JP2002105541A - Method for preventing fluctuation in plate width in continuous heat treatment fascility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing fluctuation in the plate width in a continuous heat treatment facilities for estimating the width shrinkage not only in a stationary condition but also the width shrinkage in a non-stationary condition when shifting from a preceding steel strip to a succeeding steel strip. SOLUTION: A leveler is provided inside a continuous heat treatment furnace, the width of the steel strip is measured with a plate width meter disposed at the inlet side of the continuous heat treatment furnace, the width shrinkage of a measured part in the continuous heat treatment furnace is estimated, the width shrinkage is subtracted from the measured value of the width of the steel strip to estimate the width of the steel strip on the outlet side of the continuous heat treatment furnace, and the elongation rate of the leveler is adjusted so that the estimated width of the steel strip agrees with the target value. The width shrinkage is obtained on the basis of the shape of a thermal crown and the temperature of the steel strip by calculating the temperature of the steel strip in the furnace and the temperature distribution in each hearth roll in the axial direction, and determining the shape of the thermal crown of each hearth roll on the basis of the temperature distribution in the axial direction thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing a width change of a steel strip in a continuous heat treatment facility such as a continuous annealing facility.

[0002]

2. Description of the Related Art FIG. 1 is a schematic view schematically showing an example of a continuous annealing facility. 1 is a steel strip, 2 is a payoff roll,
3 is a continuous annealing furnace, 4 is a hearth roll, 5 is a heating zone, 6 is a soaking zone, 7 is a cooling zone, 8 is an overaging zone, 9 is a cooling zone, 10
Denotes a temper rolling mill, 11 denotes a tension reel, 12 denotes an entrance looper, 13 denotes an exit looper, and 14 and 15 denote bridle rolls.

In FIG. 1, a steel strip 1 is a payoff reel 2.
It is more continuously supplied into a continuous annealing furnace 3 (hereinafter also referred to as a furnace), is supported by a large number of hearth rolls 4 provided in the furnace, and has a heating zone 5, a soaking zone 6, a cooling zone 7, an overageing After passing through the band 8 and the cooling zone 9 in order, a predetermined heat treatment is performed, and the tension reel 1 is rolled by the temper rolling mill 10.
It is wound up by 1.

[0004] The steel strip 1 runs in a furnace under a predetermined tension in order to prevent meandering, and the temperature of the steel strip in the soaking zone 6 from the exit side of the heating zone 5 is 700 ° C to 850 ° C. . Steel strips under tension under such high temperature conditions
The plastic deformation occurs due to repeated bending by the hearth roll 4. That is, the steel strip elongates in the longitudinal direction and contracts in the width direction (hereinafter also referred to as width contraction).

[0005] The steel strip to be supplied to the continuous annealing equipment is determined in consideration of the above-mentioned width reduction in the product width. If the width reduction amount is large, a width trim is required in the next process, and the yield decreases. There are problems such as an increase in work cost, and in the worst case, a product width cannot be secured due to a shortage of width. Therefore, suppression of the fluctuation of the width shrinkage amount is important for keeping the steel strip width on the exit side of the continuous annealing equipment within a predetermined dimensional tolerance, and various methods have been conventionally proposed.

Japanese Unexamined Patent Publication No. Hei 4-6226 discloses a method in which the width of a plate is measured at the entrance and the exit of an annealing furnace, and the tension in the furnace is controlled based on the width of the plate. JP-A-57-9
No. 4525 discloses that, assuming that the furnace temperature is higher and the furnace tension is larger, the amount of width shrinkage in the furnace is larger, a large tension is applied in a region where the steel band width is large, and the steel band width is reduced. A method of controlling the amount of width reduction by relaxing the tension in a narrow area is disclosed.

Japanese Patent Application Laid-Open No. 63-171835 discloses that the sectional shape and the width of a steel strip are controlled by adjusting the furnace tension and the furnace temperature based on the steel strip thickness distribution and the steel strip width. A method is disclosed.

Japanese Patent Application Laid-Open No. 8-127820 discloses a method for predicting the amount of width reduction from the yield stress, elastic modulus, number of hearth rolls, hearth roll diameter and tension of a steel strip due to a heat cycle given to the steel strip. ing.

