Vacuum furnace

Abstract

The present invention relates to a vacuum furnace. A vacuum furnace capable of increasing the amount of dissolved gas of cooling oil to perform heat treatment is provided. The vacuum furnace is provided with a heating chamber that heats a workpiece, a quenching chamber that has an oil tank that stores cooling oil in which air dissolved in advance has been reduced, and cools the workpiece heated in the heating chamber by immersing the workpiece in the cooling oil, and a supply member that supplies non-active gas dissolved in the cooling oil to the cooling oil during the workpiece is housed in the heating chamber.

Description

Technical Field

[0001] This invention relates to a vacuum furnace. Background Technology

[0002] In the heat treatment of metal parts and other workpieces, the formation of an oxide film on the workpiece surface can affect quality. Therefore, techniques for suppressing oxide film formation are known. Patent Document 1 points out the increased cost of vacuum furnaces and proposes a technique to reduce oxygen in the cooling oil during heat treatment in an atmospheric atmosphere. However, in the technology of Patent Document 1, since heat treatment is performed in an atmospheric atmosphere, the suppression of oxide film is considered insufficient. Generally speaking, a vacuum furnace for heat treatment under reduced pressure is advantageous for suppressing oxide film. Patent Document 2 discloses an apparatus for heat treatment under reduced pressure, which includes a method for injecting gas into the workpiece during immersion in cooling oil for cooling. Patent Document 3 also discloses an apparatus for heat treatment under reduced pressure, which discloses a method of injecting cooling oil into the quenching chamber during the vapor film stage of quenching and reducing the pressure of the quenching chamber during the boiling stage (sometimes referred to as the high Pascal method).

[0003] On the other hand, in a vacuum furnace, when using fresh cooling oil, the quenching chamber containing the fresh oil is depressurized for a certain period (e.g., one night), significantly reducing the air dissolved in the fresh oil. One purpose of this is to suppress the formation of an oxide film on the workpiece surface. Afterward, the fresh oil is repeatedly used for workpiece cooling, but in a vacuum furnace, the quenching chamber is depressurized while connected to the atmosphere for workpiece feeding, thus maintaining a relatively low level of air dissolved in the cooling oil.

[0004] However, if the amount of gas dissolved in the cooling oil is low, the cooling performance may sometimes decrease. Non-Patent Literature 1 points out that if the amount of dissolved gas is low, the cooling performance decreases, and explains that experiments using beakers have confirmed that if the amount of dissolved gas is increased by stirring the cooling oil, the cooling performance is restored.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 3151681

[0008] Patent Document 2: International Publication No. 2018 / 123246

[0009] Patent Document 3: Japanese Patent No. 6533146

[0010] Non-patent literature

[0011] Non-Patent Literature 1: Katsumi Ichitani, Action of Heat Treatment Oil under Reduced Pressure, "Industrial Heating", Japan, Japan Industrial Furnace Association, November 15, 2018, Vol. 43, No. 6, pp. 20-26 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Non-patent literature 1 concludes that, since increasing the amount of dissolved gas by stirring the cooling oil takes time, even with repeated decompression and stirring of the cooling oil in a vacuum furnace, the impact on the change in cooling performance caused by variations in the amount of dissolved gas is relatively small, and there is no problem in balancing the performance of the cooling oil. However, from the perspective of vacuum furnace development, there is room to improve heat treatment performance by improving the performance of the cooling oil.

[0014] The purpose of this invention is to provide a vacuum furnace that can increase the amount of dissolved gas in the cooling oil for heat treatment.

[0015] Solution for solving the problem

[0016] According to the present invention, a vacuum furnace is provided, characterized in that it comprises:

[0017] The heating chamber heats the workpiece;

[0018] A quenching chamber having an oil tank for storing cooling oil with pre-reduced dissolved air, wherein the workpiece heated in the heating chamber is immersed in the cooling oil for cooling; and

[0019] A supply component that supplies an inactive gas, which is used to dissolve in the cooling oil, to the cooling oil while the workpiece is housed in the heating chamber.

[0020] The effects of the invention

[0021] According to the present invention, a vacuum furnace capable of increasing the amount of dissolved gas in cooling oil for heat treatment can be provided. Attached Figure Description

[0022] Figure 1 This is an explanatory diagram of a vacuum furnace according to one embodiment of the present invention.

[0023] Figure 2 yes Figure 1 A diagram illustrating the quenching chamber of a vacuum furnace.

[0024] Figure 3 (A) and (B) are flowcharts representing a processing example of the control unit, and (C) is... Figure 1 A diagram illustrating the operation of a vacuum furnace.

[0025] Figure 4This is a flowchart illustrating a processing example of the control unit.

[0026] Figure 5 (A) to (F) are Figure 1 A diagram illustrating the operation of a vacuum furnace.

[0027] Figure 6 (A) to (D) are Figure 1 A diagram illustrating the operation of a vacuum furnace.

[0028] Figure 7 It is a timing diagram showing the state of the heating chamber and quenching chamber during heat treatment.

[0029] Figure 8 This is an explanatory diagram illustrating an example of when inert gases are supplied.

[0030] Figure 9 This is a flowchart illustrating another processing example of the control unit.

[0031] Figure 10 This is a timing diagram representing another state of the heating chamber and quenching chamber during heat treatment.

[0032] Figure 11 (A) to (C) are explanatory diagrams representing another example of a supply unit.

[0033] Figure 12 (A) and (B) are illustrations of another example of a supply unit.

[0034] Figure 13 This is a timing diagram representing another state of the heating chamber and quenching chamber during heat treatment.

[0035] Figure 14 This is an explanatory diagram of a vacuum furnace according to another embodiment of the present invention.

[0036] Figure 15 yes Figure 14 A diagram illustrating the operation of a vacuum furnace.

[0037] Figure 16 This is an explanatory diagram of a vacuum furnace according to another embodiment of the present invention.

[0038] Figure 17 (A) is an explanatory diagram of the test subject, and (B) is an explanatory diagram of the test content.

[0039] Figure 18 (A) to (C) are graphs representing the experimental results.

[0040] Explanation of reference numerals in the attached figures

[0041] 1~1B: Vacuum furnace, 2: Heating chamber, 3: Quenching chamber Detailed Implementation

[0042] The embodiments are described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are not intended to limit the technical solutions of the claims. Furthermore, all combinations of features described in the embodiments are not necessarily essential to the invention. Two or more features from the plurality of features described in the embodiments can also be combined arbitrarily. Additionally, the same reference numerals are used to denote the same or identical structures, and repeated descriptions are omitted.

