Machinery's Handbook, 31st Edition
2512
GREASE
100 200 300 400 500 600 Temperature ˚F
-100
-50 032
Calcium Complex
Sodium
Lithium
Aluminum Complex
Bentonite
-75
-50 -25
0
100
200
300
Temperature ˚C
Fig. 10. Temperature Limit Guidelines for Grease Grease Classification: The National Lubricating Grease Institute—NLGI, classifies grease according to a rating standard that measures the consistency of the grease. Using a penetrometer apparatus under laboratory conditions, a conical weight is dropped from a known height into the grease sample, and its depth of penetration is measured after a 5 second time period. The Table 13 rating chart shows that stiffer greases are rated with a higher NLGI code than more fluid grease with higher levels of penetration. Grease consistency largely depends on the type and amount of soap thickener blended in the grease and the oil viscosity — NOT the base oil viscosity alone. Rolling element bearings will use grease in the NLGI 1 to 3 range. Centralized grease lubricating systems favor 0 to 2 NLGI rated grease. Table 13. NLGI Grease Consistency Rating Chart NLGI Rating Description Penetration Range (0.1mm@77 ° F) 6 Brick Hard 85–115 5 Very Stiff 130–160 4 Stiff 175–205 3 Medium 220–250 2 Medium Soft 265–295 1 Soft 310–340 0 Very Soft 355–385 00 Semi Fluid 400–430 000 Semi Fluid 445–475 Grease Additives: As with oil, grease will also contain solids additives such as graph- ite, molybdenum disulphide, and PTFE for use in extreme pressure and heavy wear conditions. Lubricant Application Selecting a Suitable Lubricant.— Selecting a suitable lubricant will depend on a num- ber of factors such as type of operation (full film, boundary layer), temperature, speed, load, working environment, and machine design. Machine maintenance requirements and maintenance schedules are not always taken into account in the equipment engineer- ing design process of the lubrication system(s). Careful assessment of the conditions and consultation with a lubricant manufacturer/provider must take place to determine the
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