Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21 78~3
16662-01
~THOD AND APPARATUS FOR
JS~ MOLDING PLASTIC pl~TTt~.R~
This application is a continuation-in-part of United
States application Serial No. 08/135,829 filed October 14, 1993,
haYing a common assignee with the present application.
q~his invention relates to a method and apparatus for
5 compression molding plastic articles including closures.
1~,31.4 L ~ ' and summary of the Invention
It is common to compression mold plastic articles
including closures, as contrasted to injection molding plastic
articles. Typical patents comprise United States patents
2,072,536, 2,155,316, 2,218,456, 2,402,462, 2,891,281,
3,210,805, 4,296,061, 4,314,799, 4,343,754, 4,355,759,
4,497,765, 4,640,673, 4,755,125 and EPA 0 091 653 A2.
In the compression molding of plastic articles, there
are inherent variations that can a~fect the resultant articles.
15 One such variance is the manufacturing tolerance applied to the
tools. Accordingly, the molding sets on a machine are not
identical. Thus, when the tools are made up in the molding
position, the volume of the space between the molding surfaces
varies between mold sets. A further variance is the weight
20 and/or volume of the plastic charge that is placed within each
mold set.
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~ 2~7~3
In the above-identified patent application, there is
disclosed an invention which provides a method and apparatus
for compression molding plastic articles including closures
wherein the forming pressure can be accurately controlled;
5 wherein the forming pressure can be readily adjusted; wherein
lateral forces on the tooling are not applied directly to the
forming tool; wherein the tooling may be readily replaced;
wherein the number and size of tool stations can be readily
changed; and wherein various kinds and sizes of articles
lo including closures can be readily made by changing the tooling
and associated actuating mechanisms; wherein the tooling will
compensate for variations in pellet or charge weight, variations
in mold tooling volume in the closed mold position and wherein
a substantial overload such as a double charge of plastic can
LS be readily absorbed without overloading the tooling or the
overall apparatus.
In the above-identif ied patent application, the method
and apparatus for compression molding plastic articles including
closures includes providing co-acting sets of tools including
20 a first set for moving a core and core sleeve into engagement
with a cavity mold relative to a second set of tooling. The
first set of tooling includes an actuator between the tooling
and a fixed upper cam. ~he 3econd set of tooling includes an
actuator supporting the cavity mold and asaociated with a lower
2s fixed cam. A gas cylinder charged with atmospheric gas at a
predet~rminF~l pressure, preferably nitrogen, is provided in the
second set of tooling and controls the compression molding
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~ 21 78063
force. In a preferred form, a plurality of sets of tooling are
provided in circumferentially spaced relation on a rotating
turret supported by a central column. A common manifold supplies
the pressure at accurately controlled pressure to each of the
S nitrogen cylinders.
Each individual gas charged cylinder in association
with its individual tooling has a common predetermined pressure
as defi~ed by the system pressure, each cylinder being connected
in parallel with each of all the tooling cylinders by means of
lo connecting pipework and manifolds.
In the preferred form, each of the gas cylinaers has
a common diameter and consequently will require an equal force
to deflect each of the pistons within its respective cylinder
against the common system pressure. In the compression molding
process, it is preferred that each molded part be molded with
a constant molding force and that variations are held to a
mini This force will be sufficient to fully form the part
but no so high as to cause flashing of the material from the
adjoining mold surfaces.
It is well known in the art that volumetric variations
occur within the tooling due to manufacturing tolerances and
that the plastic material charge can vary in weight and volume.
Further, it is understood that occasional gross errors will
occur in the pellet charge volume as a result of incorrect
2s machine setting, or ag a regult of double charge of plastic, or
as a result of a prior molded part not being released ~rom the
mold prior to receiving a further charge of material.
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2 7 78063
For this reason, it is preferred to include a means
to compensate for the accumulated volumetric variance resulting
from the above phenomena while not F~Yt~e~1ing the preset molding
force established by the system pressure previously mentioned.
S Further, there is a limit of volumetric variance
beyond which the resulting part is nonfunctional as defined by
the desired geometry of the part being molded.
In a preferred form, each of the first set of tools
is advanced a common fixed stroke toward the respective cavity
o within the second set of tools to close the mold and to form
the plastic to f ill the mold. Normally the plastic charge is
within the desired weight tolerance to correctly form the part
and the pressure in the melt builds up during the forming stage
until the desired molding force is reached and the cavity is
deflected against the supporting gas cylinder to limit any
further increase in molding force. By this means, when the
desired molding force is reached, the volumetric space within
the tooling combination will remain substantially constant for
the duration of the stroke of the first set of tooling.
