JPH0225523A - Direct heating type continuous heat-treatment furnace for metal strip - Google Patents

Abstract

PURPOSE:To always maintain the prescribed heat pattern by arranging a burner for heating a strip having together with function for gas-cooling the strip in the subject treating furnace. CONSTITUTION:In heating zone 4 in a direct heating type continuous heat- treatment furnace 2, the burner 8 for heating the metal strip 1 having together with the function for gas-cooling the metal strip 1 is arranged. Then, at the time of heating the strip 1, fuel gas and air for combustion are supplied from fuel gas inlet 13 and combustion air inlet 14, respectively and burnt in a combustion chamber 10 to heat the strip 1. On the other hand, at the time of cooling the strip 1, after cutting off the fuel gas with a cut-off valve 21 and the air for combustion with a cut-off valve 23, combustion exhaust gas having the same composition as the atmosphere in the furnace and becoming low temp., after recuperator 15 is raised up to the pressure with a fan 16, sent to the air inlet 14 and discharged from outlet in the burner, to cool the strip 1.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a direct-fired continuous annealing furnace for metal strip. , eye the metal strip! ! This invention relates to a direct-fired continuous annealing furnace that can control the plate temperature.

<Prior Art> A direct-fire heating type continuous heat treatment furnace for metal strips will be explained by taking the horizontal type continuous heat treatment furnace shown in FIG. 7 as an example. It consists of a soaking zone 5, in which the metal strip 1 is transported by transport rolls 6, heated and soaked by a burner 7 to a predetermined heat pattern.

Here, the heat pattern refers to the heating rate, heating temperature, uniform P: temperature, soaking time, etc. of the metal strip 1, and is intended to impart predetermined properties to the metal strip. If the thickness of the metal strip and the passing speed in the furnace are constant, the metal strip can be heated to a specified value by controlling the furnace temperature or fuel flow rate in the pre-heating zone, heating zone, and soaking zone to a specified value accordingly. The pattern can be controlled.

<Problem to be solved by the invention> However, when metal strips of different thickness are connected,
When the thickness of the metal strip changes suddenly (the point where metal strips of different thickness are connected is called a stepped point),
Alternatively, if the sheet passing speed is suddenly changed, a predetermined heat pattern cannot be applied.

The reason for this is that the heat input to the metal strip is mainly radiant heating from the furnace wall or burner frame, and it is difficult to change the so-called furnace temperature, represented by the furnace wall temperature, in a short time.

In this way, a strip far away from a predetermined heat pattern cannot have the predetermined properties;
It cannot be made into a product.

Conventionally, in order to prevent deviations in the heat pattern, a dummy strip called a threading material was placed between the product strips to avoid temperature abnormalities in the product strips. This had the disadvantage of reducing production and causing significant energy loss.

Note that Japanese Patent Publication No. 60-5644 is a publication in which the same furnace is used for both heating and cooling means.

JP-A-58-151429, JP-A-59-938
However, these are different from the purpose of the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous heat treatment furnace capable of solving the above problems and always maintaining a predetermined heat pattern.

Means for Solving the Problems> The present invention provides a metal strip heating burner that also has a function of gas cooling the metal strip in a direct-fired continuous heat treatment furnace for the metal strip, and The burner is configured to heat or cool the metal strip, and when the burner has a cooling chamber on the outer wall of the combustion chamber and is used for cooling the metal strip, the combustion air inlet of the burner is The burner is configured to introduce cooling gas, and the burner has a gas cooling chamber provided with a plurality of jet holes on the outer wall of the combustion chamber to guide the cooling gas into the furnace along the inner wall of the combustion chamber. However, when used for cooling a metal strip, cooling gas is ejected from the ejection holes.

Effects> The effects of the present invention will be explained by taking as an example a case where the thickness of a metal strip is changed. Figure 4 shows the thickness of the metal strip in the prior art, which is larger than this.
It is a diagram showing the transition of plate temperature and furnace temperature when changing to D.
The explanation will be made assuming that the time when the plate thickness changes from 01 to D2 at the exit of the heating zone is t, and the plate passing speed is constant.

In this case, the board thickness is constant until the time is reached, so
The furnace temperature Tg+ corresponding to the plate thickness and the IJ tube temperature Ts, which corresponds to the metal thickness, are constant up to tl.

At time t1, the plate thickness instantly changes from Dl to Dt, and the plate temperature of the metal strip drops rapidly. The reason for this is that if a metal strip with a plate thickness of Dt has a furnace temperature of Tgl, Tst
(-is+), but when the stepped point passes 1. Then, since the furnace temperature is Tg+, ΔT is
This is because the value of s will be low.

Then, the furnace temperature gradually rises, and at time t2 after a time lag τ, when the furnace temperature reaches Tgz corresponding to the thickness of the plate, the metal strip reaches the temperature TsH.

Therefore, with the metal strip heating burner described later that also has the function of gas cooling the metal strip, at the time h, the plate thickness D! By heating the metal strip of D! The metal strip can be brought to a target plate temperature Tst.

Next, Fig. 5 is a diagram showing the transition of the plate temperature and furnace temperature when the thickness of the metal strip is changed from the conventional technique to the thinner plate thickness D. Thick, from D! The time at which the plate changes to (+1) is assumed to be (+1), and the threading speed is assumed to be constant.

In this case, the plate thickness is constant until time t+8.

Therefore, the furnace temperature Tg+ and metal strip temperature ↑3. is constant until time L1'.

The thickness of the metal strip increases from time (1) to D0, and the temperature of the metal strip rapidly increases ΔTs'.

Thereafter, the furnace temperature gradually decreases, and when the furnace temperature reaches Tgz corresponding to the i thickness D2 at time t% after the time lag τ', the metal strip reaches the target temperature Tgz.

Therefore, by cooling the metal strip with the thickness Dt at times t and l using a heating burner for the metal strip, which will be described later and also has the function of gas cooling the metal strip, the metal strip with the thickness Dt can be heated to the target plate. It can be made hot Tsl.

Note that when changing the strip passing speed, the metal strip can be controlled to the target strip temperature using the same method.

<Example> Embodiments of the present invention will be described based on the drawings.

FIG. 1 is an overall configuration diagram of the first invention. In FIG. 1, reference numeral 8 denotes a burner for heating the metal strip 1, which is provided in the heating zone 4 of the direct-fired horizontal continuous heat treatment furnace 2 and has the function of cooling the metal strip 1 with gas.

FIG. 2 is a sectional view of an example of the burner 8, which is the second invention. In FIG. 2, the burner 8 is connected to the combustion chamber 10.
has a water cooling chamber 12 on the outer wall 11 of the metal strip 1
When used in the cold part of the burner, the combustion air inlet 1 of the burner
Cooling gas is introduced from No. 4. In the figure, 12a is a cooling water inlet, 12b is a cooling water outlet, 13 is a fuel gas inlet, 2a is a furnace wall, and 2b is a
is an insulating material.

When heating the metal strip 1, the burner 8 supplies fuel gas and combustion air from a fuel gas port 13 and a combustion air port 14, respectively, and burns it in the combustion chamber 10 to heat the metal strip.

On the other hand, when cooling the metal strip 1, after cutting off the fuel gas with the cutoff valve 21 and the combustion air with the cutoff valve 23,
The combustion exhaust gas having the same composition as the atmosphere inside the furnace which has become low temperature after the recuperator 15 is pressurized by the fan 16, and the flow meter 17
．． Flow rate! PI section valve 18. Via the isolation valve 19, the combustion air is sent to the air supply 14 and discharged from the burner outlet to cool the metal strip.

These controls are performed by a control device 9 for the burner 8. That is, the position of the stepped point of the metal strip l is predicted by the tracking device 27, and the furnace temperature Tf measured by the furnace thermometer 24, the plate temperature Ts measured by the plate thermometer 25, and the combustion exhaust gas thermometer are calculated. Based on the exhaust gas temperature Tye and g measured in step 6 and the heat vacuum, plate thickness, and strip threading speed manually entered in advance into the metal strip information input device 28, the cooling gas flow rate control valve 18. Shutoff valve 19° Fuel gas flow rate control valve 20.
Shutoff valve 21. Combustion air flow control valve 22. The cutoff valve 23 is subjected to feedforward control.

