Wear of pure metals. Wear - metal

When friction of mating surfaces occurs, wear (wear) occurs, which is understood as the process of separating the surface material of a solid body and (or) increasing it

residual deformation during friction, manifested in a gradual change in the size and (or) shape of the body (GOST 27674-88). The property of a material to resist wear, estimated by a value inverse to the wear rate, is usually called wear resistance. As a result of wear, the dimensions of the part change, the gaps between the rubbing surfaces increase, causing beating and knocking. All this causes machine failure.

Wear is a complex physical and chemical process and is often accompanied by corrosion. Real surfaces have difficult terrain characterized by roughness and waviness. During friction, there is a discrete contact of rough bodies and, as a consequence of this, separate frictional connections arise that determine the wear process. Wear can occur due to frictional fatigue, brittle and ductile fracture, microcutting during initial interaction, destruction (including fatigue) of oxide films, deep metal tearing out, etc.

When relative movement of contacting materials occurs, a friction force arises that prevents mutual movement. The friction force is equal to where P is the normal component external force, acting on the contact surface, and is the friction coefficient. The friction coefficient (a dimensionless quantity) can be determined from the equation: where A is the coefficient, is the dynamic viscosity and and is the relative speed of movement. The lower the value, the less wear.

Typically, between the rubbing surfaces there is a thin film of oxides, which insulates the surfaces of the contacting metals. The wear mechanism and the amount of wear depend both on the properties of the material of the friction pairs and on the nature of their movement (sliding friction, rolling friction, etc.), the value of P, the speed of movement and the physico-chemical action of the medium. The different types of wear are described below. More often, corrosion-mechanical or oxidative wear occurs. Oxidative wear is called wear, in which the main influence on wear is chemical reaction material with oxygen or an oxidizing environment.

As a result of friction, a special structure containing a large number of oxides Under the secondary structure there is a highly deformed thin layer of metal with a high dislocation density. During normal oxidative wear, only the secondary structure is destroyed, after which it is easily removed

Rice. 75. Wear curve

is restored and the process is repeated many times. The presence of a secondary structure reduces wear of the surface layer. The highest wear resistance is achieved with a minimum thickness of the secondary structure, its high strength and good bonding with the base metal.

With normal oxidative wear, the friction coefficient and thickness of the collapsing layer are 0.001-0.01 mm.

Under constant friction conditions, three stages of wear take place (Fig. 75): 1 - running-in period, during which intense wear occurs, the microgeometry of the surface changes and the material is hardened; these processes provide elastic contact interaction of bodies; after running-in, an equilibrium surface roughness is established, characteristic of the given friction conditions, which does not subsequently change and is continuously reproduced; 2 - period of steady wear, during which the wear intensity is minimal for given friction conditions; 3 - period of catastrophic wear.

Oxidative wear is observed in plain bearings, shafts, bushings, piston rings, etc.

A distinction is made between friction without lubricant and friction with lubricant. Friction without lubricant is observed in friction gears, brake pairs, etc. Boundary lubrication is widely used, when an oil film with a thickness of hundredths to tenths of a millimeter is adsorbed on the surface of the part. The coefficient of friction for this case is: With liquid lubrication, the rubbing surfaces are separated by a layer of lubricant under pressure, which is load-bearing because it balances the external load. In this case, the lubricant layer has a significant thickness, friction occurs inside the oil layer, which leads to a decrease in the coefficient of friction

In other types of wear, destruction affects surface layers of greater thickness.

Types of wear. According to GOST 27674-88 there are the following types wear: mechanical, corrosion-mechanical and electrical erosion (wear caused by electric current).

Mechanical wear includes abrasive, water-abrasive, gas-abrasive, erosive, cavitation, fatigue, fretting wear and galling wear.

Abrasive wear of a material occurs as a result of the cutting or scratching action of solid bodies and (or) abrasive particles. These particles enter between contacting surfaces with lubricant or from the air, and can also appear as a result of the development of other types of wear (seizing, spalling, oxidation). Abrasive wear can occur with a predominance of oxidation processes (oxidation and subsequent destruction of oxide films) and a predominance of mechanical destruction (the introduction of abrasive particles) and surface destruction. With the oxidative form of abrasive wear, the friction coefficient and thickness of the collapsing layer are up to 0.1 mm. Abrasive wear is typical for many parts of mining, drilling, construction, road, agricultural and other machines operating in technological environments containing abrasive particles (soil, rocks being drilled, etc.).

Wear that occurs as a result of the impact of particles entrained by the fluid flow is called water jet wear. It occurs, for example, in mixers and reactor propellers, in wheels and pump housings, in screws, etc.

When abrasive particles are carried along by gas flow (for example, in chimneys and blowers), the wear they cause is called gas abrasive wear.

Cavitation wear refers to the wear of a surface due to the relative movement of a solid body in a liquid. Propellers, hydraulic turbines, machine parts subject to forced water cooling, and pipelines operate under cavitation conditions.

Fatigue wear (contact fatigue) occurs as a result of the accumulation of damage and destruction of the surface under the influence of cyclic contact loads, causing the appearance"pits" of spalling. Fatigue wear occurs during friction, rolling, or, less commonly, sliding, when the contact of parts is concentrated.

Thus, contact fatigue can be observed in heavily loaded gears and worm gears, rolling bearings, rails and tires of rolling stock railway transport etc.

Wear during fretting corrosion occurs in bolted and rivet joints, seating surfaces of rolling bearings, gears, couplings and other parts in moving contact. Even very small relative movements with an amplitude of 0.025 μm are sufficient for the formation of fretting corrosion.

The cause of wear is the continuous destruction of the protective oxide film at the points of moving contact. Friction coefficient

Sticking wear in which scuffing occurs, resulting in catastrophic wear patterns. In this case, the surface is destroyed and the rubbing parts fail.

A distinction is made between type I (cold seizure) and type II (hot seizure). Cold scuffing occurs during friction with low speeds of relative movement (up to 0.5-0.6 m/s) and specific loads that exceed in the absence of a lubricant and a protective film of oxides. Hot scuffing, on the contrary, occurs during sliding friction with high speeds and loads, when the temperature in the contact zone rises sharply (up to 500-1500 °C). During type I setting, the friction coefficient and the thickness of the collapsing layer are up to 3-4 mm, and during type II setting, respectively, up to 1.0 mm.

Electroerosive wear occurs as a result of exposure to discharges during the passage of electric current.

Acceptable types of wear: oxidative and oxidative form of abrasive wear. Unacceptable damage due to friction: setting of types I and II, fretting process, cutting and scratching (mechanical form of abrasive wear), rolling fatigue and other types of damage (corrosion, cavitation, erosion, etc.).

The intensity of linear wear is taken as the basis for the engineering characteristics of wear, where is linear wear and is the friction path. The wear rate varies from 10-13. Depending on the wear rate, 10 wear resistance classes from 0 to 9 have been introduced.

According to the type of contact interaction of friction surfaces, the classes correspond to elastic deformation, classes 6 and 7 - elastoplastic deformation, classes 8-9 - microcutting

Thus, the wear rate of cylinder liners piston rings, connecting rod and main journals of crankshafts make up cutting tools, teeth of excavator buckets -

Wear resistance classes allow the use of calculation methods for determining the service life of a rubbing pair.

Wear test methods. The wear test is carried out by the most various methods(Fig. 76). It should be borne in mind that the tests carried out different methods, are not comparable. Shown in Fig. 76 wear test circuits, reproducing conditions for the most various types wear.

Rice. 76. Schemes of various wear test methods: I, II - wear during sliding without lubrication and with lubrication; III - wear by friction with and without lubrication; IV - wear during rolling without lubrication; 1 - roll; 2 - hard alloy; 3 - shaft; 4 - disk; 5 - hard alloy ball; 6 - abrasive; 7 - disk; 8 - water; 9 - roller bearing

Massive wear is determined by the decrease in mass. Absolute mass wear is related to the friction surface area, after which linear wear is determined. The friction coefficient is calculated from the friction moment. The lower the wear, friction coefficient and heating for a given period of test time at constant pressure, the higher the wear resistance of the material. Extreme pressure properties are determined under friction conditions without lubricant. For materials with higher extreme pressure properties, there is less or no transfer of material from the insert sample to the mating surface of the roller and the coefficient of friction and temperature increase less during testing.

Tests for abrasive wear are carried out according to GOST 17367-71 by friction against fixed abrasive particles. In this case, the friction of the test and reference samples is carried out on an abrasive cloth under a static load and no heating. Relative wear resistance is determined by the formula where is the absolute linear wear of the reference and test samples, mm; - actual diameter of the reference and test samples, mm.

