JPH10158747A - Method for setting furnace temperature in heating furnace of continuous annealing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently execute the heat treatment with a small amount of consumtion of fuel, to suitably control strip temp. and to prevent the development of meandering by observing the strip temp. at the outlet side and at the center part of a heating furnace and changing the setting value of the furnace temp. so that the temp. of the metallic strip comes in a presetting range. SOLUTION: A calculator 18 for setting the furnace temp. receives the data of a comparison datum, strip thickness, strip width, kind of steel, and a target strip temp. value at the outlet side and its allowable range, etc., from a host computer 16 and the necessary data of the center strip temp. target value and the allowable value are read in. Successively, the strip temp. predicting calculation is executed and the furnace temp. value is calculated so that the strip temp. at the outlet side of the heating furnace 10 becomes the target value. The strip temp. predicting calculation at the first half part is executed based on the calculated furnace temp. successively, it is judged whether the center strip temp. comes to the target allowable range or not. When the center strip temp. does not come to the allowable range, a step width is corrected. It is judged whether or not the strip temp. at the outlet side comes to the allowable range again by the same way, and in the case of not coming to the allowable range, the step width is corrected and changed setting furnace temp. is outputted to a controller 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a furnace temperature setting method for a heating furnace of a continuous annealing furnace, and more particularly to a furnace temperature setting method for controlling the furnace temperature of the first half of the heating furnace and the entire heating furnace.

[0002]

2. Description of the Related Art In a continuous annealing furnace, it is important to prevent the occurrence of meandering and to ensure a stable passing state.
The first possible cause of the meandering is the formation of the thermal crown of the hearth roll in the first half of the heating furnace. Conventionally, a method of controlling the thermal crown itself and a method of cooling the hearth roll to prevent the thermal crown have been known. These techniques are also one of the means for preventing meandering, but there are facilities that cannot be mechanically adapted.

[0003] Therefore, a method of devising the initial crown of the hearth roll and controlling the surface temperature of the strip at the center of the heating furnace, that is, the furnace temperature in the first half of the heating furnace, suppresses the generation of the thermal crown and prevents meandering. It is considered. As a means for doing this, it is necessary to divide the heating furnace into a plurality of zones and to be able to set the furnace temperature individually in each zone.

[0004] As a method of setting the furnace temperature for each zone, for example, Japanese Patent Publication No. 59-33176 discloses a method of switching to step heat or flat heat depending on the dimensions of the strip, the type of steel, and the target sheet temperature at the exit side of the heating furnace. Discloses a method of performing efficient heat treatment with a low fuel consumption. Here, the step heat refers to a furnace temperature setting method in which a zone of a heating furnace is divided into, for example, four zones, and a furnace temperature set value is gradually increased at a certain step width from the previous zone. It refers to a furnace temperature setting method in which all zones have the same target furnace temperature. Note that a furnace temperature setting method for gradually lowering the furnace temperature set value at a certain step width from the previous zone is referred to as reverse step heat.

Japanese Patent Laid-Open No. 25555/1993 discloses that the plate temperature is measured separately in the middle part and the outlet side of the heating furnace, and the furnace temperature in the first half of the heating furnace is controlled based on the plate temperature in the middle part. There is disclosed an apparatus in which the furnace temperature in the latter half of the heating furnace is controlled based on the outlet plate temperature. Japanese Patent Application Laid-Open No. 5-271784 discloses a technique in which the furnace temperature in the first half of the heating furnace is set higher than the furnace temperature in the second half of the heating furnace. Further, JP-A-60-
JP-A-56026 and JP-A-7-126759 disclose a technique in which a heating furnace is divided into a plurality of zones, and a set furnace temperature in each zone is set so as to gradually increase from an upstream side to a downstream side. I have.

[0006]

However, the conventional method of switching to step heat or flat heat depending on the dimensions of the strip, the type of steel, and the target sheet temperature on the exit side of the heating furnace, involves fixing the heat pattern according to the object. Because it does not change the step width and does not take into account meandering prevention, if a human tries to correct the central plate temperature to prevent meandering, the outlet plate temperature will be the target plate temperature. There is a possibility that it will be greatly deviated from the above. On the other hand, when trying to guarantee the delivery side plate temperature in terms of quality, the center plate temperature cannot satisfy the allowable range, and there is a possibility that meandering may occur.

