3 Roll Bending Machine: Working Principle and Rolling Process

With the rapid development of manufacturing, coal-fired power, hydropower, nuclear power and wind power encouraged by the national clean energy policy, also closely followed, pipeline and column tower parts processing needs of large complete sets of plate rolling machine;

Offshore oil and gas, petrochemical, coal chemical industry, heavy duty high pressure vessel product has become increasingly popular, thousand tons of hydrogenation reactor, two thousand tons of coal liquefaction reactor, 10000m3 natural gas spherical tank are widely applied, which make heavy duty plate rolls specialized for rolling thick plate and high strength plate become key equipment.

3 Roll Bending Machine Working Principle

Roll bending machine also been called rounder and roller machine, which is universal forming equipment for rolling metal plate into cylinder, cone, curved and other shapes.

According to the principle of three-point forming circle, the relative position change and rotational motion of the working roll make the metal sheet produce continuous plastic deformation to obtain the predetermined shape of the workpiece.

It is widely used in boiler, shipbuilding, petroleum, chemical, metal structure and machinery manufacturing industries.

See below figure, 3 roll bending machine usually take two lower roller as active roll, can realize positive and reverse rotation. One upper roller is a follower roll, can move vertically up and down.

Roll Bending Machine Structure

  1. Movable bearing seat
  2. Hydraulic cylinder
  3. Left frame
  4. Base
  5. Upper roller
  6. Lower roller
  7. Tie rod
  8. Right frame
  9. Hydraulic cylinder
  10. Fixed bearing seat
  11. Roller gear
  12. Reducer
  13. Motor
  14. Unloading device


When rolling steel plate, the plate is placed between the upper and lower rollers, and the three cutting points that are exposed to the metal sheet by three rolls can make the plate bend into a curved or closed circle.

Therefore, the forming process of sheet metal can be regarded as the three-roll bending machine to make a continuous three-point bending process.

During processing, one end of the metal plate is feed into three-roller plate between the upper and lower roller, and then top roller bring downward displacement on the metal plate, which make the plate under it generate a certain plastic bending deformation due to compression.

When the roller is rotating, there is friction between the plate and the roll, so when the roll is rotated, the plate also moves along its longitudinal direction.

Lower roller under positive &negative rotation alternately, and rolled plate move back and forth, two lower roller rotation and the friction drive plate and roller move.

Meanwhile, the upper roller continue to add downward pressure on roller, the upper roller move back and forth on the plate.

When the plate pass the bottom of upper roller (the roller deformation zone) in turn, and stress exceeds the yield limit, it will produce plastic deformation, plate obtained the plastic bending deformation along the full length, and processed into the required shape.

Adjust the relative position between the upper and lower rolls properly, and the plate can be bent to a radius not less than the radius of the upper roller.

The following is the working principle drawing of symmetrical 3 roll bending machine.

working principle drawing of symmetrical 3 roll bending machine

Driven roller Ⅱ, Ⅲ is driven by motor and reducer, which rotating in the same direction at the same speed (or in the opposite direction).

Because of the friction between the roller and the plate, the plate is driven forward and the roller is rotated.

Adjust the position of the upper roller properly, and the roll of different curvature of the plate can be made.

If the workpiece cannot meet the desired curvature after a rolling process, the upper roller can be reduced properly, and then make the reverse rolling again and again until it is rolled into the desired shape.

As can be seen from above figure, the three rolls of the symmetrical three roller bending machine are arranged in an isosceles triangle, so in the rolling process, the two ends of the workpiece are bound to leave a straight line.

The length of the straight-line segment is about half the distance of the center of the two lower rollers. This part of the straight line is the place where the roller cannot roll, which is the biggest disadvantage of the symmetrical three-axis roller.

Despite the disadvantages of the symmetrical three roller plate bending machine, it has been widely used because of its simple structure, convenient operation and low cost.

As for the problem of eliminating the straight-line segment, it can be solved by different methods in combination with the specific situation, as shown in the table below.

Elbow pre-bendingThis method uses the die to prebend two ends of the steel plate at the pressure machine to achieve the desired curvature.
Keep allowanceAdd appropriate plate allowance at plate ends. After the two ends roll out a certain length, then cut off the remainder (also known as the straight-line segment).
Add base plate for pre-bendingThis method is performed on the roll machine, as shown in figure 3b.

However, when this method is adopted, the ability of the rolling machine should be fully considered, that is, the sum of the bending force of the work and the required gasket should be less than that of the roll plate machine.

eliminating the straight-line segment method

For another asymmetric three roller bending machine, the arrangement of the shaft roller is designed to eliminate the straight line segments on the rolling workpiece.

The characteristics of such rolling machine are two lower roller can be adjusted vertically.

Any lower shaft roller can be adjusted to the center distance of the upper roller, and the other roller is raised to the appropriate position. The starting end of the steel plate can be bent and rolled.

After half roll, change the alignment of the two lower roller, continue rolling, and eliminate the straight line segment at the end of the workpiece.

The workpiece can also be turned around, the back end become front end for rolling, which can also eliminate the line segment.


3 Roll Bending Machine Rolling Process

The following is a brief introduction to the process of a short cylinder with Dg ≥ 400mm which will help you understand the rolling process of 3 roll bending machine.


Getting the material

The material must be confirmed in accordance with the drawing and process requirements, and the material surface shall not have obvious defects. The material quality and specification shall conform to the relevant national standards and industry standards.


