JP4427024B2 - Strip rolling method - Google Patents

Description

  The present invention relates to a rolling method in which surface flaws are reduced and dimensional accuracy is improved over the entire length of a rolled material in a sizing mill used in hot finishing of strips such as wire rods and bar steels.

  In recent years, in the hot rolling of wire rods and steel bars, a sizing mill has been installed on the rear side of a finishing mill such as a block mill to improve the dimensional accuracy of the product (dimensional accuracy of the finished wire diameter). Precision rolling) has been carried out. This sizing mill includes two-way roll method, three-way roll method and four-way roll method rolling mills. Usually, four rolling mills are arranged, and these four rolling mills are driven in common, It has a block mill structure in which the roll speed of the rolling mill can be changed by a speed increaser. And in the former two rolling mills (two passes), rolling is performed at a comparatively high surface reduction ratio as in the normal rolling with a cross-sectional reduction rate (area reduction rate) of 10 to 20%, and the latter two rolling mills In (2 passes), there is a sizing mill that performs rolling with a reduced surface area of several percent. Hereinafter, the sizing mill includes all types of sizing mills described above.

  As a feature of the sizing mill, since rolling is performed with a reduced area ratio, it is possible to perform rolling with high dimensional accuracy, and since it is a block mill structure of a common drive system, it is between each rolling mill, that is, between roll stands (hereinafter, It is mentioned that the rolling is performed in a state where tension is applied to the rolled material. As described above, rolling is performed in a state where the tension between the stands is applied, so that vibrations are generated in the rolling material between the stands depending on factors such as a pass (hole type) schedule, a steel type and temperature of the rolling material, and a roll gap adjustment. There is a case. When vibration occurs in the rolled material between the stands, the rolled material comes into contact with guides for guiding the rolled material, which are attached to the exit side and the entry side of the rolling roll, and surface flaws are generated in the rolled material. Accordingly, there arises a problem that the product dimension (finished dimension) varies over the entire length of the rolled material.

As precision rolling for rolling a material to be rolled such as a wire rod or steel bar with high dimensional accuracy, for example, in Patent Document 1, two units of a two-roll system are provided on the rear stage side of the finishing mill (block mill), that is, on the downstream side in the rolling direction A sizing mill with a tandem arrangement of a first-stage rolling mill consisting of two roll stands and a second-stage rolling mill consisting of two roll stands of the same two-roll type. A precision rolling method is disclosed in which rolling is performed so that the dimensional tolerance is within ± 1%, and the reduction rolling is performed so that the reduction in area is 10% or less in the latter-stage rolling mill.
JP 2004-358515 A

  However, even if rolling is performed under the above-described rolling conditions disclosed in Patent Document 1, the final (second) roll stand and the previous (first) roll of the rear-side rolling mill with reduced surface area pass When vibration occurs in the rolled material between the stands, it causes periodic dimensional variations over the entire length of the rolled material, making it impossible to perform precision rolling.

  Therefore, an object of the present invention is to hot-roll strips such as wire rods and bar steels, and to suppress vibration of the rolled material between roll stands in the rolling process in a sizing mill installed at the subsequent stage of the finish rolling mill. Another object of the present invention is to provide a rolling method capable of reducing surface wrinkles and improving dimensional accuracy over the entire length of the rolled material.

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

That is, the method for rolling a bar according to claim 1 is a method for rolling a bar in a sizing mill that is installed on the rear side of a finish rolling mill and has at least two roll stands, and is a final roll stand of the sizing mill. Controlling the tension acting on the rolling material on the entry side of the roll stand (F-1) with respect to the direction of the force along the rolling direction acting on the roll stand (F-1) before (F). Therefore, it is characterized by keeping constant .

