Vacuum carburization device and vacuum carburization method

Abstract

To reduce carburization variation of workpieces carburized in the same lot when plural workpieces are simultaneously vacuum-carburized.SOLUTION: A vacuum carburization device 1 for simultaneously carburizing plural workpieces W comprises a treatment chamber 10, in which the workpieces W are inserted, and plural support bases 19 supporting the workpieces W. The treatment chamber 10 has a first side wall 13, a second side wall 14, and an insertion port 11 of the workpieces W. A third heater 43 extending inward of the treatment chamber 10 from a wall opposite to a ceiling wall 16 or the insertion port 11 of the treatment chamber 10 is provided in a third region A3.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a vacuum carburizing apparatus and a vacuum carburizing method. [Background technology]

[0002] As an example of heat treatment to improve the wear resistance of steel automobile parts, machine parts, etc., a carburizing process is known in which carbon is dissolved in the surface of the part (hereinafter referred to as "workpiece") to harden the surface of the workpiece. Vacuum carburizing, in which carburizing is performed in a vacuum atmosphere, is also known as a carburizing method that can reduce the amount of carbon dioxide emitted from the carburizing device that performs the carburizing process.

[0003] To reduce the cost of vacuum carburizing, it is common to carry out the process using a mass production method, and it is desirable to increase the number of workpieces per lot. Patent Documents 1 and 2 disclose vacuum carburizing equipment that performs vacuum carburizing on multiple workpieces simultaneously. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5976540 [Patent Document 2] Patent No. 6817799 Summary of the Invention [Problem to be solved by the invention]

[0005] When performing carburizing treatment with conventional vacuum carburizing equipment, a mesh-like jig on which multiple workpieces are placed is loaded into a treatment chamber, and the workpieces are heated by a heater installed near the wall surface of the treatment chamber. The temperature of the workpieces rises due to the radiant heat of the heater, but the surface area of ​​each workpiece placed on the jig that is shaded by components of the jig or other workpieces differs depending on the positional relationship with the heater, and the temperature rise rate differs for each workpiece.

[0006] For example, workpieces placed on the outer periphery of the jig, which is close to the heater, tend to heat up easily, but workpieces placed in the center of the jig, which is far from the heater, tend to be in the shadow of the jig's components or other workpieces and are difficult to heat up. This causes temperature variations among the workpieces, which leads to carburization variations among workpieces carburized in the same lot. In particular, when the jig has a multi-stage hierarchical structure, the above-mentioned carburization variations due to temperature variations are likely to occur.

[0007] Furthermore, in vacuum carburization, the rate at which carbon penetrates into the workpiece varies significantly depending on the workpiece temperature, so that the carburization variation of the workpieces in vacuum carburization is easily affected by the temperature variation of each workpiece.

[0008] As a means for reducing temperature variation, for example, supplying an inert gas into the treatment chamber and using a stirring fan to heat the workpiece by convection heat transfer can be considered. However, as the temperature in the treatment chamber increases, the atmosphere becomes thin and the effect of convection heat transfer decreases. In addition, in order to perform vacuum carburization, it is necessary to exhaust the inert gas before supplying the carburizing gas into the treatment chamber, which increases the lead time required to ensure exhaust time and requires exhaust equipment to exhaust the high-temperature inert gas. In addition, when exhausting a large amount of high-temperature gas, various measures are required, such as measures to prevent the vacuum exhaust line from overheating and measures to prevent high-temperature gas from flowing into the vacuum pump. For this reason, the method of supplying an inert gas into the treatment chamber and heating the workpiece using a stirring fan has the above-mentioned concerns and cannot be said to be a sufficient method for reducing temperature variation.

[0009] Therefore, in conventional vacuum carburizing apparatus, there is room for improvement in terms of reducing the carburizing variation caused by the temperature variation of workpieces that are carburized in the same lot.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to reduce the carburization variation of workpieces carburized in the same lot when vacuum carburizing is performed on multiple workpieces simultaneously. [Means for solving the problem]

[0011] The aspects of the present invention that solve the above problems are exemplified below. (1) A vacuum carburizing apparatus for simultaneously carburizing multiple workpieces, A processing chamber into which the workpiece is loaded; A plurality of support tables for supporting the workpiece; The processing chamber includes: A first side wall; a second side wall opposite the first side wall; The workpiece is inserted into the workpiece through a work opening provided in a wall portion other than the first side wall and the second side wall. a first heater extending inside one of two opposing wall portions of the processing chamber and parallel to the one wall portion; a second heater is provided inside the other of the two opposing wall portions and extending parallel to the other wall portion; Among the plurality of support stands, the one closest to the first side wall is defined as a first support stand, the one closest to the second side wall is defined as a second support stand, a region on the first side wall side of the first support stand in the processing space formed in the processing chamber is defined as a first region, a region on the second side wall side of the second support stand is defined as a second region, and a region on the second side wall side of the first support stand and on the first side wall side of the second support stand is defined as a third region, A vacuum carburizing apparatus, characterized in that a third heater is provided in the third area, the third heater extending inwardly from a ceiling wall of the treatment chamber or a wall portion facing the loading port of the treatment chamber. (2) The vacuum carburizing apparatus described in (1), characterized in that the third heater extends from the ceiling wall inwardly of the treatment chamber and is provided in a plurality of locations spaced apart in the loading direction of the workpiece. (3) The vacuum carburizing apparatus according to (1) or (2), wherein the third heater is located at the center of the processing chamber in the width direction. (4) a plurality of temperature measuring units for measuring the temperature within the processing chamber; A control unit that controls an output of the third heater, The third heater is provided in plurality, The vacuum carburizing apparatus according to any one of (1) to (3), characterized in that the control unit is configured to execute output control of each of the third heaters so that the temperature distribution in the treatment chamber becomes a predetermined temperature distribution based on the temperatures measured by the plurality of temperature measuring units. (5) a first gas supply pipe that discharges a carburizing gas to the first region; a second gas supply pipe that discharges the carburizing gas into the second region; a third gas supply pipe that discharges the carburizing gas to the third region is provided; The vacuum carburizing apparatus according to any one of (1) to (4), characterized in that the third gas supply pipe extends inwardly from a ceiling wall of the treatment chamber or a wall portion facing the supply port of the treatment chamber. (6) The vacuum carburizing apparatus according to (5), characterized in that the third gas supply pipe extends from the ceiling wall inwardly of the treatment chamber and is provided in a plurality of pipes spaced apart in the loading direction of the workpiece. (7) The vacuum carburizing apparatus according to (5) or (6), wherein the third gas supply pipe is located at the center of the processing chamber in the width direction. (8) The third gas supply pipe is a first discharge port that discharges the carburizing gas toward the first side wall; a second discharge port for discharging the carburizing gas to the second side wall side, The vacuum carburizing apparatus according to any one of (5) to (7), wherein the end of the third gas supply pipe is closed. (9) A plurality of the third gas supply pipes are provided, A mass flow controller is connected to each of the third gas supply pipes, The vacuum carburizing apparatus according to any one of (5) to (8), further comprising a control unit for controlling the operation of each mass flow controller so that the flow rate of the carburizing gas discharged from each of the third gas supply pipes becomes a predetermined flow rate. (10) A vacuum carburizing method for simultaneously carburizing a plurality of workpieces, comprising the steps of: A vacuum carburizing method, characterized in that the carburizing treatment is performed by heating the workpiece from outside a jig placed in a treatment chamber on which the workpiece is placed, and from inside the jig. (11) A vacuum carburizing method for simultaneously carburizing a plurality of workpieces, comprising the steps of: 11. The vacuum carburizing method according to claim 10, characterized in that the carburizing treatment is carried out by discharging a carburizing gas to the side of the jig and discharging the carburizing gas from the inside of the jig onto the workpiece. Effect of the Invention

