Note: Descriptions are shown in the official language in which they were submitted.
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PREFORM POST-MOLD COOLING METHOD AND APPARATUS
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus
for molding and cooling plastic molded articles such as
preforms made of single or multiple materials such as plastic
resins. In particular, the invention teaches a rapid injection
molding process where the molded articles, such as PET
preforms, are ejected from the mold before the cooling step is
complete. This is possible as a result of the utilization of a
new post-mold cooling process and apparatus where the preforms
are cooled internally by convection heat transfer, after being
removed from the mold and retained outside the mold area. The
present invention also teaches additional external cooling,
done through either convection or conduction heat transfer,
which may take place at least partially simultaneously with the
internal cooling.
Proper cooling of molded articles represents a very
critical aspect of the injection molding process because it
affects the quality of the article and impacts the overall
injection cycle time. This becomes even more critical in
applications where semicrystalline resins are used, - such as the
injection molding of PET preforms. After injection, the PET
resin remains in the mold cavity space for cooling for a
sufficient period of time to prevent formation of crystalline
portions and to allow the preform to solidify before being
ejected.
Two things typically happen if a preform is rapidly
ejected from a mold in order to reduce the cycle time of the
injection process. The first is that the preform is not
uniformly cooled. In most instances, the bottom portion
opposed to the mold gate is crystallized. The amount of heat
accumulated in the walls of the preforms during the injection
process will still be high enough to induce post molding
crystallinity especially in the gate area of the preform. The
gate area is a very critical spot because cooling of the mold
in this portion is not effective enough and also because the
resin in the mold cavity space is still in contact with the hot
stem of the hot runner injection nozzle. If this area of a
preform remains crystalline above a certain size and depth,
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this will weaken the quality of a blown article. The second is
that the preform will be too soft and thus can be deformed
during the next handling steps. Another critical area of a
preform is the neck finish portion which in many instances has
a thicker wall and thus retains more heat than the other
portions. This neck portion needs aggressive post-mold cooling
to prevent it from becoming crystallized. Also aggressive
cooling tends to make the neck solid enough to sustain further
manipulations.
Many attempts have been made in the past to improve the
cooling efficiency of PET injection molding systems, but they
have not resulted in a significant improvement in the quality
of the molded preforms or a substantial reduction of the cycle
time. Reference is made in this regard to the US Patent
4,382,905 to Valyi which discloses an injection molding method
where the molded preform is transferred to a first tempering
mold for a first cooling step and then to a second tempering
mold for a final cooling step. Both tempering molds are similar
to the injection mold and have internal means for cooling their
walls that make contact with the preform during the cooling
process. Valyi 1905 does not teach the provision of cooling
devices located on the means for transferring the preforms from
the molding area or additional cooling devices that circulate a
fluid coolant inside the molded parison.
US Patent 4,592,719 to Bellehache discloses an injection
molding method for fabricating PET preforms where molded
preforms are removed from the injection cores by a first
movable device comprising vacuum sucking devices for holding
the preforms and also comprising air absorption (convection)
cooling of the outer surface of the preform. A second cooling
device is used by Bellehache '719 in conjunction with a second
movable device to further cool the inside of the preforms also
by air absorption. See Fig. 22 herein. Bellehache 1719 does
not teach cold air blowing inside a preform which has a
significantly higher cooling effect with respect to sucking or
absorbing ambient air and also does not teach cooling means by
conduction heat transfer located in intimate contact with the
preforms wall and air blow means directed to the dome portion
of the preforms. Bellehache suffers from a number of
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deficiencies including less cooling efficiency, less
uniformity, longer cooling time, high potential for preform
deformation.
US Patent No. 5,176,871 and 5,232,715 show a preform
cooling method and apparatus. The molded preform is retained by
the injection molding core outside the mold area. The mold
core is cooled by a coolant that does not make contact with the
molded preform. A cooling tube larger than the preform is
placed around the preform to blow cooling air around the
preform. The principal problem with the apparatus and method
shown in these patents is that the preform is retained in the
mold core and this significantly increases the cycle time.
Also internal cooling is not achieved by direct contact between
coolant and the preform.
Further reference is made to US Patents 5,114,327,
5,232,641, 5,338,172, and 5,514,309 that teach a preform
internal cooling method using a liquid coolant. Preforms
ejected from a mold are transferred to a preform carrier
having vacuum means to retain the preforms in place without
making contact with the preforms' external wall. The preforms
carrier however does not have any cooling devices. Cooling
cores are further introduced inside the preforms retained by
the carrier and a cooling fluid is blown inside the preforms to
cool them. The coolant is further removed by the same vacuum
means that retain the preforms from the chamber surrounding the
preforms. These patents do not teach blowing cold air inside a
preform where the air freely leaves the preform after cooling.
These patents also do not teach simultaneous cooling of the
preforms internally and externally or a preform carrier having
cooling means. See Fig. 21 shown herein.
Further reference is made to Japanese Pat. Discl. 7-171888
which teaches a preform cooling apparatus and method. A molded
preforms robot carrier is used to transfer the preforms to a
cooling station. The robot includes external cooling of the
preforms walls by conduction thermal transfer using a water
coolant. The cooling station comprises a first movable transfer
robot that has a rotary hand portion including vacuum means for
holding the preforms and also external cooling of the preforms
walls by conduction thermal transfer. The molded preforms are
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transferred from the robot carrier to the hand portion. The
hand portion is moved from position A to position B where it is
rotated by 900 in order to transfer the preforms (cooled so far
only at the exterior) to a cooling tool. The cooling tool has
means to hold the preforms, devices to cool the inside of the
preforms by blowing air and devices to cool the outside of the
preforms by either blowing air or water cooling. The internal
cooling which is employed is shown in FIGS. 19 and 20 herein.
