JP2907311B2 - Method and apparatus for controlling temperature of alloying furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a steel strip immersed and passed through a galvanizing bath at a predetermined temperature to form an alloy layer composed of iron and zinc on the surface of the steel strip. The present invention relates to a method and an apparatus for controlling the temperature of an alloying furnace.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing an example of a conventional galvanizing alloying furnace. This alloying furnace for hot-dip galvanizing is disclosed in Japanese Patent Application Laid-Open No. 4-48059. A steel sheet 5 is immersed in a galvanizing bath 1 through a sink roll 3 and a zinc wiping device 4 to target the amount of zinc deposition. The value is adjusted to the value, and the alloying furnace 6 is entered. Alloying furnace 6
In the heating zone 8, the steel sheet 5 is heated by the direct-fire type burner 7, and in the soaking zone 9, the steel sheet 5 is soaked and subjected to a predetermined alloying treatment. A static pressure pad 10 is integrally installed near the discharge port at the upper end of the alloying furnace 6, and a fluid is ejected to both sides of the steel plate 5 to cause a gap between the static pressure pad 10 and the steel plate 5 in the furnace. A draft and a static pressure region are formed to confine the flow of exhaust gas from the lower part of the furnace inside the furnace.

As a fluid to be supplied to the static pressure pad 10, an atmosphere gas in the furnace immediately above the furnace entrance side is used. This gas is sucked by a suction fan 20, and a plate thermometer 15 and a plate The pressure is supplied to the hydrostatic pad 10 through the flow control valve 21 controlled by the temperature controller 13 and further through the balance control valve 11. An exhaust duct 18 having a damper 19 is provided near the furnace outlet side.

[0004] With such a configuration, the furnace sealing action,
In other words, it is possible to control the amount of air entering from the furnace entrance side, thereby realizing control of the soaking zone upper plate temperature, that is, the holding plate temperature.

[0005]

However, in the prior art shown in FIG. 4, the disturbance to the heating zone caused by changing the amount of air entering from the furnace entrance side for controlling the temperature of the upper soaking zone, that is, No consideration has been given to the occurrence of alloying processing failure due to unintended fluctuations in the heating strip temperature.

For example, if the sealing pressure of the static pressure pad is reduced, the air entering from the furnace entrance side increases, leading to a decrease in the heating effect of the heating zone, and the temperature of the heating zone cannot be maintained without increasing the amount of combustion. . On the other hand, when the sealing pressure is high, not only does the outside air intrude but the heating zone overheats,
Conversely, a state in which the heated combustion gas in the furnace blows out from the furnace entrance side may occur.

Accordingly, the range in which the sealing pressure of the hydrostatic pad can be arbitrarily changed without any inconvenience for controlling the plate temperature in the upper part of the tropical zone is extremely narrow. On the other hand, there is a problem of being totally helpless.

Further, considering a general alloying process,
Some control loop for adjusting the amount of combustion to stabilize the heating conditions in the heating zone, for example, a furnace temperature control or a sheet temperature control of the heating zone is provided. For example, in the alloying furnace shown in FIG. If a plate thermometer is added to the upper part of the heating zone 8 to control the combustion amount of the direct fire type burner 7 so that the plate temperature output from the plate thermometer becomes constant, the plate temperature is stabilized. As a means for achieving this, a double loop including a burner control loop and a static pressure pad control loop is formed, so that control loop interference occurs with each other, and as a result, the sheet temperature tends to be unstable. .

Further, since the plate temperature in the upper part of the soaking zone is controlled only by the static pressure pad provided on the exit side of the furnace, the response of the amount of inflowing air to the operation of the static pressure pad is poor, and the larger the furnace space, the larger the space inside the furnace. There is a problem that the response speed is deteriorated.

