JP2006222023A - Method for manufacturing spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing spark plug, which can improve adhesiveness of a plating layer formed on a grounding electrode. <P>SOLUTION: A grounding electrode 30 is bonded to the top surface of a main metal 50 of a metal assembly body 200. The metal assembly body 200 is fitted and fixed to the top of a supporting rod 210 by arranging the axis direction and is rotated with the axis of the supporting rod 210 in the center. A blast treatment machine carries out a blast treatment to the grounding electrode 30 by injecting an injection material 230 from a injection outlet 220 aiming at the grounding electrode 30. This removes an oxide film formed on the surface of the grounding electrode 30, and improves adhesiveness of the plating layer to the grounding electrode 30 since the surface of the grounding electrode 30 becomes uneven and the area of the surface becomes large. Even if the spark plug is used in an internal combustion engine without removing the plating layer formed on the grounding electrode 30, the plating layer does not fall off or fall out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a spark plug for an internal combustion engine.

  Conventionally, spark plugs for ignition are used in internal combustion engines. A general spark plug has a metal shell that holds an insulator having a center electrode inserted therein, and a ground electrode welded to a tip surface of the metal shell, and the other end of the ground electrode, A spark discharge gap is formed facing the tip of the center electrode. Then, a spark discharge is performed between the center electrode and the ground electrode.

  In such a spark plug, in order to improve the corrosion resistance of the metallic shell, a plating layer is formed on the surface of the metallic shell by plating. In the manufacturing process, in consideration of the productivity and cost of the spark plug, the ground electrode is welded to the metal shell, and the ground electrode is joined to the metal shell (hereinafter, the metal shell in this state is referred to as “metal fitting”). Barrel plating treatment is performed on the assembly, and a plating layer is formed on the metal shell together with the ground electrode.

  By the way, since the ground electrode is exposed to the combustion chamber of the internal combustion engine which becomes high temperature and high pressure, a nickel-based alloy is used as its material. Nickel-based alloys have the property of forming an oxide film on their surface when they come into contact with oxygen and preventing the oxidation from proceeding to the inside. Due to the formation of, the adhesion of the plating layer decreases. For this reason, when the ground electrode is bent to form a spark discharge gap after forming the plating layer, or when spark discharge is performed after assembly to the internal combustion engine, the plating layer floats (swells) or peels off. Dropout may occur. When a bridge is formed between the center electrode and the ground electrode by the plating layer that has been peeled off and dropped off, there is a risk that it may cause a misfire.

In order to prevent this, it is conceivable to perform a masking process on the ground electrode in advance before performing the plating process on the metal fitting assembly so that a plating layer is not formed on the ground electrode. However, a masking process and a process of removing the mask after the formation of the plating layer are required, so that it is not practical in view of productivity and cost. Therefore, conventionally, after performing the plating process on the metal fitting assembly without performing the masking process, the plating layer formed on the ground electrode is chemically peeled and removed (for example, see Patent Document 1) or ground and peeled off. (See, for example, Patent Document 2), the number of processes is reduced to increase productivity, and problems such as bridging are prevented from occurring.
JP 2001-68250 A JP 2003-123937 A

  However, when the plating layer of the ground electrode is chemically peeled and removed, the plating layer is removed by immersing only the ground electrode portion of the metal fitting assembly on which the plating layer is formed in the chemical solution. Due to the instability of the surface, the plating layer formed on the metal shell may be peeled off. In addition, when the ground electrode plating layer is removed by grinding using a tool such as a milling machine, the ground electrode base material may be shaved together when grinding the plating layer, so the initial dimensions cannot be obtained. There is a concern that the strength of the ground electrode may be reduced, and in particular, there is a risk of fatigue failure starting from the cutting trace of the ground electrode during bending of the ground electrode.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spark plug manufacturing method capable of improving the adhesion of a plating layer formed on a ground electrode.

  In order to achieve the above object, a spark plug manufacturing method according to a first aspect of the present invention includes a center electrode and an axial hole extending in an axial direction of the central electrode, and the central electrode is disposed inside the axial hole. A spark including an insulator to be held, a metal shell that surrounds and holds the periphery of the insulator in a radial direction, and a ground electrode that has one end joined to a front end surface of the metal shell and the other end facing the center electrode A method of manufacturing a plug, comprising: a blasting process for blasting the ground electrode; a welding process for welding one end of the ground electrode to the metal shell; and the welding process, the ground electrode and the metal shell Is a metal fitting assembly that is integrally joined to each other, and plating is performed on the metal fitting assembly in which at least the ground electrode is blasted by the blasting process. And a degree.

