Concurrent airflow of deducting equipment via
compressed air jets.
In the early 1990s, the first vertical
spiral designs made their debut, and
were almost immediately recognized as
a quantum leap from horizontal helixes,
which utilized the efficiency-limiting effects of gravity for tablet transport.
With vertical dedusting, tablets
would now be vibrated up a stainless
steel spiral by a combination of electro-
magnets and spring blades positioned
at the spiral’s base. Dust extraction ports were placed at
regular intervals along the center of the spiral, either in the
form of slots perforated directly in the central extraction
column or as suction channels under sections of the spiral
with perforations. By increasing the residence time of tablets
in the deduster and tumbling them in a variety of positions
while vibration conveyed them upward, tablets were exposed
to dust-clearing vacuums at multiple points – a stark perfor-
mance improvement over horizontal dedusting.
These vertical vibrating designs brought the additional benefit of elevating the tablets, gaining sufficient height to compensate the height loss of gravity-fed metal detectors downstream,
and the ability to discharge into taller containers.
On this first generation of elevating dedusters, tablets – and
any dust being separated from them – were moved up by vibration of the stainless steel spiral on which they were travelling.
Since the amplitude of the vibration is greater on the circumference of the spiral and smaller at the center of the spiral, tablets
tended to travel around the outer circumference of the spiral.
There was, however, a significant drawback with this process: With extraction ports placed on or near the center column, dust extraction worked in the opposite direction of the
tablet movement generated by the spiral’s vibration patterns.
So dust moved together with tablets toward the spiral’s outside circumference, and was often too far from the extraction
suction points for efficient removal. As a result, the lower
rungs of the spiral could be saturated in powder after operating only a few hours. Tablets would literally be rolling in it.
Dust has always been an unwanted byproduct of tablet manufacturing. In a perfect world, all powder
would flawlessly flow into the hopper,
and 100% of the product would emerge
as finished tablets. In practice, though,
most tablet presses are so inundated
with dust after an eight-hour run that
they form miniature snow piles on both
sides of the feeder, and build-ups of
material occur around the takeoff bar
and recirculation channel. Typically,
a noticeable amount also travels down the tablet press chute
either as free powder or on the tablet surface as residual pow-
der. In some cases, compacted burs are also
present around the edges of tablets (resulting
from the clearance between the punches and
the die) or around logos.
In short, if dust can get somewhere, it al-
most certainly will. And unwanted dust can bring
a number of adverse effects downstream from
the tablet press, including:
• A messy build up in packaging equipment resulting
in potential jams, obscured sensors or faulty
closing of packaging (blisters or strips)
• Increased amount and frequency of
necessary cleaning downstream from the
• Increased operator exposure to APIs on
• Diminished patient confidence in the end
product via unsightly dust at the bottom of
a bottle or rough burrs around tablet edges
or logos that could affect prescription com-
But to best understand the importance
of tablet dedusting – as well as the steady
technological advances that have driven the
industry – it is worthwhile to progressively
examine the past two decades, starting with
the inception of modern-day vertical dedusting equipment and techniques.
■ By Nic Michel, General Manager, North America, Pharma Technology Inc.
The evolution of dedusters shows generational progress via design innovations.
Efficiency by Design
■ 32 NOV/DEC 2014 | PHARMACEUTICAL PROCESSING
■ PHARMPRO. COM
■ TABLE TING
The PharmaFlex 750 Tablet Deduster
features a high pressure-molded polymer
spiral composed of FDA-accepted material
with a closed face surface that does not
scratch or discolor.