Note: Descriptions are shown in the official language in which they were submitted.
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Low-Pressure Molding System
Disclosed herein is also a method of extrusion molding at low, substantially
constant
melt pressures. Embodiments of the disclosed method now make possible a method
of
extrusion that gives a better and more consistent product then a conventional
extrusion
process also resulting in a more energy and cost effective than conventional
extrusion
molding processes. Embodiments of the disclosed method surprisingly allow for
the
filling of an extrusion mold cavity at lower melt pressure and e.g. having a
longer mold
profile with cooling build in enabling a straighter and more consistent
extruded profile
with less sink and a more homogenic material composition.
Furthermore, it is possible that a constant pressure method could enable a
better
temperature control/profile of the plastic during the extrusion molding
process.
Furthermore, a new innovative hot runner system having at least one cold
runner
portion in a mold component and/or mold part that is reheated during every
molding
cycle before injection of the next portion molten plastic material e.g. using
conductive
heating in whole or in part this heating form often having a short heating
processes
lasting for less than half a second.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to extrusion molding machines and methods of
producing
extrusion molded parts and, more particularly, to extrusion molding machines
that adjust
operating parameters of the extrusion molding machine during an extrusion
molding run
to account for changes in material properties and pressures of the extrusion
material
and methods of accounting for changes in extrusion molding material properties
during
an extrusion molding run and/or compounding of materials.
Disclosed herein is also a method of extrusion molding at low, substantially
constant
melt pressures. Embodiments of the disclosed method now make possible a method
of
extrusion that gives a better and more consistent product then a conventional
extrusion
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process also resulting in a more energy and cost effective than conventional
extrusion
molding processes. Embodiments of the disclosed method surprisingly allow for
the
filling of an extrusion mold cavity at lower melt pressure and e.g. having a
longer mold
profile with cooling build in enabling a straighter and more consistent
extruded profile
with less sink and a more homogenic material composition.
Furthermore, it is possible that a constant pressure method could enable a
better
temperature control/profile of the plastic during the extrusion molding
process.
Furthermore, a new innovative hot runner system having at least one cold
runner
portion in a mold component and/or mold part that is reheated during every
molding
cycle before injection of the next portion molten plastic material e.g. using
conductive
heating in whole or in part this heating form often having a short heating
processes
lasting for less than half a second.
1. Field of the Disclosure
The present disclosure relates to methods for extrusion molding, injection
molding and
blow molding, more particularly, to methods for extrusion molding at low,
substantially
constant melt pressures and controlling viscosity and melt temperature e.g.
supported
by pressure and shear heat measured before and/or after a breaker plate/plates
placed
in the extruder, injection unit and/or in a hot runner manifold where the size
and
geometry of the holes in the breaker plate/plates enables this e.g. combined
with the
breaker plate/plates being temperature controlled by heat and/or cooling
and/or
adjustable in flow hole size during the molding process. This novel process
will also
enhance the mixing of compounded materials as well as the separation of
different/contaminated plastics e.g. in recycled plastics materials.
Furthermore, a new innovative hot runner system having at least one cold
runner
portion in a mold component and/or mold part that is reheated during every
molding
cycle before injection of the next portion molten plastic material e.g. using
conductive
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heating in whole or in part this heating form often having a short heating
processes
lasting for less than half a second.
2. Brief Description of Related Technology that can be improved by the
disclosed
inventions.
Plastics extrusion is a high-volume manufacturing process in which raw plastic
is
melted and formed into a continuous profile. Extrusion produces items such as
pipe/tubing, weather-stripping, fencing, deck railings window frames, plastic
films and
sheeting, thermoplastic coatings, and wire insulation.
This process starts by feeding plastic material (pellets, granules, flakes or
powders)
from a hopper into the barrel of the extruder. The material is gradually
melted by the
mechanical energy generated by turning screws and by heaters arranged along
the
barrel. The molten polymer is then forced into a die, which shapes the polymer
into a
shape that hardens during cooling.
In the extrusion of plastics, the raw compound material is commonly in the
form of
nurdles (small beads, often called resin) that are gravity fed from a top
mounted
material hopper into the barrel of the extruder. Additives such as colorants
and UV
inhibitors (in either liquid or pellet form) are often used and can be mixed
into the resin
prior to arriving at the hopper. The process has much in common with plastic
injection
molding from the point of the extruder technology, although it differs in that
it is usually a
continuous process. While pultrusion can offer many similar profiles in
continuous
lengths, usually with added reinforcing, this is achieved by pulling the
finished product
out of a die instead of extruding the polymer melt through a die.
The material enters through the feed throat (an opening near the rear of the
barrel) and
comes into contact with the screw. The rotating screw (normally turning at
e.g. 120 rpm)
forces the plastic beads forward into the heated barrel. The desired extrusion
temperature is rarely equal to the set temperature of the barrel due to
viscous heating
and other effects. In most processes, a heating profile is set for the barrel
in which three
or more independent P ID-controlled heater zones gradually increase the
temperature of
the barrel from the rear (where the plastic enters) to the front. This allows
the plastic
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beads to melt gradually as they are pushed through the barrel and lowers the
risk of
overheating which may cause degradation in the polymer.
Extra heat is contributed by the intense pressure and friction taking place
inside the
barrel. In fact, if an extrusion line is running certain materials fast
enough, the heaters
can be shut off and the melt temperature maintained by pressure and friction
alone
inside the barrel. In most extruders, cooling fans are present to keep the
temperature
below a set value if too much heat is generated. If forced air cooling proves
insufficient
then cast-in cooling jackets are employed.
At the front of the barrel, the molten plastic leaves the screw and travels
through a
screen pack to remove any contaminants in the melt. The screens are reinforced
by a
breaker plate (a thick metal puck with many holes drilled through it) since
the pressure
at this point can exceed 5,000 psi. The screen pack/breaker plate assembly
also serves
to create back pressure in the barrel. Back pressure is required for uniform
melting and
proper mixing of the polymer, and how much pressure is generated can be
"tweaked"
by varying screen pack composition (the number of screens, their wire weave
size, and
other parameters). This breaker plate and screen pack combination also
eliminates the
"rotational memory" of the molten plastic and creates instead, "longitudinal
memory".
Breaker plates are essentially required in extruders to cover filter screens
and provide
uniform melting and mixing of the polymer before entering the extrusion mold.
The
number of holes, the diameter of the holes and the thickness of the breaker
plates has a
direct impact on the time required for the forming process.
The use of breaker plates in the extrusion process serve a dual purpose, i.e.,
create a
seal between the extruder barrel and, secondly, allow a means of building back
pressure through the use of screen packs.
However, sometimes deleterious effects take place because the screen are too
fine and
filter out some of the compound ingredients causing back pressure to escalate
during
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the course of a production run.
The remedy is to design a breaker plate with the same surface, i.e., smaller
holes and
less of them to achieve the same back pressure without screens!
Optimized breaker plates can be design with maximized number of holes e.g. of
different sizes. Providing different hole configurations for a given break
plate geometry,
the optimized design can be evaluated for stress distribution and deformation
under
different molding/extrusion conditions in different plastic materials and/or
compounded
plastic materials homogeneities/consistency in output.
The edge to edge thickness between the successive holes was also crucial, to
avoid
excessive deformation due to stress generation. With consecutive iterations
considering
the different parameters, three optimized breaker plate designs were proposed
possessing maximum number of holes as well as maintaining the stress and
deformation values within the allowable limits.
After passing through the breaker plate molten plastic enters the extrusion
mold. The
mold is what gives the final product its profile and must be designed so that
the molten
plastic evenly flows from a cylindrical profile, to the product's profile
shape. Uneven flow
at this stage can produce a product with unwanted residual stresses at certain
points in
the profile which can cause warping upon cooling. A wide variety of shapes can
be
created, restricted to continuous profiles.
The product must now be cooled, and this is usually achieved by pulling the
extrudate
through a water bath. Plastics are very good thermal insulators and are
therefore
difficult to cool quickly. Compared to steel, plastic conducts its heat away
2,000 times
more slowly. In a tube or pipe extrusion line, a sealed water bath is acted
upon by a
carefully controlled vacuum to keep the newly formed and still molten tube or
pipe from
collapsing. For products such as plastic sheeting, the cooling is achieved by
pulling
through a set of cooling rolls. For films and very thin sheeting, air cooling
can be
effective as an initial cooling stage, as in blown film extrusion.
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Plastic extruders are also extensively used to reprocess recycled plastic
waste or other
raw materials after cleaning, sorting and/or blending. This material is
commonly
extruded into filaments suitable for chopping into the bead or pellet stock to
use as a
precursor for further processing.
Normally there are five possible zones in a thermoplastic screw. Since
terminology is
not standardized in the industry, different names may refer to these zones.
Different
types of polymer will have differing screw designs, some not incorporating all
of the
possible zones.
Most screws have these three zones:
= Feed zone (also called the solids conveying zone): this zone feeds the
resin into the
extruder, and the channel depth is usually the same throughout the zone.
= Melting zone (also called the transition or compression zone): most of
the polymer is
melted in this section, and the channel depth gets progressively smaller.
= Metering zone (also called the melt conveying zone): this zone melts the
last
particles and mixes to a uniform temperature and composition. Like the feed
zone,
the channel depth is constant throughout this zone.
In addition, a vented (two-stage) screw has:
= Decompression zone. In this zone, about two-thirds down the screw, the
channel
suddenly gets deeper, which relieves the pressure and allows any trapped gases
(moisture, air, solvents, or reactants) to be drawn out by vacuum.
. Second metering zone. This zone is similar to the first metering zone,
but with
greater channel depth. It serves to re-pressurize the melt to get it through
the
resistance of the screens and the die.
Often screw length is referenced to its diameter as L:D ratio. For instance, a
6-inch
(150 mm) diameter screw at 24:1 will be 144 inches (12 ft) long, and at 32:1
it is
192 inches (16 ft) long. An L:D ratio of 25:1 is common, but some machines go
up to
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40:1 for more mixing and more output at the same screw diameter. Two-stage
(vented)
screws are typically 36:1 to account for the two extra zones.
Each zone is equipped with one or more thermocouples in the barrel wall for
temperature control. The "temperature profile" i.e., the temperature of each
zone is very
important to the quality and characteristics of the final extrudate.
Typical plastic materials that are used in extrusion include but are not
limited to:
polyethylene (PE), polypropylene, acetal, acrylic, nylon (polyamides),
polystyrene,
polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS) and
polycarbonate.
The manufacture of plastic film for products such as shopping bags and
continuous
sheeting is achieved using a blown film line.
This process is the same as a regular extrusion process up until the die.
There are three
main types of dies used in this process: annular (or crosshead), spider, and
spiral.
Annular dies are the simplest and rely on the polymer melt channeling around
the entire
cross section of the die before exiting the die; this can result in uneven
flow. Spider dies
consist of a central mandrel attached to the outer die ring via a number of
"legs"; while
flow is more symmetrical than in annular dies, a number of weld lines are
produced
which weaken the film. Spiral dies remove the issue of weld lines and
asymmetrical flow
but are by far the most complex.
The melt is cooled somewhat before leaving the die to yield a weak semi-solid
tube.
This tube's diameter is rapidly expanded via air pressure, and the tube is
drawn
upwards with rollers, stretching the plastic in both the transverse and draw
directions.
The drawing and blowing cause the film to be thinner than the extruded tube,
and also
preferentially aligns the polymer molecular chains in the direction that sees
the most
plastic strain. If the film is drawn more than it is blown (the final tube
diameter is close to
the extruded diameter) the polymer molecules will be highly aligned with the
draw
direction, making a film that is strong in that direction, but weak in the
transverse
direction. A film that has significantly larger diameter than the extruded
diameter will
have more strength in the transverse direction, but less in the draw
direction.
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In the case of polyethylene and other semi-crystalline polymers, as the film
cools it
crystallizes at what is known as the frost line. As the film continues to
cool, it is drawn
through several sets of nip rollers to flatten it into lay-flat tubing, which
can then be
spooled or slit into two or more rolls of sheeting.
Sheet/film extrusion is used to extrude plastic sheets or films that are too
thick to be
blown. There are two types of dies used: T-shaped and coat hanger. The purpose
of
these dies is to reorient and guide the flow of polymer melt from a single
round output
from the extruder to a thin, flat planar flow. In both die types ensure
constant, uniform
flow across the entire cross-sectional area of the die. Cooling is typically
by pulling
through a set of cooling rolls. In sheet extrusion, these rolls not only
deliver the
necessary cooling but also determine sheet thickness and surface texture.
Often co-
extrusion is used to apply one or more layers on top of a base material to
obtain specific
properties such as UV-absorption, texture, oxygen permeation resistance, or
energy
reflection.
A common post-extrusion process for plastic sheet stock is thermoforming,
where the
sheet is heated until soft (plastic) and formed via a mold into a new shape.
When
vacuum is used, this is often described as vacuum forming. Orientation (i.e.
ability/
available density of the sheet to be drawn to the mold which can vary in
depths from 1
to 36 inches typically) is highly important and greatly affects forming cycle
times for
most plastics.
Extruded tubing, such as PVC pipes, is manufactured using very similar dies as
used in
blown film extrusion. Positive pressure can be applied to the internal
cavities through
the pin, or negative pressure can be applied to the outside diameter using a
vacuum
sizer to ensure correct final dimensions. Additional lumens or holes may be
introduced
by adding the appropriate inner mandrels to the die.
Multi-layer tubing applications are also ever present within the automotive
industry,
plumbing & heating industry and packaging industry.
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Over jacketing extrusion allows for the application of an outer layer of
plastic onto an
existing wire or cable. This is the typical process for insulating wires.
There are two different types of die tooling used for coating over a wire,
tubing (or
jacketing) and pressure. In jacketing tooling, the polymer melt does not touch
the inner
wire until immediately before the die lips. In pressure tooling, the melt
contacts the inner
wire long before it reaches the die lips; this is done at a high pressure to
ensure good
adhesion of the melt. If intimate contact or adhesion is required between the
new layer
and existing wire, pressure tooling is used. If adhesion is not
desired/necessary,
jacketing tooling is used instead.
Coextrusion is the extrusion of multiple layers of material simultaneously.
This type of
extrusion utilizes two or more extruders to melt and deliver a steady
volumetric
throughput of different viscous plastics to a single extrusion head (die)
which will
extrude the materials in the desired form. This technology is used on any of
the
processes described above (blown film, over-jacketing, tubing, sheet). The
layer
thicknesses are controlled by the relative speeds and sizes of the individual
extruders
delivering the materials.
In many real-world scenarios, a single polymer cannot meet all the demands of
an
application. Compound extrusion allows a blended material to be extruded, but
coextrusion retains the separate materials as different layers in the extruded
product,
allowing appropriate placement of materials with differing properties such as
oxygen
permeability, strength, stiffness, and wear resistance.
Co-extrusion can also be defined as the process in which two or more plastic
materials
are extruded through a single extrusion mold. In this process, two or more
orifices are
arranged in such a manner that the conjoint merging and welding of the
extrudates
takes place and before chilling, a laminar structure form. In co-extrusion, a
separate
extruder is used to fed every material to the extrusion mold but the orifices
can be
arranged in such a manner that each extruder provides two or more plies of the
same
material.
Co-extrusion may be employed in the processes of Film Blowing, Extrusion
Coating,
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and Free Film Extrusion. The general benefit of the co-extrusion process is
that every
laminate ply imparts a required characteristic property like heat-sealability,
stiffness, &
impermeability, all of which are impossible to attain by using any single
material.
It is evident that co-extrusion is a better process than a single layer
extrusion. For
instance, in the vinyl fencing industry, co-extrusion process is used for
tailoring the
layers on the basis of whether these are exposed to weather or not. Generally,
compound's thin layer is extruded that contains high-priced weather resistant
additives.
This extrusion is done on the outside, whereas inside there is an additive
package
which is more suitable for the structural performance and impact resistance.
Advantages Of Co-extrusion
According to various internationally established and popular companies that
are using
the co-extrusion process continuously in their production procedures, there
are a
number of advantages of this process. Some of these advantages are listed
below:
= High quality mono-layer extrusion coatings in larger varieties of line
speeds and
widths
= Use of lower cost materials for filling purpose, assists in saving on the
amount of
qualitative resins
= Capability of making multi-layer as well as multi-functional structures that
too in a
single pass
= Reduction in the number of steps required in general extrusion process
= Provides targeted performance with the use of definite polymers in
particular
layers
= Reduction in setup and trim scrap
= Potential for use of a recycle layer
Disadvantages of Co-extrusion
As per a number of globally reckoned companies, there are some disadvantages
related with the process of co-extrusion. Some of these disadvantages are as
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= Minor differences in physical properties are responsible for making a
combination
desirable, but these differences are also responsible for making the
combination
incompatible
= For this process, polymers must have similar melt viscosities to sustain
a laminar
flow. All the viscosity differences may be more or less tolerable, according
to the
material location inside the composite structure along with the layers
thinness
= Requires more sophisticated extruder and its operator. This implies extra
maintenance cost of the equipment.
= Demands considerable planning as well as forethought in the system design
Extrusion coating is using a blown or cast film process to coat an additional
layer onto
an existing roll-stock of paper, foil or film. For example, this process can
be used to
improve the characteristics of paper by coating it with polyethylene to make
it more
resistant to water. The extruded layer can also be used as an adhesive to
bring two
other materials together.
Compounding extrusion is a process that mixes one or more polymers with
additives
and /or fillers to give plastic compounds. Additive and/or filler materials
can affect the
tensile strength, toughness, heat resistance, color, clarity etc. A good
example of this is
the addition of talc to polypropylene. Most of the filler materials used in
plastics are
mineral or glass-based filler materials. There are two main subgroups of
filler materials:
particulates and fibers. Particulates are small particles of filler which are
mixed in the
matrix where size and aspect ratio are important. Fibers come in many forms
and often
in small circular strands that can be very long and have very high aspect
ratios.
The feeds may be pellets, powder and/or liquids, but the compounded product is
usually
in pellet form, to be used in other plastic-forming processes such as
extrusion and
injection molding. As with traditional extrusion, there is a wide range in
machine sizes
depending on application and desired throughput. While either single- or
double-screw
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extruders may be used in traditional extrusion, the necessity of adequate
mixing in
compounding extrusion makes twin-screw extruders all but mandatory.
There are two sub-types of twin-screw extruders: co-rotating and counter-
rotating. This
nomenclature refers to the relative direction each screw spins compared to the
other. In
co-rotation mode, both screws spin either clockwise or counter-clockwise; in
counter-
rotation, one screw spins clockwise while the other spins counterclockwise. It
has been
shown that, for a given cross sectional area and degree of overlap
(intermeshing), axial
velocity and degree of mixing is higher in co-rotating twin extruders.
However, pressure
buildup is higher in counter-rotating extruders. The screw design is commonly
modular
in that various conveying and mixing elements are arranged on the shafts to
allow for
rapid reconfiguration for a process change or replacement of individual
components due
to wear or corrosive damage.
Injection Molding
The injection unit of injection molding machine is much like an extruder. The
injection
unit melts the polymer resin and injects the polymer melt into the mold. It
consists of
a barrel that is fed from one end by a hopper containing a supply of plastic
pellets. The
unit may be: ram fed or screw fed.
The injection unit consists of a granulate hopper, cylinder, screw, nozzle,
heating bands
and hydraulic drives and serves the purpose of melting and injecting the
molding
material.
A nozzle shut-off valve used in an injection molding machine for plastic. By
opening and
closing the shut-off valve with the pressure of plastic from or in the
injection unit. An
aspect relates to an improved nozzle shut-off valve for use in reciprocating
screw or
plunger type injection molding machines of the kind used to handle plastic and
elastomeric material.
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Conventional molding apparatus of the reciprocating rotating screw type
usually
includes a plasticizing cylinder or chamber having a bore, wherein the
plasticizing screw
rotates in such a manner so as to allow the solid molding material to enter
the cylinder
and be plasticized as it advances in the direction of screw feed. Attached on
one end of
the plasticizing cylinder is a nozzle in communication with a mold sprue which
leads to
the mold cavity. As the plasticized material is deposited at the metering or
front end of
the screw, it develops a back pressure that forces the screw to retract in the
cylinder
bore and when the plasticized material reaches a predetermined volume, or shot
size,
the retracting screw contacts a limit switch and stops its rotation. The shot
is now ready
for injection into the mold cavity, generally upon receipt of a signal from
the clamp,
whereupon the screw is driven forward hydraulically and/or electrically to
inject the shot.
Later, the plasticizing screw again starts to rotate and gradually retract as
a new shot is
built up in the plasticizing cylinder. Thus, the screw reciprocates once per
machine cycle
to plasticize and inject a shot of material.
Often, a shut-off valve is employed to interrupt the flow of molten material
from the
nozzle into the mold sprue. The valve offers the advantages of minimizing or
entirely
curtailing drool through cut off of material flow at the nozzle and provide
the capability to
plasticize during periods in which the mold is open. Generally, plasticizing
takes place
during part curing to prevent plasticized material from escaping.
The force to open a nozzle shut-off valve preparatory to an injection cycle by
various
arrangements of hydraulic motor, pneumatic piston and cylinder arrangements,
and the
location and orientation of the several parts.
The shut-off valve/valves can also be placed in the mold at the individual
cavity/cavities
in a valve gate hot runner system.
A hot runner system is an assembly of heated components¨hot halves, nozzles
and
gates and¨that inject plastic into the cavities of an injection mold. The
system usually
includes a heated manifold and a number of heated nozzles. The manifold
distributes
the plastic entering the mold to the nozzles, which then meter it precisely to
the injection
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points in the cavities. The hot runner is equipped with its own temperature
control
system called a hot runner controller.
A hot runner controller is a temperature controller used to control the
temperature in the
hot runner. This helps create the most consistent part(s) due to the ability
to modify the
temperature at the individual gate location thereby enabling a balanced fill
of the
cavity/cavities.
By contrast, a cold runner is simply a channel formed between the two halves
of the
mold, for the purpose of carrying plastic from the injection molding machine
nozzle to
the cavities. Each time the mold opens to eject the newly formed plastic
parts, the
material in the runner is ejected as well, resulting in waste.
A hot runner system usually includes a heated manifold and a number of heated
nozzles. The main task of the manifold is to distribute the plastic entering
the mold to
the various nozzles which then meter it precisely to the injection points in
the cavities.
Hot runner systems are fairly complicated systems, they have to maintain the
plastic
material within them heated uniformly, while the rest of the injection mold is
being
cooled in order to solidify the product quickly.
Hot runners usually make the mold more expensive to manufacture and run, but
they
allow savings by reducing plastic waste and by reducing the cycle time because
you
don't have to wait until the conventional runners freeze.
Hot runner advantages
= Shorter cycle time: No runner controlling the cooling time
= Easier to start: Without runners to remove, and auto cycle occurs faster
and more
frequently
= Fewer sink marks and under-filled parts: Unlike when plastic flows
through a cold
runner and loses heat to mold plates
= Design flexibility: Can locate the gate at many points on the part
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= Balanced melt flow: Separate melt channels are in externally heated
manifolds that
are insulated from mold plates surrounding them.
From a technical point of view, valve gate technology enables the production
of low-
stress injection molding parts, which almost always meet the requirements of a
very
low vestige. As a result, the lower degree of stress when gating with valve
gate
systems becomes relevant. When using a valve gate there is no need to control
the
vestige by trying to achieve small gate diameters. Small gate diameters of
course lead
to higher shear rates and therefore inevitably result in a higher degree of
orientation.
Areas with a high degree of orientation cause internal stress, so warping of
the part is
a high risk. For example, a gate diameter of 0.8 mm for a part with a shot
weight of 10
g results in a local shear rate of approximately 150,000 1/s. When a valve
gate with a
needle diameter of 2.5 mm is used, the shear rate in the gate area is
approximately
6,000 1/s.
Safety is another factor to consider when using valve gate systems. For
example,
valve gate systems are used to avoid stringing in fast cycling molds.
Stringing always
occurs when the melt in the gate has no chance to freeze properly within the
time
given. This can happen in fast-cycling molds as well as with large gate
diameters or
with an improper temperature control. With valve gate technology, stringing
can be
avoided in most cases. The mechanical shut-off ensures that the gate is always
sealed properly, regardless of the gating diameter. However, in case of very
large
needle diameters, even valve gate systems can cause problems. When operating
with
short cycle times the needle stores so much heat during injection that a
bonding effect
in the needle area can occur.
Using valve gates also provides a processing improvement gained by the precise
control of the shut-off time. When molding multi-point gated parts, the
formation of flow
lines can be avoided by a sequential opening of the needles. By using this
method, a
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controlled melt flow can be achieved so that a frontal meeting of flow fronts
can either
be avoided or be placed in less critical areas of the part.
Valve Gate System Gating Variations
Two important sealing principles have been established for the processing of
thermoplastics with valve gate systems. One of them is the conical needle
geometry.
During closing the conical needle moves into corresponding gate geometry in
the mold
insert. When using this principle, the closing power of the needle drive must
be limited
to avoid damage of the mold insert. When the needle closes the melt is
displaced from
the narrowing gap.
In lieu of the conical needle, the cylindrical form is often used. Here the
mold insert
normally has a conical entrance leading into a short cylindrical bore. The
melt in the
cylindrical area, which measures only some tenth of a millimeter, must be
pushed into
the part when closing the needle. Considering the low melt volume and the
shrinkage,
this normally has no effect on the molded part.
Needles protruding from the side into the gate on an angle offer some
advantages
because the melt flow is only slightly blocked in their open position.
However, because
the non-symmetrical layout of this gating method causes a higher wear, this
method
has not gained a large market acceptance.
Valve Gate System With Integrated Needle Drive
An in-line valve gate with an integrated needle drive is a general-purpose
system
compared to standard designs. Due to the construction of the nozzles, the
valve gate
can be handled like a "conventional" hot runner system. As shown in the
description
regarding function and mounting location, a fixed mold half consists of a
normal
clamping plate, a manifold frame plate including a standard manifold and a
nozzle
retainer plate. The in-line valve gate can be used as a freestanding single
tip as well.
There is no need for any changes in construction. Examples for applications
are
shown in.
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When used in stack molds, the in-line valve gate offers decisive advantages.
Since
there is no need to place the needle drive behind the manifold and to guide
the needle
through the manifold, a perfectly symmetrical positioning of the cavities can
be
achieved. This means optimal utilization of mold and machine. Furthermore, two
in-
line valve gate nozzles that are positioned exactly opposite each other can be
used for
a central leakage-free melt-transfer in stack molds without having to use an
accumulator cavity.
In large molds with deeply immersed nozzles, very long needles must be used.
At the
same time, the nozzles are screwed into the manifold. To ensure that the
desired
position of the needle is reached when the manifold is heated up and thermally
expanded, the needle must be adapted while the system is cold or jamming of
the
needle and wear in the needle guides is possible. This problem can be
eliminated by
using a valve gate system with an integrated needle drive as the final stage
of a long
nozzle. The position of the valve gate is fixed within the mold and a flexible
pipe
connects the valve gate to the manifold. Due to the fact that the needle is
contained
within the valve gate assembly, it experiences smaller growth and is not
affected by
other elements such as manifold growth.
Standard Valve Gate
The standard valve gate is of importance when a low system height is required.
Because the needle drive is positioned in the clamping plate, the total height
of the
system is similar to a normal hot runner system. However, when using this
method,
the manifold of the hot runner system must be specially adjusted to the valve
gate
system. Either additional sealing elements or at least clearance bores for the
needle
must be provided. The clearance bores must be positioned so that they do not
interfere with the melt channels in the manifold. An in-line valve gate nozzle
with a
needle drive that can be operated mechanically, hydraulically or pneumatically
is
useful in this situation.
Valve Gate for Multi-Component Applications
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The coaxial valve gate was developed using the principles of the standard
valve gate.
This technology allows the injection of two components via one injection
point. The
components may be injected both at the same time or delayed. Considering the
mold
technology, the following layer configurations are possible: inner/outer or
outer/inner
layers (simple layers) or outer/inner/outer layers (sandwich). The possibility
of using
the sandwich method for direct gating in a multi-cavity mold especially opens
up a
wide range of applications. For example, the production of pre-forms with
barrier layer
or the production of parts with thick walls (foamed core component to
counterbalance
shrinking) is possible. The use of materials with different structures for the
inner and
outer layer helps to create special haptical appearances.
In addition, the coaxial valve gate is suitable for partial hot runner
solutions as well.
For example, there are different methods that it can be used as a machine
nozzle. The
first one is the application as a "universal single nozzle" within an
additional machine
plate. This configuration allows the production of sandwich parts by using
standard
two-component machines in combination with conventional runner solutions
(three-
plate molds). In this case, the part as well as the cold runner system must
have
sufficient dimensions because due to the so-called "sandwich plate," a large
portion of
the mold daylight width cannot be utilized.
This problem is eliminated when using a two-component machine nozzle. In this
case,
a machine with special configurations must be used because both injection
units must
be connected with the coaxial valve gate nozzle. The coaxial valve gate system
facilitates the injection of both components simultaneously. Adjusting the
simultaneous
phase of the injection cycle can vary the penetration of the core component.
With a
machine configuration as mentioned above, both injection units could be used
independently for standard injection molding. For articles that must be molded
in two
different colors, the color change can be accomplished with only one shot.
Of course, two-component molding can be done with "conventional" valve gate
systems as well. One of the methods normally used is the transfer method,
requiring a
rotary table or a handling system. The other method is the core-back method.
Both are
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seldom used for layer configurations but mainly for production of articles
with
additional sealing lips, grip-areas and two-colored areas positioned next to
each other
or injected polymer windows.
"Hot runner" is a term used in injection molding that refers to the system of
parts that
are physically heated such that they can be more effectively used to transfer
molten
plastic from a machine's nozzle into the various mold tool cavities that
combine to form
the shell of your part. Sometimes they are called "hot sprues." You can
contrast the
term "hot runner" with its opposite, and the historically more common "cold
runner." Cold
runners are simply an unheated, physical channel that is used to direct molten
plastic
into a mold tool cavity after it leaves the nozzle. The primary difference is
that hot
runners are heated while cold runners are not.
While hot runners are not required for injection molding processes, they can
be useful to
ensure a higher quality part. They are particularly beneficial with
challenging part
geometries that require lower margin of error in the flow properties of the
molten plastic
(i.e. where inopportune cooling or temperature deltas might result in uneven
flow).
Further, hot runners can be beneficial in reducing wasted plastic during high
volume
shoots. Because cold runners are unheated, the channel needs to be larger and
thus
more plastic needs to be shot during each cycle. If you are shooting a large
number of
parts while iterating to get the design correct you could easily run up the
cost of plastic
above the cost of a hot runner assembly. The downside to hot runner
technology, is that
it is more expensive by default than a cold runner setup.
The advantage of hot runners is that, if designed properly, the plastic will
flow from the
machine's nozzle more uniformly into the gate locations. Agate location is the
point at
which molten plastic enters the cavity of the injection mold. Gate location,
plastic
temperature, the design of internal mold cavities, and the material properties
of the
plastic itself e.g. regrind/recycled material that will preform different than
virgin material
as well as that of the mold all have an important impact on the success or
failure of the
injection molding process.
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Hot runners are designed to maximize manufacturing productivity by reducing
cycle
time. Internally heated hot runner designs resulted in solidified plastic on
the internal
boundaries of the channel with molten plastic much more localized to the
specific heater
location. By contrast, externally heated runners utilize heated nozzles and a
heated
manifold and based on the high thermal conductivity of metal they are able to
maintain
much more even flow properties for the internal plastic.
Externally heated: This system design employs a cartridge-heated manifold with
interior flow passages. To separate it from the rest of the mold, the manifold
has several
insulating characteristics that reduce heat loss. Since it does not require a
heater that
can block the flow, and all of the plastic is molten, the externally heated
hot runner
channels have the lowest pressure drop of any runner system. This method works
better for color changes because none of the colors in the runner system
freeze. In
addition, materials do not have surfaces where they stick to and degrade ¨ an
attribute
that makes externally heated systems an excellent choice for thermally
sensitive
materials.
Internally heated: Internally heated runner systems have annulus flow passages
that
are heated by a probe and torpedo located in the passages. Taking advantage of
the
insulating effect of the rubber melt, it reduces heat loss to the rest of the
mold. However,
this system requires higher molding pressures, and color changes can be quite
challenging. In addition, materials have many places where they stick to the
surface and
degrade. You should not use thermally sensitive materials in the fabrication
process.
Heating the runner can be done through a variety of materials,
including coils, cartridge heaters, heating rods, heating pipes and band
heaters. A
complex control system ensures a consistent flow and distribution of the melt.
Insulated runners. Unheated, this type of runner requires extremely thick
runner
channels to stay molten during continuous cycling. These molds have extra-
large
passages formed in the mold plate. During the fabrication process, the size of
the
passages in conjunction with the heat applied with each shot results in an
open molten
flow path. This inexpensive system eliminates the added cost of the manifold
and drops
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but provides flexible gates of a heated hot runner system. It allows for easy
color
changes.
A three-plate mold is used when part of the cold runner system is on a
different plane
to the injection location. The runner system for a three-plate mold sits on a
second
parting plane parallel to the main parting plane. This second parting plane
enables the
runners and sprue to be ejected when the mold is opened
Injection screw
The reciprocating-screw machine is the most common. This design uses the same
barrel for melting and injection of plastic.
When the mold is closed the screw by its rotation moves the plastic forward
filling a
predeterminate volume in front of the screw while moving backwards until this
volume is
achieved and then stops its rotation. When the empty mold then is closed, and
the
screw is the used as a plunger injecting the warm plastic into the empty mold
holding
the filled mold cavity under pressure until the plastic has solidified. After
a
predetermined cooling time the mold is opened and the solidified plastic part
in the mold
is ejected and the mold closes again, and the process repeats itself.
The alternative unit involves the use of separate barrels for plasticizing and
injecting the
polymer. This type is called a screw-preplasticizer machine or two-stage
machine.
Plastic pellets are fed from a hopper into the first stage, which uses a screw
to drive the
polymer forward and melt it. This barrel feeds a second barrel, which uses a
plunger to
inject the melt into the mold. Older machines used one plunger-driven barrel
to melt and
inject the plastic. These machines are referred to as plunger-type injection
molding
machines.
Selecting Injection Molding Screws
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Using the right injection molding screws is crucial to making quality parts
consistently
and with maximum production output.
To select the right screw, details of the particular part to be molded must be
known (that
is, part material, weight, size and wall thickness). The basic mold design is
also
important so that flow length from gate, shot weight and runner system are all
taken into
consideration.
Choosing a screw without knowledge of the parts is like buying a car without
any
preference for performance and handling requirements.
The basic design of any screw has 3 zones along its length:
1. Feed zone
2. Transition zone
3. Metering zone
The feed zone conveys the solid plastic pellets which are fed from the hopper
to the
transition zone where they are compressed by a change in screw geometry. This
compression forces the pellets to melt through the action of pushing up
against each
other. This is called shearing. The metering zone then conveys the melt to the
front of
the screw ready for injection into the mold cavity.
In the transition zone the material is compressed by the change in the depth
of the
screw channels from the feed zone to the metering zone. The ratio of the
change in
depth is called the compression ratio and is usually between 2 and 3 for
plastics such
as PP and PE. The length of the transition zone is typically 4 to 7 x the
screw diameter
in a general-purpose screw.
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Another aspect of screw design is the length to diameter ratio (LID) meaning
how long it
is compared to its diameter. As an example, the L/D ratio for PP and PE is in
the range
20-30:1.
When it comes to general purpose screws, longer screws are usually preferred
because
they will produce a better-quality melt and therefore produce better quality
parts
The advantage of a general-purpose screw is that they can be used with most
plastic
materials such as PP, PE, Nylon, PET and PC so they are very flexible and good
for
molding companies that mold a variety of different materials.
The disadvantage is that, for some materials, part quality and productivity
rates will be
lower compared to more advanced injection molding screw designs such as the
barrier
screw.
This type of screw provides a better-quality melt at a faster rate compared
with a
general-purpose screw. There are many different designs of barrier screws, the
difference being in the varying of the flight depths and channel widths.
The exact design chosen must be in line with the application.
Although double flight screws have a different design, they are an alternative
to barrier
screws. They are also designed to deliver a high-quality melt at fast rates.
The design ensures the plastic is fully melted before it reaches the
compression zone,
which is not the case in a general-purpose screw.
Double flight injection molding screws can be used in technical parts for PP
and thin
wall technical parts in PA which does not plasticize well with barrier screws.
The screw diameter is important for 2 reasons. The first reason is that it
determines the
maximum available injection pressure, the smaller the diameter the higher the
available
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pressure. This is critical for parts that have thin walls and a long flow
length and for
plastic materials that are difficult to inject.
The second reason is the diameter determines the maximum shot size available.
The
smaller the diameter, the smaller the shot size.
It can be seen that there is a conflict between shot size and injection
pressure when
selecting a screw diameter. Initially it might seem advantageous to choose the
largest
diameter so that there is more flexibility in the types and size of parts that
can be made
in one machine, but this is the wrong way to think about it.
The screw diameter should be chosen in line with the application otherwise
quality
and/or productivity rates will suffer. The injection unit must be capable of
generating
enough injection pressure (with some in reserve) to maintain consistent fill
times and as
a consequence, maintain the quality.
Serious thought should be given to using a heat-treated screw and barrel as
these will
provide longer life than non-heat-treated parts. This is especially important
when the
material contains some level of reinforcement as this is much more abrasive
and will
wear out the screw and barrel sooner than material without reinforcement.
Once the screw and barrel start to wear, part quality will start to suffer,
and it will only be
a matter of time before a replacement will be needed. This is a large cost,
not just
because of the cost of the replacement screw but for the loss in production.
The tip is a non-return valve at the front of the screw which allows the melt
to pass
through during the plasticizing stage but stops the melt from back flowing
into the screw
during the injection stage.
There are 2 basic designs the ball check valve and the sliding ring check
valve. The
ring check valve is generally preferred because it allows an easier path for
the melt to
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pass through compared to a ball check valve. Therefore, a ring check valve is
suited to
shear sensitive materials such PC.
However, the disadvantage of the ring valve is their tendency to wear, so the
ring check
valve condition should be checked on a regular basis_ A typical sign of wear
is
inconsistent cushioning during processing.
The fact is, in today's competitive environment, injection molding
manufacturers need to
be making parts as efficiently as possible in order to keep manufacturing
costs down
and delivery times short.
Using the right injection molding screws for your parts will play a
significant role in this.
Plasticizing cylinder
Screw position at the end of the dosage process; the plasticized material is
in front of
the screw tip. Screw position after the injection process; the plasticized
material is
injected into the mold. A material cushion is left in front of the screw for
injection into the
mold during the holding pressure phase.
Blow molding is a specific manufacturing process by which hollow plastic parts
are
formed and can be joined together. It is also used for forming glass bottles
or other
hollow shapes.
In general, there are three main types of blow molding: extrusion blow
molding, injection
blow molding, and injection stretch blow molding.
The blow molding process begins with melting down the plastic and forming it
into
a parison or, in the case of injection and injection stretch blow molding (IS
B), a preform.
The parison is a tube-like piece of plastic with a hole in one end through
which
compressed air can pass.
The parison is then clamped into a mold and air is blown into it. The air
pressure then
pushes the plastic out to match the mold. Once the plastic has cooled and
hardened the
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mold opens up and the part is ejected. The cost of blow molded parts is higher
than that
of injection-molded parts but lower than rotational molded parts.
In extrusion blow molding, plastic is melted and extruded into a hollow tube
(a
parison). This parison is then captured by closing it into a cooled metal
mold. Air is then
blown into the parison, inflating it into the shape of the hollow bottle,
container, or part.
After the plastic has cooled sufficiently, the mold is opened, and the part is
ejected.
Continuous and Intermittent are two variations of Extrusion Blow Molding. In
continuous
extrusion blow molding the parison is extruded continuously and the individual
parts are
cut off by a suitable knife. In Intermittent blow molding there are two
processes: straight
intermittent is similar to injection molding whereby the screw turns, then
stops and
pushes the melt out. With the accumulator method, an accumulator gathers
melted
plastic and when the previous mold has cooled and enough plastic has
accumulated, a
rod pushes the melted plastic and forms the parison. In this case the screw
may turn
continuously or intermittently. With continuous extrusion the weight of the
parison drags
the parison and makes calibrating the wall thickness difficult. The
accumulator head or
reciprocating screw methods use hydraulic systems to push the parison out
quickly
reducing the effect of the weight and allowing precise control over the wall
thickness by
adjusting the die gap with a parison programming device.
Containers such as jars often have an excess of material due to the molding
process.
This is trimmed off by spinning a knife around the container which cuts the
material
away. This excess plastic is then recycled to create new moldings. Spin
Trimmers are
used on a number of materials, such as PVC, HDPE and PE+LDPE. Different types
of
the materials have their own physical characteristics affecting trimming. For
example,
moldings produced from amorphous materials are much more difficult to trim
than
crystalline materials. Titanium coated blades are often used rather than
standard steel
to increase life by a factor of 30 times.
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The process of injection blow molding is used for the production of hollow
glass and
plastic objects in large quantities. In the injection blow molding process,
the polymer is
injection molded onto a core pin; then the core pin is rotated to a blow
molding station to
be inflated and cooled. This is the least-used of the three different blow
molding
processes and is typically used to make small medical and single serve
bottles. The
process is divided into three steps: injection, blowing and ejection.
The injection blow molding machine is based on an extruder barrel and screw
assembly
which melts the polymer. The molten polymer is fed into a hot runner manifold
where it
is injected through nozzles into a heated cavity and core pin. The cavity mold
forms the
external shape and is clamped around a core rod which forms the internal shape
of the
preform. The preform consists of a fully formed bottle/jar neck with a thick
tube of
polymer attached, which will form the body. similar in appearance to a test
tube with a
threaded neck.
The preform mold opens and the core rod is rotated and clamped into the
hollow, chilled
blow mold. The end of the core rod opens and allows compressed air into the
preform,
which inflates it to the finished article shape.
After a cooling period the blow mold opens, and the core rod is rotated to the
ejection
position. The finished article is stripped off the core rod and as an option
can be leak-
tested prior to packing. The preform and blow mold can have many cavities,
typically
three to sixteen depending on the article size and the required output. There
are three
sets of core rods, which allow concurrent preform injection, blow molding and
ejection.
Compression Molding is a method of molding in which the molding material,
generally
preheated, is first placed in an open, heated mold cavity. The mold is closed
with a top
force or plug member, pressure is applied to force the material into contact
with all mold
areas, while heat and pressure are maintained until the molding material has
cured. The
process employs thermosetting resins in a partially cured stage, either in the
form of
granules, putty-like masses, or preforms.
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Compression molding is a high-volume, high-pressure method suitable for
molding
complex, high-strength fiberglass reinforcements. Advanced composite
thermoplastic
can also be compression molded with unidirectional tapes, woven fabrics,
randomly
oriented fiber mat or chopped strand. The advantage of compression molding is
its
ability to mold large, fairly intricate parts. Also, it is one of the lowest
cost molding
methods compared with other methods such as transfer molding and injection
molding;
moreover, it wastes relatively little material, giving it an advantage when
working with
expensive compounds.
However, compression molding often provides poor product consistency and
difficulty in
controlling flashing, and it is not suitable for some types of parts. Fewer
knit lines are
produced and a smaller amount of fiber-length degradation is noticeable when
compared to injection molding. Compression-molding is also suitable for ultra-
large
basic shape production in sizes beyond the capacity of extrusion techniques.
Compression molding was first developed to manufacture composite parts for
metal
replacement applications, compression molding is typically used to make larger
flat or
moderately curved parts. This method of molding is greatly used in
manufacturing
automotive parts such as hoods, fenders, scoops, spoilers, as well as smaller
more
intricate parts. The material to be molded is positioned in the mold cavity
and the heated
platens are closed by a hydraulic ram. Bulk molding compound or sheet molding
compound are conformed to the mold form by the applied pressure and heated
until the
curing reaction occurs. SMC feed material usually is cut to conform to the
surface area
of the mold. The mold is then cooled, and the part removed.
Materials may be loaded into the mold either in the form of pellets or sheet,
or the mold
may be loaded from a plasticizing extruder. Materials are heated above their
melting
points, formed and cooled. The more evenly the feed material is distributed
over the
mold surface, the less flow orientation occurs during the compression stage.
Compression molding is also widely used to produce sandwich structures that
incorporate a core material such as a honeycomb or polymer foam.
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Thermoplastic matrices are commonplace in mass production industries. One
significant
example are automotive applications where the leading technologies are long
fiber
reinforced thermoplastics and glass fiber mat reinforced thermoplastics.
In compression molding there are six important considerations that an engineer
should
bear in mind.
= Determining the proper amount of material.
= Determining the minimum amount of energy required to heat the material.
= Determining the minimum time required to heat the material.
= Determining the appropriate heating technique.
= Predicting the required force, to ensure that shot attains the proper shape.
= Designing the mold for rapid cooling after the material has been
compressed into
the mold.
Extruders for 3D printing
Types of extruders depending on the drive
Within extruders there are two types depending on the type of drive: Direct
and Bowden.
In the direct extruder, as its name suggests, the filament runs directly from
the cog of the
extruder to the HotEnd. There are even systems in which these two parts are
together.
In the Bowden extruders, on the contrary, the connection with the HotEnd is
through a
PTFE tube through which the filament passes.
The main function of the extruder is to move the filament from the reel to the
HotEnd in
the most precise way and at the speed suitable for 3D printing.
Types of extruders: Direct
The direct extruder, as its name suggests, the filament runs directly from the
cog of the
extruder to the HotEnd. There are even systems in which these two parts are
together,
as in the Titan Aero.
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The direct extruders allow the printing of rigid and flexible materials (1.75
mm and 2.85
mm) regardless of the composition of the filament. Another advantage is that
they require
low retraction lengths, reducing printing time and increasing the extruder
motor life. Its
main drawback is the inertias produced in the axis of the printer in which the
extruder
moves, caused by the weight and unbalance of the center of mass with respect
to the
axis. Another drawback can appear in closed printers and with a tempered
chamber that
can reach temperatures in the extruder motor that affect the performance of
operation.
Types of extruders: Bowden
In the Bowden extruders, on the contrary that the direct extruders, the union
with the
HotEnd is through a PTFE tube through which the filament passes.
These extruders have low inertias in the axis of displacement of the HotEnd.
The Bowden
system, since the extruder and the extruder motor are anchored to the chassis
of the 3D
printer, greatly reduce the inertias in the movement to make the impression.
This makes
it possible to produce very fast prints and at the same time of high quality.
Its main
disadvantage is the great difficulty to print flexible filaments (TPE) of
diameter 1.75 mm.
This is due to the fact that being a flexible filament it is not possible to
keep the pressure
in the filament constant along the Bowden PTFE tube until the HotEnd, since it
flexes the
filament. In Bowden systems of 2.85 mm however it is possible to print the
flexible
filaments at low speed.
Direct Extruders
Advantages:
25. Print flexible materials, both PLA Soft or TPU, and TPE in 1.75mm and
2.85mm.
= Print all kinds of materials without problems, regardless of the abrasion
presented by
certain filaments. To print 3D abrasive materials, it is recommended using a
brass nozzle
with the ruby tip that has an almost infinite life.
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= This system needs short retraction lengths to obtain good 3D prints,
which reduces the
likelihood of a jam.
= Retraction is the recoil movement of the filament necessary to prevent
dripping of
material during movements and displacements that the vacuum extruder performs
during
3D printing.
The parameters that configure the retraction are:
= Retraction distance: Length of material that recedes in the retraction
process. It
varies depending on the type of material, the type of extrusion system Direct
or
Bowden and the type of HotEnd. For flexible materials, especially for the TPE
type, retraction must be deactivated to prevent the filament from coiling on
the
extruder pinion.
= Retraction speed: Speed at which the extruder motor drives back the
filament. With this parameter its necessary to be very careful if high speeds
are
used (greater than 70mm/s) because it can mark the filament in such a way that
it's unusable to continue the 3D printing.
Disadvantages:
= Considerable inertia in the axis through which the extruder and the
HotEnd moves. This
factor is increased when you want to make 3D prints at high speeds by having
to move
the weight of the whole set (extruder, extruder motor and HotEnd), especially
if the 3D
printer has several extruders.
= Temperature problems in the electric motor of the extruder. In closed 3D
printers and with
a tempered chamber, temperatures in the extruder motor can be reached that
affect the
performance of operation.
Bowden extruders
Advantages:
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= Low inertias in the axis of displacement of the HotEnd. In the Bowden
system, since the
extruder and the extruder motor are anchored to the chassis of the 3D printer,
the inertias
in the movement to make the impression are greatly reduced. This allows for
very fast
and high-quality printing.
= High drag power of the filament. The majority of 3D printers that use
this extruder system
have a set of pinions (reducer group) that increases the drag torque of the
filament, thus
being able to move coils larger than normal.
Disadvantages:
. Problems printing with flexible filaments with a diameter of 1.75mm. This
is due to the fact
that being a flexible filament it isn't possible to keep the pressure in the
filament constant
along the Bowden PTFE tube until the HotEnd as it channels the filament. In
the 2.85mm
Bowden systems, however, it's possible to print the flexible filaments at low
speed.
Types of HotEnd depending on the diameter of the material
The HotEnd is responsible for melting the filament to make the desired piece.
It configures
the type of HotEnd (V6 or Volcano) and the nozzle depending on the diameter of
the
material, depending on the type of piece, quality and finish you want to
obtain. We classify
the extruders in the V6 and Volcano types and then we mention the advantages
and
disadvantages between these two types of HotEnd.
Advantages and disadvantages of HotEnd V6
Advantages:
= The V6 is the most versatile HotEnd on the market, valid for all types of
impressions, even
for flexible materials (especially with 2.85 / 3mm filament). With the HotEnd
V6 you can
make all kinds of parts with an exceptional finishing quality.
Disadvantages:
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= The maximum diameter of nozzle recommended for this type of extruder is
0.80mm /
1mm since for larger diameters, problems of continuity of flow usually occur.
Advantages and disadvantages of HotEnd Volcano
Advantages:
= Thanks to the parallel position of the Heater Cartridge with respect to
the nozzle, a greater
heated area is achieved, thus giving great control and stability over the
melting of the
filament. For all the above you can make 3D prints with larger diameter nozzle
(1.2mm),
which leads to shorter manufacturing times and the possibility of printing
with a higher
layer height than in the V6.
= More resistant pieces. Thanks to making higher layers with a laminar flow
(without
bubbles) the joints between the chemical bonds of the material are stronger,
giving more
rigid and resistant parts.
Disadvantages:
= Surface finish of low detail. Due to the high layer heights, the pieces
are made with steps
in areas where there are curved surfaces at different heights.
Understanding Viscosity in Extrusion
Both the power-law coefficient and the consistency index must be considered to
calculate viscosity.
Viscosity for non-Newtonian polymers is a combination of increasing
temperature and
shear rate, as described by the following relationship:
/7 = my'/
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where viscosity (ri) equals consistency index (m) times the shear rate (y) to
the power
law index (n) minus 1.
Generally, only rheology experts discuss the effects of the consistency index.
The
consistency index, or viscosity change with increasing temperature, is largely
dependent on the energy input to the polymer by shear from the screw rotation.
That
is, as the shearing raises the polymer temperature by viscous dissipation or
conversion of mechanical power to temperature, the viscosity additionally
decreases
due to the higher temperature and adds to the shear thinning. The consistency
index
describes that rate of decrease due to increased temperature.
The shear-thinning characteristics of various polymers are often categorized
solely by
the power-law coefficient, but the consistency index can have just as
significant effect
on the final viscosity and has to be considered.
As a result, two polymers of similar melt index or melt flow can have vastly
different
viscosities at the elevated shear rates during processing. Melt-index and melt-
flow
measurements by capillary rheometer are at very low shear rates, where shear
thinning is almost non-existent. Due to the multiplying effect of power-law
coefficient
and consistency index, an HDPE and a PP at identical shear rates and slightly
different temperatures can have a difference in viscosity where the HDPE is
three
times as viscous as the PP. This means that the melt temperature of the HDPE
on the
same screw design is going to be much higher than the PP.
Use of the simple viscosity calculation can greatly assist in analysis of
extruder power
requirements, melt temperature and polymer flow for different polymers without
the
use of shear-rate/viscosity graphs
Interestingly, some polymers can reach a near autogenous or adiabatic shear
rate
where the viscosity drops proportional to the shear rate or screw speed such
that
further heating through viscous dissipation is minimized and the power-
requirement
increases only a small amount.
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The actual calculation of the motor load using the calculated viscosity is
quite
complicated and generally requires computer simulation. However, the
calculated
viscosity can be a useful tool for approximation of the viscosity and the
resulting screw
power requirements when coupled with the calculations for viscous dissipation
of
different polymers on single-screw extruders of different sizes and L/D
ratios. Power-
law coefficient and consistency data can be found on the internet or from the
polymer
suppliers.
Viscosity: Definition
Viscosity as it relates to plastic injection is the measurement of how thick
or thin a
material flow. A good comparison would be the difference between molasses and
water.
If you were to pour water and molasses at the same time, water would flow much
easier
than the molasses. Molasses is thick and flows slowly. Water is thinner and
flows much
faster. Molasses would be considered to be high viscosity, and water would be
low
viscosity.
The same terminology applies in different plastic injection materials.
Materials that are
low viscosity flow thin and quick, while high viscosity materials flow thick
and slower.
For instance, nylon flows thinner and faster than styrene, thus nylon has a
lower
viscosity than styrene. Styrene falls in the middle of the material scale and
is
considered to be the mean. As such, materials that are at a higher viscosity
than
styrene are recorded as positive. Materials that are a lower viscosity than
styrene are
recorded in MSDS data as negative values.
Viscosity vs. Temperature
Temperature plays an important role in adjusting viscosity. The general rules
of thumb
are this:
= Adding heat will lower the viscosity of a material, thus making the flow
thinner and
faster. It is important to note here that higher temperatures add to cycle
time, and
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that there is a point when temperature becomes detrimental by producing more
gas
and causing degradation. Melt temperature should be measured to assure that
barrel
temperature is within the tolerances of the melt window provided by the
machine
manufacturer.
=
Reducing heat thickens the flow and slows down the fill rate. Lower
temperatures
provide faster cycle times but increase wear on plastics equipment if the
temperature
becomes too low. Again, it is important to measure melt temperature to verify
that
heats are within the melt window.
Viscosity vs. Fill Time
Viscosity has little effect on fill time. Thinner flow fronts flow easier,
however injection
speed is established through scientific procedure to be at the mean of slow to
fast. The
press controls the speed using valves, servos, etc. There is, however, a
change in the
amount of energy used to satisfy what set points establish as the correct fill
speed.
Increased energy usage can sometimes result in higher production cost, and
vice versa
for energy decreases. There are situations where one or the other may become
more
beneficial based on higher production needs or value costing.
Viscosity vs. Peak Pressure
Viscosity also has a direct relationship to peak pressure. A thicker, cooler
flow front will
result in a higher peak pressure. A thinner, warmer flow front results in a
lower peak
pressure. Thus, adding heat lowers viscosity and peak pressure while reducing
heat
increases viscosity and peak pressure.
Using Viscosity to Address Defects
This section will address several common molding defects and list methods of
using
viscosity changes to improve part quality. At no point does this article
theorize that
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viscosity is the cure all for molding defects, but there are situations where
adjusting
viscosity can improve part functions and/ or appearance. Listed here are many
of these
situations, and methods of using viscosity to improve upon or eliminate the
defect:
Sink:
There are several different types of sink, but heat sink and sinks over ribs
or deep
contours in the mold design can have a direct relationship to viscosity.
. Heat sink- Heat sink occurs when mold or material temperature are too
hot. Cycle
time can also be a factor. In some instances, lowering barrel temperature can
reduce
or eliminate heat sink conditions.
