O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

9.2 Metal-polymer systems
In almost any technique, you can find elements that form a metal-polymer friction pair: plain bearings with polymer bushings, sealing collars and polymer stuffing box seals for plungers, pistons, friction gears, brake devices, artificial joints.
Consider, from the point of view of tribology, a metal-polymer system as a metal-polymer friction pair. A friction pair is a system of two elements, the contact surfaces of which move relative to each other.
A metal-polymer friction pair is a kind of metal-polymer system, different in properties and processes occurring in it from metal-metal, polymer-polymer pairs.
A metal-polymer system is a combination of at least two bodies intended for joint work, connected by atomic-molecular forces or mechanically, one of which consists of macromolecules (polymer), and the other of atoms with shared electrons (metal).
A metal-polymer material is a semi-finished product consisting of polymers and metals fixedly interconnected by atomic-molecular forces or mechanically, and is intended for the manufacture of parts, assemblies and structures (for example, a metal sheet with a polymer coating).
A metal-polymer part is an elementary (indivisible) part of a structure or assembly made of polymers and metals or metal-polymer material (for example, a metal-polymer gear).
A metal-polymer assembly is a structural element consisting of metal and polymer or metal-polymer parts, which can also be used in various structures. (for example, metal-polymer friction unit, sliding units, metal-polymer sealing units).
Compared to metals, polymers have a lower coefficient of friction, wear out less, and are insensitive to shocks and vibrations. And at the same time, they have low, compared with metals, thermal conductivity and heat resistance.
The polymer in a metal-polymer friction pair is used directly as a friction body, or in the form of a coating - a film on the surface of another material, mainly metal. Pure polymers are not used in friction pairs; fillers, plasticizers, modifiers, etc. are introduced into them to improve their properties, and composite polymer materials are used.
The friction of polymer composite materials is accompanied by chemical reactions of oxidation, tribodestruction and structuring processes (changes in the structure of the material during friction), breaking of chemical bonds, synthesis of new phases, and other processes. All this leads to the formation of secondary structures that facilitate or hinder the process of friction of mating surfaces in friction units. The surface layers of both the metal counterbody (an element of the friction pair working together with the friction material) and the polymer composite material during friction are also in a complex stress-strain state under the action of shear stresses and deformations. The mechanochemical destruction of macromolecules in the surface layers leads to the breaking of chemical bonds, the formation of free radicals, and can also initiate adsorption plasticization of the surface layers of a polymer and conjugated metal part (according to the Rebinder effect, under the influence of an active medium (including lubricants) during friction, plasticization of the surface layer of the metal occurs).
At different modes of friction, frictional transfer of materials is possible, which consists in the transfer of a polymer material to a metal counterbody. As a result of the interaction of polymer particles with active areas of the counterbody surface, the so-called “third body” is formed - a frictional transfer film. The mechanism of formation of a transfer film depends on the mechanism of destruction of the polymer material, the degree of destruction of macromolecules, the activity of the resulting radicals and their interaction with the metal, and the mobility of molecular chains.
The structure and properties of the transfer film are of decisive importance in the mechanism of friction and wear of metal-polymer friction pairs.
Research and experience in the operation of metal-polymer tribo-couplings have shown that satisfactory operation of these matings is possible only if a stable polymer film of frictional transfer is formed on the metal counterbody. It has been established that the formation of a frictional transfer film occurs due to adhesive bonds that occur when the polymer contacts the metal. The process of adhesive bond formation can be divided into two stages.

• 
  At the first stage, the polymer molecules move to the metal surface and their certain orientation in the interfacial layer, which results in close contact between the molecules and functional groups of the polymer and metal.
  
• 
  The second stage of the process consists in the direct interaction of the polymer and metal.
  

A lot of works are devoted to the study of the mechanism of formation of frictional transfer films, but they, as a rule, are of a particular nature, since they study certain types of polymeric and composite materials.