Draw the line

When expanding, the diameter of the cylinder must be consistent with the actual diameter of the end enclosure, and the diameter of the cylinder material should be calculated according to the intermediate diameter of the cylinder.

Unfold length direction should be the same as that of steel rolling, limit position to 45 °.

The line should be reasonable, make full use of the edge material, improve the utilization of steel.

If the cylinder is welded by multiple sections, the weld shall be properly configured according to the technical requirements of equipment assembly and welding.

The welding joint edge arc spacing between butt welds of end enclosure, longitudinal weld seams of cylindrical shell section should be more than 3 times the thickness of the cylinder and not less than 100mm.

If the cylinder connect pipe, support, reinforcing ring, base plate, etc, the interpositional relation between the longitudinal and circumferential weld on cylinder should avoid hole opening on the weld seam or too close to it, and the reinforcing ring or base plate covered on weld seams.

The line drawing should be accurately, geometric mapping method should be adopted to draw vertical line, bisectrix and bisectrix instead of square master.

Set aside the necessary margin, draw edge cutting line on the metal plate first, and then draw actual material line and check the line.

Tolerance requirement for drawing line for blanking purpose:

Line drawing tolerance requirement of cylinder height H is: H±1mm

The difference between two diagonal lines △ L=L1 - L2 ≤ 2mm, length tolerance of cylinder section L±3mm

Perimeter formula:L=π(Di + S), in the formula, Di is the cylinder diameter(mm), S is cylinder thickness(mm).

After the marking, a material mark transplantation is made in the box of 100mm x 100mm in the upper right corner of the steel plate.

Blanking and edge processing:

Carbon steel plate thickness< 12mm, use shearing machine for blanking as far as possible (otherwise, use semi-automatic cutting), after cutting process, clean the slag, and deburring.

When the groove is needed, the plate thickness > 6mm shall be carried out by semi-automatic cutting machine or rolling chamfering machine;

The plate thickness is less than 6mm and the grinding method should be used.

Groove generated by flame cutting machine should clean the slag, the welding groove can not has the flaws such as crack, delamination. Before welding, the oxide, grease, slag and other harmful impurities on the surface of the welded joint shall be cleaned.

Clearance range (calculate from the groove or plate edge) ≥20mm.



When the plate is rolled, each end of the plate has a length can’t be bent due to none contact with the upper roller, which is called residual straight edge.

During symmetrical bending, the remaining straight edge is usually about half of the center distance of the lower roller, and it is also related to plate thickness.

The remaining straight edges of asymmetric bending are approximately 1/6 to 1/10 of symmetrical bending.

This part of the remaining straight edge is difficult to eliminate completely during the correction, it is easy to produce quality and equipment accident, so it should be prebent.

If there are no precurving, you can correct them with a template after the final roll.

Steel plate surface must be cleaned before bending, the roller surface must not have rust leather, wool, edges and corners, rigid particles.

For example, when rolling stainless steel, the upper and lower roller must be wrapped in a layer of tape or paint special layer, the protection layer must not have rigid particles.


Center alignment

When the plate is put into the roll plate machine, in order to prevent the skew, the workpiece should be twisted, and the workpiece main line should be parallel to the roller shaft to ensure the round rolling quality.


Rolling Circles

The circle rolling is the main process of product forming, which is divided into one feed and multi-feed process.

The number of feed times depends on the process (such as the cold roll is not allowed to exceed the allowable maximum deformation rate) and the equipment constraints (such as non-slip conditions and power conditions).

A certain amount of overwinding must be added when the spring back of cold roll is significant.

The longitudinal stagger of the cylinder end is required less than 1.5mm.

The rolling process of the plate is shown in below figure.

Schematic diagram of roll bending process

Roundness correction

The purpose of the roundness correction is to make the curvature of the whole circle as uniform as possible to improve the product quality.

Generally, the steps are as follows:

⑴ Feeding

According to experience or calculation, the roller can be adjusted to the maximum correct position of curvature.

⑵ Round rolling

Rolling the cylinder for two cycle under correction curvature, emphasize on rolling welding position to make consistent curvature of the whole circle.

⑶ Unloading

Gradually reduce the load, so that the workpiece can be rolled up several times under the reduced correction load.

2018-01-12T10:00:43+00:00 Rolling|


  1. Gowdru Manjunatha January 10, 2018 at 7:32 pm - Reply

    Hi sir/ mam. How to calculate the load required to bend a 6mm thick plate to get a 100mm diameter of shell, if the top roller has 80mm and the bottom rollers has the 70mm diameter. The distance between the two bottom rollers are 111mm. The bottom rollers are connected to a 2HP motor with gear arrangements running at 25rpm. The MS is a working plate material. Please answer it to me, if you can …

    • MachineMfg January 10, 2018 at 8:24 pm - Reply

      there is formula to calculate the rolling force as well as driven power, I will write this later, so keep following my blog post.

  2. Gowdru Manjunatha January 10, 2018 at 7:33 pm - Reply

    Please help me. I’m in problem of executing this ..

    • MachineMfg January 11, 2018 at 1:13 pm - Reply

      Pls check the newly updated blog post, it will help you.

  3. Can Berk Yucel March 21, 2018 at 9:55 pm - Reply


    Can I have this post as .pdf if it is possible?

    Best Regards.

    • MachineMfg March 22, 2018 at 8:56 am - Reply

      Why not save this page to your browser bookmark? It’s much more convenient for you to visit anytime and any place.

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