By adopting more efficient de-gating and de-risering techniques, foundries can make a significant impact on their bottom line operating costs.
Jason W. Hitchings, Comanche Technologies
Business challenges facing foundries and metal casters at the moment in areas such as fluctuating raw material prices, increasing labor wages, and the ever-changing growth rates of specific casting buyer target markets present what can best be described as a “moving target” that not only requires managers to have good aim, but also the ability to change their respective “weapon” at a moment’s notice as factors dictate. As is often the case, many of these profit-driving variables are beyond the control of a foundry or metal-casting facility and are compensated for internally by perhaps raising the end casting price, reducing the workforce, or exploring less costly or alternative raw materials where possible. As frustrating as this current business environment can be, it also presents the opportunity for production personnel to consider the metal-casting process cost variables that they DO have direct control over. Inward-looking metalcasters who successfully discover ways to reduce internal costs can reap immediate benefits through enhanced competitiveness. The question is where to start?
One of the more time & energy consuming areas for any foundry is easily the casting finishing room, which can often comprise upwards of 40% of the total production cost of an end-casting. Regardless of the type of alloy, the metal-casting process, or the casting size, it will need to be cut away from its feeder-gating in some way. Despite the impressive technical efficiency available in the form of advanced robotic arm systems and computer aided surface finishing equipment, the vast majority of foundries and metal-casting production facilities continue to rely on manually operated cutting equipment such as grinding wheels, cut-off saws, cutting torches, hydraulic de-gating wedges, etc. While there is little doubt that the high prices of automated-robotic finishing room systems prevent more widespread use with the mid-size to smaller production foundries, there remains significant potential for cost reduction and quality improvement among even manually operated cutting solutions. With respect to production scale, most small to medium sized foundries will employ 3 to 5 personnel for cleanup room activities that focus primarily on manual-cutoff and residual gating removal. The process is both time and labor intense, not to mention one of the most physically hazardous jobs in a foundry. The attractiveness of an automated robotic system is obvious, but given the high cost, they remain effectively out of reach for most small & medium sized foundry operators.
Lower Cost De-Gating
It should come as no surprise that some of the smaller, but very competitive foundries and metal-casting producers (along with a surprising number of some of the largest) have embraced the use of a variety of high temperature capable filter mesh fabrics to serve the dual-role of molten metal filter and casting de-gating aid. Holding the practical knowledge of effective, cost-reducing techniques and similar methods “close to the vest” is also what keeps these smaller, yet innovative companies competitive. At the risk of leveling the playing field, we’ll describe the technique as most widely practiced and also in comparison to the growing use of more advanced, higher performance filter mesh materials. What makes the use of filter mesh material particularly attractive among cost-conscious foundries is the lack of a requirement for significant up-front capital investment in both manual cutting equipment and the additional personnel needed to operate them. However, there is a requirement for foundry professionals to learn the technology behind and develop the practical application knowledge of these filter mesh materials in filtering and de-gating roles.
Existing Material Solutions: Silica & Fiberglass Mesh Filter Cloth Many sand casting foundries use flat cut pieces of either Silica mesh or Fiberglass mesh material by placing them in various sections of their gating network (base of the downsprue, mid-way in runners, and particularly at end casting in-gates) to capture slag & inclusions, reduce feed turbulence, and to create “break points” where desired. These break-points or “cleavage planes” are typically the same areas formerly targeted for manual cutting, but will now instead separate much more easily and with far less impact. The use of Fiberglass mesh is limited to Aluminum casting due to the relatively low temperature capability of the Fiberglass itself. For higher temperature alloys and cast metals such as iron, foundries employ resin-stiffened Silica mesh material that can withstand average pouring temperatures of approximately 2850°F / 1565°C. These application parameters are joined by equally important considerations of overall pouring weight, filter mesh to alloy contact area dimensions, and pouring time. As a general rule, the larger the alloy “flow-through” or contact areas of the filter mesh, the less the overall pouring weight and exposure time should be. Otherwise, the risk of the filter mesh breaking through or deflecting too far in the direction of molten metal flow grows considerably. Once personnel gain experience in using a filter mesh material with their own specific application variables, the benefits of additional metal filtration, reduced in-mold turbulence and far easier de-gating become evident and measurable.
As with most things, there are always “exceptions to the rule” that while inconvenient in the short term, also push the development of new technologies that ultimately may out-perform the original later on. As mentioned earlier, the use of Fiberglass mesh is limited to Aluminum applications due its maximum pouring temperature limit, and Silica mesh should not be used with Aluminum or Copper applications due to the stiffening resin’s propensity to “off-gas” and potentially create porosity defects in the former and its chemical incompatibility with the latter. Both Fiberglass and Silica mesh filter material are equally limited in their respective ability to handle significant molten metal throughput and when that limit is pushed, can cause deflection or “bulging” in the direction of molten alloy flow that results in a non-flat cleavage plane requiring additional machining to correct. As a consequence, foundries with demanding applications that fell outside the capabilities of either material have had to rely on their standard finishing room practices and other molten metal filter types until recently.
New Technology Development: CerraFlex® & CerraGlas® Filter Material – Two new filter mesh technologies have been developed by Comanche Technologies that effectively extend these de-gating & filtration techniques to foundry applications previously beyond the capabilities of standard Fiberglass and Silica mesh. CerraGlas is a proprietary ceramic-compounded Fiberglass mesh specifically designed for advanced Aluminum casting applications that is significantly stronger (reduced chance of break-through or deflection of material, resulting in a flat cleavage-plane when de-gated) and provides an average 20% increase in pouring temperature capability. CerraFlex, on the other hand, was developed for use with most cast alloys and metals that include steels, cast iron, Bronze, Aluminum, Copper and more. Capable of withstanding pouring temperatures of up to 3400°F / 1871°C, CerraFlex provides the highest rigidity and strength currently available among molten metal filter mesh materials. For foundries, these improvements translate into larger filter material contact areas, heavier pouring weights, and a much wider range of alloys and cast metals that can be filtered and more easily de-gated.
Having a wider variety of molten metal filter mesh materials available to more closely match a foundry’s specific application parameters, as is now the case, can greatly improve their chances of success in reducing cleaning room costs and improving their end casting quality at the same time. However, it is essential that such internal efforts receive strong management support and that the testing of new de-gating techniques & filter mesh materials are conducted and tracked to ensure they’re meeting the cost reduction and performance expectations of everyone involved. Finally, foundries and metal casters should expect and receive strong technical product and application support from their suppliers in these initiatives. Foundry professionals are well advised to look beyond simply finding the lowest price suppliers of Fiberglass or Silica mesh filter material as far too many have little or no metallurgical experience or resources available for a customer with technical questions about its use. Experienced foundry and metal casting procurement managers usually pose a bona-fide technical application question when screening a potential new supplier that goes beyond simple recitation of marketing literature or website bullet points and requires the supplier to show a basic familiarity with metallurgical processes related to filtration and de-gating. The quality and thoroughness (or lack thereof) of the answer will reveal far more about what the foundry can expect from that supplier in the future, aside from low priced filter mesh.
About the author:
Jason Hitchings is the general manager of Comanche Technologies, a global leader in the research & development of molten metal filtration technology and foundry processes. He can be reached at JHitchings@comanchetechnologies.com or via phone: 866-925-6750. Further information on advanced de-gating practices and molten metal filtration is available on Comanche Technology’s website: