MXPA01000425A - Spark plug tip having platinum based alloys - Google Patents

Abstract

A spark plug and method of making same, wherein the spark plug includes a platinum alloy tip portion which takes the form of a rivet or a sphere. The tip portion is annealed in an annealing furnace at a temperature between about 700°-1400°C for a time between about 5-30 minutes. The annealed tip portion is then resistance welded to an electrode of the spark plug. The annealing provides the tip portion with added resistance to corrosion and attack by lead. Preferred embodiments of the spark plug tip material comprise 80%platinum - 20%rhodium;80%platinum - 20%iridium;96%platinum - 4%tungsten;and Pt (bal) - Ir (a)%-W(b)%, where"a"ranges from about 15 to 19 percent by weight;"b"ranges from about 1 to 4 percent by weight, and the balance is comprised of platinum and incident impurities, and wherein the sum of iridium and tungsten present ranges from about 16 to19.

Description

SPARK PLUG WITH ALLOYS BASED ON PLATINUM BACKGROUND OF THE INVENTION Field of the Art This invention relates to spark plugs, and more particularly to a spark plug having a tip portion composed of platinum-based and hardened alloys to provide high resistance to lead and other corrosive elements that could affect adverse to the tip portion and therefore shorten the life of the spark plug.

Explanation Spark plugs are used in internal combustion engines to ignite fuel in a combustion chamber. The electrodes of the spark plug are subject to intense heat and an extremely corrosive atmosphere generated by the formation of a spark and combustion of the combustible air mixture. To improve the durability and resistance to erosion, spark plug electrode tips must be able to withstand high temperature and corrosive environment of the internal combustion chamber resulting from the reaction of chemical products between air, fuel and fuel additives. The SAEJ3L2 describes the specification for gasoline cars used as a fuel in the United States. Gasoline consists of mixtures of hydrocarbons derived from petroleum: saturated (50-80%), olefins (0-15%) and aromatic (15-40%). Leaded gasoline contains approximately 0.10 g Pb / gallon of fuel (0.026 g Pb / 1), and sulfur 0.15%. In unleaded gasoline there is approximately 0.05 g Pb / gallon, (0.013 g Pb / 1), 0.1% sulfur, 0.005 g P / gallon, (0.0013 g P / L). In addition, there are a number of additives incorporated in the fuel for several reasons. For example, tetramethylphenyl (TML) and tetraethyl lead (TEL) are added as antiknock agents. Compounds of carboxylic acids (acetic acid), are added as lead diluents. Aromatic amines, phenols are added as antioxidants. Organic bromine, chlorine compounds are added as rags and deposit modifiers, phosphorus and boron contain compounds that are added to reduce the surface of ignition, preignition and as trapeze machines. Metallic activators are added to reduce oxidation deterioration of the fuel by metals, such as Cu, Co, V, Mn, Fe, Cr and Pb. In addition, carboxylic acids, alcohols, amines, sulfonates, phosphoric acid salts of amines are used as oxidation prevention additives. The mechanism for ignition in an internal combustion engine is very complex and is briefly explained here. In the gasoline engine, the piston that rises compresses the air / fuel mixture, which causes an increase in pressure and temperature. The spark ignites the charge of combustible air, and the force of the advance of the frontal flame acts against the piston, compressing the load more distant unburned combustible air. The reactions of pre-flame combustion occur in the unburned combustible air mixture. Impact or detonating noise often associated with internal combustion engines occurs when an extremely rapid combustion reaction occurs at the front end of the gasoline of the forward flame advance. The formation of the pre-flame reaction products of gasoline establish the state to detonate. It is believed that the alkyl lead additive must first be decomposed in the combustion chamber to form lead oxide before it can exert its anti-detonating effect. The antiknock species must be finely dispersed in the combustion chamber to adjust the number of collisions of the critical reaction species with which the anti-detonating agent will occur. However, lead oxide deposits can cause problems with valve burns and soiling spark plugs. The deposits of lead that accumulate in the spark plug insulation cause the machine not to ignite due to the high speed at the relatively high electrical conductivity of the tank. The complete combustion of a hydrocarbon fuel with air will produce carbon dioxide (C02), water (H20) and nitrogen (N2). The air radius for fuel by weight, 14.5 / 1, is the correct chemical mixing ratio. The less air is available, some carbon monoxide (CO) and hydrogen (H2) is found in the products, while some oxygen (02) is available in the products. The atmosphere present during combustion can cause hot electrode corrosion in the spark plug. The manufacturers of copper electrode (Cu) and nickel (Ni) for spark plugs is a test in the art and has been completed in a variety of ways. For example, U.S. Patent No. 3,803,892 issued April 16, 1974 and entitled "Central Electrode Spark Plug Production Method" describes a method of extruding the copper and nickel electrodes from a flat plate of the two materials. U.S. Patent No. 3,548,472 issued December 22, 1970 and entitled "Connection Ignition and Method for Fabricating a Central Electrode therefor" illustrates a method of cold forming an outer sleeve in the form of a nickel cup by some steps , inserting a piece of copper wire into the cup and then lightly pressing the two materials together. U.S. Patent No. 3,857,145 issued December 31, 1974 and under the title "Method of Producing a Central Spark Plug Electrode" describes a process whereby a central copper core is inserted into a nickel element and attached to it by a collar portion to ensure that an electric flow path occurs. The spark plug electrodes produced by the above described methods are performed in a satisfactory manner for a relatively short period of time of handling when used in vehicles that were manufactured before the clean air implementation of the 1977 law in the United States. United. After 1977, with the modifications for the machine and fuel, the operating temperature of most vehicles increases. As a result of the changes in the machines and fuels, some of the components that operate in the machines have been subject to the corrosive effects of the exhaust gases. After a period of time of operating at higher temperatures in gas recirculation, some erosions / corrosion may occur to the nickel-based core electrode. Once corrosion takes place, the deteriorated electric flow path can result in lower fuel efficiency. Currently spark plug manufacturers for automotive vehicles commonly include an electrode that is manufactured from at least one nickel part. The electrode also commonly includes a very small tip portion that is welded to the electrode during the manufacture of the spark plug.

