JP4373993B2 - Spark plug - Google Patents

Description

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

A spark plug used for ignition of an internal combustion engine, for example, a gasoline engine for automobiles, is provided with an insulator on the outside of the center electrode and a metal shell on the outside thereof.
A ground electrode that forms a spark discharge gap with the center electrode is attached to the metal shell. And it attaches and uses to the cylinder head of an engine with the attaching screw part formed in the outer peripheral surface of a metal shell. By the way, the metal shell is generally made of an iron-based material such as carbon steel, and its surface is often galvanized for corrosion protection. Further, in order to enhance the anticorrosion performance, the surface of the galvanized layer is further subjected to chromate treatment.

  By the way, in order to galvanize the metal shell as described above, it is effective to improve the productivity to use a so-called barrel plating process. However, it is necessary to attach the ground electrode to the metal shell by resistance welding or the like as described above. However, if the attachment is performed after barrel plating, poor welding is likely to occur due to the interposition of the zinc-based plating layer (or chromate layer). Moreover, since the zinc-based plating layer is damaged at the welded portion, there is a problem that the corrosion resistance is lowered. Therefore, in general, a ground electrode is attached to the metal shell before plating, and thereafter, the metal shell in which the ground electrode is integrated is subjected to galvanization by barrel plating or subsequent chromate treatment. Yes.

  However, in the above 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. For example, an insulating chromate layer is formed on the surface where the spark gap is to be formed. And there is a drawback that the discharge performance is adversely affected. In recent years, in order to improve the spark wear resistance, a spark is formed by welding a tip mainly composed of a refractory metal such as Pt or Ir at a position corresponding to the spark gap between the center electrode and the ground electrode. Plugs are also popular. However, when such a refractory metal tip is welded to the ground electrode side, if a galvanized layer or a chromate layer as described above is formed, it causes welding failure and leads to defects such as chip peeling.

  Therefore, an electrode base surface is exposed without forming a galvanized layer on the tip side surface of the ground electrode to which the noble metal tip is welded, and a refractory metal tip is welded thereto. As a method of exposing the electrode base surface, conventionally, 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 formation of a galvanized layer on the tip is adopted. However, this method has a drawback that it is troublesome to attach a rubber tube or the like and is difficult to automate, and has a very poor efficiency. In addition, the tip portion of the ground electrode not involved in the plating process is likely to be attached with oil or dirt when handling such as attaching a rubber tube. If the refractory metal tip is welded in such a state, the bonding strength is likely to be impaired, and a defect such as tip peeling may occur.

An object of the present invention, in a form integrated with the metal shell and the ground electrode, on the basis of the spark plug manufacturing method capable of efficiently forming a galvanized layer on a portion other than the ground electrode tip, whereby a spark plug obtained, hardly the bonding strength is impaired when welding the refractory metal tip, to provide a hard spark plug to cause trouble such as peeling of the firing portion formed by turn-chip bonding is there.

Means for Solving the Problems and Effects of the Invention

A spark plug manufacturing method as an example for solving the above problems includes a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, a center electrode, And a ground electrode disposed opposite to the spark discharge gap so as to form a spark discharge gap therebetween, and discharging by welding a refractory metal tip to at least the ground electrode side at a position corresponding to the spark discharge gap. In the method of manufacturing a spark plug having a noble metal ignition part having a surface,
Prepare a bracket assembly in which the base electrode side of the ground electrode is attached to one opening of the cylindrical metal shell, and collect zinc on the outer surface of the metal shell and ground electrode of the bracket assembly as a main component. Forming a zinc-based plating layer to form a zinc-based plating layer;
While removing the zinc-based plating layer on the outer surface of the metal shell, the zinc-based plating layer of the ground electrode is peeled off at least at the tip of the electrode while the zinc-based plating layer is formed. A stripping step to be removed;
A method including a welding step of welding a refractory metal tip to the surface of the base electrode material exposed by peeling after the peeling step is completed.

  Note that in this specification, “main component” (also synonymous with “main” or “mainly”) means a component having the highest content in the material of interest.

  According to the above method, the zinc-based plating layer is collectively formed on the outer surface of the metal fitting assembly in which the base electrode side of the ground electrode is attached to the metal shell, and then the zinc-based plating layer formed on the electrode tip side. Is peeled and removed, and a refractory metal tip is welded to the surface of the base electrode material exposed by the peeling to form an ignition part. In other words, unlike the conventional case, masking with a rubber tube or the like for avoiding the formation of a plating layer at the tip of the ground electrode is not required, so a spark plug of the type that forms a refractory metal ignition part on the ground electrode is extremely efficient. Can be manufactured. In addition, after peeling of the zinc-based plating layer, adhesion of dirt, oil, and the like is less likely to occur due to the absence of the masking treatment, and the surface layer portion of the base electrode material is appropriately removed by the peeling treatment, and further purification proceeds. The effect can also be expected. As a result, the welding strength of the refractory metal tip is increased, and problems such as ignition part peeling are less likely to occur.

