Tony Midea (L) receiving his speaker award from Meeting Chair Gene Muratore

Tony graduated with his Bachelor of Science in Aeronautical Engineering from The Ohio State University and his Masters of Science in Aeronautical and Astronautical Engineering from the University of Illinois.  Tony started his working career with McDonald Douglas as Propulsion Systems Performance Manager for the F15E product line and Senior Engineer for the F-18, AV8B and T45 Projects, as well as several "black" projects.  He also worked six years with NASA doing propulsion system integration for the high speed civil transport and the two-stage-to-orbit vehicles.  Tony has been with Foseco Metallurgical for 12 years using computer simulation to develop feeding system material thermal data, optimize products and to assist foundries with product applications and computer simulations.  Currently, Tony is the Product Development/ Technical Group Manager.  Tony is the past Chairman of AFS Engineering Division Executive Committee 1A and 1B.  He is also the Past Chairman of the AFS Process Modeling Committee 1F.  Tony has written over 38 technical papers for various organizations.

Molten metal does not magically appear within a casting cavity, but rather it is poured through a conventionally designed system consisting of a sprue, runner bars and ingates, or through a direct pouring system.   Oftentimes, the difference between good castings and scrap is partly determined by the quality and consistency of the method by which the casting cavity is filled.

Quality of the metal flow means minimizing inclusion generation, and consistency means delivering molten metal to the casting cavity in the same orderly fashion, every time.  Engineers employ the Laws of Continuity and Mass Conservation to help them design good quality gating systems, and Computational Fluid Dynamic (CFD) programs are often used to evaluate and improve the design.  

No matter how good the design of the metal delivery system is, inclusions already present in the molten metal may find their way into the casting cavity.  These types of inclusions must be mechanically removed from the metal stream.  In addition, momentum caused by gravity acting upon the molten metal can be difficult to dampen, and this can result in metal damaging flow turbulence and oxide inclusions.  In many instances, these problems are difficult to solve with delivery system design alone.  

A common way to address these challenges is to use filtration devices to help trap inclusions and modify the flow stream.  It is easy to visualize how various filter structures can physically trap inclusions, but it is less obvious to visualize how they alter the metal flow itself.  But there is a straightforward explanation.  

The metal flow stream sees a filtration device as a flow discontinuity, which means that the Law of Continuity does not apply across filtration devices.  The filter acts as an obstacle to the free flowing metal, and this results in a reduction of flow momentum and velocity, much like a resistor in an electrical wire reduces the voltage.  In both cases, the discontinuity is designed to reduce and control the energy and flow of the medium.  

Historically, it has been difficult to analyze the detailed flow characteristics of individual filtration devices.  X-ray and water flow devices have typically been used, but there are severe limitations to the ability to draw quantitative results from these types of experiments.  Computational fluid dynamic codes have also been employed to varying degrees with some success^1-5, but these studies can be extraordinarily time intensive to conduct.

This paper documents the results from a new study that analyzes, using CFD, the flow through different filtration devices, and compares these results to an identical gating system without a filter.  The overall effect of the filter on the metal flow of the system is analyzed, as well as the flow characteristics just before and after the filter itself. 

Summary/Conclusions

This study analyzes, using CFD, the flow through different filtration devices, and compares these results to an identical gating system without a filter.  Pressed, cellular extruded and foam filtration devices were analyzed, in particular.

The results show that any of these three filtration methods is successful in modifying the metal flow in such a way that the metal velocity and flow energy are reduced, as compared to not using a filtration system at all.  Foam filters, which are naturally more restrictive than either extruded and/or pressed filters, are able to more significantly reduce the flow velocity, energy and turbulence, and result in the best runner bar flow characteristics of the filters tested in this study.  The extruded and pressed filters yielded similar results, except inside the filter itself and very near the filter exit.  Inside the filter, the pressed filter had higher velocities within its channels as compared to the extruded filter, thus potentially reducing its ability to successfully mechanically trap inclusions.  At the exit, the pressed filter exhibited a tendency to create flow jets, whereas the extruded filter did not, except for a row or two of channels at the bottom of the filter.