TECHNICAL ANALYSIS Chuck Coe, CLGS, CLS Deleterious particles in lubricating greases Particles in greases can be controlled with the manufacture of improved raw materials. THERE ARE A VAST NUMBER of different particle types which can be found in lubricating greases. As is well-known, there are numerous types of desirable particles in grease such as molybdenum disulﬁde, Teﬂon, graphite, etc., and many important purposes for their intentional incorporation into greases. In this article, we’ll examine the other side of the coin—particles in greases that are viewed as harmful or, at best, not serving a useful purpose. TYPES OF PARTICLES First, let us divide all particles broadly into two classes: abrasive and non-abrasive. In the abrasive category, we ﬁnd such undesirable materials as metallic ﬁnes from machining (iron, steel, copper, brass and bronze.) (Figure 1.) Other metallic par-ticles may include wear debris (iron, steel, copper, brass, bronze, lead and oxides of the same.) (Figure 2.) Corrosion of iron and its alloys creates iron oxides, which vary in hardness and, therefore, abrasiveness. Lastly, there is the ubiquitous dirt, usually composed mostly of sand or silicon. (Figure 3.) In the non-abrasive class, some of the more commonly found undesirable par-ticles consist of agglomerates of either soap or non-soap thickeners. Some cases of unintentional agglomerates of insoluble additives have been observed. Finally, we have the desirable additive solids—MoS 2 , graphite, etc. 28 The record for most snowfall in a year is 1,140 inches recorded at Mt. Baker in the North Cascades of Washington State during the 1998-99 winter.