High Friction Coating Material

A. Not sure how high the temp you have in mind. Electro nickel plated diamond will give you a finish of diamond file. Or thermo-spray, say chromium oxide with appropriate grade of powder. Need more details of your requirement.

A. If you meant a low coefficient of friction, you can try a Teflon coating :-)

If you are looking for a high coefficient of friction you can try a plasma coating.

Suerte.

A. I suggest that you try belting the different alloys together with some sort of foreigner clamp. These products come with complete instructions, so nothing is left to the imagination. I bet you will experience vast improvements in outstanding performance. Good luck.

A. I am working on a very similar problem for my company. Our compressive stress requirement is lower, 8,000 to 12,000 psi. I know of an application using tungsten carbide coating on carbon steel against non-coated carbon steel that is in the 10,000 to 12,000 psi range. It does not slip or damage the mating surfaces.

A. Hi, Jim.

As a semantics issue, I don't know if there is anything with an actual Coefficient of Friction greater than 1.0.  While a rack and pinion set can drive a force greater than the normal force between the two gears, it would not work at all if the actual coefficient approached 1.0. Similarly, there are all sorts of small scale and micro-scale interlocking arrangements, including things as low-tech as duct tape and Velcro :-)

One interesting item I recently heard of, and that Messrs. Chaw and Stevenson allude to, is "friction shims" for flanged connections, where the shims are electroless nickel plated with occluded diamond or other hard particles. The tiny hard particles dig into the opposing surface and can thus transmit torque with a coefficient of .6 and above even when the surfaces may be oily. Perhaps you could either use such shims between the mating parts, or plate one of the mating parts with the composite electroless nickel? Even then, for your needs you'd probably require a keyway, or tapered joint, or something like that since a coefficient "much greater than 1" sounds extremely unlikely. Good luck.

Regards,

No one can respond to that question until and unless you provide some better Information.

Your question is akin to asking "What is the best spice?" There's no one answer.

What is the "organic" surface?
Speed?
Pressure?
Service conditions? Dry, wet, lubricated. None or all of the above?
Temperature?
Expected life?
Optimum coefficient of friction?

Give us some information and then, maybe, we can help.

A. Regarding (static) Coefficient of Friction greater than 1.0... yes, it is easy to see many material combinations with 1.0+.

Rubber on Rubber (dry), Aluminum on Aluminum (dry), Silver on Silver (dry), Platinum on Platinum (dry) are all greater than 1.0. Not to mention thousands of coatings combinations. Note that these are all "like material" combinations, where the surface molecules have greatest "stick" (cohesion).

1.0 is not a welded joint. It is the "slope" upon which (45 degrees) an object at rest under normal gravity will be right at the threshold of "slip".

Thanks David. The coefficient of friction is the ratio between the parallel force needed to move an object and the normal force on it, and your illustration of a 45 degree angle for a coefficient of friction of 1 is the typical one and a good one. I find the subject an intriguing one because I think a combination of surface profile interlocking and/or cold welding is what we simplify and call "coefficient of friction".

Why is the coefficient of kinetic friction usually lower than the coefficient of static friction? Could it be because we're bumping along with the two surfaces not having time to seat and interlock, like a poorly meshed gear? Why is the highest friction always between identical materials if not due to cold welding or like molecules mechanically interlocking? Why does a little liquid reduce the friction -- is it because it keeps the surfaces from interlocking? I never studied friction after graduation, and wish I had :-)

Regards,

A. Hello Ted,

Spent lots of hours dealing with friction problems as a young design engineer. Here's the best problem I ever had and solved... a pliable part was being automatically inserted into an automotive assembly, with lubricant. The parts were tearing about once in 10,000 operations, a disaster in the auto industry, a recall was pending. The company asked me to come in and solve after the corporate engineering black belts had about given up after 3 months of DOE.

Took about 5 minutes for me to find the problem... a small force couple due to mis-designed tooling (geometry was wrong) was just enough to stress the material obliquely (shear and tension combined). Every so often the mold line on the part wasn't totally clean... so the stress was just enough to pinch and tear.

The black belts had attacked the problem by throwing different lubricants at it... but the root cause was faulty geometry. Pythagoras and Newton, not some chemists, were the solution.

A. Hi Conor,

Hard Anodizing the Aluminum seems the obvious choice; am I missing something?

It's not just the roughness factor that is the difference between steel and SS: SS is lousy for bonding rubber, Steel does bond very well on rubber with or without Chemlock or equivalent bonding products.

A simple CED coating on the steel will also aid the bonding of rubber on steel or aluminum.

A. I have no idea what coating might do what you want, but, AFAIK, all wheel driven Land Speed records have been set on pneumatic tires, provided by one of the major tire companies.

If you're running a jet car, then the apparent go-to material is high strength aluminum. Wheel steering doesn't count for nearly as much as aerodynamics.

But, if you're trying to reinvent the wheel, I have no clue.

A. Hi. You're beyond my depth, but it would seem to me that embedded strands of glass, carbon, or steel fibre would be necessary towards holding any thick elastomer coating onto wheels rotating at 10,000 RPM.

Regards,

A. Hi Julio!
Looks like no one has chimed in so far but if you state the exact alloys you are trying to put a coating on, as well as your current challenge and what you would like to see improved, this crew will come up with answers much easier!
Cheers!