JP4652621B2 - Spark plug manufacturing method and spark plug - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug manufacturing method and a spark plug.
[0002]
[Prior art]
For example, a spark plug used for ignition of an internal combustion engine is of a type in which an ignition part is formed by welding a tip mainly made of Pt to the tip of an electrode in order to improve spark wear resistance. However, in recent years, in order to further improve the spark wear resistance, a spark plug in which an ignition part is composed of a chip mainly composed of W (tungsten) instead of Pt is disclosed in, for example, Japanese Patent Application Laid-Open No. 59-25945, Various proposals have been made in JP-A-59-25949, JP-A-5-54955, JP-A-8-185594, and the like.
[0003]
Further, in recent years, the temperature in the combustion chamber tends to increase due to the increase in the output of the internal combustion engine, and in order to improve the ignitability, an engine of a type in which the ignition portion of the spark plug protrudes into the combustion chamber is often used. It has become like this. In addition, as part of measures for making maintenance free for automobile engines, severe demands that cannot be imagined from the previous situation, such as continuous running of 160,000 km or more without replacement of spark plugs, have come to be issued.
[0004]
[Problems to be solved by the invention]
When a W-type chip is used, since the melting point of W is as high as about 3380 ° C., the spark wear resistance is greatly improved. However, since W has a property of being easily oxidized and volatilized at a high temperature, it is long. If the high-speed traveling of time is repeated and the temperature rises above a certain temperature, there is a drawback that the ignition part is suddenly oxidized and consumed, and the spark gap interval is enlarged. In order to solve this problem, for example, in each of the above publications such as JP-A-5-54955 and JP-A-8-185594, a W-based alloy in which an additive metal such as Re or Ta is added to W is used for the chip. A method for improving the oxidative wear resistance of the ignition part has been proposed.
[0005]
Here, as a chip manufacturing method using a W-based alloy, a raw material powder obtained by adding an additive metal powder to a W powder is formed into a chip shape, and the molded body is sintered to form a chip (powder). Sintering method) was common. However, a chip made of a W-based composite material obtained by this powder sintering method has a drawback that it has low toughness and lacks mechanical strength, so that cracks are likely to occur. In addition, when using the powder sintering method, the additive amount of the additive metal to W can actually be added only about 3 to 10 wt% from the viewpoint of processing technology, and the oxidation consumption resistance may not be sufficiently improved. .
[0006]
An object of the present invention is to provide a spark plug and a method for manufacturing the same that can achieve both the oxidation wear resistance and mechanical strength of an ignition part made of a W-based composite material.
[0007]
[Means for solving the problems and actions / effects]
  In order to solve the above-described problem, the spark plug manufacturing method of the present invention includes a spark discharge gap formed between a center electrode and a ground electrode, and at least one of the spark discharge of the center electrode and the ground electrode. A spark plug manufacturing method in which an ignition part made of a W-based composite material containing W (tungsten) as a main component is provided at a position facing a gap,
  A sintering process for producing a sintered body by sintering the raw material powder of the W-based composite material;
  A hot working step for obtaining a hot working material by subjecting the sintered body to hot working so that W-based composite material particles extend in a predetermined direction;
  A chip forming step of processing the hot processed material into a chip of a predetermined shape as a chip material;
  A bonding step of bonding the chip to at least one of the center electrode and the ground electrode to form the ignition portion;TheIncludingSee
The W-based composite material contains 20 to 40 wt% of metal powder of a metal element belonging to Group 5A or 7A of the Periodic Table of Elements.It is characterized by that.
[0008]
When the ignition part is composed of a W-based composite material containing W as a main component, one or more selected from metal elements belonging to Group 5A or Group 7A of the periodic table of elements as an additive component of the W-based composite material It is effective in using Wt to suppress oxidation and volatilization of W. Specifically, for example, metal powders of these metal elements can be used.
[0009]
In the spark plug in which the ignition part is composed of a W-based composite material, the oxidation resistance consumption of the ignition part has hitherto been mainly attempted to improve mainly by adding an appropriate alloy element such as Re. Although it is certainly an effective technique, the present inventors have conducted intensive studies from the viewpoint of the metal structure, and as a result, the oxidation resistance and mechanical strength at high temperatures of the ignition part made of a W-based composite material are The chip is greatly affected by the structure of the metal crystal particles in the chip, and the structure is made into a fibrous shape in which the W-based composite material particles (metal crystal particles) are stretched in a predetermined direction, so that the oxidation resistance of the ignition part is reduced. Has been found to be remarkably improved and the mechanical strength is improved, and the present invention has been completed.
