JP4934208B2 - Spark plug insulator and spark plug manufacturing method - Google Patents

Description

  The present invention relates to an insulator for a spark plug and a method for manufacturing the spark plug.

  2 to 6 of Patent Document 1 disclose a conventional method for manufacturing an insulator for a spark plug. This manufacturing method is a manufacturing method of an insulator for a spark plug in which a through hole for inserting a center electrode and a terminal electrode is formed in the axial direction.

  In this manufacturing method, first, as a preparation step, a press pin used for forming a through hole and a mold having a cavity with an opening formed on the rear end side in the axial direction are prepared. At the rear end of the press pin, a rib-like pin-side spiral portion that spirals around its outer peripheral surface is formed.

  In the powder filling step, the raw material powder is charged into the cavity through the opening and filled. Next, after the powder filling process, as a press pin arranging process, the press pin is moved in the axial direction from the opening to arrange the press pin in the cavity. After the press pin placement step, the opening is closed with a closing member as a cavity closing step. Thereafter, as a pressure molding step, the raw material powder in the cavity is pressed together with the press pins to obtain a molded body.

  After the pressure molding process, as a demolding process, the molded body is demolded from the cavity together with the press pins. After the demolding step, the press pin is extracted from the formed body as a press pin removing step. The molded body thus obtained has an outer shape corresponding to the spark plug insulator. This molded body is ground to form an unfired insulator.

  Thereafter, the unfired insulator is fired at a temperature of about 1400-1650 ° C. Thereby, the pin hole formed by the press pin becomes a through hole. Thereafter, glaze is applied to the surface of the fired body, and finish firing is performed to form an insulator for a spark plug. This insulator for a spark plug is assembled with a center electrode, a terminal electrode, a metal shell, a resistor, and the like to form a spark plug. This spark plug is attached to the engine by a threaded portion of the metal shell, and is used as an ignition source for the air-fuel mixture supplied to the combustion chamber of the engine.

JP 2000-315563 A

  By the way, spark plugs tend to be reduced in diameter in order to save space, and further reduction in diameter is required for spark plug insulators. For this reason, it is necessary to reduce the diameter of the through hole of the spark plug insulator, and it is necessary to manufacture the spark plug insulator using the reduced diameter press pin. However, when an insulator for a spark plug is manufactured using a reduced-size press pin in the conventional manufacturing method, the resistance that the press pin receives from the raw material powder in the cavity in the press pin placement step after the powder filling step. May bend. In this case, the pin hole of the molded body does not extend straight in the axial direction, and the through hole of the spark plug insulator does not extend straight in the axial direction. For this reason, the insulator for spark plugs becomes a defective product, or the press pin must be frequently replaced, resulting in an increase in manufacturing cost.

  The present invention has been made in view of the above-described conventional situation, and can provide a method for manufacturing an insulator for a spark plug that can secure a high yield even when the diameter is reduced, and can realize a reduction in manufacturing cost. Providing is a problem to be solved.

The spark plug insulator manufacturing method of the present invention is a spark plug insulator manufacturing method in which a through hole for inserting a center electrode and a terminal electrode is formed in an axial direction,
A preparation step of preparing a press pin used for forming the through hole and a mold having a cavity having an opening formed on the rear end side in the axial direction;
A press pin disposing step of disposing the press pin in the cavity by moving the press pin from the opening toward the front end in the axial direction;
After the press pin placement step, a powder filling step of charging the raw material powder into the cavity through the opening, and filling,
After the powder filling step, a cavity closing step for closing the opening with a closing member;
After the cavity closing step, pressurizing the raw material powder in the cavity together with the press pin to obtain a molded body, and
A demolding step of demolding the molded body from the cavity together with the press pin after the pressure molding step;
After the demolding step, comprising a press pin removing step of extracting the press pin from the molded body,
The closing member is assembled so that a plurality of divided bodies surround the press pin, and has an insertion hole formed in the axial direction , and the press pin is movable in the insertion hole. ,
In the press pin placement step, the press pin is moved to the final position on the tip side in the axial direction,
In the cavity closing step, the closing member is moved to the front end side in the axial direction ,
At least in the cavity blocking step each said divided body is characterized that you configure an integral annular body (claim 1).

  In the manufacturing method of the present invention, the press pin arranging step is performed before the powder filling step. For this reason, the press pin is difficult to bend. Therefore, the pin hole of the molded body extends straight in the axial direction, and the through hole of the spark plug insulator also extends straight in the axial direction.

  Therefore, according to the manufacturing method of the present invention, it is possible to reduce the occurrence of defective products even when the spark plug insulator is reduced in diameter, and to reduce the frequency of press pin replacement. It can be ensured, and as a result, the manufacturing cost can be reduced.

  In the manufacturing method of the present invention, the closing member and the press pin are integrated, and in the press pin arranging step, the press pin is stopped before the final position on the front end side in the axial direction, and the gap in which the raw material powder can be introduced into the cavity Can be secured between the closing member and the opening, and in the cavity closing step, the press pin can be moved to the final position to close the opening with the closing member.

  In this case, the closing member and the press pin move together. In the press pin arrangement step, the press pin stops before the final position in the cavity, so that a clearance between the closing member and the opening of the mold is secured. Here, the “final position on the tip end side in the axial direction of the press pin” is a position where the press pin should be arranged in the cavity when performing the pressure forming process. For this reason, in the powder filling step, it is possible to charge the raw material powder into the cavity through the gap between the closing member and the opening of the mold. In the cavity closing step, when the press pin is moved to the final position on the tip side in the axial direction, the closing member also moves together with the press pin to close the opening of the mold. During this time, most of the press pin is disposed in the cavity before the powder filling step, so that the resistance from the raw material powder in the cavity is small and is not easily bent. According to this manufacturing method, the effects of the present invention can be realized with a simple configuration.

  Specifically, “stop before the final position” specifically means that the press pin can be used as much as possible within the range in which the raw material powder can be charged into the cavity from the gap secured between the closing member and the mold opening. Is stopped at a position close to the final position, preferably about 5 mm to 20 mm (about 4 to 16 times the outer diameter of the press pin).

  Note that the closure member and the press pin are integrated with each other, in addition to the case where the both are an integral part, and the case where the both are separate members but move together.

  In the manufacturing method of the present invention, the press pin includes a first shaft portion formed on the front end side in the axial direction, and a second shaft formed on the rear end side in the axial direction from the first shaft portion and having a larger diameter than the first shaft portion. The shaft portion may include a step portion formed between the first shaft portion and the second shaft portion. And, in the press pin arrangement process, the press pin is stopped at the position before the final position on the front end side in the axial direction, and the stroke shorter than the axial direction length of the first shaft portion is left to the final position. The press pin can be moved to the final position, and at the same time or later, the opening can be closed by the closing member.

  In this case, in the press pin arranging step, the press pin stops at a position before the final position in the cavity and leaving a stroke shorter than the axial length of the first shaft portion to the final position. In this case, the closing member may be configured to move integrally with the press pin, or may be configured to move independently of the press pin.

  When the closing member is configured to move integrally with the press pin, the press pin stops before the final position, so a gap is secured between the closing member and the mold opening, and the raw material powder is introduced into the cavity from the gap. And can be filled. In the cavity closing step, when the press pin is moved to the final position on the front end side in the axial direction, the closing member is also moved together with the press pin to close the opening of the mold.

  On the other hand, when the closing member is configured to move independently of the press pin, in the powder filling step, the raw material powder can be charged into the cavity from the opening and filled. Then, in the cavity closing step, after the press pin is moved to the final position on the axial front end side, the closing member is moved independently of the press pin to close the opening of the mold.

  In the cavity closing step, the press pin is moved to the final position on the tip side in the axial direction. The press pin has a first shaft portion, a step portion, and a second shaft portion, and the step portion moves toward the distal end side in the axial direction while compressing the raw material powder by a stroke shorter than the axial length of the first shaft portion.

  Here, in the conventional manufacturing method, in the press pin arranging step after the powder filling step, the press pin is moved in the axial direction from the opening to arrange the press pin in the cavity. For this reason, the stroke which a press pin moves to the axial direction front end side compressing raw material powder will become considerably longer than the axial direction length of a 1st axial part. According to the confirmation of the inventors, the raw material powder on the tip side of the step portion is thereby excessively compressed, and a consolidated aggregate may be generated. If it does so, the aggregate will be in the state scattered in the circumference | surroundings of a 1st axial part, a step part, and a 2nd axial part in a cavity, and the spot with a big filling density of raw material powder tends to produce around an aggregate. As a result, the spark plug insulator obtained through the pressure molding process or the like may have defects such as pinholes and lowering the insulation properties. More specifically, the first shaft portion forms a pin hole that becomes a through-hole in the so-called small-diameter portion of the spark plug insulator, and the second shaft portion is formed in the inside-diameter portion and the large-diameter portion on the front end side of the spark plug insulator. Since the pin hole is formed in the diameter part and the through hole on the rear side from these, a defect tends to occur between the tip small diameter part or the tip small diameter part and the tip side medium diameter part. Since the spark plug insulator has a thin tip small diameter portion and a thin portion between the tip small diameter portion and the tip middle diameter portion, there is a concern that the insulation may be impaired due to defects generated in these.

  In this regard, in the manufacturing method of the present invention having the above-described configuration, the stroke in which the step portion moves toward the tip end side in the axial direction while compressing the raw material powder is shorter than the axial length of the first shaft portion. According to the confirmation of the inventors, this makes it difficult for the raw material powder on the tip side from the stepped portion to be excessively compressed and to form a compacted aggregate. For this reason, it is hard to produce the spots with a large packing density of raw material powder around the 1st axial part in a cavity, a step part, and a 2nd axial part. As a result, the spark plug insulator obtained through the pressure molding process or the like is less prone to defects such as pinholes, and is less likely to suffer from a decrease in insulation. On the contrary, in the manufacturing method of the present invention, when the step portion moves by the stroke, the raw material powder around the first shaft portion is appropriately compressed and densified by the step portion in the axial direction. Defects are less likely to occur between the small diameter portion of the insulator and the small diameter portion of the tip and the medium diameter portion of the distal end.

  In the above case, the stepped portion is preferably tapered. In this case, the resistance received from the raw material powder by the stepped portion moving toward the tip end in the axial direction can be relaxed, and the degree of compression of the raw material powder around the first shaft portion can be easily adjusted.

  Further, in the above case, the closing member has an insertion hole formed in the axial direction, the press pin is movable in the insertion hole, and in the cavity closing step, after moving the press pin to the final position, The closing member can be moved to the front end side in the axial direction. Thereby, the structure which a closure member moves independently of a press pin is easily realizable. That is, the closing member and the press pin configured as separate bodies can move independently, and after the press pin reaches the final position, the closing member reaches a position where the cavity can be closed. is there.

  In the manufacturing method of the present invention, the closing member has an insertion hole formed in the axial direction, the press pin is movable in the insertion hole, and in the press pin arranging step, the press pin reaches the final position on the front end side in the axial direction. In the cavity closing step, the closing member is moved to the front end side in the axial direction (claim 1).

  With this configuration, the press pin moves independently of the closing member, and the press pin is arranged at the final position in the cavity in the press pin arranging step. The “final position” is as described above. For this reason, in the powder filling step, it is possible to charge the raw material powder into the cavity through the opening. In the cavity closing step, the closing member moves independently of the press pin, and the opening of the mold is closed by the closing member. During this time, the press pin does not receive the resistance of the raw material powder and is not easily bent. According to this manufacturing method, the effect of this invention can be implement | achieved reliably.

As a specific configuration in which the press pin is movably provided in the insertion hole, the closing member in the manufacturing method of the present invention is formed by assembling a plurality of divided bodies so as to surround the press pin, and at least a cavity closing step In Ru der what each divided body constitutes an integral annular body (claim 1). For this reason , when each divided body surrounding the press pin is separated in the radially outward direction of the press pin, the insertion hole is expanded. For this reason, even if it is a case where a part of outer peripheral surface of a press pin is thicker than an insertion hole, a press pin can move the inside of an insertion hole without a problem. Further, in the cavity closing step, each divided body forms an integral annular body and closes the opening, so that the cavity can be highly sealed.

  The configuration of the closing member is particularly effective when the pin-side spiral is formed on the rear end side of the press pin. In this case, a molded body side spiral portion in which the pin side spiral portion is transferred to the molded body is formed by the pressure molding process. For this reason, after the demolding step, as the press pin removing step, the press pin can be retracted while rotating around the axis with respect to the molded body, and the press pin can be extracted from the molded body. At this time, the pin-side spiral portion of the press pin can be moved without difficulty in the expanded insertion hole, so that the size of the manufacturing apparatus can be reduced.

In the production method of the present invention, the bottom portion of the side opposite to the opening of the cavity, it is preferable that the positioning portion for positioning the radial position of the tip of the press pin is formed (claim 2). The positioning part is, for example, a concave part into which the tip of the press pin is fitted. In this case, since the tip of the press pin is restrained so as not to be displaced in the radial direction, the press pin is more difficult to bend.

The spark plug manufacturing method of the present invention includes a step of manufacturing a spark plug insulator by the above-described spark plug insulator manufacturing method, and a step of assembling the manufactured spark plug insulator and other components. (Claim 3 ). Since the spark plug obtained by this manufacturing method can enjoy the effects of the manufacturing method of the spark plug insulator of the present invention, a high yield can be secured, and consequently the manufacturing cost can be reduced.

