Note: Descriptions are shown in the official language in which they were submitted.
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In injecting molding machines the core pin is first in-
serted into the mold cavity of an injection mold where the
surfaces of the cavity are spaced from the surfaces of the
core pin by a distance equal to the desired thickness of
plastic coating which is to be applied to the core pin. The
plastic material is then injected into the mold cavity and
the core pin thus coated with the material~
The mold is then opened and the core pin is transferred
to a blowing mold where the cavity has the shape of the
product which is to be blown. Blowing fluid under pressure
is then discharged from the core pin against the plastic
that surrounds the core pin and the plastic is blown outwardly
away from the core pin and into contact with the sides of the
mold. After a short cooling time, the blowing mold is opened
and the core pin is moved to a stripping station where the
blown article is stripped from the core pin.
In extrusion molding machines, a plastic tube is extru-
ded downwardly into an open blowing mold and a core pin ex-
tends from the extruder downwardly along the axis of the tube.
When the tube has reached a length greater than the length of
the blow mold, the mold closes and pinches the bottom of the -
tube closed while clamping the upper end of the tube tightly
around the core pin. The tube is then blown to the shape of
the mold cavity by blowing fluid discharged from the core pin
and the mold is opened to permit the extrusion of another
length of tubing. The blown molding is cut off from the tube
and the mold closes on the new length of tube to repeat the
blowing step.
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In both types of machines, the molding must remain in
the blowing mold until the plastic coos sufficiently to hold
its shape. The blowing mold is cooled by circulation of water
or other cooling fluid through cooling passages in the wall
of the mold..
The pressure of air or other fluid used to blow the
plastic must be limited in pressure. If introduced into the
blowing mold at too high pressure, the blowing fluid will
blow out the plastic wall at the weakest place or location
of greatest stress, and the temperature of the plastic must
be controlled so that the plastic is hot enough to blow at the
pr~ssure that can be safely used.
By covering the core rod with a balloon and coating the
outside of the balloon with the plastic to be blown, a number
of new results are obtained. One is that higher pressure can
- be used to blow the molding. The balloon prevents the blowing
fluid from having contact with the plastic and there is no
danger of a blowout of the plastic. Because higher pressure
can be used for blowing, plastic can be blown at lower tempera-
ture and after it has been cooled to the temperature range at
-~hich it begins to crystallize. This permits orientation of
the molecules and by having a balloon that is deformed biaxially,
the plastic of the molding is stretched both circumferentially
and axially (or in other directions at right angles to one
another) so that the molding has biaxial orientation with re-
sulting greater strength, and in the case of some plastics,
clear transparencY
Another new result is obtained if the balloon is made
~ith different wall thickness at different sections of its
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extent. There is then a sequential expansion of the different
-sections of the balloon so that corresponding sections of the
parison are blown at different times. For example, the upper
or lower portion of the molding might be blown ahead of another
portlon.
Blowing fluid, such as liquid, at temperatures substan-
tially lower than the plastic can be used and circulated
through the balloon during the blowing operation and immediate-
ly thereafter so that the molding is cooled from both the in-
side and outside to obtain substantially faster cooling and a
- shorter cycle for the machine, and increased production.
The invention is suitable for use on either injection
blow molding machines or e~trusion blow molding machines.
Other objects, features, and advantages of the invention
will appear or be pointed out as the description proceeds.
BRIEF ~ESCRIPTION OF DRAWING
In the drawing, forming a part hereof, in which like
reference characters indicate corresponding parts in all the
views:
Figure 1 is a diagrammatic view of an injection blow
molding machine with the molds, plastic, and balloon covered
core pin shown in section;
Figure 2 is a greatly enlarged sectional view of a blow-
ing mold with a differently shaped cavity from that shown in
Figure 1 and with the plastic on the core pin not yet blown;
Figure 3 is a sectional view taken on line 3-3 of Figure
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. Figure 4 is a greatly enlarged fragmentary view of a
portion of the core pi~ shown in Figure 2;
Figure 5 is a view showing diagrammatically a closed
circuit connected with the core pin of Figure 2 for supplying
cooling and blowing fluid to the core pin;
Figure 6 is a diagrammatic view of an injection blow
molding machine with a balloon covered core pin made in
accordance with this invention;
Figure 7 is a view similar to Figure 6 but showing
the blowing mold in closed position and the condition of the
plastic and balloon at the end of the blowing operation; and
FIgure ~ is an enlarged, fragmentary, detail view of
vents for the core pin of Figures 6 and 7.
DESCRIPTION OF PREFERRED EMBO~IMENT
Figure 1 shows an injection blow molding machine 10
which includes a turret 12 with four core pins, 14, 15, 16
and 17 projecting from different sides of the turret 12 at
90 angular relation to one another. The turret 12 is ro-
tated about an axis 20 wherever the core pins 14-17 are to
be transferred from one station to another.
The first station of the machine 10 is an injection
station 22 which has a mold 24 to which plastic is supplied
from an extruder 26 through a nozzle 2~. The core pin 14
e~tends into a cavity 30 of the mold 24.
The core pin 14 is covered by a balloon 32 which is
secured to the core pin in a manner which will be explained
in connection with Figures 2 and 4. The core pin 14 with the
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balloon 32 covering it, extends into the cavity 30. With the
mold 24 closed, plastic 34 is injected into the cavi~y 30 so
as to coat the entire portion of the balloon 32 which is
spaced from the surface of the mold cavity 30.
The injection mold 24 is of conventional construction
~ith passages 36 for the circulation of cooling fluid; and
the mold 24 opens to release the plastic 34. The mold opens
wlde enough so that the turret 12 can rotate and move the
core pin 14, balloon 32 and plastic 34 in a counterclockwise
direction about the center 20 into the position occupied by
the core pin 15 in Figure 1.
During this movement of the turret 12 through an angle
of 90~, the core pin 15 is moved into the position occupied
by the core pin 16 in Figure 1 and the core pin 16 is moved
. into the position occupied by the core pin lZ. The core pin
17 moves into the open mold 24 where it is ready to receive
a charge of plast~c 34 from the nozzle 2~ at the beginning of
the next cycle of the machine. The operation of the mold 24
in opening and closing; and the operation of the turret 12 in
transferring core pins from one station to another are well
understood in the injection blo~ molding machine art and no
further illustration or description of this structure is
necessary for a complete understanding of this invention.
The cecond station of the machine 10 is a conditioning
station 3~. The core pin 15 at the conditioning station 3~
has a balloon 32 ~ covered with plastic 34 ~ which was applied
to the core pin lS in the mold 24 in the manner already des-
cribed for the core pin 14. Each core pin 15 with its plastic
34' remains at the conditioning station 3~ until the next
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mo~rement of the turret 12, and durlng thi~ time the plastlc
34' c0018 to substantially the temperatur~ desired for blowing.
This cooling time ls determinet by the dwell period of the
turret 12; but the amount of cooling desired will vary with
- ~he amount of plastic 34' which i3 applied at different times
depending upon the molds which are on the machine for produc-
in~ a particular molding. The amount of coollng also dependq
on the temperature at which the blowing ls to be performed.
Thls ln turn depend~ upon the pressure that is to be used
and upon the amount of orientation of the molecules that are
required or deslred for a particular molding. Although the
d~ell time at the conditioning station 3~ ls not ~ariable
to suit the desired cooling, the extent of cooling can be
controlled at the dwell station by controllin~ the temperature
of the atmosphere surrounding the plastic 34' or by subjecting
the plastic to radiant heatlng of various degrees while at
'che conditioning station 3~.
The machine can have a blowlng station 40 at which there
18 a blowin~ mold b,2 into which the core pin 16 travelled
during the precedlng movement of the turret 12 and while the
mold 42 was open. When the mold 42 is closed, and blowing fluid
is dlscharged from openlngs 44 ln the core pin 16, a balloon
32a on the core pin 16 expandq and moves plastic 34a lnto
contact wlth the s~urfaces of a mold cavlty 46 of the mold 42.
Flgure 1 shows the balloon 32a expanded and the plastic 34a
~haped to the contour of the mold cavity 46.
The mold 42 haq passage-q 36a for cooling fluid snd lt is
nece~sary for the plastic34a to cool in the mold 42 to a
temperature low enDugh to make the plastic self-sustaining
before the artlcle molded from the plastic can be removed from
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the mold 42. This time required for the molded article to
cool has been the limiting factor on the output of injectlon
molding machines. With the present invention, the balloon 32a
can be inflated with water or other liquid at a temperature
which will cool the plastic 34a from the inside at the same
time that contact with the walls of the mold 42 cool the
plastic from the outside. By cooling the plastic from both
sides, the cooling time can be greatly reduced. This shortens
the cycle of the molding machine and greatly increases the
production.
When the article molded from the plastic 34a, which is
shown in Figure 1 as a bottle 50, has cooled to a shape sus-
taining temperature, the mold 42 is opened and the turret
12:rotates another 90 to move the core pin to a stripping
station 52 where the core pin 17 is shown with a bottle 50
held on the core pin by the neck 54 of the bottle. The core
pin 17 has a balloon 32b which is shown deflated in Figure 1,
the deflation having taken place upon completion of the cooling
at the blowing station 40 and while the core pin was travel-
ling from the blowing station to the stripping station 52.
At the stripping station 52 a stripper plate 55 mo~es into
engagement with the neck S4 of the bottle and pushes the
bottle axially along the core pin 17 to disengage the bottle
from the core pin. This completes the manufacture of the bot-
tle 50 on the molding machine.
Figyre 2 shows the core pin 16 in a mold 42' which is
similar to the mold 42 of Figure 1 except that the mold
cavity 46' is of different shape and the passages 36' for
cooling the mold are also of different shape. The balloon
32a is secured to the core pin 16 by clamping rings 56 which
clamp the material of the balloon 32a into circumferential
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grooves 57 extending around the outside surface of the core
p~n 16. Two rings 56 are shown; one outside the mold 42' and
the other inside. The mold 42' closes firmly against the
outside surface of the balloon 32a so that none of the plas-
tic material 34a can be extruded from the mold cavity between
the balloon and the clamping surface of the mold 42' which
clamps against the surface of the balloon 32a.
There is a shoulder 5~ on the core pin 16 and there is
a clearance 5~c between the core pin and the inside surface
-of the balloon 32a for some distance to the left of the shoul-
der 5~ in Figure 2. This clearance is maintained, during in-
jection of the plastic into the mold at the injection station
22 (Figure 1) by supplying fluid within the balloon 32a sub-
stantially equal to the pressure at which the plastic is in-
jected into the mold.
A circumferential air manifold 59 ex~ends around one
end of the mold 42' and the side of the manifold is closed by
a cover 60. Passages 61, at angularly spaced locations around
the mold, lead from the air manifold 59 to the outside surface
of the balloon 32a at regions where the balloon 32a can col-
lapse toward the core pin; i.e. at the region of the balloon
surface outside of clearance space 5~c.
Plastic is preventéd from entering the passage 61, at
the injection station, by maintaining enough pressure within
the balloon to prevent the plastic from collapsing the balloon
into the clearance 5~c. Less counterbalancing pressure in
the balloon is required when each passage 61 is located near
the end of the clearance 5~ as shown in Figure 2.
When the blowing operation is complete, and the blown
article has cooled enough to hold its shape, a partial vacuum
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is drawn on the core pin 16 to collapse the balloon. The
balloon cannot collapse unless air can gain entrance between
the outside surface of the balloon and the inside surface of
the blown article. The balloon 32a collapses into the clear-
ance 5~ when the vacuum is first drawn on the core pin. This
opens a clearance between the balloon and the inside surface
of the neck of the blown bottle. Air from the passages 61
rushes into this clearance between the balloon and the blown
bottle for the length of the balloon that did not expand during
the blowing operation. Beyond this the expanded balloon col-
lapses away from the blown bottle as air continues to flow to-
ward the left in Figure 2 along the outside surface of the
balloon.
Figure 2 shows the feature of blowing different parts
of the parison sequentially. In order to obtain expansion of
- some parts of the balloon 32a ahead of other parts, the walls
of the balloon 32a are thicker around the region 66 than at
other parts of the length of the balloon. Thus when the bal-
loon 32a is inflated, as indicated by the bro~en lines in
Figure 2, the part of the balloon to the left of the region
66 expands before the wall at the region 66 expands. By
controlling the stiffness or elasticity of the walls of the
balloon 32a at different regions, the plastic 34a can be blown
se~uentially as to different portions of its length.
In Figure 2, for example, the expansion of the balloon
from the dotted line position shown in Figure 2 will soon
bring the plastic into contact w~th the side of the mold
cavity at a region midway between the right and left hand ends
of the cavity. Further expansion of the balloon will stretch
the plastic in both directions from this mid region as the
left hand end of the balloon travels toward the left hand end
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of the mold cavity and as the stiffer right hand portion of
th~e balloon expands toward the right hand end of the mold
cavity. Thus the plastic is stretched both circumferentially,
with the increase in diameter of the balloon, and also axially
to produce a biaxial orientation of the plastic material if
the plastic material is blown at a temperature low enough to
permit orientation of the molecules. Since the balloon pre-
~ents the blowing fluid from having contact with the plastic
34a, the blowing fluid can be at extremely high pressure with-
out danger of brea~ing through a weak portion of the plastic
and the blowing at higher pressure permits the plastic material
34a to be blown at lower temperature at which it has begun to
crystallize.
The proportion of the core pin 16 which extends into
the cavity of the mold has a center partition 70 extending
lengthwise of the core pin as shown in dotted lines in Figure
2. Water or other blowing and cooling fluid flows into the
space on one side of the partition 70 through an inlet passage
72 and flows out of the space on the other side of the parti-
tion 70 through an exhaust passage 74. These passages commu-
nicate with tubing 76 and 7~, respectively, which are part of
a closed circuit as will be explained in connection with Figure
5. Thus the fluid supplied to the passage 72 flows out through
the openings 44 on one side of the core pin and circulates ge-
nerally circumferentially around the core pin within the in-
flating balloon 32a; and this liquid or other fluid returns
to the interior of the core pin on the other side of the '
partition 70 through the openin~s 44 that are on that side of
the partition. The blowing and cooling fluid then passes out
through the exhaust passage 74, as already explained. Figure
5 shows the core pin 16 in a mold cavity ~0 which tapers to a
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larger diameter at the far end of the mold instead of a to a
smaller diameter as shown in Figure 2. This difference depends
upon the desired shape of the article which i9 being blown.
As in the other molds, the core pin 16 is shorter than the mold
so that the plastic being blown is stretched axially as well
as circumferentially. Figure 5 shows in dotted lines indicated
by the reference characters 32b and 32c the contour of the
balloon as it expands in the mold cavity ~0 with differences
in the localized expansion as the result of greater resistance
to e~pansion toward the right hand end of the balloon.
Figure 5 also shows diagrammatically the closed circuit
through which blowing fluid from the exhaust tube 7~ travels
through a valve ~2 and cooler ~ to a blowing fluid supply
tank ~6 from which the blowing fluid is fed back by a pump
8~ to the supply tube 76.
.
- The pump ~ is driven by a motor 90 connected w~th a
power supply line 92 and having a speed control 94 for regu-
lating the rate of supply of blowing fluid to the core pin.
No attempt is made to show the automatic control for insti-
gating and stopping the flow of blowing fluid in accordance
with the cycle of the blow molding machine since this is con-
ventional. The use of the blowing fluid to supply cooling to
the inside of the molded article is one of the novel features
of this invention. The valve ~2 is shown with spring loading
96 which is adjustable to change the back pressure in the core
pin and this valve g2 is adjusted to make the back pressure
as high as desirable in order to obtain the necessary blowing
pressure. A relief valve 9~ is lnterposed in the closed
system to permit discharge from the pump ~g to flow back to
the blowing fluid supply tank ~6 through a by-pass around the
-valve ~2.
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The cooler ~4 is shown as a tube with heat radiating
plns, but this is merely representative of means for cooling
fluid passing through the tubing and any other cooling ex-
pedient can be used depending upon the amount of heat to be
d~ssipated.
Figure 6 and 7 show the application of the invention to
an extrusion molding machine. A plastic pipe 102 is extruded
downwardly from an extruder 104 through an extruder die 106
located above clamping jaws 10~. A core pin 110 extends
downward from theextruder 104 and this core pin 110 is lo-
cated within the ex~ruded tube 102 and substantially concen-
tric therewith.
A blowing mold 112 is made up of two mold sections 114
and 116 which are shown separated in Figure 6 and closed
together in Figure 7. The core pin llO is covered with a
balloon 120 in the same way as the core pins described in
Figures 1-5. -
When the tube 102 has been extruded to a length suffi-
cient to reach the bottom of the mold cavity of the mold
112, the jaws 10~ are brought together by clamping forces to
pinch the tube 102 tight around the outside surface of the
balloon 120 as shown in Figure 7; and the mold sections 114
and 116 are then brought together so that bottom edges 124
pinch the lower end of the tube 102 tightly closed with a
lower tail end of the tube projecting below the edges 124
as indicated by the reference character 102a in Figure 7.
Blowing fluid is then supplied to the core pin 110
and the balloon 120 is expanded to force- the tube 102 out-
ward into contact with the surfaces of the mold cavity formed
by the closed sections 114 and 116.
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When the plastic is fully blown in the mold 112, the
mold cools the plastic to a shape-sustaining temperature and
~he mold is then opened, the balloon ccllapsed, and the
molded bottle removed from the core pin.
Figure ~ shows the core pin 110 with vent tubes 126
opening through holes 12~ in the sides of the core pin 110
and through the sides of the balloon 120 for admitting air
between the outside of the balloon and the inside of the
blown article for collapse of the balloon.
Vent openings for permitting escape of air from molds
asethe plastic is blown, and for admitting air to break
~acuums when articles are to be removed from the molds are
provided by using openings or channels of small cross-section
that does not permit entrance of plastic into the opening.
Such vents are well-known and used in conventional blow
molding apparatus and a description of the vents-is not
necessary for a complete understanding of this invention.
The prefered embodiments of the invention have been
illustrated and described, but changes and modifications can
be made and some features can be used in different combina--
tions without departing from the invention as defined in the
claims.
