JP5276796B2 - Plasma processing furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma-treating furnace with which the temperature distribution in a material to be treated is improved and the generation of uneven treatment can be prevented. <P>SOLUTION: In the plasma-treating furnace 4, surroundings of the material 2 to be treated in a treating chamber S2 is provided with a heat-shading material 63, and in the heat shading material 63, an opening hole part 81 is arranged. Further, the opening hole part 81 is made to open/close with a cover material 83, and in this way, the heat in the heat-shading material 63 is made to exhaust to the outside. The heat-shading material 63 is arranged at the side parts and the upper part of the material 2 to be treated and the opening hole part 81 is arranged at the upper part of the material 2 to be treated. Furthermore, the inlet side of the heat-shading material 63 is provided with an inlet side heat-shading door 64 for opening/closing the inlet side and the outlet side heat-shading material 63 is provided with an outlet side heat-shading door 65 for opening/closing the outlet side, and in the inside of the heat-shading material 63, a heater 62 is provided, and in the furnace body 51, a cooling water passage 68 is included. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a plasma processing furnace for processing an object to be processed such as a steel material using plasma.

For example, in the manufacture of steel products such as crankshafts, a nitriding treatment is performed in which an iron nitride layer is formed on the surface of the steel material in order to improve the wear resistance and corrosion resistance of the steel material. An example of such a nitriding method is plasma nitriding (ion nitriding) (see Patent Documents 1 and 2). In this method, a processing gas containing nitrogen gas (N ₂ ) is supplied to a processing chamber in which an object to be processed that is a steel product is charged, and the processing object is configured by using the object to be processed that is a steel product as a cathode. Using a furnace body or the like as an anode, glow discharge is generated between the two electrodes, and an ionized process gas (nitrogen ions) is caused to collide with the object to be processed and enter the surface of the object to be processed.

  As a processing furnace for performing the nitriding treatment as described above, a furnace provided with a heat shield (heat insulating material) surrounding the object to be processed is known (see Patent Documents 1 and 2). Such a heat shield is arranged on the side or above the object to be processed in the processing chamber so as to partition the object to be processed and the furnace body. By providing such a heat shield, it is possible to suppress the heat given to the object to be processed from being dissipated to the surroundings and being absorbed by the furnace body or the like. Accordingly, the heating efficiency of the object to be processed can be improved.

Japanese Patent Laid-Open No. 7-3340 JP-A-9-268365

  However, in the conventional processing furnace, there is a problem that the temperature distribution of the object to be processed is likely to vary, and therefore processing unevenness is likely to occur. That is, when a heat shield is disposed around the object to be processed, heat is accumulated inside the heat shield and the temperature of the object to be processed may become too high. In addition, when performing processing using plasma, the processing chamber is depressurized. Even in such a depressurized state, slight heat convection occurs, so the atmosphere temperature in the processing chamber is higher on the upper side than on the lower side. It tends to rise. Therefore, when the heat shield is disposed so as to surround the side and upper side of the object to be processed, for example, the inside upper part of the heat shield (between the upper part of the object to be processed and the heat shield) is likely to become high temperature. . Therefore, the temperature of the upper part (particularly the upper central part) of the object to be processed is likely to be higher than the other parts. That is, there is a possibility that a difference in processing effect may occur between the upper portion of the object to be processed and other portions.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a plasma processing furnace that can improve the temperature distribution of an object to be processed and prevent the occurrence of processing unevenness.

In order to solve the above problems, according to the present invention, a plasma processing furnace for processing an object to be processed by generating plasma, comprising a processing chamber for storing the object to be processed, the object to be processed in the processing chamber. A heat shield disposed around the heat shield, provided with an opening in the heat shield, and provided with a lid for opening and closing the opening, between the object to be processed and the opening inside the heat shield. A temperature sensor that measures temperature; and a control unit that controls a position of the lid with respect to the opening based on a measurement value of the temperature sensor, and the control unit opens and closes the lid during plasma processing. Thus , a plasma processing furnace is provided in which the temperature between the object to be processed and the opening is adjusted .

  The heat shield may be provided on the side and above the object to be processed. The opening may be provided above the object to be processed. A heater for heating the object to be processed may be provided inside the heat shield. Furthermore, you may provide the entrance side heat shielding door which opens and closes the entrance side of the said heat shield, and the exit side heat shielding door which opens and closes the exit side of the said heat shield. The heat shield may be provided inside the furnace body and provided with a cooling water passage through which cooling water for cooling the furnace body passes.

Further, the processing chamber may be a nitriding chamber for nitriding a target object.

