JP5339369B2 - Method for manufacturing spark plug center electrode and method for manufacturing spark plug - Google Patents

Description

  The present invention relates to a method for manufacturing a center electrode used in a spark plug having a tip made of a noble metal at the tip of the center electrode, and a method for manufacturing the spark plug.

  Conventionally, a spark plug is desired to have excellent durability, and a configuration in which a noble metal tip (hereinafter also simply referred to as a tip) is arranged at the tip of a center electrode that generates spark discharge has been adopted. This configuration is based on a configuration based on the idea of adopting a material excellent in spark wear resistance as a chip against the electrode being consumed by spark discharge.

  By the way, in order to improve the spark wear resistance of an electrode, it is also known as an effective means to improve the heat drawability of the electrode. Alloys used as an electrode material for spark plugs include alloys containing Ni as a main component such as inconel (registered trademark). A material in which the content of Ni is increased for the purpose of improving the heat drawability of such an alloy is known (see, for example, Patent Document 1). Even when an electrode formed of such a material is used, it is mentioned that a tip is disposed at a tip portion that is a starting point of the spark discharge. In order to improve the heat drawability, it is more desirable to provide a core portion made of Cu or an alloy thereof having better thermal conductivity than the Ni alloy constituting the outer surface.

JP 2004-206931 A

  However, it has been confirmed that even if a spark plug is produced using a material with an actually increased Ni content, the desired durability may not be achieved. After carefully examining the cause, the chip peels off from the electrode, creating a gap between them, the chip's heat drawability deteriorates and wear increases, the chip itself drops off the electrode, etc. It turns out that there is a problem. In order to solve this problem, various conditions for welding the tip were examined, but the fundamental problem was not solved.

  Accordingly, the present invention provides a method for manufacturing a center electrode that eliminates the root cause of the above-mentioned problem, improves weldability, and prevents the above-described peeling and dropping, and a method for manufacturing a spark plug using the same. Objective.

The first configuration of the solution is as follows:
A method for producing a spark plug center electrode comprising a center electrode having a noble metal tip at its tip,
A main body part precursor that has a cup shape and contains 90% by weight or more of Ni as a main component, and a core part made of a material that is more excellent in heat conduction than the main body part precursor is fitted inside the main body part precursor. And an intermediate portion precursor made of an alloy containing Ni as a main component and having a lower Ni content than the main body portion precursor on the opposite side of the bottom surface of the main body portion precursor to the side on which the core portion is fitted. An integration step of forming a center electrode precursor by integrating three members of the main body part precursor, the core part and the intermediate part precursor by plastic working;
A tip welding step of welding the noble metal tip to an intermediate portion precursor of the center electrode precursor , and
In the integration step, when the boundary surface between the main body part precursor and the intermediate part precursor is seen in a cross section passing through the axis of the central electrode precursor, an arc shape bulging toward the intermediate part precursor side is formed. It is characterized by forming.

The second configuration of the solving means is
The difference in thermal conductivity coefficient between the main body part precursor and the intermediate part precursor is 8 W · mK or more at room temperature.

The third configuration of the solving means is
The intermediate portion precursor contains Ni in an amount of 50 wt% to 80 wt%.

The fourth configuration of the solving means is
The intermediate part precursor contains a weldability improving component selected from Fe and Cr.

Moreover, what is necessary is just to comprise a spark plug using the center electrode manufactured by the above.
According to the above means, the following operation can be obtained.

According to the first to fifth aspects of the present invention, chip peeling can be effectively suppressed. This is because the Ni content of the material constituting the main body part precursor is higher than that of the conventional Inconel, so the heat sinking is improved when the tip is welded to the electrode, and the weldability is improved. By eliminating the decline. Specifically, when the main body precursor contains 90% by weight or more of Ni, the welding strength of the member to be joined with the Ni decreases, but in the first configuration of the present invention, the tip is welded. In doing so, an intermediate part precursor made of a Ni alloy having a lower Ni content than the main body part precursor, that is, a Ni content of less than 90% by weight is interposed, so that heat during welding is excessively drawn. Thus, it is possible to realize reliable bonding between the intermediate portion precursor and the chip. And since the intermediate part precursor and the main body part precursor are integrated by plastic working such as extrusion molding, the joining property of both is not influenced by the thermal conductivity of both, and strong joining is possible. It is.

In the present invention based on the above-mentioned matters, it is needless to say that the thermal conductivity of the intermediate portion precursor is worse than that of the main body portion precursor and that the thermal conductivity coefficient is low. However, simply providing an intermediate portion precursor having a poor thermal conductivity may cause a problem in bondability when integrated by extrusion or the like, and in the present invention, it is defined by the Ni content.

