| 摘要 |
PURPOSE:To detect simply, inexpensively and resistibly against the heat of arc flame in a small space by discriminating the existance of key holes by the existance of the voltage by the arc flame caused on mutually insulated material to be welded and backing material. CONSTITUTION:Voltage VC is zero with the state of welding being started, no key hole formed and plasma arc 6 not penetrating the back face of the material 12 to be welded. However when a key hole is formed after the elapse of some hours, the plasma arc 6 penetrates the material 2 to be welded and the arc flame becomes to reach the backing material 3. With this state the voltage VC shows the voltage of some degrees with the material 2 to be welded as zero, the variation in the voltage VC caused rapidly and the variation is recognized even though there is some variation in voltage. By detecting the voltage VC the key hole is formed, plasma arc penetrates and whether uranami bead is formed or not can be discriminated.
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