[0010]
That is, according to the manufacturing method of the present invention, a chip material made of a W-based composite material for forming an ignition part is manufactured by combining sintering and hot working, whereby the acid resistance of the ignition part obtained is obtained. It is possible to improve the wear resistance without deteriorating the mechanical properties. Employing the sintering method is effective in preventing component segregation and contributes to improvement in oxidation resistance. Further, by forming the chip structure into a fibrous form in which the W-based composite material particles are stretched in a predetermined direction by hot working, the occurrence of cracks and chips is remarkably reduced, and mechanical properties such as toughness and strength are reduced. Can be further improved. In addition, since the voids in the sintered body made of the W-based composite material are crushed and reduced by compression accompanying hot working, the thermal conductivity is improved and the inside of the ignition part (chip) due to the presence of the voids Oxygen can be prevented from penetrating into the film, and oxidation resistance can be further improved. Furthermore, by passing through the hot working process, compared with the case where the molded product of metal powder is sintered and made into chips as in the past, the connection between the metal particles becomes dense, so that the spark consumption is improved, In addition, since the segregation of impurities at the grain boundaries seen during powder sintering is made uniform, the spark consumption due to grain boundary corrosion is also improved.
[0011]
The content of the metal powder made of a metal element belonging to Group 5A or Group 7A of the periodic table of elements in the W-based composite material is about 5 to 45 wt%, preferably 10 to 40 wt%. When the content is less than 5 wt%, the spark wear resistance is excellent, but the oxidation resistance may be inferior. When the content exceeds 45 wt%, the relative amount of W is lowered, so that the spark wear resistance is lowered and the oxidation resistance is reduced. May be inferior.
[0012]
As used herein, the term “ignition portion” refers to a portion of a bonded chip that has not been affected by compositional variation due to bonding (for example, a portion that is alloyed with the material of the ground electrode or the center electrode by bonding). The remaining part). The “processing” as used in the present invention is not particularly limited as long as the crystal grains of the W-based composite material to be processed can be stretched in a predetermined direction. For example, forging, rolling, and wire drawing (drawing). It can carry out by 1 type or the combination of 2 or more types. In this case, the processing needs to be performed by hot processing in which the material temperature during processing is 1650 to 1750 ° C. When the processing temperature is less than 1650 ° C., the deformation resistance of the workpiece material made of the W-based composite material is large, and the frequency of occurrence of grain boundary cracks is high, and sound processing becomes impossible. On the other hand, when the processing temperature exceeds 1750 ° C., the oxidation and volatilization of the W component becomes violent, leading to a decrease in workability. In addition, the life of jigs used for processing (forging punches, rolling rolls, or wire drawing dies) can easily be exhausted at an early stage, leading to an increase in manufacturing costs.
[0013]
The processed material is made into a chip material having a suitable shape as an ignition part by various processes. As a specific processing method, in the hot working step, the sintered body is formed into a linear or rod-shaped material (hereinafter referred to as a linear material) by at least one of hot forging, hot rolling and hot wire drawing. If the chip is obtained by cutting it into a predetermined length in the length direction (for example, by electric discharge machining), the chip manufacturing yield is high, and the axial direction of the linear material (chip Or when it becomes an ignition part, it is convenient also in obtaining the structure | tissue consisting of the flat W type composite material particle extended in the direction parallel to the axis line.
[0014]
In this case, the chip has a fibrous structure in which the W-based composite material particles extend in the chip thickness direction and the average aspect ratio of the W-based composite material particles appearing in a cross section parallel to the chip thickness direction is 5 or more. It is desirable to manufacture as what exhibits. When the aspect ratio is 5 or more, the oxidation resistance and mechanical strength can be improved particularly remarkably due to the fiber formation of the tissue. Note that an extremely large aspect ratio causes a decrease in manufacturing efficiency and a cost increase due to an increase in the number of processing steps, so that the aspect ratio is appropriately determined within a range of, for example, about 100. In the present specification, the aspect ratio refers to various pairs of parallel tangent pairs that do not cross the inside of the grain with respect to the outline of the crystal grain observed in the field of view on a predetermined cross section, as shown in FIG. When drawn in the positional relationship, it is defined as a ratio Rdmax / Rdmin between the maximum interval Rdmax and the minimum interval Rmin in the pair of tangent pairs.
