JP2001110545A - Spark plug and method for manufacturing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a spark plug which, a main attachment and a ground electrode thereof being integrated together, can effectively form a zinc galvanized layer on the portion except the leading end of the ground electrode. SOLUTION: A zinc galvanized layer 141 is uniformly formed on the outer surface of an attachment assembly in which the base end of the ground electrode 4 is installed on the main attachment 1. Then the zinc galvanized layer formed on the leading end of the electrode is removed by electrolytic separation and a metal chip with a high fusing point is welded on the surface of a base electrode material exposed by the separation, thereby forming an ignition section 32. In other words, since there is no need for masking not to form a galvanized layer on the leading end of a ground electrode, it is made possible to highly efficiently manufacture a spark plug 100 which forms the ignition section 32 on the ground electrode 4. At the same time without the intervention of masking treatment after the separation of the galvanized layer, dirt and oil content are hard to attach and the purification of the surface of the base electrode material is facilitated by the separation treatment, resulting in an increase of welding intensity of the metal chip with a high fusing point and less occurrence of the problem of the separation of the ignition section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A spark plug used for ignition of an internal combustion engine, for example, a gasoline engine for an automobile or the like, is provided with an insulator outside a center electrode and a metal shell outside the center electrode. It has a structure in which a ground electrode forming a spark discharge gap is attached to the metal shell.
The metal shell is mounted on the cylinder head of the engine by a mounting screw formed on the outer peripheral surface of the metal shell. Incidentally, the metallic shell is generally made of an iron-based material such as carbon steel, and its surface is often plated with zinc for corrosion protection. Further, in order to enhance the anticorrosion performance, the surface of the galvanized layer is further subjected to a chromate treatment.

In order to apply zinc plating to the metallic shell as described above, it is effective to use a so-called barrel plating process in terms of improving productivity. However, as described above, it is necessary to attach the ground electrode to the metal shell by resistance welding or the like. However, if the attachment is performed after barrel plating, poor welding is likely to occur due to the interposition of a zinc-based plating layer (or a chromate layer). In addition, there is a problem that the corrosion resistance is reduced because the zinc-based plating layer is damaged in the welded portion. Therefore, in general, a ground electrode is attached to the metal shell before plating, and then the metal shell with the ground electrode integrated is subjected to zinc plating or subsequent chromate treatment by barrel plating or the like. I have.

[0004]

However, in the above-mentioned method, a zinc-based plating layer or a chromate layer is also formed on the surface of the ground electrode integrated with the metal shell. The formation of the insulating chromate layer has a disadvantage that the discharge performance is adversely affected.
In recent years, in order to improve spark erosion resistance, a spark formed by welding a chip mainly composed of a high melting point metal such as Pt or Ir to a position corresponding to a spark gap between a center electrode and a ground electrode has been formed. Plugs are also widespread. However, when such a high melting point metal tip is welded to the ground electrode side, if the galvanized layer or the chromate layer as described above is formed, it causes welding failure and leads to defects such as chip peeling.

Therefore, the surface of the electrode base is exposed without forming a galvanized layer on the tip side surface of the ground electrode to which the high melting point metal tip is welded, and the high melting point metal tip is welded thereto. I have. Conventionally, as a method of exposing the electrode base surface, a method of covering the tip of the ground electrode with a rubber tube or the like so as not to come into contact with the plating solution and preventing the formation of a zinc plating layer on the tip is adopted. However, this method has a drawback that mounting a rubber tube is troublesome and difficult to automate, and is extremely inefficient. In addition, when handling such as mounting a rubber tube, oil, dirt, and the like are likely to adhere to the tip of the ground electrode that is not involved in the plating process. When the high melting point metal tip is welded in such a state, the joining strength is easily deteriorated, and a problem such as chip peeling may occur.

An object of the present invention is to provide a method of manufacturing a spark plug capable of efficiently forming a galvanized layer on a portion other than the tip of a ground electrode by integrating a metal shell and a ground electrode, and a method of manufacturing the same. A spark plug obtained by the method described above, wherein the joining strength of the high melting point metal tip is less likely to be impaired when welding the high melting point metal tip, and furthermore, the spark plug is less likely to cause problems such as peeling of a fired portion formed by the tip joining. It is in.

[0007]

In order to solve the above problems, a method of manufacturing a spark plug according to the present invention comprises a center electrode, an insulator provided outside the center electrode, and an insulator. A metal shell provided on the outside of the body, and a ground electrode disposed so as to face the spark discharge gap so as to form a spark discharge gap between the center electrode and at least a position corresponding to the spark discharge gap. A method for manufacturing a spark plug in which a refractory metal ignition portion having a discharge surface is formed by welding a refractory metal tip to a ground electrode side, wherein a base end of a ground electrode is provided at one opening of a cylindrical metal shell. Prepare a metal fitting assembly with the side attached, collectively on the outer surface of the metal shell and the ground electrode of the metal fitting assembly, a zinc-based plating layer forming step of forming a zinc-based plating layer containing zinc as a main component, So For the metal assembly where the zinc-based plating layer is formed, the zinc-based plating layer on the outer surface of the metal shell is removed, and at least the zinc-based plating layer of the ground electrode that is formed at the tip of the electrode is electrolytically peeled off. And an underlying electrode material surface exposed by the peeling after the electrolytic peeling step is completed (hereinafter, referred to as a base exposed surface)
And a welding step of welding the high melting point metal tip to the metal.

[0008] In this specification, the term "main component" (also synonymous with "main component" or "mainly") means a component having the highest content ratio in the substance of interest.

According to the above method, a zinc-based plating layer is collectively formed on the outer surface of the metal fitting assembly in which the base end of the ground electrode is attached to the metal shell, and thereafter, the zinc plating layer formed on the electrode tip side is formed. The system plating layer is removed by electrolytic peeling, and a refractory metal tip is welded to the base electrode material surface exposed by the peeling to form an ignition portion. In other words, unlike the conventional case, masking with a rubber tube or the like to prevent the formation of a plating layer at the tip of the ground electrode is not required, so that a spark plug of a type in which a refractory metal ignition portion is formed on the ground electrode is extremely efficient Can be manufactured. In addition, after the zinc-based plating layer is peeled off, since no masking treatment is interposed, adhesion of dirt and oil is less likely to occur, and the surface layer portion of the base electrode material is appropriately removed by electrolytic peeling treatment to further purify the surface. We can expect the effect to advance. As a result, the welding strength of the high melting point metal tip is increased, and problems such as peeling of the ignition portion are less likely to occur.

