8.3. Essence and economic assessment of technological processes of fuel processing
Fuel refers to solid, liquid and gaseous combustible substances that are a source of thermal energy and raw materials for the chemical industry.
As a result of chemical processing of various fuels, a huge amount of hydrocarbon raw materials is obtained for the production of plastics, chemical fibers, synthetic rubbers, varnishes, dyes, solvents, etc. For example, when coking coals, the following are obtained: benzene, toluene, xylenes, phenol, naphthalene, anthracite, hydrogen, methane, ethylene and other products. When oil is extracted, “associated” gases are released from it, which contain methane, ethane, propane, butane and other hydrocarbons used in the chemical industry.
Sources of hydrocarbon raw materials are also gases obtained as a result of oil refining (cracking, pyrolysis, reforming). These gases contain saturated hydrocarbons - methane, ethane, propane, butane and unsaturated hydrocarbons - ethylene, propylene, etc. In addition, aromatic hydrocarbons can be obtained during oil refining: benzene, toluene, xylene and their mixtures.
One of the most important types of chemical raw materials is natural gas, containing up to 98% methane. Wood and wood waste are a source of cellulose, ethyl alcohol, acetic acid, furfural and a number of other products. Shales and peat are used to produce flammable gases, raw materials for the production of oils, motor fuels, high-molecular compounds, etc.
Fuel combustion provides energy for thermal power plants, industrial enterprises, transport, and everyday life. The importance of fuel as a chemical raw material is growing every year.
Since the role of solid fuel in the global fuel balance is increasing, methods for producing cheap liquid and gaseous fuels, as well as chemical raw materials, from coal and shale are being developed all over the world.
The development of coal and nuclear energy will in the future make it possible to stop the consumption of oil and natural gas for energy purposes and completely transfer these types of fuel to industry as raw materials for the chemical industry, as well as for the synthesis of proteins and fats.
All fuels according to their state of aggregation are divided into solid, liquid and gaseous; by origin - natural and artificial (See table).
Artificial fuels are obtained by processing natural fuels.
Fuel types
|
Physical state of fuel |
FUEL |
|
|
natural |
artificial |
|
|
Wood, peat, coal, shale |
Coke, semi-coke, charcoal |
|
|
Gasoline, kerosene, naphtha, fuel oil |
||
|
Gaseous |
Natural gas, associated gases |
Coconut gas, generator gases, oil refining gases |
Solid fuels consist of combustible organic matter and non-combustible or mineral impurities and ballast. The organic part of the fuel consists of carbon, hydrogen and oxygen. In addition, it may contain nitrogen and sulfur. The non-combustible part of the fuel consists of moisture and minerals. The most important liquid fuel is oil.
Oil contains 80-85% carbon, 10-14% hydrogen and is a complex mixture of hydrocarbons. In addition to the hydrocarbon part, oil contains a small non-hydrocarbon part and mineral impurities. The hydrocarbon part of oil consists of three series of hydrocarbons: paraffin (alkanes), naphthenic (cyclenes) and aromatic (arenes).
Gaseous paraffin hydrocarbons from CH 4 to C 4 H 10 are in a dissolved state in oil and can be released from it in the form of associated gases during oil production. Liquid paraffin hydrocarbons from C 5 H 34 to C 15 H 34 make up the bulk of the liquid part of oil and liquid fractions obtained during its processing.
Solid paraffin hydrocarbons from C 16 H 34 and above are dissolved in oil and can be isolated from it.
Naphthenic hydrocarbons are represented in oil mainly by derivatives of cyclopentane and cyclohexane.
Aromatic hydrocarbons are contained in oil in the form of benzene, toluene, and xylene in small quantities.
The non-hydrocarbon part of oil consists of sulfur, oxygen and nitrogen compounds. Oxygen compounds are naphthenic acids, phenols, and resinous substances.
Mineral impurities- these are mechanical impurities: water, mineral salts, ash.
Mechanical impurities - solid particles of sand, clay, rocks - are carried out from the bowels of the earth with the flow of produced oil. Water in oil is present in two forms: free, separated from the oil during settling; in the form of persistent emulsions that can only be destroyed by special methods.
Mineral salts, such as magnesium and calcium chlorides, are dissolved in the water contained in the oil.
Ash makes up hundredths and even thousandths of a percent in oil.
Solid fuels are processed using the following methods: pyrolysis, or dry distillation, gasification and hydrogenation.
Pyrolysis occurs when fuel is heated without air access. As a result, physical processes occur, such as the evaporation of moisture, and chemical processes - the transformation of fuel components to produce a number of chemical products. The nature of the individual processes occurring during the processing of various fuels is different.
Basically, they all require heat input from outside. Reaction apparatuses are heated by hot flue gases, which transfer heat to the fuel through the wall of the apparatus or in direct contact with the fuel.
Gasification is a fuel processing process in which the organic part of it is converted into combustible gases in the presence of air, water vapor, oxygen and other gases. This process is exothermic. The gasification temperature is 900-1100 °C.
Hydrogenation is the processing of solid fuels, in which, under the influence of high temperature, under the action of hydrogen and in the presence of catalysts, chemical reactions occur, leading to the formation of products more rich in hydrogen than the feedstock. The quality and quantity of products obtained from hydrogenation depends on the type of fuel being processed, the process conditions and a number of other factors.
Oil refining methods are different and can be divided into two groups: physical and chemical.
Physical processing methods are based on the use of the physical properties of the fractions that make up the oil. No chemical reactions occur with these processing methods. The most common physical method of refining oil is distillation, in which the oil is separated into fractions.
Chemical processing methods are based on the fact that, under the influence of high temperatures and pressure in the presence of catalysts, hydrocarbons contained in oil and petroleum products undergo chemical transformations, as a result of which new substances are formed.
Thermal cracking is a chemical method of oil refining, the essence of which is the splitting of long molecules of heavy hydrocarbons included in high-boiling fractions into shorter molecules of light, low-boiling products. Thermal cracking occurs at high temperatures of 450-500 ° C and elevated pressure. Thermal cracking carried out at a temperature of 670-1200 ° C and at atmospheric pressure is called pyrolysis.
Catalytic cracking is called cracking using a catalyst. The use of a catalyst makes it possible to reduce the cracking temperature and not only increase the quantity of products obtained, but also improve their quality. Clays such as bauxite, as well as synthetic aluminosilicates containing 10-25% Al 2 O 3, SiO 2, serve as catalysts. Cracking temperature - 450 - 500 °C. The process occurs at elevated pressure.
A type of catalytic cracking is reforming. The catalyst is platinum supported on aluminum oxide.
Using the methods described above for processing natural fuels, artificial solid, liquid and gaseous fuels, as well as the most important types of petroleum products, are obtained.
As a result of coal coking, the following products are obtained:
1. Coke is a dark gray product, the porosity of which is 45-55%, and contains 97-98% carbon. Depending on the purpose it is divided into:
a) blast furnace coke - large, more than 40 mm in diameter, strong and porous. Based on sulfur content, it is divided into grades KD-I, KD-2, KD-3. Sulfur content should not exceed 1.3-1.9%;
b) foundry coke (grade KL). The lower size limit is 25 mm in diameter. The sulfur content in it is allowed no higher than 1.2-1.3%. It has lower porosity and strength compared to blast furnace coke;
c) coke nut (CO) is used for the production of ferroalloys. Size 10 - 25 mm in diameter. Coke - fraction from 10 to 20 mm - used for gasification;
d) coke breeze (fraction with a diameter of less than 10 mm) is used for agglomeration;
e) coke, unsuitable for technical needs due to the high content of ash and sulfur, as well as due to low mechanical properties, is used as fuel.
Return coke oven gas contains 60% hydrogen and 25% methane, the rest is nitrogen, carbon monoxide, carbon dioxide, oxygen, and unsaturated hydrocarbons. It is used for heating air blast in blast furnaces, for heating steelmaking, coke and other furnaces, and also serves as a raw material for the production of hydrogen and ammonia.
Crude benzene consists of benzene, toluene, xylene, carbon disulfide, phenols, etc. The substances that make up crude benzene are widely used in the production of polymers, dyes, drugs, explosives, pesticides, etc.
4. Coal tar is a mixture of aromatic hydrocarbons. It is used for the production of dyes, chemical fibers, plastics, in the pharmaceutical industry, as well as for the production of various technical oils.
Products of direct distillation of petroleum can be divided into three groups: fuel fractions, oil distillates and tar. The most valuable fuel fraction is gasoline, which contains hydrocarbons with a boiling point of 180-200 °C. Gasolines are used as components of automobile and aviation gasolines and as solvents.
Naphthas include hydrocarbons with boiling points of 105-220 °C. Light naphtha (with a boiling point of 105 - 150 °C) is used as a raw material for further processing into gasoline, and heavy naphtha is used as a component of jet fuels or solvents for the paint and varnish industry.
Kerosene is a hydrocarbon fraction with boiling points of 140-330 °C; They are used as lighting kerosene, as well as jet and diesel fuels.
Gas oil - fractions with boiling points up to 400 °C. Light gas oil (solar) is the basis of diesel fuels. Heavy gas oils are raw materials for further processing.
Fuel oil is a fraction that includes hydrocarbons, paraffin, oily and resinous substances with a boiling point above 300 °C. Light fuel oils are used as boiler fuel and gas turbine fuel; heavy ones go for further processing.
Oil distillates are fractions consisting of C20–C70 hydrocarbons. The boiling points of the substances included in their composition range from 350 to 550 °C. Oil distillates are used to produce a large number of lubricating and special oils.
Tar consists of resinous substances, paraffins and a certain amount of heavy hydrocarbons of a cyclic structure. Tar is a semi-product for the production of bitumen and coke. Some types of tar are used as softeners in the rubber industry.
The products of cracking are: cracked gasoline, cracked gases and cracked residue.
Cracking gasolines are used as components of motor gasolines. Cracking gases are used as fuel and as a raw material for the synthesis of organic compounds. The cracking residue is a mixture of resinous and asphalt substances with a certain amount of unreacted raw materials. Cracking residue is used as boiler fuel and raw material for the production of bitumen.
The technical and economic indicators of the oil refining and coke industry include: equipment productivity and power, process intensity, labor productivity, production costs, capital costs. The coke and oil refining industries are characterized by high material and energy intensity.
The cost of raw materials in the production of petroleum products is 50-75%. Consequently, the main factor influencing the cost is the reduction of costs per ton of products, which can be achieved by improving the technological processes of oil and coke refining, using catalytic processes, more advanced equipment and comprehensive automation, which leads to a reduction in capital costs, energy costs and steam, increased productivity
Polymer materials are widely used in car repairs. They have a wide range of positive properties:
- good friction and anti-friction qualities
- sufficient strength
- oil, petrol and water resistance
- maintaining the shape of the part
- ability to withstand a certain load and temperature
- ease of restoration and manufacturing of parts, etc.
Possessing valuable physical and mechanical properties, polymer materials can reduce the labor intensity of machine repair and maintenance by 20-30% and reduce the consumption of scarce materials (ferrous and non-ferrous metals, welding and surfacing materials, solder, etc.) by 40-50% . The disadvantages of polymer materials include changes in their properties depending on service life (aging), relatively low hardness, fatigue strength and heat resistance.
The following polymer materials are recommended for use in machine repair: polycaproamide (nylon), polyethylene, polystyrene, polyamide, fiberglass, epoxy resins, synthetic adhesives, sealants, anaerobic polymer materials, etc. The industry produces special first aid kits and sets of polymer materials for machine repair.
The use of polymer materials does not require complex equipment and highly qualified workers. It is possible in specialized repair enterprises, in farm workshops, as well as in the field.
The use of epoxy compositions in the restoration of parts
Epoxy resins are used very rarely in their pure form. In repair practice, epoxy compounds are used, which are multicomponent systems. The most important advantage of the composition over polymers is their increased rigidity and strength, dimensional stability, increased impact strength, adjustable friction and other properties. However, all these properties cannot be achieved in one composition.
In addition to epoxy resin, the composition, depending on the purpose, may include plasticizers, fillers, hardeners, curing accelerators, pigments and other components.
Plasticizers reduce brittleness and resistance to sudden temperature changes, but reduce thermal conductivity. Dibutyl phthalate is most often used as a plasticizer.
