JPS61199026A - Radiant tube for heat treating furnace - Google Patents

Abstract

PURPOSE:To improve the heat radiation efficiency of radiant tubes arranged in the upper part of a heat treating furnace and to prolong the life of a recuperator by vertically extending the radiant tubes downward along the side wall of the furnace. CONSTITUTION:Coils 13 placed on coil stands 14 arranged on the bottom of a heat treating furnace 10 are heated with radiant tubes 20 arranged in the upper part of the furnace 10. At this time, the tubes 20 are vertically extended downward along the side wall of the furnace 10. Not only the tops of the coils 13 but also the sides which are not sufficiently heated with the unextended radiant tubes are heated. The extended radiant tubes have improved heat radiation efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a radiant tube that is most suitable for a batch type stationary furnace type heat treatment furnace, particularly an annealing furnace.

(Prior Art) Conventionally, as shown in FIGS. 5 and 6, in the annealing furnace as described above, the charging door 2 of the furnace body 1 is opened and a plurality of coils 3. . . , 3 is moved into the furnace, and the coils 3 are placed on the coil mounting stand 4 . . . 3 at the bottom of the furnace. ...,
4, the cart is moved outside the furnace, the charging door 2 is closed, and the inside of the furnace is maintained in a reducing atmosphere. After that, a plurality of radiant tubes (heating/cooling tubes) arranged approximately horizontally at the top of the furnace are loaded. 5
．． ..., 5 is heated, and at the same time, the gas in the furnace is circulated by a fan 6, heated by a radiant duplex 5, and blown onto the coil 3 from above to raise the temperature of the coil 3 to about the A1 transformation point. After the heating process, in the cooling process, the radiant tube 5 is cooled, and at the same time, the furnace gas is circulated by the fan 6 and cooled by the cooler 7 and the radiant tube 5, and the coil 3
There is a system in which the coil 3 is cooled down to a temperature at which extraction can be performed by spraying it from above (see Japanese Patent Publication No. 52-20925).

By the way, in the annealing furnace as described above, the coil 3 is
The furnace is heated or cooled from above by the radiant heat of the radiant tube 5 at the upper part of the furnace and the furnace gas circulating inside the furnace from above to below.

That is, in the coil 3, especially the horizontally placed tight coil,
It was thought that heat conduction from the upper and lower end surfaces was good, but from the circumferential surface, heat conduction was poor due to the air gap between the plates.Also, since there is a coil mounting stand 4 below the coil 3, the coil mounting stand This is due to the fact that a strong heat source cannot be installed due to the strength of 4.

However, with the arrangement of the radiant tubes 5 as described above, the heat dissipation efficiency of the radiant tubes 5 is very poor at about 30%, so the heating time is 31 hours, as shown by the chain line a in FIG. Cooling time is 40 hours, total 71
In addition to the time required, the temperature at the outlet of the radiant tube 5 reaches 1000°C or more, as shown by the chain line in Figure 4, which significantly reduces the lifespan of the recuperator (heated gas recovery device). was there.

Therefore, when the present inventor conducted an experiment on the temperature distribution during heating of the coil 3, it was found that the coil 3a on the side wall side and the coil 3 on the center side
In case b, the heating time was 1 hour (Fig. 7(a)), the heating time was 12 hours (Fig. 7(b)), and the heating time was 20 hours (Fig. 7(b)).
In each of Figure (C)), the isothermal curve moves downward from the upper end surface of the coil 3, but at the same time it also moves from the circumferential surface to the inner diameter side, and the speed of movement in the inner diameter direction is equal to the speed of movement in the vertical direction. It has become clear that the size is about 1/2 of that of the previous year, which is much larger than expected.

(Object of the Invention) The present invention has been made based on the above-mentioned knowledge, and aims to improve the heat dissipation efficiency of the radiant tube and the life of the recuperator.

(Structure of the Invention) Therefore, the present invention provides a heat treatment furnace in which a coil placed on a coil stand at the bottom of the furnace is heated by a radiant duplex arranged approximately horizontally at the top of the furnace. tE) extending downward substantially vertically from the furnace side wall.

(Effects of the Invention) According to the present invention, the radiant tube in the upper part of the furnace is extended so that it also runs along the side wall of the furnace, so the heat dissipation efficiency of the radiant tube is improved compared to the conventional one. Since heat can be generated even from the circumferential surface of the coil, which previously had poor heat distribution, heating and cooling times have been shortened.

Furthermore, by extending the radiant duplex in this way, the temperature at the outlet of the radiant tube is significantly lowered, and the life of the recuperator is significantly improved.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIGS. 1, 2 and 3, the annealing furnace 10
is equipped with a closed furnace body +1, and has a front wall 1 of the furnace body 11.
A charging door 12 is provided in the furnace body 11, and a total of nine coils 13, three vertical and horizontal, are installed in the furnace bottom 11b inside the furnace body 11. ...
, 13 is placed horizontally on a ball-shaped coil stand 14. ...,
14 are erected.

