Better Quality Through Finer Milling

March 31, 2003
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A successful fine grinding mill combined with an advanced classifier is providing new opportunities for producing extremely fine, high quality ceramic pigments and powders.



Several years ago, Eirich Machines Inc., based in Hardheim, Germany, introduced a new agitated media mill* to improve the efficiency of fine grinding operations. The mill has since been successfully used to grind glazes, frits, pigments, ferrites and a variety of hard ceramic substances, such as heavy spar, feldspar and quartz, to sizes as small as D97≥30 mm with a relatively high throughput. However, in today’s ceramic industry, increasingly smaller particle sizes are required to further enhance product quality.

An exterior view of the new classifier.
Engineers at Eirich knew that the agitated media mill was capable of achieving smaller particles sizes. The difficulty was the classifier—early versions of the mill were used with a standard classifier that frequently became clogged when handling extremely fine powders. As a result, the system often created a bottleneck in the production process.

To overcome this challenge, Eirich engineers decided to team up with Noll GmbH in Bobingen, Germany. The resulting technology combines the proven design of the agitated media mill with an advanced dynamic classifier** capable of efficiently handling even the finest ceramic powders.

This system—which features a successful agitated media mill combined with an advanced classifier—can handle powders as fine as D97<3 mm with much higher throughputs than conventional classification technologies.

System Operation

In the new combined system, the product is fed to the mill and reduced in size by a stirred bed of ceramic beads that transfer the milling energy through shear, impact and attrition forces. The finely ground material rises to the top of the mill’s rotating pan and is drawn into a negative pressure (vacuum) air stream that passes along the new classifier’s specially designed classifying wheel. The small particles enter the wheel while the coarse and agglomerated fines continue down to the coarse classifier. Here, turbulent air forces break up the agglomerates and transport them back to the classifier. The remaining coarse material is fed back into the agitated media mill, completing the cycle (see Figure 1).

Figure 1. A schematic of the new combined system. A) The coarse and agglomerated fines are intensely mixed with air in the coarse classifier and are fed back to the classifier wheel. B) Both fine and coarse materials pass along the classifying wheel. Fine materials progress to the filter unit, while coarse materials are returned to the coarse classifier. C) Bulk bag feed and returned coarse product enter the system here. D) Product is fed into the mill's rotating grinding chamber. An extra stirrer arm insures energy input.
In conventional air classifiers, the particles first pass through the course classifier and then to the classifying wheel. However, the newly developed classifier works in exactly the opposite way—extracting the fines that are already present first, and then allowing for more intense air mixing of the remaining agglomerates. This technique enables the system to handle powders as fine as D97<3 mm with much higher throughputs than conventional classification technologies.

Proving the New Technology

To prove the new technology, Noll acquired an agitated media mill from Eirich for its toll processing subsidiary in Cologne, Germany, and began running performance tests on the combined system in December 2002. The system met with immediate success, using less energy and requiring less time to produce extremely fine particle sizes compared to more expensive jet milling technologies (see Table 1). It also generated a higher throughput of material and was able to process coarser feed materials. Additionally, since very little time was needed for the machine to produce stable results, and since no excess material was required for start-up and cleaning, much less waste material was generated during the grinding operation—a feature that is especially important for high-cost materials. As a result, the system cost less to operate than conventional technologies. Based on these results, Eirich recently began installing a combined system in its technical laboratory in Hardheim.

Tests with the new technology are ongoing, but preliminary results have shown that the system can successfully be used to grind and classify zirconium dioxide, zircon silicate, marmor, glazes/frits, aluminium oxide, calcium carbonate, and titanium dioxide minerals and pigments. Trials have also successfully been performed with other materials.

The new classifier’s specially designed polyamide classifying wheel allows small particles to enter the wheel while the coarse and agglomerated fines continue down to the coarse classifier.

A Fine Solution

Producers who have previously milled their products to very fine particle sizes in large quantities by wet or dry ball milling or in smaller quantities using jet milling can now use this new dry system to save time, energy and processing costs. Because the system uses ceramic and polymer linings and construction parts, it is especially suited for the metal-free processing of ceramic raw materials, minerals, frits and glazes. Additionally, the specially designed classifier wheel allows for higher throughputs and sharper top cuts in the finest size range. Through this technology exchange, ceramic manufacturers can achieve new possibilities in powder processing.

References:

*The MaxxMill®, developed and supplied by Eirich Machines Inc. (U.S.) and Maschinenfabrik Gustav Eirich GmbH & Co KG (Germany).

**The MultiNo®-SE, developed and supplied by Noll GmbH.

For more information:

For more information about this combined milling/classifying system, contact:

• Noll GmbH, Boschstrasse 2a, 86399 Bobingen, Germany; (49) 8234-9661516; e-mail mailto:marc.zwart@ulf-noll.de; http://www.ulf-noll.com.

• Eirich Machines Inc., 4033 Ryan Rd., Gurnee, IL 60031; (847) 406-1381; fax (847) 336-0914; e-mail mailto:eirichsales@eirichusa.com; http://www.eirichusa.com.

• Maschinenfabrik Gustav Eirich GmbH & Co KG, Wallduerner Str. 50, 74736 Hardheim,

Germany; (49) 6283-51-339; e-mail mailto:maxxmill-info@eirich.de; http://www.eirich.com.

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