Abstract: The present invention provides a method of readily manufacturing a multi-layer pipe liner bag with a good workability. A guiding tube is inserted into an outer layer composed of a tubular resin absorbent material and a plastic film coated over the outer periphery of the tubular resin absorbent material. An inner layer composed of another tubular resin absorbent material is inserted into the guiding tube, and the guiding tube is extracted with the outer layer and the inner layer being fixed. The tubular resin absorbent materials of the outer layer and the inner layer are with thermosetting resin to complete the pipe liner bag. Since the outer layer and the inner layer are manufactured separately, the manufacturing of the respective layers can be performed with a good workability. Also advantageously, the plastic film covering the outer surface of the outer layer can be prevented from scratches and so on.

Abstract: Dimpling of a workpiece by rebounding of a magnetic repulsion punch mechanism, when operated at high punching rates, is avoided by application of a damping pulse at a point at or subsequent to a mid-point of a return stroke of the punch from the workpiece and preferably within the last 10% of the return stroke. This damping pulse is preferably a fraction of the pulse width and of approximately the same amplitude as a driving pulse applying kinetic energy to the punch for causing punching of the workpiece. At high punching rates the kinetic energy of the return portion of a punching stroke is substantially determined by elastic rebounding of the punch from a guide bushing. The removal of kinetic energy during the return portion of the stroke allows the return of the punch to a position close to a rest position during a very short interval with small overshoot under control of mechanical damping.