JPH0448852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous annealing furnace for steel strips using ceramic radiant tubes.

In continuous annealing furnaces for annealing steel strips (hereinafter referred to as strips), the heating method used in vertical continuous annealing furnaces for cold-rolled steel plates, including tin plate blanks and high-strength deep-drawn steel plates, is mostly based on radiation heat transfer. is occupying. This is because the surface texture of the strip is influenced by the characteristics of the burner flame, and the surface texture of the strip is affected by the characteristics of the burner flame, and the surface texture of the strip is affected by the characteristics of the burner flame. This is due to the fact that oxide film remains (remaining oxide film) and soot build-up easily occurs.

There are two types of radiation heating methods: one using a radiant tube and one using an electric heater directly in the furnace. A conventional vertical strip heating furnace using a radiant tube is shown in FIGS. 1 and 2. Note that FIG. 2 is a sectional view of FIG. 1. In the figure, 1 is a hearth roll, 2 is a radiant tube, and 3 is a strip.

The radiant tube method mainly uses a burner for the radiant tube to pass high-temperature combustion gas into the tube to raise the tube temperature and indirectly heat the strip in the furnace filled with a protective atmosphere by radiation. It is something. However, in the case of heat-resistant steel tubes, the radiant tube temperature must currently be limited to about 1000°C or less, making rapid heating difficult. Therefore, the overall length of the furnace also increases, and the heating zone occupies a large space in the continuous annealing furnace.

Under these circumstances, the material of the radiant tube has been studied, and the application of fine ceramics, which have excellent heat resistance, has been attracting attention. However, the inherent weakness of fine ceramics, which is their brittle strength (1/100 of steel in terms of sharpy impact value), is a major disadvantage for continuous annealing furnaces for strips, and it is difficult to put them into practical use. There is no such situation. This is because in a continuous strip annealing furnace, strip breakage (in the furnace) cannot be avoided, so the radiant tubes arranged in steps inside the furnace must be made of a material that can sufficiently withstand the impact when the strip breaks. Because it has to be. Among fine ceramics, even SiC and Si ₃ N ₄ , which have high high-temperature strength, cannot withstand the impact when a sheet material strip breaks.

For the above reasons, the radiant tube temperature
At present, rapid heating furnaces using radiation have not been put into practical use as it is not possible to raise the temperature above 1000℃.

In view of the current situation, the inventors of the present invention have arrived at the present invention as a result of intensive research into a continuous annealing furnace for steel strips that uses fine ceramics to raise the tube temperature to over 1,000 degrees Celsius, and that also takes impact resistance into consideration. .

The object of the present invention is to provide a continuous annealing furnace for steel strips in which a ceramic radiant tube is installed, and a protective heat-resistant steel tube through which furnace atmosphere gas is passed is installed between the radiant tube and the steel strip. The furnace atmosphere is sucked in from the opening at the end of the heat-resistant steel tube by a heat-resistant fan installed inside or outside the furnace, passes through the tube, and is discharged back into the furnace for reflux. An object of the present invention is to provide a continuous annealing furnace for steel strip using a ceramic radiant tube.

The furnace of the present invention uses a radiant tube made of fine ceramics, uses a heat-resistant steel tube as its protector, and uses the protective atmosphere inside the furnace as a cooling means to reflux the inside of the tube. . As for the reflux method, a heat-resistant fan made of ceramics is installed inside or outside the furnace, and is driven by a drive section provided outside the furnace. The protective atmosphere is sucked in from the protective tube installed in the latter half of the furnace where the temperature of the radiant tube is high and the temperature difference with the strip is large, and is sent to the tube installed in the first half of the furnace by a heat-resistant ceramic fan. It is discharged and refluxed into the furnace through the tube end opening.

Next, a vertical continuous annealing furnace will be explained using FIGS. 3 to 5 as an embodiment of the furnace of the present invention, but the present invention is not limited thereto. Furthermore, Figure 3 shows
The overall layout of a vertical continuous annealing furnace is shown, and b shows the cross section of a. FIG. 4 shows the top roll portion inside the furnace, and b shows the cross section of a. Moreover, FIG. 5 shows the bottom roll part in the furnace, and b shows the cross section of a.
Furthermore, FIGS. 6a and 6b illustrate an example of a radiant tube protection tube and a support bar used in the continuous annealing furnace of the present invention.

