Causes of accelerated engine wear. The most common causes of premature engine wear

In this article, we will look at the three most common causes of engine component damage and describe the situations that lead to breakdowns. The most common causes of damage are abrasion of the engine due to dirt, water hammer and increased oil consumption.

Abrasive engine wear

Abrasive wear is the result of hard particles scratching or cutting the mating parts, as well as the result of dust entering the surface of the parts, introduced by air or introduced with lubricant. Most often, abrasive wear of the engine manifests itself in the form of increased oil consumption.

Examination of damaged parts reveals a different nature of damage:

• a wide matte contact patch is formed on the piston skirt both from the side of the greatest lateral load and from the opposite side;
• wear of the processing profile on the piston skirt is noted;
• thin grooves form on the piston skirt, piston rings, cylinder wall or liner in the direction of travel;
• piston rings and their grooves have wear in height;
• an increased thermal clearance is noted on the piston rings, the edges of the rings become extremely sharp;
• the working edges of the oil scraper ring wear out;
• the piston pin has grooves of a wavy profile;
• abrasive wear leaves its marks on other parts, for example, on the valve stem.
• In case of damage caused by abrasive wear, several types of defects can be distinguished:
• If only one cylinder is damaged and the first piston ring is worn significantly more than the third, then contaminants enter the combustion chamber through the cylinder intake system, that is, from above. The reason for this is either depressurization or mud deposits that were not removed before the repair work began.
• If several or all cylinders are damaged and the first piston ring is worn significantly more than the third, then contaminants enter the combustion chamber through the common intake system of all cylinders. The reasons for this situation are due to depressurization and / or a destroyed or missing air filter.
• If the third piston ring is worn significantly more than the first, then it should be assumed that the engine oil is dirty. Oil contamination occurs either because the engine crankcase has not been cleaned and/or because of a dirty oil mist separator.

Elimination of defects and prevention consists in checking the intake system for leaks, checking and replacing the air filter, before installation, the engine crankcase and suction pipes should be cleaned of dirt. Maintain cleanliness during repair work.

Water hammer

Water hammer is a powerful source of energy. And this energy can have a devastating effect on many engine components: a piston collapses or deforms, a connecting rod bends or breaks, a piston ring bridge of a damaged piston shows signs of static fracture, a piston pin breaks.

The cause of this defect is liquid (water or fuel) that has entered the combustion chamber. Since neither water nor fuel is subject to compression, water hammer causes a sudden force on the piston, piston pin, connecting rod, cylinder head, crankcase, bearings and crankshaft.

Too much liquid can end up in the combustion chamber for the following reasons: water enters the combustion chamber through the intake system (for example, when driving on a surface flooded with water); water enters the combustion chamber due to defective gaskets. Too much fuel enters the combustion chamber due to a defective injection nozzle.

Increased oil consumption

A little oil consumption is normal. It varies depending on the type of engine and its mode of operation. If the oil consumption rates prescribed by the manufacturer are exceeded, then we can talk about such a thing as increased oil consumption. Possible reasons for the increased consumption:

• Due to depressurization of the turbocharger. The oil circulation line in the turbocharger system is clogged or coked. Due to the pressure in the oil circuit that rises for this reason, oil is forced out of the turbocharger into the intake duct and into the exhaust system.
• Oil enters the combustion chamber with the fuel, for example, due to wear of the high pressure fuel pump, which is usually lubricated through the engine oil circuit.
• A leaky intake system allows dirt particles to enter the combustion chamber, which leads to increased wear.
• If the piston protrusion is incorrectly adjusted, the piston may hit the cylinder head. As a result, oscillations occur that affect the fuel injectors. At the same time, the nozzle ceases to close completely, so too much fuel enters the combustion chamber, and an overdose of fuel occurs.
• The oil has worn out. Exceeded oil change intervals result in clogging and/or destruction of the filter paper, resulting in unclean oil circulating in the oil circuit.
• Bent or twisted connecting rods lead to a violation of the movement of the piston, which entails a violation of the necessary sealing of the combustion chamber. In the most critical cases, the pumping action of the piston rings may occur. In this case, oil is actively supplied to the combustion chamber.
• If piston rings are broken, misaligned, or incorrectly installed, these circumstances can lead to insufficient sealing between the combustion chamber and the crankcase. As a result of this seal failure, oil can enter the combustion chamber.
• Cylinder head bolts not properly tightened. This can lead to deformations, and hence to a violation of the tightness of the oil circuit.
• Due to worn pistons, piston rings and cylinder contact surfaces, the volume of blow-by gases increases. And this leads to excess pressure in the crankcase. If the pressure is too high, oil mist can be forced out through the crankcase ventilation into the combustion chambers.
• Too high an oil level causes the crankshaft to sink into an oil bath, which leads to the formation of oil mist. And if the oil is too old or of poor quality, then the formation of oil foam is also possible. Then oil mist and foam, together with breakthrough gases, enter the suction channel through the engine ventilation, and hence into the combustion chambers.
• In case of malfunctions in the combustion process, fuel overflow is possible. Due to the dilution of the oil with fuel, the wear of pistons, piston rings and the working surface of the cylinders increases many times over.
• If the cylinder is misaligned, for example due to old and/or incorrectly tightened cylinder head bolts, the piston rings lose their sealing capacity between the combustion chamber and the crankcase. Thus, oil mist can enter the combustion chamber. With particularly strong deformations, it is even possible for the piston rings to act as a pump, that is, a situation where oil is simply pumped into the combustion chamber.
• Poorly machined cylinder with poor honing of its running surface interferes with the oil retention process. This leads to a significant increase in wear of such mating parts as pistons, piston rings and cylinder working surfaces, and, consequently, to insufficient sealing of the engine crankcase. When using clogged or worn honing heads, a graphite layer forms on the working surface of the cylinder. That is, there is a so-called insulating jacket. It significantly reduces the oil scraping potential, which leads to increased wear, especially during cold starts.

Untimely replacement of oil and oil filter leads to the work of friction pairs in adverse conditions. This is due to the deterioration of the properties of engine oil (its viscosity changes, additives are produced, the tendency to form deposits on parts and in the channels of the lubrication system, etc.) and a large amount of wear products in the lubrication system (a bypass valve opens in a contaminated oil filter and oil flows past the filter element).

