Typically the metal surface will be accompanied by dust oxide corrosion layer of oil contaminants salt or old paint. Dense oxide layer is an oxide layer formed in the forging steel produced by high temperature, usually attached relatively firmly, but more brittle than the steel itself, and the cathode itself, will accelerate corrosion of metal. It do not remove these substances directly affect paint adhesion of the entire layer.
Spiral steel pipe in the actual construction, long-term contact with liquid, air, soil and other media, so it need to add a layer of protection for products on corrode the metal surface to prevent corrosion and prolong the life spiral.
Spiral steel pipe into the pipe unit, the multi-channel rolling rolls, gradually rolled strip, a gap is formed with a circular opening tube, squeeze rollers to adjust the amount of reduction, so that a gap control in ~ 3mm, and to weld the ends flush.
(1)If the gap is too large, resulting in reduced proximity effect, lack of eddy heat weld together indirectly arising crystal fusion or cracking are not bad.
(2)If the gap is too small, causing the proximity effect increases, excessive heat welding, weld cause burning; or weld extruded to form a pit after rolling, affecting the quality of the weld surface.
After heating the two edges of the tube to the welding temperature, the lower squeeze rollers squeeze the metal grains to form a common mutual penetration, crystallization, forming a solid weld. If spiral pipe extrusion pressure is too small, the crystal is formed on the small number of common weld metal strength decreases, the cracking force; if the pressing force is too large, will make the extruded molten weld metal, not only reduces the weld strength, and will generate a lot of internal and external burrs, and even cause the welding seam defects ride.
Post time: Sep-12-2019