If the plastic charge was of a size less than the
lower tolerance to produce a functional part and of insufficient
size to fill the mold, then the desired molding force would not
be achieved prior to the completion of the stroke of the f irst
tooling and the resulting part could have voids, often referred
2~ to as "shorts".
Clearly, if a charge of material ~Y~t~ the maximum
tolerance to produce a quaLity part, then it is important to
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21 780b3
ensure that the tooling volume is ~ ated by further
deflection of the cavity under the control of its respective
gas cylinder in order that the mold force does not reach such
proportion as to damage the tooling or the machine.
To maintain a constant molding force within each of
successive tools, it is preferred that the force compensating
means is contained within the tool and thus in~ r~nt9~nt of any
external influences and has a minimum of moving parts to reduce
friction. It is also preferred not to use mechanical springs
lo for force compensation as they have a variance in spring rating,
are subject to failurer and cannot readily be re-set.
In the compression molding of closures having a
peripheral wall and a base portion, it is desirable to acc 'Ate
variable charges of plastic material and at the same time not
affect the aYial relationship of the male and female components
of the mold. In accordance with a further aspect of the
invention, a method and apparatus are provided by using a two
piece cavity mold having relative movement between the two
pieces wherein the relative movement is controlled by a gas
cylinder in opposition to the molding force. Such a method and
apparatus are useful in making threaded closures, double wall
closures and tamper indicating closures.
In the making of closures wherein the amount of plastic
in the peripheral wall of the closure is controlled, in accordance
2s with the invention, the method and apparatus comprises providing
lower toolinj wherein the cavity comprises two pieces, an inner
portion forming the base of the closure and an outer portion
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~ ~ t 7~0~3
which forms the peripheral wall of the closure. The outer
portion is spring loaded and the Lnner portion is supported by
gaseous pressure of a gas cylinder. 'rhe outer portion may be
actuated by an external actuator actuated by an additional cam.
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` 2~78~63
Description of the Drauings
FIG. l is a plan view of an apparatus embodying the
invention .
FIG. 2 is a sectional view taken along the line 2-2
s in FIG. 1.
FIG. 3 is a sectional view similar to FIG. 2 with
parts being removed.
FIG. 4 is a fragmentary sectional view taken along
the line 4-4 in FIG. 1.
lo FIG. 5 is a partly diagrammatic horizontal sectional
view.
FIG. 6 is a vertical sectional view of one set of
upper ana lower tooling.
FIG. 7 is a fragmentary sectional view on an enlarged
scale of the lower as3embly of the set of tooling shown in FIG. 6.
FIGS. 8-11 are fragmentary sectional views of one set
of tooling during various stages of compression molding.
FIG. 12 is a fragmentary side elevational view of a
portion of the tooling shown in FIG. 7.
FIG. 13 is a fragmentary sectional view taken along
the line 13-13 in FIG. 12.
FIG. 14 is a schematic diagram of the nitrogen system
utilized ln the invention.
FIG. 15 is a schematic diagram of a modified system.
2s FIG. 16 is a vertical sectional view of a modif ied
set of upper and lower tooling.
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21 7BOÇ3
FIGS. 17-21 are fragmentary sectional views of the
tooling shown in FIG. 16 during various stages o~ compression
molding .
FIG. 22 is a side elevational Yiew of a portion of
5 the tooling.
.
~ 21 78063
Description
Referring to FIGS. 1-3, the method and apparatu9
embodying the invention is shown as applied to a rotary apparatus
that includes a base 20, supporting a column 21 on which a
5 turret or carousel 22 is rotatably mounted by upper and lower
tapered bearings 23, 24. Turret 22 includes vertically spaced
supports comprising an annular upper support 22a, an annular
support 22b, and a lower annular support 22c. A plurality of
upper support segments 25 are mounted on upper support 22a and
lo abut to define a ring. A plurality of lower segments 26 are
mounted on the intermediate and lower support3 22b, 22c and
abut to def ine a ring . Each segment 25 supports one or more
of circumferentially spaced sets of actuators 34. Each segment
26 supports one or more actuators 52 adjacent the lower end of
15 the apparatUS. The actuators 34 are mounted for vertical
movement in housings 34a mounted upon support segments 25 which,
in turn, are aupported on an upper ring mount 22a (FIGS. 2, 3 ) .
