In the previous article (PCI May, p. 82), we described the four common methods of size reduction-impact, abrasion, cutting and compression. This article concentrates on impact machines, although many units combine two or more methods.
Hammer MillThe model 1200 Hammer Mill is the classic size reduction-by-impact machine. Fist-sized material is processed by rotating, hardened hammers. A final fineness of 400 mm (microns) can be obtained. The mills are ideal for pre-crushing and coarse grinding.
Micro Hammer-Cutter MillAs its name suggests, this desktop mill uses both swinging hammers and cutting edges to grind samples down to below 200 mm. Thousands of these versatile machines are in use in labs around the world. The Micro Hammer-Cutter Mill handles light & fibrous materials, hard rocks and ores, and many other materials.
Cross Beater MillThis mill combines impact and shearing, similar to the Micro Hammer-Cutter Mill but is designed to handle larger samples, fed semi-continuously. Material enters the grinding chamber axially where it comes into contact with high-speed cross beater tips. The action of the beaters throwing product against the serrated profile of the grinding chamber produces particles as fine as 70 mm.
Dish and Puck MillThe Dish and Puck Mill packs a powerful punch for pulverizing materials from the hardest to the most malleable ore or mineral. A heavy-duty motor operates a rotating eccentric weight that causes a specially designed puck to be thrown about inside a bowl or dish. The puck's energy is directly transferred to the material causing size reduction to 40 mm and below within minutes or sometimes seconds.
Ball MillsBall Mills come in a variety of sizes and styles; from the Planetary Ball Mill shown to small desktop units designed to handle a few grams. Whether being used for dry or wet milling, they operate by converting the energy present in a moving ball into work (size reduction) when it collides with the product. Dry ball milling can produce a final fineness to 10 mm. Wet milling can achieve sub-micron size.
Jet MillThis is a different kind of mill - it has no moving parts. Instead, it uses the energy in compressed gas to drive material into itself and the walls of the mill, creating substantial size reduction. Each particle is subjected to hundreds of small impacts, that successively grind away the product until a 5 mm or smaller fineness is achieved. Ideal when contamination can not be tolerated.
For more information on equipment, contact Glen Mills Inc., 395 Allwood Road, Clifton, NJ 07012; visit www.glenmills.com; or Circle Number 76.