JPS6321562B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an in-line rolling method in which a rotary caster, that is, a continuously cast piece having a trapezoidal cross-sectional shape is rolled directly into a billet in a continuous casting line. Conventionally, a so-called VH type rolling mill, which alternately combines vertical roll type and horizontal roll type, has been adopted and operated for the production of billets as an in-line rolling method for continuous slabs. However, in many cases, the final product is a relatively low-grade product such as a concrete bar, and the standards for the billet's cross-sectional shape and surface flaws are lax, and when we look at the semi-finished billet stage, the cross-sectional shape is extremely poor and the surface is It is normal to see many scratches. Therefore, as long as conventional rolling methods are used, it is practically difficult to produce billets of high-grade wire material from slabs with trapezoidal cross sections, and even if they were produced, the cost of removing defects in subsequent processes would be enormous. . In addition, in terms of roll durability and rolling power, the loss is extremely large and it is not economical. Next, conventional problems will be explained based on a specific example. Table 1 shows typical examples of conventional methods for rolling billets from slabs with trapezoidal cross sections.
The first and No. 3 passes use grooved rolls, and the No. 2 and No. 4 passes use horizontal rolls.

[Table] In Figure 2, Ld and Hm are given by the following formulas. Ld=√・( ₀ − ₁ ) Hm=(H ₀ +H ₁ )/2 In other words, the first problem is that the slab with trapezoidal cross section is No.
No. 1 box pass causes the material to be rolled down, but because the cross-sectional area of the lower half of the material is larger than the upper part, no.
The exit side of the pass tends to curve upward. This is blocked by the side walls of the hole mold, and as a result the material rubs strongly against the side walls of the box hole mold. As a result, scratches as shown in part 1 of Figure 4 occur on the surface of the material, and as a result, the side walls of the hole are also severely worn, and in terms of rolling power, the increase in torque due to this friction results in power loss. appears. The second problem is that the No. 2 and No. 4 passes are flat rolls, so the effect of the trapezoidal shape of the billet remains even after 4 passes, as shown in 2 in Figure 4, and the corners of the billet are also flat rolls. It will not be a uniform radius like 3 in Figure 4, but will be angular. In the figure, a: the first pass, b: the second pass, c: the third pass, and d: the fourth pass. The third problem is that there is no consideration given to rolling power. In other words, because the relationship between roll diameter and rolling reduction amount is inappropriate, Ld/Hm in Table 1 is relatively small, and the rolling pressure acting on the roll surface becomes high on the entry side of the roll bite, causing the so-called peening phenomenon. Therefore, the rolling load and torque become relatively large, which is extremely disadvantageous in terms of power. The present invention fundamentally solves these problems and provides an excellent rolling method that can be applied to billets for high-grade wire rods. It has been found that the amount of reduction in the first pass has a very large effect on the first problem, that is, the upward warping phenomenon during roll bite. Figure 3 shows the relationship. In this figure, a flat roll made of plasticine and gypsum is used to roll down a trapezoidal section from the side, and the effect of the amount of roll on upward warpage is basically investigated. It has been found that as the reduction amount increases, the warpage decreases. This tendency also appears when using the box-hole type. As shown in FIG. 3, there is a close relationship between the rolling reduction rate in the first pass and the warpage of the material at the exit side of the first pass. Warpage is maximum when the reduction rate is 17-18%,
As the rolling reduction rate is increased further, the warpage gradually decreases. Therefore, from a practical point of view to enable industrialization, in the present invention, the rolling reduction rate in the first pass is limited to 30% or more. In the conventional method, rolling is performed at or below the point shown in FIG. FIG. 4 shows the metal flow when rolling was performed using a box hole die with this reduction amount. After rolling, the upper surface of the material has some lap flaws caused by friction with the roll flange. For reference, FIG. 5 shows the metal flow when using the box hole type with the reduction amount corresponding to the points in FIG. 3. As you can see from 1 in Figure 5,
The lap flaw seen in 1 in Figure 4 is not observed.
In other words, it is shown that at least lap defects can be prevented if the rolling reduction is 35% or more. a in the diagram
is the first pass. Based on this basic fact, the present invention provides an extremely excellent rolling method shown in Table 2.

[Table] First, for the first pass, the rolling reduction ratio was set to 40% or more, and in the example, it was set to 43%. Further, the roll used was a flat roll 13 having no hole shape as shown in FIG.
Furthermore, a roller guide 12 shown in FIG. 8 was installed at close range on the front and rear surfaces. By taking the above measures, it has become possible to perform good rolling with extremely little warpage, without any scratches, and with no problem in connection to the subsequent second pass. That is, it is clear that the adoption of a large rolling reduction ratio in the first pass (point c in FIG. 3) will further improve the improvement compared to point b in the same figure, based on the basic characteristics of the upward warpage in FIG. 3B. Furthermore, since no hole mold is used, there is no restriction by the hole wall, and no scratches occur at all. Furthermore, since the upward warpage is basically slight, the material can be sufficiently properly guided by the roller guides on the front and rear surfaces. The reason for installing roller guides on the front and rear surfaces is as follows. Normally, as shown in FIG. 9A, the entry side is restrained by the weight of the material, so the exit side is warped. Therefore, for example, if a guide is installed on the exit side to suppress the upward warpage, the entry side will become upward warped as shown in FIG. 9B.
During rolling, warping is not preferable because it causes trouble. Therefore, guides are installed on the front and rear surfaces of the roll. The reason why the guide is of a roller type is to reduce frictional resistance, which is preferable in terms of power and surface flaws. Next, the second pass and the third pass will be explained. As for ensuring the product shape, which is the second problem with the conventional method, a good shape can be obtained by rolling in two successive passes using a groove die. However, the point to be kept in mind at this time is to make the relationship between the groove bottom width W of the hole mold and the width B of the input material shown in FIG. 10, that is, the margin ratio (W-B/W×100), appropriate. Specifically, between 0 and 5%, preferably between 2 and 5%.
By setting it to 3%, it is possible to significantly reduce the frictional resistance of the sidewalls of the hole. This is advantageous in terms of surface flaw power. If the margin ratio is set to 5% or more, the material collapses within the hole mold during roll bite, resulting in a shape resembling a parallelogram cross section as shown in FIG. 10, 5B, which is undesirable. FIG. 11 shows an example in which a billet was actually rolled from a slab having a trapezoidal cross section shown in Table 2. It is possible to obtain a very good product with three passes. Rolling that is advantageous in terms of rolling power, which is the third problem with the conventional method, is achieved by the following basic idea. That is,
The diameter of the roll for each pass must be appropriately selected according to the dimensions of the material, and specifically, the average value (Hm) of the height dimensions on the input and exit sides of the material, and the contact between the roll and the material Projected length of surface in rolling direction (Ld)
The roll diameter of all passes is preferably selected between 0.7 and 1.0 so that the ratio Ld/Hm does not become less than 0.5. By doing so, it is possible to prevent an abnormal increase in roll surface pressure called peening hill, advantageous characteristics can be obtained in terms of both rolling load and torque, and rolling can be performed with less energy. Table 2, which is an example of the present invention, is an example of rolling a billet (122 x 122) from a trapezoidal slab (190/230 x 140), and shows the most preferable rolling distribution. The No. 1 pass can basically reduce the warping of the material by using a large rolling reduction ratio. Also,
By using a flat roll, it is possible to basically eliminate friction with the side wall of the grooved roll. This can prevent surface flaws in the material and, as a corollary, also reduce wear on the rolls. In addition, horizontal roller type roller guides 13 shown in Fig. 7 are installed on the entry and exit sides of the No. 1 pass.
was installed, corrected the slight warping of the material, and installed No.
It becomes possible to smoothly connect to 2 paths. Although this roller guide uses a unit 14 in which the entrance and exit sides are integrated as shown in FIG. 8, it is also possible to use a unit in which the entrance and exit sides are separated. By using a box hole type for No. 2 and No. 3 passes, the product shape can be shaped extremely well. Also, regarding No. 1 and No. 2 paths with large loads,
By setting Ld/Hm to about 0.8, it becomes extremely advantageous in terms of power. Furthermore, a large rolling reduction increases Ld/Hm even with a relatively small diameter roll. In addition, the adoption of a large rolling reduction ratio in the first pass has the effect of reducing the number of passes by one, which is useful for reducing the number of stands, ie, saving equipment costs. As described above, the rolling method of the present invention provides the most rational and excellent rolling method in terms of product quality, roll durability, rolling power, equipment cost, etc.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the cross section of the material, Figure 2 is a schematic diagram of roll reduction, Figure 3A is a graph of reduction rate and warpage,
Figure 3B is a schematic diagram of upward warping, Figure 4 is an explanatory diagram of a photograph of plasticine in the rolling pass process, Figure 5 is an explanatory diagram of another photograph of plasticine in the rolling pass process, and Figure 6 is a schematic diagram of a cross section of the material. , FIG. 7 is a perspective view of the present invention,
FIG. 8 is a plan view of the present invention, FIG. 9 is an explanatory diagram of warping, FIG. 10 is an explanatory diagram of hole shapes and materials, and FIG. 11 is an explanatory diagram of the rolling pass process. 10: Material, 12: Roll, 13: Horizontal roller guide, 14: Unit.

Claims (1)

[Claims] 1. When obtaining a billet with a rectangular cross section by rolling from a billet with a trapezoidal cross section obtained by continuous casting of molten steel, the length of the bottom (two parallel sides with different side lengths) of the cross section of the slab with a pair of flat rolls is The first pass is configured to reduce the length of the long side of the two parallel sides with different side lengths of the slab cross section (ΔH/H1, where ΔH: side length decrease amount, H1 :1st
The length of the long side of the slab cross section before rolling in the pass) is 30%
In addition to performing the above rolling, entering the first pass,
A rotatable guide is provided on the exit side to suppress warping of the rolled material, and subsequent passes are sequentially applied to apply rolling in a direction perpendicular to the previous pass, and at least two successive passes are performed using a roll having a groove shape. Furthermore, the hole type margin rate (margin rate = (W-
B)/W×100, where W: groove bottom width, B:
Rolling with shaping is carried out with the width of the material on the input side being 5% or less, and the diameter of the rolling roll in each pass is determined by the average value Hm of the height dimension on the input side and exit side of the material in the relevant pass, and the rolling roll. The ratio Lb/Hm of the projected dimension Ld of the length of the contact surface of the material in the rolling direction is
A method for rolling continuously cast slabs having a trapezoidal cross-sectional shape, characterized by rolling the slabs to a diameter of 0.5 or more.