In re Hayatian

56 C.C.P.A. 715, 159 U.S.P.Q. (BNA) 523, 1968 CCPA LEXIS 244

• Court: Court of Customs and Patent Appeals
• Decided: November 14, 1968
• Docket: No. 7969
• Status: Published

Opinion

PEE CURIAM:

By order of the Court, appellant’s petition for rehearing is 'granted only to the extent of changing the language of the original opinion dated June 6,1968, as follows:

Delete the last three lines of the text on page 12 (including footnote 2) and the first four, lines on page 13, and insert therefor:

The solicitor, in response to this argument, pointed out that appellant’s major premise is contrary to Coulomb’s second law of friction for dry surfaces,² namely that for a given load the frictional force is independent of the apparent³ area of contact, and derived equations to demonstrate to the court that the Belleville washer actually has a greater frictional restraining torque than the flat washer. We conclude, without judging the scientific merit of the applicability of Coulomb’s laws of friction in all instances, that there exists sufficient controversy regarding the aspect of friction here involved so as to indicate that it is not necessarily self-evident that the flat washer is less likely to turn relative to the link than the Belleville washer.

2 Encyclopedia Americana (1964 ed.), Subject — Friction, subtopic — Coulomb’s Laws:

Most texts in mechanics are agreed upon a set of conclusions first published by Charles Augustin de Coulomb in 1785 and supplemented by extensive work of Arthur Jules Morin (1832) * * »

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The laws of Coulomb friction are: (1) The frictional force is directly proportional to the force or load pushing the two bodies together. (2) For a given load, the frictional force is independent of the area of contact. (3) The kinetic frictional' force is independent of the velocity of sliding. (4) The coefficient of friction, static or kinetic, for any pair of surfaces depends upon the nature of the materials, their hardness and smoothness.

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The first two laws of Coulomb friction must be modified since it was found by F. P. Bowden and D. Tabor in 1938 that for metals in contact the frictional force Is independent of the load and directly proportional to the actual area of contact. This area depends on the number of points in contact and is smaller than the apparent contact area. Increasing the load serves of course to increase the number of contact points. Careful tests, using the electrical conductivity of these points, indicate that the deciding factor is indeed the area and not the load.

3 It is noted that the record provides no assurance that the actual contact area for the Belleville washer would be less than that for the flat washer.