Final Technical Report Quantification and Standardization of Pattern Properties for the Control of the Lost Foam Casting Process

This project takes a fresh look at the ''white side'' of the lost foam casting process. We have developed the gel front hypothesis for foam pyrolysis behavior and the magnetic metal pump method for controlling lost foam casting metal fill event. The subject of this report is work done in the improvement of the Lost Foam Casting Process. The original objective of this project was to improve the control of metal fill by understanding the influence of foam pattern and coating properties on the metal fill event. Relevant pattern properties could then be controlled, providing control of the metal fill event. One of the original premises of this project was that the process of metal fill was relatively well understood. Considerable previous work had been done to develop fluid mechanical and heat transfer models of the process. If we could just incorporate measured pattern properties into these models we would be able predict accurately the metal fill event. As we began to study the pyrolysis behavior of EPS during the metal fill event, we discovered that the chemical nature of this event had been completely overlooked in previous research. Styrene is the most prevalent breakdown product of EPS pyrolysis and it is a solvent for polystyrene. Much of the styrene generated by foam pyrolysis diffuses into intact foam, producing a molten gel of mechanically entangled polystyrene molecules. Much of the work of our project has centered on validation of this concept and producing a qualitative model of the behavior of EPS foam undergoing pyrolysis in a confined environment. A conclusion of this report is that styrene dissolution in EPS is a key phenomenon in the pyrolysis process and deserves considerable further study. While it is possible to continue to model the metal fill event parametrically using empirical data, we recommend that work be undertaken by qualified researchers to directly characterize and quantify this phenomenon for the benefit of modelers, researchers, and workers in the field. Another original premise of this project was that foam pattern and coating properties could be used to efficiently control metal fill. After studying the structure of EPS foam in detail for the period of this contract, we have come to the conclusion that EPS foam has an inherent variability at a scale that influences metal fill behavior. This does not allow for the detailed fine control of the process that we originally envisioned. We therefore have sought other methods for the control of the metal fill event. Of those, we now believe that the magnetic metal pump shows the most promise. We have conducted two casting trials using this method and preliminary results are very encouraging. A conclusion of our report is that, while every effort should continue to be made to produce uniform foam and coatings, the use of the magnetic metal pump should be encouraged and closed loop control mechanisms should be developed for this pouring method