The main reasons for accelerated engine wear. Wear. Types of wear How the piston works

The car body is more open to various influences than any other part of it, and therefore wears out faster. Body damage or wear is one of the common reasons for contacting a car service. Large-scale body repair, including slipway, reinforcement and painting work, can only be performed by specialists in a service station, where there is all the necessary equipment, and minor damage can be repaired on your own.

The car body is more open to various influences than any other part of it, and therefore wears out faster. Body damage or wear is one of the common reasons for contacting a car service. Large-scale body repair, including slipway, reinforcement and painting work, can only be performed by specialists in a service station, where there is all the necessary equipment, and minor damage can be repaired on your own.

Causes of body damage

Body damage and wear can be caused by various causes:

• technological and structural damage associated with a violation of the technology for processing the metal of the body, paintwork, poor assembly quality, insufficiently rigid fastening of parts, flaws in the design;
• operational damage and normal wear and tear are associated with stress, static and dynamic loads that body elements are subjected to during operation. In particular, these are damages associated with metal fatigue, high-frequency vibrations of working units;
• emergency damage occurs during accidents, road accidents, collisions;
• a significant part of the damage is the result of improper maintenance of the vehicle, its storage in unfavorable conditions, the same reasons lead to accelerated wear.

The main factors leading to damage:

• corrosion - oxidation and destruction of metal. It can be caused both by precipitation, humid air and condensation, and chemically aggressive substances - electrolyte solutions, anti-ice reagents, emissions contained in the atmosphere. Contact of metal parts with parts made of other materials can also lead to corrosion. It is especially susceptible to hard-to-reach areas, gaps, bends of edges, which are difficult to thoroughly dry, ventilate and clean;
• abrasive wear - the impact on the body of solid particles contained in the polluted air or falling on it from the road surface. Abrasive wear accelerates the corrosion process;
• contact friction of doors, fenders and other metal parts in contact with each other;
• vibration leading to cracks, destruction of welded joints.

Driving on roads with poor surfaces, bumps and potholes, accompanied by jolts, impacts, vibration, is one of the main causes of body damage. If you store the car outdoors or in a damp and cold garage, do not wash or wipe dry for a long time after washing, do not treat with protective compounds, drive in an aggressive manner, carelessly, the likelihood of damage and accelerated wear increases.

According to statistics, the front part of the car body most often suffers in an accident, damage to the rear area is less common, and damage to the side areas is least recorded. The scale of accident damage is directly proportional to the speed of the colliding objects. In a collision, kinetic energy is released until it is completely extinguished, a chain reaction will develop, causing damage and destruction of body parts.

Types of wear and damage

The body is susceptible to a variety of damage resulting from one of the above factors or a combination thereof:

• deformation of body parts - dents, folds, distortions. Severe deformations of the body lead to shear of individual parts, excessive vibrations, excessive stress on the chassis, and a violation of the stability of the vehicle;
• the most serious deformations are distortions, leading to a change in the geometry of the body. As a result, the shape and size of door and window openings, the interior frame, and the trunk lid change. Doors and windows jam or, conversely, they sag;
• the displacement of the side members is another manifestation of geometry violations;
• cracks may appear at the joints of the vehicle struts with the body due to shock, vibration, improper wheel balancing. Cracks also form on the mudguard, strut, casing cardan shaft, side members, in the places of attachment of seats, shock absorbers, struts, spring brackets and a fuel tank;
• welded joints in other places are often destroyed, especially points and seams that are subject to the highest loads - the joints of the spacer with the spar, the mudguard with the arch;
• body fasteners - bolts, nuts, nut holders - may break off. If this damage is not corrected immediately, it will lead to larger problems;
• loose fit of individual body parts leads to knocks and squeaks during static load and movement;
• due to mechanical damage and exposure to aggressive substances, the paint and varnish and anti-corrosion coating is destroyed.

Even cosmetic damage to the body is fraught with danger: if a scratch touches the anti-corrosion coating, corrosion will quickly spread. Corrosion can be superficial, covering a large area, and local, extending inland. The latter is more dangerous, since it leads to the corrosive brittleness of the metal.

Changes in the geometry of the body, distortions, cracks in parts and destruction of welded joints can lead to a deterioration in vehicle handling and provoke emergency situations. Therefore, body damage of any nature (corrosive, mechanical) and scale must be repaired as soon as possible.

Ways to eliminate damage to the body

In the presence of mechanical damage, the original shape of the damaged part is restored, if possible, if it cannot be restored, then it is replaced with a new one.

The simplest category of repair is the elimination of external damage to the skin that did not affect the interior frame, subframe. If, due to deformations of the body, the distances between the attachment points of the main units have changed, it is necessary to restore the geometry. This is not always possible, sometimes the damage is so large-scale that it is more cost-effective and safer to replace the entire body. Repairs will be cheaper if you order a suitable disassembled body in good condition.

The main methods and techniques of body repair:

• preliminary rough alignment - drift;
• final alignment - straightening;
• elimination of bubbles formed during straightening by heating the metal with a torch or spot welding machine with subsequent cooling;
• soldering - sealing dents with tin solder, removing excess files with a file and polishing. It is used if the dent is small, and it is difficult to dismantle the part for punching and straightening;
• filling small dents followed by filing and polishing the filler. Usually the putty is applied in several layers;
• extraction of hollow parts using a special tool - a nail puller. Cylindrical rods resembling nails are welded to the cleaned dent, then they are pulled with a nail puller, using as a lever;
• welding cracks;
• straightening distortions using power equipment;
• Painting works.

To eliminate surface deformations, it is necessary to remove a layer of paint and mastic, completely freeing up the space for the tightening. Deep dents are aligned gradually, from the edges to the center. If parts of different hardness got into the damaged area, they start with the harder ones. If a fold has formed, start by flattening it. An anvil of the desired profile is placed under the surface to be straightened. Removable elements are best straightened on a workbench.

To straighten distortions, power equipment is needed - a jack, a hydraulic square with extension cords, inserts and chains. The chains must be attached at right angles to the damaged area so that the straightening is done in the opposite direction to the deformation. Stretching starts with the minimum stroke, then the effort gradually increases.