Japanese Patent Application Laid-Open No. 9-31550 discloses that the width shrinkage amount is predicted based on the crown amount of the hearth roll and the flatness of the steel strip on the entrance side of the annealing furnace, and when the predicted value exceeds an allowable range, the crown control is performed. A method of controlling the amount of width reduction using a roll is disclosed.

[0010]

However, Japanese Patent Application Laid-Open Nos. Hei 4-6226 and 57-94525,
In the method described in JP-A-63-171835, operating conditions such as furnace tension are set only in response to plate width fluctuations and plate thickness distributions on the furnace entrance side. There is a problem that can not be obtained. Also, in this method, even if feedback control is performed by measuring the width of the steel strip at the outlet side of the annealing furnace, since the equipment is long even after the high temperature range, the steel strip passing therethrough is not used. There is also the problem of not being able to control.

[0011] Japanese Patent Application Laid-Open No. 8-127820 and
The method disclosed in JP-A-31550 can estimate the amount of width reduction when operating conditions such as a heat cycle and a passing speed are constant. However, in continuous annealing, steel strips are sequentially connected and continuously processed.For example, when operating conditions such as dimensions and annealing temperature of a preceding steel strip and a subsequent steel strip connected to the steel strip are different. However, there is a problem that it is not possible to accurately estimate the amount of width reduction near the connection between the preceding steel strip and the following steel strip.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and its object is not only in the amount of width reduction in the steady state but also in the unsteady state such as when changing from the preceding steel strip to the succeeding steel strip. An object of the present invention is to provide a method for preventing a width change of a continuous annealing facility that can estimate a width shrinkage amount and suppress a width change on a furnace discharge side.

[0013]

SUMMARY OF THE INVENTION In a continuous annealing furnace, steel strips having different annealing temperatures and dimensions are sequentially connected, and the stripping speed is changed to give a predetermined heater pattern, and the strip is continuously processed. You. Accordingly, the temperature of the steel strip when passing through the hearth roll is not always constant, and changes with time near the connection between the preceding steel strip and the following steel strip. Therefore, the thermal crown formed on the hearth roll by contact with the steel strip changes, and the roll crown changes accordingly.

The present inventors have investigated the relationship between the roll crown and the width shrinkage using a model device simulating a continuous annealing furnace, and have obtained the following findings. FIG. 2 is a graph showing the relationship between the roll crown and the width contraction, in which the width contraction is expressed as distortion in the width direction.

(A) As shown in FIG. 2, when the roll crown changes, the distortion in the width direction, that is, the width shrinkage changes. Therefore, in a situation where the thermal clan changes with time, the width contraction amount fluctuates.

(B) In order to suppress the transient width fluctuation occurring when changing from the preceding steel strip to the succeeding steel strip, it is necessary to grasp the fluctuation of the thermal crown and to estimate the width shrinkage. (C) As shown in FIG. 2, when the tension is changed, the width contraction amount changes. Therefore, in order to suppress the fluctuation of the width reduction, it is effective to control the tension so as to cancel the fluctuation of the width reduction estimated based on the fluctuation of the thermal crown.

(D) However, when the tension is largely changed, a meandering or narrowing called a heat buckle may occur when the steel strip is passed, and there is a limit in changing the tension.

(E) If a leveler is provided in the furnace and an elongation strain is applied to the steel strip, the width of the steel strip decreases. Therefore, by adjusting the elongation rate of the leveler according to the change in the width shrinkage in the furnace, the steel strip width on the furnace exit side can be controlled to the target width.

(F) If the fluctuation of the roll crown is large, the fluctuation of the width shrinkage becomes large. Therefore, reduction of the thermal crown, which is a cause of roll crown fluctuation, is effective for suppressing width shrinkage fluctuation. Since the thermal crown is caused by the temperature distribution in the axial direction of the roll, the thermal crown can be reduced by changing the axial temperature distribution of the hearth roll to a predetermined distribution by heating the roll.

