In the flattening experiment of the second-hand welded pipe unit equipment, weld cracking often occurs. The formation of weld cracks can be divided into two types: positive pressure weld cracking and lateral pressure weld cracking. The following is for everyone to interpret the occurrence of weld cracks in second-hand welded pipe mill equipment.

(1) Cracking of positive pressure weld:

Refers to the flattening and cracking of the weld part and the direction of force on the same parallel line. The mechanism of positive pressure internal cracking of thick-walled pipe is: when the pressure is positive, the outer circle weld of the welded pipe is compressed, the inner circle weld is stretched, and the inside of the weld is easily cracked. The specific reasons are: excessive deformation of the edge of the tube blank, and the welding seam is in a ∧ shape for butt joint; the extrusion force is too small; the welding heat is not enough; the tube blank is hard, and the weld seam is easy to crack after bearing the force.

The main measures to eliminate the cracking of the positive pressure weld of the thick-walled pipe are as follows:

Appropriately relax the first forming flat roll (W plate hole, edge deformed hole pattern and comprehensive deformed hole pattern) and closed hole roller in the second-hand welded pipe unit equipment. In addition, the extrusion force should be increased during operation to increase the welding heat. And it removes the tube blank with too high hardness.

(2) Cracking of side pressure weld:

When the direction of the flattening force is 90° to the weld, the weld will be completely cracked, partially cracked or cracked. The cracking mechanism of the side pressure weld is just the opposite of the positive pressure. The surface of the side pressure weld is in tension, and the more it is pressed down, the smaller the radius of curvature of the weld position, and the greater the tensile stress of the weld surface, it is very It is easy to produce cracked welds and cause lateral pressure cracking.

The main measures to eliminate side pressure weld cracking are:

Increase the extrusion force and increase the welding heat; improve the forming quality, and strive to realize the parallel butt joint of the welds.

To do a good job in solving the weld cracking of the second-hand welded pipe unit equipment, the first thing to do is to find out the cause of the weld cracking before appropriately adjusting the forming flat roller and the closed hole roller to increase the large extrusion force and increase the welding heat to solve the problem.

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