Patent ID: 7550102
Filing Date: 2009-06-23
Classification: B23D,B26D,B29C,B29K,B29L,F16L

Abstract:
1. A method of making a substantially rigid, helically shaped, seamless, unitary, tubular structure comprising a helically shaped outer tubular member having an outwardly directed wall, a helically shaped inner tubular member having an inwardly directed wall that is radially spaced from said outer tubular member, and a plurality of helically shaped ribs disposed in an annular space between said inner and outer tubular members, wherein at least some of said ribs are in spacing and supporting relationship to said inner tubular member and said outer tubular member and wherein said structure as a whole and all elements thereof is a helically shaped seamless structure, said method comprising: melting a moldable material and extruding said melted material into a unitary, moldable extrudate comprising said moldable inner tubular member, said moldable outer tubular member, and a plurality of said moldable ribs, radially spacing said outer tubular member from said inner tubular member, disposing at least some next adjacent ribs and the portions of said inner tubular member and said outer tubular member intercepted by said next adjacent ribs so that together they form at least one helically shaped truss cell(s) having at least one of a trapezoidal and/or triangular cross section; molding said moldable extrudate into a helically shaped moldable tubular extrudate; moving said moldable extrudate in a downstream direction; applying circumferential drive to an outer surface of said extrudate such that the combination of said downstream and circumferential drives cause said extrudate to move downstream along a substantially helical path; simultaneously passing said helical shaped, moldable extrudate about internal and external sizing and cooling zones that provide sufficient cooling to solidify said extrudate as a helix; juxtaposing an inner surface of said inner tubular member with a cooling element, comprising a solid mandrel disposed within said inner tubular member for a time sufficient to cool and solidify said inner tubular member as well as a portion of said rib elements adjacent to said inner tubular member; substantially simultaneously passing said helically shaped, moldable extrudate through an external cooling means proximate to an outer surface of said outer tubular member; disposing said external cooling means and the outer surface of said outer tubular member within a cooling sleeve for a time sufficient to freeze and solidify said outer tubular member as well as a portion of said rib elements adjacent to said outer tubular member; causing said internal cooling mandrel and said external cooling means to be in simultaneous cooling relationship with said inner surface of said inner tubular member and said outer surface of said outer tubular member, respectively, until the helical inner tubular member, the helical outer tubular member and the helical rib elements have all solidified; configuring said cooling mandrel and said cooling sleeve with lengths that correspond to the time it takes for the molten helically shaped tubular article to become cool enough to be self supporting; passing cooling fluid through said extruder and at least some of said truss cells in an amount sufficient to enable said at least some truss cells to communicate with ambient fluid outside said extruder and to cool and solidify at least part of at least some of said rib elements; rotating said cooling mandrel and thereby rotating said helical inner tubular member and said helical outer tubular member relative to each other at angular velocities such that the angles said rib elements make with respect to said inner tubular member and said outer tubular member, respectively, are substantially the same when said extrudate is moldable as well as after said extrudate has been cooled and solidified; and carrying out said method under conditions such that the outer cross sectional diameter of said solid unitary helically shaped structure is not substantially larger than the outer cross sectional diameter of said moldable extrudate.