(G) In the method of suppressing the fluctuation of the width shrinkage by both reducing the thermal clan and changing the elongation by heating the roll, the amount of change in the elongation is reduced as compared with the method of adjusting only the elongation. There are advantages. For example, when the amount of change in the elongation rate is large, the thickness of the sheet may change and the thickness accuracy may be deteriorated. By reducing the amount of change in the elongation rate, a high accuracy of the thickness can be maintained.

The present invention has been completed based on the above findings, and the gist thereof is as follows. (1) A continuous heat treatment furnace that heat-treats a steel strip loaded with tension while being wound around a plurality of hearth rolls provided in the furnace, a leveler provided inside the continuous heat treatment furnace, and the continuous heat treatment furnace A method for preventing the width change of the steel strip in a continuous heat treatment facility having a width gauge provided on the entrance side of the steel strip, and measuring the width of the steel strip with the width gauge, in a continuous heat treatment furnace of the measured portion. Estimate the width shrinkage of the steel strip width, subtract the width shrinkage from the measured value of the steel strip width to estimate the steel strip width on the exit side of the continuous heat treatment furnace, so that the estimated steel strip width matches the target value. A method for preventing a change in the width of a steel strip in a continuous heat treatment facility, comprising adjusting an elongation of the leveler.

(2) A continuous heat treatment furnace for performing heat treatment while rolling and transporting a steel strip loaded with tension around a plurality of hearth rolls provided in the furnace, a leveler provided inside the continuous heat treatment furnace, A method for preventing a change in the width of a steel strip in a continuous heat treatment facility having a width gauge provided on an inlet side of a continuous heat treatment furnace, wherein the heat treatment means includes a heating means for adjusting a temperature of the hearth roll as the hearth roll. The steel strip width is measured with the sheet width meter, and the width shrinkage amount in the continuous heat treatment furnace of the measured portion is estimated, and the width shrinkage amount is subtracted from the measured value of the steel strip width to continuously perform the measurement. Estimating the steel strip width on the exit side of the heat treatment furnace, and adjusting the elongation rate of the leveler and the temperature of the hearth roll so that the estimated steel strip width matches the target value. A method for preventing band width fluctuation.

(3) The width shrinkage amount in the continuous heat treatment furnace is defined as a
(C) The method for preventing a variation in the width of a steel strip in a continuous heat treatment facility according to the above (1) or (2), wherein the estimation is performed in the following manner. a. The steel strip temperature in the furnace and the axial temperature distribution of each hearth roll are determined. b. Next, the thermal crown shape of each hearth roll is determined based on the axial temperature distribution. c. The width shrinkage is calculated based on the thermal crown shape and the steel strip temperature.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The description of the continuous heat treatment equipment according to the present embodiment will be given by taking a continuous annealing equipment as an example.

FIG. 3 is a schematic diagram showing the continuous annealing equipment according to the present embodiment. Reference numeral 20 indicates a leveler, reference numeral 21 indicates an in-furnace bridle roll, reference numerals 22, 23, and 26 indicate in-furnace plate width meters, and the same elements as those in FIG.

In FIG. 3, the continuous annealing equipment according to this embodiment goes from the entrance side to the exit side, and includes a payoff reel 2, a width gauge 22, an entrance looper 12, a continuous annealing furnace 3, and an exit looper 1.
3. It has a temper rolling mill 10 and a tension reel 11, and further has a leveler 20 inside a continuous annealing furnace and a width gauge 23 (hereinafter also referred to as a furnace width gauge) provided behind the leveler. . The continuous annealing furnace 3 includes a heating zone 5, a soaking zone 6, a cooling zone 7, an overaging zone 8 and a cooling zone 9 in order from the furnace entrance side to the exit side, and the leveler is disposed at the entrance of the heating furnace. You.

FIG. 4 is a schematic diagram showing the structure of the leveler 20 shown in FIG. Reference numeral 24 denotes a work roll, 25 denotes a backup roll, and the same elements as those in FIG. 3 are denoted by the same reference numerals.
As shown in FIG. 4, the leveler 20 includes work rolls 24, 24, 24 arranged in a staggered manner with the steel strip 1 interposed therebetween, and has in-furnace bridle rolls 21, 21 on the entrance side and the exit side. By pushing the work rolls 24, 24, 24 into the steel strip, elongation strain is given to the steel strip.

