JPH0612709B2 - Atmosphere control device for induction heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention rapidly heats a steel material to a predetermined high temperature in a short time in a process of hot working such as rolling or pressing. The present invention relates to an induction heating furnace, and more specifically, it is intended to effectively prevent generation and melting of steel material surface scale in the induction heating furnace.

[Conventional technology]

In an induction heating furnace that rapidly heats steel to a predetermined high temperature within a short period of time, the state that the oxygen gas content of the furnace atmosphere and the amount of oxidation due to the surface temperature during steel heating change
Shown in the figure.

In Fig. 5, the curve a4 shows that the oxygen gas concentration in the furnace is 20%.
Curve a5 shows that the oxygen gas concentration in the furnace is 1%
And the curve a6 shows the change characteristics when the oxygen gas concentration in the furnace is 0.1% or less.

As is clear from Fig. 5, at least 1250 steel is used.
When heating above ℃, by reducing the oxygen gas concentration in the furnace, it is possible to significantly reduce the oxidation loss of the steel material, which can greatly improve the yield and prevent product surface defects due to scale generation. Becomes

In addition, when scale that is an oxide is generated on the surface of the steel material, the scale that is this oxide has a low melting point and
Since it melts at about ℃, this molten scale not only impairs the operability of the induction heating furnace, but also causes surface defects in the steel.
There is an inconvenience that causes many problems such as ear cracking.

Therefore, the control of the atmosphere in the induction heating furnace, that is, the control of the oxygen gas concentration in the furnace, has an important meaning, and an atmosphere gas such as an inert gas is enclosed in the furnace to prevent the oxidation of the steel surface. Countermeasures have been proposed and some measures have been reported.

For example, Japanese Utility Model Publication No. 58-24397, Japanese Utility Model Publication No. 48-
Japanese Patent No. 113741 and Japanese Utility Model Laid-Open No. 48-91555 disclose the means disclosed in these prior arts.
This is a method of feeding an inert gas into the furnace, and relates to a sealing structure at the lower part of the furnace. Basically, the inert gas is fed into the furnace from the outside of the furnace to control the atmosphere inside the furnace. It is supposed to be maintained at the set level.

[Problems to be solved by the invention]

However, these conventional means described above have the following inconvenient problems.

That is, since it is necessary to open the furnace at the time of charging and discharging the steel material into the furnace, it is not possible to prevent the outside air from entering the furnace, and the atmosphere in the furnace changes the opening and closing of the furnace. A large amount of it is replaced with the outside air at every operation, that is, a large amount of oxygen gas intrudes into the furnace from the outside every time the furnace is opened and closed.

An extremely large amount of inert gas is required in order to feed the inert gas into the furnace while allowing the large amount of oxygen gas to enter the furnace and thereby reduce the oxygen gas concentration in the furnace. .

Incidentally, the initial oxygen gas concentration in the furnace is set to 10%, and the amount of inert gas fed in to reduce the oxygen gas concentration is as shown in Fig. 6 according to the experimental results.

That is, as is clear from the curve a7 in Fig. 6, in order to set the oxygen gas concentration in the furnace to 5% of the initial oxygen gas concentration, an inert gas of about 5 times the volume in the furnace space is required. It becomes.

Further, since the characteristic of the induction heating furnace is that the steel material is rapidly heated to a predetermined high temperature within a short time, the atmosphere inside the furnace must be adjusted within a short time as a matter of course. However, if it takes a long time to adjust the atmosphere in the furnace, it becomes impossible to secure the productivity of the furnace.

Therefore, in an induction heating furnace in which charging and extraction of steel materials are repeated within a short time, it is possible to adjust the atmosphere in the furnace by only replacing the atmosphere in the furnace by pushing the inert gas into the furnace. It is clear that there is a speed limit.

[Means for solving problems]

The present invention was devised to solve the above-mentioned problems in the conventional example, and when a steel material is rapidly heated by an induction heating furnace, in order to achieve effective furnace atmosphere control, a furnace gas suction operation is performed. The present invention will be described below with reference to the drawings showing an embodiment of the present invention.

