Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/190260
LESSONS IN LUBRICATION Filtergrams In contrast with ferrograms, filtergrams do not have any bias toward ferrous particles. As the oil sample is forced through a filter membrane, any particles greater than the pore size are randomly trapped on the membrane surface. However, Particles collect at random on a filtergram. bottom light transmission during analysis is poor due to the opaqueness of the filter membrane. Wear Modes Rubbing (Break-In) Wear (Abrasive Wear) As the most common type of wear, rubbing wear occurs whenever there is surface sliding contact within a machine. During initial surface contact, this type of "break-in" wear should be expected. It usually results in a smoother, low-wearing surface. Particles produced from rubbing wear typically have a platelet (two-dimensional) morphology and smooth topography. Cutting Wear (Abrasive Wear) This abnormal wear is produced when two surfaces penetrate one another. As its name suggests, particles are generated from one surface gouging the other surface, creating long, ribbon-like chunks. This wear mode is often compared to machining swarf from a lathe but on a much smaller scale. Rolling Wear (Surface Fatigue) Rolling surface contact produces surface fatigue. Particles generated from surface fatigue tend to come in the form of spalls, spherical or laminar particles. The formation of pits and spalls as a result of high load and a lowcontact surface area leads to the shaping and sizing of these particles as they are forced out of their original setting. This type of wear typically occurs with components of rolling motion contact, such as in the case of ball bearings. Rolling and Sliding Wear Combined (Surface Fatigue and Abrasive Wear) This abnormal combination of wear modes is caused by fatigue 42 | September - October 2013 | www.machinerylubrication.com and scuffing. It is commonly associated with gear systems, particularly along the pitchline of gear teeth as well as in conditions with too high of a load or speed and excessive heat generation. For example, the surface contact of gear teeth is a combination of rolling and sliding motion. This combined wear mode region, along with the effects of lubricant contaminants, can generate a complex fusion of wear debris. Severe Sliding Wear A severe level of wear occurs in excessive loads and high speeds between contacting surfaces. When surface stresses are too great because of increased load and/or speed on the surface contact area, the Striations indicate sliding motion area becomes unstable and large particles break away, further increasing the wear rate. Chemical/Corrosive Wear Corrosive wear is frequently labeled as fretting corrosion, erosion, stress fatigue, etc. These particles are often too small to distinguish individually and are usually the result of improper fluid properties or heavy contamination from water, acid, salt or bacteria. Heat also plays a major role in corrosion. Most lubricants have rust/corrosion-inhibiting additives to combat the effects of chemical wear. Particle Morphology and Topography Since wear particles detach from internal machine surfaces in a variable manner, their morphology and topography are unique. However, they also fit certain patterns based on the actions by which they become detached.