JP4291484B2 - Spark plug and method of manufacturing spark plug - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug and a manufacturing method thereof.
[0002]
[Prior art]
In the spark plug as described above, a type in which an ignition part is formed by welding a tip mainly made of Pt to the tip of an electrode is used in order to improve spark wear resistance. However, in recent years, in order to further improve the spark wear resistance, a spark plug in which an ignition part is constituted by a chip mainly composed of Ir instead of Pt is disclosed in, for example, Japanese Patent Laid-Open Nos. 63-257193 and 3 Various proposals are made in JP-A-1475, JP-A-5-54953, JP-A-9-7733, JP-A-10-32076, JP-A-10-74575, JP-A-10-22052, and the like.
[0003]
However, in recent years, the temperature in the combustion chamber tends to increase due to the high performance of the internal combustion engine, and in order to improve the ignitability, many types of engines in which the ignition portion of the spark plug protrudes into the combustion chamber are also used. It has become like this. Recently, as part of measures to make maintenance free for automobile engines, severe demands that cannot be imagined from the previous situation, such as continuous running over 160,000 km without replacement of spark plugs, have come to be issued. ing.
[0004]
[Problems to be solved by the invention]
When Ir-based chips are used, the durability is greatly improved. However, since Ir has the property of being easily oxidized and volatilized at a high temperature, if it is repeatedly run for a long time at a high temperature, it will rise above a certain temperature. There is a drawback that the ignition part is rapidly consumed and the spark gap interval is enlarged. In order to solve this problem, JP-A-9-7733, JP-A-10-32076, JP-A-10-74575, and JP-A-10-22052 disclose ignition by adding Rh or Pt to Ir. A method for improving the oxidation resistance of the part has been proposed. However, it is not always sufficient in situations where a design that further increases the temperature of the ignition part is required, such as increasing the ignition part at the tip of the center electrode in order to improve durability in harsh usage environments at higher temperatures, or to improve ignitability. It is hard to say that a good effect has been obtained.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug in which an ignition portion is formed by joining Ir-based chips, and a spark plug that is extremely excellent in oxidation resistance consumption of the ignition portion, and a method for manufacturing the spark plug.
[0006]
[Means for solving the problems and actions / effects]
The spark plug of the present invention includes a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a ground electrode disposed so as to face the center electrode. And an ignition part that is fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap, the ignition part having Ir as a main component and a carbon content of 40 ppm or less. Or it is comprised by the composite material which has this Ir type metal as a main component.
[0007]
  Further, the method of the present invention for producing the spark plug is as follows:AboveAt the position corresponding to the spark discharge gapAboveWith the center electrodeAboveBased on the tip by welding a tip made of an Ir-based metal having Ir as a main component and a carbon content of 40 ppm or less or a composite material containing the Ir-based metal as a main component to at least one of the ground electrode Form an ignition partWith
Prior to the welding, the tip or the tip material for producing the tip is subjected to a decarbonization heat treatment in a reduced-pressure atmosphere or a hydrogen atmosphere in order to remove a carbon component in the Ir-based metal,
The atmosphere of the decarbonizing heat treatment has an oxygen partial pressure of 2.7 × 10. ^-2 A reduced pressure atmosphere of Pa or less or an oxygen partial pressure of 2.7 × 10 ^-2 Pa or less and hydrogen partial pressure is 5 × 10 ⁴ A hydrogen atmosphere of Pa or higher,
The temperature of the decarbonizing heat treatment is adjusted in a range of 1610 ° C. or more and 2000 ° C. or less.It is characterized by that.
[0008]
As used herein, the term “ignition part” refers to a part of a joined chip that is not affected by compositional variation due to welding (for example, a part that is alloyed with the material of the ground electrode or the center electrode by welding). The remaining part).
[0009]
Conventionally, in a spark plug in which an ignition part is made of an Ir-based metal, attempts have been made mainly to improve the oxidation resistance by adding an appropriate alloy element such as Rh. Although it is certainly an effective technique, the present inventors have conducted intensive studies on the content of impurity elements mixed from raw materials and the like in addition to the amount of alloy element components to be actively added. The oxidation resistance at high temperature of the ignition part made of a metallic metal is greatly affected by the impurity carbon contained in a trace amount, and the content level is controlled to 40 ppm or less by weight content, thereby The inventors have found that the oxidation wear resistance is remarkably improved, and have completed the present invention.
[0010]
If the carbon content in the Ir-based metal constituting the ignition part exceeds 40 ppm, the effect of improving the oxidation resistance and wear resistance of the ignition part due to the reduction of the carbon content is not significant, and in particular, the suppression of oxidation consumption due to the addition of alloy components, etc. If not taken into account, the exhaustion of the ignition part at a high temperature becomes significant, leading to a decrease in durability. The carbon content in the Ir-based metal is desirably 20 ppm or less, more desirably 10 ppm or less, and further desirably 5 ppm or less.
[0011]
The chip for forming the ignition part or the chip material for manufacturing the chip may be a melting material manufactured by melting and solidifying an Ir-based metal material, or a raw material powder mainly composed of an Ir-based metal. It is good also as a sintered material obtained by shape | molding this into a predetermined shape and sintering this. The chip material can be made into a chip by applying predetermined processing. “Processing” as used herein means what is made by rolling, forging, wire drawing (drawing), cutting, cutting (including electric discharge machining), or punching alone or in combination. And In this case, processing such as rolling, forging, or punching can be performed by so-called hot processing (or warm processing) performed by raising the temperature of the alloy to a predetermined temperature. The processing temperature depends on the alloy composition, but is preferably 700 ° C. or higher, for example. For example, if the molten material is processed into a plate shape by hot rolling, and then the plate material is punched into a predetermined shape by hot punching to form a chip, the chip manufacturing efficiency is remarkably improved, and the chip manufacturing is performed. Unit price can be greatly reduced. It is also possible to form a chip by processing the molten alloy into a linear or rod shape by hot rolling or hot forging and then cutting it into a predetermined length in the length direction.
[0012]
As a method of reducing the carbon content of the chip or a chip material for manufacturing the chip, it is naturally considered to use a chip material having as little impurity carbon content as possible. However, high-purity raw materials are expensive, and high-purity raw materials are used even if there is a possibility of contamination by carbon inevitably mixed from a carbon source such as a crucible during melting. However, there is a possibility that the carbon content level cannot be reduced to the expected value.
[0013]
Therefore, when the carbon content of the chip or the chip material for manufacturing the chip is unexpectedly increased to a value exceeding 40 ppm, this is performed in a reduced-pressure atmosphere or a hydrogen atmosphere prior to welding. The decarbonization heat treatment is very effective in removing or reducing the carbon component in the Ir-based metal. In the case of a melting material, it is also effective to hold the molten metal in hydrogen (or a hydrogen-containing gas composed of hydrogen and an inert gas such as argon) or blow hydrogen or hydrogen-containing gas into the molten metal. It is.
[0014]
On the other hand, in the sintered material, when the carbon content level in the Ir-based metal raw material powder, for example, for producing a molded body is high, the raw material powder before the molding is used to remove the carbon component, Powder decarbonization heat treatment can be performed in a reduced-pressure atmosphere or a hydrogen atmosphere. In addition, when using a sintered material, the sintering may be a sintering process (hereinafter referred to as a decarbonized sintering process) that also serves as a decarbonizing process for an Ir-based metal in a reduced pressure atmosphere or a hydrogen atmosphere. it can. Note that at the end of the powder decarbonization heat treatment or decarbonization sintering process, the carbon content level in the raw material powder may be 40 ppm or less, and even if this level exceeds 40 ppm, What is necessary is just to give the carbon content level of the chip | tip or chip | tip raw material finally obtained to 40 ppm or less by performing a decarbonization heat processing.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A spark plug 100 as an example of the present invention shown in FIG. 1 and FIG. 2 is formed at a distal end of a tubular metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip portion 21 protrudes. One end of the noble metal ignition part (hereinafter also simply referred to as the ignition part) 31 is connected to the center electrode 3 and the metal shell 1 provided inside the insulator 2 by welding or the like, and the other end side is A ground electrode 4 or the like is provided that is bent back to the side and disposed so that the side surface faces the tip of the center electrode 3. Further, the ground electrode 4 is formed with an ignition part 32 that faces the ignition part 31, and a gap between the ignition part 31 and the opposing ignition part 32 is a spark discharge gap g.
