Heat treatment furnace

Abstract

In a heat treatment furnace, which includes a preheating chamber equipped with a modified gas generator such as a gas burner, a heating chamber downstream of the preheating chamber, and a conveying means for placing the workpiece to be heat-treated into the preheating chamber and the heating chamber, and is configured to exhaust the modified gas generated by the combustion of the modified gas generator and supply it into the furnace as furnace atmosphere gas through a modified gas supply passage, the present invention provides a configuration that makes it possible to further increase the rate at which the workpiece to be heat-treated rises during the preheating stage. [Solution] A heat treatment furnace 10 according to one embodiment of the present disclosure is provided with a high-frequency induction heating coil 26 located upstream of a gas burner 52, which is a modified gas generator, and connected to an AC power supply 96.

Description

Technical Field

[0001] The present disclosure relates to a heat treatment furnace.

Background Art

[0002] Conventionally, heat treatment furnaces have been put into practical use in which a gas burner (or combustion burner) is disposed in a preheating chamber, the combustion heat thereof is used as a heat source for preheating, and exhaust gas generated by combustion of the gas burner is utilized as furnace atmosphere gas.

[0003] For example, Patent Document 1 discloses a heat treatment furnace that utilizes exhaust gas generated by combustion of a combustion burner as furnace atmosphere gas, and preheats an object to be treated with heat from the combustion burner. Specifically, in this heat treatment furnace, a heat-generating gas generator having a combustion burner is disposed in a temperature raising zone adjacent to a heating zone, a mixed gas obtained by mixing raw material gas (butane, propane, etc.) and air is combusted by the combustion burner, the object to be treated is preheated by the combustion heat, the converted gas discharged from the combustion burner is cooled and dehydrated by a heat exchanger, further cooled and dehydrated by a refrigerator, adjusted for dew point, supplied to the heating zone and the cooling zone, and used as furnace gas for non-oxidizing treatment of the object to be treated.

[0004] Further, Patent Document 2 discloses a heat treatment furnace in which, without using an inert gas such as nitrogen gas or argon gas as furnace atmosphere gas, converted gas generated by combustion of a gas burner is caused to absorb carbon dioxide and moisture by a CO2 absorber, so as to be utilized as furnace atmosphere gas that brings the inside of the furnace into a non-oxidized state. In this heat treatment furnace, the gas burner is provided in a preheating chamber on the upstream side of the heating chamber, and the object to be heat-treated carried into the preheating chamber is preheated by the combustion heat from the gas burner.

[0005] Furthermore, Patent Document 3 discloses a heat treatment furnace that was devised to further pursue energy saving effects, based on the heat treatment furnaces described in Patent Documents 1 and 2. The heat treatment furnace of Patent Document 3 has a pre-chamber, a preheating chamber, a heating chamber, and a cooling chamber arranged in a continuous manner. Heaters are provided in the preheating chamber and the heating chamber, and the workpiece to be heat-treated, which is transported on a mesh belt conveyor, is preheated in the pre-chamber and preheating chamber and then heated in the heating chamber for heat treatment. The preheating chamber is equipped with a gas burner, and the workpiece to be heat-treated is preheated by the combustion heat of the gas burner. The modified gas generated by the combustion of the gas burner is supplied into the heat treatment furnace as the furnace atmosphere gas through a modified gas supply passage. A modified gas combustion device is provided in the pre-chamber. The modified gas combustion device burns the modified gas that has been used as the furnace atmosphere gas flowing from the downstream side to the upstream side in the heat treatment furnace, and the heat of this combustion preheats the workpiece to be heat-treated being transported in the pre-chamber. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 58-27323 [Patent Document 2] Japanese Patent Publication No. 2014-74566 [Patent Document 3] Japanese Patent Publication No. 2017-166721 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, in order to make more effective use of the combustion heat mentioned above in the preheating chamber, it is necessary to increase the travel speed (conveying speed) of the mesh belt conveyor and increase the processing rate of heat-treated materials per unit time in the preheating chamber. However, in order to heat the heat-treated materials to a sufficiently uniform temperature through preheating in the preheating chamber, it is necessary to keep the heat-treated materials in the preheating chamber for a certain period of time.