. Sink over ribs/ details: Sinks over ribs can be related to two different
situations:
1. Material in the rib can still be too hot, leading to a sink over the rib.
In this case,
lowering viscosity may improve the condition by lowering heat in the rib area.
2. Sink can also be caused by material flowing across the rib too slow,
leading to an
over pack condition that causes a pull sink as the part ejects. In this
situation,
increasing heat can promote thinner flow, flowing faster across the rib and
packing it
out less. As the part ejects, the rib being packed less allows for better
removal of the
part.
Flash:
There are several situations where flash can be directly attributed to
viscosity. For
instance, hair line flash can be a sure sign that material is too viscous, and
a
temperature reduction is needed to improve the condition. In some situations
where a
mold has parting line damage, reducing heat can actually improve flash that
was a
direct result of that damage.
Knit Lines:
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Knit lines occur when different flow fronts come together as plastic flows
through the
part cavities. In the case of mold details, knits will occur on the lee side
of a detail.
Picture a rock in a stream. as the water rushes against it, the rock causes
resistance.
The water flows around the rock, knitting back together as the two flow fronts
meet each
other in the rear the faster the water flows, the longer it takes for the two
flow streams to
reassemble as one. The same applies when molding around a detail. Faster flow
results
in longer thinner knits. Slower flow results in thicker and shorter knits. In
terms of
viscosity, higher heat equals faster flow and lower heat equals slower flow.
If packing
around a detail is causing cracks/ shorts/ burns on the knit line, reduce the
heat to
improve knit line seal and strength.
As noted above, there are many situations where viscosity can be used as a
tool to
correct poor molding conditions. When standardizing process, start off with
lower level
viscosity as determined by melt temperature, and then make adjustments using
higher
temperatures when viscosity appears to be directly related to molding issues.
This
assures that cycle times are optimal, thus leading to higher efficiency. Low
scrap and
high efficiency will lead to higher returns off of your molded products.
Plastic recycling is the process of recovering scrap or waste plastic and
reprocessing
the material into useful products. Since the majority of plastic is non-
biodegradable,
recycling is a part of global efforts to reduce plastic in the waste stream,
especially the
approximately 8 million metric tons of waste plastic that enters the Earth's
ocean every
year.
Compared with lucrative recycling of metal, and similar to the low value of
glass
recycling, plastic polymers recycling is often more challenging because of low
density
and low value. There are also numerous technical hurdles to overcome when
recycling
plastic. Materials recovery facilities are responsible for sorting and
processing plastics
but have struggled to do so economically as of 2019.
When different types of plastics are melted together, they tend to phase-
separate, like
oil and water, and set in these layers. The phase boundaries cause structural
weakness
and delamination in the resulting material, meaning that polymer blends are
useful in
only limited applications. The two most widely manufactured plastics,
polypropylene and
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polyethylene, behave this way, which limits their utility for recycling. Each
time plastic is
recycled, additional virgin materials must be added to help improve the
integrity of the
material. So, even recycled plastic has new plastic material added in. The
same piece
of plastic can only be recycled about 2-3 times before its quality decreases
to the point
where it can no longer be used.
Centrifugation
One of the most common pieces of equipment used to separate materials into
subfractions in a biochemistry lab is the centrifuge. A centrifuge is a device
that spins
liquid samples at high speeds and thus creates a strong centripetal force
causing the
denser materials to travel towards the bottom of the centrifuge tube more
rapidly than
they would under the force of normal gravity.
Induction heating is an accurate, fast, repeatable, efficient, non-contact
technique
for heating metals or any other electrically conductive materials.
An induction heating system consists of an induction power supply for
converting line
power to an alternating current and delivering it to a workhead, and a work
coil for
generating an electromagnetic field within the coil. The work piece is
positioned in the
coil such that this field induces a current in the work piece, which in turn
produces heat.
The water-cooled coil is positioned around or bordering the work piece. It
does not
contact the work piece, and the heat is only produced by the induced current
transmitted through the work piece. The material used to make the work piece
can be a
metal such as copper, aluminum, steel, or brass. It can also be a
semiconductor such
as graphite, carbon or silicon carbide.
For heating non-conductive materials such as plastics or glass, induction can
be used to
heat an electrically conductive susceptor e.g., graphite, which then passes
the heat to
the non-conducting material.
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Induction heating finds applications in processes where temperatures are as
low as
100 C (212 F) and as high as 3000 C (5432 F). It is also used in short heating
processes lasting for less than half a second and in heating processes that
extend over
several months.
Induction heating is used both domestic and commercial cooking, in several
applications such as heat treating, soldering, preheating for welding,
melting, shrink
fitting in industry, sealing, brazing, curing, and in research and
development.
How Does Induction Heating Work?
Induction produces an electromagnetic field in a coil to transfer energy to a
work piece
to be heated. When the electrical current passes along a wire, a magnetic
field is
produced around that wire.
Key Benefits of Induction
The benefits of induction are:
= Efficient and quick heating
= Accurate, repeatable heating
= Safe heating as there is no flame
= Prolonged life of fixturing due to accurate heating
Methods of Induction Heating
Induction heating is done using two methods:
The first method is referred to as eddy current heating from the I2R losses
caused from
the resistivity of a work piece's material. The second is referred to as
hysteretic heating,
in which energy is produced within a part by the alternating magnetic field
generated by
the coil modifying the component's magnetic polarity.
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Hysteretic heating occurs in a component up to the Curie temperature when the
material's magnetic permeability decreases to 1 and hysteretic heating is
reduced. Eddy
current heating constitutes the remaining induction heating effect.
When there is a change in the direction of electrical current (AC) the
magnetic field
generated fails, and is produced in the reverse direction, as the direction of
the current
is reversed. When a second wire is positioned in that alternating magnetic
field, an
alternating current is produced in the second wire.
The current transmitted through the second wire and that through the first
wire are
proportional to each other and also to the inverse of the square of the
distance between
them.
When the wire in this model is substituted with a coil, the alternating
current on the coil
generates an electromagnetic field and while the work piece to be heated is in
the field,
the work piece matches to the second wire and an alternating current is
produced in the
work piece. The I2R losses of the material resistivity of the work piece
causes heat to be
created in the work piece of the work piece's material resistivity. This is
called eddy
current heating.
Plastics processors today encounter many barriers to an autonomous injection
molding operation. This is because the levers that control the stability of
the operation
are often varying in ways that are either difficult, or in some cases
impossible, for the
processor to control. Overcoming these challenges requires: 1) a robust
process that
can withstand the normal variations in materials, mold, machine, and
environment;
and 2) a control system that can intelligently adapt to the variations that
are outside
The iMFLUX technology:
Works by controlling the filling process by actual plastic pressure filling
and packing
the mold using a low and constant plastic pressure. The key to making the
process
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work is a proprietary control system that eliminates flow hesitations, packs
the part as
it fills, and reduces pressure loss within the mold. This allows plastic to
flow much
slower than conventional processing techniques, and results in a process with
lower
pressure, shorter cycle time, and the ability to adapt in real time as molding
conditions
vary.
iMFLUX controls the filling process by maintaining plastic pressure at a
lower, and
more constant pressure. In so doing, the process is inherently less
susceptible to
variations that shut down a conventional process.
The reason the process is so robust is that it actively controls plastic
pressure during
molding, which is the number-one factor impacting the quality and consistency
of an
injection molded plastic part. This overcomes the inconsistency of
conventionally
controlled processing where screw velocity is maintained constant, but plastic
pressure varies as material and molding conditions change. When it comes to
autonomous molding, the iMFLUX technology is steering the process based on
what
really matters¨plastic pressure¨a massive advantage.
iMFLUX can adapt the process to handle variations, even variations well
outside of the
normal range, much easier than can be achieved with a conventional process.
This is
possible because the iMFLUX is a simple process, essentially pressure and
time. On
traditional injection molding, adapting to changes requires modifying several
variables¨injection velocity, transfer position (or cavity pressure), holding
pressure,
and holding time. What's more, the holding time itself must accommodate
variations
that have complex interactions.
The iMFLUX technology, adjustments are limited essentially to plastic pressure
(how
much pressure is driving the plastic in to the mold) and time (how long is
this pressure
applied). The simplicity of the process enables iMFLUX to create highly
advanced
control algorithms that can handle variations well beyond what is practical on
the
conventional injection molding technology.
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The ability to reliably process variable materials is one of the industry's
biggest needs,
since processors are being asked to run more and more recycled and lower-cost
materials. Often these materials have varying viscosity, making them very
difficult to
handle. Conventional injection molding is set up to run parts at a static set
of process
conditions, and as even relatively small material variations occur, process
adjustments
are needed to maintain part quality. Recent advances in technology have made
it
easier to manage material variations on conventional injection molding,
however,
that process is still inherently unstable due to its sensitivity to transfer
position and
pressure. The iMFLUX technology is much less susceptible to such changes,
since it
has no transfer position and adjusts in real time to variations in material
rheology.
Blocked Cavities:
A traditional molding process is set to inject a certain volume of plastic
into a mold,
regardless of the ability of the mold to accept this volume. This can create
issues if a
gate becomes blocked, or if a part is not ejected completely, leaving nowhere
for the
plastic to go. Depending on the number of mold cavities and cavity volumes,
this will
result in bad parts and potential damage to the mold.
The iMFLUX technology works differently, since it is continuously controlling
the
process and monitoring plastic pressure. If a mold cavity becomes blocked, the
system immediately recognizes this change and profiles the injection velocity
to match
what is needed for the current state of the mold. Not only does this prevent
tool
damage, the process actually makes good-quality parts in the remaining
cavities.
Similar to automated braking on your car, the system understands when to slow
the
movement of the screw to optimally fill the cavity. This feature is
particularly helpful
with multicavity molds where the processor needs to keep a mold running at
less than
full cavitation. In this case, the mold cavities can simply be turned off
without the need
to develop a new modified process. This is not possible in conventional
injection
molding.
Leaky Check-Rings & Worn Barrels:
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Consistent check-ring functioning is necessary with traditional velocity-based
process
control to maintain a consistent polymer volume at transfer. Even small
variations can
cause big issues with part quality. Using the iMFLUX technology, a leaking
check ring
has virtually no impact on the process, since the process is completely
reliant on
plastic pressure with real-time feedback. If the check ring leaks, iMFLUX
simply
accelerates the screw to compensate for the leakage. Conventional injection
molding relies on static process settings and cannot make dynamic adjustments
for
inconsistent check-ring performance. Using iMFLUX technology these adjustments
is
not necessary, as long as the press can build plastic pressure, a completely
repeatable process can be obtained. This is true whether the repeatability
issues are
consistent shot-to-shot, or sporadic in nature. To achieve truly autonomous
molding
the process must be able to adapt to these kinds of common variations, or it
cannot be
effective in achieving a stable, repeatable process.
An advanced feature released by iMFLUX earlier this year, called Auto-
Viscosity
Adjust (AVA), enables the iMFLUX technology to manage even larger variations
than
the base iMFLUX technology. The new feature can handle viscosity shifts of 50
MFI
or more. AVA works by detecting viscosity changes, then modifying filling
pressure to
achieve the same filling time shot-to-shot. The process adjusts in real time
without
needing operator input. This is true regardless of the source of variation,
which can
include regrind variation, percentage of regrind, colorant changes, moisture
level of
the material, or temperature variation. Basically, if the machine can melt it,
the iMFLUX technology can process it.
Another feature just released enables the control system to compensate for
material
density shifts, even shot-to-shot. Called Precision Shot, the technology works
by first
building shot pressure to a predetermined threshold, followed by metering the
shot
into the mold. This feature is only possible when controlling the process
using plastic
melt pressure, enabling the system to accurately determine that the check ring
has
seated and that the target compression of the melt has been achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
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The embodiments set forth in the drawings are illustrative and exemplary in
nature and
not intended to limit the subject matter defined by the claims:
FIG. 1 illustrates a diagrammatic front view of a plastic extrusion machine
according to
one or more embodiments shown and described herein;
FIG. 2 is a illustration of a breaker plate for extrusion molding at low,
substantially
constant pressure in accordance with an embodiment of the disclosure;
FIG. 3 is a illustration of a blow molding machine for molding at low,
substantially
constant pressure in accordance with another embodiment of the disclosure;
FIG. 4 is a schematic illustration of a parison entering a blow mold;
FIG. 5 is a schematic illustration of a bottle blow mold process for molding
at low,
substantially constant pressure in accordance with another embodiment of the
disclosure;
FIG. 6 illustrates a diagrammatic front view of a plastic injection molding
machine
according to one or more embodiments shown and described herein;
FIG. 7 illustrates a diagrammatic front view of a hot runner mold that could
be improved
by the method of injection molding at low, substantially constant pressure in
accordance
with an embodiment of the disclosure;
FIG. 8 illustrates a diagrammatic front view of a more detailed hot runner
mold;
FIG. 9 illustrates a diagrammatic view of the iMFLUX low-pressure process
molding
thick-to-thin-to-thick in this PP demo part. This application requires
automatic control
software and sensors that provide absolutely constant filling pressure, with
no hesitation
enabling a 0.030 inch. Diameter runner having a 3-inch long "filament" portion
before
entering and filling the cavity of the part without freezing.
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DETAILED DESCRIPTION
All pressures disclosed herein are gauge pressures, which are pressures
relative to
ambient pressure.
Disclosed herein is a method of injection molding at low, substantially
constant melt
pressures. Embodiments of the disclosed method now make possible a method of
injection molding that is more energy¨and cost¨effective than conventional
high-
velocity injection molding process. Embodiment of the disclosed method
surprisingly
allow for the filling of a mold cavity at low melt pressure without
undesirable premature
hardening of the thermoplastic material in the mold cavity and without the
need for
maintaining a constant temperature or heated mold cavity. As described in
detail below,
one of ordinary skill in the art would not have expected that a constant
pressure method
could be performed at low pressure without such premature hardening of the
thermoplastic material when using an unheated mold cavity or cooled mold
cavity.