It is a front view (partial sectional view) of a spark plug to which an insulator is applied according to the manufacturing method of the insulator for a spark plug of Reference Example 1. It is a front view of a press pin in connection with the manufacturing method of the insulator for spark plugs of Reference Example 1. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of the reference example 1, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of the reference example 1, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of the reference example 1, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of the reference example 1, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of the reference example 1, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of the reference example 1, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of an Example, and shows the manufacturing process of an insulator. FIG. 10 is a cross-sectional view showing the XX cross section of FIG. 9 according to the method for manufacturing the spark plug insulator of the embodiment. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of an Example, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of an Example, and shows the manufacturing process of an insulator. It is explanatory drawing which concerns on the manufacturing method of the insulator for spark plugs of an Example, and shows the manufacturing process of an insulator. It is explanatory drawing which shows the manufacturing process of an insulator in the manufacturing method of the insulator for spark plugs of the reference example 2. FIG. It is explanatory drawing which shows the manufacturing process of an insulator in the manufacturing method of the insulator for spark plugs of the reference example 2. FIG. 6 is a graph illustrating a test example according to the method for manufacturing the spark plug insulator of Reference Example 2.

  Hereinafter, after first explaining Reference Example 1, an embodiment embodying the present invention will be described with reference to the drawings. In each figure (excluding FIG. 10), the vertical direction is defined as the axial direction, and the lower side of each of the spark plug 100, the press pins 50, 250, the cavity 83, and the spark plug insulator 2 is defined as the tip side. Similarly, the upper part of each is defined as the rear end side.

(Reference Example 1)
The manufacturing method of Reference Example 1 is a method of manufacturing the insulator 2 which is a specific embodiment of the spark plug insulator. Since the insulator 2 constitutes the spark plug 100, the overall configuration of the spark plug 100 will be described first.

  The spark plug 100 includes a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip protrudes, and a center electrode provided inside the insulator 2 with the tip protruding. 3, and a ground electrode 4, etc., which is disposed so that one end is coupled to the metal shell 1 by welding or the like and the other end is bent back to the side, and the side surface thereof faces the tip of the center electrode 3. ing.

  A spark discharge gap g is formed between the ground electrode 4 and the center electrode 3. The metal shell 1 is formed in a cylindrical shape by a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw portion 7 and a tool engaging portion 1e are formed on the outer peripheral surface thereof. Yes. The screw portion 7 is for attaching the spark plug 100 to an engine (not shown). The tool engaging portion 1e has a hexagonal shaft cross-sectional shape, and a tool such as a spanner or a wrench is engaged when the metal shell 1 is attached. Further, the center electrode 3 and the ground electrode 4 are made of Ni alloy or the like, and a core material 3a such as Cu or Cu alloy for radiating heat is embedded as necessary.

  The insulator 2 is made of an insulating material mainly composed of alumina or the like, and a through hole 6 for inserting the center electrode 3 and the terminal electrode 13 is formed in the axial direction. The center electrode 3 is inserted and fixed at the front end side of the through hole 6, and the terminal electrode 13 is inserted and fixed at the rear end side of the through hole 6. In addition, the resistor 15 is disposed between the terminal electrode 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal electrode 13 via conductive glass seal layers 16 and 17, respectively. The resistor 15 is formed as a resistor composition obtained by mixing glass powder and conductive material powder (and ceramic powder other than glass as necessary) and sintering by hot pressing or the like.

  The axial sectional diameter of the center electrode 3 is set smaller than the axial sectional diameter of the resistor 15. And the through-hole 6 is the circular cross-section hole-shaped 1st part 6a which penetrates the center electrode 3, and the circular cross-section hole shape formed in larger diameter than this in the back side (drawing upper side) of the 1st part 6a. And a second portion 6b. The terminal electrode 13 and the resistor 15 are accommodated in the second portion 6b, and the center electrode 3 is inserted into the first portion 6a. The rear end portion of the center electrode 3 is formed with an electrode fixing convex portion 3b protruding outward from the outer peripheral surface thereof. At the connecting position between the first portion 6a and the second portion 6b of the through hole 6, a convex portion receiving surface 6c for receiving the electrode fixing convex portion 3b of the center electrode 3 is formed in a tapered surface or a rounded surface shape. Has been.

  The inner peripheral surface of the second portion 6b of the through hole 6 has a drawing taper (for example, about 5/1000 to 5/100) that becomes larger in diameter toward the rear side in the axial direction in order to make it easier to pull out a press pin 50 described later. Is granted. On the other hand, the inner peripheral surface of the first portion 6a is provided with a taper with a smaller angle than that of the second portion 6b, or is substantially free of a taper.

  In addition, if the specific dimension of the outer shape of the insulator 2 is exemplified, the total length of the insulator 2 is, for example, about 30 to 75 mm, and the average inner diameter of the second portion 6b of the through hole 6 is, for example, 2 to 5 mm. Similarly, the average inner diameter of the first portion 6a is, for example, about 1 to 3.5 mm. The insulator 2 is further reduced in diameter in order to save space of the spark plug 100 and improve performance such as heat generation characteristics.

  Next, a method for manufacturing the insulator 2 will be described. The insulator 2 described above is a book in which a preparation process, a press pin arrangement process, a powder filling process, a cavity closing process, a pressure forming process, a demolding process, and a press pin removing process are performed in this order. It is manufactured by the manufacturing method of the invention. Hereinafter, each step will be described.

<Preparation process>
In the preparation step, a press pin 50 and a forming die 80 are prepared.

  As shown in FIG. 2, the press pin 50 is a metal shaft used to form the through hole 6. More specifically, the press pin 50 has a first shaft portion 51 for forming the first portion 6a of the through hole 6 shown in FIG. A second shaft portion 52 for forming the second portion 6b of the hole 6 is formed. Further, a step portion 53 corresponding to the convex receiving surface 6c of the through hole 6 in FIG. 1 is formed between the first shaft portion 51 and the second shaft portion 52.

  The outer peripheral surface of the second shaft portion 52 is provided with a taper taper (corresponding to the taper taper of the second portion 6b, for example, about 5/1000 to 5/100) that increases in diameter toward the rear side in the axial direction. ing. On the other hand, the outer peripheral surface of the first shaft portion 51 is provided with a taper taper smaller than the second shaft portion 52 (corresponding to the taper taper of the first portion 6a) or substantially provided with a taper taper. It has become a form that is not. The average outer diameter of the first shaft portion 51 corresponds to the average inner diameter of the first portion 6 a, 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 press pin 50 may be selected according to the type of insulator to be created. In particular, a thin pin having a small diameter of about 2.5 mm to 3.6 mm is used as the size of the second shaft portion 52. Can be done.

  Since the press pin 50 is a very thin shaft body as described above, for example, a material having a high rigidity such as a cemented carbide or an alloy is used so as not to cause problems such as bending during a pressure molding process or the like. It consists of tool steel.

  On the rear end side of the second shaft portion 52 of the press pin 50, a flange-shaped end surface forming portion 55 that forms a rear end side end surface of the molded body PC, which will be described later, is integrally formed. A head portion 56 having a female screw portion 57 formed in the direction is integrally formed. As shown in FIG. 3 etc., the upper holder part 86 is rotatably fitted on the outside of the head part 56.

  As shown in FIG. 2, a rib-like pin-side spiral portion 54 is formed on the rear end side outer peripheral surface of the second shaft portion 52. Note that the spiral winding direction of the pin-side spiral portion 54 is opposite to the spiral winding direction of the female screw portion 57.