Measuring wear by loss of mass or volume of a part is not applicable to machine parts. In this case, wear is determined by the content of wear products in the lubricant ( chemical analysis), micrometric measurement method

parts before and after wear, by the artificial base method, when a depression is applied to the wearing surface, by reducing the size of which the amount of wear is judged, by the surface activation method, based on a decrease in radioactivity during wear of a part, in which a radioactive volume 0.05 thick is created in a given area -0.4 mm by irradiation with charged or other particles.

For contact fatigue testing, three-roller, two-contact machines are used, in which the test sample is rolled under pressure between two shafts (rollers), as well as machines in which a flat surface is subjected to contact loading when rolling with balls. Contact fatigue wear is characterized by a limited limit of fatigue chipping, i.e., the maximum normal cycle stress at which destruction of the surface layers of the test metal is not observed for a given test base. The contact endurance limit is determined on the basis of cycles (depending on the material). The criterion for failure is the onset of progressive spalling, which can lead to spalling over the entire surface. Minimum size chipping should exceed half of the semi-minor axis of the contact area. Based on the test results, a contact fatigue curve is constructed.

Wear is usually understood as a gradual undesirable change in the surface of solids, occurring primarily due to the mechanical pressure of small particles of material.

Scientific research into the wear of metals and conventional alloys has been carried out for approximately more than 40 years, and metal-ceramic hard alloys for about 20 years.

Numerous methods and laboratory testing instruments have been developed to compare wear performance of alloys. At first it was assumed that each material should have a specific wear resistance inherent only to it. However, it soon became clear that the problem of wear is more complex than previously thought and depends on various factors. A complicating point in this case is the fact that most wear-resistant materials do not have a homogeneous, but clearly heterogeneous structure.

Factors that determine wear

To reduce wear metal material and regulating it with the help of alloying additives, it is necessary to identify those individual factors that influence the course of the wear process. It is necessary, however, to take into account that the wear process of metal-ceramic hard alloys based on metal carbides, manufactured by sintering with the resulting structural features, often proceeds differently than for other metal materials.

Factors that significantly influence the durability of hard materials and hard alloys include: hardness, bending strength, compressive strength, heat resistance and structure, and in some cases also corrosion resistance and scale resistance. The development of cutting materials from carbon steels (high-speed steels and stellites occupy an intermediate position) to modern metal-ceramic hard alloys, the high wear resistance of which compared to steels is associated with a high content of tungsten carbides, titanium, tantalum, vanadium, etc., took place taking into account knowledge the listed factors.

Since the wear of a material largely depends on its hardness, it was first of all necessary to carefully study this factor. It is very difficult to explain the concept of “hardness”. Typically, hardness is defined as a property of a material associated with resistance to penetration of another body or deformation, cutting, scratching, or abrasion.

Other features of the hardness problem are highlighted in the works.

The most widely used methods for testing carbide alloys for hardness include the diamond cone (Rockwell) and diamond pyramid (Vickers) indentation methods. When applying these methods, it is necessary to take into account that all cast and sintered metal-like materials, and therefore metal-ceramic hard alloys, consist of a mass of homogeneous or dissimilar crystals. When determining macrohardness by conventional methods, too many crystals are covered (in the case of finely dispersed hard alloys, over a thousand). Thus, the macrohardness test provides only an average value of the hardness of the material. In this regard, for alloys with a heterogeneous structure, for example bearing alloys, high-speed steels with a high content of carbides and metal-ceramic carbide alloys, it is impossible to obtain a clear idea of ​​the individual components of the structure based on macrohardness. Only with the help of recently created instruments for determining macrohardness was it possible to determine the hardness of individual components of the structure; To determine the hardness of individual components, you can also use the Birnbaum method. Data on the relationship between macrohardness, microhardness, scratch microhardness (according to Birnbaum) and the classical values ​​of mineral hardness on the Mooca scale are given in table. 43. For comparison in table. 43 also shows data for various components of the structure of steel and hard alloys.

Hot hardness also has a significant effect on the wear of cutting carbide alloys during cutting and carbide dies during hot wire drawing. The hot hardness of alloys of the WC-Co type and the WC-TiC-Co type has already been mentioned above. As the cobalt content increases, the hot hardness decreases, and the addition of TiC slightly increases it. About the great influence that hot solids have

Table 43

The hardness of different* minerals, as well as steel

Hardness

Methods

Microhardness

Solid. b HB, kg/mm2

Mineral or hard material

By K pool KlOO I

According to Knoop KlOO (14]

Vickers, kg/mm’

By Khrushov, KGImmCH\

Hardness HB, kg/mm’

