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POROSITY
- Pattern is improperly sprued. Sprues may be too thin, too long or not attached in the proper location, causing shrinkage porosity.
- Not enough metal reservoir to eliminate shrinkage porosity.
- Metal contains gas.
- Mold is too hot.
- Too much moisture in the flux.
- Too much remelt being used. Always use at least 50% new metal.
- Metal is overheated.
- Poor mold burnout.
FINS OR FLASH ON CASTINGS
- Flask was disturbed while investment was setting.
- Base was removed too soon.
- Flask was allowed to partially dry before dewaxing.
- Incorrect dewaxing or a furnace malfunction.
- Flask burned out and allowed to cool below (500oF (260oC) before casting reheating, flask allowed to cool between dewax and placement in preheated oven.
- Flask was improperly handled or dropped.
- Speed was set too high on centrifugal casting machine.
- Patterns were placed on one plane. The should be staggered on top rack.
- Incorrect water powder ratio was used.
- Not enough investment was placed over the patterns.
- Flask was placed too close to heat source in burnout oven.
- Flasks were not held at low burnout temperature long enough.
INCLUSIONS (FOREIGN PARTICLES) IN CASTINGS
- Patterns were improperly sprued to wax base or tree or not filleted, causing investment to break at sharp corners during casting.
- Flask was not sufficiently cured before placing into burnout oven.
- Improper dewaxing cycle was used.
- Flask was not cleaned from prior cast.
- Loose investment in sprue hole.
- Molten metal contains excess flux or foreign oxides.
- Crucible disintegrating or poorly fluxed.
- Improperly dried graphite crucible.
- Investment was not mixed prpoerly or long enough.
- Contaminants in wax pattern.
- Flask was not held at low burnout temperature long enough.
- Flask was placed too close to heat source in burnout oven.
ROUGH CASTINGS
- A poor quality pattern
- Flask was not sufficiently cured before placing into burnout oven.
- Flask was held in steam dewax too long.
- Metal, flask or both were too hot.
- Patterns were improperly sprued.
- Flask was placed too close to heat source in burnout oven.
BUBBLES OR NODULES ON CASTINGS
- Vacuum pump is leaking air.
- Vacuum pump has water in the oil.
- Vacuum pump is low on oil.
- Investment not mixed properly or long enough.
- Invested flasks were not vibrated during vacuum cycle.
- Vacuum extended past working time.
SPALLING (an area of the mold wall flakes into the mold cavity)
- Flask was placed into a furnace at low temperature (below 300oF or 150oC) for an extended period.
- Flask was placed too close to the source of heat.
- Sharp corners are struck by metal at high centrifugal velocities.
- Improper burnout cycle was used.
NON-FILL OR INCOMPLETE CASTINGS
- Metal was too cold when cast.
- Mold was too cold when cast.
- The burnout was not complete.
- Pattern was improperly sprued, creating tubulence when csting in a centrifugal casting machine.
- Centrifugal casting machine had too high revolution per minute.
GROWTH-LIKE ROUGH CASTING THAT RESISTS REMOVAL IN PICKLING SOLUTION
- Burnout temperature too high.
- Mold temperature was too high when casting.
- Metal temperature was too high when casting.
SHINY CASTINGS
- Carbon residue was left in the mold, creating a reducing condition on the surface.
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