Sockets fored in plastics pipes in continuous production - using combined heater and expander permitting rapid operation

摘要

A method of forming sockets, optionally also beadings, on lengths of extruded plastics tube which are cut from the continuous extrusion in the production line is as follows: the stages of heating, expanding of the socket and cooling are all carried out in immediate succession, pref. merging one into another. The pipe may be moved forward either continuously or intermittently, along a straight or curved path. The heating, expanding and cooling devices are pref. all arranged coaxially one after another, the first two being formed as a single unit, in which the heating mandrel. constitutes the centering device for the expanding mandrel and is permanently inside the tube during the expansion. Where the heating mandrel operates by radiant heat, its external diameter is slightly smaller than that of the pipe, whereas when it operates by direct conduction, it can be expanded to bring it into contact with the interior of the tube. The unit is connected by a rod to a piston rod of a symmetrical jack, which pushes two such units outwards in opposite directions so that two sockets are simultaneously formed in the ends of two pipes which have just been separated by cutting.