Machine parts made of polymers. Methods and equipment for the production of polymer containers and packaging. The main fields of application of plastics in mechanical engineering

Mechanical engineering is one of the few basic sectors of the national economy that determines the development of the entire economy as a whole, as was specially emphasized at the XXVI Congress of the CPSU. Our party has always given priority attention to the development and improvement of mechanical engineering - from the five-year industrialization plan, even earlier, from the GOELRO plan to today... In all modern developed countries, the volume of mechanical engineering production is more than a quarter of the total volume of industrial production, fixed assets of mechanical engineering and metalworking - almost a quarter of all fixed assets; this industry employs between one third and one half of all industrial workers. And this is natural, a simple list of mechanical engineering subsectors convincingly confirms its basic role. Here is the list: power engineering; electrical; machine-tool and tool industry; instrumentation; tractor and agricultural engineering; transport; automobile and aviation industry; shipbuilding, etc. Another convincing fact: in 1970 the machine building of the USSR produced more than 30,000 items.

It is not surprising that this industry is the main consumer of almost all materials produced in our country, including polymers. Usage polymer materials in mechanical engineering is growing at a rate that has no precedent in all of human history. For example, in 1978, the mechanical engineering of our country consumed 800,000 tons of plastics, and in 1960 - only 116,000 tons. It is interesting to note that ten years ago, 37-38% of all plastics produced in our country were sent to mechanical engineering, and by 1980, the share of mechanical engineering in the use of plastics had dropped to 28%. And the point here is not that the need could decrease, but that other sectors of the national economy began to use polymer materials in agriculture, in construction, in light and food industries, etc. even more intensively.

At the same time, it is appropriate to note that in recent years, the function of polymeric materials in any industry has also somewhat changed. More and more important tasks began to be entrusted to polymers. More and more relatively small, but structurally complex and responsible details machines and mechanisms, and at the same time, polymers began to be used more and more often in the manufacture of large-sized body parts of machines and mechanisms carrying significant loads. Below we will talk in more detail about the use of polymers in the automotive and aviation industries, but here we will only mention one remarkable fact: a few years ago an all-plastic tram went around Moscow. And here's another fact: a quarter of all small ships - cutters, lifeboats, boats, etc. - are now built from plastics.

Until recently, the widespread use of polymeric materials in mechanical engineering was hampered by two seemingly generally recognized drawbacks of polymers: their low (compared to branded steels) strength and low heat resistance. Overcoming the temperature limit is described in the chapter "Steps to the Future". As for the strength properties of polymeric materials, this milestone was overcome by the transition to composite materials, mainly glass and carbon fiber reinforced plastics. So now the expression "plastic is stronger than steel" sounds quite reasonable. At the same time, polymers have retained their position in the mass production of a huge number of those parts from which a particularly high strength is not required: plugs, fittings, caps, handles, scales and housings for measuring instruments. Another area specific to polymers, where their advantages over any other materials are most clearly manifested, is the area of interior and exterior decoration.We have already mentioned this when talking about construction.

The same can be said about mechanical engineering. Almost three quarters of the interior trim passenger cars, buses, planes, river and sea vessels and passenger cars is now made from decorative plastics, synthetic films and fabrics, artificial leather, etc. Moreover, for many machines and devices only the use of anti-corrosion finishing synthetic materials ensured their reliable, long-term operation. For example, repeated use of a product in extreme physical and technical conditions (space) is ensured, in particular, by the fact that its entire outer surface is covered with synthetic tiles, moreover, glued with synthetic polyurethane or polyepoxy glue. And the apparatus for chemical production? They have such aggressive environments inside that no branded steel would withstand. The only way out is to make the inner lining of platinum or PTFE film. Plating baths can only work if they themselves and the suspension structures are coated with synthetic resins and plastics.

Polymer materials are also widely used in such a branch of the national economy as instrument making. The highest is obtained here economic effect on average, 1.5-2.0 times higher than in other branches of mechanical engineering. This is explained, in particular, by the fact that most of the polymers are processed in instrumentation by the most progressive methods, which increases the level useful use(and no waste) of thermoplastics, increases the replacement rate of expensive materials. Along with this, the costs of living labor are significantly reduced. The simplest and most convincing example is the manufacture of printed circuits: a process that is inconceivable without polymer materials, and with them fully automated.

There are other sub-sectors where the use of polymeric materials provides both the saving of material and energy resources and the growth of labor productivity. Almost complete automation was provided by the use of polymers in the production of brake systems for vehicles. It is not for nothing that almost all functional parts of brake systems for cars and about 45% for railway rolling stock are made of synthetic press materials. About 50% of rotating parts and gears are made from durable engineering plastics.In the latter case, two different trends can be noted. On the one hand, there are more and more reports about the manufacture of gear wheels for tractors from nylon. Scraps of old fishing nets, old stockings and a mess of nylon fibers are melted and molded into gears. These gears can operate almost without wear in contact with steel, in addition, the system does not require lubrication and is almost silent. Another trend is the complete replacement of metal parts in gearboxes with CFRP parts. They also show a sharp decrease in mechanical losses, a long service life.

Another area of application of polymeric materials in mechanical engineering, worthy of a separate mention, is the manufacture of metal-cutting tools. As use expands durable steels and alloys, more and more stringent requirements are imposed on the processing tool. And here, too, plastics come to the rescue of the tool maker and machine operator. But not quite ordinary plastics of ultra-high hardness, such that they dare to argue even with diamond. The king of hardness, the diamond, has not yet been dethroned from his throne, but things are moving towards that. Some oxides (for example, from the genus cubic zirconia), nitrides, carbides, already today demonstrate no less hardness, and, moreover, a greater thermal resistance. The trouble is that they are still more expensive than natural and synthetic diamonds, and besides, they have a "royal vice" - they are mostly fragile. So, in order to keep them from cracking, each grain of such an abrasive is surrounded by polymer packaging, most often from phenol-formaldehyde resins. Therefore, today three quarters of abrasive tools are manufactured using synthetic resins.

These are just a few examples and the main trends in the introduction of polymer materials in the mechanical engineering sub-industry. The automobile industry now occupies the very first place in terms of the growth rate of the use of plastics among other sub-sectors. Ten years ago, from 7 to 12 types of different plastics were used in cars; by the end of the 70s, this number exceeded 30. From the point of view of chemical structure, as one would expect, the first places in terms of volume are occupied by styrene plastics, polyvinyl chloride and polyolefins. They are still slightly inferior to them, but they are actively catching up with polyurethanes, polyesters, acrylates and other polymers. The list of car parts that are made from polymers in certain models these days would take more than one page. Bodies and cabins, tools and electrical insulation, interior trim and bumpers, radiators and armrests, hoses, seats, doors, hoods, etc., etc. Moreover, several different companies abroad have already announced the start of production of all-plastic vehicles. The most common trends in the use of plastics in the automotive industry are generally the same as in other sub-sectors. First, it saves materials: waste-free or low-waste forming of large blocks and assemblies. Secondly, thanks to the use of lightweight and lightweight polymeric materials, the total weight of the car is reduced, which means that fuel will be saved during its operation. Thirdly, made as a whole, the blocks of plastic parts significantly simplify assembly and save labor.

