Assessing dynamic characteristics for friction draft gears with worn wedge shoes

A friction draft gear model was developed to assess the degraded dynamic characteristics of worn draft gears in the vehicle impact condition. It presents an approach to simulate multiple typical wear profiles of wedge shoes and reflect their effects on the draft gear performance. Based on the rated design indexes and existing overhaul regulations of MT-2 type friction draft gears in China, the safety wear limits for wedge shoes with different wear profiles were classified and assessed. The results indicate that wedge shoes with uniform or concave wear can significantly worsen draft gear performance, and the existing maintenance limit of 1 mm only applies to wedge shoes with uniform wear but not to the most common wedge shoes with concave wear. Also, for wedge shoes with concave wear, when the wear area covers 50%, 75%, and 100% of the total main friction surface, the corresponding safety wear limits are 0.5 mm, 0.8 mm, and 1.3 mm, respectively. Therefore, it is proposed to design multiple graded and dynamic maintenance limits to ensure the service safety of MT-2 type friction draft gears.