The use of low-quality oil causes accelerated wear and rapid engine failure. An oil that does not have the full range of properties necessary for normal lubrication of friction pairs does not prevent the formation of scoring and destruction of the working surfaces of highly loaded parts (gas distribution mechanism parts, piston rings, piston skirts, crankshaft liners, turbocharger bearings, etc.). The increased tendency of low-quality oils to form tarry deposits can lead to clogging of oil channels and leave friction pairs without lubrication, which will cause their accelerated wear, scoring and seizure. Similar effects are possible if an oil is used that does not correspond to this engine in terms of quality (API, ACEA classifications, etc.). For example, when a cheaper SF/CC oil is used instead of the recommended API SH/CD class oil.

The unsatisfactory condition of the air or fuel filter (defects, mechanical damage), as well as various leaks in the intake system connections, lead to the ingress of abrasive particles (dust) into the engine and intense wear, primarily of cylinders and piston rings.

Untimely repair of engine malfunctions or incorrect adjustments will accelerate the wear of parts. For example, a "knocking" camshaft is a source of continuous contamination of the lubrication system with metal particles.

Incorrect ignition timing, malfunctions of the carburetor or engine management system, the use of spark plugs that are not suitable for the engine cause detonation and pre-ignition, threatening to destroy the pistons and surfaces of the combustion chambers.

Overheating of the engine due to malfunctions in the cooling system can lead to deformation of the cylinder head (cylinder head) and the formation of cracks in it.

The oil film in friction pairs with insufficient cooling becomes less durable, which leads to intensive wear of rubbing parts.

In diesel engines, piston burnouts and other serious defects occur as a result of malfunctions of the fuel equipment.

Vehicle operating modes also affect the rate of engine wear. The operation of the engine mainly at maximum loads and crankshaft speeds can significantly reduce its resource (by 20–30% or more). Exceeding the permissible number of revolutions leads to the destruction of parts. About 70% of engine wear occurs during start-up.

A cold start especially contributes to a decrease in the resource if the engine is filled with oil with an inappropriate viscosity-temperature characteristic. At a temperature of -30 degrees, it is equivalent (in terms of wear) to a run of several hundred kilometers. This is due, first of all, to the high viscosity of the oil at low temperatures - it takes more time for it to flow (pump) to the friction pairs.

Short trips on a cold engine in winter contribute to the formation of deposits in the lubrication system and corrosive wear of pistons, their rings and cylinders.

During the operation of any production equipment, there are processes 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 depreciation management and timely renewal of fixed assets.

Definition of wear

Wear or aging is a gradual decrease in the performance of products, assemblies or equipment as a result of a change in their shape, size or physical and chemical properties. These changes occur gradually and accumulate over the course of operation. There are many factors that determine the rate of aging. 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 cost of products also decreases.

Types of wear

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

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

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

Some types of aging are divided into subspecies, such as abrasive.

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-building mechanisms;
• Agreecultural machines. Agreecultural equipment;
• construction and production of building materials.

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

gas abrasive

This subspecies of abrasive wear differs from it in that solid abrasive particles move in a gas stream. The surface material crumbles, cuts off, deforms. Found in equipment such as:

• pneumatic pipelines;
• blades of fans and pumps for pumping contaminated gases;
• nodes of blast-furnace installations;
• components of solid propellant turbojet engines.

Often, gas-abrasive action is combined with the presence of high temperatures and plasma flows.

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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 liquid flow.

These are affected by:

• hydrotransport systems;
• HPP turbine units;
• cleaning equipment components;
• mining equipment used for washing ore.

Sometimes hydroabrasive processes are exacerbated by the impact of an aggressive liquid medium.

cavitation

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 active factor in the cavitation destruction of surfaces. Such destruction occurs on the propellers of large and small vessels, in hydraulic turbine and process equipment. The situation can be complicated by the impact 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 convergence of surface areas at a distance that allows the forces of interatomic interaction to manifest themselves. It 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 surface zones from the part. Loaded rubbing pairs are subject to adhesive aging: bearings, shafts, axles, sliding liners.

Thermal

The thermal form 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 plasticity temperature. Damage is expressed in crushing, melting and changing the shape of the part. Typical for highly loaded units of heavy equipment, rolls of rolling mills, hot stamping machines. It can also occur in other mechanisms if the design conditions for lubrication or cooling are violated.

fatigue

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

Fretting

Fretting is a phenomenon of micro-destruction of parts that are in close contact under conditions of low-amplitude vibration - from hundredths of a micron. Such loads are typical for rivets, threaded connections, dowels, slots and pins connecting the parts of mechanisms. As fretting aging increases and metal particles peel off, the latter act as an abrasive, aggravating the process.

There are other less common specific types of aging.

Wear types

The classification of types of wear in terms of the physical phenomena that cause it in the microcosm is supplemented by a systematization of macroscopic consequences for the economy and its subjects.

In accounting and financial analytics, the concept of depreciation, which reflects the physical side of phenomena, is closely related to the economic concept of equipment depreciation. Depreciation means both reducing the cost of equipment as it ages, and attributing part of this reduction to the cost of manufactured products. This is done in order to accumulate funds on special depreciation accounts for the purchase of new equipment or its partial improvement.

Depending on the causes and consequences, physical, functional and economic are distinguished.

Physical deterioration

This implies the direct loss of design properties and characteristics of a piece of equipment in the course of its use. This loss can be either total or partial. In the event of partial wear and tear, the equipment undergoes a refurbishment that returns the properties and characteristics of the unit to its original (or other, predetermined) level. In case of complete wear and tear, the equipment is subject to write-off and dismantling.

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

• First. Equipment wears out during planned use in compliance with all the rules and regulations established by the manufacturer.
• Second. The change in properties is due to improper operation or force majeure factors.
• Emergency. A hidden property change causes 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 serviceable and can produce products, but the use of new technologies or more advanced models that appear on the market makes the use of obsolete ones economically unprofitable. Functional wear can be:

• Partial. The machine is unprofitable for a complete production cycle, but is quite suitable for performing some limited set of operations.
• Complete. Any use results in damages. Unit to be decommissioned and dismantled

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. Leads to the need to restructure the entire technological chain with a complete or partial renewal of the composition of fixed assets.

