The real title of this article was “When in Doubt . . . Don’t Mix Bearing Lubricants.” The original three-page article was written by John Rumierz and was printed in the August, 2000, issue of Plant Engineering. John listed three key concepts; I am going to cover two or them:
• Do not relubricate bearings before checking compatibility.
• Never mix greases with different thickeners.
Included in the article was a “Workbench Test for Compatibility:
• Pour equal quantities of the test greases into a container
• Stir with a screwdriver
• If the mixture turns runny and pours easily from the container, or hardens into a sludge-like consistency, the two greases are likely to be incompatible.”
“Whether the lubricants involved are oils or greases, questions of compatibility often come down to a judgment call. In some situations, test results or factory-floor experience may offer adequate
assurances to bearing users that two lubricants can be combined without harmful effects. Otherwise, technicians should follow a simple rule: When in doubt…don’t mix lubricants!”
What is grease? The article said, “A lubricating grease is produced by suspending a mineral oil or synthetic oil in a thickener, which carries the oil within a network of fibers. . . . As a general rule, greases that have different thickeners, such as lithium or polyurea, should never be mixed. . . . in extreme cases the base oil will bleed completely out of the grease mass.”
This seems to say that what I have done (and I bet that many have
done the same thing!) is risky. That is, adding lubricant to a bearing.
A better procedure would be to disassemble the joint, clean it thoroughly,
and relubricate it.
DON’T MIX HYDRAULIC OIL
This is very similar to the above, so I kept them together. This came from NAEVT’s The Technician for March/April, 2000, from a column by Don Henry (Canada). “Mixing brands or grades of motor
oil is never recommended, but at least you are going to dump out most of the motor oil during a change. This, of course, is not the case with hydraulic oil, and mixing of brands of hydraulic oil can cause some big headaches. The problem occurs because of the different additive packages used in the oil to make it perform better. Additives are used for many reasons. One is to disburse air out of the oil and another is to remove foam from the top of the oil. But not all brands of hydraulic oils use the same chemicals to do this, and sometimes these different additives will work against each other and the oil will foam excessively. This could put air bubbles in the hydraulic oil, and the effect will be spongy controls.”
— Ted Elder
Silver Trumpet – 2016 Vol. 2