[0012] According to the present invention, when vacuum carburizing is performed on a plurality of workpieces simultaneously, it is possible to reduce the variation in carburizing of the workpieces carburized in the same lot. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a vacuum carburization apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the cross section AA of FIG. [Diagram 3] FIG. 3 is a cross-sectional view of FIG. 2 taken along line BB. [Figure 4] FIG. 13 is a diagram for explaining an arrangement region of a third heater. [Diagram 5] FIG. 13 is a diagram for explaining an arrangement region of a third heater. [Figure 6] FIG. 6 is an explanatory diagram showing a schematic configuration of a vacuum carburization apparatus according to a second embodiment. [Figure 7] FIG. 7 is a view showing a cross section CC of FIG. [Figure 8] FIG. 8 is a cross-sectional view of FIG. [Figure 9] 4 is a cross-sectional view of a third gas supply pipe taken along the pipe axis direction. FIG. [Figure 10] FIG. 10 is a cross-sectional view of FIG. 9 . [Figure 11] 13 is a diagram showing another example of the configuration of the third gas supply pipe. FIG. [Figure 12] 13 is a diagram showing another example of the configuration of the third gas supply pipe. FIG. [Figure 13] FIG. 13 is a diagram showing temperature measurement positions in a processing chamber in a heating test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted.

[0015] First Embodiment Fig. 1 is an explanatory diagram showing a schematic configuration of a vacuum carburizing apparatus according to the present embodiment, Fig. 2 is a diagram showing a cross section taken along line AA in Fig. 1, Fig. 3 is a diagram showing a cross section taken along line BB in Fig. 2.

[0016] The vacuum carburizing apparatus 1 includes a furnace body 2 and a treatment chamber 10 for performing carburizing treatment on a workpiece W made of steel parts such as automobile parts and machine parts. The treatment chamber 10 is, for example, a rectangular parallelepiped case, and is disposed inside the furnace body 2. In the drawings, the X direction is the width direction of the treatment chamber 10, the Y direction is the depth direction of the treatment chamber 10, and the Z direction is the vertical direction. The X direction, Y direction, and Z direction are perpendicular to each other. In this embodiment, the Y direction is also the loading direction of the workpiece W into the treatment chamber 10.

[0017] A loading port 11 for loading the workpiece W into the processing chamber 10 is formed in the side wall on the near side in the depth direction (negative side in the Y direction) of the four side walls of the furnace body 2 and the processing chamber 10. If the two side walls adjacent to the front side wall 12 on which the loading port 11 is formed are called the first side wall 13 and the second side wall 14, the first side wall 13 and the second side wall 14 face each other and extend parallel to the YZ plane. In other words, the loading port 11 described above is formed in a wall portion other than the first side wall 13 and the second side wall 14. The rear side wall 15 facing the front side wall 12 is a side wall that constitutes the rear side of the processing chamber 10 and extends parallel to the XZ plane.

[0018] Heat insulating materials 18 are provided on the inside of the side walls 12 to 15, the ceiling wall 16, and the bottom wall 17 of the treatment chamber 10. An openable and closable door (not shown) with heat insulating material is attached to the furnace body 2 on the charging port 11 side, and when the carburizing treatment is performed, the workpiece W is charged into the treatment chamber 10 and then the door is closed to block the charging port 11.

[0019] The heat insulating material 18 on the bottom wall 17 side is provided with a plurality of columnar support tables 19 for supporting the workpieces W. The plurality of support tables 19 are arranged at intervals along the width direction (X direction) of the processing chamber 10 and also along the loading direction (Y direction) of the workpieces W. The periphery of the lower end of each support table 19 is covered with the heat insulating material 18, and a jig 20 is placed on the upper end of each support table 19.

[0020] In this specification, the jig refers to a structure on which the workpiece W or a tray containing the workpiece W is placed, and the workpiece W, which is the object to be carburized, is carburized while being placed in the tray. When the workpiece W is large, the workpiece W may be placed directly on the jig 20 without using a tray. The tray may also be configured in a mesh shape so as not to impede the flow of gas in the furnace.

[0021] The jig 20 according to this embodiment has a multi-stage hierarchical structure, with mesh-like trays arranged at intervals in the vertical direction (Z direction). The trays are connected to each other via supports, forming three stages of workpiece W placement areas, and the workpiece W is indirectly supported by the support base 19 via the jig 20.

