Heat treatment device, temperature control auxiliary mechanism in heat treatment device, and temperature control method

Abstract

Provided is a heat treatment device including a heat treatment chamber for heat-treating a workpiece, and having a temperature control auxiliary mechanism attached to the heat treatment chamber. The temperature control auxiliary mechanism has an outer pipe inserted from the outside to the inside of the heat treatment chamber, and an inner pipe movably inserted into the outer pipe. The distal end of the outer pipe is closed, the distal end of the inner pipe is open, the outer pipe is provided with a discharge port outside the heat treatment chamber, and a heat insulating material that divides an internal space of the outer pipe into the distal end side and the base end side is attached to the outer circumferential surface of the inner pipe.

Description

Heat treatment apparatus, temperature control auxiliary mechanism for heat treatment apparatus, and temperature control method

[0001] The present invention relates to a heat treatment apparatus, a temperature control assist mechanism in the heat treatment apparatus, and a temperature control method.

[0002] Carburizing and quenching processes are widely used to harden the surfaces of workpieces, such as automotive and machine parts made of various steel materials, to improve their wear resistance and fatigue strength. Among these processes, vacuum carburizing offers advantages in terms of quality, such as the fact that it is processed under reduced pressure, preventing the formation of grain boundary oxidation and the resulting incompletely quenched layer, and that it provides excellent carburizing uniformity in areas with small pores and thickness variations. Furthermore, vacuum carburizing is increasingly being used as a solution to recent social constraints on resources and the environment, due to its advantages of improving energy efficiency and reducing CO2 emissions.

[0003] The carburizing process is outlined below. In an inert gas atmosphere, the temperature is raised to a temperature range where the crystal grains of the component material undergo no coarsening. This is followed by a vacuum evacuation process, a carburizing process, and a cooling process to the pre-hardening temperature. Following the carburizing process, hardening at the same carburizing temperature range can lead to cracking and significant distortion of the component's shape. Therefore, it is common to lower the temperature to a temperature suitable for hardening in the same carburizing chamber. Therefore, when considering the efficiency of the entire carburizing process, shortening the time required for the heating and cooling processes—that is, improving the heating and cooling rates—has a significant impact on reducing the total processing time.

[0004] In relation to the aforementioned process requirements, there is a trend toward improved insulation performance for the entire equipment in order to reduce energy consumption in heat treatment equipment and heat treatment processes. While improved insulation performance offers benefits such as shortening the time required for the temperature rise process and reducing the energy required to maintain temperature in the carburizing process, it also increases the time required for the temperature fall process. In other words, when switching from the temperature rise / soaking process to the temperature fall process, improved insulation performance has a disadvantage in terms of heat exchange during cooling in the temperature fall process.

[0005] In order to reduce the impact of the heat treatment process for metal parts on climate change, improving the energy efficiency of the entire heat treatment process is an urgent issue, and technology is needed that can simultaneously improve the insulation of heat treatment furnaces and shorten the time required for the cooling process.

[0006] For example, Patent Document 1 discloses a method in which the heat shield wall surrounding a vacuum heat treatment furnace is made of a material with excellent heat insulation properties, and cooling pipes are provided inside and on the outer wall surface of the heat shield wall to circulate a cooling medium, thereby enabling rapid switching between heating and cooling.

[0007] Japanese Unexamined Patent Publication No. 2-192592

[0008] However, in the technology of Patent Document 1, the cooling piping is arranged inside or on the outer wall of the heat shield wall, and when a cooling medium is circulated, it is the heat shield wall that is directly cooled, and the atmosphere inside the furnace is cooled according to the temperature drop of the heat shield wall, so the cooling effect is small. In vacuum carburizing, a cooling method with a greater cooling effect was required in the cooling process from the carburizing temperature to the quenching start temperature as described above.

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a means for improving the cooling efficiency in the temperature-lowering process while maintaining the thermal insulation of the heat treatment chamber at the same level as in the past.

