JPS60181242A - Continuous annealing method of steel strip - Google Patents

Abstract

PURPOSE:To suppress surely heat buckle and meandering by correcting the thermal crown of hearth rolls so as to be maintained within the range of the upper limit crown rate to suppress heat buckle and the lower limit crown rate to prohibit meandering. CONSTITUTION:The size and set temp. of a steel strip 1 are put from a generator 7 for annealing specifications to a calculator 8 which calculates a heat treating temp. and furnace temp. and outputs the same to a setter 9 to perform operation and outputs also the same to a deciding device 10. The device 10 makes decision by taking in the steel strip temp. from a thermometer 13 and outputs a signal to a device 11 for deciding hearth roll temp. if said temp. is satisfactory. Said device feeds a signal to a learning device 12 to correct the temp. and feeds the same to the calculator 8 and if said temp. is not satisfactory. On the other hand, the device 11 makes decision by taking in the actually measured temp. at the end and central part of a hearth roll 6 and continues the operation as it is is said temp. is satisfactory. Said device corrects the temp. in the device 12 and feeds the same to the calculator 8 if the temp. is not satisfactory. The meandering and heat buckle of the strip 1 are prevented by repeating the above- mentioned procedure.

Description

Detailed Description of the Invention Technical Field The present invention relates to a continuous annealing method for steel strips, and in particular, the technology described in this specification is for roll crown control to suppress meandering and heat buckling of the north roll in a vertical continuous annealing furnace. The following is a proposal on how to smoothly operate a continuous annealing furnace.

BACKGROUND OF THE INVENTION In general, continuous annealing of a copper strip imparts predetermined material properties by passing the steel strip under appropriate temperature conditions, threading speed, and tension. In the case of a continuous annealing furnace, particularly a vertical furnace, a large number of hearth rolls are installed in the upper and lower parts of the furnace, and the copper strip is passed through these hearth rolls. FIG. 1 shows an example of a typical vertical continuous annealing furnace. In the figure, ■ is a copper zone, 2 is a heating zone, 8 is a soaking zone, 4 is a slow cooling zone, 5 is a rapid cooling zone, and 6 is a hearth roll. The steel strip 1 is connected to the heating zone 8~
While being conveyed through the quenching zone 5 in the directions of arrows A and B, it comes into contact with a large number of hearth rolls 6 and is simultaneously maintained at the required temperature and speed and heat-treated.

However, when a copper strip is heat treated in such a vertical continuous annealing furnace, depending on the shape of the steel strip, the tension balance in the furnace, or the temperature conditions, the copper strip may shift relative to the line center and may be damaged in some places. This may cause the mark to shift laterally. When this lateral shift becomes large, the copper strip meanderes, and furthermore, problems arise in that the edge portion of the copper strip is damaged or broken due to contact with the furnace wall.

Therefore, in order to prevent such lateral deviation, the second
As shown in the figure, the round is given - one throttle 6
is used. A force F acts on the steel strip 1 in the width direction of the steel strip 1 by the hearth roll with such a round toward the center as shown by the arrow. occurs and meandering is corrected.

However, this self-centering ability F. If it is too large, heat buckling will occur in the copper band. This is the self-centering force F that moves from both sides of the steel strip toward the center. Because of this, the copper strip buckles in the width direction near its center, and the buckled part wraps around the 111 roll.Therefore, conventionally, 111 roll has the ability to correct meandering and prevent heat buckling. Its own crown lid! A proposal has been made to increase the distance by 114 m.

For example, JP-A No. 57-177980, Utility Model Application No. 58-1
The technique disclosed in No. 0646 proposes adjusting the hearth roll by heating and cooling it, and the technique disclosed in Utility Model Application Publication No. 55-172869 proposes that a bending device is provided to perform a-ru crown sectioning. There is. However, in order to apply these known techniques to actual operations, a crown measuring device and a crown controlling device must be installed for each roll, which increases costs and requires delicate mutual adjustment between rolls. In reality, many problems remained.

Purpose of the Invention The purpose of the present invention is to provide a continuous annealing method that reliably suppresses heat buckling and meandering caused by excess or deficiency of crown amount, which cannot be achieved with conventional techniques. The gist of the present invention is as set forth in the claims at the beginning of this specification.

Structure of the invention The throttle installed in the vertical continuous annealing furnace is
Initially, it is low at the center where it contacts the steel strip and high at its ends. Figure 8 shows an example of measuring the temperature distribution in the axial direction of a hearth roll.
also shows a low value.

A thermal crown occurs on the hearth roll due to the difference in thermal expansion that occurs with temperature as seen in this temperature distribution.

