Letter 37023

Want graphite type coating on the surface of cured rubber [Ohio] 

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I want to extruded a rubber article the has a coating of graphite or similar material on the surface. This coating must be bonded to the surface of the rubber part, for it will see some wear in actual use. This coating will give lubricity to the surface of the rubber part so that there is no drag on a glass or metal obstacle. This product line would involve considerable linear feet of extrusion.

Alice Uminska
- Middlefield, OH, USA

Alice, a possible solution to your problem is called dry film lube. Do a Google search, There are two major companies. This includes graphite, molydisulfide and possibly some other stuff. There are numerous formulations. Some require baking at moderate temperatures some do not. I have no clue as to how well it will stick to "rubber".

James Watts
- FL

Alice,
Just an idea since extrusion is not my field. Have you considered double extrusion? First, with base material, then with graphite impregnated rubber skin over the base. I don´t think paints or conventional coatings over rubber will offer good durability.

Guillermo Marrufo
Monterrey, NL, Mexico

The post above is about "dual durometer extrusion" where two or even three different vinyl compositions can be extruded into one structure simultaneously. For example A flexible vinyl low friction seal compound can be place right on a rigid window frame extrusion. Similar things can be done with rubber compositions.

For rubber, you can compound in surface modified UHMW. UHMW stands for "ultra high molecular weight polyethylene" - they leave off the PE usually. This will anchor and give wear resistance and lubricity. Talc or graphite are alternatives. Some oils added to rubber compositions will exude to the surface and lubricate.

If this is a small one time application, epoxy will grip rubber fairly well and can be loaded up with any of the solid lubes above. But you have to use a more flexible epoxy and this sometimes can be accomplished by doubling up on hardener. You might consider Molybdenum disulfide but this is now viewed as a heavy metal.

Easiest to apply but with lower durability is soap, dry silicon spray, dry Teflon spray, dry graphite spray, spray on mold releases....anything slippery that does not attack the rubber part.

Jack Wells
- Austin, Texas, USA

I am having the same problem trying to coat rubber rollers to bring down the friction and reduce the grip. My rollers should have been vulcanized with greater hardness to have a smoother grip.

The suggestions sent to you are helpful to me as well, I will try them out and report them back to you.

Is there a tool to measure friction on a rubber roller?

Eduardo Salomon
- Miami

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