[0043] <First Implementation Method>

[0044] <Structure of a Vacuum Furnace>

[0045] Figure 1 This is an explanatory diagram of a vacuum furnace 1 according to an embodiment of the present invention. Figure 2 This is an explanatory diagram of the quenching chamber 3 of vacuum furnace 1. Figure 1 This shows the structure of vacuum furnace 1 from the side. Figure 2 This shows the structure of vacuum furnace 1 from the front view.

[0046] The vacuum furnace 1, comprising a heating chamber 2 and a quenching chamber 3 arranged sequentially, is a device for heat treating a workpiece W. The workpiece W is, for example, a plurality of mechanical parts housed in a basket. The heating chamber 2 is divided by a shell 20, inside which is an insulated container 21 formed of insulating material. The insulated container 21 is kept airtight. On the other hand, a door 21a is provided on the quenching chamber 3 side, allowing the workpiece W to be fed into and out of the insulated container 21 when the door 21a is open. The door 21a is moved by an actuator (not shown).

[0047] A conveying unit 22 for conveying workpiece W is provided at the bottom of the insulated container 21. The conveying unit 22 is a unit that forms a furnace bed and moves the workpiece W in and out of the insulated container 21. In this embodiment, it is a roller conveyor. However, the conveying unit 22 is not limited to a roller conveyor, but may also be a chain conveyor or a forklift robot.

[0048] Multiple heaters 23 are also provided inside the heat-insulating container 21. The heaters 23 can be used to heat the inside of the heat-insulating container 21 to heat the workpiece W that is stopped on the conveying unit 22. A circulating fan 24 is provided in the heating chamber 2. The blades of the circulating fan 24 are arranged inside the heat-insulating container 21 to circulate the gas inside the heat-insulating container 21.

[0049] A carburizing gas supply unit 7 is provided in the heating chamber 2. The carburizing gas supply unit 7 includes a gas storage section 70 and a control valve V5. The gas storage section 70 stores compressed gas (e.g., acetylene gas) for carburizing. When the control valve V5 is opened, carburizing gas can be supplied to the heat-insulating container 21.

[0050] The quenching chamber 3 is divided by the housing 30. An opening 31a, serving as the inlet and outlet for the workpiece W, is formed in the wall on its front side. An opening 31b, for conveying the workpiece W between the quenching chamber 3 and the heating chamber 2, is formed in the partition wall between the two chambers. The opening 31a is opened and closed by a door 34, and the opening 31b is opened and closed by a door 35. Doors 34 and 35 are moved by an actuator (not shown).

[0051] The quenching chamber 3 includes an upper conveying chamber 31 and a lower oil tank 32. Cooling oil is stored in the oil tank 32. A conveying unit 33 is provided in the conveying chamber 31. In this embodiment, the conveying unit 33 is a roller conveyor. However, the conveying unit 33 is not limited to a roller conveyor and may also be a chain conveyor.

[0052] The conveying unit 33 is raised and lowered using the lifting unit 36. The lifting unit 36 ​​includes an actuator 36a and a lifting device 36b connecting the actuator 36a and the conveying unit 33. Figure 1 Conveying unit 33 and Figure 2 The dashed line indicates the transport position and is in Figure 2 The conveying unit 33 is raised and lowered between the immersion positions indicated by solid lines. The lifting device 36b is, for example, a chain, and the actuator 36a is a fluid cylinder that sends the lifting device out and pulls it in. The workpiece W on the conveying unit 33 is lowered to the immersion position by the conveying unit 33 and immersed in the cooling oil. The lifting unit 36 ​​can also continuously raise and lower the conveying unit 33 (i.e., the workpiece W) over short distances near the immersion position. A heater 37 is provided in the oil tank 32, and the temperature of the cooling oil 32a can be adjusted by the heat generated by the heater 37.

[0053] Multiple circulation units 39 are provided in the oil tank 32. Each circulation unit 39 has a drive source 39a, such as a motor, located outside the oil tank 32, and blades 39b located inside the oil tank 32, serving as a stirring unit for stirring the cooling oil 32a. Inside the oil tank 32, multiple L-shaped or J-shaped circulation passages 38 are formed by passage walls 38w. Each circulation passage 38 is a cylindrical passage with an inlet 38a and an outlet 38b. The inlet 38a is located in the upper part of the oil tank 32, and the outlet 38b is located in the lower part of the oil tank 32, particularly below the conveying unit 33 at the immersion position.

[0054] Blade 39b is positioned within circulation passage 38, and through its rotation, such as Figure 2 As indicated by the middle arrow, a circulating flow is generated from inlet 38a to outlet 38b. The cooling oil flowing out of outlet 38b causes the cooling oil around workpiece W to circulate, improving the cooling performance of workpiece W.

[0055] The vacuum furnace 1 includes a pressure reduction unit 5 and a non-reactive gas supply unit 6. The pressure reduction unit 5 includes a vacuum pump 50 and control valves V1 and V2. By operating the vacuum pump 50 and opening the control valves V1, pressure reduction can be achieved in the quenching chamber 3, for example, by evacuating the quenching chamber 3. Additionally, pressure reduction can be achieved within the insulation container 21 by opening the control valves V2, for example, by evacuating the insulation container 21. The vacuum pump 50 is shared by the heating chamber 2 and the quenching chamber 3. However, it is also possible to have a separate vacuum pump for each chamber.

[0056] The inert gas supply unit 6 includes a gas supply source 60 and control valves V3, V4, and V6, and is a unit for supplying inert gases such as nitrogen. The gas supply source 60 is, for example, a tank for storing compressed gas containing inert gases. When control valve V3 is opened, inert gases are supplied from the gas supply source 60 to the delivery chamber 31 of the quenching chamber 3, enabling repressurization of the quenching chamber 3. When control valve V4 is opened, inert gases are supplied from the gas supply source 60 to the heat insulation container 21 of the heating chamber 2, enabling repressurization of the heat insulation container 21.

[0057] For cooling oil 32a, in order to reduce the amount of oxygen dissolved in it, the dissolved air is reduced beforehand by depressurization, resulting in a decrease in the amount of dissolved gas. As a result, the cooling performance of cooling oil 32a is reduced. When control valve V6 is opened, inactive gas is supplied to cooling oil 32a. By supplying inactive gas to cooling oil 32a, it is dissolved, thereby increasing the amount of dissolved gas in cooling oil 32a and improving its performance. It should be noted that in this embodiment, the gas supply source 60 is shared by the delivery chamber 31, oil tank 32, and heat insulation container 21. However, it is also possible for each chamber to have its own gas supply source.

