JPS63260601A - Method for forming billet end - Google Patents

Abstract

PURPOSE:To minimize the crop loss of a billet after sheet rolling by pressing the tail and front ends of a bloom by blooming rolls several times in blooming rolling and then performing the billet rolling. CONSTITUTION:A continuous ingot delivered from a blooming mill 3 is pressed down by rolling rolls 4 to peel scales on long sides. Then, the bloom is turned 90 deg. by a manipulator and is pressed down to peel scales on short sides. The 90 deg. turning and rolling by the rolling rolls 4 are repeated to form a bloom having prescribed dimensions. In this stage, a fish tail 11 gradually develops. The bloom is rolled into a billet 9 by rolling rolls of a billet rolling mill 5 and the shearing machine 6 cut off the fish tail 11 developed by adding metal flow. As for end part pressing the bloom rolling, the tail end is pressed at the initial and last stages and the front end is subjected to taper pressing from the initial stage to later stages. Thus, the crop loss by cutting off the fish tail is minimized.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a blooming method, which aims to prevent the growth of fishtails at the end of the bloom and minimize billet truncation losses after subsequent billet rolling. The present invention relates to a blooming rolling method. In particular, pressure is applied to prevent the growth of fishtails during blooming from continuous billets to booms, and pressure is applied in advance during blooming to eliminate the growth of fishtails during slab rolling. This invention relates to a steel billet end forming method.

(Prior art) Continuous slabs in an as-cast state supplied from a continuous caster in a steelmaking factory are charged into a heating furnace in a hot slab state and bloomed by blooming, and then turned into slabs. It is rolled into billets.

During this blooming, a fishtail grows at the end of the continuous billet, and then the metal flow of billet rolling is applied to cut off the end of the billet. This is the main cause of a decrease in the yield of blooming because the long pieces are cut off and only long pieces are produced.

Conventionally, methods for reducing fishtail include methods by improving rolling schedules such as zero-piece bus rolling and pultrusion rolling, ■ "bloom preforming method" disclosed in JP-A-58-1920601, and ■ JP-A-60. -238004
A method such as the "blossom rolling method" disclosed in Japanese Patent Publication No.

(Problems to be Solved by the Present Invention) However, although the method (2) has the effect of reducing crop loss compared to normal rolling, both methods have certain limitations and problems.

In method (2), the edges of the bloom are preformed by pressing using a press tool or a roll for blooming prior to blooming, but this also has certain limitations, and the billet rolling in the next step is not possible. In some cases it is insufficient.

In addition, press machines are expensive and have economic problems, and when newly introduced to preform the edges of the bloom, it is difficult to layout the existing rolling line, and it also poses a large maintenance burden. . Further, press preforming causes a large build-up of the edge portion at the end of the bloom, resulting in poor stability during the next rolling and problems in that the edge portion may fold inward.

In method (2), the edges of the bloom are press-preformed using a blooming roll prior to blooming, but this also has certain limits, and if the next step is billet rolling. is insufficient. (This corresponds to conventional method No. 2 shown in FIGS. 1 and 2.) (Problems to be solved by the invention) The present invention was proposed in view of the above-mentioned circumstances.
The purpose of this is to form the bloom end using the existing blooming rolls to eliminate the promotion of fishtails at the 7th bloom stage, and to form the bloom end in consideration of the metal flow of billet rolling in the next process. It is an object of the present invention to provide a method for forming the end of a steel billet that can improve the yield by adding forming and eliminating the promotion of fishtails at the billet stage.

(Means for Solving the Problems) In the method for forming the end of a steel billet according to the present invention, in order to prevent the formation of fishtails during the bloom stage, the bloom end surface is pressed by the bloom end face and the blooming roll at the early stage of blooming rolling. After pressing at a distance that corresponds to the position, one end of the bloom is tapered in the longitudinal direction, taking into consideration the metal flow in the next process of billet rolling, and the other end is rolled in the width direction after blooming. By applying pressure, it is intended to eliminate the fishtail after rolling the billet.

To explain this in detail based on FIGS. 1 and 2, the as-cast continuous slab supplied from the continuous caster 1 of the manufacturing factory is mostly in the hot slab state. It is charged into a heating furnace 2, baked to a predetermined temperature, and then sent to a blooming mill 3.

