| 摘要 |
PROBLEM TO BE SOLVED: To surely ensure ignitability as well as a long service life by suppressing production of internal cracks of a discharge tip in a spark plug. SOLUTION: An iridium ingot is subjected to hot grooved roll process with plural stages and a hot dice wire drawing process with plural stages to form an wire rod. If the temperature of the roll and the dice is within the range of 710-1,080 deg.C and a wire drawing speed is within the range of 800-1,400 mm/ minute, internal cracks exceeding 0.03 mm is not produced. If the temperature of the roll and the dice and the wire drawing speed are within the range of 710-920 deg.C and 900-1,100 mm/minute respectively, no internal crack is produced. A spark plug having a discharge tip manufactured by cutting this wire rod and attached to its center electrode is excellent in durability.
|
