Note: Descriptions are shown in the official language in which they were submitted.
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COOLING TUBE AND METHOD OF USE THEREOF
TECHNICAL FIELD
The present invention relates, in general, to cooling tubes and
is particularly, but not exclusively, applicable to cooling
tubes used in a plastic injection-molding machine to cool
plastic parts, such as plastic parisons or preforms. More
particularly, the present invention relates to a structural
configuration of these cooling tubes, and also to method of
manufacturing and using such tubes, for example in the context
of a manufacturing process for preforms made from
polyethyleneterephthalate (PET) or the like.
BACKGROUND OF THE INVENTION
In order to accelerate cycle time, molding machines have
evolved to include post mold cooling systems that operate
simultaneously with the injection molding cycle. More
specifically, while one injection cycle is taking place, the
post mold cooling system, typically acting in a complementary
fashion with a robotic part removal device, is operative on an
earlier formed set of molded articles that have been removed
from the mold at a point where they are still relatively hot,
but sufficiently solid to allow limited handling.
Post mold temperature conditioning (or cooling) molds, nests or
tubes are well known in the art. Typically, such devices are
made from aluminum or other materials having good thermal
conductivity properties. Further, it is known to use fluid-
cooled, cooling tubes for post-mold temperature conditioning of
molded plastic parts, such as plastic parisons or preforms.
Typically, such tubes are formed by conventional machining
methods from solid stock.
To improve cooling efficiency and cycle time performance, EP
patent 0 283 644 describes a multi-position take-out plate that
has a capacity to store multiple sets of preforms for more than
one injection cycle. In other words, each set of preforms is
subjected to an increased period of accentuated conduction
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cooling by retaining the preforms in the cooling tubes for more
than one injection cycle. With increased cooling, the quality
of the preforms is enhanced. At an appropriate point in time, a
set of preforms is ejected (usually by a mechanical ejection
mechanism) from the take-out plate onto a conveyor to allow a
new set of preforms to be inserted into the now vacant set of
cooling tubes.
European patent EP 0 266 804 describes an intimate fit cooling
tube for use with an end-of-arm-tool (EOAT). The intimate fit
cooling tube is water cooled and is arranged to receive a
partially cooled preform. More particularly, after the preform
has undergone some cooling within the closed mold, the mold is
opened, the EOAT extended between the cavity and core sides of
the mold and the preform off-loaded from a core into the
cooling tube that then acts to cool the exterior of the preform
through thermal conduction. As the preform cools it will
shrink and slide further inside the tube to fit snugly therein.
A problem with the known cooling tube arrangements, is that the
preform (at some point, if not from the point of introduction)
looses contact with the internal side walls of the cooling
tube, which loss of thermal contact lessens cooling efficiency
and causes uneven cooling. As will be understood, uneven
cooling can induce part defects, including deformation of
overall shape and crystallization of the plastic (resulting in
areas that are visibly hazed). Furthermore, lack of contact can
cause ovality across the circumference of the preform, while
the loss of the cooling effect can mean that a preform is
removed from the cooling tube at an excessively high
temperature. In addition to causing surface scratching and
overall dimensional deformation, premature removal of a preform
at an overly high temperature can also result in the semi-
molten exterior of preform sticking either to the tube or
another preform; all of these effects are clearly undesirable
and result in part rejection and increased costs to the
manufacturer. It is therefore desirable to configure the
cooling tube to include a means to achieve and/or maintain
contact between the outer surface of the preform and the
internal side walls of the cooling tube.
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U.S. Patent No. 4,047,873 discloses an injection blow mold in
which the cavity has a sintered porous sidewall that permits a
vacuum to draw the parison into contact with the cooling tube
sidewall.
U.S. Patent No. 4,047,873 discloses a method and apparatus for
producing bi-axially oriented blow molded articles wherein the
steps of longitudinal and radial expansion are performed
sequentially in a longitudinal stretching mold and a radial
stretching blow mold, respectively. In particular, a method is
described for the longitudinal stretching of the parison in the
longitudinal stretching mold which comprises a cavity formed in
a porous structure, and a plurality of pressure control zones
configured therealong.
Japanese patent publication 56113433 discloses a process for
producing hollow parts that includes the steps of extrusion
molding of a foam parison into a vacuum forming mold comprising
a cavity formed in a porous structure, and subsequently vacuum
forming the parison into the hollow part whereby the foam cells
in the hollow part do not collapse.
German patent publication DE 197 07 292 describes a method and
apparatus for producing aseptic bottles that includes the steps
of extrusion molding of a parison into a vacuum forming mold,
and subsequently expanding the parison in the mold by vacuum
suction whereby germs do not enter into the bottle as is the
case with conventional blow molding.
U.S. Patent No. 4,208,177 discloses an injection mold cavity
containing a porous element that communicates with a cooling
fluid passageway subjecting the cooling fluid to different
pressures to vary the flow of fluid through the porous plug.
U.S. Patent Nos. 4,295,811 and US 4,304,542 disclose an
injection blow core having a porous metal wall portion.
A "Plastics Technology Online" article entitled "Porous Molds'
Big Draw", by Mikell Knights, printed from the Internet on July
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27, 2002, discloses a porous tooling composite called METAPOR'~.
The article discloses the technique of polishing this material
to close slightly the pores to improve the surface finish and
reduce the porosity.
An article from International Mold Steel, Inc., entitled
"Porous Aluminum Mold Materials", by Scott W. Hopkins, printed
from the Internet on July 27, 2002, also discloses porous
aluminum mold materials. The materials and applications
disclosed in the above two articles refer to vacuum
thermoforming of plastics in the mold itself, in which
preheated sheets of plastic are drawn into a single mold half
via a vacuum drawn through the porous structure of the mold
half.