An upper set of tooling 27 is associated with each
actuator 34 and includes a movable assembly 27a mounted on the
20 lower end of actuator 34 and a fixed assembly 27b mounted on a
portion 26a of segment 26 that is fixed to support 22b (FIG. 6).
A fixed annular cam 29 is supported by columns 30 (FIGS. 1, 4)
and is associated with the upper actuators 34. Actuator 34,
in turn, has a cam roller 35 at its upper end for engaging the
25 cam 2 9 .
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A set of lower tooling 28 i8 mounted on each lower
actuator 52. A fixed annular cam 31 is supported on base 20 and
is associated with the lower actuators 52.
Each lower assembly 28 of tooling includes a female
mold assembly 51 and a cooling water manifold 51a. Each actuator
52 has a roller 60 on its lower end for engaging cam 31 (FIG. 6).
Referring to FIG. 6, the fixed assembly 27b is mounted
on a segment portion 26a of the segment 26. The movable assembly
27a comprises a mold plunger or core 41 spring loaded upwardly
lo by springs 45, a core sleeve 42 and a stripper sleeve 44 urged
downwardly by stripper springs 43. The core 41 is made in
several sections and def ines a male mold.
Referring to FIGS. 6 and 7, each actuator 52 is mounted
in a support body 50 forming a part of segment portion 26b.
The mold 51 has limited relative movement with respect to the
actuator 52 and is yieldingly urged upwardly by cavity springs
53 which act upon lift pins 54. The lower actuator 52 further
includes a plunger 55 that engages a holding spring plug 56
which in turn engages the piston 57 of a nitrogen cylinder 39.
A centering spring 59 is interposed between the holding spring
plug 56 and the plunger 55. The nitrogen cylinder 39 is provided
with nitrogen at an accurately detF~ ne~l pressure supplied to
the area or chamber 61 below the nitrogen chamber 39 through a
connector 62 having an orif ice.
2s In this tooling style, the molding force is applied
through the core sleeve 42 and the core 41 attached to the core
sleeve 42 by a lost motion connection, the core 41 being biased
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~ 21 78063
upward by the array of springs 45 . The upper cam 29 is f ixed
and the core sleeve 42 thus moves downward a f ixed stroke as
controlled by the upper cam 29.
Referring to FIGS. 12 and 13, provision is made for
5 rapid removal of the cavity mold 51 and comprises a yoke 80
having spaced arms 81 that engage annular groove 83 in the
actuator 52 and groove 82 in the cavity mold 51. Grooves 83
in actuator 52 are snugly engaged by arms 81. Groove 82 in
cavity mold 51 has a greater axial width such that the cavity
lo mold 51 has limited axial movement relative to the actuator 52.
Spring loaded plungers 84 on the arms 81 extend inwardly to
engage the periphery of mold 28. Yoke 80 includes a handle 85
to facilitate grasping the yoke 80.
The one piece cavity mold 51 is located on the lower
tooLing actuator 52, but is free to move axially a limited
amount relative to actuator 52 by the construction 3hown in
FIGS. 12 and 13 and the cavity mold 51 is held up by the array
of springs 53 within the lower tooling actuator 52. These
springs 53 are limited in stroke by the lift pins 54, which
20 bottom out on a lift pin retainer 54a. The cavity mold 51 rests
on the plunger 55, which is retained to limit its upward travel.
The plunger 55 contacts the holding spring plug 56 and a spring
59 is f itted between ~he two c _ ~nts. The holding spring
plug 56, in turn, contacts the piston rod 57 of nitrogen cylinder
2s 39.
Referring to FIG. 7, nitrogen cylinder 39 is normally
fully outstroked, maintaining the holding spring plug 56 against
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2 1 78063
the locating stop surface 52a in the lower tooLing actuator 52.
The plunger 55, when free, will be moved up by the center spring
59 until it reaches a stop surface 52b within the lower tooling
actuator 52.
Referring to FIG. 6, provision is made for lowering
the upper actuator 34 and comprises the first roller 35 on the
upper end thereof for engaging the upper cam 29 to cause the
downward movement of the male mold as8embly 32. In addition,
a second roller 70 is provided for rotation about the same axis
lo as roller 35 that engages a second fixed upper cam 72 (FIG. 2)
for lifting the upper tooling 27 during the operating cycle in
order .
