Note: Descriptions are shown in the official language in which they were submitted.
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HOT RUNNER WITH REMOVABLE GATE PAD
FIELD
[0001]This application relates to hot runner assemblies for injection molding
machines and to pads for locating a hot runner nozzle tip relative to a mold.
BACKGROUND
[0002] Injection molding is a process by which a molding material is injected
into a
mold and then cooled to form a solid molded article. A molding material, such
as,
for example, polyethylene terephthalate (PET) is placed in a plasticizing
unit, which
heats the molding material into a molten, flowable state. Molten molding
material is
then conveyed through a distribution network, often referred to as a "hot
runner",
and delivered to a mold through a nozzle.
[0003] Flow of molding material out of the nozzle is controlled at a gate. A
valve
stem in the nozzle may be extended to seal the gate and retracted to open the
gate. Unfortunately, typical designs are prone to wear due to misalignment and
are
difficult to service or replace.
SUMMARY
[0004] An example hot runner assembly for delivering molding material to a
mold
cavity of an injection molding machine through a mold inlet comprises: a
manifold
plate; a nozzle extending through the manifold plate, the nozzle having a
nozzle
outlet; a gate pad having an inlet end with an inlet opening and an outlet end
with a
gate aperture and a passage through said gate pad from the inlet opening to
the
gate aperture, the gate pad removably attached to the manifold plate so that
the
nozzle is received in the passage and the nozzle outlet is in communication
with
the mold inlet through the gate aperture; a valve stem within the nozzle,
movable
between an extended position, in which the valve stem seals the gate aperture
to
prevent flow of molding material therethrough, and a retracted position.
[0005] An example gate pad for an injection molding machine comprising a
manifold plate, a nozzle extending through the manifold plate and a valve stem
1
Ff= 31.
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within the nozzle movable between an extended position in which the valve stem
extends through an outlet of the nozzle and a retracted position, comprises: a
body
having an inlet end with an inlet opening and an outlet end with a gate
aperture,
and a passage through the body from the inlet opening to the gate aperture;
the
inlet end removably attachable to the manifold plate so that the nozzle is
received
in the passage through the inlet opening and the outlet of the nozzle is in
communication with the gate aperture, wherein the valve stem seals the gate
aperture in the extended position.
[0006] An example method of disassembling an injection molding machine
comprising a mold and a hot runner having a manifold plate comprises:
extending a
valve stem within a nozzle of the hot runner to form a seal with a gate
aperture in a
gate pad attached to the manifold plate, thereby preventing flow of molding
material
through the gate aperture; removing the mold from the hot runner with the seal
intact.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] In the figures, which illustrate by way of example only, embodiments of
this
invention:
[0008] FIG. 1 is a top schematic view of an injection molding machine;
[0009] FIG. 2A is an enlarged cross-sectional view of a sub-assembly of the
injection molding machine of FIG. 1 in a first operational state;
[0010] FIG. 2B is an enlarged cross-sectional view of the sub-assembly of FIG.
2A
in a second operational state;
[0011] FIG. 3 is an enlarged cross-sectional view of another sub-assembly of
the
injection molding machine of FIG. 1;
[0012] FIG. 4 is an enlarged cross-sectional view of another sub-assembly of
the
injection molding machine of FIG. 1;
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[0013] FIG. 5 is an enlarged cross-sectional view of an alternate sub-assembly
of
an injection molding machine;
[0014] FIG. 6 is an enlarged cross-sectional view of an alternate sub-assembly
of
an injection molding machine; and
[0015] FIG. 7 is an enlarged cross-sectional view of an alternate sub-assembly
of
an injection molding machine.
DETAILED DESCRIPTION
[0016] FIG. 1 depicts an example embodiment of an injection molding machine
100
for forming molded articles from molding material. Molding machine 100 has a
stationary platen 102 and a movable platen 104. A hot runner 106 and mold 108
are mounted between platens 102, 104. Hot runner 106 is mounted to stationary
platen 102. Mold 108 comprises a mold cavity plate 110 mounted to hot runner
106, and a mold core plate 112 mounted to moveable platen 104.
[0017] Moveable platen 104 is movable between a closed position, depicted in
FIG.
1, and an open position (not shown) in which movable platen 104 is withdrawn
away from stationary platen 102 along axis a-a (hereinafter referred to as the
longitudinal axis).
