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MARCH 2016 187
AR T I C L E
Dalian Field
Dalian Field – China
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Fax: +86 411 83192716
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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