Process and apparatus to injection mold continuous lengths of hollow plastic articles

A method of making ribbed pipe in a stepwise manner, comprising the successive steps of:

• (a) forming a length of pipe by injection molding a moldable material in a cavity between a collapsible mandrel and a plurality of female mold elements;
• (b) disengaging said plurality of female mold elements from said length of pipe;
• (c) advancing the collapsible mandrel in an axial direction downstream to partially eject said length of pipe from the cavity;
• (d) collapsing said collapsible mandrel to disengage from said length of pipe;
• (e) retracting the collapsible mandrel to its original position;
• (f) engaging said plurality of female mold elements to clamp an inner end of said length of pipe at a position near the second end of the cavity;
• (g) expanding said mandrel thereby closing the second end of said cavity;
• (h) injecting further moldable material into said cavity to form a further length of pipe and homogeneously welding said further moldable material to the inner end of the partially ejected length of pipe;
• (i) repeating steps b-h to form pipe of a desired length.

An apparatus for continuous injection molding ribbed pipe in a stepwise manner, comprising:

• a collapsible mandrel;
• a plurality of female mold elements removably positioned about the periphery of said collapsible mandrel forming a cavity therebetween;
• means for injecting moldable material into the cavity between the collapsible mandrel and the plurality of female mold elements to form a length of pipe;
• means for advancing and guiding said formed length of pipe downstream.