[0008] The present disclosure aims to provide a configuration that enables a higher rate of heating of the workpiece during the preheating stage in a heat treatment furnace, which comprises a preheating chamber equipped with a modified gas generator such as a gas burner, a heating chamber downstream of the preheating chamber, and a conveying means for placing the workpiece to be heat-treated into the preheating chamber and the heating chamber, and is configured to exhaust the modified gas generated by the combustion of the modified gas generator and supply it into the furnace as a furnace atmosphere gas through a modified gas supply passage. [Means for solving the problem]

[0009] One aspect of this disclosure is: In a heat treatment furnace comprising a preheating chamber equipped with a modified gas generator, a heating chamber downstream from the preheating chamber, and a conveying means for placing objects to be heat-treated so as to be transported to the preheating chamber and the heating chamber, the modified gas generated by the combustion of the modified gas generator is exhausted and supplied into the furnace as furnace atmosphere gas through a modified gas supply passage, A high-frequency induction heating coil, located upstream of the aforementioned modified gas generator and connected to an AC power supply. It is equipped with Heat treatment furnace To provide.

[0010] According to the heat treatment furnace with the above configuration, the object to be heat-treated placed on the conveying means can be actively heated by a high-frequency induction heating coil, then preheated in a preheating chamber, and then sent to the heating chamber. Therefore, the rate at which the object to be heat-treated rises during the preheating stage can be increased compared to a furnace without a high-frequency induction heating coil. For example, this makes it possible to increase the travel speed of the conveying means.

[0011] Preferably, the modified gas generator is provided on one side of the conveying means in the vertical direction, and the high-frequency induction heating coil is provided on the other side of the conveying means in the vertical direction, opposite to the side on which the modified gas generator is provided. With this configuration, the high-frequency induction heating coil can actively heat the object to be heat-treated placed on the conveying means from the vertical side opposite the modified gas generator with respect to the conveying means. Therefore, compared to the case where a high-frequency induction heating coil is not provided, the temperature of the object to be heat-treated can be brought closer to a more uniform temperature more quickly or to a more uniform temperature.

[0012] Preferably, the high-frequency induction heating coil is provided at a distance of at least a first predetermined distance from the conveying means. This configuration makes it possible to prevent or suppress overheating of the conveying means.

[0013] Preferably, the high-frequency induction heating coil is provided to heat the workpiece in the atmosphere, and the pre-chamber, located downstream of the high-frequency induction heating coil and upstream of the preheating chamber, is equipped with a modified gas combustion device configured to burn the modified gas used as the furnace atmosphere gas and preheat the workpiece with the heat of combustion. In this case, the high-frequency induction heating coil is preferably located at a distance of a second predetermined distance or more from the upstream end of the pre-chamber in the transport direction. With this configuration, even if the pre-chamber is provided, it is possible to prevent or suppress overheating of, for example, the outer wall of the pre-chamber.

[0014] Preferably, the high-frequency induction heating coil is provided to heat the workpiece in the atmosphere and is located at a distance of at least a third predetermined distance from the upstream end of the preheating chamber in the transport direction. This configuration prevents or suppresses, for example, overheating of the outer wall of the preheating chamber. The third predetermined distance may be the same as or different from the second predetermined distance mentioned above. [Effects of the Invention]

[0015] According to the above aspect of the present disclosure, a heat treatment furnace having the above configuration is provided, which makes it possible to further increase the temperature rising rate of the object to be heat-treated in the preheating stage, as compared with the case where no high-frequency induction heating coil is provided. [Brief Description of the Drawings]

[0016] [Figure 1] This is a schematic configuration diagram showing the configuration of a heat treatment furnace according to an embodiment of the present disclosure. [Figure 2] This is a cross-sectional view of the preheating chamber in the heat treatment furnace of Fig. 1. [Figure 3] This is a cross-sectional view of the front chamber in the heat treatment furnace of Fig. 1. [Figure 4] This is a view of the high-frequency induction heating unit and its surroundings in the heat treatment furnace of Fig. 1, as viewed downward from the upper side in the vertical direction. [Figure 5] This is an enlarged view of the high-frequency induction heating unit and its surroundings in the heat treatment furnace of Fig. 1. [Figure 6] This is an enlarged view of the high-frequency induction heating unit and its surroundings in the heat treatment furnace of a modified example. [Modes for Carrying Out the Invention]

[0017] Hereinafter, embodiments according to the present disclosure will be described based on the accompanying drawings. The same reference numerals are assigned to the same components (or configurations), and their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0018] FIG. 1 shows a schematic configuration of a heat treatment furnace 10 according to an embodiment of the present disclosure. In this heat treatment furnace 10, a carry-in table 12, a high-frequency induction heating section 13, a front chamber 14, a preheating chamber 16, a heating chamber 18, a cooling chamber 20, a rear chamber (outlet chamber) 22, and a carry-out table 24 are sequentially and continuously provided from the upstream side toward the downstream side in the direction in which the workpiece W to be heat-treated is conveyed by a conveying means (hereinafter referred to as "conveying direction" or "longitudinal direction") CD. This heat treatment furnace 10 preheats the workpiece W conveyed by the conveying means in the high-frequency induction heating section 13 provided with the high-frequency induction heating coil 26, the front chamber 14 and the preheating chamber 16, and heats the workpiece W in the heating chamber 18 to perform heat treatment. This heat treatment furnace 10 can be used for annealing, quenching and the like with its original configuration or with additional functions. The carry-in table 12 extends to substantially the same position as the high-frequency induction heating section 13 provided with the high-frequency induction heating coil 26 in the conveying direction CD of the workpiece W to be heat-treated, or extends upstream from the high-frequency induction heating section 13.