[0015]
As another method, the hot working includes a hot rolling process, and the hot working material is formed as a plate material based on the hot rolling process, and the thickness direction from the plate material is the chip thickness direction. For example, the chip can be manufactured by hot punching or electric discharge machining. The method is also highly efficient, and is composed of flat W-based composite material particles that are elongated in the plate surface direction of the plate-like material (in the direction perpendicular to the axis line when it becomes a chip or an ignition part). Convenient for obtaining tissue.
[0016]
In this case, the chip exhibits a fiber particle structure in which the W-based composite material particles extend in the direction of the chip main surface and the average aspect ratio of the W-based composite material particles appearing in a cross section orthogonal to the chip main surface is 5 or more. It is desirable to be manufactured as a product. When the aspect ratio is 5 or more, it is possible to particularly remarkably improve oxidation resistance and mechanical strength by flattening the tissue. Also in this case, extremely increasing the aspect ratio causes a decrease in manufacturing efficiency and a cost increase due to an increase in the number of processing steps, so that the aspect ratio is appropriately determined within a range of, for example, about 100.
[0017]
  Next, the spark plug of the present invention can be manufactured by the above manufacturing method, a spark discharge gap is formed between the center electrode and the ground electrode, and at least one of the sparks of the center electrode and the ground electrode. A spark plug provided with an ignition part made of a W-based composite material containing W as a main component at a position facing the discharge gap,
  The W-based composite material particles forming the ignition part have a structure stretched in a predetermined direction.And
The W-based composite material contains 20 to 40 wt% of metal powder of a metal element belonging to Group 5A or Group 7A of the Periodic Table of Elements.It is characterized by that.
  According to this, by making the W-based composite material particles (metal crystal particles) forming the ignition part into a structure stretched in a predetermined direction, the mechanical properties such as the toughness and strength of the ignition part are improved as well as the improvement in oxidation resistance. The properties are improved and the occurrence of defects such as cracks and chips is significantly reduced. Furthermore, the processing to make the W-based composite particles stretched reduces the number of vacancies in the ignition part made of W-based composite materials (due to the use of the sintering method) and improves thermal conductivity. In addition, oxygen can be prevented from entering the ignition portion (chip) due to the presence of the vacancies, so that the oxidation resistance and wear resistance can be further improved. The W-based composite material particles may contain one or more selected from metal elements belonging to Group 5A or Group 7A of the Periodic Table of Elements. In this case, oxidation and volatilization of W can be further suppressed.
[0018]
The W-based composite material forming the ignition part has a surface facing the spark discharge gap as an ignition surface, and a direction perpendicular to the ignition surface is defined as a height direction of the ignition part. It is desirable that the W-based composite material particles appear in a cross section parallel to the firing portion height direction and have a structure having an average aspect ratio of 5 or more while extending in the portion height direction. Further, when the W-based composite material particles are to be stretched in a predetermined direction along the ignition surface, the ignition surface appears along a cross-section perpendicular to the ignition surface along the extending direction of the W-based composite material particles. It is desirable to exhibit a structure in which the average aspect ratio of the W-based composite material particles is 5 or more.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A spark plug 100 as an example of the present invention shown in FIG. 1 and FIG. 2 is formed at a distal end of a tubular metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip portion 21 protrudes. One end is joined to the center electrode 3 and the metal shell 1 provided inside the insulator 2 in a state where the ignition portion 31 is protruded, and the other end is bent back to the side. Includes a ground electrode 4 disposed so as to face the tip of the center electrode 3. Further, the ground electrode 4 is formed with an ignition part 32 that faces the ignition part 31, and a gap between the ignition part 31 and the opposing ignition part 32 is a spark discharge gap g.
[0020]
The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, for example, and has a hole 6 for fitting the center electrode 3 along its own axial direction. The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw for attaching the plug 100 to an engine block (not shown) on its outer peripheral surface. Part 7 is formed.
[0021]
The chip adherent surface forming portion of the center electrode 3 and the ground electrode 4, in this embodiment, at least the surface layer portion thereof is made of a heat-resistant alloy containing Ni or Fe as a main component. "Means the component having the highest mass content, and does not necessarily mean" the component occupying 50% by mass or more "). For example, as a heat-resistant alloy containing Ni as a main component, INCONEL600, INCONEL601, or the like can be used.
[0022]
On the other hand, the ignition part 31 and the opposing ignition part 32 are mainly composed of a W-based composite material containing W as a main component, and the W-based composite material includes a group 5A metal element (V, Nb, Ta) or One or more additive metals selected from Group 7A metal elements (Mn, Tc, Re) are included, and the particles have a structure stretched in a predetermined direction. Thereby, even in an environment in which the temperature of the center electrode 3 and the ground electrode 4 is likely to rise, the spark consumption and mechanical strength of the ignition parts 31 and 32 can be improved, and oxidation of the W component can be achieved.・ Deterioration is extremely effectively suppressed by volatilization. Moreover, the weldability with respect to the electrode which consists of the above heat-resistant alloys is also favorable. In addition, it is good also as a structure which abbreviate | omits any one of the ignition part 31 and the opposing ignition part 32. FIG. In this case, the spark discharge gap is between the ignition part 31 and the side surface of the ground electrode 4 that does not have the ignition part, or between the ignition part 32 and the tip surface of the center electrode 3 that does not have the ignition part. g will be formed. Further, the opposing ignition part 32 on the ground electrode 4 side may be made of a material other than the W-based composite material such as a noble metal or a noble metal alloy mainly containing Pt, Ir, or Rh.
[0023]
As described above, the additive metal element component that can be added to the W-based composite material constituting the ignition parts 31 and 32 is a group 5A metal element (V, Nb, Ta) or a group 7A metal element (Mn, Tc, Re). One or more selected from can be contained. By adding these components, it becomes possible to improve the oxidation consumption resistance. In particular, Nb has an extremely high effect of improving the oxidation consumption resistance at high temperatures of the ignition parts 31 and 32.
[0024]
As the W-based composite material, for example, an alloy containing W as a main component and Nb as an additive metal in a range of 5 to 45 wt% can be used. By using the alloy, the consumption of the ignition part due to oxidation and volatilization of the W component at a high temperature is further effectively suppressed, and as a result, a spark plug having higher durability is realized.
[0025]
Here, as the content of Nb in the alloy increases within the above range, the oxidation / volatilization suppressing effect of the ignition parts 31 and 32 is enhanced. In this respect, the effect of suppressing oxidation and volatilization is most remarkable when the Nb content is 10 to 40 wt%, more preferably 20 to 35 wt%, and most preferably 25 to 30 wt%. However, in the present invention, since the effect of suppressing oxidation consumption due to the W-based composite material particles constituting the ignition portions 31 and 32 being stretched in a predetermined direction is large, the stretched structure is obtained even if the Nb content is relatively small. Even when compared with a conventional spark plug in which the ignition part is formed of a W-based composite material having no form, a good oxidation / volatilization effect is achieved. As a result, it is possible to realize a spark plug having excellent oxidation resistance and wear resistance of the ignition part 31 or 32 while reducing the content of relatively expensive Nb.
[0026]
An alloy containing W as a main component and Re as an additive metal in the range of 5 to 45 wt% can also be used as the W-based composite material. By using the alloy, the consumption of the ignition part due to the oxidation and volatilization of the W component at a high temperature is effectively suppressed, and as a result, a spark plug excellent in durability is realized. If the Re content in the alloy is less than 5 wt%, the effect of suppressing the oxidation and volatilization of W becomes insufficient, and the ignition part tends to be consumed, so that the durability of the plug may be lowered. On the other hand, if the Re content exceeds 45 wt%, the melting point of the alloy may decrease, and the durability of the plug may also decrease.
[0027]
Examples of the spark plug manufacturing method of the present invention will be described below.
As shown in FIG. 3A, a disc-shaped chip 31 ′ made of an alloy composition constituting the ignition part 31 (see FIGS. 1 and 2) is superimposed on the tip surface of the center electrode 3, and The ignition part 31 is formed by forming an all-around laser welded part (hereinafter also simply referred to as a welded part) 10 along the outer edge of the joint surface by laser welding and fixing it. Further, the opposing ignition part 32 (see FIGS. 1 and 2) aligns the tip 32 'with the ground electrode 4 at a position corresponding to the ignition part 31, and similarly welds 20 along the outer edge of the joint surface. And are fixed to each other.
[0028]
A manufacturing method of these chips 31 ′ and 32 ′ (hereinafter, when the chips 31 and 32 are generically referred to, the symbols “154” to “155” may be used) will be described below. First, as shown in FIG. 4 (a), a raw material powder (W-based composite material powder) P having a predetermined composition containing W as a main component is blended, and this is formed into a predetermined shape as shown in FIG. 4 (b). After molding, it is sintered. The raw material powder P can be a composite of an additive metal powder composed mainly of a W metal powder and composed of an additive metal element such as Nb or Re.
[0029]
FIG. 5 (a) shows a raw material powder P mainly composed of W metal powder formed by pressing or the like to form a compact 140, which is sintered in a sintering furnace FS as shown in FIG. 5 (b). This is an example of obtaining a block-shaped sintered body 150. Moreover, as shown in FIG.5 (c), the cylindrical powder compact 130 can be made and this can be sintered and the cylindrical sintered body 135 can also be made. This form is advantageous when processing into a linear or rod-like shape having a circular cross section, for example.
[0030]
Next, the sintered body obtained as described above is hot-worked. For example, the cylindrical sintered body 135 obtained as shown in FIG. 5C is subjected to hot rotary forging using a rotary hammer (hot swaging: the method itself is known), hot wire. After rolling (using a grooved roll that forms a roll hole mold: the method itself is a known one) or a combination thereof to draw in the axial direction to form a rod-shaped material, wire drawing as shown in FIG. 6 (a) Drawing is further performed by hot drawing using a die to obtain a linear material 153 as shown in FIG. The linear material 153 is formed to have a circular axial cross section, and the structure thereof is a fibrous material in which crystal grains of a W-based composite material are stretched in the longitudinal direction of the material, as shown in FIG. Become. The average aspect ratio (Rdmax / Rdmin) of the crystal grains of the W-based composite material is 5 or more in a cross section parallel to the longitudinal direction of the linear material 153 (the cross section AA including the central axis of the material in the drawing).
[0031]
On the other hand, as shown in FIG. 8A, a block-shaped sintered body 150 shown in FIG. 4B (or a bar-shaped material 151 forged from it shown in FIG. 8C) is used as a rolling roll pair. By hot rolling the sintered material, a plate-shaped material 152 shown in FIG. 4 (d) can be obtained. In the plate-like material 152, the crystal grains of the W-based composite material are stretched in a direction along the main surface MT of the plate by hot working. The crystal particles of the W-based composite material have a flat particle structure having an average aspect ratio (Rdmax / Rdmin) of 5 or more in a cross section LT along the extending direction and orthogonal to the main surface.
[0032]
Next, the plate-like material 152 or the linear material 153 that is the hot-worked material obtained as described above is processed into chips having a predetermined shape. For example, if the plate-like material 152 of FIG. 4D is punched in the thickness direction by hot punching, a chip 154 as shown in FIG. 4E can be formed. In this case, as shown in FIG. 10A, in the chip 154, the crystal particles of the W-based composite material extend in the direction along the end surface (chip main surface) CP in the chip thickness direction and along the extending direction. In addition, a flat particle structure in which the average aspect ratio of the crystal grains of the W-based composite material appearing in the cross section AS orthogonal to the chip main surface is 5 or more is exhibited.
[0033]
In FIG. 1, the tip 154 is joined to the center electrode 3 and / or the ground electrode 4 by welding so that the tip thickness direction coincides with the axial direction O of the center electrode 3, thereby forming the ignition portion 31 or 32. . Specifically, a method of forming the annular welded portion 10 or 20 (see FIG. 3) along the outer peripheral surface of the chip by laser welding, or a method of using resistance welding can be exemplified. As shown in FIG. 3 (b), the ignition parts 31 and 32 have W-based composite material crystal particles with the surface facing the spark discharge gap g (derived from the chip main surface) as the ignition surface. While extending along a predetermined direction J parallel to the ignition surface, it exhibits a flat particle structure in which the average aspect ratio of the crystal grains of the W-based composite material appearing in the cross section orthogonal to the ignition surface is 5 or more.
