SPECIAL STORY FEED & ADDITIVE MAGAZINE March 2022 61 About Arthur vom Hofe Arthur vom Hofe is CPM Europe’s Segment Manager Feed & Oilseeds. He has been already involved in the front line since the early nineties when representing the company for pelleting and particle size reduction equipment. Throughout this time, he has gained valuable experience of feed production processes across the world. Hammer pattern Hammer patterns (the number and distribution of the hammers on the rotor) and positions (setting the hammer closer to or further from the screen) have a profound effect on the performance of any Hammer Mill. Because different materials grind differently, the ideal number of hammers and clearance to the screen will need to be adjusted according to each application. For course grinding it is most efficient to grind with a limited number of hammers, but for fine grinding applications it is best to use an extra heavy hammer pattern to achieve the very fine finished products desired. If the rotor is equipped with a larger number of pins (12), the total number of hammers is increased significantly. This without putting an excessive number of hammers on (four or eight) pins, which could lead to high stress and the possible failure of the rotor plates. Grinding chamber shape Finally, we do have to realize that the speed differential between the product and the hammer determines the impact, which is required to reduce the particle size of the incoming product. A tear-drop shaped Hammer Mill chamber will maintain the speed differential better than traditional circular chambers. This is because the rotation of the product in the chamber didn’t escape after the first hit is effectively reduced. STEP GRINDING The most flexible grinding solution is a system with a Roller Mill in combination with a large diameter speed controlled Hammer Mill. The feed miller can basically produce every desired particle size. From a course mash feed with minimal fines to a very fine grind, all from the same high capacity grinding line. The Roller Mill will produce course mashes or will prebreak the materials before they are processed with the Hammer Mill. Pre-breaking the material with the Roller Mill before going to the Hammer Mill saves over 25% on total energy consumption. This also means that when placing a Roller Mill before an existing Hammer Mill, the capacity is increased with 30-40%. A positive side effect is that the lifetime of the Hammer Mill wear parts (and with that the consistency of the grind) is enormously extended (x4 or more) due to the pre-breaking action of the Roller Mill. If in a step grinding system a traditional Hammer Mill is used instead of a CPM Champion teardrop shape, it is necessary to use screens between the two machines to experience the benefits. Sifting provides additionally the possibility to remove the oversized fibrous husks from the Roller Mill ground mash and grind them with the Hammer Mills. A sustainable feed industry is constantly looking for the best way to process feed, to have the best yield with use of lowest amount of energy and lowest amount of raw materials. In this article we focused on the ways how to optimize the particle size in the grinding process of the feed mill. However, there is still much to learn in order to understand the animal biology and the effect of particle size on its nutrition to be able to define what the most optimal particle size.
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