Fast Fettling

November 29, 2002
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A new robotic pressing/fettling system provides fast, precise fettling of even difficult, irregular-shaped items.

The robot first positions the item in front of a dry grinding device equipped with a grinding belt or disc, then rotates it to a sponging unit with counter-rotating sponge reels.
Medard de Noblat in Limoges, France, has manufactured porcelain tableware for more than 160 years. For most of the 1990s, the company was still forming its products using traditional bench casting. However, when it secured a large order from Hermes de Paris several years ago, the company realized that it would have to implement a new forming technology to meet the high quality demands of this new customer. While a number of other tableware companies had switched to high-pressure casting due to the technology’s significant quality improvements compared to bench casting, products made through high-pressure casting sometimes deformed after firing. Not wanting to risk this type of defect, the company opted instead for an isostatic pressing system from SAMA Maschinenbau GmbH, headquartered in Germany. The quality of isostatically pressed items is generally better than products produced through high-pressure casting. However, conventional isostatic pressing systems offer limited movement, making it difficult to fettle non-round, multi-sided, rectangular and irregular-shaped products. SAMA’s system has overcome this challenge by incorporating robotic fettling technology that uses specially developed software and six axes to allow customized programming and virtually unrestricted movement of the objects being fettled. The system’s flexibility also ensures that no dust or slip can get in the product during the vertical working stage. In the new system, the isostatically pressed items are placed in a centering device, which feeds the items to the fettling robot. The robot first positions the item in front of a dry grinding device equipped with a grinding belt or disc, then rotates it to a sponging unit with counter-rotating sponge reels. A second sponging unit equipped with a sponge belt or reel handles the final sponging. The robot then replaces the finished item on the centering device and picks up the next item to be fettled. The flexibility of the system ensures that the highest possible edge quality is attained, regardless of the shape or size of the item being fettled. Medard de Noblat installed its first isostatic pressing/robotic fettling system in 1998, and it has also recently commissioned a second system.

Automating the Technology

At Medard de Noblat, the robotic fettling systems are still “off-line”—i.e., the pressed articles are manually removed from the press and placed on the centering device. However, in a newly patented, large flatware isostatic line installed at Rosenthal’s Rothb?hl (Germany) factory, this process is fully automatic. The horizontal pressing plant produces Rosenthal’s range of square, rectangular and irregular shaped articles, which measure up to 500 mm (20 in.) wide and 150 mm (6 in.) tall in the green state. The pressed items first drop from the press onto a discharge belt and are transported to a pre-centering device. Next, a vacuum sucker transfers the items to the flash breaking (rim trimming) station, where the extra “rim” created by the isostatic pressing process is automatically removed. The vacuum sucker then moves the items to the position recognition station, where a digital camera transfers the determined coordinates to the appropriate fettling robot. A total of three robots are used to achieve the nominal output of approximately 350-400 articles per hour. Each robot carries out its tasks “quasi-autonomously”—i.e., each robot controls one dry and two wet processing stations. At the end of the cycle, each robot places the finished items back on the rotating table. These items are transferred to a foot polishing station and are then stacked in preparation for bisque firing.

Achieving Positive Results

The enhanced quality of isostatic pressing, combined with the high flexibility and precision (± 0.1 mm) of the robotic fettling technology, has enabled Medard de Noblat and Rosenthal to greatly increase their product quality while reducing the amount of labor required to produce their products. Both companies have also been able to increase their assortment of irregular-shaped items, thereby enhancing their positions in the highly competitive tableware market. In fact, Rosenthal directly attributes an increase in orders from Portugal, Italy and the U.S. to the enhanced manufacturing flexibility provided by the new system. With the new isostatic pressing/robotic fettling system, tableware manufacturers can quickly and easily manufacture even difficult, irregular-shaped products that meet the high quality standards of today’s consumers.

For More Information:

For more information about isostatic pressing and/or robotic fettling technology, contact SAMA Maschinenbau GmbH, Germany, a division of SACMI Whiteware, Schillerstrasse 21, D-95163 Weissenstadt, Germany; (49) 09253 889-0, ext. 151; fax (49) 09253-1079; e-mail elke.silkens@sama-online.com; or visit www.sama-online.com or www.sacmi.com.

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