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SAND CASTING

SAND CASTING

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SAND CASTING

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  1. SAND CASTING

  2. Ceramic Moulding • This process use a method very near to plaster mold casting. Plaster, plastic, wood, metal or rubber is used for making the pattern. A ceramic slurry comprising zircon, fused silica and a bonding agent is first poured over the pattern. Like rubber it hardens quickly. It is then peeled of the pattern and reassembled as a mold. The volatile materials are removed in a low temperature oven. Ceramic mold, with high temperature pours is obtained after it is baked in a furnace at about 1000 °C (1832 °F) .

  3. Features of Ceramic Moulding • More accurate in dimension • Surface finish is good • Wall thickness is small • Weights is less • Patterns are Reusable and cheap.

  4. Pressure Die Casting • Pressure Die casting is the process of forcing molten metal under high pressure into mold cavities (which are machined into dies). Most pressure die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, and tin based alloys, although ferrous metal die castings are possible. The die casting method is especially suited for applications where a large quantity of small to medium sized parts are needed with good detail, a fine surface quality and dimensional consistency.

  5. Pressure Die Casting

  6. Open Hearth Furnace

  7. Electric Furnace

  8. Sand Casting Defects • Porosity • Fins or Flash on Castings • Inclusion(foreign material/sand) in Castings • Rough castings • Bubbles or Nodules on castings • Spalling (an area of the mold wall flakes into the mold cavity) • Non fill or Incomplete castings • Mould shift • Blow Holes • Pin Holes • Shrinkage cavity

  9. 13. Shrinkage cavity 14. Hot Tears (Cracks) 15. Cold shut and misrun 16. Internal Air Pocket

  10. 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.

  11. FINS OR FLASH ON CASTINGS • Flask was disturbed while investment was setting. • Base was removed too soon. • Flask was allowed to partially dry before de-waxing. • Incorrect de-waxing or a furnace malfunction. • Flask burned out and allowed to cool below (500oF (260oC) before casting reheating, flask allowed to cool between de-wax 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

  12. 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 de-waxing 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 properly 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.

  13. ROUGH CASTINGS • A poor quality pattern • Flask was not sufficiently cured before placing into burnout oven. • Flask was held in steam de-wax too long. • Metal, flask or both were too hot. • Patterns were improperly sprued. • Flask was placed too close to heat source in burnout oven.

  14. 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.

  15. SPALLING (an area of the mold wall flakes into the mold cavity) • Flask was placed into a furnace at low temperature (below 300oC 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.

  16. NON-FILL OR INCOMPLETE CASTINGS • 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.

  17. POROSITY FLASH MOULD SHIFT

  18. SHORT CASTING INCLUSION GAS