In short, the roll crown that affects the occurrence of meandering and heat buckling in the steel strip must be considered in addition to the initial crown originally given to the roll itself, as well as the thermal crown mentioned above. Regarding crown control to suppress or prevent heat crown, there is no effective method other than adjusting the heat crown described above.

Note that the total crown ΔD can be expressed as follows.

(4) ΔD=ΔD1+ΔDt ・・・・・・■−ΔD□tenα・
d・ΔT ・・・・・・■′−ΔDi ten α・d・(TR
c-TRE)...■"Here, ΔD: Initial crown ΔDt: Thermal crown α: Thermal expansion straw d: Plate thickness ΔT= TRO-THE TRO: Hearth roll center temperature TRE: Hearth roll end temperature total What substantially influences the fluctuation of the crown ΔD is the thermal crown ΔDt in the above equation 0, and if this thermal crown is perfectly controlled, the occurrence of the meandering and heat buckling can be suppressed or prevented.

For example, in the first half of the heating zone 2 of the annealing furnace, the temperature of the steel strip 1 is low, so the temperature THE at the end of the roll is much higher than the temperature TRo at the center, and as a result, the total crown ΔD shown in equation 0 points in the smaller direction. , the self-centering force is weakened and meandering is more likely to occur. Therefore, by controlling the thermal crown ΔD, the above-mentioned problem can be avoided.

In short, during annealing, the total crown ΔD, especially the thermal crown ΔD, is the upper limit crown ΔD11 at which heat buckling does not occur. The lower limit crown ΔDL may be controlled within a range in which meandering does not occur.

DL
...The problem is solved by setting the lower limit temperature (meandering prevention crown 1) TH...the upper limit temperature (heat buckle suppressing crown amount).

As a result, the present invention provides thermal crown setting model equations for copper strip temperature, temperature at the center and both ends of the roll, with furnace temperature, heat treatment rate, and plate thickness as parameters, for thermal crown control. The temperature in the furnace and the heat treatment speed are determined while sequentially correcting the measured value of the copper strip to fall within the range of the upper limit crown amount for suppressing heat buckling and the lower limit crown amount for preventing meandering, and the copper strip is continuously heat treated. It is a continuous annealing method.

FIG. 4 is a flowchart of the method of the present invention. First, the dimensions of the copper strip to be subjected to heat treatment and the set (target) copper strip temperature are determined. Here, the predicted steel strip temperature Ts is TB k-qax + TG + ast HV-B +
aa +++++... ■Where, To: Furnace temperature ■: Heat treatment rate B: Plate thickness a0 to a8: Coefficient Also, setting (target) - - Regarding the roll end temperature TRE and the hearth roll center temperature TRc , THE
'q b 1 ・TG 10 b s ・V-B + b
a ・・・・■(7) TRe ” CI・TG+ c 2・V−B+0.・
...■ However, b□ to b8 and C□ to c8 can be expressed by model formulas consisting of coefficients.

Next, the temperature T'G of the copper strip is measured, and it is determined whether the measured value T'o is within the allowable range of the set steel strip temperature using equation (2).

TsL<T's<TsH Here, T: Lower limit temperature (meandering prevention crown L amount) TsH: Upper limit temperature (heat buckle suppressing crown amount) T's: Set steel strip temperature And as a result of the judgment, equation 0 is satisfied. If not, modify the model formula 〇 by changing the coefficient a1 i 82 * aB in the formula ■, and then adjust the furnace temperature T again. , the heat treatment speed V is reset and annealing is performed.

As a result of the determination, if the formula (■) is satisfied, then-- Measure the temperatures at the ends and center of the scroll, and determine whether these (8) actually measured temperatures satisfy the above formula 0, If it is satisfied, the operation will continue, but if it is not satisfied, it will be 0.
The coefficients b□, bg and C□, c2°c8 of formula 0 were modified, but the model formula 〇 was not corrected.

By (2), the furnace temperature TG and J degree V are set again and the heat treatment is continued.

Correction of each of the above coefficients is preferably performed by learning control. For example, if the coefficient to be corrected is a, based on the following formula, 'n+1 -aan + (1-α)an-1°゛°°゛°■0 〈α〈1 By adopting the method explained above, the predicted steel strip temperature T
5 and hearth roll end and center predicted temperatures T, T
The difference between these measured values is reduced by the learning RE RC control, so the furnace temperature TG and processing speed V
By controlling the roll crown, it is possible to indirectly control the roll crown without impairing predetermined material properties.

Next, an example of the apparatus according to the present invention will be explained based on FIG. 1
Reference numeral 6 indicates a fallen belt, and 6 indicates a no-throttle roll, which has thermometers embedded in at least two locations, one at the end and the center (the thermometer is not shown). 7 is an annealing specification generator, 8 is a computing unit, and 9 is a furnace condition setting device.