Referring to FIG. 6, provision is made for lifting
the lower actuator 52 and comprises a roller 60 on actuator 52
that engages the lower cam 31. In addition, a second roller 74
is provided for rotation about the same axis as roller 60 and
engages a second fixed lower cam 77 for insuring that the cavity
mold 51 is in its lowest position to receive a pellet of plastic.
Operation
Referring to FIGS. 6-11, the operation includes a
series of steps:
Position 1~1 Open
FIGS. 6-7 show the tooling open condition with the
upper tool assembly 27 up and the lower tool assembly 28 down.
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21 78063
Position #2 Closing of Mold
As shown in FIG. 8, af ter a charge or pellet of
thermoplastic material i8 delivered to the female mold, the
lower tooling actuator 52 is raised a fixed stroke by the lower
cam 31, and the cavity 51 contacts the stripper sleeve 44 (FIG.
9 ) . The stripper sleeve springs 43 initially overpower the
weaker cavity springs 53, and subsequently the small spring 59
(FIG. 6) in the plunger 55 until the clearances are taken up
and the nitrogen cylinder 39 oppose8 any further compression
o of the cavity. At this point the stripper sleeve 44 is forced
upward against springs 43 for the r -ind~r of the lower tooling
upward stroke.
Position #3 Moldinq
Referring to FIG. 10, the upper tooling is now lowered
a fixed stroke to form the part, as controlled ~y the fixed
upper forming cam 29. When the forming pressure increases to
equal the force of the nitrogen cylinder 39, then the piston 57
of the nitrogen cylinder 39 moves to limit the molding force on
the tooling. This forces the cavity 51 to lower, and causes
the gtripper gleeve gprings 43 to move the stripper sleeve 44
downward in unison with the cavity 51, until the upper tool
stroke is completed.
Position ~3 Eoldinq
Referring to FIG. 11, a holding pressure is achieved
2s through the parallel sections of the cams 29, 31, under control
of the nitrogen cylinder 39. ~o relative axial movement of the
tooling takes place during this phase.
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21~78~63
Position #4 Lowered EIolding Force Section
Referring to FIG. 11, a lesser holding force i5
achieved by a relief step in the upper cam 29 only, which allows
the core sleeve 41 to become free from the cam 29. This causes
5 the piston 57 of nitrogen cylinder 39 to outstroke until the
holding spring plug 56 bottoms out. The cavity 51 is
simultaneously lifted by the nltrogen cylinder 39, and the core
sleeve 42 along with the core 41 are lifted by the cavity 51.
The holding force is now maintained by the weight of the upper
o actuator 34 and the tooling pin assembly. The cavity springs 53
in the lower actuator 52 play no role in this part of the cycle
and remain compressed by the higher rated stripper sleeve springs
43. The small sprLng 59 on the inner shaft 55 is also ineffective
at th i s t ime .
5 Position #5 Cavity Stripping
During stripping of the closure from cavity 51, the
lower tooling actuator 52 is lowered, leaving the closure on
the molding core 41. If a threaded closure has been molded,
then normally the stripeer sleeve springs 43 would not overcome
20 the closure strip force required, and would remain compressed,
and the stripper sleeve 44 would not move down.
The core sleeve 42 is subsequently withdrawn by direct
upward cam action due to engagement of roller 70 with second
upper cam 71 ~FIG. 2 ) . The resistance of the closure to stripping
2s from the threads causes the core 41 to stay down, until its
lost motion with the core sleeve 42 is taken up. At this time,
the core 41 i~ also E>ulled up by the action of the core sleeve
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21 78063
42, causing the core sleeve 42 to compress the array of core
sleeve springs 45, and the part to be stripped fram the core 41
as the stripper sleeve springs 43 overcome the stripping force.