In the method of separately calculating and setting the furnace temperatures of the first half and the second half of the heating furnace based on the measured values of the plate temperature at the middle part and the outlet side of the heating furnace, the balance between the furnace temperature and the first half is maintained. When a variety of varieties are produced in the latter half, the control of the target furnace temperature cannot be performed in time for the next material, or the creaking of the furnace zone itself may adversely affect the equipment.

In addition, the method of setting the furnace temperature in the first half of the heating furnace to a high level is, in practice, limited in use because the set temperature cannot be reached in the first half and the capacity is exceeded, or the predicted outlet plate temperature is insufficient. And the fuel efficiency is not good.

In the method in which the heating furnace is divided into a plurality of zones and the furnace temperature is set so that the set furnace temperature in each zone gradually increases, the step width is not changed. However, there is a problem that the furnace temperature set value cannot be corrected when the temperature does not satisfy the allowable range.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has been designed to appropriately control the plate temperature at the center and the outlet side of the heating furnace while performing efficient heat treatment with a small amount of fuel. It is an object of the present invention to provide a technology that can set a temperature, prevent the occurrence of meandering, and improve quality and sheet passing property.

[0011]

According to the present invention, a heating furnace of a continuous annealing furnace for continuously heating a metal strip is divided into a plurality of zones in a traveling direction of the metal strip, and a different furnace temperature is set for each zone. In the furnace temperature setting method in the heating furnace of the continuous annealing furnace, which heats the traveling metal strip and controls the sheet temperature of the metal strip on the heating stripping side, the sheet temperature on the heating furnace exit side and the center of the heating furnace are controlled. Monitoring and changing the furnace temperature set value in accordance with the monitored sheet temperature so that the sheet temperature of the metal strip falls within a predetermined range respectively set at the heating furnace outlet side and the heating furnace central part. Thus, the above-mentioned problem has been solved.

Further, the furnace temperature set value is changed from step heat to flat heat according to the monitored plate temperature while changing the step width.

Further, the furnace temperature set value is changed from flat heat to reverse step heat in accordance with the monitored plate temperature while changing the step width.

Hereinafter, the process leading to the present invention will be described.

The present inventors first set the furnace temperature in the first half of the heating furnace using a sheet thermometer installed in the center of the heating furnace, and set the furnace temperature in the second half of the heating furnace using a sheet thermometer installed on the exit side of the heating furnace. Attempts were made to set them separately, but the relationship between the target sheet temperatures at the center of the heating furnace and the outlet side varied depending on the material.

That is, since the purpose is only to prevent meandering in the central part of the heating furnace, there is no great difference depending on the material, but since the quality of the material is assured at the outlet side, the destination, the purpose of use, etc. The target plate temperature varies greatly depending on the target. Therefore, if the furnace temperature is set using the target plate temperature at the center of the heating furnace and at the outlet side as it is, there is a risk that the furnace temperature setting in the first half of the heating furnace may suddenly fall below the lower limit.

Conventionally, step heat and flat heat are fixed depending on the type of steel and size, and there is no method of changing the step width even in the case of step heat.

Therefore, in the present invention, the step width is changed little by little on the assumption that the furnace temperature does not vary greatly from the entrance side to the exit side using step heating.

According to the present invention, while monitoring the sheet temperature at the center of the heating furnace and the exit side of the heating furnace, the setting of the furnace temperature is changed so as to appropriately control the respective sheet temperatures. Even when there are many changes in the furnace temperature setting, the transition is smooth, meandering can be prevented, and the material of the product can be guaranteed.

When the furnace temperature of the heating furnace is set using step patterns such as step heat, flat heat, and reverse step heat, and the step width is modified, the furnace temperature in each zone becomes higher than necessary. Since it can be set so that it does not fall apart, the step pattern and the furnace temperature rise and fall smoothly, making it easy to change the furnace temperature setting when passing many types of materials in a short cycle with the highest possible combustion effect .

Since the sheet temperature at the center is intended to prevent meandering, the target sheet temperature at the center can be said to satisfy the target unless it falls below the target value (that is, the target at the center). Sheet temperature = lower limit of allowable value.) The target plate temperature on the delivery side is also set with upper and lower allowable ranges according to the material,
The current furnace temperature is set within the allowable range.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing equipment including a heating furnace of a continuous annealing furnace to which the present invention is applied.

In FIG. 1, reference numeral 10 denotes a heating furnace which forms the main body of the continuous annealing equipment. A continuous strip-like strip 12 welded in the heating furnace 10 passes through the heating furnace 10. These strips 12 are continuously fed in the direction of arrow A as the rolls 14 inside and outside the heating furnace 10 rotate, and rapidly heated toward the exit side of the heating furnace 10 by radiant heat from a radiant tube burner, for example. Is done.

