Abstract
Welding of magnetized steels has long been a problem in the welding industry. When welding is attempted in the presence of a magnetic field, the welding arc becomes deflected. This phenomenon is known as arc blow. Arc blow can cause significant weld defects, it can reduce productivity, and it is frustrating to the welder. Sometimes weld joint magnetism is so great that control methods must be used to produce a satisfactory weld. In 1991, Newport News Shipbuilding (NNS) developed and built six magnetic field negators (patent applied for) for their welding department. Each unit consists of a small hand-carried electromagnet and power supply that operates off any standard 110/120 volt ac power source. The lightweight system is designed to counteract magnetic fields up to 200 milli-tesla (mT) (2000 gauss) across a 13 mm (0.5 in.) weld joint in 25-mm-thick (1 in.) steel. Through laboratory and production testing, the magnetic field negator has demonstrated the ability to neutralize local areas of high residual magnetism, resulting in a considerable reduction of magnetism-related weld quality problems.
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