TPT January 2021

AR T I C L E

Dalian Field

Impor tance of rigidity for complex CNC-CFS square-square pipe mill production By Gao Guowu, chief engineer, FD Machinery, China

Since the advent of the first CFS square-square pipe mill in 2000, FD has never stopped its research. The first generation CFS square-square pipe mill was manually adjusted. Figure 1 shows a CFS- I 20x20mm-60x60mm square-square pipe mill with wall thickness 0.8-2.5mm, built in 2004. As can be seen from the figure, there are many quad-headed shafts and hand wheels on the equipment for adjusting the roll positions. The key factor for CNC-CFS square-square pipe mills (automatic square-square flexible pipe mills) is the accurate calculation and adjustment of the roll position. Using hardware and software technology, and modern automation equipment, this is not difficult. More crucial is that the equipment must have enough rigidity to maintain this position non-change on different loads that include steel pipe specifications, materials, production speed and so on. It is difficult to manually correct when considering so many factors. When using a detection device to make closed-loop control, its complexity is unimaginable and it is not realistic for a large system with nearly 100 digital axes. Only the improvement of the rigidity of the equipment can reduce the impact of load changes on the roll position, which is the best solution in this case.

Figure 2

Figure 3

The second generation CFS was built with electric adjustment. Figure 2 shows the CFS- II 200x200mm-500mmx500mm square-square mill, with thickness 5mm-20mm, built in 2005. As can be seen from the figure, there are many motors, reducers, knobs and display screens on the equipment for adjusting and displaying the roll positions. The CFS- I and CFS- II are adjusted by operators according to the data sheet, which will take time and be prone to errors. When making small specification products, the maximum wall thickness should be reduced because of the sharp decrease of shaft rigidity. For example, when producing 200 x 200mm steel pipe, the wall thickness can only be 10mm, rather than 20mm. This is the crucial defect of these two structures. The third generation CFS is adjusted automatically. Figure 3 shows CNC-CFS- III 80x80mm-200mmx200mm square- square tube mill with wall thickness 3-10mm, built in 2012. As can be seen from the figure, there are a lot of adjustment motors and reducers on the equipment, but there are no knobs and displays.

Figure 1

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JANUARY 2021