Next, FIG. 3 is a sectional view of one embodiment of the burner 8, which is the third invention. In FIG. 3, the burner 8 has a gas cooling chamber 33 provided in the outer wall 30 of the combustion chamber 29 with a plurality of ejection holes 32 for guiding the cooled gas into the furnace along the inner wall 31 of the combustion chamber 29. The cooling gas supplied to the gas port 34 is ejected from the ejection hole 32. In addition,
Components that are the same as those in FIG. 2 are given the same numbers, and their explanations will be omitted.

When heating the metal strip l, the fuel gas population is 13. Fuel gas and combustion air are supplied from the combustion air ports 14 respectively, and the metal strips 1 are combusted in the combustion chamber 29.
heat up. At this time, since the combustion exhaust gas that has become low temperature after the recuperator 15 is supplied to the gas cooling chamber 33 through a pipe (not shown), the inner wall 31 is maintained at a relatively low temperature.

On the other hand, when the metal strip 1 is being cooled, the fuel gas is cut off by the cutoff valve 20. After cutting off the combustion air with the cutoff valve 23,
The combustion exhaust gas having the same composition as the atmosphere inside the furnace which has become low temperature after the recuperator 15 is pressurized by the fan 16, and the flow meter 17
．． Flow control valve 18. Via the isolation valve 19, the combustion air is sent to the air supply 14 and discharged from the burner outlet to cool the metal strip.

In the above embodiments, low-temperature combustion exhaust gas discharged into the chimney 35 was used as the cooling gas, but it is also possible to use the atmosphere directly as the cooling gas. However, when the atmosphere is discharged into the furnace, there is a problem in that the percentage of oxygen in the atmosphere inside the furnace increases. In particular, when steel strip is heat-treated in a non-oxidizing furnace, the rate of oxidation of the steel strip increases, which is undesirable, and it is appropriate to use combustion exhaust gas.

<Effects of the Invention> As explained above, the method of the present invention can control the temperature of the metal strip to the target plate temperature when changing the furnace temperature by changing the thickness of the metal strip or the threading speed. Yield can be improved and energy wastage can be prevented, which is particularly effective in high-mix, low-volume production.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of an embodiment of the first invention, Fig. 2 is a sectional view showing an embodiment of the burner of the second invention, and Fig. 3 is an embodiment of the burner of the third invention. Figure 4 is a graph showing changes in the plate temperature and furnace temperature of the metal strip near the stepped point when the plate thickness changes from small to large, and Figure 5 shows the changes in plate thickness from large to small. FIG. 6 is an explanatory diagram of a direct-fired horizontal continuous heat treatment furnace. DESCRIPTION OF SYMBOLS 1... Metal strip, 2... Direct-fired horizontal continuous heat treatment furnace, 8... Burner for heating the metal strip, which also has the function of gas cooling the metal strip, 9... Control device, 10
．． 29... Combustion chamber 11.30... Burner outer wall, 1
2...Water cooling chamber, 13...Fuel gas inlet, 14.
...Combustion air inlet, 33...Gas cooling chamber, 3
2... spout.

Claims (3)

[Claims] (1) In a direct-fired continuous heat treatment furnace for metal strips,
A direct-fire heating type continuous heat treatment furnace for metal strips, characterized in that a burner for heating the metal strip is provided which also has a function of cooling the metal strip with gas, and the burner is configured to heat or cool the metal strip. . (2) Claim (1) wherein the burner has a water cooling chamber on the outer wall of the combustion chamber, and when the burner is used to cool the metal strip, cooling gas is introduced from the combustion air inlet of the burner.
) Direct-fire heating type continuous heat treatment furnace. (3) When the burner has a gas cooling chamber provided on the outer wall of the combustion chamber with a plurality of injection holes for guiding cooling gas into the furnace along the inner wall of the combustion chamber, and is used for cooling the metal strip,
Claim (1) wherein cooling gas is ejected from the ejection hole.
1) The direct-fired continuous heat treatment furnace described above.