JP2004186152A - Sparking plug and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sparking plug which can solve the problem that the chip of a noble metal is difficult to weld on a discharge portion in its earth electrode because an Al-aggregation layer is formed on the surface layer of an alloy used for the earth electrode though the use of the alloy containing not less than 0.8 wt% of Al with the main component of Ni is effective in improving the performance of the sparking plug, and on the other hand if tried to remove the Al-aggregation layer completely, that a steep rise in a working cost is taken place, . <P>SOLUTION: In this sparking plug, a noble metal chip 5 is welded onto at least an earth electrode 4 in a counter electrodes with the chip being disposed in a position facing a center electrode. Here, the opposing electrodes are composed of the center electrode and the earth electrode 4, and disposed in an opposing and spaced relationship with each other with a spark discharge gap formed therebetween. In addition, the base material of the earth electrode 4 is made of the alloy that contains not less than 0.8 wt% of Al with a main component of Ni and further has an Al-aggregation layer 4a in its surface layer, and the area occupancy ratio of Al-aggregation X in the region within 20 μm beneath the noble metal chip 5 in the half section including the welded noble metal chip 5 is not more than 30%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a spark plug and a manufacturing method thereof.

  As shown in FIG. 2, the spark plug 1 is fixed to the cylindrical metal shell 2, the center electrode 3 protruding from the cylinder through the center of the metal shell 2, and the cylindrical end of the metal shell 2 by welding or the like. And a ground electrode 4 having a free end bent into a key shape and opposed to the center electrode 3. The opposed surfaces of the center electrode 3 and the ground electrode 4 are discharge portions, and a discharge portion in which noble metal tips 5 and 5 such as platinum nickel alloy are welded is put into practical use.

  In order to improve the performance of the internal combustion engine, an improvement in the performance of the spark plug 1 is required, and in order to improve the performance of the spark plug 1, an improvement in the high temperature oxidation resistance of the ground electrode 4 is required. As a material that can satisfy such a requirement, there is an alloy containing Ni as a main component and containing 0.8 wt% or more of Al. However, since such an alloy is heat-treated in a nitrogen atmosphere in the production process, the aluminum component in the alloy is aluminum nitride and forms an agglomerated layer on the surface of the alloy, and this Al agglomerated layer forms the ground electrode 4 of the alloy. Is preventing the use of.

  That is, when the above alloy is adopted as the base material of the ground electrode 4, when the noble metal tip 5 is welded to the discharge part, the heat of the welding promotes the oxidation of the surface of the Al aggregated layer on the surface of the base material, and at the welding interface. Since aluminum oxide is formed, the weldability of the noble metal tip 5 is lowered, that is, the noble metal tip 5 is peeled off from the ground electrode 4. In addition, it is conceivable that the noble metal tip 5 is welded after completely removing the Al agglomerated layer, but this increases the processing cost of the base material, which increases the price of the ground electrode 4.

  According to a first aspect of the present invention, there is provided a spark plug formed by welding a noble metal tip to at least a ground electrode of a center electrode and a ground electrode, which are opposed to each other with a spark discharge gap therebetween, and a surface facing the center electrode. An alloy having a main component of Ni and containing 0.8 wt% or more of Al and having an Al aggregated layer on its surface layer is used as a base material of a ground electrode, and is 20 μm below a half-section noble metal tip including a welded noble metal tip. Provided is a spark plug in which the area occupancy of Al agglomerates is 30% or less in the cross-sectional area of the range.

  In addition, the spark formed by welding a noble metal tip to at least the ground electrode of the center electrode and the ground electrode, which are opposed to each other with a spark discharge gap therebetween, and on the surface facing the center electrode. A method for manufacturing a plug, wherein an alloy containing Ni as a main component and containing Al in an amount of 0.8 wt% or more and having an Al agglomerated layer on its surface is used as a base material for a ground electrode, and the surface layer is first ground to obtain an Al agglomerated material. While the layer is thinned, the precious metal tip is superimposed on the base material, and the polymerization part is heated to mainly melt the base material, and press the precious metal tip in the molten state to remove the molten Al aggregated layer. Provided is a method for manufacturing a spark plug in which a noble metal tip is allowed to settle and thereby the noble metal tip is joined to an alloy layer below the surface layer.

