JPS6058767B2 - Heating control method for multiple annealing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating control method for a multiple annealing furnace used for annealing cold rolled coils, etc. More specifically, the present invention relates to a heating control method for a multiple annealing furnace used for annealing cold rolled coils, etc. This paper proposes a heating control method that can reduce fuel consumption by controlling heating.

FIG. 1 is a schematic plan view of a direct-fired dual-type tight coil annealing furnace, and FIG. 2 is a schematic cross-sectional view taken along the line ■--■ in FIG. Reference numeral 1 denotes a cold-rolled coil as a workpiece, and the coils 1 are stacked in four stages with their axes perpendicular via a convector plate 2, and the whole is covered with an inner cover 3, forming four sets. stack of 5,,50,50
, 50 are formed.

Such stacks 5, - 50 are arranged side by side, and the entire stack is covered by the portable furnace body 4. A burner 5 is provided at the bottom of the long side wall of the furnace body 4.
A burner 5 for heating each stack 5, 50, 53, 54 is connected to a fuel supply source via a fuel control valve 81, 82, 83, 84, respectively.
Heating control can be performed individually for each of 2, 53, and 54. One thermometer 62 or the like is installed for each stack at the upper part of the long side wall of the furnace body 4, so that the ambient temperature of each stack, that is, the furnace temperature TF around each stack can be measured. In addition, in order to measure the temperature (hereinafter referred to as base temperature) TB of the lower end surface of the coil 1 at the bottom of each stack, one thermometer 72 or the like is inserted through the convector plate 2 at the bottom for each stack. installed. Furnace temperature TF measured for each stack 5 to 50
and base temperature TB are both input to the control device 9, and based on these measured values and the set values of the furnace temperature and base temperature set in advance in the control device 9, the control device 9 controls the temperature for each stack. Fuel control valves 81 to 8 to control the heating
4 outputs a control signal for adjusting the opening degree. Conventionally, this heating control was performed as follows.

First, the first stage of heating control is to raise the temperature inside the furnace from room temperature to a predetermined temperature, and to adjust the opening degree of the fuel control valve 81 and the like in order to maintain this temperature. That is, until the furnace temperature TF measured by the thermometer 6 reaches its set value positive, the fuel control valve 8
The 1st class is open, and after TF reaches TV, TF is
When the furnace temperature TF rises, or after TF reaches 〒V, the temperature of the coil 1 rises and the actually measured base temperature TB becomes the set value. When τR is reached, the process moves to the second stage of heating control. In this second stage control, the fuel control valve 81, etc. is closed when the base temperature TB is higher than the positive set value, and opened when TB is below ■. This is temperature control based on the base temperature. Fig. 3 shows an example of the time transition of the furnace temperature TF and base temperature TB when performing the above-mentioned control using stacks Sl, S2,
It is shown for S4. The furnace temperature TF increases relatively quickly.
Moreover, the temperature around each stack rises uniformly to reach a predetermined temperature, but the heat from the burner 5 is transferred to the inner cover 3, and further radiated and convected from the inner cover 3 to each coil, so the base temperature TB increases. The temperature is slow, and each stack has a different heating rate. This is because, due to the coil production process, it is not possible to form coils of the same shape and weight for all stacks, and each stack has a different heat capacity. Therefore, the switching point from the first stage to the second stage of heating control is shown in Figure 3 as Cl,
As shown by C2 and C4, each stack is different, and in some cases, the difference is as much as one (transfer) interval. On the other hand, since it is necessary to secure a soaking period of a certain amount of time or more for coil annealing, the end point of the soaking period must be determined based on the stack whose base temperature reached the set value the latest. In the case of Fig. 3, it is necessary to set the end of the soaking period at the time when a certain annealing time t- determined by the annealing conditions has elapsed from C1, and for stacks other than stack S1, excessive This caused overheating and wasted fuel. The present invention has been made in view of the above circumstances, and the present invention calculates heat transfer to the coil during the heating process of the coil in the annealing furnace, and performs heating control to equalize the temperature of the lowest temperature coil in each stack. By doing so, it is an object of the present invention to provide a heating control method for a multiple annealing furnace, which allows the coils of all stacks to reach the annealing temperature almost simultaneously, thereby reducing the amount of fuel used, which was wasted in the past. purpose.

A heating control method for a multiple annealing furnace according to the present invention is a heating control method for a multiple annealing furnace that is equipped with a separate heating means for each of n groups of objects to be heated, each consisting of a plurality of objects to be heated. While heating according to the heat pattern, the temperature Tl, T2 of the lowest temperature heated object in the group of heated objects
...T.

Tl, T2 ... The j-th heated body group related to the minimum value Tm, n in TO is operated according to a predetermined heat pattern, and the other heated body groups are operated according to each heated body group. T1 in order to equalize the temperature of the lowest temperature heated body in the heating body group.
One Tmi. (However, the furnace is operated by modifying the heat pattern by a value determined in relation to i=1, 2...n; i+.j). The method of the present invention will be specifically explained below based on the drawings.

FIG. 4 is a schematic cross-sectional view of a direct-fired double tight coil annealing furnace, and FIG. 5 is a block diagram of the apparatus used to carry out the method of the present invention, shown together with a schematic plan view thereof. The structure of the annealing furnace itself is similar to that shown in FIGS. 1 and 2, and the same parts are given the same reference numerals. That is, the coils 1 are stacked in four tiers with their axial directions perpendicular to each other with convector plates 2 in between, and the entire structure is covered with an inner cover 3. And these four stacks Sl, S2, S3,
The S cover body is covered with the furnace body 4. The burner 5 installed opposite to the lower part of the long side wall of the furnace body 4 has fuel control valves 81, 82,
83 and 84 allow heating control for each stack. In addition, thermometers 61, 62, 63, and 64 are installed at the upper part of the side wall of the furnace body 4, respectively, in order to measure the furnace temperatures TFl, TF2, TF3, and TF4 around each stack Sl, S2, S3, and S4. Furthermore, the base temperature TBL, TB2
, TB3 and TB4, thermometers 71 and 72 are used, respectively.
, 73, 74 connect the detection unit to each stack Sl, S2, S
3. It is installed in contact with the lower end surface of the lowest coil of S4. and thermometers 61 and 7 for each stack.
1 (or 62 and 72, 63 and 73, 64 and 74)
The detection signals of the input interface 111 (or 1
12, 113, 114), and is corrected based on the characteristics of each thermometer 61, 71, etc. at the input interface 111, etc., to obtain the furnace temperature 'I' for each stack.
The temperature is converted into quantities equivalent to Fl, etc. and the base temperature TBl, etc., and further A/D (analog/digital) converted, and taken in at a fixed sampling period (for example, 2 times) to the coil temperature calculation device 12 consisting of a microcomputer. To go.

Data regarding each coil specification such as the plate width, plate thickness, inner diameter, outer diameter and material (steel type) of each coil 1 charged into the annealing furnace is inputted into the coil temperature calculation device 12 from the constant manual input device 14. The coil temperature calculation device 12 calculates the heat transfer for the coil 1 as described later based on the measured value such as the furnace temperature TFl detected by each thermometer 61 etc. and the constant according to the coil specifications, and calculates the heat transfer for the coil 1 as described later. Calculate the temperature of 13 is an arithmetic and control unit, and input interfaces 111, 11
Furnace temperature TFl for each stack from 2,113,114
etc. and base temperature TBl are input, and the constant manual input device 14 inputs the initial set values of the furnace temperature and base temperature.
and below are input, and furthermore, the calculated temperature values of all the coils in the furnace are input from the coil temperature calculation device 12.

Based on these input signals, the arithmetic and control unit 13 determines each stack Sl, S2, S3, S4 at the sampling time t.
Setting value of furnace temperature for each feather? (t), n? (t),
(t), Ti; 7 (t) or base temperature set value 1
? (t),1? (t), ding? (t), and the signal (t) are calculated, and these are calculated as the furnace temperature measurement values TFl(t), TF2(t), TF
3(t), TF4(t) or base temperature measurement value TBl(
t), TB2(t), TB3(t), and TB4(t), as well as fuel control devices 151 and 152 corresponding to each stack.
, 153, 154. The fuel control device 151 etc. outputs a control signal to the fuel control valve 81 etc. to adjust the opening degree of the fuel control valve 81 etc. in order to match the set value of the furnace temperature or base temperature with the measured value. Next, the contents of the calculation in the coil temperature calculation device 12 will be explained.

