Abstract
At any time there are anomalies and difficulties in the prediction of friction, and these are accentuated if one of the surfaces is deformable, as in flexible piston seals, since the surface strain introduces an additional variable. Such surfaces, although exhibiting the three usual kinds of friction—dry, boundary, and film—show peculiar characteristics at low speeds, when the friction is usually less than that at higher speeds. The static friction itself depends on the time during which the surfaces have been in contact, and preliminary work indicates that there is a law connecting these two quantities, the probable form of which is given in the paper.
The experiments suggest that the total friction force need be no greater than 1 per cent of the force on a 3-inch diameter piston at pressures of the order of 2,000 lb. per sq. in. (and may be much less in the case of specially shaped seals) though the accuracy of prediction is unlikely to be better than ± 10 per cent.
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