[0019] In the heat treatment furnace 10, a mesh belt conveyor 30 driven by a motor 28 is disposed as a conveying means for conveying the workpiece W to be heat-treated in the conveying direction CD through the inside of the heat treatment furnace 10. The mesh belt conveyor 30 is an endless belt. Note that the conveying means is not limited to the mesh belt conveyor 30, and may be configured with various known structures.

[0020] FIG. 2 shows a cross-sectional view of the preheating chamber 16 in the heat treatment furnace 10, taken along a cross section perpendicular to the conveying direction CD. As shown in FIG. 1 and FIG. 2, the preheating chamber 16 and the heating chamber 18 are arranged in direct communication with each other, each has a rectangular shape in a cross-sectional view perpendicular to the conveying direction CD, and is formed such that the periphery thereof is surrounded by a heat insulating wall 32 made of ceramic fiber. The heat insulating wall 32 is formed by being attached to the inner surfaces of the outer walls 34 on both sides, the upper and lower outer walls 36, 38, etc. of the heat treatment furnace 10. Note that the heat insulating wall 32 is not limited to being made of ceramic fiber, and may be made of, for example, heat-resistant bricks.

[0021] For example, as shown in Figure 2, in the preheating chamber 16 and heating chamber 18, multiple crossbeams 40 extending in a direction perpendicular to the transport direction CD (width direction) are installed between the outer walls 34 on the lower insulating wall 32. Furthermore, multiple longitudinal beams 42 extending in the transport direction CD through the preheating chamber 16 and heating chamber 18 are arranged on the crossbeams 40. These crossbeams 40 and longitudinal beams 42 are arranged to intersect each other, forming a support structure. This support structure, in which the crossbeams 40 and longitudinal beams 42 are arranged to intersect each other, supports the mesh belt conveyor 30 that carries the heat-treated object W from below.

[0022] As shown in Figures 1 and 2, in the preheating chamber 16 and heating chamber 18, multiple heaters 46 extending in the width direction below the upper insulating wall 32 are arranged at intervals in the conveying direction CD. Furthermore, in the heating chamber 18, multiple heaters 46 extending in the width direction above the lower insulating wall 32 and below the vertical beam member 42 are arranged at intervals in the conveying direction CD. These heaters 46 are resistance heaters and can heat the object W to be heat-treated.

[0023] The modified gas inlet 48, described later, is shown as one for the heating chamber 18 in Figure 1, but there may be more than one, and it may also be provided not only in the heating chamber 18, but also in the preheating chamber 16, the cooling chamber 20, etc. In this case, the inlet 48 is located near the downstream end of the heating chamber 18. The modified gas supplied into the furnace from the inlet 48 flows from the downstream side to the upstream side of the furnace due to the action of the gas flow forming section GF, described later, and can flow to the pre-chamber 14. A different form of flow forming section (not shown) may be provided, and a predetermined flow rate of nitrogen gas or an inert gas, etc., may be supplied into the furnace from the downstream side to the upstream side of the heating chamber 18. This allows the modified gas supplied to the heating chamber 18 to flow actively upstream from the heating chamber 18 to the preheating chamber 16, and further to the pre-chamber 14. Also, since the inlet 48 is located near the downstream end of the heating chamber 18, a sufficient amount of modified gas can be supplied to the cooling chamber 20 adjacent to the heating chamber 18.

[0024] Furthermore, a flame curtain forming device 50, which is a type of curtain forming device, is provided to suppress the inflow of air from the upstream side of the pre-chamber 14 into the pre-heating chamber 16 and the heating chamber 18, and the tunnel that connects them to the cooling chamber 20 and transports the heat-treated material W together with them, i.e., the pre-chamber 14 which constitutes the inside of the furnace. The flame curtain forming device 50 is equipped with a burner device 50a. The burner device 50a is positioned at the upstream end of the pre-chamber 14, specifically in the lower part of the upstream inlet of the pre-chamber 14, and the burner device 50a generates a flame from below to above the mesh belt conveyor 30, thereby forming a flame curtain, i.e., a flame curtain. The flame curtain forming device 50 is not limited to this configuration and may have other configurations. Also, for example, in addition to the configuration that forms a combustion gas, i.e., a flame curtain, as in the flame curtain forming device 50, the curtain forming device may be configured to form a gaseous curtain using at least a part of an inert gas and / or nitrogen gas.

