JP2024080372A - Atmospheric heat treatment furnace - Google Patents

Abstract

To provide an atmosphere heat treatment furnace capable of preventing the intrusion of outside air into the furnace by holding the furnace internal pressure above atmospheric pressure and suppressing the use of excessive pressure adjustment gas.SOLUTION: An atmosphere heat treatment furnace 10 has a pressure detector 68 for detecting furnace internal pressure, pressure adjustment gas introducing means, and furnace internal pressure control means 80 including a pressure control part 72 for adjusting the amount of pressure adjustment gas introduced into the furnace through the pressure adjustment gas introducing means. When the difference between the detected temperature and the target temperature detected by a temperature detector 28 is equal to or greater than a predetermined value, the furnace internal pressure control means 80 executes sequence control for setting the introduction amount of the pressure adjustment gas to a predetermined amount, and when the difference between the detected temperature and the target temperature is less than a predetermined value, it executes feedback control for feeding back the pressure detected by the pressure detector 68 to adjust the introduction amount of the pressure adjustment gas.SELECTED DRAWING: Figure 3

Description

This invention relates to an atmospheric heat treatment furnace suitable for use in heat treatment of steel materials, etc.

In an atmospheric heat treatment furnace using an endothermic gas, a drop in furnace pressure can cause problems such as deterioration of the atmosphere due to the intrusion of outside air and abnormal combustion. For this reason, in conventional atmospheric heat treatment furnaces, a constant amount of inert gas such as _N2 is fed into the furnace as a pressure adjusting gas so that the furnace pressure is higher than atmospheric pressure (see, for example, Patent Document 1 below).

However, the pressure inside the furnace fluctuates depending on the heating/cooling conditions and the amount of endothermic gas being fed, and the pressure inside the furnace also drops during cooling or when endothermic gas is not being fed. If an attempt is made to maintain the pressure inside the furnace, for example during cooling, by feeding a constant amount of pressure regulating gas, excessive pressure regulating gas will be fed into the furnace during heating. Excessive feeding leads to increased use of inert gas (pressure regulating gas) and dilution of the endothermic gas, resulting in increased operating costs.

JP 2010-132997 A

In light of the above circumstances, the present invention aims to provide an atmospheric heat treatment furnace that can maintain the pressure inside the furnace at or above atmospheric pressure, preventing outside air from entering the furnace, and suppressing the use of excessive pressure adjustment gas.

The atmospheric heat treatment furnace according to the first aspect of the present invention is defined as follows:
A furnace body,
An atmosphere control means for controlling the flow rate of an atmosphere adjusting gas supplied into the furnace so that a carbon potential index value determined from the CO concentration and the _CO2 concentration in the furnace atmosphere becomes a predetermined value;
an in-furnace temperature control means including a temperature detector for detecting an in-furnace temperature, a heating means, and a temperature control unit for adjusting a control output for the heating means so that the detected temperature received from the temperature detector approaches a target temperature;
a pressure detector for detecting the pressure inside the furnace, a pressure adjusting gas introduction means, and an in-furnace pressure control means including a pressure control unit for adjusting the amount of the pressure adjusting gas introduced into the furnace through the pressure adjusting gas introduction means;
having
The furnace pressure control means is
When a difference between the detected temperature detected by the temperature detector and the target temperature is equal to or greater than a predetermined value, or when a control output for the heating means is equal to or greater than a predetermined value, a sequence control is executed to set the pressure adjusting gas introduction amount to a predetermined amount;
When the difference between the detected temperature and the target temperature is less than a predetermined value, or when the control output for the heating means is less than a predetermined value, feedback control is executed to adjust the amount of the pressure regulating gas introduced by feeding back the detected pressure detected by the pressure detector.

According to the atmospheric heat treatment furnace of the first aspect thus defined, the amount of pressure adjustment gas introduced is adjusted by feeding back the detected pressure, so that the amount of pressure adjustment gas used can be reduced compared to the case where a constant amount is continuously introduced into the furnace.
Here, it is recognized that the detection value (detection pressure) detected by the pressure detector may vary widely under a specific heating condition. In the atmospheric heat treatment furnace of the first aspect, by selectively using a sequence control that does not use the detection value by the pressure detector and a feedback control that uses the detection value by the pressure detector according to the heating condition, it is possible to avoid problems caused by the variation in the detection value of the furnace pressure, while maintaining the furnace pressure at or above atmospheric pressure to prevent the intrusion of outside air into the furnace and suppress the use of excessive pressure adjustment gas.

Here, the pressure detector may be configured to include a plurality of pressure detectors.
In this case, the furnace pressure control means can further include a low selector which selects the smallest detection value among the detection values received from each pressure detector and outputs it as the detected pressure in the furnace (second aspect).

When the pressure detectors are configured to be multiple, the furnace pressure control means can further include a transmission anomaly determination unit that determines that there is an anomaly in the transmission from the pressure detector when the difference between the detection values transmitted from the two selected pressure detectors is equal to or greater than a predetermined value for a predetermined period of time or longer (third aspect).

The fourth aspect of the present invention is defined as follows:
In any one of the first to third aspects, in an atmospheric heat treatment furnace, a gas introduction pipe for introducing the atmospheric adjustment gas and the pressure adjustment gas into the furnace;
a flow rate detector for detecting a flow rate of the atmosphere adjusting gas;
a valve opening degree calculation unit that calculates a valve opening degree of the pressure regulating gas supply means necessary for preventing flashback in the gas introduction pipe as a control output;
a high selector that outputs the larger of the control output calculated by the feedback control and the control output calculated by the valve opening degree calculation unit as a control output for the pressure regulating gas supply means;
It further comprises:

According to the atmospheric heat treatment furnace of the fourth aspect thus defined, at least the flow rate required to avoid flashback is maintained in the gas introduction pipe, so that flashback can be avoided when the amount of pressure adjustment gas introduced is suppressed by feedback control.

1 is a diagram showing a schematic overall configuration of an atmospheric heat treatment furnace according to an embodiment of the present invention; 2 is a schematic diagram showing elements related to temperature control in the atmospheric heat treatment furnace of FIG. 1. 2 is a schematic diagram showing elements related to control of the atmosphere and pressure in the atmospheric heat treatment furnace of FIG. 1. FIG. 4 is a functional block diagram illustrating a configuration of a pressure control unit. FIG. 5 is a functional block diagram illustrating a configuration of a feedback control execution unit in FIG. 4 . 11 is a diagram showing a change in detected pressure during heat treatment using the atmospheric heat treatment furnace of the present embodiment, together with a heat pattern, etc. FIG. This is a modified example that further adds a function for preventing flashback in the gas introduction pipe. This is a modified example in which a plurality of pressure detectors are provided. FIG. 13 is an explanatory diagram of an alarm output unit when a plurality of pressure detectors are provided.

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the schematic overall configuration of an atmospheric heat treatment furnace according to one embodiment of the present invention. In the figure, 10 is a batch-type atmospheric heat treatment furnace used for annealing wire coils, steel bars, etc., and a heating chamber 13 is formed inside a box-shaped furnace body 12. An entrance/exit 14 is formed at one end in the longitudinal direction of the furnace body 12, and the workpiece to be heated is loaded into the furnace (heating chamber 13) through the entrance/exit 14 by a group of rollers 15. The entrance/exit 14 can be opened and closed by a door 17 connected to a drive unit 16.

The heating chamber 13 is equipped with multiple radiant tube burners 20 and ceiling fans 24 arranged along the conveying direction (longitudinal direction), and is connected to a gas inlet pipe 19 for introducing various gases.

Figure 2 is a schematic diagram showing elements related to the furnace temperature control in the atmospheric heat treatment furnace 10. As shown in the figure, the atmospheric heat treatment furnace 10 is equipped with a temperature detector 26, multiple radiant tube burners 20 as heating means, and a temperature control unit 43. These constitute the furnace temperature control means 45 in the present invention.

The temperature detector 26 detects the temperature inside the furnace and transmits the temperature information to the temperature control unit 43. There are no particular limitations on the type of temperature detector 26, but known thermocouples and radiation thermometers can be used taking into account the measurable range, responsiveness, etc.

The radiant tube burner 20 is equipped with a pipe-shaped tube body 21 and a combustion burner 22 arranged coaxially in the hollow part at one end of the tube body 21. A fuel supply pipe 30 and an air supply pipe 36 are connected to the combustion burner 22, and a flow control valve 33 is provided on the main pipe 31 side of the fuel supply pipe 30, and a flow control valve 39 is provided on the main pipe 37 side of the air supply pipe 36. Manual valves 34, 40 are provided on each branch pipe 32, 38 of the fuel supply pipe 30 and the air supply pipe 36, and the valve opening is adjusted in advance so that fuel gas and combustion air are supplied evenly to each combustion burner 22.

