Vacuum carbon impregnation equipment

Abstract

To provide a vacuum carburization apparatus which reduces variation of carburization in upstream and downstream sides without excessively supplying carburization gas.SOLUTION: A vacuum carburization apparatus includes a furnace body 2 accommodating a work-piece 8, a plurality of supply ports 41, 42, 43 which supply gas into the furnace body 2, a carburization gas flow rate controller 13 which controls a supply flow rate of carburization gas G1, a plurality of open-close valves 31, 32, 33 which are disposed between the carburization gas flow rate controller 13 and the supply ports, respectively, and open and close a flow passage of the gas, and an exhaust port 51 which discharges the gas within the furnace body 2. At least one of the plurality of open-close valves is closed to carry out a vacuum carburization treatment.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vacuum carburizing apparatus.

Background Art

[0002] As conventional technologies of vacuum carburizing apparatuses, for example, Patent Document 1 and Patent Document 2 disclose injecting carburizing gas unidirectionally from a plurality of supply ports. Patent Document 3 discloses switching the supply of carburizing gas through a large number of installed supply ports with a time difference. Patent Document 4 discloses providing a supply port targeting locations where carburizing gas is difficult to reach.

[0003] Incidentally, in a vacuum carburizing apparatus, since carburizing gas flows from the upstream side (supply port side) to the downstream side (discharge port side), the carburizing gas is consumed first by workpieces on the upstream side, so the carburizing gas concentration on the downstream side becomes lower than the carburizing gas concentration on the upstream side. For this reason, carburizing gas is often supplied in excess of the appropriate amount calculated from the total surface area of the workpieces, so that an appropriate carburizing gas concentration can be obtained even on the downstream side.

Prior Art Literature

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problem to be Solved by the Invention

[0005] If the amount of carburizing gas supplied exceeds the appropriate amount, running costs increase, and the amount of carbon-based components adhering to the furnace and exhaust system increases, leading to more frequent equipment maintenance. On the other hand, if the amount of carburizing gas supplied is insufficient, carburized workpieces are more likely to occur downstream where the carburizing gas does not reach easily.

[0006] A vacuum carburizing apparatus is desired that reduces carburizing variations in the upstream and downstream sides without supplying excessive carburizing gas.

[0007] Therefore, the object of this invention is to provide a vacuum carburizing apparatus that reduces carburizing variations on the upstream and downstream sides without supplying an excessive amount of carburizing gas. [Means for solving the problem]

[0008] To solve the above problems, a vacuum carburizing apparatus according to one aspect of this invention is provided. A furnace body for housing the workpiece, Multiple supply ports for supplying gas to the inside of the furnace body, A carburizing gas flow controller controls the supply flow rate of carburizing gas, A plurality of on-off valves are disposed between the carburizing gas flow controller and the supply port, respectively, to open and close the gas flow path, The furnace body is equipped with an outlet for discharging gas from inside the furnace body, The vacuum carburizing treatment is performed by closing at least one of the plurality of on-off valves. [Effects of the Invention]

[0009] According to this invention, a high-concentration carburizing gas that enables proper vacuum carburizing treatment is delivered to the downstream side without supplying an excessive amount of carburizing gas, thereby reducing variations in carburizing both upstream and downstream. [Brief explanation of the drawing]

[0010] [Figure 1]This figure schematically illustrates the vacuum carburizing apparatus and vacuum carburizing process according to Embodiment 1. [Figure 2] Figure 1 illustrates another vacuum carburizing process using the vacuum carburizing apparatus shown in Figure 1. [Figure 3] This diagram illustrates the purging process that follows vacuum carburizing. [Figure 4] This figure schematically illustrates a vacuum carburizing apparatus according to Embodiment 2. [Figure 5] This figure illustrates the purging process using the vacuum carburizing apparatus shown in Figure 4. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the vacuum carburizing apparatus 1 according to the present invention will be described with reference to the drawings. In the following description, terms indicating specific directions or positions (for example, terms including "up," "down," "right," "left," "front," and "rear") will be used as needed. The use of these terms is for the purpose of facilitating the understanding of this disclosure with reference to the drawings, and the meaning of these terms does not limit the technical scope of this disclosure. Furthermore, the terms "upstream side" and "downstream side" are used, with reference to the direction of gas flow, with the side of the gas supply port being called the "upstream side" and the side of the gas discharge port being called the "downstream side." In addition, the following description is essentially illustrative and is not intended to limit this disclosure, its applications, or its uses. Furthermore, the drawings are schematic, and the ratios of each dimension do not necessarily correspond to reality. In the drawings, black-filled valves indicate the closed state, and white-filled valves indicate the open state. In the drawings, the flow of carburizing gas is shown by dashed lines, and the flow of purge gas is shown by solid lines.

[0012] [Embodiment 1] The vacuum carburizing apparatus 1 according to Embodiment 1 will be described with reference to Figure 1. Figure 1 is a schematic diagram illustrating the vacuum carburizing apparatus 1 and the vacuum carburizing process according to Embodiment 1.

[0013] As shown in Fig. 1, the vacuum carburizing apparatus 1 is an apparatus that accommodates a workpiece 8, which is a material to be treated, inside a furnace body 2, heats the workpiece at a predetermined temperature, and performs vacuum carburizing treatment by carburizing gas G1 flowing inside the furnace body 2 under reduced pressure.