  The “noble metal tip” means a small piece formed with a noble metal component as a main component, and examples thereof include conventionally known Ir—Pt alloys, Ir—Rh alloys, and Pt—Ni alloys. Moreover, it does not necessarily need to consist only of a noble metal and may contain a base metal and an oxide.

1 is an overall view (partial sectional view) of a spark plug 1 manufactured according to the present invention. It is a figure explaining the manufacturing process of the center electrode which is the principal part of this invention. (A) is a precursor, (b) is a state in which the precursors are integrated (before plastic working), (c) is a tip of a product formed into a central electrode shape by plastic working, (d) Is a noble metal tip 31 bonded to the tip.

Embodiments will be described below with reference to the drawings.
FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the axis X direction of the spark plug 1 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side as the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  A shaft hole 4 is formed through the insulator 2 along the axis X. A center electrode 5 is inserted and fixed on the front end side of the shaft hole 4, and a terminal electrode 6 is inserted and fixed on the rear end side. A resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 in the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seals 8 and 9, respectively.

  The center electrode 5 protrudes from the tip of the insulator 2, and the terminal electrode 6 is fixed in a state of protruding from the rear end of the insulator 2. Further, a noble metal tip 31 is joined to the center electrode 5 at the tip thereof by welding.

  On the other hand, the insulator 2 is formed by firing alumina or the like as is well known, and in its outer portion, the rear end side body portion 10 formed on the rear end side, and the rear end side body portion 10 A large-diameter portion 11 that protrudes outward in the radial direction on the distal end side, a middle trunk portion 12 that is smaller in diameter than the large-diameter portion 11 on the distal end side, and the middle trunk portion 12. Is also provided with a leg length portion 13 formed to have a smaller diameter on the distal end side. Of the insulator 2, the large-diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the leg length portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  The metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 15 for attaching the spark plug 1 to the engine head is formed on the outer peripheral surface thereof. Further, a seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted into a screw neck 17 which is the rear end of the screw portion 15 and has no thread. . Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the engine head is provided. A caulking portion 20 for holding the insulator 2 is provided.

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. As a result, the airtightness in the combustion chamber is maintained, so that air-fuel mixture, exhaust gas, etc. entering the gap between the leg length 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 do not leak to the outside. It has become.

  Further, in order to more completely fix the insulator 2 to the metal shell 3, annular ring members 23 and 24 are provided between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3. Between the ring members 23 and 24, powder of talc (talc) 25 is filled. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  Further, a ground electrode 27 having a substantially L shape is joined to the distal end portion 26 of the metal shell 3. That is, the ground electrode 27 is welded at its rear end to the front end portion 26 of the metal shell 3, and the front end side is bent back so that the side surface faces the front end portion (the noble metal tip 31) of the center electrode 5. Are arranged as follows. The ground electrode 27 may be formed of a Ni-based alloy, and is formed of Inconel 601 (registered trademark) in this embodiment.

  Further, a noble metal tip 32 is joined to the ground electrode 27 so as to face the noble metal tip 31. A gap between the noble metal tips 31 and 32 is a spark discharge gap 33. In the present embodiment, the noble metal tip 31 is made of a known noble metal material (for example, a Pt—Ir alloy), and the noble metal tip 32 is made of a Pt-20Ir-5Rh alloy. .

  The center electrode 5 includes a core portion 5A made of Cu or Cu alloy, a main body portion 5B made of Ni alloy, and an intermediate portion 5C made of Ni alloy different from the main body portion 5B. By the manufacturing method described below, the boundary surface between the main body portion 5B and the intermediate portion 5C has a curved shape that bulges toward the tip of the center electrode 5 (to the tip portion 5C side), that is, an arc shape in a cross section along the axis X. It is formed to draw. In the present embodiment, the main body portion 5B is made of a high Ni-containing alloy containing 90% or more of Ni, while the intermediate portion 5C is made of, for example, Inconel 600 (registered trademark) whose Ni content is 80% or less. Yes.