[0018] With moveable platen 104 in the closed position, mold cavity plate 110
and
core plate 112 abut one another and may be pressed together by a force exerted
on the platens.
[0019] In the closed position, a plurality of mold cavities 114 are defined
between
cavity plate 110 and core plate 112. Molten molding material may be injected
under pressure into mold cavities 114 and cooled to form molded parts. Two
such
cavities are depicted in FIG. 1, but mold 108 may have any number of cavities.
[0020] Cavities 114 receive molten molding material from a plasticizing unit
116
through hot runner 106. Plasticizing unit heats molding material to a desired
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temperature sufficient to render the molding material in a flowable state.
Plasticizing unit 116 may, for example, compress solid pellets of molding
material
with a screw or augur, heating the material and urging it toward cavities 114.
Other
suitable plasticizing units are well known to those skilled in the art.
[0021] Hot runner 106 comprises a backing plate 118 mounted to stationary
platen
102. A sprue bushing 126 is received through the backing plate and coupled to
a
manifold 124, for example using bolts or the like. Sprue bushing 126 has an
inner
passage for receiving molten molding material from plasticizing unit 116.
[0022]A manifold plate 120 is mounted to backing plate 118, for example, using
bolts or other suitable fasteners. A manifold pocket 122 is defined between
manifold plate 120 and backing plate 118. Manifold 124 is disposed within
manifold
pocket 122. Manifold 124 is attached to backing plate 118 and manifold plate
120
using alignment pins (not shown). The alignment pins may align manifold 124 to
backing plate 118 but may allow manifold 124 to float in the longitudinal
direction of
injection molding machine 100. Thermally-insulating spacers (not shown) may be
provided between manifold 124 and backing plate 118, manifold plate 120.
[0023]Manifold 124 has an inlet in fluid communication with sprue bushing 126
to
receive molding material. The inlet branches into a plurality of conduits (not
shown)
that run internally within manifold 124 from sprue bushing 126 to each of a
plurality
of nozzles 128, to deliver molding material thereto. Nozzles 128 may form part
of
larger assemblies, which may for example include one or more heaters (not
shown)
or seals (not shown).
[0024] Nozzles 128 are mounted to manifold 124, by conventional methods, well-
known to those skilled in the art. Nozzles 128 may, for example, be mounted
using
preloaded spring packs and aligning features such as pins. Each nozzle 128
extends through a passage 144 in manifold plate 120 to a corresponding cavity
114
to supply molding material thereto. Two nozzles 128 are depicted in FIG. 1,
however any number may be present.
[0025] Each of manifold plate 120, cavity plate 110 and core plate 112 have
alignment bores 103 extending longitudinally therethrough. Alignment pins 101
are
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mounted to backing plate 118, for example, using bolts or other suitable
fasteners
(not shown). Alignment pins 101 extend through alignment bores 103 to maintain
relative alignment between backing plate 118, manifold plate 120, cavity plate
110
and core plate 112.
[0026] FIGS. 2A-2B depict an example nozzle 128 in greater detail. As
illustrated,
nozzle 128 includes a housing 130 and a tip 132 threaded into housing 130.
Housing 130 and tip 132 define a continuous sealed internal passage 134
leading
to a nozzle outlet 136. Nozzle tip 132 tapers towards the end of nozzle 128. A
thermal insulating member 158 is disposed at the outlet end of nozzle tip 132
when
assembled. Thermal insulating member 158 has an aperture therethrough
corresponding to nozzle outlet 136.
[0027]A valve stem 138 is received in internal passage 134. Valve stem 138 is
movable between an extended position, as depicted in FIG. 2A, and a retracted
position, depicted in FIG. 2B. Valve stem 138 is movable by an actuator (not
shown), housed in backing plate 118. The actuator may, for example, be a
linear
actuator, such as a pneumatic, hydraulic or electric actuator. In its extended
position, valve stem 138 extends through nozzle outlet 136. In its retracted
position, valve stem 138 is withdrawn within internal passage 134 and is clear
of
nozzle outlet 136. The width of valve stem 138 is slightly less than that of
nozzle
outlet 136 so that, in its extended position, valve stem 138 substantially
blocks
nozzle outlet 136, but need not contact nozzle outlet 136 or form a positive
seal
therewith. In an example embodiment, there may be approximately 200 microns of
clearance between valve stem 138 and nozzle outlet 136.
[0028] Nozzle 128 is mounted to manifold 124 and is received in passage 144 of
manifold plate 120 without contacting manifold plate 120.
[0029]A gate pad insert 146 is removably attached to manifold plate 120 and
fits
over nozzle 128 to maintain alignment of nozzle 128 relative to manifold plate
120.
In some embodiments, gate pad insert 146 has a generally cylindrical body,
with an
inlet end 147 and an outlet end 149.
[0030] Inlet end 147 has external threads 148 which matingly engage threads
150
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in manifold plate 120 proximate the end of passage 144. Inlet end 147 thus
serves
as a retention element to removably attach gate pad insert 146 to manifold
plate
120.
[0031] Gate pad insert 146 includes external shoulder 168 and flange 170,
which
protrude outwardly. Shoulder 168, which may be annular, is received in a
corresponding pocket defined in manifold plate 120 at the end of passage 144.
Shoulder 168 bears tightly against manifold plate 120 and maintains alignment
of
gate pad insert 146 relative to manifold plate 120.
[0032] Flange 170 abuts the face of manifold plate 120 and maintains the
correct
longitudinal position of gate pad insert 146 relative to manifold plate 120.
That is,
flange 170 limits the distance gate pad insert 146 can be threaded into
manifold
plate 120.
[0033] Gate pad insert 146 has an internal passage 152 therethrough. Passage
152 tapers longitudinally from a wide inlet at its upstream end to a narrow
gate
aperture 160 at its downstream end. As used herein, the terms "upstream÷ and
"downstream" refer to the direction of flow of molding material. That is,
"downstream" is the direction toward cavities 114, and "upstream" is the
direction
toward plasticizing unit 116.
[0034] Nozzle 128 is received in passage 152 of gate pad insert 146. Passage
152
may include a shoulder 154. Upstream of shoulder 154, the width of passage 152
is much greater than that of nozzle 128 to permit a heater, such as a coil
heater to
be installed around nozzle 128, and to maintain an air gap between nozzle 128
and
gate pad 146. Downstream of shoulder 154, passage 152 is dimensioned to
tightly
fit nozzle 128. Gate pad 146 forms a seal 135 with nozzle housing 130
downstream of shoulder 154.
[0035] Proximate gate aperture 160, passage 152 may have a tapered shape
approximately complementary to that of nozzle tip 132. Thus, the end of nozzle
tip
132 is tightly received in passage 152 so that nozzle outlet 136 and valve
stem 138
align with gate aperture 160. A thermal insulating member 158 may be
compressed between nozzle tip 132 and gate pad insert 146, so that thermal
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insulating member 158 abuts the wall of passage 152. Thermal insulating member
158 may be formed, for example, from high-temperature resistant plastic and
may
form a thermal barrier between nozzle 128 and gate pad 146.
[0036] Gate aperture 160 is sized correspondingly to valve stem 138 so that,
in its
extended position valve stem 138 is received in gate aperture 160 and forms a
seal
therewith (FIG. 2A). Conversely, in its retracted position, valve stem 138 is
clear of
gate aperture 160 (FIG. 2B).
[0037]The tapered shapes of nozzle tip 132 and passage 152 may cooperate to
guide nozzle 128 into the correct position in gate pad insert 146 as gate pad
insert
146 is attached to manifold plate 120 by advancing inlet end 147 into passage
144.
[0038] Nozzle 128 is aligned with a mold cavity 114 to supply molding material
thereto. Mold cavity 114 may be defined by a mold cavity insert 140 received
in
cavity plate 110, and a mold core insert (not shown) received in core plate
112
(FIG. 1). Mold cavity insert 140 and the mold core insert define the outer and
inner
surfaces, respectively, of a part molded in cavity 114. Specifically, mold
cavity
insert 140 has a molding surface 141 which defines the outer surface of molded
parts. Mold cavity insert 140 has an inlet 142 (FIG. 2B) through which molding
material may be introduced into mold cavity 114.