[0014] The gases used in the present invention are carburizing gas G1 and purge gas G2. The carburizing gas G1 is a hydrocarbon gas that reacts on the surface of the workpiece 8 to generate carbon, and is, for example, acetylene gas. Further, the purge gas G2 is used for driving out low-concentration carburizing gas G1, whose concentration has been reduced after being used for the vacuum carburizing treatment when performing carbon diffusion treatment after the vacuum carburizing treatment, out of the furnace body 2 for replacement, and is an inert gas such as nitrogen.

[0015] In the vacuum carburizing apparatus 1, during the vacuum carburizing treatment, the carburizing gas G1 is supplied into the furnace body 2 through a carburizing gas supply source 11, and is discharged to the outside of the furnace body 2 by a vacuum pump 4. In the case of vacuum carburizing treatment, a substantially constant reduced pressure state of, for example, about 1 kPa is maintained inside the furnace.

[0016] The vacuum carburizing apparatus 1 comprises at least a furnace body 2, a plurality of supply ports 41, 42, 43, a carburizing gas flow rate controller 13, a purge gas flow rate controller 23, a plurality of opening / closing valves 31, 32, 33, and a discharge port 51.

[0017] The furnace body 2 accommodates the workpiece 8 and has, for example, a substantially rectangular parallelepiped shape. A plurality of supply ports 41, 42, 43 are disposed in the furnace body 2, for example, a first supply port 41, a second supply port 42, and a third supply port 43 are disposed. Gases such as the carburizing gas G1 and the purge gas G2 are supplied into the furnace body 2 through the first supply port 41, the second supply port 42, and the third supply port 43. As the discharge port 51, for example, a first discharge port 51 is disposed in the furnace body 2. The gas that has flowed inside the furnace body 2 is constantly discharged through the first discharge port 51.

[0018] The furnace body 2, although not shown in the figures, includes a heating section such as a heater, a thermometer for measuring the internal temperature of the furnace, a pressure gauge for measuring the internal pressure of the furnace, and a jig for arranging multiple workpieces 8. A gas supply unit 7 is located upstream of the furnace body 2, and a gas discharge unit 9 is located downstream of the furnace body 2. The gas supply unit 7 includes a carburizing gas supply unit 10 and a purge gas supply unit 20.

[0019] The carburizing gas supply unit 10 comprises a carburizing gas supply source 11, a carburizing gas on / off valve 12, and a carburizing gas flow controller 13, extending from the upstream to the downstream side. The carburizing gas supply source 11 consists of a gas cylinder or the like containing a carburizing gas G1 such as acetylene gas. The carburizing gas on / off valve 12 is a valve that opens and closes the carburizing gas flow path through which the carburizing gas G1 flows, and is, for example, a solenoid valve whose opening and closing is controlled by a control unit (not shown). The carburizing gas flow controller 13 is a flow control valve that controls the supply flow rate of the carburizing gas G1, and is, for example, a mass flow controller that controls the supply flow rate by measuring the mass flow rate of the carburizing gas G1. The carburizing gas flow path from the carburizing gas supply source 11 to the carburizing gas flow controller 13 is connected by piping.

[0020] The purge gas supply unit 20 includes a purge gas supply source 21, a purge gas on / off valve 22, and a purge gas flow controller 23, extending from the upstream to the downstream side. The purge gas supply source 21 consists of a gas cylinder or the like containing purge gas G2 such as nitrogen gas. The purge gas on / off valve 22 is a valve that opens and closes the purge gas flow path through which the purge gas G2 flows, and is a solenoid valve whose opening and closing is controlled by a control unit (not shown). The purge gas flow controller 23 is a flow control valve that adjusts the flow rate of the purge gas G2, and is a mass flow controller that measures the mass flow rate of the purge gas G2 to control the flow rate. The purge gas flow path from the purge gas supply source 21 to the purge gas flow controller 23 is connected by piping.

[0021] A confluence channel 14 is formed by a carburizing gas flow path located downstream of the carburizing gas flow controller 13 and a purge gas flow path located downstream of the purge gas flow controller 23. The confluence channel 14 is connected to a branch channel 15 at the confluence point. The branch channel 15 is formed by multiple flow paths leading from the confluence point to multiple supply ports 41, 42, and 43. These confluence channel 14 and branch channel 15 are constructed using piping.

[0022] Multiple on-off valves 31, 32, and 33 are provided, for example, a first on-off valve 31, a second on-off valve 32, and a third on-off valve 33. Each on-off valve 31, 32, and 33 is a valve that opens and closes the gas flow path, and is, for example, a solenoid valve whose opening and closing is controlled by a control unit (not shown). The first on-off valve 31 is provided in the branch flow path from the carburized gas flow controller 13 to the first supply port 41, the second on-off valve 32 is provided in the branch flow path from the carburized gas flow controller 13 to the second supply port 42, and the third on-off port 33 is provided in the branch flow path from the carburized gas flow controller 13 to the third supply port 43.

[0023] Multiple supply ports 41, 42, and 43 are provided on the upstream wall surface of the furnace body 2 (the left wall surface in Figure 1). For example, a first supply port 41, a second supply port 42, and a third supply port 43 are provided as multiple supply ports 41, 42, and 43. Each supply port 41, 42, and 43 is composed of a nozzle fitted into a through-hole formed in the wall surface, and gas is supplied into the interior of the furnace body 2 through each supply port 41, 42, and 43. Each supply port 41, 42, and 43 is spaced apart in the intersecting direction (up and down direction in Figure 1) that intersects the gas flow direction (left to right direction in Figure 1).

