JP2009252441A - Insulator for spark plug and method of manufacturing the same, as well as spark plug and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulator for a spark plug capable of achieving more detailed grade management and enough traceability without bringing about deterioration of corrosion resistance of main metal fittings or mechanical strength of an insulator, by aiming at improvement of visibility of a mark and increase of an information amount, as well as a spark plug with an insulator for a spark plug, and to provide a method of manufacturing the same. <P>SOLUTION: The spark plug 1 includes an insulator 2 with an axial hole 4, the main metal fittings 3 fitted outside the insulator 2, a center electrode 5 insertion-fitted into the axial hole 4, and a grounding electrode 27 forming a spark discharge gap 33 against a tip of the center electrode 5. The insulator 2 is formed by cutting a molded item obtained by compression molding raw-material powder mainly composed of alumina, and then, baking the cut molded item, before which, a mark 30 by a laser is attached on the surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spark plug used for an internal combustion engine and a manufacturing method thereof, and an insulator for a spark plug used for a spark plug and a manufacturing method thereof.

  A spark plug for an internal combustion engine is attached to an internal combustion engine (engine) and used for ignition of an air-fuel mixture in a combustion chamber. Generally, a spark plug is provided on the outer periphery of an insulator having an axial hole, a center electrode inserted through the front end of the axial hole, a terminal electrode inserted through the rear end of the axial hole, and the insulator. A metal shell and a ground electrode provided at the tip of the metal shell and forming a spark discharge gap with the center electrode are provided. Further, the surface of the metal shell is subjected to galvanization or nickel plating in order to improve the corrosion resistance.

  By the way, a mark including information such as the type and lot number of the spark plug is attached to the surface of the spark plug. Conventionally, the mark can be generally engraved on the surface of the metal shell, but with the engraving, the surface of the metal shell may be peeled off and the corrosion resistance of the metal shell may be reduced. is there. On the other hand, it is conceivable to engrave the mark on the surface of the insulator, but in this case, there is a concern that the mechanical strength of the insulator is reduced.

Therefore, a technique for marking the surface of an insulator with ink has been proposed (see, for example, Patent Document 1).
Japanese Patent Application Laid-Open No. 9-276992

  However, when the above technique is employed, ink bleeding or the like may occur, and the printed mark may become unclear. In consideration of the blur and the like, characters and the like must be made relatively large, and the amount of information per unit surface area of the mark becomes relatively small. For this reason, detailed information including the type and production lot of the spark plug cannot be included in the mark, and there is a risk that detailed product management of the spark plug and traceability in the event of a failure may not be sufficiently achieved. There is.

  The present invention has been made in view of the above circumstances, and an object thereof is to improve the visibility of the mark and increase the amount of information without causing a decrease in the corrosion resistance of the metal shell and the mechanical strength of the insulator. Accordingly, it is possible to provide an insulator for a spark plug that can realize finer product type management and sufficient traceability, a manufacturing method thereof, and a spark plug including the insulator for a spark plug and a manufacturing method thereof. is there.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The insulator for a spark plug of this configuration is a spark plug formed by cutting a molded body obtained by compression molding a raw material powder mainly composed of alumina and then firing the molded body that has been cut. An insulator for
Before firing, the surface is marked with a laser.

  The “mark” is displayed by a figure, a letter, a number, a sign, a symbol, a design, or the like, for example, identification information indicating a spark plug type or lot number, a product mark, It has information for specifying the production line through which the spark plug insulator has passed (the same applies hereinafter).

  According to the configuration 1, the surface of the insulator is marked with a laser. Therefore, compared with the case where a mark is engraved on the surface of the metal shell or the insulator, it is possible to suppress a decrease in corrosion resistance and mechanical strength. In addition, there is no risk of bleeding or the like, and visibility can be improved as compared with the case of marking with ink. Moreover, since it becomes possible to mark a minute character etc., the information amount per unit area which a mark has can be increased. As a result, more detailed information can be included in the mark, and fine varieties of spark plugs and excellent traceability can be realized.

  By the way, since the insulator for spark plugs after firing has a relatively high strength, when marking with a laser, it is necessary to irradiate the insulator with a laser having a relatively high energy. However, by irradiating with a high energy laser, the marked part and the insulator structure in the vicinity thereof may be destroyed, and the mechanical strength and the withstand voltage performance may be lowered. In general, a glaze layer may be formed on the surface of a predetermined portion of a spark plug insulator after firing so as to improve the strength. However, it is difficult to mark an insulator on which a glaze layer is formed with a YAG laser marker having a relatively high glass permeability, and the types of laser markers that can be marked are limited.

  In this regard, according to the present configuration 1, marking by a laser is performed before firing the insulator. Here, since the insulator before firing has relatively low strength, the insulator can be marked by laser irradiation with relatively low energy. As a result, it is possible to suppress the destruction of the insulator structure located around the mark, and it is possible to more reliably prevent the mechanical strength and withstand voltage performance of the insulator from being lowered. Moreover, since marking is performed on the insulator before the glaze layer is formed, marking can be performed with various laser markers such as a YAG laser marker.

  Configuration 2. The spark plug insulator of this configuration is characterized in that, in the above configuration 1, the mark includes information on at least one of a production line at the time of compression molding and a production line at the time of cutting.

  “Production line information” includes information for identifying (specifying) a specific production line among a plurality of production lines in various production processes, production date, production time information, etc. (Hereinafter, the same applies).

  In recent years, the manufacturing process has become complicated due to an increase in the types of spark plugs and the manufacturing process. Therefore, it is conceivable to ensure traceability of the insulator manufacturing process by marking information about the manufacturing line on the spark plug insulator. Here, in the process of manufacturing the insulator, in the process before firing the insulator, that is, in the compression molding process or the cutting process, defects (for example, cracks or through holes) are likely to occur in the insulator. For this reason, it is conceivable to mark the information about the production line in the compression molding process and the cutting process with ink on the insulator before firing. However, baking the insulator causes volatilization of the ink exposed to high temperatures, which may cause the mark to become unclear or the mark to disappear.

  In this regard, according to the present configuration 2, a mark including information on the production line is attached by a laser before firing the insulator. For this reason, even after going through the firing process, it is possible to suppress the occurrence of defects such as the mark becoming unclear or disappearing, and as a result, the compression molding process and the cutting process where the occurrence frequency of defects is relatively high. The production line that caused the failure, the time when the failure occurred, and the like can be specified. As a result, it is possible to effectively perform improvement work on the specified production line, and to improve production quality.

  Configuration 3. The insulator for a spark plug of this configuration is characterized in that, in the above configuration 1 or 2, the mark is attached to the surface of the large-diameter portion that protrudes outward in the radial direction of itself.

  According to the configuration 3, the spark plug insulator is formed with the large-diameter portion bulging in the radial direction. Here, the large diameter portion is formed thicker than other portions of the insulator. Therefore, by marking the surface of the large-diameter portion, it is possible to more reliably prevent a decrease in mechanical strength and withstand voltage performance of the insulator due to the marking.

  Configuration 4. A spark plug of this configuration includes the insulator for a spark plug according to any one of the above configurations 1 to 3.

  According to the said structure 4, about the spark plug provided with a cylindrical metal shell etc., the effect similar to the said structure 1 etc. will be show | played.

Configuration 5. The spark plug of this configuration is the metal shell provided with the threaded portion provided on the outer periphery of the spark plug insulator in the above-described configuration 4 and screwed to the outer periphery of the spark plug in the mounting hole of the engine head of the internal combustion engine. And having
The outer diameter of the thread portion is M12 or less.

  In the spark plug in which the outer diameter of the thread portion is relatively small, that is, M12 or less, the spark plug insulator provided inside the metal shell is also relatively small in diameter. For this reason, the surface area of the insulator to which the mark can be attached becomes relatively small, and as a result, the amount of information held by the mark may be relatively small. In addition, the insulator having a reduced diameter is likely to have a defect in a manufacturing process (particularly, a cutting process).

  In this respect, according to the above configuration 5, since a relatively small character or the like can be marked with a laser, even a small-diameter insulator with a relatively small surface area has a mark having a sufficient amount of information. Can be attached. In addition, by adopting the above configuration 1 or the like, it is possible to achieve excellent traceability for a small-diameter insulator that is likely to cause a defect, and therefore, it is possible to further improve the production quality.

Configuration 6. The spark plug of this configuration has a metal shell provided on the outer periphery of the spark plug insulator in the above configuration 4 or 5,
Of the insulator for a spark plug, the mark is attached to a surface of a portion covered with the metal shell.

  According to the configuration 6, the mark is attached to the portion covered by the metal shell. As a result, with respect to the completed spark plug, for example, it is not possible to visually recognize the mark attached from the viewpoint of realizing traceability in the manufacturing process. As a result, the appearance quality can be improved.

Configuration 7. The manufacturing method of the insulator for spark plugs of this structure is the manufacturing method of the insulator for spark plugs in any one of the structures 1 to 3,
A compression molding process in which a raw material powder mainly composed of alumina is compression molded to form a molded body;
Cutting the molded body into a predetermined insulator shape, and forming a non-fired insulator; and
A firing step of firing the unfired insulator to obtain an insulator for a spark plug;
Including
In the pre-stage of the firing step, a mark by a laser is applied to the surface of the molded body or the surface of the unfired insulator.

  According to the structure 7, the insulator for a spark plug that exhibits the same effect as the structure 1 and the like can be more reliably manufactured.

Configuration 8. A manufacturing method of the spark plug insulator of the present configuration is the manufacturing method of the spark plug insulator according to the above configuration 7,
Including an inspection step of inspecting the spark plug insulator,
The mark includes information about at least one of a production line in the compression molding process and a production line in the cutting process,
In the inspection step, when a failure is determined, information on the production line of the mark attached to the spark plug insulator subjected to the failure determination is stored in an information storage device. And

  According to the configuration 8, in the inspection process, information on the production line of the mark attached to the spark plug insulator that has been determined to be defective is stored in the information storage device. Thereby, based on the stored information, for example, it is possible to identify a production line that is likely to cause a defect, and to effectively improve the line. As a result, the production quality can be further improved.

Configuration 9 A spark plug manufacturing method of this configuration is the spark plug manufacturing method according to any one of the above configurations 4 to 6,
A compression molding process in which a raw material powder mainly composed of alumina is compression molded to form a molded body;
Cutting the molded body into a predetermined insulator shape, and forming a non-fired insulator; and
A firing step of firing the unfired insulator to obtain an insulator for a spark plug;
Including
In the pre-stage of the firing step, a mark by a laser is applied to the surface of the molded body or the surface of the unfired insulator.

  According to the above configuration 9, the same operational effects as the configuration 7 are basically obtained.

Configuration 10 A manufacturing method of the spark plug of this configuration is the manufacturing method of the spark plug according to the above configuration 9,
Including an inspection step of inspecting the spark plug insulator,
The mark includes information about at least one of a production line in the compression molding process and a production line in the cutting process,
In the inspection step, when a failure is determined, information about the production line of the mark attached to the spark plug insulator subjected to the failure determination is stored in an information storage device. And

  According to the said structure 10, the effect similar to the said structure 8 will be show | played fundamentally.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1 and the upper side is the rear end side.

