"prequalified shielding gases"

Date 05-22-2007 00:57

CO2 would not be spray arc. Spray arc only occurs with an argon rich gas (80% or more - some books say 90% or more) and a amperage setting above the transition current which is dependant on the wire size and wire feed speed).

Anything below this argon % would be considered globular or short circuit and short circuit is not prequalified under D1.1.

Documenting this would be the correct % of argon in the shielding gas and the amperage settings above that transition current for that electrode diameter.

By jerrykroll (**)

Date 05-22-2007 01:15

I am still looking for a definitive source - code requirement if you will - that specifies spray arc parameters - a text reference is not "code" - common practice is not "code" - how do we really define and recognize spray arc "to code" ?

By jerrykroll (**)

Date 05-22-2007 11:34

Thanks for the review and information.
My problem is that one of my clients (overseas) is stating they have established a qualified
welding procedure for spray arc using a CO2 rich (CO2/Argon) mix.

I have seen many tables with parameters - many excellent one from electrode manufactureres.
They all state gas mix used, v/a/wfs, etc., all rich in Argon (85%+)

I am still interested in learning if, or how, the D1.1 would allow a prequalified spray arc procedure
with a CO2/Argon mix, using a higher percentage of CO2 than Argon, and if so to what degree.

Also for what it's worth - the A5.18 Spec. for Electrodes qualifies the electrode tensile properties (ER70S-6) using straight CO2, but states in a footnote
"that this does not preclude the use of gas blends of Ar/O2, or Ar/CO2". (no % stated though)

By MBSims

Date 05-22-2007 03:39 Edited 05-22-2007 03:49

No code that I have ever used has clearly defined transfer modes for GMAW. AWS D1.1 Paragraph 1.3 refers to AWS A3.0, supplemented by Annex K, for terms and definitions. The following definitions appear in A3.0 for transfer modes:

Short circuiting transfer, gas metal arc welding. Metal transfer in which molten metal from a consumable electrode is deposited during repeated short circuits.

Globular transfer, gas metal arc welding. The transfer of molten metal in large drops from a consumable electrode across the arc.

Spray transfer. gas metal arc welding. Metal transfer in which molten metal from a consumable electrode is propelled axially across the arc in small droplets.

Pulsed spray transfer, gas metal arc welding. A variation of spray transfer in which the welding power is cycled from a low level to a high level, at which point spray transfer is attained, resulting in lower average voltage and current.

These definitions do not clearly define the parameters at which the transfer mode changes. The is some technical guidance in the AWS Welding Handbook Volume 2 Chapter 4 on transfer modes and the "transition current" at which the change from globular transfer to spray transfer mode occurs. It says that a predominately argon rich shielding gas is required to achieve spray transfer. Table 4.1 provides transition currents for different sizes and electrode materials: