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186

M

ARCH

2016

AR T I C L E

Dalian Field

xx

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