JPH0361726B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a furnace temperature setting method for a continuous heating furnace for heating slabs and the like.

[Technical background of the invention and its problems]

A continuous heating furnace (hereinafter referred to as a furnace) that heats slabs, etc. must be operated to heat the heated material to a temperature suitable for subsequent processes while minimizing energy consumption, and to ensure the target production volume. is required. The biggest problem in operating this type of furnace is that when multiple materials with different dimensions are heat-treated in the same furnace, the load inside the furnace will fluctuate, so it is difficult to obtain a predetermined heating temperature. The issue is how to set the furnace temperature.

This will be explained in more detail with reference to FIG. Inside a furnace 1 equipped with a burner 2, slabs S ₁ , S ₂ , ..., S _i , ..., So as materials to be heated are arranged in order from the extraction port 3 side to the charging port side, and the _slabs S If the dimension of _i , for example, the thickness is different from other slabs, then the thinner slab S ₁ ~ _{S i-1} , S _i+1 ~ S _o
If the furnace temperature is set to target the thickness of the slab S i , the thick slab S _i will be insufficiently baked, which will cause major problems in the subsequent process.
On the other hand, if the furnace temperature is set for a thick slab S _i , the relatively thin slabs S ₁ ~ _{S i-1} , S _i+1 ~ _{S o} will be overcooked, which not only increases the scale but also wastes energy. I will do it.

As is well known, it takes a considerable amount of time for the actual temperature of the furnace to reach the set point.
It is impossible to set the temperature for each individual slab.

For this reason, in the past, at least one of the slabs S ₁ to _{S i-1} and S _i+1 to _{S o} would be overcooked, taking into account the characteristics of the furnace and knowing that the one closest to slab S _i would be overcooked. The operator had set the furnace temperature of the heating furnace so that S _i reached the target extraction temperature.

In this way, when the operator sets the furnace temperature, he must be familiar with all the dimensional information, current temperature information, target extraction temperature information, extraction pitch information, etc. for all slabs in the furnace. However, operations that rely on the operator's intuition naturally have limitations, and it has been impossible to precisely set the furnace temperature.

Taking these circumstances into account, the material to be heated is heated to a temperature suitable for subsequent processes without relying on the intuition of the operator, while minimizing energy consumption. The applicant has already proposed a furnace temperature setting method for a continuous heating furnace that can appropriately set the furnace temperature in the future when there are restrictions or when there are furnace temperature restrictions for heating in the succeeding slab. (Refer to Japanese Unexamined Patent Publication No. 1983-45325). An outline of this furnace temperature setting method will be explained below.

Furnaces generally have a large heat capacity and time constant;
If the furnace temperature is controlled by feedback control, it is not possible to obtain appropriate temperature control results. Therefore, feedforward control, which sets the furnace temperature by predicting the furnace condition at a future time from the furnace condition at the current time, becomes effective.

FIG. 4 is a diagram showing the state in which _the slabs S _{1 to S o} shown in FIG. Let t ₁ be the current time for explanation purposes. Similarly, time t ₁ is the future time when slab S _i reaches the extraction port, and slab S _i is extracted at time t _i+1 . Also,
The interval Δt _i between each time is the extraction pitch, and this time pitch Δt _i is determined by the time required for rolling in the subsequent process, the capacity of the furnace, or the product production volume, etc. In some cases, the target extraction It can be stretched slightly to maintain temperature.

As shown in FIG. 4, the slab S ₁ is at the extraction port from the current time t ₁ to the future time t ₂ , and similarly, the slab S _i is at the extraction port from the future time t _i to the future time t _i+1. It will be in the furnace.

In this case, by constantly detecting the furnace temperature and measuring the temperature at the time of charging and the time in the furnace of each slab, the current temperature of all slabs can be calculated, and then the time that slab S ₁ stays in the furnace at the extraction port can be calculated. i.e. t ₂ − _{t 1}
=Δt It is possible to determine a future furnace temperature that will bake this slab S ₁ to the target extraction temperature in ₁ hour.

In this way, if the furnace temperature for Δt ₁ hour is determined, then the future time t ₂ when the slab S ₂ reaches the extraction port
It is possible to calculate the future temperature of slab S ₂ ~ S _{o at} , and then bake this slab S ₂ to the target extraction temperature during the time that slab S ₂ is in the furnace at the extraction port, that is, t ₃ − t ₂ = Δt ₂ hours. It is possible to determine the future furnace temperature.

Similarly, the future temperature of the slab S _i at the future time t _i when the slab S _i reaches the extraction port can be calculated, and the time that the slab S _i is in the furnace at the extraction port, that is _{, t i +1} − It is possible to calculate the future furnace temperature at which the temperature will reach the target extraction temperature in time t _i =Δt _i .

Note that the current temperature or future furnace temperature of the slabs S ₁ to _{S o} and the temperature during the time they are in the furnace at the extraction port can be calculated using a well-known slab heat transfer model formula.

The following equation is used as this slab heat transfer model equation.

q=σ・φ _cg {(θ _g +273) ⁴ − (θ _s +273) ⁴ } ...(1) θ _s (Δt)=θ _s +q/K ₁・Δt ...(2) However, q: slab θ _g : Furnace temperature θ _s : Current temperature of the slab σ : Stephan-Boltzmann constant φ _cg : Heat absorption coefficient related to furnace temperature and slab θ _s : (Δt) : Slab temperature after time Δt k ₁ : These are constants related to the properties and dimensions of the slab.Equation (1) above is the radiation heat transfer equation that expresses the relationship between the furnace temperature θ _g and the slab's current temperature θ _s , and equation (2) is the equation that calculates the slab temperature. It is.

As is clear from these equations (1) and (2), by giving the temperature of each slab at the time of charging the slab into the furnace, the detected furnace temperature, and the furnace time, all slabs in the furnace S ₁
It is possible to know the current temperature of ~S _o . Further, by providing the current temperature of the slab S ₁ , the target extraction temperature, and the extraction pitch, it is possible to determine the future furnace temperature θ _g,2 that achieves the target extraction temperature.

Next, regarding slab S ₂ , by substituting its current temperature, the future furnace temperature determined for slab S ₁ , the target extraction temperature and extraction pitch of slab S ₂ into equations (1) and (2) above, , the future furnace temperature θ _g,2 that achieves the target extraction temperature of this slab S ₂ is determined.

Below, in the same way, the furnace temperature at a future time Δt _j when any slab S _j in the furnace is in the furnace at the extraction port is calculated for slabs S ₁ to S _{j -1 that are in the furnace closer to the extraction port than slab S j.} It can be determined from the future furnace temperature determined by the above, the current temperature and target extraction temperature of slab S _j , and each scheduled extraction time of slabs S ₁ to _{S j-1} .

Figure 5 shows the future furnace temperature θ _g calculated in this way.
is expressed with time t on the horizontal axis.

By the way, if the thickness of the slabs S ₁ to _i-1 in the furnace is relatively small and the thickness of the succeeding slab S _i is significantly larger than that of the preceding slabs S ₁ to _{S i-1} , the fifth As shown in the figure, the future furnace temperatures θ _g,1 , θ _g,2 , ..., θ _g,i-1 determined for slabs S ₁ to _{S i-} 1 are relatively low on average. On the contrary, the future furnace temperature θ _g,i determined for the slab S _i may become significantly higher. In other words, unless the future furnace temperature during the time when the slab S _i is in the extraction port is set to a very high value θ _g,i , the target extraction temperature of the preceding slab may not be achieved.

Normally, a furnace has a maximum furnace temperature (hereinafter referred to as allowable furnace temperature) θ _g,nax that is allowable for operation, and when θ _g,i > θ _g,nax, the actual furnace temperature is increased to θ _g,i. It is clear that the slab S i cannot be burnt and therefore the slab S _i will be underburned.

If it is predicted that such underburning will occur, the furnace temperature is changed to the allowable furnace temperature θ _g,nax earlier than time t _i , and some slabs in the furnace between the extraction ports are lower than slab S _i . Even if the slab is slightly overcooked, the number of overcooked slabs can be kept to a minimum, and the slab
It must be ensured that the target extraction temperature is obtained for S _i . The timing for changing this future furnace temperature to the allowable furnace temperature θ _g,nax may be determined as follows.

Curve B (solid line) shown in Figure 6 shows the predicted temperature trajectory from current time t ₁ to extraction time t _i+1 of slab S _i , which was predicted to be underburned, and curve A (dotted line) shows the furnace temperature. Assuming that the furnace temperature is maintained at the allowable temperature, the _slab is heated from the scheduled extraction time t _i+1 to the current time t 1 in order to obtain the target extraction temperature θ _s,i,REF at the scheduled extraction time t _{i+1 of} the slab S i. It shows a temperature trajectory calculated by making the temperature of S _i correspond to time.

Normally, the temperature of slab S _i increases by absorbing heat as shown in curve B, but curve A starts from the target extraction temperature θ _s,i,REF and changes from future time t _i+1 to current This is the trajectory as heat is released towards time _t1 . The temperature of the slab, which decreases while emitting heat in this manner, can be easily calculated by subtracting the second term from the first term on the right side of equation (2). That is, the following equation may be used instead of equation (2).

