U.S. patent application number 11/115210 was filed with the patent office on 2005-08-25 for cooling tube with porous insert.
Invention is credited to Neter, Witold, Niewels, Joachim Johannes, Romanski, Zbigniew, Unterlander, Richard Matthias, Uracz, Tomasz.
Application Number | 20050186375 11/115210 |
Document ID | / |
Family ID | 31992393 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050186375 |
Kind Code |
A1 |
Neter, Witold ; et
al. |
August 25, 2005 |
Cooling tube with porous insert
Abstract
An injection-molding machine cooling tube, which cools molded
plastic parts, includes a porous cooling tube having an outer
surface and an inner surface. Preferably, the porous cooling tube
has a porosity in the range of 3-20 microns. A cooling fluid
passageway is preferably disposed adjacent the porous cooling tube
outer surface and is configured to carry a cooling fluid to extract
heat from the porous cooling tube. Fluid flow structure, preferably
a vacuum, is configured to cause a molded plastic part inside the
porous cooling tube to expand into contact with at least a portion
of the inner surface of the porous cooling tube.
Inventors: |
Neter, Witold; (Newnan,
GA) ; Niewels, Joachim Johannes; (Thornton, CA)
; Unterlander, Richard Matthias; (Nobleton, CA) ;
Uracz, Tomasz; (Everett, CA) ; Romanski,
Zbigniew; (Mississauga, CA) |
Correspondence
Address: |
KATTEN MUCHIN ROSENMAN LLP
525 WEST MONROE STREET
CHICAGO
IL
60661-3693
US
|
Family ID: |
31992393 |
Appl. No.: |
11/115210 |
Filed: |
April 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11115210 |
Apr 27, 2005 |
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10766037 |
Jan 29, 2004 |
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10766037 |
Jan 29, 2004 |
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10246916 |
Sep 19, 2002 |
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6737007 |
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Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
B29C 48/09 20190201;
B29C 45/0053 20130101; B29C 2045/7214 20130101; Y10T 428/1352
20150115; B29C 49/06 20130101; B29C 45/7207 20130101; B29C 48/11
20190201; B29C 2035/1616 20130101; B29C 49/6427 20130101; B29C
48/0017 20190201; B29C 49/4205 20130101; B29L 2031/60 20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B32B 001/08 |
Claims
1-21. (canceled)
22. A molded plastic article, comprising: a closed end: an open
end; an inside surface; and an outside surface; a portion of the
outside surface having a profile corresponding substantially to a
porous cooling cavity inside surface which has interstitial spaces
that are configured to provide, in use, a low pressure sufficient
to cause the molded plastic article to expand and contact the
cooling cavity inside surface, the portion of the molded plastic
article outside surface having surface finish which corresponds
substantially to the interstitial spaces of the porous cooling
cavity.
23. A molded plastic article with a shape of at least a portion of
its outside surface defined by a profiled inside surface of a
porous member, the molded plastic article formed by the process of:
(i) receiving a malleable molded plastic article into the porous
member; (ii) evacuating the air surrounding the molded plastic
article through a plurality of interstitial spaces that are
configured along the inside surface of said porous member causing
the portion of the outside surface of the molded plastic article to
move into contact with the profiled inside surface of the porous
member, 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; whereby the portion of
the outside surface of the molded plastic article takes on a
surface finish that corresponds substantially to the interstitial
spaces of the porous cooling cavity.
24. The molded plastic article according to claim 22, wherein the
porous member is formed of a porous substrate with the profiled
inside surface having interstitial spaces preferably within a range
of about 3 to 20 microns. (i) receiving a malleable molded plastic
article into the porous member; (ii) evacuating the air surrounding
the molded plastic article through a plurality of interstitial
spaces that are configured along the inside surface of said porous
member causing the portion of the outside surface of the molded
plastic article to move into contact with the profiled inside
surface of the porous member, 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; whereby the portion of the outside surface of
the molded plastic article takes on a surface finish that
corresponds substantially to the interstitial spaces of the porous
cooling cavity.
25. The molded plastic article according to claim 22, wherein
molded plastic article is a preform.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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 polyethylenetetraphthlate (PET) or the like.
[0003] 2. Related Art
[0004] 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.
[0005] 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.
[0006] 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 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.
EP patent 0 283 644 is incorporated herein by reference.
[0007] In many other cooling tube arrangements, 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 these effects are clearly undesirable and
result in part rejection and increased costs to the
manufacturer.
[0008] European patent EP 0 266 804 describes an intimate fit
cooling tube that is held within an end-of-arm-tool (EOAT) of a
robot. The intimate fit cooling tube is water cooled and is
arranged to receive a preform shortly after it has attained the
glass-transition temperature that allows handling of its form
without catastrophic deformation. 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 by a
conduction process. However, as the preform cools it will shrink
and therefore may loose contact across its entire circumference
with the cooling tube yielding an uneven cooling effect.
[0009] U.S. Pat. Nos. 4,102,626 and 4,729,732 are further 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
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.
[0010] 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 tube
assembly to form cooling channels therebetween.
[0011] U.S. Pat. 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.
[0012] U.S. Pat. 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.
[0013] U.S. Pat. Nos. 4,295,811 and U.S. Pat. No. 4,304,542
disclose an injection blow core having a porous metal wall
portion.
[0014] A "Plastics Technology Online" article entitled "Porous
Molds' Big Draw", by Mikell Knights, printed from the Internet on
Jul. 27, 2002, discloses a porous tooling composite called
METAPOR.TM.. The article discloses the technique of polishing this
material to close slightly the pores to improve the surface finish
and reduce the porosity.
[0015] An article from International Mold Steel, Inc., entitled
"Porous Aluminum Mold Materials", by Scott W. Hopkins, printed from
the Internet on Jul. 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.
SUMMARY OF THE INVENTION
[0016] According to a first aspect of the present invention,
structure and/or steps are provided for a tube assembly for
operating on a malleable molded plastic part. The tube assembly
comprising a porous tube having a profiled inside surface, and a
vacuum structure configured to cooperate with the porous tube to
provide, in use, a reduced pressure adjacent the inside surface.
The reduced pressure causes an outside surface of the malleable
molded plastic part, locatable within the tube assembly, to contact
the inside surface of the porous insert so as to allow a
substantial portion of the outside surface of the malleable part,
upon cooling, to attain a profile substantially corresponding to
the profile of the inside surface. In an embodiment of the
invention, the porous tube is cylindrically-shaped, and the vacuum
structure is provided by locating the porous tube in a tube body
and by providing at least one vacuum channel adjacent the outside
surface of the porous tube, in use, for connection to a vacuum
source.
[0017] The inside surface of the porous tube having an internal
profile that is substantially (if not highly and accurately
toleranced to) the final dimensions of the molded part, the porous
tube of the various embodiments of the present invention
effectively causes, under cooling, a re-shaping of the molded part
to its exact final shape defined by the profile of the insert.
Indeed, the reduced pressure/effective vacuum acting through the
porous material essentially acts to draw the malleable preform into
the final shape whilst ensuring that cooling is optimized by
continuous surface contact with a thermally efficient heat
dissipation material and path.
[0018] According to a second aspect of the present invention,
injection molding machine structure and/or steps are provided with
a molding structure that molds at least one plastic part.
Furthermore, at least one porous cooling cavity is configured to
hold and cool the at least one plastic part after it has been
molded by the molding structure. At least one vacuum channel is
respectively configured to provide a lower-than-ambient pressure to
the at least one porous cavity to cause the at least one plastic
part to contact the inside surface of the at least one porous
cavity.
[0019] According to a third aspect of the present invention, a
method for shaping a malleable molded plastic part including the
steps of: (i) receiving the molded plastic part into a porous tube;
(ii) providing a reduced pressure adjacent a profiled inside
surface of the porous tube causing a portion of an outside surface
of the molded plastic part to move into contact therewith and
thereby attain a substantially corresponding shape; and (iii)
extracting heat from the molded plastic part through a heat
dissipation path to solidify the molded plastic part at least to
the extent required to ensure that the shape of the outside surface
of the molded plastic part is preserved; and (iv) ejecting the
molded plastic article; wherein the outer surface of the molded
plastic part is provided with a final shape that is defined by the
profiled inside surface profile of the porous tube.
