Intermediate Bulk Containers in
Plastic Compounding
Guest article by Carl Andrews, General Manager, Matcon USA Inc.
 Today’s
producers and users of plastics require a multitude of ‘properties’
from their plastic compounds ranging from, resistance to ultraviolet
decay, rigidity, temperature resistance, purity and colors to name
but a few. To achieve the desired properties of plastic compounds a
wide variety of raw ingredients are used. These additives are
normally in powder form and contain differing handling and flow
characteristics.
Modern compounding manufacturing
facilities are now designed using Intermediate Bulk Container (IBC)
systems for material handling, formulation, dispensing, filling,
discharging and blending. Product is fed to the extruders via
loss-in-weight feeders either directly and/or by adopting pre-mix or
master-batch techniques. These methods can be described in the
following stages.
- Addition of raw ingredients
- Production and use of pre-blended
additives
- Compounding with master batch
Addition of Raw Ingredients
Many compounding facilities rely on
gravimetric or volumetric feeders to deliver the correct recipe of
additives to the extruder. The feeders meter into the extruder in a
continuous mode to ensure constant and accurate quality of the end
product throughout the campaign and for all sub-sequent campaigns.
For consistent high accuracy feeding
of the additives into the extruder, it is essential to use
gravimetric type feeders. This ensures a constant flow rate to the
extruder on a minute-by-minute second-by-second basis and ensures
accuracy is maintained throughout the production run. Experience has
shown that screw type LIW feeders are the most accurate units for
this purpose.
All LIW feeders need to be filled
periodically. Refilling is usually achieved from a secondary '
refill hopper ' located above the feeder utilizing flow by gravity
into the unit as required. Although the feeder has a continuous feed
into the extruder, it is refilled on a ' batch ' basis. This feed
rate to the extruder is calculated on a ' weigh loss ' basis. Since
the feeder needs a finite volume in its hopper it requires to be
filled on a periodic basis.
During this ' refill ' mode the
feeder is seeing material being added, this being contrary to the
normal control mode. To compensate for this ' in accuracy ' the
feeder controller has a special software program which keeps the
overall feed rate within the accuracy demanded. To maintain the
overall accuracy the refill 'feed rate' should be between 9 and 10
times the maximum feed rate of the feeder and should be refilled
between 8-12 times per hour. For high feed rate feeders, it is
possible to refill up to 25 times per hour. In such cases the refill
should be done from the static hopper using a Metering Valve with
the desired accuracies. This would then be considered as a bulk
feed.
Production and Use of Pre-Blended
Additives
When dealing with a need for blended
product the compounder will be faced with the choice of blending on
site or using a toll processor, however many chemical produces are
finding ways by which seemingly unstable materials can now be
homogenized and stabilized for shipment and storage.
Although the base price of such
blends is higher per pound to purchase, there are great savings to
be made by reducing the number of feeders on each line. If on site
blending is considered, the use of "in-bin" blending systems can
eliminate a lot of dust generation and reduce down time due to
cleaning.
Compounding with Master Batch
In the majority of compounding
applications it is also usual to feed a masterbatch through to the
extruder. Master batch is a highly colored plastic pellet, which is
used, in small quantities with the bulk polymers to achieve
consistency in color. Ingredients are again fed through a mixer and
loss in weight feeder as with other process methods.
Pigment Production - Environmental
and Containment Issues
 Many
of the larger pigment producers specialize in one or two specific
colors. This means that cross contamination of materials during
handling at these facilities should be minimal. Material containment
is though still an important environmental issue and must be
considered during the design of an IBC system and process to ensure
plant cleanliness and operator safety, etc.
It is important to note that some of
these pigments are very expensive and may be in the region of
several hundreds of dollars per pound, therefore any spillage or
dust is undesirable. Using containment filling and discharge the
pigment producer reduces costs in several key areas; waste of
materials, labor, cleaning of equipment and facility, operator
safety with the benefit of increased productivity.
Figure caption: Dust
containment is a major issue particularly with violently colored
pigments and masterbatch producers have perhaps the biggest problem!
Therefore, dust containment from an operator and environment point
of view is important. Pharmaceutical qualities are therefore
applicable and often used in this industry.
Damage to super sacks or bags when
being handling by fork truck, etc. and transportation should also be
considered. Suitable IBC systems should only be considered if they
offer both containment filling and can guarantee the complete
discharge of the material from the container.
Most industries containment is now a
pressing issue. It is extremely important when dealing with
controlled substances highly scented product or high color pigments.
Containment can be expressed in two ways, one that describes cross
contamination this can be measured in ppm (parts per million) the
other is the measure of airborne dust by weight, this is measured in
micrograms per cubic meter. Few discharge aids have the unique
advantages of a cone valve system, where discharge and containment
technology are all built in.
Considerations of Materials
Handling Over Containment
Most additive powders exhibit
difficult flow characteristics. These can be very cohesive and often
subject to rat holing and bridging in static hoppers/containers.
Until recently refill hoppers have almost always been static, or in
a few cases flexible big bags/super sacs have been used. Both these
methods have proven to be unreliable and come with their own house
keeping issues. Where static hoppers are used it is often necessary
to provide external extraction devices to ensure that the powder
discharges from the hopper. These can be in the form of vertical or
horizontal agitators, air jets or external or internal vibrators.
Often these may prove to be ineffective, noisy, degrade or segregate
the product. It is very important that blended materials do not
segregate during the filling and discharging operation.
 Figure
caption: Levels of hygiene and cleanability are much higher at
this end of the industry due the fact that even small trace elements
of say red pigment in a white masterbatch are unacceptable (this
could be 1 ppm). Typically cone valve discharge stations are
produced to pharmaceutical quality, possibly with "Clean In Place"
and/or quick release couplings for "Clean Off Place", these
principles can also be used for the containment transfer system. IBC
wash stations and wash booths are available and are normally used as
part of the overall compounding system to complete an automated and
environmentally friendly production facility.
Where hand filling takes place
splitting sacks and dumping product causes dust issues and debris
must be moved from the area. Also the storage of bags and drums
around the hopper area is an unnecessary hazard. This can be
eliminated with the use of IBC systems Conclusion IBC's throughout
the Plastic compounding chain. It can be seen that there is an
enormous advantage to using IBC technology within the plastics
compounding industry and a further advantage to use cone valve
technology. Difficult to flow product can be accurately and
predictable fed down into Gravimetric feeders, Rigid IBC’s can be
used as blending vessels, containment can be introduced to areas
where environmental conditions dictate and there are no disposal,
housekeeping or ergonomic consideration.
Conclusion - IBC's Throughout the
Plastic Compounding Chain
It can be seen that there is an
enormous advantage to using IBC technology within the plastics
compounding industry and a further advantage to use cone valve
technology. Difficult to flow product can be accurately and
predictable fed down into gravimetric feeders, rigid IBC’s can be
used as blending vessels, containment can be introduced to areas
where environmental conditions dictate and there are no disposal,
housekeeping or ergonomic consideration.
Contact Our Author
Mr. Carl Andrews
General Manager
Matcon USA, Inc.
233 North Delsea Drive
Sewell, New Jersey 08080
Phone:
856-256-1330
Fax: 856-256-1329
Web site:
http://www.matconibc.com/
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