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Vikas
Shukla
engineeringinsider
The plastic is synthetically produced non-metallic compounds. Plastic
can be moulded into various forms and hardened for commercial use.
The plastic products are easily seen. The plastic products we use like
jars, protective caps, bottles, toys, kitchen utensils, accessories and many
more.
We cannot imagine world without plastic products. The keyboard and
mouse we use is also made with plastic moulding. The plastic part of chairs
which you sit is also made with same process.
The process is just simple. The molten liquid plastic is inserted into
a mould like the plastic bottle. After that it is left for cooling and after
that the final product is ready.
The moulds are used to form various plastic products like cabinets,
barriers, barricades, traffic signage, garden pots and many more.
If you want to start a plastic moulding process, you should have to
understand the different processes first.
Choose one of the plastic moulding processes according to your budget,
resources and expertise. Below there are various processes for plastic
moulding.
Blow Moulding
In the blow moulding process the air pressure is used to inflate the
molten plastic into mould cavity.
This process is used to make one-piece hollow plastic products like
bottles and containers.
The blow moulded items are widely used in consumer beverages and
manufacturers arrange the production for maximum numbers.
The blow moulding process has two steps:
· Starting the process with making the tube of molten plastic called
parison.
· Inflate the parison into the final shape.
The Parison is formed from extrusion or injection moulding techniques.
Extrusion Blow Moulding
Manufacturers used extrusion blow moulding for high-production
operations for making plastics bottles. The process is automatic and combines
with operations like bottle filling and labelling. The blown containers must be
rigid. The rigidity is depends on various factors like wall thickness.
The extrusion blow moulding process contains below steps.
· Extrude the Parison.
· Cut the Parison from top and seal at the bottom and the two halves of
mould come together.
· After inflate the plastic tube took the mould cavity’s shape.
· Open the mould and remove final product.
Injection Moulding
The injection blow moulding process contains the injection of mould
the parison instead of extrusion. It has low production rate then the extrusion
process.
The process has below steps.
· Injection-mould the parison around a blowing rod.
· The parison is transferred to a blow mould.
· Inflate the soft polymer to the mould.
· Open the mould and remove the product.
Stretch Blow Moulding
The manufacturers use the variations of injection blow moulding known
as stretch blow moulding.
In this technique the blowing rod is extending downward into the
injection moulded parison and this stretch the plastic and create a more
stressing of polymer than conventional injection blow moulding.
The final product is more rigid, higher transparency and it is more
impact-resistant.
The Polyethylene terephthalate (PET) is most widely used material for
plastic injection moulding.
The PET is polyester with low permeability and the stretch-blow-moulding
process gives strength and it is ideal for making containers for carbonated
beverages.
The Stretch blow moulding steps:
· Injection moulding
· Stretching
· Blowing
Blow Moulding Materials and Products
The polyethylene (PE) is a ideal for blow moulding process as it has
high density and high molecular weight polyethylene.
Materials used for blow moulding:
· Polypropylene
· Polyvinylchloride (PVC)
· Polyethylene terephthlate
Rotational Moulding
Rotational moulding or rotomoulding use gravity inside a ratatin mould
to create a hollow form.
This technique is used also as an alternative of blow moulding to make
large, hollow shape.
This is used for thermosplastic polymers but now thermoset and
elastomer are more common.
The rotomoulding is better than blow moulding for more complex
external geometries, large parts and for lower production quantities.
The rotomoulding process has below steps.
· First load a predetermined amount of polymer powder into a split mould
cavity.
· Heating and rotating the mould on two perpendicular axes so the powder
can coat the mould’s internal surfaces equally and make sure to make uniform
thickness layer.
· Open the mould and unload the ready product.
The speed during process is slow. The process is done with gravity not
with centrifugal force and this coat the mould surfaces.
The Rotomolding Moulds
The rotomoulding process is simple and less expensive than injection
moulding and blow moulding. But the production cycle took more time around 10
minutes. To minimize time there is three station moulding machine.
First Station – In this station, unloading of final product and load
the powder for next step in the cavity.
Second Station – Heating station where hot-air convection heats the
mould as rotate and temperature inside reaches up to 375o C depends on polymer
and item moulded.
Third Station – The third station is cooling station that cools the
mould with cold air or spray of water to solidify the plastic moulding inside.
The products are made with rotational moulding.
Toys, Boat and canoe hulls, Sandboxes, small swimming pools, Buoys and
other floatation items, truck body parts, automotive dashboard, fuel tanks.
Furniture, garbage cans, fashion mannequins, containers, storage tanks and many
more.
The material used for roto moulding
· Polyethylene, mainly HDPE
· Polyproplene
· Acrylonitrile butadiene styrene (ABS)
· High-impact polystyrene
The plastic moulding process is technical process which cannot be done
by everyone. It requires knowledge about various materials and knows the
process in every stage.
So it is advisable to study the business and market of your final
product.
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Blow Moulding |
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