Turning to FIG. 2, a method for manufacturing the center electrode 5 will be described.
First, the precursors 5A ′, 5B ′, and 5C ′ to be the core portion 5A, the outer layer 5B, and the intermediate portion 5C are prepared (FIG. 5a). The precursor 5B ′ is formed in a bottomed cylindrical shape (so-called cup shape). The precursor 5A ′ is formed into a shape having a body portion 5A′1 inserted into the inner hole 5B′1 of the precursor 5B ′ and a head portion 5A′2 having a larger outer diameter. The precursor 5C ′ is formed in a disk shape having a surface (5C′2) having substantially the same shape as the bottom 5B′2 of the precursor 5B ′. These precursors 5A ′, 5B ′, and 5C ′ are combined and inserted into a mold, and are integrated by plastic processing such as extrusion (FIG. 5b). The outer shape of the integrated precursor is adjusted by cutting or the like to form the center electrode 5 (FIG. 5 c), and is welded to a separately prepared cylindrical noble metal tip 31 to be integrated with the noble metal tip 31. 5 is assembled to the insulator 2 (FIG. 5d). In the welding of the center electrode 5 and the noble metal tip 31, the noble metal tip 31 is superimposed on the tip of the center electrode 5 (specifically, the tip of the intermediate portion 5C), and further, laser welding, electronic The noble metal tip 31 and the center electrode 5 are joined by performing beam welding or resistance welding. Prior to extrusion molding, a combination of the precursors 5A ′, 5B ′, 5C ′ is subjected to vacuum annealing, and a precursor 5A ′ made of Cu or a Cu alloy and a precursor 5B ′ made of a high Ni-containing alloy. The Cu component and the Ni component may be diffused on the joint surface.

  On the other hand, the noble metal tip 32 opposed to the noble metal tip 31 is positioned at a predetermined position of the ground electrode 27 and temporarily welded by resistance welding, and then spotted by a laser beam along the outer edge of the joint surface. Welded. Thereby, a melted portion in which the noble metal material and the Ni alloy are melted is formed, and the ground electrode 27 and the noble metal tip 32 are joined. In the present embodiment, the noble metal tip 32 is arranged on the ground electrode 27. However, when the cost is more important than the performance in the spark plug 1, the noble metal tip 32 may be omitted.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated. First, the metal shell 3 is processed in advance. That is, a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material) is formed by forming a through-hole by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a ground electrode 27 made of a Ni alloy is resistance-welded to the front end surface of the metal shell intermediate. Next, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained. The metal shell 3 to which the ground electrode 27 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment. When joining the noble metal tip 32 to the tip of the ground electrode 27, it is preferable from the viewpoint of welding strength that the surface treatment is eliminated by polishing or the like at the place where the noble metal tip 32 is joined and then welded.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, by using a raw material powder mainly composed of alumina 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.

Then, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seals 8 and 9. The glass seals 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared one is injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. After that, the terminal electrode 6 is pressed from the rear and then baked in a firing furnace. At this time, the glaze layer may be simultaneously fired and formed on the surface of the rear end side body portion 10 of the insulator 2, or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are assembled as described above. More specifically, it is fixed by caulking the opening on the rear end side of the metal shell 3 formed relatively thin inward in the radial direction, that is, by forming the caulking portion 20.

  Finally, the ground electrode 27 is bent to adjust the spark discharge gap 33 between the noble metal tip 31 provided at the tip of the center electrode 5 and the noble metal tip 32 provided on the ground electrode 27. Is done.

  Thus, the spark plug 1 having the above-described configuration is manufactured through a series of steps. Thus, it is possible to realize a spark plug in which a noble metal tip is arranged at the tip of the center electrode main body (main body portion), which is excellent in heat dissipation and uses a relatively large Ni component. As a spark plug, it is possible to manufacture a spark plug that does not peel off and fall off.

Next, the effect of the present invention will be confirmed.
First, Ni alloys having different Ni contents, which are assumed to be used as the center electrode of the spark plug or have been used as the center electrode of the spark plug, were prepared (Table 1).

  Various combinations of the various Ni alloys shown in Table 1 were used as the material of the main body or the intermediate part constituting the center electrode, and various center electrode samples were produced through the above-described manufacturing method (Table 2). The prepared samples differ only in the materials of the main body and the intermediate portion, and the other dimensions, the material of the core and the noble metal tip, etc. are the same in any sample.

Spark plugs were produced using these various samples, and evaluated from two viewpoints of chip peeling and chip sweating.
“Chip peeling” means that the center electrode sample is subjected to 1000 cycles of heating and cooling for 2 minutes (900 ° C.)-Cooling 1 minute (room temperature), and the chip is removed from the center electrode after the test, or the appearance and cross section For items that can be judged as having no peeling or no problem in actual use even when peeling is confirmed, `` ○ '', if there is a problem such as dropping or peeling, “×”.
“Chip sweating” refers to the production of a spark plug using a center electrode sample, attachment to an actual engine, durability for 100 hours under a predetermined condition where the center electrode temperature is about 800 ° C. If there is no malfunction (sweat phenomenon) in which the components of the evaporated chip are reattached due to reattachment, “○” is indicated. If the sweat phenomenon is confirmed, “×” is indicated. Items that could be judged as causing no problems were evaluated as “△”.

