What are the methods for cutting spiral welded steel pipes

Currently, the most common method for cutting spiral welded steel pipes is plasma cutting. This process generates a large amount of metal vapor, ozone, and nitrogen oxide fumes, severely polluting the surrounding environment. The key to solving the fume problem is how to completely draw the plasma fumes into a dust collection device to prevent air pollution.

However, the difficulties in dust collection during plasma cutting of spiral welded steel pipes are:

1. Cold air from outside the machine's gaps enters the suction inlet at a large volume, making the total amount of fumes and cold air inside the spiral-welded steel pipe exceed the effective airflow of the dust collector, thus making complete absorption of the cutting fumes impossible.

2. During cutting, the plasma gun nozzle blows air in two opposite directions simultaneously, causing fumes to escape from both ends of the spiral welded steel pipe. The suction port installed in one direction on the spiral welded steel pipe is unlikely to effectively collect the fumes.

3. Because the part of the spiral welded steel pipe being cut is far from the dust collection suction inlet, the airflow reaching the suction inlet is insufficient to remove the fumes.

Therefore, the design principles for dust collection hoods used in spiral welded steel pipe cutting are as follows:

1. The air volume drawn into the dust collector must be greater than the total amount of fumes and dust generated by plasma cutting and the air inside the pipe. This should create a certain amount of negative pressure within the spiral welded steel pipe and minimize the entry of large amounts of outside air to effectively draw the fumes into the dust collector.

2. The fumes should be blocked after the cutting point of the spiral welded steel pipe. Cold air should be prevented from entering the spiral welded steel pipe at the suction inlet as much as possible. A negative pressure chamber should be created inside the spiral welded steel pipe to prevent fumes from escaping. Crucially, the fume-blocking device must be reliably designed and manufactured, not affecting normal production, and easy to use.

3. The shape and installation location of the suction inlet. To achieve the desired effect, the suction inlet must draw in a significant amount of fumes and dust from inside the spiral welded steel pipe. Adding a baffle after the plasma gun cutting point will trap the fumes and dust inside the spiral welded steel pipe, allowing them to be completely removed after a buffer period.

Specific measures for cutting spiral welded steel pipes: Install a dust baffle on the internal trolley of the spiral welded steel pipe, positioned approximately 500mm from the plasma gun cutting point. Pause briefly after the spiral welded steel pipe is cut to ensure complete dust absorption. Note that the dust baffle must be accurately positioned after cutting. Furthermore, to ensure the rotation of the trolley supporting the dust baffle matches the steel pipe's rotation, the angle of the trolley's wheels must be consistent with the angle of the inner rollers. This method can be used for plasma cutting of large-diameter spiral welded steel pipes with a diameter of approximately 800mm; for pipes with a diameter less than 800mm, where the dust cannot escape from the outlet direction, an internal baffle is unnecessary. However, an external baffle must be installed at the dust inlet of the forming machine to prevent cold air from entering.