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Volumetric
Filling
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When volumetrically
filling the auger stop signal is controlled from a shaft encoder
monitoring the number of auger revolutions or a timer.
The choice
of system is dependent upon the speed required, batch size/changeover
times and budget available. The upper speed limit for semi automatic
filling is dictated by the time taken to manually handle the container.
If two seconds is allowed for picking up the container, presenting
it to the filling nozzle and putting it down again, a one second
fill time will restrict the output to 20 fills per minute. Others
factors will limit the output further, for example:
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| 1.
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Larger fill
weight |
| 2.
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Slow auger rpm
required due to a tendency to damage the product or generate dust. |
| 3.
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Small container
neck opening restricting the auger diameter. |
| 4.
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Container handling
difficulties, bags/sacks etc. |
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When filling
rigid containers automatically the same restrictions apply. The
speed may be further limited by the need to lift or vibrate the
container at the point of fill. A simple pneumatic lift is used
to provide a clean neck-entry fill, whereas an air-over-oil system
provides the constant rate of descent required for bottom-up filling.
Vibration may be required during the fill to settle a granular product
that would not otherwise fit into the container.
Oral suspension
antibiotic filling into glass/plastic bottles, a common pharmaceutical
macro-dosing application (see above) typically runs at between
15 and 30 containers per minute on a single head in-line system.
Doubling the number of filling heads has the effect of virtually
doubling the output. Containers are indexed through two-at-a-time,
each head filling 100% into alternate containers.
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Further increases
in speed can be made by utilising a four head system; two lanes
each with two heads, but when higher outputs still are required
rotary filling technology is employed.
When speed
is the main criteria for selecting a rotary solution, the most frequently
chosen solution is the continuous motion rotary machine with either
intermittent or continuous filling. Containers are fed into a rotary
turret possessing the requisite number of transfer funnels. The
neck of the container is engaged with the bottom nozzle of the transfer
funnel, either by lifting the container or by lowering the funnel
on a cam rail. The fill is made as the transfer funnels pass underneath
the auger filling head.
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The transfer
funnel is often vibrated to ensure complete transfer from funnel
to container. It can be seen from the above diagram that in order
to avoid spillage of powder between the transfer funnels the dosing
has to be intermittent, i.e: stopped between the trailing edge of
one funnel and the leading edge of the next. With the auger size
being determined by the fill accuracy required and the auger rpm
restricted to the maximum possible for meeting that accuracy without
damaging the powder, the turret has to be slowed from its theoretical
maximum to compensate for this stop/start effect. The addition
of a "knife-edge" plate, a circular plate with cut-outs above each
funnel separated by a blade-edge, permits continuous dosing and
can increase the output from around 100 containers per minute to
300cpm.
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