[0010] An object of the present invention is to solve the above-mentioned problems, so that even when the operating conditions and the like change and the load of the alloying furnace fluctuates, no disturbance is given to the heating zone and even if a large load fluctuation occurs. An object of the present invention is to provide a method and an apparatus for controlling the temperature of an alloying furnace capable of controlling the holding plate temperature with good responsiveness and stably.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a method for controlling the temperature of an alloying furnace, which is divided into a heating zone and a holding zone sequentially along the direction of transport of the metal strip. Detecting the temperature of the zone and obtaining a temperature deviation from the target temperature value, and converting the temperature deviation into a target external air introduction amount value to the holding zone and a target furnace pressure value of the heating zone through a conversion table. A step of detecting the amount of outside air introduced into the holding zone to determine a deviation from the target outside air introduction amount value, a step of controlling the amount of outside air introduced into the holding band based on the deviation, and Detecting the pressure in the tropical furnace and obtaining a pressure deviation from the target pressure in the furnace, and supplying the combustion exhaust gas from the heating zone to the static pressure sealing means provided at the downstream of the conveyance of the heating zone. The amount of exhaust gas supplied to the vehicle based on the pressure deviation A temperature control method of the alloying furnace, characterized in that it comprises a degree.

Further, the present invention provides a temperature control device for an alloying furnace, which is divided into a heating zone and a holding zone sequentially in the direction of transport of the metal zone, and detects the temperature of the metal zone in the downstream portion of the holding zone. Temperature detecting means for performing the operation, a temperature adjusting means for outputting a temperature deviation between an output from the temperature detecting means and a target temperature value, and a temperature deviation output from the temperature adjusting means, A conversion table for converting the outside air introduction amount value and the target furnace pressure value of the heating zone,
Outside air introduction means for introducing outside air into the holding zone, outside air introduction amount detecting means for detecting the outside air introduction amount into the holding band, and the output from the outside air introduction amount detection means and the target outside air introduction amount value Outside air introduction amount adjusting means for outputting a deviation,
Outside air introduction amount control means for controlling the outside air introduction amount introduced into the holding zone based on the deviation, pressure detection means for detecting the furnace pressure in the heating zone, output from the pressure detection means and the target A pressure adjusting means for outputting a pressure deviation from a furnace pressure value, an exhaust gas supply means for supplying combustion exhaust gas from a heating zone to a static pressure sealing means provided at a downstream portion of the heating zone, and An exhaust gas supply amount control means for controlling an exhaust gas supply amount to be supplied to the pressure sealing means based on a pressure deviation outputted from the pressure adjusting means. .

[0013]

According to the present invention, the combustion exhaust gas from the heating zone is supplied to the static pressure sealing means provided at the downstream of the heating zone to control the amount of exhaust gas to be supplied from the heating zone to the holding zone. The amount of exhaust gas flowing into the system, that is, the amount of heat, is controlled. Further, the outside air is introduced into the holding zone to cool the inside of the furnace of the holding zone, and the degree of cooling is controlled by controlling the amount of outside air introduced. The exhaust gas supply amount and the outside air introduction amount are obtained by detecting the temperature of the metal strip in the downstream portion of the holding zone, obtaining the temperature deviation from the target temperature value, and obtaining the target furnace temperature of the heating zone obtained through the conversion table. Each is controlled by the pressure value and the target outside air introduction amount value to the holding zone. When the temperature in the furnace of the holding zone is decreased, the amount of exhaust gas flowing into the holding zone can be increased to increase the temperature in the furnace. On the other hand, when the temperature in the furnace of the holding zone increases, The temperature inside the furnace can be lowered by increasing the amount of outside air introduced. Therefore, the furnace temperature of the holding zone can be controlled by a combination of the two methods, so that various furnace temperature fluctuations can be controlled responsively and stably. In addition, by setting the contents of the conversion table to desired characteristics, it is possible to prevent the exhaust gas supply amount from suddenly changing and adversely affecting the control loop in the heating zone.

