World Grain -- December 2013 - 58

feeDoPeratIonS

mixers have the mixing advantages of a
single shaft mixer with the added ability to cross mix the ingredients between
each of the assemblies.
If paddles are used, they can be
overlapped to create a fluidizing zone
between the two shaft assemblies.
These mixers have the advantage
of both lengthwise mixing as in the
single shaft type and cross mixing between the assemblies.
These combined mixing actions provide for full or complete mixing in as
little as a minute or less depending on
the ingredients being used.
Single shaft horizontal mixers are designed to be full for proper mixing action. This means that the mixture should
fill to the point that the top of the ribbon
or paddles is covered. If they are overfilled, the materials above the ribbon or
paddle tips do not get mixed well and often just float on top of the mixing action.
The twin shaft horizontal mixers, due
to their cross mixing actions, can properly mix batches that fill only a portion
of the mixer volume. This works nicely
for mixing various size batches in the
same mixer. In some cases, using a twin
shaft horizontal mixer, the batch size
can be as small as 10% to 20% of the
full mixer capacities.

Drum mixer
Another mixer is the drum type. It is
a horizontal cylinder turned by an external drive. There are no rotating internal
parts. The mixing is done by a series of
vanes attached to the interior surface
of the drum. As the drum rotates, these
vanes cause a free-fall action that folds,
divides and combines the ingredients
into a uniform mix that is blended by
the constant rotating motion. Without
internal moving parts, the mixer is able
to gently mix breakable ingredients or
materials such as flaked grains. It also
is able to mix hard to handle ingredients
due to its mixing action.
This mixer is charged and discharged
through openings located high on the front
(end) of the drum. Liquids may be added
by spraying the liquid onto the tumbling
ingredients using a liquid addition accessory. The drum uses much less energy than
the standard horizontal or vertical mixer
as no rotating shafts are used internally.
This mixer can also do small batches.
When liquids are added into any mixer, they must be sprayed into the mix so
they actually are sprayed on to the ingredients and not on to the surfaces of the
mixer itself. For batch mixes, it is best
to limit the amount of liquid added to
no more than 4% maximum of the batch

weight, but higher liquid addition rates
are often possible in horizontal paddle
mixers and drum mixers.
Summary
When choosing a batch mixer, it is
important to know the types and characteristics of materials to be mixed,
the amount(s) of liquids to be added in
the mixture during mixing, the sizes of
batches required, and the time available
for the mixing operation to meet production requirements.
It is wise to look at different mixer
manufacturers and options before deciding on the correct batch mixer for your
needs. Most manufacturers will gladly
run a test for you to confirm the suitability of their equipment.
In a future article we will look at continuous mixing system equipment.
Fred Fairchild is feed science professor emeritus
in the Department of Grain Science and Industry
at Kansas State University. Prior to coming to
Kansas State in 1994, he worked in the industry
designing, constructing and commissioning
numerous mill facilities. He is a licensed
professional engineer. He can be reached by
e-mail at fjf@k-state.edu.
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