  According to a second aspect of the present invention, there is provided a spark plug manufacturing method according to the first aspect of the present invention, wherein the blasting process applied to the ground electrode in the blasting process is performed between a powder and a liquid. It is characterized by using a wet blasting method in which the mixture is sprayed.

  According to a third aspect of the present invention, there is provided a spark plug manufacturing method according to the first or second aspect of the invention, wherein, in the blasting process, the ground electrode is subjected to a blasting process for 1 period. It is more than second and less than 90 seconds.

  According to a fourth aspect of the present invention, there is provided a spark plug manufacturing method according to any one of the first to third aspects, wherein in the plating step, nickel or zinc is formed on the surface of the metal fitting assembly. And a chromate film layer is formed on the surface of the metal layer.

  In the spark plug manufacturing method according to the first aspect of the present invention, the oxide film formed on the surface of the ground electrode can be removed by blasting the ground electrode welded integrally with the metal shell. . Furthermore, the surface of the ground electrode can be formed in an uneven shape, and the surface area can be increased. And if the plating process is performed on the ground electrode with the oxide film removed and the surface area increased, the adhesion of the plating layer can be improved as compared with the case where the blasting process is not performed. If a ground electrode with a highly adhesive plating layer is formed, it is difficult for the plating layer to peel off or drop off even if it is used in an internal combustion engine. It is possible to reduce the risk of being lost. In addition, if there is no risk of peeling or falling off of the plating layer, it is not necessary to perform a step of removing the plating layer of the ground electrode by grinding or chemical treatment in the spark plug manufacturing process, thereby improving the productivity of the spark plug. be able to.

  The ground electrode from which the oxide film has been removed by the blasting process may be joined to the metal shell by the welding process. However, after the welding process is performed first and the ground electrode is joined to the metal shell, the blasting process is performed. The oxide film on the surface of the ground electrode may be removed.

  By the way, when stress is applied to the metal, the crystal slips, and the resistance to the slip surface gradually increases. When this resistance is increased to some extent, the metal is plastically deformed, so that the hardness increases, so-called work hardening occurs. When a force is applied to the ground electrode by blasting, the hardness of the ground electrode increases due to this work hardening. If blasting is performed on a ground electrode having a Vickers hardness of HV180, the hardness can be HV200 or higher, and the strength of the ground electrode can be increased.

  Moreover, in the spark plug manufacturing method of the invention according to claim 2, in addition to the effect of the invention according to claim 1, the surface of the ground electrode is made smoother and the powder particles are reduced from remaining on the surface. It becomes possible to do. The blasting process is a process in which the processed surface is washed or worn by projecting a granular material (abrasive material also called a projecting material) onto the processed surface. By performing this blasting process as a wet blasting process in which powder and liquid are mixed, liquid acts on the processed surface, so that it acts as a cushion, and the granular material is stuck into the processed surface and remains. Can be suppressed. The ground electrode with less residue can improve the bonding strength of the plating layer, and a spark plug with improved adhesion of the plating layer to the ground electrode can be manufactured.

  In the spark plug manufacturing method of the invention according to claim 3, in addition to the effect of the invention according to claim 1 or 2, the period of blast treatment applied to the ground electrode is 1 second or more and 90 seconds or less. Thus, the oxide film formed on the surface of the first electrode can be surely removed, and the surface area of the ground electrode can be increased. If the duration of the blast treatment is less than 1 second, there is a possibility that a sufficient treatment time for removing the oxide film from the surface of the ground electrode cannot be obtained. Further, even if the blasting period is 90 seconds or less, sufficient adhesion of the plating layer can be obtained, and even if the blasting process is performed for a longer period, the adhesion of the plating layer does not change. May decrease.

  Further, in the spark plug manufacturing method of the invention according to claim 4, in addition to the effect of the invention according to any of claims 1 to 3, a metal layer mainly composed of nickel or zinc is formed on the surface of the metal fitting assembly. By forming, the corrosion resistance of the metal fitting assembly can be improved. Furthermore, by forming a chromate film layer on the surface of the metal layer, the metal layer can be protected, and the corrosion resistance of the main metal fitting assembly can be further improved. In the present invention, the “main component” indicates that the component occupies 70% by weight or more of the total components contained.