Referring to FIG. 14, the control system for supplying
5 nitrogen to each of the cylinders can be more readily understood
by reference to this gchematic. The designation LOAD represents
cylinders which are connected to a rotary coupling R (FIG. 2 )
on the turret 22 that, in turn, is connected through a pressure
control module and a pressure regulator and shut-of f valve to
lo a source of nitrogen such as a gas cylinder. Lines L such as
hoses extend from the rotary coupling R (FIG. 1) to couplings C
of the nitrogen cylinders 39 (FIG. 6). In the preferred form,
the pressure control module includes a solenoid operated valve
to exhaust gas to atmosphere, and a second solenoid valve to
15 admit pressurized gas from the nitrogen gas cylinder. The
interface is a computer and interactive screen to allow an
operator to select a desired system pressure setting by direct
input, or the setting could be established automatically by a
menu selection from the computer. Preferably, the pressure
20 signal reference to the logic control represents a high and a
low pressure limit, and the logic control continually compares
the feedback signal from a pressure transducer representing the
actual system pressure at any one time. When a pressure is
detected above the high limit setting, the logic control
25 energizes the first solenoid valve to exhaust gas from the
system until the system pressure is within limits. Conversely,
a system pressure lower than the low limit causes the second
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~ 21 78~63
solenoid valve to operate and to admit high pressure nitrogen
from the gas cylinder until the system pressure i5 again within
the preset limits.
Although the above description represents a preferred
S form of the pressure control module, other control systems may
be used in which this control is achieved, and it it not intended
to limit the scope of the invention.
FIG. 5 is a composite sectional view at various
horizontal sections. In the lower left guadrant of FIG. 5,
there is shown how a plurality of segments 25 are mounted on
the turret and each supports the actuators 34 of f ive sets of
upper tooling. In the lower left quadrant, there is shown how
a plurality of segments 25 each supporting f ive sets of upper
tooling 27 on the actuators. In the upper left quadrant there
is shown how a plurality, shown as f ive, of the actuators 52
of lower sets of lower tooling 28 are provided on segments 33.
Thus, if it is desired to vary the size or number of sets of
tooling, the segments can support more or less sets depending
on the size.
During normal operation, the molding force control
is achieved with minimal compression of the gas cylinder, for
example, on the order of .030 in. ~his control is maintained
despite small variations in the volumetric capacity of the
closed molds, and despite small variations in the weight of the
delivered pellets. On the occasion of inadvertent loading of
double pellets into a particular mold tool or due to incorrect
setting of the mean pellet weight delivery for the particular
--16--
` ~17~063
mold, then the gas cylinder within the affected tooling will
individually compress to absorb the additional stroke of the
cavity and could compress to limit the molding force to an
amount as preset by the gas system pressure up to an amount,
for example, of approximately 0. 500 in. If the pellet weight
is outside the specified range for the part being molded, then
the resulting part will be defective, but the machine loading
will be limited by the molding force control described above,
and thus machine damage will be eliminated.
0 Further, inasmuch as the cylinders within the tools
are linked by a common system, and i~ ^u~ h as the system volume
is much greater than the change in volume of the system during
normal forming operation, (in excess of 1000:1) then the system
pressure is substantially constant and each tooling is
~5 consequently controlled to the same preset molding force.
Thus, each set of tooling is controlled fully
throughout the molding cycle since the same predet~rmine~ force
is applied to a set of tooling at all times. In addition, each
set of tooling is controlled without adversely affecting ad jacent
or other sets of tooling.
The advantages of the present invention can thus be
summar i zed as f ollows:
a) Precise force control is provided on each set
of tooling.
2s b) The predet.-rmin~d force is applied to each set
of tooling during the forming and holding
portions of each cycle.
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2 t 78063
c) The force is sub5tantially constant at all times.
d) The pressure control of one set of tooling does
not adversely affect any other tooling in the
array .
S e) The u5e of 5eparate actuators which eliminates
side load on the upper tooling.
f ) The ability to readily change molding tooling.
g) The ability to readily change the number and
size of tooling to form articles of variou5 sizes
and weights.
h) The use of continuous cams which require minimal
maintenance .
Although in a preferred form gas cylinders are
provided, in accordance with another aspect of the invention
lS the cylinders may comprise hydraulic fluid cylinders supplied
through a rotary coupling as shown schematically in FIG. 15.
The hydraulic cylinders aesignated as LOAD are connected through
the rotary coupling to a gas pressurized accumulator and the
system is supplied with oil from a low volume pump with an
20 adjustable pressure limiting valve. The gas charged accumulator
provides for rapid changes in system volume as a result of
piston displacement within the respective cylinders and avoids
the need for a larger volume pump. If the gas charged accumulator
is of sufficient capacity, then the resulting pressure control
2s within the system would be substantially constant.
This system could function in a similar manner to the
preferred form of the invention and the pressure could be
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2~ 78063
remotely controlled by using a servo pilot operated pressure
relieving valve. Uowever, it has a disadvantage in situations
where possible oil contamination is a concern.