  As the stripping process, physical removal methods such as ion etching and shot blasting are possible, but the zinc-based plating layer is chemically stripped by immersing the ground electrode on which the zinc-based plating layer is formed in a stripping solution. If the removal method is employed, the efficiency can be further increased. In addition, due to the etching effect of the stripping solution, the surface of the base electrode material can be further easily cleaned.

  As such a chemical peeling removal method, specifically, a method of electrolessly peeling the zinc-based plating layer by immersing the ground electrode on which the zinc-based plating layer is formed in an acidic peeling solution is exemplified. it can. As such an acidic stripping solution, one containing at least one of nitric acid, hydrochloric acid, sulfuric acid and organic acid is excellent in the stripping / removing effect of the zinc-based plating layer, and can be used effectively in the present invention. . In particular, an acid solution in which nitric acid and hydrochloric acid are mixed is not only excellent in the peeling effect of the zinc-based plating layer, but also is a base electrode made of a Ni-based metal material (for example, a Ni alloy such as a Ni-based heat-resistant alloy) or an Fe-based heat-resistant alloy. When the material is configured, it is difficult to damage the ground, and discoloration is unlikely to occur. Further, the weldability of the surface of the base metal material after the treatment to the refractory metal tip is also good.

  As a method of peeling only the zinc-based plating layer on the tip side of the ground electrode, peel off the ground electrode so that the base end is exposed above the liquid surface by a predetermined length and the remaining tip is located in the stripping solution. It is reasonable to immerse in the liquid and peel off the zinc-based plating layer only at the immersed part. According to this, the zinc-based plating layer can be peeled over the desired length on the tip side only by adjusting the immersion depth of the ground electrode in the stripping solution.

  For example, when the spark plug is of a type in which the ground electrode is bent sideways and a spark discharge gap is formed between the bent ground electrode tip and the center electrode tip. Specifically, the following method is effective. That is, a metal fitting assembly in which the ground electrode before bending is attached so as to extend linearly in the axial direction of the main metal fitting is used, and the metal fitting assembly is directed downward on the side on which the earth electrode is attached. And the tip of the ground electrode is immersed in a stripping solution. According to this method, if the liquid level of the stripping solution is kept constant, the holding position in the height direction of the metal shell is fixed by a jig or the like, and the zinc-based plating layer always having a constant length. There is an advantage that the peeling region can be easily formed.

  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 weld surface (exposed surface) on the base metal material side formed by peeling of the zinc-based plating layer is activated by acid stripping, interdiffusion between the tip and the base metal material occurs during resistance welding. It becomes easy to progress, and the welding strength of the obtained ignition part is greatly increased. Such an effect is particularly remarkable when the base metal material is made of a Ni-based metal (for example, a Ni alloy such as a Ni-based heat-resistant alloy) or a Fe-based heat-resistant alloy.

For example, in the case where the ground electrode material layer of the ground electrode is made of Ni-based metal mainly composed of Ni or Fe-based metal mainly composed of Fe, the structure of the spark plug obtained by the above manufacturing method is as follows :
In a form facing the center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a spark discharge gap between the center electrode and the center electrode. A ground electrode arranged,
Zinc including an outer surface of the metallic shell and an outer surface of the base end portion of the ground electrode joined to the metallic shell, including a zinc-based plating layer mainly composed of zinc and a chromate layer covering the surface of the zinc-based plating layer The exposed portion of the base electrode material layer is formed of Ni-based metal mainly composed of Ni or Fe-based metal mainly composed of Fe at the tip portion of the ground electrode while being covered with the chromate layer,
And, the noble metal ignition part is formed by welding a Pt-based metal tip mainly composed of Pt on the ground electrode side at a position corresponding to the spark discharge gap of the exposed part of the base electrode material layer,
In addition, the average thickness of the diffusion layer formed corresponding to the bonding interface between the noble metal firing portion and the ground electrode can be 10 μm or more.

  That is, since the interdiffusion between the chip and the underlying metal material is facilitated, the average thickness of the diffusion layer formed corresponding to the bonding interface between the noble metal firing portion and the ground electrode is secured to 10 μm or more. As a result, the joining strength of the ignition part is significantly increased. As a result, problems such as chip peeling are less likely to occur even during high-load operation.

By the way , in order to further improve the corrosion resistance of the metal shell , it is effective to perform a chromate treatment step of forming a chromate layer on the zinc-based plating layer. Then, the method may be embodied regardless of whether to form a spark portion made of a refractory metal ground electrode, arrangement of the spark plug of the present invention corresponding to this,
A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a spark discharge gap are formed between the center electrode and the center electrode. A ground electrode arranged in a shape,
A zinc-based plating layer containing zinc as a main component, and a chromate layer covering a surface of the zinc-based plating layer, the outer surface of the metal shell and the outer surface of the base end portion of the ground electrode joined to the metal shell And an exposed portion of the base electrode material layer on which the zinc-based plating layer is not formed is formed on the tip end side in the axial direction of the ground electrode.
In the zinc chromate layer, the chromate layer is formed so as to cover an end surface in the axial direction of the ground electrode of the zinc-based plating layer.
And as a manufacturing method for this spark plug,
A grounding disposed opposite to the center electrode so as to form a spark discharge gap between the insulator provided outside the center electrode, the metal shell provided outside the insulator, and the center electrode. In a method for producing a spark plug comprising an electrode,
Prepare a metal fitting assembly in which the base electrode side of the ground electrode is attached to one opening of the cylindrical metal shell, and one zinc is the main component of the metal shell of the metal fitting assembly and the outer surface of the base electrode base portion. Forming a zinc-based plating layer, and without forming a zinc-based plating layer on the remaining portion excluding the base end portion of the ground electrode, with the underlying electrode material surface exposed,
It can be carried out by immersing the entire outer surface including the base electrode material surface of the metal fitting assembly on which the zinc-based plating layer is formed in a chromate treatment solution and subjecting the zinc-based plating layer to chromate treatment.

