During the operation of any production equipment, processes occur that are associated with a gradual decrease in its performance characteristics and changes in the properties of parts and assemblies. As they accumulate, they can lead to a complete stop and serious damage. To avoid negative economic consequences, enterprises organize a process for managing wear and tear and timely updating fixed assets.
Wear detection
Wear, or aging, is a gradual decrease in the performance characteristics of products, components 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. Negatively affects:
- friction;
- static, pulsed or periodic mechanical loads;
- temperature conditions, especially extreme ones.
The following factors slow down aging:
- Constructive decisions;
- use of modern and high-quality lubricants;
- compliance with operating conditions;
- timely maintenance, scheduled preventative repairs.
Due to a decrease in performance characteristics, 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 type - damage to the surface by small particles of other materials;
- cavitation, caused by the explosive collapse of gas bubbles in a liquid medium;
- adhesive appearance;
- oxidative species caused by chemical reactions;
- thermal view;
- fatigue appearance caused by changes in the structure of the material.
Some types of aging are divided into subtypes, such as abrasive.
Abrasive
It consists in the destruction of the surface layer of the material during contact with harder particles of other materials. Characteristic for mechanisms operating in dusty conditions:
- mining equipment;
- transport, road construction mechanisms;
- Agreecultural machines. Agreecultural equipment;
- construction and production of building materials.
You can counteract it by using special hardened coatings for rubbing pairs, as well as by promptly changing the lubricant.
Gas abrasive
This subtype of abrasive wear differs from it in that solid abrasive particles move in the gas flow. The surface material crumbles, is cut off, and is deformed. Found in equipment such as:
- pneumatic lines;
- fan and pump blades for pumping contaminated gases;
- domain installation nodes;
- components of solid fuel turbojet engines.
Often, gas abrasive effects are combined with the presence of high temperatures and plasma flows.
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Waterjet
The effect is similar to the previous one, but the role of the abrasive carrier is performed not by a gaseous medium, but by a liquid flow.
The following are susceptible to this effect:
- hydrotransport systems;
- hydroelectric power station turbine units;
- components of washing equipment;
- mining equipment used for washing ore.
Sometimes waterjet processes are aggravated by exposure to an aggressive liquid environment.
Cavitation
Pressure drops in the liquid flow flowing 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 ships, in hydraulic turbines and technological equipment. The situation can be complicated by exposure to 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, periodic convergence of surface areas occurs at a distance that allows the forces of interatomic interaction to manifest themselves. The interpenetration of atoms of substance of one part into the crystalline structures of another begins. 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 bearings.
Thermal
The thermal type of aging consists of the destruction of the surface layer of a material or a 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. Characteristic for highly loaded components of heavy equipment, rolls of rolling mills, hot stamping machines. It can also occur in other mechanisms when the design conditions for lubrication or cooling are violated.
Fatigue
Associated with the phenomenon of metal fatigue under variable or static mechanical loads. Shear stresses lead to the development of cracks in the materials of parts, causing a decrease in strength. Cracks in the near-surface layer grow, unite and intersect with each other. This leads to erosion of small scale-like fragments. Over time, this wear can cause the part to fail. It is found in components of transport systems, rails, wheel sets, mining machines, building structures, etc.
Fretting
Fretting is the phenomenon of microfracture of parts in close contact under conditions of low-amplitude vibration - from hundredths of a micron. Such loads are typical for rivets, threaded connections, keys, splines and pins connecting 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.
Types of wear
The classification of types of wear and tear from the point of view of the physical phenomena that cause it in the microcosm is complemented by systematization according to the macroscopic consequences for the economy and its subjects.
In accounting and financial analytics, the concept of wear and tear, which reflects the physical side of phenomena, is closely related to the economic concept of depreciation of equipment. Depreciation refers to both the decline in value of equipment as it ages and the attribution of a portion of that decline to the cost of the products produced. This is done with the aim of accumulating funds in special depreciation accounts for the purchase of new equipment or partial improvement of it.
