Method of producing seamless tubular articles having an arcuate portion along the tubular axis

A method for producing a seamless tubular article having an arcuate portion along its tubular axis that leads into at least one straight portion, said method comprising the steps of:

• providing partable mating die members having mold cavity portions which cooperate, when said die members are closed, to define a cavity having an arcuate section that leads into at least one straight section configured to the external shape of the article to be formed;
• downwardly extruding a length of tubular parison of heated pliable thermoplastic resin having an outside diameter slightly less than the outside diameter of the article to be formed;
• while the tubular parison continues to be extruded downwardly, causing relative movement between the depending end of and the remainder of said tubular parison while still pliable, first in a direction lateral to the tubular axis of said parison as downwardly extruded and then in an upward direction generally opposed to the tubular axis of said parison as extruded to cause a portion of said parison to sag into a loop that has the general shape of the arcuate portion of the article being formed, but to cause a straight portion of said tubular parison, having the general shape of the straight portion of the article being formed and into which the arcuate parison portion leads, to remain;
• closing said die members about said tubular parison with said arcuate and said straight portions lying inside said mold cavity;
• introducing a blow molding duct into said parison to provide communication with the interior thereof;
• introducing fluid under pressure through said duct to force the parison wall outwardly into contact with the surface of said mold cavity;
• separating said die members after the plastic has cooled sufficiently to rigidify;
• and
• stripping the molded tubular article from said die cavity portions.

A method of producing a seamless tubular article having an arcuate portion along its tubular axis that leads into at least one straight portion, said method comprising the steps of:

• providing shiftable mating die members partable in a direction perpendicular to the direction of shift and having mold cavity portions which cooperate when said die members are clamped together to define a mold cavity having an arcuate section that leads into at least one straight section configured to the external shape of the article to be formed;
• downwardly extruding a depending tubular parison of heated thermoplastic resin having an outside diameter slightly less than the outside diameter of the article to be formed;
• grasping the leading end of said parison while it advances downwardly and thereby causing relative movement between the depending end of and the remainder of said tubular parison in the parting plane of said die members while said parison is still pliable first in a direction lateral to the tubular axis of said parison as downwardly extruded and then in an upward direction generally opposed to the tubular axis of said parison as extruded to cause said parison to sag into a loop intermediate its length into the general shape of the arcuate portion of the article to be formed and to cause it to have a straight portion having the general shape of the straight portion of the article to be formed into which the arcuate parison portion leads;
• shifting said die members while parted to a position flanking the arcuate and straight portions of said parison and then closing said members with said arcuate and straight parison portions lying inside said mold cavity;
• severing said enclosed arcuate and straight portions from the remainder of the parison and shifting said closed die members away from the region where it would interfere with the continued extrusion of the remainder of the parison;
• introducing a blow molding duct into the severed end of the parison in said mold cavity to provide fluid communication with the parison interior;
• introducing fluid under pressure through said duct to force the parison walls outwardly into contact with the surface of said mold cavity;
• parting said die members after the plastic has cooled sufficiently to rigidify;
• and
• stripping the molded tubular article from said die members.