θ _s (Δt) = θ _s −q/k ₁・Δt ...(3) Thus, as is clear from Fig. 6, the slab
To bake S _i to the target extraction temperature, assuming that the heating furnace is maintained at an allowable furnace temperature, the target extraction temperature θ _s,i,REF is obtained at the scheduled extraction time of slab S _i .
The slab from this scheduled extraction time to the current time.
The temperature of S _i is calculated in correspondence with time, and the point in time when this temperature matches the temperature of slab S _i that will be heated based on the future furnace temperature determined for slabs S ₁ to _{S i-1}
If the future furnace temperature determined for slabs S ₁ to _{S i-1} at t _AB is changed to the allowable furnace temperature θ _g,nax , the number of overburned slabs can be minimized and the slab S _i can be baked to the target extraction temperature.

On the other hand, depending on an extremely thick slab or past heating history, there may be no intersection between the curves A and B indicating the temperature trajectory described above. In this case, even if the furnace temperature is raised to the allowable furnace temperature θ _g,nax immediately after the current time t _i , the target extraction temperature cannot be secured at the scheduled extraction time t _{i +1} .

As shown in FIG. 7, for the slab S _i that is predicted to be undercooked, the scheduled extraction time _{t i +1} of the slab S _i is set so that the target extraction temperature is obtained at the scheduled extraction time.
Temperature trajectory A calculated from to the current time _t1
If the temperature trajectory B of slab S _i calculated based on the predetermined future furnace temperature does not have an intersection, that is, even if the temperature is immediately raised to the allowable furnace temperature θ _g,nax from the current time t ₁ , the target If the extraction temperature cannot be obtained, there is no other option than to make the slab S _i wait at the extraction port. In other words, the target extraction temperature θ _s,i,REF can be ensured only by extending the scheduled extraction time t _i+1 of the slab S _i .

However, even if the scheduled extraction time is extended, the extended time must be kept as short as possible in relation to the subsequent process, so the extraction time extension process is performed using the following method.

First, all future furnace temperatures determined for slabs S ₁ to _{S i} are changed to the allowable furnace temperature, and the temperature when heated at the allowable furnace temperature θ _g,nax from the current time t ₁ (in Fig. 7) is changed. The temperature trajectory C) is calculated as a function of time, and the slab temperature θ _s,i,A at the scheduled extraction time t _i+1 is determined.

Next, using the slab temperature θ _s,i,A and the target extraction temperature θ _s,i,REF , the extension time ΔT is calculated by the following equation.

ΔT=K・(θ _s,i,REF −θ _s,i,A )/q……(4) Where, q: Transfer rate determined by furnace temperature and slab temperature K: Determined by physical property values of slab It is a coefficient.

In this way, even if the slab S _i , which is predicted to be under-baked, is made to wait at the extraction port in order to be baked to the target extraction temperature, the waiting time will be kept to a minimum, and the processing time in the subsequent process will be significantly reduced. It is possible to prevent the situation from occurring.

By the way, in actual operations, heating constraints may be present in slabs placed in the same zone as slab S _i , both now and in the future. For example, in the case of special materials, there are restrictions on the set value of the furnace temperature due to restrictions on the material.

As shown in _Fig . 8, it is assumed that the k-th slab S _ik is placed in the furnace closer to the extraction port than the slab S _i and is subject to heating restrictions.
Let θ _g,lin1 be the furnace temperature for suppressing the temperature of S _ik below the limit value. Similarly, the first slab S _{i+ l} , which is located closer to the charging port than slab S _{i, is located within the same control zone as this slab S i ,} and has heating constraints. The furnace temperature to keep the temperature of the slab S _i+l below the limit value is θ _g,lin2 .

