Page 209 - CITS - Welder - Trade Theory

WELDER - CITS

4 Electrode stick-out
5 Width and depth of the flux
6 Materials
7 Joint design

8 Joint edges and edge preparation
9 Fit up
10 Tack welds.
1 Welding Current: Welding Current is the most influential process variable. It controls the rate at which the
electrode is melted, the depth of fusion and the amount of base metal melted. Excessively high current
produces a digging arc and the weld may melt through the backing, causing Burn- through, Other side effects
are undercuts, highly narrow weld seam and large heat affected zone. Too low a current produces an unstable
arc.
The optimum ranges of current for different wire diameters are given below:

Wire dia (mm) Current range (amps)

1.6 150-350

2.0 200-400
2.4 250-500

3.15 300-650

4.0 450-800

5.0 600-1000
6.3 700-1300

Welding Voltage: The welding voltage is a function of the arc gap. This primarily determines the shape of the
fusion zone and reinforcement. High welding voltage produces a wider, flatter, less deeply penetrated weld. The
wider bead increases the flux consumption and decreases the resistance to porosity caused by rust or scale.
However, a wide bead can accommodate a poor joint fit up. Excessively high voltage produces a hat shaped bead
which is prone to cracking.
Low are voltage produces a stiffer arc and improves the penetration in a deep groove joint. However, slag removal
is poor in such cases. Excessively low voltages produce a high, narrow bead with very difficult slag removal.

Welding Speed: The welding head travel speed has main influence on the weld size and penetration. Very
high travel speeds decrease the wetting action and increases the possibility of undercuts, arc blow, porosity and
uneven bead shapes. Since travel speed determines the amount of weld metal deposited per unit length of the
weld, the bead shape is essentially controlled by the welding speed. Too low a travel speed increases the heat
input into the weld, produces a heavy reinforcement and causes slag inclusions. However porosity is decreased
since sufficient time is permitted for the gases to escape to the atmosphere.
Electrode stick-out: This plays an important role for current densities higher than 80,000 amps/in². The electrode
stick-out is the length of the wire extending beyond the tip of the contact tube above the work piece. Higher stick
out imparts resistance heating to the wire before it enters the arc, hence deposition rate is increased. Too high a
stick out would soften the wire and stiffness of the wire would be lost.
Width and Depth of Flux: The depth of the flux layer affects the shape and penetration of the weld. If the flux
layer is too shallow, the arc is exposed resulting in a porous weld. If the layer is too deep, the weld is rough and
uneven. Porosity may result as the gases generated during welding cannot escape to the atmosphere.
Materials: Plain carbon steels which can be readily welded using standard procedures and speeds depends
some extent on rigidity of the joint.
Fillet welds for example are somewhat more critical in regard to weld cracking than are butt welds because of
inherent rigidity of the joint. Due to this reason the fillet weld and lap welds are restricted to 45,000 to 60,000

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CITS : C G & M - Welder - Lesson 61-76