JPS5952933B2 - Continuous furnace for sequential heat treatment of strip coils - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous furnace for sequential heat treatment of strip coils, and particularly aims to propose a new continuous furnace of this kind in which the gas in the furnace is appropriately treated to eliminate its harmful effects. It is.

In general, an atmospheric gas containing N2 is often used for heat treatment of rolled strip coils of metals, especially silicon steel strips, in the form of coils, especially annealing in a non-oxidizing atmosphere. Cover with matzuru,
The atmospheric gas is supplied to the inside of the matsufuru, and indirect heating is performed outside the matsufuru using an electric heater or a radiant tube, or sometimes direct heating is performed by a direct-fired burner using gas or liquid fuel.

Here, so-called sand seals, ceramic wool seals, etc. are generally applied to the hem of the matsufuru, and it is difficult to achieve a complete seal. During the heat treatment, the atmosphere gas supplied to the Matsufuru passes through the hem seal and leaks into the furnace. As a result, the high-temperature interior of the furnace becomes an atmosphere similar to that inside the Matsufuru, and the above-mentioned gas is contained in the heat treatment atmosphere gas. When the furnace gas contains N2, there is a risk that the gas inside the furnace will come into contact with the outside air and cause an explosion, which is a particular concern in continuous furnaces where heat treatment proceeds between the sequential insertion and rapid advance of a large number of strip coils into the furnace. be done.

Therefore, in the past, double barrier layers 2 and 3 were provided on the upper and outlet sides of the continuous furnace 1 shown as a typical example of a trolley-type tunnel furnace in Figures 1 and 2, respectively, and the barrier compartments 4 and 5 were A complicated operation such as replacing the inside with an inert atmosphere such as N2 gas is required every time a strip coil is loaded or unloaded. Piping and wiring that penetrate the furnace wall that looks like hail 6
．． In order to ensure the sealing around the double barrier layer 2.3 or even the double barrier layer 2.3 itself, the furnace construction structure had to be complicated.

In the figure, 8 is a trolley, 9 is a matsufuru, 10 is a hem seal, 1
1 is a strip coil, 12 is an electric heater, 13 is a supply pipe for heat treatment atmosphere gas, and 14 is a coupler for connecting and disconnecting the coils.

In addition to the above, if atmospheric gas containing N2 leaks into the furnace, it will penetrate the furnace wall and impair its insulation properties, resulting in a reduction in thermal efficiency. The above-mentioned sealing measures generally prevent flammable gases such as CO from escaping out of the furnace, even when using them as the heat treatment atmosphere gas.
This is also requested because it is considered essential in terms of safety and health management.

The applicant company's prior development efforts in this regard include, for example, as shown in Japanese Patent Application Laid-Open No. 54-96408.
Numerous benefits have been brought about by introducing preheated air into the furnace and igniting and burning the combustible components in the gas inside the furnace to render it harmless.

This invention is the result of further development efforts based on the results, and has made it possible to more appropriately and easily treat leaked combustible gas, especially in the low temperature range inside the furnace.

In other words, especially when attempting to burn flammable gas in the low-temperature region indicated by a in Figure 1, an ignition system is essential, and the difficulty of preventing and managing the ignition system has been solved particularly advantageously. It is something to do.

This invention uses a strip coil covered with Matsufuru.
There is an inlet opening where matsufuru is sealed and sequentially charged into the furnace, an outlet opening where the matsufuru are sent from the heating zone through the soaking zone to the cooling zone and then taken out, and the high temperature area inside the furnace. It consists of a tunnel furnace equipped with a barrier layer between the upper and lower temperature regions, and a supply system that introduces atmospheric gas containing flammable gas into the inside of the Matsufuru that are successively fed through the furnace, and a seal at the bottom of the Matsufuru. A series of strip coils each having an air supply system for completely combusting the flammable gas leaked into the furnace in the high temperature region of the furnace and diluting it to a concentration below the flammability limit in the low temperature region of the furnace. This is a continuous furnace for heat treatment.

In carrying out this invention, the heat source applied to the high temperature range of the continuous furnace may be an electric heater or a radiant tube as usual, but instead of a direct-fired burner that uses gas or liquid fuel at least in part, It is possible to use the combustion air in excess of the stoichiometric mixture ratio for complete combustion of the flammable gas leaking into the furnace in the high temperature range.

