JPH02274821A - Method for feeding atmospheric gas in continuous heat treatment furnace - Google Patents

Abstract

PURPOSE:To prevent invasion of atmospheric gas into slow cooling and rapid cooling zones an to prevent deterioration of surface characteristic of a steel strip by feeding the atmospheric gas in a furnace from the slow cooling and the rapid cooling zones and exhausting the gas from heating zone and soaking zone in the continuous heat treatment furnace for the steel strip composed of the heating zone, soaking zone, slow cooling zone and rapid cooling zone. CONSTITUTION:A steel strip 11 is continuously annealed through a continuous heat treatment furnace consisting of the heating zone 1 having radiant tube 5, the soaking zone 2 having electric heater 6, the slow cooling zone 3 having cooling tube 7 and the rapid cooling zone 4 having jet cooler 8. In this case, the atmospheric gas in the furnace is fed into the furnace from supplying holes 9 arranged to the rapid cooling zone 4 and the slow cooling zone 3 and exhausted to out of the furnace from gas exhaust pipes 10 arranged to the soaking zone 2 and heating zone 1. The oxidization on the surface of the steel strip with the steam caused by steam generated in the furnace and CO gas generated with decomposition of rolling oil coming into the slow cooling zone 3 and rapid cooling zone 4 does not occur, and further, the development of flow on the surface of the steel strip 11 with seal material at throut part between the zones is prevented and the continuous annealing material for the steel strip having excellent surface characteristic is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for introducing atmospheric gas into a continuous heat treatment furnace.

[Prior Art] In general, a continuous incineration furnace for strips, for example, a strip, usually has a heating zone, a soaking zone, a slow cooling zone, and a rapid cooling zone, each of which is heated to create a desired atmosphere. Continuous annealing of strips is carried out.When continuously annealing strips that require particularly strict control of the surface properties, it is necessary to create a desired atmosphere gas in each zone in the continuous annealing furnace. The atmospheric gas in the slow cooling zone and rapid cooling zone must be clean. In response to this need, proposals have been made in the past to prevent the mixing of atmospheric gases in the furnace by adding innovations to the joints of the respective bands in a continuous annealing furnace. The apparatus shown in FIGS. 3 and 4 is disclosed. 31 is a soaking zone, and 32 is a slow cooling zone. A throat 33 connects the soaking zone 31 and the slow cooling zone 32.

34 is an atmospheric gas diffusion tube, and a furnace pressure adjustment damper 36 is provided at its upper end. 37 is a gas blowing device. Reference numeral 38 denotes an L-shaped sealing material made of fiber, and the throats 33 are provided inside the upper wall at intervals with the atmospheric gas diffusion pipe 34 interposed therebetween. Projections 39 are provided on the lower wall of the throat 33 at intervals.

The protrusion 39 is covered with a sealing material made of fiber. A hearth roll 35 is provided at the stepped portion of the protrusion 39. This mechanism prevents atmospheric gas from the soaking zone 32 from entering the soaking zone 31 side, or conversely, preventing atmospheric gas from soaking zone 31 from mixing into the slow cooling zone 32 side.

Conventionally, the device for introducing atmospheric gas into a continuous annealing furnace is the second (21st)
The heating zone, soaking zone,
It is supplied to both the slow cooling zone and the rapid cooling zone from approximately the same location. If there is no sealing mechanism for the throat 33,
Atmospheric gas mixes between each band.

[Problems to be Solved by the Invention] However, the sealing mechanism has a problem in that the L-shaped sealing material made of fibers rubs against the strip, causing scratches on the surface of the strip.

[Means for Solving the Problems] A method for introducing atmospheric gas into a continuous heat treatment furnace according to the present invention is a method for introducing atmospheric gas into a continuous heat treatment furnace having at least a heating zone, a soaking zone, and a cooling zone. The method is characterized in that the atmospheric gas is introduced from the cooling zone and the atmospheric gas is diffused from the heating zone or the soaking zone.

[Function] Since the present invention is constructed as described above, it is possible to avoid the problem of causing scratches on the surface of the strip due to friction between the sealing material and the strip, and to improve the surface quality of the strip. Prevent harmful components from entering cooling zones such as slow cooling zones and rapid cooling zones.

