Fine Fireclay: Great Expectations
World sanitaryware production is dominated by vitreous china, but fine fireclay (FFC) is an increasingly important segment of the market. Despite the recent economic crisis, FFC has continued to grow as a rising number of producers view it as a profitable option.
Even with the success of FFC in Europe, it has met difficulties in penetrating the North and South American markets. However, the historical context-as well as the technical and market forces that have driven its growth-illustrates that fine fireclay has great potential in the Americas.
A Little HistorySanitaryware bodies typically fall into three categories: traditional fireclay, which was the original type of body used for industrial sanitaryware production in the West; vitreous china, which currently dominates the global market; and fine fireclay, which arrived on the market more recently. When modern sanitaryware production began a little over a century ago, the traditional fireclay body was the only option available.
Fireclay bodies consisted of a blend of crushed fireclay with pre-fired refractory brick clay grog and sand, resulting in a medium-to-coarse grain texture that required coating with an engobe before glaze application. These bodies were then fired at about 2280°F to produce a piece with high porosity and water absorption levels of up to 13%. Fireclay pieces also tended to suffer from greenspots and pyrite burnout as a result of contamination from low clay processing levels, further increasing the need for a good engobe.
The development of vitreous china was, in large part, a result of the demand for fine-grained ware that do not require an engobe and provided a more easily cleaned surface. Unlike fireclay, these bodies are typically made of a blend of plastic clays, a fluxing agent such as feldspar, and quartz as a filler. Pieces are then coated with an impervious vitreous glaze to produce ware with water absorption of less than 0.5% of the dry weight.
Raw MaterialsIn fine fireclay, the pre-fired or calcined clay is the single most important component and can account for over 40% of the body. Notable regional variations occur in FFC recipes because many producers choose to make use of locally available raw materials. Within the Americas, a number of options could be adapted to provide excellent performance in an FFC body.
Within Imerys Ceramics, the low-alumina sanitaryware-specific chamotte provided by the group's AGS plant in southwest France is favored. The chamotte remains inert in the FFC body as it is pre-fired at 2500-2900°F, acting as a skeleton that produces pieces with reduced deformation and shrinkage. Imerys Ceramics technical specialists collaborate with FFC producers to ensure that the balance of chamotte, plastics and other components is correct; when successful, the total shrinkage can be as low as 4%.
FFC casting bodies are typically prepared as high-density slips that demand fluid ball clays and kaolins. At high slip densities, the bodies need to be fast casting, strong and plastic to tolerate handling following demolding. It is also essential to have rheologic stability to obtain a consistent casting performance. In addition, the firing of large FFC pieces often requires bodies with low carbon content due to the risk of black coring and the burnout of volatiles.
With these many variables, it can sometimes be a challenge to achieve the right balance for the optimum conditions within a specific plant. For this reason, Imerys Ceramics developed Hycast FFC(tm), a strong shredded ball clay specially blended to provide an optimal FFC performance. However, as this clay is suitable for both conventional and pressure casting and also for use in vitreous china systems, sanitaryware producers (particularly those that work with both types of bodies) benefit from the product's versatility. Similar ball clays are available through the Imerys Ceramics North American ball clay portfolio.
The other main component of an FFC body is kaolin, which provides the fired whiteness and is, on the whole, used to determine the casting rate. FFC does not require specific kaolin properties that differ significantly from vitreous china. It is therefore likely that North and South American sanitaryware manufacturers already use kaolins that would be suitable for FFC.
The FutureDespite the lack of penetration beyond Europe and the Middle East, major advances are taking place within the FFC segment. This year, Imerys Ceramics developed Super Fine Fireclay™, which the group believes to be the next generation for FFC bodies. It offers good fluidity and a much finer particle size than an ordinary FFC body. This means that sanitaryware manufacturers can continue to produce elaborate designs and functional pieces in a variety of shapes and sizes without the handling problems associated with FFC due to its medium-to-coarse grain texture.
In addition, when compared to the usual FFC bodies, this innovation improves the glaze application process because its finer particle size results in pieces that are much smoother to the touch and are visibly whiter. Ultimately, Super Fine Fireclay offers a final product that has a finish very similar to that of vitreous china while still enabling the design capabilities of FFC.
For additional details regarding fine fireclay, contact Imerys, North America Ceramics at 100 Mansell Ct. E., Suite 300, Roswell, GA 30076; (770) 594-3689; fax (770) 645-3460; or visit www.imerys-ceramics.com.