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SECTION BENDING

Section bending also called profile bending, uses a section bending machine that is done in a wide variety of metals in various ways.

(The section rolling process bends the profile according to the principle of three points forming a circle.)

WHAT IS SECTION BENDING?

bending process
Cold Bending and Hot Bending Process

Section bending also called profile bending or section rolling, uses a section bending machine that is done in a wide variety of metals in various ways..
There are two main processes – cold bending and hot bending (induction bending).

Roll bending is the most common section bending process and plate roll bending process in cold section rolling of metal profile.

Video of section bending (aluminum and steel)

Cold section bending

The cold roll bending process (section rolling process) is a suitable technique for curving (rolling) structural steel sections, pipe and tubes, and flanges where very tight radius bends or ‘elbows’ are generally not required.

The cold roll forming process 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.

:: Read More :

The section bending process can be implemented in many ways. The section rolling process can only be realized by a section roller. The principle of roll bending is to form a circle at three points. The commonly used model is a three-roll section rolling machine.

Cold section bending is suitable for bending metal profiles

Profile bending machines (section rolling machines) use a technique called cold rolling, also known as ring rolling to produce quality curved sections in a cost-effective way.
Large sweeping curves, and varying radius curves, such as ellipses, tight bends, rings, and coils, can be achieved for a wide range of sections and material types.

  1. Bent Tube Profiles; Bent tube is used for numerous applications, from agricultural equipment to roof trusses. Section bending can bent round, square, or rectangular tubes in all sizes and materials
  2. Bent Pipe Profiles: Cold section bending process can bend pipe profiles with a diameter of fewer than 20 inches, work with most grades of carbon steel pipe and aluminum pipe, and can create custom profiles from both full and halfpipe.
  3. Bent Bar Profiles: Can create custom-bent profiles from bars in all sizes and shapes: round, half-round, square, hexagonal, and rectangular. Section rolling process can custom-bend metal bar the “easy way” (on the y-y axis) and the “hard way” (x-x axis) with equal precision.
  4. Bent Beam Profiles: Using the section rolling process can produce custom bent beam profiles of any size, creating even the largest bent beams with superior precision and repeatability. Section rolling processes are “the hard way” and “the easy way” bending methods.
  5. Bent Channel Profiles: the section bending process can bent channels with flanges out, flanges in, or “the hard way.”
  6. Bent Tee Profiles: Bent tee profiles “stem in,” “stem out,” or “stem up,” with minimal distortion, Its section rolling process is similar to ring rolling angle.
  7. Bent Angle Iron Profiles: The section rolling process can be ring rolling in nine orientations to custom-bent angle profiles with minimal distortion.
  8. Bent Steel Section Profiles: Complete section bending services, custom-bent profiles from standard mill shapes, and more.
  9. Custom Profiles from Rolled Plate: Accurately roll steel and aluminum plates into full cylinders, full cones, and cylinder cone segments, as designs require.

The roll bending (section rolling) of the section bending is used to conduct continuous three-point bending of the metal profiles to make the profile produce plastic deformation and reach the required bending radius.

The curving of profile bending machine (also called section bending machine, section rolling machine, or section bender) shapes—angles, bars, beams, channels, tees, pipe, and tube, are all part of section bending.

:: Read More: Glossary of common bending-rolling terms, taken from Design Guide 33.

How to bend a profile with an angle roll?

3-roller section bending machine is the main force of metal profile, the machine has two fixed rollers, while the upper vertical roller is positioned accordingly in order to complete the desired bending. By changing the relative position and rotating movement of the working roller, continuous plastic deformation is achieved in order for the workpiece to receive a predetermined shape.

Important reading:2021 update: Read before operation of profile bending machine

Bending process of profile bending machine
Bending process of roll cold bending

While bending, the workpiece is positioned between the lower and upper rollers of the section rolling machine. After placing the metal profile (bar, angle, h beam, tube and pipe, u channel) between the rollers, the upper roller is lowered to secure the workpiece, and at the same time, it has achieved sufficient pressure on the sheet, generating plastic bending. When rotating the roller there is friction between the metal profile and the roller, so the profile moves along its longitudinal direction. At the same time, the upper roller adds pressure to the workpiece.

When the roller crosses the lower limit of the upper roller (the roller deformation zone) in one turn and the pressure exceeds the bending limit, plastic deformation occurs and the sheet is folded to its desired dimensions by its entire length. By adjusting the relative position between the lower and upper rolls, the sheet can be folded to a diameter that is not less than the diameter of the upper roller.

In the picture above you can see the principle of the symmetrical circular section bending machine with 3 rollers.

Rollers 2 and 3 move in the same direction and at the same speed. Because of the friction between the sheet metal and the rollers, the workpiece moves in advance. By adjusting the position of the upper roller, the desired bending angle can be achieved. If the workpiece does not achieve the proper curvature after the first bending, it can be adjusted and started the process in the opposite direction until the desired shape is achieved.

How to reduce the end flat part of cold rolling profiles?

What is the flat part of a cold rolling bending?

After bending (section rolling) due to the position of the rollers on the workpiece inevitably remains a flat part at the ends of the metal profile. This flat part is approximately half the length of the gap between the centers of the lower rollers.

How to reduce it?

Although the appearance of a straight part is considered to be a flaw of a symmetrical roller with 3 rollers, their simple structure, comfortable use, and low price still make them the most wanted model of roll metal section bending machines.

In addition, there are methods which we can use in order to easily eliminate this problem. You can find some of them below:

Pre-bending

This solution involves bending the edges of the workpiece on a press brake or roll bender before the roll bending process.

If the metal profile ends can be bent prior to rolling, then no extra material is required. This process is called “pre-bending.”

Pre-bending can be done with a radius die in a press brake or done in a 3-roll or 4-roll section bending machine, plate roll. How thick a plate you can pre-bend is controlled by the maximum pressure that can be applied by the top roll of the machine.

More specifically, the capacity of an angle roll machine is defined by the maximum thickness and the minimum radius combinations that can be pre-bent for a given profile of maximum width. Pre-bending saves time. You do not have to cut then roll, cut then roll, etc. Pre-bending also eliminates flat spots and material waste.

Adding a “base” for the workpiece during the pre-bending

This method involves the installation of a “base” together with a workpiece designed for bending and performing the edge pre-bending process on the circular bending machine itself. The application of this method should take into account the possibilities of the circular bending machine and calculate the strength of the applied force on the “base” and the workpiece.

Leaving allowance at the ends – if you add appropriate allowance at plate ends before the bending, you can, after the bending, cut off those parts into a desired bending shape.

Asymmetrical model

Regarding the asymmetrical models of roll bending machines with 3 rollers, the position of the rollers is better adapted to eliminate the flat edges of the sheet, in which case the lower rollers can also be mounted vertically.

Thus, in a model with an asymmetric position of the rollers, the lower rotating roller can be lifted up to the middle of the gap between the two rollers, while the other can be positioned in the appropriate position so that the starting part of the metal profile can be folded to form a circle. The flat edge can be eliminated on both sides by turning the rollers in half of the bending process by folding the back of the profile. Additionally, the workpiece can also be turned around after completion of one bending cycle and then the back part will become the front and both flat edges will be eliminated.

5 points of attention for profile bending

  1. In the process of roll bending, the deformation mode of the metal profile is equivalent to that of free bending.
  2. The curvature of the roll bending part depends on the relative position between the rollers, the thickness of the metal profile, and the mechanical properties.
  3. Due to the existence of bending elastic recovery, the curvature of the roll bending part cannot be equal to that of the upper roller.
  4. The most important characteristic of the section rolling method is its strong versatility.
  5. Generally, there is no need to add process equipment to the section rolling machine, and only rollers suitable for different section shapes and sizes are needed for rolling bending of profiles.

Application of section rolling process

The applications for bent metal profiles are varied. Cover a broad spectrum of industry, including; building, tunnels, bridges, civil excavations, architectural features, pipe and mechanical works for materials handling and storage, machinery, etc.

  • Metal joinery
  • Construction metallers
  • Metal construction
  • Metal furniture manufacturing
  • Equipment for industrial facilities (chemical, petrochemical, pharmaceutical, food, etc.)
  • Manufacture of agricultural machinery
  • Equipment for railway, naval, military, nuclear, and energy sectors
  • Equipment parts for agricultural machinery,
  • rail, naval, military, nuclear, and energy sectors
  • Manufacture of parts for gates and fences
  • Manufacture of protective equipment parts such as rails, fences, handrails, bumpers, etc …
  • Manufacturing of urban furniture parts

How to choose the right profile bending machine

Before purchasing a new section rolling machine, must make a responsible assessment of their purchases.

Adding new equipment obviously requires cost considerations.
However, if the new equipment is not as productive as the old one, then the investment will be ruined.

According to a study, a considerable part of the procurement is ignoring the production capacity of the equipment and the impact of equipment maintenance, so that the newly added equipment cannot meet the production needs.

3 key points for choosing the right angle rolls

You can into the following 3 points for the reference in the procurement of profile rolling equipment:

  1. To determine the proper profile bending machine, it is critical that yield strength, thickness, and diameter (or radius) of the profiles are all considered because, for example, a higher yield or tighter diameter will require more pressure to form.
  2. When determining which section bending machine is best suited for the task one has at hand, it is important to research what each profile bending machine is designed to do, and to understand the materials that one will be working with. Manufacturers can usually provide detailed information about their machines, such as capacity and yield.
  3. Compare the manufacturer’s information about how much force a machine can produce and what kind of metals it is designed to handle, and compare this to your site’s mill certificates or other relevant information to see which section bending machine best fits your needs.

Of course, you can also choose a correct angle roller through the following methods:

section Rolling & Bending

Select the metal profile to be bent

Next, you will find relevant information, including the processing capabilities of different profile bending machines manufactured by BIT related to the project you care about.

What can BIT provide for profile bending?

BIT section bending machine now has the leading capacity worldwide in section bending and gives customers the confidence to design structures with minimal limitations. BIT can provide bending of standard angles, bars, beams, channels, pipes, tubes, and tees and is able to bend aluminum extrusions—even if it is a complex shape—in order to meet customers’ needs.

Our profile bending machine models and bending dimensions

Our profile bending machine can bend up to the section modulus: 1700 cm3

Section bending machine (Angle roll) with 4 rolls

In addition to machine tools for roll bending with 3 rollers, there are on the market machines for roll bending with 4 rollers. They offer quicker and easier management.

bending process of four-roll section bending machine
bending process of four-roll section bending machine

Principle

The principle of operation of the angle roll machine with 4 rolls is similar to the machine with 3 angle rollers, with the main difference being that the additional roller is used for better input of the material and execution of the process of pre-bending.

During bending, the upper and lower rollers are static, the material is firmly positioned between them, and the side rollers move and bend the material. In order to eliminate the flat edges of the material, the lower roller moves upward to hold the material firmly, and the side roller moves and occupies the position for pre-bending.

Unlike a section bending machine with 3 rollers, where during the pre-bending it is assumed that the material is lowered when entering the machine, in the rolling machine with 4 rollers, the material is positioned horizontally, allowing the use of motorized horizontal material holders when inserting materials in certain models. In addition, the input of materials can be carried out on both sides, so the machine can be placed next to the wall and save space.

Advantage

The advantage of a profile bending machine with 4 rollers has a unique complete bending process. The machine accepts the material in one stroke, performs the pre-bending, and continues to bend the profile. This system does not require an operator to remove, turn and then straighten the material after pre-bending, as is the case with 3-rollers section bending machines.

The material remaining in the machine makes the machine with 4 rollers up to 50% more efficient compared to 3-roller models and allows the material to bend at the desired diameter immediately after pre-bending. The bending of the flat edge starts after bending the material in one direction.

The side rollers are positioned to the left and to the right of the bottom roller and have their own axes. The independent axis of each roller allows perfect bending. The “rear” side roller (located on the other side of the material insertion) also has a rear end stop function and aligns the material. This feature allows the operator to work without the assistance of other people. Bending in the shape of the coupe is also possible on the machine with 4 rollers. The side rollers can be positioned in the corner for making the coupling and the bottom roller can be lifted to hold and position the material.

What is the principle of cold rolled section bending?

The most common profile roll bending process is the 3-roll roll bending process:

section bending process
Section Bending Process
section bending curving steel
section bending curving steel
Section Rolling Process
Section Rolling Process

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 plateaux have 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 emphasizing that at most radii found in structural applications, the changes are modest.

For normal low carbon steel and including structural steel, the strain-induced during the bending process produces no real problems, as the material exerts the same elastic characteristics in the elastic range.

Strain curve

As mentioned, during the rolling bending process, the material must have exerted on it 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. 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.

Ductility

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.

Visible distortion

Usually, the most important effect of the bending process is aesthetics, not structure. The steel on the outside of the curve tends to stretch (and therefore thinner), while the steel on the inside of the curve tends to become thicker.

The bending process may produce some visible deformation in the section. For example, the hollow section is thinner, and the bending process will cause visible ripples on a smaller radius. Therefore, our expert team will often suggest when it is better to provide a thicker The thickness reduces the impact caused by the bending process of the wall part.

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.

List of the BIT profile bending machine bend radii

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.

View our Specification page

Sections radius curves

In general, sections, tubes, and hollow sections can be curved into single radius curves, multi-radius curves, parabolic or elliptical curves, or even coordinates.

They can also, within limits, be curved in two places or form spirals.

There are, however, a number of physical constraints which limits the degree to which three-dimensional curvature is possible in practical terms.

View Tolerance Information page

Hot section bending

Hot bending generally refers to different types of induction bending. Hot bending is highly effective at bending pipes because they are fast, precise, and makes few errors.

induction bending h beam
induction bending H beam

The induction bending process, also known as high-frequency bending, incremental bending, or hot bending, uses inductors to locally heat steel by induction. This results in a narrow heat band in the shape to be bent. The shape is firmly held by a clamp at the desired radius, which is mounted on a free pivoting arm. The shape is pushed through the inductor by an accurate drive system which causes the hot section to form the induction bend at the set radius. The best part is then cooled by water, forced or still air to fix the bent shape.

Hot bending process of the section bending

Hot bending is generally only referring to different types of induction bending.

Induction bending is a highly effective way of section bending, as it is fast, precise, and with few errors. The induction bending process is performed by heating a certain point of the section up where it then can be bent without much effort. It doesn’t require any filler material and the result of the bending tends to keep distortion to a minimum.

Many induction benders have also chosen this type of bending because of its energy sufficiency. After the heating process has been done, the bending doesn’t take a lot of time at all.

Features of the hot section bending process

Induction bending is a very effective method of section bending because it is fast, accurate, and almost error-free.

The induction bending process is performed by heating a certain point of the metal profiles, which can then be bent effortlessly. It does not require any filling material, and the result of bending tends to keep deformation to a minimum.

Many induction bending machines also choose this type of bending because of its sufficient energy. The heating process is the most time-consuming element of the process, after the heating process is completed, bending does not require much time at all.

Advantages of the hot section bending process

The hot section bending process has the incomparable adaptability of cold bending.

  • For example, the straight line distance between two adjacent elbows on a pipe can be kept small, and even continuous bending can be carried out without leaving straight pipe sections;
  • Can process materials with poor cold ductility into elbows;
  • It can process elbows that require a lot of mechanical energy during cold bending and can bend brittle materials that are easy to break during cold bending. Hot bending can be bent into a small radius elbow on the pipe.
  • For carbon steel pipes and most alloy steel pipes, the bending radius of hot bending is much smaller than that of cold bending, and the bending radius can be as small as 0.7 to 1.5 times the outer diameter of the pipe.

Disadvantages of hot section bending

  • The downside of hot section bending may be that the material must be cooled later, increasing the time spent on each pipe, and the machines tend to be more expensive than cold section bending machines.
  • The negative aspects of hot section bending can be that the material does have to cool off afterward, adding to the time spent on each pipe and that the machines tend to be more expensive than cold section bending appliances.
  • The equipment is complex, the processing cost is high, the production efficiency is low, and the surface finish is poor.
  • For copper pipes, the cold section bending process is used, which eliminates the possibility of “hydrogen disease” due to the elimination of high-temperature heating.

Induction metal profile bending

Hot bending or induction bending:
While there are slight variances to different hot section bending methods, nearly all are a form of induction bending.

This method precisely heats the metal profiles using an induction heating coil before applying pressure to make the intended bend.

It requires much less physical force than cold bending methods and can produce bends of similar or higher quality with no filler materials, mandrils, or other additions used to avoid distortion.

What is induction bending?

Induction Bending is a precisely controlled and efficient section bending technique. Local heating using high frequency induced electrical power is applied during the induction bending process. Pipes, tubes, and even structural shapes (channels, W & H sections) can be bent efficiently in an induction bending machine. Induction bending is also known as hot bending, incremental bending, or high-frequency bending. For bigger pipe diameters, when cold bending methods are limited, Induction bending is the most preferable option. Around the pipe to be bent, an induction coil is placed that heats the pipe circumference in the range of 850 – 1100 degrees Celsius.

Induction bending metal

The induction bending technology allows the bending of an almost unlimited variety of materials.

The only requirement is that they can be heated by induction.

Common material groups are:

CARBON STEELS
  • Low alloyed steels
  • High alloyed steels
  • Fine-grain steels
STAINLESS STEELS
  • Austenitic
  • Martensitic
  • Ferritic
  • Duplex
OTHER
  • Special alloys
  • Clad pipe
  • Aluminum
  • Titanium

View processing capabilities all of our profile bending machines here