By the way, the same advantages stimulate the widespread use of polymer materials in the aviation industry. For example, replacing aluminum alloy With graphite plastic in the manufacture of the wing slat, the number of parts can be reduced from 47 to 14, fasteners - from 1464 to 8 bolts, weight is reduced by 22%, and the cost is reduced by 25%. In this case, the safety margin of the product is 178%. Helicopter blades, fan blades jet engines are recommended to be made from polycondensation resins filled with aluminosilicate fibers, which allows to reduce the weight of the aircraft while maintaining strength and reliability. According to English patent No. 2047188, coating the bearing surfaces of aircraft or blades of helicopter rotors with a layer of polyurethane with a thickness of only 0.65 mm increases their resistance to rain erosion by 1.5-2 times. Tough requirements were set before the designers of the first Anglo-French supersonic passenger aircraft "Concorde". It was calculated that friction against the atmosphere would heat the outer surface of the aircraft to 120-150 ° C, and at the same time, it was required that it did not succumb to erosion for at least 20,000 hours. fluoroplastic film. Concorde designers experienced no less difficulties in solving issues of sealing fuel and hydraulic systems. And here a way out of the predicament was provided by polysiloxane and fluorocarbon elastomers, sealants and mastics. By the way, about elastomers. In the course of presenting information on the use of polymer materials in mechanical engineering, we practically did not touch upon this type of polymer. But they are also widely used in the form of cuffs and oil seals, gaskets, tubes and tires. The oil and petrol resistance of these seals, gaskets and hoses is very important for a car, which is ensured by the use of acrylonitrile butadiene, polychloroprene and similar rubbers. But recently, in connection with the rise in prices for petroleum products, reports began to appear about the use of a new fuel in cars - alcohol. In this regard, it can be assumed that in the near future, automakers will demand alcohol-resistant rubbers from Chemists. It is not so difficult to create such rubbers and other polymeric materials; the driver would be alcohol-resistant. Well, now let's move on to describing several colorful and little-known cases of the use of polymer materials in mechanical engineering. (TSB, 3rd ed., Vol. 15; Plast. World, 1979, 37, No. 2).

Cutting thread

Can a steel bar be cut with synthetic thread? For this to succeed, it is necessary that the thread be super-strong and highly hard, or the steel softens. And why is it necessary? The same blank can be cut with a hardened hacksaw blade. But the trouble is that after such a sawing, harmful residual stresses and deformations remain in the steel. And steel and other metals can be softened with special chemical reagents - each metal has its own chemicals. The synthetic filament will only carry these chemicals to the cutting site. This is the method developed by Polish chemists. The thread moves along the surface of the workpiece being cut at a frequency of 24 strokes per minute. At the end of each stroke, the reaction products of the solvent with the metal are removed, the thread is impregnated with a fresh portion, and it makes a reverse stroke. (Young technician, 1965, No. 8).

Plastic rockets

The shell of the rocket engine is made of carbon fiber, wound on a pipe; carbon fiber tape pre-impregnated with epoxy resins. After curing the resin and removing the auxiliary core, a pipe is obtained with more than two-thirds of carbon fiber, sufficiently strong in tension and bending, resistant to vibration and pulsation. It remains to fill the blank with rocket fuel, attach the compartment for instruments and cameras to it, and you can send it in flight. (Compsites, 1981, 12, no. 1).

Plastic sluice

On one of the canals in the Bygdoszcz region, the first in Poland (and probably the first in the world) all-plastic sluice was installed. The gateway works flawlessly.

The plastic parts are designed for over 20 years of service life. Oak beams had to be replaced every 6 years. (Science and Life, 1969, no. 3).

Welding without heating

How do I attach two plastic panels to each other? Can be glued, but then it is necessary to equip workplace ventilation system. You can screw or rivet, but then you need to drill holes ahead of time. It can be welded if both panels are thermoplastic, but even here you cannot do without ventilation, and besides, due to local overheating, the connection may turn out to be destructive and fragile. Most The best way and equipment for it, was developed by the French company "Brunson". An ultrasound generator with a power of 3 kW, a frequency of 20 kHz, "sound guides" - sonotrodes - that's all. The tip of the sonotrode, vibrating, penetrates the upper part of the fastened parts up to 8 mm thick, plunges into the lower one and carries along the upper polymer melt. The energy of ultrasonic vibrations is converted into heat only locally, and spot welding is obtained. The same method and the same equipment are also suitable for "bricking" various fasteners and fittings in plastic. The most effective application of ultrasonic welding in the production of electric lighting equipment, car trim parts, ventilation systems in the construction of tanks, in the aircraft industry, etc. Ultrasonic welding is especially recommended in the manufacture of products from polyolefins, styrene plastics, polyamides, polycarbonates, various vinyl and acrylic resins. (Offic. Plast et caoutch. 1979, 26, no. 275).

Polyurethanes against bullies

This post needs no comment:

"Polyurethane coatings have high hardness, durability over 10 years and good gloss. Their use may solve the problem of durable painting of subway cars in New York. On such coatings it is impossible to write or draw with either a pencil or a felt-tip pen, which significantly reduces the cost of cleaning of wagons ". (Mod. Paint and Coat, 1979, 69, No. 11).

Universal plastics

An original point of view on the practical application of polymeric materials, in particular in instrument making, was recently expressed by a columnist for the English magazine World of Plastics.

In his opinion, all the variety of requirements for the properties of plastics can be satisfied with eight polymers: ABS copolymer, nylon, phenolic resins, polyethylene and polypropylene, polyurethane foam and polyvinyl chloride.

The author noted that the ratio of cost to volume has been regularly increasing for all materials in recent years, but for synthetic organic polymers this growth is slower than for steel, aluminum and glass. The author considers the main advantages of plastics when used in instrument making:

1. Parts made of polymeric materials can be molded without their subsequent processing, since during the molding process the required color is provided and appearance finished product.

2. The designer is given the opportunity to develop parts with complex configurations with significant savings in labor time and cost.

3. The characteristics of thermal and electrophysical properties inherent in polymeric materials prevent damage to electrical devices and reduce their heat transfer.

4. Thanks to the light weight of plastic products, transport costs are reduced and their handling is easier.

The author also claims that plastics are most widely used in five groups of devices: in large-sized structures; household electrical appliances; radio electronics; conditioners and humidifiers. It is for these five groups, the observer claims, that eight basic polymers are enough, and immediately illustrates this with examples of the latest exhibits of refrigerators, washing machines and dishwashers, fans, vacuum cleaners, radio installations, televisions, calculating machines, laboratory equipment, etc., up to to homemade oil extractors, toasters and coffee makers. Unfortunately, the list of polymers from which these devices are made turns out to be much wider than the eight-term list given at the beginning of the review. There are acetal resins, and various polyesters, and polycarbonate, and polyphenylene oxide, etc., besides, many more, as a rule, are not in pure form, but as part of compositions with each other and various fibrous and powdery fillers.

Polymers the products of the chemical combination of identical molecules in the form of repeating units are called. Polymer molecules consist of tens and hundreds of thousands of atoms. Polymers include: cellulose, rubbers, plastics, chemical fibers, varnishes, adhesives, films, various resins and etc.

By their origin, polymeric materials are divided into natural and synthetic ... Natural ones include: starch, rosins, proteins, natural rubber, etc. The bulk of polymeric materials used in modern industry are synthetic polymers. They are obtained by polymerization reactions (without the formation of by-products), for example, the production of polyethylene, and polycondensation (with the formation of by-products), for example, the production of phenol-formaldehyde resins.

The production of polymers by the polymerization reaction is carried out as follows. The polymerization reaction is organic matter containing double bonds in the molecule. Under the influence of light, heat, pressure, or in the presence of catalysts, molecules of substances by opening double bonds combine with each other, forming a polymer.

