Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR BLOW MOLDING LARGE REINFORCED
PLASTIC PARTS
BACKGROU11TD OF THE INVENTION
The present invention relates to blow molding methods and apparatuses, and,
more
particularly, a blow molding method and apparatus for producing large,
reinforced plastic parts.
Recently, there has been an increase in the demand and applications for large,
molded
plastic parts, specifically parts that are greater than about 2 lbs. in weight
and having a total
surface area of greater than about 400 sq. inches. As a result, some of these
parts have become
l0 quite complex. One example of this can be seen in radiator supports for
automobiles. Design
engineers are now integrating many features into the radiator support to
reduce tooling and
manufacturing costs.
The usefulness of blow molding techniques for forming such parts has not been
practical due to the structural characteristics of the plastic material
conventionally used in
blow molding techniques. That is, the ability to blow molding large complex
parts is limited
by the fact that the parts produced can be only so large or so thin before the
parts lose their
structural integrity and impact resistance.
Heretofore, in order to reinforce various large complex plastic parts, such
parts would
conventionally be reinforced by mineral fillers or glass fibers. However, such
reinforcement
cannot be used effectively in blow molding operations, because the glass
fibers limit parison
expansion characteristics and also have a deleterious effect on the blow
molding assembly
itself. Furthermore, such reinforcement has a deteriorating effect on impact
resistance of the
part.
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SUMMARY OF THE INVENT10N
It is an object of the present invention to overcome the problems noted above.
In achieving this object, the present invention provides a method for blow
molding large,
plastic parts. Accordingly, the present invention provides a method for
molding large parts,
comprising the steps of providing a reinforced plastic melt comprising at
least one
thermoplastic material and reinforcement particles dispersed within the at
least one
thermoplastic material, the reinforcement particles comprising less than 15%
of a total
volume of the plastic melt, and at least 50% of the reinforcement particles
having a thickness
of less than about 20 nanometers, and at least 99% of the reinforcement
particles having a
thickness of less than about 30 nanometers; communicating a tubular formation
of the plastic
melt to a mold assembly having a mold cavity defined by mold surfaces, the
mold surfaces
corresponding to a configuration of the part to be molded, an amount of the
plastic melt
communicated to the mold assembly being sufficient to form a part having a
weight of at least
2 pounds and a total surface area of at least 400 sq. inches; applying
pressurized gas to an
interior of said tubular formation to expand the tubular formation into
conformity with the mold
surfaces; solidifying the plastic melt to form the part; and
removing said part from said mold assembly.
It is also an object of the invention to blow mold particular parts for
automotive
applications, which has heretofore been impractical.
In one embodiment, a substantially hollow, integrally formed radiator and
light support
structure for a motor vehicle is formed from at least one thermoplastic
material and
reinforcement particles dispersed within the at least one thermoplastic
material. The
reinforcement particles comprise less than 15% of a total volume of the
integrally formed
radiator and light support structure, at least 50% of the reinforcement
particles have a
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thickness of less than about 20 manometers, and at least 99% of the
reinforcement particles
have a thickness of less than about 30 manometers. The structure comprises a
radiator frame
portion, having apertures for securing a motor vehicle radiator to the support
structure. A pair
of light receiving recesses of the support structure are constructed and
arranged to mount
headlights for the motor vehicle. The recesses have apertures for receiving
electrical
connecting portions of the lights.
In another embodiment, there is provided a hollow, sealed front end bumper
that
comprises at least one thermoplastic material and reinforcement particles
dispersed
within the at least one thermoplastic material. The reinforcement particles
comprise
less than I S% of a total volume of the bumper, at least 50% of the
reinforcement
particles have a thickness of less than about 20 manometers, and at least 99%
of the
reinforcement particles having a thickness of less than about 30 manometers. A
fluid
consuming component is constructed and arranged to be mounted on and used by
the
motor vehicle. A conduit communicates the fluid consuming component with the
sealed
interior of the hollow bumper, thus permitting said hollow sealed bumper to
serve as a
fluid reservoir for the fluid consuming component.