[0010] As a method of chemically peeling and removing the zinc-based plating layer, the ground electrode on which the zinc-based plating layer is formed is immersed in an acidic electrolyte to thereby electrolessly peel the zinc-based plating layer. It is also possible. However,
According to the method of the present invention employing the electrolytic peeling treatment, the following effects that cannot be achieved by electroless peeling are obtained. When the zinc plating layer is covered with the chromate layer in the chromate layer forming step to form a zinc chromate layer, in the electroless treatment with an acidic electrolytic solution, the peeling itself is difficult because the chromate layer acts as a protective film for the zinc plating layer. Becomes However, according to the electrolytic peeling treatment, it is possible to collectively remove a zinc chromate layer composed of a zinc-based plating layer and a chromate layer covering the same.

In the electroless treatment using an acidic electrolytic solution, when the ground electrode is immersed in the electrolytic solution, the dissolution reaction of the zinc-based plating layer starts to progress immediately. The dissolution reaction does not stop immediately because the liquid remains. Therefore, the dissolution proceeds excessively not only in the zinc-based plating layer but also in the base metal layer, and defects such as surface roughness are likely to occur. In addition, in the acidic electrolyte, when the content of the acidic component is increased in order to increase the dissolving power, the zinc-based plating layer in a portion that is not immersed in the liquid is eroded due to evaporative components and splashes from the liquid. As a result, the corrosion resistance of the metal shell may be reduced. However, in the electrolytic stripping process, the dissolution reaction does not proceed rapidly unless current is supplied, so that the thickness of the stripped layer can be easily controlled, and surface roughening due to the progress of dissolution in the base metal layer does not easily occur.

Further, the zinc-based plating layer covering the outer surface of the metal shell is not easily affected by evaporation components from the liquid, splashes, and the like. As a result, the corrosion resistance of the zinc-based plating layer can be significantly increased. Specifically, the following corrosion resistance level is realized as a spark plug in which a zinc chromate layer is formed on the surface of a metal shell. That is, JISH850
2 in the corrosion resistance test method for plating specified in 2.
Endurance time until white rust resulting from corrosion of the zinc-based plating layer of the zinc chromate layer covering the metal shell appears at least 10% of the entire surface of the zinc chromate layer when the "neutral salt spray test method" is performed. For more than 48 hours.

In the electrolytic stripping treatment, by adjusting the electrolytic potential, a reaction in which the dissolution of zinc is promoted and the dissolution of the underlying metal material layer is suppressed can be easily realized. Thereby, the base metal material layer hardly dissolves, and the zinc-based plating layer can be peeled sufficiently to perform an ideal treatment. As a result, the weldability of the high melting point metal tip to the exposed base surface is further enhanced.

The pH of the electrolytic solution used for electrolytic stripping is 6 to 8
It is desirable to adjust to the range. When the pH of the electrolytic solution is less than 6, the dissolution of the zinc-based plating layer tends to proceed due to the natural oxidation potential of the solution itself even when no current is supplied, and it becomes difficult to control the peeling thickness, or Roughness and an oxide layer may be formed on the exposed surface, which may adversely affect the weldability of the high melting point metal tip. In addition, there is a concern that the corrosion resistance of the metal shell may be deteriorated due to the zinc-based plating layer being attacked in undesired portions due to the influence of liquid scattering or the like. On the other hand, when the pH exceeds 8, the stripping reaction rate is reduced, which may cause inconveniences such as reduced efficiency and insufficient stripping. The pH of the electrolyte is more desirably 6.
It is preferable to adjust the value in the range of 5 to 7.5.

The energization time for electrolytic stripping is determined by the thickness of the zinc-based plating layer in the region of the ground electrode to be stripped, while the etching thickness of the underlying electrode material layer underlying the stripped zinc-based plating layer is determined. Is preferably adjusted to be less than 1.0 μm. When the etching thickness of the base electrode material layer is 1.0 μm or more, the weldability of the refractory metal tip may be adversely affected by the surface roughness of the base exposed surface.

For example, when the ground electrode material layer of the ground electrode is Ni
When composed of a base heat-resistant alloy, almost all of the zinc-based plating layer is peeled off, and an electrolytic peeling treatment is performed so that excessive etching of the underlying metal material layer is suppressed. A groove-like pattern having a depth greater than the average roughness level of the crystal grain surface is formed along the crystal grain boundary of the electrode material layer. When the exposed surface of the base is in such a state, the welding strength of the ignited portion obtained by welding the high melting point metal tip is increased. It is unlikely to occur.

As a method of peeling off only the zinc-based plating layer on the front end side of the ground electrode, a ground end is exposed so as to have a predetermined length above the liquid surface, and the remaining front end is located in the electrolytic solution. It is reasonable to immerse the electrode in an electrolytic solution and peel off the zinc-based plating layer only in the immersed portion. According to this, only by adjusting the immersion depth of the ground electrode with respect to the electrolytic solution, the zinc-based plating layer can be peeled off over the desired length corresponding to the immersion depth on the ground electrode tip side.

For example, the spark plug is of a type in which the ground electrode is bent back to the side, and a spark discharge gap is formed between the bent back end of the ground electrode and the center electrode. In some cases, the following method is effective. That is, as the bracket assembly, one in which the ground electrode before bending is attached so as to extend linearly in the axial direction of the metallic shell is used, and the side where the ground electrode is attached to the bracket assembly faces downward. And the tip of the ground electrode is immersed in the electrolytic solution.
According to this method, if the liquid surface height of the electrolytic solution is kept constant, the holding position in the height direction of the metal shell is fixed by a jig or the like, so that a zinc-based plating layer having a fixed length is always provided. There is an advantage that the peeling region of the above can be easily formed.

In the spark plug, a refractory metal ignition portion having a discharge surface can be formed by welding a refractory metal tip to at least the ground electrode at a position corresponding to the spark discharge gap. In this case, the ignition portion can be formed by electrolytically peeling off the zinc-based plating layer of the ground electrode, and then welding a high melting point metal tip to the base electrode material surface exposed by the peeling. Since the welding surface (exposed surface) on the base metal material side formed by peeling of the zinc-based plating layer is activated by electrolytic peeling, mutual diffusion between the chip and the base metal material proceeds during resistance welding. And the welding strength of the resulting ignited portion is greatly increased.

Next, if a Pt-based metal tip containing Pt as a main component is used as the high melting point tip on the ground electrode side, welding can be easily performed by resistance welding. In addition, since the welding surface (exposed surface) on the base metal material side formed by peeling of the zinc-based plating layer is activated by electrolytic peeling, mutual diffusion between the chip and the base metal material during resistance welding is prevented. It easily progresses, and the welding strength of the obtained ignition part is greatly increased. Such an effect is particularly remarkable when the underlying metal material is made of a Ni-based metal (for example, a Ni alloy such as a Ni-based heat-resistant alloy) or an Fe-based heat-resistant alloy.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. 1 and 2 show an embodiment of a spark plug according to the present invention.
The spark plug 100 has a state in which a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip protrudes, and a high melting point metal firing part 31 formed at the tip. One end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like, and the other end is bent back to the side, and the side surface faces the tip of the center electrode 3. And a ground electrode 4 and the like arranged so as to be connected to each other. Further, a Pt-based metal firing portion (also regarded as one of the high melting point metal firing portions) 32 facing the high melting point metal firing portion 31 is formed on the ground electrode 4. And a gap between the Pt-based metal firing portion 32 is a spark discharge gap g.