Fillers are introduced to improve physical and mechanical properties and reduce internal stresses arising due to the difference in the linear expansion coefficients of metal and polymer. Fillers are divided into binders (fiberglass, fabrics) and powdered (iron powder, aluminum powder, cement, talc, graphite, etc.).
Polyethylene polyamine is often used as a hardener for epoxy resins.
Epoxy compositions are a universal repair material. They are used for sealing cracks, cavities, holes, restoring moving and fixed joints, and gluing parts. The composition of the composition depends on the required properties and operating conditions. To secure bushings, rings, and screws during restoration using additional repair parts, a composition without fillers is used. For 100 parts (by weight) of ED-16 epoxy resin, take 10 parts of dibutyl phthalate and 12 parts of polyethylene polyamine. When sealing cracks, holes, and restoring bearing seats, fillers are introduced into the compositions.
The preparation of the composition is as follows. The epoxy resin in the container is heated to a temperature of 70-80°C, the required amount is poured into the vessel, a plasticizer is added and the two-component composition is mixed. Then, if necessary, add filler, previously dried for 2-3 hours at a temperature of 100-120°C, and mix the composition thoroughly. The hardener is added before using the composition.
The prepared composition must be used within 20-25 minutes.
Sealing cracks and holes
Epoxy compositions are used to seal cracks in body parts that do not pass through holes for bushings, bearing seats, threaded holes, no more than 200 mm long. After determining the size of the crack, its edges are drilled with a drill with a diameter of 3 mm, and the crack along its entire length is cut at an angle of 60-70°, to a depth of 2-3 mm (for a wall thickness of more than 5 mm). If the wall thickness is less than 2 mm, the crack is not cut. The surface of the part is cleaned to a metallic shine at a distance of 40 mm on both sides of the crack and degreased with acetone. The prepared composition is applied to the surface and compacted with a spatula. To seal small cracks (up to 20 mm), use a composition without filler. When restoring cast iron parts with holes and cracks longer than 20 mm, use the following composition. For 100 parts (by weight) of ED-16 resin, take 15 parts of dibutyl phthalate, 120 parts of iron powder and 11 parts of polyethylene polyamine. To restore body parts made of aluminum alloys, instead of iron powder, aluminum powder (25 parts) is used as a filler.
A crack 20-150 mm long on body parts or tanks is sealed with an epoxy composition reinforced with fiberglass or technical calico. The first fabric overlay should cover the crack by 20-25 mm on both sides, and the second should cover the first by 10-15 mm. After applying the first layer of epoxy composition, apply the first overlay and roll it into place. A thin layer of the composition is applied to the surface of the lining and a second lining is applied, which is also rolled with a roller. A layer of the composition is again applied to the second overlay and left to cure.
Rice. Options for sealing cracks: a - with epoxy; b - epoxy composition reinforced with fiberglass; c - epoxy compound and metal lining.
Cracks in body parts longer than 150 mm are sealed using a lining made of sheet steel 1.5-2.0 mm thick. The cleaned surfaces of the part, lining and screws are coated with an epoxy composition.
Curing of the composition is carried out at a temperature of 18-20 C for 72 hours. It is allowed to cure at a temperature of 20 C for 12 hours, and then according to one of the following modes: at 40 C - 48 hours; at 60 C" - 24 hours; at 80 C" - 52 hours; at 100 C" - 3 hours.
Holes in body parts, radiator tanks, and fuel tanks are repaired by applying overlapping patches using epoxy compositions. For small holes, the lining is made of fiberglass. Thin-walled parts are restored by applying a sheet steel overlay. Holes in body parts are sealed by overlapping metal plates with screws. The steel flashing can be secured with an epoxy compound that penetrates the additional drillings.
Restoration of mounting holes
Epoxy compositions are used for repairing fixed mating parts of the housing-bearing, housing-bushing type, if the gap in the mating does not exceed 0.1 mm. Before applying the composition, the mating surfaces of the hole in the housing and bushing (bearing) are cleaned and degreased. After drying, apply the composition (without filler) to the prepared surfaces in a layer no more than 0.5 mm thick. After 10-15 minutes, the sleeve (bearing) is pressed into the hole and curing is carried out according to one of the above modes.
Bonding parts with synthetic adhesives
For gluing, adhesives VS-YUT and type BF, 88N, etc. are used. Glue VS-YUT is used for gluing linings to brake pads and clutch discs. In addition, it can be used for gluing metals, fiberglass and other materials. Curing mode: pressing pressure of the bonded surfaces - 0.2-0.4 MPa, temperature - 175-185°C, duration - 1.5-2.0 hours.
Adhesives BF-2, BF-4, BF-6 are used for gluing metals, wood, etc.
BF-6 glue produces more elastic joints, so it is used for gluing felt, felt, fabrics and other materials. Bonding mode: pressure - 0.5-1.0 MPa, temperature - 140-160°C, duration - 1.0-1.5 hours. BF-52T glue is used for the same purposes as VS-YUT glue.
For gluing rubber and rubber to metal, glue 88H is used.
The surfaces to be bonded are cleaned of dirt and old polymer materials. Metal surfaces are cleaned to a metallic shine and degreased with acetone or gasoline. After drying the parts, apply a layer of glue 0.10-0.15 mm thick to the surfaces to be glued and keep at room temperature for 10-15 minutes. Then apply a second layer of glue and dry the parts. The end of drying is checked “touch”. A rubber block, cleaned with acetone, is applied to the glue layer. If it does not stick, the surfaces to be glued are placed one on top of the other and compressed with special devices. The part, together with the accessories, is placed in a special cabinet for heat treatment (hardening of the adhesive composition) and kept for 40 minutes. To reduce residual stresses in the adhesive joint, the parts are cooled together with the cabinet to a temperature of 80-100°C, and then in air to a temperature of 20-25°C for 2-3 hours and removed from the fixtures.
This technology is used to glue friction linings onto brake pads and discs.
The use of elastomers in restoring fits
Repair of bearing units often involves restoring the original tension. Failure to fit is caused by the crushing of surface irregularities during pressing and removal of bearings and due to rotation of the bearing ring during machine operation. To restore seats for bearings in holes and on shafts, as well as for bushings and gears with wear of no more than 0.06 mm, GEN-150(B) or 6F elastomers are used.
The technological process includes the following operations: preparing the solution, cleaning and degreasing worn surfaces, applying the solution to prepared surfaces, heat treatment and assembling components. Solutions are prepared according to the following recipe: one part (by weight) of the GEN-150(B) elastomer and 6.2 parts of acetone; or 2 parts 6F elastomer, 5 parts acetone and 5 parts ethyl acetate.
The elastomer solution is applied to the surface of the part in a fume hood with a brush. Overlapping layers when applying the solution is not allowed. The film thickness of one layer is 0.01 mm. The coated part is kept for 20 minutes and then placed in a drying oven for heat treatment. Heat treatment is carried out at a temperature of 120 C for 30 minutes. Each subsequent layer until the required thickness is obtained is applied after heat treatment of the previous one. Before assembly, the surface of the elastomer-coated part is lubricated with graphite lubricant, and the surrounding part is heated to a temperature of 120-140°C.
Sleeve bearing bushings and other parts are manufactured by injection molding. The main technological properties of plastics are: fluidity, the ability of the material to fill a mold at a certain temperature and pressure; shrinkage - reduction in the size of the finished part compared to the corresponding mold dimensions; curing speed, which depends on the properties and ratio of resin and hardener, as well as the temperature at which the curing process occurs. Polycaproamide having sufficient strength and durability...
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RESTORATION OF MACHINE PARTS USING POLYMER MATERIALS
Types of polymer materials and their scope of application
Polymers, plastics and other artificial composite materials are widely used in the production, maintenance and repair of machines.
Polymers these are high-molecular organic compounds of artificial or natural origin, usually having an amorphous structure.
Plastics composite materials made on the basis of polymers, capable of taking a certain shape at a given temperature and pressure, which is maintained under operating conditions. Depending on the number of components, plastics can be single-component (simple) or multi-component (composite). Simple ones are, for example, polyethylene, polystyrene, consisting of synthetic resin. In composite plastics (phenoplasts, aminoplasts, etc.), the resin is a binder for other components. They are fillers, plasticizers, hardeners, accelerators (activators), dyes, lubricants and other components that give the plastic the necessary properties.
The share of additional components can reach 70%. This makes it possible to create composite materials that, in accordance with production needs, have a combination of certain properties: sufficient strength, vibration resistance, good chemical resistance to acids, alkalis and other aggressive media, high friction or antifriction, noise-absorbing, dielectric, thermal insulation and other properties.
In the repair industry, polymer materials are used for: sealing cracks, holes and cavities in parts; gluing; restoration of the shape and size of worn parts; sealing joints; manufacturing of wearing parts or their individual parts.
Depending on the ability to return to its original state under the influence of temperature, thermosetting and thermoplastic polymer materials are distinguished.
Thermoplastic materials or thermoplasticsWhen the temperature rises, they transform into a plastic state, and when cooled, they restore their properties. Therefore, they can be recycled many times. Using various thermal methods, thermoplastics are applied to the surfaces of parts in the form of coatings for various purposes (anti-friction, protective, insulating, etc.). Some thermoplastics (polyamides such as caprolactan, AK-7, etc.) are used to produce sleeve bearings and other parts by injection molding.
An important performance property of thermoplastics isthermal stabilitythe time during which a thermoplastic can withstand a certain temperature while maintaining its properties. The main technological properties of plastics are: fluidity (the ability of a material to fill a mold at a certain temperature and pressure); shrinkage (reduction in the dimensions of the finished part compared to the corresponding dimensions of the mold); curing speed, which depends on the properties and ratio of resin and hardener, as well as the temperature at which the curing process occurs.
Polyethylene, polycaproamide, fluoroplastic and other thermoplastics are widely used in repairs.
Polyethylene It is characterized by good ductility, which is maintained even at low temperatures, which allows it to be used for the manufacture and restoration of flexible products (pipes) and protective coatings.
Polycaproamide, Having sufficient strength and resistance to the effects of alkalis and various fuels and lubricants, it is used as a structural material for the manufacture of gears and bushings, and for the application of wear-resistant coatings to parts.
Fluoroplastic , due to its high melting point (327 °C), low coefficient of friction, high wear resistance and virtually no adhesion in contact with metals, it is used for the manufacture of sleeve bearings operating at temperatures up to 250 °C. In terms of chemical resistance, it surpasses all materials, which determines a wide range of its use in various aggressive environments. The lack of adhesive interaction with metals makes it difficult to use fluoroplastic for applying protective coatings to them by spraying. Therefore, mechanical fastening of fluoroplastic linings to restored products is usually used.
Thermoset materialsor thermosets (textolite, fiberglass, fiberglass, epoxy compositions, etc.) are distinguished by the fact that when heated as a result of chemical reactions, they irreversibly transform into a solid, infusible and insoluble state. They may collapse if reheated. Thermosetting plastics used in repairs include compositions including epoxy (ED-16, ED-20), phenol-formaldehyde and other resins, hardeners, plasticizers and other components.
When mixed with hardener (polyethylene polyamine, aromatic amines, etc.) the epoxy resin becomes solid and insoluble. This process, depending on the hardener, can occur at different temperatures. For example, when boron fluoride is used as a hardener, hardening occurs at a negative temperature. As the proportion of hardener increases, the fragility of the composite material increases, and when it decreases, the hardening process lengthens, therefore, to obtain a high-quality polymer material, it is necessary to follow the recommendations established in the instructions for the ratio of resin and hardener. This also applies to other components of the polymer composition.
Plasticizers (dibutyl phthalate, triethylene glycol, thiokol, etc.) serve to increase the impact strength and strength of the composite material, reduce its sensitivity to thermal cyclic stress, impart elasticity and other required properties.
Inorganic fillers(metal powder, graphite, quartz and mica flour, talc, asbestos, carbon fibers, glass fiber, fiberglass, etc.) and organic (paper, cellulose, wood flour, cotton fabric, etc.) allow you to control the physical and mechanical properties of the composite material to increase strength, wear resistance, heat resistance, etc. For example, by changing the ratio between the content of metallic and non-metallic powders, it is possible to reduce the shrinkage of the applied polymer coating and the difference in the values of the coefficients of linear expansion of the part and the coating, and by introducing graphite, increase its wear resistance. The use of fibrous fillers makes it possible to obtain fiberglass, fiberglass and other high-strength materials based on phenol-formaldehyde resins, which are widely used for the manufacture of machine parts.
