Page 81 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

A Quick Guide to Welding and Weld Inspection

(absorb moisture) and therefore must be kept dry and pre-
heated before use to remove the moisture. Agglomerated
fluxes give better mechanical properties to the welded joint
than fused fluxes and are used in low hydrogen applications.
Fused fluxes are formed by melting their constituents
together at high temperature and then cooling them to form a
glass-like flux. The granules are solid and feel like grains of
sand when rolled between the fingers. They are moisture
resistant, easy to use, give good weld profiles and have good
slag detachability, but the weld metal properties are not as
good as those using agglomerated fluxes. These are ideally
used in general purpose applications.
Fluxes are also classified as basic or acidic, which refers to
the ratio of basic oxides to acidic oxides that they contain.
The higher the basicity then the greater the flux moisture
absorption and related difficulty in removing it.
Agglomerated fluxes will be basic whereas the fused fluxes
will tend to be acidic. An increase in basicity will increase
toughness but reduce arc stability, reduce weld profile and
make slag removal more difficult. The flux with the highest
basicity giving good arc stability, acceptable weld profile and
slag removal should normally be chosen.

Applications
Because of the deep penetration and high deposition rates
achievable with SAW it is commonly used in heavy
fabrication environments such as shipbuilding and pressure
vessel manufacture.
Typical defects
Typical defects associated with this process are shrinkage
cavities formed where high weld depth/width (> 2:3) ratios
are present, solidification cracking caused by high dilution
levels with parent material or a high depth/width ratio,
porosity due to damp fluxes or insufficient flux depth,
hydrogen cracking from damp flux and lack of fusion from
arc-blow or an incorrect technique.

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 66 of 66