A circulation fan 15 is provided at the bottom of the rear wall 11c of the furnace main body 11.
A cooler 17 is provided at the upper part of the rear wall 11c, and is moved by a drive device 16 so as to be retracted outside the furnace during the heating process and thrust into the furnace during the cooling process.

On the other hand, the furnace upper lid in the furnace main body 11 has both side walls l.
A plurality of radiant tubes 20 projecting in a U-shape from ie and Iff to the center of the furnace. . . , 20 are arranged substantially horizontally at predetermined intervals in the longitudinal direction of the furnace, and each radiant tube 20 . ..., 20 are both side walls 11e, l
It extends substantially vertically downward along le to near the furnace bottom 11b.

And each radiant tube 20. ..., 20, one end opening 20a, . . . , 20a has a burner 21, =-,
21 are respectively provided, and the other end ports 20b, .
....

20b is connected from the collecting pipe 22 to the collecting recuperator 23 on the upper surface of the furnace main body 11.

With the above configuration, the charging door 12 of the furnace body 11 is opened, the trolley loaded with the coil 13 is driven into the furnace, the coil 13 is transferred onto the coil placement stand I4, and the trolley is moved out of the furnace. The furnace is run, the charging door I2 is closed, and the inside of the furnace is maintained in a reducing atmosphere.

Then, the radiant duplex 20 is heated by the burner 21, and at the same time, the circulation fan 15 is driven.

Then, the upper end surface of the coil 13 on the coil stand 14 is heated by the radiant heat from the horizontal portion 20c of the radiant tube 20, and at the same time the peripheral surface is heated by the radiant heat from the vertical portion 20d. The air is blown upward, passed between the horizontal parts 20c of the radiant tube 20, heated, and blown onto the upper end surface of the coil 13, passed around the circumferential surface of the coil 13, and passed between the coil mounting bases 14 and into the fan 15. It gets sucked in and circulates.

At this time, since the radiant duplex 20 is longer than the conventional one by the vertical portion 20d, the effective heat radiation area is significantly increased.

For example, in the conventional case, the tube effective length was 5.6 meters and the effective heat radiation area was 72.6 m, but in this case, the tube effective length is lo, 3 m, and the effective heat radiation area is 132.21 m.
”, and the effective length is 1.841. The effective heat radiation area is 1.8
The heat dissipation efficiency is doubled, and the heat dissipation efficiency is improved by about 14% compared to the conventional method.

Therefore, the coil 13 is heated not only from the upper end surface but also from the circumferential surface, which has poor heat distribution, so that the heating time is 27 hours, as shown by the solid line C in FIG.
), which is about 4 hours shorter than the previous version.

On the other hand, after the heating process, in the cooling process, air is passed through the radiant tube 20 and at the same time the cooler 17
rush into the furnace and drive the circulation fan 15.

Then, similarly to the heating process, the end face and peripheral surface of the coil 13 are cooled by the radiant heat from the horizontal part 20c and the vertical part 20d of the radiant tube 20, while the coil 13 is cooled by the furnace gas circulated by the fan 15. Because of the effective cooling, the cooling time to the extraction temperature (approximately 80°C or less) is 37 hours, as shown by the solid line C in Figure 4, which is approximately 3 hours shorter than the conventional method (JL line a). .

Therefore, the heating and cooling time is reduced by a total of 7 hours compared to the conventional method, and the productivity is improved by about lθ%.

Furthermore, since the vertical portion 20d of the radiant tube 20 is extended, the outlet temperature of the radiant tube 20 is
As shown by the solid line d in FIG. 4, the maximum temperature is 800°C, which is lower by an average of 300°C than the conventional one (dashed line b), and the life of the recuperator 23 is improved.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an annealing furnace according to the present invention, FIG. 2 is a plan view inside the furnace of FIG. 1, FIG. 3 is a front sectional view of FIG. 1, and FIG.
The figure is a graph showing the relationship between coil temperature and heating gas temperature.
FIG. 5 is a side sectional view of a conventional annealing furnace, FIG. 6 is a front sectional view of FIG. 5, and FIGS. 7(a) to 7(c) are heating temperature distribution diagrams of the coil. IO... Annealing furnace, 11... Furnace body, 13... Coil, 14... Coil mounting stand, 20... Radiant tube, 20c... Horizontal part, 20d... Vertical part. Patent applicant: Agent of Kobe Steel, Ltd.
Patent Attorney Previously 葆 Two idiots Figure 1 Figure 2 Figure 3rIA Figure 4 KI FJ+h+ Figure 5 → Figure 6 Figure 7 (a) ("C1 Figure 7 (c) (@C)

Claims (1)

[Claims] (1) In a heat treatment furnace in which a coil placed on a coil stand at the bottom of the furnace is heated by a radiant tube placed approximately horizontally at the top of the furnace, the radiant tube is moved approximately downward along the furnace side wall. A radiant tube for a heat treatment furnace characterized by vertical extension.