In another embodiment, there is provided a substantially hollow, integrally
formed bumper and radiator and light support structure assembly for a motor
vehicle.
The assembly is formed from at least one thermoplastic material and
reinforcement
2o particles dispersed within the at least one thermoplastic material. The
reinforcement
particles comprise less than 15% of a total volume of the support structure
assembly,
at least 50% of the reinforcement particles have a thickness of less than
about 20
manometers, and at least 99% of the reinforcement panicles have a thickness of
less
than about 30 manometers. The integrally formed assembly includes i) a hollow
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radiator frame portion, and apertures formed in the frame portion for securing
a motor
vehicle radiator to the frame portion, ii) a pair of light receiving recesses
constructed and
arranged to mount for the motor vehicle. Apertures are formed in the recesses
for
connecting the lights with an electrical power source, and iii) a hollow
bumper portion
constructed and arranged to be mounted to a front end of a motor vehicle.
Other objects and advantages of the present invention will become apparent
from the
following detailed description.
BRIEF DESCRIPTION OF THE DRAWING
to A preferred embodiment of the present invention is described herein with
reference to
the drawing wherein:
FIGS. 1-3 are cross sectional views of a blow molding assembly, and
illustrating various
steps used in a blow molding operation in accordance with one aspect of the
present invention;
FIG. 4 is a perspective view of a blow-molded combination radiator support and
light
IS support structure in accordance with a further aspect of the present
invention;
FIG. 5 is a perspective view of a motor vehicle, with certain components
removed to
better reveal others, and illustrating the combination of a hollow bumper,
fluid consuming
component, and conduit for communicating the bumper with the fluid consuming
component in
accordance with yet a further aspect of the present invention;
20 FIG. 6 is an enlarged perspective view of the front end of the motor
vehicle illustrated in
FIG. 5; and
FIG. 7 is a perspective view of an integral, blow-molded bumper and radiator
support
and headlight support assembly in accordance with yet another aspect of the
present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Illustrated in Figure 1 is a blow molding assembly, generally indicated at 10,
in
accordance with the present invention. The assembly 10 includes an extruder
nozzle 12
connected with a tubular head assembly 14. The tubular head assembly 14 is
provided with
an internal tubular core 18. An ejecting mechanism 24 is disposed in the space
between the
tubular head assembly 14 and the core 18.
A hot plastic melt 20 is supplied through an extruder nozzle 12 into the
tubular head
assembly 14. A hot plastic preform 25 is produced in the cavity between the
core 18 and the
assembly 14. During this process the lower end of the head assembly 14 is
firmly engaged by
1o a movable base plate 26, constituting the upper portion of a hydraulic ram
structure, for
sealing the lower end of the cavity between core 18 and head assembly 14. The
blow
molding assembly further comprises a mold assembly 29, which has internal mold
surfaces
defining a die cavity. The die surfaces correspond to the external surface
shape of the part to
be blow molded. In the preferred embodiment, the mold assembly comprises parts
capable of
relative movement therebetween. More specifically, two mold parts 36 and 37
form side
walls of the die cavity, and the base plate 26 forms the bottom wall when the
base plate 26 is
moved to its lowered position as illustrated in Figure 2.
In operation, the mold assembly 29 starts in the open configuration, as shown
in
Figure 1. The base plate 26 is pressed firmly against the head assembly 14 and
closes the
latter so that the preform 25 can be formed. The movable base plate 26 is then
moved
downwardly to drop a parison 41 of the hot plastic melt 20 (see Figure 2). The
ejecting ram
mechanism 24 can be thrust forward to assist parison formation. At about the
same speed as
the preform 25 is ejected, the base plate 26 is lowered, while supporting the
bottom of the
tubular parison 41, and the second mold assembly 29 is closed. At the same
time,
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compressed air or other gases or vapors under pressure are then blown through
bore 38 in the
core 18, so that the parison 41 is blown out and pressed firmly against the
walls or surfaces 43
defining the cavity 44 of the mold assembly 29, the parison thus assuming the
shape of the
mold cavity. The amount of plastic melt 20 communicated in the form of tubular
parison 41
to the mold assembly is sufficient to form a part having a weight of at least
2 pounds and a
total surface area of at least 400 sq. inches, as the present invention is
primarily concerned
with larger parts of this magnitude. Smaller parts are not benefited vis-a-vis
reinforcement to
the same extent as larger parts (smaller parts usually do not require the same
degree of
structural integrity as larger parts).
