Note: Descriptions are shown in the official language in which they were submitted.
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IN31e CTIO~ ~OLDI~IG APPARATllS ~ITEI DIRIECT
GAS (::O~E~CTIOL~ TO ~J~L~ Hl~B131R
BACKGROUND OF THE INVENTION
1 This invention relates generally to injection
molding and more particularly to valve gated gas assisted
apparatus for making plastic products having a hollow or
gas filled central portion.
Providing a flow of gas along with the
pressurized melt to form hollow plas~ic produc~s is known
in the art and is generally referred to as l'gas assisted
injection moldingnO An early example is shown in U.S,
patent number 4,101,617 to Friederich which issued July
18, 1978O More recent arrangements are shown in European
patent application serial number 09360tl89 to Engel
Maschinenbau GOmOb3HO published March 28 t 1990 and U.S,
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patent number 4,917,594 to Gellert which issued April 17,
1990. It is very desirable for many applications that
these systems be valve gated, but the previous valve gated
gas assisted systems have had the disadvantage that
relatively complicated arrangements have been necessary to
supply the gas to the reciprocating valve pin or member.
This has increased the manufacturing cost and resulted in
malfunctions during use.
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10 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 valve gated gas assisted injection molding
apparatus having a flexible gas supply line connected
directly to the valve member~
To this end, in one of its aspects, the
invention provides valve gated gas assisted injection
molding apparatus having a heated nozzle with a rear end,
the nozzle being seated in a well in a cavity plate wi.th
the rear end abutting against a heated manifold, a melt
passage extending to convey pressurized melt from an inlet
in the manifold to a gate extending through the cavity
plate to a cavity, the nozzle having a central bore
extending therethrough~ an elongated valve member having a
forward end and a rear end being received in the central
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1 bore of the nozzle whereby a portion of the melt passage
extends in the central bore around a forward portion of
the valve member, and valve member actuating means to
reciprocate the valve member between a retracted open
position and a forward closed position in which the
forward end of the valve member is seated in the gate, the
improvement wherein the elongated valve member has a
hollow central passage extending therethrough, to the
forward end of the valve member, a flexible gas supply
line being connected to the valve member to supply
pressurized gas to the central passage according to a
predetermined cycle to provide during injection, a stream
of gas from the forward end of the valve member flowing
through the gate into the cavity, with melt from the
portion of the melt passage around the valve member
flowing around the stream of gas into the cavity.
Further objects and advantages of the invention
will appear from the following description, taken toge~her
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional view of a portion of a
valve gated injection molding system according to one
embodiment of the invention showing the melt passage;
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1 Figure 2 is a sectional view taken along line 2-
2 in Figure 1 showing the valve member actuating
mechanism;
Figure 3 is a similar partial view showing the
valve member in the closed position;
Figure 4 is a partial isometric view of the
valve member according to this embodiment of the
invention;
Figure 5 is a sectional view of a portion of an
injection molding system according to another embodiment
of the invention; and
Figure 6 is a sectional view of a por~ion of
Figure 5 showing the piston in the open position.
DETAILED DESCRIPTION OF THE DRAWI~GS
Reference is first made to Figures 1 to 3 which
shows a valve gated gas assisted injection molding system
or apparatus having a melt passage 10 which extends from a
central inlet 12 in a manifold 14, through a central bore
16 of a heated nozzle 18 and a ga~e 20 to a cavity 22~ In
this embodiment the melt passage 10 branches from the
central inlet 12 into two channels 24 around the valve
member actuating mechanism and rejoins in a valve member
bushing 26 which is seated in the nozzle 18. ~s can be
seen, a portion 27 of the melt passage 10 extends towards
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1 the gate 20 along a valve member 28 in the central bore 16
which is considerably larger in diameter than the valve
member 28.
