JP4773932B2 - Manufacturing method of spark plug - Google Patents

Description

  The present invention relates to a method for manufacturing a spark plug used for ignition of an internal combustion engine, and more particularly to a method for manufacturing an insulator constituting the spark plug.

  In general, in a spark plug used for an internal combustion engine such as an automobile engine, a long insulator is held in a state of being inserted into a cylindrical metal shell, and is formed on the insulator. A center electrode that forms a spark discharge gap facing the ground electrode welded to the front end side of the metal shell and a terminal electrode that applies a high voltage to the center electrode are inserted into the shaft hole.

  Such an insulator is formed by press-molding the prepared raw material powder, forming a molded body having a hole to be a shaft hole, and grinding the outer surface of the obtained molded body to have a predetermined insulator shape. Then, it is manufactured by firing.

In the conventional grinding process for grinding the molded body, as shown in FIG. 11, the molded body 50 is supported in a state where the insertion pin P5 is inserted from the rear end side of the hole formed along the axial direction. It is rotated in a direction indicated by an arrow F5 in FIG. On the other hand, the grinding rotary roller (rotary grindstone) 55 for grinding the molded body 50 has a peripheral surface 55a formed in a shape corresponding to the outer shape of the insulator, and is in the same direction as the arrow F5 by a rotation mechanism (not shown). Is rotated in the direction indicated by the arrow F6 in FIG. Then, by bringing the molded body 50 into contact with the peripheral surface 55a of the rotating grinding roller 55 for grinding, the outer shape of the molded body 50 is ground into a shape corresponding to the insulator (see, for example, Patent Document 1).
JP 2001-176737 A

  In recent years, spark plugs have tended to be downsized and reduced in diameter due to the increase in the area occupied by intake and exhaust valves in the combustion chamber accompanying the increase in the output of internal combustion engines. It is requested.

  However, with regard to the insulator, it is necessary to ensure the clearance between the metal shell provided to prevent side fire and the predetermined electric resistance, so even if the material is highly insulating. There is a limit to reducing the thickness from the outer peripheral surface to the shaft hole. As a result, the influence of the diameter reduction of the insulator appears as the diameter reduction of the shaft hole.

  For this reason, when the molded body is ground in the insulator manufacturing process, a relatively small diameter insertion pin to be inserted into the hole of the molded body must be employed. As a result, the insertion pin bends due to the frictional force that the molded body receives from the rotating grinding roller, causing eccentricity (decrease in coaxiality) and hole misalignment on the tip side of the molded body to be ground. There is a risk that.

  Such a problem is more likely to appear more remarkably in recent years because the longer the spark plug that is being lengthened, the longer the insulator.

  The present invention has been made in view of the above circumstances, and the purpose thereof is to form a molded body having a hole portion to be a shaft hole of the insulator with a raw material powder in manufacturing the insulator. An object of the present invention is to provide a spark plug manufacturing method capable of suppressing the eccentricity of the molded body and the axial displacement of the hole that occur when the molded body is ground into an insulator shape.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

Configuration 1. The manufacturing method of the spark plug of this configuration is as follows:
A molding step of molding the raw material powder into a molded body having a hole to be a shaft hole;
A predetermined insertion pin is inserted into the hole of the molded body to rotatably support the molded body, and the molded body is brought into contact with a rotating rotating roller for grinding, and a pressing means is brought into contact with the molded body. A grinding step of supporting the molded body against the frictional force received from the grinding roller and grinding the outer peripheral surface of the molded body;
Through a firing step of firing the ground compact,
A method of manufacturing a spark plug including an insulator formed by inserting and fixing a center electrode and a terminal electrode, wherein the hole portion is a shaft hole,
The grinding step includes
The position where at least one pressing means comes into contact with the molded body from the position where the rotating roller for grinding comes into contact with the molded body is 180 ° in the rotation direction of the molded body around the insertion pin. The position is shifted by a predetermined angle which is largely smaller than 270 °.

  In other words, the rotation direction of the molded body with the insertion pin as the axis from the position where the at least one pressing means contacts the molded body from the position where the grinding rotary roller contacts the molded body. The position is shifted by a predetermined angle larger than 90 ° and smaller than 180 ° in the opposite direction.

