Three-Mechanism Grinding Mill achieves finer, more uniform particles

A newly introduced cryogenic grinding mill from Air Products and Chemicals Inc. (Allentown, Pa.; www.airproducts.com/ultrafine) can generate consistent yields of particles between 45 and 250 μm, and in some applications can achieve particle sizes of 10 μm. The ultrafine grinding mill also achieves narrower particle size distributions than conventional impact mills.

Known as the PolarFit ultrafine-grinding mill (diagram), the cryogenic grinder employs a combination of size-reduction strategies — impact, particle attrition and particle-particle collisions — in one machine to reach finer particle sizes and raise yields within a particular size range. “We set out to design a highly flexible machine,” says technology manager Jon Trembley, “and one that both lowers energy input and makes efficient use of liquid nitrogen” (to remove heat generated by the grinding process).

The PolarFit mill has an easily adjustable grinding gap, and is intended for low-maintenance operation.

Before being launched at last month’s PTX Canada tradeshow in Toronto, the PolarFit mill had undergone an internal analysis program, processing 2–3 tons of material at a time while being compared to competing products. The product performed well for various cryogenic size-reduction applications, including plastics, pigments, powder coatings, thermoplastic elastomers, spices and other food products. The PolarFit mill is available with grinding rotors in three standard sizes — 200, 400 and 800 mm, as well as in custom-made sizes.

CHEMICAL ENGINEERING ♦ WWW.CHE.COM ♦ AUGUST 2011