Further, as described in claim 3, a recess for inserting a noble metal tip is formed on a surface of the ground electrode facing the center electrode, and the noble metal tip is inserted into the recess and welded. A method for manufacturing a spark plug is provided.
According to a fourth aspect of the present invention, there is provided the spark plug manufacturing method according to the second or third aspect, wherein at least the thickness of the Al aggregated layer of the discharge part is ground to 20 μm or less.
In addition, as described in claim 5, the spark plug manufacturing method according to any one of claims 2 to 4, wherein the Al aggregated layer is ground by a mechanical grinding means.
Further, as described in claim 6, the spark plug manufacturing method according to any one of claims 2 to 4, wherein the Al aggregated layer is ground by a chemical grinding means.

  According to the first aspect of the present invention, a high-performance spark plug having high-temperature oxidation resistance can be provided at a low price. That is, even when a nickel alloy having an Al agglomerated layer on the surface layer, which is superior in high temperature oxidation resistance but is a factor that inhibits weldability of the noble metal tip, is used as a base material, it is 20 μm below the noble metal tip having a half cross section including the welded noble metal tip. If the area occupancy of the Al aggregate is 30% or less in the cross-sectional area of the range, the weldability of the noble metal tip is good even if such an Al aggregate is present. This means that if the Al agglomerate in the above range is as small as 30% or less in area occupancy, the state where there is little aluminum oxide to the extent that the weldability is not impaired even at the weld interface between the noble metal tip and the ground electrode base material. This is because it can be produced. In addition, if this is used to grind the base material while leaving an Al agglomerated layer satisfying such conditions before welding, the grinding cost can be reduced compared to the case where the Al agglomerated layer is completely removed, and what kind of welding is performed. The excellent effect that reliable welding can be performed also to the method is obtained.

  Further, according to the invention described in claim 2, since a method is adopted in which the noble metal tip is pressure settled on the molten base material and the Al aggregate layer is pushed away by the noble metal tip itself, the Al aggregate on the base material surface is welded. Even if there are more than the above conditions, the noble metal tip can be welded so as to satisfy the above conditions. Therefore, the cost for grinding the Al aggregated layer can be further reduced.

  Further, as in claim 3, if a recess for inserting the noble metal tip is formed on the surface of the ground electrode facing the center electrode, and the noble metal tip is inserted into the recess and welded, the Al of the entire base material is formed. The processing cost of the base material can be further reduced than when the agglomerated layer is thinly ground. Further, according to the weldability test, if the thickness of the Al agglomerated layer in the discharge portion is 20 μm or less as described in claim 4 in the manufacturing method of claim 2, weldability having no practical problem can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings. 1 (a) is an enlarged half sectional view of the base material, FIG. 1 (b) is an enlarged half sectional view of the base material showing a state in which the Al aggregated layer is ground, and FIGS. 1 (c) and 1 (d) are welded. FIG. 2 is a front view of the main part of the spark plug, FIG. 3 is an enlarged half cross-sectional view of the main part of the ground electrode after noble metal tip welding, and FIG. 4 is an enlarged main part of the ground electrode showing a peeled state. FIG.

  As already described in the section of the prior art, the spark plug 1 includes a cylindrical metal shell 2, a center electrode 3 that protrudes from the cylinder through the center of the metal shell 2, and a cylinder end of the metal shell 2. And a ground electrode 4 fixed by welding or the like and having a free end bent into a key shape and opposed to the center electrode 3. A spark discharge gap is formed between the center electrode 3 and the ground electrode 4, and the opposing surfaces of the center electrode 3 and the ground electrode 4 are discharge parts. A noble metal tip 5 such as an alloy or a platinum iridium alloy is welded.

  Next, a method for manufacturing the spark plug 1 will be described. However, since a known manufacturing method is applied as it is except for the portion related to the ground electrode 4 of the spark plug 1, the description thereof is omitted.

