Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF INVENTION
The invention generally relates to the art of injection moulding and more
specifically to
systems for removing hollow plastic articles from an injection moulding
machine, especially
preforms made from polyethylene terephthlate (PET) which are subsequently blow
moulded into
end-user containers.
BACKGROUND OF INVENTION
Each cycle of an injection moulding machine produces a plurality of preforms
which must
be removed from the machine in order to enable the next cycle to commence. The
preforms
which must be removed from the injection moulding machine are quite hot due to
the fact that
the inj ection moulding operation is earned out at high temperatures and the
preforms are only
superficially or partially cooled during the injection moulding cycle. This
incomplete cooling
causes the preform to exhibit a temperature gradient wherein the inner and
outer skin
temperatures of the preform are relatively cool in order to solidify the
preform for short-term
handling. However, as PET preforms typically have relatively thick walls,
e.g., about 4 to 6 mm,
a substantial amount of heat remains trapped or stored in the interior of the
preform walls.
Accordingly, the preforms have to be carefully handled upon removal from the
injection
moulding machine as otherwise the escaping heat could lead to the deformation
of the preform
should it be unduly stressed, or to "sticking" problems that arise when
insufficiently cooled
preforms are brought into contact with one another. (Of course, it is always
possible to lengthen
the period of the injection moulding cycle to thereby allow the preforms more
time to cool in the
machine; however, that would be counteractive to the goal of achieving high
throughput).
An example of a prior art system for preform removal and cooling is disclosed
in U.S.
Patent No. RE33,237 to Delfer. This system employs a robot-controlled take-out
plate assembly
having a plurality of cooled tubes or single-ended cavities formed therein,
with the number of
such cavities corresponding to a multiple of at least two times the number of
preforms produced
per injection moulding cycle. The extra set o~r sets of cavities in the Delfer
take-out plate
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assembly allows preforms to be held and cooled in the take-out plate for a
corresponding number
of additional injection moulding cycles, thereby permitting the preforms a
greater of amount time
to be cooled before being transported for further processing.
The structure of such apreform removal and handling system, detailed for
instance in U.S.
S Patent No. 4,729,732 to Schad et. al., U. S. Patent No. 4,173,448 to Rees
et. al., and U. S. Patent
No. 5,447,42f to Gesner et al., comprises an air pressure means and a cooling
means. The air
pressure means provides a vacuum or pressurized air to each tube or cavity of
the take-out
assembly. The vacuum enables preforms to be removed by suction from the
moulding machine
and held in the take-out plate cavities during ~~ransfer to a receiving
station. Conversely, the
pressurized fluid assists in ejecting preforms stored within the take-out
plate cavities. The
cooling means circulates cooling fluid throughout the take-out plate in order
to chill the preforms
temporarily stored therein.
This type of preform removal and handling system tends to be relatively
expensive and
difficult to maintain for a number of reasons. First, the air pressure means
and the cooling means
each require the provision of extraneous equipment, such as air pumps and heax
exchangers, as
well equipment that may be integrate into the take-out plate such as valves
and the like. Second,
the air pressure and cooling means require that intricate integrated channels,
bores and manifolds
be milled into the take-out plate in order to distribute the appropriate
fluids to each of the preform
holding cavities or tubes. This requirement tends to make the take-out plate,
which is precisely
crafted, difficult and expensive to manufacture. Third, as the cavities or
tubes of the take-out
plate are typically designed to encompass the bodies of the preforms, the
plate tends to be
relatively thick and heavy. The robotic positioning device thus requires
relatively powerful
motors in order to quickly position the take-out plate in a stable manner.
Finally, this type of
system tends to require relatively frequent maintenance due to its complexity.
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SUMMARY OF INVENTION
The invention presents an alternative prefonn removal and handling system and
a take-out
plate assembly which does not incorporate the complexities of the prior art
thereby providing the
advantages of low cost and reduced maintenance requirements.
S According to one aspect of the invention, injection moulding apparatus for
producing
hollow plastic articles is provided. The apparatus includes an injection
moulding machine
having interlockable male and female mould portions for forming a first number
of hot hollow
plastic articles in an inj ection moulding cycle, and means for reciprocating
the mould portions
between a mould-closed position and a mould-open position. A conveyor is
spaced apart from
the injection moulding machine, and features receptacles for holding the hot
hollow plastic
articles in an upright position in order to let hot air disposed in the
interior of each hot hollow
plastic article to rise unheeded, the number of such receptacles being at
least equal to the first
number of hollow plastic articles produced in the injection moulding cycle. A
transfer
mechanism quickly removes the hot hollow plastic articles from the injection
moulding machine
1 S when it is in the mould-open position and deposits the hot hollow plastic
articles upright in the
conveyor receptacles.
