Articles
General Casting Tips for Karat Golds
By Stuller Technical Team | January 30, 2012
Melt Temperature Recommendations For Various Casting Methods- Vacuum assist casting: 100° to 200° F over Melt Temperature.
- Centrifugal/sling casting: 50° to 125° F over Melt Temperature.
- Pieces with less detail require lower superheats.
- Experience is the best guide.
Flask Temperature Recommendations For Various Casting Methods
- Smaller pieces (findings) and pieces with great detail (filigree rings) require higher flask temperatures 1100°F to 1300°F.
- Large pieces (gent's rings) and pieces with few details require a lower flask temperature, 800°F to 1000°F.
- White golds generally require flask temperatures on the high end of the recommendations.
- Centrifugal casting tends to have flask temperatures on the lower end of the recommendations
- Large and small pieces on a single tree require flask temperatures closer to those needed for light pieces.
- Experience is the best guide.
About The Metal
- Ratios in excess of 50% scrap are not recommended.
- Clean metal thoroughly before using (no investment).
- Purge system periodically. Start fresh every 6 months.
- The weight of the metal in the button and tree should at least equal the weight of the pieces cast.
Investing Procedures
Ratios of Investment to Water
- Follow instructions of the supplier.
- Pieces with great detail may need a slightly greater amount of water for investment.
Vacuuming Investment
- Make sure you have a good vacuum.
- Vibrate table to help remove trapped air.
Burnout Cycle
- Don't move invested trees too early (wait 1 hour)
- Follow instructions of investment supplier.
- Check that temperature read was accurate.
- The casting flask temperature (final step) should be maintained for at least one hour before the first flask is removed.
Proper Spruing and Gating
- Improper spruing is the leading cause of shrinkage porosity.
- Don't use chock gates. They cut off the feed metal.
- Place sprue (gates) at heaviest cross sections of the piece.
- Use runners to heavy areas if they are separated by thin cross sections.
- Flair the gate at the connection to the piece. This will help reduce turbulence in the metal flow.
- Don't put pieces too close together.
- Smooth all surfaces to avoid sharp corners which may break off during casting (i.e. connections between main sprue and gates; and gates and piece).
Breakout
- Don't rush to break out. Place flask in shaded area, quench when red glow is no longer visible in button.
- Clean investment off thoroughly if you plan on reusing the scrap. Investment in the melt will cause porosity problems over time.
- IF breaking out dry by hammering, be sure flask is well below 600°F to help reduce potential cracking.
