Analysis of the main causes of the deterioration of the quality of the bent pipe and the method of attention:

1. When purely bent, the outer wall of the inner layer of the inner layer is subjected to tensile stress &1 and thinned under the action of external force M, and the inner side is under compressive stress. The effect is thickened, and the combined forces N1 and N2 change the cross section of the tube. Based on this factor, the main cause of the deterioration of the bend quality is RX and SX. Therefore, in GBJ235-82, the RX value and the amount of external thinning under various pressure levels are clearly defined, in order to control RX. With the value of SX, thus ensuring quality.

2. As mentioned in the preceding article, when the material is bent, the outer side of the material is pulled, and the position of the inner pressed neutral shaft is different from the method of bending. In the top bending type (compression bending), the neutral axis is about 1/1 from the outer wall. At 3 places, the neutral shaft is at 2/3 of the outer wall when working in a turning (back bend). Therefore, the thin-walled pipe is curved, and it is advantageous to use the spin bending method.

3, the accuracy of the bending tire is also one of the factors affecting the quality of the bending tube. When manufacturing the bent tires, in addition to the specification and size requirements to be controlled within a certain tolerance range, the user is also required to select the corresponding bending tire according to the curved pipe diameter during use. 4. The bendability and surface corrosion of the pipe itself may also affect the quality of the pipe. During on-site construction, the operator also needs to know the material of the pipe being processed, the processing performance and the judgment of the surface corrosion.