Note: Descriptions are shown in the official language in which they were submitted.
CA 02676615 2014-03-06
. CWCAS-210
Aftercooling Apparatus and Method for Aftercooling Preforms
Field of the Invention
The invention relates to an aftercooling apparatus for preforms. The invention
also
relates to a method for aftercooling preforms with a threaded portion, a blow-
molded
part and a neck ring.
Background of the Invention
In practical applications, three aftercooling systems have attained dominance
for the
production of preforms:
- According to a first concept, the still hot preforms are transferred
directly to the cooling sleeves of an aftercooling. The aftercooling has
several cooling positions commensurate with the number of preforms
of an injection molding cycle,
- According to a second concept, the preforms are removed from the
open molds using a lightweight removal robot which does not provide
cooling, and are then transferred to an aftercooling where they are
aftercooled.
- According to a third concept proposed by the applicant, the robotic
function is divided into a removal gripper with water-cooled removal
sleeves and an additional transfer gripper for transfer to an
aftercooling.
According to recent developments, the injection molding machine cycle time is
further shortened by removing the preforms from the molds in a soft state with
an
unstable shape. However, previously less noticeable problems are now becoming
more important. Physical effects cause cooling inside the walls of the
preforms to
be uneven:
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¨ When the preforms are removed from the open molds, thermal stress and
shrinkage stress occur in the preforms due to temperature difference inside
the preforms, in particular in the wall of the preforms, which causes
dimensional changes.
¨ Each mechanical intervention and each handling by robotic grippers can
cause dimensional damage.
¨ The same applies when the preforms are in a horizontal position in the
aftercooling.
Accordingly, each intervention during aftercooling becomes an extremely
delicate
task. In the fabrication of injection-molded parts with injection molding
machines,
the cool-down time is a determining factor for the duration of a full cycle.
The first
and main cooling effect still takes place in the injection molds. Both mold
halves are
intensely water-cooled during the injection molding process, so that the
temperature
of the injection-molded parts, while still in the mold, can be lowered at
least in the
marginal layers from, for example, 280 C to a range of about 70 C. The
temperature drops in the outer layers very quickly below the so-called glass-
transition temperature of about 80 C. The actual injection molding process up
to the
removal of the injection-molded parts could recently be cut almost in half,
while
retaining optimal qualities of the preforms. The preforms must be solidified
in the
mold halves to a degree that they can be gripped by the removal aids and
transferred to a removal device. The shape of the removal device matches the
outside dimension of the injection-molded parts. The intense water cooling in
the
mold halves causes, according to physical principles, a time delay of the
temperature drop reaching the core region of the preform wall. Accordingly,
the
aforementioned about 70 C cannot be uniformly attained across the entire cross-
section. As a result, rapid re-heating over the material cross-section occurs
from
the inside to the outside as soon as the intense water cooling through the
molds is
interrupted. For two reasons, it is therefore most important to aftercool the
preforms
outside the mold. Dimensional changes, but also surface damage, such as
pressure points, etc., during aftercooling must be prevented. Cooling in the
higher
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temperature range must also be prevented from being too slow to avoid locally
detrimental crystal formation caused by reheating. The goal is a uniform
amorphous
state in the material of the finished preform. The residual temperature of the
finished
preforms should be so low that no pressure or adhesion damage occurs at the
contact points even in large packages with thousands of loosely supplied
injection-
molded parts. The surface temperature of the finished injection-molded parts
must
not exceed 40 C even after slight reheating. Aftercooling after removal of the
hot,
dimensionally unstable preforms from the injection mold is very important for
maintaining dimensional stability.
In WO 2004/0415110, the applicant proposes an intense cooling station and an
aftercooling station, with the intense cooling station having cooling pins
that can be
inserted into the preforms for cooling the inside. The interior shape of the
cooling
sleeves is here matched to the corresponding interior shape of the injection
mold,
such that the preforms after removal from the molds can be inserted with as
little
play as possible until completely contacting the cooling sleeves. If the
preforms are
in a horizontal position in the first aftercooling phase, then they tend to on
a
corresponding bottom part of the cooling sleeve. The preforms are then cooled
more strongly at the bottom due to a more intense cooling contact in the lower
region, which induces stress in the preform, causing the preform tends to
assume
an oval shape. If individual preforms are easily deformed during the first
aftercooling phase due to the shortened cooling time in the injection molds,
then the
corresponding dimensional changes in already solidified preforms can no longer
be
corrected. According to a preferred embodiment disclosed in WO 2004/0415110,
an inflation pressure can be generated inside the preforms through targeted
control
of suction and blow air, and the not yet solidified preform can be brought
into
complete contact to the entire inner wall surface of the cooling sleeve. After
the
preforms fully contact the inner wall surface of the cooling sleeve, the
contact across
this area is maintained during several seconds, producing a calibration effect
for
each individual preform. The calibration effect produces a high production and
quality standard during the production of the preforms that was not attainable
with
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conventional technology. The preforms are thereby brought again to the exact
dimensions shortly after being removed from the injection molds. Any
dimensional
changes introduced after the first critical handling from the injection molds
into the
cooling sleeves are compensated. Calibration of the preforms allows removal of
the
preforms from the molds at still higher temperatures, thereby shortening the
injection molding cycle time even further.
WO 2004/0415110 proposes two different solutions for producing an inflation
pressure. According to a first variant, a sealing ring is arranged on a
cooling pin or
on a blow nozzle, which is brought into contact on the conical transition in
the
interior of the preform. According to the second variant, the blow nozzle has
ring-
shaped seals intended for contacting the end face of the open rim of the
preform.
The inflation pressure hereby operates on the entire preform. Both solutions
disadvantageously require in practice and with multiple injection molds
having, for
example, 100 to 200 mold cavities very high precision for guiding and moving
all
blow nozzles.
