LIQUID AIR WELDER MANUAL

A slight side to side movement of the welding torch helps to achieve consistent penetration when making butt welds in the flat position.Įffect of welding positions in GMA welding galvanized steel Penetration of the weld in galvanized steel is less than for uncoated steel so that slightly wider gaps must be provided for butt welds. The increased heat input helps to burn away the extra zinc at the front of the weld pool. The reduction in speed is related to the thickness of the coating, the joint type and the welding position, and is generally of the order of 10 to 20 per cent.įillet welds in steel with thicker galvanized coatings may be welded more readily if the current is increased by 10 amps. GMA welding speeds should be lower than on uncoated steel to allow the galvanized coating to burn off at the front of the weld pool. A 92% Ar/5% CO 2/3% O 2 mixture has been found to provide excellent results on galvanized sheet up to 3.0mm thickness.Ĭonditions for GMA welding galvanized steel using a short-circuiting arc and both Ar/CO 2 and CO 2 shielding gases are given below. The use of a spatter release compound as discussed below under ‘ Appearance of GMA welds in galvanized steel’, may be worthwhile.Īlternatively, the more expensive argon/CO 2 or argon/CO 2/O 2 mixes provide adequate weld penetration, a superior weld bead, and far less spatter. Galvanized steel is welded satisfactorily using the GMA process and pure carbon dioxide shielding gas which provides excellent weld penetration, but considerable weld spatter. Shielding gas for GMA welding galvanized steel The process is used for welding thin sheet and for positional welding of all thicknesses. Short circuiting transfer occurs about 100 times per second producing a characteristic buzzing sound as the arc is extinguished and reignited. The end of the wire dips into the molten weld pool while a globule of metal is being transferred, causing a short circuit which momentarily extinguishes the arc. Short circuiting transfer sometimes known as ‘dip transfer’, in which lower currents and voltages are used. This is the high current/high voltage form of the process which is used in the flat position on plate thick enough to prevent burn-through from the larger weld pool and higher heat input.Ģ. Spray transfer, in which globules of metal are detached from the wire and propelled across the stable arc. Welding parameters provide for two different types of metal transfer in GMA welding:ġ. When the arc is lengthened, current is reduced and the wire is consumed at a lower rate, again maintaining the original pre-set arc length. The constant voltage type power sources employed offer instantaneous self adjustment of the arc so that the arc length remains constant even when the operator varies the distance between the electrode and the work piece – power sources are designed to increase welding current as the arc length shortens and the wire burns off at a higher rate to maintain the original arc length. The high current density resulting from the small diameter of the wire is in the region of 200 amperes per square millimetre. A small diameter consumable wire electrode of 0.8mm to 1.6mm is fed automatically to the weld torch. The weld takes place in a protective gas shield. Some reduction in welding speed is required, see ‘Welding conditions’ below. Arc stability is excellent and is not affected by the galvanized coating. In the GMA welding of galvanized steel the presence of the zinc coating has no effect on weld properties although some weld spatter is produced as discussed below under ‘ Appearance of GMA welds in galvanized steel’.

As with all welding proper ventilation and fume exhaust is essential (please see Chapter 13 of WTIA Technical Note 7). Prolonged breathing of these fumes can cause side effects which last about 24 hours. The zinc oxidises in the air to a fine white powder. Welding galvanized steel vaporizes the zinc near the arc (zinc boils before steel melts). It is particularly suited to the welding of thinner materials. GMA welding, also known as CO 2 – (13X) or MIG/MAG welding, is a versatile semi-automatic welding process which is convenient and easy to use. Information has also been supplied by Liquid Air Australia Limited and Welding Industries of Australia. Recommendations are based on Australian practice and terminology.

LIQUID AIR WELDER MANUAL

Work sponsored by International Lead Zinc Research Organization, New York and carried out by E N Gregory of The Welding Institute, Cambridge, England, has been used in recommendations on gas metal arc welding (GMAW) and manual metal arc welding (MMAW). Closer control of welding conditions than for uncoated steel is usually necessary but procedures are simple and well established. Galvanized steels are welded easily and satisfactorily by most commonly practised welding techniques.

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