JPS5818401B2 - Continuous heating furnace control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of heating a hot steel billet in a continuous heating furnace, for example in a hot coil rolling process.

The continuous heating furnace used in the above-mentioned hot coil rolling process is charged with steel billets at room temperature (approximately 25°C), and the temperature inside the furnace is controlled so that the steel billets are heated to a temperature suitable for rolling. ) has been done.

However, in recent years, in order to reduce the fuel consumption rate (the amount of fuel used per unit amount of steel billets), it has become common practice to charge billets into a heating furnace as warm billets immediately after blooming or continuous casting without cooling them. So-called hot charge rolling is being carried out.

In this case, the temperature at which the hot steel billet is charged into the heating furnace varies depending on the elapsed time after blooming or continuous casting or the dimensions of the steel billet, and varies by about 200 to 700°C.

Since only room temperature billets were charged into conventional heating furnaces, there was no need to consider differences in charging temperature when controlling the furnace temperature; Even when charging was started, no consideration was given to the above-mentioned difference in charging temperature.

For this reason, even if hot steel billets were charged, it was not possible to achieve a sufficient reduction in fuel consumption.

In view of the above-mentioned points, the present invention aims to reduce fuel consumption by determining the charging temperature of hot steel billets in advance and controlling the temperature inside the furnace according to changes in this charging temperature. It is an object of the present invention to provide a side leg method of a continuous heating furnace that can be obtained.

The present invention controls the temperature inside the heating furnace according to the temperature of the hot steel billet, and the temperature of the hot billet can be measured in various ways. The case of calculating by time will be described in detail based on FIG.

Continuously cast steel billets are cut into predetermined billet sizes after continuously casting molten steel.

At this time, the temperature of the steel billet is maintained at a constant value (approximately soo'c) by a water cooling side attached to the continuous casting equipment, and the temperature of the steel billet is measured by a thermometer.

A steel billet that is charged into a continuous heating furnace as a hot steel billet is charged into a heating furnace several hours after being cut.

At this time, the cutting time of the hot steel piece, the temperature of the steel piece at that time,
The charging temperature θin is calculated using the following heat transfer equation based on the time of charging into the continuous heating furnace and the dimensions of the billet.

δθ δ2θ C・ρ・−=λ・□ δt ax2 θ(t, x): Material temperature t: Time (time elapsed from cutting time) X: Thickness direction coordinate (0≦X≦H/2) ρ: Material Density C: Specific heat of material λ: Material thermal conductivity H: Initial condition of warm slab thickness θ (0, x) = 00 θ0: Boundary condition of billet temperature at the end of continuous casting (t, -)=O ax Z ■ Surface - λ・−・θ(t, O)=4.88・εy θ(t, O)+273 θair+273C()
'-()4) 100 100 ε: Emissivity with the atmosphere θair: Ambient temperature When the elapsed time until the charging time is tin, the average temperature in the thickness direction is used as the charging temperature θin as shown in the following formula. do.

θ1n = f02θ (tin This is to control the furnace temperature.

Next, controlling the furnace temperature will be explained based on FIG. 2.

[First stage] Calculate the rolling time (tAi) for the hot steel billet from the hot steel billet on the most extraction side to the charged billet.

This is determined from the dimensions of each warm steel billet and the dimensions of the product to be rolled.

[Second Stage] Due to constraints in the rolling operation, the gap time (tGi) from the completion of rolling of each hot steel billet to the start of rolling of the next warm steel billet is determined.

[Third Step] The extraction pitch tpi from each hot steel piece extraction to the next hot steel piece extraction is calculated by tAi +tGi.

[Fourth stage] Calculate the travel time from the extraction pitch tpi to the charging temperature and θin until the charged steel billet is extracted, and calculate the time t1 until leaving the preheating zone and the time t1 until leaving the first heating zone. time t2,
The time t3 until leaving the second heating zone and the time t4 until extraction are determined.

[Fifth Step] Assuming the furnace temperature Ti of each zone, the temperature of the steel billet at the time of extraction is calculated using the following formula.

δ a2 C・ρ・−θ(tXx)=λ−θ(tXx)・・・■δ
t 1) x2 θ Boundary condition - λ - e (t, o) = QRad...
・・・=・■θλ Ti+273 QRad=4.88ΦCG ((−□) 400 θ(tXo)273 −()') Four-curve song■ 00 Initial condition θ(o, t)=θin ・・・・・・
・・・・・・・・・■Here, ΦcG is the overall heat transfer coefficient,
t is the elapsed time from charging, X is the coordinate in the thickness direction of the hot steel slab, and the surface is assumed to be x=o.

