quote:

Originally posted by Rennie:
Hello,
Kindly allow me to continue with this thread. Referring to an HVAC fan/motor, the manufacturer/supplier recommends grease Shell Alvania 3 or a BP equivalent of Energrease LS3. According to the grease specs this is an NLGI 3.

Since the fans run 24/7 it doesn't really matter that the grease is so thick, because it will stay hot. I certainly wouldn't have expected to need a grease that thick unless perhaps the fans are made to tolerate a mounting with the axis vertical? That could be why the grease is so thick. Anyway, a modern polyurea grease is compatible with lithium-based grease.

The effect of using any other grease with polyurea under any condition is catastrophic failure. Most likely a state of saponification will result and your two greases will become some non-lubricating watery mystery. I'm going to consult a few senior tribologists in my co. and get a handle on the grade 3 grease issue and will report that back promptly. I was an eye witness to a grease failure when lithium complex grease was added to an electric motor shipped with polyurea.

quote:

Originally posted by Monolec:
The effect of using any other grease with polyurea under any condition is catastrophic failure.

The grease company literature that I have been perusing differentiates between 'old' polyurea and 'new' polyurea. In fact, I've seen the 'new' polyurea referred to as 'di-urea' which has to be the ickiest name for a grease ever. Anyway, the 'new' polyurea is listed by these grease companies as being compatible with metal-based greases, unlike the 'old' polyurea.

Mike:

The problem is actually that the 'soap,' (base) polyurea, does not play well with others.

I am linking (the attachment is too large) the presentation that I gave at PdM-2005 on greasing electric motor basics:

http://www.motordiagnostics.com/papers/Bearing%20Greasing.pdf

I hope you find this helpful.

Additional information can be found in the 2006 history section in http://www.motordiagnostics.com/presentations.htm which are free to download and use, including the paper that goes with the presentation.

Sincerely,
Howard

Mike,

The conventional polyurea thickener is pretty much incompatible with everything regardless of whether the base oil is mineral or synthetic. The newer "polyurea" thickened greases are called, as you point out, "di-urea". I agree that the new name could have been chosen better but these thickeners are also referred to as shear stable and the formulation makes them pretty compatible across the board with the lithium and calcium family thickeners. As with all changes in grease, you have to check the chemical compatibility of the base oil. I have seen the earlier polyurea thickened greases turn to rocks when mixed with lithium complex thickened greases and the fluid leached out of the bearing area in short order. At least with those you knew very quickly that you had made a mistake.

I have been investigating greases for different applications in our facilities and suggest you contact your lubricant supplier (technical side not sales) and get data on tests done to show the compatibility. I have done this and am quite satisfied with the results.

Ken Culverson

quote:

Originally posted by DaiWei:
I have been investigating greases for different applications in our facilities and suggest you contact your lubricant supplier (technical side not sales) and get data on tests done to show the compatibility. I have done this and am quite satisfied with the results.

I have done this, and I have standardized on two greases, both from the same manufacturer, and both lithium-based. One is a non-EP grease used solely for electric motors, and the other is an EP synthetic for everything else. I had planned to go with a polyurea for the electric motors due to the evidence that polyurea is very common in electric motors, and the new stuff seems pretty nice, indeed, but my biggest, most expensive and most important motors are General Electric DC drives (200 and 500HP) and the documentation for them specifies a lithium-based non-EP grease, so I figured I might as well go with that for all of my electric motors, then every grease I use is lithium-based. I haven't regretted the decision so far, but time will tell.

Make sure, if any of them are sent out for repair, that you specify the type of grease the repair shop uses. I have been involved in a number of cases where the repair shop has been unaware and put in their standard grease and have had incompatibility issues in the field.

Howard

Here is a chart that supports the comments about shear stabilized polyurea thickener being more compatible with others than the old polyurea
http://www.mpc-home.com/GreaseCompatibility.pdf

In fact, the bottom row for shear stabilized polyurea suggests it is more compatible accross a spectrum of grease thickeners than any of the others lsited. Not incompatible with any... borderline compatible with only a few... compatible with most. Then again, I have been cautioned against relying on these charts due to subtle differences within a categroy. The only way to judge compatibility for sure is by doing the worked penetration test on a sample combining both types of grease.

I asked one of my technical advisors about this. The prevailing data most important to grease spec in this case is " DN value. DN =Bearing RPM and bearing diameter in millimeters. Use the shaft diameter for journal bearings and the pitch diameter for anti friction bearings. The pitch diameter (dm)is the arithmetic mean of the outer diameter of the bore. Experience with various bearing sizes and speeds is also factored into the range of DN values for various grease consistencies and physical properties such as tackiness.For DN of 0-75,000--tacky w/ heavy oil. 75,000-150,000--tacky w/ medium oil @ NLGI#2. 150,000--250,000 smooth,medium oil,light tack, NLGI#1 or NLGI grade 0.250,000-350,000--smooth texture w/ light to medium oil. If you calculate the info with this formula for DN value the answer is a tacky, medium oil #2 grease. Hope this helps.This info was relayed via a major bearing OEM.