THE INFLUENCE OF MATERIALS ON THE DURABILITY OF SLIDING BEARINGS

ABSTRACT

The article discusses the importance of angular contact bearings in the crankshaft of an autotractor engine and consideration of methods for increasing the durability of their work, which makes it possible to increase the efficiency of bearings and prevent wear during high loads of an internal combustion engine. An assessment of the materials for the manufacture of plain bearings and their influence on the operation of the bearing itself is given.

АННОТАЦИЯ

В статье рассматривается значение радиально упорного подшипника скольжения в коленчатым вале автотракторным двигателе и рассмотрение методов повышения долговечности их работы, позволяющих повысить эффективность работы подшипников и предотвращения износа в период высоких нагрузок двигателя внутреннего сгорания. Приведена оценка материалов изготовления подшипников скольжения и их влияние на работу самого подшипника.

Keywords: plain bearing, internal combustion engine, bearing, engine crankshaft, wear

Ключевые слова: подшипник скольжения, двигатель внутреннего сгорания, вкладыш, кoленчатый вал двигателя, износ.

The bearings of the crankshaft of the engine operate mainly in the hydrodynamic lubrication regime. In a properly designed and manufactured bearing, this mode can only be violated during start-up, with a decrease in oil viscosity, instantaneous overloads, violation of its supply, etc. During normal operation of a tractor diesel engine of medium tension, the minimum value of the oil layer thickness is 7-8 microns.

In forced models of internal combustion engines, the thickness of the hydrodynamic film is reduced to 4 microns. This thickness is limiting, since local violations of the hydrodynamic regime are possible, caused by the ingress of abrasive particles into the gap, the dimensions of which exceed the size of the gap. It does not follow from this that during normal operation of the bearing, when the friction surfaces are lubricated with a layer of oil, wear does not occur. Plastic deformation may occur, caused by high hydrodynamic pressures developed by the oil layer. The maximum value of hydrodynamic pressure is 2.5 - 3 times higher than the average pressure of external forces acting on the bearing. Contact polarization, thermoelectric phenomena on friction surfaces separated by a liquid 2 film, are the cause of the electrostatic component of wear. A particularly important factor is also the corrosion of the anti-friction layer.

The task of increasing the durability of plain bearings of an internal combustion engine cannot be considered only from the point of view of improving the design and improving the physicochemical properties of a plain bearing. To solve this problem, it is also necessary to take into account the second component of the investigated friction pair - the surface of the crankshaft journal and the crankshaft itself. Only with this approach to the solution, the modes and operating conditions of the designed product are determined: it determines the types of process fluids used during operation; frequency and duration of operation cycles; the main parameters that determine the state of the object and their limiting values, indicating the inadmissibility of its further use.

The main factors in the design and manufacture of the sliding liner of an internal combustion engine are its design (the liners can be thick-walled and thin-walled) and the quality of its anti-friction coating. Initially, the requirement to ensure high rigidity of the liner was satisfied by using thick-walled liner, which have a thickness of 4 - 6 mm or more. However, such liners did not provide good contact with the bearing bed, which made it difficult to remove heat and reduce fatigue strength [4].

In addition, the thick anti-friction layer is subject to displacement under load. In modern engines, thin-walled liners are increasingly being used. These are flexible designs, but due to their tight fit to the bed, the rigidity is provided by the bearing as a whole. At the same time, heat is very well removed to the engine mass and lowers the temperature of the anti-friction film. Thin-walled liners are good for mass production as they are stamped from tape, but require high precision and alignment of bearing assemblies. The most common materials for pouring liners are alloys based on aluminum, copper, tin, zinc, and lead. The choice of anti-friction alloy should be determined to a greater extent by its compatibility with the oil. The suitability of an oil for engine bearings is practically determined by its anti-corrosion properties and viscosity. For example, babbitt sliding liners are currently unpromising due to their low fatigue strength and corrosion resistance. For the most part, alloys containing lead have these disadvantages. Lead bronze, which has high mechanical characteristics and hardness than babbits, is widely used, but worse in workability.

In autotractor engines, three-layer bearings are used: anti-friction filling from the SOS-6-6 alloy (6% antimony, 6% tin, 88% lead), a thin-walled steel base and a cermet or copper-nickel sublayer.

On tractor diesel engines, bimetallic liners have found their application: antifriction alloy ASM (3.5 - 4.5% - antimony, 0.5 - 0.7% - magnesium, the rest - aluminum), applied by rolling onto a rigid steel base, with an intermediate underlayer of aluminum foil or pure aluminum. Such bimetallic bearings are used in most domestic tractor diesel engines. Their durability is 4 - 5 thousand hours. The thickness of the anti-friction layer is 0.7 - 0.8 mm, i.e. they can be considered thick-walled.  However, the transition in diesel engines to a thinner fill has not yet justified itself due to the deformability of the shafts, which are subject to heavy loads.

Table 1 below shows the antifriction materials that have found their application in the manufacture of plain bearings of an internal combustion engine. The design of the engine on which it is installed also has a great influence on the durability of the bearing shells. It is known from the theory of engine calculation that in in-line internal combustion engines, compared to V-shaped ones, the loads on the connecting rod bearings are greater than on the main bearings, and their wear is correspondingly higher. However, this theory is not always correct. So, on the D-243 tractor diesel engine, the connecting rod bearings wear out less than the main bearings, regardless of the fact that the load on them is higher. This is due to the additional purification of oil in the cavities of the connecting rod journals. Similar phenomena take place in engines.

Таблица 1. Материалы для гидродинамических подшипников скольжения

Table 1.

Materials for hydrodynamic plain bearings

To a large extent, the degree of wear and the ratio of wear of the main and connecting rod bearings depend on the supply of oil from the main line to the crankshaft. Thus, the experimental change in the surface of the crankshaft journal made it possible to obtain the following advantages: to reduce the average temperature in the oil layer by 10.7%; increase the minimum oil layer thickness by 62%; reduce the power spent on friction in the bearing by 28%; reduce heat release due to friction forces by 52%.

Conclusion: Thus, the service life of plain bearings can be increased in various ways. The effectiveness of one or another method depends on the type of engine on the materials of manufacture of the bearings themselves.

Список литературы:

1. Дорохов А.Ф., Абачараев И.М., Абачараев М.М., Шихсаидов Б.П. Конструкторскотехнологические разработки по повышению ресурса и экономичности двигателя внутреннего сгорайия//Двигателестроение. - 2004. -№1.-С.20-22
2. Гаркунов Д.Н. Триботехника (износ и безызносность). М: Издательство МСХА, 2001. - 616 с.
3. Дроздов Ю.Н. и др. Трение и износ в экстремальных условиях: Справочник / Ю.Н. Дроздов, В.Г. Павлов, В.Н. Пучков. М.: Машиностроение, 1986.-224 с.
4. Анализ металлов; Справочник/Лазарев А.И., Харламов И.П. М.: Металлургия, 1987. - 320 с.
5. Денисов А.С. Басков В.Н. Особенности изнашивания деталей при переменных режимах работы агрегатов//Двигателестроение. - 2003. - № 4, — С.46-48