The production of national standard spiral welded pipes generally adopts spiral welding forming, with commonly used shape transitions.
(1) Spiral inner hole transition method. The advantage of this method is that the mold design is convenient, and the outer mold can be made of a general round tube mold. Due to the consistency between the cross-sectional shape of the core rod and the shape of the finished inner hole, the preparation of the forming process is also extremely simple. When using this method for forming, the outer mold adopts a pre formed or tapered die with a small taper angle and a tapered shaft to improve the effect of inner hole forming. Its disadvantages are as follows.
National standard welded pipe product display pictures
① The shaft is subjected to high stress, making it difficult to produce spiral welded pipes with smaller inner diameters.
② In order to allow the shaft to enter the inner hole of the spiral welded pipe, the inner diameter of the deformation specification should be determined according to the diameter of the outer circle welded pipe on the clear surface of the finished inner hole. Therefore, the deformation specification is often chosen larger than other transition methods.
③ Due to the fact that the thick wall is in an empty state during the entire forming process, additional tensile stress is relatively high; The greater the amount of wall reduction, the greater the additional tensile stress, and even internal cracking may occur at thick walls. Therefore, in process design, the deformation should be appropriately reduced, the number of passes should be increased, and internal cracking should be prevented.
(2) The equal wall pipe transition method is generally used to produce national standard spiral welded pipes. Its advantages include good forming effect, the use of conical molds, increased single pass wall reduction, reduced deformation specifications and forming passes. The process preparation is divided into two steps. Firstly, the required cross-sectional size of the equal wall pipe is determined based on the shape of the finished product and the maximum wall thickness. Then, the deformation specification is determined based on the equal wall pipe process preparation.
(3) National standard spiral welded pipe transition method. When hollow drawing the national standard spiral welded pipe in a circular mold, the wall thickness changes very little, mainly due to plastic bending around the national standard steel pipe. The shape of the inner hole of the steel pipe after empty drawing is not quite correct, and it needs to be shaped by shaft drawing. This method is suitable for pulling thick walled small section internal welded pipes because the core rod of the shaping process has less force and can prevent internal cracking. But the process planning is more complex and there are many passes. When formulating the process, the required cross-sectional dimensions of the welded pipe are determined based on the shape and size of the finished product, and then the bending specifications are determined according to the national standard for spiral welded pipes.