[0024] A first outlet 51 is provided on the downstream wall of the furnace body 2 (the right-hand wall in Figure 1) as an outlet. The first outlet 51 is composed of a nozzle fitted into a through-hole formed in the wall, and gas from inside the furnace body 2 is discharged through the first outlet 51. The first outlet 51 is positioned approximately in the center in the direction of intersection (vertical direction in Figure 1) that intersects the direction of gas flow.

[0025] In the discharge channel located downstream of the first discharge port 51, an exhaust valve 6 and a vacuum pump 4 are arranged as a gas discharge section 9, extending from the upstream side to the downstream side. The exhaust valve 6 is a valve that opens and closes the exhaust channel, and is a solenoid valve that is controlled to open and close by a control unit (not shown). The vacuum pump 4 evacuates the inside of the furnace body 2. The discharge port 51 and the exhaust valve 6, and the exhaust valve 6 and the vacuum pump 4 are connected by piping. When vacuum carburizing and purging are performed, the inside of the furnace is maintained in a reduced pressure state by these processes. Also, when maintaining the inside of the furnace in a substantially constant reduced pressure state, for example, the exhaust valve 6 is opened, and its opening degree is controlled by a control unit (not shown).

[0026] In the vacuum carburizing apparatus 1 described above, when all of the on-off valves 31, 32, and 33 are opened and the carburizing gas G1 is supplied in a dispersed manner from all of the supply ports 41, 42, and 43, the flow rate of the carburizing gas G1 slows down, making it difficult for the carburizing gas G1 to reach the downstream workpiece 8. As a result, the contact time with the carburizing gas G1 at the downstream workpiece 8 is shortened, and the concentration of the carburizing gas G1 at the downstream workpiece 8 decreases as the carburizing gas G1 is consumed, making it easier for non-uniformity to occur between the carburizing process at the upstream and downstream ends.

[0027] Therefore, as Embodiment 1 to solve this problem, a vacuum carburizing process using the vacuum carburizing apparatus 1 described above will be explained with reference to Figures 1 and 2.

[0028] Figure 1 shows that, under constant supply flow rates of carburizing gas G1 by the carburizing gas flow rate controller 13, the carburizing gas shut-off valve 12 is opened and the purge gas shut-off valve 22 is closed in the gas supply unit 7, and one of the multiple shut-off valves 31, 32, and 33 is opened while the remaining shut-off valves are closed. For example, the first shut-off valve 31 is opened while the second shut-off valve 32 and the third shut-off valve 33 are closed. The carburizing gas flow rate controller 13 supplies an appropriate amount of carburizing gas G1 as the supply flow rate, calculated from the total surface area of ​​the workpieces 8 placed inside the furnace body 2.

[0029] The carburizing gas flow rate controller 13 keeps the supply flow rate of carburizing gas G1 constant, and the second on-off valve 32 and the third on-off valve 33 are closed. All on-off valves 31, 32, and 33 are connected to each of the three branched flow paths 15. Therefore, carburizing gas G1 is ejected through the first supply port 41 connected to the open first on-off valve 31, but the carburizing gas G1 is ejected more forcefully than when all on-off valves 31, 32, and 33 are open and the gas is ejected in a dispersed manner. As the flow velocity of the carburizing gas G1 ejected from the first supply port 41 increases, a high concentration of carburizing gas G1 reaches the workpiece 8 located downstream of the first supply port 41 (in other words, located on the side of the first discharge port). At this time, even if the flow velocity of the carburizing gas G1 increases, the supply of an appropriate amount of carburizing gas G1 calculated from the total surface area of ​​the workpiece 8 is maintained. As the carburizing gas G1 forcefully ejected from the first supply port 41 diffuses within the furnace, an appropriate amount of carburizing gas G1 is supplied to the workpiece 8 located away from the first supply port 41. This condition is continued for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41. As a result, a high concentration of carburizing gas G1 that enables appropriate vacuum carburizing treatment is delivered to the downstream side without supplying an excessive amount of carburizing gas G1, thereby reducing carburizing variations in the upstream and downstream sides.

[0030] The carburizing gas G1 ejected vigorously from the first supply port 41 diffuses within the furnace, but if it is ejected from only one location, the concentration distribution of the carburizing gas G1 will be uneven in the direction intersecting the flow direction of the carburizing gas G1. Therefore, at predetermined valve switching intervals, for example, the second on-off valve 32 is opened while the first on-off valve 31 and the third on-off valve 33 are closed. The carburizing gas G1 is then vigorously ejected through the second supply port 42, which is connected to the open second on-off valve 32. As the flow velocity of the carburizing gas G1 ejected from the second supply port 42 increases, high-concentration carburizing gas G1 reaches the workpiece 8 located downstream of the second supply port 42. This condition is maintained for a predetermined time, and vacuum carburizing treatment is performed through the second supply port 42.

[0031] Then, at predetermined valve switching intervals, for example, the third on-off valve 33 is opened while the first on-off valve 31 and the second on-off valve 32 are closed. Carburizing gas G1 is forcefully ejected through the third supply port 43 connected to the open third on-off valve 33. As the flow velocity of the carburizing gas G1 ejected from the third supply port 43 increases, a high concentration of carburizing gas G1 reaches the workpiece 8 located downstream away from the third supply port 43. This state is continued for a predetermined time to perform vacuum carburizing through the third supply port 43.

