Wearing of case hardened shaft wearing in delrin and/or UHMW polyethylene holder

[tlyter]

I am trying to determine the cause of a wear issue on our machine. We have a 440c idler bar that rests in a slotted block made of delrin or UHMW conductive Polyethylene holder. The shaft rotates at ~1500 rpm. I am getting wear on the shaft that produces brown dust. The shaft is 8mm and the holder slot width is 8.3mm. The shaft is meant to be removeable to remove paper jams. Any ideas? Images attached.

 

[btrueblood]

I'm assuming the delrin is also a conductive material? The rotation of the shaft at 1500 rpm is generating heat which decomposes the delrin, releasing the carbon or whatever particulate material generates the conductivity, the resulting particulate and decomposed plastic is abrasive and wears the shaft. You could consider using a lubricated material (oil bearing sintered plastic or sintered bronze?), or change the mount to accept a roller bearing; this may or may not be conductive enough to make the static dissipate to your satisfaction, which might require some separate mechanism (wiper brush?) to provide a dissipation path.

 

[moon161]

What he said.

 

[EdStainless]

Or look at grades of PEEK that are loaded for both lubricity and conductivity. If you need to choose a plastic based on lubricity and add a second system for static dissipation, though metal bushings should take care of both.
You need less friction for that rotation speed, the plastic will wear and then the debris will cause the shaft to wear.


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P.E. Metallurgy, Plymouth Tube

 

[1gibson]

Spring loaded metal pin at the center of the shaft face to deal with conductivity? Groove or slot somewhere in the bearing contact area (4 or 8 o'clock) to help clear debris?

Pin could be as simple as a flat metal plate with a dimple pressed into it, makes contact with the metal screws to ground to the machine body, rely on the plate flexibility for the spring action. Leave a knockout behind the bushing so the plate has room to move a bit.

 

[dvd]

Max P, max V, max PV?

PV data chart