[0016]
The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, for example, and has a hole 6 for fitting the center electrode 3 along its own axial direction. The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw for attaching the plug 100 to an engine block (not shown) on its outer peripheral surface. Part 7 is formed.
[0017]
The chip adherent surface forming portion of the center electrode 3 and the ground electrode 4, in this embodiment, at least the surface layer portion thereof is made of a heat-resistant alloy containing Ni or Fe as a main component. "Means the component with the highest weight content, and does not necessarily mean" the component occupying 50% by weight or more "). As the heat-resistant alloy containing Ni or Fe as a main component, the following can be used.
(1) Ni-base heat-resistant alloy: In this 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.
[0018]
(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.
[0019]
On the other hand, the ignition part 31 and the opposing ignition part 32 are mainly composed of a metal containing Ir as a main component (Ir-based metal). The ignition parts 31 and 32 made of the Ir-based metal each have a carbon content of 40 ppm or less, desirably 20 ppm or less, more desirably 10 ppm or less, and even more desirably 5 ppm or less in terms of weight content. As a result, even in an environment where the temperature of the center electrode 3 is likely to rise, it is possible to improve the wear resistance of the ignition parts 31 and 32 and to reduce the wear extremely effectively due to oxidation and volatilization of the Ir component. It is suppressed. Moreover, the weldability with respect to the above heat-resistant alloys is also favorable. In addition, it is good also as a structure which abbreviate | omits any one of the ignition part 31 and the opposing ignition part 32. FIG. In this case, a spark occurs between the ignition part 31 and the side surface of the ground electrode 4 that does not have the ignition part, or between the opposing ignition part 32 and the front end surface of the center electrode 3 that does not have the ignition part. A discharge gap g is formed. Further, the opposing ignition part 32 on the ground electrode 4 side may be composed of a noble metal other than an Ir-based metal, such as a noble metal mainly composed of Pt.
[0020]
The Ir metal constituting the ignition parts 31 and 32 can contain at least one of Pt, Rh, Ru, Re, Nb, and Hf as an additive metal element component. Thereby, the oxidation consumption resistance at high temperature of the ignition parts 31 and 32 is further improved. However, in the present invention, since the effect of suppressing oxidative consumption by reducing the carbon content in the Ir-based metal constituting the ignition parts 31 and 32 to the aforementioned level is great, the content of the additive metal element component is reduced. Even if it is not increased so much, the oxidation and volatilization suppression of the ignition part becomes considerably remarkable. This is advantageous in that the added amount can be reduced when the added metal element component is an expensive noble metal such as Pt, Rh, Ru, or Re. In this respect, it is desirable that the Ir-based metal has an Ir content of 85% by weight or more, and the balance is substantially the above-described additive metal element component.
[0021]
For example, the following materials can be used as the Ir-based metal constituting the ignition parts 31 and 32.
(1) An alloy containing Ir as a main component and containing Rh in the range of 1 to 50% by weight (but not including 50% by weight) is used. By using the alloy, the consumption of the ignition part due to the oxidation and volatilization of the Ir component at a high temperature is further effectively suppressed, and as a result, a spark plug having higher durability is realized.
[0022]
When the Rh content in the alloy is less than 1% by weight, the effect of suppressing Ir oxidation and volatilization due to the addition of Rh is not significant. On the other hand, when the Rh content is 50% by weight or more, the melting point of the alloy is lowered, and the durability of the plug is similarly lowered.
[0023]
Here, as the content of Rh in the alloy increases within the above range, the oxidation / volatilization suppressing effect of the ignition parts 31 and 32 is enhanced. In this respect, the effect of suppressing oxidation and volatilization is most prominent when the Rh content is 7 to 30% by weight, more preferably 15 to 25% by weight, and most preferably 18 to 22% by weight. However, in the present invention, the effect of suppressing oxidation consumption by reducing the carbon content in the Ir-based metal constituting the ignition parts 31 and 32 to the aforementioned level is great, so even if the Rh content is relatively small. Compared with the conventional spark plug in which the ignition portion is made of Ir-based metal, an oxidation / volatilization effect that is equal to or higher than that is achieved. As a result, it is possible to realize a spark plug excellent in oxidation resistance and wear resistance of the ignition part 31 or 32 while reducing the content of expensive Rh. For example, when the Ir content in the Ir-based metal is 85 wt% or more as described above, the Rh content is desirably 1 to 15 wt%, more desirably 3 to 10 wt%. It is desirable to adjust.
[0024]
(2) An alloy mainly containing Ir and containing Pt in the range of 1 to 50% by weight is used. By using the alloy, consumption of the ignition part due to oxidation and volatilization of the Ir component at high temperature is further effectively suppressed, and as a result, a spark plug having higher durability is realized. When the Pt content in the alloy is less than 1% by weight, the effect of suppressing Ir oxidation and volatilization becomes insufficient, and the ignition part is easily consumed, so that the durability of the plug is lowered. On the other hand, when the Pt content is 50% by weight or more, the melting point of the alloy is lowered, and the durability of the plug is similarly lowered. For example, when the Ir content in the Ir-based metal is 85% by weight or more as described above, the Pt content is desirably 1 to 15% by weight, and more desirably 3 to 10% by weight. It is desirable to adjust.
[0025]
(3) An alloy containing Ir as a main component and containing 0.5% by weight or more of Nb is used. By using the alloy, consumption due to oxidation and volatilization of the Ir component at a high temperature is further effectively suppressed, and as a result, a spark plug having higher durability is realized. When the Nb content in the alloy is less than 0.5% by weight, the effect of suppressing Ir oxidation and volatilization by adding Nb becomes insignificant. The Nb content is desirably 1% by weight or more, and more desirably 5% by weight or more.
[0026]
In this case, it is more preferable to use an alloy containing Nb in a range below the solid solubility limit with respect to Ir. When Nb is contained exceeding the solid solubility limit with respect to Ir, Ir₃A brittle intermetallic compound such as Nb is formed, which may cause problems in durability and impact resistance of the ignition part. For example, since the solid solubility limit of Nb with respect to Ir at room temperature is about 6% by weight, when Nb is contained alone, it can be said that it is desirable to set the content to be smaller than the above values. However, if the formation amount of the intermetallic compound is below a certain level and the effect on the durability of the ignition part is small, the Nb content may be a value slightly exceeding the solid solubility limit. Absent. From the above, when Nb is contained alone, for example, the content is 7% by weight or less, preferably 6% by weight or less.
[0027]
(4) An alloy containing Ir as a main component and containing Rh in a range of 0.1 to 30% by weight and further containing at least one of Ru and Re in a range of 0.1 to 17% by weight in total is used. Thereby, consumption of the ignition part due to oxidation and volatilization of the Ir component at a high temperature is further effectively suppressed, and as a result, a spark plug having higher durability is realized. When the Rh content is less than 0.1% by weight, the effect of suppressing the oxidation and volatilization of Ir becomes insufficient, and the ignition part is easily consumed, so that the wear resistance of the plug cannot be secured. On the other hand, if the content of Rh exceeds 30% by weight, the melting point of the alloy containing Re or Ru is lowered, and the spark wear resistance is impaired, so that the durability of the plug cannot be ensured. Therefore, the content of Rh is adjusted within the above range.