[0010] One aspect of the present invention for achieving this object is a heat treatment apparatus having a heat treatment chamber for heat treating a workpiece, the heat treatment chamber having a temperature control auxiliary mechanism attached thereto, the temperature control auxiliary mechanism having an outer pipe inserted from the outside to the inside of the heat treatment chamber and an inner pipe inserted movably inside the outer pipe, the outer pipe having a closed tip and an open tip, the outer pipe having an exhaust port outside the heat treatment chamber, and an insulating material attached to the outer surface of the inner pipe that divides the internal space of the outer pipe into a tip side and a base side.

[0011] The heat treatment device may include a drive mechanism for moving the inner tube and the heat insulating material.

[0012] Another aspect of the present invention is a temperature control auxiliary mechanism provided in a heat treatment apparatus having a heat treatment chamber for heat-treating a workpiece, the temperature control auxiliary mechanism comprising an outer pipe inserted from the outside to the inside of the heat treatment chamber, and an inner pipe inserted movably into the outer pipe, the tip of the outer pipe being closed and the tip of the inner pipe being open, the outer pipe being provided with an exhaust port outside the heat treatment chamber, and an insulating material attached to the outer surface of the inner pipe that divides the internal space of the outer pipe into a tip side and a base side.

[0013] Another aspect of the present invention is a temperature control method for a heat treatment chamber using the above-mentioned heat treatment apparatus, characterized in that, in a temperature-raising and soaking process, inside the external pipe, the insulating material is moved to the position of the insulating wall of the heat treatment chamber, and the supply of refrigerant from the internal pipe to the inside of the external pipe is stopped, and in a temperature-lowering process, inside the external pipe, the insulating material is moved to the outside of the outlet, refrigerant is supplied to the internal pipe, and the supplied refrigerant flows from the inside of the external pipe to the outlet.

[0014] According to the present invention, in a heat treatment process, it is possible to improve the cooling efficiency in the temperature lowering process while maintaining the thermal insulation of the heat treatment chamber at the same level as in the past.

[0015] 1 is a perspective view of a heat treatment chamber; FIG. 2 is an explanatory diagram of a heat treatment apparatus showing a state in which a workpiece is loaded into the heat treatment chamber; FIG. 3 is an explanatory diagram showing the basic configuration of a temperature control auxiliary mechanism; FIG. 4 is an explanatory diagram showing the following states (1) and (2) regarding the operation of the temperature control auxiliary mechanism: (1) A state in which the tip of the inner pipe is inserted up to the tip of the outer pipe inside the outer pipe; (2) A state in which the heat insulating material has moved to the outside of the discharge port inside the outer pipe; and FIG. 5 is a diagram showing an outline of the carburizing process carried out in the examples and comparative examples. and FIG. 6 is a comparative graph of temperature changes during temperature reduction in the examples and comparative examples.

[0016] Hereinafter, examples of embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments.

[0017] <Configuration of Heat Treatment Apparatus> Fig. 1 is a perspective view of a heat treatment chamber 10 provided in a heat treatment apparatus 1 according to an embodiment of the present invention. Fig. 2 is an explanatory diagram of the heat treatment apparatus 1 showing a state in which a workpiece W, which is an object to be treated, is loaded into the heat treatment chamber 10. As shown in Fig. 1, the heat treatment chamber 10 has a substantially cylindrical shape, and multiple heaters 12 are inserted vertically (in the Z-axis direction in Fig. 1) into the heat treatment chamber 10 from above.

[0018] The underside of the heat treatment chamber 10 has an open loading port 13, and a scissor lifter 14 is disposed below the heat treatment chamber 10 to load a workpiece W into the heat treatment chamber 10 through this loading port 13. FIG. 2 shows a state in which the support base 15 of the scissor lifter 14 is raised and the workpiece W placed on the support base 15 is loaded into the heat treatment chamber 10. When the support base 15 is raised in this manner, the loading port 13 on the underside of the heat treatment chamber 10 is blocked and insulated by the support base 15. Note that with the support base 15 of the scissor lifter 14 lowered, the workpiece W can be placed on the support base 15 below the heat treatment chamber 10, and then the support base 15 of the scissor lifter 14 can be raised as shown in FIG. 2 to load the workpiece W into the heat treatment chamber 10.

