TPT March 2016

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186 MARCH 2016
AR T I C L E Dalian Field
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Double-car cut-off machine aims to
help increase competitive power
over the next 20 years
By Guowu Gao, chief engineer at FD Machinery
Performance and applications
Double-car flying saw: as the name implies there are two
cutting cars equipped in one production line and they operate
as per their own control model and finish the cutting on
pipes or open profiles alternately. Because of the use of two
independent cutting cars on the same line the job that was
originally performed by one cutting car is replaced by two
cutting cars. The duty cycle of one car is twice as long as a
single car and overall cutting time is more than doubled. Due
to the extension of cutting time the saw blade life
is extended as well as the cut end quality, which is
better than before. Therefore, if the cutting time and
incision quality remain unchanged the line speed is
also improved. The most common choice is for the
speed, blade life and cutting quality to be improved
at the same time to make the line speed and cutting
time increase together.
It is well known that the bottle-neck for line speed
in tube and pipe and roll-forming mills is often the
flying saw because the mill speed can be improved
without limit and technology such as the HF welder
can be upgraded to meet the requirements of any
high speed mill currently in operation (although
most roll-forming mills are not equipped with a
welder), and high-speed pipe packing machines
can solve product collection problems with ease.
FD Machinery has been developing a new double-car
flying saw since 2014. The first saw has already been
commissioned for an ERW pipe mill at Mitwalli Steel
Products Co in Saudi Arabia, with line speed up to
150m/min.
The machine has now been successfully in production
since the middle of last year. The second set of saws will
be installed at a similar mill and will be put into production
in early 2016 for the same company. The third set will
operate at up to 200m/min and will be used at APL India
for an existing mill.
The flying saw has been praised by the customers thanks
to its excellent performance in increasing line speed and
due to the longer saw blade life achieved.
Only the flying saw is limited because the process of cut-to-
length on 4-8m tubes cannot be accurately completed in a short
space of time, so the line speed is always restricted. Taking
a Dia76mm pipe mill as an example, when wall thickness of
3mm for tube, 60x60mm or pipe Dia76mm, if it is equipped
with single car flying saw the line speed economically can be
50-60m/min. When wall thickness is 1mm for tube 20x20mm
or pipe DIa25mm it can be 100-120m/min.
A few pipe mill makers call for higher line speed, but this is
at the expense of saw blade life and incision quality without
practical usage or benefits. Pipe mills with double-car flying
saws can have a speed of 120-150m/min and 200-240m/min
or higher for the above-mentioned size tube production with
saw blade life and incision quality that is not decreased.
The benefits of double-car flying saws is not only in improving
the maximum line speed but also in levelling line speed
features to make line speed of cutting big size and thick wall
thickness tubes similar to that of small size thin wall thickness
in a single line. This is a more meaningful improvement for
those who mainly produce big sizes. The producer can use the
new flying saw to get double the efficiency it could previously,
and the ratio of investment and benefit is cost-effective.
When speaking about line speed usually we assume it is for
6m product lengths, but some tube and pipe makers may
produce 3m or shorter lengths. For a line equipped with
single-car flying saw, a fall of the speed in production will be
far more than that of the length shortened, which will not only
seriously affect the efficiency of the production line, but also
Double-car flying saw