JPH03140415A - Method for determining material heating-up curve in heating furnace - Google Patents

Abstract

PURPOSE:To improve dimensional accuracy at the time of rolling by picking up two kinds of temp. conditions, that is, temp. conditions in a skid part and temp. conditions in a part between skids in the method for introducing a slab into a continuous heating furnace having plural control zones and controlling the slab extraction temp. to the desired temp. CONSTITUTION:The average temps. of a slab in skid parts and in the parts between skids are determined, respectively, from the temp. prediction mathematical model of a slab, and the sensitivities of the slab extraction temp. to respective furnace temps. are determined from the above average temps., predicted residual in-furnace time, and the furnace temps. in respective zones by using an average slab temp. sensitivity formula at the time of extraction. Then, modified furnace temps. are determined by executing a modified furnace temp. computing formula from the sum total of the above sensitivities in respective zones and their deviations so that the deviations between the predicted extraction temp. of the slab heated at the above furnace temps. and the desired extraction temps. in the above skid parts are reduced to zero. Further, the computing of the slab sensitivity to the degree of soaking is performed from of extraction so that the degree of soaking, as the difference of the average temp. of the temps. in the parts between the above skid parts from the average temp. of the temps. in the above skid parts, reaches the desired temp. Successively, the final controlled furnace temps. in the respective zones are determined from the above modified furnace temp. computing formula.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for determining a material temperature rise curve of a heating furnace in a hot rolling line.

[Conventional technology]

FIG. 4 is an explanatory diagram showing a process for determining the charging temperature of a steel billet based on elapsed time in the conventional continuous heating furnace control method disclosed in, for example, Japanese Patent Publication No. 58-18401. This invention controls the temperature inside the heating furnace according to the temperature of the steel billet. Various methods of measuring the temperature of the steel billet have been carried out, but when it is determined by the elapsed time from the time of ingot formation to the time of charging into the heating furnace. I will explain about it.

First, continuously cast steel billets are cut into predetermined billet sizes after continuously casting molten steel. At this time, the temperature of the steel billet is controlled to a constant value (approximately 800° C.) by water cooling control attached to the continuous casting device and measured by a thermometer. A steel billet that is charged into a continuous heating furnace as a hot steel billet is charged into a heating furnace several hours after being cut. At this time,
The charging temperature θin is calculated using the following heat transfer equation based on the cutting time of the steel slab, the temperature of the steel slab at the time, the time of charging into the continuous heating furnace, and the dimensions of the steel slab.

boundary condition ■Center 0 surface However, θ(t, x): material temperature t: Time (elapsed time since disconnection time) time) X; Thickness direction coordinate (0≦x<H/ 2) P; material density C: Material specific heat λ; material thermal conductivity H: Slab thickness initial conditions θ(0,x)=θ.

θ0: Billet temperature at the end of continuous casting ε: Emissivity with the atmosphere θ□, ;Ambient temperature When the elapsed time until the charging time is t, the charging temperature θi11 in the thickness direction is calculated as shown in the following equation. Adopt the average temperature.

Once the charging temperature θ, 7 is determined, the charging temperature θ is determined in the heating furnace.
5. Using 5 as an initial value, control the furnace temperature of the multiple zones so that the predicted extraction temperature of the steel billet matches the target extraction temperature, and calculate the heat transfer equation for each zone based on the remaining furnace time of each zone until extraction. If there is a deviation from the target value, correct the assumed furnace temperature again and repeat the calculation until it matches. Find the set furnace temperature. Determine the temperature rise curve of the material.

[Problem to be solved by the invention]

The conventional method for determining the material temperature rise curve for a heating furnace is as described above, so it is necessary to use trial and error to determine the amount of correction when there is a deviation between the predicted and desired furnace temperature. , Also, since the heat transfer equation is solved, the slab (steel billet) in the furnace
When the number of books is large, it takes a long time to calculate the total, so it is not suitable for online use. In addition, when considering the rolling process, there were problems such as a decrease in dimensional accuracy during rolling because no consideration was given to the temperature difference between the skids (sliding members) and the skid part (hereinafter referred to as soaking degree).

