JP2018104723A - Plasma nitriding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a scattering of nitride layer thickness of work-pieces using a plasma nitriding apparatus of a simple structure, because there is a difference of nitride layer thickness between work-pieces located in the central part of a furnace and work-pieces located in the upper part and the lower part of the furnace in a conventional plasma nitriding apparatus.SOLUTION: A plasma nitriding apparatus 1 for nitriding work-pieces W having a furnace body 1a serving as an anode and the work-pieces W serving as a cathode includes a jig 2 which is electrically connected to a power source 8 so as to serve as the cathode and on which the work-pieces W are mounted, and an auxiliary heating member 9 with electric conductivity that is arranged between the jig 2 and the ceiling part 1b of the furnace body 1a and electrically connected to the power source 8 so as to serve as the cathode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plasma nitriding apparatus for performing a plasma nitriding process on automobile parts, other machine parts, etc. (hereinafter “work”).

  Conventionally, it is known to perform nitriding as a hard processing method for increasing the hardness of a workpiece. Although there are processing methods such as gas nitriding and plasma nitriding as work nitriding methods, plasma nitriding apparatuses such as Patent Document 1 and Patent Document 2 are used when performing plasma nitriding. Nitriding using a plasma nitriding apparatus is performed by heating a work housed in a furnace to a predetermined temperature and then converting the processing gas for nitriding to plasma. Usually, the workpiece in the plasma nitriding apparatus is heated to the target nitriding temperature by self-heating of the workpiece by glow discharge or by heating using a heater in addition to self-heating.

Japanese Patent Laid-Open No. 9-3646 JP 2005-2444 A

  When the inside of the furnace of the plasma nitriding apparatus is divided into three in the height direction and these are called the upper part of the furnace, the central part of the furnace, and the lower part of the furnace, heat is accumulated in the central part of the furnace in the conventional plasma nitriding apparatus. It was easy and the center part in the furnace was hotter than the upper part in the furnace and the lower part in the furnace. As a result, the nitride layer thickness varies between the workpiece located in the center of the furnace and the workpiece located in the upper and lower parts of the furnace.

  On the other hand, it is also conceivable to use the heater provided in the furnace to heat the upper part and the lower part of the furnace whose temperature is relatively lower than the central part of the furnace. However, the location where the heat accumulation occurs varies depending on the shape and number of workpieces housed in the furnace and the method of arranging the workpieces on the jig. For example, even when the same plasma nitriding equipment is used, when different types of workpieces are nitrided, the jig suitable for the workpiece depends on the shape of the workpiece and the number of workpieces processed per lot. The shape may change. In such a case, the temperature distribution in the furnace is different from the temperature distribution of the nitriding treatment of the previous lot. That is, the position of the heat reservoir in the furnace can be changed for each type. Therefore, in order to eliminate the temperature difference in the furnace, even if only the low temperature part is heated with the heater, the heater wire arrangement must be changed to the optimum one for each processing lot, and the work load is reduced. Become very large.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress a nitride layer variation of a workpiece with a plasma nitriding apparatus having a simple configuration.

  The present invention that solves the above-mentioned problems is a plasma nitriding apparatus that performs nitriding of a workpiece using a furnace body as an anode and a workpiece as a cathode, and is electrically connected to a power source so that the workpiece is placed and becomes a cathode And a conductive auxiliary heating member that is disposed between the jig and the ceiling of the furnace body and is electrically connected to the power source so as to serve as a cathode. It is characterized by that.

  The “subsidiary heating member having conductivity” in the present invention only needs to have conductivity that can function as a heat source by self-heating by glow discharge.

  The variation of the nitrided layer of the workpiece can be suppressed with a plasma nitriding apparatus having a simple configuration.

1 is a diagram showing a schematic configuration of a plasma nitriding apparatus according to an embodiment of the present invention. It is a figure which shows the jig | tool shape of the plasma nitriding apparatus which concerns on embodiment of this invention. It is a figure which shows the arrangement | positioning state of the workpiece | work mounted on the jig | tool based on embodiment of this invention. It is a figure which shows schematic structure of the plasma nitriding apparatus of a comparative example.