The tip portion is commonly of the shape of a sphere or rivet, the process of cooling form also serves to reduce the resistance of the tip to erosion. Currently, there is a need and desire to develop a long life (above 150,000 miles) for spark plugs for internal combustion engines that are suitable for use with lead and lead-free fuels. There is also a need for a long life spark plug that can be manufactured by current manufacturing procedures, which is not appreciably more expensive than spark plugs currently manufactured, and which includes an electrode that is manufactured to be highly resistant to lead attack and other corrosive elements to operate at high temperatures. There is also a need for a long life spark plug that can be manufactured without significantly increasing the complexity of the assembly process used in the manufacture of the spark plug.

COMPENDIUM OF THE INVENTION. The invention relates to a spark plug with a long life and a method of manufacturing it. The spark plug contains at least one electrode, and preferably a pair of electrodes, each of which includes a tip portion welded thereto. The tip portion contains a rivet-shaped portion or sphere containing a platinum alloy. In a preferred embodiment, the tip portion is composed of platinum, iridium and tungsten. During fabrication, the tip portion is tempered in a tempering furnace at a temperature within a range of about 900-1400 ° C. The tempering furnace is preferably charged with argon, nitrogen or subjected to a vacuum, and the tip portion is kept in the furnace for a period of time preferably within the range of about 5-15 minutes. This produces a tip portion that has a fine grain microstructure. Subsequently, the tip portion is allowed to cool, or near to, room temperature and is then placed in a welded device. The tip portion is then aligned with the electrode and then a resistance welded to the electrode. The same procedure is preferably performed on both. The central and base electrodes of the spark plug. The hardened purta portions have a high resistance to attack by lead and other corrosive elements commonly experienced in combustion chambers of internal combustion engines. The result of a spark plug that has an extremely long life (up to approximately 150,000 miles or more). The aperture established between the two spark plug electrodes is further maintained substantially constant for the life of the spark plug after the tip portions of each of the electrodes are substantially unaffected by the gases produced in the combustion chambers of a spark plug machine. internal combustion.

BRIEF DESCRIPTION OF THE DRAWINGS The various advantages of the present invention will become apparent to a person skilled in the art by reading the following specification and appended claims and making reference to the following drawings in which: Figure 1 is an elevation view of a portion of a spark plug. according to the preferred embodiment of the present invention that incorporates a hardened tip portion in each of the central and base electrodes thereof; Figure 2 is a side view elevation of a platinum alloy sphere before it is resistively welded to one of the spark plug electrodes; Figure 3 is a side elevation view of an aluminum alloy rivet according to the preferred embodiment of the present invention before it is welded to one of the spark plug electrodes; Figure 4 is a flow diagram of the steps used to treat at high temperature and secure the portion attached to a spark plug electrode; Fig. 5 is a simplified drawing of a welding tool being used to resistively solder the tip portion to the center electrode of the spark plug, where the tip portion contains a rivet-shaped tip portion.; Figure 6 is a simplified side view of a welding tool that is used to resistively weld the tip portion to the side electrode of the spark plug, where the tip portion consists of a spherical tip portion; Figure 7 is a micrograph of a rough grain 80% Pt-20% platinum-based alloy of a tip portion of a spark plug after 75 hours of exposure to leaded fuel during a SPEAD test; Figure 8 is a micrograph of a fine grain 80% Pt-20% Rh tempered, of a tip portion of platinum-based alloy after it has been exposed for 75 hours to the fuel with lead during a SPEAD test; Figure 9 is a graph indicating the hardness of a hardened 80% Pt-20% in an alloy after being subjected to a tempering temperature for 5 minutes; and Figure 10 is a graph indicating the hardness of a hardened 80% Pt-20% Rh of an alloy after it is subjected to a tempering temperature for 5 minutes.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES With reference to Figure 1, a spark plug 10 is illustrated according to the preferred embodiment of the present invention. The spark plug 10 includes an annular metallic housing 12 having filaments 14 formed thereon, a central electrode 16 having a tip portion 18, an insulator 20 and a side or base electrode 22. The central electrode 16 is placed inside the insulator 20, it is turned inside the metallic housing 12. As is well known, it is desirable to maintain the distance between the tip portion. 18 and the side electrode 22, hereinafter referred to as the "hollow" 24, constant over the life of the spark plug 10. The tip portion 18 has hitherto been fabricated from platinum (Pt), which has been found to provide good resistance to erosion carried by the spark in the presence of combustible gases present in the combustion chambers of an internal combustion engine. However, the tip portion of plate 18, which is shown in figure 1 in the form of a sphere, is still susceptible to being attacked by lead, which is present in some fuels that are still used with internal combustion engines. . The erosion and deterioration of the tip portion can cause the gap 24 to widen, thereby weakening the spark that the spark plug 10 produces.

It has been found that iridium (Ir) has excellent resistance to the attack of a large range of molten metals. According to the preferred embodiments of the tip portion 148 described herein, they are preferably composed of 80% platinum-20% iridium, or 80% platinum-20% rhodium or 80% platinum-4% tungsten. Alternatively, the tip portion can be composed of the following alloys: Pt (almost 81%) - Go (almost 18%) - (almost 1%); Pt (almost 81%) - Go (almost 15%) - W (almost 4%); or Pt (at least about 80%) - Go (less than about 20%) and W (less than about 4%). It is also appreciated that the amount of iridium, rhodium or tungsten can vary significantly, and that the approximately expressed hundreds may vary if desired. Referring now to Figures 2 and 3, two embodiments of the tip portion 18 of the present invention are shown. Figure 2 illustrates the tip portion in the shape of a sphere 18a. The diameter of the sphere can vary significantly but is preferably within the range of about 381 um - 1.14 mm (0.015 - 0.045 inches), and more preferably about 0.760 um (0.030 inches). Figure 3 illustrates the tip portion 18 in the form of a rivet 18b. The rivet 18b includes a head 28 having a coatinua, hemispherical outer surface 30 and a flat portion 32. A final part 34 extends from the end portion 32 and has a flat outer surface 36. Referring now to Figure 4 , a flow diagram 38 illustrates the steps performed in the high temperature treatment and welding of the tip portion 18 to the electrode 16. Initially, a tip portion of platinum iridium, platinum rhodium or tungsten platinum is obtained, as indicated in step 40. The tip portion can be in the form of a sphere or rivet. Top portions are commercially available from a company number such as Engelhard Corporation Johnson Matthey and Sigmund Cohn Corporation. Further with reference to Figure 4, a suitable tip portion 18 is first chosen, as indicated in step 40. The tip portion 18 is then hardened in a tempering furnace at a temperature preferably within the range of about 700 ° -1400 ° C and for a period of time preferably between about 5-30 minutes, and more preferably for a time between about 5-15 minutes, as indicated in step 42. After the tempering is finished, the tip portion tempered 18 is removed from the tempering furnace and allowed to cool to room temperature, as indicated in step 44. Referring now to figures 4 and 5, the tip portion 18b is then placed in a welded device, as indicated in step 46. In Figure 5, the welded device is designed by a reference numeral 54 and has a void 56. The void 56 is formed to maintain so a sphere shape or a rivet shape of the tip portion on a flat upper surface 58. Figure 6 illustrates a welded device 54a suitable for maintaining the rivet sphere shape 18a. The electrode 16 can then be included on an outer portion 16a made of nickel and copper core 16b. A lower flat surface 16c is positioned to face the rivet-shaped tip portion 18b. In step 48 in Fig. 4, the electrode 16 of the spark plug is aligned with the tip portion, as also shown in Fig. 5. A welded electrode 60 is then aligned on the spark plug electrode 16, as indicated in Figs. step 50 (and in figure 5) and tip portion 18b is then resistively welded to the spark plug electrode as indicated in step 52. Figure 6 shows steps 46-50 for the sphere-shaped tip portion 18a which is attached to the base electrode 16 of the spark plug 10. The hardened tip portion 18 exhibits substantially high resistance to corrosion and erosion on a tip portion that has not been quenched. Referring briefly to Figure 7, a micrograph illustrates a portion of a tip portion of iridium platinum 18 that has been tempered at 1750 ° C for five minutes and at 800 ° C for 15 minutes, after it has been subjected to a test SPEAD (Accelerated Durable Spark Plug Electrode) for 75 hours on a dynamometer. The average grain size of the tempered 80% Pt-20% Ir is approximately 250 um in figure 7. Some erosion of the tip 80% platinum-20% iridium along the grain boundaries that has resulted in the loss of the tip material. Figure 9 shows the hardening hardness of the spheres and rivets 80% Pt-20% Ir after being subjected to a tempering temperature for 15 minutes. The hardened hardness 80% Pt-20% Ir is approximately 320-340 Hv. Upon tempering, the deformed structure will be recrystallized and the hardness will be decreased. The fine grain structure of 80% Pt-20% Ir can be obtained at tempering temperatures in the range of 1200 ° C to 1400 ° C, and produces a hardness of between 260-290 Hv. The roughness of the grain structure of 80% Pt-20% Ir can be obtained at the tempering temperature of 1700 ° C, and produce a hardness of between 280 to 300 Hv. The hollow grown of a roughness of grain 80% Pt-20% Go of the tip of spark plug after the test of machine SPEAD is approximately 2.5 times that of a fine grain 80% Pt-20% Go of the tip of the spark plug . In addition the spark enhancement of the erosion resistance can be achieved by the addition of 1 to 4% (by weight) of tungsten to the platinum-iridium alloy. For example, the gap grows from a fine grain 80% Pt-20% Go from the tip of the spark plug after a machine test SPEAD is approximately three times what a fine grain 81% Pt-18% Ir-1% the tip of the spark plug. As compared to the grain roughness 80% Pt-20% Go the tip of the spark plug, a factor of 7.5 times the spark erosion resistance has been achieved in the fine degree 81% Pt-18% Ir-1 % W of the tip of the spark plug. Figure 8 is a micrograph of a tip portion 18 of platinum rhodium after it has been subjected to the SPEAD test for 75 hours on leaded fuel. The average sphere grain size tempered at 950 ° C for 15 minutes of 80% Pt-20% Rh is approximately 45 um. The fine grain loss 80% Pt-20% Rh of the tip material is small. The hardness of unhardened spheres and rivets 80% Pt-20% Rh is approximately 300-310 Hv. Upon tempering, the deformed structure will be recrystallized, and the hardness will be decremented. The fine grain structure of 80% Pt-20% Rh can be obtained at tempering temperatures in the range of 800 ° C to 1000 ° C, which produces a hardness of between 200-230 Hv. The roughness of the grain structure of 80% Pt-20% Rh can be obtained from a tempering temperature of 1250 ° C, which produces a hardness of between 170 to: .80 Hv. The gap that grows from a rough grain 80% Pt-20% Rh from the tip of the spark plug after a SPEAD machine test is approximately 6.5 times that of a fine grain 80% Pt-20% Rh from a spark plug tip . The manufacturing method described herein allows the platinum alloy tip portions to be constructed with significantly more erosion resistance than the puma portions previously developed. The realization of tempering over the peak portions to the preferred temperature range and preferred time period described herein significantly defines the grain of the structure, which minimizes erosion and corrosion of the grain boundary and significantly increases its resistance to spark erosion in the presence of lead and other corrosive elements. As a result, the gap 24 is substantially maintained over the life of the spark plug. The tip portion and manufacturing method described herein also does not appreciably add to the construction cost of the spark plug: it requires the use of materials that are not already widely available commercially. Accordingly, the spark plug of the present invention can still be manufactured economically and without adding significant costs and manufacturing processes. Those skilled in the art can now appreciate from the foregoing description that the broad teaching of the present invention can be implemented in a variety of ways. Therefore, while this invention has been described in particular connection to examples thereof, the real field of the invention should not be limited from other modifications that are apparent to the expert who practices it on a study of the drawings, specification and following claims.

