Machinery's Handbook, 31st Edition
GREASE Application 2515 The method of grease lubrication will depend on the greased bearing design; bearings can be hand-packed, manually-lubricated with a terminating style grease gun, or automati- cally greased. Open rolling bearings are received with a rust inhibiting compound from new and must be pre-packed on assembly— DO NOT remove bearings from their packaging until ready to use, and DO NOT spin dry bearings as this will significantly degrade the life of the bearing. Shielded or sealed bearings usually arrive pre-packed from the manufacturer—always specify your preferred grease to your bearing supplier when or- dering. The initial amount of grease is determined by adjusting the volume according to the known speed and load. For operating temperatures above 180 ° F (80°C) the bearing is packed to 25 percent of the full pack volume. For temperatures below 180 ° F (80°C), the guideline for pack volume is shown in Table 17 and is based on the bearing surface speed in operation calculated as: (5) where dn = bearing surface speed factor, metric, mm dn Dn SD RPM or # =
Dn = bearing surface speed factor, US customary, in. SD = shaft diameter of the bearing bore, mm or in. RPM = velocity, rotations per minute at full speed Table 17. Bearing Packing Guidelines dn (mm) Dn (in.)
% Full Pack
From
To
From
To
0
50,000 100,000 150,000 200,000
0
2,000 4,000 6,000 8,000
100 75 50 33 25
50,000 100,000 150,000 200,000+
2,000 4,000 6,000 8,000+
For vibration applications, do not fill more than 60% of full pack When hand packing, work the grease with fingers around all the rolling elements; the bearing can be dismantled to make this operation easier. The grease should fill the immedi - ate bearing area. Before renewing grease in an existing bearing, the bearing must be re- moved and washed in kerosene or any suitable degreasing product. Once clean, the bearing is lightly coated in mineral oil, being careful not to spin the bearing at this point. Once filled with the appropriate amount of grease in the bearing area, the bearing can be hand spun to fling off grease excess, which is wiped away with a lint-free clean cloth. Free spacing in the housing should be filled from 30 to 50 percent. Overfilling bearings with grease is the leading cause of bearing lubrication-related failures. Over greasing causes the lubricant to “churn,” which in turn “spikes” the bearing internal temperature, significantly reducing the bearing life using considerably more energy to overcome fluid friction. Bearings designed to be lubricated by a grease handgun or automated delivery system will have a grease port built into the bearing housing and raceway. Grease lubrication intervals will depend on temperature and speed. Fig. 12 provides guidelines for renewing grease based on speed. Bearings running at high temperature extremes will require more frequent application based on the temperature, load, speed, and type of grease used. When replenishing grease always use new clean grease of the exact same specification, from the same manufacturer. Mixing different greases can lead to compatibility problems causing detriment to the bearings. If changing to a new grease specification or manufacturer, consult with the new manufacturer for the correct change out procedure. Lubrication Delivery Methods and Systems.— Numerous methods and systems are used to deliver oil and grease to bearing points. Automated centralized systems work on the premise of delivering a very small amount of lubrication on an almost continual basis,
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