EP 900 135 proposes a concept similar to the aforementioned second variant.
Sealing of the open rim presumes a certain pressing force and also sufficient
dimensional stability of the threaded part. To prevent dimensional changes of
the
threaded part, the preforms must be left in the injection molds until reaching
a higher
dimensional stability. However, this works against shortening the injection
molding
cycle time.
US 2005/0147712 proposes a method for processing a preform, wherein the
preform can be brought into contact with an inner wall of a cooling device by
a
vacuum. To this end, a cooling device insert for generating the required
vacuum is
constructed to be porous. In addition to the vacuum applied to the outside of
the
preform, an overpressure can be produced in the interior of the preform, for
example
with a pin, which is also - at least partially - porous or has a membrane
which
pushes the preform outwardly, against the inner side of the cooling device.
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CWCAS-210
Based on extensive investigations, it was recognized that calibration of the
still hot,
dimensionally unstable preforms immediately after withdrawal of the removal
robot
from the open mold halves has significant advantages. However, this success
was
not observed with all types of preforms. For example, with preforms having an
unsupported threaded region in relation to the cooling sleeves, the problems
with
dimensional stability could not be solved. The inventor has recognized that
with
increasingly shorter machine cycle times, the entire open end side can be
subject to
a significant handling risk during aftercooling, and not only because the
threaded
portion protrudes from the cooling sleeve and can therefore no longer be
cooled by
the cooling sleeve. This happens regardless if the preform is calibrated or
not.
US 2005/0194709 discloses a cooled removal sleeve for preforms which at least
in
certain sections are not in direct contact with the cooled removal sleeve. It
is
proposed to cool those regions which are not in direct contact by applying air
cooling, with an air flow being supplied to the preforms from openings in the
cooling
sleeve.
It is therefore an object of the invention to develop a method and an
apparatus
which ensures highest quality parameters and maximal dimensional stability of
the
preform during aftercooling, in particular with respect to handling, at least
with
typical preforms, and provides the shortest possible cycle time.
Summary of the invention
The aforementioned object is attained with an aftercooling apparatus for
preforms,
wherein the still dimensionally unstable preforms are removed with a removal
gripper from the open mold halves of an injection molding machine and can be
at
least partially aftercooled in water-cooled removal or cooling sleeves,
wherein air
blowing devices are integrated in the cooling sleeves in the region of the
outer open
end side of the preforms, via which air blowing devices the outer skin, at
least in an
unsupported region of the preforms, can be cooled with cooling air. The
preforms
can be air-cooled and hence solidified after insertion into the cooling
sleeves from
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the outside in the transition region between the threaded portion and the neck
ring
and/or to the transition region between the neck ring and the blow-molded
part, and
the preforms can be calibrated after retraction of the cooling sleeves from
the open
mold halves by way of compressive or sealing rings, which are applied on
nipples,
within a single injection cycle.
The apparatus may include a controller, by which the air blowing device can be
activated from the time the preform is transferred to the removal or cooling
sleeves.
The quantity of cooling air and/or the temperature of the cooling air may be
controlled, wherein the maximum values can preferably be adjusted immediately
after the preform is transferred from the open mold halves.
The water-cooled removal sleeves may include cooling channels disposed in the
region between the threaded portion and the blow-molded part or the
cylindrical
shaft, for a corresponding outside cooling of the preforms, and also an air
fitting for
the cooling channels.
Depending on the geometric design of the preforms, the ventilation channels
are
arranged in the region between the threaded portion and the neck ring and/or
in the
transition region between the neck ring and the cylindrical blow-molded part.
The water-cooled removal sleeves may be fabricated from standardized
components, such that depending on the situation, guide rings for the
ventilation
channels for cooling the transition region between the threaded portion and
the neck
ring and/or for cooling the transition region between the neck ring and the
cylindrical
blow-molded part can be inserted.
The apparatus may include a device with a plurality of nipples, each nipple
having
an insertion part into the preforms, and that the insertion parts of the
nipples have
radially expandable compressive or sealing rings which can be introduced into
the
preforms.
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The compressive rings may be constructed as radially expandable, in particular
floatingly supported sealing rings, by which a mechanically generated,
adjustable
sealing force can be produced in the direction of the interior wall of the
preforms, for
building up an expansion pressure in the interior space of the blow-molded
part of
the preforms.
The nipples can be inserted with a controlled position into the preforms with
the, in
particular, floatingly supported compressive or sealing rings into a
selectable optimal
sealing location in a region between threaded portion and blow-molded part.
The preforms can be transferred, while still in a hot, dimensionally unstable
state,
from the injection mold for aftercooling to water-cooled removal sleeves, and
calibrated to exact outside dimensions using compressed air introduced through
the
nipples which can be inserted into the preforms.
The nipples may be arranged on a common actuating plate, with which controlled
drive means may be associated for insertion and positioning of the compressive
or
sealing rings at an optimal insertion depth or at an optimal location for the
sealing
rings in the preforms or in the removal or cooling sleeves.
The apparatus may further include a controllable removal gripper having at
least a
number of water-cooled removal sleeves that corresponds to the number of
injection
molding positions of the injection molds, preferably a 3-fold to 4-fold number
of the
number of injection molding positions in a mold.
The apparatus may further include a removal gripper with the water-cooled
removal
sleeves, a transfer gripper with nipples as well as an aftercooling with a
number of
cooling positions, which corresponds to three to four times the number of
injection
molding positions, wherein the blow-molded part of the preforms can be
calibrated
in the removal sleeves, and the preforms can be transferred in a predetermined
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exact shape within each injection cycle with the transfer gripper to the
aftercooling
and after finish-cooling to a removal device.