[0034]
On the other hand, the chip | tip 155 can be manufactured by cut | disconnecting the linear raw material 153 of FIG.4 (d) to a predetermined space | interval in a length direction by electrical discharge machining etc. FIG. As shown in FIG. 10 (b), the chip 155 includes W-based composite material crystals that appear in a cross section AS parallel to the chip thickness direction, while crystal grains of the W-based composite material extend in the chip thickness direction. It exhibits a fibrous structure in which the average aspect ratio of the particles is 5 or more. The tip 155 is also joined to the center electrode 3 and / or the ground electrode 4 by welding as shown in FIG. The W-based composite material crystal particles are stretched along a direction J parallel to the axis O, and the average aspect ratio of the W-based composite material crystal particles appearing in a cross section parallel to the extending direction is 5 or more. Presents an organization.
[0035]
The above-mentioned chips 154 and 155 shown in FIGS. 10A and 10B have a diameter dc of about 0.4 to 1.2 mm and a thickness tc of about 0.5 to 1.5 mm, for example. As a result, the outer diameters of the ignition parts 31 and 32 also have the same dimension dc.
[0036]
[Experimental example]
In order to confirm the effect brought about by the configuration of the spark plug 100 of the present invention, the following experiment was conducted. First, as a raw material powder, Ta powder, Nb powder, and Re powder having an average particle size of about 10 μm are respectively 5, 10, 20, 30, 40, 45, and 50% by weight with respect to W powder having an average particle size of about 10 μm. Dry mixing was performed. Each of these raw material powders is molded at a pressure of 200 kg / mm²Was pressed at room temperature to form a green compact. Next, this compact was sintered in a vacuum at 3000 ° C. for 20 hours to obtain a rod-shaped sintered body having a length of about 30 mm, a width of 20 mm, and a height of 100 mm.
[0037]
Next, the following hot working was performed on the sintered body. First, forging pressure 5 × 10 while maintaining the material temperature at 1500 ° C.⁵kg / cm²Then, preliminary forging was performed on a prismatic bar having an axial cross-section of 10 mm square. Subsequently, it rolled by the hot wire rolling process using a grooved roll until a cross section became 1.5 mm square. In addition, the groove roll temperature at the time of rolling was maintained in the range of 680-750 degreeC, and raw material temperature in the range of 1300-1400 degreeC.
[0038]
Then, the material temperature is maintained at 1300 to 1400 ° C., the wire diameter is 0.9 mm by hot forging, and the die temperature is maintained at 680 to 750 ° C. and the wire temperature is 1300 to 1400 ° C. Then, hot wire drawing was performed until the final wire diameter became 0.6 mm. The wire thus obtained was cut into a thickness of 0.8 mm in the axial direction by electric discharge machining to obtain a disk-shaped chip having a diameter of 0.6 mm and a thickness of 0.8 mm.
[0039]
The obtained chip was polished so that a cross-section including the central axis appeared and the structure was observed. As a result, the crystalline particles of the W-based composite material were stretched in the thickness direction of the chip to form a fibrous structure. all right. When the average aspect ratio of the crystal grains of the W-based composite material was measured in the cross section, it was found to be about 50.
[0040]
Each chip was subjected to an oxidation consumption resistance test. That is, after each chip was left at 1100 ° C. for 20 hours in the air, the remaining amount of oxidation was calculated from the ratio of the area of the unoxidized portion to the area of the cross section of each chip. Specifically, the chip surface area X when each chip is viewed in plan from the discharge surface side is obtained in advance, and each chip is left in the atmosphere at 1100 ° C. for 20 hours. In the case of ultrasonic cleaning, the surface area Y of the chip (unoxidized portion) when the remaining chip (unoxidized portion) is viewed in plan from the discharge surface side is obtained, and the chip (unoxidized portion) relative to the chip surface area X is obtained. Oxidized portion) The remaining amount of oxidation was calculated from the ratio of the surface area Y. The results are shown in FIG. In the graph of FIG. 11, the horizontal axis indicates the amount of Ta, Nb, and Re added, and the vertical axis indicates the amount of residual oxidation. Thus, it can be seen that the chip with the added amount of Ta, Nb, Re of 5 to 45 wt%, which is the range of the present invention, shows that the oxidation consumption is suppressed, and further when the added amount is about 10 to 40 wt%. It turns out that it is preferable. Note that the W metal with no added metal disappeared in 5 hours.