Another problem with known cooling tubes is that they are
expensive and time-consuming to make and assemble. Further,
the operational mass (i.e. including cooling water) of the
cooling tube is of particular concern considering that a
typical robot take-out system may include one or more sets of
cooling tubes in an array, and therefore the cumulative mass
supported by the robot quickly becomes a significant operating
and/or design consideration (i.e. inertia or momentum
considerations for the robot). Moreover, the robot typically
operates to remove many tens of preforms in a single cycle
(with present PET systems producing up to one hundred and
forty-four preforms per injection cycle) so the energy expended
by the robot and the technical specification of the robot are
unfortunately relatively high. The provision and operation of a
high specification robot therefore impose considerable
financial cost penalties on an end user. It is therefore
desirable to configure and manufacture the cooling tube
according to a simplified structure and method, respectively.
Furthermore, it is desirable to configure the cooling channels
as relatively open channels in an effort to reduce the
operational mass of the cooling tube.
U.S. Patent Nos. 4,102,626 and 4,729,732 are typical of prior
art systems in that they show a cooling tube formed with an
external cooling channel machined in the outer surface of the
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tube body, a sleeve is then assembled to the body to enclose
the channel and provide an enclosed sealed path for the liquid
coolant to circulate around the body.
WO 97/39874 discloses a tempering mold that has circular
cooling channels included within its body.
EP 0 700 770 discloses another configuration that includes an
inner and outer cooling tube assembly to form cooling channels
therebetween.
U.S. Patent No. 5,870,921 discloses an extrusion die for use in
producing aluminum alloy articles of extruded shapes or tube
having a void with defined internal dimension.
SiJNMARY OF THE INVENTION
According to a first aspect of the present invention, structure
and/or steps are provided for a tube assembly for operating on
a relatively hot, and hence malleable, molded plastic part
after it has been molded by a molding structure. The tube
assembly includes a porous member having a profiled inside
surface for receiving an outside surface portion of the molded
plastic part. The inside surface is preferably profiled to
substantially correspond with the outside surface portion of
the molded plastic part to be cooled. The tube assembly also
includes a vacuum structure configured to cooperate with the
porous member to provide a reduced pressure adjacent the inside
surface. In operation, the reduced pressure causes the outside
surface portion of the malleable molded plastic part, locatable
within the tube assembly, to contact the inside surface of the
porous member so as to allow a substantial portion of the
outside surface portion of the malleable part, upon cooling, to
attain a profile substantially corresponding to the profile of
the inside surface, and wherein a substantial disfiguring of
the shape of the outside surface portion of the at least one
plastic part is prevented.
According to a second aspect of the present invention,
structure and/or steps are provided for a porous cooling cavity
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that is configured to cooperate with a vacuum structure for
receiving and cooling a relatively hot, and hence malleable,
molded plastic article after it has been molded by a molding
structure. The porous cooling cavity includes a porous member
formed from a porous material. The porous member including (i)
an inside surface that is profiled to substantially reflect a
shape of a portion of an outside surface of the molded plastic
article, and (ii) a vacuum coupling structure. The vacuum
coupling structure of the porous member is configured to
cooperate with the vacuum structure to provide, in operation, a
reduced pressure adjacent the inside surface of the porous
member to cause the portion of the outside surface of the
malleable molded plastic article to contact the inside surface
of the porous member so as to allow the outside surface portion
of the malleable part, upon cooling, to maintain a profile
substantially corresponding to the profile of the inside
surface and thereby a disfiguring of the shape of the outside
surface portion of the molded article is substantially
prevented.
According to a third aspect of the present invention, structure
and/or steps are provided for an end-of-arm tool configured to
be carried by a robotic arm in an injection molding machine.
The end-of-arm tool includes a carrier configured to be coupled
to the robotic arm, the carrier carrying at least one molded
article cooling device. The at least one molded article cooling
device includes a porous member having a porous inside surface
that is profiled to substantially reflect a shape of a portion
of an outside surface of a relatively hot, and hence malleable,
molded article. The end-of-arm tool further includes an
evacuation structure configured to evacuate the air through the
porous member. In operation, the porous member supports the
evacuation of air through the porous inside surface to cause
the malleable molded article within the porous member to expand
to come into contact therewith, wherein a substantial
disfiguring of the shape of the outside surface portion of the
at least one plastic part is prevented.
According to a fourth aspect of the present invention,
structure and/or steps are provided for an injection mold
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robot. The injection mold robot includes an arm member
configured to be disposed adjacent an injection molding
machine, a carrier configured to be coupled to the arm member,
the carrier carrying at least one molded article cooling
device. The at least one molded article cooling device includes
a removable porous member having a porous inside surface that
is profiled to substantially reflect a shape of a portion of an
outside surface of a relatively hot, and hence malleable,
molded article. The injection mold robot further includes an
evacuation structure configured to evacuate the air through the
at least one porous member. In operation, the porous member
supports the evacuation of air through the porous inside
surface to cause the malleable molded article within the at
least one porous member to expand to come into contact
therewith, wherein a substantial disfiguring of the shape of
the outside surface portion of the at least one plastic part is
prevented.
According to a fifth aspect of the present invention, structure
and/or steps are provided for an injection molding machine. The
injection molding machine includes a molding structure that
molds at least one relatively hot, and hence malleable, plastic
part. The injection molding machine further including at least
one porous cooling cavity having a profiled inside surface that
is configured to hold and cool the at least one plastic part
after it has been molded by the molding structure. The inside
surface is profiled to substantially correspond with the
outside surface portion of the at least one plastic part to be
cooled. The injection molding machine also includes at least
one vacuum channel that is configured to provide a lower-than-
ambient pressure to the inside surface. In operation, the
lower-than-ambient pressure adjacent the inside surface causes
an outside surface portion of the at least one plastic part to
contact the inside surface of the at least one porous cavity,
wherein a substantial disfiguring of the shape of the outside
surface portion of the at least one plastic part is prevented.