[0025] Now, a gas burner 52 for generating modified gas is provided in the preheating chamber 16. Since this gas burner 52 is substantially the same as the configuration already proposed by the present inventors (see, for example, Patent Document 3), only its outline will be described here, particularly based on Figure 2. Note that the gas burner 52 is an example of a modified gas generating device.

[0026] The gas burner 52 is positioned vertically below, or below, the mesh belt conveyor 30 within the preheating chamber 16. The gas burner 52 comprises a burner body 54 made of a radiant tube, a supply cylinder 56, an exhaust passage 58 formed around the supply cylinder 56, a raw material gas supply cylinder 60, and a spark rod 62 provided inside the raw material gas supply cylinder 60.

[0027] Inside the burner body 54, pilot fuel gas for combustion is supplied from a pilot fuel gas source 64 through a fuel gas supply cylinder 60, and a premixed gas, which is a mixture of air and fuel gas (i.e., fuel gas), is taken in from a supply cylinder 56 and supplied to the burner body 54. Butane, propane, etc., are used as the fuel gas.

[0028] Then, within the burner body 54, the pilot fuel gas is ignited by applying voltage to the spark rod 62, which is the ignition means, with the spark power supply 66. After combustion by ignition, combustion is maintained by the premixed gas.

[0029] The combustion heat from the gas burner 52 heats the material W to be treated, which is brought into the preheating chamber 16. The modified gas produced by this combustion passes through the exhaust passage 58, preheats the premixed gas taken in at the preheating section 68, and is then discharged from the gas burner 52. The modified gas produced in this way is, for example, a heat-generating modified gas such as DX gas, and contains CO, CO2, H2, H2O, and N2.

[0030] As shown in Figure 1, the modified gas discharged from the gas burner 52 is supplied to the heating chamber 18 through the inlet 48 via the modified gas supply passage 70. A water-cooled heat exchanger 72 and a refrigeration dewatering machine 74 are sequentially arranged in the modified gas supply passage 70.

[0031] As the modified gas passes through the modified gas supply path 70, it is cooled to about 40°C in the water-cooled heat exchanger 72, then cooled to about 5°C and dehydrated in the refrigeration dewaterer 74, and then sent into the heating chamber 18.

[0032] The preheating chamber 16, heating chamber 18, and cooling chamber 20 are arranged in this order along the transport direction CD and are in communication with each other. Therefore, the refrigeration dewatering machine 74 may be connected to the cooling chamber 20 in addition to the heating chamber 18, and the denatured gas, which has been cooled and dewatered as described above, may be supplied directly from the refrigeration dewatering machine 74 to the heating chamber 18 and the cooling chamber 20.

[0033] Furthermore, the modified gas supply line 70 is not limited to the water-cooled heat exchanger 72 and the refrigeration dewatering machine 74; any equipment suitable for the desired heat treatment may be installed. For example, a CO2 adsorption device may be installed in place of either or both of the water-cooled heat exchanger 72 and the refrigeration dewatering machine 74, or in addition to them.

[0034] Figure 3 shows an enlarged cross-sectional view of the pre-chamber 14 in the direction CD of the conveying direction. As shown in Figures 1 and 3, and especially in Figure 3, the pre-chamber 14, which communicates with the upstream side of the preheating chamber 16, is equipped with a modified gas combustion device 76. The aforementioned gas flow forming section GF is configured to include this modified gas combustion device 76. The gas flow forming section GF is configured so that the modified gas from the heating chamber 18 flows toward the pre-chamber 14. The modified gas combustion device 76 includes a partition wall 78, an air introduction pipe 80, and an exhaust gas outlet 82. The specific configuration of the pre-chamber 14 equipped with the modified gas combustion device 76 will be described below.

[0035] The front chamber 14 is divided vertically by a nearly horizontal partition wall 78 that extends in the transport direction CD. The partition wall 78 vertically separates at least half of the front chamber 14, in this case at least half of the front chamber 14 on the downstream side in the transport direction, more specifically at least 70% of the front chamber 14 on the downstream side in the transport direction. By providing the partition wall 78, the front chamber 14 is roughly divided into the space above the partition wall 78 (upper space) 78u and the space below the partition wall 78 (lower space) 78d. The lower space 78d is directly connected to the preheating chamber 16, and the upper space 78u is connected to the preheating chamber 16 via the lower space 78d. Below the partition wall 78, that is, the lower space 78d, is the loading chamber 84 where a mesh belt conveyor 30 (not shown in Figure 3) is located, and it is directly connected to the preheating chamber 16.

[0036] The upper space 78u above the partition wall 78 is a modified gas combustion chamber 86 surrounded by a ceramic fiber insulation wall 32. The leading end of the modified gas combustion chamber 86 in the transport direction CD is closed, and an exhaust gas outlet 82 is provided facing upward. The exhaust gas generated by combustion in the modified gas combustion chamber 86 is discharged through the exhaust gas outlet 82.

[0037] The base end of the front chamber 14 in the transport direction, i.e., the upstream end, serves as an inlet 88 for the heat-treated material W into the furnace, and a hood 90 is attached above it. An opening 92 is provided at the bottom of the hood 90, forming part of the aforementioned inlet 88, and an exhaust gas section 94 is formed above it.

[0038] An exhaust gas outlet 95 is provided above the exhaust gas section 94, facing upward. Furthermore, the aforementioned air introduction pipe 80 is attached to the front wall of the hood 90, facing into the modified gas combustion chamber 86, so as to penetrate the exhaust gas section 94 in the conveying direction CD. The air introduction pipe 80 is an air introduction member that guides air into the upper space 78u. The air introduction pipe 80 is provided so as to extend in the conveying direction CD of the heat-treated object W, and extends toward the upper space 78u through the space 78m connecting the upper space 78u and the lower space 78d in the partition wall 78. The tip of each air introduction pipe 80 extends downstream of the upstream end of the partition wall 78 in the conveying direction of the heat treatment furnace 10. However, the tip of the air introduction pipe 80 may be designed to terminate at the same position as or just before the upstream end of the partition wall 78 in the conveying direction CD of the heat treatment furnace 10. The extension length of the tip of the air intake pipe 80 should be designed to facilitate the smooth flow of the modified gas from below to above the partition wall 78. The number of air intake pipes 80 may be one or more.

[0039] Since the gas flow forming section GF is configured with the modified gas combustion device 76 as described above, the modified gas used as the furnace atmosphere gas in the heat treatment furnace 10, particularly in the heating chamber 18 and the preheating chamber 16, is pulled towards the modified gas combustion chamber 86 and flows from downstream to upstream in the transport direction CD. The modified gas then flows into the modified gas combustion chamber 86 from, for example, the base end side, i.e., the upstream side, of the input chamber 84 of the pre-chamber 14, which is a degreasing chamber, and reacts with the air introduced from the air introduction pipe 80 in the modified gas combustion device 76 to burn in the modified gas combustion chamber 86. The burned gas, i.e., exhaust gas, is then mainly discharged from the exhaust gas outlet 82. The exhaust gas may also be discharged from the exhaust gas outlet 95.

[0040] Furthermore, it is preferable to install exhaust gas purification devices, such as catalytic converters, at the exhaust gas outlets 82 and 95.

[0041] Furthermore, as shown in Figures 1 and 2, the burner device 50a described above is provided below the opening 92 of the hood 90. Therefore, the frame curtain formed by the burner device 50a of the frame curtain forming device 50 prevents the modified gas flowing from downstream to upstream toward the front chamber 14 in the transport direction CD from being discharged directly from the inlet 88 of the heat treatment furnace 10, and also assists in promoting the flow of modified gas from the downstream side.

[0042] The cooling chamber 20 is equipped with cooling means, such as a water cooling system (not shown), to cool the heat-treated object W that has passed through the heating chamber 18 at a predetermined cooling rate.

[0043] In addition, various modifications are possible to the heat treatment furnace 10 with the above configuration. For example, the following modifications may be made: Although a partition door is not provided between the preheating chamber 16 and the heating chamber 18, one may be provided. Similarly, although a partition door is not provided between the heating chamber 18 and the cooling chamber 20, one may be provided.

[0044] As described above, each heater 46 provided in the preheating chamber 16 and the heating chamber 18 is controlled so that the temperature of the room in which it is installed reaches the corresponding target temperature. A control device (not shown) is provided to control the operation of each of these heaters 46 and / or gas burners 52, etc., so that the furnace temperature, furnace atmosphere gas, etc. are controlled to reach a desired state.

[0045] Various sensors may be provided in the heat treatment furnace 10 for the control of the control device. It is preferable to provide an oxygen sensor capable of measuring the partial pressure of oxygen, but various other sensors such as a temperature sensor capable of measuring temperature may also be provided. For example, a hydrogen sensor capable of measuring the partial pressure of hydrogen, a dew point sensor capable of measuring the dew point inside the heat treatment furnace 10, a CO sensor capable of measuring the partial pressure of carbon monoxide, a CO2 sensor capable of measuring the partial pressure of carbon dioxide, etc. may be provided.

