JP5775378B2 - Strip rolling method - Google Patents

Description

  The present invention relates to free size rolling in continuous rolling of strips, and is an invention related to rolling technology for forming strips having a wide range of product dimensions without changing the roll hole shape.

Conventionally, in hot rolling of steel bars, that is, wire rods and bar steels, a raw material (billet) having a predetermined length is heated to a target temperature in a heating furnace and then sequentially extracted and rolled one by one. Such conventional rolling has the following problems.
(1) In the rolling of a wire rod, the final finish rolling speed reaches 100 m / s or more, and a misroll may occur due to the tip of the rolled material striking a guide or the like on the entrance side of the rolling mill. The misroll due to this stagnation may occur as long as there is a tip of the rolled material, and is more likely to occur as the rolling speed increases, and thus there is a limit to improving the productivity.
(2) In order to control the surface scale and material, the rolled material is water-cooled after finish rolling, but a non-water-cooled part is set from the viewpoint of preventing misrolling caused by the resistance of the cooling water, particularly at the tip of the rolled material. Has been. For this reason, the non-water-cooled portion at the tip of the rolled material is discarded, and there is a limit to improving the rolling yield.
(3) Generally, a block mill is used in the final finish rolling mill, and rolling is performed by applying tension to the rolled material between roll stands of the block mill. In this tension rolling, since the tension is not applied between the rolling mills (roll stands) at the leading end and the trailing end of the rolled material, the product dimensions vary. For this reason, together with the above (2), the front end portion and the rear end portion are cut off from the viewpoint of product dimensions.

  In recent years, as a means for solving these problems, for example, as described in Patent Document 1, also in the rolling of strip steel, the trailing end of the preceding rolled material that has started rolling, and the subsequent rolling extracted from the heating furnace A continuous rolling method has been developed in which the tips of the materials are sequentially joined and rolled endlessly. By adopting this continuous rolling method, the number of passes through the tip is reduced, the rate of misrolling is reduced, the amount of cut off at the tip and rear ends of the rolled material is reduced, and productivity and yield are improved. .

JP 2000-5802 A

  However, in the strip rolling that is formed into a wire rod or steel bar with a hole roll, a hole roll having a different shape is required for each target product dimension, and the rolling amount for each product dimension is often relatively small. Even if continuous rolling is performed, it is necessary to change rolls for each product dimension. This production loss due to the roll change time cannot be avoided even if continuous rolling is performed, and there is a problem that the effect of improving the productivity by continuous rolling cannot be sufficiently achieved. Also, unlike the case of plate rolling, where the target plate thickness can be controlled only by changing the roll gap, in the case of strip rolling, the conventional sizing can be used to form a product with the target dimensions only by changing the roll gap. There was a limit even if the free size rolling technology by rolling was used.

Therefore, the object of the present invention is to establish a technique for reducing the production loss due to roll change accompanying the product diameter change after realizing the yield improvement at the leading and trailing ends of the rolled material and the reduction of misroll, which are the advantages of continuous rolling. That is.

  In order to solve the above problems, the present invention employs the following configuration.

The rolling method of the bar steel according to claim 1 is a rolling method of the bar steel which continuously rolls without stopping rolling by joining the preceding material and the succeeding material of the billet extracted from the heating furnace as the material to be rolled. The target product diameter is changed without stopping the rolling, and a predetermined tension of less than 100 MPa is applied to the rolled material between the final finish rolling mill and its upstream rolling mill, and the roll clearance of the final finish rolling mill is changed from the reference gap. The product diameter is lowered by a predetermined amount, and the product diameter is changed during rolling in accordance with the target product diameter .

  In recent layouts of wire rod factories, as shown in FIG. 1, for example, there are several rolling mills as final rolling mills on the rear stage side of a block mill 5 installed as a finishing rolling mill. A sizing mill 6, which is a rolling mill with a reduced surface area for the purpose of improving accuracy, is installed.