3 and 4 show an embodiment of the present invention in which an electric heater is used as a heat source, and the double barrier layers 2, 3, which are indispensable in the above-mentioned prior art, and therefore the barrier chambers 4, 5 are eliminated. These have been completely abolished and replaced with a single plate-shaped barrier layer 2.
', 3' together with an intermediate partitioning barrier layer 15 that partitions the low-temperature area a from the high-temperature area in the furnace,
1 and 2 except that an air supply system 16 opened at the bottom of the furnace in the high temperature zone and low temperature zone a, and an exhaust system 17 similarly placed at the top of the furnace. The structure is almost the same as the one described above.

In FIG. 3, 18 is an exhaust pipe, 19 is a stack, and 20 is a fan.

In addition, in FIG. 5, the heat treatment atmosphere gas is also supplied from the supply pipe 13.
An example of an attachment/detachment operation system for supplying air to the piping 6 into each Matsufuru 9 is shown. A supply pipe 13 is connected to the gas main pipe 22 by a flexible pipe 21, and the supply pipe 13 is connected to a predetermined position in the furnace. A coupler 14 that airtightly fits each of the pipes 6 hanging down from the bogie 8 to be stopped is provided, and an elevating cylinder 23 is provided for the attachment/detachment operation of the coupler. have them do it.

Note that the coupler 14 may be provided with a self-closing valve that controls the air supply stop at this time.

The air supply system 16 is connected to a high temperature region a and a low temperature region a of the continuous furnace 1.
It is possible to use separate and independent systems for these, but if it is possible to distribute the air supply amount as described later, a common pressurizing source may be used.

To operate the continuous furnace configured as described above, air is first supplied into the furnace from the air supply system 16, and then preparations are made to raise the temperature of the heating zone and then the soaking zone to a predetermined temperature, and then the door 2' is opened and the trolley 8 is opened. Then, the strip coil 11 surrounded by Matsufuru 9 is charged into the furnace, and the heat treatment step of introducing a heat treatment atmosphere gas containing flammable gas into the interior of Matsufuru 9 is successively carried out, until the high temperature region is filled. Later, the intermediate barrier layer15
Further, when the low temperature region a is filled, the outlet insulation layer 3' is also opened and closed at the same time as the input insulation layer 2', and the next coil is loaded and the processed coil is taken out at the same time.

During this operation, the flammable gas that passed through the hem seal of Matsuful 9 and leaked into the furnace had an ignition temperature of 57°C in the high temperature range, since the heat treatment temperature is generally 760°C or higher.
When H2 at 0° C. is used as an atmospheric gas, it also burns immediately.

The amount of air supplied here is that the concentration of N2 that burns is 4% to 74% of the air ratio, so the amount of air supplied is 0.4% to H21m3.
~24 m3, and the combustion exhaust gas is discharged from the exhaust system 17 to the stack 19 via the exhaust pipe 18.

The N2 gas leaking from the hem of the Matsuful 9 in the cooling zone, that is, the low-temperature area a, is diluted to 4% or less, which is the lower limit of combustion, by a particularly large amount of air sent from the air supply system 16, and is exhausted without being combusted. It is discharged from the system 17 through the stack 19 into the atmosphere.

In this case, the amount of air blown into the low temperature area inside the furnace is N2 gas 1
m” requires 24 m3 or more.

Thereafter, in the same manner, the materials to be annealed are sequentially charged into the furnace and passed through the heating zone and the cooling zone a in the furnace, and then taken out from the furnace through the outlet shutoff door 3' to complete the annealing.

If the method of the present invention is used to completely treat N2 gas leaking into the furnace, no particularly complicated furnace control is required.

In other words, the amount of N2 gas supplied into Matsufuru is
When supplying air in the range of 0.5 to 8 m3/h per piece, in high temperature range, the amount of air supplied per piece of Matsufuru is 2 to 1.
If it is in the range of 2 m/h, it falls within the combustion range of N2 of 4 to 74%, so the fan 20 may have a constant discharge rate.

