tion of different phenomena, densifying the feed mash, shearing and mixing alter the
structure to such an extent that binding between feed particles in the pelleting process is
enhanced. This explains the observed trend of increased pellet hardness and durability
(Table 5) o f ex p an de r-pelleted feeds. Especially in the case of raw materials which may
impair pellet quality, the use of an expander leads to increased durability. For raw
materials having good pelleting ability like wheat, the additional energy consumption
during expander pelleting may not be justified. Energy consumption of a press connected
in series with an expander decreases compared to the energy consumption of a
pellet press without an expander. However, total energy consumption was significantly
Table 5
The effect of pelleting and expander-pelleting on durability and specific energy consumption of the press and
expander for corn and wheat (after Robohm, 1991)