The steel strip 1 is continuously supplied from the pay-off reel 2, and the width of the steel strip is continuously measured by a strip width meter 22 (also referred to as a furnace entry side width gauge) provided on the furnace entrance side. And is supported by a large number of hearth rolls 4 provided in the furnace, and sequentially passes through a heating zone 5, a soaking zone 6, a cooling zone 7, an overaging zone 8 and a cooling zone 9, thereby performing a predetermined heat treatment. After being applied, it is temper-rolled and wound up by a tension reel 11. At this time, the steel strip 1 is given an elongation strain by the leveler 20 and the steel strip width is continuously measured by the furnace inner width meter 23. The continuous annealing furnace and the leveler used in the present invention are not limited to the examples shown in FIGS. 3 and 4, and a known device can be used.

FIG. 5 is a flowchart showing an example of the procedure of the method of the present invention. As shown in the drawing, the present invention measures the width of the steel strip with the furnace width meter at the furnace entrance side and estimates the width shrinkage amount in the continuous annealing furnace of the measured portion, and subtracts the width shrinkage amount from the width. The width of the steel strip on the exit side of the continuous annealing furnace is estimated by using the method, and the elongation of the leveler is adjusted so that the estimated width of the steel strip becomes a target value. Here, the width shrinkage is obtained from the operating conditions, the steel strip temperature, the axial temperature distribution of the roll, the thermal crown, and the roll shape in order. It is estimated from the width contraction amount at.

The width shrinkage is calculated using a model in which the steel strip in the furnace is divided in the longitudinal direction (hereinafter referred to as a divided model).
FIG. 6 is a diagram illustrating an example of the division model. Reference numeral 30 denotes a hearth roll, and 31 denotes a steel strip.

As shown in FIG. 6, N hearth rolls 3
0 is arranged above and below the furnace, and the steel strip 31 is divided into N parts in the longitudinal direction at each hearth roll position. Calculate the heat flow in and out of each split section. In the illustrated example, the steel strip is divided at each hearth roll position. However, by further dividing between the hearth rolls and increasing the number of divisions, the calculation accuracy can be improved. Hereinafter, a procedure for estimating the width shrinkage amount using the model shown in FIG. 6 and suppressing the fluctuation of the steel strip width on the furnace exit side will be described with reference to FIG. Note that the symbol i represents a divided section (i = 1 to
N), a symbol j indicates a time step, and a symbol k indicates a width direction position of the hearth roll.

Calculation of temperature of steel strip: There are several methods for calculating the temperature of the steel strip, but the following is preferred as an embodiment of the present invention in terms of calculation accuracy. From the line speed, plate thickness, plate width, steel type, furnace temperature at calculation start time τ ₀ , time δτ
Steel strip temperature T of each divided section (hereinafter also referred to as section) after elapse
_{S is obtained} by equation (1).

[0033]

(Equation 1) Here, δV: volume (δL × W × t), δQ: area (δ
L × W × 2) and thermal energy (heat transfer from the furnace to the steel strip, heat radiation and heat transfer with the rolls) during δτ, δL: length of each divided section, c: Steel strip specific heat, t: steel strip thickness, W: steel strip width.

The accuracy of calculation can be improved by measuring the steel strip temperature in the above section using a radiation thermometer or the like, and verifying and correcting the steel strip temperature calculated by the above equation (1) based on the measured value. it can.

Calculation of the hearth roll axial temperature distribution: Several calculation methods can be considered at this time, but the following method is preferable because the above calculation results can be used. Based on the steel strip temperature calculated by the above equation (1), the temperature distribution inside the hearth roll is calculated in consideration of contact heat transfer with the steel strip, heat transfer from the furnace, and radiant heat. Hearth roll (hereinafter,
Is simply divided into a radial direction and an axial direction.
l: radial division position, m: axial division position,
The roll internal temperature T _l , _m is calculated from the following discrete equation (2) obtained from the heat balance inside the roll.

[0036]

(Equation 2) Accordingly, the average temperature in the thickness direction of the roll body at the axial position k (hereinafter also referred to as roll temperature) is (2)
Calculated by averaging the roll internal temperature determined by the formula in the thickness direction. Roll temperature T _R of the total roll by repeating these calculations similarly for all rolls (i, j, k), i.e. the axial temperature distribution of all the roll is determined by the following equation (3).