1o Preferably, the mold assembly 29 is provided with appropriate water cooling
lines and
a temperature control unit in conventional fashion for regulating the
temperature of the mold
assembly.
After the part 46 has solidified, the mold assembly 29 is opened, and the part
46 is
removed.
In accordance with the present invention, the plastic melt 20 (and thus the
resultant
part) comprises at least one thermoplastic material and reinforcement
particles dispersed
within the at least one thermoplastic material. The reinforcement particles
comprise less than
IS% of a total volume of the plastic melt 20, at least 50% of the
reinforcement particles have
a thickness of less than about 20 nanometers, and at least 99% of the
reinforcement particles
2o have a thickness of less than about 30 nanometers. In accordance with the
method described
above, a tubular formation in the form of parison 41 of the plastic melt is
communicated to the
mold assembly 29. The mold surfaces 43 correspond to a configuration of the
part to be
molded. Pressurized gas is applied through conduit or port 38 to an interior
of the tubular
formation 41 to expand the tubular formation into conformity with the mold
surfaces 43. The
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plastic melt when forced imo conformity with surfaces 43 is then permitted to
solidify (e.g, by
cooling the mold assembly 29) to form the pan 46. The solidified part is then
removed from the
mold assembly 29 and after the mold assembly 29 is opened.
The reinforcement filler particles. also referred to as"nanoparticles" due to
the
magnitude of their dimensions, each comprise one or more generally flat
platelets. Each
platelet has a thickness of between 0.7-1.2 nanometers. Generally, the average
platelet
thickness is approximately 1 nanometer thick. The aspect ratio (which is the
largest
dimension divided by the thickness) for each particle is about 50 to about
300.
The platelet particles or nanoparticles are derivable from larger layered
mineral
1o particles. Any layered mineral capable of being intercalated may be
employed in the present
invention. Layered silicate minerals are preferred. The layered silicate
minerals that may be
employed include natural and artificial minerals. Non-limiting examples of
more preferred
minerals include montmorillonite, vermiculite, hectorite, saponite,
hydrotalcites, kanemite,
sodium octosilicate, magadite, and kenyaite. Mixed Mg and A1 hydroxides may
also be
used. Among the most preferred minerals is montmorillonite.
To exfoliate the larger mineral particles into their constituent layers,
different methods
may be employed. For example, swellable layered minerals, such as
montmorillonite and
saponite are known to intercalate water to expand the inter layer distance of
the layered
mineral, thereby facilitating exfoliation and dispersion of the layers
uniformly in water.
2o Dispersion of layers in water is aided by mixing with high shear. The
mineral particles may
also be exfoliated by a shearing process in which the mineral particles are
impregnated with
water, then frozen, and then dried. The freeze dried particles are then mixed
into molten
polymeric material and subjected to a high sheer mixing operation so as to
peel individual
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t .
1
platelets from multi-platelet particles and thereby reduce the particle sizes
to the
desired range.
The plastic melt 20 utilized in accordance with the present invention are
prepared by combining the platelet mineral with the desired polymer in the
desired
ratios. The components can be blended by general techniques known to those
skilled
in the art. For example, the components can be blended and then melted in
mixers or
extruders. Preferably, the plastic melt 20 is first manufactured into pellet
form. The
pellets are then plasticized in an extruder to form the plastic melt 20 which
is supplied
through extruder nozzle 12.
Additional specific preferred methods, for the purposes of the present
invention, for forming a polymer composite having dispersed therein exfoliated
layered particles are disclosed in U.S. Patent Nos. 5,717,000, 5,747,560,
5,698,624,
and WO 93/1 I 190. Additional background information is disclosed in the
following
U.S. Patent Nos. 4,739,007 and 5,652,284.
