Vacuum heat treatment furnace

Abstract

To provide a vacuum heat treatment furnace capable of suppressing unstable control of furnace internal pressure when the amount of atmosphere gas introduced into the furnace is reduced under a low vacuum atmosphere.SOLUTION: The vacuum heat treatment furnace 1 is provided with a vacuum heating chamber 4 in which a workpiece W is heated in a vacuum atmosphere and a vacuum control means 6 for bringing the vacuum heating chamber 4 into a prescribed vacuum state. The vacuum control means 6 has a pressure sensor 26 for measuring the pressure in the vacuum heating chamber 4, an atmospheric gas introducing means 27 for introducing an atmospheric gas into the vacuum heating chamber 4, a vacuum pump 32 for evacuating the vacuum heating chamber 4, an exhaust system 33 for connecting the vacuum heating chamber 4 and the vacuum pump 32, and an adjusting gas introducing means 35 for introducing an adjusting gas into the exhaust system 33.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a vacuum heat treatment furnace suitable for use in heat treating metal materials such as steel. [Background technology]

[0002] In the manufacture of stainless steel rods, pipes, etc., bright heat treatment is generally carried out in a non-oxidizing atmosphere mainly consisting of hydrogen gas. In relation to such bright heat treatment, Patent Document 1 below describes a method for performing bright heat treatment at a pressure of several torr to 1000 kJ / cm2 using a heat treatment apparatus equipped with a gas supply pipe for supplying atmospheric gas into a furnace and a vacuum pump for exhausting the gas inside the furnace. -3 The document describes a method in which an object to be treated is heat-treated under a low vacuum of Torr while continuously supplying and exhausting an atmospheric gas.

[0003] According to such a bright heat treatment method, by maintaining a low vacuum in the furnace, -4 This prevents the evaporation of alloy components such as Cr that occurs under high vacuum conditions exceeding 1000kJ / cm², and hazardous gases released due to harmful substances (moisture and oxide scale) contained in the workpieces and furnace materials are exhausted to the outside of the furnace by a vacuum pump, thereby reducing the impact of hazardous gases on the brilliance of the workpieces. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Jikko No. 52006-52 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since hydrogen gas and Ar gas used as atmospheric gases in bright heat treatment are expensive, if the atmospheric gas is continuously supplied into the furnace as described above, this will result in an increase in running costs. In order to reduce the amount of atmospheric gas used, it is possible to reduce the amount of atmospheric gas introduced into the furnace depending on the amount of harmful gas generated inside the furnace, but the adjustment range of the exhaust capacity of the vacuum pump is not wide. Therefore, if the amount of atmospheric gas introduced into the furnace is reduced beyond the adjustment range of the vacuum pump considering the required maximum exhaust capacity, the amount of exhaust gas from the furnace cannot be reduced accordingly, resulting in excessive exhaust of gas inside the furnace and the risk of unstable control of the furnace pressure.

[0006] The present invention has been made in light of the above circumstances and aims to provide a vacuum heat treatment furnace that can prevent the control of the furnace pressure from becoming unstable when the amount of atmospheric gas introduced into the furnace is reduced under a low vacuum atmosphere. [Means for solving the problem]

[0007] The vacuum heat treatment furnace according to the first aspect of the present invention is defined as follows: A vacuum heat treatment furnace for heat treating a workpiece made of a metal material, a vacuum heating chamber in which the workpiece is heated in a vacuum atmosphere, and a vacuum control means for maintaining the vacuum heating chamber in a predetermined vacuum state; The vacuum control means a pressure sensor for measuring the pressure in the vacuum heating chamber; atmospheric gas introducing means for introducing atmospheric gas into the vacuum heating chamber; a vacuum pump for evacuating the vacuum heating chamber; an exhaust system provided outside the furnace and connecting the vacuum heating chamber and the vacuum pump; a conditioning gas introducing means for introducing a conditioning gas into the exhaust system; It has.

[0008] According to the vacuum heat treatment furnace of the first aspect defined as above, even if the vacuum heating chamber cannot be brought to the specified vacuum state by simply reducing the rotation speed of the vacuum pump, the amount of gas exhausted from the vacuum heating chamber can be adjusted to the exhaust amount required to bring the vacuum heating chamber to the specified vacuum state by introducing an adjustment gas into the exhaust system connecting the vacuum pump and the vacuum heating chamber. Therefore, according to the vacuum heat treatment furnace of the first aspect, even when performing bright heat treatment in which atmospheric gas is continuously introduced into the vacuum heating chamber under a low vacuum atmosphere, it is possible to reduce the amount of atmospheric gas introduced into the vacuum heating chamber while maintaining a predetermined low vacuum state, thereby suppressing an increase in running costs.

