The spiral steel pipe feeds the strip into the welded pipe unit. After rolling by multiple rollers, the strip is gradually rolled up to form a circular tube blank with an opening gap. 3mm, and make both ends of the welding joint flush.
1. If the gap is too large, the proximity effect will be reduced, the eddy current heat will be insufficient, and the intergranular bonding of the weld will be poor, resulting in unfused or cracked.
2. If the gap is too small, the proximity effect will increase, the welding heat will be too large, and the welding seam will be burned; or the welding seam will form a deep pit after extrusion and rolling, which will affect the surface quality of the welding seam.
After the two edges of the tube blank are heated to the welding temperature, under the extrusion of the extrusion roller, the common metal grains are formed to penetrate and crystallize each other, and finally, a firm weld is formed. If the extrusion force of the spiral steel pipe is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracks will occur after being stressed; if the extrusion force is too large, the molten metal will be squeezed out of the weld seam. It not only reduces the strength of the weld, but also produces a large number of internal and external burrs, and even causes defects such as welding laps.