SU1738395A1 - Method of transit rolling of strip - Google Patents

Abstract

SUMMARY OF THE INVENTION: after rolling in the slab, the slab cant be turned through 180 ° C. During transport by the heat sink, the temperature difference between the top and bottom of the slab is 20-30 ° C. Rolling in the rough reversing stand of the hot rolling mill is carried out with a difference of circumferential speeds of the upper and lower rolls of 8-12%. Bending sla is prevented. 1 tab.

Description

The invention relates to the field of hot rolling of strips and can be used in metallurgical plants, which include a rolling mill (rolling mill) and a hot rolling mill.

A known method of transit rolling a strip includes rolling an ingot on slabing, transporting the slab and subsequent rolling on a broadband mill, and the transportation of the slab is carried out in thermally insulated carriages to reduce heat loss.

The disadvantage of this method is the complexity of its implementation in existing workshops both for technical and organizational reasons, which is associated with the replacement of transporting devices with insulated trolleys. In addition, such a replacement requires large capital expenditures.

There is also known a method of rolling a strip with an upper pressure, consisting in using rolls of different diameters of 2-6 mm. This method is used to compensate for uneven heating or cooling of the strip.

This method does not provide for the implementation of transit rolling of a strip at operating technological complexes, including slabing and a continuous broadband hot rolling mill.

The closest in technical essence to the claimed is the method of transit rolling of the strip selected as a prototype, including heating the ingot, rolling the ingot on the slab, transporting the slab to the hot rolling mill, rolling it in a reversing stand and subsequent rolling.

The disadvantage of this method is to reduce its performance due to the bending of the slab during rolling in the reversing stand of the roughing group of the mill stands. The slab bending occurs in the rolling process in the stand due to different deformation conditions on the side of the upper and lower work rolls. In this case, the longitudinal axis of the slab is bent to form

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swelling down, which makes it impossible to further rolling such a slab. The bent slab is either straightened on the roller table or removed. All this reduces the productivity of the mill.

The aim of the invention is to increase the productivity of the hot rolling mill by reducing its downtime due to the bending of the slab during rolling in the roughing reversing mill stand.

The goal is achieved by the method of transit rolling a strip, including rolling an ingot on a slab, transporting and rolling a slab in a hot rolling mill, after rolling on a slab, turning the slab over 180 °, then during transportation of the slab By controlling the heat sink, the upper temperature of the slab is higher than its lower temperature by 20–30 ° C, and rolling in the reversing stand of the mill is performed with an excess of the peripheral speed of the upper roll over the speed of the lower roll by 8-12%.

The invention is illustrated by the following example.

In slab 1150, ingots with a mass of 16.9–20 tons are rolled. Before rolling, ingots are heated to 1260–1350 ° С depending on the steel grade in the heating pits heated by the coke-domain mixture.

After the ingot has been rolled in the slab cage, a slab thickness of 180–250 mm and a width of 1250–1760 mm is obtained. After rolling out of the cage, the rolled slab is turned by 180 °. In addition, the upper and lower sides of the table are swapped. After turning, the temperature of the upper slab is higher than the temperature of the lower slab at 40-50 ° C (the temperature of the upper slab is 1150-1190 ° C, the temperature of the bottom is 1120-1150 ° C). During transportation, the bottom is cooled by air, and the bottom is cooled by the water-cooled rolls of the roller table. The amount of water supplied to cool the rollers of the roller table varies from 100-1000 l / h per roller. With such a regulation, the cooling rate of the bottom of the transported slab changes. The amount of water supplied is controlled according to the indications of pyrometers, ensuring that the top of the slab exceeds the temperature of the bottom by 10-40 ° C. Then the slab is rolled in a reverse cage of the rough group of the 2500 mill in three passes. Work rolls of the reversing stand have an individual adjustable drive. The peripheral speed of the work rolls is varied in the range of 1-1.5 m / s.

In the rolling process, the ratio of the circumferential speeds of the upper and

lower work rolls. The speed of the upper roll is higher than the speed of the lower roll by 6-15%. From the reversing stand, the roll is fed to the subsequent stands of the rough and finishing groups of the mill 2500, where it is rolled to the finished size.

The results of the transit rolling strip are presented in the table.

Analysis of the results of the transit rolling of strips shows that compliance with the modes recommended in the technical solution ensures high hourly productivity of hot rolling mill 2500 within 840-930 t / h (see experiments 1,2,8,9). The exclusion of the canting by 180 ° (see experiments 3, 4, 5) results in the temperature of the bottom slab being higher than the temperature of the top in front of the reversing stand, even under conditions of maximum cooling from the bottom. At the same time, despite the wide ratio of the speeds of adjustment of the working rolls of the reversing stand (from speeding the top roll over the lower speed by 10% (run 3) to speeding the bottom roll over the top roll by 9% (run 5), the slab bends, impeding its rolling, which leads to the necessity of straightening the slab and reducing the productivity of the mill to 90-120 t / h.

The deviation from the recommended excess temperature of the slab above the lower temperature by 20-30 ° C in front of the reversing stand and the deviation from the recommended excess of the peripheral speed of the upper roll over the lower speed by 8-12% in the reversing stand causes the slab to bend in the process. its rolling and, as a result, reducing the productivity of the mill to 370-480 t / h (experiments 6, 7, 10, 11).

Rolling in the prototype method (experiments 12,13,14} dramatically reduces the mill's productivity (up to 50-80 t / h) due to the large bend of the slab when rolling in a reversing stand, which makes it necessary / periodically to turn off take it off rolling.

The invention provides high productivity of the hot rolling mill by preventing bending of the slab when rolling it in the reverse mill stand, which is currently one of the main reasons that prevent the industrial development of a progressive method of transit rolling of metallurgical enterprises that have It includes servicing conveyor conveyors and a hot rolling mill with a reversing stand in the roughing group. In addition, the invention provides savings

fuel by reducing the number of slabs heated in the furnaces of the hot rolling mill, and saves metal by eliminating its carbon loss in the furnaces of the mill. During transit rolling, the quality of the metal is improved by increasing its toughness. In addition, there is the possibility of rolling slabs of greater mass and size, which, due to their size, cannot be placed and heated in the methodical furnaces of the hot rolling mill.

Claims (1)

The invention of the method of transit rolling strip, including rolling of an ingot on slabing, transporting and rolling a slab in a hot rolling mill, characterized in that, in order to increase the productivity of the hot rolling mill by reducing its downtime due to the bending of the slab during rolling in the roughing reversing mill stand, turning is carried out after rolling slab 180 °, then in the process of slab transport, by adjusting the heat sink, the temperature of the upper slab is above the lower temperature by 20-30 ° C, and rolling in the reversing mill stand is performed at an excess of peripheral speed and the upper roll above the speed of the lower roll by 8-12%,