What is section bending?
Section bending, also called profile bending, is done in a wide variety of metals in various ways. There are two main processes – cold bending and induction bending, our machine is cold bending.
Cold bending is accomplished by passing the steel member back and forth between sets of rolls. The point load applied by the central roller is sufficient to take the steel past its yield point and introduce a permanent set.
We use a technique called cold rolling, also known as ring rolling to produce quality curved sections in a cost effective way. Large sweeping curves, varying radius curves, such as ellipses, tight bends, rings and coils, can be achieved for a wide range of sections and material types.
Cold rolling is a suitable technique for curving (rolling) structural steel sections, pipe and tube, and flanges where very tight radius bends or 'elbows' are generally not required. Applications cover a broad spectrum of industry, including; building, tunnels, bridges, civil excavations, architectural features, pipe and mechanical works for materials handling and storage, and machinery etc.
BIT section bending machine now have the leading capacity worldwide in section bending and gives customers the confidence to design structures with minimal limitations.
First of all, the curving of standard mill shapes—angles, bars, beams, channels, tees, pipe, and tube, are all part of section bending. It is also the case that aluminum extrusions, even extremely complex sections of aluminum, can be rolled and formed into a ring. Then there are steel sections that are cold formed; for example, an angle can be formed out of plate in a press brake and then bent to a prescribed radius. In this case, special tooling would be required to ensure that the two legs of the angle stay the same length throughout the bending process. Other steel sections that can be formed and then bent into a ring or ring segment include channels, outward wing channels, and inward wing channels. Section bending, therefore, comprises all types of profile bending. Steel tube bending is one of the most common types of profile bending.
Our profile bending machine models and bending dimensions
Our profile bending machine can bend up to the section modulus: 1700 cm3
To bend sections, there are two main processes – cold bending and induction bending. Cold bending is accomplished by passing the steel member back and forth between sets of rolls. The point load applied by the central roller is sufficient to take the steel past its yield point and introduce a permanent set.
The bending takes place between three points. As the diagram shows, no bending takes place until the section touches all three points or rollers.
Cold bending takes the material past its yield point which strain hardens the steel to some degree. Some of the yield plateau has to be used, so in general plastic design is not recommended. The toughness of the steel can also change, particularly at small radii. It is worth emphasising that at most radii found in structural applications, the changes are modest.
For normal low carbon steels and including structural steel, the strain induced during the bending process produces no real problems, as he material exerts the same elastic characteristics in the elastic range.
As mentioned, during the rolling bending process, the material must have exerted on it a stress greater than its yield strength or elastic limit. This is the maximum stress that the material can be subjected to and still spring back, or return to its original length. The yield point or elastic limits is shown as point ‘A’ on the figure below, a typical stress-strain curve. A stress less than the yield strength will not permanently bend the material. The amount of stress to apply to the material being bent is in area ‘C’, which is the plastic region. These lines show how, when the stress is removed, the material will spring back to a length somewhat smaller than when the stress was being applied.
The steel sections become work hardened when using the cold bending process. The amount of work hardening is dependent on the radius required and the geometry of the section. The results in a ‘flattened-out’ stress-strain curve as shown in the diagram above. A tensile test on a sample of steel that has been cold-roller bent will show a small loss in ductility, but a higher Ultimate Tensile Strength, which results in a loss of some ductility. Even though there is a loss of some ductility, for normal structural applications, the effect is minimal and can be ignored.
Often, the most important effects of the curving process are aesthetic, rather than structural. The steel on the outside of the curve tends to get stretched (and therefore thinner) whilst the steel on the inside of the curve tends to become thicker. There can be some visible distortion on sections caused by the bending process, for example with thin hollow sections, the bending process can cause visible ripples at small radii, therefore our expert staff will more that often advise when it is more appropriate to supply a thicker wall section to reduce the impact caused by the bending process.
Minimum radius and tolerance:
The minimum radius to which a section can be bent without any meaningful distortion depends on the section properties and bending methods being used.
As the years have gone by these minimum radii have been reduced as new techniques have been developed, so the minimum has continued to get smaller
Normal bending tolerances for single radius bends are in line with those specified in the National Structural Steelwork Specification.
It is not easy to provide a definitive and comprehensive list of the radii to which every section can be curved. There are large numbers or standard sections (each with different bending characteristics), there are different methods of bending (hot and cold), and the end-uses vary widely. Also, with continuing technical developments, ‘minimum radii’ also change.The minimum radius you need to bend is best to view our bending machine specifications before purchase.
In general, sections, tubes and hollow sections can be curved to single radius curves, to multi-radius curves, to parabolic or elliptical curves, or even to co-ordinates. They can also, within limits, be curved in two places or to form spirals. There are, however, a number of physical constraints which limits the degree to which three-dimensional curvature is possible in practical terms. It is important therefore, that any requirements for three-dimensional bends are discussed in detail at enquiry stage.
BIT section bending machine provides a uniquely comprehensive cold section bending service, providing the following decisive advantages:
Bending capacity to be able to handle the largest sections that can be produced in the mill
The world’s largest capacity range
Sections up to 35m long
The most advanced bending systems available
Any size order is achievable
Multiple bends possible
Faster and more energy efficient
BIT section bending machine can provide bending of standard angles, bars, beams, channels and tees and able to bend aluminum extrusions—even if it is a complex shape—in order to meet of customers needs. Ensure that bent sections maintain the radius necessary to successfully match your specifications.
Section bending has been used to create a large range of products, including microwave and other antennas.
Aluminum extruded sections can be seen in microwave, point-to-point antennas. Other complex aluminum sections are used as turrets for machine gun mounts on military equipment.
Formed channels can often be seen on the corners of the luggage conveyors at airports. Curved unistrut inward-wing-channel sections can be seen guiding the rollers holding up the curtains around a hospital bed or supporting hooks for shirts in a laundry. Curved formed angles can be seen as the base for tanks.
Other applications can include roller guides for holding up hospital bed curtains, supporting hooks for laundry or even the base of tanks.