[0032] Then, at predetermined valve switching intervals, for example, the first on-off valve 31 is opened again, while the second on-off valve 32 and the third on-off valve 33 are closed. Carburizing gas G1 is forcefully ejected through the first supply port 41 connected to the open first on-off valve 31. As the flow velocity of the carburizing gas G1 ejected from the first supply port 41 increases, a high concentration of carburizing gas G1 reaches the workpiece 8 located downstream away from the first supply port 41. This state is continued for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41.

[0033] In this way, the closed state of any two of the multiple on-off valves 31, 32, and 33 is sequentially switched. In other words, the open state of any one of the multiple on-off valves 31, 32, and 33 is sequentially switched. As a result, vacuum carburizing treatment through the first supply port 41, vacuum carburizing treatment through the second supply port 42, and vacuum carburizing treatment through the third supply port 43 are sequentially switched at a predetermined valve switching interval. This switching operation is repeated multiple times. The predetermined valve switching interval is determined according to the furnace pressure and the supply flow rate of the carburizing gas G1. However, if the valve switching interval is too long, uneven carburizing is likely to occur due to the uneven distribution of the concentration of the carburizing gas G1, as described above. Also, if the valve switching interval is too short, uneven carburizing is likely to occur because the high-concentration carburizing gas G1 does not easily reach the workpiece 8 located downstream. Therefore, a suitable valve switching interval is, for example, 1 second to 15 seconds. This suppresses the uneven distribution of the carburizing gas G1 concentration inside the furnace body 2, thereby reducing uneven carburizing.

[0034] Figure 2 illustrates another vacuum carburizing process using the vacuum carburizing apparatus 1 shown in Figure 1. Figure 2 shows that, under constant supply flow rates of carburizing gas G1 by the carburizing gas flow rate controller 13, the carburizing gas shut-off valve 12 is opened and the purge gas shut-off valve 22 is closed in the gas supply unit 7, and any two of the multiple shut-off valves 31, 32, and 33 are opened while the remaining shut-off valves are closed. For example, the second shut-off valve 32 and the third shut-off valve 33 are opened while the first shut-off valve 31 is closed. The carburizing gas flow rate controller 13 supplies an appropriate amount of carburizing gas G1 as the supply flow rate, calculated from the total surface area of ​​the workpiece 8 placed inside the furnace body 2.

[0035] The supply flow rate of carburizing gas G1 by the carburizing gas flow rate controller 13 is constant, and the first on-off valve 31 is closed. Therefore, carburizing gas G1 is ejected through the second supply port 42 and the third supply port 43 connected to the open second on-off valve 32 and the third on-off valve 33, respectively, but the carburizing gas G1 is ejected more forcefully than when all on-off valves 31, 32, and 33 are open. As the flow velocity of the carburizing gas G1 ejected from the second supply port 42 and the third supply port 43 increases, high-concentration carburizing gas G1 reaches the workpiece 8 located downstream, away from the second supply port 42 and the third supply port 43. This condition is maintained for a predetermined time, and vacuum carburizing treatment is performed through the second supply port 42 and the third supply port 43. This allows a high concentration of carburizing gas G1 to be delivered to the downstream side without supplying an excessive amount of carburizing gas G1, enabling proper vacuum carburizing treatment and reducing variations in carburizing both upstream and downstream.

[0036] The carburizing gas G1 ejected vigorously from the first supply port 41 diffuses within the furnace, but if it is ejected from only one location, the concentration distribution of the carburizing gas G1 will be uneven in the direction intersecting the flow direction of the carburizing gas G1. Therefore, at a predetermined valve switching interval, for example, the first on-off valve 31 and the third on-off valve 33 are opened, and the second on-off valve 32 is closed. The carburizing gas G1 is then vigorously ejected through the first supply port 41 and the third supply port 43, which are connected to the open first on-off valve 31 and the third on-off valve 33, respectively. As the flow velocity of the carburizing gas G1 ejected from the first supply port 41 and the third supply port 43 increases, high-concentration carburizing gas G1 reaches the workpiece 8 located downstream, away from the first supply port 41 and the third supply port 43. This condition is maintained for a predetermined time, and vacuum carburizing treatment is performed through the first supply port 41 and the third supply port 43.

[0037] Then, at predetermined valve switching intervals, for example, the first on-off valve 31 and the second on-off valve 32 are opened and the third on-off valve 33 is closed. Carburizing gas G1 is forcefully ejected through the first supply port 41 and the second supply port 42, which are connected to the first on-off valve 31 and the second on-off valve 32, respectively, which are open. As the flow velocity of the carburizing gas G1 ejected from the first supply port 41 and the second supply port 42 increases, a high concentration of carburizing gas G1 reaches the workpiece 8 located downstream, away from the first supply port 41 and the second supply port 42. This state is continued for a predetermined time to perform vacuum carburizing through the first supply port 41 and the second supply port 42.

[0038] Then, at predetermined valve switching intervals, for example, the second on-off valve 32 and the third on-off valve 33 are opened again, and the first on-off valve 31 is closed. Carburizing gas G1 is forcefully ejected through the second supply port 42 and the third supply port 43, which are connected to the open second on-off valve 32 and the third on-off valve 33, respectively. As the flow velocity of the carburizing gas G1 ejected from the second supply port 42 and the third supply port 43 increases, a high concentration of carburizing gas G1 reaches the workpiece 8 located downstream, away from the second supply port 42 and the third supply port 43, respectively. This state is continued for a predetermined time, and vacuum carburizing is performed through the second supply port 42 and the third supply port 43.

