All Glossary

Sanitary ware

A type of porcelain zircon-glazed ceramic that includes bathtubs, sinks, toilets, etc.

Key phrases linking here: sanitary ware, sanitaryware - Learn more

Details

This is a very large industry worldwide, second only to ceramic tile in clay and energy use. The knowledge of how to make sanitaryware can be found on every industrial continent, especially Asia. Chaozhou, China has hundreds of sanitary ware factories and Morbi, India has 300. However many other countries have very highly developed processes and innovative products (e.g. the Middle East, Italy, Germany and Spain).

Some of the factories in Asia-Pacific are less automated, use lower-quality materials and rely on local hot climates for drying. It is also common to have few technical people on staff (requests we get for technical assistance generally come from these types of companies). At the other end of the spectrum, the modern form of manufacture is barely recognizable when compared to a few decades ago.

Most sanitary ware is fired at high temperatures (e.g. 1280-1290C) and is made from porcelain bodies resembling the standard 4x25 recipe (feldspar, kaolin, silica, ball clay). Ware fired lower (e.g. 1200C) requires that body to have more feldspar (e.g. 30-35%), this must be at the expense of quartz and clay. Grog or powder made from rejects is also often included. Ware is glazed using zircon opacified feldspar-based recipes. The hiding power of the zircon glaze enables compromises in the body recipe (e.g. trading some of the kaolin and ball clay for locally available materials).

The manufacture of sanitaryware pushes many ceramic processes to their limit (thick casting, high mass drying and firing, thick glaze layers, highly deflocculated slips, etc.) and product loss or defects is common.

Many other advanced products and applications of porcelain have grown out of the creativity and attention to detail of the sanitaryware industry.

Related Information

Sanitaryware tunnel kiln control panel

In this plant, they are firing a 20-hour cycle. In sanitary ware this is considered fast firing. This kiln is a combination drier and furnace, it is 96 meters long. It has a pre-heating zone, firing zone, and cooling zone. In this plant, after the firing zone ware is cooled quickly, from 1200-800C, to ensure a glossy glaze surface. Each car takes 13 hours to reach a peak temperature of 1200C. The panel displays the temperature of 24 points in the tunnel.

Over deflocculated slip causes instability in toilet tank

Sanitary ware factories optimize their slips to have the lowest possible specific gravity for production volume reasons. Potters would be happy with 1.7 SG whereas numbers approaching 1.9 SG are common in factories. They often teeter on the edge of issues like this (sections softening causing localize warping) and inexperienced technicians can be unaware of the critical balances needed to prevent loss in production.

Zircon glazes cover well but they have a problem

This sanitary ware tank lid was made in China. Notice how thick the white glaze is being applied to cover the iron containing body below. This is a testament to how opaque a zircon opacified glaze can be. Zircon often causes crawling (likely due to a combination of the effects of its fine particle size on drying properties and its tendency to stiffen the melt). Extra measures and constant attention to detail (e.g. glaze thickness, slurry rheology, avoidance of sharp contours on ware) are needed with such glazes.

Oversize particles in a typical manufactured porcelain body

Example of the oversize particles from a 100 gram wet sieve analysis test of a powdered sample of a porcelain body made from North American refined materials. Although these materials are sold as 200 mesh, that designation does not mean that there are no particles coarser than 200 mesh. Here there are significant numbers of particles on the 100 and even 70 mesh screens. These contain some darker particles that could produce fired specks (if they are iron and not lignite); that goodness in this case they do not. Oversize particle is a fact of life in bodies made from refined materials and used by potters and hobbyists. Industrial manufacturers (e.g. tile, tableware, sanitaryware) commonly process the materials further, slurrying them and screening or ball milling; this is done to guarantee defect-free glazed surfaces.

Crawling sanitary ware glaze sourcing Al2O3 from only feldspar

The original recipe had a very low clay content, sourcing almost all of its Al₂O₃ from feldspar instead. Although the glaze slurry was maintained at 1.78 specific gravity (an incredibly high value) and thus would have had very low shrinkage, it did not stick and harden well enough to the ware. Why? Lack of clay content in the glaze. The fix was to source much more of the Al₂O₃ from kaolin instead of feldspar. The reduction in feldspar shorted the glaze on KNaO and SiO₂ so these were sourced from a frit and pure silica instead (the calculations to do this were done in Insight-live.com). The change also provided opportunity to substitute some of the KNaO with lower expansion CaO. This reduced the thermal expansion and reduced crazing issues.

Example of COE curves considered a good fit for body and glaze

These are from a sanitaryware plant in India. Long-term glaze fit is essential for their products. The glaze thus needs to be under some compression. That means the body must have a slightly higher coefficient of thermal expansion (COE) than the glaze. These two charts were created on the same dilatometer by the same person using well-defined procedures (the glaze and clay each have their own procedures). A history of measurements and associated knowledge of how the data relates to the quality of the fired products provides a context to interpret these reports. In other words, technicians have learned that the difference shown here is what is required to achieve optimal glaze fit for this specific body/glaze combination. Of course, some sort of database system (e.g. lab notebook, an account at insight-live.com) is needed to record the history of testing to be able to effectively compare the past with the present.

Amazing things that sanitaryware producers can make

These "one piece closets", shown in the background photo, weigh up to 45kg (100lb). In this factory, they fire cold-to-cold, in a tunnel kiln, in about 20 hours. Total shrinkage of the product is 12% (so the moulds are made 12% bigger). They are porcelain so dry hardness is fairly low - but they need to dry and shrink while doing so - without cracking. And, as porcelain, they have a high firing shrinkage - yet need to fire with minimal warping and no cracks - despite the weight. They also have to perform in use every day for decades (they must withstand a minimum 400 kg load). The glaze has be to durable and it absolutely cannot craze, shiver or leach. The engineers, mold makers and kiln designers that make these possible are amazing. But so are the production personnel - not just because of conditions in the plants (e.g. heat, humidity, noise) but also the need to keep costs down yet still produce a good product. That means incorporating as much local material, dry and fired scrap as possible. While some plants have pressure-casting lines, the cost is high so most still use traditional plaster molds - it is heavy and demanding work.

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