This invention was made to solve the above-mentioned problems, and it is possible to determine the temperature in a short time, and also to improve the dimensional accuracy during rolling by incorporating two types of temperature conditions at the skid part and between the skids. The purpose of this study is to obtain a method for determining the material temperature rise curve in a heating furnace.

[Means to solve the problem]

The method for determining a material temperature rise curve for a heating furnace according to the present invention calculates two types of slab average temperatures between the skid part and the skid using a slab average temperature calculation formula, and uses a prediction model to determine the slab temperature at the time of extraction with respect to the furnace temperature. Sensitivity is determined by calculating the slab sheep average temperature sensitivity formula during extraction. Furthermore, in order to converge the deviation between the extraction target and the predicted slab extraction temperature to zero, a modified furnace temperature calculation formula is executed to determine the temperature increase curve.

[Effect]

The method for determining the material temperature rise curve of a heating furnace in this invention is to determine the average temperature of two types of slabs between the skirad section and the skid in order to quickly control the temperature inside the furnace, which changes depending on the slab charged into the continuous heating furnace. This method uses a model that predicts the temperature and a sensitivity calculation at the time of extraction to perform convergence calculations and determine the temperature rise curve, which reduces calculation time and improves rolling dimensional accuracy.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure shows a conceptual diagram of a heating furnace. In order to maintain each predetermined tropical zone stably, the temperature of the tropical zone is controlled into three zones, for example, a pre-heating zone, a heating zone, and a soaking zone.

FIG. 3 is a block diagram showing a heating furnace control system. In the figure, 20 is a current temperature calculation means, 21 is a temperature rise curve calculation means, and 22 is a set furnace temperature calculation means, which controls the furnace temperature setting means 106. Information is given to the current temperature calculation means 20 as a parameter from the material information means 102.

Further, 101 is a heating furnace divided into zones and has multiple sets of fuel flow rate controllers 103, and is equipped with a furnace temperature detector 104 and a combustion burner 105 to enable independent temperature control for each zone. There is.

Next, a calculation method for determining a material temperature increase curve will be described with reference to the flowchart in FIG. First, the slab average temperature θ1. and equations (1) and (2) for the set furnace temperature θJl.
As shown in the formula.

θ,1=θ5. +(θgl-θ, +-+)eXp(-α
Jlt+/H)... (1)...
(2) Here, θ, I: aJI: θ, I: Cp: t: γ: H Nislab average temperature correction coefficient setting Furnace temperature specific heat prediction Remaining furnace time Specific gravity Slab thickness σ: Stefan-Boltzmann constant i: Band ( L=1.3) j Niskid part/skid gap (j=1.2) The above equation (1) is based on the predicted remaining time 1+, slab thickness H1, set furnace temperature θ1. If given, the average temperature of each strip exit side slab θ1
is calculated (slab temperature prediction formula model).

First, in step ST1, each zone furnace temperature initial value θ11 is set using table values. In addition, if the slab average temperature sensitivity equation during extraction of equation (3) is used, each zone furnace temperature θ3. The slab average temperature sensitivity for each zone furnace temperature can be determined by partial differentiation.

F, , = a e , , /aθ,k ・
(3) (j = 1.2 k = 1.3) In step ST2, the slab average temperature θJl (skid part) during extraction is determined from equations (1) and (2), and in step ST3, equation (4) is calculated. Check whether you are satisfied or not.

θ, 3+ Σ F +k·Δθgk=θ13^1 (target value) (4) Next, in step ST4, equation (3) is partially differentiated to find the sensitivity. Here, in step ST5, the correction amount Δθ of the corrected furnace temperature is determined as shown in equation (5). (modified furnace temperature calculation formula).

(6) The gain β of the corrected furnace temperature can be found using the formula.

= e13AI' -〇(6) θ, , wax , upper limit value of furnace temperature set for each zone θ , ff1l
n, the lower limit of the furnace temperature set in each zone, and the gain β as ・(5
), the correction amount Δθ,5 is found.

θ1. Add the correction amount obtained by equation (5) to (θ1.+
Δθ11→θ, 1). Then, the processing in steps ST2 to ST5 is repeated until formula (4) is satisfied.