[0009] In addition, in this invention, the vacuum heat treatment furnace can be configured as a continuous heat treatment furnace by being equipped with a transport means for transporting the workpiece, an inlet purge chamber provided upstream of the vacuum heating chamber in the transport direction and in which vacuum purging of the chamber is performed, and a cooling chamber provided downstream of the vacuum heating chamber in the transport direction and in which cooling of the workpiece is performed (second aspect).

[0010] Furthermore, a preheating chamber in which the workpiece is heated in a vacuum atmosphere can be provided between the inlet purge chamber and the vacuum heating chamber (third aspect). According to this third aspect, the workpiece is heated in a vacuum atmosphere in the preheating chamber prior to heat treatment in the vacuum heating chamber, thereby making it possible to remove moisture, oils, and oxide scale from the surface of the workpiece in advance, and to suppress the generation of harmful gases in the subsequent vacuum heating chamber.

[0011] Furthermore, in the vacuum heat treatment furnace of the first aspect of the present invention, it is possible to configure the vacuum heat treatment furnace to include a heat insulating wall surrounding the periphery of the vacuum heating chamber, a vacuum vessel containing the heat insulating wall, and a cooling gas introducing means for introducing a cooling gas into the vacuum heating chamber (fourth aspect). According to this fourth aspect, a series of heat treatments, including a heating treatment under vacuum followed by a cooling treatment using a cooling gas, can be performed on a workpiece accommodated in the vacuum heating chamber.

[0012] Here, openings for cooling gas circulation, which are opened and closed by doors, can be provided in a pair of side walls of the heat insulating wall spaced apart on the furnace opening side and the furnace inner side (fifth aspect). In this way, a flow of cooling gas can be formed along the longitudinal direction of an elongated workpiece housed in the vacuum heating chamber in a manner extending from the furnace opening side to the furnace inner side, and distortion of the workpiece during cooling can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic overall configuration of a vacuum heat treatment furnace according to an embodiment of the present invention. [Figure 2] 2 is a view showing a state in which the openable / closable cover of the vacuum heat treatment furnace of FIG. 1 is separated from the end of the furnace shell. [Figure 3] 3 is a cross-sectional view of the vacuum heat treatment furnace of FIG. 1 taken along line III-III. [Figure 4] 10 is a diagram showing a jig that is loaded into the vacuum heat treatment furnace together with the workpiece. FIG. [Figure 5] 2 is a schematic diagram showing elements related to a vacuum control means in the vacuum heat treatment furnace of FIG. 1. FIG. [Figure 6] 3 is an explanatory diagram illustrating an example of furnace pressure control in the vacuum heat treatment furnace. FIG. [Figure 7] 3 is an explanatory diagram of a cooling process in the vacuum heat treatment furnace. FIG. [Figure 8] 10 is a diagram showing a modified example in which a cooling gas introduction nozzle is further provided in the vacuum heat treatment furnace. FIG. [Figure 9] FIG. 10 is a diagram showing a schematic overall configuration of a vacuum heat treatment furnace according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a diagram showing the overall configuration of a vacuum heat treatment furnace according to one embodiment of the present invention. In the figure, reference numeral 1 denotes a single-chamber heat treatment furnace for performing bright heat treatment on a workpiece W, and includes a furnace shell 2 as a vacuum container, a vacuum heating chamber 4 provided inside the furnace shell 2, vacuum control means 6 (see Fig. 5) for controlling the vacuum heating chamber 4 to a predetermined vacuum state, and cooling gas introduction means 8 for introducing cooling gas into the vacuum heating chamber 4.

[0015] The furnace shell 2 is a pressure-resistant, cylindrical vacuum vessel with a bottom, and is placed sideways so that the central axis of the cylinder is horizontal. An open lid 10 is airtightly attached to one open end 2a of the furnace shell 2 with a seal ring.

