Cutting method of thick wall spiral steel pipe

　　At present, the most common cut-off method of spiral steel pipe manufacturers is plasma cutting. When cutting, there will be a lot of metal vapor, ozone, nitrogen oxide smoke, which will seriously pollute the surrounding environment. The key to deal with the smoke and dust problem is how to inhale all the plasma dust into the dust removal equipment, and then avoid air pollution.

　　The difficulties of dust removal in plasma cutting of spiral steel pipe are as follows:

　　1. When the nozzle of the plasma gun is cut, the air blows out in two opposite directions together, and then the smoke and dust will come out from both ends of the steel pipe. However, it is difficult to recover the smoke and dust from the suction port installed in one direction of the steel pipe.

　　2. The cold air outside the suction port enters the suction port from the open space of the machine, and the air volume is very large, so that the total amount of smoke and cold air in the steel pipe is greater than the effective air volume inhaled by the dust remover, and then it is impossible to completely absorb the smoke and dust.

　　3. Because the cutting part is far away from the dust suction inlet, it is difficult for the wind force reaching the suction inlet to stir the dust.

　　Therefore, the design principle of dust hood is as follows:

　　1. The air volume inhaled by the dust remover should be greater than the total amount of dust and air inside the pipe caused by plasma cutting. A certain amount of negative pressure cavity should be formed inside the steel pipe, and the outside air should not be allowed to enter the steel pipe as much as possible, so as to effectively suck the dust into the dust collector.

　　2. The smoke and dust shall be blocked in the future direction of the steel pipe cutting point, and the cold air shall be avoided to enter the steel pipe at the suction inlet as far as possible. A negative pressure chamber shall be formed in the internal space of the steel pipe, so as to prevent the smoke and dust from coming out. The key is that the equipment for preventing smoke and dust shall be designed and manufactured firmly, which will not affect the normal production and be convenient for use.

　　3. The shape of the suction inlet and the position of the device. It is necessary to let the suction inlet suck more smoke and dust inside the steel pipe into the pipe to achieve the effect. A baffle is added in the future direction of the plasma gun cutting point to keep the dust inside the steel pipe, and the smoke can be completely sucked out after buffering for a period of time.

　　Specific measures:

　　The dust baffle is installed on the traveling car inside the steel pipe and placed at about 500mm from the cutting point of the plasma gun. After the steel pipe is cut off, the smoke and dust are completely absorbed. Pay attention to the accurate positioning of the smoke baffle after cutting. In addition, in order to make the traveling car supporting the smoke baffle consistent with the rolling of steel pipe, the angle of the traveling wheel of the traveling car must be consistent with that of the inner roll.

　　This method can be used for plasma cutting of large diameter spiral welded pipe with a diameter of about 800mm; when the diameter is less than 800mm and the pipe diameter is small, the smoke can not come out from the pipe outlet direction, so it is unnecessary to install internal baffle. However, there must be an external baffle to block the entry of cold air at the smoke suction inlet of the former.