  First, the ground electrode 4 is made of an alloy containing Ni as a main component and containing 0.8 wt% or more of Al as a base material. As shown in FIG. 1A, this type of alloy has an Al aggregate layer 4a having an Al aggregate X (aluminum nitride and aluminum oxide) generated by heat treatment in the production process on the surface layer of the alloy layer 4b. FIG. 1 (a) shows the state of the cross section of the alloy observed by SEM. This surface layer is ground to thin the Al agglomerated layer 4a (grinding step). Specifically, it is good to grind until the Al aggregated layer 4a becomes 20 μm or less. The means for grinding may be either mechanical grinding means by a polishing machine or the like, and chemical grinding means by pickling with hydrofluoric acid or aqua regia, electrolytic polishing or the like.

Next, as shown in FIG. 1 (c), the ground electrode 4 is placed on the holding jig 6a of the electric resistance welder, and a noble metal tip 5 processed into a thin disk shape is formed on a portion corresponding to the discharge portion of the ground electrode 4. Put it on. Then, a pressing jig 6b of an electric resistance welding machine is placed on the noble metal tip 5, and a current of about 1,100 A is applied between the electrode holding jig 6a and the pressing jig 6b while pressing with a pressure of about 284 to 304N. Then, the superposed portion of the base metal of the noble metal tip 5 and the ground electrode 4 is heated (welding process). The base material of the ground electrode 4 has a melting point of 1,350 ° C. to 1,400 ° C., whereas the melting point of the noble metal tip 5 is 1,840 ° C. to 1,880 ° C., which is higher than that. Melt. Accordingly, as shown in FIG. 1 (d), the noble metal tip 5 sinks while pressing and melting the molten Al aggregate layer 4a under the pressure of the pressing jig 6b. Then, when the noble metal tip 5 is substantially flush with the base material, the pressing jig 6b is raised. Thus, the welding process is completed, and the noble metal tip 5 pushes away the Al agglomerated layer 4a and joins it to the alloy layer 4b below the surface layer.
The above electric resistance welding may be performed in an Ar atmosphere (specifically, a so-called Ar-rich state in which Ar gas is blown onto the welded portion). By doing so, the phenomenon that the aluminum nitride of the Al agglomerated layer changes into aluminum oxide due to heat during welding is less likely to occur, and as a result, the amount of aluminum oxide at the weld interface can be reduced. Of course, the Ar gas may be replaced with another inert gas.

The cross-section of the ground electrode 4 after welding the noble metal tip 5 is as shown in FIG. 3, and the cross-sectional area in the range of approximately 20 μm below the noble metal tip 5 of the half cross section including the noble metal tip 5 indicated by hatching in FIG. When the area occupancy of the Al aggregate X is 30% or less, the welding result is good. This is because if the Al agglomerate X in the above range is a small area occupancy ratio of 30% or less, the aluminum oxide to the extent that the weldability is not impaired even at the weld interface between the noble metal tip 5 and the base material of the ground electrode 4. This is because it is possible to create a state in which there is little.
The area occupation ratio of the Al aggregate X can be calculated by, for example, an image processing apparatus manufactured by Keyence Corporation. In addition, since the area occupation ratio may be 30% or less, it may not be necessary to calculate the entire 20 μm range below the noble metal tip 5. For example, a plurality of portions with a large amount of Al aggregate X are arbitrarily selected, and the area occupancy of Al agglomerate X is calculated for a unit area of 5 μm square at those locations, and the average area occupancy must exceed 30%. For example, the area occupancy rate cannot be less than 30% in the entire hatched portion in FIG. Therefore, in such a case, the calculation of the Al agglomerates X may be terminated at that time, and by doing so, the area occupation rate calculation operation can be shortened.

  The ground electrode 4 manufactured as described above is welded to the cylindrical end of the metal shell 2. The above process may be performed after the ground electrode 4 is welded to the cylindrical end of the metal shell 2.