  As shown in FIGS. 3 to 6, the molding die 80 is a device that performs molding generally called “rubber press”. “Rubber press” is a molding method in which a powder such as a ceramic material is filled in a rubber mold and a high molding pressure is applied from the outer periphery to produce a homogeneous molded body.

  More specifically, in the molding die 80, a cylindrical inner rubber die 82 having a cavity 83 penetrating in the axial direction inside is provided in a cylindrical outer rubber die 81 disposed in the molding die body 80a. It is the structure arranged in. The opening below the cavity 83 (on the tip side in the axial direction) is closed by a bottom lid 84 and a lower holder 85. On the other hand, an opening 89 is formed above the cavity 83 (on the rear end side in the axial direction). As shown in FIG. 5, the opening 89 is closed by fitting the rear end side of the press pin 50 integrated with the upper holder portion 86 in the cavity closing step, which will be described later. Is sealed.

<Press pin placement process>
In the press pin arrangement step, as shown in FIG. 3, the press pin 50 in a state where the tip of the rotary shaft 87 is screwed to the female screw portion 57 and the upper holder portion 86 is fitted outside the head portion 56. It is arranged in the cavity 83 by moving from the opening 89 toward the tip end side in the axial direction. Here, a position where the press pin 50 is to be disposed in the cavity 83 when the pressure forming step shown in FIG. 5 is performed is defined as a “final position”. 3 to 6, the position of the tip in the axial direction in a state where the press pin 50 is disposed at the final position is displayed as the final position E. In the reference example 1, in the press pin arranging step, the press pin 50 is stopped before the final position E on the axial front end side (for example, about 5 mm to 20 mm), and the upper holder portion 86 and the opening 89 of the cavity 83 are A gap S1 in the vertical direction is formed between them. In this state, the tip of the press pin 50 is lifted upward by a length corresponding to the gap S1 from the case where the press pin 50 is disposed at the final position E.

<Powder filling process>
In the powder filling process, as shown in FIG. 4, the raw material powder GP is charged and filled into the cavity 83 from the gap S <b> 1 between the upper holder portion 86 and the opening 89 of the cavity 83.

Here, the raw material powder GP is specifically prepared as follows. First, alumina powder (average particle diameter of 1 to 5 μm) and additive element materials such as Si component, Ca component, Mg component, Ba component or B component, which are sintering aids, are blended at a predetermined ratio, and are hydrophilic. A forming base slurry is prepared by adding and mixing a binder (for example, PVA or acrylamide-based binder) and water. In addition, each additive element type raw material, for example, Si component is SiO ₂ powder, Ca component is CaCO ₃ powder, Mg component is MgO powder, Ba component is BaCO ₃ powder, and B component is H ₃ BO ₃ powder (or an aqueous solution may be used). ). Then, the raw material powder GP as the green granule for molding is manufactured by spray-drying the green slurry for molding by a spray drying method or the like.

  The raw material powder GP manufactured in this way is adjusted so as to contain moisture within a range of 1.5% by weight or less by adjusting the conditions during spray drying (for example, the drying temperature and spray rate). Moisture blending loosens the binding force of the powder particles in the granulated particles, promotes the crushing of the granulated particles during pressing, and swells the hydrophilic binder blended in the molding substrate to cause caking. The main purpose is to effectively extract the properties and increase the strength of the molded body PC.

  The lower limit value of the moisture content of the raw material powder GP varies depending on the particle size distribution and the like of the raw material powder GP, but is appropriately set to such an extent that the above effects are not insufficient. In addition, when the amount of water exceeds 1.5% by weight, the fluidity of the granulated product may be deteriorated and difficult to handle. More preferably, the water content is adjusted within a range of 1.3 wt% or less.

  The blending amount of the hydrophilic binder in the raw material powder GP is preferably adjusted in the range of 0.5 to 3.0% by weight. When the blending amount of the hydrophilic binder is less than 0.5% by weight, the strength of the molded body PC is insufficient and handling becomes difficult, and cracks and chips may easily occur. On the other hand, if it exceeds 3.0% by weight, the binder removal time during firing becomes longer, leading to a decrease in the production efficiency of the insulator, and the residual amount of impurity components (for example, carbon) derived from the binder in the insulator. May increase, leading to a decrease in performance (eg, dielectric strength voltage).

  As shown in FIG. 4, the raw material powder GP adjusted to the above state avoids the press pin 50 disposed in the cavity 83, so that the gap between the upper holder portion 86 and the opening 89 of the cavity 83 is reduced. The material is introduced into the cavity 83 and is deposited from the bottom to the top in the cavity 83. When a predetermined amount of the raw material powder GP is filled in the cavity 83, the process proceeds to the next step.

<Cavity closing process>
In the cavity closing step, as shown in FIG. 5, the press pin 50 that has been stopped in the cavity 83 due to the trouble of the final position E is inserted to the final position E. Then, the opening 89 is closed by fitting the rear end side of the press pin 50 in which the upper holder portion 86 is integrated, and as a result, the cavity 83 is sealed. Here, as described above, since the raw material powder GP is adjusted so that the moisture content falls within a predetermined range, it is not in a dry and smooth state. For this reason, when the press pin 50 is moved to the front end side in the axial direction in the raw material powder GP, the press pin 50 receives a certain amount of resistance from the raw material powder GP. However, in Reference Example 1, the insertion distance of the press pin 50 during the cavity closing process is a very short distance corresponding to the gap S1. For this reason, the resistance that the press pin 50 receives from the raw material powder GP during the cavity closing step can be greatly reduced. Here, the upper holder portion 86 corresponds to a closing member that closes the opening 89.

<Pressure forming process>
In the pressure molding step, as shown in FIG. 5, the raw material powder GP in the cavity 83 is pressed together with the press pins 50 to obtain a molded body PC.

  More specifically, the hydraulic pressure FP is applied radially inward to the outer peripheral surface of the outer rubber mold 81 through a pressurized liquid passage 80b formed in the mold body 80a. Then, the outer rubber mold 81 and the inner rubber mold 82 are elastically deformed so as to reduce the diameter, and the cavity 83 is also reduced. For this reason, the raw material powder GP filled in the cavity 83 is pressurized and compressed by applying the hydraulic pressure FP indirectly through the outer rubber mold 81 and the inner rubber mold 82. As a result, the raw material powder GP in the cavity 83 is solidified in a form integrated with the press pin 50, and a compact PC is obtained.

  At this time, the hydraulic pressure FP is preferably adjusted in the range of 30 to 150 MPa. When the hydraulic pressure FP is less than 30 MPa, the strength of the molded body PC is insufficient and handling becomes difficult, and cracks, chips and the like are likely to occur. On the other hand, if it exceeds 150 MPa, the life of the outer rubber mold 81 and the inner rubber mold 82 may be shortened, leading to an increase in cost.