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

In addition to physical, temporal and natural factors, the safety of equipment characteristics is indirectly influenced by economic factors:

• Falling demand for manufactured goods.
• inflation processes. Prices for raw materials, components and labor resources are growing, at the same time, there is no proportional increase in prices for the company's products.
• Competitor price pressure.
• An increase in the cost of credit services used for operating activities or for the renewal of fixed assets.
• Non-inflationary price fluctuations in the commodity markets.
• Legislative 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 causes and ways to determine wear

In order to determine the degree and causes of depreciation, a commission on fixed assets is created and operates at each enterprise. Equipment wear is determined by one of the following methods:

• observation. Includes visual inspection and complexes of measurements and tests.
• According to the service life. It is defined as the ratio of the actual period of use to the normative one. The value of this ratio is taken as the amount of wear in percentage terms.
• an enlarged assessment of the state of the object is made using special metrics and scales.
• Direct measurement in money. The cost of acquiring a new similar unit of fixed assets and the cost of refurbishment is compared.
• return on further use. The decrease in income is estimated, taking into account all the costs of restoring properties, compared with theoretical income.

Which of the methods to apply in each specific case is decided by the fixed assets commission, guided by regulatory documents and the availability of initial 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;
• reducing balance method;
• by the total period of production use;
• in accordance with the volume of output.

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 Abrasion
• 1.2 Fatigue wear
• 1.3 Seizure wear
• Conclusion

Introduction

During the operation of the car, as a result of the impact on it of a number of factors (impact of loads, vibrations, moisture, air flows, abrasive particles when dust and dirt get on the car, temperature effects, etc.), an irreversible deterioration of its technical condition occurs due to wear and damage to its parts, as well as a change in a number of their properties (elasticity, plasticity, etc.). wear hydroerosive abrasive

The change in the technical condition of the car is due to the operation of its components and mechanisms, the influence of external conditions and storage of the car, as well as random factors. Random factors include hidden defects in car parts, structural overload, etc.

The main permanent causes of changes in the technical condition of the vehicle during its operation were wear, plastic deformation, fatigue failure, corrosion, as well as physical and chemical 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 condition of machines and justify measures aimed at reducing the intensity of wear of machine parts, it is necessary to determine the type of surface wear in each specific case. To do this, it is necessary to set the following characteristics: type of relative displacement of surfaces (friction contact scheme); the nature of the intermediate medium (type of lubricant or working fluid); main 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 nature of relative oscillations with an average amplitude of 0.02-0.05 mm).

According to the type of intermediate medium, wear is distinguished during friction without lubricant, during friction with a lubricant, during friction with an abrasive material. Depending on the properties of the materials of parts, lubricant or abrasive material, as well as on their quantitative ratio in interfaces, various types of surface destruction occur during operation.

Wear is divided into the following types: mechanical (abrasive, hydro and gas abrasive, erosive, hydro and gas erosive, cavitation, fatigue, jamming 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 influences on the friction surface.

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

Electroerosive wear of the surface as a result of exposure to discharges during the passage of electric current is called electroerosive wear. In machines, this type of wear is found in electrical equipment elements in generators, electric motors, and also in electromagnetic starters.

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

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

1.1 Abrasion

Abrasive is the mechanical wear of a 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 is abrasive in nature. Such wear is found in the details of pivot joints, open plain bearings, parts of the working bodies of road machines, parts of running gears, etc.

The main source of abrasive particles getting into 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 µm, i.e. commensurate with the gaps in the interfaces of road machines. The main components of 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 erosive, hydro-gas-erosive and cavitation wear from hydro- and gas-abrasive wear.

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

Hydroerosive (gas-erosive) wear is erosive wear as a result of the action of a liquid (gas) flow.

Cavitation wear is called hydroerosive wear when a solid body moves relative to a liquid, in which gas bubbles collapse near the surface, which creates a local increase in pressure or temperature. Wear of this type is most common in pipeline elements and in manifolds in the absence of abrasive particles in the working fluid or gas. For road and construction machines, erosive types of wear are not typical.

1.2 Fatigue wear

Fatigue is called mechanical wear as a result of fatigue failure during repeated deformation of microvolumes of the material of the surface layer. Such wear is observed in most road vehicle interfaces as a concomitant type of wear. It occurs both in rolling friction and in sliding friction.

The process of fatigue wear is usually associated with repeatedly repeated stress cycles in rolling or sliding contact. In the process of surface interaction, stress fields arise in their upper layers. Scheme of stress distribution at the contact of the cylinder with the 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 (microprofile, dirt, dents, scratches, scuffs); load distribution in mating (elastic deformation, misalignment of parts, clearance); type of friction (rolling, sliding or rolling with slipping); 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 also 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 the microvolumes of the material, which occurs under the action of repeated compressive and tensile forces.

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

Fatigue wear of the material can be moderate and progressive. The usual moderate wear for most friction pairs is not dangerous, 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 manifests itself in the interaction of parts made of elastomeric materials. The elastic properties of these materials make it possible to reproduce the roughness of the opposite solid surface during sliding, which, in turn, leads to repeated cyclic loading of the material. If the hard surface irregularities are rounded and do not cause abrasion, 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 under the action of cyclic stresses for a long time.

1.3 Seizure wear

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

In the mechanism of wear during seizing, an important role is played by the atomic-molecular interaction of the materials of parts, which occurs when the surfaces approach each other. Unlike wear of other types, 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 quite quickly and leads to severe forms of damage (seizures and shells).

The process of formation of metallic 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 seizing process also depends on the properties of these oxides. Protective films that are firmly connected to the base metal and are able to quickly recover when destroyed prevent the metals from seizing.

Wear due to seizing of metals occurs as a result of a violation of the rule of a positive gradient of mechanical properties in depth under conditions of friction without lubricant or with an insufficient amount of it. Rolling friction under boundary lubrication also exhibits wear caused by material seizing and seizing. Seizing occurs when the lubricating film is locally broken and 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 flashes, etc.

