JP2716551B2 - Heating furnace material heating curve determination method - Google Patents

Description

Description: FIELD OF THE INVENTION 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 view of a process for obtaining the charging temperature of a conventional hot slab according to the elapsed time, for example, disclosed in Japanese Patent Publication No. 58-18401. The continuous cast billet is cut into predetermined billet dimensions after continuously casting molten steel. At that time, the slab temperature was kept at a constant value (approximately 80
0 ° C), and the slab temperature is measured by a thermometer. A slab charged to a continuous heating furnace as a hot slab is charged to the heating furnace several hours after cutting. At this time,
Based on the cutting time of the slab, the slab temperature at the time, the charging time into the continuous heating furnace, and the slab dimensions, the charging temperature θ _in is calculated by the following heat transfer equation.

θ (t, x): Material temperature t: Time (elapsed time from cutting time) x: Coordinates in thickness direction (0 ≦ x ≦ H / 2) ρ: Material density C: Material specific heat λ: Material thermal conductivity H: Slab thickness Initial condition θ (0, x) = θ ₀ θ ₀ : Slab temperature at the end of continuous casting Boundary condition Center surface ε: emissivity to atmosphere θ _air : atmosphere temperature When the elapsed time until the charging time is defined as t _in , the average temperature in the thickness direction is adopted as the charging temperature θ _in as _{in the} following equation.

Once the charging temperature θ _in is obtained, the charging temperature θ _in the heating furnace is obtained.
The furnace temperature in each zone is controlled so that the predicted extraction temperature of the slab coincides with the target temperature using _in as an initial value.

[Problems to be solved by the invention]

Since the conventional method of determining a material heating curve of a heating furnace is performed as described above, once there is a deviation between the prediction and the target at the assumed furnace temperature, the correction must be performed by trial and error, and Since the heat transfer equation is solved, it takes a long time to calculate if the number of slabs in the furnace increases, and it is not suitable for online use. Furthermore, when the rolling process is considered, there is a problem that it is difficult to obtain dimensional accuracy during rolling because a temperature difference between the skids and the skid portion (hereinafter, referred to as a soaking degree) is not particularly considered.

The present invention has been made in order to solve the above-described problems, and has a short calculation time, and improves the dimensional accuracy of rolling in consideration of two types of temperatures (between a skid portion and a skid). It is intended to obtain a method for determining a heating curve.

[Means for solving the problem]

The method for determining a heating temperature curve of a heating furnace according to the present invention includes estimating a current temperature of a slab by a current temperature calculating means using material information and an actual furnace temperature, and based on the estimated slab temperature, a distance between a skid portion and a skid. Each control exit temperature is predicted by each exit temperature prediction means, and when the predicted control exit temperature is different from the target temperature, the slab temperature sensitivity calculation means calculates the temperature sensitivity of the slab to each zone furnace temperature by the slab temperature sensitivity calculation means, If the target extraction temperature is not satisfied based on the deviation with respect to the target temperature and the temperature sensitivity, the correction furnace temperature calculation means using a different algorithm corresponding to each of the target extraction temperatures depending on whether the target soaking degree is satisfied or not. The temperature is calculated, and the prediction of the temperature on the exit side, the calculation of the slab temperature sensitivity, and the calculation of the corrected furnace temperature are repeated to perform the convergence calculation and set the furnace temperature.

(Operation)

Regarding the setting of the furnace temperature in the present invention, the first
The current material temperature is calculated from the material information and the actual furnace temperature by the current temperature calculating means. Secondly, each outgoing side temperature predicting means predicts each outgoing side temperature from the current material temperature, and if the result is different from the target value, the slab temperature sensitivity calculating means calculates the slab temperature sensitivity with respect to each furnace temperature. . Subsequently, third, the corrected furnace temperature is calculated by the corrected furnace temperature calculating means based on the deviation from the target and the sensitivity, and the temperature rise curve is determined. Therefore, control with high dimensional accuracy can be performed.