The temperature control unit 43 adjusts the control output for the radiant tube burner 20 so that the detected temperature received from the temperature detector 26 approaches a preset heat pattern (target temperature) during operation. A control signal corresponding to this control output is sent to the flow control valves 33 and 39, which increase or decrease the opening of these flow control valves 33 and 39 to control the heat of the combustion burner 22. In addition, when cooling the inside of the furnace, the supply of fuel gas is stopped and only air is circulated inside the tube body 21.

In addition, in this example, the temperature control unit 43 outputs information regarding the difference between the detected temperature detected by the temperature detector 26 and the target temperature to the pressure control unit 72 described later.

Such a temperature control unit 43 can be realized, for example, by a PLC (Programmable Logic Controller) equipped with a data processing unit, a memory unit, a communication I/F unit, etc., or a temperature regulator. Similarly, the atmosphere control unit 66 and pressure control unit 72 described below can also be realized by a PLC or various regulators.

Next, the atmosphere control in the furnace will be described. In this example, an endothermic modified gas is used as the atmosphere gas. The endothermic modified gas is generally called RX gas, and is mainly composed of CO, _H2 , and _N2 . In this example, the RX gas is used, and the carbon potential index value (PF) determined by the ratio of _CO2 % to the square of CO% in the atmosphere gas in the furnace shown in the following formula (1) is controlled to a target value, thereby making it possible to create an atmosphere in the furnace in which decarburization or carburization does not occur.
PF=(CO%) ² / _CO2 %...Equation (1)

As shown in FIG. 3, an RX gas supply pipe 47, _N2 gas supply pipes 48, 49, 50 and an air supply pipe 51 are connected to the gas inlet pipe 19 connected to the furnace body 12, and a check valve 54 is connected to a gas delivery pipe 53 connected to the furnace body 12.

The RX gas supply pipe 47 supplies the RX gas generated by the RX gas generator 56 to the gas inlet pipe 19 and introduces the gas into the furnace via the gas inlet pipe 19, and is equipped with a flow rate control valve 58 and a flow rate detector 59.
The N ₂ gas supply pipe 49 supplies N ₂ gas from an N ₂ gas supply source 61 to the gas introduction pipe 19 and introduces the N 2 gas into the furnace via the gas introduction pipe 19 , and is equipped with a flow rate control valve 64 .
The air supply pipe 51 supplies air from an air supply source 62 into the furnace via a gas introduction pipe 19, and is equipped with a flow rate control valve 63.
The RX gas supply pipe 47, the N ₂ gas supply pipe 49 and the air supply pipe 51 are used to introduce various gases into the furnace in PF control using a carbon potential index value (PF).

In FIG. 3, 65 is an analyzer, and 66 is an atmosphere control unit.
The analyzer 65 measures the CO ₂ gas concentration (CO ₂ %) and CO gas concentration (CO %) inside the furnace, and sends the measurement signals to an atmosphere control unit 66 .
The atmosphere control unit 66 is connected to the analyzer 65 as well as the flow rate control valves 58, 64, and 63 on the RX gas supply pipe 47, _N2 gas supply pipe 49, and air supply pipe 51. The atmosphere control unit 66 receives a measurement signal from the analyzer 65, calculates the carbon potential index value (PF) shown in the above formula (1), and further calculates a control output corresponding to the opening degree of each flow rate control valve so that the calculated actual PF value follows the reference value (PF setting pattern shown in FIG. 6(B)) of the carbon potential index value previously selected according to the furnace temperature in the atmospheric heat treatment furnace 10 and the heat treatment content of the work. Then, control signals corresponding to these control outputs are input to the flow rate control valves 58, 64, and 63, respectively, and the flow rates of the RX gas, _N2 gas, and air introduced into the furnace through these flow rate control valves are adjusted.

Next, the furnace pressure control will be described. In this example, a control for maintaining the furnace pressure at atmospheric pressure or higher is performed separately from the PF control. The pressure detector 68, _N2 gas supply pipe 48, and pressure control unit 72 shown in FIG. 3 are used for this purpose.

The pressure detector 68 detects the pressure inside the furnace and transmits a signal corresponding to the detected pressure value (detection value). The detection value may be absolute pressure or the pressure difference from atmospheric pressure. For example, a manometer may be used as the pressure detector 68.

The _N2 gas supply pipe 48 supplies _N2 gas from an N2 gas supply source 61 to the gas inlet pipe 19 during furnace pressure control, and introduces the _N2 gas into the furnace via the gas inlet pipe 19, and is equipped with a flow rate control valve 69. The gas inlet pipe 19, the _N2 gas supply pipe 48, and the flow rate control valve 69 correspond to the pressure adjusting gas introduction means of the present invention.

The pressure control unit 72 is connected to the temperature control unit 43, the pressure detector 68, and the flow rate control valve 69 on the N ₂ gas supply pipe 48, and outputs a control output corresponding to the valve opening degree to the flow rate control valve 69.
As shown in FIG. 4 , the pressure control unit 72 includes a control switching unit 74 , a sequence control execution unit 75 , and a feedback control execution unit 76 .
The sequence control execution unit 75 outputs a predetermined control output as a control output for the flow rate adjustment valve 69 .
On the other hand, as shown in FIG. 5, the feedback control execution unit 76 is configured as a PID control system consisting of a proportional action unit 77A, an integral action unit 77B, a differential action unit 77C and an adder unit 77D, and executes feedback control based on the difference between the target pressure value SP1 set in the target pressure setting unit 78 and the detected pressure value PV1 from the pressure detector 68, to calculate a control output MV1 for the flow rate control valve 69 (0%≦MV1≦100%).

When obtaining a control output for the flow rate adjustment valve 69 , the control switching unit 74 determines whether to execute the sequence control execution unit 75 or the feedback control execution unit 76 based on the heating information received from the temperature control unit 43 .
In detail, when the difference between the detected temperature and the target temperature in the heating information received from the temperature control unit 43 is equal to or greater than a predetermined value (i.e., when the variation in the detected pressure becomes large), the sequence control execution unit 75 executes sequence control by outputting a predetermined control output to set the amount of pressure adjustment gas introduced to a predetermined amount.
On the other hand, when the difference between the detected temperature and the target temperature is less than a predetermined value (i.e., when the variation in the detected pressure is small), the feedback control execution unit 76 feeds back the detected pressure to calculate a control output and executes feedback control to adjust the amount of pressure adjustment gas introduced.

As described above, in this embodiment, the pressure detector 68, the gas inlet pipe 19 as a pressure regulating gas introduction means, the _N2 gas supply pipe 48, the flow rate control valve 69, and the pressure control unit 72 constitute the furnace pressure control means 80 of the present invention.

Next, the control operation of the heat treatment (for one batch) performed in the atmospheric heat treatment furnace 10 will be described.
After the workpiece to be heated is loaded into the furnace (heating chamber 13) through the entrance/exit 14, the door 17 is closed and a series of heat treatments is started, at which point _N2 gas for purging is introduced into the furnace through the _N2 gas supply pipe 49, and atmospheric heating is started by the burner 20 so as to follow the heat pattern shown in Fig. 6(A). Here, at the beginning of heating (the section shown by t1 in the figure), the inside of the furnace is in the low temperature range and there is a large temperature difference between the target temperature based on the heat pattern and the detected temperature, so a control output close to 100% is output from the temperature control unit 43 to the burner 20, and rapid heating is performed.
When such rapid heating is being performed, the value detected by the pressure detector 68 may vary widely as shown in Fig. 6C, making it difficult to obtain an accurate furnace pressure. For this reason, the furnace pressure control means 80 executes sequence control during this period, and introduces a preset amount of pressure adjustment gas into the furnace to maintain the furnace pressure at or above atmospheric pressure and prevent outside air from entering the furnace. The amount of pressure adjustment gas introduced by sequence control can be a constant flow rate per hour.

After that, when the furnace atmosphere temperature rises and the difference between the target temperature based on the heat pattern and the detected temperature becomes small (the section indicated by t2 in the figure), the introduction of RX gas is started based on the setting pattern of the index value of the carbon potential (PF setting pattern shown in FIG. 6(B)). When the t2 section is entered, the variation in the detection value detected by the pressure detector 68 is suppressed to a small value, so that the furnace pressure control means 80 executes feedback control and adjusts the amount of pressure adjustment gas introduced. While this feedback control is being executed, the amount of pressure adjustment gas (amount of N2 gas) introduced through the pressure adjustment gas supply means can be reduced according to the increase in the furnace pressure due to the heating and expansion of the atmospheric gas and the increase in the furnace pressure due to the introduction of the _RX gas into the furnace.

As described above, according to the present embodiment of the atmospheric heat treatment furnace 10, by selectively using sequence control that does not use the detection value of the pressure detector 68 and feedback control that uses the detection value of the pressure detector 68 depending on the heating state, it is possible to avoid problems caused by variations in the detection value of the pressure inside the furnace, while maintaining the pressure inside the furnace at or above atmospheric pressure, preventing outside air from entering the furnace, and suppressing the use of excessive pressure adjustment gas.

Next, a modification of this embodiment will be described.
7 shows a modified example which further adds a function for preventing backfire in the gas introduction pipe 19. When air and RX gas are simultaneously fed into the furnace through the gas introduction pipe 19, if the total flow rate of gas flowing through the gas introduction pipe 19 is too small, there is a risk of a backfire phenomenon in which a flame flows backward through the gas introduction pipe 19. In order to prevent such a backfire phenomenon, it is necessary to increase the opening of the flow control valve 69 of the pressure regulating gas introduction means to maintain a certain flow rate or more.

In this modification, as shown in FIG. 7, a valve opening calculation unit 82 and a high selector 84 are added to the pressure control unit 72 .
The valve opening calculation unit 82 outputs the opening of the flow rate control valve 69 of the pressure regulating gas introduction means required to prevent flashback. The valve opening calculation unit 82 outputs the opening of the flow rate control valve 69 required to prevent flashback from the RX gas flow rate information as a control output MV2 (0%≦MV2≦100%) based on a broken line function (see FIG. 7B) showing the relationship between the flow rate of the RX gas previously obtained and the opening of the flow rate control valve 69 of the pressure regulating gas introduction means. When the control output MV2 obtained by the valve opening calculation unit 82 and the control output MV1 calculated by the furnace pressure control are input to the high selector 84, the high selector 84 outputs the larger of these two control outputs as the control output for the flow rate control valve 69.

In this manner, at least the flow rate required to avoid flashback is maintained in the gas introduction pipe 19, so that flashback can be avoided when the _N2 gas for maintaining the furnace pressure is suppressed by feedback control.

Next, another modified example different from the example shown in FIG. 7 will be described.
Although the atmospheric heat treatment furnace in the above embodiment is provided with one pressure detector, it is possible to provide multiple pressure detectors in some cases. In this case, it is desirable to adopt the smallest detection value among the detection values received from the pressure detectors as the detection pressure in the furnace from the viewpoint of preventing the intrusion of outside air into the furnace.
For example, in the case where two pressure detectors 68A, 68B are provided for detecting the furnace pressure as shown in FIG. 8(A), a signal extraction unit 86 and a low selector 88 are provided in the pressure control unit 72 as shown in FIG. 8(B), and the detection value signals transmitted from the pressure detectors 68A, 68B are extracted by the signal extraction unit 86 at a predetermined sampling interval (e.g., 100 ms) and with a predetermined number of moving average terms (e.g., 10) to calculate a moving average, and the low selector 88 receives these moving averages and outputs the smallest moving average among the received moving averages as the detected pressure inside the furnace.

In addition, when two pressure detectors 68A, 68B are used for detecting the furnace pressure, an alarm output unit 90 can be further provided, as shown in Figure 9, to detect and alarm any abnormal transmission caused by a malfunction of the pressure detector itself.
The alarm output unit 90 in FIG. 9 is equipped with a signal extraction unit 91 and a transmission abnormality judgment unit 92, in which the detection value signals transmitted from the pressure detectors 68A, 68B are extracted by the signal extraction unit 91 at a predetermined sampling interval (e.g., 100 ms) and with a predetermined number of moving average terms (e.g., 10) to obtain a moving average, and the obtained moving average signal is sent to the transmission abnormality judgment unit 92.
The transmission abnormality judgment unit 92 compares the two moving averages, and if the difference between them remains greater than a predetermined value for a predetermined period of time or more, it judges that there is an abnormality in the transmission from one of the pressure detectors and outputs a transmission abnormality detection signal.

In Fig. 9, 95 is an AND operation section, 94 is a NOT operation section, and 96 is an on-delay timer. The alarm output section 90 is capable of receiving a heat treatment in progress signal, a door closing completion signal, and a disconnection signal from the pressure detectors 68A and 68B in addition to signals from the pressure detectors 68A and 68B, and outputs an alarm output signal when a transmission abnormality detection signal is output from the transmission abnormality determination section 92 in a state in which the heat treatment in progress signal and the door closing completion signal are received but a disconnection signal is not received. Since the detected pressure fluctuates greatly for a while after the door is closed and heat treatment is started as shown in Fig. 6, alarm monitoring is performed after the set time has elapsed by the on-delay timer 96 for waiting for stabilization.
By using the alarm output unit 90 configured in this manner, it is possible to know from the alarm output signal that there is a high possibility that either of the pressure detectors 68A, 68B is malfunctioning.
While the example in Figure 9 above is an example equipped with two pressure detectors, even if there are three or more pressure detectors, malfunctions in the pressure detectors can be detected by comparing the pressure detectors two by two.

Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be configured in various modified forms without departing from the spirit of the present invention.
(1) For example, in the above embodiment, the difference between the detected temperature and the target temperature is used as heating information for switching between sequence control and feedback control. However, it is also possible to use control output information for the heating means (burner) instead.
(2) In the above embodiment, the atmosphere heat treatment furnace has an inlet and an outlet at one end of the furnace body in the longitudinal direction, but the present invention can also be applied to a straight-through type atmosphere heat treatment furnace in which the inlet is provided at one end of the furnace body in the longitudinal direction and the outlet is provided at the other end. In such a case, it is also possible to configure the furnace so that pressure detectors are provided near the inlet and the outlet, respectively.

10 Atmospheric heat treatment furnace 12 Furnace body 19 Gas introduction pipe 20 Radiant tube burner (heating means)
26 Temperature detector 43 Temperature control unit 45 Furnace temperature control means 48 _N2 gas supply pipe (pressure adjustment gas introduction means)
59 Flow rate detector 66 Atmosphere control unit 69 Flow rate control valve (pressure adjustment gas introduction means)
68 Pressure detector 72 Pressure control unit 80 Furnace pressure control means 82 Valve opening degree calculation unit 84 High selector 88 Low selector 92 Transmission abnormality determination unit MV1, MV2 Control output

Claims (4)

A furnace body,
An atmosphere control means for controlling the flow rate of an atmosphere adjusting gas supplied into the furnace so that a carbon potential index value determined from the CO concentration and the _CO2 concentration in the furnace atmosphere becomes a predetermined value;
an in-furnace temperature control means including a temperature detector for detecting an in-furnace temperature, a heating means, and a temperature control unit for adjusting a control output for the heating means so that the detected temperature received from the temperature detector approaches a target temperature;
a pressure detector for detecting the pressure inside the furnace, a pressure adjusting gas introduction means, and an in-furnace pressure control means including a pressure control unit for adjusting the amount of the pressure adjusting gas introduced into the furnace through the pressure adjusting gas introduction means;
having
The furnace pressure control means is
When a difference between the detected temperature detected by the temperature detector and the target temperature is equal to or greater than a predetermined value, or when a control output for the heating means is equal to or greater than a predetermined value, a sequence control is executed to set the pressure adjusting gas introduction amount to a predetermined amount;
When the difference between the detected temperature and the target temperature is less than a predetermined value, or when the control output for the heating means is less than a predetermined value, a feedback control is performed in which the detected pressure detected by the pressure detector is fed back to adjust the amount of the pressure adjustment gas introduced. A pressure detector including:
2. The atmospheric heat treatment furnace according to claim 1, wherein said furnace pressure control means further comprises a low selector which selects the smallest detection value among detection values received from each pressure detector and outputs the selected value as the detection pressure inside said furnace. A pressure detector including:
2. The atmospheric heat treatment furnace according to claim 1, wherein the furnace pressure control means further comprises a transmission anomaly determination unit that determines that there is an anomaly in the transmission from the pressure detector when a state in which a difference between the detection values transmitted from the two selected pressure detectors is equal to or greater than a predetermined value continues for a predetermined time or longer. a gas introduction pipe for introducing the atmosphere adjusting gas and the pressure adjusting gas into a furnace;
a flow rate detector for detecting a flow rate of the atmosphere adjusting gas;
a valve opening degree calculation unit that calculates a valve opening degree of the pressure regulating gas supply means necessary for preventing flashback in the gas introduction pipe as a control output;
a high selector that outputs the larger of the control output calculated by the feedback control and the control output calculated by the valve opening degree calculation unit as a control output for the pressure regulating gas supply means;
The atmospheric heat treatment furnace according to claim 1 , further comprising:

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