Gas circulation method for a heat treatment furnace, gas circulation apparatus, and heat treatment furnace equipped therewith

Abstract

This invention provides a configuration that enables the more effective use of hydrocarbon gases and non-oxidizing gases in a heat treatment furnace to perform heat treatment on steel. [Solution] A gas circulation method for a heat treatment furnace 10 according to one aspect of the present invention includes a first step of supplying a hydrocarbon gas and a non-oxidizing gas in a predetermined component ratio to a heating chamber 12; a second step of passing the gas that has passed through the heating chamber through a contaminant removal device 82; and a third step of adding at least one of the hydrocarbon gas and the non-oxidizing gas to the gas that has passed through the contaminant removal device 82 so that the component ratio of the hydrocarbon gas and the non-oxidizing gas in the gas that has passed through the contaminant removal device 82 approaches the predetermined component ratio, and supplying it to the heating chamber 12. The hydrocarbon gas is preferably an unsaturated hydrocarbon gas, and may include at least one of ethylene gas, propylene gas, butylene gas, and acetylene gas.

Description

Technical Field

[0001] The present invention relates to a gas circulation method for a heat treatment furnace, a gas circulation device, and a heat treatment furnace provided with the same.

Background Art

[0002] Conventionally, heat treatment of steel has been performed according to the following procedure. First, the temperature is raised while purging the inside of a heat treatment furnace containing a workpiece (object to be treated) with nitrogen gas. Next, when the temperature inside the heat treatment furnace reaches a predetermined temperature, the supply of the purging nitrogen gas is stopped, and a conversion furnace gas is supplied into the heat treatment furnace. Then, the inside of the heat treatment furnace is maintained in a conversion furnace gas atmosphere, and the workpiece is heated to a predetermined temperature in this conversion furnace gas atmosphere, held for a certain period of time, and cooled at a predetermined cooling rate.

[0003] However, the above heat treatment method requires the generation of a conversion furnace gas in a conversion furnace, and for example, has a problem that maintenance management of the conversion furnace is troublesome. Therefore, through intensive research by the present applicants, a method of heat treatment based on nitrogen gas without using a conversion furnace has been developed (see Patent Document 1).

[0004] The heat treatment method disclosed in Patent Document 1 raises the temperature while purging the inside of the heat treatment furnace with nitrogen gas, and when the furnace internal temperature reaches a predetermined temperature, the flow rate of the nitrogen gas supplied into the heat treatment furnace is decreased, and a hydrocarbon gas having a double bond with 2 to 4 carbon atoms is added to the nitrogen gas and supplied into the heat treatment furnace, and the addition amount of this hydrocarbon gas is controlled based on the methane concentration in the exhaust gas discharged from the heat treatment furnace. Thereby, an attempt is made to control the amount of carbon in the workpiece using a hydrocarbon gas having a double bond with 2 to 4 carbon atoms that decomposes at a low temperature. And Patent Document 1 discloses that when using propylene gas as the hydrocarbon gas, depending on the airtightness of the furnace, decarburization is observed on the surface of the workpiece when the addition amount of propylene is less than 1%, and carburization is observed on the surface of the workpiece when the addition amount of propylene exceeds 2%, and therefore it is desirable to control the addition amount of propylene to 1 to 2% in the annealing operation.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-127814 [Overview of the project] [Problems that the invention aims to solve]

[0006] The heat treatment method described in Patent Document 1 relates to a batch-type heat treatment furnace, including a bell-type furnace, and not to a continuous-type heat treatment furnace. Furthermore, in this heat treatment method, the gas inside the heat treatment furnace is exhausted through an exhaust gas passage, which presents challenges in terms of efficient resource utilization.

[0007] The object of the present invention is to provide a configuration that enables the more effective use of hydrocarbon gases and non-oxidizing gases such as nitrogen gas in a heat treatment furnace, such as a continuous heat treatment furnace, to perform heat treatment on steel. [Means for solving the problem]

[0008] A first aspect of the present invention is, A first step involves supplying a hydrocarbon gas and a non-oxidizing gas in a predetermined component ratio to a heating chamber, A second step involves passing the gas that has passed through the aforementioned heating chamber through a contaminant removal device, A third step involves adding at least one of the hydrocarbon gas and the non-oxidizing gas to the gas that has passed through the contamination removal device so that the component ratio of hydrocarbon gas and non-oxidizing gas in the gas that has passed through the contamination removal device approaches the component ratio within the predetermined range, and then supplying it to the heating chamber. including, Gas circulation method for heat treatment furnaces To provide.

[0009] According to the gas circulation method for a heat treatment furnace of the first embodiment having the above configuration, a gas containing hydrocarbon gas and a non-oxidizing gas in a predetermined component ratio can be circulated as the furnace atmosphere gas, thereby enabling heat treatment of steel by making more effective use of hydrocarbon gas and non-oxidizing gas.

[0010] A second aspect of the present invention is, A mixed gas generating unit that generates a gas containing a hydrocarbon gas and a non-oxidizing gas in a predetermined component ratio, A supply unit that supplies the gas from the mixed gas generation unit toward the heating chamber, A pump that sends the gas that has passed through the heating chamber to the mixed gas generation unit via a circulation path, A contaminant removal device installed in the aforementioned circulation path and Equipped with, The mixed gas generation unit adds at least one of the hydrocarbon gas and the non-oxidizing gas to the gas that has passed through the contamination removal device so that the component ratio of the hydrocarbon gas and the non-oxidizing gas in the gas that has passed through the contamination removal device approaches the component ratio within the predetermined range. Gas circulation system for heat treatment furnaces To provide.

[0011] According to the gas circulation device for a heat treatment furnace of the second embodiment having the above configuration, a gas containing hydrocarbon gas and non-oxidizing gas in a predetermined range of component ratios can be circulated as the furnace atmosphere gas, thereby enabling heat treatment of steel by making more effective use of hydrocarbon gas and non-oxidizing gas.

[0012] Preferably, the non-oxidizing gas is nitrogen gas. Also preferably, the hydrocarbon gas is an unsaturated hydrocarbon gas. The hydrocarbon gas may contain at least one of ethylene gas, propylene gas, butylene gas, and acetylene gas.

[0013] The present invention also applies to a heat treatment furnace equipped with the aforementioned gas circulation device. Furthermore, the present invention also applies to a continuous heat treatment furnace equipped with the aforementioned gas circulation device. [Effects of the Invention]

[0014] According to the above first aspect or the above second aspect of the present invention, since the above configuration is provided, in a heat treatment furnace such as a continuous heat treatment furnace, it becomes possible to more effectively utilize a hydrocarbon gas and a non-oxidizing gas to perform heat treatment of steel.

Brief Description of Drawings

[0015] [Figure 1] It is a schematic configuration diagram of a part of a heat treatment furnace according to an embodiment of the present invention.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments according to the present invention will be described based on the attached drawings.

[0017] FIG. 1 shows a schematic configuration of a part of a heat treatment furnace 10 according to an embodiment of the present invention. The heat treatment furnace 10 includes a heating chamber 12. More specifically, the heat treatment furnace 10 includes a quenching heating chamber 12 and a quenching oil tank 14. A quenching oil tank 14 is provided on the downstream side of the quenching heating chamber 12. As is clear from FIG. 1, the quenching oil tank 14 is located on the lower side in the vertical direction than the quenching heating chamber 12. Although not shown in FIG. 1, the heat treatment furnace 10 includes a tempering heating chamber on the downstream side of the quenching oil tank 14.

[0018] A mesh belt conveyor 16 is provided in the quenching heating chamber 12 as a conveyance means for the work W, that is, a conveyance device. The mesh belt 18 of the mesh belt conveyor 16 is an endless belt and is wound around a first roller 20, a second roller 22, and the like. The mesh belt 18 can circulate and move inside the quenching heating chamber 12. Here, the first roller 20 is a driving roller and is driven electrically. However, the first roller 20 may be referred to as a driving drum, and for example, at this time, the second roller 22 which is a driven roller may be referred to as a driven drum.

