Wear and tear of industrial equipment parts. Types of defects and wear of car parts

During operation, the equipment and its elements, being subjected to various influences, change in condition, size and properties. These changes can proceed smoothly (regular change) and abruptly (irregular change). The reasons for these changes are wear phenomena, estimated by changing the geometric dimensions of machine elements, their mass, or by some other indirect signs (wear due to shape changes without mass loss, etc.).

Wear- a process that leads to a change not only in the external, but also in the strength characteristics of machine elements, which gradually reduces their reliability and leads to failures in operation.

The most intensive wear process occurs in the conjugated elements of machines, especially when they are mutually moving. On fig. 7 shows the main factors that determine the wear processes in machines.

Rice. 7. Main factors determining wear processes in machines and equipment.

Wear- the result of wear, manifested in the form of separation or permanent deformation of the material of the part. The consequence of wear, as a rule, is a violation of interfaces, kinematic connections and the operation of parts of a given unit or mechanism as a whole.

Machine wear can be mechanical, molecular-mechanical, corrosion-mechanical, corrosion.

Mechanical wear occurs as a result of mechanical influences and includes the following types of wear: abrasive, hydroabrasive, gas-abrasive, erosive, fatigue, cavitation.

abrasive wear occurs as a result of the cutting and scratching action of solid particles. These particles, which have entered from the outside or separated (chipped, planed, etc.) from mutually contacting and rubbing parts, significantly increase their wear.

Waterjet wear occurs as a result of the action of solid particles trapped in the flow of an oily liquid that serves as a lubricant between parts.

Gas-abrasive wear arises as a result of the action of solid particles trapped between rubbing parts with gas flows.

erosion wear surfaces of parts occurs as a result of exposure to liquid or gas flows containing excessively small solid particles or inclusions.

Gas-abrasive wear is typical for internal combustion engines, and erosive wear is typical for its parts: valve system, injector nozzles, carburetor jets, etc.

fatigue wear occurs as a result of repeated deformation of the material of the parts. It arises and develops in the most stressed, mainly working, surface layers of parts due to the long-term action of loads, especially those that are variable in value and direction. In this type of wear, the cause of parts failures are fatigue cracks that begin to develop in that part of the surface where tensile stresses act, and, as a rule, from the place where various kinds of risks, nicks, and delaminations appeared.

cavitation wear manifests itself in the relative movement of solids in a liquid medium. Most often, it is observed in the liners of the cylinder block, cooling and lubrication systems of internal combustion engines, blades of oil and water pumps, etc.

Molecular mechanical wear occurs as a result of the simultaneous action of mechanical and molecular or atomic forces. Due to their unevenness and roughness, the mutually contacting and rubbing surfaces of the mating parts have contacts through which significant specific loads are transmitted, therefore, breaks in the lubricating film (oils, ointments) are possible, and at high relative speeds of movement of the surfaces of the parts, excessive heating occurs, leading to the evaporation of the lubricating oil film or ointments and to the setting of particles in contact parts. In the future, separation and destruction of the places of setting of parts occurs. In this case, a recess is formed on one of the surfaces, and a protrusion is formed on the other, i.e. transfer of metal from one surface to another.

The considered type of wear is observed in the process of running-in parts and elements of machines.

Corrosion-mechanical wear occurs during the friction of materials that have entered into chemical interaction with the environment (air oxygen and other gases). Under the action of an aggressive oxidizing environment, oxide films are formed on the mutually contacting and rubbing surfaces of the parts, which are removed as a result of mechanical friction, and the surfaces freed from these films are oxidized again, etc., i.e. wear process takes place. An example is the wear of parts of the cylinder-piston group of engines due to the presence in the environment of such corrosion agents as sulfuric, sulphurous and organic acids.

The most significant influence on the wear process is exerted by friction forces, causing mechanical and other types of wear of mutually contacting surfaces. Moreover, the wear resulting from friction is a whole series of simultaneously occurring processes: abrasion, crushing, oxidation, etc.

Process abrasion occurs when one part of the machine or its element slides relative to another. This phenomenon is called friction of the first kind and occurs due to the fact that the contacting surfaces, as a rule, have irregularities (roughness) that prevent the free movement (sliding) of one part over another. The process of abrasion is the more intense, the more rough the contacting surfaces. Wear intensity increases if abrasive or other inclusions get between the contacting surfaces.

The process of abrasion also occurs during mutual rolling of the surfaces of machine parts under load and during impacts. This phenomenon is called friction of the second kind. It occurs due to the fact that, as a result of rolling or impacts, microcracks, and often macrocracks, appear on the surfaces of the contacting parts, with their subsequent development in depth and the formation of a thin metal film, which subsequently crumbles and peels off, resulting in the so-called wear at major destruction. The causes of such wear can be surface fatigue, as well as structural damage to the metal of the contacting surfaces due to heat and shock. The considered type of mechanical wear often appears on the working surfaces of gear and worm gears, rolling bearings, various support devices, etc.

Fig.8. Wear in mating parts: a - increase in wear; b - wear rate

Corrosion wear- destruction of metal parts of machines under the influence of the environment, especially moistened. Destruction in this type of wear begins, as a rule, from the outer surfaces, gradually penetrating deep into. The most common type of corrosion is rusting, i.e. combination of metal with atmospheric oxygen. As a result of corrosion, the unpainted surfaces of the metal parts of machines are first covered with a dark coating, and then with deep (if the necessary measures are not taken) corrosive flaws, while the metal parts acquire a spongy fragile structure. Parts of machines with a low carbon content are subjected to the greatest damage and wear as a result of corrosion. The intensity of corrosion increases in the presence of a number of gases and liquids containing acids and alkalis.

There are two types of corrosion wear processes: chemical And electrochemical.

Chemical corrosion manifests itself under the influence of atmospheric oxygen and various gases (carbon dioxide, sulfur dioxide), as well as liquids that do not conduct electric current (oils and ointments of oil refining, various resins). The intensity of chemical wear of parts depends on the quality of the materials from which they are made, the degree of oxidation at high temperatures and operating conditions (neutral or aggressive environment, etc.).

Electrochemical corrosion occurs in media that conduct electric current, i.e. in electrolytes - solutions of salts, acids, alkalis, as well as in a humid atmosphere and soil.

The pattern of increasing wear of equipment elements, especially in their joints, is expressed by a curve that has three clearly defined sections that characterize the periods of operation of the joints (Fig. 8):

I- the running-in period, when the joints wear out very intensively, but the wear rate gradually decreases;

II- the period of normal operation, when the conditions on the surface of the articulated parts become constant, and wear proceeds at a constant rate;

III- the period of emergency, most intensive wear, when wear (clearances) reach unacceptable values.

The period of normal operation of a piece of equipment (assembly unit, parts, etc.):

(31)

where - the duration of the running-in parts; - wear corresponding to the maximum allowable wear (clearance) in the interfaces of parts; - wear corresponding to the end of running-in parts; tg- coefficient characterizing the rate of wear of parts.

The following main factors influence the wear rate of a normal period of operation: operating conditions - pressure, nature of loads, relative speeds, temperatures, etc.; properties of materials, their variability in work; mating conditions, the nature of the contact of mating elements, the quality of processing of the material from which these elements are made; timeliness and quality of technical services; compliance of the used fuels and lubricants.

In addition to wear, the phenomena of plastic deformation of equipment elements are possible due to unacceptable loads on these elements.

Changes in machines and their elements are expressed by the following functional dependence:

where - operational factors (the nature and characteristics of the production of works, modes of use of machines, climatic conditions, etc.); - design factors (kinematic and dynamic features of machines, properties of materials from which their elements are made, etc.); - technological factors (type of materials from which machine elements are made, methods and quality of their processing, etc.); - subjective features and qualifications of the personnel servicing the machine (drivers, mechanics, tankers, etc.).

Wear and tear in machines and their elements are divided into moral and physical.

Obsolescence- decrease in the cost of equipment under the influence of technical progress.

This type of wear has two forms of manifestation. Obsolescence of the first form is the depreciation of machines due to the constant growth of labor productivity in the industries that produce these machines, as well as manufacturing products, materials, etc. for them. The area of distribution of this form of obsolescence is determined by the rate of technical progress of that sector of the national economy and related industries that produce these machines or components for them, materials, etc.

Loss of equipment value due to obsolescence of the first form:

(33)

where is the initial cost of the equipment, rub.; - the replacement cost of the machine or the cost of its complete reproduction at the time of physical wear and tear, taking into account the appearance of more advanced designs, rub.

Replacement cost of equipment after a certain time T:

(34)

where is the initial cost of the car, rub.; R- the average annual increase in labor productivity in the industry and related industries that produce the specified type of equipment.

Obsolescence of the second form is the depreciation of equipment due to the emergence of new technology, i.e. machines similar or close to them, but more advanced designs. An indicator of the obsolescence of this form is the coefficient of reduction in the cost of machines due to technical progress, expressed as a fraction of its original cost:

(35)

Physical deterioration arises as a result of mechanical molecular-mechanical and corrosion-mechanical wear and consists of the wear of structural and non-structural elements of machines. Physical wear appears both as a result of the direct action of machines and their elements (wear as a result of the direct action of machines), and as a result of the indirect action of equipment and its individual elements (wear as a result of equipment inactivity - during downtime, when they are affected by atmospheric and other adverse conditions ). Depreciation is determined as a percentage: new elements in the equipment (parts, assembly units, etc.) are taken as 100% serviceability, and worn ones, the use of which is impossible, are taken as 100% wear.

