Welding Practice - The Hong Kong Polytechnic University

Welding Practice
mixture. The fuel gases which may be used include acetylene, butane, coke gas.
ethylene hydrogen, natural gas, propane, and other petroleum derivatives or
mixtures. Because acetylene in combination with oxygen produces the hottest
flame, oxy-acetylene welding is the most commonly used of these processes. The
equipment required for gas welding is simple and compact, making it especially
useful for maintenance or site work where portability is an advantage. However
the rate of welding is slower with gas than with arc welding and the lower heat of
gas welding limits its use. For production purposes, it is ideally suited to lightgauge
metals work, as in aircraft and automotive assemblies of sheet and tube,
or to the welding of metals which have low melting points, such as copper and
its alloys.
2.1 Arc Welding
Arc welding is a fusion process in which the welding rod is cast into the
previously fused space between the metals to be joined. The heat necessary to
melt the metal and welding rod is obtained from an electric arc struck between
the rod (electrode) and the work, a temperature of 3500-4000°C being obtained
near the crater (Fig 3) of the arc.
There are many types of arc welding processes, some of the common ones
are outlined below.
Page 3
IC Professional Training