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Common surface defects of welded pipes in second-hand large welded pipe mills

Common surface defects of welded pipes in second-hand large welded pipe mills

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  • Release time:2021-09-01 10:18
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【概要描述】When the second-hand large-scale welded pipe unit is making welded pipes, pipe surface scars are common defects of welded pipes, and the actual expression forms are such as crushing, indentation and dark lines and scratches. The following is an explanation of the formation of surface defects of welded pipes.

Common surface defects of welded pipes in second-hand large welded pipe mills

【概要描述】When the second-hand large-scale welded pipe unit is making welded pipes, pipe surface scars are common defects of welded pipes, and the actual expression forms are such as crushing, indentation and dark lines and scratches. The following is an explanation of the formation of surface defects of welded pipes.

  • Sort:Solution
  • Auth:
  • Source:
  • Release time:2021-09-01 10:18
  • Pvs:
Detail

When the second-hand large-scale welded pipe unit is making welded pipes, pipe surface scars are common defects of welded pipes, and the actual expression forms are such as crushing, indentation and dark lines and scratches. The following is an explanation of the formation of surface defects of welded pipes.

 

Second-hand large welded pipe unit

 

Crush:

It refers to the damage of the roll pass of the second-hand large welded pipe unit to the surface of the tube blank. There are many types of crushing injuries, but the causes are nothing more than the following:

 

(1) The bottom line of the pass of a pair of rolls is adjusted higher than the bottom line of the rolling; the whole rolling line causes uneven undulations;

(2) The vertical roll is too tight;

(3) The vertical roll has an elevation angle;

(4) The new hole pattern may be that the edge chamfer of the hole pattern is too small or the chamfer angle does not meet the requirements;

(5) The high-strength blank tube has large resilience, large deformation and friction resistance, and the edge of the hole pattern is very easy to "bite" the tube blank;

(6) The vertical roller in front of the flat roller does not exert enough lateral force on the tube blank, which causes the wider tube blank to enter the flat-roll pass of a fixed width, and the tube blank is "sheared" by the pass;

(7) The flat roll is low, causing the tube blank to be crushed by the lower edge of the vertical roll pass;

(8) The vertical roll deviates from the rolling center line, causing the tube blank to be crushed in the flat roll.

 

Indentation and dark line:

Indentation and dark lines are actually the product of crushing, and the principle of generation is basically the same. Only the main performance is more subtle. It is invisible without careful observation and the touch is not obvious. However, they have a dangerous impact on the quality of the surface of the welded pipe. Have.

 

The indentation usually appears as a 5-10mm reflective tape, which is especially obvious when looking at the light source. The refractive index of the light at the indentation is different from other positions.

 

The essence of the dark line is that the linear scars produced in the front were not found in time, and were "flattened" by the subsequent rolls. Roughly, there is no problem; but carefully check it carefully, wipe it with sandpaper, and use your fingernail to trace the tube surface circumferentially, or you can see or feel the existence of dark lines. Dark lines are more concealed and difficult to detect than indentations.

 

Second-hand large welded pipe unit

 

Scratch:

The key is the damage caused to the tube blank in the process by the rollers that do not move or the relative speed difference is large, and the characteristic is related to the speed difference. For example, the vertical roller bearing is damaged, which causes the vertical roller to rotate and scratch the pipe surface; the linear velocity of the rolling diameter position on the pass is different from the linear velocity of other parts, and the position with a larger speed difference is compared with the moving forming tube blank. There is a certain relative movement between them, and the pipe surface will be scratched after the friction reaches a certain level. The scratch feature of the former is that there is a straight vertical line on the tube surface; the feature of the latter is that there are irregular arcs on the tube surface that are connected to each other like "nail marks". "Nail prints" mostly occur at the two edges, bottom and middle of the forming tube. The edge and bottom of the tube correspond to the position where the speed difference of the forming vertical roll is the largest, and the middle corresponds to the position where the speed difference of the forming flat roll is the largest .

 

The second-hand large-scale welded pipe unit realizes the removal of "nail marks", which can be solved from two aspects: hole type and adjustment:

From the perspective of pass design, without affecting the actual effect of the overall deformation, bold removal of the pass is not only harmless to the molding, but also can never cause scratches.

 

From the perspective of adjustment, if there are indentations under the vertical roll tube blank, reduce the vertical roll; if there are indentations on both sides of the flat roll tube blank, tighten the vertical roll before the flat roll or relax the flat roll appropriately. If there is an indentation on one side of the tube blank after exiting the flat roller, it should be calibrated to the center line of the vertical roller before the flat roller.

 

 

 

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