  At the time of grinding, a dynamic frictional force is applied in the tangential direction at the contact point with the grinding rotary roller, and a reaction force of the force pressing the compact against the grinding rotary roller is applied in the normal direction. However, when the grinding rotary roller and at least one pressing means are brought into contact with the molded body in the above positional relationship as in the configuration 1, the dynamic frictional force in the contact direction and the reaction force in the normal direction are caused by at least one pressing means. Grinding can be performed in a state where the molded body is supported against the above.

  Therefore, according to the above configuration 1, when the molded body is ground, even if a relatively small diameter insertion pin is inserted into the hole of the molded body, the molded body is formed from the rotating rotating roller for grinding. Generation | occurrence | production of the malfunction that an insertion pin will bend by the frictional force etc. which a body receives can be suppressed. As a result, it is possible to suppress the occurrence of eccentricity and axial misalignment of the hole on the tip side of the molded body to be ground.

Configuration 2. The manufacturing method of the spark plug of this configuration is as follows:
A molding step of molding the raw material powder into a molded body having a hole to be a shaft hole;
A predetermined insertion pin is inserted into the hole of the molded body, the molded body is rotatably supported, the molded body is brought into contact with a rotating grinding rotary roller, and a rotating presser rotating roller is attached to the molded body. A grinding step of applying a rotational force against the friction force received from the grinding rotary roller to contact the molded body and grinding the outer peripheral surface of the molded body;
Through a firing step of firing the ground compact,
A method of manufacturing a spark plug including an insulator formed by inserting and fixing a center electrode and a terminal electrode, wherein the hole portion is a shaft hole,
The grinding step includes
The position where the pressing rotary roller contacts the molded body is greater than 180 ° in the rotational direction of the molded body with the insertion pin as the axis from the position where the grinding rotary roller contacts the molded body. The position is shifted by a predetermined angle smaller than 270 °.

  In other words, from the position where the pressing rotary roller contacts the molded body, from the position where the grinding rotary roller contacts the molded body, the rotation direction of the molded body with the insertion pin as an axis. Is a position shifted in the opposite direction by a predetermined angle greater than 90 ° and less than 180 °.

  Therefore, according to the said structure 2, the effect similar to the said structure 1 is show | played.

Configuration 3. The manufacturing method of the spark plug of this configuration is the above configuration 1 or 2,
In the grinding step,
The molded body is supported from both sides in the axial direction.

  According to the said structure 3, stability can be improved by supporting a molded object from an axial direction both sides in a grinding process, and the effect of the said structure 1 or 2 can be improved more. As an example of the shape of the molded body to which the configuration 3 is more effectively applied, a shape in which the diameter of the portion of the hole portion with which the insertion pin abuts is 3.0 mm or less can be given. The insertion pin is preferably one that does not bend due to the reaction force from the grinding roller when grinding the molded body. However, if an insertion pin made of an excessively hard material is used, the reaction force from the grinding rotation roller is reduced. There is a risk of breakage when received. In general, an alloy called a cemented carbide may be used. Further, the longer the overall length of the molded body, the easier it is to bend when receiving a reaction force from the rotating roller for grinding. For this reason, it can be said that this configuration 3 is more effectively applied to the insulator having an axial length of 68 mm or more. In addition, as a shape of the finished product as a spark plug, it can be said that the screw diameter of the metal shell is M10 or less, and the length from the tip surface of the largest diameter portion of the insulator to the tip of the insulator is 30 mm or more. .

  As described above, the present invention for eliminating the eccentricity and axial misalignment of the molded body serving as the insulator is desirably provided as a final process in the grinding of the molded body, that is, a finishing process. Paradoxically, in the grinding process before the finishing process, that is, the so-called roughing process, it is not always necessary to support the compact from both sides in the axial direction. This is because even if some eccentricity or shaft misalignment occurs in the roughing process, it can be adjusted in the finishing process.

  In the roughing process, it is possible to process not only the outer peripheral surface of the molded body but also the tip part by supporting the molded body with a cantilever only from the rear end side without supporting the molded body from both sides in the axial direction. It becomes. By simultaneously processing in this way, the processing time can be shortened. Then, after the rough cutting step, the finish cutting step is performed with both ends, thereby eliminating problems such as eccentricity and shaft misalignment.

  The following configuration 4 includes the above configuration.