Thermosetting plastics are used to seal dents, cracks, pores and cavities in parts made of metallic and non-metallic materials, to restore seating surfaces for bearings in body parts, as well as to manufacture new parts.
Depending on the properties, plastics can be processed into parts in a viscous flow state (injection molding, extrusion, pressing), in a highly elastic state (stamping, pneumatic and vacuum molding); in the solid state (processing, cutting, gluing, welding) and other methods.
The use of polymer materials in machine repair, compared to other restoration methods, makes it possible to reduce labor intensity by 20-30% and the cost of repairs by 15-20%, as well as eliminate complex technological processes typical for the application of metal materials and their processing. The consumption of structural materials (often scarce and expensive non-ferrous metals and stainless steels) and, accordingly, the weight of parts are significantly reduced (by 40-50%). At the same time, polymer materials do not reduce the fatigue strength of the parts they restore, which in many cases makes it possible not only to replace welding or surfacing, but also to restore parts that are either impossible to restore by other technological methods, or unprofitable, or this involves difficult working conditions.
The practical use of polymer materials usually does not require complex technological equipment, which is important in repair production conditions.
Disadvantages of polymer materialscompared to metals are lower strength, intensive aging, low thermal conductivity and thermal resistance of individual materials.
Elastomers and sealants. To seal and restore seating of fixed joints, elastomers and sealants, including anaerobic ones, are used. Elastomers are produced in the form of sheets 2 x 5 mm thick, from which a working solution is prepared using acetone. To do this, the required amount of elastomer is divided into small pieces, which are poured into a glass container with the amount of acetone calculated in accordance with the instructions and kept in it until dissolved. The resulting solution must be stored in tightly closed containers. Convenient ready-to-use elastomers based on cold-curing rubber, which are two-component materials supplied in liquid or paste form. They are used to restore rubber coatings of parts, hoses, insulation, as well as for casting non-standard shapes of cuffs, seals and gaskets.
The surface of the part to be coated is subjected to sandblasting or grinding until it is completely clean and gives it increased roughness to improve adhesion to the coating. Before applying the coating, the prepared surface is degreased with a special product or acetone. Both components of the applied material (base and activator) are mixed together to ensure homogeneity of the mixture and remove air from it. When eliminating large cracks and chips, it is recommended to reinforce the coating with fiberglass, which increases its strength.
The most effective sealing material is sealants based on polymers and oligomers. Thermoplastic and thermosetting sealants, drying and non-drying, polymerizing, vulcanizing and non-hardening, are used.
Table 4.11
Anaerobic sealantsare one-component materials that contain acrylic and methacrylic esters and hydrogen peroxide. They are effective for sealing threaded and flanged connections of pneumatic and hydraulic systems using a variety of mating surface materials. At the same time, in addition to sealing, the strength and rigidity of the connections increases, gaps are eliminated (0.2 x 0.7 mm) and surfaces are protected from corrosion. The time for complete polymerization for different sealants is from 24 to 72 hours. Start of operation is possible immediately after curing. When choosing a sealant brand, the gap between the parts being sealed and the ambient temperature, which affects the viscosity of the composition, are taken into account.
Anaerobic sealants are also effective in impregnating (sealing) small cracks and pores in workpieces produced by casting and pressure methods, and in welds. In this case, the sealant is applied without the use of an activator to a cleaned and degreased surface with defects 2 x 3 times every 15 x 20 minutes. To speed up the curing of the sealant, the product is kept at a temperature of 6090 °C for 0.52 hours.
In the repair industry, anaerobic compositions of the types DN, Anaterm, Unigerm, etc. are widely used. They are compositions that can remain in a fluid state for a long time and harden in the absence of contact with atmospheric oxygen. Curing time depends on ambient temperature, and maximum strength of the cured material is achieved after 24 hours.
These compositions have high penetrating ability and therefore are able to fill micro-irregularities and micro-cracks in parts, gaps in the joints between them equal to 0.05 x 0.2 mm. During polymerization, they transform into a solid stable state with the formation of a durable compound that is resistant to temperature changes in the range -60... +150 °C and aggressive environmental influences. This allows you to impregnate and seal pores in cast and pressed workpieces, and reliably fix the relative position of parts in various joints (smooth flat and cylindrical, threaded, profile, etc.). In this case, the mating parts can be made of different materials in any combination.
The use of anaerobic materials when assembling fixed joints is very effective. For example, when installing bearings using anaerobic material, not only is corrosion and other damage to the seating surfaces eliminated, but the bearing rings also ensure backlash-free mating with them. After removing a bearing installed in this way, the seating surface remains clean, and subsequent repairs only require reapplying sealant without treating it.
Anaerobic materials do not interact with water, solvents, lubricants and provide reliable anti-corrosion protection of sealed parts. This can significantly increase the reliability of structures. It is also important that most of these materials are environmentally friendly.
Before applying anaerobic sealant, the part must be thoroughly cleaned of contaminants using appropriate methods (mechanical, chemical, etc.) and degreased.
Adhesive materials. Adhesive materials are often solutions of various synthetic resins in organic solvents. They are produced in the form of components mixed before use, as well as in the form of film, powder, and granules. In the repair industry, epoxy adhesive materials are more often used, which is due to their high adhesion and neutrality with respect to the materials being glued, low shrinkage, and resistance to corrosion and other influences. Fiberglass reinforcement expands the scope of application of these adhesive materials and makes it possible to eliminate large holes and cracks in parts operating at temperatures of -70... +120 °C. The disadvantage of epoxy adhesive compositions is the toxicity of the components.
Acrylic adhesives (types AN, KV), cyanoacrylic (types TK, KM, MIG) and silicone are also widely used, which make it possible to firmly connect parts made of various materials to each other, seal gaps and cracks, reduce vibration and noise, produce seals and gaskets of any kind. forms. A feature of cyanoacrylic adhesives is their rapid curing (for most brands, the setting time is 1 minute). The operating temperature of adhesive joints can vary from -50 to +250 °C.
The use of adhesive compositions makes it possible to glue parts together, eliminate cracks up to 150 mm long, and holes up to 2.5 cm in area 2 , chips, corrosion-erosion and other damage, as well as create wear-resistant graphite and other coatings.
Compared to welding, it is possible to connect parts made of dissimilar materials in the absence of internal stresses and warping, using simpler technological equipment, with less labor intensity and repair costs.
Metal polymersare two-component composite materials, which consist of 70x80% fine metal powders (nickel, chromium, zinc) and special oligomers (polymers with low molecular weight), which upon curing form polymer coatings of increased strength due to the use of surface energy of the materials. Metal polymers are characterized by high adhesion to various metal and non-metallic materials, including plastics, with the exception of fluoroplastic and polyethylene, which allows them to produce high-quality cold molecular welding, which is one of the progressive high-tech methods for restoring machine parts. It is performed using composite metal-polymer materials that can be processed by cutting.
In addition, these materials reliably protect machine parts from corrosion and erosion in aggressive environments with high humidity and evaporation. Their operating temperature is in the range -60... +180 °C with a maximum heat resistance of up to 200×220 °C. The tensile strength of modern metal polymers is (MPa): in compression 120 x 145, in bending 90 x 110, in shear 15 x 25. Important advantages of metal-polymer materials are the absence of volume change during polymerization and their elasticity, which eliminates the negative influence of differences in the coefficients of linear expansion of the part materials and coating.
Thanks to these properties, metal polymers make it possible to create high-strength joints of various materials using cold welding, restore the size, shape and integrity of parts, apply wear-resistant coatings with a self-lubricating effect to their working surfaces, and solve other repair problems.
Metal polymers are used to eliminate emergency leaks in pipelines and containers, restore seats for rolling bearings on the shaft and in the housing, threaded connections and “broken” keyways, eliminate defects in cast iron and steel castings (sinks, cracks), repair housing parts (potholes, chips, etc.), as well as to protect machine parts from corrosion, abrasive wear, and erosion.
Advantages of using metal polymers:
no thermal or mechanical impact on the restored surface, special technological equipment or protective environment are required;
environmentally friendly working conditions, since the metal polymer components used do not contain and do not form volatile toxic substances when interacting with each other and with the coated material;
fire safety of repair and restoration work.
Application of polymer materials to parts
In the repair industry, polymer coatings are applied to parts using the gas-flame method, as well as by melting the powder in a fluidized state.
Gas flame sprayingpowder polymer materials are carried out in installations similar to the spraying of powder metal materials. Surfaces to be coated are thoroughly cleaned of all types of contaminants and oxides, and surfaces not to be coated are protected with foil or asbestos screens. Before spraying, the part is coated with a heat-insulating primer and heated with a gas burner to a temperature exceeding the melting point of the polymer powder, which protects the coating from cracking after cooling.
When spraying, the polymer powder is fed into the gas flame of an injection gas burner and, in a molten state, is applied to the surface of the part with a jet of compressed air under a pressure of 0.4 x 0.6 MPa. The powder melts under the action of a gas flame and a preheated product. Special powders are used, for example, TPF-37, PFN-12, as well as polyethylene, nylon, polystyrene and various compositions of these and other polyamide materials with fillers. The thickness of the coating can reach 10 mm. In one pass, a surface with a width of 20 x 70 mm is covered. After applying the coating, it is additionally heated with a burner flame or in a heating device and rolled with a metal roller to compact it.
When spraying non-metallic materials, the part is often not heated, but coated with a special glue that provides stronger adhesion of the coating to the product.
When repairing cars, flame spraying of polymer materials is used to seal minor defects in parts and weld marks, apply anti-friction, anti-corrosion, electrical insulating, heat insulating and decorative coatings.
Fluidized Powder Bed Coating. The polymer coating on the parts is created by melting a powder with a particle size of 0.1 x 0.15 mm, which is in a fluidized state, under the influence of the heat of a preheated part. Varieties of this method differ in the method of transferring the deposited powder into a fluidized state. Of these, vortex, vibration and combined methods have been used.
With the vortex method the fluidized (vortexed) state of the powder is created by a flow of air or inert gas. The equipment consists of chamber 2 (Fig. 4.65), which is divided into two parts by a porous partition 6 and filter 5, which ensures the flow of air from the bottom of the chamber to the top. In the upper part of the chamber, a layer of fused powder is poured onto the filter, the thickness of which must be at least 100 mm. Filter 5 prevents the powder from clogging the holes in the partition and pouring it from the top of the chamber to the bottom.
Rice. 4.65. Installation diagram for vortex spraying of a polymer coating: 1 cylinder; 2 camera; 3 powder; 4 sprayed part; 5 fabric filter; 6 porous partition; 7 exhaust device; 8 suction device
From cylinder 1, an inert gas is supplied under a pressure of 0.1 x 0.2 MPa to the lower part of the chamber, which, after passing through the partition and filter, brings powder 3 into a suspended (fluidized) state.
The restored part 4, heated to a temperature above the melting point of this polymer, is placed in a fluidized layer of polymer powder, which, in contact with the heated part, melts, forming a thin-layer coating on it. Areas not to be covered must be insulated with foil, liquid glass or other easily removable material.
Depending on the heating temperature of the part, the time it is in the powder, thermal conductivity and its melting point, the thickness of the coating can be 0.08 x 1 mm. A high-quality coating is formed regardless of the complexity of the part’s shape, which is a significant advantage of this method. It is used to create anti-friction and protective coatings.
To relieve internal stresses, the part after coating is heated and kept in oil at a temperature of 150 x 160 ° C for 15 x 60 minutes.
Vibration methodthe fluidized state of the deposited powder is created by transmitting vibrations to the chamber with a special vibrator with a frequency of 50 x 100 Hz. This provides a more uniform and high-quality coating up to 1.5 mm thick. Compared to the vortex vibration method, it is more economical, since compressed air is not required, and due to the fact that the part is not cooled by a gas flow, the associated loss of heat accumulated during heating before coating is eliminated. Due to this, all other things being equal, a greater thickness of the formed coating is ensured. After coating, the part is placed in a reflow chamber.
