JP3252751B2 - Strip width control method in cold tandem rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cold rolling a metal plate, and more particularly, to a method for connecting a plurality of coils to perform continuous rolling, which is capable of breaking a plate at a connection point between a preceding coil and a following coil. The present invention relates to a cold rolling method for preventing a sheet width from being changed due to a change in a rolling speed.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand from customers for improving the quality accuracy of plate materials (hereinafter simply referred to as "rolled plates") manufactured by rolling various materials.

[0003] In the field of cold rolling, many means for improving flatness such as plate thickness accuracy and flatness and bending have been constructed, and high-precision rolling has been made possible. However, the improvement of the plate width accuracy is not enough. If the strip width after rolling is smaller than expected, dimensional defects will occur. If the width of the sheet is rolled beforehand to avoid the width shortage, the extra width must be removed after the rolling, so that the productivity and the yield are reduced.

[0004] When a coil is tandem-rolled using a plurality of rolling mills, a change in rolling speed causes a change in sheet width. The plate width becomes wider at the time of deceleration, and becomes smaller at the time of speed increase. At the coil connection point when connecting multiple coils and performing continuous rolling,
In some cases, coils of different dimensions (thickness and width) are connected, and the inner and outer peripheries of the hot-rolled coil to be connected are also unstable in terms of material and contain many nonmetallic inclusions and surface flaws, so the plate breaks. It is also a part where the occurrence of liability is likely to occur. The risk of plate breakage is particularly high in a later stage where the plate thickness is reduced, the material is hardened, and the tension is increased and rolled. For this reason, when the coil connection point is rolled, it is passed at a reduced speed. It has been observed that large width fluctuations occur during this deceleration, and improvement measures are desired.

A method for controlling the tension between stands to adjust the sheet width to a target value in response to fluctuations in the rolling speed is disclosed in Japanese Patent Application Laid-Open No. Hei 5-
No. 76916. In this method, it is necessary to increase the tension in order to prevent the plate width from spreading at the reduction portion. For this reason, there is a problem that the probability of breakage is further increased at the coil connection portion during continuous rolling where there is a risk of breakage even under normal operating conditions.

Japanese Unexamined Patent Publication (Kokai) No. 62-296904 discloses a method of adjusting a sheet width fluctuation amount to a target value by controlling a sheet crown ratio. In this method, when rolling is performed so that the sheet crown ratio, which is a value obtained by dividing the sheet crown amount by the sheet thickness at the center of the sheet width, is increased, the sheet width is increased, and conversely, rolling is performed so that the sheet crown ratio is reduced. In this case, the width of the rolled metal plate is reduced.

FIG. 9 schematically shows a change in flat shape that occurs in response to a change in thickness distribution in the width direction of the sheet due to rolling.
Strip crown amount (C) is the difference of the plate thickness (h _c) and the thickness of the plate end portion in the width direction of the plate width direction central portion _{(h e) (h c -h} e), the strip crown ratio (gamma) It is obtained as _{(h c -h e) ÷ h} c. FIG. 9 (a) shows a case where rolling is performed so that the sheet crown ratio becomes larger than before rolling, and the flat shape after rolling tends to have an ear wave. FIG. 9 (b) shows a case where rolling is performed so that the sheet crown ratio becomes small, and the flat shape after rolling tends to elongate in the middle.

When the plate width is controlled by the method disclosed in Japanese Patent Application Laid-Open No. 62-296904, when the plate width is increased, the flat shape becomes an ear wave, and when the plate width is reduced, the middle shape is elongated. Become. As described above, in order to suppress the spread of the sheet width caused by the deceleration near the connection point where the sheet width is likely to fluctuate because the speed is reduced during continuous rolling, it is necessary to control the flat shape to have middle elongation. Becomes However, when rolling is performed in the middle elongation shape, the tension is concentrated on the end portion of the sheet width, and the sheet is easily broken from the end portion of the sheet width. The method disclosed in Japanese Patent Application Laid-Open No. 62-296904 does not take into account any breakage that easily occurs during cold rolling in which the tension between stands is increased, and there is a problem in applying this method as it is. .

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of controlling a sheet width in cold tandem rolling which can prevent a change in the sheet width without a trouble such as a sheet break even if the rolling speed is changed. It is to be.

[0010]

The gist of the present invention is as follows.
The present invention relates to a method for controlling a sheet width in cold tandem rolling.

