In Awanti Polymoulds is
a Mould Makers in Pune, India
we mainly working on blow moulding is the process of forming a molten tube of
thermoplastic material i.e. Polymer or resin) & placing the parison or
preform within a mould cavity and inflating the tube with compressed air, to
take the shape of the cavity and cool the part before removing from the mould.
Any hollow thermoplastic part can be blow moulded.
Parts are not just limited to bottles, where there is one opening
and it is usually smaller in diameter or size than the overall body
dimensions. These are some of the most common shapes used in consumer
packaging, however there are other typical types of blow moulded parts,
including, but not limited to:
- Industrial
bulk containers
- Lawn, garden
and household items
- Medical
supplies and parts, toys
- Building
industry products
- Automotive-under
the hood parts
- Appliance components
History of
Blow Moulding
The actual concept or theory of blow moulding came from the glass blowing
process. As early as the 1880’s there was a patented method of extruding
a Celluloid polymer into a parison and blow moulding a part. Early
methods and materials to blow plastics into shapes were very crude and not
suitable for mass production. It wasn’t until the late 1930’s that the
first commercial machines and products were developed for the manufacturing of
blow moulded bottles. The major event that triggered and fuelled the
early years of commercial blow moulding was the development of low and high
density polyethylene suitable for blow moulding and consumer packages.
From this, there was an explosion of blow moulded products and equipment in
both Europe and North America.
Blow Moulding
Manufacturing Processes
There are three main types of blow moulding:
- Extrusion
blow moulding
- Injection
blow moulding
- Injection stretch blow moulding
The main differences among them are the method of forming the
parison; either by extrusion or injection moulding, the size of the parison and
the method of movement between the parison and blow moulds; either stationary,
shuttling, linear or rotary.
In Extrusion Blow Moulding-(EBM) the
polymer is melted and the solid extruded melt is extruded through a die to form
a hollow tube or parison. Two halves of a cooled mould are then
closed around the parison, pressurized air is introduced through a pin or
needle, inflating it into the shape of mold, thus producing a hollow
part. After that all hot plastic has cooled at required stage, the mould
is opened and the part is removed.
In EBM there are two basic methods of extrusion, Continuous and
Intermittent. In continuous, the parison is extruded continuously and the
mould moves to and away from the parison. In Intermittent, plastic is
accumulated by the extruder in a chamber, then forces through the die to form
the parison. The molds are typically stationary under or around the
extruder.
Let’s take a ex. of the Continuous Process are Continuous Extrusion
Shuttle machines and Rotary Wheel machines. Intermittent extrusion
machines can be Reciprocating Screw or Accumulator Head. Various factors
are considered when selecting between the processes and the size or models
available.
Ex. of parts made by the EBM process include many hollow products,
such as bottles, industrial parts, toys, automotive, appliance components and
industrial packaging.
With respect to the Injection Blow Systems – (IBS) process,
the polymer is injection molded onto a core within a cavity to form a hollow
tube called a preform. The preforms rotate on the core rod to the blow mould
or moulds at the blowing station to be inflated and cooled. This process
is typically used to make small bottles, usually 16oz/500ml or less at very
high outputs. The process is divided into three steps: injection, blowing
and ejection, all done in an integrated machine. Parts come out with
accurate finished dimensions and capable of holding tight tolerances—with no
extra material in the formation it is highly efficient.
Ex. Of IBS parts are
pharmaceutical bottles, medical parts, and cosmetic and other consumer product
packages.
Injection
Stretch Blow Moulding- (ISBM) the Injection Stretch Blow
Moulding- (ISBM) process is similar to the IBS process described above, in
that the preform is injection moulded. The moulded preform is then
presented to the blow mould in a conditioned state, but before final blowing of
the shape, the preform is stretched in length as well as radially. The
typical polymers used are PET and PP that have physical characteristics that
are enhanced by the stretching part of the process. This stretching gives
the final part improved strength and barrier properties at much lighter weights
and better wall thicknesses than IBS or EBM—but, not without some limits such
as handled containers, etc.. ISBM can be divided into the One
Step and Two Step process.
In the One Step process both preform manufacture and
bottle blowing are performed in the same machine. This can be done in
three or four station machines, (Injection, Conditioning, Blowing and
Ejection). This procedure and equipment can handle low to high volumes of
various shape and size bottles.
In the Two Step process the plastic is first moulded
into the preform using an injection moulding machine separate from the blow moulder.
These are produced with the necks of the bottles, including threads on the open
end of the closed end hollow preform. These preforms are cooled, stored,
and fed later into a re-heat stretch blow moulding machine. In the Two
Step Reheat Blow process, the preforms are heated (typically using infrared
heaters) above their glass transition temperature, then stretched and blown
using high-pressure air in the blow moulds.
The Two Step process is more suited to very high volumes of
containers, 1 litter and under, with very conservative use of resin providing
great strength, gas barrier and other features.
Materials
suitable for Blow Moulding
Examples of Blow Moulding Polymers in single layer or multiple
layer structures or combinations include such materials as: (i) High Density
Polyethylene, (ii) Low density Polyethylene, (iii) Polypropylene, (iv)
Co-polyester, (v) PET, (vi) PVC, (vii) Nylon, (viii) EVOH, (ix) EVA, (x TPE,
(xi) COP and COC, (xii) Polycarbonate, (xiii) Polystyrene, (ix) ABS, etc
Awanti
Polymoulds is a brand in High Speed Bottle Mould Manufacturing
in India
and plus it is an industry leader in blow moulding. No other partner
offers our comprehensive family of technologies to perfectly match your
application needs. For more information visit our website
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