Combined (vibration-vortex) methodis a combination of those discussed above. In this method, a chamber containing fluidized gas and powder is oscillated using a special device with a frequency of 50×100 Hz and an amplitude of up to 10 mm. This improves the quality of the coating and makes it possible to apply coatings of greater thickness than with the vortex or vibration method.
The advantages of the vortex-vibration method compared to the vortex and vibration methods are as follows:
reliable and more uniform fluidization of the powder throughout the entire volume, including powders prone to sticking and clumping;
increase up to 2 times the ratio of the volume of powder in a fluidized state to the volume of bulk powder;
good fluidization of the mixture of polymer powders and fillers and the absence of their separation during coating formation;
uniform height of the part and increased coating thickness under the same conditions.
Restoring the integrity of parts and the tightness of dismountable joints
Using polymer materials they restore integrity parts by sealing defects in the form of cracks and holes or gluing.
Cracks in body partseliminated using adhesive compositions based on epoxy resins and other materials. They are selected depending on the material of the part and the size of the cracks. There are adhesive compositions for repairing cast iron, steel, aluminum and plastic parts, some of them are listed in table. 4.11. When restoring parts operating under vibration conditions, up to 30% of finely ground mica and rubber are added to epoxy compounds.
The use of polymer materials gives good results only with careful preparation of the surface in the defect area. To ensure reliable adhesion of the polymer to the part, its surface must be thoroughly cleaned of dirt, cleaned and degreased. To improve the adhesion of the polymer to the surface of the part, increased roughness is created on it. Traces of paint and corrosion on the prepared surface are not allowed.
Typical technology for sealing cracks in a body partincludes the following operations:
1. Preparing the part for repair. It includes: drilling holes with a diameter of 2.5 x 3 mm at the ends of the crack; chamfering (for wall thickness over 1.5 mm) along cracks at an angle of 6070° to a depth of 13 mm; cleaning the surface adjacent to the crack with a width of 25 x 30 mm to a metallic shine; degreasing the cleaned surface. For cracks up to 50 mm in length, the chamfer may not be removed.
2. Preparation of the polymer material in accordance with the recommendations for this material. For example, an epoxy composition is prepared in the following sequence: heating the epoxy resin to a liquid state; mixing it in a certain proportion with a plasticizer; introduction of the necessary fillers into the composition and thorough mixing. Immediately before use, the hardener is added to the epoxy composition and thoroughly mixed. The resulting composition should be used within 20×30 minutes.
3. Apply a polymer composition corresponding to the material of the part and rub it into the crack. The epoxy composition hardens at room temperature or with the use of additional heat after partial curing and exposure to a temperature of 80 ° C. Heating the part immediately after applying the composition is not allowed, as it leads to swelling, uneven thickness and insufficient strength.
4. Tightness test of a sealed crack under a pressure of 0.3 x 0.4 MPa. Water seepage through a sealed crack is not allowed.
To increase the strength of the connection when the length of cracks is more than 30 mm, fiberglass overlays are used, which are laid in several layers with glue applied between them. They are pre-cleaned in boiling water for 2×3 hours and degreased with acetone. The first overlay should overlap the crack by 15 x 20 mm, and each subsequent one should overlap the contour of the previous overlay by 5 x 10 mm. Each pad is rolled with a roller to remove air from under it and seal the joint. The number of overlays depends on the length of the crack and usually does not exceed three. Lag linings are not allowed.
If the crack length is more than 150 mm, an additional metal plate with a thickness of 1.5 x 2 mm is used to cover the crack by 40 x 50 mm. It is installed on an adhesive composition, followed by mechanical fastening to the part being restored with screws located at a distance of 50x70 mm from each other.
Parts with holes are also repaired with the installation of overlays. For holes with a diameter of up to 25 mm, they are made of fiberglass, and for larger diameters, metal plates are used, which must fit tightly to the part. To do this, they are attached with screws, and additional drillings are provided in the plate and the body wall, which are filled with an adhesive composition that, after curing, increases the strength of sealing the hole.
The considered method of sealing cracks and holes can be used if the defects are located on the flat surfaces of the parts. On shaped surfaces, these defects are usually eliminated by welding or a combined method, when a layer of epoxy composition is applied to the weld to seal it.
Good results when sealing cracks are obtained by using shaped tightening inserts followed by sealing the crack by applying a polymer material.
Gluing when repairing machines, it is used to connect together parts of a part or different parts made of the same and different (metallic and non-metallic) materials. Adhesives of types BF, BC, VK, epoxy compounds, etc. are used. The gluing technology includes preparing the surfaces to be joined, applying an adhesive composition to them, connecting the parts together and, if necessary, heat treatment to completely cure it and increase its strength.
Surface preparation for gluing is carried out in the same way as when sealing cracks. To ensure the same thickness of the adhesive layer, a more careful fit of the bonded surfaces to each other is required, and their roughness after cleaning should be approximately Rz = 20 µm for better adhesion to the adhesive.
For gluing metal parts together, adhesives BF-2 and BF-4 are used, which are alcohol solutions of thermosetting resins. They have heat resistance up to 80 ° C, and the shear strength of the adhesive joint is 40 x 60 MPa. The glue is applied in 2 x 3 layers so that their total thickness is 0.1 x 0.2 mm. With a greater thickness, the adhesion force of the glue to the part decreases by 1.5 x 2 times. The parts to be glued are compressed together under a pressure of 0.5 x 1 MPa and in this state are kept at a temperature of 140 x 150 ° C for 0.5 x 1 hour.
BF-2 glue is also used for assembling fixed joints with a gap between mating parts of up to 0.15 mm. For larger gaps, an epoxy compound is used, which is applied in one layer.
VS-10T glue, which is a solution of synthetic resins in organic solvents, is used for gluing friction linings operating at temperatures -60... +100 °C.
Restoration of fixed cylindrical and threaded connections
Recoverycylindrical connectionstype bearing ring housing, cylindrical cup housing, polymer compositions, elastomers and anaerobic sealants are used. In all cases, the surfaces are cleaned to bare metal, degreased with acetone and dried. Two methods are used to restore such compounds using polymeric materials.
The first method is characterizedin that the polymer material is cured after the joint is assembled. It is usually used with a gap in the connection of up to 0.2 mm. A polymer material (epoxy composition A or metal polymer) is applied to the surface of the part, which is kept for a certain time in the open air for preliminary curing, the joint is assembled, excess applied material is removed, and the material remaining between the parts being connected is cured. As a result, a gap-free connection of parts is created.
Second way differs in that the applied polymer material is processed, usually by boring, after it has cured to obtain the nominal or repair size of the restored surface. More effective and easier to implement compared to boring is the method of restoring seating surfaces in body parts using the methoddimensional calibrationholes coated with polymer material. Calibration is carried out after its partial curing and eliminates the operation of boring the hole being restored.
When using this method, the following basic operations are performed: cleaning and degreasing the hole being restored; applying a polymer material 1 x 1.5 mm thick to the prepared surface and partially curing it; calibration of the restored hole; final curing of the applied material and quality control of the coating.
Calibration of the polymer coating 1 (Fig. 4.66) is carried out on pressing equipment, special stands or metal-cutting machines (vertical drilling or lathe) using a mandrel 2, which, under the influence of force P, is pushed without relative rotation through the hole being restored. The mandrel is pre-lubricated with oil or technical grease to reduce friction.
The calibration method allows you to form a hole coated with a polymer composition to a given (nominal or repair) size of the connection of parts, ensuring high productivity and stable quality of restoration.
When repairing fixed bearing connections (housing-bearing, shaft-bearing, etc.), elastomers and sealants are also often used. The elastomer is applied layer by layer with a certain time interval between layers until the desired coating thickness is obtained. The thickness of one layer is within 0.01 x 0.015 mm, and its permissible total thickness depends on the brand of material applied and the technology used. If necessary, heat treatment of the coating is carried out, the regime of which depends on its composition. Fixed joints coated with elastomer or sealant are assembled by pressing with an interference fit of 0.01 x 0.03 mm.
Due to the low thickness of one coating layer, the use of elastomers is also effective for restoring fixed connections when the fit is loose, for example, between a bearing ring or sleeve and a housing.
When the mounting hole in the housing part wears out, the elastomer is applied to the surface of the outer ring of the bearing (cup) until the required fit in the connection is obtained.
Often, the seating surfaces in the housings are restored by gluing in bushings made with the required precision using epoxy compound A. In this case, subsequent mechanical processing is not required. The mounting holes are also restored using polymeric materials and rolled bushings. The sleeve is glued into the hole to be restored and, after partial curing of the polymer material, it is rolled out to the required size.
To fix the bearing rings in the housing or on the shaft using anaerobic sealants, the prepared surfaces of the mating parts are covered with a layer of sealant of equal thickness. To increase the accuracy of the restored connection, the mating parts are centered relative to each other using a special device and kept in it at room temperature until the anaerobic material acquires strength to ensure that the relative position of the mating parts is maintained outside this device. Depending on the brand, the sealant acquires full strength after 3 x 24 hours. The brand of sealant is selected depending on the gap in the connection. For example, the maximum gap in the connection when using AN-1 sealant is 0.07 mm, and AN-6 sealant 0.7 mm. As the thickness of the sealant layer increases, the durability of the connection decreases. To increase strength and expand technological capabilities, fillers are introduced into sealants.
For restoration of threaded surfaces and connectionsEpoxy compounds, metal polymers and sealants are used.
The technology for restoring threaded surfaces by cold welding using metal polymers is simple and low in labor intensity. The threaded surface of the reference bolt is moistened with a special release liquid (a two percent solution of poly-isobutylene in gasoline) and coated with a metal polymer, for example, a repair composite material. The bolt is then screwed into the cleaned and degreased threaded hole being restored. Thanks to the release liquid, the metal polymer adheres only to the material of the part being restored. After the metal polymer has hardened, the bolt is unscrewed from the hole. High quality restoration of threaded surfaces is possible only with the correct choice of polymer material based on its properties and operating conditions of the threaded connection.
Severely worn threaded holes in body parts are often restored by installing screws, for more reliable fastening of which epoxy composition A is used in the part.
If there is slight wear, the threaded connection is restored by applying an epoxy compound to the prepared threaded surfaces of both parts of the connection. For wear of up to 0.3 mm, use composition E or an anaerobic sealant, and for wear of more than 0.3 mm, use compositions B or C, depending on the material of the part. To lock threaded connections, anaerobic sealant or composition E is used. The effectiveness of using these materials depends on compliance with their curing regime and the requirements for surface preparation.
Restoration of parts by pressing
Pressing is used to repair parts using plastic. The part to be restored is placed in a mold, the working cavity of which has the dimensions of the new part, and plastic is fed into it. For thermosetting plastics, compression molding is used, and for thermoplastic plastics, injection molding is used.
At compression pressingthe restored part 7 (Fig. 4.67) is installed, based on element 6, in the lower part 5 of the mold on support 9. The upper part 3 of the mold is installed on the lower part and thermosetting powder is poured through hole 2, which is melted by heating device 4.
Rice. 4.67. Compression pressing scheme: 1 punch; 2 loading opening; 3 upper part of the mold; 4 heating device; 5 lower part of the mold; 6 base element; 7 detail; 8 ejector; 9 support; 10 layer of plastic
Under the influence of pressure created by punch 1, the powder melt fills the free cavities in the mold, resulting in a plastic layer 10 being created on part 7. After cooling, the part is removed from the mold by ejector 8.
At injection moldingThe thermoplastic polymer material is melted in an injection molding machine and fed under pressure through sprue 1 (Fig. 4.68) into a mold, between the upper 2 and lower 3 parts of which the restored part 4 is preliminarily installed. Before filling the mold with polymer material, it is heated to a temperature of 80 100 °C. As a result of filling the free space in the mold with polymer material, it forms a layer 10 of the required thickness on the part 4. Pressing can be used to restore bearing shells, water pump impellers, etc.
Features of mechanical processing of polymer coatings
Features of mechanical processing of polymer coatings are determined by their properties. Due to the abrasive effect of fillers, wear on cutting tools when processing polymer materials can be greater than when processing metals. The low thermal conductivity of the polymer material causes more intense heat removal from the cutting zone through the cutting tool, which requires its reliable cooling. To cool the tool and simultaneously remove chips, it is recommended to use compressed air rather than cutting fluid. To avoid chipping of the coating under the influence of cutting forces, it is necessary to use sharply sharpened tools. The diameter of the drill should be chosen 0.5 x 0.15 mm larger than the diameter of the hole indicated in the drawing, since the diameter of the hole drilled in the polymer is usually reduced.
