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PROCESSING OF THERMOSET RESINS

DIE CASTING:
This is very simple and common method to produce solid part from liquid thermoset
resin. The liquid along with curing agent and other additives is mixed using a glass
rod or mechanical stirrer, is subjected to vacuum to remove bubbles and is poured in
a heated mould to take its shape. The resin is allowed to cure or mould further
heated in oven to complete the crosslinking of resin. Once curing is complete, the
mould is cooled and the sample removed. The mould is made of inexpensive
material like aluminium or plaster of Paris.
ROTATIONAL CASTING:
This process is used to produce hollow products such as balls, dolls others. The
process is similar to Rotational moulding process for thermoplastics except that the
liquid thermoset resin along with curing agent and other additives is used as raw
material. The heated mould is rotated simultaneously on 2 axis to form the product.
The mould is then cooled and opened to remove the product.
COMPRESSION MOULDING
Compression moulding consists of charging a plastics powder or preformed plug
into a heated mould cavity. The mould consists of two halves, the lower half usually
is a cavity (female) and the upper half has a projection (male) which exactly fits into
the cavity when the mould is closed. The material in mould is subjected to heat and
pressure from hydraulic press which gets squeezed or compressed in gap between
the two halves and excess material flows out of the mould as a thin film known as
'flash. The material goes through a chemical change (curing) that causes it to
harden into its desired shape. After curing, the mould opens and the part is ejected.
This technique is used for large mouldings and some sheet products. Compression
moulding is a batch process and is a rather slow process as opposed to continuous
process used to make Radio & appliance knobs, ash trays & electrical parts, utensil
handles, electronic component, and connectors out of thermoset materials.
DMC / SMC: Materials used for CM are either in the form of a dough-like substance
called Dough Moulding Compound (DMC) or in sheet form called Sheet Moulding
Compound (SMC), in form of a plastic sheet that has not been cured. Both forms are
composed of resin, chopped glass fibres, a catalyst and a release agent.
Shaping of SMC/DMC is achieved by placing a measured amount of DMC /SMC into
the heated female mould, (the yoke). The heated male side of the mould (the plug)
closes forcing the material into the mould cavities. The heat from the mould cures
and hardens the compound. When the material has cured and hardened sufficiently,
the plastic moulded product is ejected from the mould.
Compression moulding considerations: Proper amount of material, the
minimum amount of energy required to heat the material, appropriate heating
technique and its time requirement. Predict the force requirement and mould design
to facilitate rapid cooling after material compression.

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