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

Rice. 8.1. The nature of mechanical wear of parts:
a - bed and table guides, b - internal surfaces of the cylinder, c - piston, d, d - shaft, f, g - wheel teeth, h - screw and nut threads, and - disc friction clutch; 1 - table, 2 - bed, 3 - skirt, 4 - jumper, 5 - bottom, 6 - hole, 7 - bearing, 8 - shaft neck, 9 - gap, 10 - screw , // -- screw; And - places of wear, P "acting forces
in the air, water vapor, in contact with colder metal parts, is deposited on them in the form of condensate, which causes corrosion, i.e., the destruction of the metal due to chemical and electrochemical processes developing on its surface. Under the influence of corrosion, deep corrosions are formed in the parts, the surface becomes spongy, and loses mechanical strength. These phenomena are observed, in particular, in parts of hydraulic presses and steam hammers operating in steam or water.
Typically, corrosion wear is accompanied by mechanical wear due to the mating of one part with another. In this case, the so-called corrosion-mechanical and, i.e., complex and wear occurs.
The nature of the mechanical wear of parts. Mechanical wear of equipment parts can be complete if the entire
the surface of the part, or local, if any part of it is damaged (Fig. 8.1, a-i).
As a result of the wear of the guides of the machine tools, their flatness, straightness and parallelism are violated due to the action of unequal loads on the sliding surface. For example, the rectilinear guides 2 of the machine (Fig. 8.1, a) under the influence of large local loads become concave in the middle part (local wear), and the short guides 1 of the table mating with them become convex.
Cylinders and piston liners in engines, compressors, hammers and other machines also wear out unevenly (Fig. 8.1, b). Wear occurs in the area of movement of the piston rings and manifests itself in the form of wear of the inner walls of the cylinder or liner. The shape of the cylinder bore is distorted - deviations from cylindricity and roundness (barrel shape) are formed, scratches, scuffs occur
* and other defects. In the cylinders of internal combustion engines, their upper part, which experiences the highest pressures and the highest temperatures, is subjected to the greatest wear. In forging and pressing equipment, on the contrary, the greatest wear appears in the lower part of the cylinder - where the piston is located during impacts. Piston wear (Fig. 8.1, c) manifests itself in abrasion and scuffing on the skirt Shaft wear (Fig. 8.1, d, E) is manifested by the occurrence of various defects: the shafts become bent, twisted, and also broken due to material fatigue; teases form on their necks; cylindrical necks become conical or barrel-shaped. Deviations from roundness are also acquired by the holes of plain bearings and bushings. The uneven wear of the necks of the shafts and the surfaces of the holes in the bushings during the rotation of the shaft is the result of the action of various loads in different directions. If only the force of gravity acts on the shaft during rotation, then wear appears in the lower part of the bearing (see Fig. 8.1, d, left).
In gears, the teeth wear out most often: scuffs form, the teeth change their shape, size and break out. Breakage of teeth, the appearance of cracks in the spokes, rim and hub of gears, wear of mounting holes and keys occurs for three main reasons: 1) gear overload; 2) ingress of foreign bodies into it; 3) incorrect assembly (for example, mounting gears on a shaft with misaligned axes).
The lead screws have a trapezoidal or rectangular thread. The threads of the screw and its nut wear out, the turns become thinner (Fig. 8.1, Z.). Thread wear on screws is usually uneven
* Seizure - damage to the friction surface in the form of wide and deep grooves in the direction of sliding. dimensional, since the vast majority of parts processed on machines have a shorter length than the lead screw. The part of the thread that works more wears out more. Lead screw nuts wear faster than screws. The reasons for this are as follows: the thread of the nuts is inconvenient to clean from contamination; nuts in some cases are unsatisfactorily lubricated; for a nut associated with a screw, all threads are involved in the work, while for a screw only a small part of its turns, equal to the number of turns of the nut, work at the same time.
In disc couplings, as a result of the action of friction forces, the ends of the discs are subjected to the greatest wear (Fig. 1, i); their surfaces are abraded, scratches, scuffs appear on them, flatness is disturbed.
In threaded connections, the thread profile most often wears out, as a result, the gap increases in them. This is observed in

Rice. 2. Wear of rolling bearings:
a - due to misalignment, b - when turning the inner ring on the shaft, c - due to excessive tightness, d - due to a faulty stuffing box; And - places of wear at the mates not only running, but also clamping, for example, clamping screws of often unscrewed mounting bolts. Wear of threaded connections is the result of insufficient or, conversely, excessive tightening of screws and nuts; wear is especially intense if the working connection perceives large or alternating loads: bolts and screws are stretched, the thread pitch and its profile are distorted, the nut begins to “seize”. In these cases, emergency breakdowns of the connection parts are possible. The edges of bolt heads and nuts most often wear out because they are unscrewed with the wrong wrenches.
In keyed connections, both the keys and the keyways wear out. Possible reasons for this phenomenon are loosening of the fit of the part on the shaft, improper fitting of the key in the socket.
In rolling bearings, due to various reasons (Fig. 8.2, a-d), working surfaces are subject to wear - pockmarks appear on them, peeling of the surfaces of treadmills and balls is observed. Under the action of dynamic loads, their fatigue failure occurs; under the influence of excessively tight fits of bearings on the shaft and in the housing, the balls and rollers are pinched between the rings, as a result of which distortions of the rings during installation and other undesirable consequences are possible.
The different sliding surfaces are also subject to characteristic wear patterns (Figure 8.3). During the operation of gears, due to contact fatigue of the material of the working surfaces of the teeth and under the action of shear stresses, chipping of the working surfaces occurs, i.e. separation of particles of the material