In the production of high frequency welded pipe machine, the forming joint state of the tube blank directly affects the quality of the weld, and the parallelism of the butt surface of the welded joint is particularly important. In the process of seam welding of steel pipes, the parallelism of the seam is mainly ensured by adjusting the reduction amount of the upper roller of the squeeze roller and the gap between the two upper rollers.

1. The hole type characteristics of the welding extrusion roller

The hole radius of the upper extrusion roller of the welded extrusion frame is about 10% larger than that of other extrusion rollers. Therefore, a gap is generated between the outer surface of the upper extrusion roller and the ideal circular section of the steel pipe, which is commonly known as "Heel Gap".

In actual forming, the section of the steel pipe cannot be an ideal circle. In the general case of high frequency welded pipe machine, due to insufficient deformation of the edge of the strip, the section is likely to be peach-shaped.

If the upper squeezing roll adopts the same hole radius as other squeezing rolls, when the V-shaped seam is eliminated by adjusting the reduction amount of the upper squeezing roll, the outer surface of the upper squeezing roll will be strongly pressed against the surface of the steel pipe It is easy to cause scars on the pipe surface and form a more serious V-shaped seam.

Therefore, the setting of "heel gap" is to effectively eliminate the V-shaped seam phenomenon by adjusting the reduction amount of the upper extrusion roller according to the actual characteristics of the tube blank forming. The position and shape of the "heel gap" are shown in Figure 1.

2. Adjustment method of the upper squeeze roller

When the position of the squeeze roller is set according to the standard hole pattern, if it is found that the forming seam is V-shaped, the pressing amount of the upper squeeze roller can be adjusted within the range of "heel gap". The adjustment method is shown in Figure 2. 

The limit of the reduction amount of the upper squeeze roll is that the outer surface of the upper squeeze roll causes a shallow indentation on the surface of the steel pipe. As a rule of thumb, when this reduction limit is reached, a parallel (I-shaped) formed seam is usually formed, even with higher strength tubing.

When the high frequency welded pipe machine applies the above experience, the gap between the two upper squeeze rollers must be set strictly according to the design value. A change in this gap will directly cause a change in the "heel gap". If the gap is not strictly set according to the design value every time the roll is changed, it is difficult to achieve reproducibility in the adjustment of the hole pattern.

For the same reason, when performing asymmetric adjustment of the top roll to eliminate misalignment, be sure to adjust only the top roll on the console side, and keep the top roll on the other side fixed as a reference. If the upper rollers on both sides are adjusted arbitrarily, the gap between the upper rollers may be gradually moved away from the set value.