All-Russian Scientifi c and Research Institute of Tube Industry - RosNITI (Chelyabinsk, Russia):

Vydrin A. V., Dr. Eng., Prof., Deputy General Director on Scientific Work, e-mail: vydrinav@rosniti.ru
Chernykh I. N., Scientific Researcher, e-mail: chernyh@rosniti.ru

Longitudinal mandrel rolling of seamless tubes is conducted in the stands with grooved rolls. So-called “classic” roll pass design (with oval or round reduction area and radial or straight groove flank) is used for tube rolling in the modern mills. Pass shape and deformation procedure have eff ect on precision of tube wall thickness in its cross section and on origination and transformation of surface defects. Deformation of tube shape in the cross section perimeter of deformation area in a single stand occurs in equal conditions. Longitudinal rolling of lead billets on floating mandrel has been conducted using experimental unit. Artificial defects of cylindric form have been applied on surface of the billets, and these billets have been rolled in two passes. Different combinations of roll pass designs have been used; deformation procedures (elongation coefficients), typical for roughing stands of modern tube rolling mills have been applied. The scheme for processing of experimental data has been
proposed and deformation non-uniformity, variation of wall thickness along the line of pass split and relative wall thickness deviation were examined. The relationship between wall thickness variation along pass split line was obtained. Transformation of defects (variation of square, length and orientation of defects relating to the rolling line) in the areas along the perimeter of deformation area were researched. It was shown that actual elongation coeffi cient in the pass and deformation procedures in the concrete deformation area are the determining factors for transformation of defects, independently to pass kind. Relation between reduction in deformation area has also the effect on transformation of defects in the out-of-contact area and on variation of wall thickness along split line.

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