Podcast
Questions and Answers
What is the main purpose of wax elimination or burnout?
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?
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?
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?
What happens if wax elimination is incomplete?
What causes the air in the mold cavity to be driven out when the molten metal enters?
What causes the air in the mold cavity to be driven out when the molten metal enters?
Which gases are formed when organic materials like wax are decomposed at high temperatures?
Which gases are formed when organic materials like wax are decomposed at high temperatures?
What is necessary for the formation of gases during wax elimination?
What is necessary for the formation of gases during wax elimination?
What results from the presence of any foreign material in the mold cavity?
What results from the presence of any foreign material in the mold cavity?
What should be done if castings are incomplete or the margins irregular due to foreign materials?
What should be done if castings are incomplete or the margins irregular due to foreign materials?
What are waxes primarily composed of?
What are waxes primarily composed of?
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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