[0058] An injection section 61 is provided at the top of the pipe from the control valve V6 to the oil tank 32. Inactive gas is injected into the cooling oil 32a from the injection section 61. By injecting inactive gas into the cooling oil 32a, its dissolution efficiency can be improved. A micronization section 62 is provided in the injection section 61 to refine the bubbles of the inactive gas injected from the injection section 61. The micronization section 62 is, for example, made of a porous material. The micronization section 62 can be a mechanism that generates micron-sized or nano-sized bubbles. By refining the bubbles of the inactive gas, the dissolution efficiency relative to the cooling oil 32a can be improved.

[0059] The location where the inactive gas is supplied relative to the cooling oil 32a can be chosen arbitrarily, but in this embodiment, it is set within the circulation passage 38. By injecting the inactive gas into the circulation passage 38, the circulating flow of the cooling oil 32a mixes with the inactive gas, thereby improving the dissolution efficiency of the inactive gas. Moreover, the circulating flow is a downward flow from the inlet 38a to the outlet 38b, which is a flow away from the liquid surface (oil surface) of the cooling oil 32a. By injecting the inactive gas into this flow, premature escape of the inactive gas from the oil surface to the outside of the cooling oil 32a can be suppressed. Furthermore, in this embodiment, the inactive gas is injected upstream of the blade 39b in the flow direction of the circulating flow within the circulation passage 38. After injection, the inactive gas mixes with the cooling oil 32a by means of the blade 39b, thereby improving the dissolution efficiency of the inactive gas relative to the cooling oil 32a. The circulation unit 39 can operate continuously or only during the quenching of the workpiece W and during the supply of inactive gas to the cooling oil 32a.

[0060] The control unit 9 automatically controls the vacuum furnace 1. The control unit 9 includes a processing unit, a storage unit, and an input / output interface. The processing unit, represented by a CPU, is a processor that executes programs stored in the storage unit. The storage unit, such as ROM, RAM, or a hard disk, stores information required for control in addition to the programs executed by the processing unit. The input / output interface facilitates the transmission and reception of signals between the processing unit and external devices.

[0061] The input / output interface receives the detection results from sensors 90, including those measuring pressure and temperature in each chamber and sensors detecting the conveying position of workpiece W. Based on these results, the processing unit outputs control signals to the actuators of fluid equipment such as motors and control valves in the vacuum furnace 1, driving them accordingly. An operation panel 91 is connected to the control unit 9. The operation panel 91 is, for example, a touchpad. Users can use the operation panel 91 to perform various settings and operation instructions for the vacuum furnace 1.

[0062] <Control Example>

[0063] This section describes a control processing example executed by the processing unit of control unit 9. It should be noted that, unless otherwise specified, all control valves and doors are closed.

[0064] <Settings>

[0065] Figure 3(A) is a flowchart illustrating an example of processing user action settings. In S1, a setting screen is displayed on the operation panel 91. The setting screen displays various setting items, for example, in the form of a menu. The user can recall the desired setting item and input the setting content. As an action setting that the user can set, for example, the conditions for supplying inactive gas from the injection unit 61 to the cooling oil 32a can be listed. As these supply conditions, the timing of supplying inactive gas, the supply time, or the supply method (continuous, intermittent), etc., can be listed.

[0066] In step S2, user input on the operation panel 91 related to the settings is received. In step S3, the settings input in step S2 are saved in the storage unit. The process then concludes. The vacuum furnace 1 is then operated according to the saved settings.

[0067] Vacuuming of new oil

[0068] When the cooling oil 32a is new, the dissolved oxygen content is relatively high. Therefore, as a preparatory treatment for the heat treatment of workpiece W, the dissolved air in the cooling oil is reduced in advance by the decompression unit 5. Figure 3 (B) indicates the processing example executed by the processing unit of control unit 9, which is executed according to the user's instructions. Figure 3 (C) is an operation diagram of vacuum furnace 1.

[0069] In S11, the user's start instruction is received. Processing begins with new oil collected in oil tank 32. In S12, vacuum pump 50 is activated, and control valve V1 is opened to evacuate the quenching chamber 3. Figure 3 As schematically shown in (C), the gas inside the quenching chamber 3 is discharged. The pressure inside the quenching chamber 3 is reduced to less than 10 Pa, for example. Dissolved oxygen in the fresh oil is removed and exhausted to the outside of the furnace through the pressure reducing unit 5.

[0070] In S13, it is determined whether the termination condition is met. The termination condition is, for example, the elapsed time or the user's end date. In the case of the elapsed time, for example, about half a day to one day, dissolved air can be sufficiently removed from the cooling oil 32a. If the termination condition is met, proceed to S14, close the control valve V1, stop the vacuum pump 50, and end the vacuuming process.

[0071] <Examples of heat treatment>

[0072] This section illustrates a series of heat treatments for workpiece W. Figure 4 This indicates a processing example executed by the processing unit of control unit 9. Figure 5 (A) Figure 6 (D) is an operational diagram of vacuum furnace 1. In S21, workpiece W is fed into quenching chamber 3. Figure 5(A) indicates the operation of vacuum furnace 1 at this time. After the inactive gas is supplied to the quenching chamber 3 through the inactive gas supply unit 6 to make the quenching chamber 3 reach atmospheric pressure, the door 34 is opened, and the workpiece W is sent from outside the furnace into the quenching chamber 3. The quenching chamber 3 is now open to the atmosphere.

[0073] In S22, the vacuum chamber 3 is evacuated using the pressure reduction unit 5. Figure 5 (B) indicates the operation of vacuum furnace 1 at this time. Vacuum pump 50 is activated, control valve V1 is opened, and the pressure in quenching chamber 3 is reduced. For example, the pressure in quenching chamber 3 is reduced to less than 10 Pa. When workpiece W is fed in, the air entering quenching chamber 3 is discharged out of the furnace. At this time, the air dissolved in cooling oil 32a is also degassed and discharged out of the furnace, suppressing the increase of dissolved oxygen in cooling oil 32a due to atmospheric opening when workpiece W is fed in.

[0074] In S23, workpiece W is conveyed from quenching chamber 3 to heating chamber 2. Figure 5 (C) indicates the operation of vacuum furnace 1 at this time. Doors 35 and 21a are opened, and conveying units 33 and 22 are driven to convey workpiece W to heating chamber 2.

[0075] Next, as part of the processing in heating chamber 2, in S24, the vacuum chamber 2 is evacuated using the pressure reducing unit 5, and the heating process is performed in S25. As part of the processing in quenching chamber 3, in S26, the inactive gas is supplied to the conveying chamber 31 using the inactive gas supply unit 6, thereby pressurizing the quenching chamber 3. Figure 5 (D) indicates the operation of vacuum furnace 1 at this time.

[0076] The vacuum pump 50 is activated, and control valve V2 is opened to depressurize the heating chamber 2. When the workpiece W is conveyed to the heating chamber 2, air may sometimes enter; therefore, this air is discharged outside the furnace. The pressure in the heating chamber 2 is reduced to, for example, less than 10 Pa, but around 50 Pa, before heating begins by heater 23. In parallel, control valve V3 is opened, and inert gas is supplied to the conveying chamber 31 via inert gas supply unit 6, pressurizing the quenching chamber 3. This pressurization is used to suppress degassing of the inert gas and promote dissolution when it is subsequently supplied to the cooling oil 32a.

[0077] In parallel with the heating treatment (S25) in heating chamber 2, in S27, control valve V3 is closed to stop the supply of inactive gas to delivery chamber 31, while control valve V6 is opened to supply inactive gas to cooling oil 32a. Figure 5(E) indicates the operation of vacuum furnace 1 at this time. It is possible to increase the amount of dissolved gas while maintaining a low dissolved oxygen content in cooling oil 32a. The heating process in heating chamber 2 includes a step of supplying carburizing gas into the heat-insulating container 21 by opening control valve V5 using carburizing gas supply unit 7.

[0078] Corresponding to the end of the heat treatment (S25) in heating chamber 2, in S28, control valve V6 is closed to stop the supply of inactive gas to cooling oil 32a. In S29, in order to balance the gas pressure between heating chamber 2 and quenching chamber 3 (e.g., a pressure slightly lower than atmospheric pressure), control valves V3 and V4 are opened, and inactive gas is supplied to conveying chamber 31 and heat insulation container 21 using inactive gas supply unit 6. Figure 5 (F) indicates the operation of vacuum furnace 1 at this time, supplying inactive gas to delivery chamber 31 and insulation container 21 respectively. The supply of inactive gas to cooling oil 32a ends.

[0079] In S30, workpiece W is conveyed from heating chamber 2 to quenching chamber 3. Figure 6 (A) indicates the operation of vacuum furnace 1 at this time. Doors 21a and 35 are opened, and conveying units 22 and 33 are driven to convey workpiece W to quenching chamber 2. If the conveying of workpiece W is completed, doors 21a and 35 are closed, and vacuum is applied to the heat insulation container 21 using pressure reduction unit 5.

[0080] In S31, the workpiece W is quenched. Figure 6 (B) indicates the operation of vacuum furnace 1 at this time. Using lifting unit 36, the conveying device 33, together with the workpiece W, is lowered to the immersion position. The workpiece W is immersed in cooling oil 32a and is rapidly cooled.

[0081] If quenching is completed, the lifting unit 36 ​​is used to raise the conveying device 33 together with the workpiece W to the conveying position, and in S32, the workpiece W is sent out of the furnace. Figure 6 (C) and Figure 6 (D) indicates the operation of vacuum furnace 1 at this time. For example... Figure 6 As shown in (C), control valve V3 is opened, and inactive gas is supplied to the delivery chamber 31 via inactive gas supply unit 6, restoring the quenching chamber 3 to atmospheric pressure. Then, as... Figure 6 As shown in (D), door 34 is opened, and workpiece W is sent out of the furnace using conveyor 33. The heat treatment of workpiece W is then complete.

[0082] In S33, it is determined whether there is a next workpiece W to be processed. If there is a next workpiece W, the process returns to S21 and repeats the same process.

[0083] Reference Figure 7 ,illustrate Figure 4The state of vacuum furnace 1 in the heating process. Figure 7 This is a timing diagram showing the timing of the supply of inactive gas to cooling oil 32a ("inactive gas supply"), the pressure change in quenching chamber 3 ("quenching chamber pressure"), the pressure reduction timing in quenching chamber 3 ("quenching chamber depressurization"), the pressure change in heating chamber 2 ("heating chamber pressure"), and the pressure reduction timing in heating chamber 2 ("heating chamber depressurization"). Figure 7 The proposed steps are as follows: After the workpiece is fed into the heating chamber 2, the heating treatment proceeds through a series of processes: heating and homogenization → carburizing → diffusion → cooling → homogenization. The workpiece is then transferred to the quenching chamber 3, and after oil cooling, it is removed from the furnace. It should be noted that "workpiece feeding" here refers to the transfer of workpiece W from the quenching chamber 3 to the heating chamber 2.

[0084] In the "workpiece feeding" step, the air pressure in the quenching chamber 3 is reduced to pressure P1 (e.g., less than 10 Pa) by vacuuming in S22. At time t1, the workpiece W is conveyed from the quenching chamber 3 to the heating chamber 2. When the workpiece W is conveyed to the heating chamber 2, after doors 35 and 21a are closed, the heating chamber 2 is evacuated in S24. The heating chamber 2 is essentially always reduced to a vacuum state (e.g., less than 10 Pa), but there is a possibility that a small amount of air may enter the heating chamber 2 when the workpiece W is conveyed from the quenching chamber 3 to the heating chamber 2. Therefore, as a precaution, the heating chamber 2 is evacuated (degassed).

[0085] After doors 35 and 21a are closed, the gas pressure in the quenching chamber 3, which has been reduced to pressure P1 (e.g., less than 10 Pa) by vacuuming in S22, is increased to pressure P2 in S26 to promote the dissolution of inactive gases relative to cooling oil 32a. Pressure P2 is, for example, between 1 kPa and 9000 kPa, preferably between 10 kPa and 2000 kPa, and more preferably in the range of 30 kPa to 90 kPa. Figure 7 In the example, we assume that the pressure is lower than atmospheric pressure (around 30 kPa) as pressure P2.

[0086] If the gas pressure inside heating chamber 2 is below 50 Pa, heater 23 is activated to begin heating the workpiece W. If the temperature inside heating chamber 2 is a predetermined temperature, heater 23 is activated to maintain that temperature for homogenization (to achieve uniform heat distribution). Meanwhile, in parallel with the start of workpiece W heating, inactive gas is supplied to cooling oil 32a in quenching chamber 3. The gas pressure in quenching chamber 3 is increased to pressure P2, thus promoting the dissolution of inactive gas relative to cooling oil 32a compared to the state of less than 10 Pa immediately after vacuuming.

