Electromagnetic Filters for Ceramics

Since the first ceramics were produced, iron and iron-bearing minerals have caused defects. The problematic minerals occur naturally in the raw materials, with additional fine iron accidentally introduced during transportation, storage or processing.

Effective removal often involves several stages of magnetic separation. However, the introduction of High-Intensity Electromagnetic Filters proved ground-breaking in terms of removing even the finest and weakest magnetic particles. Bunting is one of the world’s leading designers and manufacturers of magnetic separators for the recycling and waste industries. The Bunting European manufacturing facilities are in Redditch, just outside Birmingham, and Berkhamsted, both in the United Kingdom.

Traditional Magnetic Separators

Small electromagnetic bowl filters have been commonplace in ceramics plants for decades. The small bowl-type electromagnets, often producing a background magnetic field of around 1500 gauss, were an industry-standard, removing coarser magnetic particles from ceramic slips and glazes.

Figure 1 – Small Electromagnetic Filter in a ceramics plant

In the late 1980s, the introduction of permanent Rare Earth Magnets dramatically improved the separation of magnetic particles. Rare Earth Tube Magnets, with a nominal surface magnetic strength of 9000 gauss, captured fine and weakly magnetic particles. However, they required manual and frequent cleaning, which often did not occur. As the magnetics built up on the surface of the Tube Magnets, so the separation efficiency reduced.

Higher Intensity Electromagnetic Filters

With a drive towards improved efficiencies to combat increasing competition from the Far East, European ceramics producers sought improved separation of problematic iron.

Figure 2 – High-intensity Electromagnetic Filter

The High-Intensity Electromagnetic Filter provided the answer. The magnetic field is generated in a similar way to the old small electromagnetic bowl filters, but that was where the similarity ceased. The new magnetic separation technology generated background magnetic fields of between 5,000 and 6,500 gauss and this field intensity was further enhanced on the cross-points of a centrally-located magnetic stainless-steel matrix to between 10,000 and 12,000 gauss.

The increased magnetic intensity enabled the capture of the finest iron and also para-magnetic minerals. When the central matrix was cleaned, the flushed-out fine magnetics appeared almost oil-like.

The valve and pipework design of the Electromagnetic Filter also enabled automatic cleaning of the magnetics from the matrix. On a timed sequence, commonly every 20 minutes for glaze, the feed would stop, the electromagnetic coil would turn off, and water would flush through the matrix. After approximately 2 minutes, the cleansed Electromagnetic Filter would be back in operation.

Cleansing Ceramic Glaze and Body

Initially, the focus was on ceramic glaze, especially with the growing demand for high-white ceramic sanitaryware and tableware. The Electromagnetic Filter, complete with pipework, valves, and control, could be mounted on a wheeled frame and easily moved to an individual glaze storage tank. Once connected, the glaze would be continuously passed through the Electromagnetic Filter, ensuring the maximum possible removal of iron and weakly magnetic particles. Care had to be taken with some coloured glazes whose pigments were, indeed, magnetic.

Then ceramic producers started assessing the ceramic body. Iron contamination in the body of a fired ceramic weakens the structure, causing cracks and breaks. Also, iron in the body damaged moulds and caused defects in the surface finish of the biscuit and the smoothness of the glaze.

Figure 3 – High-intensity Electromagnetic Filter in the Redditch Customer Experience Centre

The processing volume of ceramic body was far higher than glaze and batch feeding was not possible in many plants. Subsequently, Bunting developed larger Electromagnetic Filters and set up a flip-flop operation where one was always working whilst the other was cleaning. This provided a continuous flow of ceramic body and automated cleaning. This technique was also used in many mineral processing plants purifying silica sand and feldspar.

Improving European Ceramic Competitiveness

Ceramic producers using Electromagnetic Filters found a dramatic decrease in rejects due to iron contamination as well as an improvement in the whiteness. Such a focus on improved processing and end-product quality was vital as Europe competed with a growing number of high-volume, lower-quality and low-priced imports from the Far East.

Whether the production is of ceramic tiles or technical ceramics, the Electromagnetic Filter has become a key part of the manufacturing process in many European ceramics operations. For further information, please contact us on press@buntingeurope.com or visit our website: Bunting-Redditch – www.mastermagnets.com