  In this case, it is desirable to perform the chromate treatment step after the peeling step. For example, when chemical detachment is performed by immersion in a stripping solution, if the detachment process is performed after completion of the chromate treatment process, the formed chromate layer becomes a protective film, making it difficult to separate the zinc plating layer. It may become. When peeling is performed after the chromate layer is formed, as shown in FIG. 6 (d), the boundary position between the exposed surface (140a) of the base metal material and the remaining layers (141, 142) is In some cases, the end surface of the zinc-based plating layer 141 is exposed, and corrosion of the zinc-based plating layer is likely to proceed. However, if the chromate treatment is performed after the zinc-based plating layer 141 is peeled off, it can be covered with the chromate layer (142) including the end surface of the zinc-based plating layer (141) as shown in FIG. Corrosion resistance can be further increased.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to examples 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 cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip 21 protrudes, and a refractory metal ignition part 31 formed at the tip. In the state, one end of the center electrode 3 provided inside the insulator 2 and the metal shell 1 is coupled by welding or the like, and the other end is bent back to the side. A ground electrode 4 and the like arranged to face each other are provided. The ground electrode 4 is formed with a Pt-based metal ignition part (also considered as one of the refractory metal ignition parts) 32 facing the refractory metal ignition part 31, and these refractory metal ignition parts 31. And the Pt-based metal ignition part 32 is a spark discharge gap g.

  The “ignition part” as used in the present specification is a part of the bonded member that is not affected by the composition variation due to welding (for example, alloyed with the material of the ground electrode or the center electrode by welding). The remaining part excluding the part).

  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. A terminal fitting 13 is inserted and fixed on one end side of the through hole 6, and the center electrode 3 is inserted and fixed on the other end side. A resistor 15 is disposed 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 through the conductive glass seal layers 16 and 17, respectively.

  The metal shell 1 is formed in a cylindrical shape from a metal such as carbon steel, and constitutes a housing of the spark plug 100. On the outer peripheral surface thereof, there is a screw portion 7 for attaching the plug 100 to an engine block (not shown). Is formed. In addition, 1e is a tool engaging part which engages tools, such as a spanner and a wrench, when attaching the metal shell 1, and has a hexagonal axial cross-sectional shape. On the other hand, a ring-shaped wire packing 62 that engages with the rear peripheral edge of the flange-shaped protrusion 2e is disposed between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, and further 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 crimping portion 1d is formed by crimping the opening edge of the metal shell 1 toward the packing 60 inward. It is fixed with respect to the insulator 2.

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

  Next, a zinc plating layer 41 (zinc-based plating layer) for corrosion prevention is formed on the entire outer surface of the base layer (for example, carbon steel) 40 of the metal shell 1, and the outer side thereof is covered with a chromate layer 42, and zinc A chromate layer is formed. Similarly, a zinc chromate layer comprising a galvanized layer 45 and a chromate layer 46 is also formed on the outer surface of the gasket 30. As shown in FIG. 1, the galvanized layer 41 and the chromate layer 42 on the metal shell 1 side cover up to the base end portion of the ground electrode 4, and the remaining distal end side of the ground electrode 4 The surface of the metal material 140 is exposed. The chromate layer 142 is formed so as to cover the end face in the axial direction of the ground electrode 4 of the galvanized layer 141.

  The galvanized layer and the chromate layer of the metal shell 1 and the gasket 30 are both formed by the same method, and will be described below representatively on the metal shell 1 side. The galvanized layer 41 is formed by a known electrolytic galvanizing method, and has a thickness of about 3 to 10 μm, for example. If this thickness is less than 3 μm, sufficient corrosion resistance may not be ensured. On the contrary, a film thickness exceeding 10 μm is excessive in terms of ensuring corrosion resistance, and the plating time is lengthened and the production efficiency is lowered, leading to an increase in cost.

  On the other hand, the chromate layer 42 may use a commonly used yellow chromate film. However, the yellow chromate film suffers from the fact that part of the chromium component is contained in the form of hexavalent chromium, thereby protecting the environment. In recent years, when the interest in is increasing globally, it has gradually been shunned. From this viewpoint, it is desirable to use a trivalent chromium-based chromate layer in which 95% by weight or more of the chromium component contained is trivalent chromium.

