Instruction manual

OPERATING_MANUAL_MC20V.DOC 18.03.11 KS Seite 25
3.14. About casting metal:
Because of high costs casters do not like to use every time fresh alloy. For some
alloys customers mix „second hand metal“ up to 50%, mainly Au, Ag based alloys.
Never use finished jewellery pieces. The alloy composition is not known,
solder in casting material will give no good casting result.
Never mix two alloys, even if they have the same contents of gold
All already cast metal should be very clean, sand blasting and pickling are
adequate methods. Caution: rest of glass beads, investment material or rests
of acid are unwanted. Clean in ultrasonic in distilled water.
Alloys with zinc content: give much more fresh metal to „old“ metal.
Alloys with high carat (Pt 950, Au 21/22/24 ct) can be re-used to 100%
Pd 950 is a very reactive metal. No chance to melt it twice. Use fresh metal!
Prevent oxidation by melting under vacuum and inert gas only.
Never use boric acid for melting!
3.15. Hints for castings in difficulty-to-cast metals
Brass, gold 8/9/10 ct, some alloys gold
14ct
These alloys have a high content of zinc.
Some of the zinc evaporates 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
evaporate zinc. After reaching full
vacuum, push another time start
(vacuum will be released by gas). After
reaching casting temperature, cast
immediately.