<Demolding process>
In the demolding step, as shown in FIG. 6, the molded body PC is demolded from the cavity 83 together with the press pins 50. More specifically, when the application of the hydraulic pressure FP is canceled, the outer rubber mold 81 and the inner rubber mold 82 are elastically restored to return to the original shape, and the reduced cavity 83 also returns to the original shape. Thereby, the outer peripheral surface of the compression-molded molded body PC and the inner peripheral surface of the cavity 83 are separated from each other, and a space is formed therebetween. The molded body PC is attached to the press pin 50 by pulling up the press pin 50 integrated with the rotary shaft 87 and the upper holder portion 86 toward the rear end side in the axial direction with respect to the outer rubber mold 81 and the inner rubber mold 82. Withdrawn from the cavity 83 in a state.

<Press pin removal process>
In the press pin removing step, as shown in FIG. 7, the press pin 50 is extracted from the molded body PC. More specifically, when molding is performed using the press pin 50 in which the pin-side spiral portion 54 is formed, on the rear end side of the inner cylindrical surface of the molded body PC facing the second shaft portion 52 of the press pin 50, A shaped body side spiral portion 20a having a shape obtained by inverting the pin side spiral portion 54 (that is, a groove shape) is formed. The molded body side spiral portion 20a is often removed by cutting or the like, but if it is not removed, it remains as the spiral portion 20 in the fired insulator 2 as shown in FIG.

  As shown in FIG. 7, in a state where the molded body PC pulled up from the cavity 83 is held by an air chuck (not shown), the rotating shaft 87 screwed into the female screw hole 57 of the press pin 50 is driven by a motor or the like (not shown). It is rotated in a direction to be tightened into the female screw hole 57 by a source. Then, the press pin 50 rotates around the axis with respect to the molded body PC, and the press pin 50 is screwed up and lifted in the extraction direction based on the screw action caused by the engagement between the pin side spiral portion 54 and the molded body side spiral portion 20a. To do.

  That is, since the press pin 50 is slowly raised while rotating by the screwing action of the screw, excessive friction between the press pin 50 and the inner cylindrical surface of the molded body PC facing the outer peripheral surface of the press pin 50. It becomes difficult to generate force, and as a result, the press pin 50 can be pulled out smoothly without damaging the molded body PC. Further, since the second shaft portion 52 of the press pin 50 is tapered, a gap can be secured with respect to the inner cylindrical surface of the molded body PC by simply raising the press pin 50 slightly, and the press pin 50 can be easily pressed. The pin 50 can be released. Note that by forming a release layer such as a hard carbon release film on the outer peripheral surface of the press pin 50, the press pin 50 may be more easily extracted.

  As shown in FIG. 8, the molded body PC in which the above steps are finished and the press pin 50 is extracted is processed into an outer shape corresponding to the insulator 2 by processing the outer surface by grinder cutting or the like, Baking is performed at a temperature of 1400 to 1650 ° C. Thereby, the inner cylinder surface of the molded body PC facing the outer peripheral surface of the press pin 50 becomes the through hole 6. Then, the glaze is further applied and finish firing is performed to complete the insulator 2 shown in FIG. The spark plug 100 is completed by assembling the insulator 2 obtained in this manner with another constituent member such as the metal shell 1. The spark plug 100 is attached to the engine at the screw portion 7 and is used as an ignition source for the air-fuel mixture supplied to the combustion chamber.

  Here, as described above, the manufacturing method of the spark plug insulator of Reference Example 1 performs the press pin placement step before the powder filling step to place the press pin 50 in the cavity 83 while ensuring the clearance S1. Deploy. Next, in the powder filling step, the raw material powder GP is introduced into the cavity 83 from the gap S <b> 1 so as to avoid the press pins 50 arranged in the cavity 83, and filled in the cavity 83. For this reason, in the subsequent cavity closing process, the distance for inserting the press pin 50 to the final position E is a very short distance corresponding to the gap S1, and the resistance that the press pin 50 receives from the raw material powder GP in the cavity closing process. Can be significantly reduced. For this reason, the press pin 50 becomes difficult to bend, and the inner cylinder surface of the molded body PC facing the outer peripheral surface of the press pin 50 is formed so as to extend straight in the axial direction. As a result, the through-hole 6 of the insulator 2 also extends straight in the axial direction.

  Therefore, according to the manufacturing method of Reference Example 1, it is possible to reduce the occurrence of defective products and reduce the frequency of replacement of the press pins 50 in the manufacture of the insulator 2 with a reduced diameter. As a result, this manufacturing method can secure a high yield for the insulator 2 and, in turn, can reduce the manufacturing cost of the spark plug 100.

  In the manufacturing method of Reference Example 1, the upper holder portion 86 as the closing member and the press pin 50 are integrated. In the press pin arrangement step, the press pin 50 is stopped before the final position E, and a gap S1 in which the raw material powder GP can be charged into the cavity 83 is secured between the upper holder portion 86 and the opening 89, The raw material powder GP is charged into the cavity 83 from the gap S1 and filled. Further, in the cavity closing step, when the press pin 50 is moved to the final position E, the upper holder portion 86 is also moved integrally with the press pin 50 to close the opening 89. This manufacturing method having such a simple configuration can easily obtain the effects of the present invention.

(Example)
The manufacturing method of the embodiment is a method of manufacturing the insulator 2 as in Reference Example 1. However, instead of the press pin 50 and the upper holder portion 86 of Reference Example 1, the press pin 250 and the upper holder portion 286 are replaced. Adopted. For this reason, due to the difference in the configuration of these members, the above-described steps also have differences. Hereinafter, differences from the manufacturing method of Reference Example 1 will be mainly described, and description of steps similar to those of Reference Example 1 will be omitted or simplified. Also, the same components as those in Reference Example 1 are denoted by the same reference numerals, and the description thereof is omitted.

  Hereinafter, the manufacturing method of the insulator 2 of an Example is demonstrated, referring FIGS. 9-13.

<Preparation process>
In the preparation step, as shown in FIG. 9, a press pin 250 and a forming die 80 are prepared. Since the molding die 80 is the same as that of the reference example 1, description thereof is omitted.

  Similar to the press pin 50 of Reference Example 1, the press pin 250 is formed with a first shaft portion 51, a step portion 53, a second shaft portion 52, and a pin-side spiral portion 54. However, the end surface forming portion 55 and the head portion 56 in the press pin 50 of Reference Example 1 are not formed on the press pin 250. Instead, the press pin 250 is integrally formed with a cylindrical shaft-shaped rotating shaft portion 287 that extends from the rear end of the second shaft portion 52 to the rear side in the axial direction. The rotating shaft portion 287 corresponds to the rotating shaft 87 of the reference example 1, and is rotated by a driving source such as a motor (not shown).

  As shown in FIG. 9 and the like, an upper holder portion 286 is disposed on the outer peripheral side of the rotating shaft portion 287. As shown in FIG. 10, the upper holder portion 286 is configured by three divided bodies 286 a, 286 b, and 286 c having fan-shaped cross sections, and is disposed so as to surround the outer peripheral surface of the rotating shaft portion 287. A central space surrounded by the divided bodies 286a, 286b, and 286c serves as an insertion hole 286d through which the rotation shaft portion 287 is inserted.

  And as shown to Fig.10 (a), if each division body 286a, 286b, 286c leaves | separates from the rotating shaft part 287 to radial direction, the insertion hole 286d will be diameter-expanded. For this reason, the rotating shaft part 287 becomes relatively movable in the axial direction within the insertion hole 286d.

  On the other hand, as shown in FIG. 10B, when each of the divided bodies 286a, 286b, and 286c approaches the rotating shaft portion 287, the insertion hole 286d is in close contact with the rotating shaft portion 287, and the divided bodies 286a, 286b, and 286c are An annular body is formed by combining them integrally. In such a state, each of the divided bodies 286a, 286b, and 286c is configured to close the opening 89 and seal the inside of the cavity 83 in a cavity closing process described later.

  Further, as shown in FIG. 9, the press pin 250 is formed with a protruding portion 251 a that protrudes in a substantially conical shape from the first shaft portion 51 toward the distal end side in the axial direction. A concave portion 284a into which the tip of the protruding portion 251a is fitted is formed at the center of the upper surface of the bottom lid 84 corresponding to the protruding portion 251a.

<Press pin placement process>
In the press pin arrangement step, as shown in FIG. 9, first, the press pin 250 and the upper holder portion 286 are arranged above the opening 89 of the mold 80. Then, the divided bodies 286a, 286b, and 286c of the upper holder portion 286 are separated from the rotary shaft portion 287 in the radially outward direction, and the insertion hole 286d is in a state in which the diameter has been increased. At this time, a vertical gap S <b> 2 is formed between the upper holder portion 286 and the opening 89. In the embodiment, since the press pin 250 and the upper holder portion 286 are independently movable in the axial direction, a gap S2 larger than the gap S1 in the reference example 1 can be formed.

  Next, in the insertion hole 286d, the rotary shaft portion 287 is moved to the axial front end side, whereby the press pin 250 is inserted into the cavity 83 from the opening 89 and moved to the final position on the axial front end side. Here, when performing the pressure molding step shown in FIG. 12, the position where the press pin 250 should be disposed in the cavity 83 is defined as the “final position”. Unlike the reference example 1, in the embodiment, as shown in FIG. 11, the press pin 250 is arranged at the final position in the stage of the press pin arrangement process. At this time, the tip of the protruding portion 251 a is fitted into the concave portion 284 a of the bottom lid 84. For this reason, the tip of the press pin 250 is restrained, and it becomes difficult to displace in the direction (radial direction) orthogonal to the axis. The concave portion 284a corresponds to a positioning portion that positions the radial position of the tip of the press pin 250.

<Powder filling process>
In the powder filling step, as shown in FIG. 11, the raw material powder GP is charged and filled into the cavity 83 from the gap S2 between the upper holder portion 286 and the opening 89 of the cavity 83 so as to avoid the press pin 250. .

<Cavity closing process>
In the cavity closing step, as shown in FIG. 11, the upper holder portion 286 in a state where the insertion hole 286 d is expanded is moved to the front end side in the axial direction. Then, as shown in FIG. 12, the front end side of the upper holder portion 286 is fitted into the opening 89 of the cavity 83 to close the opening 89. At this time, as shown in FIG. 10 (b), the divided bodies 286a, 286b and 286c are in close contact with each other to form an integral annular body and close the opening 89, so that the cavity 83 is securely sealed. And Here, unlike the cavity closing process of the reference example 1, in the cavity closing process of the embodiment, the press pin 250 does not move, so the press pin 250 does not receive resistance from the raw material powder GP. Here, the upper holder portion 286 corresponds to a closing member that closes the opening 89.

<Pressure forming process>
In the pressure molding step, as shown in FIG. 12, the raw material powder GP in the cavity 83 is pressed together with the press pins 250 to obtain a molded body PC. Details are the same as those in Reference Example 1, and thus description thereof is omitted.

<Demolding process>
In the demolding step, by releasing the application of the hydraulic pressure FP in the state shown in FIG. 12, the reduced cavity 83 is returned to its original shape, and the outer peripheral surface of the compression molded body PC and the inside of the cavity 83 are restored. Separate the peripheral surface. Then, the press pin 250 in a state where the divided bodies 286a, 286b, and 286c of the upper holder portion 286 are in close contact with each other is pulled up with respect to the outer rubber mold 81 and the inner rubber mold 82 in the axial direction. As a result, the molded body PC is pulled out of the cavity 83 in a state of being attached to the press pin 250.

<Press pin removal process>
In the press pin removing step, as shown in FIG. 13, the press pin 250 is extracted from the molded body PC. More specifically, as shown in FIG. 10A, each of the divided bodies 286a, 286b, and 286c of the upper holder portion 286 is separated from the rotary shaft portion 287 in the radially outward direction, and the insertion hole 286d is expanded in diameter. To do. Then, as shown in FIG. 13, in a state where the molded body PC pulled up from the cavity 83 is held by an air chuck (not shown), the rotating shaft portion 287 of the press pin 250 is counterclockwise by a driving source such as a motor (not shown). Rotate around. Then, the press pin 250 rotates around the axis with respect to the molded body PC, and as described above, is extracted from the molded body PC based on the screw action caused by the engagement between the pin-side spiral portion 54 and the molded body-side spiral portion 20a. At this time, the pin-side spiral portion 54 of the press pin 250 can move within the insertion hole 286d whose diameter has been increased without any problem, and thus the size of the manufacturing apparatus for the insulator 2 can be reduced.

  The molded body PC from which the above steps have been completed and the press pin 250 has been removed is cut and baked to form the insulator 2 and assembled to the spark plug 100 as in the case of Reference Example 1.

  Here, in the manufacturing method of the spark plug insulator of the embodiment, the press pin 250 can be moved in the insertion hole 286d by increasing the diameter of the insertion hole 286d of the upper holder portion 286 as a closing member. For this reason, as described above, the manufacturing method moves the press pin 250 to the final position in the cavity 83 independently of the upper holder portion 286 in the press pin arranging step performed before the powder filling step, It is possible to easily secure the clearance S <b> 2 between the upper holder portion 286 and the opening 89.

  And this manufacturing method throws raw material powder GP into the cavity 83 from the gap S2 so as to avoid the press pin 250 arranged at the final position in the cavity 83 in the powder filling step, and into the cavity 83. Fill. Thereafter, in the cavity closing step, the upper holder portion 286 moves independently of the press pin 250 and closes the opening 89 by the upper holder portion 286. For this reason, in the cavity closing step, the press pin 250 does not move and does not receive resistance from the raw material powder GP. For this reason, the press pin 250 becomes more difficult to bend.

  Therefore, the manufacturing method of the embodiment can achieve the same effects as the manufacturing method of Reference Example 1 more reliably than the manufacturing method of Reference Example 1.

  Further, in this manufacturing method, the tip of the press pin 250 is restrained in the cavity 83 by the concave portion 284 a as a positioning portion formed on the bottom lid 84 of the mold 80. For this reason, in the pressure molding process, even if a compressive force in the direction perpendicular to the axis acts on the press pin 250 when the cavity 83 shrinks, the radial position of the tip end of the press pin 250 is difficult to be displaced. For this reason, the press pin 250 is more difficult to bend.

(Reference Example 2)
The manufacturing method of Reference Example 2 is a method of manufacturing the insulator 2 as in Reference Example 1, but the press pin placement step (shown in FIG. 3) and the powder filling step (shown in FIG. 4) of Reference Example 1 Is changed as shown in FIGS. Hereinafter, differences from the manufacturing method of Reference Example 1 will be mainly described, and description of steps similar to those of Reference Example 1 will be omitted or simplified. Also, the same components as those in Reference Example 1 are denoted by the same reference numerals, and the description thereof is omitted.

<Preparation process>
In the preparation step, as in the first reference example, the press pin 50 and the forming die 80 are prepared. As explained in the preparation step of Reference Example 1, the press pin 50 is formed on the axial end side with respect to the first shaft portion 51 formed on the front end side in the axial direction, and is formed on the rear end side in the axial direction with respect to the first shaft portion 51. A second shaft portion 52 having a larger diameter than 51, and a step portion 53 formed between the first shaft portion 51 and the second shaft portion 52. As shown in FIG. 2, the stepped portion 53 is tapered so as to connect the first shaft portion 51 and the second shaft portion 52 having different outer diameters.

<Press pin placement process>
In the press pin arrangement step, as shown in FIG. 14, the press pin 50 in a state where the tip of the rotary shaft 87 is screwed to the female screw portion 57 and the upper holder portion 86 is fitted outside the head portion 56. It is arranged in the cavity 83 by moving from the opening 89 toward the tip end side in the axial direction. Here, similarly to the reference example 1, when the pressure forming step shown in FIG. 5 is performed, a position where the press pin 50 should be disposed in the cavity 83 is defined as a “final position”. 14 and 15, the position of the tip in the axial direction when the press pin 50 is disposed at the final position is displayed as the final position E. In the reference example 2, in the press pin arranging step, the press pin is located at the position before the final position E on the tip end side in the axial direction and leaving the stroke F shorter than the axial length T of the first shaft portion 51 up to the final position E. 50 is stopped. As a result, a vertical gap S <b> 3 is formed between the upper holder portion 86 and the opening 89 of the cavity 83. In this state, the tip of the press pin 50 is lifted upward by the stroke F from the case where the press pin 50 is disposed at the final position E.

<Powder filling process>
In the powder filling step, as shown in FIG. 15, the raw material powder GP is put into the cavity 83 from the gap S3 between the upper holder portion 86 and the opening 89 of the cavity 83 so as to avoid the press pin 50 arranged in the cavity 83. In

  As explained in the powder filling step of Reference Example 1, since the raw material powder GP is manufactured by spray drying the molding base slurry by a spray drying method or the like, condition adjustment during spray drying (for example, drying temperature and spray speed) Etc.) is adjusted so as to contain water within a range of 1.5 wt% or less. For this reason, if the raw material powder GP is excessively compressed, a consolidated aggregate is likely to be formed.

  When the charged raw material powder GP is accumulated from the lower side to the upper side in the cavity 83 and a predetermined amount of the raw material powder GP is filled in the cavity 83, the process proceeds to the next step.

<Cavity closing process>
In the cavity closing step, the press pin 50 is inserted to the final position E as shown in FIG. Then, the opening 89 is closed by fitting the rear end side of the press pin 50 in which the upper holder portion 86 is integrated, and as a result, the cavity 83 is sealed. Here, as described above, since the raw material powder GP is adjusted so that the moisture content falls within a predetermined range, it is not in a dry and smooth state. For this reason, when the press pin 50 is moved to the front end side in the axial direction in the raw material powder GP, the press pin 50 receives a certain amount of resistance from the raw material powder GP. At this time, the stepped portion 53 moves toward the tip end side in the axial direction while compressing the raw material powder GP by the stroke F.

<Pressure forming process>
In the pressure molding step, as in Reference Example 1, as shown in FIG. 5, the raw material powder GP in the cavity 83 is pressed together with the press pins 50 to obtain a molded body PC.

<Demolding process>
In the demolding step, the molded body PC is demolded from the cavity 83 together with the press pins 50 as shown in FIG.

<Press pin removal process>
In the press pin removing step, as in Reference Example 1, as shown in FIG. 7, the press pin 50 is extracted from the molded body PC.

  The molded body PC from which the above steps have been completed and the press pin 50 has been removed is cut and baked to form the insulator 2 and assembled to the spark plug 100 as in the case of Reference Example 1.

  Here, in the manufacturing method of the spark plug insulator of Reference Example 2, the press pin 50 includes the first shaft portion 51, the second shaft portion 52, and the step portion 53 having the above-described configuration. . And as above-mentioned, the press pin arrangement | positioning process is implemented before a powder filling process, and the press pin 50 is arrange | positioned in the cavity 83, ensuring the clearance gap S3. Next, in the powder filling step, the raw material powder GP is introduced into the cavity 83 from the gap S3 so as to avoid the press pins 50 arranged in the cavity 83, and filled in the cavity 83. For this reason, in the subsequent cavity closing process, the distance for inserting the press pin 50 to the final position E becomes a very short stroke F, and the resistance that the press pin 50 receives from the raw material powder GP in the cavity closing process is greatly reduced. can do.

  Therefore, the manufacturing method of Reference Example 2 can also achieve the same effects as the manufacturing method of Reference Example 1.

  Further, in this manufacturing method, the stroke F in which the stepped portion 53 moves toward the tip end side in the axial direction while compressing the raw material powder GP is shorter than the axial length T of the first shaft portion 51. As a result, the raw material powder GP on the tip side of the stepped portion 53 is not excessively compressed, and a compacted aggregate is hardly generated. For this reason, it is hard to produce the spots with a large filling density of raw material powder GP around the 1st axial part 51 in the cavity 83, the step part 53, and the 2nd axial part 52. FIG. As a result, the insulator 2 obtained through the pressure molding process or the like is less likely to have defects such as pinholes and is less likely to have a problem that the insulating properties are lowered. On the contrary, in the manufacturing method of Reference Example 2, when the stepped portion 53 moves by the stroke F, the raw material powder GP around the first shaft portion 51 is appropriately compressed and densified by the stepped portion 53 in the axial direction. Therefore, defects are less likely to occur between the distal end small diameter portion 2a (shown in FIG. 1) of the insulator 2 and the distal end small diameter portion 2a and the distal end side intermediate diameter portion 2b (shown in FIG. 1). The tip small-diameter portion 2a is positioned on the tip end side in the axial direction of the insulator 2, and has a thin cylindrical shape with a taper. A center electrode 3 is disposed on the inner peripheral side of the tip small diameter portion 2a. The distal-end-side intermediate diameter portion 2b is positioned on the rear end side in the axial direction of the insulator 2 from the distal-end small-diameter portion 2a, and has a thick cylindrical shape having a larger diameter than the distal-end small-diameter portion 2a. The rear end in the axial direction of the center electrode 3 and the resistor 15 are disposed on the inner peripheral side of the front end side middle diameter portion 2b. The distal end small diameter portion 2a and the distal end side intermediate diameter portion 2b are bent, and the wall thickness largely varies locally. The insulation 2 of the insulator 2 is further improved by making it difficult for defects to occur between the distal end small-diameter portion 2a of the insulator 2 and the distal end small-diameter portion 2a and the distal-end-side intermediate diameter portion 2b having such a configuration. Can do.

