Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title: GAP SEAL BETWEEN NOZZLE COMPONENTS
FIELD OF THE INVENTION
This invention relates to an injection molding apparatus, and more
particularly to a nozzle seal for an injection molding apparatus.
BACKGROUND OF THE INVENTION
A hot runner injection molding apparatus typically includes nozzles that
are heated to maintain melt therein at a controlled temperature. The nozzles
are typically in contact with a mold component that defines one or more mold
cavities. The mold cavities in the mold component are filled with melt that
first
passes through the nozzles. The mold component is then typically cooled in
order to solidify the melt in the mold cavities, thus forming a plurality of
molded parts, which are then ejected from the mold cavities.
Because the nozzles are typically heated, and the mold component is
cooled for at least a portion of an injection molding cycle, it is desirable
to
have a relatively low heat transfer from the nozzles into the mold component.
Many nozzle constructions have been proposed in the past to address this
issue. Examples of such a nozzle construction is shown in US Patent Nos.
5,492,467 and 5,554,395, both to Hume et al.
The '467 patent teaches a hot runner nozzle having a nozzle body, an
insert which is positioned in the nozzle body, and a bushing that surrounds
the insert. The bushing contacts the mold component, to form a seal
therebetween. The bushing and the insert are spaced apart so that a gap
exists between them. During the injection process, molten material fills the
gap between the insert and the bushing. With this configuration, some heat is
lost from the insert, through the molten material, through the bushing and
finally into the mold component. Furthermore, the molten material itself can
make the disassembly of the nozzle difficult and time consuming.
The '395 patent teaches a multi-piece nozzle tip assembly including a
tip piece, a tip surrounding piece and a mold component contact piece. The
tip surrounding piece surrounds the tip piece and retains the tip piece in the
nozzle. The tip surrounding piece is spaced from the tip piece. A mold
component contact piece is provided between the tip piece and the mold
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component, to inhibit melt from filling the space between the tip piece and
the
tip surrounding piece. However, heat can be lost from the tip piece through
the seal and into the mold component. In particular, the heat losses occur
near the downstream end of the insert, where control over the temperature of
the melt is particularly important.
Thus, there is a continuing need for new nozzle constructions that have
further improved heat transfer efficiency.
SUMMARY OF THE INVENTION
In a first aspect, the invention is directed to a nozzle for an injection
molding apparatus. The nozzle includes a nozzle body, a heater, a tip, a tip
surrounding piece. The nozzle body defines a nozzle body melt passage,
which has an inlet that is adapted to be downstream from and in
communication with a melt source. The heater is connected to said body for
heating melt in said nozzle body melt passage. The tip defines a tip melt
passage that is downstream from and in communication with said nozzle body
melt passage. The tip melt passage has an outlet that is upstream from a
gate in a mold component. The tip includes a tip sealing surface. The tip
surrounding piece includes a first tip surrounding piece sealing surface. The
first tip surrounding piece sealing surface and said tip sealing surface are
separated by a gap. The gap is sized to inhibit the flow of melt between said
first tip surrounding piece sealing surface and said tip sealing surface.
In a second aspect, the present invention is directed to an injection
molding machine that incorporates the nozzle described above.
DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention and to show more
clearly how it may be carried into effect, reference will now be made by way
of
example to the accompanying drawings, in which:
Figure 1 is a sectional side view of a portion of a nozzle in accordance
with a first embodiment of the present invention;
Figure 2 is a sectional side view of a portion of a nozzle in accordance
with a second embodiment of the present invention;
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Figure 3 is a magnified view of a sealing portion of the nozzle shown in
Figures 1;
Figure 4 is a sectional side view of a portion of a nozzle in accordance
with a third embodiment of the present invention;
Figure 5 is a sectional side view of a portion of a nozzle in accordance
with a fourth embodiment of the present invention;
Figure 6 is a sectional side view of a portion of a nozzle in accordance
with a fifth embodiment of the present invention;
Figure 7 is a sectional side view of a portion of a nozzle in accordance
with a sixth embodiment of the present invention; and
Figure 8 is a sectional side view of an injection molding apparatus
having a plurality of nozzles in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In a hot runner injection nozzle system, there are two critical areas
where there is a heat loss. One area is between the nozzle and the injection
manifold, and the other area is between the nozzle and the mold component
in the area of the gate.
Reference is made to Figure 1, which shows a nozzle 10, in
accordance with a first embodiment of the present invention. Nozzle 10 is for
transferring melt from a runner in a manifold in a hot runner injection
molding
apparatus to a mold cavity 11 in a mold component 12. Mold cavity cooling
channels 13 may optionally be included in mold component 12.
Nozzle 10 includes a body 14, a tip 16, a tip surrounding piece 18, a
heater 22, and may include an optional thermocouple 26. The body 14 has a
body melt passage 28 that passes therethrough. The nozzle 10 includes a
viscosity seal 48 which is a seal made between two surfaces which do not
contact each other.
The tip 16 may be removably connectable to the body 14. The tip 16
defines a tip melt passage 30 therethrough that is downstream from and in
fluid communication with the body melt passage 28. The tip melt passage 30
may exit from tip 16 into a chamber 32 that surrounds nozzle tip 16. A gate
34 transfers melt from the chamber 32 into the mold cavity 11.
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Melt passes from a melt source, through one or more runners in a
runner component such as a manifold, through the nozzle body melt passage
28, through the tip melt passage 30, through the chamber 32, through the
gate 34 and finally into the mold cavity 11. The centre of the gate 34 defines
5, an axis 35, which is parallel to the direction of flow of melt through gate
34,
into the mold cavity 11.
The exit from the tip melt passage into the chamber 32 is shown at 36.
Exit 36 may be concentric with respect to axis 35, as shown in Figure 1.
Because the melt flows through the tip 16, the tip 16 can be used to
transfer heat from the heater 22 to the melt. To facilitate the heat transfer,
the
tip 16 is preferably made from a thermally conductive material, such as
Beryllium-Copper.
Because of the melt flow through tip 16, the tip 16 may be exposed to a
highly abrasive environment, and it may be desirable to make the tip 16 from
a wear resistant material. An example of a material that is both thermally
conductive and wear resistant is Tungsten Carbide. The tip 16 may be made
in accordance with the teachings in US Patent No. 5,658,604 (Gellert et al.),
which discloses the construction of a nozzle tip using Tungsten Carbide.
The tip 16 may be positioned within a bore 37 in the nozzle body 14.
Depending on the material selected for the tip 16, a threaded portion can be
relatively difficult to machine. Furthermore, such a threaded portion can be
brittle and subject to premature failure, depending on the material of
manufacture for the tip 16. Thus, by making the tip 16 threadless, a greater
number of materials are available for its manufacture.
Furthermore, by making the tip 16 threadless, some cost of
manufacture is saved for the tip 16 and correspondingly for the body 14,
relative to a threaded tip.
The tip surrounding piece 18 may retain the tip 16 in place in the
nozzle body 14. Because the melt that contacts the tip surrounding piece 18
is generally slower moving than the melt flowing through the tip 16, the tip
surrounding piece 18 may be made from a material that is less wear resistant
than that of the tip 16. Accordingly, the tip surrounding piece 18 may be
made from a material that is relatively easily machined with threads.
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The tip surrounding piece 18 may contact the mold component 12, as
shown in Figure 1. To reduce heat losses from the tip 16 and from the nozzle
body 14 into the mold component 12, the tip surrounding piece 18 may be
made from a material that has a thermal conductivity that is lower than that
of
the material for the nozzle tip 16, depending on the specific requirements of
the molding application. Alternatively, the tip surrounding piece 18 may be
made from a material that has a thermal conductivity that is similar to that
of
the nozzle tip 16.
The tip surrounding piece 18 may be removably attachable to the
nozzle body 14. For example, the tip surrounding piece 18 may include a
threaded portion 40 for mating with a corresponding threaded portion 41 on
the nozzle body 14. The threaded portion 40 as shown in Figure 1 is an
external thread, however, it is alternatively possible for the tip surrounding
piece to include an internal thread to mate with an external thread on the
nozzle body 14.
The tip surrounding piece 18 may also include a tool engagement
portion 42, for receiving a tool (not shown), for the installation and removal
of
the tip surrounding piece 18 with respect to the nozzle body 14.
The tip surrounding piece 18 may include a jam surface 44 for mating
with a shoulder 45 on the tip 16. When the tip surrounding piece 18 is
attached to the nozzle body 14, the jam surface 44 mates with the shoulder
45 on the tip 16, to retain the tip 16 in place in the bore 37. The jam
surface
44 and the shoulder 45 may cooperate to form a mechanical seal.
The tip surrounding piece 18 further includes a first tip surrounding
piece sealing surface 46, which cooperates with a tip sealing surface 47 on
the tip 16 to form a viscosity seal 48, which may also be referred to as a gap
seal. The first surrounding piece sealing surface 46 and the tip sealing
surface 47 are separated from each other by a gap G.
Due to the viscosity of the melt in the chamber 32, the proximity of the
first tip surrounding piece sealing surface 46 and the tip sealing surface 47
inhibits melt from flowing between the first tip surrounding piece sealing
surface 46 and the tip sealing surface 47. Thus, the gap G, in conjunction
with the viscosity of the melt, acts as a seal.