  According to the present invention, the heat of the object to be processed can be dissipated through the opening from the inside to the outside of the heat shield. By opening and closing the opening with the lid, it is possible to switch between a state in which the heat of the object to be processed is dissipated through the opening and a state in which the heat is not dissipated. Thereby, the temperature of the to-be-processed object near opening can be adjusted. That is, it is possible to improve the temperature distribution of the object to be processed and prevent the occurrence of processing unevenness.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments according to the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the plasma nitriding system 1 includes three processing chambers that house and process the object 2, that is, a heating chamber S <b> 1 that heats (preheats) the object 2. A nitriding chamber S2 for nitriding the object to be processed 2 heated in the heating chamber S1 by generating plasma, and a cooling chamber S3 for cooling the object to be processed 2 nitrided in the nitriding chamber S2 are provided. The heating chamber S1, the nitriding chamber S2, and the cooling chamber S3 are provided in the heating furnace 3, the nitriding furnace 4 (plasma processing furnace), and the cooling unit 5, respectively, and are arranged in a row in the lateral direction (substantially horizontal direction, transport direction D). These are arranged in this order from the entrance side. In addition, the plasma nitriding system 1 includes a target object transport mechanism 6 that moves the target object 2 in a predetermined transport direction D and transports the heating chamber S1, the nitriding chamber S2, and the cooling chamber S3 in this order. (See FIG. 2). Furthermore, on the entrance side of the heating furnace 3, a carry-in machine 11 for carrying the workpiece 2 into the heating chamber S1 is provided. On the outlet side of the cooling unit 5, a carry-out machine 12 that receives the workpiece 2 carried out from the cooling chamber S <b> 3 is provided. A shutter chamber 15 is provided between the heating furnace 3 and the nitriding furnace 4. A shutter chamber 16 is provided between the nitriding furnace 4 and the cooling unit 5. Outside the heating furnace 3, the nitriding furnace 4, and the cooling unit 5, a control unit 17 that controls the operation of each unit of the plasma nitriding system 1 and a power supply unit 18 that supplies a voltage to each unit of the plasma nitriding system 1 are provided. (See FIG. 1).

  In the present embodiment, the object to be processed 2 is a plurality of metal products such as a crankshaft or a camshaft, for example, and is supported by a support member 2a (a tray or the like) having conductivity such as metal, and the support member 2a. It is designed to be transported integrally. The material of the workpiece 2 is a steel material such as carbon steel or alloy steel in the case of a crankshaft, and is cast iron or the like in the case of a camshaft.

The heating furnace 3 includes a furnace body 21, and the internal space of the furnace body 21 is a heating chamber S1. On the entrance side of the furnace body 21, a carry-in port 22 for the workpiece 2 and a shutter 23 for opening and closing the carry-in port 22 are provided. On the outlet side of the furnace body 21, a carry-out port 25 for the object to be processed 2 and a shutter 26 for opening and closing the carry-out port 25 are provided. The shutter 26 moves in the shutter chamber 15. The heating chamber S1 includes a chain conveyor 31 (see FIG. 2) that conveys the object 2 to be processed in the heating chamber S1, and a heating chamber heater (not shown) that heats the object 2 in the heating chamber S1 by radiant heat. ), A stirring mechanism 34 (fan) for stirring the atmosphere in the heating chamber S1 is provided. Further, in the heating chamber S1, a heating chamber pressure-reducing mechanism 42 that depressurizes (evacuates) the inside of the heating chamber S1, and heating for supplying, for example, nitrogen gas (N ₂ ) as a heating gas or a purge gas into the heating chamber S1. A chamber gas supply path 43 is connected (see FIG. 2).

  The nitriding furnace 4 has a so-called horizontal furnace structure. For example, the nitriding furnace 4 includes a furnace body 51 having a substantially cylindrical shape with the length direction (axial direction) directed in the transport direction D, and the internal space of the furnace body 51 is nitrided. It is chamber S2. The furnace body 51 is made of metal (conductor). On the entrance side of the furnace body 51, a carry-in port 52 for the workpiece 2 and a shutter 53 for opening and closing the carry-in port 52 are provided. The shutter 53 moves in the shutter chamber 15 (see FIG. 2). On the outlet side of the furnace body 51, a carry-out port 55 for the object to be processed 2 and a shutter 56 for opening and closing the carry-out port 55 are provided. The shutter 56 moves in the shutter chamber 16.

  As shown in FIGS. 3 and 4, the nitriding chamber S <b> 2 is provided with a chain conveyor 61 for conveying the object 2 to be processed in the nitriding chamber S <b> 2 and a heater 62 (nitriding chamber heater) for heating the object 2 by radiant heat. It has been. Furthermore, a heat shield 63 (nitriding chamber heat shield) that suppresses the heat generated by the heater 62 from diffusing and being taken away by the furnace body 51 and the like, an inlet side heat shield door 64 that opens and closes the inlet side of the heat shield 63, An outlet side heat shielding door 65 that opens and closes the outlet side of the heat shield 63 is provided. Moreover, the to-be-processed object raising / lowering mechanism 66 which raises / lowers the to-be-processed object 2 with respect to the chain conveyor 61 within the nitriding chamber S2 is provided. The workpiece lifting mechanism 66 is provided with an electrode body 67. The furnace body 51 has a built-in cooling water passage 68 through which cooling water for cooling the furnace body 51 passes.

  The heater 62 is provided inside a heat shield 63 (side walls 63a and 63b described later). In the example shown in the drawing, the heat shield 63 is provided on the side of the object 2 along the inner surface of the heat shield 63, and the object 2 is heated from both sides. For example, an electric heater or the like may be used as the heater 62. In this case, AC power is supplied to the heater 62 from the power supply unit 18. In the illustrated example, a plurality of heaters 62 are provided on both sides of the object to be processed 2 so that the temperature of the object 2 can be controlled by dividing the periphery of the object 2 into a plurality of zones. In other words, by adjusting the amount of heat generated by each heater 62, the temperature distribution inside the heat shield 63 (processing temperature distribution during nitriding) can be controlled.

