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Lubrication Tips for Reliability Professionals

June 26, 2001 Subscribers: 7,442

Q & A

"How do you know when you have added enough grease?"

While there is no easy answer to the question of manual grease relubrication cycles and volumes, it does not have to be a mystery. The best policy, of course, is to measure the size of the bearing shaft, width and bearing outer diameter and grease gun output per stroke, then calculate the amount required. This SKF formula is easy to use:

Gq = 0.114 DB

Where:

Gq = Grease quantity in ounces
D = Bearing outside diameter in inches
B = Total bearing width in inches

If a simple formula is not available, estimate the number of shots based on the shaft diameter for bore diameters up to 6”.

For example: Estimate the number of inches in the shaft. Multiply that number by itself to get a rough estimate of the number of shots from the grease gun. Apply the last half of these shots slowly, and at the point that you begin to experience resistance, stop pumping.

This rule of thumb does not hold for bearings with bore diameters of greater than 6”.

Today's Tip

• If you use several greases at your facility, then it is important that all of your greases are compatible with one another. A safe first assumption is that they are not compatible unless proven otherwise. To confirm compatibility, have your supplier or an independent lab run a shear stability test on the greases individually and then repeat the test using a mixture of the products that you wish to cross-check. Ideally, you would like to see little to no change in the consistency of the greases either separately or after mixing.

  ASTM D217 provides a high level of confidence about how compatible the products are under ideal conditions. Actual plant conditions, such as high temperature, contaminants and loading, can exaggerate problems with incompatibility.

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Book Bits

Every engine, hydraulic pump, gear set or other component very slowly wears as it operates, and these tiny, sub-micronic particles of such elements as iron and copper, become catalysts which slowly attack the oil, causing acids to form. These tiny metal contaminants, combined with carbon soot particles resulting from the combustion process in engines, also circulate in the system and through their abrasive action, create more wear. These solid particles become just like a fine grinding compound and will slowly scratch and score bearing surfaces, turbocharger bearings, crankshaft journals, cylinder liners, and hydraulic pump and valve surfaces.

For more information about the book "The Practical Handbook of Machinery Lubrication" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=55

Copyright © 2001, Noria Corporation. All rights reserved. Please do not reprint or host on your website without explicit permission. However, if you found this newsletter helpful, we grant you permission, and strongly encourage you, to e-mail it to a business associate or a friend. Thank you. The presence of advertising in Lube-Tips does not constitute an endorsement of the products or services in such ads. Further, because results will vary widely based on a number of factors, Noria Corporation cannot warrant the results, the accuracy or the completeness of any material published herein.

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