JPH0711343A - Method for controlling atmosphere in continuous annealing furnace - Google Patents

Abstract

PURPOSE:To prevent gas in a heating zone from mixing into a cooling zone by arranging a CO gas analyzer near the inlet of a shield tunnel and blowing new atmospheric gas from the lower part of the tunnel according to this indication. CONSTITUTION:The CO analyzer 5 is set near the inlet of the shield tunnel 4 formed with a partition wall 3 between the heating zone 1 and the cooling zone 2. At the time of operating, the condition of gas in the heating zone accompanied with the band steel 8 is detected with an analyzer 5. Successively, the new atmospheric gas supplying quantity cancelling the flowing gas in the heating zone is calculated with a CO concn. controller 6. The new atmospheric gas is blown toward the shield tunnel 4 from an atmospheric gas injection nozzle 9 at the furnace bottom through an atmospheric gas flow rate controller 7. By this method, as the atmosphere in the heating zone 1 can be separated from the cooling zone 2, CO is not carried into the cooling zone 2 and the contamination of the band steel caused by deposit of CO can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atmosphere control device for a continuous annealing furnace.

[0002]

2. Description of the Related Art Generally, as a method of sealing an atmosphere in a continuous annealing furnace, there is known a method of providing a seal roll or a seal tunnel as disclosed in JP-A-2-4926.

[0003]

The method using a seal roll is such that, when the roll is brought into contact with the steel strip, the steel strip is damaged if the peripheral speed of the roll does not match the strip speed, and the strip is stretched in the width direction. There is a problem that there is a gap in the part where there is no gap, and when the steel strip thickness changes, the roll will be damaged unless the change is detected accurately.

Further, in the method of isolating the atmosphere by utilizing the difference in specific gravity by the seal tunnel, when the steel strip speed increases, the atmosphere gas accompanying the steel strip flows, so that the upstream side (heating zone) of the steel strip. There is a problem that the atmospheric gas mixes into the downstream side (cooling zone). As a result, a gas flow from the heating zone to the cooling zone occurs, and the CO gas in the heating zone mixes in the cooling zone. Therefore, C is deposited in the cooling zone due to the reaction CO + H ₂ → C + H ₂ O in the cooling zone. However, there is a problem that it causes stains on the steel strip.

An object of the present invention is to provide an atmospheric gas control device that solves the above problems.

[0006]

In order to solve the above problems, the present invention provides a sealing tunnel (a partition wall is provided at each end of a path through which a steel strip flows from top to bottom), and the accompanying flow of the strip is cooled. The state of entering the zone is detected by a CO analyzer, and new atmospheric gas is injected from the bottom of the furnace so as to cancel this accompanying flow, and the CO concentration in the seal tunnel is controlled to a low value. Here, in the heating zone, H _{2 in the} furnace
The following reactions occur due to O and C contained in the steel strip, and the heating zone atmosphere gas contains H ₂ O + C → H ₂ + CO CO. Therefore, the amount of wake flow from the heating zone can be judged by the CO concentration in the seal tunnel.

That is, according to the present invention, in a continuous annealing furnace for continuously annealing a steel strip, a path in which the steel strip flows from the top to the bottom is provided between the final heating zone and the cooling zone, and the steel strip in the pass is joined to the steel strip. A partition wall is provided between the tropical zone and between the steel strip and the cooling zone of the path, a gas analyzer is provided near the entrance of the seal tunnel formed by these two walls, and atmospheric gas is blown out near the exit. It is an atmosphere control device for a continuous annealing furnace, which is provided with a nozzle and controls an input amount of an atmosphere gas according to an instruction value of a gas analyzer.

[0008]

According to the present invention, the atmospheric gas flowing from the heating zone to the cooling zone in the seal tunnel can be detected by measuring the CO concentration in the seal tunnel. When the CO concentration is high, new atmosphere gas is introduced from the cooling zone to the heating zone so as to cancel the accompanying flow. This allows
In addition to the sealing effect due to the original density difference of the seal tunnel,
Due to the effect of the flow of the new atmosphere gas, the flow of the atmosphere gas from the heating zone to the cooling zone can be blocked.

The amount of input gas is CO in the seal tunnel.
Since the control is performed according to the concentration, it is possible to balance the accompanying flow and the input gas amount for any steel strip velocity, and it is possible to reliably isolate the atmospheres of the heating zone and the cooling zone.

[0010]

FIG. 1 is a flow chart showing an embodiment of the present invention. A partition wall 3 is provided between the heating zone 1 and the cooling zone 2,
A seal tunnel 4 is formed. The steel strip 8 runs in the seal tunnel from top to bottom. The new atmosphere gas is blown from the bottom of the seal tunnel 4 by the nozzle 9. The blowing method may be a method of directly charging into the furnace bottom, but it is more preferable that a nozzle for canceling the accompanying flow is provided as shown in FIG.

A CO analyzer 5 is installed near the entrance at the top of the seal tunnel to continuously measure the CO concentration in the seal tunnel. The concentration controller 6 calculates the input amount of atmospheric gas from the measured CO concentration value, and sets the input amount setting value to the flow rate controller 7.
Give to. When the CO concentration is high, the concentration and flow controller increases the input amount of the atmospheric gas, and when the CO concentration is low, the atmospheric gas flow amount is decreased.

The supplied atmospheric gas becomes a flow from the lower part to the upper part of the seal tunnel due to the flow velocity at the time of injection and the draft generated by the heat obtained from the steel strip. Therefore, if the flow from the lower part to the upper part is large, the CO concentration in the upper part will decrease,
By the control by the controller described above, the accompanying flow and the input atmosphere gas can be balanced, and as a result, the atmosphere of the heating zone and the atmosphere of the cooling zone can be isolated.

By inputting the steel strip velocity to the concentration controller 6, the atmosphere isolation can be achieved more reliably.

[0014]

According to the present invention, since the CO analyzer is provided near the entrance of the upper part of the seal tunnel and the input amount of the atmospheric gas is controlled according to the CO concentration, the heating zone can be used regardless of the steel strip speed. The atmosphere in the cooling zone can now be reliably isolated, and CO in the heating zone atmosphere is no longer brought into the cooling zone.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of an atmosphere control device of the present invention.

FIG. 2 is an explanatory view showing an embodiment of an atmosphere gas injection nozzle.

[Explanation of symbols]

 1 Heating Zone 2 Cooling Zone 3 Partition Wall 4 Seal Tunnel 5 CO Analyzer 6 CO Concentration Controller 7 Atmosphere Gas Flow Controller 8 Steel Strip 9 Atmosphere Gas Injection Nozzle

Claims (1)

[Claims] 1. A continuous annealing furnace for continuously annealing a steel strip, wherein a path through which the steel strip flows from top to bottom is provided between a final heating zone and a cooling zone, and between the steel strip and the heating zone of the pass, and A partition wall is provided between the steel strip and the cooling zone of the pass, a gas analyzer is provided near the entrance of the seal tunnel formed by these two walls, and a charging nozzle for blowing atmospheric gas is provided near the exit. An atmosphere control device for a continuous annealing furnace, which controls an input amount of an atmosphere gas according to an instruction value of a gas analyzer.