JPS6220828A - Continuous annealing furnace - Google Patents

Abstract

PURPOSE:To suppress the cross-interferences between furnaces and to improve the operability of the furnaces of a continuous annealing furnace successively provided with a preheating furnace, direct fire furnace and indirect heating furnace by providing intermediate chambers between the furnaces to prevent the transfer of in-furnace gases between the furnaces. CONSTITUTION:The preheating furnace 11, the direct fire furnace 12, the indirect heating and soaking furnace 13 and a gas jet cooling installation 14 are successively installed in succession of an inlet side installation to form the continuous annealing furnace. The 1st intermediate chamber 15a is provided between the preheating chamber 11 and the direct fire furnace 12. The 2nd intermediate chamber 15b is provided to the return part in the upper part of the furnace 12 and the 3rd intermediate chamber 15c is installed between the furnace 12 and the furnace 13. The transfer of the in-furnace gas to the other furnaces is obviated by such mechanism even if there is a fluctuation of the gaseous pressure in the furnaces. Since inverting rolls are enclosed by the intermediate chambers, the rolls are protected against the high temp. of the furnaces.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a continuous annealing furnace for continuously annealing, for example, a thin S4 strip.

[Conventional technology]

FIG. 6 is an explanatory diagram showing an example of a conventional continuous annealing furnace.
In the figure, (1) (inlet side equipment), (2) heating and soaking furnace installed following this input side equipment, and (3) gas racket cooling installed following this heating and soaking furnace. Facility,(
4) (Cooling equipment installed following the gas-cooling equipment next door, (5) Over-aging furnace installed following this cooling equipment, (6) Over-aging furnace installed following the tobacco over-aging furnace. This is a steel tapping facility.The entry side facility (1) is equipped with a cleaning facility, and inside the heating/soaking furnace (2) is a radian I-tube (RT) which is an indirect heating source. is provided and filled with a mixed gas of N 2 + H□,
The cooling equipment (4) uses internal water-cooled rolls and the like.

In the above continuous annealing furnace, the vocal cords (7) are connected to the entrance equipment (1
In step 1, the surface is cleaned by the cleaning equipment W11ζ, enters the heating and soaking furnace (2), and is indirectly heated by a radiant tube in a N2 + H2 gas atmosphere in the heating and soaking furnace (2). It enters the cooling equipment (3) where it is cooled by a gas jet, enters the cooling equipment (4) where it is contact cooled by internal water-cooled rolls, enters the overaging furnace (5) where it is overaged, and then exits. Steel equipment (6) (where it is wound up into a roll.

Conventional continuous annealing furnace as mentioned above (heating and equalization)
F (In 2+, the N4 band (7) is annealed by indirect heating, so the annealing ability is insufficient, the annealing cost is high, and it is difficult to heat high-quality products, so it is difficult to satisfy the necessary annealing conditions. In this case, it is possible to increase the annealing capacity by increasing the length of the heating/soaking furnace (2).
When making a soaking furnace (2), the heating and soaking furnace (2)
It would be quite large, and the equipment cost and running cost would also be huge! MN annealing costume)
The problem arises that - is increased.

In view of these problems, Japanese Patent Publication No. 58-22524 proposes a continuous annealing furnace using direct flame heating.

This continuous annealing furnace is an impinging jet direct-fired furnace that rapidly heats the steel strip to the soaking temperature through convection heat transfer and blast furnace radiation by colliding high-temperature combustion gas and/or high-temperature combustion flame against the front and back surfaces of the steel strip. A second radiant preheating furnace is introduced which introduces high-temperature exhaust gas from the direct-fired furnace and preheats it to a rapid heating start temperature by radiant heat transfer, and introduces low-profile exhaust gas from the preheating furnace and injects it onto the steel strip. The first step is to preheat the steel strip to room temperature due to convection heat transfer.
It consists of a convection preheating furnace. Since this continuous annealing furnace employs a direct heating method, the heating efficiency is much higher than that of the above-mentioned indirect heating method continuous annealing furnace.

[Problem that the invention seeks to solve]

However, since this continuous annealing furnace anneals the steel strip with direct flame,
There is a problem that the surface of the n4 band is oxidized.

