Asymmetric three-roller sheet-bending systems in steel-pipe production

Abstract

Various attachments are used to produce components of particular configurations from metal sheet. In particular, sheet-bending roller systems may be classified in terms of the number of rollers (two, three, or four); the type of drive (mechanical, pneumatic, electromechanical, hydraulic); and the roller configuration (symmetric, asymmetric). Three-roller systems are used for the production of cylindrical, oval, and conical components by bending the metal sheet. They may be employed to manufacture pipes, channels, airways, shells, barrels, and sheathes. The operation of three-roller sheet-bending systems is based on the rotation of rollers in opposite directions, so that the sheet is captured and bent to the specified radius. To facilitate sheet supply and the release of the products bent into closed circles, the three-roller sheet-bending systems are combined with a removable front shaft applying a pressure that may be adjusted. In the three-roller systems, the diameter of the upper roller is about 1.5 times that of the lower rollers. In shaping, the rollers perform reversible motion. The upper roller may be raised and lowered to regulate the diameter of the circle produced. In this approach, extremely small sheet sections remain flat. This problem is eliminated by bending the ends of the sheet in a press or in a roller mill. In the present work, a mathematical method is proposed for determining the forces and torques in cold flexure of thick steel sheet on three-roller sheet-bending systems. The calculations permit the determination of the reaction of the roller supports, the residual stress in the wall of the steel sheet, the proportion of the plastic deformation over the sheet thickness, and the relative deformation of longitudinal surface fibers of the sheet in flexure as a function of the roller radius, the roller spacing, the reduction of the sheet by the upper roller, the sheet thickness, the Young’s modulus, the yield point, and the strengthening modulus of the steel sheet. The results may be used at metallurgical and manufacturing plants in the production of large-diameter steel pipe for major pipelines.