Reference numeral 16 denotes comparison data such as sheet thickness, sheet width and steel type for the material to be manufactured, and the heating furnace 1 for the material.
0 This is a higher-level computer for giving the target plate temperature at the center and the delivery side and the allowable upper and lower limits.

Reference numeral 18 denotes a furnace temperature setting computer for setting a specific furnace temperature. The furnace temperature setting computer 18 obtains the target of specific gravity, specific heat, center temperature of the target material, and its allowable value based on the material standard from the host computer 16. Further, the furnace temperature setting computer 18 determines whether the material is heated in basically what step pattern, that is, whether the furnace temperature is the same in all zones in a flat shape, the furnace temperature is increased in a step shape, If so, read the initial conditions such as how many degrees in the step width the furnace temperature should be increased. The furnace temperature setting computer 18 performs a sheet temperature prediction calculation based on these initial conditions. That is, as a result of determining the furnace temperature so as to satisfy the sheet temperature at the exit side of the heating furnace 10, if the sheet temperature at the center is insufficient, the step pattern is corrected and the sheet temperature prediction calculation is performed again, and these sheet temperatures are calculated. The final result of repeating the temperature prediction and the furnace temperature correction is output as a furnace temperature value to a controller 20 that controls the furnace temperature of the heating furnace 10.

The heating furnace 10 is divided into, for example, four zones Z1, Z2, Z3, and Z4 as objects for setting the furnace temperature. In each zone, a thermometer 22 is provided for an upper portion and a lower portion, and the furnace temperature is measured. The result of the furnace temperature measurement by the thermometer 22 is taken into the controller 20. In each zone, a plurality of combustion gas pipes 24, a combustion gas flow rate measuring device 26, and a combustion gas flow rate valve 28 are provided as necessary, and are controlled by controllers 20 installed in the respective sections. The furnace temperature in each zone is adjusted by opening and closing a combustion gas flow valve 28 by feedback from a combustion gas flow meter 26 provided separately for the upper and lower parts of each zone.

In addition to the above, plate thermometers 30, 32 and 34 for measuring the plate temperature of the surface of the strip 12 are provided on the entrance side of the heating furnace 10, the central part of the heating furnace and the exit side of the heating furnace. The value is taken into the furnace temperature setting computer 18 and used for the sheet temperature prediction calculation. The feed speed of the strip 12 by the roll 14 or the like is measured by a line speed detector 36, and the speed is also taken into the furnace temperature setting computer 18 and used for the sheet temperature prediction calculation.

Hereinafter, the operation of the present embodiment will be described.

FIG. 2 is a flowchart showing the flow of calculation processing performed by the furnace temperature setting computer 18 in the first embodiment.

In the first embodiment, a step heat having a step width of a ° C. becomes an initial value. Even after the correction, the furnace temperature in the first half is higher than that in the reverse step. If not.

First, in step 100, the furnace temperature setting computer 18 receives data such as comparison data, sheet thickness, sheet width, steel type, outlet side target sheet temperature value and its allowable range from the host computer 16. Next, in step 102, other data necessary for the furnace temperature setting calculation, such as the target value of the central plate temperature, the allowable value thereof, and the initial value of the step pattern, are read.

In the next step 104, a sheet temperature prediction calculation is performed. Among them, a furnace temperature value is calculated according to the step pattern so that the sheet temperature at the exit side of the heating furnace 10 becomes a target value. In this case, a heat absorption model using the entire furnace temperature as one is used. At this point, it is not known whether the center sheet temperature is satisfactory. Therefore, in the next step 106, a plate temperature prediction calculation for the first half of the furnace is performed based on the furnace temperature just calculated. That is, how many degrees Celsius up to the center by the calculated furnace temperature
Calculate until the plate temperature is heated. In this case, a heat absorption model for only the first half of the furnace is used.

In the next step 108, it is determined whether or not the center plate temperature is within the target allowable range. If the central plate temperature satisfies this allowable range, the next step 110
Then, the set furnace temperature is output to the controller 20 and the calculation is terminated.