  The spark plug 1 includes a cylindrical insulator 2 as an insulator for a spark plug, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. On the side, a leg length part 13 formed with a smaller diameter than this is provided. Moreover, in this embodiment, the said large diameter part 11 is formed more thickly than the other site | part (the rear end side trunk | drum 10, the middle trunk | drum 12, and the leg long part 13). In addition, most of the large-diameter portion 11, the middle trunk portion 12, and the leg long portion 13 of the insulator 2 are accommodated in the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the leg length portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14. In addition, since the outer diameter of the screw part 15 of the metal shell 3 to be described later is relatively small as M12 or less, the insulator 2 inserted in the metal shell 3 is also relatively small in diameter.

  Further, the insulator 2 is formed with a shaft hole 4 penetrating along the axis CL1, and a center electrode 5 is inserted and fixed to the tip end side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Furthermore, the center electrode 5 has a rod shape (cylindrical shape) as a whole, and its tip end surface is formed flat and protrudes from the tip of the insulator 2.

  A terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface thereof. Yes. In addition, a seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the engine head is provided. A caulking portion 20 for holding the insulator 2 is provided. In the present embodiment, the outer diameter of the screw portion 15 is relatively small, such as M12 or less (for example, M10 or less).

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. Thereby, the air tightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  Further, the front end portion 26 of the metal shell 3 is bent back at the front end, and a ground electrode 27 whose side surface faces the front end portion of the center electrode 5 is joined. The ground electrode 27 has a two-layer structure including an outer layer 27A and an inner layer 27B. In the present embodiment, the outer layer 27A is made of a Ni alloy [for example, Inconel 600 and Inconel 601 (both are registered trademarks)]. On the other hand, the inner layer 27B is made of a copper alloy or pure copper, which is a better heat conductive metal than the Ni alloy. Further, a spark discharge gap 33 is formed between the tip of the center electrode 5 and the tip side surface of the ground electrode 27.

  Furthermore, in this embodiment, as shown in FIG. 2, a mark 30 is attached to the surface of the large diameter portion 11 of the insulator 2 by a laser marker. In the present embodiment, the mark 30 has information on a production line on which the insulator 2 is produced (for example, information for specifying a production line that has passed through a compression molding process or a cutting process described later, Information on date and production time).

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated. First, the metal shell 3 is processed in advance. That is, a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material) is formed by forming a through-hole by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a ground electrode 27 made of a Ni-based alloy or the like is resistance-welded to the distal end surface of the metal shell intermediate body. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained. The metal shell 3 to which the ground electrode 27 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

On the other hand, the insulator 2 is formed separately from the metal shell 3. More specifically, first, a raw granule for molding is prepared using, for example, a raw material powder mainly composed of alumina and containing a binder or the like. And in a compression molding process, a cylindrical molded object is obtained by performing rubber press molding with respect to the said shaping | molding raw material flow. Next, in the cutting process, the obtained molded body is ground to obtain an insulator-shaped unfired insulator. Then, the laser marker against a portion corresponding to the large diameter portion 11 of the resulting unfired insulator (for example, a YAG laser marker, CO ₂ laser marker or the like) by the mark 30 is attached. At this time, the mark 30 is attached by laser irradiation with relatively low energy. Next, in the firing step, the unfired insulator with the mark 30 is put into a firing furnace and fired to obtain the insulator 2. Furthermore, the obtained insulator 2 is inspected in an inspection process. More specifically, with respect to the inspection process, the rod-shaped first electrode is inserted into the shaft hole 4 of the insulator 2 while the second electrode is disposed outside the insulator 2 so that the second electrode has a high height. By applying a voltage, a potential difference is generated between both electrodes. When spark discharge (flashover) occurs through the opening of the shaft hole 4, it is determined as “good”, and when flashover occurs without passing through the opening of the shaft hole 4, Since it is a through discharge that has passed through a minute hole or the like of the insulator 2, it is determined as “defective”. For the insulator 2 determined to be “defective”, information about the production line of the mark 30 attached to the insulator 2 is stored and accumulated in an information storage device (not shown).

