Today we've got a very informative article on grinding by Willem de Vaan, General Director, Wynveen
International BV.
Full text follows or read online here
by Willem de Vaan, General Director, Wynveen International BV, The Netherlands
Together with mixing and pelleting, grinding is one of the important
processes when producing animal feed.
Traditionally, hammer mills are used in the feed industry for grinding
raw materials, which is mainly caused by the relatively simple construction and
high variation in particle reduction compared to other techniques used at
roller mills and crackers.
Roller mills and crackers showed better results when it comes to
energy consumption, but the new designed mills feature adjustable pre-breaker
plates, variable speed drives and automatic screen change systems.
This results in an energy saving which brings the hammer mill again in
a favoured position, certainly when taking in consideration the relatively high
costs for wearing parts on roller mills and crackers. Given the fact that a
hammer mill also allows grinding of mixed products, it becomes clear that hammer
mills still are the majority.
Wynveen International BV has a rich tradition in manufacturing
machines and equipment for the animal feed industry, petfood industry and fish
industry.
Recently the company has moved into its new premises, which means a
doubling of the office and production floor compared to the old building. With
this new office Wynveen International BV is prepared of the future and has made
the logical next step to meet the growth targets it is aiming for. With its new
website, introduced during the opening of the new building, one can see in a
glance what capabilities can be offered.
Besides the design and delivery of complete turnkey feed mills,
Wynveen International BV is manufacturing the main equipment like hammer mills,
mixers, coater and sifters and conveying equipment.
Wynveen International BV is
manufacturing hammer mills in a wide range.
The features of the of hammer mills that can be delivered are:
Big diameter 1200mm - 1500rpm
Diameter 650mm - 3000rpm
Capacities from 2t/h up to 60t/h
Frequency controlled drives
Manual or automatic screen exchange
With or without adjustable breaker plates
Two directions of rotation possible
Motor capacities up to 400kW
Open rotor design
Temperature control on main bearings and chamber
Feeder with magnet and stone trap
Ergonomic design
Already, five years ago, the Wynveen hammer mill underwent a complete
makeover and there was the idea to develop a hammer mill that will be prepared
for the future and can deal with the challenges of the future. This means
minimal energy consumption and the possibility to answer to the need of the
various applications required in nowadays-feed mills.
Most animal feed mills are looking for a grinding concept that can
produce the particle size that fits with the specific required coarseness of
ingredients needed for the feed to produce.
The latest version of the Wynveen hammer mills type GHM has a grinding
chamber diameter of 1200mm, which gives at a speed of only 1500rpm a hammer tip
speed at the ideal level of approximately 90m/seconds. The length of the chamber
can vary from 750 to 1250mm, depending on the required capacity. The low speed
gives a lower noise level, less wear and tear and lower bearing load compared
to a 3000-rpm hammer mill.
To suit the various demands in feed mill capacities, Wynveen
International BV can deliver hammer mills that can deal with different
capacities from two tones/hour up to 60 tones/hour. For the smaller capacities
the 3000-rpm versions are still used.
In the enclosed table you will find the various possibilities. By
introducing frequency control on the motor, it became possible to grind ideal
structures and particle size. In fact you can create a new screen set-up but
still using the same screen perforation. When using a high speed you are able
to create fine grinding, while with a lower speed a coarser grinding is
achieved.
Frequent
changing
To answer the growing need for producing a great number of recipes,
the screens need to be changed frequently, for which reason Wynveen has
designed the GHM version with an optional automatic screen change system. This
gives more possibilities to grind on various perforations without the need to
stop the motor during production and loose a lot of production time. Wynveen has
chosen to make use of the ergonomic design already available at the hammer
mills with manual screen exchange, which means a horizontal movable screen
cassette in which 4 screens (so also four different perforations selectable)
are mounted.
The big advantage versus vertical screen exchange is the space needed.
Often an upper hopper is positioned above the hammer mill, which
reduces the possibilities for vertical screen exchange. To avoid dust and waste
of product during exchange of the screen, while the motor is still running, it
is important to maintain, an under pressure in the grinding chamber of the
hammer mill. Special inflatable sealing’s with labyrinth ensure a correct
tightness of the sealing in operation and stop’s the product leaving the
grinding chamber.
To minimise energy consumption adjustable breaker plates are
introduced.
Tests have proven that hardly any grinding takes place below the level
of the main shaft. By designing two adjustable breaker plates in the top of the
machine, an energy saving of approximately 30–35 percent compared to the old
designs has been achieved.
The lower part of the hammer mill is executed with screens; by making
use of the gravity force a good discharge of product is possible. The idea of
adjustable breaker plates was to create an asymmetric form (ellipse instead of
circle) in the grinding chamber. Because of this the product is forced to leave
their natural flow and, because of the centrifugal force the product will hit
the breaker plate, as a result it is bounced back and then again gets a hit of
the hammer.
So a more frequent frontal collision is achieved between hammers,
breaker plates and product. By making the breaker plates adjustable we can
create this ellipse in both directions.
The hammer mills of Wynveen International BV allow a drive motor up to
400kW.
Furthermore, a so-called open rotor has been designed with two
functions. One is to create sufficient stiffness and balance and secondly to
minimise the temperature increase while grinding.
For monitoring purposes the main bearings and the chamber are fitted
with temperature sensors. All components can also be delivered in an Atex
execution. To make use of all four corners of the hammers and reduce the
downtime of the machine, the direction of rotation of the hammer mill can be
changed and the rotor has double holes for the hammer axles. To ensure a good
product entrance to the mill, a feeder is developed which contains an
integrated, (automatically cleaned) magnet and a stone trap.
This will make sure that possible metal parts and/or stones are
prevented from ending up in the feed mix. The combination of the two makes the
feeder unique.
Risk analyses
To meet the latest stringent guidelines of CE regulations, Wynveen
International BV has conducted a risk analyses for its hammer mills.
This has been done for both non-hazardous environments and ATEX
environments. To meet both as a standard, the hammer mills are equipped with
proper earthing and sensors to detect possible increase of heat. Where required
we make use of a pressure release membrane and/or flame arrestors.
For reducing the noise and vibration our hammer mills are provided
with shock absorbers.
Much attention was spent to the ergonomic aspect. By designing two big
doors, the hammer mills are very easy accessible for screen and hammer
exchange. Both doors easily roll sideways via a rail and wheels and are
equipped with safety switches to make sure that no mistakes can be made during
maintenance.
Other important points to keep in mind when designing a grinding plant
are not only the right choice of hammer mill, but also the correct energy
efficient motor type and very important, an adequate aspiration set-up.
Especially the last item needs special attention.
The capacity of the aspiration fan should not only be in the right
relation to the screen area of the mill but also depends on products, which
have to be ground. Depending on the air volume, the necessary filter surface
can be determined.
In general, reverse air cleaned filters are used, which allow for an
air load on the filter cloth of approximately two m3/minute of air per m2 of filtering
area.
Finally, it is important that the filter unit is not directly
positioned beside the outlet product stream of the hammer mill to make sure
that a good airflow and aspiration is safeguarded.
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