Seizure wear is most common in gears. According to the ability to resist 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, oblique and spiral teeth; hypoid and helical gears with the lowest extreme pressure resistance. This is due to the fact that in hypoid and helical gears, the greatest slip of the teeth is noted in the engagement. Seizure wear also occurs in ball and roller bearings, and 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 a chemical interaction with the medium. At the same time, new, less durable chemical compounds are formed on the metal surface, which are removed with wear products during the mating process. Corrosion-mechanical wear includes oxidative wear and wear during fretting corrosion.

Wear is called oxidative wear, in which the main influence on the destruction of the surface is exerted by the chemical reaction of the material with oxygen or an oxidizing environment. It occurs during 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.

Wear during fretting corrosion is the corrosion-mechanical wear of contacting bodies with small oscillatory relative displacements. This type of wear differs from wear during fretting 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 the manifestation of a chemical reaction of the materials of parts and wear products with oxygen. Taking this into account, it is not difficult to draw an analogy between the mechanisms of wear development during fretting and fretting corrosion.

Wear during fretting and fretting corrosion usually occurs on the mating surfaces of shafts with wheel disks pressed on them, couplings and rolling bearing rings; on axles and wheel hubs; on the bearing surfaces of the springs; on tightened joints, fitted surfaces of keys and grooves; on the supports of motors and gearboxes. A necessary condition for the occurrence of fretting corrosion is the relative slip of the mating surfaces, which can be caused by vibration, reciprocating movement, periodic bending or twisting of the mating parts. The fretting process is accompanied by setting, oxidation, corrosion, and fatigue failure of microvolumes.

As a result of fretting corrosion, the endurance limit of the surface decreases by 3-6 times. Rubbing, metal sticking, tears, shells, as well as surface microcracks are formed on the surfaces of parts at the interfaces. A distinctive sign of wear due to fretting corrosion is the presence of shells on the friction surfaces, in which compressed oxides with a specific color are concentrated. In contrast to other types of wear, during fretting corrosion, the wear products in their bulk cannot leave the contact zone of the working surfaces of the parts.

Wear during fretting corrosion entails a violation of the dimensional accuracy of the connection (if part of the wear products finds a way out of the contact zone) or seizing 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 displacement of surfaces and a friction path (0.025 mm) equivalent to the oscillation amplitude at an oscillation frequency of up to 30 Hz and higher; localization of surface damage on the areas of actual contact due to small relative displacements; active oxidation

When elastomeric materials interact with metal parts, a setting phenomenon is also observed. The elastomer wears out if the coefficient of friction between it and the hard surface is high enough and the tensile strength of the elastomer 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. Next, there is a gradual tearing out of a part of the elastic material of the elastomer, which is in a state of setting with a solid surface. In this case, the elastomer layer separated from the surface is twisted into a roller and forms a wear particle. The wear rate of the elastomer in this case depends significantly on the temperature, load and type of lubricant. By selecting a lubricant taking into account external conditions and the elastic properties of the elastomer, this type of wear can be completely eliminated.

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

The first stage is accompanied by the destruction of protrusions and oxide films due to cyclically repeated oscillatory relative displacements of the contacting surfaces under the action of high loads. There are processes of hardening of materials and plastic deformation of the protrusions of microroughnesses, causing the surfaces to approach each other. The convergence of surfaces causes molecular interaction and metal seizing at individual points of contact. Destruction due to fatigue of the protrusions and setting 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 action of air oxygen and moisture. An electrolytic medium is created between the surfaces, which intensifies the process of oxidation of metal surfaces and their corrosion 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 softened surface layers of metals begin to be intensively destroyed at a gradually increasing rate. The process has a corrosion-fatigue fracture character.

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

2. The main causes of wear and damage to bodies

Wear and damage to bodies can be caused by a variety of 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, body elements and assemblies experience dynamic stresses from bending in the vertical plane and twisting, loads from their own weight, the weight of cargo and passengers.

Significant stresses also contribute to the wear of the body and its components, which arise as a result of the vibration of the body, not only when it moves over irregularities and possible shocks and shocks when hitting these irregularities, but also due to engine operation and errors in balancing the rotating components of the vehicle chassis (especially 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 car does not have a chassis frame, or partially when the body is installed on the frame.

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

There are two main groups of damage and malfunctions in the bodies of cars that come in for overhaul: damage that occurs as a result of an increase in changes in the state of the body.

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

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

Typical types of wear and damage to the body during the operation of the car 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 of the metal body of the body.

In the metal parts of the body, 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 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, roofs, etc.). Corrosion develops especially strongly in places that are difficult to access for inspection and cleaning in small gaps, as well as in flanging and bending of edges, where moisture periodically getting into them can persist for a long time.

So, dirt, salt and moisture can accumulate in wheel arches, stimulating the development of corrosion; the bottom of the body is not sufficiently resistant to the influence of factors that cause corrosion. The corrosion rate is greatly influenced by the composition of the atmosphere, its pollution with various impurities (emissions from industrial enterprises, such as sulfur dioxide resulting from fuel combustion; ammonium chloride released into the atmosphere due to evaporation of the seas and oceans; solid particles in the form of dust), and as well as ambient temperature, etc. Solid particles contained in the atmosphere or falling on the surface of the body from the roadway also cause abrasive wear of the metal surface of the body. With an increase in temperature, the corrosion rate increases (especially in the presence of aggressive impurities and moisture content in the atmosphere).

Winter coatings of roads with salt to remove snow and ice, as well as the operation of the car on the sea coast, lead to an increase in car corrosion.

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

Thus, studies have shown that when steel comes into contact with polyisobutylene, the metal corrosion rate per day is 20 mg/m2, and when the same steel comes into contact with silicone rubber, it is 321 mg/m2 per day.

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

Contact friction also leads to the appearance of corrosion on the surface of body parts, which takes place under the simultaneous action of a corrosive environment and friction, during the oscillatory movement of two metal surfaces relative to each other in a corrosive environment. Doors along the perimeter, wings at the points of their attachment to the body with bolts and other metal parts of the body are subject to this type of corrosion.

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 coverage, also leads to corrosion of the body.