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, the Ni-based alloy is forged, and an inner layer 5A made of a copper alloy is provided at the center of the Ni-based alloy to improve heat dissipation.

  Then, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared material is injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. After being heated, it is baked and hardened by pressing with the terminal electrode 6 from behind while heating in a firing furnace. At this time, the glaze layer may be fired simultaneously on the surface of the rear end side body portion 10 of the insulator 2 or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are assembled as described above. More specifically, it is fixed by caulking the opening on the rear end side of the metal shell 3 formed relatively thin inward in the radial direction, that is, by forming the caulking portion 20.

  Finally, the ground electrode 27 is bent to adjust the spark discharge gap 33 between the tip of the center electrode 5 and the tip of the ground electrode 27.

  Thus, the spark plug 1 having the above-described configuration is manufactured through a series of steps.

  As described above, according to the spark plug 1 (insulator 2) in the present embodiment, the surface 30 of the insulator 2 is marked with the laser marker. Therefore, compared with the case where a mark is engraved on the surface of the metal shell 3 or the insulator 2, it is possible to suppress a decrease in corrosion resistance and mechanical strength. In addition, there is no risk of bleeding or the like, and visibility can be improved as compared with the case of marking with ink. Moreover, since it becomes possible to mark a minute character etc., the information amount per unit area which the mark 30 has can be increased. As a result, more detailed information can be included in the mark 30, and fine product type management and excellent traceability of the spark plug 1 can be realized.

  Further, marking with a laser is performed before firing the insulator 2. Here, since the insulator 2 (unfired insulator) before firing has a relatively low strength, the insulator 2 (unfired insulator) can be marked by laser irradiation with relatively low energy. As a result, the insulator structure located around the mark 30 can be prevented from being destroyed, and the mechanical strength and withstand voltage performance of the insulator 2 can be prevented more reliably. Moreover, since marking is performed on the insulator 2 before forming the glaze layer, it is possible to perform marking with various laser markers such as a YAG laser marker.

  Further, a mark 30 including information about the production line is attached by a laser marker before firing the insulator 2. For this reason, even if it passes through a baking process, generation | occurrence | production of the malfunction that the mark 30 becomes unclear or disappears can be suppressed, and by extension, the compression molding process and cutting work with which the malfunction occurrence frequency is comparatively high. In the process, it is possible to identify the production line that has caused the failure, the time when the failure occurred, and the like. As a result, it is possible to effectively perform improvement work on the specified production line, and to improve production quality.

  In addition, by marking the surface of the large-diameter portion 11 formed thicker than other parts of the insulator 2, the mechanical strength and withstand voltage of the insulator 2 associated with the mark 30 attached. It is possible to more reliably prevent the performance from being deteriorated.

  Moreover, since the large diameter part 11 will be covered with the metal shell 3 in the spark plug 1 at the time of completion, the mark 30 cannot be visually recognized. As a result, the appearance quality can be improved.

  In addition, since a relatively small character or the like can be marked by a laser, a sufficient amount of information can be obtained even with an insulator 2 having a relatively small diameter and a relatively small surface area as in this embodiment. A mark 30 can be attached. In addition, excellent traceability can be achieved for the insulator 2 with a reduced diameter, which is likely to cause defects, and the production quality can be further improved.

  Further, in the inspection process, information about the production line of the mark 30 attached to the insulator 2 that has been determined to be defective is stored and accumulated in the information storage device. Thereby, based on the stored / accumulated information, for example, it is possible to specify a production line that is likely to cause a defect, and to effectively improve the line. As a result, the production quality can be further improved.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the said embodiment, although the mark 30 is attached | subjected to the surface of the large diameter part 11 of the insulator 2, the site | part to which the mark 30 is attached is not limited to the surface of the large diameter part 11. Therefore, the mark 30 may be provided on the surface of the rear end side body part 11, the middle body part 13, or the like.

