Improving Dewax Performance
Using a progression of controlled tests, Pine Tree Castings incrementally improved its investment casting dewaxing process while maintaining productivity and minimizing capital expenditures.
Mark Oles, Pine Tree Castings, Newport, N.H. I
nvestment caster Pine Tree Castings, Newport, N.H., had a chronic dewaxing problem. A high percentage of its molds leaked during pouring because
of cracks that developed during the flash firing process. The facility had to dip the molds after firing to seal the cracks. Special shell building and firing techniques were necessary to minimize excess metal, flash, bulge and residue defects. Eliminating the mold crack- ing would eliminate those extra steps, increase casting yields and improve throughput at dewax. The metalcaster uses three push-
through flash fire ovens to dewax its molds. In flash firing, dewaxing and mold firing are combined in one op-
eration. The wax must be completely combusted to obtain a clean mold. The investment caster identified many potential contributors to its mold leak- ing problem. Its process used highly- filled, highly conductive pattern- and stick-wax, multiple layers of low permeability prime coats, and poorly controlled ovens. Pine Tree Castings did not want
the solution to come at the detriment of another department. All potential solutions would need to be viewed on their ability to reduce cracking, as well as on total cost impact. The investment caster wanted to account for all areas that could be affected, including: • wax injection rates; • wax material cost;
• shell material cost; • dewax mold handling; • energy consumption; • mold repair; • metal leakage during pouring; • casting scrap and salvage; • capital costs.
Statistical Approach Pine Tree Castings used the cone
mold test to investigate a broad range of potential solutions. Cone patterns were made by melting wax in a small glue pot and pouring it into a mold. After cooling, the large outside diameter was carefully finished to a specific radius. An extruded gate was attached to the face of the small diameters. In the tests, the gate size
Figs. 1 and 2. The cones used in Pine Tree Castings’ tests were inspected for interior and exterior cracks, which were rated for severity based on their size and location.
28 MODERN CASTING / August 2010
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