JP3289296B2 - Heating furnace heating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a heat treatment furnace, and more particularly to a method for heating a thick steel plate using a high-temperature, high-speed jet burner. And a method for heating the object to be heated so that the object has a desired temperature.

[0002]

2. Description of the Related Art Typical heat treatments for thick steel plates (hereinafter referred to as "thick plates") include a quench treatment (quenching treatment) in which heating is performed at a relatively high temperature and a quota treatment (releasing distortion during rolling. Or a process aimed at adjusting the structure of the material to be heated, also referred to as a normalizing process) or a tempering process (tempering process) of heating at a relatively low temperature. Quenching and quoting are performed at a temperature of about 900 ° C.
This is performed at a temperature of about 10 ° C. That is, these processing temperatures are determined in detail by the quality and composition of the steel sheet to be manufactured.

It should be noted that every time the above-mentioned heat treatment is performed, the generation of scratches on the surface of the thick plate due to the generation of oxide scale and the failure of the product performance due to the uneven temperature.

Therefore, in order to pay attention to these points, in the high-temperature treatment such as the quench treatment and the norma treatment, indirect heating in a nitrogen N ₂ atmosphere in the furnace is performed. Fire heating is performed. In each of these processes, radiant heating (heating by heat radiation) is generally performed with the aim of making the furnace temperature distribution uniform.

FIG. 9 shows an example of the structure of a quota furnace for performing the quota processing.

[0009] As shown in FIG. 9, in this norma furnace, a steel plate 10 as an object to be heated is transferred from a transport roller table 12.
Conveyed above. Heat is radiated from the radiation heating tube (radiant tube) 14 to the steel plate 10 to
Heat. In FIG. 9, the radiation heating tube 14 is
The burner section 16 is built in, and the frame (flame) from the burner section 16 is prevented from coming into contact with the furnace atmosphere. or,
Reference numeral 18 denotes a furnace wall.

In the norma furnace, nitrogen N ₂ is introduced into the furnace so that the surface of the steel sheet 10 is not oxidized.

In this norma furnace, a frame is radiated from the burner section 16 into the radiant heat tube 14 so that the heating tube 1
The steel sheet 10 is indirectly heated by the radiant heat from 4.

Therefore, a heat treatment furnace such as a norma furnace for performing indirect heating using a radiant heating tube is called a radiant tube type indirect heating heat treatment furnace.

[0010] In the case of performing the heat treatment, the furnace temperature is generally not set higher than the heat treatment temperature because the non-uniform temperature distribution of the object to be heated causes a defect in the material of the object to be heated. In this case, in radiant heating, the heat transfer efficiency is poor, and the heating time is inevitably long. Further, in the radiant heating, even when the furnace temperature is set high in a low-temperature portion of the object to be heated, the temperature of the object to be heated usually cannot exceed the heat treatment temperature.

However, when the operation fluctuates due to an operation trouble or the like, particularly when the heat load is reduced,
It becomes impossible to easily lower the furnace temperature, and in such a case, the object to be heated may be overheated.

[0012] On the other hand, a direct-fired reduction burner, which is a jet burner that emits a reducing frame directly into a furnace, has recently been developed for use in a cold-rolled thin steel sheet process line. The direct fire reduction burner achieves an effect of greatly shortening the line length by improving heat transfer performance including a convection heat transfer effect.

[0013] Such a direct flame reduction burner can be applied to heat treatment of a thick plate, and by using this burner, the heat treatment line can be shortened and running costs and construction costs can be greatly reduced. . In addition, the positive use of the convection heat transfer makes it possible to respond to the furnace temperature change in a shorter time than a radiant tube type indirect heat treatment furnace that requires a long time to change the furnace temperature. In addition, it is effective for making the chance free by changing the plate thickness and the plate width.

[0014]

However, in a jet burner such as the direct-fire reduction burner, when a high-temperature frame having a reducing performance is caused to collide with the surface of an object to be heated by direct fire, overheating occurs. There is a problem that the surface temperature of the object to be heated may be higher than the heat treatment temperature.

That is, when the object to be heated is a cold-rolled thin steel sheet having a small thickness, the temperature difference between the surface where heat diffusion into the inside in the thickness direction is fast and the center of the thickness is not so large. Hard to overheat.