  As shown in FIGS. 4 and 5, the heat shield 63 has a substantially U-shape when viewed from the transport direction D, and the heat shield 63 is held by the chain conveyor 61 or the workpiece lifting mechanism 66. Side walls 63a and 63b provided on the sides (both sides in the width direction of the object 2) and an upper plate part 63c provided above the object 2 are provided. That is, it is provided around the object to be processed 2 in the nitriding chamber S2 so as to surround the side and upper side of the object to be processed 2. In other words, the side part of the object to be processed 2 and the side wall part of the furnace body 51 are divided into left and right by the side wall part 63a (63b), and the space between the upper part of the object to be processed 2 and the ceiling part of the furnace body 51 is divided. The upper plate portion 63c is provided so as to be partitioned vertically. Further, as shown in FIG. 5, an inlet-side passage port 63 d through which the object to be processed 2 passes is provided on the inlet side of the heat shield 63 in the transport direction D. On the outlet side of the heat shield 63 in the transport direction D, an outlet-side passage port 63e through which the object to be processed 2 passes is provided. The heat shield 63 may be formed of a highly heat insulating material (heat insulating material).

  The side wall parts 63a and 63b have a flat plate shape oriented substantially vertically (parallel to the transport direction D). In the example shown in FIG. 4, the side wall parts 63 a and 63 b are provided above the upper surface of the chain conveyor 61. That is, it is provided so as to cover the entire sides of the object 2 held by the chain conveyor 61 or the object lifting mechanism 66.

  The upper plate portion 63c has a flat plate shape that is oriented substantially horizontally (parallel to the transport direction D). An opening 81 is provided in the central portion of the upper plate portion 63c (that is, above the workpiece 2 held by the chain conveyor 61 or the workpiece lifting mechanism 66). In the illustrated example, the opening 81 is formed in a substantially rectangular shape, and overlaps with the upper center of the workpiece 2 disposed at a predetermined position when performing nitriding in a plan view as viewed from above. In the position.

  An opening wall body 82 is provided at the peripheral edge of the opening 81. The opening wall body 82 is erected from the peripheral portion of the opening 81 toward the outside (above the upper plate portion 63 c), and is provided in a rectangular frame shape along the entire peripheral portion of the opening 81.

A lid 83 that opens and closes the opening 81 (the upper opening of the opening wall 82) is provided above the opening 81 and the opening wall 82. In the illustrated example, the lid 83 has a substantially rectangular flat plate shape and is oriented substantially horizontally. Moreover, it is supported by the lower end part of the cover body raising / lowering mechanism 84 (cover body moving mechanism) attached to the ceiling part of the furnace body 51, and it raises / lowers along a substantially vertical direction by the action | operation of the cover body raising / lowering mechanism 84. It is like that. That is, between the closing position P _L1 (see FIG. 6) that closes the opening 81 close to the opening wall body 82 and the opening position P _L2 that moves above the closing position P _L1 and opens the opening 81, It can be moved up and down. Note that the lid 83 may be made of a highly heat-insulating material. The lid lifting mechanism 84 may be configured to use a cylinder mechanism such as an air cylinder, for example.

The entrance-side heat shielding door 64 (see FIG. 3) has a substantially flat plate shape and is provided substantially perpendicular to the side wall portions 63a and 63b and the upper plate portion 63c (perpendicular to the transport direction D). Moreover, it is supported by an entrance side door elevating mechanism (for example, a cylinder mechanism) (not shown) attached to the ceiling portion of the furnace body 51, and ascends and descends along a substantially vertical direction by the operation of the entrance side door elevating mechanism. It has become. That is, the side wall portions 63a, 63 b, an inlet closed position _{P I1} which closes the inlet-side passage hole 63d in proximity to the inlet side of the edge portion of the upper plate portion 63c, it moves upward in the inlet closing position _{P I1} inlet side between the inlet opening position P _I2 to open the passage port 63d, it has become vertically movable. Inlet closing position P _I1 inlet-side heat shielding door 64 disposed is provided so as to divide back and forth in the conveying direction D between the entrance 52 and the rear portion of the workpiece 2 (inlet side portion). In addition, you may comprise the entrance-side heat shielding door 64 with a material with high heat insulation.

The outlet side heat shielding door 65 has a substantially flat plate shape, and is provided substantially perpendicular to the side wall parts 63a and 63b and the upper plate part 63c (perpendicular to the transport direction D). Further, it is supported by an outlet side door elevating mechanism (for example, a cylinder mechanism) (not shown) attached to the ceiling portion of the furnace body 51, and moves up and down along a substantially vertical direction by the operation of the outlet side door elevating mechanism. It has become. That is, the side wall portions 63a, 63 b, and the outlet closing position _{P O1} for closing the outlet-side passage hole 63e in proximity to the edge of the outlet side of the upper plate portion 63c, the outlet side moves upward of the outlet closing position _{P O1} between the outlet opening position P _O2 for opening the passage port 63e, which is a vertically movable. The outlet side heat shielding door 65 disposed at the outlet closing position _PO1 is provided so as to partition the front part (side part on the outlet side) of the workpiece 2 and the carry-out port 55 in the transport direction D in the front-rear direction. . In addition, you may comprise the exit side heat shielding door 65 also with a material with high heat insulation.

