JP2012171008A - Temper rolling method, temper rolling apparatus, and manufacturing method of steel strip - Google Patents

Abstract

[PROBLEMS] To control the surface roughness with a target value accurately even if there is no problem such as constant load control, and there is no expensive online surface roughness meter, even if there is a fluctuation in the coil. To provide a temper rolling method for steel strip.
The temper rolling is carried out by adjusting the rolling load and / or the exit side tension so that the roughness transfer parameter p represented by the following formula is constant.
p = α · p _p + β · f
However, p _p : peak surface pressure (MPa), f: advanced rate (%), α, β: constant.
[Selection] Figure 1

Description

  The present invention relates to a temper rolling method, a temper rolling apparatus, and a steel strip manufacturing method.

  In general, temper rolling of a steel strip is performed by annealing a cold-rolled steel strip finished to a target thickness by a cold rolling process, and then subjecting the steel strip to a light reduction of, for example, about 1% elongation using a temper rolling mill. Is done by. In some cases, temper rolling may be performed after applying a surface treatment such as hot dip galvanization or electrotin plating to the cold-rolled steel strip after annealing. When the temper rolling is performed, the steel strip is stretched uniformly, thereby correcting the shape of the steel strip and adjusting the mechanical properties of the steel strip (for example, yield point elongation, tensile strength, elongation, etc.). Therefore, temper rolling is important for adjusting the shape of the steel strip or adjusting the mechanical properties of the steel strip, and also adjusting the properties such as the surface roughness of the steel strip. It is one of the important purposes of rolling.

  The diameter of the work roll used for such temper rolling is usually about 300 to 700 mm, and the thickness of the steel strip used for temper rolling is about 0.15 to 3.0 mm. When the strip is temper-rolled, a work roll having a very large diameter with respect to the steel strip thickness is used. Also, temper rolling is a dry rolling method in which steel strip is rolled without supplying lubricant to the work roll, or in order to prevent adhesion of steel strip material to the work roll surface, a lubricant with low lubricity is used for the work roll. A rolling method is used in which the steel strip is rolled by supplying to the steel. In other words, when temper rolling a steel strip, it is common not to use a lubricant with high lubricity for the purpose of reducing the friction coefficient, and the friction coefficient between the work roll and the steel strip surface is very high. It is assumed that it will grow.

  Conventionally, when it is important to control the surface roughness of a steel strip within a target range, after determining the average surface pressure, that is, the rolling load, by a method such as Patent Document 1, for example, when rolling in a coil The roll gap and the rolling tension were changed so that the rolling load always coincided with the rolling load. This is generally called constant load control.

  Patent Document 2 discloses a method of correcting the rolling force and the exit side tension based on the surface roughness of the temper rolling mill and the actual elongation measured by an online surface roughness measuring device. . Patent Document 3 also discloses a method of automatically controlling the rolling load so that the surface roughness measured by the surface roughness measuring device on the exit side of the temper rolling mill falls within a predetermined range. Further, Patent Document 4 discloses a method of measuring the surface roughness continuously or intermittently to correct the elongation rate, the entry side tension, and the exit side tension (or a friction coefficient in the case of a wet type). Here, the correction of the elongation rate is the correction of the reduction.

JP 59-107701 A JP-A-5-154526 JP-A-5-277533 JP 2008-6453 A

  Among the above-mentioned conventional patents, with the constant load control, it is difficult to control the surface roughness after rolling to a target value. One factor is due to the wear of the roll. Usually, fluctuations in the surface roughness are suppressed by applying hard chromium plating to the roll surface. However, with respect to plate thickness fluctuations and hardness fluctuations in the coil, even if the load is constant, fluctuations in surface roughness may be large and deviate from the target value. Further, in the method described in Patent Document 1, when the roll diameter is different, the steel sheet surface roughness may not be a target value.

  The methods disclosed in Patent Documents 2 and 3 are based on the premise that the surface roughness is continuously measured on the exit side of the temper rolling mill, and must include an expensive online surface roughness meter, Equipment costs are high.

  In the method disclosed in Patent Document 4, intermittent measurement may be possible, and an on-line surface roughness meter is not necessarily required. However, in order to perform intermittent measurement, the line is stopped and an operator performs measurement on the inspection table. Work is required, and work efficiency and production efficiency are low.