Configuration 4. The manufacturing method of the spark plug of this configuration is the above configuration 1 or 2,
In the molding step,
While the molded body is molded in a state where the hole is closed at the tip,
In the grinding process,
While inserting the insertion pin into the hole from the rear end side of the molded body and supporting the molded body from the rear end side, the outer peripheral surface of the molded body is subjected to roughing and the molding is performed. A roughing step of dropping the tip of the body and penetrating the hole,
A finishing cutting step of finishing the outer peripheral surface of the molded body with the insertion pin inserted into the hole of the molded body and supporting the molded body from both sides in the axial direction. Features.

  According to the above configuration 4, in the rough cutting process, the molded body is supported by cantilever in order to scrape off the tip portion, and in the finish cutting process, the molded body is supported by both ends in order to perform processing with higher stability. As a result, it is possible to suppress the occurrence of the above-described problems, that is, the occurrence of eccentricity or axial misalignment of the hole at the tip side of the molded body.

Configuration 5. The manufacturing method of the spark plug of this configuration is the above configuration 4,
A tip portion shaving step for shaving the tip of the molded body in a state where the molded body is supported from the rear end side in a stage after the roughing process and before the finishing shaving process. It is characterized by performing.

  According to the configuration 5, the insertion pin is inserted from the front end surface of the molded body by performing the tip end cutting process in a state where the molded body is supported in a cantilevered manner before the finishing cutting process for supporting the molded body with both ends. It is not necessary to project the tip, and the tip can be processed more easily. On the other hand, when the tip portion cutting step is performed in a state where the molded body is supported in a cantilever stage after the finish cutting step, there is a concern about the occurrence of the above-described problem.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the spark plug obtained by the spark plug manufacturing method of the present invention will be described. FIG. 1 is a partially broken front view showing a spark plug.

  The spark plug 1 is composed of a long insulator 2, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  A shaft hole 4 is formed through the insulator 2 along its own central axis. A center electrode 5 is inserted and fixed on the front end portion (lower end portion in FIG. 1) of the shaft hole 4, and a terminal electrode 6 is inserted and fixed on the rear end portion side. A resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 in the shaft hole 4, and both ends of the resistor 7 are connected to the center electrode 5 via the conductive glass seal layers 8 and 9. And the terminal electrode 6 are electrically connected to each other.

  More specifically, the shaft hole 4 of the insulator 2 includes a small-diameter hole portion 4a formed on the distal end side, and a large-diameter hole portion 4b formed larger in diameter on the rear side of the small-diameter hole portion 4a. It is configured. And the taper surface or the R-shaped convex part receiving surface 4c is formed in the connection part of the small diameter hole part 4a and the large diameter hole part 4b.

  The terminal electrode 6 and the resistor 7 are accommodated in the shaft hole 4 of the insulator 2 in a state of being inserted into the large diameter hole portion 4b, and the center electrode 5 is accommodated in the state of being inserted into the small diameter hole portion 4a. ing. The center electrode 5 protrudes from the tip of the insulator 2, and the terminal electrode 6 protrudes from the rear end of the insulator 2. A fixing convex portion 5a is formed at the rear end portion of the center electrode 5 so as to protrude outward from the outer peripheral surface thereof, and the fixing convex portion 5a is locked to the convex portion receiving surface 4c. Thus, the center electrode 5 is fixed.

  On the other hand, the insulator 2 includes a corrugation portion 10 formed on the rear end side in the outer shape portion, a flange-shaped large diameter portion 11 formed to protrude outward in the circumferential direction at a substantially central portion in the axial direction, and the large portion. A middle body portion 12 formed with a smaller diameter on the distal end side than the diameter portion 11 and a leg length portion 13 formed with a smaller diameter on the distal side than the middle body portion 12 are provided. Of the insulator 2, the distal end side including the large-diameter portion 11, the middle trunk portion 12, and the leg long portion 13 is accommodated in a metal shell 3 formed in a cylindrical shape.

  The metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface thereof. A seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Furthermore, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the engine head is formed at the rear end of the metal shell 3.

  A substantially L-shaped ground electrode 21 is welded to the tip end face 20 of the metal shell 3. The ground electrode 21 is attached with a predetermined spark discharge gap 22 between the discharge surface 21 a at the tip of the ground electrode 21 and the tip of the center electrode 5.

  Next, a method for manufacturing the spark plug 1, particularly a method for manufacturing the insulator 2, which is a characteristic part of the present invention, will be described in detail.

  In the manufacturing process of the insulator 2, first, an additive element material that functions as a sintering aid is blended with the alumina powder as a main component to prepare a raw material powder. Then, a green binder slurry is obtained by adding and mixing a hydrophilic binder and water as a solvent to the obtained raw material powder. Then, the forming substrate slurry is spray-dried by a spray drying method or the like, and adjusted to a granular forming substrate granulated product.

  In the subsequent molding step, the obtained green granulated material for molding is filled in a rubber press mold and is subjected to rubber press molding with a press pin inserted, thereby forming the original shape of the insulator 2 as shown in FIG. A cylindrical molded body 30 is obtained. A hole 31 to be the shaft hole 4 is formed in the molded body 30 by the press pin. However, the hole 31 is closed at the tip of the molded body 30 after press molding.

  Next, a grinding step of grinding the outer shape of the obtained molded body 30 into a shape corresponding to the insulator 2 is performed. In the grinding process according to the present embodiment, a roughing process, a tip part cutting process, and a finish cutting process are sequentially performed. Here, these steps will be described in detail with reference to FIGS. FIG. 2 is a schematic cross-sectional view for explaining the shape of the molded body 30 and its supporting form in the rough cutting process, and FIG. 3 explains the shape of the molded body 30 and its supporting form in the finishing cutting process. It is a cross-sectional schematic diagram for this. FIG. 4 is a schematic diagram for explaining the contact position relationship between the compacting body 30 and a grinding rotary roller used in grinding and a pressing rotary roller as a pressing means.

  In the roughing process, roughing is performed on the outer peripheral surface of the molded body 30 by the roughing rotating roller 35 for roughing shown in FIG. 2, and the tip of the molded body 30 is scraped off and the hole 31 is penetrated. .

  In this roughing process, as shown in FIG. 2, the insertion pin P1 is fitted into the hole 31 from the rear end side of the molded body 30, and the molded body 30 is processed while being rotatably supported from the rear end side. Is done.

  The grinding roller 35 used in the roughing process has a peripheral surface 35a substantially corresponding to the outer shape of the insulator, and an abrasive layer is formed on the peripheral surface 35a. And the rotation roller 35 for grinding rotates to the direction shown by the arrow F2 in FIG.2, 4 centering on the rotating shaft center G2 parallel to the axial direction of the shaft center G1 of the penetration pin P1 by the drive of the motor which is not shown in figure. It is like that.

  On the other hand, the presser rotating roller 37 is made of silicon resin or the like having a large frictional resistance with the molded body 30 and is driven by a motor (not shown) to rotate in a rotational axis parallel to the axial direction of the axis G1 of the insertion pin P1. It rotates about G3 in the direction shown by arrow F3 in FIGS.

  The insertion pin P1 is made of a material having high rigidity, such as a cemented carbide, so that deformation is less likely to occur during grinding. The insertion pin P1 includes a small-diameter shaft portion corresponding to the small-diameter hole portion 4a of the insulator 2 and a large-diameter shaft portion corresponding to the large-diameter hole portion 4b. It has a corresponding shape. An annular pressing rubber 33 is attached to the insertion pin P1 to facilitate positioning of the molded body 30 during grinding, or the grinding rotary roller 35 comes into contact with the insertion pin P1 and both are damaged. Or prevent it.

  In the tip portion cutting step subsequent to the rough cutting step, the tip corner portion of the molded body 30 is cut into an R surface by a grinding rotary roller for cutting the tip portion (see FIG. 5).

  In the tip portion cutting step, as in the rough cutting step, the insertion pin P1 is fitted into the hole 31 from the rear end side of the molded body 30, and the molded body 30 is rotatably supported from the rear end side. Processing is performed at. As shown in FIG. 5, the grinding rotary roller 39 used when the tip portion is cut is formed in the longitudinal direction of the molded body 30 (left and right direction in FIG. 5) in order to form the tip surface of the insulator 2. The substantially right-angled surface 39 a can be shaped so as to abut the tip of the molded body 30. Further, since the molded body 30 is cantilevered from the rear end side during this processing, the hole portion 31 penetrates when the portion that becomes the front end surface of the insulator 2 is formed. However, since it does not protrude from the surface on which the insertion pin P1 is formed and does not come into contact with the substantially right-angled surface 39a of the grinding roller 39, the surface 39a reaches the rotation axis G1. Can be left as