Polymer grinding is performed with abrasive wheels at a cutting speed of 30×40 m/s. For processing thermoplastics, it is recommended to use not solid abrasive material, but circles made from thick linen, cloth and flannel circles. The diameter of the circles is 300 x 500 mm, thickness is 80 x 90 mm. They are impregnated with an abrasive paste of finely ground pumice with water. Grinding should be carried out with light pressure on the wheel to the surface to be processed to prevent heating of the coating.
For grinding thermosetting materials, white electrocorundum with a grit size of 46 and a hardness of SM-1 is used. Cutting depth up to 0.5 mm, workpiece movement speed 0.5 m/min, cutting speed 35 m/s.
When using polymer materials, especially epoxy compositions and synthetic adhesives, it is necessary to strictly observe safety precautions, since many of the components included in their composition are toxic and flammable.
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1. Literature review on the topic “Polymer materials for agricultural partsagricultural equipment" 2
2. Review of patent research on the topic: “Compositions and technology of polymer parts used in automotiveand agricultural machinery" 15
3. Experimental and technological part: “Development of technological equipment and technology for manufacturing polymer parts for agricultural equipmentnatural equipment" 21
Literature 29
1. Literature review on the topic “Polymer materials for parts of agricultural equipment”
Natural polymers, mainly of plant origin (wood, rubber, flax, jute fibers, resins, etc.) have been used by humans since ancient times. However, only in the 20th century, thanks to the development, first of all, of chemistry, physics, and materials processing technology, new artificial (synthetic) polymer materials were created, the fundamental issues of deep transformation of the structure of natural polymers were resolved, and as a result, a huge number of unique materials were created. A new vast field of materials science has been created - the science of the structure, properties and technology of polymers and plastics.
The term “polymer materials” is a general term. It unites three broad groups of synthetic materials, namely: polymers, plastics and their morphological variety - polymer composite materials (PCMs) or, as they are also called, reinforced plastics. What is common to the listed groups is that their obligatory part is the polymer component, which determines the basic thermal deformation and technological properties of the material. The polymer component is an organic high-molecular substance obtained as a result of a chemical reaction between the molecules of the original low-molecular substances - monomers.
Polymers are usually called high-molecular substances (homopolymers) with additives introduced into them, namely stabilizers, inhibitors, plasticizers, lubricants, antirads, etc. Physically, polymers are homophasic materials. They retain all the physical and chemical properties inherent in homopolymers.
Plastics are polymer-based composite materials containing dispersed or short-fiber fillers, pigments and other bulk components. Fillers do not form a continuous phase. They (dispersed medium) are located in a polymer matrix (dispersed medium). Physically, plastics are heterophase isotropic materials with physical macroproperties identical in all directions.
Polymer reinforced materials are a type of plastic. They differ in that they use not dispersed, but reinforcing, that is, reinforcing fillers (fibers, fabrics, tapes, felt, single crystals), which form an independent continuous phase in the PCM. Certain varieties of such PCMs are called laminated plastics. This morphology makes it possible to obtain plastics with very high deformation-strength, fatigue, electrical, acoustic and other target characteristics that meet the highest modern requirements.
Synthetic or natural high-molecular compounds are used as binders in the production of polymer materials, including synthetic resins, high-molecular compounds or products of their processing, for example, cellulose ethers, bitumens, etc.
Resins used for the manufacture of plastics can be thermosetting or thermoplastic, which determines their main technological and operational properties.
Many plastics (mostly thermoplastics) consist of a single binder. Such materials include polyethylene, polystyrene, polyamides, organic glass, nylon, etc. A feature of thermoplastic materials is their ability to soften when heated and harden again when cooled. Moreover, these processes are reversible and occur the same way with each heating and cooling cycle. The structure of the material does not change, and no chemical reactions occur in it.
Thermoplastic materials are characterized by low density, good formability, and resistance to fuels and lubricants. Polyethylene has a heat resistance of up to 50°C, frost resistance of up to -70°C, and is chemically resistant, but is susceptible to aging. It is used for the manufacture of films, pipes, containers, and household items. Polypropylene has higher strength properties, but has lower frost resistance (down to minus 20?). Areas of application close to polyethylene. Polystyrene is a hard, transparent, compact material. Used for the manufacture of parts of devices and machines (handles, housings, pipes, etc.). Polyurethanes and polyamides: nylon, nylon are used for the manufacture of high-strength threads and films. Plexiglas are transparent solids used in aircraft, automotive, and instrument making.
Thermoplastics also include fluoroplastic - unique materials with a very low coefficient of friction. They are used for valves, taps, pumps, bushings, gaskets, etc.).
When heated, thermosetting materials soften only in the initial period of time, and then harden at the heating temperature due to the occurrence of irreversible chemical reactions in their structure, as a result of which such material remains hard and does not soften upon repeated heating to sufficiently high temperatures. Representatives of thermosetting materials are phenol-formaldehyde, glyphthalic, epoxy resins, unsaturated polyesters, etc. The nature of the chemical reactions leading to irreversible hardening can be of a different nature. It can be stimulated by the addition of special substances - hardeners - to the resins, or it can occur only due to thermal activation - when heated. However, in both cases, a feature of thermosetting plastics is the irreversible nature of the change in the basic properties of the material.
The basis of thermosetting plastics are thermosetting polymers. Various inorganic materials are used as fillers. Depending on the type of filler, such materials are divided into powder, fibrous and layered. Powder materials use wood or cellulose flour, ground quartz, talc, cement, graphite, etc. as fillers. Such plastics have uniform properties in all directions and are well pressed. Disadvantage - low resistance to shock loads. They are used for the manufacture of body parts of devices, technological equipment in foundries (models) or lightly loaded parts of dies. Fiber plastics (fibers) have high strength properties, especially glass fibers, since, in essence, they are composite materials and take advantage of the properties of both the base and the fibers used to create these materials. Laminated plastics, like fiberglass, are composite materials. They are characterized by the highest strength and, at the same time, plastic properties. There are textolites (filler - cotton fabric), getinax (filler - paper), laminated plastics (wood veneer), fiberglass (fiberglass fabric). Textolite has increased wear resistance. Can be used to make gears, cams, bearings and other heavily loaded parts.
These materials contain much to make a person’s life and the world around him more beautiful, comfortable, and prosperous. Polymer materials are lightweight (5-7 times lighter than metals and alloys). Calculations have established that replacing a number of metal parts of a passenger car with carbon fiber reinforced epoxy resin reinforced with carbon fibers will reduce the weight of the car by 40%; it will become more durable; Fuel consumption will decrease and corrosion resistance will sharply increase. They can be easily painted in a variety of colors, they can be shiny or matte, transparent or translucent, or fluorescent. These materials do not break down in aggressive environments in which metal products are subject to intense corrosion. Organic polymers are fabric equivalent, i.e. in their chemical structure they are close to human skin, hair, and muscle tissue, which allows them to be used in reconstructive surgery and allows you to create interiors in which a person feels as comfortable as possible.
Polymer materials are easily processed and therefore, products of the most bizarre shapes can be created from them without much expense. Thanks to the development of polymer materials science, new technologies have been developed: gluing, sealing products, etc. Finally, only polymers have high elasticity - the ability to large reversible deformations, most clearly manifested in rubbers.
Polymer materials are being introduced into life very clearly, making it possible to solve not only technical issues, but also aesthetic problems. Today we can talk about the existence of certain principles, proven provisions that must be taken into account when artistic designing and creating plastic products.
When using polymers, it is possible to directly, simply and effectively solve both aesthetic and functional problems. An example would be the evolution of bottles in perfumery or containers in medicine, where they simultaneously become atomizers or droppers, etc.
The following can also be added to the main advantages of polymer materials:
a) high manufacturability, thanks to which labor-intensive and expensive operations of mechanical processing of products can be eliminated from the production cycle;
b) minimum energy intensity, due to the fact that the processing temperatures of these materials are, as a rule, 150-250 ° C, which is significantly lower than that of metals and ceramics;
c) the ability to produce several products at once, including complex configurations, in one molding cycle, and in the production of molded products to conduct the process at high speeds;
d) almost all processes for processing polymer materials are automated, which can significantly reduce wage costs and improve the quality of products.
However, polymer materials also have some disadvantages that must be taken into account when producing polymer products.
Polymers are dielectrics and accumulate static electricity. If a plastic product is large in size, it can actively attract dust, dirt, and be discharged onto a person when touched. We have to solve the problems of removing static electricity.
When making plastic products, deep textured relief is not allowed, since dirt accumulates in these places and it may be impossible to wash it off.
The polymer product should not have sharp corners, edges, or narrow crevices; the choice of material must be made taking into account the conditions of processing technology and operation. Thus, polymers and plastics are materials with specific properties and capabilities, primarily because they have an unusual chemical composition and structure.
Equipment for processing plastics is used to convert the original polymer material into products with predetermined performance characteristics. The design and manufacture of machines and units for plastic processing is carried out at enterprises in various branches of mechanical engineering.
Most methods for processing plastics involve the use of molding processes for products from polymers that are in a viscous-flowing state - injection molding, pressing, extrusion, etc. Some processes are based on the material achieving a highly elastic state at the time of molding - pneumatic vacuum molding. The industry uses methods of molding from polymer solutions and dispersions.
Processing of polymer materials includes three main groups of processes: preparatory, forming and finishing.
Preparatory cycle processes are necessary to improve the technological properties of processed raw materials, as well as to obtain semi-finished products and blanks used in the main processing methods. Such processes include grinding, granulating, drying, tabletting, and preheating.
Forming processes are the processing processes by which plastic products are manufactured. Two groups of these processes can be distinguished: continuous (extrusion, calendering) and periodic (injection molding, vacuum pneumatic molding, blow molding, spraying, pressing and a number of others). The production of fiberglass products is carried out using methods that vary in hardware and technological design. The technological process for manufacturing fiberglass products consists of the following operations: preparing the binder and filler, combining the binder and filler, and molding the product.
Finishing processes are designed to give finished products a certain appearance and create a permanent connection of individual elements of a plastic product. These include the processes of mechanical processing of manufactured products, painting and metallization of their surfaces, welding and gluing of individual parts.
Recently, polymer materials have been actively used both for the manufacture and restoration of parts for agricultural equipment. In repair practice, plastics are applied to the surfaces of parts to restore their dimensions, increase wear resistance and improve sealing. At the same time, the plastic coating reduces friction noise and increases the corrosion resistance of the product. A thin layer of plastic practically does not deteriorate the strength properties of the metal and makes the part pliable, i.e. the ability to take the shape of the mating part, which leads to a sharp increase in the contact area. Plastics are applied by injection molding, hot pressing, vortex, flame and centrifugal methods.
Repairing agricultural machinery using polymer materials, compared to other methods, makes it possible to restore parts with high quality and reduce:
labor intensity - by 20-30%;
material costs - by 40-50%;
cost of work - by 15-20%.
When restoring parts, the most widely used are acrylic and polyamide plastics, textolite, and wood-laminated plastics. Textolite and wood-laminated plastics are used to restore worn surfaces of machine guides, manufacture gears, plain bearings, bushings and other parts with rubbing working surfaces.
In repairs, acrylic plastics are widely used, containing acrylic resins as binding materials - products of the polymerization of methyl methacrylate and the copolymerization of methyl methacrylate with styrene. These include: actylate ATS-1, butacryl, epoxy-acrylic plastics SKHE-2 and SKHE-3.
These thermoplastic, rapid-curing, cold-curing plastics are produced by mixing powder and liquid. The prepared mass, which has the consistency of sour cream, hardens without heating or pressure.
Such plastics are used when restoring worn-out products as a wear compensator to restore broken dimensional chains of machine tools and machines. Plastics are used to restore: circular guides of rotary machine beds, adjusting wedges and clamping bars of mechanisms of all types of equipment, including mechanical presses. They are also used to repair spindle bearings of turret heads of turret lathes; holes, bushings, seats of gears and pulleys; hydraulic pump parts; rocker mechanisms and other parts of metal-cutting equipment. The plastic solution is also used for gluing materials.
