Grease lubrication is usually suitable for medium and low speed applications where the bearing operating temperature is lower than the limit temperature of grease. No antifriction bearing grease is suitable for all applications. Each grease has only limited performance and characteristics. Grease consists of base oil, thickener and additives. Bearing greases usually contain petroleum based oils thickened with a metal soap. In recent years, organic and inorganic thickeners have been added to synthetic base oils. Table 26 summarizes the composition of typical greases. Table 26 Grease composition, base oil thickener additive grease, mineral oil, synthetic hydrocarbon ester, perfluorinated oil, silicone, lithium, aluminum, barium, calcium and soap soap (inorganic) microgel (clay), carbon black, silica gel, PTFE soap free (organic) polyurea compound antirust agent dye viscosity agent metal passivator antioxidant anti-wear extreme pressure additive calcium based and aluminum based grease have excellent water resistance and are suitable for industrial applications that need to prevent water intrusion. Lithium based grease has many uses and is suitable for industrial applications and wheel end bearings.
Synthetic base oils, such as esters, organic esters and silicones, when used with common thickeners and additives, the * * working temperature is usually higher than that of petroleum based oils. The operating temperature of synthetic grease can range from - 73 ° C to 288 ° C. The following are the general characteristics of thickeners commonly used with petroleum based oils. Table 27 General characteristics of thickeners used with petroleum based oils typical drop point * * temperature and water resistance of thickeners using the thickeners in table 27 with synthetic hydrocarbon or ester based oils can increase the * * operating temperature by about 10 ° C.
°C °F °C °F
Lithium base 193 380 121 250 good
Composite lithium base 260 + 500 + 149 300 good
Composite aluminum matrix 249 480 149 300 excellent
Calcium sulfonate 299 570 177 350 excellent
Polyurea 260 500 149 300 good
The use of polyurea as thickener is the most significant progress in the lubrication field in more than 30 years. Polyurea grease has shown excellent performance in a variety of bearing applications, and has become a recognized ball bearing pre lubricant in a short time. The torque of bearing is very important under low temperature starting conditions. Some grease can only work normally when the bearing is running, but it will cause too much resistance to the starting of the bearing. In some small machines, it may not start when the temperature is very low. In such a working environment, the lubricating grease is required to have the characteristics of low-temperature starting. If the operating temperature range is wide, synthetic grease has obvious advantages. The grease can still make the starting and running torque very small at a low temperature of - 73 ° C. In some cases, these greases will perform better than lubricants in this regard. An important point about grease is that starting torque is not necessarily a function of grease consistency or comprehensive performance. Starting torque is more like a function of the individual performance of a specific grease, which should be determined by experience.
High temperature: the high temperature limit of modern grease is usually a comprehensive function of the thermal stability and oxidation resistance of base oil and the effectiveness of oxidation inhibitors. The temperature range of grease is determined by the dropping point of grease thickener and the composition of base oil. Table 28 shows the temperature range of grease under various base oil conditions. After years of grease lubricated bearing test, the empirical method shows that the service life of grease will be halved for every 10 ° C increase in temperature. For example, if the service life of a grease at 90 ° C is 2000 hours, when the temperature rises to 100 ° C, the service life decreases to about 1000 hours. Conversely, after reducing the temperature to 80 ° C, the service life is expected to reach 4000 hours.
Synthetic base oils, such as esters, organic esters and silicones, when used with common thickeners and additives, the * * working temperature is usually higher than that of petroleum based oils. The operating temperature of synthetic grease can range from - 73 ° C to 288 ° C. The following are the general characteristics of thickeners commonly used with petroleum based oils. Table 27 General characteristics of thickeners used with petroleum based oils typical drop point * * temperature and water resistance of thickeners using the thickeners in table 27 with synthetic hydrocarbon or ester based oils can increase the * * operating temperature by about 10 ° C.
°C °F °C °F
Lithium base 193 380 121 250 good
Composite lithium base 260 + 500 + 149 300 good
Composite aluminum matrix 249 480 149 300 excellent
Calcium sulfonate 299 570 177 350 excellent
Polyurea 260 500 149 300 good
The use of polyurea as thickener is the most significant progress in the lubrication field in more than 30 years. Polyurea grease has shown excellent performance in a variety of bearing applications, and has become a recognized ball bearing pre lubricant in a short time. The torque of bearing is very important under low temperature starting conditions. Some grease can only work normally when the bearing is running, but it will cause too much resistance to the starting of the bearing. In some small machines, it may not start when the temperature is very low. In such a working environment, the lubricating grease is required to have the characteristics of low-temperature starting. If the operating temperature range is wide, synthetic grease has obvious advantages. The grease can still make the starting and running torque very small at a low temperature of - 73 ° C. In some cases, these greases will perform better than lubricants in this regard. An important point about grease is that starting torque is not necessarily a function of grease consistency or comprehensive performance. Starting torque is more like a function of the individual performance of a specific grease, which should be determined by experience.
High temperature: the high temperature limit of modern grease is usually a comprehensive function of the thermal stability and oxidation resistance of base oil and the effectiveness of oxidation inhibitors. The temperature range of grease is determined by the dropping point of grease thickener and the composition of base oil. Table 28 shows the temperature range of grease under various base oil conditions. After years of grease lubricated bearing test, the empirical method shows that the service life of grease will be halved for every 10 ° C increase in temperature. For example, if the service life of a grease at 90 ° C is 2000 hours, when the temperature rises to 100 ° C, the service life decreases to about 1000 hours. Conversely, after reducing the temperature to 80 ° C, the service life is expected to reach 4000 hours.
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