[0022] Each of the second and third trays of the jig 20 has a gap in the center in the width direction (X direction), and the gap extends along the depth direction (Y direction) of the processing chamber 10. In other words, a groove 21 is formed in the center of the width direction of the jig 20, penetrating from the third tray of the jig 20 to the top surface of the first tray, and the groove 21 extends along the depth direction of the processing chamber 10. By having the groove 21 in the jig 20, it is possible to avoid interference between the jig 20 and a third heater 43 described later when the jig 20 carrying the workpiece W is loaded into the processing chamber 10.

[0023] Furthermore, by having the jig 20 have the grooves 21, oil can easily flow into the grooves 21 during oil quenching, which is a process following the carburizing process, and quenching variations within a lot can be reduced compared to when a jig without the grooves 21 is used. In addition, by allowing oil to easily flow into the grooves 21, each workpiece W can be cooled more uniformly, and the amount of distortion of each workpiece caused by the quenching process can be reduced. As a result, it is possible to reduce the cost of secondary processing for distortion correction.

[0024] When the workpieces W are loaded into the processing chamber 10 using the jig 20, first, a plurality of workpieces W are placed on the jig 20, and the jig 20 is placed on the forks (not shown) of a transport device installed outside the processing chamber 10. Next, the forks move forward with the bottom surface of the jig 20 (the bottom surface of the first tray) supported by the forks, and the jig 20 moves above the support base 19. Next, the forks move down, and the jig 20 is transferred from the forks to the support base 19. Then, the forks move back with the jig 20 placed on the top surface of each support base 19, and the workpieces W placed on the jig 20 are loaded into the processing chamber 10.

[0025] The structure of the jig 20 is determined appropriately depending on the shape, size, number, etc. of the workpieces W. In addition, the structure of the jig 20 is not limited to a multi-stage hierarchical structure, and may be, for example, a tray-like or basket-like structure having only one stage in which the workpieces W are placed.

[0026] Next, a description will be given of the first gas supply pipe 31 and the second gas supply pipe 32 which supply the carburizing gas into the processing chamber 10. The carburizing gas is, for example, acetylene gas, ethylene gas, propane gas, butane gas, or a mixture of these gases.

[0027] A first gas supply pipe 31 that discharges carburizing gas to the workpiece W is provided on the first side wall 13 of the processing chamber 10. The first gas supply pipe 31 penetrates the furnace body 2 and the first side wall 13 of the processing chamber 10, and the tip of the first gas supply pipe 31 is located between the heat insulating material 18 provided on the inside of the first side wall 13 and the outer periphery of the jig 20. In addition, the end of the first gas supply pipe 31 opposite to the tip side is connected to a carburizing gas supply source (not shown) such as a cylinder in which carburizing gas is stored.

[0028] 1, a plurality of first gas supply pipes 31 are provided at intervals in the vertical direction (Z direction) in accordance with the height of each workpiece W placed on the jig 20. In addition, as shown in FIG 2, a plurality of the first gas supply pipes 31 are also provided at intervals in the depth direction (Y direction) of the processing chamber 10.

[0029] A second gas supply pipe 32 that discharges carburizing gas is provided on the second side wall 14 of the processing chamber 10. The second gas supply pipe 32 penetrates the furnace body 2 and the second side wall 14 of the processing chamber 10, and the tip of the second gas supply pipe 32 is located between the heat insulating material 18 provided on the inside of the second side wall 14 and the outer periphery of the jig 20. In addition, the end of the second gas supply pipe 32 opposite to the tip is connected to a carburizing gas supply source (not shown) such as a cylinder in which carburizing gas is stored.

[0030] 1, the second gas supply pipes 32 are provided at intervals in the vertical direction (Z direction) in accordance with the height of each workpiece W placed on the jig 20. Moreover, as shown in FIG 2, the second gas supply pipes 32 are also provided at intervals in the depth direction (Y direction) of the processing chamber 10.

[0031] The material for the above-mentioned gas supply pipes 31 to 32 may be selected from, for example, carbon, ceramics, stainless steel, molybdenum, tungsten, alumina, etc., but it is preferable to select alumina, which is less likely to deteriorate during burnout processing performed as a periodic maintenance operation.

[0032] The first gas supply pipe 31 and the second gas supply pipe 32 have been described above.

[0033] 2, a thermocouple 40 is provided on the first side wall 13 in the processing chamber 10 as a temperature measuring unit for measuring the temperature inside the processing chamber 10. The thermocouple 40 is inserted through the furnace body 2 and the first side wall 13, and the tip of the thermocouple 40 is located inside the heat insulating material 18 on the first side wall 13 side. A plurality of thermocouples 40 are installed at intervals along the depth direction (Y direction) of the processing chamber 10, and the temperatures of a front region, a central region, and a back region in the depth direction of the processing chamber 10 are measured.

[0034] Note that, like the first side wall 13 side, a thermocouple 40 may also be installed on the second side wall 14 side, but if the structure inside the processing chamber 10 is symmetrical, the temperature distribution in the depth direction inside the processing chamber 10 tends to be similar on the first side wall 13 side and the second side wall 14 side. Therefore, by using the temperature measurement results of the thermocouple 40 on the first side wall 13 side, it is possible to estimate the temperature distribution in the entire depth direction inside the processing chamber 10.

[0035] (heater) Next, the first heater 41, the second heater 42, and the third heater 43 that heat the workpiece W placed in the processing chamber 10 will be described.

[0036] 1, a first heater 41 for heating the workpiece W from above the jig 20 is provided near the ceiling wall 16 in the processing chamber 10. The first heater 41 has, for example, a straight tube shape or a U-shape, and extends in the width direction (X direction) of the processing chamber 10 inside the heat insulating material 18 on the ceiling wall 16 side. The first heater 41 penetrates the first side wall 13 and the second side wall 14 and is fixed to each of the side walls 13, 14. As shown in FIG. 3, a plurality of first heaters 41 are installed at intervals along the depth direction (Y direction) of the processing chamber 10.

[0037] 1, a second heater 42 for heating the workpiece W from below the jig 20 is provided near the bottom wall 17 in the processing chamber 10. The second heater 42 has, for example, a straight tube shape or a U-shape, and extends in the width direction (X direction) of the processing chamber 10 inside the heat insulating material 18 on the bottom wall 17 side. The second heater 42 penetrates the first side wall 13 and the second side wall 14 and is fixed to each of the side walls 13, 14. As shown in FIG. 3, a plurality of second heaters 42 are installed at intervals along the depth direction (Y direction) of the processing chamber 10.