[0028]
On the other hand, when the total content of Ru or Re is less than 0.1% by weight, the effect of suppressing consumption due to oxidation and volatilization of Ir due to the addition of these elements becomes insufficient. On the other hand, if the total content of Ru or Re exceeds 17% by weight, the ignition part tends to wear out and sparks are easily consumed, and sufficient durability of the plug cannot be ensured. Therefore, the total content of Ru and Re is adjusted within the above range, preferably 0.1 to 13% by weight, more preferably 0.5 to 10% by weight. Note that only one of Ru and Re may be added alone, or both may be added in combination.
[0029]
One of the reasons why Ru or Re is contained in the alloy improves the wear resistance of the ignition part. For example, by adding these components, a stable and dense oxide film is formed on the alloy surface at a high temperature. It is estimated that Ir, which is very volatile with a single oxide, is fixed in the oxide film. And it is thought that this oxide film acts as a kind of passive film and suppresses the progress of oxidation of the Ir component. In addition, in the state where Rh is not added, even if Ru or Re is added, the oxidation volatility at high temperatures of the alloy is not improved so much. Therefore, the oxide film is made of Ir- (Ru, Re) -Rh system or the like. It is also considered that this is a composite oxide, which is superior to an Ir- (Ru, Re) -based oxide film in terms of denseness or adhesion to the alloy surface.
[0030]
If the total content of Ru or Re is excessively increased, it is presumed that spark consumption proceeds by the following mechanism rather than volatilization of Ir oxide. In other words, the influence of the denseness of the oxide film to be formed or the adhesion to the alloy surface decreases, and the total content exceeds 17% by weight. And, when the impact of spark discharge of the spark plug is repeatedly applied, it is considered that the formed oxide film is easily peeled off, whereby a new metal surface is exposed and spark consumption is likely to proceed.
[0031]
Further, the following important effects can be achieved by addition of Ru and / or Re. That is, by including Ru and / or Re in the alloy, it is possible to sufficiently ensure wear resistance even when the Rh content is significantly reduced as compared with the case of using an Ir—Rh binary alloy, As a result, a high-performance spark plug can be configured at a lower cost. In this case, the content of Rh is preferably 0.1 to 3% by weight, more preferably 0.1 to 1% by weight.
[0032]
(5) Use an alloy mainly containing Ir and containing at least one of Pt, Re, and Pd in a range of 1 to 30% by weight and further containing Rh in a range of 1 to 49% by weight. Constituting with an alloy containing Pt, Re, or Pd in the above range mainly composed of Ir effectively suppresses consumption due to oxidation and volatilization of the Ir component at a high temperature, and the alloy further contains Rh in the above range. By doing so, the processability is dramatically improved. As the chip, a chip formed by subjecting a molten alloy obtained by blending and melting raw materials to have a predetermined composition to a predetermined process can be used. In addition, "processing" here shall mean what is made by at least one of rolling, forging, cutting, cutting, and punching alone or in combination.
[0033]
When the Rh content is less than 1% by weight, the effect of improving the workability of the alloy cannot be sufficiently achieved, and for example, cracks and cracks are likely to occur during processing, resulting in a decrease in material yield when manufacturing chips. Connected. In addition, when a chip is manufactured by hot punching or the like, wear or damage of a tool such as a punching blade is likely to occur, resulting in a decrease in manufacturing efficiency. On the other hand, if it exceeds 49% by weight, the melting point of the alloy is lowered and the durability of the plug is lowered. Therefore, the content of Rh is preferably adjusted within the above-described range, and is preferably adjusted within a range of 2 to 20% by weight. In particular, when the total content of Pd to Pt is 5% by weight or more, the alloy becomes further brittle, and unless a predetermined amount or more of Rh is added, chip manufacturing by processing becomes extremely difficult. In this case, Rh is added in an amount of 2% by weight or more, desirably 5% by weight or more, and more desirably 10% by weight or more. When the content of Rh is 3% by weight or more, Rh may not only improve workability but also have an effect on the suppression of oxidation and volatilization of Ir components at high temperatures.
[0034]
If the total content of Pt or Pd is less than 1% by weight, the effect of suppressing Ir oxidation and volatilization becomes insufficient, and the chip is easily consumed, so that the durability of the plug is lowered. On the other hand, when the content exceeds 30% by weight, the melting point of the alloy decreases, the durability of the plug also decreases (for example, when Pd alone is added), or the content of expensive Pt or Pd increases. Although the material cost of the chip increases, there arises a problem that the chip consumption suppressing effect cannot be expected so much. In view of the above, the total content of Pt to Pd is preferably adjusted in the above range, and preferably in the range of 3 to 20% by weight.
[0035]
Examples of the spark plug manufacturing method of the present invention will be described below.
That is, as shown in FIG. 9, a disc-shaped chip 31 ′ made of an alloy composition constituting the ignition portion 31 (FIG. 1) is superposed on the tip surface 3s of the center electrode 3, and further on the outer edge of the joint surface. The ignition part 31 is formed by forming an all-around laser welded part (hereinafter also simply referred to as a welded part) 10 by laser welding and fixing it. Further, the opposing ignition part 32 (FIG. 1) aligns the tip 32 ′ (FIG. 12) with the ground electrode 4 at a position corresponding to the ignition part 31, and similarly welds 20 along the outer edge of the joint surface. And are fixed to each other.
[0036]
These chips 31 ′ and 32 ′ (hereinafter, when the chips 31 and 32 are generically referred to, the symbol “150” may be used) are obtained by blending and dissolving each alloy component so as to have a predetermined composition. For example, the molten material is processed into a plate material by hot rolling, and the plate material is formed by punching into a predetermined chip shape by hot punching, or an alloy is hot rolled, hot forged, or hot drawn. After processing into a linear or rod-shaped material, a material formed by cutting it into a predetermined length in the length direction can be used. Moreover, what was shape | molded spherically by the atomizing method etc. can also be used. As the chip 150, for example, a chip having a diameter dc of 0.4 to 1.2 mm and a thickness tc of 0.5 to 1.5 mm is used. As a result, for example, as shown in FIG. 7A, the outer diameter D of the ignition portion 31 also has the same dimensions.
[0037]
As shown in FIG. 3, the chip 150 or the chip material 300 or 210 for manufacturing the chip 150 is subjected to a decarbonizing heat treatment in a reduced-pressure atmosphere or a hydrogen atmosphere prior to welding. It is effective in removing the carbon component therein. FIG. 3A shows an example of decarbonizing heat treatment in the heat treatment furnace FK in a state where the plate material 300 is processed into the rod-shaped material 210 and further FIG. 3C is processed into the chip 150. ing.
[0038]
Desirable conditions for this decarbonization heat treatment are as follows. First, the decarbonization heat treatment atmosphere has an oxygen partial pressure of 2.7 × 10.^-2A reduced pressure atmosphere of Pa or less or an oxygen partial pressure of 2.7 × 10^-2Pa or less and hydrogen partial pressure is 5 × 10⁴A hydrogen atmosphere of Pa or higher is desirable. When performed in a reduced pressure atmosphere, the oxygen partial pressure is 27 × 10³If it exceeds Pa, the Ir component in the Ir-based metal may be reduced by oxidation or volatilization. The oxygen partial pressure is more desirably 1.4 × 10.^-2It is good to set it as Pa or less.
[0039]
Further, the decarbonizing effect is more remarkable in the decarbonizing heat treatment in a hydrogen atmosphere. As the atmospheric gas, hydrogen gas or a hydrogen-containing gas composed of hydrogen and an inert gas such as argon can be used. However, the hydrogen partial pressure in the atmospheric gas is 5 × 10⁴If it is less than Pa, a sufficient decarbonizing effect cannot be expected. The hydrogen partial pressure is 1.2 × 10⁵When Pa is exceeded, the processing cost including equipment may increase. The hydrogen partial pressure is more desirably set higher than the atmospheric pressure. In this way, hydrogen in the furnace always flows in the direction of leaking out of the furnace, so that fluctuations in the furnace atmosphere as the process proceeds can be suppressed.
