We have some Siemens 50 hp motors that I need to know what type of grease is in them. I looked on their website and all it states is a high temp tested polyurea grease. Can you mix synthetics with polyureas. I'm asking because normal procedure for this facility is to use sealed bearings in our motors. These motors have single shielded bearings (a suprise to management) and to the best of my knowledge have not been periodically greased for the 10 years I have been here (YIKES). I made a vibe call on one of them and when we changed out the bearings one had spalls on the inner race and both had practically no lube.

Mixing can be a problem. It can change the consistency to result in higher or lower penetration than the original greases which may result in grease flowing out of the bearing or grease hardening and becoming useless. The only no-risk way to do it is to only combine identical (same manufacturer) greases or ones that have been tested for compatibility. You could sample the grease to try to find out but that would seem to be a lot of effort.

There is some risk but not too much if you at least have similar same gelling agent and base oil. Since we suspect they have used Polyurea based, I would suggest Mobil Polyrex EM would be fairly low risk for incompatibility.

Thanks Pete,
Thats pretty much what I was thinking, but never hurts to ask.

Roy,
Is is fairly typical for motors 50HP and above to be supplied with single shielded or open bearings. If the motor is more than 5 years old, the probability that the grease in the bearings is Chevron SRI #2 approaches 100%. All of the major bearing manufacturers supplied SRI in their bearings up until a few years ago, and it was the most commonly specified grease for motor bearings by a large number of motor manufacturers. Even if the grease is not SRI, any polyurea grease should be compatible... Chevron SRI and Mobil Polyrex EM can be mixed with no problem. Polyurea greases are also marginally compatible with Sodium Soap and Calcium complex greases. Don't use a synthetic unless you clean out all of the old grease!

quote:

Don't use a synthetic unless you clean out all of the old grease!

I heard that comment from someone else lately and I'm sure it's right but I don't understand it. I was under the impression that the majority of compatibility problems were related to the thickener (change in penetration of the mixture). What kind of problems arise due to incompatibility of the oil?

Incompatibility of the oil in greases can be a real problem, mainly due to additives. PH can be affected, and then acids start to form. Some of the synthetic greases have PAO with ester additive carriers, some have PAO with mineral oil additive carriers, and some have pure ester based oil. A couple of synthetic greases have Alkylated Naphthalene based or alkyl benzene oils. It is extremely difficult to figure out the oil compatibilities from different synthetic greases, let alone with mineral oil based grease, so I don't usually recommend putting synthetic grease in anything unless it has been cleaned out first.

Thanks for the info Ed. Our plants started operation in 1988. In 1996 an evaluation was done to standardize on Mobilith SHC100 (Lithium complex thickener, Synthetic Hydrocarbon base oil with VG-100) for virtually all of our greased bearings (which came from a variety of manufacturers and shops). I don't think we went in and changed any bearings to changeout grease. Sounds like we may have a compatibility nightmare. I'll have to look in Lube notes and see if they have any more details.