Embodiments of the disclosed method also allow for the formation of quality
injection
molded parts that do not experience undesirable sink or warp without the need
to
balance the pre-injection mold cavity pressure and the pre-injection pressure
of the
thermoplastic materials. Thus, embodiments of the disclosed method can be
performed
using atmospheric mold cavities pressures and eliminate the need for including
pressurizing means in the mold cavity.
Embodiments of the method can also produce quality injection molded parts with
significantly less sensitivity to variations in the temperature, viscosity,
and other such
properties of the thermoplastic material, as compared to conventional high-
pressure
injection molding process. In one embodiment, this can advantageously allow
for use of
thermoplastic materials formed from recycled plastics (e.g., post-consumer
recycled
plastics), which inherently have batch-to-batch variation of the material
properties.
Additionally, the low melt pressures used in the disclosed method can allow
for use of
low hardness, high thermal conductive mold cavity materials that are more cost
effective
to manufacture and are more energy efficient. For example, the mold cavity can
be
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formed of a material having a surface hardness of less than 30 Rockwell C (Rc)
and a
thermal conductivity of greater than 30 BTU/HR FT F. In one embodiment, the
mold
cavity can be formed of an aluminum alloys, such as, for example aluminum
alloys 6061
Al and 7075 Al.
Embodiments of the disclosed method can further allow for the formation of
high quality
thin-walled parts. For example, a molded part having a length of molten
thermoplastic
flow to thickness (L/T) ratio of greater than 100 can be formed using
embodiments of
the method. It is contemplated the embodiments of the method can also form
molded
parts having an L/T ratio greater than 200, and in some cases greater than
250.
Molded parts are generally considered to be thin walled when a length of a
flow channel
divided by a thickness of the flow channel T is greater than 100 (i.e.,
UT>100).
A sensor may be located near the end of fill in the mold. This sensor may
provide an
indication of when the melt front is approaching the end of fill in the mold.
The sensor
may sense pressure, temperature, optically, or other means of identifying the
presence
of the polymer. When pressure is measured by the sensor, this measure can be
used to
communicate with the central control unit to provide a target "packing
pressure" for the
molded component. The signal generated by the sensor can be used to control
the
molding process, such that variations in material viscosity, mold
temperatures, melt
temperatures, and other variations influencing filling rate, can be adjusted
for by the
central control unit. These adjustments can be made immediately during the
molding
cycle, or corrections can be made in subsequent cycles. Furthermore, several
readings
can be averaged over a number of cycles then used to make adjustments to the
molding process by the central control unit. In this way, the current
injection cycle can
be corrected based on measurements occurring during one or more cycles at an
earlier
point in time. In one embodiment, sensor readings can be averaged over many
cycles
so as to achieve process consistency.
Once the mold is completely filled, the melt pressure and the mold pressure,
if
necessary, are reduced to atmospheric pressure at time and the mold cavity can
be
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opened. During this time if using an injection molding machine, the
reciprocating
screw stops traveling forward. Advantageously, the low, substantially constant
pressure
conditions allow the shot comprising molten thermoplastic material to cool
rapidly inside
the mold, which, in various embodiments, can occur substantially
simultaneously with
venting of the melt pressure and the mold cavity to atmospheric pressure.
Thus, the
injection molded part can be ejected from the mold quickly after filling of
the mold cavity
with the shot comprising molten thermoplastic material.
Melt Pressure
As used herein, the term "melt pressure" refers to a pressure of the molten
thermoplastic material as it is introduced into and fills a mold cavity of a
molding
apparatus. During filling of substantially the entire mold cavity, the melt
pressure of the
shot comprising molten thermoplastic material is maintained substantially
constant at
less than 6000 psi. The melt pressure of the shot comprising molten
thermoplastic
material during filling of substantially the entire mold cavity is
significantly less than the
injection and filling melt pressures used in conventional injection molding
processes and
recommended by manufacturers of thermoplastic materials for use in injection
molding
process. Other suitable melt pressures include, for example, less than 5000
psi, less
than 4500 psi, less than 4000 psi, and less than 3000 psi. For example, the
melt
pressure can be maintained at a substantially constant pressure within the
range of
about 1000 psi to less than 6000 psi, about 1500 psi to about 5500 psi, about
2000 psi
to about 5000 psi, about 2500 psi to about 4500 psi, about 3000 psi to about
4000 psi,
and about 3000 psi to less than 6000 psi.
As described above, a "substantially constant pressure" refers to a pressure
that does
not fluctuate upwardly or downwardly from the desired melt pressure more than
30% of
the desired melt pressure during filling of substantially the entire mold
cavity with the
shot comprising molten thermoplastic material. For example, the substantially
constant
pressure can fluctuate (either as an increase or decrease) from the melt
pressure about
0% to about 30%, about 2% to about 25%, about 4% to about 20%, about 6% to
about
15%, and about 8% to about 10%. Other suitable fluctuation amounts include
about 0,
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2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, and 30%. The melt pressure
during
filling of substantially the entire mold cavity can increase or decrease,
respectively, for
example, at a constant rate, and be considered substantially constant so long
as the
maximum increase or decrease in the melt pressure during filling of
substantially the
entire mold cavity is no greater than the 30% of the desired melt pressure. In
yet
another embodiment, the melt pressure during filling of substantially the
entire mold
cavity can increase over a portion of time and then decrease over a remaining
portion of
time. This fluctuation will be considered a substantially constant pressure so
long as the
maximum increase or decrease in the melt pressure during filing is less than
30% of the
desired melt pressure.
The melt pressure of the thermoplastic material filling into the mold cavity
can be
measured using, for example, a pressure transducer disposed at the filling
point. The
location in the molding apparatus where the molten thermoplastic material
enters the
mold cavity. For example, for a molding apparatus having a single mold cavity
coupled
to a nozzle, the filling point can be at or adjacent to the nozzle.
Alternatively, for a
molding apparatus having a plurality of mold cavities and a runner system for
transporting the molten thermoplastic material from the nozzle to each of the
mold
cavities, the filling points can be the points of contact between the runner
system and
each of the individual mold cavities. The molten thermoplastic material is
maintained at
the substantially constant melt pressure as it is transported through the
runner system.
In general, the runner system is a heated runner system that maintains the
melt
temperature of the shot comprising molten thermoplastic material as it is
transported to
the mold cavities.
The melt pressure of the thermoplastic material during filling of
substantially the entire
mold cavity can be maintained, for example, by measuring the melt pressure
using a
pressure transducer disposed at the nozzle and maintaining a constant pressure
at the
nozzle. In another embodiment, the melt pressure of the shot comprising
thermoplastic
material during filing of substantially the entire mold cavity can be measured
using a
pressure transducer disposed in the mold cavity opposite the gate.
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In another embodiment, once substantially the entire mold cavity is filled,
the melt
pressure can be increased to fill and pack the remaining portion of the mold
cavity.
Maintaining Substantially Constant Pressure
A closed loop controller and/or another pressure regulating devices may be
used
instead of the closed loop controller. For example, a pressure regulating
valve (not
shown) or a pressure relief valve (not shown) may replace a controller to
regulate the
melt pressure of the molten thermoplastic material. More specifically, the
pressure
regulating valve and pressure relief valve can prevent over pressurization of
the mold.
Another alternative mechanism for preventing over pressurization of the mold
is to
activate an alarm when an over pressurization condition is detected.
Thus in another embodiment, the molding apparatus can include a pressure
relief valve
disposed between an breaker plate and the mold cavity. The pressure relief
valve has a
predetermined pressure set point, which is equal to desired melt pressure for
the filling
of the mold. The melt pressure during the filling of the mold cavity is
maintained
substantially constant by applying a pressure to the molten thermoplastic
material to
force the molten thermoplastic material through the pressure relief valve at a
melt
pressure higher than the predetermined set point. The pressure relief valve
then
reduces the melt pressure of the thermoplastic material as it passes through
the
pressure relief valve and is introduced into the mold cavity. The reduced melt
pressure
of the molten thermoplastic material corresponds to the desired melt pressure
for filling
of the mold cavity and is maintained substantially constant by the
predetermined set
point of the pressure release valve.
In one embodiment, the melt pressure is reduced by diverting a portion of
thermoplastic
material to an outlet of the pressure relief valve. The diverted portion of
the
thermoplastic material can be maintained in a molten state and can be
reincorporated
into the injection system, for example, through the heated barrel.
Mold Cavity Pressure
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As used herein, the "mold cavity pressure" refers to the pressure within a
closed mold
cavity and/or an open extrusion mold, and/or blow molding mold. The mold
cavity and/or
an open extrusion mold, and/or blow molding mold. Pressure can be measured,
for
example, using a pressure transducer placed inside the mold cavity and/or an
open
extrusion mold, and/or blow molding mold. In embodiments of the method, prior
to
introducing molten thermoplastic material into the mold cavity and/or an open
extrusion
mold, and/or blow molding mold., the mold cavity pressure is different than
the pressure
of the molten thermoplastic material. For example, the mold cavity pressure
can be less
than the pressure of the molten thermoplastic material. In another embodiment,
the
mold cavity pressure can be greater than the pressure of the molten
thermoplastic
material. The mold cavity pressure can have a pressure greater than
atmospheric
pressure. In yet another embodiment, the mold cavity can be maintained at a
vacuum
prior to and/or during filling.
In various embodiments, the mold cavity and/or breaker plate pressure can be
maintained substantially constant during filling of substantially the entire
mold cavity
with the shot comprising molten thermoplastic material. The term
"substantially constant
pressure" as used herein with respect to a melt pressure of a thermoplastic
material,
means that deviations from a baseline melt pressure do not produce meaningful
changes in physical properties of the thermoplastic material. For example,
"substantially
constant pressure" includes, but is not limited to, pressure variations for
which viscosity
of the melted thermoplastic material do not meaningfully change. The term
"substantially constant" in this respect includes deviations of up to
approximately 30%
from a baseline melt pressure. For example, the term "a substantially constant
pressure
of approximately 4600 psi" includes pressure fluctuations within the range of
about 6000
psi (30% above 4600 psi) to about 3200 psi (30% below 4600 psi). A melt
pressure is
considered substantially constant as long as the melt pressure fluctuates no
more than
30% from the recited pressure.
For example, the substantially constant pressure can fluctuate (either as an
increase or
decrease) from the melt pressure about 0% to about 30%, about 2% to about 25%,
about 4% to about 20%, about 6% to about 15%, and about 8% to about 10%. Other
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suitable fluctuation amounts include about 0, 2, 4, 6, 8, 10, 12, 14, 16, 18,
20, 22, 24,
26, 28, and 30%. The mold cavity pressure can be maintained substantially
constant at
a pressure greater than atmospheric pressure.
The mold cavity can include, for example, one or more vents for maintaining
the mold
cavity pressure substantially constant. The vents can be controlled to open
and close in
order to maintain the substantially constant mold cavity pressure.
In one embodiment, a vacuum can be maintained in the filling of substantially
the entire
mold cavity with the molten thermoplastic. Maintaining a vacuum in the mold
cavity
during injection can advantageously reduce the amount of melt pressure
required to fill
the cavity, as there is no air to force from the mold cavity during filling.
The lack of air
resistance to the flow and the increased pressure drop between the melt
pressure and
the end of fill pressure can also result in a greater flow length of the shot
comprising
molten thermoplastic material.
Mold Temperature
In embodiments of the method, the mold cavity is maintained at room
temperature or
cooled prior to filling of the mold with the molten thermoplastic material.
While the mold
surfaces may increase in temperature upon contact with the molten
thermoplastic
material, an internal portion of the mold cavity spaced at least 2 mm, at
least 3 mm, at
least 4 mm, at least 5 mm, at least 6 mm, at least 7 mm, at least 8 mm, at
least 9 mm,
or at least 10 mm from the most immediate surface of the mold cavity
contacting the
thermoplastic material is maintained at a lower temperature. Typically, this
temperature
is less than the no-flow temperature of the thermoplastic material. As used
herein, the
"no-flow temperature" refers to the temperature at which the viscosity of the
thermoplastic material is so high that it effectively cannot be made to flow.
In various
embodiments, the internal portion of the mold can be maintained at a
temperature of
less than 100 C. For example, the internal portion can be maintained at a
temperature
of about 10 C. to about 99 C., about 20 C. to about 80 C., about 30 C. to
about 70
C., about 40 C. to about 60 C., and about 20 C. to about 50 C. Other
suitable
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temperatures include, about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,
70, 75, 80,
85, 90, 95, or 99 C. In one embodiment, the internal portion is maintained at
a
temperature of less than 50 C.
Heretofore, when filling at low constant pressure, the filling rates were
reduced relative
to conventional filling methods. This means the polymer would be in contact
with the
cool molding surfaces for longer periods before the mold would completely
fill. Thus,
more heat would need to be removed before filling, and this would be expected
to result
in the material freezing off before the mold is filled. It has been
unexpectedly discovered
that the thermoplastic material will flow when subjected to low, substantially
constant
pressure conditions despite a portion of the mold cavity being below the no-
flow
temperature of the thermoplastic material. It would be generally expected by
one of
ordinary skill in the art that such conditions would cause the thermoplastic
material to
freeze and plug the mold cavity rather than continue to flow and fill the
entire mold
cavity. Without intending to be bound by theory, it is believed that the low,
substantially
constant pressure conditions of embodiments of the disclosed method allow for
dynamic
flow conditions (i.e., constantly moving melt front) throughout the entire
mold cavity
during filling. There is no hesitation in the flow of the molten thermoplastic
material as it
flows to fill the mold cavity and, thus, no opportunity for freeze-off of the
flow despite at
least a portion of the mold cavity being below the no-flow temperature of the
thermoplastic material. Additionally, it is believed that as a result of the
dynamic flow
conditions, the molten thermoplastic material is able to maintain a
temperature higher
than the no-flow temperature, despite being subjected to such temperatures in
the mold
cavity, as a result of shear heating. It is further believed that the dynamic
flow conditions
interfere with the formation of crystal structures in the thermoplastic
material as it begins
the freezing process. Crystal structure formation increases the viscosity of
the
thermoplastic material, which can prevent suitable flow to fill the cavity.
The reduction in
crystal structure formation and/or crystal structure size can allow for a
decrease in the
thermoplastic material viscosity as it flows into the cavity and is subjected
to the low
temperature of the mold that is below the no-flow temperature of the material.
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In various embodiments, the mold can include a cooling system that maintains
the
entire mold cavity at a temperature below the no-flow temperature. For
example, even
surfaces of the mold cavity which contact the molten thermoplastic material
can be
cooled to maintain a lower temperature. Any suitable cooling temperature can
be used.
For example, the mold can be maintained substantially at room temperature.
Incorporation of such cooling systems can advantageously enhance the rate at
which
the as-formed plastic part leaves the mold.
Thermoplastic Material
A variety of thermoplastic materials can be used in the low, substantially
constant
pressure injection molding methods of the disclosure. In one embodiment, the
molten
thermoplastic material has a viscosity, as defined by the melt flow index of
about 0.1
g/10 min to about 500 g/10 min, as measured by ASTM D1238 performed at a
temperature of about 230 C and a weight of 2.16 kg. For example, for
polypropylene the
melt flow index can be in a range of about 0.5 g/10 min to about 200 g/10 min.
Other
suitable melt flow indexes include about 1 g/10 min to about 400 g/10 min,
about 10
g/10 min to about 300 g/10 min, about 20 to about 200 g/10 min, about 30 g/10
min to
about 100 g/10 min, about 50 g/10 min to about 75 g/10 min, about 0.1 g/10 min
to
about 1 g/10 min, or about 1 g/10 min to about 25 g/10 min. The MFI of the
material is
selected based on the application and use of the molded article. For examples,
thermoplastic materials with an MFI of 0.1 g/10 min to about 5 g/10 min may be
suitable
for use as preforms for Injection Stretch Blow Molding (ISBM) applications.
Thermoplastic materials with an MFI of 5 g/10 min to about 50 g/10 min may be
suitable
for use as caps and closures for packaging articles. Thermoplastic materials
with an
MFI of 50 g/10 min to about 150 g/10 min may be suitable for use in the
manufacture of
buckets or tubs. Thermoplastic materials with an MFI of 150 g/10 min to about
500 g/10
min may be suitable for molded articles that have extremely high LIT ratios
such as a
thin plate. Manufacturers of such thermoplastic materials generally teach that
the
materials should be injection molded using melt pressures in excess of 6000
psi, and
often in great excess of 6000 psi. Contrary to conventional teachings
regarding injection
molding of such thermoplastic materials, embodiments of the low, constant
injection
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molding method of the disclosure advantageously allow for forming quality
injection
molded parts using such thermoplastic materials and processing at melt
pressures
below 6000 psi, and possibly well below 6000 psi.
The thermoplastic material can be, for example, a polyolefin. Exemplary
polyolefins
include, but are not limited to, polypropylene, polyethylene,
polymethylpentene, and
polybutene-1. Any of the aforementioned polyolefins could be sourced from bio-
based
feedstocks, such as sugarcane or other agricultural products, to produce a bio-
polypropylene or bio-polyethylene. Polyolefins advantageously demonstrate
shear
thinning when in a molten state. Shear thinning is a reduction in viscosity
when the fluid
is placed under compressive stress. Shear thinning can beneficially allow for
the flow of
the thermoplastic material to be maintained throughout the injection molding
process.
Without intending to be bound by theory, it is believed that the shear
thinning properties
of a thermoplastic material, and in particular polyolefins, results in less
variation of the
materials viscosity when the material is processed at low pressures. As a
result,
embodiments of the method of the disclosure can be less sensitive to
variations in the
thermoplastic material, for example, resulting from colorants and other
additives as well
as processing conditions. This decreased sensitivity to batch-to-batch
variations of the
properties thermoplastic material can also advantageously allow post-
industrial and
post-consumer recycled plastics to be processed using embodiments of the
method of
the disclosure. Postindustrial and post-consumer recycled plastics are derived
from end
products that have completed their life cycle and would otherwise have been
disposed
of as a solid waste product. Such recycled plastic, and blends of
thermoplastic
materials, inherently have significant batch-to-batch variation of their
material
properties.
The thermoplastic material can also be, for example, a polyester. Exemplary
polyesters
include, but are not limited to, polyethylene terphthalate (PET). The PET
polymer could
be sourced from bio-based feedstocks, such as sugarcane or other agricultural
products, to produce a partially or fully bio-PET polymer. Other suitable
thermoplastic
materials include copolymers of polypropylene and polyethylene, and polymers
and
copolymers of thermoplastic elastomers, polyester, polystyrene, polycarbonate,
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poly(acrylonitrile-butadiene-styrene), poly(lactic acid), bio-based polyesters
such as
poly(ethylene furanate) polyhydroxyalkanoate, poly(ethylene furanoate),
(considered to
be an alternative to, or drop-in replacement for, PET), polyhydroxyalkanoate,
polyamides, polyacetals, ethylene-alpha olefin rubbers, and styrene-butadiene-
styrene
block copolymers. The thermoplastic material can also be a blend of multiple
polymeric
and non-polymeric materials. The thermoplastic material can be, for example, a
blend of
high, medium, and low molecular polymers yielding a multi-modal or bi-modal
blend.
The multi-modal material can be designed in a way that results in a
thermoplastic
material that has superior flow properties yet has satisfactory chemo/physical
properties. The thermoplastic material can also be a blend of a polymer with
one or
more small molecule additives. The small molecule could be, for example, a
siloxane or
other lubricating molecule that, when added to the thermoplastic material,
improves the
flowability of the polymeric material.
Other additives may include foaming agents and other expanding additives,
inorganic
fillers such calcium carbonate, calcium sulfate, talcs, clays (e.g.,
nanoclays), aluminum
hydroxide, CaSiO3, glass formed into fibers or microspheres, crystalline
silicas (e.g.,
quartz, novacite, crystallobite), magnesium hydroxide, mica, sodium sulfate,
lithopone,
magnesium carbonate, iron oxide; or, organic fillers such as rice husks,
straw, hemp
fiber, wood flour, or wood, bamboo or sugarcane fiber.
Other suitable thermoplastic materials include renewable polymers such as
nonlimiting
examples of polymers produced directly from organisms, such as
polyhydroxyalkanoates (e.g., poly(beta-hydroxyalkanoate), poly(3-
hydroxybutyrate-co-3-
hydroxyvalerate, NODAX (Registered Trademark)), and bacterial cellulose;
polymers
extracted from plants, agricultural and forest, and biomass, such as
polysaccharides
and derivatives thereof (e.g., gums, cellulose, cellulose esters, chitin,
chitosan, starch,
chemically modified starch, particles of cellulose acetate), proteins (e.g.,
zein, whey,
gluten, collagen), lipids, lignins, and natural rubber; thermoplastic starch
produced from
starch or chemically starch and current polymers derived from naturally
sourced
monomers and derivatives, such as bio-polyethylene, bio-polypropylene,
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polytrimethylene terephthalate, polylactic acid, NYLON 11, alkyd resins,
succinic acid-
based polyesters, and bio-polyethylene terephthalate.
The suitable thermoplastic materials may include a blend or blends of
different
thermoplastic materials such in the examples cited above. As well the
different materials
may be a combination of materials derived from virgin bio-derived or petroleum-
derived
materials, or recycled materials of bio-derived or petroleum-derived
materials. One or
more of the thermoplastic materials in a blend may be biodegradable. And for
non-blend
thermoplastic materials that material may be biodegradable.
Exemplary thermoplastic resins together with their recommended operating
pressure
ranges are provided in the following chart:
Injection Pressure Material Material Full Name Range (PSI) Company Brand
Name pp Polypropylene 10000-15000 RTP RTP
100 Imagineering series Plastics Poly- propylene Nylon 10000-18000 RTP RTP
200 Imagineering series Plastics Nylon ABS Acrylonitrile 8000-
20000 Marplex Astalac Butadiene ABS Styrene PET Polyester 5800-14500 Asia AIE
PET International 401F Acetal 7000-17000 API
Kolon Kocetal Copolymer PC Polycarbonate 10000-15000 RTP RTP
300 Imagineering series Plastics Poly- carbonate PS Polystyrene 10000-
15000 RTP RTP 400 Imagineering series Plastics SAN Styrene 10000-15000 RTP RTP
500 Acrylonitrile Imagineering series Plastics PE LDPE & 10000-15000 RTP RTP
700 HDPE Imagineering Series Plastics TPE Thermoplastic 10000-15000 RTP RTP
1500 Elastomer Imagineering series Plastics PVDF Polyvinylidene 10000-
15000 RTP RTP 3300 Fluoride Imagineering series Plastics PTI Poly- 10000-
15000 RTP RTP
4700 trimethylene Imagineering series Terephthalate Plastics PBT Polybutylene
10000-
15000 RTP RTP 1000 Terephthalate Imagineering series Plastics PLA Polylactic
Acid 8000-15000 RTP RTP 2099 Imagineering series Plastics
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While the molten thermoplastic material maintaining the melt pressure of the
molten
thermoplastic material at a substantially constant pressure of less than 6000
psi,
specific thermoplastic materials benefit from the invention at different
constant
pressures. Specifically: PP, nylon, PC, PS, SAN, PE, TPE, PVDF, PTI, PBT, and
PLA at
a substantially constant pressure of less than 10000 psi; ABS at a
substantially constant
pressure of less than 8000 psi; PET at a substantially constant pressure of
less than
5800 psi; Acetal copolymer at a substantially constant pressure of less than
7000 psi;
plus poly(ethylene furanate) polyhydroxyalkanoate, polyethylene furanoate (aka
PEE) at
substantially constant pressure of less than 10000 psi, or 8000 psi, or 7000
psi or 6000
psi, or 5800 psi.
As described above, a low and substantially constant pressure method can
achieve one
or more advantages over conventional molding processes e.g. being cost
effective and
having a efficient process that eliminates the need to balance the pre-
injection
pressures of the mold cavity and the thermoplastic materials, a process that
allows for
use of atmospheric mold cavity pressures and, thus, simplified mold structures
that
eliminate the necessity of pressurizing means, the ability to use lower
hardness, high
thermal conductivity mold cavity materials that are more cost effective and
easier to
machine, a more robust processing method that is less sensitive to variations
in the
temperature, viscosity, and other material properties of the thermoplastic
material, and
the ability to produce quality injection molded parts at low pressures without
premature
hardening of the thermoplastic material in the mold cavity and without the
need to heat
or maintain constant temperatures in the mold cavity.
Parts molded using a conventional, higher pressure process usually have a
reduced
number of oriented bands when compared to a part molded using a low constant
pressure process.
Parts molded using a low constant pressure process may have less molded-in
stress. In
a conventional process, the velocity-controlled filling process combined with
a higher
transfer or switchover to pressure control may result in a part with high
levels of
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undesirable molded-in stress. If the pack pressure is set too high in a
conventional
process, the part will often have an over-packed gate region.
Moreover, one skilled in the art will recognize the teachings disclosed herein
may be
used in the construction of stack molds, multiple material molds including
rotational and
core back molds, in combination with in-mold decoration, insert molding, in
mold
assembly, and the like.
While particular embodiments have been illustrated and/or described herein, it
should
be understood that various other changes and modifications may be made without
departing from the spirit and scope of the claimed subject matter. Moreover,
although
various aspects of the claimed subject matter have been described herein, such
aspects need not be utilized in combination. It is therefore intended that the
appended
claims cover all such changes and modifications that are within the scope of
the claimed
subject matter.
The method and/or machinery could also use constant low-pressure molding in an
injection blow molding process, by controlling the filling process by actual
plastic
pressure filling and packing the mold and/or part of the mold using a low and
constant
plastic pressure, that eliminates flow hesitations, packs the part as it
fills, and reduces
pressure loss within the mold as it fills, the polymer is injection molded
onto a core pin;
then the core pin is rotated to a blow molding station to be inflated and
cooled. The
process is divided into three steps: injection, blowing and ejection.
The method and/or machinery could also use constant low-pressure molding in an
extrusion blow molding process, by controlling the filling process by actual
plastic
pressure filling and packing the mold and/or part of the mold using a low and
constant
plastic pressure, that eliminates flow hesitations, packs the part as it
fills, and reduces
pressure loss within the mold as it fills, plastic is melted and extruded into
a hollow tube
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(a parison). This parison is then captured by closing it into a cooled metal
mold. Air is
then blown into the parison, inflating it into the shape of the hollow bottle,
container, or
part. After the plastic has cooled sufficiently, the mold is opened, and the
part is ejected.
Continuous and Intermittent are two variations of Extrusion Blow Molding. In
continuous
extrusion blow molding the parison is extruded continuously and the individual
parts are
cut off by a suitable knife. In Intermittent blow molding there are two
processes: straight
intermittent is similar to injection molding whereby the screw turns, then
stops and
pushes the melt out. With the accumulator method, an accumulator gathers
melted
plastic and when the previous mold has cooled and enough plastic has
accumulated, a
rod pushes the melted plastic and forms the parison. In this case the screw
may turn
continuously or intermittently. With continuous extrusion the weight of the
parison drags
the parison and makes calibrating the wall thickness difficult. The
accumulator head or
reciprocating screw methods use hydraulic systems to push the parison out
quickly
reducing the effect of the weight and allowing precise control over the wall
thickness by
adjusting the die gap with a parison programming device.
The method and/or machinery could also use constant low-pressure molding in
extruders
for 3D printingTypes of extruders (depending on the drive) by controlling the
process by
actual plastic pressure leaving the nozzle, e.g. having an adjustable nozzle
and/or
breaker plate/pressure valve enabling the nozzle to distribute its material at
a low and
constant plastic pressure, that eliminates flow hesitations. Within extruders
for 3D
printing there are two types depending on the type of drive: Direct and
Bowden. In the
direct extruder, as its name suggests, the filament runs directly from the cog
of the
extruder to the HotEnd. There are even systems in which these two parts are
together.
The method and/or machinery could also have a constant low-pressure extrusion
in an
injection molding machine given the constant low-pressure molding by
controlling the
filling process by actual plastic pressure filling and packing the mold and/or
part of the
mold using a low and constant plastic pressure, that eliminates flow
hesitations, packs
the part as it fills, and reduces pressure loss within the mold as it fills
using at least
one breaker plate to build the necessary back pressure needed to keep a
constant low
pressure. The holes in the breaker plate would automatic create some friction
heat and
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having a heat sensor on both sides of the breaker plate would enable a better
control
and uniformity of the plastic material passing through the breaker plate e.g.
also having
the breaker plate temperature controlled by cooling and/or heating measures
The method and/or machinery could also have a constant low-pressure extrusion
in an
injection molding machine where the breaker plate and/or pressure valve could
be
added to the injection unit and/or being built in to a manifold being bolted
on to the mold
in the machine and/or being part of such mold e.g. built in to a hot runner
manifold. The
apparatus holding the breaker plate and/or pressure valve could also be
controlling
shear heat and/or measuring the temperature of the material entering and/or
leaving the
obstacle/pass way creating the shear heat e.g. the breaker plate potentially
having the
possibility to control the passage size creating the shear heat. This could
include the
control of heat, cooling, pressure and flow speed to achieve the desired
output
The method and/or machinery could also have a breaker plate in the injection
unit of an
injection molding machine given the constant low-pressure molding using at
least one
breaker plate to control the uniformity of the material composition including
temperature.
A breaker plate could also be placed in the hot runner manifold of the mold in
the
injection molding machine. Here having the benefit that the hot runner system
already
was set up for temperature control. And now it would also be possible to
control friction
heat e.g if the holes in the breaker plate was matching the size of the gates
into the
cavity/cavities.
The method and/or machinery could also have a constant extrusion with at least
on
breaker plate having traps build in enabling separation of materials of
different density,
viscosity e.g. also with temperature deviations like having hot and cooler
areas for the
material to pass this made possible given the constant low pressure.
Consistent low
pressure protects the plastic material from degenerating and makes it much
better to
recycle both coming from virgin material as well as going through the
recycling process.
When different types of plastics are melted together, they tend to phase-
separate, like
oil and water, and set in these layers. The phase boundaries cause structural
weakness
and delamination in the resulting material, meaning that polymer blends are
useful in
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only limited applications. The two most widely manufactured plastics,
polypropylene and
polyethylene, behave this way, which limits their utility for recycling. Each
time plastic is
recycled, additional virgin materials must be added to help improve the
integrity of the
material. So, even recycled plastic has almost always new plastic material
added in.
The same piece of plastic can only be recycled about 2-3 times before its
quality
decreases to the point where it can no longer be used. Consistent low pressure
protect
the plastic material from degenerating and makes it much better to recycle and
when
processed through an extruder under consistent low pressure it could e.g. be
possible
to direct dissimilar materials in a fixed direction enabling separation and/or
centering of
the unwanted and/or wanted material into the center core of a given extruded
profile
minimizing surface blemishes and delamination of the extruded product.
The method and/or machinery could also have a constant extrusion with at least
on
breaker plate having traps build in enabling enhanced mixing/compounding of
materials
of different density, viscosity e.g. also with temperature deviations like
having hot and
cooler areas for the material to flow through positioning e.g. additives like
glass fiber or
blowing agent in the center of the melt flow enabling enhanced surface on the
finished
parts, this made possible given the constant low pressure. Consistent low
pressure also
enabling a longer profile in the extrusion mold with extra cooling due to the
no hesitation
in the flow front enabling straighter and more homogenic extruded profiles
leaving the
extruder.
The method and/or machinery could also have a constant extrusion with at least
on
breaker plate having traps build in enabling separation of materials of
different density,
viscosity e.g. in a twin extruder e.g. with dissimilar screws e.g. also with
temperature
deviations like having hot and cooler areas/zones in the extruder for the
material to pas
through. This made possible given the constant low pressure that has proven an
excellent success rate going thick to thin and back to thick without
hesitation in uneven
fill rates in cavities in injection molds. Consistent low pressure furthermore
protects the
plastic material from degenerating and makes it much better to recycle both
coming
from virgin material as well as going through the recycling process.
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The method and/or machinery could also have a constant extrusion in an
injection
molding machine given the constant low pressure molding allowing a traditional
injection
unit to have much larger and more humogen plasticizing output extruding the
plastic into
the cavity/cavities than just injecting the plasticized material is in front
of the screw tip,
also needing a material cushion left in front of the screw for injection into
the mold
during the holding pressure phase.
The method and/or machinery could also have a constant extrusion in an
injection
molding machine given the constant low pressure molding using at least one
breaker
plate to build the necessary back pressure needed to keep a constant low
pressure
when using the extrusion feature on a injection unit on a traditional
injection molding
machine. This would also enable a given injection molding machine to have a
much
wider range of shot weight without the degeneration of the material in the
injection unit.
The method and/or machinery could also have a constant extrusion in an
injection
molding machine given the constant low pressure molding using at least one
breaker
plate to build the necessary back pressure needed to keep a constant low
pressure
when using the extrusion feature on an injection unit on a traditional
injection molding
machine. E.g. combining the extrusion feature with injecting the plasticized
material is in
front of the screw tip thereby increasing the material that can be introduced
into the
cavity/cavities in the machine and e.g applying a constant extrusion of the
material
using the space in front of the screw to hold a cushion while the mold open
and closes
and/or during the holding pressure phase of the molding process. These
features could
also be used in one of the three main types of blow molding: extrusion blow
molding,
injection blow molding, and injection stretch blow molding.
The method and/or machinery could also have a blow mold that has a cavity that
fills
(e.g. neck and thread on a bottle) due to the low constant fill without
hesitation where
the material packs as it fills where after filling neck and thread turns into
extrusion e.g.
by mechanically opening space for the extrusion, and/or injection of a parison
by
controlling the filling process during the actual plastic pressure filling and
packing the
mold and/or part of the mold using a low and constant plastic pressure, that
eliminates
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flow hesitations, packs the part as it fills, and reduces pressure loss within
the mold as
it fills. The parison is then clamped into a mold and air is blown into it.
The air pressure
then pushes the plastic out to match the mold. Once the plastic has cooled and
hardened the mold opens up and the part is ejected.
The method and/or machinery could also have a constant extrusion in an blow
molding
machine given the constant low pressure molding using at least one breaker
plate
and/or pressure valve to build the necessary back pressure needed to keep a
constant
low pressure enabling it to pack e.g. the entry area (the neck and thread
portion) of a
bottle blow mold as it fills, where after it acts as an extrusion mold for the
rest of the
parison. The parison is then clamped into a mold and air is blown into it. The
air
pressure then pushes the plastic out to match the mold. Once the plastic has
cooled
and hardened the mold opens up and the part is ejected.
The method and/or machinery could also have a constant extrusion in an blow
molding
machine given the constant low pressure molding using at least one breaker
plate
and/or pressure valve to build the necessary back pressure needed to keep a
constant
low pressure enabling it to pack e.g. the entry area (the neck and thread
portion) of a
bottle blow mold as it fills this packable portion of the blow mold e.g.
having slides
and/or core pulls being movable in respect to the rest of the blow mold.
The method and/or machinery could also have a constant low pressure extrusion
in an
blow molding machine given the constant low pressure molding using at least
one
breaker plate and/or pressure valve to build the necessary back pressure
needed to
keep a constant low pressure enabling and/or controlling the filling process
by actual
plastic pressure filling and packing the mold and/or part of the mold using a
low and
constant plastic pressure, that eliminates flow hesitations, packs the part as
it fills, and
reduces pressure loss within the mold as it fills it to pack material in part
and/or in full
using one of the three main types of blow molding: extrusion blow molding,
injection
blow molding, and injection stretch blow molding.
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The method and/or machinery could also have a constant extrusion in an blow
molding
machine given the constant low pressure molding using at least one breaker
plate
and/or pressure valve to build the necessary back pressure needed to keep a
constant
low pressure enabling it to pack the material better and more consistent in
parison
and/or preform enabling a better blow molded product.
The method and/or machinery could also have a constant low pressure extrusion
in an
blow molding machine given the constant low pressure molding using at least
one
breaker plate to build the necessary back pressure needed to keep a constant
low
pressure enabling it to pack e.g. the entry area (the neck and thread portion)
of a bottle
blow mold as it fills.
The method and/or machinery controlling the filling process by actual plastic
pressure
filling and packing the extrusion mold and/or part of the mold using a low and
constant
plastic pressure, that eliminates flow hesitations, packs the part as it
fills, and reduces
pressure loss within the mold as it fills could also have a compression
molding feature
compressing the initial plastic profile as it comes out the extrusion tool
from one or more
angles/surfaces
The method and/or machinery could also have a compression molding feature
having
one or more compressing wheels with continues compressing cavities and/or
cores
shaping the initial plastic profile as it comes out the extrusion tool from
one or more
angles/surfaces
The method and/or machinery could also have a continues low pressure label
applied to
the plastic profile as it comes out the extrusion tool from one or more
angles/surfaces
The method and/or machinery could also have a continues low barrier label
applied to
the plastic profile as it comes out the extrusion tool from one or more
angles/surfaces
The method and/or machinery could also have a continues stamping/cutting
and/or
shaping of parts from the plastic profile as it comes out the extrusion tool
from one or
more angles/surfaces
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The method and/or machinery could also have a continues stamping/cutting
and/or
shaping of parts from the plastic profile as it comes out the extrusion tool
having the
excess material from the plastic profile returned into the extruder for a
continues re-use
The method and/or machinery could also have a continues stamping/cutting
and/or
shaping of pre-foamed preforms for e.g. shoe soles from the plastic profile as
it comes
out the extrusion tool from one or more angles/surfaces followed by the
preform getting
placed in a heated mold cavity for the final expansion and/or compression
The method and/or machinery could also have a continues stamping/cutting
and/or
shaping of parts from the plastic profile as it comes out the extrusion tool
from one or
more angles/surfaces where one of the operations is pressing a hinge function
into the
profile and bending the hinge stretching the plastic molecules into the
opening direction
enhancing the function and lifetime of the hinge
The method and/or machinery could also have a new innovative hot runner system
due
to the possibilities of the constant low-pressure technology controlling the
filling process
by actual plastic pressure filling and packing the mold and/or part of the
mold using a
low and constant plastic pressure, that eliminates flow hesitations, packs the
part as it
fills, and reduces pressure loss within the mold as it fills. Having proved
that it enables
filling of unbalanced and/or different size cavities. Therefore, the manifolds
of this new
hot runner system would need less height since it would not need the extra
layers to
balance the different hot runner drops. The new system could e.g. have small
breaker
plates of e.g different configuration to e.g accommodate a straight feed line
to e.g ten
hot runner drops.
The method and/or machinery could also have a new innovative hot runner system
due
to the constant low-pressure technology that has proved that it enables
filling of
unbalanced and/or different size cavities. Therefore, the manifolds of this
new hot
runner system would need less height and could have more cavities feed by hot
runner
drops in a given mold plate due to the design freedom in having the need for a
balanced
feed system as current hot runner systems have for injection molding today.
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The method and/or machinery could also have a new innovative hot runner system
due
to the constant low-pressure technology that has proved that it enables
filling of
unbalanced and/or different size cavities. Therefore, the manifolds of this
new hot
runner system could enable extrusion molding and the different forms of blow
molding
to benefit from these new hot runner systems that in standard injection molds
with cold
runners have shown how long thin cold runner lines can feed thick walled parts
in
cavities without any and/or very little hesitation in the fill pattern.
The method and/or machinery could also have a new innovative hot runner system
based on the possibilities of the constant low-pressure technology enabling
e.g. a 0.030
inch. Diameter runner Having a 3-inch long "filament" portion before entering
and filling
the cavity of the part without freezing diameter and length can vary depending
on part
size and choice of material. Having at least one cold runner portion that is
reheated
during every molding cycle before injection of the next portion molten plastic
material
making the thin filament molten again and given a relative thin diameter of
the filament it
can be reheated relative fast eliminating the use of expensive standard hot
runner
drops.
The method and/or machinery could also have a new innovative hot runner system
based on the possibilities of the constant low-pressure technology enabling
e.g. a 0.030
inch. Diameter runner Having a 3-inch long "filament" portion before entering
and filling
the cavity of the part without freezing diameter and length can vary depending
on part
size and choice of material. Having at least one cold runner portion that is
reheated
during every molding cycle before injection of the next portion molten plastic
material
making the thin filament molten again and given a relative thin diameter of
the filament
it can be reheated relative fast
For heating non-conductive materials such as plastics, induction can be used
to heat an
electrically conductive susceptor e.g., graphite, which then passes the heat
to the non-
conducting material. Induction produces an electromagnetic field in a coil to
transfer
energy to a work piece to be heated. The material used to make the work piece
can be
a metal such as copper, aluminum, steel, brass or aloeids and mixed materials
created
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for strength and conductivity. It can also be a semiconductor such as
graphite, carbon
or silicon carbide. Induction heating finds applications in processes where
temperatures
are as low as 100 C (212 F) and as high as 3000 C (5432 F).
Other heating applications can be used to reheat the filament parts of the
mold and in it
might also be possible to use this new innovative hot runner system for high
pressure
injection molding application. The filament part could also be a more
traditional form of
gate design that resides in a mold part/component that can be reheated a
predetermined time during each injection molding cycle.
The method and/or machinery could also have a new innovative hot runner system
having conductive heating as heating source in whole or in part e.g. in
combination with
a traditional heated hot runner manifold. The conductive heating as heating
source in
whole or in part could also be used in combination with a three plate molds
that are
used when part of the cold runner system is on a different plane to the
injection location.
The runner system for a three-plate mold sits on a second parting plane
parallel to the
main parting plane. This second parting plane enables the runners and sprue to
be
ejected when the mold is opened.
The conductive heating as heating source in whole or in part could also be
used in
combination with insulated runners that normally are unheated, this type of
runner
requires extremely thick runner channels to stay molten during continuous
cycling.
These molds have extra-large passages formed in the mold plate. During the
fabrication
process, the size of the passages in conjunction with the heat applied with
each shot
results in an open molten flow path. This inexpensive system eliminates the
added cost
of the manifold and drops but provides flexible gates of a heated hot runner
system. It
allows for easy color changes.
The abovementioned suggestions are meant to be used in both as standalone and
in
combinations and in part combinations not limited to any of the described
molding
technologies in creation of new patent claims for current and/or dependent
patent
applications.
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