  Hereinafter, an embodiment of a spark plug manufacturing method embodying the present invention will be described with reference to the drawings. First, the structure of a spark plug 100 as an example of a spark plug manufactured by the spark plug manufacturing method of the present embodiment will be described. FIG. 1 is a partial cross-sectional view of a spark plug 100. In FIG. 1, in the direction of the axis O of the spark plug 100, the side on which the center electrode 20 is provided is described as the front end side of the spark plug 100, and the side on which the connection terminal 40 is provided is described as the rear end side.

  As shown in FIG. 1, the spark plug 100 generally includes an insulator 10, a metal shell 50 that holds the insulator 10, a center electrode 20 that is held in the shaft hole 12 of the insulator 10, and a metal shell. The ground electrode 30 is joined to the front end portion 31 of the center electrode 20 so as to be opposed to the front end portion 22 of the center electrode 20, and the connection terminal 40 is provided on the rear end side of the insulator 10.

  First, the insulator 10 constituting the insulator of the spark plug 100 will be described. As is well known, the insulator 10 is formed by firing alumina or the like, and is a cylindrical insulating member having an axial hole 12 in the axis O direction. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 is formed on the rear end side. Further, a corrugation portion 16 for increasing a creepage distance is formed further on the rear end side than the rear end side body portion 18. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the front end side from the flange portion 19. A small leg length portion 13 is formed. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is assembled to an internal combustion engine (not shown).

  Next, the center electrode 20 will be described. In the center electrode 20, a metal core 23 made of copper or a copper alloy for promoting heat dissipation is embedded in the center of an electrode base material made of a nickel-based alloy such as Inconel (trade name) 600 or 601. It is a rod-shaped electrode. The center electrode 20 is electrically connected to the connection terminal 40 held on the rear end side of the shaft hole 12 via the sealing material 4 and the resistor 3 provided inside the shaft hole 12. The rear end 42 of the connection terminal 40 is exposed from the rear end of the insulator 10, and a high voltage cable (not shown) is connected to the rear end 42 via a plug cap (not shown). A high voltage is applied to 20.

  Next, the metal shell 50 will be described. The metal shell 50 is a cylindrical metal fitting for holding the insulator 10 and fixing the spark plug 100 to an internal combustion engine (not shown). The metal shell 50 holds the insulator 10 so as to surround the flange portion 19, the distal end side trunk portion 17, and the leg length portion 13 from the rear end side barrel portion 18 in the vicinity of the flange portion 19 of the insulator 10. The metal shell 50 is formed of a low carbon steel material, and includes a tool engaging portion 51 to which a spark plug wrench (not shown) is fitted, and a screw portion 52 to be screwed into an engine head provided on an internal combustion engine (not shown). ing. Further, the metal shell 50 has a caulking portion 53 on the rear end side of the tool engaging portion 51. By caulking the caulking portion 53, the step portion 15 formed between the front end side body portion 17 and the leg long portion 13 of the insulator 10 is attached to the plate packing 8 on the step portion 56 formed on the inner periphery of the metal shell 50. The metal shell 50 and the insulator 10 are integrated. In order to complete sealing by caulking, an annular shape is formed between the inner peripheral surface in the vicinity of the caulking portion 53 of the metal shell 50 and the outer peripheral surface of the rear end side body portion 18 in the vicinity of the flange portion 19 of the insulator 10. Ring members 6 and 7 are interposed, and talc (talc) 9 powder is filled between the ring members 6 and 7. Further, a flange 54 is formed at the center of the metal shell 50, and the gasket 5 is inserted into the vicinity of the rear end side (upper part in FIG. 1) of the screw 52, that is, the seat surface 55 of the flange 54. Yes.

  Next, the ground electrode 30 will be described. The ground electrode 30 is made of a metal having high corrosion resistance. As an example, a nickel-based alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 30 has a substantially rectangular cross section perpendicular to the longitudinal direction of the ground electrode 30 and has a bent rectangular bar-like outer shape. And the base 32 of the base end side of a square bar shape is joined to the front end surface 57 of the front end side of the axial direction of the metal shell 50 by resistance welding. On the other hand, the tip 31 of the ground electrode 30 opposite to the base 32 is bent so as to face the tip 22 of the center electrode 20, and a spark discharge gap is formed between the two. The base 32 corresponds to “one end of the ground electrode” in the present invention, and the tip 31 corresponds to “the other end of the ground electrode” in the present invention.

  In spark plug 100 of the present embodiment, plating is performed on metal shell 50 and ground electrode 30 joined to metal shell 50, and a plating layer is formed on the surfaces of metal shell 50 and ground electrode 30. . The plating layer is formed in two layers, and a metal layer 80 containing zinc as a main component is formed on the surfaces of the metal shell 50 and the ground electrode 30. Further, a chromate film layer 85 in which 98% by weight or more of the contained chromium component is trivalent chromium is formed on the surface of the metal layer 80.

  Next, when manufacturing the spark plug 100 having such a configuration, a series of steps for performing plating on the metal fitting assembly in which the metal shell 50 and the ground electrode 30 are joined will be described. In addition, it demonstrates centering around the manufacturing method of the principal part of this Embodiment, and abbreviate | omits or simplifies description about a well-known part.

  First, the insulator 10 is formed by using alumina as a main raw material, grinding and so on to obtain a predetermined shape, and firing at a high temperature. On the other hand, the rod-shaped center electrode 20 and the ground electrode 30 are made of the nickel-based alloy described above. Note that when the center electrode 20 is formed, the metal core 23 is inserted. The center electrode 20, the sealing material 4, the resistor 3, the connection terminal 40 previously produced by plastic working or the like are integrally formed on the formed insulator 10 by a glass sealing process. In this glass sealing step, a glaze layer may be formed on the surface of the insulator 10.

  The metal shell 50 is made by using a steel material and performing plastic working, cutting, or rolling to a predetermined shape. At this time, the metal shell 50 is formed with a tool engaging portion 51, a screw portion 52, a flange portion 54, and the like having a predetermined shape.

  Then, the base 32 of the ground electrode 30 is joined by resistance welding to the distal end surface 57 of the cylindrical metal shell 50 before assembling the insulator 10 or the like to form the metal fitting assembly 200 (see FIG. 2) (welding). Process). The ground electrode 30 is in a rod-like state before being bent, and is joined with its distal end portion 31 directed toward the distal end side in the axial direction of the metal shell 50.

  Next, as shown in FIG. 2, the metal shell 50 is attached to the tip of the support bar 210 with the axial direction perpendicular to the rear end side (the caulking portion 53 side of the metal shell 50). Fix by aligning the directions. And it rotates so that it may become 0-20 rotations per minute centering | focusing on the axis | shaft of the support rod 210. FIG. Further, the injection port 220 of the blasting machine (not shown) is directed toward the ground electrode 30 so that the injection direction with respect to the ground electrode 30 becomes an dip angle of 0 to 90 °. Then, the ground electrode 30 is subjected to blasting using a so-called dry blasting method in which a spray material 230 as a granular material is blown from the ejection port 220 with air for a predetermined time (blasting process). At this time, the sprayed spray material 230 collides with the ground electrode 30 to remove the oxide film formed on the surface of the ground electrode 30, and the surface of the ground electrode 30 is formed to be uneven.

  In addition, as the injection material 230 injected from the injection port 220 of a blast processing machine (not shown), the granular material which consists of glass, a metal, a ceramic, etc. can be used. For example, when using the granular material formed from the SUS bead as the spray material 230, it is desirable that the time for performing the blast treatment is 10 to 20 seconds. As will be described later, if the blast treatment is performed for 1 second or more per processed surface, an effect sufficient for removing the oxide film can be obtained. The distance between the ejection port 220 and the ground electrode 30 is preferably 10 to 200 mm.

  And the metal-plating assembly 200 by which the blasting process was performed with respect to the ground electrode 30 performs the plating process by a barrel apparatus (not shown) (plating process). First, the metal fitting assembly 200 is immersed in a zinc plating bath containing zinc as a main component, and the metal layer 80 is formed on the surface of the metal fitting assembly 200. Next, the metal fitting assembly 200 is immersed in a chromate treatment bath to form a chromate film layer 85 on the surface of the metal layer 80. That is, in the plating process, the metal layer 80 and the chromate film layer 85 are formed on the surface of the metal shell 50 and on the surface of the ground electrode 30 joined to the metal shell 50.

  Next, after drying the metal fitting assembly 200 subjected to the plating treatment, the insulator 10 in which the center electrode 20 and the like are integrated uses the above-described plate packing 8, ring members 6 and 7, talc 9 and the like. The caulking portion 53 is formed to be assembled to the metal fitting assembly 200. Next, the ground electrode 30 is bent as shown in FIG. 1, and when the spark plug 100 is assembled, the tip 31 of the ground electrode 30 and the tip 22 of the center electrode 20 face each other to form a spark discharge gap. To form. The metal layer 80 is formed on the surface of the ground electrode 30 whose surface area is increased by removing the oxide film by blasting and further forming the surface to be uneven. For this reason, the adhesiveness with the base material of the ground electrode 30 is high, and the bending (swelling), peeling, or dropping off due to the bending process does not occur. The insulator 10 holding the center electrode 20 is inserted into the metal fitting assembly 200 processed in this way, and the spark plug 100 is completed by crimping.