  In general, in a block mill, since the rolling mill (roll) interval is short, loops cannot be formed and no tension can be obtained. (Roll) tension is applied. When tension is applied to the entry side and the exit side of the rolling mill, the breadth after rolling (width dimension after rolling-width dimension before rolling) decreases. When tension is added between the rolling mills in the two rolling mills, the width dimension increases because the tension between the rolling mills becomes zero when the tail end passes through the first rolling mill. Therefore, in rolling wire rods, the tension between rolling mills is adjusted as close to no tension as possible in order to prevent dimensional fluctuations of the product. On the other hand, between the block mill and the sizing mill, if tension is applied to the rolled material, the width of the rolled material increases as soon as the tail end of the rolled material passes through the block mill, and the target product dimensional accuracy Cannot be realized. For this reason, the rotation speed of the mill motor is adjusted between the block mill and the sizing mill so that tension does not act on the rolled material as much as possible.

  In the sizing mill, the last two stands usually use a “round” roll hole type with a reduced surface ratio, and the same roll hole type can be rolled over a relatively wide range of product dimensions only by changing the roll gap. There is an advantage that can be done (free size rolling). Molding a product with a diameter smaller than the standard hole mold size can be achieved by reducing the roll gap of the 4 stands (or the final 2 stands), but the smaller the roll gap, that is, the larger the area reduction ratio. As the width increases, the rolled material protrudes from the hole mold, and there is a limit to the product size range that can be rolled.

  As described above, in continuous rolling in which the preceding and succeeding materials of the billet extracted from the heating furnace are joined and rolled, there is no tail end of the rolled material until the end of continuous rolling. Even if tension is applied to the rolled material between the block mill and the sizing mill, the problem that the width dimension increases at the tail end of each billet is eliminated. In addition, when the tension on the entry side of the sizing mill changes, this tension propagates to the tension between the stands in the sizing mill, and the width spread rate at each stand of the sizing mill decreases (see Non-Patent Document 1). Even if the roll gap of the final finish rolling mill is reduced and reduced, it can be formed into a target shape without biting the rolled material from the hole mold, and the product size range that can be rolled, that is, the free size rolling range can be expanded.

Kushida et al .: R & D Kobe Steel Engineering Reports / Vol.56, No.3 (Dec.2006), P.16

The rolling method of the strip according to claim 2 is provided with a moving speed measuring device for measuring the moving speed of the material to be rolled between the final finish rolling mill and the upstream rolling mill, and the tip of the material to be rolled V0 is the moving speed of the tip of the material to be rolled until it exits the upstream rolling mill and bites into the final finish rolling mill, and the tip of the rolled material bites into the final finishing mill. After that, when the moving speed of the intermediate portion of the material to be rolled until the rear end portion of the material to be rolled passes through the upstream rolling mill is V1, the material to be rolled after leaving the final finish rolling mill A movement speed ratio R = (V1−V0) / V0 × 100 is obtained in advance over the entire length, and the movement speed ratio V0m and the movement speed ratio R measured by the movement speed measuring device in actual operation are obtained. Using the equation (1)
V1a = V0m + V0m × R / 100 --------- (1)
After the front end of the material to be rolled is caught in the final finish rolling mill, the target moving speed V1a of the intermediate portion of the material to be rolled until the rear end of the material to be rolled passes through the upstream rolling mill is obtained. The rolling between the final finishing mill and the upstream rolling mill is controlled by controlling the rotational speed of the drive motor of the final finishing mill so that the moving speed V1 of the material to be rolled becomes the target moving speed V1a. A predetermined tension is applied to the material.

  As disclosed in Patent Document 2 by the inventors of the present application, the moving speed ratio R at which the dimensions are uniform over the entire length of the rolled material after leaving the final finish rolling mill is obtained in advance by experiments and measured. By calculating the target moving speed V1a using the moving speed V0m of the rolling material tip and the moving speed ratio R, the end of the rolling material is bitten into the final finish rolling mill by a simple calculation process. As a result, it is possible to control the drive motor of the final finish rolling mill, so there is no uncontrolled part compared to the conventional technology, there is no dimensional variation over the entire length of the product, and high-precision dimensional control is possible. Become.

