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What is a Roll Bender?

By Mal Baxter
Updated: May 17, 2024

A roll bender is a piece of equipment that curves tube and pipe with larger center line diameters. It does this by means of opposing rollers, in which a pipe is slotted through and worked back and forth, until the desired curvature is obtained. Typically, the pipe is fed through three rollers in a trianglular arrangement; the arc of the circle is determined by adjustment to a third opposing roller. These machines come in sizes from table top to heavy machinery. Some are hand-cranked, and others offer digital control in order to repeat jobs in production processes.

A pipe, extrusion, or other solid material passes through the roll 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 rollers usually complete the task. Double pinch machines provide adjustable rolls against a fixed upper roll, while initial pinch types require the alternate bending of pipe ends. The equipment generates slight arcs to coils and circles in various schedules and lengths of pipe.

Techniques for operating a roll bender must take into account pipe material to allow for the pressures needed to produce the desired arc. Geometric arrangement creates a cubic polynomial, which approximates an arc between the rollers and section of pipe where force is applied. The resulting plastic and elastic deformation is mitigated by a spring-back effect after leaving the rollers. This is indicated by a given material's elastic compliance relative to its ductility, that is, the inverse of its stiffness. Some metals have higher ductility to elasticity ratio and are more easily shaped.

While bending remains a gradual process, advances in machine capacities increase production speeds. How effectively a roll bender will handle stock thicknesses and gauges of material depends upon the interaction between machine power and stiffness of the material. This equipment is capable of converting metal sheets into cylinders and cones of varying elliptical degrees. Round, square, or rectangular pipes, angle iron, and flat tubing can all be manipulated through this workpiece.

The proper roll bender for a given process is indicated by several key factors. These include projected thicknesses, widths, and tolerances of the target material. Minimum desired diameters also factor in, as small-diameter tubes can harden in multi-pass rolling.

Size of the bending rolls is determined by the yield point ranges of material and the force needed to deform them. This can also be affected by the face of the bend; rectangular tubing can be bent the easy way, along its flat side, or the hard way, along its narrow edge. In production processes, it is also necessary to assess the scope of production runs and job completion times.

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