  When the chromate layer 42 is a trivalent chromium-based chromate film, for example, in the case of a conventional trivalent chromium-based chromate film such as a glossy chromate film commonly called UNIQLO or a blue chromate film layer, the film thickness is maximum. Since it is as thin as about 0.1 μm, sufficient corrosion resistance and heat resistance may not be ensured for the metal shell in the main use environment of the spark plug. Therefore, by securing the film thickness of the chromate layer 42 to 0.2 μm or more, the anticorrosion performance of the chromate film mainly composed of trivalent chromium can be greatly improved, and sufficient durability against corrosion can be imparted to the metal shell. become able to. In addition, the corrosion resistance of the metal shell 1 can be sufficiently maintained even in an environment unique to a spark plug that easily rises in temperature and is susceptible to acid attack. If the thickness of the chromate layer 42 is less than 0.2 μm, the anticorrosion performance and the heat resistance cannot be sufficiently secured. On the other hand, if the film thickness exceeds 0.5 μm, cracks are likely to occur in the layer (for example, during processing during assembly), or the layer may easily fall off, leading to a loss of corrosion protection performance. The thickness of the chromate layer 42 is desirably 0.3 to 0.5 μm. The chromate layer 42 is preferably substantially free of hexavalent chromium.

Next, the center electrode 3 and the ground electrode 4 are made of a heat-resistant alloy containing Ni or Fe as a main component as a metal material that forms the base of the zinc chromate layer. For example, the following can be used as the heat-resistant alloy mainly composed of Ni or Fe.
(1) Ni-base heat-resistant alloy: In the present specification, Ni is contained in an amount of 40 to 85% by weight, and the main component of the balance is one or more of Cr, Co, Mo, W, Nb, Al, Ti and Fe. The heat-resistant alloy consisting of 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); p138)). Do not do):
ASTROLOY, CABOT 214, D-979, HASTELLOY C22, HASTELLOY C276, HASTELLOY G30, HASTELLOY S, HASTELLOY X, HAYNES 230, INCONEL 587, INCONEL 597, INCONEL 600, INCONEL 601, INCONEL 617, INCONEL 706, INCONEL 706, INCONEL 706 , INCONEL X750, KSN, M-252, NIMONIC 75, NIMONIC 80A, NIMONIC 90, NIMONIC 105, NIMONIC 115, NIMONIC 263, NIMONIC 942, NIMONIC PE11, NIMONIC PE16, NIMONIC PK33, PYROMET 860, RENE 41, RENE 95, SSS 113MA, UDIMET 400, UDIMET 500, UDIMET 520, UDIMET 630, UDIMET 700, UDIMET 710, UDIMET 720, UNITEP AF2-1 DA6, WASPALOY.

(2) Fe-based heat-resistant alloy: In the present specification, Fe is contained in an amount of 20 to 60% by weight, and the balance is mainly one or more of Cr, Co, Mo, W, Nb, Al, Ti and Ni. The heat-resistant alloy consisting of 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), p138)). Do not do);
A-286, ALLOY 901, DISCALOY, HAYNES 556, INCOLOY 800, INCOLOY 801, INCOLOY 802, INCOLOY 807, INCOLOY 825, INCOLOY 903, INCOLOY 907, INCOLOY 909, N-155, PYROMET CTX-1, PYROMET CTX-3, S-590, V-57, PYROMET CTX-1, 16-25-6, 17-14CuMo, 19-9DL, 20-Cb3.

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

  Next, the refractory metal ignition part 31 on the side of the center electrode 3 (and thus the chip 31 ′ for forming the refractory metal ignition part 31) has a high melting point mainly composed of any one of Ir, Rh, Pt, W, Re, and Ru. It is mainly composed of a metal, for example, a refractory metal mainly composed of Ir. Use of these refractory metals can improve the wear resistance of the ignition part even in an environment where the temperature of the center electrode is likely to rise. Moreover, the weldability with respect to the above heat-resistant alloys is also favorable. On the other hand, the Pt-based metal ignition part 32 on the ground electrode side (and thus the chip 32 ′ for forming the Pt-based metal ignition part) is not only Pt but also Pt—Ni alloy (for example, Pt-1 to 30 wt% Ni alloy), Pt -Ir alloy, Pt-Ir-Ni alloy, etc. The Pt-based metal ignition part 32 is formed by bonding a Pt-based metal tip 32 ′ by resistance welding to an exposed surface (underlying metal material surface) of the underlying metal material layer 140 that is not covered with the zinc chromate layer.

  When the refractory metal ignition part 31 is mainly composed of Ir, since Ir has a property of being easily oxidized and volatilized in a high temperature region, if it is used as it is in the ignition part, it is caused by oxidation and volatilization rather than spark consumption. There is a drawback that wear is a problem. Therefore, the refractory metal ignition part 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 part can be improved.