[0016] A heat insulating material 12 is disposed inside the furnace shell 2, and the heat insulating material 12 forms a cylindrical heat insulating wall 13 with both ends closed. The inner area surrounded by the heat insulating wall 13 is the vacuum heating chamber 4, and gas inside the vacuum heating chamber 4 is sucked and exhausted through an exhaust system 33 shown in Fig. 5, creating a vacuum state (reduced pressure state). The vacuum heating chamber 4 is provided with a hearth 15 for holding the workpiece W, and a heater 17 is disposed along the inner surface of the insulating wall 13 as a heating means for heating the workpiece W (see Figures 1 and 3).

[0017] In this embodiment, the side wall 13a and bottom wall 13c that constitute part of the insulating wall 13 are separable from the other parts of the insulating wall 13. The side wall 13a, bottom wall 13c and hearth 15 of the insulating wall 13 are placed on a cart 19 together with the opening / closing lid 10. In this embodiment, as shown in Fig. 2, the opening / closing lid 10 and the like are moved leftward in the drawing along rails 20 to open the entrance / exit 14 on the throat side, allowing the workpiece W to be charged through the entrance / exit 14.

[0018] In this embodiment, a rod-shaped or pipe-shaped stainless steel material can be exemplified as the workpiece W. In this case, the workpiece W is loaded into the vacuum heating chamber 4 while being held by a jig 22 shown in FIG. The jig 22 is configured to include a plurality of plate-shaped mounting plates 23 arranged in the vertical direction and a plurality of short column-shaped spacers 24 erected on each mounting plate 23, and the workpiece W is accommodated in an individual accommodation space 25 partitioned by the mounting plates 23 and the spacers 24. The mounting plates 23 and spacers 24 that make up the jig 22 are made of heat-resistant steel or C / C composite that is resistant to thermal deformation at high temperatures, and by placing the workpiece W on the mounting plates 23 that have been machined to a predetermined flatness, it is possible to suppress shape transfer to the workpiece W due to deformation of the jig. Each workpiece W held by the jig 22 is accommodated in the vacuum heating chamber 4 so that its longitudinal direction is aligned with the depth direction of the furnace.

[0019] Next, we will explain the vacuum control means 6 that puts the vacuum heating chamber 4 into a predetermined vacuum state. As shown in Figure 5, the vacuum control means 6 includes a pressure sensor 26, atmospheric gas introduction means 27 that introduces atmospheric gas into the vacuum heating chamber 4, a vacuum pump 32 that evacuates the vacuum heating chamber 4, an exhaust system 33 that connects the vacuum heating chamber 4 and the vacuum pump 32, adjustment gas introduction means 35 that introduces adjustment gas into the exhaust system 33, and a control unit 40, and while introducing and evacuating the atmospheric gas into the vacuum heating chamber 4, the inside of the vacuum heating chamber 4 is put into a predetermined low vacuum state (for example, approximately 100 Pa) during heat treatment.

[0020] The pressure sensor 26 detects the pressure inside the vacuum heating chamber 4 and transmits a signal corresponding to the detected pressure value (detected value).

[0021] The atmospheric gas introduction means 27 is configured to include an atmospheric gas introduction pipe 29 that introduces the atmospheric gas (in this example, hydrogen and Ar gas) from the atmospheric gas supply source 28 into the furnace (more specifically, the vacuum heating chamber 4), and a mass flow controller 30 that is provided on the atmospheric gas introduction pipe 29 and adjusts the flow rate of the atmospheric gas.

[0022] As shown in Figure 5, the vacuum heating chamber 4 is provided with a suction port 33a of an exhaust system 33 connected to a vacuum pump 32, and gas inside the vacuum heating chamber 4 is sucked in through the suction port 33a, creating a vacuum state (reduced pressure state) inside the vacuum heating chamber 4. An adjustment gas introduction means 35 for introducing an adjustment gas into the exhaust system 33 is connected to the exhaust system 33 connecting the vacuum heating chamber 4 and the vacuum pump 32. The adjustment gas introduction means 35 is configured to include an adjustment gas introduction pipe 37 that introduces an adjustment gas (nitrogen gas in this example) from an adjustment gas supply source 36 into the exhaust system 33, and a mass flow controller 38 that is provided on the adjustment gas introduction pipe 37 and adjusts the amount of adjustment gas introduced.

[0023] The control unit 40 can be realized by, for example, a PLC (Programmable Logic Controller) equipped with a data processing unit, a storage unit, a communication I / F unit, etc. The control unit 40 is connected to the pressure sensor 26, the vacuum pump 32, the mass flow controller 30 on the ambient gas inlet pipe 29, and the mass flow controller 38 on the adjustment gas inlet pipe 37, and outputs a control output to the mass flow controllers 30 and 38 corresponding to their openings, and outputs a control output to the vacuum pump 32 corresponding to its rotation speed.