After straightening, residual stress may remain, which, when the vehicle is moving, is transmitted to the bushings and shock absorbers and often leads to their separation. To avoid this, body straightening with significant deformations should be carried out with removed mechanical units. If, due to deformation, access to them is limited, it is necessary to perform preliminary straightening without removing these units. Stretching is recommended to be accompanied by percussion of the folds. After finishing the straightening, the entire straightened section is tapped with a straightening hammer through a wooden spacer to relieve internal stress.

The frameless body, in which the base does not detach from the skeleton, can only be repaired at a service center using special equipment with a rigid base. It is also better to paint in a special spray booth; you cannot do it outdoors, since dust and midges will immediately adhere to fresh paint. If paintwork is carried out in the garage, you must first do the cleaning there.

Before painting, it is better to disassemble the body into separate parts for better painting over hard-to-reach areas. Damaged areas are thoroughly cleaned from corrosion, primed with acid soil. The entire painted surface is sanded with a machine or manually using sandpaper, degreased, processed from a spray gun with an acrylic primer. After the soil has dried, the surface is sanded again. Usually three layers of paint are applied, its viscosity decreases with each layer.

In addition to the inevitable damage to the car body and its natural wear and tear, inevitable during operation, there may be accidents and damage associated with improper care, accelerated wear. Any damage to the bodywork must be repaired as soon as possible, as it can trigger a chain of new faults. The work on straightening the dents can be done in the garage with your own hands, and in case of serious violations of the body geometry, it is better to contact a service where there is the necessary power equipment.

1. Nominal. (REINFORCED) Mileage 0-15 thousand km. Driving in city mode (driving - standing) disturbs the temperature balance of the cooling system, leading to uneven expansion of rubbing parts. There is a very fast grinding of friction pairs with the loss of metal and the formation of scoring.

2. Current. (ACCEPTABLE) Mileage 15-60 thousand km. The car has become dynamic. Running in - running in! But there was oil consumption. The accumulated deposits (carbonization) under the rings form quite serious seizure marks on the cylinders. What have we done to reduce friction?
Operating a car in city mode (driving - standing) is like skating on asphalt, not on ice. The main function of the oil is to remove up to 80% of the heat from the piston, on the surface of which the working mixture burns out at t 1200 ° C (gasoline). The oil loses its viscosity due to high temperatures. And to separate the rubbing surfaces, a strong oil film is required.

3. Critical. (LIMIT) Mileage 60-120 thousand km. The accumulated carbon deposits (coke) under the rings and in the grooves do not allow them to be amortized. Rings, valves burn. Oil consumption increases sharply. Direct contact of the rings with the cylinder surface is created. Honors are being erased, the wear is catastrophic.

4. Beyond. Mileage over 120 thousand km. The engine loses over 70 grams of metal. Avalanche deposits reduce all parameters: pressure, "compression". Cap is required. repair with troubleshooting of parts. After the cap. repair, it is necessary to process suprotek + molecular pile, to increase the resource by 2-3 times.

How wear occurs:

Full wear is the loss of more than 70 grams of metal by the engine

1. Frequent starts during night heating

2. Incorrect running-in of a new or overhauled engine in high hydrodynamic friction mode (driving in tightness at high loads). It's all the fault of city traffic jams

3. Engine overheating. In 99% of cases, overheating occurs due to poor heat dissipation - internal overheating. The dashboard does not detect such overheating

4. Coking is the main factor How this process takes place Heavy fractions of hydrocarbons of unburned fuel and varnish deposits of oil are formed into more viscous ones, and under the action of t - into solid ones. Hard-to-remove resinous coke formations (carbon deposits) are capable, due to lacquer transformations of the oil, to adhere to the metal surface and clog cavities.

The oil scraper rings scrape off the carbon together with oil from the cylinder surface, while part of the carbon is removed into the filter, part is deposited on the inner surface of the engine, the other part clogs the grooves of the piston rings, while the mobility is lost.

The resulting coking:
1.increases oil consumption
2.Reduces over-piston pressure (compression ratio)
3.Passing gases into the crankcase oxidize the oil very quickly, it darkens and loses its function

The main negative physical phenomena,
destroying the engine, creating wear:

- Flotation- destruction and pateria of metal
- Cavitation- "buggy" cooling system
- Surge- unstable engine operation (rpm float)
- Blasting state - detonation, overheating
- Lining- the formation of very strong carbon deposits on the pistons

Carrying out early diagnostics in new and used cars, further service maintenance in our center will save time and money.

During the operation of any production equipment, processes occur associated with a gradual decrease in its performance and a change in the properties of parts and assemblies. Accumulating, they can lead to a complete stop and serious damage. To avoid negative economic consequences, enterprises organize the process of wear management and timely renewal of fixed assets.

Determination of wear

Wear, or aging, is a gradual decrease in the performance characteristics of products, assemblies or equipment as a result of changes in their shape, size or physical and chemical properties. These changes occur gradually and accumulate during operation. There are many factors that determine the rate of aging. Have a negative impact:

• friction;
• static, impulse or periodic mechanical loads;
• temperature regime, especially extreme.

The following factors slow down aging:

• Constructive decisions;
• the use of modern and high-quality lubricants;
• compliance with operating conditions;
• timely maintenance, scheduled preventive maintenance.

Due to the decrease in performance, the consumer value of the products is also reduced.

Wear types

The rate and degree of wear is determined by friction conditions, loads, material properties and design features of the products.

Depending on the nature of external influences on the materials of the product, the following main types of wear are distinguished:

• abrasive appearance - surface damage by small particles of other materials;
• cavitation caused by the explosive collapse of gas bubbles in a liquid medium;
• adhesive appearance;
• oxidative form caused by chemical reactions;
• thermal appearance;
• fatigue due to structural changes in the material.

Some types of aging are broken down into subtypes, such as abrasive aging.

Abrasive

It consists in the destruction of the surface layer of the material during contact with harder particles of other materials. Typical for mechanisms operating in dusty conditions:

• mining equipment;
• transport, road construction mechanisms;
• Agreecultural machines. Agreecultural equipment;
• construction and production of building materials.

It can be counteracted by using special hardened coatings for rubbing pairs, as well as by changing the lubricant in a timely manner.