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

  The plasma nitriding apparatus 1 according to this embodiment shown in FIG. 1 is a so-called vertical plasma nitriding apparatus in which the length of the furnace body 1a is long in the height direction. The plasma nitriding apparatus 1 has a cylindrical furnace body 1 a, a jig 2 on which a workpiece W is placed, a cathode base 3 on which the jig 2 is placed, and a support member 4 that supports the jig 2 and the cathode stage 3. It has. The furnace shape of the plasma nitriding apparatus 1 is not particularly limited.

  The jig 2 is a multistage jig on which workpieces W are placed in a layered manner, and each stage of the jig 2 is a conductive member in which a notch 5a is provided in a part of the outer periphery as shown in FIG. It is comprised with the disk 5 which consists of (SUS304, SS400 etc.). In the present embodiment, the shapes of the disks 5 constituting each step of the jig 2 are substantially the same. A processing gas passage port 5b through which a processing gas for nitriding supplied in the furnace passes is formed at the center of the disk 5. Due to the presence of the processing gas passage port 5b, the processing gas easily spreads to each workpiece W, and the effect of suppressing variation in the nitriding quality of the workpiece W is enhanced.

  Further, the disc 5 is provided with three openings 5c formed on the same circumference. A circular column member 7 made of a conductive member (SUS304, SS400, etc.) extending in the height direction from the bottom plate 6 at the lower end of the jig is passed through each opening 5c. 5 is fixed to the support member 7. Work pieces W are arranged on each stage of the jig 2 as shown in FIG. Further, the column member 7 is electrically connected to the cathode table 3 through the bottom plate 6. Note that the shape of the jig 2 is appropriately changed depending on the shape and number of the workpieces W, the arrangement method of the workpieces W on the jig, and the like. Further, the shape of the support member 4 is not limited to a circular shape.

  The cathode stage 3 on which the jig 2 is mounted is connected to a glow discharge power source 8 provided outside the furnace so as to become a cathode when energized. The bottom plate 6 at the lower end of the jig is in contact with the cathode base 3, whereby the jig 2 is electrically connected to the glow discharge power source 8 via the cathode base 3. On the other hand, an auxiliary heating member 9 that assists heating of the workpiece W is attached to the upper end portion of the jig. The auxiliary heating member 9 is, for example, one circular iron-based member made of SUS304, SS400 or the like which is an example of a metal member. The auxiliary heating member 9 has such a diameter that each workpiece W placed on the jig 2 is hidden in a plan view as shown in FIG. In FIG. 3, only the outline of the auxiliary heating member 9 is indicated by a two-dot chain line, and the specific shape is not shown. The auxiliary heating member 9 having such a shape is fixed at the tip portions of the three support members 7 as shown in FIG. As described above, since the column member 7 is electrically connected to the cathode base 3, the auxiliary heating member 9 attached to the tip of the column member 7 is also electrically connected to the glow discharge power source 8 via the cathode table 3. Is in a state of being connected to. That is, the auxiliary heating member 9 also becomes a cathode when energized. The furnace body 1a is connected to a glow discharge power source 8 so as to become an anode when energized.

  The auxiliary heating member 9 at the upper end of the jig, the bottom plate 6 at the lower end of the jig, and the disk 5 at each stage of the jig are connected via the column member 7 so that the members of the jig 2 are integrated. Move. When carrying in such a jig | tool 2 in a furnace, the auxiliary | assistant heating member part of the jig | tool 2 in the state in which the workpiece | work W was mounted is lifted with a crane etc., and the inlet provided in the side of the furnace body 1a is provided. The jig 2 is carried into the furnace from (not shown) and placed on the cathode table 3.

  The distance between the auxiliary heating member 9 and the uppermost stage of the jig is appropriately changed according to the amount of heat generated by the auxiliary heating member 9, but it is desirable that the distance be the same as the interval between the stages of the jig 2. Thereby, the plasma conditions of the workpieces W arranged in each stage are constant, and variations in the nitriding quality of the workpieces W are suppressed. Note that “same” in the above “same interval” does not mean strictly the same, but includes substantially the same concept. For example, a difference of about several millimeters that occurs when manufacturing the plasma nitriding apparatus 1 is allowed as “the same interval”. In the present embodiment, the auxiliary heating member 9 is formed in a disc shape, but the shape of the auxiliary heating member 9 is appropriately changed depending on the shape and number of the workpieces W, the arrangement method of the workpieces W on the jig, and the like. The Further, the number of auxiliary heating members 9 is not particularly limited, and for example, a plurality of auxiliary heating members 9 may be provided on the same plane. However, when the jig 2 is divided into three parts in the height direction, and these are referred to as a jig upper step, a jig middle step, and a jig lower step, the auxiliary heating of the jig upper step is more effectively performed. The auxiliary heating member 9 is preferably formed so as to cover the jig 2 so that the workpieces W placed on the jig 2 are not exposed in plan view.

  A heater 10 for accelerating the temperature rise of the workpiece W is arranged in a cylindrical shape along the inner wall of the furnace body 1a on the side of the jig 2 placed on the cathode table 3. The heater 10 has a height that matches the overall height of the jig 2. An upper thermocouple 11, a center thermocouple 12, and a lower thermocouple 13 are provided in the vicinity of the upper portion, the center portion, and the lower portion of the heater 10, respectively. The thermocouples 11, 12, and 13 are provided with thermocouple holding columns 14. It is fixed to. The upper thermocouple 11 is configured to control the approximate temperature of the upper stage of the jig, the central thermocouple 12 is configured to control the approximate temperature of the middle stage of the jig, and the lower thermocouple 13 is controlled to the approximate lower temperature of the lower stage of the jig. Even if these thermocouples 11, 12, 13 are provided, the wire arrangement of the heaters 10 in each processing lot is the same arrangement, so the heat caused by the difference in the shape of the jig 2 etc. It is not easy to intensively heat a portion having a low temperature in accordance with the change in the accumulation location.

  The plasma nitriding apparatus 1 according to the present embodiment is configured as described above. Although explanation is omitted, the plasma nitriding apparatus 1 has a necessary configuration as a plasma nitriding apparatus such as a supply pipe and an exhaust pipe of a processing gas for nitriding treatment.

  When plasma nitriding is performed with this plasma nitriding apparatus 1, heat tends to be accumulated in the middle part of the jig, but in the plasma nitriding apparatus 1 of the present embodiment, the auxiliary heating member 9, the column member 7 and the bottom plate 6 are Since it is in a state of being electrically connected to the glow discharge power source 8 via the cathode base 3, electricity flows through the auxiliary heating member 9 and self-heats by glow discharge. As a result, a heat source is generated at the upper end of the jig 2, and the upper part of the jig whose temperature is relatively lower than that of the middle part of the jig is heated. As the temperature of the upper stage part of the jig increases, the temperature difference between the upper stage part of the jig and the middle stage part of the jig and the lower stage part of the jig increases, and heat easily moves to the lower stage part of the jig. As a result, the temperature of the lower part of the jig also becomes higher than before.

  By performing the plasma nitriding process in such a state, it is possible to suppress variations in the nitride layer thickness of the workpieces W arranged on the jig upper stage, the jig middle stage, and the jig lower stage. In other words, it is possible to suppress variations in nitriding quality within the same lot.

  Further, in the plasma nitriding apparatus 1 of the present embodiment, the auxiliary heating member 9 functions as a heat source by self-heating by glow discharge when heating the upper jig part, so that dedicated heating for heating the upper jig part is performed. There is no need to provide a mechanism. That is, according to the plasma nitriding apparatus 1 of the present embodiment, it is possible to suppress variations in the nitride layer thickness of the workpieces W arranged in each stage without complicating the apparatus structure.

  Further, normally, since covering the upper portion of the jig 2 may cause the flow of the raw material gas to be not uniform, a member that is likely to interfere with the gas flow is not provided above the jig 2. Even if a member that covers the upper side of the jig 2 is provided, a member used for a common purpose in different processing lots is not attached to each jig to reduce the number of parts, but as a component of the furnace. It is common to attach to the furnace shell. However, when such a member is fixedly supported on the furnace shell, the member acts as an anode, and arc discharge occurs when the anode and the cathode (for example, the uppermost stage of the jig) are close to each other. As described above, there is common technical knowledge that a member that normally covers the upper side of the jig 2 is not provided. However, in the present embodiment, the auxiliary heating member 9 that covers the upper side of the jig 2 is provided. The plasma nitriding apparatus 1 is configured so that becomes a cathode. Thereby, the disk 5 and the auxiliary heating member 9 constituting the uppermost stage of the jig 2 become the cathode when energized, and the upper stage of the jig can be heated in a state where arc discharge hardly occurs.

  In this embodiment, an iron-based member is used as the auxiliary heating member 9, but other members may be used as long as they are conductive members. However, for example, when a member such as a copper plate is used, the copper component of the copper plate during the plasma treatment may be mixed into the workpiece W, and the quality as the nitriding member may be deteriorated. It is preferable to use a system member. The auxiliary heating member 9 is not limited to a plate-like member. In addition, although it is not essential to provide the heater 10, it is preferable to provide the heater 10 in order to promote the temperature rise of the workpiece W and shorten the processing time.

  Further, in the present embodiment, the auxiliary heating member has been described by taking the vertical plasma nitriding apparatus 1 as an example. However, even in the case of the horizontal plasma nitriding apparatus 1 in which the length of the furnace body 1a is long in the horizontal direction, auxiliary heating is performed. A member 9 can be provided. Further, in the present embodiment, the multi-stage jig 2 capable of placing the workpieces W in a hierarchical manner is used, but the jig 2 may not be multi-stage. For example, in the state where a workpiece is placed on the jig 2, when one workpiece has a height that reaches from the lower part in the furnace to the upper part in the furnace, in the conventional plasma nitriding apparatus, the temperature of the central part in the furnace Is higher than the temperature in the furnace upper part and the furnace lower part, the variation of the nitride layer thickness increases between the work center part and the work upper part and work lower part. On the other hand, according to the plasma nitriding apparatus 1 as in the present embodiment, the auxiliary heating member provided at the upper end of the jig functions as a heat source even when nitriding such a workpiece. The temperature can be increased. As a result, it is possible to reduce the nitride layer variation between the work center and the work upper part and work lower part.

  That is, the jig 2 on which the workpiece W is placed is electrically connected to a power source so as to be a cathode, and the auxiliary heating member 9 having conductivity is disposed between the jig 2 and the ceiling portion 1b of the furnace body 1a. If the plasma nitriding apparatus 1 is configured to be electrically connected to a power source so that the auxiliary heating member 9 becomes a cathode, the temperature of the work W located in the upper part of the furnace can be raised, It becomes possible to suppress variations in the nitrided layer thickness of the workpiece W located at the upper part, the central part in the furnace, and the lower part in the furnace.

  As mentioned above, although 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.

  Plasma nitriding of a plurality of automobile gears was performed using the plasma nitriding apparatus according to the present invention. The plasma nitriding apparatus according to the present invention is a furnace configured as shown in FIG. More specifically, the jig 2 is a multi-stage jig on which the workpieces W are placed in a hierarchy, and the disks 5 constituting each stage of the jig 2 are formed of SS400. Each disk 5 is fixed to a column member 7 extending in the height direction from the bottom plate 6 at the lower end of the jig. The support member 7 is formed of SS400, and the support member 7 is electrically connected to the cathode base 3 through the bottom plate 6. The cathode stage 3 on which the jig 2 is mounted is connected to a glow discharge power source 8 provided outside the furnace so as to become a cathode when energized. The bottom plate 6 at the lower end of the jig is in contact with the cathode base 3, whereby the jig 2 is electrically connected to the glow discharge power source 8 via the cathode base 3. A heater 10 is disposed along the inner wall of the furnace body 1a on the side of the jig 2 placed on the cathode base 3.

  An auxiliary heating member 9 made of SS400 is attached to the upper end portion of the column member 7. That is, the auxiliary heating member 9 is disposed between the uppermost stage of the jig and the ceiling portion 1b of the furnace body 1a. The auxiliary heating member 9 is a single iron-based member having a circular shape, and has a shape that covers the jig 2 so that the workpieces W placed on the jig 2 are not exposed in plan view. Further, the distance between the auxiliary heating member 9 and the uppermost stage of the jig is the same as the distance between the stages of the jig 2.

  In the plasma nitriding apparatus 1 having such a configuration, since the conductive auxiliary heating member 9 is electrically connected to the glow discharge power source 8 via the conductive support member 7 and the cathode base 3, Sometimes it becomes the cathode. The furnace body 1a is connected to a glow discharge power source 8 so as to become an anode when energized.

  The plasma nitriding apparatus according to the present invention as an embodiment is configured as described above. The plasma processing conditions using this plasma nitriding apparatus are the same as in the prior art, and after passing through the exhaust process and the decompression process, the furnace pressure is 180-600 Pa and the glow current density is 1.0-1.0 in the temperature raising process and the nitriding process. Adjustment was made within the range of 2.6 A / m2. Moreover, as atmosphere gas in a furnace, nitrogen and hydrogen gas were supplied, and the flow rate ratio of these gases was set to be nitrogen: hydrogen = 2: 1. Furthermore, the control temperature of the heater provided so as to correspond to the upper part of the jig, the middle part of the jig, and the lower part of the jig is set to 520 ° C., and the temperatures obtained from the upper stage thermocouple, middle stage thermocouple, and lower stage thermocouple are set. Based on the temperature control.

  Further, for comparison with the plasma nitriding apparatus according to the present invention, the plasma nitriding process of the gear is performed under the same plasma processing conditions using the plasma nitriding apparatus 50 provided with no auxiliary heating member as shown in FIG. did. The conventional plasma nitriding apparatus 50 has the same configuration as that of the plasma nitriding apparatus according to the present invention except that no auxiliary heating member is provided. The arrangement of the gears mounted on each stage of the jig is the same arrangement.

  After carrying out the plasma nitriding treatment of the gears, the gears were extracted one by one from the upper part of the jig, the middle part of the jig, and the lower part of the jig. The gears extracted from each stage are gears that are arranged at the same position in plan view. Thereafter, the tooth of each extracted gear was cut perpendicularly to the tooth surface, the cut surface of the cut tooth was mirror-polished, and the cut surface was observed with an optical microscope at a magnification of 400 times. Based on the image information thus obtained, the nitrided layer thickness at the tooth surface portion of the gear was measured. The measurement results of the nitride layer thickness are as shown in Tables 1 and 2 below.

  In the conventional plasma nitriding apparatus, there is a difference of 1.5 μm in the nitride layer thickness between the gear in the middle part of the jig with the thickest nitride layer thickness and the gear in the upper part of the jig with the smallest nitride layer thickness. occured. On the other hand, in the plasma nitriding apparatus according to the present invention, there was only a difference of 0.9 μm between the gear at the upper part of the jig and the gear at the middle part of the jig. That is, by providing the auxiliary heating member at the upper end of the jig, the variation in the nitrided layer thickness of the nitrided product could be reduced.

  The present invention can be applied to plasma nitriding treatment of a workpiece.

DESCRIPTION OF SYMBOLS 1 Plasma nitriding apparatus 1a Furnace body 1b Top part 2 of furnace body 3 Jig 3 Cathode stand 4 Support member 5 Disc 5a Notch 5b Process gas passage port 5c Opening 6 Bottom plate 7 Strut member 8 Glow discharge power source 9 Auxiliary heating member DESCRIPTION OF SYMBOLS 10 Heater 11 Upper thermocouple 12 Center thermocouple 13 Lower thermocouple 14 Thermocouple holding column 50 Conventional plasma nitriding apparatus W Workpiece

Claims (5)

A plasma nitriding apparatus for performing nitriding treatment of the workpiece using a furnace body as an anode and a workpiece as a cathode,
A jig on which the workpiece is placed and electrically connected to a power source to become a cathode;
A plasma nitriding apparatus comprising: a conductive auxiliary heating member that is disposed between the jig and the ceiling of the furnace body and is electrically connected to the power source so as to serve as a cathode. The jig is a multi-stage jig on which the workpiece is placed in a hierarchy, and has a support member extending in the height direction from the lower end of the jig,
The plasma nitriding apparatus according to claim 1, wherein the auxiliary heating member is attached to an upper end portion of the support member.   The plasma nitriding apparatus according to claim 2, wherein a distance between the auxiliary heating member and the uppermost stage of the jig is the same as an interval between the stages of the jig.   The plasma according to any one of claims 1 to 3, wherein the auxiliary heating member is formed so as to cover the jig so that the workpiece placed on the jig is not exposed in a plan view. Nitriding equipment.   The plasma nitriding apparatus according to any one of claims 1 to 4, wherein the auxiliary heating member is an iron-based member.

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