Furthermore, similarly, the slab S _i is in the furnace in a zone closer to the charging port than the zone in which the slab S i is in the furnace, and from the slab S _i (l
+m) It is assumed that the actual slab S _i+l+n is subject to heating restrictions, and the furnace temperature for keeping the temperature of the slab S _i+l+n below the limit value is θ _g,lin3 . In such a case, when determining the future furnace temperature of slab S _{i ,}
Since the preceding slab S _ik and the succeeding slab S _i+l , which are subject to heating restrictions, are in the same control zone as the furnace temperature θ _{g,nax , the furnace temperature cannot be set to the allowable furnace temperature θ g,nax} .
Until the preceding slab S _ik is extracted, the preceding slab
It is possible to set the lower limit furnace temperature (hereinafter referred to as the minimum limit furnace temperature) of the limit furnace temperature θ _{g ,lin1} of S _ik and the limit furnace temperature θ g,lin2 of the subsequent slab S _i+l . be.
After the preceding slab S _ik is extracted, the subsequent slab
The limiting furnace temperature θ _g,lin2 of S _i+l can be set. moreover,
If slab S _{i +l+n} , which is in the furnace in a zone closer to the charging port than the zone in which slab S i is in the furnace and is subject to heating restrictions, is in the same control zone as slab S _i , the time _Until slab _{S i is} extracted _from It is possible to set it to a warm temperature. Therefore, in this case, before the scheduled extraction time t _i-k+1 of the slab S _ik , the slab temperature is at the lowest limit furnace temperature between the limit furnace temperature θ _g,lin1 and the limit furnace temperature θ _g,lin2 .
From the scheduled extraction time t _ik-1 of S _ik , the slab S _i+l+n
The limiting furnace temperature θ _g,lin2 is maintained until the time t _n when the slab S _i is in the same control zone as the slab S i, and the limiting furnace temperature θ _g,lin2 and the limiting furnace temperature θ _g,lin3 after the time t _n . Assuming that the furnace temperature is maintained at the lowest limit among the two, the temperature of slab S _i is changed over time so that the target extraction temperature θ _s,i,REF is obtained at the scheduled extraction time t _i+1 of slab S _i . Calculate the corresponding
This temperature was determined for slabs S ₁ to S _i-1 at the time when it matched the temperature of slab S _i to be heated based on the future furnace temperature determined for slabs S ₁ to _{S i-1} Before the scheduled extraction time t _i-k+1 of the slab S _ik , the future furnace temperature is set to the lowest limit furnace temperature of the limit furnace temperature θ _g,lin1 and the limit furnace temperature θ _{g,lin2 .} From time t _i-k+1 to time t _n , the limit furnace temperature is θ _g,lin2 , and at time t _n , the lowest limit furnace temperature between the limit furnace temperature θ _g,lin2 and the limit furnace temperature θ _g,lin3 is set.
You can change each one.

Figure 9 is a diagram showing the timing of changes in the furnace temperature in the future. Curve A shows the time t n when slab S _{i + l + n} enters the same control zone as slab S _i and the time t _{n when slab S i + l + n} enters the same control zone as slab S _i . The time between scheduled extraction time t _i+1 is set to the lowest limit furnace temperature of limit furnace temperature θ _g,lin2 and limit furnace temperature θ _g,lin3 , and time is set from scheduled extraction time t _i-l+1 of slab S _ik . up to t _n to the limiting furnace temperature θ _g,lin2 ,
It is assumed that before the scheduled extraction time t _i-k+1 of slab S _ik , the furnace temperature is maintained at the lowest of the limit furnace temperature θ _g,lin1 and the limit furnace temperature θ _{g ,lin2} , and In order to obtain the target extraction temperature θ _g,i,REF at the scheduled extraction time t _i+1 , the temperature of _{the slab S i was} calculated in correspondence with time from the scheduled extraction time t i+1 to the current time t ₁ . The temperature trajectory is shown, and curve B is the slab temperature calculated based on the future furnace temperature determined in advance for slabs S ₁ to _{S i-1.}
It shows the temperature trajectory of S _i .

Thus, the time t _AB where curve A and curve B intersect
, slab S _ik extracts the future furnace temperature predetermined for slabs S ₁ to _{S i-1} to the lowest limit furnace temperature between limit furnace temperature θ _g,lin1 and limit furnace temperature θ _g,lin2. At time t _i-k+1, the future furnace temperature determined in advance for slabs S ₁ to _{S i-1} is set to the limit furnace temperature θ _g,lin2 , and slab S _i+l+n
The future furnace temperature determined in advance for slabs S ₁ to _{S i-1} at the time t _n when S is in the same control zone as slab S _i is defined as the limit furnace temperature θ _g,lin2 and the limit furnace temperature θ _g, If you change each to the lowest limit furnace temperature of _lin3 , the slab
S _ik , slab S _i+l and slab S _i+l+n can be reliably prevented from being overcooked, and the target extraction temperature of slab S _i can be ensured.

In the above furnace temperature setting method, slabs with heating restrictions are targeted for which the furnace temperature limit value can be easily specified, but in actual heating furnace operation, slabs with heating restrictions are As such, there are slabs for which it is difficult to easily specify the furnace temperature limit value. In the above-described furnace temperature setting method, it is difficult to satisfy the heating constraints for such slabs for which it is difficult to easily specify the furnace temperature limit value.

