Metal Properties Jewelry Casting Tips & Tricks- Romanoff

Notes on the properties of some metal alloys

Brass, gold 8/9/10 kt, some alloys gold 14 kt:

These alloys have a high content of zinc. Some of the zinc evapo- rates during the heating phase. If vacuum is used in the melting chamber, much more zinc would evaporate. To prevent this problem there is a small trick

Put the metal in the cold crucible, set in flask at the same time. Push button start (heating) and start (vacuum) again immediately. Now a vacuum is built up, but the metal, still not liquid, cannot evapo- rate zinc. After reaching full vacuum, push another time start (vacu- um will be released by gas). After reaching casting temperature, cast immediately

Palladium 950:

Palladium should be melted in the same type of crucible like plati- num. Palladium has a strong reaction with oxygen. That's why we recommend to "wash" the chamber atmosphere as follows: Set "power" to 0.0 kW (0 %). Put in metal, set in flask. Push button Start (want to heat, but set point power is zero = no heating possible). After then Start again = vacuum comes. After reaching vacuum, another push on Start: vacuum will be released by ARGON gas. Make only ONE washing cycle, because palladium ex- tracts the oxygen from the crucible ceramic. Change setting of power to 3.5 kW (100 %). Wait until metal is mol- ten completely and cast immediately

IMPORTANT: Use Argon gas for palladium castings!

Platin:

Set heating power to 3.5 kW (100%).

Use the special ceramic crucible for Platinum. Put metal into the (cold) cruci- ble. Push “Start” once for heating, set in flask and lock chamber. Push “Start” second time to start the vacuum.

Full vacuum is reached inside the gypsum in about 30 seconds (see timer). After metal is melted totally, wait for max. 8 seconds and cast. This will extend the life time of the crucible!

Adjust your process in that way, that in the moment of pouring out the Pt. and the end of evacuation time (at least 30 seconds) of the flask are concurrently.

Important hint:

Pt., melted in a standard Pt.-crucible, is absorbing silicate out of the crucible
material. As more often you re-melt same batch of metal, as more silicate will
be absorbed. This makes Pt. brittle.

Help: Coating of the inside of the crucible by use of liquid zircon oxide!

After casting: leave flask under set parameters for approx. 240 seconds.

Cobalt-chromi-um,steel alloys

Set heating power to 2.8 kW (80%).

Use the ceramic crucible for steel.

Put in crucible, set in flask. Push “Start” twice to start heating and vacuum. If full vacuum is there for at least 30 seconds (see timer) increase heating power to 3.5 kW (100 %) and cast when metal is ready.

One more problem of NiCr, CoCr and steel alloys: some alloys tend to splash in melted condition and under vacuum. In this case, it is useful to change set- ting of melting pressure to -0.80 bar