[0019] The heaters 12 described above are arranged in two rows so as to be positioned on both sides of the workpiece W that has been placed on the support base 15 of the scissor lifter 14 and carried into the heat treatment chamber 10. In addition, a temperature control assistance mechanism 12a, which will be described later, is provided in each row of heaters 12. In the example shown in FIG. 1 , the temperature control assistance mechanism 12a is arranged in the center of the row of heaters 12 that is arranged in the X-axis direction on both sides of the workpiece W. Note that the temperature control assistance mechanism 12a is not limited to being arranged in the center of the row of heaters 12, and may be arranged in any position.

[0020] Furthermore, an agitating fan 16 is provided at the upper interior portion of the heat treatment chamber 10. A motor 17 for rotating the agitating fan 16 is attached to the upper exterior surface of the heat treatment chamber 10.

[0021] The entire heat treatment chamber 10 is composed of a heat insulating wall 20. A gas inlet 21 is provided on the side of the heat treatment wall 20 to supply processing gas into the heat treatment chamber 10. An exhaust pipe 22 and an opening 23 are provided on the front side of the heat treatment chamber 10. A pusher 24 is inserted into the opening 23 from the front of the heat treatment chamber 10, so that the workpiece W inside the heat treatment chamber 10 can be transported to the next cooling chamber 25. A door 26 is provided on the rear side of the heat treatment chamber 10, which is opened and closed when the workpiece W is transported to the next cooling chamber 25 by the pusher 24.

[0022] The cooling chamber 25 is equipped with an elevator rack 30 that receives the workpiece W transported from the heat treatment chamber 10. An oil tank 31 is provided below the elevator rack 30, and as the elevator rack 30 descends, the workpiece W is immersed in the oil tank 31 and cooled. In addition, a door 32 that is opened and closed when the workpiece W is transported from the cooling chamber 25 to the outside is provided on the rear surface of the cooling chamber 25.

[0023] In particular, the workpiece W has an outer dimension designed to fit the inner dimensions of the heat treatment chamber 10, and the internal structure is changeable to accommodate parts to be heat treated of various shapes and sizes within the outer dimension. For example, there are trays for efficiently placing multiple parts to be heat treated on the workpiece W, and a typical structure allows these trays to be placed three-dimensionally within the workpiece W. Furthermore, the heater 12 is arranged to surround the side of the workpiece W within the heat treatment chamber 10, but is positioned so as not to interfere with the workpiece W so that the workpiece W can be smoothly loaded into the heat treatment chamber 10 and transported from the heat treatment chamber 10 to the cooling chamber 25. This design ensures that the movement of the workpiece W during the heat treatment process is not hindered.

[0024] 3 and 4, the structure and operation of the temperature control assist mechanism 12a according to an embodiment of the present invention will be described. The temperature control assist mechanism 12a has an outer pipe 40 inserted from the outside to the inside of the heat treatment chamber 10, and an inner pipe 41 inserted movably into the outer pipe 40. The outer pipe 40 penetrates the insulating wall 20 of the heat treatment chamber 10, with the base end (upper part) of the outer pipe 40 located outside the heat treatment chamber 10 and the tip end (lower part) of the outer pipe 40 located inside the heat treatment chamber 10. The tip (lower end) of the outer pipe 40 is closed, and an exhaust port 42 located outside the heat treatment chamber 10 is provided at the upper side of the outer pipe 40.

[0025] The tip (lower end) of the inner pipe 41 is open, and a heat insulating material 43 that divides the internal space of the outer pipe 40 into a tip side (lower end side) and a base side (upper end side) is attached to the outer peripheral surface of the inner pipe 41. Outside the heat treatment chamber 10, a drive mechanism 45 such as a cylinder device is attached to the side of the outer pipe 40, and by operating this drive mechanism 45, the inner pipe 41 and the heat insulating material 43 are slid up and down together inside the outer pipe 40.