The term "ignited portion" as used herein refers to a portion of the joined fixed members which is not affected by the composition fluctuations caused by welding (for example, the material of the ground electrode or the center electrode by welding). The remaining part excluding the alloyed part)
Shall be referred to.

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a through hole 6 for fitting the center electrode 3 along its own axial direction. . The terminal fitting 13 is inserted and fixed to one end of the through hole 6, and the center electrode 3 is inserted and fixed to the other end of the through hole 6. A resistor 15 is arranged between the terminal fitting 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 fitting 13 via conductive glass seal layers 16 and 17, respectively.

The metal shell 1 is formed of a metal such as carbon steel in a cylindrical shape, and forms a housing of the spark plug 100 and has a plug 100 on its outer peripheral surface.
Is formed on the engine block (not shown). Reference numeral 1e denotes a tool engagement portion that engages a tool such as a wrench or a wrench when the metal shell 1 is attached, and has a hexagonal axial cross-sectional shape. On the other hand, between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, a ring-shaped wire packing 62 that engages with the rear peripheral edge of the flange-shaped protrusion 2e is arranged. On the rear side, a ring-shaped packing 60 is arranged via a filling layer 61 such as talc. Then, the insulator 2 is pushed forward toward the metal shell 1 and, in this state, the opening edge of the metal shell 1 is swaged inward toward the packing 60 to form a swaged portion 1d. It is fixed to the insulator 2.

A gasket 30 is fitted into the base end of the screw 7 of the metal shell 1. The gasket 30 is a ring-shaped part obtained by bending a metal plate material such as carbon steel, and the screw portion 7 is screwed into a screw hole on the cylinder head side to form a flange-shaped gas seal portion 1f on the metal shell 1 side. Between the screw hole and the opening peripheral portion of the screw hole, it is compressed in the axial direction and deformed so as to be crushed, and serves to seal a gap between the screw hole and the screw portion 7.

Next, a zinc plating layer 41 for corrosion protection is formed on the entire outer surface of the underlayer (for example, carbon steel) 40 of the metal shell 1.
(A zinc-based plating layer) is formed, and further outside thereof is covered with a chromate layer 42 to form a zinc chromate layer. Similarly, a zinc chromate layer composed of a galvanized layer 45 and a chromate layer 46 is also formed on the outer surface of the gasket 30.

The zinc plating layer and the chromate layer of the metal shell 1 and the gasket 30 are all formed by the same method. Hereinafter, the metal shell 1 will be described as a representative. The zinc plating layer 41 is formed by a known electrolytic zinc plating method, and has a thickness of, for example, 3
About 10 to 10 μm. If the thickness is less than 3 μm, corrosion resistance may not be sufficiently secured. Conversely, 10
A film thickness exceeding μm is an excessive specification from the viewpoint of ensuring corrosion resistance, and also increases the plating time and reduces the production efficiency, leading to an increase in cost.

On the other hand, a commonly used yellow chromate film may be used for the chromate layer 42. However, the yellow chromate film suffers from the fact that a part of the chromium component is contained in the form of hexavalent chromium. In recent years, interest in environmental protection has been increasing on a global scale, and has been gradually shunned. In this respect, the chromate layer is
It is desirable to use a trivalent chromium-based chromate layer in which 95% by weight or more of the contained chromium component is trivalent chromium.

When the chromate layer 42 is formed of a trivalent chromium-based chromate film, for example, in the case of a conventional trivalent chromium-based chromate film such as a blue chromate film layer or a conventional chromate film such as a blue chromate film layer, the formed film thickness is obtained. Is as thin as about 0.1 μm at the maximum, so that sufficient corrosion resistance and heat resistance to the metal shell may not be secured in the main use environment of the spark plug in some cases. Therefore, by securing the thickness of the chromate layer 42 to 0.2 μm or more,
The anticorrosion performance of the chromate film mainly composed of trivalent chromium is greatly improved, and the metal shell can be given sufficient durability against corrosion. In addition, the corrosion resistance of the metal shell 1 can be sufficiently maintained even in an environment peculiar to a spark plug in which the temperature is likely to rise and an acid attack is likely to occur. When the thickness of the chromate layer 42 is 0.2
If it is less than μm, sufficient anticorrosion performance and heat resistance cannot be ensured. On the other hand, if the thickness exceeds 0.5 μm, cracks may occur in the layer (for example, during processing in assembling or the like) or the layer may easily fall off, leading to impairment of the anticorrosion performance. The thickness of the chromate layer 42 is desirably 0.3 to 0.5 μm. It is desirable that the chromate layer 42 does not substantially contain hexavalent chromium.

Next, the center electrode 3 and the ground electrode 4 are made of Ni as a metal material forming the base of the zinc chromate layer.
Alternatively, it is made of a heat-resistant alloy containing Fe as a main component.
For example, the following can be used as a heat-resistant alloy containing Ni or Fe as a main component. Ni-base heat-resistant alloy: In this specification, Ni is contained in an amount of 40 to 85% by weight, and the balance is mainly composed of Cr, Co, Mo, W, and N.
b, a general term for heat-resistant alloys composed of one or more of Al, Ti and Fe. Specifically, the following can be used (both are trade names; for the alloy composition,
Literature (Revised 3rd Edition Metal Data Book (Maruzen); p138)
And will not be described in detail): ASTR
OLOY, CABOT 214, D-979, HASTELLOY C22, HASTELLOY C
276, HASTELLOY G30, HASTELLOY S, HASTELLOY X, HAYN
ES 230, INCONEL 587, INCONEL 597, INCONEL 600, INC
ONEL 601, INCONEL 617, INCONEL 625, INCONEL 706, I
NCONEL 718, INCONEL X750, KSN, M-252, NIMONIC 75,
NIMONIC 80A, NIMONIC 90, NIMONIC 105, NIMONIC 11
5, NIMONIC 263, NIMONIC 942, NIMONIC PE11, NIMONIC
PE16, NIMONIC PK33, PYROMET 860, RENE 41, RENE 9
5, SSS 113MA, UDIMET 400, UDIMET 500, UDIMET 520,
UDIMET 630, UDIMET 700, UDIMET 710, UDIMET 720, UN
ITEP AF2-1 DA6, WASPALOY.

