Hot-rolling equipment and a method of hot-rolling a slab

Abstract: A hot-rolling equipment includes a continuous casting apparatus (2), a simplified heating oven (3) disposed immediately after an outlet of the continuous casting apparatus (2), a sizing press (4) disposed immediately after an outlet of the simplified heating oven (3), and rough rolling mills (6). The sizing press (4) is installed at an inlet side of the rough rolling mills (6). The continuous casting apparatus (2), simplified heating oven (3), sizing press (4) and rough rolling mills (6) are linearly arranged. A hot-rolling method for slab (S) includes the steps of heating a slab material transferred from the continuous casting apparatus (2) in the simplified heating oven (3) installed immediately after an outlet of the continuous casting apparatus (2), and contracting and reducing the width of the slab (S) by the sizing press (4) installed immediately after an outlet of the simplified oven (3).

Description: The present invention relates to a hot-rolling equipment according to the precharacterising part of claim 1 and a method according to the precharacterising part of claim 3 of hot-rolling a slab and, more particularly, to a hot-rolling equipment and method in which a sizing press intended to reduce the width of a slab plate is provided at an inlet side of rough rolling mills and the slab material transferred from a continuous casting apparatus is subjected to reduction in width, after which the resulting slab is rolled. With a recent standardization of slab material width in the continuous casting apparatus, there has been a demand for change in width of slab plate in the succeeding rolling step. To satisfy this demand, such a sizing press as is disclosed in Japanese Patent Unexamined Publication No. 59-101201 has been adopted. This sizing press has a pair of press tool parts or mold parts which reciprocate laterally with respect to the travelling direction of a slab to press the same in the widthwise direction. Thus, the slab can be greatly reduced in width. An example of the hot-rolling equipment with such a sizing press is disclosed in Japanese Patent Unexamined Publication No. 60-115302. In this hot-rolling equipment disclosed in this official gazette, the sizing press is disposed between a heating oven and a finish rolling mill. And the slab material, which has been once cooled during the transfer of it from the continuous casting apparatus, is heated by the heating oven up to a temperature of 1100°C or more which permits hot-rolling to be made effective. Thereafter, the slab is transferred to the sizing press in which it is subjected to reduction in width in the widthwise direction. Thereafter, the slab is hot-rolled by the finish rolling mill. In the above-described conventional hot-rolling equipment, the press tool of the sizing press is caused to contact with the slab kept at a temperature as high as 1100°C or more for pressing fabrication. Usually, therefore, the press tool is water-cooled down to a temperature of 500°C or 600°C or less so as to ensure the heat-resistant strength. Accordingly, a high temperature difference acts on the portions of contact between side edges of the slab and the press tool parts, so that the slab is cooled only at its side edges. This raises, for example, a problem that, in the succeeding rolling step, side edge cracks, non-uniformity in temperature in the widthwise direction, etc. occurs with the result that a decrease in the thickness precision in the widthwise direction (tendency for a central part of slab to extend) occurs. US-A-4 651 550 discloses a hot-rolling equipment and a hot-rolling method comprising the precharacterizing features of claim 1 and claim 3, respectively, and the additional feature of forming loops of the hot thin slab at the inlet and the outlet sides of the sizing press. JP-A 62-114702 discloses a hot-rolling equipment wherein rough rolling mills are disposed immediately after an outlet side of a sizing press. SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of side edge cracks of the slab during the rolling operation performed in a hot-rolling equipment in which the slab width is reduced and thereafter the slab is rolled. Another object of the present invention is to make small the area of arrangement of a hot-rolling equipment, thereby enabling reduction or saving of energy as well as reduction in equipment in cost. To attain the above object, the present invention provides a hot-rolling equipment having the features of claim 1. Further, the present invention provides a hot-rolling method for a slab, having the features of claim 3. DESCRIPTION OF THE DRAWINGS Fig. 1A is a plan view of a hot-rolling equipment in accordance with a first embodiment of the present invention; Fig. 1B is a side view of the hot-rolling equipment shown in Fig. 1A; DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 1A and 1B, a hot-rolling equipment (10) in accordance of the present invention is shown. This hot-rolling equipment (10) is composed of a steel-making section and a rolling section. The steel-making section is constituted by a continuous casting apparatus (2) while the rolling section by a heat holding oven (3) disposed immediately after an outlet of the continuous