In the cold tandem rolling using a plurality of rolling mills, the influence of the rolling load and the control amount of the shape control means on the variation of the width of the material to be rolled for each steel type, each thickness and the width of the material, The effect of the rolling load and the shape control amount on the difference in the elongation strain between the plate width end and the center and the relationship between the rolling speed and the rolling load are obtained in advance for each stand, and in response to the change in the rolling speed, A shape that is necessary to keep the sum of the plate width fluctuations generated at each stand within the specified range, and that the difference in the elongation strain rate at the end and the center of the plate width generated at each stand does not fall below the specified limit value A width control method in cold tandem rolling, wherein an appropriate control amount of the control means is calculated for each stand, and the shape control means of each stand is controlled according to the calculated value.

The present invention has been completed on the basis of the following findings regarding the plate width fluctuation occurring during cold rolling.

(1) FIG. 8 shows the results of a study conducted by the inventor of the present invention on the state of fluctuations in the sheet width caused by the fluctuations in the rolling conditions during cold rolling, using an experimental rolling mill. FIG. As shown in FIG. 8, the sheet width decreases as the rolling speed increases, the tension increases, the rolling reduction decreases, and the roll bending force increases. When the rolling speed, the tension or the rolling reduction changes, the rolling load also changes. Therefore, the influence of the above-mentioned rolling conditions on the variation in the sheet width can be approximately arranged as a relationship with the rolling load.

(2) As shown in FIG. 8 (e), there is a proportional relationship between the amount of change in the sheet crown ratio due to rolling and the amount of change in the sheet width. Since the sheet crown amount is affected by the distribution of the roll gap formed between the upper and lower work rolls, the control amount of the means for controlling the amount of deflection of the work roll (for example, the bending force of a work roll bender. There is also a proportional relationship between the "control means" and "shape control amount") and the sheet width fluctuation amount. If the shape is controlled by a method that does not directly affect the rolling load, such as the roll bending method that controls the bending of the roll by applying a bending moment in the axial direction of the roll, the sheet crown can be changed without changing the rolling load. Can be changed.

(3) By predicting a change in the sheet width from a change in the rolling load caused by the change in the speed, and adjusting the shape control amount so as to cancel the change in the sheet width, the change in the sheet width due to the change in the speed is suppressed. You can do it.

When the crown is changed, the flat shape changes. When adjusting the shape control means in the direction in which the sheet crown ratio increases, there is a possibility that the sheet is broken due to the concentration of tension at the end of the sheet. In particular, if the thickness of the sheet is controlled to increase the sheet crown ratio at the subsequent stage of the tandem rolling mill in which the sheet is thin and the tension is high, the risk of breakage increases.

In order to prevent this, the above (1) to (3)
In addition to the above, rolling is performed under the following conditions (4) and (5).

(4) When changing the rolling speed in cold tandem rolling, the crown ratio is adjusted mainly by the former stand. During deceleration, the width of the plate is reduced by adjusting the shape control means in the direction in which the plate crown ratio decreases. When speeding up, return to the original. Since the front stand has a large plate thickness, a plate crown control effect, that is, a plate width control effect is large. When the sheet thickness is large, the flat shape is hard to change even if the sheet crown ratio is greatly changed during rolling. For this reason, if the sheet crown ratio is reduced in the front stand, the center elongation is less likely to occur as compared to the rear stand, and the risk of breakage is small because the sheet thickness is thicker than the rear stand. As described above, by performing the necessary width adjustment in the former stand, the latter stand can perform rolling while maintaining a flat shape optimal for the sheet passing property.

(5) The latter stand is preferably rolled with an ear wave tendency in order to prevent the plate from breaking. For this reason, a lower limit is set for the elongation-strain difference represented by “elongational strain at the end of the width of the sheet” − “elongational strain at the position of the center of the sheet width”. The elongation strain difference is a value indicating the difference in elongation strain in the width direction of the sheet when the sheet is rolled when the sheet is rolled. I do. The elongation-strain difference can be adjusted by changing the shape control amount. If the elongation-strain difference becomes excessively negative, tension is concentrated on the plate edge in the subsequent stand, and the possibility of breakage increases. In order to avoid this, a lower limit is set for the elongation-strain difference. The control amount of the shape control means of each stand is
The range is determined so that the difference in elongation strain resulting from the shape control is equal to or greater than the above lower limit. This can prevent breakage at the subsequent stand.

