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Questions and Answers
What is the purpose of using the correct ratio of oxygen to acetylene in oxy-acetylene flame?
In electric melting, what is the role of the water-cooled coil?
Which zone of the flame of a blowtorch is responsible for oxidizing the alloy?
Why is it recommended to use twice the amount of gold required for the framework during casting preparation?
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What is the average weight range of a mandibular partial denture casting in terms of gold weight?
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What are the three purposes served by the burnout operation?
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Why should the torch be removed simultaneously when releasing the casting machine in gold casting?
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What are the two techniques used to remove the wax?
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Which type of casting machine uses gas oxygen blowtorch as a heating source?
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What happens if too little force is used in the casting process?
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Why is it important to eliminate all traces of wax from the mold in the burnout process?
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In the context of casting machines, what does 'induction method' provide?
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Study Notes
Oxy-Acetylene Flame
- Control is necessary to achieve the correct ratio of oxygen to acetylene to prevent oxidation (too much oxygen) or carbon pick-up (too much acetylene)
Electric Melting
- Properties:
- Machine driven by an electric motor that produces a high-frequency current
- Current passes through a water-cooled coil, generating heat in the alloy
- Cooling of the coil is essential to prevent it from melting during the process
- Water pressure of approximately 25 is required to cool the coil satisfactorily
Induction Melting
- Provides a rapid and accurate method of melting metal
- Composition of the flame of a blowtorch:
- Mixing zone: cool, colorless zone
- Combustion zone: greenish-blue zone where partial combustion takes place, making it an oxidizing zone
- Reducing zone: dim-blue tip, the hottest zone
- Oxidizing zone: where combustion between the gas and surrounding air occurs, making it an oxidizing zone
Casting
- Procedure:
- Prepare the casting machine by cleaning or lining the crucible with asbestos and winding and locking it in position
- Stack the gold in the crucible to melt uniformly, using twice the amount required for the framework
- Melt the gold using a gas-air torch, specifically the reducing area of the flame
- Remove the casting ring from the oven and place it in the casting machine, avoiding overheating the gold
- Release the casting machine and remove the torch simultaneously
- Burnout and Casting:
- Burnout: removal of wax from the mold by heat, serving three purposes:
- Drives off moisture in the mold
- Vaporizes and eliminates the pattern, leaving a cavity in the mold
- Expands the mold to compensate for metal contraction on cooling
- Techniques for removing wax:
- Slow technique: gradual temperature increase
- Rapid technique: heating to 200°C for 30 minutes
- Burnout: removal of wax from the mold by heat, serving three purposes:
- Types of casting machines:
- Centrifugal casting machine
- Air pressure:
- Gas oxygen blowtorch
- Electric muffles surrounding the metal
- Induction method: rapid and accurate melting of metal
- Importance of controlled force:
- Too little force: mold not completely filled
- Too much force: excessive turbulence, entrapment of gases in the casting, or mold fracture
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Description
Test your knowledge about burnout and casting techniques in the manufacturing process. Learn about the process of removing wax from a mold using heat and the purposes of the burnout operation. Explore different techniques for eliminating wax and optimizing the casting process.
