Grease Greasing ErieBearings（油脂和润滑ErieBearings）.pdf

GREASE GREASING What is Grease? The definition of grease issued by the American Society for Testing Materials (ASTM) is: “A solid to semi-fluid product of dispersion of a thickening agent in a liquid lubricant. Other ingredients imparting special properties may be included”. There are three main components of grease: 1. Thickening or gelling agent (i.e. soap, clay or polyurea) 2. Oil which provides the lubrication 3. Additives (i.e. anti-oxidants, corrosion preventative agents, anti-weld EP additives) Thickening Agent The thickening agent or soap performs a fairly complex function but simply put, “holds” the oil until required and then “releases” the oil to lubricate the bearing. The consistency of grease depends on this thickening agent. Consistencies vary from NLGI 000 through to NLGI 6. NLGI 000 grease is very soft while NLGI 6 grease is like a solid block. Typically, motor grease is NLGI 2. For high temperature applications an NLGI 3 grease is often used. The oil “held” by the thickening agent performs the lubricating function and is usually mineral oil but can also be synthetic. The base viscosity of this oil is very important and is often one of the most commonly overlooked parameters of grease. Grease typically contains oils from ISO 10 (for arctic duty type grease) through ISO 510 (10 mm2/S – 600 2 O O mm /S at 40 C). Typically motor bearings operate at 40 – 50 C above ambient. O O Assuming an ambient of 40 C and an operating temperature of 40 C, the total temperature is 80OC. This reduces the actual viscosity of the oil such that for example, a 2 O base oil of ISO 99 has a viscosity of 20 mm /S (centistokes) at 80 C. Base Oils The importance of base oils is the most often ignored and yet on