A STUDY ON THE LOAD LEVEL INFLUENCE ON PARTICULATE MATTER EMISSIONS FROM THE SLIDING CONTACT BETWEEN A LOW STEEL FRICTION MATERIAL AND CAST IRON

摘要

In 2013 the road transport contribution to PM10 and PM2.5 emissions in the EU region counted for 11% and 16% respectively of the total emission. Related to these road transport emissions, the non-exhaust fraction equals almost the 50% of the exhaust one. A major contributor to the non-exhaust fraction is the wear particles generated from disc brakes. The purpose of this paper is to investigate how different load levels, i.e. contact pressures, can affect the particle concentration, the particle size distribution as well as the temperature distribution of a typical pad to rotor material combination (low-steel pad material and cast iron disc) found in European braking system. Tests were conducted in a pin-on-disc machine, specially designed for airborne particulate research. A clean chamber technique was used ensuring that measured airborne particulates were only generated from the sliding contact in the pin-on-disc machine. In addition, an insulating plate placed between the disc and the rotating base allows the system to reach up to 350°C, without using any external heating source. The same constant sliding speed was used for all tests (1.3 m/s) ensuring the same sliding distance with the specific test time of 3h. The testing time was chosen to get a long enough steady state periods. The load was applied to the contacting pairs with dead weights varying from 1 kg to 7 kg giving an average contact pressure range of 0.29 MPa to 1.95 MPa. The concentration and the size distribution were measured using an Electrical Low Pressure Impactor (Dekati ELPI+) covering a size range from 6 nm to 10 μm. The frictional heating was measured using thermocouples placed 3 mm from the contact surface in both pin and disc. Also the friction coefficient and the wear rate were determined using a load cell measuring the frictional load and a LVDT measuring the wear depth change. The results show a stable stationary particle generation for the low loads compared to a more transient response with short periods of high concentration levels for the higher loads. This gives evidence of a temperature limit in the production of airborne particulates generated from disc brake material combinations. Above this temperature limit around 200°C a sharp increase in the total concentration number can be detected. Future studies will be devoted to a study of different pad to rotor material combinations.