Plant Services - January 2008 - (Page 44) Power Transmission EFFICIENCY example, if the starting radial clearance is 0.008 in. and the recommended clearance reduction is 0.003 in., then the clearance should be reduced until a feeler blade measuring 0.005 in. is the largest blade that can fit through the gap. 4. Don’t drag the rollers periences more drag when wading in waist-deep water than in ankle-deep water, overlubrication causes more frictional churning and drag inside the bearing, resulting in higher internal friction and operating temperatures and a loss of lubricant viscosity. After measuring the initial radial clearance with the bearing under load, raise the shaft with a jack to unload the bearing. Then the locknut can be tightened and the bearing driven up the adapter sleeve. Inadvertently loading the bearing at this point causes the bearing rollers to drag across the roller paths, thus scoring the roller paths and damaging the bearing before it’s even operational. Verify that the bearing is unloaded by rotating the bearing’s outer ring manually; it should easily turn within the housing bore. Once the bearing has been driven a certain distance up the adapter sleeve, lower the shaft to take another bearing clearance measurement. Repeat this process until you’ve achieved the desired clearance reduction. After installation, completely pack the bearing with grease. Fill the base of the pillow block to a level equal with the bottom of the shaft. Newer pillow block varieties sometimes have cast-in markings to indicate the correct grease level. Don’t overfill the pillow blocks. Just as a person ex- Relube software can estimate the recommended relubrication interval and grease quantity based on factors including bearing type, size and fan speed. 5. Add the lube Fan bearings should be periodically relubricated. It’s best to relubricate with smaller grease quantities at more frequent intervals. Relube software can estimate the recommended relubrication interval and grease quantity based on factors including bearing type, size and fan speed. These programs can reduce the risk of overfilling when relubricating. For example, if the relubrication program recommends adding 1 oz. of grease every month, the best approach would be to inject 1/4 oz. weekly. Once the fan bearings are back in operation, monitor them for changes in vibration and operating temperature. Bearing lubricant can retain heat, causing operating temperatures to rise. If you detect high temperatures, change out the old grease, thoroughly clean the fan bearings and housings, and refill with the initial grease filling. Even if operating temperatures remain normal, it’s a good idea to annually replace old grease during planned maintenance shutdowns. John Clark is an applications engineer at SKF USA Inc., based in Kulpsville, Pa. Contact him for more information on fan bearing installation, lubrication and maintenance at john.p.clark@skf.com and (215) 513-4884. More resources at www.PlantServices.com/thismonth Installing bearings – “Proper bearing removal and replacement” Bearing designs – “Bearing misalignment” Mothballing equipment – “Mothballing equipment when demand falls” Lubes & bearing failure – “Bearing lube basics” Fan vibrations – “Don’t allow fan wheels to work with bad vibes” High-temp fan bearings – “Preventing fan failure at high temperatures” For more, search www.PlantServices.com using the keywords bearing, fan and grease. 44 www.PLANTSERVICES.com January 2008 http://www.PlantServices.com/thismonth http://www.sulmac-deway.com http://www.PlantServices.com http://www.sulmac-deway.com http://www.PLANTSERVICES.com
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