Process for forming helical screw threads having a flank with zero or negative inclination
OwnerCharles Marcon, Jean Poullaininventors
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Abstract
A process for forming a helical screw thread comprising a flank with negative inclination on the wall of a rotationally symmetrical body (19) such as a metal pipe or tube. A first phase involves producing a screw thread having flanks with a positive inclination and then a second phase involves modifying the inclination of one of the flanks (24) by plastic deformation to make it negative (32). For that purpose, use is made of a roller (26) mounted on an inclined axis (X2--X2), which rolls against the flank of the thread.
Claims18
A process for forming on the wall of a rotationally symmetrical body, an inside or outside helical screw thread comprising a flank with zero or negative inclination, characterised by producing in a first phase, using a method such as machining, rolling or the like, a screw thread in which the flanks of each thread (23, 24) have positive inclination and then in a second phase, using a forming means, producing plastic deformation without removing material of the thread flank (24) which will be load-bearing in use, said deformation imparting a zero or negative inclination (32) to said flank.
In combination with a forming apparatus having means for causing the axis of a rotationally symmetrical forming roller to rotate with a relative helical movement around a rotationally symmetrical body for forming on the wall of a rotationally symmetrical body an inside or outside helical screw thread comprising a flank with zero or negative inclination, a rotationally symmetrical forming roller (26) having at least one substantially frustoconical forming zone operatively mounted on said forming apparatus with said frustoconical forming zone in deforming contact with the flank of the helical screw thread to be imparted with zero or negative inclination.
Dependencies are inferred from the claim text.