[Example] An example of the present invention will be described below with reference to the drawings. 1st
The figure shows a top view of the continuous heat treatment furnace of the present invention. In Figure 0, the vertical furnace has a built-in hearth roll that allows the steel strip 113 to run. It has a configuration in which it is divided into a rapid cooling zone 4 in series. The heating/cooling means in each zone includes, for example, a radiant tube 5 in heating zone 1, an electric heater 6 in soaking gP2, and a cooling tube 7 in slow cooling zone 3.
A jet cooler 8 is used in the rapid cooling zone 4. Atmospheric gas inlets 9 are provided at two checkpoints in the slow cooling zone 3 and at two locations in the rapid cooling zone 4, for a total of four locations.Atmospheric gas is fed from these four atmospheric gas inlets 9. Two pipes 10 are placed in the heating zone 1, and two in the soaking zone 2.
There are a total of four atmospheric gas diffusion pipes, each with a total of 2g, and the atmospheric gas is diffused from these four atmospheric gas diffusion pipes. The reason for providing four diffusion tubes above and below is that a large amount of atmospheric gas can be diffused in the lower part and further in the upper diffusion tube, so that complete diffusion can be achieved. When the steel strip 11 is in a furnace and the oxide film on the surface layer of the steel strip 11 is reduced by a reducing gas such as H2, F e O+ H2 = F
H and O are generated in the furnace through a reaction typified by e + H20.

Rolling oil is used during rolling in a cold strip mill, and may adhere to the steel strip 11 and may remain slightly even after electrolytic cleaning. The rolling oil adhering to the steel strip 11 is exposed to high temperatures in the heating zone 1 and the soaking zone 2, and decomposes to generate Co and H2O. slow cooling zone 3
And in the quenching zone 4, H2O may oxidize the surface of the steel strip 11. Here, the above-mentioned Co ,H
This prevents 2O from entering the slow cooling zone 3 and the rapid cooling zone 4, and prevents the surface properties of the steel strip 11 from being damaged. A conventional method of supplying atmospheric gas is shown in FIG. 2. In the conventional method of supplying atmospheric gas, atmospheric gas was uniformly supplied to each surface. Furthermore, the conventional sealing mechanism for the throat 33 had a problem in that the sealing material and the strip rubbed against each other in R1, causing scratches on the surface of the strip 11, but the method of introducing atmospheric gas of the present invention solves this problem. points are also resolved.

FIG. 5 shows the relationship between the H2O content in the slow cooling zone 3 and the line speed. Region 1 corresponds to the conventional atmospheric gas injection method. Area 2 corresponds to the case where, among the atmospheric gas introduction methods used for comparison, the atmospheric gas was only diffused from the heating zone or the soaking zone. Region 3 corresponds to the case where the atmospheric gas injection method of the present invention is used.

[Effects of the Invention] Since the present invention is configured as described above, it is possible to avoid the problem of causing scratches on the surface of the strip, and to remove components that damage the surface properties of the strip from an annealing zone or a quenching zone. This prevents the surface of the strip from entering the cooling zone such as a continuous heat treatment furnace from mechanical scratches or
Since it is free from chemical attack and chemical contamination, it has become possible to manufacture high-grade strips.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view of a continuous heat treatment furnace according to an embodiment of the present invention, Fig. 2 is a vertical sectional view of a continuous heat treatment furnace in which a conventional atmospheric gas injection method is implemented, and Fig. 3 is a conventional continuous heat treatment furnace. 4 is an enlarged view of the sealing mechanism shown in FIG. 3, and FIG. 5 is an explanatory diagram showing the sealing mechanism of the throat section of It is a figure showing the effect of the present invention. 1...Heating zone, 2...Soaking zone, 3...Low cooling zone, 4
...Rapid cooling zone, 5...Radiant tube, 6...
Electric heater, 7... Cooling tube, 8...
Jet cooler, 9... Atmosphere gas inlet, 10
...Atmosphere gas diffusion pipe, 11...Steel strip, 3
DESCRIPTION OF SYMBOLS 1... Soaking zone, 32... Slow cooling zone, 33... Throat, 34... Atmosphere gas diffusion pipe, 35... Hearth roll, 36... Furnace pressure adjustment damper 37... Gas Blowing device, 38...Sealing material.

Claims (1)

[Claims] In a method of supplying atmospheric gas to a continuous heat treatment furnace that has at least a heating zone, a soaking zone, and a cooling zone, the atmospheric gas is supplied from the cooling zone and the atmospheric gas is diffused from the heating zone or the soaking zone. A method for introducing atmospheric gas into a continuous heat treatment furnace, characterized in that: