Evaluation of an improved centrifugal casting machine
A Type III gold alloy, a silver-palladium alloy, and a base metal alloy were cast in two different centrifugal casting machines. With the number of complete cast mesh squares as an indicator of castability, the Airspin casting machine produced superior castings with all three alloys. The base metal alloy produced the greatest number of complete squares with both casting machines.he last wax process was introduced to dentistry by 
Taggart in 1907.’ Since that time millions of cast
restorations have been made, most with a broken-arm
centrifugal cast machine. In the past decade, partly in
response to the widely fluctuating price of precious
metals, particularly gold, and partly because of a search
for metals with improved physical properties, a vast
number of alloys of disparate composition have been
used.2 
The introduction of the new alloys, many of which
exhibit higher melting temperatures and dramatically
reduced specific gravities, has created considerable inter-
est in casting technology. Early studies on castability of
different types of alloys noted the difficulty in casting
low gold, nongold, and base metal alloys when conven-
tional materials and techniques were used.3-5
The castability of an alloy is defined by its ability to
completely fill the mold created by the elimination of a
pattern.6 Castability depends on a complex number of
variables that include melting range, mold temperature,
and the initial acceleration of the casting machine.7*8
Theoretically, with no limit to the flame temperature or
potential mold temperature, all alloys are ultimately
castable. In dentistry however, casting techniques are
limited by the disruption of casting investment at exces-
sive burnout temperatures and by breakdown of the
alloy at excessive melting temperatures.
One potential method to improve the castability of an
alloy at conventional temperatures is to increase the rate
of acceleration of the centrifugal casting machine. An
important point is that the molten metal fills the mold
quickly, and the ultimate speed attained by a casting
*Assistant Professor and Chairman, Biomaterials Science, Department
or Restorative Dentistry.
**Certified Dental Technician.
THE JOURNAL OF PROSTHETIC DENTISTRY
machine is relatively unimportant compared with the
initial acceleration. A new casting machine (Airspin
Pneumatic Caster, Airspin Mfg. Co., Van Nuys, Calif.)
that demonstrates an improved initial acceleration has
recently been developed (Fig. 1). The Airspin unit is a
vertical-motion centrifugal casting machine that is rap-
idly accelerated by the operation of a pneumatic cylinder
and piston. Compressed gas is applied to the piston to
move it within the cylinder, and a connected drive chain
engages a drive wheel coupled to the casting arm (Fig.
2). Movement of the piston through a drive stroke is
thereby coupled to rotate the casting arm and provide
such rapid acceleration that the mold is filled with
molten metal before substantial cooling can take
place.9
This study was conducted to determine if use of this
device resulted in improved castability of dental alloys
when compared with using a conventional broken-arm
casting machine. Castability of three different dental
alloys was compared.
MATERIAL AND METHODS
A nylon mesh 11 X 11 mm with 0.1 mm filaments was
used as the pattern for the castings. Each pattern
contained 100 complete squares. The sprue was attached
to 4 squares so that only 96 test squares remained. This
pattern was chosen based on results of a preliminary
study that revealed that it was impossible to completely
cast the entire pattern with a 0.1 mm filament with
either a Type III gold or a base metal alloy when the
Airspin machine was used (Fig. 3). Castability was
determined by the number of complete squares cast in a
pattern.6
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