Still, IO is a copper band temperature determiner, 11 is a...-throll temperature determiner, and 12 is a learning device. 18 is a copper band thermometer, and 14 is an output device. Based on the steel strip dimensions and the set (target) steel strip temperature manually input from the annealing specification generator 7, the calculation device 8 calculates the heat treatment rate V and furnace temperature T using the 0-0 formula. is calculated and output to the setting device 9. Based on this, a continuous annealing operation will be performed, and on the other hand, a setting completion signal is output to the copper strip temperature determiner 10. Next, steel strip lake degree determination′
A10 takes in the temperature of the copper band from the thermometer 18 and makes a determination using the formula (2). If satisfied, a signal is output to the Heath roll temperature determiner 11. If it is not satisfied, a signal is output to the learning device 12, and this learning device j2 calculates the coefficients a0 to
a8 is modified based on the 0 formula, the modified result is sent to the arithmetic unit 8, and the above procedure is repeated. On the other hand, if the formula (2) is satisfied, the no-throttle temperature determiner 11 that receives the signal takes in the measured temperatures at the ends and center of the hearth roll, and makes a determination based on the formula (0). If satisfied, the -1=-
Continue operation without changing the i furnace = r condition, but if it is not satisfied, use the learning device 12 to change the coefficients of formulas s, , b
2. b8, and correct C□r 02 + CB. Next, the result is sent to the arithmetic unit 8, and the above procedure is repeated again.

Note that the output device 14 is, for example, an alarm device such as a buzzer, and may be configured to sound when the roll temperature does not satisfy the 0 formula.

Example An example is shown in which during continuous annealing, the model equations 〇, ■, and 0 regarding the heat crown, whose parameters are "furnace temperature TG, processing speed V, and plate thickness", were modified by learning control. .

First, FIG. 6 shows the relationship between the furnace temperature TG and the hearth roll end temperature T□, and gives an example of the model formula 〇.

Further, FIG. 7 shows the relationship between the roll center temperature TRE and the product of the heat treatment rate fl) and the plate thickness (B), and gives an example of the model formula 〇. Furthermore, Figure 8 shows 1 furnace temperature TG
This shows the relationship between the product of the heat treatment rate (v) and the plate thickness (B), and is a specific example of the operation of the model formula (2).

Fig. 9 shows the relationship between the temperature difference ΔT'' TRo-TRE, meandering, and the heat buckle. Smooth continuous annealing is possible if controlled.

Effects of the Invention According to the present invention, by continuing the operation while sequentially correcting the model formulas (■ to ■) described above, it is possible to reduce yield deterioration due to heat buckling to 1.5%, and also to reduce the yield deterioration due to meandering. The occurrence frequency of rosette fractures was also suppressed from 2.4 times/month to 0.5 times/month, making it possible to operate the continuous annealing furnace in a more or less smooth manner.

(12)

[Brief explanation of drawings]

Fig. 1 is a route diagram of the vertical continuous annealing furnace, Fig. 2 is a front view of the nozzle to -throttle roll, Fig. 8 is an axial temperature distribution diagram of the -11th roll, and Fig. 4 is the method of the present invention. 5 is a block diagram for explaining the method of the present invention, FIG. 6 is a graph showing the relationship between the furnace temperature and the roll end temperature, and FIG. 7 is the product of speed and plate thickness. Figure 8 is a graph showing the relationship between roll center temperature and the product of speed and plate thickness. Figure 9 is a graph showing the relationship between temperature difference, meandering, and heat buckling. It is a graph showing a relationship. 1...Steel strip 2...Heating zone 8...Soaking zone 4...Slow cooling zone 5...! Cold zone 6...No1-throll? ...Annealing specification generator 8...Arithmetic unit 9...Furnace condition setting device
lO... Steel Temperature Judgment Device] 1... Bathroom Temperature Judgment Device 12... Learning Device 1B... Copper Band Thermometer 1
4... Output "a. Patent applicant: Kawasaki Steel Corporation -9A'1)-

Claims (1)

[Claims] L In a method of continuously annealing a copper strip in a vertical continuous annealing furnace under roll crown control of no-throttle rolls, the temperature of the copper strip is determined using the furnace temperature, heat treatment rate, and plate thickness as parameters, ---throttle center. The temperature in the furnace and the heat treatment rate are adjusted while sequentially modifying the thermal crown setting model formula for each temperature at both ends, so that the measured values fall within the range of the heat buckle suppression upper limit crown amount and the meandering prevention lower limit crown amount. A continuous annealing method for a copper strip, characterized by determining and continuously heat-treating the copper strip.