Note: Descriptions are shown in the official language in which they were submitted.
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INJ~CTION MOLDING SYSTEM WITD GAS
PLOW T~ROUGD VALVE GATE
1 BACKGROUND OF THE INVENTION
This invention relates to injection molding and
more particularly to a valve gated system for making
plastic products with a gas filled central portion.
Molding hollow plastic products by injecting
pressurized gas in the center of a stream of melt is
described in U.S. patent number 4,101,617 to Friederich
which issued July 18, 1978. However, this previous
arrangement has the disadvantage, particularly for large
131 18~3
1 size products which require a larger diameter gate, that
the gate cannot be shut off. Consequently melt drooling
when the mold opens and increased cycle time become
problems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to
at least partially overcome the problems of the prior art
by providing a gas injection system which is valve gated.
To this end, in one of its aspects, the
invention provides a valve gated hot runner injection
molding system having a heated nozzle seated in a well in
a cavity plate, the nozzle having a central bore extending
therethrough to receive an elongated valve member with a
forward end and a rear end and to provide a melt passage
which extends in the central bore around at least at
forward portion of the valve member to convey melt to a
gate extending through the cavity plate to a cavity, and
valve member actuating means to reciprocate the valve
member longitudinally between a retracted open position
and a forward closed position in which the forward end of
the valve member is seated in the gate having the
improvement wherein the elongated valve member is hollow
and receives centrally therein an elongated pin having a
forward end and a rear end, the pin being securely mounted
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1 in a fixed position wherein the forward end is centrally
received in the gate with a space therearound which
provides a stream of melt with a hollow center flowing
into the cavity when the valve member is retracted to the
open position, the pin having a hollow central portion
extending from an inlet near the rear end of the pin to an
outlet at the forward end of the pin, whereby pressurized
gas received at the inlet to the hollow pin flows through
the outlet into the hollow center of the stream of melt
flowing into the cavity.
Further objects and advantages of the invention
will appear from the following description, taken together
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional view of a portion of an
injection molding system according to one embodiment of
the invention showing the valve member in the open
position,
Figure 2 is a similar sectional view showing the
valve member in the closed position,
Figure 3 is a partial sectional view at a right
angle to Figure 1,
Figure 4 is an enlarged sectional view showing
the area of the gate, and
131 1893
1 Figure 5 is a sectional view of a portion of an
injection molding system according to another embodiment
of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
_ _
Reference is first made to Figure 1 which shows
- a valve gated injection molding system according to one
embodiment of the invention having a nozzle 10 seated in a
well 12 in a cavity plate 14. The nozzle 10 has a central
bore 16 which is aligned with a gate 18 which extends
through the cavity plate 14 to a cavity 20. The nozzle 10
is accurately located in this position by an insulating
flange 22 which seats against a circumferential shoulder
24 and by a nozzle seal insert 26. The nozzle seal insert
26 which is screwed into the forward end 28 of the nozzle
10 has a cylindrical nose portion 30 which is received in
a seat 32 around the gate 18 and a tapered bore 34 which
is an alignment with and extends from the central bore 16
of the nozzle 10 to the gate 18. Electric plate heaters
36 as described in Gellert's Canadian patent application
serial number 589,783 filed February 1, 1989 entitled
"Profiled Plate Heaters for Injection Molding Nozzles" are
mounted on opposite sides of the nozzle 10 to heat the
nozzles 10. The cavity plate 14 is cooled by pumping
cooling water through conduits 38 and an insulative air
131 1893
1 space 40 is provided between the heated nozzle 10 and the
surrounding cooled cavity plate 14.
A manifold 42 is secured to the rear end 44 of
the nozzle 10 by bolts 46. The manifold 42 and the nozzle
10 are held in place by a locating collar 48 which is
fastened to the back plate 50 by bolts 52. The back plate
50 is, in turn, mounted to the cavity plate 14 by bolts
which are not shown. As seen in Figure 3, the manifold 42
is heated by electric plate heaters 54 attached to
opposite sides 56. The heated manifold 42 is thermally
separated from the surrounding cooled back plate 50 by an
insulative air space 58, with only minimum contact with
the locating collar 48.
The central bore 16 of the nozzle 10 has a
hollow elongated steel valve member 60 extending centrally
therein. In this embodiment, the valve member 60 has a
generally uniform cross section extending from a rear end
62 to a forward end 64. As can be seen, the hollow valve
member 60 has an elongated steel pin 66 extending through
it. The pin 66 has a forward end 68 and a rear end 70
which extends rearwardly into the manifold 42 where it is
secured by a set screw 72. This fixes the pin 66 in a
position in which the forward end 68 extends centrally
through the gate 18. The valve member 66 is similarly
secured to a movable actuating yoke 76 by double set
131 1893
1 screws 78. The steel yoke 76 extends transversely through
an opening 80 in the manifold 42. The outer ends 82 of
the yoke 76 are each connected by a screw 84 to a rod 86
extending from a pneumatically actuated piston 87 in a
cylinder 88 seated in the back plate 50. A high pressure
seal 89 extends around each piston rod 86 to prevent
- leakage. The pair of pistons 87 are activated in unison
according to a predetermined cycle to reciprocate the yoke
76 and the valve member 60 between the retracted open
position shown in Figure 1 and the forward closed position
shown in Figure 2 in which the forward end 64 of the valve
member is seated in the gate 18.
