Braking Performance of Fe-Based and Cu-Based Powder Metallurgy Pads Paired with C/C-SiC Disk on Full-Scale Dynamometer

Abstract

In this study, the friction performance of copper-based (Cu-PM) and iron-based (Fe-PM) powder metallurgy pads was systematically compared and analyzed by performing a braking test paired with a C/C-SiC disk on a full-scale flywheel brake dynamometer, including coefficient of friction (COF), wear rate (Wr), and worn surface under dry and wet tests. The test procedure simulated the braking conditions on high-speed trains with initial brake speeds (IBS) from 50 km/h to 200 km/h, as well as under various brake clamping forces (F_B). During dry tests, both pads exhibited high levels of COF. The mean value of average COF (µ_m) for the Cu-PM pad was 0.371, which was slightly higher than that of 0.358 from the Fe-PM pad. The stability of µ_m over the IBS ranged from 68% to 82% for Cu-PM pads under different F_B, while it was from 82% to 85% for Fe-PM pads. However, during the wet tests, the mean value of µ_m dropped to 0.207 for Cu-PM pads, and with the minimum µ_m of 0.062; whereas, they were 0.344 and 0.188 for Fe-PM pads, respectively, showing a significant difference in the friction performance between the two pads. Additionally, the W_r of the Cu-PM pad was 0.110 cm³/MJ during dry tests, which was 17.3% lower than that of 0.133 cm³/MJ observed for the Fe-PM pad. After the brake test with the Cu-PM pad, the friction film primarily covered the Si/SiC-rich region of the disk, effectively inhibiting the plowing of SiC hard asperities onto the pad surface. However, the friction film predominantly covered the fiber-rich region of the disk after the test with the Fe-PM pad, and the exposure of hard Si/SiC-rich asperities would continuously plow the pad during braking and resulted in furrows on the surface of the Fe-PM pad. In terms of wear mechanisms, adhesion wear was the primary mechanism on the contact surfaces of the Cu-PM pad and the C/C-SiC disk, while abrasion dominated the interaction between the Fe-PM pad and the C/C-SiC disk. This study provides valuable insights for the application of C/C-SiC brake disks on trains.

Keywords:

• C/C-SiC disk
• powder metallurgy pad
• flywheel brake dynamometer
• dry condition
• wet condition

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

Additional information

Funding

Financial support from the Beijing Science and Technology Planning Project under Contract Z201100008420013 is gratefully acknowledged.