[0040]
Next, the temperature of the decarbonizing heat treatment is preferably adjusted in the range of 1200 to 2000 ° C. When the temperature is lower than 1200 ° C., a sufficient decarbonizing effect cannot be achieved. On the other hand, when the temperature exceeds 2000 ° C., it is difficult to soften or melt the Ir-based metal, which causes welding or deformation of the chip or chip material being processed. More desirably, the temperature of the decarbonizing heat treatment is adjusted in the range of 1400 to 1950 ° C.
[0041]
Further, the decarbonization from the Ir-based metal in the chip or the chip material proceeds with the holding time of the decarbonization heat treatment. Therefore, it is necessary to set the holding time sufficiently long so that the final carbon content is 40 ppm or less. However, the necessary and sufficient heat treatment holding time varies depending on the decarbonization heat treatment temperature and the atmosphere, and also on the carbon content level before the decarbonization heat treatment. Naturally, it is necessary to set the heat treatment holding time longer for those having a high carbon content level before the heat treatment. However, as a guideline, in order to reduce the carbon content to the above level, it can be said that it is desirable to maintain the temperature of the decarbonizing heat treatment for at least about 1 hour. Further, when the heat treatment temperature is low, the decarbonization rate decreases, and conversely, when the heat treatment temperature is high, the decarbonization rate increases. Therefore, when performing the same amount of decarbonization, the higher the heat treatment temperature, the shorter the decarbonization time. In this case, assuming that the temperature of the decarbonization heat treatment is TC (° C.) and the heat treatment holding time is th (hours), TC ≧ 1200, and TC × thh is 1950 or more. It can be said that it is desirable to reduce the carbon content.
[0042]
The carbon content of the chip or chip material is desirably 120 ppm or less before the decarbonization heat treatment. If the carbon content of the chip or chip material exceeds 120 ppm before the decarbonizing heat treatment, the carbon content of 40 ppm or less is finally secured even if the holding time of the decarbonizing heat treatment is set to a considerably long time. It may be difficult to do.
[0043]
The method of decarbonizing the chip or the chip material as described above is effective for both the melting material and the sintered material described later. In the case of a sintered material, various organic additives may be added as a molding aid (for example, a binder or a lubricant). The organic additive serves as a carbon source, and the resulting chip or chip material contains The carbon content may increase. However, by subjecting this to a decarbonization heat treatment as described above, the carbon content can be reduced, and as a result, an ignition part having excellent oxidation resistance and wear resistance can be obtained.
[0044]
Next, as shown in FIG. 4, the chip 150 (or the chip material 135) may be a sintered material obtained by forming a raw material powder mainly composed of an Ir-based metal into a predetermined shape and then sintering it. . In FIG. 4A, first, a raw material powder P mainly composed of an Ir-based metal powder is formed by pressing or the like to form a compact 140, which is sintered in a sintering furnace FS as shown in FIG. As a result, an example of a chip 150 is shown. Further, as shown in FIG. 4 (c), a rod-shaped powder compact 130 is formed, and this is sintered to form a rod-shaped sintered material 135. Further, as shown in FIG. It can also be cut into chips 150. In any case, the raw material powder P can be subjected to a powder decarbonization heat treatment in a reduced pressure atmosphere or a hydrogen atmosphere at a stage before molding, and decarbonization can be performed by performing sintering in a reduced pressure atmosphere or a hydrogen atmosphere. It is also possible to achieve (decarbonization sintering treatment).
[0045]
In the powder decarbonization heat treatment, the oxygen partial pressure is 2.7 × 10^-2A reduced pressure atmosphere of Pa or less or an oxygen partial pressure of 27 × 10³Pa or less and hydrogen partial pressure is 5 × 10⁴It is desirable to carry out at a temperature of 1200 to 2000 ° C. in a hydrogen atmosphere of Pa or higher. When performed in a reduced pressure atmosphere, the oxygen partial pressure is 2.7 × 10^-2If it exceeds Pa, the Ir component in the raw material powder may be reduced by oxidation, volatilization or the like. The oxygen partial pressure is more desirably 1.4 × 10.^-2It is good to set it as Pa or less. Moreover, when performing in a hydrogen atmosphere, the hydrogen partial pressure is 5 × 10 5.⁴If it is less than Pa, a sufficient decarbonizing effect cannot be expected. The hydrogen partial pressure is 1.2 × 10⁵When Pa is exceeded, the processing cost including equipment may increase. The hydrogen partial pressure is more desirably set higher than the atmospheric pressure. In this way, hydrogen in the furnace always flows in the direction of leaking out of the furnace, so that fluctuations in the furnace atmosphere as the process proceeds can be suppressed. Further, if the temperature of the powder decarbonizing heat treatment is less than 1200 ° C., a sufficient decarbonizing effect cannot be achieved. On the other hand, when the temperature exceeds 2000 ° C., it becomes difficult to soften or melt the Ir-based metal, and the powder particles are welded and aggregated and cannot be used for molding. The temperature of the powder decarbonization heat treatment is more desirably adjusted in the range of 1400 to 1900 ° C.
[0046]
Further, the decarbonization sintering treatment has an oxygen partial pressure of 2.7 × 10.^-2A reduced pressure atmosphere of Pa or less or an oxygen partial pressure of 27 × 10³Pa or less and hydrogen partial pressure is 5 × 10⁴It is desirable to carry out in the range of 1400-2000 degreeC in hydrogen atmosphere of Pa or more. When sintering in a reduced pressure atmosphere, the oxygen partial pressure is 2.7 × 10^-2If it exceeds Pa, the Ir component in the raw material powder may be reduced by oxidation, volatilization or the like. The oxygen partial pressure is more desirably 1.4 × 10.^-2It is good to set it as Pa or less. Moreover, when performing in a hydrogen atmosphere, the hydrogen partial pressure is 5 × 10 5.⁴If it is less than Pa, a sufficient decarbonizing effect cannot be expected, and the hydrogen partial pressure is 1.2 × 10.⁵When Pa is exceeded, the processing cost including equipment may increase. The hydrogen partial pressure is more desirably set higher than the atmospheric pressure. In this way, hydrogen in the furnace always flows in the direction of leaking out of the furnace, so that fluctuations in the furnace atmosphere as the process proceeds can be suppressed. Next, when the temperature of the decarbonization sintering process is less than 1400 ° C., sintering is impossible and a sufficient decarbonization effect may not always be achieved. On the other hand, if the temperature exceeds 2000 ° C., it is difficult to avoid the softening or melting of the Ir-based metal, resulting in welding or deformation of the resulting chip or chip material. More desirably, the temperature of the decarbonization sintering treatment is adjusted in the range of 1400 to 1950 ° C. The holding time at the decarbonizing heat treatment temperature is preferably in the range of 0.5 to 5 hours. If the holding time is less than 0.5 hours, a sufficient decarbonizing effect cannot be expected, and if it exceeds 5 hours, the production efficiency is lowered due to the longer sintering time. In addition, when an organic binder is added to the powder, diffusion of the carbon component into the Ir metal constituting the powder may progress, leading to an increase in the carbon content in the metal. Furthermore, the crystal grains of the sintered body may grow excessively by Ostwald, leading to insufficient strength.
[0047]
Next, an example of a welding method will be described. In addition, since the welding method for forming said ignition parts 31 and 32 is substantially the same, it demonstrates in detail below centering on the ignition part 31 by the side of the center electrode 3. FIG. As shown in FIG. 9 (a), the tip surface 3s of the center electrode 3 is used as a chip fixing surface, and a chip 31 'is overlapped thereon to form an overlapping assembly 70. With respect to the overlapping assembly 70, An all-around laser welded portion 10 that extends over the tip 31 ′ and the tip-fixed surface is formed along the tip outer peripheral surface. At this time, as a laser welding light source, a pulsed laser light source (for example, a YAG laser light source) having an energy per pulse of 1.5 to 6 J, a pulse length of 1 to 10 milliseconds, and a pulse generation frequency of 2 to 20 pulses / second. ) 50 is used. As shown in FIG. 6, the all-around laser welded portion 10 formed using the above-described size tip 31 ′ is flat in the overlapping direction of the tip 31 ′ and the tip-fixed surface. The maximum outer peripheral dimension dmax when viewed is less than 2.0 mm, and does not reach the discharge surface 31a in the thickness direction of the chip 31 ′. In addition, it is desirable that the outer peripheral maximum dimension dmax is 0.4 mm or more. If dmax is less than 0.4 mm, it is difficult to form a uniform weld even if the laser beam is considerably reduced, and this may hinder the formation of a normal ignition part.