[Purpose of the invention]

The present invention has been made in order to eliminate the above-mentioned disadvantages, and the present invention has been made to limit the furnace temperature to keep the upper surface temperature and lower surface temperature within the limit values for materials to be heated whose upper surface temperature and lower surface temperature are limited. Continuous furnace furnace that allows for better setting of future upper and lower furnace temperatures to bake to the target extraction temperature while meeting heating constraints, even when values cannot be easily specified by the operator. The purpose is to provide a temperature setting method.

[Summary of the invention]

In order to achieve the above object, the present invention provides a heating furnace with a large number of materials to be heated S ₁ , S ₂ , ..., S _i-1 , S _i , S _i+1 in order from the extraction side to the charging side. ,…,S _o-1 , S _{o
Assuming that} there exists
The future furnace temperature determined for ~S _i-1 , the current temperature of the heated material S _i , the target extraction temperature of this heated material S _i , and the scheduled extraction time of the heated material S ₁ ~ _{S i} In the furnace temperature setting method for a continuous heating furnace, which sets the future furnace temperature during the time when the material to be heated S _i is in the furnace until the material to be heated S i is extracted, at each time until the material to be heated S _i is extracted. , specify the upper and lower surface temperatures of the heated material in the same control zone as time S _i , and set the upper and lower surface temperatures of the heated material S _i to the upper limits of the specified surface temperature. Calculate the limit furnace temperature to keep it below, assume that the furnace temperature is maintained at the limit furnace temperature, and perform future extraction so that the target extraction temperature is obtained at the scheduled extraction time of the material to be heated S _i When the temperature of the material to be heated S i matches the temperature of the material to be heated S _i to be heated based on the future furnace temperature determined for the materials to be heated S ₁ to S _i-1 from the scheduled time to the current time, the material to be heated S ₁ to _{S i-1} is changed to the limit furnace temperature.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

In the future temperature change timing shown in FIG. 9, the curve A shows the time t _n when slab S _i+l+n enters the same control zone as slab S _i and the scheduled extraction time t _i+ of slab S _i . Assuming that the furnace temperature is maintained at the lowest limit furnace temperature determined by the limit furnace temperature θ _g,lin2 and the limit furnace temperature θ _g,lin3 in the time interval (t _n ~ _{t i +1} ) between ₁ and 1, In order to obtain the target extraction temperature θ _s,i,REF at the scheduled extraction time t _i +1 of the slab S _i , the temperature of the slab S _i is adjusted in time from the scheduled extraction time t _i+1 to the time t _n . This is the temperature trajectory calculated by

As an embodiment of the present invention, the above-mentioned limit furnace temperature θ _g,lin3 for suppressing the temperature of the slab S _i+l+n below the limit value is provided.
Considering the case where it is difficult to specify directly, here, instead of the limiting furnace temperature θ _g,lin3 , we specify the upper limit value θ _ss,nax of the upper and lower surface temperatures of the slab S _i+l+n. Then, the limit furnace temperature θ _g,lin3 shall be calculated from the specified upper limit value of the surface temperature, and the method is shown below.

FIG. 1 shows the predicted temperature trajectory of slab S _i+l+n from current time t ₁ to extraction time t _i+l+n+1 of slab S _i+l+n . Curve B ₁ is the locus of the upper and lower surface temperatures and the locus of the lower surface temperature of the slab S _i+l+n (Here, since the heating from the upper and lower parts is equal, the locus of the upper surface temperature and the locus of the lower surface temperature) are consistent),
Curve B ₂ shows the trajectory of the average temperature of slab S _i+l+n .
In addition, curve A ₁ in the figure _represents the time interval (t _{c ~
The} furnace temperature is maintained at the limit furnace temperature θ _g,lin3 calculated from the upper limit value θ _ss ,nax at the time interval (t' _AB ~
t _c ), assuming that the furnace temperature is maintained at the allowable furnace temperature _g,nax , the target extraction temperature θ s _,i+l is set at the scheduled extraction time t _i+l+n+1 of the slab S _i+l+n. Extract fixed time to get _+n,REF
A temperature trajectory calculated by making the upper surface temperature and lower surface temperature of slab S _i+l+n correspond to time from t i+l _+n+1 to the current time t ₁ is shown. Similarly, curve A ₂ is from the scheduled extraction time t _i+l+n+1 of slab S _i+l+n to the current time.
The temperature trajectory of the average temperature of the slab S _i+l+n calculated toward t ₁ is shown. Time t _c indicates the time when the upper surface temperature and lower surface temperature of slab S _i+l+n become higher than the upper limit value θ _ss,nax .

