A roll bender uses opposing rollers to bend pipes and tubes without deforming the cross section. The correct bender depends on material thickness, width, and tolerances, as well as desired minimum diameters and production runs. The size of the bend rolls is determined by the yield strength ranges of the material and the force required to deform them. Advances in machine capabilities increase production speed.
A roll bender is a piece of equipment that bends pipes and tubes with larger centerline diameters. It does this by means of opposing rollers, into which a tube is inserted and worked back and forth, until the desired curvature is obtained. Typically, the pipe is fed through three rollers arranged in a triangular arrangement; the arc of the circle is determined by the adjustment of a third opposite roller. These machines are available in sizes from tabletop to heavy machinery. Some are hand cranked and others offer digital control to repeat jobs in manufacturing processes.
A tube, extrusion, or other solid material passes through the bender repeatedly in a bending process that gradually alters the axis of the material. This process preserves the integrity of the pipe without deformation to the cross section. Three or four reels usually complete the task. Dual-crimp machines provide adjustable rolls against a fixed top roller, while initial-crimp types require alternating crimping of the tube ends. The equipment generates light coil arcs and circles in various schedules and tube lengths.
Techniques for operating a roll bender must take into account the pipe material to allow for the pressures needed to produce the desired arc. The geometric arrangement creates a cubic polynomial, which approximates an arc between the rollers and the section of pipe where the force is applied. The resulting plastic and elastic deformation is mitigated by a springback effect after exit from the rolls. This is indicated by the elastic compliance of a given material relative to its ductility, i.e. the inverse of its stiffness. Some metals have a higher ductility-to-elasticity ratio and are more easily shaped.
While bending remains a gradual process, advances in machine capabilities increase the speed of production. How effectively a roll bender will handle stock thicknesses and material thicknesses depends on the interaction between machine horsepower and material stiffness. This equipment is capable of converting sheets into cylinders and cones of varying degrees of ellipticity. Round, square or rectangular, angled and flat tubing can all be manipulated through this piece.
The correct bender for a given process is indicated by several key factors. These include the expected thicknesses, widths and tolerances of the target material. Desired minimum diameters are also taken into account, as small diameter pipes can harden in multi-pass rolling.
The size of the bend rolls is determined by the yield strength ranges of the material and the force required to deform them. This can also be affected by the face of the curve; rectangular tubing can be bent the easy way, along its flat side, or the hardest way, along its narrow edge. In manufacturing processes, you also need to evaluate the scope of production runs and the time to complete jobs.
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