[0038] A third heater 43 is provided on the ceiling wall 16 of the processing chamber 10 to heat the surrounding workpiece W inside the jig 20. The third heater 43 penetrates the furnace body 2 and the ceiling wall 16 at the center in the width direction (X direction) of the processing chamber 10 and extends from the ceiling wall 16 toward the bottom of the processing chamber 10. Specifically, the third heater 43 extends from the ceiling wall 16 to near the top surface of the first tray of the jig 20 placed on the support table 19.

[0039] In other words, the lower end of the third heater 43 is located below half the height of the processing space S in the processing chamber 10 and above the upper ends of the multiple support stages 19. The processing space S is a region in the processing chamber 10 that is filled with carburizing gas, and in this embodiment, the processing space S is the space inside the heat insulating material 18 arranged inside the side walls 12 to 15, the ceiling wall 16 and the bottom wall 17.

[0040] 3, the third heater 43 is a U-shaped heater. The shape of the third heater 43 may be, for example, a straight tube shape, but is preferably U-shaped from the viewpoint of simplification of maintenance work and power supply components.

[0041] As shown in FIG. 2, the third heaters 43 are provided at intervals along the depth direction (Y direction) of the processing chamber 10, and heat each workpiece W lined up along the depth direction (Y direction) of the processing chamber 10 from the center of the jig 20.

[0042] The heating element of each of the heaters 41 to 43 may be made of, for example, carbon, nichrome wire, molybdenum, tungsten, silicon carbide, or the like. It is preferable to select silicon carbide (SiC), which is less likely to deteriorate during burnout processing.

[0043] In this embodiment, the heaters 41, 42 are installed so as to extend in the width direction (X direction) inside the opposing ceiling wall 16 and bottom wall 17, but the heaters 41, 42 may be installed so as to extend, for example, in the depth direction (Y direction) of the processing chamber 10. Furthermore, for example, the heaters 41, 42 may be installed so as to extend in the vertical direction (Z direction) or the depth direction (Y direction) of the processing chamber 10 inside the opposing first side wall 13 and second side wall 14.

[0044] That is, the first heater 41 can be installed in the processing chamber 10 near one of the opposing wall portions so as to extend parallel to the one wall portion, and the second heater 42 can be installed near the other wall portion so as to extend parallel to the other wall portion.

[0045] An exhaust pipe (not shown) for exhausting the atmosphere inside the processing chamber 10 is connected to the processing chamber 10, and the exhaust pipe is equipped with equipment such as a pressure gauge (not shown) and a vacuum pump (not shown).

[0046] The vacuum carburizing apparatus 1 includes a control unit 50. The control unit 50 is, for example, a computer equipped with a CPU, a memory, etc., and has a program storage unit (not shown). Various programs for controlling a series of processes performed by the vacuum carburizing apparatus 1 are stored in the program storage unit.

[0047] For example, the program storage unit stores a program for controlling the output of the third heater 43 so that the temperature distribution in the processing chamber 10 becomes a predetermined temperature distribution based on the temperatures measured by the multiple thermocouples 40. By controlling the output of the third heater 43 in this manner, it is possible to enhance the effect of reducing the temperature variation between the workpieces W arranged on the outer periphery of the jig 20 and the workpieces W arranged in the center of the jig 20. The "predetermined temperature distribution" is set appropriately depending on the structure of the jig 20, the shape and arrangement of each workpiece W, etc.

[0048] The above-mentioned program may be recorded in a computer-readable storage medium and installed in the control unit 50 from the storage medium.

[0049] The vacuum carburizing apparatus 1 according to this embodiment is configured as described above. In this vacuum carburizing apparatus 1, the third heater 43 is disposed in the widthwise center of the treatment chamber 10, and the heating element of the third heater 43 extends from the ceiling wall 16 of the treatment chamber 10 toward the inside of the treatment chamber 10. When performing carburizing treatment, each workpiece W disposed around the third heater 43 is heated. Therefore, when performing carburizing treatment, the workpiece W is heated from the outside of the jig 20 by the first heater 41 and the second heater 42, and the workpiece W is heated from the inside of the jig 20 by the third heater 43.

[0050] This makes it easier to uniformly heat the workpieces W arranged on the outer periphery of the jig 20 and the workpieces W arranged in the center, reducing the temperature variation of the workpieces W carburized in the same lot. As a result, it becomes possible to reduce the carburization variation caused by the temperature variation, improve the yield, and reduce the carburization cost.

[0051] Furthermore, since the third heater 43 can heat the jig 20 from the inside, it is possible to increase the temperature rise rate of each workpiece W arranged near the center of the jig, where the temperature rise rate is the slowest. This makes it possible to shorten the lead time for a series of carburizing treatments, thereby improving productivity and reducing energy costs.

[0052] In this embodiment, the third heater 43 is provided only in the center of the processing chamber 10 in the width direction, but multiple third heaters 43 may be provided in the width direction (X direction) depending on the structure of the jig 20 and the arrangement of the workpieces W. Furthermore, for example, when the structure of the jig 20 is not symmetrical or when the arrangement of the workpieces W is not symmetrical, the third heater 43 does not need to be provided in the center of the processing chamber 10 in the width direction.

[0053] In either case, if it is possible to heat the workpiece W from inside the jig 20 by the third heater 43, the effect of reducing the carburization variation described above can be obtained. For this reason, the arrangement area of ​​the third heater 43 to obtain the effect of reducing the carburization variation is defined, for example, as follows.

[0054] (Third heater placement area) 4 and 5 are diagrams for explaining the arrangement region of the third heater 43. First, as shown in Fig. 4, of the multiple supports 19 for placing the jig 20, the support closest to the first side wall 13 is defined as the first support 19a, and the support closest to the second side wall 14 is defined as the second support 19b.

[0055] Next, the area in the processing space S formed in the processing chamber 10 on the first side wall 13 side of the first support table 19a is defined as a first area A1, the area on the second side wall 14 side of the second support table 19b is defined as a second area A2, and the area on the second side wall 14 side of the first support table 19a and on the first side wall 13 side of the second support table 19b is defined as a third area A3.

