JP2007227187A - Spark plug for internal combustion engine and manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug comprising an ignition part having a first main component of Pt and a second component of Ir, which hardly causes trouble such as cracking, peeling or dropping-out of the ignition part. <P>SOLUTION: In this spark plug, an ignition part 31 is provided at a tip of a central electrode 3, an ignition part 32 opposed to the ignition part 31 is provided at a tip of a grounding electrode 4, and the gap between both the ignition part 31 and 32 corresponds to a spark discharge gap 33. Each of the ignition parts 31 and 32 comprises Pt as the main first component and Ir as the second component. The chip-like ignition parts 31 and 32 have an average value of crystal grain orientation ratio of 0.5 or less and a Vickers hardness of 300 Hv or less by performing a predetermined heat treatment thereto after plastic working. Consequently, enlargement of grain size of the crystal grains is suppressed, whereby deterioration of the mechanical strength is suppressed, and internal cracking resulted from working distortion can be consequently solved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, as a spark plug for an internal combustion engine such as an automobile engine, for example, a tip-like ignition part made of a noble metal alloy is welded to a tip part of a center electrode or a ground electrode. As a typical method for producing the ignition part, after obtaining a rolled plate material of a noble metal alloy, a method of obtaining a relatively thin chip by punching this into a disk shape, and a rod-shaped material by hot wire drawing There is a method of obtaining a chip having a relatively large thickness by cutting the chip after obtaining the chip.

  Regardless of which method is used, the resulting chip is subject to various types of processing, particularly plastic processing, which causes processing strain (sometimes referred to as “residual stress”), and the processing is performed even after chip welding. Distortion may remain. In addition, when such processing distortion exists, there is a concern that abnormal wear of the chip, internal cracks, and the like may be caused, leading to deterioration of durability as a spark plug, bridging phenomenon of a spark discharge gap, and the like. .

Incidentally, in recent years, it has been proposed to employ a precious metal material mainly composed of iridium (Ir) as a material constituting the ignition portion. Among them, there is a technique of softening the surface layer region by annealing (heat treatment) at 900 to 1700 ° C. on a chip mainly composed of Ir (see, for example, Patent Document 1). In the technique disclosed in Patent Document 1, Ir is an excellent material in terms of spark consumption, but in view of the fact that it is likely to cause oxidation and volatilization, recrystallization of the surface layer region is promoted, Oxidation and volatilization are suppressed by increasing the particle size.
Japanese Patent Laid-Open No. 11-154583

  However, when the ignition part is made of a noble metal material whose main component is platinum (Pt), for example, the ignition part uses Pt as the main first component and iridium as the second component. In such a case, the technique disclosed in Patent Document 1 cannot be applied as it is. That is, when the ignition part uses Pt as the main first component, volatilization or the like is not a problem. However, if the crystal grain size is increased, the following various problems may occur.

  Compared to the case where the ignition part composed of crystal grains grown and coarsened is composed of crystal grains which are not coarsened, the portion where each of the crystal grains is in contact decreases, There is a problem that the mechanical strength of the ignition part itself decreases because the bonding force between the crystal grains constituting the ignition part decreases.

  In addition, when the proportion of coarse grains with large particle sizes increases in the ignition part, the path of corrosion that progresses along the boundary between the crystal grains from the surface of the ignition part (grain boundary) is simplified. Therefore, this intergranular corrosion tends to proceed to the relatively inner part of the ignition part. As intergranular corrosion progresses, the portion where the crystal grains come into contact with each other decreases in a form that is broken by the advanced corrosion, and the bonding strength between the crystal grains in the ground electrode also decreases, and the ignition part itself The problem that mechanical strength falls will be produced.

  As a result, the ignited part due to the coarsened crystal grains partially peels off the structure of the ignited part, and as a result, the ignited part falls off. In particular, in the ignition part on the side of the ground electrode that is likely to be exposed to higher temperatures, the above-mentioned problem is more likely to appear.

  Note that the above problem is not only in the case where a chip-like ignition part mainly composed of Pt is provided in the center electrode and the ground electrode, but also in the case where the ground electrode itself is composed of a material mainly composed of Pt. Can also happen.

  The present invention has been made in view of the above circumstances, and the object thereof is related to a spark plug including an ignition part or the like in which the main first component is Pt and the second component is Ir. It is an object of the present invention to provide a spark plug for an internal combustion engine and a method for manufacturing the same, which can reduce the occurrence of problems such as peeling and dropping.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

Configuration 1. The spark plug of this configuration is joined to the center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, the metal shell, and a tip portion of the center electrode A spark plug for an internal combustion engine having a spark discharge gap between the tip of the center electrode and the tip of the ground electrode,
The ignition part provided at least one of the front end portion of the center electrode and the front end portion of the ground electrode has a main first component Pt, a second component Ir, and a cross-sectional structure observed. When the two parallel lines are drawn while changing the positional relationship with the particles so as to contact the outline and do not cross the inside of the outline of the particle appearing on the cross section, When the maximum value of the distance between parallel lines is the maximum diameter dmax of the particles, and the minimum value is the minimum diameter dmin, the average value of the ratios dmin / dmax of the minimum diameter dmin to the maximum diameter dmax for each particle in a given cross section. Is 0.5 or less.