Preferably, the thermoplastic used for the purposes of the present invention
is
a polyolefin or a blend of polyolefins. The preferred polyolefin is at least
one
member selected from the group consisting of polypropylene, ethylene-propylene
copolymers, thermoplastic olefins (TPOs), and thermoplastic polyolefin
elastomers
(TPEs).
The exfoliation of layered mineral particles into constituent layers need not
be
complete in order to achieve the objects of the present invention. The present
invention contemplates that at least 50% of the particles should be less than
about 20
nanometers in thickness and, thus, at least 50% of the particles should be
less than
about 20 platelets stacked upon one another in the thickness direction. In
addition, at
least 99% of the reinforcement particles should have a thickness of less than
about 30
nanometers. With this extent of exfoliation, with a loading of less than 15%
by
volume, the benefits of the nanoparticles begin
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to accrue with meaningful effect for many large thin pan applications. For
example, such
loading of nanoparticles will provide a desired increase in the modulus of
elasticity by about
50-70% over conventional fillers.
More preferably, at least 50 % of the particles should have a thickness of
less than 10
nanometers. At this level, an additional increase of about 50-70% in the
modulus of elasticity
is achieved in comparison with the 50% of particles being less than 20
nanometer thick as
discussed above. This provides a level of reinforcement and impact resistance
that would be
highly suitable for most motor vehicle bumper applications.
Preferably, at least 70% of the panicles should have a thickness of less than
5
t0 nanometers, which would achieve an additional 50-70% increase in the
modulus of elasticity
in comparison with the 50% of less than 10 nanometer thickness exfoliation
discussed above.
This provides ideal reinforcement and impact resistance for large thin parts
that must
withstand greater degrees of impart. It is always preferable for at least 99%
of the particles to
a thickness of less than about 30 nanometers (i.e., less than about 30 layers
or platelets thick),
as particles greater than this size act as stress concentrators..
It is most preferable to have as many particles as possible to be as small as
possible,
ideally including only a single platelet.
As noted above, the preferred aspect ratio (which is the largest dimension
divided by
the thickness) for each particle is about 50 to about 300. At least 80% of the
particles should
2o be within this range. If too many particles have an aspect ratio above 300,
the material
becomes too viscous for forming parts in an effective and efficient manner. If
too many
particles have an aspect ratio of smaller than 50, the particle reinforcements
will not provide
the desired reinforcement characteristics. More preferably, the aspect ratio
for each particle is
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between 100-200 . Most preferably, at least 90% of the particles have an
aspect ratio within
the 100-200 range.
Generally, in accordance with the present invention, the plastic melt 20 and
hence the
parts to be manufactured should contain less than 15% by volume of the
reinforcement
particles of the type contemplated herein. The balance of the pan is to
comprise an
appropriate polyolefin material and suitable additives. If greater than 15% by
volume of
reinforcement filler is used, the viscosity of the composition becomes too
high and thus
difficult to mold.
Turning now to FIG. 4, there is shown a substantially hollow, integrally
formed radiator
~ o and light support structure for a motor vehicle, generally indicated at
50, and manufactured in a
blow molding operation in accordance with the present invention. The structure
50 is formed
from at least one thermoplastic material and reinforcement particles dispersed
within the at
least one thermoplastic material. The reinforcement particles comprise less
than 15% of a
total volume of the integrally formed radiator and light support structure 50,
at least 50% of
the reinforcement particles have a thickness of less than about 20 manometers,
and at least
99% of the reinforcement particles have a thickness of less than about 30
manometers. The
structure 50 comprises a radiator frame portion 52, having apertures 54 for
securing a motor
vehicle radiator (not shown for sake of clarity) to the support structure 50.
A pair of light
receiving recesses 56 of the support structure 50 are constructed and arranged
to mount
2o headlights (not shown for sake of clarity) for the motor vehicle. The
recesses 56 having
apertures 58 for receiving electrical connecting portions of the lights.
As shown, the support structure can be nestingly received with respect to a
motor
vehicle fascia, indicated at 60.