casting apparatus, a sizing press (4) disposed immediately after an outlet of the heat holding oven, a reheating oven (5) disposed immediately after an outlet of the sizing press, and a plurality of rough rolling mills (6) disposed at the outlet side of the reheating oven. The heat holding oven (3) serves to prevent a decrease in temperature of a high-temperature slab material S produced in the continuous casting apparatus (2), or to reheat the slab plate subjected to temperature drop to its original temperature. The sizing press (4) serves to reduce the width of the slab S having been drawn out of the heat holding oven (3). The reheating oven (5) serves to heat the widthwise reduced slab up to a temperature suitable for the next rolling step. Between the sizing press (4) and the reheating oven (5), there are disposed a transfer means (7) for transferring the width-reduced slab to the reheating oven, and a charging table (8) for charging the slab from the transfer means into the reheating oven. The rough rolling mills (6) serve to roll the reheated slab to a predetermined thickness. Between each rolling mill (6) there is disposed a rough rolling table (11) for conveying or transferring the slab S which has been rolled in a preceding one of the two rough rolling mills (6). Crop shear and a finish rolling mill (not shown) are disposed at the outlet side of the rough rolling mill group. In operation, the slab material which has been produced in the continuous casting apparatus (2), is cut to a predetermined length by a cutter (2a) and then the resulting slab is conveyed to the heat holding oven (3) while it is kept at high temperature. In the heat holding oven (3), each slab is heated by means of burners (3a). Thus, the side edge portions of the slab, which are liable to drop in temperature, are prevented from experiencing a temperature drop. The temperature, by which the slab temperature has already been reduced, is raised to the original temperature of the side edge portions of the slab, whereby the respective temperatures of the slab interior, slab side edge portions and slab surface layers are made uniform. Since the heating in the heat holding oven (3) is effected by utilizing the latent heat in a solidified piece of the slab material produced in the continuous casting apparatus (2), only a small amount of heat input sufficiently serves the purpose. The slab S thus heated is transferred to the sizing press (4) by means of table rollers (3b). In the sizing press (4), the slab S is transferred to, and positioned at, a zone of molding (4a) by pinch rollers (4d). Then, electric motors (4b) are driven to rotate so as to cause rotation of eccentric shafts (4c). As a result, a pair of mold parts (4a) are moved in a direction transverse to the travelling direction of the slab S at right angles thereto to thereby press the slab S and reduce the width thereof. It is to be noted that each mold part (4a) has, as shown in Fig. 1A, an inclined portion (4a') inclined with respect to the travelling direction of the slab S and a parallel portion (4a'') parallel to the travelling direction of the slab S. Since the slab S is prevented from dropping in temperature at its side edge portions in the heat holding oven (3), even when it is reduced in width by the sizing press (4), its side edge portions are prevented from being cracked. Accordingly, it is possible to set the width dimension at any given value, thus to perform an effective width reduction of the slab. The side edge portions of the slab S, which have been contacted with the mold parts (4a) in the sizing press (4), are cooled and thus their temperatures are lowered. The slab S thus made low in temperature is placed on transfer beams (7a) of the transfer means (7) and is conveyed to the changing table (8). Thus, the slab is placed on the charging table (8a). and then is put into the reheating oven (5). In the reheating oven (5), the side edge portions of the slab S is reheated to make uniform the temperature of the slab S. The amount of heat to be input as well as the time length in which heat is to be input, in the reheating oven (5), may also be small because the interior of the slab is kept at a high temperature and it suffices to reheat the side edge portions of the slab. The slab S thus reheated in the reheating oven (5) is transferred to the rough rolling mills (6) by a drawing table (9). Between the rough rolling mills (6), the slab S is conveyed on a rough rolling table (11). Thus, the slab S is rolled to a predetermined thickness by the rough rolling mills (6). At this time, the side edge portions of the slab, which have dropped in temperature in the sizing press (4), have already been completely restored to its original temperature by reheating in the reheating oven (5), so that the slab temperature is uniformized. For this reason, any side edge crack of the slab attributable to the temperature drop at the side edge portions thereof would not occur. In addition, the decrease in precision of thickness in the widthwise direction (tendency for a central part of slab to extend in excess) can also be suppressed. This makes it possible to prepare a slab with no side edge crack as well as with a uniform thickness. The steel sheet thus prepared by being