Castings
Several factors effect the quality of metal
castings. Some of these factors are listed below:
- Coefficients of thermal
conductivity
- Thermal expansion and
contraction,
- Chemistry
- Precision of molds and dies
- Shrinkage allowances
- Dryness of molds
- Casting design
- Method of pouring liquid metal
- Design of gates and risers
Imperfections in castings may not be of
concern for many types of service. They are commonly referred to as casting
defects since castings are not perfect. This is unfortunate as
imperfections beyond engineering design specifications should be considered
defects, while imperfections within engineering design specifications should
not be considered defects.
Some casting imperfections may have no
effect on the function or service life of castings. Many imperfections are
easily corrected by blast cleaning or grinding. Other imperfections
may be acceptable in some locations.
It is not uncommon for engineers to zone a
casting drawing. Depending on the criticality of the location or zone the
same imperfection would be judged acceptable in one location while
unacceptable in another location. |
Casting Discontinuities
Some common casting
deficiencies are:
Casting failures can be due
to various causes. Some castings fail due to design deficiencies, while
other castings fail due to casting deficiencies.
 Casting Failure Analysis
Casting failures can be due
to various causes. Improper loading or environment may contribute to
the cause of failure. Casting imperfections may or may not contribute to
the cause of failure. Some imperfections may be commonly occurring
discontinuities or anomalies that are normally expected to be present in
castings. Other imperfections are casting defects that result in failure
of the casting. Failure analysis can determine the cause of the casting
failure and determine if a casting imperfections was the primary or contributing
cause of failure.
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