Hardness HRC

Sclerometric hardness

Structural components of steel or hard alloys

2700 2770- 4440

Cementite, stellite

Fused ZrO2

Metal-ceramic hard alloys, double carbides, carbides*1

Silicon carbide

Boron carbide

2800(2500- 3000)

2560*g(2150-2900)

Metal-ceramic hard alloys, carbides and solid solutions of carbides*3

¦——————— „_ with 1 ^o/ binders - double carbide 2Fe3C, 3Cr4C, TaC carbides, - solutions* carbide

Z0mTpTmokTpT^^e=e%=kie5tve^eVYasplkvD, s, -15* ligaments; carbides WC, Т.С, ZrC, hard

For wear rates of carbide cutters during cutting, see below (see also data on alumina-based cutting ceramics).

If the hardness of, for example, diamond, corundum, silicon carbide, boron carbide and refractory metal carbides such as tungsten and titanium carbides were the only factor determining their wear resistance, then these hard materials themselves would be suitable as cutting materials, for dies as well as for rotary and percussion drilling. This, however, happens only in limited cases, and only in those work processes where great mechanical strength is not required from the material. During fine turning and grinding, i.e., with low cutting forces and a small chip cross-section, diamond is many times superior to hard alloys. For rough turning, i.e., with high cutting forces, large chip cross-sections and intermittent cutting, it is completely unsuitable. In fine drawing dies, diamond is superior to all other materials. However, with large die diameters it cannot withstand high pressure to the surface and splits easily. Diamond is well suited for rotary drilling of rock, but is less suitable for impact drilling than metal-ceramic hard alloys. Boron carbide is not suitable for rough cutting and drawing due to its low strength. As a material for sandblasting nozzles, boron carbide is superior (in cases where the nozzles operate at moderate pressure) to all other materials, including five times more durable hard alloys.

Thus, in most cases where wear resistance is required, it is also necessary to take into account the compressive strength, the flexural strength and the heat resistance of the material as decisive factors. In table 44 shows data on hardness, bending strength and compressive strength of various hard materials, as well as metal-ceramic hard alloys of the WC-Co and WC-TiC-Co type. Very hard diamond and boron carbide have at the same time relatively low strength characteristics. Zin-

Hardness, bending strength and compressive strength of hard materials and hard alloys

*’ Microhardness. *g Cast or hot pressed. "Sintered or hot pressed.

Tercorundum and cast tungsten carbide closely match each other in their mechanical properties. In terms of tensile strength in bending and compression, metal-framed hard alloys are partially superior to some best brands steels With an increase in cobalt content, the bending strength of hard alloys increases with a simultaneous decrease in hardness; this can also be seen from a comparison with cast and sintered pure tungsten carbide.

The heat resistance of metal-ceramic hard alloys is exceptionally high, even at those temperatures at which high-speed steel is unsuitable from this point of view. This can be explained, on the one hand, by the structural strength of the rigid carbide frame and, on the other hand, by the sufficient heat resistance of the binder phase. For the same reason, metal-ceramic hard alloys are superior to steels in hot upsetting.

In some types of equipment (pumps for pumping out acids, valves in the chemical industry, etc.), parts made of hard alloys, in addition to mechanical wear, are also exposed to chemical reagents. In this regard, it is necessary to know the corrosion resistance of the material.

The resistance of hard alloys to chemical influences, according to Daville, is determined, on the one hand, by the stability of the carbide component and, on the other hand, by the stability of the metal binder. Refractory carbides are usually resistant to hydrochloric, sulfuric and hydrofluoric acids; at the same time, they are sensitive to the effects of oxidizing acids such as Nitric acid. Due to the fact that the metals used as a binder for carbide components are in most cases soluble in acids, the acid resistance of such alloys is determined primarily by the acid resistance of the binder phase. The corrosive effect of non-oxidizing acids, therefore, does not consist in uniform removal of the surface layer, but in leaching of the binder metal. In this case, either a carbide framework remains, or disintegration occurs into individual carbide grains.

Controlling factors that determine wear

Once researchers were convinced that hardness, flexural strength, high-temperature resistance and microstructure were determinants of wear, the question arose as to how these factors could be influenced.

Hardness can be adjusted by changing the binder content or the degree of dispersion of the carbide and binder phases. According to Meyer and Eilander, it is possible by reducing the grain size of the WC phase from 2-5 to 0.5-1 μm to increase the hardness of WC-Co alloys from 89-90 to 92-93 HRA. Conversely, as a result of too high a temperature or too long a sintering time, large carbide crystals are formed. This reduces the hardness and wear resistance of hard alloys.

Another method of increasing the hardness of metal-ceramic hard alloys is based on introducing solid solutions of carbides into the charge instead of pure carbides. According to the work, isomorphic metal carbides of groups IVa and Va of the periodic system (TiC, ZrC, VC, NbC and TaC) are characterized by complete mutual solubility. The only exception is ZrC-VC.

According to more recent data, hafnium carbide behaves similarly to zirconium carbide. Thus, in the HfC-VC system, solubility is limited. Carbides of metals of groups IVa and Va dissolve well carbides of metals of group VIa (for example, WC and Mo2C). On the contrary, carbides of metals of group VIa either do not dissolve carbides of groups IVa and Va at all, or, if they dissolve them, it is in an insignificant amount. In the structure, for example, of hard alloys WC-TiC-Co or WC-TiC-TaC (NbC), -Co is formed along with the binding y-phase and a-phase (pure WC or a solid solution of extremely small amounts of TiC-TaC-NbC in WC ) also the solid solution TiC-WC or TiC-TaC (NbC) - WC (p-phase). In this case, the solid solution p is, as a rule, somewhat harder than the a phase. The highest hardness of solid solutions is obtained, as a rule, when a certain ratio of WC: TiC ' is observed. This phenomenon is also observed in solid solutions of Mo2C-TiC and others.

Flexural strength, like hardness, is highly dependent on the bond content. With the same binder content, the flexural strength can be changed by changing the degree of dispersion of the particles of the carbide or binder phase, as well as the sintering mode. In WC-TiC-Co hard alloys, the presence of TaC (NbC) in the solid solution phase significantly increases the bending strength.

High-temperature resistance can be improved by reducing the binder content or by forming a solid solution in the carbide or binder phase. TiC, TaC, TaC-NbC, VC, Cr3C2 or Mo2C are mainly added to WC, and to cobalt small quantities Fe, Ni, Cr or Mo. In some cases, WC, which is the main component in wear-resistant carbide alloys, is replaced with solid solutions of these carbides.

The microstructure of carbide-binder hard alloys can vary over a wide range, i.e., from minimal component grain size (carbide phase grain size 0.5-1 μm) to very coarse (carbide phase grain size 5-50 μm). With grain refinement and an increase in the degree of dispersion, the hardness increases and, conversely, plasticity is apparently maximum in WC-Co alloys with 8-10% Co and a uniform grain size of 5-6 microns. Strong porosity, especially the presence of macropores in the structure, causes more severe wear. Hard alloys of the WC-Co type with a reduced content of fixed carbon (in WC), containing the m) phase, have greater hardness and greater wear resistance, but at the same time, greater brittleness than the corresponding alloys with excess carbon.

Methods for testing hard alloys for wear resistance

The wear resistance of hard alloys is determined by various methods depending on the purpose of the alloys. In most cases, only relative digital wear values ​​are determined.

High-performance carbide alloys intended for cutting various materials are tested by turning. At a constant depth of cut ii feed, durability is determined, i.e., the time until the turning tool becomes dull, depending on the cutting speed. Based on the data obtained, resistance curves are constructed (see Chapter IV). The characteristic wear phenomena of a turning cutter are as follows: on the rear surface there is a chamfer wear strip, on the front surface there is so-called crater formation.

If a hard alloy is used to reinforce tools for chip-free machining, as well as for tools operating under shock loads and under loads associated with scratching, abrasive action, etc., other methods for determining wear are used.

In the Nieberding testing machine, spherical ground samples move under a certain load on a rotating steel or cast iron disk (you can also use sandpaper) from the middle to the edge. As a result, the sample makes a spiral path of a certain length. Wear bands appear on the test sample, from which the degree of wear can be easily determined. The wear of the hard alloy under the described test conditions is almost impossible to account for and amounts to about ‘Before the wear of high-speed steel.

Unambiguous results can be obtained using a Skoda-Savina car. A rotating carbide disc grinds tightly clamped steel or carbide test pieces. The results of testing hard alloys of various porosities on this machine are given in Table. 45. The volume of the hole increases as the porosity of the carbide increases. At the same time, the so-called “Savin wear index” increases accordingly. Under the same test conditions, the wear of high-speed steel is approximately five to six times greater.