  In order to evaluate the adhesion of the plating layer formed on the ground electrode 30 of the spark plug 100 manufactured as described above, the following evaluation test was performed.

[Example 1]
First, the evaluation test about the adhesiveness of the plating layer by the presence or absence of a blast process was done. In this evaluation test, the blasted metal fitting assembly subjected to the welding process, the blasting process, and the plating process described in the present embodiment and the blasting-free metal fitting assembly subjected to the welding process and the plating process were used as samples. 7 each were prepared. The ground electrode was made of Inconel (trade name) 600, and joined to the metal shell by resistance welding. Thereafter, a blasting treatment for 30 seconds was performed on the ground electrode of the sample of the bracket assembly with the blasting treatment. Blasting was performed by a dry blasting method, and SUS beads having a particle size of # 150 (74 to 105 μm) made of SUS304 were used as the propellant. In this embodiment, blasting is performed at a projection pressure of 0.3 to 0.5 MPa. In addition, the metal plating layer is formed on the surface of the metal fitting assembly using a zinc plating bath containing zinc as a main component for the plating treatment, and then the metal fitting assembly is applied to the chromate treatment bath using trivalent chromate. Was immersed to form a chromate film layer. Thereafter, it was washed with water and dried.

  And in order to make it easy to generate | occur | produce a plating defect with respect to a pair of 6 types of samples of a metal fitting assembly with a blasting process and a metal fitting assembly without a blasting process, 260,280,300,320,340, The heat treatment at 360 (° C.) was performed for 15 minutes. Moreover, the sample which did not heat-process as a comparative example was prepared. After heating, each sample was cooled to room temperature, and as shown in FIG. 3, the tip of the ground electrode was bent outward (in a direction away from the axis O) until the axis of the ground electrode of each sample became a right angle. And the surface of the bending position R of the ground electrode was observed with a 10 × magnifier.

  In the evaluation of the adhesion of the plating layer, as shown in FIG. 4, the surface state of the ground electrode bending position R is good, and the plating layer does not float (swell), peel off or drop off. (Indicated by A in the figure) was evaluated as “◎”. Moreover, the thing (it shows with B in a figure) in which the goosebump-like float (swelling) generate | occur | produced was evaluated as "(circle)". A horizontal stripe-like crack that occurred and partly peeled (indicated by C in the figure) was evaluated as “Δ”. And what peeled completely (it shows with D in a figure) was evaluated as "x". The results of this evaluation test are shown in Table 1.

  As a result of the evaluation test, the sample of the metal assembly without blasting treatment was evaluated as “◎” when the heat treatment was not performed and the plating layer did not float (swell), peeled off, or dropped off. Moreover, in the sample which heat-processed at 260 degreeC, the goosebump-like float (swelling) generate | occur | produced in the plating layer, but it was evaluated as "(circle)" without peeling and dropping. In the sample subjected to the heat treatment at 280 ° C., cracks in the form of horizontal stripes were generated in the plating layer, and peeling was caused in part. And in the sample which heat-processed above 300 degreeC, peeling generate | occur | produced completely and was evaluated as "x".

  On the other hand, in the case of the blasted metal fitting assembly sample, when the heat treatment was not performed or when the heat treatment was performed at 260 ° C. to 320 ° C., the plating layer was not lifted (swelled), peeled off, or dropped off. It was evaluated as “◎”. And in the sample which heat-processed above 340 degreeC, the goosebump-like floating (swelling) generate | occur | produced in the plating layer, but it was evaluated as "(circle)" without peeling and dropping.

  From this result, the adhesion of the plating layer to the base material of the ground electrode is improved by blasting the ground electrode to remove the oxide film formed on the surface and increasing the surface area and then plating. As a result, it was found that the occurrence of peeling and dropping can be prevented.

[Example 2]
Next, the evaluation test about the adhesiveness of the plating layer by the time which performs a blast process was done. In this evaluation test, seven types of metal fitting assemblies that were subjected to the welding process, the blasting process, and the plating process described in this embodiment were produced as samples. The material of the ground electrode of the sample and the plating conditions are the same as in Example 1. In the blasting process, blasting was performed for each sample for 0, 1, 10, 30, 60, 90, and 120 seconds in the same manner as in Example 1.