According to the invention, there is provided an exhaust gas supply means for supplying combustion exhaust gas from the heating zone to a static pressure sealing means provided at a downstream portion of the heating zone, and a control means for controlling the amount of exhaust gas supplied. By providing the exhaust gas supply amount control means, the amount of exhaust gas flowing from the heating zone to the holding zone, that is, the heat amount can be controlled. Furthermore, by providing outside air introduction means for introducing outside air to the holding zone, and outside air introduction amount control means for controlling the amount of outside air introduced, the outside air is introduced into the holding zone and the By cooling the air and controlling the amount of outside air introduced,
The degree of cooling can be controlled. Further, by providing a temperature detecting means for detecting the temperature of the metal belt in the downstream portion of the holding belt, and a temperature adjusting means for outputting a temperature deviation between the output and the target temperature value, Is adopted as a control parameter, and by providing a conversion table for converting the temperature deviation into a target furnace pressure value in the heating zone and a target outside air introduction amount value into the holding zone, the exhaust gas supply amount and the outside air introduction amount can be reduced. Each is controlled. Therefore, the furnace temperature in the holding zone can be controlled by two combinations of the heat supply and the degree of cooling, so that various furnace temperature fluctuations can be controlled with good responsiveness and stably. Also, by setting the contents of the conversion table to desired characteristics, it is possible to prevent a sudden change in the exhaust gas supply amount from adversely affecting the temperature control loop in the heating zone.

[0015]

FIG. 1 is a block diagram showing the configuration of a temperature control device for an alloying furnace according to an embodiment of the present invention. The alloying furnace 40 sequentially moves the heating zone 41, the holding zone 42, and the like along the transport direction (from bottom to top in FIG. 1) of the metal strip 30 such as a steel plate.
It is divided into a cooling zone 43 and is installed immediately above the plating bath 31 for storing a molten metal 32 such as molten zinc. After the metal strip 30 conveyed at a predetermined speed is immersed in the plating bath 31, the conveyance direction is changed vertically upward by the sink roll 33, and is adjusted to a predetermined plating adhesion amount by a wiping device 34 such as a high-pressure nozzle. Enters the heating zone 41 of the alloying furnace 40. Heating zone 41
In the above, after the metal strip 30 is heated to a temperature necessary for the alloying treatment by a burner 44 such as a direct fire type burner,
After being carried into the holding zone 42, the soaking process is performed for a certain period of time, alloying proceeds from the surface to a predetermined depth, and further, the cooling zone 43
And cooled to the temperature required for the subsequent processing.

FIG. 3 is a graph showing an example of a heat treatment pattern of the alloying furnace. When the metal strip 30 passes through the heating zone 41, the metal strip 30 is heated to the plate temperature Ta, and thereafter is maintained at a substantially constant temperature in the holding zone 42.
b, and is cooled in the next cooling zone 43.

A heating zone 41 is provided downstream of the heating zone 41.
A static pressure sealing device 49 for controlling a draft effect between the metal band 30 and the holding band 42 is provided by adjusting a pressure in a static pressure region formed between the static pressure sealing device 49 and the metal band 30. The amount of exhaust gas flowing from the heating zone 41 to the holding zone 42, that is, the amount of heat flowing into the holding zone 42, can be controlled. Exhaust gas to be supplied to the static pressure sealing device 49 is sucked from a suction duct 46 provided in the heating zone 41 by a suction fan 47 and supplied through a flow control valve 48 controlled by a pressure controller 51. You.

On the other hand, the combustion amount of the burner 44 in the heating zone 41 is determined by a burner control unit 45 based on the output of a sheet thermometer TA for detecting the temperature of the metal zone provided immediately after the static pressure sealing device 49. Controlled.

A separate sheet thermometer TB is provided downstream of the holding zone 42 in the conveyance direction. The temperature of the sheet temperature output from the sheet thermometer TB and the target temperature value output from the temperature setting section 53 are further increased. A temperature controller 52 that outputs a temperature control manipulated variable by control calculation based on the deviation is provided.

