Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED INJECTION MOULDING NOZZLE AND TIP
Field
This invention relates to nozzles and nozzle tips for injection moulding of
plastic, and
in particular, but not exclusively, to a "hot runner" type of nozzle.
Background
In "hot runner" style injection moulding, molten plastic is injected into a
mould cavity
through a heated nozzle. The plastic flows through a tip, which is typically
made
from a relatively highly thermally conductive material. The heated tip itself
is typically
spaced apart from the mould to avoid direct contact between the tip and the
cooled
mould, and is positioned relative to the gate opening of the mould by a
locating
means such as a locating nut. The nut is often made from a material which has
relatively poor thermal conductivity such as titanium, in order to insulate
the tip from
the mould.
Present designs of nozzles, and in particular nozzle tips, have a number of
disadvantages.
Many nozzles of the prior art raise the temperature of the plastic within the
nozzle to
a peak many tens of degrees higher than the optimum injection temperature in
order
to ensure that it exits the nozzle at around the correct temperature. This may
be
particularly undesirable when modern composite plastics are used, as some of
these
materials may have a relatively narrow range of temperatures (i.e. "operating
window") within which the plastic stays molten, but does not degrade.
The temperature of the nozzles of the prior art is monitored and controlled in
order to
ensure that the temperature of the plastic exiting the nozzle is within a
required
range.
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The temperature variation within the nozzles of the prior art has
traditionally been so
great that the position of the sensor taking this measurement has been
critical in
order to achieve a representative measurement.
The plastic material commonly flows out of the tip from one or more outlets at
or
substantially adjacent a distal end of the tip. In use, pressure forces a
small amount
of the molten plastic upwards towards the nozzle forming a "bubble" or resin
layer to
insulate the exposed portion of the tip in the space between the tip, a
locating nut
engaged therewith, and/or the mould gate, potentially resulting in "hang up"
areas of
stagnant plastic. If there is a change in the plastic material being used in
the
injection moulding system, for example a change in the colour of the plastic,
material
remaining in this space can contaminate the new plastic for one or more drops
since
it is not quickly flushed out by the new material. Accordingly, it may be
necessary to
remove and clean the nozzle thoroughly before changing material.
Due largely to the placement of the outlets at the distal end of the tip,
injection
moulding tips of the prior art generally have a smaller mass and/or outer
surface
area than might otherwise be desirable to maintain the temperature of the
molten
plastic as it is injected into the mould, and may cause unnecessary or
undesirable
stagnation, circulation or flow paths of the molten plastic.
Furthermore, injection moulding nozzle tips of the prior art have
traditionally had a
conical shape at the distal end. Any misalignment of the tip with respect to
the gate
of a mould, in particular if the nozzle is positioned too close to the gate,
significantly
reduces the spacing between the tip and gate, and thus the size of the opening
through which the plastic material is injected into the mould. This can affect
the
injection pressure and thus the quality of the moulding.
Object of the Invention
It is therefore an object of the invention to provide an injection moulding
nozzle
and/or a nozzle tip which overcomes or ameliorates at least one problem of the
nozzles/tips of the prior art, or at least to provide the public with a useful
choice.
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Further objects of the invention will become apparent from the following
description.
Summary of Invention
Accordingly in one aspect the invention may broadly be said to consist in an
injection
moulding nozzle tip comprising:
a substantially elongate main member;
an inlet provided at a proximal end of the main member;
a tapered apex portion provided at a distal end of the main member;
one or more outlets provided in the main member between the proximal end
and the tapered apex portion; and
a fluid flow path between the inlet and the or each outlet.
Preferably the tapered apex portion comprises the distal end of a bulbous
portion of
the tip provided at the distal end of the main member, whereupon the one or
more
outlets are provided between the proximal end and the bulbous portion of the
tip.
Preferably the diameter of the widest part of the bulbous portion is greater
than the
diameter of the main member at or adjacent the or each outlet.
Preferably the tapered apex portion has a substantially concave shape, wherein
the
angle of the outer surface with respect to a main axis of the main member
reduces
towards the distal end.
Preferably the concave shape comprises a concave cone having an inwardly-
curved
conical outer surface.
Alternatively the concave shape may comprise a plurality of substantially
linear
and/or curved surfaces.
Preferably the main member is adapted to engage with a locating nut at or
adjacent
the distal end, and an interchangeable nozzle body at or adjacent the proximal
end,
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the locating nut being adapted to locate the tip with respect to a mould gate
and the
nozzle body being adapted to engage with a manifold of an injection moulding
system, wherein the tip comprises an integrated injection moulding tip and
connector
between the nozzle body and the locating nut.