In step 108, when the center plate temperature does not satisfy the allowable range, that is, as shown in FIG.
If the center plate temperature is lower than the center allowable range M1 even though the outlet side plate temperature is within the allowable range M2, in step 112, it is determined whether or not the step width is 0 (that is, the step width is not 0). Judge whether or not it is flat heat). If the step width is not 0, the process proceeds to step 114, where the step width is changed from the initial value a shown in FIG. 3A to 1/2 so that it becomes a / 2 shown in FIG. To fix. Thus, the step width is reduced by half.
As shown in FIG. 4A, the furnace temperature in the second half zone decreases by the amount corresponding to the decrease in the step width, and the furnace temperature in the first half zone increases accordingly. This ultimately means shifting the combustion load to the first half zone.

Returning again to step 104, the exit sheet temperature and the center sheet temperature are calculated again in the same manner using the corrected step pattern. At this time, as shown in FIG. 4B, if the central plate temperature is insufficient in the allowable range M1 at the center, the step width is again increased to 1 in step 114 as shown in FIG. / 2 is corrected to a / 4. as a result,
If the central plate temperature satisfies the allowable range M1 at the center as shown in FIG. 5B, the process proceeds to step 110, where the set furnace temperature is output to the controller 20, and the calculation is terminated.

As described above, the step width is corrected by the initial value a.
, A → a / 2 → a / 4 → 0, and gradually reduce the order.
(A) and (b) as shown in FIG.

As shown in FIGS. 7 (a) and 7 (b), if the central plate temperature is insufficient in the allowable range M1 even in the flat heat, the step width is set to 0 in step 112.
That is, after confirming that the heat is flat, it is determined in step 116 whether or not the calculated outlet sheet temperature is within the commanded upper limit. If the outlet sheet temperature has not reached the upper limit, the target value of the outlet sheet temperature is increased by ΔT ° C. in Step 118 as shown in FIG. 8A, and the outlet sheet temperature and the center sheet temperature are calculated again. This is intended to raise the central sheet temperature by the shortage by increasing the target sheet temperature on the delivery side within a materially acceptable range. Then, the target value of the outlet sheet temperature is changed to a high value within the upper limit value, and FIG.
When the central plate temperature satisfies the allowable range M1 as shown in (a) and (b), the set furnace temperature is output to the controller 20 in step 110, and the calculation is terminated.

If the exit sheet temperature exceeds the upper limit in step 116, the quality at the exit side cannot be guaranteed because the sheet temperature is too high, and the sheet temperature is too low at the center. Therefore, in the next step 120, the abnormality is notified and the processing is terminated.

FIGS. 7 to 9 show the case where the step width is corrected starting from the step heat and the step width is corrected to reach the flat heat, and the center plate temperature is still insufficient. The same applies even when the furnace temperature setting is not allowed.

Next, a second embodiment of the present invention will be described.

In the second embodiment, flat heat is set as an initial value, and a reverse-step furnace temperature setting is allowed.

The flowchart of the calculation process in this case is as follows.
In step 112 of FIG. 2, it is confirmed that the reverse step width is within the allowable range (−b ° C.), and in step 114, the reverse step width is changed from 0 → (−b / 4) → (−b / 2) → All steps are the same as those in the flowchart of FIG. 2 except that the correction is performed in the order of (−b). Considering this replacement, the operation of the second embodiment will be described with reference to the flowchart of FIG.

Steps 100 to 106 are the same as in the first embodiment. In step 108,
As shown in FIG. 10 (b), when it is determined that the central plate temperature value is below the allowable range M1 at the center, the process proceeds to step 112, and whether the reverse step width is within the allowable range (-b). Judge. If the reverse step width is 0, the process proceeds to step 116, where it is determined whether the outlet sheet temperature calculator is within the upper limit value. If the reverse step width is within the upper limit value, in step 118, as shown in FIG. The temperature is increased by ΔT ° C. within the range up to the upper limit. At this time, as shown in FIG. 11B, even in the calculation of the flat heat, if the center plate temperature does not satisfy the allowable range M1 at the center, the step 1 is performed.
At 14, the reverse step width is changed to -b / 4. At this time, if the center sheet temperature does not satisfy the allowable range M1 at the center, the reverse step width is changed from 0 → (−b / 4) → (−b /
2) The allowable range of the reverse step width in the order of (-b) (-
Correct the reverse step width until b). Then, as shown in FIGS. 12A and 12B, if the center plate temperature satisfies the allowable range M1 at the center, step 110 is executed.
Outputs the set furnace temperature to the controller 20 and terminates the calculation.