Gas abrasive

This subtype of abrasive wear differs from it in that solid abrasive particles move in the gas stream. Surface material crumbles, shears off, deforms. Found in equipment such as:

• pneumatic lines;
• fan and pump blades for pumping contaminated gases;
• nodes of blast-furnace installations;
• components of solid propellant turbojet engines.

Often, the gas abrasive effect is combined with the presence of high temperatures and plasma streams.

Download GOST 27674-88

Waterjet

The impact is similar to the previous one, but the role of the abrasive carrier is performed not by the gaseous medium, but by the flow of liquid.

Are subject to such effects:

• hydrotransport systems;
• HPP turbine units;
• components of precoating equipment;
• mining equipment used to wash ore.

Sometimes hydroabrasive processes are aggravated by exposure to an aggressive liquid medium.

Cavitational

Pressure drops in the liquid flow around the structure lead to the appearance of gas bubbles in the zone of relative rarefaction and their subsequent explosive collapse with the formation of a shock wave. This shock wave is the main factor of the cavitation destruction of surfaces. Such destruction occurs on propellers of large and small ships, in hydro turbine and technological equipment. The situation can be complicated by the effect of an aggressive liquid medium and the presence of an abrasive suspension in it.

Adhesive

With prolonged friction, accompanied by plastic deformations of the participants in the rubbing pair, there is a periodic approach of the surface areas at a distance that allows the forces of interatomic interaction to manifest themselves. Begins the interpenetration of the atoms of the substance of one part into the crystal structures of another. The repeated occurrence of adhesive bonds and their interruption lead to the separation of the surface zones from the part. Loaded rubbing pairs are subject to adhesive aging: bearings, shafts, axles, sliding bushings.

Thermal

The thermal type of aging consists in the destruction of the surface layer of the material or in the change in the properties of its deep layers under the influence of constant or periodic heating of structural elements to the plastic temperature. Damage is expressed in crushing, melting and changing the shape of the part. Typical for high-loaded units of heavy equipment, rolls of rolling mills, hot stamping machines. It can also be found in other mechanisms when the design conditions for lubrication or cooling are violated.

Fatigued

It is associated with the phenomenon of metal fatigue under alternating or static mechanical loads. Shear stresses lead to the development of cracks in the materials of parts, causing a decrease in strength. The cracks in the near-surface layer grow, merge and intersect with each other. This leads to the erosion of small scale-like fragments. Over time, this wear can lead to the destruction of the part. It is found in the nodes of transport systems, rails, wheelsets ah, mining machines, building structures, etc.

Fretting

Fretting is the phenomenon of microfracture of parts in close contact under conditions of vibration of small amplitude - from hundredths of a micron. Such loads are typical for rivets, threaded connections, keys, splines and pins connecting the parts of the mechanisms. With increasing fretting aging and detachment of metal particles, the latter act as an abrasive, aggravating the process.

There are other, less common specific types of aging.

Wear types

The classification of the types of wear from the point of view of the physical phenomena causing it in the microcosm is supplemented by the systematization according to the macroscopic consequences for the economy and its subjects.

In accounting and financial analytics, the concept of depreciation, which reflects the physical side of the phenomena, is closely related to the economic concept of equipment depreciation. Depreciation refers to both the reduction in the cost of equipment as it ages, and attributing some of this reduction to the cost of production. This is done with the aim of accumulating funds on special depreciation accounts for the purchase of new equipment or its partial improvement.

Depending on the causes and consequences, a distinction is made between physical, functional and economic.

Physical deterioration

This refers to the direct loss of design properties and characteristics of a piece of equipment during its use. This loss can be either complete or partial. In the event of partial wear and tear, the equipment undergoes refurbishment, returning the properties and characteristics of the unit to its original (or other, pre-agreed) level. If the equipment is completely worn out, it must be written off and dismantled.

In addition to the degree, physical wear is also divided into genders:

• First. The equipment wears out during planned use in accordance with all the rules and regulations established by the manufacturer.
• Second. Changes in properties are caused by improper use or force majeure factors.
• Emergency. Latent change of properties leads to a sudden crash.

The listed varieties are applicable not only to the equipment as a whole, but also to its individual parts and assemblies.

This type is a reflection of the process of obsolescence of fixed assets. This process consists in the appearance on the market of the same type, but more productive, economical and safe equipment. The machine or installation is physically still quite functional and can produce products, but the use of new technologies or more advanced models that appear on the market makes the use of outdated ones economically unprofitable. Functional wear can be:

• Partial. The machine is not profitable for a complete production cycle, but it is quite suitable for performing a certain limited set of operations.
• Complete. Any use leads to damage. The unit is subject to write-off and dismantling

Functional wear is also subdivided according to the factors that caused it:

• Moral. Availability of technologically identical but more advanced models.
• Technological. Development of fundamentally new technologies for the production of the same type of product. It leads to the need to restructure the entire technological chain with full or partial renewal of the composition of fixed assets.

In the event of a new technology, as a rule, the composition of the equipment is reduced, and the labor intensity decreases.

In addition to physical, temporary and natural factors, economic factors also have an indirect effect on the safety of equipment characteristics:

• Falling demand for manufactured goods.
• Inflationary Processes. Prices for raw materials, components and labor resources are growing, at the same time, a proportional increase in prices for the company's products does not occur.
• Competitor pricing pressure.
• Increase in the cost of credit services used for operating activities or for the renewal of fixed assets.
• Non-inflationary price fluctuations in commodity markets.
• Legal restrictions on the use of equipment that does not meet environmental standards.

Both real estate and production groups of fixed assets are subject to economic aging and loss of consumer qualities. Each enterprise maintains registers of fixed assets, which take into account their depreciation and the course of depreciation accumulations.

The main reasons and how to determine wear

To determine the degree and causes of wear and tear, a commission on fixed assets is created and operates at each enterprise. Equipment wear is determined in one of the following ways:

• Observation. Includes visual inspection and measurement and test complexes.
• By the term of operation. It is defined as the ratio of the actual term of use to the normative one. The value of this ratio is taken as the amount of wear in percentage terms.
• an integrated assessment of the state of an object is carried out using special metrics and scales.
• Direct measurement in money. The cost of acquiring a new, similar unit of property, plant and equipment is compared with the cost of refurbishment.
• profitability of further use. The decrease in income is estimated, taking into account all the costs of restoring properties in comparison with the theoretical income.

