Electrodes & Operation
MMA Electrodes
An MMA electrode consists of a metal core wire covered with a flux coating, which is extruded concentrically around the core wire. The metal core may be carbon steel, alloy steel, stainless steel, nickel alloy, copper alloy, cast iron, aluminium alloy, or even special hard-facing alloys. The coating may contain many different metallic and non-metallic compounds, including oxides, carbonates, fluorides, organic materials and metal powders, all held together with silicate binders.
There are also some electrodes that are constructed differently, such as a tubular design, where the fluxing and alloying compounds are held within a metal tube, usually made of steel.
At one end of the electrode an amount of flux is removed from the core wire to allow it to be held in the electrode holder. At the other end, the flux is chamfered away from the core wire to allow easy striking. It is also common practice with many types of electrode to coat this end of the electrode in a graphitic solution, which again is to aid arc-striking.
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OperationOnce an arc has been struck between the electrode and the workpiece, the electrode will start to melt. The welder must move the electrode towards the workpiece to maintain a constant arc length in the direction the weld is required. During welding, the core wire melts to form a weld pool. This melts at a faster rate than the coating around it. The core wire normally provides most of the alloying for the weld metal, although there are some, such as iron-powder electrodes, where a high proportion of the available weld metal is carried in the coating. The electrode coating performs many functions, including:
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