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

Figure 1 - Surface corrosion on a car fender.

Figure 2 - Pitting on a car.

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

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

Body cracks occur upon impact due to a violation of the body metal processing technology (multiple impact processing of steel in a cold state), poor build quality during the manufacture or repair of the body (significant mechanical forces when connecting parts), as a result of the use of low quality steel, the influence of metal fatigue and corrosion with subsequent mechanical load, assembly defects of units and parts, as well as insufficiently strong unit design.

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

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

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

1 - cracks in the mudguard; 2 - violation of the welded connection of the spacer or mudguard with the frame spar; 3 - cracks in the strut; 4 - cracks on the front panel and mudguards of the front wheels; 5 cracks on the pillars of the wind window; 6 - deep dents on the windshield rack panel; 7 - skew of the opening of the wind window; 8 -- separation of the front seat bracket; 9 - cracks on the casing of the base of the body; 10 - violation of welded joints of body parts; 11 - curvature of the gutter; 12 - dents on the outer panels, covered with parts on the inside, irregularities remaining after straightening or straightening; 13 - local corrosion in the lower part of the rear window; 14 - detachment of the rear pillars in the attachment points or cracks in the pillars; 15 and 16 - local corrosion of the trunk lid creek; 17 -- separation of the trunk lock bracket; 18 - local corrosion in the rear of the base of the body; 19 - dents on the bottom panel of the tailgate in the places where the rear lights are attached; 20 - local corrosion in the lower part of the mudguard; 21 - corrosion coating and other minor mechanical damage; 22 - local corrosion of the wheel arch; 23 -- curvature of the mudguard of the rear wing; 24 - violation of the welded seam in the connection of the mudguard with the arch; 25, 32 - cracks in the base in the places where the seats are attached; 26 - local corrosion on the rear door pillar and on the base of the body. exciting power rear spar; 27 -- cracks on the base of the body at the attachment points of the rear spring brackets and others; 28 - dents on the rack panel and the curvature of the center pillar; 29 - separation of the holders of the retainer plates and the hinges of the body door; 30 - local corrosion in the lower part of the middle pillar of the sidewall; 31 - local corrosion and cracks in the spars of the base of the body; 33 -- distortions of doorways of bodies; 34 - continuous corrosion of the thresholds of the base; 35 - dents on the spars of the base of the body (breaks are possible); 36 - thread failure on the plates for fixing the latch and door hinges; 37 - tearing off the door latch cover; 38 - dents (possibly with breaks) on the body side panel; 39 -- local corrosion at the bottom of the A-pillar; 40 - violation of the anti-corrosion coating; 41 - separation of the nut-holders; 42 - curvature of the cross member No. 1; 43 - cracks on the bulkhead plate at the attachment points of the strut; 44 - separation of the bracket for fastening the front buffer; 45 - cracks on the radiator shield; 46 - local corrosion on the brace of the amplifier; 47 -- cracks in the attachment points of the spar; 48 -- weakening of the rivet connection of the bracket; 49 - making holes for the finger of the spring earring and the front bracket for mounting the rear spring; 50 - separation of the amplifier of the side member of the base of the body; 51 - wear of the shock absorber mounting hole; 52 - cracks in the places where the fuel tank brackets are attached; 53 - dents with sharp corners or breaks on the bottom panel; 54 - solid corrosion on the lower rear panel; 55 - cracks in the places where the shock absorbers are attached; 56 - cracks on the casing of the cardan shaft

Destruction of welded joints in units, the details of which are connected by spot welding, as well as in continuous welds of the body, can occur due to poor-quality welding or the effects of corrosion and external forces: vibration of the body under the action of dynamic loads, uneven distribution of goods during loading and unloading of bodies.

The destruction data are shown in Figure 4.

Figure 4 - Destruction of welded joints under the influence of corrosion

Wear due to friction occurs in fittings, hinge pins and holes, upholstery, rivet and bolt 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 poor-quality work (assembly, repair, etc.).

The concentration of stresses in the joints of individual elements of the body in the 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.

Body structures usually provide for the necessary rigid connections, reinforcement of individual sections with additional parts, extrusion of stiffeners.

However, in the course of long-term operation of the body and in the process of its repair, individual weak links in the body body may be revealed, which require strengthening or changes in the design of the nodes in order to avoid the occurrence of secondary breakdowns.

Conclusion

The change in the technical condition of the car is significantly influenced by the operating conditions: road conditions (technical category of the road, type and quality of the road surface, slopes, uphill slopes, curvature radii of the road), traffic conditions (heavy city traffic, traffic 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 in winter, which increase corrosion), as well as transport conditions ( vehicle loading).

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

These include such damage as fatigue wear and corrosion-mechanical wear.

To reduce corrosion of car parts and, first of all, the body, it is necessary to maintain their cleanliness, timely care for the paintwork and its restoration, and perform anti-corrosion treatment of body cavities and other parts subject to corrosion.

To prevent fatigue failures and plastic deformations, it is necessary to strictly follow the rules for operating a car, avoiding its operation at limiting modes and with overloads.

List of sources used

1 Fundamentals of performance of technical systems studies. 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.: OGU, 2010. - 586 p.

4 Improving the durability of transport vehicles: textbook. manual for universities / V. A. Bondarenko [and others]. - M. : Mashinostroenie, 1999. - 144 p.

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

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A sad story: from an engine (new, moderately used or overhauled) they expected many years and many hundreds of thousands of kilometers of reliable and honest work, but it immediately began to smoke, lost power, began to act up at startup, ate oil and eventually got up.

Now the vast majority uses cars that were created in countries that are decades ahead of us in the mass motorization of the population. And these cars are built on principles close to those that exist in aviation - DIAGNOSTICS ACCORDING TO REGULATIONS.
Those who have been abroad know that there most often people come to the service with a question, see if everything is in order. This is especially the case in Germany.

Engine. What is the most common cause of premature engine wear?