An outside air duct 56 for introducing outside air for lowering the ambient temperature in the holding band 42 is provided at an intermediate portion of the holding band 42, and the outside air is blown by a suction fan 54 and is sent to a temperature controller. The manipulated variable output by 52 is passed through a conversion table 70 and sent through a flow control valve 55 controlled by a flow controller 71 to be a target outside air flow value. Therefore, the plate thermometer TB and the temperature controller 5
2. A control loop including the conversion table 70, the flow controller 71, and the flow control valve 55 performs cooling control based on the amount of outside air blown so that the plate temperature at the downstream portion of the conveyance of the holding zone 42 becomes constant.

Further, the temperature control manipulated variable output from the temperature controller 52 is converted into a target pressure value in the heating zone furnace through a conversion table 57 having a step-like characteristic curve showing a hysteresis characteristic. Even when the target pressure value is changed via the change rate limiter 80, the target pressure value is input to the next stage pressure controller 51 as a small change in the target pressure value so as not to adversely affect the burner control of the heating zone. Further, the output of the pressure gauge PA provided in the heating zone 41 is input to the pressure controller 51. The pressure controller 51 performs a control operation based on the pressure deviation and controls the opening degree of the flow control valve 48 by a pressure control operation amount output to control the amount of exhaust gas supplied to the static pressure sealing device 49, thereby controlling static pressure. The degree of sealing of the pressure sealing device 49 is changed to control the amount of exhaust gas flowing from the heating zone to the holding zone, that is, the amount of heat.

Between the holding zone 42 and the cooling zone 43, there is provided a static pressure sealing device 62 for suppressing a draft effect between the two, and like the static pressure sealing device 49 of the heating zone 41,
The amount of gas flowing into the cooling zone 43 from the holding zone 42 is suppressed by the pressure in the static pressure region formed between the static pressure sealing device 62 and the metal zone 30.

External air blown from a blower fan 60 is supplied to the static pressure sealing device 62 through a flow control valve 61. By adjusting the opening of the flow control valve 61, the static pressure sealing device 62 is opened. The degree of sealing of the device 62 can be adjusted.

Next, a method for controlling the temperature of the alloying furnace according to one embodiment of the present invention will be described with reference to FIG.
First, using the sheet thermometer TB, the temperature of the metal strip 30 in the downstream portion of the conveyance of the holding strip 42 is detected, and the temperature is calculated by a control calculation based on a temperature deviation from a target temperature predetermined by the temperature control unit 53. The control operation amount is obtained by the temperature controller 52.

The manipulated variable output from the temperature controller 52 is input to a conversion table 70 for converting into a target outside air introduction value into the holding zone, and is converted into a target outside air introduction value. The flow rate of the outside air introduced into the holding zone is detected by the flow meter 72, and the control calculation is performed by the flow controller 71 based on the flow difference between the output of the flow meter 72 and the target outside air flow rate output from the conversion table 70. Perform the flow control operation amount. The degree of cooling of the atmosphere inside the holding zone 42 is controlled by adjusting the opening degree of the flow rate control valve 55 based on the flow control operation amount thus obtained and controlling the amount of outside air supplied to the holding zone 42. ing.

The manipulated variable output from the temperature controller 52 is converted into a target pressure value through a conversion table 57 having a step-like characteristic curve showing a hysteresis characteristic.

FIG. 2 is a graph showing an example of a characteristic curve of the conversion table 57. In this graph, the X axis indicates the temperature control operation amount output from the temperature controller, the Y axis indicates the target pressure value in the heating zone furnace, and when the temperature control operation amount is input to the conversion table, P0 to P5 The target pressure value is converted into a target pressure value of six levels, and a larger target pressure value is output as the temperature control operation amount becomes larger as a whole. Further, in order to prevent the output from becoming unstable even if the temperature control manipulated variable fluctuates slightly in the vicinity of the level step, a hysteresis of ΔH is given in terms of the temperature control manipulated variable. In this way, even if the temperature of the metal strip 30 in the downstream portion of the transport of the holding strip 42 fluctuates slightly, signal processing is performed so that the output target pressure value does not fluctuate greatly. For example, hunting in the control loop is prevented. It is possible.