Coil temperature calculation device 12, specifications of each coil and thermometer 6
Furnace temperature measurement values TFl, T detected by 1, 62, 63, 64
Based on F2, TF3, and TF'4, heat transfer calculations of the coil 1 due to burner heating are performed to calculate the temperature of each coil. Thermal energy generated when the fuel ejected from the burner 5 burns inside the furnace body 4 is partially consumed as sensible heat of the exhaust gas or heat stored in the furnace, but most of it becomes sensible heat of the inner cover 3. The heat held by the heated inner cover 3 is transferred to the atmospheric gas within the inner cover 3, and is also radiantly transferred to the four stages of coils 1 loaded within the inner cover 3. The outer peripheral surface of the coil 1 is heated not only by radiation heat transfer from the inner cover 3 but also by convective heat transfer from the high temperature atmospheric gas. In addition, a base fan (not shown) installed below the center of the lowest coil of the four-stage coil 1 allows the atmospheric gas inside the inner cover 3 to flow upward from the center of the coil 1. Since this is forced to circulate, the temperature of the atmospheric gas inside the inner cover 3 is substantially uniform, and the inner circumferential surface of the coil is heated by convective heat transfer as well as the outer circumferential surface by the high-temperature atmospheric gas. The upper and lower end surfaces of the coil 1 are in contact with the convector plate 2, except for the upper end surface of the uppermost coil.
The convector plate 2 itself is heated by atmospheric gas, and the end face of the coil 1 is heated by the convector plate 2.
Heated by contact heat transfer from As a heat conduction equation to simulate such a heat transfer phenomenon, the following (
1) A Fourier heat conduction differential equation expressed in a two-dimensional cylindrical coordinate system as shown in the equation is used.

However, r: radial direction of two-dimensional cylindrical coordinates (R, z)
Variable Z: Axial variable of two-dimensional cylindrical coordinates (R, z) t: Time T: Coil temperature (°C) at time t, function of R, z; T = T (R, z) λR, λ2: Coils in r direction and z direction respectively
Thermal conductivity of C, ρ: specific heat and density of the coil, respectively, or since the coil is approximated as a cylinder, the boundary is the outer circumferential surface,
The inner peripheral surface and the upper and lower end surfaces.

As mentioned above, heat transfer on the outer circumferential surface of the coil is radiant heat transfer from the inner cover 3'' and convection heat transfer from the atmospheric gas, and heat transfer on the inner circumferential surface is convective heat transfer from the atmospheric gas. The boundary conditions for the outer circumferential surface and inner circumferential surface are shown below (2).
, (3). However, Rl, r2: coil inner diameter and coil outer diameter Tc: atmospheric gas temperature T1: inner cover temperature T, l, T, 2: coil surface temperature at the coil inner circumferential surface and outer circumferential surface, respectively, and z function; Tsl=T(
Rl, z), T, l = T (R2, z) Hl, h2: Heat transfer coefficient between the inner and outer circumferential surfaces of the coil and the ambient gas, respectively σ: Stephan's Boltzmann constant E: Coil outer circumferential surface and inner cover Regarding the heat absorption rate between the coil and the coil end surface, all parts except the top end surface of the uppermost coil are in contact with the convector plate 2.
Since the convector plate 2 receives convective heat transfer from the atmospheric gas and is heated to approximately the same temperature as the atmospheric gas temperature Tc, the boundary conditions at the upper and lower end surfaces of the coil are such that the convector plate 2 does not exist. First, assuming that atmospheric gas occupies the space between the upper and lower coils, and that the end faces of the coils receive convective heat transfer from the atmospheric gas, each coil can be approximated by equations (4) and (5) below, respectively. Expressed as

However, Zl, Z2: lower end surface and upper end surface of the coil, respectively.
If the r coordinate axis is set at the lower end surface of the coil, then Zi・=o. T,3,
T, 4: Surface temperature of the coil at the lower and upper end surfaces of the coil, respectively, as a function of r; T$3=T(R
,Zl),T$4=T(R,z2)H3,ll4:
The heat transfer coefficient between the lower and upper end surfaces of the coil and the ambient gas, respectively.Here, in the boundary condition equations (2) to (5) above, the temperature Tc of the ambient gas and the temperature T of the inner cover are determined by the furnace temperature. Measured values TFl(t), TF2(t), TF
3(t) and TF'4(t).

Then, all formulas (1) to (5) are coil temperature T = T
Since the equation relates only to (R, z), by converting equation (1) into a difference equation and performing numerical calculations based on the boundary conditions expressed by equations (2) to (5), the measured value of the furnace temperature can be calculated. TFl
The temperature distribution of the coil at the time t when (t) etc. are input is determined. Such heat transfer calculations are performed for each of the four coils in the stack, and similar heat transfer calculations are performed for the other stacks based on the coil specifications and furnace temperature measurements for the other stacks. The arithmetic unit 12 calculates the temperature of the coils by performing heat transfer calculations on all coils in the furnace each time data is input from the input interfaces 111, 112, 113, and 114, that is, at each sampling time. Therefore, the temperature distribution inside the coil becomes higher as it approaches the inner and outer surfaces of the coil and upper and lower end surfaces of the coil, and becomes lower as it approaches the center of the coil in the thickness direction (r direction) and width direction (Z direction). 13 selects the lowest temperature in each coil from the temperature calculation values for all coils in the furnace inputted from the coil temperature calculation device 12, and selects the lowest temperature for each of the four coils of each stack Sl, S2, S3, S4 from the lowest temperature, Furthermore, its minimum value, that is, each stack Sl, S
The temperatures Tl, T2, T3, and T4 of the coil having the lowest temperature portion in 2, S3, and Sl are selected, and the minimum value Tmin among these lowest temperatures T1 to T4 is selected.

Next, the correction amount ΔTl, ΔT2, ΔT3, Δ of the set value of the furnace temperature or base temperature of each stack Sl, S2, S3, S4
Each of T4 is calculated, for example, as shown in equation (6) below. however,
α, β: Constants Note that the minimum coil temperature T is the minimum value T. For a stack of nin, ΔT, is 0.

For example, the lowest coil temperature T4 of stack S4 is T1 to T4.
T4=T. nin, and ΔT4=0. As described above, the arithmetic and control device 13 finds the stack with the minimum coil temperature based on the coil temperature calculation value inputted from the coil temperature calculation device 12 at each sampling point of the input interface 111, etc., and compares the furnaces of other stacks. While calculating the correction amount of the temperature or base temperature set value, the sampling time t is calculated as follows.
The output data to the fuel control device 151 etc. in is calculated.

(1) First stage of heating control Measured value of base temperature TBl(t) (1=1, 2, 3, 4
) until it reaches its initial setting value, heating control is performed based on the furnace temperature.

Therefore, the sampling time T. ．． , the furnace temperature setting value Tm (Tm) and the furnace temperature measurement value TF, (t
) (T.n) to the fuel control devices 151, 152, 153,
The furnace temperature setting value ↑L (Tm) is output to 154, and the furnace temperature setting value ↑L (Tm) is calculated as shown in the following equation (7). However, ↑已(
Tm): Furnace temperature setting value at sampling time Tml ゛n■(T...-1): Previous sampling time (
Trn. −1) Furnace temperature setting value and heating start time T
.

Furnace temperature setting value at 〒 Color (TO) indicates its initial setting value ↑
There is p. Further, for the stack in which the minimum coil temperatures T1 to T4 exhibit the minimum value among these, the set value is the same as the set value at the previous sampling time Tm-1. For example, if T4 is the minimum value among T1 to T4, the furnace temperature setting value V4 (T.) for stack S4 is 〒4
Equal to (Tn, -1). In addition, the furnace temperature measurement value TF, (T
m) is the sampling time T. This is the measured value of the furnace temperature input from the input interfaces 111, 112, 113, and 114 at n. (2) Second stage of heating control Measured value of base temperature TB, (t) (1=1, 2, 3, 4
) is its initial setting value τ100.

Once the temperature is reached, heating control is performed based on the base temperature. Therefore, at the sampling time TTTl, the base temperature setting value Mr. T (T.) and the base temperature measurement value TBl (Tm) at the time are used in the fuel control devices 151 and 15.
Outputs to 2,153,154, but base temperature set value T
The decoy (T..) is obtained by performing a modified calculation as shown in equation (8) below. However, T decoy (T.): sampling point T. Base temperature set value Tday (T..-1) at previous sampling time T. , -1. Note that for stacks whose coil minimum temperatures T1 to T4 have the minimum value among these, the set value is the base temperature set value at the previous sampling time T. ．． -1 is the same as the setting value.

For example, if T4 is the minimum value among T1 to T4, the base temperature setting value 1■ (T..) for stack S4
is equal to ↑100, (T..-1). Furthermore, the base temperature measurement value TBs (Tm) is input to the input interfaces 111, 112, 113, 114 at the sampling time Tm.
This is the measured value of the base temperature input from. Therefore, the measured value TBi(t) of the base temperature of all the stacks S is the initial setting value ■. When the heating control of the stack with the slowest base temperature temperature rise reaches the second stage, when a certain annealing time t- has elapsed, all fuel controls are activated to end the heating. Device 151, 152, 1
A signal for closing the fuel control valves 81, 8, 83, and 84 is output to the fuel control valves 53 and 154. fuel control device 151,
152, 153, and 154 are based on the set value (t) of the furnace temperature and the measured value TF, (t) inputted from the arithmetic and control unit 13 at each sampling time as described above, or the setting of the base temperature. Based on the value Ding (t) and the measured value TB, (t), in order to match the measured value and the set value, the opening adjustment signal of the fuel control valve 81 etc. by PID calculation or (setting value)
An opening/closing signal is output to the fuel control valve 81, which opens when ≧(measured value) and closes when (set value)<(measured value).

When controlling the heating of an annealing furnace with such a device,
First, the initial setting values 1■, ■0 of the furnace temperature and base temperature set in the constant manual device 14, and the measured values of the furnace temperature and base temperature measured with the thermometers 61, 71, etc. immediately after the start of heating ( (close to room temperature at the beginning of heating) TF, (TO)T
B, (TO) (1 = 1, 2, 3, 4) is the arithmetic and control unit 1
3 is input.

7 Then, at the start of heating, TB, (TO) <issue 0, so the initial set value TP of the furnace temperature and the measured value TFl (TO) are output from the arithmetic and control device 13 to the fuel control device 151, etc.
The first stage of furnace temperature control is started.

Next, at time t1 when a certain sampling period (for example, 2 samples) has elapsed after the start of heating by the burner 5, the measured values of the furnace temperature and base temperature at that time 'IFi(t1), TBi
(t1) is input to the coil temperature calculation device 12 and the calculation control device 13 from the input interface 111 etc., and the coil temperature calculation device 12 inputs each specification of the in-furnace coil and each stack S, which are input from the constant human power device 14. A heat transfer calculation is performed based on the measured value of the furnace temperature τFi (t1), and the temperature distribution of all the coils is determined. This temperature calculation value is input to the arithmetic and control unit 13, the minimum coil temperature T, in each stack is determined, and the minimum value T. ．． The stack corresponding to in is found. Next, the arithmetic and control unit 13 calculates the furnace temperature setting value τ', (chi) at the sampling time t1 according to equations (6) and (7) (T, is T.
For the stack corresponding to , the setting value is equal to the setting value at the time of the previous sampling), and this TPi(tu) is sent to the fuel control devices 151, 152 together with the respective furnace temperature measurement values TF′ (t1).
, 153, 154. Thereafter, at each sampling time T2, t3, t4..., the corrected furnace temperature set value and measured value are outputted to the fuel control device 151, etc. as described above, and the coils in the furnace are adjusted to the lowest coil of each stack. The temperature is raised while being controlled so that the temperature is uniform. And is the base temperature measurement value ゛M, (Tk) its initial setting value ↑? If the temperature reaches 100, the subsequent heating control for that stack is changed to the second stage base temperature control.

For example, in the case of this stack S1, the arithmetic and control device 13 outputs the initial set value dW and the measured value TBl (Tk) of the base temperature to the fuel control device 151. Then, at the next sampling time point Tk+1, the correction amount ΔT in equation (6) is obtained from the coil temperature calculation value based on the measured furnace temperature value TFl (T, +1) at that time point, and this ΔT1 and ?(T,)), the base temperature set value (Tkya,) is calculated from equation (8), and the fuel control device 15
1, that one (T8l) and the base temperature measurement value ゛田, (T
k+1). In this way, for the stack S, each subsequent sampling time Tk+2, tk+3
. . . The corrected base temperature set value and measured value are output from the arithmetic and control unit 13, but other stations, tanks S2,
Is the base temperature measurement value for S3 and S4 also the initial setting value T? Each time Tu. At the point in time when
3, 154 to output a heating end signal to end the annealing of the coil. In addition, if heating cannot be controlled individually for all stacks, that is, if the fuel supply systems and fuel control valves for two or more stacks are not independent, each stack that shares these fuel controls, etc. The lowest value among the measured values of the furnace temperature and base temperature may be used for heating control.

Next, the results of heating control of a dual tight coil annealing furnace using the method of the present invention will be explained.

In Fig. 6, the horizontal axis shows the elapsed time after the start of heating, and the vertical axis shows the temperature, and the changes in the furnace temperature and base temperature are shown with a solid line for the stack S1 and a broken line for the stack S2.
Further, the stack S4 is represented by a dashed dotted line. Since the stack S3 shows a temperature increase curve that is almost the same as that of the stack S2, the illustration of the stack S3 is omitted. As is clear from the figure, the base temperature is increasing at approximately the same rate for each stack, and the time point when switching from furnace temperature control to base temperature control is C for stacks Sl, S2, and S4, respectively.
As shown by "1, C"2, and C"4, it can be said that each stack is at approximately the same time. Therefore, after the stacks other than stack S1, which has the slowest temperature increase rate, switch to base temperature control, , the so-called wasted firing time until the stack S1 is switched is extremely short, and the amount of fuel wasted is extremely small.By the way, the plate thickness is 0.7 to 1.5 WrIt1 plate thickness 9
17-1065 ro, coil outer diameter 1890-2530-,
Coils with various specifications showing a variation range of coil inner diameter 590 m were tested under various conditions: furnace temperature target value (initial setting value) 780°C, base temperature target value (initial setting value) 690°C, annealing time 1 (g). When coil annealing is performed, the fuel consumption rate, that is, the amount of fuel used under such coil annealing conditions, is reduced by about 9% compared to the conventional method. As detailed above, in the case of the method of the present invention, the minimum temperature of the coil in each stack is determined by calculating the heat transfer based on the measured value of the furnace temperature at each sampling point of the furnace temperature and the base temperature. The stack showing the minimum value is found, and while the base temperature is being raised (furnace temperature control period), the furnace temperature set value is corrected to lower the heating rate of stacks other than this stack. The temperature rise time is almost uniform for all stacks, the wasted firing time is extremely shortened, and unnecessary fuel consumption during this time can be reduced. Also, the period during which the base temperature is held constant (base temperature control period) Since the base temperature setting value other than the stack, which indicates the minimum coil minimum temperature, is adjusted to a lower value while ensuring the temperature required for annealing, it is possible to reduce fuel consumption for stacks with good heating efficiency, etc. , the present invention has a remarkable effect on reducing the fuel consumption of a multiple annealing furnace.

[Brief explanation of the drawing]

Figure 1 is a schematic plan view of a dual tight coil annealing furnace;
The figure is a schematic cross-sectional view taken along line H-■ in Figure 1, Figure 3 is a graph showing an example of the time course of the furnace temperature and base temperature using the conventional heating control method, and Figure 4 is a double tight coil annealing. FIG. 5 is a schematic cross-sectional view of the furnace, FIG. 5 is a block diagram of the apparatus used to carry out the method of the present invention, and FIG. 6 is a graph showing the effects of the method of the present invention. 1... Coil, 2... Convector plate, 3... Inner cover, 4... Furnace body, 61, 62, 63, 64, 71, 72, 73, 74
...Thermometer, 81, 82, 83, 84...
・Fuel control valve, 111, 112, 113, 114...
... Input interface, 12 ... Coil temperature calculation device, 13 ... Calculation control device, 14 ... Constant human power device, 1151, 152, 153, 154 ...
...Fuel control device.

Claims (1)

[Claims] 1. In a heating control method in a multiple annealing furnace, which is equipped with a separate heating means for each of n groups of objects to be heated, which are made up of a plurality of objects to be heated, while heating according to a predetermined heat pattern, The temperatures T_1, T_2...T_n of the lowest temperature heated objects in the group of heating objects are calculated, and T_1, T
_2... The jth heated object group related to the minimum value T_m_i_n in T_n is operated according to a predetermined heat pattern, and for other heated object groups, the lowest temperature heated object in each heated object group is operated. Ti-T_m_ to equalize the temperature
A heating control method for a multiple annealing furnace, characterized in that the furnace is operated by modifying the heat pattern by a value determined in relation to i_n (where i=1, 2...n; i≠j).