Page 407 of 561

WIRE WELDING

Spray-Arc

The spray-Arc is recognized by a relatively intense arc between the welding wire and the work piece. The metal transfer is in the form of a continuous spray of molten metal droplets from the wire tip through the arc to the surface of the melted pool. The arc is almost spatter free and provides deep penetration in the base material. The deposit rate is high, and this arc type is recommended for material thickness above 3 mm. To obtain a spray-arc it is necessary to have welding current above a certain minimum value, the transition current. This current level depends on the shielding gas, (consisting of minimum 80% Argon or Helium), the alloy and the size of the welding wire. As a guideline a 0.8 mm solid steel wire will provide a spray arc if the welding current is above approximately 150 Ampere. At currents below this level the steady spray will consist of gradually larger droplets until a spray no longer can be maintained, and the short-arc is established.

Short Arc

is also called short circuit transfer. No metal is transferred through the arc with this technique, but is instead

Spray-arc welding

transferred through rapid short circuits between wire and work piece. The wire touches the work piece and the welding current increases immediately, melting of a drop of filler material. As this drop is melted off the arc is re-established, heating wire tip and base material until the wire feed speed again pushes the wire into contact with the work piece. This sequence repeats itself continuously approximately 100 times per second, providing a concentrated arc with low heat input to the work piece and rapidly solidifying deposit. The short-arc method is therefore excellently suited for sheet metal welding, and also for bridging large gaps in poorly aligned joints. The rapidly solidifying deposit also makes short-arc welding easy in any welding position.

4.03

Short circuiting (short arc welding)

406