On the other hand, the pressure gauge PA detects the pressure inside the furnace at the upstream portion of the heating zone 41 in the conveyance, and the output of the pressure gauge PA is compared with the target pressure value output from the conversion table 57 via the rate-of-change limiter. Pressure controller 51 based on pressure deviation
Control operation is performed to obtain the pressure control operation amount. Based on the pressure control operation amount thus obtained, the flow control valve 4
8, the degree of sealing of the static pressure sealing device 49 is changed by controlling the amount of exhaust gas to be supplied to the static pressure sealing device 49 provided upstream of the heating zone 41 in the conveying direction. The amount of exhaust gas flowing into the system, that is, the amount of heat, is controlled.

In such a temperature control method, when the temperature of the metal band 30 in the downstream portion of the conveyance of the holding band 42 decreases, the output of the plate thermometer TB decreases, and the output of the manipulated variable of the temperature controller decreases. Then, first, the output of the conversion table 70 decreases, and the target outside air introduction value immediately given to the flow controller 71 decreases, and the outside air introduction amount becomes larger than the target outside air introduction amount. The operation output decreases, the opening of the flow control valve 56 decreases, and the holding band 42
The amount of outside air introduced into the air supply, that is, the degree of cooling is immediately reduced. Furthermore, the target pressure value output from the conversion table 57 decreases stepwise, and the furnace pressure increases with respect to the target pressure, so that the operation amount output of the pressure controller decreases and the opening of the flow control valve 48 decreases. Become smaller, static pressure sealing device 49
The amount of exhaust gas supplied to the heating zone 41 decreases, the degree of sealing decreases, and the amount of exhaust gas flowing from the heating zone 41 to the holding zone 42, that is, the amount of heat, increases. Then, the ambient temperature in the holding zone 42 increases due to the reduction in the degree of cooling and the increase in the amount of heat, and the temperature of the metal zone 30 in the downstream portion of the holding zone 42 is controlled to increase.

Conversely, assuming that the temperature of the metal band 30 at the downstream portion of the holding band 42 is increased, the metal band 30 operates in the opposite direction to the above-described operation, and the temperature of the metal band 30 at that portion decreases. Controlled in the direction. Therefore, the temperature of the metal strip 30 at the downstream of the transport of the holding zone 42 is controlled to be stable by the combination of the cooling and the heat supply.

On the other hand, in the heating zone, when the output of the sheet thermometer TB is controlled stably by the above-described operation, the change in the furnace pressure PA of the heating zone 41, that is, the amount of air entering from the furnace entrance side is Since the control is performed so as to change only little by little while avoiding a sudden change, the change is absorbed by the burner control unit 45, and the output of the plate thermometer TA is also stably controlled.

That is, the characteristic curve of the conversion table 57 is stepwise and has a hysteresis characteristic, and the target pressure value of the heating zone 41 is changed at a relatively small ratio, thereby controlling the plate temperature of the heating zone 41. Eliminating bad effects on loops.

With the above operation, the heating strip temperature TA and the holding strip temperature TB in the alloying furnace are stably controlled, and the heat treatment pattern shown in FIG. 3 is stably obtained.

[0034]

As described in detail above, according to the present invention, since the atmosphere temperature in the holding zone of the alloy furnace is controlled responsively and stably, the temperature of the metal zone in the holding zone becomes substantially constant, The alloying treatment on the surface of the band is performed very stably. Therefore, it is possible to improve the quality of the metal strip and the production yield. Furthermore, it becomes easy to adjust the heat treatment pattern in the alloying furnace with good reproducibility, and it is possible to improve the degree of freedom of production and shorten the time for adjusting the operating conditions.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a temperature control device for an alloying furnace according to one embodiment of the present invention.