In the blooming mill 3, the continuous slabs sent therein are first rolled down with rolling rolls 4 to peel off the scale on the long sides. After that, 90 pieces of continuous cast pieces are placed on the table surface using a manipulator.
Rotate once and press down to peel off the scale on the surface of the short piece.

This will remove most of the scale. After that, the continuous slab is rotated 90 degrees by a manipulator,
Rolling with the rolling rolls of the rolling mill 5 is repeated to form a bloom of a predetermined size. In the figure, 6 indicates a shearing machine, and 7 indicates a dispensing/dispensing device. (This corresponds to conventional method 1 in Fig. 1.) In this rolling bath process, as is well known, the metal flow during blooming comes into contact with the roll 4 as shown in Fig. 4(a). Because the surface of the steel piece 8 is larger than the center,
Fishtail 11 gradually grows. This occurs in the same way on both the short and long sides of the early continuous cast piece, and the overall shape is a superimposed fishtail. After that, it is made into a bloom of a predetermined size and sent to a billet rolling mill.

In the billet rolling mill 5, the billet 9 is rolled into a long billet 9 by rolling rolls of several stands, and the fishtail 11 that has grown by adding metal flow due to this rolling is passed through the shearing machine 6 as shown in FIG. 4(b). The long piece is then cut off and divided into several pieces of predetermined length to produce finished products. For this reason, it is extremely important to minimize the occurrence of fishtails in order to achieve a high yield in a blooming rolling mill.

FIG. 3 shows an explanatory diagram of metal flow between the conventional method and the present invention. In the first conventional method, the tail and front fishteal are left behind after blooming and billet rolling, and this results in crop loss. In conventional method 2, in order to reduce this tail and front fishtail,
Before blooming, strong reduction pressing is performed using a press device or a blooming roll. This also becomes h2 after blooming and billet rolling, which becomes crop loss.

The present invention aims at reducing crop loss in order to prevent the formation of fishtails at the tail and front, and without using heavy pressure pressing (H2 in the figure) as in conventional method No. 2. In order to press with this strong reduction, in the case of a press machine, the pressure is about 2000 to 3000T, which increases the cost.In addition, when using rolls for blooming, it is necessary to take measures such as reinforcing the reduction cylinder. The amount of wear will also be large. In the rolling method of the present invention, initial and last pressing is performed on the tail side, and taper rolling is performed in the middle to late stages of the initial pressing on the front side. The reason why the methods are different for the tail and front is due to the difference in metal flow during billet rolling, as shown in Figure 3.

It can be said that the present invention divides the second conventional method into two steps. That is, H2>H3>H3, there is no need to strengthen the reduction cylinder for blooming, and the amount of roll wear is significantly different compared to conventional method 2. As a result of the above, >h2>h3, and the crop loss is minimized in the present invention.

As shown in L5 diagram (a), the pressing position is determined from the relationship 2Δh = (r − -) tan θ, and Δh =
In the case of 90mm, u#200mm. The reason why the position b in the figure is optimal is that it is only at point b that the pressing area S effectively becomes the convex shape 81 in the figure. In the case of a, the pressing area S becomes small, and in the case of C, the convex shape of S becomes small.

Further, when pressed as shown in FIG. 5(b), the center of the steel piece becomes concave as shown in S2, so such a method should not be adopted.

The actual pressing position is, when Δh = 90mm,
It is necessary to keep fi in the range of 170 to 230 mm, which is equivalent to setting Δh to 60 to 120 mm as shown in FIG.

FIG. 6 shows an explanatory diagram of the difference in metal flow between the conventional method and the present invention. In this case, the initial pressing has to be divided into several times because there are limits on the amount of pressing due to the blooming function and restrictions on the hole shape, and it is important to take this into consideration when creating a pass schedule.

(Example) Next, the present invention will be explained in detail based on examples.

Example 1 Using a blooming mill, continuous slabs were subjected to bloom edge forming under the conditions shown below by varying the amount of pressing, and the crop shape was investigated by changing the timing of pressing. The results are shown in Figure 7.
It is shown in FIG.