Claims (10)

1. A method for constructing an electrode for a spark plug using a preformed tip portion, of the method comprising the steps of: tempering the tip portion to a temperature within a range of about 900-1400 ° C for a predetermined period of time to obtain a fine grain microstructure; placing the tip portion in an element; aligning the tip portion with the electrode; and welding the tip portion to the electrode. The method of claim 1 wherein the step of tempering the tip portion by the predetermined time comprises tempering the tip portion for a time of between about 5-15 minutes. 3. The method of claims 1-2, wherein the step of tempering the tip portion comprises placing the tip portion in a tempering furnace containing argon. 4. The method of claims 1-2, wherein the step of tempering the tip portion comprises placing the tip portion in a tempering furnace containing nitrogen. 5. The method of claims 1-2, wherein the step of tempering the tip portion comprises placing the tip portion in a tempering furnace subject to a vacuum. A method for constructing an electrode for a spark plug using a preformed tip portion of platinum, of the method comprising the steps of: tempering the tip portion to a temperature within a predetermined temperature in the range for a period of time between 5-15 minutes to produce a fine grain microstructure; allowing the tip portion to cool to the desired temperature; placing the tip portion in an element; aligning the tip portion with the electrode; and the resistance to welding of the tip portion to the electrode. The method of claim 6, wherein the predetermined temperature comprises a temperature within a range of between about 900-1400 ° C. 8. The method of claims 6-7, wherein the tempering step of the tip portion produces a fine grain microstructure equal to or less than about 40 um. 9. A spark plug consisting of: an insulator; a central electrode placed in the part inside the insulator; a base electrode; each of the electrodes includes a tip portion secured thereto; and within each of the tip portions contains a hardened tip portion to provide a fine grain microstructure equal to or less than about 45 um. 10. The spark plug of claim 9 wherein each of the tip portions contains a fine grain microstructure of approximately 40 um.