The vertical continuous annealing furnace of the present invention has a large number of hearth rolls 1 and ceramic radiant tubes 2. Two or more heat-resistant steel tubes 4 are arranged between the ceramic radiant tube 2 and the strip 3 in the height direction of the furnace, and a plurality of support bars 5 are attached to the tubes in the horizontal direction to support them. Then, the support bar 5 is supported by the furnace support bracket 6. The bracket has a structure that allows the bar to be inserted into an oval opening to accommodate expansion of the tube 4. The tube 4
are arranged between the radiant tube 2 and the strip 3 for each train, and each tube is assembled at the suction header 7 or blowout header 8 provided at the bottom of the furnace body, and the suction header 7 is connected to the connecting pipe. 9 to the suction side of a ceramic blower (or super heat-resistant steel blower) 10. On the other hand, the discharge side of the blower 10 is connected to the blow-off header 8 through a communication pipe 11. The drive motor 12 of the blower 10 is installed outside the furnace, and the drive shaft is isolated from the air outside the furnace by a sealing device. The headers 7, 8 are made of heat-resistant steel and are attached to the furnace casing by support supports. Ceramic blower 10 is similarly supported from the furnace casing or hearth. The blower drive shaft and motor are connected by a flexible joint. The support bar 5 has a 6th-a
The cross section is not limited to the circular cross section shown in the figure, but may be a rectangular cross section as shown in FIG. 6-b. Further, a plate-like rib or the like may be welded to the connection portion with the tube 4 as a suitable stiffener. The blower can be installed anywhere within the furnace, but considering maintenance etc., it was chosen to be at the bottom of the furnace, but it can also be installed outside the furnace. The headers 7 and 8 can also be installed not only in the lower part of the furnace but also in the upper part of the furnace so that the tube 4 can be suspended. It is also possible to provide a plurality of openings 13 in the longitudinal direction on the surface of the tube 4 connected to the discharge side of the blower 10 on the side facing the strip. (See FIG. 6-a) As mentioned above, although the ceramic radiant tube 2 can withstand high temperatures of 1000 DEG C. or higher, it is brittle and cannot withstand the impact when the strip breaks.
Therefore, in the present invention, a heat-resistant steel tube 4 provided on the strip side of the ceramic radiant tube 2 is devised so that the impact when the strip breaks is not directly transmitted to the radiant tube.

The effect of the present invention is that the radiant tube made of ceramics can be put to practical use, so that the radiant tube can be maintained at high temperatures (1000°C or higher).
As a result: (1) the strip can be rapidly heated by radiation in a protective atmosphere; (The heating rate can be increased.) (2) The size of the heating furnace can be small.

There are other effects.

The radiant tube 2 is protected by the tube 4 from direct impact when the strip 3 breaks. On the other hand, the tube 4 itself is a tube made of heat-resistant steel, and is connected to a ceramic blower 10 in the furnace to flow the protective atmosphere in the furnace into the tube. protected from radiation by intra-tube convection heat transfer. The protective atmosphere inside the furnace is small compared to the surface temperature of the radiant tube and does not exceed 1000℃, so tube 4
It has sufficient effect on protective cooling. The tubes 4 in the furnace are divided into two groups, the first half and the second half, and are connected to the blower 10 by a suction header 7 that collects the tubes 4 in the first half or the second half, and the tubes 4 in the furnace are connected to the blower 10 through the opening at the top of the support bar 5. Breathe in the atmosphere. On the other hand, the second half or first half of the tube 4 connected to the blow-off header 8 causes the furnace atmosphere discharged by the blower to flow into the tube to obtain a cooling effect. The atmosphere in the furnace that has passed through the blow-out tube 4 is discharged into the furnace from the top opening of the tube 4. Cooling of the tube 4 is most effective if the suction side is set in the second half of the furnace where the radiant tube temperature is set high and the air is blown into the first half of the furnace. Further, the support bar 5 for supporting the tube 4 on the furnace wall can also be provided with a ventilation hole at the connection part with the tube, so that the atmosphere inside the furnace can be flowed into the inside, and a cooling effect can be expected as needed.
Furthermore, by providing a plurality of vertically aligned openings on the surface of the tube 4 connected to the discharge side of the blower 10 facing the strip, a gas jet blowing action is generated, and the following effects are expected. can. That is, by adding heat transfer by convection to heat transfer by radiation alone, the production conditions of the treated strip (e.g. line speed, plate thickness,
This speeds up the transient response to changes in the strip width, etc., and reduces the amount of wasted strip.

[Brief explanation of the drawing]

FIG. 1 shows a conventional vertical strip heating furnace, and FIG. 2 is a sectional view of FIG. 1. 3 to 5 show a vertical continuous annealing furnace which is an embodiment of the present invention. FIG. 3 shows the overall layout, FIG. 4 shows the top roll portion in the furnace, and FIG. 5 shows the bottom roll portion in the furnace. FIG. 6 shows an example of a radiant tube protection tube and support bar used in the continuous annealing furnace of the present invention.

Claims (1)

[Claims] 1. A continuous annealing furnace for steel strips equipped with a ceramic radiant tube, in which a protective heat-resistant steel tube through which furnace atmosphere gas is passed is installed between the radiant tube and the steel strip. A ceramic radiant, characterized in that a heat-resistant fan installed outside the furnace sucks in the furnace atmosphere from the opening at the end of the heat-resistant steel tube, passes it through the tube, and discharges it back into the furnace for reflux. Continuous annealing furnace for steel strips using tubes.