[0087] During the supply of inactive gas to the cooling oil 32a, the undissolved inactive gas causes the pressure in the conveying chamber 31 to rise. Therefore, the pressure reducing unit 5 periodically reduces the pressure in the quenching chamber 3 to maintain the pressure in the quenching chamber 3 at pressure P2. The pressure rise in the quenching chamber 3 itself is not a particular problem, but when conveying the workpiece W from the heating chamber 2 to the quenching chamber 3, it is necessary to restore the heating chamber 2 (especially the insulation container 21) and the quenching chamber 3 to pressure P3 (e.g., 80 kPa to 90 kPa) to achieve pressure balance. At this time, in order to easily control the pressure in the quenching chamber 3, the pressure in the quenching chamber 3 is maintained at pressure P2. Figure 7 During the period when "inactive gas supply" is in progress, the "quenching chamber pressure" pulsation reflects the reduction in the pressure rise in the delivery chamber 31 caused by the inactive gas that is not dissolved in the cooling oil 32a, and the pressure reduction in the quenching chamber 3 by the pressure reducing unit 5.

[0088] During the heat treatment, the heat-insulated container 21 is maintained in a vacuum state (less than 10 Pa). In this embodiment, a vacuum pump 50 is used to depressurize each chamber. When the capacity of the vacuum pump 50 is small, it is sometimes difficult to depressurize multiple chambers simultaneously. Therefore, a depressurization unit 5 is used to alternately depressurize in the two chambers in such a way that the depressurization timing of "quenching chamber depressurization" and "heating chamber depressurization" do not overlap.

[0089] During the carburizing process, carburizing gas is supplied to the insulation container 21 via the carburizing gas supply unit 7, increasing its pressure. To control the pressure inside the insulation container 21, the pressure reduction unit 5 is used only for reducing the pressure in the insulation container 21 during the carburizing process. Therefore, the supply of inactive gas to the cooling oil 32a is temporarily stopped during the carburizing process. Of course, the supply of inactive gas to the cooling oil 32a can also be carried out during the carburizing process.

[0090] After the diffusion process, during the cooling process, the driving of a portion of the heaters 23 is stopped, allowing the temperature inside the insulated container 21 to gradually decrease to the predetermined temperature. After the subsequent homogenization process, the heating treatment in the heating chamber 2 is completed. Then, in order to transfer the workpiece W from the heating chamber 2 to the quenching chamber 3, both the quenching chamber 2 and the heating chamber 3 are restored to pressure P3. When the workpiece W is transferred from the heating chamber 2 to the quenching chamber 3, it is immersed in cooling oil 32a (oil cooling). Afterward, the workpiece is removed from the furnace. The heating chamber 2 is then evacuated again using the pressure reduction unit 5.

[0091] It takes time to dissolve the inactive gas in the cooling oil 32a and increase the amount of dissolved gas. In this embodiment, during the period when the workpiece is in the heating chamber 2, the inactive gas can be supplied to the cooling oil 32a to increase the amount of dissolved gas. In this embodiment, the supply of the inactive gas to the cooling oil 32a is carried out during heating and homogenization, diffusion, cooling, and homogenization. As a result, the supply time can be ensured to be, for example, about 60 to 120 minutes, and combined with the direct injection of inactive gas from the injection section 61 into the cooling oil 32a, the amount of dissolved gas in the cooling oil 32a can be sufficiently increased.

[0092] <Second Implementation Method>

[0093] Reference Figure 8 This is another example illustrating the timing of supplying inactive gases to cooling oil 32a. As mentioned above, it takes time for the amount of dissolved gas to increase and dissolve in the cooling oil 32a, so the user can appropriately set the supply timing based on factors such as the heat treatment time.

[0094] Figure 8 The example of EX1 illustrates an example of supplying inactive gas to cooling oil 32a during the first half of the heat treatment period (the period close to the time when the workpiece W is fed into the heating chamber 2, for example, until heating and homogenization). Figure 8 The example of EX2 represents an example in which an inactive gas is supplied to the cooling oil 32a during the latter half of the heat treatment period (the period close to the time when the workpiece W is sent out of the quenching chamber 3, for example, until diffusion, cooling, homogenization, etc.). Although either EX1 or EX2 can be used, the example of EX2, which is closer to the quenching period, is advantageous considering that the dissolved gas in the cooling oil 32a may degas.

[0095] Figure 8 The example of EX3 illustrates the supply of inactive gas to the cooling oil 32a in a manner that is divided into the first half and the second half of the heating process. This is the same supply timing as the first embodiment, suitable for situations where there is an obstacle to the supply of inactive gas during the heating process. Figure 8 The example of EX4 illustrates the supply of inactive gas to the cooling oil 32a during the middle period of the heat treatment. This is suitable for situations where the supply of inactive gas is hindered during the first or second half of the heat treatment.

[0096] Example EX5 illustrates an example where the supply of inactive gas to cooling oil 32a begins at the heat treatment stage, the workpiece W is conveyed to the quenching chamber 3, and the supply ends just before immersion in cooling oil 32a. This facilitates ensuring a longer supply time.

[0097] In the examples so far, during the quenching of workpiece W (the period when workpiece W is not immersed in cooling oil 32a), inactive gas is not supplied to cooling oil 32a. This has the advantage of stabilizing the properties of cooling oil 32a during quenching. Alternatively, it is also possible to employ... Figure 8 The timing of the supply. In the illustrated example, an example is shown where the supply of inactive gas to the cooling oil 32a begins from the heat treatment stage and continues during the quenching of the workpiece W (while the workpiece W is immersed in the cooling oil 32a). This makes it easy to ensure a longer supply time.

[0098] In either example, by utilizing the time that the workpiece W is present in the heating chamber 2 to supply inactive gas to the cooling oil 32a, time can be ensured for increasing the amount of dissolved gas in the cooling oil 32a.

[0099] <Third Implementation Method>

[0100] In the first embodiment Figure 4 In the example, for each workpiece W (or whenever the quenching chamber 3 is opened to the atmosphere in S21), an inactive gas is supplied to the cooling oil 32a in S27. This is advantageous in maintaining a sufficient amount of dissolved gas in the cooling oil 32a.

[0101] However, it is also possible to supply non-reactive gas to the cooling oil 32a for each of the multiple workpieces W. Figure 9 This is a flowchart illustrating this example. Only applicable to... Figure 4 The following example illustrates different processing methods. In this example, inactive gas is supplied to the cooling oil 32a for every three workpieces W processed. The number of workpieces W processed can also be set by the user.

[0102] After workpiece W is fed into heating chamber 2 in S23, processing steps S41 to S43 are performed as part of the processing on the quenching chamber 3 side. In S41, it is determined whether the variable N, representing the number of times workpiece W has been processed, is 3. If N = 3, proceed to S42; if N ≠ 3, proceed to S43. In S42, variable N is reset to 0, and processing steps S26 to S28 are skipped, proceeding to S29.