The above publication states that a heat absorbing coating agent is applied to the steel strip in advance during annealing.

It is unclear whether this is useful for preventing oxidation of the steel strip, but in order to prevent the oxidation of the steel strip, it seems necessary to apply some kind of oxide film I): agent to the surface of the steel strip. .

In particular, when a steel strip is heated to a high temperature in a direct-fired furnace and subjected to high-temperature annealing, the surface of the steel strip is severely oxidized. Even if an attempt is made to reduce this oxide film with the atmospheric gas (H2+H2) in a soaking furnace, roll pickup will occur on the roll immediately after the direct firing furnace, and the surface of the steel strip will be damaged. Furthermore, in order to reduce the above-mentioned oxide film, it is necessary to increase the H2 concentration in the atmospheric gas, but doing so poses problems in terms of safety and the varnish surface. From the above points, in the continuous annealing furnace with a direct-fired furnace currently in operation, heating is only performed to about 400 to 500°C in the direct-fired furnace.

Furthermore, in the conventional method, regarding the furnace gas, the atmospheric gas in the radiant tube soaking zone (indirect heating) flows into the direct-fired furnace, and the mixture of the combustion exhaust gas from the direct-fired furnace and the above atmospheric gas flows into the preheating furnace, and the final is being discharged. In this case, individual? There is a problem in that mutual interference occurs due to flow rate fluctuations in the ff region, and furnace pressure fluctuations are severe and cannot be fully managed. Furthermore, when the steel strip is preheated by introducing combustion exhaust gas containing unburned components into the preheating furnace, the temperature of the exhaust gas at the outlet of the preheating furnace becomes low, making it difficult to completely burn the unburned components.

[Means for solving the t81 problem] The continuous annealing furnace according to the present invention includes a pre-2A furnace, a direct-fired furnace, and a
In this continuous annealing furnace, which has a contact heating and soaking furnace in this 111a and continuously anneales a thin steel strip, an intermediate chamber is provided between each of the furnaces to prevent movement of gas in the furnace.

Further, in the continuous annealing furnace according to another invention of this application, the continuous annealing furnace has a preheating furnace, a direct-fired furnace, and an indirect scorching furnace in this 1+10, and continuously anneales the R steel strip. An intermediate chamber is provided to prevent the movement of internal gas, and an afterburning chamber is provided between the direct-fired furnace and the preheating furnace to completely burn the combustion exhaust gas in the direct-fired furnace and supply it to the preheating furnace. It is.

[Effect]

In this invention, an intermediate chamber is provided between each furnace to prevent the movement of gas in the furnace, so even if the gas pressure in the furnace fluctuates, the gas in the furnace will not move to other furnaces. Mutual interference between each furnace due to fluctuations in gas pressure within the furnace should be suppressed.

Further, in another invention of this application, an afterburning chamber is provided between the direct-fired furnace and the preheating furnace, so that the combustion exhaust gas in the direct-fired furnace is completely combusted and supplied into the preheating chamber. The combustion exhaust gas in the combustion chamber is completely combusted in the afterburning chamber, so that its temperature rises, and this combustion exhaust gas with increased temperature is supplied into the preheating chamber,
Preheating of the steel strip is promoted.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The oil removal device of the input side equipment can be omitted, and the other cooling equipment, overaging furnace, and exit side equipment (these are the same as those of the continuous annealing furnace described in the prior art, and their explanation will be omitted.

In Figure 1, (11) is a preheating furnace installed following the entrance equipment, (12) is a direct-fired furnace installed following this preheating furnace, and (13) is a direct-fired furnace installed following this direct-fired furnace. indirect heating soaking furnace, (January is the gas jet cooling equipment installed following this indirect heating soaking furnace, and after this gas jet cooling equipment () + 4 is the 15 cooling equipment, overaging furnace, and The side equipment is installed in this order.

A first intermediate chamber (+5a) is located between the preheating furnace (II) and the direct-fired furnace (12), and a second intermediate chamber (15b) is located at the folded upper part of the direct-fired furnace (12). A third intermediate chamber (+5c
l are provided respectively.

Figure 2 shows intermediate chambers (15a), (15b), (1
Please explain the structure of 5c) in detail. In the figure, (+5)
t, an intermediate chamber, (1G) a roll that supports the steel strip (7) in this intermediate chamber, (17) a seal plate facing the steel strip (7) with a small gap, and (18) a steel The seal rolls (19) facing each other with the band (7) in between are ff44'i (
A seal plate (17), a seal roll (18), and a labyrinth seal (19) are provided in this order in the direction away from the roll (16). It is possible to make the roll gap of the seal roll (18) as close as possible.

The seal roll (18) may be internally water-cooled or may not be water-cooled. If water cooling is not used, use one made of heat-resistant steel or ceramic. The labyrinth seal (19) protects the seal roll (is) from heat radiation from the high part in the furnace.
It is for sliding doors, and is made of refractory material. The seal plate (17) is used as a final seal and is not necessarily essential. However, seal roll (18
) Since it is installed directly, it can be placed quite close to the steel strip (7), and therefore the sealing effect is great. The distance between the seal plate (17) and the labyrinth seal (19) is 50-10
It should be approximately 0 mm. In these seals, first, the labyrinth seal (191) roughly seals, the seal roll (18) provides a temporary seal, and the seal plate (191) seals the rough seal.
7) will be further sealed.

In FIG. 1, the temperature of the first intermediate chamber (15a) between the preheating furnace (1]) and the direct-fired furnace (12) is not very high, at most 300'cQπ, and the roll maintenance A ( [
No particular measures are required. The atmosphere in the first intermediate chamber (15a) may be a reducing gas (lI20N2) or a combustion exhaust gas. However, sufficient sealing is required to make the +7.4 furnaces form independent squares.

In the example in Fig. 1, a two-pass direct-fired furnace (I2) is shown, and an intermediate chamber (15bl) is provided between each pass.This second intermediate chamber (+5b) and the third For roll security reasons, it is preferable that the middle room (15c) has a title atmosphere (1120N2), especially for the third middle room (15c).
c) must be a reducing atmosphere to prevent the direct-fired furnace combustion exhaust gas from entering the soaking furnace (13).

Between the direct-fired furnace (12) and the preheating furnace (11), there is a direct-fired furnace (
12) Complete combustion of the combustion exhaust gas in the preheating furnace (11)
An afterburning chamber (2o) is provided which supplies the inside of the tank. Exhaust gas at the outlet of the direct-fired furnace (12);
The temperature is 0 to 1200° C., which is above the spontaneous ignition temperature of the unburned material, and the unheated material can be easily combusted by simply supplying air in the afterburning chamber (20). The afterburning chamber (20) increases the temperature of the exhaust gas and promotes preheating of the steel plate without dissipating unburned portions of the exhaust gas into the atmosphere. On the exit side of the afterburning chamber (20), there are two systems, one going to the preheating furnace (11) and the other going to the discharge side, and by adjusting the valves (21) and (22), an appropriate amount of exhaust gas is preheated. You will be led to room (1]).

In the direct-fired furnace (12), a reductive heating burner capable of reductive heating is provided on the side of the soaking furnace (]3), which is capable of reductive heating in an area with a length corresponding to 1710 or more of the effective furnace length of the direct-fired furnace (12). is installed. A preferred embodiment of the reduction heating burner of the present invention can be fired at high temperatures even in a heating furnace! 11! (850°C or higher). The reason why it is possible to increase the heating temperature in this heating furnace is because a premix burner is used. This is because, in order to heat the nIJ band without oxidation, it is necessary to collide a high-temperature combustion flame with an air ratio of 1.0 or less against the copper band. The limit temperature that can be heated without oxidation depends on the flame temperature, and the higher the flame temperature, the higher the limit temperature that can be heated without oxidation. In a premix burner, since air and combustion are mixed in advance, the mixed air and fuel cannot be preheated, and therefore, the flame strength is uniquely determined by the fuel type. It is possible to increase the flame temperature by enriching 0□, but this increases the possibility of explosion of the premixture, making it impractical.

