There are relatively many failures of used welded pipe units, and the causes of failures are also more complicated. Often, one result is caused by multiple reasons, or one cause can cause several results. Some failures are tricky to deal with. Let's start with a brief description of the scratch accident.

Scratch

The scratches of the tube blank in the used welded pipe units are mainly caused by two parts, ① scratches of the guide mechanism. ② the extrusion welding mechanism is scratched.

① Scratches of the guide mechanism

Scratches on the guide parts generally occur on both sides of the tube blank. If the guide structure with the guide sleeve is not properly adjusted, there will also be frictional scratches on the upper and lower surfaces of the tube blank. large and continuous. The main reason is that the height position of the guide sleeve is incorrect, or after the upper and lower guide roller bearings are damaged, the tube blank cannot be well controlled, so that it is formed after friction with the guide sleeve. In addition, when the guide roller deviates too much from the rolling center line, and the relative difference between the axes of the guide sleeve and the guide roller is too large, it will also cause scratches on both sides of the tube blank.

② The extrusion welding mechanism is scratched

The scratches caused by the extrusion roller mainly occur at the bottom of the tube blank, and the reasons are roughly as follows:

(1) The hole type does not match

Weld extrusion structures include two-roll, three-roll and four-roll. As long as the combined hole patterns do not match, it is easy to cause scratches on the surface of the tube blank, and the two-roll structure is particularly prominent. There are many factors that cause the hole pattern to not match. Take the two-roller structure as an example, such as bearing damage; axial movement of the roller; different hole size;

(2) Highly matched

The lower edge of the extrusion roll pass should be consistent with the height of the rolling line, while the height of the guide roll is determined by the wall thickness of the tube blank. If the height of the guide roller is reduced to a certain limit, the edge fillet of the squeeze roll pass will cause scratches to the bottom of the tube blank, especially after the R fillet of the squeeze roll pass is sharpened, the scratches will more likely to happen.

(3) Insufficient squeezing force on the squeezing roller

Especially for the two-roller structure of the extrusion roller device, when the upper extrusion force is insufficient, under the action of the tension of the tube blank, the roller shaft will have an upper elevation angle, so that the rounded corners of the edge R of the hole shape protrude, thereby causing the lower part of the tube blank. scratched. When the rounded corners of the squeeze roll hole type R are sharpened, the occurrence of scratching accidents will be aggravated.

The scratches of the tube blank in the used welding pipe units are mainly caused by two parts, ① the guiding mechanism and ② the extrusion welding mechanism. As a result, the extrusion welding mechanism can be divided into (1) the hole type does not match (2) height matches (3) insufficient squeezing force on the squeezing roller.