On the other hand, when the object to be heated has a relatively large thickness (thick steel plate), a temperature distribution is generated from the surface toward the center of the thickness. For example, as shown in FIG.
Even if the average temperature in the thickness direction is not equal to or higher than the heat treatment temperature, the vicinity of the surface may exceed the heat treatment temperature. As described above, when the temperature near the surface exceeds the heat treatment temperature, there is a possibility that the above-described problems may occur on the surface, such as generation of scale and insufficient performance of the product.

The present invention has been made in order to solve the above-mentioned conventional problems, and enables rapid heating of an object to be heated while preventing generation of surface oxides. An object of the present invention is to provide a method for heating a heat treatment furnace, which can prevent heating, prevent frame loss (loss), and economically use fuel.

[0018]

According to the present invention, there is provided a method for heating an object to be heated in a heat treatment furnace such that the object is heated to a desired temperature. A jet burner is provided to heat the object to be heated and to diffuse heat into the object to be heated so that the center temperature of the object to be heated becomes a desired temperature while preventing overheating of the surface of the object to be heated.
Heating means to alternately perform heating, the thickness of the object to be heated and the transport speed
Depending on the degree, the jet burner is selectively thinned out for a predetermined time.
The combustion zone and the non-combustion zone are alternately formed and heated.
Thus , the above-mentioned problem is solved.

In the present invention, in the soaking zone of the heat treatment furnace, the object to be heated can be soaked by radiant heating means.

[0020]

[Action] When a heated object is continuously heated by a jet burner such as a direct flame reduction burner, if the object to be heated is a thick steel plate, overheating occurs near the surface in the thickness direction (surface layer portion, etc.)
Product quality problems such as generation of oxide scale and failure to achieve product performance occur.

Accordingly, the inventor has conceived of providing a portion for diffusing heat from the surface layer portion to the inside of the heating material, heating the surface by the injection burner, and then heating by the next jet burner after the surface layer temperature decreases. . That is, heating and thermal diffusion are performed alternately.

If such a process of alternately performing the heating and the thermal diffusion is represented by a temperature distribution between the surface and the center of the steel sheet, for example, a temperature change state as shown in FIG. 1 is obtained. In order to achieve such a temperature change situation, a jet burner is installed in a temperature-raising portion (indicated by reference numeral A in FIG. 1) in the heat treatment furnace, and a burner is provided in a surface temperature decreasing portion (indicated by reference numeral B in FIG. 1). If you do not install it will be good.

That is, as shown in FIG. 2, for example, a row group of the jet burners 22 is arranged (arranged) at a portion x of a certain distance l (ell) in the heat treatment furnace with respect to the conveying direction of the article 10 to be heated. ). This portion x is a convection heating portion for convection heating by, for example, a direct flame reduction flame (flame). The combination of the convection heating portion x and the non-heating portion y can prevent overheating of the surface of the material to be heated. The combination of these parts x and y is determined by the thickness of the material to be heated, for example, the steel plate, and the transport speed.

However, if the arrangement of the group of jet burners is fixed by the combination of the convection heating portion x and the non-heating portion y, the following problem occurs.

That is, when the object to be heated is a steel plate having a considerably large thickness, for example, a steel plate having a thickness of more than 100 mm, the heating rate of the steel plate does not depend on the atmosphere in the furnace and the speed of heat transfer on the steel plate surface. It is governed by the heat diffusion inside the steel sheet. This control is due to the thermophysical properties of the steel sheet itself, and it is impossible to avoid this control.

Therefore, the arrangement of the jet burners with the convection heating portion x and the non-heating portion y fixed as described above is applied to a relatively thin steel plate.

On the other hand, for a thick steel plate, it can be said that the heating time is determined by the heat diffusion due to the physical properties inside the steel plate rather than the burner arrangement.

Further, if the arrangement of the heated portion x and the non-heated portion y of the burner is fixed, it is impossible to fluctuate the operation or to optimally heat the material to be heated having a wide thickness. Become.