In other words, even if the N2 gas supply amount changes in the range of 0.5 to 5.11 = /h, if the supplied air amount is within the range of 2 to 12 m3/h, it will always be 4 to 74% as shown below. fall within range.

When N2: 0.5m3/h, the required air volume is set as
”/h or more, a fan with a constant discharge amount may be used.

In other words, in order to dilute N2 gas to a range where it will not burn, N2
It is best to keep the concentration below 4%.

Therefore, the amount of dilution air when the amount of N2 supplied is at its maximum is sufficient for the amount of N2 gas below that amount.

That is, for a supplied N2 quantity of 0.5 to 5 m"/h, the lower limit of the supplied air quantity is:

If the fan is above this value, a certain amount of fan can feed the necessary and sufficient air into the furnace.

Therefore, safety measures such as providing a backup unit for both fans 20 and always having a diesel generator on hand as a power source in case of a power outage are sufficient.

Although the above embodiments of the invention have been described with respect to a continuous furnace consisting of a direct tunnel furnace, it goes without saying that the same method can be applied to a rotary hearth type continuous furnace.

For the sake of clarity, a continuous furnace using a rotary hearth 8' is shown in FIG. 6, with common numbers and symbols attached to the same structures as those already described, so that the operation and effect will be easily understood.

■ In conventional furnaces, N leaks from the Matsufuru into the furnace.
In order to prevent combustible gases such as 2 from coming into contact with air, the inlet and outlet of a continuous furnace are separated from the inside of the furnace by double shutoff doors that can be opened and closed, and each of these rooms is equipped with N2, etc. A large amount of inert gas is required, and sealing between the inlet chamber or the outlet chamber and the opening/closing door that separates the inside of the furnace from the outside air, or
Whereas seals for piping and wiring penetrating from outside the furnace to the inside of the furnace, such as couples for measuring furnace temperature, atmospheric gas, and supply gas pipes, had a complicated structure, the method of the present invention reduces the furnace structure. becomes extremely simple.

■ The thermal conductivity of a heat insulating material in an N2 atmosphere is much higher than that in air or combustion gas, reaching 2 to 2.7 times, increasing the heat radiated from the furnace body. Even when atmospheric gas is used, there is no stagnation in the furnace, which greatly contributes to improving thermal efficiency.

■ 2.572kcal/ms by N2 gas combustion
- Since the calorific value of N2 can be used to raise the furnace temperature, when using C gas to heat the furnace, you can save approximately 0.6 m'' of C gas for 1 m'' of N2 gas, and even when using kerosene. N
This leads to an energy saving of approximately 0.31 for 1 m'' of 2 gases, and an even more significant energy saving effect is achieved when using electric heaters or radiant tubes.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an example of a conventional continuous atmosphere heat treatment apparatus for metal strip coils, FIG. 2 is a cross-sectional view thereof, FIG. 3 is a longitudinal cross-section of a continuous heat treatment apparatus according to the present invention, and FIG.
The figure is a cross-sectional view, FIG. 5 is an explanatory diagram showing an atmospheric gas supply piping system, and FIG. 6 is a plan layout diagram of a rotary hearth type continuous furnace. 1...Continuous furnace, 2', 3'...Shiya fault at each opening on the exit side, 6...Piping, 9...
...Matsuful, 10...Hem sticker, 15...
. . . Intermediate isolation layer, 13 . . . Atmosphere gas supply pipe, 16 . . . Air supply system.

Claims (1)

[Claims] 1 An entry opening where strip coils covered with Matsufuru are sequentially charged into the furnace with a Matsufuru hem seal applied, and an exit opening where the strip coils are sent from the heating zone in the furnace through the soaking zone to the cooling zone and then taken out. The furnace consists of a tunnel furnace that is equipped with a barrier layer between the high-temperature region and the low-temperature region in the furnace, and an atmospheric gas containing flammable gas is introduced into the matsufuru, which are successively fed through the furnace. Air supply system that completely burns the combustible gas leaked into the furnace through the supply system and the Matsufuru hem seal in the high-temperature region of the furnace, and dilutes it to a concentration below the flammability limit in the low-temperature region of the furnace. A continuous furnace for sequential heat treatment of strip coils, characterized in that it has a system.