[0024] FIG. 6 is an explanatory diagram of an example of furnace pressure control in a vacuum heat treatment furnace 1. FIG. 6(A) shows the change in the amount of harmful gases emitted due to harmful substances (moisture and oxide scale) in the workpiece W and furnace materials. As shown in the figure, a large amount of harmful gases is emitted in the initial stage D1 of the heat treatment as heating begins. To prevent an increase in the oxygen partial pressure in the furnace due to harmful gases, it is necessary to introduce a large amount of atmospheric gas into the vacuum heating chamber 4 in the initial stage D1 of the heat treatment and exhaust the atmospheric gas containing harmful gases to the outside of the furnace to dilute the harmful gases in the vacuum heating chamber 4. On the other hand, since less harmful gases are generated in the later stage D2 of the heat treatment, the amount of atmospheric gas introduced can be reduced compared to the initial stage D1 of the heat treatment.

[0025] Therefore, as shown in FIG. 6(B), the control unit 40 adjusts the opening of the mass flow controller 30 so that the amount of ambient gas introduced is large in the early stage D1 of the heat treatment and is small in the later stage D2 of the heat treatment. In addition, the control unit 40 PID controls the rotation speed of the vacuum pump 32 based on the pressure value detected by the pressure sensor 26 so as to maintain a predetermined low vacuum state (e.g., 100 Pa) inside the vacuum heating chamber 4. As a result, as shown in Figure 6(C), in the early stage D1 of the heating process, the rotation speed of the vacuum pump 32 is high and a large amount of atmospheric gas is exhausted from the vacuum heating chamber 4. On the other hand, in the later stage D2 of the heating process, as the amount of atmospheric gas introduced decreases, the rotation speed of the vacuum pump 32 gradually decreases and the amount of gas exhausted from the vacuum heating chamber 4 also decreases.

[0026] Figure 6(D) shows the amount of adjustment gas introduced. At the beginning D1 of the heating process when a large amount of atmospheric gas is being introduced into the vacuum heating chamber 4, the adjustment gas mass flow controller 38 is closed. Thereafter, as the amount of introduced atmospheric gas decreases and the rotation speed of the vacuum pump 32 reaches a preset lower limit P1 (see Figure 6(C)), the control unit 40 opens the adjustment gas mass flow controller 38 and controls the amount of adjustment gas introduced so that the pressure in the vacuum heating chamber 4 becomes a target low vacuum pressure (e.g., 100 Pa).

[0027] Specifically, when the pressure in the vacuum heating chamber 4 drops below the target low vacuum pressure, the amount of adjustment gas introduced is increased, the amount of exhaust from the vacuum heating chamber 4 is reduced, and the pressure in the vacuum heating chamber 4 is increased. Also, when the pressure in the vacuum heating chamber 4 rises above the target vacuum pressure, the amount of adjustment gas introduced is reduced, the amount of exhaust from the vacuum heating chamber 4 is increased, and the pressure in the vacuum heating chamber 4 is reduced. In this way, even if the amount of ambient gas introduced into the vacuum heating chamber 4 decreases and exceeds the adjustment range of the vacuum pump 32, it is possible to avoid the problem of the control of the furnace pressure becoming unstable and making it impossible to maintain the desired low vacuum state.

[0028] Next, we will explain the cooling gas introduction means 8. The cooling gas introduction means 8 is configured to include a circulation fan 42 shown in Figure 1, a gas cooler 49, and a pair of openings 46A, 46B provided in the heat insulating wall 13.

[0029] The circulation fan 42 is disposed inside the furnace shell 2 in a region near the other end wall 2b opposite the open / close lid 10. The circulation fan 42 rotates around a rotation axis extending horizontally in the drawing from a motor 43 attached to the other end wall 2b, sucks in cooling gas through an intake port 44, and ejects the cooling gas radially outward from the outer periphery of the fan.

[0030] A pair of left and right side walls of the insulating wall 13, more specifically a pair of side walls 13a, 13b spaced apart on the furnace opening side and the furnace inner side, are provided with openings 46A, 46B for circulating cooling gas, which are opened and closed by door bodies 47A, 47B, respectively. When the door bodies 47A and 47B are moved by a drive mechanism (not shown) to open the openings 46A and 46B as shown in Figure 7 and the circulation fan 42 is rotated, a circulation flow of cooling gas is formed, as shown by the arrows in Figure 7, including an outward path that flows from left to right within the vacuum heating chamber 4 and a return path that flows from right to left in the area between the furnace shell 2 and the insulating wall 13.