In value terms, the physical wear and tear of equipment is determined (% of the cost of reproduction):

(36)

where is the estimated cost of equipment repair, rub.; - replacement cost of equipment or the cost of complete reproduction of equipment at the time of its physical deterioration, taking into account the appearance of more advanced designs, rubles; a is the relative value of residual wear, which is established from the experimental data of the repair of such equipment, %.

Repair of equipment is expedient if the cost of restoring equipment is less than the cost of acquiring a new one, i.e.< , где - стоимость нового оборудования. При этом нельзя не учитывать степени совершенства конструкции, соответственно, и технико -экономических показателей как старого, так и нового оборудования.

General depreciation of equipment due to physical and moral depreciation as a share of the initial cost:

Fig. 9 Graph of the total wear of a machine, consisting of elements that are replaceable or completely renewable at various service lives (according to aggregated indicators)

The total wear of equipment is determined by two methods - analytical And graphic. The most obvious is the graphical method.

On the horizontal axis (Fig. 9), the full service life of the machine T (accepted according to the standard service life tables) is plotted, and on the vertical axis - the maximum indicator of total wear. First, the wear of the main non-replaceable and non-renewable element of equipment (main frame, bed, etc.) is determined with the absolute wear value . A straight line drawn from the origin to the point represents the line of total wear of the element in question. By the end of the life of the equipment, this element will be completely worn out over time (partial wear

The service life of machine elements is taken according to the results of an experimental check, test data or according to regulatory reference books.

When determining the total wear, the following order is followed: make a list of all structural and non-structural elements of the machine; determine their service life; select constructive and non-constructive elements in groups so that each of them can be considered as one enlarged element; determine the service life and cost of all simultaneously replaceable or renewable elements of each of these groups; make a table and calculate the total wear for any interval of use of the machine or build a wear graph based on aggregated indicators.

In determining the life or cost of enlarged elements and the frequency of their renewal, data on the frequency and average cost of the corresponding maintenance and repair, together with the average cost of the spare parts replaced, can be used.

The tendency to depreciation is inherent in many types of property accounted for in the company, including fixed assets. About what are the types of depreciation of fixed assets and how to determine it, will be discussed in the publication.

The concept and types of depreciation of fixed production assets (OPF)

OPF - assets designed for operation in production for a long time (more than 1 year) and wear out in the course of work.

Depreciation is considered to be the gradual loss of consumer qualities of an object and, accordingly, its value. It happens in different ways. Some objects wear out due to obsolescence and dilapidation of constituent materials, mechanical wear, metal fatigue under the influence of production processes, natural phenomena and other factors, while others - due to the loss of expediency of use and a decrease in economic efficiency in use. And since production assets wear out for completely different reasons, they classify this phenomenon in accordance with them.

Based on the above criteria, the types of depreciation of fixed assets include physical and moral depreciation.

Obsolescence of fixed assets

The obsolescence of the fixed assets is found in the depreciation of the fixed assets, as a result of the appearance of technical innovations, sometimes long before the end of the JFS. Distinguish obsolescence of the 1st and 2nd orders.

The first category includes depreciation caused by an increase in labor productivity in the industries producing OF. This process leads to a reduction in the cost of manufactured objects that already have increased competitiveness due to lower prices.

Obsolescence of fixed assets of the 2nd order occurs as a result of the creation of the most cost-effective fixed assets, the emergence of new facilities that increase production productivity.

Obsolescence can be partial or complete. Partial depreciation is recognized, which is a shared loss of the consumer value of the object. Depending on the specifics of production, it is possible to prevent partial obsolescence of an object by using it in other operations where efficiency will be higher.

Complete obsolescence is the complete depreciation of the object. In such cases, its use in production becomes unprofitable.

Physical depreciation of fixed assets

The physical deterioration of the OS means the loss of use value. Distinguish between productive and unproductive wear. Productive is characterized by loss of value, which is the result of operation, unproductive wear and tear is an invariable attribute of objects that are under conservation for various reasons, such as the impossibility of use, natural aging, etc.

Physical deterioration can be complete or partial. In full, OS items are replaced by new assets as the lifespan has expired and the cost of the OS has fully passed into the price of the products being released. An example is capital construction, when an erected building replaces a worn one. Partial physical depreciation implies the possibility of further operation of the object, carrying out repair work, reconstruction, if appropriate, or the implementation of appraisal work to determine the percentage of depreciation of the object and establish the possibility of its operation or sale.

Wear Calculation Methods

The degree of physical wear and tear of fixed assets depends on such factors as the intensity and duration of operation, the characteristic features of the OS designs and the circumstances of work. We will consider methods for calculating the depreciation of buildings, since they most often require professional evaluation.

In the special literature on assessment, 5 methods for calculating the physical deterioration of buildings are described. These are the methods:

cost compensation;
chronological age;
effective age;
expert;
breakdowns.

Consider the features of each of them.

Cost compensation consists in equating the amount of depreciation to the cost of its elimination, which is an excellent justification for the amount of depreciation. The disadvantage of the method is its laboriousness of calculations, especially for large buildings.
With the chronological calculation method, the formula is used:
And physical \u003d B x / B ss x 100, where B x is the age of the object in fact, B ss is the service life of the building according to the standard.

Let's calculate the physical deterioration of the building, example:

Let us determine the depreciation of a building that has served 750 months with a standard service life of 1200 months.

And physical \u003d 750 / 1200 x 100 \u003d 62.5%

The advantage of the method is the simplicity of calculation, but it does not take into account the repairs and replacements that took place during operation, which often happens in practice. Therefore, this method is considered effective for calculating depreciation in the first years of OS operation; if the building is more than 10 years old, you should not use it .;
Calculation by the effective age method has 3 variations:
And physical \u003d V e / V ss x 100%, where where V e is the effective age of the object, i.e. the expert evaluates the structure by appearance.

And physical \u003d (V ss - V ost) / V ss x 100%

And physical \u003d (1 - B st / V ss) x 100%, where B st - the remaining life of the building.

Substituting the initial data of the previous example into the formulas and adding the expert's estimate of 720 months, we get the values:

And physical \u003d 720 / 1200 x 100 \u003d 60%

And physical \u003d (1200 - 450) / 1200 x 100 \u003d 62.5%

And physical \u003d (1 - 450 / 1200) x 100 \u003d 62.5%

The disadvantage of the method is the impossibility of a strong justification of the effective age of the structure. There is a large calculation error (this can be seen from the first formula).
The expert method is based on the rating scale for depreciation, proposed in the "Rules for assessing the physical depreciation of residential buildings" VSN 53-86r. Its value is determined by external damage to the elements. This method is used by BTI employees when issuing registration certificates. Wear is determined by the formula:
And physical \u003d ∑ (I k x HC k) x 100%, where I k is the amount of wear of a certain element in the building, calculated according to the rules of VSN 53-86r, UV k is the specific gravity of this element in the building.

The specified NLA describes in detail the expert methodology, we introduce only the principle of calculation. The expert method is the most commonly used.
The breakdown method proposes the establishment of physical depreciation as a whole by summing the depreciation values for individual groups, expressed in:
- Correctable wear (deferred repair);
- Irreparable wear of short-lived (i.e., repeatedly replaced during operation) elements;
- Irreparable wear and tear of long-lived (recovery of which is possible only with the overhaul of the building) elements.

Practical work No. 1

"Independent study and note-taking of the topic: "Wear of parts of industrial equipment""

The essence of the phenomenon of wear

The service life of industrial equipment is determined by the wear of its parts.- a change in the size, shape, mass or state of their surfaces due to wear, i.e. residual deformation from permanent loads or due to destruction of the surface layer during friction.

The wear rate of equipment parts depends on many factors:

Ø conditions and mode of their work;

Ø material from which they are made;

Ø the nature of the lubrication of rubbing surfaces;

Ø specific force and sliding speed;

Ø temperature in the interface zone;

Ø state of the environment (dustiness, etc.).

Wear amount characterized by established units of length, volume, mass, etc.

Depreciation is determined:

Ø by changing the gaps between the mating surfaces of parts, \

Ø leakage in seals,

Ø decrease in the accuracy of processing the product, etc.

Wear is:

ü normal and

ü emergency.

Normal or natural is called wear that occurs during the correct, but long-term operation of the machine, i.e. as a result of using a given resource of its operation.

emergency or progressive, called wear, which occurs within a short time and reaches such proportions that further operation of the machine becomes impossible.

At certain values of changes resulting from wear, wear limit, causing a sharp deterioration in the performance of individual parts, mechanisms and the machine as a whole, which causes the need for its repair.

Wear rate - this is the ratio of the values of the characterizing quantities to the time interval during which they arose.

The essence of the phenomenon of friction

The primary cause of wear of parts (especially mating and rubbing against each other) is friction.

Friction - the process of resistance to relative movement that occurs between two bodies in the areas of contact of their surfaces along the tangents to them, accompanied by the dissipation of energy, i.e., its transformation into heat.

In everyday life, friction is both beneficial and harmful.

Benefit lies in the fact that due to the roughness of all objects without exception, as a result of friction between them, slip does not occur. This explains, for example, that we can move freely on the ground without falling, objects do not slip out of our hands, a nail holds firmly in the wall, a train moves along rails, etc. The same friction phenomenon is observed in the mechanisms of machines, whose work is accompanied by the movement of interacting parts. In this case, friction gives negative result - wear of mating surfaces of parts. Therefore, friction in mechanisms (with the exception of the friction of brakes, drive belts, friction gears) is an undesirable phenomenon.

Types and nature of wear parts

Types of wear are distinguished in accordance with the existing types of wear -

Types of wear:

Ø mechanical(abrasive, fatigue ),

Ø corrosive and etc.

Mechanical wear is the result of the action of friction forces when sliding one part over another.

With this type of wear, abrasion (cutting) of the surface layer of the metal and distortion of the geometric dimensions of the jointly working parts occur. Wear of this type most often occurs during the operation of such common interfaces of parts as a shaft - bearing, frame - table, piston - cylinder, etc. It also appears during rolling friction of surfaces, since sliding friction inevitably accompanies this type of friction, however, in such cases, wear is very small.

The degree and nature of mechanical wear of parts depend on many factors:

Ø physical and mechanical properties of the upper layers of the metal;

Ø working conditions and the nature of the interaction of mating surfaces; pressure; relative speed of movement;

Ø conditions for lubrication of rubbing surfaces;

Ø degree of roughness of the latter, etc.

The most destructive effect on the details has abrasive wear, which is observed in cases where the rubbing surfaces are contaminated with small abrasive and metal particles.

Usually, such particles get on the rubbing surfaces during the processing of cast billets on the machine, as a result of wear of the surfaces themselves, dust ingress, etc.

They retain their cutting properties for a long time, form scratches and scuffs on the surfaces of parts, and, when mixed with dirt, act as an abrasive paste, as a result of which intensive rubbing and wear of mating surfaces occurs. The interaction of the surfaces of parts without relative movement causes metal crushing, which is typical for keyed, splined, threaded and other connections.

Mechanical wear can also be caused by poor maintenance of the equipment, for example, irregularities in the supply of lubrication, poor quality repairs and non-compliance with its deadlines, power overload, etc.

During operation, many machine parts (shafts, gear teeth, connecting rods, springs, bearings) are subjected to long-term action of variable dynamic loads, which have a more negative effect on the strength properties of the part than static loads.

fatigue wear is the result of variable loads acting on the part, causing fatigue of the material of the part and its destruction. Shafts, springs and other parts are destroyed due to fatigue of the material in the cross section. In this case, a characteristic type of fracture is obtained with two zones - the zone of developing cracks and the zone along which the fracture occurred. The surface of the first zone is smooth, while the second zone is shelled and sometimes granular.

Fatigue failure of the material of a part does not necessarily lead to its failure immediately. It is also possible that fatigue cracks, peeling and other defects may occur, which, however, are dangerous, as they cause accelerated wear of the part and mechanism.

To prevent fatigue failure, it is important to choose the right cross-sectional shape of a newly manufactured or repaired part: it should not have sharp transitions from one size to another. It should also be remembered that a rough surface, the presence of scratches and scratches can cause fatigue cracks.

Seizure wearoccurs as a result of sticking (“seizing”) of one surface to another.

This phenomenon is observed with insufficient lubrication, as well as significant pressure, at which two mating surfaces approach each other so closely that molecular forces begin to act between them, leading to their seizure.

Corrosive wear is the result of wear of parts of machines and installations that are under the direct influence of water, air, chemicals, temperature fluctuations. For example, if the air temperature in industrial premises is unstable, then every time it rises, the contained

Rice. one. The nature of mechanical wear of parts:

but- bed and table guides, b- internal surfaces of the cylinder,

in- piston, d, d- shaft, e, w- 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, 11 - screw;

AND- places of wear, R- active efforts

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 occurs, i.e. complex, wear.

The tires of a car are the only element of the vehicle that connects it to the road. Often car owners forget that rubber is the most important element of a car that directly affects. But when the tires wear out, every driver regretfully understands that it's time to spend money on buying new tires. . After all, sometimes tire wear can indicate a possible malfunction of the car. In this case, replacing the rubber with a new one may not help. For example, with some types of breakdowns, your new tires may wear out prematurely in a short time. Let's take a look at ten of the most by which it is quite possible to determine the cause of this wear and tear, eventually finding out the technical condition of the vehicle.

1. Wear of the rubber tread in the center (in the middle)

What it looks like: With this type, as a rule, the tread in the middle of the tire is worn the most (example in the photo).

Cause: If the tire wears the most in the center of the wheel, then this indicates that the central part of the tread had the most contact with the road surface, compared to the tread closer to the edges of the rubber. Therefore, the car on which this rubber was installed did not have sufficient grip with the road surface. Accordingly, the traction of the machine was insufficient.

Most often, such wear indicates that the tire was not properly inflated. That is, the tire pressure did not correspond to the pressure recommended by the car manufacturer. This type of wear indicates that the owner of the car did not check the pressure even with sudden changes in temperature outside, at which the pressure in the tires can change significantly.

The fact is that while the tires are cold (for example, after a frosty night), the tire pressure may be lower than the manufacturer recommends. But after the start of the movement, the pressure in the tires begins to rise from the heating of the air in it. As a result, after a certain distance traveled, tire pressure may exceed the maximum allowable rate recommended by the automaker. As a result, the pumped tire unevenly adheres to the road surface, as a result of which uneven tire wear in the center of the tread will be observed.

Some motorists often advise to improve handling and reduce fuel consumption, on the contrary, to pump over the wheels. But this is not justified. Yes, in this way you can reduce fuel consumption a little and even improve handling a little, but in the end you will pay for it with faster tread wear.

That is, saving a little money on fuel, you will pay a lot more.

2. Tire bulging (bulging) and side wall cracks

What it looks like: Cracks and bulges on the side wall of the tires.

Cause: This usually comes from hitting a pothole (hole) in the road, a curb, etc. Usually the tire is well protected from such impacts. But if the tire is under-inflated or over-inflated, there is a great danger that the tire will be damaged as a result of the impact. Large cracks on the side wall of the tire that run along the rim of the wheel indicate that it has been operated with insufficient pressure for a long time. Small cracks on the side surface of the rubber indicate external damage or the age of the rubber (due to age, the rubber compound begins to chemically break down, causing the tire to begin to crack).

A herniated tire looks like a bulge on the surface of the rubber. Most often, a protrusion (hernia) appears on the side wall of the tire. Herniated rubber is associated with internal damage (rubber layer). This usually happens due to a side part hitting a curb, pole, etc. Most often, after an impact, a hernia (protrusion) of the wheel does not immediately appear. That is, after a stroke, you can see a hernia only after a week or even after a month.

If you notice cracks or hernia on tires, then you need to buy new tires as soon as possible.

Remember that it is very dangerous to use rubber with a hernia..

3. Dents in rubber

What it looks like: According to long-term observations, rubber with dents looks like in the photo. That is, the tire has the form of tubercles and dents.

Cause: This type of tire is usually associated with (wear or damage to the elements of the chassis of the car). Due to a malfunction of the suspension, shock mitigation on bumps is insufficient. As a result, the tire experiences an overload from impacts, taking on the maximum load. But the load is distributed unevenly over the entire tread surface. As a result, some areas of the tread take on more load than others, which contributes to the formation of dents and bumps on the tires.

Most often, this appearance of used tires is associated with poor shock absorbers. Although it is worth noting that any parts of the suspension that have failed can cause this kind of wear.

We advise you in case of detection of such deformation of the tires, to make a complete suspension and racks of the car in the technical center. We do not recommend dealing with a similar problem at a tire fitting, i.e. in order to determine the cause of the change in the shape of the wheels. It is not uncommon when tire workers do not know what can cause irregularities (dents, bumps) on the tread surface.

Most often, tire workers claim and believe that this is the cause of improper camber. But this is not a fact. As we have already said, this reason may be due to the failure of the shock absorber (s).

4. Diagonal dent with signs of tread wear

What it looks like: Diagonal dent on the tread surface with uneven wear on the tire surface.

Cause: Most often this problem occurs on the rear wheels, where the camber is incorrectly set. Also, such a deformation of the wheel may be associated with an insufficient rotation interval, and also, sometimes such a change in the appearance of the tire may be associated with the frequent transportation of heavy loads in the trunk or in the car.

A heavy load can change the geometry of the suspension, resulting in diagonal deformation of the rubber tread surface.

5. Excessive tread wear at the edges

What it looks like: The inner and outer tread has increased wear, while the middle of the tread is significantly less worn.

Cause: This is a sure sign of insufficient. That is, the pressure does not correspond to the norm recommended by the car manufacturer. Remember that this is the most dangerous tire condition. The fact is that with reduced pressure in the tire, it is subject to greater bending. According to the laws of physics, this means that when the wheel rotates, the tire will accumulate more heat. As a result, the rubber will not evenly adhere to the road surface and, accordingly, we will get uneven rubber wear.

Also, insufficient pressure in the tires will lead to the fact that the rubber will not sufficiently soften the blows on the road, which will naturally directly affect the suspension. Over time, this hard impact on the suspension can lead to premature suspension failure, as well as affect the wheel alignment.

How to avoid the problem of under-inflated (insufficient) tires: We again return to the fact that every driver should regularly check the air pressure in the tires, that is, every month or every time after a sharp change in temperature outside. Also remember that cold tires (when parked at night) may show pressures lower than those recommended by the vehicle manufacturer. But during a long trip, due to the heating of the air, the pressure may exceed the norm.

The fact is that this system usually warns you of a change in tire pressure, either when there is a sharp pressure fluctuation (for example, a sharp drop in tire pressure by more than 25 percent), or when there is a significant decrease in pressure for a long time.

In other words, the tire pressure warning system can only be activated when the tire pressure is significantly lower than necessary. This means that you run the risk of driving for a long time on wheels with insufficient air pressure.

6. Convex side tread wear

What it looks like: The side blocks of the tread, usually similar to the plumage of birds, have. The lower edges of the tread blocks are rounded, while the higher edges of the blocks are sharp. Note that you cannot visually notice this kind of wear. This can be understood only when examining the tread from the edge and by touch, i.e. with hands.

Cause: With this type of tread wear, check the ball joints and wheel bearing first.

It is also necessary to check the stabilizer bushing, which, in case of failure, can lead to improper operation of the suspension stabilizer, which will eventually lead to this type of wear on the rubber tread.

7. Flat wear spots

What it looks like: One spot on the wheel has more wear than the other.

Cause: Single spots of increased wear on the surface of the tire are often found when forced hard braking or skidding, or when taxiing out of a situation in order to avoid an impact (for example, if an elk or other animal did not unexpectedly run onto the road). Especially such wear will be visible after heavy braking with simultaneous skidding, if the car is missing.

The fact is that when braking hard and taxiing in order to get away from the impact, a car without ABS is more prone to skidding with locked wheels, which will lead to something like this type of worn spot on the tire tread.

Also, similar stains can appear in cars that have been parked for a long time.

Remember that when you park your car for a long time, you risk tires where wear spots will appear on the tires of your car due to the uneven distribution of the weight of the car on them. The fact is that during parking, the rubber tread does not completely come into contact with the surface and, as a result, a certain section of rubber is deformed from a long parking.

8. Wear on the leading edge of the tread

What it looks like: The leading edge of the tread block is worn and the rear of the tread has sharper corners. Please note that this type of wear may not be visible during visual inspection. Therefore, check the protector with the edge by hand. If you notice that some tread corners are sharper (like hacksaw teeth) compared to other tread edges that are smoother, then this is real wear and not the norm, as many drivers usually assume.

Cause: This is the most common tire wear. Since this type of tire wear is very common and many car owners think that this is the norm, it is not. In fact, this wear indicates that the wheel has insufficient rotation. Therefore, it is necessary.

Most often, the reason is associated with the wear of the suspension elements (salint blocks), with the wear of the ball bearings, and also due to the wear of the wheel bearing.

9. Unilateral tire wear

What it looks like: One side of the tire is worn more than the other.

Cause: Usually, with this type of wear, the cause may be an incorrect alignment of the collapse of the car. This type of uneven wear of the rubber tread is due to the fact that it does not stand exactly on the road surface due to improper wheel alignment.

In order to set the wheel exactly in relation to the road surface, it is necessary to adjust the wheel alignment.

Also, similar wear can occur with damaged springs, ball joints, suspension bushings. In particular, one-sided uneven wear of the tread may appear when transporting heavy loads by car.

In addition, some models of powerful sports cars have a special wheel alignment, which leads to a similar uneven tire wear. But this is rare.

10. Tire wear to indicator

What it looks like: Many tires have wear indicators between the tread. As a rule, these are special inserts that help you determine when it is necessary to change tires for new ones. Usually the height of these inserts is lower than the height of the tread. As soon as the tire tread is equal in height to the wear indicators, it is necessary to purchase.

Cause: Typically, tire replacement should occur after the tread depth is lower than recommended by the tire manufacturer. It's not always easy to tell by eye. Therefore, many tire manufacturers install wear indicators on tires (between the tread). As soon as the tread height wears down to the height that the indicators have, then it's time to change the wheels to new ones.

A rubber tread with a certain depth is necessary in order to divert water from the tire and prevent the car from hydroplaning on wet roads.

If your tires do not have a wear indicator, then you can measure the tread depth yourself in order to understand whether it is time to buy new tires. To do this, you need to use a coin, which must be inserted into the tread with an edge and measure the depth with it. You can read more about traditional tire wear here or check out our infographic.

Attention! For summer tires, the minimum tread depth must be at least 1.6, 2 or 3 mm (depending on the rubber manufacturer).

For winter tires, the minimum safe tread height should be at least 4-6 mm.

The types of wear are distinguished in accordance with the existing types of wear - mechanical (abrasive, fatigue), corrosion, etc.