Which of the methods to apply in each specific case is decided by the commission on fixed assets, guided by regulatory documents and the availability of background information.

Accounting methods

Depreciation deductions designed to compensate for the aging processes of equipment can also be determined using several methods:

• linear or proportional calculation;
• diminishing balance method;
• by the total period of production use;
• in accordance with the volume of manufactured products.

The choice of methodology is carried out during the creation or deep reorganization of the enterprise and is fixed in its accounting policy.

Operation of equipment in accordance with the rules and regulations, timely and sufficient deductions to depreciation funds allow enterprises to maintain technological and economic efficiency at a competitive level and delight their consumers with quality goods at reasonable prices.

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• Introduction
• 1.1 Abrasive wear
• 1.2 Fatigue wear
• 1.3 Wear when seized
• Conclusion

Introduction

During the operation of the car, as a result of exposure to a number of factors (exposure to loads, vibrations, moisture, air currents, abrasive particles when dust and dirt hit the car, temperature effects, etc.), its irreversible deterioration occurs. technical condition associated with wear and damage of its parts, as well as a change in a number of their properties (elasticity, plasticity, etc.). wear erosive abrasive

A change in the technical condition of a car is due to the operation of its components and mechanisms, the impact of external conditions and storage of the car, as well as random factors. Random factors include hidden defects in vehicle parts, structural overloads, etc.

The main permanent reasons for the change in the technical state of the vehicle during its operation were wear, plastic deformation, fatigue damage, corrosion, as well as physicochemical changes in the material of parts (aging).

1. Types of destruction of metal surfaces

In order to effectively manage the processes of changing the technical state of machines and justify measures aimed at reducing the intensity of wear of machine parts, it is necessary to determine the type of wear of surfaces in each specific case. For this, it is necessary to set the following characteristics: type of relative displacement of surfaces (frictional contact scheme); the nature of the intermediate medium (type lubricant or working fluid); basic wear mechanism.

In machine interfaces, there are four types of relative movement of the working surfaces of parts: sliding, rolling, impact, oscillation (movement having the character of relative oscillations with an average amplitude of 0.02-0.05 mm).

By the type of intermediate medium, wear is distinguished by friction without lubricant, by friction with a lubricant, and by friction with an abrasive material. Depending on the properties of the materials of the parts, lubricant or abrasive material, as well as on their quantitative ratio in the mates, in the process of operation, surface destruction of various types occurs.

Wear is divided into the following types: mechanical (abrasive, hydro and gas abrasive, erosion, hydro and gas erosion, cavitation, fatigue, jam wear, fretting wear); corrosion-mechanical (oxidative, wear during fretting corrosion); wear under the action of electric current (electroerosive).

Mechanical wear occurs as a result of mechanical action on the friction surface.

Corrosion-mechanical wear is a consequence of mechanical stress, accompanied by chemical and (or) electrical interaction of the material with the environment.

Erosion is called erosive wear of a surface as a result of exposure to discharges during the passage of an electric current. In machines, this type of wear is found in electrical equipment in generators, electric motors, as well as in electromagnetic starters.

In real operating conditions of machine interfaces, several types of wear are observed simultaneously. However, as a rule, it is possible to establish the leading type of wear, limiting the durability of parts, and to separate it from the rest, accompanying types of surface destruction, which insignificantly affect the performance of the interface.

The mechanism of the main type of wear is determined by examining the worn surfaces. Observing the nature of the manifestation of wear of the friction surfaces (the presence of scratches, cracks, traces of chipping, destruction of the oxide film) and knowing the indicators of the properties of the materials of the parts and the lubricant, as well as data on the presence and nature of the abrasive, the intensity of wear and the mode of operation of the interface, it is possible to fully justify the conclusion on the type of wear of the interface and to develop measures to increase the durability of the machine.

1.1 Abrasive wear

Abrasive is the mechanical wear of the material as a result of the mainly cutting or scratching action of abrasive particles on it, which are in a free or fixed state. Abrasive particles, having a higher hardness than metal, destroy the surface of parts and dramatically increase their wear. This type of wear is one of the most common. In road vehicles, more than 60% of wear cases are abrasive. Such wear is found in the parts of pivot joints, open plain bearings, parts of the working bodies of road machines, parts undercarriage and etc.

The main source of abrasive particles entering machine interfaces is the environment. 1 m3 of air contains from 0.04 to 5 g of dust, 60 ... 80% consisting of suspended particles of minerals. Most of the particles have sizes d = 5 ... 120 microns, i.e. commensurate with the gaps in the interfaces of road vehicles. The main components of the dust: silicon dioxide SiO2, iron oxide Fe2O3, compounds of Al, Ca, Mg, Na and other elements.

When determining the type of wear of machine elements, it is necessary to distinguish erosion, hydro-gas erosion and cavitation wear from hydro and gas abrasive wear.

Erosive is the mechanical wear of the surface as a result of the action of the flow of liquid and (or) gas.

Hydroerosive (gas erosion) wear is erosive wear resulting from the action of a liquid (gas) flow.

Cavitation wear is called hydroerosive wear when a solid moves relative to a liquid, in which gas bubbles collapse near the surface, which creates a local increase in pressure or temperature. This type of wear is most often found in pipeline elements and collectors in the absence of abrasive particles in the working fluid or gas. For road and construction machines erosional wear is not typical.

1.2 Fatigue wear

Fatigue is the mechanical wear as a result of fatigue failure during repeated deformation of microvolumes of the surface layer material. This wear is seen in most road vehicle mates as a concomitant wear. It occurs both with rolling friction and sliding friction.

The fatigue wear process is usually associated with repetitive stress cycles in rolling or sliding contact. In the process of interaction of surfaces in their upper layers, stress fields arise. Scheme of stress distribution at the contact of a cylinder with a plane, calculated by the finite element method. In the process of friction, maximum compressive stresses arise on the working surface of the parts, and directed tangential stresses m propagate along the depth of the material of the part with a maximum at a certain distance from the point of contact.

The intensity of fatigue wear is determined by the following factors: the presence of residual stresses and surface stress concentrators (oxides and other large inclusions, dislocations); surface quality (micro-profile, dirt, dents, scratches, scuffs); load distribution in the interface (elastic deformations, misalignment of parts, clearance); type of friction (rolling, sliding or rolling with slippage); the presence and type of lubricant.

There are two models of the material fatigue wear process. The theory of fatigue wear, developed by a group of scientists led by I.V. Kragelsky. According to this theory, wear particles from the friction surface can be separated without the introduction of microprotrusions of one part into the surface layers of another mating part. Wear can occur due to fatigue of microvolumes of the material, which occurs under the action of multiple compressive and tensile forces.

Fatigue wear is most often observed under conditions of high contact loads with simultaneous rolling and sliding of one surface on another. In such conditions, for example, gear wheels, heavily loaded gear wheels and rolling bearings, gear rims work. Fatigue wear of the working surfaces of parts is accompanied by an increase in noise and vibration levels as wear increases.

Fatigue wear of the material can be moderate and progressive. Normal moderate wear is not hazardous for most friction pairs, and parts with fatigue damage can be used for a long time. Progressive wear occurs at high contact stresses, is accompanied by intense destruction of the surface and can lead to breakage of parts (for example, a gear tooth).

With intense abrasive wear of the working surfaces, their destruction occurs faster than the formation of fatigue cracks, therefore, as a rule, pitting is not observed in such cases.

Fatigue wear also occurs when elastomeric parts interact. The elastic properties of these materials make it possible to reproduce the roughness of the opposing hard surface during sliding, which, in turn, leads to repeated cyclic loading of the material. If the protrusions of the irregularities of the hard surface are rounded and do not cause abrasive wear, then damage can occur in the subsurface layers of the elastomer under the action of repeated compressive, tensile and alternating shear stresses. This fatigue mechanism causes wear of a relatively low intensity, which increases significantly when cyclic stresses are applied for a long time.

1.3 Wear when seized

Wear when seizing occurs as a result of seizure, deep pulling out of the material, transferring it from one friction surface to another and the impact of the resulting irregularities on the mating surface. The wear of this kind is one of the most dangerous and destructive. It is accompanied by a strong connection of the contacting areas of the friction surfaces. In the process of friction, the relative movement of surfaces leads to the tearing of metal particles from one surface and enveloping them onto another, harder surface.

In the mechanism of seizing wear, an important role is played by the atomic-molecular interaction of the materials of the parts, which occurs when the surfaces come together. Unlike other types of wear, which require a certain time for the development of the process and the accumulation of destructive damage, when seizing, the destruction of the surface occurs quickly enough and leads to severe forms of damage (scuffs and shells).

The process of the formation of metal bonds depends on the properties of the mating surfaces (their nature, hardness), as well as on the methods of their processing. In the presence of oxide films on the surface of metals, the galling process also depends on the properties of these oxides. Protective films, which are firmly bonded to the base metal and are able to quickly recover when destroyed, prevent the seizure of metals.

Wear due to metal galling occurs due to violation of the positive gradient rule mechanical properties in depth under conditions of friction without lubricant or with insufficient lubricant. In rolling friction under boundary lubrication conditions, wear is also observed due to material seizure and galling. Seizure occurs when the lubricating film breaks locally and a metallic contact is established. This is possible not only when the supply of lubricant is stopped, but also due to a general overload of the interface, a sharp increase in the oil temperature in the surface layers, local temperature outbreaks, etc.

Seizing wear is most common in gears. According to their ability to withstand seizing under the same loading conditions, gears of all types can be arranged in the following order: cylindrical gears with internal and external gearing; bevel gears with straight, bevel and spiral teeth; hypoid and screw drives with the lowest extreme pressure resistance. This is due to the fact that in hypoid and helical gears, the greatest sliding of the teeth is observed in the engagement. Seizing wear is also found in ball and roller bearings, in heavily loaded rolling bearings.

1.4 Corrosion-mechanical wear

Corrosion-mechanical wear is characterized by the process of friction of a material that has entered into chemical interaction with the medium. In this case, new, less durable chemical compounds are formed on the metal surface, which are removed with wear products during the operation of the interface. Corrosion-mechanical wear includes oxidative wear and wear during fretting corrosion.

Oxidative wear is called wear, in which the main effect on the destruction of the surface is exerted by the chemical reaction of the material with oxygen or an oxidizing environment. It occurs with rolling friction with or without lubricant. The rate of oxidative wear is low and amounts to 0.05 ... 0.011 μm / h. The process is activated with increasing temperature, especially in a humid environment.

Fretting corrosion wear is the mechanical-corrosion wear of contacting bodies at small oscillatory relative displacements. This type of wear differs from wear during fretting of mechanical wear of contacting bodies with small oscillatory relative displacements. The main difference is that fretting wear occurs in the absence of an oxidizing environment without a chemical reaction of the materials of parts and wear products with oxygen. Taking this into account, it is easy to draw an analogy in the mechanisms of wear development during fretting and fretting corrosion.

Fretting and fretting corrosion wear usually occurs on the mating surfaces of shafts with pressed-on wheel disks, couplings and rolling bearing rings; on axles and wheel hubs; on the support surfaces of the springs; on tight joints, fitted surfaces of keys and grooves; on the supports of motors and gearboxes. A prerequisite Fretting corrosion is the relative slip of mating surfaces, which can be caused by vibration, reciprocating movement, periodic bending or twisting of mating parts. The fretting process is accompanied by seizure, oxidation, corrosion and fatigue destruction of microvolumes.

As a result of fretting corrosion, the surface endurance limit is reduced by 3-6 times. On the surfaces of parts in the places of mates, abrasions, adhesions of metal, tears, cavities, as well as surface microcracks are formed. A distinctive feature of wear due to fretting corrosion is the presence of cavities on the friction surfaces, in which pressed oxides with a specific color are concentrated. Unlike other types of wear during fretting corrosion, wear products in their bulk cannot leave the contact zone of the working surfaces of parts.

Wear during fretting corrosion entails a violation of the dimensional accuracy of the joint (if part of the wear products finds a way out of the contact zone) or seizure and jamming of detachable joints (if the wear products remain in the friction zone). Fretting corrosion is characterized by a low speed (about 3 mm / s) of the relative movement of surfaces and a friction path (0.025 mm) equivalent to the vibration amplitude at a vibration frequency of up to 30 Hz and above; localization of surface damage on the areas of actual contact due to small relative displacements; active oxidation

When elastomeric materials interact with metal parts, the seizure phenomenon is also observed. An elastomer will wear out if the coefficient of friction between it and the hard surface is large enough and the elastomer's tensile strength is low. If the surface layers of the material are in a state of maximum deformation, then a scratch or a small crack appears in the direction perpendicular to the sliding direction. Further, there is a gradual tearing out of a part of the elastic material of the elastomer, which is in a state of adhesion to a hard surface. In this case, the layer of elastomer, separated from the surface, is rolled into a roller and forms a wear particle. The rate of wear of the elastomer in this case depends significantly on the temperature, load and type of lubricant. By selecting the lubricant taking into account the external conditions and the elastic properties of the elastomer, this type of wear can be completely eliminated.

The wear process of friction corrosion under conditions of friction without lubricant can be divided into three stages.

The first stage is accompanied by the destruction of protrusions and oxide films due to cyclically repeating oscillatory relative displacements of the contacting surfaces under the action of high loads. The processes of hardening of materials and plastic deformation of the protrusions of microroughnesses occur, causing the surfaces to converge. The convergence of surfaces causes molecular interaction and seizure of the metal at separate points of contact. Fatigue failure of the protrusions and seizure nodes generates wear products, some of which are oxidized. This stage is characterized by increased wear with a monotonically decreasing wear rate.

At the second stage, fatigue damage accumulates in the surface layers. A corrosive environment is formed in the friction zone under the influence of atmospheric oxygen and moisture. An electrolytic environment is created between the surfaces, which intensifies the process of oxidation of metal surfaces and their corrosive destruction. This stage is characterized by the stabilization of the wear process, a decrease in the wear rate compared to the wear rate at the first stage.

At the third stage, due to fatigue corrosion processes, the weakened surface layers of metals begin to intensely break down with a gradually increasing rate. The process has a corrosion-fatigue nature of destruction.

The intensity of surface destruction during fretting corrosion depends on the amplitude and frequency of vibrations, load, material properties of parts and the environment.

2. The main causes of wear and damage to bodies

Body wear and damage can be caused by various reasons. Depending on the cause of the malfunction, they are divided into operational, structural, technological and arising from improper storage and care of the body.

During operation, the elements and units of the body experience dynamic stress from bending in the vertical plane and twisting, loads from their own weight, the mass of cargo and passengers.

The wear of the body and its components is also facilitated by significant stresses that arise as a result of body vibrations not only when it moves over irregularities and possible jolts and impacts when hitting these irregularities, but also due to engine operation and errors in balancing the rotating components of the vehicle chassis (in particular cardan shafts), as well as as a result of the displacement of the center of gravity in the longitudinal and transverse directions.

Loads can be absorbed by the body completely if the vehicle does not have a chassis frame, or partially when the body is installed on the frame.

Studies have shown that variable voltages act on body elements during vehicle operation. These stresses cause fatigue accumulation and lead to fatigue failure. Fatigue failures begin in the area of ​​stress accumulation.

There are two main groups of damages and malfunctions in the car bodies of cars being overhauled: damage arising as a result of increasing changes in the state of the body.

These include natural wear and tear that occurs during normal technical operation of the vehicle due to constant or periodic exposure to the body of such factors as corrosion, friction, decay of wooden parts, elastic and plastic deformation, etc.; malfunctions, the appearance of which is associated with human action and are a consequence of design flaws, factory imperfections, violations of body care standards and rules of technical operation (including emergency ones), poor-quality body repair.

In addition to normal physical wear and tear, when operating the car in difficult conditions or as a result of violation of the norms of maintenance and prevention, accelerated wear and tear may occur, as well as the destruction of individual parts of the body.

Typical types of wear and damage to the body during vehicle operation are metal corrosion that occurs on the surface of the body under the influence of chemical or electromechanical influences; violation of the density of riveted and welded joints, cracks and breaks; deformation (dents, distortions, deflections, warpage, bulges).

Corrosion is the main type of wear on the metal body of the body.

In metal body parts, the most common type of electrochemical corrosion occurs, in which the metal interacts with an electrolyte solution adsorbed from the air, and which appears as a result of both direct ingress of moisture on the unprotected metal surfaces of the body, and as a result of the formation of condensate in its inter-sheathing space ( between the inner and outer panels of doors, sides, roof, etc.). Corrosion develops especially strongly in places that are difficult to inspect and clean in small gaps, as well as in flanges and bends of edges, where moisture that periodically gets into them can persist for a long time.

So, in the wheel arches, dirt, salt and moisture can collect, stimulating the development of corrosion; the underbody is not sufficiently resistant to corrosion factors. The corrosion rate is greatly influenced by the composition of the atmosphere, its contamination with various impurities (emissions from industrial enterprises, such as sulfur dioxide formed as a result of fuel combustion; ammonium chloride that enters the atmosphere due to the evaporation of seas and oceans; particulate matter in the form of dust), and also the ambient temperature, etc. Solid particles contained in the atmosphere or falling on the surface of the body from the roadbed also cause abrasive wear of the metal surface of the body. As the temperature rises, the corrosion rate increases (especially in the presence of aggressive impurities and moisture content in the atmosphere).

Winter road surfaces with salt to remove snow and ice, as well as vehicle operation on the seashore, lead to increased vehicle corrosion.

Corrosion damage in the body also occurs as a result of contact of steel parts with parts made of some other materials (duralumin, rubbers containing sulfur compounds, plastic based on phenolic resins and others, as well as as a result of metal contact with parts made of very wet sawn timber containing a noticeable amount of organic acids (formic acid, etc.).

Thus, studies have shown that upon contact of steel with poly-isobutylene, the rate of metal corrosion per day is 20 mg / m2, and upon contact of the same steel with silicone rubber - 321 mg / m2 per day.

This type of corrosion is observed in the places where various rubber seals are installed, in the places where chrome-plated decorative parts fit the body (headlight rims, etc.).

The appearance of corrosion on the surface of body parts is also caused by contact friction, which occurs with the simultaneous action of a corrosive environment and friction, with the vibrational movement of two metal surfaces relative to each other in a corrosive environment. This type of corrosion is susceptible to doors around the perimeter, fenders at the points of their attachment to the body with bolts and other metal parts of the body.