[0046] Furthermore, as described above, the heat treatment furnace 10 is provided with a high-frequency induction heating section 13 equipped with a high-frequency induction heating coil 26. The high-frequency induction heating section 13, or the high-frequency induction heating coil 26, is located upstream of the preheating chamber 16, and in this case, particularly upstream of the front chamber 14. The high-frequency induction heating coil 26 is configured to heat the workpiece W in the atmosphere. The high-frequency induction heating coil 26 is connected to an AC power supply 96. Therefore, an AC current flows through the high-frequency induction heating coil 26. The frequency of the AC current for high-frequency induction heating should be set according to the dimensions and material of the workpiece W. The frequency can be set to, for example, 1kHz to 20kHz, with 5kHz to 10kHz being good, and preferably 6kHz to 8kHz, but it is not limited to these ranges. The frequency may be, for example, several tens of kHz to several hundred kHz.

[0047] As shown in Figure 1, the high-frequency induction heating coil 26 is installed on the vertically upper side of the mesh belt conveyor 30. Therefore, by passing an alternating current through the high-frequency induction heating coil 26, the heat-treated object W placed on the mesh belt conveyor 30 can be heated from its vertically upper side.

[0048] Figure 4 shows a view of the high-frequency induction heating section 13 and its surroundings in the heat treatment furnace 10, viewed from the vertically upward direction. As shown in Figures 1 and 4, and especially in Figure 4, the high-frequency induction heating coil 26 is a flat coil. Specifically, the high-frequency induction heating coil 26 has a generally meandering shape on a plane, that is, it has a configuration that extends on a plane so as to be repeatedly folded back and extend in the conveying direction CD. The high-frequency induction heating coil 26 has folded sections 26s located on both sides of the mesh belt conveyor 30 and extends over a width greater than the entire width of the mesh belt conveyor 30 (the width in the width direction perpendicular to the conveying direction CD, which is the direction of movement of the mesh belt conveyor 30). Therefore, in this case, the majority of the high-frequency induction heating coil 26 extends in a direction intersecting the conveying direction CD, and in this case in the width direction perpendicular to it. By passing an alternating current through the high-frequency induction heating coil 26, a magnetic field is generated around the heat-treated object W placed on the mesh belt conveyor 30, allowing the heat-treated object W to be heated from above. However, the number of folded portions 26s of the high-frequency induction heating coil 26 is not limited to that shown in Figure 4. Furthermore, in Figure 4, the spacing of the high-frequency induction heating coils 26 in the transport direction CD is generally constant, but this is not limited to this; for example, the spacing may become sparser at the upstream and downstream ends of the transport direction CD, and denser in between. The high-frequency induction heating coil 26 is made of copper, and cooling water flows inside it.

[0049] As shown in Figure 5, the high-frequency induction heating coil 26 is installed so as to be at least a predetermined distance (hereinafter referred to as the first predetermined distance) L1 from the mesh belt conveyor 30 in the vertical direction. The first predetermined distance L1 is preferably determined to prevent or suppress overheating of the mesh belt conveyor 30, for example, to prevent or suppress the mesh belt conveyor 30 from being heated above a predetermined temperature.

[0050] Furthermore, as shown in Figure 5, the high-frequency induction heating coil 26 is positioned at a predetermined distance (hereinafter referred to as the second predetermined distance) L2 or more from the upstream end 14u of the front chamber 14 in the transport direction CD. In this case, the upstream end 14u of the front chamber 14 corresponds to the entrance 88 for the heat-treated material W into the furnace. This second predetermined distance L2 is preferably set to prevent or suppress overheating of the outer wall of the front chamber 14, for example, to prevent or suppress the outer wall of the front chamber 14 from being heated above a predetermined temperature.

[0051] According to the heat treatment furnace 10 having the above configuration, the object to be heat-treated W, which is placed on the mesh belt conveyor 30 and transported in the transport direction CD, can be preheated, that is, heated and heated up, as follows before reaching the heating chamber 18.

[0052] First, the object to be heat-treated W is placed on the mesh belt conveyor 30 via the loading table 12 and then proceeds to the high-frequency induction heating section 13, which is equipped with a high-frequency induction heating coil 26. The high-frequency induction heating coil 26 is positioned vertically above the mesh belt conveyor 30 so as to be at least a first predetermined distance L1 away from the mesh belt conveyor 30, so that the upper part of the object to be heat-treated W is heated more strongly than its lower part. The object to be heat-treated W, heated in the high-frequency induction heating section 13, moves to the pre-chamber 14.