According to a sixth aspect of the present invention, structure
and/or steps are provided for a method for cooling a relatively
hot, and hence malleable, molded plastic part, wherein a
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substantial disfiguring of the shape of the outside surface
portion of the at least one plastic part is prevented. The
method includes the steps of: (i) receiving the molded plastic
part into a porous cooling cavity that includes an inside
surface that is profiled to substantially correspond with an
outside surface portion of the molded plastic part to be
cooled; (ii) providing a reduced pressure adjacent the profiled
inside surface of the porous cooling cavity causing the outside
surface portion of the molded plastic part to move into contact
therewith and thereby attain a substantially corresponding
shape; (iii) extracting heat from the molded plastic part
through a heat dissipation path to solidify the molded plastic
part to the extent that the shape of the outside surface is
preserved; and (iv) ejecting the molded plastic article.
According to a seventh aspect of the present invention,
structure and/or steps are provided for forming a molded
plastic article. The molded article having a shape of at least
a portion of its outside surface defined by an inside surface
of a porous cooling cavity that is profiled to substantially
reflect a shape of a portion of an outside surface of a
relatively hot, and hence malleable, molded article to be
cooled. The molded plastic article formed by the process of:
(i) receiving the malleable molded plastic article into the
porous cooling cavity; (ii) evacuating the air surrounding the
molded plastic article through a plurality of interstitial
spaces that are configured along the inside surface of the
porous cooling cavity causing the portion of the outside
surface of the molded plastic article to move into contact with
the profiled inside surface and thereby to attain a shape
substantially corresponding to the profiled inside surface; and
(iii) extracting heat from the molded plastic article through
a heat dissipation path to solidify the molded plastic article
sufficiently such that the outer shape of the molded plastic
article is preserved; wherein the portion of the outside
surface of the cooled molded plastic article takes on a surface
finish that corresponds substantially to the interstitial
spaces of the porous cooling cavity.
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According to an eighth aspect of the present invention,
structure and/or steps are provided for a cooling tube for
cooling a portion of an injection molded article received
therein. In accordance with a preferred embodiment, the cooling
tube includes an extruded tube body having an inside surface
and an outside surface, and a plurality of cooling channels
disposed therebetween that arranged in a longitudinal direction
of said tube body. The cooling tube further including a
connecting channel configured between said cooling channels for
interconnecting said cooling channels into at least one cooling
circuit, a seal configured at each end of tube body for closing
said cooling channels, and an inlet and an outlet in said tube
body for said at least one cooling channel. The cooling tube
also includes a plug disposed in a distal end of said tube
body. The inside surface of said tube body and an inside
surface configured on said plug being machined to provide a
profiled cavity that substantially conforms with a profile of
an outer surface of said portion of said molded article.
According to a ninth aspect of the present invention, a method
for extruding the cooling tube includes the steps of: (i)
extruding a tube body having an inside surface, an outside
surface, and a plurality of cooling channels disposed
therebetween that arranged in a longitudinal direction of said
tube body; (ii) machining the inside surface of the tube body
to substantially conform with the outer surface of the molded
article; (iii) configuring a connecting channel between the
cooling channels; and (iv) forming the plug.
The present invention advantageously provides a cooling tube
structure that functions to cool rapidly and efficiently a
just-molded plastic part located within the cooling tube,
thereby improving robustness of the preform and generally
enhancing cycle time. Moreover, in the context of cooling PET
and the unwanted production of acetaldehyde arising from
prolonged exposure of the preform to relatively high
temperatures, the rapid cooling afforded by the present
invention beneficially reduces the risk of the presence of
unacceptably high levels of acetaldehyde in the finished
plastic product, such as a drink container. Beneficially, the
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FIG. 8 depicts a section through the cooling tube assembly of a
third alternate embodiment.
FIG. 9 is a sectional view of a cooling tube according to a
preferred embodiment of the present invention;
FIG. 10 is a view along section 'A-A' of FIG. 9 cooling tube;
FIG. 11 is an isometric view of a cooling tube porous insert;
and
FIG. 12 is a sectional view of a cooling tube according to an
alternative embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The present invention will now be described with respect to
embodiments in which a porous cooling tube is used in a plastic
injection molding machine, although the present invention is
equally applicable to any technology in which, following part
formation, cooling of that part is undertaken by a cooling tube
or the like. For example, the present invention can find
application in a part transfer mechanism from an injection
molding machine and a blow-molding machine.
FIG. 1 shows a typical injection molding machine 10 capable of
co-operating with a device supporting the cooling tube of the
present invention. During each injection cycle, the molding
machine 10 produces a number of plastic preforms (or parisons)
corresponding to the number of mold cavities defined by
complementary mold halves 12, 14 located within the machine 10.
The injection-molding machine 10 includes, without specific
limitation, molding structure such as a fixed platen 16 and a
movable platen 18. In operation, the movable platen 18 is moved
relative to the fixed platen 16 by means of stroke cylinders
(not shown) or the like. Clamp force is developed in the
machine, as will readily be appreciated, through the use of tie
bars 20, 22 and a machine clamping mechanism 35 that typically
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generates a mold clamp force (i.e. closure tonnage) using a
hydraulic system. The mold halves 12, 14 together constitute a
mold generally having one or more mold cavities 22, 24, with
the mold halves 12, 14 each located in one of the movable
platen 14 and the fixed platen 16. A robot 26 is provided,
adjacent the fixed 16 and movable platen 14, to carry an end of
arm tool (EOAT) 28, such as a take-out plate. The take-out
plate 28 contains a number of preform cooling tubes 30 at least
corresponding in number to the number of preforms 32 produced
in each injection cycle, and may be a multiple thereof. In use,
in a mold open position (as shown in FIG. 1), the robot 26
moves the take-out plate into alignment with, typically, a core
side of the mold and then waits until molded articles (e.g.
preforms 32) are stripped from respective cores into
respectively aligned cooling tubes 30 by operation of a
stripper plate 33.
Cooling tubes 30 are generally shaped to reflect the external
profile of the molded article (e.g. preform 32), so in the
context of a PET preform the cooling tubes 30 are preferably
cylindrically-shaped, open-ended, hollow tubes, each having a
channel at the base thereof connected to a vacuum or suction
unit 34 operational to draw and/or simply hold the preforms 32
in the tubes 30.
Generally, the take-out plate 28 will be cooled either by
connection to a suitable thermal sink and/or by a combination
of techniques, including internal water channels, as will be
understood.
FIG. 2 shows a cooling tube assembly 50 comprising an inner
porous insert 52 made, preferably, of a material such as porous
aluminum having a porosity in the range of about 3 to 20
microns. The porous properties of the substrate are generally
achieved from either its material configuration or a chemical
removal (or adjustment) treatment process in which interstitial
spaces are induced into the substrate, thereby producing an
internal structure that is somewhat analogous to either
honeycomb or a hardened sponge. The present invention can make
use of communicating channels through the substrate material
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having a size outside the range of 3 to 20 microns, albeit that
readily commercially available materials, such as METAPOR7 and
PORCERAX- (both manufactured by the International Mold Steel
Corporation), are discussed with respect to the preferred
embodiments described herein. Porosity is, in any event, a
function of surface finish, and machining of working of the
surface can affect porosity through the material, as will be
understood. In a preferred embodiment, the inner porous insert
52 is made from a structure having definite strength and
mechanically resilient properties, although the inner porous
insert could also be made from substances like graphite. It is
preferably that the inner porous insert 52 is a thermal
conductor, with it being particular preferably that the thermal
conduction properties are good, e.g. a metal-based or sintered
composite material.
As will be understood, METAPOR" is combination of aluminum and
epoxy resin having a mix ratio of between about 65-90% aluminum
powder and 35-10% epoxy resin.
A typical cooling tube assembly 50 may have an internal length
dimension of about 100 millimetres (mm), with an interior
diameter of about 25mm and an outer diameter of about 40mm,
with these dimensions reflecting the size of the molded
article. Of course, tubes may be made of different diameters
and lengths to suit the particular preform shape being cooled.
From a practical perspective, the porous insert 52 is
preferably located in a tube body 54, which is surrounded by a
sleeve 56. Cooling channels (or passageways) 58 are optionally
cut or otherwise formed adjacent to the tube body 54, and
convey a cooling fluid (e.g. air, gas, or liquid) to cool the
body 54 and the insert 52, thus drawing heat from the molded
plastic part in the porous insert 52. Each cooling channel
preferably configured to have a cross-section comprising a
plurality of arcuate, elongated slots which extend around
greater than 50% of a circumference of an inside diameter of a
respective cooling cavity. Alternatively, the tube body 54
could simply be directly thermally coupled to a heat sink to
reduce a combined overall weight of the tubes and end-of-arm-
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tool 28, provided that the heat sink is capable of drawing
sufficient heat from a preform in unit time.
Seals 60-62 between the sleeve 56 and the tube body 54 -contain
the cooling fluid in the grooves 58. Channels 66 are cut or
otherwise formed in the exterior surface of porous insert 52
and provide a means to apply a vacuum through the porous
structure of the porous insert 52.
Other than the channels 66, the outer surface of the porous
insert 52 is configured such that a good surface contact is
maintained between the insert 52 and the tube body 54, thereby
to optimize heat transfer from the porous insert to the molded
plastic part. The vacuum is applied through the porous insert
such that a freshly loaded molded plastic part 32, shown in
FIG. 3, is caused to expand in size to touch an inner surface
82 of the porous insert, as shown in FIG. 4. Thus, heat is
conducted from the molded plastic part 32 to and through the
porous insert 52 to the cooled tube body 54. It is noted that
the position of a dome portion 80 of the preform 32 is
exaggerated in FIG. 3 and that FIG. 3 is representative of a
time when the preform is being introduced into the cooling tube
assembly 50.
Under application of suction or vacuum, a lower-than-ambient
pressure is present outside of insert 52, thus causing air to
flow through the porous insert 52 from the inside surface 82
thereof and into channels 66. This suction, in turn, causes a
lower-than-ambient pressure at the outer surface of the molded
plastic part, causing it to move into contact with the inner
surface 82 of the porous insert 52.
In a PET environment with a METAPOR insert having 3-20 micron
interstitial spaces, operational vacuum pressures for the
system are achievable within the range of about 254 to 762
millimeters (10 to 30 inches) of mercury (using a U3.6s Becker
evacuation pump). However, it will be understood that the
applied vacuum pressure is a ultimately determined by (and is a
function of) the mechanical properties of the plastics
material.
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A positive pressure may also be applied (by means of a fluid
injector and lip seals) to the inside of the preform, to cause
the preform to contact at least a portion of the cooling tube
inside surface, although this requires a sealed system. Any
appropriate pressure differential may therefore be applied
between the inside surface of the cooling tube and the outside
surface of the plastic part, depending on the shape of the part
and the cycle time provided for the cooling. It is preferred
that the entire outer surface of the preform (cylindrical outer
surface and spherical outer surface at the distal tip, i.e. the
dome 80) contact the porous insert cooling tube, although an
outer profile of the preform may, in fact, prevent this along,
for example any inwardly tapering portion 84 proximate the neck
finish of the preform 32. However, the cooling tube and vacuum
structure may be designed to bring any portion(s) of the
preform into contact with the cooling tube, depending on the
plastic part design and the portion(s) thereof needing cooling.
Further, the vacuum (or positive pressure) may be applied in
one, two, or three or more stages to effect various cooling
profiles of the plastic part. For example, a thick portion of a
preform may be brought into immediate contact with the cooling
tube, while a thinner portion of the preform may be brought
into contact with the cooling tube at a later time. In general,
the preform is in contact with the cooling tube 50 for
sufficient time only to allow robust handling of the preform
without any fear of damage arising, with this dependent upon
preform material, size and cross-sectional profile.
