heat treatment furnace

Abstract

A heat treatment furnace capable of suppressing variations in the flow rate of cooling gas within a treatment chamber during gas cooling is provided. [Solution] A heat treatment furnace (1) includes a treatment chamber (4) partitioned by a heat insulating wall (16) and accommodating a workpiece (W) to be treated, and a cooling means (8) for circulating a cooling gas into the treatment chamber (4) through a pair of gas vent openings (17A, 17B) formed in opposing heat insulating walls (16a, 16b) of the treatment chamber (4) to cool the workpiece (W). The heat treatment furnace (1) further includes a flow rectifier (45) installed in the gas vent openings (17A, 17B) and forming a plurality of individual openings (46) within the gas vent openings (17A, 17B), and when the longitudinal width of the gas vent openings (17A, 17B) is L and the lateral width is S, the opening ratio of a central region (47) of the gas vent openings (17A, 17B) having a longitudinal dimension of 1 / 2L and a lateral dimension of 1 / 3S is within a range of 0.17 to 0.85 relative to the opening ratio of a region (48) other than the central region (47).

Description

[Technical Field]

[0001] The present invention relates to a heat treatment furnace capable of subjecting a workpiece to a heating treatment and a gas cooling treatment. [Background technology]

[0002] For example, a heat treatment furnace is known that has a single treatment chamber defined by a heat insulating wall within the furnace shell, and that can subject a workpiece contained in the treatment chamber to a gas cooling treatment after a heating treatment. Such a heat treatment furnace is equipped with a heating means for heating the workpiece contained in the treatment chamber, and a cooling means for cooling the workpiece by circulating a cooling gas into the treatment chamber through a pair of gas vents formed in opposing heat insulating walls of the treatment chamber (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-231969 Summary of the Invention [Problem to be solved by the invention]

[0004] In the heat treatment furnace described above, the opening area of ​​the gas vent port is made large so that sufficient cooling gas can be supplied to the workpiece in the treatment chamber during gas cooling. However, if the gas vent port is simply an opening, the flow of cooling gas tends to be biased toward the center of the gas vent port, resulting in a problem of variation in the flow rate of the cooling gas within the treatment chamber. SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a heat treatment furnace capable of suppressing variations in the flow rate of cooling gas within the treatment chamber during gas cooling. [Means for solving the problem]

[0005] The heat treatment furnace of the present invention is defined as follows: a treatment chamber defined by a heat insulating wall within the furnace shell and accommodating the workpiece; a heating means for heating the workpiece accommodated in the processing chamber; a cooling means for circulating a cooling gas into the processing chamber through a pair of gas vents formed in opposing insulating walls of the processing chamber to cool the workpiece; A heat treatment furnace for subjecting the workpiece to a heating treatment and a gas cooling treatment, comprising: a flow straightening plate disposed in the gas vent port portion and forming a plurality of individual openings within the gas vent port portion; When the longitudinal width of the gas vent portion is L and the lateral width is S, the opening ratio of the central region of the gas vent portion, which has a longitudinal dimension of 1 / 2L and a lateral dimension of 1 / 3S, is in the range of 0.17 to 0.85 compared to the opening ratio of the other regions excluding the central region.

[0006] According to the heat treatment furnace of the present invention defined in this manner, the inflow of cooling gas near the center of the gas vent port, where the gas flow tends to concentrate, is suppressed, and the variation in the flow rate of the cooling gas within the treatment chamber during gas cooling can be suppressed.

[0007] In the heat treatment furnace of the present invention, the individual openings may be formed in the shape of holes, lattices, or slits. In this case, the hole diameter, lattice width, or slit width of the individual openings in the central region may be smaller than the hole diameter, lattice width, or slit width of the individual openings in the other regions.

[0008] In addition, in the heat treatment furnace of the present invention, a baffle plate can be arranged so as to block the space between the outer surface of the insulating wall near the gas vent portion and the inner surface of the furnace shell in a vertical cross-sectional view perpendicular to the central axis of the furnace shell. In this way, the amount of cooling gas that does not pass through the gas vent port and instead flows around into the space between the outer surface of the heat insulating wall and the inner surface of the furnace shell can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing the internal structure of a heat treatment furnace according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 3] 2 is a diagram showing a state in which cooling gas is circulated in a direction different from that shown in FIG. 1 in the heat treatment furnace of the same embodiment. [Figure 4] FIG. 10 is a plan view of the gas vent portion to which the flow straightening plate is attached. [Figure 5] 10A and 10B are explanatory diagrams for evaluating variations in the flow rate of a cooling gas in a processing chamber. [Figure 6] FIG. 10 is a diagram of a modified example in which a baffle plate is added to the space between the outer surface of the insulating wall and the inner surface of the furnace shell. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present invention will be described in detail below with reference to the drawings. In the following description, a vacuum heat treatment furnace will be used as an example of the heat treatment furnace of the present embodiment.

