Note: Descriptions are shown in the official language in which they were submitted.
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THREE-PIECE MOLDING MANIFOLD
Field of the Invention
The present invention relates to molding manifolds, particularly to hot runner
manifolds for distributing molten materials to mold cavities_
Background of the Invention
Multi-cavity molding, in particular for injection molding, is widely used for
manufacturing multiple parts in a single mold during each cyGe. Manifolds are
required to direct molten material, e.g. plastics and metals, to a number of
outlet ports
through flow channels so that the molten material can be directed to multiple
cavities
to form parts. Hot runner manifolds use electric heating elements to keep the
temperature of flow channels at the melting temperature of the molten
material.
During a production run, the heated material remains molten in the flow
channels
between shots, hence reducing material waste in the runner system and reducing
the
amount of finishing work required for the final parts.
Hot runner manifolds are widely used and may be the only economic way to
manufacture multiple small parts in one shot. As the hot nrnner manifolds
require
embedded electric heating elements to keep the material molten in flow
channels, it is
critical to ensure that a sound seal is obtained around the flow channels to
reduce or
eliminate leaking of molten material to the heating elements or the outside of
the
manifold. In addition, the manifold design preferably allows the heating
elements to
be placed in such a way that an even temperature gradient across the mold can
be
achieved.
United States Patent 5,496,168 issued March 5, 1996 to Renwick describes a
hot runner manifold in which matching grooves are machined in opposing
surfaces of
two steel plates to fomn flow channels as well as separated heating element
channels.
Heating elements and their channels are furnace brazed together, while the
matching
surfaces of the two steel plates are brazed to form an integrated manifold.
This design
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is complex requiring an inordinate amount of machining to produce the filling
ducts/recesses and air ducts leading to heating element channels, and the
brazing
ducts leading to one matching surface. Further, considerable amount of worN;
is
require to tack-weld individual filling tubes in a recess over each filling
duct, fill braze
powder into the ducts/tubes, and machine out filling tubes after furnace
brazing.
Furthermore, expensive vacuum furnace equipment is require to braze the
heating
elements and braze the two halves of the manifold into an integrated unit.
Still further,
brazing requires heating the entire manifold to about 1925°F, which
deteriorates the
mechanical properties of the manifold material and may cause deformation of
the
entire manifold. Yet further, the entire procedure to produce the integrated
manifold
requires a longer production cycle. Finally, furnace brazing may induce excess
brazing material to leak into the flow channel, which will require expensive
polishing
procedures to clean.
United States Patent 4,648,546 issued March 10, 1987 to Gellert describes a
composite plate method of manufacturing an integrated hot runner manifold. A
manifold having two-halves is machined with matching grooves for flow
channels, and
another channel is machined on the upper external surface for the heating
elements.
Furnace brazing is used to seal the heating elements with the channels and to
seal the
matching surfaces of the two halves of the manifold.
United States Patent 4,761,343 issued August 2, 1988 to Gellert describes a
manifold system having a bridging composite plate manifold interconnecting a
number
of support composite plate manifolds with different flow passage orientations
to
improve streamlined and uniform flow and reduce pressure drop while allowing
flexibility of system design for different applications.
United Stated Patent 5,227,179 issued July 13, 1993 to Benenati describes a
manifold assembly having interlocking components to contain the high pressure
generated in the injection molding presses. A duct structure is designed to
provide
passages for the heated plastic. The duct contains a tubular member for flow
channel,
which is embraced by a two-half interlocking conduit cover. Four heating
elements are
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embedded and sealed below the external surfaces at the four corners of the two
halves to heat the flow channel. Manufacturing of the individual duct and
interNock
elements is very tabor intensive.
United States Patent 6,749,422 issued June 15, 2004 to Yu describes a hot
runner manifold having two separable halves with matching grooves to form flow
channels. Molten plastic flows through ground channel pipes within the
grooves. The
flow channels are heated by heaters located in grooves on the external surface
of
manifold halves. The pipes are covered by copper plates, which act to improve
heat
transfer from the heaters to the flow channels to keep the plastic in a molten
state.
Manufacturing interconnected channel pipes is complex and expensive.
In United States Patents 4,648,546, 4,761,343, 5,227,179 and 6,749,422, all
flow channels are located at the matching surfaces of two halves of the
manifold, while
heating element channels are located on external surfaces. While reducing the
risk of
plastic leaking into the heater element channels, these designs are costly to
manufacture, undesirably large and/or inefficient at heating the flow
channels.
United States Patent 6,099,292 issued August 8, 2000 to McGrevy describes a
hot runner manifold having a single block with flow channels machined therein.
A
serpentine groove is machined into the surface of the block to accept a heat
conductive assembly, the heat conductive assembly being a conduit having a
heater
element therein. The serpentine groove and heat conductive assembly
essentially
parallels the path of the flow channels in the block. In this design, the
manifold is a
single block and the heater element is on the outside surface of the block.
While
reducing the risk of plastic leaking into the heater element channels, this
design is
costly to manufacture and inefficient at heating the flow channels.
German Patent Publication 10243387 published March 18, 2004 to Holger
describes a hot runner manifold system in which a first hot runner system may
be
connected to a second hot runner system. Each hot runner system may be a
single
block with grooves therein or two halves with grooves between them. Electric
heater
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elements are used to heat the flow channels. There is no provision for sealing
the flow
channels away from the heater elements.
Japanese Patent Publications 5200786 and 5200787 both published August 10,
1993 to Katsutoshi et al, describe a hot runner manifold having two halves in
which
leakage of resin from the runner is prevented by means of a core inserted into
recessed grooves that surround the hot runner in both halves of the manifold.
A
recession in the core collects resin that leaks between the two halves and the
pressure
of the resin forces the core to tightly fit into the recessed grooves thereby
forming a
seal to prevent further leakage of the resin. Such a sealing method is not
efficient and
prone to failure. Furthermore, this design permits resin to pool in the
recession and
permits resin pooled in the recession to bleed back into the hot runner
channel
contaminating subsequent shots of resin. Thus, this design limits the ability
to change
resin type or color without disassembling the entire manifold.
Despite advances that have been made in the art, there remains a need for
improved manifolds for distributing molten material to mold cavities, in
particular
improved hot runner manifolds in which leakage of molten material from the
runners is
reduced.
Summary of the Invention
There is provided a molding manifold comprising: one or more inlet ports and
one or more outlet ports; a first half having one or more flow grooves; a
cover piece
having one or more flow grooves complementary to the flow grooves of the first
half,
the cover piece covering the one or more flow grooves of the first half, the
flow
grooves of the first half and cover piece together forming flow channels for
distributing
molten material from the one or more inlet ports to the one or more outlet
ports, the
cover piece engaged with the first half to reduce or eliminate leakage of
molten
material out of the flow channels; a second half having a cavity for receiving
the cover
piece, the second half securable to the first half; and, one or more heater
grooves in
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the first half, second half or both the first half and second half for
receiving one or
more heating elements for heating the flow channels.
The cover piece covers the flow grooves of the first half so that molten
material
is contained within the flow channels. The cover piece is engaged with the
first half
5 preferably by welding, bolts, clamps, pressure from the second half, an
adhesive, or a
combination thereof. Flow channels formed from the flow grooves of the first
half and
the cover piece are preferably hermetically sealed at an interface between the
first half
and the cover piece to completely prevent leakage of molten material out of
the flow
channels. The hermetic seal should be able to withstand the pressure generated
by
the molten material in the flow channels. In one embodiment, the cover piece
is
welded to the first half at the interface between the cover piece and the
first half.
