Method for forming tube with thickened socket end

Claim 1

METHOD FOR FORMING A SOCKETED TUBE MADE OF A PLASTIC MATERIAL WHICH IS RIGID IN AN UNHEATED CONDITION, THE TUBE HAVING OPPOSITE INNER AND OUTER SIDES AND BEING PROVIDED WITH A THICKENED END BY DEFORMING THE TUBE WHICH HAS BEEN BROUGHT INTO A CONDITION IN WHICH DEFORMATION IS POSSIBLE BY APPLYING HEAT, COMPRISING THE STEPS OF: A. HEATING THE END PART OF THE TUBE UP TO A TEMPERATURE ABOVE THE DEFORMATION TEMPERATURE OF THE PLASTIC MATERIAL, B. THICKENING THIS END PART OF THE TUBE WITHOUT SUBSTANTIALLY CHANGING THE DIAMETER OF THE INNER SIDE BY SUBJECTING THE SAME TO AN UPSETTING OPERATION BY DEFORMING THE TUBE BETWEEN A FIRST SUPPORTING WALL POSITIONED WITHIN THE TUBE AND A SECOND SUPPORTING WALL POSITIONED OUTSIDE OF THE TUBE, WITH THE FIRST AND SECOND WALLS BEING ARRANGED WITH A PREDETERMINED SPACING BETWEEN THEM AND SO DEFORMING THE TUBE UNTIL THE INNER SIDE AND OUTER SIDE OF THE THICKENED PART ARE SUPPORTED BY THE FIRST AND SECOND SUPPORTING WALLS, C. COOLING AT LEAST THE OUTER SIDE OF THE THICKENED PART OF THE TUBE DOWN SO AS TO HAVE A TEMPERATURE AT LEAST 10* LOWER THAN THE TEMPERATURE OF THE THICKENED MASS SO THAT ON REMOVAL OF THE SECOND SUPPORTING WALL THE THICKENED PART SUBSTANTIALLY RETAINS ITS FORM, WHILE ON THE OTHER HAND COOLING IS PERFORMED SUCH THAT AFTER REMOVAL OF THE SECOND SUPPORTING WALL, THE HEAT IN A PARTICULAR INNER CROSSSECTIONAL AREA SUFFICES TO BEING THIS ENTIRE CROSS-SECTIONAL AREA UP TO AT LEAST THE TEMPERATURE OF DEFORMATION, AND D. SUBSEQUENTLY WIDENING THE THICKENED PART TO FORM A SOCKET.