JPH0967618A - Method for controlling atmospheric dew point in decarburize-annealing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately execute the direct control of a dew point in a furnace by utilizing an estimated dew point model prepared from various kinds of conditions, at the time of controlling the dew point in a continuous decarburize-annealing furnace for a grain oriented silicon steel sheet. SOLUTION: At the time of annealing the grain oriented silicon steel sheet in the continuous decarburize-annealing furnace for steel sheet which is classified as a heating zone, decarburizing zone, reducing zone and cooling zone, a model expression for estimating the infurnace dew point in the heating zone is prepared from a humidifier set value, infurnace atmosphere gas quantity, sheet width of the steel sheet coil and steel sheet radiation rate based on the measured value of the dew infurnace point in the heating zone at the stationary time. Characteristic of the dew point in the furnace at the time of changing the humidifier set value is observed, and based on the data, an approximated dynamic characteristic model with a useless time and the temporary delay is prepored. The humidifier set value for achieving a target value of the dew point in the furnace decided for each kind of steel is calculated from the dew point estimation model and set to the humidifier, and since the dew point in the furnace is easily and directly controlled, the unevenness of the film oxidation quantity in the steel sheet is regulated within the target value with excellent control accuracy and the annealing yield is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an atmospheric dew point in a continuous strip decarburization annealing furnace.

[0002]

2. Description of the Related Art A continuous annealing furnace for strips includes a heating furnace, a soaking furnace, and a cooling zone, and a heating zone, a decarburizing zone, a reduction zone, and a cooling zone. In each zone, continuous annealing or continuous decarburizing annealing is performed with a desired atmosphere gas. For continuous annealing of strips whose surface quality needs to be controlled strictly, those which require decarburization, and those whose oxide layer on the steel sheet surface needs to be controlled, for example, heating zone, decarburization zone , Each zone of the reduction zone must have a predetermined atmosphere, for example, the dew point is maintained in a specific range, and a specific component in the atmospheric gas composition is always kept at a constant concentration, so that it is appropriate for the processing purpose of each zone. is there.

Japanese Patent Application No. 5-25688 filed earlier
In the method for controlling the atmosphere flow in the continuous annealing furnace of No. 3, the opening / closing degree of the outlet of the atmosphere gas flowing into the furnace is controlled, and the dew point in the furnace is controlled. In addition, JP-A-5-78
Japanese Patent Publication No. 736 discloses a method of stabilizing the dew point in the furnace by supplying atmospheric gas all at once from the latter stage of the furnace. In any case, these conventional techniques are methods of indirectly controlling the dew point in the furnace by adjusting the amount of atmospheric gas flowing into the furnace.

[0004]

The conventional indirect dew point control method as described above has the following problems. (1) In the control of the dew point by adjusting the amount of atmospheric gas, the control becomes complicated and it is difficult to improve the control accuracy. (2) It takes a long time to reach the target value when the dew point is changed. (3) There is a possibility that the formula expressing the relationship between the atmospheric gas amount and the dew point may deviate.

The problem to be solved by the present invention is to provide a method that is easy to control and has excellent control accuracy by directly controlling the dew point in the furnace.

[0006]

In order to solve the above problems, an atmosphere dew point control method for a decarburizing annealing furnace according to the present invention, in controlling the dew point of a continuous decarburizing annealing furnace for grain-oriented electrical steel sheets,
Create a model to estimate the dew point of one point in the heating zone in the furnace based on the atmospheric gas flow rate, the dew point of the humidifier, the plate width of the steel plate, the emissivity of the steel plate, and the furnace temperature of the soaking zone, and based on the model Thus, the dew point of the humidifier is determined so as to achieve a predetermined dew point target value for each steel type.

[0007]

In the present invention, dew point control is performed in the following steps.

(1) A model formula for estimating the dew point in the heating zone furnace from the set value of the humidifier, the amount of atmospheric gas in the furnace, the coil plate width, and the steel plate emissivity based on the measured value of the dew point in the heating zone furnace at a constant time create. 〇 Model formula In-furnace dew point = A, humidifier set value + B, atmospheric gas amount + C, coil plate width + D, steel plate emissivity + E, furnace temperature + F (1) formula

(2) The characteristics of the dew point in the furnace when the set value of the humidifier was changed were observed (see FIG. 2), and based on this data,
A dynamic characteristic model that approximates dead time and temporary delay is created (see FIG. 3).