  However, the grinding rotary roller for pressing the tip and the pressing rotary roller are the same as the rotating rotary roller 35 and the pressing rotary roller 37 used in the roughing process, but the shape is slightly different. Things are used. However, the rotation direction is the same as that of the grinding rotary roller 35 and the pressing rotary roller 37. In other words, the grinding rotary roller used in the tip cutting process rotates around the rotation axis G2 in the direction indicated by the arrow F2, and the presser rotation roller rotates around the rotation axis G3 in the direction indicated by the arrow F3. To do.

  In the next finish-cutting step, a finish-cutting process is performed on the outer peripheral surface of the molded body 30 by the finishing grinding rotary roller 36 shown in FIG.

  In the finish cutting step, as shown in FIG. 3, in addition to the insertion pin P1, the insertion pin P2 is further fitted into the hole 31 from the distal end side of the molded body 30 to support the molded body 30 from both sides in the axial direction. Processing is performed in the state.

  The insertion pin P2 is made of a material having high rigidity like the insertion pin P1, but the insertion pin P2 is different from the insertion pin P1 in terms of shape, and has only a small diameter shaft portion corresponding to the small diameter hole portion 4a of the insulator 2. It has a shape. An annular presser rubber 34 for preventing the molded body 30 from falling off is attached to the insertion pin P2.

  The grinding rotary roller 36 and presser rotary roller 38 used in the finishing process are the same as the rotary rotary roller 35 and presser rotary roller 37 used in the roughing process, although the materials are the same. Somewhat different is used. For example, the grinding roller 36 has a peripheral surface 36a corresponding to the outer shape of the insulator (the molded body 30 shrinks when fired, so the dimensions thereof are different). A grain layer is formed. However, the rotation direction is the same as that of the grinding rotary roller 35 and the pressing rotary roller 37. That is, the grinding rotary roller 36 rotates about the rotational axis G2 in the direction indicated by the arrow F2 in FIGS. 3 and 4, and the presser rotary roller 38 rotates about the rotational axis G3 as shown by the arrows in FIGS. Rotate in the direction indicated by F3.

  Based on the above configuration, in each step, as shown in FIG. 4, the compact 30 is brought into contact with the rotating grinding rollers 35, 36 and the like, and the rotating presser rollers 37, 38 and the like are molded. By applying a rotational force rotating in the direction indicated by the arrow F1 in FIGS. 2 to 4 against the friction force received from the grinding rotary rollers 35, 36 and the like by contacting the compact 30 and the compact 30. Grinding is performed.

  Next, with reference to FIG. 4, the arrangement configuration of the molded body 30, the grinding rotary roller 35, and the pressing rotary roller 37 on an orthogonal plane orthogonal to the axial direction of the axis G1 of the insertion pin P1 will be described. The positional relationship among the molded body 30, the grinding rotary roller 35, and the pressing rotary roller 37 is such that the grinding rotary roller 35 and the pressing rotary roller 37 are different rollers (for example, the grinding rotary roller 36 and the pressing rotary roller 38). The same positional relationship may be used even when the item is replaced with ().

  In this embodiment, the shaft center G1 of the insertion pin P1 and the rotation shaft center G2 of the grinding roller 35 and the like are positioned on substantially the same horizontal plane, and the rotation shaft center G3 of the presser rotation roller 37 and the like are both shaft centers G1. , G2 is positioned slightly below. More specifically, the position S1 where the pressing rotary roller 37 and the like come into contact with the molded body 30 is 180 ° in the rotation direction F1 of the molded body 30 from the position S2 where the grinding rotary roller 35 and the like come into contact with the molded body 30. The position is shifted by a predetermined angle A that is larger and smaller than 270 °. In the present embodiment, the predetermined angle A is set to 225 °. That is, a straight line connecting the shaft center G1 of the insertion pin P1 and the rotation shaft center G3 of the pressing roller 37 or the like is inclined by 45 ° in the rotation direction F1 of the molded body 30 with respect to the horizontal line connecting both the shaft centers G1 and G2. is doing.

  The molded body 30 that has undergone the grinding step (finishing step) as described above is removed from the insertion pins P1 and P2, and then sent to the next firing step.

