How is Grease Analysis Different to Oil Analysis?

Rafe sits down with Rich Wurzbach – President at MRG Laboratories to discuss all things regarding grease analysis and grease sampling.

Rafe Britton: How are those tests different from a standard slate of oil analysis tests? Typically with oil analysis you’ll receive results for oxidation by infrared, nitration, water and a couple of others. And then generally the bulk of the results come from ICP, a measure of all the different metals within the sample. One of the differences is going to be that with grease, we’ve also got the thickener component. So maybe if we can talk through some of the different tests that you might do and how does the presence of a thickener effect the results there? 

Rich Wurzbach: Sure. So it affects the tests you might do and how you do them.

Differences in how the laboratory prepares samples

It also affects how the sample is handled in the laboratory. When you have an oil sample, one of the first things you do when you get it in a laboratory is you shake it up vigorously to re-suspend the particulate, the moisture, to try to create a homogeneous distribution within that oil sample.

Because if you’re going to do more than one test, you’re going to be taking a point piece here and a piece there and so forth. And you want whatever that is to be evenly distributed throughout. But you could shake a grease container all day long and you’re not going to move anything around. So the is reality that you need to deal with the heterogeneity of your material in a grease.

Differences in ferrous content testing

For example one of the tests that you would do would be a ferrous content test. And we often do this with oil samples as well. Sometimes we are happy to measure using ICP iron levels in our metals. But other times we’re looking at ferrous content because we want to see small particles and large particles, and really get a sense of the wear of the components, the bearings, the gears. In grease, we need to measure that differently because it might be heterogeneous.

So we have a device that uses an induction coil, where you take the entire grease thief and drop it into that coil. And it measures from top to bottom, the representative nature of how much ferrous material is there; large, small and everything in between. And that’s a device called the FerroQ.

Rafe Britton: Right off the bat, that’s that’s different. That would be, analogous to the PQ index?

Rich Wurzbach: Yes, it would be.

And I know some folks have tried to put a grease sample next to a PQ device, but if you understand how PQ works it’s not gonna work well. And it’s not going to be reliable for grease because in a PQ the material in that fluid is responding to that magnetic field and changing in response to it.

Whereas materials aren’t moving in the grease and you can’t redistribute. And they’re not going to respond to that field. So this is a different kind of induction method that is really focused in, on the unique properties of priests. 

Differences measuring viscosity

So you mentioned viscosity. We can’t use the traditional methods to measure viscosity, but we do have a very important measure to do for used grease and that is the consistency of the grease. As you mentioned, what can happen over time is that thickener can break down and the grease can become soft.

Sometimes you can have the thickener separate from the oil. There can be conditions where the grease dries out or hardens or when we start mixing greases together, really strange things happen in terms of that performance. So to be able to evaluate that consistency change from what the new grease should be, that’s where that grease the analyzer comes into play, and we have to measure it in a way that measures the non-Newtonian fluid properties.

And that’s called the dye extrusion test. 

Rafe Britton: So you can actually do that with relatively small sample quantities. You were talking about what a one gram? 

Rich Wurzbach: Yep. That’s why I talked about being an integrated process. When you expect a laboratory to do meaningful analysis with only one gram, conserving that material is really important. And even every time you transfer a grease, it’s hard to get it all off of whatever you’re transferring.