[0039] As described above, the closed state of any one of the multiple on-off valves 31, 32, and 33 is sequentially switched. In other words, the open state of any two of the multiple on-off valves 31, 32, and 33 is sequentially switched. As a result, vacuum carburizing treatment through the first supply port 41 and the second supply port 42, vacuum carburizing treatment through the second supply port 42 and the third supply port 43, and vacuum carburizing treatment through the first supply port 41 and the third supply port 43 are sequentially switched at a predetermined valve switching interval. This switching operation is repeated multiple times. Similar to the embodiment described with reference to Figure 1, the predetermined valve switching interval is determined according to the furnace pressure and the supply flow rate of the carburizing gas G1, and a suitable valve switching interval is, for example, 1 second to 15 seconds. Compared to the embodiment described with reference to Figure 1, the flow velocity of the carburizing gas G1 is slower, but the flow velocity of the carburizing gas G1 is faster than when all on-off valves 31, 32, and 33 are open.

[0040] Next, with reference to Figure 3, we will explain the purging process that follows the vacuum carburizing process described above using Figures 1 and 2. Figure 3 is a diagram illustrating the purging process that follows the vacuum carburizing process.

[0041] Figure 3 shows that under reduced pressure with a nearly constant furnace pressure, the carburizing gas shut-off valve 12 is closed and the purge gas shut-off valve 22 is opened in the gas supply section 7, and all shut-off valves 31, 32, and 33 are opened to perform purging. In other words, Figure 3 shows how, during purging, the carburizing gas G1 that was previously present in the furnace is gradually pushed out toward the discharge port 51 by the purge gas G2 flowing from the upstream side to the downstream side of the furnace.

[0042] In the vacuum carburizing apparatus 1 described above, a vacuum carburizing treatment is performed under reduced pressure to penetrate carbon into the surface layer of the workpiece 8. Subsequently, a diffusion treatment is performed to thermally diffuse the carbon from the surface layer into the interior of the workpiece 8. The vacuum carburizing treatment and diffusion treatment are repeated until a predetermined carburizing depth and surface carbon concentration are reached. In the diffusion treatment, carbon is thermally diffused by heating to a predetermined temperature under reduced pressure, for example, by interrupting the flow of carburizing gas G1 and switching to the flow of inert purging gas G2. That is, the diffusion treatment includes a purging treatment to expel the carburizing gas G1 used during the vacuum carburizing treatment.

[0043] When replacing carburizing gas G1 with purging gas G2, in other words, when switching from vacuum carburizing to diffusion processing, if the supply flow rate of purging gas G2 is about the same as that of carburizing gas G1, the purging gas G2 will quickly reach the first exhaust port 51, shortening the time that carburizing gas G1 remains on the side of the first outlet 51 (downstream side), and also increasing the dilution of carburizing gas G1 downstream. Therefore, even when replacing carburizing gas G1 with purging gas G2, carburizing defects are more likely to occur in the downstream workpiece 8.

[0044] Therefore, when replacing the carburizing gas G1 with the purging gas G2, the purging gas flow controller 23 is controlled so that the supply flow rate of the purging gas G2 is less than the supply flow rate of the carburizing gas G1. In other words, the purging process performed after the vacuum carburizing process has a low-flow purging period in which the supply flow rate of the purging gas G2 is reduced. As the purging gas G2 slowly reaches the first exhaust port 51, the time that the carburizing gas G1 remains on the side of the first outlet 51 (downstream side) is increased, and the dilution of the carburizing gas G1 on the downstream side is delayed. As a result, the contact time between the workpiece 8 and the carburizing gas G1 on the downstream side is increased, and the decrease in the concentration of the carburizing gas G1 on the downstream side is suppressed, thereby suppressing the occurrence of carburizing defects in the workpiece 8 on the downstream side.

[0045] The low-flow purging period, which involves reducing the supply flow rate of purge gas G2, is defined, for example, as the time required for the concentration of carburizing gas G1 inside the furnace body 2 to fall to 5% or less, starting from the start of supplying purge gas G2. This is because the effect of the carbon surface reaction decreases significantly when the concentration of carburizing gas G1 falls below 5%. In this way, the purging process can be quantitatively controlled by defining the low-flow purging period.

[0046] [Embodiment 2] The vacuum carburizing apparatus 1 according to Embodiment 2 will be described with reference to Figure 4. Figure 4 is a schematic diagram illustrating the vacuum carburizing apparatus 1 according to Embodiment 2.

[0047] The vacuum carburizing apparatus 1 according to Embodiment 2 is characterized in that multiple supply ports 41, 42, 44, and 45 are arranged on one side and the other side of the furnace body 2, and discharge ports 51 and 52 are arranged on the intersecting side and the other side of the furnace body 2 where the two sides intersect. The differences from the vacuum carburizing apparatus 1 according to Embodiment 1 described above will be explained in detail.

[0048] One side gas supply unit 7 is located upstream of one side of the furnace body 2 (left side in Figure 4), and this unit includes a carburizing gas supply unit 10 and a purge gas supply unit 20. Another side gas supply unit 7 is located upstream of the other side of the furnace body 2 (right side in Figure 4), and this unit includes a carburizing gas supply unit 10 and a purge gas supply unit 20.

