JPH07100826B2 - Continuous annealing furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous annealing furnace used in hot dip galvanizing lines and the like.

[0002]

2. Description of the Related Art Usually, a hot-dip galvanizing line is provided with a continuous annealing furnace, in which a steel strip is annealed to a desired temperature and then immersed in a plating bath.

A continuous annealing furnace for a plating line is disclosed in Japanese Patent Publication No.
No. 2-57692, Japanese Patent Publication No. 62-59168, Japanese Patent Publication No. 1-21204, and Japanese Patent Publication No. 1-2185.
No. 2, JP-A-1-283352, and JP-A No. 2-8331.

As shown in FIG. 2, such a continuous annealing furnace is provided with a direct heating furnace (hereinafter referred to as DFF) 3 and a radiant tube furnace (hereinafter referred to as RTF) 5. The DFF 3 is a vertical heating furnace having a large number of burners, and has a role of directly blowing a reducing flame onto a steel strip to heat it. The RTF 5 is provided on the downstream side of the DFF 3, and in a reducing atmosphere, for example, an atmosphere in which a mixed gas of hydrogen gas and nitrogen gas is replaced, the steel strip is reciprocated up and down a plurality of times, and the steel strip is dried in a dry state. Has a role of soaking.

In this case, the combustion waste gas of the DFF 3 is RT
When it enters the F5, the reducing atmosphere of the RTF5 is destroyed by the moisture in the waste gas, so that the lower roll chamber 4 is provided at the lower part of the furnace and the gas flow is always from the side of the RTF5 to the DFF.
A large amount of reducing gas is supplied into the RTF 5 so as to flow toward the 3 side (from the downstream side to the upstream side of the steel strip conveying path), and the internal pressure of the RTF 5 is set to be lower than that in the lower roll chamber 4. Is also high.

In addition, a part of the waste gas of DFF3 is in the upper region.
A bypass passage 6 having an ejector 7 is provided in the upper part of the furnace in order to prevent the so-called roll pick-up from penetrating into the roll chamber 2 and oxidizing the roll surface to roughen the surface of the steel strip. ing. The reducing gas in the RTF 5 is supplied to the upper roll chamber 2 through the bypass passage 6, and nitrogen gas is blown from the nitrogen gas supply source 8 to oxidize the roll in the upper roll chamber 2. To prevent.

[0007]

However, since the upper bypass passage 6 is not intended to prevent the backflow of the waste gas, the backflow of the waste gas occurs via the lower roll chamber 4. That is, due to various operational conditions and fluctuations that exceed the pressure control response of the lower roll chamber 4, the gas flow may temporarily flow back from the DFF 3 toward the RTF 5.

Such backflow is caused when the zone ignition of the DFF 3 is performed or when the combustion amount of the DFF 3 is rapidly increased.
It occurs because the pressure in the lower roll chamber 4 temporarily exceeds that of the RTF 5.

When the combustion exhaust gas of the DFF 3 flows back toward the RTF 5, the dry reducing atmosphere of the RTF 5 is destroyed and the surface of the steel strip is oxidized, which adversely affects the subsequent plating process and deteriorates the quality of the product. . Since the furnace volume after the RTF is large, it usually takes a long time to recover the reducing atmosphere. During this period, the deterioration of product quality is a serious loss.

On the contrary, when the partial zone of the DFF 3 is extinguished or the combustion amount is drastically lowered, the internal pressure of the lower roll chamber 4 is instantly lowered from the control pressure, and this is directly fed to the atmosphere furnace after RTF 5. Cause furnace pressure fluctuations, and
There is a risk of invasion of outside air from the cable.

At the same time, the DFF3 of the atmosphere gas of the RTF5
The flow rate to the air flow temporarily increases and reduces the reducing power of the DFF flame. The reduction in the reducibility of DFF3 directly affects the product quality.

Further, a sudden change in the internal pressure of the lower roll chamber 4 becomes a disturbance of the furnace pressure control, which increases the recovery time until the stable control. The influence on the furnace pressure controllability has the same problem as in the DFF zone ignition.

The present invention has been made in order to solve the above-mentioned problems, and the influence of fluctuations on the DFF side does not substantially affect the RTF side, which enables stable operation and improves product quality. It is an object of the present invention to provide a continuous annealing furnace that can be used.

