JP2009084633A - Plasma nitriding treatment device, and continuous type plasma nitriding treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous type plasma nitriding treatment device where temperature control for the body to be treated can be performed correctly as possible, and uniform nitriding treatment can be efficiently performed to the whole of the body to be treated. <P>SOLUTION: Nitriding chamber heaters 26 are arranged on both the right and left sides in the carrying direction of the body W to be treated in a nitriding chamber 2, the right side heater 26R and the left side heater 26L are divided into the front/back sides and upper/lower sides of the carrying direction, respectively. The plasma nitriding treatment device is further provided with: thermocouples 33 measuring the temperature of the region corresponding to each divided heater 29 in the body W to be treated; and control parts 36 individually controlling the calorific power in each divided heater 29 in such a manner that the measured temperature of each thermocouple 33 reaches the preset objective temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a plasma nitriding apparatus for nitriding an object to be processed such as a steel material. The present invention also relates to a continuous plasma nitriding method.

  As a plasma nitriding apparatus for continuously nitriding an object to be processed such as a steel material, heating chambers, nitriding chambers (glow discharge processing chambers), cooling chambers, etc. are arranged in series in a horizontal direction. An apparatus for transferring an object to be processed is known in which an intermediate door is provided between the chambers (see the section of the prior art in Patent Document 1).

  There is also known a plasma nitriding apparatus provided with a heater for heating an object to be processed in a plasma nitriding chamber defined by a furnace wall having a coolant passage (see Patent Document 2).

  Furthermore, an apparatus that includes a heater that heats an object to be processed in the plasma nitriding chamber and that is divided into upper, middle, and lower parts and that can individually control each of the divided heaters is known (the conventional technique of Patent Document 3). Section).

As a typical example of the object to be processed, as shown in FIG. 2 of Patent Document 2, a plurality of objects to be processed such as a steel crankshaft are supported by a support member such as a frame or a tray. An aggregate of single objects to be processed can be mentioned.
JP 59-96259 A JP 2005-2444 A JP 2004-238705 A

  In general, in the plasma nitriding process, when the object to be processed is heated by glow discharge, the temperature of the central part of the object to be processed is more likely to rise than the peripheral part of the object to be processed due to self-heating of the object to be processed. It is difficult to uniformly heat the entire treatment body. For example, as described above, in the case where an aggregate of single objects to be processed is used as an object to be processed, the closer to the central part of the aggregate in the aggregate, the more easily affected by self-heating from surrounding single objects to be processed. A large temperature difference will occur between the processing object alone in the vicinity of the wall.

  In Patent Document 3, the heater for heating the object to be processed is divided into upper, middle, and lower parts, and each divided heater can be individually controlled so as to equalize the temperature of the object to be processed. This relates to a batch furnace. Therefore, it is presumed that the heater is arranged in an annular shape so as to surround the entire lateral circumference of the object to be processed. Therefore, it cannot be applied as it is to a continuous plasma nitriding apparatus that requires the object to pass through.

  Moreover, since the thing of patent document 3 is equipped with the sealed chamber which accommodates a to-be-processed object, and the temperature of the outer side of this sealed chamber is measured with the thermocouple provided corresponding to each said division | segmentation heater, It is unsuitable for accurately controlling the temperature of the object itself.

  The present invention has been made in view of the above-described circumstances, and can control the temperature of the object to be processed as accurately as possible, and can efficiently perform uniform nitriding on the entire object to be processed. An object of the present invention is to provide a continuous plasma nitriding apparatus and method that can be applied.

  In order to solve the above-described problems, a plasma nitriding apparatus according to the present invention is a plasma nitriding apparatus that performs a plasma nitriding process on a workpiece, and includes a nitriding chamber heater that heats the workpiece in the nitriding chamber. Chamber heaters are disposed on the left and right sides in the transfer direction of the object to be processed in the nitriding chamber, and the nitriding chamber heater has a plurality of divided heaters divided forward and backward and vertically in the transfer direction. A thermocouple that measures the temperature of the body and a control unit that individually controls the amount of heat generated by each of the divided heaters are provided.

  According to the present invention, the object to be processed is heated (self-heated) by glow discharge that generates plasma in the nitriding chamber, and is also heated by the nitriding chamber heater from the left and right sides in the transport direction. Here, in the present invention, the nitriding chamber heater is divided into a plurality of parts before and after and in the upper and lower directions in the transport direction, and the temperature of the object to be processed is measured by the thermocouple. And each said control part controls the emitted-heat amount of each said division | segmentation heater separately. Thereby, the whole object to be processed can be controlled to the target temperature or a temperature close thereto at the time of nitriding. Therefore, uniform nitriding treatment can be efficiently performed on the entire object to be processed.

  The nitriding chamber heaters are arranged on both the left and right sides in the conveying direction of the object to be processed in the nitriding chamber, so that the nitriding chamber heater does not interfere with the transfer of the object to be processed.

  As a preferred embodiment, the nitriding chamber is defined by a furnace wall having a coolant passage, a heat insulating material is disposed on the furnace wall side of each of the divided heaters, and each of the divided heaters and each of the heat insulating materials. Is exemplified by a case in which is covered with a common heat conduction case (claim 2).

  In this case, the heat generated by the divided heater is radiated by the heat conduction case to heat the object to be processed. Therefore, the object to be processed is uniformly heated over a wide range by each divided heater.

  Moreover, since the said heat insulating material is arrange | positioned at the said furnace wall side of the said divided heater, it is suppressed that the heat_generation | fever from a divided heater is taken away by the said furnace wall. In addition, if the temperature rises too much in a certain region of the object to be processed, the heat generation amount of the divided heater corresponding to that region is controlled to drop, but at this time, the heat is transferred to the furnace wall side through the heat conduction case. Since heat dissipation is promoted, the temperature drop speed of the object to be processed is high. Therefore, the temperature control of the object to be processed can be performed quickly.

  In plasma nitriding, abnormal discharge is likely to occur when the glow voltage is increased because the glow discharge is lowered and increased in a certain vacuum state. However, in such a case and when abnormal heating occurs for other reasons, Heat can be quickly released to the water-cooled furnace wall through the conduction case. With the conventional heater structure, it is difficult to quickly release heat.

  As a preferred embodiment, a mode in which the object to be processed is transported in the order of a heating chamber, the nitriding chamber, and a cooling chamber and plasma nitriding treatment is performed in the nitriding chamber (Claim 3).

  With the above structure, a plurality of objects to be processed can be sequentially moved to the heating chamber, the nitriding chamber, and the cooling chamber, and the processing in each chamber can be performed continuously and in parallel, so that high mass productivity is achieved.

  As another preferred embodiment, in the nitriding chamber heater, a mode in which each of the left side heater and the right side heater has a plurality of divided heaters divided in the front and rear and the top and bottom in the transport direction (Claim 4). .

  As another preferred embodiment, a mode in which the thermocouple is a plurality of thermocouples that measure the temperature of the object to be processed in a region corresponding to each of the divided heaters is exemplified.

  The configurations of the fourth and fifth aspects are preferable because finer temperature control is possible.

  In another preferred embodiment, the thermocouple is insulated from a furnace wall, and the thermocouple is disposed close to the object to be processed up to a minimum distance where there is no influence of discharge with the object to be processed. An example of measuring the temperature in the vicinity of the object to be processed will be exemplified (claim 6).

  Thermocouples are affected by discharge and may be damaged, and accurate temperature measurement may not be possible. In addition, conventionally, for example, a heat-resistant window is opened in the furnace body and the object to be processed is measured with a radiation thermometer from the outside so as not to be affected by the discharge, but there is a problem with the accuracy of the radiation thermometer itself. In addition, since the measurement place is limited due to the structure, it is difficult to measure the temperature accurately. In the present embodiment, the thermocouple is insulated from the furnace wall, and the thermocouple is brought close to the object to be processed up to a minimum distance (for example, about 5 to 20 mm) that is not affected by discharge with the object to be processed. By arranging and measuring the temperature in the vicinity of the object to be processed, the temperature can be measured with sufficiently high accuracy, and the temperature management of the object to be processed can be performed accurately.

  On the other hand, the method of the present invention for solving the above-described problem is a continuous plasma nitriding method in which the object to be processed is continuously transferred to the nitriding chamber and plasma nitriding is performed. Dividing the heat-dissipating nitriding chamber heaters provided only on both the left and right sides in the conveyance direction of the treatment body into a plurality of front and rear and top and bottom in the conveyance direction, and measuring the temperature of the region corresponding to each divided heater in the workpiece, Nitriding is performed by individually controlling the amount of heat generated by each of the divided heaters so that all of the region of the object to be processed has a preset target temperature.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  1 is a schematic plan view of a part of a plasma nitriding apparatus according to an embodiment of the present invention, in which a part thereof is a horizontal section, FIG. 2 is a sectional view taken along the line II-II in FIG. 1, and FIG. FIG. 4 is a front view of the heater, and FIG. 4 is a sectional view taken along arrows IV-IV in FIG.

  As shown in FIG. 1, a plasma nitriding apparatus according to an embodiment of the present invention includes a heating chamber 1 that heat-treats (preheat-treats) a workpiece W, and a treatment that is heat-treated in the heating chamber 1. A nitriding chamber 2 for nitriding the body W by generating plasma and a cooling chamber 3 for cooling the object to be processed W nitrided in the nitriding chamber 2 are provided. These chambers are provided in a line along the conveying direction of the workpiece W in the above order. A first shutter chamber 4 is provided between the heating chamber 1 and the nitriding chamber 2. Similarly, a second shutter chamber 5 is provided between the nitriding chamber 2 and the cooling chamber 3. Is provided.

  The object to be processed W is, for example, an assembly of objects to be processed which is formed by supporting a plurality of objects to be processed on a support member such as a frame or a tray. Examples of the object to be treated include metal products such as a crankshaft or a camshaft. The material of the single object to be processed 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 chamber 1 will be described. The heating chamber 1 is defined inside the heating furnace 6. On the entrance side of the heating furnace 6, a carry-in port 7 for the workpiece W and a carry-in shutter 8 that opens and closes the carry-in port 7 are provided. On the outlet side of the heating furnace 6, a carry-out port 9 for the workpiece W and a carry-out shutter 10 that opens and closes the carry-out port 9 are provided. The carry-out shutter 10 moves up and down in the first shutter chamber 4.

  The heating chamber 1 is provided with a chain conveyor 11 that conveys the workpiece W and a heating chamber heater 12 that heats the workpiece W in the heating chamber 1 by radiant heat. The heating chamber 1 has a heat shield 13 that suppresses the heat generated by the heating chamber heater 12 from diffusing toward the furnace wall, and a blower mechanism (blower fan) 14 that stirs the atmosphere in the heating chamber 1. Provided in the furnace wall of the heating furnace 6 is a coolant passage 15 for circulating coolant, and the coolant passage 15 communicates with a coolant source 15a.

  The heating chamber 1 is connected to a heating chamber decompression path 16 for decompressing (evacuating) the heating chamber 1, and the heating chamber decompression path 16 is connected to a decompression mechanism 17 including a vacuum pump and the like. Furthermore, the heating chamber 1 is connected to a heating chamber gas supply path 18 for supplying, for example, nitrogen gas as a heating gas or a purge gas to the heating chamber 1, and the heating chamber gas supply path 18 is connected to a heating gas supply. Connected to source 19.

  Next, the nitriding chamber 2 will be described with reference to FIGS. The nitriding chamber 2 is defined inside a horizontal cylindrical nitriding furnace 20 (so-called horizontal plasma nitriding furnace). The nitriding furnace 20 is made of metal (conductor). On the entrance side of the nitriding furnace 20, a carry-in port 21 for the workpiece W and a carry-in shutter 22 for opening and closing the carry-in port 21 are provided. The carry-in shutter 22 moves up and down in the first shutter chamber 4. On the exit side of the nitriding furnace 20, a carry-out port 23 for the workpiece W and a carry-out shutter 24 that opens and closes the carry-out port 23 are provided. The carry-out shutter 24 moves up and down in the second shutter chamber 5.

  In the nitriding chamber 2, a chain conveyor 25 that conveys the workpiece W, a nitriding chamber heater 26 that heats the workpiece W in the nitriding chamber 2 by radiant heat, and the workpiece W on the chain conveyor 25. And a workpiece lifting mechanism 27 (see FIG. 2) that lifts up at a predetermined position. The furnace wall of the nitriding furnace 20 has a built-in coolant passage 28 for circulating a coolant, and the coolant passage 28 communicates with a coolant source 28a.

  The nitriding chamber heaters 26 are disposed only on the left and right sides in the conveyance direction of the workpiece W in the nitriding chamber 1, and each of the left heater 26L and the right heater 26R is divided into a plurality of front and rear and top and bottom in the conveyance direction. ing. Each divided heater 29 is a component of the heater unit 30 as shown in FIGS.

  Each of the heater units 30 includes the divided heater 29, a heat insulating material 31 disposed on the furnace wall side of the divided heater 29, a heat conduction case 32 that covers both the divided heater 29 and the heat insulating material 31, It has. As the divided heater 29, an electric heating element such as a strip shape or a coil shape can be used. The heat conduction case 32 is formed of a metal such as stainless steel having good heat conductivity and heat resistance against the nitriding temperature. A thermocouple insertion hole 30a for inserting a thermocouple 33 described later is formed through the central portion of each heater unit 30.

  Heat generated from the divided heater 29 becomes radiant heat by the heat conducting case 32 and heats the object W to be processed. Further, the heat insulating material 31 suppresses the heat generated from the divided heater 29 from being taken away by the furnace wall when the workpiece W is heated. The heat conduction case 32 also has an effect of efficiently dissipating the heat on the object to be processed W side to the furnace wall side and efficiently controlling the temperature drop of the object to be processed W.

  A plurality of heater units 30 are arranged on the left side of the object to be processed W in the nitriding chamber 2 side by side in the front-rear and top-bottom directions with respect to the conveyance direction of the object to be processed. Are also arranged side by side in front and rear and top and bottom. In the present embodiment, each of the rectangular parallelepiped heater units 30 shown in FIGS. 3 and 4 includes three in the front-rear direction and three in the vertical direction on the left and right sides of the workpiece W, as shown in FIGS. Two are arranged in an orderly manner without a large gap between them. Each heater unit 30 on the left side and each heater unit 30 on the right side face each other substantially in parallel with the workpiece W interposed therebetween.

  As shown in FIG. 2, in the nitriding chamber 2, thermocouples 33 that measure the temperatures of the regions corresponding to the respective divided heaters 29 (the respective heater units 30) in the workpiece W are provided with the respective divided heaters. 29 is provided correspondingly. Each thermocouple 33 is disposed insulated from the furnace wall. In addition, each thermocouple 33 is close to the object to be processed up to a minimum distance (for example, about 5 to 20 mm) that is not affected by the discharge so that the temperature of each part of the object to be processed W can be measured as accurately as possible. Let them be arranged. Thereby, temperature measurement with sufficiently high accuracy can be performed for each part of the workpiece W, and temperature management of the workpiece can be accurately performed.

  Each thermocouple 33 is connected to a power controller 35 including a thyristor, a transistor, and the like via a temperature controller 34, and each power controller 35 is connected to each of the divided heaters 29. Each of the temperature regulators 34 and each of the power controllers 35 is a control unit 36 that individually controls the amount of heat generated by each of the divided heaters 29 so that the measured temperature of each thermocouple 33 becomes a preset target temperature. Function. That is, in order to control the measured temperature of each thermocouple 33 to a preset target temperature, each temperature regulator 34 supplies a control signal to each power controller 35, and each power controller 35 The electric power supplied to each divided heater 29 is adjusted.

  In the left and right heaters 26L and 26R, the pair of divided heaters facing each other with the workpiece W interposed therebetween may be controlled as being parallel to each other on the circuit.

  As shown in FIG. 2, an upper heat insulating material 37 closes the upper end of the left heater 26L (an assembly of six left heater units) and the right heater (an assembly of six right heater units). ing. An opening 38 is provided at the center of the upper heat insulating material 37, and a lid 39 that opens and closes the opening 38 is provided above the opening 38. The lid 39 is connected to a lid lifting mechanism 40 attached to the ceiling portion of the nitriding furnace 20, and moves up and down by the operation of the lid lifting mechanism 40. Thereby, the opening degree of the opening 38 is adjusted, and the temperature control of the object to be processed W (particularly, the center of the upper surface of the object to be processed W) is performed. However, in the present invention, since the amount of heat generated by each of the divided heaters 29 can be individually controlled, the temperature of the object to be processed can be sufficiently controlled without the temperature control by the opening 38.

  As shown in FIG. 1, at the time of nitriding, the inlet side heat insulation door 41 closes the gap between the inlet side ends of the left heater 26L and the right heater 26R. The entrance-side heat insulating door 41 moves up and down by the operation of an entrance-side door elevating mechanism (not shown). When the entrance-side heat insulating door 41 is in the lowered position, the inlets between the left and right heaters 26L, 26R are closed, and when the inlet-side heat insulating door 41 is in the raised position, between the left and right heaters 26L, 26R. The entrance is opened.

  Similarly, at the time of nitriding, the outlet side heat insulation door 42 also closes between the outlet side end portions of the left heater 26L and the right heater 26R. The outlet side heat insulating door 42 moves up and down by the operation of an outlet side door lifting mechanism (not shown). When the outlet side heat insulating door 42 is in the lowered position, the outlet between the left and right heaters 26L, 26R is closed, and when the outlet side heat insulating door 42 is in the raised position, between the left and right heaters 26L, 26R. The exit is opened.

  As shown in FIG. 2, at the upper part of the nitriding furnace 20, door accommodating portions 43a and 43b that allow the inlet side heat insulating door 41 and the outlet side heat insulating door 42 to rise are formed to protrude upward. ing.

  As shown in FIG. 2, the workpiece lifting mechanism 27 includes an electrode body 44 that supports the lower surface of the workpiece W and applies a voltage to the workpiece W, and the electrode body 44 is placed in the nitriding chamber. 2 is provided with an elevator 45 that moves up and down in 2 and an insulator 46 that insulates the electrode body 44 from the elevator 45.

  The electrode body 44 is disposed between the chain belts 25 in the nitriding chamber 2 and is disposed between the inlet-side heat insulating door 41 and the outlet-side heat insulating door 42 in a plan view (when viewed from above). It is installed. The electrode body 44 is formed in a frame shape or a lattice shape so that the processing gas is smoothly supplied also to the lower portion of the object to be processed W.

  Connected to the electrode body 44 is a cathode of a DC power supply 47 for plasma provided outside the nitriding chamber 1. On the other hand, the anode of the DC power supply 47 for plasma is connected to, for example, the furnace wall of the nitriding furnace 20. The cathode and the anode are insulated by the insulator 46 to prevent the occurrence of abnormal discharge such as voltage drop or arc discharge due to short circuit. When the object to be processed W, which is a conductor, is supported by the electrode body 44 and the insulator 46 and the electrode body 44 are raised by the elevator 45, the object to be processed W is lifted from the chain conveyor 25, and the electrode It will be in the state insulated from parts other than the body 44. FIG.

  The elevator 45 is supported by an elevator drive unit 48 provided below the nitriding furnace 20, an elevator support bar 49 provided so as to penetrate the bottom of the furnace body, and an upper end part of the elevator support bar 49. And an elevating plate 50. The electrode body 44 is supported on the elevating support plate 50 through the insulator 46.

  As shown in FIG. 1, the nitriding chamber 2 is connected to a nitriding chamber pressure reducing path 51 for depressurizing (evacuating) the inside of the nitriding chamber 2. The nitriding chamber decompression path 51 is connected to a decompression mechanism 52 including, for example, a vacuum pump or the like outside the nitriding chamber 1. Further, the nitriding chamber 2 is supplied with a nitriding chamber gas supply path 53 for supplying a hydrocarbon gas such as nitrogen gas, hydrogen gas, propane gas, ammonia gas or the like into the nitriding chamber 2 as a processing gas or a purge gas. And the nitriding chamber gas supply path 53 is connected to a nitriding chamber gas supply source 54. The nitriding chamber gas supply path 53 is provided with an open / close valve 55 for opening and closing the nitriding chamber gas supply path and a flow rate adjusting unit (mass flow controller) 56 for adjusting the supply amount of the nitriding chamber gas. In FIG. 1, only one nitriding chamber gas supply source 54 is shown for simplification, but actually, there are a plurality of gas supply sources in parallel with each other corresponding to the plurality of types of gases. The nitrogen gas supply path 53 is communicated.

  Next, the cooling chamber 3 will be described with reference to FIG. The cooling chamber 3 is defined inside the refrigerator 57. On the inlet side of the cooler 57, a carry-in port 58 for the workpiece W and a carry-in shutter 59 for opening and closing the carry-in port 58 are provided. The carry-in shutter 59 moves up and down in the second shutter chamber 5. On the outlet side of the cooler 57, a carry-out port 60 for the workpiece W and a carry-out shutter 61 for opening and closing the carry-out port 60 are provided.

  The cooling chamber 3 is provided with a chain conveyor 62 that conveys the workpiece W and a blower mechanism (blower fan) 63 that stirs the atmosphere in the cooling chamber 3. A number of cooling fins 64 for promoting heat exchange are provided on the inner wall of the cooling chamber 3. A cooling fluid passage 65 for circulating a cooling fluid is built in the furnace wall of the cooling chamber 57, and the cooling fluid passage 65 communicates with a cooling fluid source 65a.

  The cooling chamber 3 is connected to a cooling chamber decompression path 66 for decompressing (evacuating) the cooling chamber 3, and the cooling chamber decompression path 66 is connected to a decompression mechanism 67 including a vacuum pump and the like. Further, a cooling chamber gas supply path 68 for supplying, for example, nitrogen gas as a cooling gas or a purge gas to the cooling chamber 3 is connected to the cooling chamber 3, and the cooling chamber gas supply path 68 is supplied with a cooling gas supply. Connected to source 69.

  A roller conveyor 70 is disposed in the first shutter chamber 4 and the second shutter chamber 5. These roller conveyors 70, together with the chain conveyor 11 in the heating chamber 1, the chain conveyor 25 in the nitriding chamber 2, and the chain conveyor 62 in the cooling chamber 3, constitute a series of workpiece transfer mechanisms.

  The plasma nitriding apparatus is automatically controlled by a command from a control unit (not shown). The control unit includes, for example, a general-purpose computer, and performs control for automatically processing the object to be processed according to a predetermined processing program based on detection values of various detection sensors (not shown).

  Next, a processing method using the plasma nitriding apparatus will be described.

  After the entrance shutter 8 of the heating chamber 1 is opened and the workpiece W is carried into the heating chamber 1, the entrance shutter 8 is closed. Thereby, the heating chamber 1 is sealed. The workpiece W is transported by the chain conveyor 11 and stopped at a predetermined heating position in the heating chamber 1.

  When the heating chamber 1 is in a sealed state, the inside of the heating chamber 1 is decompressed to a substantially vacuum state by the operation of the decompression mechanism 17. Thereafter, nitrogen gas is supplied into the heating chamber 1 through the heating chamber gas supply path 18. Thereby, while oxidizing atmosphere is discharged | emitted from the inside of the heating chamber 1, the pressure in the heating chamber 1 becomes higher than a substantially vacuum state.

  In the heating chamber 1 in this state, the workpiece W is heated by the heat generated by the heating chamber heater 12. As described above, since the pressure in the heating chamber 1 is higher than the vacuum state, the heat from the heating chamber heater 12 is easily transmitted to the object to be processed W through the processing atmosphere, and the object to be processed is Heating of W can be performed efficiently. The temperature of the heating chamber 1 is controlled to a predetermined processing temperature (for example, about 500 ° C.) by adjusting the amount of heat generated by the heating chamber heater 12. In addition, the atmosphere in the heating chamber 1 is agitated by the air blowing mechanism 14, and the temperature distribution in the heating chamber 1 is made uniform. By such a process, the to-be-processed object W is heated to about 500 degreeC, for example.

  On the other hand, the inlet 21 and the outlet 23 are closed and sealed by the shutters 22 and 24, respectively, and the nitriding chamber 2 is brought into a reduced pressure state (for example, about 133.3 Pa) by the operation of the pressure reducing mechanism 52 of the nitriding chamber 1. . Further, the inside of the nitriding chamber 1 is purged with nitrogen gas through the nitriding chamber gas supply path 53. The temperature of the nitriding chamber 1 is raised to a predetermined temperature (for example, about 500 to 550 ° C.) by the heat generated by the nitriding chamber heater 26. The temperature control in the nitriding chamber 1 is performed by adjusting the heat generation amount of the nitriding chamber heater 26 and the flow rate of the cooling water in the coolant passage 28.

  When the heat treatment in the heating chamber 1 is completed, the decompression mechanism 17 of the heating chamber 1 is operated again, and the inside of the heating chamber 1 is decompressed to the same extent as the pressure of the nitriding chamber 2. Thereafter, the carry-out port 9 of the heating chamber 1 and the carry-in port 21 of the nitriding chamber 2 are opened, and the heating chamber 1 and the nitriding chamber 2 are communicated with each other via the first shutter chamber 4. In the nitriding chamber 2, the inlet side heat insulating door 41 is moved upward, and the inlets between the left and right heaters 26L, 26R are opened. At this time, the electrode body 44 is lowered to a position lower than the upper surface of the chain conveyor 25 in the nitriding chamber 2 by the operation of the elevating drive unit 48. Supply of voltage by the DC power supply 47 for plasma is stopped, and no discharge is generated.

  In such a state, the workpiece W is transported from the heating chamber 1 to the nitriding chamber 2 through the first shutter chamber 4, and the electrode body 44 is moved by the chain conveyor 25 in the nitriding chamber 2. It is stationary at the upper position. When the workpiece W is carried into the nitriding chamber 2, the carry-in port 21 of the nitriding chamber 2 is closed, and the inside of the nitriding chamber 2 is sealed again.

  Thereafter, a processing gas containing nitrogen gas (for example, a mixed fluid such as nitrogen gas, hydrogen gas, propane gas, and ammonia gas) is supplied into the nitriding chamber 2 through the nitriding chamber gas supply path 53. Thereby, the pressure in the nitriding chamber 2 is increased to a predetermined processing pressure (for example, about 400 to 1067 Pa).

  Further, in the nitriding chamber 2, the entrance-side heat insulating door 41 is closed, and the workpiece W on the chain conveyor 25 includes the left and right heaters 26L and 26R, the upper heat insulating material 37, the inlet-side heat insulating door 41, and the outlet. It will be in the state enclosed by the side heat insulation door 42. FIG. In this state, the elevating support rod 49 is raised by driving the elevating drive unit 48, and the elevating plate 50, the insulator 46, and the electrode body 44 are integrally raised. Thus, the workpiece W is pushed up from the chain conveyor 25 while being supported by the electrode plate 44, and is held at a predetermined nitriding height position indicated by a solid line in FIG.

  Thereafter, a voltage is applied by the plasma direct current power source 47, and nitriding is performed. That is, the electrode body 44 and the workpiece W serve as a cathode, the furnace body serves as an anode, glow discharge occurs between the two electrodes, and plasma is generated. The processing gas in the nitriding chamber 2 is ionized, and the ionized processing gas (nitrogen ions) collides with the workpiece W and enters the surface thereof. Thereby, an iron nitride layer is formed on the surface of the workpiece W.

  While the nitriding process is being performed, the processing temperature in the nitriding chamber 2 is the heat generated by the nitriding chamber heater 26, the heating by glow discharge (the heat generated by the ionized processing gas colliding with the workpiece W), and the cooling liquid. By controlling the flow rate, temperature, and the like of the cooling water in the passage 28, for example, a predetermined temperature of about 500 to 550 ° C. is maintained.

  In the present embodiment, each of the left heater 26L and the right heater 26R is divided into a plurality of front and rear and top and bottom in the transport direction, and each divided heater 29 (each heater unit 30 in the workpiece W). ) Is measured by the thermocouple 33. And each said control part 36 controls the emitted-heat amount of each said division | segmentation heater 29 separately so that the measured temperature may become the preset target temperature. Thereby, the whole to-be-processed object W is maintained at target temperature or the temperature close | similar to it at the time of nitriding. Therefore, uniform nitriding treatment can be efficiently performed on the entire workpiece W.

  In general, in the plasma nitriding process, when the object to be processed is heated by glow discharge, the temperature of the central part or the upper part of the object to be processed is more likely to rise than the peripheral part of the object to be processed due to self-heating of the object to be processed. In contrast, in the present embodiment, the amount of heat generated from the divided heater 29 (heater unit 30) corresponding to the peripheral region of the workpiece W is controlled to be relatively large. The amount of heat generated from the divided heater 29 (heater unit) corresponding to the central region of W (the central region in the front-rear direction and the central region in the left-right direction) is controlled to be relatively small. In addition, the upper divided heater of the workpiece W is controlled so that the amount of heat generated is smaller than that of the lower divided heater. As a result, the entire workpiece W converges to a preset target temperature. Since there are no heaters before and after the workpiece W, these regions are heated by the front and rear divided heaters 29 (heater units) of the heaters 26L and 26R on the left and right sides. Therefore, it is preferable that the number of divisions in the front-rear direction of the left and right heaters 26L, 26R is at least three in the front, middle, and rear. Also, the number of heater divisions in the vertical direction is preferably 2 or more.

  In the illustrated example, the left and right heaters 26L and 26R are each composed of six divided heaters 29 (heater units 30). However, if the number of heater divisions is increased, finer control is possible. . As described above, if the heater is not divided as described above, sufficient temperature control cannot be performed in the plasma nitriding process.

  In the present embodiment, the nitriding chamber heaters 26 are disposed only on the left and right sides of the nitriding chamber 2 in the conveying direction of the workpiece W, so that the nitriding chamber heater 26 does not interfere with the conveyance of the workpiece W.

  In the present embodiment, the nitriding chamber 2 is defined by a furnace wall having a coolant passage 28, and a heat insulating material 31 is disposed on the furnace wall side of each divided heater 29. Each of the heat insulating materials 31 is covered with a common heat conduction case 32 to form a heater unit 30. With this configuration, the heat generated from the divided heater 29 is radiated by the heat conduction case 32 to heat the workpiece W. Therefore, the workpiece W is uniformly heated over a wide range by each divided heater 29.

  Since the heat insulating material 31 is disposed between the divided heater 29 and the furnace wall, the heat generated from the divided heater 29 is prevented from being taken away by the furnace wall, and the heating efficiency is high. In addition, when the temperature rises excessively in a certain area of the workpiece W, the amount of heat generated by the divided heater 29 corresponding to that area is automatically controlled to drop. Since heat dissipation to the furnace wall side is promoted, the temperature drop speed of the workpiece W is high. Therefore, the temperature control of the workpiece W can be performed quickly.

  Further, the central portion of the upper portion of the object to be processed W whose temperature is likely to rise can be controlled by operating the lid lifting mechanism 40 and adjusting the opening of the opening 38 of the upper heat insulating material 37. it can.

  As described above, since the plasma nitriding process is performed at a temperature of about 500 ° C. and under reduced pressure, the heating by the radiant heat of the heater and the heat conduction by the gas are not large, that is, the heat is not easily transmitted to the object to be processed. It is in a very difficult state to control. Further, the object to be processed self-heats due to glow discharge, which also adds to the difficulty of temperature control. Therefore, in the past, it has been difficult to suppress temperature variation due to the location of a single object to be processed and to accurately control temperature, but the configuration of this embodiment dramatically improves the accuracy of temperature control. It was possible to improve the temperature variation significantly.

  Further, in the plasma nitriding method, heat is generated by collision of ionized gas with the surface of the object to be processed, so that the temperature of the object to be processed does not increase unless the object to be processed has a certain amount or more. . However, if the size of the object to be processed is increased by enlarging the set of objects to be processed, the temperature difference between the vicinity of the center of the object to be processed and the peripheral part will become larger. In contrast, according to the present system in which the nitriding chamber heater 26 is used in combination, a number of divided heaters 29 are used as the nitriding chamber heater 26, and the amount of heat generated is controlled for each divided heater 29, the size of the workpiece W can be increased. Regardless of the package shape, the entire workpiece can always be nitrided at a uniform temperature, that is, with as little variation in temperature between the workpieces as possible. It was possible to suppress the variation of.

  According to the tests by the inventors of the present invention, the temperatures of various regions of the object to be processed W during the nitriding process in the nitriding chamber 2 (for example, nine temperature measurement locations) When the target temperature is set to 520 ° C., it is within a variation range of about 15 ° C. above and below the target temperature at the beginning of the nitriding process (about 30 ° C. in total), and about 7 each above and below the target temperature as the nitriding time elapses. It converged within a variation range of about -8 ° C (about 15 ° C in total). According to the literature (“Ion nitriding method”, Hishiko Yamanaka chopsticks, published by Nikkan Kogyo Shimbun Co., Ltd.), the temperature difference of each part of the object to be processed during ion nitriding is due to the fact that the object itself generates heat. There are cases where the temperature is around 100 ° C. between the vicinity and the portion close to the furnace wall. Compared with this, it will be understood that the temperature uniformizing effect of the workpiece W according to the present embodiment is remarkable.

  In addition, the temperature variation was also investigated for commercially available furnaces, but the temperature variation was the best, and it was about 25 ° C. (total 50 ° C.) with respect to the target temperature even when the nitriding time was stable. This is significantly different from about 7-8 ° C. (15 ° C. in total) of the present application. This furnace is a vertical mold with a heater, and has the same structure as that of Patent Document 2.

  Further, according to the temperature control of the present invention, mass production or automation of plasma nitriding, which has been difficult in the past, can be performed, and a stable product can be supplied in large quantities.

  When the nitriding process in the nitriding chamber 2 is completed as described above, the supply of voltage by the plasma DC power supply 47 is stopped, and the glow discharge is stopped. Further, the workpiece W is returned onto the chain conveyor 25 by the driving of the elevating drive unit 48. Thereafter, the outlet side heat insulating wall 42 is raised, and the outlet sides of the left and right heaters 26L, 26R are opened. Further, the carry-out port 23 of the nitriding chamber 2 is opened, and the workpiece W is transferred from the nitriding chamber 2 to the cooling chamber 3 through the second shutter chamber 5.

  When the nitriding chamber 2 and the cooling chamber 3 are communicated with each other, the inside of the cooling chamber 3 is preferably purged with nitrogen gas. Thereby, it is possible to prevent the oxidizing atmosphere from flowing from the cooling chamber 3 to the nitriding chamber 2. The purging of the cooling chamber 3 can be performed by depressurizing the cooling chamber 3 by operating the decompression mechanism 67 and supplying nitrogen gas through the cooling chamber gas supply path 68.

  In the cooling chamber 3, the indoor atmosphere is cooled by the cooling water supplied to the coolant passage 65, and the cooling of the workpiece W is promoted by the cooling fins 64. In addition, the atmosphere in the cooling chamber 3 is agitated by the blower mechanism 63, the temperature distribution in the cooling chamber 3 is made uniform, and cooling can be performed quickly. By such a cooling process, the object to be processed is lowered, for example, from about 500 to 550 ° C. to about 100 to 150 ° C.

  When the cooling process is completed, the carry-out port 60 is opened, and the workpiece W is carried out from the cooling chamber 3. As described above, a series of processing steps in the plasma nitriding system is completed.

1 is a schematic plan view in which a part of a plasma nitriding apparatus according to an embodiment of the present invention is a horizontal section. It is II-II arrow sectional drawing of FIG. It is a front view of a division | segmentation heater. FIG. 4 is a cross-sectional view taken along arrow IV-IV in FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating chamber 2 Nitriding chamber 3 Cooling chamber 26 Nitriding chamber heater 26L Left side heater 26R Right side heater 28 Coolant passage 29 Split heater 31 Heat insulating material 32 Heat conduction case 33 Thermocouple (thermometer)
36 Control unit (heat generation control unit)

Claims (7)

  A plasma nitriding apparatus for plasma nitriding a target object (W), comprising a nitriding chamber heater (26) for heating the target object (W) in the nitriding chamber (2), the nitriding chamber heater (26) ) Are arranged on both the left and right sides in the transfer direction of the object to be processed (W) in the nitriding chamber (2), and the nitriding chamber heater (26) is divided into a plurality of heaters before and after the transfer direction and vertically. A thermocouple (33) that measures the temperature of the object to be processed (W), and a controller (36) that individually controls the amount of heat generated by each of the divided heaters (29), A plasma nitriding treatment apparatus comprising:   The nitriding chamber (2) is defined by a furnace wall having a coolant passage (28), a heat insulating material (31) is disposed on the furnace wall side of each divided heater (29), and each divided heater ( 29. The plasma nitriding apparatus according to claim 1, wherein 29) and each of the heat insulating materials (31) are covered with a common heat conduction case (32).   The said to-be-processed object (W) is conveyed in order of a heating chamber (1), the said nitriding chamber (2), and a cooling chamber (3), and is plasma-nitrided in the said nitriding chamber (2). Plasma nitriding equipment.   In the nitriding chamber heater (26), each of the left side heater (26L) and the right side heater (26R) has a divided heater (29) divided into a plurality of front and rear and top and bottom in the transport direction. 4. The plasma nitriding apparatus according to 3.   The thermocouple (33) is a plurality of thermocouples (33) for measuring the temperature of the workpiece (W) in a region corresponding to each of the divided heaters (29). The plasma nitriding apparatus according to item.   The thermocouple (33) is insulated from the furnace wall, and the thermocouple (33) is disposed close to the object to be processed (W) to a minimum distance that is not affected by discharge with the object to be processed (W). The plasma nitriding apparatus according to claim 1, wherein the temperature in the vicinity of the object to be processed (W) is measured.   A continuous plasma nitriding method for performing a plasma nitriding process by continuously transferring an object to be processed (W) to a nitriding chamber (2), wherein the object to be processed (W) is formed in the nitriding chamber (2). The nitriding chamber heaters (26) provided on both the left and right sides in the transport direction are divided into a plurality of front and rear and top and bottom in the transport direction, and the temperatures of the regions corresponding to the divided heaters (29) in the workpiece (W) are measured. A continuous plasma nitriding method in which nitriding is performed by individually controlling the amount of heat generated by each of the divided heaters (29) so that all of the region of the object to be processed (W) reaches a target temperature.

Images