There are several variables which when changed can have an effect on the weld appearance and mechanical properties:
• Welding current.
• Type of flux and particle distribution.
• Arc voltage.
• Electrode angle (leading, trailing).
• Polarity.
• Single, double or multi wire-system.
3.1 Welding current
• Increasing current increases penetration and wire melt-off rate
Welding current effect on weld profile (2.4mm electrode diameter, 35V arc voltage and 61cm/min travel speed)
• Excessively high current produces a deep penetrating arc with a tendency to burn-through, undercut or a high, narrow bead prone to solidification cracking.
• Excessively low current produces an unstable arc, lack of penetration and possibly a lack of fusion.
3.2 Arc voltage
Arc voltage adjustment varies the length of the arc between the electrode and the molten weld metal. If the arc voltage increases, the arc length increases and vice versa. The voltage principally determines the shape of the weld bead cross section and its external appearance.
350A 500A 650A
Arc voltage effect on weld profile (2.4mm electrode diameter, 500A welding current and 61cm/min travel speed)
Increasing the arc voltage with constant current and travel speed will:
• Produce a flatter and wider bead
• Increase flux consumption
• Tend to reduce porosity caused by rust or scale on steel
• Help to bridge excessive root opening when fit-up is poor
• Increase pick-up of alloying elements from the flux when they are present Excessively high arc voltage will:
• Produce a wide bead shape that is subject to solidification cracking
• Make slag removal difficult in groove welds
• Produce a concave shaped fillet weld that may be subject to cracking
• Increase undercut along the edge(s) of fillet welds
• Over alloy the weld metal, via the flux
Reducing the arc voltage with constant current and travel speed will:
• Produce a ‘stiffer’ arc which improves penetration in a deep weld groove and resists arc blow
Excessively low arc voltage will:
• Produce a high, narrow bead
• Cause difficult slag removal along the weld toes
3.3 Travel speed
If the travel speed is increased:
25V 35V 45V
Travel speed effect on weld profile (2.4mm electrode diameter, 500A welding current and 35V arc voltage)
3.4 Electrode size
Electrode size affects:
• Weld bead shape and depth of penetration at a given current: A high current density results in a stiff arc that penetrates into the base metal.
Conversely, a lower current density in the same size electrode results in a soft arc that is less penetrating.
• Deposition rate: At any given amperage setting, a small diameter electrode will have a higher current density and deposition rate of molten metal than a larger diameter electrode. However, a larger diameter electrode can carry more current than a smaller one, so the larger electrode can ultimately produce a higher deposition rate at higher amperage.
Electrode size effect on weld profile (600A welding current, 30V arc voltage and 76cm/min travel speed)
3.5 Electrode extension
The electrode extension is the distance the continuous electrode protrudes beyond the contact tip. At high current densities, resistance heating of the electrode between the contact tip and the arc can be utilised to increase the electrode melting rate (as much as 25-50%). The longer the extension, the greater the amount of heating and the higher the melting rate (see below )
30.5 cm/min 61cm/min 122cm/min
3.2mm 4.0mm 5.0mm
3.6 Type of electrode
An electrode with a low electrical conductivity, such as stainless steel, can with a normal electrode extension, experience greater resistance heating.
Thus for the same size electrode and current, the melting rate of a stainless steel electrode will be higher than that of a carbon steel electrode.
3.7 Width and depth of flux
The width and depth of the layer of granular flux influence the appearance and soundness of the finished weld as well as the welding action. If the granular layer is too deep, the arc is too confined and a rough weld with a rope-like appearance is likely to result, it may also produce local flat areas on the surface often referred to as gas flats. The gases generated during welding cannot readily escape and the surface of the molten weld metal is irregularly distorted. If the granular layer is too shallow, the arc will not be entirely submerged in flux. Flashing and spattering will occur. The weld will have a poor appearance and may show porosity.
4 Storage and Care of Consumables
Care must be given to fluxes supplied for SAW which, although they may be dry when packaged, may be exposed to high humidity during storage. In such cases they should be dried in accordance with the manufacturer's recommendations before use, or porosity or cracking may result.
Ferrous wire coils supplied as continuous feeding electrodes are usually copper-coated. This provides some corrosion resistance, ensures good electrical contacts and helps in smooth feeding. Rust and mechanical damage should be avoided in such products, as they interrupt smooth feeding of the electrode. Rust will be detrimental to weld quality generally since it is a hygroscopic (may contain or absorb moisture) material and thus can lead to hydrogen induced cracking.
Contamination by carbon containing materials such as oil, grease, paint and drawing lubricants is especially harmful with ferrous metals. Carbon pick-up in the weld metal can cause a marked and usually undesirable change in properties. Such contaminants may also result in hydrogen being absorbed in the weld pool.
Welders should always follow the manufacturer's recommendations for