[0103] In this embodiment, since the inactive gas is supplied to the cooling oil 32a for each of the plurality of workpieces W, it is possible to prevent the unnecessary supply of inactive gas.

[0104] <Fourth Implementation Method>

[0105] In the first embodiment, an example was described in which the pressure in the quenching chamber 3 was maintained at a pressure P2 (<P3) during the supply of the inert gas to the cooling oil 32a. However, the pressure P2 may also be higher than the pressure P3 during the recompression. If the pressure P2 is higher, the dissolution of the inert gas in the cooling oil 32a is promoted.

[0106] Figure 10 represents instead of Figure 7 the state of the vacuum furnace 1 during the heat treatment in this embodiment. Aspects different from the Figure 7 example will be described.

[0107] In this embodiment, in order to promote the dissolution of the inert gas in the cooling oil 32a, the pressure in the quenching chamber 3 evacuated to a pressure P1 (e.g., less than 10 Pa) in S22 is increased to a pressure P2' in S26. The pressure P2' is, for example, about 130 kPa. During the supply of the inert gas to the cooling oil 32a, the inert gas that has not dissolved in the cooling oil 32a causes the pressure in the transfer chamber 31 to rise. Therefore, the decompression unit 5 periodically decompresses the quenching chamber 3 to maintain the pressure in the quenching chamber 3 at the pressure P2'.

[0108] During the recompression ( Figure 4 S29), the decompression unit 5 decompresses the pressure in the quenching chamber 3 to the pressure P3 to balance it with the pressure in the heating chamber 2.

[0109] <Fifth Embodiment>

[0110] In the first embodiment, as the inert gas supply unit 6, the gas supply source 60 is shared by the transfer chamber 31, the heat insulation container 21, and the oil tank 32. However, a dedicated unit for supplying the inert gas to the cooling oil 32a in the oil tank 32 may be provided.

[0111] Figure 11 (A) of

[0112] shows an example. The illustrated inert gas supply unit 6A includes a gas supply unit 63, a tank T storing the inert gas, and check valves 67a and 67b. The gas supply unit 63 includes a cylinder (Japanese: シリンダ) 65 and an actuator 64 that reciprocates a piston 65a in the cylinder 65. The actuator 64 includes, for example, a fluid circuit or an electric motor.

[0113] ​​When piston 65a moves in the D1 direction, a negative pressure is created inside cylinder 65, and check valve 67a opens, drawing inert gas from tank 66 into cylinder 65. At this time, check valve 67b closes. If piston 65a moves in the D2 direction, check valve 67b opens, supplying the inert gas in cylinder 65 to cooling oil 32a in oil tank 32. By continuously reciprocating piston 65a in the D1 and D2 directions, inert gas can be supplied to cooling oil 32a in oil tank 32. This increases the amount of dissolved gas in cooling oil 32a.

[0114] Figure 11 (B) represents another example. The inactive gas supply unit 6B shown in the figure is... Figure 11 The inactive gas supply unit 6A has the same structure as (A), but the source of the inactive gas supply is different. The suction port 65b of the inactive gas supply unit 6B is connected to the conveying chamber 31 via a check valve 67a. Except when the workpiece W is being fed in or out (… Figure 4 In addition to S21 and S32, the inactive gas supply unit 6 fills the delivery chamber 31 with inactive gas. The inactive gas supply unit 6B uses the delivery chamber 31 as a source of inactive gas.

[0115] Figure 11 (C) represents another example. Figure 11 The inactive gas supply unit 6C of (C) is a unit built into the quenching chamber 3, which is a gas pump that delivers the inactive gas in the delivery chamber 31 to the cooling oil 32a in the oil tank 32.

[0116] Figure 12 (A) represents yet another example. Figure 12 The inactive gas supply unit 6D of (A) includes an ejector 68 and a liquid delivery pump 69. The ejector 68 is disposed inside the quenching chamber 3, and the liquid delivery pump 69 is disposed outside the quenching chamber 3. The ejector 68 has a main body 681 forming a straight oil passage and a gas passage portion 682 intersecting the oil passage. The oil passage of the main body 681 has an inlet 681a and an outlet 681b.

[0117] The main body 681 is immersed in cooling oil 32a, and the gas passage 682 extends from the main body 681 to the oil surface of the cooling oil 32a and communicates with the delivery chamber 31.

[0118] The main body 681 has a cylindrical space 681c formed in a manner that surrounds the oil passage, and the space 681c is connected to the gas passage section 682. The space 681c and the oil passage are connected by a plurality of gas passages 681d.

[0119] The pump 69 draws in cooling oil 32a from the oil tank 32 and sprays the drawn-in cooling oil 32a into the inlet 681a of the injector 68. The sprayed cooling oil 32a passes through the main body 681 and is injected into the oil tank 32 from the outlet 681b. As the cooling oil 32a passes through the main body 681, a negative pressure is generated in the space 681c and the gas passage 681d. The inactive gas in the delivery chamber 31 is mixed with the cooling oil 32a passing through the main body 681 via the gas passage 682, the space 681c, and the gas passage 681d. The cooling oil 32a mixed with the inactive gas is then injected from the outlet 681b. In this way, inactive gas can be supplied to the cooling oil 32a, increasing the amount of dissolved gas in the cooling oil 32a.

[0120] Figure 12 (B) represents another example. Figure 12 The inactive gas supply unit 6E of (B) is related to Figure 12 The inactive gas supply unit 6D of (A) has the same structure, but the injector 68 is located outside the quenching chamber 3.

[0121] The ejector 68 and the delivery pump 69 constitute a circulation section that returns the cooling oil 32a discharged from the oil tank 32 to the oil tank 32. Inert gas is supplied to the cooling oil 32a in the ejector 68, which is located midway through the circulation path. The cooling oil 32a mixed with the inert gas is injected into the oil tank 32 via the outlet 681b and the piping 69a. Alternatively, instead of the piping 69a, the cooling oil 32a mixed with the inert gas can be injected into the delivery chamber 31 via the piping 69b. The injected cooling oil 32a falls onto the cooling oil 32a in the oil tank 32 and mixes with it.

[0122] <Sixth Implementation Method>

[0123] Figure 11 (B) Figure 12 Since the inactive gas supply units 6B to 6E of (B) are supplied with inactive gas from the delivery chamber 31, the gas pressure in the quenching chamber 3 does not rise even when inactive gas is supplied to the cooling oil 32a. Therefore, in order to maintain a constant gas pressure in the quenching chamber 3, it is not necessary to depressurize the quenching chamber 3. On the contrary, if the inactive gas dissolves in the cooling oil 32a, the gas pressure in the quenching chamber 3 will decrease. Therefore, the control valve V3 is opened to supply inactive gas from the gas supply source 60 to the delivery chamber 31. Figure 13 It means to substitute Figure 7 A timing diagram showing the state of the vacuum furnace 1 during the heat treatment in this embodiment. (Explanation and...) Figure 7 Examples from different aspects.