The porosity of the porous insert 52 can be lowered to improve
the surface finish (i.e. inner surface 82) of the porous insert
52 in contact with the molded plastic part and thereby minimize
any marking of the molded part's surface. Reducing the porosity
of the insert 52 also, however, reduces the flow of air passing
therethrough. A modest flow reduction can be tolerated since
this does not greatly impede the effect of the vacuum created
or diminish its intensity, especially since, once the molded
part's surface contacts the insert, all airflow ceases. The
airflow rate only affects the speed at which the vacuum is
created when the molded part 32 initially enters the tube 52.
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Porosity reduction is achieved by milling and grinding
procedures, whereas additional process steps of stoning or
electric discharge can clear debris from surface interstitial
spaces to increase porosity. In any event, flow rate through
the material is a function of both applied pressure and
porosity, as will be readily understood.
Inside the cooling tube 50, due to the partially cooled, but
still malleable, state of the molded part on entry into the
molded plastic part, the vacuum will cause the molded plastic
part to expand in diameter and perhaps length. The molded part
is subjected to a vacuum applied to most of its external
surface, while its internal surface is exposed to ambient
pressure.
In FIG. 5, support ledge 100 of the molded part 32 prevents the
part from entering further into the tube 50 as the part cools
and shrinks. In this case, the vacuum draws the closed end of
the part further into the tube while the support ledge prevents
the opposed end from following. In all embodiments the vacuum
causes the part to change shape to substantially eliminate the
clearance that initially exists between the part's outer
surface and the corresponding inner surface of the porous
insert 52.
In the case of molded plastic parts having diametric features,
such as the inwardly tapered portion 84, these will not be
substantially altered in shape during this expansion phase. The
configuration and size of the internal dimensions of the porous
insert 52 are made such that the diameter matches or is
slightly larger than the corresponding diameter of the part
being cooled, thus preventing substantial disfiguring of the
plastic part shape.
End seal 104 (of FIG. 3) at the open end of the cooling tube 50
provides a means to initially establish (and as necessary
maintain) the vacuum within the assembly. If there are sections
of the porous insert 52 that do no engage with portions of the
preform, such as region 106 shown in FIG. 4 below support ledge
100, then the end seal 104 is required to ensure that the
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molded part remains in contact with the inner wall 82 and
thereby to resist the effect of shrinkage of the part as it
cools, otherwise the end seal 104 may be omitted. If the vacuum
were not present, shrinkage of the part would cause a
separation between the part's outer wall and the inner cooling
wall of the insert 52 (and hence a resulting loss of suction),
thereby greatly impeding the transfer of heat from the part to
the insert 52 and into the cooling tube. Thus, the continuing
provision of the vacuum ensures intimate contact between the
molded part's outer surface and the insert's inner wall 82 is
maintained to maximize cooling performance.
Returning to FIG. 3, the cooling tube assembly 50 is preferably
fastened to a carrier or take-out plate 110 by a screw 112. The
insert 52 is retained in the assembly by a collar 114, which is
threaded onto the end of the tube body 54 or fastened or
otherwise coupled by any other conventional means. A cooling
fluid channel inlet 116, and a cooling fluid channel outlet 118
are provided in the carrier plate 110. A vacuum channel (or
passageway) 120 is also provided in the carrier plate 110.
After sufficient cooling time has elapsed, the vacuum is
replaced with pressurized airflow (by inversion of the vacuum
pump function), and the part is ejected from the cooling tube
assembly 50 by this pressure.
FIGs. 5 and 6 show an alternative embodiment for a cooling tube
150 in which the tube body 54 and the sleeve are 56 replaced
with an extruded tube that contains integral cooling channels.
An aluminum extrusion 152 forms the tube body and contains
integral cooling channels 154 that are alternately connected to
each other by grooves 156 at each end of the tube. Sealing
rings 158 close the ends of the tube to complete the cooling
circuit's integrity. A porous aluminum insert 160, having
external grooves 162 that act as a channel for the vacuum, is
located (inside the cooling tube 150) by a spacer 164 and a
collar 166 attached to the tube by a thread or any other
conventional fastening mechanism. The tube assembly is fastened
to the carrier plate 110 by any suitable external clamping
means, such as a bolt 168 and clamp 800. This alternative
17
H-675-0-WO CA 02493961 2005-07-06
embodiment has a lower cost of manufacture and an improved
cooling efficiency by virtue of its extruded body component.
FIG. 7 shows a second alternative embodiment for cooling a
molded part having a different shape. In this arrangement, the
end seal (reference numeral 104 of FIG. 3) between the top of
the cooling tube and the underside of the support ledge 100 is
not necessary. A porous insert 200 is held within the extruded
tube 152 by a collar 201 that is threaded 202 onto the top of
the cooling tube (in this case the extruded tube 152) or
fastened by any suitable means. The collar 201, typically made
from aluminum or the like, extends inwardly to conform to the
inner profiled shape 204 of an open end of the insert 200 that
matches, or is slightly larger, than that of the part being
cooled. The collar 201 provides a seal of sufficient efficacy
to allow the vacuum applied to the porous insert to cause the
part to expand in size to intimately fit against the inner
surface of the insert and cool. In some cases it is preferred
that the part has a looser fit in the tube when first entering
it. In this event, FIG. 8 shows how a lip seal 210 can provide
the necessary initial sealing to permit a vacuum to become
effective after the loading of a looser fitting part.
Methods of constructing and using the cooling tubes (in an
operational environment) of the present invention to accentuate
cooling and part formation have been described above. Briefly,
a porous cooling tube constructed in accordance with one of the
X:*W.=3iuents of the present invention is manufactured by milling
'-or extruding a cooling tube assembly having a porous cooling
t~ insert una, optional but preferable, cooling fluid
channO~~.T" -.: '~he porous insert may be polished, painted, or
otherwi sc+. to reduce poraeF# ty and provide a finer f ini sh
~
to the ext~io~'~t the molded part. The cooling fluid channels
" ; ,0
may be wholly en~,t4~'
1-*-, 'nside the tube, or may be formed by
placing a s'Leeve over'-," -'~annels formed in the outer surface
,,.~ .
of the porous irivert. Vac~. ~ M;Tels may be milled or extruded
., ..: . .., ., 7.,:.~" .
orr---a5i,- au.ter surface of the or may be provided
with separate structur"e-&6~a~_'t acrous insert outer
surface. The closed end of the coo.L."'.~ ~:,ay be machined
40intcL the tube, or may comprise a plug open end
18
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of a cooling cylinder. Appropriate seals are then fitted to
either end of the cooling tube to provide the required pressure
management, as described above.
In operation, the just-molded plastic part is extracted from a
mold cavity and inserted into the cooling tube and preferably
sealed therein. Then, a vacuum (or partial vacuum) is applied
through the porous insert from the outer surface thereof to the
inner surface thereof, causing the plastic part to expand in
length and diameter to contact the inner surface of the porous
insert. The cooling fluid circulates through the cooling
channels, extracting heat from the porous insert, which
extracts heat from the molded part. When sufficient cooling is
complete (when the exterior surfaces of the molded part have
solidified and achieved sufficient rigidity), the vacuum is
released and the molded part is ejected, for example, into a
bin for shipping. If desirable, a positive pressure can be
applied through the vacuum channels to force the molded part
from the cooling.tube.
Thus, what has been described is a novel cooling tube assembly
for the improved cooling of partially cooled molded parts that
provides a means to maintain intimate surface contact between
the part's external surface and the internal cooled surface of
the tube during the cooling cycle. The disclosed post mold
cooling device preferably uses a vacuum to slightly expand the
part to contact the cooled surface and to maintain contact as
part cools, thereby counteracting shrinkage that tends to draw
the part away from the cooled surface.
The present invention may also be described with respect to
embodiments in which the cooling tube includes an extruded
tube. The extruded cooling tube has particular use in a plastic
injection molding machine, although the present invention is
equally applicable to any technology in which, following part
formation, cooling of that part is undertaken by a cooling tube
or the like. For example, the present invention can find
application in a part transfer mechanism from an injection
molding machine and a blow-molding machine.
19
H-675-0-WO CA 02493961 2005-07-06
FIG. 9 shows a sectional view through a cooling tube 350 of an
embodiment of the present invention. The cooling tube 350
preferably comprises an extruded one-piece tube 352 with an
outside surface 384, an inside surface 382 for operating on the
preform 32. The cooling tube 350 includes a cooling circuit
for cooling inside surface 382 that includes longitudinally
oriented cooling channels 354 formed by extrusion between the
inside surface 382 and the outside surface 384 of the tube 352.
The cooling channels 354 are connected together in a desired
flow configuration by any number of connecting channels 356,
and the cooling circuit connected to a source and sink of
coolant through inlet and outlet channels 390 and 392. The
connecting channels 356 are located at the top and base of tube
352, between the outside surface 384 and the inside surface
382, and extend between two or more cooling channels 354. The
connecting channels 356 are closed on one side by sealing rings
358. The sealing rings 358, including seals 359, are retained
in a groove at the top and base of the cooling tube 350 by snap
rings 366 or other known fastening means. The cooling tube 350
further includes a central plug 364 inserted into its base and
retained by shoulder 367, the central plug 364 including a
contoured inside surface 303 for supporting and otherwise
operating on the bottom of a preform 32. The central plug 364
also includes a pressure channel 394, for connection to a
vacuum source, for the purpose of assisting in the transfer of
a preform 32 into the cooling tube 350. The coolant inlet and
outlet channels 390 and 392 of the cooling circuit being
provided in the central plug 364.
The tube 352 preferably comprises a one-piece extruded tube
with longitudinal cooling channels 354 that may have a cross
sectional profile selected from a wide range of shapes. Using
conventional machining techniques (e.g. milling) to machine the
channels 354 with the shape shown in FIG. 10 is generally not
practical beyond a length of about 4 times the diameter of the
cutter being used, thereby limiting the length of cooling tube
made by this method to an unsuitably small range. Therefore, an
extruded tube can be identified as one having an integral
cooling channel having a length generally greater than four
times the minor diameter of the cooling channel 354, or one as
CA 02493961 2005-07-06
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having a substantially constant non-cylindrical cooling channel
354 shape.
The cooling channels 354 formed in the extrusion process
provides channels for cooling fluid to circulate in the tube,
extracting heat from the preform 32 through the tube inside
surface 382. The cooling tube may include four cooling channels
354 (as shown in FIG. 10). The shapes of channels 354 are
preferably arcuate-shaped, elongated slots that present a
larger cooling surface area than drilled holes. Preferably, the
cumulative angular extent of all elongated slots is greater
than 180 degrees, the angular extent of each elongated slot
being the measure of the contained angle of an arc concentric
with the cooling tube with its terminus points defining a
maximum arc length through the elongated slot. Such a shape
works to optimize thermal transfer from a preform 32 due to the
coolant distribution that extends around a substantial portion
of, and in proximity to, the inside surface 382 that contacts
the preform 32, and also due from the high volume flow rate of
coolant supported by the large cross sectional profile of the
coolant channel 53. Further, the preferred coolant channel 354
cross-sectional profile provides for a relatively lightweight
cooling tube 350, that results in an overall mass reduction in
the carrier plate assembly 11 that may be considerable given
that some carrier plate assemblies include upwards of 432 tubes
(i.e. a carrier plate assembly with, 3 sets of 144 cooling
tubes), thereby allowing a lighter duty and hence lower cost
robot to be used and/or allowing the plate to move faster
thereby saving some cycle time and reducing energy consumption.
In an alternative embodiment of the invention, the four arcuate
shape channels shown in FIG. 10 could be changed to only two
larger arcuate shapes (not shown) so that one channel
represents the input and the other the output, thereby
simplifying the connecting channels 356.
