Effect of pressure on the behavior of cathode spots in oxide removal by are discharge

The cathode spots of a vacuum arc have smart properties such as preferential attack against oxides and their selective removal. Recently cathode spots have been used for cleaning metal surface before the application of coating or prior to surface modification. The effects of pressure on the cleaning action of the cathode spots were investigated in a wide pressure range from 10 to 2000 Pa of insert atmosphere. Experiments were carried out by using hot rolled steel plates, the surfaces of which were covered with thick oxide of 5-10 μm. Experimental observation revealed the following results: (1) The vacuum arc phenomenon of cathode spots is confirmed even under a pressure as high as 20000 Pa. (2) The number of cathode spots on the oxide surface increased with the increase of pressure in the range of 10 ˜2000 Pa. (3) The removal rate of oxide decreased with the increase of pressure. AI pressures higher than 10000 Pa, the cleaning action (oxide removal) by the cathode spots was only negligibly observed. (4) The cathode spot energy density may possibly decrease with an increase in pressure. (5) The higher the pressure increase, the smaller area the movement of the cathode spots was restricted to. The cleaning area decreased with the increase of pressure.