Casting Gold Temps


#1

So I am a newbie trying to get into casting gold in a simple pour furnace. I am able to get the printer and plaster to work perfectly. However, when I melt the gold at the temps specified by the manufacture (RioGrande - 18K White Gold), the gold doesn’t flow thru the part until it freezes. I am only trying to make a simple ring band, so I don’t think I need additional spurs. I just poured at 2200F and it still froze in the mold. Other than the furnace limits, is there any limit to how you can melt the gold?

Any advice from anyone else who went thru this process?


#2

number one- you want the mold to be HOT. investment molds are usually pored fresh from the furnace after melting out the wax.

number two- Is your mold VENTED? you are not pouring molten gold into an Empty mold, you are pouring it into a mold that is already filled - with air.
you need to make provision in your mold for the air to come out as the metal flows in. A GATE for metal to flow in. And one or more VENTS that the air can escape thru.
Investment allows the gas that comes out of the metal as it cools to escape thru the mold wall… but its not porous enough to allow the air to pass thru as fast as you need the metal to flow in,

number Three- for small castings you need a centrifugal casting machine to place a pressure head in the metal so that it will move quickly into the mold.
They make small ,spring wound centrifugal casting machines you can clamp to a desktop and that will handle ring sized molds.


#3

Thank you! I solved the issue.

For anyone other newbie reading this in the future, the key things to running a regular furnace while casting gold is:

  1. FL is not kidding when they say that you need at least a 12 hour burnout. Even at 11 hours, there are still traces of ash in the mold.
  2. Metal needs to heat in the furnace for around 45 mins to 1 hour. Meaning, just because the crucible is glowing doesnt mean that the metal is ready to pour.
  3. The casting temps on the spec sheets I am told are for centrifugal casting. You need to increase it by around 200 degrees to make sure that you flow the metal properly.
  4. Immediately pour metal from the furnace as quickly as possible. Any delay causes dramatic temperature drops which effect flowing of the metal thru the mold.

#4

yes- when we pour bronze- we heat it at least 250 degrees hotter than the pouring temp. This is because in the less than a minute it takes to get the crucible out of the furnace and over to the molds, its gonna lose that much heat.

pulling a crucible out of a 2,000 degree furnace into 80 degree room air is like immersing a piping hot cup of coffee into liquid nitrogen.

You might want to get yourself a centrifuge… static pours of small volume are fraught with miscasts and porosity.
Moreover, you want head pressure to keep feeding metal into the mold as the metal shrinks.

In large volume casting you rely on the fact that the mold is taller and the cup pretty massive and the pure weight of the metal for head pressure, but even then we often design an elevated gate to help give us the pressure needed to keep the metal feeding as it thickens.