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 


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. 


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 


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. 


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