[0037]

(Equation 3) Here, l ₂ : roll outside coordinates, l ₁ : roll inside coordinates,
It is.

The roll temperature at each point is measured by a temperature sensor provided inside the roll, and based on the measured value, the roll temperature calculated by the above equation (3) is verified and corrected to improve the calculation accuracy. be able to.

The thermal crown calculation: from the roll temperature T _R, determine the increase in temperature [Delta] T _k in the axial direction each position, in terms of the force p _k acting isotropically radially at each position discretized, Assuming that force _pk is applied to the cylindrical part of the roll,
The roll bulge / dent shape at that time is calculated. p
_k is calculated from the temperature rise amount ΔT _k by the following equation (4).

[0040]

(Equation 4) When x is the coordinate in the roll axis direction, the roll bulge / dent shape cr _k (x) is calculated by the following equation (5).

[0041]

(Equation 5) here,

[0042]

(Equation 6) It is. Here, h _S : roll body thickness, ν: Poisson's ratio of the roll, E: elastic modulus of the roll, and R ₀ : roll radius.

Therefore, the thermal clan Cr is represented by the following equation (6) as the sum of the equations (5). Incidentally, assuming that the roll temperature is symmetrical, p _k = p _−k may be set.

[0044]

(Equation 7) Here, k _e is the number of divisions of the roll barrel side.

Calculation of roll shape: The initial roll crown and the like are added to the thermal crown obtained by equation (6),
From the following equation (7), a width direction distribution R (i, j, k) of the roll radius representing the roll shape is obtained.

[0046]

(Equation 8) Here, Cr _int is the initial crown shape, and Crw is the flexure shape due to the effect of the constraint of the axle portion of the roll.

Calculation of width reduction: The width reduction can be obtained as the sum of the width reduction generated when passing through the hearth roll and the width reduction between the hearth rolls, ie, the free span. If the roll has a crown, the elongation differs at the width direction position. Therefore, in calculating the elongation, the steel strip is divided in the width direction, and the elongation strain is calculated for each of the divided strips in consideration of the roll crown at that position. The increment of elongation strain of each strip formed by passing the roll once is the increment of elongation strain by bending calculated by the following equation (8) and the elongation strain by bending back calculated by the following equation (9). The sum with the increment.

[0048]

(Equation 9) Here, σ _T : tension, σ _X0 : two-dimensional yield stress.

Therefore, the ratio of the strain distribution in the width direction is calculated by the function f
Expressed as ₁ , the widthwise strain δε _WR generated when passing through the hearth roll is given by equation (10). The function f ₁ satisfies 0 <f ₁ <0.5 obtained by experiment.

[0050]

(Equation 10) The increment of the elongation strain of each strip in the free span is calculated by equation (11).

[0051]

[Equation 11] here,

[0052]

(Equation 12) It is.

Therefore, assuming that the ratio of the strain distribution in the width direction is a function f ₂ , the width contraction δε _WF in the free span is (1
It is given by equation 3). Incidentally function f ₂ is obtained by experimentation and is 0 <f ₂ <0.5.

[0054]

(Equation 13) The width contraction amount ε _w on the furnace exit side is a sum of all the divided sections of the width direction distortion at the time of passing through the hearth roll given by the equation (10) and the width distortion at the free span given by the equation (13). It is calculated by equation (14).

[0055]

[Equation 14] Estimation of the steel strip width on the furnace exit side: The steel strip width is measured with the furnace width meter on the furnace entrance side, and the width shrinkage of the measured part in the furnace is calculated as (1
The width of the steel strip on the furnace exit side is estimated by estimating with the equation 4) and subtracting the width reduction amount from the steel strip width.

