TPT July 2007

5.2 Control system functions

• Synchronised position control maintains the symmetry between rolls and the rolling centreline, to avoid damages to chocks and bearings • Separation force measurement computes the average and differential values of the rolling forces using the pressure transducers installed on the hydraulic capsules • Capsule position control regulates the position of the rolls by comparing position pre-set and position feedback and set-up for roll changeover • During rolling, automatic variation of the roll positioning takes place in accordance with a calculated rule, in order to compensate the temperature disuniformity over the tube length • Impact compensation increases the gap between the rolls during the entrance of the shell into each stand, thus reducing excessive thickness on the tube head end. The impact peak compensation on mechanical components limits the stress on the roll bearings and reduces the mandrel and rolls consumption • A general damage prevention system (automatic roll emergency opening), based on automatic gap increase, limits the overload and enables the tube end to be rolled. There is also an emergency capsules control to avoid strong deformation of the pipe and consequent damage to mechanical parts, mandrel and rolls 6. FQM™ integration in the rolling line A typical material flow, together with the process control installed, is a central part of the system. The billet, cut into multiple lengths of the rolling length, are re-heated to 1,280°C in the re-heating furnace, rotary hearth type or walking beam type. After the re-heating, the piercing of the billet is undertaken in a cross rolling mill to form a round hollow shell. The cross rolling mill mainly consists of two opposite and equi-rotating rolls, suitably shaped in order to rotate and advance the billet against a plug. The external deformation of the material is contained by means of lateral rotating disks or fixed shoes (at 90° in respect to the rolls). The internal plug determines the internal material deformation. The cone shape and divergent orientation of the work rolls require no abrupt change of ovality and twist direction of the material during rolling. They help achieve the following benefits:

› Figure 8 and 9 : A side view of a 5-stand FQM (top and above)

5.1 Major system features

Master speed control enables the coordinated increase and decrease of motor speed references. This speed control is carried out by always ensuring comparative balance of the set drive speeds during the rolling process. An essential element of the system is wall thickness measurement; gauging of the thickness of the rolled material is provided and the set of the proper roll gap opening performed. The process control system analyses the data produced by the wall thickness gauge located at the extractor stand exit. Based on the results, the mill mathematical model updates the speed and gap parameter set points to improve the quality of the rolled pipes. Impact drop compensation acts to minimise the length of pipe rolled at speeds that are different from pre-set values by using auto-adaptive parameters, relying on real-time calculation algorithms. The core of the process control is the installation of hydraulic capsules, which are fully managed by the system. On each roll cartridge three independent hydraulic capsules are mounted, one per roll. The main function of the control system of the hydraulic capsules, controlled by servo-valves, is to move the stand rolls. The position of the cylinders and pressure of the chambers are measured in real time by dedicated transducers and used by a dedicated high-speed control system, capable of controlling and maintaining the set position.

fi Figure 10 : Material flow during rolling in a 5-stand FQM

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J uly /A ugust 2007