[0031] The gas cooler 49 is disposed in the furnace shell 2 in the region on the other end wall 2b side opposite the opening / closing lid 10, at a position between the side wall 13b of the insulating wall and the circulation fan 42. The gas cooler 49 lowers the temperature of the cooling gas, which has become hot after passing through the workpiece W in the vacuum heating chamber 4, by heat exchange.

[0032] Next, we will explain a series of heat treatment operations in the vacuum heat treatment furnace 1, taking the case of bright annealing as an example. After the workpiece W is loaded into the vacuum heating chamber 4 through the entrance / exit 14 (see FIG. 2), the open / close lid 10 is closed, and first, the air inside the furnace is exhausted to the outside by the vacuum pump 32. In the subsequent heat treatment, the workpiece W is heated to a target temperature (e.g., 800°C) by the heater 17 and then soaked. In the initial stage D1 of the heat treatment (see FIG. 6), a large amount of atmospheric gas is introduced into the vacuum heating chamber 4 through the atmospheric gas introduction means 27, and the atmospheric gas is exhausted by the vacuum pump 32 so that the vacuum heating chamber 4 is in a predetermined low vacuum state (e.g., approximately 100 Pa), and a non-oxidizing atmospheric state is maintained inside the chamber.

[0033] In the later stage D2 of the heat treatment, the atmospheric gas continues to be introduced into and exhausted from the vacuum heating chamber 4, maintaining the chamber in a non-oxidizing atmosphere. However, in the later stage D2 of the heat treatment, the amount of atmospheric gas introduced is reduced compared to the early stage D1, thereby reducing the amounts of hydrogen and Ar gas used as the atmospheric gas. When the rotation speed of the vacuum pump 32 reaches a preset lower limit P1 as the amount of introduced atmospheric gas decreases, an adjustment gas is introduced into the exhaust system 33 connecting the vacuum pump 32 and the vacuum heating chamber 4, and the amount of adjustment gas introduced is controlled so that the pressure in the vacuum heating chamber 4 is maintained at a target low vacuum pressure (e.g., 100 Pa).

[0034] In the cooling process following the heating process, the vacuum heating chamber 4 is restored to pressure with atmospheric gas, the doors 47A and 47B are moved to open the openings 46A and 46B, and the cooling gas inside the furnace shell 2 is circulated by the circulation fan 42 to cool the workpiece W accommodated in the vacuum heating chamber 4. After the cooling process, the opening / closing lid 10 is opened and the workpiece W is carried out of the furnace, completing a series of operations related to the heat treatment of the workpiece W.

[0035] As described above, according to the vacuum heat treatment furnace 1 of this embodiment, even if the vacuum heating chamber 4 cannot be brought into the specified vacuum state by simply reducing the rotation speed of the vacuum pump 32, by introducing an adjustment gas into the exhaust system 33 connecting the vacuum pump 32 and the vacuum heating chamber 4, the amount of gas exhausted from the vacuum heating chamber 4 can be adjusted to the exhaust amount required to bring the vacuum heating chamber 4 into the specified vacuum state. Therefore, according to the vacuum heat treatment furnace 1 of this embodiment, even when bright heat treatment is performed in a low vacuum atmosphere by continuously introducing atmospheric gas into the vacuum heating chamber 4, it is possible to reduce the amount of atmospheric gas introduced into the vacuum heating chamber 4 while maintaining a predetermined low vacuum state, thereby suppressing an increase in running costs.

[0036] In addition, the vacuum heat treatment furnace 1 of this embodiment includes a heat insulating wall 13 surrounding the vacuum heating chamber 4, The furnace is equipped with a furnace shell 2 containing an insulating wall 13 inside and a cooling gas introduction means 8 for introducing cooling gas into the vacuum heating chamber 4, and a series of heat treatments, including heating treatment under vacuum followed by cooling treatment using cooling gas, can be performed on the workpiece W contained in the vacuum heating chamber 4.