[0026] As shown in FIG. 4A , the drive mechanism 45 is operated to lower the inner pipe 41 within the outer pipe 40, and the tip of the inner pipe 41 is inserted close to the tip of the outer pipe 40. When the tip of the inner pipe 41 is inserted close to the tip of the outer pipe 40, the supply of refrigerant into the inner pipe 41 is stopped. When the tip of the inner pipe 41 is inserted close to the tip of the outer pipe 40, the heat insulating material 43 attached to the circumferential surface of the inner pipe 41 moves to the position of the heat insulating wall 20 of the heat treatment chamber 10. By moving the heat insulating material 43 to the position of the heat insulating wall 20 of the heat treatment chamber 10, the interior of the heat treatment chamber 10 is insulated from the outside. Note that when the tip of the inner pipe 41 is inserted close to the tip of the outer pipe 40, the tip of the inner pipe 41 may not reach the tip of the outer pipe 40, and the tip of the inner pipe 41 may be open inside the outer pipe 40. Alternatively, the tip of the inner tube 41 may be tightly fitted to the tip of the outer tube 40 and closed.

[0027] 4(2), when the drive mechanism 45 is operated to raise the inner pipe 41 inside the outer pipe 40 and move the insulating material 43 to the outside of the outlet 42, the tip of the inner pipe 41 is opened. As a result, a refrigerant is supplied from the inner pipe 41 to the inside of the outer pipe 40 as described below, and the refrigerant is further discharged from the inside of the outer pipe 40 to the outside through the outlet 42. Furthermore, as the insulating material 43 moves upward away from the position of the insulating wall 20 of the heat treatment chamber 10, the inside of the heat treatment chamber 10 is cooled by outside air.

[0028] To ensure heat resistance and corrosion resistance, the outer tube 40 may be protected by a ceramic material such as silicon carbide (SiC), aluminum oxide (Al2O3), mullite (a compound of aluminum oxide and silicon dioxide), carbon, etc. These materials are selected from the viewpoint of ensuring mechanical strength as well as heat resistance and corrosion resistance against the temperature and carburizing atmosphere within the heat treatment chamber 10, with silicon carbide (SiC) being the most suitable.

[0029] The entire heat treatment apparatus 1 is controlled by a control device 50 .

[0030] <Temperature Control Method> Next, as an example of a temperature control method according to an embodiment of the present invention, a vacuum carburization treatment of the workpiece W in the heat treatment apparatus 1 will be described.

[0031] (Loading Process) First, before loading the workpieces W, nitrogen gas, which is an example of an inert gas, is supplied into the heat treatment chamber 10 from the gas inlet 21, and the interior of the heat treatment chamber 10 is filled with a nitrogen atmosphere. In order to prevent oxidation of the workpieces W when loading the workpieces W, it is preferable to perform the above-mentioned pre-adjustment of the atmosphere. At this time, the pressure inside the heat treatment chamber 10 is, for example, 1×10 4 ~1.5 x 10 5 At this point, the temperature control assist mechanism 12a is set to a state in which, as shown in Fig. 4(1), the drive mechanism 45 is operated to lower the inner pipe 41 inside the outer pipe 40, and the heat insulating material 43 attached to the circumferential surface of the inner pipe 41 is moved to the position of the heat insulating wall 20 of the heat treatment chamber 10 (operating state during temperature increase and soaking). As will be described in detail later, the supply of the refrigerant (refrigerant gas) is stopped.

[0032] Next, the support base 15 of the scissor lifter 14 descends, thereby opening the loading port 13 provided at the bottom of the heat treatment chamber 10, and the workpiece W, which has been transported from outside the furnace by a transport means such as a roller conveyor (not shown), is supported on the support base 15. Next, a signal instructing the scissor lifter 14 to rise is output from the control device 50, and the support base 15 rises. As a result, the support base 15 comes into close contact with the loading port 13 at the bottom of the heat treatment chamber 10, closing the loading port 13, and the workpiece W is loaded into the heat treatment chamber 10.

[0033] In addition, from the viewpoint of preventing outside air from flowing into the heat treatment chamber 10, it is preferable to maintain the pressure inside the heat treatment chamber 10 at a pressure equal to or higher than atmospheric pressure by adjusting the amount of nitrogen gas supplied from the time the loading port 13 is opened until it is closed again.

[0034] (Temperature-raising process) After the workpiece W is loaded into the heat treatment chamber 10, the heat treatment chamber 10 is evacuated. This evacuation expels any air remaining in the heat treatment chamber 10, thereby suppressing oxidation of the workpiece W during the temperature rise of the heat treatment chamber 10. Note that this evacuation reduces the pressure inside the heat treatment chamber 10 to 1×10 3 It is preferable that the pressure is 5×10 Pa or less. 2 Pa or less.