[0048]
The above-mentioned various heat-resistant alloys used as electrode materials have a low thermal conductivity of about 30 W / m · K or less at 800 ° C., and have the property of being easily heated during laser welding. However, by using a laser beam having an energy per pulse of 1.5 to 6 J and a pulse length of 1 to 10 milliseconds, 2 to 20 pulses, which is a much higher pulse generation frequency than the conventional method. / Sec can be used to form the all-around welded portion 10 with high uniformity. Specifically, the minimum width lmin and the maximum width lmax of the all-around laser welded portion 10 in the direction in which the chip is overlapped with the chip fixing surface, in this case, in the direction of the center axis O of the chip 31 ′ or the center electrode 3 The ratio lmin / lmax can be 0.7 or more (preferably 0.9 or more).
[0049]
FIG. 8A shows a developed view of the projected image when the laser weld 10 is projected onto a cylindrical surface coaxial with the central axis O (having a diameter equal to the outer diameter of the discharge surface 31a). The above lmin and lmax are shown. Further, in the direction of the central axis O, the minimum distance hmin from the outer edge TL of the discharge surface 31a to the edge closer to the discharge surface 31a of the laser weld 10 is TL to the discharge surface 31a of the laser weld 10. It is desirable that hmin / hav be 0.7 or more similarly, assuming that the distance to the integration center line UCm of each edge on the near side is the average ignition portion thickness hav. As a result, for example, at the position where hmin is reached (in many cases, the position where the welded portion 10 is the widest (lmax)), the precious metal ignition portion is only slightly consumed and exposure to the discharge surface of the welded portion occurs, and ignition occurs. Problems that cause mistakes and the like are effectively prevented.
[0050]
In addition, the ignition portion 31 fixed to the tip surface of the center electrode 3 has a markedly improved resistance to oxidation by reducing the carbon content level in the Ir-based metal as described above. Therefore, as a mode in which the temperature is more likely to rise, even if the thickness of the central electrode 3 in the axial direction is increased to about 0.4 to 1.0 mm, oxidation consumption is effectively suppressed, and consequently the life of the ignition part 31 is increased. Can be stretched. In this case, the thickness of the ignition part 31 is represented by hmin in FIG.
[0051]
Next, as shown in FIG. 7A, the welded portion 10 has a donut-like shape when both side portions sandwiching the central axis O of the welded portion 10 are not connected in the radial direction (in this case, the welded portion 10 has a donut shape). ) Can measure the chip thickness tc from the axial cross section after welding. However, as shown in FIG. 8B, when the welded portions on both sides are connected in the radial direction (the welded portion 10 has a disk shape), as shown in FIG. A reference line CM is set at an intermediate position between the integral center lines UCm and LCm on both side edges of the part 10 and the distance H between the reference line CM and the outer edge TL of the discharge surface 31a is estimated as the chip thickness tc.
[0052]
Here, the tip diameter dc is appropriately set in the range of 0.4 to 1.2 mm according to the durability and ignition performance required for the spark plug. However, since the tip is generally expensive, the amount of use thereof is as much as possible. In order to reduce the thickness, the thickness tc is preferably set to a relatively small value of 0.5 to 1.5 mm as described above. The average ignition part thickness hav is preferably 0.2 to 1.0 mm. The reason for this is that when hav is less than 0.2 mm, the precious metal ignition part is only slightly consumed and exposure to the discharge surface of the welded part occurs, which may reduce the durability of the spark plug. On the other hand, if hav exceeds 1.0 mm, when the life of the spark plug is reached due to the gap expansion, the spark plug is replaced with a considerable amount of chips remaining, which increases waste. is there. Assuming this, for example, when the chip thickness tc can be confirmed even after welding, the ratio hav / tc to the average ignition portion thickness hav and the chip thickness tc is approximately 0.13 to 2.0. It can be said that it is desirable. However, as shown in FIG. 8B, in the case where the edge on the side opposite to the discharge surface of the tip 31 ′ is located so as to protrude to the base end side from the welded portion 10, hav / tc is Even if it is 0.2 to 1.0, regardless of the arrival of the lifetime, there will be a problem that all the protruding portions are wasted.
[0053]
On the other hand, in order to improve the peel resistance from the center electrode of the tip, it is desirable that the distance between UCm and LCm is the average weld width lav and that lav is 0.4 mm or more. From the same point of view, when the both side portions sandwiching the central axis of the welded portion are not connected in the radial direction as shown in FIG. 8C, tc-hav is preferably 0.2 mm or more. On the other hand, as shown in FIG. 8D, when both side portions in the radial direction are connected to each other, on the joint surface between the welded portion 10 and the ignition portion 31 from the discharge surface 31a in the axial direction of the center electrode 3. Tc3−tc2 where tc2 is the dimension up to the position where the weld 10 is the thinnest and tc3 is the dimension until the position where the weld 10 is the thinnest on the joint surface between the weld 10 and the center electrode 3 It is desirable that it be 0.2 mm or more.
[0054]
When the chip 31 ′ is formed in a disk shape as in the embodiment, as shown in FIG. 9B, the overlapping assembly 70 of the chip 31 and the center electrode 3 is replaced with a laser light source 50. On the other hand, the method of irradiating the pulsed laser beam LB toward the outer peripheral surface of the chip while rotating relatively around the chip center axis O is a reasonable method for uniformly forming the entire laser welding part as described above. Is. In this case, only one of the assembly 70 or the laser light source 50 may be rotated, or both may be rotated (for example, in directions opposite to each other).
[0055]
In this case, it is desirable to adjust the rotational speed as follows. First, the relative rotational speed of the overlapping assembly 70 and the laser light source 50 is preferably 10 rpm or more (preferably 12 rpm or more) when only one laser light source 50 is used. In order to perform all-around welding, the assembly 70 and the laser light source 50 must be rotated relative to each other for at least one turn. When the relative rotation speed is less than 10 rpm, the welding time for one turn and therefore one piece is required. In some cases, the piece time for manufacturing the spark plug becomes longer and does not necessarily give an advantage over the conventional method.
[0056]
On the other hand, although it is the upper limit value of the relative rotational speed, when the overlapping assembly 70 is rotated, in order to prevent deformation and scattering due to the centrifugal force of the molten metal generated during welding, the maximum is about 240 rpm (four rotations per second). It is better to keep it on. On the other hand, the centrifugal force applied to the welded portion 10 increases substantially in proportion to the outer peripheral maximum dimension dmax, and is considered to increase substantially in proportion to the square of the rotational angular velocity. The rotational speed of the overlay assembly 70 is:
Vmax = 5π (2 / dmax) 1/2 (unit: radians / second) (1)
It is desirable to set it below the value Vmax determined by (however, the unit of dmax is mm).
[0057]
According to the above formula (1), Vmax can be increased as dmax decreases. For example, when dmax = 2.0 mm, Vmax is approximately 150 rpm, but when dmax = 1.5 mm, Vmax = 173 rpm, and when dmax = 0.7 mm, Vmax = 253 rpm. Further, when both the assembly 70 and the laser light source 50 are rotated to form an intended relative rotational speed, if the rotational speed on the center electrode side can be increased, the amount of the rotational speed must be slightly complicated. The rotational speed of the mechanism on the laser light source 50 side that is not present can be reduced (or non-rotated), and as a result, the mechanism on the laser light source 50 side can be simplified or the rotation burden can be reduced.
