TPT July 2007

109

uly

ugust

2007

sizes and steel grades. There is also a better yield, with improved

quality in the shape of the tube end leading to a reduction in

cropping.

Because of a wider wall thickness range capability on the same

mandrel, the total number of mandrels required to cover the

complete size range is reduced. Consequently, there is a reduced

mandrel inventory and less frequent mandrel size changeover.

There is also a significantly reduced consumption of mandrels and

rolls because of lower average and peak pressures.

There is a higher degree of stability of the material flow during

rolling, which reduces accidents and the losses for cobbles. This

increase in efficiency leads to better productivity and yield.

4. Technical profile of the

FQM™ retained mandrel mill

The FQM™ mill is mainly comprised of

rolling units and cartridges – each one

with 3 driven rolls – supported by chocks

and mounted in a shifting slide inside the

cartridge. Each cartridge is comprised of

two cast shells. The design of the cartridge

allows the radial extraction of the shifting

slides, containing chocks and rolls, without

the necessity to open the cartridges into

two halves.

Due to the geometry of the mill the

required adjustment to roll position before

or after profile redressing can be undertaken directly with the

hydraulic capsule. The hydraulic capsules are mounted outside

the container and engaged/disengaged to the roll during the roll

changeover procedure.

The mandrel supporting units are installed inside the container.

These units guarantee optimum operation, by means of three self-

centring rolls, with adjustable positioning in accordance to mandrel

size, and oil-hydraulically operated for opening/closing the mandrel

centring and support during rolling.

The number and position of mandrel supporting stands depends on

the mill configuration. For example, on a 5-stand mill the mandrel

supporting stands are installed at the inlet and outlet of the first

rolling unit, between the third and the fourth rolling unit and at the

outlet of the last rolling unit.

The roll cartridges and the mandrel supporting units are inserted in

a fixed and rigid cylindrical container and sit on side supports inside

the container. Due to his geometry the container is designed to react

uniformly to the three separating forces acting in radial direction.

For the roll changeover all the rolling units and the mandrel

supporting units are pushed along the rolling axis toward the mill

exit. The changeover is performed with a side-shifting type car.

5. FQM™ process control

Seamless tube plants are configured as distinct technological

areas in which different jobs can take place at the same time.

Each technological area has its own process control system that

is integrated with the others via level 3 automation. The following

goals can be achieved with this process control system:

• Enhanced dimensional quality of the final product

• Improved operator independence for better production quality

• Improved consistency of production quality

• Maximised yield of the plant

• Simplified start-up for new production configurations

A suitable integration and process automation system is essential

to match the high quality performance and results gained from 3-roll

pass design. The Danieli automation system is supported by ‘fast’

data collection of the main process variables. During the rolling

process all data is gathered from level 1 and used for process

tracking, process tuning and input for level 2 models.

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Figure 6

Advantages of the FQM process: comparison between 2-roll RMM (left) and 3-roll FQM (right)

Figure 7

A mandrel supporting stand from the FQM container