Aquatic animals have various feeding habits and feed intakes. For example, fish swallow feeds so they need about 40 minutes to intake feeds. However, shrimps nibble feeds so they need three to six hours to intake feeds.

1. September | October 2013
Grinding equipment for aquatic feed pellets
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3. A
quatic animals have various
feeding habits and feed intakes.
For example, fish swallow feeds
so they need about 40 minutes
to intake feeds. However, shrimps nibble
feeds so they need three to six hours to
intake feeds.
The digestive tract of aquatic animals is
relatively short so they have poor digestive
ability. For example, fish have no salivary
glands in the oropharyngeal cavity which helps
seek, intake and swallow feeds. So the func-
tions of tearing and grinding feeds degenerate.
Fish dissolve and digest feeds from the
feed surface so aquatic feeds with small
particles are convenient for digestion and
absorption.
These characteristics mean that aquatic
feed pellets should have good stability and
water resistance; be easy to digest; and be the
fineness specific growth stages.
In order to produce ideal aquatic feed pel-
lets, feed ingredients, processing technology
and equipment especially the grinding process,
should be carefully considered.
Nutrition sources for feed pellets
Raw materials for pellets should con-
sider not only the nutritional values but
also the need for good stability in water.
Protein, which ensures the growth and
reproduction of aquatic animals, is an
essential of aquatic feed pellets. It accounts
for 25-50 percent of the feed formula
with wheat and wheat by-products as the
main sources of protein. If the viscosity of
protein is increased when heated, then the
pelletizing performance is improved and
the stability is good.
Starch is the most common carbohydrate
used in aquatic feed pellets. To ensure the
stability of feed pellets in water, the starch
content of sinking feed pellets should be up
to 10 percent and that of floating feed pellets
should be about 20 percent.
Coarse fat is a good source of high quality
energy. The crude fat level includes the fat of
feed ingredients and that of added fat. The
added fat has great influence on the pelletizing
effect but too much fat will make the feed pellet
loose and influence the stability. For this reason,
the content of added fat should not exceed 3
percent.
Fishmeal is widely used in aquatic feed
pellets. High quality fishmeal has good water
resistance qualities.
Similarly, rapeseed dregs contain high
coarse fibre which is conducive to improving
the water resistance of aquatic feed pellets.
Among the commonly used feed ingredients
cotton pulp, fishmeal and soybean meal, have
good water resistance characteristics while
the water tolerance of corn, bran and rice
bran is poor.
Adding moderate binders can improve
water resistance. There are two kinds of
binders: natural substances such as sodium
lignin sulphonate and align, and chemical sub-
stances such as carboxymethyl cellulose and
sodium polyacrylate.
So when designing feed formula the raw
materials should be highly nutritious and have
good water resistance properties.
Why is grinding so important?
The aquatic feed pellet has high require-
ments in terms of particle size and viscosity
so the processing technology is important.
In general, feed ingredients for aquatic feed
pellet should be ground to 40 meshes. For
special aquatic animals such as shrimps, turtles,
eels and other small animals, the raw materials
should be super-finely ground so as to pass
through a 100 mesh screen. The fine crushing
granularity can improve the utilization rate of
aquatic feed pellet.
Aquatic animals have simple digestive sys-
tem and the residence time of feed in the gut
is short so pellets containing large particles are
Grinding equipment for aquatic feed pellets
by Joyce Li, customer service, Amisy Machinery, China
Table 1
10 | InternatIOnal AquAFeed | September-October 2013
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5. not conducive to easy digestion. The finer the
crushing granularity, the larger the surface area
which contacts with the digestive enzyme thus
the digestibility is increased.
Raw materials come in different shapes
and thicknesses. So if they are not ground
before processing, the finished pellets can
lack a balanced nutritional quality and have
poor stability in water. Table 1 shows the
relationship between the grinding fineness and
stability in water.
Feed pellets have little viscosity when
ground to a large particle size. The crushing
fineness also has an effect on the following
processes such as mixing and steam modulat-
ing and the fineness of pulverization has great
influence on stability. When the grain fineness
is perfect, the raw materials can be fully
mixed and the swelling property of materials
converge making for good stability.
Finer particle sizes will have a larger
surface area which can be fully modulated,
making better-formed pellets. Although finer
particle size is conducive to producing feed
pellets with good stability, the grain size
should not be too fine otherwise the pel-
leted feeds are fragile. The proportions of
coarse grain, medium grain and fine grain
should be appropriate so that during the
pelleting period the fine grain can fill the
space between the coarse grains. This means
that the contact area between particles is
increased and the pelletizing performance is
improved.
Choosing the appropriate
grinding equipment is crucial
Controlling the grinding fineness has a
direct influence on the stability of aquatic feed
pellet and the production cost. The impor-
tance of cost should not be underestimated;
electricity consumption during the grinding
process accounts for 50-70 percent of the
total power consumption.
Choosing the appropriate grinding equip-
ment is also critical. Different aquatic animals
have different requirements in terms of par-
ticle size of feed ingredients which requires
corresponding grinding equipment. Hammer
mills are widely used in the feed industry and
in aquatic feeds. The hammer mill consists of
hammers, a rotor, the grinding surface and
sieve. The hammer is the main working part
whose shape, size, quantity and line speed has
a great influence on the grinding efficiency and
grinding fineness. When the linear velocity of
hammer blade is slower, the grinding efficiency
and production efficiency are low.
A quicker line speed will improve grind-
ing efficiency. However, too high a speed
will make the material speed fast, reduce
Figure 1
September-October 2013 | InternatIOnal AquAFeed | 11
FEATURE
Extruder OEE for the Production of Fish FeedExtruder OEE for the Production of Fish Feed
AMANDUS KAHL GmbH & Co. KG, Dieselstrasse 5-9, D-21465 Reinbek / Hamburg,
Phone: +49 40 727 71 0, Fax: +49 40 727 71 100, info@amandus-kahl-group.de www.akahl.de

6. the grinding efficiency, increase the power
consumption and increase the energy con-
sumption of products. The optimal line speed
should consider factors such as the power
consumption, grinding fineness, noise and
production efficiency.
The number of hammers has a great
effect on the grinding fineness and crushing
efficiency. Out simply, more hammers means
faster and finer grinding. Fewer hammers
results in a coarser product.
Mesh screen and sieves are related to
the grinding fineness. Figure 1 shows the
relationship between grinding fineness of
corn, bean pulp and the mesh screen
diameter. The smaller the diameter of
mesh screen, the finer the grinding fineness
and the lower the output. In turn, when
the diameter is big, the grinding fineness is
coarse and the output is high. The size of
mesh screen diameter is determined by the
required size of the final pellet so in the
context of meeting the grinding fineness
of feed pellets a sieve with big diameter
should be adopted so as to improve the
crushing efficiency and reduce energy con-
sumption.
Studies show that when the sieve area is
increased by 9 percent, the grinding efficiency
can be improved by 35 percent and the
electricity consumption can be reduced by 13
percent. So choosing the appropriate sieve
area can improve the output.
In addition, the thickness of sieve influ-
ences the sieving ability of materials. There
is a corresponding and restrictive relationship
between the sieve thickness and the diameter
of mesh screen: sieve thickness is less than or
equal to the diameter of mesh screen.
The fineness requirement of ordinary
aquatic feed pellet is 40-60 mesh. In order
to achieve the ideal crushing fineness and
avoid the super-fine grinding of materi-
als, the grinding surface shape should be
changed. A water drop grinding surface is
widely adopted in producing the aquatic
feed pellets. A water drop sieve shape can
increase the effective sieve area, destroy
the circulation layer of materials so as
to change the material motor direction,
increase the frequency of hammer grind-
ing the materials and improve crushing
efficiency.
Grinding machine options
Machine for fine grinding have a higher
spindle speed, more hammers numbers and a
wider grinding surface than models for coarse
grinding.
The Amisy series of AMS-ZW-29C,
AMS-ZW-38C and AMS-ZW-50C hammer
mills can be used for coarse grinding of feed
ingredients.
The main
differences
of the three
models are
the grinding
room width,
hammer
blade quan-
tity, power.
The wider the
grinding room,
the higher the
crushing effi-
ciency. More
hammers
will produce
finer prod-
ucts though
of course the
higher power
means the
more output.
The Amisy
series of
AMS-ZW-
60B and
AMS-ZW-
80B ham-
mer mills are
mainly used
for fine grind-
ing. The out-
put differenc-
es between the two models are related
to the power, grinding room width and
hammer numbers.
The AMS-ZW-80B model has more ham-
mers, a wider grinding surface and greater-
power than that of the AMS-ZW-60B. This
means that the output of AMS-ZW-80B is
greater than that of AMS-ZW-60B.
Both the series use the water drop
design to ensure a larger space for grind-
ing and to improve crushing efficiency.
The crushing fineness differences between
the two models mainly lie in the spindle
speed, hammer numbers and grinding sur-
face width.
Producing fine feeds
As mentioned previously, aquatic animals
such as shrimps, eels and turtles require fine
feeds. For these animals, grinding fineness
must be up to 80 mesh. Ordinary hammer
mills cannot reach this fineness so ultra
fine feed grinding equipment is necessary.
To achieve the required small particle size,
ingredients should be crushed twice. An
initial coarsely grinding can be done by a
hammer mill with a second grind on an
ultra fine mill.
Ultra fine grinding equipment uses the
blade type. The grinding chamber and
grading room of Amisy’s AMSSWFL42,
AMSSWFL75, AMSSWFL102 and
AMSSWFL128 models are located in the
same machine body so that crushing, grad-
ing and separation can be completed simul-
taneously. The main differences between
the three models lie in feeding motor
power, sieving motor power, rotor diame-
ter and rotor speed. When the rotor speed
is faster the grinding fineness is finer but the
grinding efficiency and output are accord-
ingly reduced. Compared with other feed
hammer mills, the ultra fine feed crushing
mill has a lower output because the rotor
speed is faster.
The main index to evaluate the working
efficiency of feed grinding equipment is the
grinding fineness, output and power consump-
tion. Grinding fineness has great influence on
the feed utilization, production properties
of aquatic animals, feed pellet quality and
production cost.
Considering factors such as the mesh
screen, hammer quantity, spindle speed, grind-
ing surface size and choosing the appropriate
power based on the composite factors, grind-
ing can produce homogenous pellets, improve
output and reduce the electricity consump-
tion and production costs.
More InforMatIon:
Email: service@feed-pellet-mill.com
Website: www.feed-pellet-mill.com
12 | InternatIOnal AquAFeed | September-October 2013
FEATURE
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7. September-October 2013 | InternatIOnal AquAFeed | 13
FEATURE
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8. www.aquafeed.co.uk
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Volume 16 Issue 5 2013 - sePTemBeR | oCToBeR
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EXPERT TOPIC
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