(3) The humidifier set value for achieving the target value of the in-furnace dew point determined for each steel type is calculated from the dew point estimation model in step (1) and set in the humidifier. Humidifier set value = (target dew point in furnace-B-atmosphere gas amount + C-coil plate width + D-steel plate emissivity + E-furnace temperature + F) / A (2) formula

(4) At the time of steel type switching, each humidifier set value is calculated in advance from each furnace dew point target value, and the temporal change of the heating zone furnace dew point is calculated from the dynamic characteristic model obtained in step (2). Estimate, compare this result with the time transition of the dew point target value, calculate the humidifier setting change timing that minimizes the variation by trial and error based on the following equation, and set it to the humidifier based on this result.

[0012]

[Equation 1]

[0013]

EXAMPLES Examples of the present invention will be specifically described below.
FIG. 1 is a schematic diagram showing the configuration of a continuous decarburization annealing furnace for carrying out the dew point control method according to the present invention. In the figure,
A continuous annealing furnace 1 comprises a heating zone 2 and a soaking zone 3 in this embodiment. Reference numeral 4 is a humidifier for supplying atmospheric gas having a high dew point of 50 to 70 ° C., and gas is supplied to the heating zone 2 and the soaking zone 3 from the latter stage of the furnace. The strip 5 is passed through the furnace in the direction of the arrow. Heating zone 2,
When the dew point in the soaking zone 3 changes, the measured values indicated by the dew point measuring devices 6 and 7 also change. When the measured value deviates from the target value, the controller 8 adjusts the hot water temperature of the humidifier,
Operates to the target dew point. The target value 9 is
It is calculated and set by the computer 10 using a model formula. By such an operation, the dew point in the decarburization annealing furnace is kept constant. When changing the dew point target value due to steel type switching,
The control accuracy is improved by calculating the time until the target value is reached and the timing that minimizes the difference between the process response and the target value, and performing the setting change at this timing.

Experimental examples for showing the effects of the present invention are shown below.

(1) Control Conditions Coil Specifications: Plate Thickness 0.50 mm or Less (0.26 mm) Plate Width 1500 mm or Less (700 mm) Component Carbon 20 ppm or More (500 ppm) (Before Decarburization) Threading Speed: 50 m / min to 150 m / Min (120 m / min) Furnace temperature: 800 ° C to 1000 ° C (820 ° C) Dew point in the furnace: 40 ° C to 80 ° C (60 ° C)

(2) Model formula A = 1.0 B = 1.2 × 10 ⁻³ C = −2.
0 × 10 ⁻³ D = 2.0 E = 6.0 × 10 ⁻³ F = 10

(3) Consideration a) Variation in dew point Inventive example ± 2.21 ° C. or less Conventional example ± 2.58 ° C. b) Variation in film oxidation amount Inventive example ± 4% Conventional example ± 10%

[0018]

As described above, the present invention has the following effects. (1) By directly controlling the dew point in the furnace, the control was easy, the control accuracy was improved, the variation in the film oxidation amount was within the target value, and the yield was significantly improved. (2) The time until the target dew point converges can be shortened.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a continuous annealing furnace for carrying out a dew point control method according to the present invention.

FIG. 2 is a graph showing a target dew point in the furnace and a dew point transition at the time of calculation.

FIG. 3 is a graph showing a target value of a dew point in a furnace and a dew point transition at the time of setting.

[Explanation of symbols]

1 continuous annealing furnace, 2 heating zones, 3 soaking zone, 4 humidifier, 5 steel plate, 6,7 dew point detector, 8 controller, 9
Target value, 10 calculator

Claims (1)

[Claims] 1. When controlling the dew point of a continuous decarburization annealing furnace for grain-oriented electrical steel sheets, based on the atmospheric gas flow rate, the dew point of the humidifier, the sheet width of the steel sheet, the emissivity of the steel sheet, and the soaking temperature of the soaking zone. Create a model to estimate one dew point in the heating zone in the furnace,
A dew point control method for a decarburizing annealing furnace, wherein the dew point of the humidifier is determined so as to achieve a predetermined dew point target value for each steel type based on the model.