Insulator for spark plug, and method for manufacturing spark plug

[0030] Example 1

[0031] The manufacturing method of Example 1 is a method of manufacturing the insulator 2, and the insulator 2 is an insulator for spark plugs. Since the spark plug 100 includes the insulator 2, first, the overall configuration of the spark plug 100 will be explained.

[0032] The spark plug 100 includes: a cylindrical metal shell 1; an insulator 2 fitted into the metal shell 1 so that its front end protrudes; a center electrode 3 provided in the insulator 2 with its front end protruding; and The ground electrode 4 is configured such that one end of the ground electrode 4 is joined to the metal shell 1 by welding or the like and the other end is bent laterally so that one side of the other end faces the front end of the center electrode 3.

[0033] A spark discharge gap g is formed between the ground electrode 4 and the center electrode 3. The metal shell 1 is formed of a metal such as low carbon steel in a cylindrical shape, and forms a casing for the spark plug 100. The outer peripheral surface of the metal shell 1 is formed with a threaded portion 7 and a tool engaging portion 1e. The threaded portion 7 is used to mount the spark plug 100 to an unshown engine. The tool engaging portion 1e has a hexagonal shaft cross-sectional shape, and when the metal shell 1 is mounted to the engine, the tool engaging portion 1e is engaged with a tool such as a wrench or a wrench. The center electrode 3 and the ground electrode 4 are made of Ni alloy or the like, and if necessary, a core material 3a such as Cu or Cu alloy for improving heat dissipation can be buried.

[0034] The insulator 2 is made of an insulating material mainly including alumina or the like. The insulator 2 is formed with a through hole 6 extending in the axial direction. The center electrode 3 is inserted and fixed into the front end side of the through hole 6, and the terminal electrode 13 is inserted and fixed into the rear end side of the through hole 6. The resistor 15 is arranged inside the through hole 6 and between the terminal electrode 13 and the center electrode 3. Both ends of the resistor body 15 are electrically connected to the center electrode 3 and the terminal electrode 13 via conductive glass sealing layers 16 and 17, respectively. The resistor body 15 is formed of a resistor composition, which is obtained by mixing glass powder and conductive material powder (using ceramic powder instead of glass powder if necessary) and sintering the resulting mixture by a hot press or the like.

[0035]The diameter of the center electrode 3 (in a cross section perpendicular to the axial direction) is set to be smaller than the diameter of the resistor 15. The through hole 6 has a first portion 6a and a second portion 6b each in the form of holes having a circular cross-sectional shape. The second part 6b is arranged on the rear side (upper side in the figure) of the first part 6a and has a larger diameter than that of the first part 6a. The terminal electrode 13 and the resistor body 15 are housed in the second part 6b, and the center electrode 3 is inserted into the first part 6a. The rear end of the center electrode 3 is formed with an electrode fixing lug 3b protruding outward from the outer peripheral surface of the center electrode 3. A convex portion receiving surface 6c for receiving the electrode fixing convex portion 3b of the center electrode 3 is formed at the connection position between the first portion 6a and the second portion 6b of the through hole 6 in the form of a tapered surface or an arched surface.

[0036] In order to facilitate the removal of the pressing pin 50 described later, an extraction taper (for example, about 5/1000) whose diameter increases toward the rear side in the axial direction is formed on the inner peripheral surface of the second portion 6b of the through hole 6. To 5/100). On the other hand, an extraction taper angle is formed on the inner peripheral surface of the first portion 6a that is smaller than the extraction taper angle of the second portion 6b, or the extraction taper is hardly formed on the inner peripheral surface of the first portion 6a.

[0037] In addition, if the specific dimensions of the outer shape of the insulator 2 are exemplified, for example, the overall length of the insulator 2 is 30mm to 75mm, and the average inner diameter of the second portion 6b of the through hole 6 is about 2mm to 5mm. Similarly, the average length of the first portion 6a The inner diameter is, for example, about 1 mm to 3.5 mm. In order to save space for the spark plug 100 or improve its performance such as heat generation characteristics, the diameter of the insulator 2 can be made smaller.

[0038] Next, a method of manufacturing the insulator 2 will be explained. The above-mentioned insulator 2 is manufactured by a manufacturing method including a sequential manufacturing step, a pin arranging step, a powder filling step, a cavity closing step, a pressure forming step, a demolding step, and a pin removing step. Hereinafter, each step will be explained.

[0039] Preparation steps

[0040] In the preparation step, the pressing pin 50 and the forming die 80 are prepared.

[0041] Such as figure 2 As shown, the pressing pin 50 is a metal shaft member for forming the through hole 6. In more detail, the pressing pin 50 is formed on the front end side for forming figure 1 The first shaft portion 51 of the first portion 6a of the through hole 6 and the second shaft portion 52 for forming the second portion 6b of the through hole 6 in the middle. The second shaft portion 52 continues from the rear side of the first shaft portion 51. Between the first shaft portion 51 and the second shaft portion 52 and figure 1 The convex portion receiving surface 6c of the through hole 6 corresponds to the step portion 53.

[0042] An extraction taper (for example, an extraction taper of approximately 5/1000 to 5/100 corresponding to the extraction taper of the second portion 6b) that increases in diameter toward the rear side in the axial direction is formed on the outer peripheral surface of the second shaft portion 52. An extraction taper angle smaller than the extraction taper angle of the second shaft portion 52 (corresponding to the extraction taper of the first portion 6a) is formed on the outer peripheral surface of the first shaft portion 51, or substantially on the outer peripheral surface of the first shaft portion 51 Does not form a take-out taper. The average outer diameter of the first shaft portion 51 corresponds to the average inner diameter of the first portion 6 a of the through hole 6, and the average outer diameter of the second shaft portion 52 corresponds to the average inner diameter of the second portion 6 b of the through hole 6. The size of the pressing pin 50 can be selected according to the type of insulator to be manufactured. Especially when a thin insulator is to be manufactured, a small-diameter pressing pin whose diameter size of the second shaft portion 52 is approximately 2.5 mm to 3.6 mm can be used.

[0043] Since the pressing pin 50 is such a very thin shaft member, for example, the entire pressing pin is made of a material with high rigidity such as cemented carbide, alloy tool steel, etc., so that steps such as pressure forming steps do not occur. Problems such as bending.

[0044] A flange-shaped end surface forming portion 55 is integrally formed at the rear end of the second shaft portion 52 of the pressing pin 50, and the flange-shaped end surface forming portion 55 is used to form the rear end surface of the blank PC described later. A head 56 having an internal threaded portion 57 extending in the axial direction is integrally formed on the rear side of the forming portion 55. Such as image 3 As shown, the upper holding portion 86 is rotatably fitted to the outside of the head 56.

[0045] Such as figure 2 As shown, a rib-shaped pin-side spiral portion 54 is formed on the outer peripheral surface on the rear end side of the second shaft portion 52. The spiral winding direction of the pin-side spiral portion 54 is opposite to the spiral winding direction of the female thread portion 57.

[0046] Such as Figure 3 to Figure 6 As shown, the forming die 80 is configured to perform a forming method generally referred to as "rubber pressing." "Rubber pressing" is a forming method in which powders such as ceramic materials are filled into a rubber mold and a high fluid pressure is applied from the outer periphery of the rubber mold to produce a homogeneous green body.

[0047] In more detail, the forming mold 80 is configured such that the cylindrical inner rubber mold 82 is substantially concentrically arranged inside the cylindrical outer rubber mold 81, and the outer rubber mold 81 is arranged in the forming mold member 80a. The inner rubber mold 82 defines a cavity 83 passing through the inner rubber mold 82 in the axial direction. The opening on the lower side (the front end side in the axial direction) of the cavity 83 is closed by a bottom lid 84 and a lower holding portion 85. An opening 89 is formed above the cavity 83 (rear end side in the axial direction). Such as Figure 5 As shown, when the rear end of the pressing pin 50 integrally formed with the upper holding portion 86 is fitted into the opening 89 in a cavity closing step described later, the opening 89 is closed. In this way, the inside of the cavity 83 is in a sealed state.

[0048] Pin configuration steps

[0049] Such as image 3 As shown, in the step of arranging the pressing pin, the tip of the rotating shaft 87 is screwed into the female threaded portion 57, and the pressing pin 50 is axially advanced from the opening 89 toward the tip side of the forming die 80 to place the upper holding portion 86 The pressing pin 50 in a state of being fitted to the outside of the head 56 is arranged in the cavity 83. Here, will be Figure 5 In the illustrated pressure forming step, the position of the pressure pin 50 arranged inside the cavity 83 is defined as the "final position". in Figure 3 to Figure 6 , The position of the front end (the front end side in the axial direction) of the pressing pin 50 in the final position is indicated by E. In Embodiment 1, in the pressing pin arrangement step, the advancement of the pressing pin 50 is stopped before reaching the final position E (for example, the axial distance between the front end of the pressing pin 50 and the final position E is about 5 mm to 20 mm) Therefore, a gap S1 is formed between the upper holding portion 86 and the opening 89 of the cavity 83 in the vertical direction (axial direction). That is, in this state, the front end of the pressing pin 50 is spaced from the final position E to provide the gap S1.

[0050] Powder filling step

[0051] Such as Figure 4 As shown, in the powder filling step, the raw material powder GP is filled into the cavity 83 through the gap S1 between the upper holding portion 86 and the opening 89 of the cavity 83.

[0052] For example, raw meal powder GP is prepared as described below. First, by mixing alumina powder (with an average particle diameter of 1 μm to 5 μm) and a sintering aid such as Si component, Ca component, Mg component, Ba component, or B component by mixing alumina powder in a predetermined ratio, and adding A hydrophilic binder (for example, PVA (polyvinyl alcohol) or acrylamide-based binder) and water are mixed and mixed to form a base slurry for molding. For additive element-based raw materials, for example, SiO can be used 2 Mixed with Si component in powder form, it can be CaCO 3 Ca is mixed in the form of powder, Mg can be mixed in the form of MgO powder, and BaCO 3 The Ba component can be mixed in the form of H 3 BO 3 The component B is mixed in the form of powder (or an aqueous solution). In addition, the base slurry for molding is spray-dried by a spray drying method or the like to produce raw meal powder GP as a base granulated material for molding.

[0053] The raw meal powder GP manufactured in this manner is adjusted by adjusting the conditions (for example, drying temperature, spray speed, etc.) during spray drying so that the raw meal powder GP contains 1.5% by weight or less of water. The main purpose of mixing water is to reduce the binding force of the powder particles in the granulated particles, to promote the rupture of the granulated particles under pressure, and to expand the hydrophilic binder mixed with the molding substrate to show its effectiveness. The adhesiveness, thereby increasing the strength of the green PC.

[0054] Although the lower limit of the water content of the raw meal powder GP differs depending on the particle size distribution of the raw meal powder GP, etc., the lower limit is appropriately set to a level that does not make the above effect insufficient. If the water content exceeds 1.5% by weight, the fluidity of the granulated material decreases, and handling becomes difficult. More desirably, the water content is adjusted to a range of 1.3% by weight or less.

[0055] The mixing amount of the hydrophilic binder in the raw meal powder GP may preferably be adjusted to 0.5% to 3.0% by weight. If the blending amount of the hydrophilic binder is less than 0.5% by weight, the strength of the green PC becomes insufficient, the handling becomes difficult, and cracks, chipping, etc. are likely to occur. If the blending amount exceeds 3.0% by weight, the de-binder treatment time at the time of sintering becomes longer, which leads to a decrease in the production efficiency of the insulator. In addition to this, the residual amount of impurity components (for example, carbon) derived from the binder in the insulator may increase, which results in a decrease in performance (for example, dielectric voltage resistance).

[0056] Such as Figure 4 As shown, the raw meal powder GP adjusted to the above state is charged into the cavity 83 from the gap S1 between the upper holding portion 86 and the opening 89 of the cavity 83 to accumulate upward from the lower portion of the cavity 83. In this way, the raw meal powder GP is filled into the cavity 83 and surrounds the pressing pin 50 arranged in the cavity 83. After a predetermined amount of raw meal powder GP is filled into the cavity 83, the next step is performed.

[0057] Mold cavity occlusion step

[0058] Such as Figure 5 As shown, in the cavity closing step, the pressing pin 50 stopped in the cavity 83 before reaching the final position E is inserted to reach the final position E. Meanwhile, when the rear end of the press pin 50 integrally formed with the upper holding portion 86 is fitted into the opening 89, the opening 89 is blocked. In this way, the inside of the cavity 83 is in a sealed state. Here, since the raw meal powder GP is adjusted so that its water content is within the aforementioned predetermined range, the raw meal powder is not in a dry and loose state. Therefore, when the pressing pin 50 moves toward the front end side of the mold 80 in the axial direction in the raw meal powder GP, the pressing pin 50 receives a certain magnitude of resistance from the raw meal powder GP. However, in Example 1, the insertion distance of the pressing pin 50 in the cavity closing step is a very short distance, that is, the distance from the tip of the pressing pin 50 stopped in the powder filling step to the final position E, which is approximately equal to the gap S1 corresponds. Therefore, the resistance from the raw powder GP that the pressing pin 50 receives in the cavity closing step can be significantly reduced. Here, the upper holding portion 86 may serve as a closing member for closing the opening 89.

[0059] Pressure forming step

[0060] Such as Figure 5 As shown, in the pressure forming step, the green powder GP in the cavity 83 and the pressing pin 50 are pressed together to obtain a green body PC.

[0061]In more detail, the fluid pressure FP is applied to the outer peripheral surface of the outer rubber mold 81 in the radial direction via the pressurized fluid passage 80b formed in the forming mold body 80a, so that the outer rubber mold 81 and the inner rubber mold 82 are elastically deformed to reduce Their diameter and cavity 83 volume. Therefore, the fluid pressure FP is indirectly applied to the raw meal powder GP via the outer rubber mold 81 and the inner rubber mold 82, thereby compressing the raw meal powder GP filled in the cavity 83. As a result, the raw powder GP of the cavity 83 is solidified in an integral form with the pressing pin 50, thereby obtaining a green body PC.

[0062] In this case, it is preferable to adjust the fluid pressure FP in the range of 30 MPa to 150 MPa. If the fluid pressure FP becomes less than 30 MPa, the strength of the green body PC becomes insufficient, handling becomes difficult, and cracks, chipping, etc. are likely to occur. If the hydraulic pressure exceeds 150 MPa, the life of the outer rubber mold 81 and the inner rubber mold 82 may be shortened, which may result in an increase in cost.

[0063] Demoulding step

[0064] Such as Figure 6 As shown, in the demolding step, the blank PC and the pressing pin 50 are released from the mold cavity 83 together. In more detail, when the application of the fluid pressure FP is released, the outer rubber mold 81 and the inner rubber mold 82 elastically return to their original shapes, so that the cavity 83 also returns to its original shapes. Therefore, the outer peripheral surface of the blank PC is detached from the inner peripheral surface (inner rubber mold 82) of the cavity 83 to provide a space therebetween. With respect to the outer rubber mold 81 and the inner rubber mold 82, the pressure pin 50 integrally combined with the rotating shaft 87 and the upper holding portion 86 is pulled out toward the rear end side of the mold 80 in the axial direction, and the pressure of the blank PC is adhered thereto. The pin 50 is pulled out from the cavity 83.

[0065] Pin removal steps

[0066] Such as Figure 7 As shown, in the pressing pin removal step, the pressing pin 50 is taken out of the blank PC. In more detail, when the blank PC is obtained using the pressing pin 50 having the pin-side spiral portion 54, the blank PC is formed with the blank-side spiral portion 20 a accordingly. The blank side spiral portion 20a has the reverse shape of the pin side spiral portion 54 (that is, a groove shape), and is located at the rear end of the inner cylindrical surface of the blank PC opposite to the second shaft portion 52 of the pressing pin 50 . In addition, the blank-side spiral portion 20a is often removed by cutting or the like. However, such as figure 1 As shown, if the body-side spiral portion 20a is not removed, the body-side spiral portion 20a remains as the spiral portion 20 in the insulator 2 after sintering.

[0067] Such as Figure 7 As shown, in a state where the blank PC pulled out from the mold cavity 83 is held by an air chunk (not shown), it is fastened on the rotating shaft 87 by a driving source such as a motor (not shown). The rotating shaft 87 screwed on the female screw hole 57 of the pressing pin 50 is rotated in the direction into the female screw hole 57. Therefore, the pressing pin 50 rotates about the axis with respect to the blank PC, so that the pressing pin 50 is loosened from the blank PC body by the thread action between the pin-side spiral portion 54 and the blank-side spiral portion 20a. Therefore, the pressing pin 50 moves upward in the take-out direction while rotating.

[0068] That is, since the pressing pin 50 slowly moves upward during the rotation by means of the screw, it is prevented from being generated between the outer circumferential surface of the pressing pin 50 and the inner cylindrical surface of the blank PC opposite to the outer circumferential surface of the pressing pin 50 Excessive friction. Therefore, the pressing pin 50 can be smoothly taken out without damaging the green body PC. In addition, since the second shaft portion 52 of the pressing pin 50 is formed with a take-out taper, when the pressing pin 50 is slightly moved upward with respect to the blank PC, a gap between the pressing pin 50 and the inner cylindrical surface of the blank PC can be ensured. Therefore, the pressing pin 50 can be easily released. In addition, a mold release layer such as a hard carbon-based mold release layer may be formed on the outer peripheral surface of the press pin 50 to further facilitate the removal of the press pin 50.

[0069] Such as Figure 8 As shown, the outer surface of the blank PC from which the above-mentioned steps have been completed and the pressing pin 50 has been taken out is machined by a grinder or the like to be trimmed into a shape corresponding to the insulator 2, and then heated at 1400°C to 1650°C Sintered at a temperature. Therefore, the inner cylindrical surface of the blank PC that once opposed the outer peripheral surface of the press pin 50 becomes the through hole 6. Next, the glaze is further applied to the green body, and the green body is finally sintered by coating the glaze on the green body, thereby completing figure 1 Insulator 2 shown. The insulator 2 obtained in this way is assembled to other constituent members such as the metal shell 1 to complete the spark plug 100. The spark plug 100 is mounted to the engine using the threaded portion 7, and the spark plug 100 is used as an ignition source of the air-fuel mixture supplied into the combustion chamber.

[0070] As described above, in the manufacturing method of the spark plug insulator according to Embodiment 1, the pressing pin arrangement step is performed before the powder filling step so that the pressing pin 50 is arranged in the cavity 83 while ensuring the gap S1. Next, in the powder filling step, the raw material powder GP is charged into the cavity 83 from the gap S1 to be filled into the cavity 83 around the pressing pin 50 arranged in the cavity 83. In the subsequent cavity closing step, the distance by which the pressing pin 50 is inserted to the final position E becomes a very short distance substantially corresponding to the gap S1. Therefore, in the cavity closing step, the resistance from the raw powder GP received by the pressing pin 50 can be significantly reduced. Therefore, the bending of the pressing pin 50 is prevented, and the inner cylindrical surface of the blank PC opposite to the outer peripheral surface of the pressing pin 50 can be formed to extend straight in the axial direction. Therefore, the through hole 6 of the insulator 2 also extends straight in the axial direction.

[0071] According to the manufacturing method of Embodiment 1, when the insulator 2 having a small diameter is manufactured, the generation of defective products can be reduced, and the replacement frequency of the pressing pin 50 can be reduced. That is, this manufacturing method can ensure a high yield of the insulator 2, and can achieve a low manufacturing cost of the spark plug 100.

[0072] According to the manufacturing method of Embodiment 1, the upper holding portion 86 serving as the blocking member is integrated with the pressing pin 50. In the pin arranging step, the pin 50 is stopped before reaching the final position E to ensure a gap S1 between the upper holding portion 86 and the opening 89 that is sufficient to supply the raw powder GP into the cavity 83. The raw material powder GP is supplied from the gap S1 and filled into the cavity 83. In addition, when the pressing pin 50 is moved to the final position E in the cavity closing step, the upper holding portion 86 moves integrally with the pressing pin 50 to close the opening 89. The manufacturing method with such a simple configuration can easily provide operational effects.

[0073] Example 2

[0074] Although the manufacturing method of the second embodiment is similar to the manufacturing method of the first embodiment, the pressing pin 250 and the upper holding portion 286 are used in the second embodiment instead of the pressing pin 50 and the upper holding portion 86 in the first embodiment. Therefore, due to the difference in the structure of these components, the above steps also have different points. Hereinafter, the description will be focused on differences from the manufacturing method of Embodiment 1, and the description of the same steps as those of Embodiment 1 will be omitted or simplified. The same reference numerals are used to indicate the same configurations as in Embodiment 1, and the description of these same configurations is omitted.

[0075] Below, will refer to Figure 9 to Figure 13 The method of manufacturing the insulator 2 according to Embodiment 2 will be described.

[0076] Preparation steps

[0077] Such as Picture 9 As shown, in the preparation step, the pressing pin 250 and the forming die 80 are prepared. Since the molding die 80 is the same as the molding die in the first embodiment, the description of the molding die 80 is omitted.

[0078] Similar to the pressing pin 50 of Embodiment 1, the pressing pin 250 is formed with a first shaft portion 51, a stepped portion 53, a second shaft portion 52, and a pin-side spiral portion 54. The pressing pin 250 is not formed with the end face forming portion 55 and the head 56 in the pressing pin 50 of the first embodiment. Instead, the pressing pin 250 is integrally formed with a columnar shaft portion 287 extending from the rear end of the second shaft portion 52 toward the rear side in the axial direction. The rotating shaft portion 287 corresponds to the rotating shaft 87 of Embodiment 1, and is adapted to be rotated by a driving source such as a motor (not shown).

[0079] Such as Picture 9 As shown by the others, the upper holding portion 286 is provided around the outer peripheral surface of the rotating shaft portion 287. Such as Figure 10A with Figure 10B As shown, the upper holding portion 286 is composed of three split members 286a, 286b, and 286c each having a fan-shaped cross section. These sub-members 286a, 286b, and 286c are arranged to surround the outer peripheral surface of the shaft portion 287. The central space surrounded by the sub-members 286a, 286b, and 286c serves as an insertion hole 286d through which the shaft portion 287 can be inserted.

[0080] Such as Figure 10A As shown, when the sub-members 286a, 286b, and 286c are separated radially outward from the shaft portion 287, the diameter of the insertion hole 286d increases. In this state, the shaft portion 287 passing through the insertion hole 286d is movable in the axial direction with respect to the upper holding portion 286.

[0081] Such as Figure 10B As shown, when the sub-members 286a, 286b, and 286c are close to the shaft portion 287, the insertion hole 286d is brought into close contact with the shaft portion 287, so that the sub-members 286a, 286b, and 286c are combined into one body to form an annular member. The sub-members 286a, 286b, and 286c in this state can close the opening 89 in the cavity closing step described below, thereby sealing the inside of the cavity 83.

[0082] Such as Picture 9 As shown, the pressing pin 250 is formed with a protruding portion 251a that protrudes in the axial direction from the first shaft portion 51 toward the front end in a substantially conical shape. A recess 284a is formed in the center of the upper surface of the bottom cover 84 to correspond to the protrusion 251a. The tip of the protrusion 251a can be fitted into the recess 284a.

[0083] Pin configuration steps

[0084] In the pressing pin arrangement step, first, the pressing pin 250 and the upper holding portion 286 are arranged above the opening 89 of the forming die 80. Next, the sub-members 286a, 286b, and 286c of the upper holding portion 286 are separated radially outward from the shaft portion 287 to increase the diameter of the insertion hole 286d. In this case, a gap S2 in the vertical direction is formed between the upper holding portion 286 and the opening 89. In the second embodiment, since the pressing pin 250 and the upper holding portion 286 can move relative to each other in the axial direction independently of each other, a gap S2 larger than the gap S1 of the first embodiment can be formed.

[0085] Then, the rotating shaft portion 287 moves toward the front end in the axial direction with respect to the insertion hole 286d, thereby inserting the pressing pin 250 into the cavity 83 from the opening 89 until the pressing pin 250 reaches the final position on the front end side in the axial direction. Will be in progress Picture 12 The position of the pressing pin 250 in the cavity 83 during the illustrated pressure forming step is defined as the "final position". Such as Picture 9 with Picture 11 As shown, unlike Embodiment 1, in Embodiment 2, the pressing pin 250 is arranged at the final position in the pressing pin arrangement step. When the pressing pin 250 is arranged in the final position, the front end of the protrusion 251a is fitted into the recess 284a of the bottom cover 84. Therefore, the pressing pin 250 is restricted, and the displacement in the direction perpendicular to the axis (radial direction) is prevented. The recessed portion 284a is used as a positioning portion for positioning the radial position of the tip of the pressing pin 250.

[0086] Powder filling step

[0087] Such as Picture 11 As shown, in the powder filling step, the raw material powder GP is filled into the cavity 83 from the gap S2 between the upper holding portion 286 and the opening 89 of the cavity 83 around the pressing pin 250.

[0088] Mold cavity occlusion step

[0089] Such asPicture 11 As shown, in the cavity blocking step, the diameter of the insertion hole 286d will be as Figure 10A The upper holding portion 286 in the enlarged state as shown moves toward the front end in the axial direction so as to Picture 12 The opening 89 is blocked as shown. Through the movement of the upper holding portion 286, the front end of the upper holding portion 286 is fitted into the opening 89 of the cavity 83, so that the diameter of the insertion hole 286d is gradually reduced and finally the sub-members 286a, 286b, and 286c are brought into close contact with each other. Constitute a Figure 10B Annular body shown. Therefore, the inside of the cavity 83 is reliably sealed. Here, unlike the cavity closing step of Embodiment 1, the pressing pin 250 does not move in the cavity closing step of Embodiment 2. Therefore, the pressing pin 250 does not receive any resistance from the raw meal powder GP. The upper holding portion 286 serves as a closing member for closing the opening 89.

[0090] Pressure forming step

[0091] Such as Picture 12 As shown, in the pressure forming step, the green powder GP in the cavity 83 and the pressing pin 250 are pressed together to obtain a green body PC. Since the details of the pressure forming step are the same as the pressure forming step of Embodiment 1, the description of the pressure forming step is omitted.

[0092] Demoulding step

[0093] In the demolding step, release as Picture 12 The application of the fluid pressure FP in the state shown causes the contracted cavity 83 to return to its original shape, and the outer circumferential surface of the blank PC is released from the inner circumferential surface of the cavity 83. In addition, the pressing pin 250 and the blank PC in a state where the sub-members 286a, 286b, and 286c of the upper holding portion 286 are in close contact with each other are pulled out together in the axial direction with respect to the outer rubber mold 81 and the inner rubber mold 82. Therefore, the pressing pin 250 with the blank PC thereon is pulled out from the cavity 83.

[0094] Pin removal steps

[0095] Such as Figure 13 As shown, in the pressing pin removal step, the pressing pin 250 is taken out of the blank PC. In more detail, such as Figure 10A As shown, the sub-members 286a, 286b, and 286c of the upper holding portion 286 are separated radially outward from the shaft portion 287 to increase the diameter of the insertion hole 286d. Such as Figure 13 As shown, in a state where the blank PC pulled out from the mold cavity 83 is held by an air chunk (not shown), the pressing pin is rotated counterclockwise by a driving source such as a motor (not shown). 250 of the shaft 287. Therefore, the pressing pin 250 rotates about the axis relative to the blank PC, and as described above, the pressing pin 250 is taken out from the blank PC by means of the screw action between the pin-side spiral portion 54 and the blank-side spiral portion 20a. Since the pin-side spiral portion 54 of the pressing pin 250 can be moved without difficulty in the insertion hole 286d having an increased diameter, the size of the manufacturing apparatus of the insulator 2 can be reduced.

[0096] Similar to Embodiment 1, the green body PC from which the above-mentioned various steps have been completed and the pressing pin 250 has been taken out is cut and sintered into the insulator 2 and assembled to the spark plug 100.

[0097] According to the method of Embodiment 2, by increasing the diameter of the insertion hole 286d of the upper holding portion 286 as the blocking member, the pressing pin 250 can be moved in the insertion hole 286d. That is, the pressing pin 250 and the upper holding portion 286 can move independently of each other. Therefore, in this manufacturing method, as described above, even if the pressing pin 250 is moved to the final position in the cavity 83 in the pressing pin arranging step before the powder filling step, the upper holding portion 286 and the opening 89 can be easily secured. The gap between S2.

