From "Lubrication Fundamentals"

If simple precautions are not observed, contamination of lubricants with subsequent damage to machines can occur during storage or during transfer of oil or grease from the original container to the dispensing equipment, or to the equipment being lubricated. Pumps, oil cans, grease guns, measures, funnels, and other dispensing equipment must be kept clean at all times and covered when not in use. Where operating conditions justify them, centralized dispensing or lubrication systems that keep the lubricants in closed systems and, therefore, protected against contamination, are highly recommended.

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QUESTION: In the case of an oil that has operated for an extended period of time with depleted antioxidant additives, how might the properties of that oil change?

Get the answer.

"We are in the process of changing oil suppliers. Our current supplier tells us that their oil will not mix and be compatible with the new suppliers. The new supplier tells us it will. How do we determine who is telling the truth?"

Unless one understands the chemistries of the various products in use, one cannot exclusively state that the products are compatible without stability testing to prove compatibility.

Rotary Pressure Vessel Oxidation Stability (RPVOT) tests are useful for this investigation for oils. RPVOT is a good measure for comparing 'pure' oil stability to 'mixed' oil stability. Commission a test series with the original oil, the replacement oil, a then a mixture of the existing product with the replacement product in a mixture ratio of 90% to 10%, 50% to 50%, and 10% to 90%. The results are reported in minutes until oxidation occurs.

Common test times are in the low hundreds to low thousands of minutes. Longer test times indicate better resistance to oxidation and chemical degradation.

There is a similar tests for greases. Additionally, worked stability tests using similar mixture ratios and at least 10,000 stroke intervals (ASTM D217-A) could help to verify grease thickener compatibility. If there are no substantial difference between the test duration intervals then there is a great likelihood that the products are compatible, and can be mixed without undue concern.

If there is appreciable difference in the test results, and the results do not denote an improvement in oxidation resistance (this is possible), then you should consider clean changes for all the systems to be converted.

As a general rule it would be best not to mix old and new products from different brands.

Mike Johnson, Noria Corporation

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