[0011] FIG. 1 is a cross-sectional view showing the internal structure of a vacuum heat treatment furnace 1 according to one embodiment of the present invention. As shown in the figure, the vacuum heat treatment furnace 1 has a treatment chamber 4 formed inside a furnace shell 2 serving as a vacuum container, for accommodating the workpiece W. The vacuum heat treatment furnace 1 is a single-chamber heat treatment furnace that enables the workpiece W accommodated in the treatment chamber 4 to be subjected to a heat treatment under vacuum followed by a gas cooling treatment, and is configured to include a heater 6 as a heating means for heating the workpiece W, and a cooling means 8 for gas cooling the workpiece W.

[0012] The furnace shell 2 is configured as a pressure-resistant vacuum vessel having a substantially cylindrical shape, and is placed sideways so that the central axis P of the cylinder is horizontal. An open / close lid 10 is airtightly attached to one end of the cylindrical furnace shell 2 (the left end in FIG. 1) with a seal ring. The furnace shell 2 is provided with a suction port 11 connected to a vacuum pump 12, and the inside of the furnace shell 2 is placed in a vacuum state (reduced pressure state) by sucking air from inside the furnace shell 2 through the suction port 11.

[0013] The furnace shell 2 of the vacuum heat treatment furnace 1 is also provided with a supply port 13 for supplying nitrogen gas as a non-oxidizing gas into the interior. A nitrogen gas supply device 14 is connected to the supply port 13, and the nitrogen gas supplied through the supply port 13 is supplied into the furnace shell 2 including the treatment chamber 4.

[0014] A heat insulating material 15 is disposed inside the furnace shell 2, and the heat insulating material 15 forms a box-shaped heat insulating wall 16. The processing chamber 4 is formed in the inner area surrounded by the heat insulating wall 16. The side wall 16c constituting part of the insulating wall 16 is detachable from the other part of the insulating wall 16, and is connected to the opening / closing lid 10 by a connecting member 19 so that it can move integrally with the opening / closing lid 10. When the opening / closing lid 10 is opened, the side wall 16c of the insulating wall 16 is also detached from the other part of the insulating wall 16, making it possible to load and unload the workpiece W into and from the processing chamber 4.

[0015] As shown in Figure 1, in the area on the left side of the processing chamber 4, a convection heating fan 26 is provided to stir and circulate the nitrogen gas supplied into the processing chamber 4 and promote the temperature rise of the workpiece W during the temperature rise period, and a motor 27 to rotate this fan is attached to the opening / closing lid 10.

[0016] Gas vents 17A and 17B for passing cooling gas are provided as openings penetrating the insulating material in the thickness direction in the upper wall 16a and the lower wall 16b of the insulating wall 16. In this embodiment, the gas vents 17A and 17B have the same shape and dimensions and are provided at positions that overlap each other in a plan view.

[0017] 2 is a cross-sectional view taken along line II-II in FIG. 1. As shown in the figure, shutter mechanisms 22 are provided directly above gas vent port 17A and directly below gas vent port 17B. Shutter mechanism 22 includes a shielding plate 23 that opens and closes gas vent port 17A or 17B, and a cylinder device 24 that opens and closes shielding plate 23. Shielding plate 23 is composed of halves 23a and 23b, which move in opposite directions from near the center of gas vent port 17A or 17B, respectively, to open gas vent port 17A or 17B (FIG. 2 shows gas vent port 17A or 17B in an open state).

[0018] The shutter mechanisms 22 provided on the top and bottom close the gas vent openings 17A and 17B with shielding plates 23 when the workpiece W is heated by the heater 6. On the other hand, when the workpiece W is gas-cooled, the operation is controlled so as to open the gas vent openings 17A and 17B.

[0019] The processing chamber 4, which is partitioned by the heat insulating wall 16, is provided with a heater 6 as a heating means, and also with a stand 20 on which the workpiece W is placed. The stand 20 is configured to include a pair of rod-shaped members 20a spaced apart from each other in the left-right direction of FIG.

