WEAR AND TEAR OF SPLINE JOINTS IN VEHICLES

ABSTRACT

The article presents a brief review of the destruction of contacting parts as a result of the occurrence and development of fretting corrosion. The optimal options for preventing fretting corrosion are also given.

The article reflects the regularities of changes in the concentration of wear products falling out into the oil of the unit, based on the results of theoretical and experimental studies of spline joints of half axles of rear axles of cars in operating conditions, depending on the rate of accumulation of wear products.

As a result of occurrence and development of fretting corrosion the service life of many assemblies is limited by wear or destruction of contacting parts, occurring at oscillating motion of contacting surfaces. Exactly the same movement occurs in spline joints of half axles of rear axles of «UZAUTO MOTORS» JSC vehicles.

АННОТАЦИЯ

В статье представлен краткий обзор разрушения контактирующих деталей в результате возникновения и развития фреттинг-коррозии. Также приведены оптимальные варианты предотвращения фреттинг-коррозии.

В статье нашли свое отражение закономерности изменения концентрации продуктов износа, выпадающих в масло агрегата, основанные на результатах теоретических и экспериментальных исследований шлицевых соединений полуосей задних мостов автомобилей в эксплуатационных условиях, в зависимости от скорости накопления продуктов износа.

В результате возникновения и развития фреттинг-коррозии ресурс работы многих узлов ограничивается износом или разрушением контактирующих деталей, происходящие при колебательном движении контактирующих поверхностей. Точно такое же движение происходит в шлицевых соединениях полуосей задних мостов автомобилей АО «UZAUTO MOTORS».

Keywords: Wear, fretting corrosion, friction, oxidation, adsorptions, particles, isolation, ultradispersion.

Ключевые слова: Износ, фреттинговая коррозия, трение, окисление, адсорбция, частицы, изоляция, ультрадисперсия.

The national economy of the Republic of Uzbekistan uses various machines and mechanisms, the overwhelming majority of which are motor vehicles. Due to the fact that they work in difficult conditions, in most cases it is off-road and dusty conditions, there is intensive contamination of lubricants of the rear axles of the vehicle. For this reason there is wear of parts of the units at a high rate, and the number of failures occurring in the rear axles is 23.3% of the total number of failures, the cost of funds for the elimination of failures is 24.3% of the total cost of repair of machines. Therefore, it is required periodic assessment of technical condition and express-diagnostics of wear of parts of aggregates of the above mentioned machines and mechanisms in the process of their operation, allowing to predict the occurrence of failure of aggregates, due to wear of their parts. In most cases, half axles are installed in the satellite with the help of splines. They have a relative displacement equal to the gap between the teeth of the splines of the axle and satellite. Therefore, the parts fail as a result of wear and buckling of the splined joints and their lateral collision. Here, the amount of wear corresponding to 10 mm of spline length is 0.05-0.08% of the total amount of wear products falling out of the gears. The inner ring of the bearing is mounted on the half-axle without relative movement, therefore no wear products fall out from this connection into the oil of the machine.

The fatigue strength under the influence of fretting corrosion can decrease several times, the generalised approach under friction conditions allows us to distinguish three main stages of fretting corrosion development. At the first stage of fretting corrosion, hardening of the contact surfaces and cyclic fluidity of the surface layers are observed; most of the protrusions of the actual contact interact with others plastically. This is facilitated by the adhesion of juvenile metal in the contacting irregularities after the destruction of natural oxide films. The protrusions and sheared interlocking nodes destroyed by fatigue create primary fracture products, of which some are oxidised. However, metallic wear particles make up the majority of the products at this stage. Oxidation reactions accelerate the transition of the surface layers into an ultradispersed state.

Fatigue damage continues to accumulate at the second stage of fretting corrosion in the subsurface layers. In the friction zone a corrosive-active medium is simultaneously formed due to adsorption of oxygen and moisture on oxides. At this stage, the wear rate is low and is mainly associated with the destruction of oxide films formed on friction surfaces, with the amount of wear products in the friction zone of oxide films reaching an equilibrium value due to the fact that the exit of particles from the contact zone is balanced by their emergence.

Under such conditions, a special (mechanochemical) mechanism of intensification of oxidation of metallic surfaces acts due to the fact that under alternating contact interactions a reactive fine-dispersed structure appears in the thinnest surface layers. A protective role can be played by the reduction of the rate at formation of a mixed structure (of metal and oxides). We can call the incubation period the second period of fretting corrosion. Pre-hardened layers under optimum conditions experience more moderate cyclic loads and fatigue damage, aggravated by corrosion processes, accumulates in the formed contact.

The third stage of fretting-corrosion, preliminarily loosened by fatigue and corrosion processes, is associated with the final destruction of damageability zones. These stages are called stages of corrosion-fatigue fracture, taking into account the possibility of electrochemical processes. During this period the surface layers of metal, which have been subjected to cyclic deformations for a long time, become so hardened that they lose their stability and their progressive separation begins, which is manifested in the growth of wear rate. Destruction of contacting surfaces due to fretting corrosion increases with the growth of test duration (Fig. 1.)

As the number of cycles increases, the pattern of fretting corrosion development may change depending on material properties, sliding amplitude and specific load. The wear rate of steel is high, especially during the run-in period, and then it decreases. The figure below shows the dependence of the spline wear rate on the number of loading cycles. L_c

Figure 1. Influence of the number of loading cycles on values of wear of splines of rear axle half axles of the vehicle

Although lubrication does not usually prevent fretting corrosion completely, any lubricant is better than no lubricant at all. Oil- or grease-based greases are most effective when they are fully immersed in the friction zone and isolate the surfaces from air oxygen.

Conclusions: According to specialists of UzMIS (Machine Testing Station) of the Republic of Uzbekistan, experimental studies show that the mass of wear products accumulated in the oil of rear axles for one period of replacement, according to spectral analysis is 52.2 grams on the epyura of wear parts 51.641 grams. The mass of wear products for the same period was: gears on the wear of gear teeth 30.7 grams; spline joints 9.2 grams; rolling bearings 11.741 grams. Thus arithmetic average resource: gears on wear of teeth 10087 hours; spline joints - 8334 hours; rolling bearings -7041 hours.

The mechanism of spline joint wear is also disclosed. It is established that the wear products from the spline joint in the oil of the unit fall out as a result of fretting -corrosion of the rubbing surfaces. The amount of wear products grows according to linear regularity with increasing cycles of loading of spline joint.

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