TPT July 2007

› Figure 11 (above left) : Into the heart of the FQM process; Figure 12 (above right): a diagram displaying the FQM’s automatic mandrel cycle

the outer diameter takes place with a simultaneous wall thickness variation. The change of the wall thickness depends on the longitudinal tension (stretching) acting on the tube during reduction. The mill is equipped with a series of closely spaced three-roll stands (in accordance with the required OD reduction). The three rolls, individually driven and with adjustable roll stands, are used in the last stand position. The Kocks sizing or stretch reducing blocks are the state-of-the-art in 3-roll technology for tube rolling, with stands featuring three input drive shafts, and radially adjustable or non-adjustable rolls with quick roll change. Restrictions normally experienced with conventional stretch reducing mills are completely eliminated and overcome in the Kocks design. This leads to the following improvements:

• Minimise the surface strain due to the torsion and circumferential shear deformation • Suppress the ‘forging’ effect (by increasing roll velocity the shell is pulled in the direction of rolling) • Improves the shell OD surface (due to the speed match between roll and shell)

The cone-type cross roll piercing characteristics are:

• High elongation • High expansion levels • Capacity to pierce a wide range of steel grades • High concentricity and wall uniformity • Excellent inner and outer surface quality

After the piercing of the billet, the shell is rolled in the FQM™ and the finishing of the tubes into the required final sizes is performed in a sizing or a stretch-reducing block. It is here that the reduction of fi Figure 13 : A complete view of a five-stand FQM™ (Fine Quality Mill) for a 350,000t/y 7" seamless pipe mill (Buttrio, Italy)

• Higher rolling forces and torque • Shorter stand spacing • Quick roll changing (30 min per stand) • Radial adjustment of rolls • No special roll lathe is required • Investment is considerably reduced

7. Conclusion FQM™ is the core of the seamless pipe production process selected by Danieli. The innovative features of the mill are fully integrated in the deformation path of the complete rolling line, either for new installation or for revamping of an existing installation. The best result is achieved when a complete new rolling line, from the billet re-heating furnace, usually rotating hearth type, to cooling bed is installed, allowing Danieli to balance the deformation path among the piercing mill, the RMM and the sizing/stretch reducing mill.

Danieli Centro Tube – Italy Fax : +39 02 2624 5486 Email : r.giannatasio@danieli.it Website : www.danielicorp.com

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J uly /A ugust 2007