FIG. 2 is a graph showing an example of a characteristic curve of a conversion table 57 of FIG.

FIG. 3 is a graph showing an example of a heat treatment pattern of an alloying furnace.

FIG. 4 is a structural view showing an example of a conventional galvanizing alloying furnace.

[Explanation of symbols]

 REFERENCE SIGNS LIST 30 metal strip 31 plating bath 32 molten metal 33 sink roll 34 wiping device 40 alloying furnace 41 heating zone 42 holding zone 43 cooling zone 44 burner 45 burner control unit 46 suction duct 47 suction fan 48 flow control valve 49 static pressure sealing device 51 Pressure controller 52 Temperature controller 53 Temperature setting unit 54 Suction fan 55 Flow control valve 56 Outside air duct 57 Conversion table 60 Ventilation fan 61 Flow control valve 62 Static pressure sealing device 63 Suction duct 64 Suction fan 70 Conversion table 71 Flow controller 72 Flow meter 80 Change rate limiter

──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyuki Takezaki, 5th Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd. Inside Sakai Works (72) Inventor Kazuhiro Majima 5th, Ishizunishi-cho, Sakai-shi, Osaka Nissin Steel (72) Inventor Hozumi Akita 1-1-30 Oyodonaka, Kita-ku, Osaka-shi, Osaka Prefecture Inside Kansai Branch of Toshiba Corporation (72) Inventor Hiroyuki Suzuki 1--1, Oyodonaka, Kita-ku, Osaka-shi, Osaka 1-30 Toshiba Corporation Kansai branch office (56) References JP-A-2-30745 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. A method for controlling the temperature of an alloying furnace, which is divided into a heating zone and a holding zone sequentially along a direction in which the metal strip is conveyed, comprising:
A step of obtaining a temperature deviation from the target temperature value; a step of converting the temperature deviation into a target outside air introduction amount value to the holding zone and a target furnace pressure value of the heating zone through a conversion table; A step of detecting the amount of outside air introduced to obtain a deviation from the target outside air introduction value, a step of controlling the amount of outside air introduced to the holding zone based on the deviation, and a step of detecting the furnace pressure in the heating zone. A step of obtaining a pressure deviation from the target furnace pressure value, and an exhaust gas supply amount when supplying combustion exhaust gas of the heating zone to a static pressure sealing means provided in a downstream portion of the heating zone in the conveyance.
Controlling the temperature based on the pressure deviation. 2. A temperature control device for an alloying furnace, which is sequentially divided into a heating zone and a holding zone along a conveying direction of the metal zone, wherein a temperature of the metal zone at a downstream portion of the holding zone is detected. Temperature detecting means, temperature adjusting means for outputting a temperature deviation between an output from the temperature detecting means and a target temperature value, a temperature deviation outputted from the temperature adjusting means, a target outside air introduction amount to the holding zone. Conversion table for converting the temperature and the target furnace pressure value of the heating zone, the outside air introduction means for introducing outside air to the holding zone, and the outside air introduction amount detection for detecting the outside air introduction amount to the holding zone Means, an outside air introduction amount adjusting means for outputting a difference between an output from the outside air introduction amount detection means and a target outside air introduction value, and controlling the outside air introduction amount introduced into the holding zone based on the difference. Means for controlling the amount of outside air introduced; Pressure detecting means for detecting a tropical furnace pressure; pressure adjusting means for outputting a pressure deviation between an output from the pressure detecting means and the target furnace pressure value; Exhaust gas supply means for supplying to the static pressure sealing means provided at the downstream of the heating zone, and controlling the amount of exhaust gas supplied to the static pressure sealing means based on the pressure deviation output from the pressure adjusting means. A temperature control device for an alloying furnace, comprising: