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Figure 10-4 Examples of Porosity
is gas pores found in the solidified weld bead. As seen in Figure 10-4, these
pores may vary in size and
are generally distributed in a random manner. However, it is possible that porosity
can only be found at the
weld center. Pores can occur either under or on the weld surface.
The most common causes of porosity
are atmosphere contamination, excessively oxidized work piece
surfaces, inadequate deoxidizing alloys
in the wire and the presence of foreign matter. Atmospheric
contamination can be caused by:
1) Inadequate shielding
gas flow. 2) Excessive
shielding gas flow. This can cause aspiration of air into the gas stream.
3) Severely clogged
gas nozzle or damaged gas supply system (leaking hoses, fittings, etc.)
4) An excessive wind
in the welding area. This can blow away the gas shield.