  The present invention has been made in order to solve the above-mentioned problems, and does not cause problems such as constant load control, and even if there is no expensive on-line surface roughness meter, even if there are fluctuations in the coil, steel is used. It is an object of the present invention to provide a temper rolling method and a temper rolling apparatus that can accurately control the surface roughness of a strip to a target value, and a steel strip manufacturing method.

  The present inventors also conducted experiments relating to temper rolling and calculations based on the finite element method (FEM) to examine factors that have a dominant influence on the roughness transfer of temper rolling.

  First, in temper rolling, since the roll diameter is very large and the elongation of the steel strip is about 1%, the change in the thickness of the steel strip before and after rolling depends on the roll diameter and the length in the rolling direction of the roll bite. Is significantly smaller than Therefore, it was found that the surface pressure distribution is not significantly different from the surface pressure distribution in the case where the elastic cylinder known as the Hertz's elastic contact formula contacts the rigid body plane. Therefore, the peak surface pressure is an important factor.

  Since the method described in Patent Document 1 does not take into account the above knowledge, the average surface pressure is a factor, and therefore the accuracy of the surface roughness of the steel sheet is not sufficient. Since the diameter of the work roll used for temper rolling is not always constant, the steel sheet surface roughness can be accurately predicted by changing the factor from the average surface pressure to the peak surface pressure.

  It was also found that the advance rate has a great influence on the roughness transfer of temper rolling. That is, the present inventors have newly found that even when the load is constant (that is, the peak surface pressure is constant), the surface roughness changes as the advance rate changes. In the method described in Patent Document 1, such an advanced rate is not considered, and it is difficult to say that the accuracy of the surface roughness of the steel strip is sufficient.

The advance rate f is expressed by the following equation (1) using the exit side plate speed V _S (mpm) and the roll peripheral speed V _R (mpm). Usually, the exit side plate speed is detected by a plate speedometer installed on the exit side of the rolling mill, a rotational speed of a bridle roll installed on the exit side of the temper rolling mill for the purpose of controlling tension, and the like.
f = {(V _S / V _R ) −1} × 100 [%] (1)

  Furthermore, the present inventor found that the temper rolling has a small elongation rate and a large friction coefficient, so that the work roll and the steel plate surface are almost completely fixed in the roll bite, but very little in the vicinity of the inlet and outlet. It has been found that relative slip occurs, and in particular, relative slip near the exit promotes the transfer of roughness, and that the advanced rate correlates well with this relative slip amount. Although it is very difficult to measure the relative slip near the exit online, the advance rate is well correlated with the relative slip, so we decided to use the advance rate as the second factor.

  In Patent Documents 2 to 4, on-line surface roughness measurement is premised, but in general, the output of an on-line surface roughness meter varies greatly, and filter processing such as moving average is required for use in control. As a result, the fluctuation of the steel sheet surface roughness measured by the online surface roughness meter is mainly due to the above-mentioned roll wear, and such fluctuation is corrected by monitoring the advance rate as in the present invention. Can do.

  Including intermittent measurement as shown in Patent Document 4, measuring the steel sheet surface roughness at the temper rolling mill outlet side has a particularly low set-up accuracy and makes the steel sheet surface roughness within a predetermined range from the coil tip. This is effective when it is difficult to fit, but this can be dealt with by considering the peak surface pressure as in the present invention since the influence of the roll diameter is mainly large.

This invention is made | formed based on the said knowledge, and provides the following (1)-(3).
(1) A temper rolling method in which temper rolling is performed on a steel strip after cold rolling and annealing, and the rolling load and the roughness transfer parameter p represented by the following formula are constant. A temper rolling method comprising temper rolling by adjusting the exit side tension.
p = α · p _p + β · f
However,
p _p : Peak surface pressure (MPa)
f: Advanced rate (%)
α, β: constants.
(2) A temper rolling apparatus for performing temper rolling on a steel strip after cold rolling and annealing, for controlling the tension on the entry and exit sides of a rolling stand having a work roll for rolling the steel strip. A temper rolling apparatus comprising: a bridle roll; and a control unit that adjusts a rolling load and / or an exit side tension so that a roughness transfer parameter p represented by the following formula is constant.
p = α · p _p + β · f
However,
p _p : Peak surface pressure (MPa)
f: Advanced rate (%)
α, β: constants.
(3) A steel strip manufacturing method in which a steel strip is manufactured by cold-rolling and annealing a raw material and then temper-rolling the raw steel strip, and the temper rolling is represented by the following equation: A method for producing a steel strip, wherein the rolling load and / or the exit side tension are adjusted so that the roughness transfer parameter p is constant.
p = α · p _p + β · f
However,
p _p : Peak surface pressure (MPa)
f: Advanced rate (%)
α, β: constants.

