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Pharmaceutical
Taking the strain
Uses of sieves in the pharmaceutical industry and the increased demand
for containment. By Rob O’Connell, Russell Finex
A sieve or screener is an essential part of every pharmaceutical Where sieves are used?
production process, particularly as product quality and integrity Most pharmaceutical processes are HACCP (Hazard Analysis and
are so important. The use of a sieve safeguards against Critical Control Point) controlled. This means that an analysis of
customer compensation or litigation as it eliminates all the process is carried out in terms of where hazards can occur.
oversized contamination. It therefore ensures that ingredients Critical control points are identified and some form of prevention
and finished products are quality assured during production and is put in place. Sieving equipment will help considerably at any of
before use or despatch. these points where there is a risk that contamination could enter
However, the design of sieving equipment has had to undergo the process. This is commonly known as control sieving or
radical changes in recent years to overcome the new demands security check screening of powders.
of companies manufacturing pharmaceuticals. These demands These critical control points are found in many different areas
include improving productivity, product quality and most of the production process. On the primary side an example is
importantly improving the health and safety of the operators of where raw ingredients are de-bagged because of the potential
sieves and screeners. The latest generation of sieve has made for parts of the bag to be accidentally introduced into the
large improvements to the safety by effectively containing the process. Another example on the primary side is where mixing
powders being processed therefore adhering to occupational or blending takes place as this is another potential area for
exposure limits. contamination to get into the powder. On the secondary side
In basic terms a sieve consists of a housing containing a many pharmaceutical companies consider the finished powder
removable wire mesh of a defined aperture size. This assembly packaging area critical and place a sieve here to prevent
is vibrated by an electric motor so particles which are small contamination and therefore customer complaints.
enough to pass through the mesh apertures do so and any
particles or contamination that are too big remain on the top. Features and benefits of check screening sieves
Most units used in the pharmaceutical industry tend to be Sieves used for check screening are designed to be extremely
circular in shape and of a high quality Good Manufacturing simple to operate and maintain, with the emphasis on making
Practice (GMP) design. Stainless steel mesh with a high them easy to strip down and clean effectively. Their compact
tolerance on the apertures is also specified to give excellent design means that they can be placed in small or restricted
product quality. height areas of the production process – possibly where a sieve
was not originally deemed necessary but is now essential.
Compact Airlock Sieve
The sieve mesh itself is a removable item so the aperture size
of the mesh can be changed according to the powder being
processed. Modern units use mesh that is securely bonded with
adhesive to a frame which gives a much higher tension in the
mesh than older styles that secured the frame with a clip or
screws. Having a consistent and high tension level gives better
throughputs and reduces blinding or blocking of the sieve
apertures. Another recent development is the use of FDA
approved adhesive to bond the sieve mesh to the frame.
All other contact parts of the sieve are manufactured from
stainless steel and can be polished to very low Ra (surface
roughness) values to ensure good flow properties and easy
cleaning. These components are simple to remove and wash in
an autoclave or other cleaning vessel thus removing any chance
of cross contamination between different batches of material.
Ultrasonic deblinding system
Most powders can be screened quickly and accurately by a
standard sieve, however, some pharmaceutical powders may be
sticky or have irregular shaped particles, which can cause mesh-
blinding problems. The method of ultrasonically exciting the
stainless steel mesh wires of a powder screening machine by
high-frequency, low-amplitude vibration to prevent apertures
16 Solids & Bulk Handling • August 2007 www.solidsandbulk.co.uk
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