This patent does not teach a cooling method where internal and
external cooling are performed as soon as possible from the
moment the preforms are ejected from the mold and into a
carrier plate. It also does not teach simultaneous internal
and external cooling of the preforms while they are retained by
the movable robot carrier. Therefore, this cooling method is
not fast enough and does not prevent crystallinity formation
outside the mold.
Figures 19 and 20 show known methods of internally cooling
preforms where a cooling device is located outside the preform
and is used to blow cool air inside the preform. Because the
air nozzle is located outside the preform, the incoming cold
air flow will inevitably interfere and mix at least partially
with the outcoming warm flow. This will significantly reduce
the cooling efficiency. If the cooling device is on the same
axis with the preform, the approach of Figure 19 is ineffective
because there is no air circulation in the preform. If the
cooling device is laterally shifted as in Figure 20, internal
air circulation is achieved, but this is still ineffective
because one side of the preform is better and faster cooled
than the other. The coolant has a quasi-divergent flow profile
with a non-symmetrical profile. This profile is very
ineffective and it does not allow to concentrate the cooling
fluid/gas towards the sprue gate or dome portion.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to
provide a method and apparatus for producing preforms which
have improved cooling efficiency.
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It is a further object of the present invention to provide
a method and apparatus as above which produce preforms having
improved quality.
It is yet another object of the present invention to
provide a method and apparatus as above which reduce overall
cycle time.
The foregoing objects are obtained by the apparatus and
method of the present invention.
In one embodiment, the innovative molding and cooling
method of the present invention includes removing the preforms
from the mold before the preforms are fully cooled inside the
mold, i.e. the preforms retain a certain amount of heat that
may potentially crystallize the sprue gate portion, the neck
finish portion or the entire preform; retaining the preforms
outside the molding area; and internally cooling the preforms
by convection heat transfer so that crystallization does not
occur in any of those regions.
In another embodiment, the innovative molding and cooling
method of the present invention comprises removing the preforms
from the mold before the preforms are fully cooled inside the
mold, i.e. they still retain a certain amount of heat that may
potentially crystallize the sprue gate portion, the neck finish
portion or the entire preform; retaining the preforms outside
the molding area; internally cooling the preforms by convection
heat transfer so that crystallization does not occur in any of
the aforementioned regions, said cooling step comprising
placing the coolant in direct contact with the preform; and
externally cooling the preforms by convection heat transfer so
that crystallization does not occur in any of the
aforementioned regions. The external cooling step may be
performed simultaneously, at least partially simultaneously, or
sequentially, with respect to the internal cooling step.
In yet another embodiment, the innovative molding and
cooling method of the present invention comprises removing the
preforms from the mold before the preforms are fully cooled
inside the mold, i.e. they still retain a certain amount of
heat that may potentially crystallize the sprue gate portion,
the neck finish portion, or the entire preform; retaining the
preforms outside the molding area; internally cooling the
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preforms by convection heat transfer so that crystallization
does not occur in any of those regions, said internal cooling
step comprising placing the coolant in direct contact with the
preform; and externally cooling the preform by conduction heat
transfer so that crystallization does not occur in any of the
aforementioned regions. The external cooling step may be
performed simultaneously, at least partially simultaneously, or
sequentially with respect to the internal cooling.
In each of these embodiments, the preforms are ejected
from the mold and are retained external to the mold by means
independent of the mold such as for example a movable take-off
plate. Such independent retention means may retain one batch
of molded preforms or several batches of preforms
simultaneously. When several batches are held by the
independent means, the batches will have different temperatures
because they were molded at different times. According to the
present invention, the molded preforms will be cooled in
different sequences internally and externally using the cooling
method of the present invention. In each embodiment of the
present invention, internal cooling is done using means, such
as cooling pins, that enter at least partially inside the
preform and circulate coolant therein. Cooling is
preferentially done by a quasi-symmetrical flow of coolant
delivered inside the preform that can be directed towards the
portions of the preforms that need more cooling than the
others, such as the sprue gate and the neck finish. In a
preferred embodiment of the present invention, the coolant is
directed toward the bottom or dome portion of the preform so as
to create an annular flow of coolant.
In certain embodiments of the present invention, the
innovative internal cooling of the preforms is supplemented by
external cooling that can be done in several ways. For
example, the external cooling can be done on a take out plate
(single or multiple position) that has cooling means operative
using either conductive (cooled water) or convection (air/gas)
heat transfer. It also can be done on a take out plate (single
or multiple position) that does not have cooling means whereby
the preforms are only partially in contact with their holders.
In this way, cooling gas/air can be delivered by an independent
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cooling device to directly touch the outer surface of the
preforms.
Yet in another embodiment, the preforms are retained in a
take-out plate that does not have any cooling means and are
solely cooled internally by the new cooling pins of the present
invention.
The innovative cooling approach of the present invention
in one embodiment may be achieved by removing the preforms or
molded articles from the mold, holding the preforms or molded
articles in a robot take-off-plate having a system for cooling
the exterior surfaces of the preforms or molded articles, and
thereafter engaging cooling means inside the preform or molded
article to effect simultaneous cooling of the exterior and
interior surfaces. According to the present invention, an
additional cooling step is introduced whereby the temperature
of the preform is reduced using heat transfer by convection,
such as by circulating a cooling gas inside the preform.
The method and apparatus according to the present
invention, as previously discussed, can be advantageously used
to prevent crystallization in the most critical areas of
preforms, namely the bottom part or the dome portion where the
sprue gate is located and the neck portion. Further, the
cooling method and apparatus of the present invention can be
integrated into an injection-blow molding machine where the
cooled preforms with no crystallinity are further temperature
conditioned and blown into bottles.
In accordance with one aspect of the present invention, a
method for preventing crystallization in an injection molded
preform by enhanced out of the mold cooling comprises injecting
a molten material into a mold formed by two mold halves or
plates which in a mold open position are spaced apart so as to
define a molding area; cooling the molten material while in the
mold cavity space formed by the mold halves up to a temperature
substantially close to the crystal-glass transition temperature
of the molten material so that the molded article can be
mechanically handled outside the mold without suffering any
geometrical deformation; opening the mold halves by a distance
sufficient to allow a molded article carrier to be moved
between the two mold halves; ejecting the molded articles from
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the mold and transferring them to the movable carrier; cooling
the molded articles while they are in the movable carrier by
heat transfer conduction to reduce crystallinity whereby the
coolant is blown air; and further internally cooling the molded
articles by convection heat transfer until each molded article
is substantially free of any crystallized portion. The same
method can be implemented using a movable carrier including
convective heat transfer means for external cooling.
In accordance with one aspect of the present invention,
the apparatus for forming a de-crystallized, injection molded
article comprises a mold having two mold halves which can be
moved between a mold closed position and a mold open position;
means for injecting molten material into the mold while the
mold halves are in the mold closed position; means for cooling
the molten material in the cavity space formed by the mold
halves up to a temperature substantially close the crystal-
glass transition temperature of the molten material so that the
molded article can be mechanically handled outside the mold
without suffering any geometrical deformation; means for
opening the mold so that the mold halves are spaced apart a
distance sufficient to allow a molded article carrier to be
moved in between the two mold haves; means for ejecting the
molded articles from the mold; means for transferring the
molded articles to the movable carrier; said carrier having
means for holding the preforms and for cooling the molded
articles by heat transfer conduction to reduce crystallinity;
and means for further internally cooling the molded articles by
convection heat transfer until each molded article, preferably
the entire article, is substantially free of any crystallized
portion, particularly in the mold gate area. The same method
can be implemented using a movable carrier with conductive heat
transfer means for external cooling.
As used herein, the terms "take-off plate", t'take-out
plate" and "end of arm tool" are used interchangeably and refer
to the same structure(s).
Other details of the method and apparatus of the present
invention, as well as other objects and advantages attendant
thereto, are set forth in the following detailed description
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and the accompanying drawings in which like reference numerals
depict like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing the preform temperature vs. time
during and after the injection step;
Fig. 2 is a schematic representation of a preform in the
mold;
Figs. 3(a) and 3(b) show the temperature gradient across
the walls of a molded preform during cooling;
Fig. 3c shows the temperature profile along the preform
walls.
Fig. 4 is a sectional view showing a prior art injection
mold;
Fig. 5 is a sectional view showing a movable robot
including an end-of-arm-tool (EOAT) device placed in the
molding area between the stationary and movable mold plates;
Figs. 6(a) and 6(b) are side views showing an embodiment
of the present invention including a robot take-off-plate (or
end of arm tool, EOAT) and a frame holding cooling pins;
Figs. 6(c) and 6(d) are front views of the embodiment of
Figs. 6(a) and 6(b);
Figs. 7(a) - 7(d) shows the frame and the cooling pins
according to a first embodiment of the present invention;
Figs. s(a) - (g) shows several cooling pin designs
according to the present invention;
Figs. 9(a) and 9(b) illustrate a more detailed view of the
cooling pins according to two embodiments of the present
invention;
Fig. 10(a) shows a preform having crystallized zones as
they are generated in prior art methods;
Fig. 10(b) shows a preform without crystallized zones as
it results after the method of the present invention;
Figs. 11(a) - 11(1) show another embodiment of the frame
and cooling pins according to the present invention;
Fig. 12 is a sectional view of a system wherein air
cooling channels are incorporated into the mold halves;
Figs. 13(a) and 13(b) are side views of another embodiment
of the cooling system of the present invention;
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Fig. 14 is a top view of an injection molding system
having another embodiment of the cooling system of the present
invention;
Fig. 15 is a sectional view of yet another embodiment of
the cooling system of the present invention showing the
mechanism for cooling the interior of the molded articles
attached to the take-off-plate;
Fig. 16 illustrates an embodiment of the present invention
wherein a take-off plate with no cooling means is used to
remove the molded preforms from the molding area;
FIG. 17 illustrates the construction of an alternative
cooling pin in accordance with the present invention;
FIGS. 18(a) and (b) illustrate the construction of yet
another alternative cooling pin in accordance with the present
invention;
FIGS. 19 and 20 illustrate prior art methods for cooling
the interior of a preform;
FIG. 21 illustrates another prior art system for cooling
the interior and the exterior of a preform;
FIG. 22 illustrates a prior art system using the sucking
of ambient air to cool a preform; and
FIG. 23 illustrates an alternative frame construction with
cooling pins on multiple surfaces of the frame.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, Fig. 1 is a graph showing
the evolution of preform temperature vs. time during and after
the injection step. Fig. 2 is a schematic representation of a
preform while it is in the mold. As can be seen from this
figure, cooling while in the mold is typically effected by
cooling tubes 12 and 14 positioned within the mold cavity 16
and the mold core portions 18 respectively. As a result,
cooling is effected from both sides of the preform 11.
Further, as shown in Fig. 2, the mold cavity plate 16 typically
has a gate region 20 at which the bottom part or the dome
portion 22 of the preform 11 is formed. The preform has a neck
finish portion 13 which sometimes has a thick wall which is
difficult to cool to prevent crystallinity.
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Figs. 3(a) and 3(b) show the temperature gradient across
the walls of a molded preform during cooling. Fitj. 3(a) shows
the temperature gradient inside the mold, while Fig. 3(b) shows
the temperature gradient outside the mold. Fig. 3(c) shows the
temperature profile along the preform walls. The temperature
spike represents the temperature in the dome or sprue gate
portion of the preform.
Referring now to Fig. 4, an injection mold is provided
which includes a stationary mold half or plate 32 having an
array of mold cavities 34 and a movable mold half or plate 36
having an array of mold cores 38. The mold cavity plate 32 is
in fluid communication with a manifold plate (not shown) that
receives molten material from an injection unit (not shown) of
an injection molding machine. The mold cavities 34 receive the
molten material from hot runner nozzles (not shown), such as
for example a valve gated nozzle (not shown), through mold
cavity gates 40. The mold cavities are each surrounded by
cooling means 42 for cooling the molten material in the cavity
space formed by the mold core 38 and the mold cavity 34 when
the mold plates 32 and 36 are in a mold closed position. The
cooling means 42 are preferably formed by cooling channels
embedded within the mold plate 32 for conducting a cooling
fluid. As previously discussed, the mold cores 38 and the mold
cavities 34 form in the mold closed position a plurality of
mold cavity spaces (not shown) that are filled with molten
material through the mold gates 40 during the injection step.
The mold cores 38 also include means 44 for cooling the molten
material in the cavity space. The cooling means 44 preferably
comprise a cooling tube within each mold core. The mold core
plate 36 further includes an ejector plate 46 which is used to
remove the molded preforms 48 from the mold cores 38. The
operation of the ejector plate 46 is well known in the prior
art and does not form part of the present invention. In fact,
the ejector plate 46 may comprise any suitable ejector plate
known in the art.
According to the current invention, any molten plastic,
metal or ceramic material can be injected into the mold cavity
space and cooled into a desired article using the mold system
of Fig. 4. In a preferred embodiment of the current invention,
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the molten material is PET and the molded article is a preform.
According to the present invention however, the molded article
can also be a preform made of more than one material, such as
for example virgin PET, recycled PET and an appropriate barrier
material such as for example EVOH.
As is known in the art, a preform is molded by closing the
mold, injecting the molten material into the cavity space,
initiating cooling of the cavity space, filling the cavity
space, holding the molten material under pressure, performing
final in-mold cooling, opening the mold, ejecting the
solidified articles or preforms from the cores and transferring
the articles or preforms to a take-off plate. According to
the present invention, in order to reduce the overall cycle
time, the residence time of the preform in the mold has to be
minimal so that the mold is able to produce batches of preforms
as fast as possible. The problem with a reduced residence time
in the mold is that the cooling time has to be reduced, but in
such a manner that the molded articles or preforms are solid
enough to withstand all the subsequent handling steps without
deformation. A reduced cooling time is a problematic option
because the articles or preforms are not sufficiently and
uniformly cooled by the cooling means 42 and 44. The amount of
heat retained by the article or preform after being cooled
inside the mold for a reduced time and immediately after
opening the mold is very significant and depends on the
thickness of the molded article or preform. This internal heat
has the potential to generate crystallized portions at the
sprue gate area or dome portion of the molded article or
preform, the neck finish portion of the molded article or
preform, or the entire preform. In order to prevent the
crystallization of the molded article or preform, a very
aggressive cooling method has to be used. During cooling,
attention must be paid so as to control the shrinkage of the
molded articles which can adversely affect their final
dimensions.
Fig. 5 illustrates one embodiment of a robot take-off
plate 60 which can be used in the cooling method of the present
invention. The take-off plate 60 includes a plurality of
hollow holders or receptacles 62 which can be water cooled
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tubes. Typical take-off plates which may be used for the take-
off plate 60 are shown in US Patent No. 5,447,426 to Gessner et
al. and in US Reissue Patent No. RE 33,237 to Delfer, III. In
operation, the mouth of a plurality of holders 62 are aligned
with the mold cores 38 of the mold plate 36. Transfer of the
molded articles 48 to the holders 62 is effected by operation
of the ejector plate 46. According to the present invention,
the take-off plate 60 can be provided with a number of holders
62 equal to the number of mold cores 38 or a larger number of
holders 62 such as a multiple of the number of mold cores, for
example three or four times the number of mold cores. By
having more holders 62 than the number of cores 38, it is
possible to retain some of the molded articles for a time
longer that a single molding cycle and thereby increase the
cooling time while maintaining a high output of molded
articles. The method of the present invention can be carried
out irrespective of the relative number of molded articles
retained by the holders 62. Nevertheless, in the preferred
embodiment of the invention, the robot take-off plate 60 has a
number of holders 62 which represent three times the number of
cores 38. This means that the take-off plate 60 does not
always carry a number of preforms or molded articles equal to
the number of holders 62. This also means that a single batch
of preforms can be moved back more than once into the mold area
between the mold core and cavity plates to pick up other
batches of molded articles, while being cooled by intimate
contact between the hollow tubes 64 within the take-off plate,
which tubes 64 carry a cooling liquid such as water, and the
external wall of the preforms as shown in more detail in the
aforementioned US Patent No. 5,447,426. The heat transfer
between the tubes 64 and the hot molded articles released from
the mold is performed through conduction. More particularly,
any solid material incorporating any cooling means can be used
and brought into intimate contact with the exterior wall of the
molded articles to cool the molded articles. By using a
cooling system based on heat transfer through conduction
implemented through an intimate contact between the molded
article or preform and the cooling means, the shape of the
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article or preform is maintained without deformations or
scratches caused by handling.
If desired, the conductive cooling means 64 employed in
the take-off plate can be replaced by a convective heat
transfer means. Any suitable convective heat transfer means
known in the art may be used with the take-off plate 60 to
effect cooling of the exterior surfaces of the molded articles
or preforms carried by the take-off plate 60.
Referring now to Figs. 6(a) and 6(b), an additional
cooling device 70 is used in conjunction with the robot take-
off plate 60 to enhance the post-mold cooling efficiency by
allowing simultaneous cooling of the interior and exterior
surfaces of the molded articles or preforms by convective heat
transfer and thus reduce the cycle time and improve the quality
of the preforms. The additional cooling device 70 includes an
array of elongated cooling pins 74 whose role is to deliver a
cooling fluid inside the molded articles held by the take-off
plate 60. In a preferred embodiment of the present invention,
the cooling fluid is mostly directed and delivered directly
into the dome (sprue gate) portion 22 of the molded article or
preform, which portion has the highest chance to become
crystalline due to the reduction of the cooling time in the
mold. The cooling fluid is introduced so as to create an
annular flow pattern. According to the present invention, the
cooling fluid could be any appropriate coolant, such as for
example a liquid or a gas. In a preferred embodiment of the
present invention, the cooling fluid is pressurized air
delivered at through a channel 90 located inside the cooling
pin 74. This aspect of the present invention is shown in more
detail in Fig. 9(a).
Fig. 9(a) illustrates a cooling pin 74 in accordance with
the present invention positioned within a preform or molded
article 48 being cooled. In order to create an optimum flow of
the cooling agent, the cooling pin 74 is introduced deep inside
the preform 48 so that the coolant can reach the dome or sprue
gate portion 22. More than that, the cooling pin 74 acts as an
additional cooling core. The cooling pin 74 also contributes
to the creation of an annular flow pattern which has a higher
cooling potential than other cooling flow patterns. Also by
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using the novel cooling pin 74, the incoming blown cold air and
outcoming warm air are completely separated and thus prevents
mixing of the two.
As shown in Fig. 9(a), the cooling pin 74 is positioned
centrally within the preform or molded article, preferably so
that the central axis 220 of the cooling pin 74 is aligned with
the central axis 222 of the preform. As can be seen from this
figure, the outer wall 224 of the cooling pin 74 in an upper
region UP is spaced from the inner wall 226 of the preform by a
distance D. Additionally, the outlet nozzle 92 of the cooling
pin 74 is spaced from the inner wall 228 of the dome portion 22
by a distance d. In order to create the desired annular flow
pattern of cooling fluid, it is preferred that the ratio of d:D
be within the range of about 1:1 to about 10:1. It is also
highly desirable that the outlet nozzle 92 of the cooling pin
be formed by a divergent nozzle construction. While it is
preferred to use a divergent nozzle for the outlet 92, it is
possible to form the outlet 92 from a straight walled nozzle
construction.
Because cooling pin 74 goes deep inside the preform and
behaves like a cooling core as well, the pattern of outcoming
warm air that freely escapes from the preform has an annular
shape.
While a preferred construction for the cooling pin has
been shown in Fig. 9(a), as shown in Figs. 8(a) through 8(g),
17 and 18, the cooling pins 74 can have various sizes and
shapes to achieve various cooling effects. For example, as
shown in Fig. 8(a), the lower portion LP of the cooling pin may
have a diameter D2 which is different from the diameter D, of an
upper portion UP of the pin. As shown in Figs. 8(a) through
8(c), the upper portion UP of the pins may have different
shapes. Referring to Fig. 8(d), the cooling pin 74 may have
lateral outlets 82 for discharging a cooling fluid onto side
walls of the molded article where crystallinity may occur. As
shown in Fig. 8(e), the cooling pin 74 could have helical
grooves 84 to obtain specialized cooling effects. Similarly in
Fig. 8(f) and 8(g), the cooling pin 74 could have a plurality
of ribs 86 spaced about its periphery or a plurality of contact
elements 88.
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Figs. 18a and 18b illustrate a cooling pin 74 having a
plurality of radial conduits 230 for delivering coolant on
areas of the preform other than the dome portion 22 such as the
neck finish portion or the body portion. The radial conduits
230 may be spaced along the length of the cooling pin so as to
direct coolant against particular areas of a preform 48.
The cooling pins 74 can be made from any suitably
thermally conductive or thermally insulative material. If
desired, as shown in Fig.17, the cooling pin 74 may be made
from a porous material 232 so that additional coolant can be
spread in a very uniform manner on areas of a preform other
than the dome or sprue gate portion 22.
In a preferred embodiment of the present invention, the
design of the cooling pin 74 is intended to concentrate maximum
cooling at the sprue gate or dome portion 22 of the molded
article 48 and thus aggressively focus the cooling fluid to
cool this region. In this way, molded articles such as
preforms free of crystallized areas in the sprue gate or dome
portion 22 can be formed.
An alternative pin construction with a cold air blowing
system which can be used in the apparatus of the present
invention is illustrated in Fig. 9(b). As shown therein, the
pin 74 has a cold air blowing channel 90 having an outlet 92
for directing cold air against the interior surfaces of the
molded article 48, preferably the dome or sprue gate portion 22
of the molded article. The channel 90 communicates with a
source of cold air (not shown) via the inlet 94. The cooling
pin 74 is further provided with a vacuum channel 96 for
removing the cooling air from the interior of the molded
article 48. The vacuum channel 96 may be connected to any
desired vacuum source (not shown). As can be seen in Fig.
9(b), the cooling pin 74 is mounted on a portion of a frame 98
by sliding pads 100, which are used for pin self-alignment, and
a fastening means such as nut 102. The nut 102 can be secured
to the element 104 which has an exterior threaded portion (not
shown).
Referring now to Figs. 6 and 7, the array of cooling pins
74 is mounted onto a cooling frame 98 which can be made of a
lightweight material such as aluminum. According to the
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CA 02326449 2004-07-05
present invention, the cooling frame 98 can be operated in
either a vertical or a horizontal position. In both cases, the
frame 98 is movable towards the take-off plate 60 when the
take-off plate 60 reaches its final out of mold position. Any
suitable means known in the art may be used to move the frame
98 so as to advance it at a high speed so that the cooling pins
74 can be immediately introduced inside the molded article. In
a preferred embodiment of the present invention, the frame 98
is moved using hydraulic cylinders 110. According to the
present invention, the number of cooling pins 74 can be the
same or less than the number of receptacles 62 in the take-off
plate 60. According to the present invention, the take-off
plate 60 is provided with means for holding the molded
articles or preforms 48 within the receptacles 62 such as
suction means (not shown), and with means for ejecting the
preforms from the take-off plate. The holding means and the
ejection means may be those disclosed in the aforementioned US
Patent No. 5,447,426. As shown in Figs. 6(c) and 6(d), the
cooling frame 98 is provided with a plurality of spaces 112.
The spaces 112 allow finally cooled molded articles or preforms
ejected from the take-off plate 60 to be dropped onto a
conveyor 114 for transportation away from the system. In a
preferred embodiment of the present invention, the fully cooled
preforms 48 are dropped onto the conveyor 114 through the
spaces 112 by laterally shifting the cooling pins 74 relative
to the receptacles 62 holding the preforms that have to be
ejected from the take-off-plate 60. This is the case when the
cooling frame is in a horizontal position. When the cooling
frame is in a vertical position, it does not interfere with the
preforms dropped by the take-off-plate.
Referring now to Figs. 7(a) and 7(b), a first array of
cooling pins 74 is illustrated. As can be seen in Fig. 7(b),
the cooling pins 74 each have cooling air passageways 90 which
communicate with a source of cooling air (not shown) via the
passageway 122. Incorporated into the passageway 122 are a
number of air valves 124 which can be used to regulate the flow
of cooling air. In this way, variable amounts of cooling air
can be supplied to the cooling pins 74.
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Referring now to Fig. 7(c), it is also possible to
directly provide each cooling pin 74 with air frQm a source of
cooling fluid (not shown) via a simple passageway 126. Still
further, as shown in Fig. 7(d), if desired, the passageway 126
could be connected to the fluid conduit 120 in each of the
cooling pins via a flexible conduit 128.
According to one embodiment of the present invention, the
cooling pins 74 enter the preforms retained by the take-off
plate 60 in a few steps, and at each step the preforms that are
molded at different times are at different temperatures. In
order to optimize the overall cooling step and to avoid the
waste of coolant, during the first step of cooling the preforms
are very hot and thus a maximum amount of cooling air is
delivered by the pins. In the second and the subsequent steps,
the amount of cooling air directed by the pins engaging the
first molded preforms is substantially less than the amount
directed towards the newly molded and hotter preforms. In
order to further optimize the cooling process, any known
suitable temperature sensors, such as a thermocouples, can be
used to measure the temperature of the preforms before and
after cooling them so that adjustments of the cooling rate can
be done without interrupting the molding cycle. In a preferred
embodiment, thermocouples (not shown) connected to some cooling
control means (not shown) are located in the take-off plate 60
adjacent to each preform. By monitoring the temperature of
each preform, some adjustments can be made to the amount of
cooling air delivered to all cooling pins 74 or to some of the
cooling pins 74. This may also compensate for any cooling
inefficiencies or non-uniformity of the conduction cooling
means located in the take-off plate.
Referring now to Figs. 10(a) and 10(b), Fig. 10(a) shows a
preform 48, in sectional view, molded by a prior art system.
As shown therein, the preform 48 may have crystalline areas in
four different zones including the dome portion 22 and the neck
portion 13. Fig. 10(b) on the other hand shows a preform 48,
in section view, which has been manufactured using the system
of the present invention. As shown therein, there are no areas
of crystallinity.
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Another embodiment of the present invention is shown in
Figs. 11(a) through 11(1) where the take-off plate 60' is
always maintained in a vertical position during the entire
molding cycle. This eliminates a complicated motor and makes
it lighter and thus faster to move in and out of the mold space
formed between the mold halves or mold plates 32 and 36. The
cooling frame 98' used in this system has an additional
function and an additional movement. First of all, the pins
74' use blowing air to cool the molded articles or preforms and
sucking air to extract the molded articles or preforms from the
take-off plate 60'. The preforms are be held on the pins 74'
by the vacuum and removed from the tubes 62' within the take-
off plate 60' during a back movement. The cooling frame 98'
has a movement to approach and move back from the take-off-
plate 60' and further has a rotation to move from a vertical to
a horizontal position parallel to a conveyor 114' to allow the
preforms to be ejected from the pins 74' by stopping the
vacuum. According to the present invention, any suitable means
known in the art can be used to rotate the cooling frame 98'
with the pins 74'. According to a preferred embodiment of the
invention shown in Figs. 11(a) through 11(1), a stationary cam
130 is used as a very simple means to convert the translation
of the frame into a rotation so that the preforms held by the
cooling frame can be dropped onto a conveyor 114'. As shown in
Fig. 11(h), the cooling pins 74' can engage the preforms by
vacuum and remove them from the take-off plate 60'. Next the
preforms are dropped from the pins 74' onto a conveyor.
The operation of the innovative cooling apparatus of the
present invention can be understood from Figs. 6(a) through
6(d). After the in-mold cooling process which is shortened up
to the point where the articles or preforms reach a
solidification status that prevents their deformation, the mold
is opened and the take-off plate 60 is moved into the molding
area between the mold core plate 36 and the mold cavity plate
32. Relative movement between the mold core and mold cavity
plates may be performed in any manner known in the art using
any suitable means (not shown) known in the art. After the
take-off plate 60 reaches the out of the mold position, the
cooling pins 74 are engaged with the molded articles for
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WO 99/50039 PCT/US98/14972
cooling, especially in the dome area 22 of each article or
preform.
While the take-off plate 60 has been described as having
water cooled means for conduction cooling of the exterior
surfaces of the preforms within the holders 62, there are times
when one would want to not start cooling of the exterior
surfaces when the preforms are first placed within the take-off
plate. To this end, means may be provided to control cooling
within the take-off plate so that such cooling does not start
until after internal cooling of the preforms has begun and/or
finished. For example, suitable valve means (not shown) may be
incorporated into the take-off plate to prevent flow of a
cooling fluid until a desired point in time. In this way,
internal and external cooling of the preform may be preformed
simultaneously, at least partially simultaneously, or
sequentially.
