Application of magnetization measurements to wear debris analysis

Abstract

Spectrometric oil analysis for total wear metal amounts is often used to monitor lubricated machinery. In many cases iron is the dominant wear metal, and spectrometric analysis gives good results for total iron. However, iron may be present in several forms such as metal particles, oxides, carbides, sulfates and dissolved ions. A breakdown of total iron into the amounts and forms of iron present should give further valuable insight into wear phenomena taking place inside the machine. In this paper the use of magnetization measurements on samples of used oils and oil filters to obtain information on the forms of iron present in wear debris from lubricated machines is introduced. The measurement technique is described and the magnetic properties of some iron species that might be expected in wear debris are reviewed. This technique provides information on both ferromagnetic and paramagnetic species through the observation of various magnetic properties. Several illustrative examples are included. The ability of this technique to detect the paramagnetic as well as the ferromagnetic components is important because it is often found that the majority of the iron in wear debris is paramagnetic. A correspondence between the measured ferromagnetic component and ferrography is also shown for some cases.