[0020] Next, we will explain the cooling means 8. As shown in Figure 1, the cooling means 8 is composed of a circulation fan 31, a gas cooler 35 that lowers the temperature of the cooling gas by heat exchange, a circulation direction switching plate 37, and an air direction adjusting plate 41, and uses nitrogen gas supplied into the furnace shell 2 as the cooling gas to cool the workpiece W contained in the treatment chamber 4. The circulation fan 31 is disposed inside the furnace shell 2 in a region near the other end wall 2b opposite the open / close lid 10. The circulation fan 31 rotates around a rotation axis extending horizontally in the drawing from a motor 32 attached to the other end wall 2b, sucks in cooling gas through an intake port 33, and ejects the cooling gas radially outward from the outer periphery of the fan.

[0021] The circulation direction switching plate 37 is a member that opens and closes a pair of upper and lower openings 39A and 39B provided on the gas flow path between the processing chamber 4 and the circulation fan 31, and is rotatable around an axis 38 by a drive mechanism not shown. 1, by closing the lower opening 39B with the lower circulation direction switching plate 37 and opening the upper opening 39A with the upper circulation direction switching plate 37, the cooling gas passing through the processing chamber 4 can be set to a first cooling gas circulation direction in which the flow of the cooling gas is upward (see the gas flow indicated by the arrows in the figure). Also, by closing the upper opening 39A and opening the lower opening 39B, it is possible to switch to a second cooling gas circulation direction in which the flow of the cooling gas passing through the processing chamber 4 is downward (see FIG. 3).

[0022] The wind direction adjusting plate 41 is provided between the processing chamber 4 and the furnace shell 2 at a position facing the gas vent ports 17A and 17B, and is rotatable around an axis 42 by a drive mechanism not shown. A plurality of airflow direction adjusting plates 41 can be arranged near gas vent ports 17A and 17B. In this embodiment, as shown in Fig. 1, a first airflow direction adjusting plate 41A is provided near the center of the opening of gas vent ports 17A and 17B, and a second airflow direction adjusting plate 41B is provided near the opening edge of gas vent ports 17A and 17B on the side away from circulation fan 31. These airflow direction adjustment plates 41A, 41B change the direction of the cooling gas that is blown out from the circulation fan 31 and flows through the space between the processing chamber 4 and the furnace shell 2 approximately parallel to the central axis P, and guide the cooling gas to the gas vent portions 17A, 17B.

[0023] 4 is a diagram showing gas vent port 17B formed in lower wall 16b of heat insulating wall 16. As shown in the figure, in this embodiment, a rectifying plate 45 is attached to close gas vent port 17B through which cooling gas passes. Below, gas vent port 17B and the rectifying plate 45 attached to gas vent port 17B will be described. However, in the vacuum heat treatment furnace 1 of this embodiment, which is capable of switching the circulation direction of the cooling gas, a similar rectifying plate 45 is also attached to gas vent port 17A formed in upper wall 16a.

[0024] The flow straightening plate 45 is a member attached to the gas vent port 17B to vertically direct the flow of gas passing through the gas vent port 17B and adjust the flow rate. The flow straightening plate 45 is a plate-shaped member made of a C / C composite (carbon composite material) that is less susceptible to strength loss in high-temperature environments, and has a plurality of individual slit-shaped openings 46 formed therein that penetrate the plate in the thickness direction.

[0025] In order to prevent the gas flow from concentrating near the center of gas vent portion 17B in the first cooling gas circulation direction shown in Figure 1 and the flow rate of the gas flow from becoming extremely high near the center, the width dimension and arrangement pitch of individual openings 46 are taken into consideration so that the opening rate K1 in central region 47 of gas vent portion 17B shown in Figure 4 is smaller than the opening rate K2 in other regions 48 excluding central region 47. Here, the aperture ratio is calculated as B / A, where A is the area of ​​the target region and B is the total area of ​​the individual apertures present in the target region.

[0026] Here, when the longitudinal width of gas vent port 17B is L, the lateral width is S, and the opening center of gas vent port 17B is O, central region 47 is a rectangular region symmetrical with respect to longitudinal center line PL and lateral center line PS passing through opening center O, with the longitudinal dimension being 1 / 2L and the lateral dimension being 1 / 3S. Central region 47 is indicated by a two-dot chain line in the drawing. The other region 48 is the entire region of the gas vent port portion 17B (a rectangular region having a longitudinal width L and a lateral width S in FIG. 4) excluding the central region 47. In this embodiment, the ratio (K1 / K2) of the aperture ratio K1 in the central region 47 to the aperture ratio K2 in the other region 48 excluding the central region 47 is set to a range of 0.17 to 0.85. To obtain the effect of suppressing concentrated inflow from the center of the gas vent portion 17B, the aperture ratio ratio K1 / K2 needs to be 0.85 or less. However, if the aperture ratio K1 is too low compared to the aperture ratio K2, the required amount of cooling gas cannot be supplied into the processing chamber 4, so the aperture ratio ratio K1 / K2 needs to be 0.17 or more. A more preferable range for the aperture ratio ratio K1 / K2 is 0.17 to 0.68.

