JPH04280929A - Continuous annealing furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This 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 equipped with a continuous annealing furnace, in which the steel strip is annealed to a desired temperature and then immersed in a plating bath.

[0003] Continuous annealing furnaces for plating lines were developed by
2-57692, Japanese Patent Publication No. 62-59168, Japanese Patent Publication No. 1-21204, Japanese Patent Publication No. 1-21852
JP-A No. 1-283352, and JP-A No. 2-8331.

[0004] Such continuous annealing furnaces include direct-fired heating furnaces (
A radiant tube furnace (hereinafter referred to as RTF) and a radiant tube furnace (hereinafter referred to as RTF) are provided. A DFF is a vertical heating furnace having a large number of burners, and is used to heat a steel strip by directly spraying a reducing flame onto the steel strip. RTF
is installed on the downstream side of the DFF, and is used to level the steel strip in a dry state while moving the steel strip up and down several times in a reducing atmosphere, for example, an atmosphere substituted with a mixed gas of hydrogen gas and nitrogen gas. It is for heating.

In this case, if the combustion gas of the DFF enters the RTF, the reducing atmosphere of the RTF will be destroyed by the moisture in the combustion gas, so a roll chamber with a constant pressure control is provided at the bottom of the furnace. with the gas flow always changing from RTF to DF
A large amount of reducing gas is supplied into the RTF so that it flows toward F (from the downstream side to the upstream side of the steel strip conveyance path), and the internal pressure of the RTF is made higher than that of the roll chamber. There is.

[0006]

[Problems to be Solved by the Invention] However, in conventional continuous annealing furnaces, due to various operating conditions and fluctuations that exceed the responsiveness of pressure control in the roll chamber, the gas flow temporarily changes. A so-called reverse flow that flows from the DFF to the RTF (from the upstream side to the downstream side of the steel strip conveyance path) may occur.

[0007] In other words, backflow occurs when the DFF zone ignites or when the combustion amount of the DFF increases rapidly.
This is caused by the pressure in the chamber temporarily exceeding that of the RTF.

[0008] When the combustion exhaust gas from the DFF flows back toward the RTF, the dry reducing atmosphere of the RTF is destroyed and the surface of the steel strip is oxidized, which adversely affects the subsequent plating process and causes a decline in product quality. . Since the volume inside the furnace after RTF is large, it usually takes a long time to recover the reducing atmosphere. Deterioration in product quality during this period results in significant losses.

On the other hand, when extinguishing a part of the DFF zone or rapidly reducing the combustion amount, the internal pressure in the roll chamber drops instantaneously below the control pressure, and this directly flows into the atmosphere furnace after the RTF. This causes fluctuations in the furnace pressure, leading to the risk of outside air entering through the seals of various parts of the furnace body. At the same time, the flow rate of the RTF atmosphere gas to the DFF temporarily increases, reducing the reducing power of the DFF flame. Decreased reducibility in DFF directly affects product quality.

Further, a sudden change in the roll chamber pressure causes a disturbance in the furnace pressure control, increasing the recovery time until stable control is achieved. The effect on furnace pressure controllability is similar to that of the DFF zone.

[0011] This invention was made to solve the above problems, and the influence of fluctuations on the DFF side does not substantially affect the RTF side, allowing stable operation and improving product quality. The purpose of the present invention is to provide a continuous annealing furnace that can perform continuous annealing.

0012

[Means for solving the problem] Conventionally, since the amount of atmospheric gas flowing into the RTF is large, even if backflow occurs temporarily, the combustion gas of the DFF is relaxed by a large amount of reducing gas, and the DFF and No special sealing measures were taken in the roll room between RTFs.

[0013] However, recent customers have high quality demands, and in order to meet these demands, the inventors have developed a method to lower the atmosphere between the DFF and RTF in accordance with operational fluctuations. We conducted extensive research on how to shut it off in our room.

[0014] The continuous annealing furnace according to the present invention has a direct-fire heating zone that heats the object to be treated using a direct-fire reducing flame, and a non-oxidation soaking zone that soaks the object to be treated in a reducing atmosphere. In a continuous annealing furnace, a roll is provided between the direct-fired heating zone and the non-oxidizing soaking zone and transports the object to be processed from the direct-fired heating zone to the non-oxidizing soaking zone. A pair of roll chambers, a seal chamber that is provided between the roll chambers and surrounds the conveyance path of the object to be processed, and the internal pressure of the direct fire heating zone and the non-oxidation soaking zone or the furnace. It is characterized by comprising a gas supply means for supplying a non-oxidizing gas into the sealing chamber according to operating conditions.

[0015]

[Operation] In the continuous annealing furnace according to the present invention, a seal chamber is provided between the roll chambers, and when the internal pressure of the direct-fired heating zone exceeds the internal pressure of the non-oxidizing soaking zone by more than a certain value, gas is supplied. A non-oxidizing gas is supplied to the sealing chamber by the means. For this reason,
The atmosphere between the open heating zone side and the non-oxidizing soaking zone side is blocked in the sealing room, so that the reducing atmosphere in the non-oxidizing soaking zone is not destroyed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, the communication duct 14 is connected to D
It is provided horizontally between the DFF 12 and the RTF 21 at the lowest part of the FF 12, and includes a pair of roll chambers 15, 18 and a seal chamber 17.

The upstream roll chamber 15 contains transport rolls 15a, and the steel strip 3 vertically transported from the DFF 12 is changed in its transport direction to horizontal by the transport rolls 15a. There is. In addition, the downstream roll chamber 18 is also
The steel strip 3 is conveyed horizontally from the upstream side via the sealing chamber 17, and the conveying direction is changed vertically by the conveying roll 18a, and further conveyed to the RTF 21. It has become. Note that the seal chamber 17 is
The roll joint portion 16 is connected to each roll chamber 15, 18, respectively.

A gas supply source 26 communicates with the inside of the seal chamber 17 via a pipe 27. A shutoff valve 25 is installed in the pipe 27.
is provided. The output section of the comparator 24 is connected to the power switch of the cutoff valve 25. The detection circuits of the pressure sensors 13 and 22 are connected to the input section of the comparator 24, respectively.

The first pressure sensor 13 is provided at a suitable location in the DFF 12 and has the role of detecting the furnace pressure of the DFF 12. The second pressure sensor 22 is provided at a proper location in the RTF 21 and has the role of detecting the furnace pressure of the RTF 21 .

The comparator 24 compares the detection signals received from the first and second pressure sensors 13 and 22, and shuts off when the voltage difference between the two (value that can be converted into differential pressure) exceeds a predetermined value. It has the role of issuing a command signal to the valve 25. In the steady operating state, the internal pressure of the RTF 21 exceeds that of the DFF 12, so gas flows from the RTF 21 toward the DFF 12 in the communication duct 14.

By the way, when there is a zone ignition or a sudden increase in combustion amount in the DFF 12, the DFF 12
Due to the increase in internal pressure, the pressure in the roll chamber 15 may exceed the internal pressure in the RTF 21, and the combustion exhaust gas from the DFF 12 may flow back toward the RTF 21 through the communication duct 14.

However, at this time, the shutoff valve 25 opens and nitrogen gas flows into the seal chamber 17 from the supply source 26, and the atmosphere between the DFF 12 side and the RTF 21 side is shut off by the nitrogen gas, so a large amount of Combustion gas containing moisture will no longer enter the RTF 21. That is, when the furnace pressure of the DFF 12 rises and exceeds the furnace pressure of the RTF 21, and the differential pressure between the two becomes approximately 20 to 30 mmHg or more, the first and second
The difference value (voltage difference) between the detection signals input from the pressure sensors 13 and 22 to the comparator 24 exceeds a predetermined set value, and based on this, a command signal is sent to the shutoff valve 25, and the switch is turned OFF.
The purge gas flows into the seal chamber 17. Note that a limit switch is used as the switch of the cutoff valve 25,
The shutoff valve 25 remains open for a certain period of time.

Furthermore, when the DFF 12 is extinguished, R
A large amount of reducing gas tries to flow from the TF21 side to the DFF12 side, but in this case as well, the extinguishing conditions are set to the cutoff valve 25.
The shutoff valve 25 is opened for a predetermined period of time,
Let nitrogen gas flow into the seal chamber 17, and RTF2
1 to the DFF 12.

According to the above embodiment, RT due to backflow prevention
In addition to maintaining the F21 furnace atmosphere, RTF21
Since it is possible to prevent excessive gas from flowing from the side to the DFF 12 side, the atmosphere inside the DFF 12 furnace is maintained at a desired atmosphere, and smooth operation from an unsteady state to a steady state can be achieved.

[0026]

[Effects of the Invention] According to the present invention, since the atmosphere between the open heating zone and the non-oxidizing soaking zone is blocked by the purge gas, the dry reducing atmosphere in the non-oxidizing soaking zone is not destroyed, and the surface of the steel strip is kept clean. Therefore, oxidation of the surface of the steel strip can be effectively prevented and the plating adhesion is not impaired, so that a plated steel sheet of good quality can be obtained.

[Brief explanation of the drawing]

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

[Explanation of symbols]

3; Steel strip, 10; Continuous annealing furnace, 11; Preheating furnace, 12; Direct-fired heating zone (direct-fired heating furnace), 13, 22; Pressure sensor, 1
4; Communication duct, 15, 18; Roll chamber, 17; Seal chamber, 21; Non-oxidation soaking zone (radiant tube heating furnace)
, 24; Comparator, 25; Shutoff valve, 26; Gas supply source, 4
0; Molten metal bath

Claims (1)

[Claims] 1. A continuous annealing furnace having a direct flame heating zone that heats the object to be treated using a direct flame reducing flame and a non-oxidizing soaking zone that soaks the object to be treated in a reducing atmosphere. a pair of roll chambers provided between the fire heating zone and the non-oxidizing soaking zone and equipped with rolls for transporting the object to be processed from the direct flame heating zone toward the non-oxidizing soaking zone; , a seal chamber provided between the roll chambers and surrounding the conveyance path of the object to be processed, and an internal pressure in the direct fire heating zone and the non-oxidation soaking zone;
Alternatively, a continuous annealing furnace comprising a gas supply means for supplying a non-oxidizing gas into the sealing chamber according to operating conditions of the furnace.