2. Engine overheating.

The accumulation of soot is a gradual process. There are many reasons and we all analyzed them. For some types of engines this is more relevant, for others less so. The problem is most acute for engines with direct fuel injection.
It is often said that engines have become less reliable. And I would put it differently. Engines have become more demanding both on our fuel and in our conditions, carbon deposits must be cleaned every 10 thousand, then there will be no problems.
In addition, fuel equipment sensor errors, air filter clogging, and much more greatly affect the accumulation of soot.
Overheat. This phenomenon rarely occurs suddenly. It usually "sneaks" very gradually in the form of small smudges of antifreeze, which can be both noticeable and manifest as a puddle under the car, or antifreeze getting into the combustion chamber, which can most often be seen only with an endoscope through the spark plug hole.

"Opening" of several engines with similar symptoms at first glance always gives a more or less similar picture - severe wear of the cylinder-piston group. However, catastrophic wear is not always a direct consequence of long and intensive operation. Often the piston group, and with it the entire engine, die suddenly. In such cases, it is extremely important to understand what exactly caused this wear in order to eliminate the cause during the repair. Otherwise, the repair turns into an endless and hopeless elimination of consequences.

Let's look at a few typical examples:

Intensive wear as a result of the fuel washing off the lubricant from the cylinder walls.

Errors in the operation of the fuel equipment, a “pouring” nozzle, misfiring or inaccuracies in setting the injection advance angle lead to the formation of an excess amount of unburned fuel in the over-piston space. Getting on the cylinder walls, fuel particles mix with the oil film, significantly reducing its lubricating properties. As a result, in the most stressed upper zone of the cylinder, the piston rings operate under conditions of insufficient lubrication.

Significant excess fuel

It is able to completely wash off the oil film, and the operating conditions of the rings in this case are close to the dry friction mode. In such cases, intensive wear of the piston rings is observed, with the formation of a characteristic sharp edge. The cylinder liner in the upper zone of operation of the rings acquires critical wear (about 0.2 mm) literally in 500 - 800 km of run. The piston skirt is not seriously affected at the initial stage. Later, characteristic dark spots with vertical scoring appear on the piston skirt, indicating friction zones in conditions of insufficient lubrication. When examined under a microscope on the piston skirt, it is possible to detect embedded particles of wear products of the piston rings. The engine oil of a “dead” engine for the reasons described above usually has significant fuel impurities. So, along with the black smoke of the over-enriched exhaust, not only soot and unburned diesel fuel fly out into the pipe, but also a significant part of the engine resource.

Quick and sad consequences are caused by abrasive getting into the engine.

It is not difficult to calculate that for every minute of operation, a naturally aspirated diesel engine pumps through itself an amount of air equal to the product of the working volume and 1/2 revolution. For example, V slave is 12 liters, revolutions are 2000 rpm, i.e. 12 m2 per minute or 720 m3 per hour. A very low concentration of solid particles in such a volume of air consumed is enough for the accumulated abrasive to literally eat the engine from the inside. Inaccurate installation of the air filter, loose clamps, cracks in the connecting corrugations, the possibility of air being sucked into the engine past the filter - all this leads to a quick death of the motor from the "road" abrasive.

Risk of technical abrasive entering the motor during maintenance or repair.

A tractor in a dusty field and a luxurious boat in neutral waters can be equally subject to such misfortunes. How many times have you seen how the desire of a diligent owner of a passenger car to “polish” the intake manifold with a sandpaper, or competently and accurately grind the carburetor body parts on the plate, leads to an almost instantaneous (200 - 500 km) death of the engine. It is impossible to remove the technical abrasive by “rinsing with gasoline”. In the modern practice of engine repair, the very desire to grind something (for example, valves) is bewildering, but nevertheless, in such an insidious way, abrasive particles sometimes manage to get into the engine.

Then the following picture is formed: solid particles entering the friction zone cause intense wear. Piston rings wear intensively not only in radial thickness, but also in height. In this case, the first compression ring receives the maximum wear, since it is it that is exposed to solid particles in the first place. Intensive wear of the first ring in height appears as a result of the accumulation of solid particles in the gap between the ring and the annular groove of the piston. The end surfaces of the ring quickly receive significant deviations from the original geometric shape and dimensions. The rapidly increasing gap causes intense breaking of the annular groove.
When an abrasive enters the engine, intense wear of the working surfaces of the rings is accompanied by the formation of numerous vertical scratches. On the edges of the rings there is a micro breakage or microburrs. The zone of maximum cylinder wear is usually lower than in the case of wear due to excess fuel described above and is approximately at the middle of the operating height of the cylinder. The working area of ​​the piston skirt is damaged in the form of numerous vertical scratches, giving the piston skirt a matte gray color. When examined under a microscope, embedded solid particles are found on the piston skirt - the killers of the motor and the culprits of this type of wear.

The number of such inclusions on the piston skirt is usually not large - only a few points per 1 cm2, however, if we take into account that a small part of the total about 200,000 double strokes, even a small amount of hard inclusions on the piston skirt becomes obvious, which clearly indicates the abrasive nature of intensive wear. The often notorious bath of gasoline, in which yesterday<сполоснули>lapped valve, and today the mechanic of another shift washed something before assembling the motor and is the true reason<необъяснимых>wear.

The last, and perhaps the most obvious indicator of the presence of abrasive wear is

The nature of the damage to the piston pin.

Judge for yourself: if a finger with a surface hardness of usually around 54:60 HRC received abnormally large wear in a short time, turning in<алюминиевых>piston bosses, therefore particles were present in the friction zone that were much harder than the material of the piston pin itself. In practice, it happened, unfortunately, to analyze cases with malicious application of powders or pastes to motors.

In this situation. An absolute boon would be the creation of a serious specialized scientific and expert laboratory. But until such an organization has been created, transport workers and repairmen have to deal with many controversial situations on their own.

By themselves, defects in the mechanical part of the engine, as you know, do not appear. Practice shows: there are always reasons for damage and failure of certain parts. It is not easy to understand them, especially when the components of the piston group are damaged.

The piston group is a traditional source of trouble for the driver operating the car and the mechanic repairing it. Overheating of the engine, negligence in repairs - and please - increased oil consumption, blue smoke, knocking.

When "opening" such a motor, scuffs on pistons, rings and cylinders are inevitably found. The conclusion is disappointing - expensive repairs are required. And the question arises: what was the fault of the engine, that it was brought to such a state?

