方管斷面設計時要考慮兩個主要因素：一個是斷面的安全性；另一個是斷面的經濟性。為了斷面安全，我們要求H型鋼的腰厚與高度之比應不小于1/45。對作柱用的H型鋼，是用扭轉半徑與其質量之比來表示其經濟性。性理論用來計算靜態結構，如倉庫、房屋、橋梁等是可行的，但對運動構件如車輪等就不太適用，這時人們往往采用塑性理論。它主要用于靜載荷平面梁和受到彎曲應力的框架結構，其要求如下：對于高層建筑，還需要進行更細致的計算。塑性設計方法在動載荷情況下，通常是按許用應力不小于動載荷再乘以許用應力的安全系數的方法進行許用應力的計算。在一個軸受彎曲的情況下，可用公式a=W動/W許進行計算。用塑性方法代替性方法計算強度，可以提高構件的承載能力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%.

由于方管成型在機組設備和冷彎工藝上有著共同性，模輥的組合化是生產標準化，系列化型材的必然選擇。這幾年國內機組上組合模輥發展很快，也出現了許多技術創新，大大降低了模輥投入成本，提高了機組效益。可是基本上是對原有模輥的局部改進，加了一些墊圈，組合方式缺乏科學性，結構大同小異，換輥時間長。

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.