Depending on the causes and consequences, they distinguish between physical, functional and economic.
Physical deterioration
This refers to the direct loss of the design properties and characteristics of a piece of equipment during its use. Such loss may be either total or partial. In case of partial wear, the equipment undergoes restoration repairs, returning the properties and characteristics of the unit to the original (or other pre-agreed) level. If the equipment is completely worn out, it must be written off and dismantled.
In addition to degree, physical wear and tear is also divided into types:
- First. Equipment wears out during planned use in compliance with all standards and regulations established by the manufacturer.
- Second. Changes in properties are due to improper operation or force majeure factors.
- Emergency. Hidden changes in properties lead to sudden emergency failure.
The listed varieties apply 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 of the appearance on the market of the same type, but more productive, economical and safe equipment. The machine or installation is still physically in good working order and can produce products, but the use of new technologies or more advanced models appearing on the market makes the use of outdated ones economically unprofitable. Functional wear can be:
- Partial. The machine is unprofitable for a complete production cycle, but is quite suitable for performing a certain limited set of operations.
- Full. Any use results in damages. The unit is subject to write-off and dismantling
Functional wear is also divided 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 rebuild the entire technological chain with a complete or partial update of the composition of fixed assets.
If a new technology appears, as a rule, the composition of the equipment is reduced and the labor intensity decreases.
In addition to physical, temporary and natural factors, the safety of equipment characteristics is also indirectly influenced by economic factors:
- Fall in demand for manufactured goods.
- Inflationary processes. Prices for raw materials, components and labor resources are rising, while at the same time there is no proportional increase in prices for the company's products.
- Price pressure from competitors.
- An increase in the cost of credit services used for operating activities or for updating fixed assets.
- Non-inflationary price fluctuations in raw materials markets.
- Legal restrictions on the use of equipment that does not meet environmental standards.
Both real estate and production groups of fixed assets are susceptible to economic aging and loss of consumer qualities. Each enterprise maintains registers of fixed assets, which take into account their depreciation and the progress of depreciation accumulations.
The main reasons and ways 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 complex measurements and tests.
- According to service life. It is defined as the ratio of the actual period of use to the standard one. The value of this ratio is taken as the amount of wear in percentage terms.
- a comprehensive assessment of the condition of an 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 restoration repairs are compared.
- profitability of further use. The reduction in income is estimated taking into account all the costs of restoring properties in comparison with the theoretical income.
Which method to use in each specific case is decided by the fixed assets commission, guided by regulatory documents and the availability of source information.
Accounting methods
Depreciation charges, designed to compensate for the aging processes of equipment, can also be determined using several methods:
- linear or proportional calculation;
- reducing balance method;
- by total period of production use;
- in accordance with the volume of products produced.
The choice of methodology is made during the creation or deep reorganization of an enterprise and is enshrined in its accounting policies.
Operation of equipment in accordance with rules and regulations, timely and sufficient contributions 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.
The main reasons for accelerated engine wear
Late replacement of oil and oil filter leads to the operation of friction pairs in unfavorable conditions.
This is due to the deterioration of the performance properties of the engine oil (its viscosity changes, additives are produced, the tendency to form deposits on parts and in the channels of the lubrication system increases, etc.) and a large number of wear products in the lubrication system (in an extremely dirty oil filter, the bypass opens valve and oil passes by the filter element).
Using 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 scuffing 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, scuffing and jamming. Similar effects are possible if an oil that does not meet the quality class of the given engine (API, ACEA classification, etc.) is used. For example, when instead of the recommended oil according to API class SH/CD, a cheaper SF/CC is used.
Poor air or fuel filter condition(defects, mechanical damage), as well as various leaks in the intake system connections lead to the entry of abrasive particles (dust) into the engine and intense wear, primarily of the cylinders and piston rings.