Leveler elongation rate control: The leveler elongation rate is adjusted such that the steel strip width on the furnace exit side (hereinafter also referred to as an estimated value) estimated by the above method matches the target value. That is,
If the estimated value is higher than the target value, increase the growth rate,
When the elongation is smaller than the target value, by adjusting the elongation so as to reduce the elongation, it is possible to prevent the width variation on the furnace discharge side due to the variation in the width shrinkage. For example, a target width on the leveler exit side (hereinafter, also referred to as a target level on the leveler exit side) is calculated by adding the width reduction amount to the target value of the steel strip width on the furnace exit side, and is measured by a furnace inner width meter. Adjust the elongation of the leveler so that the steel strip width is the target width on the leveler exit side. Alternatively, when the continuous annealing equipment is not equipped with a furnace width gauge, the elongation rate at the leveler and the amount of width shrinkage accompanying the elongation rate for each condition such as steel strip material, temperature, and dimensions May be experimentally determined in advance, and the elongation may be adjusted from this relationship so that the estimated value matches the target value.

FIG. 7 is a flowchart showing an example of the procedure of another method of the present invention. Another method of the present invention is to provide a heating means for adjusting the temperature of the hearth roll inside the hearth roll, estimate the steel strip width on the furnace exit side, and extend the steel strip width so as to match the target value. The rate and the hearth roll temperature are simultaneously controlled, or the elongation rate is controlled first, and if not enough, the hearth roll temperature is further controlled.

The width of the steel strip on the furnace exit side is determined in the same manner as described above.
It can be obtained from the steel strip width measured by the furnace entrance side width gauge and the width reduction calculated by the equation (14). The temperature control of the hearth roll can be performed by using a heating roll having a heating means provided therein as the hearth roll.

In the control of the elongation rate of the leveler and the temperature control of the hearth roll, for example, the temperature of the hearth roll is controlled so that the estimated value of the steel strip width on the furnace exit side matches the target value, and the steel strip on the furnace exit side is controlled. The target width on the leveler exit side is calculated by adding the width contraction amount to the target width value, and the elongation rate of the leveler is controlled so that the steel strip width measured by the furnace width gauge becomes the target level on the leveler exit side. I do. Alternatively, the relationship between the elongation rate at the leveler and the amount of width shrinkage accompanying the elongation rate is experimentally obtained in advance for each condition such as the material, temperature, and dimensions of the steel strip, and the steel strip width on the furnace exit side is estimated. The hearth roll temperature is controlled so that the value matches the target value, and the leveler exit side target width is obtained, and the leveler exit side target width estimated from the above relationship is set to the leveler exit side target width. Control elongation.

FIG. 8 is a schematic view showing an example of the structure of a heating roll. The heating roll 40 includes a plurality of heaters 41 and a plurality of temperature sensors 42 in the internal width direction. By adjusting the output of each heater while measuring the temperature distribution inside the roll with a temperature sensor, it is possible to change the temperature distribution in the roll width direction. By changing the temperature distribution in the width direction of the roll so as to reduce the thermal crown, the fluctuation of the width shrinkage amount can be suppressed. Therefore, in such a modified example, in addition to the change in the elongation, the change in the widthwise temperature distribution of the roll by heating the roll can more effectively suppress the fluctuation of the steel strip width on the furnace exit side. That is, even when the thickness accuracy is deteriorated only by changing the elongation, it is possible to prevent the thickness accuracy from being deteriorated by using the roll heating in combination and to more effectively suppress the fluctuation of the steel strip width on the furnace exit side. it can.

For example, when raising the annealing temperature,
By heating the outer side of the roll in advance, the increase of the thermal crown can be suppressed. When the sheet width is widened, the thermal crown per sheet width when the width is changed to a wide one can be reduced by heating the outside of the roll width in advance to increase the temperature. Moreover, meandering and heat buckle caused by the roll crown are suppressed.

In the description of this embodiment, the case where the continuous annealing equipment shown in FIG. 3 is used as the continuous heat treatment equipment is taken as an example. However, the present invention is not limited to this mode, and can be similarly applied to a continuous heat treatment facility provided with a continuous heat treatment furnace for performing heat treatment while transporting a steel strip loaded with tension around a hearth roll and transporting it.

[0063]

(Embodiment 1) FIG. 9 is a schematic view showing the basic structure of a continuous annealing model sheet passing apparatus (referred to as a model passing apparatus). Reference numerals R1 to R12 denote hearth rolls, 35 denotes a heating device, 36 denotes a heating furnace, and the same elements as those in FIG. 3 are denoted by the same reference numerals.