JP 2004-66263 A

  The strip rolling method according to claim 3 is characterized in that the moving speed measuring device is a Doppler speedometer.

  In this invention, in continuous rolling of the bar steel, tension is applied to the rolled material between the sizing mill as the final finish rolling mill and the block mill as the upstream rolling mill, and the roll gap of the final finish rolling mill is reduced. Therefore, even if the roll gap of the final finish rolling mill is reduced and reduced, the rolled material can be formed into a target shape without biting from the hole mold, and the free size rolling range can be expanded.

  Further, a moving speed ratio R at which the dimension becomes uniform over the entire length of the rolled material after leaving the final finish rolling mill is obtained in advance by experiments or the like, and the measured moving speed V0m of the rolled material tip and the moving speed are obtained. By determining the target moving speed V1a using the ratio R, the drive motor control of the final finishing mill can be performed from the moment when the end of the rolled material is bitten into the final finishing mill by a simple calculation process. Compared with the prior art, an uncontrolled portion does not occur at the tip, and there is no dimensional variation over the entire length of the product, and highly accurate dimensional control is possible.

It is explanatory drawing which shows an example of a layout of a wire rod factory. (A) It is explanatory drawing which shows the cross-sectional shape of the rolling material of each sizing mill stand exit side (reference conditions). (B) Same as above (Example of the present invention) (c) Same as above (Example of the present invention) (d) Same as above (Comparative example)

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1 as an example of the layout of the wire factory, the billet as the material to be rolled is extracted after being heated to the required hot rolling temperature in the heating furnace 1, and the rough rolling mill row 2 and intermediate rolling are extracted. The rolling is sequentially performed in the machine trains 3 and 4, the finish rolling start temperature is adjusted by water cooling in the water cooling zone 8, and finish rolling is performed in the block mill 5. And the to-be-rolled material 11 which raised the temperature by finish rolling is water-cooled by the water-cooling zone 9, the rolling start temperature is adjusted, and after final rolling by the sizing mill 6 for the purpose of improving dimensional accuracy, etc., The winding temperature is adjusted by the adjustment cooling, and the winding is taken up by the winder 7, and after necessary adjustment cooling is performed, the coil is converged into a coil shape to obtain a product.

  The billet of the rolled material is welded by a joining device (not shown) on the exit side of the heating furnace 1, and the billet is a lot such as a steel type or an order quantity, for example, by a reference hole mold corresponding to one product dimension D0. Rolled continuously in units. Next, when the product dimension is changed from D0 to D1 depending on the order quantity, the block mill 5 and the block mill 5 and the sizing mill 6 are set so that the tension acting on the material to be rolled 11 becomes a preset value. The roll rotation speed of the upstream rolling mill is uniformly reduced. Simultaneously with the adjustment of the roll rotational speed, the roll gap of the sizing mill 6 is changed to a preset value, so that the reference hole mold corresponding to the product dimension D0 can be used without changing the hole mold. Products can be rolled continuously in lot units such as steel grades and orders. Since the transition of the target product dimension from the product dimension D0 to D1 proceeds without stopping rolling, if a dimension close to the product dimension D0 using the reference hole mold is selected as the transitioned product dimension D1, it is accompanied by the dimension transition. The dimensional variation of the product when the tension setting between the block mill 5 and the sizing mill 6 is changed and when the roll gap is changed in the sizing mill 6 can be absorbed within the dimensional tolerance.

  In order to shorten the length of the rolled material in which the dimensional variation occurs when the tension and the roll gap are changed, that is, to reduce the length of the rolled material as much as possible, the final rolling speed is decreased by uniformly adjusting the number of rotations of all rolling mills during the dimensional transition. May be. This uniform adjustment of the rotation speed can be performed by changing the motor rotation speed of the rolling mill so that the ratio of roll diameter × roll rotation speed is constant in the adjacent rolling mills. At the time of the product dimension transition, the block mill 5-sizing is performed based on the difference between the actual width dimension of the product measured by an online dimension measuring device (not shown) installed on the exit side of the sizing mill 6 and the target width dimension. You may feedback-control the rotation speed ratio between the mills 6, ie, the tension | tensile_strength which acts on the rolling material in the meantime. It is desirable to control the rotation speed ratio by adjusting the motor rotation speed of the sizing mill 6.

