Conventionally, large H-shaped steels are generally produced by rough rolling a beam blank, a bloom or a slab produced by continuous casting, etc., by using a breakdown mill and then conducting intermediate rolling or finish rolling in a universal mill, etc. FIG. 1 shows the layout of the most typical shape-steel mill. It includes a breakdown mill BD comprising grooved horizontal rolls 1 and 2 that together form a vertical pair, an intermediate universal mill UR equipped with horizontal rolls 3 and 4 and vertical rolls 5 and 6 that are so arranged as to oppose one another in the vertical and horizontal directions, respectively, an edger mill E equipped with horizontal rolls 7 and 8 that together form a vertical pair, and a finish universal mill UF equipped with horizontal rolls 9 and 10 and vertical rolls 11 and 12 that are so arranged as to oppose one another in the vertical and horizontal directions, respectively. As shown at the intermediate and lower stages of FIG. 1, a predetermined shape steel is rolled and produced by using the shape steel mill by carrying out a plurality of reverse passes at the breakdown mill BD, a plurality of reverse passes at the intermediate universal mill UR and the edger mill E and a single pass at the finish universal mill UF.
FIG. 2 shows a shape steel mill which is proposed in Japanese Unexamined Patent Publication (Kokai) No. 52-88565 and makes the setup of the conventional shape steel mill compact in FIG. 1, and the finish universal mill UF is installed in the proximity of the edger mill E. The rolling pass schedule of this rolling mill is shown at the lower stage of FIG. 2. In other words, after a reverse rolling is carried out in a plurality of passes at the breakdown mill, reverse rolling is carried out in a plurality of passes at the intermediate universal mill UR and the edger mill E, and one-pass rolling is thereafter carried out at the finish universal mill UF.
FIG. 3 shows a shape steel rolling mill proposed in Japanese Unexamined Patent Publication (Kokai) No. 63-52701. According to this prior art technology, the intermediate universal mill UR, the edger mill E and the finish universal mill UF are disposed adjacent to one another, and the H-shaped steel is produced by passing the blank through these mills in a plurality of passes. In the drawing, reference numeral 14 denotes a heating furnace.
In the rolling mill of the prior art example shown in FIG. 1, the upper and lower horizontal rolls 3 and 4 of the intermediate universal mill UR have the shape represented by the solid lines shown in FIG. 4(a), and the flange of the H-shaped steel as the to-be-rolled material is opened to both sides. (Hereinafter, rolling of the H-shaped steel into such a shape will be called "X-shape rolling".) The horizontal roll 3 (and the horizontal roll 4, too) is worn out in the course of use as indicated by dash lines in FIG. 4(b) but when grinded, the roll 3 can secure a predetermined width b and can be used for the to-be-rolled material 15 of the H-shaped steel having the same size.
On the other hand, the width b1 of the upper and lower horizontal rolls 9 and 10 of the finish universal mill UF has a predetermined shape in a radial direction so as to be match with the final product of the H-shaped steel as shown in FIG. 5(a), and the H-shaped steel as the to-be-rolled material is rolled into an H shape (hereinafter, rolling of the H-shaped steel into such a shape will be called "H shape rolling") by using the upper and lower horizontal rolls 9 and 10 and the right and left vertical rolls 11 and 12. However, this width b1 changes to a width b2 in the course of use for a predetermined time as shown in FIG. 5(b) and even when it is grinded and modified, the predetermined roll width b1 cannot be secured. Therefore, the rolls are used for rolling of a product of a smaller product size in the next rolling operation. In other words, there remains the problem that the roll consumption of the finish universal mill is inferior to the roll consumption of the intermediate universal mill UR.
Next, in the rolling mill described in Japanese Unexamined Patent Publication (Kokai) No. 52-88565 shown in FIG. 2, the finish universal mill UF is disposed closer to the edger mill E so that it can be installed in a narrower space, but shaping of rolling is fundamentally the same as the prior art example shown in FIG. 1. However, the roll consumption unit of the finish universal mill UF is inferior and eventually, the running cost is high. For this reason, the finish universal mill UF is used for rolling in only the final single pass.
In Japanese Unexamined Patent Publication (Kokai) No. 63-52701 shown in FIG. 3, a plurality of normal and reverse rolling passes are carried out by using the intermediate universal mill UR, the edger mill E and the finish universal mill UF. Therefore, the improvement of the roll consumption unit of the finish universal mill UF described above is not made. Therefore, the rolling mill of Japanese Unexamined Patent Publication (Kokai) No. 63-52701 proposes a negative counter-measure of setting the surface reduction ratio of the finish universal mill UF to 15 to 55% of that of the intermediate universal mill.
Further, as X shape rolling and H shape rolling are repeated, the flange of the H-shaped steel is repeatedly turned up and down, but if the thickness of the flange of the H-shaped steel is as great as 60 to 80 mm at the initial stage of the reverse pass, a biting error occurs to invite miss-rolling, and this renders a critical problem which inhibits productivity.