[0014]

Conventionally, since the amount of atmospheric gas to the RTF is large, even if a reverse flow occurs temporarily, a large amount of reducing gas relaxes the combustion gas of the DFF. No special sealing measures were taken in the roll room during the RTF.

However, there is a recent high demand for quality from consumers, and in order to meet such demand, the inventors have set the atmosphere between DFF and RTF in accordance with the fluctuation in operation. I conducted a diligent study on shutting off in a room.

The continuous annealing furnace according to the present invention has an open flame heating zone for heating an object to be treated by using a direct reduction flame and an oxidation-free soaking zone for soaking the object in a reducing atmosphere. In a continuous annealing furnace, provided above the open flame heating zone,
An upper roll chamber having a roll for feeding the object to be processed to the open flame heating zone and a lower part of the open flame heating zone for transferring the object to be treated from the open flame heating zone to the non-oxidizing soaking zone. Lower roll chamber provided with a roll for sending toward, a seal mechanism provided in the lower roll chamber, and a bypass communicating from the lower roll chamber to the upper roll chamber. And a passage. Furthermore, it is desirable to provide a gas supply means in the middle of the bypass passage and supply a non-oxidizing gas into the bypass passage.

[0017]

In the continuous annealing furnace according to the present invention, since the seal mechanism is provided in the lower roll chamber, waste gas containing moisture passes through the lower roll chamber from the open flame heating zone. It will not enter the non-oxidizing soaking zone.

Further, since the bypass passage is provided between the lower roll chamber and the upper roll chamber, the internal pressure of the open flame heating zone rises and a large amount of waste gas flows into the lower roll chamber. In this case, the waste gas is released to the upper roll chamber via the bypass passage without flowing into the non-oxidizing soaking zone. Therefore, in the lower roll chamber, the atmosphere between the direct-fired heating zone side and the non-oxidizing soaking zone side is shut off, and the reducing atmosphere of the non-oxidizing soaking zone is not destroyed.

[0019]

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

As shown in FIG. 1, the upper roll chamber 10 is D
The roll 10 provided in the upper part of the FF 12 and in the upper roll chamber
By a, the feeding direction of the steel strip 9 is changed from horizontal to vertical. The upstream side of the upper roll chamber 10 communicates with a preheating furnace (not shown). A waste gas passage 11 is provided between the upper roll chamber 10 and the DFF 12, and the DFF 1
2 combustion waste gas is exhausted.

The lower roll chamber 14 is horizontally installed between the DFF 12 and the RTF 21 at the bottom of the DFF 12.
It has two small rooms 15 and 18. By the way, the height difference between the upper roll 10 and the lower roll chamber 14 is about 20 m.

The small chamber 15 on the upstream side has a conveying roll 15a therein, and the steel strip 9 vertically conveyed from the DFF 12 can be changed in the conveying direction horizontally by the conveying roll 15a. . In addition, the small room 18 on the downstream side also has a transport roll.
The steel strip 9 that has a built-in roll 18a is horizontally transported from the upstream side, the transport direction is changed to a vertical direction by the transport roll 18a, and the steel strip 9 is further transported to the RTF 21. Inside the RTF 21, a plurality of pairs of upper and lower rolls 21a are provided. The steel strip 2 reciprocates up and down in the RTF 21, and is uniformly heated by a reducing gas composed of a mixed gas of hydrogen gas and nitrogen gas.

A seal mechanism 17 is provided inside the lower roll chamber 14, and the seal mechanism 17 effectively seals the downstream small chamber 18 from the upstream small chamber 15. The seal mechanism 17 has enough rectangular boxes (not shown) for the steel strip 9 to pass through. A heat insulating member (not shown) is packed in the gap between the seal box and the inner wall of the roll to prevent ventilation from the upstream small chamber 15 to the downstream small chamber 18.

The bypass passages 22 and 24 communicate with the lower roll chamber 14 and the upper roll chamber 10, respectively.
The bypass passage 22 communicates with the upstream small chamber 15 of the lower roll chamber 14. In this case, the bypass passage 22 may be communicated with the downstream small chamber 18. Further, the bypass passage 24 communicates with an appropriate place in the upper roll chamber 10.

