The intermediate coiling device “coil-box” manufactured by firm “Hatch Steltech” (Canada), was designed according to the technical assignment of the Works. Taking into consideration all the last developments and experience in this field, and also the peculiarities of the existing equipment, the ‘coil-box’ was installed on the intermediate rolling table of hot rolling strip mill 1680 to widen the range of products, increase the share of hot-rolled coils of weight up to 16 tons and increase the mill productivity.
Its peculiarities are the possibilities of coiling and de-coiling of small coil weights (4,5 — 8,0 tons), the presence of heat screens to reduce heat losses when working in the regime of oscillation (alternating rotation) during delay in the mill line, operations of cutting the transfer bar to size during de-coiling.
Work of the intermediate coiling device “coil-box” in the conditions of high speed feeding of metal into the finishing group is of great importance when the pause between feedings before the first finishing stand is approximately 5 seconds. Several technical solutions are being solved: simultaneous coiling and de-coiling of transfer bars, absence of draw bar, acceleration and maximum possible transportation speed of the transfer bars, usage of high-speed hydraulics, exact positioning of the coil, effective programmable control and tracing of the transfer bars in all the sections of the mill from the roughing scale breaker to the first stand of the finishing group.
Intermediate coiling device “coil-box” works, as a rule, automatically. The control programme coordinates all the following operations. The controller traces the movement of the transfer bar regarding measurement of speed, position, direction and time, using hot metal detectors and signals of the mill control system and also the input data, set by the operator. The control system of the intermediate coiling device “coil-box” traces the movement of all the slabs from the moment they approach the roughing scale breaker up to the moment the tail part of the transfer bar comes out of the first finishing stand. Thanks to the intermediate coiling and de-coiling of transfer bars with simultaneous changing over of the front and back ends of the transfer bars, the transfer bar temperature levels out along its length before the finishing group of stands. As the results of the carried out research have shown, averagely, when rolling the whole assortment of strips with weight up to 16 tons the actual surface temperature difference along the length of the transfer bars before the finishing group of stands has decreased from 490C up to 200C. Due to this the temperature difference at the end of rolling has decreased along the length from 260C to 90C. Apart from that the transfer bar loses heat, and the working conditions of the finishing stand equipment improve.
Commissioning of the coiling device ‘coil-box’ excluded length limiting of transfer bars by the length of the intermediate rolling table which used to exist on the mill between the roughing and finishing group of stands and allowed to reduce the thickness of transfer bars for the finishing group from 27-28 mm up to 23-25 mm. It also provides reduction of the load. In its turn it allowed to widen the assortment of hot-rolled strips from double weight coils, particularly thin profiles of thickness 1,8-2,4 mm.
Improvement of the rolling temperature conditions leads to improvement of the geometrical dimension of rolled strips. Distribution of thickness value along the length of the strip has become more uniform.
Rolling of double weight coils provides increase of productivity of the continuous hot strip mill 1680 and reduction of metal losses with crop ends, efficiency of production during processing of double-weight hot-rolled coils in cold rolling shop No.1. Metal losses with crop ends in pickling lines of cold rolling shop No.1 reduce from 6,0 to 3,5%, productivity of rolling mills and other shop aggregates also increases. At present mastering of the technology of rolling thin cold-rolled coils of thickness 0,5 and 0,6 mm from double-weight hot-rolled coils of thickness 2,0 and 2,2 mm.
Starting from the commissioning of ‘coil-box’ 2,3 million tons of hot-rolled strips have been rolled. In 2008-2009 the share of strips with weight up to 16 tons has increased by 52-58% against 38% in 2007, including in cold rolling shop No.1 from 47,5 up to 55,8%. Growth of production in 2008 only due to mastering of a new assortment of strips of double weight (including thin hot-rolled strips of thickness 1,8-2,0 mm) amounted to 180,9 thousand tons.
Installation of the coiling device ‘coil-box’ of firm “Hatch Steltech” on the intermediate rolling table of mill 1680 together with the modernization of the shearing aggregate and installation of the motor of stands No.2 of continuous hot strip mill 1680 with regulated speed, erection in cold rolling shop No.1 of a new hydrochloric acid pickling line NTA-4 will allow to completely transfer to rolling of coils weighing up to 16 tons; reduce 1,5-2,0 times metal losses with crop ends; increase the production of mill 1680 and production of continuous 4-high cold-rolling mill in cold rolling shop No.1 and other aggregates.
Vyacheslav PANCHENKO, Head of the hot rolling group of the research rolling laboratory of the Works’ Central Laboratory.