[0056] From the viewpoint of reducing the above-mentioned variation in carburization, the third heater 43 is provided in the third area A3 so as to extend downward from the ceiling wall 16. This makes it possible to heat the workpieces W from inside the jig 20, and reduces the temperature variation of the workpieces W carburized in the same lot, thereby reducing the variation in carburization.

[0057] In the above example, multiple third heaters 43 were provided at intervals in the depth direction (Y direction) of the processing chamber 10, but only one third heater 43 may be provided. Even in this case, it is possible to reduce temperature variation of the workpieces W carburized in the same lot, compared to a vacuum carburizing apparatus with a conventional structure in which the workpieces W cannot be heated from inside the jig.

[0058] However, when a large number of workpieces W are carburized in the same lot, a plurality of workpieces W are arranged in a line along the depth direction of the jig 20. For this reason, from the viewpoint of heating each workpiece W more uniformly, it is preferable to provide a plurality of third heaters 43 along the depth direction within the processing chamber 10.

[0059] Furthermore, in the above example, the third heater 43 is disposed so as to extend from the ceiling wall 16 of the processing chamber 10 to the inside of the processing chamber 10, but the third heater 43 may be disposed so as to extend, for example, from the rear side wall 15 of the processing chamber 10 to the inside of the processing chamber 10. Even when the third heater 43 is installed on the rear side wall 15, the workpieces W around the third heater 43 can be heated from inside the jig 20, thereby obtaining the effect of reducing temperature variation of the workpieces W carburized in the same lot.

[0060] <Second embodiment> Fig. 6 is an explanatory diagram showing a schematic configuration of a vacuum carburizing apparatus 1 according to a second embodiment. Fig. 7 is a diagram showing a CC cross section of Fig. 6. Fig. 8 is a diagram showing a DD cross section of Fig. 7. The vacuum carburizing apparatus 1 according to this embodiment includes a third gas supply pipe 33 in addition to the first gas supply pipe 31 and second gas supply pipe 32 described in the first embodiment.

[0061] (Third gas supply pipe) The third gas supply pipe 33 is provided in the ceiling wall 16 of the processing chamber 10. The third gas supply pipe 33 penetrates the furnace body 2 and the ceiling wall 16 at the center in the width direction (X direction) of the processing chamber 10, and extends from the ceiling wall 16 downward in the processing chamber 10. Specifically, the third gas supply pipe 33 extends from the ceiling wall 16 to near the upper surface of the first tray of the jig 20 placed on the support table 19.

[0062] In other words, the lower end of the third gas supply pipe 33 is located below half the height of the processing space S in the processing chamber 10 and above the upper ends of the multiple support stages 19. The processing space S is a region in the processing chamber 10 that is filled with the carburizing gas, and in this embodiment, the processing space S is the space inside the heat insulating material 18 arranged inside the side walls 12 to 15, the ceiling wall 16 and the bottom wall 17.

[0063] 7, the third gas supply pipes 33 are provided at intervals along the depth direction (Y direction) of the processing chamber 10, and discharge the carburizing gas onto the side surfaces of each of the workpieces W lined up along the depth direction (Y direction) of the processing chamber 10. Moreover, the third gas supply pipes 33 and the third heaters 43 are arranged alternately along the depth direction (Y direction) of the processing chamber 10.

[0064] 8, the upper end of each of the third gas supply pipes 33 is connected to a carburizing gas supply source (not shown), and a mass flow controller 34 is provided on the carburizing gas supply path of each of the third gas supply pipes 33. The operation of these mass flow controllers 34 is preferably controlled by the control unit 50 so that the flow rate supplied to each of the third gas supply pipes 33 becomes a predetermined flow rate. This makes it easier to uniformly supply the carburizing gas to the workpieces W arranged on the outer periphery of the jig 20 and the workpieces W arranged in the center of the jig 20, thereby improving the effect of reducing the variation in carburizing.

[0065] The above-mentioned "predetermined flow rate" is appropriately set depending on the structure of the jig 20, the shape and arrangement of the workpiece W, and the like. The flow rates of the respective third gas supply pipes 33 may be the same or different.

[0066] 9, the third gas supply pipe 33 has a shape in which the lower end is closed, and a first discharge port 35 and a second discharge port 36 are formed on the side surface of the pipe body. The first discharge port 35 is an opening for discharging the carburizing gas toward the first side wall 13 side of the above-mentioned processing chamber 10, and the second discharge port 36 is an opening for discharging the carburizing gas toward the second side wall 14 side.

[0067] The first discharge ports 35 and the second discharge ports 36 are each formed at intervals along the axial direction of the third gas supply pipe 33. In addition, as shown in Fig. 10, the first discharge ports 35 and the second discharge ports 36 are each formed at intervals along the circumferential direction of the third gas supply pipe 33.

[0068] The number and arrangement of the first discharge port 35 and the second discharge port 36 are appropriately changed depending on the structure of the jig 20 and the arrangement of the workpieces W. However, in order to more uniformly supply the carburizing gas to each of the workpieces W in the center of the jig located around the third gas supply pipe 33, it is preferable to provide at least one each of the first discharge port 35 and the second discharge port 36.

[0069] The material for the above-mentioned gas supply pipes 31 to 33 may be, for example, carbon, ceramics, stainless steel, molybdenum, tungsten, alumina, etc., but it is preferable to select alumina, which is less likely to deteriorate during burnout processing performed as a periodic maintenance operation.

[0070] The third gas supply pipe 33 has been described above.

[0071] In the vacuum carburizing apparatus 1 according to this embodiment, a third gas supply pipe 33 is disposed in the center in the width direction within the treatment chamber 10, and when performing the carburizing treatment, carburizing gas can be discharged to each workpiece W disposed around the third gas supply pipe 33. Therefore, when performing the carburizing treatment, carburizing gas is supplied to the workpiece W from the side of the jig 20 by the first gas supply pipe 31 and the second gas supply pipe 32, and carburizing gas is supplied to the workpiece W from the inside of the jig 20 by the third gas supply pipe 33.