  As a cause of the vibration of the rolled material between the roll stands described above, it is considered that the force acting on the rolled material between the stands is on the compression side. However, in general, a pass schedule in which compressive force acts on the rolled material between the stands is not adopted, and a pass schedule designed so that an appropriate tension acts on the rolled material between the stands. Adopted. Even when a pass schedule designed so that an appropriate tension acts is applied, vibrations may occur in the rolled material depending on the temperature and material (steel type) of the rolled material. As a result of investigating the cause of this vibration, the present inventors have found that in a roll stand where vibration has occurred, the force along the rolling direction acting on the roll housing (hereinafter also referred to as the force in the rolling direction) becomes zero. Nearly, it was found that such a state was caused by a change in the direction of the force acting on the rolled material during rolling. That is, since the force along the rolling direction acting on the roll housing is close to zero, the direction of the force along the rolling direction acting on the roll housing is likely to fluctuate during rolling. The rolling material vibrates due to movement along the direction. In particular, when the movement of the upper and lower rolls incorporated in the roll stand along the rolling direction is not uniform, the vibration of the rolled material becomes more remarkable.

The balance of the force acting on the roll housing along the rolling direction, that is, the direction of the force, is generally possible by changing the hole shape, the speed increasing ratio between the roll stands, and hence the tension between the stands. In particular, in the sizing mill having the extremely low surface area as described above, in order to suppress the vibration of the rolled material, as described above, the roll stand (F-1) one before the final roll stand (F). It is important to keep the direction of the force acting along the rolling direction constant so as not to fluctuate due to various rolling factors. Here, the force along the rolling direction includes both the traveling direction of the rolled material and the force in the opposite direction.
By adjusting the rolling speed between the roll stand (F-1) and one upstream roll stand, the tension acting on the rolled material during this period is controlled, thereby acting on the roll stand (F-1). The direction of the force along the rolling direction can be kept constant. When this tension control is performed, it is desirable that the sizing mill pre-stage rolling mill and the ultra-reduced surface ratio post-side rolling mill are driven individually.

  The rolling method of the strip according to claim 2 is characterized in that the force along the rolling direction acting on the roll stand (F-1) is applied to the entry side tension (TN1) of the roll stand (F-1) and the entry side rolled material. It is obtained by the difference between the product TN1 × S1 with the cross-sectional area (S1) and the product TN2 × S2 with the exit-side tension (TN2) and the exit-side rolled material cross-sectional area (S2).

  The method for rolling steel bars according to claim 3 is characterized in that the force along the rolling direction acting on the roll stand (F-1) is directly measured using a strain gauge.

The method for rolling steel bars according to claim 4 is characterized in that the magnitude of the force along the rolling direction acting on the roll stand (F-1) before the last roll stand (F) is 10 kgf or more. And

  Thus, by increasing the force along the rolling direction acting on the roll stand (F-1) to 10 kgf or more, the influence of the fluctuation factor of the rolling condition is suppressed, and the force acts along the rolling direction. Force can be kept stable in a certain direction. In addition, the force along the rolling direction acting on the roll housing is obtained by measuring the tension between the stands and the rolled material size, thereby calculating the product of the entry side tension (TN1) of the roll stand and the entry side rolled material cross-sectional area (S1). It can be determined by TN1 × S1 and the difference (TN1 × S1−TN2 × S2) between the product TN2 × S2 of the exit side tension TN2 and the exit side rolled material cross-sectional area (S2). It is also possible to measure directly by attaching a strain gauge to the roll housing.

In the present invention, a sizing mill having at least two roll stands installed on the rear stage side of a finish rolling mill of a hot rolling mill row for wire rods and bar steels, between the roll stands depending on the temperature and material of the rolled material. As a result of investigating the cause of vibration in the rolled material, in particular, the direction of the force along the rolling direction acting on the roll stand (F-1) immediately before the final roll stand (F) of the sizing mill is 1 it turned out during rolling of the rolled material it is important to keep constant, controlling the tension acting on the rolled material between those the roll stand (F-1) and one upstream of the roll stand Thus, the direction of the force along the rolling direction is kept constant. This effectively suppresses the vibration of the rolled material between the stands in the sizing mill, especially during the rolling process by the latter-stage rolling mill, thereby reducing surface flaws and generating dimensional variations over the entire length of the rolled material. Thus, it is possible to improve the dimensional accuracy.