[0035] The above-mentioned vacuum evacuation may be omitted if the steel type of the workpiece W is a type that is not easily oxidized, or depending on the required level of carburizing quality, etc.

[0036] After the heat treatment chamber 10 is evacuated to a vacuum atmosphere by the above-described evacuation, the evacuation is stopped and nitrogen gas is supplied into the heat treatment chamber 10. Then, when the pressure inside the heat treatment chamber 10 reaches a predetermined pressure (for example, 3×10 4 After the pressure reaches 100 bar (Pa), the supply of nitrogen gas is stopped.

[0037] While supplying the nitrogen gas, the heater 12 and stirring fan 16 are operated to raise the temperature inside the heat treatment chamber 10 to the predetermined carburizing temperature (930°C). During this temperature raising process, the heat treatment chamber 10 is not in a vacuum atmosphere but in a nitrogen gas atmosphere, which makes it easier for the temperature inside the heat treatment chamber 10 to rise, and the temperature raising time can be shortened. The carburizing temperature is set appropriately depending on the steel type of the workpiece W and the structure inside the furnace, and in the case of vacuum carburizing, it is set to, for example, 730 to 1200°C.

[0038] (Soaking step) After the temperature inside the heat treatment chamber 10 reaches a predetermined carburizing temperature, evacuation is performed again. This evacuation allows the workpiece W to be soaked in heat before the carburizing process of the workpiece W is started. This evacuation reduces the pressure inside the heat treatment chamber 10 to 1×10 3 It is preferable to set the pressure to 5×10 Pa or less. 2 Pa or less.

[0039] The soaking step may be omitted. In this case, evacuation is started during the temperature-raising step. In this case, the "time for the temperature-raising step" is the time from when the charging port 13 is closed in the charging step to when the supply of the carburizing gas, which will be described later, is started.

[0040] On the other hand, if the soaking step is omitted and evacuation is started midway through the temperature increase step, convection heat transfer does not occur after the heat treatment chamber 10 is filled with a vacuum atmosphere. In such an environment where convection heat transfer does not occur, temperature variations in the workpiece W are likely to occur during the temperature increase step. Therefore, in order to suppress temperature variations in the workpiece W and improve the carburizing quality, it is preferable to perform the soaking step after sufficiently heating the workpiece W in an inert gas atmosphere.

[0041] 4(1) shows the operation of the movable temperature control auxiliary mechanism during the temperature-raising and soaking process. During the temperature-raising and soaking process, the inner pipe 41 serving as the refrigerant gas inlet pipe is lowered, and the heat insulating material 43 fixed to the inner pipe 41 and the portion of the heat treatment chamber 10 covered with the heat insulating wall 20 are integrated, thermally isolating the inside and outside of the heat treatment chamber 10.

[0042] In addition, the supply of refrigerant gas is set to be stopped. In Fig. 4(1), the tip of the inner pipe 41 serving as a refrigerant gas inlet pipe is in contact with the bottom surface of the outer pipe 40, thereby cutting off communication between the inner pipe 41 and the outlet 42. However, the tip of the inner pipe 41 may be open inside the outer pipe 40 without reaching the tip of the outer pipe 40. Even if refrigerant gas remains in the inner pipe 41 when the tip of the inner pipe 41 is open inside the outer pipe 40, the presence of the insulating material 43 prevents the refrigerant gas from contributing to heat exchange between the inside and outside of the heat treatment chamber 10. In other words, the state shown in Fig. 4(1), in which the insulating material 43 is arranged integrally with the insulating wall 20 and the flow of refrigerant gas is blocked, is the most advantageous state for thermal insulation between the inside and outside of the heat treatment chamber 10.

[0043] (Carburizing and Diffusion Process) After the heat treatment chamber 10 is evacuated to a vacuum, a carburizing gas (e.g., acetylene gas) is supplied into the heat treatment chamber 10, which has reached the carburizing temperature, while continuing to evacuate. At this time, the pressure inside the heat treatment chamber 10 is 1×10 5 Pa or less, and in this state, vacuum carburizing of the workpiece W is initiated. Then, after maintaining this state for a certain period of time, the supply of the carburizing gas is stopped and the workpiece W is subjected to a diffusion treatment.