Therefore, in order to cope with such operation fluctuations and the like and expand the processing, the idea is to arrange the jet burners relatively densely and to install the burners in each row so that they can be used independently. did. As a result, for example, as shown in FIG.
In addition to 24), it is possible to form a non-burning zone 26 that does not burn. By this non-combustion zone 26,
The same location as the non-heating portion y shown in FIG. 2 can be secured.

In the heat treatment furnace, the transporting roll for the object to be heated is provided, for example, as shown by reference numeral 20 in FIG.

The present invention has been made by focusing on the above points.

According to the present invention, an appropriate combustion zone and a non-combustion zone are formed by selectively using a jet burner depending on the size of the material to be rolled, for example, the thickness of a thick steel plate. can do. This makes it possible to optimally heat operation fluctuations and objects to be heated having a wide range of plate thicknesses.

Therefore, the object to be heated can be heated quickly (at a high speed), the generation of surface oxides can be prevented, flame loss can be prevented, and the use of fuel can be economically achieved.

As shown in FIG. 4, the jet roll burner 22 cannot be provided at the portion where the transport roll 20 is installed, so that large heat transfer cannot be expected. Also, if the surface temperature of the object to be heated approaches the heat treatment temperature, the probability of overheating increases greatly by convection heating, so in the soaking part in the heat treatment furnace, radiant heating (for example, using a radiant tube, etc.) It is preferable to adopt a procedure for making the furnace temperature equal to the heat treatment temperature.

Therefore, if the radiant heating means is provided in the soaking zone of the heat treatment furnace, the oxidation of the surface of the object to be heated can be surely prevented. In this manner, the advantage of the conventional radiant heating can be maintained, and the non-oxidizing convection heat transfer technology using the recently developed direct-fired reduction burner can be applied to achieve the reform of the steel plate heat treatment furnace.

[0036]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In this embodiment, the present invention is applied to a heat treatment furnace in which the jet burner rows 12 as shown in FIG. 3 are relatively densely arranged and are installed so that each row can be used alone. The jet burners 2 in the jet burner row 12 are controlled in accordance with the thickness of the steel sheet 10 so that the center temperature of the steel sheet 10 becomes a desired temperature while preventing the surface of the steel sheet 10 from being overheated.
2 is selectively thinned out.

In the heat treatment furnace according to the embodiment, a combustion zone and a non-combustion zone are realized by the selective use of the jet burner 22 as described above.

As a result, as shown in FIG.
The center temperature can be raised to the target value without the surface temperature of 0 exceeding the target heat treatment temperature.

Therefore, it is possible to prevent oxide scale from being generated on the surface of the steel plate 10 and prevent the components of the steel plate 10 from being unreached, thereby improving the product quality.

Next, an example in which a heating time is shortened by performing a tempering process in a heat treatment furnace according to the present invention will be described.

In this case, the thickness of the steel sheet was 20 mm, and the tempering temperature was 600 ° C. The jet burner was a direct fire reduction burner, which was commercially available. FIG. 5 shows the heating performance of the burner. The convective heat transfer coefficient obtained by this burner is about 150 to 200 kcal / m ² hr ° C. Therefore, on the other hand, the heating capacity in the radiant tube radiant heating is about 50 kcal / m in terms of convection heat transfer.
² hr ° C. Therefore, the heating performance of the jet burner is:
It has about three to four times the radiant tube.

Here, for comparison, FIG. 6 shows an example of a conventional steel plate which is heated by radiant heating.

It can be seen that as the temperature difference between the furnace temperature and the steel sheet temperature becomes smaller, the temperature rise of the steel sheet becomes extremely worse. As shown in FIG. 6, since the thickness of the steel sheet is relatively thin, only a slight temperature difference is generated between the surface layer and the center in the initial stage of heating, and there is little concern that only the surface layer is overheated.

FIG. 7A shows an example of a heating time when a steel sheet is heated using the direct fire reduction burner.

As shown in FIG. 7A, when the steel sheet temperature is 55
The convection heat transfer of the jet burner was used up to 0 ° C, and after 550 ° C, conventional radiant heating was employed to prevent overheating. The total heating time was 30 minutes. On the other hand, the steel plate was heated to 595 ° C by radiant heating with a radiant tube.
As a result, the total heating time was 49 minutes. Thus, the present invention reduces the heating time by about 40%.

The example shown in FIG. 7A shows an example in which the plate thickness is small and a non-combustion zone is not required.

On the other hand, FIG. 7B shows an example of heating a thick steel plate.

In this case, the thickness of the steel plate is 80 mm.
In addition, the total time during which the steel sheet is transported in the row group in which the direct fire reduction burners are arranged is 9 minutes, and the transport time of the combustion zone in the row group is 6 minutes, and the non-thermal firing zone is 3 minutes. The direct burner burner is selected and used. By such selective use, the steel sheet was heated to 510 ° C. by convective heat transfer by a direct-fire reduction burner, and from 510 ° C. to 595 ° C., was heated by the radiant heating.

As a result, the total heating time was 130 minutes. On the other hand, the total heating time is 199 minutes in the heating using only the radiant heating according to the conventional method. Thus, according to the present invention, the heating time is reduced by 35%.

FIG. 8 shows a comparison between the surface temperature and the center temperature of the thick steel plate shown in FIG. When the center temperature reaches 510 ° C., conventional radiation heating is performed. From FIG. 8, the surface temperature was 595 ° C. during heating.
Below, it can be seen that overheating has not occurred.

In the above-described embodiment, a steel plate is exemplified as the object to be heated. However, the object to be heated according to the present invention is not limited to this steel plate. The present invention can be implemented. For example,
The present invention can be applied to a heat treatment for a steel ingot serving as a material of a steel sheet.

Further, in the present invention, the heating of the object to be heated by the heat treatment furnace is performed, and the heat treatment furnace naturally includes a heating furnace generally referred to.

In the above-described embodiment, the zone where the jet burner is burned is described as the heating zone. However, the present invention is not limited to this. Can be heated.

[0055]

As described above, according to the present invention, the object to be heated can be quickly heated, surface oxides can be prevented, flame loss can be prevented, and fuel consumption can be reduced. Excellent effects such as being able to be achieved are obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a temperature rise of an object to be heated when heating and non-heating are repeated for explaining the principle of the present invention.

FIG. 2 is a side view similarly showing an example in which a section in which jet burners are arranged and a section in which the jet burners are not arranged are provided in the conveying direction of a material to be heated.

FIG. 3 is a side view showing a configuration example of a heat treatment furnace in which a row group of jet burners in a heating zone (combustion zone) and a non-heating zone (non-combustion zone) according to the present invention is similarly arranged. .

FIG. 4 is a side view of an essential part showing an example in which a jet burner is provided between transport rolls.

FIG. 5 is a diagram showing the performance of a jet burner employed in an embodiment of the present invention.

FIG. 6 is a diagram for explaining the operation of the embodiment.
It is a diagram which shows the example of a temperature rise when a thin plate is heated by the conventional method.

FIG. 7 is a diagram showing an example of a heating time when a steel sheet is heated by the conventional method and the method of the present invention.

FIG. 8 is a diagram showing an example of the heating time by a change in the temperature of the steel sheet.

FIG. 9 is a front sectional view showing a configuration example of a conventional norma furnace.

FIG. 10 is a diagram showing an example of a change in a surface temperature and a center temperature of a material to be heated heated by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Steel plate, 12 ... Jet burner row group, 20 ... Conveyance roller, 22 ... Jet burner, 24 ... Heating zone, 26 ... Non-heating zone.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21D 1/52

Claims (2)

(57) [Claims] 1. A method of heating an object to be heated in a heat treatment furnace so that the temperature of the object to be heated becomes a desired temperature, wherein a jet burner is provided at a predetermined interval in a pre-tropical zone or a heating zone of the heat treatment furnace. Heating the object to be heated such that the center temperature of the object to be heated becomes a desired temperature while preventing overheating of the surface of the object ;
Heating means for alternately diffusing heat into the object to be heated is adopted.
The jet burner according to the thickness of the object to be heated and the conveying speed.
Selective thinning, combustion zone, non-combustion zone at predetermined intervals
Are alternately formed and heated. 2. The method for heating a heat treatment furnace according to claim 1, wherein in the soaking zone of the heat treatment furnace, the object to be heated is soaked by radiant heating means.