3 and 4 show the reductive heating characteristics of this reductive heating burner. FIG. 3 shows the relationship between the reduction heating limit temperature at which the steel material can be heated in a reduced state and the air ratio. Preheated air crystallinity 4
00℃, using fuel and (7) C gas, it can be heated to about 950℃.
The reduction time required to reduce a steel plate with an oxide film of 0A to about 20 to 30A is measured, and the reduction time is approximately 1.5 seconds at a steel plate temperature of 600℃, 0.8 seconds at 700℃, and 750℃.
It takes about 0.5 seconds at ℃.

Heat the steel strip in a direct-fired furnace (12) from 250℃ to 700℃ for about 1 hour.
When heating for 5 seconds, it takes about 1.5 seconds to heat from 650°C to 700°C, as shown in FIG. At this time, 250℃
When a steel strip is heated from 650℃ to 650℃ using a general burner at an air ratio of 1.0 or less, at this heating rate, the oxide film formed is 200 to 400℃.
It is about 8.

Therefore, it can be seen that sufficient reduction can be achieved by using a reduction heating burner for heating from 650°C to 700°C.

When this section is converted into a furnace length, it is approximately 1710 of the furnace length. Therefore, approximately I/1 of the furnace length is placed in the area on the side of the soaking furnace (13).
A reduction heating burner may be provided for the length of 0, and a general diffusion burner may be provided for the other portions.

The atmospheric gas in the third intermediate chamber (15c) and the soaking furnace (13
) flows into the reduction heating region of the direct-fired furnace (12), its reduction ability will be reduced. That is, the temperature of these atmospheric gases is the scorching temperature in the Bm band (700
~900℃), and the combustion gas temperature in the reductive heating region (
1,400 to 1,600° C.), and if atmospheric gas were to enter, the gas temperature in the reduction heating region would drop, significantly reducing the reduction ability. For this purpose, a second afterburning chamber (19) is provided, and a third intermediate chamber (19) is provided.
5c) and the atmospheric gas of soaking F (13) is guided to the second afterburning chamber (23), this problem can be solved.

〔Effect of the invention〕

Since this invention is configured as explained above, even if the gas pressure in the furnace fluctuates, the gas in the furnace will not move to other furnaces, and mutual interference between the furnaces due to fluctuations in the gas pressure in the furnace will not occur. This has the effect of improving the operability of each unit. In addition, since the reversing roll is surrounded by an intermediate chamber, it has the effect of being protected from the high heat of each house.

In addition, another invention of this application has the effect that the combustion exhaust gas is completely combusted in the afterburning chamber and then supplied to the preheating chamber, so that the temperature of the combustion exhaust gas reaches an upper limit and the preheating of the steel strip is promoted. .

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the present invention, Fig. 2 is an enlarged view of the main part of Fig. 1, Figs. 3 to 5 are graphs showing the characteristics of the reduction heating burner, and Fig. 6 (This is an explanatory diagram showing an example of a conventional Keizoku annealing furnace. In the figure, (71j) is a steel strip, (11) is a preheating furnace, (
12) is a direct-fired furnace, (I3) is a soaking furnace, (14) is a gas jet cooling equipment, (15) is an intermediate chamber, (17) is a seal plate, (18) is a seal roll, and (19) is a labyrinth.
Seal, (20) is the afterburning chamber.

Claims (4)

[Claims] (1) It has a preheating furnace, a direct-fired furnace, and an indirect heating furnace in this order,
A continuous annealing furnace for continuously annealing thin steel strips, characterized in that an intermediate chamber is provided between each of the furnaces to prevent movement of gas within the furnace. (2) Claim 1, wherein the direct-fired furnace has a reduction heating burner on the side of the indirect heating furnace.
Continuous annealing furnace as described in section. (3) In a continuous annealing furnace that has a preheating furnace, a direct-fired furnace, and an indirect heating soaking furnace in this order and continuously anneales thin steel strips, an intermediate chamber is provided between each of the furnaces to prevent the movement of gas in the furnace. A continuous annealing furnace characterized in that an afterburning chamber is provided between the direct-fired furnace and the preheating furnace to completely combust the combustion exhaust gas in the direct-fired furnace and supply it to the preheating furnace. (4) The continuous annealing furnace according to claim 3, wherein the direct-fired furnace has a reduction heating burner on the side of the indirect heating soaking furnace.