[0019] The quenching heating chamber 12 includes a heater 24 as heating means, that is, a heating device. A plurality of heaters 24 are provided. Here, each heater 24 extends in a direction orthogonal to the conveyance direction of the workpiece W, that is, in the width direction. In FIG. 1, the heaters 24 are provided above and below the quenching heating chamber 12, respectively, but may also be provided on the left and right side portions in the width direction. The workpiece W conveyed by the mesh belt conveyor 16 passes through the heating space (heating region or heating area) HS between the heaters 24. The heaters 24 are not limited to being provided above and below the quenching heating chamber 12, and of course, may be provided in various arrangements or arrays, such as only on one of them, for example. Further, the heater 24 may be an electric heating type heating device or a combustion heating type heating device. Examples of the combustion heating type heating device include a radiant tube burner. The radiant tube burner is a burner that burns fuel in a radiant tube and heats by the radiant heat thereof.

[0020] A gas supply unit 26 is provided which is configured to supply an in-furnace atmosphere gas to the quenching heating chamber 12. The gas supply unit 26 is configured to supply a gas containing a hydrocarbon-based gas and a nitrogen gas into the quenching heating chamber 12 as the in-furnace atmosphere gas. The gas supply unit 26 will be described later.

[0021] The internal structure of the quenching heating chamber 12 is made of graphite-based material. As shown in Figure 1, a partition wall, or muffle 34, is provided to separate the conveying space, i.e., the heating space HS, through which the workpiece W is transported by the mesh belt conveyor 16, from the heater 24. This muffle 34 is made of graphite-based material, and in this case, it is made of graphite. The sheet-like, or plate-like, graphite, or graphite plate, used as the muffle 34 can be manufactured, for example, by cold isohydrodynamic forming (CIP). Therefore, the workpiece W is transported by passing through a tunnel surrounded by the graphite muffle 34, in an atmosphere heated by the radiant heat of the graphite muffle 34. The muffle 34, which is an internal structure of the quenching heating chamber 12, may be entirely made of graphite-based material, but at least a part of it may be made of graphite-based material. Also, here, the tunnel defining the heating space HS is composed of graphite muffle 34 around its entire circumference, but only a part of the tunnel may be composed of muffle 34. Furthermore, part or all of the muffle 34, which is an internal structure of the quenching heating chamber 12, may be made of other graphite-based materials, specifically, C / C composite, which is a graphite-based material. Furthermore, at least a part of the internal structure of the quenching heating chamber 12 other than the muffle may be made of graphite-based materials. By making at least a part of the internal structure of the quenching heating chamber 12 from graphite-based materials, the amount of oxidizing gas in the furnace is intended to be less than a predetermined amount.

[0022] Here, the mesh belt 18 is also made of a graphite-based material, more specifically, graphite. However, like the muffle 34, the mesh belt 18 may also be made of other graphite-based materials, such as a C / C composite. However, the mesh belt 18 is not limited to being made of a graphite-based material, and may be made of a heat-resistant metal belt, for example. Furthermore, the conveying device is not limited to one that uses the mesh belt 18, and may be configured as a roller conveying device.

[0023] An outside air blocking structure 36 is applied to the input end (leftmost in Figure 1) of the mesh belt conveyor 16. The outside air blocking structure 36 has an inlet throttling section 36a on the side where the mesh belt 18 enters the furnace, and an outlet throttling section 36b on the side where the mesh belt 18 exits the furnace. As shown in Figure 1, the inlet throttling section 36a and the outlet throttling section 36b are brought close to each other, effectively creating a single inlet and outlet for the mesh belt 18. This prevents the suction of outside air into the furnace due to the pressure difference between the inlet and outlet of the mesh belt 18 when they are separated, thereby stabilizing the atmosphere inside the furnace.

[0024] Furthermore, multiple curtain bodies 36c are provided at the input end of the mesh belt conveyor 16. The curtain bodies 36c are flexible and, although they are sheet-like in this case, may have other shapes, such as linear or string-like. The multiple curtain bodies 36c are suspended so as to hang down from the top to the bottom in the vertical direction. In this case, the curtain bodies 36c are made from nickel-based thin sheet material. However, the curtain bodies 36c may be manufactured from other materials, such as carbon-based materials, glass-based materials, ceramic-based materials, or metal materials such as steel or titanium-based materials that have sufficient strength and flexibility at heat treatment temperatures.