  Further, in this manufacturing method, by appropriately adjusting the taper angle of the stepped portion 53 having a tapered shape, the resistance received from the raw material powder GP by the stepped portion 53 moving to the axial front end side in the cavity closing step can be reduced. At the same time, it is easy to adjust the degree of compression of the raw material powder GP around the first shaft portion 51. More specifically, the taper angle of the stepped portion 53 is more preferably about 20 ° to 70 °.

  Here, the test example which confirms the effect of the reference example 2 was implemented as follows.

(Test example)
In the test example, an aggregate formed by compacting the raw material powder GP was prepared. The raw material powder GP has a particle size of about 50 to 160 μm, whereas the prepared aggregate has a particle size of about 2 to 5 mm. In the powder filling step, aggregates were intentionally mixed into the raw material powder GP filled in the cavity 83. Then, each said process was implemented and five test products 1-1 and 1-2 as the insulator 2 were obtained respectively. At this time, in the test sample 1-1, an aggregate was mixed in a region in the cavity 83 corresponding to the distal end side middle diameter portion 2b of the insulator 2. In the test product 1-2, aggregates were mixed in a region in the cavity 83 corresponding to the large diameter portion 2c (shown in FIG. 1) of the insulator 2. The large-diameter portion 2c has a flange shape that is positioned on the rear end side in the axial direction of the insulator 2 from the tip-side medium diameter portion 2b and has a larger diameter than the tip-side medium diameter portion 2b. In addition, ten test samples 1-3, which are standard products in which aggregates are not mixed into the raw material powder GP in the powder filling step, were also prepared.

  Next, with respect to the above test products 1-1 to 1-3, the penetration voltage at the tip small diameter portion 2a was measured. Specifically, the center electrode 3 and the terminal electrode 13 are not assembled, and a test rod-shaped electrode is inserted into the through-hole 6 for the insulator 2 having no glaze layer formed on the surface, An annular electrode (having a hole in the metal plate that allows insertion of the tip small diameter portion 2a) is arranged on the outer peripheral side of the tip small diameter portion 2a, and a high voltage is applied between them to reduce the voltage. The voltage was changed from the voltage side to the high voltage side, and the voltage at which the insulation by the tip small diameter portion 2a was broken (that is, the penetration voltage of the insulator) was measured. The voltage value obtained by the measurement is the average voltage value and fluctuation of “there is an agglomerate” (left side) in FIG. 16 for a total of ten test samples 1-1 and five test samples 1-2. For the ten test products 1-3, the average voltage value and the fluctuation width were similarly shown as “standard (no aggregate)” (right side) in FIG.

  As a result, as shown in FIG. 16, in the test product 1-3 as a standard product, the fluctuation width of the through voltage was within about ± 5% when the average value of the 10 through voltages was used as a reference. On the other hand, in the test samples 1-1 and 1-2 in which aggregates are mixed, the average value of the penetration voltage is about 4% lower than the average value of the standard product, and the penetration voltage is low. The deflection width toward the direction was about -10% when the average value of the standard product was used as a reference, and was considerably low (the highest penetration voltage was equivalent to the standard product).

  As is apparent from the results of this test example, in the case where aggregates are mixed in the process of manufacturing the insulator 2, the insulator 2 having a low penetration voltage can be manufactured. On the other hand, if it is the manufacturing method of Reference Example 2, the aggregate which is the cause is difficult to mix in, and as a result, the insulator which avoids that insulation property becomes low while the through-hole 6 is formed straight is formed. In addition, the press pin is unlikely to be bent, and as a result, a high yield can be secured.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments and can be appropriately modified and applied without departing from the spirit thereof.

  For example, in the manufacturing method of Reference Example 2, the press pin 250 and the upper holder part 286 of the embodiment may be adopted instead of the press pin 50 and the upper holder part 86. Although illustration is omitted, in this case, in the press pin arrangement step, a stroke F that is shorter than the final position E on the front end side in the axial direction and shorter than the length T in the axial direction of the first shaft portion 51 is left to the final position E. The press pin 250 is stopped at the position. At this time, a vertical gap S <b> 2 is formed between the upper holder portion 286 and the opening 89. In the cavity closing step, the press pin 250 is inserted to the final position E, and then the opening 89 is closed by the upper holder portion 286. Such a manufacturing method can also exhibit the same effects as the manufacturing method of Reference Example 2.

  The present invention is applicable to a spark plug.

DESCRIPTION OF SYMBOLS 3 ... Center electrode 6 ... Through-hole 13 ... Terminal electrode 2 ... Insulator for spark plugs (insulator)
50, 250 ... Press pin 51 ... First shaft portion 52 ... Second shaft portion 53 ... Step portion 80 ... Mold 83 ... Cavity 86, 286 ... Closure member (upper holder portion)
89 ... Opening 100 ... Spark plug 284a ... Positioning part (concave part)
286a, 286b, 286c ... divided body 286d ... insertion hole GP ... raw material powder PC ... molded body S1, S2, S3 ... gap where raw material powder can be put into the cavity E ... final position F ... length in the axial direction of the first shaft portion Stroke shorter than length T: Length in the axial direction of the first shaft

Claims (3)

A method for manufacturing an insulator for a spark plug in which a through hole for inserting a center electrode and a terminal electrode is formed in an axial direction,
A preparation step of preparing a press pin used for forming the through hole and a mold having a cavity having an opening formed on the rear end side in the axial direction;
A press pin disposing step of disposing the press pin in the cavity by moving the press pin from the opening toward the front end in the axial direction;
After the press pin placement step, a powder filling step of charging the raw material powder into the cavity through the opening, and filling,
After the powder filling step, a cavity closing step for closing the opening with a closing member;
After the cavity closing step, pressurizing the raw material powder in the cavity together with the press pin to obtain a molded body, and
A demolding step of demolding the molded body from the cavity together with the press pin after the pressure molding step;
After the demolding step, comprising a press pin removing step of extracting the press pin from the molded body,
The closing member is assembled so that a plurality of divided bodies surround the press pin, and has an insertion hole formed in the axial direction , and the press pin is movable in the insertion hole. ,
In the press pin placement step, the press pin is moved to the final position on the tip side in the axial direction,
In the cavity closing step, the closing member is moved to the front end side in the axial direction ,
Method for producing at least the cavity blocking step in each said divided body is integral to configure the annulus an insulator for a spark plug according to claim Rukoto. Wherein the said opening and bottom of the opposite side of the cavity, the production method of an insulator for a spark plug according to claim 1, wherein the positioning portion is formed for positioning the radial position of the tip of the press pin. A step of producing an insulator for a spark plug by the method for producing an insulator for a spark plug according to claim 1 or 2 ,
A method for manufacturing a spark plug, comprising the step of assembling the manufactured insulator for a spark plug and another constituent member.

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