[0049] As shown in Figure 4, if the furnace body 2 has, for example, a roughly rectangular parallelepiped shape, the first supply port 41 and the second supply port 42 connected to the gas supply unit 7 on one side are arranged on the wall surface of one side of the furnace body 2, and the fourth supply port 44 and the fifth supply port 45 connected to the gas supply unit 7 on the other side are arranged on the wall surface of the furnace body 2 on the other side. For example, the first supply port 41 and the fourth supply port 44 face each other, and the second supply port 42 and the fifth supply port 45 face each other.

[0050] A first outlet 51 is located on one intersecting side of the furnace body 2 (upper side in Figure 4), and a second outlet 52 is located on the other intersecting side of the furnace body 2 (lower side in Figure 4). For example, the first outlet 51 and the second outlet 52 face each other. A first discharge channel located downstream of the first outlet 51 and a second discharge channel located downstream of the second outlet 52 are connected at a discharge confluence point. In the discharge channel, an exhaust on / off valve 6 and a vacuum pump 4 are arranged as a gas discharge section 9, running from the upstream side to the downstream side.

[0051] In the vacuum carburizing apparatus 1 described above, the carburizing gas G1 does not reach the workpieces 8 located in the intermediate region of the furnace body 2 as effectively as it does the workpieces 8 located near the first and second supply ports 41 and 42, and the fourth and fifth supply ports 44 and 55. As a result, the contact time with the carburizing gas G1 is shortened for workpieces 8 located in the intermediate region of the furnace body 2. Furthermore, the carburizing gas G1 is consumed by the workpieces 8 located near the first and second supply ports 41 and 42, and the fourth and fifth supply ports 44 and 55, which lowers the concentration of the carburizing gas G1 in the intermediate region of the furnace body 2. Consequently, non-uniformity is more likely to occur between carburizing in the areas near the supply ports 41, 42, 44, and 45 and carburizing in the intermediate region of the furnace body 2.

[0052] Therefore, as a second embodiment to solve this problem, a vacuum carburizing process using the vacuum carburizing apparatus 1 described above will be explained with reference to Figure 4.

[0053] Figure 4 shows that, under the assumption that the supply flow rate of carburizing gas G1 by the carburizing gas flow rate controllers 13,13 on one side and the other side is approximately constant, the carburizing gas on-off valves 12,12 on one side and the other side are opened and the purge gas on-off valves 22,22 on one side and the other side are closed at the gas supply units 7,7 on one side and the other side. It also shows that one of the on-off valves 31,34:32,35 on the opposing sides is opened and the on-off valve on the other side is closed. For example, the first on-off valve 31 on one side and the fourth on-off valve 34 on the other side are opened, while the second on-off valve 32 on one side and the fifth on-off valve 35 on the other side are closed. The carburizing gas flow rate controllers 13,13 on one side and the other side supply an appropriate amount of carburizing gas G1 as the supply flow rate, calculated from the total surface area of ​​the workpieces 8 placed in the furnace body 2.

[0054] The supply flow rate of carburizing gas G1 by the carburizing gas flow controllers 13, 13 on one side and the other side is kept approximately constant, and the second on-off valve 32 on one side and the fifth on-off valve 35 on the other side are closed. Therefore, carburizing gas G1 is forcefully ejected through the first supply port 41 on one side, which is connected to the open first on-off valve 31, and carburizing gas G1 is forcefully ejected through the fourth supply port 44 on the other side, which is connected to the open fourth on-off valve 34.

[0055] The carburizing gas G1 ejected from the first supply port 41 on one side and the carburizing gas G1 ejected from the fourth supply port 44 on the other side collide in an intermediate region located roughly midway between the one and other sides of the furnace body 2. As a result, a high concentration of carburizing gas G1 reaches the workpiece 8 located near the first supply port 41 on one side, the workpiece 8 located near the fourth supply port 44 on the other side, and the workpiece 8 located in the intermediate region of the furnace body 2. This condition is maintained for a predetermined time, and vacuum carburizing is performed through the first supply port 41 and the fourth supply port 44. This ensures that a high concentration of carburizing gas G1 is delivered to the intermediate region of the furnace body 2, enabling appropriate vacuum carburizing without supplying excessive amounts of carburizing gas G1, thereby reducing carburizing variations regardless of the workpiece's position within the furnace body 2.

[0056] Then, at predetermined valve switching intervals, for example, the second on-off valve 32 on one side and the fifth on-off valve 35 on the other side are opened, while the first on-off valve 31 on one side and the fourth on-off valve 34 on the other side are closed. Carburizing gas G1 is forcefully ejected through the second supply port 42 on one side, which is connected to the open second on-off valve 32, and carburizing gas G1 is forcefully ejected through the fifth supply port 45 on the other side, which is connected to the open fifth on-off valve 35. The carburizing gas G1 ejected from the second supply port 42 on one side and the carburizing gas G1 ejected from the fifth supply port 45 on the other side collide in the intermediate region of the furnace body 2. As a result, high-concentration carburizing gas G1 reaches the workpiece 8 located in the intermediate region of the furnace body 2. This state is continued for a predetermined time, and vacuum carburizing is performed through the second supply port 42 and the fifth supply port 45.

[0057] Then, at predetermined valve switching intervals, for example, the first on-off valve 31 and the fourth on-off valve 34 are opened again, while the second on-off valve 32 and the fifth on-off valve 35 are closed. Similarly to the above, the carburizing gas G1 ejected from one side of the first supply port 41 and the carburizing gas G1 ejected from the other side of the fourth supply port 44 collide in the intermediate region of the furnace body 2, and high-concentration carburizing gas G1 reaches each workpiece 8 located in the intermediate region of the furnace body 2. This state is continued for a predetermined time, and vacuum carburizing is performed through the first supply port 41 and the fourth supply port 44.

[0058] As described above, the on-off valve on one side and the on-off valve on the other side are sequentially switched to open and close. Therefore, the vacuum carburizing process through the first supply port 41 and the fourth supply port 44 and the vacuum carburizing process through the second supply port 42 and the fifth supply port 45 are sequentially switched at a predetermined valve switching interval, for example, at intervals of 1 to 15 seconds. This switching operation is repeated multiple times.

[0059] Next, with reference to Figure 5, we will explain the purging process that is performed after the vacuum carburizing process described above using the vacuum carburizing apparatus 1 shown in Figure 4. Figure 5 is a diagram illustrating the purging process using the vacuum carburizing apparatus 1 shown in Figure 4.

[0060] Figure 5 shows that under reduced pressure with a nearly constant furnace pressure, the purging process is performed by closing the carburizing gas shut-off valve 12 and opening the purge gas shut-off valve 22 in the gas supply section 7, and opening all shut-off valves 31, 32, 34, and 35.

[0061] Similar to the description of the purging process in Embodiment 1, when replacing carburizing gas G1 with purge gas G2, the purge gas flow controllers 23, 23 on one side and the other side are controlled so that the supply flow rate of purge gas G2 is less than the supply flow rate of carburizing gas G1. As the purge gases G2, G2 on one side and the other side slowly reach the intermediate region, the time that the high-concentration carburizing gas G1 remains in the intermediate region of the furnace body 2 is extended, and the dilution of carburizing gas G1 in the intermediate region of the furnace body 2 is delayed. As a result, the contact time between the workpiece 8 and the carburizing gas G1 in the intermediate region of the furnace body 2 is extended, and the decrease in the concentration of carburizing gas G1 can be suppressed, thereby suppressing the occurrence of carburizing defects in the workpiece 8 located in the intermediate region of the furnace body 2. The low-flow purging period, in which the supply flow rate of purge gas G2 is reduced, is defined, for example, as the time required for the concentration of carburizing gas G1 inside the furnace body 2 to become 5% or less, starting from the start of supply of purge gas G2. This is because when the concentration of carburizing gas G1 is reduced to 5% or less by the purge gas G2, the effect of the carbon surface reaction is significantly reduced. In this way, the purging process can be quantitatively controlled by specifying the low-flow purge period.

[0062] Although specific embodiments of this invention have been described, this invention is not limited to the above embodiments and can be implemented with various modifications within the scope of this invention.

[0063] In the vacuum carburizing apparatus 1 of the above embodiment, multiple on-off valves 31, 32, 33 are arranged on the side of multiple supply ports 41, 42, 43, and at least one of these on-off valves is closed to increase the flow velocity of the carburizing gas G1 ejected from the open supply ports. Alternatively, one supply port may be provided, along with multiple discharge ports and multiple on-off valves corresponding to the multiple discharge ports, and at least one of these on-off valves may be closed to increase the flow velocity of the carburizing gas G1 discharged from the open discharge ports (in other words, sucked up by the vacuum pump 4), thereby increasing the flow velocity of the carburizing gas G1 ejected from the supply ports.

[0064] In the above embodiment, the furnace body 2 is shown to have a substantially rectangular parallelepiped shape, but for example, the furnace body 2 can also have a substantially cylindrical shape, with a plurality of supply ports 41, 42, and 43 arranged on one side of the cylindrical shape and an outlet port 51 arranged on the other side.

[0065] In the above embodiment, the valve switching interval for each on-off valve may be the same predetermined time, or it may be different depending on the ease with which the carburized gas G1 flows inside the furnace body 2.

[0066] In the above embodiment, the carburizing gas flow controller 13 and the purge gas flow controller 23 may be used in combination.

[0067] In the above embodiment, the first discharge port 51 may be installed at multiple locations on the furnace body 2.

[0068] In the above embodiment, pressure control using the exhaust valve 6 is shown as an example to maintain a substantially constant reduced pressure state inside the furnace. However, pressure control may also be performed by providing a separate pressure control valve or by controlling the exhaust capacity of the vacuum pump 4. Furthermore, if the reduced pressure state is maintained, it is not necessary to control the inside of the furnace to a substantially constant level.

[0069] The first discharge port 51 and the second discharge port 52 may be arranged on either side of the furnace body 2, that is, on one side of the intersection (upper side in Figure 4) or the other side of the intersection (lower side in Figure 4).

[0070] The supply flow rate of the carburizing gas G1 is determined by calculating an appropriate amount based on the total surface area of ​​the workpieces 8 placed inside the furnace body 2. This appropriate amount is intended to be the amount that enables uniform carburizing of the workpieces 8, and in reality, it is a constant multiple of the amount calculated from the total surface area of ​​the workpieces 8.

[0071] This invention and its embodiments can be summarized as follows:

[0072] A vacuum carburizing apparatus 1 according to a first aspect of this invention is A furnace body 2 that houses workpiece 8, Multiple supply ports 41, 42, 43:41, 42, 44, 45 for supplying gas to the inside of the furnace body 2, A carburizing gas flow controller 13 controls the supply flow rate of carburizing gas G1, A plurality of on-off valves 31, 32, 33:31, 32, 34, 35 are respectively disposed between the carburizing gas flow controller 13 and the supply port to open and close the gas flow path, The furnace body 2 is equipped with outlets 51:51,52 for discharging gas from inside the furnace body, The vacuum carburizing treatment is performed by closing at least one of the aforementioned plurality of on-off valves 31, 32, 33:31, 32, 34, 35.