Delayed troubleshooting of engine problems or incorrect adjustments will accelerate wear of parts. For example, a knocking camshaft is a source of continuous contamination of the lubrication system with metal particles. Incorrect setting of the ignition timing, malfunction of the carburetor or engine management system, or the use of spark plugs that do not match the engine cause detonation and glow ignition, which threatens to destroy the pistons and surfaces of the combustion chambers.
Engine overheating due to malfunctions in the cooling system can lead to deformation of the cylinder head (cylinder head) and the formation of cracks in it. With insufficient cooling, the oil film in friction pairs becomes less durable, which leads to intense wear of the 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. Operating the engine primarily at maximum loads and crankshaft speeds can significantly reduce its service life (by 20-30% or more). Exceeding the permissible speed leads to destruction of parts.
About 70% of engine wear occurs during the starting mode. A cold start especially contributes to a reduction in service life if the engine is filled with oil with an inappropriate viscosity-temperature characteristic. At a temperature of -30oC 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 reach (pump) the friction pairs.
Short trips with a cold engine in winter contribute to the appearance of deposits in the lubrication system and corrosive wear of pistons, their rings and cylinders.
VIII. CONCLUSION OF THE COMMANDER OF THE MILITARY UNIT
VII. COMMISSION PROPOSALS
VI. VOLUME OF IMPROVEMENTS COMPLETED
V. CAUSES OF EARLY WEAR OR DAMAGE
IV. TECHNICAL CONDITION
___________________________________________________________________________________________________________________________________________________________
(No. of amendment bulletins)
______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Chairman of the commission: __________________________________________________
Members of the commission: ____________________________________________________________________________
(position, military rank, signature, surname)
____________________________________________________________________________
(position, military rank, signature, surname)
The act was drawn up in ____ copies.
copy No. 1 __________
copy No. 2 __________
copy No. 3 __________
(SENIOR MANAGER)
M.P. ______________________________________________________________________________________________________________
(position, military rank, signature, surname)
Passed: ________________________________________________________________
(position, military rank, signature, surname)
Accepted: ______________________________________________________________
(position, military rank, signature, surname)
"____" ________________ 200 g.
1. The act is intended to document the established technical condition, need for repairs and decommissioning of weapons and equipment, recorded by numbers and technical condition.
2. The act is drawn up by a commission of a military unit (formation), association:
when transferring weapons and equipment within a military unit (warehouse) - in one copy and approved by the unit commander (head of the warehouse);
when transferring weapons (equipment) from one military unit to another, delivery to a repair unit (enterprise) of an association (center) - in triplicate and approved by the commander of the military unit. The first copy of the act is presented to the higher management body of the relevant service, the second is sent along with the weapons (equipment), the third remains in the military unit;
when transferring weapons (equipment) to a lower category of a previously established period, extending the service life and service life - in duplicate. Both copies are submitted to the higher management body of the relevant service. After approval by the senior commander, the first copy of the act is returned to the military unit (to the warehouse);
when decommissioning weapons (equipment) removed from the equipment of troops, as well as those that became unusable during testing or after the expiration of the established service life - in two copies. Both copies of the act are sent in the prescribed manner for approval to the chief who has the right to do so. After approval, the first copy is returned to the military unit (warehouse);
when writing off lost or prematurely deteriorated weapons (equipment) - in two copies and approved by the commander of the military unit (head of the warehouse). The first copy, along with the application, is sent to the senior supervisor to receive an inspection certificate.
The signature of the commander of the military unit in Section VIII and the signature of the commander who approved the act are certified with mastic official seals.
3. In column 2 of section I of the act, the first line records the basic model of weapons (equipment, equipment) for which the act is drawn up. The following lines record its components, counted by numbers (engines, units, guns, launchers, machine guns, electronic receiving and transmitting devices, components, etc.), technical documentation.
4. Section III of the act records missing parts and spare parts (the incompleteness card is attached to the act), as well as technical documentation and fuel transferred with weapons (equipment). The tire numbers and the percentage of their wear are also recorded here.
5. Section IV records: the date and place of failure of weapons (equipment); technical condition during external inspection, engine start and mileage test (operating mode).
