Clutches with Cork Inserts. [l"RO"M AUTO CAR.]

Progress, Volume II, Issue 10, 1 August 1907, Page 378

Clutches with Cork Inserts. [l"RO"M AUTO CAR.]

A clutch with cork inserts is still more or less of a novelty. Further light is thrown on the matter by a report of tests made under Professor Hollis at Harvard, U.S.A. This has been sent us by the British- American Co. of Widdrington Road, Coventry, who refit clutches in this way. It seems from the Harvard tests that the co-efficient of friction between two cast iron surfaces was approximately half what it was when one of the cast iron plates was provided with compressed cork inserts, which were forced into holes in the cast iron, and only allowed to project l-32in. above the surface of the metal. The claims for cork are very well put by the British- American Co., and as we have at present no practical experience with cork used in this way, we cannot do better than quote them : " The theory of action and explanation of the phenomenon is this • Cork not only has twice the co-efficient of friction of leather or metal, but it strongly grasps the surface with which it comes in contact, in such a way that it gathers up dust abraded particles and globules of oil which, under other conditions, act as rollers and diminish the friction and cause slipping by keeping the surfaces apart, so that it will be seen that by the use of these inserts the surfaces are brought into intimate contact and the friction thus doubled. The cork used is solid natural cork, specially selected and specially prepared, and is forced under high compression into sockets made to receive it. It is held in place by its own expansion, and the curious result is found that it wears down no faster than the solid material in which it is embedded, and that it retains its frictional and other qualities under constant service for many years. It differs from ordinary frictional surfaces by the fact that it is impervious to air, water, and oil, and its great frictional quality is neither diminished nor affected by air, moisture, atmospheric conditions, water, oil or other lubricants, so that but little reflection will be needed to show the enormous advantage gained over every other friction-producing material by the use of these inserts. Automobile "clutches of either the cone type, or of the metal-to-metal disc variety can be enormously improved in their gripping power by the use of cork insertions. In metal-to-metal disc clutches they are used in alternate discs or in place of leather in leather-faced disc clutches." We may add that the cork inserts are also recommended for brakes as well as clutches the corks being fitted into the faces of the brake drums. The consequent increase of holding power is considerable.