The Study Of Suppressing Railway Disc Brake Squeal Noise By Grooved Surface Texturing

Brake squeal noise generated by the railway disc brake is one of the important parts of the railway noise, which seriously affects the normal operation of railway industry and consequently results in the detrimental effect on the people and surrounding environment. Therefore, railway disc brake squeal has become a worldwide problem in present. It is reported that the interface characteristic is a key factor in affecting the squeal noise, and the surface topography plays a significant role in the generation of brake squeal. However, the knowledge about the effect of groove-textured surface on brake squeal is very limited. Therefore, it is worthwhile to study the relationship between groove-textured surface and brake squeal, which will contribute to further investigating the generation of brake squeal and seeking potential way to reduce brake squeal.In this work, two kinds of surface modifications of discs in the form of:grooves at parallel regular intervals (i.e. parallel grooves), and grooves at radial regular angular intervals (i.e. radial grooves) were manufactured on the disc surfaces, respectively. Experimental tests of friction noise were performed in a pad-on-disc configuration to study the capability of grooved surface in reducing squeal noise. Moreover, a customized sample with parallel grooves distributed on only half of the disc surface is manufactured, and the corresponding experimental and numerical study was performed to detect the evolution of vibration and noise from smooth surface to groove textured surface in one disc sample, and further validate the effect of grooves on the squeal generation. Furthermore, an experimental set-up was developed to simulate the high-speed train disc brake according to the similarity principle. This set-up is able to study the brake squeal noise related to the contact materials, interface characteristics and speed etc. By using this set-up, the bake noise generated from two kinds of train brake contact pairs (i.e. composite material pad/cast iron disc and powder metallurgy pad/forged steel disc) were studied. Moreover, groove-textured surfaces with radial regular angle intervals grooves were manufactured on the forged steel discs, and the corresponding experimental test was performed to further demonstrate the ability of grooved disc in suppressing the brake noise, by comparing the case of smooth surface. The conclusions are summarized as follows:1. The results of the experimental tests showed that the disc surface topography with grooved modifications had a good potential in reducing squeal noise. Moreover, the configurations of grooves have effect on the vibration and noise characteristics of contact surface. The level of vibration and noise was found to decrease with the increase of the groove width for both kinds of the disc surfaces having parallel and radial grooves.2. For the disc sample with parallel grooves on only half of its surface, it was found that grooves on the contact surface can suppress the squeal noise generation of the friction system. Moreover, the grooves were found to be able to play a storage cavity role in trapping wear debris and change the wear features of the disc surface. The numerical results of the detailed finite element model showed that the grooves on the disc surface can significantly affect the contact pressure distribution of the pad surface during the friction process, and redistribute the concentrated interface pressure and consequently suppress squeal generation.3. A scaling test rig on the basis of the parameters of the high-speed train was developed according to the similarity principle. This test rig can be used to conduct both the drag and in-stop braking tests. Moreover, the test rig can further be used to investigate the relationship between the friction materials, interfacial characteristics, speed and brake squeal, by adjusting the parameters of the test rig, such as the rotational speed, inertia, brake pressure and radius etc.4. The phenomena of railway disc brake squeal noise were reproduced on the scaling test rig, which verified the feasibility of the method. The results showed that higher sound pressure with more complicated frequency composition were generated from the powder metallurgy pad/forged steel disc system, comparing to that of the composite material pad/cast iron disc system. Moreover, the surface of forged steel disc underwent more severe wear, which can be characterized by the accumulation of the wear debris.5. The squeal noise tests were performed in the scaling test rig by comparing both the smooth and groove-textured forged steel disc surfaces. The results showed that the squeal noise generated from the groove-textured disc surface could be significantly reduced. Moreover, the grooves exist on the disc surface allowed an easier removal of wear debris from the friction interface into the grooves, and which was able to improve the tribological consequences.