[0041]
In addition, a desktop spark test was performed on the chips containing the above Nb in each addition amount. That is, using each chip, the spark plug ignition portion 31 and the opposing ignition portion 32 shown in FIG. 1 are formed so that the spark discharge gap g has a width of 0.8 mm, and the plug is attached to the test chamber. Then, an AC voltage with a frequency of 60 Hz was applied for 200 hours at a chamber internal pressure of 0.4 MPa and a maximum voltage of 30 kV, and the amount of increase in the width of the spark discharge gap g was measured. Note that the atmosphere in the chamber was a nitrogen atmosphere. The result is shown in FIG. Thus, it can be seen that the chip in which the amount of Nb added is 5 to 45 wt%, which is the range of the present invention, has a small gap increase and a very good resistance to oxidation and consumption.
[0042]
On the other hand, an actual machine durability test was performed on each of the above chips and a chip (same component composition) obtained by sintering a powder molded product without performing hot working. That is, the ignition part 31 and the opposing ignition part 32 of the spark plug 100 shown in FIG. 1 are formed using the above chips so that the spark discharge gap g has a width of 0.8 mm, and the spark consumption by the actual machine is reduced. A sex test was performed. In other words, the plug is attached to a gasoline engine (displacement 2000 cc), unleaded gasoline is used, the throttle is fully opened, the engine is operated at 5000 rpm for 400 hours (equivalent to traveling 50,000 km), and the spark discharge gap g The amount of magnification was measured. The center electrode temperature during the test was measured using a known temperature measuring plug. As a result, the center electrode temperature in the vicinity of the tip surface position of the metal shell 1 of the spark plug 100 shown in FIG. Met. The results are shown in FIG. Compared to a chip with only sintering, a chip whose structure is fibrous by further hot working after sintering has a very good result because the gap increase is small and the oxidation consumption resistance is greatly improved. It can be seen that is obtained.
[0043]
Next, a chip (W-30Nb hot forged product) obtained by adding 30 wt% Nb and the above hot working, and a chip obtained by molding and sintering without adding 30 wt% Nb and performing the above hot working A strength test was performed on (W-30Nb sintered product). That is, in addition to preparing the spark plug 100 shown in FIG. 1 in which the ground electrode 4 is not coupled to the metal shell 1, four chips each using the above-mentioned chips are prepared for each chip. In the apparatus as shown in FIG. 14, the spark plug in this state is fixed, the weight (200 g) is swung up to an angle θ = 15 ° to 45 °, and dropped in a pendulum manner at an initial speed of zero every 2.5 °. An impact was applied to the surface (ignition part 31), and the presence or absence of cracks or chips in the chip was examined. An alumina plate is fixed to the surface of the weight that contacts the chip. The results are shown in FIG. FIG. 15 is a plot of the weight angle at which cracking and chipping occurred for each chip. Compared with a chip of only sintering, in a chip whose structure is fibrous by further hot working after sintering, It can be seen that the weight angle at which chipping occurs is large, that is, the impact resistance is improved.
[0044]
In addition, 10 wt% of Nb powder is added to W powder, 5 kinds of raw material powders are added 5, 10, 15, 20, and 25 wt% of Re powder, and 20 wt% of Nb powder is added to W powder, and Re powder is further added. Each of the three types of raw material powders to which 5,10,15 wt% was added was sintered and hot-worked in the same manner as described above to produce ternary (W-Nb-Re) chips. For each of these chips, the oxidation remaining amount was calculated by the same oxidation resistance consumption test as described above. The results are shown in FIG. It can be seen that the ternary chip consisting of W, Nb, and Re also has good oxidation resistance as well as the binary chip consisting of W and Nb.
[Brief description of the drawings]
FIG. 1 is a partial front sectional view showing an embodiment of a spark plug according to the present invention.
FIG. 2 is an enlarged sectional view showing the main part.
FIG. 3 is an enlarged sectional view showing FIG. 2 in a further enlarged manner.
FIG. 4 is a schematic view showing an example of a method for manufacturing a firing portion forming chip.
FIG. 5 is a schematic view showing an example of chip forming and sintering methods.
FIG. 6 is an explanatory view schematically showing a step of making W-based composite material particles into a fibrous form and a structure of the obtained material.
