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 mold.
- 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 beginners.
- 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 email@example.com. and Rio Grande, Albuquerque, NM; (800) 545-6566 www.riogrande.com.
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.