The central plug 364 preferably includes a contoured inside
surface 303 shaped to substantially match that of the part
being cooled. The central plug 364 is preferably made from
aluminum, and functions to cool the gate area of the preform,
21
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H-675-0-WO
to define a channel for the vacuum, and to facilitate the
coupling of the cooling channels to the carrier plate 11, where
necessary. Provision for the pressure channel 394 is preferably
at the plug's center. In one embodiment, the central plug 364
is retained between the shoulder 367 of the cooling tube and
the take-out plate 28. A tube fastener 368, such as a screw or
bolt, is provided to couple the cooling tube 350 to the take-
out plate 28. Alternate means of assembling the plug 364 and
fastening the cooling tube 350 to the take-out plate 28 may be
used.
Exemplary physical dimensions of a cooling tube 350 for an
arbitrary preform 32 according to the present invention suggest
a representative length of about 100mm long, an interior
diameter of about 25mm, and outer diameter of about 41mm. For
such an arbitrary cooling tube, the cooling channels 354 are
preferably about 1-4mm in thickness, about 80mm in
circumference, and about 100mm (preferably the same length as
tube) in axial length. Of course, tubes of different diameters
and lengths would be made to suit the geometry of any preform
32, and hence wide variations in the coolant channel 354
dimensions are possible. The cooling tube 350 is preferably
made from Aluminium.
According to the present invention, an extruding process is
used to form a tube 352 including the cooling channels and a
hole, the hole preferably sized to be smaller than any of the
plastic parts destined for cooling in the tube. The extrusion
process is consistent with known techniques. The tube 352 is
then cut to length and the molding surface and any other
desired features (such as connecting channels 356, sealing ring
358 grooves, and any coolant inlet/outlet or pressure channels,
coupling structure, etc.) are then machined. The central plug
364 is then machined, including adding desired features (such
as coolant 390, 392 and pressure channel 394). The central
plug 364 with all necessary seals is then installed into the
cooling tube 350, and the sealing rings 358 with seals 359
installed into the sealing ring grooves in the top and bottom
of the cooling tube 350, so that the entire assembly is ready
for installation onto the take-out plate 28.
22
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H-675-0-WO
In a preferred embodiment, the connecting channels 356 at the
top end of the tube 352 may be provided by machining through
alternate separation walls (not shown) of the cooling channel
354. At the take-out plate 28 (bottom) end of the tube 352,
similar alternate separation walls (not shown) are machined to
connect the cooling channels 354 and provide connections to the
cooling fluid inlet channel 390 and the cooling fluid outlet
channel 392. Alternately, the cooling channels 354 in the tube
wall could be connected directly to the corresponding ports in
the take-out plate 28.
In an alternative embodiment of the present invention (not
shown) the cooling tube is extruded to define a cylindrically-
shaped tube with an inside surface, an outside surface, and at
least one cooling channel 354 formed on the outer surface of
the tube 352. A tubular sleeve fits-around the tube 352
thereby enclosing the cooling channels 354. Seals are provided
between the tube 352 and sleeve to provide a water-tight
connection. The cooling channels may be connected as
previously described in the preferred embodiment of the
invention.
In an alternative embodiment of the present invention (not
shown) the cooling tube is extruded to define a cylindrically-
shaped tube with an inside surface, an outside surface, and at
least one cooling channel 354 formed on the outer surface of a
tubular sleeve that fits-around the tube 352 thereby enclosing
the cooling channels 354. Seals are provided between the tube
352 and sleeve to provide a water-tight connection. The
cooling channels may be connected as previously described in
the preferred embodiment of the invention.
In operation, the cooling tube is used similarly to that
described in US 4,729,732. It is preferred that the internal
dimensions of the cooling tube are slightly smaller than the
external dimensions of the preform being cooled. Thus, as the
preform shrinks, its external size is reduced, and a vacuum
acting through the central plug draws the part further into the
cooling tube so that an intimate fit or contact of the
23
H-675-0-WO CA 02493961 2005-07-06
preform's external surface is maintained with the inside
surface of the cooling tube. Alternately, the internal
dimensions of the cooling tube can be manufactured to be the
same size or slightly larger than the external size of the
preform being cooled, so as to permit a flow of air to be drawn
past the part's external surfaces by the vacuum.
In more detail, after the preforms are formed in the injection
molding machine, the mold opens by stroking the movable platen
18 away from the fixed platen 16, and the robot arm (carrying
the carrier plate assembly 11) moves between the mold halves 12
and 14 so that the cooling tubes 30 can receive a set of
preforms 32 that are ejected from cores 23. Applied suction may
be used to encourage transfer of the preforms 32 from the cores
23 to the cooling tubes 30, and/or to retain the preforms
therein. The carrier plate assembly 11 is then moved out from
between the mold halves 12, 14, and then orientated so that the
carrier plate assembly 11 is sequentially or selectively placed
adjacent to a cooling station, a receiving station, or a
conveyor. The preforms may then be transferred thereto.
In addition to the improved cooling performance of the cooling
tube, there is a substantial benefit in reduced cost of
manufacture. An extruded cooling tube according to the present
invention can benefit from a cost reduction relative to
conventionally manufactured tube due to substantially reduced
machining requirements.
In an alternative embodiment of the invention (not shown) the
cooling tube assembly 350 of FIG. 9 may be modified to include
a tubular porous insert 452, as shown in FIG. 11, along the
inside surface 482 for vacuum forming a preform 32 and to
improve preform 32 cooling efficiency due to a better heat
conduction interface (i.e. larger surface area contact and more
intimate fit). The porous insert 452 includes an inner surface
482 and outer surface 483, the inner surface 482 contoured to
correspond substantially with the final desired molding surface
of the preform 32, the outer surface 483 may be segmented by a
set of longitudinally directed pressure channels 466. The
pressure channels 466 provide a conduit for establishing a
24
H-675-0-WO CA 02493961 2005-07-06
region of very low vacuum pressure in proximity to the portion
of the porous insert 452 between the inside surface 482 and the
outside surface 483 and thereby to evacuate air through the
porous structure of the porous insert 450 for the purpose of
drawing a deformable preform 32 into contact with the contoured
inside surface 482 of the porous insert 452, thereby vacuum
forming the preform 32. The porous insert 452 is preferably
made from a highly thermally conductive material, such as
aluminum. The material selection for the porous insert further
characterized by the requirement for a porous structure with a
porosity preferably in the range of about 3-20 microns.