A method for manufacturing the spark plug 100 will be described.
First, the zinc chromate layer is formed on the metal shell 1 as follows. To the metal shell 1, the base end side of the ground electrode 4 is attached by welding to the opening on the side of the mounting screw 7, thereby forming a metal fitting assembly W. At this stage, the ground electrode 4 is before bending 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 into a holding container 202 whose wall surface is configured to be liquid-permeable by a net, a perforated plate, or the like, and a galvanizing bath in the plating layer 200 is inserted. It is immersed in L1. A counter electrode 203 is disposed in the plating bath L1. If the DC power supply 204 is energized between the metal fitting assembly W and the counter electrode 203 via the energizing electrode 205 in the holding container 202 while rotating the holding container 202 around the horizontal rotation axis by the motor 201, 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 rotating barrel plating as described above.

  When galvanizing is performed as described above, the galvanized layer 141 is formed on the entire surface of the ground electrode 4, that is, the entire surface of the underlying metal material layer 140, as shown in FIG. As shown in FIG. 2, a noble metal tip, for example, a Pt-based metal tip 32 ′ is welded to the tip of the ground electrode 4 to form the ignition portion 32, but the galvanized layer 141 remains formed. The zinc melts into the welded portion, leading to a significant decrease in the joint strength of the ignition portion 32. Therefore, the galvanized layer 141 formed on the ground electrode 4 is peeled only at the tip side in the process shown in FIG.

  This apparatus has a stripping tank 210 in which a stripping solution, for example, an acidic stripping solution L3 containing hydrochloric acid and nitric acid is accommodated. The upper surface opening of the peeling tank 210 is closed by a holding plate 212 in which an assembly insertion port 212a is formed. Then, the screw portion 7 of the assembly W is inserted in the assembly insertion port 212a in the axial direction so that the ground electrode 4 faces down, and is supported by the inner edge portion of the assembly insertion port 212a in the gas seal portion 1f. The On the other hand, the peeling liquid L3 is supplied from a peeling liquid tank (not shown) from the peeling liquid supply port 214 of the peeling tank 210 by a pump 213. Then, the liquid level is detected by the liquid level sensor 211 provided in the tank, and when the liquid level is lowered, the control unit 212 operates the pump 213 with reference to the detection signal of the sensor 211, The height of the liquid surface SH of the stripping solution L3 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 fixed length on the base end side protruding above the liquid level SH, and the tip side is It is immersed in the stripping solution L3. Thereby, as shown in FIG.6 (b), the zinc plating layer 141 of an immersion part is melt | dissolved and peeled. At this time, the exposed surface 140a of the base metal material layer 140 is also activated by acid etching.

  For example, when an aqueous solution of nitric acid and hydrochloric acid is used as the stripping liquid L3, the blending amount of nitric acid is 10 to 30% by weight and the blending amount of hydrochloric acid is 20 to 30% by weight in order to produce the stripping effect without excess or deficiency. It is good to do. Further, the ratio WHCl / WHNO3 of the hydrochloric acid blending amount WHCl (wt%) and the nitric acid blending amount WHNO3 (wt%) should be about 0.5 to 4 to determine the finished state of the base metal material layer after peeling. Desirable for good.

  The height from the opening end face of the threaded portion 7 of the metal shell 1 to the liquid level SH is preferably adjusted to be 1 mm or more, for example. When the height is less than 1 mm, the peeling liquid L3 comes into contact with the end surface of the metal shell 1 with only slight liquid level fluctuation, and the galvanized layer 141 is peeled off to an undesired portion on the metal shell 1 side. Even if the stripping solution L1 does not come into contact, it is likely to be affected by the vapor containing the acid component, which is not desirable in terms of ensuring corrosion resistance.

  When peeling of the galvanized layer 141 is completed, this is once washed and dried, and chromate treatment is performed. In this embodiment, the chromate treatment tank 200 shown in FIG. 4 (the same reference numerals are assigned to the parts common to FIG. 3), and the chromate treatment liquid L2 is filled therein and the treatment is performed by the barrel method. Is going. However, the chromate treatment to be performed is of a non-electrolytic type, and no electrode or power source for energization is provided (in addition, the electrolytic chromate treatment can be performed. In this case, an apparatus similar to FIG. Adopt the configuration).

  As the chromate treatment liquid L3, a dense and thick trivalent chromium-based chromate layer, which is difficult to obtain by a general chromate treatment method, is obtained by using a mixture of a trivalent chromium salt and a complexing agent for trivalent chromium. Thus, a trivalent chromium-based chromate layer of 0.2 to 0.5 μm can be easily formed. Details of such a chromate treatment solution are disclosed in German Published Patent Publication DE19638176A1. Below, the outline is demonstrated.

  As described above, in the process of forming the chromate layer, oxidation elution of the base metal (for example, zinc) first occurs in the treatment bath, and the eluted base metal component reacts with the solution containing chromate ions to form trivalent. The theory is that chromium mainly forms a polymer complex by hydroxyl or oxygen bridges and precipitates and deposits on the surface of the underlying metal in a gel state. In this case, in order for the chromate layer to grow, the elution of the base metal and the reaction / deposition of the eluted base metal and chromate ions in the bath must proceed in parallel. However, if the chromate layer is deposited to some extent, the elution reaction of the base metal layer, which is a heterogeneous reaction through the interface with the bath solution, is hindered, and the growth of the layer is stagnated.

  According to the disclosure of the above-mentioned German published patent publication, in order to increase the thickness of the layer, the rate of dissolution of the base metal and layer precipitation due to the reaction between the dissolved base metal component and trivalent chromium is increased. However, it is important to reduce the rate of reverse dissolution of the deposited chromate layer as much as possible. And in said method, it is thought that layer precipitation is accelerated | stimulated by adding a suitable complexing agent in a bath and complexing trivalent chromium, and a film thickness increase is attained.

  Complexing agents include various chelating agents (dicarboxylic acid, tricarboxylic acid, oxyacid (hydroxyl dicarboxylic acid or hydroxytricarboxylic acid etc .: for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, corkic acid Aceleic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, tartaric acid, citric acid, malic acid, ascorbic acid and the like are effective, but other complexing agents may be used. The complexing agent is as described in the German Patent Publication.

  In order to increase the layer thickness, it is also effective to raise the temperature of the chromate treatment bath to about 20 to 80 ° C. If the bath temperature is less than 20 ° C., the effect of increasing the layer thickness due to the temperature rise is hardly expected. If the bath temperature is 80 ° C. or more, the evaporation of water from the bath is intense, and thus it becomes difficult to control the bath conditions. Further, the immersion time of the object to be processed (metal shell, gasket, etc.) in the chromate bath is preferably 20 to 80 seconds. If the immersion time is less than 20 seconds, there may be a case where a sufficient film thickness of the chromate layer cannot be secured. On the other hand, if the immersion time exceeds 80 seconds, the formed chromate layer becomes too thick, and the layer is cracked (for example, during processing during assembly), or the layer is liable to fall off. May be damaged.

  On the other hand, in order to promote 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 precipitated layer does not become intense. A desirable pH range is, for example, about 1.5 to 3. Moreover, in order to suppress remelting of the layer formed by precipitation, it is effective to incorporate a hydroxide such as nickel, cobalt or copper which is difficult to remelt into the layer. For this purpose, the metal compound can be dissolved and blended in the chromate treatment bath.

  On the other hand, as a result of further studies by the present inventors, a predetermined amount of sodium salt (for example, sodium nitrate) is added to the chromate treatment bath so that the content of the sodium component in the chromate layer is 2 to 7% by weight. It has been found that it becomes easier to form a dense chromate layer in a thick film by blending it into the thick film. Although the detailed mechanism is unknown, it is presumed that when sodium ions are taken into the chromate layer, the dissolution of the chromate layer into the treatment bath is less likely to occur. If the content of the sodium component in the chromate layer is out of the range of 2 to 7% by weight, it may be difficult to ensure the 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 preferably 2 to 6% by weight.

  Note that when a zinc chromate layer is formed on the gasket 30, the same method is used except that the metal shell 1 (or assembly W) is replaced with a gasket in the above-described process, except that no peeling treatment is performed. Applicable.

  Now, in the above chromate treatment, as shown 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 is immersed in the chromate treatment solution. However, as shown in FIG. 6C, the chromate layer 142 is formed only on the surface of the galvanized layer 141 where the substitution reaction with zinc can proceed, and on the exposed surface 140a of the underlying metal material, The formation of the chromate layer hardly proceeds. On the other hand, in the galvanized layer 141, the formation of the chromate layer also proceeds at the end face, and finally the galvanized layer 141 is covered by the chromate layer 142 including the end face, and the exposed portion hardly occurs. Needless to say, this is advantageous in suppressing the progress of corrosion of the galvanized layer 141 when the spark plug is used.

  Next, returning to FIG. 2, an example of a method for forming the ignition portions 31 and 32 will be described. The formation of the ignition parts 31 and 32 is completed before the insulator 2 or the center electrode 3 is assembled to the metal shell 1. First, in the center electrode side refractory metal ignition part 31, after positioning a tip (for example, disk-shaped) made of a refractory metal constituting the ignition part 31 on the tip surface of the center electrode 3, an annular weld bead is placed. By forming 10, the chip is joined to the center electrode 3 to form the ignition part 31.

  On the other hand, the Pt-based metal ignition part 32 on the ground electrode 4 side is formed as follows. First, as shown in FIG. 7, the same positioning recess 4 a is formed on the side surface of the ground electrode 4 at a position corresponding to the ignition part 31 on the center electrode 3 side. Then, for example, the Pt-based metal rod is rounded 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 4b. Fit in. Subsequently, the ground electrode 4 and the tip material 32 ′ are sandwiched between the energizing electrodes 150, 150 and energized by a welding power source (not shown) to form a layered diffusion layer (welded portion) 32 a.

  When the ignition part 32 is formed on the side surface of the ground electrode 4, the tip 32 ′ may be joined by laser welding, but the laser beam is generated with the tip 32 ′ positioned on the laterally extending electrode 4. Since it is necessary to relatively rotate the part and the electrode 4 in the circumferential direction of the chip 32 ′, it is somewhat troublesome. However, if a Pt-based metal is used as the material for the ignition part, the melting point is lower than that of Ir or the like, so that sufficient bonding strength can be achieved even if a simple welding method such as resistance welding is employed.

  Moreover, in the general spark plug used with the polarity which makes the center electrode 3 side negative, the ignition part formed in the front-end | tip part of the center electrode 3 is easy to raise 31 temperature, and also the attack of the positive ion derived from a spark discharge The ignition part 32 on the ground electrode 4 side is less susceptible to positive ion attack than the ignition part 32 on the center electrode 3 side. Difficult to progress. Therefore, the ignition part 32 on the ground electrode 4 side has a sufficient wear resistance level even with a Pt-based metal, and even if resistance welding is employed, problems such as peeling hardly occur. Furthermore, the Pt-based metal has good workability, and it is easy to manufacture a metal member for forming the ignition part.

  Now, in the ignition part 32 formed in this way, the exposed surface 140a on the base metal material side formed by peeling of the galvanized 141 layer is activated by acid peeling, so that the chip 32 ′ and the base are exposed during resistance welding. Interdiffusion with the metal material layer 140 tends to proceed. As a result, the average thickness of the diffusion layer 32a formed corresponding to the bonding interface between the ignition part 32 and the ground electrode 4 can be increased, specifically, this can be ensured by 10 μm or more. The joint strength of the part 32 can be significantly increased.

  The thickness of the diffusion layer 32a is defined as follows. First, as shown in FIG. 7 (b), a cross section perpendicular to the ignition surface 32a is taken at the junction between the ignition portion 32 and the base metal material layer 140, and the cross section orthogonal to the ignition surface 32b is taken on the cross section. Set the analysis line in the direction. Then, by X-ray microanalysis (EPMA) along the analysis line, characteristic X-rays of Pt as the main component of the ignition portion 32 and the main component of the base metal material layer 140, here, Ni. Measure the line analysis profile of the intensity distribution. The obtained line analysis profile desirably removes a minute intensity fluctuation component having a wavelength of less than 1 μm by filtering in order to remove noise.

  Next, as shown in FIG. 8, the average Pt characteristic X-ray intensity in the ignition portion 32 is set to IPt1, and the Ni characteristic X-ray intensity is set to INi2, while the average Ni of the base metal material layer 140 is set to The intensity of the characteristic X-ray is INi1, and the intensity of the Pt characteristic X-ray is IPt2. Next, the Pt and Ni line analysis profiles obtained along the analysis line are plotted on the coordinate plane represented by the characteristic X-ray intensity I on the vertical axis and the distance x measured along the analysis line on the horizontal axis. Represented by The x-coordinate of the intersection of the Ni line analysis profile PFNi and the straight line representing I = INi1-0.01 (INi1-INi2) is x1, and the same Pt line analysis profile PFPt and I = IPt2 + 0.01 (IPt-IPt2) The x coordinate of the intersection with the straight line to be represented is defined as x2, and (x1 + x2) / 2 = xm1. Similarly, the x coordinate of the intersection of the Pt line analysis profile PFPt and the straight line representing I = IPt1−0.01 (IPt−IPt2) is x3, the Ni line analysis profile PFNi, and I = INi2 + 0.01 (INi1). -Xi2 is defined as (x3 + x3) / 2 = xm2, where the x coordinate of the intersection with the straight line representing -INi2) is x4. The thickness t of the diffusion layer is defined by t≡ | xm1−xm2 |. When the measurement value of t varies depending on the set position of the analysis line, it is desirable to measure a plurality of points while changing the position of the analysis line and obtain an average value thereof.

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

Experimental example

  Hereinafter, the following experiment was performed in order to confirm the effect of the present invention. First, an INCONEL 600 wire (1.5 mm × 2.8 mm square cross section) was prepared as a material for the ground electrode 4 and cut to a length of 14 mm. On the other hand, using the cold forging carbon steel wire SWCH8A defined in JIS G3539 as a 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 INCONEL 600 wire was joined to this by resistance welding to produce an assembly W shown in FIG. Then, the assembly W was subjected to electrolytic galvanization using a known alkali cyanide bath by the barrel plating apparatus of FIG. 3 to form a galvanized layer having a thickness of about 6 μm.

  Next, aqueous solutions containing nitric acid or hydrochloric acid with various compositions shown in Table 1 were prepared as stripping solutions, and the galvanized layer was stripped from the ground electrode 4 by the method shown in FIG. However, the height from the opening end surface of the threaded portion 7 of the metal shell 1 to the liquid level SH was 1 mm, and the immersion time was 120 seconds.

The assembly W from which the galvanized layer had been peeled was washed and chromated using the apparatus shown in FIG. However, the chromate treatment bath is 50 g of chromium (III) chloride (CrCl ₃ .6H ₂ O), 3 g of cobalt nitrate (II) (Co (NO ₃ ) ₂ ) and sodium nitrate per liter of deionized water. (NaNO ₃ ) was dissolved in a ratio of 100 g and malonic acid 31.2 g, and the bath was maintained at a liquid temperature of 60 ° C. with a heater, and the pH of the bath was adjusted to 2.0 by addition of an aqueous caustic soda solution. . The immersion time in the chromate treatment solution was 60 seconds, washed with water and dried, and then dried with warm air at 80 ° C. When the thickness of the formed chromate layer was measured by SEM, it was about 0.30 μm, and the end surface portion of the galvanized layer 141 was also covered with the chromate layer 142 as shown in FIG. It was confirmed. For comparison, a test product in which the galvanized layer was not peeled was also prepared (Table 1: Test product 2).