  Center electrodes (samples Nos. 3 to 5) composed of materials 1 to 3 having a Ni content of 90% by weight or more in the main body and materials 4 to 8 having a Ni content of less than 90% in the middle part. , 7-9, 11-13, 15-17) all had good test results without causing chip peeling and chip sweating abnormalities.

  Sample No. In the spark plug using 19 center electrodes, almost no peeling occurred after the test, but a slight sweating was observed. This is because the Ni content of the material 8 constituting the intermediate portion is relatively small so as to be less than 40% by weight and 50% by weight, and thus the tip was likely to become hot during the test and the sweating phenomenon was likely to occur. It is done. On the other hand, No. 1 made of material 7 having a Ni content of 50% by weight. This was not the case for 15-17. From this, it was confirmed that it is more desirable that the intermediate portion has Ni of 50% by weight or more.

  Sample No. 1 in which the intermediate part and the main part are both made of material 1 is used. The intermediate part 1 and the body part 1 are integrated by extrusion, but except for this point, the structure is the same as that of the center electrode of a conventional spark plug. For this reason, the problem of chip | tip peeling will arise like the conventional spark plug. For comparison, the reverse configuration of the present invention, that is, sample No. The configuration of 2 resulted in both chip peeling and chip sweating abnormalities, and this also confirmed the significance of the present invention.

  From the above test results, it seems that the effect is different between the material 3 and the material 4, that is, the Ni content is 80% by weight as a critical. However, the upper limit of the Ni content of the intermediate part that realizes the present invention is not necessarily limited to 80% by weight. The confirmed results are shown in Table 3. The confirmation method is a test method different from the aforementioned “chip peeling” evaluation. The test is a method in which a sample of the center electrode is prepared in the same manner as described above, a cooling cycle is performed in which heating is performed for 2 minutes (1000 ° C.)-Cooling 1 minute (room temperature), and the number of cycles leading to peeling is compared. is there. Table 3 shows the composition of the confirmed alloy and the result of this test.

  Sample A, which has the same composition as the intermediate part and the main part, corresponds to the same structure as the center electrode of the conventional spark plug, but an intermediate made of an alloy having a lower Ni content than the main part. In all of the samples (samples B to F), the number of cycles leading to chip peeling increased with respect to sample A.

  As mentioned above, although this invention was demonstrated based on one Example, in implementing this invention, it is not limited to the said Example, The change in the range which does not deviate from the main point is possible suitably.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Insulator 3 Metal shell 5 Center electrode 5A (Center electrode) Core part 5B (Center electrode) Main body part 5C (Center electrode) Intermediate part 27 Ground electrode 31 Noble metal tip (Center electrode side)

Claims (5)

A method for producing a spark plug center electrode comprising a center electrode having a noble metal tip at its tip,
A main body part precursor that has a cup shape and contains 90% by weight or more of Ni as a main component, and a core part made of a material that is more excellent in heat conduction than the main body part precursor is fitted inside the main body part precursor. And an intermediate portion precursor made of an alloy containing Ni as a main component and having a lower Ni content than the main body portion precursor on the opposite side of the bottom surface of the main body portion precursor to the side on which the core portion is fitted. An integration step of forming a center electrode precursor by integrating three members of the main body part precursor, the core part and the intermediate part precursor by plastic working;
A tip welding step of welding the noble metal tip to an intermediate portion precursor of the center electrode precursor;
I have a,
In the integration step, when the boundary surface between the main body part precursor and the intermediate part precursor is seen in a cross section passing through the axis of the central electrode precursor, an arc shape bulging toward the intermediate part precursor side is formed. A method for manufacturing a center electrode for a spark plug, characterized by comprising: The method for manufacturing a center electrode for a spark plug according to claim 1, wherein a difference in thermal conductivity coefficient between the main body portion precursor and the intermediate portion precursor is 8 W · mK or more at room temperature. . The method for manufacturing a center electrode for a spark plug according to claim 1 or 2, wherein the intermediate portion precursor contains 50 wt% or more and 80 wt% or less of Ni . The method of manufacturing a spark plug center electrode according to any one of claims 1 to 3, wherein the intermediate portion precursor contains a weldability improving component selected from Fe and Cr. . A spark plug is formed using the center electrode according to any one of claims 1 to 4.
A method of manufacturing a spark plug characterized by the above.

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