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An advantage to including a viscosity sea148 is that the manufacturing
tolerances for sealing surfaces 46 and 47 are less demanding, relative to a
typical mechanical sealing portion. A further advantage is that because melt
does not pass through the gap seal 48, an air space 49 is maintained
between the tip 16 and the tip surrounding piece 18. The air space 49
provides an insulative layer to reduce heat transfer between the tip 16 and
the
tip surrounding piece 18.
The gap seal 48 can maintain the air space 49 without the need for
contact between the tip 16 and any other component, particularly contact at or
near the outlet end of the tip 16, where melt temperature is particularly
important. By avoiding such contact between the tip 16 and another
component, the heat losses from the tip 16 are reduced.
The Gap G is preferably between approximately .02 and approximately
.07 mm if it the only seal and is not combined with a mechanical seal. If the
jam surface 44 on the tip surrounding piece 18 and the shoulder 45 on the tip
16 form a mechanical seal, the gap G may be approximately .15 mm with a
range of approximately .05 to .35 mm. It will be noted that the gap G required
to inhibit the flow of melt is dependent on the specific molding application.
The rheological properties of the melt at the injection temperature, such as
its
viscosity, determine the maximum gap G that provides the desired seal.
The tip surrounding piece 18 may further include a second tip
surrounding piece sealing surface 50, which mates with a mold component
sealing surface 52 to form a nozzle-mold component seal 54. The nozzle-
mold component seal 54 inhibits the leakage of melt out of the chamber 32.
The nozzle-mold component seal 54 may be any suitable kind of seal, such
as, for example, a mechanical seal, or a viscosity seal, or a combination of
both.
The tip surrounding piece 18 may include a tip surrounding piece
alignment surface 56, which mates with a mold component alignment surface
58 to align the nozzle 10 with respect to the gate 34. In the embodiment
shown in Figure 1, the tip surrounding piece alignment surface 56 and the
second tip surrounding piece sealing surface 50 may be the same surface.
Also, the mold component alignment surface 58 and the mold component
sealing surface 52 may be the same surface.
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Reference is made to Figure 2, which shows a nozzle 100 that
includes a tip 102. Tip 102 differs from tip 16 in that tip 102 has a melt
passage 104 with an exit 106 that is off-centre from the axis 35 of the gate
34. Nozzle tip 102 is used to extend the heating surface in contact with the
melt flow into the gate 34, to maintain the temperature of the melt close to
the mold cavity 11.
Thus, a nozzle in accordance with the present invention may have a
tip that inserts into the gate 34 and has an off-centre melt passage exit
with respect to the axis 35, or alternatively has a tip that has a concentric
melt passage exit with respect to the axis 35.
Reference is made to Figure 3, which shows a magnified view of the
viscosity seal 48 in the embodiments of Figures 1 and 2.
Reference is made to Figure 4, which shows a nozzle 200 in
accordance with a third embodiment of the present invention. The nozzle
200 includes the nozzle tip 16, a tip surrounding piece 217, a mold
component contact piece 218, the heater 22, and may include the optional
thermocouple 26.
The tip surrounding piece 217 may be similar to the tip surrounding
piece 18. In the embodiment shown in Figure 4, the tip surrounding piece
217 is positioned between the tip melt passage, which is shown at 219 and
the heater 22 along a portion of the length of the tip melt passage 219.
Thus the tip surrounding piece 217 is preferably made from a thermally
conductive material to reduce losses between the heater 22 and the tip 16.
The tip surrounding piece 217 may be made from such materials as Be-Cu,
Aluminum, Molybdenum or suitable Molybdenum alloys.
Along a portion of the length of the tip surrounding piece 217, there
may be direct contact with the tip 16, to further improve the heat transfer.
Along the remainder of the length of the tip surrounding piece 18, however,
is provided a first tip surrounding piece sealing surface 220, which
cooperates with a tip sealing surface 221 to form a gap seal 222. Along the
length of the gap seal 222, an air space 223 is defined, and the sealing
surfaces 220 and 221 are separated by the gap G.
The mold component contact piece 218 may be joined to the tip
surrounding piece 217 and may seal therewith against melt leakage. The
mold component contact piece 218 may form a seal with the mold
component
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12, to inhibit melt leakage therepast from chamber 32, and may also serve to
align the nozzle 10 with respect to the gate 34. The seals formed between
the mold component contact piece 218 and the tip surrounding piece 217, and
between the mold component contact piece 218 and the mold component 12
may be any suitable kinds of seals, such as mechanical seals.
