Pourable Ceramic Core Recipe For Direct Pattern Contact
Patent Filed: July 10, 2014 (PDF)
Stage of Development:
Prototypes developed and tested in commercial foundry
Investment casting is a common technique used to produce high-quality cast metal parts. Generally, a pattern made of a low melting point material such as wax is coated in a heat resistant shell material. Once the shell is cured, the pattern is burned or melted from the shell leaving a cavity in which to pour molten metal. The process of forming the shell used in investment casting involves repeated steps of dipping the pattern in a liquid slurry and refractory material up to seven times per shell with adequate time for air drying between dips to ensure structural integrity is maintained. This process typically lasts several days from first pattern dip to molten metal pour. Occasionally patterns used for investment casting contain deep cores with complex geometries that will not dry properly using standard practices. Traditional core materials produce extreme exothermic reactions as they cure and cannot be poured directly against typical pattern materials used in the industry without damaging the surface of the pattern and subsequent cast part. There is a need for new quick dry shell materials that exhibit a decreased exothermic cure and can therefore be applied directly to the pattern. The shell material must also be compatible with standard practices including low impact shell removal.
Researchers at the University of Wisconsin – Whitewater and collaborators have developed a new high viscosity refractory material that forms a ready-to-pour ceramic core in as little as 30 minutes. This newly developed core material has the advantage of being able to cure quickly without generating a strong exothermic reaction upon curing. The low curing temperatures allow the new core material to be poured directly into the deep cavities of a pattern without causing pattern surface deformation. The new refractory core material greatly decreases the time from coating pattern to pour as the material can be exposed to temperatures up to 3,200 degrees fahrenheit after 30 minutes of curing at room temperature. In addition, the refractory bonds well with traditional investment casting shell materials. When high temperatures are applied during the casting process the strength of the refractory material is reduced, thereby enhancing the ability to remove the investment casting material from the cast product while still accurately reproducing fine details of the pattern. Shell removal can be accomplished with high pressure water as opposed to hammering or the use of abrasives, creating a lower impact process of removal.
Cores for investment casting that can be injected under pressure as well as poured directly into the deep complex cavities of pattern.
-Ultrafast dry time
-One step application
-Easy removal of refractory cores from final cast part
-Broad range of thermal tolerance
-Pot life ranges from 5-13 minutes
-Shelf life is approximately one year