[0025] At the discharge end of the mesh belt conveyor 16 (i.e., the end on the second roller 22 side in Figure 1), a quenching oil tank 14 is provided downstream of the quenching heating chamber 12. At the discharge end of the quenching heating chamber 12 (on the right side in Figure 1), a chute 13 extending vertically is provided. The chute 13 is located below the falling space within the heating space HS, where the workpiece W falls after passing the downstream end of the mesh belt conveyor 16. The chute 13 extends into the quenching oil tank 14. The chute 13 does not reach the oil level S of the quenching oil tank 14, but it may extend into the oil of the quenching oil tank 14. The quenching oil tank 14 is in communication with the quenching heating chamber 12 via the chute 13.

[0026] The heat treatment furnace 10 further includes an oil inflow prevention means OP configured to prevent oil (e.g., oil mist) from flowing from the quenching oil tank 14 into the quenching heating chamber 12. The oil inflow prevention means OP, which may also be called an oil inflow prevention device, here includes a fluid curtain forming section 40. Specifically, as the oil inflow prevention means OP, a fluid curtain forming section 40 is provided, configured to form a fluid curtain C between the quenching heating chamber 12 and the quenching oil tank 14. The fluid curtain forming section 40 is provided on the chute 13. Here, the fluid curtain forming section 40 is configured to form an oil curtain, but it may also be configured to form an air curtain with nitrogen gas, for example. In this case, the supply port 46, which will be described later, can become a gas supply port and can be connected to a tank of nitrogen gas or the like.

[0027] The fluid curtain forming section 40 includes an oil curtain forming device 42 configured to form an oil curtain C between the quenching heating chamber 12 and the quenching oil tank 14. An oil passage 43 is provided for drawing oil from the oil tank 14. An oil pump 44 is provided in this oil passage 43. The oil passage 43 has an oil supply port 46 located at the position of the chute 13. The oil curtain forming device 42 includes a flow straightening member 48 to straighten the flow of oil coming out of the oil supply port 46 and form the oil curtain C. The flow straightening member 48 is provided to extend between an oil outlet 49 provided in the chute 13 and the oil supply port 46. The flow straightening member 48 has a smooth concave curved surface 48a. Oil flowing out of the oil supply port 46 can flow along the concave curved surface 48a, thereby forming an oil curtain C as shown in Figure 1.

[0028] Furthermore, the fluid curtain forming section 40 includes an oil receiving section 50 provided between the quenching heating chamber 12 and the quenching oil tank 14 to receive the oil curtain C. The oil receiving section 50 is positioned opposite the flow straightening member 48 of the oil curtain forming device 42 to receive the oil curtain generated by the oil curtain forming device 42. More specifically, the oil receiving section 50 is provided to open into the chute 13. The oil receiving section 50 is provided in a predetermined position to receive the oil curtain C without the oil curtain C directly colliding with the oil surface S of the quenching oil tank 14. Below it, the oil receiving section 50 is connected to the quenching oil tank 14. The oil receiving section 50 also includes a foam suppression section 52. The foam suppression section 52 is provided to suppress, preferably eliminate, oil foam generated as a result of receiving the oil curtain C. Here, the foam suppression section 52 is configured as a member having oil passages in a labyrinth structure, but it may be various devices or structures that provide such a foam suppression effect.

[0029] Furthermore, the quenching oil tank 14 is equipped with a conveyor 54 for transporting the workpiece W from the quenching oil tank 14 to a tempering heating chamber (not shown).

[0030] Now, let's further explain the gas supply unit 26 mentioned above. In this heat treatment furnace 10, a mixed gas containing hydrocarbon gas and nitrogen gas is supplied to the quenching heating chamber 12 as the furnace atmosphere gas. The gas supply unit 26 comprises a mixed gas generation unit 60 and a supply unit 62 that supplies the mixed gas generated in the mixed gas generation unit 60 to the quenching heating chamber 12.

[0031] The mixed gas generation unit 60 comprises a first tank 64 for hydrocarbon gas and a second tank 66 for nitrogen gas (N2). The first tank 64 is filled with propylene (C3H6) gas as the hydrocarbon gas. The hydrocarbon gas in the first tank 64 is not limited to propylene gas, and various unsaturated hydrocarbon gases may be used, for example, it may contain at least one of ethylene gas, propylene gas, butylene gas, and acetylene gas. The gas in the second tank 66 is nitrogen gas, which is a neutral gas, but it is not limited to nitrogen gas, and various non-oxidizing gases may be used, or it may be an inert gas. The second tank 66 may also be a nitrogen gas generator.

[0032] Furthermore, the mixed gas generation unit 60 includes a mixing chamber 68 into which gases are supplied and mixed from the first tank 64 and the second tank 66, respectively. The mixing chamber 68 is equipped with a stirring blade 70. The stirring blade 70 is driven by a motor (not shown). The amount of propylene gas supplied from the first tank 64 to the mixing chamber 68 is adjusted by the opening and closing control of a control valve 72. The amount of nitrogen gas supplied from the second tank 66 to the mixing chamber 68 is adjusted by the opening and closing control of a control valve 74. The gas generated in the mixing chamber 68, i.e., the mixed gas, is supplied to the quenching heating chamber 12 via a supply port 62a of a supply unit 62 provided in the heating chamber 12, and the amount supplied is adjusted by the opening and closing control of a control valve 76 of the supply unit 62. The supply port 62a is provided to supply the gas from the mixing chamber 68, i.e., the mixed gas, into the quenching heating chamber 12 from the downstream end of the quenching heating chamber 12, so that the mixed gas flows from the downstream side to the upstream side in the quenching heating chamber 12. The gas flow from the mixing chamber 68 to the quenching heating chamber 12 is generated by the pressure difference between them, but is not limited to that; the supply unit 62 may also be equipped with a pump.

[0033] The component ratio of hydrocarbon gas and nitrogen gas in the mixed gas should be within a predetermined range. The mixed gas generation unit 60 is configured to generate a mixed gas containing hydrocarbon gas and nitrogen gas within this predetermined component ratio. The operation of control valves 72 and 74 is controlled and coordinated accordingly.

[0034] Here, workpiece W is steel. The component ratio of hydrocarbon gas and nitrogen gas in the mixed gas should be determined within a predetermined range, taking into account decarburization or carburization on the surface of workpiece W. At a predetermined high temperature, when the amount of oxidizing gas in the furnace falls below a predetermined amount, propylene (C3H6) decomposes as shown in equation (1) below to produce methane (CH4), hydrogen (H2), and carbon (C). C3H6→ CH4+H2+2[C] (1)

[0035] This [C] is nascent carbon, and the amount of this [C] is correlated with the amount of methane gas and hydrogen gas, respectively, and affects the decarburization or carburization of the surface of the workpiece W. Therefore, the decarburization or carburization treatment of the surface of the workpiece W can be controlled by adjusting the component ratio of hydrocarbon gases and nitrogen gas in the mixed gas based on at least one or both of the amounts of methane gas and hydrogen gas.

[0036] Furthermore, in the heat treatment furnace 10, which is a continuous heat treatment furnace, the furnace atmosphere gas is circulated. In other words, the gas supply unit 26 of the heat treatment furnace 10 is configured as a gas circulation device GC.

[0037] The upstream end 78u of the circulation path 78 opens at the upstream end of the quenching heating chamber 12. The downstream end 78d of the circulation path 78 opens into the mixing chamber 68 of the mixed gas generation unit 60. A pump 80 is provided in the circulation path 78. By operating the pump 80, the gas that has passed through the quenching heating chamber 12 can be sent to the mixing chamber 68 of the mixed gas generation unit 60 via the circulation path 78.