Mechanical wear is the result of friction forces when one part slides over another. With this type of wear, abrasion (cutting) of the surface layer of the metal and distortion of the geometric dimensions of the jointly working parts occur. Wear of this type most often occurs during the operation of such common mates of parts as a shaft - a bearing, a frame - a table, a piston - a cylinder, etc. It also appears during rolling friction of surfaces, since this type of friction is inevitably accompanied - there is also sliding friction, but in such cases, wear is very small.

The degree and nature of mechanical wear of parts depend on many factors: the physical and mechanical properties of the upper layers of the metal; working conditions and the nature of the interaction of mating surfaces; pressure; relative speed of movement; conditions for lubrication of rubbing surfaces; the degree of roughness of the latter, etc. The most destructive effect on the parts is abrasive wear, which is observed in cases where the rubbing surfaces are contaminated with small abrasive and metal particles. Usually, such particles fall on rubbing surfaces during the processing of cast billets on a machine, as a result of wear of the surfaces themselves, dust ingress, etc. They retain their cutting properties for a long time, form scratches, scuff marks on the surfaces of parts, and also, mixing with dirt, they act as an abrasive paste, as a result of which intensive rubbing and wear of mating surfaces occurs. The interaction of the surfaces of parts without relative movement causes metal crushing, which is typical for keyed, slotted, threaded and other connections.

Mechanical wear can also be caused by poor maintenance of the equipment, for example, irregularities in the supply of lubrication, poor repair and failure to meet its deadlines, power overload, etc.

In. during operation, many machine parts (shafts, gear teeth, connecting rods, springs, bearings) are subjected to long-term action of variable dynamic loads, which have a more negative effect on the strength properties of the part than static loads. Fatigue wear is the result of variable loads acting on a part, causing fatigue of the part material and its destruction. Shafts, springs and other parts are destroyed due to fatigue of the material in the cross section. In this case, a characteristic type of fracture is obtained with two zones - the zone of developing cracks and the zone along which the fracture occurred. The surface of the first zone is smooth, while the second one is shelled and sometimes granular.

Fatigue failure of the material of the part does not necessarily lead to its failure immediately. It is also possible the occurrence of fatigue cracks, peeling and other defects, which, however, are dangerous, as they cause accelerated wear of the part and mechanism. To prevent fatigue failure, it is important to choose the right cross-sectional shape of a newly manufactured or repaired part: it should not have sharp transitions from one size to another. It should also be remembered that a rough surface, the presence of scratches and scratches can cause fatigue cracks.

Seizure wear occurs as a result of sticking (“seizing”) of one surface to another. This phenomenon is observed with insufficient lubrication, as well as significant pressure, at which two mating surfaces approach each other so closely that molecular forces begin to act between them, leading to their seizure.

Corrosive wear is the result of wear of parts of machines and installations that are under the direct influence of water, air, chemicals, and temperature fluctuations. For example, if the air temperature in industrial premises is unstable, then every time it rises, the contained

Rice. one.

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 erosions 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-mechanics occurs, i.e., complex and wear.

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. 1, a-i).

As a result of wear of the guide machines, 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. 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. 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 * and other defects occur. 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. 1, c) manifests itself in abrasion and scoring on the skirt

The wear of the shafts (Fig. 1, d, e) is manifested by the appearance of various defects: the shafts become bent, twisted, and also broken due to material fatigue; bullies 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 its gravity acts on the shaft during rotation, then wear appears in the lower part of the bearing (see Fig. 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. 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 strongly. 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; I - wear points

interfaces not only running, but also clamping, for example, clamping screws of frequently 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 the heads of bolts 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. 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 (Fig. 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 tangential stresses, chipping of the working surfaces occurs, i.e. separation of particles of the material

Fig.3.

a - chipping, b - peeling, c - corrosion, d - erosion, e - scratches, e - scuffing, g - sticking, h - deep tearing of the material and its transfer from another friction surface rial, leading to the formation of pits on the friction surface (Fig. 3, a). The destruction of the working surfaces of the teeth due to intense chipping (Fig. 3, b) is often called flaking (there is a separation from the friction surface of the material in the form of scales).

On fig. 3c shows a surface damaged by corrosion. The surface of the cast iron powder ring (Fig. 3, d) is damaged due to erosion wear, which occurs when the piston moves in the cylinder relative to the liquid; gas bubbles in the liquid burst near the piston surface, which creates a local increase in pressure or temperature and causes wear on parts. The surface of the brake drum (Fig. 3, e) shows the risks that appear when a solid body or solid particles act on a rotating drum. Seizures (Fig. 3, f) are formed as a result of seizing surfaces during friction due to the action of molecular forces between them. On fig. 3, g shows the working surface of the part with foreign particles adhering to it, and in fig. 3, h - the surface of the part with wear during jamming as a result of setting - deep tearing of the material and its transfer from another friction surface.