When painting cars, the surfaces of the body, carefully prepared for painting, can be contaminated with wet hands and polluted air. This, with insufficient quality coating, also leads to corrosion of the body.

The process of corrosion of bodies occurs either uniformly over a large area (surface corrosion is shown in Figure 1), or corrosion goes into the thickness of the metal, forming deep local destruction - cavities, spots in individual points of the metal surface (pitting corrosion is shown in Figure 2).

Figure 1 - Surface corrosion on a car wing.

Figure 2 - Pitting on a car.

Continuous corrosion is less dangerous than local, which leads to the destruction of metal parts of the body, their loss of strength, to a sharp decrease in the corrosion fatigue limit and to corrosion brittleness characteristic of the body lining.

Depending on the operating conditions conducive to corrosion, body parts and assemblies can be subdivided into those having open surfaces facing the roadbed (bottom of the floor, fenders, wheel arches, door sills, bottom of the radiator lining), into having surfaces that are located in within the volume of the body (frame, trunk, top of the floor), and on surfaces that form a closed isolated volume (hidden parts of the frame, bottom of the outer door cladding, etc.).

Cracks in the body occur on impact due to a violation of the metal processing technology of the body (shock multiple processing of steel in a cold state), poor assembly quality during the manufacture or repair of the body (significant mechanical forces when joining parts), as a result of the use of low quality steel, the influence of metal fatigue and corrosion with subsequent mechanical stress, assembly defects of assemblies and parts, as well as insufficiently strong assembly structure.

Cracks can form in any part or part of a metal enclosure, but most often in areas subject to vibration.

Figure 3 shows the main damage to the body on the example of a GAZ-24 car.

Figure 3 - Damage found in the body of the GAZ-24 "Volga"

1 - cracks on the mudguard; 2 - violation of the welded joint of the strut or splash guard with the frame spar; 3 - cracks in the spacer; 4 - cracks on the front panel and front wheel mudguards; 5 cracks in the pillars of the windshield; 6 - deep dents on the pillar panel of the wind window; 7 - skew of the wind window opening; 8 - separation of the bracket front seat; 9 - cracks on the body base casing; 10 - violation of welded joints of body parts; 11 - curvature of the gutter; 12 - dents on the outer panels, covered with parts with inside, irregularities left after straightening or straightening-13 - local corrosion in the lower part of the rear window; 14 - separation of the tail racks at the attachment points or cracks on the racks; 15 and 16 - local corrosion of the trunk lid stream; 17 - separation of the trunk lock bracket; 18 - local corrosion in the rear of the base of the body; 19 - dents on the lower panel of the tailgate at the attachment points rear lights; 20 - local corrosion in the lower part of the mudguard; - 21 - coating of corrosion and other minor mechanical damage; 22 - local corrosion of the wheel arch; 23 - curvature of the rear wing mudguard; 24 - violation of the welded seam in the joint of the mudguard with the arch; 25, 32 - cracks in the base at the seat attachment points; 26 - Local corrosion on the rear door pillar and on the base of the body. exciting rear spar booster; 27 - cracks on the base of the body at the points of attachment of the brackets of the rear springs and others; 28 — Dents on the pillar panel and bent B-pillar; 29 - separation of the holders of the plates of the retainer and the hinge of the door of the body; 30 - local corrosion in the lower part of the middle pillar of the sidewall; 31 - local corrosion and cracks in the side members of the body base; 33 - distortions of doorways of bodies; 34 - continuous corrosion of the base sills; 35 - dents on the side members of the body base (breaks are possible); 36 - breakdown of the thread on the plates for fastening the retainer and door hinges; 37 - separation of the door lock cover; 38 - dents (possibly with gaps) on the body side panel; 39 - local corrosion in the lower part of the front pillar; 40 - violation of the anti-corrosion coating; 41 - separation of guy-carriers; 42 - the curvature of the cross member No. 1; 43 - cracks on the bulkhead at the strut attachment points; 44 - detachment of the bumper front attachment bracket; 45 - cracks on the radiator shield; 46 - local corrosion on the brace of the amplifier; 47 - cracks in the spar attachment points; 48 - loosening of the riveted connection of the bracket; 49 - the development of holes for the spring shackle pin and the front bracket for attaching the rear spring; 50 - separation of the body base spar amplifier; 51 - wear of the shock absorber mounting hole; 52 - cracks in the attachment points of the fuel tank brackets; 53 — Dents with sharp corners or tears on the bottom panel; 54 - continuous corrosion on the lower rear panel; 55 - cracks in the attachment points of the shock absorbers; 56 - cracks on the propeller shaft cover

Destruction of welded joints in nodes, parts of which are connected by spot welding, as well as in solid welded seams of the body, can occur due to poor-quality welding or exposure to corrosion and external forces: body vibration under dynamic loads, uneven distribution of loads during loading and unloading of bodies.

Fracture data are shown in Figure 4.

Picture 4 - Failure of welded joints under the influence of corrosion

Frictional wear occurs in fittings, hinge pins and holes, upholstery, riveted and bolted holes.

Dents and bulges in the panels, as well as deflections and distortions in the body appear as a result of permanent deformation upon impact or poorly performed work (assembly, repair, etc.).

The concentration of stresses in the joints of individual elements of the body in openings for doors, windows, as well as at the joints of elements of high and low rigidity can cause the destruction of parts if they are not reinforced.

In the structures of the bodies, the necessary rigid connections are usually provided, the reinforcement of individual sections with additional parts, and the extrusion of stiffeners.

However, in the process of long-term operation of the body and in the process of its repair, individual weak links in the body body may come to light, which require reinforcement or changes in the design of the units in order to avoid the appearance of secondary breakdowns.

Conclusion

Changes in the technical condition of the vehicle are significantly influenced by the operating conditions: road conditions (technical category of the road, type and quality of road surface, slopes, uphill and downhill gradients, radius of curvature of the road), traffic conditions (intensive city ​​traffic, driving on country roads), climatic conditions (ambient temperature, humidity, wind loads, solar radiation), seasonal conditions (dust in summer, dirt and moisture in autumn and spring), aggressiveness of the environment (sea air, salt on the road to winter time intensifying corrosion), as well as transport conditions (vehicle loading).

As a result of the essay, the main types of destruction of the car body of the car were studied.

These include fractures such as fatigue wear and mechanical corrosion wear.