  According to the present invention, even when there is a difference in the work roll diameter, a hardness variation of the steel strip, a load variation due to a plate thickness variation, or a tension variation, the variation in the steel strip roughness is suppressed and the target value is achieved. be able to. In addition, it is not necessary to introduce an expensive measuring machine such as an on-line surface roughness meter, the equipment cost can be reduced, and since intermittent roughness measurement is not necessary, workability and productivity are good.

It is a schematic block diagram which shows typically the temper rolling equipment which can implement the temper rolling method which concerns on this invention.

Hereinafter, modes for carrying out the present invention will be described.
In the present embodiment, the hot-rolled material is cold-rolled and annealed, and then the material steel strip is temper-rolled to produce a desired steel strip.

  Cold rolling and annealing may be carried out according to conventional methods, and the conditions are not particularly limited. Moreover, there is no restriction | limiting in particular in the material of a steel strip, It can apply also to the steel strip to which hot dipping and electroplating were given.

  The temper rolling is performed using a temper rolling facility including one or more rolling stands provided with a work roll whose surface roughness is adjusted to 0.5 to 10 μm with an average roughness Ra by dull processing.

  Roughness can be imparted to the work roll surface by performing dull processing on the work roll surface. Here, as a dull processing method, a shot blast processing method, an electric discharge dull processing method, a laser dull processing method, an electron beam dull processing method, or the like can be used. Further, as a countermeasure against wear, the roll after the dull processing may be subjected to chrome plating.

The above-mentioned average roughness Ra is based on “JIS B 0601 (2001)”, and only the reference length is extracted from the surface roughness curve in the direction of the average line, and the x-axis is extracted in the direction of the average line of the extracted portion. Is a value expressed by the following equation (2) in micrometers (μm) when the y-axis is taken in the direction of the vertical magnification and the roughness curve is expressed by y = f (x). .

  In addition, as a value of the surface average roughness Ra of the said work roll in this invention, it is good also as the value of Ra calculated | required by the above Formula (2) in the representative position on the surface of a work roll, and multiple positions on the surface of a work roll. It is good also as a value which averaged the value of Ra measured in. In the case of using the average value of a plurality of positions, for example, at least a portion of the work roll contacting with the steel strip has four points at 90 ° intervals in the circumferential direction and three points at the center and both ends in the width direction. An average value may be used. Moreover, an evaluation length of 4 mm and a cutoff of 0.8 mm are usually used. The measurement direction is preferably the axial direction (width direction).

  Further, the value of the steel strip surface average roughness Ra may be, for example, Ra obtained by the above formula (2) at a representative position such as the center in the width direction, or an average of values measured at a plurality of positions on the steel strip surface. It is good.

ただし、
π：円周率
Ｒ：ワークロール半径（ｍｍ）
ν_Ｒ：ポアソン比（ワークロール）
Ｅ_Ｒ：ヤング率（ワークロール）（ＧＰａ）
である。 The peak surface pressure p _p (MPa) can be obtained by the following equation (3) using the rolling load P (kN) measured by the load cell and the width W (mm) of the steel strip to be rolled.

However,
π: Circumference ratio R: Work roll radius (mm)
ν _R : Poisson's ratio (work roll)
E _R : Young's modulus (work roll) (GPa)
It is.

Further, the advanced rate f is obtained by the following equation (4).
f = {(V _S / V _R ) −1} × 100 [%] (4)
However,
V _S : Delivery side plate speed (mpm)
V _R : rolling speed (work roll peripheral speed) (mpm)
It is. The delivery side plate speed (steel strip speed) can be measured by the rotational speed of the bridle roll on the delivery side of the rolling mill or by installing a plate speed meter. The work roll peripheral speed may be obtained from the work roll outer peripheral length by calculating the work roll rotational speed from the drive motor rotational speed and the gear ratio of the speed reducer.

