JPS61163219A - Method and device for heat treatment of metallic strip in direct fire type continuous heat treatment furnace - Google Patents

Abstract

PURPOSE:To prevent the flawing on the surface of a metallic strip by providing floating devices in a heat treatment furnace, ejecting the high-temp. gas generated out of the furnace from the bottom surface side of the strip and heat-treating the catenary-supported strip. CONSTITUTION:The floating devices 4a, 4b, 4c are provided in the direct fire type continuous heat treatment furnace 1 and a floating device 5 is provided to the outside of the furnace. The metallic strip 3 is heat-treated by side firing burners 6 while said strip is catenary-supported in the furnace 1 between an out-of-furnace roll 2 on the inlet side and the floating device 5 on the outlet side. The high temp. gas is ejected from the devices 4a, 4b, 4c to the bottom surface side of the strip 3. The high-temp. gas is the out-of-furnace gas different of the in-furnace gas obtd. by introducing air and gaseous fuel through conduits 10a, 13a into a heater 11a to burn the air and fuel and supplying the resultant gas through a conduit 12a to the device 4a (the same holds true of the other devices 4b, 4c). The use of rolls is thus abolished and the flawing on the surface of the strip 3 in the furnace is prevented.

Description

[Detailed Description of the Invention] (Industrial Application Field) This specification refers to the heat treatment of metal strips that have strict requirements for surface quality, such as stainless steel strips, automotive steel plates, and other strip materials such as aluminum and copper. I
The following describes the results of research and development aimed at effectively avoiding contact scratches caused by passing J-tube through a heat treatment furnace.

Stainless steel strips, steel plates for automobiles, etc. are metal strips that require strict surface beauty, and when these metal strips are subjected to continuous heat treatment, extreme care must be taken to prevent scratches from forming on the surface. The same applies to strip materials such as aluminum and copper.

(Prior art) As a continuous annealing furnace for stainless steel copper strips, the
The one described in Publication No. 26723 is typical, and in order to prevent surface scratches from forming on the stainless steel strip, asbestos furnace rolls are used, and the number of rolls is minimized to provide so-called catenary support. The tension applied to the steel strip can be reduced.

However, since this catenary-type continuous annealing furnace uses rolls in the furnace, it is difficult to pick up scratches (metallic scratches).
Since it is impossible to completely eliminate the oxidized scale of the J-tube that adheres to and grows on the rolls, causing scratches on the surface of the IJ-tube, frequent replacement of the rolls in the furnace is necessary, which impairs the operating rate of the furnace. This is one of the factors.

Although it depends on the steel type, the maximum furnace temperature is usually 1100℃~11
On the other hand, asbestos rolls have a heat resistance temperature of about 600 to 700 degrees Celsius, which requires water cooling inside the rolls, which results in high heat loss, which is not desirable from an energy-saving perspective, and also causes temperature unevenness in stainless steel strips. There are also disadvantages.

On the other hand, in order to continuously heat-treat strip materials such as aluminum and copper, the gas in the furnace is circulated by a fan, and the circulating furnace gas is jetted against the strip material from fluid pressure pads placed opposite to each other toward the top and bottom surfaces of the strip material. A type of heat treatment furnace has been proposed in which floating support of the strip material is combined with heating, and this furnace has come to be used in drying and baking furnaces in coating lines for cold-rolled steel sheets.

In this case, although surface flaws such as pick-up do not occur on the strip material, sufficient floating edges cannot be removed, so only thin strips or strips with low specific gravity can be used. This is because when a pair of upper and lower fluid pressure pads is used to uniformly heat the upper and lower surfaces of the strip, static pressures Pu and Pd are generated on the upper and lower surfaces of the strip, respectively, and the difference between these The metal strip will be levitated by P = Pd - P u, but since the static pressure depends on the flow rate of the fluid, it is necessary to circulate the high-temperature furnace gas under high pressure.
Due to problems such as heat resistance, lifespan, and cost of the pressurizing fan, the number of floating blades must be limited. Therefore, a large number of fluid pressure pads are required with a narrow installation interval between the fluid pressure pad pairs. There are disadvantages to doing so.

(Problems to be Solved by the Invention) To solve the problem of surface scratches caused by pick-up, which is inevitable in catenary support of IJ tubes, the jetting force of high-temperature gas different from that of the furnace gas can be effectively utilized. It is an object of the invention to make possible a particularly advantageous avoidance.

(Means for solving problems) The above objectives are suitably achieved by the following steps.

In a direct-fired continuous heat treatment furnace for metal strip, high-temperature gas generated separately from the furnace gas is ejected toward the lower surface of the metal strip from at least one flotation device placed inside the heat treatment furnace. A method for heat treating a metal strip in a direct-fired continuous heat treatment furnace (first invention), in which a predetermined heat treatment is performed while the strip is catenary-supported inside the heat treatment furnace.

