Report on Fiber Enhanced Slurry Developments
Abstract
One of the most exciting new developments for the investment casting industry is the use of organic fiber. Dan Duffey and Robert Shaw (son of the inventor of the “Shaw Process”) were issued a UK Patent and three US Patents covering the use of organic fibers for use in investment casting slurries.
Introduction
Originally, Buntrock Industries, Inc. licensed this technology, but has since purchased the three US patents. The major advantages of incorporating the fiber into an investment casting slurry are:
- Thicker shell build for each coat. This frequently means that the shell can be constructed with less dips.
- More uniform shell build around corners and sharp radii. The University of Birmingham in cooperation with Rolls Royce developed a special edge test for evaluating the MOR strength around the trailing edge of airfoil shapes. The fibers tend to wrap themselves around sharp corners of the assembly and reinforce the “weakest points of shell construction.” For Rolls, this edge breaking test was much more predictive of shell cracking than the standard 3 point break MOR test.
- The fibers are believed to prevent crack propagation.
- Due to the above reasons, shell molds are less crack prone and this has been verified by D.O.E. tests at a number of foundries.
- Since the fibers are organic, they burn out during the furnacing cycle. The hollow channels from the vacated fibers significantly increase permeability and improve knock-out. Caustic leaching is also improved, as the chemical solution now has paths within the shell to penetrate and remove shell material.
Much of the current work has centered around a special organic fiber with about a 1.5mm length (both the length and diameter of the fiber are important). Although other types of fibers and lengths are possible, this particular one seems to work well for back-up slurries and is the one we suggest for your evaluation.
In order to achieve better economics, we have developed other additives which enhance slurry rheology and increase the shell build per coat. A very excellent candidate is our Carb-O-Sil refractory. This product was developed by Wesbond and its use with fibers is covered in a recently issued Buntrock Industries US Patent (#6814131); this patent also protects the art of blending fiber and refractory materials to form a convenient pre-blend. Additional US patents have issued (US# 6991022 and US# 7,004,230) to further protect this technology.