An ejector 23 is provided between the bypass passage 22 and the passage 24. A supply port of a gas supply source 26 communicates with the ejector 23 via a damper 25. Nitrogen gas is stored in the gas supply source 26.
The damper 25 has opening / closing and flow rate adjusting functions. next,
The operation of the above device will be described.

When the DFF 12 is ignited, the internal pressure of the DFF 12 rises and exceeds the internal pressure of the RTF 21, and the combustion waste gas enters the lower roll chamber 14. However, the waste gas is blocked by the seal device 17 and does not flow into the RTF 21 on the downstream side. In addition, the small room 15 on the upstream side of the roll room 14
When the internal pressure of rises, the ejector 23 operates and sucks the internal gas of the small chamber 15. As a result, the internal pressure of the upstream small chamber 15 drops, the differential pressure with the downstream small chamber 18 is maintained, and backflow is prevented.

At this time, the damper 25 is opened and nitrogen gas is supplied from the supply source 26 to the bypass passage 24. The inflow of nitrogen gas increases the suction force through the bypass passages 22 and 24, and the exhaust from the small chamber 15 becomes smooth. It should be noted that the damper 25 is provided with a limit switch, and the damper 25 is opened for a fixed time.

Furthermore, when the DFF 12 is extinguished, R
A large amount of reducing gas tries to flow into the DFF 12 side from the TF 21 side, but in this case as well, the fire extinguishing condition is set by the damper 25.
Built in the closing condition of, the damper 25 opens for a predetermined time,
Nitrogen gas is allowed to flow into the bypass passages 22 and 24 to prevent the reducing gas from flowing from the RTF 21 to the DFF 12.

According to the above embodiment, RT is prevented by backflow prevention.
In addition to maintaining the F21 furnace atmosphere, RTF21
Since it is possible to prevent an excessive gas inflow from the DFF12 side to the DFF12 side, the atmosphere in the DFF12 furnace is maintained at a desired atmosphere, and the unsteady state can be smoothly operated to the steady state.

[0030]

According to the present invention, since the atmosphere between the open flame heating zone and the non-oxidizing soaking zone is shut off by the seal device in the lower roll chamber, a dry reducing atmosphere of the non-oxidizing soaking zone is created. It is not broken and the surface of the steel strip is kept clean. In addition, the lower
The waste gas that has entered the chamber is routed through the bypass passage to the upper roll.
As it escapes to the room, the effect of protecting the atmosphere of non-oxidizing soaking zone is enhanced. For this reason, it is possible to effectively prevent the oxidation of the surface of the steel strip, the plating adhesion is not impaired, and it is possible to obtain a plated steel sheet of good quality. Further, since the gas is made to flow into the upper roll chamber through the bypass passage, the roll in the upper roll chamber is cooled by gas, and the pickup of the roll is effectively prevented.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a continuous annealing furnace according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a conventional continuous annealing furnace.

[Explanation of symbols]

9: Steel strip, 10: Upper roll chamber, 12: Open flame heating zone (D
FF), 14; lower roll chamber, 17; seal mechanism, 2
1; non-oxidizing soaking zone (RTF), 22, 24; bypass passage, 23; ejector, 25; damper, 26; gas supply source.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akihiko Nakamura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Noboru Taguchi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside the Steel Pipe Co., Ltd. (72) Inventor Michiaki Tsutsumi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Inside Steel Pipe Co., Ltd. (72) Hideo Iwasaki 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Incorporated (56) References JP-A-2-236229 (JP, A) JP 60-46162 (JP, B2)

Claims (1)

[Claims] 1. A continuous annealing furnace having a direct fire heating zone for heating an object to be treated using a direct flame reducing flame, and a non-oxidizing soaking zone for soaking the object to be treated in a reducing atmosphere. An upper roll chamber provided above the fire heating zone and provided with a roll for feeding the object to be treated to the open flame heating zone, and provided below the open flame heating zone to treat the article to be treated directly A lower roll chamber provided with a roll for sending from the fire heating zone toward the non-oxidizing soaking zone, a seal mechanism provided in the lower roll chamber, and the lower roll chamber through the A continuous annealing furnace having a bypass passage communicating with the upper roll chamber.