6. Section V records the causes of premature wear or damage and the investigation performed. The base sample on which the system is mounted is given a separate report on its technical condition, and the category and type of repair required is determined. In this case, an additional copy of the act is sent to the head of the service, which takes into account the basic sample.
7. When producing vehicle certificate forms, the following are not printed: the reverse side of the first sheet; the name of the second, third and fourth details of paragraphs 4, 8 and paragraph 6 of section II; Section VI.
8. When drawing up an act for writing off production equipment in Section VIII, if necessary, the chief accountant (head of the financial service) confirms its book value and the amount of depreciation.
The main question of this article is whether driving at low speeds leads to premature wear of the engine? And what modes are the most “wear-inducing”...
The organization of expert tests is, in general, clear. The engine is the same: a VAZ eight-valve engine. A stand, equipment, gasoline and several cans of oil - each test cycle requires its replacement. The task is simple - you need to “travel” the same distance, at the same speed, but using different engine operating modes. On different gears...
How to achieve this? You can drive at the same speed, maintaining engine speeds of 1500, 2500, and even 4000 rpm. The higher the speed, the lower the gear; it is important that the power produced by the engine is the same. It’s easy to do this at the stand - we measure the torque using a dynamometer, the speed is known - therefore, we know the power. We multiply “speed” by engine hours, which we also record – that’s the mileage.
With wear it is more difficult - every time, after running the engine at a fixed time for a given time, the engine will have to be disassembled and weighed the main parts that form the friction units, these are bearing shells and piston rings. Plus, there is additional intermediate control, which we will carry out by determining the content of wear products in oil samples. If they found chromium, it means that the first piston rings are wearing out; found iron - cylinders and shaft journals; tin has appeared - it will determine the wear rate of the bearing liners (since it is part of the anti-friction layer); aluminum is a consequence of wear on the pistons and camshaft bearings.
The engine worked at the specified constant modes with approximately the same power, 50 hours each. Not much for the resource, but we get wear rates, and then by simple extrapolation we estimate the approximate service life of the motor. At the same time, the engine speed during the test cycles varied from 1200 to 4000, that is, more than three times. And then the load on the motor was increased - and the cycle was run again. And then - more... The result was a voluminous table, where for each point of the regime its own wear rate was recorded, and divided by units - bearings and rings.
This is how the average wear rate of the first piston rings of the engine changes when the operating mode changes.
“Black zones” of active wear were immediately revealed. The most serious ones are when a large load is applied at low speeds, and with high oil temperatures. The wear rate in this mode is maximum - both for bearings and piston rings with cylinders. Engine specialists call this area zone of towing modes.
With increasing speed, the wear zone immediately began to decrease and somewhere at 1800 rpm it disappeared. All friction units “floated” onto oil films, direct contact between the surfaces of the parts disappeared - and with it the wear rate became almost zero. But we must understand that zero wear rate on the graphs does not mean that it does not exist, just wear in these modes is less than the measurement error. In practice, of course, this is not entirely true. Microparticles of dust, wear products, soot that have slipped through the oil filter will cause some wear here too.
And so - connecting rod bearing shells
As the crankshaft speed increases, the wear zone begins to appear and grow again. In our case - already somewhere from 3800 rpm modes under heavy load, and further - it progresses. Moreover, here the wear of bearings and piston rings with cylinders behaves differently. The crankshaft bearings begin to feel high speeds most quickly. Why? The fact is that with increasing speed, the load on the bearings increases sharply - the pressure of inertial forces depends on the speed squared. But the rings again begin to wear out at high rotation speeds - around 4500 rpm, and there this is mainly due to an increase in oil temperature.
Where is the most favorable area for engine operation? In the VAZ V8s we tested (no matter whether carburetor or injection, eight- or sixteen-valve), the optimal speed zone at which the engine is able to absorb any load without any damage to itself is approximately 2000...3000 rpm. Here we take into account that the initial state of the engine can be different, and so can motor oils... The principle is simple - the more worn out the engine is, the higher the lower and the lower the upper boundaries of the wear-free zones. The higher the oil viscosity, the lower the engine speed can be safely loaded. But there are no exact numbers - it’s very individual.
