The Crown Expander: Pelleting without a Pelleting Press

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Our customers operate more than 600 expanders worldwide. In the U.S.A. for example, turkey fattening feed is expanded before pelleting in most cases. The annular gap expander has proved to be a good solution also in other fields such as starch modification or the oilseeds-processing industry. And last but not least, we have developed our Kahl extruder on the basis of the expander. With the extruder even higher mechanical energy inputs and modification degrees can be realised, and the products – fish feed, petfood, and snacks – can be pelleted or given other defined shapes.

For quite some time, there has been a clear tendency towards coarse grinding of feed.

AMANDUS KAHL remembered that in the annular gap expander, coarse grinding structures remain largely unchanged, although the product is exposed to a strong pressure and kneading effect. The pressure load in the expander acts on all sides of the coarse particles. The homogeneous pressure distribution on the entire particle circumference is supported by embedding these coarse particles in a pasty moist matrix of fine particles. Another advantage lies in the fact that the finer particles are agglomerated during expansion and thus are transformed into coarse structures.

It occurred to our engineers that they might equip the expander outlet with an annular die similar to that of a pelleting press. A die without pan grinder rollers to be more precise, as they wondered: Should the high internal pressure of the expander not be able to press the finished product right through the round or oblong bores in the die ring, thus making the pressing and crushing effect of pan grinder rollers superfluous? A rotating cutter was designed, meant to cut the product strands leaving the die to uniform pellet lengths.

So the »Crown Expander« was born. The machine owes its name to the crown form of the first dies which were provided with slits instead of bores.

One important component of the annular gap expander remained unchanged in the Crown expander: The hydraulically moveable cone. This cone can be moved into and out of the crown die at the outlet end. Depending on the position of the cone in the die, more or less die bores are open for the production of pellets. Thus the pelleting process is easy to control by simply varying the cone position – in contrast to conventional extrusion processes which require die changes or far more complicated control mechanisms.

The results obtained so far, have met every expectation, which means that we succeeded in the proverbial »squaring of the circle«: The Crown expander produces pellets or other regularly shaped structures while preserving coarse particles and simultaneously agglomerating fine and finest components. The positive nutritional effect of expansion is an additional advantage which traditional pelleting does not offer.

The crown expander – an ideal example of a successful further development taking into account aspects of animal nutrition and process technology.