To reduce corrosion of car parts and, first of all, the body, it is necessary to maintain their cleanliness, take timely care of the paintwork and its restoration, perform anti-corrosion treatment of hidden body cavities and others. corroded details.

To prevent fatigue damage and plastic deformation, the rules for operating the vehicle should be strictly observed, avoiding its operation at extreme conditions and with overloads.

List of sources used

1 Fundamentals of the performance of technical systems textbook. for universities V.A. Zorin Academy, 2009 .-- 206 p.

2 Reliability of vehicles "Fundamentals of the theory of reliability and diagnostics" / V. I. Rassokha. - Orenburg: OSU Publishing House, 2000 .-- 100 p.

3 Reliability of mobile machines / K.V. Shchurin; Ministry of Education and Science Ros. Federation .: OSU, 2010 .-- 586 p.

4 Increased durability transport vehicles: textbook. manual for universities / V. A. Bondarenko [and others]. - M.: Mechanical Engineering, 1999 .-- 144 p.

5 Fundamentals of the theory of reliability vehicles: study-method. hands. for correspondence students forms of teaching specialties "150200, 230100" / V. I. Rassokha. - Orenburg: OSU, 2000 .-- 36 p.

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The fact that the engine is the heart of a car is clear to everyone, and it is natural for every motorist to want to extend his life. Engine failures occur, both due to the fact that something is clogged or misaligned in the engine, and due to wear. The latter has much more dire consequences. But wear, as a rule, does not come suddenly, and according to individual manifestations it can be established that the engine, as it were, crossed the line that separates the natural wear accompanying any normal operation from the intensive one, in which there is a rapid and irreversible destruction of the engine.

The main reasons for premature wear are:

1. "Dry friction" in contact pairs of mating parts

This, in turn, is due to the fact that the oil film, which must always separate the entire set of friction points that touch each other, moving parts, is squeezed out and at these points an avalanche-like destruction of the metal immediately begins. In addition, a sharp increase in temperature in the "dry friction" zone leads to the heating of the metal and a change in its properties, which in turn will cause further, even sharper destruction, even if the root cause is eliminated. To put it simply, the engine turns out to be irretrievably "screwed up". By the way, in this situation, many have a strong desire to quickly sell a car for a reasonable price.

What are the main reasons leading to "dry friction"? There are only two of them. This is either too high specific pressure in the places of friction from excessive gaps or sharp dynamic loads leading to the breakdown of the oil film, or "oil starvation" due to problems in the lubrication system.

2. Engine overheating

Every year, with the onset of warm days, many motorists meet on the road with the hoods raised, from under which steam is falling. However, not everyone understands how dangerous even short-term overheating is for the engine. Let's dwell on this in more detail. Most vulnerability from the point of view of overheating is the cylinder - piston group. The maintenance of the required temperature conditions is ensured by the cooling liquid, which must continuously remove heat from the heating zone to the radiator. The heat released in the combustion chamber, when heat removal is stopped, is capable of raising the temperature in the combustion chamber several times in a few seconds. Wherein piston rings, due to their smaller mass and geometry, they expand faster than the cylinder walls and turn into a kind of cutting tool that leaves deep nadirs on the cylinder walls.

The rings themselves lose their elasticity from overheating, as a result of which the engine loses power, begins to consume oil and without major repairs it is no longer possible to get rid of this trouble. According to our observations, even a one-time overheating of the engine never goes without consequences. And even short-term overheating, if it does not cause the above-described consequences, then the valve stem seals will most likely have to be changed after that. For this reason, when buying a car, it is more expedient to ask not about its mileage, but about whether the engine has overheated. This is especially true for cars whose engines are significantly boosted and have more intense temperature conditions.

A typical mistake of many of our motorists is the desire to reach home, despite the fact that the temperature arrow is moving towards the red zone. But do not forget that the temperature sensor is most often located in the radiator area. Now imagine that for one of many reasons, the movement of the coolant has slowed down or stopped altogether. In this case, a vapor lock immediately forms in the channels of the washing cylinders and the temperature reaches critical values ​​in a few seconds, while the arrow just starts to move to the right. The situation is even worse for cars with only indication in the form of a light bulb.

A separate cause of many overheating is the influence of the air conditioner. First, an additional radiator appears in the path of the air flow that cools the engine radiator, which heats up a lot. Secondly, when the air conditioner is on, the engine receives a fairly high additional load. And thirdly, all this is sharply aggravated when the engine is idling, when the circulation rate of the coolant is minimal, and the share of the power taken by the air conditioner from the engine in this mode is close to 50%. In this case, the cooling of the radiators is provided only by an electric fan, which also creates an additional load. Not surprisingly, very often when checking prestigious cars, we find traces of increased engine wear at low mileage. The reason for this was most likely the fact that when a noble car owner chilled out in an air-conditioned office in hot weather, his chauffeur did the same in his car for hours.

How, in practical terms, to avoid such phenomena and thereby extend the engine life? If you bought a new car, then everything is simple - follow the instructions. If the car is supported, then the smallest details are fundamentally important, indicating how the car was used before you and what is the degree of its wear today. According to our statistics, after in the course of "pre-sale" examinations, at least 60% of potential buyers refuse to buy this car precisely based on the results of the engine check.

Many people hope in such situations for the help of special additives. Here you need to be extremely careful and use them as potent drugs only as prescribed by specialists. A long-term study of this issue allows us to conclude that the use of some additives for preventive purposes can end very badly, but on the other hand, the targeted use of some additives for a "well-established purpose" gives a positive result.

In conclusion, I would like to give the owners of used cars a few recommendations that could prevent its premature failure:

1.Do not rest until you establish for sure the true reasons for such manifestations as the consumption of antifreeze and oil, as well as extraneous sounds from the engine, and even more so any signs of a decrease in oil pressure.

2. Under no circumstances should the engine run even for a short time when the arrow of the temperature gauge approaches the red zone. The temperature display system has an inertia of about 3-5 minutes, during which the cost of damage to your car can be several times higher than the cost of a tow truck or tow truck.

3. The greatest loads, and therefore wear and tear, fall on the connecting rod-piston group of the engine during sharp accelerations, therefore only owners of relatively fresh and sufficiently powerful cars can not deny themselves the pleasure of starting with slipping.