The aforementioned object is also attained with a method for aftercooling of
preforms with a threaded portion, a blow-molded part and a neck ring, which
are at
least partially aftercooled in water-cooled cooling sleeves while still in a
hot,
dimensionally unstable state, wherein the outer skin of at least a part of
outer open
unsupported end sides of the preforms is cooled with cooling air via air
blowing
devices integrated in the cooling sleeves. The preforms after insertion into
the
cooling sleeves are air-cooled from the outside in the transition region
between the
threaded portion and the neck ring and/or up to the transition region between
the
neck ring and the blow-molded part and thereby solidified, and are calibrated
within
a single injection cycle after withdrawal of the cooling sleeves from the open
mold
halves by way of compressive or sealing rings disposed on nipples.
The blow-molded parts of the preforms may be calibrated after insertion of
preforms
into the cooling sleeves and the withdrawal from the open mold halves within
the
duration of a single injection cycle, the preforms are calibrated on the
interior wall of
the cooling sleeves to the exact outside dimensions by compressed air with
continuously increasing pressure.
The compressed air for the calibration may continuously rise in pressure from
the
start of the calibration, so that the outside skin of the preform is further
cooled down,
wherein the rise of the air pressure is attained by increasing the control
voltage of a
control valve of in the compressed air supply.
The nipples may be inserted into the preforms with the compressive or sealing
rings
with a controlled position into a selectable optimal sealing location in a
region
between the threaded portion and the blow-molded part.
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The nipples may be inserted into the preforms with the compressive or sealing
rings
with a controlled position up to the transition region between the threaded
portion
and the neck ring or to the transition region between the neck ring and the
blow-
molded part.
The method may further include the steps wherein a) compressive or sealing
rings
attached on nipples are inserted with controlled positioning into each of the
preforms
in the region between the threaded portion and the blow-molded part, wherein
b)
the compressive or sealing rings are expanded up to the contact with the inner
wall
of the preforms, and c) the interior space of the blow-molded part is sealed
to the
outside by generating a force directed radially in the direction of the inner
wall.
An outside cooling of the preforms with air may start immediately after
transfer of
the preforms to the cooling sleeves in the region between the threaded portion
and
the cylindrical blow-molded part.
Application of cooling air for the preform may be controlled such that the
maximum
cooling effect starts immediately after the transfer of the preform.
For preforms with a widening neck, the transition region between the threaded
portion and the neck ring may be air-cooled from the outside.
For preforms with a neck portion that tapers on the outside, this region of
the
preforms may be air-cooled from the outside.
The aftercooling apparatus according to the invention is characterized in that
blowing devices are integrated in the cooling sleeves in the region of the
outer open
end sides of the preforms, through which the outer skin, at least of an
unsupported
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region of the preforms, can be solidified with cooling air. The preforms can
also be
calibrated within a single injection molding cycle, after withdrawal of the
cooling
sleeves from the open mold halves, by compressive or sealing rings (56) that
are
mounted on nipples (30).
The method of the invention is characterized in that the outer skin, at least
of a part
of the outer open unsupported end sides of the preforms, are cooled with
cooling air
through air blowing devices integrated in the cooling sleeves and thereby
solidified.
In addition, the preforms are calibrated, after withdrawal of the cooling
sleeves from
the open mold halves, within a single injection molding cycle by way of
compressive
or sealing rings mounted on nipples.
The inventor has recognized that calibration after insertion of the hot
preforms into
the cooling sleeves with a substantially cylindrical or slightly conical blow-
molded
part results in significant progress in the manufacture of conventional
preforms. The
interior space of the preform, at least of the blow-molded part, must be
mechanically
sealed for calibration. However, the force of the compressed air used for the
calibration, as well as the mechanical sealing force, creates new problems, if
the
region of the open end of the preform wall sections is not supported by the
inner
wall of the cooling sleeves. It is also important to note that the outside of
the open
end of the preform can already be solidified immediately after transfer from
the open
mold halves to the cooling sleeves, as soon as the air cooling is integrated
in the
cooling sleeves. This produces a time improvement of, for example, 1 to 2
seconds
to make the respective threaded region dimensionally stable by additionally
cooling
the outside with cooling air. Cooling the blow-molded part immediately from
the
outside could be disadvantageous because the calibration would then require a
higher air pressure. Water-cooling the cooling sleeves has an immediate effect
in
the cylindrical region of the neck ring due to the direct wall contact, which
turned out
to be successful from the beginning. The entire region of the neck ring should
be
air-cooled and solidified from the outside until the mechanical forces can no
longer
impair dimensional stability due to the sealing forces. In a particular
preferred
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CWCAS-210
embodiment, the outer air cooling location for calibration is selected to be
located
approximately vis-à-vis the inside sealing force of the compressive or sealing
rings.
The novel aftercooling solution for calibration and/or handling starts
preferably with
the concept of a Thermos bottle closure. Both applications have a sensitive
wall
material. In one case, the material is glass, in the other case an easily
deformable
plastic. With the solution according to the invention, the sealing location
need not
be defined with the highest precision. The substantial advantage of the novel
invention is that the entire cycle time can be substantially reduced, while
meeting all
quality criteria and while the efficiency of the injection molding machine can
be
increased by between 15% and 20%. The preforms can be unmolded sooner, i.e.,
when the preforms are still substantially dimensionally unstable.
In practice, there are a large variety of preforms which may require special
treatment.
- Particularly delicate are preforms which have a conically tapered neck
piece
between the cylindrical blow-molded part and the neck ring.
- Another delicate preform has in a widened portion in the corresponding
neck
section.
With the new invention, dimensional stability can be fully maintained even
when the
dry cycle time is significantly shortened. This means that a reserve remains
for a still
shorter machine cycle time when the particular air cooling of the outer, open
end
side is employed. Field tests have shown that the machine cycle time can be
reduced by 15% with clear preforms and by 20% with colored preforms.
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PCT/EP2008/050840 CA 02676615 2009-07-24
Advantageously, when calibrating, the pressure of the compressed air increases
continuously from the start of the calibration. In this way, shrinkage can be
continuously compensated even when the preform continues to solidify.
Preferably,
the compressed air supply can be reproducibly controlled by a programmed
increase of the control voltage of a control valve and a corresponding
increase of
the calibration pressure.
In a particularly preferred embodiment, a cooling aggregate is associated with
the
aftercooling apparatus for producing low-temperature air, in particular at a
temperature below 0 C. A pressure generator for the cooling air is associated
with
the aftercooling apparatus, which generates a cooling air pressure of less
than 2
bar, preferably less than 1.2 bar. Advantageously, the application is
controlled,
wherein the aftercooling apparatus includes a controller by which the air
blowing
device can be activated immediately, from the moment the preform is
transferred to
the removal or cooling sleeves. Application of low-temperature air has two
significant advantages: firstly, immediately after transfer of the preforms,
which are
removed from the molds while still hot, an immediate and more intense
solidification
of the outer skin can be attained in the region of the opening. This means
that
before any mechanical intervention through handling or calibration, this
region which
is especially at risk, is solidified to a degree so as to prevent an oval
shape or local
swelling. The low-temperature air advantageously also reduces the quantity of
cooling air. The air pressure can be reduced, for example from 4 bar to only 1
bar.
Accordingly, the same effect can be attained with a much smaller air quantity
than
with ambient air. In particular, the quantity and temperature of the low-
pressure air
can be purposely controlled.
According to a particularly advantageous embodiment of the novel invention, it
is
proposed that the air blowing device is implemented as air channels directed
to the
outer, open-ended side of the preforms. Preferably, the aftercooling apparatus
includes a controller for switching the apparatus on and off, by which the air
blowing
device can be activated from the moment the preform is transferred to the
removal
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or cooling sleeves as well as during the calibration phase. The solution of
the
invention can be applied in the field of aftercooling wherever there is a risk
of
handling-related damage.
In a particularly advantageous embodiment, a gripper has a plurality of
nipples with
a corresponding insertion part into the preforms, wherein the insertion parts
of the
nipples have radially expandable compressive or sealing rings which can be
inserted into the preforms. The compressive rings are preferably implemented
as a
radially expandable sealing rings, by which a sealing force can be generated
via a
bore in the nipples in the interior of the blow-molded part of the preforms
directed
towards the inner wall of the preforms for building up an inflation pressure.
In a
particularly preferred embodiment, the inflation pressure is controlled by
starting
with a minimum pressure, which then increases to the optimal pressure.
According to another important concept of the invention, the nipples can be
inserted
into the preforms, with control of their position, to a selectable optimal
sealing
location in the region between the threaded part and the blow-molded part.
Different
shapes of the transition between the threaded part and the blow-molded part
can
then be taken into consideration. The best sealing location is identified at
the
beginning of each production. After insertion of the nipples, the outer wall
of the
entire blow-molded part of the preform must be in wall contact with the
corresponding inner wall of the removal sleeve. Preferably, the preforms are
already
inserted into the removal sleeves during transfer with the removal sleeves
until a
complete and full inner wall contact of the entire blow-molded part, including
the
closed bottom part, is attained. During the duration of several injection
molding
cycles, the preforms are aftercooled in the water-cooled cooling sleeves of an
aftercooling, wherein the calibration is performed during the time of a single
injection
molding cycle or limited by the duration of a single injection molding cycle.
The
preforms can be removed from the cooling sleeves without any problems.
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With respect to the apparatus, each nipple has two tubular parts which can
move
relative to one another. A support shoulder is fixedly attached at each end.
With
the two aforedescribed solutions, each nipple includes air channels through
which
compressed air can be controllably supplied into the interior space of the
blow-
molded parts of the preforms. The actuating plate is moved by controlled
actuating
means with respect to the platform for synchronous activation of the
compressive or
sealing rings. The actuating means have only a supporting function during the
calibration. The compressive or sealing rings, when compressed, are held at
the
inside of the preform. A small force of the actuating means for the actuating
plate is
already sufficient for providing a good seal. Advantageously, the nipples are
arranged on a platform by way of a common actuating plate, by which the
nipples
are inserted in or withdrawn from the preforms as well as positioned inside
the
removal sleeves. To this end, controlled drive means are associated with the
platform for positioning the compressive or sealing rings with an optimal
insertion
depth or at an optimal location.
According to a preferred embodiment, the preforms are removed from the removal
sleeves and transferred to cooling sleeves of an aftercooling when reaching
sufficient dimensional stability, but within the time of a single injection
molding cycle.
After calibration, the compressive or sealing rings can be released and the
pressure
relieved from the interior space of the blow-molded parts. A vacuum can be
generated via the air channels and the nipples, with the preforms being
transferred
to the aftercooling by way of the nipples. The nipple does not have a cooling
function. Preferably, during the short calibration time, no air is exchanged
between
the interior of the preform and the ambient air. The nipples are provided with
air
channels, through which a vacuum can be generated in the preforms for removal
of
the preforms. The air channel for compressed air and suction can be identical
inside
the nipple. Preferably, the tubular sections are movable inside one another,
wherein
the inner tubular section has at least one air channel. For the concept of the
first
solution approach, the apparatus has a controllable removal gripper with a
number
of removal sleeves, with the number of removal sleeves corresponding to at
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the number of injection positions of the injection mold. The apparatus has an
air
connection for controllable admission of compressed air to produce an
inflation
pressure inside the preforms for calibrating the preforms, as well as a
fitting to
control suction, whereby after switching from inflation pressure to vacuum the
preforms can be removed from the removal sleeves with the help of the nipples.
With this concept, the apparatus includes, in addition to the removal gripper,
an
aftercooling and a transfer gripper for transferring or switching the preforms
from the
removal gripper to the aftercooling, for finish cooling of the preforms,
independent of
the injection molding cycle.
