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#725 Rich Yellow All-Purpose Alloy for 18K - 1 oz. (28 grams).
- Can be used for sheet, plate and wire fabrication
- Can also be used for investment casting if desired
#725 Alloy
Purpose
- Mix Alloy # 725 with fine gold to obtain 18K rich yellow gold for sheet, plate and wire fabrication.
- Can also be used for investment casting if desired.
Melting
- #725 Alloy and fine gold should be melted together in a clean crucible. Put alloy in the bottom of the crucible and fine gold on top.
- Initial melting temperature should be 1070°C / 1958°F.
- Drop temperature somewhat before pouring as listed below.
- Boracic acid flux may be used to keep the metal clean during the melting process.
- The metal should be mixed well with a stirring rod before pouring to assure a good mix.
Pouring Temperature for Ingots
Pouring
- Metal should be poured into a preheated, vertical graphite, or lightly lubricated iron mold.
- A steady, even pouring motion should be used, slowing down at the end of the pour to prevent shrinkage in the top of the ingot.
- Use a round rod mold for wire, and a 2-piece, L-shaped mold for plate and sheet.
Quenching
- The metal ingot should be removed from the mold and quenched immediately in pickle solution or water.
- For heavy ingots, a one-minute cool-down before quenching prevents quench cracking.
Fabrication
- The metal ingot should be cleaned of all adhering oxide or fluxes before rolling.
- The ingot should be rolled or drawn to a 50% reduction in size before annealing. After annealing, continue the reduction at 50% before annealing again.
- Clean the ingot after each anneal.
- Keep the rolls, dies and metal clean to prevent defects in the finished stock.
Annealing
- Annealing temperature 704°C / 1300°F for 20 minutes.
- Quench immediately in water or pickle solution.
- A boracic acid fire coat should be applied before annealing in an open atmosphere oven to protect the metal from heavy oxidation.
- Avoid over-annealing wire or plate stock, as this can cause excessive grain growth, creating an orange peel effect on the surface of finished goods.
Re-Melting
- Use a 50% scrap to fresh mix when remelting to prevent oxide build-up in the metal.
Investment Casting
- Pre-alloy #725 and fine gold, and pour into water to make shot.
Pre-Alloying Temperature
- 1060° - 1070° C / 1940° - 1958° F.
Casting Temperature
- 1010° - 1020° C / 1850° - 1868° F.
Flask Temperature
- A slightly higher temperature is recommended.
Quench Time
- Wait 5 to 15 minutes before quenching flasks.
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