JP2009016255A - Plug material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plug material reducing discharge voltage and maintaining the voltage reduced state for a long time and to provide its manufacturing method. <P>SOLUTION: The almost cylindrical plug material constitutes a center electrode of an ignition plug and includes a boundary phase of a first metal and a cell phase of a second metal partitioned from the boundary phase in its sectional structure. The first and second metals have different anti-spark consuming properties. A metal of low anti-spark consuming property is preferentially consumed to form a recess defining an edge, thereby reducing the discharge voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a material constituting a center electrode of a spark plug. Specifically, the present invention relates to a plug material having a low discharge voltage and capable of maintaining the state for a long period of time, and a manufacturing method thereof.

Conventionally, Pt, Ir, and alloys thereof have been used as a constituent material of a center electrode that is a main member of a spark plug for an internal combustion engine. Since these metals have a high melting point and excellent resistance to spark consumption and oxidation, they have a long life even in a high-temperature and high-oxidation atmosphere in the combustion chamber. In addition to the use of these metals / alloys alone as a structure of the center electrode, an example using a clad material combining two kinds of materials is also known recently (for example, Patent Document 1). Precious metals such as Pt and Ir are both high melting point materials, but when compared strictly, spark wear resistance and oxidation resistance are different, so using these clad materials makes the best use of their respective strengths. Can do.
JP 2002-359052 A

  By the way, the properties required for this type of plug material are preferentially the above-mentioned wearability and oxidation resistance, but the discharge voltage is as important as these. Even if it is excellent in spark erosion resistance, the center electrode is consumed with use, and the discharge voltage may change greatly due to its shape change, resulting in a misfire phenomenon. Accordingly, a discharge voltage that is appropriately reduced and has stable discharge characteristics is required. In this regard, few conventional plug materials have been developed from this point of view.

  Therefore, the present invention provides a plug material that can reduce the discharge voltage and maintain the state for a long period of time. Also provided is a method by which the plug material can be produced efficiently.

  Although the discharge voltage of the spark plug varies depending on the environmental conditions, the discharge voltage tends to decrease when the shape of the center electrode is such that an edge (corner) appears. The reason why the discharge characteristics change due to wear is that the shape of the center electrode is rounded due to wear. The present inventors conducted extensive research and found a structure having more edges because the discharge voltage is reduced based on a plug material in which two kinds of metals and alloys are combined.

  That is, the present invention relates to a substantially cylindrical plug material constituting a center electrode of a spark plug, and in the cross-sectional structure thereof, a boundary phase made of a first metal and a second metal partitioned by the boundary phase The first metal and the second metal are plug materials made of a plurality of cell phases and having different resistance to spark consumption.

  The plug material according to the present invention has, for example, a cross-sectional structure as shown in FIG. 1, includes a boundary phase, and forms a cell phase divided by the boundary phase. Each phase consists of metals with different resistance to spark consumption. In this plug material, since the metal with low spark wear resistance is preferentially consumed, an edge appears due to a dent caused by the consumption. Since the edge length thus generated is longer than that of a conventional simple clad material, the discharge voltage can be reduced. In addition, since the phase made of a metal with high spark wear resistance will eventually wear out, the end surface of the center electrode becomes flat. Appear. In this way, it is possible to reduce and stabilize the discharge voltage while repeating the appearance of the edge, the flattening due to wear, and the reappearance of the edge.

  In the present invention, metals / alloys having different spark wear resistance are selected and combined as constituent materials of the boundary phase and cell phase. The boundary phase (first metal) is made of a metal having low spark wear resistance. The cell phase (second metal) may be composed of a metal having a high resistance to spark consumption, or a reverse combination. This is because, as shown in FIG. 2, in any case, the edge appears due to the consumption of the metal having low spark consumption. In the present invention, it is preferable to arrange a metal having a high resistance to spark consumption in the cell phase. This is because when the boundary phase is consumed, the cell phase is likely to remain in a needle shape and stabilize the discharge voltage.

  The specific material of the first metal and the second metal is preferably a metal / alloy that can be used as a plug material, and an alloy including a noble metal is preferable. The noble metal alloy preferably contains at least one of platinum, iridium, and rhodium. The composition of each noble metal is platinum: 5 to 100% by weight, iridium: 10 to 100% by weight, rhodium: 0.1 to 50% by weight. % Alloy is preferred. In addition to these noble metals, those added with 0.1 to 15% by weight of at least one of iron, nickel, and chromium are also applicable.

  In the selection of the first metal and the second metal based on the spark wear resistance, since the iridium content and the spark wear resistance are correlated, the above composition should be based on the iridium concentration. Is preferred. Specifically, it is preferable to determine the composition of each metal so that the Ir concentration of the first metal is 5% by weight or less as compared with the Ir concentration of the second metal. Examples of the combination of the first metal and the second metal include those shown in Table 1 below.

  In the cross-sectional shape as described above, in order to lower the discharge voltage, the cell phase area is preferably 2 to 80% of the total cross-sectional area. This is because if the cross-sectional area is too large, the discharge voltage does not decrease. Further, when importance is attached to wear resistance, the area of the cell phase is preferably 50% or more with respect to the total cross-sectional area.

  As shown in FIG. 4, the plug material according to the present invention may have a coating layer made of the first metal on the outer peripheral side surface thereof. This coating layer is made of the first metal and communicates with the boundary phase.

  In the cross-sectional shape of the plug material according to the present invention, as examples of the shape of the boundary phase and the cell phase, as shown in FIG. 1, the cell phase has a substantially rhombus shape having flat extension portions on all sides, and a tridental shape. In which a cell phase is formed (FIG. 3A), a cell phase having a different shape is formed (FIGS. 3B and 3C), and the like. Among these, as the shape of the cell phase becomes thinner and more complicated, the length of the edge at the time of wear increases, but since the manufacturing tends to become difficult if the cell phase is complicated, what kind of shape should be made? Is determined by a balance with manufacturing efficiency.

  Next, the manufacturing method of the plug material according to the present invention will be described. The plug material manufacturing method according to the present invention includes a plurality of first metal bars or wire rods and a second metal bar or wire rod bundled in parallel, and the bundled rod rods or wire rods are drawn. Or a plurality of bars or wires made of the second metal coated with the first metal are bound in parallel, and the bound bars or wires are drawn.

  Each of these manufacturing methods uses a bar or wire as a raw material, and the first and second metals are processed by processing the bound bar or wire until the respective materials are integrated by drawing. The boundary phase and the cell phase are formed while deforming. According to these methods, the boundary phase can be easily formed, and a cell phase having a complicated shape such as a honeycomb shape can also be formed.

  Here, the former method using the two kinds of rods or wires made of the first and second metals (FIG. 5 (A)) is a massive cell phase at the center of the boundary phase as shown in FIG. It is useful for forming a shape having On the other hand, the latter method (FIG. 5B) using a bar or wire made of the second metal covered with the first metal is useful for forming a narrow and narrow boundary phase.

  In these production methods, in any case, it is preferable that the side surfaces of the bound bars or wires, or at least one of the end portions are welded and then drawn. This is to facilitate handling during processing.

  Further, in these methods, before the drawing process, the bound bar or wire can be inserted into the cylindrical material made of the first metal, and the cylindrical material can be drawn (FIG. 6A). According to this method, a plug material having a coating layer on the outer peripheral side surface can be easily manufactured. The first and second metals may be reversed. (Fig. 6B)

  In the present invention, the first metal and the second metal are preferably combined such that the hardness difference between them is 100 Hv or less. This is because if the hardness difference is too large, the soft material is preferentially deformed during processing and extends in the longitudinal direction of the wire, making it difficult to obtain a dimension and shape as designed.

  As described above, the plug material according to the present invention has a reduced discharge voltage and can maintain it for a long period of time. Moreover, the plug material manufacturing method according to the present invention can efficiently manufacture a plug material having a relatively complicated cross-sectional shape.

  Hereinafter, preferred embodiments of the present invention will be described.

First Embodiment : Four Pt-20 wt% Ir alloy wires having a diameter of 8 mm were prepared and arranged on the outer periphery of an Ir-10 wt% Rh alloy wire having a diameter of 11 mm. And the side surface of each wire was laser-welded. The welding conditions were an output of 250 kW, a pulse width of 3.5 msec, and an OFF time of 2.0 msec.

  Next, the bound wire was heated to 1200 ° C. and processed to a diameter of 8 mm by hot swaging. Furthermore, wire drawing (plug material) having a diameter of 1.2 mm was manufactured by performing a drawing process while performing heat treatment. In this drawing process, a heat treatment at 1200 ° C. was performed every time 30% processing was performed with a cross-section reduction rate. The manufactured plug material had a cross-sectional shape as shown in FIG. 1, and the center part of an Ir-10 wt% Rh alloy as a cell phase had a square shape of about 0.6 mm square. At this time, the area ratio of the cell phase to the plug material cross-sectional area was 35%.

Second Embodiment : Ir-10 wt% Rh alloy wire with a diameter of 5.9 mm is covered with a Pt-20 wt% Ir alloy pipe with an outer diameter of 9 mm and an inner diameter of 6 mm and heated to 1200 ° C. After processing to a diameter of 4 mm by aging, heat treatment was performed at a temperature of 1200 ° C. for 1 hour for removal of processing strain and diffusion bonding, and further drawing was performed to 2.3 mm and coated with a Pt-20 wt% Ir alloy. An Ir-10 wt% Rh alloy wire was produced.

  Next, seven of these coated wires were bundled and covered with a Pt-20 wt% Ir alloy pipe having an outer diameter of 9 mm and an inner diameter of 7 mm, followed by hot swaging. Then, a wire rod (plug material) having a diameter of 1.2 mm was manufactured by performing a drawing process while performing heat treatment. At the time of drawing, a heat treatment at 1200 ° C. was performed every time 30% was processed with a cross-section reduction rate. The manufactured plug material has a cross-sectional shape as shown in FIG. 6A, and has a honeycomb-shaped boundary phase made of Pt-20 wt% Ir alloy and a polygonal shape made of seven Ir-10 wt% Rh alloys. A cell phase was formed. The width of the cell phase was about 0.2 mm. At this time, the area ratio of the cell phase to the plug material cross-sectional area was 25%.

Third Embodiment : Here, the plug material was manufactured by reversing the metals constituting the boundary phase and the cell phase with respect to the first embodiment. Four wires of Ir-10 wt% Rh alloy with a diameter of 8 mm are prepared, these are arranged on the outer periphery of a Pt-20 wt% Ir alloy wire with a diameter of 11 mm, and the wire rods which are welded and bound are drawn and plugged The material was manufactured. The wire welding conditions and the drawing process conditions were the same as in the first embodiment. The manufactured plug material had a cross-sectional shape as shown in FIG. 1, and the central portion of the Pt-20 wt% Ir alloy as the cell phase was a square shape of 0.6 mm square. At this time, the area ratio of the cell phase to the plug material cross-sectional area was 35%.

Comparative Examples 1 and 2 : As a comparison with the above embodiment, Ir-10 wt% Rh alloy wire and Pt-20 wt% Ir alloy wire, which are conventional plug materials, were prepared. The wire diameter is 1.2 mm.

Discharge test : A discharge test was performed on the plug materials according to the embodiments and comparative examples. In this test, each wire was cut into 30 mm, opposed to each other with a gap of 1 mm, discharged for 300 hours, and the average value and the maximum value of the discharge voltage were measured. Table 2 shows the results.

  From Table 2, it can be seen that the plug material according to the first to third embodiments has an average discharge voltage reduced as compared with the comparative example. Moreover, the difference between the average value and the maximum value according to the first to third embodiments is also low, and it can be seen that stable discharge characteristics are maintained.

The figure which shows an example of the cross-section of the plug material which concerns on this invention. The figure explaining the state where the plug material which concerns on this invention was consumed. The figure which shows another example of the cross-section of the plug material which concerns on this invention. The figure which shows an example of the cross-section in the case of having the coating layer of the plug material which concerns on this invention. The figure explaining the manufacturing method of the plug material which concerns on this invention. The figure explaining the manufacturing method of the plug material which concerns on this invention.

Claims (11)

A substantially cylindrical plug material constituting a center electrode of a spark plug, comprising a boundary phase made of a first metal and a cell phase made of a second metal separated by the boundary phase in the cross-sectional structure thereof. The first metal and the second metal are plug materials that are different in resistance to spark consumption. The first metal and the second metal are platinum: 5 to 100% by weight, iridium: 10 to 100% by weight, rhodium: 0.1 to 50% by weight, or the noble metal alloy Is a noble metal alloy in which at least one of iron, nickel, and chromium is added in an amount of 0.1 to 15% by weight,
The plug material according to claim 1, wherein the Ir concentration of the first metal is 5% by weight or less as compared with the Ir concentration of the second metal. The plug material according to claim 1 or 2, wherein an area ratio of the second metal to a cross-sectional area of the plug material is 2 to 80%. The cell phase has a substantially rhombic or substantially trigonal polygonal shape having a flat extension toward the outer periphery, and a plurality of phases divided by the cell phase are formed. The plug material according to crab. The plug material according to any one of claims 1 to 3, wherein the boundary phase has a honeycomb shape by dividing a plurality of cell layers. The plug material according to any one of claims 1 to 5, further comprising a coating layer made of a first metal on an outer peripheral side surface. It is a manufacturing method of the plug material in any one of Claims 1-5, Comprising: The bar or wire which consists of a some 1st metal, and the bar or wire which consists of a 2nd metal in parallel A method for producing a plug material, in which the rods or wires that are bound and bound are drawn. It is the manufacturing method of the plug material in any one of Claims 1-6, Comprising: The bar or wire which consists of a 2nd metal coat | covered with the 1st metal was bound in parallel, and the said bound A plug material manufacturing method for drawing a rod or wire. The method for producing a plug material according to claim 7 or 8, wherein the side surface or at least one end of the bound bar or wire is welded and then drawn. The method for producing a plug material according to claim 8 or 9, wherein, prior to the drawing process, the bound bar or wire is inserted into a cylindrical material made of a first metal, and the cylindrical material is drawn. The manufacturing method of the plug material of Claim 7-10 processed using the material whose hardness difference of a 1st metal and a 2nd metal is 100 Hv or less.

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