Fig. 16 illustrates another embodiment wherein a take-off
plate 60" with no cooling means is used to remove the molded
preforms from the molding area. The take-off plate 60" may
have preform holders 62" sufficient in number to accommodate
either a single batch or multiple batches of preforms. The
preforms are retained by vacuum means (not shown) that through
the openings 240 suck on the sprue gate or dome portion 22 of
the preforms 48. The preforms are also retained by the holders
62" which can have any desired configuration that allows the
preforms to be directly cooled using a cooling gas/air. The
holders 62" are preferably stiff enough to retain the preforms
and have perforations or other openings 242 and 244 where the
holders do not have any direct contact with the preforms. By
having these kind of holders that only partially cover the
outer surface of the preforms, the preforms can be cooled on
their outer surfaces, while they are additionally cooled
internally by the cooling pins 74. In this case, the cooling
step comprises the transfer of the preforms from the mold to
the take-off plate 60", the movement of the take-off plate 60"
outside the molding area, to the cooling area which is adjacent
the molding area. At the cooling area, the preforms 48 are
internally cooled using the frame 98 and the cooling pins 74
that enter at least partially inside the preforms. At the same
CA 02326449 2004-07-05
time, the preforms 48 retained by the take-off plate 60" have
their exterior surfaces convectively cooled by an additional
cooling station 250 that blows a coolant fluid towards the
preform holders. As shown in Fig. 16, the additional cooling
station 250 has a plurality of nozzles 252, 254, and 256 for
blowing coolant toward the outer surfaces of the preforms. The
nozzles 252, 254, and 256 blow cooling fluid through windows
258 in the take-off plate 60" and onto the outer surface of the
preforms via windows or openings 242 and 244 in the preform
holders. The nozzles 252, 254 and 256 blow cooling fluid
through openings 242 and 244 in the preform holders 62" and
onto the outer surface of the preforms. While the additional
cooling station 250 has been shown as having nozzles for
cooling two preforms, it should be recognized that in actuality
the cooling station 250 may have as many nozzles as needed to
cool the outer surfaces of any desired number of preforms.
The use of the additional cooling station 250 allows the
preforms 48 to be simultaneously cooled inside and out using
cooling means that are independent from the take-off plate 60".
This approach makes the take-off plate 60" very light, very
fast and easy to service. If desired, the preform holders 62"
may grip the preforms solely around the neck portion, thus
leaving a more open window for the blown cooling fluid to cool
the outer portion of the preforms.
According to another embodiment of the invention, the
take-off plate may include external cooling means using blown
air or may include no cooling means. In both cases, internal
cooling is achieved using the novel cooling method and
apparatus of the present invention.
The innovative cooling method and apparatus of the present
invention are extremely beneficial for cooling preforms molded
in high cavitation molds. It is well known that the
temperature of the molten resin flowing through a mold varies
quite substantially for a variety of reasons including: (a)
non-uniform heating of the hot runner manifold; (b) formation
of boundary layers inside the manifold's melt channels; (c)
non-uniform mold cavity cooling; and (d) insufficient cooling
at the mold gate area. One consequence of the temperature
variations across the mold is that the cooling time has to be
21
CA 02326449 2004-07-05
adjusted at the local level so that the hottest preforms are
cooled before any crystallinity occurs in the final preforms.
In order to prevent formation of crystallized zones, the
cooling system of the present invention is able to provide a
different cooling pattern that can be tuned according to the
temperature signature of each mold. Sensors in the take-off
plate 60 can be provided to regulate the amount of cooling from
each cooling pin 74. Another consequence of the non-uniform
temperature inside the mold is that in most cases the gate
sprue area located on the dome section 22 of the preforms is
the hottest part of the molded preform. Because this sprue
gate portion is more slowly cooled in the mold closed position,
chances are that this portion will be highly crystalline if the
in-mold cooling is too long or if no additional cooling is
provided outside the mold. According to the present invention,
the cooling pins 74 blowing cold air inside the preform
immediately adjacent the sprue gate area is a novel operation
that prevents in a very efficient manner the formation of
crystallized areas in the preform.
The innovative cooling method and apparatus of the present
invention are also beneficial for compensating for the cooling
inefficiency of the take-off plate. It may happen that due to
the imperfect contact between the hot molded article and the
cooling tube, the temperature of the molded article held by the
take-off plate may vary across the plate. According to the
present invention, the temperature sensors located in the take-
off plate or the cooling frame can be used to provide
information to a cooling control unit that varies the amount of
cooling fluid directed to each preform.
The adaptive cooling approach mentioned so far is also
beneficial because it can take into account the fact that the
temperature pattern of the molded preforms can vary during the
day, the function of the specific resin used, the function of
the machine settings, or due to local variations in the
thickness of the preforms caused by improper valve stem
actuation in the hot runner nozzle or due to uneven core shift
in the mold cavities. These situations are neither predictable
nor easy to fix; however, the present invention provides a
22
CA 02326449 2004-07-05
mechanism to tune the post-molding cooling step for each cavity
based on the temperature of each molded article or preform.
A significant reduction of the cycle time for the benefit
of increasing the post molding cooling time can be achieved by
simplifying the design and the movements of the take-off plate
and the cooling frame. This has to take into account very
critical assembling, servicing and operation constraints such
as rigidity, movement accuracy, alignment between the cooling
pins and the molded articles or preforms on the take-off-plate
and vibrations. Also the location of the cooling frame with
the pins has to be decided in such a manner to reduce the "foot
print" of the entire machine.