The nozzle 18 is seated in a well 30 in the
cavity plate 32 by an insulation flange or bushing 34
which abuts against a circumferential shoulder 36. This
accruately locates the nozzle 18 with the central bore 16
in alignment with the gate 20 and provides an insulative
air space 38 between the nozzle 18 and the surrounding
cavity plate 32. The nozzle 18 has an electrical heating
element 40 which is integrally cast into it and the cavity
plate 32 is cooled by pumping cooling water through
cooling conduits 42. An injection molding nozzle seal 44
as described in Gellert's U.S. patent number 4,286,941
which issued September 1, 1981 is seated in the nose
portion 46 of the nozzle 18 and bridges the air space 38
around the gate 20 to prevent the air space 38 filling
with melt.
The manifold 14 is secured in correct alignment
to the nozzle 18 by bolts 48. The nozzle 18 and manifold
14 are in turn held in place by a locating ring 50 which
is secured by bolts 52 extènding through the support plate
54 into the cavity plate 32.
The valve member bushing 26 i5 securely seated
in an opening 56 in the rear end 58 of the nozzle 18 and
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1 has a valve member bore 60 extending therethrough in
alignment with the central bore 16 through the nozzle
18. As described in UOS~ patent number 4,433,969, the
valve member bore 60 which extends into a rearwardly
projecting portion 62 of the valve pin bushing 26 is of
sufficient length and fits snugly enough around the valve
member 28 to seal against leakage of the pressurized melt :
around the valve member 28 as it reciprocates. As can be :
seen, the valve member bushing 26 is shaped to connect the -
two channels 24 of the melt passage 10 to the central bore
16 through the nozzle 18. The valve member bushing 26 and
the opening 56 in which it is seated in the nozzle 18 are
oblong shaped to accurately align it, and the rearwardly
projecting portion 62 has two outwardly facing flat
surfaces 64.
The elongated valve member 28 has a hollow
passage 66, a rear end 68 and a forward end 70 which seats
in the gate 20 in the forward closed position. As seen in
Figure 4, in this embodiment, the rear end 68 of the valve
: 20 member 28 has an enlarged connector portion 72 with a
threaded opening 74 to receive a fitting 76 from a
flexible gas supply line 78. The valve member 28 also has
an enlarged flange portion 80 which is spaced from the
connector portion 72. The flange portion 80 has a flat
face 82 which is aligned with a flat face 84 of the
connector portion 72.
1 The manifold has an electrical heating element
86 which is integrally brazed into it and has a radial
opening 88. The slot 88 receives the rearwardly
projecting portion 62 of the valve member bushing 26 and a
r`ack member 90. The rack member 90 has two inwardly
facing flat surfaces 92 which slid against the outwardly
acing flat surfaces 64 of the rearwardly projecting
portion 62 of the bushing 26. The valve member 28 extends
through a groove 94 in the rack member 90, with the
enlarged flange portion 80 being engageably received in a
transverse slot 96. The rack member 90 also has a toothed
portion 98 with a row of outwardly facing teeth 100. The
opening 88 in the manifold 14 extends radially outward to
receive a pinion lever member 102 which is pivotally ~ ;:
mounted on a pivot pin 104 which extends into the manifold .
14 on opposite sides of the opening 88. The pinion member
102 also has teeth 106 which engage the teeth 100 of the
rack member 90 and a pivot lever arm 108 which extends ;~
outwardly through the mouth 110 of the opening 88. The
pivot lever arm 108 is connected by a rod 112 to a double- ~ :
acting piston 114 which is driven by air received through
hoses (not shown) leading to connectors 116 to reciprocate
in a pivotally mounted cylinder 118. While the pivot ;
lever arm 108 is curved in this embodiment to match the
location of the cylinder 118 and piston 114, other ~ -
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1 suitable arrangements can be used to drive the pinion
lever member 102.
In use, the system is assembled as shown and
electrical power is applied to the heating elements 40,86
to heat the manifold 14 and the nozzle 18 to a
predetermined operating temperature. Pressurized melt
from a molding machine (not shown~ is introduced into the
melt passage 10 through the central inlet 12 and a
pressurized gas such as nitrogen or air is applied through
gas supply line 78 according to a predetermined cycle.
