JPH0585621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heating control method for a direct-fired heating zone in a continuous heat treatment furnace for metal strip.

(Prior Art) Conventionally, quantitative determination of the oxide film on the surface of a steel strip heated in a direct-fired heating zone in a continuous heat treatment furnace for metal strips, such as a non-oxidation heating furnace, has been carried out off-line by sample testing. For this reason, in the heating zone, an estimated operation is performed in which heating is controlled based on the air-fuel ratio (air/gas ratio), furnace temperature, plate temperature, etc.

(Problems to be Solved by the Invention) In the conventional heating control method described above, the steel strip surface quality is judged as good or bad through off-line sample tests, and heating control is performed based on this, which requires a great deal of labor. There were problems in that it took a long time to process, caused a lot of production loss, and it was not always possible to obtain a steel strip with an appropriate surface quality.

The present invention has been made to address these conventional problems, and aims to provide a heating control method for a direct-fired heating zone that reduces labor and makes it possible to obtain a steel strip with an appropriate surface quality. It is.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a continuous heat treatment furnace for metal strips in which at least one of the temperature within the furnace of the direct-fired heating zone and the temperature of the metal strip exiting the heating zone is improved. The temperature of one of the metal strips is detected, and the furnace temperature of the heating zone is controlled based on this detected temperature, while the thickness of the oxide film on the surface of the metal strip is detected at the point where it exits the heating zone, and the thickness of the oxide film on the surface of the metal strip is detected based on this detected value. hand,
At least one of the air-fuel ratio of the direct fire burner of the heating zone and the furnace temperature of the heating zone is controlled by interruption.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a continuous furnace for a continuous galvanizing line to which the heating control method for a direct-fired heating zone according to the present invention is applied. The process continues from the non-oxidizing furnace 3 forming the tropical zone through a connecting section 5 containing a deflector roll 4 to a subsequent heating reduction zone 6, through which the steel strip 1, which is the material to be treated, is passed. be.

Furthermore, an in-furnace thermometer 7 is installed in the non-oxidation furnace 3 to be able to detect the temperature inside the furnace, and a material thermometer 8 is provided at the place exiting the non-oxidation furnace 3 to be able to detect the temperature of the steel strip.
Similarly, at the exit from the non-oxidation furnace 3, a non-contact type oxide film thickness meter 9 is provided which can detect the thickness of the oxide film on the surface of the steel strip without contact.

Based on the values detected by the furnace thermometer 7, material thermometer 8, and oxide film thickness meter 9, the furnace temperature controller 10, control selection judgment function section 11, and cross limit function (in any case , an air flow controller 13 via an air/gas ratio controller 12 with a function to ensure that a defined air/gas ratio is not disturbed.
and a flow rate controller 14 to control the furnace temperature of the heating zone and the air/gas ratio.

Next, a heating control method for the direct-fired heating zone in the apparatus configured as described above will be explained.

First, the furnace temperature controller 10 compares a predetermined set value with the detected value by the oxide film thickness meter 9, and if the detected oxide film thickness is within the allowable limit,
Perform the usual furnace temperature regime.

That is, the furnace temperature controller 10 compares the predetermined steel strip temperature with the detected value by the material thermometer 8, and if this detected value is higher, the air flow controller 13 and the gas flow controller 14 so as to reduce the air/gas flow rate by
In the opposite case, the air flow controller 13 and the gas flow controller 14 are controlled to increase the air/gas flow rate.

Further, the furnace temperature controller 10 compares the predetermined furnace temperature setting with the value detected by the furnace thermometer 7, and depending on whether this detected value is higher or the opposite, the same applies as described above. air flow controller 13
It is also possible to control the gas flow rate controller 14.

On the other hand, if the value of the oxide film thickness detected by the oxide film thickness meter 9 exceeds the allowable limit, the air/gas ratio controller 12 controls the air/gas flow rate to be changed by the air/gas flow rate controller 13 and the flow rate controller 14. and controlling the air flow controller 13 and the gas flow controller 14 so that the air/gas ratio controller 12 changes the air-fuel ratio. It is now possible to do this by interrupting.

Note that the oxide film thickness gauge 9 in FIG. 1 may be provided between the two deflector rolls 4 of the connection section 5 instead of at the outlet of the non-oxidizing furnace 3.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, at least one of the temperature inside the direct-fired heating zone in a continuous heat treatment furnace for metal strip and the temperature of the metal strip exiting this heating zone is detected. While controlling the furnace temperature of the heating zone based on this detected temperature, the thickness of the oxide film on the surface of the metal strip is detected at the point where it exits the heating zone, and based on this detected value, the temperature of the heating zone is controlled. At least one of the air-fuel ratio of the direct fire burner and the furnace temperature of the heating zone is controlled by interruption.

Therefore, it is possible to control heating so as to maintain an appropriate oxide film thickness, and it is possible to improve work efficiency.

[Brief explanation of the drawing]

FIG. 1 is a control system diagram of a continuous furnace for a continuous galvanizing line to which the heating control method according to the present invention is applied. 1... Steel strip, 2... Burner, 3... Non-oxidation furnace,
7... Furnace thermometer, 8... Material thermometer, 9... Non-contact oxide film thickness gauge, 10... Furnace temperature controller,
11... Control selection judgment function section, 12...
Air/gas ratio controller, 13... air flow controller, 14... gas flow controller.

Claims (1)

[Claims] 1. In a continuous heat treatment furnace for metal strips, at least one of the temperature inside the direct-fired Japanese heat treatment furnace and the temperature of the metal strip exiting this heating zone is detected, and the furnace temperature of the heating zone is determined based on this detected temperature. At the same time, the thickness of the oxide film on the surface of the metal strip is detected at the point where it exits the heating zone, and based on this detected value, the air-fuel ratio of the direct fire burner in the heating zone and the inside of the furnace in the heating zone are controlled. 1. A heating control method for a direct-fired heating zone, characterized in that at least one of the temperatures is controlled in an interrupt manner.