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Casting and Its Defects

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Introduction to Casting

  • - Definition:
  • A manufacturing process where molten metal is poured into a mold to form a desired shape after solidification.
  • - Importance:
  • Used for producing complex shapes, large parts, and a variety of materials.

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Types of Casting Processes

  • 1. Sand Casting - Suitable for large, intricate parts using sand molds.
  • 2. Die Casting - High-pressure metal injection into a steel mold for mass production.
  • 3. Investment Casting - Wax model coated with ceramic for fine detail and accuracy.
  • 4. Centrifugal Casting - Rotating mold for cylindrical parts.
  • 5. Continuous Casting - Continuous production of metal shapes, mainly used for steel.

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Common Casting Defects

  • - Porosity
  • - Cold Shut
  • - Shrinkage Cavity
  • - Misruns
  • - Hot Tears
  • - Inclusions
  • - Blowholes
  • - Metal Penetration
  • - Mold Shift
  • - Surface Roughness

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Porosity

  • - Cause: Gas entrapment or shrinkage during solidification.
  • - Effects: Weakens mechanical properties.
  • - Prevention:
  • - Degas molten metal.
  • - Use vacuum casting.
  • - Optimize pouring rate.

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Cold Shut

  • - Cause: Incomplete fusion of metal streams due to low pouring temperature.
  • - Effects: Weak joint areas.
  • - Prevention:
  • - Increase pouring temperature.
  • - Improve mold design.

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Shrinkage Cavity

  • - Cause: Insufficient molten metal to compensate for volume reduction.
  • - Effects: Internal voids in the casting.
  • - Prevention:
  • - Use risers.
  • - Design an effective gating system.

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Misruns

  • - Cause: Premature solidification before the mold is filled.
  • - Effects: Incomplete casting.
  • - Prevention:
  • - Increase mold and metal temperature.
  • - Ensure smooth metal flow.

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Hot Tears (Hot Cracks)

  • - Cause: Stresses during cooling and solidification.
  • - Effects: Cracks in the casting.
  • - Prevention:
  • - Optimize cooling rates.
  • - Ensure uniform mold temperature.

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Inclusions

  • - Cause: Foreign materials (slag, sand) in the casting.
  • - Effects: Weakens mechanical strength.
  • - Prevention:
  • - Filter molten metal.
  • - Maintain mold cleanliness.

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Blowholes

  • - Cause: Trapped air or gases during solidification.
  • - Effects: Surface or subsurface voids.
  • - Prevention:
  • - Improve mold venting.
  • - Use dry molds.

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Metal Penetration

  • - Cause: Molten metal seeps into the mold material.
  • - Effects: Rough casting surface.
  • - Prevention:
  • - Use finer sand.
  • - Compact molds properly.

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Mold Shift

  • - Cause: Misalignment of mold halves.
  • - Effects: Dimensional inaccuracies.
  • - Prevention:
  • - Ensure accurate mold alignment.
  • - Secure molds tightly.

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Surface Roughness

  • - Cause: Poor mold surface or metal turbulence.
  • - Effects: Reduced surface finish quality.
  • - Prevention:
  • - Improve mold preparation.
  • - Control metal flow.

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Conclusion

  • - Summary:
  • - Casting is vital for manufacturing complex parts.
  • - Understanding defects helps improve product quality.
  • - Key Takeaways:
  • - Identify causes and implement preventive measures to reduce casting defects.