Here, if we pay attention to the time t _j that is between the time t _c and the scheduled extraction time t _i+l+n+1 of the slab S _i+l+n , the time
Slab a certain time interval Δt (extraction pitch) before t _j
The average temperature θ _SM (t _j −Δt) of S _{i + l + n} is calculated from the above equation (3) as follows: θ _SM (t _j −Δt) = θ _SM (t _j ) − (q _u + q _l )/K ₁ Δt ……(5) However, θ _SM (t _j ): Slab average temperature at time t _j Δt: Fixed time interval (extraction pitch) q _u : Upper heat transfer amount q _l : Lower heat transfer amount K ₁ : Properties of slab, It can be expressed as a constant related to dimensions.

At this time, the upper surface temperature θ _ss,u (t _j ) of the slab S _i+l+n at time t _j is calculated from the slab average temperature θ _SM (t _j ) and the upper heat transfer amount q _u by thermal conduction _analysis . _,u (t _j )=θ _SM (t _j )+K ₂ q _u (6) However, K ₂ can be expressed as a constant determined by the slab. Similarly, the lower surface temperature θ _ss,l
(t _j ) can be expressed as θ _ss,l (t _j ) = θ _SM (t _j ) + K ₂ q _l ……(7) using the slab average temperature θ _SM (t _j ) and the lower heat transfer amount _q l I can do it. Here, the upper heat transfer amount q _u when the upper surface temperature reaches the upper limit value θ _ss,nax is obtained from equation (6) by the slab average temperature θ _SM (t _j ) at time t _j and the upper surface temperature upper limit value θ _{ss ,nax} , it can be expressed as q _u =1/K ₂ {θ _ss,nax −θ _SM (t _j )} (8). Similarly, when the lower surface temperature reaches the upper limit value θ _ss,nax, the lower heat transfer amount q _u is calculated from equation (7) by the slab average temperature θ _SM (t _j ) at time t _j and the upper limit value of the lower surface temperature θ Using _ss,nax , it can be expressed as q _l =1/K ₂ {θ _ss,nax −θ _SM (t _j )} (9).

On the other hand, considering the radiation heat transfer amount q from the furnace to the slab, the radiation heat transfer amount q can be calculated from the above equation (1) using the furnace temperature θ _q and the slab surface temperature θ _ss according to the Stephan-Boltzmann law. =σφ _cg {(θ _g +273) ⁴ −(θ _ss +273) ⁴ }……(
10) can be expressed as

Equation (10) focuses on the radiation between the furnace temperature θ _g and the slab surface temperature θ _ss , but considering normal heating furnace operation, the average slab temperature θ is used instead of the surface temperature θ _s . Simulations have shown that the heat transfer amount q can be calculated with a highly accurate approximation by using the following equation using _SM . In other words, the formula for heat transfer using the average slab temperature θ _SM is: q=σφ _cg {(θ _g +273) ⁴ −(θ _SM +273) ⁴ }・(1−K ₃ ) ……(11) However, K ₃ : Expressed as a constant determined by the type of slab and average temperature.

Equation (11) shows the upper furnace temperature θ _g,u and the average slab temperature θ _SM (t _j ).
Substituting , the upper heat transfer amount q _u is expressed as q _u =σφ _cg [θ _g,u +273} ⁴ −{θ _SM (t _j )+273} ⁴ ]・(1−K ₃ ) ……(12). Similarly, the lower heat transfer amount q _l is calculated using the lower furnace temperature θ _g,l and the average slab temperature θ _SM (t _j ): q _l =σφ _cg [{θ _g,l +273} ⁴ −{θ _SM (t _j )+273} ⁴ ]・(1−K ₃ ) ...(13)

From equation (12), the upper furnace temperature can be calculated using the upper heat transfer amount q _u and the average slab temperature θ _SM (t _j ): θ _g,u = [q _u /σφ _cg (1−K ₃ ) + {θ _SM (t
_j ) +273} ⁴ ] ^1/4 −273...(14) Similarly, from equation (13), the lower furnace temperature is
Using the lower heat transfer amount q _l and the slab average temperature θ _SM (t _j ), θ _g,l = [q _u /σφ _cg (1−K ₃ ) + {θ _SM (t _j
)+273} ⁴ ] ^1/4 −273……(15)

Using the above relational expression, the value of the limit furnace temperature θ _g,lin3 between time (t _j −Δt) and time t _j can be calculated from the upper limit value of the surface temperature of slab S _i+l+n θ _ss,nax. It can be calculated. To calculate it, first, from equations (8) and (9),
The upper heat transfer amount q _u and the lower heat transfer amount q _l when the slab surface temperature is set to the upper limit value θ _ss,nax are determined. Next, we will calculate the upper heat transfer amount q _u , the lower heat transfer amount q _l and the time determined above.
From equation (5) using the slab average temperature θ _SM (t _j ) at t _j ,
Slab average temperature θ _SM 4 (t _j −Δt) at time (t _j −Δt)
seek. Similarly, the upper heat transfer amount q _u and the lower heat transfer amount q _{l
( 1 _}
4) Calculate the upper and lower furnace temperatures from equation (15),
This furnace temperature is defined as the limit furnace temperature θ _g,lin3 .

In the above embodiment, both the upper limit value of the upper surface temperature and the upper limit value of the lower surface temperature of the slab S _i+l+n are set to θ _ss,nax , but the upper limit value of the upper surface temperature is set to θ _ss,u, Even if the lower surface temperature upper limit value is specified independently for _nax and lower surface temperature limit value θ _ss,l,nax , the upper furnace temperature limit value θ _g,u,lin3 and the lower furnace temperature limit value θ _g,l can be set using the same procedure as above. _,lin3
can be calculated independently.

FIG. 2 shows the configuration of a temperature setting device for carrying out the furnace temperature setting method according to the present invention. This temperature setting device is an extraction pitch calculation device 1 that calculates the scheduled extraction time of all slabs in the furnace according to the post-process.
1. Slab temperature calculation device 12 that calculates the current temperature of all slabs from the time when the material to be heated is charged into the heating furnace; Future furnace temperature calculation device 13 that calculates the future furnace temperature sequentially from the slab closest to the extraction port; a slab surface temperature upper limit value table 15 that stores the specified upper limit value of the upper surface temperature of the slab and the specified upper limit value of the lower surface temperature of the slab; A limit furnace temperature calculation device 16 that calculates a limit furnace temperature from the slab surface temperature upper limit value stored in the slab surface temperature upper limit value table 15;
A furnace temperature table 17 that stores the limit furnace temperature of special slabs for which no upper limit surface temperature is specified, a limit furnace temperature calculated by the limit furnace temperature calculation device 16, and an allowable furnace stored in the furnace temperature table 15. A minimum limit furnace temperature calculation device 18 that calculates the minimum limit furnace temperature at each time until all slabs in the furnace are extracted from the temperature and limit furnace temperature, Furnace temperature change timing calculation device 19 that determines the timing to change the furnace temperature to the minimum limit furnace temperature and changes the scheduled extraction time for slabs where the target extraction temperature cannot be obtained even if the furnace temperature is changed from the current time to the minimum limit furnace temperature. , a storage device 20 for storing future furnace temperatures, and this storage device 20
It consists of an output device 21 that outputs the future furnace temperature stored in the heating furnace 22 to the heating furnace 22.

The operation of the furnace temperature setting device shown in FIG. 2 will be explained below.

When an extraction signal for extracting a slab or a signal generated at regular intervals is applied as a starting signal G to the extraction pitch calculation device 11 and the slab temperature calculation device 12, the extraction pitch calculation device 11 is activated according to the type of post-process and the required time. On the other hand, the slab temperature calculation device 12 calculates the current temperature of all the slabs based on the detected furnace temperature and the furnace time of each slab.

Next, the future furnace temperature calculation device 13 uses the signals from the extraction pitch calculation device 11 and the slab temperature calculation device 12, as well as each slab target extraction temperature, to
First, starting with the slab closest to the extraction port, the future furnace temperature for the time it will be in the furnace at the extraction port is determined, and then the future furnace temperature for the time that the subsequent slab will be in the furnace for the future time in the extraction port is sequentially determined. In this case, the future furnace temperature during the time when slab S ₁ is in the extraction port is the current temperature of slab S ₁ ,
The target extraction temperature for slab S ₁ and the scheduled extraction time for slab S ₁ are determined, and the future furnace temperature for the time when slab S ₂ is in the extraction port is determined by the future furnace temperature determined for slab S ₁ and the scheduled extraction time for slab S 1. It is determined by the current furnace temperature of _S2 , the target extraction temperature of Slab _S2 , and the scheduled extraction time of Slabs _S1 and _S2 . Thereafter, the future furnace temperatures of all slabs are determined in the same manner.

On the other hand, if there is a limit to the slab surface temperature or if there is a furnace temperature limit to the slab, the limit furnace temperature calculation device 16 calculates the slab surface temperature upper limit value stored in the slab surface temperature upper limit value table 15.
The limit furnace temperature calculated by and the furnace temperature table 17
The minimum restriction furnace temperature is determined by the minimum restriction furnace temperature calculation device 18 from the allowable furnace temperature and the restriction furnace temperature stored in .

The under-burning determination device 14 is a future furnace temperature calculation device 1.
Compare the future furnace temperature determined in step 3 with the minimum limit furnace temperature determined by the minimum limit furnace temperature calculation device 18, and if the future furnace temperature exceeds the minimum limit furnace temperature,
This slab is determined to be under-burned, and a command is given to the furnace temperature change timing calculation device 19 to change the furnace temperature in the future.

Thus, the furnace temperature change timing calculation device 19
calculates the temperature of slab S _i corresponding to time from this scheduled extraction time to the current time so that the target extraction temperature can be obtained at the scheduled extraction time of slab S _i that is determined to be insufficiently burnt. Temperature is Slab S ₁ ~
When the temperature of the heated slab S _i matches the future furnace temperature determined in advance for S _i-1 , the minimum furnace temperature is converted to the minimum furnace temperature determined by the minimum furnace temperature calculation device 18. do. However, if the future furnace temperature of slab S _i exceeds the minimum limit furnace temperature and the target extraction cannot be secured even if _the furnace temperature is maintained at the minimum limit furnace temperature from the current time, _the All future furnace temperatures determined in this manner are changed to the minimum limit furnace temperature, and the time that slab S _i stays in the furnace at the extraction port is extended so that slab S _i reaches the target extraction temperature.

Next, the storage device 20 stores the future furnace temperature of all the slabs including the changed future furnace temperature and the scheduled extraction time of all the slabs including the changed scheduled extraction time, and sends these to the output device 21. Along with giving to
The feedback is fed back to the future furnace temperature calculation device 13 and used as data for determining the future furnace temperatures of slabs following these slabs.

In this way, it is possible to implement the furnace temperature setting method for baking a slab whose surface temperature is limited to the target extraction temperature, as explained using FIGS. 9 and 1.

〔Effect of the invention〕

As detailed above, according to the furnace temperature setting method of the present invention, even if there is a slab in the furnace whose upper limit of surface temperature is restricted, the surface temperature can be maintained below the upper limit. This makes it possible to bake the slab to the target extraction temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between time and temperature for explaining the furnace temperature setting method of the present invention, and FIG. 2 shows the configuration of a furnace temperature setting device that implements the furnace temperature setting method of the present invention. Block diagram, Figure 3 is a sectional view showing the arrangement of materials to be heated in a general continuous heating furnace, Figure 4 is
The figure is an explanatory diagram showing changes in the arrangement state of the heated materials in Figure 3, and Figures 5, 6, 7, and 9 are time and temperature diagrams for explaining the conventional furnace temperature setting method. Figure 8 is a cross section showing the arrangement of heated materials when there is a heated material whose furnace temperature is restricted in the preceding heated material and the trailing heated material. It is a diagram. DESCRIPTION OF SYMBOLS 1... Continuous heating furnace, 2... Burner, _S1 -S _o ... Material to be heated, 11... Extraction pitch calculation device, 12... Slab temperature calculation device, 13... Future furnace temperature calculation device, 14...
Insufficient baking determination device, 15... Slab surface temperature upper limit value table, 16... Limit furnace temperature calculation device from the slab surface temperature upper limit value, 17... Furnace temperature table, 18... Minimum limit furnace temperature calculation device, 19... Furnace temperature change timing Arithmetic device, 20... Storage device, 21... Output device, 2
2...Continuous heating furnace.

Claims (1)

[Claims] 1. A large number of materials to be heated S ₁ , S ₂ , ..., S _i-1 , S _i , S _i+1 ,
..., S _o-1 , S _o exist, focus on a specific material to be heated S _i , and determine the values for the materials to be heated S ₁ to _{S i-1} located in the furnace on the extraction side. the future furnace temperature, the current temperature of the material to be heated S _i , and this material to be heated.
Based on the target extraction temperature of S _i and the scheduled extraction time of the materials to be heated S ₁ to S _i , the continuous heating furnace is configured to set the future furnace temperature during the time the material to be heated is in the furnace until the extraction of the material to be heated S _i . In the furnace temperature setting method, at each time until the material to be heated S _i is extracted, the upper limit value of the surface temperature of the upper and lower parts of the material to be heated in the furnace in the same control zone as the material to be heated S _i is specified. , Calculate the limit furnace temperature for suppressing the upper and lower surface temperatures of the material to be heated S _i to below the specified upper limit of the surface temperature, and assume that the furnace temperature is maintained at the limit furnace temperature. , the future furnace temperature determined for the materials to be heated S ₁ to _{S i-1} from the future scheduled extraction time to the current time so that the target extraction temperature is obtained at the scheduled extraction time of the material to be heated S _i The future furnace temperature determined for the materials to be heated S ₁ to S _i-1 is changed to the limit furnace temperature at the time when the temperature of the material to be heated S _i is heated based on How to set the furnace temperature of a continuous heating furnace.