  Here, “main first component” refers to the component having the highest mass ratio in the material, and “second component” refers to the component having the second highest mass ratio in the material. (Hereinafter, the same applies to each configuration). Note that the ignition portion does not necessarily mean that the first component and the second component are included, and may contain a component not specifically defined above (for example, a third component).

  According to the above configuration 1, the ignition portion provided at least one of the tip portion of the center electrode and the tip portion of the ground electrode has the main first component as Pt and the second component as Ir. Thus, by using the noble metal alloy having a relatively high melting point as the ignition part, the consumption of the ignition part is suppressed, and thus the life is extended. By the way, the material which comprises the said ignition part is formed through plastic processing etc., and the material immediately after passing through plastic processing has comparatively high hardness. In addition, the crystal grains constituting the material have a shape deviated far from the spherical shape and oriented in a predetermined direction, and processing strain remains, resulting in abnormal chip wear and internal cracking. It can be done. In order to eliminate such processing distortion, it is conceivable to perform heat treatment. However, in the case where Pt is the main first component of the ignition part as in the present configuration 1, recrystallization is promoted when the heat treatment is performed at a high temperature for a long time, and the crystal grain size becomes large. There is concern about a decrease in mechanical strength due to interfacial corrosion. In view of this point, in the configuration 1, an ignition portion in which an increase in crystal grain size is suppressed is employed. That is, when the heat treatment is excessively performed, the crystal grain size tends to increase. In this case, the aspect ratio of the crystal grains also approaches “1”. In other words, as the cross-sectional structure along the orientation direction is observed as the heat treatment is performed, the outer shape of the particle appearing on the cross section is in contact with the outer shape line and does not cross the inside of the particle. When various parallel lines are drawn while changing the positional relationship with the particles, the maximum value of the distance between the parallel lines is the maximum diameter dmax of the particles, and the minimum value is the minimum diameter dmin. The ratio dmin / dmax of the minimum diameter dmin with respect to the maximum diameter dmax for each particle in the cross section in FIG. In this regard, in the present configuration 1, the average value of the ratio dmin / dmax of the minimum diameter dmin to the maximum diameter dmax when the cross-sectional structure along the alignment direction is observed (referred to as “alignment ratio average value” for convenience) is “0. 5 "or less. Therefore, in the ignition part of Configuration 1, it is difficult for the mechanical strength to decrease due to grain coarsening and the mechanical strength to decrease due to intergranular corrosion, and durability can be improved. In addition, the ignition part in this structure 1 may be provided as a chip | tip joined to the base material which comprises a center electrode and a ground electrode like the past, and these base materials themselves may be comprised from the said noble metal alloy.

  Configuration 2. The spark plug of this configuration is characterized in that, in the above configuration 1, the ignition part having the main first component as Pt and the second component as Ir is provided on the ground electrode side.

  When using the spark plug, the ignition part on the ground electrode side is closer to the combustion chamber of the internal combustion engine than the ignition part on the center electrode side, and is more easily exposed to high temperatures during use. On the other hand, since it is cooled to the same degree as the center electrode at low temperatures, it is in a situation where it is exposed to a severe environment with a larger temperature difference. For this reason, peeling and corrosion at the grain boundaries are likely to occur on the ground electrode side as compared with the center electrode side, which may lead to abnormal consumption and internal cracking. In this respect, since the ignition part is provided on the ground electrode side as in the above-described configuration 2, even if the ignition part is exposed to a higher temperature, a defect caused by grain boundary delamination with respect to the ignition part on the ground electrode side Can be effectively suppressed.

  Configuration 3. The spark plug of this configuration is characterized in that, in any one of the above configurations 1 and 2, the ignition part in which the main first component is Pt and the second component is Ir has a Vickers hardness of 300 Hv or less. .

  As described above, the material immediately after the plastic working has a relatively high hardness and may have a working strain remaining. On the other hand, in the said structure 3, it is set as Vickers hardness 300Hv or less by performing predetermined heat processing. For this reason, the processing distortion is eliminated, and problems such as abnormal consumption of the ignition part and internal cracks can be prevented. In addition, when the material in which the main first component is Pt and the second component is Ir exceeds the Vickers hardness of 300 Hv, it may not be sufficient to eliminate the processing strain. There is a risk of causing cracks.

  Configuration 4. The spark plug of this configuration is characterized in that, in the above configuration 3, the ignition part in which the main first component is Pt and the second component is Ir contains 5 mass% to 40 mass% of Ir. To do.

  When the Ir content is less than 5% by mass, since the hardness of the original material (immediately after the plastic working) is relatively low, even if the Vickers hardness of the configuration 3 is not more than 300 Hv, Heat treatment may not be sufficient, and processing distortion may remain in the ignition part. On the other hand, when the content of Ir exceeds 40% by mass, since the hardness of the original material (immediately after the plastic working) is relatively high, when trying to satisfy the requirement of Vickers hardness of 300 Hv or less in the above configuration 3, Too much heat treatment. For this reason, recrystallization is promoted, and there is a concern that the mechanical strength is lowered due to the coarsening of crystal grains and the mechanical strength is lowered due to intergranular corrosion.

  In this regard, according to the present configuration 4, the content of Ir is set within an appropriate range, and the operational effects of the above-described configuration 3 are more reliably achieved.

  The spark plug described above can be manufactured by various methods. For example, the spark plug can also be manufactured by a method as shown in the following configuration 5.

Configuration 5. The spark plug manufacturing method of the present configuration includes a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the metal shell. A ground electrode disposed to face the tip of the center electrode, and has a spark discharge gap between the tip of the center electrode and the tip of the ground electrode, and the ground electrode is a main first component. Is set to Pt and the second component is set to Ir, or the tip portion of the ground electrode is provided with a chip-like ignition portion having the main first component set to Pt and the second component set to Ir. A method for producing a spark plug for an internal combustion engine, comprising:
A grounding electrode having the main first component as Pt and the second component as Ir, or a tip-like ignition part having the main component as Pt and the second component as Ir is provided at the tip. A metal shell assembly is obtained by welding the ground electrode to the metal shell, and then a heat treatment process is performed in which the metal shell assembly is subjected to heat treatment.

  According to the above-described configuration 5, the metal shell assembly is obtained by welding the ground electrode whose main first component is Pt and whose second component is Ir to the metal shell (note that the spark plug including the assembly is provided). Is suitably used, for example, in a gas engine or the like placed under more severe conditions). Alternatively, a metal shell assembly is obtained by welding a ground electrode comprising a tip-shaped ignition portion having a first first component of Pt and a second component of Ir at the tip portion to the metal shell ( The spark plug provided with the assembly is preferably used for a general gasoline engine, for example). Thereafter, the metal shell assembly is subjected to heat treatment in a heat treatment step. By this heat treatment, the processing distortion of the ignition part in which the first component is Pt and the second component is Ir is eliminated, and problems such as internal cracks in the ignition part can be prevented.

  In addition, “a primary ignition component having Pt as the first first component and Ir being the second component, or a tip-like ignition having the first component as Pt and the second component as Ir at the tip. The ground electrode provided with a portion has two parallel lines in contact with the outer shape line of the particle appearing on the cross-section when the cross-sectional structure is observed, so as not to cross the particle, When various values are drawn while changing the positional relationship with the particles, the maximum value of the distance between the parallel lines is the maximum diameter dmax of the particles, and the minimum value is the minimum diameter dmin. The heat treatment may be performed so that the average value of the ratio dmin / dmax of the minimum diameter dmin to the maximum diameter dmax is 0.5 or less. Thus, the mechanical strength reduction can be more reliably suppressed by appropriately performing the heat treatment.

  By the way, the case where the aspect of the ground electrode is the former, that is, the case where the metal shell assembly is obtained by welding the ground electrode whose main first component is Pt and whose second component is Ir to the metal shell is mentioned. As a result, the metal shell is often made of a base metal, and welding between the metal shell, which is the base metal, and a ground electrode made of a noble metal alloy may not always be sufficient. In this respect, since heat treatment is performed after welding as in Configuration 4, the familiarity of the welded portion between the metal shell and the ground electrode is further improved, and as a result, the joint strength between the two is also improved. Can do.

  Furthermore, it can also be set as the spark plug shown in the following structure 6.

Configuration 6. The spark plug of this configuration includes a center electrode having an inner ignition portion, and a ground electrode welded with a chip-like outer ignition portion forming a spark discharge gap between the center electrode, and the outer ignition portion is A spark plug for an internal combustion engine in which the main first component is Pt and the second component is Ir;
The outer ignition portion is formed through plastic working, and when the cross-sectional structure is observed, two parallel lines are formed so that the outer shape of the particles appearing on the cross section is in contact with the outer shape line and does not cross the inside of the particle. When various lines are drawn while changing the positional relationship with the particle, the maximum value of the distance between the parallel lines is the maximum diameter dmax of the particle, and the minimum value is the minimum diameter dmin. Heat treatment is performed such that the average value of the ratio dmin / dmax of the minimum diameter dmin to the maximum diameter dmax for each particle is 0.5 or less and the Vickers hardness is 300 Hv or less.

  According to the structure 6, since it heat-processes so that it may become Vickers hardness 300Hv or less, the work distortion of an outer side ignition part is eliminated and malfunctions, such as an internal crack, can be prevented. In addition, when observing the cross-sectional structure, the parallel lines of the particles appearing on the cross-section are in contact with the external lines and the two parallel lines are changed so as not to cross the particles. However, when various values are drawn, the maximum value of the distance between the parallel lines is the maximum diameter dmax of the particles, and the minimum value is the minimum diameter dmin, the minimum diameter dmin with respect to the maximum diameter dmax of each particle in a predetermined cross section. Since the heat treatment is performed so that the average value of the ratio dmin / dmax is 0.5 or less, it is possible to suppress a decrease in mechanical strength.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the spark plug 100 of this embodiment includes a metal shell 1, an insulator 2, a center electrode 3, and a ground electrode 4. The metal shell 1 has a cylindrical shape, and an insulator 2 is held inside thereof. The tip of the insulator 2 protrudes from the metal shell 1. Further, the center electrode 3 is provided inside the insulator 2 in a state in which a firing portion (inner firing portion) 31 provided at the tip is projected. Further, the ground electrode 4 is disposed so that the base end portion thereof is welded to the metal shell 1, the front end side thereof is bent back, and the side surface thereof faces the front end portion of the center electrode 3. The ground electrode 4 is provided with an ignition part (outside ignition part) 32 facing the ignition part 31. A gap between the ignition part 31 and the ignition part 32 is a spark discharge gap 33.

  The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and a hole 6 is formed inside the insulator 2 along the axial direction of the insulator 2. 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 the spark plug 100 is attached to an outer cylinder of the engine cylinder head (not shown). A threaded portion 7 is formed.

  As shown in FIG. 2, the main body 3a of the center electrode 3 and the main body 4a of the ground electrode 4 are made of a nickel (Ni) alloy or the like. On the other hand, the ignition part 31 and the opposing ignition part 32 are made of a noble metal alloy whose main first component is platinum (Pt) and whose second component is iridium (Ir) (this will be described later). To do).

  The main body 3a of the center electrode 3 is reduced in diameter at the tip side, and the tip surface is formed flat, and a disk-shaped chip made of an alloy composition constituting the ignition portion 31 is overlapped thereon, and The ignition portion 31 is formed by forming the welded portion B1 along the outer edge portion of the joint surface by laser welding, electron beam welding, resistance welding or the like and fixing it. Further, the ignition part 32 opposite to this is formed by aligning the chip on a predetermined position of the ground electrode 4, and similarly forming the welded part B2 along the outer edge part of the joining surface and fixing it. The In addition, it is good also as a structure which abbreviate | omits any one (the chip part) among the ignition parts 31 and the ignition parts 32 facing this. In this case, a spark discharge gap 33 is formed between the ignition part 31 and the ground electrode body 4a or between the opposing ignition part 32 and the center electrode body 3a. However, for the purpose of the present invention, it is desirable to provide at least the ignition part 32 on the side of the ground electrode 4 that is easily exposed to higher temperatures.

  Next, the manufacturing method of these chip-like ignition parts 31 and 32 is demonstrated. First, each alloy component is blended and melted to have a predetermined composition in which the main first component is Pt and the second component is Ir, and an ingot is formed with respect to the melted alloy, and then forging, groove roll Roll. Thereafter, as a first technique, as shown in FIG. 3A, there is a method of obtaining a rolled plate material 201 and then punching it to obtain a disk-shaped chip 202 having a relatively small thickness. As a second method, as shown in FIG. 4 (a), a rod-shaped material 203 is obtained by hot wire drawing and then cut into a predetermined length to obtain a columnar chip 204. There is.

  The chips 202 and 204 obtained by any one of the above methods are subjected to plastic processing, and processing distortion (residual stress) may occur during the plastic processing or the like. In the present embodiment, in order to remove the processing distortion, the ignition parts 31 and 32 are configured after the chips 202 and 204 are subjected to a predetermined heat treatment in the process of manufacturing the spark plug 100 described later.

  However, if heat treatment is performed at a too high temperature for a long time, recrystallization is promoted, the crystal grain size increases, and the mechanical strength of the chips 202 and 204 decreases. In view of this point, in this embodiment, for example, heat treatment is performed at 900 ° C. to 1100 ° C. (preferably 920 to 1000 ° C.) for 1 hour in a vacuum or an inert gas atmosphere or a reducing atmosphere such as a hydrogen atmosphere. Applied. Thereby, it is suppressed that the crystal grain size increases.

  More specifically, when the rolled plate material 201 is obtained and punched out to obtain the disk-shaped chip 202 as in the first method shown in FIG. 3A, FIG. As shown in FIG. 2, the particles (crystal grains) are oriented in the horizontal direction in the figure by plastic working (rolling). Further, as in the second method shown in FIG. 4A, when the rod-shaped material 203 is obtained and then cut into a predetermined length to obtain the chip 204, as shown in FIG. 4B. In addition, the crystal grains are oriented in the longitudinal direction of the bar (the vertical direction in the figure). Here, when the heat treatment is excessively performed, the crystal grain size tends to increase, and in this case, the aspect ratio of the crystal grains also approaches “1”. In other words, as the cross-sectional structure along the orientation direction is observed as the heat treatment is performed, the outer shape of the particles appearing on the cross section is in contact with the outer shape as shown in FIG. 5, for example. The maximum value of the distance between the parallel lines when the two parallel lines are drawn while changing the positional relationship with the particle so as not to cross the inside of the particle is the maximum diameter dmax of the particle, and also the minimum value. When the minimum diameter dmin is set, the ratio dmin / dmax of the minimum diameter dmin to the maximum diameter dmax for each particle in a predetermined cross section approaches “1”. In this respect, in this embodiment, the average value of the ratio dmin / dmax of the minimum diameter dmin to the maximum diameter dmax (hereinafter referred to as “orientation ratio average value” for convenience) when the cross-sectional structure along the alignment direction is observed is “ The heat treatment is performed under relatively mild conditions so as to be 0.5 "or less.

  Moreover, the ignition parts 31 and 32 of this embodiment are heat-processed so that it may become Vickers hardness 300Hv or less. As a result, the processing distortion is eliminated, and problems such as abnormal consumption of the ignition part and internal cracks are prevented.

  Furthermore, although the ignition parts 31 and 32 of this embodiment set Pt as a main 1st component and Ir as a 2nd component, the said Ir is contained 5 mass% or more and 40 mass% or less especially. When Ir is contained in an amount of less than 5% by mass, since the hardness of the original material (immediately after the plastic working) is relatively low, heat treatment is sufficient even if the Vickers hardness is 300 Hv or less. However, there is a possibility that processing distortion remains in the ignition part. On the other hand, when the Ir content exceeds 40% by mass, the hardness of the original material (immediately after undergoing plastic working) is relatively high. Therefore, if the Vickers hardness of 300 Hv or less is to be satisfied, the heat treatment is performed. Too much done. Therefore, recrystallization is promoted, the crystal grain size becomes large, and there is a possibility that the problem of a decrease in mechanical strength may occur.

  Next, the manufacturing method of the spark plug 100 comprised as mentioned above is demonstrated. First, the metal shell 1 is processed in advance. That is, a metal material (for example, an iron-based material such as S15C or S25C or a stainless steel material) formed in a cylindrical shape is formed through holes by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, the ground electrode 4 made of a nickel (Ni) alloy (for example, an Inconel alloy) is resistance-welded to the tip portion of the metal shell intermediate. During the welding, so-called “sag” is generated, and after the “sag” is removed, the threaded portion 7 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 1 to which the ground electrode 4 is welded is obtained. The metal shell 1 to which the ground electrode 4 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  Further, a tip for constituting the above-described ignition portion 32 is joined to the tip portion of the ground electrode 4 by resistance welding, laser welding, or the like. In addition, in order to make welding more reliable, plating removal of a welding site is performed prior to the welding, or masking is performed on a planned welding site during a plating process. Further, the tip may be welded after assembling described later.

  On the other hand, the insulator 2 is molded separately from the metal shell 1. For example, by using a raw material powder mainly composed of alumina or aluminum nitride and containing a binder or the like, a green granulated material for molding is prepared, and rubber press molding is used to obtain a cylindrical molded body. The obtained molded body is ground and shaped. Then, the shaped one is put into a firing furnace and fired. The insulator 2 is obtained by performing various grinding | polishing processes after baking.

  In addition to the metal shell 1 and the insulator 2, the center electrode 3 is manufactured. That is, a Ni-based alloy is forged, and a copper core is provided at the center to improve heat dissipation. And the chip | tip for comprising the ignition part 31 mentioned above is joined to the front-end | tip part by resistance welding, laser welding, etc.

  The insulator 2 and the center electrode 3 obtained as described above and a terminal fitting (not shown) are sealed and fixed by a glass seal (not shown). As a glass seal, borosilicate glass and metal powder are generally mixed and adjusted. After the adjusted material is injected into the inner hole of the insulator 2, the terminal fitting is pressed from the rear. Then, it is baked and hardened in a firing furnace. At this time, the glaze layer may be fired simultaneously on the surface of the body portion on the rear end side of the insulator 2, or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 provided with the center electrode 3 and the terminal fitting, respectively, produced as described above, and the metal shell 1 provided with the ground electrode 4 are assembled. More specifically, with respect to the rear end portion of the metal shell 1 formed to be relatively thin, cold insulation or hot crimping is performed, so that the insulator 2 is connected to the rear end portion of the metal shell 1 from the circumferential direction. Are held so as to be surrounded.

  Finally, the ground electrode 4 is bent to perform a process for adjusting the spark discharge gap 33 between the center electrode 3 (the ignition part 31) and the ground electrode 4 (the ignition part 32).

  Thus, the spark plug 100 having the above-described configuration is manufactured through a series of steps.

  As described above, according to the present embodiment, the ignition portions 31 and 32 are heat-treated so that the above-described “orientation ratio average value” is equal to or less than “0.5”. Therefore, it is possible to make it difficult for mechanical strength to decrease due to grain coarsening and mechanical strength to decrease due to intergranular corrosion.

  Moreover, the ignition parts 31 and 32 are made into Vickers hardness 300Hv or less by heat-processing. For this reason, processing distortion is eliminated and problems such as abnormal wear and internal cracks can be prevented. In particular, Ir as the second component is contained in an amount of 5% by mass to 40% by mass. For this reason, the said effect by satisfy | filling the requirement that the said Vickers hardness is 300 Hv or less is show | played more reliably.