The cover piece may have any desired size and shape. To promote better
sealing, the cover piece preferably has a shape and dimensions that just
covers the
flow grooves of the first half. Thus, the surface area of the interface
between the cover
piece and the first half is as small as possible while permitting total
coverage of the
flow grooves of the first half. Enough of an interface should be provided so
that a
good seal can be obtained while reducing the possibility of molten material
bleeding
into the interface between the cover piece and first half. The exact shape and
dimensions of the cover piece are a matter of choice by one skilled in the art
considering the specific application of the manifold and the specific means
for
engaging the cover piece with the first half.
Where welding is used to engage the cover piece with the first half, it is
advantageous to bevel the edges of the cover piece and the first half's flow
grooves at
the interface. Beveling the edges leads to a good weld line without leaving a
ridge that
could interfere with the way in which the cover piece is accommodated in the
cavity of
the second half.
The cover piece is received in a cavify of the second half. Preferably, the
size
and shape of the cavity is complementary to the size and shape of the cover
piece so
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that the cover piece just fits within the cavity. The cavity may be open-
topped such
that the top surface of the cover piece is flush with or protrudes from the
top surface of
the second half, or the cavity may surround the cover-piece on three sides. In
other
embodiments, the cavity may be designed so that the second half surrounds the
cover
piece at strategic locations with other locations being flush with or
protruding from the
surface of the second half. In embodiments where the top of the cover-piece is
at
least partially covered by the second half, pressure exerted by the second
half when it
is secured to the first half may serve to engage the cover piece with the
first half. The
second half should not cover the flow grooves of the cover piece.
The second half is securable to the first half by securement means, for
example
by welding, bolts, clamps, adhesives or a combination thereof. Preferably, the
second
half has a size and shape complementary to the first half.
Heater grooves in the first half, second half or both the first and second
halves
receive heating elements for heating the flow channels. The heater grooves
preferably
follow a similar path as the flow channels. The heater grooves are preferably
as close
as possible to the flow channels to provide more efficient heating. The cover
piece
should not cover the heater channels in order to keep the flow channels
separate from
the heater channels. Since the cover piece reduces or eliminates leakage of
molten
material out of the flow channels, there is no need to braze the heater
grooves or the
heating elements in the heater grooves. The heating element is preferably an
electric
heater coil commonly used in the art. The heater grooves preferably have
openings at
the edge of the manifold for contact with a power source.
Preferably, the first and second halves have complementary heater grooves on
their inner surtaces. Together, the heater grooves of the first and second
halves form
one or more heater channels for housing the heater elements.
The inlet ports receive molten material from a source. The inlet ports are in
fluid communication with the flow channels and the flow channels distribute
the molten
material to the outlet ports, which are in fluid communication with the flow
channels.
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From the outlet ports molten material is fed into mold cavities for forming
objects.
There may be any number of inlet and outlet ports. Inlet and outlet ports may
be
located anywhere on the manifold. The nature of the molding operation will
dictate
numbers and locations of the inlet and outlet ports.
Preferably, the inlet and outlet ports are oriented parallel to each other and
perpendicular to the flow channels. Preferably, the inlet ports are on the top
of the
manifold and the outlet ports on the bottom. Preferably, the bottom surface of
the
manifold is an outside surface of the first half and the top of the manifold
is an outside
surtace of the cover piece, the second half or both the cover piece and second
half.
Preferably the inlet ports are in the cover piece. In one embodiment, there is
a single
inlet port in the cover piece. The number of outlet ports depends on the
number of
parts desired to be made in one shot. Preferably, the outlet ports are in the
first half.
The molten material may comprise, for example, a plastic (e.g. thermoplastic
polymers, elastomers, rubbers, composite polymers, blends thereof, etc.) or a
metal
(e.g. aluminum, magnesium). The parts of the manifold, i.e. the first half,
second half
and cover piece, may comprise any suitable material for the particular molding
operation desired. For example, for injection molding of plastics the parts of
the
manifold may comprise, for example, P20 or H13 tool steel, Ramax 2 tool steel
or 420
stainless steel. For die casting of metals, the parts of the manifold may
comprise, for
example, H 13 tool steel.
