METHOD FOR MAKING SCREW JOINT Russian patent published in 1994 - IPC

FIELD: pipe manufacture. SUBSTANCE: following volumetric heat treatment and thread cutting the couplings are delivered to installation for surface machining by strips. Loop-type inductor-sprayer is applied to threaded portion, then heating and cooling are turned successively on and off. After the first strip the coupling is turned through an angle set by the width of hardened and nonhardened strips and the process is repeated, thus forming a series of strips on lock threads, said strips being arranged parallel to one another and uniformly around the circumference. Threaded end of pipe is delivered into inductor-sprayer so that basic plane of thread passes exactly through the middle of inductor-sprayer. Rotation of pipe, heating and cooling of its threaded end are carried out in succession. Low-temperature tempering is performed either on entire pipe or on its threaded end alone. EFFECT: higher efficiency. 1 tbl