Note: Descriptions are shown in the official language in which they were submitted.
91~1
INJECTION MOLDING SYSTEM ~AVING OFFSET
VALVE PIN BIASING MEC~ANISM
BACKGRO~ND OF THE INVENTION
~his invention relates generally to injection
molding and more particu]arly to a central entry valve
gated system having offset valve member biasing mechanism.
Spring loaded elongated valve member actuators
are well known in the art. An early example is shown in
U.S. Patent number 2,940,123 to Beck et al. which issued
June 14, 1960. With the trend to higher injection
pressures and reduced component size, providing sufficient
space to locate the spring is a serious problem,
'
.
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1 particularly with a center entry system where the melt
passage extends through the manifold out around the rear
portion of the valve member. Center entry systems having
a radially offset pivotal actuating mechanism are known as
shown in the applicant's U.S. patent number 4,286,941
which issued September 1, 1981. Another way of dealing
with this problem is shown in U.S. patent number 4,380,426
to Wiles which issued April 19, 1983 which discloses a
center entry system with a pneumatically actuated piston
connected to the driven end of the valve member.
It is also known to provide an injection molding
nozzle with a nose portion extending forward into the
cavity plate to form the gate as shown in the applicant's
U.S. patent number 4,579,520 which issued April 1, 1986.
A valve member which extends into the cavity and closes in
the rearward direction is shown in the applicant's U.S.
patent number 4,521,179 which issued June 4, 1985. Valve
members which provide flexing gates are described in U.S.
patent number 4,380,422 to Von Holdt which issued
April 19, 1983 and "Hot-Runner 'Flex Gate' Fills Large
Parts Fast with Low Stress", Plastics Technology, July
1988, p 21-23. Thus, the previous actuating mechanisms
either have relatively costly piston actuators, are too
cumbersome for the space available, or do not provide
sufficient force to close a large diameter gate.
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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 one or more valve member biasing mechanisms
which extend radially outward from the valve member.
To this end, in one of its aspects, the
invention provides a valve gated center entry hot runner
injection molding system having a heated nozzle which is
secured to a heated manifold, the heated nozzle being
received in a cavity plate, said nozæle having a forward
nose portion which extends through an opening in the
cavity plate to the cavity, the nozzle having a central
bore with a rear portion and a forward portion which
extends through the nose portion of the nozzle to form a
gate having a forward mouth, an elongated valve member
which extends through the central bore in the nozzle and
reciprocates longitudinally between a retracted closed
position and a forward open position, the valve member
having a forward portion, a central portion which extends
through the rear portion of the central bore, and a rear
portion which extends into a central opening in the
manifold and a melt passage to convey pressurized melt
from a central inlet in the manifold to the gate which
extends through the manifold and nozzle around the rear
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l portion of the valve member to join a s?ace around the
forward portion of the valve member in the forward portion
of the central bore which leads to the gate, the central
portion of the valve member fitting in he rear portion of
the central bore to prevent substantial leakage of the
pressurized melt around the reciprocati~g valve member,
the improvement wherein the valve member has an enlarged
forward end which seats in the mouth of the gate in the
retracted closed position, and a biasin~ mechanism is
mounted in the manifold, the biasing me-hanism including
biasing means mounted in the manifold and lower means
extending to receive a force from the b-asing means and
apply a force to the valve member in th~ rearward
direction.
Further objects and advantages of the invention
will appear from the following descript~on, taken together
with the accompanying drawings.
BRIEF DESCRIPTIO~ OF THE DR~WINGS
_ _ _
Figure l is a sectional view of a portion of an
injection molding system according to o~e embodiment of
the invention showing the configuration of the melt
passage,
Figure 2 is a split section view at a right
angle to Figure 1 showing the biasing mechansims in the
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1 open and closed positions,
Figure 3 is a cut-away isometric view showing
the relationship of the melt passage and the biasing
mechanisms in more detail, and
Figure 4 is a similar split section view showing
another embodiment of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Reference is first made to Figure 1 which shows
a valve member 10 which is received in a central bore 12
in a nozzle 14 which is secured by bolts 16 to a manifold
18. The manifold 18 has a locating flange 20 which is
seated against a circumferential shoulder 22 of a cavity
plate 24 to locate the nozzle 14 in a well 26 in the
cavity plate 24 with an insulative air space 28 between
the heated nozzle 14 and the cooled cavity plate 24. The
locating flange 20 has openings 30 through it to reduce
heat loss to the surrounding cavity plate 24. The nozzle
14 and manifold 18 are also located laterally by a forward
nose portion 32 of the nozzle 14 being received in a
matching cylindrical opening 34 through the cavity plate
24 and by the rear end 36 of the manifold 18 being
received in a matching opening in a locating collar 38.
The locating collar 38 is held securely in place by bolts
40 which extend through the back plate 42 into the cavity
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1 plate 24.
The central bore 12 through the nozzle 14 has a
rear portion 44 and a larger diameter forward portion 46
which extends through the nose portion 32 of the nozzle to
form a gate 48 with a forward mouth 50. The valve member
10 has a forward portion 52, a central portion 54 which
extends through the rear portion 44 of the central bore
12, and a rear portion 56 which extends into a central
opening 58 in the manifold 18. As can be seen, the
forward portion 52 of the valve member 10 is smaller in
diameter than the surrounding forward portion 46 of the
central nozzle bore 12 which provides a melt flow space 60
between them, expect that the forward portion 52 of the
valve member has an enlarged forward end 62 which seats in
the mouth 50 of the gate 48 in the retracted closed
position. The enlarged end 62 of the valve member 10 has
a flat forward face 64 which aligns with the same side 66
of the cavity 68 in the closed position. The central
portion 54 of the valve member 10 has a number of spaced
ridges 70 which fit in the rear portion 44 of the central
nozzle bore 12 through the nozzle 14 to prevent leakage of
pressurized melt around the reciprocating valve member 10.
In this embodiment, the nozzle 14 is heated by
plate heaters 72 which are secured on opposite sides as
seen in Figure 2. The manifold 18 is heated by an
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1 electrical heating element 74 which is integrally cast
into it. The cavity plate 24 is cooled by pu~ping cooling
water through cooling conduits 76. In this large volume
application with the forward face 64 of the valve member
extending to the cavity 68, it is desirable to provide
more cooling to the enlarged end 62 of the valve member
10. Thus, a twisted partition 78 is mounted in the hollow
valve member 10, and a circulation of cooling water is
provided between inlet and outlet pipes 80,82 which extend
laterally from the rear portion 56 of the valve member 10
through lateral openings 84,86 in the manifold 18. Thus,
cooling water flows into the valve member 10 through the
inlet pipe 80, forward along one side of the twisted
partition 78 to the enlarged end 62 where it crosses over
and flows rearwardly along the other side of the twisted
partition and back out through o~tlet pipe 82.
As seen in Figure 1, a melt passage 88 extends
to convey pressurized melt from a central inlet 90 at the
rear end 36 of the manifold 18 to the gate 48. The
passage 88 splits into two branches 92 which extend around
the opening 58 in the manifold and join the space 60
around the forward portion 52 of the valve member 10.
While the forward portion 52 of the valve member 10 is
shown in this embodiment as being smaller in diameter than
the central portion 54, this is not necessarily the
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1 case. The important thing is that the forward portion 46
of the central nozzle bore 12 must be sufficiently larger
than the forward portion 52 of the valve member 10 to
provide the space 60 with a sufficient cross-sectional
area to convey the melt received through the split
branches 92 of the melt passage 88. When the injection
pressure of the melt forces the valve member 10 to the
forward open position, the melt then flows through the
gate 48 outwardly around the enlarged head 62 of the valve
member 10 into the cavity 68.
Reference will now be made to Figure 3 in
describing the two valve member biasing mechanisms 94
which are located on opposite sides of the central opening
58 in the manifold which receives the rear portion 56 of
the valve member 10. In this embodiment of the invention
the two biasing mechanisms 94 and the two branches 92 of
the melt passage 88 are equally angularly spaced in an
alternating arrangement around the valve member 10. This
balances the lateral forces on the valve member and the
branches 92 of the melt passage 88 extend between the
biasing mechanisms 94 so as to not unduely increase the
necessary diameter of manifold 18 and the nozzle 14.
Each biasing mechanism 94 includés a coiled
compression spring 96 which is seated in a cylindrical
opening 98 in the manifold 18 and a lever member lOG which
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1 extends radially inward from the spring 96. As can be
seen, the lever member 100 has an outer end 102 with a
locating tit 104 which receives the spring 96 and an inner
end 106 which extends into a notch 108 in a split ring ~10
which extends around the rear portion 56 of the valve
member 10. The lever member 100 extends radially in a
slot 112 in the manifold and is shaped to provide a
fulcrum 114 near the inner end 106 which abuts against the
rear end 116 of the nozzle 14. The split ring 110 has an
inner portion 118 which is seated in a channel 120 which
extends around the rear portion 56 of the valve member
10. Thus, when the spring 96 forces the outer end 102 of
the lever member 100 forward, the lever member 100 pivots
around the fulcrum 114 and retracts the split ring 110 and
the valve member 10 to which it is engaged. The position
of the fulcrum 114 provides a mechanical advantage to the
force transmitted from the spring 96 to the valve member
10. Consequently, the travel of the valve member 10 is
considerably less than that of the outer end of the lever
member 100 which receives the spring. Of course, the
springs 96 and lever member 100 on opposite sides of the
split ring 110 are of equal sizes so as to apply balanced
forces to the valve member.
In use, the system is assembled as shown and
electrical power is applied to the plate heaters 72 and
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1 the terminal 122 of the heating element 74 to heat the
nozzle and manifold 18 to a predetermined operating
temperature. Pressurized melt from a molding machine (not
shown) is introduced into the melt passage 88 through the
S central inlet 90 according to a predetermined cycle. When
injection pressure is applied, the force of the melt on
the enlarged end 62 of the valve member overcomes the
spring force and drives the valve member 10 forward until
the forwardly facing shoulder 124 of the split ring 110
stops against the rear end 116 of the nozzle 14 in the
open position. The melt then flows through the melt
passage 88 and the gate 48 until the cavity 68 is
filled. When the cavity 68 is filled, the combination of
the back pressure of the melt in the cavity 68 and the
force of the springs 96 drives the valve member 10 to the
retracted closed position in which the enlarged forward
end 62 is seated in the matching mouth 50 of the gate
48. The injection pressure is then released and after a
short cooling period, the mold is opened to eject the
molded products. After ejection, the mold is closed,
injection pressure is reapplied which reopens the gate
48. This cycle is repeated continuously with a frequency
dependent upon the size of the cavity and the type of
material being molded. As can be seen, the travel of the
valve member 10 is relatively short, but large cavities
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l can be filled quickly because of the large diameter of the
enlarged end 62 of the valve member and the mouth 50 of
the gate 48. The shape of the enlarged end 62 and the
mouth causes the pressurized melt to flare outwardly as it
S enters the cavity 6B. This produces a radial molecular
orientation of the melt which is advantageous in
increasing the strength of products having certain
configurations.
Figure 4 shows an alternate embodiment of the
invention having only a single biasing mechanism 94. It
has been found that during normal continuous operation,
when the cavity 68 fills up with pressurized melt, the
back pressure of the melt in the cavity against the
forward face 64 of the valve member 10 is sufficient to
drive the valve member 10 to the retracted closed position
without the additional force of the biasing mechanism
94. However, the biasing mechanism 94 is necessary to
avoid the valve member 10 being frozen in the oipen
position when the system is shut down. This would cause
considerable difficulty in getting the system operational
again. Otherwise, this embodiment is the same as the
embodiment described above and the description need not be
repeated.
While the description of the injection molding
system with offset valve member biasing mechanisms has
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1 been given with respect to a preferred embodiment, it is
not to be construed in a limitiny sense. Variations and
modifications will occur to those skilled in the art. For
instance, it is apparent that the shape of the springs 96
and lever members 100 can be changed. Also the shape of
the valve member 10, the central bore 12 and the opening
58 in the manifold 18 in which it is received can be
varied. Reference is made to the appended claims for a
definition of the invention.
