Analysis of Tribotechnical Properties and Comparative Evaluation of Polymeric Materials and Rubbers Used in Rolling Stock

Rubber materials are widely used in friction assemblies of railway rolling stock. Rubbers are used oil seals, other various seals, shock absorbers, corrugated hoses, sleeves, sealing rings, etc. During operation, rubbers are exposed to various mechanical influences that cause wear, cracks, abrasion, dents, burnthroughs, etc., which can lead to the failure of the entire unit and unforeseen unscheduled repairs of the rolling stock. Any failure on the route together with unplanned repairs incur heavy economic losses.Currently, the issue of wear of rubbers in rubber-steel tribopairs has not been sufficiently studied in case of supply of lubricant to the friction zone and of wear caused by a free and fixed abrasive. There is ongoing research on the possibility of replacing rubber products with other polymeric materials, which have shown significantly better results in tribological tests, both in terms of friction coefficients and in the wear mechanism. The data obtained will make it possible to choose the most optimal options for materials that can act as a replacement for standard rubber products in rolling stock friction assemblies.The paper presents the results of tribological tests of thermoplastic polyurethanes (TPU), ultra-high-molecular-weight polyethylene (UHMWPE) and polypropylene (PP2015) in comparison with rubber based on nitrile butadiene rubber (NBR). The tests were carried out according to two schemes: «plane (tested sample) – bushing» and «plane (tested sample) – generatrix of a rubber disk with supply of abrasive grain to the friction zone». The objective of the work is to determine the dependence of the change in friction coefficients on load and sliding speed, as well as the dependence of seizure pressures of tribo-pairs on speed, weight loss of samples after wear tests with a free and fixed abrasive, the morphology of wear surfaces, and wear mechanisms of polymer materials and rubbers.

Development of a New Finishing Process Combining a Fixed Abrasive Polishing with Magnetic Abrasive Finishing Process

High quality, highly efficient finishing processes are required for finishing difficult-to-machine materials. Magnetic abrasive finishing (MAF) process is a finishing method that can obtain a high accuracy surface using fine magnetic particles and abrasive particles, but has poor finishing efficiency. On the contrary, fixed abrasive polishing (FAP) is a polishing process can obtain high material removal efficiency but often cannot provide a high-quality surface at the nano-scale. Therefore, this work proposes a new finishing process, which combines the magnetic abrasive finishing process and the fixed abrasive polishing process (MAF-FAP). To verify the proposed methodology, a finishing device was developed and finishing experiments on alumina ceramic plates were performed. Furthermore, the mechanism of the MAF-FAP process was investigated. In addition, the influence of process parameters on finishing characteristics is discussed. According to the experimental results, this process can achieve high-efficiency finishing of brittle hard materials (alumina ceramics) and can obtain nano-scale surfaces. The surface roughness of the alumina ceramic plate is improved from 202.11 nm Ra to 3.67 nm Ra within 30 min.