DEFINITION OF SPRAY TRANSFER KELVIN LONGDEN PROCEDURES DEPARTMENT
PRESENTATION OVERVIEW • Modes of metal transfer • Factor affecting metal transfer • Spray transfer data • Guidelines for spray transfer
MODES OF METAL TRANSFER • Short-Circuiting Transfer (GMAW-SC) • Globular Transfer (GMAW-GL) • Spray Transfer (GMAW-SP) • Pulsed Transfer (GMAW-P)
SHORT-CIRCUITING TRANSFER MODE (GMAW-SC) • Repetitive short-circuits (the arc is extinguished) between the wire and the welding puddle. • The parameters are at their lowest range for the GMAW process • Application in all positions for thin sheet and for the root pass welding of pipe. • Difficult to apply successfully to thicker materials because of the low values of amperage and voltage may result in fusion problems. • Not prequalified.
GLOBULAR TRANSFER (GMAW-GL) • Droplet transfer is nonaxial with a diameter larger that the wire size. • In argon-rich gases this mode of metal transfer occurs with parameters below the spray transition but above that for short-circuiting. • Spatter can be excessive, rough-looking beads, glass-like silica island formations. • Limited use compared to short-circuit and spray transfer modes. • Not considered prequalified.
SPRAY TRANSFER (GMAW-SP) • Molten metal is transferred across the arc in a continuous stream of fine droplets. • The arc is stable. • Current and voltage above critical transition values and the use of argon-rich gas mixtures. • High deposition rates and desirable fusion and penetration characteristics. • Considered prequalified.
PULSED TRANSFER (GMAW-P) • Periodic surges or pulses of current above the transition value for spray transfer which causes the detachment of droplets. • Between the current pulses, the arc is maintained by a relatively low background current. • Average current can be well below the transition value - weld appearance resembling that obtained in spray transfer. • Not prequalified
METAL TRANSFER ACROSS THE ARC IN GMAW • The mode of the weld metal transfer is determined by the following factors: • Welding current • Electrode size • Electrode composition • Electrode stick out • Shielding gas
GAS MIXTURES FOR GMAW FOR CARBON STEELS • The gas mixtures commonly used for gas metal arc welding of carbon steel are: • Argon / Oxygen - 98% Ar / 2% O2 , 95%Ar / 5% O2 • Argon / Carbon dioxide - 90% Ar / 10% CO2 , 85% Ar / 15% CO2 , 75% Ar / 25% CO2 • Argon / Carbon dioxide / oxygen - 91% Ar / 5% CO2 / 4% O2, 90% Ar / 8% CO2 / 2% O2,
Group A - Lows Energy Mixes Argon + 1-10% oxygen Argon + 2-10% CO2 Argon + 1-10% oxygen + 2-10% CO2 Group B – Medium Energy Mixes Argon + 14-20% CO2 Argon + 1-5% oxygen + 14-20% CO2 GMAW Gases That Produce Similar Results
Spray Transfer Guidelines • Shielding Gas – Argon rich - maximum 20% CO2 • Welding parameters in accordance with graphs • Look and sound of the arc