How to control the forming of welded pipe?

1. Weld gap control of welded steel pipe
The strip steel is sent to the welded pipe unit, and after multi-roll rolling, the strip steel is gradually rolled into a round tube billet with openings and gaps. Adjust the reduction amount of the extrusion roller, control the gap of the weld seam at 1~3mm, and make the two ends of the weld seam flush. If the gap is too large, the proximity effect will be reduced, the heat of the eddy current will be insufficient, and the intergranular bonding of the weld will be poor, resulting in lack of fusion or cracking. If the gap is too small, the proximity effect will be increased, and the welding heat will be too large, causing the weld to burn. Or the weld seam forms deep pits after extrusion and rolling, which affects the surface quality of the weld seam.

2. Welding temperature control of welded pipe
The welding temperature is mainly affected by the high-frequency eddy current thermal power. For low carbon steel, the welding temperature is controlled at 1250~1460℃, which can meet the penetration requirements of 3~5mm pipe wall thickness. In addition, the welding temperature can also be achieved by adjusting the welding speed. When the input heat is insufficient, the heated weld edge cannot reach the welding temperature, and the metal structure remains firm, forming incomplete fusion or incomplete penetration. When the input heat is insufficient, the edge of the heated weld seam exceeds the welding temperature, resulting in overburning or droplet, which makes the weld seam form a fusion hole.

3. Control of extrusion force
After the two sides of the tube blank are heated to the welding temperature, under the extrusion of the extrusion roller, the metal grains formed together penetrate and crystallize each other, and finally form a firm weld. If the extrusion force is too small, the number of eutectics formed is small, the strength of the weld metal decreases, and cracks occur after stress. If the extrusion force is too large, the metal in the molten state will be squeezed out of the weld, which will not only reduce the strength of the weld, but also produce a large number of internal and external burrs, and even cause defects such as welds. welding ring.

4. Adjustment of the position of the high-frequency induction coil
The high frequency induction coil should be located as close as possible to the extruder. The induction coil is far away from the extrusion machine, the effective heating time is longer, the heat-affected zone is wider, and the weld strength is reduced. On the contrary, the edge of the weld is not heated enough, and the shape is poor after extrusion

5. There will be weld scars after welding and extrusion, which need to be removed. The cleaning method is to fix the tool on the frame, and scrape the weld marks flat by the rapid movement of the welded pipe. Burrs inside the weld.
Pipes are generally not removed.