The fixed pin 66 has a hollow central portion 90
which extends to convey gas from an inlet towards the rear
end 70 of the pin 66 to an outlet at the forward end 68 of
the pin 66. As best seen in Figure 4, the outlet is
formed by a porous stainless steel portion 94 which is
securely welded in a seat 96 at the forward end 68 of the
in 66 and projects into the cavity 20. The porous portion
94 is formed by sintering stainless steel powder which
allows a sufficient flow of gas outward into the cavity
20, while preventing melt from the cavity 20 flowing back
in to the hollow central portion 90. The inlet to the
hollow central portion 90 of the fixed pin 66 is provided
by a lateral opening 98 through one side of the valve
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131 1893
1 member 60 which connects to a circumferential space 100
around a reduced diameter portion 102 of the fixed pin
66. This space 100 is, in turn, connected to the hollow
central portion 90 of the pin 66 by diagonally extending
ducts 104. The length of the reduced diameter portion 102
of the fixed pin 66 is at least equal to the travel of the
valve member 66 to provide a continuous connection to the
opening 98 throughout the travel of the valve member 66.
The yoke 76 has a gas duct 106 which extends laterally
outward from the opening 98 through the valve member 60 to
a connector 108 from a gas supply hose 110. As can be
seen, in this embodiment, a specially shaped bushing 112
is provided around the screw 84 to the piston rod 86 so
the gas duct 106 can bypass the screw 84.
As seen in Figure 3, a melt passage 114 extends
to convey pressurized melt from a central inlet 116 at the
rear end 118 of the manifold 42 to the gate 18. The
passage 114 splits into two passages 120 to bypass the
transverse opening 80 through the manifold 42 in which the
yoke 76 reciprocates and join a space 122 around the
outside of the valve member 60 in the central bore 16. A
sealing sleeve 124 seated around the valve member 60 in
the central bore 16 at the rear end 44 of the nozzle 10
prevents leakage of the pressurized melt as the valve
member 60 reciprocates. The sleeve 124 also helps to
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1 31 1 893
1 locate the nozzle 10 relative to the manifold 12 and to
centrally locate the valve member 60 and the fixed pin 66
inside it.
In use, the system is assembled as shown and
electrical power is applied to the leads 126,128 to the
plate heaters 36,54 to heat the nozzle 10 and the manifold
42 to a predetermined operating temperature. Pressurized
melt from a molding machine (not shown) is injected into
the melt passage 114 through the central inlet 116
according to a predetermined cycle. A pressurized gas
such as nitrogen or air is applied through the hose 110
and pneumatic pressure is also appli~d to the cylinder 88
according to the cycle. Thus, when the pneumatic pressure
actuates the yoke 76 and the valve member 60 to the
retracted open position, injection melt pressure and gas
pressure are applied. This produces a stream 130 of melt
which flows into the cavity 20 through a space 132 around
the porous portion 94 at the forward end 68 of the fixed
pin 66. The stream 130 of melt has a hollow center 134
into which the pressurized gas flows through the porous portion
94 in the forward end 68 of the fixed pin 66. As seen in
Figure 1, this produces a melt bubble 136 which expands
until it contacts the walls of the cavity 20. After there
is a build up of gas pressure in the filled mold, the
pistons 87 drive the yoke 76 and the valve member 60 to
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131 1893
1 the forward closed position shown in Figure 2 in which the
forward end 64 of the valve member 60 is seated in the
gate 18. Injection pressure is then released and after a
short cooling period, the gas pressure is released and a
suction can be applied so the walls do not blow when the
mold is opened. The mold is then opened along the parting
line 74 to eject the hollow molded product. After
ejection, the mold is closed and pneumatic pressure is
reapplied to the cylinders 88 to withdraw the valve member
60 to the open position and injection and gas pressure are
reapplied to refill the cavity 20. This cycle is repeated
continuously with a frequency dependent upon the size of
cavity and type of material being molded.
Figure 5 illustrates an injection molding system
lS according to another embodiment of the invention. The
elements of this embodiment which are common to the first
embodiment described above are described and illustrated
using the same reference numerals. In this case, the
nozzle 10 is similarly seated in well 12 in the cavity
plate 14. However, in this embodiment, the nozzle 10 has
a cylindrical nose portion 140 which is received in an
opening 142 through the cavity plate 14 to provide the
tapered gate 18 leading to the cavity 20. The nozzle 10
is heated by an integral helical electrical heating
element 144 and has an insulative air space 40 between it
~ ~ lo - 1 3 1 1 8 9 ~
1 and the surrounding cavity plate 14 which is cooled by
pumping cooling water through conduits 38. The nozzle 10
is secured by bolts 46 to a manifold 42. The manifold 42
and the nozzle 10 are secured in place by a locating
collar 48 which is fastened to the cavity plate 14 by
bolts 146. The manifold 42 is also heated by a helical
electric heating element 148 which is integrally brazed
into it.
The nozzle 10 has a central bore 16 with a rear
portion 150 and a larger diameter forward portion 152
which leads to the gate 18. A hollow elongated steel
valve member 60 is received in the central bore 16 in the
nozzle 10. The valve member 60 has a forward portion 154,
a central portion 156 which extends through the rear
portion 150 of the central bore 16, and a rear portion 158
which extends into a central opening 160 in the manifold
42. As can be seen, the forward portion 154 of the valve
member 60 is smaller in diameter than the surrounding
forward portion 152 of the central nozzle bore 16 which
provides a melt flow space 122 between them. A melt
passage 114 extends to convey pressurized melt from a
central inlet 116 at the rear end 118 of the manifold 42
to the gate 18. The passage 114 splits into two branches
(not shown) which extend out around the opening 160 in the
manifold and join the space 122 around the valve member 60
131 1893
1 in the central bore 16. The central portion 156 of the
valve member 60 has a number of spaced ridges 162 which
fit in the rear portion 150 of the central nozzle bore 16
through the nozzle 10 to prevent leakage of pressurized
melt around the reciprocating valve member 60.
The rear portion 158 of the valve member 60
which extends into the central opening 160 in the manifold
42 has a smaller diameter neck portion 164 around which a
split ring 166 is mounted. The split ring 166 has two
opposing segments which are received in the opening 160
around the neck portion 164 of the valve member 66 as
described in detail in Gellert's Canadian patent
application serial number 601,623 filed June 2, 1989
entitled "Injection Molding System Valve Member Split
Ring". One of the segments of the split ring 166 has a
notch 168 to receive the inner end 170 of a pivotal lever
member 172. In this embodiment of the invention, the
lever member 172 is part of the valve member actuating
mechanism which applies a force through the split ring 166
to reciprocate the valve member 60 between a retracted
open position and a forward closed position in which the
forward end 64 of the valve member 60 is seated in the
gate 18. In this embodiment, the lever member 172 which
pivots around pivot pin 174, is driven by a pneumatic
piston 176 to which pressurized air is applied according
to a controlled cycle.
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131 1893
1 The hollow valve member 60 has a hollow
elongated steel pin 66 extending through it. While the
valve member 60 reciprocates, as described above, the pin
66 is fixed in place by its rear end 70 being secured in
the manifold by a double set screw 72. As can be seen, in
this fixed position, the forward end 68 of the fixed pin
66 extends centrally through the gate 18. The fixed pin
66 has a hollow central portion 90 which conveys gas from
an inlet near the rear end 70 of the pin 66 to an outlet
at the forward end 68 of the pin 66. The outlet is
provided by a number of small holes 178 at the forward end
68 of the pin. The holes 178 are large enough to allow a
sufficient flow of gas outward into the cavity 20, but
small enough to prevent melt from the cavity 20 flowing
back in through the holes 178. The inlet to the hollow
central portion 90 of the fixed pin 66 is similarly
provided by a slot 180 extending radially through the pin
66 near the rear end 70. The slot 180 in the rixed pin 66
is long enough to be in continuous with a lateral opening
98 in one side of the reciprocating valve member 60. The
lateral opening 98 in the valve member receives a gas
conduit 182 which extends outwardly through an opening 184
in the manifold 42 to connect to a conventional gas supply
(not shown).
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131 1893
1 The operation of this embodiment of the
invention is similar to that described above in regard to
the first embodiment with the valve member 60 being
actuated by the lever member 172 and the pressurized gas
flowing in through the conduit 182. However, in this
embodiment, the valve member 60 is only driven to the
forward closed position by the actuating mechanism and is
driven open by the melt injection pressure. However, in
other embodiments, the actuating mechanism can be double
acting as well as single acting.
While the description of the valve gated
injection molding system with gas flow through a central
fixed pin has been given with respect to preferred
embodiments, it is not to be construed in a limiting
sense. Variations and modifications will occur to those
skilled in the art. For instance, alternate
configurations can be provided to fix the pin 66 in place
and to supply the gas to the hollow central portion 90.
Also, different actuating mechanism can be used to
reciprocate the valve member 60 between the open and
closed positions. Also the porous portion 94 can be
replaced by a flat portion seated in the forward end 68 of
the pin with small tapered holes cut through it with a
laser drill. Reference is made to the appended claims for
a definition of the invention.
