Innovations in Kiln Furniture
Over the past several years, a number of new kiln furniture systems have appeared on the market. At least three of these—a lightweight system; a non-stick ceramic body; and a process for producing low thermal mass, high strength kiln furniture*—are a result of Dyson’s dedication to the ceramic industry. These new systems are increasing energy efficiency, reducing production time and improving the overall manufacturing process for ceramic manufacturers around the world.
Lightweight Kiln FurnitureWith high fuel prices and the never-ending need for increased production, the drive toward lighter weight kiln furniture has heightened drastically over the past several years. This has especially been true in the bone china industry, where the refractory-to-ware ratio is often quite high. With traditional kiln furniture, some bone china manufacturers might be firing with a refractory-to-ware ratio as high as 6:1 or 7:1, which means that most of the energy in the firing process is being used to fire the refractories rather than the ware.
In the spring of 2000, a new system was introduced** that combines standard cordierite/mullite formulations with lightweight refractory aggregate, providing up to 40% savings in refractory weight. This weight reduction enables shorter firing cycles and increased fuel savings for bone china manufacturers and other secondary kiln furniture users. The refractory was formulated to provide excellent thermal shock properties and retains a low reversible thermal expansion (2.8 x 10-6/°C), ensuring a long refractory life.
Perhaps even more importantly, the lighter weight of the system is easier for operators to handle compared to conventional kiln furniture. “Many companies have gone for the lighter weight furniture in a big way on the basis of ergonomics—it’s less weight that operators have to lift,” says Dr. John Gallimore, divisional, technical and R&D manager for Dyson Ceramic Systems.
Non-Stick Ceramic BodyAnother innovation has recently been developed for manufacturers of tableware, who typically fire their bisque on alumina-coated cordierite kiln furniture. The alumina coating prevents the bisque from sticking to the kiln furniture, but frequent recoating is usually required. Depending on the desired quality of the pieces being fired, some manufacturers might have to recoat their kiln furniture every 20 to 25 cycles or more to give their bisque an adequate kiln furniture surface during the firing process. While the recoating process itself only takes a few minutes, all of the setters, profiles or batts must be taken out of the system and removed to a designated area to be recoated. The furniture may also need to be cleaned and flinted before recoating. This results in an inefficient, labor-intensive process that reduces manufacturers’ production capabilities.
In the fall of 2000, a new non-stick, high-alumina ceramic body was developed for use as cup chums and profile setters. This new body eliminates the need to wash and recoat the kiln furniture components between runs, saving manufacturers both time and wear and tear on their kiln furniture.
Unlike traditional alumina bodies, where there is often a high thermal mismatch between the ware that’s sitting on the kiln furniture and the kiln furniture itself, the high-alumina body of the new kiln furniture was modified so that the reversible thermal expansion closely matches that of typical tableware bodies (4.0 x 10-6/°C). This modification prevents the ware from sticking and increases the kiln furniture’s durability. Instead of the cracking, crawling or peeling that can result from using traditional alumina coatings and that necessitates the need to recoat, the new furniture remains smooth and defect-free, cycle after cycle.
A six-month trial period at a UK manufacturer of bone china tableware has proven the benefits of this new kiln furniture. The company was having to recoat its old cup chums as often as every six or seven passes through the kiln. With the new furniture, the company has achieved over 150 passes without recoating.
“The major benefits are really the savings in labor, downtime and material costs that can be achieved with the non-stick furniture,” says Ray Spooner, new product development manager for Dyson Ceramic Systems. “If you have a kiln solely for firing cups, as many as 50,000-60,000 cup chums might go through that kiln. If you have to recoat those cup chums every six or seven passes, you’ll need an army of people to accomplish the process. And then there’s the possibility that some of the chums will be damaged during handling and recoating.
“It’s difficult to quantify just how much it costs to recoat kiln furniture because it’s always done in-house. Nobody really sits down and works out what the true cost is. But in this age of trying to push through as much production as possible, using a non-stick body can have tremendous benefits. From the tableware manufacturer’s point of view, it made their process more consistent because the kiln can now operate without stopping all the time for recoating,” Spooner says.
The Dycor ProcessRecognizing the need for more durable, thinner and lighter weight refractories in the ceramic industry, researchers have devoted themselves to advancing the way kiln furniture is made in an effort to meet these needs. This has resulted in a new kiln furniture manufacturing process that provides increased refractory homogenization with a significant improvement in strength. Called the Dycor process, the method is licensed through CERAM Research in Stoke-on-Trent, UK, and involves mixing the ceramic powders in a polymer carrier, then processing that formula under very high shear. In addition to increasing refractory strength, the process provides a 20% improvement in creep resistance.
Kiln furniture made through this new process provides benefits in both primary and secondary applications. Extruded hollow batts can be produced thinner than conventional systems but with the same load-bearing capacity. Rolled/calendared solid batts can also be produced thinner. Additionally, the process can be used to produce extruded hollow beams that provide an attractive alternative for applications where silicon carbide is over-engineered.
“Using the Dycor process allows the strength of typical cordierite beams to be doubled. While the beam still won’t match the strength of silicon carbide, it can be used in certain areas where people are using silicon carbide—a much more expensive system—where they don’t necessarily need to,” says Gallimore. “For instance, in a sanitaryware kiln, two main beams run the length of the kiln car, and several shorter beams sit across these two beams. The shorter beams could be produced using the Dycor process to significantly reduce the manufacturer’s costs.”
In secondary kiln furniture applications, a variety of shapes can be made by placing a rolled/calendared sheet over a former and applying light pressure. This technique provides the advantage of using conventional presses, tools and dies with lower pressures, extending tool life. Additionally, thinner sections can be used, which makes the refractories easier to handle and saves energy consumption in the kiln.
“We are in the process of designing the plant needed to produce kiln furniture using the Dycor process, but all the test results we’ve been given are far beyond anything that we could have imagined,” says Spooner. “We’ve taken a product in the green state, manufactured through this process, and hit it repeatedly on a desk and have been unable to break it. To see the test done is unbelievable.”
While the new forming process is primarily being used to extrude batts, the potential also exists to pelletize the material in the process and use it as a granulate to fill conventional dies. This would enable the process—and its related benefits—to be carried over into every type of kiln furniture used in the ceramic industry.
“Using the Dycor process, we can reduce the refractory thickness but still maintain the same level of strength. For instance, we can reduce the size of a 1-in. thick batt down to about a 1⁄2-in. thick with the same mechanical and thermal strength. This will provide ergonomic benefits, fuel savings and time savings in the firing cycle, as well as other benefits,” says Spooner. “It’s an exciting time to be in this industry.”
For More InformationFor more information about these and other kiln furniture innovations, contact Dyson Ceramic Systems, Shelton New Road, Hartshill, Stoke-on-Trent, Staffordshire ST4 0EP, UK; (44) 1782-711511; fax (44) 1782-742019; e-mail firstname.lastname@example.org; or visit htpp://www.dyson-ceramic-systems.com.
Editor's NoteDyson Ceramic Systems is just one of the companies dedicated to meeting ceramic manufacturers’ kiln furniture needs. For a list of additional kiln furniture suppliers, see Ceramic Industry’s Data Book & Buyers’ Guide in print or online. Previous articles on kiln furniture can also be found on our website by clicking on “Editorial Archives” and entering “kiln furniture” in the search field.
*These three systems are patent-pending by Dyson Ceramic Systems.
**The lightweight system was originally introduced by Hewitt Refractories and is now being offered through Dyson Ceramic Systems.