FIG. 7 is a diagram illustrating an aspect ratio of crystal grains.
FIG. 8 is an explanatory view schematically showing a step of flattening W-based composite material particles and a structure of the obtained material.
FIG. 9 is a diagram schematically showing a state in which pores in a sintered body disappear due to compression by processing.
FIG. 10 is an explanatory diagram showing some examples of chip structures.
FIG. 11 is a graph showing the results of a binary oxidation resistance test.
FIG. 12 is a diagram showing the results of a desktop spark test.
FIG. 13 is a diagram showing results of an actual machine durability test.
FIG. 14 is a schematic diagram showing an apparatus for performing a strength test.
FIG. 15 is a diagram showing the results of a strength test.
FIG. 16 is a graph showing the results of a ternary oxidation resistance consumption test.
[Explanation of symbols]
1 metal shell
2 Insulator
3 Center electrode
4 Ground electrode
31 ignition part
31 'chip
32 Opposing firing parts
g Spark discharge gap

Claims (8)

Ignition made of a W-based composite material containing W as a main component at a position where a spark discharge gap is formed between the center electrode and the ground electrode and at least one of the center electrode and the ground electrode faces the spark discharge gap. A spark plug manufacturing method provided with a section,
A sintering process for producing a sintered body by sintering the raw material powder of the W-based composite material;
A hot working step for obtaining a hot working material by subjecting the sintered body to hot working so that W-based composite material particles extend in a predetermined direction;
A chip forming step of processing the hot processed material into a chip of a predetermined shape as a chip material;
See containing and a bonding step to the firing portion by joining the tip to at least one of said ground electrode and said center electrode,
The spark plug manufacturing method, wherein the W-based composite material contains 20 to 40 wt% of a metal powder of a metal element belonging to Group 5A or Group 7A of the Periodic Table of Elements . By stretching the sintered body by the hot working, the hot working material is formed as a linear or rod-shaped material (hereinafter collectively referred to as a linear material), and the linear material is The method for manufacturing a spark plug according to claim 1, wherein the tip is formed by cutting at predetermined intervals in the longitudinal direction. The chip exhibits a fibrous structure in which W-based composite particles extend in the chip thickness direction and the average aspect ratio of the W-based composite particles appearing in a cross section parallel to the chip thickness direction is 5 or more. The method for manufacturing a spark plug according to claim 2 , wherein the spark plug is manufactured as a product. The hot working includes a hot rolling step, and the hot working material is formed as a plate-like material based on the hot rolling step, and the plate thickness direction from the plate-like material is the chip thickness direction. The method for manufacturing a spark plug according to claim 1, wherein the chip is processed. The chip extends in a direction along an end face (hereinafter referred to as a chip main surface) in the chip thickness direction, and the W-based composite material particle appears in a cross section parallel to the extending direction and perpendicular to the chip main surface direction. The manufacturing method of the spark plug of Claim 4 manufactured as what exhibits the flat particle structure whose average aspect-ratio of W type composite material particle | grains is 5 or more. Ignition made of a W-based composite material containing W as a main component at a position where a spark discharge gap is formed between the center electrode and the ground electrode and at least one of the center electrode and the ground electrode faces the spark discharge gap. A spark plug provided with a portion,
Particles of the W-based composite material of the said spark portion, have a tissue stretched in a predetermined direction,
The spark plug characterized in that the W-based composite material contains 20 to 40 wt% of a metal powder of a metal element belonging to Group 5A or Group 7A of the Periodic Table of Elements . The W-based composite material forming the ignition part has a surface facing the spark discharge gap as an ignition surface, and a direction perpendicular to the ignition surface is an ignition part height direction. The spark plug according to claim 6 , wherein the spark plug exhibits a fibrous structure in which an average aspect ratio of the W-based composite material particles extending in the vertical direction and appearing in a cross section parallel to the ignition portion height direction is 5 or more. The W-based composite material forming the ignition part has the surface facing the spark discharge gap as an ignition surface, and the W-based composite material particles extend in a predetermined direction along the ignition surface. The spark plug according to claim 6 , which exhibits a structure in which an average aspect ratio of the W-based composite material particles appearing in a cross-section along the extending direction of the composite material particles and perpendicular to the ignition surface is 5 or more.

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