| 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.
-
Boric 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 boric 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 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 - 15 minutes before quenching flasks.
|
