اول صفحة من burn out
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Questions and Answers

What is the main purpose of wax elimination or burnout?

  • To reduce the wax's volume
  • To cool down the investment
  • To melt the wax for reuse
  • To create a cavity for molten metal casting (correct)
  • What does the temperature reached by the investment determine?

  • The hardness of the final casting
  • The viscosity of molten metal
  • The melting point of wax
  • The thermal expansion to compensate for casting shrinkage (correct)
  • Why is a much higher temperature required for complete wax elimination?

  • To melt the wax
  • To expand the investment
  • To vaporize all traces of wax (correct)
  • To solidify the molten metal
  • What happens if wax elimination is incomplete?

    <p>Small bits of wax residue prevent complete casting formation</p> Signup and view all the answers

    What causes the air in the mold cavity to be driven out when the molten metal enters?

    <p>The pores in the investment</p> Signup and view all the answers

    Which gases are formed when organic materials like wax are decomposed at high temperatures?

    <p>Carbon dioxide, water, nitrogen oxides</p> Signup and view all the answers

    What is necessary for the formation of gases during wax elimination?

    <p>Presence of a sufficient supply of oxygen</p> Signup and view all the answers

    What results from the presence of any foreign material in the mold cavity?

    <p>Incomplete or irregular margins in the casting</p> Signup and view all the answers

    What should be done if castings are incomplete or the margins irregular due to foreign materials?

    <p>Repeat the casting with a new wax pattern</p> Signup and view all the answers

    What are waxes primarily composed of?

    <p>Carbon, hydrogen, oxygen, and nitrogen</p> Signup and view all the answers

    Study Notes

    Wax Elimination (Burn Out)

    • Wax elimination involves heating the investment in a controlled furnace to vaporize the wax, creating a cavity for molten metal casting.
    • The temperature reached determines thermal expansion, necessary to compensate for casting shrinkage.
    • Although wax melts at low temperatures, complete elimination requires much higher temperatures.
    • Incomplete wax elimination leaves residue in the mold's fine margins, preventing a complete casting.

    Importance of Complete Wax Elimination

    • Incomplete wax elimination slows or prevents air/gas removal from the mold cavity, resulting in incomplete castings or irregular margins.
    • If this occurs, the casting process should be repeated with a new wax pattern.

    Formation of Gases

    • Waxes, being organic materials, are composed of carbon, hydrogen, oxygen, and nitrogen.
    • When heated to high temperatures, waxes decompose into gases: carbon dioxide (CO2), water (H2O), and nitrogen oxides (NO2).
    • Gas formation depends on sufficient oxygen, high oven temperature, and adequate heating time.
    • Insufficient oxygen availability can hinder gas formation in the mold cavity.

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