Further, the porous insert 452 may be advantageously
manufactured in a process that includes the step of extrusion.
Yet another alternative embodiment of the invention is shown in
FIG. 12, wherein a cooling tube assembly 450 for vacuum forming
a preform 32 is provided. The cooling tube assembly 450
includes a tube 454 that may be machined from available tube
stock, however an extruded tube such as tube 352 (as
exemplified in FIG. 9) may also be used. The tube 454 includes
an insert bore 455 for receiving a porous insert 452, as
exemplified in FIG. 11. The porous insert 452 is retained in
the tube 454 by a central plug 464, the central plug 464
received in a first and second plug bore 457, 458 of the tube
454. The central plug 464 is further retained in the tube 454
by its shoulder 467 bearing against the step between the first
and second plug bore 457, 458. The shoulder 467 on the central
plug 464 corresponds to a step in the diameter of the central
plug 464 with a narrowed portion at its upper end that provides
an annular channel 465 between the central plug 464 and the
second plug bore 458 of the tube 454. The annular channel 465
connects the pressure channels 466 of porous insert 452 with a
channel 420 that is formed in the central plug 464 that is in
turn connected in use to a first vacuum channel in take-out
plate 28. The central plug 464 includes a contoured inside
surface 403 that substantially corresponds to the dome portion
of preform 32 that may be used for forming and cooling the
region. The central plug 464 further includes inlet and an
outlet coolant channel 490, 492, and a pressure channel 494,
for connection to coolant inlet and outlet channels 116, 118
CA 02493961 2005-07-06
x-675-0-Wo
and a second pressure channel in the take-out plate 28
respectively. The inlet and outlet channels 490, 492 of the
central plug 464 are further connected to a cooling groove 493
formed on the outer surface of the tube 454 thereby forming a
cooling circuit. The cooling tube assembly 454 further
includes a sleeve 456 that is retained on the outer surface of
the tube 454. Seals 459 are also provided between the sleeve
456 and tube 454, and between the central plug 464 and the tube
454 to provide air and water tight connections between
components forming the cooling tube assembly 450. The tube 454
further includes a groove at its open and for receiving an end
seal 404 that provides in use an airtight seal between the
preform support ledge 100 and the cooling tube assembly 450 for
enclosing the volume formed between the preform 32 and cooling
tube assembly 450, thereby enabling the development of the
required low vacuum forming pressure. The primary components
of the cooling tube assembly 450 are preferably made from a
highly thermally conductive material, such as aluminum. The
operation of the cooling tube assembly 454 installed on the
take-out plate 28 of the carrier plate assembly 11 will now be
described. The take-out plate 28 provides cooling fluid inlet
and outlet channels and first and second vacuum channels to
correspond with the ports on the central plug 464. In use, a
preform 32 is drawn into the cooling tube assembly 450 by a
relatively high flow rate suction acting through the pressure
channel 494 that further retains the preform 32 once the
preform support ledge 100 is sealed against the end seal 404
thereby stopping air flow. A high vacuum is then applied
through the vacuum channel 420 in the central plug 464, then
through the annular channel 465 and pressure channels 466,
whereupon the vacuum acts through the porous wall of the porous
insert 452. The volume of air between the preform 32 and the
inner surface 482 of the porous insert 452 is at least
partially evacuated to cause the drawing of the preform outer
surface into contact with the porous insert 452. Once in
contact with the porous insert 452, the preform 32 is cooled by
conduction, its heat moving through a path from the preform
outer surface to the porous insert 452, to the tube 454, and to
the circulating coolant. Once enough heat has been removed
from the preform 32 to ensure that it will retain its shape,
26
CA 02493961 2005-07-06
H-675-0-WO
the high vacuum acting through the vacuum channels 466 is
released and a positive pressure is applied through the
pressure channel 494 to assist in the ejection of the preform
32.
Thus, what has been described is an extruded cooling tube for a
plastic part, a porous insert for use with a cooling tube
assembly for vacuum forming preforms, various advantageous
embodiments of cooling tube assemblies, methods of making the
afore mentioned, and a method of using a cooling tube assembly,
which will greatly reduce the cost of such tubes in injection
molding and/or improve the quality of the molded preform 32.
All U.S. and foreign patent documents, and articles, discussed
above are hereby incorporated by reference into the Detailed
Description of the Preferred Embodiment.
The individual components shown in outline or designated by
blocks in the attached Drawings are all well-known in the
injection molding arts, and their specific construction and
operation are not critical to the operation or best mode for
carrying out the invention.
While the present invention has been described with respect to
what is presently considered to be the preferred embodiments,
it is to be understood that the invention is not limited to the
disclosed embodiments. For example, whilst the preferred
embodiment of the present invention discusses the present
invention in terms of a porous insert, it will be appreciated
that the insert could, in fact, be realized by a thermally
conductive but porous coating applied to a profiled housing,
although use of an insert benefits ease of manufacture and
assembly. The application of the cooling technology is not, as
will be understood, limited to size or weight (of, e.g.
preforms), with the defining criteria being the ability to
establish a vacuum to encourage contact of an outer surface of
the molded article with the inner surface of the porous
profiled substrate. Furthermore, while the cooling tube
assembly of the present invention has been described in the
context of a plastic injection molding machine, it will be
27
CA 02493961 2005-07-06
H-675-0-WO
appreciated that it is equally applicable to any technology in
which, following part formation, cooling of that part is
undertaken by a cooling tube or the like, e.g. in a part
transfer mechanism between an injection molding machine and a
blow-molding machine. The scope of the following claims is to
be accorded the broadest interpretation so as to encompass all
such modifications and equivalent structures and functions.
28
