Machinery Lubrication

Machinery Lubrication Jan Feb 2013

Machinery Lubrication magazine published by Noria Corporation

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Page 23 of 76

GREASES BY STEFFEN BOTS, OELCHECK , GERMANY Grease Analysis: Early Warning System for Failures and Proactive Maintenance Tool T Taking oil samples on a regular basis as part of a maintenance strategy has become state of the art. Oils are tested with regards to their condition, possible contamination and wear. Laboratory results and evaluations by experienced engineers can support the identification of upcoming component failures, prove whether maintenance actions like filtration or dehydration work properly and help establish condition-based oil drain intervals. It's a different story when it comes to grease. In the past, continuous trend-based grease monitoring was not a common practice even though the majority of installed bearings are grease lubricated and have a substantial impact on the reliability of the equipment. However, a change in philosophy seems to be occurring with a trend toward more routine grease analysis. This has been driven by technical issues and supported by positive experiences with oil analysis programs. In addition, there have been many examples from the field where grease analysis has proven to provide important information about grease, including the amount of wear, contamination, consistency, bleeding behavior and condition of the base oil and additives. Since grease properties often change significantly during operation and that the contamination and wear information is concentrated within a relatively small volume that's not affected by filtration or diluted by a huge oil reservoir, grease analysis can be a very effective condition-monitoring tool. In many cases, grease analysis was initially performed only after damage or an accident, but trend analyses of grease samples have shown that trouble with grease or bearings can be recognized in advance with a good grease analysis program. The Proper Sampling Technique Elemental Analysis For a valid grease sample, the proper sampling technique is required. It obviously is much more difficult to take a representative grease sample from a bearing than to take an oil sample. To take a grease sample, remove the inspection screw on a slew bearing or take off the grease nipple from a rolling-element bearing. Cut the sampling tube in a length that is appropriate 24 to enter the bearing and reach an area for taking a meaningful sample. Mount the clean tube on a syringe and press the opening of the tube onto the corresponding greased area. Use the syringe to pull the used grease into the sampling tube (at least 1 centimeter). For some applications, it may be necessary to repeat the procedure on different sampling points of the same bearing. Approximately 1 gram of grease is enough for analysis. Be sure to watch for any color changes to avoid taking fresh grease too close to the regreasing point. Grease samples can be analyzed by optical emission spectroscopy (OES) according to the rotrode principle. Up to 21 elements can be evaluated to obtain information regarding wear, contamination and additives. These include: • Wear metals (iron, chromium, tin, copper, lead, nickel, aluminum, molybdenum and zinc) January - February 2013 | To take a grease sample, use a syringe to pull used grease into the sampling tube. For trend analysis, samples should always be taken at the same points. A sample of the fresh grease should also be sent as a reference sample for all future analysis.

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