METHOD FOR CHANGING THE THICKNESS OF A BODY EXTRUDED WITH A CONSTANT THROUGHPUT, AND DEVICE FOR CARRYING OUT THE METHOD

摘要

Extrusion of thermoplastic pipe with periodic variations in wall thickness produced by running an extruder and a separate drawn off machine eash at constant throughput rates and varying the distance between the two units to modify the effective draw-off rate from the extruder, and hence the profile wall thickness. Either the extruder or draw-off unit is stationary and the other is mounted on a power driven carriage capable of converging the two units relatively rapidly resulting in thick wall section extrusion during convergence, and parting the units slowly to produce greater lengths of thin-walled profiles. Used for producing thick-walled zones in pipe at intervals suitable for radial dilation to produce socket mouths which match the pipe walls for thickness at suitable pipe length intervals. The extruder operates under stable conditions and the draw off unit can operate at an optimum speed for grip on the profile surface, providing better dimensional and structural reproducibility than systems which vary extrusion or draw-off rates.