  Further, when the spark plug 100 is used, the ignition part 32 on the ground electrode 4 side is more easily exposed to a higher temperature than the ignition part 31 on the center electrode 3 side, and the problem of grain boundary separation is more concerned. By the way. In this respect, in the present embodiment, since at least the ignition part 32 on the ground electrode 4 side has the above-described configuration, even if it is exposed to a high temperature, the problem caused by the grain boundary separation is more effective. Can be suppressed.

  Next, in order to confirm the above-described effects, various samples were prepared by changing various conditions, and various evaluations were attempted. The experimental results are described below. In addition, Tables 1-3 which show each evaluation result show the relative evaluation in each evaluation test, and even if a judgment is x, it does not necessarily indicate that it cannot be used as a product.

  First, while the main first component is Pt, an alloy containing 20% by mass of Ir as the second component is prepared, and the above-mentioned orientation ratio average is obtained by varying the heat treatment conditions. Sample chips with different values were prepared (Samples 1 to 3). The evaluation results of these samples are shown in Table 1.

表１に示すように、Ｉｒの含有量が同じでも、配向比平均値が異なることで、引張強度に相違が生じることが明らかとなった。すなわち、配向比平均値が「０．５」を上回るサンプル１（配向比平均値＝「０．７」）については、引張強度が著しく低いものとなってしまったのに対し、配向比平均値が「０．５」以下であるサンプル２，３については、十分な引張強度が得られた。ここで、引張強度とあるのは、機械的強度に準ずるものであり、一般的に引張強度が高ければ機械的強度も高い傾向にある。すなわち、引張強度が著しく低い（表中×印）場合には、チップ内で割れや剥離が発生し易いと判定することができる。

As shown in Table 1, it became clear that even if the Ir content is the same, the tensile strength differs depending on the orientation ratio average value. That is, the sample 1 whose orientation ratio average value exceeds “0.5” (orientation ratio average value = “0.7”) has a significantly low tensile strength, whereas the orientation ratio average value For Samples 2 and 3 having a value of “0.5” or less, sufficient tensile strength was obtained. Here, the term “tensile strength” refers to mechanical strength. Generally, the higher the tensile strength, the higher the mechanical strength. That is, when the tensile strength is remarkably low (indicated by x in the table), it can be determined that cracking or peeling is likely to occur in the chip.

  Therefore, from the above experimental results, when the crystal grain size is increased, the mechanical strength is reduced, and the crystal grains are partially peeled off and dropped (prone to cracks originating from the grain boundaries), It can be seen that the durability is remarkably lowered, while the mechanical strength can be prevented from being lowered and the durability can be ensured by appropriately performing the heat treatment while suppressing the increase in the crystal grain size.

  Next, while changing the content of Ir as the second component in various ways, the heat treatment time was varied, and sample chips having different hardnesses were prepared (Samples 4 to 12). Table 2 shows the evaluation results of these samples.

表２に示すように、Ｉｒの含有量が異なると、引張強度や、チップ内剥離の有無に影響が及ぶことが明らかとなった。ここで、チップ内剥離とあるのは、任意の断面を顕微鏡観察した際、チップ内で剥離を起こしていることをいい、当該チップ内剥離は、加工歪み（残留応力）に起因して起こりうるものである。つまり、チップ内剥離あり（表中×印）の場合には、加工歪みが大きいと判定することができる。尚、表中△印は、チップ内剥離が僅かながら発生してしまったことを示す。また、Ｉｒの含有量が同じで、かつ、配向比平均値が「０．５」以下であっても、硬度が異なることで、チップ内剥離の有無に影響が及ぶことが明らかとなった。

As shown in Table 2, it has been clarified that the different Ir contents affect the tensile strength and the presence or absence of peeling in the chip. Here, in-chip peeling means that peeling occurs in the chip when an arbitrary cross section is observed with a microscope, and the in-chip peeling can occur due to processing strain (residual stress). Is. That is, when there is peeling within the chip (x mark in the table), it can be determined that the processing strain is large. In addition, (triangle | delta) mark in a table | surface shows that peeling in chip | tip has generate | occur | produced a little. It was also found that even if the Ir content is the same and the orientation ratio average value is “0.5” or less, the hardness is different, which affects the presence or absence of in-chip peeling.

  That is, even if the orientation ratio average value is “0.4”, the sample 4 with an Ir content of less than 5% by mass (Ir content = 3% by mass) caused slight peeling in the chip. Moreover, about the sample 8 (Ir content = 45 mass%) whose Ir content exceeds 40 mass%, the tensile strength was remarkably low. In contrast, Samples 5, 6, and 7 having an average orientation ratio value of “0.4” and an Ir content of 5 mass% to 40 mass% (Ir content = 5, 20, 40 mass) %), The tensile strength was sufficient, and no chip peeling occurred.