According to another advantageous embodiment, the apparatus has an
aftercooling
constructed as a removal robot with a plurality of cooling positions in
relation to the
injection positions of the injection molds. The preforms to be transferred hot
are
here inserted into respective unoccupied cooling positions, calibrated,
intensely
cooled and ejected after finish cooling. The nipples can here support, with
controlled
and compressed air, the ejection of the finish-cooled preforms from the
removal
sleeves as well as the transfer to a conveyor belt. According to the second
embodiment, the press or sealing rings can likewise be relieved after
calibration, the
pressure in the interior space of the blow-molded parts can be vented, the
nipples
withdrawn and held in a waiting position, until the aftercooling is
repositioned for a
new charge of preforms of the subsequent injection molding cycle.
In both embodiments, the preforms are calibrated with compressed air and the
calibration time is limited by the injection molding cycle. Pressing and
calibration of
the still soft preforms has significant advantages:
- Firstly, by firmly pressing the outer skin of the preforms against the
inner, water-
cooled removal sleeve, maximum heat transfer and maximum cooling effect is
ensured.
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- Secondly, with the calibration, the outside dimensions of the preforms
are
reestablished exactly and remain intact during the subsequent solidification
of
the shape.
- Thirdly, the physical quality parameters are guaranteed by rapidly
crossing of the
so-called glass-transition temperature.
- Fourthly, by producing of a strongly cooled and solidified outer material
layer,
sufficient dimensionless stability of the preforms for subsequent handling by
the
removal sleeves in the cooling sleeves of an aftercooling and the following
ejection to a conveyer belt is achieved.
According to another particularly preferred embodiment of the apparatus, the
water-
cooled removal sleeves have in the region between the threaded portion and the
blow-molded part ventilation channels for a corresponding outside cooling of
the
corresponding preform region, also an air fitting for the ventilation
channels.
Depending on the geometrical shape of the preforms, the ventilation channels
are
arranged in the transition region between the threaded portion and the neck
ring
and/or in the transition region between the neck ring and the blow-molded
part.
Preferably, the water-cooled removal sleeves are constructed from standardized
parts, such that depending on the particular situation, customized guide rings
for the
ventilation channels for cooling the transition region between the threaded
portion
and the neck ring and/or the transition region between neck ring and blowing
portion
can be implemented.
With respect to the method, it is also proposed to employ outside cooling of
the
preforms with air in the region between the threaded portion and the blow-
molded
part immediately after transfer of the preforms to the cooling sleeves of the
removal
gripper until the end of the calibration. Compressive or sealing rings are
attached to
the nipples for the calibration and preferably introduced in a position-
controlled
manner into the preforms up to the transition region between the threaded
portion
and the neck ring or up to the transition region between the neck ring and the
blow-
molded part. In combination, the preforms are already cooled from the outside
after
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insertion into the cooling sleeves and during the calibration, also from the
outside, to
the transition region between the threaded portion and the neck ring and/or up
to the
transition region between the neck ring and the blow-molded part, and
solidified.
Advantageously, the outer skin of the preforms is more strongly solidified
immediately after transfer from the open mold halves to the cooling sleeves,
and
before the calibration on the critical unsupported portions of the preforms,
so that
the mechanical gripper forces do not adversely affect on the corresponding
regions.
With preforms having a widening neck, the transition region between the
threaded
portion and the neck ring is air-cooled from the outside. The preforms are
hereby
inserted until the neck rings contact the front face of the cooling sleeves,
wherein
the cooling sleeves are configured so that a minimum gap, preferably in a
range of
hundredths of millimeters, remains between the bottom part of the preforms and
the
corresponding bottom part of the cooling sleeves, which can then be eliminated
by
the calibration.
Brief Description of the Drawings
The invention will now be described in more detail with reference to several
exemplary embodiments.
Figure 1 shows schematically the novel invention in a ready position before
calibration of the preforms;
Figure 2a shows a nipple optimally inserted in a preform in the region of the
open
end side of the preform;
Figure 2b shows on an enlarged scale a nipple with a floating compressive or
sealing ring;
Figure 3a shows outside cooling of the transition region between threaded
portion
and blow-molded part of the preforms;
Figure 3b shows a partial section of Figure 3a on an enlarged scale;
Figure 4a shows an enlarged portion of external air cooling;
Figure 4b shows external air cooling in a preform with a widening neck
section;
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Figures 5a, 5b and 5c show once more in schematic diagrams an optimal location
for applying the compressive or sealing rings and the exterior cooling,
wherein in Figures 5b and 5c the delicate, unsupported regions are
additionally externally cooled with air;
Figure 6a shows a differently constructed thick-wall preform with
corresponding
positioning of the nipple and the sealing ring, respectively;
Figure 6b shows the solution of Figure 6a, however with the inflation pressure
removed and the sealing ring relieved;
Figure 6c shows removal of a preform with the nipple operating as a support
nipple;
Figure 7 show schematically an example for the first solution approach with
additional aftercooling;
Figure 8 shows schematically an example for the second solution approach,
with
the removal robot constructed as an aftercooling;
Figure 9 shows a thermal profile, recorded on a preform produced without
calibration;
Figure 10a shows an exemplary test of a preform calibration; and
Figure 10b shows a defective preform, wherein the transition region that was
not
supported in the cooling sleeve, is not solidified according to the
invention.
Detailed Description
Figure 1 shows a situation after retraction of the removal device 11 from the
open
mold halves 8 and 9 and the start of the calibration as well as of intense
cooling.
The platform 17 with the nipples 30 is here already in a ready position for
insertion
travel into the preforms 10 as indicated by arrow 31. The platform 17 is
supported
on a support console 36 via an arm 14 disposed on a travel device 32 and
linear
guide rails 33 and is moved parallel to the machine axis 37 with a linear
drive 34.