The roughness transfer parameter p can be calculated from the peak surface pressure and the advanced rate obtained as described above by the linear expression shown in the following expression (5).
p = α · p _p + β · f (5)
Α and β are constants given as roughness parameters.
During rolling, the roughness transfer parameter p is calculated at a certain control cycle based on the actually measured load and the actually measured advanced rate, and the rolling load and the exit side tension can be controlled so as to be constant. .

When the variation amount of the roughness transfer parameter p is small, for example, when the variation amount is 5% or less as a guide, it is desirable to control by the output side tension. For example, when p becomes large, if the exit side tension is reduced, the advance rate f becomes small and the value of p is corrected. Changing the exit side tension large change in forward slip f, the peak surface pressure p _p hardly changes.

If the parameter p changes suddenly and exceeds the above-mentioned standard fluctuation amount, the change in the output tension is stopped (the output tension is fixed at the current value), and the load is applied until the parameter p returns to the target value. To change. For example, when p becomes very large, when the load is lowered, both p _p and f become small and the value of p is corrected.

The roughness parameters (constants) α and β are preferably determined in advance according to the steel type, plate thickness, roll surface roughness, roll processing method, and the like. Further, it is preferable that the data is constantly updated using the actual measurement data. For example, temper rolling experiments with varying rolling load and exit side tension were performed, and the steel sheet roughness transfer rate (surface roughness of rolled steel sheet / roll surface roughness) was measured. By investigating the correlation with the pressure p _p and the advanced rate f (multiple regression analysis), α and β can be obtained. It goes without saying that α and β can be obtained as a function of operation data such as steel type (deformation resistance value, etc.), sheet thickness, roll usage distance, and the like.

  In addition, a target value of the roughness transfer parameter p may be set in advance and controlled so as to be the target value. The parameter value at a certain stage during rolling is set as a lock-on value, and this value is set as the target value. You may control as.

  FIG. 1 is a schematic configuration diagram schematically showing a temper rolling facility capable of performing a temper rolling method according to an embodiment of the present invention. The temper rolling equipment shown in FIG. 1 includes a rolling stand 3 having a work roll 2 whose surface is dulled, a bridle roll 4 for controlling the tension on the entry / exit side, and a controller 5 for controlling the roughness transfer parameter p. I have. In FIG. 1, the control part 5 has shown the content of the control with the block. In FIG. 1, the steel strip is rolled from the left to the right, and related equipment such as a coil payout equipment existing on the left side and a coil winding equipment existing on the right side are omitted.

In the control unit 5, roughness transfer parameter p, a peak surface pressure p _p sought (3) than the load detection value of the load cell 6, the exit-side bridle speed and roll speed (work roll peripheral velocity) (4) Based on the advanced rate f obtained by the equation, it is obtained every moment by the equation (5). The obtained roughness transfer parameter p can be adjusted to the target value by changing the load or the outlet side tension of the hydraulic reduction cylinder 7 by general PI control based on the deviation Δp from the target value.

  The gain of PI control can be determined only by adjustment by test threading, or as shown in FIG. 1, an influence coefficient gain determined by preliminary threading or the like in advance may be provided.

  In FIG. 1, the rolling stand 3 is shown as a four-stage stand, but the present invention is not limited to the four-stage type, and the same applies to a two-stage, six-stage or cluster-type rolling stand. Has temper rolling effect.

  In addition, the temper rolling equipment to which the present invention is applied is sufficient if it has at least one rolling stand provided with upper and lower work rolls 2 whose surfaces are dulled, within the range allowed by the necessity and installation space. There is no limit to increasing the number of rolling stands back and forth accordingly. Needless to say, the present invention can be applied to these increased rolling stands as needed.