[0072] On the other hand, for example, in a vacuum carburizing apparatus that does not have the third gas supply pipe 33, carburizing gas is supplied only from the side of the jig 20 by the first gas supply pipe 31 and the second gas supply pipe 32. At this time, the carburizing gas discharged from the first gas supply pipe 31 and the second gas supply pipe 32 flows from the outer periphery toward the center of the jig 20, but as the carburizing gas reaches the center of the jig, it comes into contact with the components of the jig 20 and each workpiece W, impeding the flow of the carburizing gas.

[0073] In contrast to this, in the vacuum carburizing apparatus 1 according to this embodiment, the third gas supply pipe 33 is provided, so that carburizing gas can be supplied from inside the jig 20, and therefore carburizing gas can be supplied to each workpiece W arranged in the center of the jig 20, which is difficult for carburizing gas to reach from the sides of the jig 20. This makes it possible to supply carburizing gas from which carbon components have not been consumed to each of the workpieces W arranged on the outer periphery of the jig 20 and the workpieces W arranged in the center, thereby enhancing the effect of reducing carburizing variations in each workpiece W carburized in the same lot.

[0074] In addition, as a means for reducing the variation in carburizing in a vacuum carburizing apparatus that does not have the third gas supply pipe 33, for example, there is a method of increasing the amount of carburizing gas discharged from the first gas supply pipe 31 and the second gas supply pipe 32, and supplying more than the theoretically required amount of carburizing gas into the processing chamber 10. This makes it possible to supply carburizing gas in a state in which the carbon components have not been consumed and have not been thermally decomposed to the center of the jig 20.

[0075] However, excessive supply of carburizing gas into the treatment chamber 10 not only increases the treatment cost, but also increases the frequency of sooting in the treatment chamber 10. When sooting occurs in the treatment chamber 10, burnout treatment is performed as a regular maintenance operation to burn off the soot adhering to the inside of the treatment chamber 10. Since carburizing treatment of the workpiece cannot be performed during burnout treatment, excessive supply of carburizing gas results in reduced productivity.

[0076] In addition, in vacuum carburizing, pulse control is sometimes used to suppress cementite precipitation on the extreme surface of the workpiece W by repeating the supply of carburizing gas and evacuation, but if the evacuation speed is slow when an excess of carburizing gas is supplied, it is easy for the carburizing gas that has not been pyrolyzed and the pyrolysis gas to coexist in the treatment chamber 10. In that case, if the pyrolysis gas floats near the workpiece W, it becomes difficult for the carburizing gas that has not been pyrolyzed to come into contact with the workpiece W, which can cause problems such as uneven carburization of the workpiece W and a decrease in the carburization speed of the workpiece W. To address these problems, a large vacuum pump can be used to evacuate the gas in the treatment chamber 10 in a short time, but there is a concern that this would increase the initial cost of the equipment and the running cost.

[0077] In addition, when the carburizing gas is floating in the treatment space S, the carburizing gas loses its carburizing ability due to thermal decomposition, so that part of the carburizing gas supplied into the treatment chamber 10 does not contribute to the carburizing of the workpiece W. Therefore, if the carburizing gas is supplied in excess of the theoretically required amount, the amount of carburizing gas lost due to thermal decomposition increases, and the carburizing efficiency decreases. In other words, the amount of carburizing gas required to obtain the desired carburizing quality increases, and the running costs also increase. In particular, since acetylene gas that can be used as the carburizing gas is expensive, the method of supplying an excess of acetylene gas used as the carburizing gas into the treatment chamber 10 significantly increases the running costs.

[0078] The vacuum carburizing apparatus 1 according to the second embodiment is equipped with the third gas supply pipe 33, which eliminates the need for excessive supply of carburizing gas as described above, and therefore in addition to reducing variations in carburizing, can also reduce running costs.

[0079] In this embodiment, the third gas supply pipes 33 and the third heaters 43 are arranged alternately along the depth direction (Y direction) of the processing chamber 10. As a result, in the widthwise center of the jig 20, the amount of carburizing gas discharged to each of the workpieces W lined up along the depth direction and the temperature of each of the workpieces W tend to become uniform, improving the effect of reducing the variation in carburizing.

[0080] In addition, in this embodiment, the third gas supply pipe 33 is provided only in the center of the processing chamber 10 in the width direction, but a plurality of third gas supply pipes 33 may be provided in the width direction (X direction) depending on the structure of the jig 20 and the arrangement of the workpieces W. Furthermore, for example, when the structure of the jig 20 is not symmetrical or when the arrangement of the workpieces W is not symmetrical, the third gas supply pipe 33 does not have to be provided in the center of the processing chamber 10 in the width direction.

[0081] In either case, if it is possible to supply carburizing gas from inside the jig 20 by the third gas supply pipe 33, the effect of reducing the carburizing variation described above can be obtained. For this reason, in order to obtain the effect of reducing the carburizing variation, it is preferable that the third gas supply pipe 33 is provided so as to extend downward from the ceiling wall 16 in the third area A3. This makes it possible to discharge the carburizing gas from inside the jig 20, thereby reducing the carburizing variation of the workpieces W carburized in the same lot.

[0082] The first gas supply pipe 31 is disposed at a position where the carburizing gas can be discharged to the first area A1, and the second gas supply pipe 32 is disposed at a position where the carburizing gas can be discharged to the second area A2. This allows the carburizing gas to be supplied from the side of the jig 20.

[0083] 6, the carburizing gas is discharged into the first area A1 by discharging it from the first gas supply pipe 31 attached to the first side wall 13 into the processing chamber 10, but for example, the first gas supply pipe 31 may be attached to the ceiling wall 16 in the first area A1. If the carburizing gas is discharged downward from the first gas supply pipe 31 attached to the ceiling wall 16 in the first area A1, the carburizing gas is discharged into the first area A1 in the processing chamber 10, and the carburizing gas can be supplied from the side of the jig 20. For the same reason, the second gas supply pipe 32 may be attached to the ceiling wall 16 in the second area A2.

[0084] (Another configuration example of the third gas supply pipe) Next, other configuration examples of the third gas supply pipe 33 will be described.

[0085] First, the carburizing gas supplied to the third gas supply pipe 33 is supplied from the upper end side of the third gas supply pipe 33, and therefore the pressure loss increases toward the tip of the third gas supply pipe 33. Therefore, the amount of carburizing gas discharged from each of the discharge ports 35, 36 decreases toward the tip of the third gas supply pipe 33, and the amount of carburizing gas discharged varies depending on the positions of the discharge ports 35, 36 in the axial direction of the pipe.

[0086] Therefore, in order to reduce the variation in the amount of carburizing gas discharged in the axial direction of the pipe, it is preferable that the hole diameters of the first discharge port 35 and the second discharge port 36 are larger the closer they are to the tip of the third gas supply pipe 33, as shown in Fig. 11. This increases the amount of carburizing gas discharged from the discharge ports 35, 36 at the tip side of the third gas supply pipe 33, and even if pressure loss occurs inside the pipe, the variation in the amount of carburizing gas discharged from the third gas supply pipe 33 in the axial direction of the pipe can be reduced.

[0087] The third gas supply pipe 33 may have a double pipe structure as shown in Fig. 12. The third gas supply pipe 33 in the example of Fig. 12 is composed of an inner pipe 33a to which carburizing gas is supplied and an outer pipe 33b surrounding the inner pipe 33a. A third discharge port 37 for discharging the carburizing gas to the inside of the outer pipe 33b is formed on the side surface of the inner pipe 33a, and the above-mentioned first discharge port 35 and second discharge port 36 are formed on the side surface of the outer pipe 33b. The third discharge port 37 of the inner pipe 33a is formed at a different height from the first discharge port 35 and second discharge port 36 of the outer pipe 33b.

[0088] In the third gas supply pipe 33 having a double pipe structure, even if the amount of carburizing gas discharged from the inner pipe 33a varies due to pressure loss occurring in the inner pipe 33a, the carburizing gas discharged from the inner pipe 33a is temporarily filled in the outer pipe 33b, so that the variation in the amount of discharge is reduced. In other words, the carburizing gas is discharged from the outer pipe 33b in a state in which the variation in the amount of discharge caused by pressure loss in the inner pipe 33a is reduced, so that the carburizing gas is supplied to each workpiece more uniformly, and the effect of reducing the variation in carburizing can be improved.

[0089] In the above example, the tip of the third gas supply pipe 33 is closed, and the first discharge port 35 and the second discharge port 36 are formed on the side surface of the pipe, but the third gas supply pipe 33 may be a pipe with an open tip like a nozzle, without any discharge port on the side surface of the pipe. Even with such a third gas supply pipe, carburizing gas can be discharged from inside the jig 20 to the surrounding workpieces W, so that the carburizing variation of the workpieces W carburized in the same lot can be reduced compared to a vacuum carburizing apparatus of a conventional structure in which carburizing gas cannot be discharged from inside the jig.

[0090] Furthermore, in the above example, multiple third gas supply pipes 33 were provided at intervals in the depth direction (Y direction) within the processing chamber 10, but only one third gas supply pipe 33 may be provided. Even in this case, it is possible to reduce the carburizing variation of the workpieces W carburized in the same lot, compared to a vacuum carburizing apparatus of a conventional structure in which the carburizing gas cannot be discharged from inside the jig.

[0091] However, when a large number of workpieces W are carburized in the same lot, a plurality of workpieces W are arranged side by side along the depth direction of the jig 20. For this reason, from the viewpoint of supplying the carburizing gas to each workpiece W more uniformly, it is preferable to provide a plurality of third gas supply pipes 33 along the depth direction within the treatment chamber 10.

[0092] Furthermore, in the above example, the third gas supply pipe 33 is disposed so as to extend from the ceiling wall 16 of the processing chamber 10 to the inside of the processing chamber 10, but the third gas supply pipe 33 may be disposed so as to extend, for example, from the rear side wall 15 of the processing chamber 10 to the inside of the processing chamber 10. Even when the third gas supply pipe 33 is installed on the rear side wall 15, the carburizing gas can be discharged from the inside of the jig 20 to the workpieces W around the third gas supply pipe 33, thereby obtaining the effect of reducing the carburizing variation of the workpieces W carburized in the same lot.

[0093] Although the embodiment of the present invention has been exemplified above, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention.

[0094] For example, the components of the above-described embodiments may be combined in any manner. Any combination will naturally provide the functions and advantages of each of the components in the combination, and will also provide other functions and advantages that will be apparent to those skilled in the art from the description of this specification. EXAMPLES

[0095] Heating tests were carried out using the vacuum carburizing apparatus 1 shown in Figures 1 to 3 and a vacuum carburizing apparatus (not shown) that was not equipped with the third heater 43 of the vacuum carburizing apparatus 1. The treatment chamber in each vacuum carburizing apparatus was treatment chamber 10a having a rectangular parallelepiped treatment space with length L in the depth direction (X direction) shown in Figure 13, width b and height h.

[0096] At positions P1 to P5 in the processing chamber 10a, the temperature is measured by a temperature sensor during a heating test. Positions P1 to P4 are the positions of the diagonal end points of the rectangular parallelepiped processing space, and position P5 is the position of the intersection of two diagonals of a plane parallel to the XZ plane at the position 2 / L. In the following description, the "periphery temperature" in the processing chamber 10a is the average temperature of the temperatures measured at positions P1 to P4, and the "center temperature" is the temperature measured at position P5.

[0097] In the heating test, first, the inside of the processing chamber 10a at room temperature is heated with a heater in a vacuum atmosphere, and the temperature difference between the peripheral temperature and the central temperature in the processing chamber 10a is measured when the peripheral temperature in the processing chamber 10a reaches 600° C. Next, the heater temperature is set constant, and the soaking time from the point when the peripheral temperature in the processing chamber 10a reaches 600° C. until the peripheral temperature and the central temperature become substantially the same temperature is measured.

[0098] Next, the heater temperature setting is changed to further heat the inside of the processing chamber 10a. After that, the temperature difference between the peripheral temperature and the central temperature in the processing chamber 10a is measured when the peripheral temperature in the processing chamber 10 reaches 850°C. Next, the heater temperature setting is kept constant, and the soaking time from when the peripheral temperature in the processing chamber 10a reaches 850°C until the peripheral temperature and the central temperature become substantially the same temperature is measured.

