Development Prizes: New Materials
High wear resistant Fe-sintered alloy slider for high-speed trains
A prize was awarded to Fine Sinter Co Ltd. for the development of a high wear resistant slider for high-speed trains (Fig. 4). The slider, or contact strip, is designed to collect electric currents and transmit them to train vehicles through a pantograph from the trolley wire. The basic requirements for the slider are high wear resistance and a low level of attack on the trolley wire. Among many expendables in railway vehicles, the slider is most frequently replaced and, consequently, represents one of the highest costs in train maintenance. Recently, increases in train running speeds have made it necessary to improve the wear resistance of sliders at high speeds.
The aim of this development was to significantly decrease slider wear and to reduce the level of attack on the trolley wire, through the provision of good lubrication, and to maintain good mechanical properties. In order to increase wear resistance in the high-speed range, while maintaining good lubrication and high mechanical properties, a MnS-containing, free-cutting Fe powder was used as the matrix and a complex mixture of Fe-based and Cr-based hard particles was added. In addition, by avoiding the sulfurisation treatment used in conventional sliders, an improvement of more than 40% on lead-times was achieved without any cost increase.
A wear test at 300 km/h relative running speed found that slider wear was improved by 38% and the level of wear on the trolley wire was equal to or better than that of a conventional slider.
Development of an Fe-Cu system oil-impregnated sintered bearing with excellent high pressure resistance and wear resistance
Diamet Corporation won a further award for the development of a bearing that is designed to form part of the armature used in an electronically controlled wiper motor, as a typical application example (Fig. 5).
In order to improve pressure and wear resistance, the company targeted excellent sliding and lubricating performance with higher hardness and strength than conventional Fe-Cu system oil-impregnated sintered bearings.
For better sliding characteristics, the developed bearing material incorporated a large amount of copper (exceeding the solubility limit in iron) and had a microstructure with a large fraction of copper phases. In addition, as a result of optimising the raw material particle size of the copper powder and graphite and the sintering conditions, the material has become an Fe-Cu system composite structure, in which undissolved copper phases and free graphite are dispersed and distributed, resulting in high hardness and high strength. Furthermore, Diamet succeeded in securing the dimensional accuracy of the sizing process by making the dimensional change rate in sintering almost zero (< 0.1%).
The developed bearing material is said to achieve a wear resistance of more than four times that of a conventional bearing, under the electronically controlled wiper motor operating conditions. The material has high hardness and high strength, but also has excellent lubricating properties, sliding performance and dimensional accuracy. Diamet stated that there is no other example of this type of bearing material in the marketplace.