[0038] A contaminant removal device 82 is provided in the circulation path 78. The contaminant removal device 82 has a filter. The contaminant removal device 82 is positioned so that the gas that has passed through the quenching heating chamber 12 and reached the circulation path 78 passes through the contaminant removal device 82. In particular, the contaminant removal device 82 is positioned so that the gas that has passed through the quenching heating chamber 12 and reached the circulation path 78 passes through the contaminant removal device 82 first. In the heat treatment furnace 10 of this embodiment, when a predetermined time has elapsed since the gas that has passed through the quenching heating chamber 12 has passed through the contaminant removal device 82, the filter of the contaminant removal device 82 is replaced. Note that the contaminant removal device 82 is not limited to having a filter, and for example, it may also have a component having a labyrinth structure flow path in addition to or instead of a filter. The reason for providing the contaminant removal device 82 is that, in addition to methane (CH4) and hydrogen (H2), carbon (C) is produced during the thermal decomposition of propylene (see formula (1) above), and the excess carbon, such as soot, is removed. Focusing particularly on the soot that is to be removed, the contaminant removal device 82 may also be called a soot removal device. Furthermore, the contaminant removal device 82 may be provided to remove residue (e.g., carbides) derived from the Bonde coating of the workpiece W, for example.

[0039] The circulation path 78 is further equipped with a cooler 84 and a CO2 adsorbent 86. The cooler 84 is provided to cool the gas and dehydrate it. The CO2 adsorbent 86 is provided to reduce the CO and CO2 concentrations in the gas.

[0040] Furthermore, sensors D1, D2, and D3 are provided in the circulation path 78. For example, sensor D1 is a temperature sensor, sensor D2 is a sensor for detecting methane gas concentration, and sensor D3 is a sensor for detecting hydrogen gas concentration. Based on the outputs from these sensors D1, D2, and D3, the amounts of propylene gas and nitrogen gas added to the gas that has passed through the contaminant removal device 82 are controlled. In other words, the control valves 72 and 74 are controlled so that the component ratio of hydrocarbon gases and nitrogen gas in the gas that has passed through the quenching heating chamber 12 and further through the contaminant removal device 82 approaches the component ratio within the predetermined range mentioned above. Note that the sensors are not limited to sensors D1, D2, and D3; for example, only sensor D2, or only sensors D1 and D2, may be used. Also, sensors that detect hydrocarbon gases, in this case propylene gas and / or components derived therefrom, and / or other components related thereto, are not limited to methane gas concentration and hydrogen gas concentration, and the control valves 72 and 74 are controlled based on the output from these sensors. For example, sensors that detect CO concentration, CO2 concentration, oxygen concentration, etc., may be provided, and the control valves 72 and 74 may be controlled based on these sensors or their outputs.

[0041] Furthermore, to further prevent oxidation of the oil surface S in the quenching oil tank 14, a second supply port 88 is provided near the outlet of the quenching heating chamber 12, through which nitrogen gas from the second tank 66 is supplied. The supply of nitrogen gas from the second supply port 88 is controlled by opening and closing a control valve 90. The second supply port 88 is located downstream of the supply port 62a.

[0042] As described above, the heat treatment furnace 10 includes a mixed gas generation unit 60 that generates a mixed gas containing hydrocarbon gas and nitrogen gas in a predetermined component ratio, a supply unit 62 that supplies the mixed gas generated in the mixed gas generation unit 60 toward the heating chamber 12, a pump 80 that sends the gas that has passed through the heating chamber 12 to the mixed gas generation unit 60 via a circulation path 78, and a contaminant removal device 82 provided in the circulation path 78. The mixed gas generation unit 60 includes a first tank 64, a second tank 66, a mixing chamber 68, and control valves 72 and 74. These control valves 72 and 74 are controlled based on the output from sensors D1, D2 and D3. Therefore, the mixed gas generation unit 60 can add at least one of hydrocarbon gas and nitrogen gas to the gas that has passed through the contaminant removal device 82 so that the component ratio of hydrocarbon gas and nitrogen gas in the gas that has passed through the contaminant removal device 82 approaches the predetermined component ratio mentioned above. In other words, the heat treatment furnace 10 performs a gas circulation method for the heat treatment furnace, which includes a first step of supplying hydrocarbon gas and nitrogen gas in a predetermined component ratio to the heating chamber 12, a second step of passing the gas that has passed through the heating chamber 12 through a contaminant removal device 82, and a third step of adding at least one of hydrocarbon gas and nitrogen gas to the gas that has passed through the contaminant removal device 82 so that the component ratio of hydrocarbon gas and nitrogen gas in the gas that has passed through the contaminant removal device 82 approaches the predetermined component ratio, and then supplying it to the heating chamber 12. Therefore, a gas containing hydrocarbon gas and nitrogen gas in a predetermined component ratio can be circulated as the furnace atmosphere gas, and thus it becomes possible to perform heat treatment on a steel workpiece W by making more effective use of hydrocarbon gas and nitrogen gas. Thus, the gas supply unit 26 of the heat treatment furnace 10 according to one embodiment is configured as a gas circulation device GC.