  In the firing step, the molded body 30 that has been ground is fired within a firing temperature range of 1450 ° C to 1700 ° C. Then, further glaze is applied and finish baking is performed, and the insulator 2 is completed.

  The spark plug 1 is completed by inserting and fixing the center electrode 5 and the terminal electrode 6 to the insulator 2 manufactured in this way and attaching the insulator 2 to the metal shell 3.

  As described above in detail, during grinding, the grinding rotary roller 35 and the press rotary roller 37 and the like are brought into contact with the molded body 30 in the above positional relationship, so that the press rotary roller 37 and the like rotate the grinding rotary roller. The molded body 30 can be supported against the dynamic frictional force received from 35 and the like. Therefore, in this embodiment, when the molded body 30 is ground, the insertion pin P1 or the like can be used even when a relatively small diameter is employed as the insertion pin P1 or the like that is inserted into the hole 31 of the molded body 30. Generation | occurrence | production of the malfunction that it will bend can be suppressed. As a result, it is possible to suppress the occurrence of eccentricity and axial misalignment of the hole on the tip side of the molded body 30 to be ground.

  Moreover, since the molded body 30 is supported from both sides in the axial direction in the finish cutting step, the above-described effects can be obtained more reliably. Furthermore, since the tip portion cutting step is performed in a state where the molded body 30 is supported in a cantilever manner before the finish cutting step, the tip portion can be processed more easily.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  (A) In the above embodiment, the insulator shown in FIG. 1 is given as an example of an insulator to which the present invention is applied. Of course, the present invention is also applied to grinding of insulators having other outer shapes. can do.

  (B) In the above-described embodiment, the roughing step, the tip portion cutting step, and the finishing cutting step are sequentially performed in the grinding step. However, all these steps may be performed in one step by one grinding rotary roller. Further, the tip portion cutting step may be performed after the rough cutting step and the finish cutting step. In this way, the tip can be finished more beautifully. In addition, when grinding the molded body 30 having a configuration in which the hole portion 31 penetrates in the tip portion in advance, the molded body 30 may be supported from both sides in the axial direction in all steps as well as the finish cutting process. .

  (C) In the above embodiment, the outer peripheral surface shape of the pressing rotary roller 37 is described as a surface having irregularities corresponding to the molded body 30, but the outer peripheral surface shape of the pressing rotary roller 37 is not limited in any way. Absent. Further, it is not necessary to press all over the axis of the molded body, and only a thick portion may be pressed so that the molded body 30 does not break when a pressing force (load) is applied. For example, as shown in FIG. 6, as a pressing rotary roller, a first pressing roller 37A disposed corresponding to a portion to be the large diameter portion 11 of the insulator 2, and a molded body from the first pressing roller 37A. It is good also as a structure which supports the molded object 30 in multiple places according to the difference in the thickness of the molded object 30, such as providing the 2nd pressing roller 37B arrange | positioned at the front end side of 30.

  In the example shown in FIG. 6, the first pressing roller 37 </ b> A and the second pressing roller 37 </ b> B are configured to rotate around the same rotation axis (rotation axis G <b> 3). The rotation shafts of the plurality of pressing rollers that support the molded body 30 may be different from each other. For example, in the example shown in FIGS. 7 and 8, the first pressing roller 37A and the second pressing roller 37B are configured to rotate about different rotation axes. In this case, the first pressing roller 37A is rotated for grinding with respect to the compact 30 by rotating in the direction indicated by the arrow F3a in FIGS. 7 and 8 around the rotation axis G3a by driving a motor (not shown). A rotational force that rotates in the direction indicated by the arrow F1 in FIGS. The rotation axis G3a of the first pressing roller 37A is positioned on substantially the same horizontal plane as the axis G1 of the insertion pin P1 and the rotation axis G2 of the grinding rotation roller 35.

  On the other hand, the second pressing roller 37B rotates in the same direction as the first pressing roller 37A (the direction indicated by the arrow F3b in FIGS. 7 and 8) around the rotation axis G3b due to the frictional force received from the molded body 30. To do. Further, the position S1 where the second pressing roller 37B comes into contact with the molded body 30 is the same as the pressing rotary roller 37 of the above embodiment, from the position S2 where the grinding rotary roller 35 comes into contact with the molded body 30. The position is shifted by 225 ° in the rotation direction F1 of the molded body 30.