[0037] Furthermore, in the vacuum heat treatment furnace 1 of this embodiment, openings 46A and 46B for cooling gas circulation, which are opened and closed by doors 47A and 47B, respectively, are provided in a pair of side walls 13a and 13b spaced apart on the furnace opening side and the furnace inner side of the heat insulating wall 13. Therefore, a flow of cooling gas can be formed along the longitudinal direction of the long workpiece W housed in the vacuum heating chamber 4 in a manner extending from the furnace opening side to the furnace inner side, and deformation of the long workpiece W during heat treatment (more specifically, during cooling) can be suppressed.

[0038] FIG. 8 shows a modified example in which a cooling gas introduction nozzle 51 is further provided in the vacuum heat treatment furnace 1. In the vacuum heat treatment furnace 1, if the loading space for the workpiece W in the vacuum heating chamber 4 is widened, the outer periphery of the workpiece W will significantly extend outside the openings 46A and 46B provided in the side wall of the insulating wall 13, as shown in Figure 8(A), which raises concerns about delayed cooling of the outer periphery. In such a case, in addition to the openings 46A and 46B that circulate cooling gas in the axial direction of the heat treatment furnace, it is also possible to arrange cooling gas introduction nozzles 51 that spray cooling gas toward the outer periphery of the workpiece W along the inner periphery of the vacuum heating chamber 4, as shown in Figures 8(A) and (B).

[0039] 9 shows a schematic overall configuration of a vacuum heat treatment furnace according to another embodiment of the present invention, in which 1B is a continuous vacuum heat treatment furnace in which workpieces W are continuously heat-treated. The vacuum heat treatment furnace 1B has a generally cylindrical steel furnace body 54 that extends horizontally in Fig. 9. An inlet 56 for charging materials is formed on the left side of the furnace body 54, and an outlet 57 for unloading materials is formed on the right side of the furnace body 54. Doors 58 and 59 are provided at the inlet 56 and outlet 57, respectively, and are opened and closed by air cylinder-type opening and closing devices 72.

[0040] The interior of the furnace body 54 is divided into sections along the direction in which the workpiece W is transported: an inlet-side purge chamber 60, a preheating chamber 62, a vacuum heating chamber 64, and a cooling chamber 66. Each chamber is equipped with a pressure-resistant furnace shell, and each chamber can be placed in a vacuum state (reduced pressure state) by sucking out gas from the chamber using a vacuum pump. Air cylinder-type opening / closing devices 73 are provided between each chamber, specifically between the inlet-side purge chamber 60, the preheating chamber 62, the vacuum heating chamber 64, and the cooling chamber 66, respectively, and drive doors 74, 75, and 76 at the openings of each chamber to open and close. These doors enable the openings of each chamber to be airtightly closed.

[0041] Furthermore, partitioned chambers 77 are formed between the chambers. The partitioned chambers 77 airtightly isolate the areas between the chambers (for example, between the inlet-side purge chamber 60 and the preheating chamber 62), including the areas where two opposing doors (for example, doors 74, 74 shown in FIG. 9) move up and down, from the outside, and prevent outside air from entering the chambers when the doors at the openings of the chambers are opened.

[0042] 9, conveying rollers 91 are arranged in parallel along the conveying direction in each chamber of the vacuum heat treatment furnace 1B. The rollers 91 may be made of metal such as heat-resistant steel or C / C composite rollers. A plurality of rollers 91 arranged in each of the entrance-side purge chamber 60, the preheating chamber 62, the vacuum heating chamber 64, and the cooling chamber 66 constitute roller groups 93, 94, 95, and 96, respectively. Each of these roller groups is independently driven, and sequentially transports the workpiece W placed in the entrance-side purge chamber 60 downstream in the transport direction (to the right in the drawing).

[0043] The inlet-side purge chamber 60 is a section that prevents atmospheric air from entering the preheating chamber 62. A degassing pipe 79 extending from a vacuum pump 78 and a nitrogen gas supply pipe 80 connected to a nitrogen gas source (not shown) are connected to the inlet-side purge chamber 60. When the workpiece W is loaded through the inlet 56 and the door 58 is closed, the atmospheric air inside the inlet-side purge chamber 60 is exhausted to the outside of the chamber via the vacuum pump 78. When the pressure is restored, nitrogen gas is supplied into the chamber through the pipe 80 to restore atmospheric pressure.

[0044] The preheating chamber 62 is a section in which the workpiece W is heated to a predetermined target temperature under high vacuum, and is formed in an area inside a heat insulating wall 81 made of a heat-resistant heat insulating material. The preheating chamber 62 is provided with a heater 84 as a heating means, and is connected to a degassing pipe 86 extending from a vacuum pump 85, and the preheating chamber 62 is kept at a predetermined vacuum pressure (for example, 10 -3 The preheating chamber 62 is also connected to a pipe 83 for supplying nitrogen gas.

[0045] Prior to heat treatment in the subsequent vacuum heating chamber 64, the workpiece W is heated in the preheating chamber 62 under high vacuum, thereby removing moisture, oils, and oxide scale from the surface of the workpiece W. This prevents the atmospheric gas from reacting with scale and being consumed in the subsequent vacuum heating chamber 64, and reduces the amount of atmospheric gas sent to lower the oxygen partial pressure. To enhance the effect of removing scale and the like, it is desirable to heat the workpiece W to 750°C or higher in the preheating chamber 62 in an atmosphere of 10 Pa or less. It is also possible to use a metal reflector as part or all of the insulation surrounding the preheating chamber 62. Unlike fibrous insulation, this significantly reduces the accumulation of harmful substances (such as moisture and oil) that adversely affect brilliance in the furnace material.

[0046] Next, the vacuum heating chamber 64 is a section in which the workpiece W is heat-treated in a low vacuum and non-oxidizing atmosphere, and is formed in an area inside a heat insulating wall 88 made of a heat-resistant insulating material. The vacuum heating chamber 64 is provided with a heater 90 as heating means. The vacuum heating chamber 64 also has a pressure sensor 26 that measures the pressure inside the vacuum heating chamber 64, atmospheric gas introducing means 27 that introduces atmospheric gas (hydrogen and Ar gas) into the vacuum heating chamber 64, a vacuum pump 32 that evacuates the vacuum heating chamber, an exhaust system 33 that connects the vacuum heating chamber 64 and the vacuum pump 32, and an adjusting gas introducing means 35 that introduces an adjusting gas into the exhaust system 33, which together form a vacuum control means 6 that keeps the vacuum heating chamber 64 in a predetermined vacuum state. Since the components of the vacuum control means 6 are the same as those of the vacuum heat treatment furnace 1, the same reference numerals will be used to indicate the respective components, and their description will be omitted here. In this vacuum heating chamber 64, the vacuum control means 6 introduces and exhausts atmospheric gas, while maintaining the interior of the vacuum heating chamber 64 in a predetermined low vacuum state (for example, 100 Pa) during the heat treatment.

[0047] The cooling chamber 66 is a section for cooling the heat-treated workpiece W. The cooling chamber 66 is connected to a degassing pipe 102 extending from a vacuum pump 101 and a cooling gas introduction pipe 103 connected to a nitrogen gas source or an Ar gas source (not shown). The cooling chamber 66 is also equipped with a gas cooler 105 for cooling the ambient gas and a fan (not shown) for circulating the ambient gas, making it possible to cool the workpiece W by circulating the ambient gas as a cooling gas.

[0048] Next, a series of heat treatment operations in the vacuum heat treatment furnace 1B will be explained using the case of bright annealing as an example. First, the roller group 93 is driven to load the workpiece W into the entrance-side purge chamber 60. After the door 58 is closed, the pressure is reduced using the vacuum pump 78, and the air inside the chamber is discharged to the outside.

[0049] After the evacuation of the entrance purge chamber 60 is completed, the exit door 74 of the entrance purge chamber 60 and the entrance door 74 of the preheating chamber 62 are opened, the roller groups 93 and 94 are driven, the workpiece W is transported into the preheating chamber 62, and the door 74 is closed. -3 The workpiece W is heated to about 800°C under a high vacuum of about Pa, and moisture, oil, and oxide scale are removed from the surface of the workpiece W.

[0050] After heating in the preheating chamber 62 is completed, the preheating chamber 62 and the vacuum heating chamber 64 are maintained at approximately the same vacuum pressure, and the exit door 75 of the preheating chamber 62 and the entrance door 75 of the vacuum heating chamber 64 are opened, and the roller groups 94, 95 are driven to transport the workpiece W into the vacuum heating chamber 64, and the door 75 is closed. The workpiece W transported into the vacuum heating chamber 64 is heat-treated at a predetermined temperature (800 to 1200°C) in a low vacuum atmosphere (approximately 100 Pa) while suppressing evaporation of Cr. At this time, in the same manner as in the above embodiment, atmospheric gas (hydrogen and Ar gas) is introduced into and exhausted from the vacuum heating chamber 64, ensuring brilliance.