When polymers are prepared by polycondensation, two monomer products are reacted to form a polymer and a by-product.

Among polymeric materials, a special place belongs to plastics. This is a material that contains high molecular weight synthetic resins as the main component. They are obtained by chemical synthesis of the simplest substances extracted from such available raw materials as coal, lime, air, oil.

The main advantage of using plastics compared to other materials, it is the ease of processing them into a product. Their inherent plastic properties make it possible, using automatic press machines, automatic casting machines, etc., to produce hundreds of parts of complex configurations per hour. At the same time, the consumption of materials is minimal (there is practically no waste), the number of machines and maintenance personnel is reduced, and energy consumption is reduced. In view of this, much less investment is required in organizing the production of plastic products.

Plastics processing methods and manufacturing plastic products depend on the ratio of plastics to temperature. Allocate thermoplastic and thermosetting plastics .

To thermosetting includes plastics that soften when heated to a certain temperature, and then turn irreversibly into an infusible and insoluble state. Thermosetting plastics, once cured, cannot be recycled and are therefore called irreversible. Phenoplastics are an example of thermosetting plastics. Products from thermosetting plastics are produced by pressing in molds. The latter have an internal cavity corresponding to the shape and dimensions of the future product, and usually consist of two detachable parts - a matrix and a punch. The die is fixed on the bottom plate of the press, the punch - on the movable slide of the press. A measured amount of press powder, heated to 90 - 120 ° C, is fed into the matrix, which has a temperature required for pressing. Under the influence of heat from the heated matrix, the polymer softens and acquires the necessary plasticity. Under the action of the punch, the softened material fills the cavity of the mold. At the same time, complex chemical transformations take place in the thermosetting resin, leading to the formation of an infusible material. The product hardens in a pressurized mold. After a certain holding time, the product is removed from the mold. Temperature, pressure and pressing time are determined by the properties of the materials to be pressed. In addition, extrusion or extrusion is also used to process thermosetting plastics. This method produces products of a flat (sheets, films) or cylindrical (rods, pipes) shape.

To obtain products from thermoplastic plastic, the following methods are used: injection molding, extrusion (extrusion) and sheet forming ... Their use is due to the thermoplasticity of the material.

The most applicable method for processing thermoplastic plastics is injection molding. It is carried out on special injection molding machines. Powdered or granular polymer is fed into a heated cylinder of an injection molding machine, where it is melted. When cooled, the thermoplastic polymer solidifies and takes on the appearance of a part.

Also, when processing plastics into products, molding, stamping, mechanical cutting, blowing of hollow products are used. All methods are characterized by a short technological cycle, low labor costs and ease of automation.

Synthetic fibers obtained from synthetic high molecular weight resins. A large group is made up of polyamide fibers - nylon, nylon. They are characterized by high strength, elasticity, alkali resistance, electrical insulation resistance. Polyester fibers include lavsan. It is used for the production of fabrics, knitwear, electrical insulating materials. Differs in high mechanical strength.

Technological process obtaining chemical fibers includes the following stages:

1) preparation of the spinning mass;

2) fiber spinning;

Finishing.

Rubber- a typical representative of high molecular weight (polymer) compounds. It is the main component of rubber, it is of plant origin (natural) and synthetic. The most widely used in industry is synthetic rubber. His chemical composition and the structure, as well as physical properties can be very diverse and very different from the properties of natural rubber, which is the advantage of synthetic rubbers.

The main raw materials for the production of synthetic rubbers are associated petroleum gases, ethyl alcohol and acetylene. The main production methods are polymerization and polycondensation. During processing, rubbers are converted into rubber. It is characterized by high elasticity, resistance to abrasion, bending, gas and water tightness, high electrical insulating properties, resistance to aggressive media.

Rubber are obtained by adding a number of components (ingredients) to the rubber. This mixture is then vulcanized. Vulcanization consists in the formation of bridges between linear rubber molecules and obtaining a three-dimensional spatial molecular structure. This structure leads to an increase in the thermal stability and strength of the material, to a decrease in its solubility and an increase in chemical resistance. The most common vulcanizer is sulfur, which also determines the hardness of rubber. Also, various fillers are introduced both to improve the properties (soot, zinc white, kaolin, antioxidants) and to reduce the cost (chalk, talc).

Rubber products are made: by extrusion, stamping, injection molding, dipping models in latex, etc. Rubber products are divided according to purpose and operating conditions.

V chemical industry the largest costs are for raw materials and account for an average of 60 - 70% of the prime cost, and for fuel and energy - about 10%. Depreciation deductions are 3 - 4%, wage the main production workers range from 3 to 20% of the cost of production and depends on the type of production.

Repair of parts with polymers.

Other ways to restore parts.

Literature:

Main:

1. Machine repair / Ed. Telnova N.F. - M .: Agropromizdat, 1992, 560 p .: ill. [P. 193..210]

2. Technology for the repair of machinery and equipment. Under total. ed. I. S. Levitsky. 2nd ed., Rev. and add. M .: "Kolos", 1975.

Additional:

Car repair / 0.I. Sidashenko, O. A. Naumenko, A. Ya. Poic'kyi ta sh .;

Ed. 0.I. Sidashenka, A. Ya. Poliskiy. - K .: Harvest, 1994.- 400s. [With. 138..143]

Basic polymer materials.

When repairing machines, polymer materials are widely used both for manufacturing and for restoring parts. This is due to the fact that they have a number of valuable properties (low bulk density, significant strength, good chemical resistance, high antifriction and dielectric properties, vibration resistance, rather high heat resistance of some of them, etc.).

The use of polymers makes it possible in many cases to avoid complex technological processes when restoring parts, such as welding, surfacing, electroplating, etc. The technology of using polymers is simple and available for implementation at repair enterprises.

The basis of plastics (plastics) is an artificial (synthetic) or natural resin, which plays the role of a binder and determines their chemical, mechanical, physical and other properties.

Various plastics are made by adding fillers, plasticizers, hardeners, colorants, and other materials to the resin.

TO polymeric Materials include plastics, which, like plastics, are divided into two large groups: thermosetting (thermosetting plastics) and thermoplastic (thermoplastics).

Reaktoplasts soften when heated and can be molded by pressing or other methods. After further heating, certain chemical transformations take place, and they become solid, dense, insoluble and infusible. It is impossible to reuse thermosets for their intended purpose.

Thermoplastics They soften when heated, formed by injection molding, and then, after cooling, harden, retaining their shape. When reheated, thermoplastics become soft and fusible, which means they can be reused.

Fillers are used to improve physical and mechanical, dielectric, frictional or antifriction properties, to increase heat resistance and reduce shrinkage of polymer materials, as well as to reduce the cost. Metal surveillance is used as fillers; Portland cement, cotton fabrics, fiberglass, paper, asbestos, mica, graphite, etc.

Plasticizers- dibutyl phthalate, camphor, oleic acid, dimethyl - and di-ethyl phthalate and others - give polymers elasticity, viscosity and fluidity during processing.

Hardeners- amines, magnesia, lime and others - contribute to the transition of polymers into a solid and insoluble state.

Dyes- nigrosine, ocher, mummy, red lead and others - give polymers a certain color.

Among the many polymeric materials used in the repair of cars, polyamides, polyethylene, fiberglass, fiberglass, styracryl, compositions based on epoxy resins, etc. are gaining more and more importance.

