Note: Descriptions are shown in the official language in which they were submitted.
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INJECTION MOLDING TORPEDO WITH
DIAGONAI- I~EIIT BORE
BACKGROUND OF THE INVENTION
This invention relates generally to injection
molding and more particularly to a torpedo having a tip and
a diagonally extending melt bore to be mounted at the
forward end of an injection molding nozzle. ~
Seating a torpedo having a conical surface ~ ;
leading to a forward tip in a heated nozzle to control the -
build up of excessive friction heat in the area of the gate
is well known as one type of hot tip gating. The forward '~
end of the nozzle is separated from the cavity plate -~
through which the gate extends by an insulative air space ~ -
which usually is bridged to prevent the melt escaping into
the air space. In one previous type seen in the
applicant's U.S. patent number 4,450,999 which issued May
29, 1984, the torpedo has a central shaft with a forward
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tip which is ronnected by a number of radial ribs to an
outer collar which bridges the insulative air space. The
melt flows through a number of channels extending between
the ribs around the central shaft to the gate. In another
previous type seen in the applicant's U.S. patent number
5,028,227 which issued July 2, 1991, the ribs extend
inwardly from a mounting ring or flange which is secured in
place by a gate insert which bridges the air space between
the forward end of the nozzle and the cavity plate. A
similar arrangement is shown in the applicant's Canadian
patent application serial number filed
September 22, 1992 entitled "Injection Molding Nozzle with
Thermocouple Receiving Torpedo", but in that case the outer
collar is retained in place by a cylindrical nozzle seal
and there is only a single rib extending in to the central
shaft. All of these previous torpedoes have a central
shaft held in place by one or more radial ribs. The metal
ribs necessarily have a thin cross-section which restricts
heat transfer through them. Also, the previous torpedoes
having a ribbed configuration are relatively costly to
manufacture. The applicant's U.S. patent number 4,583,284
which issued April 22, 1986 shows a nozzle having a tip and
a melt bore having a diagonal portion, but there is no
provision for a replaceable torpedo.
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SUMMARY OF THE INVENTION
Accordingly, it is an object of the present
invention to at least partially overcome the disadvantages
of the prior art by providing a replaceable torpedo which
is economical to make and has a tip with a rapid response
to temperature changes.
To this end, in one of its aspects, the invention
provides an injection molding torpedo to be mounted at the
forward end of a nozzle, the nozzle having a melt passage
with an inner surface and a predetermined diameter
extending therethrough in alignment with a gate, the
forward end of the nozzle having a seat with a forward
facing shoulder and an inner surface extending around the
melt passage to receive the torpedo, the torpedo comprising
a main portion having a reax end, a forward portion
extending from the main portion, and a melt bore extending
therethrough, the main portion having a rearward facing
surface to abut against the forward facing shoulder in the
nozzle to seat the torpedo in the seat in the nozzle, the
forward portion having a conical surface with a forward tip
to extend centrally in alignment with the gate and provide
a space around the conical surface leading to the gate, the
melt bore extending from the rear end with a diagonal
portion extending to the conical surface to convey melt
from the melt passage in the nozzle to the space around the
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conical surface leading to the gate. ;
Further objects and advantages of the invention
will appear from the following description taken together
with the accompanying drawings.
¦ BRIEF DESCRIPTION OF THE__RAWINGS
¦ Figure 1 is a sectional view of a portion of an
injection molding system showing a torpedo according to a
first preferred embodiment of the invention,
Figure 2 is an exploded isometric view showing
the torpedo and nozzle seal in position for insertion in
the nozzle seen in Figure 1,
Figure 3 is a sectional view showing the torpedo
¦ retained in position by a gate insert, and
1 15 Figure 4 is a sectional view showing a torpedo
¦ according to a second preferred embodiment of the
invention.
¦ DETAILED DESCRIPTION OF_THE INVENTION
Reference is first made to Figures 1 and 2 which
show a portion of a multi-cavity injection molding system
~ having several nozzles 10 to convey pressurized plastic
'I melt to respective gates 12 leading to different cavities
14 in the mold 16. The mold 16 includes a cavity plate 18
and a back plate 20 which is secured to the cavity plate 18
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by screws 22. Other molding configurations may have a
variety of other plates or parts, depending on the
application. The mold 16 is cooled by pumping cooling
water through cooling conduits 24 extending in the cavity
plate 18 and the back plate 20. An electrically heated
steel melt distribution manifold 26 is mounted between the
cavity plate 18 and the back plate 20 by a central locating
ring 28 and insulative and resilient spacer members 30.