[0044] (Temperature Dropping / Second Soaking Step) After the diffusion process is completed, the evacuation is stopped, and nitrogen gas is supplied to the heat treatment chamber 10 while stirring the atmosphere in the heat treatment chamber 10 with the stirring fan 16. At the same time, the temperature control auxiliary mechanism 12a is set to the operating state for temperature drop. That is, the inner pipe 41 as the refrigerant gas introduction pipe and the heat insulating material 43 are in an elevated state, and the supply of refrigerant gas is started. Then, when the pressure inside the heat treatment chamber 10 reaches a predetermined pressure (for example, 5×10 4 After the pressure reaches 1 Pa, the supply of nitrogen gas is stopped. This state is maintained for a certain period of time, and the temperature of the workpiece W is lowered and a secondary soaking treatment is performed.

[0045] 4(2) shows the operating state of the temperature control assist mechanism 12a during the temperature-lowering process. During the temperature-lowering process, the inner pipe 41 and the insulating material 43 are raised to the top. In this state, the inner pipe 41 is connected to the inside of the outer pipe 40, which serves as an exhaust pipe and is coaxially arranged outside the inner pipe 41. During the temperature-lowering process, refrigerant gas is supplied to the inner pipe 41. The supplied refrigerant gas passes through the outer pipe 40 arranged inside the heat treatment chamber 10 and is discharged into the heat treatment chamber 10 through the outlet 42. Heat exchange occurs between the refrigerant gas flowing through the outer pipe 40 and the atmosphere inside the heat treatment chamber 10 via the outer pipe 40. During the temperature-raising and soaking process, the insulating material 43, which separated the inside and outside of the heat treatment chamber 10, is also positioned outside the heat treatment chamber 10 as the inner pipe 41 is raised. This reduces the insulating properties of this portion, thereby assisting in lowering the temperature inside the heat treatment chamber 10. In this embodiment, the outer tube 40 and the inner tube 41 are arranged coaxially to form a double-tube structure, but the configuration of the temperature control assistance mechanism 12a is not limited to this.

[0046] In the above description, the atmosphere inside the external pipe 40 and the atmosphere inside the heat treatment chamber 10 are not always in communication with each other. However, when N gas, an example of an inert gas, is used as the refrigerant gas, it is also possible to adopt a configuration in which the lower end of the external pipe 40 is open. In such an apparatus configuration, N gas, which is the refrigerant gas, is introduced directly into the heat treatment chamber 10 while adjusting the pressure inside the heat treatment chamber 10. This not only enables heat exchange between the refrigerant gas and the atmosphere inside the heat treatment chamber 10 via the external pipe 40, but also increases the cooling rate by combining the cooling effect of the supply and exhaust of N gas.

[0047] (Transportation process) After the temperature of the workpiece W has been reduced and the secondary soaking process has been completed, the door 26 installed on the side wall of the heat treatment chamber 10 is opened, and the workpiece W is transported from the heat treatment chamber 10 to the cooling chamber 25. The door 26 is then closed. The workpiece W transported to the cooling chamber 25 is quenched in the oil tank 31 and then transported out of the cooling chamber 25.

[0048] The above steps complete the vacuum carburizing treatment of one lot of workpieces W. When the next lot of workpieces W is loaded into the heat treatment chamber 10, the above-described loading step is carried out again. That is, nitrogen gas is supplied into the heat treatment chamber 10, and the loading port 13 is opened when the pressure inside the heat treatment chamber 10 is equal to or higher than atmospheric pressure. This eliminates a pressure difference between the inside and outside of the heat treatment chamber 10, or the pressure inside the heat treatment chamber 10 is higher than the pressure outside the heat treatment chamber 10, making it difficult for outside air to flow into the heat treatment chamber 10 when the loading port 13 is opened.

[0049] After the loading port 13 is opened, the support table 15 of the scissor lifter 14 is lowered to its initial position, and the next workpiece W to be carburized is placed on the support table 15. The workpiece W is then subjected to vacuum carburizing treatment in accordance with the processing flow shown in Figure 5. By repeating this process, the subsequent workpieces W are also subjected to vacuum carburizing treatment in sequence.

