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M

ARCH

2016

187

AR T I C L E

Dalian Field

Dalian Field

– China

Tel: +86 411 83192715

Fax: +86 411 83192716

Email:

fd@fdmachinery.com

Website:

www.fdmachinery.com

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.

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.

Double-car flying saw equipped on pipe mill

Double-car flying saw in operation