voestalpine bohler URANOS 3200 PME Instrucciones De Uso página 34

Welding polarity
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.
Most materials, except for aluminium (and its alloys) and mag-
nesium, are welded with this polarity.
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 com-
pared with metals.
High currents cannot be used, since they would cause excessive
wear on the electrode.
7.2.1 Steel TIG welding
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:
Ø electrode (mm)
1.0
1.6
2.4
The electrode must be sharpened as shown in the figure.
(°)
30
60÷90
90÷120
34
current range (A)
15÷75
60÷150
130÷240
current range (A)
0÷30
30÷120
120÷250
Filler metal
The filler rods must have mechanical characteristics comparable
to those of the parent metal.
Do not use strips obtained from the parent metal, since they
may contain working impurities that can negatively affect the
quality of the welds.
Shielding gas
Tipically, pure argon (99.99%) is used.
Welding Ø Electrode
current (A) (mm)
6-70 1.0
60-140 1.6
120-240 2.4
7.2.2 Copper TIG welding
Since TIG welding is a process characterized by high heat con-
centration, it is particularly suitable for welding materials with
high thermal conductivity, like copper.
For TIG welding of copper, follow the same directions as for TIG
welding of steel or special instructions.
7.3 Continuous wire welding (MIG/MAG)
Introduction
A MIG system consists of a direct current power source, wire
feeder, wire spool, torch and gas.
MIG manual welding system
The current is transferred to the arc through the fusible elec-
trode (wire connected to positive pole); in this procedure the
melted metal is transferred onto the workpiece through the arc
stream. The automatic feeding of the continuous filler material
electrode (wire) is necessary to refill the wire that has melted
during welding.
Gas nozzle Argon flow
n° Ø (mm) (l/min)
5-6
4/5 6/8.0
6-7
4/5/6 6.5/8.0/9.5
7-8
6/7 9.5/11.0