Fergana polytechnic insitute mechanical engineering faculty department of mechanical engineering and automation

Figure 8.1. Construction scheme of rubber molecules: 
a – raw rubber; b - vulcanized rubber 
In most cases, vulcanization is the chemical cross-linking of sulfur with 
rubber. 5-7% sulfur is added for ordinary rubber, 30-35% for hard rubber-ebonite. 
There are two types of vulcanization: a) hot; b) cold. Hot vulcanization in 
hydropresses at a temperature of 140-145 
0 
C, under a pressure of 25-75 kg/cm 
2 for 2-
40 min. 
carried out in time intervals. Special personal vulcanizers are used for aviation 
details (camera, camera). 
Cold vulcanization is used for thin-walled products. In this case, Fig. 8.1. 2-
3% sulfur is held in a sulfur-carbon solution with chlorine for several minutes. No 
sulfur added. 

- light can also vulcanize. The most interesting thing is that if both 
sulfur and 

light are given, the process will speed up again. 
As a result of vulcanization, strength and flexibility are increased. Some 
physico-chemical properties also increase: wear resistance, resistance to various 
solvents, electrical conductivity. 

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It should be remembered that rubber is prone to wear. In this case, the physico-
chemical and mechanical properties of rubber decrease. 
Wear is accelerated under sunlight, under the influence of temperature, under 
the influence of oxidants (oxygen, ozone), under the influence of internal stresses. 
It is necessary to pay attention to these during use and storage. 
should be stored indoors in rooms where sunlight does not touch, at a 
temperature of 5-20 
0 C, and humidity of 40-65%.
In the remaining points, depending on the type of rubber, special technical 
requirements are observed. 
Non-metallic materials are based on polymers. Effective use of non-metallic 
materials in machine building leads to great economic gains. Polymer materials are 
substances made up of many units whose macromolecules have the same structure. 
The molecular weight of polymers varies from 5000 to 1000,000. Such a large-sized 
macromolecule has a great influence on all the properties of the polymer with its 
composition and shape . 
Polymer macromolecules form chains made up of individual links. The cross-
sectional size of the chain is several thousand angstroms, and the length is several 
thousand angstroms. Therefore, the macromolecule is flexible. Flexibility of the 
macromolecule is a property of the polymer. 
Covalent bonds (chemical bonds) between the atoms forming the chain of 
macromolecules, and Van der Waalps forces act between the molecules. These 
molecular forces are 10...50 times smaller than covalent bond forces. Thus, polymers 
are characterized by strong bonds in their macromolecules and weak bonds between 
them. 
If macromolecules of the same composition differ in size, the physico-
chemical properties of the polymer are spread, such a phenomenon is called 
polydispersity . If the macromolecule has the same composition, it is called a 
copolymer. In some cases, the macromolecule of a polymer can be composed of 
homogeneous sections (blocks) that are repeated in a row, and such a polymer is 
called a block copolymer. 

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During the synthesis of polymers, other monomers can be attached to the main 
molecular chain, and the resulting polymer is called a copolymer. If the chains of 
the macromolecule are made of the same atoms, the polymer is called homoseparate, 
if it is made of different atoms, it is called a heteroseparate polymer. 
Polymers are divided into natural (natural rubber, mica, cellulose, asbestos, 
natural graphite) and synthetic polymers. Synthetic (artificial) polymers are of great 
practical importance, because different properties can be achieved by changing their 
composition and structure during their synthesis. 
Polymer substances can be classified according to their composition, 
macromolecule shape, phase state, polarity, and resistance to heating. According to 
their composition, polymers are divided into organic, inorganic and elementoorganic 
types. Of these, organic polymers are widely used. 
If the polymer macromolecule is composed of carbon atoms, it is called a 
carbocyclic polymer. In heterojunction polymers, carbon atoms are bonded to atoms 
of other elements. For example, oxygen atoms increase the flexibility of 
macromolecules (fibers, films), phosphorus and chlorine increase the fire resistance 
(flammability) of the polymer (rubber, hermetic), fluorine atoms increase the 
chemical stability of the polymer, etc. 
Organic polymers include resins and rubbers. 
Inorganic ( 
Si, Ti, Al, ... 
) substances are included in macromolecules of 
elemento-organic polymers. These polymers have the following structure: 
… – Si – O – Si - … 
R 
R 
R 
R 
Inorganic polymers include silicate glass, ceramics, mica, asbestos. These 
polymers do not have a carbon skeleton. The basis of the polymer is metal oxides . 
Composite materials made of different groups of polymers are also used in 
technology (for example, glass and plastic). 

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The properties of the polymer are also affected by the structure of its 
macromolecule. According to the shape of the macromolecule, there are linear, 
branched, mesh-like polymers ( Fig . 8. 2).