JPS6133884B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of controlling temperature while making constant furnace temperature correction in a multi-zone continuous heating furnace. A multi-zone continuous heating furnace usually consists of a pre-heating zone, a heating zone, and a soaking zone.
The purpose is to heat a steel billet (referred to as a "steel billet") to a predetermined temperature required for rolling. At the same time, in order to make full use of the rolling capacity, it is necessary to operate the rolling line in such a way that billets can be supplied to the rolling mill without stopping the rolling line. However, in actual operation, the steel billets charged into the heating furnace vary in size and steel type, and the required heating temperature for each steel billet is also not uniform. For this reason, it is impossible to individually control the temperature of each steel billet, and it is difficult to avoid overheating or underheating depending on the size of the steel billet. In actual furnace temperature control, the furnace temperature is set so that the furnace temperature in the charging side zone (preparation zone) is low and the furnace temperature in the extraction side zone (soaking zone) is high. Therefore, the furnace temperature is controlled based on the steel slab that is least likely to be heated in each zone, which results in overheating of other steel slabs, which reduces fuel consumption and steel quality. It cannot be said that this is necessarily satisfactory. In order to deal with this situation, various proposals regarding furnace temperature control of continuous heating furnaces have been made in recent years.
For example, a weighting coefficient that differs depending on the position in the furnace is considered for the deviation between the average temperature and the target temperature for each piece of steel in the furnace, and these are combined to determine the performance index.
There is a method of controlling the output of the heating means depending on the magnitude of the figure of merit (Japanese Patent Publication No. 29403/1983). However, even if such a method of adding different weighting coefficients depending on the position in the furnace is used, it is difficult to achieve sufficient furnace temperature control because the response of the actual billet temperature to changes in furnace temperature is extremely slow. Can not. Alternatively, the required furnace temperature is determined for each strip and each slab, and the representative furnace temperature is determined for each zone from the required furnace temperature group, and then the required furnace temperature group is determined. It is also known to control the temperature by selecting the highest temperature as the representative temperature when the temperature is below a certain limit determined by the quality of the billet and other conditions (Japanese Patent Publication No. 51-30526). However, this method also controls the furnace temperature by targeting the steel slabs that are the most difficult to heat, so improvements in fuel consumption cannot be expected, and the steel slabs located on the exit side of each zone Because the residence time in that zone is short, when there are large changes in the dimensions of the slab in the furnace, extraction temperature, etc., the amount of furnace temperature correction will increase (especially noticeable in the charging side zone), and the actual This method has the disadvantage that not only is it difficult to control the furnace temperature, but also its accuracy is deteriorated. The present invention has been made to solve the above-mentioned problems regarding temperature control of a multi-zone continuous heating furnace. That is, the present invention is a method for controlling the furnace temperature in each zone in a multi-zone continuous heating furnace, in which the temperature of each steel billet located in each zone is determined by the ambient temperature in that zone,
In addition to determining the furnace characteristics and the dimensions, thermal properties, and thermal history of each billet, the time required for each billet to be transferred a certain distance from its current position is determined by calculating the time required for each billet to be transferred a certain distance from its current location to all locations on the extraction side of the billet. The target billet temperature is obtained from the position, dimensions, and extraction pitch of the billet, and the target billet temperature is obtained at a position where each billet is moved a certain distance from its current position, the predicted billet temperature at that position, the transfer time, and the current belt temperature. The amount of furnace temperature correction (ΔT _li ) in each zone for each slab is determined from the furnace temperature of the zone on the extraction side and the weighting coefficient (ω _li ) is calculated for the amount of furnace temperature correction (ΔT _li ). Then, the furnace temperature correction amount (ΔT _l ) in each zone is calculated using the following formula. [However, n represents the number _of steel slabs in the 1st zone] or the gradient α (dω _{li /} dΔT _li ) is made smaller in the charging side band and larger in the extraction side band, or the ΔT _li
The furnace temperature is controlled by determining the furnace temperature correction amount (ΔT _l ) from the above formula, and the furnace temperature in each zone is controlled by this procedure. By doing so, we were able to heat the billet to the optimum temperature for rolling with the minimum fuel consumption, and also succeeded in stabilizing productivity and quality. According to the furnace temperature control method according to the present invention, first, the temperature of each billet in each zone is determined, and the time required for each billet to be transferred a certain distance in the future is determined, and the temperature and transfer of the billet are determined. Based on the required time, calculate how much the furnace temperature needs to be corrected in order for each billet to reach the specified temperature at the position where it has been transferred a certain distance, and calculate the weighted average by adding weight depending on the amount of correction. The furnace temperature correction amount is a value obtained by adding different weights depending on each band or the size of the correction amount and taking a weighted average. Below, an example of calculation of each billet temperature in each band will be explained first. The temperature of each billet in the furnace (θ _li ) can be determined by numerical analysis using the one-dimensional forward difference method, and inside the billet is expressed by the following equation. θ ^j+1 _k = Θ(θ ^j _k+1 +θ ^j _k−1
−2θ ^j _k )+θ ^j _k … [] In the above formula, θ ^j _k is the internal position kΔx of the steel piece (however,
Δx is a minute section of the internal position of the steel billet), time jΔt
(However, Δt is a numerical solution of temperature in a minute interval of time), and Θ is Θ=a・Δt/(Δx) ²
(However, a is the temperature diffusivity). Furthermore, if the heat flux at the slab boundary is q(t), the slab boundary condition is expressed by the following equation. θ ^{j + 1} _p = 2・Θ・θ ^j ₁ + (1−2Θ) θ ^j _p
+2AΘq(t) ...[] [In the formula, A = Δx/λ, λ is the thermal conductivity] Furthermore, the overall heat absorption rate is φ _CG and the furnace atmosphere temperature is
If Tg, the above heat flux q(t) is calculated by the following formula []
It is expressed as q(t)=4.88φ _CG [(Tg+273/100) ⁴ − (θ〓+273/100) ⁴ ] ...[] The above overall heat absorption rate (φ _CG ) depends on the heating furnace shape and operating conditions. It is a value that changes, and the furnace atmosphere temperature Tg is determined using a temperature detector such as a thermocouple. The average temperature θ _li for each steel piece in each band is determined by the above formulas [] to []. This calculation is performed at predetermined time intervals or each time a billet is charged or extracted. Next, find the time (τ) required for each piece of steel to move a certain distance (d) and reach the position (Li). Assuming that the steel pieces in the furnace are numbered 1, 2, ...k, in order from the extraction side, the required time for transfer (τ) can be calculated using the following formula. In the above formula, K is the billet number and P _K is the billet extraction pitch. In addition, Mmax is calculated by the following formula, where SB _K is the width of the steel billet and G _K is the gap between the billets. is the maximum value of the number M of steel slabs that holds true. C is
This is the scheduled extraction stop time before extraction of the Mmax steel billet. Therefore, if the position (Li) belongs to the next band, the transfer time (τ) is divided into the transfer time (τ _l ) in the current band and the transfer time (τ _l+1 ), (τ _l+2 )... and calculate in the same way as the above formula [ ]. Each billet temperature (θ _li ) determined by the above calculation,
Using the time (τ) [τ = τ _l + τ _l+1 +...] required for each piece of steel to move by distance (d) and reach position (Li), each piece of steel moves by distance (d) and reaches position (Li). The calculation procedure for determining the furnace temperature correction amount (ΔT _li ) required to reach the target temperature will be explained. Note that to simplify the explanation, it is assumed that a position (Li) that is separated by a distance (d) belongs to the current band. First, the temperature (θ ^p _li ) of the steel billet at the position (Li) is calculated and predicted using the following formula for the steel billet in the furnace. θ ^P _li =f(T _l , T _l+1 , τ _l , τ _l+1 ,
θ _li ) … [] [In the formula, T _li is the current furnace temperature of the l-th zone, and τ _l is the current furnace temperature of the l-th zone.
The residence time of the strip, θ _li represents the current billet temperature] Next, ^the position (Li ) is determined by the following _formula [ ^] . Δθ ^P _li = f(T _l +ΔT ^P , T _l+1 , τ _l , τ _l+1 , θ _li )−f(T _l , T _l+1 , τ _l , τ _l+1 , θ _li )... [] Similarly, when only the furnace temperature of the zone on the extraction side (zone 1+1) of the zone is changed by a minute amount (ΔT ^P ), the amount of rise in temperature of the steel billet at the position (Pi) (Δθ
^P _l+1,i ) is calculated using the following formula []. Δθ ^P _l+1,i = f(T _l , T _l+1 +ΔT ^P , τ _l , τ _l+1 , θ _li ) − f(T _l , T _l+1 , τ _l , τ _l+1 , θ _li ) ...[] On the other hand, when setting the furnace temperature of the billet retention zone,
The furnace temperature change ratio β of each zone takes into consideration the dimensions of the steel billet remaining in the current 1st zone and the next 1+1th zone, the extraction temperature conditions, the current burner load of both zones, the furnace temperature, etc. Determine _l (=ΔT _l+1 /ΔT _l ). Next, the amount of furnace temperature correction (ΔT
_li ) is calculated using the following formula [] including the above change ratio. ΔT _li =(θ ^m _li −θ ^P _li )ΔT ^P /(Δθ ^P _l
i
+β _l Δθ ^P _l+1,i ) …[] [In the formula, θ ^m _li represents the target temperature of the steel slab at the position (Li)] Through the above calculation procedure, the amount of furnace temperature correction (ΔT _li ), then calculate the furnace temperature correction amount (ΔT _l ) in the customer area. In this case, since the furnace temperature correction amount (ΔT _li ) differs depending on each steel slab, a weighting coefficient (ω _li ) is given depending on the magnitude. Figure 1 shows the amount of furnace temperature correction (Δ
T _li ) and the weighting coefficient (ω _l
This is a graph schematically showing the relationship of _i ), and the coefficient (ω _li ) is determined by taking into account the burner capacity in each zone, the heat transfer characteristics in the furnace, the structure of the steel slab in the furnace, the extraction pitch, etc.
It is determined by the magnitude of the furnace temperature correction amount (ΔT _li ) for each slab. By determining the weighting coefficients in this way and performing weighted averaging as shown in the following equation, the furnace temperature correction amount (ΔT _l ) is obtained. [In the formula, n represents the number of steel slabs in the 1st zone] Next, the furnace temperature correction amount (ΔT
_l ), the gradient α of the weighting coefficient (ω _li ) is
A case where (dω _li /dΔT _li ) is changed and introduced in each band will be explained. Table 1 shows the effect on the billet extraction temperature when the furnace temperature of each zone is changed. In addition, the same table shows that under the general furnace temperature setting conditions where the thickness of the steel slab is 160 to 250 mm and the furnace time is 120 to 270 minutes.
This figure shows the average degree of influence that changes in furnace temperature in each zone have on extraction temperature.

[Table] As is clear from the table above, changes in the charging side zone furnace temperature have little effect on the billet extraction temperature. This is because changes in the temperature of the steel billet due to changes in the furnace temperature are alleviated during the transition process of the billet to the extraction side. On the other hand, it can be seen that the degree of influence of the furnace temperature change in the extraction side zone is large, and it has a large effect on the steel billet extraction temperature. From this, the closer the zone is to the extraction side, the more weight should be given to the steel pieces that are less likely to be heated in that zone, so that the steel pieces whose heating state deviates significantly from the average should be reflected more greatly in the furnace temperature setting. On the other hand, in the zone near the charging side, this is not so necessary, and it is sufficient to adopt a more average furnace temperature setting. However, in this case, it goes without saying that a certain limit should be placed so that the extraction temperature of each steel billet falls within an allowable rolling range. FIG. 2 is a graph schematically showing the relationship between the weighting coefficient (ω _li ) according to the degree of influence on the extraction temperature described in Table 1 and the furnace temperature correction amount (ΔT _li ), and ( i) is the first heating zone, (ii) is the second heating zone, (iii)
indicates the weighting coefficient for the third heating zone, and (iv) indicates the weighting coefficient for the soaking zone. In other words, at the time when the furnace temperature correction amount (ΔT _li ) for each slab is determined, as shown in the figure, even if there is a large difference in ΔT _li in the charging side zone, the weighting coefficient (ω _li ) is Not much difference,
By reducing the weight gradient α (dω _li /dΔT _li ), the amount of furnace temperature correction (ΔT _l ) for that zone is determined on average using the above [formula]; on the other hand, a relatively large weight gradient is set for the zone on the extraction side. is used to calculate the amount of furnace temperature correction (ΔT
_l ) to determine. In the past, in heating furnace operations aimed at reducing fuel consumption, furnace temperatures have been set to lower the charging side furnace temperature and increase the extraction side furnace temperature; In furnace temperature control, the deviation of each billet temperature from the target value in each zone is reflected in the furnace temperature control on an average basis, so heating is more rational from the standpoint of fuel consumption. Operation is possible. By the way, when using the above-mentioned furnace temperature control method, the heating temperature may deviate significantly from its target value if there is a significant change in the composition of the steel slabs in the furnace. In such a case, the above weight gradient (α)
It is possible to use a method in which ΔT li is varied by the magnitude of the furnace temperature correction amount (ΔT _li ) for each piece of steel. In this method, when the furnace temperature correction amount (ΔT _li ) is positive, the weight is By increasing the slope (α) and decreasing it when it is negative, using an appropriate slope will reduce the influence of the billet temperature that does not heat above the target and the billet temperature that heats above the target on the furnace temperature correction. It is something to be adjusted. By operating in this way, you can control the furnace temperature only for slabs that are difficult to bake to the target, such as thick slabs or high-temperature extraction slabs, or evenly control the furnace temperature for all slabs. Various controls such as those incorporated into the control can be arbitrarily and easily implemented by selecting the weight gradient. Figures 4 [] and [] are graphs showing the results of controlling the furnace by setting the weight gradient (α) at three levels as shown in the above formula [] as an example of the above-mentioned furnace temperature control. be. α=-D (When ΔT _li ≧0)〓 [X] α=-1/D (When ΔT _li <0) [However, D is 0.1, 0.5, and 1.0] In each figure, the curve is billet extraction temperature guarantee control (D=
0.1), B indicates the intermediate value control (D=0.5), and C indicates the average value control (D=1.0). Area (a) is the slab thickness
Steel billets of 180mm in diameter, 200mm in (b), and 180mm in (c) are charged. As shown in the figure, by changing the weight gradient (α), it is possible to perform control that guarantees the extraction temperature of all billets, control that makes the temperature of all billets in the band match the target temperature on average, or It can be seen that the furnace temperature control can be carried out as desired, such as intermediate control. The concrete operation of each furnace temperature control may be performed by adjusting the ordinary heating means based on the furnace temperature correction amount (ΔT _l ) determined for each zone. As described above, according to the present invention, the temperature of each steel billet in each band when it reaches a position in front a certain distance away is predicted, and the temperature of each billet is predicted so that the value matches the target temperature. The amount of furnace temperature correction (ΔT _li ) is calculated for each slab, and the amount of furnace temperature correction (ΔT
T _l ) is determined, so by changing the weighting coefficient according to the situation of the steel pieces in the furnace at the time, it is possible to significantly reduce the fuel consumption rate compared to the conventional furnace temperature control method, and it is possible to reduce the extraction Target temperature can be guaranteed. Such accurate furnace temperature control also provides effects such as improving the productivity of the rolling process and improving product quality by preventing skid marks and the like.

[Brief explanation of the drawing]

Figure 1 shows the furnace temperature correction amount (ΔT _li ) and the weighting coefficient (ω _l
Figure 2 is a graph showing the relationship between the furnace temperature correction amount (ΔT _li ) and weighting coefficient (ω _li ) for each zone, and Figure 3 is a graph showing the relationship between the furnace temperature correction amount (ΔT _li ) for each zone. An explanatory diagram showing the relationship between the weighting coefficient (ω _li ) when the weighting coefficient (ω li ) is changed according to the value, and FIGS. 4 [ ] and [ ] are graphs showing a specific example of furnace temperature control according to the present invention.

Claims (1)

[Claims] 1. The temperature of each steel slab located in each zone of a multi-zone continuous heating furnace is determined based on the ambient temperature in that zone, the furnace characteristics,
In addition to determining the dimensions, thermal properties, and thermal history of each billet, the time required for each billet to be transferred a certain distance from its current position is determined from the positions of all billets located on the extraction side from that billet. , a target steel billet temperature at a position obtained from the dimensions and extraction pitch, and transferred by a certain distance from the current position of each steel billet, a predicted steel billet temperature at that position, and the transfer time;
Based on the furnace temperature of the current zone and its extraction side zone, the amount of furnace temperature correction (Δ
T _li ) is determined, a weighting coefficient (ω _li ) is determined for the furnace temperature correction amount (ΔT _li ), and the furnace temperature correction amount (ΔT _l ) in each zone is calculated using the following formula. [In the formula, n represents the number of steel slabs in the lth zone.] A furnace temperature control method for a multi-zone continuous heating furnace, characterized in that the temperature is determined by: 2. The temperature of each steel slab located in each zone of the multi-zone continuous heating furnace is calculated based on the ambient temperature within that zone, the furnace characteristics,
In addition to determining the dimensions, thermal properties, and thermal history of each billet, the time required for each billet to be transferred a certain distance from its current position is determined from the positions of all billets located on the extraction side from that billet. , a target steel billet temperature at a position obtained from the dimensions and extraction pitch, and transferred by a certain distance from the current position of each steel billet, a predicted steel billet temperature at that position, and the transfer time;
Based on the furnace temperature of the current zone and its extraction side zone, the amount of furnace temperature correction (Δ
T _li ) is calculated, and then the weighting coefficient (ω _l
i ) and its weight gradient (α) [α=dω _li /
dΔT _li ] is set to be small in the charging side zone and large in the extraction side zone, or to be changed according to the correction amount (ΔT _li ), and the furnace temperature correction amount (ΔT _l ), the following formula [However, in the formula, n represents the number of steel slabs in the lth zone.] A furnace temperature control method for a multi-zone continuous heating furnace, characterized in that the temperature is determined by: