JPS6323846B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides extraction temperature,
By setting the extraction pitch and rolling speed to optimal values, the total cost required to commercialize the unit weight of the slab (hereinafter referred to as cost)
The present invention relates to a hot rolling control method that aims to minimize the

In continuous hot rolling, it goes without saying that the aim should be to reduce the cost required to produce a unit weight of a slab as much as possible. Efforts have already been made to minimize costs in equipment.

However, concrete developments regarding the pursuit of minimum costs for continuous hot rolling as a whole have yet to be made.

The present invention was made in view of the above-mentioned current situation, and it is an object of the present invention to provide a control method that minimizes the product cost in a hot strip mill.

In a hot strip mill, predetermined input information includes the size and temperature of the slab charged into the heating furnace and the size and temperature of the product coil at the completion of rolling, and these input values cannot be changed. However, based on this input information, it is usually possible to freely select the method of baking in a heating furnace and the method of rolling on a mill line until a predetermined product is manufactured.

In a heating furnace, as shown in Figure 1, given the slab size and charging temperature, the fuel consumption Q _FUEL required to bake a unit weight of slab is a function of the target extraction temperature T _EXT and target extraction pitch τ. Yes Q _FUEL = ₁ (T _EXT , τ) ...(1) It can be expressed as. That is, as the target extraction temperature increases, the fuel cost required to bake to that temperature increases, and even if the target extraction temperature is the same, the fuel cost tends to decrease as the extraction pitch increases.

On the other hand, in the mill line, as shown in Figure 2A, the temperature of the slab extracted from the heating furnace is conveyed to the coiler while being rolled. As a result, the temperature gradually decreases. If the temperature drop curve when the slab extracted at the extraction temperature T _EXT1 is rolled and transported at a certain rolling speed V _a is 1a, then the same extraction temperature
When the rolling speed is set to V _b which is higher than V _a at T _EXT1 , the temperature drop curve becomes 1b, and the temperature after extraction from the heating furnace is higher than that of curve 1a. on the other hand,
Naturally, when a slab extracted at a lower extraction temperature T _EXT2 is rolled and conveyed at the same rolling speed V _a , the temperature drop curve 2a becomes lower than a slab extracted at an extraction temperature T _EXT1 . In addition, the rolling power Q _KW required to roll a slab unit weight on the mill line is a function of the material temperature and rolling speed at that time, so the rolling power consumption Q _KW is Q _KW = ₂ (T _EXT , V) ...(2) It can be expressed as. Note that in equation (2), V represents the rolling/conveying speed. This situation is shown in Figure 2B.

On the other hand, the amount of cooling water used for the unit weight of the slab used in the mill line, _QWAT , tends to increase as the extraction temperature _TEXT increases and as the extraction pitch decreases, as shown in Figure 3. In other words, in order to maintain good mechanical properties of the product coil, the finish rolling exit temperature FDT and the temperature CT just before coiling in the coiler are kept at approximately the specified temperature, so the higher the extraction temperature _TEXT , the more steel plate cooling water is required. shall be. Furthermore, as the extraction pitch τ becomes smaller, more roll cooling water is required to suppress the temperature rise of the mill rolls and table rolls. Therefore, the amount of cooling water used Q _WAT can be expressed as Q _WAT = ₃ (T _EXT , τ) ...(3).

As mentioned above, the heating furnace fuel Q _FUEL consumed to heat, roll and coil the unit weight of the slab is
Rolling power Q _KW , cooling water Q _WAT , target extraction temperature
It can be seen that T _EXT is expressed as a function of target extraction pitch τ and rolling speed V.

On the other hand, rolling efficiency (total tonnage rolled per unit time) TPH can be similarly expressed as a function of extraction pitch τ as shown in Figure 4: TPH = ₄ (τ) ...(4).

In this way, when evaluating the hot strip mill as a whole, the elements to be evaluated are the fuel consumption in the heating furnace Q _FUEL required for the unit weight of the slab, the power consumption in the mill line Q _KW , and the cooling water usage in the mill line. If we take the quantity Q _WAT , convert these evaluation quantities into the cost required to produce the unit weight of the slab, and use the sum as one cost evaluation standard J ₁ , then J ₁ = w ₁・K ₁ Q _FUEL + w ₂ K ₂ Q _KW +w ₃ K ₃ Q _WAT …(5)

In the above equation, K ₁ , K ₂ , K ₃ : Cost for heating furnace fuel unit consumption, electricity unit consumption in mill line, and cooling water unit consumption respectively w ₁ , w ₂ , w ₂ : Reheating furnace fuel This is a weighting factor for consumption cost, mill line power consumption cost, and cooling water consumption cost. On the other hand, it is necessary to take rolling efficiency TPH as another element to evaluate, and cost evaluation standard J ₁
In order to calculate the sum, the rolling efficiency evaluation standard J ₂ can be expressed as J ₂ =w ₄ ·TPH (4). However, w ₄ is the conversion factor between rolling efficiency and cost.

Therefore, the overall evaluation standard J is taken as J=J ₁ +J ₂ ...(7).

Rewriting equation (7) using equations (1), (2), (3), and (4), J=W ₁ K ₁ Q _FUEL +W ₂ K ₂ Q _KW +W ₃ K ₃ Q _WAT +W ₄ TPH =W ₁ K _{1 1} (T _EXT , τ) + W ₂ K _{2 2} (T _EXT , V) + W ₃ K _{3 3} (T _EXT , τ) + W _{4 4} (τ) = (T _EXT , τ, V) ……(8 ) becomes. That is, the evaluation criterion J is a function of the heating furnace target extraction temperature T _EXT , the heating furnace target extraction pitch τ, and the rolling/conveying speed V on the mill line. In addition, the values of K ₁ , K ₂ , and K ₃ in the above formula (8) are as follows for each factory:
Furthermore, it is necessary to assume that the values will change over time, and it is natural that the values of w ₁ , w ₂ , w ₃ , and w ₄ will vary depending on the demands of the time.

Now, if we consider the manipulated variables T _EXT , τ, and V as one X plane, and show the relationship with the evaluation criterion J, we get curved surface B in Figure 5. In other words _, as shown in area A in Figure 5, the manipulated variables ^T _{EXT , τ} ^{, and} V are ^determined by hardware capacity constraints and operational ^{constraints .} There are constraints such as (9), and each has a possible range. In addition, in equation (9), the suffix is L:
Lower limit value U: means the upper limit value.

Therefore, while satisfying this constraint (9), (8)
The values of the manipulated variables T _EXT 〓, τ〓, V〓 that minimize the evaluation criteria given by the formula are calculated using a nonlinear optimization method, and each value of the manipulated variables is calculated using the obtained optimal value. The heating furnace and mill line should be operated so that the heating furnace target extraction temperature T _EXT 〓, target extraction pitch τ〓, and rolling/conveying speed V〓 are achieved.

As described above, according to the present invention, in optimizing the operation of the entire hot strip, the target extraction temperature of the slab extracted from the heating furnace, the target extraction pitch, and the rolling-conveying speed of the steel plate in the mill line are selected as operating variables. As a criterion for evaluating the optimality of operation, we calculated the sum of the total cost of fuel consumption in the heating furnace, power consumption cost and cooling water consumption cost in the mill line, and rolling efficiency for the unit weight of the slab, and used a nonlinear optimization method. The target extraction temperature, target extraction pitch, and rolling/conveying speed, which are operating variables, are determined so as to minimize the evaluation criteria using This allows optimum operation of the hot strip mill as a whole, from the heating furnace to the winder.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between fuel consumption per slab unit weight and target extraction temperature, Figure 2 A is a characteristic diagram showing the state of slab temperature drop after extraction in the heating furnace, Figure 2 Loss slab unit Figure 3 is a characteristic diagram showing the relationship between rolling power consumption per unit weight and target extraction temperature, Figure 3 is a characteristic diagram showing the relationship between cooling water consumption per slab unit weight and target extraction temperature, Figure 4 is a characteristic diagram showing the relationship between rolling efficiency and target extraction temperature. FIG. 5 is a characteristic diagram showing the relationship with the extraction pitch, and is a curved surface diagram showing the relationship with the evaluation criteria, with the heating furnace target extraction temperature, the heating furnace target extraction pitch, and the rolling conveyance speed as one X plane.

Claims (1)

[Claims] 1 In continuous hot rolling, the fuel consumption Q _FUEL required to bake the unit slab weight in the heating furnace to the target extraction temperature T _EXT is the target extraction temperature T _EXT of the heating furnace.
and the extraction pitch τ function Q _FUEL = (T _EXT , τ), the power consumption Q _KW required to roll a unit slab weight to a predetermined size is determined by the above target extraction temperature T _EXT
and the function Q _KW = ₂ (T _EXT , V) of the rolling speed V, the amount of cooling water used Q _WAT required to roll a unit slab weight is calculated as the function Q _WAT = of the above target extraction temperature T _EXT and extraction pitch τ. ₃ (T _EXT , τ), the total tonnage TPH of the slab rolled per unit time is the function of extraction pitch τ TPH = ₄ (τ), and the above fuel consumption Q _FUEL , electricity consumption Q _KW , cooling water consumption
The above target extraction temperature is set so that the sum of cost evaluation standard J ₁ , which converts Q _WAT into the cost required to produce the slab unit weight, and evaluation standard J ₂ for the total slab tonnage TPH rolled in the above unit time is the minimum. In hot continuous rolling, the heating furnace and mill line are operated and operated according to the target extraction temperature, extraction pitch, and rolling speed obtained by calculating T _EXT , extraction pitch τ, and rolling speed as operating variables. Optimal rolling control method.