Page 70 - SSAB Welding Handbook Edition 2

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12.0 The use of shielding gas Welding handbook

Short circuiting transfer
©SSAB

Welding gun

Shielding gas
Consumable
electrode
Droplet
Arc
Weld pool Base metal

Drop begins Drop advances Drop touches weld Circuit is broken;
to form towards base pool, causing short another drop begins
metal circuit to form
Fig. 12.2: Illustation of short arc welding.

Other welding parameters also influence the Each droplet grows to a comparatively large size
emergence of the arc types, including the chemical during the metal transfer and then short circuits,
composition of the shielding gas, the diameter of giving a momentarily high current. The droplet leaves
the consumable and the stick-out length of the wire the wire and the arc is struck again, see fig. 12.2. The
from the contact nozzle. metal transfer leaves the wire assisted by the surface
energy in the melt. Short arc welding can be identified
Short arc occurs during welding with relatively low by its characteristic sparkling sound.
heat inputs. This arc allows for versatile welding
operations, including:
Spray arc welding normally has a rather high heat
4 Out of position welding, making all types of input which leads to higher productivity compared to
welding positions conceivable. short arc welding. This arc has a degree of stability
4 Welding of joints with a wide range of plate that contributes to a very low level of spatter. Spray
thicknesses, including the complete thickness arc can be performed in the horizontal position for
range of the Hardox and Strenx grades. solid wires, flux cored wires and metal cord wires.
Using rutile flux-cored wires gives the advantage of
Some general drawbacks for short arc welding welding in positions other than the horizontal. The
include: high heat input means that the range of suitable
4 Relatively low welding productivity. single plate thicknesses for this technique is limited
4 The tendency toward an unstable arc. Therefore, to approximately 5 mm and above. The exception is
special care should be taken in order to achieve pulsed arc welding, which can weld joints of thinner
suitable welding parameters. A good general single plate thicknesses.
measure is to apply a short arc length to promote a
stabilized arc performance. The metal droplet transfer has a higher frequency
4 The increased risk for lack of fusion when welding compared to short arc welding and the size of each
in heavy plate thicknesses, due to the low heat metal droplet is small. In spray arc welding there are
input. no short circuits and the droplet leaves the wire as a
small droplet or a spray through the arc, according to
Short arc welding is characterized by a metal transfer fig. 12.3.
from the consumable, where each droplet short-
circuits the arc. The droplet transfer has a low
frequency of approximately 50-200 Hz.

70 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.