passed through the rough rolling mills (6) is conveyed to the succeeding rolling step including finish rolling mills. According to this embodiment, since the heat holding oven is installed immediately after the outlet of the continuous casting apparatus, the temperature drop at the side edge portions of the high temperature slab material produced in the continuous casting apparatus is prevented or compensated for by reheating, so that it is possible to directly reduce the width of the high temperature slab by the sizing press. Therefore, in the hot-rolling equipment provided with the sizing press, it becomes possible to effect hot direct rolling by directly connecting the rough rolling mills to the continuous casting apparatus. In addition, since the reheating oven is installed at the outlet side of the sizing press, it is possible to uniformize the temperature of the slab cooled at its side edge portions by its contact with the press tool and thereby prevent the occurrence of any crack at the side edge portions of the slab in the rolling step executed with use of the rough rolling mills, thus ensuring a slab with a uniform thickness. In addition, since the method of rolling is a hot direct rolling, the amount and time length of heat input in the reheating oven can be greatly reduced as compared with the conventional heating oven. In addition, since the heat holding oven is so arranged as to reheat or heat the slab by utilizing the latent heat in a solidified piece of the high-temperature slab material produced in the continuous casting apparatus, the amount of heat to be input in the heat holding oven may also be small. This enables reduction in size of the equipment and, at the same time, reduction in cost of the equipment and reduction in the required energy. In connection with the invention, explanation has been made of the flow of the hot charge rolling (HCR) employing the reheating oven. According to the present invention, since the high temperature slab material produced in the continuous casting apparatus is directly reduced in width by the sizing press, the improved rolling followed by no edge crack of the slab becomes possible. Further, since the direct transfer rolling in which the steel-making step is directly connected to the rolling step is carried out, not only the production process from the creation of steel to a product but also the facilities to be installed can be reduced in scale. In addition, reduction in cost of the facilities becomes possible. In addition, energy saving effect can be obtained by utilizing the high temperature of cast piece of base material.

Claims: A hot rolling equipment (10) including a sizing press (4) for reducing the width of a slab (S), the sizing press being disposed at the inlet side of rolling mills (6), the slab material supplied from a continuous casting apparatus (2) being rolled after being passed through the sizing press (4), and a heat holding oven (3) disposed immediately at the outlet side of said continuous casting apparatus (2), characterized in that said heat holding oven (3) is disposed at the inlet side of said sizing press (4) for uniformalizing the temperatures of the interior, surface layers and side edge portions of a high-temperature slab material (S) produced in the continuous casting apparatus (2), whereby the high-temperature slab material is immediately subjected to reduction in width by said sizing press (4), and a reheating oven (5) is disposed between the outlet side of said sizing press (4) and the inlet side of said rolling mills (6) for uniformalizing the temperatures of the slab material, of which side edge portions are cooled by the contact with said sizing press (4), whereby the slab material, the temperature of which is uniformalized, is subjected to rolling by said rolling mills (6). A hot-rolling equipment as claimed in claim 1, in which said sizing press (4) has a pair of mold parts (4a) for pressing said slab (S) by their lateral reciprocating movements with respect to the travelling direction of said slab (S), said pair of mold parts (4a) being so arranged as to contact with said slab (S) having first surface portions (4a') converging in the travelling direction of said slab (S) and second surface portions (4a'') parallel to the travelling direction of said slab (S). A hot-rolling method for a slab (S) of a slab material fed from a continuous casting apparatus (2) by using a hot-rolling equipment including said continuous casting apparatus (2), a heat holding oven (3), a sizing press (4), and rough rolling mills (6), characterized by the steps of heating said slab material transferred from said continuous casting apparatus (2), in said heat holding oven (3) disposed immediately after an outlet of said continuous casting apparatus (2), contracting and reducing the width of said heated slab (S) by said sizing press (4) disposed immediately after an outlet of said heat holding oven (3), reheating said width-contracted and reduced slab (S) in a reheating oven (5), and rolling said reheated slab (S) to a predetermined thickness in rough rolling mills (6).

Inventors: MURAMATSU YUTAKA, TAJIMA SADAYOSHI, MURAMATSU, YUTAKA, TAJIMA, SADAYOSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: B21B1
IPC codes: B21B1