Using the model passing device shown in FIG. 9, the heating device 35 sets the furnace A zone at 830 ° C. and the B zone at 500 ° C.
The preceding material and the following material of the material SPCC were continuously passed at a constant speed under the passing conditions shown in Table 1 as the atmosphere heated.

[0065]

[Table 1] First, after running a steel strip having a width of 250 mm, a steel strip having a width of 350 mm was continuously run. According to the procedure shown in FIG. 5, the width shrinkage amount is estimated based on the calculation of the thermal crown shape change, including the transitional state when the plate width is changed from the width of 250 mm to the width of 350 mm. From the steel strip width measured by the width gauge 22 installed on the entrance side, the steel strip width on the exit side of the heating furnace 36 (hereinafter, also referred to as the furnace exit side) is estimated,
The leveler outlet side target value is determined such that the steel strip width on the furnace outlet side matches the target value, and the leveler 20 is adjusted so that the steel strip width measured by the furnace inner width meter 23 becomes the leveler outlet side target value. The elongation was adjusted. For comparison, a test (comparative example) in which the elongation rate of the leveler was constant was also performed. The width of the steel strip was measured by a strip width meter 26 provided on the furnace exit side, and a difference between the steel strip width and a target value (hereinafter, also referred to as a width fluctuation amount) was obtained. Table 2 shows the width variation.

[0066]

[Table 2] As shown in Table 2, in the comparative example, the width per sheet width was increased, the crown per sheet width was increased, and the width fluctuation amount tended to increase until the thermal crown of the roll became stable. In the example of the present invention, the width fluctuation amount in the transient state of the plate width change was significantly suppressed as compared with the comparative example. (Example 2) The model threading device shown in FIG. 9 was used, and the heating rolls shown in FIG. 8 were used for the hearth rolls (R2, R4, R6, R8, R11).
And the following material were continuously passed at a constant speed, and the width variation was investigated.

First, after running a steel strip having a width of 250 mm, a steel strip having a width of 350 mm was continuously run. According to the procedure shown in FIG. 7, the width shrinkage amount is estimated based on the calculation of the thermal clan shape change including the transitional state at the time of changing the width of the plate width. Estimate the steel strip width on the furnace exit side from the steel strip width measured in 22,
Control the roll temperature so that the steel strip width on the furnace exit side matches the target value, obtain the leveler exit side target value, and the steel strip width measured by the furnace inner width meter becomes the leveler exit side target value. The elongation of the leveler was controlled as described above. For comparison, a test (comparative example) in which the elongation was constant and the temperature was not controlled was performed. Table 3 shows the results of the investigation of the width variation on the outlet side of the furnace in the same manner as described above.

[0068]

[Table 3] As shown in Table 3, in the comparative example, the plate width was increased,
Until the crown per plate width increased and the thermal clan of the roll became stable, the width variation tended to increase. In the example of the present invention, the width fluctuation amount in the transient state of the plate width change was significantly suppressed as compared with the comparative example. (Example 3) In the continuous annealing equipment having the basic configuration shown in FIG. 3, the present invention is applied to a condition in which a low carbon steel, steel strip having a thickness of 1.0 mm and a width of 1200 to 1300 mm is passed at an annealing temperature of 800 to 820 ° C. The effect was verified. The width shrinkage amount on the exit side of the continuous annealing furnace was estimated in the manner shown in FIG. 5, and the elongation rate of the leveler was controlled so that the width became a target value. Plate width meter 2 provided on the furnace exit side
The steel strip width was measured in 6 and the difference (width variation) between the steel strip width and the target value was determined.

FIG. 10 shows the distribution of the width variation. In addition, the comparative example in the figure is a case where the elongation rate of the leveler is constant.
Since the width shrinkage varies under the condition that various steel strips coexist, the variation in the width variation increases in the comparative example as shown in FIG. 10, but the width variation in the present invention example is greatly reduced. And a substantially uniform width was obtained. Accordingly, the plate width accuracy was improved, and excellent effects were confirmed, such as the trim margin of the in-line trim which was conventionally set to be large in consideration of the width fluctuation can be reduced by about 1.8 mm on both sides.