A furnace atmosphere control device for an induction heating furnace according to the present invention is a steel material.
Suction device 12 that sucks and discharges the furnace gas after inserting and sealing the heated steel material 15 into the furnace body 1 of the induction heating furnace that reheats 15 in the atmospheric gas, and the furnace gas suction by this suction device 12 A gas supply device 8 for supplying an atmosphere gas using an inert gas into the furnace body 1 after the discharging operation, an analyzer 6 for analyzing and detecting the oxygen gas concentration in the furnace body 1, and an analysis result signal of the analyzer 6. A controller 7 for controlling the amount of atmospheric gas supplied to the inside of the furnace body 1 of the gas supply device 8 in order to keep the oxygen gas concentration in the furnace body 1 below a predetermined constant value according to S1. There is.

The analyzer 6 constantly samples the gas in the furnace body 1 and analyzes and detects the concentration of oxygen gas in the collected gas. The detected value of the concentration of oxygen gas is constantly controlled as a signal S1. It is output to the container 7.

The controller 7 is composed of a microcomputer or the like, and according to the signal S1 from the analyzer 6, the gas supply device 8
The supply amount of the atmospheric gas into the furnace body 1 is controlled.

[Action]

The in-furnace atmosphere control device according to the present invention is configured as described above. Next, the basic operation of the present invention device will be described in order.

The analyzer 6 samples the furnace gas from the sampling port 5 formed in the furnace body 1, continuously analyzes and detects the oxygen gas concentration in the furnace gas, and outputs the detection signal S1 to the controller 7 Is output to.

From this state, the skid portion 3 loaded with the steel material 15 rises to load the steel material 15 into the furnace body 1 and at the same time seal the furnace body 1.

When the sealing of the furnace body 1 is achieved, a current is supplied to the heating coil 2 to start the induction heating operation of the steel material 15. At the same time when the heating operation of the induction heating furnace is started, the control start signal S2 is sent to the controller 7. Is output.

That is, the control start signal S2 is output to the controller 7 by the door closing signal.

When the control start signal S2 is input, the controller 7 outputs the control signal S3 according to the signal S1 to the gas supply device 8 and the suction device 12.

Due to the input of the control signal S3 from the controller 7, the gas supply device 8 first shuts off the supply path of the atmospheric gas into the furnace body 1, while the suction device 12 operates to remove the gas in the furnace body 1. Aspirate and discharge.

After the suction device 12 has been operated for a desired time, the suction device 12 is stopped, and at the same time, the gas supply device 8 is operated to feed an atmospheric gas into the furnace body 1 to restore the pressure inside the furnace body 1 and then analyze it. The input value of the atmospheric gas from the gas supply device 8 into the furnace body 1 is controlled by the control signal S3 so that the analysis value by the total 6, that is, the oxygen gas concentration becomes equal to or less than the preset target concentration, and thus the constant oxygen gas is maintained. The induction heating operation of the steel material 15 below the concentration is achieved.

〔Example〕

In the case of the embodiment shown in FIG. 1, the side wall of the furnace body 1 is provided with a suction / charge port 4 for sucking the gas inside the furnace and for charging the atmospheric gas into the furnace body 1, and A furnace body gas sampling port 5 is formed on the top wall of the opening 1.

The sampling port 5 is formed on the top wall of the furnace body 1 because the temperature inside the furnace is at a level considerably higher than the temperature outside the furnace, and therefore the gas inside the furnace flows upward in the furnace due to the draft effect. Therefore, it is considered that the atmosphere in the upper part of the furnace is more representative.

However, this is generally true, and it goes without saying that it can be arbitrarily determined depending on the peculiarities of the equipment.

The in-furnace gas sampled from the sampling port 5 is introduced into the analyzer 6 to analyze and grasp the components in the in-furnace gas.

Since the purpose of the device of the present invention is to make the inside of the furnace body 1 as non-oxidized as possible, it is necessary to control the oxygen gas concentration in the furnace. A total (eg, zirconia type) is optimal.

From the oxidation weight loss characteristics shown in Fig. 5, it is desirable that the oxygen gas concentration be 1% or less for heating above 1250 ° C, as the control target value of the oxygen gas concentration in the furnace.

The analysis / detection value of oxygen gas concentration by this analyzer 6 is a signal
It is input to the controller 7 as S1.

A gas supply device 8 and a suction device 12 for the suction / input port 4
Are connected in parallel, and the gas supply device 8 includes an inert gas source 9 as an atmospheric gas, a flow rate control valve 10, and a flow meter.
11 and the suction device 12 is composed of a vacuum pump 13 and a switching valve 14.

The embodiment shown in FIG. 1 is operated in the following order.

First, the steel material 15 is loaded on the skid portion 3 and lifted up, so that the steel material 15 is loaded into the furnace body 1.

Next, when the lower door (not shown) is stopped at the raised position, a door closing signal is transmitted, the flow rate control valve 10 is closed, the switching valve 14 is opened, and the vacuum pump 13 is started.

The door open signal may be directly input to the flow rate control valve 10, the switching valve 14 and the vacuum pump 13.
In the case of the embodiment shown in FIG. 1, a start command signal S2 is input to the controller 7, and the controller 7 sends the control signal S3 according to the input of this signal S2 to the flow control valve 10, the switching valve 14 and the vacuum pump 13. Output to.

This control signal S3 is output as a "closed" signal to the flow rate control valve 10 and is output as a "closed" signal to the switching valve 14 at the beginning when it is transmitted according to the input of the command signal S2. Then, it is output to the vacuum pump 13 as a start signal.

When the suction / discharge of the gas in the furnace by the vacuum pump 13 progresses and the analysis value of the oxygen gas concentration by the analyzer 6 becomes less than or equal to the preset target value and the induction heating furnace enters the steady operation, the controller 7 Signal S3, the vacuum pump 13 is stopped, the switching valve 14 is closed, and the flow rate control valve 10 is fully opened.

When the flow rate control valve 10 is fully opened, an inert gas source 9 supplies atmospheric gas such as nitrogen gas into the furnace body 1 at a stroke,
The pressure inside the furnace body 1 is restored, and after the pressure inside the furnace body 1 is restored, the opening of the flow control valve 10 is adjusted so that the analysis value by the analyzer 6 becomes a preset target value. 9 to furnace body 1
Control the amount of atmospheric gas input into the inside.

The case where the switching valve 14 is opened / closed by the signal S3 from the controller 7 has been described. However, the opening / closing of the switching valve 14 and the start / stop control of the vacuum pump 13 require that the internal volume of the furnace body 1 be constant. Therefore, it is possible to control with the timer starting from the point of time when the door closing signal is transmitted.

However, during the above-mentioned series of control operations, even if the in-furnace gas is continuously sucked for an appropriate fixed time, the oxygen gas concentration in the in-furnace gas does not decrease or a certain amount of atmospheric gas or more If the oxygen gas concentration in the furnace gas does not decrease even after the gas is charged into the furnace body 1, it is considered that a serious problem has occurred in the sealing performance of the induction heating furnace. The operator can be notified by means of a display, etc., and fundamental measures can be implemented early.

Next, an example of one implementation result is shown.

As shown in Fig. 2, the internal dimensions of the furnace body 1 are that the length R1 is 1250.
With a width R3 of 450 mm and a height R2 of 1800 mm, the dimensions of the steel material 15 charged and heated in the furnace body 1 are that the length K1 is
It measures 12200 mm, width K3 is 215 mm, and height K2 is 1300 mm.

Therefore, the volume inside the furnace body 1 excluding the volume of the steel material 15 is 6.7 m.
It becomes ³ .

The heating pattern for steel material 15 is 30 minutes heating, 5
The temperature distribution characteristic curve a1 of the steel material 15 has a form as shown in FIG.

The steel material 15 is hot-charged for the purpose of reducing the electric power consumption of the induction heating furnace, and the surface temperature of the steel material 15 is continuously measured by the radiation thermometer attached to the furnace wall of the furnace body 1. It is warm.

In this specific example, the heating temperature of the steel material 15 is
Since it is as high as 1300 ° C, as is clear from Fig. 5, it is necessary to control and control the oxygen gas concentration in the furnace gas to 1% or less in order to suppress the oxidation loss to a sufficiently small value.

At the start of heating the steel material 15 (when charging is completed in Fig. 3,
At time t1 in FIG. 4), the oxygen gas concentration in the furnace becomes high due to the invasion of outside air into the furnace body 1 by opening the lower door.

In this specific example, the oxygen gas concentration in the furnace gas is set to 1% or less during the furnace gas suction time of about 5 minutes (from time t1 to time t2 in FIG. 4).

As is clear from the steel material surface temperature change curve a1 shown in Fig. 3, the surface temperature of the steel material 15 is about 1100 ° C 5 minutes after the start of heating. Since it is not necessary to lower the suction speed quickly, the suction speed is set to the above-mentioned time.

As is clear from Fig. 4, after completion of the gas suction in the furnace (time point
After t2), a large amount of nitrogen gas, which is the atmospheric gas, is rapidly injected into the furnace because it is necessary to restore the internal pressure to the positive pressure of atmospheric pressure + α (α is about +1 mmH ₂ O).

After the time t3 when the recompression in the furnace is achieved, the control of the amount of the atmospheric gas introduced into the furnace is started according to the analysis value of the oxygen gas in the furnace gas, and the operation is steady.

In addition, the oxygen gas concentration curve a3 clearly shows that the oxygen gas concentration in the furnace gas is controlled within the range of 0.5 to 1% in the high temperature region where the surface temperature of the steel material 15 is easily oxidized at 1250 ° C or higher. Shows.

〔The invention's effect〕

As is clear from the above description, the furnace atmosphere control device for an induction heating furnace according to the present invention can reduce the oxygen gas concentration in the furnace gas to a sufficiently low target value or less within an extremely short time. The rapid heating of steel material within a short time, which is a characteristic of the induction heating furnace, can be fully utilized, and thus high productivity of the furnace can be secured.

In addition, the amount of atmospheric gas consumed to bring the oxygen gas concentration in the furnace gas below the target value can be made much smaller than in the conventional case, thereby reducing the amount of atmospheric gas consumed. In addition, it is possible to reduce the size and simplification of the equipment related to the atmosphere gas, which is highly economical.

Furthermore, it is known in advance that the degree of decrease in the oxygen gas concentration in the furnace gas due to the suction and discharge of the furnace gas has a substantially constant characteristic. The gas tightness of the furnace can be detected early and surely, and thereby good steel heating can be achieved. Therefore, it is possible to replace the gas in the furnace in a short time. It is possible to reduce the required amount of input gas, and the inside of the furnace is cooled by pushing gas replacement and the heating efficiency of the furnace is reduced, but in the device of the present invention with a small amount of pushing gas, it is possible to improve the furnace efficiency It is the one that exhibits the excellent effect of.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the configuration of the device of the present invention. FIG. 2 is a perspective view of a furnace body showing a specific example for carrying out the function of the device of the present invention. FIG. 3 is a diagram showing the characteristics of the surface temperature of the steel material by the induction heating furnace. FIG. 4 is a supply amount change curve diagram of the inert gas into the furnace and an oxygen gas concentration change characteristic diagram in the furnace showing an example of the control operation by the device of the present invention. FIG. 5 is a diagram showing the relationship between the furnace temperature and the surface oxidation loss of steel. FIG. 6 is a diagram showing the relationship between the oxygen gas concentration in the furnace and the replacement amount of the gas in the furnace. DESCRIPTION OF SYMBOLS 1; Furnace body, 2; Heating coil, 3; Skid part, 4; Suction / inlet port, 5; Sampling port, 6; Analyzer, 7; Controller, 8;
Gas supply device, 9; Inert gas source, 10; Flow control valve, 1
1; flow meter, 12; suction device, 13; vacuum pump, 14; switching valve, 15; steel material.

Claims (1)

[Claims] 1. A suction device for sucking and discharging the furnace gas after inserting and sealing the heated steel material into an induction heating furnace for reheating the steel material in an atmospheric gas, and a furnace gas suction and discharge operation by the suction device. A gas supply device for supplying an inert gas atmosphere gas into the furnace later, an analyzer for analyzing and detecting the oxygen gas concentration in the furnace, and an oxygen gas concentration in the furnace according to the analysis result signal of the analyzer. A furnace atmosphere control device for an induction heating furnace, comprising: a controller for controlling an amount of atmosphere gas supplied to the furnace of the gas supply device so as to be equal to or less than a preset constant value.