[0039] Mold cavity insert 140 defines a recess 166 for receiving outlet end
149 of
gate pad insert 146. Outlet end 149 is generally cylindrical and has a lateral
surface 162 and flat end surface 164. Flat end surface 164 tightly abuts and
forms
a seal with cavity insert 140. Recess 166 may be sized to provide some
clearance
between recess 166 and lateral surface 162. Clearance between recess 166 and
lateral surface 162 allows for tolerance of some misalignment between gate pad
insert 146 and cavity insert 140 without gate pad insert 146 rubbing against
cavity
insert 140. In some embodiments, clearance between lateral surface 162 of
outlet
end 149 and recess 166 may be within approximately 0.5 mm to 1.0 mm.
[0040] One or both of cavity insert 140 and outlet end 149 of gate pad insert
146
may have chamfered corners 172. Chamfered corners may help guide outlet end
149 into recess 166.
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[0041] Inlet 142 of mold cavity insert 140 is aligned with gate aperture 160
of gate
pad insert 146, and thus, with nozzle outlet 136 and valve stem 138. Inlet 142
is
slightly larger than gate aperture 160, so that, within the alignment
tolerance
permitted by outlet end 149 and recess 166, gate aperture 160 and inlet 142
are
always in communication. That is, inlet 142 is sized so that, at the maximum
misalignment condition, gate aperture 160 and inlet 142 remain in flow
communication. Likewise, inlet 142 is sized so that valve stem 138 does not
contact mold cavity insert 140. That is, at the maximum misalignment
condition,
valve stem 138 can be moved to its extended position without contacting mold
cavity insert 140. In an example, the radius of inlet 142 may be larger than
that of
gate aperture 160 by approximately the same amount as or more than recess 166
is wider than outlet end 149 of gate pad insert 146. That is, if recess 166 is
sized to
provide 0.5 mm of clearance on each side of outlet end 149, the radius of
inlet
aperture 142 may be approximately 0.5 mm greater than that of gate outlet 160,
or
more.
(0042] As best shown in FIG. 2A, in its extended position, valve stem 138
extends
through nozzle outlet 136, seal member 158, gate aperture 160 and inlet 142.
Gate
aperture 160 is dimensioned to form a seal with valve stem 138 in the extended
position of valve stem 138, preventing molding material from flowing out of
nozzle
128. Backflow of molding material out of cavity 114 may be prevented by the
seal
formed between flat end surface 164 against cavity insert 140 and by the seal
between valve stem 138 and gate aperture 160.
[0043] Conversely, with valve stem 138 in its retracted position, as shown in
FIG.
2B, molding material is free to flow out of nozzle 128, through nozzle outlet
gate
aperture 160 and inlet 142 and into cavity 114.
(0044] The components of hot runner 106 and mold 108, including gate pad 146,
cavity insert 140 and nozzle 128, may be formed from metal. For example, the
components may be formed from stainless steel, such as 420 stainless steel.
Other metals may be used in other embodiments. As will be appreciated, the
components of injection molding machine 100 may be subjected to significant
mechanical and thermal loads during operation and may be subjected to
frictional
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wear due to movement of components. Accordingly, suitable materials are those
which have sufficient strength and surface hardness. All components may be
formed from identical materials, such as identical stainless steel alloys, or
different
components may be formed from different materials. For example, gate pad
insert
may be formed from a metal selected for relatively low thermal conductivity,
such
as titanium, and the cavity insert 140, or a part thereof, may be formed from
a metal
selected for high thermal conductivity, such as beryllium copper.
Alternatively, gate
pad 146 and cavity insert 140 may be formed of a combination of metals having
different thermal conductivities. Alternatively or additionally, components
may be
selected to have differing hardness so that certain components wear more than
others. For example, gate pad insert 146 may be formed of a softer metal than
valve stem 138 so that gate aperture 160 tends to wear, rather than valve stem
138, as the two rub together. The wear surfaces of gate pad 146 and valve stem
138 could be coated with wear-resistant coatings, such as diamond-chrome,
chrome, nickel-cobalt or cobalt, or other suitable coatings well known to
those
skilled in the art.
[0045] In use, injection molding machine 100 is operated in molding cycles. At
the
beginning of a molding cycle, moveable platen 104 is in its closed position as
depicted in FIG. 1 and force is exerted on the platens 102, 104 to urge mold
cavity
plate 110 and mold core plate 112 together. At least some of this force may be
borne by gate pad insert 146, urging flat end surface 164 against mold cavity
insert
140, which may thereby form a seal between flat end surface 164 and mold
cavity
insert 140. Valve stem 138 is withdrawn to its retracted position, shown in
FIG. 2B,
and molding material is injected under pressure through nozzle 128 and into
cavity
114. Molding material travels through nozzle outlet 136, gate aperture 160 and
inlet 142.