[0124] In this embodiment, the pressure reduction unit 5 only reduces the pressure on the quenching chamber 3. Figure 4The vacuum is drawn in S22, after which pressure reduction in quenching chamber 3 is not required. Pressure reduction unit 5 is specifically used for pressure control of heating chamber 2 (insulated container 21).

[0125] The supply of inactive gas to the cooling oil 32a also takes place during the carburizing process. The supply of inactive gas to the cooling oil 32a causes a decrease in the gas pressure within the quenching chamber 3. Therefore, at times t2 and t3, control valve V3 is opened, supplying inactive gas from the gas supply source 60 to the delivery chamber 31. This maintains the gas pressure within the quenching chamber 3 at pressure P2.

[0126] <Seventh Implementation Method>

[0127] The above-described embodiments can also be used in combination with the high-pascal method. Figure 14 This is an explanatory diagram showing one example of a vacuum furnace 1A. Vacuum furnace 1A is formed by adding a high-Pascal unit 10 to vacuum furnace 1. The high-Pascal unit 10 includes a secondary tank 11 storing cooling oil 32a, a pressurized tank 12 storing compressed gas containing inactive gases, and a vacuum tank 13. The vacuum tank 13 is connected to a vacuum pump 50 via a control valve V14. By opening the control valve V14, the vacuum pump 50 reduces the pressure, thereby pre-evacuating the vacuum. The vacuum tank 13 is also connected to the upper part of the delivery chamber 31 via a control valve V15. By opening the control valve V15, the vacuum tank 13 draws gas from the delivery chamber 31, thus reducing the pressure in the quenching chamber 3. Multiple sets of vacuum tanks 13 and control valves 14 and 15 are provided.

[0128] The auxiliary tank 11 is connected to the pressurized tank 12 via control valve V12, and also to the oil tank 32 via control valve V11. The pressurized tank 12 has an internal pressure of at least atmospheric pressure. By opening control valves V11 and V12, the compressed gas in the pressurized tank 12 pressurizes the auxiliary tank 11, allowing cooling oil 32a from the auxiliary tank 11 to be supplied to the oil tank 32 for a short time. The auxiliary tank 11 is also connected to a vacuum pump 50 via control valve V13. By opening control valve V13, the vacuum pump 50 depressurizes the auxiliary tank 11, allowing a portion of the cooling oil 32a in the oil tank 32 to return to the auxiliary tank 11.

[0129] An example of controlling the high-Pascal unit 10 during quenching is explained. For example... Figure 14 As shown, the lifting unit 36 ​​lowers the conveying unit 33 and the workpiece W together to the immersion position, immersing the workpiece W in cooling oil 32a. Approximately simultaneously, control valves V12 and V11 are opened, supplying cooling oil 32a from the auxiliary tank 11 into the oil tank 32. Thus, as... Figure 15As illustrated, the level of the cooling oil 32a in the quenching chamber 3 rises to the upper part of the conveying chamber 31. That is, in this embodiment, the conveying chamber 31 also temporarily forms an oil tank. In addition, the pressure in the quenching chamber 3, which is connected to the pressurized tank 12 and the auxiliary tank 11, rises due to Pascal's principle.

[0130] Subsequently, during the boiling stage in the critical region and the convection stage after the boiling stage, control valve V15 is opened to connect vacuum tank 13 to the conveying chamber 31, thereby reducing the pressure in the quenching chamber 3. At this time, multiple sets of vacuum tanks 13 and each vacuum tank 13 in control valves 14 and 15 are gradually connected to the conveying chamber 31. As a result, the pressure in the quenching chamber 3 can be reduced proportionally to the cooling rate of the workpiece W. After all vacuum tanks 13 are connected to the conveying chamber 31, when transitioning from the boiling stage to the convection stage, each control valve 14 is opened to connect vacuum pump 50 to the conveying chamber 31, and the vacuum pump 50 is used to reduce the pressure in the quenching chamber 3.

[0131] Through the above, quenching is performed. In the high-Pascal quenching process, during the vapor film stage, the amount of cooling oil 32a is increased, and the quenching chamber 3 is pressurized. This suppresses the formation of a vapor film on the surface of the workpiece W, allowing for a faster cooling rate. Furthermore, the quenching chamber 3 can be depressurized at a rate proportional to the cooling rate of the workpiece W. Therefore, the transition of heat transfer from nucleation boiling to convection is delayed. This ensures the uniform heat distribution of the workpiece W before it enters the hazardous area.

[0132] After quenching, in preparation for the next quenching, control valve V15 is closed, and each vacuum tank 13 is evacuated. Control valves V12 and V14 are closed, and control valve V13 is opened. Vacuum pump 50 is used to depressurize the auxiliary tank 11, allowing cooling oil 32a to return from oil tank 32 to the auxiliary tank 11. Afterward, control valves V11 and V12 are closed.

[0133] <Eighth Implementation Method>

[0134] The vacuum furnaces 1 and 1A in the above embodiments are configured such that: a workpiece W is fed from outside the furnace into the quenching chamber 3, the workpiece W is transported from the quenching chamber 3 to the heating chamber 2, and the heat-treated workpiece W is discharged from the quenching chamber 3. However, it is also possible to adopt a configuration in which: the workpiece W is fed from outside the furnace into the heating chamber 2, and the heat-treated workpiece W is discharged from the quenching chamber 3. Figure 16 This is one example.

[0135] The shell 20 of the heating chamber 2 of the vacuum furnace 1B has an opening 20a on the wall opposite to the quenching chamber 3, which serves as the inlet for the workpiece W. The opening 20a is opened and closed by a door 25. The door 25 is moved by an actuator (not shown). The wall of the heat insulation container 21A, which replaces the heat insulation container 21, opposite the opening 20a, is made of a door 21b that can be opened and closed.

[0136] In vacuum furnace 1B, workpiece W is first sent into heating chamber 2. After heat treatment, it is conveyed to quenching chamber 3 for quenching. After quenching, it is sent out of the furnace from quenching chamber 3.

[0137] In this embodiment, while the workpiece W is in the heating chamber 2, supplying an inactive gas to the cooling oil 32a can increase the amount of dissolved gas in the cooling oil 32a.

