Importance

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Abstract

A bell end in an extruded pipe having a transition phase of greater than 35° is formed by thermoforming. The transition phase acts as a pipe stop system to prevent over insertion of another pipe into the bell end. The process includes heating the first end of the pipe, pushing the pipe onto a mandrel having a sloped portion with a forming angle of more than 35° and applying pressure to conform the pipe to the shape of the working surface of the mandrel. The heating step includes heating an end of the pipe where the transition phase will be formed in a preliminary pre-heater, while the pipe is still warm from the extrusion process, and then immediately thereafter in a heating box. Preferably, the end of the pipe, and in particular the portion of the pipe corresponding to the longitudinal position where the transition phase will be formed, will be heated to an average temperature of at least 100° F. and more preferably 200° F. and still more preferably at 300° F. The number of heating zones in the heating unit and the duration of heating is selected to be comparable to the time required to extrude the pipe so that the overall thermoforming process can be performed substantially continuously with the pipe extrusion.

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First Claim