The following mechanisms are suitable for implementing this method:

Metal strip heat treatment apparatus in a direct-fired continuous heat treatment furnace, which is equipped with at least one flotation device in the furnace, and blows out high-temperature gas from the flotation device by a high-temperature gas generator disposed outside the furnace (second invention) ).

FIG. 1 shows a direct-fired continuous heat treatment furnace according to the present invention,
In the figure, 1 is the furnace body, 2 is the outside roof, 3 is the metal strip, 4.5 is the flotation device for supporting it, 6 is the side-fired direct fire burner, and 7 is the preheating zone on the entrance side of the furnace body 1. ,
8 is a flue. Although the illustration shows a case where a plurality of flotation devices 4 are arranged, distinguished by subscripts a, b, and 'c, at least one or more flotation devices are installed inside the furnace body 1 and spread between them,
Also, between the inlet side outer furnace roll 2 and the outlet side flotation device 5
A predetermined heat treatment is performed using a side firing burner 6 while supporting the metal strip 3 catenarily between the metal strips 3 and 3.

In this invention, the gas ejected from the flotation device 4 does not use the in-furnace gas, but instead provides a separate high-temperature gas generator outside the furnace, and the high-temperature gas generated from this is sent from the flotation device to the lower surface of the IJ tube. By ejecting the metal strip, a sufficient flow rate can be secured, and even a metal strip with a large thickness can be supported without contact, and the supporting force can be made sufficiently large, so the number of flotation devices 4 installed can be reduced. That's enough.

(Function) According to the present invention, the static pressure Pc (kg/cm2) generated on the IJ tube 3 by the flotation device 4 is
In the area shown in the figure, it is expressed by the following formula.

pc=ρv2βh (1+(1+cos θ)−)
(1,) where ρ: Original fluid density (kgf 5ec2
/m') V: Flow velocity at the jet curvature (m/5ec) θ: Inclination angle of the jet nozzle t: Slit width (m) h: Flying height (m) Also, the force F (kgf) received by the strip 3 is as follows: Expressed by the formula.

F = A - P C (2) Δvarnish) Area (m2) of the IJ knob that receives static pressure. Therefore, the metal strip 3 levitates under the floating height where its own weight and the force calculated by equation (2) match. It will be supported. This floating blade F is proportional to the square of the flow velocity. However, with the conventional method of circulating the gas in the furnace as mentioned earlier, the flow rate cannot be increased due to limitations in the fan capacity due to equipment costs, heat resistance, etc., whereas this invention A generator 9 is separately provided outside the furnace,
Since high-temperature gas is supplied to the flotation device 4 from this, restrictions or restraints originating from the gas temperature can be eliminated.

That is, if low-temperature gas is heated to a desired temperature by the heating device 11 between the booster fan and the flotation device 4 and then supplied to the flotation device 4, the flow velocity at this time has the following relationship.

Here, vl: Inlet flow rate of the heating device vo: Outlet flow rate TI of the heating device; Inlet temperature of the heating device To: Outlet temperature of the heating device The inlet temperature is 30°C and the outlet temperature is 850°C. Then, the flow velocity becomes approximately 1.93 times, and therefore the floating blade becomes approximately 3
．． It becomes seven times.

Furthermore, compared to a pair of hydraulic pressure pads according to the prior art, the floating blade becomes larger due to the fact that the downward force exerted by the upper hydraulic pressure pad does not work.

From the above, the present invention allows continuous heat treatment of thick metal strips as well.

Incidentally, a conventional example of a catenary-type heat treatment furnace is shown in FIG. 3, and 4a/, 4b/, and 4c/ are furnace rolls, and the flotation device 4 according to the present invention has the same arrangement pitch as this.
It is sufficiently possible to support a thick metal IJ tube by simply installing a (b) The contribution rate to the IJ tube heat treatment is significantly reduced, and temperature unevenness in the metal strip 3 does not occur. In Fig. 4, 15 is a heating gas nozzle 16 is a fan for pressurizing the gas in the furnace;
7 is a reheater. In other words, in the present invention, with respect to the flotation device 4, only the flotation blade needs to be considered, so various controls in heat treatment are very simple.

(Example) An example of application of the present invention to a direct-fired continuous heat treatment furnace for stainless steel strips will be described with reference to FIG.

Floating device 4 is provided with hot gases as combustion gases generated by the air guided in this example by conduit 10 contributing to the formation of a burner flame (not shown) in a combustion chamber as heating device 11. It can be supplied through a conduit 12 and ejected toward the metal strip 3 for catenary support, while being subjected to a predetermined heat treatment by a side-fired direct-fired burner 6. In the figure, 13 is a fuel gas conduit.