In addition, the furnace temperature T is T=Ti t, ≦・t≦ti (however, to=o)
・・・It is given by ■.

From the above formulas ■, ■, ■, ■, ■, the hot steel billet temperature θo at the time of extraction
Find ut.

&out=H/2'・2θ(t,, x) dx °
°゛■H: Warm steel billet thickness [Sixth stage] If the hot steel billet temperature θout at the time of extraction matches the target value θaim, the furnace temperature Ti assumed in the fifth stage is adopted, and the furnace temperature side leg Output to device.

A known furnace temperature sterilization device controls the fuel flow rate so that the furnace temperature reaches a set temperature Ti.

Also, θout and θaim do not match and θout becomes θai.
If it is higher than m, the heat loss due to the exhaust gas can be reduced by lowering the furnace temperature on the charging side where the exhaust gas flue is located, so Ti is assumed to be lower and the process returns to step 5.

Conversely, if θout is lower than θaim, the furnace temperature T4 on the extraction side farthest from the flue is assumed to be higher for the same reason as described above, and the process returns to the fifth step.

In this way, the temperature in the heating furnace is determined based on the charging temperature θin so that the hot steel billet temperature θout at the time of extraction becomes the target value θaim.

By outputting the furnace temperature determined as described above as the furnace temperature measurement result, the furnace temperature is adjusted according to changes in the charging temperature.

Next, an embodiment of the method of the present invention will be described based on FIGS. 3 to 6.

FIG. 3 shows the temperature distribution of the hot steel piece determined by the formula 0, and is an example of an elapsed time of 6 hours.

In the case of the example shown in FIG. 3, θin=540°C and the surface temperature is 480°C.

Figure 4 shows an example in which the furnace temperature was determined by implementing the present invention on hot steel slabs after an elapsed time of 6 hours and 12 hours.
The charging temperature of the hot steel billet was 540° C. and the charging temperature of the hot steel billet after 12 hours was 300°C, but both were 1250°C at the time of extraction.

Also, Figure 5 is an example of calculation when the temperature on the surface of a hot steel piece is measured as a substitute for calculating the charging temperature using formulas ``■'' and ``■''. The set value of the furnace temperature is 50°C in the preheating zone and the first heating zone.
The extraction temperature is set at about 1260°C.

On the other hand, without calculating the hot steel billet charging temperature using formulas ① and ②, and without measuring the surface temperature,
If the temperature in the furnace is specified as 00℃, the set value of the furnace temperature will be as shown in Figure 6, and the extraction temperature will be 1280℃, resulting in an extremely large loss in terms of thermoeconomics. As a second best method when the single charging temperature cannot be calculated,
Perform upper surface temperature measurements.

Although the above explanation was limited to continuously cast billets, it is also important to check whether the blooming rolled material reaches a predetermined temperature (approximately 1250°C) at the end of blooming, or the temperature of the billet at that point is measured. It is natural that exactly the same thing can be done with the elapsed time from the end time of block rolling.

As described above, the present invention accurately grasps the charging temperature of hot steel billets to be charged into a continuous heating furnace, and controls the temperature inside the furnace based on this charging temperature. This makes it possible to set an appropriate temperature in the furnace for the charging temperature, and has the excellent effect of significantly reducing the fuel consumption in the heating furnace.

□

[Brief explanation of the drawing]

The drawings show an embodiment of the method of the present invention, and Fig. 1 is an explanatory diagram showing the process when the charging temperature of hot steel billet is determined from the elapsed time, and Fig. 2 is a step-by-step diagram of the method for controlling the temperature inside the furnace. Figure 3 is an explanatory diagram showing the temperature distribution after 6 hours, Figure 4 is the furnace temperature measurement result when the present invention was applied to hot steel slabs after 6 and 12 hours. Explanatory diagram showing the fifth
The figure is an explanatory diagram showing an example of calculation when the temperature on the surface of a hot steel piece is measured, and FIG. 6 is an explanatory diagram showing the set value of the furnace temperature when the charging temperature is uniformly defined.

Claims (1)

[Claims] 1. When heating hot steel billet charged into a continuous heating furnace, the temperature at the end of blooming or continuous casting of the hot steel billet and the elapsed time from the time of charging into the heating furnace to the time of charging shall be determined. Either find the charging temperature or directly measure the temperature of the hot billet with a thermometer at the time of charging, and then derive the charging temperature using a relational expression calculated based on this charging temperature (θin). The furnace temperature on the charging side is the lowest among the possible combinations of temperatures of each furnace zone such that the extraction temperature ((9out)) of the hot steel billet is equal to the preset target value (θaim)ic of the hot steel billet. A sterilization method for a continuous heating furnace, which is characterized by adjusting the temperature of each furnace zone.