[0099] The results of the heating test carried out under the above conditions are shown in Table 1 below.

[0100] [Table 1]

[0101] As shown in Table 1, when the third heater was installed, the temperature difference between the peripheral and central temperatures in the processing chamber was smaller both at the time the temperature was raised to 600° C. and at the time the temperature was raised to 850° C., compared to when the third heater was not installed. Furthermore, when the third heater was installed, the soaking time for soaking the peripheral and central temperatures at 600° C. and at 850° C. were both shortened, and the lead time from starting heating inside the processing chamber to completing soaking at 850° C. was shortened.

[0102] Therefore, according to the results of this heating test, the vacuum carburizing apparatus equipped with the third heater can reduce the temperature variation between the periphery and center of the treatment chamber by making it easier to heat the center of the treatment chamber. Therefore, even when performing vacuum carburizing, the workpieces can be heated from the center of the jig on which multiple workpieces are placed, reducing the temperature variation between the workpieces placed on the periphery of the jig and those placed in the center of the jig.

[0103] The above describes the embodiments of the present invention. The effects described in this specification are merely explanatory or exemplary and are not limiting. In other words, the technology disclosed herein may provide other effects that are apparent to a person skilled in the art from the description of this specification, in addition to or in place of the above effects. [Industrial Applicability]

[0104] The present invention can be applied to a vacuum carburizing apparatus for a workpiece, and can also be applied to other heat treatment apparatuses, such as a gas carburizing apparatus and a nitriding apparatus. [Explanation of symbols]

[0105] 1 Vacuum carburizing equipment 2 Furnace body 10 Processing Room 10a Processing Room 11 Charging port 12 Front side wall 13 First side wall 14 Second side wall 15 Rear side wall 16 Ceiling Wall 17 Bottom wall 18 Insulation 19 Support stand 19a 1st support stand 19b 2nd support stand 20 Jig 21 Groove 31 First gas supply pipe 32 Second gas supply pipe 33 Third Gas Supply Pipe 33a inner tube 33b outer tube 34 Mass Flow Controller 35 1st discharge port 36 2nd outlet 37 Third discharge port 40 Thermocouple 41 First heater 42 Second heater 43 Third heater 50 Control section A1 1st area A2 second area A3 3rd area W work

Claims

1. A vacuum carburizing apparatus for simultaneously carburizing multiple workpieces, A processing chamber into which the workpiece is loaded; A plurality of support tables for supporting the workpiece; The processing chamber includes: A first side wall; a second side wall opposite the first side wall; The workpiece is inserted into the workpiece through an inlet provided in a wall portion other than the first side wall and the second side wall. a first heater extending inside one of two opposing wall portions of the processing chamber and parallel to the one wall portion; a second heater is provided inside the other of the two opposing wall portions and extending parallel to the other wall portion, Among the plurality of support tables, the support table closest to the first side wall is defined as a first support table, and the support table closest to the second side wall is defined as a second support table. A region on the first side wall side of the first support table in the processing space formed in the processing chamber is defined as a first region, a region on the second side wall side of the second support table is defined as a second region, and a region on the second side wall side of the first support table and on the first side wall side of the second support table is defined as a third region, A vacuum carburizing apparatus, characterized in that a third heater is provided in the third area, the third heater extending inwardly from a ceiling wall of the treatment chamber or a wall portion facing the loading port of the treatment chamber.

2. 2. The vacuum carburizing apparatus according to claim 1, wherein the third heater extends from the ceiling wall inwardly of the treatment chamber and is provided in a plurality of units spaced apart from one another in a loading direction of the workpiece.

3. 3. The vacuum carburizing apparatus according to claim 1, wherein the third heater is positioned at a center portion in the width direction of the processing chamber.

4. A plurality of temperature measuring units for measuring the temperature within the processing chamber; A control unit that controls an output of the third heater, The third heater is provided in plurality, 3. The vacuum carburizing apparatus according to claim 1, wherein the control unit is configured to execute output control of each of the third heaters so that a predetermined temperature distribution is achieved in the treatment chamber based on the temperatures measured by the plurality of temperature measuring units.

5. a first gas supply pipe that discharges a carburizing gas into the first region; a second gas supply pipe that discharges the carburizing gas into the second region; a third gas supply pipe that discharges the carburizing gas to the third region is provided; 3. The vacuum carburizing apparatus according to claim 1, wherein the third gas supply pipe extends from a ceiling wall of the treatment chamber or a wall portion facing the supply port toward the inside of the treatment chamber.

6. 6. The vacuum carburizing apparatus according to claim 5, wherein the third gas supply pipe extends from the ceiling wall to the inside of the treatment chamber, and a plurality of the third gas supply pipes are provided at intervals in the loading direction of the workpiece.

7. 6. The vacuum carburizing apparatus according to claim 5, wherein the third gas supply pipe is located at a center portion in a width direction of the processing chamber.

8. The third gas supply pipe is a first discharge port that discharges the carburizing gas toward the first side wall; a second discharge port for discharging the carburizing gas to the second side wall side, 6. The vacuum carburizing apparatus according to claim 5, wherein the end of the third gas supply pipe is closed.

9. A plurality of the third gas supply pipes are provided, A mass flow controller is connected to each of the third gas supply pipes, 6. The vacuum carburizing apparatus according to claim 5, further comprising a control unit for controlling the operation of each mass flow controller so that the flow rate of the carburizing gas discharged from each of the third gas supply pipes becomes a predetermined flow rate.

10. A vacuum carburizing method for simultaneously carburizing a plurality of workpieces, comprising the steps of:

1. A vacuum carburizing method, comprising the steps of: heating the workpiece from the outside of a jig placed in a treatment chamber on which the workpiece is placed; and heating the workpiece from the inside of the jig.

11. A vacuum carburizing method for simultaneously carburizing a plurality of workpieces, comprising the steps of:

11. The vacuum carburizing method according to claim 10, wherein the carburizing treatment is carried out by discharging a carburizing gas to a side of the jig and discharging the carburizing gas from inside the jig onto the workpiece.

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