The flotation device 5 is in charge of flotation and support of the metal strip 3 by air injection, for example, on the outlet side of the furnace body 1, but it may be a roll as in the conventional case as long as there is no risk of scratching.

According to FIG. 1, flotation devices 4 were installed at intervals of 10 m.

At this time, the maximum furnace temperature is 1100 to 1150°C, so
The flotation device 4 had a heat-resistant structure made of heat-resistant steel (5ONi to 3QCr steel) with a 10° firebrick coating on the outside.

In addition, coke oven gas (calorific value 4300 kcal/N
m3) at a pressure of 2300 mm If20.
At the same time, the combustion air is supplied to the burner from
Air at a pressure of 2500 mm H 2 O, preheated to 00° C., was supplied through conduit 10 . The high temperature gas obtained by this high temperature gas generator 9 is supplied to the flotation device 4, and the thickness is 3 to 10 m.
m.

Stainless steel strip with a width of 1000 to 1500 mm at speed 3
When the stainless steel strip was passed through and annealed at 0 m/min, it floated stably under a lift with a floating height of about 20 to 30 mm directly above the flotation device 4, which prevented the occurrence of surface flaws in the furnace. I was able to eliminate all of them.

At this time, the temperature of the combustion gas is controlled within the range of 800-1100°C, and the pressure inside the flotation device 4 is controlled within the range of 1000-2000°C.
It was mmf120.

In this embodiment, the high-temperature gas ejected from the flotation device 4 is not the method of pressurizing low-temperature gas in advance and raising its temperature to high-temperature gas through heat exchange, as mentioned above, but directly uses combustion gas after combustion. , so the use of a fan was unnecessary.

In addition, in this embodiment, combustion gas was individually supplied from one combustion gas generator 9 to one flotation device 4, but after concentrating it in one gas generator 9,
The high temperature gas may be distributed and supplied to a plurality of floating devices 4.

Furthermore, in this embodiment, the catenary support of the metal IJ tube 3 is entirely carried out by the flotation device 4, but the flotation device 4 is used only in the areas where people can easily access the area, for example, the high temperature part, and the rest remains as before. It may also depend on the roll.

Morinko Hatada is applicable not only to continuous annealing of stainless steel strips, but also to various horizontal heat treatment furnaces such as non-oxidizing furnaces for continuous hot-dip galvanizing lines and drying and baking furnaces for color coating lines. It is possible to do so.

(Effects of the Invention) According to the present invention, the following numerous effects can be obtained.

(1) The floating blade can be dramatically enlarged, so
Thick metal strips can also be supported floatingly.
Therefore, by abolishing the use of rolls, it is possible to completely eliminate surface flaws in the furnace.

(2) For the same reason as above, it is possible to eliminate the maintenance required for rolls, and there is no need to stop the furnace when replacing rolls, which has the effect of improving production efficiency, improving energy consumption, and reducing the burden on workers. Significant.

(3) Furnace length can be shortened by eliminating the need for rolls.

For example, compared to the case shown in FIG. 3, it is possible to shorten the length by about 5 to 6 m.

(4) Since the metal strip is supported in a catenary-like manner, the number of flotation devices can be reduced, which simplifies the control inside the furnace. In other words, the flotation device has the functions of supporting and heating the metal strip, but since the flotation blades can be made large, there is no need to provide them at narrow intervals as shown in Figure 4, and the contribution rate of the flotation device to the heating of the metal strip can be reduced. Can be made smaller. Therefore, when changing the heat treatment conditions, the change can be made without much consideration of the flotation device.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of application of the present invention to a continuous annealing furnace for stainless steel copper strips, Fig. 2 is a diagram explaining the principle of a flotation device, and Fig. 3 is a sectional view of a conventional continuous annealing furnace for stainless steel copper strips. FIG. 4 is a sectional view and an AA sectional view of a heat treatment furnace using a conventional fluid pressure pad. 1...Furnace body 2...Furnace outer roll 3...
・Metal strip 4...Flotation device 6...Side-fired open fire burner

Claims (1)

[Claims] 1. In a direct-fired continuous heat treatment furnace for metal strips, high-temperature gas generated separately from the furnace gas from at least one flotation device disposed inside the heat treatment furnace, 1. A method of heat treating a metal strip in a direct-fired continuous heat treatment furnace, characterized in that the metal strip is ejected toward the lower surface thereof, and a predetermined heat treatment is performed while the strip is catenary-supported inside the heat treatment furnace. 2. Equipped with at least one or more flotation devices in the furnace,
1. A continuous heat treatment apparatus for metal strip in a direct-fired continuous heat treatment furnace, characterized in that high-temperature gas produced by a high-temperature gas generator disposed outside the furnace is ejected from a flotation device.