Contaminants in Used Oils and Their Problems

Abstract

Contaminants in hydraulic and lubricating oils are harmful to lubrication. Therefore, contamination control of hydraulic and lubricating oils has been implemented in many factories and oil cleanliness standards of hydraulic and lubricating oils have been established as criteria for oil contamination control. There are two types of oil cleanliness standards: one is based on particle count and the other on gravimetric analysis. NAS 1638, ISO 4406, SAE AS4059, and JISB9930 belong to the former and ASTM D4898 and JISB9931 to the latter. The par tide count defines oil cleanliness by counting the number of particulate contaminants in the certain size ranges, and the gravimetric analysis shows the weight of contaminants remaining, on a membrane filter disc after a certain quantity of oil was filtered under vacuum, the oil was washed out, and the membrane filter disc was completely dried. Recently, there is a ten dency that particle count dominates the technology to judge oil cleanliness. Of course, it is important to quantify the number of particulate contaminants in oils. However, all particles are not contaminants, as particles like graphite and MoS2, which are countable by particle count, are good additives for lubricants. Therefore, it is very important for us not only to judge oil cleanliness by the particle count but also to know without prejudice what they are. This article discusses some methods to separate contaminants, what contaminants are, and how much they are.