Thinest casting depends on how you are getting the metal into the mould
Three methods Gravity, Centrifugal force and air pressure.
Gravity is the oldest but you need large sprues to get the metal in an
it's logical that it wont go far in the mould without help! so thicke
pattern and assistance Next oldest is swinging the mould after puttin
the Molten metal in scary but it used to be done We learned that one a
College! few years ago Steam pressure by damp asbestos pressing near th
freshly poured metal forms a seal and steam forces metal into th
mould.
OK all dangerous but allow thinner patterns.
More modern ways involve centrifugal casting machines either verticall
or horizontally. usually spring wound, melt the metal and hit the butto
metal flies in the mould and pattern is cast 0.3-5mm and less again w
are talking small patterns here moulds two -3 inches with castin
fitted inside.
Theory of casting is that the pattern should fit in your mould! th
sprues mounted so the metal can flow easily into the pattern and tha
you can easily cut them off. The reservoir usually spherical in shap
must be close to the centre of the mould ie the heat centre with th
reservoir last to cool and close to the pattern this is a trade off
reason for this is that get your metal in to the casting and as i
cools it contracts you must be able to supply molten metal into you
casting otherwise voids form as porosity or worse still parts of yo
pattern is missing. it doesn't matter if voids form in your reservoir
Check out dental suppliers sites for details of techniques particularl
if your patterns are small also jewellery sites. both use Gold bu
dental metal workers also use nonprecious metals so may be mor
appropriate to you. secnd hand machinery is available though pricey bu
hey you may be lucky.
Keep your mould as hot as poss near that of the meting point of th
metal so it doesn't cool in the casting and cast as quick as poss.
email me if you want any other info.
graha
--
Grahammo
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