Attention point of cold bending of angle flanges

Angle iron is a common standard structural steel shape. Angles are L-shaped cross sections made by hot or cold rolling at the mill.

angle flanges
angle flanges

Cold bending is done on machines commonly called profile bending machine (also called angle roller or section benders) . These machines might have three or four rolls that induce the curvature of the steel sections as they pass through the tooling.

Angle iron has high strength, stiffness, toughness, and ductile properties. However, it does not actually bend very easily. The most natural way to bend an angle iron is apex in or out but most angle rings are rolled being in or out. What happens is that the bending causes the angle to twist. The reason is that the vertical leg of the angle is being bent the “easy-way” or like a belt, while the horizontal leg is being bent the “hard-way” like a washer. The twist is caused because the neutral-axis is somewhere between the two legs. All the material inside the neutral axis compresses while all material outside the axis stretches.

Angles can be used in agricultural equipment, pneumatic conveying systems, tank stiffeners, manholes, construction equipment, angle rings for ductwork, antenna or satellite housings, and also helical strakes. Angles can be rolled into rings in different orientations. They can be rolled leg-in (stiffeners), leg-out (flanges), apex-in (wheels), apex-out, off-axis and lastly helical (stringers or strakes).

Bending angle product is the angle ring. The majority of angle rings are also called angle flanges. Angle flanges are rolled leg out and are commonly provided with or without bolt holes.

All forming angle iron, regardless of scale, involves some kind of plastic deformation. Material expansion occurs on the outside surface of the bent angle, compression on the inside, and you need to know how to deal with both. The limits of material ductility will be the controlling factor for the minimum bend radius.

The strains associated with the plastic deformation when cold forming can cause the material to strain-harden. This can change the material’s mechanical properties in the area of the bend, where plastic deformation is occurring. At this point, ductility and resistance to fracture will need to be considered.

When bending thick angle iron, you need to abide by a minimum inside bend radius. This will minimize the effects of strain hardening and cracking at the bend.

A Simple Rule of Thumb
There’s a rule of thumb to determine a steel’s minimum bend radius: Divide 50 by the material’s tensile reduction percentage as specified by your supplier. This value will vary by grade.

If the steel has a tensile reduction value of 10 percent, divide 50 by that value: 50/10 = 5. Next, subtract 1 from that answer: 5 – 1 = 4. Now, multiply that answer by the plate thickness. If the material is 0.5 in. thick: 4 × 0.5 = 2. So in this case, the minimum inside bend radius is 2 times the material thickness.

Note that this is just a rule of thumb.