To reduce the heat transfer from the nozzle 200 into the mold
component 12, the mold component contact piece 218 may be made from a
material that is comparatively less thermally conductive than that of the tip
surrounding piece 18. For example, the mold component contact piece 218
may be made from titanium, H13, stainless steel, mold steel or chrome steel,
for example. As another alternative, the mold component contact piece 218
may be made from ceramic. Other suitable materials for the mold component
contact piece 218 are disclosed in US Patent No. 5,879,727 (Puri). Puri
discloses such materials for use as an insulative layer for a nozzle.
1c
Reference is made to Figure 5, which shows a nozzle 300 in
accordance with a fourth embodiment of the present invention. Nozzle 300
includes the nozzle body 14, the nozzle tip 16, a tip surrounding piece 318, a
nozzle guide 320 and may include the optional thermocouple 26.
The tip surrounding piece 318 may be similar to the tip surrounding
piece 18, and includes a first tip surrounding piece sealing surface 322,
which
cooperates with the tip sealing surface 47 to form a gap seal 324 therewith.
The sealing surfaces 322 and 47 are separated by the gap G.
The tip surrounding piece 318 further includes a second tip surrounding
piece sealing surface 350, which cooperates with the mold component sealing
surface 52 to form another viscosity seal 360, to inhibit melt leakage out of
the
chamber 32. Because the sealing surfaces 350 and 52 do not contact, the
heat transfer between the nozzle 300 and the mold component 12 is further
reduced. Also, because the sealing surfaces 350 and 52 do not contact each
other, the nozzle guide 320 can be included as an alignment means for the
nozzle 300 in the mold component 12. The nozzle guide 320 has an outer
edge 370 that aligns nozzle 300 in a bore 380 of mold component 12.
Reference is made to Figure 6, which shows a nozzle 400 in
accordance with a fifth embodiment of the present invention. The nozzle 400
is similar to nozzle 300 and includes the tip 16, a tip surrounding piece 418,
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the heater 22 and may include the optional thermocouple 26. The tip
surrounding piece 418 includes a first tip surrounding piece sealing surface
420 which cooperates with the tip sealing surface 47 to form a viscosity seal
422 therebetween. The sealing surfaces 420 and 47 are separated by the
gap G.
The tip surrounding piece 418 also includes a second tip surrounding
piece sealing surface 424 that cooperates with the mold component sealing
surface 52 to form a nozzle seal 426. The nozzle seal 426 may include a first
seal portion 427 that is a viscosity seal and a second seal portion 428 that
is a
mechanical seal. The second portion 428 of the nozzle seal may also serve
as an alignment means for aligning the nozzle 400 with respect to the gate 34.
Reference is made to Figure 7, which shows a nozzle 500 in
accordance with a sixth embodiment of the present invention. The nozzle 500
includes a nozzle body 501, a tip 502, a tip surrounding piece 504, the heater
22 and may include the optional thermocouple 26.
The nozzle body 501 may be similar to the nozzle body 14 and defines
a nozzle body melt passage 505 therethrough. The tip 502 may be similar to
the tip 16 and may define a tip melt passage 506 therethrough that is
downstream from and in fluid communication with the nozzle body melt
passage 505. The tip 502 may include a first threaded portion 508 which
cooperates with a second threaded portion 510 on the nozzle body 501.
The tip surrounding piece 504 may be similar to the tip surrounding
piece 18, and may include a first tip surrounding piece sealing portion 512,
which cooperates with a tip sealing surface 514 to form a viscosity seal 516
therebetween. The sealing surfaces 512 and 514 are separated by the gap
G.
The tip surrounding piece 504 does not, in the embodiment shown in
Figure 7, retain the tip 502 in place in the nozzle body 501. By eliminating
contact between the tip 502 and the tip surrounding piece 504, and by
including the viscosity seal 516 therebetween, heat losses from the tip 502
are reduced.
The tip surrounding piece 504 may include a second tip surrounding
piece sealing portion 516 with cooperates with the mold component sealing
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surface 52 to form a nozzle seal 518 therewith to inhibit melt leakage out of
the chamber 32.
Reference is made to Figure 8, which shows an injection molding
apparatus 600, that includes a runner component 602, the mold component
12 and a plurality of nozzles 606 in accordance with the present invention.
The runner component 602 includes a plurality of runners 608, which
transfer melt from a main runner inlet 610 to the nozzles 606. The runner
component 602 may be heated by a heater 612.
The nozzles 606 transfer melt from the runner component to the mold
component 12. The nozzles 606 may be any of the nozzle embodiments
described above and shown in Figures 1-7.
It will be appreciated that the particular configuration of the viscosity
sealing portion may be selected depending on the specific molding
application, including the rheological properties of the melt, such as its
viscosity at the injection temperature.
While the above description constitutes the preferred embodiments, it
will be appreciated that the present invention is susceptible to modification
and change without departing from the fair meaning of the accompanying
claims.
