WELDING VARIABLES
The following major process variable play an important role in shaping the weld bead and the resultant weld metal in submerged arc welding:
- a. Welding current
- b. Welding voltage
- c. Welding speed
- d. Electrode stick out or wire extension
- e. Height of the flux layer
- f. Joint design
- g. Electrode polarity
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 joint may melt through the backing, causing burn through. Other side effects are high current undercuts, highly narrow weld seam and large Heat Affected Zone (HAZ). Too low a welding current produces an unstable arc in the cavity.
Welding voltage
The welding voltage is a function of arc gap. This primarily determines the shape of the fusion zone and reinforcement. The High welding voltage produces a wider, flatter and 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 arc 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 poor bead shape resulting in very difficult slag removal.
Welding speed
The welding speed has an important influence on the weld bead size and penetration. Very high travel speeds decrease the welding action and increases the possibility of undercuts, arc blow, porosity and uneven bead shapes. Since welding speed, i.e. 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 advantageously reduced since sufficient time is permitted for the gases to escape into the atmosphere during slag metal reactions.
Electrode stick out
Stick out or electrode extension plays an important role for current densities higher than 80,000 amps / sq. inch. The electrode stick out is the length of the wire extending beyond the tip of the contact tube upto the surface of 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 at higher temperatures resulting in improper bead formation.