Fe-based heat-resistant alloy: In the present specification, Fe is contained in an amount of 20 to 60% by weight, and the remainder is mainly composed of Cr, Co,
A heat-resistant alloy comprising one or more of Mo, W, Nb, Al, Ti and Ni is generically referred to. Specifically, the following can be used (all are trade names; the alloy composition is described in the literature (Revised 3rd Edition Metal Data Book (Maruzen), p. 138); A-286, ALLOY 901, DISCALOY, HAYNES 55
6, INCOLOY 800, INCOLOY 801, INCOLOY 802, INCOLOY
807, INCOLOY 825, INCOLOY 903, INCOLOY 907, INCOLO
Y 909, N-155, PYROMET CTX-1, PYROMET CTX-3, S-59
0, V-57, PYROMET CTX-1, 16-25-6, 17-14CuMo, 19-9D
L, 20-Cb3.

In this embodiment, INCONEL 600 is used for both the center electrode 3 and the ground electrode 4 (however, a Cu-based metal layer for improving heat drawing may be inserted inside). The approximate composition is as follows: Ni: 76% by weight-Cr: 15.5% by weight-Fe: 8% by weight.

Next, the refractory metal firing portion 3 on the side of the center electrode 3
1 (and thus a chip 31 'for forming it)
Is mainly composed of a high melting point metal containing Ir, Rh, W, Re or Ru as a main component, for example, a high melting point metal containing Ir as a main component. By using these refractory metals, even in an environment where the temperature of the center electrode tends to increase, the wear resistance of the ignition portion can be improved. Further, the weldability to the above-mentioned heat-resistant alloy is also good. On the other hand, the Pt-based metal firing portion 32 on the ground electrode side (and, consequently, the chip 32 ′ for forming it) is
In addition to a simple substance, it is composed of a Pt-Ni alloy (for example, Pt-1 to 30% by weight Ni alloy), a Pt-Ir alloy, a Pt-Ir-Ni alloy, or the like. The Pt-based metal firing portion 32 is formed by joining a Pt-based metal tip 32 ′ by resistance welding to an exposed surface (base metal material surface) of the base metal material layer 140 that is not covered by the zinc chromate layer.

When the high melting point metal ignition portion 31 is mainly composed of Ir, since Ir has a property of easily oxidizing and volatilizing in a high temperature range, if Ir is used as it is in the ignition portion as it is, it is more oxidative than spark exhaustion. -There is a disadvantage that consumption due to volatilization is a problem. Therefore, the high-melting point metal ignition portion is mainly composed of an Ir alloy containing Ir as a main component and one or more of Pt, Rh, Ru, Pd and Re added thereto, thereby oxidizing such Ir. Volatilization can be effectively suppressed, and the wear resistance of the ignition portion can be improved.

A method for manufacturing the spark plug 100 will be described. First, a zinc chromate layer is formed on the metal shell 1 as follows. The base end side of the ground electrode 4 is attached to the opening of the metal shell 1 on the side of the mounting screw portion 7 by welding to form a metal assembly W. At this stage, the ground electrode 4 has not yet been bent, and is in a state of linearly extending in the axial direction of the metal shell 1. This is galvanized by barrel plating using a barrel plating apparatus 199 shown in FIG. In the barrel plating apparatus 199,
A plurality of metal fitting assemblies W are inserted in a stacked state into a holding container 202 whose wall surface is formed through a liquid such as a net or a perforated plate, and immersed in a galvanizing bath L1 in the plating layer 200. The counter electrode 203 is disposed in the plating bath L1. While rotating the holding container 202 about a horizontal rotation axis by the motor 201, the metal fitting assembly W and the counter electrode 203 are connected via the current-carrying electrode 205 in the holding container 202.
When the DC power supply 204 is energized, the metal fitting assembly W is galvanized on the entire outer surface including the ground electrode 4. As the barrel plating, swing barrel plating can be adopted in addition to the rotary barrel plating as described above.

When the peeling of the galvanized layer 141 is completed, it is washed and dried once and subjected to a chromate treatment. In this embodiment, a chromate treatment tank 200 shown in FIG. 4 (the same parts as those in FIG. 3 are denoted by the same reference numerals) is used.
Here, the chromate treatment liquid L2 is filled and the treatment is performed by the barrel method. However, the chromate treatment to be performed is of a non-electrolytic type, and no electrodes or a power supply for conducting electricity are provided. (However, the electrolytic chromate treatment can be performed. In this case, an apparatus similar to FIG. 3 is used.) Configuration may be adopted).

As the chromate treatment liquid L3, a mixture of a trivalent chromium salt and a complexing agent for trivalent chromium is used to obtain a dense and thick film of trivalent chromium, which is difficult by a general chromate treatment method. A system chromate layer can be formed, and a trivalent chromium-based chromate layer having a thickness of 0.2 to 0.5 μm can be easily formed. Such a chromate treatment solution is disclosed in German Published Patent Application DE19.
Details are disclosed in 638176A1. The outline will be described below.

As described above, the process of forming the chromate layer is as follows.
Oxidation and elution of the underlying metal (for example, zinc) occurs first in the treatment bath, and the eluted underlying metal component reacts with a solution containing chromate ions, and trivalent chromium is converted into a polymer form by a hydroxyl group or an oxygen bridge. It is a common theory that the main mechanism is to form a complex and precipitate and deposit in a gel state on the surface of the underlying metal. in this case,
In order for the chromate layer to grow, elution of the underlying metal and
Reaction between the eluted base metal and chromate ions in the bath
Deposition must proceed in parallel. However, when the chromate layer is deposited to some extent, the elution reaction of the underlying metal layer, which is a heterogeneous reaction via the interface with the bath liquid, is prevented, and the growth of the layer is stagnated.

According to the disclosure of the above-mentioned German published patent application, in order to increase the thickness of the layer, the rate of dissolution of the base metal and the precipitation of the layer by the reaction between the dissolved base metal component and trivalent chromium are determined. It is important to minimize the rate of reverse dissolution of the deposited chromate layer while increasing In the above-described method, it is considered that the layer precipitation is promoted by adding an appropriate complexing agent to the bath to complex trivalent chromium, and the film can be made thicker.

As complexing agents, various chelating agents (dicarboxylic acid, tricarboxylic acid, oxyacid (hydroxyl dicarboxylic acid or hydroxylic tricarboxylic acid, etc .: for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid) , Coric acid, aseleic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, tartaric acid, citric acid,
It is effective to use malic acid, ascorbic acid, etc., but other complexing agents may be used. The complexing agents that can be used are as described in the aforementioned German patent publication.