  Embodiments of the present invention will be described below with reference to the accompanying FIGS. 1 to 3 together with examples.

  FIG. 1 shows a layout of a finish rolling mill row of a wire rod and bar (bar-in-coil) rolling line. As the finishing mill 1, a block mill in which roll stands (normally 8 to 10) each incorporating a plurality of two-way rolls 1 a to 1 g are alternately arranged with a 90 ° roll axis is installed. It is a block mill in which a roll stand (four in the embodiment) in which a plurality of two-way rolls 2a to 2d are incorporated on the rear stage side, that is, the downstream side in the rolling direction, is alternately inclined by 90 ° roll axis. A sizing mill 2 is installed as a final finish rolling mill. A water cooling zone 3 is installed between the finish rolling mill 1 and the sizing mill 2. FIG. 2 schematically shows the roll arrangement of the sizing mill 2, and roll stands (F-3), (F-2), (F-1), F comprising two-way rolls 2a to 2d, respectively. However, the roll stands (F-3), (F-2), (F-1), and the two-way rolls 2a to 2d of F are provided respectively for the 90 ° roll axis. Commonly driven by the motor M via a speed increaser (not shown).

  The billet extracted from the heating furnace passes through the rough rolling mill row and the intermediate rolling mill row, and the cross-sectional area decreases sequentially. This rolled material 5 is the finish rolling mill 1 and the required entry side dimension to the sizing mill 2. Rolled into Then, the rolled material that has passed through the finish rolling mill 1 is adjusted to a required entry temperature by the water cooling zone 3 and introduced into the sizing mill 2. In this sizing mill 2, rolling is performed at a normal area reduction ratio of 10% or more in the roll stands (F-3) and (F-2) of the preceding rolling mill in the same manner as in the finish rolling mill (block mill) 1. With the roll stand (F-1), F, which is a subsequent-stage rolling mill, rolling is performed with a reduced area ratio of several percent or less, and finished to a product size that satisfies the target dimensional tolerance.

The force along the rolling direction acting on each roll stand of the sizing mill was measured when rolling from 155 square billet (low alloy steel) to a product size of Φ5.5 mm. As shown in Table 1, the measurement of the force along the rolling direction is as follows: roll stand (F-1) (NO. 3st) immediately before the final roll stand (F) (NO. 4st) of the sizing mill 1 When the roll gap of the upstream roll stand (F-2) (NO.2st) of the roll stand (F-1) is adjusted so that the force Tf in the upstream or downstream direction acting on the roll is 10 kgf or more. (NO.1, Reference Example), when the tension acting on the rolling material on the entry side of the roll stand (F-1) is controlled by changing the speed increase ratio of each speed increaser (NO.2, Example) In particular, three cases were carried out when no adjustment / control was performed (NO. 3, comparative example).

From Table 1, in the case of NO.3 (comparative example) in which no adjustment or control is performed, the rolling direction force acting on the roll stand (F-1) is 5 to -5 kgf, and the rolling direction is one force. It changed during rolling of the material, and vibration occurred between this roll stand (F-1) and the final roll stand (F), and periodic dimensional fluctuations were observed in one rolled material. In contrast, in No. 1 ( reference example), the roll of the roll stand (F-2) on the upstream side thereof has an absolute value of 10 kgf or more in the rolling direction acting on the roll stand (F-1). Since the gap was adjusted, a constant force acts on the roll stand (F-1) in the direction of -10 to -20 kgf (upstream direction of rolling), and the roll stand (F-1) and the final roll stand (F) No vibrations and accompanying dimensional fluctuations and surface flaws occurred between the two), and the target dimensional tolerance was satisfied. In No. 2 (Example), the tension of the rolled material on the entry side was controlled so that the direction of the force acting on the roll stand (F-1) was constant. ), A constant force acts in the direction of −40 to −37 kgf (upstream direction of rolling), and vibration occurs between the roll stand (F-1) and F as in the case of NO.1 ( reference example). And the surface flaws accompanying it did not occur, and the target dimensional tolerance was satisfied. Thus, the force in the rolling direction acting on the roll stand (F-1) can be measured online using a strain gauge, and can be constantly monitored, and based on the measurement results, The roll gap of the roll stand (F-1) and / or the roll stand on the upstream side thereof can be feedback controlled so that the direction of force in the rolling direction is constant without fluctuation. Incidentally, the force in the rolling direction acting on the roll stand (F-1) is, NO.1 (Reference Example) shown in Table 1, the sign of the rolling upstream (force in the case of NO.2 (Example) It is also possible to control the roll gap or / and the tension so as to be constant not only in the minus (−) side but also in the rolling downstream direction (the sign of the force is on the plus (+) side).