[0058]
According to the formula (1), when dmax <0.78 mm, Vmax is larger than the above-described desirable upper limit of 240 rpm. However, according to the study of the present inventor, even in the case of the small-diameter chip as described above, the welded portion 10 that is completely continuous in the circumferential direction is formed using a laser beam having an energy of 1.5 to 6 J per pulse. In this case, at least five pulse weld beads must be formed for one turn. 240 rpm is 4 revolutions per second, and even when 20 pulses / second, which is the upper limit value of the pulse generation frequency described above, is used, 5 pulses can be finally hit per second. Therefore, if the rotational speed becomes higher than this, the weld bead 10d is intermittently formed in the circumferential direction, and it may be impossible to complete the formation of the pulse weld bead continuous in the circumferential direction during one rotation. Therefore, from the viewpoint of the formula (1), even if a rotational speed exceeding 240 rpm is possible, it can be said that it is advantageous to keep the rotational speed at about 240 rpm. However, when it is permitted to perform welding after the second rotation, the welded portion 10 that is continuous in the circumferential direction can be formed by shifting the formation angle phase of the weld bead 10d.
[0059]
On the other hand, when the laser light source 50 side is rotated, the rotation speed is preferably set to 90 rpm or less in order to suppress the occurrence of laser beam irradiation position blurring and the like.
[0060]
When the thickness tc of the tip 31 'is small as described above, it is effective to irradiate the pulsed laser beam LB obliquely from above in order to form the welded portion 10 so as not to reach the discharge surface 31a. Specifically, as shown in FIGS. 9B and 9C, the intersection edge Q between the chip fixed surface (in this case, the front end surface of the center electrode 3) and the chip outer peripheral surface within the spot of the laser beam LB. It is desirable to irradiate the overlapping assembly 70 with the pulsed laser light LB so that the irradiation angle θ with respect to the chip adherence surface is in the range of 0 ° to 60 ° (for example, 45 °).
[0061]
In order to facilitate positioning and fixing of the chip 31 ′ to the chip fixing surface, as shown in FIG. 9D, a positioning recess 3 a corresponding to the outer shape of the chip is formed on the chip fixing surface, and the positioning is performed. It is also possible to make the overlapping assembly 70 by fitting the chip 31 ′ into the recess 3 a. In this case, in order to perform welding joint reliably, it is preferable to irradiate the pulsed laser beam LB toward the intersection edge Q between the opening peripheral edge of the recess 3a and the chip outer peripheral surface.
[0062]
Next, Ir-based metal chips or chip materials that have been kept at a high temperature for a long time due to a decarbonizing heat treatment often have crystal grains that are coarsened due to crystal growth. In this case, when the crystal grains are excessively coarsened, when the ignition portion 31 is formed by joining the tip 31 ′ by laser welding in which rapid heating and rapid cooling are repeated, for example, as shown in FIG. There is a case where the chip 31 ′ is destroyed due to a boundary crack or the like. Therefore, in consideration of this, it is desirable that the average particle diameter of the Ir-based metal constituting the ignition portion 31 (and thus the tip 31 ') be 100 μm or less. An average particle size of less than 5 μm is often not practical because it is difficult to realize due to restrictions in the manufacturing process, or even if it can be realized, the cost is extremely high. Note that in this specification, two parallel lines that are in contact with the outer shape line and do not cross the crystal grain with respect to the outer shape line of the crystal grain observed on the polished surface of the material, Is defined as the maximum value of the distance between the parallel lines when variously drawn while changing the positional relationship, and the average grain size means the average value of the grain sizes of the many crystal grains thus obtained And
[0063]
As a specific method for crystal grain refinement, there is a method of processing and heat-treating the chip or chip material after the decarbonization heat treatment. For example, in the case of a plate material, it is processed by rolling or the like to a size (plate thickness tP) slightly larger than a final desired size (for example, plate thickness tF), and then decarbonized heat treatment is performed. As a result, the crystal grains become coarse, but by reworking them again, for example, by hot rolling as shown in FIG. 5, the so-called dynamic recrystallization phenomenon is used to refine the grains. Can be achieved. If the desired dimensions (for example, plate thickness tF) are finally obtained by this processing, it is more efficient. On the other hand, defects may be introduced into the chip or the chip material by cold or warm working, and the defects may be annealed to be recovered and recrystallized to refine crystal grains.
[0064]
  In addition, the material constituting the chip is a group 3A (so-called rare earth element) of the periodic table of elements.OrOxides of metal elements belonging to Group 4A (Ti, Zr, Hf) (including complex oxides)One ofIn the range of 0.1 to 15% by weight. As a result, since the oxide particles pin the crystal grain boundaries, the crystal grain growth during the decarbonization heat treatment (or during the decarbonization sintering process) is suppressed, and the coarsening of the crystal grains as described above is prevented. Can do. Further, consumption due to oxidation and volatilization of the additive metal element components, particularly Ir, Ru, and Re, is further effectively suppressed. When the content of the oxide is less than 0.1% by weight, the effect of suppressing the coarsening of grains by the addition of the oxide or the effect of preventing the oxidation and volatilization of the added metal element component may not be sufficiently expected. On the other hand, if the oxide content exceeds 15% by weight, the thermal shock resistance of the chip may be impaired. As the oxide, Y₂O₃Is preferably used, but in addition to this, La₂O₃, ThO₂, ZrO₂Etc. can be preferably used. In addition to oxides, inorganic material particles such as carbides, nitrides and borides can also be included. In this case, the carbon content in the Ir-based metal phase forming the matrix of the inorganic material particles is 40 ppm or less. It needs to be.
[0065]
Next, in the Ir-based metal constituting the ignition parts 31 and 32, when the concentration distribution of the added metal element component has a stripe-like density, as shown in FIG. The ignition parts 31 and 32 can be formed so that the direction is substantially parallel to, for example, the voltage application direction (that is, the discharge direction) in the ignition parts 31 and 32 (hereinafter referred to as a parallel mode). According to this, the following effects are achieved.
{Circle around (1)} When a stripe-like density distribution occurs, the directivity of the alloy crystal orientation tends to occur in the direction of the density stripe J. For example, regions having a large concentration difference of the additive metal element component also have a difference in thermal expansion coefficient, and when the thermal cycle is repeated in the ignition parts 31 and 32, the ignition parts 31 and 32 are caused by peeling along the light and shade stripe J. May wear out. It is also conceivable that peeling progresses due to local corrosion near the boundary of the light and shade stripe J. However, in any case, as shown in FIG. 2 (d), this separation occurs in the voltage application direction which is the direction of the gray stripe J in the parallel mode, that is, in the interval direction of the spark discharge gap g. The alloy crystals of the ignition portions 31 and 32 are relatively easy to maintain the dimension in the gap interval direction. Accordingly, there is an advantage that the spark discharge gap g is unlikely to change even if a certain amount of wear proceeds. In addition, if the alloy crystal structure extending in the direction of the light and shade stripe J is not in the form of a plate but in the form of a fiber, it can be said that it is more advantageous because the progress of peeling becomes slow.
[0066]
(2) In the case of a so-called parallel type spark plug in which the side surface of the ground electrode is opposed to the front end surface of the center electrode, as shown in FIG. The directions are matched, and the orientation of the alloy crystal is easily aligned in this direction. As a result, the ignition part 31 has good heat conductivity in the axial direction of the center electrode 3 and contributes to the improvement of the heat extraction characteristics of the ignition part. In addition, the ignition portion 31 is formed by cutting a rod-shaped alloy (which can be easily manufactured by rotary forging or wire drawing) into a ring by electrical discharge machining or the like, in which fibrous crystal grains are grown along with the above-described light and dark stripes in the longitudinal direction. Chips can be manufactured. For example, waste is hardly generated during chip manufacturing, and the manufacturing yield can be improved.