[0053] In the anteroom 14, the workpiece W is preheated by the combustion heat from the modified gas combustion device 76 installed therein. This preheating heats not only the workpiece W inside the furnace but also the mesh belt conveyor 30. Since the workpiece W is in contact with the mesh belt conveyor 30, the lower part of the workpiece W is heated more strongly than the upper part due to heat transfer from the mesh belt conveyor 30.

[0054] Similarly, in the preheating chamber 16, the heat from the gas burner 52 and the heating from the heater 46 further heat not only the workpiece W inside the furnace but also the mesh belt conveyor 30. Since the workpiece W is in contact with the mesh belt conveyor 30, the lower part of the workpiece W is heated more strongly than the upper part due to heat transfer from the mesh belt conveyor 30. In particular, in the preheating chamber 16, the gas burner 52 is located vertically below the mesh belt conveyor 30. Therefore, the mesh belt conveyor 30 is strongly heated by the heat from the gas burner 52, and the lower part of the workpiece W is strongly heated not only by heat transfer from the mesh belt conveyor 30 but also by the heat from the gas burner 52.

[0055] The upper part of the heat-treated object W is strongly heated by the heating that occurs when alternating current is passed through the high-frequency induction heating coil 26, while the lower part is strongly heated by preheating in the front chamber 14 and preheating chamber 16. As a result, the temperature inside the heat-treated object W can approach a uniform temperature more quickly, or reach a substantially uniform temperature more quickly, compared to the case where only preheating is performed in the front chamber 14 and preheating chamber 16. Therefore, compared to the case where only preheating is performed in the front chamber 14 and preheating chamber 16, combining heating or preheating in the high-frequency induction heating section 13 with the preheating in the front chamber 14 and preheating chamber 16 makes it possible to rapidly and uniformly heat the heat-treated object W. In other words, this makes it possible to suitably increase the rate at which the heat-treated object W rises to a predetermined heating temperature in the heating chamber 18. As a result, the travel speed (conveying speed) of the mesh belt conveyor 30 can be increased. Furthermore, this configuration increases the heating rate of the object to be heat-treated W, and also shortens the length of the transport direction CD of the pre-chamber 14 and / or preheating chamber 16.

[0056] The following describes some of the characteristic features of the heat treatment furnace 10 having the above configuration, and the effects and benefits thereof.

[0057] The heat treatment furnace 10 comprises a preheating chamber 16 equipped with a gas burner 52, which is a modified gas generator; a heating chamber 18 downstream of the preheating chamber 16; and a mesh belt conveyor 30 on which the workpiece W to be heat-treated is placed to be transported to the preheating chamber 16 and the heating chamber 18. The heat treatment furnace 10 is also configured to exhaust the modified gas generated by the combustion of the gas burner 52 and supply it into the furnace as the furnace atmosphere gas through a modified gas supply passage 70. A high-frequency induction heating coil 26 connected to an AC power supply 96 is located upstream of the pre-chamber 14, which is upstream of the preheating chamber 16. In other words, the high-frequency induction heating coil 26 is located upstream of the gas burner 52, which is a modified gas generator. With this heat treatment furnace 10, by passing an AC current through the high-frequency induction heating coil 26, the workpiece W placed on the mesh belt conveyor 30 is actively heated, and then the workpiece W can be preheated in the preheating chamber 16 and sent to the heating chamber 18. Therefore, compared to the case where the high-frequency induction heating coil 26 is not provided, the rate of heating of the object to be heat-treated W in the upstream stage of the heating chamber 18, i.e., the preheating stage, can be more effectively increased.

[0058] The gas burner 52 is located on the vertically lower side of the mesh belt conveyor 30, and the high-frequency induction heating coil 26 is located on the vertically upper side of the mesh belt conveyor 30, opposite to the side where the gas burner 52 is located. With this configuration, the high-frequency induction heating coil 26 can actively heat the heat-treated object W placed on the mesh belt conveyor 30 from the vertically opposite side of the gas burner 52, relative to the mesh belt conveyor 30. As a result, the temperature of the heat-treated object W can be brought closer to a more uniform temperature more quickly or to a more uniform temperature compared to when the high-frequency induction heating coil 26 is not provided. In addition, a modified gas combustion device 76 is located on the vertically upper side of the mesh belt conveyor 30 in the pre-chamber 14, and the gas burner 52 is located on the vertically lower side of the mesh belt conveyor 30 in the pre-heating chamber 16. In the heat treatment furnace 10, combustion in the gas burner 52 is actively carried out to generate modified gas, so the heating from below by the gas burner 52 is stronger than the heating by the modified gas combustion device 76. Therefore, in this heat treatment furnace 10, a high-frequency induction heating coil 26 is installed on the vertically upper side of the mesh belt conveyor 30 to heat the workpiece W placed on the mesh belt conveyor 30 from the opposite side of the gas burner 52.