[0098] According to this manufacturing method, in the powder filling step, the raw material powder GP is charged into the cavity 83 from the gap S2 to fill the cavity 83 around the pressing pin 250 provided in the final position in the cavity 83. In the cavity closing step, the upper holding portion 286 moves independently of the pressing pin 250 to close the opening 89. Therefore, in the cavity closing step, the pressing pin 250 does not move, and does not receive any resistance from the raw powder GP. That is, the bending of the pressing pin 250 is prevented.

[0099] Therefore, the manufacturing method of Example 2 can also show the same operational effects as the manufacturing method of Example 1, and is more reliable than the manufacturing method of Example 1.

[0100] In addition, in this manufacturing method, the front end of the pressing pin 250 is restricted in the cavity 83 by the recess 284 a formed at the bottom cover 84 of the molding die 80 as a positioning portion. In the pressure forming step, when the cavity 83 shrinks, even if a compressive force in a direction perpendicular to the axis acts on the pressure pin 50, the radial position of the front end of the pressure pin 250 can be prevented from shifting. That is, the bending of the pressing pin 250 is prevented.

[0101] Example 3

[0102] Although the manufacturing method of embodiment 3 is similar to that of embodiment 1, as Figure 14 with 15 As shown, the pin configuration steps of Example 1 are changed (such as image 3 Shown) and powder filling steps (such as Figure 4 Shown). Hereinafter, the description will focus on the differences from the manufacturing method of Embodiment 1, and the description of the same steps as those of Embodiment 1 will be omitted or simplified. In addition, the same configurations as those of Embodiment 1 are designated by the same reference numerals, and the description of these same configurations is omitted.

[0103] Preparation steps

[0104] In the preparation step, similar to Example 1, the pressing pin 50 and the forming die 80 are prepared. As described in the preparation procedure of Example 1, the pressing pin 50 has: the first shaft portion 51 on the front end side in the axial direction; and is closer to the rear end side than the first shaft portion 51 in the axial direction. The second shaft portion 52 with a larger diameter; and the step portion 53 between the first shaft portion 51 and the second shaft portion 52. Such as figure 2 As shown, the step portion 53 is formed into a tapered shape to connect the first shaft portion 51 and the second shaft portion 52 having different outer diameters.

[0105] Pin configuration steps

[0106] Such as Figure 14 As shown, in the pressing pin arrangement step, the front end of the rotating shaft 87 is screwed into the internal thread portion 57 of the pressing pin 50, and the upper holding portion 86 is assembled to the outside of the head 56 of the pressing pin 50. The pressing pin 50 in this state is set in the cavity 83 by advancing the pressing pin 50 in the axial direction from the opening 89 toward the front end. Here, similar to Example 1, will be Figure 5 The position where the pressure pin 50 is arranged inside the cavity 83 in the illustrated pressure forming step is defined as the "final position". in Figure 14 with Figure 15 In the figure, E is used to indicate the position of the front end of the pressing pin 50 in the final position. In Embodiment 3, in the step of disposing the pressing pin, the pressing pin 50 is stopped at a position in the axial direction away from the final position E by a stroke F which is shorter than the axial length T of the first shaft portion 51. Therefore, a gap S3 is formed between the front end of the upper holding portion 86 and the opening 89 of the cavity 83 in the radial direction perpendicular to the up-down direction (axial direction). That is, in this state, the front end of the pressing pin 50 is lifted from the final position E by the stroke F, and the front end of the upper holding portion 86 is lower than the opening 89 of the cavity 83 in the vertical direction.

[0107] Powder filling step

[0108] Such as Figure 15 As shown, in the powder filling step, the raw material powder GP is filled into the cavity 83 from the gap S3 between the upper holding portion 86 and the opening 89 of the cavity 83 around the pressing pin 50 provided inside the cavity 83.

[0109] As described above, in the powder filling step of Example 1, the base slurry for molding is spray-dried by the spray drying method or the like to produce the raw meal powder GP. Therefore, by adjusting the conditions during spray drying (for example, drying temperature, spraying speed, etc.), the raw meal powder is adjusted so that the water content is 1.5% by weight or less. Therefore, if the raw meal powder GP is excessively compressed, a consolidated aggregate is likely to be generated.

[0110] In the powder filling step, the charged raw meal powder GP is accumulated upward from the lower part of the mold 80 in the cavity 83. After filling a predetermined amount of raw meal powder GP into the mold cavity 83, the next step is performed.

[0111] Mold cavity occlusion step

[0112] In the cavity occlusion step, it is similar to the first embodiment, such as Figure 5 As shown, the pressing pin 50 is inserted to reach the final position E. At the same time, when the rear end of the pressing pin 50 integrated with the upper holding portion 86 is fitted into the opening 89, the opening 89 is blocked. Therefore, the inside of the cavity 83 is in a sealed state. Here, since the raw meal powder GP is adjusted so that its water content is within the above-mentioned predetermined range, the raw meal powder will not be in a dry and loose state. Therefore, when the pressing pin 50 moves toward the front end side in the axial direction in the raw meal powder GP, the pressing pin 50 receives a certain amount of resistance from the raw meal powder GP. In this case, the stepped portion 53 moves toward the front end by the stroke F in the axial direction while compressing the raw meal powder GP.

[0113] Pressure forming step

[0114] In the pressure forming step, similar to Example 1, such as Figure 5 As shown, the raw powder GP in the cavity 83 and the pressing pin 50 are pressed together to obtain a green body PC.

[0115] Demoulding step

[0116] In the demolding step, similar to Example 1, such as Figure 6 As shown, the blank PC and the pressing pin 50 are removed from the cavity 83 together.

[0117] Pin removal steps

[0118] In the step of removing the pin, it is similar to Example 1, as Figure 7 As shown, the pressing pin 50 is pulled out of the blank PC.

[0119] Similar to Embodiment 1, the green body PC from which the above-mentioned various steps have been completed and the pressing pin 50 has been taken out is cut and sintered into the insulator 2 and assembled to the spark plug 100.

[0120] In the method of manufacturing an insulator according to Embodiment 3, the pressing pin 50 has the first shaft portion 51, the second shaft portion 52, and the step portion 53 as described above. Furthermore, as described above, the pressing pin arrangement step is performed before the powder filling step, so that the pressing pin 50 is arranged in the cavity 83 while ensuring the gap S3. Next, in the powder filling step, the raw material powder GP is charged into the cavity 83 from the gap S3 and the cavity 83 is filled around the pressing pin 50 arranged in the cavity 83. Therefore, in the subsequent cavity closing step, the pressing pin 50 can be inserted a very short distance, that is, the stroke F to reach the final position E. Therefore, in the cavity closing step, the resistance from the raw powder GP received by the pressing pin 50 can be significantly reduced.

[0121] Therefore, the manufacturing method of Example 3 can also exhibit the same operational effects as the manufacturing method of Example 1.

[0122]In the manufacturing method according to Embodiment 3, the stroke F for moving the stepped portion 53 toward the front end side in the axial direction while compressing the raw meal powder GP is shorter than the axial length T of the first shaft portion 51. Therefore, the raw meal powder GP closer to the front end side than the step portion 53 is prevented from being excessively compressed, and the generation of compacted aggregates is also prevented. Therefore, there is almost no variation in the density of the raw powder GP around the first shaft portion 51, the second shaft portion 52, and the step portion 53 in the cavity 83. Therefore, defects such as pinholes are hardly generated in the insulator 2 obtained through the pressure forming step, and the occurrence of deterioration of insulation performance is prevented. In addition, in the manufacturing method of Embodiment 3, when the step portion 53 is moved by the stroke F, the raw meal powder GP around the first shaft portion 51 is appropriately compressed and densified in the axial direction by the step portion 53. Therefore, the small-diameter portion 2a (such as figure 1 Shown), or at the tip small-diameter portion 2a and the tip-side mid-diameter portion 2b (such as figure 1 Shown) will not produce defects. The tip small-diameter portion 2a is located on the tip side in the axial direction of the insulator 2, and is formed in a tapered thin-walled cylindrical shape. The center electrode 3 is arranged on the inner peripheral side of the tip small-diameter portion 2a. In the insulator 2, the front end side middle diameter part 2b is located closer to the rear end side than the front end small diameter part 2a in the axial direction, and the front end side middle diameter part 2b is formed as a thick wall having a larger diameter than the front end small diameter part 2a. Cylindrical shape. The rear end of the center electrode 3 in the axial direction and the resistor 15 are arranged on the inner peripheral side of the middle diameter portion 2b on the front end side. The tip small-diameter portion 2a is offset from the tip-side middle-diameter portion 2b to form a stepped portion with a changed wall thickness. No defect is generated between the front end small diameter portion 2a of the insulator 2 having such a structure and between the front end small diameter portion 2a and the front end side middle diameter portion 2b. Therefore, the insulation performance of the insulator 2 can be further improved.

[0123] According to this manufacturing method, the taper angle of the tapered step portion 53 can be appropriately adjusted to control the raw material received by the step portion 53 when the step portion 53 is moved toward the front end side in the axial direction in the cavity closing step. The resistance of the powder GP and the degree of compression of the stepped portion 53 compress the raw powder GP around the first shaft portion 51. Specifically, the taper angle of the step portion 53 is preferably about 20° to 70°.

[0124] The test example for confirming the operational effect of Example 3 was performed as follows.