JP6713919B2 - Sintered body manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a sintered body, and more particularly to a method for manufacturing a sintered body in which a ceramic compact is fired while being suspended from a firing jig.

In the spark plug, an insulator made of ceramics such as alumina insulates the metal shell from the electrode. The insulator is a sintered body obtained by firing a long ceramic molded body. Patent Document 1 discloses a method of firing a ceramic molded body by using a bottomed cylindrical firing jig having a funnel-shaped receiving port. In the technique disclosed in Patent Document 1, after the end of the ceramic molded body that expands in a tapered shape is supported by the receiving port, the receiving port is covered with a lid and the firing jig is sealed. The ceramic molded body is fired while being suspended from a firing jig arranged in the furnace. Accordingly, it is possible to prevent buckling of the lower portion of the sintered body that occurs when the ceramic molded body is placed and fired.

JP-A-3-88279

However, in the above-mentioned conventional technique, since the firing jig is sealed, the heat transfer from the furnace to the ceramic molded body is conducted from the receptacle of the firing jig to the end of the ceramic molded body and the firing jig. From the heat radiation to the ceramic compact. Since a temperature difference is likely to occur between the end portion of the ceramic molded body and the other portion, there is a problem that the shrinkage rate during firing is likely to vary and the sintered body is easily deformed.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a sintered body that can suppress deformation during sintering.

In order to achieve this object, in the method for producing a sintered body of the present invention, a ceramic molded body including a second portion having a diameter larger than that of the elongated first portion is molded by a molding step. By the firing step, the firing jig is placed in the furnace and the ceramic molded body is fired with the first portion suspended in the vertical direction of the firing jig. The firing jig has a bottomed cylindrical wall portion whose lower end side is closed and an inclined surface whose upper end surface narrows toward the lower end side and which is formed continuously or intermittently in an annular shape. And a support portion fixed to the inside of the. The firing jig supports the outer peripheral edge of the second portion of the ceramic molded body on the inclined surface. In the firing process, the firing jig has a first space surrounded by the ceramic molded body, the wall portion and the support portion in a state where the outer peripheral edge of the second portion is in contact with the inclined surface, and a first space inside the furnace outside the first space. It is provided with a hole that connects the two spaces.

According to the method for producing a sintered body of the first aspect, the hole communicates the first space formed by the firing jig and the ceramic molded body with the second space inside the furnace outside the firing jig . The heat transfer from the furnace to the ceramic molded body is due to heat conduction from the inclined surface of the firing jig to the outer peripheral edge of the second part of the ceramic molded body and heat radiation (radiation) from the firing jig to the ceramic molded body. In addition, due to the convective heat conduction in the first space and the second space communicating with each other through the holes, it is possible to prevent a temperature difference from occurring in the ceramic molded body suspended by the firing jig. Therefore, it is possible to prevent variation in shrinkage rate of the ceramic molded body during firing and to suppress deformation of the sintered body during firing.

According to the method for producing a sintered body of claim 2, since the hole is provided in the wall, in addition to the effect of claim 1, heat can be easily transferred to the first part of the ceramic molded body by convection heat conduction. There is an effect that can be done.

According to the method for producing a sintered body according to claim 3, since the hole is provided in the supporting portion, in addition to the effect of claim 1 or 2, the convection heat conduction is applied to the first portion of the ceramic molded body. There is an effect that it can be easily heated.

According to the method for producing a sintered body according to claim 4, since the inclined surface is continuously provided, when the first part of the ceramic molded body is suspended, the entire circumference of the outer peripheral edge of the second part is reduced. Contact the inclined surface. As a result, in addition to the effect according to any one of claims 1 to 3, there is an effect that the ceramic molded body can be stably supported.

According to the method for producing a sintered body of claim 5, the inclined surface is provided intermittently. The hole portion is a gap between the ceramic molded body supported by the intermittent inclined surface and the support portion. Therefore, in addition to the effect of any one of claims 1 to 3, there is an effect that heat can be easily transferred to the second portion of the ceramic molded body by convective heat conduction.

According to the method for producing a sintered body according to claim 6, the ceramic molded body has an outer diameter smaller than that of the second portion, and includes a third portion provided on the opposite side of the first portion with the second portion interposed therebetween. I have it. Since the outer diameter of the third part is smaller than that of the first part, it is difficult to raise the position of the center of gravity of the ceramic molded body on which the first part is suspended. Therefore, in addition to the effect according to any one of claims 1 to 5, there is an effect that the ceramic molded body can be stably supported.