[0043] Although the heat treatment furnace 10 is a continuous heat treatment furnace, the present invention is not limited to application to a continuous heat treatment furnace. The gas circulation method and gas circulation device GC of the heat treatment furnace according to the present invention may each be applied to a batch-type heat treatment furnace.

[0044] Although embodiments and modifications thereof according to the present invention have been described above, the present invention is not limited thereto. Various substitutions and modifications are possible as long as they do not depart from the spirit and scope of the invention as defined by the claims of this application. [Explanation of Symbols]

[0045] 10 Heat treatment furnace 12. Hardening heating chamber 14. Quenching oil bath 16 Mesh Belt Conveyor 18 Mesh belt 24 Heater 26 Gas Supply Department 60 Mixed gas generation unit 62 supply ports 68 Mixing room 78 Circulation route 80 pumps 82 Contamination Removal Device 84 Cooler 86 CO2 adsorption machine C Oil Curtain GC gas circulation system

Claims

1. A first step involves supplying a hydrocarbon gas and a non-oxidizing gas in a predetermined component ratio to a heating chamber, A second step involves passing the gas that has passed through the heating chamber through a contaminant removal device, A third step involves adding at least one of the hydrocarbon gas and the non-oxidizing gas to the gas that has passed through the contamination removal device and supplying it to the heating chamber, so that the component ratio of hydrocarbon gas and non-oxidizing gas in the gas that has passed through the contamination removal device approaches the component ratio within the predetermined range. including, A method for circulating gas in a heat treatment furnace.

2. The non-oxidizing gas is nitrogen gas. The aforementioned hydrocarbon gas is an unsaturated hydrocarbon gas. A method for circulating gas in a heat treatment furnace according to claim 1.

3. The hydrocarbon gas includes at least one of ethylene gas, propylene gas, butylene gas, and acetylene gas. A method for circulating gas in a heat treatment furnace according to claim 1 or 2.

4. A mixed gas generating unit that generates a gas containing a hydrocarbon gas and a non-oxidizing gas in a predetermined component ratio, A supply unit that supplies the gas from the mixed gas generation unit toward the heating chamber, A pump that sends the gas that has passed through the heating chamber to the mixed gas generation unit via a circulation path, A contaminant removal device installed in the aforementioned circulation path and Equipped with, The mixed gas generation unit adds at least one of the hydrocarbon gas and the non-oxidizing gas to the gas that has passed through the contamination removal device so that the component ratio of the hydrocarbon gas and the non-oxidizing gas in the gas that has passed through the contamination removal device approaches the component ratio within the predetermined range. Gas circulation system for a heat treatment furnace.

5. The non-oxidizing gas is nitrogen gas. The aforementioned hydrocarbon gas is an unsaturated hydrocarbon gas. A gas circulation device for a heat treatment furnace according to claim 4.

6. The hydrocarbon gas includes at least one of ethylene gas, propylene gas, butylene gas, and acetylene gas. A gas circulation device for a heat treatment furnace according to claim 4 or 5.

7. A heat treatment furnace equipped with a gas circulation device for the heat treatment furnace according to claim 4 or 5.

8. A continuous heat treatment furnace equipped with a gas circulation device for the heat treatment furnace according to claim 4 or 5.

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