[0067]
On the other hand, as shown in FIG. 2 (c), the firing portions 31, 32 are formed so that the direction of the gray stripe J is substantially orthogonal to the voltage application direction (ie, the discharge direction) in the firing portions 31, 32, for example. (Hereinafter referred to as an orthogonal aspect). In this case, although the effect peculiar to the said parallel aspect cannot be expected, the consumption itself of the ignition parts 31 and 32 is suppressed instead, and the increase suppression effect of a spark discharge gap width improves further. That is, since the direction of the gray stripe J intersects with the direction in which the discharge voltage is applied, the boundary of the gray stripe J is hardly exposed on the ignition surface 31a. As a result, it is presumed that peeling due to local corrosion near the boundary between light and shade stripes is suppressed, and that the ignition parts 31 and 32 are less likely to progress.
[0068]
[Experimental example]
In order to confirm the effect of the present invention, the following experiment was conducted.
(Experimental example 1)
An alloy having a composition of Ir-5 wt% Pt was prepared by blending and dissolving a predetermined amount of Pt metal (carbon content 90 ppm) to Ir metal (carbon content 120 ppm). This alloy was hot-rolled at a temperature of 700 ° C. and processed into a plate having a thickness of 0.5 mm. Next, the obtained plate material was hot punched (processing temperature 1700 ° C.) to obtain a disk-shaped chip having a diameter of 0.7 mm and a thickness of 0.5 mm. The carbon content of the chip at this stage was about 100 ppm. The carbon content in the Ir metal was measured by analyzing the combustion gas by infrared absorption while burning the sample in an oxygen stream. The analytical apparatus used was Horiba Seisakusho Co., Ltd., EMIA-510 / 520, and the calibration curve was prepared using the JSS1202-2 low carbon steel standard sample of the Japan Iron and Steel Institute. The measurement was performed in a state of being enclosed in a Sn capsule in order to prevent oxidation during heating of the chip sample (the capsule weight is about 1 g with respect to the chip weight of about 0.4 g). In addition, as the Sn capsule, a carbon capsule whose carbon content was previously found to be 16 ppm or less was used.
[0069]
Subsequently, the above chip was subjected to a decarbonizing heat treatment under various conditions, and the carbon content in the chip after the heat treatment was analyzed by the same method as described above. In FIG. 10, various heat treatment temperatures were set within a range of 1040 to 2100 ° C., and various heat treatment times were set within a range of 1 to 5 hours. Also, the heat treatment is performed in the furnace with a degree of vacuum of 7.0 × 10.^-3After exhausting to Pa, hydrogen gas (purity 99.99%) was introduced, and the hydrogen gas partial pressure was adjusted to atmospheric pressure (1.06 × 10 6 by adjusting the flow rate thereof.⁵Pa). The results are shown in FIG.
[0070]
That is, the carbon content decreases as the heat treatment temperature TC (° C.) becomes higher and as the heat treatment time th (hour) becomes longer. In particular, the carbon content under the condition that TC × th satisfies 1950 or more. It can be seen that is reduced to 10 ppm or less. Note that the chip was deformed under the condition that the heat treatment temperature TC exceeded 2000 ° C.
[0071]
The chips after the above-described various treatments were held at 1050 ° C. for 20 hours in the air, and then the oxidation resistance was evaluated by measuring the weight loss of each test piece. The result is shown in FIG. That is, the chip having a carbon content of 40 ppm or less by adjusting the conditions of the decarbonizing heat treatment has greatly improved oxidation resistance, and particularly good results are obtained when the carbon content is 20 ppm or less or 10 ppm or less. I understand that.
[0072]
Next, in FIG. 12, the heat treatment temperature is fixed at 1800 ° C., the heat treatment time is fixedly set at 5 hours, and the oxygen partial pressure measured with a mass flow meter is adjusted to 0.7 to 27 by adjusting the degree of vacuum in the furnace. × 10^-2The results are shown in the case of decarbonizing heat treatment when the hydrogen gas partial pressure is adjusted to Pa and hydrogen gas partial pressure is set to atmospheric pressure, and when hydrogen gas is not introduced. The graph in the figure shows the evaluation results of the oxidation resistance performed by the same method as described above, and the table shows the analytical value of the carbon content in the chip after the heat treatment. In the case of introducing hydrogen, decarbonization progresses well even if the oxygen partial pressure is slightly increased, and the final carbon content level is also low. Correspondingly, it can be seen that the lower the ultimate carbon content level, the better the oxidation resistance.
[0073]
(Experimental example 2)
By blending and dissolving a predetermined amount of Pt metal (carbon content 90 ppm) or Rh metal (carbon content 80 ppm) to Ir metal (carbon content 120 ppm), Ir-5 wt% Pt, Ir-10 weight An alloy having a composition of% Rh and Ir-20 wt% Rh was prepared. In addition, an appropriate amount of graphite powder was blended at the time of dissolution so that the carbon content in the obtained ingot would be various values. This alloy was processed into a chip under the same conditions as in Experimental Example 1 (a disk shape having a diameter of 0.7 mm and a thickness of 0.5 mm), and the carbon content of the chip was measured. It was.
[0074]
Subsequently, the chip was subjected to decarbonization heat treatment with the heat treatment temperature fixed at 1800 ° C. and the heat treatment time fixed at 5 hours. In the heat treatment, the degree of vacuum in the furnace is 1.4 × 10.^-2After exhausting to Pa, hydrogen gas (purity 99.99%) was introduced, and the hydrogen gas partial pressure was adjusted to atmospheric pressure by adjusting the flow rate. When the carbon content in the chip after heat treatment was analyzed by the same method as described above, the carbon content was various values of 0.5 to 50 ppm.
[0075]
Using the above chip, the sparking portion 31 and the opposing firing portion 32 of the spark plug 100 shown in FIG. 1 are formed so that the spark discharge gap g has a width of 1.1 mm, and the spark wear resistance by the actual machine A test was conducted. That is, the plug was attached to a 6-cylinder gasoline engine (DOHC, displacement of 2500 cc), the throttle was fully opened, and the engine was operated for 200 hours at an engine speed of 5500 rpm, and the amount of expansion of the spark discharge gap g was measured. FIG. 13 is a graph plotting the gap increase after endurance against the carbon content in the chip. Even when the chip is formed with any alloy, when the carbon content is 40 ppm or less, the gap increase is small and the oxidation resistance is remarkably improved. Especially when the carbon content is 20 ppm or less or 10 ppm or less, It can be seen that very good results are obtained.
[0076]
(Experimental example 3)
A base metal alloy having a composition of Ir-5 wt% Pt was prepared by blending and dissolving a predetermined amount of Ir metal (carbon content 120 ppm) and Pt metal (carbon content 90 ppm). And it was pulverized so that it might become an average particle diameter of 3 micrometers by ball-milling (solvent: ethanol) using a pot. In addition, Y having an average particle diameter of 7 μm₂O₃After blending 1.7% by weight of the powder, water as a solvent and polyvinyl alcohol (PVA) as a binder are added and mixed, and then dried to form a molding powder, which is molded into a predetermined disc shape. Then, a metal-oxide composite material chip was prepared by sintering. Sintering was performed at 1950 ° C. for 1 hour in an atmospheric hydrogen atmosphere. The obtained sintered material chip has a disk shape with a diameter of 0.7 mm and a thickness of 0.5 mm.
[0077]
For this chip, the heat treatment temperature was various values of 1000 to 2000 ° C. (the temperature was raised from room temperature to each heat treatment temperature in 1 hour), the heat treatment time was fixed at 10 hours, and the vacuum in the furnace Degree 1.4 × 10^-2The decarbonization heat treatment was performed in an atmosphere adjusted to Pa and further introduced with hydrogen gas and the partial pressure of hydrogen gas being atmospheric pressure, and the oxidation resistance was evaluated by the same method as in Example 1. The graph in FIG. 14 shows the evaluation result, and the table shows the analysis value of the carbon content after heat treatment in the chip. That is, the chip having a carbon content of 40 ppm or less by adjusting the conditions of the decarbonizing heat treatment has greatly improved oxidation resistance, and particularly good results are obtained when the carbon content is 20 ppm or less or 10 ppm or less. I understand that.
[0078]
(Example 4)
A base metal alloy having a composition of Ir-5 wt% Pt was prepared by blending and dissolving a predetermined amount of Ir metal (carbon content: 120 ppm) and Pt metal (carbon content: 90 ppm). And it was pulverized so that it might become an average particle diameter of 3 micrometers by ball-milling (solvent: ethanol) using a pot. Next, with respect to this powder, the heat treatment temperature is set to various values of 400 to 900 ° C., the heat treatment time is fixedly set to 10 hours, and the degree of vacuum in the furnace is set to 1.4 × 10 6.^-2The powder was decarburized and heat-treated in an atmosphere adjusted to Pa and further introduced with hydrogen gas to make the hydrogen gas partial pressure atmospheric pressure. Then, water as a solvent and polyvinyl alcohol (PVA) as a binder are added to the treated powder and mixed, then dried to form a green powder for molding, which is molded into a predetermined disc shape and sintered. As a result, a chip having a composition of Ir-5 wt% Pt was produced. Sintering was performed at 1950 ° C. for 1 hour in an atmospheric hydrogen atmosphere. The obtained sintered material chip has a disk shape with a diameter of 0.7 mm and a thickness of 0.5 mm.
[0079]
The obtained chip was evaluated for oxidation resistance by the same method as in Example 1. The graph in FIG. 15 shows the evaluation result, and the table shows the analysis value of the carbon content after heat treatment in the chip. That is, the chip having a carbon content of 40 ppm or less by adjusting the conditions of the decarbonizing heat treatment has greatly improved oxidation resistance, and particularly good results are obtained when the carbon content is 20 ppm or less or 10 ppm or less. I understand that.
[Brief description of the drawings]
FIG. 1 is a partial front sectional view showing an embodiment of a spark plug according to the present invention.
FIG. 2 is an enlarged sectional view showing the main part.
FIG. 3 is a schematic diagram showing an example of a decarbonizing heat treatment method for a chip for forming an ignition part or a chip material.
FIG. 4 is a schematic view showing an example of a manufacturing method of a chip or chip material that performs a decarbonized sintering process.
FIG. 5 is a schematic diagram showing a process of refining the structure of a chip material by a thermomechanical treatment.
6 is an enlarged perspective view and a plan view of the front end side of the center electrode front end portion of the spark plug of FIG.
7 is a longitudinal sectional view of FIG. 2 and a longitudinal sectional view of a modified example thereof.
FIG. 8 is a development explanatory view of an all-around welded portion.
9 is a manufacturing process explanatory diagram of a center electrode side ignition portion of the spark plug of FIG. 1;
10 is a graph showing the relationship between decarbonization heat treatment conditions and the carbon content in the chip after treatment in Experimental Example 1. FIG.
FIG. 11 is a diagram showing the decarbonization heat treatment conditions, the carbon content in the chip after the treatment, and the results of the corresponding oxidation resistance test.
FIG. 12 is a diagram showing the atmosphere of the decarbonizing heat treatment, the carbon content in the chip after the treatment, and the results of the corresponding oxidation resistance test.
13 is a graph showing the results of an actual machine durability test of Experimental Example 2. FIG.
14 is a diagram showing the atmosphere of decarbonization heat treatment, the carbon content in the chip after the treatment, and the results of the corresponding oxidation resistance test in Experimental Example 3. FIG.
15 is a graph showing the atmosphere of powder decarbonization heat treatment, the carbon content in the chip after the treatment, and the results of the corresponding oxidation resistance test in Experimental Example 3. FIG.
[Explanation of symbols]
1 metal shell
2 Insulator
3 Center electrode
4 Ground electrode
31 ignition part
31 'chip
32 Opposing firing parts
g Spark discharge gap

Claims (17)

A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, a ground electrode disposed so as to face the center electrode, and the center electrode and the ground An ignition part fixed to at least one of the electrodes and forming a spark discharge gap,
The spark plug is composed of an Ir-based metal whose main component is Ir and a carbon content of 40 ppm or less or a composite material whose main component is the Ir-based metal.   The spark plug according to claim 1, wherein a carbon content in the Ir-based metal is 20 ppm or less.   The spark plug according to claim 1, wherein a carbon content in the Ir-based metal is 10 ppm or less.   The spark plug according to any one of claims 1 to 3, wherein the Ir-based metal contains at least one of Pt, Rh, Ru, Re, Nb, and Hf as an additive metal element component.   The spark plug according to claim 4, wherein the Ir-based metal contains Pt in a range of 1 to 50% by weight.   The spark plug according to claim 4 or 5, wherein the Ir-based metal has an Ir content of 85 wt% or more.   The spark plug according to claim 6, wherein the Ir-based metal contains Pt in a range of 1 to 15% by weight. The ignition part contains any of oxides (including complex oxides) of metal elements belonging to Group 3A or Group 4A of the Periodic Table of Elements within a range of 0.1 to 15% by weight. Item 8. The spark plug according to any one of Items 1 to 7.   The spark plug according to any one of claims 1 to 8, wherein an average particle diameter of a material constituting the ignition portion is 5 to 100 µm. In order to manufacture the spark plug according to any one of claims 1 to 9,
At least one of said center electrode and said ground electrode at a position corresponding to the spark discharge gap, a main component Ir, and the carbon content is mainly the following Ir-based metal or the Ir-based metal 40ppm composite By welding a tip made of material, and forming an ignition portion based on the tip ,
Prior to the welding, the tip or the tip material for producing the tip is subjected to a decarbonization heat treatment in a reduced-pressure atmosphere or a hydrogen atmosphere in order to remove a carbon component in the Ir-based metal,
The atmosphere of the decarburization heat treatment, the oxygen partial pressure of 2.7 × ¹⁰ -2 Pa or less of vacuum atmosphere, or an oxygen partial pressure of 2.7 × ¹⁰ -2 A is Pa or less hydrogen partial pressure 5 × 10 ⁴ A hydrogen atmosphere of Pa or higher,
The spark plug manufacturing method is characterized in that a temperature of the decarbonizing heat treatment is adjusted in a range of 1610 ° C. or more and 2000 ° C. or less . The spark plug manufacturing method according to claim 10, wherein a carbon content of the chip or the chip material is 120 ppm or less before the decarbonizing heat treatment . The spark plug manufacturing method according to claim 10 or 11, wherein the chip material after the decarbonizing heat treatment is processed and heat-treated for crystal grain refinement . The spark plug manufacturing method according to any one of claims 10 to 12, wherein the chip material is a melting material manufactured by melting and solidifying the Ir-based metal raw material . The spark according to any one of claims 10 to 12, wherein the chip or the chip material is obtained by forming a raw material powder mainly composed of an Ir-based metal into a predetermined shape and then sintering the powder. Plug manufacturing method. The spark plug manufacturing method according to claim 14, wherein the raw material powder is subjected to powder decarbonization heat treatment in a reduced pressure atmosphere or a hydrogen atmosphere in order to remove a carbon component before the molding . The powder decarbonization heat treatment, following the reduced-pressure atmosphere of oxygen partial pressure of 2.7 × ¹⁰ -2 Pa, or oxygen partial pressure 2.7 × ¹⁰ -2 Pa or less was hydrogen partial pressure of 5 × ¹⁰ 4 Pa The method for producing a spark plug according to claim 15, which is performed in the above hydrogen atmosphere at a temperature in the range of 1200 to 2000 ° C. The sintering is performed under a reduced pressure atmosphere having an oxygen partial pressure of 2.7 × 10 ⁻² Pa or lower, or an oxygen partial pressure of 2.7 × 10 ⁻² Pa or lower and a hydrogen partial pressure of 5 × 10 ⁴ Pa or higher. The spark plug manufacturing method according to any one of claims 14 to 16, wherein the spark plug is performed in a hydrogen atmosphere at a temperature of 1400 to 2000 ° C for 0.5 to 5 hours .

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