Analysis of the main reasons for the decline in the quality of the bend pipe and the attention methods:
1. In the case of pure bending, under the effect of external force distance M, the outer arm wall of the pipe is thinned by the effect of tensile stress & 1 on the outer arm wall of the neutral layer, and the inner side is subjected to compressive stress. The result is thickened, and the combined forces N1 and N2 change the cross-section of the tube. Based on this factor, the main reason for the decline in the quality of the elbow is RX and SX. Therefore, in GBJ235-82, the RX value and the thinning amount of the outer side under various pressure levels are clearly stipulated, and the intention is to control RX. With the value of SX, then ensure the quality.
2. As mentioned in the previous article, when the pipe is bent, the outside of the material is pulled, and the position of the neutral axis under pressure on the inside is different from the way the pipe is bent. In the top bending (compression and bending) operation, the neutral axis is about 1/2 from the outer wall.
3. When working in the turning (return bending type), the neutral axis is 2/3 away from the outer wall. Therefore, the thin-walled pipe is tortuous, and it is beneficial to use the bending method.
3. The precision of the bent tire is also one of the factors that affect the quality of the bent pipe. In the manufacture of bent tires, in addition to the standard size required to be controlled within a certain tolerance range, we also require users to select the corresponding bent tires according to the bent pipe diameter during use.
4. The bendability and surface corrosion of the pipe itself may also affect the quality of the bend. During on-site construction, the operator also needs to understand the information of the processed pipeline, the processing performance and make judgments on the appearance of corrosion.
5. Now supply R. (Bending radius/pipe outer diameter) relationship curve (as shown in Figure 3), for users to refer to when selecting the relationship between pipe diameter and wall thickness. This figure focuses on reflecting the influence of the relative bending radius and relative wall thickness on the quality of the bent pipe. According to the acceptance criteria for pipe processing: the cold-formed steel pipe is 4D for medium and low pressure and 5D for high pressure. Therefore, our bending tire design is R=4D (determined in special cases), so as far as the pipe bending machine produced by our factory is concerned, it is mainly to select the relative wall thickness SX. The upper part of the figure is the area without a mandrel, and the middle part of the figure It is the general mandrel area, and the lower part of the figure is the special mandrel area. Because the design and manufacture of special mandrels are very difficult, and the operation is not convenient, so our factory generally does not supply them. Special circumstances can be negotiated separately.
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