WELDING THEORY - OD1650 - LESSON 1/TASK 1
In some processes, the flux selected for use with a welding rod has important effects on
weldability. Also, the electrode covering influences the weld obtained in certain steels. Molten
steels have a tendency to absorb hydrogen from the surrounding atmosphere and to expel it when
they solidify. Some types of electrode coverings send a lot of hydrogen into the atmosphere
surrounding the arc and the molten puddle. This hydrogen is enough to cause microscopic
cracks in the heat-affected zone of some steels. To eliminate this problem, low-hydrogen
electrodes have been developed to weld the newer high-tensile steels.
Joint design also influences the weldability of a metal. Several factors must be considered when
selecting a joint design. They include the welding process, the thickness of the material to be
welded, and the purpose the joint is to serve.
Thin sheets of metal can be butted together without special preparation other than cleaning; but
heavy plates must be beveled or grooved to make a satisfactory joint. Again, the design used is
related to the purpose; that is, the way the load or stress is applied, the erosive or corrosive
conditions it must resist, and the joint efficiency. The term "joint efficiency" is used to indicate
the strength of a welded joint as compared with the strength of the unwelded base metal.
Each of the welding processes has a technique or procedure peculiar to that process. Often the
technique varies with the kind or size of the filler metal used, or the kind of weld being made.
The incorrect use of a technique, or the use of the wrong technique, may lead to defects that
make the joint unsatisfactory.
Conclusion. This information on welding processes is provided to give a brief
introduction to welding. A shop drawing is the universal language used to convey all the
necessary information that an individual would need to perform these welding processes.
Special symbols are furnished on shop drawings to show the kinds of welds to be used. The
following subparagraphs will contain data on the use and function of welding symbols.