Grease Compatibility

[SuperSalad]

I've been saying for years that most of the compatibility charts out there aren't accurate anymore and that thickener type isn't the only detail to consider. I'm pretty sure it's well known in the industry (at least in my own veil of influence), but its still nice to see it in a more public forum.
How to Determine Grease Compatibility and Why It's Important

 

[Ducked]

Seems good, though I bet it'll be a long while before the results of such testing become generally available, if they ever do.

One bit I don't get, but its so basic that I must be missing something.

"The resulting mixture is analyzed by Fourier transform infrared (FTIR) spectroscopy to note any reaction or unexpected oxidation of the components in the grease."

OK, that makes sense. Oxidation products are detected. However, it goes on:-

"The grease is also evaluated by elemental spectroscopy to assess unexpected final ratios of additives as compared to the anticipated averaging of values seen in the original products, adjusting for mixing ratios."

Assuming there are no nuclear reactions, how can the elemental makeup of the mixed grease change? Where do the missing elements go?

Only thing I can think of is they get adsorbed onto surfaces in the test equipment.

 

[Food Scientist]

Originally Posted By: Ducked

"The grease is also evaluated by elemental spectroscopy to assess unexpected final ratios of additives as compared to the anticipated averaging of values seen in the original products, adjusting for mixing ratios."

Assuming there are no nuclear reactions, how can the elemental makeup of the mixed grease change? Where do the missing elements go?

Only thing I can think of is they get adsorbed onto surfaces in the test equipment.


I read that as "Hey we are checking the amount of additives and verifying that our theoretical calculations were correct."

 

[Ducked]

Originally Posted By: SVTCobra
Originally Posted By: Ducked

"The grease is also evaluated by elemental spectroscopy to assess unexpected final ratios of additives as compared to the anticipated averaging of values seen in the original products, adjusting for mixing ratios."

Assuming there are no nuclear reactions, how can the elemental makeup of the mixed grease change? Where do the missing elements go?

Only thing I can think of is they get adsorbed onto surfaces in the test equipment.


I read that as "Hey we are checking the amount of additives and verifying that our theoretical calculations were correct."


I read it as "The grease is also evaluated by elemental spectroscopy to assess unexpected final ratios of additives as compared to the anticipated averaging of values seen in the original products, adjusting for mixing ratios." because that is what it says.

Taken at face value, a change in the proportion of elements, (which seems to be what they are describing, but can't be) seems to require them to disappear or be created, which (for non-nuclear reactions) is impossible.

 

[Ducked]

A closer examination of table 3 (reporting elemental analysis of 2 greases and a 50-50 mixture) and the comments on it, doesn't help much. They say:-

"Table 3 reveals the differences in elemental spectroscopy values for the reference greases and the 50-50 mixture. The areas highlighted in yellow show the contrast between the greases and evidence of mixing."

The first bit is OK, but if they are mixing the sample in the rig described, why do they need "evidence of mixing", and what is this "evidence of mixing" anyway?

A 50-50 mix would be expected to give the arithmetic mean of the two values reported for the greases analysed separately. In fact it ranges from 100% less than expectation for Lead and Aluminium (not detected in the mixture at all) to 300% more than expectation for Boron. Calcium is 122% more than expectation.

Assuming its thoroughly mixed, and the elements aren't volatile, adsorbed, or otherwise lost from the system, I'd guess some of this deviation from expectation is due to the accuracy limits for the detection method, plus maybe some interference effects on the detection (i.e. an artefact).

I'm not clear what, if anything, it tells us about operational incompatability.

 

[SuperSalad]

I think they are simply comparing the calculated average to a measured result to verify that the two greases are completely miscible/mixable with one another. If for some reason they do not totally mix than a single sample would have variable elemental results from the calculated average.

If instead, the two greases are uniformly mixed, then the average values and the measured values should correlate. So my take from it is that the test is to:

1. Verify that the greases did mix uniformly during the simulation.
2. The two grease additive systems are compatible enough for proper mixing.

 

[Ducked]

OK, that makes sense. I was assuming uniform mixing, whereas that's what they were testing for.

My DUH!

Is mixing necessary for compatability?

Seems possible the two greases could function OK independently, but I suppose "old" grease could prevent "new" grease from getting to the wearing surfaces.

 

[SuperSalad]

Yeah even if the two greases didn't mix and still worked to their full capacity, it would probably result in uneven wear on that part which would be less desirable than more, but even, wear.

 

[Shannow]

Something that I've observed over many years, and quite a few not so good experiences is that grease manufacturers will over-exaggerate the compatibility of their greases to make a sale, reasoning that a 20L drum of their grease hooked up to your machine is better than someone else's, and that for the (brief???) period of mixing, not MUCH bad stuff will happen.

Depending on how close to the line of safety that the gear is operating, this final assumption may not be actually true.

We've had great results replacing regular greases with Miobilith SHC series.

We've had woeful results with greases containing MoS2, Graphite and/or teflon...again, those applications are more close to the wire than a system that can survive forever on Li soap.