Hereinafter, the present invention will be described based on examples.
Rolling was performed by the temper rolling mill shown in FIG. Here, a work roll having a diameter of 600 mm and a barrel length of 1400 mm was used, and a backup roll having a diameter of 2000 mm and a barrel length of 1400 mm was used. The material of the work roll was 5% chromium forged steel. The surface of the work roll was finished to a surface average roughness Ra = 2.5 μm by a shot blast method. As the steel strip for temper rolling, a low carbon steel having a plate thickness of 0.8 mm, a plate width of 1200 mm, an average roughness Ra measured in the width direction of the surface of 0.3 to 0.5 μm, and a yield stress of 200 MPa was used. Rolling speed was constant _{V R} (outer circumferential speed of the work rolls) in 200Mpm. In the figure, so that it actually measure the strip velocity (plate velocity) V _S by the rotation speed of the rolling mill exit side bridle roll (in four upper left). The set values were a rolling load of 4 kN / mm, an elongation of 1%, and front and rear tensions of 98 MPa. The target roughness was 1.2 ± 0.2 μm in terms of average roughness Ra.

  The steel strip is rolled by 10 km in accordance with the conventional technique described in Patent Document 1 and the method of the present invention, and the steel sheet roughness after rolling at 100 points at a pitch of 100 m is measured to be within the target roughness range. The probability of fitting was investigated.

  In the prior art, the surface roughness of the steel strip is controlled so that the tension is constant and the load becomes a target value. It was 85% that was within the target roughness range. On the other hand, in the method of the present invention, first, preliminary rolling is performed, and the rolling load is set to 5 conditions of + 5%, + 3%, ± 0%, −3%, −5% of the set value, and the front tension (exit tension). Were changed under the same five conditions, and the advanced rate f [%] and the steel sheet roughness transfer rate (rolled steel plate roughness / roll roughness) were measured for a total of 25 conditions. The peak surface pressure [MPa] was calculated based on the above equation (3) with the Young's modulus of the work roll as 205.8 GPa and the Poisson's ratio as 0.3. Table 1 shows each condition, measurement, and calculation result.

The contribution ratio (slope) of _pp and f to the change in the steel sheet roughness transfer rate is obtained by the least square method based on the above equation (5), and α = 0.000707 and β = 2 are determined. The value of the condition closest to the target roughness was input and the roughness transfer parameter p = 0.9 was set as the target value. Table 1 also shows the p value under each condition using the values of α and β.

  When the fluctuation was smaller than 3% with respect to the fluctuation of the roughness transfer parameter p, the front tension (exit tension) was changed. In the case of a rapid fluctuation exceeding 3%, the rolling load was changed by changing the load without changing the front tension (exit tension). From the results shown in Table 1, the influence coefficient gain in FIG. 1 is 367 [MPa] when the outlet side tension is changed, and 7.93 [kN / mm] when the rolling load is changed. That is, in the closed loop of the control in FIG. 1, the PI is changed so that the error of 1.0 with respect to the target of the p value is changed by 367 [MPa] for forward tension and 7.93 [kN / mm] for rolling load. Input to the controller. As a result, it was within the target roughness range at all measurement points.

  From the above, it was confirmed that the steel sheet surface roughness produced by temper rolling can be controlled within the target roughness range by using the method according to the present invention. Thus, since the yield is improved by using the method of the present invention, it can be expected to bring about an industrially useful effect.

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Work roll 3 Rolling stand 4 Bridle roll 5 Control part 6 Load cell 7 Rolling cylinder

Claims (3)

A temper rolling method in which temper rolling is performed on a steel strip after cold rolling and annealing, and the rolling load and / or the output are set so that the roughness transfer parameter p represented by the following formula is constant. A temper rolling method comprising adjusting the side tension and performing temper rolling.
p = α · p _p + β · f
However,
p _p : Peak surface pressure (MPa)
f: Advanced rate (%)
α, β: constants. A temper rolling apparatus for performing temper rolling on a steel strip after cold rolling and annealing, a rolling stand having a work roll for rolling the steel strip, and a bridle roll for controlling the tension on the entry and exit sides A temper rolling apparatus comprising: a control unit that adjusts a rolling load and / or an exit side tension so that a roughness transfer parameter p represented by the following formula is constant.
p = α · p _p + β · f
However,
p _p : Peak surface pressure (MPa)
f: Advanced rate (%)
α, β: constants. A steel strip manufacturing method in which a steel strip is manufactured by cold rolling and annealing a material and then temper rolling the material steel strip, wherein the temper rolling is a roughness transfer represented by the following formula: A method for producing a steel strip, wherein the rolling load and / or the exit side tension is adjusted so that the parameter p is constant.
p = α · p _p + β · f
However,
p _p : Peak surface pressure (MPa)
f: Advanced rate (%)
α, β: constants.

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