Friction Type D
During the initial phase of wear in of type D, the contact pressures at the low pressures flanks are much higher than in the middle of the seal. This will cause the surface profile of the seal will wear more at its flanks than in the centre. The seal will than have a slight arrow form on its contact surface. The sealing length is then gradually changed from the whole seal width to half. Even after this arrow form is obtained, the contact pressure at the flanks is higher than in the centre of the width, why the slight arrow form can be maintained.