TPT March 2016

AR T I C L E

Dalian Field

affect the welding and product quality for welded open profile due to the large speed fall. If the double-car flying saw is equipped for a production line, the line speed may be a little lower but the drop range of speed is much less dramatic than that of a single-car flying saw. Furthermore, for products that are inappropriate for quick cutting, a double-car flying saw can be equipped to increase the line speed. Below we analyse how the double-car flying saw can extend cutting time. It will be starting from distribution between the one-piece cycle and cutting time. One-piece cycle refers to the time for cutting off one piece of pipe. For example, when the line speed is 120m/min and length is set at 6m, one-piece cycle = 1 minute / 120m/min x 6m x 60s = 3s. The 3s operations of a single-car flying saw includes seven steps: saw car synchronisation, cutting jaw clamping, car head moving forward, cart head moving backward, cutting jaw unclamping, car returning and car waiting. The distribution of cutting time is to divide the 3s into the above seven steps. Experience tells us that only 0.6s to 0.8s is used for blade feeding; big size products cannot be cut off during such short time. But if it is cut by double-car flying saw the line speed is still at 120m/min, the cut-to-length of products is 6m the cutting length for each cutting car will be 12m not 6m and the one-piece cycle = 1 minute / 120m/min x 12m x 60s = 6s. The extra 3s are all put onto the blade feeding operation, the feeding time is changed from 0.6s to 0.8s, to 3.6s to 3.8s, and the cutting time is increased six times. Considering cart travel limit the cutting time can be increased three times, an economical speed of double-car flying saw when it is used to cut wall thickness 3mm of square 60x60mm tube or round 76mm pipe will be equal to the speed for a single-car flying saw when it is used to cut wall thickness 1mm of square 20x20mm tube or round 25mm pipe. During the above operations the line speed is 100-120m/min. The above analysis assumes that the cutting cycle has not changed, and only cutting time is changed to get line speed when producing big size products. Below we assume that one- piece cycle is not changed to get line speed when producing small size products: one-piece cycle is 3s, cut-to-length is still 12m for one cart, the line speed will be up to 240m/min (= 60s/min / 3s x 12m = 240m/min). Another important feature for the double-car flying saw is blade change cycle – this is increased by one time according to output because the original one-car job is now separated by two cars. This means that shut-down time for blade changing is decreased one time, therefore the loss due to shut-down time and waste by shut-down are reduced by half. With some special production lines – such as those with high steel grade, thick wall thickness, big sizes and difficult cutting of tube and pipe – cutting can become an even bigger bottleneck. This problem can be solved by the use of a double-car flying saw. In order to meet with different cutting requirements the milling cut can be performed by using this saw. It can also be used for other cutting purposes, which can be done with the installation of different cutting devices such as flame cutting, plasma cutting and laser cutting.

Double-car flying saw equipped on pipe mill

Double-car flying saw in operation

If this kind of double-car flying saw cannot meet the requirements of line speed or short length cutting, the number of cars can be increased for the purpose.

Conclusion High investment efficiency and profit are of course important for producers, and the double-car flying saw may be the best model in terms of low investment for high returns. While factory space, construction of the factory building and staff numbers remain unchanged, output can be increased two-fold by choosing or changing to use this kind of double- car flying saw. It may be that one-car flying saws will be not chosen in tube and pipe production facilities in the not-too-distant future.

Dalian Field – China Tel: +86 411 83192715 Fax: +86 411 83192716 Email: fd@fdmachinery.com Website: www.fdmachinery.com

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M ARCH 2016