Wear mechanism of disc-brake block material for new type of drilling rig

Abstract

To improve friction and wear performance and service life of the disc-brake pair material of a drilling rig, a new type of asbestos-free frictional material with better performance for disc-brake blocks is developed, and its wear mechanism is investigated by friction and wear experiments. Topography and elementary components of the brake block’s wear surface are analyzed by employing SEM and EDAX patterns, revealing its tribological behaviour and wear mechanism. When the frictional temperature is lower, the surface film of the brake block is thinner, dense, smooth with plasticity, and divided into the mixture area, Fe-abundant area, carbon-abundant area and spalling area. The mixture area consists of various constituents of frictional pairs without ploughing and rolling trace. The Fe-abundant area mainly consists of iron and other constituents. The carbon-abundant area is the zone where graphite and organic fibre are comparatively gathered, while the spalling area is the zone where the surface film is spalled and its surface is rough and uneven, with a loose and denuded state. During the period of high frictional temperature, the frictional surface is also divided into the mixture area, Fe-abundant area and spalling area. In this case, the mixture area consists of abrasive dust from friction pairs, and the surface film is distributed with crumby hard granules, exiguous oxide, carbide granules and sheared slender fibre. The Fe-abundant area is mostly an oxide layer of iron with a flaky distribution. Fracture and spalling traces as well as an overlapping structure of multilayer surface films can be easily found on the surface film. The components of the spalling area are basically the same as that of the matrix. At the beginning of wear, the hard peaks from the friction surface of the disc-brake plough on the surface of the brake block. With increasing frictional temperature, the friction surface begins to soften and expand, and oxidized wear occurs at the same time. During the high-temperature wear period, severely influenced by friction heat, obvious softening and plastic flow can be found on the friction surface of the brake block, its anti-shearing ability is weakened, and adhesive wear is intensified. Thermal decomposition of cohesive material in the brake block is simultaneously strengthened, so that constituents shed due to loss of adhesion. Organic fibre is in a flowing state and obviously generates drawing, shearing, carbonization and oxidization. In addition, thermal cracking, thermal oxidization, carbonization and cyclization of organic substances on the surface of brake block can make the friction surface produce pores or cracks, thus fatigue wear occurs.

References

1. Yi Maozhong Han Zhihai Chen Hua et al.The study on the brake friction characteristic ofplasma sprayed fe-ni-co-wc coatingTribology 1996 16(2)150155
2. Wang Xinhua Zhang Siwei Fan Qiyun Experimental study in screening and matching of disc brakepair materials of drilling rig. Tribology 2002 22(3)197201
3. Zhang Siwei Wang Xinhua Fan Qiyun et al.Investigation of the tribological performance offriction pair for disc brake of drilling rigScience in China (Series A) 2001 44(Supplement)253258
4. Fan Qiyun Zhang Siwei Li Weiming Thermal design, a new concept of the disc brake designOil Field Equipment 1995 24(3)2225
5. Jia Xian Zhou Benlian Chen Yongtan et al.Study on worn surface layers of the friction pairvonsisting of semimetallic friction materials and grey cast iron.Tribology 1995 15(2)171176
6. Wang Bozhan Yao Anyou Research on meerschaum brake-frictionmaterial and analysis of its friction and wear mechanismIn: Proceedings of the 5^th National Symposium on Tribology, Part I 1992 591–596
7. Zhang Mingzhe Liu Yongbing Yang Xiaohong The progress in the tribologial investigation of automotivefriction materialsTribology 1999 19(4)379384