How does this compare with motors of other sizes? There is one catch here... In principle, the friction units of the motor sense not the revolutions, but the linear speeds of movement of the surfaces of the parts. There is such a motor parameter - average piston speed, is the product of the piston stroke and the crankshaft speed divided by thirty. The range that we obtained approximately corresponds to average piston speeds of 5...7 m/s. This means that for “long-stroke” engines, for which the piston stroke is larger than the diameter, the zone of optimal conditions will shift to the region of lower speeds. Hence their “elasticity”. For “short-stroke” ones, the zone of optimal modes will shift to the area of higher speeds.
By the way, it is precisely this range of changes in average piston speeds that is usually used to determine the main operating zones of engines with large resources. Marine diesel engines, diesel generators, etc.
So, take your size, follow the basic steps, and approximately get your safe speed range. But this is approximately true...
But in general, the conclusion is clear. Both low-speed modes with heavy loads and extreme speeds are harmful to the engine. Alexander Shabanov
All parts lose their original characteristics during operation. The reason for this is WEAR - the process of changing spare parts, as a result of which the mechanism loses its original properties.
Visual signs of wear: changes in the size and structure of the surfaces of parts.
Types of wear parts
Changing the characteristics of used spare parts is a process that is the result of their interaction and use. Some changes occur even during normal operation of the mechanisms. Such changes are called NATURAL and are introduced when the node starts.
2 types of unnatural wear of parts:
- NORMAL
It is a consequence of improper operation and installation violations. Leads to gradual equipment failures and deterioration of the technical condition of the facility.
- EMERGENCY
As the numerical values of normal wear and tear increase, objects and mechanisms become completely unusable.
Factors that influence wear rates:
- Mechanism design
- Precision and cleanliness of processing
- Strength of the material of a specific part and those in contact with it
- Lubricant quality
- Operating conditions of the unit (regularity, nature of the load, temperature, pressure)
- Maintenance frequency
Reasons for wear of parts
All reasons can be combined into 3 groups:
- Physical/Mechanical
It is a consequence of high loads and the impact of friction between one part and another. Contacting parts wear out and cracks, scratches, and roughness appear on their surfaces.
- Thermal/molecular mechanical
Parts working together experience overheating due to high speeds and specific pressures. Due to a sharp increase in temperature, setting and subsequent destruction of the molecular bonds of particles inside the metal occurs. Parts warp and melt.
- Chemical/ corrosive
It is observed on the surface of metal parts as a result of exposure to water, air, and chemicals. Processes of corrosion and corrosion of the metal occur. To avoid this, it is recommended to use .
It is worth understanding that the cause of wear and tear of parts is not one single factor, but several interrelated ones.
How to restore worn parts?
Basic methods for restoring parts:
- Restoration by mechanical and metalworking
Suitable for parts with flat contacting surfaces. The worn area is processed (sanded, ground, etc.) and transferred to the next size. Mechanical processing is used separately and as a final stage of other methods.
- Upgrade by welding and surfacing
By surfacing durable metals, the dimensions of damaged parts are restored.
- Restoring a part by metallization
The size of the worn part is restored by applying molten metal in a thin (from 0.03 mm) and thick (over 10 mm) layer.
- Galvanic surfacing (chrome plating)
Applying chromium in a thin layer (up to 1 mm) ensures resistance to mechanical abrasion. The method is similar to metallization, but less universal. Restored parts do not withstand dynamic loads well.
- Strengthening and bonding with plastic
Plastics make it possible to obtain fixedly connected units, as well as to stop the wear of parts. Unlike previous methods, metal and non-metallic parts can be restored with plastic. The cost of repairs with plastics is significantly lower. Using modern casting materials, it is possible to restore a part with complex and non-standard geometry.