As described above, in the second embodiment, the case where the plate temperature of the central part and the outlet side of the heating furnace 10 cannot be satisfied even in the calculation of the flat heat, and the transition to the reverse step heat in which the furnace temperature in the first half zone is increased. The concept of shifting the combustion load to the first half to increase the combustion load in the first half zone because the central plate temperature is insufficient is common to the first embodiment.

Although the second embodiment starts with the flat heat as an initial value, a reverse step furnace temperature may be set as an initial value.

In the above-described embodiment, since the sheet temperature at both the central portion of the heating furnace and the outlet side is satisfied, the material at the outlet side is guaranteed, and meandering which is likely to occur in the first half of the heating furnace is prevented. Is now available. Also, in this embodiment, it is possible to maintain the balance of combustion by using a combustion pattern such as step heat or flat heat, and to smoothly perform the transition even when there are many furnace temperature setting changes in various types. It became.

[0048]

As described above, according to the present invention,
Since the plate temperature at both the center and the outlet side of the heating furnace is satisfied, the material at the outlet side is guaranteed, meandering that tends to occur in the first half of the heating furnace is prevented, and the stable flow is maintained while maintaining the combustion balance. It has become possible to produce products with good board and quality.

The purpose of maintaining the center sheet temperature is to prevent meandering. However, when it is desired to guarantee a temperature control curve (heat cycle) in the heating furnace for other purposes, the sheet temperature at the time of passing through the center is limited. It is valid.

The furnace temperature of the heating furnace is set based on a step pattern of step heat, flat heat and reverse step heat. In order to set the furnace temperature in each zone so that it does not vary more than necessary, a step pattern and a furnace are used. There is also an effect that the furnace temperature setting can be easily changed when a wide variety of materials are passed in a short cycle while the temperature is smoothly changed up and down and the effect of combustion is as high as possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a heating furnace of a continuous annealing furnace to which the present invention is applied.

FIG. 2 is a flowchart showing the flow of processing according to the first embodiment of the present invention;

FIG. 3 is an explanatory diagram showing initial values in a process of setting a furnace temperature from step heat to flat heat in the first embodiment.

FIG. 4 is an explanatory diagram showing a case where a step width is reduced to １ ／ in the same process.

FIG. 5 is an explanatory diagram showing a case where the step width is reduced to に お い て in the same process.

FIG. 6 is an explanatory diagram showing a case where a flat heat occurs in the same process.

FIG. 7 is an explanatory diagram showing a process of a furnace temperature setting calculation in the case of flat heat in the first embodiment.

FIG. 8 is an explanatory diagram showing a case where the furnace temperature is increased in the same process.

FIG. 9 is an explanatory diagram showing a case where a target value at the center is achieved in the same process.

FIG. 10 is an explanatory diagram showing initial values in a process of a furnace temperature setting calculation from flat heat to reverse step heat in the second embodiment.

FIG. 11 is an explanatory diagram showing a case where the furnace temperature is increased in the same process.

FIG. 12 is an explanatory diagram showing a case where reverse step heating is performed in the same process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Heating furnace 12 ... Strip 14 ... Roll 16 ... Host computer 18 ... Calculator for furnace temperature setting 20 ... Controller 22 ... Thermometer 24 ... Combustion gas piping 26 ... Combustion gas flow measuring device 28 ... Combustion gas flow valve 30, 32, 34 ... Sheet thermometer 36 ... Line speed detector

Claims (3)

[Claims] A heating furnace of a continuous annealing furnace for continuously heating a metal strip is divided into a plurality of zones in a running direction of the metal strip, and a different furnace temperature can be set for each zone. In the furnace temperature setting method for the heating furnace of the continuous annealing furnace for heating and controlling the sheet temperature of the metal strip on the heating outlet side, the sheet temperature on the outlet side of the heating furnace and the central part of the heating furnace is monitored, In the central part of the heating furnace, the furnace temperature set value is changed according to the monitored sheet temperature so that the sheet temperature of the metal strip falls within a predetermined range respectively set in advance. Furnace temperature setting method for heating furnace of continuous annealing furnace. 2. The apparatus according to claim 1, wherein the furnace temperature set value is changed from step heat to flat heat according to the monitored plate temperature while changing a step width. Furnace temperature setting method for heating furnace of continuous annealing furnace. 3. The apparatus according to claim 1, wherein the furnace temperature set value is changed from flat heat to reverse step heat in accordance with the monitored sheet temperature while changing the step width. Temperature setting method in the heating furnace of the continuous annealing furnace to be changed.