Advantages of ring die pellet mills: First, ring die pellet mills do not suffer uneven
roller and die wear as the inner and outer edge of the rollers cover the same
distance. For this reason, ring die pellet mills are preferred for large scale production
as the long-term costs from roller and die replacement are perceived to be lower.
Ring die pellet mills are also preferred for large-scale production for energy efficiency
reasons. Roller slip in flat die pellet mills causes extra friction during the pelleting
process, thereby using more energy during production. Yet this friction is not entirely
disadvantageous, as friction results in more heat, which is needed to produce quality
pellets. All ring die pellet mills come complete with a conditioner and variable speed
feeding.
Disadvantages of ring die pellet mills: The first obvious disadvantage of the ring die
pellet mill is its size and weight. This is usually not a problem for large-scale
production, yet is often problematic for small-scale production. Also, changing rollers
and dies in a ring die pellet mill is a far more labor intensive process. The dies in
particular are large and heavy, in most cases requiring lifting equipment for removal
or replacement. Also roller adjustment is more difficult, as a majority of ring die pellet
mills require manual roller adjustment which can only be accessed by opening the
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pellet mill chamber. However this is not always the case, as some now come with
optional remote roller adjustment at extra cost. Overall, ring die pellet mills are more
costly than flat die mills, as the machines themselves and the dies and rollers are
generally more expensive than flat die pellet mills. Finally, the user can’t view the
pelleting process, as the die and roller are encased behind a solid door, thereby only
allowing indirect methods to quickly obtain information for troubleshooting.
Die and roller interaction
The die and rollers interact to create a wedge of feed at the nip in the pellet mill. The
three main forces in this process are:
1) Roll force: The force from the roll acting on the material. This force acts on the
material relative to the contact point with the die. It is a force that acts to compress
and extrude the material.
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