[0059] Furthermore, the high-frequency induction heating coil 26 is positioned at a distance of at least a first predetermined distance L1 from the mesh belt conveyor 30. This configuration makes it possible to prevent or suppress overheating of the mesh belt conveyor 30.

[0060] The high-frequency induction heating coil 26 is provided to heat the workpiece W in the atmosphere, and the pre-chamber 14, located downstream of the high-frequency induction heating coil 26 and upstream of the pre-heating chamber 16, is equipped with a modified gas combustion device 76 configured to burn the modified gas used as the furnace atmosphere gas and preheat the workpiece with the heat of combustion. The high-frequency induction heating coil 26 is located at a distance of at least a second predetermined distance L2 from the upstream end of the pre-chamber 14 in the transport direction CD. With this configuration, it is possible to prevent or suppress overheating of the outer wall of the pre-chamber 14.

[0061] While embodiments of this disclosure have been described above, this disclosure is not limited to such embodiments. Various substitutions and modifications are possible, as long as they do not deviate from the spirit and scope of this disclosure as defined by the claims of this application.

[0062] For example, the heat treatment furnace according to this disclosure does not need to have a pre-chamber 14. In this case, as shown in Figure 6, a preheating chamber 16 is located directly downstream of the high-frequency induction heating section 13, and an inlet 88 for the workpiece W to be heat-treated may be provided in the preheating chamber 16. In this case, the high-frequency induction heating section 13 equipped with the high-frequency induction heating coil 26 is provided to heat the workpiece W in the atmosphere, and is preferably located at a predetermined distance (hereinafter referred to as the third predetermined distance) or more from the upstream end of the preheating chamber 16 in the transport direction CD. With this configuration, for example, it is possible to prevent or suppress overheating of the outer wall of the preheating chamber 16. Note that this third predetermined distance may be the same as or different from the second predetermined distance L2 described above.

[0063] Furthermore, in the above embodiment, a gas burner 52 is provided on the vertically lower side of the mesh belt conveyor 30 in the preheating chamber 16, and a high-frequency induction heating coil 26 is provided on the vertically upper side of the mesh belt conveyor 30 in the high-frequency induction heating section 13. This relationship may be reversed. In other words, it is also possible to configure the gas burner 52 to be positioned on the vertically upper side of the mesh belt conveyor 30 and the high-frequency induction heating coil 26 to be positioned on the vertically lower side of the mesh belt conveyor 30. Thus, it is preferable that the gas burner 52, which is a modified gas generator, is provided on one vertical side of the mesh belt conveyor 30, and the high-frequency induction heating coil 26 is provided on the other vertical side of the mesh belt conveyor 30, opposite to the side on which the gas burner 52 is provided. [Explanation of Symbols]

[0064] 10 Heat treatment furnace 13. High-frequency induction heating section 14 Vestibule 16 Preheating chamber 18 Heating chamber 26. High-frequency induction heating coil 30 Mesh Belt Conveyor 52. Gas burner (modified gas generator)

Claims

1. In a heat treatment furnace comprising a preheating chamber equipped with a modified gas generator, a heating chamber downstream from the preheating chamber, and a conveying means for placing objects to be heat-treated so as to be transported to the preheating chamber and the heating chamber, the modified gas generated by the combustion of the modified gas generator is exhausted and supplied into the furnace as furnace atmosphere gas through a modified gas supply passage, A high-frequency induction heating coil, located upstream of the aforementioned modified gas generator and connected to an AC power supply. It is equipped with Heat treatment furnace.

2. The modified gas generating device is provided on one side of the conveying means in the vertical direction, The high-frequency induction heating coil is provided on the other side of the conveying means in the vertical direction, opposite to the side where the modified gas generator is provided. The heat treatment furnace according to claim 1.

3. The high-frequency induction heating coil is provided so as to be at least a first predetermined distance away from the transport means. A heat treatment furnace according to claim 1 or 2.

4. The aforementioned high-frequency induction heating coil is provided to heat the object to be heat-treated in the atmosphere, A pre-chamber located downstream of the high-frequency induction heating coil and upstream of the preheating chamber is equipped with a modified gas combustion device configured to burn the modified gas used as the furnace atmosphere gas and preheat the object to be heat-treated by the heat of combustion. The high-frequency induction heating coil is located at a distance of at least a second predetermined distance from the upstream end of the front chamber in the transport direction. A heat treatment furnace according to claim 1 or 2.

5. The aforementioned high-frequency induction heating coil is provided to heat the object to be heat-treated in the atmosphere and is located at a distance of at least a third predetermined distance from the upstream end of the preheating chamber in the transport direction. A heat treatment furnace according to claim 1 or 2.

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