The hardened plastic is wear-resistant, works well in combination with cast iron, steel, bronze, the coefficient of friction in the absence of lubricant is 0.20-0.18, and when the required amount of antifriction additives is introduced into the composition, it decreases to 0.143. Plastics with such additives can work without lubrication.
Hardened plastic is resistant to alkalis of any concentration, gasoline, turpentine, fresh and sea water, mineral and vegetable oils. The plastic layer can be removed by heating to 150-200C and further burning or cutting.
The viscosity of plastics varies depending on their purpose. To do this, powdered, fibrous and layered fillers from metallic and non-metallic materials are introduced into the plastic solution.
To increase performance properties (reduce the coefficient of friction and increase wear resistance), graphite powder is introduced into the plastic (up to 10%, mass fraction).
In repair practice, nylon grades A and B have become widespread. This is a solid white material with a yellow tint, which has high strength, wear resistance, oil and gasoline resistance, as well as good anti-friction properties. The main disadvantages of nylon are low thermal conductivity, heat resistance and fatigue strength. The maximum permissible operating temperature of nylon coverings should not exceed plus 70-80°C and minus 20-30°C.
The surfaces of bushings, shafts, liners and other parts are repaired with a nylon coating.
Figure 1. Scheme of applying nylon to the worn surface of a part using injection molding: 1 - upper part of the mold; 2 - sprue channel; 3 - lower part of the mold; 4 - part being repaired; 5 - nylon layer
Repair of worn surfaces of parts using nylon is in most cases carried out by injection molding on special injection molding machines. The essence of the process is that a layer of nylon is applied under pressure to a specially prepared worn surface of the part. The worn part is installed in a mold (Fig. 1) and molten nylon is pumped under pressure into the gap formed between the part and the wall of the mold. Then the mold is opened, the part is removed, and the sprues and flash are removed from it. If necessary, the nylon covering is mechanically processed until the required dimensions are obtained. To improve quality, the finished part is thermally treated in an oil bath at a temperature of 185-190°C and kept at this temperature for 10-15 minutes.
When applying nylon, it is heated to 240--250°C and supplied under a pressure of 4-5 MPa (40-50 kgf/cm). The mold together with the part is preheated to a temperature of 80-100°C. The coating thickness is recommended from 0.5 to 5 mm. Injection molding is carried out using thermoplastic automatic machines, injection molding machines, etc. This method is technologically simple and does not require complex equipment and accessories.
Nylon (in the form of a powder 0.2-0.3 mm in size) can be sprayed onto the surface of the part. The essence of this method is that powdered nylon is applied to the prepared and heated surface of the part. When hitting a heated part, particles of powdered nylon melt, forming a plastic coating.
When repairing fixed joints of rolling bearings, GEN-150V elastomer and 6F sealant are often used. The first consists of SKP-40S nitrile rubber and VGU resin. The second is a product of a combination of butadiene rubber SKP-40 with PKU resin based on substituted phenolavinyl acetate resin. Before applying the coating, the surfaces of the parts are mechanically cleaned and degreased.
The coating is applied in different ways: by pouring, brushing, or centrifugally, depending on the design of the parts and the means of application. Heat treatment of the coating from the GEN-150V solution is carried out at a temperature of 115? for 40 minutes, from a solution of 6F sealant - at a temperature of 150 ... 160? within three hours. The durability of fixed connections depends on the speed of operation. The main reason for the operation of seats without a polymer coating is fretting corrosion. The nature of wear changes significantly according to the fit of bearings coated with a 6F sealant solution. The polymer coating completely prevents metal contact and the development of fretting corrosion, and this significantly reduces the rate of loss of functionality of the seats, especially in body parts.
Adhesive compositions based on epoxy resin are important for restoring the functionality of cast iron body parts with cracks. The main binding component of these compositions is epoxy resin grade ED-6 or ED-5. The most commonly used resin is ED-6. It is a transparent viscous mass of light brown color. To prepare a composition based on ED-6 resin, 10-15 parts of dibutyl phthalate (plasticizer), up to 160 parts of filler and 7-8 parts of polyethylene polyamine (hardener) are added per 100 parts (by weight) of resin. The filler used is: iron powder (160 parts), aluminum powder (25 parts), grade 500 cement (120 parts). The epoxy resin is heated in a container to a temperature of 60-80°C, a plasticizer is added, then a filler. The hardener is introduced immediately before use, since after this the composition must be used within 20-30 minutes. Compositions based on epoxy resins are used for repairing parts operating at temperatures from -70 to +120°C. They are used to seal cracks and holes in body parts, to restore fixed fits and threaded connections.
When sealing cracks, their boundaries are determined and the surfaces are prepared. The boundaries of the crack are usually drilled with a drill with a diameter of 2-3 mm and chamfered at an angle of 60-70° to a depth of 2-3 mm along the crack along its entire length (Fig. 2, a). The surface is cleaned at a distance of 40-50 mm on both sides of the crack to a metallic shine and notches are made. Then degrease with acetone.
The patch is cut out of fiberglass of such a size that it covers the crack by 20-25 mm. A composition based on epoxy resins is prepared immediately before its use and applied with a brush or spatula to a surface with a thickness of about 0.1-0.2 mm (Fig. 2, b). After this, a patch is applied and rolled with a roller (Fig. 2, c).
Figure 2. Scheme of sealing cracks: a - surface preparation; b - filling with epoxy resin composition; c - rolling the lining with a roller; 1 - composition layer; 2 - overlay; 3 - roller
A layer of glue is again applied to the surface of this overlay, and then another one is placed, which overlaps the previous one by 10-15 mm, rolled with a roller and another layer of adhesive coating is applied. For curing, adhesive coatings are kept for 72 hours at a temperature of 20 °C, or 3 hours at a temperature of 100 °C. During operation, the body parts are subject to significant alternating mechanical and temperature loads, which lead to peeling of the coating and loss of the required tightness by the parts. To avoid unwanted delamination, metal plates are used and secured with bolts.
Adhesive materials not only provide the ability to firmly connect parts made of different materials, but also seal gaps and cracks; seal lights, windows, hoses and pipes; isolate electrical contacts; eliminate vibration and noise; used for the manufacture of seals and gaskets of any shape.
Glue welding of large-sized thin-walled structures shows good quality indicators. This area is completely new for Russia and all CIS countries. The fact is that thin-walled structures and body panels of agricultural vehicles, after resistance spot welding, are still sealed using various mastics, primers and plastisols. This is a rather labor-intensive operation, and in the case of gaps larger than 0.5 mm, it is usually not possible to achieve high-quality sealing. Glue-welding technology not only ensures good sealing of the weld, but also increases the strength of the joint by 1.5 times.
The connection is made in this way: a layer of glue is applied to the surfaces to be connected, then they are placed one on top of the other and spot welded. The adhesive layer absorbs most of the load, and thanks to this, the weld point is unloaded, its performance improves, which significantly increases the fatigue strength and rigidity of the joint. As a result, the number of welding points can be reduced by 30-50 pieces. and accordingly reduce labor and energy costs for welding work.
The adhesive materials used in this technology are paste-like one- or two-component compositions. Moreover, one-component ones cure at 410-430K (140-160?), which in some cases makes it possible to combine the drying of the glue with the drying of the paint and varnish coating applied to the finished product. It is also important that glue welding does not require preliminary cleaning of the surfaces to be joined. Finally, glue-welded assembly technology also solves the issues of corrosion protection of the weld.
2. Review of patent research on the topic: “Compositions and technology of polymer parts used in automotive and agricultural machinery”
A review of patent research was carried out at a depth of 14 years (1998-2012), 8 patents were discovered on this topic:
Patent for invention No. 94903 (patent start date April 22, 2009) describes a useful model of an injection mold, which relates to foundry production of products, mainly from thermoplastic polymer, by injection molding, mainly thick-walled products. The technical solution of the invention can also apply to the production of products from other materials.
The purpose of the utility model is to increase the efficiency of using a mold for injection molding. The problem is solved by the fact that the mold for injection molding contains detachable parts 1 and 2, in one of which there is a forming cavity 4 and an ejector 5 is located, and in the other there is a nozzle 9. It has distinctive features: the forming cavity 4 is made with variable volume using a movable sign in the form of a piston 6, which is also an ejector. At least one forming mark 7 can be passed through the piston 6.
It is also possible to make the shape of the surface of the piston 6 and the mating surface of the forming cavity 4 different from cylindrical.
The patent for invention No. 2312766 (patent start date 01/30/2006) describes a method for manufacturing a mold insert, in particular for the manufacture of mold inserts for producing angle-type products, and can be used in their production, both by pressing and and injection molding. The technical result of the claimed invention is the creation of a method for manufacturing mold liners, which makes it possible to increase productivity, quality and manufacturing accuracy, and also allows you to vary the shape and size of the working part of the liner. The technical result is achieved by a method for manufacturing a mold liner, in which the body of the liner is made longitudinally split. The barrel-shaped working surface of its parts - half-liners - is performed by turning from one workpiece on a mandrel specially designed for this purpose. The parameters of the barrel-shaped surface are selected based on the following conditions: the height of the barrel is equal to the diameter of the liner, the radius of the generatrix of the barrel is equal to half the diameter of the liner, the radius of the equator of the barrel is greater than or equal to the radius of the generatrix of the barrel, but less than or equal to the diameter of the liner.
Patent for invention No. 2446187 (patent start date 06/17/2010) describes a method for producing a polymer nanocomposite, which involves mixing a thermoplastic with a filler - detonation synthesis nanodiamond (DND) in a thermoplastic melt in the elastic instability mode. To do this, choose a temperature and shear stress that ensure a Weissenberg number of at least 10. The ratio of components is as follows, wt.%: thermoplastic - 95-99.5, DND - 0.5-5. The invention makes it possible to obtain a polymer nanocomposite with increased elastic modulus, hardness, impact strength, and tensile strength. Such materials can be used for the manufacture of housings, polymer friction pairs (gears, bearings, etc.), as well as in the aerospace industry, as they have increased mechanical properties and resistance to aggressive environments.
Invention patent No. 2469860 (patent start date July 17, 2009) describes a device for producing three-dimensional objects by solidifying powder or liquid material. The replaceable frame of the device for manufacturing a three-dimensional object (3) contains a frame (1) and a platform (2) located in the frame (1) with the possibility of vertical movement, while the frame (1) and the platform (2) form the working space of the said device. The replacement frame is configured to be inserted into and removed from said device, wherein said device is designed to produce a three-dimensional object (3) by solidifying a powder or liquid material (3a) intended for producing said object (3) layer by layer at locations in each layer corresponding to the cross section of the object to be manufactured (3). On the inner side facing the workspace, the frame (1) contains glass-ceramic plates (13). The technical result consists in ensuring the heating of the working space to high temperatures due to the small coefficient of thermal expansion of glass-ceramic plates.
Patent for invention No. 2470963 (patent start date 06/12/2009) describes reactor thermoplastic polyolefins with high fluidity and excellent surface quality, which include (A) a matrix of propylene homo- or copolymer, the mass fraction of which is from 40 to 90% with ISO 1133 MFR index (230°C, 2.16 kg rated load)? 200 g/10 min, and (B) an elastomeric copolymer of ethylene and propylene, the mass fraction of which is from 2 to 30%, with an intrinsic viscosity IV (according to ISO 1628 in decalin as a solvent)? 2.8 dl/g with an ethylene mass fraction of more than 50 and up to 80% and (C) elastomeric copolymer of ethylene and propylene, the mass fraction of which is from 8 to 30%, with intrinsic viscosity IV (according to ISO 1628 in decalin as a solvent) from 3.0 to 6.5 dl/g and with a mass content of propylene from 50 to 80%. Reactor thermoplastic polyolefins are produced in a multi-stage polymerization process involving at least 3 sequential stages, in the presence of a catalyst system including (i) a Ziegler-Natta procatalyst, which includes a lower alcohol transesterification product and a phthalic acid ester, (ii) ) an organometallic cocatalyst, and (iii) an external donor represented by formula (I), Si(OCH2CH3)3(NR lR2), where the values of R1 and R2 are specified in the claims. Also disclosed is a multi-stage process for the production of these polyolefins, comprising either a combination of one loop and two or three gas phase reactors, or a combination of two loop and two gas phase reactors connected in series. The polyolefins of the invention are used to produce injection molded products for the automotive industry. The invention also relates to molded articles obtained from reactor thermoplastic polyolefins. Polyolefins can be used to injection mold large profiles that do not exhibit ripples and exhibit both a good toughness/stiffness balance and good flow.
Patent for invention No. 2471811 (patent start date 10/02/2008) describes a method for producing propylene polymers. The resulting propylene polymer has a melt flow rate (230°C, 2.16 kg) above 30 g/10 min. The method is carried out in the presence of a catalyst system comprising (A) a solid catalyst component containing Mg, Ti, a halogen and an electron-donating compound selected from succinates; (B) an aluminum alkyla cocatalyst; and (C) a silicon compound of formula R1Si(OR)3 in which R1 is branched alkyl and R is independently C1-C10 alkyl. A method for producing propylene polymer compositions and heterophasic compositions is also described. The technical result is the production of propylene polymers that simultaneously have a wide molecular weight distribution and a high melt flow rate.
Patent for invention No. 2471817 (patent start date January 10, 2012) describes a method for producing polyamide-6 by emulsion polymerization of caprolactam. The method includes preparing a reaction mass from caprolactam, water as an initiator and polyethylsiloxane liquid, heating it, preliminary holding, main holding at 210-215°C, cooling and separating the resulting granules, wherein the reaction mass is first prepared from caprolactam and water, heated to 210-215°C, preliminary exposure is carried out at 210-215°C for 6-7 hours, and polyethylsiloxane liquid, preheated to 210-215°C, is introduced into the reaction mass before the main exposure, which is carried out for 5-15 hours. The technical result is to improve the quality of the target product and reduce energy costs.
Patent for invention No. 2471832 (patent start date November 5, 2007) describes a method for producing a polyamide fire-resistant composition, in particular suitable for the production of molded products. The polyamide-based composition contains melamine cyanurate and novolac. The composition is suitable for the production of molded products with high dimensional stability and used in electrical or electronic connection technology, such as breakers, switches, connecting devices.
The Applicant has discovered that a polyamide composition with low novolac content and relatively low content of melamine cyanurate, a melamine derivative, provides optimal results in the areas of fire resistance and water reabsorption. Contrary to what was known to date, novolac does not change the flame retardant properties of the polyamide composition containing a melamine derivative.
Additionally, in a polyamide composition, novolac and melamine cyanurate act synergistically, although the two compounds used as a flame retardant agent typically act differently. In fact, novolac is known as an agent involved in the formation of a carbon layer that insulates the polyamide matrix from the flame. Melamine cyanurate, on the other hand, is known for its effect on the controlled breaking of polyamide bonds, causing the formation of droplets of molten polyamide, thus preventing the spread of fire.
3. Experimental and technological part: “Development of technological equipment and technology for manufacturing polymer parts for completing agricultural equipment.”
The development of technological equipment begins with studying the initial data for a specific polymer product. Input data includes the following:
drawing of the product indicating the location of the inlet sprue channel, traces of the connector of forming parts, ejectors, etc.;
type of production (mass, serial, etc.);
annual product production program in units;
product service life;
mechanical loads;
equipment that can be used to manufacture the product (presses, thermo- or thermoset machines, high-frequency generators, thermostats, etc.);
equipment technical characteristics data not contained in catalogs (use of non-standard nozzles, adapter plates, pedestals, etc.);
auxiliary equipment and devices (pullers of cassettes, products, loading devices, devices for screwing up products or signs, etc.) and their passport data.
Figure 3. Tension roller K 02.001
The tension roller part K 02.001 (Fig. 3) is an element of the tensioner KM 15.010 for chain drives in the KTN-2VM, KST-1.4, KST-1.4M potato diggers and in the KL-1.4 and PL-1 onion diggers manufactured at JSC "Agropromselmash" Type of production - small-scale, annual product production program - 4600 - 5000 pcs. in year. The service life of the product is 5 years. The operating mode of the polymer section of the enterprise is one-shift. Mechanical load is dry friction, since it is advisable not to use lubricants, due to the fact that harvesting machines operate in conditions of sand dust, which, settling on the lubricant, will accelerate wear. The part has relatively small dimensions: the largest diameter is 65 mm, height is 48 mm, weight is 0.112 kg.
Figure 4. Tension sprocket KM 15.040
Currently, instead of the tension roller K 02.001, the tension sprocket KM 15.040 is used (Fig. 4), which is an assembly unit consisting of two parts:
sprocket crown K 07.604, workpiece material - circle? 120 mm steel 45, weight 0.5 kg;
hub KM 15.010.611, workpiece material - circle? 56 mm st 3, weight 0.28 kg.
Manufacturing the tension sprocket KM 15.040 is a rather labor-intensive technological process. Both the hub and the crown first undergo a procurement operation, which consists of cutting the blanks on saws. Next comes primary turning. After this, teeth are cut on the crown and it is subjected to heat treatment. Next, the crown of the sprocket is welded together with the hub into a single whole, and then comes the finishing turning operation, where the seat for the bearing is bored.
To manufacture the tension roller K 02.001, you will need an injection mold with a connector in two planes, but given the small-scale production, the manufacture of such a mold will be impractical. Therefore, after analyzing the technical documentation of JSC Agropromselmash, I came to the conclusion that it would be more expedient to make the roller smooth, so after turning we can get both the tension roller K 02.001 and the roller KB 08.050.001. The roller KB 08.050.001 was purchased, since in 2012, in our production, the Lidchanin-1 potato harvester was developed and put into production, where it goes to the bulkhead table in the amount of 156 pieces. But given the small production of combines, about 20 units. per year, it was decided to develop an injection mold for the production of a smooth roller K 00.001 and a technology for the production of a tension roller K 02.001 and a roller KB 08.050.001.
When choosing a material, the main priority is anti-friction properties and impact resistance, so I choose Grodnamid anti-friction PA6-LTA-SV30.
There are a large number of computer programs for modeling parts, finished products, and technological equipment for their production: AutoCAD, Solid Works, Compass 3-d and others. Since this part is small in size and does not require special manufacturing precision, we choose an inexpensive product. This is a three-dimensional modeling computer program from the Russian company Askon: KOMPAS-3D V12. The main methodological source is the “Handbook for the design of equipment for plastic processing” edited by A. P. Panteleev, Yu. M. Shevtsov and I. A. Goryachev.
According to the product drawing, we draw a 3-d model and find out the mass-center characteristics of the part:
Mass M = 137.46 g;
Area S = 195.8 cm2;
Volume V = 134.774 cm3.
According to Panteleev’s reference book, the injection molding machine D 3134 - 500P with an injection volume of 500 cm3, KuASY (Table 6, p. 22), is suitable for the manufacture of this product, which we select, since it is available at the enterprise.
We calculate the number of castings and the required clamping forces based on the technical parameters of the injection molding machine using reference literature data (Table 6, page 22).
Number of castings (formula 7, p. 66):
no = В1Qн /Qиk1 = 0.7 500/134.774 1.02 = 2.546,
where b1 = 0.7 is the machine utilization factor; Qн = 500 cm3 - nominal volume of the machine; Qi = 134.774 cm3 - volume of one product; k1 = 1.02 - coefficient taking into account the volume of the gating system per product.
Required clamping force (formula 5, page 65):
Po = 0.1 q Fpr no k2 k3 = 0.1 32 97.9 2 1.1 1.25 = 861.52 kN?2500 kN,
where q = 32 MPa is the pressure of the plastic in the forming socket; Fpr = 97.9 cm2 - area of projection of the product onto the mold parting plane; no = 2 - number of products in the mold; k2 = 1.1 - coefficient taking into account the area of the gating system in plan; k3 = 1.25 - coefficient that takes into account the use of the maximum clamping force of the slabs by 80 - 90%.
Based on the calculations obtained, it can be seen that on an injection molding machine D 3134 - 500P with an injection volume of 500 cm3, it is possible to cast 2 products simultaneously. This is possible based on the injection volume and the required clamping force.
When starting to develop a mold, first of all it is necessary to correctly position the product in it, while choosing the optimal number of products to be cast. To do this, one should take into account the specific production conditions (including instrumental production), the product production plan, the required degree of mechanization and automation of the mold,
Basic requirements for the position of the product:
the plan projection of a product or group of products should be located symmetrically relative to the axis of the press connector (injection molding machine);
It is necessary to orient the product in such a way that during casting, after the mold is separated, it remains in its movable part;
The final choice of product location must be linked to the location of the gating system inlet, the cooling system and the presentation of the product.
Figure 5. Layout of parts in the mold.
Based on the calculations obtained, we draw the layout of the products in the mold (Fig. 5). After selecting the layout of the product in the injection mold, we begin to design the elements of the injection mold in the Compass 3-d software. From the reference literature (Table 7, p. 24) we select the connecting dimensions of the installation elements of the injection molding machine, the stroke length of the movable plate, as well as the maximum dimensions of the injection mold. We choose 45 steel as the material for the semi-matrices and sign plates, assign heat treatment - hardening, followed by tempering. For the remaining plates (top and bottom, backing plate, pusher plates) we choose material St 3. Columns, sprue and guide bushings, ejectors are made of U8 steel with subsequent heat treatment.
First, we draw the upper and lower half-matrices, placing the products in them according to the chosen scheme. The thickness of the semi-matrices is tentatively assumed to be 50 mm, based on the fact that the minimum size of the assembled mold should be 250 mm. We also preliminarily assume that the upper and lower plates will be 30 mm each.
The approximate stroke of the moving part of the Lx mold can be determined using the formula for a part that requires the use of rod ejectors (page 325)
Lx = I + c = 48 + 60 = 108 mm< LM = 500 мм,
where I is the height of the part; c is a value that takes into account the height of the central sprue, the clearance required to remove the part, etc.; in molds with a rod and point-rod gating system, the value c is taken equal to 60 mm; LM = 500 mm -- stroke of the machine plate (given in the machine passport).
One of the main elements of the mold is the gating system, which is used to connect the cylinder to the mold and fill it.
d1 = dc +(0.4 - 0.6) = 4 +0.5 = 4.5 mm.
The optimal length L of the central sprue channel depends on its diameter d1 and is 20 - 40 mm. The central sprue channel must be made conical. The cone angle is determined by the shrinkage of the polymer and its adhesive properties. Recommended cone angle b = 3°. It should be noted that the radius of the sleeve sphere r must be made 1 mm larger than the radius of the machine nozzle sphere r1 for normal fit of the sleeve to the nozzle when closed. Directly behind the bushing, a special nest with a reverse cone is usually provided to catch the first cooled portion of the mass and hold the gating system in the movable part of the mold.
Distribution channels are located in both halves. The cross-sectional area of the distribution channel is determined by the empirical formula (p. 326):
Frk? = = 16.235 mm2,
where Fnp = 3.14 3.122 = 32.47 mm2 - the largest cross-sectional area of that part of the channel that precedes the calculated one; nрк = 2 -- number of branching distribution channels.
The most favorable cross-sectional shape of such channels is round, because they have the smallest contact surface of the mass with the channel walls, which ensures the least pressure and heat loss.
The cross-section of the inlet channel, depending on the gating system adopted, can be trapezoidal, round (point gates), or annular. The area of this section is determined by the formula (p. 328):
Fvk? = = 8.49 mm2,
where F0 = 3.14 2.33 = 16.98 mm2 -- cross-sectional area of the inlet of the main channel; nвк = 2 -- number of inlet channels.
The cross-sectional area of the ventilation ducts is determined by the following empirical formula:
F, = 0.05 V = 0.05 134.774 = 6.739 mm2,
where V = 134.774 cm3 - volume of the part without cavities, fittings; 0.05 is a coefficient having the dimension cm-1.
Ventilation ducts are made rectangular with a width smaller than the width of the inlet duct and a depth of 0.03 to 0.06 mm. Channels are made in the mold after testing it only when the cross-section of the gaps in the movable joints is less than the calculated value Fв.
Having simulated individual elements of the form using a computer program, we assemble them into a single whole, visually assessing discrepancies and gaps. As we assemble the modeled injection mold, we adjust the thickness of the slabs. The stroke length of the ejectors is determined by the selection method, while checking the consistency of the movement of individual elements. Based on the obtained 3-D models, design and technological documentation necessary for the manufacture of technological equipment is created.