Table 45

Wear of hard alloys determined on a Skoda-Savina machine

Hardness HV

Sample number

Hole volume, mm1- South, after

Wear amount V1-3000

Surface Appearance (X 32)

The Savin wear test method was used by P. Grodzinsky to determine the microwear of hard alloys. Using a small diamond-metal disk rotating at a certain speed,

An incision is made in a hard alloy sample under load. The length and width of this cut, measured under a microscope, characterize the wear resistance of the alloy. Black developed a device for testing wear-resistant carbide alloys. In the device, the test sample, fixed in a rotating clamp, is abraded with wet quartz sand or carborundum powder. The device gives well comparable, although very relative wear indicators. In table 46 shows data on the wear resistance of various solid materials. The standard for comparison is ordinary carbon steel with a wear index of 1.

Table 46

Wear coefficients of various materials determined by Black’s sandblasting method

The subject of numerous studies recently has been wear and abrasion testing of pure carbides, borides, and other hard materials and, finally, surfacing hard alloys. In this case, they were tested at high temperatures various materials to determine the possibility of their use for bearing parts subject to wear at high temperatures.

When testing wear, especially on carbide grinding balls, the Norman and Loeb method can also be used. During long-term tests in practical conditions During grinding, ball wear is determined by weight loss or reduction in diameter. The wear of balls made of hard alloys of the WC-Co type is 50 times less than the wear of molybdenum steel balls usually used for grinding under the same conditions.

The wear test method used by Miligan and Ridgway, as well as Amman, by shot peening (steel shot) of test specimens, which has proven itself when testing grinding wheels, provides well comparable results for hard alloys. The data obtained were sufficiently confirmed when comparing carbide nozzles for sandblasting with nozzles made of tool steel under operating conditions. The method has undergone further improvement; in addition, appropriate test fixtures were created.

Table data 40 indicate unequal amounts of wear during sandblasting of hard alloys of unequal composition and different hard materials.

Tungsten-free cermet hard alloys, especially alloys based on TiC-VC and TiC- - Mo2-C, made by hot pressing, are equivalent to tungsten-cobalt hard alloys. The use of hot pressing increases the strength and hardness of these alloys and therefore improves their wear resistance.

Boron carbide is particularly resistant to sandblasting, which makes it possible to use sintered products containing boron carbide. However, one must take into account its low bending strength. The new method of wear testing of, for example, carbide turning tools (see above) or carbide dies uses instruments that measure the radioactivity of the removed chips or material being drawn, which is a good measure of the wear of the carbide.

Radioactivity is determined by a Geiger counter or autoradiographically.

Wear of metals due to friction against more soft materials, V including due to the mechanical impact of a liquid or gas jet, it primarily represents damage not to the metal itself. The process of corrosion erosion should be represented as the occurrence of two coupled processes: mechanical wear of the protective film and chemical or (in the case of electrically conductive external environment) electrochemical interaction of metal with an aggressive environment.
Metal wear is reduced compared to wear in a hydrocarbon mixture, its electrical conductivity increases, which reduces the risk of accumulation static electricity.
The influence of the ratio between the volumes of crushed material and the inter-ball space on the productivity of the mill.| The influence of the shape of grinding media on the intensity of vibration grinding / - rods. 2 - cylinders. Metal wear is an important economic indicator.
The wear and tear of metals is a problem of great scientific and economic importance. The works of foreign researchers are also of great importance - Bowden, Tibor, Ridner, Fing, Lancaster, etc. Comprehensive reviews of the most important research on wear carried out in the USSR and other countries have been published in the literature. To date, there is no general theory of friction and wear, with the help of which it would be possible to explain the experimentally observed patterns of wear and predict the behavior of various metals in relation to their wear when friction conditions change and mechanical characteristics metals
Wear of metals in some cases is also accompanied by the wedging effect of lubricant entering microcracks; structural changes surface layers resulting from increased temperatures on the friction surface; electrical and other phenomena.
Wear of non-lubricated metals depending on pressure (according to Mailender and Dees); mild steel gliding on hard chrome steel.
Typically, the wear of metals is less, the higher their hardness.
Typically, the wear of metals is less, the higher their hardness.
The absolute progressive wear of metal deposited with different grades of electrodes, taking into account wear during running-in, is shown in Fig.
Samples for wear testing on an MI type machine. The degree of wear of metals and alloys is usually determined by the coefficient of friction, the heating temperature of the materials during wear testing, and the weight loss during wear testing.
Wear products of metals during friction in hydrocarbon environments are higher oxides fl], formed during oxidation reactions between the deformed metal and free oxygen contained in the liquid.
When metals wear, the oil film is most affected by the temperature on the friction surface.
Friction and wear of metals, plastics and elastomers are discussed in detail in a number of monographs and reviews, therefore, without pretending to cover the problem completely, in this chapter we will try to briefly summarize the main results that can be used to predict the wear of rubber in products. Wear, being the result of friction, depends on the latter in different ways, which is determined by the conditions and mode of friction, the composition and design of the rubbing materials, implemented by the friction mechanism.

