A Study of the Arc Welding Phenomena at Reduced Gas Pressures (Report 4)
Characteristics of Arc and Penetrations under Axial Gas Flow
1971 Volume 40 Issue 3 Pages 211-220
Details
1971 Volume 40 Issue 3 Pages 211-220
The electrical and thermal characteristics of tungsten arc under axial gas flow in argon atmosphere of 18 to 760 mmHg are examined and various penetration shapes formed in the specimens of copper, aluminum, mild steel and stainless steel at the above mentioned ambient pressures are discussed in relation to the arc characteristics.
The facts elucidated are as follows.
1) At reduced gas pressure, elliptical "Cathode Zone", which is highly ionized and has a higher energy density compared to the arc column, is deformed to the conical shape by the axial gas stream. Arc voltage is considerably high in this case.
2) The velocity of axial gas stream increases with decreasing gas pressure and with increasing arc current. In our equipment, it becomes larger than the sound velocity under the gas pressure lower than 100 mmHg.
3) Under axial gas flow, two types of arc exist, namely "H Type" and "L Type". "H Type arc" has a higher arc voltage and in this case arc is kept at the tip part of the cathode electrode. On the other hand, "L Type arc" has a lower arc voltage and the arc covers much area of the cathode electrode.
4) At reduced gas pressure, potential gradient of arc column in "H Type arc" is nearly equal to that in "L Type arc" and is larger than that in the arc in statistic atmosphere. The sum of anode drop and cathode drop, VA+VK, in "H Type arc" is higher than that in "L Type arc". The difference of VA+VK between two types is presumed to depend on the surface condition of the cathode electrode.
5) At reduced gas.pressure molten metal is rapidly removed by the strong gas stream. As a result solid groove is formed in the metal specimen. It must be mentioned that when the cathode zone touches to the specimen, the contact zone at the specimen melts very rapidly. In this case deeply arc-gouged or sharply arc-cut groove is formed. The width of the groove corresponds to the contact diameter of the cathode is zone on the specimen.