[Desktop chip weldability test 1]
In order to confirm the effect of the present invention, the following desktop chip weldability test was performed.
(A) “Inconel 601” (registered trademark), which is a commercially available nickel alloy, is used as the base material of the ground electrode 4 and processed into a 1.3 mm × 2.7 mm flat material, and the thickness of the Al agglomerated layer 4a 11 types were manufactured in increments of 5 μm from 0 μm to 50 μm, and 5 types of each were manufactured. In addition, the specific additive element and addition amount (wt%) of the base material are as follows.
[Si: 0.23 Cr: 21.9 Mn: 0.20 Al: 1.37 Fe: 14.6 Ni: 61.7]
(B) The noble metal tip 5 was made of a Pt-20Ir alloy and processed into a disk shape having a diameter of 1.1 mm and a thickness of 0.4 mm.
(C) In the welding process, a commercially available electric resistance welder was used, and the noble metal tip 5 was pressed with a pressure of 294 N while flowing a current of 1,100 A between the electrode holding jig 6 a and the pressing jig 6 b.
(D) The condition of “heating at 900 ° C. for 2 minutes—air cooling for 1 minute” was repeated 1000 times for the ground electrode 4 manufactured as described above, and then the peeling state of the noble metal tip 5 was observed. The results are shown in Table 1. Incidentally, the degree of peeling represented the ratio of the length L ₂ was peeled off to the length L ₁ of the welded portion, as shown in FIG. 4 as a percentage (%).

  As a result of the weldability test 1, it was confirmed that welding was possible by precipitating the noble metal tip 5 even if the Al aggregated layer 4a was left thin, that is, the Al aggregated layer 4a was not completely removed. In particular, if the thickness of the Al agglomerated layer 4a is 20 μm or less, peeling of the noble metal tip 5 is suppressed to 20% or less, so that a high quality spark plug can be stably provided. On the other hand, when the thickness of the Al agglomerated layer 4a is 21 μm to 30 μm, peeling of 21% to 50% occurred, but the evaluation of whether this value is good or not depends on the required quality level and is evaluated as usable. There is also a case. Even if the thickness of the Al aggregated layer 4a is 21 μm to 30 μm, the weldability can be significantly improved by slightly increasing the thickness of the noble metal tip 5.

[Desktop chip weldability test 2]
In order to confirm the relationship between the area occupancy of the Al agglomerate X and the weldability of the noble metal tip 5, the following desktop tip weldability test was performed.
(A) “Inconel 601” (registered trademark), which is a commercially available nickel alloy, is used as the base material of the ground electrode 4, which is processed into a 1.3 mm × 2.7 mm flat material, and the thickness of the Al agglomerated layer 4 a A variety of types were manufactured. In addition, the specific additive element and addition amount (wt%) of the base material are as follows.
[Si: 0.25 Cr: 20.0 Mn: 0.20 Al: 1.5 Fe: 15.0 Ni: 63]
(B) The noble metal tip 5 was made of a Pt-20Ir alloy and processed into a disk shape having a diameter of 1.1 mm and a thickness of 0.4 mm.
(C) In the welding process, a commercially available electric resistance welder was used, and the noble metal tip 5 was pressed with a pressure of 294 N while flowing a current of 1,100 A between the electrode holding jig 6 a and the pressing jig 6 b.
(D) For the ground electrode 4 manufactured in the above manner, the condition of “heating at 900 ° C. for 2 minutes—air cooling for 1 minute” was repeated 1000 times, and then the noble metal tip 5 having a half cross section including the welded noble metal tip 5 In the cross-sectional area in the range of 20 μm below, the area occupancy of the Al aggregate X and the peeling state of the noble metal tip 5 were observed. The results are shown in Table 2. Incidentally, the degree of peeling represented the ratio of the length L ₂ was peeled off to the length L ₁ of the welded portion, as shown in FIG. 4 as a percentage (%).

  As a result of the weldability test 2, welding of the noble metal tip 5 is performed when the area occupancy of the Al agglomerates X is 30% in the cross-sectional area in the range of 20 μm below the noble metal tip 5 having a half cross section including the welded noble metal tip 5. It was confirmed that the characteristics were within the usable range.

