Welding Processes Handbook
This explanatory guide to the commercially significant and commonly-used welding processes covers the design of welded joints, quality assurance and costing, and can be applied to all instruction levels.
TABLE OF CONTENTS Welding Processes Handbook
Chapter 6: Metal Arc Welding with Coated Electrodes
6.1 Description of the Method
Manual Metal Arc welding (MMA) is often referred to as Shielded Metal Arc Welding (SMAW) or stick electrode welding. It was the predominant form of fusion welding until the beg0inning of the 1980s. Electrode rods consist of a wire core with an external coating. They are made in a range of core diameters, with each diameter being intended for a particular current range. Welding involves striking an arc between the electrode and the workpiece, with the heat of the arc melting the electrode (i.e. the filler material), and with the coating melting to form a protective slag.
The equipment required is simple, as shown in Figure 6.1, which means that the method is straightforward to use. It is particularly suitable for jobs such as the erection of structures. It can also be used outdoors, as opposed to other methods requiring shielding gas, which are unsuitable in wind. However, its arc time factor is relatively low, due to the time required for chipping away slag after welding and changing the electrodes.
Figure 6.1: Schematic diagram of manual metal arc welding.
6.2 Equipment
Power Sources
When welding with coated electrodes, the required current is set at the power source. The welding current must be kept within certain limits even though the arc length may vary. The short-circuit current should not be more than about 60 % higher than the current setting, in order to avoid spatter from the short-circuiting of the arc caused by the droplets of...
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