1-1. Grease lubrication

Grease is made by mixing and dispersing a solid of high oil-affinity (called a thickener) with lubricant oil (as a base), and transforming it into a semi-solid state. As well, a variety of additives can be added to improve specific performance. Base oil Mineral oil is usually used as the base oil for grease. When low temperature fluidity, high temperature stability, or other special performance is required, diester oil, silicon oil, polyglycolic oil, fluorinated oil, or other synthetic oil is often used. Generally, grease with low viscosity base oil is suitable for applications at low temperature or high speed; grease with high viscosity base oils is suitable for applications at high temperature or under heavy load. Thickener Thickeners are an important factor to determine grease performance. Table 9-1 shows the properties of common thickeners. Table 9-1 Characteristics of thickeners Thickener Operating temperature range Rotational speed range Mechanical stability Water resistance Pressure resistance Lithium soap -30 to 120 Medium to high Excellent Good Good Calcium soap -10 to 70 Low to medium Fair to good Good Fair Sodium soap  0 to 110 Low to high Good to excellent Bad Good to excellent Urea compounds -30 to 150 Low to high Good to excellent Good to excellent Good to excellent Bentone -10 to 150 Medium to high Good Good Good to excellent Fluorine compounds -40 to 250 Low to medium Good Good Good

Additives Major additives and their uses are as follows:   Extreme pressure agentsWhen bearings must tolerate heavy or impact loads.   Oxidation inhibitorsWhen grease is not refilled for a long period.