[0051] Next, after the heat treatment in the vacuum heating chamber 64 is completed, the interior of the vacuum heating chamber 64 is vacuumed to the same degree as the cooling chamber 66, the exit door 76 of the vacuum heating chamber 64 and the entrance door 76 of the cooling chamber 66 are opened, the roller groups 95, 96 are driven to transport the workpiece W to the cooling chamber 66, and the door 76 is closed. After the pressure is restored with the atmospheric gas in the cooling chamber 66, the workpiece W is cooled by circulating the atmospheric gas while being cooled by the gas cooler 105. After cooling, the door 59 is opened and the workpiece W is carried out, completing the series of operations related to the heat treatment of the workpiece W.

[0052] As described above, the vacuum heat treatment furnace 1B of this embodiment is equipped with a conveying means (rollers 91) for conveying the workpiece, an inlet purge chamber 60 located upstream of the vacuum heating chamber 64 in the conveying direction and in which vacuum purging of the chamber is performed, and a cooling chamber 66 located downstream of the vacuum heating chamber 64 in the conveying direction and in which cooling of the workpiece W is performed, and the vacuum heat treatment furnace 1B can be configured as a continuous heat treatment furnace.

[0053] In the vacuum heat treatment furnace 1B of this embodiment, a preheating chamber 62 is provided between the inlet purge chamber 60 and the vacuum heating chamber 64, in which the workpiece W is heated in a vacuum atmosphere. Prior to heat treatment in the vacuum heating chamber 64, the workpiece W is heated under high vacuum to remove moisture, oil, and oxide scale from the surface of the workpiece, thereby suppressing the generation of harmful gases in the subsequent vacuum heating chamber 64.

[0054] Although the embodiments of the present invention have been described in detail above, these are merely examples. For example, the vacuum heat treatment furnace of the present invention can be applied to heat treatments other than bright heat treatment. Furthermore, the treatment conditions and gas types used during heat treatment can be changed as appropriate depending on the purpose of the heat treatment, the steel type of the workpiece, etc., and various modifications can be made to the present invention without departing from the spirit of the present invention. [Explanation of symbols]

[0055] 1,1B Vacuum heat treatment furnace 2 Furnace shell (vacuum vessel) 4,64 Vacuum heating chamber 6 Vacuum control means 8 Cooling gas introduction means 13,88 Insulated walls 13a,13b side wall 26 Pressure Sensor 27 Atmospheric gas introduction means 32 Vacuum pump 33 Exhaust system 35 Adjustment gas introduction means 46A,46B opening 47A, 47B door body 60 Inlet side purge chamber 62 Pre-heating chamber 66 Cooling room 91 Roller (conveying means) W Processing object

Claims

1. A vacuum heat treatment furnace for heat treating a workpiece made of a metal material, a vacuum heating chamber in which the object to be treated is heated in a vacuum atmosphere; a vacuum control means for controlling the vacuum heating chamber to a predetermined vacuum state; Equipped with The vacuum control means a pressure sensor for measuring the pressure in the vacuum heating chamber; atmospheric gas introducing means for introducing atmospheric gas into the vacuum heating chamber; a vacuum pump for evacuating the vacuum heating chamber; an exhaust system provided outside the furnace and connecting the vacuum heating chamber and the vacuum pump; a conditioning gas introducing means for introducing a conditioning gas into the exhaust system; A vacuum heat treatment furnace having a

2. a conveying means for conveying the object to be treated; an inlet-side purge chamber provided upstream of the vacuum heating chamber in the conveying direction, in which vacuum purging of the interior of the chamber is performed; a cooling chamber provided downstream of the vacuum heating chamber in a conveying direction, in which the object to be treated is cooled; The vacuum heat treatment furnace of claim 1 , comprising:

3. 3. The vacuum heat treatment furnace according to claim 2, further comprising a preheating chamber provided between the inlet purge chamber and the vacuum heating chamber, in which the workpiece is heated in a vacuum atmosphere.

4. a heat insulating wall surrounding the vacuum heating chamber; a vacuum vessel containing the heat insulating wall therein; a cooling gas introducing means for introducing a cooling gas into the vacuum heating chamber; The vacuum heat treatment furnace of claim 1 , comprising:

5. 5. The vacuum heat treatment furnace according to claim 4, wherein a pair of side walls of the heat insulating wall spaced apart from each other on the furnace opening side and the furnace inner side are provided with openings for circulating cooling gas, which are opened and closed by doors.

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