  The workpiece lifting mechanism 66 has an electrode body 67 for applying a voltage to the workpiece 2, a lift 112 that lifts and lowers the electrode body 67 in the nitriding chamber S <b> 2, and the electrode body 67 is insulated from the lift 112. And an insulator 113. The electrode body 67 is provided inside the chain conveyor 61 (between the chain belts) in the nitriding chamber S2 (see FIG. 6). A cathode of a plasma power supply 115 (DC power supply) provided outside the nitriding chamber S2 is connected to each electrode body 67 via a wiring or the like. On the other hand, the anode of the plasma power source 115 is connected to the furnace body 51 through wiring or the like, for example. Note that the cathode (electrode body 67) and the anode (furnace body 51, etc.) of the DC power supply 115 are insulated by an insulator 113. That is, by providing the insulator 113, the cathode and the anode of the DC power source 115 are short-circuited to reduce the voltage, and abnormal discharge such as arc discharge occurs to reduce processing efficiency. Yes. In addition, when the object to be processed 2 is supported by the electrode body 67 and the insulator 113 and the electrode body 67 are raised by the elevator 112, the object to be processed 2 is lifted from the chain conveyor 61 and insulated from portions other than the electrode body 67. It is possible to make it. The insulator 113 is made of a material having high heat resistance, high electrical insulation, etc., such as ceramics.

Further, as shown in FIG. 3, a nitriding chamber pressure reducing path 131 for reducing the pressure (evacuating) inside the nitriding chamber S2 is connected to the nitriding chamber S2. The nitridation chamber decompression path 131 is connected to the decompression mechanism 132 (nitridation chamber decompression mechanism) including a vacuum pump or the like outside the nitridation chamber S2. Further, for example, nitrogen gas (N ₂ ), hydrogen gas (H ₂ ), hydrocarbon gas such as propane gas (C ₃ H ₈ ), ammonia gas (NH ₃ ) or the like is treated or purged into the nitriding chamber S2. A nitriding chamber gas supply path 133 is provided as supply gas. The nitriding chamber gas supply path 133 is connected to the nitriding chamber gas supply source unit 134 outside the nitriding chamber S2. The nitriding chamber gas supply source unit 134 is provided with a nitrogen gas supply source 141, a hydrogen gas supply source 142, a propane gas supply source 143, and an ammonia gas supply source 144.

As shown in FIG. 2, the cooling unit 5 includes a casing 151, and an internal space of the casing 151 is a cooling chamber S <b> 3. On the entrance side of the housing 151, a carry-in port 152 for the workpiece 2 and a shutter 153 for opening and closing the carry-in port 152 are provided. The shutter 153 moves in the shutter chamber 16. On the outlet side of the housing 151, a carry-out port 155 for the object to be processed 2 and a shutter 156 for opening and closing the carry-out port 155 are provided. The cooling chamber S3 is provided with a chain conveyor 161 that conveys the workpiece 2 in the cooling chamber S3 and an agitation mechanism 164 (fan) that agitates the atmosphere in the cooling chamber S3. Further, the cooling chamber S3 includes a cooling chamber decompression mechanism 172 that decompresses (evacuates) the inside of the cooling chamber S3, and a cooling chamber that supplies, for example, nitrogen gas (N ₂ ) as a cooling gas or a purge gas into the cooling chamber S3. A gas supply path 173 is connected.

  As shown in FIG. 2, the workpiece transfer mechanism 6 includes the roller provided in the chain conveyor 31 in the heating chamber S1, the chain conveyor 61 in the nitriding chamber S2, the chain conveyor 161 in the cooling chamber S3, and the shutter chamber 15. 181 and a roller 182 provided in the shutter chamber 16.

  The functional elements of each part of the above-described plasma nitriding system 1 are controlled by commands from the control unit 17 (see FIG. 1). The control unit 17 includes, for example, a general-purpose computer, and is configured to perform control for automatically processing the workpiece 2 according to a predetermined processing recipe. That is, under the control of the control unit 17, a heating process, a nitriding process, and a cooling process described later can be automatically performed. Although not shown, the plasma nitriding system 1 includes a thermometer, a pressure gauge, and the like for detecting the temperature and pressure of the heating chamber S1, the temperature and pressure of the nitriding chamber S2, the temperature in the cooling chamber S3, and the pressure, respectively. The detection sensor is provided, and the detection value is transmitted to the control unit 17. That is, the control unit 17 controls each unit of the plasma nitriding system 1 based on the detection value of each detection sensor.

  Next, a plasma nitriding (ion nitriding) processing method using the plasma nitriding processing system 1 configured as described above will be described. First, the workpiece 2 is carried into the heating chamber S1. That is, the workpiece 2 is conveyed from the carry-in machine 11 to the heating chamber S <b> 1 through the carry-in port 22, and is transferred onto the chain conveyor 31.

When the inlet 22 is closed and the inside of the heating chamber S1 is sealed, the inside of the heating chamber S1 is depressurized by the operation of the heating chamber decompression mechanism 42 and is in a substantially vacuum state (for example, about 0.1 Torr (about 13.3 Pa). )). Thereafter, nitrogen gas is supplied into the heating chamber S <b> 1 through the heating chamber gas supply path 43. Thus, the oxidizing atmosphere (O ₂ ) is discharged from the heating chamber S1, the inside of the heating chamber S1 is purged with nitrogen gas, and the processing pressure (pressure in the heating chamber S1) is, for example, about 500 Torr (about 66.7 kPa). Degree). And the to-be-processed object 2 on the chain conveyor 31 is heated to about 500 degreeC by the heat_generation | fever of the heater which is not shown in figure, for example.

  On the other hand, in the nitriding chamber S2, the carry-in port 52 and the carry-out port 55 of the nitriding chamber S2 are closed by the shutters 53 and 56, respectively, and the nitriding chamber S2 is sealed, and the nitriding chamber S2 is operated by the operation of the decompression mechanism 132 The inside of S2 is in a decompressed state (for example, about 1 Torr (about 133.3 Pa)). Further, nitrogen gas is supplied into the nitriding chamber S2 through the nitriding chamber gas supply path 133. That is, the pressure in the nitriding chamber S2 is reduced in a nitrogen gas atmosphere. Further, the temperature in the nitriding chamber S <b> 2 is raised to a predetermined temperature (for example, about 500 ° C. to 550 ° C.) by the heat generated by the heater 62. The cooling water channel 68 is appropriately supplied with cooling water. That is, the temperature in the nitriding chamber S2 is controlled to a predetermined temperature by adjusting the heat generation amount of the heater 62 and the flow rate of the cooling water in the cooling water channel 68.

When the heat treatment in the heating chamber S1 is completed, the pressure reducing mechanism 42 is operated again, and the pressure in the heating chamber S1 is reduced to the same level as the pressure in the nitriding chamber S2 (for example, about 1 Torr). Thereafter, the carry-out port 25 and the carry-in port 52 are opened, and the heating chamber S1 and the nitriding chamber S2 are communicated with each other through the shutter chamber 15. In the nitriding chamber S2, the inlet side heat shielding door 64 is moved to the inlet opening position _PI2 , and the inlet side passage port 63d is opened.

  In this state, the workpiece 2 is moved along the transport direction D, and is transported from the heating chamber S1 to the nitriding chamber S2 through the carry-out port 25, the shutter chamber 15, and the carry-in port 52. That is, the workpiece 2 is transferred from the chain conveyor 31 to the chain conveyor 61. When the workpiece 2 is carried into the nitriding chamber S2, the carry-in port 52 of the nitriding chamber S2 is closed, and the inside of the nitriding chamber S2 is again sealed.

  The object to be processed 2 carried into the nitriding chamber S2 is transported to a predetermined position inside the heat shield 63 through the inlet-side passing port 63d by the driving of the chain conveyor 61, and is then stopped. The inlet side passage port 63d and the outlet side passage port 63e of the heat shield 63 are closed by the inlet side heat shielding door 64 and the outlet side heat shielding door 65, respectively. Further, the electrode body 67 is raised by driving the object lifting mechanism 66, and the object to be processed 2 held on the chain conveyor 61 is pushed up by the electrode body 67. That is, the object to be processed 2 is separated from the chain conveyor 61 upward and is placed on the electrode body 67 inside the heat shield 63, and the parts other than the electrode body 67 (elevator 112, furnace body 51, chain 51). It is electrically insulated from the conveyor 61 or the like. In this way, the object to be processed 2 is stationary at a predetermined height while being supported by the object lifting mechanism 66, and is surrounded by the heat shield 63, the inlet side heat shield door 64, and the outlet side heat shield door 65. (Ie, the entire side portion of the object to be processed 2 is surrounded by a member having high heat shielding properties, and the upper portion of the object to be processed 2 is covered by the upper plate portion 63c). By carrying out like this, it can suppress that a heat | fever is dissipated from the to-be-processed object 2, and the to-be-processed object 2 can be heated now efficiently.

  Further, when the object to be processed 2 is carried into the nitriding chamber S2, the inlet 52 is closed, and the inside of the nitriding chamber S2 is sealed, a processing gas containing nitrogen gas in the nitriding chamber S2 through the nitriding chamber gas supply path 133 ( For example, a mixed fluid such as nitrogen gas, hydrogen gas, propane gas, and ammonia gas) is supplied. As a result, the pressure in the nitriding chamber S2 is increased to a predetermined processing pressure (for example, about 3 Torr to 8 Torr (about 400 Pa to 1067 Pa).

  Thus, in the state where the processing gas is supplied into the nitriding chamber S2 and the workpiece 2 is supported by the electrode body 67, a voltage is applied by the DC power source 115 to perform nitriding. That is, the electrode body 67 and the object to be processed 2 serve as cathodes, the furnace body 5 serves as an anode, glow discharge occurs between the two electrodes, and plasma is generated. That is, the processing gas in the nitriding chamber S2 is ionized. The ionized processing gas (nitrogen ions) collides with the object 2 and enters the surface of the object 2. Thereby, an iron nitride layer is formed on the surface of the workpiece 2.

  During the nitriding process, the processing temperature in the nitriding chamber S2 and the temperature of the object to be processed 2 are the heat generated by the heater 62 and the heating by glow discharge (heating by the ionized processing gas colliding with the object to be processed 2). ), By controlling the cooling by the cooling water channel 68, the temperature is adjusted to a predetermined temperature (for example, about 500 ° C. to 550 ° C.).

  Furthermore, the temperature distribution inside the heat shield 63 can be suitably adjusted by opening and closing the opening 81. That is, in a horizontal processing furnace such as the nitriding furnace 4, the temperature distribution in the processing chamber tends to be generally worse than that in the vertical processing furnace, and the upper portion (particularly the opening 81) of the workpiece 2 tends to be deteriorated. The upper central portion located in the vicinity of the upper part of the heat shield tends to become hot, but by opening the opening 81, the heat in the heat shield 63 is released through the opening 81 and is easily absorbed by the furnace body 51 (cooling water channel 68). Become.

For example, when the temperature of the upper center portion of the workpiece 2 rises above a predetermined upper limit temperature set in advance, the lid 83 is moved to the opening position _PL2 , the opening 81 is opened, and the upper portion of the workpiece 2 is What is necessary is just to make it the state in which the heat of a center part is thermally radiated outside the heat shield 63. If it does so, the temperature of the upper center part of the to-be-processed object 2 can be reduced, and it can approach the temperature of other parts (parts other than the upper center part of the to-be-processed object 2). On the contrary, when the temperature of the upper center portion of the object to be processed 2 is lower than a predetermined lower limit temperature (a temperature lower than the upper limit temperature), the lid 83 is moved to the closing position _PL1 , and the opening is opened. 81 may be closed so that the heat of the upper center portion of the object to be processed 2 is switched to a state where the heat is not radiated outside the heat shield 63. If it does so, the temperature of the upper center part of the to-be-processed object 2 can be raised, and it can approximate the temperature of another part. By opening and closing the opening 81 in this manner, the temperature of the upper central portion of the workpiece 2 can be maintained at a temperature within a predetermined range (between the upper limit temperature and the lower limit temperature). Further, it is possible to prevent the temperature at the upper center of the object to be processed 2 from becoming too high or low with respect to other parts, and to improve the uniformity of the temperature distribution of the object to be processed 2 in the nitriding process. As a result, it is possible to prevent processing unevenness from occurring.

As described above, when the nitriding process in the nitriding chamber S2 is completed, the supply of voltage by the DC power supply 115 is stopped, and the glow discharge is stopped. Further, the electrode body 67 and the object to be processed 2 are lowered by driving the object to be processed lifting mechanism 66. Then, the workpiece 2 is transferred from the electrode body 67 to the chain conveyor 61, and the electrode body 67 is lowered below the chain conveyor 61 and the workpiece 2. Further, the outlet-side heat shielding door 65 is moved to the outlet opening position P _O2, the outlet-side passage hole 63e is opened. Furthermore, the carry-out port 55 and the carry-in port 152 are opened, and the nitriding chamber S2 and the cooling chamber S3 are communicated with each other through the shutter chamber 16.

  In this state, the workpiece 2 is moved along the transport direction D, and the pressure is reduced in advance from the inside of the heat shield 63 through the outlet-side passage port 63e, the transport port 55, the shutter chamber 16, and the transport port 152. It is conveyed to chamber S3. That is, the workpiece 2 is transferred from the chain conveyor 61 to the chain conveyor 161. When the workpiece 2 is carried into the cooling chamber S3, the carry-in port 152 of the cooling chamber S3 is closed, and the inside of the cooling chamber S3 is sealed.

  The object to be processed 2 carried into the cooling chamber S3 is conveyed to a predetermined position in the cooling chamber S3 by the driving of the chain conveyor 161, and is stopped. Further, nitrogen gas is supplied to the cooling chamber S3 through the cooling chamber gas supply path 173, the inside of the cooling chamber S3 is increased to a predetermined processing pressure (for example, about 500 Torr), and cooling processing is performed. The heat radiated from the workpiece 2 is transmitted to cooling water in a cooling water passage (not shown) via nitrogen gas in the cooling chamber S3, the casing 151, and the like, and is exhausted from the cooling unit 5 together with the cooling water. By this cooling treatment, the temperature of the workpiece 2 is lowered from about 500 ° C. to 550 ° C. to about 100 ° C. to 150 ° C.

  When the cooling process is completed, the carry-out port 155 is opened, and the workpiece 2 is transferred from the cooling chamber S3 to the unloader 12 through the carry-out port 155 by driving the chain conveyor 161. As described above, a series of processing steps in the plasma nitriding processing system 1 is completed.

  In the plasma nitriding system 1, a plurality of objects to be processed 2 can be continuously processed in parallel. That is, a plurality of objects to be processed 2 can be processed continuously and efficiently while performing heat treatment in the heating chamber S1, nitriding treatment in the nitriding chamber S2, and cooling treatment in the cooling chamber S1.

  As described above, in the nitriding furnace 4 of the plasma nitriding treatment system 1, the opening 81 is provided in the heat shield 63, so that the atmosphere inside the heat shield 63 and the heat of the object to be processed 2 can be reduced. The heat shield 63 can be diffused through the opening 81 from the inner side to the outer side (furnace body 51 side). By opening and closing the opening 81 with the lid 83, it is possible to switch between a state in which the atmosphere inside the heat shield 63 and the heat of the object to be processed 2 are dissipated through the opening 81 and a state in which the heat is not dissipated. Thereby, the atmosphere in the vicinity of the opening 81 and the temperature of the object to be processed 2 (the temperature of the upper central portion facing the opening 81) can be adjusted. That is, the temperature distribution of the atmosphere in the heat shield 63 and the temperature distribution of the object to be processed 2 can be improved, and the uniformity of the temperature distribution can be improved. As a result, the processing unevenness of the object to be processed 2 can be prevented.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  For example, in the above embodiment, a crankshaft made of an iron-based alloy, a camshaft, and the like are illustrated as the object to be processed 2, but the object to be processed 2 is not limited to this, and the present embodiment is applicable to various materials. Applicable to plasma nitriding.

  The shape, arrangement, and the like of the heater 62, the heat shield 63, the opening 81, the opening wall 82, the lid 83, and the like provided in the nitriding furnace 4 are not limited to the above embodiment. For example, the heater 62 may be provided not only on the side of the workpiece 2 in the nitriding chamber S2, but also on the upper side. Further, the inlet side heat shielding door 64 and the outlet side heat shielding door 65 are not necessarily provided. That is, the nitriding treatment may be performed in a state where the inlet side passage port 63d and the outlet side passage port 63e are opened. The opening wall body 82 is not necessarily provided. In other words, the lid 83 may be brought into direct contact with the heat shield 63 to close the opening 81. The position of the opening 81 is not limited to the position overlapping the upper center of the workpiece 2 and may be provided at another location.

In the above embodiment, the method for adjusting the temperature distribution of the workpiece 2 by moving the lid 83 to the closed position P _L1 and the opening position P _L2 has been described. You may make it move to the several position more than a location in steps, and you may make it move to arbitrary positions. That is, the opening degree of the opening 81 (the distance between the opening 81 and the lid 83) may be adjusted stepwise or arbitrarily.

For example, as shown in FIG. 7, the height of the lid body 83 with respect to the opening 81 can be adjusted in four stages, that is, the lid body 83 is disposed above the closing position P _L1 and the closing position P _L1 to open the opening 81. first open position P _L3 which _opened, to be moved to the first second open position P _L4 higher than the opening position P _L3, second third opening position P _L5 higher than the opening position P _L4 May be. In this case, the opening degree of the opening 81 is minimized (zero) when placing the lid 83 in the closed position P _L1, maximized when placing the lid 83 to the third opening position P _L5. Further, the amount of heat dissipated from the upper portion of the object to be processed 2 through the opening 81 (the amount of heat absorbed by the furnace body 51) increases as the opening degree of the opening 81 increases. That is, when the lid 83 is disposed at the third opening position _PL5 , the heat radiation amount is maximized. Therefore, by adjusting the position of the lid 83, the amount of heat radiation can be adjusted, and as a result, the temperature distribution in the heat shield 63 and the temperature distribution of the workpiece 2 can be controlled.

  Further, as shown in FIG. 7, a temperature sensor 185 for measuring the temperature (atmosphere temperature) of the nitriding chamber S2 may be provided, and the position of the lid 83 may be adjusted based on the measured value. In the example shown in FIG. 7, the temperature sensor 185 is disposed inside the thermal shield 63 so as to measure the temperature between the upper central portion of the workpiece 2 and the opening 81. That is, the temperature of the upper center portion of the workpiece 2 can be predicted from the measured value of the temperature sensor 185. Further, the measured value of the temperature sensor 185 is transmitted to the control unit 17. The control unit 17 controls the position of the lid 83 with respect to the opening 81 based on the measurement value of the temperature sensor 185. That is, based on the measured value of the temperature sensor 185, a control command is transmitted to the lid lifting mechanism 84, and the lid lifting mechanism 84 adjusts the position of the lid 83 according to the control command transmitted from the control unit 17. . For example, control is performed so that the measured value of the temperature sensor 185 becomes a target value (a temperature between a preset upper limit temperature and a lower limit temperature). If it does in this way, the temperature of to-be-processed object 2 can be adjusted appropriately.

Further, the control unit 17 may calculate the difference (deviation amount) between the measured value of the temperature sensor 185 and the target value, and determine the opening degree of the opening 81 based on the deviation amount. For example, when the deviation amount is small, the lid 83 may be disposed at the first opening position _PL3 to reduce the heat dissipation amount. When the deviation amount is large, the lid 83 may be disposed at the second opening position _L4 to increase the heat radiation amount. When the deviation amount is larger, the lid 83 may be disposed at the third opening position _PL5 to maximize the heat radiation amount. Thus, the larger the deviation amount, the larger the opening degree of the opening 81 may be controlled. If it does so, the temperature distribution in the heat shield 63 and the temperature distribution of the to-be-processed object 2 can be adjusted appropriately more accurately.

  Furthermore, the configuration of the nitriding furnace 4 is a continuous processing system such as the plasma nitriding processing system 1 shown in the above embodiment (including a plurality of processing chambers, such as a heating process, a process using plasma, a cooling process, etc. The present invention is not limited to a system that performs a plurality of types of processing in different processing chambers), and can also be applied to a batch-type plasma processing system (a system that performs a plurality of types of processing in the same processing chamber). That is, for example, the present invention can be applied to a configuration in which heat treatment and nitriding treatment are performed in the same processing chamber, or a configuration in which heating treatment, nitriding treatment, and cooling processing are performed in the same processing chamber.

  Further, the configuration of the nitriding furnace 4 is not limited to the horizontal furnace as described in the above embodiment (a structure in which the object to be processed is moved in the lateral direction and is carried in / out from the side of the processing chamber). The present invention can also be applied to a furnace (a structure in which an object to be processed is moved up and down and carried in and out from below a processing chamber).

  FIG. 8 shows an example of a batch type vertical nitriding furnace 190. In FIG. 8, elements having the same functional configuration as the elements in the above-described embodiment are denoted by the same reference numerals. The nitriding furnace 190 includes a furnace body 191 having a substantially cylindrical shape whose length direction (axial direction) is substantially vertical, and the internal space of the furnace body 191 is a nitriding chamber S2. The furnace body 191 is made of metal, and a loading / unloading port 192 for the object to be processed 2 and a shutter 193 for opening / closing the loading / unloading port 192 are provided at the bottom of the furnace body 191. Further, the nitriding furnace 190 includes a heater 62, a heat shield 63, a cooling water channel 68 (a cooling water channel for cooling the furnace body 191), an opening 81, an opening wall body 82, a lid 83, A lid lifting mechanism 84 and the like are provided. Moreover, the to-be-processed object raising / lowering mechanism 196 which carries in / out to the nitriding chamber S2 through the loading / unloading port 192 by moving the to-be-processed object 2 up and down is provided.

  The heat shield 63 provided in the nitriding furnace 190 has a substantially rectangular parallelepiped shape with an open bottom. That is, the entire side portion of the object 2 to be processed (the object 2 to be processed disposed at a predetermined position when performing the nitriding process) held by the object lifting mechanism 196 in the nitriding chamber S2 is surrounded and processed. It is formed so as to surround the upper part of the body 2. The opening 81 is provided at a position so as to overlap the upper center of the workpiece 2 held by the workpiece lifting mechanism 196 when viewed from above. Further, similarly to the workpiece lifting mechanism 66, the workpiece lifting mechanism 196 includes an electrode body 67, an insulator 113, and the like. Also in such a configuration of the nitriding furnace 190, the opening 81 is opened and closed by the lid 83, whereby the amount of heat dissipated through the opening 81 can be adjusted, and the temperature distribution of the workpiece 2 can be suitably controlled.

  In addition to the plasma nitriding process, the present embodiment can be applied to various processes using plasma such as a plasma carburizing process and a plasma carbonitriding process. That is, the plasma processing furnace is not limited to a nitriding furnace (plasma nitriding furnace), and may be a plasma carburizing furnace, a plasma carbonitriding furnace, or the like.

  The present invention can be applied to a plasma processing furnace or the like that performs surface treatment of metal products and the like.

1 is a schematic plan view of a plasma nitriding system according to an embodiment. It is a schematic longitudinal cross-sectional view of a plasma nitriding system. It is a longitudinal cross-sectional view of a nitriding furnace. It is a longitudinal cross-sectional view (schematic cross-sectional view by the II line | wire in FIG. 3) of a nitriding furnace. It is a perspective view explaining the composition of a heat shield, an opening, and a lid. It is explanatory drawing which expanded and showed the structure of the thermal-shielding body and the to-be-processed object raising / lowering mechanism. It is the longitudinal cross-sectional view which showed embodiment which adjusts the position of a cover body in 4 steps. It is a longitudinal cross-sectional view of a vertical furnace.

Explanation of symbols

D Transport direction S1 Heating chamber S2 Nitriding chamber S3 Cooling chamber 1 Plasma nitriding system 2 Processed object 3 Heating furnace 4 Nitriding furnace 5 Cooling unit 6 Processed object transport mechanism 17 Control unit 62 Heater 63 Heat shield 64 Entrance side heat shield Door 65 Outlet side heat shielding door 81 Opening 82 Opening wall body 83 Lid body 84 Lid body lifting mechanism

Claims (6)

A plasma processing furnace for processing an object to be processed by generating plasma,
A processing chamber for storing the object to be processed;
A heat shield disposed around the object to be processed in the processing chamber;
Providing an opening in the thermal shield;
Providing a lid for opening and closing the opening ;
A temperature sensor that measures the temperature between the object to be processed and the opening inside the thermal shield, and a control unit that controls the position of the lid relative to the opening based on a measurement value of the temperature sensor; With
The said control part adjusts the temperature between the said to-be-processed object and the said opening by opening and closing the said cover body during plasma processing, The plasma processing furnace characterized by the above-mentioned . The thermal shield is provided on the side and upper side of the object to be processed,
The plasma processing furnace according to claim 1, wherein the opening is provided above the object to be processed. The plasma processing furnace according to claim 1, wherein a heater for heating the object to be processed is provided inside the heat shield. It has an entrance side heat shielding door which opens and closes the entrance side of the heat shield, and an exit side heat shield door which opens and closes the exit side of the heat shield. The plasma processing furnace described. The thermal shield is provided inside the furnace body,
The plasma processing furnace according to any one of claims 1 to 4, further comprising a cooling water passage through which cooling water for cooling the furnace body is passed. The plasma processing furnace according to any one of claims 1 to 5, wherein the processing chamber is a nitriding chamber for nitriding a target object .

Images