The main polymer materials used in the repair business are characterized by the following properties.

Nylon resin(caprolactam) grades A and B - solid horny material of white or yellowish tinge. Supplied in the form of granules. Ultimate strength: in compression 70-80 MPa, in tension 60-65 MPa, in bending 80 MPa.

Caprolactam They are used for the manufacture and restoration of parts with high antifriction properties (bearings, gear wheels, bushings, rollers, liners), seals, gaskets, etc.

The main disadvantage of nylon is low thermal conductivity, heat resistance and fatigue strength (6.5 MPa). The maximum permissible operating temperature of nylon parts or coatings in air should not exceed plus 70-80 ° C and minus 20-30 ° C.

Polyethylene High pressure grade G1E-150 is a hard, horny material of milky white color. Supplied in the form of granules. Ultimate tensile strength 12-16 MPa, compression 12.5 MPa, bending 12-17 MPa.

Polyethylene of this brand has high dielectric properties, significant resistance to the action of acids and alkalis, good resistance in the environment of various oils, insignificant moisture absorption.

Polyethylene PE-150 They are used for insulation of wires, cables, parts of high-frequency devices, radio equipment, lining of apparatus, tanks, metal coating. Polyethylene films are used as packaging material.

Low-pressure polyethylene of grades L, E and P is a hard, horny material of milky white color. It is released in the form of granules. Tensile strength 22-27 MPa (for grade L), 22-35 MPa (for grade E), 22-45 MPa (for grade P). It is used for the manufacture and restoration of wheels, covers, casings, tubes, etc. Press powders FKP-1 and FK. P-2 Available in powder form. The ultimate static bending strength for FKP-1 powder is 50-60 MPa. It is used for the manufacture of parts with increased mechanical strength and impact resistance (flanges, covers, flywheels, gears, pulleys, handles, etc.).

FKP-2 powder Has a flexural strength of 75-85 MPa. This powder is used for the manufacture of parts with increased impact and bending strength (flanges, gears, pulleys, cams, etc.).

Clay BF-2- homogeneous viscous liquid of dark brown color. It can glue metals and non-metallic materials operating at temperatures from -60 ° to + 180 ° C, phenolic-formaldehyde plastics, textolite, fiberglass, getinax, amiplasts, fiber, glass, ebonite, wood, plywood, fabrics, leather, ceramics, etc. etc.

Ultimate tensile strength of glued samples: steel-steel 28.5-38.5 MPa; steel-porcelain 10 MPa, steel-glass 13.9 MPa; duralumin-duralumin 6.5-10 MPa. Compounds resistant to water, alcohol, gasoline, kerosene, mineral acids. The glue is produced in a ready-to-use form.

Glue BF-6 Used for gluing fabrics, felt, etc. VS-10T glue-Homogeneous transparent liquid of dark red color, without impurities and precipitation. They can glue together and in any combination various metals and non-metallic materials (steel, cast iron, aluminum, copper and their alloys, fiberglass, heat-resistant foams, as well as asbestos-cement materials), operating at a temperature of 200 ° C for 200 hours and at a temperature 300 ° C for 5 hours. Ultimate shear strength (steel ZOKhGSA - steel ZOKhGSA) is at a temperature of 20 ° C-15-17 MPa, at a temperature of 200 ° C - 6.0-6.5 MPa and at a temperature of 300 ° C - 3.5-4.0 MPa.

Repair of parts

Repair of parts with cracks and holes. Cylinder blocks, cylinder heads, gearbox housings and other parts are repaired using epoxy resins.

Widely used Epoxy resin ED-16- transparent viscous mass of light brown color. In a hermetically sealed container at room temperature, it can be stored for a long time.

The resin hardens under the action of a hardener, as the latter are aliphatic amines, aromatic amines (AF-2), low molecular weight polyamides (L-18, L-19 and L-20). The most common is considered Polyethylene polyamine- a viscous liquid from light yellow to dark brown.

To increase the elasticity and impact resistance of the cured epoxy resin, a plasticizer should be added to its composition, for example, dibutyl phthalate, a yellowish oily liquid.

With the help of fillers, the physical and mechanical, frictional or antifriction properties are improved, the heat resistance and thermal conductivity are increased, and the cost is reduced. These include cast iron, iron and aluminum powders, asbestos, cement, quartz sand, graphite, fiberglass, etc.

The epoxy composition is prepared as follows. The container with ED-16 epoxy resin is heated in a heating cabinet or containers with hot water to a temperature of 60 ... 80 ° C and the bath is filled with the required amount of resin. A plasticizer (dibutyl phthalate) is added to the latter in small portions, thoroughly stirring the mixture for 5 ... 8 minutes. Then the filler is also introduced - 8 ... 10 minutes.

The prepared composition can be stored for a long time. Immediately before its use, pour in a hardener and mix for 5 minutes, after which the epoxy composition should be used within 20 ... 25 minutes.

The quality of epoxy coatings largely depends on the composition and composition. Cracks up to 20 mm long are closed In the following way.

Using a magnifying glass of 8 ... 10-fold magnification, the boundaries of the cracks are determined and holes with a diameter of 2.5 ... 3.0 mm are drilled at its ends. Along it along the entire length, a chamfer is removed at an angle of 60 ... 70 ° C to a depth of 1.0 ... 3.0 mm. If the thickness of the part is less than 1.5 mm, then chamfering is not recommended. The surface is cleaned at a distance of 40 ... 50 mm from the crack to a metallic sheen. Degrease the surfaces of the crack and the cleaned area, wiping them with a swab soaked in acetone.

After drying for 8 ... 10 minutes, the surface of the part is degreased again and dried again.

Detail 1 (Fig. 1, a) Placed so that the cracked surface 2 Up to 20 mm long was in a horizontal position, and epoxy is applied with a spatula 3 On the surface of the crack and the cleaned area.

Crack 20 ... 150 mm long (fig. 1.6) Close up in the same way, but after applying the epoxy 3 An additional pad is placed on it 4 Made of fiberglass. The latter covers the crack from all sides by 20 ... 25 mm. Then the pad is rolled on with a roller 5. A layer of the composition is applied to the surface, and a second pad is applied B (Fig. 1, c) With an overlap of the first by 10 ... 15 mm. Next, roll it in with a roller and apply the final layer of epoxy

Fig. 1 Crack sealing scheme:

1 - detail; 2 - crack; one— Epoxy composition; 4 and 6-fiberglass plates; 5 - roller; 7 — Metal plate; 8 ~ bolt.

For cracks longer than 150 mm (Fig. 1, d) An epoxy is applied with a metal overlay and bolted to it. The surface preparation and crack preparation is the same as for a crack less than 150 mm in length.

Cover 7 is made of sheet steel with a thickness of 1.5 ... 2.0 mm. It should cover the crack by 40 ... 50 mm. Holes with a diameter of 10 mm are drilled in the pad. The distance between their centers along the crack is 60 ... 80 mm. The centers must be at least 10 mm from the edges of the cover.

The patch is placed on the crack. Punch the centers of the holes on the parts, remove the cover, drill holes with a diameter of 6.8 mm and cut the threads into them 1M8X1. The surfaces of the part and overlays are cleaned to a metallic sheen and degreased.

Holes on the parts are repaired using the same compound with the overlapping or flush overlapping of metal overlays. In the first case (Fig. 2, a) The sharp edges of the hole are dulled and the surface of the part around the hole is cleaned to a metallic sheen at a distance of 10 ... 20 mm.

