CALCULATION OF PARAMETERS OF THE ASYMMETRICAL THREE-ROLLER SHEET-BENDING ROLLS IN STEEL PIPES PRODUCTION

Abstract

To produce articles of various confi guration from the metal sheet, a variety of devices are used. One of them is the sheet-bending rolls, which can be classifi ed according to several characteristics: number of rollers (two-, three- and four-rollers), type of the drive (mechanical, pneumatic, electromechanical and hydraulic) and by mutual arrangement of the rollers (symmetrical and asymmetrical). The three-roller sheet-bending rolls are used for the manufacturing of cylindrical, oval and conical shapes by bending of sheet’s metal. Using them, we produce pipes, gutters, air condition lines, shells, barrels and all kinds of covers. The working principle of the threeroller sheet-bending rolls is based on the oppositely directed rotation of the rollers, whereby the grip of the sheet material and bending by a given radius are taken place. To facilitate the sheet feeding and the extraction of products, bent into a closed circle, the three-roller sheet-bending rolls are equipped with the removable and adjustable to clamp front shaft. In the three-roller mill the upper roller’s diameter is about 1.5 times larger than the lower rollers’ diameter. In the process of forming, the rollers are making the reverse movement during which the upper roller may be raised and lowered to adjust the diameter of the moldable workpiece. In this shaping method the extreme small parts of the sheet remain fl at. This defect is eliminated by the bending of billet’s ends at the press or at the rolling mill. In this paper the mathematical method for determining the forces and bending moments at the cold bending of thick steel sheet on the three-roller sheet-bending rolls is proposed. The calculations allow us to determine the support reaction of rollers, residual stresses in the wall of the steel sheet, the proportion of plastic deformation on the sheet thickness and relative deformation of the longitudinal surface fi bers of the sheet under bending depending on the rollers’ radius, pitches bet ween the rollers, magnitude of the sheet reduction by the upper roller, the sheet thickness, as well as the elastic modulus, the yield stress and the hardening modulus of sheet’s steel. The research results can be used at the metallurgical and machine works in production of steel largediameter pipes for main pipelines.