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Turning now to FIGS. 5 and 6. there is shown a hollow, sealed front end
bumper, generally indicated at 70. The bumper 70 is shown mounted to the front
end of
a motor vehicle, generally indicated at 7?. The hollow bumper comprises at
least one
thermoplastic material and reinforcement particles dispersed within the at
least one
thermoplastic material. The reinforcement particles comprise less than 15% of
a total
volume of the bumper, at least 50% of the reinforcement particles have a
thickness of
less than about 20 manometers, and at least 99% of the reinforcement particles
have a
thickness of less than about 30 manometers. A fluid consuming component, such
as a
conventional windshield wiper fluid spraying assembly, generally indicated at
74 in FIG.
5, is constructed and arranged to be mounted on and used by the motor vehicle.
A
conduit 76 communicates the fluid consuming component with the sealed interior
of the
hollow bumper 70, thus permitting said hollow sealed bumper to serve as a
fluid
reservoir for the fluid consuming component (e.g., the wiper fluid spraying
assembly
74).
The fluid consuming component to which the bumper 70 is communicated may
be other components in the motor vehicle as well, such as the radiator 78,
which may be
communicated with the interior of the bumper 70 by conduit 80 (see FIG. 5).
It should also be appreciated that the bumper 70 may be divided so as to have
two separate compartments. For example, in FIG. 6 it can be appreciated that
the
interior of bumper 70 is divided into compartments 84 and 86, with the
compartment 84
communicating with the wiper spray assembly 74 via conduit 76, and the
compartment
86 communicating with radiator 78 via conduit 80. Separate compartment filler
necks
88 and 90 are provided for filling compartments 84 and 86, respectively, with
the
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appropriate fluids. Doors 92 and 94 are pivotally mounted close off access to
necks 88
and 90, respectively, and to permit access to the necks when filling is
desired.
Turning now to FIG. 7, there is shown a substantially hollow, integrally
formed bumper
and radiator and light support structure assembly for a motor vehicle,
generally indicated at 100.
The assembly 100 is formed from at least one thermoplastic material and
reinforcement
particles dispersed within the at least one thermoplastic material. The
reinforcement particles
comprise less than 15% of a total volume of the support structure assembly, at
least 50% of
the reinforcement particles have a thickness of less than about 20 nanometers,
and at least
99% of the reinforcement particles having a thickness of less than about 30
nanometers. The
integrally formed assembly includes i) a hollow radiator frame portion 102,
and apertures 104
formed in the frame portion for securing a motor vehicle radiator (not shown
for sake of clarity)
to the frame portion 102, ii) a pair of light receiving recesses 106
constructed and arranged to
mount lights (not shown for sake of clarity of illustration) for the motor
vehicle. Apertures 108
are formed in the recesses 106 for connecting the lights with an electrical
power source, and iii)
a hollow bumper portion 110 constructed and arranged to be mounted to a front
end of a motor
vehicle.
By utilizing plastic melt with the loading of nanoparticles discussed above
(e.g., less
than 15% of a total volume of the plastic melt), higher modulus of elasticity
of conventional
large plastic parts can be achieved, and thus be manufactured with a reduced
wall thickness
2o while maintaining the same required impact resistance. In one example, the
modulus of the
material used to form a bumper is increased to between about 200,000 to about
500,000 PSI.
In accordance with the present invention, by adding the exfoliated platelet
material in
accordance with the above, the modulus of the large, thin part can be
increased without
significantly losing impact resistance. Because the modulus is increased,
large thin parts,
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such as bumpers, can be made thinner than what was otherwise possible. More
specifically,
bumpers for automobiles must have sufficient impact resistance or toughness to
withstand
various standard automotive impact tests.
For example, an automotive bumper must withstand a typical dart (puncture
type)
impact test wherein the bumper will not crack or permanently deform upon
impact of at least
200 inch pounds force at a temperature of -30°C or lower. In a
conventional IZOD impact
test, it is desirable for the bumper to withstand at least 10 ft pounds/inch
at room temperature
and at least 5 ft pounds/inch at -30°C. In order to withstand cracking
at such force levels, the
modulus for the conventional bumper is typically between about 70,000 to about
150,000
t0 pounds per square inch. (PSn. In accordance with the present invention, the
modulus can be
increased by a factor of 2 to 3 times, without significantly effecting the
impact resistance.
In addition to the above mentioned benefits, use of the nanoparticle
reinforced plastic
melt enables the coefficient of linear thermal expansion to be reduced to less
than 40 x 10-6
inches of expansion per inch of material per degree Fahrenheit
(IN/IN)/°F, which is less than
60% of what was previously achievable for thermoplastic motor vehicle bumpers
that meet
the required impact tests. As a further benefit, the surface toughness of the
bumper can be
improved. The improved surface toughness provided by the nanoparticles greatly
reduces
handling damage and part scrap. It also eliminates the need for the extra
packaging and
protective materials and the labor involved.
In addition, it is possible to double the modulus of polymers without
significantly
reducing toughness. Thus, it is possible to produce parts like bumpers using
20-35% thinner
wall sections that will have comparable performance. The use of nanoparticles
can provide
the mechanical, thermal, and dimensional property enhancements, which are
typically
obtained by adding 20-50% by weight of glass fibers or mineral fillers or
combinations
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thereof to polymers. However, only a few percent of nanoparticles are required
to obtain
these property enhancements.
As a result of the fact that such low levels of nanoparticles are required to
obtain the
requisite mechanical properties, many of the typical negative effects of the
high loadings of
conventional reinforcements and fillers are avoided or significantly reduced.
These
advantages include: lower specific gravity for a given level of performance,
better surface
appearance, toughness close to that of the unreinforced base polymer, and
reduced anisotropy
in the molded parts.
It is preferable for these parts to have reinforcement particles of the type
described
1o herein comprising about 2-10% of the total volume of the panel, with the
balance comprising
the polyolefin substrate. It is even more preferable for these exterior panels
to have
reinforcement particles of the type contemplated herein comprising about 3%-5%
of the total
volume of the panel.
In accordance with another specific embodiment of the present invention, it is
contemplated that the blow molding apparatus can be used to make large, highly
reinforced
parts having a modulus of elasticity of 1.000,000 or greater. Conventionally,
these parts
typically require loadings of 25-40% by volume of glass fiber reinforcement.
This amount of
glass fiber loading would result in a high viscosity of any melt pool that
could be used in the
blow molding apparatus of the present invention and would thus render the blow
molding
2o apparatus disclosed herein largely impractical for such application.
Use of the plastic melt 20 as described above enables the blow molding
apparatus
disclosed herein to manufacture large parts that can be provided with impact
resistance
characteristics that were not previously attainable. For example, the blow
molding system of
the present invention is able to manufacture large parts having a modulus of
elasticity of
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greater than 1,000,000 PSI by use of the plastic melt reinforced with loadings
of 8-15% by
volume of nanoparticles, with at least 70% of the nanoparticles having a
thickness of 10
nanometers or less. As with the above described embodiment, the plastic melt
used has
substantially the same material composition as the pan to be manufactured.
In this case of molding large parts with a modulus of elasticity greater than
1,000,000
PSI, it may be desirable to use engineering resins instead of polyolefins.
Such engineering
resins may include polycarbonate (PC), acrylonitrile butadiene styrene (ABS),
a PC/ABS
blend, polyethylene terephthalates (PET), polybutylene terephthalates (PBT),
polyphenylene
oxide (PPO), or the like. Generally, these materials in an unreinforced state
have a modulus
of elasticity of about 300,000 PS1- 350,000 PS1. At these higher loadings of
nanoparticles
(8-15% by volume), impact resistance will be decreased, but to a much lower
extent than the
addition of the conventional 25-40% by volume of glass fibers.
Although certain embodiments of the invention have been described and
illustrated
herein, it will be readily apparent to those of ordinary skill in the art that
a number of
~5 modifications and substitutions can be made to the blow molding system
disclosed and
described herein without departing from the true spirit and scope of the
invention.
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