The base material of the hot rolled sheet is continuously cast slab. The base material demand of the Hot Rolling Mill is met by self-produced and imported slabs. Before being rolled into sheet, the slabs are heated to the temperature required for hot forming (1200 - 1270 °C) in two suitable pusher type furnaces operating with sliding rails (fired by a mixture of any ratio of natural gas and coke oven gas) and in one natural gas-fired walking-beam furnace. The energy efficiency of the furnaces is ensured by the recuperators used to preheat combustion air and to recycle the physical heat capacity of the flue gas.
The slabs heated to the temperature of hot forming are rolled by the rougher into transfer bars with a thickness of 24 - 36 mm (depending on the gauge, width and quality of the rolled sheet). The reversing roughing mill is composed of one vertical, so-called edging mill stand and one horizontal two-high mill stand. The primary scale developed during heating and the secondary scale developed during roughing is removed from the slab surface by the descaling system that operates with industrial water at pressure of 140 bars.
The coil-box upstream the finishing mill is used for coiling the transfer bar and homogenizing its temperature, but it also plays a significant role in the fact that the volume of raw coils produced by the Hot Rolling Mill may be as high as 25 tons.
In order to improve specific steel consumption, a transfer bar-cropping optimization system operates between the coil-box and the finishing mill. The continuous finishing mill has a configuration of six four-high mill stands and is used for the rolling of strips with a maximum width of 1540 mm. The gauge control system operating at the finishing mill ensures the dimensional accuracy of hot rolled products.
By controlling the temperature of the hot rolled strip, the interstand cooling system, as well as the laminar strip cooling system installed on the discharging roller table downstream the finishing mill contribute to setting the adequate mechanical properties of raw coils.
Wide strips with a thickness of 1.2 - 18 mm are coiled using a downcoiler with a maximum capacity of 25 tons. Almost one third of the hot rolled raw coils produced is transferred to the pickling plant in the Cold Rolling Mill to be processed. The rest of the raw coils is sold in the form of sheet, slit coil or wide strip with plain or patterned surface finish.
