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heated before introduction into a mould to remove moisture content. These moulds
can be simple designs or have intricate patterns. If choosing a press, it is important to
ensure that the platens and daylight (mould-opening height) can be accommodated.
The hot material becomes malleable and takes the set pattern of the mould easily.
The moulded part is cooled inside the mould and then removed. If the raw material
is in powder form there could be flash (excess material) that must be trimmed or
buffed. Most presses are usually hydraulic because high pressure is often required
for moulding.
In general, only solid parts are moulded so the density and material distribution will
be consistent throughout each moulded part. It is also possible to have a multi-cavity
mould to produce many smaller parts that can be assembled into one large part later.
12.3 Brief History of Compression Moulding
In 1847, a plastic processing company was the first use compression moulding to
mould small parts, particularly for domestic purposes. Undoubtedly, the machines
would have been hand-operated ones and steam would have been heating medium. By
the early 1900s, compression moulding had come a long way, with much-improved
technology, and plastic product processors had begun to use thermosetting resins.
Before that, the resin materials used in compression moulding were shellac-based
thermoplastics. The first patented compression-moulding machine with a huge
development in technology was in the 1930s. However, even these machines can be
barely compared with modern machines, which are well advanced in technology, more
efficient and available in manual, semi-automatic or automatic operation.
12.4 Raw Materials for Compression Moulding
As the prices of polymer resins continue to increase, manufacturers of plastic products
have been looking for more cost-effective pathways. For compression moulders, the
availability of thermoplastic PCRH and thermosetting PCRH ash will solve this
problem to a great extent. Both types of resins will give products with better properties
and be less expensive.
12.4.1 Thermoplastic Polymeric Composite Resins
It is more common to thermosetting resins than thermoplastic resins in compression
moulding, but new technology is making it possible to use PCRH. For ease of
moulding, these composite resins are available in the form of pellets in their
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