The cover plate is made of sheet steel with a thickness of 0.5, .. 0.8 mm. It should cover the hole by 10 ... 20 mm. The edges of the hole and the area of the surface cleaned around it are degreased and dried for 8 ... 10 minutes.

Fig. 2 Scheme of sealing holes with overlaying:

A - flush; b— Overlap; 1 and b - metal plates; 2 and 5 - layers of epoxy composition; 3 - wire; 4— Fiberglass overlay; 7— Bolt.

A wire with a diameter of 0.3 ... 0.5 mm and a length of 100 ... 150 mm is attached to the center of the lining. Lining is made of fiberglass along the contour of the hole. A thin layer of epoxy is applied after the secondary degreasing of the edges of the hole and the cleaned area and drying.

Install the pad 1 Under the hole and secure with wire 3. Then laid on the pad 1 Pad 4 From fiberglass, roll it on with a roller, apply an epoxy compound, lay a second glass cloth patch and roll it on with a roller. The operations for applying the epoxy composition and laying the glass cloth linings are repeated until the hole is filled along the entire wall thickness. Layer 2 of the epoxy composition is applied to the upper pad and cured. In the second case (fig. 2.6) The sharp edges of the hole are dulled, the surface of the part is cleaned around it at a distance of 40 ... 50 mm to a metallic sheen. The cover is made of steel with a thickness of 1.5 ... 2.0 mm. It should cover the hole by 40 ... 50 mm. Drill holes in it with a diameter of 10 mm. The distance between them along the perimeter of the hole is 50 ... 70 mm. The centers should be 10 mm from the edges of the trim. Drill holes with a diameter of 6.8 mm into parts and cut threads into them 1M8X1. The surface of the lining in contact with the part is cleaned to a metallic sheen. Degrease the surfaces of the part and linings, and then apply a thin layer of epoxy to them. After that, the leaks and sagging of the epoxy composition are cleaned and the quality of the repair is checked. 3. Ways to restore parts Sealing cracks in body parts. This operation is performed by mechanical means: pinning, curly inserts and patching. Sealing cracks Pinning- a very time-consuming operation and requires high qualifications of a locksmith. It is used in the repair of parts subject to tightness conditions (gearbox housings, rear axles, water jackets of cylinder blocks). The essence of this method is that the crack along its entire length is sealed with threaded pins.

The latter are made of red copper or bronze. First, the ends of the crack are drilled, the threads are cut into them and the pins are installed. Then, in the order shown in Figure 2.50, drill holes and install the remaining pins. It is recommended to rake the ends of the pins, and solder the repaired surfaces. Cracks with a length of 50 mm or more should not be repaired with pins.

Rice. 3. Scheme of sealing cracks with pins.

Sealing cracks with curly inserts allows you to restore not only the tightness of the part, but also its strength.

The repair technology includes obtaining a special groove in the parts and pressing a pre-made figured insert into it (fig. 4). The main parts of the equipment, on which the quality of work depends, are the jig for drilling the groove holes and the shaped insert itself. Cracks are sealed with sealing and tightening shaped inserts, which are made of mild steel 20 or Art. 3.

Fig.4 Types of figured inserts: a and b - sealing; c, d, d, AND E - constricting; g - drilling holes across the crack.

Filling the crack with sealing figured inserts is as follows.

Having retreated from the end of the crack in the direction of its continuation by 4 ... 5 mm, holes with a diameter of 4.6 mm are drilled for parts with a wall thickness of up to 12 mm and a diameter of 6.6 mm over 12 mm to a depth of 3.5 and 6.5 mm, respectively.

Then, holes are also drilled sequentially along the crack using a special conductor. The latter is rearranged and fixed each time along the drilled hole. In addition, holes are made across the crack - two on each side every five holes.

First, transverse and then longitudinal inserts are installed in the groove, having previously lubricated the end and side surfaces with epoxy Compound, And rivet them.

Filling the cracks with figured constriction inserts is similar to the method discussed above. The figured groove for the tightening figured insert is made only across the crack. With the help of a special jig, six holes with a diameter of 3.5 mm are drilled to a depth of 10 or 15 mm (depending on the wall thickness of the part) in increments of more than 0.1 ... 0.3 mm, with three holes on one side and three on the other.

The bridge between the holes is removed with a special punch in the form of plates 1.8 or 3.0 mm thick. A shaped insert is pressed into the resulting groove, having previously degreased the surfaces and lubricated them with an epoxy compound.

The crack is pulled together due to the difference in the sizes of the steps between the axes of the holes of the figure groove and the figured insert. “In this way, it is recommended to restore the partitions between the cylinders of the crankcase, gearbox housings and repair cracks in the cylinder heads.

A set of equipment OR-11362 has been developed, which includes two improved conductors. They are used to repair the outer walls of parts and inner cylindrical surfaces, differ from the existing ones in their versatility, simplicity of the device and low labor intensity during operation.

Repair of threaded connections. The operability of threaded connections is restored by two methods: Changing the original size A worn out threaded part (method of repair dimensions) and Without changing it(methods of surfacing and welding, setting additional parts, replacing part of a part).

The latter is considered more progressive, that is, without changing the dimensions of the thread (under the nominal size), since this does not violate interchangeability and does not reduce the strength of the connection.

The external thread is restored in several ways. Torn off threads (less than 2 threads) and nicks are removed by sweeping with a threading tool and locksmithing.

Usually, bolts with worn heads, stripped threads of more than 2 threads, as well as worn threads are rejected. When repairing threads on shafts, replace the worn out threaded part of the part or weld metal onto the surface different ways.

The main disadvantage of surfacing should be considered a decrease in the fatigue strength of the part (from 10 to 30%) and the possibility of burn-through of thin-walled parts. Threaded holes have the following main defects: breakdown, clogging, crushing and chipping of individual turns, wear along the inner and average diameters, etc. Various methods are used to repair them. (fig. 5).

The main disadvantage of welding holes with subsequent drilling and threading of nominal size is a large heat-affected zone, which leads to chilling of cast iron, cracking and warping, a change in the structure of the material and a decrease in thread strength by almost half. Cutting a threaded hole at a new location is only possible if its location can be changed without violating the interchangeability of the connection (drum hub, etc.).

Stabilization of threaded connections with a polymer composition is used when the total wear of the stud-body connection is not more than 0.3 mm. The installation of a spiral insert in the repair of critical parts and assemblies has been widely used.

Rice. 5. Methods for repairing threaded connections

Features of technological processes for the manufacture of polymeric materials depend on their composition and purpose. The main technological factors are certain temperature and power, forming 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.

The main methods of plastics processing: rolling, calendering, extrusion, pressing, casting, coating, impregnation, watering, spraying, welding, gluing, etc.

Mixing compositions is a homogenous enhancement process
the distribution of all ingredients over the volume of the polymer, sometimes with additional dispersion of particles. Mixing can be batch and continuous. The design and operation of the mixers depend on the type of mixed materials (free-flowing or pasty).

Rolling is an operation in which plastic is formed in the nip between rotating rolls (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 roller and cut 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 it is cut with a knife in the form of a narrow continuous tape.

Rolling allows you to benignly mix the components of plastics in order to obtain a homogeneous mass, while the polymer, as a rule, is transferred to a viscous state due to an increase in temperature during grinding. With repeated passing of the mass through the rollers, plasticization occurs, i.e., the combination of the polymer with the plasticizer by means of accelerated mutual penetration. The rollers allow grinding and crushing plastic components. This is ensured by the fact that when moving in the gap, the materials are compressed, crushed and abraded, since the rollers can rotate at different peripheral speeds.

