方管断面设计时要考虑两个主要因素：一个是断面的安全性；另一个是断面的经济性。为了断面安全，我们要求H型钢的腰厚与高度之比应不小于1/45。对作柱用的H型钢，是用扭转半径与其质量之比来表示其经济性。性理论用来计算静态结构，如仓库、房屋、桥梁等是可行的，但对运动构件如车轮等就不太适用，这时人们往往采用塑性理论。它主要用于静载荷平面梁和受到弯曲应力的框架结构，其要求如下：对于高层建筑，还需要进行更细致的计算。塑性设计方法在动载荷情况下，通常是按许用应力不小于动载荷再乘以许用应力的安全系数的方法进行许用应力的计算。在一个轴受弯曲的情况下，可用公式a=W动/W许进行计算。用塑性方法代替性方法计算强度，可以提高构件的承载能力14%。

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%.

由于方管成型在机组设备和冷弯工艺上有着共同性，模辊的组合化是生产标准化，系列化型材的必然选择。这几年国内机组上组合模辊发展很快，也出现了许多技术创新，大大降低了模辊投入成本，提高了机组效益。可是基本上是对原有模辊的局部改进，加了一些垫圈，组合方式缺乏科学性，结构大同小异，换辊时间长。

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.