In operation, metal wear is estimated in kilograms (or grams) per 1 ton of ground fuel or silt; ta 1 / set-hour of energy expended 1 n; grinding, as well as in kg/t balls, loading the greedy ones into the drum.
Main types of wear of metals, Kyiv - Moscow, Mashgiz.
Note that the wear of metals is described by a formula similar to (1).
During sliding friction, wear of metals in fuels is directly proportional to the bulk temperature of the fuel up to approximately 120 C. At higher temperatures, an inflection of the curve is observed, and the rate of increase in wear decreases with increasing temperature. The critical load for metal setting decreases with increasing fuel temperature.
From work on metal wear it is known that a very small fraction of friction energy is spent on abrasion; This explains the lack of a direct relationship between friction and wear.
The calculated determination of the depth of metal wear when the oxide film is completely removed from the surface is difficult task.
The problems of corrosion and mechanical-erosive wear of metal are solved comprehensively using technological, special ways protection ( protective coatings, corrosion inhibitors, electrochemical protection) and modern means control of the aggressiveness of corrosive environments and the effectiveness of protection methods. The corrosion protection method is selected on the basis of a feasibility study, taking into account the availability of material, technical, labor and other resources. This takes into account the stage of field development, the associated aggressiveness of the transported medium and the forecast of its changes over time.
During friction and wear of metals, various physical, chemical and mechanical processes arise and occur on the surface and in surface volumes, which determine the intensity and nature of wear.
When friction and wear of metals occur on the surface and in surface volumes, various physical, chemical and mechanical processes occur. Depending on the friction conditions, each of these processes has a different speed. The process that has the highest speed under given friction conditions will be predominant, determining the type of wear. By changing the friction conditions, one can slow down or accelerate one or another process and thereby cause one or another type of wear.
Such a diverse influence of the considered factors on the wear of metals does not allow us to establish the reason for the high wear resistance of iron coatings. However, research still makes it possible to identify the nature of the influence of certain properties of coatings on their wear resistance.
Thus, the processes of wear of metals and the deterioration of the thermal stability of fuels are interrelated. This is also confirmed by the fact that almost all antioxidant additives, and especially additives that improve the thermal stability of fuels, are also anti-wear. The quality of additives varies only based on the temperature limits of their effectiveness. Their role is to protect the metal through adsorption or chemisorption on its surface. At the same time, the destruction of the metal from corrosion processes and its catalytic effect on oxidation processes in the fuel are limited. In general, the effect of additives limits the formation of a finely dispersed solid phase in the fuel, the subsequent enlargement of its particles, and therefore reduces the risk of the negative impact of the formed solid phase on the wear of abrasive metals.
The abrasiveness of dust characterizes the intensity of metal wear at the same gas velocities and dust concentrations. It depends on the hardness, shape, size and density of the particles.
Wear of grinding media various shapes and linings when grinding quartz sand.
As can be seen from the metal wear graph, in the process of grinding quartz sand to different dispersion (Fig. 13), the degree of wear of balls is significantly lower than that of rods or cylinders.
Currently, the mechanism of wear of metals and its patterns are most fully explained by the molecular mechanical theory. Based on her general provisions, some new patterns of metal wear and ways to reduce it have been established.
One of the conditions for reducing metal wear in the case of molecular interaction, as indicated in the work, is the creation of a negative gradient mechanical properties in depth. Under such conditions, metal wear has a polishing-dust-like character.
In the process of friction and wear of metals, the following occurs: elastic and plastic deformation of microroughnesses and plastic flow in solid surface layers, leading to plastic wear - a change in the size of rubbing bodies without noticeable destruction of their surface; repeated microplastic deformations during periodic encounters of microroughnesses, leading to fatigue failure of surfaces; change in the mechanical and physical properties of the surface layers of the metal due to deep plastic deformation.
The abrasiveness of dust characterizes the intensity of metal wear at the same gas velocities and dust concentrations. It depends on the hardness, shape, size and density of the particles.
The ability of hydrocarbons of different structures to reduce wear of metals during friction and reduce friction has still been studied very little. There is some data on the antiwear properties of naphthenic and aromatic hydrocarbon fractions isolated from oils.
X-ray diffraction pattern of the initial surface of a sample made of Armco iron (visible. The explanation of the influence of secondary structures on the wear of metals is associated with the classification of metals according to their wear resistance, developed by the authors, as well as taking into account the existence of groups of metals (first and second groups), during friction of which oxide films are formed that have a complex of properties that increase wear resistance, and with the presence of groups of metals (third and fourth groups), during friction of which oxide films are formed that have a low complex of properties, as a result of which the wear rate increases.
The influence of the composition of the lubricating medium on the corrosion-mechanical wear of the metal is due to a number of factors, among which the main ones are the adsorption decrease in the strength of the surface layers of the metal due to the Rebinder effect, the disjoining pressure of thin layers of liquid in cracks, chemical corrosion aggressiveness and the ability of additives to create strong tri-hydrates during friction. bochemical films, the ability of the lubricating medium to inhibit electrochemical corrosion and hydrogenation of the metal.
Using the basic expression for the depth of metal wear (5.14), it is possible to solve some practical problems related to the wear of pipes on the heating surfaces of the boiler.
Solid contaminants include metal wear products, as well as dust and dirt that can enter the tank from the atmosphere if there is no filter on the air line.
The dependence of the wear of heat-treated U10A steel on specific pressure (according to P.K. Topekha. The influence of specific pressure on the intensity of corrosion-mechanical wear of metals and alloys has been studied very poorly. According to work 40], corrosion-mechanical wear of gray cast iron is directly is proportional to the specific pressure up to a certain value of the latter, after which the amount of wear increases sharply. For alloy cast iron, a more complex dependence of wear on the specific pressure is observed.
The extreme pressure effect is necessarily based on the wear of the modified metal; therefore, wear-free operation of friction units of machines and mechanisms in boundary and elastohydrodynamic friction modes when using oils with such additives is practically impossible. Rosenberg, who notes that even under conditions of boundary lubrication, a wear-free friction regime can be ensured if the oil with the additive forms boundary films on the metal.
The conclusions regarding the effect of abrasive hardness on metal wear are as follows: if the hardness of abrasive grains significantly exceeds the hardness of the metal, then wear does not depend on the difference in hardness of the abrasive and metal; if the hardness of the abrasive grains is lower than the hardness of the metal, then wear depends on the difference in hardness and quickly decreases as this difference increases.

