Glossary - M
Welding with equipment which performs the welding operation under the constant observation and control of a welding operator. The equipment may or may not load and unload the workpieces. See automatic welding. A header with outlets or branches to which a number of cylinders of gas may be connected. A welding operation performed and controlled completely by hand. See automatic welding, machine welding and semi-automatic welding. A trade name for a fuel gas which is a stabilised mixture of Methylacetylene and Propadiene. It comprises three carbon atoms and four hydrogen atoms, C3H4. A hard brittle microstructure which forms if steel is heated and then cooled very rapidly. The process whereby a solid becomes a liquid under a change in temperature or pressure An opaque, lustrous, elemental chemical substance that is good conductor of heat and electricity, usually malleable, ductile, and more dense than other elemental substances. A composite tubular metal electrode consisting of a metal sheath and a core of various powdered materials, producing no more than slag islands on the face of a weld bead. External shielding may be required. A fuel gas and a member of the paraffin family. It is the simplest hydrocarbon molecule comprising one carbon atom and four hydrogen atoms, CH4. A small crack in weld metal or HAZ, only visible under a microscope. MIG welding stands for Metal Inert Gas welding. The MIG process uses the heat generated by an electric arc to fuse the joint area. The arc is formed between the tip of a consumable, continuously fed filler wire and the workpiece. A term used to describe the general range of carbon and carbon manganese steels used for fabrication. These steels typically contain - 0.05 - 2% carbon, 0.3 - 2% manganese and up to 0.6% silicon. MMA stands for Manual Metal Arc, an electric arc welding process in which the arc is struck between a covered metal electrode and the workpiece. Shielding of the weld pool is provided by the decomposition of the electrode covering and the electrode is consumed to provide filler metal. Weight of one molecule of a substance in units of atomic weight. Molecular weight may be computed by summing the atomic weights of the component atoms of a molecule.
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