Reference is made in this regard to Figs. 13(a) and 13(b)
which show another embodiment of the present invention where
the take-off plate 60 remains in a vertical position during the
additional air cooling step, i.e. parallel to the mold plates
32, 26. The cooling frame 98 is translated towards the take-
off plate 60 and the cooling pins 74 enter the molded articles
or preforms 48. After all the preforms are cooled, the cooling
frame 98 is retracted, the take-off plate 60 is rotated at 900
and parallel to a conveyor 114 and then the cooled preforms are
removed from the plate 60. This approach simplifies the design
of the cooling frame which does not need rotation means and
means to prevent its interference with the preforms ejected
from the plate.
Further reference is made to Fig. 14 which shows another
embodiment of the invention where the robot take-off plate 60
comprises additional translation means 150 to move the preforms
48 along an axis parallel to their axis of revolution. This
additional movement of the preforms 48 simplifies the cooling
frame 98 which remains substantially stationary during the
cooling process. As shown in Fig. 14, the take-off plate 60 or
other means for holding the preforms is translated along the
axis X towards the stationary cooling frame 98. After the
cooling step, the take-off plate 60 is rotated by 90 so that
it faces the conveyor 114 and thus the cooled preforms are
ejected.
Further reference is made to Fig. 15 which shows novel air
cooling means attached to the take-off-plate 60. The approach
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WO 99/50039 PCT/US98/14972
shown in this figure eliminates the need for a separate frame
for holding the cooling pins and thus reduces the;size of the
cooling system and thus of the injection molding machine. The
new cooling pins 174 have an approximate U-shape and can be
moved all together parallel to the preforms 48 so that they can
be introduced inside the preforms and moved out of the preforms
using a thin strip 176 actuated by piston BB or any other known
means. The pins 174 can be also rotated around an axis "A"
parallel to the preform so that they can be brought into or
removed from axial alignment with the preforms. This
simultaneous rotation of all the pins 174 can be achieved using
any suitable means known in the art. According to the
invention, the U-shaped cooling pins 174 have an ARM "A" that
enters the preform, an ARM "C" parallel to ARM "A" that is used
for moving ARM "A", and an ARM "B" that connects ARM "A" to ARM
"C". The rotation of the pins around the axis A of ARM "C" can
be done in various ways. As shown in Fig. 15, this can be done
using an elongated rack 178, operated by piston AA, that is in
engagement with pinions 180 attached to the ARM "C" of each
cooling pin. The same rotation can be done using frictional
means, one in translation and the other in rotation. During
the transfer of the preforms 48 from the cores 38 to the
cooling tubes 62 of the take off plate 60, the U-shaped cooling
pins 174 can be "parked" in a dedicated location located
adjacent each cooling tube 62, so that they do not interfere
with the moving preforms and less space is needed to open the
mold. Immediately after the preforms 98 are retained in the
take-off plate 60, the cooling pins 174 attached to the plate
60 are moved forward by the piston BB and the strip 176 and
when they reach a certain height which allows ARM "A" to be on
top of the preform, they are rotated in axial alignment with
the preforms and finally introduced inside the preforms through
the retreat of the piston BB. The permanent contact between
the strip 176 and each ARM "C" is provided by a coil spring 182
which operates against shoulder 181 or any other appropriate
means. A flexible tube 184 is used to supply blowing air to
each cooling pin through ARM "C". This design of the cooling
pins attached to the take-off plate brings the following
advantages: simplif ies'and reduces the size of the cooling
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WO 99/50039 PCT/US98/14972
system, improves the cooling rate because inside cooling starts
immediately after the preforms are in the take-off plate,
inside cooling can be done during the movement of the take-off
plate and practically continuously for as long as the preforms
are also cooled by the take-off plate. During the ejection of
the cooled preforms, the cooling pins must be again rotated
towards their initial position so that they are no longer
aligned with the preforms.
Further reference is made to Fig. 12 which shows air
cooling means comprising cooling channels 210 incorporated in
the mold halves 32, 36 that allow cooling of the preforms held
by the mold cores, during and immediately after opening the
mold and before the take-off plate enters the molding area.
This additional cooling step will further solidify the preform
before the take-off plate is brought into the mold area and
before they are transferred to the take-off plate.
According to another embodiment of the present invention,
that can be easily understood from other drawings in this
application, the robot and the take-off plate retain only a
single batch of preforms. After the injection steps, the take-
off plate is parked outside the mold area and cooling air or
refrigerated air is blown inside each preform from the cooling
pins. The cooled preforms are ejected form the take-off plate
that will be brought back into the molding area without
carrying any preforms.
Fig. 23 illustrates an alternative construction of the
frame 98 for holding the cooling pins 74. As shown in this
figure, the frame 98 may have cooling pins 74 on two opposed
surfaces. Further, the frame may rotate about a first axis 300
and a second axis 302 which is perpendicular to the first axis
300. Any suitable means (not shown) known in the art may be
used to rotate the frame 98 about the axes 300 and 302.
By providing this type of construction, it is possible to
have a first set of cooling pins 74 engage the preforms 48 in a
take-off plate 60 and begin internal cooling of the preforms.
The preforms 48 may then be transferred out of the holders 62
in the take-off plate 60 onto the pins 74. The frame 98 can
then be rotated about one or more of the axes 300 and 302,
while internal cooling of the preforms 48 is being carried out
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by the pins 74. After the first set of preforms has reached
the left-hand position shown in Fig. 23, a second set of
cooling pins 74 may engage a second set of preforms 48 held in
the take-off plate 60. If desired, the left-hand set of
preforms 48 can have their exterior surfaces convectively
cooled using a cooling station 304 having a plurality of
nozzles (not shown) for blowing cold air onto the exterior
surfaces. If desired, the frame 98 may have a preform
retaining plate 308 attached to it.
26