Preferably at least a portion of the proximal end of the main member is
adapted for
disposal internally of the nozzle body, and at least a portion distal end of
the main
member is adapted for disposal internally of the locating nut.
Preferably the proximal and distal ends of the main member each comprise a
threaded portion adapted to engage with complementary threaded portions of the
nozzle body and locating nut, respectively.
Preferably the threaded portions have an external diameter less than that of a
central
portion of the main member provided between said threaded portions, wherein
the
central portion has an external surface adapted to contact a heating means.
According to a second aspect, the invention may broadly be said to consist in
an
injection moulding nozzle assembly comprising an injection moulding nozzle tip
according to any one of the preceding statements.
Further aspects of the invention will become apparent from the following
description.
Drawing Description:
A number of embodiments of the invention will now be described by way of
example
with reference to the drawings in which:
Figure 1 is a perspective view of a nozzle including a tip according to the
present
invention;
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Figure 2 is a cross section of an example embodiment of a nozzle according to
the
invention, also showing two alternative nozzle bodies in addition to that
engaged with
the tip; and
5 Figure 3 shows a cross section of the distal end of the tip, the locating
nut, and the
gate to a mould.
Detailed Description of the Drawings
Throughout the description like reference numerals will be used to refer to
like
features in different embodiments.
Referring to Fig. 1, an injection moulding nozzle according to the present
invention is
shown generally referenced 100.
The nozzle 100 includes a nozzle body 1 with a channel 2 therethrough
providing a
fluid path between an inlet 2a and an outlet 2b. A tip, substantially
comprising the
shank or main member 3, is positioned adjacent and engaged with the nozzle
body
1. The main member 3 includes a channel 4 therethrough providing a fluid flow
path
between an inlet 4a at a proximal end and at least one outlet 4b towards a
distal end
of the tip.
When in the correct position, as shown in Figure 2, the inlet 4a of the tip
substantially
aligns with the outlet 2b of the nozzle body, so that, in use, molten plastic
is able to
flow from a manifold or machine nozzle (not shown), through the channels 2 and
4,
and then into a mould (not shown) via the one or more outlet apertures 4b
provided
in the tip. In the illustrated embodiment, two outlet apertures 4b are
visible, although
the tip may comprise one or more such outlets.
The main member 3 in some embodiments may comprise a tip liner and a sleeve
(not shown) as described in PCT Patent Application No. PCT/NZ2007/000094
(published under No. WO 2007/123428) assigned to the assignee of the present
application, the contents of which are herein incorporated by reference.
According to
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the preferred embodiment, however, the main member 3 is provided as a single
piece as shown. The nozzle 100 will typically also be provided with a housing
or
cover (not shown) which is preferably attached to or integral with a heating
means
such an electrical element in intimate thermal contact with the main member 3,
in
particular a central portion thereof having a larger diameter and an outer
surface
which is preferably flush with those of the nozzle body 1 and locating nut 6.
The main member 3 of the tip is in use aligned relative to a mould gate 8 by
engagement with a locating means such as a locating nut 6, as shown in detail
in
Fig. 3. In a preferred embodiment the main member 3 has externally threaded
portions to engage a first threaded portion at the proximal end of the main
member 3
with the nozzle body 1 and a second threaded portion towards the distal end of
the
main member 3 for engagement with the locating nut 6, so that the main member
3
extends internally into both the nozzle body 1 and the locating nut 6 at
respective
ends.
The main member 3 is preferably made from a material which has a high thermal
conductivity, typically being higher than the nozzle body I and the locating
means 6.
In a preferred embodiment the main member 3 may be made from special wear-
resistant materials having a high thermal conductivity several times that of
steel, or
such other suitable material as may be known to those skilled in the art to
have a
suitable thermal conductivity and yield temperature. In at least one
embodiment the
tip is constructed from special materials that are at least approximately
three to five
times more thermally conductive than the nozzle body 1 and/or the housing.
In one embodiment the main member 3 has at least a central cylindrical
external
surface of greater diameter than the threaded portions, the central
cylindrical surface
being provided for intimate thermal contact with the heating means. Therefore,
the
tip has first and second portions of reduced diameter (which may coincide with
the
threaded portions as illustrated) adjacent to the inlet and outlet,
respectively, and a
central portion of increased diameter which contacts the heating means. Heat
is
thus applied to the tip through the larger diameter central portion of the
main
member 3, rather than heat being applied at either end of the tip as is the
case in
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certain tips of the prior art. Thus heat loss through to the mould is reduced
relative
to nozzles in which the heating means extends further towards the outlet of
the
nozzle, and the high thermal conductivity of the main member 3 allows a high
proportion of the heat absorbed from the heating means to flow into the
plastic in the
flow path 4 along the entire length thereof.
Although the tip is described throughout this document by way of example as
having
a generally circular cross-section of various diameters along its length, in
particular
including cylindrical and conical portions, the invention is not limited to
such shapes
and many variations or modifications are possible without departing from the
scope
of the invention.
The tip has a sufficient mass that it can act as a thermal reservoir. That is,
it has a
large thermal capacity compared to the plastic in the flow path 4. If the
temperature
of the plastic flowing through the tip is momentarily cooler than the required
temperature then the main member 3 preferably retains sufficient energy that
is able
to heat the plastic without a significant drop in the temperature of the tip.
Injection moulding nozzle tips of the prior art typically have a conical
tapered apex
portion 5 with outlet apertures provided close to the apex and thus the mould
gate 8.
However, according to the present invention the outlet apertures 4b are
provided at
or adjacent the base of the tapered portion 5 further towards the proximal end
of the
tip than is the case in nozzle tips of the prior art. The outlet apertures 4b
may
therefore be said to be provided in the main member 3 between the tapered
portion
5 and the proximal end of the tip, yet typically in a region of the tip
substantially
enclosed by the locating nut 6, e.g. substantially adjacent the threaded
portion
adapted to engage the locating nut 6. The outlet apertures 4b are therefore
provided
at the "top" of the cavity or bubble area between the tip and the locating nut
6 where
a bubble or resin layer insulating the tip from the mould forms in use,
providing a
substantially continuous fluid flow path along the full length of the bubble
area or
cavity between the tip and locating nut 6, as shown in Fig. 1. This encourages
continual flushing of the molten plastic and eliminates or at least minimizes
"hang up"
areas where plastic may stagnate or circulate.
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The position of the outlet apertures 4b means that the tapered portion of the
tip,
absent of any channel 4 or outlets 4b, also has the advantage of having a
greater
mass adjacent the mould gate and therefore may better regulate the temperature
of
the molten plastic as it is injected into the mould. It also aids in creating
a unified
melt flow since it allows greater time/distance for the melt flows from each
outlet 4b
to consolidate before reaching the gate.
According to a preferred embodiment, the tapered portion 5 comprises the
distal end
of an enlarged or bulbous portion 7 of the tip provided at or towards the
distal end of
the main member 3, wherein the one or more outlets 4b are provided between the
proximal end and the bulbous portion 7 of the tip. The bulbous portion 7 is
thus
provided between the or each outlet aperture 4b and the tapered portion 5, and
comprises a portion of the tip which has a diameter greater than that of the
main
member 3 at or adjacent the outlet apertures 4b. The tip therefore widens
towards
the distal end of the tip past the or each outlet 4b before narrowing to a
point in the
tapered apex portion 5.
The bulb is preferably shaped to create a cavity or melt flow area between the
tapered apex portion 5 and the gate 8 having a relatively long constant
section that
decreases in diameter, aiding to unify the melt before it exits the gate, thus
reducing
flow lines. At least a part of the tapered portion 5 may therefore be shaped
to
substantially match the contours of the mould gate 5 adjacent the apex.
The increased mass of the bulb not only helps retain heat in the tip, in
particular at
the apex adjacent the gate, while also increasing the outer surface area and
friction
for improved heat conductance, thus regulating the temperature of the molten
plastic
material after leaving the outlet aperture(s) 4b, but also occupies a
substantial part of
the gate chamber to such an extent that undue pressure losses are avoided. The
bulbous shape of the tip downstream from the outlet apertures 4b also helps
guide
the melt flow as it sweeps most of the plastic around the enlarged portion to
minimise circulation in the space between the tip and locating nut 6 and/or
mould
gate.
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The locating means (e.g. locating nut 6) may, if required, have a lower
thermal
conductivity than the tip to insulate the tip from the mould and may, for
example, be
made from steel or titanium. However, because the tip transfers heat so well
to the
flow path 4 and molten plastic flowing therethrough, it is not generally
necessary to
provide a locating means having a relatively low thermal conductivity. In some
embodiments a more conductive locating means may be used to assist in
dissipating
the heat generated by shear as the plastic leaves the outlet aperture(s).