[0073] According to the above embodiment, since the carburizing gas G1 is vigorously supplied from any of the supply ports 41, 42, 43:41, 42, 44, 45, a high concentration of carburizing gas G1 that enables appropriate vacuum carburizing treatment is delivered to the downstream side without supplying an excessive amount of carburizing gas G1, thereby reducing carburizing variations in the upstream and downstream sides.

[0074] Furthermore, the vacuum carburizing apparatus 1 according to the second embodiment is, The vacuum carburizing treatment is performed under the condition that the supply flow rate of the carburizing gas G1 by the carburizing gas flow rate controller 13 is constant.

[0075] According to the above embodiment, a more precise vacuum carburizing process becomes possible.

[0076] Furthermore, the vacuum carburizing apparatus 1 according to the third embodiment is, The closing of any of the above-mentioned on-off valves 31, 32, 33:31, 32, 34, 35 is sequentially switched.

[0077] According to the above embodiment, since the carburizing gas G1 is supplied sequentially from one of the supply ports 41, 42, 43:41, 42, 44, 45, carburizing variations in the intersecting direction that crosses the flow direction of the carburizing gas G1 can be reduced.

[0078] Furthermore, the vacuum carburizing apparatus 1 according to the fourth embodiment is, according to the third embodiment described above, The valve switching interval for switching the opening and closing of the aforementioned on-off valves 31, 32, 33:31, 32, 34, 35 is between 1 second and 15 seconds.

[0079] According to the above embodiment, the bias in the concentration distribution of the carburizing gas G1 inside the furnace body 2 can be suppressed, and uneven carburizing can be suppressed.

[0080] Furthermore, the vacuum carburizing apparatus 1 according to the fifth embodiment is, in any one of the first to fourth embodiments described above, The system further includes a purge gas flow rate controller 23 that controls the supply flow rate of purge gas for purging the carburizing gas G1 used during the vacuum carburizing process, The purging process includes a low-flow purging period in which the supply flow rate of the purge gas G2 is reduced.

[0081] According to the above embodiment, the purge gas G2 slowly reaches the exhaust ports 51:51,52, and the high-concentration carburizing gas G1 remains on the side of the exhaust ports 51:51,52 for a longer period of time, thereby suppressing the occurrence of carburizing defects in the downstream workpiece 8. Therefore, without supplying an excessive amount of carburizing gas G1, a high-concentration carburizing gas G1 that enables appropriate vacuum carburizing treatment is delivered to the downstream side, thereby reducing carburizing variations in the upstream and downstream sides.

[0082] Furthermore, the vacuum carburizing apparatus 1 according to the sixth embodiment is, The low-flow purging period is defined as the time required for the concentration of the carburizing gas G1 inside the furnace body 2 to fall to 5% or less, starting from the commencement of supply of the purge gas G2.

[0083] According to the above embodiment, when the concentration of carburizing gas G1 is reduced to 5% or less by the purge gas G2, the effect of the carbon surface reaction is significantly reduced, so the purging treatment can be quantitatively controlled by specifying a low-flow purging period. [Explanation of Symbols]

[0084] 1...Vacuum carburizing equipment 2…Furnace body 4… Vacuum pump 6… Exhaust valve 7…Gas supply department 8...Work 9...Gas discharge section 10...Carburizing gas supply unit 11…Carburized gas supply source 12...Carburized gas shut-off valve 13...Carburized gas flow controller 14… Confluence channel 15… Branch channel 20... Purge gas supply unit 21…Purge gas supply source 22... Purge gas shut-off valve 23... Purge gas flow controller 31...First shut-off valve (shut-off valve) 32... Second shut-off valve (shut-off valve) 33... Third shut-off valve (shut-off valve) 34…Fourth shut-off valve (shut-off valve) 35…5th shut-off valve (shut-off valve) 41…First supply port (supply port) 42...Second supply port (supply port) 43... Third supply port (supply port) 44…Fourth supply port (supply port) 45... Fifth supply port (supply port) 51...1st discharge port (discharge port) 52…Second discharge port (discharge port) G1...Carburizing gas G2... Purge gas

Claims

1. A furnace body for housing the workpiece, Multiple supply ports for supplying gas to the inside of the furnace body, A carburizing gas flow controller controls the supply flow rate of carburizing gas, A plurality of on-off valves are disposed between the carburizing gas flow controller and the supply port, respectively, to open and close the gas flow path, An outlet for discharging gas from inside the furnace body, The system includes a control unit that controls the opening and closing of the plurality of on-off valves, The supply port is provided only on one side wall of the furnace body. The aforementioned outlet is provided on the other wall surface opposite to the one wall surface. A vacuum carburizing apparatus characterized in that the vacuum carburizing process is performed by closing at least one of the plurality of on-off valves by the control unit.

2. The vacuum carburizing apparatus according to claim 1, characterized in that the vacuum carburizing treatment is performed under the condition that the supply flow rate of the carburizing gas by the carburizing gas flow rate controller is constant.

3. The vacuum carburizing apparatus according to claim 1, characterized in that the control unit sequentially switches the closing of at least one of the plurality of on-off valves.

4. The vacuum carburizing apparatus according to claim 3, characterized in that the valve switching interval for switching the closing of the plurality of on-off valves is 1 second to 15 seconds.

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