Any welds used to between the cover piece and first half, or between the first
half and second half preferably comprise a welding material that is compatible
with the
material which comprises the manifold parts. Suitable welding processes are
generally known to one skilled in the art, for example gas tungsten arc
welding
(GTAW) and shielded metal arc welding (SMAW). Care should be taken during
welding to ensure proper closure of the intertace between the first half and
the cover
piece without distorting the flow channels. Good welding technique ensures
that the
cover piece will fit properly into the cavity of the second half after
welding, and
produces weld lines that resist internal pressure in the flow channels without
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developing warps or cracks. Any bolts used preferably match the strength and
coefficient of expansion of the materials used in the manifold parts. Any
adhesives
used should be compatible with the parts of the manifold.
A process for fabricating a molding manifold comprises: machining a first half
to include a plurality of outlet ports and to include flow grooves for flow
channels in
fluid communication with the outlet ports; machining a cover piece to include
an inlet
port and to include flow grooves in fluid communication with the inlet port,
the flow
grooves of the cover piece complementary to the flow grooves of the first
half;
machining a second half to include a cavity for receiving the cover piece;
machining
heater grooves into the first half, the second half or both the first and
second halves;
engaging the cover piece on the first half so that the flow grooves of the
first half and
the flow grooves of the cover piece match up to form sealed flow channels for
molten
material; placing one or more heater elements in the heater channels; placing
the
second half on the first half so that the cover piece fits within the cavity;
and, securing
the second half to the first half.
In a preferred process for fabricating a manifold of the present invention, a
first
half is machined to include flow grooves for flow channels, heater grooves for
heating
elements and outlet ports for molten material. A cover piece is machined to
include an
inlet port and complementary flow grooves to the flow grooves in the first
half. The
size of the cover piece is designed to cover the width of the flow channels
plus enough
distance on each side of the flow channel for welding (e.g. about 0.125 inch).
The
heater grooves are machined in the first half as close as possible to the flow
grooves
leaving enough room for a weld between the cover piece and the first half. A
second
half having the same perimeter dimensions as the first half is machined to
include a
cavity within which the cover piece may fit, and to include complementary
heater
grooves to the heater grooves in the first half.
After the individual parts of the manifold are machined, the cover piece is
placed vn the first half so that the complementary flow grooves match up. A
hermetically sealed weld is produced continuously around the perimeter of the
cover
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piece to seal the cover piece to the first half. Heating elements (e.g.
electric heating
coils) are placed in the heater grooves of the first half. The second half is
placed aver
the first half such that the complementary heater grooves match up with the
heating
elements encapsulated therein, and the cover piece matches up with and fits
within
the cavity. The second half is then secured to the first half, for example by
stitch
welding at points along the perimeter where the first and second halves meet.
The
cover piece may also be stitch welded to the second half if desired should the
cover
piece be flush with or protrude beyond the outside surface of the second half.
The
manifold is then machined to its final dimension.
Three-piece molding manifolds of the present invention advantageously provide
greater versatility in design permitting use in a greater variety of
applications.
Advantageously, manifolds of the present invention seal flow channels away
from
heating elements while permitting a variety of methods of securing the halves
of the
manifold together. This provides the option of being able to open the manifold
and
replace the heating elements without having to damage the manifold. Brazing of
the
heater channels, brazing of the heating elements in the heater channels and
brazing of
the two halves together is not required thereby greatly simplifying design and
machining of the manifold. Further, since no brazing is required, time
consuming post-
brazing polishing is also not required. Manifolds may be manufactured more
quickly at
less cost without a reduction in performance of the manifold.
Further features of the invention will be described or will become apparent in
the course of the following detailed description.
