Конструкциялық материалдар және термоөңдеу Конструкционные материалы и термообработка Constructional materials and heat treatment Учебное пособие для специальности: 5В071200– «Машиностроение»

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Corrosion resistance, technological effectiveness and other characteristics of 
metal materials even more often don't meet increasing requirements of 
automotive industry when developing new models and technologies. Therefore 
modern materials science is occupied with development of new materials on the 
basis of the nonconventional materials, fuller use of secondary resources. The 
important role belongs to creation of new machine-building materials on the 
basis of synthetic, natural and artificial binding. Among the most widespread 
and perspective materials - polymers and plastics. 
By origin, polymers are divided on: 
- natural. 
- synthetic. 
- artificial. 
Typical representatives of natural polymers are cellulose, starch, natural 
rubber. 
Synthetic polymers represent a synthesis product - purposeful receiving 
difficult substances from simpler. The nomenclature of synthetic polymers 
constantly replenishes. 
Artificial polymers are received by processing (modifying) of the natural. For 
example, artificial polymer - nitrocellulose is received by cellulose nitridation. 
On a chemical composition of macromolecules, polymers are distinguished: 
- organic. 
- inorganic. 
- organometallic. 
To organic polymers we refer the connections which molecules contain atoms 
of carbon, hydrogen, nitrogen, oxygen and sulfurs which are the part of the main 
chain and lateral groups of polymer. 
Inorganic polymers are connections which don't contain in structure of 
macromolecules of carbon atoms. 
In the course of receiving polymeric connection, monomeric links are built in a 
certain chain. On character of a structure of polymeric chains we distinguish 
polymers of linear, branched and mesh structure. 
Polymeric materials change the properties under the influence of temperature. 
On this sign polymers are subdivided on: 
- thermoreactive. 
- thermoplastic. 
Thermoreactive polymers (thermosettings) when heating above certain, 
characteristic for this purpose like polymer, temperatures, become not fusible 
and almost insoluble. 
Temroplastichnye polymers (thermolayers) possess property repeatedly to 
pass when heating to the melted condition. 
Thermoplastic and thermoreactive polymers. 

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In relation to heating, polymers are subdivided on thermoplastic and 
thermoreactive. 
Thermoplastic polymers have linear or branched structure of molecules. When 
heating they are softened, can melt, when cooling harden. This process is 
reversible. 
Thermoreactive polymers in an initial stage of education have linear structure. 
When heating they are softened. Further the spatial structure is formed, polymer 
comes into a thermostable firm fortune. 
Features of polymers structure define their properties. High molecular weight 
leads to impossibility of transition to a gaseous state or formation of low-viscous 
liquids. Thermostable polymers are not softened. Polymers can be in three stable 
conditions: vitreous, highly elastic and plastic. 
Vitreous - is a firm amorphous condition where there is no movement of links 
and movement of macromolecules. The highly elastic condition is characterized 
by ability of a material to big reversible changes of a form under the influence of 
insignificant loadings. The plastic condition reminds a liquid state with big 
viscosity. 
Polymers grow old (spontaneous and irreversible their major mechanical 
properties change) under the influence of light, oxygen (ozone), humidity, 
warmth, long storage. Processes of aging are accelerated under the influence of 
mechanical tension. The essence of aging is concluded in difficult chain reaction 
with education of free radicals. Polyethylene, polyamide fibers are steadiest 
against influence of high atmospheric temperatures and moisture. For aging 
delay in polymers add stabilizers. For example, service life of the polyethylene 
stabilized by soot, increases till 5 years, polyvinylchloride has term of services 
till 25 years. 
Properties of polymers. 
Only two aggregate states are peculiar to polymeric materials: firm and liquid. 
Transfer of a polymeric material to a gaseous state without destruction of 
communications in the main chain of macromolecules is impossible. 
Polymeric materials can be in four physical conditions: 
- crystal 
- vitreous 
- hyperelastic 
- plastic. 
Condition of polymers at which a front view of deformations are big elastic 
deformations, call hyperelastic. At a fluidity temperature impact on polymer of 
mechanical loading leads to development in it irreversible deformation - 
condition of viscosity. 

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Important feature of polymeric materials is the combination of high specific 
durability and big reversible deformations. This property is caused by existence 
in macromolecules of polymers of two types of communications - strong 
intramolecular (interatomic) and weaker intermolecular. 
The durability of polymeric materials is an interval of time from the moment 
of load application before material destruction. Functional dependence of 
polymeric materials durability on a breaking point from which follows is 
established that durability of polymeric materials changes in time and depends 
on temperature. Therefore at a choice of polymeric materials according to 
operational characteristics it is necessary to consider not only a maximum load, 
but also time during which the material doesn't collapse. 
Durability of polymeric materials significantly depends on structure which 
they get in the course of processing. The method of polymers hardening by 
orientation of macromolecules is widely used. 
Modifying of polymers. 
To improvement of polymeric materials properties we apply their physical and 
chemical modifying - introduction in structures: 
- stabilizers, 
- softeners, 
- greasings, 
- fire-retarding agents, 
- dyes, 
- alloying elements. 
For increase of plasticity and elasticity of polymeric material at its processing, 
before operation into its structure we enter softeners (air of acids and glycols, 
polyair, chlorine-containing connections). To plasticization of rubbers we apply 
oil refining products (paraffin, ceresin, petroleum oils) and coal, vegetable oils, 
fatty acids. 
Anti-softeners providing increase of connection rigidity of macromolecules 
at introduction of small additives with polar groups in vitreous polymers possess 
effect opposite to plasticization. 
To protection of polymeric materials against aging we apply stabilizers. The 
principle of operation of stabilizers is based on suppression of destruction 
processes of polymeric macromolecules under the influence of external factors. 
We distinguish stabilizers of the following types: 
- antioxidants (slowing-down thermal and thermooxidizing destruction), 
- antiozonant (slowing down ozone aging), 
- light stabilizers (interfering photooxidizing destruction under the influence of 
sunshine), 
- anti rads (interfering destruction of a polymeric material as a result of radiation 
destruction), 