Finally, using the set furnace temperature θ, 1 found in step ST5, the correction coefficient H between the skid section and the skid is input as the average slab temperature θ, l of each strip side skid section/between the skids.
is calculated using equation (1).

Then, in step ST7, θ, 3 is θ, AIM, θ2
° is θ1. It is checked using equation (7) whether AIM+Δθ and Al11 are satisfied.

... (7) Here, 80g+=c+ ・Δθg□ ...
(8)... (9) In step ST8, equation (1) is partially differentiated to obtain the skid portion/inter-skid slab sensitivity from equation (3).

In step ST9, the corrected furnace temperature (correction amount) is obtained by simultaneously applying equations (7), (8), and (9). Then, the correction amount obtained in step ST5 is added to the set furnace temperature θ, l. Thus, (1), (3).

Repeat equations (7) and (8) to obtain 013. Perform convergence calculations while correcting Δ01k so that θ23 becomes the target value, and set the furnace temperature θ. Determine. The temperature rise curve of the material is determined by this set furnace temperature.

Next, based on one embodiment of the present invention (heating furnace control) will be explained with reference to FIG.

In FIG. 3, the heating furnace 10 is divided into a plurality of control zones.
1, a combustion burner 105 and a furnace temperature detector 104 are arranged, and the flow rate is controlled by a fuel flow rate controller 103 so as to reach the set temperature for each control zone set by the furnace temperature setting means 106. . Reference numeral 102 denotes a material information means, which instructs the furnace temperature setting means 106 with material information such as the dimensions, weight, extraction temperature, and conveyance information of the material in the furnace.

The furnace temperature setting means 106 includes a current temperature calculation means 20, a temperature increase curve calculation means 21, and a set furnace temperature calculation means 22, and is activated periodically. The current temperature calculation means 20 calculates the current material temperature using the actual furnace temperature based on the material information.

The temperature increase curve calculation means 21 determines the temperature increase curve for each material as described above. The set furnace temperature calculation means 22 instructs the determined furnace temperature to the fuel flow rate controller 103.

[Effects of the Invention] As described above, according to the present invention, there is a model that predicts two types of slab average temperatures between the skid section and the skid, and the sensitivity of the slab temperature during extraction to the furnace temperature is calculated using the prediction model. Since the material temperature rise curve is determined using the calculation formula to be obtained and the calculation algorithm that converges the deviation from the target to zero, calculation time is shortened, making it suitable for online control of heating furnaces and improving the accuracy of slab rolling dimensions. This has the effect of being able to determine the temperature rise curve.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the general configuration of a heating furnace, FIG. 2 is a flowchart showing a calculation method for determining a material temperature rise curve according to an embodiment of the present invention, and FIG. 3 is a diagram according to an embodiment of the present invention. FIG. 4 is a block diagram illustrating a heating furnace control system, and is an explanatory diagram illustrating a conventional process for determining the slab charging temperature based on elapsed time. In the figure, Sr1 and Sr1 are slab temperature calculations, Sr4
．． Sr1 is slab sensitivity calculation, Sr1. Sr1 is a modified furnace temperature calculation.

Claims (1)

[Claims] Load the slab into a continuous heating furnace with multiple control zones,
In a method for determining a material temperature rise curve for a heating furnace in which the extraction temperature of a slab is controlled to a target temperature, the average temperature of the slab in the skid portion and between the skids is determined by the slab average temperature calculation formula using the temperature prediction formula model of the slab, The sensitivity of the slab extraction temperature to each furnace temperature is calculated from the slab average temperature, predicted remaining furnace time, and furnace temperature of each zone using the slab average temperature sensitivity formula at the time of extraction, and the predicted extraction temperature of the slab heated at the above furnace temperature is calculated. A corrected furnace temperature calculation formula is executed using the sum of the sensitivities of each zone and the deviation so as to make the deviation between the extraction target temperature of the skid part and the extraction target temperature of the skid part zero, and the corrected furnace temperature is calculated between the skids and the skid part. The slab sensitivity calculation for the soaking degree is performed using the slab average temperature sensitivity formula at the time of extraction so that the soaking degree, which is the difference between the average temperatures of A method for determining a material temperature rise curve for a heating furnace, characterized in that a zone controlled furnace temperature is determined.