As described above, the shape control means of the front stand is adjusted to cope with the sheet width fluctuation caused by the speed change by controlling the sheet crown amount control effect and reducing the possibility of sheet breakage. In the latter stand where the tension is concentrated on the plate edge and the plate is likely to break, the shape control means is controlled so that a flat shape suitable for threading is obtained.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in more detail and specifically.

FIG. 1 is an explanatory view of a control procedure when the control method of the present invention is applied to a five-stand tandem rolling mill.

FIG. 2 is a block diagram showing a control system of the control method of the present invention.

In the present invention, in cold tandem rolling,
For each steel type, plate thickness at the entrance side of each stand, and plate width, the following relational expression representing the effect of the rolling load and the control amount of the shape control means on the plate width variation of the rolled material, and the plate width of the rolled material The following relational expression expressing the effect of the rolling load and the shape control amount on the difference in elongation strain between the end and the central part, and the relational expression expressing the relationship between the rolling speed and the rolling load are obtained in advance for each stand by a regression equation or the like. Keep it.

A limit value of a control amount of the shape control means is calculated based on an equation based on a predicted amount of load fluctuation caused by deceleration and a lower limit value of the elongation-strain difference which is determined separately from the passing property and the like. In addition, the shape control amount required to make the sum of the plate width fluctuation amount caused by the load fluctuation in all the stands to 0 is calculated based on the formula, and within the limit range of each stand obtained by the formula, the shape control amount of each stand is calculated. Determine the correction value of the control amount. At the time of rolling, the shape control amount is changed in accordance with the above-mentioned correction amount in accordance with the timing at which the sheet passing speed is reduced near the coil connection point.

Hereinafter, a method of deriving a relational expression necessary for implementing the sheet width control method of the present invention will be described.

Assuming that the amount of change in the sheet crown ratio and the amount of change in the sheet width caused by the change are proportional, the relationship between the two is expressed by the following equation. The subscript "i" shown below
Means the i-th stand.

ΔWi = ai · Δγi where ΔW: sheet width variation Δγ: sheet crown ratio change a: constant determined by sheet thickness, sheet width, and steel type.

Assuming that the sheet crown ratio change amount is proportional to both the rolling load change amount and the shape control change amount, these relations at the i-th stand are expressed by equations.

Δγi = αi · ΔPi−βi · ΔFi where ΔP: fluctuation amount of rolling load ΔF: change amount of shape control α, β: constant determined by plate thickness, plate width, steel type Regarding the sign of the control amount, the direction in which the middle extension shape is formed is positive.

The sheet width fluctuation amount caused by the change in the rolling load and the shape control amount can be obtained as an equation from an equation.

ΔWi = ai (αi · ΔPi−βi · ΔFi) --- On the other hand, “elongational strain at end of width” − “elongational strain at center of width”
Assuming that the variation of the elongation-strain difference represented by is in a proportional relationship with each of the rolling load variation and the variation of the shape control amount,
Elongation difference (λi) after rolling at the i-th stand
Is represented by the following equation.

Λi = λi0 + mi · ΔPi−ni · ΔFi ----- Here, λi0 means an elongation-strain difference (an initial value of the elongation-strain difference) before a load or a shape control amount is changed. It is obtained by calculation at the time of initial setting. mi and ni are constants determined by the thickness and the type of steel.

If the lower limit value of the elongation-strain difference λi (min) is separately set for each stand in order to maintain a good threading property, the following equation derived from the equation using the load variation ΔP during deceleration can be obtained. Limit value of the shape control amount at the i-th stand (Δ
Fi (max)) is obtained.

[0035]

(Equation 1)

Various methods are conceivable for determining the correction amount ΔFi of the shape control for each stand. For example, each stand has a direction in which the difference in elongation strain becomes larger than the limit value ΔFi (max) obtained from the equation. With a margin of ΔF ',
A method of setting the shape control amount ΔFi represented by the equation is preferable.

ΔFi = ΔFi (max) −ΔF ′ --- Therefore, for the i-th stand, the shape control amount obtained from the lower limit value of the elongation-strain difference is represented by the following equation.

[0038]

(Equation 2)

Further, the total sum of the plate width fluctuation amounts for each stand (Σ
Since ΔWi) needs to be 0, the shape control correction amount for each stand is determined so as to satisfy the range of the following equation derived from the equation.

[0040]

(Equation 3)

Here, Σ indicates that the sum is calculated for all the stands.

