Author: Foseco
Foundry filtration has progressed significantly since Foseco first introduced ceramic foam filters to the casting industry over four decades ago. Since then, they have become firmly established as a critical component in the casting of high-quality parts with the latest advances extending their efficacy and use to even very large castings.
The 1980s was a decade of big hair and ground breaking sci-fi movies. It was also the decade that saw the launch of several landmark technologies, which would go on to shape modern life: from the Sony Walkman and the CD to the original Apple Macintosh computer, the release of Microsoft Windows 1.0, and the first mobile phones. At the same time, another development with long-lasting impact was taking place in the foundry sector as Foseco introduced the first ceramic foam casting filters in 1982.
In the more than forty years since, the company’s knowledge and understanding of filtration has advanced considerably. The application of filters has now been established in castings of less than 100g to more than 25 tonnes, with a range of materials now used as the ceramic base depending on the alloy to be cast and the required temperature performance. In this article, we look back at the history of casting filtration from the first filters to the latest developments using additive manufacturing (3D printing).
1982 SEDEX iron casting filters
1983 SIVEX filters for non-ferrous casting
1984 SEDEX and SIVEX F filters first on show at GIFA
1988 STELEX S filters for steel casting
1989 KALPUR direct pour sleeves with integral filters
1991 STELEX ZR filters
1992 SIVEX FC filters
2003 STELEX PrO filters
2010 HOLLOTEX CFU filter unit
2015 STELEX ZR ULTRA filters
2019 HOLLOTEX Shroud
2023 STELEX Optiflow3D additive manufactured filters
The first three decades
It began in 1982 with the launch of the SEDEX iron casting filters; these were quickly followed by SIVEX F filters for aluminium casting in 1983. STELEX S filters for steel casting were launched in 1988. These three brands remain at the core of Foseco’s filtration offering today. The 1980s also saw one other related development: KALPUR direct pour sleeves were launched in 1989. Integrating a ceramic foam filter into the sleeve, these eliminated the need for gating systems and allowed production times to be reduced.
New STELEX Optiflow3D filter range
Foseco’s R&D centres have dedicated test foundries for filter development trials
Innovation continued through the 1990s. STELEX ZR filters were launched in 1991, comprising a zirconia ceramic foam for improved mechanical strength and filtration capacity in steel and large ductile/grey iron casting applications up to pouring temperatures of 1 680°C. They quickly became the standard and Foseco discontinued production of the original STELEX S filter in 1996. The STELEX range was further expanded in 2003 with the launch of STELEX PrO lightweight carbon-bonded filters.
Into the new Millenium, steel filtration took a further step forward with the launch of the HOLLOTEX CFU technology for heavy and complex casting applications that demand a high metal flow rate and quality, fast filling time, and consistent pouring temperature. Comprising seven STELEX ZR filters with capacities up to 12 tonnes, the HOLLOTEX CFU unit is designed to first swirl the melt around the outer edge of the unit. This ensures rapid and complete priming of all filters and thus promotes steady and uninterrupted filling of the mould. This centrifugal force also reduces the rate of clogging for a high filter capacity.
The HOLLOTEX Shroud was introduced to the market in 2019
Metal stream shrouding and filtration of steel castings with HOLLOTEX Shroud
For aluminium casting, Foseco introduced the SIVEX FC non-ceramic foam filters in 1992. The new filters are made from a lighter material than the original SIVEX F filters, which means that when returns containing used filters are used in remelting, the filters float to the top of the molten aluminium and can be easily removed by skimming. They are also phosphate-free, eliminating the risk of phosphorus pick-up during remelt.
Bringing us up to date: STELEX ZR ULTRA and STELEX Optiflow filters
Despite this continuous innovation and the fact filters had been around for more than three decades, by the mid-2010s uptake in steel casting was still low. According to the 48th Census of World Casting production, just 8% of the global steel casting tonnage was filtered. A Foseco market study at this time highlighted the need for a steel casting filtration system that provided more consistency and efficiency in demanding casting applications. The result was the development of the STELEX ZR ULTRA filter in 2015.
SIVEX FC filters are non-ceramic foam filters used in light metal casting
Foseco application engineers can assist customers with the development of methoding solutions to optimise pattern layout, optimise yield and ensure effective inclusion removal and smooth mould filling
STELEX filters are produced in Tamworth, UK
Comprising an improved zirconia-based ceramic foam held within a ceramic frame, STELEX ZR ULTRA filters are lower in weight yet still able to withstand the impact and passage of molten steel. This reduces pore blockages and allows a consistent performance at finer porosities; the filters are also more robust and less friable, reducing the incidence of filter-related defects.
Most recently, in 2023, Foseco launched its STELEX Optiflow3D product range of additive manufactured filters. Additive manufacturing overcomes restrictions placed on filter design by traditional production techniques, allowing almost limitless options in terms of filter structure, porosity, and shape. As a result, filters with higher capacities are becoming possible, reducing the number of filters needed per casting. In one application, a STELEX Optiflow3D delivered molten iron at almost double the capacity (7kg/cm2) usually considered safe for ceramic foam filters; it also reduced returns by 10% and fettling area by 75%. This opens the possibility of filtering very large castings, which are still commonly unfiltered due to the complexity of applying the large number of filter units needed.
The HOLLOTEX Shroud
A final innovation is the HOLLOTEX Shroud, which was introduced to the market in 2019. This comprises a nozzle, gasket, and tubular pouring shroud, inserted through a filter box, which is installed in the mould at the base of the casting. The shroud effectively prevents the melt from contact with the atmosphere during pouring, reducing the risk of oxidation or gas enrichment and assisting foundries to exceed the latest casting quality expectations.
STELEX ZR ULTRA filters enable even higher filtration efficiency to be achieved through the use of finer pore filters
SEDEX is a range of silicon carbide based ceramic foam filters designed for use in grey and ductile iron applications to provide a smooth laminar flow of molten metal and prevent the ingress of slag, magnesium reaction products, inoculant residues or sand grains into the mould cavity
Shrouds have proven themselves in single and series casting applications. For example: when pouring a 1 200kg mining truck wheel hub, six castings were poured from one ladle, all passing inspection with almost no defects detected using magnetic particle inspection. The parts passed through the production process with no delay or additional rework expenses.
A better way to cast
The past forty years of filter innovation has helped foundries keep up with rising demands for:
• Improved casting quality and performance standards.
• Casting larger and more complex shapes.
• Reduced scrap and improve yield.
• Improved efficiency and effectiveness of inclusion removal.
By 2003, Foseco could write that filters had become “fundamental to the production of high-quality […] components at optimum cost.” Two decades on and that statement has never been truer with filters now available for a wider range of casting applications than ever before and delivering performance that could only have been dreamed of back in those first early days of filtration.
Please add the contact details: For more information contact Foseco on TEL: 011 903 9500 or visit www.foseco.com