The rollers used for surface finishing and sizing must have a smooth, polished surface. By the nature of the work, the rollers are of periodic and continuous action, and by the method of temperature control, they are heated (by steam or electricity) and cooled (by water).

Calendering is the process of forming an endless tape of a given thickness and width from a softened polymer mixture, once passed through a nip between rollers.

Designs of calenders differ mainly depending on the type of processed mass - rubber compounds or thermoplastics. The calender rolls are made of high quality chill cast iron. The working surface of the roll is ground and polished to a mirror finish. The rolls are heated with steam through the inner central cavity and peripheral channels.

As a rule, calendering is carried out in combination with rolling in one production line.

Extrusion is an operation in which a certain profile is given to plastic products by forcing a heated mass through a die (forming hole). The extrusion method is used to obtain profile (molded) construction products, pipes, sheets, films, linoleum, poroizol and many others. Dimensions (edit) cross section 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. Extrusion machines of two types 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 body of the machine is a screw (worm), which mixes the mass and advances it through the profiling head (mandrel). The mass is fed into the machine in the form of granules, beads or powder. The softening of the material occurs due to the heat supplied from the heaters, which are installed in several zones.

Heating J

Rice. 14.4. Extrusion machine working diagram:

1 - loading hopper; 2 - auger; 3 - head; 4 - calibrating nozzle; 5 - pulling device; b - mandrel; 7 - filter

SHAPE * MERGEFORMAT

Rice. 14.5. Stamping (press-forming) scheme: a) loading of press material; 6) closing the mold and pressing; c) pushing out the product; 1 - press material; 2 - heated mold die; 3 - heated punch; 4 - press slider; 5 - electric heater; 6 - product; 7 - ejector

Compression is a method of molding products in heated hydraulic presses. Distinguish between molding in molds (Fig. 14.5) - in the manufacture of products from press powders and flat pressing in multi-storey presses - in the manufacture of sheet materials, plates and panels. Pressing is mainly used in the processing of thermosetting polymer compositions (phenolic, aminoplasts, etc.).

For pressing building sheet materials and panels, multi-storey hydraulic presses force from 10 to 50 tons, heated by heated water or steam. Pressing on multi-storey presses consists of the following operations:
press loading, plate clamping, heat treatment under pressure, pressure relief, unloading. The method of flat pressing is used to form chipboards, paper laminates, tekstolites, wood-laminated plastics, three-layer glued panels. Molds are used to manufacture parts of sanitary and electrical equipment, parts for finishing built-in equipment, window and door devices, parts of construction machines and mechanisms.

Foaming is a method of making porous sound-insulating and elastic sealing plastics. The porous structure of plastics is obtained as a result of the foaming of liquid or viscous-flowing 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 injecting or dissolving gaseous and volatile substances in the polymer.

Foaming can take place in a closed volume under pressure and without pressure, as well as in open molds or on the surface of a structure.

Lubrication 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 is linoleum, pavinol, linkrust, etc. Usually the base moves and the screed is stationary; only its slope and clearance are regulated. The applied and leveled mass usually goes through a heat treatment stage to soften and better adhere it to the base.

Impregnation consists in dipping the base (fabric, paper, fibers) in an impregnating solution followed by drying. This operation is carried out in vertical and horizontal impregnating machines. Adhesive films (bakelite) are obtained by the impregnation method, decorative films(urea-melamine), as well as panels based on glass, asbestos and cotton fabrics, from which textolites are subsequently obtained.

Watering is the process by which plastic mass is distributed thin layer on a metal tape or drum and, hardening, is removed in the form of a thin film. This process is often associated with the evaporation of solvents. In this way, for example, cellulose acetate transparencies are obtained.

Casting. There are two types of casting: simple in molds and under pressure. In simple casting, the liquid composition or melt is poured into molds and solidified by polymerization, polycondensation or cooling. An example is the casting of floor tiles from thermosetting plastics, the production of organic glass and decorative items from polymethyl methacrylate. By cooling the melt during simple casting, some simple products are obtained from polyamides (polycaprolactam).

Injection molding is used in the manufacture of thermoplastic products. The polymer is heated to a viscous state in the heating cylinder of the injection molding machine (Fig. 14.6) and is injected by a plunger into a split mold cooled with water.

The pressure under which the melt is injected can reach 20 MPa. In this way, products are made from polystyrene, cellulose ethers, polyethylene, polyamides. Injection molding is characterized by a fast cycle, while this type of processing operations are automated.

Molding is the processing of sheet, film, 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 forming from sheets include stamping, blow molding and vacuum forming (Figure 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 - rack; 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 a die and a punch, and compressed under pressure up to 1 MPa. In this way, parts of sewage systems from vinyl plastic, light caps from plexiglass for coatings of industrial buildings, profile parts from textolite for building structures are manufactured.

During pmevmo-forming, the sheet is fixed along the contour of the matrix and heated to a slight sagging. Then heated air, compressed to 7-8 MPa, press the sheet to the surface of the matrix. A variation of this method is free blowing. In this way, light caps, containers, rings made of polyacrylates, parts of ventilation systems and chemically resistant equipment made of polyvinyl chloride are obtained.

During vacuum forming, the sheet is fixed along the contour of the hollow shape, heated and 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, vinyl polymers.

Spraying is a method of applying powdered polymers to the surface, which, when melted, adhere to it, and upon cooling, form a strong coating film. Distinguish between gas-flame, vortex and pseudo-liquefied spraying. During flame spraying, the polymer powder (polyethylene, polyamide, polyvinyl butyrol), passing through the flame, melts and, falling onto the surface in drops, adheres, forming a layer of the required thickness.

Welding and gluing are used to connect plastic blanks to obtain products of a given shape. Welding is used to join thermoplastic plastics - polyethylene, polyvinyl chloride, polyisobutylene, etc. By the method of heating the ends to be joined, air (heated air), high-frequency, ultrasonic, radiation, contact welding are distinguished.

Bonding is used to bond both thermoplastic and thermosetting plastics. In the simplest case, an organic solvent can serve as an adhesive for thermoplastic plastics, which causes swelling of the abutting ends of the parts and their sticking together under compression. More often, special adhesives are used. Depending on the production conditions and the required connection speed, cold and hot curing adhesives are used.

products from flat

polymer blanks: equipment

and technology

One of the main methods of processing polymeric materials are methods of thermoforming products from flat (sheet or film) blanks. Thermoforming combines several technological methods: vacuum, pneumatic, mechanical, as well as some other types of molding of heated polymer sheet or film blanks, while their various combinations are possible.

The widespread use of thermoforming processes is explained by the simplicity, compactness, and relative cheapness of the equipment and technological equipment used. Thermoforming is used primarily in the production of containers and packaging for the food, perfumery, pharmaceutical, chemical, oil industries, disposable tableware, as well as a number of hollow polymer products with various technical purposes. Many types of polymer products, for example, large-sized and thin-walled complex configurations, can be produced only by pneumatic or vacuum forming methods. All of the above reasons make it possible to adequately compete for thermoforming processes with other alternative methods of manufacturing products from polymer materials.

1.BASIC THERMOFORMING METHODS

The implementation of thermoforming methods is quite simple: a sheet or film polymer blank is heated to a temperature of a highly elastic state, and then, by deforming it in various ways, the latter is given the required shape, which is fixed by cooling the molded product.

Depending on the method of creating the driving force of the process of deformation of the workpiece into a finished product, the following methods of thermoforming of plastics are distinguished: vacuum, pneumatic, hydraulic, mechanical, combined.

During vacuum forming (Fig. 1) a flat workpiece 3 made of thermoplastic polymer material, pressed along the perimeter to the working chamber of the vacuum forming machine by a clamping frame 2 , first with a heating device 1 heated to a highly elastic state (Fig. 1 a). Then (Fig. 1 b) in the cavity formed by the surfaces of the workpiece 3 and forming matrix 4 (or forming punch), create a vacuum, as a result of which, due to the resulting pressure drop

Fig. 1. Diagram of the implementation of the vacuum forming process: 1 2 - clamping frame;

3 4 - forming matrix;
5 - molded product

the product is being molded 5 ... After cooling the product to the temperature of its dimensional stability, the latter is removed from the forming tool (removed from the forming tool), having previously opened the clamping frame 2 .

The implementation of pneumatic molding processes differs from vacuum molding only in that the pressure drop is created due to the use of compressed gas as a working medium, as a rule, compressed air, with an excess pressure of up to 2.5 MPa.

In hydraulic forming, the role of the working medium is played by the heated liquid, which is pumped in by a pump under a pressure of 0.15-2.5 MPa.

Mechanical forming (mechanical thermoforming) (Fig. 2) differs from pneumatic processes

molding in that giving a flat heated blank 3 shape of the finished product 5 carried out at the expense

its mechanical drawing with a metal punch 4 .

Fig. 2 Scheme of the implementation of the mechanical thermoforming process: 1 - heating device; 2 - clamping frame;

3 - flat polymer blank; 4 - forming punch;

5 - molded product

It should be noted that modern technologies production also provides for the combination of different methods of forming products, for example, pneumatic vacuum, pneumatic mechanical, etc.

Among all types of pneumatic and vacuum forming, three main ones can be distinguished: positive, negative and free. In positive shaping (punch shaping), the inner surface of the product exactly reproduces the shape or pattern of the shaping tool. Negative molding (molding in a matrix) makes it possible to obtain products, the outer surface of which exactly reproduces the shape or pattern of the inner surface of the matrix. Free forming is carried out in the armhole of the clamping frame of the machine without the use of a forming tool. In addition to the main ones listed, there are other types of technological processes for thermoforming products from flat polymer blanks.

2. EQUIPMENT USED FOR

IMPLEMENTATION OF THERMOFORMING PROCESSES

The entire range of molding machines that implement technological processes for thermoforming products from flat polymer blanks is divided according to the following criteria: molding method, type of control, type of processed material, purpose, number of positions.

The molding method, as already noted, is determined by the method of creating a driving force for the process of deforming the original blank into a finished product.

The type of molding equipment control determines the degree of automation of the plastic molding process. There are three main types of control: manual machines, semi-automatic machines, automatic machines.

Hand-operated machines are used in small-scale production. All the necessary operations (cutting and fixing the workpiece, heating it, molding, cooling and removing the workpiece) are performed by the operator.

In semi-automatic machines, the workpiece is clamped and the finished product is removed manually, and the remaining operations (heating, molding, cooling) are performed according to a predetermined program.

Automatic machines do not require the presence of an operator, and all operations are carried out automatically.

According to the type of material being processed (the type of flat polymer blanks used), the molding equipment is divided into classes: machines working with individual sheet or film blanks; machines working with roll material; cars,

fed by a sheet or film coming directly from a calender or extruder. It should be noted that feeding machines with separate flat workpieces requires the introduction of technological cycle additional operation - preliminary cutting of workpieces, which increases total time cycle. Typically, individual workpieces are fed on manual or semi-automatic machines.

Roll blanks feed the molding equipment, which operates in automatic mode.

Forming machines fed by sheet or film coming directly from a calender or extruder are usually part of automatic lines. A flat workpiece made of polymer material arriving from the calender is processed on a molding equipment and sent for further processing or to a warehouse.

According to their purpose, molding machines are divided into universal, specialized, combined.

A wide range of products of all sizes is produced on universal machines in small series. They are designed to work with single and multi-cavity molds and process a variety of thermoplastic materials.

Specialized machines are designed for the production of only a certain type of products from a specific polymer material.

Combined molding machines produce medium and large series of products. When the nomenclature of manufactured products changes, the equipment is readjusted.

According to the number of positions, molding machines are divided into the following classes: single-position, two- and three-position, multi-position.

On single-station equipment, all technological operations are carried out on the same section of the machine.

The division of technological operations into two or three sections speeds up the production process and is carried out, respectively, on two- or three-position machines.

On multi-position machines, all technological operations of the production of products are carried out simultaneously. Such equipment is most applicable in industrial production and is characterized by high performance. In turn, multi-position machines are divided into carousel, belt and drum machines.

The multi-position carousel machine uses the carousel principle. The workpiece moves in a circle, successively going through the stages from fixing, heating and forming to cooling and removing the finished product.

The belt principle is usually used when the machine is powered by roll material. The belt with the formed products after the forming machine moves further along the conveyor for further processing.

Drum-type machines also use roll material.

Molding equipment for the implementation of thermoforming processes is often equipped with additional devices: for trimming, punching holes, punching, pre-drawing, etc. Such equipment can be part of technological lines for the production and filling of polymer containers and packaging.

More detailed information about the device and principles of operation of various types of equipment used for the implementation of technological processes of thermoforming of products from flat polymer workpieces are presented in other literary sources [2 - 7, 9].

3.BASIC TECHNOLOGICAL PARAMETERS

THERMOFORMING PROCESSES

The main technological parameters that determine the course of thermoforming processes of products from flat polymer blanks and ultimately affect the quality finished products, are: the temperature of the workpiece used, the temperature of the forming tool, the working pressure drop during molding, the speed of molding, the cooling rate of the molded workpiece, the geometry of the molded product, the properties of the polymer raw materials used, the properties and thermodynamic parameters of the working media, etc.

Since the processes of processing polymers into products and parts are, first of all, deformational, the choice of the optimal temperature for each specific method of their processing should, taking into account its specifics, be based on the features of the deformation behavior of the materials used. These features are easily established from the analysis of the thermomechanical curve, the typical form of which for amorphous polymer is shown in Fig. 3. Analysis of the given thermomechanical curve shows that polymer materials are characterized by three pronounced regions that determine different degrees of their deformability and

Fig. 3. Thermomechanical curve of amorphous polymer:

T C- glass transition temperature; T T- pour point; 1, 2, 3 - areas of glassy, highly elastic and viscous-flowing relaxation states of the polymer, respectively

corresponding to various relaxation (thermomechanical) states of polymers: glassy, highly elastic and viscous. The glassy state of polymers is characterized by the absence of movement of macromolecular chains or their segments. Thermal motion in a material manifests itself only in the vibrations of atoms. The application of an external load to the polymer under such conditions can only lead to a change in its macromolecular structure of the average interatomic distances and bond angles of chemical bonds. Therefore, the deformation behavior of polymers in this state and ordinary elastic solids is no different, and the deformations developing in such conditions in polymers are completely elastically reversible.