(Example of the invention)

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1, for example, in a hot coil rolling process,
This figure shows an outline of a continuous heating furnace for heating a slab with a continuous heating furnace.
Is a tropical zone, and 4 is a slab that is charged from the left side of the continuous heating furnace and passes in the direction of the arrow.

Next, a method of calculating the set furnace temperature and the material temperature rise curve will be described. First, in order to estimate the average temperature of the slab 4 at the current position in the furnace after the slab 4 is charged, the heat transfer equation of the equation (1) is solved at regular intervals.

The boundary condition is solved by equation (2).

Here, λ: thermal conductivity T: slab internal temperature C _p : specific heat U, D: upper and lower slabs γ: specific gravity H: slab thickness q: heat flux T is converted to an average temperature.

n: Number of slab mesh divisions Thus, the current slab average temperature is obtained. Based on this temperature, the temperature of each zone control furnace is calculated by the following average temperature prediction model for each zone, and the material temperature rise curve is determined.

θ _ji = θ _gi + (θ _ji-1 −θ _gi ) exp (−α _i t _i / H) …… (4) Here, θ _ji : average slab temperature a _i : adjustment coefficient θ _gi : set furnace temperature C _p : specific heat t _i : predicted furnace time γ: specific gravity H: slab thickness σ: STEFAN-BOLTZMAWN constant i: band (i = 1,3) j: between the skid portion and the skid (j = 1,2) In the equation (4), given t _i , H, θ _gi , the average slab temperature θ _ji on each banding side can be obtained.

Further, by _performing partial differentiation with each zone setting furnace temperature θ _gi , the average slab temperature sensitivity at the time of extraction with respect to each zone setting furnace temperature is obtained.

F _ji = θ _j3 / θ _gi (j = 1, 2 i = 1, 3) (6) The target values are the extraction target temperature θ _out ^* and the target soaking degree Δθ _out ^*.
And are represented by equations (7) and (8).

| Θ ₁₃ −θ _out ^* | Δθ _D (7) θ ₂₃ −θ ₁₃ Δθ _out ^* (8) As for the constraint of the target, the expression (8) is loose and the expression (7) is severe, so that (8) The equation may be satisfied first, and each zone control furnace temperature is calculated by the following two methods.

(I) When the warm steel slab exists in the pre-tropical zone When neither equation (7) nor (8) is satisfied When only equation (7) is not satisfied Using equation (9) or (10), the correction Δ for each zone setting furnace temperature
θ _gi is obtained, and the correction Δθ _gi is added to the initial zone setting furnace temperature θ _gi to correct each zone setting furnace temperature θ _gi .

Then, after correction of each band set furnace temperature theta _gi, the respective band set furnace temperature theta _gi (4), by substituting calculated (5), again (7),
Step ST determines whether or not the judgment condition of equation (8) is satisfied.
Judge with 5 and 6. Then, (7), when not satisfied (8) of the determination condition, adds the correction amount [Delta] [theta] _gi "to each band set furnace temperature theta _gi, then modifying each band setting oven temperature theta _gi, The corrected zone setting furnace temperature θ _gi is substituted into the equations (4) and (5) and calculated, and it is determined again in steps ST5 and ST6 whether or not the determination conditions of the equations (7) and (8) are satisfied. (7)
By repeating until the determination condition of Expression (8) is satisfied, each zone setting furnace temperature θ _gi is obtained.

(Ii) When a hot slab exists in the heating zone When neither equation (7) nor (8) is satisfied When only (7) is not satisfied (Iii) When the hot slab exists in the solitary tropics θ ₁₃ + F ₁₃ · Δθ _g3 = θ _out ^* (13) In the case of (i), the formula (9) or (10), and in the case of (ii) ( In the case of equation (11), equation (12), or (iii), Δθ _gk obtained in equation (13) is added to the initial θ _gk , and again (4),
By repeating the process of calculating the expression (5) and checking the expressions (7) and (8), each zone setting furnace temperature is obtained.

Here, C ₁₁ , C ₂₁ , C ₂₂ , C ₂₃ , C ₃₁ , and C ₃₂ are adjustment coefficients.

