F-0317 Investigation of contaminants in hydraulic and lubricating oils by colorimetric analysis

Abstract

Contaminants in hydraulic and lubricating oils are harmful to lubrication. There are two types of oil cleanliness standards; one is based on particle count like NAS 1638, ISO 4406, SAE AS4059 and JIS B9930, the other gravimetric analysis like ASTM D4898 and JIS B9931. The particle count method can tell us the number of particles of certain size ranges and the gravimetric method. the gross weight of contaminant in a certain quantity. But they cannot tell us what the contaminants are. When oils are used in machines for a long time, oils will be oxidized. As oil oxidation products are of molecular size, it is difficult to check by particle count. The authors have investigated the color of contaminants collected on membrane filters by a colorimetric device and found that the color of the contaminants in used oils showed a certain tendency.