  Next, a Pt tip ((diameter: 1.5 mm, thickness: 0.2 mm)) was joined to the tip portion (exposed surface) of the ground electrode 4 by resistance welding shown in FIG. However, the welding conditions were such that the pressure load between the current-carrying electrodes 150 and 150 was 40 kgf and the secondary current was 1 kA For comparison, the assembly before the zinc chromate treatment was also applied to the ground electrode 4. The chip was welded (Table 1: Test sample 1).

  Thus, the assembly which formed the ignition part 32 was evaluated as follows. First, with regard to the appearance of the ground electrode 4 after the chromate treatment, in particular, the peeling boundary part of the galvanized layer was visually observed, △ when the large discoloration was observed, ◯ when the discoloration was hardly observed, and no discoloration at all What was not observed was evaluated as (double-circle).

  As for the corrosion resistance, the “5. Neutral salt spray test method” in the plating corrosion resistance test method defined in JISH8502 was performed for up to 48 hours. The evaluation was x when white rust derived from corrosion of the galvanized layer appeared about 10% or more of the total area of the zinc chromate layer. Although white rust was generated, the area ratio was less than 10%. The case where the occurrence of white rust was not recognized was rated as ◎.

  As for weldability, a cycle in which the ground electrode 4 was heated with a burner for 2 minutes so that the maximum temperature reached 900 ° C. and then allowed to cool at room temperature for 1 minute was repeated 1000 times, and the cross-sectional structure was observed with an optical microscope. By observing, the case where chip peeling occurred was evaluated as x, and the case where peeling was not particularly recognized was evaluated as ◎.

  As can be seen from these results, both the salt spray test and weldability of the galvanized layer that had been acid peeled and then chromated were excellent. In particular, those using a nitric acid / hydrochloric acid aqueous solution as the stripper have a good appearance. On the other hand, it can be seen that those that are not plated or chip-welded without performing plating peeling of the ground electrode 4 (test samples 1 and 2) have poor weldability.

  Note that the thickness of the diffusion layer 32a was measured for the test product 1 and the test product 6 by the method already described with reference to FIG. 8 (however, the electron probe spot diameter was 1 μm). The line analysis profile by EPMA is shown in FIG. (A) has shown the profile of the test article 6 which is this invention goods, and thickness t of the diffusion layer was about 22 micrometers. On the other hand, (b) shows the profile of the test product 1 as a comparative product, and it can be seen that the thickness t of the diffusion layer is as small as about 10 μm. Before welding, when the carbon abundance on the surfaces to be welded of the ground electrodes of both test products was measured by X-ray photoelectron spectroscopy, the surface carbon abundance of the test product 6 was 1/4 or less that of the test product 1. I understood it. This is because the surface carbon abundance of the base metal material layer 140 of the ground electrode 4 is reduced and activated due to the plating peeling, and the interdiffusion with the Pt-based metal tip 32 ′ during resistance welding is promoted. It is thought that.

BRIEF DESCRIPTION OF THE DRAWINGS The longitudinal half sectional view which shows the spark plug which is one Example of this invention. The longitudinal cross-sectional view which shows the principal part of FIG. Process explanatory drawing of the electrolytic zinc plating by barrel plating. Process explanatory drawing of the chromate process by a barrel method. Explanatory drawing of a peeling process. The figure explaining the formation process of the zinc chromate layer in this invention in contrast with the conventional process. Process explanatory drawing which shows the method of forming an ignition part in a ground electrode by resistance welding. The figure which shows the definition of the thickness of a diffused layer. The figure which shows the example of a measurement of the diffused layer thickness by an EPMA line analysis profile.

Explanation of symbols

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

Claims (2)

A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a spark discharge gap are formed between the center electrode and the center electrode. A ground electrode arranged in a shape,
A zinc-based plating layer containing zinc as a main component, and a chromate layer covering a surface of the zinc-based plating layer, the outer surface of the metal shell and the outer surface of the base end portion of the ground electrode joined to the metal shell And an exposed portion of the base electrode material layer on which the zinc-based plating layer is not formed is formed on the tip end side in the axial direction of the ground electrode.
In the zinc chromate layer, the chromate layer is formed so as to cover an end face in the axial direction of the ground electrode of the zinc-based plating layer. A noble metal ignition part is formed by welding a Pt-based metal tip containing Pt as a main component at least on the ground electrode side at a position corresponding to the spark discharge gap,
And spark plug of claim 1, wherein the thickness of the diffusion layer is 10μm or more, which is formed corresponding to the bonding interface between the ground electrode and the noble metal spark portion.