The melt distribution manifold 26 has a cylindrical inlet
portion 32 and is heated by an integral electrical heating
element 34. An insulative air space 36 is provided between
the heated manifold 26 and the surrounding cooled cavity
plate 18 and back plate 20. A melt passage 38 having a
common inlet 39 in the inlet portion 32 of the manifold 26
branches outwardly in the manifold 26 and extends through
each nozzle 10 to the gates 12.
Each nozzle 10 has a forward end 40 and a rear
end 42 which abuts against the melt distribution manifold
26. An electrical heating element 44 extends helically
around the centrally extending melt passage 38 and has an
external terminal 48 to which power leads 50 are connected.
The nozzle 10 is received in a well 52 in the cavity plate
18 and is located in this position by having a circular
insulation flange 54 which is seated against a matching
shoulder 56 in the well 52 in the cavity plate 18. The
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nozzle 10 has an enlarged portion 58 adjacent its forward
end 40 with a bore 60 into which a thermocouple element 62
extends to monitor the operating temperature adjacent the
forward end 40 of the nozzle lO. The central melt passage
38 which extends from the manifold 26 through each nozzle
10 is aligned with the gate 12 extending through the cavity
plate 18 to the cavity 14. The central melt passage 38
through the nozzle 10 has an inner surface 64 with a
predetermined diameter. The forward end 40 of the nozzle
10 has a seat 66 with a forward facing shoulder 68 and a
cylindrical inner surface 70 in which a torpedo 72
according to the invention is mounted.
In this embodiment, each torpedo 72 has a main
portion 74 with an outer surface 76 and a forward portion
78 with a conical surface 80 extending to a forward tip 82.
The outer surface 76 has a circular mounting flange 84
extending outwardly around it. The torpedo 72 is
accurately seated in position with the forward tip 82 in
alignment with the gate 12 by the mounting flange 84 being
secured in the seat 66 by a hollow nozzle seal 86 which is
seated against the cavity plate 18 to extend around the
gate 12. The forward end 40 of the heated nozzle 10 is
separated from the cooled cavity plate 18 by an insulative
air space 88, and in this embodiment the nozzle seal 86
bridges the air space 88 to prevent pressurized melt
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leaking into it. The manifold 26, nozzles 10, torpedoes
72, and nozzle seals 86 are securely retained in this
position against the melt injection pressure by force from
the screws 22 which is applied to the manifold 26 through
the spacer members 30.
The nozzle seal 86 has a circular removal flange
92 which extends outwardly into the air space 88 and is
spaced from the forward end 40 of the nozzle 10 to provide
for removal of the nozzle seal 86 by prying it out with a
screwdriver or other similar tool. The circular mounting
flange 84 has a rearward facing surface 94 which abuts
against the forward facing shoulder 68 of the seat 66. The
outer surface 76 of the main portion 74 of the torpedo 72
has a first cylindrical portion 96 which extends rearwardly
from the circular mounting flange 84 to the rear end 98 and
fits in contact with the inner surface 64 of the melt
passage 38 through the nozzle 10. The outer surface 76 of
the main portion 74 of the torpedo 72 also has a second
cylindrical portion 100 which extends forwardly from the
mounting flange 84 to the conical surface 80 and fits in
. contact with the surrounding nozzle seal 86 which in turn
fits in contact with the inner surface 70 of the seat 66.
Each torpedo 72 also has a melt bore 102 with a
rear portion 104 which extends centrally from the rear end
98 and a diagonal portion 106 which extends from the rear
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portion 104 to the conical surface 80. The rear portion
104 tapers inwardly from a diameter at the rear end 98
which is equal in diameter to and in alignment with the
melt passage 38 through the nozzle 10 to avoid turbulence
in the melt flow. The melt from the melt passage 38 flows
through the melt boxe 102 in the torpedo into a space 108
around the conical surface 80 which leads to the gate 12.
The torpedo is made of a highly heat conductive metal such
as a beryllium copper alloy or molybdenum. The
configuration of the torpedo 72 and the extent of contact
with the surrounding nozzle 10 and nozzle seal 86 provides
the forward tip 82 with a rapid response to temperature
changes during the injection cycle.
