JPH0213018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrode material that is used as a chip electrode in the spark discharge portion of the center electrode or ground electrode that forms the spark gap of a spark plug. Conventionally, as a method of reducing the electrode wear of spark plugs, spark plugs have been made using electric welding means to form noble metal chip electrodes such as heat-resistant and oxidation-resistant platinum or platinum alloys in the spark discharge part. Compared to spark plugs with discharge parts made of base metals, they wear out less and can extend their lifespan. In this case, the chip electrode is used in a thin film of 0.1 to 0.7 mm in consideration of economic constraints and durability. By the way, when actually used inside an engine, the temperature of this thin film part can reach over 900 to 1000 degrees Celsius.
Although the corrosive atmosphere is extremely harsh,
In particular, platinum-based alloys are extremely unstable against corrosion in reducing atmospheres at temperatures above 900°C.
For example, in the case of pure platinum, crystal grain growth is extremely fast, starting at temperatures above 400°C, and starting at temperatures above 900°C.
If the temperature exceeds ℃, a thin film of 0.5 mm may grow to the size of one grain, and when used in an engine, corrosion progresses along the grain boundaries, causing so-called grain boundary fracture, which causes cracks. platinum-iridium alloy (Ir5~20), which is also known as spark plug electrode material.
(wt%), the addition of iridium increases the crystal grain growth temperature to 700-880℃, slows coarsening and reduces damage to the electrode, but it still satisfies the durability as a spark plug electrode. I couldn't do it. In order to prevent grain boundary fracture as described above, the present invention has sufficient stability even at the operating temperature of engines of 900 to 1000 degrees Celsius, has a low corrosion rate, and can significantly improve electrode life. The purpose of this invention is to provide electrode materials for spark plugs that can be used. The present invention consists of platinum with 15.0-25.0% by weight of iridium and 0.1-5.0% by weight of tungsten, or 15.0-25.0% by weight of iridium and tungsten selected from livedenum, rhodium, rhenium, ruthenium, cobalt, iron, manganese and nickel. A platinum alloy containing at least one kind of platinum in an amount of 0.1 to 5.0% by weight and a sum of iridium in a range of 20.0 to 30.0% by weight effectively prevents coarsening of crystal grains at high temperatures. That is. In the present invention, the reason why iridium is set at 15.0% by weight or more is to ensure the effect of preventing coarsening of crystal grains at temperatures above 900°C, and adding more than 25.0% by weight results in hardness, poor workability, and poor mass productivity. This is because the amount of tungsten added to iridium or at least one of molybdenum, rhodium, rhenium, ruthenium, cobalt, iron, manganese, and nickel is limited to 0.1 to 5.0% by weight. This is because, if the amount exceeds 5.0% by weight, processability will similarly become difficult. The present invention will be explained below with reference to Examples. Example 1 Ingots were produced by melting platinum alloys having compositions No. 1 to No. 17 shown in Table 1, hot-formed, and rolled to a thickness of 0.5 mm. Next, each sample was left in an electric furnace at a predetermined temperature for 1 hour to determine the crystal grain growth temperature based on the crystal structure. The results are shown in Table 1, and the coarsening temperature of crystal grains in all of the samples Nos. 6 to 17 of the present invention was higher than 900℃ compared to the conventional samples Nos. 1 to 3, and the platinum surface can effectively prevent abnormal erosion. Incidentally, when iridium was added alone in samples No. 4 and No. 5, the effect of suppressing coarseness was excellent, but the bonding strength at the welded part with the electrode material was poor, and when iridium was added in an amount of 25.0% by weight or more, workability was extremely deteriorated.

【table】

[Table] Example 2 Furthermore, No. 7 of the present invention and No. 1 of the conventional example in Table 1
In each case, samples with a thickness of 0.5 were used, and these samples were electrically welded to the tip of the center electrode to form a spark plug.
As a result of a durability test conducted under the conditions of 3000 rpm x 4/4, the platinum surface of conventional example No. 1 corroded after 100 to 150 hours, while the present invention No. 7 showed no abnormalities on the alloy surface even after 500 hours. I stopped talking. As mentioned above, the platinum alloy that is the electrode material for the spark plug of the present invention has an engine operating temperature of 900 to
It prevents decomposition and abnormal erosion at temperatures above 1000℃ and remains stable for long periods of time, offering excellent durability as a spark plug electrode. In addition, it can be manufactured into thin film small-diameter members with the same workability as conventional platinum alloys, and can be joined with almost the same weldability as conventional platinum alloys.

Claims (1)

[Claims] 1 15.0 to 25.0% by weight of iridium, 0.1 to 5.0% by weight of tungsten, or 0.1 to 5.0% by weight of tungsten plus at least one selected from molybdenum, rhodium, rhenium, ruthenium, cobalt, iron, manganese and nickel, and An electrode material for a spark plug in which the sum of iridium is within the range of 20.0 to 30.0% by weight and the balance is platinum.