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Porosity occurs when the gases produced by the weld flux insufficiently shield the molten weld metal. An overexposed weld bead absorbs nitrogen, oxygen, and hydrogen from the atmosphere; these gases form tiny voids in the weld bead and are released while the weld cools. Poor fusion also affects the strength of the weld and is often easily visible.
The symbolic representation of a V weld of chamfered plates in a technical drawing. The symbols and conventions used in welding documentation are specified in national and international standards such as ISO 2553 Welded, brazed and soldered joints -- Symbolic representation on drawings and ISO 4063 Welding and allied processes -- Nomenclature of processes and reference numbers.
The poor overlap does not allow the slag from the previous weld to melt out and rise to the top of the new weld bead. It can also occur if the previous weld left an undercut or an uneven surface profile. To prevent slag inclusions, the slag should be cleaned from the weld bead between passes via grinding, wire brushing, or chipping. [21]
Most weld purging is carried out on joints made by the TIG or GTAW arc welding process. [6] When the laser welding process is chosen, joints or welds being made on reactive materials will need to be carried out and in the case of electron beam welding, this is carried out in a vacuum, in which case purging takes place by complete evacuation of all gas.
Shielded metal arc welding process, showing slag. Welding flux is a combination of carbonate and silicate materials used in welding processes to shield the weld from atmospheric gases. When the heat of the weld zone reaches the flux, the flux melts and outgasses.
Weld mapping is the process of assigning information to a weld repair or joint to enable easy identification of weld processes, production (welders, their qualifications, date welded), quality (visual inspection, NDT, standards and specifications) and traceability (tracking weld joints and welded castings, the origin of weld materials).
Spray transfer GMAW. Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) and metal active gas (MAG) is a welding process in which an electric arc forms between a consumable MIG wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to fuse (melt and join).
A submerged arc welder used for training Close-up view of the control panel A schematic of submerged arc welding Pieces of slag from submerged arc welding exhibiting glassy surface due to silica (SiO 2). Submerged arc welding (SAW) is a common arc welding process. The first SAW patent was taken out in 1935.