Open ended extrusion of plastic tubing with internal - pressure maintained by a magnetically supported

摘要

A floating mandrel made of ferromagnetic material is supported axially within extruding plastic tubing by a series of electromagnetic poles of opposed signs. The mandrel has several sections almost as large in diameter as the tubing bore; these have the cumulative effect of restricting loss of the pressurised (4 atm.) gas (air) supplied at the extrusion nozzle for maintaining the tubing section in an extended state. Pref. the tubing follows a curved path at some point between the extruder and the magnetic unit and between the magnetic unit and the product cut-off device (a travelling saw) to prevent ejection of the mandrel should the electromagnets be de-energised.