In order to increase the layer thickness, it is effective to raise the temperature of the chromate treatment bath to about 20 to 80 ° C. If the bath temperature is lower than 20 ° C., the effect of increasing the layer thickness by increasing the temperature can hardly be expected, and if the bath temperature is higher than 80 ° C., control of bath conditions becomes difficult due to severe evaporation of water from the bath. Further, the immersion time of the object to be treated (metal shell, gasket, etc.) in the chromate bath is preferably set to 20 to 80 seconds. If the immersion time is less than 20 seconds, the thickness of the formed chromate layer may not be sufficiently secured. On the other hand, the immersion time is 8
When the time exceeds 0 seconds, the formed chromate layer becomes too thick, cracks may occur in the layer (for example, during processing in assembling or the like), or the layer may easily fall off, which may impair the anticorrosion performance. is there.

On the other hand, in order to promote the dissolution of the base metal, it is effective to lower the pH of the chromate treatment solution within a range in which the re-dissolution of the layer on which the precipitate is formed does not become intense. A desirable pH range is, for example, about 1.5 to 3. In order to suppress the re-dissolution of the layer on which the precipitate has been formed, it is effective to incorporate a hardly re-dissolved hydroxide such as nickel, cobalt or copper into the layer. For this purpose, the compounds of the above metals are dissolved in a chromate treatment bath.
Can be blended.

On the other hand, as a result of further studies by the present inventors, the content of the sodium component in the chromate layer was 2 to 7%.
% Sodium salt (e.g.,
It has been found that by blending sodium nitrate, etc.) in the chromate treatment bath, it is easier to form a dense chromate layer into a thick film. Although the detailed mechanism is unknown, it is presumed that if sodium ions are taken into the chromate layer, the chromate layer is less likely to be redissolved in the treatment bath. The content of the sodium component in the chromate layer is 2 to 7% by weight.
If the thickness is out of the range, it may be difficult to secure a thick film of the chromate layer to 0.2 μm or more. The content of the sodium component in the chromate treatment layer is more desirably 2 to 6% by weight.

When the zinc plating and the chromate treatment are performed as described above, as shown in FIG.
1 and the chromate layer 142 are formed on the entire surface of the ground electrode 4, that is, on the entire surface of the base metal material layer 140. As shown in FIG. 2, a noble metal tip
For example, the Pt-based metal tip 32 'is welded to
Is formed, but if the galvanized layer 141 and the chromate layer 142 are still formed, the components of these layers are mixed in the welded portion, leading to a large decrease in the joining strength of the ignition portion 32. Therefore, in the step shown in FIG. 5, only the leading end portion of the zinc plating layer 141 and the chromate layer 142 formed on the ground electrode 4 are peeled off.

This apparatus has an electrolytic stripping tank 210 containing an electrolytic solution L3. The upper opening of the electrolytic stripping tank 210 is closed by a holding plate 212 in which an assembly insertion opening 212a is formed. Then, the assembly insertion port 212a
The screw portion 7 of the assembly W so that the ground electrode 4 is at the bottom.
Is inserted in the axial direction, and is supported by the inner edge of the assembly insertion opening 212a at the gas seal portion 1f. On the other hand, the pump 213 is supplied from the electrolyte supply port 214 of the electrolytic stripping tank 210.
Supplies the electrolyte L3 from an electrolyte tank (not shown). Then, the liquid level sensor 211 provided in the tank detects the liquid level, and when the liquid level decreases, the control unit 212 operates the pump 213 with reference to the detection signal of the sensor 211, Liquid level S of electrolyte L3
The height of H is kept constant.

As a result, the position of each assembly W in the height direction is fixed by the holding plate 212, and the ground electrode 4 has a predetermined length on the base end side protruding above the liquid surface SH. The tip side is immersed in the electrolytic solution L3. In addition, a counter electrode 215 is disposed in the electrolytic stripping tank 210, and the direct current power supply 216 supplies electricity to the metal shell 1 side as positive (anode) and the counter electrode 215 side as negative (cathode). As shown in c), the galvanized layer 141 in the immersed portion is electrolytically peeled off. At this time, the exposed surface 140a of the base metal material layer 140 is also activated by being subjected to electrolytic etching. The mechanism of the electrolytic stripping of the zinc chromate layer is assumed as follows. That is, as shown in FIG. 6A, when the electrolytic solution L3 penetrates through the pinhole 142a formed in the chromate layer 142, the inner zinc plating layer 141 is formed by electrolysis as shown in FIG. Eroded. When the dissolution of the zinc plating layer 141 progresses, the chromate layer 142 drops off, and the newly exposed surface of the zinc plating layer 142 comes into contact with the electrolytic solution L3 to further promote electrolytic erosion. It is considered that the electrolysis of the galvanized layer 141 is repeated, and the peeling proceeds.

The pH of the electrolytic solution L3 is adjusted to a neutral range of 6 to 8 (preferably 6.5 to 7.5). As a result, the zinc plating layer 141, which is easily acid-dissolved, does not dissolve unless current is applied, and the surface roughness of the exposed surface 140a due to excessive dissolution is effectively prevented. Electrolyte L3
Is, specifically, a sulfate ion,
Those containing at least one of nitrate ions and organic acid ions can be suitably used. By containing sulfate ions, the electrolytic stripping efficiency is enhanced, and even when a chromate layer is formed, the desired stripping amount can be obtained in a short time. In addition, nitrate ions have an effect of allowing the stripping treatment to proceed uniformly. Particularly, when a chromate layer is formed, the chromate layer is partially broken to prevent the contact between the internal zinc-based plating layer and the electrolytic solution. Since it promotes, it is possible to obtain a smooth underlayer exposed layer which is less likely to cause uneven peeling.
The total mixing ratio of sulfate ions and nitrate ions in the electrolytic solution is preferably selected, for example, in the range of 0.5 to 250 g / liter. If the compounding ratio is less than 0.5 g / liter, the conductivity of the liquid cannot be sufficiently ensured, and if the current is forcibly applied, problems such as roughening of the substrate are caused. On the other hand, a compounding ratio exceeding 250 g / liter leads to unnecessary cost increase of the liquid.

From the viewpoint of maintaining both smoothness and electrolytic stripping efficiency, the electrolytic solution desirably contains both sulfate ions and nitrate ions, and has a molar concentration of sulfate ions CSO ₄ . , Molar concentration of nitrate ion CN
It is preferable to use one whose ratio CSO ₄ / CNO ₃ to O ₃ is adjusted in the range of 4/1 to 40/1. CSO ₄ / CNO ₃ is 40
If it exceeds / 1, it may be particularly difficult to achieve uniform and smooth peeling of the zinc chromate layer. If it is less than 4/1, the electrolytic peeling efficiency may be insufficient, leading to a decrease in productivity. From the viewpoint of maintaining the pH of the electrolytic solution in the neutral region as described above, it is desirable to mix these acid ions in the form of a soluble neutral compound such as a sodium salt or a potassium salt.

Next, the organic acid ion can function as a polarization improver for maintaining the concentration polarization, and contributes to the uniform dissolution of the zinc-based plating layer and the smoothing of the underlying exposed layer. As the organic acid ion, for example, a carboxylic acid ion such as acetic acid, oxalic acid, malonic acid, citric acid, gluconic acid, tartaric acid and the like can be used. These acid ions are also desirably formulated in the form of a soluble neutral compound such as a sodium salt or a potassium salt.

Using the above electrolytic solution L3, for example,
By performing electrolysis under the condition that the current density per unit is about 0.4 to 0.7 A, the zinc chromate layer can be efficiently separated. If the current density is less than 0.4 A / piece, it takes too much time to peel off the zinc chromate layer, and problems such as layer residual easily occur. On the other hand, when the current density exceeds 0.7 A / piece, surface roughness of the exposed portion of the underlying metal is likely to occur. In addition, when the thickness of the zinc plating layer 141 and the chromate layer 142 is about the above-mentioned level, the energization time is preferably about 100 to 180 seconds. The temperature of the electrolytic solution is preferably set to 20 to 40 ° C. from the viewpoint of sufficiently securing the current density while suppressing excessive evaporation of the electrolytic solution.

The height from the opening end face of the threaded portion 7 of the metal shell 1 to the liquid surface SH is preferably adjusted to be, for example, 1 mm or more. When the height is less than 1 mm, the electrolytic solution L3 comes into contact with the end face of the metal shell 1 due to slight fluctuation of the liquid level, and the zinc plating layer 141 is easily peeled to an undesired portion on the metal shell 1 side. However, it is not desirable in terms of ensuring corrosion resistance.

In the above-described electrolytic stripping process, by adjusting the electrolytic potential, the base metal material layer 140 hardly dissolves, and an ideal process in which the zinc plating layer 141 is sufficiently stripped can be performed. As a result, the weldability of the high melting point metal tip to the exposed base surface is further enhanced. Then, during the energization time of the electrolytic stripping, the zinc plating layer 142 was almost completely stripped in the region of the ground electrode 4 where the electrolytic stripping was to be performed, and the etching thickness of the base electrode material layer 140 was 1.0 μm.
It is adjusted to be less than m. Then, by adjusting the current density so as to suppress excessive etching of the base metal material layer 140, the crystal grain boundary of the base electrode material layer is formed on the base exposed surface 140a as shown in FIG. Along the GB, a groove-shaped pattern EG having a depth greater than the average roughness level of the crystal grain surface is formed. When the base exposed surface 140a is in such a state, the ignition portion 32
The welding strength of FIG. 2 is increased. When the electrolytic stripping process is completed, the metal shell 1 is washed and dried, and is sent to a welding process for forming a spark part.

In the case where a zinc chromate layer is formed on the gasket 30, the metal shell 1 may be used in the above process.
By replacing the gasket (or the assembly W), the same method can be applied except that the electrolytic stripping process is not performed.

Returning to FIG. 2, an example of a method for forming the firing portions 31 and 32 will be described. The formation of these firing parts 31, 32
The assembly is completed before the insulator 2 or the center electrode 3 is attached to the metal shell 1. First, regarding the high melting point metal firing portion 31 on the center electrode side, after a tip (for example, a disk-shaped one) made of the high melting point metal constituting the firing portion 31 is positioned on the tip end surface of the center electrode 3, an annular welding bead is formed. By forming 10, the tip is joined to the center electrode 3 to form a firing portion 31.

On the other hand, the Pt-based metal firing portion 3 on the ground electrode 4 side
2 is formed as follows. First, as shown in FIG. 7, a similar positioning recess 4a is formed on the side surface of the ground electrode 4 at a position corresponding to the firing portion 31 on the center electrode 3 side. Then, for example, a Pt-based metal rod is cut into a circle by electric discharge machining or the like, or a disk-shaped Pt-based metal chip (hereinafter, also simply referred to as a chip) 32 ′ formed by punching a Pt-based metal plate is positioned in the positioning recess 4 b. To fit. Subsequently, the ground electrode 4 and the tip material 32 ′ are sandwiched between the current-carrying electrodes 150, 150, and a current is supplied from a welding power source (not shown) to form a layered diffusion layer (welded portion) 32 a.

When the ignition portion 32 is formed on the side surface of the ground electrode 4, the tip 32 'may be joined by laser welding. However, the tip 32' is positioned on the electrode 4 extending in the lateral direction. Since the laser beam generator and the electrode 4 need to be relatively rotated in the circumferential direction of the chip 32 ', it is somewhat troublesome. However, if a Pt-based metal is used as the material of the ignition portion, the melting point is lower than that of Ir or the like, so that a sufficient joining strength can be achieved even when a simple welding method such as resistance welding is used.

In a general spark plug used with a negative polarity on the side of the center electrode 3, the ignition portion formed at the tip of the center electrode 3 easily rises in temperature by 31 and positive ions derived from spark discharge However, since the ignition portion 32 on the ground electrode 4 side has a smaller temperature rise and is less susceptible to the attack of positive ions, the ignition portion 32 on the side of the center electrode 3 is as small as the ignition portion 31 on the center electrode 3 side. Wear is difficult to progress. Therefore, the ignition part 32 on the ground electrode 4 side is P
Even a t-based metal has a sufficient level of wear resistance, and even if resistance welding is employed, problems such as peeling hardly occur. further,
Pt-based metals have good workability and are easy to manufacture metal members for forming ignition parts.

The ignition portion 32 thus formed
Since the exposed surface 140a on the base metal material side formed by peeling of the zinc plating 141 layer is activated by electrolytic peeling, mutual diffusion between the chip 32 'and the base metal material layer 140 during resistance welding is reduced. Easy to progress. As a result, it becomes possible to increase the average thickness of the diffusion layer 32a formed corresponding to the joint interface between the ignition portion 32 and the ground electrode 4, and more specifically, to secure the average thickness of 10 μm or more. The joining strength of the portion 32 can be greatly increased.

The thickness of the diffusion layer 32a is defined as follows. First, as shown in FIG.
A cross section orthogonal to the ignition surface 32a is taken for the joint between the metal and the base metal material layer 140, and the ignition surface 32
An analysis line is set in a direction orthogonal to b. Then, along with the analysis line, electron beam microanalysis (Electron Probe
A line analysis profile of a characteristic X-ray intensity distribution of Pt as a main component of the ignition portion 32 and a main component of the base metal material layer 140, here, Ni, is measured by Micro Analysis (EPMA). In the obtained line analysis profile, it is desirable that a minute intensity fluctuation component having a wavelength of less than 1 μm is removed by filtering in order to remove noise.

Next, as shown in FIG. 8, the average intensity of the Pt characteristic X-ray in the ignition portion 32 is IPt1 and the intensity of the Ni characteristic X-ray is INi2, while the base metal material layer 140
The average intensity of the Ni characteristic X-rays is denoted by Ni1, and the intensity of the Pt characteristic X-rays is denoted by IPt2. Next, each line analysis profile of Pt and Ni obtained along the analysis line is plotted on a coordinate plane represented by the characteristic X-ray intensity I on the vertical axis and the distance x measured on the horizontal axis along the analysis line. Expressed by Ni
Line analysis profile PFNi and I = INi1-0.01
The x coordinate of the intersection with the straight line representing (INi1-INi2) is x1,
Similarly, the Pt line analysis profile PFPt and I = IPt2 +
The x coordinate of the intersection with the straight line representing 0.01 (IPt-IPt2) is defined as x2 and (x1 + x2) / 2 = xm1.
Similarly, a Pt line analysis profile PFPt and I
= X Pt1 of the intersection with the straight line representing IPt1-0.01 (IPt-IPt2), Ni line analysis profile PFNi and I
= XNi2 + 0.01 (x3 + x3) / 2 = xm2 where x is the x coordinate of the intersection with the straight line representing (INi2−INi2). Then, the thickness t of the diffusion layer is t≡ | xm1-x
m2 |. When the measured value of t fluctuates depending on the set position of the analysis line, it is desirable to perform measurement at a plurality of points while changing the position of the analysis line, and obtain the average value thereof.

When the formation of the ignition parts 31 and 32 is completed,
If the insulator 2 and the center electrode 3 are assembled to the metal shell 1, and the ground electrode 4 is bent so that the ignition portion 31 and the ignition portion 32 face each other in the positional relationship shown in FIG. The spark plug 100 shown in FIG. 1 is completed.

The electrolytic peeling treatment may be performed after the galvanizing treatment shown in FIG. In this case, the chromate treatment is performed after the galvanized layer 141 is peeled off by the electrolytic peeling treatment. In this case, in FIG. 4, the entire surface of the assembly W, including the tip-side surface of the ground electrode 4 from which the galvanized layer 141 has been peeled off, is immersed in the chromate treatment liquid. The chromate layer 142 is formed only on the surface of the zinc plating layer 141 where the substitution reaction with zinc can proceed, and the formation of the chromate layer hardly proceeds on the exposed surface 140a of the underlying metal material. As a result, as shown in FIG. 9, in the galvanized layer 141, the formation of the chromate layer also proceeds on the end face thereof, and finally the zinc plated layer 141 is covered with the chromate layer 142 including the end face, and the exposed portion is formed. It hardly occurs. Thus, the progress of corrosion of the galvanized layer 141 when the spark plug is used is more effectively suppressed.

[0063]

EXPERIMENTAL EXAMPLES The following experiments were conducted to confirm the effects of the present invention. First, as the material of the ground electrode 4, INCONEL
600 wires (1.5 mm × 2.8 mm square cross section) were prepared and cut to a length of 14 mm. On the other hand, JISG353
Using the carbon steel wire for cold heading SWCH8A specified in No. 9 as a raw material, the metal shell 1 having the shape shown in FIG. 1 was manufactured by cold forging. The nominal diameter of the threaded portion 7 of the metal shell 1 was 14 mm, and the axial length was about 19 mm. Next, the above-mentioned wire of INCONEL 600 was joined thereto by resistance welding to produce an assembly W shown in FIG. Then, as an example product, the assembly W was subjected to electrolytic zinc plating using a known alkaline cyanide bath by the barrel plating apparatus of FIG. 3 to form a zinc plating layer having a thickness of about 6 μm.

Next, after cleaning the assembly W, the assembly shown in FIG.
The chromate treatment was performed using the device. However,
The bath is treated with chlorine chloride per liter of deionized water.
Rom (III) (CrCl₃・ 6H₂O) 50 g, nitric acid
Baltic (II) (Co (NO₃) ₂3 g), sodium nitrate
(NaNO₃) Of 100 g, malonic acid 31.2 g
The bath is built up by dissolving together, and the liquid temperature 6
While maintaining the temperature at 0 ° C, the pH of the bath was adjusted to a sodium hydroxide aqueous solution.
And adjusted to 2.0. Chromate treatment solution
Immersion time is 60 seconds, and after washing and drying,
Dried by wind. The thickness of the formed chromate layer is S
It was about 0.30 μm as measured by EM.

Next, 200 g of ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) was added to 1 L of deionized water.
A bath was prepared by mixing 10 g of ammonium nitrate (NH ₄ NO ₃ ) at a ratio of 20 g of citric acid, and an electrolytic solution adjusted to pH 7.0 with aqueous ammonia was prepared. Then, the zinc chromate layer was peeled off from the ground electrode 4 by the method shown in FIG. However, the height from the opening end face of the screw portion 7 of the metal shell 1 to the liquid level SH is 1.5 m.
m. The electrolytic stripping was performed under a constant voltage of 8 V for about 120 seconds. The current density per assembly during electrolytic stripping of the zinc chromate layer was 0.1%.
It was maintained at 4-0.7A. On the other hand, for comparison, after forming the galvanized layer 141, a mixture of hydrochloric acid, nitric acid and water in a ratio of 1: 0.5: 2 was used as an acid stripping solution.
The zinc plating layer 141 is electrolessly peeled off by immersing the tip of the ground electrode 4 in this for 120 seconds.
Was also subjected to chromate treatment using the same chromate treatment bath as described above to prepare a test sample.

FIG. 10 is an SEM photograph (magnification: 800 times) of the ground electrode 4 after processing on the exposed surface of the underlayer.
Is an example product, and (b) is a comparative product. In the example product,
It can be seen that a groove-like etching pattern having a depth greater than the average roughness level of the crystal grain surface is formed along the crystal grain boundary. On the other hand, in the comparative example product, no etching pattern along the crystal grain boundary is particularly observed.

Next, the tip (exposed surface) of the ground electrode 4
To Pt chip ((diameter 1.5mm, thickness 0.2mm)
Are joined by resistance welding shown in FIG.
2 was formed. However, welding conditions are as follows:
The pressing load between 150 was 40 kgf, and the secondary current was 1 kA. The assembly in which the ignition portion 32 was formed was evaluated as follows. First, the vertical section of the ground electrode 4 is represented by S
When the etching thickness of the underlying electrode material layer at the peeled portion was measured by EM observation, it was almost 0 in the example product, but the etching proceeded by about 10 μm in the comparative example product.

The corrosion resistance was measured according to JIS H850.
2 in the corrosion resistance test method for plating specified in 2.
Neutral salt spray test method "for up to 48 hours. When the white rust resulting from the corrosion of the galvanized layer was evaluated based on what percentage of the total area of the zinc chromate layer appeared, the example product showed little white rust, while the comparative example product showed little white rust. The occurrence of white rust was observed at an area ratio of about 10%.

Next, regarding the weldability, a cycle of heating the ground electrode 4 with a burner for 2 minutes so that the maximum temperature reached 900 ° C., and then allowing it to cool at room temperature for 1 minute was repeated 1000 times. The condition was evaluated by visual observation with an optical microscope. As a result, cracks were observed at the joints in the comparative example product and signs of chip peeling were observed, but there was no particular abnormality in the example product.

[Brief description of the drawings]

FIG. 1 is a longitudinal half sectional view showing a spark plug according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a main part of FIG. 1;

FIG. 3 is an explanatory view of a process of electrolytic zinc plating by barrel plating.

FIG. 4 is an explanatory view of a process of chromate treatment by a barrel method.

FIG. 5 is an explanatory view of an electrolytic peeling step.

FIG. 6 is a diagram supposing and illustrating a peeling process of a zinc chromate layer by electrolytic peeling.

FIG. 7 is a process explanatory view showing a method for forming a firing portion on a ground electrode by resistance welding.

FIG. 8 is a diagram showing the definition of the thickness of a diffusion layer.

FIG. 9 is a longitudinal half sectional view showing a modified example of the spark plug of FIG. 1;

FIG. 10 is an SEM photograph showing a state of a base exposed surface of an example product and a comparative example product in an experimental example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Ground electrode 30 Gasket 41,45 Galvanized layer 42,46 Chromate layer 100 Spark plug

Claims (12)

[Claims] A spark discharge gap is formed between a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the center electrode. A ground electrode disposed opposite to the ground electrode, a refractory metal firing portion having a discharge surface by welding a refractory metal tip to at least the ground electrode side at a position corresponding to the spark discharge gap. A method of manufacturing a formed spark plug, comprising: preparing a metal assembly in which a base end of the ground electrode is attached to one opening of the cylindrical metal shell; and a metal shell and a ground electrode of the metal assembly. A zinc-based plating layer forming step of collectively forming a zinc-based plating layer containing zinc as a main component on the outer surface of the metal shell; An electrolytic stripping step of removing, by electrolytic stripping, at least one of the zinc-based plating layers of the ground electrode, which is formed at the tip of the electrode, while removing the plating layer; and exposing by stripping after the electrolytic stripping step is completed. A welding step of welding the refractory metal tip to the base electrode material surface thus formed. 2. The method according to claim 1, further comprising: forming a chromate layer that covers a surface of the zinc-based plating layer. In the electrolytic stripping step, a zinc chromate layer including the zinc-based plating layer and a chromate layer that covers the zinc-based plating layer is formed. The method for manufacturing a spark plug according to claim 1, wherein the spark plug is removed at a time. 3. The method for producing a spark plug according to claim 2, wherein the pH of the electrolytic solution used for the electrolytic stripping is adjusted within a range of 6 to 8. 4. The zinc-based plating layer is almost entirely stripped in the region of the ground electrode where the electrolytic stripping is to be performed, and the etching thickness of a base electrode material layer that forms the base of the stripped zinc-based plating layer is reduced. The method for manufacturing a spark plug according to claim 2, wherein the energization time of the electrolytic peeling is adjusted so as to be less than 1.0 μm. 5. A method in which the ground electrode is immersed in the electrolyte so as to be energized so that the base end is exposed above the liquid surface by a predetermined length and the remaining tip is located in the electrolyte. ,
The method for manufacturing a spark plug according to any one of claims 1 to 4, wherein the zinc-based plating layer is subjected to electrolytic peeling only in the immersed portion. 6. The spark plug, wherein the ground electrode is bent laterally, and the spark discharge gap is formed between the bent end of the ground electrode and the end of the center electrode. And a metal assembly in which a ground electrode before bending is attached so as to extend linearly in the axial direction of the metal shell, and the metal assembly is attached to the ground electrode. 6. The method for manufacturing a spark plug according to claim 5, wherein the end of the ground electrode is immersed in the electrolytic solution while the side of the ground electrode is held downward. 7. The spark plug, wherein a refractory metal ignition portion having a discharge surface is formed by welding a refractory metal tip to at least the ground electrode at a position corresponding to the spark discharge gap, After electrolytically peeling off the zinc-based plating layer of the ground electrode,
The method for manufacturing a spark plug according to any one of claims 1 to 6, wherein the refractory metal tip is welded to a surface of the base electrode material exposed by the peeling. 8. The method for producing a spark plug according to claim 1, wherein the electrolytic solution contains at least one of a sulfate ion and a nitrate ion and an organic acid ion as main components of an acid anion. 9. The electrolyte contains both sulfate ions and nitrate ions, and has a sulfate ion molar concentration CSO.
₄ and method of manufacturing a spark plug according to claim 8, wherein the use of what ratio CSO ₄ / CNO ₃ the molar concentration CNO ₃ of nitrate ions is adjusted within a range of 4 / 1-40 / 1. 10. A base electrode material layer of the ground electrode, which underlies the zinc-based plating layer, is made of a Ni-based heat-resistant alloy or Fe.
The method for producing a spark plug according to any one of claims 1 to 9, wherein the spark plug is made of a base heat-resistant alloy. 11. A spark discharge gap is formed between a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the center electrode. A ground electrode disposed opposite to the base metal, wherein an outer surface of the metal shell and a base end outer surface of the ground electrode joined to the metal shell are zinc-based plating mainly composed of zinc. And a zinc chromate layer including a chromate layer covering the surface of the zinc-based plating layer,
At the tip of the ground electrode, a base exposed surface is formed, which forms a base for the zinc chromate layer and exposes a base electrode material layer made of a Ni-base heat-resistant alloy. By welding the refractory metal tip at the position corresponding to the gap, a refractory metal ignition portion having a discharge surface is formed, and “5. Neutral salt spray test” in the corrosion resistance test method for plating specified in JIS 8502. Method, the durability time required for white rust resulting from corrosion of the zinc-based plating layer of the zinc chromate layer covering the metal shell to appear by 10% or more of the entire surface of the zinc chromate layer is 4 hours.
A spark plug characterized by being at least 8 hours. 12. A spark discharge gap is formed between a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the center electrode. A ground electrode disposed opposite to the base metal, wherein an outer surface of the metal shell and a base end outer surface of the ground electrode joined to the metal shell are zinc-based plating mainly composed of zinc. And a zinc chromate layer including a chromate layer covering the surface of the zinc-based plating layer,
At the tip of the ground electrode, a base exposed surface is formed, which forms a base for the zinc chromate layer and exposes a base electrode material layer made of a Ni-base heat-resistant alloy. Along the crystal grain boundary of the electrode material layer, a groove-like pattern having a depth greater than the average roughness level of the crystal grain surface is formed, and the refractory metal is formed at a position corresponding to the spark discharge gap. A spark plug, wherein a high melting point metal ignition portion having a discharge surface is formed by welding a tip.