Continuous Production Process for 3D Printed Ceramic Foundry Filters

Many of the metal components that are ubiquitous in our everyday lives – in cars, aeroplanes, buildings, machinery and more – are made by casting molten metal into specific shapes and sizes. Impurities in the metal can lead to defects that render a component unusable or even cause it to fail, so filtration is a crucial part of the production process.

Conventional filters are most commonly made from ceramic materials moulded around polyurethane foam to create ‘pores’. However, there are several problems with this technique. “The random structure of foam means there’s no guarantee of pore size and reproducibility. In addition, the foam is burned off during firing, which can not only emit toxic fumes but also means new foam is required for the production of each filter,” explains Mike Leaney, Director of foundry filter manufacturer CAT International Ltd. “For a large filter manufacturer, millions of pounds of polyurethane are literally going up in smoke each year.”

With funding from the Transforming Foundation Industries Challenge, CAT International Ltd is developing an alternative: a ceramic filter created with a 3D printer without the need for polyurethane foam. “3D printing gives us complete control over the cellular structure – shape, pore size and flow path – so a filter can be engineered to improve performance and efficiency,” says Leaney.

The project was two-fold: investigating a ceramic formulation that could be used to fabricate filters and the 3D-printing process, also known as Additive Manufacturing (AM).

The team worked with the Manufacturing Technology Centre, Coventry, to identify software that could generate an adaptable lattice structure. “Enhancing the uniformity and performance of filters, alongside an increase in the ability to apply them to larger castings, gives a better tensile performance of the cast metal, leading to energy savings from increased yields, potential light-weighting and defect repair,” says Leaney.

Another key benefit of the AM process is scalability. Meeting an increasing demand for large-format components, such as the offshore wind turbine market, is constrained by current processes. “Our technology enables us to increase a filter’s flow rate and capacity. Manufacturing something like a wind turbine requires more and more metal through filters. AM offers the potential to reconfigure a filter and create something bespoke for these newer applications,” says Leaney.

One of the problems with 3D printing ceramic is shrinkage during firing. Building on CAT International Ltd’s earlier ceramic innovations, the project team developed a novel formulation containing pre-sintered material for printing, followed by a coating to strengthen the final structure. “The result is a ceramic that doesn’t shrink, doesn’t affect pore size, and is strong enough to handle metal at 1700 degrees.”

AM production of ceramic parts is still in its infancy and is constrained by the capital cost of large-scale 3D printing equipment. However, Leaney believes the pace of development around this technology, coupled with increasing usage applications, could revolutionise the industry. “It’s not just filters; foundries could produce other ceramic parts they require but are currently importing, such as gating. The technology has potential applications for the ceramics industry, too, such as commercial potteries,” he says. “These sectors use high volumes of raw material and increasing amounts of energy – our technology can potentially improve their environmental performance and bottom line.”

“3D-printing gives us complete control over the cellular structure – shape, pore size and flow path – so a filter can be engineered to improve performance and efficiency.”

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