Controlled pneumatic pressure is applied to the cylinder
118 to operate the piston 114 according to a matching
cycle. When the piston 114 pivots the pinon lever member
102 to the open position shown in Figure 3 the rack member
90 and the valve member 28 slide rearwardly to withdraw
the forward end 70 from the gate 20. Then, injection melt
pressure and gas pressure are applied. This produces a
stream 120 of gas which flows from the forward end 70 of
the valve member 28 through the gate 20 into the cavity 22
with melt from the adjacent portion 27 of the melt passage
10 flowing around it. As seen in Figure 2, this produces
a melt bubble 122 which expands until it contacts the
walls of the cavity 20. After there is a build up of gas
pressure in the filled cavity 20, the piston 114 drives
the pinion lever member 102 and the valve member to the
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1 forward closed position shown in Figure 1 in which the
forward end 70 of the valve member 28 is seated in the
gate 20. Injection pressure is then released, and after a
short cooling period, the gas pressure is released and a
suction can be briefly applied so the walls do not blow
when the mold is opened. The forward end 70 of the valve
member has a porous portion 124 which is formed by
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sintering stainless steel powder. This allows the gas to ~ -
flow outward to the cavity 22, while preventing the melt
from flowing back in to plug the hollow passage 66. The
mold is then opened along the parting line 126 to eject
the hollow molded product. After ejection, the mold is
closed and hydraulic pressure is reapplied to the cylinder
118 to withdraw the valve member 28 to the open position ;~
and injection and gas pressure are reapplied to refill the ~ ~
cavity 22. This oycle is repeated continuously with a -
frequency dependent upon the size of cavity and type of
material being molded. As seen in Figures 2 and 3, in
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this embodiment, the gas supply line 78 has several loops
2Q 128 in it to provide additional flexability for its
connection to the valve member 28 which reciprocates ~-
between the open and closed positions.
Figures 5 and 6 illustrates an injection molding
system according to another embodiment of the invention. ~ -
The elements of this embodiment which are common to the
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1 first embodiment described above are described and
illustrated using the same reference numerals. In this
case, the nozzle 18 is similarly seated in well 30 in the
cavity plate 32. However, in this embodiment, the valve
member actuating means is a piston 130 which reciprocates
in a cylinder 132, rather than the rack and pinion
mechanism described above. The cylinder 132 is seated in
a back plate 134 and hydraulic pressure is applied through
hydraulic fluid lines 136 to reciprocate the piston 130
according to a predetermined cycle. The piston 130 has a
neck portion 138 which extends through a V-shaped
hydraulic seal 140. The piston also has central bore 142
which is threaded adjacent the rear end to receive the ;
valve member 28.
The elongated valve member 28 has a hollow
central passage 66 extending from the forward end to the
rear end 68. While the forward end is not shown, it is
the same as that described above in the first
embodiment. In this embodiment, the valve member 28 has
an enlarged connector portion 72 which extends through an
opening 144 through a cap 146 which is screwed into the
cylinder 132. Another hydraulic seal 148 is seated in the
cap 146 to prevent leakage of hydraulic fluid as the valve
member 28 reciprocates. An L-shaped connector fitting 150
is screwed into an opening 152 in the rear of the
connector portion 72 to connect to the gas supply line 78.
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1 In this embodiment of the invention, the heated
nozzle 18 is one of several nozzles in a multi-cavity
system. The melt passage 10 extends through an elongated
manifold 154 having an integral heating element 156. The
melt passage 10 extends diagonally through the valve
member bushing 26 to join the central bore of the nozzle
18 as described in U.S. patent number 4,433,969 to Gellert
which issued February 2B, 1984.
The operatlon cf this embodiment is similar to
that described above in regard to the first embodiment- ;
with the valve member 28 being actuated by the piston 130
to which it is connected. As seen in Figure 6, in this
embodiment, the gas supply line 78 does not have any
loops. If the line 78 is made of a suitable flexible
material such as braided high pressure hydraulic hose and
it is long enough, it has been found to have sufficient
flexability to provide for the continuous movement of the
valve member 28.
While the description of the valve gated gas
assisted injection molding system has been provided with
regard 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, the gas `~
supply line 78 can have a single longitudinal loop to
provide the necessary flexibility. The forward end 70 of
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1 the valve member 28 can have a number of laser cut holes
instead of porous portion 124. Reference is made to the
appended claims for a definition of the invention.
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