Brief Description of the Drawings
In order that the invention may be more clearly understood, embodiments
thereof will now be described in detail by way of example, with reference to
the
accompanying drawings, in which:
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Fig. 1 is an exploded perspective view of a three-piece 4-port manifiold in
accordance with the present invention showing a first half, a cover piece and
a second
half;
Fig. 2 is an exploded perspective view of the manifold of Fig. 1 in an upside
5 down orientation showing the cover piece inserted within a cavity of the
second half;
Fig. 3 is a perspective view showing the manifold of Fig. 1 in an assembled
configuration;
Fig. 4 is a top view of the first half of the manifold of Fig. 1;
Fig. 5 is a bottom view of the cover piece of the manifold of Fig. 1;
10 Fig. 6 is a bottom view of the second half of the manifold of Fig. 1;
Fig. 7 is an exploded cross-sectional view through A-A of Fig. 3;
Fig. 8 is a top schematic view of a three-piece 24-port manifold in accordance
with the present invention;
Fig. 9 is a cross-sectional view taken through B-B of Fig. 8;
Fig. 10 is an exploded cross-sectional view of an arm of alternate embodiment
of a manifold of the present invention;
Fig. 11 is an exploded cross-sectional view of an arm of another alternate
embodiment of a manifold of the present invention; and,
Fig. 12 is an exploded cross-sectional view of an arm of yet another alternate
embodiment of a manifold of the present invention.
Description of Preferred Embodiments
Referring to Figs. 1-7, a three-piece 4-port manifold comprises first half 10,
cover piece 20 and second half 30. First half 10 comprises flow grooves 11
radiating
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from a central point and terminating in outlet ports 12. Outlet ports 12 are
perpendicular to flow grooves 11 and open out to the bottom of first half 10.
First half
also has heater groove 13 for receiving an electrical heating coil (not
shown).
Heater groove 13 terminates at openings 14 through which the terminals of the
heater
5 coil may protrude out the side of first half 10.
Cover piece 20 comprises flow grooves 21 complementary to flow grooves 11
on first half 10. When assembled as shown in Fig. 3, flow grooves 11 match up
with
flow grooves 21 as illustrated in Fig. 7 to form flow channels through which
molten
plastic may flow. Cover piece 20 comprises central inlet port 22 for receiving
molten
10 plastic perpendicular to flow grooves 21. Cover piece 20 is just large
enough to
accommodate flow grooves 21 and cover flow grooves 11 without covering any
part of
heater groove 13. The interface between the cover piece and the first half is
sealed
using welding, cyanoacrylate adhesive or some other fastening methods when the
manifold is assembled.
Top half 30 comprises cavity 31 having a size and shape complementary to
cover piece 20. As best seen in Figs. 2, 3 and 7, cover piece 20 fits snugly
in cavity
31 so that the top of the cover piece is flush with the top of the second
half. Second
half 30 also comprises heater groove 33 complementary to heater groove 13 on
first
half 10. When the manifold is assembled as shown in Fig. 3, heater groove 31
matches up with heater groove 11 as illustrated in Fig. 7 to form a heater
channel
within which the electrical heating coil (not shown) is encapsulated. Heater
groove 31
terminates in openings 34 through which the terminals of the heater coil may
protrude
out the side of second half 10. Openings 14 and 34 match up when the manifold
is
assembled. The perimeter of second half 30 has a complementary shape to the
perimeter of first half 10. Top half 30 is secured to first half 10 by stitch
welding at
interface 39 (Fig. 3).
In use, the assembled manifold has an electrical heater coil encapsulated in
the
heater channel formed from heater grooves 13 and 33. A shot of molten plastic
is
injected into inlet port 22 and molten plastic is distributed through four
flow channels
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formed from flow grooves 11 and 21 to be forced out through the four outlet
ports 22
into four mold cavities where plastic objects are formed. The mold cavities
are
replaced with empty mold cavities and another shot of molten plastic is
delivered in the
same manner. The heater coil keeps the plastic molten during the process so
that
shots may be made consecutively without opening the manifold. Should the
heater
coil malfunction, the second half of the manifold may be separated from the
first half to
replace the heater coil without opening the flow channels, therefore, the
manifold may
be used again.