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- anti tiring (slowing-down processes of fatigue phenomena in a material). 
Stabilizers enter in small amounts (0,01-2% on weight) at synthesis or 
processing of polymers. 
Polyethylene. 
Typical representative of polyolefins subgroup. Depending on polymerization 
conditions (pressure, type of catalyst, temperature) we receive a product of 
various molecular weight. 
Distinguish polyethylene: 
- high pressure and low density. 
- low pressure and high density. 
- average pressure. 
- high-molecular low pressure. 
Polyethylene possesses a number of valuable properties: moisture - and gas-
tight, does not bulk up in water, elastic in a wide interval of temperatures, steady 
against effect of acids and alkalis, possesses very good dielectric properties. 
Combination of high chemical firmness, satisfactory mechanical properties to 
technological effectiveness of processing (it is processed in all known ways: by 
molding under pressure, machining, vacuum forming, welding, etc.) and low 
cost determines its broad application in mechanical engineering, radio 
engineering, chemical industry. 
Polyethylene of low pressure possesses the bigger mechanical durability and 
rigidity and is used for production of pipes, hoses, sheets, film, details of radio 
equipment, and various capacities. Molding under pressure produce gates, 
cogwheels working with small loading. Polyethylene of high pressure is applied 
as a packing material in the form of film or in the form of unbreakable container 
(bottle, canisters, and boxes). 
However in view of insufficient mechanical durability to production of details 
of cars it is applied restrictedly. The main lack of polyethylene - its low heat 
resistance, from it is recommended to use products at temperatures not over 
80ºС. 
Polypropylene. 
Polypropylene - is a synthetic polymer, characterized by melting temperature 
near 170ºС. In comparison with polyethylene, differs higher impact strength, 
durability, wear resistance, possesses high dielectric properties, low steam and 
gas permeability, it is steady against effect of boiling water and alkalis, but 
possesses low thermo - and light resistance. It is applied to production of the 
details working in contact with aggressive liquids. 
Vinyl plastic. 

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Advantages of vinyl plastics are high mechanical properties, chemical 
firmness, technological effectiveness of processing in products, workability 
cutting. 
Working temperature of vinyl plastic is from 0 to +40ºС, at sharp fluctuations 
of temperature is jarred on, and when heating above 40ºС it is softening and 
loses rigidity. Vinyl plastic at lowered temperatures becomes fragile. It does not 
burn, but at a temperature 120-140ºС starts being softened that is used when 
welding products from vinyl plastic. Decomposition temperature 160-200ºС. It 
is inclined to aging under the influence of atmospheric actions and chemical 
reagents. 
Vinyl plastic is let out mainly in the form of sheets and profile hire (pipes, 
bars, corner, etc.). Products from vinyl plastic produce expression, stamping at a 
temperature 130ºС, machining, welding, gluing together by perchlorovinyl glue. 
Capacities in chemical mechanical engineering, cases and separators for 
storage batteries, gates, valves, fitting for pipelines, details of pumps and fans 
and other products are produced from vinyl plastic. 
Caprone. 
Caprone gained the greatest distribution as rather cheap and least scarce 
material from many brands of polyamides. Its main advantage as constructional 
material is the combination of high durability, deterioration, warm and chemical 
firmness with technological effectiveness of processing in a product. 
Wear resistance of caprone is several times higher, than steel, cast iron and 
some non-ferrous metals. The best antifrictional properties caprone with 
addition of 3-5% of graphite possesses. 
For production of details from caprone and other polyamides most we widely 
use molding metol under pressure. Caprone is well processed by cutting, sticks 
together and weldable. Details of antifrictional appointment, bearings, 
cogwheels, arms, handles, covers, cases, pipeline fittings are made from it. 
Polystyrene. 
Polystyrene represents a product of polymerization of styrene. 
There are the following types of polystyrene and materials on its basis: 
- general purpose. 
- shock-resistant. 
- foaming. 
- styrene copolymers. 
Polystyrene of the general appointment is the colourless transparent material 
possessing absolute water resistance, high electroinsulating properties, light 
resistance and hardness. Polystyrene is resistant to a mold, to alkaline and sour 

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environments. The main application of polystyrene - radio equipment details, 
irresponsible constructional details, products of a household purpose. 

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