It's not the engine's fault, of course. It is simply necessary to foresee what these or those interventions in its work lead to. After all, the piston group of a modern engine is “thin matter” in every sense. The combination of the minimum dimensions of parts with micron tolerances and the enormous forces of gas pressure and inertia acting on them contributes to the appearance and development of defects, ultimately leading to engine failure.

In many cases, simply replacing damaged parts is not the best engine repair technique. The reason for the appearance of the defect remained, and if so, then its repetition is inevitable.

To prevent this from happening, you need to think several moves ahead, calculating the possible consequences of your actions. But this is not enough - it is necessary to find out why the defect occurred. And here, without knowledge of the design, operating conditions of parts and processes occurring in the engine, as they say, there is nothing to do. Therefore, before analyzing the causes of specific defects and breakdowns, it would be nice to know ...

How does a piston work?

The piston of a modern engine is a seemingly simple detail, but it is extremely responsible and complex at the same time. Its design embodies the experience of many generations of developers.

And to some extent, the piston forms the appearance of the entire engine. In one of the previous publications, we even expressed such an idea, paraphrasing a well-known aphorism: “Show me a piston, and I will tell you what kind of engine you have.”

So, with the help of a piston in the engine, several problems are solved. The first and main thing is to perceive the pressure of the gases in the cylinder and transfer the resulting pressure force through the piston pin to the connecting rod. This force is then converted by the crankshaft into engine torque.

It is impossible to solve the problem of converting gas pressure into torque without reliable sealing of the moving piston in the cylinder. Otherwise, a breakthrough of gases into the engine crankcase and oil from the crankcase into the combustion chamber are inevitable.

To do this, a sealing belt with grooves is organized on the piston, in which compression and oil scraper rings of a special profile are installed. In addition, special holes are made in the piston to discharge oil.

But this is not enough. During operation, the bottom of the piston (fire zone), in direct contact with hot gases, heats up, and this heat must be removed. In most engines, the cooling problem is solved using the same piston rings - heat is transferred through them from the bottom to the cylinder wall and then to the coolant. However, in some of the most loaded designs, additional oil cooling of the pistons is done, supplying oil from below to the bottom using special nozzles. Sometimes internal cooling is also used - the nozzle supplies oil to the internal annular cavity of the piston.

For reliable sealing of cavities from the penetration of gases and oils, the piston must be held in the cylinder so that its vertical axis coincides with the axis of the cylinder. All sorts of distortions and "shifts" that cause the "hanging" of the piston in the cylinder, adversely affect the sealing and heat transfer properties of the rings, increase the noise of the engine.

The piston skirt is designed to hold the piston in this position. The requirements for the skirt are very contradictory, namely: it is necessary to provide a minimum, but guaranteed, clearance between the piston and the cylinder both in a cold and in a fully warmed up engine.

The task of designing a skirt is complicated by the fact that the temperature coefficients of expansion of the materials of the cylinder and piston are different. Not only are they made of different metals, their heating temperatures vary many times over.

To prevent the heated piston from jamming, modern engines take measures to compensate for its thermal expansion.

First, in the cross section, the piston skirt is shaped like an ellipse, the major axis of which is perpendicular to the axis of the pin, and in the longitudinal section, it is a cone, tapering towards the bottom of the piston. This shape allows the skirt of the heated piston to conform to the cylinder wall, preventing jamming.

Secondly, in some cases, steel plates are poured into the piston skirt. When heated, they expand more slowly and limit the expansion of the entire skirt.

The use of light aluminum alloys for the manufacture of pistons is not a whim of designers. At high speeds, typical for modern engines, it is very important to ensure a low mass of moving parts. Under such conditions, a heavy piston will require a powerful connecting rod, a “mighty” crankshaft and an overly heavy block with thick walls. Therefore, there is no alternative to aluminum yet, and you have to go to all sorts of tricks with the shape of the piston.

There may be other "tricks" in the piston design. One of them is a reverse cone at the bottom of the skirt, designed to reduce noise due to the “relaying” of the piston in dead spots. A special microprofile on the working surface helps to improve the lubrication of the skirt - microgrooves with a pitch of 0.2-0.5 mm, and a special anti-friction coating helps to reduce friction. The profile of the sealing and fire belts is also defined - here is the highest temperature, and the gap between the piston and the cylinder in this place should not be large (there is an increased likelihood of gas breakthrough, the risk of overheating and breakage of the rings) or small (there is a high risk of jamming). Often, the resistance of the fire belt is increased by anodizing.

All that we have said is far from a complete list of requirements for a piston. The reliability of its operation also depends on the parts associated with it: piston rings (dimensions, shape, material, elasticity, coating), piston pin (clearance in the piston bore, method of fixation), cylinder surface condition (deviations from cylindricity, microprofile). But it is already becoming clear that any, even not too significant, deviation in the operating conditions of the piston group quickly leads to defects, breakdowns and engine failure. In order to repair the engine in the future with high quality, it is necessary not only to know how the piston is arranged and works, but also to be able to determine by the nature of the damage to the parts why, for example, a scuff has occurred or ...

Why did the piston burn out?

An analysis of various piston damages shows that all causes of defects and breakdowns are divided into four groups: cooling failure, lack of lubrication, excessively high thermal and force effects from gases in the combustion chamber, and mechanical problems.

At the same time, many causes of piston defects are interrelated, as are the functions performed by its various elements. For example, defects in the sealing belt cause overheating of the piston, damage to the fire and guide belts, and scuffing on the guide belt leads to a violation of the sealing and heat transfer properties of the piston rings.

Ultimately, this can cause burnout of the fire belt.

We also note that with almost all malfunctions of the piston group, increased oil consumption occurs. With severe damage, thick, bluish exhaust smoke, a drop in power and difficult starting due to low compression are observed. In some cases, the sound of a damaged piston is heard, especially on a cold engine.

Sometimes the nature of the defect in the piston group can be determined even without disassembling the engine according to the above external signs. But more often than not, such an “indiscriminate” diagnosis is inaccurate, since different causes often give almost the same result. Therefore, the possible causes of defects require a detailed analysis.