Those
skilled in the art will recognize the circumstances in which the heat
generated by
shear is likely to require the use of a locating means which has relatively
good
thermal conductivity.
According to at least one embodiment of the invention, the outer surfaces of
the
tapered apex portion of the tip have a substantially concave cross-section in
the
generally longitudinal direction, wherein the angle of the outer surface of
the tapered
apex portion with respect to the main or longitudinal axis of the elongate
main
member 3 reduces towards the distal end of the tip. This concave shape may
comprise a concave cone having an inwardly-curved generally conical outer
surface,
or may alternatively comprise any other suitable shape or shapes having a
reduced
angle adjacent the apex. For example, the tapered apex portion of the tip may
alternatively resemble a first cone-shaped portion at the apex and having a
relatively
smaller angle with respect to the longitudinal axis, provided on one or more
truncated cone portions having relatively larger angles towards the outlet
apertures
4b. Those skilled in the art will appreciate that the concave-shaped tapered
apex
portion may therefore comprise a plurality of substantially linear and/or
curved outer
surfaces or cross-sections.
The purpose of the concave tip is to provide an apex area which is relatively
small in
diameter with respect to the gate of a mould with which the nozzle/tip is
engaged in
use. Variations in the alignment of the tip with respect to the gate, in
particular due
to thermal expansion of the tip, will therefore have a reduced affect on the
size of the
opening through which the plastic material is injected into the mould. The
concave
tip, as opposed to a standard conical or convex tip, also increases the volume
of
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material that can feed the gate area, thereby reducing shear on the materials
and
avoiding overheating of the tip during injection. Accordingly, the concave
tip, alone
or in combination with the aforementioned features, may give rise to improved
or
more consistent material flows and injection pressure, resulting in reduced
5 manufacturing times and/or improved mould product quality.
As previously described, the injection moulding nozzle tip of the present
invention is
adapted to engage at opposing ends with a nozzle body 1 and a locating nut 6,
preferably by way of externally threaded portions of the main member 3. The
nozzle
10 body 1 in turn is adapted to engage with a manifold (not shown) of an
injection
moulding system which distributes the plastic material to the or each nozzle
of the
system, while the locating nut 6 also engages or abuts with a mould gate 8 to
couple
the tip therewith and define a fluid flow path to the mould cavity. The main
member
3 therefore preferably forms an integrated tip and connector between the
nozzle
body 1 and locating nut 6.
Substituting an alternative nozzle body, e.g. nozzle body I la or I lb of Fig.
2, for the
nozzle body 1 shown engaged with the main member 3, the tip can be configured
for
engagement with a range of manifolds and may therefore be easily retrofitted
to a
number of different injection moulding systems. Thus, any injection moulding
system
can benefit from the advantages of a tip according to various embodiments of
the
present invention. Alternatively, or additionally, a tip/connector according
to the
present invention may be replaced by removing and replacing the tip from the
nozzle
body 1 and locating nut 6, without the need for necessarily replacing those
components.
Those skilled in the art will appreciate that the present invention may
therefore be
said to consist in an injection moulding tip and/or an injection moulding
nozzle,
manifold, or system including a tip as described herein.
From the foregoing it will be seen that the present invention provides an
injection
moulding nozzle and a tip therefor which is capable of improved injection
characteristics and heat transfer between a heater and molten plastic flowing
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through the nozzle. The main member conducts heat from an external surface
internally to the fluid flow path and projects internally of the body and the
locating
means so that heat is transferred efficiently to the molten plastic along the
substantial length of the main member, which includes a tapered apex beyond
one
or more outlet apertures to contact and transfer heat to the plastic prior to
injection
into the mould.
Unless the context clearly requires otherwise, throughout the description, the
words
"comprise", "comprising", and the like, are to be construed in an inclusive
sense as
opposed to an exclusive or exhaustive sense, that is to say, in the sense of
"including, but not limited to".
Although this invention has been described by way of example and with
reference to
possible embodiments thereof, it is to be understood that modifications or
improvements may be made thereto without departing from the scope of the
invention. The invention may also be said broadly to consist in the parts,
elements
and features referred to or indicated in the specification of the application,
individually or collectively, in any or all combinations of two or more of
said parts,
elements or features. Furthermore, where reference has been made to specific
components or integers of the invention having known equivalents, then such
equivalents are herein incorporated as if individually set forth.
Any discussion of the prior art throughout the specification should in no way
be
considered as an admission that such prior art is widely known or forms part
of
common general knowledge in the field.
