Precious Metals & Bench
Choose the right wax to ensure a better casting
Casting is known more formally as lost-wax casting. The waxes
used are an essential element of the process. Unless you choose
the correct wax for each job, consistent quality casting is almost
impossible. You should be familiar with three types of wax for
most casting jobs:
- Carving wax, which is used to carve the original model.
- Injection wax, which is melted and injected into the rubber
- Treeing wax, which is used in setting the sprue tree. This
article will look at the first two types of wax. We'll examine
waxes used in the sprueing process in a future article.
John Henkel of J.A. Henkel Inc. has been in the modelmaking,
casting and finishing business for 23 years. He says one of the
most important things to consider in choosing a carving wax is
the configuration and level of detail of the piece you're casting.
Most waxes sold today come in different colors, and the properties
of the different colored waxes vary from one manufacturer to
another. However, there are some generalities:
- The hardest carving waxes, often in shades of green, are
good for sharp, clear details. The drawback, Henkel says, is
they are brittle and break more easily than others during carving.
He uses hard waxes himself, but he doesn't recommend them for
- A medium hardness wax often in shades of purple, red
or blue is stronger and less brittle than the hardest
waxes, while still allowing good detail. This is the kind
of carving wax Henkel uses most often and recommends for most
of his students and customers who carve their own models.
- Softer waxes, often in shades of blue, are good for carving
flat or larger objects such as belt buckles or brooches. They
are very strong and durable. He points out that when you make
pieces where a softer wax is appropriate for the body, details
can be carved separately in harder wax and then attached.
You'll find even more injection waxes than carving waxes on the
market. But again, the important consideration is the piece you're
going to cast. Understanding the three basic components of injection
waxes and their characteristics will help you make the right
choice for anything you want to cast:
- Paraffin is responsible for a wax's flow or fluidity. The
more paraffin the wax contains, the more fluid it will be when
melted. This is important when doing highly detailed work.
- Beeswax (natural or synthetic) is made of larger crystals
than paraffin and gives wax flexibility and strength. This type
of wax is especially good for intricate filigree designs and
other pieces with thin areas where strength is important.
- Carnauba imparts to wax hardness and carvability. This is
important if you plan to work with the wax model after you take
it out of the rubber mold.
According to Henkel, commercially produced waxes have a combination
of these components. The ratio of the components determines the
characteristics of that particular wax. Experienced casters sometimes
mix different waxes to obtain exactly the properties they need
for a certain project. See the box below for an explanation of
some of the important terms you'll want to discuss with your
wax supplier. These terms and others can be found on page 83
of Rio Grande's 1999 catalog.
The manufacturers and distributors of carving and injection waxes
can provide answers to all of your questions. Henkel suggests
you shop around, talk with the suppliers and let them help you
choose a selection of waxes that will be right for all the modelmaking
you need to do.
Sources: J.A. Henkel Inc., Brunswick, MA; (207) 729-3599
firstname.lastname@example.org. and Rio Grande, Albuquerque, NM; (800)
Carvability: The ability of a wax to be carved or filed without gumming up tools. Harder waxes are usually best for carving.
Flexibility: The ability of a wax to be deformed without breaking or shattering. Usually the more flexible the wax, the less carvable.
Flow: The ability of the wax to fill cavities and accurately reproduce detail.
Flow Temperature: The temperature at which a wax is liquid enough to flow into the mold.
Memory: The ability of the wax to be deformed and then return to its original shape.
Shrinkage: The relative amount of volume lost when the wax changes from molten to solid form. Generally, the higher the flow temperature, the greater the chance of shrinkage.
|Rio Grande's purple
Plast-O-Wax Plus is designed to offer good surface quality,
crisp detail and minimal shrinkage. Cost, $5.75 per pound when
you order 5 to 29 pounds.
|Rio Grande says Rio Turquoise Wax
yields bright surfaces and good pattern readability. Cost, $4.40
per pound for 5 to 9 pounds.
|Rio Grande's Rio Jade Wax is designed
for excellent memory to help retain shape. Good flexibility.
Cost, $4.40 per pound when you order 5 to 9 pounds.
Copyright © 1999 by Bond Communications.