When analyzing the results of studies of the effect of the weighting agent on metal wear on the MACT-I machine, it should be borne in mind that the entry of abrasive into the frictional contact zone on this machine is difficult due to the small contact area.
The influence of cleaning heating surfaces of steam boilers on metal wear // Thermal power engineering.
Dependence of the wear rate of a friction pair steel C45 - steel C45 at a pressure of 1 MPa on the sliding speed at a relative air humidity of 5% (curve / and 50% (curve 2). All the given data on the effect of humidity on the wear of metals were obtained by Uetz in 1968, when hydrogen wear was not yet known.
Numerous attempts are known from the literature to present the patterns of wear of metals and alloys in the form of mathematical formulas relating the intensity of wear to the load, physical properties materials and the environment in which this friction pair wears out.
This scheme reflects the adsorption-corrosion-fatigue nature of destruction and wear of metal in a lubricating environment and is a phenomenological description of the mechanism of this destruction and wear, taking into account factors determined by the composition of the lubricating environment. Depending on the operating conditions, the nature of the load, the material and design of a particular machine component, the role of the factors indicated in the diagram may be different. However, the significance of each of these factors seems sufficient to be included in general scheme And considerations in relation to specific case development, analysis of the mechanism of action and use of lubricants effective in conditions of corrosion-fatigue wear.
In table 14 shows summary data on metal wear at high temperatures. Metals are arranged in the table in increasing order of their wear resistance. The wear values ​​are given as the average of tests of six samples of each metal grade.
Coefficient B takes into account the influence of the initial stage of corrosion on metal wear and equal to the ratio corrosion depth - during the period between complete removal of the oxide film from the surface in the initial stage of corrosion to the value at the main stage of corrosion.
The term relative specific wear or relative wear refers to the wear of metal in g/kWh or kg/kWh of energy consumed by the shredder.
Characteristics of idle speed. When choosing the diameter of the balls, it should be taken into account that metal wear increases with decreasing diameters. Operational practice has shown, for example, that a ball diameter of 30 mm is beneficial for ash, and 40 mm for coal near Moscow.