With the above processing, the set furnace temperature and the material temperature rise curve are determined.

Next, the heating furnace control operation according to one embodiment of the present invention will be described with reference to the flowchart of FIG. 2 and the block diagram of the continuous heating furnace of FIG.

First, a combustion burner 105 and a furnace temperature detector 104 are arranged in the heating furnace 101 divided into a plurality of control zones, and the temperature is set to a set temperature for each control zone set by the furnace temperature setting means 106. Next, the fuel flow controller 103 operates to control the fuel flow. The material information means 102 instructs the furnace temperature setting means 106 of material information such as the size, weight, extraction temperature, and furnace transfer information of the material in the furnace.

The furnace temperature setting means 106 includes a current temperature calculating means 20, each outgoing side temperature predicting means 21, a slab temperature sensitivity calculating means 22, and a corrected furnace temperature calculating means 23, and is started periodically.

First, the current temperature calculation means 20 calculates the current material temperature by referring to the actual furnace temperature based on the material information output from the material information means 102 (step ST1). Next, the initial furnace temperature obtained from the calculation result is set (step ST2).
Each outgoing side temperature prediction means 21 predicts each outgoing side temperature based on the current material temperature (step ST3). (Steps ST6 and ST7), modified furnace temperature calculation means 2
If the target extraction temperature is not satisfied based on the deviation from the target and the sensitivity using 3, the corrected furnace temperature is obtained by a different algorithm depending on whether the target soaking degree is satisfied or not (step ST8). ~ ST10). The set furnace temperature thus determined is instructed to the fuel flow controller 103 (step ST11).

〔The invention's effect〕

As described above, according to this case, the present temperature calculating means for obtaining the current material temperature, and the respective outlet temperature predicting means for predicting each outlet temperature when the material leaves the furnace, If the value is different from the target value, the slab temperature sensitivity calculation means for calculating the sensitivity of the slab temperature and finally the temperature correction is performed by the corrected furnace temperature calculation means, so that it is directly solved using the heat transfer equation for the prediction calculation As a result, the calculation time is shortened, and since the temperature rise curve is determined so as to satisfy the two target values of the extraction temperature and the soaking degree, high-precision control is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a continuous heating furnace according to one embodiment of the present invention, FIG. 2 is a flowchart showing an operation sequence of the present invention, FIG. 3 is a control system diagram of the heating furnace according to one embodiment of the present invention, FIG. FIG. 4 is an explanatory diagram of the elapsed time of the charging temperature of the conventional hot steel slab. 4 is a slab, 20 is a current temperature calculating means, 21 is each band temperature predicting means, 22 is a slab temperature sensitivity calculating means, 23 is a corrected furnace temperature calculating means, and 101 is a heating furnace. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A method for determining a material temperature rise curve of a heating furnace for determining a temperature rise curve when a slab is charged into a heating furnace having a plurality of furnace temperature control zones and continuously heated. Into a heat transfer equation, a current temperature calculating means for estimating a current average temperature of the slab, and a current average temperature of the slab estimated by the current temperature calculating means, and substituting the current average temperature prediction model for each band. By means of each exit temperature prediction means for predicting each control exit temperature between the skid portion and the skid, and when the predicted control exit temperature is different from the target temperature, each exit slab average temperature is obtained. Slab temperature sensitivity calculation means for calculating the temperature sensitivity for each zone setting furnace temperature by partially differentiating the average temperature of each stripping side slab with each zone setting furnace temperature, and the slab temperature sensitivity calculation means If the target extraction temperature is not satisfied with respect to the temperature sensitivity, the modified furnace using a different algorithm corresponding to the in-furnace temperature control zone where the hot slab exists, depending on whether or not the target soaking degree is satisfied. A heating furnace material characterized by comprising a corrected furnace temperature calculating means for obtaining a temperature, repeatedly performing a converging operation by repeatedly performing each outgoing side temperature prediction, a slab temperature sensitivity calculation and a corrected furnace temperature calculation, and setting a furnace temperature. How to determine the heating curve.