There are two main factors to be considered in the design of square pipe section: one is the safety of the section, the other is the economy of the section. For the sake of section safety, the ratio of waist thickness to height of H-beam should be no less than 1/45. For H-section steel used as column, its economy is expressed by the ratio of torsion radius to its mass. Sex theory can be used to calculate static structures such as warehouses, houses and bridges, but it is not suitable for moving components such as wheels. At this time, people often use plastic theory. It is mainly used for static load plane beams and frame structures subjected to bending stress. Its requirements are as follows: for high-rise buildings, more detailed calculation is needed. In the case of dynamic load, the allowable stress is usually calculated by multiplying the allowable stress by the safety factor of the allowable stress. In the case of bending of an axle, the formula a=W/W may be used for calculation. By using the plastic method to calculate the strength, the bearing capacity of the component can be increased by 14%.
Because square tube forming has commonality in unit equipment and cold bending process, the combination of die roll is the inevitable choice for standardization of production and serialization of profiles. In recent years, the combined die rolls on domestic units have developed rapidly, and many technological innovations have emerged, which greatly reduces the input cost of die rolls and improves the unit efficiency. However, it is basically a partial improvement of the original die roll, with some washers added. The combination mode is lack of scientific nature, the structure is much the same, and the roll change time is long.
