The Properties of Tungsten Electrode in TIG Arc Welding
Current Cayacity and Consumption
1963 Volume 32 Issue 10 Pages 1006-1017
Details
1963 Volume 32 Issue 10 Pages 1006-1017
In this paper, the author intends to determine the current capacity and consumption of tungsten electrode in TIG arc welding for the purpose of establishing the standard (JIS) of the electrode.
From this work, the following conclusions are obtained :
(1) The current capacity of pure tungsten electrode under DCSP depends on Joule's heat and consequently on the stick-out length of electrode, and is formulated by experiment as Im=220× (α/le×102)3/4, where a is the cross section of electrode in cm2 and le is the stick-out length of. electrode in cm. The current capacity of thoriated tungsten in argon shielded DCSP arc is rather a little less than that of pure tungsten.
(2) The DCRP current capacity has not a definite critical value, but is determined from a practial standpoint.
(3) The failure of electrode due to over current in the AC TIG arc occurs in two ways ; that is, of S.P. type in smaller diameter electrode and of R.P. type in larger diameter electrode. The AC capacity depends largely on the amount of DC component, and their relation is given by Im=Im0/(1-αPd), where Im0 is the maximum allowable current in the case of balanced AC, Pd is the ratio of DC component to effective value of AC component and a is a theoretically given coefficient. The AC capacity of thoriated tungsten is considerably larger than that of pure tungsten.
(4) From careful measurements using water-cooled Cu anode or aluminum plate as a work piece and preventing start spattering, the electrode consumption under DCSP steady arc is found to be a few mg/30 min. and seems to be caused through pure evaporation. The electrode consumption for AC arc under the same condition is 2 to 3 times the value mentioned above.
(5) For, the arc when using steel plate as base electrode, the consumption is nearly 10 times that for DCSP arc with water cooled Cu anode, and especially in the case of the AC arc successive spattering sometimes accompanies.
(6) At the start of DCSP arc, the spattering of electrode is caused when applying nearly maximum allowable current suddenly to pure, tungsten which was once used. Start spattering is not caused by (a) thoriated tungsten (b) pure, virgin tungsten, (c) arc starting with smaller current.
(7) The start spattering is found to occur succeedingly for about 1/4sec. following the arc ignition, and seems to be caused by the cavity formed at the tip of electrode and the thermal shock.