[0050] The above describes a vacuum carburizing method using the heat treatment apparatus 1 according to this embodiment. The heat treatment apparatus 1 can be summarized as follows. The heat treatment apparatus 1 includes a temperature control auxiliary mechanism 12a, which is composed of a heat insulating material 43 and refrigerant piping (external pipe 40 and internal pipe 41) through which a refrigerant flows. The temperature control auxiliary mechanism 12a is designed to change the thermal insulation state of the heat treatment chamber 10 and the refrigerant flow path for cooling the heat treatment chamber 10 between processes requiring high thermal insulation in the heat treatment chamber 10, such as a temperature-raising and soaking process, and processes requiring cooling in the heat treatment chamber 10, such as a temperature-lowering process. For example, during the temperature-raising and soaking process, the thermal insulation performance of the heat treatment chamber 10 is maintained by having the heat insulating material 43 function as part of the insulating wall 20, and the supply of refrigerant gas to the external pipe 40 is stopped to maintain the heat treatment chamber 10 at a high temperature. In addition, in the temperature reduction process, the insulating performance of the heat treatment chamber 10 is reduced by raising the insulating material 43, and by supplying refrigerant gas to the external pipe 40, heat exchange between the atmosphere in the heat treatment chamber 10 and the refrigerant gas is actively carried out, thereby promoting temperature reduction.

[0051] The carburizing process was carried out using the temperature control assist mechanism 12a according to the embodiment of the present invention. The carburizing process conditions are outlined in Figure 5. The following explanation will focus on the entire process, from the end of the carburizing and diffusion process to the temperature before quenching begins.

[0052] The product subjected to the carburizing treatment was an automobile gear part, and the product weight was 400 kg, and the total weight including the jig was 630 kg.

[0053] The heater 12 and temperature control auxiliary mechanism 12a in the device were configured such that the two heaters on both sides of the heater 12 were replaced with temperature control auxiliary mechanisms 12a as described with reference to Figure 1. The diameter of the inner pipe 41 was 35 mm, the diameter of the outer pipe 40 was 125 mm, the heat insulating material was glass wool, and the heat insulating material was installed so as to fill the space between the inner pipe 41 and the outer pipe 40, with a length of 370 mm in the vertical direction.

[0054] After the carburizing and diffusion process was completed, i.e., at the end of the carburizing and diffusion process in Fig. 5, the output of the heater 12 was stopped, and N gas was started to be supplied at a flow rate of 500 L / min to restore the pressure to normal by supplying an inert gas into the heat treatment chamber 10. The pressure was restored to atmospheric pressure in approximately 300 seconds.

[0055] Simultaneously with the start of the N2 gas supply, the internal pipe 41 of the temperature control auxiliary mechanism 12a was moved from the position shown in Figure 4(1) to the position shown in Figure 4(2). Simultaneously with the start of the change in the internal pipe 41 position, compressed air used in the factory was also supplied as refrigerant gas through the internal pipe 41 at a flow rate of 1600 L / min. The supplied compressed air passed from the lower end of the internal pipe 41 through the external pipe 40 and was discharged to the outside through the outlet 42 at the top of the external pipe 40. The temperature of the supplied compressed air was room temperature. The cooling time required from the start of the N2 gas supply to reach 885°C, 15°C higher than the quenching start temperature of 870°C, was 1285 seconds. The results are shown in Table 1.

[0056]

[0057] After the temperature reached 885°C, the supply of compressed air to the inner tube 41 was stopped in order to avoid an unnecessarily rapid temperature drop at the quenching start temperature of 870°C and to avoid further temperature instability due to temperature control. The change in temperature inside the heat treatment chamber 10 before, during, and after the temperature drop process is shown by the thin solid line in Figure 6. Comparative Example

[0058] As in the example, after the carburizing and diffusion process was completed, the heater 12 output was stopped, and N gas was supplied at a flow rate of 500 L / min to restore atmospheric pressure to the heat treatment chamber 10 by supplying inert gas. The differences from the example were that the inner tube 41 was positioned at the downward end and the supply of compressed air from the cooling compressor was stopped. The cooling time required to reach 885°C after the start of N gas supply was measured and was found to be 1,913 seconds. Comparing this result with the results of the example shown in Table 1 above, the cooling time was 49% longer. As in the example, the temperature transition in the comparative example is shown by the dotted line in Figure 6.