This apparatus is effective because it is passible to handle the hot hollow
plastic articles,
such as PET preforms, for a period of less than approximately 15 seconds
before the heat trapped
in the interior of the walls of the hollow plastic article manages to spread
out to the inner and
outer skins of the article and soften the skins to a point where the article
can no longer be actively
manipulated. However, within this time period, the transfer mechanism deposits
the hot hollow
plastic articles into the receptacles of the conveyor, where the articles are
held for cooling and not
actively manipulated or unduly stressed. The hot hollow plastic articles are
held in an upright
position when disposed on the conveyor in order to efficiently cool the hollow
plastic article. If
the hollow plastic articles were held in an upside down manner, the closed end
of the article
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would trap sufficient heat in the hollow interior of the article to cause the
above mentioned
deformation and/or sticking problems.
The transfer mechanism preferably comprises a substrate, and a retractable
clamping
means, connected to the substrate, for gripping the first number of hot hollow
plastic articles from
S the injection moulding machine when in the mould-open position and for
releasing the gripped
articles. The substrate may comprise a carrier plate having a plurality of
bores therein, and the
clamping means may comprise jaw clamps, co-axial with each bore, with each jaw
clamp being
slidably mounted on the carrier plate for movement in a direction
substantially normal to the
corresponding bore. A motive means, such as a robot, aligns and juxtaposes the
clamping means
with the hot hollow plastic articles disposed on one of the mould portions
when the moulding
machine is in the mould-open position. The motive means also aligns and
juxtaposes hot hollow
plastic articles held by the clamping means with the conveyor receptacles in
order to deposit the
former into the latter.
The transfer mechanism of the present invention provides a mechanically stable
system
for the removal and handling of hot plastic articles from the injection
moulding machine. In
contrast to some prior art systems, the transfer mechanism of the present
invention does not
incorporate complicated cooling and air pressure means. Moreover, the
substrate of the transfer
mechanism can be made relatively thin and light thereby enabling the use of
more economically
efficient motors to be employed in the motive means.
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BRIEF DESCRIPTION OF DRAWINGS
For the purposes of description, but not of limitation, the invention will now
be explained
in greater detail with reference to the accompanying drawings, wherein:
Figures lA - 1 C are perspective view illustrations of an injection moulding
apparatus in
accordance with the preferred embodiment, each of which illustrates a prefers
ed transfer
mechanism of the apparatus in a different operative position;
Figures 2A, 2B and 2C are partial cross-sectional views of the injection
moulding
apparatus taken along line I-I in Figure 1;
Figure 2D is a partial cross-sectional view of the transfer mechanism taken
along line II-II
in Figure 1 C;
Figure 2E is a partial cross-sectional view of a preferred conveyor employed
in the
injection moulding apparatus taken along line Il(I-III in Figure 1C;
Figure 3 is a fragmentary, perspective view of a portion of the transfer
mechanism;
Figure 4 is a front view also showing hidden details of a similar portion of
the transfer
mechanism shown in figure 3;
Figure 5 is an exploded view of a portion of the transfer mechanism shown in
figure 3;
and
Figures 6A - 6C are schematic diagrams illustrating various preferred patterns
for storing
hot hollow plastic articles onto the conveyor.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
An inj ection moulding apparatus 10 for producing hollow plastic articles such
as PET
preforms is shown in Figs. lA to 1C. The apparatus 10 includes an injection
moulding machine
12 and a hopper 14 for receiving PET pellets which are heated to produce PET
resin that is
injected into moulds provided by the injection moulding machine as is well
known in this art.
The inj ection moulding machine 12 includes interlockable male and female
mould
portions 16A and 16B. Referring additionally to the partial cross-sectional
views of Figs. 2A and
2B, the male mould portion 16A carries a plurality of elongate cores 18
designed to penetrate
corresponding cavities 20 in the female mould portion 16B and thereby provide
a plurality of
moulds. The mould portions 16A and 16B reciprocate between a mould-closed
position and a
mould-open position for each injection moulding cycle of the machine 14. In
the mould-closed
position, a number of elongate hollow preforms ~ 8 are produced, the exact
shape of each article
corresponding to the intersticial shape between a given core%avity. In the
mould-open position,
a gap 22 is present between the male and female mould portions 16A and 16B and
the recently
moulded, hot, hollow preforms must be removed from the machine 12 in order to
enable the next
injection moulding cycle to commence.
The injection moulding apparatus 10 includes a conveyor 24 which is spaced
apart from
the injection moulding machine 12. The conveyor includes a web 25 and
receptacles 26,
discussed in greater detail below, for holding the hot hollow preforms in an
upright position in
order to efficiently cool the performs. The number of receptacles 26 is at
least equal to the
number of preforms produced in each injection moulding cycle, and preferably
more, as discussed
in greater detail below. The conveyor 24 holds the preforms for a
predetermined time period,
preferably a multiple of injection moulding cycles, in order to give the
preforms sufficient time
to cool and stabilize. As the conveyor 24 proceeds in a forward direction,
preforms at the head
of the conveyor simply fall out of the receptacles 26 as the web 25 curves at
about point 27 to
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begin its return path. At this point, the preforms can be collected or
transferred by other conveyor
means (not shown) for further processing, such as blow moulding, etc.
The inj ection moulding apparatus 10 includes a transfer mechanism 28 for
quickly
removing the hot hollow prefonms from the injection moulding machine 12 when
it is in the
mould-open position and for depositing these preforms upright in the conveyor
receptacles 26,
as shown for example in Figure 2E. The transfer mechanism 28 comprises a frame
or substrate,
such as a take-out or carrier plate 30, and a retractable clamping means such
as split ring clamps
32, discussed in greater detail below, for gripping and holding all of the
preforms produced in
an injection moulding cycle. A motive means, such as a three-axis gantry robot
34, aligns and
juxtaposes the clamping means 32 with the hot preforms disposed on the male
moulding portion
16A when the injection moulding machine 12 is in the mould-open position. The
motive means
also aligns and juxtaposes hot preforms held by the clamping means 32 with the
conveyor
receptacles 26 in order to deposit the hot preforms into the receptacles. The
movement of the
carrier plate 30 as provided by the motive means is partially depicted in
Figs. 1 A, 1 B and 1 C,
and, in cross-sectional view, by Figs. 2C, 2D and 2E.
The clamping means, as described in greater detail below, exerts some pressure
onto the
recently moulded and still quite hot PET preforms which typically have a skin
temperature of
about 10 to 30 degrees Celsius, depending on the operating characteristics of
the machine 12, and
a much higher internal temperature, e.g. about 200 degrees Celsius.
Nevertheless, it: is possible
to apply a small amount of pressure to the PET preforms and thus handle them
for a short time
period before the heat trapped in the interior of the preform walls manages to
diffuse or radiate
to the inner and outer skins of the preforms and soften the skins to a point
where they are no
longer "set" and the preform can no longer be gripped or otherwise actively
manipulated. This
time period will vary depending on the length of the injection moulding cycle,
the skin
temperature, the temperature of operation, and the cooling efficiency of the
injection moulding
machine. A typical time period within which tine preforms may be handled is
approximately 5
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to 10 seconds. Accordingly, within this time period, the transfer mechanism 28
deposits the
preforms into the receptacles 26 of the conveyor 24, where the preforms are
temporarily stored
until they stabilize. The preforms are not actively manipulated or unduly
stressed when stored
on the conveyor 24. The hot hollow preforrns are held in an upright position
when disposed on
the conveyor in order to let hot air disposed in the interior of each preform
to rise unheeded and
hence allow the preform to cool sufficiently without the need for an
extraneous cooling means.
The upright positioning is important because if the hollow PET preforms were
held in an upside
down manner, the closed end of the preform would trap sufficient heat in the
hollow interior
thereof to thereby cause the preform to possibly deform and/or stick to other
preforms when
eventually brought into contact with one another.
Referring additionally to Figs. 2C, 3, 4 and 5, the structures of the take-out
or carrier plate
30 and the clamping means are shown in greater detail.
The carrier plate 30 comprises a plurality of bores 36 therein arranged in a
pattern
corresponding to the pattern of elongate cores 18 present on the male portion
16A of the injection
moulding machine 12. Each bore 36 is sized larger in diameter than a
predetermined portion 3 5
of a corresponding preform exposed in the gap 2.2 between the male and female
mould portions
when the injection moulding machine 12 is in the mould-open position. Thus, as
shown in the
cross-sectional view of Fig. 4C, preforms 38 disposed on the male mould
portion 16A can freely
penetrate corresponding carrier plate bores 36.
The plate 30 features one split ring or jaw clamp 32 for each carrier plate
bore 32. Each
clamp 32 is co-axially aligned with its corresponding bore 36 and is slidably
mounted on the take
out plate, as described in greater detail below, for movement in a direction
39 normal to the bore.
