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Polymeric Processing Techniques
MDP 462
Lecture 9
Blow Molding
Both of extrusion and injection molding processes are used to
make hollow, seamless parts out of thermoplastic polymers.
It is a molding process in which air pressure is used to inflate
soft plastic into a mold cavity
It is an important industrial process for making one-piece
hollow plastic parts with thin walls, such as bottles and similar
containers
Since many of these items are used for consumer beverages for
mass markets, production is typically organized for very high
quantities
The technology is borrowed from the glass industry with which
plastics compete in the disposable or recyclable bottle market
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Blow molding is accomplished in two steps:
Fabrication of a
Inflation of the
starting tube of
tube to the
molten plastic,
desired final
called a
shape
parison/preform
Preform
Hollow (usually circular) pipe section
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Forming the
parison/preform
Injection
Extrusion
molding
Bottle Forming
Extrusion Injection Stretch blow
blow molding blow molding molding
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(1)extrusion of parison;
(2) parison is pinched at the top and sealed at the bottom around a metal
blow pin as the two halves of the mold come together;
(3) the tube is inflated so that it takes the shape of the mold cavity;
(4) mold is opened to remove the solidified part
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The Excess
When a bottle is produced using this blow molding
method, excess material is created when the mold closes
around the parison.
Flash at the bottom (called the tail), the top (the moil),
and for handled ware - a “handle slug” needs to be
trimmed.
Typically, the flash is removed upon mold release
(trimmed in mold) to complete a finished bottle or jar.
to complete a finished bottle or jar.
For bottle with handles (handle ware), offset neck and
special circumstances, the flash is extracted via a
secondary operation downstream.
Blow molded trash can being removed from mold (before
final trimming)
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Identifying EBM Bottles
Bottles are easily identifiable by their pinch
off line across the base of the bottle
This 'line' is created as the mold cavity closes
on the parison and the tail is trimmed off
Extrusion Blow Molding
Equipment
Intermittent Continuous
extrusion extrusion
equipment equipment
Reciprocating Accumulator Rotary Shuttle
screw machinery head machinery machinery machinery
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https://www.youtube.com/watch?v=Ylfv_2RnFwo
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Rotary Method Blow Molding
Several to dozens of molds are clamped to a rotating wheel,
which revolves to enable the parison to be supplied into each
mold in a continuous sequence. The mold is closed and air is
blown in to form the parts shape
To make large quantities of
product;
Size of mold can be range
from small bottles up to 30
liter drum;
Multiple molds and parisons
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Labeling
Advantages
Lower mold costs compared to ISBM or IBM and the capability of
forming handles.
Multi-layer capability, EBM bottles can have up to 7 layers of
materials that include virgin plastic resin layers that encase a post-
consumer recycled layer, barrier layer, and adhesive layers to bond
the other layers together.
Other capabilities unique to EBM includes IML (in mold labeling),
window stripe on bottles, angled and offset necks, handle ware, and
multiple necks.
In terms of logistics and cost benefits, EBM mold fabrication time is
often shorter and relatively inexpensive compared to other blow
molding methods, and many EBM manufacturers have
interchangeable mold parts which allow the same bottle to be
molded with different neck finishes, body, or embossment inserts.
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Bottle Forming
Extrusion Injection Stretch blow
blow molding blow molding molding
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Injection Blow Molding
In this process, the starting parison is injection molded
rather than extruded.
(1) parison is injected molded around a blowing rod;
(2) Injection mold is opened and parison is transferred to a blow mold;
(3) soft polymer is inflated to conform to the blow mold; and
(4) blow mold is opened, and blown product is removed.
Injection
Blow
Molding
Machine
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“Zero Cooling” design moves preform cooling from
the injection station to the conditioning station,
allowing for overlapping cooling and injection of a
new shot
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In Injection Blow Molding
A preform, that is Because the neck and
injection molded first, threads are injection
looks like a miniature molded when the
version of the final preform is made, they
product, comprised of are produced very
the finished size neck accurately, enabling
with threads and a an excellent seal with
small, thick walled the cap, also known as
lower section, which the closure (all
will be blown into the closures are injection
final shape. molded), which means
an excellent leak-
proof-seal
Injection Blow Molding
Compared to its extrusion-based competitor, injection
blow molding usually has the following advantages:
(1) higher production rate,
(2) greater accuracy in the final dimensions,
(3) less wasteful of material
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Injection vs. Extrusion Blow Molding
Injection blow molding is often preferred for small,
complex bottles, such as those in medical applications.
Larger containers can be produced with extrusion blow
molding because the mold in injection molding is so
expensive for large preform.
Also, extrusion blow molding is technically more feasible
and economical for multi-layer bottles used for storing
certain medicines, personal care products, and various
chemical compounds.
Bottle Forming
Extrusion Injection Stretch
blow blow blow
molding molding molding
Single- Two- stage
stage
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Stretch blow molding is best known for producing PET bottles
commonly used for water, juice and a variety of other products.
Stretch blow molding has been used since the early 1970's and has
grown in existence with the primary use for making carbonated
beverage bottles.
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Stretch Blow
Molding
One of the major advantages of
stretch blow molding is the ability to
stretch the preform in both the hoop
direction and the axial direction
This biaxial stretching of material
increases the tensile strength, barrier
properties, drop impact, clarity, and
top load in the container
With these increases it is usually
possible to reduce the overall weight
in a container by 10 to 15 percent less
then when producing a container in
another way
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Single-Stage, Three-Stations Injection
Stretch Blow Molding Machines
https://www.youtube.com/watch?v=AAvOYz7qOsw
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Two-stage stretch blow molding
In this process, the machinery
injection molds a preform, which is This allows companies to either
then transferred within the machine to make or buy their own
another station where it is blown and preforms.
then ejected from the machine.
Because of the relatively high
This type of machinery is generally cost of molding and equipment,
called injection stretch blow molding this is the best technique for
(ISBM) and usually requires large producing high volume items
runs to justify the very large expense such as carbonated beverage
for the injection molds to create the bottles.
preform and then the blow molds to
finish the blowing of the container.
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The preform is already injected molded in first
stage
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Presentation
One can easily identify the difference by looking at
the bottom of the bottle. If u see a circular dimple it
means it is IBM and if u see a line at the bottom
then it is EBM
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EBM VS IBM
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