From the equation, the unknown number corresponding to the number of stands △
For Fi and one unknown △ F ′, equations for the number of stands and one equation are derived. If these are solved as simultaneous linear equations, ΔFi and ΔF ′ can be uniquely obtained.

The constants ai, αi, βi, mi and ni may be obtained in advance by experiments or numerical calculations.

FIG. 3 is a conceptual diagram for explaining a method of determining the shape control amount for each stand described above.

FIG. 4 is a diagram showing an example of setting the lower limit of the elongation-strain difference at each stand. FIG. 4A shows an example of the present invention. As shown in the figure, the rear stand of the tandem rolling mill, in which the tension between stands is high and the thickness of the stand is reduced and the risk of breakage increases, is preferably passed through with an ear wave tendency. Is limited to a relatively high elongation difference. In addition, as described above, in a post-stage stand where the plate thickness is reduced, the effect of changing the plate width is small even if the shape is controlled. For these reasons, it is preferable that the width compensation at the time of speed change is performed in the former stand,
In the case of a five-stand rolling mill, the rolling is preferably performed in three front stands, more preferably up to two front stands.

The shape control change amount at the time of deceleration is determined in advance based on preset conditions such as the speed and the shape control amount in the steady portion.
The amount of load change occurring at the target speed in the deceleration section is predicted and calculated. When the coil connection point approaches, the shape control amount is changed to a predetermined value in synchronization with the rolling speed at the timing of deceleration.

The shape control means for controlling the sheet width may be any method capable of changing the roll interval profile online, such as roll bending, change of roll crown, change of roll cross angle, change of roll, etc. Any may be used.

[0048]

【Example】

(Example 1) Using a five-stand cold tandem rolling mill,
The effect of the strip width control method of the present invention was verified. As a shape control method, an increment type work roll bender having a maximum capacity of 50 tons / chock was used, and a method of determining a shape control change amount for each stand employed a method shown in the formula. Using a four-high rolling mill having a work roll diameter of 400 mm, a backup roll diameter of 1400 mm, and a roll body length of 1800 mm, a normal steel coil having a thickness of 4 mm and a width of 1200 mm was used. 30 rolling reduction from 1 to 4 stands
%, No. 5 stands rolled at 5% reduction and 0.9
A 1 mm steel plate was used. Rolling oil viscosity at 40 ° C .: 4
A 0 cst mineral oil-based rolling oil was used in the emulsion, and the rolling speed in the steady portion: 1000 m / min, and the rolling speed in the reduction portion: 100 m / min.

The coefficients of the relational expressions for calculating the sheet width, shape, load variation and the like when changing the rolling conditions were estimated by numerical calculations from the actual values during operation. Note that the coil used for rolling was edge-trimmed before rolling to use a base material having a uniform width over the entire length. The strip width after rolling was measured by an optical strip width meter installed on the exit side of the rolling mill.

FIG. 4 shows a preset lower limit value of the elongation strain difference of each stand. (A) is an example of the present invention, and the lower stand set the lower limit value of the elongation-strain difference so as to have an ear wave tendency in order to prevent plate breakage (hereinafter referred to as “condition 1”). (B) is a comparative example, in which the lower limit value of the elongation-strain difference of each stand is substantially equal so that a plate width control amount equivalent to the condition 1 is obtained under the condition of the lower limit value of the elongation-strain difference. (Hereinafter referred to as “condition 2”). Using these lower limits, the shape control change amount for each stand was determined from the formula and the following formula. In the comparative example, the roll bending force of any of the stands was not changed.

FIG. 5 shows the change in the speed at the exit side of the rolling mill, the measured value of the sheet width, and the roll bending force (WRBF) of each stand when the rolling speed is changed during the rolling.
In the example of the present invention under the condition 1 shown in (a), the roll bending force changes in response to the load fluctuation accompanying the speed fluctuation, and the sheet width fluctuation amount at the acceleration / deceleration section measured at the rolling mill exit side is reduced. It is getting smaller. On the other hand, FIG.
In the comparative example, a maximum width of about 2 mm occurs in the acceleration and deceleration portions. From this result, it is apparent that the width variation can be suppressed by appropriately performing the shape control means in the acceleration / deceleration section by the method of the present invention.

(Example 2) The effect of the present invention was clarified by applying the method of the present invention to rolling of a large number of coils. The rolling mill used was the 5-stand cold tandem rolling mill described in Example 1, and had a thickness of 2.5 to 5.5 mm and a width of 800 to 1600.
The effect of applying the method of the present invention when continuously rolling a low-carbon steel base material of 0.5 mm to 0.5 to 1.5 mm was confirmed.
The lower limit of the elongation-strain difference is set as two types (conditions 1 and 2) shown in FIGS. 4A and 4B, and the lower limit of the elongation-strain difference is set. Were set as in the condition 1, but the shape width variation and the breakage ratio were investigated for a total of three cases in which the shape control was not corrected when the speed was changed (condition 3). The shape control at the time of the speed change was obtained from the equation. The plate width control accuracy was evaluated based on the difference in plate width between the steady portion and the deceleration portion in the same coil.

FIG. 6 shows a frequency distribution table of the sheet width variation when rolling is performed under each condition. FIG. 7A shows an embodiment according to the present invention, and shows a case where the lower limit value of the elongation rate difference for each stand is set to Condition 1 described above. (B) is a comparative example, in which the lower limit of the elongation difference rate for each stand is set to the above-described condition 2. (C) is the case of condition 3 in which no control was performed as a comparative example. FIG. 7 shows the ratio of the number of sheet breaks that occurred during rolling when rolling was performed under these conditions.

As shown in FIG. 6 (a) and the result of condition 1 in FIG. 7, under the condition 1 of the present invention example, the deviation of the sheet width fluctuation amount is small, and the sheet breakage occurrence rate is low and good. . However, when rolling is performed under the condition 2 in which the shape constraint condition (elongation strain difference limit) at each stand is constant, the sheet width deviation is slightly larger than the condition 1. This depends on the dimensions of the steel plate
This is because the control amount of the shape control means was insufficient due to a small set value of the lower limit of the elongation-strain difference in the former stage stand, and sufficient control could not be performed in some cases. In the case of the condition 2, the number of sheet breaks increased to about three times that of the condition 1. Under Condition 3, which is a comparative example in which the shape control during deceleration is not performed, the number of sheet breaks is low, but the deviation of the sheet width fluctuation is large.

[0055]

According to the present invention, in cold tandem rolling, strip breakage at a connection point between a leading coil and a trailing coil is prevented, and a change in strip width due to a change in rolling speed is prevented, thereby achieving a stable operation. It is possible to manufacture a metal plate with excellent dimensional accuracy by the above operation.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a control procedure when a control method of the present invention is applied to a five-stand tandem rolling mill.

FIG. 2 is a block diagram showing a control system according to a control method of the present invention.

FIG. 3 is a conceptual diagram illustrating a method of determining a shape control amount for each stand according to the present invention.

FIG. 4 is a diagram illustrating a setting example of a lower limit value of an elongation-strain difference for each stand according to the embodiment of the present invention. (A) shows an example of the present invention, and (b) shows a comparative example.

FIG. 5 is a diagram showing a state of shape control and a change in a sheet width according to a change in a rolling speed when cold tandem rolling is performed according to the embodiment of the present invention. (A) shows an example of the present invention, and (b) shows a comparative example.

FIGS. 6A and 6B are graphs showing the state of plate width fluctuation in the deceleration section in a frequency distribution according to the embodiment of the present invention, wherein FIG. 6A shows an example of the present invention, and FIGS. It is a figure showing a result.

FIG. 7 is a diagram showing a comparison of the frequency of occurrence of sheet breakage during rolling between an example of the present invention and a conventional method.

FIG. 8 is a diagram showing experimental results on the relationship between fluctuations in various rolling conditions and changes in the resulting sheet width.

FIG. 9 is an explanatory diagram showing a relationship between a change in a sheet crown in rolling and a flat shape.

Claims (1)

(57) [Claims] In cold tandem rolling using a plurality of rolling mills, the effect of a rolling load and a control amount of a shape control means on a sheet width variation of a material to be rolled, for each steel type, sheet thickness, and sheet width; The effect of rolling load and shape control amount on the difference in elongation strain between the end portion and the central portion of the sheet width and the relationship between rolling speed and rolling load are determined in advance for each stand, and changes in the rolling speed occur at each stand. Appropriate shape control means in a range that is necessary to keep the sum of plate width fluctuations within a predetermined range, and that the difference in elongation strain rate between the end portion and the center portion of the plate width generated at each stand does not fall below a predetermined limit value. A control amount for each stand, and controlling the shape control means of each stand according to the calculated value.