[0138] <Ninth Implementation Method>

[0139] The test specimen was used to conduct a quenching test. Figure 17 (A) is a sectional view and a right view of the test specimen 100. The test specimen 100 is a cylindrical steel specimen (50 mm in diameter, 100 mm in length, SCM435). The test specimen 100 has three openings on its end face, into which thermocouples 101 to 103 are installed. Thermocouple 101 is positioned near the outer periphery of the end face, thermocouple 103 is positioned near the center of the end face, and thermocouple 102 is positioned near a distance of 4 / 100 of the diameter from the center of the end face.

[0140] In the quenching test, the test piece 100, along with the data recorder, was heated to approximately 900°C and then immersed in cooling oil. The temperature readings of each thermocouple 101–103 were recorded by the data recorder over a predetermined period. The test was conducted under four conditions. Figure 17 (B) is an explanatory diagram of the test procedure. "Pressure" refers to the gas pressure in the quenching chamber during quenching. "High Pascal method" indicates whether the high Pascal method described in the seventh embodiment is applied. "Inactive gas supply" indicates whether an inactive gas is injected into the cooling oil before quenching to increase the amount of dissolved gas. If "yes", nitrogen is supplied to the cooling oil as an inactive gas for 90 minutes.

[0141] Figure 18 (A) Figure 18 (C) represents the test result. Figure 18 (A) represents the test results of thermocouple 101. Figure 18 (B) represents the test results of thermocouple 102. Figure 18 (C) indicates the test result of thermocouple 103. Additionally, R1 corresponds to number 1, R2 to number 2, R3 to number 3, and R4 to number 4.

[0142] Comparing the test results (R1 and R3) of test numbers 1 and 3, respectively, without the high-Pascal method, it can be seen that the cooling rate of R3 is faster than that of R1. The faster the cooling rate, the harder the quenched material. This can be understood as improving the cooling performance of the cooling oil by increasing the amount of dissolved gas through the injection of inactive gas.

[0143] Comparing the test results (R2 and R4) of tests No. 2 and No. 4, which implemented the high Pascal method, it can be seen that the cooling rate of R4 is faster than that of R2. This is understandable, as in the case of the high Pascal method, the cooling performance of the cooling oil is improved by increasing the amount of dissolved gas through the injection of inactive gas into the cooling oil.

[0144] <Other Implementation Methods>

[0145] In the above embodiments, the case of carburizing oil quenching treatment as a heating treatment in heating chamber 2 is exemplified, but the content of the heating treatment is not limited to carburizing oil quenching treatment, and can be applied to a variety of heating and cooling treatments that use liquids (such as quenching oil) (e.g., vacuum oil quenching, solution treatment, precipitation hardening, etc.).

[0146] The above describes the implementation of the invention, but the invention is not limited to the above implementation and various modifications and alterations can be made within the scope of the spirit of the invention.

Claims

1. A control method of a vacuum furnace, the vacuum furnace comprising: a heating chamber that heats a workpiece; a quenching chamber that has a sump that stores cooling oil in which dissolved air is previously reduced, and cools the workpiece heated in the heating chamber by immersing the workpiece in the cooling oil; a decompression means that decompresses the quenching chamber; and a supply means that supplies a non-active gas used for dissolving in the cooling oil to the cooling oil, the control method of the vacuum furnace characterized by comprising: a decompression process that decompresses the quenching chamber by the decompression means each time the quenching chamber is opened to the atmosphere; and a supply process that supplies the non-active gas to the cooling oil by the supply means each time the quenching chamber is opened to the atmosphere during the workpiece is housed in the heating chamber.

2. The control method of the vacuum furnace according to claim 1, characterized in that the supply means is caused not to supply the non-active gas to the cooling oil during the workpiece is immersed in the cooling oil in the quenching chamber.

3. The control method of the vacuum furnace according to claim 1, characterized by comprising a setting process that enables a user to set a supply condition in which the supply means supplies the non-active gas.

4. The control method of the vacuum furnace according to claim 1, characterized by comprising a process of pressurizing the quenching chamber by supplying a non-active gas before the supply means supplies a non-active gas to the cooling oil.

5. The control method of the vacuum furnace according to claim 4, characterized in that the quenching chamber after the pressurizing is lower in air pressure than the atmospheric pressure.

6. The control method of the vacuum furnace according to claim 1, characterized by supplying a non-active gas to a space above the cooling oil in the quenching chamber, and taking in the non-active gas in the space by the supply means and supplying the non-active gas to the cooling oil in the supply process.

7. The control method of the vacuum furnace according to claim 6, characterized in that the supply means is built in the quenching chamber.

8. The control method of the vacuum furnace according to claim 1, characterized in that the supply means comprises a jetting portion that jets the non-active gas, and a refining means that refines bubbles of the non-active gas jetted from the jetting portion is provided in the jetting portion.

9. The control method of the vacuum furnace according to claim 1, characterized in that the vacuum furnace comprises: a passage wall that is provided in the sump and forms a circulation passage that circulates the cooling oil in the sump; and a circulation means that is provided in the circulation passage and stirs the cooling oil to generate a circulation flow of the cooling oil, and the supply means supplies the non-active gas to the circulation passage in the supply process.

10. The control method of the vacuum furnace according to claim 1, characterized by comprising a process of feeding the workpiece from outside the furnace to the heating chamber via the quenching chamber.

11. The control method of the vacuum furnace according to claim 1, characterized by ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The process includes, as a preparation process for heat treatment of the workpiece, a process of reducing air dissolved in the cooling oil in advance by decompression by the decompression member.

12. The control method of a vacuum furnace according to claim 1, wherein The supply member has a circulation section that returns the cooling oil discharged from the oil tank to the oil tank, and The supply member supplies the cooling oil circulating in the circulation section with non-active gas.

13. A vacuum furnace, characterized by provided with: a heating chamber that heats a workpiece; a quenching chamber that has an oil tank that stores cooling oil in which air dissolved in advance has been reduced, and cools the workpiece heated in the heating chamber by immersing the workpiece in the cooling oil; a decompression member that decompresses the quenching chamber, a supply member that supplies non-active gas for dissolving in the cooling oil to the cooling oil; and a control member, The control member has a processor and a storage device that stores a program for the processor to execute, The program causes the processor to execute the following processes: a decompression process that decompresses the quenching chamber by the decompression member each time the quenching chamber is opened to the atmosphere, and a supply process that supplies the non-active gas to the cooling oil by the supply member during a period in which the workpiece is housed in the heating chamber each time the quenching chamber is opened to the atmosphere, The supply member supplies non-active gas into the oil tank.

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