According to the method for manufacturing a sintered body according to claim 7, the ceramic molded body has an outer diameter smaller than that of the second portion, and includes a third portion provided on the opposite side of the first portion with the second portion interposed therebetween. I have it. Since the outer diameter of the third part is larger than that of the first part, the range in which the angle of the inclined surface with respect to the vertical direction can be set is large by suspending the first part, as compared with the case where the third part is suspended. it can. Therefore, in addition to the effect of any one of claims 1 to 5, there is an effect that the degree of freedom in designing the inclined surface can be increased.

According to the method for producing a sintered body of claim 8, the inclined surface is a curved surface that is convex upward. Since the outer diameter of the outer peripheral edge of the second portion of the ceramic molded body is reduced by firing, the contact position of the outer peripheral edge of the second portion on the inclined surface is lowered due to shrinkage during firing. When the ceramic molded body descends, the axis of the ceramic molded body may be inclined with respect to the vertical direction and the sintered body may be deformed. However, if the inclined surface is a curved surface that is convex upward, the inclined surface is lower. It is possible to reduce the amount of lowering of the second portion due to shrinkage during firing, as compared with the case of a convex curved surface or a flat surface. As a result, it is possible to reduce the possibility that the sintered body is deformed in a state where the shaft is tilted. Therefore, in addition to the effect according to any one of claims 1 to 7, it is possible to suppress the generation of a defective sintered body where the shaft is tilted. There is.

It is one side sectional drawing of the spark plug in one embodiment of the present invention. It is a top view of the baking jig in a 1st embodiment. FIG. 3 is a sectional view of the firing jig taken along the line III-III in FIG. 2. FIG. 3 is a cross-sectional view of a firing jig and a ceramic molded body arranged in a furnace. It is sectional drawing of the firing jig and the ceramic molded body which expanded the part shown by V of FIG. FIG. 6 is a cross-sectional view of a firing jig and a ceramic molded body taken along line VI-VI in FIG. 5. It is sectional drawing of the baking jig and ceramic molded object in 2nd Embodiment. FIG. 8 is a sectional view of a firing jig and a ceramic molded body taken along line VIII-VIII of FIG. 7. It is sectional drawing of the baking jig and ceramic molded object in 3rd Embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-sided sectional view of a spark plug 10 according to an embodiment of the present invention. In FIG. 1, the lower side of the paper is referred to as the front end side of the spark plug 10, and the upper side of the paper is referred to as the rear end side of the spark plug 10. The spark plug 10 includes an insulator 11.

The insulator 11 is a tubular member formed of ceramics such as alumina having excellent mechanical properties and insulating properties at high temperatures. The insulator 11 is formed with a shaft hole 12 penetrating along the axis O. The insulator 11 has a body portion 13, a large-diameter portion 14, a middle body portion 15 and a long leg portion 16 which are connected from the rear end side to the front end side along the axis O.

The body portion 13 is a cylindrical portion at the rear end of the insulator 11. The large diameter portion 14 is an annular portion having an outer peripheral edge having a diameter larger than that of the body portion 13. The middle body portion 15 is a cylindrical portion having a smaller diameter than the body portion 13 and the large diameter portion 14. The leg long portion 16 is a cylindrical portion having a diameter smaller than that of the middle trunk portion 15. The insulator 11 has a reduced diameter portion 17 formed at the boundary between the middle body portion 15 and the long leg portion 16 so that the outer diameter is reduced toward the distal end side. The center electrode 20 is arranged in the shaft hole 12 at the tip of the middle body portion 15 and the inner portion of the long leg portion 16.

The center electrode 20 is a rod-shaped member extending along the axis O, and copper or a core material containing copper as a main component is covered with nickel or a nickel-base alloy. The center electrode 20 is held by the insulator 11 and its tip is exposed from the shaft hole 12.

The terminal fitting 21 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (for example, low carbon steel). The terminal fitting 21 is fixed to the rear end of the insulator 11 in a state where the front end side is press-fitted into the shaft hole 12. The terminal fitting 21 is electrically connected to the center electrode 20 inside the shaft hole 12. The metal shell 30 of the insulator 11 is fixed to the distal end side of the outer periphery of the insulator 11 with a space in the axis O direction from the metal terminal 21.

The metal shell 30 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel or the like). The metallic shell 30 has a threaded portion 31 formed on the outer peripheral surface on the front end side. The metal shell 30 is attached to the engine by connecting the screw portion 31 to the screw hole of the engine (not shown). The metal shell 30 has a shelf portion 32 formed on the inner circumference of the screw portion 31 in the radial direction and protruding inward in the radial direction.

The metallic shell 30 is provided on the rear end side of the screw portion 31 with a ring-shaped seat portion 33 that projects outward in the radial direction in a flange shape. A gasket 36 that prevents leakage of combustion gas from a screw hole of the engine is arranged between the seat portion 33 and the screw portion 31. The metal shell 30 is provided with a tool engagement portion 34, which is engaged with a tool such as a wrench, on the rear end side of the seat portion 33. The screw part 31 is rotated by the tool engaged with the tool engagement part 34.

The metal shell 30 has an engaged portion 35 connected to the rear end of the tool engaging portion 34. The engaged portion 35 is a portion in which the rear end edge of the metal shell 30 is bent inward. In the insulator 11, two ring members 37 are arranged on the outer periphery of the body 13 at intervals in the axis O direction. The ring member 37 is arranged inside the tool engaging portion 34 of the metal shell 30 in the radial direction, and the space surrounded by the ring member 37, the body portion 13 and the tool engaging portion 34 is filled with powder 38 such as talc. There is. The engaged portion 35 engages with the rear end portion of the large diameter portion 14 of the insulator 11 via the ring member 37 and the powder 38.

In the metallic shell 30, the engaged portion 35 is bent inward with the reduced diameter portion 17 of the insulator 11 engaged with the shelf portion 32, and the engaged portion 35 is connected to the large diameter portion 14 of the insulator 11. Engage. Due to the bending of the engaged portion 35, the metal shell 30 is crimped and fixed to the insulator 11. The insulator 11 is held by the metal shell 30 with the large-diameter portion 14 and the reduced-diameter portion 17 sandwiched by the engaged portion 35 and the shelf portion 32 from both sides in the axis O direction.

The ground electrode 39 is a metal member (for example, a nickel-based alloy) that is joined to the tip of the metal shell 30. In the present embodiment, the ground electrode 39 is formed in a rod shape, and the tip side is bent and faces the center electrode 20. The ground electrode 39 forms a spark gap with the center electrode 20.

The spark plug 10 is manufactured by the following method, for example. The insulator 11 is created by firing a compact formed from raw material powder. First, a raw material powder is prepared by mixing alumina as a main component and a compound of an element such as Si, Mg, Ca, or Ba that functions as a sintering aid. A hydrophilic binder such as polyvinyl alcohol and a solvent such as water are added to the raw material powder and mixed to prepare a slurry. The slurry is dried by a spray drying method or the like to prepare a granulated product. In the molding step, the obtained granulated product is pressure-molded or injection-molded to obtain a ceramic molded body 60 (described later). In the firing step, the ceramic molded body 60 is fired to obtain the insulator 11.

Next, the center electrode 20 is inserted into the shaft hole 12 of the insulator 11. The center electrode 20 is arranged so that its tip is exposed from the shaft hole 12 to the outside. After the terminal fitting 21 is inserted into the shaft hole 12 to secure the continuity between the terminal fitting 21 and the center electrode 20, the metal shell 30 to which the ground electrode 39 is joined in advance is attached to the outer circumference of the insulator 11. The spark plug 10 is obtained by bending the ground electrode 39 so that the ground electrode 39 faces the center electrode 20.

A method for manufacturing the insulator 11 (sintered body) will be described with reference to FIGS. 2 to 6. 2 is a plan view of the firing jig 40 in the first embodiment, and FIG. 3 is a sectional view of the firing jig 40 taken along the line III-III in FIG. The firing jig 40 is made of a refractory material such as alumina, magnesia, and spinel.

As shown in FIGS. 2 and 3, the firing jig 40 includes a bottom plate 41, a cylindrical wall portion 42 mounted on the bottom plate 41, and a plate-shaped support portion 43 mounted on the wall portion 42. Equipped with. By mounting the wall portion 42 on the bottom plate 41, the wall portion 42 is formed in a bottomed tubular shape having a closed lower end. Further, by mounting the support portion 43 on the wall portion 42, the support portion 43 is fixed inside the wall portion 42. The support portion 43 has an opening 44 that is circular in a plan view. The opening 44 penetrates the support portion 43 in the plate thickness direction (vertical direction in FIG. 3 ),
The support portion 43 includes a plurality of (four in the present embodiment) ridges 45 that protrude inward from the opening 44 and extend linearly in the vertical direction. An annular inclined surface 46 that narrows from the upper end side of the opening 44 toward the lower end side is intermittently formed in the support portion 43 by the plurality of protrusions 45. In this embodiment, the inclined surface 46 is linearly inclined with respect to the vertical direction.

The support portion 43 is formed with a hole portion 47 penetrating in the plate thickness direction (vertical direction in FIG. 3). The wall portion 42 is formed with a hole portion 48 penetrating in the plate thickness direction (direction perpendicular to the plane of FIG. 3). The size and number of the holes 47 are appropriately set within a range in which the mechanical strength of the support 43 can be maintained. Similarly, the size and number of the holes 48 are appropriately set within a range in which the mechanical strength of the wall 42 can be maintained. The shapes of the holes 47 and 48 can be set arbitrarily.

In the present embodiment, for the sake of convenience, a case where one intermittently formed annular inclined surface 46 is provided on the support portion 43, that is, a case where one ceramic molded body 60 is supported on the support portion 43 will be described. However, it is not necessarily limited to this. It is naturally possible to form a plurality of inclined surfaces 46 on the support portion 43, that is, to support a plurality of ceramic molded bodies 60 on the support portion 43, within a range in which the strength of the support portion 43 can be secured.

4 is a cross-sectional view of the firing jig 40 and the ceramic molded body 60 arranged inside the furnace 50, and FIG. 5 is a cross-sectional view of the firing jig 40 and the ceramic molded body 60 in which a portion indicated by V in FIG. 4 is enlarged. 6 is a cross-sectional view of the firing jig 40 and the ceramic molded body 60 taken along the line VI-VI of FIG. In FIG. 5, the ceramic molded body 60 before firing is shown by a solid line, and the insulator 11 (sintered body) obtained by firing the ceramic molded body 60 is shown by an imaginary line (two-dot chain line).

As shown in FIG. 4, the furnace 50 includes a heat insulating material 51 for forming a furnace wall and a ceiling, a heating element 52 arranged along the furnace wall, a carriage and a belt that move in a furnace space surrounded by the heat insulating material 51. And a moving member 53 such as a roller. The furnace 50 is a continuous furnace that is continuous in the longitudinal direction (direction perpendicular to the plane of FIG. 4). By moving the moving member 53 on which the firing jig 40 is arranged, the firing jig 40 passes through the pre-heat zone, the heating zone, and the cooling zone of the furnace 50. The ceramic molded body 60 supported by the firing jig 40 is fired at a maximum temperature of about 1600° C. in the heating zone.

As shown in FIG. 5, the ceramic molded body 60 has an elongated first portion 61, a second portion 62 having a larger diameter than the first portion 61, and an outer diameter smaller than that of the second portion 62. The third portion 63 is provided on the opposite side of the first portion 61 with the portion 62 interposed therebetween. The outer diameter of the third portion 63 is larger than that of the first portion 61. The elongated shape means a rod shape or a cylindrical shape in which the length of the object is longer than the thickness of the object.

The firing jig 40 supports the outer peripheral edge 64 (corner portion) of the second portion 62 of the ceramic molded body 60 on the inclined surface 46, and suspends the first portion 61 in the vertical direction. The third portion 63 of the ceramic molded body 60 projects upward in the vertical direction with respect to the support portion 43. The first portion 61 constitutes the middle body portion 15, the leg portion 16 and the shelf portion 32 after the firing. The second portion 62 of the ceramic molded body 60 constitutes the large diameter portion 14 of the insulator 11 after firing. The third portion 63 of the ceramic molded body 60 constitutes the body portion 13 of the insulator 11 after firing.

The ceramic molded body 60 is fired in a state where the first portion 61 is suspended by the support portion 43, and is lowered by its own weight due to contraction during firing. In the ceramic molded body 60, the outer diameter of the second portion 62 is reduced by firing, so that the contact position of the outer peripheral edge 64 (corner portion) on the inclined surface 46 is lowered.

As shown in FIG. 6, a plurality of protrusions 45 are spaced apart from each other and protrude toward the inside of the opening 44, so that the inclined surface 46 is formed intermittently. As a result, the hole portion 49 formed by the gap between the second portion 62 of the ceramic molded body 60 and the support portion 43 (the gap between the adjacent protrusions 45) is formed.

Returning to FIG. 4, description will be made. In the firing jig 40, the first portion surrounded by the ceramic molded body 60, the bottom plate 41, the wall portion 42 and the support portion 43 in a state where the second portion 62 contacts the inclined surface 46 and the ceramic molded body 60 is suspended. It is partitioned into a space 65 and a second space 66 inside the furnace 50 outside the first space 65. The hole 47 formed in the support portion 43, the hole portion 48 formed in the wall portion 42, the gap (the hole portion 49) between the second portion 62 of the ceramic molded body 60 and the support portion 43 is the same as the first space 65. It communicates with the second space 66.

As a result, the heat transfer from the furnace 50 to the ceramic molded body 60 is conducted from the inclined surface 46 of the firing jig 40 to the second portion 62 of the ceramic molded body 60, and the heat transfer from the firing jig 40 to the ceramic molded body 60 is performed. In addition to heat radiation (radiation) to the part 61 and convective heat conduction from the furnace 50 to the third part 63 of the ceramic molded body 60, the first space 65 and the second space 65 communicating with the holes 47, 48, 49 are provided. Due to convective heat conduction in the space 66. Therefore, it is possible to prevent the temperature difference from occurring in the ceramic molded body 60 suspended by the firing jig 40. Therefore, it is possible to prevent variation in shrinkage rate of the ceramic molded body 60 during firing, and it is possible to suppress deformation of the sintered body (insulator 11) during firing.

Since the outer peripheral edge 64 of the second portion 62 of the ceramic molded body 60 linearly contacts the inclined surface 46 of the firing jig 40, the contact area can be reduced. Therefore, the influence of heat conduction from the inclined surface 46 of the firing jig 40 to the second portion 62 of the ceramic molded body 60 can be reduced, while the influences of heat radiation and convection heat conduction can be relatively increased. As a result, the temperature difference between the first portion 61, the third portion 63, and the second portion 62 of the ceramic molded body 60 can be further reduced, and the density of the sintered body can be prevented from becoming nonuniform.

In the ceramic molded body 60, the contact position of the outer peripheral edge 64 (corner portion) on the inclined surface 46 is lowered due to contraction during firing, so that the portion rubbed by the inclined surface 46 is the outer peripheral edge 64 (corner portion) of the second portion 62. Part)) only. As a result, it is possible to reduce scratches (rounded corners, etc.) that may occur on the large diameter portion 14 of the insulator 11 by rubbing against the inclined surface 46. Moreover, since the inclined surface 46 is formed intermittently, the contact area can be reduced as compared with the case where the inclined surface is continuous. Therefore, the scratches generated on the insulator 11 can be reduced.

Since there is a gap (hole 49) between the second portion 62 and the support portion 43 of the ceramic molded body 60 supported by the inclined surface 46 which is intermittently formed, the hole portion 49 has the first space 65 and the second space. It communicates with 66. As a result, the heat can be easily transferred to the second portion 62 of the ceramic molded body 60 by the convective heat conduction between the first space 65 and the second space 66 by the hole portion 49.

Since the hole portion 48 is provided in the wall portion 42 of the firing jig 40 that faces the heating element 52 arranged on the furnace wall, the ceramic molded body is formed by convective heat conduction by the fluid heated by the heating element 52. The heat can be easily transferred to the first portion 61 of 60.

Since the hole portion 47 is provided in the support portion 43 of the firing jig 40, heat can be easily transferred to the first portion 61 of the ceramic molded body 60 by convective heat conduction. In particular, since the holes 47 and 48 are formed in the wall 42 and the support 43, the fluid that has entered the first space 65 of the firing jig 40 from the holes 48 moves from the holes 47 to the second space 66. Can be made. As a result, convective heat conduction can be activated, and heat can be evenly transferred to the ceramic molded body 60.

The outer diameter of the third portion 63 of the ceramic molded body 60 is larger than that of the first portion 61, that is, the outer diameter of the first portion 61 is smaller than that of the third portion 63. Compared to the case where the three parts 63 are suspended, the lower end of the inclined surface 46 can be moved away from the ceramic molded body 60, and the inclined surface 46 and the first part 61 can be less likely to interfere with each other. As a result, the range in which the angle of the inclined surface 46 with respect to the vertical direction can be set can be increased. Therefore, the degree of freedom in designing the inclined surface 46 can be increased. Further, by making the outer diameter of the first portion 61 smaller than the outer diameter of the third portion 63, the first portion 61 can be easily inserted into the inclined surface 46.

Next, a second embodiment will be described with reference to FIG. In the first embodiment, a case has been described in which the annular inclined surface 46 that narrows toward the lower end side is intermittently formed in the support portion 43 in the circumferential direction. Further, in the first embodiment, the case where the inclined surface 46 inclines linearly with respect to the vertical direction has been described.

On the other hand, in the second embodiment, a case where the annular inclined surface 72 is continuously formed in the circumferential direction on the support portion 71 will be described. Further, a case where the inclined surface 72 is a curved surface that is convex upward will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

FIG. 7 is a sectional view of the firing jig 70 and the ceramic molded body 60 according to the second embodiment. FIG. 7 is a cross-sectional view of the firing jig 70 cut in the vertical direction in a state where the second portion 62 of the ceramic molded body 60 is supported by the firing jig 70, similarly to FIG. FIG. 8 is a sectional view of the firing jig 70 and the ceramic molded body 60 taken along the line VIII-VIII of FIG. 7. The support portion 71 having the inclined surface 72 is placed on the upper end of the wall portion 42.

As shown in FIG. 7, the annular inclined surface 72 formed on the support portion 71 of the firing jig 70 is a curved surface convex upward. Holes (not shown) penetrating in the plate thickness direction are formed in the wall portion 42 and the supporting portion 71 of the firing jig 70. Since holes are formed in the wall portion 42 and the support portion 71, heat transfer by convective heat conduction between the first space 65 (see FIG. 4) and the second space 66, as in the first embodiment. You can

Since the outer diameter of the outer peripheral edge 64 of the second portion 62 of the ceramic molded body 60 is reduced by firing, the contact position of the outer peripheral edge 64 on the inclined surface 72 is lowered due to contraction during firing. When the ceramic molded body 60 descends, the axis of the ceramic molded body 60 may be tilted with respect to the vertical direction and the sintered body (insulator 11) may be deformed, but the inclined surface 72 is a curved surface convex upward. Then, the amount of lowering of the second portion 62 due to the contraction during firing can be reduced as compared with the case where the inclined surface is a curved surface or a flat surface that is convex downward (see FIG. 5 ). As a result, it is possible to reduce the possibility that part of the outer peripheral edge 64 of the descending second portion 62 will be caught by the inclined surface 72, and reduce the possibility that the insulator 11 will be deformed when the shaft is inclined. Therefore, it is possible to suppress the generation of a defective sintered body (insulator 11) whose axis is inclined.

As shown in FIG. 8, since the inclined surface 72 is continuously provided in the circumferential direction, when the first portion 61 of the ceramic molded body 60 is suspended, the outer peripheral edge 64 (corner portion) of the second portion 62 is suspended. ) Contacts the inclined surface 72 all around. Therefore, the outer peripheral edge 64 of the second portion 62 that linearly contacts the inclined surface 72 can be stably supported.

Further, since the entire circumference of the outer peripheral edge 64 of the second portion 62 contacts the inclined surface 72, the contact area can be increased as compared with the case where part of the circumference of the outer peripheral edge 64 of the second portion 62 contacts the inclined surface. .. As a result, the load per unit area that the second portion 62 receives from the inclined surface 72 due to the self-weight of the ceramic molded body 60 is increased by the second portion 62 when a part of the outer peripheral edge 64 of the second portion 62 contacts the inclined surface. It can be made smaller than the load per unit area received by the portion 62. Therefore, it is possible to reduce scratches that may be generated on the large diameter portion 14 of the insulator 11 by rubbing the inclined surface 72.

Next, a third embodiment will be described with reference to FIG. In the first and second embodiments, the case where the outer diameter of the third portion 63 of the ceramic molded body 60 is larger than the outer diameter of the first portion 61 has been described. On the other hand, in the third embodiment, a case will be described in which the ceramic molded body 90 in which the outer diameter of the third portion 93 is smaller than the outer diameter of the first portion 91 is fired. The same parts as those in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

FIG. 9 is a sectional view of the firing jig 80 and the ceramic molded body 90 according to the third embodiment. FIG. 9 is a cross-sectional view of the firing jig 80 cut in the vertical direction in a state where the second portion 92 of the ceramic molded body 90 is supported by the firing jig 80, similarly to FIG. In FIG. 9, the ceramic molded body 90 before firing is shown by a solid line, and the insulator 11 (sintered body) obtained by firing the ceramic molded body 90 is shown by an imaginary line (two-dot chain line). The supporting portion 81 of the firing jig 80 on which the inclined surface 82 is formed is placed on the upper end of the wall portion 42.

As shown in FIG. 9, an annular inclined surface 82 is intermittently formed on the supporting portion 81 of the firing jig 80. Holes (not shown) penetrating in the plate thickness direction are formed in the wall portion 42 and the supporting portion 81 of the firing jig 80. Since holes are formed in the wall portion 42 and the support portion 81, heat transfer by convective heat conduction between the first space 65 (see FIG. 4) and the second space 66 is performed, as in the first embodiment. You can

The ceramic molded body 90 has a long first portion 91, a second portion 92 having a larger diameter than the first portion 91, and an outer diameter smaller than that of the second portion 92. The third portion 93 is provided on the opposite side of the first portion 91. The outer diameter of the third portion 93 is smaller than that of the first portion 91.

The firing jig 80 supports the outer peripheral edge 94 (corner portion) of the second portion 92 of the ceramic molded body 90 on the inclined surface 82, and suspends the first portion 91 in the vertical direction. The third portion 93 of the ceramic molded body 90 projects upward in the vertical direction with respect to the support portion 81. The first portion 91 constitutes the body portion 13 of the insulator 11 after firing. The second portion 92 of the ceramic molded body 90 constitutes the large diameter portion 14 of the insulator 11 after firing. The third part 93 of the ceramic molded body 90 constitutes the middle body part 15, the leg long part 16 and the shelf part 32 of the insulator 11 after firing.

Since the third portion 93 of the ceramic molded body 90 has an outer diameter smaller than that of the first portion 91, it is difficult to raise the position of the center of gravity of the ceramic molded body 90 on which the first portion 91 is suspended. Therefore, the firing jig 80 can stably support the ceramic molded body 90.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications are possible without departing from the spirit of the present invention. It can be easily guessed. For example, the shapes, sizes, and the like of the insulator 11, the ceramic molded bodies 60, 90, and the firing jigs 40, 70, 80 are not limited to this, and can be set appropriately.

In each of the above-described embodiments, the ceramic molded bodies 60 and 90 for manufacturing the insulator 11 of the spark plug 10 have been described. However, the application of the sintered body obtained by firing the ceramic molded body is not necessarily limited to the spark plug. The usage of the sintered body can be set as appropriate.

In each of the above embodiments, the case where the furnace 50 for firing the ceramic molded bodies 60 and 90 is a continuous furnace has been described, but the present invention is not limited to this. It is naturally possible to manufacture a sintered body using a batch furnace in which a certain amount of the ceramic molded bodies 60 and 90 are housed and fired.

In each of the above embodiments, the case where the wall portion 42 of the firing jig 40, 70, 80 and the bottom plate 41 are formed separately has been described, but the present invention is not limited to this. It is naturally possible to form the bottom plate 41 and the wall portion 42 as an integrally molded product.

Further, by using the moving member 53 in the case of a continuous furnace or the shelf plate in the case of a batch furnace, the lower end portion of the opening of the wall portion 42 of the firing jigs 40, 70, 80 is closed to close the wall portion 42 with a bottomed cylinder. If the first space 65 can be formed by forming the shape, it is possible to omit the bottom plate 41.

In each of the above-described embodiments, the case where the opening 44 is provided in the plate-shaped support portions 43, 71, 81 and the inclined surfaces 46, 72, 82 are formed inside the opening 44 has been described, but the present invention is not limited to this. is not. It is naturally possible to provide a plurality of arms (supporting portions) projecting inward on the wall portion 42, and to form an inclined surface that narrows toward the lower end side of the wall portion 42 on the end surfaces of the plurality of arms. .. In this case, the gap between the arms protruding from the wall 42 becomes a hole provided in the support portion.

In each of the above-described embodiments, the case where the holes 47 and 48 are formed in both the wall 42 and the supporting portions 43, 71 and 81 has been described, but the present invention is not limited to this. Of course, it is possible to omit the hole in either one of the wall portion 42 and the support portions 43, 71, 81. Further, when the gap between the ceramic molded bodies 60, 90 and the support portion 43 is the hole portion 49, both the wall portion 42 and the hole portions 47, 48 of the support portions 43, 71, 81 can be omitted.

In each of the above-described embodiments, a part or a plurality of parts of the configuration of another embodiment can be added to the embodiment or a part or a plurality of parts of the configuration of the embodiment can be exchanged. For example, it is naturally possible to make the inclined surface 72 described in the second embodiment intermittently like the inclined surface 46 described in the first embodiment. As a result, heat can be easily transferred to the second portion 62 of the ceramic molded body 60 by convective heat conduction.

Similarly, it is naturally possible to make the inclined surface 46 described in the first embodiment and the inclined surface 82 described in the third embodiment continuous like the inclined surface 46 described in the second embodiment. Is. As a result, it is possible to stably support the outer peripheral edges 64 and 94 of the second portions 62 and 92 that linearly contact the inclined surface.

Further, it is naturally possible to fire the ceramic molded body 90 described in the third embodiment using the firing jigs 40 and 70 described in the first embodiment and the second embodiment. Also in this case, the position of the center of gravity of the ceramic molded body 90 can be prevented from rising, so that the ceramic molded body 90 can be stably supported.

In the above embodiment, the case where the engaged portion 35 of the metal shell 30 is engaged with the rear end portion of the large diameter portion 14 via the ring member 37 and the powder 38 has been described, but this is not always the case. It is not limited. It is of course possible to omit the ring member 37 and the powder 38 and engage the engaged portion 35 of the metal shell 30 with the rear end portion of the large diameter portion 14 of the insulator 11.

Although the insulator 11 used in the spark plug 10 in which the ground electrode 39 faces the tip of the center electrode 20 has been described in the above embodiment, the structure of the spark plug is not necessarily limited to this. It is of course possible to apply the technique of the present embodiment to other spark plugs including the insulator 11. Other spark plugs include, for example, a spark plug in which the ground electrode 39 faces the side surface of the center electrode 20, a multi-pole spark plug in which a plurality of ground electrodes 39 are joined to the metal shell 30, and a spark plug protruding in the axial direction from the center electrode. Examples of the metal plug include a spark plug in which a ring-shaped ground electrode is arranged at the tip of the metal shell, a spark plug in which the ground electrode 39 is omitted and the center electrode is covered by a bottomed cylindrical insulator.

In addition, "a method of manufacturing a sintered body obtained by firing a ceramic molded body, comprising: a ceramic molded body having a long first portion and a second portion having a diameter larger than that of the first portion; A molding step of molding, a bottomed cylindrical wall portion having a closed lower end side, and an inclined surface which is an inclined surface whose upper end surface narrows toward the lower end side and which is continuously or intermittently formed into an annular shape. A state in which the outer peripheral edge of the second portion of the ceramic molded body is supported on the inclined surface of the firing jig including a support portion fixed to the inside of the wall portion, and the first portion is suspended in the vertical direction. And a firing step in which the firing jig is placed in a furnace to fire the ceramic molded body, and the inclined surface is a curved surface convex upward.” It is an invention included in the embodiment.

The present invention has the following effects. That is, in the ceramic molded body whose outer diameter of the outer peripheral edge of the second portion is reduced by firing, the contact position of the outer peripheral edge of the second portion on the inclined surface is lowered due to contraction during firing. When the ceramic molded body descends, the axis of the ceramic molded body may be inclined with respect to the vertical direction and the sintered body may be deformed. However, if the inclined surface is a curved surface that is convex upward, the inclined surface is lower. It is possible to reduce the amount of lowering of the second portion due to shrinkage during firing, as compared with the case of a convex curved surface or a flat surface. As a result, it is possible to reduce the possibility that the sintered body is deformed in a state where the shaft is tilted, and thus it is possible to suppress the generation of a defective sintered body in which the shaft is tilted.

11 Insulator (sintered body)
40, 70, 80 Firing jig 42 Wall part 43, 71, 81 Support part 46, 72, 82 Inclined surface 47, 48, 49 Hole part 50 Furnace 60, 90 Ceramic molded body 61, 91 First part 62, 92 2nd part 63,93 3rd part 64,94 Outer peripheral edge 65 1st space 66 2nd space

Claims (8)

A method for manufacturing a sintered body obtained by firing a ceramic molded body,
A forming step of forming the ceramic formed body including a long first portion and a second portion having a diameter larger than that of the first portion;
It has a bottomed cylindrical wall portion with a closed lower end side, and an inclined surface whose upper end surface narrows toward the lower end side and which is formed continuously or intermittently in an annular shape, and is fixed to the inside of the wall portion. And a supporting portion for supporting the outer peripheral edge of the second portion of the ceramic molded body on the inclined surface of the firing jig, and suspending the first portion in the vertical direction. And a firing step of firing the ceramic molded body by placing it in a furnace,
The firing jig includes a first space surrounded by the ceramic molded body, the wall portion and the support portion in a state where the outer peripheral edge of the second portion is in contact with the inclined surface in the firing step, and the firing. A method for manufacturing a sintered body, comprising a hole communicating with the second space inside the furnace outside the jig . The method for manufacturing a sintered body according to claim 1, wherein the hole is provided in the wall. The method for manufacturing a sintered body according to claim 1, wherein the hole is provided in the support. The method for producing a sintered body according to claim 1, wherein the inclined surface is continuously provided. The inclined surface is provided intermittently,
The method for manufacturing a sintered body according to claim 1, wherein the hole portion is a gap between the ceramic molded body supported by the intermittent inclined surface and the support portion. The ceramic molded body has a third portion having an outer diameter smaller than that of the second portion and provided on the opposite side of the first portion with the second portion interposed therebetween.
The method for producing a sintered body according to claim 1, wherein the third part has an outer diameter smaller than that of the first part. The ceramic molded body has a third portion having an outer diameter smaller than that of the second portion and provided on the opposite side of the first portion with the second portion interposed therebetween.
The method for producing a sintered body according to claim 1, wherein the third part has an outer diameter larger than that of the first part. The method for manufacturing a sintered body according to claim 1, wherein the inclined surface is a curved surface that is convex upward.

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