การพัฒนาแท่งห้ามล้อสำหรับอุตสาหกรรมรถไฟไทย

Abstract

This reseach was to investigated and developed high phosphorous cast iron brake shoes. The investigations found that state railway of Thailand had been used LV4 and DR2 brake shoes of 150,000 pieces/year (485 Baht/piece), which there were quality and service Life problems of these brake shoes and affecting the cost of state railway of Thailand. Therefore, this research focused on the development of brake shoe casting in order to improve their mechanical properties and microstructures, including reduce defects. In addition, the brake performane will increase and service life extend leading to decrease the maintanance cost. This research found that chemical compositions and mold designs affected to microstructures, porosities, hardness, and wear of casting brake shoes. Adding high phosphorous into cast iron resulted in the formation of the FeP phase. As a result, the hardness increased and the friction coefficient decreased, which affected the braking distance. On the other hand, the addition of carbon and 0.3%wt silicon inoculant contributed to form the graphites which lubricated during braking and reduce sticking between wheel and brake shoe. It was found the back plate placed above the molding box was cavitatation higher than that of below the molding box. Cross-section area ratio between the sprue and the ingate (As:A) should be in the range of 1.2-1.6 and the ingate was suitable size. The brake shoe casting part had a good quality. In view of the economic worthiness, the riser should be designed in a smaller size and appropriate propotion. However, the riser could compensate the liquid metal in the first stage of liquid feeding. Pouring temperture of liquid metal at over 1,300°C had more tubular shrinkage cavities than that of lower poring temperature and small shrinkage cavity size distributed throughout the brake shoe casting part. On the other hand, the microstructures of high phosphorous cast irons did not change after heat treatment at temperature of 800-930°C, but their hardness increased This research could produce brake shoes with hardness of 220+20HB, porosity of 8% and wear of 3-4 g (according to the ASTM G65).