If the polymer material is heated to a temperature exceeding its glass transition temperature, then it passes into the next relaxation state - highly elastic, when mobility of individual segments of the polymer macromolecular chain appears, and the material becomes softer and more elastic. However, there is still a

Supramolecular formations abundantly existing in its structure, for example, microblocks, prevent the relative displacement of molecular chains as a whole. Application of an external load to the polymer in this state

leads to a change (decrease) in the configurational entropy of the state of macromolecules, which, "unrolling" from a statistical coil, only orient themselves in the direction of the applied load, while the thermal motion of the chain links counteracts the external load. When the load is removed, the chains return to their original state, and therefore, the highly elastic deformation, as well as elastic, is a completely reversible deformation, but unlike the latter, it has an entropic nature.

With further heating of the polymer above a certain temperature, called the pour point, the supramolecular formations become so unstable that it becomes possible for a relative displacement of the chains of macromolecules relative to each other when an external load is applied to it. The latter circumstance ensures the flow of polymer media in this state, while the deformations of the flow are irreversible, and the state of the polymer itself is called viscous. It should be especially noted that the deformation of polymers in a viscous-flow relaxation state does not at all mean that the deformations developing in them are exclusively flow deformations.

Depending on the modes and kinematics of deformation, the rheological properties of polymer media in the latter, along with flow deformations, highly elastic deformations of a certain level develop.

Since all thermoforming processes provide for the stage of heating the workpiece, the surface of which is in a free state, so that the workpiece does not have the opportunity to strongly deform at this technological stage under the action of gravitational forces, it is heated until the polymer reaches a highly elastic state. Heating the billet to a viscous-flow state leads to its sufficiently fast gravitational drawing (sagging) and, as a consequence, to the impossibility of implementing the stage of forming the product. On the other hand, the temperature of the preform being formed should not be near the boundary of the glassy and highly elastic states of the polymer, since during the forming of the article, in this case, its incomplete shaping is possible. Thus, the working temperature of the moldable polymer blank is one of the main technological parameters that determine the implementation of thermoforming processes. Table 1 shows the approximate temperature conditions at which thermoforming of polymer products from flat workpieces in industry is carried out.

In addition, it should be noted the importance of implementing the process of heating the workpieces itself. Firstly, this process is quite lengthy and amounts to approximately

50-80% of the total molding cycle time of the product. Secondly, the heating of the workpieces should be carried out so that the temperature at all points of their surface at any time is the same. Uneven heating leads to uneven deformation of the workpiece in the process of its molding into a product and the formation of folds on the surface of the latter. As a result of uneven heating, separate overheated areas may form on the surface of the preform, and during molding, rupture of the preform may occur in these areas.

The temperature of the forming tool affects the cooling process of the formed product. Obviously, it must be below the glass transition temperature of the polymer, otherwise the preform will not cool sufficiently and the product may lose its shape. It is also obvious that the lower the temperature of the forming tool, the faster the cooling and the higher the productivity of the forming equipment.

Table 1

But at very low temperatures of the forming tool, hypothermia spots appear on the surface of the molded product, and its tendency to warp increases.

With pneumatic methods of forming products, such technological parameters of these processes, as the current values of the pressure drop required for their implementation, the rate of molding (shaping) of the product, which is determined by time, and the pressure of the compressed gas flowing into the working cavity, are interrelated.

The current operating pressure drop realized during the molding of the product is determined by the elastic characteristics of the polymer material, the wall thickness of the original workpiece, as well as the elastic deformations developing during its molding into the product. The use of "rigid" polymeric materials or preforms having a relatively large thickness requires the creation of relatively large pressure drops to ensure sufficient forming of the article.

For "soft" material or thin-walled workpieces, create high speeds their deformation can lead to mechanical destruction (rupture) of the latter during the molding process.

When implementing pneumoforming processes, a working (compressed) gaseous medium is fed into a closed working cavity, at least one of the surfaces of which is the surface of a flat workpiece with a source gas located there. general case may not be identical to the original gas environment. In practice, as a rule, the source and working gas media are identical.

Based on the foregoing, it is easy to understand that the time for forming a product is determined not only by the operating pressure drop, which, in the general case, depends on the properties of the material being processed, the geometric parameters of the original workpiece and the molded product, thermodynamic parameters of the gas media used, as well as some design parameters of the equipment used. and pneumocommunication systems. The maximum permissible time for forming a product is determined by the cooling of the workpiece in the process of its deformation: the temperature of the workpiece should not have time to drop to such a level at which the molding of the product becomes impossible. The minimum time for forming a product is determined by the maximum possible deformation rates of the workpiece, at which material rupture can occur.

During the implementation of vacuum forming processes (Fig. 1), the gaseous medium located there is evacuated from the closed working chamber of the vacuum forming machine with the forming equipment installed in it on the movable table, thus creating a pressure drop between the outer and inner surfaces of the flat workpiece.

The latter, being deformed under the action of the generated driving force, comes into contact with the shaping surfaces of the shaping tool (dies, punches, etc.), which ensures the implementation of the shaping process of the product. As in the case of blow molding, the rate of deformation of the workpieces during their vacuum forming depends on the time of forming the product.

First, it should be noted that not in all cases vacuum forming equipment is able to ensure stable retention of the vacuum created in the working chamber (and, consequently, the pressure drop) during the molding process. It is known that stable retention of the generated vacuum is possible only in those cases when the volume of the receiver, where the gas is evacuated from the working chamber, exceeds its initial volume by at least eight times.

Secondly, if, under natural (atmospheric) conditions, the specified condition for the implementation of the vacuum forming process is not met, then it is necessary to resort to the combined - pneumatic vacuum method of its molding, for which it is necessary to create an initial excess pressure in the working chamber of the equipment and above the outer surface of the workpiece.

Taking into account the foregoing, it is easy to understand that the technological time of forming products from flat blanks in the vacuum method of their production depends not only on the properties of the processed polymeric materials, the geometric parameters of the blanks and molded products used, the thermodynamic parameters of gaseous working media, but is also significantly determined by some constructive parameters of the equipment used and the forming tool.

When implementing the processes of mechanical thermoforming (Fig. 2), the time of forming the product (and, consequently, the rate of deformation of the workpiece) is determined by the speed of movement of the forming tool 4 , wherein optimal choice the latter is due to the same problems that are characteristic of other previously discussed molding methods.

As already noted, the cooling rate of molded products, determined by the time of their cooling in a known temperature range, affects the value of residual stresses in the material. Relatively rapid cooling of the molded product reduces the cycle time of its production, but leads to "freezing" of residual stresses in the material, as a result of which the product has low dimensional stability during operation. With relatively slow cooling, the residual stresses partially relax, increasing the dimensional stability of the product, but this increases the cycle time of the latter.

It is known that polymeric materials have relatively low thermal conductivity. Therefore, the efficiency of cooling the molded articles essentially depends on the conditions of heat transfer from the cooled polymer material to the cooling medium realized in practice.

The cooling time of the product essentially depends on the average integral value of its wall thickness. The latter concept is introduced in connection with the fact that the deformation of flat blanks during the shaping of products from them is characterized by significant heterogeneity, as a result of which the molded products have a very noticeable difference in thickness (heterogeneity of the wall thickness). The difference in thickness of polymer products impairs their presentation and such important performance characteristics as strength, stiffness, vapor and gas tightness. The thickness variation of the molded products practically does not depend on the properties of the processed polymers, but significantly depends on the implemented molding method and the geometry of the products.

The time of the technological or working cycle for the production of a particular type of product depends, first of all, on the implemented method of forming them, the equipment used, and may include a wide variety of elements.

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