Innovative Dewax Method Unlocks Potential for Investment Casters
Totally new methods are infrequent in a mature industry like investment casting. However, just such an advance has occurred for the dewax process. This patent pending technique involves an inverted directional solidification approach. Wax is removed with little or no stress on the shell. By using this technique, it is possible to remove several constraints placed on the investment caster that are in place to prevent or reduce shell cracking.
For the past half century the main methods of removing wax from investment casting shells in the USA has been the steam autoclave. The distant second most popular method is flash fire dewax. These two methods have been used to remove wax from an estimated 90-95% of all investment casting shells made during this time. The remaining few percent were accomplished by hot wax dewax, microwave dewax, and vapor dewax. The later three have significant environmental or technological issues that limit their suitability
All of these methods, while substantially different, have one thing in common. Energy to melt the wax is applied in a relatively uniform manner at one time to the entire shell. This uniformity of applied energy has long been recognized as a problem leading to shell cracking. One method used to overcome the cracking is the common use of two different waxes for patterns and gating. The gating wax typically is required to have a melt point 10 degrees Fahrenheit below that of the pattern wax to help reduce cracking of the shell from internal wax pressure. Several other methods have been developed to also help prevent cracking.
A recent patent applied for invention, which Buntrock Industries has acquired rights to market the technology, removes the wax much differently than the current and past methods of removing wax. Instead of applying energy uniformly to the entire shell at once, energy is applied to a small horizontal band around the shell. The band is then progressively moved up the shell. This process has its origin in the metallurgy of directional solidification. This directional wax removal applies less stress to the ceramic shell because the entire wax is not being heated. Only a small portion of the wax is heated at one time and liquid wax merely runs out without building pressure. Figure 1 shows a schematic diagram of how directional wax melting is different from traditional dewax methods.