Literature
polymer material automotive part
Doy M., Edwards S. - Dynamic theory of polymers. Per. from English - M.: “Mir”, 1998.
Kryzhanovsky V.K., Burlov V.V., Panimatchenko A.D., Kryzhanovskaya Yu.V., - Technical properties of polymer materials. - St. Petersburg. "Profession", 2005.
Mirzoev R.G., Kugushev I.D., Braginsky V.A. et al. - Fundamentals of design and calculation of plastic parts and technological equipment for their manufacture. - L. “Mechanical Engineering” 1972.
A.P. Panteleev, Yu.M. Shevtsov, I.A. Goryachev - Handbook for designing equipment for plastic processing. - M.: “Mechanical Engineering”. 1986
Tager A. A., - Physico-chemistry of polymers. - M. "Chemistry", 1968.
“Technical properties of polymer materials” Educational reference pos. VC. Kryzhanovsky, V.V. Burlov, A.D. Panimatchenko, Yu.V. Kryzhanovskaya.-St. Petersburg, Publishing House “Profession”, 2003.
“Design of injection molds in 130 examples.” Edited by Dipl.-Ing. E. Lindner, Ph.D. those. Sciences P. Unger. St. Petersburg 2006
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Manufacturing technology of candlestick parts and assemblies, choice of materials. Justification of the technology for manufacturing parts, selection of technological transitions and operations. The sequence of manufacturing an artistic product using pressure processing of parts.
course work, added 01/04/2016
Assessment of product manufacturability. Review of methods for manufacturing parts. Process route operations. Justification of the assortment of workpieces and the method of its production. Calculation of cutting conditions during turning. Development of technological equipment.
course work, added 01/12/2016
Technological map for making a pencil holder. Selection of material, technological route for processing parts at a minimum of reduced costs, equipment and technological equipment. Feasibility study of the product manufacturing process.
presentation, added 04/06/2011
Methodology for performing kinematic, force and strength calculations of units and parts of power equipment. Features of the choice of materials, type of heat treatment for components and parts of power plant equipment, as well as their support systems.
course work, added 12/14/2010
Determination of the labor intensity of work on the production of thin-sheet parts. Calculation of the number of personnel. Calculation of the amount of required technological equipment. Site layout. Development of a schedule for technological preparation of production.
course work, added 12/02/2009
Purpose and design features of the “gear” and “cover” parts. Selection and justification of methods for obtaining blanks; chemical, mechanical and technological properties of steel. Selection of equipment and accessories for casting parts; analytical calculation.
course work, added 09/18/2013
Calculation and development of the design of technological equipment for the manufacture of the Corrugation product. Calculation of nesting equipment. Design of form-building cavities. Calculation of shrinkage and final dimensions of forming parts. Thermal calculation of equipment.
course work, added 08/23/2014
Features of the technology for manufacturing standard structures using the example of a tank body. Studying the nature of connecting parts to each other, choosing a welding method and equipment. Methods of transportation, installation and fastening of parts, properties of materials.
Features of technological processes for the production of polymer materials depend on their composition and purpose. The main technological factors are certain temperature and power factors that form products, for which various equipment is used. Basically, production consists of the preparation, dosage and preparation of polymer compositions, which are then processed into products, and stabilization of their physical and mechanical properties, sizes and shapes is ensured.
Basic methods of plastic processing: rolling, calendering, extrusion, pressing, casting, coating, impregnation, pouring, spraying, welding, gluing, etc.
Mixing compositions is a process of increasing uniformity
the distribution of all ingredients throughout the volume of the polymer, sometimes with additional dispersion of particles. Mixing can be periodic or continuous. The design and nature of operation of mixers depend on the type of materials being mixed (loose or pasty).
Rolling is an operation in which plastic is molded in the gap between rotating rollers (Fig. 14.2). The processed mass 2 is passed several times through the gap between rollers 1 and 3, mixed evenly, then transferred to one roll and cut off with a knife 4. On continuous rollers, the mass is not only passed through the gap, but also moves along it, and at the end of the process is cut off with a knife in the form of a narrow continuous strip.
Rolling allows you to properly mix plastic components in order to obtain a homogeneous mass, while the polymer, as a rule, is transferred to a viscous-flowing state due to an increase in temperature during grinding. When the mass is repeatedly passed through rollers, plasticization occurs, i.e., the combination of the polymer with the plasticizer through accelerated mutual penetration. Rollers allow you to grind and crush plastic components. This is ensured by the fact that when moving in the gap, the materials are compressed, crushed and abraded, since the rolls can rotate at different peripheral speeds.
The rollers used for final surface finishing and calibration must have a smooth polished surface. According to the nature of their work, rollers can be periodic or continuous, and according to the method of temperature control - heated (steam or electricity) and cooled (water).
Calendering is the process of forming an endless tape of a given thickness and width from a softened polymer mixture, passed once through the gap between the rolls.
Calender designs vary mainly depending on the type of mass being processed - rubber compounds or thermoplastics. Calender rolls are made from high-quality die cast iron. The working surface of the roll is ground and polished to a mirror finish. The rolls are heated by steam through the internal central cavity and peripheral channels.
As a rule, calendering is performed in combination with rolling in one production line.
Extrusion is an operation in which plastic products are given a certain profile by pressing a heated mass through a mouthpiece (shaping hole). The extrusion method is used to produce profile (molded) building products, pipes, sheets, films, linoleum, foam insulation and many others. The cross-sectional dimensions of products manufactured by extrusion lie in a wide range: pipe diameter 05-250 mm, sheet and film width 0.3-1.5 m, thickness 0.1-4 mm. Extrusion machines are also used for mixing compositions and granulating plastics. Two types of extrusion machines are used: screw machines with one or more screws and syringe machines. The most widespread are screw, or worm, extruders (Fig. 14.4). The working part of the machine is a screw (worm), which mixes the mass and moves it through the profiling head (mandrel). The mass is fed into the machine in the form of granules, beads or powder. Softening of the material occurs due to the heat coming from heaters, which are installed in several zones.
Heating J
Rice. 14.4. Scheme of operation of the extrusion machine:
1 - loading hopper; 2 - auger; 3 - head; 4 - calibrating nozzle; 5 - pulling device; b - mandrel; 7 - filter
SHAPE * MERGEFORMAT
Rice. 14.5. Scheme of stamping (compression molding): a) loading of press material; 6) closing the mold and pressing; c) pushing out the product; 1 - press material; 2 - heated mold matrix; 3 - heated punch; 4 - press slider; 5 - electric heater; 6 - product; 7 - ejector
Pressing is a method of molding products in heated hydraulic presses. A distinction is made between molding in molds (Fig. 14.5) - in the manufacture of products from press powders, and flat pressing in multi-story presses - in the manufacture of sheet materials, slabs and panels. Pressing is used primarily in the processing of thermosetting polymer compositions (phenoplasts, aminoplasts, etc.).
For pressing building sheet materials and panels, multi-story hydraulic presses with a force of 10 to 50 tons, heated by heated water or steam, are used. Pressing on multi-story presses consists of the following operations:
loading the press, closing the plates, heat treatment under pressure, releasing pressure, unloading. The flat pressing method is used to form particle boards, paper laminates, tek-stolits, wood laminates, and three-layer glued panels. Molds are used to produce parts for sanitary and electrical equipment, parts for finishing built-in equipment, window and door fittings, parts for construction machines and mechanisms.
Foaming is a method of producing porous sound-insulating and elastic sealing plastics. The porous structure of plastics is obtained as a result of foaming of liquid or viscous compositions under the influence of gases released during the reaction between components or during the decomposition of special additives (porophores) from heating. Foaming of substances - foam stabilizers by injection or dissolution of gaseous and easily evaporating substances in the polymer.
Foaming can occur in a closed volume under pressure or without pressure, as well as in open forms or on the surface of a structure.
Coating is an operation in which a plastic mass in the form of a solution, dispersion or melt is applied to a base - paper, fabric, felt, leveled, decoratively processed and fixed. An example would be coated linoleum, pavinol, linkrust, etc. The applied mass is leveled with a special squeegee knife, which regulates the thickness of the layer and the degree of indentation. Typically the base moves but the screed blade does not move; Only its inclination and clearance are adjustable. The applied and leveled mass usually undergoes a heat treatment stage to soften it and better adhere it to the base.
Impregnation consists of dipping the base (fabric, paper, fibers) into an impregnating solution, followed by drying. This operation is carried out in vertical and horizontal impregnation machines. The impregnation method is used to produce adhesive films (bakelite), decorative films (urea-melamine), as well as panels based on glass, asbestos and cotton fabrics, from which textolites are subsequently obtained.
Casting is a process in which the plastic mass is spread in a thin layer on a metal belt or drum and, once hardened, is removed as a thin film. This process is often associated with the evaporation of solvents. In this way, for example, transparent cellulose acetate films are obtained.
Casting. There are two types of casting: simple in molds and under pressure. In simple casting, a liquid composition or melt is poured into molds and solidified as a result of polymerization reactions, polycondensation, or due to cooling. Examples include the casting of floor tiles from thermosets, the production of organic glass and decorative products from polymethyl methacrylate. By cooling the melt during simple casting, some simple products from polyamides (polycaprolactam) are obtained.
Injection molding is used in the manufacture of thermoplastic products. The polymer is heated to a viscous-flowing state in the heating cylinder of the injection molding machine (Fig. 14.6) and is injected with a plunger into a split mold cooled by water.
The pressure under which the melt is injected can reach 20 MPa. In this way, products are made from polystyrene, cellulose ethers, polyethylene, and polyamides. Injection molding is characterized by a fast cycle time, and in this type of processing operations are automated.
Molding refers to the processing of sheet, film, and tubular plastic blanks in order to give them a more complex shape and obtain finished products. Molding is carried out mainly by heating. The main methods of sheet molding include stamping, pneumatic molding and vacuum molding (Fig. 14.7).
Rice. 14.7. Vacuum forming scheme: a) negative form; b) positive form; c) preliminary drawing of the workpiece with a punch; d) preliminary pneumatic drawing of the workpiece; I-1II - molding positions; 1 - blank; 2 - negative form; 3 - stand; 4 - clamping frame; 5 - punch; 6 - positive form; 7 - forming chamber
When stamping, blanks are cut out of sheets, heated, placed in a mold between the matrix and the punch, and compressed under pressure up to 1 MPa. In this way, parts of sewer systems are made from vinyl plastic, light caps from plexiglass for coverings of industrial buildings, and profile parts from textols for building structures.
In pneumatic molding, the sheet is fixed along the contour of the matrix and heated until it slightly sag. Then, heated air, compressed to 7-8 MPa, presses the sheet to the surface of the matrix. A variation of this method is free blowing. In this way, light hoods, containers, rings made of polyacrylates, parts of ventilation systems and chemically resistant equipment made of polyvinyl chloride are produced.
In vacuum forming, a sheet is fixed along the contour of a hollow mold, heated, and a vacuum is created in the cavity. Under the influence of atmospheric pressure, the sheet is pressed against the surface of the mold. In this way, parts of sanitary equipment are made from impact-resistant polystyrene, polyacrylates, and vinyl polymers.
Spraying is a method of applying powdered polymers to a surface, which, when melted, stick to it, and when cooled, form a durable coating film. There are gas-flame, vortex and fluidized spraying. With gas flame spraying, polymer powder (polyethylene, polyamide, polyvinyl butyrol), passing through the flame, melts and, falling onto the surface in drops, sticks, forming a layer of the required thickness.
Welding and gluing are used to connect plastic workpieces to obtain products of a given shape. Welding is used to join thermoplastic plastics - polyethylene, polyvinyl chloride, polyisobutylene, etc. Based on the method of heating the joined ends, a distinction is made between air (heated air), high-frequency, ultrasonic, radiation, and contact welding.
Bonding is used to join both thermoplastic and thermoset plastics. In the simplest case, the adhesive for thermoplastic plastics can be an organic solvent, which causes the abutting ends of the parts to swell and stick together when compressed. More often, special adhesives are used. Depending on the production conditions and the required joining speed, cold- and hot-curing adhesives are used.
