Thin-wall welded pipes are mainly used for threading pipes, furniture pipes, transformer pipes, decorative pipes and so on. The used Φ76mm welded pipe units usually adopts the horizontal and vertical alternate arrangement and the hole pattern of the single radius circular deformation method. When producing thin-walled welded pipes and extremely thin-walled pipes, it is easy to produce strip edge waves and bulges, and the welding is very unstable, which is not conducive to Control the quality of thin-walled tube forming and welding.

Welding of thin-wall welded pipe

The welding of thin-walled pipes mainly includes irregular left and right dislocation of the weld, fine cracks and overburning.

The reasons for the dislocation of the irregular weld seam are in addition to the common factors such as the overturning of the forming tube, the excessive extrusion force, the swing of the squeeze roller caused by the central axis of the squeeze roller being stressed, and the height of the squeeze roller. Special attention should be paid to the used Φ76mm welded pipe units:

(1)The tube that exits the guide roller should be a flat oval shape. Because the vertical elliptical tube, or the tube with a high-up margin that is too large relative to the squeeze roller, will cause excessive pressure between the upper edge of the tube and the upper edge of the squeeze roller and become unstable, resulting in irregularities. The left and right are misaligned. The first solution is to appropriately increase the reduction in the closed hole to make the tube blank into a flat oval shape.

(2)The opening angle should be enlarged as much as possible. An elliptical tube with a larger opening angle can increase the friction on both sides of the squeeze roller, and at the same time, with the help of the partial rebound force of the opening angle, the edge of the tube can be kept stable in the squeeze roller, so as to avoid the dislocation of the welding seam. Therefore, when designing the pass, the allowance of the pass should be fully considered, and the guide blade should be wider.

(3) The lower edge of the squeeze roller should be slightly higher than the height of the rolling center line to achieve the purpose of increasing the pressure on the lower edge of the tube and reducing the pressure on the upper edge of the tube. The pressure rollers remain symmetrical and parallel to the left and right.

The main reasons for thin-walled pipes to produce fine cracks and overburning are:

(1)The closed hole blade scratches the edge of the tube blank, and the edge of the tube blank appears uneven whistle edge phenomenon, and cracks and cracks occur in the lack of meat.

(2)The influence of the edge shape of the slitting belt. When the edge of the steel strip is metal flowing downward, that is, when the two edges of the steel strip are bent down and enters the forming machine, the upper part of the weld is slightly insufficient. When the squeezing force is small, the welding is not good and it is easy to produce fine cracks.

(3) The opening angle is small. When the opening angle is small, the proximity effect is significant. Because the steel strip is thin, it is easy to produce reflow inclusion defects or over-burning.

In conclusion:

The main difficulty of the used Φ76mm welded pipe units to produce thin-walled pipes is the waves and bulges caused by the edge extension during forming, the dislocation of the weld seam, fine cracks and overburning during welding.

Through the use of W-shaped hole design, vertical roller set, and reasonable deformation distribution and adjustment technology, the forming and welding of thin-walled tubes can be well controlled.