Each clamp 32 includes jaws 40A and 40B disposed on opposing sides of the
bore. The jaws
40A and 40B feature an inner perimeter 42 designed to substantially exactly
match the shape of
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a pre-determined periphery 44 of the preform 38 when the jaws are closed,
thereby enabling the
clamp 32 to grip the hot preform 38 without damage.
Means are provided for reciprocating each clamp 32 between a gripping or
closed position
and an open position. In the preferred embodiment, such reciprocating means
comprises a double
acting piston 46, tie rods 48A and 48B, channel-shaped clamp rails 52A and 52B
which
respectively connect to clamp jaws 40A and 40B, and articulating means SO
connecting the tie
rods 48A and 48B to the piston 46.
The tie rods 48A and 48B are respectively disposed in channels 54A and 54B
milled into
one of the faces of the carrier plate 30.
Elongate slots 56 in the carrier plate 30 enable tie rods 48A and 48B to be
respectively
fastened to the clamp rails 52A and 52B via fastening screws 58A and 58B. Each
pair of clamp
rails 52A and 52B respectively straddles a row or column of bores 36. Clamp
jaws 40A and 40B
are respectively disposed within the channels 60 of the clamp rails 52A and
52B and are
floatingly connected thereto. The floating connections are provided by bolts
62, which are
threaded into jaws 40A and 40B and which pass through, but are not threaded
to, eyelets 64
located in a central wall 66 of clamp rails 52A and 52B. Each clamp jaw 40A
and 40B also
includes bores 70 for partially housing compression springs 72 mounted between
the central wall
66 and the body of each clamp jaw. The floating connections enable a given
pair of jaws 40A
and 40B to gently grasp the hot pre-forms 3 8.
The articulating means 52 comprises double-legged bell cranks 74 having legs
76A and
76B respectfully connected to the tie rods 48A and 48B. The cranks 74 are
pivotably connected
to links 78 that are attached to the double acting piston 46.
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In operation, whenever the double acting piston 46 is actuated from one
position or pole
to the other, the articulating means force tie rods 48A and 48B to move in
opposite directions
relative to another. The clamp rails 52A and 52B, and hence jaws 40A and 40B,
will move in
correspondence with the tie rods 48 and 48B since these components are
interconnected as
described above. In this manner, piston 46 can be operated to reciprocate
clamps 32 between the
closed or gripping position and the open position.
Fig. 2E, illustraxes the structure of conveyor 24 and receptacles 26 in
greater detail. The
web 25 of the conveyor is formed from a plurality of substantially flat metal
slats 80, each of
which features a number of holes 82. The holes 82 are sized to accept an
elongate body 84 of
preform 38, but are smaller than a flange 86 present on the upper end of the
preform. Thus, as
shown in Fig. 2E, flange 86 of the preform rests against the top periphery of
the slat when the
preform is disposed on the conveyor.
The conveyor 24 preferably comprises a greater number of receptacles 26 than
the number
of preforms produced in an injection moulding cycle in order to efficiently
make use of the space
on the conveyor and allow the preforms a longer time period in which to cool
before being
displaced from the conveyor. For instance, Fig. 6A, shows the conveyor 24
being configured for
a three-position diagonally offset a drop pattern 90. In the illustrated
embodiment, the injection
moulding machine 12 features a 6 x 2 (row, column) preform production pattern.
In this
embodiment, the transfer mechanism 28 is programmed to deposit preforms
produced in a first
injection moulding cycle in receptacles labelled "A". The conveyor web is then
incrementally
advanced for a distance equal to the height of two rows in the pattern 90.
Preforms produced in
the next injection moulding cycle are then deposited in receptacles labelled
"B". The conveyor
web is again advanced as before, so that preforms associated with the next
injection moulding
cycle are deposited in receptacles labelled "C". The next advance of the
conveyor web restarts
the drop cycle wherein the next batch of prefornns are deposited in
receptacles "A"'.
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Fig. 6B, illustrates an alternative, laterally oi~set drop pattern 92. In this
embodiment, the
transfer mechanism 28 is programmed to deposit three, or alternatively some
other number, of
consecutive batches of prefornls in laterally offset receptacle groups A, B, C
before the conveyor
web is advanced for a distance equal to the length of the pattern.
Fig. 6C, illustrates another alternative, single position sequential drop
pattern 94, wherein
the conveyor web is advanced for a distance eclual to the length of the
production pattern after
each batch A, B, C of preforms is deposited onto the conveyor.
Still further alternative drop patterns can combine any of three illustrated
embodiments
shown in Figs. 6A to 6C.
It will be appreciated by persons skilled in the art that the present
invention is not limited
by what has been particularly shown and described herein as numerous
modifications and
variations may be made to the preferred embodiment without departing from the
spirit and scope
of the invention.
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