voestalpine bohler welding URANOS NX 2200 PMC Manual De Instrucciones página 99

Under many operating conditions, it is useful to be able to use two preset welding currents and to be able to switch easily from
one to the other (BILEVEL).
Welding polarity
Characteristics of TIG welds
The TIG procedure is very effective for welding both carbon and alloyed steel, for first runs on pipes and for welding where good
appearance is important.
Straight polarity is required (D.C.S.P.).
Preparing the edges
Careful cleaning and preparation of the edges are required.
Choosing and preparing the electrode
You are advised to use thorium tungsten electrodes (2% thorium-red coloured) or alternatively cerium or lanthanum electrodes
with the following diameters:
(DC-)
3-20 A
15-80 A
70-150 A
150-250 A
250-400 A
400-500 A
500-750 A
750-110 A
D.C.S.P. (Direct Current Straight Polarity)
This is the most used polarity and ensures limited wear of the electrode (1), since 70% of the
heat is concentrated in the anode (piece).
Narrow and deep weld pools are obtained, with high travel speeds and low heat supply.
D.C.R.P. (Direct Current Reverse Polarity)
The reverse polarity is used for welding alloys covered with a layer of refractory oxide with
higher melting temperature compared with metals.
High currents cannot be used, since they would cause excessive wear on the electrode.
D.C.S.P.-Pulsed (Direct Current Straight Polarity Pulsed)
welding pool width and depth.
The welding pool is formed by the peak pulses (Ip), while the base current (Ib) keeps the arc
and consequently a reduced risk of hot cracks and gas inclusion.
Increasing the frequency (MF) the arc becomes narrower, more concentrated, more stable and
the quality of welding on thin sheets is further increased.
Current range
(DC+)
-
-
10-20 A
15-30 A
25-40 A 100-180 A
40-55 A 160-240 A
55-80 A 190-300 A
80-125 A 325-450 A
(AC) Ø
3-20 A 0,5 mm
20-30 A 1,0 mm
30-80 A 1,6 mm
60-130 A 2,4 mm
3,2 mm
4,0 mm
4,8 mm
6,4 mm
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OPERATING INSTRUCTIONS
Electrode
30°
30-60°
60-90°
90-120°
120-150°
150-180°
150-180°
150-180°
EN