Fig. 8 is a schematic representation of a three-piece 24-port manifold 40
having
24 outlet ports 42 (only one labeled) in the first half in fluid communication
with a
plurality of flow channels 41. A single central inlet port 45 in the cover
piece is in 1'luid
communication with the flow channels and receives molten plastic from an
injection
machine. Molten plastic injected into the inlet port is distributed through
the flow
channels and out the 24 outlet ports into 24 mold cavities. Four heater coils
44 (only
one labeled) in four heater channels 43 (only one labeled) follow the general
path of
the flow channels and maintain the plastic in the flow channels in a molten
state. The
second half is secured to the first half by a plurality of bolts 46 (only one
labeled).
Fig. 9 depicts a cross-section through B-B of Fig. 8 illustrating the
relationship
between first half 47, cover piece 48 and second half 49 of the manifold. Flow
channel
41 is formed from matching flow grooves in cover piece 48 and first half 47.
Heater
channel 43 is formed from matching heater grooves in first half 47 and second
half 49.
Cover piece 48 has a size that just covers flow channel 41 without covering
heater
channel 43. Cover piece 48 and first half 47 have beveled edges 53 at the
interface
between the cover piece and the first half. Beveled edges 53 permit welding at
the
interface to produce hermetically sealed weld lines 52 that are flush with the
edge of
cover piece 48. This permits cover piece 48 to fit snugly into a cavity in
second half 49
while permitting second half 49 and first half 47 to meet perfectly. Top half
49 overtops
cover piece 48 to provide further engagement of cover piece 48 with first half
47.
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Figs. 10-12 illustrate exploded cross-sectional views of three alternate
embodiments of
manifolds of the present invention having cavities and cover pieces with
different
shapes and constructions.
The embodiment illustrated in Fig. 10 has cover piece 65 and complementary
cavity 67 that are generally trapezoidal in cross-section. The sloping edges
of the
trapezoid permit second half 68 to apply pressure to cover piece 65 when
second half
68 is secured to first half 60 to provide better sealing engagement of the
cover piece to
the first half. Flow grooves 61 in the first half match flow grooves 63 in the
cover piece
to form flow channels. Heater groove 62 in the first half matches heater
groove 68 in
the second half to form a heater channel.
The embodiment illustrated in Fig. 11 has cover piece 75 that fits into roofed
cavity 77 in second half 78. Such an arrangement permits second half 78 to
apply
pressure to cover piece 75 when second half 78 is secured to first half 70 to
provide
better sealing engagement of the cover piece to the first half. Flow grooves
71 in the
first half match flow grooves 73 in the cover piece to form flow channels.
Heater
groove 72 in the first half matches heater groove 76 in the second half to
form a heater
channel.
The embodiment illustrated in Fig. 12 has cover piece 85 that fits into roofed
cavity 87 in second half 88. Such an arrangement permits second half 88 to
apply
pressure to cover piece 85 when second half 88 is secured to first half 80 to
provide
better sealing engagement of the cover piece to the first half. Further, roof
89 of cavity
87 is removable to provide access to cover piece 85 and to facilitate
placement of
second half 88 over cover piece 85 when assembling the manifold. Flow grooves
81
in the first half match flow grooves 83 in the cover piece to form flow
channels. Heater
groove 82 in the first half matches heater groove 86 in the second half to
form a heater
channel.
Other advantages which are inherent to the structure are obvious to one
skilled
in the art. The embodiments are described herein illustratively and are not
meant to
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14
limit the scope of the invention as claimed. Variations of the foregoing
embodiments
will be evident to a person of ordinary skill and are intended by the inventor
to be
encompassed by the following claims.
