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Bending Process of Metal Cylinder with Plate Rolling Machine

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The plate rolling process is a process of continuous three-point roll bending of metal plates by means of a plate rolling machine.

4 steps of the plate roll bending process

Simply speaking, the coiling process can be divided into four steps

Pre-bending

Pre-bending, when the plate is rolled, there is a length at both ends of the plate that does not bend because it cannot contact the upper roller, which is called the unbend end flat. The size of the unbend end flat that cannot be bent is related to the structure and bending form of the bending machine (symmetric bending, asymmetric bending).

Adjust the metal plate position

The purpose of adjusting the position of the metal plate is to make the central axis of the metal plate parallel to the roller axis to prevent skew.

Roll bending

Roll bending processing is the main process of product forming, which is divided into two types: one-time feeding and multiple feeding. Rolling the thick plates is often used for multiple feeding. The number of feeds depends on process constraints (such as the maximum allowable deformation during cold rolling) and equipment constraints (such as non-slip conditions and power conditions).

Correct roundness

The final work is to correct the roundness of the roll forming. The purpose of correcting the roundness is to make the curvature of the whole circle as uniform as possible to ensure product quality.

Example introduction of plate rolling process of 3-roll plate rolling machine

Bending process - Plate rolling processing technology of short cylinder with diameter ≥400mm.

Metal sheet plate

The material must be confirmed according to the drawings and process requirements, and the surface of the material must not have obvious defects. The quality and specifications of materials shall comply with relevant national standards and industry standards.

Design requirements for plate rolling process drawings

  • When expanding the diameter, the diameter of the cylinder must be consistent with the actual diameter of the end shield, and the diameter of the cylinder material should be calculated according to the middle diameter of the cylinder.
  • The extended length direction should be the same as that of rolled steel, and the limit position is 45°.
  • The wiring should be reasonable, make full use of edge materials, and improve the utilization rate of steel.
  • When the cylinder is multi-stage welded, the welding seam should be reasonably configured according to the technical requirements of equipment assembly and welding.
  • The edge-arc spacing of the welded joints between the butt welds of the end shell and the longitudinal welds of the cylinder shell section should be greater than 3 times the thickness of the cylinder and not less than 100mm.
  • If the cylinder is connected to pipes, brackets, reinforcement rings, bottom plates, etc., the insertion relationship of the longitudinal and circumferential welds of the cylinder body should avoid the welding seam opening or be too close, and the reinforcement ring or bottom plate should cover the welding seam. Welds.
  • To draw lines accurately, vertical lines, bisectors, and bisectors should be drawn using geometric mapping, not a square master.
  • With the necessary margins, draw the edge cut line on the sheet metal first, then draw an actual material line and check the line.

Blanking line tolerance requirements

The line drawing tolerance requirement of the cylinder height H is: H±1mm

The difference between the two diagonals △L=L1-L2≤2mm, the length tolerance of the cylindrical section is L±3mm

Circumference formula: L=π(Di + S), where Di is the diameter of the cylinder (mm), and S is the thickness of the cylinder (mm).

After marking, make a material mark transplant in a 100mm×100mm box in the upper right corner of the steel plate.

Blanking and edge treatment

If the thickness of the carbon steel plate is less than 12mm, use shears as far as possible to cut the material (otherwise use semi-automatic cutting). After cutting, clean the slag and deburr.

When grooving is required, a semi-automatic cutting machine or chamfering machine should be used for plate thickness>6mm;

If the thickness of the plate is less than 6mm, the grinding method should be adopted.

The groove produced by the flame cutting machine should be cleaned of slag, and the welding groove should not have defects such as cracks and delamination. Oxides, grease, slag, and other harmful impurities on the surface of welded joints should be removed before welding.

Gap range (calculated from groove or edge of the plate) ≥ 20mm.

Bending Process of Metal Cylinder with Plate Rolling Machine

Check before roll bending

Before roll bending, the surface of the metal sheet must be cleaned, and the roller surface must not have rust, wool, edges and corners, and hard particles.

For example, when rolling stainless steel, the upper and lower rollers must be covered with a special layer of tape or paint, and the protective layer must not have hard particles.

Center align

When the metal sheet (plate) is put into the plate rolling machine, in order to prevent skew, the workpiece should be twisted, and the main line of the workpiece should be parallel to the roller axis to ensure the rounding quality.

Pre-bending

When the metal plate is rolled, each end of the plate has a length that can be unbent, called the unbend flat, because it is not in contact with the upper roller.

When section bending symmetrically, the remaining unbend flat is usually about half of the center distance of the lower roller, which is also related to the thickness of the plate.

The unbend flat of an asymmetrical bend is approximately 1/6 to 1/10 of the symmetrical bend.

This part of the residual unbend flat is difficult to completely eliminate during the calibration process, and it is easy to produce quality and equipment accidents, so it should be prevented.

If there is no prebend, you can use a template to correct it after the final roll.

Roll bending

Spheronization is the main process of product forming, which is divided into two processes: single-feed and multi-feed.

The number of feeds depends on the process (eg cold rolling does not allow to exceed the maximum allowable deformation rate) and equipment constraints (eg skid conditions and power conditions).

When the spring-back of the cold coil is obvious, a certain amount of overcoil must be added.

The longitudinal dislocation of the cylinder end is required to be less than 1.5mm.

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

Plate roll bending process

Roundness correction

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

In general, the steps are as follows:

Feeding

According to experience or calculation, the scroll wheel can be adjusted to the maximum correct curvature position.

Rounded

Roll the cylinder for two cycles under the corrected curvature, focusing on rolling the welding position, so that the curvature of the entire circle is consistent.

Unloading

Gradually reduce the load so that the workpiece can be rolled up several times with a reduced corrective load.