  The embodiments of the present invention have been described above, but the present invention is of course not limited to the above embodiments. For example, in the embodiment, the entire surface layer of the ground electrode 4 is ground to thin the Al agglomerated layer 4a. However, as shown in FIG. 5, a shallow recess 7 for inserting the noble metal tip 5 into the discharge part of the ground electrode 4 is formed. The noble metal tip 5 may be fitted into the recess 7 and welded. In this case, even if the thin Al aggregation layer 4a remains at the bottom of the recess 7, the weldability is not adversely affected as in the embodiment.

Further, in the embodiment, electric resistance welding is used as a method of welding the noble metal tip 5 to the base material. However, in the cross-sectional area in the range of 20 μm below the surface of the base material, the area occupation ratio of the Al aggregate X is 30% or less. As long as the Al agglomerated layer 4a is ground in advance so that the area occupancy of the Al agglomerate X is clearly 30% or less after welding, the precious metal tip 5 is hardly pressurized, that is, the precious metal The noble metal tip 5 can also be welded by laser welding, ultrasonic welding, or the like, which is a welding method in which the extruding action of the Al agglomerated layer 4a by the tip 5 can hardly be expected. However, the present invention is best performed by electric resistance welding in terms of ease of implementation and cost.
In the embodiment, nickel alloy “Inconel 601” (registered trademark) is used as the base material of the ground electrode 4, but “Inconel 600” (registered trademark) may be used.

(A) is an enlarged half sectional view of the base material, (b) is an enlarged half sectional view of the base material showing a state where the Al agglomerated layer is ground, and (c) and (d) are half sectional views for explaining the welding process. is there. It is a principal part front view of a spark plug. It is a principal part expanded half sectional view of the ground electrode after noble metal chip welding. It is a principal part expanded half sectional view of the ground electrode which shows a peeling state. It is a disassembled perspective view of the ground electrode which shows another form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spark plug 3 ... Center electrode 4 ... Ground electrode 4a ... Al aggregated layer 4b ... Alloy layer 5 ... Noble metal tip 7 ... Concave X ... Al aggregate

Claims (6)

A spark plug in which a noble metal tip is welded to a surface of at least the ground electrode of the center electrode and the ground electrode that are opposed to each other with a spark discharge gap therebetween, and facing the center electrode,
An alloy having Ni as a main component and containing Al in an amount of 0.8 wt% or more and having an Al agglomerated layer on its surface layer is used as a base material for a ground electrode, and is cut within a range of 20 μm below a half-section noble metal tip including a welded noble metal tip A spark plug characterized in that, in the area, the area occupancy of Al aggregates is 30% or less. A spark plug manufacturing method in which a noble metal tip is welded to a surface of at least a ground electrode of a center electrode and a ground electrode that are opposed to each other across a spark discharge gap, and the surface of the center electrode is opposed to the ground electrode,
An alloy having Ni as a main component and containing Al in an amount of 0.8 wt% or more and having an Al aggregated layer on its own surface layer is used as a base material for the ground electrode. First, the surface layer is ground to make the Al aggregated layer thin, and then a noble metal. The base material is mainly melted by stacking the chip on the base material and the superposition part is heated, and the precious metal chip is settled while pushing away the molten Al aggregate layer by pressing the precious metal chip in the molten state. A method for manufacturing a spark plug, characterized in that a chip is bonded to an alloy layer below a surface layer.   3. A method for manufacturing a spark plug according to claim 2, wherein a recess for fitting a noble metal tip is formed on a surface of the ground electrode facing the center electrode, and the noble metal tip is fitted into the recess and welded. .   4. The method for producing a spark plug according to claim 2, wherein at least the thickness of the Al aggregated layer in the discharge part is ground to 20 [mu] m or less.   The spark plug manufacturing method according to any one of claims 2 to 4, wherein the Al agglomerated layer is ground by a mechanical grinding means.   The spark plug manufacturing method according to any one of claims 2 to 4, wherein the Al agglomerated layer is ground by a chemical grinding means.

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