Elydraulic systems without the gag charged accumulator
5 would not be as effective as the preferred form of the invention
as the hydraulic fluid is substantiAlly incompressible and
cannot be controlled or function as effectively as a gas system
wherein the fluid is compressible.
It can thus be seen that there has been provided a
lo method and apparatus for compression molding plastic articles
including closures wherein the forming pressure can be accurately
controlled; wherein the forming pressure can be readily adjusted;
wherein lateral forces on the tooling are not applied directly
to the forming tool; wherein the tooling may be readily replaced;
5 wherein the number and size of tool stations can be readily
changed; and wherein various kinds and sizes of articles
including closures can be readily made by changing the tooling
and associated actuating m~-~hAni~ -; wherein the tooling will
c ,^n~Ate for variations in pellet or charge weight, variations
20 in mold tooling volume in the closed mold position and wherein
a substantial overload such as a double charge of plastic can
be readily absorbed without overloading the tooling or the
overall apparatus.
FIGS. 16-23 show a modified form of upper and lower
25 tooling useful in making closures and the like to ac.~ ~qAte
variations in charges and provide for distribution of any
additional material to a specific portion of the closure. In
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21 78063
such tooling, the lower tooling 28a is supported on actuator
52 and comprises a female mold assembly 51b comprising a spring
loaded outer or peripheral part 51c and an inner portion 51d
supported and acted upon by a nitrogen gas cylinder 39, which
5 functions in the same manner as the nitrogen cylinder 39 described
in connection with FIGS. 1-15. The outer portion 51c i8 cooled
by a cooling water manifold 51e and the inner portion 51d is
cooled by a cooling water manifold 51f. The lower tooling
assembly 28a is removably mounted on the actuator 52 in the
o same manner ag the first form as described with reference to
FIGS. 12 and 13.
In this form, the upper tooling assembly 27c has no
stripper sleeve springs in contrast to the form shown in FIGS.
6-11, and the stripper sleeve 44a is ~ree to float in an axial
5 direction within the restraint~, as presently described. As
~hown in FIGS. 19 and 20, the upper tooling housing 27c provides
for limiting relative movement of the actuator 34 to the stripper
sleeve 44a as in its downward fixed stroke, the upper actuator
34 contacts the sleeve spacer 200 which, in turn, contacts the
20 stripper sleeve 44a. This contact occurs toward the end of the
stroke of the upper tooling actuator 34. In this form, the
upper actuator 34 is directly connected to the core sleeve 42a
which i5 in limiting sliding contact with the core 41a. The
core is spring loaded upwardly toward the core sleeve and is
2s consequently lowered simultaneougly with the core sleeve and
core .
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2 1 78063
. ~
The tooling actuators 34 and 52 are identical and
common to all forms of tooling. In this form, the inner portion
51d forms the top of the closure and slides within outer portion
51c which forms the side of the closure. The outer portion 51c
5 is separately spring loaded within the actuator 52 by the similar
array of springs 53 as described in the form of tooling shown
in FIGS. 6-11. The inner portion 51d is resting on the plunger
55a as does the one piece cavity style of tooling shown in FIGS.
1-15. The actuator 34 strokes are the same as actuator 34 in
0 that f orm.
A typical plastic closure that can be made by the
tooling shown in FIGS. 16-21 comprises a base wall and a
peripheral skirt having internal threads and may be of the type
shown in United States Patent 5,265,747, incorporated herein
5 by reference. A liner may be added to the closure after the
closure is compression molded.
Operation
Referring to FIGS. 16~23r the operation comprises the
f ollowing 8 teps:
20 Pogition #1 Open
FIG. 16 illustrates the tooling in the open position.
Position #2 ALiqnment
Referring to FIG. 19, the cavity 51c is advanced
upwardly to the stripper sleeve 44a by a fixed stroke and lifts
25 the stripper sleeve 44a until the stripper sleeve 44a reaches
its upper limit of travel. At this time, the stripper sleeve
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44a and the outer cavity portion 51c are resisted from movement
and the cavity springs 45 are compressed for the r~ i n~lPr of
the lower tooling stroke.