  If a plurality of pressing rollers are used in this way, a roller having a diameter corresponding to the difference in thickness of the molded body 30 can be employed. Accordingly, in a location such as the vicinity of the tip portion where the thickness of the molded body 30 is relatively thin, the position S1 where the pressing roller contacts the molded body 30 without bringing the pressing roller into contact with the grinding rotation roller 35 is obtained. The molded body 30 can be brought closer to a position directly below the molded body 30, that is, a position shifted by 270 ° from the position S 2 where the grinding rotary roller 35 contacts, and the molded body is more reliably resisted by the dynamic friction force received from the grinding rotary roller 35. 30 can be supported.

  In the case where a plurality of pressing rollers are provided, the number is not limited to the above two but may be three or more, and at least one of them is in the above range, that is, the position where the grinding rotary roller 35 contacts the molded body 30. If it is the structure which contacts with respect to the molded object 30 in the range larger than 180 degrees and smaller than 270 degrees from S2 to the rotation direction F1 of the molded object 30, the effect similar to the said embodiment will be show | played.

  In the roughing process, the belt may be pressed instead of a roller to improve the piece time. For example, as shown in FIG. 9, instead of the pressing rotary roller 37 of the above embodiment, a belt B1 hung between two tension rollers 41a and 41b is used as a pressing means to support the molded body 30. Also good. In this case, since the molded body 30 can be supported by surface contact using the bending of the belt B1, the molded body 30 can be supported more firmly than the roller. When the belt B1 is employed as the pressing means, the center position in the rotation direction F1 of the molded body 30 is the position S1 where the pressing means (belt B1) in this configuration contacts the molded body 30 in the contact surface with the molded body 30. It corresponds to. Note that the surface of the belt B <b> 1 may be substantially flat, or may have an uneven shape that follows the outer peripheral shape of the molded body 30, similar to the pressing rotary roller 37 and the like. Of course, the belt B1 may be used as the pressing means not only in the roughing process but also in the finishing process.

  (D) In the above-described embodiment, in the finish cutting step, the molded body 30 is supported by the two insertion pins P1 and P2 from both sides in the axial direction. When the molded body 30 having the above-described configuration is ground, the molded body 30 may be supported from both sides in the axial direction by supporting one insertion pin protruding from both front and rear end portions of the molded body 30 from both sides. . For example, as shown in FIG. 10, an insertion pin P <b> 3 that fits into the hole 31 from the rear end side of the molded body 30 and protrudes from the distal end portion of the molded body 30 is employed, and the protruding distal end portion is supported by the support member 40. It is good also as composition to do.

  (E) In the above embodiment, the rotation direction of the molded body 30 is determined from the position S1 where the pressing rotary roller 37 or the like contacts the molded body 30 and from the position S2 where the grinding rotary roller 35 or the like contacts the molded body 30. It is set at a position shifted by 225 ° to F1. Not limited to this, the position S1 where the presser rotating roller 37 and the like come in contact with each other is shifted from the position S2 where the grinding rotary roller 35 and the like come into contact with the rotation direction F1 of the molded body 30 in a range larger than 180 ° and smaller than 270 °. As long as it is a different position, it may be another position.

  (F) In the above embodiment, the rotational axis G2 of the grinding rotary roller 35 and the rotational axis G3 of the presser rotary roller 37 are arranged in parallel to the axial direction of the axial center G1 of the insertion pin P1. ing. Not limited to this, the rotational axis G2 such as the grinding rotary roller 35 and the rotational axis G3 such as the pressing rotary roller 37 may be arranged to be inclined with respect to the axial direction of the axis G1 of the insertion pin P1. . Even in such a configuration, the rotation of the molded body 30 from the position S1 where the pressing rotary roller 37 or the like contacts the molded body 30 is changed from the position S2 where the grinding rotary roller 35 or the like contacts the molded body 30. As long as the position is shifted by a predetermined angle A in the direction F1 larger than 180 ° and smaller than 270 °, it is possible to obtain the same effect as the above embodiment.

  (G) Although the straight line connecting the axis G1 of the insertion pin P1 and the rotation axis G2 of the grinding rotary roller 35 is described as a horizontal line in the above embodiment, this straight line may not be horizontal.

