10 Questions
What is the main purpose of wax elimination or burnout?
To create a cavity for molten metal casting
What does the temperature reached by the investment determine?
The thermal expansion to compensate for casting shrinkage
Why is a much higher temperature required for complete wax elimination?
To vaporize all traces of wax
What happens if wax elimination is incomplete?
Small bits of wax residue prevent complete casting formation
What causes the air in the mold cavity to be driven out when the molten metal enters?
The pores in the investment
Which gases are formed when organic materials like wax are decomposed at high temperatures?
Carbon dioxide, water, nitrogen oxides
What is necessary for the formation of gases during wax elimination?
Presence of a sufficient supply of oxygen
What results from the presence of any foreign material in the mold cavity?
Incomplete or irregular margins in the casting
What should be done if castings are incomplete or the margins irregular due to foreign materials?
Repeat the casting with a new wax pattern
What are waxes primarily composed of?
Carbon, hydrogen, oxygen, and nitrogen
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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