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Coefficient of friction with steel greater than 0.9

I an a design engineer in the automotive field, working on a development project. I am looking for a material that has a coefficient of friction (static) with steel of 0.9 or greater. This material needs to be able to be formed, cut, punched, etc into a "washer" size piece (24 mm by about 1.0 mm thick) OR be a coating for powder metal/plate steel. If someone knows of such a material, I would appreciate any information you could forward.

brad p [last name deleted for privacy by Editor]
- Ontario, Canada

Since the coeff. of friction request (0.9) is kind of unusual, I wonder if you meant it to be 0.1. Because higher the coefficient, greater is the friction.

Mandar Sunthankar
- Fort Collins, Colorado

Soft rubber tires on dry asphalt might get you 0.9. Anything on steel, I can't picture it, but I'll bet the railroads would be interested.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Well Ted, you just gave us the nearest answer. A rubber coated steel disk may be? Brad could try a few similar coatings.

Mandar Sunthankar
- Fort Collins, Colorado

It's not difficult to achieve a coefficient of friction greater than 1. Take a magnet as an example or metals that share electrons.

Larry P [last name deleted for privacy by Editor]
- Dothan, Alabama

While that is good food for thought, Larry, I'm not sure that it's correct. Coefficient of friction is, I believe, defined as Frictional force Normal force (perpendicular force), and a magnet increases the normal force. Welding the two pieces together will certainly stop them sliding on each other, but I wouldn't call that a coefficient of friction.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Can you put "teeth" on the material so it would mesh as gears do? Alternatively, can pressure be applied against the material as in the operation of an automobile clutch?

Paul F [last name deleted for privacy by Editor]
- Colorado

What about static coefficient of rubber on steel? The conformable rubber embeds microscopically and Mu is over 1.0. Some pressure is required for this to take place, but I've seen it occur when rubber is used as a vibration damper between steel parts.

Ken K [last name deleted for privacy by Editor]
- Richmond, Indiana, USA

If it is a washer between flat steel surfaces a double-sided tape of minimum thickness may serve your purpose if temperature is suitable

- Pune, India

Mr. Mooney,

I believe that Larry P is correct in his statement. While the frictional force does depend on the normal force, it also depends on the coefficient of friction. The coefficient of friction is determined by the interaction between the matter of the two surfaces involved. A magnetic interaction is one type of interaction that can be considered here.

Justin Irving
- Philadelphia, Pennsylvania
April 1, 2008

April 2, 2008

Hi, Justin. There is no doubt that magnetism can reduce slippage. When I was a kid, and that's a long time ago, Lionel added "magnetraction" to toy trains so the engine could pull a huge train without it's wheels slipping.

I am not an expert on this subject, so I don't want to engage in an "is not" / "is so" / "is not" argument on it; I'd much prefer if someone could point to a book as the referee. I was taught that F = uN, so if the magnetic attraction increases the Normal force, it increases the Frictional force without involving a change in u. But maybe the magnetism works in other ways than just increasing the Normal force :-)


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

January 29, 2009

Hi Ted,

You have it right there. The equation is F = uN. That is "Force", not weight. The magnetic attraction would add some force. This can be added to the force caused by the weight of the object.

However, magnetic force is usually tiny compared to just simply adding more weight, unless you happen to be going up a vertical wall. Or if you are working with very small objects, or you have a magnet that has a few million gauss strength.

Jeffrey Teo
- Singapore

In order for drag racing cars (wheel driven, not turbine powered) to accelerate faster than 1 g, they must produce a coefficient of friction between the tires and the tarmac that is greater than 1.

Chris Walter
- Traverse City Michigan
June 11, 2009

Yes, Chris. The present world record of 4.428 seconds would seem to indicate an acceleration of 4.18 g's, which would require a co-efficient of friction far in excess of 1.

But when rubber tires are "burned out" so that they are actually melting into the asphalt and fusing with it, maybe it's legitimate to question whether we are actually talking about coefficient of friction anymore or we're talking glue :-)


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
June 11, 2009

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