  FIG. 3 shows a sizing mill 2S according to another embodiment, in which roll stands (F-3), (F-2), (F-1), and F each having two-way rolls 2a to 2d are alternately arranged. The roll stands (F-3) and (F-2), and the rear roll stands (F-1) and F of the former stage rolling mill are respectively provided with a speed increaser (not shown). Are commonly driven by the electric motor M separately. And the dimension measuring device 4 is installed between the roll stands (F-3) and (F-2) of the former stage side rolling mill and the roll stands (F-1) and F of the latter stage side rolling mill. Dimensional measurements such as material height and width are possible. The sizing mill 2S of this driving system is different from the sizing mill 2 in that the roll stand 2a, 2b on the front stage side has a reduction area ratio of several% or less in addition to rolling with a normal area reduction ratio of 10% or more. Rolling can also be performed. Since the roll stands (F-3) and (F-2) of the former stage rolling mill and the latter stage roll stand (F-1) and F are separately driven in common, the former stage rolling mill and the latter stage rolling mill Control of the number of rotations can be performed separately, and the tension control acting on the rolling material on the entry side of the roll stand (F-1) (NO.3st) before the last roll stand (F) (NO.4st) Becomes easier. In addition, when rolling at an extremely reduced surface ratio is performed with the front roll side stands (F-3) and (F-2) of the sizing mill 2S, the front roll side stand (F-2) before the last roll stand (F-2). The direction of the force along the rolling direction acting on the corresponding roll stand (F-3) is the same as in the case of the roll stand (F-1) on the rear stage side of the sizing mill 2S. It is desirable to keep constant by controlling the tension acting on the roll stand and to suppress the vibration generation between the roll stands (F-3) and (F-2).

  The rolling method described above can be applied not only to the above-described two-way roll type sizing mill but also to a three-way roll type or a four-way roll type sizing mill.

It is explanatory drawing which shows the finishing rolling mill row | line of a strip rolling. It is explanatory drawing which shows typically the sizing mill of the finish rolling mill row | line | column of FIG. It is explanatory drawing which shows typically the sizing mill of another form of the finishing rolling mill row | line | column of FIG.

1: Finish rolling mill 1a-1g: Two-way roll 2, 2S: Sizing mill 2a-2d: Two-way roll 3: Water-cooled zone 4: Dimension measuring instrument 5: Rolled material

Claims (4)

A method for rolling steel bars in a sizing mill that is installed on the rear stage side of a finish rolling mill and has at least two roll stands, the roll stand (F−) before the last roll stand (F) of the sizing mill The direction of the force along the rolling direction acting on 1) is kept constant by controlling the tension acting on the rolling material on the entry side of the roll stand (F-1). A method of rolling steel bars.   The force along the rolling direction acting on the roll stand (F-1) is a product TN1 × S1 of the entry side tension (TN1) of the roll stand (F-1) and the entry side rolled material cross-sectional area (S1). The strip rolling method according to claim 1, wherein the method is determined by a difference between the exit side tension (TN2) and the product TN2 × S2 of the exit side rolled material cross-sectional area (S2).   The method according to claim 1, wherein a force along the rolling direction acting on the roll stand (F-1) is directly measured using a strain gauge. The magnitude | size of the force along the rolling direction which acts on the roll stand (F-1) before one last roll stand (F) is 10 kgf or more, Any one of Claim 1 to 3 characterized by the above-mentioned. The rolling method of the described bar steel.

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