[0020] According to a fourth aspect of the present invention,
structure and/or steps are provided for a tube assembly for
operating on a malleable molded plastic part. The tube assembly
comprising a tube body, and a porous insert located in the tube
body. The porous insert includes an inside surface and an outside
surface, the inside surface profiled to reflect at least a portion
of the profile of the molded plastic part. The tube assembly
further includes at least one vacuum channel in fluid communication
with the porous insert. The vacuum channel configured for
connection, in use, with a vacuum source to provide a reduced
pressure adjacent the inside surface to cause an outside surface of
the malleable molded plastic part, locatable within the tube
assembly, to contact the inside surface so as to allow a
substantial portion of the outside surface of the malleable part,
upon cooling, to attain a profile substantially corresponding to
the profile of the inside surface. The tube assembly also includes
a cooling structure configured for connection, in use, with a heat
dissipation path for cooling the molded plastic part in contact
with the inside surface of the porous insert.
[0021] Preferably, the porous insert has porosity in the range of
about 3-20 microns. A cooling fluid passageway is disposed in the
tube body adjacent the porous insert and is configured to carry a
cooling fluid to extract heat from the porous insert.
[0022] According to another aspect of the present invention,
structure and/or steps are provided for a tube assembly. The tube
assembly comprising a tube with an inside surface provided on a
porous substrate, and a fluid flow structure. The fluid flow
structure is configured to cooperate with the porous substrate to
cause, in use, a malleable molded plastic part, locatable within
the tube assembly, to be drawn into contact with the inside surface
so as to allow a substantial portion of an outside surface of the
malleable part, upon cooling, to attain an outside profile
substantially corresponding to the profile of the inside
surface.
[0023] According to an embodiment of the invention, the porous
substrate includes an inside surface and an outside surface, the
inside surface profiled to reflect at least a portion of the
profile of the molded plastic part; and a vacuum channel located
adjacent the outer surface, the vacuum channel supporting, in use,
an initial establishment of a differential pressure from the
outside surface of the porous substrate to the inside surface
thereof, to induce contact, in use, between the received molded
plastic part and the inside surface.
[0024] According to yet another aspect of the present invention,
structure and/or steps are provided for an end-of-arm tool. The
end-of-arm tool comprising a carrier plate for mounting, in use, to
a robot in a molding system, and at least one tube assembly
arranged on the carrier plate. The tube assembly is configured for
receiving, in use, a molded plastic part. The tube assembly
comprising a porous tube having an inside surface and an outside
surface, the inside surface profiled to reflect at least a portion
of the profile of the molded plastic part, and a vacuum structure.
The vacuum structure is configured to cooperate with the porous
tube to provide, in use, a reduced pressure adjacent the inside
surface to cause an outside surface of a malleable molded plastic
part, locatable within the tube assembly, to contact the inside
surface of the porous insert so as to allow a substantial portion
of the outside surface of the malleable part, upon cooling, to
attain a profile substantially corresponding to the profile of the
inside surface.
[0025] According to a further aspect of the present invention,
structure and/or steps are provided for a molded plastic part with
the shape of at least a portion of its outside surface defined by a
profiled inside surface of a porous tube. The molded plastic part
is formed by the process of: (i) receiving a malleable molded
plastic part into the porous tube; (ii) reducing pressure adjacent
the profiled inside surface of said porous tube causing the portion
of the outside surface of the molded plastic part to move into
contact with the profiled inside surface of the porous tube,
thereby to attain a shape substantially corresponding to the
profiled inside surface; and (iii) extracting heat from the molded
plastic part through a heat dissipation path to solidify the molded
plastic part sufficiently such that the outer shape of the molded
plastic part is preserved. Whereby the portion of the outside
surface of the molded plastic part takes on a surface finish
reflecting that of the profiled inside surface of the porous
insert. Preferably, the porous tube is formed of a porous substrate
with the profiled inside surface having interstitial spaces
preferably within a range of about 3 to 20 microns.