[0046]After injection is completed, valve stem 138 is moved to its extended
position, as shown in FIG. 2A. Valve stem 138 forms a seal with gate aperture
160
and seal member 158, stopping the flow of molding material out of nozzle 128.
The
seal between valve stem 138 and gate aperture 160 cooperates with the tight
fit
between flat end surface 164 and mold cavity insert 140 to prevent molding
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material from flowing out of mold cavity 114.
[0047] Injection molding machine 100 is held in its closed position and valve
stem
138 is held in its extended position while molding material in cavity 114 is
cooled.
After cooling is complete, injection molding machine 100 may be removed, and
the
newly-molded part may be removed from cavity 114. Injection molding machine
100 may then be returned to the closed state to begin a new molding cycle.
[0048] During operation of injection molding machine 100, hot runner 106 and
the
components thereof are heated to an elevated temperature, referred to as the
process temperature, for maintaining the molten state of the molding material.
Conversely, mold 108 and its components typically are actively cooled, to
promote
cooling and setting of molding material after injection into a mold. It
therefore may
be desired to maintain nozzle 128 at a high temperature, and mold cavity plate
110
and cavity insert 140 at a low temperature. Conveniently, gate pad insert 146
may
provide some thermal insulation between nozzle 128 and cavity plate 110 and
cavity insert 140.
[0049]As will be apparent, repetitive motion of valve stem 138 between its
extended and retracted positions may cause valve stem 138 to rub against
nozzle
tip 132 and gate pad insert 146, which may cause wearing of valve stem 138,
nozzle outlet 136 or gate aperture 160.
[0050] Conveniently, installation of gate pad insert 146 brings valve stem 138
into
more precise alignment with gate aperture 160 by more precisely aligning
nozzle tip
132 in passage 152. This may limit rubbing of valve stem 138 against gate pad
insert 146, which may in turn limit wearing of valve stem 138 or gate aperture
160.
[0051] Moreover, since valve stem 138 forms a seal with gate aperture 160,
inlet
142 of cavity 114 need not seal with valve stem 138 and thus may be
dimensioned
so that it is slightly larger than valve stem 138. This may provide clearance
which
may limit or eliminate rubbing between valve stem 138 and cavity insert 140.
[0052] If wear occurs, hot runner 106 or mold 108 of injection molding machine
100
may be disassembled and reassembled to replace gate pad insert 146 or cavity
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insert 140. Alternatively or additionally, hot runner 106 and mold 108 may be
removed from stationary platen 102 and movable platen 104 to install a
replacement hot runner 106 and mold 108 or to perform maintenance. To that
end,
FIGS. 3-4 depict intermediate states of assembly of hot runner 106 and mold
108.
[0053] Hot runner 106 is assembled by mounting backing plate 118 to stationary
platen 102, and mounting manifold 124 to backing plate 118 (see FIG. 1).
Nozzles
128 may be mounted to manifold 124 and manifold plate 120 may be mounted to
backing plate 118. As noted above, components may be secured to one another
using bolts or other suitable fasteners. Alignment pins 101 fixed to backing
plate
118 are received in corresponding bores (not shown) in manifold plate 120 to
ensure correct location of manifold plate 120 relative to backing plate 110.
[0054] Each gate pad insert 146 may be attached to manifold plate 120. One
gate
pad insert 146 is attached at the end of each passage 144 and receives the end
of
one nozzle 128. As depicted in FIG. 3, gate pad insert 146 is attached to
manifold
plate 120 by advancing threads 148 of inlet end 147 along corresponding
threads
150 in manifold plate 120 proximate the end of passage 144. As inlet end 147
of
gate pad insert 146 advances into manifold plate 120, the end of nozzle 128 is
received in internal passage 152 of gate pad insert 146. If nozzle 128 is
misaligned
prior to gate pad insert 146 being threaded, the complementary tapered shapes
of
internal passage 152 and nozzle tip 132 cooperate to center nozzle 128 within
gate
pad insert 146 by aligning nozzle 128 in gate pad insert recess 152. Thus,
once
gate pad insert 146 is fully threaded into manifold plate 120, valve stem 138
is
aligned with gate aperture 160. Simultaneously, shoulder 168 is received in
its
corresponding notch in passage 144, centering and squaring gate pad insert
146.
