Effective Precision Straightening of Thin-Walled Tube Metals

23 July 2019

Thin-walled tube metals are employed in a wide number of large-scale applications. Whether the tubes find their way into pipe networks or aerospace frames, they need to exhibit one key dimensional attribute. Long and gifted with a shaped cross-section of some kind, the thin-walled metal conduits must be straight as an arrow. And there’s the rub, for thinner metal tubes material have a habit of deforming, of sagging and bending.

Thin-Walled Metal Tubes Flex

Unless the alloy used to make metal tubing is super-hard, it’s going to sag. And that harder-than-nails structure wouldn’t exactly improve matters. Rigid and brittle, the tubing would probably fracture as soon as it was exposed to stress. No, when a slightly malleable metal tube is rolled into life, it’ll naturally sag. Depending on the alloy type, plus the thickness of the tube walls and its overall length, that bend quotient will become locked inside the material. That’s not an acceptable form, especially if the conduits are being installed on a framework that absolutely requires a high-tolerance fit. That aforementioned aerospace application is a patently obvious example of such precision-based dimensional tolerances. Placed in the centre of some advanced aircraft’s wing, a military contractor isn’t about to accept a group of badly warped metal tubes.

Let’s Straighten Matters Out With Heat

Even the manufacturing phase can impart problematic side-effects. If the rolled alloy used to fabricate thin-walled metal tubes doesn’t possess a uniform grain shape, it’ll warp. The bends and twists might be so small, so slight, that a visual inspection misses the defect, but a contractor’s quality assurance department won’t miss the deformation. A partially austenitized material backbone competes with cold worked stress. Alternatively, the rolling equipment has introduced a bend, or maybe there’s a thermal expansion problem that’s messing up the linear attributes of the tube. Whatever the reason, a normalizing heat treatment process can remove the undesirable dimensional imperfections. The same procedure homogenizes the metal grain so that the thin-walled tubing can exit the heat treatment chamber as a stress-free length of uniformly straightened tubing.

The cross-sectional geometry of a long, thin-walled tube can also severely worsen matters. If the metal is rolled into a circular form, the residual stresses are less likely. Rolled and formed into an extruded square, cold worked stress is considerably easier to accumulate. Then there’s the rolling machine, which can impart a bend. Thermal expansion effects and intergranular disparities are another two of the more troublesome deformation culprits. In any event, considering the number of high-tolerance applications for thin-walled metal tubing, tube straightening heat treatment services are in high demand.

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