JPS5910978B2 - Continuous annealing furnace heating zone temperature control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the temperature of a heating zone in a continuous annealing furnace.

Continuous galvanizing equipment for cold-rolled steel sheets passed through a continuous annealing furnace has recently become more sophisticated and faster, and as a result galvanized steel sheets of various materials have come to be manufactured.

In response to this situation, continuous annealing furnaces have a large heat capacity in the heating zone using radiant tubes, so when trying to lower the set temperature according to the characteristics of the processed steel plate, it takes a long time and the line speed Coupled with the fact that the line speed is fast, the quality of the product steel sheet tends to become unstable during this time, and when the line speed slows down or is stopped, the steel sheet often gets overheated in the furnace, causing damage to the steel sheet. Tensile fractures were frequently experienced.

Therefore, this invention provides rapid cooling of the heating zone of a continuous annealing furnace via a radiant tube. Become capable,
In this way, we propose a temperature control method for the heating zone of a continuous annealing furnace that makes it easy to lower the annealing temperature in accordance with the characteristics of the treated steel sheet.

This invention is based on heat-resistant steel commonly used as radiant tubes in continuous annealing furnaces, such as ACI standard HL equivalent products (
Cr28-32%, Nil8-22%, Si2% or less, CO. 2 to 0.6%) without causing any particular problems when combustion exhaust gas, saturated steam, air, or inert gas is introduced as a cooling gas instead of combustion gas.
This is based on the knowledge that it can be used for rapid cooling of the heating zone in this way.

This invention controls the cooling of the heating zone of a continuous annealing furnace by incorporating into the temperature control system of the heating zone of the radiant tube of a continuous combustion furnace, the introduction of combustion exhaust gas saturated steam air or inert gas that controls rapid cooling of the radiant tube. By realizing this, it is possible to quickly change the annealing atmosphere temperature setting, which makes it possible to process steel plates appropriately even at line speeds, and to prevent overheating of treated steel plates when the line speed is reduced or stopped. Otherwise, breakage can be effectively avoided.

FIG. 1 shows a cross section of the heating zone of the continuous annealing furnace, and FIG. 2 illustrates the temperature control system of the radiant tube.

In the figure, 1 is a continuous annealing furnace, 2 is its heating zone, and 3 is a continuous annealing furnace.
is a radiant tube.

The radiant tube 3 connects the combustion pipe 5 and the combustion air pipe 6 to the burner 4, and radiates the sensible heat of the high-temperature combustion gas generated in the burner 4 to the heating zone 72 to heat it, and the waste gas is used as waste heat. Collect it and then direct it to the chimney 3' without doing so.

In this invention, a cooling gas piping 7 connected to the radiant tube 3 is provided at <<, and the back flow of combustion gas is blocked by a check valve V as shown in the illustrated example.

Normally, fuel and combustion air are sent to the burner 4 through pipes 5 and 6, where they are burned in the Rajant tube 3, and the waste gas is released into the atmosphere.

Therefore, the combustion gas does not flow into the cooling gas pipe 7 due to the chatter valve vl.

To explain the temperature control system shown in FIG. 2 in detail, normally a thermocouple 8 measures the temperature inside the furnace or the temperature of a radiant tube, a converter 9 converts it into a current signal, and the signal is sent to a temperature controller 10. is transmitted to the alarm meter 14.

The combustion air control valve 11 is actuated by the signal from the temperature controller 10 to adjust the combustion air pressure, and the fuel control valve 12 is a ratio control valve that follows the combustion air pressure in proportion.

This control system is equipped with a sequencer 18 and a combustion command 1.
A rapid cooling command 19 is incorporated in addition to a slow cooling command 17 that utilizes adjustment signals from a temperature controller 6 and a temperature controller 10.

Now, the combustion command 16 is stopped by the gradual cooling command 17, and then the combustion air pressure control valve 11 and the fuel control valve 12 are stopped.
Combustion stops.

At the same time, the signal from the temperature controller 10 passes through the gradual cooling command 17 and enters the cooling gas regulating valve 13 to adjust the cooling gas pressure.

In addition, when a rapid cooling command 19 is issued from the sequence source 18, the combustion command 16 and slow cooling command 17 are stopped, and the rapid cooling solenoid valve 15 is activated.

Due to the operation of this rapid cooling solenoid valve, the cooling gas control valve 13 is fully opened, and the radiant tube is rapidly cooled.

By this rapid cooling operation, the temperature of the radiant tube and the ambient temperature of the radiant tube heating zone are lowered, and when the set value of the rapid cooling temperature setter 20 is reached, the rapid cooling command 19 is stopped.

At this point, the operation or temperature controller 1 is activated by the gradual cooling command.
0 gives a combustion command and allows selection of cooling or combustion of the radiant tube heating zone.

The key points of temperature control according to the present invention will be shown.

First, FIG. 3 shows an example of the effect when the line is stopped, and when comparing the downward curve of the ambient temperature, the cooling effect is approximately three times greater.

Also in FIG. 4, a cooling effect of 5 times is similarly exhibited.

As an example of the effect during operation, as shown in Figure 5, the set temperature (7
The time it takes to reach 60°C has been reduced by one-third.

Similarly, as shown in FIG. 6, the time required to reach the set temperature (760° C.) has been shortened to one-half.

As described above, according to the present invention, it is possible to reach the target temperature for the annealing curve in about one-third of the time taken by the conventional method. There is no need to adjust or change the line speed.

2 Due to this rapid cooling, the time required to reach the target temperature is short, so quality can be stabilized in a short period of time.

3. It is possible to prevent steel plates from breaking due to overheating that occurs when the line is stopped or at low speeds.

It goes without saying that the method of the present invention can be used not only in a continuous galvanizing annealing furnace but also in any annealing furnace of radiant tube heating type.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the heating zone of a continuous annealing furnace.
FIG. 2 is an explanatory diagram of temperature control differences, and FIGS. 3 to 6 are graphs of specific examples of temperature control. 3...Radiant tube, 1...Cooling gas piping.

Claims (1)

[Claims] 1. A temperature control method for the heating zone of a continuous annealing furnace, which is characterized by forcibly introducing cooling gas into the radiant tube of the continuous annealing furnace.