[0059] In both the Example and the Comparative Example, the slope of the temperature decrease with time changes during the first 180 seconds after the start of cooling. The reason for this change is thought to be that the gas pressure, primarily nitrogen, in the heat treatment chamber 10 is low during the initial 300 seconds required for the pressure to return to normal within the heat treatment chamber 10, making it difficult for the cooling effect of gas convection to work. The same reason is why the cooling temperature curves for the Example and the Comparative Example move in almost the same direction during this period; it is thought that the low pressure within the heat treatment chamber 10 makes it difficult for the effect of the temperature control assist mechanism in the Example to be seen during this period.

[0060] Detailed explanation of the temperature transitions in the temperature rise and soaking steps will be omitted, but there was no difference between the working example and the comparative example in terms of the temperature rise rate and the stability of soaking.

[0061] As described above, in the working example of the present invention, the structure of the temperature control auxiliary mechanism in the temperature drop process was changed from that in the temperature increase and soaking processes, and further, by introducing compressed air as the refrigerant gas into the inner tube, it was possible to shorten the cooling time from the starting temperature of 930°C to the target temperature of 850°C from 1913 seconds to 1285 seconds.

[0062] The present invention provides a means for achieving both the insulation and cooling efficiency required for each process of a heat treatment device by using a temperature control auxiliary mechanism that combines insulation material and refrigerant piping in temperature control in a heat treatment chamber.

[0063] W Work 1 Heat treatment device 10 Heat treatment chamber 12 Heater 12a Temperature control auxiliary mechanism 13 Loading port 14 Scissor lifter 15 Support base 16 Stirring fan 17 Motor 20 Heat insulating wall 21 Gas inlet 22 Exhaust pipe 23 Opening 24 Pusher 25 Cooling chamber 26 Door 30 Elevator rack 31 Oil tank 32 Door 40 Outer pipe 41 Inner pipe 42 Exhaust port 43 Heat insulating material 45 Drive mechanism 50 Control device

Claims

1. A heat treatment apparatus having a heat treatment chamber for heat-treating a workpiece, the heat treatment apparatus comprising: a temperature control auxiliary mechanism attached to the heat treatment chamber; the temperature control auxiliary mechanism comprising: an outer pipe inserted from the outside to the inside of the heat treatment chamber; and an inner pipe inserted into the outer pipe so as to be freely movable; the tip of the outer pipe is closed; the tip of the inner pipe is open; the outer pipe is provided with an exhaust port outside the heat treatment chamber; and an insulating material attached to the outer peripheral surface of the inner pipe that divides the internal space of the outer pipe into a tip side and a base side.

2. The heat treatment apparatus according to claim 1, further comprising a drive mechanism for moving said inner tube and said insulating material.

3. A temperature control auxiliary mechanism provided in a heat treatment device having a heat treatment chamber for heat-treating a workpiece, the temperature control auxiliary mechanism comprising: an outer pipe inserted from the outside to the inside of the heat treatment chamber; and an inner pipe inserted so as to be freely movable inside the outer pipe, wherein the tip of the outer pipe is closed and the tip of the inner pipe is open, the outer pipe is provided with an exhaust port outside the heat treatment chamber, and a heat insulating material is attached to the outer peripheral surface of the inner pipe to divide the internal space of the outer pipe into a tip side and a base side.

4. A temperature control method for a heat treatment chamber using the heat treatment apparatus according to claim 1, wherein, in a temperature-raising and soaking step, the heat insulating material is moved to the position of the heat treatment chamber's heat insulating wall inside the external pipe, and the supply of refrigerant from the internal pipe to the inside of the external pipe is stopped; and, in a temperature-lowering step, the heat insulating material is moved to the outside of the outlet inside the external pipe, and the refrigerant is supplied to the internal pipe and the supplied refrigerant is allowed to flow from the inside of the external pipe to the outlet.

5. The temperature control method according to claim 4, wherein the refrigerant is air or an inert gas.