In the article, the points of load application effecting the pads and other parts of the freight car three-element bogie during braking is considered theoretically using the example of the 2D diagram of the brake rigging. The special differences between the operating conditions of the first and second triangles of the car brake rigging and their effect on the wear of the pads when the train is moving without braking are described. The different operating conditions of the triangles are described to establish a causal relationship regarding the abnormal wear of the brake pads of the three-element bogies. For the first time, a calculation algorithm of a more accurate approach to theoretical calculations was proposed to determine the actual pressing forces in the brake pads on the wheels of the bogies. It proves the existence of the theoretical error, which is now inherent to the design models of freight cars brake rigging elements. The obtained algorithmic equations will help assess the wear of the brake pads and its effect on the stress-strain state in order to guarantee the railway traffic safety during the relevant theoretical and practical studies.
The article presents a new scientific approach to the problem related to the specific nature of the adverse biplanar critical friction wear profile of brake pads which is quite common in cars of Ukrzaliznytsya JSC, as well as in many countries where the so-called three-element bogies are used. In order to study the dual wear of brake pads during the operation, the statistical material was collected and processed in the specialized software STATISTIKA to obtain graphical dependences that confirm the results of theoretical research. In the conducted studies, the concept of dual friction wear of brake pads was first discovered as a phenomenon and introduced. The stages of formation of especially harmful wear on the working surfaces of brake pads causing the complex formation of adverse specific dual wear are shown. A new concept of the duality coefficient of frictional wear of brake pads has been introduced, and a formula for its calculations has been proposed, which has been tested in the calculations of the values of brake pressures of pads with dual wear to support the analytical studies.
The complex of operational studies and theoretical research was performed on the occurrence of harmful wear that changes geometrical parameters of the useful contact area of the brake pads of freight cars at various established standard clearance between the pad and the wheel, which significantly impairs the braking efficiency of trains. The inspections of the mechanical part of the brakes attracted attention to the abnormal wear of the brake pads of the freight cars, which occurs because the common centre of gravity of the pad and the brake shoe, which are on the pendular suspension, do not coincide with the centre of the hole in the brake strut for any pad. The results of calculations using the coordinate method performed in the Mathcad software environment and the graphical one performed in AutoCAD to determine the geometrical parameters of the formation of the upper harmful wear of the pad depending on the standard clearance between the wheel and the brake pad were compared to proved theoretically that the error between them does not exceed 5-7%.
Наука та прогрес транспорту. Вісник Дніпропетровського національного університету залізничного транспорту, 2020, № 2 (86) Creative Commons Attribution 4.
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