| 摘要 |
<p>In one working operation or in directly successive working operations a tube 2 is extruded having at least two layers of different materials and the wall thickness thereof is structured to be wave-shaped or undulatory, i.e. has thick portions and thin portions at intervals. The thus formed tube sections are then cut from the tube to form the individual inner liners 50. The periodic variation in wall thickness is obtained either by altering the infeed of at least one material, or by constricting the flow passage through the extrusion head, or by changing the withdrawal speed of the tube. The materials are preferably two different rubbers. <IMAGE></p> |