[0026] 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 acid aldehyde 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 acid aldehyde in the
finished plastic product, such as a drink container. Beneficially,
the present invention seeks to maintain a required and defined
shape of the molded part, such as a preform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Exemplary embodiments of the present invention will now be
described with reference to the accompanying drawings, in
which:
[0028] FIG. 1 is a plan view of a typical injection molding machine
including a robot, and end-of-arm tool;
[0029] FIG. 2 depicts a section through a cooling tube assembly
according to a preferred embodiment of the present invention;
[0030] FIG. 3 depicts a sectional, but exaggerated view, through
the cooling tube assembly of the FIG. 2 embodiment, with a freshly
molded part just loaded;
[0031] FIG. 4 depicts a section through the cooling tube assembly
of the FIG. 2 at a later point in time;
[0032] FIG. 5 depicts a section through the cooling tube assembly
of an alternate embodiment;
[0033] FIG. 6 depicts a view on section 5-5 of FIG. 5;
[0034] FIG. 7 depicts a section through the cooling tube assembly
of a second alternate embodiment; and
[0035] FIG. 8 depicts a section through the cooling tube assembly
of a third alternate embodiment.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY
EMBODIMENTS
[0036] 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.
[0037] 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.
[0038] 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 (not shown) that typically 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.
[0039] 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.
[0040] 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.
[0041] 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 having a size outside the
range of 3 to 20 microns, albeit that readily commercially
available materials, such as METAPOR.TM. and PORCERAX.TM. (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.
[0042] As will be understood, METAPOR.TM. is combination of
aluminum and epoxy resin having a mix ratio of between about 65-90%
aluminum powder and 35-10% epoxy resin.
[0043] A typical cooling tube assembly 50 may have an internal
length dimension of about 100 millimetres (mm), with an interior
diameter of about 25 mm and an outer diameter of about 40 mm, 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.
[0044] 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-tool 28, provided that the heat sink is capable of
drawing sufficient heat from a preform in unit time.
[0045] Seals 60-63 between the sleeve 56 and the tube body 54
contain the cooling fluid in the grooves 4. 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.
[0046] 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 1 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.
[0047] 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.
[0048] In a PET environment with a METAPOR.TM. insert having 3-20
micron interstitial spaces, operational vacuum pressures for the
system are achievable within the range of about 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.
[0049] Of course, rather than applying a vacuum from the outside of
the preform, a positive pressure may 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.
[0050] 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. 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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 and to continue to cause
the part 8. 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 molded parts remains in contact with the inner
wall 82 and thereby to resist the effect of shrinkage of the part 8
as it cools, otherwise the end seal 104 may be omitted. If the
vacuum were not present, shrinkage of the part 8 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.
[0055] Returning to FIG. 3, the 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 11-8 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 tube assembly 50 by this pressure.
[0056] 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. This alternative embodiment has a lower
cost of manufacture and an improved cooling efficiency by virtue of
its extruded body component.
[0057] 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 152, 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.
[0058] 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
embodiments of the present invention is manufactured by milling or
extruding a cooling tube assembly having a porous cooling tube
insert and, optional but preferable, cooling fluid channels. The
porous insert may be polished, painted, or otherwise treated to
reduce porosity and provide a finer finish to the exterior of the
molded part. The cooling fluid channels may be wholly enclosed
inside the tube, or may be formed by placing a sleeve over open
channels formed in the outer surface of the porous insert. Vacuum
channels may be milled or extruded on an outer surface of the
porous insert, or may be provided with separate structure adjacent
the porous insert outer surface. The closed end of the cooling tube
may be machined into the tube, or may comprise a plug fitted into
one open end 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.
[0059] In operation, the just-molded plastic part is extracted from
a mold cavity and carried by the carrier plate to a cooling station
where one or a plurality of cooling tubes are positioned. The
plastic part is 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.
[0060] 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.
[0061] All U.S. and foreign patent documents, and articles,
discussed above are hereby incorporated by reference into the
Detailed Description of the Preferred Embodiment.
[0062] 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.
[0063] 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. To the contrary, the invention is intended
to cover various modifications and equivalent arrangements included
within the spirit and scope of the appended claims. 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. 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.
* * * * *