  In order to make each sample produced in this way in a state in which defective plating is likely to occur, a heat treatment at 300 ° C. was performed for 15 minutes in a thermostatic bath. And the ground electrode of each sample was bent like Example 1, and the surface of the bending position R was observed with the 10 times magnifier (refer FIG. 3). Evaluation on the adhesion of the plating layer was also performed in the same manner as in Example 1 (see FIG. 4). The results of this evaluation test are shown in Table 2.

  As a result of the evaluation test, the sample that was not subjected to blasting (0 second) was completely peeled off and evaluated as “x”. Moreover, in the sample which performed the blasting process for 1 second or 10 seconds, although the goosebump-like float (swelling) generate | occur | produced in the plating layer, there was no peeling and dropping, and it evaluated as "(circle)". The sample subjected to the blast treatment for 30 seconds or more was evaluated as “◎” without floating (blowing), peeling, or dropping off in the plating layer.

  From this result, if the ground electrode is subjected to blasting for at least 1 second to remove the oxide film formed on the surface and the plating is performed after increasing the surface area, the plating layer on the base material of the ground electrode It was found that the adhesion was improved and the occurrence of peeling and dropping could be prevented.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the present embodiment, the ground electrode 30 is joined to the metal shell 50 and then the blast process is performed on the ground electrode 30. However, the ground electrode that has been subjected to the blast process may be joined to the metal shell. As shown in FIG. 5, the blast processing may be performed on the electrode material 330 before being formed by cutting and using the blast processing machine 300. When the electrode material 330 is conveyed along the axial direction by the conveying roller 310, as shown in FIG. 6, the two injection ports 320 of the blasting machine 300 are arranged in two directions orthogonal to the axis and facing each other. The spray material 360 mixed with water is sprayed with air toward the electrode material 330. At this time, it is preferable that the injection direction of the injection port 320 is a direction toward two corners that are diagonal to the axial cross section of the electrode material 330. By doing so, the spray material 360 can collide over the entire outer peripheral surface of the electrode material 330. Note that the blasting machine 300 that performs the blasting process using the wet blasting method preferably includes a dryer 340 that dries the electrode material 330 wetted by the blasting process.

  In this embodiment, the blasting process for the ground electrode 30 uses a so-called dry blasting method in which the spray material 230 is sprayed with air. However, the spray material 230 is mixed with a liquid such as water and sprayed with air. A so-called wet blasting method may be used.

  In addition, the metal layer 80 formed in the plating process is formed by performing a plating process using a zinc plating bath containing zinc as a main component. It may be formed.

  The present invention can be applied to a spark plug used in an internal combustion engine.

1 is a partial cross-sectional view of a spark plug 100. FIG. It is a figure which shows a blast processing process. It is a figure for demonstrating the method of performing the evaluation test of the adhesiveness of a plating layer. It is a figure for demonstrating the evaluation criteria of the adhesiveness of a plating layer. It is a figure which shows the modification of a blasting process. It is a figure which shows the modification of the blasting process seen from the arrow direction in the dashed-dotted line PP of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Insulator 12 Shaft hole 20 Center electrode 30 Ground electrode 31 Tip part 32 Base part 50 Main metal fitting 57 Front end surface 80 Metal layer 85 Chromate film layer 100 Spark plug 200 Metal fitting assembly

Claims (4)

A central electrode, an axial hole extending in the axial direction of the central electrode, an insulator that holds the central electrode inside the axial hole, and a metal shell that surrounds and holds the radial periphery of the insulator; A method of manufacturing a spark plug having one end joined to a front end surface of the metal shell and the other end having a ground electrode facing the center electrode,
A blasting process for blasting the ground electrode;
A welding step of welding one end of the ground electrode to the metal shell,
A metal fitting assembly in which the ground electrode and the metallic shell are joined and integrated by the welding process, and at least the ground electrode subjected to the blasting process by the blasting process, A spark plug manufacturing method comprising: a plating step of performing plating.   2. The spark plug manufacturing method according to claim 1, wherein the blasting process applied to the ground electrode in the blasting process uses a wet blasting method in which a mixture of powder and liquid is sprayed. 3.   3. The method for manufacturing a spark plug according to claim 1, wherein in the blast treatment step, a period during which the ground electrode is subjected to a blast treatment is 1 second or more and 90 seconds or less. In the plating step,
On the surface of the metal fitting assembly, a metal layer mainly composed of nickel or zinc;
The spark plug manufacturing method according to any one of claims 1 to 3, wherein a chromate film layer is formed on a surface of the metal layer.

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