1. Typical arc ignition process by high-speed movies

former page

Cleaning action is essential when arc ignites in temperature condition. An electrode is in room temperature before arc generation, and its surface is coverd by oxide. Right picture shows an example of cleaning action on pure tungsten electrode. A voltage of power source used was insufficient to generate welding arc. Then, only the cleaning action occured during high-frequency ignitor was active. The surface of the electrode before ignition looked very clean. But the surface is fully covered by tungsten oxide. That is the reason why cleaning action occured.
There are many debrises on the surface of used electrode on arc welding process, because of its excessive temperature cycle. There are four typical patterns of ignition behaviors.

Typical cleaning action at arc ignition stage
(1)typical	(2)normal	(3)used	(4)no shield
(5)used	(6)normal	(7)used	(8)no shield

Left hand-side movies show typical cleaning actions. Oxide layer on the cathode is cleaned form cathode top to the upper region. But this is rare case. I have only one movie listed top-left image. Cathode spots appear randomly in normal case. First break down sometimes occur at the cathod top. However, the percentege of their occurences are abou 50% or less. The first break-down usually occurs on side of the cathode which used before. The third movies are normal case for used catodes. there are too many factors those affect arc ignition process. They are cathode materials, surface conditions and geometry for the cathode. Nature of shielding gas is another important factor for arc ignition behavior. A nature of base metal is also an importan facotr for it.
Right-hand side movies are typical cases, those don't have cleaning action. Arc area is fulfiled by air in those cases. The cathode top temperature reaches enough temperature to emit enough current, because of oxidation reaction on the top.

Arc ignition movies on various base metal conditions
(1)anode spot	(2)oxide	(3)Active flux	(4)on Fe

Cleaning actions are restricted by base metal surface conditions. However, exceptions are always occure. (1) High speed movies(525kfps) at arc ignition stage. Video viewrate is 30fps, so time span enlarges about 14,000times. This is helium shield condition. The cathode temperature reaches enough high at once. But, there remains some cleaning action even in almost steady state.
(2) An anode spot appears on the base metal, immidiately. And it reaches soon in stable arc condition. Cleaning action is not so many.
(3) Active flux is painted on the base metal heavily. A strong plume flushes from the base metal immidiately. Cleaning action is not major in this case.
4) Arc ignites on mild steel with black skin surface(Fe2O3). Cleaning action is not major in this case.

next page�@�@�@2016.10.9open,�@2016.10.10revised