Position #3 Moldinq
Referring to FIGS. 16 and 20, the upper tooling 27
(FIG. 16) is then lowered a fixed stroke to form the closure,
the limiting mold pressure is reached, the nitrogen cylinder 39
is compressed, allowing the inner cavity portion 51d to move
downward until the upper tooling stroke is completed tFIG. 20).
o Simultaneously, as shown in FIGS. 19 and 20, the upper tooling
housing 27c provides for limiting relative movement of the
actuator 34 to the stripper sleeve 44a as in its downward f ixed
stroke, the upper actuator 34 contacts the sleeve spacer 200
which, in turn, contacts the stripper sleeve 44a. This contact
occurs toward the end of the stroke of the upper tooling actuator
34. In this form, the upper actuator 34 is directly connected
to the core sleeve 42a which is in limiting sliding contact
with the core 41a. The core is spring loaded upwardly toward
the core sleeve and is consequently lowered simultaneously with
the core sleeve and core.
At the completion of the forming stage, the core
sleeve 42a, stripper sleeve 44a and outer cavity portion 51c
are at a fixed axial relationship ~FIG. 21). This does not
vary with variations in material weight. This is a major
2s advantage of this method.
Position #3 EIoldinq
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21 78~63
This is accomplished through the parallel sections
of the cams under control of the nitrogen cylinders. No relative
movement takes place during this phase.
Position #4 Lowered E~oldinq Force Section
A step up in the upper cam causes the upper actuator
34, the core 41a and core sleeve 42a to rise as it is lifted by
the nitrogen cylinder. The outer cavity portion 51c is, in
turn, lifted by its array of springs 53 as the stripper sleeve
44a is allowed to move up with the core sleeve 42a. The spring
lo plug 56 (FIG. 18 ) limits the outward stroke of the nitrogen
cylinder. The inner cavity is now held up by the much reduced
force of the smaller spring 59 in the cavity holder plunger 55,
in opposition to the weight of the upper tooling 27 and the
upper actuator 34,
Position #5 Cavity Strip
During stripping, the lower tooling actuator 52 is
lowered, leaving the closure on the molding core. The stripper
sleeve 44a remains aligned with the closure skirt and it has
no opposing springs.
During the retraction of the core sleeve 42a, the
stripper sleeve 44a reaches its limit of travel as limited by
the sleeve spacer 200. At this time, the stripper sleeve 44a
acts to strip the closure as the core sleeve 42a continue3 to
retract, withdrawing the core 41a. A8 there are nQ stripper
2s sleeve springs, the stripper sleeve 44a does not have a snap
action and the resulting smooth stripping action occurs.
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~ 2~ 78~63
This form of method and apparatus provides the
desirable control of the molding force to tolerate variable
changes of material and to ~c- '~ te potential overload of
the machine and tooling resulting from an excessive charge of
plastic being trapped within the closing tooling. Further, the
method and apparatus provides that the compensating means will
not affect the axial relationship of the male and female
component5 of the mold in the case of normal variation of the
plastic charge. The split cavity of the method and apparatus
lo accomplishes these objective3 by allowing the inner cavity to
move when sufficient molding force is generated to compress the
nitrogen cylinder against the preset sy3tem pres~ure.
In summary, this form of method and apparatus has the
following advantages:
1) Use of two piece cavity construction whereby the
inner portion is axially slidably connected to an outer portion
and whereby the inner portion engages a fluid powered cylinder,
preferably nitrogen powered, such that molding force is constant
throughout the molding operation and preferably is controlled
by a common 8y8tem pre38ure applied to the cylinder and all
other cylinders in adjacent toolings.
2) The apparatus wherein the lower tooling actuator
including the nitrogen cylinder and the cavity actuating means
are interchangeable with the two main tooling styles described
2s above; both the split cavity as described here and the one piece
cavity as described above and in the aforementioned application
Serial No. 08/135,829, incorporated herein by reference, without
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21 7~063
any adjustment or changing of parts other than the wetted mold
surfaces and their individual assemblies.
Thus the forms of tooling shown in FIGS. 16-23 have
the following advantages:
S 1) Use of an auxiLiary actuator with an anti rotation
means external and ; n~p~n~ nt of any tooling members.
2) A method of actuating a tooling by means of dual
actuating shafts whereby the two shafts are axially displaced
from each other and in independent axial sliding connection
lo with each other and where both shafts are restrained from
rotation one by the other.
3 ) A method of operating an auxiliary actuating
shaft whereby its axial relationship to the main actuating shaft
is controlled by a cam track and this cam track is interchangeable
for various desired tooling actions.
It can thus be seen that there has been provided a
method and apparatus wherein plastic articles such as plastic
closures can be compression molded to ac.; - '~te variable
charges of plastic material without affecting the axial
relationship between the male and female components of the mold.
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