Violation of piston cooling is perhaps the most common cause of defects. This usually occurs when the engine cooling system malfunctions (chain: “radiator-fan-fan switch-on sensor-water pump”) or due to damage to the cylinder head gasket. In any case, as soon as the cylinder wall ceases to be washed from the outside by liquid, its temperature, and with it the temperature of the piston, begin to rise. The piston expands faster than the cylinder, moreover, unevenly, and eventually the clearance in certain places of the skirt (usually near the pin hole) becomes equal to zero. Seizure begins - the seizure and mutual transfer of materials of the piston and cylinder mirror, and with further engine operation, the piston jams.

After cooling, the shape of the piston rarely returns to normal: the skirt is deformed, i.e. compressed along the major axis of the ellipse. Further operation of such a piston is accompanied by knocking and increased oil consumption.

In some cases, the piston burr extends into the sealing belt, rolling the rings into the piston grooves. Then the cylinder, as a rule, turns off from work (compression is too low), and it is generally difficult to talk about oil consumption, since it will simply fly out of the exhaust pipe.

Insufficient piston lubrication is most often characteristic of starting conditions, especially at low temperatures. Under such conditions, the fuel entering the cylinder washes away the oil from the cylinder walls, and scoring occurs, which are usually located in the middle part of the skirt, on its loaded side.

Double-sided scuffing of the skirt usually occurs during prolonged operation in the oil starvation mode associated with malfunctions of the engine lubrication system, when the amount of oil falling on the cylinder walls decreases sharply.

The lack of lubrication of the piston pin is the reason for its jamming in the holes of the piston bosses. This phenomenon is typical only for designs with a pin pressed into the upper head of the connecting rod. This is facilitated by a small gap in the connection between the pin and the piston, so the "sticking" of the fingers is more often observed in relatively new engines.

Excessively high thermal force effect on the piston from hot gases in the combustion chamber is a common cause of defects and breakdowns. So, detonation leads to the destruction of the jumpers between the rings, and glow ignition - to burnouts.

In diesel engines, an excessively large fuel injection advance angle causes a very rapid increase in pressure in the cylinders (“rigidity” of work), which can also cause breakage of the jumpers. The same result is possible when using various fluids that make it easier to start a diesel engine.

The bottom and fire belt can be damaged if the temperature in the diesel combustion chamber is too high, caused by a malfunction of the injector nozzles. A similar picture also occurs when the piston cooling is disturbed - for example, when the nozzles supplying oil to the piston, which has an annular internal cooling cavity, coke. Seizure that occurs on the top of the piston can also spread to the skirt, trapping the piston rings.

Mechanical problems, perhaps, give the largest variety of piston group defects and their causes. For example, abrasive wear of parts is possible both “from above”, due to dust entering through a torn air filter, and “from below”, when abrasive particles circulate in the oil. In the first case, the cylinders in their upper part and the compression piston rings are the most worn, and in the second case, the oil scraper rings and the piston skirt. By the way, abrasive particles in the oil can appear not so much from untimely maintenance of the engine, but as a result of the rapid wear of any parts (for example, camshafts, pushers, etc.).

Rarely, piston erosion occurs at the “floating” pin hole when the retaining ring pops out. The most likely causes of this phenomenon are the non-parallelism of the lower and upper heads of the connecting rod, which leads to significant axial loads on the pin and the “knocking out” of the retaining ring from the groove, as well as the use of old (lost elasticity) retaining rings when repairing the engine. The cylinder in such cases turns out to be damaged by a finger so much that it can no longer be repaired by traditional methods (boring and honing).

Sometimes foreign objects can get into the cylinder. This most often occurs with careless work during engine maintenance or repair. A nut or bolt, caught between the piston and the head of the block, is capable of many things, including simply “failing” the piston bottom.

The story about defects and breakdowns of pistons can be continued for a very long time.

Electronics.
Here everything is most often manifested even more clearly. Most of the failures at the beginning manifest themselves in the form of mistakes that are erased and the person leaves reassured. But practice has shown that any, the most insignificant deviation from the norm is a sign of a certain trend. For a long time, you can ignore the light "pokes" of the box, which are easily eliminated by flashing or, in extreme cases, the prevention of the board. But quickly enough it will lead to the need to rebuild the box.

Timing errors are often a sign of chain wear, gears, and then end with a bulkhead of the motor for hundreds of thousands of rubles. Works such as replacing the timing belt should generally be carried out “in automatic mode” up to a mileage of 80 thousand. Everyone knows what happens when it breaks.

Having the opportunity to compare how much those who have not turned off the old algorithm of approach to car maintenance in their minds and those who “come for diagnostics” spend on car maintenance, I can say that the costs of the former in total during the time they own a car are about 30 50% is usually more than the latter.

The rules are very simple and follow from the features of the piston group and the causes of defects. However, many drivers and mechanics forget about them, as they say, with all the ensuing consequences.

Although this is obvious, during operation it is still necessary:

1. maintain the power supply, lubrication and cooling systems of the engine in good condition, service them in time,

2. do not overload a cold engine,

3. avoid the use of poor quality fuel, oil and inappropriate filters and spark plugs.

When repairing, it is necessary to add and strictly follow a few more rules. The main thing, in our opinion, is that one should not strive to ensure minimum piston clearances in the cylinders and in the locks of the rings. The epidemic of "small gap disease", which once struck many mechanics, is still not over. Moreover, practice has shown that attempts to "tighter" install the piston in the cylinder in the hope of reducing engine noise and increasing its resource almost always end in the opposite: piston scuffing, knocking, oil consumption and repeated repairs. The rule “better clearance is 0.03 mm more than 0.01 mm less” always works for any engine.

The rest of the rules are the same:

quality spare parts

correct processing of worn parts,

thorough washing and careful assembly with mandatory control at all stages.

Initially, smart people put a two-row chain and twin gears. The load on each tooth and link of the chain was small and there were no problems with chains in nature.

Now, under the slogan of reducing weight and metal consumption, as well as ecology, engines have become the way we see them.

After 120 thousand run, it is necessary to change without exception without waiting for the marks to leave and break or jump.

Departure of the mark from the norm even by a millimeter is the reason for replacement.

Andrey Goncharov, expert of the Car Repair section