| Synopsis of Casting Machines (7/07) |
Casting machines are an integral part of the equipment
used in any dental laboratory. They are used to melt and cast a variety of
alloys. It is reported that casting machines produce castings that are denser
and more accurate than conventional torch casting methods.
There are a number of casting machines on the market
today. They vary in size, shape, construction, and functional casting method
(centrifugal, vacuum, injection). Selecting which type of casting machine to
purchase can be difficult. One major factor in the selection process is to
determine dental laboratory needs and intended uses. For example, a number of
casting machines are designed for casting removable partial denture frameworks
in the dental laboratory. Others are specifically designed to cast fixed
restorations.
Casting machines use various heating methods to melt an
alloy. Arc heating involves the use of an electric arc where heat is
transferred by conduction, convection, or radiation. Induction heating occurs
when an electrically conductive material is placed in a varying magnetic field.
An electrical current is induced directly into the part being heated. It is
reported that induction heating can reduce or eliminate the need for skilled
operators in applications such as brazing and soldering. In addition, induction
heating is a clean form of heating which does not emit unpleasant odor or heat.
Casting methods may be a concern for a number of
laboratories. Centrifugal casting uses an articulated arm that freely spins
around a vertical axle, which is driven by an electric motor or a spring.
Vacuum casting uses similar methods, however with vacuum casting the molten
metal is driven into the mold by atmospheric pressure, while the vacuum removes
trapped air that would impede the free flow of the liquid casting material.
Gas/air-pressure injection often used with vacuum casting uses a combination of
various gases under pressure to improve the quality of the casting and minimize
porosity in the metal. A computer program regulates the various cycles involved
in the casting process.
Casting machines are available in small tabletop style,
recessed style (in-counter mounting) and floor mounted. A number of units are
equipped with a digital read out display, a viewing window and an internal
memory that holds user-defined programs that specify start temperature, melting
temperature, melting time, casting, and cooling time. Additional safety
features include a self-monitoring system and diagnostic programs to manage
internal operations.
The purpose of this synopsis is to provide useful information giving federal service customers a starting point for researching and purchasing a casting machine. Casting machines with the most features per manufacturer were selected. Additional models, if available from the manufacturer are listed with the item number only. The information in the table has been provided by the manufacturer or obtained from the Internet.
(MSgt Young)