The backside of the linear drive 34 is anchored on a bracket of the support
plate 4.
When the linear drive 34 is activated, the nipples 30 are moved towards and
away
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from the removal device 11 (as indicated by arrow 31). Adjustment means 18,
whose sole function it is to squeeze and relieve the compressive and sealing
rings
56, are associated with the actuating plate 16.
Figures 1 and 7 show schematically an injection molding machine for preforms
with
the following major elements: a machine bed 1 on which a support platen 4 and
a
fixed platen 2 and an injection unit 3 are supported. A movable platen 5 is
supported
for axial displacement on the machine bed 1. The two platens 2 and 4 are
connected with one another by tie rods 6 which extend through the movable
platen
5. A drive unit 7 for generating the clamping pressure is arranged between the
support platen 4 and the movable platen 5. The fixed platen 2 and the movable
platen 5 each carry a mold half 8 and 9, respectively, between which a
plurality of
cavities can be formed for producing a corresponding number of sleeve-like
injection-molded parts. The injection-molded parts 10 are produced in the
cavities
formed between mandrels 26 and cavities 27. After the mold halves 8 and 9 are
opened, the sleeves-like injection-molded parts 10 adhere to the mandrels 26.
The
same injection-molded parts 10 in the finished cooled state are illustrated in
the
upper left section of Figure 7, just after being ejected from an aftercooling
device 19.
The upper tie rods 6 are shown with broken lines to better illustrate the
details
between the opened mold halves. According to the solution shown in Figures 1
and
7, the four process steps for injection-molded parts 10 at the end of the
injection
molding process according to a first solution approach are as follows:
"A" indicates removal of the injection-molded parts or preforms 10 from the
two mold
halves. The parts which are still plastic are here received by a removal
device 11
(Figure 1) recessed in a space between the opened mold halves and raised with
the
removal device 11 into the position "B".
"B" indicates the phase of the calibration and intense cooling.
"B"/"C" indicates transfer of the preforms 10 from the removal device 11 to a
transfer
gripper 12, and transfer of the preforms 10 from the transfer gripper 12 to an
aftercooling device 19, according to the first solution approach.
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"D" indicates ejection of the cooled preforms 10, which are now in a
dimensionally
stable state, from the aftercooling device 19.
Figures 1 and 7 show schematically snapshots of the major handling steps
according to the first solution approach. In position "B", the vertically
stacked
injection-molded parts 10 are received by the transfer gripper 12 and 12',
respectively, and brought into a vertical position by rotating the transfer
device in the
direction of arrow P, according to phase "C". The transfer gripper 12 consists
of a
platform 17 which can be rotated about an axis 13. The platform 17 carries an
actuation plate 16, which are arranged parallel to one another in spaced-apart
relationship. The actuating plate 16 can be extended parallel to the plafform
by a
drive or by adjusting means 18, so that in the position "B" the sleeve-like
injection-
molded parts 10 can be withdrawn from the removal device 11 and placed into
the
aftercooling device 19 located above in the rotated position "C". The
respective
transfer is accomplished by changing the distance "S" between the actuating
plate
16 and the platform 17. The injection-molded parts 10, while still hot, are
finished-
cooled in the aftercooling device 19 and, after the aftercooling device 19 is
moved,
ejected in position "D" and thrown onto a conveyor belt 20. The reference
symbol 23
indicates the water cooling with corresponding supply and drain lines, which
are
conventional and indicated by arrows to simplify the drawing. The reference
symbols 24/25 indicates the air side, wherein 24 refers to blowing in or
supplying
compressed air and 25 refers to vacuum or drawing off air (Figures 6a and 6c).
Figure 2a illustrates the direct relationship between the function of the
nipples 30 as
calibration nipples and the conical section 47 of a preform 10. The
corresponding
conical outer part of the preform 10 is specially cooled immediately after
removal
from the open mold halves 8, 10, and the unsupported outer wall layer is
solidified
inside the cooling sleeve 21 (Figure 3b). This gives the entire preform
sufficient
dimensional stability at the tapered transition 47. Against the outside, the
air guiding
ring 114 is held inside the head portion 143 of the cooling sleeve 21. During
installation, the air guiding ring 114 with the inner sleeves 144 of the
cooling sleeve
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21 is inserted from left to right. The cooling air is indicated by arrows 145,
145'.
Figures 2a and 3b, respectively, show that the cooling air is operative before
the
compressive or sealing ring 56 makes contact with the preform.
Figure 2b shows the insertion part of the nipple 30 according to Figure 6a on
an
enlarged scale. A particularly preferred feature is the floating support of
the
compressive or sealing ring 56. The compressive ring 56 is held at both ends
by
loose support rings 100. The two loose support rings 100 have an inside
diameter
"D" which is larger than the outside diameter "d" of the support tube 52 by a
slight
play. Play "Sp" also exists in the longitudinal direction between the support
ring 100
and the connecting piece 80. In this way, the compressive or sealing ring 56,
when
inactive, attains a freedom of movement similar to slight tumbling or
floating. This
provides automatically an optimal annular sealing location, e.g., 57, 57' or
57" on the
compressive or sealing ring 56.
Figures 3a and 3b show outside cooling of preforms 10xx in the not-uncritical
transition 47 between the threaded portion 44 and the blow-molded part 43.
Many
preforms 10xx have an outer conical taper 110 in this region. This conical
taper 110
is disadvantageous because the region 47 of the taper vis-à-vis of the cooling
sleeve 21 is unsupported, so that there is no contact with the inner wall 111
of the
cooling sleeves. Cooling air can be blown in through an air fitting 112 and
vented to
the outside through a cooling channel 113. This additional cooling has the
significant
advantage that it can be effectively used from the first instance when the
preforms
are transferred to the cooling sleeves 21 and additionally during the entire
calibration time. The additional solidification of the outside of the affected
preform
counteracts a possible deformation caused by the pressing force of the
compressive
or sealing ring 56. The most striking structural difference to a "normal"
cooling
sleeve is that an air guiding ring 114 is arranged in the open mouth region.
An
annular cooling channel is arranged around the corresponding preformed part on
the inside of the air guiding ring 114 from the location of the air fitting
112 to the vent
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location 113'. Cooling air then flows intentionally across the entire conical
outside of
the preforms to the end face of the neck ring 137.
Figures 4a and 4b show a preform 10x with a conically widened neck piece 136.
With this type of preform, the widened neck piece is already part of the blow-
molded
part and contacts during calibration the inner wall of the cooling sleeve 130.
The
inner wall of the cooling sleeve provides the preform 10x with the defined
exterior
shape. The entire blow-molded part of the preform 10x makes contact with the
neck
ring 137. The optimal sealing location of the compressive or sealing ring 56
is in the
region of the cylindrical section in the region of the neck ring 137 (Figure
5b).
However, this part is at risk of being deformed during expansion of the
compressive
or sealing ring 56, because this part is only partially supported from the
outside.
The additional outside air cooling (KL) becomes therefore important. The outer
skin
of the thread 44 attains a greater rigidity due to the air cooling of the
threaded
portion 44 and the neck ring 137, regardless if the preform is calibrated or
not.
Figure 4b shows another interesting conceptual embodiment. The cooling sleeve
is
constructed of standardized components and consists of an inner cooling sleeve
130, an outer cooling sleeve 131 and a jacket sleeve 132, as well as a head
ring
133 which is used to form the air channels (gap Sp). The inner cooling sleeve
130
is designed commensurate with the shape of the preform 10, 10x, 10xx, with a
corresponding head ring 133 or 114 being applied. Reference symbol 138
indicates
the lowest thread pitch, 134 the base of an actuating plate, and 135 the
sealing
rings. According to Figures 4a and 4b, the cooling sleeve 10x is designed such
that
after insertion of the preforms into the cooling sleeves, a minimal gap 139 of
several
tenths of millimeters remains at the bottom part. Conversely, the neck ring
137
should fully rest on the end face of the cooling sleeve already during
insertion.
Frequently, as shown in Figure 5a, external cooling may be unnecessary with a
completely cylindrical blow-molded part. Because it is desirable to further
shorten
the machine cycle time, the threaded portion of preforms with a cylindrical
blow-
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molded part may advantageously be strengthened early on, so as to prevent
damage to the thread during any handling in conjunction with aftercooling.
Figure 5b shows a preform having an increased diameter in the region of the
open
end. This preform is no longer supported in the cooling sleeve in the region
of the
neck ring 137 and the thread. Advantageously, the outer skin of the
aforementioned
region is solidified with cooling air immediately after transfer from the
injection molds
to a removal gripper.
Figure 5c shows a solution intended to prevent deformation, in particular
bulging of
the affected section, when the corresponding blow-molded part is tapered
(Figure
10b), in particular with extremely short cycle times below 10 seconds and with
thicker preform walls. The section treated with cooling air is typically
between 3 and
cm for typical preforms for PET bottles with a fill volume of 1-2 liter,
wherein the
thread itself has a length of approximately 2 cm.
As seen from the foregoing, the preforms 10, 10x, 10xx have from the moment of
the removal from the open mold halves:
- Always the best cooling conditions;
- The preform is pressed against the inner cooling surfaces of the removal
sleeves
40, except for a short interruption, immediately after being moved from the
open
mold halves to the cooling sleeves until insertion of the nipples 30 during
the
calibration phase;
- The short interruption for a 100% contact of the preform 10 is
compensated by
the longer calibration;
- After calibration, the preforms 10, 10x, 10xx are always dimensionally
stable.
The preforms 10, 10x, 10xx therefore retain their outside geometric dimensions
after calibration until in the finished cooled state.
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An effect with maximum intensity is produced by optimizing the design of the
water
cooling loops
in the injection molds,
in the region of the injection molding cavities and in the injection molding
mandrel, as well as
in the removal sleeve,
The goal is not to finish-cool the preforms 10, 10x, 10xx within a single
injection
molding cycle. However it is desired to bring the preforms 10, 10x, 10xx to a
state
at the end of the aftercooling process, which takes about two to three times
longer,
where they can be poured, stored and transported.
This leads to substantial advantages:
a prerequisite for an extreme shortening of the cycle time,
hence a further increase of the productivity of the injection molding machine,
maximal dimensional stability of the preforms, and
the best possible qualitative properties of the preforms, for example with
respect to the crystallinity, dimensional stability and freedom from damage.
Figures 6a, 6b and 6c show calibration and removal of the preforms 10 from the
removal sleeves 40 with the nipples 30 operating as holding nipples. Vacuum
can
be applied to the interior space of the blow-molded part through the nipple 30
(Figure 6a) and the preform 10 is suctioned against the nipple 30 (- sign)
according
to Figure 6b. A centering ring 58 which exactly matches the open end of the
preform 10 is disposed at the rear end of the support tube 52, for precisely
holding
the preforms of the nipples 30. On the opposite side of the preform 10,
compressed
air is applied to the closed end of the preform (+ sign) according to Figure
6c. The
preform 10 strikes a stop 50 on the actuating plate 16 and can be completely
removed from the removal sleeve 40 and transferred, for example, to the
aftercooling, or ejected according to a second solution approach by switching
to
compressed air.
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Figure 6a illustrates schematically regulation of the compressed air supply.
