Next-Generation Investment Casting Filter Cups

Jan. 22, 2010
A new filter design achieve higher molten-metal throughput with no decrease in filtration level among other benefits.

The CerraFlex TorrentFlow™ Filter Cup increases the working temperature threshold to a new maximum — 3,500°F.

Investment casting professionals have learned to balance the need for high levels of molten metal filtration (removing dross, slag and other impurities) against a concurrent desire for higher metal throughput. Given the filtration options of ceramic cellular/foam or silica-mesh filter cups and their respective performance characteristics, it’s rarely a straightforward exercise. This is because performance factors such as throughput rate, relative level of filtration efficiency, and others can vary significantly from one type of filter to the next. As a result, it’s not difficult to find investment casters who regularly use all three filter types depending on the needs of each specific application.

Incredibly, it had been long while since the last significant technical innovation was made in any of the existing filter types. This was not because metalcasters simply stopped asking for improvements from suppliers, but rather that the available filters had become cash-cow products for foundry consumables manufacturers — at least until recently. Long familiar with metal filtration and its technical challenges, the R&D team at ComancheTechnologies created a “wish-list” on metal filtration from leading U.S. investment casters, and used the findings to help define the performance targets of their next generation of investment casting filter cups.

Their outstanding desired enhancement was “increased throughput,” but with this caveat: “no decrease in filtration level.” So although there was initial disappointment among the research team at not discovering some new and unmet, market-driven performance need, it was quickly replaced by their confidence in understanding what would define success. Ultimately, it was achieved through a two-pronged strategy of 1) redesigning the geometric shape of the filter cup, and 2) modifying the mesh material itself.

Extensive foundry testing proved conclusively that the product development team had delivered a revolutionary new filter cup. Extensive test results tallied an average 20% boost in full-production throughput, a higher temperature threshold, and a dramatic increase in active filtration area.

The CerraFlex TorrentFlowTM Filter Cup, a proprietary, “next generation” of high-performance filter technology incorporates a tailored zirconia refractory coating that effectively increases the working temperature threshold several hundred degrees to a new maximum of 3,500°F (1,927°C.) This refractory composition significantly enhances the rigidity and overall strength of the filter cup, providing the ability to handle increased pouring times and heavier metal flow. The TorrentFlow design also incorporates a distinctive interstitial space between the inner wall of the pouring cone and the outer edge of the filter cup that is custom-calculated per each cup and pouring cone pair, to deliver an effective filtration area increase of up to 78% over the traditional filter cup design.

Although the notable improvements in throughput and filtration area achieved with the TorrentFlow filter design successfully met the two most favored performance needs, as identified by extensive customer research, it’s worth noting some of the lesser-known but highly valuable additional benefits that are unique to filter cups in general:

Enhanced Hot-Top Performance – Filter cups can easily be removed from the pouring cone prior to the addition of hot topping, so that the filter material does not hamper the feedback of the molten metal. Ceramic filters placed in the base of the pouring cone can impede the metal feedback from the hot-topping’s exothermic reaction because they cannot be easily removed.

Liquid Impurity Capture – As molten metal is poured into the filter cup, the heavier, denser impurities of slag and dross typically sink to the bottom of the cup and are captured in the mesh. At the same time, liquid slags and dross will remain floating on the surface of the molten metal as it drains gently through the filter material. The “swirling” flow driven by the cup’s geometry traps the liquid slag at the bottom of the filter cup, at which point the operator can remove the filter cup entirely, ensuring the liquid slag does not enter the casting.

Formation of Fayalite – Unique to silica mesh filter cups is the formation of Fayalite (Fe2SiO4) on its surface, when used in ferrous applications. As molten ferrous metal makes contact with the silica mesh, proprietary surface coatings decompose instantly and form a sticky, viscous coating that enhances the ability of the cloth to capture even micron-sized inclusions.

No Requirement for Pre-Heat – Unlike ceramic foam and cellular screen filters, TorrentFlow and CerraFlex filter cups do not require any pre-heating in the investment pouring cone, and thus are easily salvaged should any problems occur with the investment prior to pouring.

Pouring Cone Cost Savings – Because TorrentFlow and CerraFlex filter cups are held in place at the top of the pouring cone, investment casters can reduce costs by eliminating the need for pouring cones custom-made to fit a specific size ceramic foam or cellular filter, and instead use the less expensive, standard pouring cones.

"Given the difficult economic climate we're all facing right now, our hope is that this new generation of filter cups provide investment casters another tool to reduce scrap rates and push down production costs in order to be more competitive in the global market," says Jason Hitchings, General Manager of Comanche Technologies. "We chose AMETEK Foundry Products as the exclusive manufacturer for the TorrentFlow filter cup line, as they've already done an incredible job in ramping up the production of our CerraFlex products. Comanche’s technology strategy of incremental improvement over complete process redesign seems to resonate with our customers, and provides a smoother new product adoption path."

Jason Hitchings is the general manager for Comanche Technologies. Contact him at [email protected], or visit