[0055]As shown in FIG. 4, cavity insert 140 is installed into a bore 111 in
cavity
plate 110 and cavity plate 110 is mounted to manifold plate 120. Cavity insert
140
is slid into cavity plate 110 and held in cavity plate 110, for example by
using a
washer and screw. Alignment pins 101 may be received in corresponding bores
103 in cavity plate 110 to ensure correct location of cavity plate 110
relative to
manifold plate 120.
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[0056]Alignment of cavity plate 110 with manifold plate 120 likewise aligns
cavity
insert 140 with gate pad insert 146, since the latter is aligned with manifold
plate
120 by shoulder 168.
[0057]As cavity plate 110 is secured to manifold plate 120, outlet end 149 of
gate
pad insert 146 is received in recess 166 of cavity insert 140. As noted above,
end
surface 164 of gate pad insert 146 tightly abuts mold cavity insert 140, and
some
clearance exists between lateral surface 162 of gate pad insert 146 and cavity
inset
140. Due to the clearance between lateral surface 162 of gate pad insert 146
and
cavity insert 140, some misalignment may occur between manifold plate 120 and
cavity plate 110 without lateral surface 162 of gate pad insert 146 rubbing
against
cavity insert 140.
[0058] If misalignment occurs during assembly, chamfered corners 172 of gate
insert pad 146 and cavity insert 140 may help to guide outlet end 149 of gate
pad
insert 146 into recess 166. Specifically, chamfered corners 172 may slide
against
one another to help guide gate pad insert 146 into recess 166 of cavity insert
140.
Once cavity plate 110 is installed and gate pad insert 146 is received in
recess 166
of cavity insert 140, nozzle outlet 136, valve stem 138 and gate aperture 160
align
with inlet 142 of cavity insert, to provide fluid communication between
aperture 160
and inlet 142.
[0059] The core side of mold 108 is assembled by mounting mold core plate 112
to
movable platen 104 and closing injection molding machine 100 (see FIG. 1).
Alignment pins 101 are received in bores 103 in mold core plate 112 to
maintain
correct positioning of mold core plate 112 relative to cavity plate 110 and
manifold
plate 120.
[0060] To replace or repair components, hot runner 106 may be partially or
fully
disassembled.
[0061] To repair or replace gate pad insert 146, injection molding machine 100
is
opened and cavity plate 110 is removed. Gate pad insert 146 may then be
removed and replaced or repaired. Specifically, gate pad insert 146 may be
removed by detaching its retention device, namely, backing threads 148 off
from
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threads 150.
[0062] Conveniently, gate pad insert 146 does not form any part of mold cavity
114.
That is, molding surface 141 is defined entirely by cavity insert 140. As
such,
fabrication of gate pad insert 146 may require relatively little custom
machining and
gate pad insert 146 may be produced relatively quickly and inexpensively
compared to cavity insert 140. Moreover, gate pad insert 146 may be replaced
or
repaired without removing cavity insert 140 from cavity plate 110.
[0063] Gate pad insert 146 may reduce or prevent contact between valve stem
138
and cavity insert 140 and therefore may reduce or prevent wear of cavity
insert 140.
Cavity insert 140 is typically custom-machined to define molding surface 141.
Accordingly, replacement of cavity insert 140 may be relatively expensive and
long
lead times may be required to perform custom machining. Thus, avoiding a need
to
replace cavity insert 140 may represent significant cost savings.
[0064] Nevertheless, it may periodically be desired to replace or perform
maintenance on cavity insert 140 or to replace cavity plate 110 and cavity
insert
140 with another cavity plate and insert. To do so, injection molding machine
100
may be stopped in its open position, with valve stem 138 in its extended
position
and sealing gate aperture 160. Cavity plate 110 may then be removed. Cavity
insert 140 may then be removed from cavity plate 110 and repaired or replaced,
or
another cavity plate with another cavity insert may be installed.
Conveniently, it
may be possible to perform such maintenance or replacement of cavity insert
140
without breaking the seal between valve stem 138 and gate aperture 160.
