To bend tubing that is rectangular is a more difficult process than round tube bending, (everything else being equal e.g. surface area, radius, wall thickness, and material type.) As with almost all bending, the tighter the bend, the more difficult the bend. The same holds true regarding wall thickness: the thinner, the more difficult, assuming the bending machine has the power to curve the thicker sections.
Unlike round tubing, however, rectangular tubing can be rolled off-axis as in the case of the Little Village Academy where the 14 x 4 x 3/8 rectangular tubing is rolled to inside radii from 17 to 21 ft. with a 10.9 degree pitch (pictured at right).
More commonly, rectangular tube is bent either the "hard way" (x-x axis) or the "easy way" (y-y axis). It is usually the case however, that even though more pressure is required to bend a tube the hard way, the resultant curved member is less likely to distort precisely because it is more rigid than a section curved the easy way. Easy way bending more likely will result in the inside diameter becoming somewhat concave.
Without the correct tooling, machinery, method and skilled operator, the bending of rectangular tubing can result in distortion, the most common of which is concavity on the inside diameter of the section. There are cases, however, where an OEM account wants significant concavity on the inside diameter because in certain applications the concavity makes the section actually stronger.
With the correct tooling, machinery and procedures excellent quality can be achieved even with tight-radius, thin-wall rectangular tube bending. For example, Chicago Metal Rolled Products has curved 16 x 8 x ½ rectangular tube the easy way to an 11ft inside radius. Over the years we have seen a significant increase in the use of rectangular tube bending in our work. The demand for bending aliminum round tubing has also increased.
We bend tube from 1 x 1/2 to 20 x 12 and virtually every size in between, using dozens of machines and hundreds of die sets to bend rectangular tubing. A variety of methods and techniques are used including rotary draw bending with mandrels, three-roll bending, four-roll bending, and compression bending. With these techniques, these machines, and this tooling, customers are seldom if ever given a tooling charge.
In addition to rectangular tube bending, we also do ancillary operations including saw cutting, drilling, and welding.
Bent rectangular tube is used in OEM applications like roll-over protection, framework, bumpers, and playground equipment. All kinds of structures now are built with rectangular tubes that are bent: roofs, trellises, canopies, arches, balconies, and portals. Like round and square tubing, rectangular tubing can be formed into a helix--most often for circular staircases.
Contact us for more information on metal tube bending.