  From this, when the Ir content is less than 5% by mass, even if the Vickers hardness (Hv) (hereinafter simply referred to as “hardness”) is 300, the original hardness is relatively low and sufficient. It can be seen that heat treatment cannot be performed and residual stress remains in the chip. Further, if the Ir content exceeds 40% by mass, even if the hardness is 300, the original hardness is relatively high, and if heat treatment is performed to such an extent that the hardness is reduced, the number of crystal grains increases. As a result, the average value of the orientation ratio exceeds “0.5” and the durability is remarkably lowered. On the other hand, the Ir content is set to 5% by mass or more and 40% by mass or less, and the heat treatment is appropriately performed while suppressing an increase in the grain size of the crystal without leaving a residual stress in the chip. It can be seen that abnormal wear and internal cracks can be prevented and sufficient durability can be secured.

  Further, even if the Ir content is the same as 20% by mass and the orientation ratio average value is “0.5” or less, the samples 11 and 12 having a hardness exceeding 300 (hardness = 320, 350) On the other hand, in-chip peeling occurred, but in Samples 9 and 10 (hardness = 260, 280) having a hardness of 300 or less, the tensile strength was sufficient and peeling in the chip did not occur. Therefore, even if the Ir content is in the range of 5% by mass or more and 40% by mass or less, if the hardness exceeds 300, it cannot be said that heat treatment is still sufficient, and residual stress may remain in the chip. Recognize. On the other hand, by appropriately performing the heat treatment while suppressing the increase in the grain size of the crystal so that the Ir content is in the range of 5 mass% to 40 mass% and the hardness is 300 or less, It can be seen that sufficient durability can be ensured without leaving a residual stress on the chip, and suppressing a decrease in mechanical strength.

  In the examples and experimental examples described above, an alloy (Pt—Ir system) containing Pt as the main first component and containing Ir as the second component has been described. Without being limited to the original system, a third component, a fourth component, and the like may be included separately.

  Then, next, various sample chips containing the third component and possibly the fourth component were prepared (samples 13 to 18). Table 3 shows the evaluation results of these samples.

表３に示すように、第３成分として、ロジウム（Ｒｈ）や、Ｎｉなどを含有させることとしてもよい（サンプル１３，１４）。また、第３成分に加え、第４成分を含有させることとしてもよい（サンプル１５，１６）。但し、第３成分等を含有させてもよいが、上述したように、硬度が３００以下である必要があるし、もちろん配向比平均値が「０．５」以下である必要がある。硬度が３００を超えるサンプル１７（硬度＝４００）については、チップに残留応力が残ってしまい、チップ内剥離が発生してしまった。また、配向比平均値が「０．５」を上回るサンプル１８（配向比平均値＝０．６）については、引張強度が著しく低いものとなってしまった。これに対し、第３成分等が含有されていたとしても、硬度が３００以下であり、配向比平均値が「０．５」以下であるサンプル１３〜１６については、チップに残留応力を残すことなく十分な耐久性を確保できることがわかる。

As shown in Table 3, rhodium (Rh), Ni, or the like may be included as the third component (samples 13 and 14). In addition to the third component, a fourth component may be included (samples 15 and 16). However, although a third component or the like may be contained, as described above, the hardness needs to be 300 or less, and of course, the orientation ratio average value needs to be “0.5” or less. For sample 17 having a hardness exceeding 300 (hardness = 400), residual stress remained on the chip, and peeling within the chip occurred. Further, the sample 18 having an orientation ratio average value exceeding “0.5” (orientation ratio average value = 0.6) had a remarkably low tensile strength. On the other hand, even if the third component or the like is contained, residual stress is left on the chip for samples 13 to 16 having a hardness of 300 or less and an orientation ratio average value of “0.5” or less. It can be seen that sufficient durability can be secured.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  (A) In the above embodiment, a case where a tip that has already been subjected to heat treatment (for forming the ignition part 32) is welded to the tip of the ground electrode 4 is illustrated. The tip before the heat treatment may be welded in advance, the ground electrode 4 to which the tip is welded is subjected to heat treatment, and then the ground electrode 4 may be welded to the tip portion of the metal shell intermediate. Further, the tip before the heat treatment is pre-welded to the ground electrode, and the ground electrode 4 welded to the tip is welded to the distal end portion of the metal shell intermediate to form the metal shell assembly, The assembly may be subjected to heat treatment.

  (B) Moreover, in the said embodiment, although it has set it as the structure which welds the chip-shaped ignition parts 31 and 32, in the spark plug used for a gas engine etc., the whole ground electrode makes 1st component Pt. In addition, it is possible to employ a material in which the second component is Ir. In this case, the main first component may be Pt and the second component Ir may be heat-treated and then welded to the metal shell, or may be heat-treated after welding. .

  In the latter case, a metal shell assembly is obtained by welding a ground electrode having a main first component of Pt and a second component of Ir to the metal shell, and then heat treatment is performed together with the metal shell assembly in the heat treatment step. Will be given. By this heat treatment, the processing distortion of the ignition part in which the first component is Pt and the second component is Ir is eliminated, and problems such as internal cracks in the ignition part can be prevented. In addition, by appropriately performing the heat treatment, it is possible to suppress defects caused by a decrease in mechanical strength.