Accordingly, as will be appreciated by skilled persons, it may also be
possible to
maintain plasticizing unit 116 in its operating state. That is, molding
material within
plasticizing unit 116, manifold 124 and nozzle 128 may be maintained in its
molten
state, at a molding process temperature, without being evacuated from
injection
molding machine 100. This may reduce the length of time for which molding
operation of injection molding machine 100 is stopped in order to repair or
replace
mold components.
[0065] As depicted in FIGS. 2A-2B and 3-4, inlet end 147 of gate pad insert
146
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includes threads 148 which serve as a retention element to removably attach
the
gate pad insert to manifold plate 120. In other embodiments, gate pad inserts
may
have different retention elements.
[0066] FIG. 5 depicts one such gate pad insert 246, attached to a manifold
plate
220. Gate pad insert 246 and manifold plate 220 are similar to gate pad insert
146
and manifold plate 120, with like features being indicated with like numerals.
[0067] Gate pad insert 246 includes a body with an inlet end 247 and an outlet
end
249. Inlet end 247 is slightly wider than passage 244 of manifold plate 220 so
that
inlet end 247 and passage 244 form an interference fit. In an example, inlet
end
247 may be approximately 5-10 microns wider than passage 244. Inlet end 247 is
pressed into passage 244 and is removably retained therein. Thus, inlet end
247
serves as a retention member to removably attach gate pad insert 246 to
manifold
plate 220. Due to the interference fit between inlet end 247 and passage 244,
pressing inlet end 247 into passage 244 also centers gate pad insert 246
relative to
passage 244. Gate pad insert 246 a flange 270 that abuts manifold plate 220
when gate pad insert 246 is attached thereto. Flange 270 may be annular, for
example, if gate pad insert 246 is circular in cross-section. Flange 270
limits the
distance inlet end 247 can be inserted into passage 244 and holds gate pad
insert
246 square to manifold plate 220.
[0068] FIG. 6 depicts another gate pad insert 346, attached to a manifold
plate 320.
Gate pad insert 346 and manifold plate 320 are similar to gate pad insert 146
and
manifold plate 120, with like features being indicated with like numerals.
[0069] Gate pad insert 346 includes a body with an inlet end 347 and an outlet
end
349. Inlet end 347 has an annular notch 352 in which a lock ring 348 is
retained.
Manifold plate 320 has a corresponding annular notch 350 defined in the wall
of
passage 344. Inlet end 347 may be inserted into passage 344 so that lock ring
348
is received in notch 350. Lock ring 348 then attaches gate pad insert 346 to
manifold plate 320. Gate pad insert 346 may be removed by applying force to
gate
pad insert 346 sufficient to dislodge lock ring 348 from notch 350.
[0070] FIG. 7 depicts three gate pad inserts 446 attached to a manifold plate
420.
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Each gate pad insert has an inlet end 447 and an outlet end 449. Each inlet
end
447 is configured to be received within a corresponding passage 444 of
manifold
plate 420. Each outlet end 449 is configured to be received in a recess 166 of
a
cavity insert 140 (FIG 2A).
[0071] Each gate pad insert 446 has a flange 470 protruding outwardly. Flanges
470 abut manifold plate 420. A series of bolts 448 serve as retention elements
to
removably attach gate pad inserts 446 to manifold plate 420. Specifically,
each bolt
448 is received in a corresponding bore 450 in manifold plate 420. The head of
each bolt can overlie flanges 470 of two adjacent gate pad inserts 446 and,
when
tightened against manifold plate 420, squeezes flanges 470 against manifold
plate
420 to attach gate pad inserts.
[0072]As depicted, gate pad inserts 146/246/346/446 are cylindrical, as is the
corresponding recess 152 in mold cavity insert 140. However, in other
embodiments, gate pad inserts may have other geometries. For example, a gate
pad insert may be conical or frustoconical, tapering toward the gate aperture.
The
mold cavity insert would be configured to define a mating recess. Other gate
pad
geometries are possible. Suitable gate pad shapes which permit gate pads to be
matingly received in a corresponding recess in the mold cavity insert, and
which
allow the gate aperture and mold cavity inlet to be aligned will be apparent
to those
skilled in the art.
[0073] Of course, the above described embodiments are intended to be
illustrative only and in no way limiting. The described embodiments are
susceptible
to many modifications of form, arrangement of parts, details and order of
operation.
The invention, rather, is intended to encompass all such modification within
its
scope, as defined by the claims.