[0070]

According to the present invention, it is possible to suppress a fluctuation in width which occurs transiently due to a change in the size of a steel strip or a heat treatment temperature such as an annealing temperature. Therefore, the plate width accuracy is greatly improved over the entire length of the steel strip, and it is possible to prevent deviation of the steel strip width tolerance. Also, the trim cost can be reduced, and the yield is improved. Furthermore, by using roll heating together,
The effect of suppressing the width fluctuation is further enhanced, and the induction of meandering and the like can be prevented. The significance of the present invention having such an effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a continuous annealing facility.

FIG. 2 is a graph showing a relationship between a roll crown and width reduction.

FIG. 3 is a schematic diagram illustrating an example of a continuous annealing facility according to the present embodiment.

FIG. 4 is a schematic view showing a configuration of the leveler shown in FIG.

FIG. 5 is a flowchart showing an example of a procedure of the method of the present invention.

FIG. 6 is a diagram illustrating an example of a division model.

FIG. 7 is a flowchart showing an example of a procedure of another method of the present invention.

FIG. 8 is a schematic diagram showing a structural example of a heating roll.

FIG. 9 is a schematic diagram showing a basic configuration of a continuous annealing model threading device.

FIG. 10 is a graph showing distribution of width fluctuation.

[Explanation of symbols]

 1, 31: steel strip 2: pay-off reel 3: continuous annealing furnace 4, 30, R1 to R12: hearth roll 5: heating zone 6: uniform tropical zone 7: cooling zone 8: overaging zone 9: cooling zone 10: tempering Rolling Mill 11: Tension Reel 12: Inlet Looper 13: Outlet Looper 14, 15: Bridle Roll 20: Leveler 21: Furnace Bridle Roll 22: Strip Width Meter (Entry Side Strip Width Meter) 23: Strip Width Meter (Inside Furnace) 24: Work roll 25: Backup roll 26: Plate width gauge 35: Heating device 36: Heating furnace 40: Heating roll 41: Heater 42: Temperature sensor

Claims (3)

[Claims] 1. A continuous heat treatment furnace for performing heat treatment while winding and transporting a steel strip loaded with tension around a plurality of hearth rolls provided in the furnace, a leveler provided inside the continuous heat treatment furnace, A method for preventing a width change of a steel strip in a continuous heat treatment facility having a width gauge provided on an inlet side of a heat treatment furnace, wherein the width of the steel strip is measured by the width meter, and the continuous heat treatment furnace of the measured part is provided. Estimate the width shrinkage within, and estimate the steel strip width on the exit side of the continuous heat treatment furnace by subtracting the width shrinkage from the measured value of the steel strip width, and the estimated steel strip width matches the target value A method for preventing a change in the width of a steel strip in a continuous heat treatment facility, wherein the elongation of the leveler is adjusted as described above. 2. A continuous heat treatment furnace for performing heat treatment while winding and transporting a tension-loaded steel strip around a plurality of hearth rolls provided in the furnace, a leveler provided inside the continuous heat treatment furnace, A method for preventing a width change of a steel strip in a continuous heat treatment facility having a width gauge provided on an inlet side of a heat treatment furnace, wherein a roll provided with heating means for adjusting a temperature of a hearth roll as the hearth roll is provided. Using, while measuring the steel strip width with the width meter, estimate the amount of width shrinkage in the continuous heat treatment furnace of the measured site, subtract the width shrinkage from the measured value of the steel strip width, continuous heat treatment Estimating the steel strip width on the furnace exit side, and adjusting the elongation of the leveler and the temperature of the hearth roll so that the estimated steel strip width matches the target value. Width fluctuation prevention method. 3. The amount of width shrinkage in the continuous heat treatment furnace is defined as a to c below.
3. The method according to claim 1, wherein the steel strip width variation is prevented in the continuous heat treatment equipment. a. The steel strip temperature in the furnace and the axial temperature distribution of each hearth roll are determined. b. Next, the thermal crown shape of each hearth roll is determined based on the axial temperature distribution. c. The width shrinkage is calculated based on the thermal crown shape and the steel strip temperature.