  (B) In the above embodiment, the mark 30 includes information about the production line on which the insulator 2 is manufactured. The mark 30 is an identification indicating a spark plug type, lot number, product mark, and the like. Information may be included. Moreover, both the information about a manufacturing line and the said identification information may be included.

  (C) In the above embodiment, the insulator 2 has a relatively small diameter, but the shape of the insulator 2 is not particularly limited.

  (D) In the above-described embodiment, the case where the ground electrode 27 is joined to the distal end surface of the distal end portion 26 of the metal shell 3 is embodied. The present invention can also be applied to the case where the ground electrode is formed so as to cut out a part of a certain end fitting (for example, JP-A-2006-236906). Alternatively, the ground electrode 27 may be joined to the side surface of the distal end portion 26 of the metal shell 3.

  (E) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

It is a partially broken front view which shows the structure of the spark plug of this embodiment. It is a front view which shows the mark etc. of an insulator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spark plug 2 ... Insulator as insulator for spark plugs 3 ... Main metal fitting 11 ... Large diameter part 15 ... Screw part 30 ... Mark

Claims (10)

An insulator for a spark plug formed by cutting a molded body obtained by compression molding a raw material powder containing alumina as a main component and then firing the cut molded body,
An insulator for a spark plug, characterized in that a laser mark is applied to the surface before firing.   The insulator for a spark plug according to claim 1, wherein the mark includes information on at least one of a production line at the time of compression molding and a production line at the time of cutting.   The insulator for a spark plug according to claim 1, wherein the mark is attached to a surface of a large-diameter portion that is formed to protrude outward in the radial direction of the spark plug.   A spark plug comprising the insulator for a spark plug according to any one of claims 1 to 3. Provided on the outer periphery of the spark plug insulator, and on the outer periphery of the spark plug insulator, has a metal shell provided with a threaded portion for screwing into the mounting hole of the engine head of the internal combustion engine,
The spark plug according to claim 4, wherein an outer diameter of the screw portion is M12 or less. While having a metal shell provided on the outer periphery of the spark plug insulator,
6. The spark plug according to claim 4, wherein the mark is attached to a surface of a portion covered with the metal shell in the spark plug insulator. A method for producing an insulator for a spark plug according to any one of claims 1 to 3,
A compression molding process in which a raw material powder mainly composed of alumina is compression molded to form a molded body;
Cutting the molded body into a predetermined insulator shape, and forming a non-fired insulator; and
A firing step of firing the unfired insulator to obtain an insulator for a spark plug;
Including
A method for producing an insulator for a spark plug, characterized in that, in the pre-stage of the firing step, a mark by a laser is applied to the surface of the molded body or the surface of the unfired insulator. It is a manufacturing method of the insulator for spark plugs according to claim 7,
Including an inspection step of inspecting the spark plug insulator,
The mark includes information about at least one of a production line in the compression molding process and a production line in the cutting process,
In the inspection step, when a failure is determined, information on the production line of the mark attached to the spark plug insulator subjected to the failure determination is stored in an information storage device. A method for manufacturing an insulator for a spark plug. A spark plug manufacturing method according to any one of claims 4 to 6,
A compression molding process in which a raw material powder mainly composed of alumina is compression molded to form a molded body;
Cutting the molded body into a predetermined insulator shape, and forming a non-fired insulator; and
A firing step of firing the unfired insulator to obtain an insulator for a spark plug;
Including
A method for manufacturing a spark plug, characterized in that, in the pre-stage of the firing step, a laser mark is applied to the surface of the molded body or the surface of the unfired insulator. It is a manufacturing method of the spark plug according to claim 9,
Including an inspection step of inspecting the spark plug insulator,
The mark includes information about at least one of a production line in the compression molding process and a production line in the cutting process,
In the inspection step, when a failure is determined, information about the production line of the mark attached to the spark plug insulator subjected to the failure determination is stored in an information storage device. A method for manufacturing a spark plug.

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