As to the tension between the block mill 5 and the sizing mill 6, as described in Patent Document 2, the tip of the material to be rolled until the tip of the material to be rolled bites into the sizing mill (final finishing rolling mill) 6. Part moving speed (V0) and the intermediate part of the material to be rolled until the trailing edge of the material to be rolled passes through the block mill (upstream rolling mill) after the tip of the material has been caught in the sizing mill 6 The moving speed (V1) is measured with a moving speed measuring device (not shown) such as a Doppler speedometer installed between the block mill and the sizing mill, and the moving speed ratio R = (V1-V0) / V0 is calculated. Can also be used to control. That is, a moving speed ratio R = (V1−V0) / V0 × 100 at which the dimension becomes uniform over the entire length of the rolled material after leaving the sizing mill (final finish rolling mill) 6 is obtained in advance. Using the moving speed V0m of the material to be rolled measured by the moving speed measuring device and the moving speed ratio R, according to the equation (1),
V1a = V0m + V0m × R / 100 --------- (1)
The target moving speed V1a of the material to be rolled after the leading end of the rolled material is caught in a sizing mill (final finishing rolling mill) is obtained, and sizing is performed so that the moving speed V1 of the material to be rolled becomes the target moving speed V1a Controlling the tension acting on the material to be rolled between the sizing mill (final finishing rolling mill) and the block mill (upstream rolling mill) 5 by controlling the rotational speed of the drive motor of the mill (final finishing rolling mill). Can do. From the results of numerical analysis and actual machine experiments conducted by the present inventors, when the tension between rolling mills between the block mill and the sizing mill exceeded 120 MPa, the rolled material was sometimes disconnected. Although this disconnection depends on the steel type and temperature of the rolled material in addition to the tension, the tension between the block mill 5 and the sizing mill 6 is preferably less than 100 MPa from the above analysis and experimental results.

  Each sizing mill stand (# 1 (No.1std) to # 4 (No.4std)) by numerical analysis when the product dimension Φ11.5mm is the standard product dimension and the rolling conditions in the sizing mill are as shown in Table 1. 2A to 2D show the cross-sectional shape of the rolled material on the side, and Table 2 shows the analysis results of the product dimensions and the tension between stands in the sizing mill.

  As shown in Table 1 (No. 1), the rolling conditions when the product diameter is 11.5 mm, that is, the tension between the block mill and the sizing mill (= 0), and the roll gap of each sizing mill stand were used as the standard rolling conditions. . In this reference rolling condition, as shown in FIG. 2A, the material to be rolled 11 is properly filled in the hole molds 12a to 12d of the respective stands (# 1 to # 4) (the materials to be rolled 11a to 11d). . When changing the product dimensions using the cavities 12a to 12d under the standard rolling conditions, for example, when changing the product diameter to 11.0 mm as in No. 4 (comparative example), each stand (# 1 to # 1) is used. The roll gap of # 4) is lowered by 0.5 mm from the reference roll gap (reference gap). When rolled under these conditions, the product dimensions are good in both dimensional tolerance and deviation (Table 2, No. 4), but as shown in FIG. 2 (d), the bite from the hole mold 12a is # 1. Dashi occurs (arrow pointing part). When biting of the material to be rolled 11a occurs, the biting portion is pressed by the hole mold 12b of the next stand (# 2), and folding flaws are generated in the material to be rolled 11b. In addition, a negative inter-stand tension, that is, a compressive force acts between the sizing mills # 1 (1std) to # 2 (2std), and there is a concern about occurrence of misroll or vibration between the stands. Naturally, when the target product diameter is a smaller dimension, the above phenomenon becomes more remarkable.

  On the other hand, in the inventive example No. 2, in order to change the product diameter to 11.0 mm, each stand (# 1 (No. 1std) to # 4 (No. 1) is used as in the comparative example No. 4. 4std)) is reduced by 0.5mm. However, in the case of the present invention example, as shown in Table 1 (No, 2), between the final finish rolling mill and the upstream rolling mill, that is, between the block mill and the sizing mill (= the sizing mill No. 1std inlet side) ), The above-mentioned appropriate tension of 100 MPa or less is applied. Therefore, as shown in FIG. 2 (b), the material to be rolled is placed on each stand (# 1 to # 4) are properly filled (rolled materials 11a to 11d), and tension is applied between the stands of # 1 to # 4, and no compression force is applied. Thus, even if the product dimensions are changed during rolling, there is no problem such as the occurrence of folding wrinkles or misrolls, and it is possible to realize rolling with high dimensional accuracy using a sizing mill.

  Further, in the present invention No. 3, in order to set the target product diameter to 10.5 mm, the roll gap of each stand (# 1 (No.1std) to # 4 (No.4std)) is changed to the reference roll gap ( It is reduced by 0.7 to 1.0 mm from the reference gap). Thus, even if the target product diameter is further reduced, an appropriate tension of 100 MPa or less is applied to the entry side of the sizing mill # 1, so as shown in FIG. The material to be rolled properly fills the hole molds 12a to 12d of the stands (# 1 to # 4) (rolled materials 11a to 11d) without causing biting or disconnection in the process. No tension is applied between the stands and no compressive force is applied, and high-dimensional precision rolling by a sizing mill can be realized as in the case of the No. 2 invention example. In addition, although the said Example is an analysis result in case a final finish rolling mill is a sizing mill, even if a final finish rolling mill is a block mill, the present invention is applied and the same effect is acquired.

1: Heating furnace 2: Rough rolling mill row 3, 4: Intermediate rolling mill row 5: Block mill 6: Sizing mill 7: Winding machine 8, 9.10: Water cooling zone 11, 11a to 11d: Rolled material 12a to 12d: Hole type

Claims (3)

In the rolling method of the bar steel which joins the preceding material and the subsequent material of the billet extracted from the heating furnace to be a material to be rolled, and continuously rolls without stopping rolling,
The target product diameter is changed without stopping rolling, and a predetermined tension of less than 100 MPa is applied to the rolled material between the final finish rolling mill and its upstream rolling mill,
A rolling method for steel bars, wherein a roll gap of a final finish rolling mill is lowered from a reference gap by a predetermined amount, and a product diameter is changed during rolling in accordance with the target product diameter . Between the final finish rolling mill and the upstream rolling mill, a moving speed measuring device for measuring the moving speed of the material to be rolled is provided, and the tip of the material to be rolled leaves the upstream rolling mill, The moving speed of the leading end of the material to be rolled until it is caught in the final finish rolling mill is V0, and the trailing end of the rolled material after the leading end of the rolled material is bitten in the final finishing rolling mill. Is the moving speed at which the dimension is uniform over the entire length of the material to be rolled after leaving the final finishing mill, where V1 is the moving speed of the intermediate portion of the material to be rolled until it exits the upstream rolling mill. A ratio R = (V1−V0) / V0 × 100 is obtained in advance, and using the moving speed V0m measured by the moving speed measuring device and the moving speed ratio R, the equation (1)
V1a = V0m + V0m × R / 100 --------- (1)
After the front end of the material to be rolled is caught in the final finish rolling mill, the target moving speed V1a of the intermediate portion of the material to be rolled until the rear end of the material to be rolled passes through the upstream rolling mill is obtained. The rolling between the final finishing mill and the upstream rolling mill is controlled by controlling the rotational speed of the drive motor of the final finishing mill so that the moving speed V1 of the material to be rolled becomes the target moving speed V1a. 2. A method for rolling steel bars according to claim 1, wherein a predetermined tension is applied to the material.   The strip rolling method according to claim 2, wherein the moving speed measuring device is a Doppler speedometer.

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