Metal Pick Up (MPU) on friction surfaces is considered to be one of the biggest issues in the friction industry. This paper reports observation results of microstructure of MPU and its surroundings.
Frictional tests are conducted with a friction composite containing steel fibres and a disk rotor of cast grey iron by using an inertia dynamometer. The friction composite after testing is carefully fixed with a mounting resin in order to make it easy to keep the microscopic crosssections of the friction interface intact. The observation sample is cut, rubbed with emery paper and chemically etched. Microscopic analysis is conducted by using a Scanning Electron Microscope (SEM). Chemical information of the microstructure is analysed by using a backscattered electron detector and an EDS micro analyser.
It is found that some kinds of metallurgical processes occur. MPU consists of a number of sub-micron-sized metal debris of iron. Steel fibres just under the MPU change their crystalline structure into martensite. Furthermore, this paper offers new information about the decomposition of tin sulphide into tin metal or iron-tin alloy and the attachment of the metal lump onto the friction composite, adding to conclusions found in previous works.
This study is limited in the analytical results of a kind of MPU created in a certain kind of the friction couple, the friction composite classified in a Low-steel and the disk rotor with a certain chemical composite of cast iron. However, this study helps frictional engineers to understand the mechanism of MPU creations as well as a method of microscopic observation for friction interfaces.
Shogo Kamada, Kousuke Inada, Kenji Kakihara - Otsuka Chemical Co., Ltd.