TIPS ON USING THE HANDI – MELT TYPE ELECTRIC FURNACE FOR CASTING GOLD AND SILVER ALLOYS

The small electric resistance melting furnaces are often used for casting gold and silver jewelry in small shops. The temperature read outs on the small electric furnaces are somewhat erroneous due to the thermocouple location under the crucible. The temperature read -out is the crucible temperature not the metal temperature. Many of the problems encountered with these units are due to the metal being too cold.

When using silicon deoxidized alloys the castings may come out with porosity and oxidation due to being cast too cold. The metal temperature is usually 75 to 100 degrees F. cooler than the read-out temperature on the furnace. The best rule of thumb on these units is to set the furnace 100 degrees F. above the recommended casting temperature. This procedure has proven quite successful with this design of melting furnace resulting in good castings.

BORIC ACID FLUX – is recommended for use in Handi-Melt type furnaces. It is helpful to coat the inside of the crucible with boric acid flux before using to prolong crucible life and keep the metal clean.

Use a small amount of boric acid to clean the molten metal before casting.

STIR THE METAL WELL BEFORE CASTING – This will insure a homogeneous mix and avoid karat variations in the castings. The gold in karat gold alloys has a tendency to be somewhat richer in the bottom of the crucible when the metal is molten due to the force of gravity. Stirring well before pouring will provide a good mix.

Note: Always Skim surface of metal to remove oxides before Stirring. Stirring in oxides can cause inclusions and cloudy surface finish.

SLIGHTLY HIGHER TEMPERATURES MAY NEED TO BE USED FOR SMALL MELTS – When very small amounts of metal are cast, the metal may chill on the way out of the crucible causing cold shuts and partial fills of the casting. Larger amounts of metal have more mass and hold the heat better.

USE A SEPARATE CRUCIBLE FOR EACH ALLOY – This will avoid contamination problems.

REPLACE CRUCIBLES WHEN THEY BECOME WORN OR HAVE A LOT OF SLAG BUILDUP.