Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02767603 2012-02-15
TO WHOM IT MAY CONCERN:
Be it known that I, Earl Master Towzey III, residing in the City of
Montgomery, County of
Montgomery, State of Alabama, a citizen of the United States of America, have
invented a new and
novel
PROCESS FOR DECREASING THE MOLD RESIDENCE
TIME IN EXTRUSION BLOW MOLDING
the following of which is a specification.
This application claims priority from U.S. Provisional Patent application
serial number
61/379,415, filed on September 2, 2010 which is incorporated herein by
reference in its entirety.
BACKGROUND OF THE INVENTION
Extruded blow mold articles are manufactured by melting a thermoplastic
material and
extruding it under high pressure through a die and mandrel forming a molten
parison curtain. The
molten parison is blown into the shape of the article using high pressure air.
In the process, there is a need to cool the inside of the mold cavity and the
article in the mold to
solidify the article in the desired shape. The cooling of the blown articles
is limited to the cooling of the
exterior side of the blown article as there is no known process for cooling
the insides of such articles in
an extrusion blow molding process. In addition to providing the shape of the
article, the molds also
serve the function of cooling the article.
The molds are cooled by plumbing a heat transfer fluid (usually cooling water,
chilled water or a
mixture of chilled water and glycol) to the jacket of the mold. There is some
prior art that uses cooled air
to blow a container producing a blown article that Is initially slightly
cooler than using air at elevated
temperatures. However, this is of marginal benefit as the air is quickly
warmed by the parison and offers
no continuing benefit. There is some injection molding processes that use a
continuing flow of liquefied
gas blowing on the exterior of the article to provide some convective cooling
affect. The cooling of the
blown article is usually the single longest part of the blow molding cycle. it
can thus be observed, that it
takes some extended period of time to cool articles in blow molding operations
by these methods.
THE INVENTION
Thus, what is disclosed and claimed herein is a process for decreasing the
mold residence time
in extrusion blow molding, wherein pressurized air is used to expand a plastic
into a blow molded article.
The process comprises providing an extrusion blow molding mold having a mold
cavity, with a
liquefied gas inlet into the mold cavity. Then, providing pressurized air to
the mold cavity through the
liquefied gas inlet during the blow molding of the article and stretching the
parison into the desired
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shape controlled by the interior mold surfaces. Also, providing a high
pressure liquefied inert gas, to the
interior of the blown article and allowing the liquefied gas to expand into a
saturated gas at a reduced
pressure, providing an evaporative cooling effect to the Interior of the blown
article.
In another embodiment, there is a system for molding an article from plastic
by extrusion blow
molding, the system comprising an extrusion blow molding system, wherein the
system has a mold. The
mold has a mold cavity, and affixed in the mold cavity, a means of providing
pressurized molding air and
high pressure liquefied gas to the mold cavity.
There Is a first control valve and a control on the inlet of the mold used to
control the flow of
blow air to the mold cavity through the blow pin body. There is at least one
outlet port out of the mold
for release of air and liquefied gas from the mold. The outlet is timed with
the blow molding cycle to
remain closed until after the article is blown and cooled.
In yet another embodiment, there is a control component for providing high
pressure liquefied
gas to an extrusion blow molding system. There is a control component
comprising a first valve on the
inlet of the mold and a control for a first valve to control the flow of
liquefied gas entering a mold cavity.
There is also a restricting orifice, expansion valve, control valve or other
throttling device used to drop
the pressure of the liquefied gas allowing it to expand into a saturated
gaseous state at very low
temperatures, instantaneously into the interior of the blown article. In
addition, there is at least one
outlet for release of the air and gas.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is schematic of existing state of the art showing a typical operation
to provide high
pressure blow air to the mold cavity and its release.
Figure 2 is a schematic of the Invention showing the operation to provide high
pressure air and
high pressure liquefied gas to the mold cavity, and the release.
DETAILED DESCRIPTION OF THE INVENTION
liquefied gases useful in this invention include any inert liquefied gas such
as nitrogen, carbon
dioxide, argon or refrigerant liquefied gases such as Freon. In this
invention, blow air is introduced to
the mold cavity to blow the container shape. The blow air is then shut off.
The liquefied gas is then
introduced into the mold cavity used by blow molding machines while
simultaneously opening the
controlled pressure vent.
The pressure of the liquefied gas is instantaneously reduced across the
throttling device
allowing it to evaporate and cool into a saturated gas at very low
temperatures on the order of about
0 F to about -100 F. The controlled pressure vent allows a continuous flow of
the liquefied gas quickly
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displacing the blow air from the Interior of the blown article and the
evaporative cooling affect quickly
cooling of the article from the Inside out while the mold cools the article
from the outside In.
Because extrusion blow molding cycle times are limited to how quickly the
article can be cooled
in order to remove the flash, this invention is a significant step forward in
providing reduced cycle times
for blow molding operations, and especially for blow molding containers.
In this Invention, it Is necessary to modify traditional blow molding systems.
Blow molding
systems typically operate by providing a parison of molten plastic to the mold
cavity, which are two
separated halves. The parison is clamped by the two halves of the mold coming
together and then
compressed air is injected into the clamped parison, which forces the soft
plastic out against the inside
configuration of the mold cavity. Since the mold is cooled by cooling water
flowing through its jacket
and the parison is cooled from contact with the mold wall, it takes a few
seconds for the re-configured
parison to cool and stabilize.
This invention provides cooling to the inside of the blown article in addition
to the cooling
provided by the molds to the external sides. The container Is blown using high
pressure air blown into
the center of the molten parison stretching the polymer to the mold walls.
Then liquefied gas is
introduced to the center of the parison cooling as it expands Into a gaseous
state.
Turning now to Figure 1, there is shown a typical schematic of a blow molding
operation using
high pressure air, wherein there is shown a source of high pressure air 1,
control of such air by timers
(not shown) thorough pressure reducing valves 3 and the like in a control
module 13, to an air manifold
assembly 4 containing two solenoid valves 5 and 8. Valves 5 and 8 control the
main air supply for the
blow air and valve 8 controls pre-blow air. The air is moved to one or more
blow pin bodies 9. Blow pin
bodies 9 are the components that actually provide the air to the parison.
During Injection of the air, the
blow pin cylinders 9 project downwardly in the mold, into the soft plastic. As
soon as the article has
expanded to the walls of the mold and has been cooled, the blow pin cylinders
9 rise out of the molded
article and the pressurized air is released and vented into the atmosphere as
is shown by the vent and
release assembly 12. It is contemplated within the scope of this invention to
allow the pressure to
release without any control therefor.
The same movement is used for providing the liquefied gas to the
parison/molded article as can
be observed from Figure 2. In addition to the high pressure air assembly,
there is a liquefied gas
assembly 10 shown therein in which the liquefied gas source 11 supplies
liquefied gas to the blow pin
bodies 9. Note that the high pressure air supply is merged (point P) with the
liquefied gas supply prior to
providing either to the blow pin bodies 9.
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In this invention, a source tank of the liquefied gas to be used is plumbed
into the molding
operation such that the liquefied gas can enter the parison through the same
inlet tube. The equipment
will also need to be equipped with a liquefied gas control valve 13 that will
control the flow of liquefied
gas to the interior of the blown article and a throttling device 14 that is
used to instantly drop the
pressure of the liquefied gas expanding it to a saturated gas. Control valve
15 and pressure control 16
for the release of the air and expanded gas mixture from the mold cavity at
some pressure below the
pressure of the blow air and the pressure of the liquefied gas. This allows
for the continuous flow and
evaporation of the liquefied gas into the mold cavity during the cooling
cycle.
There is also a control valve 17 timed with the blow mold cycle to open after
dosing the inlet of
the air and the liquefied gas for the release of pressure in the mold cavity
at the conclusion of the
cooling cycle and prior to the opening of the molds and release of the blown
article.
The liquefied gas valve should be mounted dose to the blow pins on the blow
molding machine (from
about 4 to 6 feet) in order to provide instantaneous entry of the liquefied
gas when needed. Flexible
tubes or lines convey the liquefied gas from the source tank to the valve and
from the valve to each
blow pin adapter on the blow molder. The liquefied gas should be adjustable
between 60 psi and 120 psi
to be effective.
Also, the same set up should be provided for the high pressure blowing air. As
can be observed,
each blow pin cylinders 9 should have two inlets, one for compressed air, and
one for the liquefied gas.
Two timers (not shown) have to be placed into the controller of the blow
molder. One is for pre blow air
which is turned on as the parison is extruded in order to position it for
molding. The second controls the
blow air used to stretch the parison. The pre blow air and blow air are turned
off by the timers
immediately after the article is blown. An additional timer opens the control
valve on the liquefied gas
and simultaneously opens the pressure controlled vent valve. This allows for
the continuous flow of
liquefied gas into the blown article. A throttling device on the inlet of the
liquefied gas instantly drops
the pressure of the liquefied gas allowing it to evaporate and cool. This
quickly displaces the blow air
and cools the article from the inside out. Once the article is cooled the time
closes the control valve on
the liquefied gas inlet and opens the vent valve releasing the pressure to the
atmosphere. The molds
then open and the cooled article is then removed from the molds.
Thus, the blow molding machine will call for the liquid liquefied gas
immediately following the
blow portion of the cycle and then disposes of the liquefied gas to the
atmosphere along with the
compressed air from inside the molded article after cooling is complete.
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it Is contemplated within the scope of this invention to provide the liquefied
gas flow into the
flow of the compressed air through a common manifold, instead of providing the
liquefied gas and air
to the blow pin bodies. This would require a backflow preventer to be
installed between the main blow
valve and the liquid insert liquefied gas line attached to the manifold.
S The timing of this operation is such that the compressed air to the parison
happens first, as a
direct flow of the liquefied gas without the air would result in freezing the
parison such that it could not
be expanded. Thus, the general order is that the blow molder will call for the
liquefied gas; it expands
when the valves open, traveling down into the blow manifold or the blow pins,
mixing with the
compressed air and cooling the air to between -40 F and -100 F. The super
cooled liquefied gas/ air
mixture hits the previously stretched parison that is against the mold cavity
wall, cooling it very rapidly.
When the timers finish, the air/liquefied gas mixture exhausts to the
atmosphere. The blown
articles come out of the machine colder than standard machine operations can
perform. The CPU of an
extrusion blow molding machine will call for the liquid liquefied gas. There
is no need for human
interaction except to set the parameters of the machine. Using liquefied gas
has no affect on the blown
article other than super cooling It. Current cooling is limited to how cold
the compressed air can be
made, or how cold the molds can be kept.
Current blow molding machines cool the container predominately from the
outside using chilled
water to cool the mold. Chilled water is generally limited to 20 to 44 degrees
Fahrenheit. It cannot go
any colder without risking freezing the chilled water lines and causing icing
of the mold cavities and,
cause related process issues such as condensation on the molds, causing water
marks that weaken the
structure of the molded article. Providing chilled water at these temperatures
is very costly due to the
energy required by the chiller to cool the heat transfer fluid.
The use of this invention makes the temperature of the atmosphere inside of
the article
between -40 and -100 F very quickly. The faster you move the formed article
temperature down to
ambient room temperature or lower, the faster it can come out of the mold and
be trimmed, and be
prepared to package and sell.
This invention can dramatically decrease the cycle time required to produce a
blow molded
article. This can lower the required capital outlay to achieve a given
capacity. In addition, the faster
cooling can be used to lighten the container saving raw material which is the
single largest cost of the
container. And finally, the faster cooling allows the neck of the container to
be formed more constantly
eliminating downstream processing issues.
Liquefied gases are relatively inexpensive and are readily available in the
market place.
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