Micro/Macro Pitting Rig (MPR)
The MPR is an innovative, compact test measurement designed to study a range of failure mechanism and to investigate rolling contact fatigue at realistic contact pressure.
The MPR is a computer controlled three-contact disc instrument in which there are three ‘counterface’ rings of equal diameter positioned apart with a smaller diameter roller located in the middle and in contact with all the rings. This arrangement allows the test roller to be subjected to a large number of rolling contact cycles in a short period of time and hence significantly reduces testing time. At a typical entrainment speed of 3.5 m/s, the central test roller will experience approximately one million contact cycles per hour.
The MPR has an on-board processor, which allows the speed, slide-roll ratio, temperature, and load to be automatically controlled. Two servo-controlled motors are used to control the speeds of the rings and the roller separately. A dip lubrication system is used to supply lubricant into the contacts. A temperature probe is inserted into the test chamber with the tip of the probe close to the contact region.
The load is applied by means of a motorized ball-screw, acting through a loading arm. Strain gauges are attached on the loading arm to measure the applied load. The MPR is equipped with a piezoelectric accelerometer which is used to measure the vibration in the contact. Once a macro-pit propagates on the test roller, the increased measured vibration level is detected by the control system and the test is stopped automatically. The number of cycles to failure (“Life”) is recorded.
The test head design allows a test to be stopped at any time, the load removed and the rotation stopped. The central roller can then be withdrawn for inspection, without disturbing either the lubricant or the three rings. The roller specimen can then be placed back in position and the test can continue. This is particularly useful in the study of both micro-pitting and macro-pitting, where physical examination of the specimen is essential.
Application of MPR
White Etching Cracks (WECs)
Screener test for lubricant formulations