1) Heating temperature: 1180°C 2) Continuous slab dimensions: 240HX 375' mm 3) Blooming roll diameter: 1050φ [l1m4) Blooming finishing dimension: 180φnun 5) Billet finishing dimension: 122φmm Figure 7 is for blooming rolling This shows the crop loss weight when changing the pressing amount when the bloom end is pressed by a roll at the beginning of blooming rolling.As the pressing amount increases, the shape becomes flatter than concave, and the crop loss weight changes. However, if the amount of pressure is too large, it will become convex and the crop loss weight will increase. Therefore, when pressing is actually performed, the pressing amount is 90 m, which reduces the crop loss weight.

Figure 8 shows the crop loss weight when the timing of pressing with the blooming rolls is changed.Among these, the all-process pressing has the lowest weight of blackthroat, but this is actually not efficient. Since the deterioration is noticeable, initial pressure is actually being implemented.

Example 2 In addition to initial pressing, taper rolling and pressing after finishing the blooming (last pressing) were performed using a blooming mill to investigate the crop shape. The results are shown in FIG. 9 and FIG. 1O.

As shown in FIG. 11, this taper rolling is carried out only on the front side in consideration of the metal flow of billet rolling. Also, pressing after blooming is carried out only on the tail side, taking into consideration the metal flow of billet rolling.

Fig. 9 shows the front crop weight when Taber rolling on the front side is performed using the blooming rolls, and as a result, Δhxfl is 20 mm x 300 [oII
+ was good.

Figure 10 shows the crop weight when pressing after finishing the blooming on the tail side (last pressing) is carried out using a blooming roll. As a result, it was found that a pressing amount of 40 mm is good. Ta.

As a result of carrying out the above, the shape of the billet end became good as shown in FIG. 11, and the crop loss was also reduced.

FIG. 12 shows conventional method No. 1. This is a comparison of the crop loss weight between Part 2 and the present invention. As is clear from the figure, it can be seen that the method of the present invention can significantly reduce the crop loss weight.

(Effects of the Invention) According to the present invention described above, it is possible to minimize crop loss with the current equipment as compared to the conventional method.

In addition, as shown in Fig. 11, cracks in the shape of the billet end are eliminated by the present invention, so when the next process includes a rolling line and a process of crop cutting,
By sharing the crop, a significant improvement in the blooming yield can be expected. Furthermore, crop loss can be appropriately and economically reduced using existing equipment without introducing a special dedicated press.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the blooming procedure of the conventional method and the present invention;
The figure is a schematic explanatory diagram of a blooming and rolling line to which the method of the present invention is applied, Figure 3 is an explanatory diagram of the metal flow of the conventional method and the present invention, and Figure 4 is a schematic diagram of the metal flow of conventional blooming and billet rolling. An explanatory diagram of the flow, Fig. 5 is an explanatory diagram of the pressing position of the present invention, Fig. 6 is an explanatory diagram of the metal flow of the conventional and the present invention, and Fig. 7 is a crop when the amount of pressure at the bloom end is changed. loss ff
1ffi, Figure 8 is a graph showing the relationship with crop loss weight when the timing of pressing is changed, and Figure 9 is a graph showing the relationship with crop loss weight when front side taper rolling is performed. FIG. 1O is a graph showing the relationship with crop loss weight when the last pressing amount after blooming is changed, FIG. 11 is an explanatory diagram of the shape of the billet end obtained by the present invention, FIG. 12 is a graph comparing the crop loss weight 1 between the conventional method and the present invention. DESCRIPTION OF SYMBOLS 1... Continuous casting machine, 2... Heating furnace, 3... Blooming rolling machine, 4... Roll for blooming rolling, 5... Billet rolling machine, 6
... shearing machine, 7 ... dispensing device, 8 ... steel billet, 9
... Billet, 10-... Bloom, l l-... Fishtail.

Claims (1)

[Claims] Bloom is produced from continuous slabs using a reversible blooming mill,
In the method for preventing the growth of fishtails in the process of manufacturing a billet using a billet rolling machine and then cutting the crops at both ends using a shearing machine, the tail and front of the bloom end are removed during the above-mentioned blooming process. 1. A method for forming the end of a steel billet, which comprises performing multiple stages of pressing using blooming rolls, and then rolling the billet.