Process for thermally bonding plastic tubes

Claim 1

A process for thermally bonding together first and second tubings made of a plastic material with a bond area having a narrow width; said process comprising the steps of: providing a stepped mandrel wire having a small diameter portion the outer diameter of which corresponds to the inner diameter of the first plastic tubing to be utilized, a larger diameter portion having an outer diameter which corresponds generally to the outer diameter of the first plastic tubing, and a shoulder separating the stepped portions; feeding one end of the first plastic tubing over the small diameter portion of the mandrel wire; feeding the end of the second plastic tubing over the larger diameter portion of the mandrel wire to a position where it overlaps the end of the first plastic tubing fed onto the small diameter portion of the mandrel wire from a direction opposite that in which the first plastic tubing was fed over the mandrel wire; feeding a section of shrink tubing having an inner diameter sufficient to be received over the second plastic tubing to a position where the overlapped first and second tubings are centrally located within the section of shrink tubing; placing the plastic tubing assembly comprising the mandrel wire, one end of the first plastic tubing, one end of the second plastic tubing, and the shrink tubing into a specially configured preheated die assembly including chill blocks; heating a narrow circumferential portion of the assembly to cause the shrink tubing section to shrink and force the second tubing against the first tubing which is being melted by the heating to thermally bond the plastic tubings together; allowing the heated bonded tubings to cool; and after cooling, removing the shrink tubing and mandrel wire.