In use, the injection molding system is assembled
as shown in Figure 1. While only a single cavity 14 has
been shown for ease of illustration, it will be appreciated
that the melt distribution manifold 26 normally has many
more melt passage branches extending to numerous cavities
14 depending on the application. Electrical power is
applied to the heating element 34 in the manifold 26 and to
the heating elements 44 in the nozzles 10 to heat them to
a predetermined operating temperature. Pressurized melt
from a molding machine (not shown) is then injected into
the melt passage 38 through the common inlet 39 according
to a predetermined cycle in a conventional manner. The
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pressurized melt flows through each nozzle 10 and the melt
bore 102 of the aligned torpedo 72 into the space 108
around the conical surface 80 and then through the aligned
gate 12 to fill the respective cavity 14. After the
cavities 14 are filled, injection pressure is held
momentarily to pack and then released. After a short
cooling period, the mold is opened to eject the molded
products. After ejection, the mold is closed and injection
pressure is reapplied to refill the cavities 14. This
cycle is continuously repeated with a frequency dependent
on the size and shape of the cavities 14 and the type of
material being molded. For initial start-up of the molding
process, heat from the heating element 44 in each nozzle 10
¦ is conducted forwardly through the torpedo 72 to the tip 82
aligned with the gate 12. During injection, the torpedo 72
conducts excess heat which is generated by friction of the
melt flowing through the constricted area of the gate 12
rearwardly to avoid stringing and drooling of the melt when
the mold opens for ejection. After the melt has stopped
flowing, solidification in the gate is enhanced by the
removal of the excess friction heat through the torpedo 72.
In many applications, ambient heat in the melt from the
machine cylinder and friction heat is sufficient to keep
the system functioning after start-up. This heat prevents
the melt completely freezing in the zrea of the gate 12 and
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11
forming a solid plug which would interfere with injection
when injection pressure is reapplied after the mold is
closed. The configuration of the torpedo 72 according to
the invention does not have restricted cross-sections of
the conductive metal through which the heat must flow and
there are large areas of contact between the torpedo 72 and
the surrounding nozzle 10 and nozzle seal 86. This
provides the forward tip 82 with a rapid response to these
changes in temperature during the injection cycle and thus
cycle time can be reduced.
Reference is now made to Figures 3 and 4 to
describe other applications and embodiments of the
invention. As many of the elements are the same as those
described above, common elements are described and
illustrated using the same reference numerals. Referring
first to Figure 3, the configuration of the torpedo 72 is
the same as that described above, but it is secured in
place in the seat 66 in the forward end 40 of the nozzle 10
by a hollow gate insert 110 rather than by a nozzle seal.
The gate insert 110 has a tapered forward portion 112
seated in a tapered opening 114 which extends through the
cavity plate 18 to the cavity 14. The gate insert 110 has
a cylindrical rear portion 116 which extends into the seat
66 in the forward end 40 of the nozzle 10 and fits in
contact with the surrounding inner surface 70 of the seat.
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12
The torpedo 72 is retained in place by the circular
mounting flange 84 being secured between the forward facing
shoulder 68 of the seat 66 and the rear portion 116 of the
gate insert 110. The gate insert 110 bridges the air space
88 between the forward end 40 of the nozzle 10 and the
cavity plate 18 and also has a circular removal flange 118.
The first cylindrical portion 96 of the outer surface 76 of
the main portion 74 of the torpedo 72 fits in contact with
the inner surface 64 of the melt passage 38 through the
nozzle 10, and the second c,vlindrical portion 100 of the
outer surface 76 fits in contact with the surrounding gate
insert 110. Thus, in use, the tip 82 of the torpedo 72
will have the same rapid response to thermal requirements
during the injection cycle described above.
Another embodiment of the invention is shown in
Figure 4 in which the rear end 98 of the main portion 74 of
the torpedo 72 abuts against the forward facing shoulder 68
of the seat 66. The first cylindrical portion 96 of the
outer surface 76 which extends from the rear end 98 fits in
contact with the inner surface 70 of the seat 66. The
second cylindrical portion 100 is smaller in diameter than
the first cylindrical portion 96 and extends forwardly from
a shoulder 120 which extends inwardly from the first
cylindrical portion 96. A nozzle seal 86 as described
above abuts against this shoulder 120 and the second
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cylindrical portion 96 fits in contact with the surrounding
nozzle seal 86. Of course, the melt bore 102 through the
torpedo also has the central rear portion 104 and the
diagonal portion 106 extending to the conical surface 80
which is relatively easy to machine and provides the
torpedo 72 with a greater area of highly conductive metal
for heat transfer to and from the forward tip 82
While the description of the torpedo 72 has been
given with respect to preferred embodiments, it will be
evident that various other modifications are possible
without departing from the scope of the invention as
understood by those skilled in the art and as defined in
the following claims.
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