Machinery's Handbook, 31st Edition
GREASE
2511
100 200 300 400 500 600 Temperature ˚F
-100
-50 032
Mineral
Poly-alph-olefin (PAO)
Poly Alkylene Glycol (PAG)
Di Ester
Polyol Ester
Extended Range Due to Additve Package. Normal Use
Silicone
-75
-50 -25
0
100
200
300
Temperature °C
Fig. 9. Temperature Limit Guidelines for Oil. to form the thickening agent. Varying the oil, additive package, and soap blend produces many unique types of grease formulated for a variety of operating conditions. Greases are classified according to their soap base as depicted in Table 12. Grease works in a similar way to a sponge; as the temperature of the grease rises, the oil bleeds from the soap filler and performs the lubricating function to the balls, raceways, and sliding surfaces. Inversely, once the grease cools down, the oil is soaked back up into the soap filler, which essentially acts as a semi-fluid container for the lubricating oil. An important step in selecting the correct grease is determining if the base oil viscos- ity is suitable for the application. For example, grease designed for heavily loaded, high temperature applications will probably use a heavy viscosity oil base, whereas general- purpose grease is more likely to use a medium viscosity oil base. Table 12. Grease Types and Their Properties Type Appearance Pump- ability Heat Resistance Temperature Range Water Resistance Compatibility with other greases Calcium (Lime Soap) Buttery Fair Fair 230 ° F (110 ° C) Excellent Excellent Sodium (Soda Soap) Fibrous Fair Very Good 250 ° F (120 ° C) Poor Good Calcium Complex Stringy Fair Good 350 ° F (175 ° C) Very Good Fair Lithium Buttery Excellent Good 350 ° F (175 ° C) Excellent Excellent Aluminum Complex Stringy Good Excellent 350 ° F (175 ° C) Excellent Poor Lithium Complex Buttery Excellent Excellent 375 ° F (190 ° C) Very Good Excellent Barium Fibrous Very Good Excellent 380 ° F (193 ° C) Excellent Fair Bentonite (non-soap) Buttery Good Excellent 500 ° F (260 ° C) Good Poor Urea Buttery Good Excellent > 500 ° F (260 ° C) Excellent Excellent Grease properties may change according to the additive package used At sustained high temperatures, grease will soften substantially and could leak or drop from the bearing unless rated specifically for high temperature applications. High tem peratures rapidly oxidize the lubricant causing the soap to harden; higher temperatures require more frequent application of grease. Lower temperatures can be just as detrimen- tal because the grease “stiffens” considerably as temperatures near –20 ° F (–30 ° C). At this temperature the rolling elements no longer rotate and they drag across the raceway. Under heavier loads this effect causes “smearing” of the bearing surfaces leading to pre - mature bearing failure. Grease temperature guidelines by type are shown in Fig. 10.
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