It is a partially broken front view which shows the whole spark plug of this embodiment. It is a cross-sectional schematic diagram for demonstrating the shape of the molded object in the rough cutting process, its support form, etc. FIG. It is a cross-sectional schematic diagram for demonstrating the shape of the molded object, its support form, etc. in a finishing cutting process. It is a schematic diagram for demonstrating arrangement | positioning structure of a molded object, the rotation roller for grinding, and the rotation roller for pressing. It is a cross-sectional schematic diagram for demonstrating the shape etc. of the rotating roller for grinding used when performing a tip part cutting process. It is a cross-sectional schematic diagram for demonstrating the support form of the molded object in another embodiment. It is a cross-sectional schematic diagram for demonstrating the support form of the molded object in another embodiment. It is a schematic diagram for demonstrating arrangement | positioning structure of the molded object in another embodiment, the rotating roller for grinding, and the pressing roller. It is a schematic diagram for demonstrating the support form of the molded object in another embodiment. It is a cross-sectional schematic diagram for demonstrating the shape of the insertion pin in another embodiment, its support form, etc. It is a perspective view of the molded object and the rotating roller for grinding for demonstrating the conventional grinding process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Spark plug, 2 ... Insulator, 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 6 ... Terminal electrode, 30 ... Molded object, 31 ... Hole part, 35, 36 ... Rotary roller for grinding, 37 , 38: Rotating roller for pressing, G1: Shaft center of inserting pin, G2: Rotating shaft center of rotating roller for grinding, G3: Rotating shaft center of rotating roller for pressing, F1: Rotating direction of molded body, F2: For grinding Rotating roller rotation direction, F3... Rotating roller rotating direction.

Claims (5)

A molding step of molding the raw material powder into a molded body having a hole to be a shaft hole;
A predetermined insertion pin is inserted into the hole of the molded body to rotatably support the molded body, and the molded body is brought into contact with a rotating rotating roller for grinding, and a pressing means is brought into contact with the molded body. A grinding step of supporting the molded body against the frictional force received from the grinding roller and grinding the outer peripheral surface of the molded body;
Through a firing step of firing the ground compact,
A method of manufacturing a spark plug including an insulator formed by inserting and fixing a center electrode and a terminal electrode, wherein the hole portion is a shaft hole,
The grinding step includes
The position where at least one pressing means comes into contact with the molded body from the position where the rotating roller for grinding comes into contact with the molded body is 180 ° in the rotation direction of the molded body around the insertion pin. A method for manufacturing a spark plug, characterized in that the position is shifted by a predetermined angle which is largely smaller than 270 °. A molding step of molding the raw material powder into a molded body having a hole to be a shaft hole;
A predetermined insertion pin is inserted into the hole of the molded body, the molded body is rotatably supported, the molded body is brought into contact with a rotating grinding rotary roller, and a rotating presser rotating roller is attached to the molded body. A grinding step of applying a rotational force against the friction force received from the grinding rotary roller to contact the molded body and grinding the outer peripheral surface of the molded body;
Through a firing step of firing the ground compact,
A method of manufacturing a spark plug including an insulator formed by inserting and fixing a center electrode and a terminal electrode, wherein the hole portion is a shaft hole,
The grinding step includes
The position where the pressing rotary roller contacts the molded body is greater than 180 ° in the rotational direction of the molded body with the insertion pin as the axis from the position where the grinding rotary roller contacts the molded body. A spark plug manufacturing method characterized in that the position is shifted by a predetermined angle smaller than 270 °. In the grinding step,
The method of manufacturing a spark plug according to claim 1, wherein the molded body is supported from both axial sides. In the molding step,
While the molded body is molded in a state where the hole is closed at the tip,
In the grinding process,
While inserting the insertion pin into the hole from the rear end side of the molded body and supporting the molded body from the rear end side, the outer peripheral surface of the molded body is subjected to roughing and the molding is performed. A roughing step of dropping the tip of the body and penetrating the hole,
A finishing cutting step of finishing the outer peripheral surface of the molded body with the insertion pin inserted into the hole of the molded body and supporting the molded body from both sides in the axial direction. The method of manufacturing a spark plug according to claim 1 or 2, characterized in that   A tip portion shaving step for shaving the tip of the molded body in a state where the molded body is supported from the rear end side in a stage after the roughing process and before the finishing shaving process. The method for manufacturing a spark plug according to claim 4, wherein:

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