[0027] To obtain a predetermined aperture ratio ratio K1 / K2, the arrangement pitch of the individual apertures 46 formed in the central region 47 can be made larger than that of the individual apertures 46 formed in the other regions 48. Furthermore, the width H1 of the individual apertures 46 formed in the central region 47 shown in FIG. 4 can be made smaller than the width H2 of the slit-shaped individual apertures 46 formed in the other regions 48.

[0028] The effect of attaching the rectifying plate 45 configured in this way to the gas vent openings 17A and 17B can be confirmed by the following simulation.

[0029] (simulation) For nine examples (one comparative example and eight examples) with different configurations of the rectifying plates attached to the gas vents 17A and 17B, the cooling gas pressure was 600 kPa.abs and the cooling fan air volume was 7.5 m 3 The flow rate of the cooling gas flowing through the processing chamber 4 was simulated under the condition of 1 / s. 5, in a vertical projection view, the area inside the processing chamber 4 overlapping with the gas vent openings 17A and 17B was divided into nine sections in the longitudinal direction and four sections in the lateral direction to obtain a total of 36 small sections 50, and the gas flow speeds were determined in these sections, and the wind speed difference, which is the difference between the maximum and minimum values, the standard deviation of the wind speeds, and the air volume, which is the total amount of gas that passed through each small section 50, were calculated. The results are shown in Table 1 below.

[0030] [Table 1]

[0031] Comparative Example 1 in Table 1 is an example in which a conventionally known lattice-shaped straightening plate is attached to the gas vent opening, and the opening ratio in the central region is 1.0 compared to the opening ratio in other regions. Example 1 is an example in which a straightening plate having individual round openings is attached to the gas vent portion, and Examples 2 to 8 are examples in which a straightening plate having individual slit-shaped openings as shown in Fig. 4 is attached to the gas vent portion. In Examples 1 to 8, the arrangement pitch and width of the individual openings formed in the central region shown in Fig. 4 are changed, and the opening ratio in the central region is made to differ from the opening ratio in other regions by a range of 0.17 to 0.85.

[0032] The results shown in Table 1 reveal that Examples 1 to 8 all have smaller wind speed differences and wind speed standard deviations of the cooling gas circulating within the processing chamber compared to Comparative Example 1. As shown in Table 1, when prioritizing based on wind speed differences, Examples 4 to 8, which have opening ratios of 0.68 or less, are particularly favorable.

[0033] Next, the heat treatment operation by the vacuum heat treatment furnace 1 of this embodiment will be described. First, the workpiece W is carried into the treatment chamber 4 with the opening / closing lid 10 and the side wall 16c of the heat insulating wall 16 of the vacuum heat treatment furnace 1 open, and then the opening / closing lid 10 and the side wall 16c of the heat insulating wall 16 are closed.

[0034] When the opening / closing lid 10 and the side wall 16c of the heat insulating wall 16 are closed, vacuum suction is performed using the vacuum pump 12, and the air inside the furnace is discharged to the outside of the furnace.

[0035] After evacuation is complete, nitrogen gas is introduced, and with the shielding plate 23 of the shutter mechanism 22 closed, the fan 26 is rotated to rapidly heat the chamber to a predetermined temperature by convection heating under normal or pressurized pressure.

[0036] After the convection heating is completed, the furnace is again evacuated, and heat treatment is carried out at a predetermined target temperature (for example, 850° C.) in a vacuum atmosphere.

[0037] After the heating process is completed, the shielding plate 23 of the shutter mechanism 22 is opened to open the gas vent ports 17A and 17B, and nitrogen gas is introduced into the furnace as a cooling gas. The cooling gas is then circulated by rotating the circulation fan 31 to perform a gas cooling process. In the gas cooling process, the cooling gas is circulated in a first cooling gas circulation direction in which the cooling gas flows upward within the processing chamber 4, thereby cooling the workpiece W within the processing chamber 4. In some cases, the circulation direction switching plate 37 can be rotated to switch the cooling gas circulation direction to a second cooling gas circulation direction in which the cooling gas flows downward within the processing chamber 4, thereby cooling the workpiece W.

[0038] After the gas cooling process is completed, the openable / closable lid 10 and the side wall 16c of the heat insulating wall 16 are opened, and the workpiece W is removed from the processing chamber 4, completing the series of heat treatment operations in the vacuum heat treatment furnace 1.

[0039] According to the vacuum heat treatment furnace 1 of this embodiment, the opening ratio in the central region 47 of the gas vent openings 17A, 17B is set within a range of 0.17 to 0.85 relative to the opening ratio in the region 48 excluding the central region 47, which suppresses the inflow of cooling gas near the centers of the gas vent openings 17A, 17B where the gas flow tends to concentrate, thereby suppressing variations in the flow rate of the cooling gas within the treatment chamber 4 during gas cooling. As a result, problems such as distortion of the workpiece W caused by variations in the flow rate of the cooling gas can be reduced.

[0040] Furthermore, in the vacuum heat treatment furnace 1 of this embodiment, the individual openings 46 of the straightening plate 45 are slit-shaped, and the slit width of the individual openings 46 in the central region 47 is narrower than the slit width of the individual openings 46 in the other regions 48. This increases the resistance of the cooling gas when it passes through the central region 47, and more effectively reduces the flow rate of the cooling gas passing through the central region 47.

[0041] FIG. 6 shows a modification of this embodiment in which a baffle plate is added to the space between the outer surface of the heat insulating wall and the inner surface of the furnace shell. When the straightening plates 45 are attached to the gas vents 17A and 17B as in the above embodiment, the opening area of ​​the gas vents 17A and 17B through which the cooling gas can pass is substantially reduced. Therefore, there is a concern that an increase in the amount of cooling gas that does not pass through the gas vents 17A and 17B but instead flows around into the space between the outer surface of the insulating wall 16 and the inner surface of the furnace shell 2 is likely. In the example of Fig. 6, in a vertical cross-sectional view perpendicular to the central axis P (see Fig. 1) of the furnace shell 2, a baffle plate 55 is arranged to block the space between the outer surface of the insulating wall 16 and the inner surface of the furnace shell 2 near the gas vent 17A, and a baffle plate 56 is arranged to block the space between the outer surface of the insulating wall 16 and the inner surface of the furnace shell 2 near the gas vent 17B. In this way, the flow of cooling gas that wraps around into the space between the outer surface of the insulating wall 16 and the inner surface of the furnace shell 2 is stopped by the baffles 55 and 56, and as a result, the amount of gas supplied into the processing chamber 4 through the gas vents 17A and 17B can be increased compared to when the baffles 55 and 56 are not present.

[0042] Although the embodiments and modifications of the present invention have been described in detail above, these are merely examples. For example, in the above embodiment, the individual openings formed in the straightening plate are slit-shaped, but the individual openings can also be circular or have other shapes than slits. Furthermore, in the above embodiment, the straightening plate is disposed at the gas vent port, but in some cases it can be attached to the charge, jigs, etc. inside the furnace. For example, the present invention can be configured in various modified forms without departing from the spirit of the invention. [Explanation of symbols]

[0043] 1 Vacuum heat treatment furnace (heat treatment furnace) 2 Furnace shell 4 Processing chamber 6 Heater (heating means) 8 Cooling means 16 Insulated walls 17A, 17B Gas vent 45 Rectifier plate 46 Individual Openings 47 Central area 48 Other Areas 55,56 Baffle plate H1 Individual opening width H2 Individual opening width K1,K2 Aperture ratio W Processing object

Claims

1. a treatment chamber defined by a heat insulating wall within the furnace shell and accommodating the workpiece; a heating means for heating the workpiece accommodated in the processing chamber; a cooling means for circulating a cooling gas into the processing chamber through a pair of gas vents formed in opposing insulating walls of the processing chamber to cool the workpiece; A heat treatment furnace for subjecting the workpiece to a heating treatment and a gas cooling treatment, comprising: a flow straightening plate disposed in the gas vent port portion and forming a plurality of individual openings within the gas vent port portion; a central region of the gas vent portion having a longitudinal dimension of 1 / 2L and a transverse dimension of 1 / 3S, the opening ratio of which is within a range of 0.17 to 0.85 relative to the opening ratios of other regions excluding the central region, where the longitudinal width of the gas vent portion is L and the transverse width of the gas vent portion is S.

2. 2. The heat treatment furnace according to claim 1, wherein the individual openings are hole-, lattice-, or slit-shaped, and the hole diameter, lattice width, or slit width of the individual openings in the central region is smaller than the hole diameter, lattice width, or slit width of the individual openings in the other regions.

3. 3. The heat treatment furnace according to claim 1, wherein, in a vertical cross-sectional view perpendicular to the central axis of the furnace shell, a baffle plate is arranged so as to block a space between the outer surface of the insulating wall near the gas vent portion and the inner surface of the furnace shell.

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