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Feeders: Dosing devices also known as Feeders or Metering Devices, generally
provide for the introduction of a measured amount of material, typically an additive
or colour and regrind to an existing flow or quantity of material into the extruder.
They can be accommodated on the throat of processing machine, where it is
triggered or speed-governed by the processing machine itself or within a fully
automated, multi-component blender. In either case, dosing can be employed by
volume or by weighing.
Volumetric feeders control flow by discharging a consistent volume of material.
They are best used when bulk density is consistent, long term feed accuracy is not
critical, and feeder performance does not need to be documented.
Gravimetric feeders control material flow by weight, for greater feed accuracy, and
therefore require a scale. In addition to improving process quality, gravimetric
feeders can document material content in the end product.
Resin Dryers: Some polymers being hygroscopic in nature need to be heated to a
certain temperature before processing them to allow the moisture to escape and
reduce moulding defects. Methods are:
Industrial Oven: The material is heated by placing them trays and placing the trays
in an industrial oven which heats them to the set temperature. However, this method
is viable only when the batch size is small and where processing machines requiring
large quantities of preheated raw material continuously, industrial ovens become
unviable.
Hopper Dryers: The second method involves the use of a Hopper Dryer which
attaches to a hopper. The dryer consists of three major parts viz. the heater, the
blower, the temperature controller. Hot air flows upward through the hopper
containing the feed pellets removing moisture. This eliminates frequent loading and
unloading of the material as in ovens reducing contaminations, is convenient and
efficient.
Dehumidifying or Desiccant Bed Dryer: A desiccant is a material that attracts and
holds moisture, acts like a sponge drawing moisture from the air. Like other types of
dryers, it heats the air to the specified drying temperature; however, the air is
circulated in a closed-loop system. Desiccant dryers pass moisture-laden air
through a desiccant (a moisture-removing material e.g. silica gel) to produce warm
dry air, which is then passed through the polymer. The air then removes moisture
from the granules and is recycled back to the dryer for further drying and reuse.
Colour Mixers: They are used to dry mix additives, fillers, dry colours (pigments)
and specialty chemicals with the resin to achieve homogeneity before loading to
hopper of machine. Mixers consist of one or two barrels with pulley which is
attached to pulley of motor by rubber belt. On switching on the motor the barrel(s)
starts rotating thus mixing the resin and the pigment inside.
High Speed mixers: They consist of a large tank for holding the plastic raw
material, at the bottom which are the set of high speed mixing blades which are
connected to a pulley - motor assembly. The motor causes the twin blade assembly
at the bottom to rotate which in turn churns the material inside at high speeds. As a
result of this the raw material heats up and the vapour begins to escape. They are
common where recycled plastics are used. Colour may be added to the high speed
mixer itself if needed to eliminate the use colour mixers altogether.

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