Patent ID: 7021106

Claim:
A plug tool for forming internally helically ribbed tube, comprising a plug including a plug body for being rotatably disposed in a die orifice of a drawing die and having a central longitudinal axis, a plurality of external grooves equally spaced about said central longitudinal axis, and a plurality of external lands in alternating arrangement with said grooves, each of said plurality of grooves terminating at a forward groove end and at a rearward groove end on said plug body, each of said plurality of lands terminating at a forward land end and at a rearward land end on said plug body, said grooves extending longitudinally along said plug body at a helix angle to said central longitudinal axis and closely corresponding to internal helical ribs formed in tubing drawn longitudinally over and relative to said plug body in a forward direction through the die orifice as said plug body rotates within the die orifice and the tubing, each of said plurality of grooves having a cross-section normal to said groove defined by a root surface and a pair of flank surfaces extending angularly outwardly away from one another from said root surface to land surfaces of adjacent ones of said lands, each of said pair of flank surfaces including a forward flank surface facing in opposition to the forward direction of draw for the tubing over said plug body and extending angularly outwardly from said root surface at an angle, and a rearward flank surface facing toward the forward direction of draw for the tubing over said plug body, said rearward flank surface extending angularly outwardly from said root surface at an angle less steep than said angle of said forward flank surface.