Friction in general
The wear in process for all Metseal piston seals are done between surface materials that can be looked at as hard and rigid, which in principle has a decisive significance for the friction and the wear. In contrast to soft or semi- hard conventional seals in polymeric materials, the Metseal metal seal can neither elastically be pressed down in the dales of the cylinder bore surface nor be chemically fastened to the cylinder bore surface. The wear in for the Metseal seals creates flat surfaces, consisting of plateau's with very good surface roughness, in a original surface which can be both proportionately rough or proportionately less rough. When the plateaus are formed, the surfaces can not go down in each other and have lateral contact, but just have contact plateau against plateau. When this has occurred, the friction normally is decreased to about half. The plateau's surfaces then usually look like a mirror. Metseal of today do not have all the scientific know-how to be able to explain all friction phenomenon, but are working according to following hypothesis that is explaining our test result. The contact surfaces of the seals are manufactured with best possible surface finish (Ra) and an ultimate bearing resistance (Mr). The aim is that the contact surface shall be as close as possible to an already worn in seal, already when it is delivered. The seal will then very rapidly get a plateau- like look and a surface profile (Ra and Rz) that thoroughgoing is much better than the cylinder surface. Very early one then will get surface contact just plateau against plateau. When the surfaces slide against each other, friction and heat is developed. The pressure media, that exists principally is in the dales of the cylinder bore surface, is rapidly heated, whereupon pressure in the media will occur. Thus because the media to a big part is trapped in the surface profile. One will then get a film development or a reduction of contact pressure and friction. The possible creation of film is different from the hydrokinetical film that one always will have in soft seals in polymeric material and to a certain extent even the Metseal seal types.