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Dark squares and dark debris

Dark squares and dark debris

(OP)
I am working on a tribometer for my capstone engineering project. The goal is to diagnose and eliminate the "contaminated" debris on the counter-face. Our motors have about 2 rpm difference which causes the 1/4" dia. sample to rub in an elliptical pattern resulting in a square wear surface. The issue is that the counter-faces are being discolored (oxidation?) and in some instances the sample actually is scratching the surface.

Two of the samples in the results I am uploading were UHMW-PE GUR 4150 and one sample (the one with notably darker and finer debris) is nylon.
The counter-faces are both stainless steel polished to 1200 grit sandpaper.
The pressure on each pneumatic air cylinder is 1.5 MPa.
This specific test ran 16 hours.
The samples were prepared in a compression mold in an oven at 400F.
I'm uploading a brief video to show how the machine works.

My main question is: Why are the counter-faces and debris being discolored. We expect the stainless steel to remain polished and the debris to be the same color as the untested samples.

(I apologize for my reflection on the counter-faces in the pictures)

http://files.engineering.com/getfile.aspx?folder=c...

http://files.engineering.com/getfile.aspx?folder=c...

RE: Dark squares and dark debris

What is the specific material and alloy being polished?
What temperature was it formed at, polished at?
What lubricants were on it, or embedded in it, prior to polishing, during forming (pressing, or rolling?) or welding?

Does this happen everytime, very seldom, about half the time?
Who did the polishing when it happens? Same shift, same time of night (or day), same crew, different crew, same machine and same polishing compound and actuator, first run of the day, first run after lunch? First run after changing polishing lubricant? Last run before changing lubricant?

RE: Dark squares and dark debris

?? You've asked this question before, since I have copies of your picture and video downloaded previously. As this is a student project, expect to have your posting removed again.

You say this is a tribometer, but what is the MAIN product of friction?

What force are you actually applying to the samples?
What temperature do they reach?

TTFN
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