  In the case of the latter modification, that is, when a metal shell assembly is obtained by welding a ground electrode whose main first component is Pt and whose second component is Ir to the metal shell, the metal shell is obtained. Is often made of a base metal, and welding between the metal shell, which is the base metal, and a ground electrode made of a noble metal alloy may not always be sufficient. In this respect, as described above, since heat treatment is performed after welding, the familiarity of the welded portion between the metal shell and the ground electrode is further improved, and as a result, the joint strength between the two can be improved. it can.

  (C) In the above embodiment, no particular reference was made to the lower limit value of the Vickers hardness (Hv) of the ignition parts 31 and 32, but the condition that the average value of the orientation ratio is not more than "0.5" is satisfied. If so, the lower limit is not subject to any particular numerical limitation. However, from the viewpoint of ensuring a predetermined strength, it is desirable that the Vickers hardness (Hv) is at least 200 or more, more preferably 250 or more.

  (D) The type of the spark plug is not particularly limited to that of the above embodiment. Therefore, for example, it may be embodied in a type having 2 to 4 ground electrodes.

It is a partially broken front view which shows the structure of the spark plug of this embodiment. It is a partial expanded sectional view of the spark plug shown centering on an ignition part. (A) is a perspective view which shows the state which stamped the disk-shaped chip | tip from the rolled plate raw material, (b) is a fragmentary perspective view which shows typically the orientation state of the crystal grain of a chip | tip. (A) is a perspective view which shows the state which obtained the cylindrical chip | tip by cut | disconnecting a rod-shaped raw material to predetermined length, (b) is a fragmentary perspective view which shows typically the orientation state of the crystal grain of a chip | tip. . It is explanatory drawing which shows typically the maximum diameter and minimum diameter of the particle | grains in a chip | tip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal fitting, 2 ... Insulator, 3 ... Center electrode, 4 ... Ground electrode, 31 ... Igniting part, 32 ... Ignition part, 33 ... Spark discharge gap.

Claims (6)

A center electrode;
An insulator provided outside the center electrode;
A metal shell provided outside the insulator;
A ground electrode that is joined to the metal shell and has a tip portion disposed so as to face the tip portion of the center electrode;
A spark plug for an internal combustion engine having a spark discharge gap between a tip portion of the center electrode and a tip portion of the ground electrode,
The ignition part provided in at least one of the tip part of the center electrode and the tip part of the ground electrode has platinum as the main first component, iridium as the second component, and
While observing the cross-sectional structure, with respect to the outline of the particle appearing on the cross-section, two parallel lines that are in contact with the outline and do not cross the inside of the particle are changed while changing the positional relationship with the particle. When the maximum value of the distance between the parallel lines when drawn is the maximum diameter dmax of the particles, and the minimum value is the minimum diameter dmin, the ratio of the minimum diameter dmin to the maximum diameter dmax for each particle in a predetermined cross section. A spark plug for an internal combustion engine, wherein an average value of dmin / dmax is 0.5 or less.   2. The spark plug for an internal combustion engine according to claim 1, wherein the ignition portion in which the main first component is platinum and the second component is iridium is provided on the ground electrode side.   The spark plug for an internal combustion engine according to claim 1 or 2, wherein the ignition part in which the main first component is platinum and the second component is iridium has a Vickers hardness of 300 Hv or less.   4. The spark plug for an internal combustion engine according to claim 3, wherein the ignition part in which the main first component is platinum and the second component is iridium contains 5% by mass or more and 40% by mass or less of iridium. . A center electrode;
An insulator provided outside the center electrode;
A metal shell provided outside the insulator;
A ground electrode that is joined to the metal shell and has a tip portion disposed so as to face the tip portion of the center electrode;
Having a spark discharge gap between the tip of the center electrode and the tip of the ground electrode;
The ground electrode has a main first component of platinum and a second component of iridium, or a tip having a main first component of platinum at the tip of the ground electrode and a second component of iridium. A method for producing a spark plug for an internal combustion engine comprising a ignitable ignition part,
A grounding electrode having platinum as the main first component and iridium as the second component, or a tip-like ignition portion having iridium as the second component and platinum as the main first component at the tip. A method for producing a spark plug for an internal combustion engine, comprising: a heat treatment step of heat treating the metal shell assembly together with the metal shell assembly after the metal shell assembly is obtained by welding the ground electrode to the metal shell. A central electrode having an inner ignition part;
A ground electrode welded with a chip-like outer ignition portion that forms a spark discharge gap with the center electrode, and the outer ignition portion uses platinum as a main first component and iridium as a second component. A spark plug for an internal combustion engine,
The outer ignition portion is formed through plastic working, and when the cross-sectional structure is observed, two parallel lines are formed so that the outer shape of the particles appearing on the cross section is in contact with the outer shape line and does not cross the inside of the particle. When various lines are drawn while changing the positional relationship with the particle, the maximum value of the distance between the parallel lines is the maximum diameter dmax of the particle, and the minimum value is the minimum diameter dmin. The average value of the ratio dmin / dmax of the minimum diameter dmin to the maximum diameter dmax for each particle is 0.5 or less, and
A spark plug for an internal combustion engine, which is heat-treated so as to have a Vickers hardness of 300 Hv or less.

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