The
compressed air supply for calibration is adjusted via a voltage-controlled
control
valve 35, 38 by way of the voltage in Volt with controller 39, wherein a
continuous
increase of the inflation pressure is contemplated, preferably from the start
of the
calibration. The shrinkage of the preform 10 due to the cooling effect from
the
cooling sleeve 21 can hereby be compensated and rapid solidification of the
outer
skin can be attained. The preform 10 can be pressed in an optimal manner
against
the inner wall of the cooling sleeve for the entire duration of the
calibration, without
causing bulges in the region of the unsupported regions or damage resulting
from
handling of the preforms.
Figure 7 shows a station at the end of the injection process with open mold
halves 8
and 9, respectively. The temperature of the preforms 10 was lowered in the
mold
using a maximum cooling effect. The preforms 10 may still be dimensionally
unstable and may quickly be deformed when subjected to the smallest external
force, if they are immediately ejected after the mold is opened. At the end of
the
injection process, the removal device is already in the start position (Figure
1) and
can be lowered between the open mold halves without a time delay after the
mold is
opened. In the solution illustrated in Figure 7, an independent aftercooling
device in
19 is employed, in which the still hot preforms 10 are finish-cooled during 3
to 4
injection molding cycles. A transfer gripper 12 transfers in phase "B"/"C" of
Figure 7
the preforms 10 to the aftercooling device 19. The preforms are aftercooled in
water-cooled sleeves.
Referring back to Figure 7, the horizontal plane is indicated with EH and the
vertical
plane with EV. The horizontal plane EH is defined by the coordinates X and Y,
whereas the vertical plane is defined by the coordinates Y and Z. The Z-
coordinate
is oriented vertically and the X-coordinate is oriented perpendicular thereto.
The
transfer gripper 12 executes a rotation and a linear motion in the X-
coordinate. In
addition, the transfer gripper 12 can be configured with a controlled motion
in the Y-
coordinate. Because the transfer gripper 12 already performs a controlled
motion in
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the X-coordinate, the preforms 10 residing on the nipples of the transfer
gripper 12
can be exactly positioned in the X-direction by a suitable
controlled/regulated
movement. For transferring the preforms 10 to the aftercooling 19, the
aftercooling
19 is here moved in the X-direction to a fixed position, the transfer gripper
12 is
controlled/regulated in the Y-direction and moved to the respective desired
position.
In the preferred embodiment, the motion means for the aftercooling 19 are
controllable/regulatable for the two coordinates X and Y for assuming exact
positions for transfer of the preforms 10. The transfer gripper 12 is here set
to a
fixed transfer position.
The discussions above make reference to the entire disclosure of WO
2004/041510
and PCT 2007/000319.
In the positions illustrated in Figures 7 and 8, the two mold halves 8 and 9
are in an
open position, so that the aftercooling 60 can move into the unobstructed
space 62
between the mold halves. The aftercooling 60 has a total of three movement
axes, a
horizontal movement axis along the Y-coordinate, a vertical movement axis
along
the Z-coordinate, and a rotation axis 63, which are coordinated by a machine
controller 19. The rotation axis 63 is only used for ejecting the finish-
cooled
preforms 10 onto a conveyor belt 20. The rotation axis 63 is supported with
respect
to a base plate. Movement means for vertical movement is a vertical drive 65.
The
vertical drive 65 is slideably disposed on a base plate 66 of a horizontal
drive 67.
The horizontal drive 67 has an AC servo motor with a vertical axis. The base
plate
66 is supported for back-and-forth movement on two parallel slide rails by way
of
four sliding bodies. The base plate 66 has on the right side of the drawing a
vertical
base plate section, on which the vertical drive 65 is anchored. The vertical
drive 65
also has an AC servo motor with a horizontal axis.
The aftercooling device according to Figure 8 has several rows arranged in
parallel.
In the illustrated example, 12 cooling sleeves 21 are illustrated in a
vertical row.
The cooling sleeves 21 can be arranged much more tightly with reference to the
conditions in the injection molds. Accordingly, not only several parallel
rows, but in
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addition an offset between the rows is proposed. The cooling tubes for a first
injection molding cycle are then indicated with numbers 1, for a second
injection
molding cycles with numbers 2, etc. If in the example with four parallel rows
all rows
number 3 are filled, then the rows with the number 1 are prepared, as
described
before, for ejection onto the conveyor belt 20. The remainder is performed in
the
same way during the entire production time. In the illustrated example, the
entire
aftercooling time is in the order of three to four times the injection molding
time. The
air pressure or vacuum conditions in the aftercooling device 19 must be
controllable
by rows, so that at a certain time all rows 1, or 2, etc. can be activated
simultaneously. In addition to the accuracy for controlling the movement of
the
aftercooling 19 and the platform 17, the acceleration and deceleration
functions
should also be optimally controlled. Visualization is performed in a command
device
of the machine controller or the machine computer 90, respectively. Any aspect
of
the movements can be optimized, for example start and stop, as well as
acceleration and deceleration, and speed and distance.
Figure 9 shows a heat profile, recorded on a preform 10xx, which was produced
without calibration. The large temperature difference of 62.8 C to 45.7 C is
evident.
This results in a radial temperature difference of 17.1 C at the end of the
shaft of the
preform, which caused an oval outer shape during the first cooling process.
This
undesired oval outer shape can only be reduced or prevented by a longer
cooling
time in the mold. In the illustrated example, the illustrated heat profile
was
measured with a cycle time of 13.5 seconds. The quality was about 0.2 mm,
which
is just inside the tolerance limit.
Figure 10a shows an exemplary test where the preform 10xx is calibrated with
cooling air. The temperature distribution is in a much narrower range of only
3.9 C,
whereby the cycle time was reduced from 13.5 seconds to 11.5 seconds. The
eccentricity of the oval shape was only 0.05 mm instead of 0.2 mm. This shows
that
with the invention, more precise preforms can be produced with a shorter cycle
time.
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Figure 10b shows a preform 10xx, where outside cooling according to the
invention
was not employed. The calibration pressure was too high, so that the preform
bulged in the unsupported conical region.
24
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