Study On Welding Torch And Welding Technology Of Steel Pipe High Speed MAG Tack-welding

In the two-stage production process of spiral pipe, a continuous, thick-wire, large current, high-speed welding method is used at the first process stage. And the performance of welding torch and the quality of welding technology directly affects the efficiency of steel pipe production. Since the development of two-stage method is very late in China, few studies is related, so there are some questions urged to be resolved, specifically in the following areas. First, because the conventional welding torch is very easy adhered by spatter, the welding pool is poor protected and the bead quality can not be guaranteed. Secondly, the welding torch is hard to be cleaned, as there is no suitable way to be adopted. At last, as for the high-speed welding technology, the bead is prone to undercut and humping weld defects with the welding speed increasing. And because of the limitations of welding speed, the efficiency of steel pipe is seriously affected, which restricts the advantages of the two stage production process.In order to solve the problems above, this paper firstly analyzed the cause of the problem existed in conventional MAG welding torch. On the basis above, the welding torch was redesigned from the nozzle material and torch structure. Finally we got a new air-cooling MAG welding torch, which has the functions of preventing spatter adhesion and self-cleaning. Recently, the new torch has been successfully applied for patent in China. And it has also been widely used in the tack-welding process of spiral steel pipe. Make the efficiency of pipe production improved by 30% or more.In terms of high-speed MAG welding technology, the arc shape images were taken by Sony DSC-W290 and the photos of droplet transfer and metal flow of welding pool were taken by FastCam Ultima 512, together with the current and voltage waveforms were collected by high-speed data acquisition system. By analyzing these pictures and waveforms, this paper mainly focused on the undercut and humping bead formation mechanism.And then, the mechanism was proved by uphill and downhill welding. On the basis of above research, this paper analyzed the affection of welding parameters. And believed that low-voltage, large current, oxidizing gas and downhill welding can all these factors promote high-speed MAG welding get a fine weld. And under the guidance of the above conclusions, this paper obtained perfect bead under different welding speeds and achieved reliable welding not less than 5.5m/min for the welding speed. Now, some of the welding parameters have been provided to the steel pipe manufacturers, made a good production efficiency.