Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02451256 2003-11-27
SPACER FOR ELECTRICALLY DRIVEN
MEMBRANE PROCESS APPARATUS
Field of the Invention
The present invention relates to electrically driven membrane process devices
and, in
particular, to components used to assist in defining flow passages in such
devices.
Description of the Related Art
Water purification devices of the filter press type which purify water by
electrically
driven membrane processes, such as electrodyalisis or electrodeionization,
comprise individual
compartments bounded by opposing ion exchange membranes. Typically, each of
the
compartments is defined on one side by a membrane disposed to the preferential
permeation of
dissolved cation species (canon exchange membrane) and on an opposite side by
a membrane
disposed to the preferential permeation of dissolved anion species (anion
exchange membrane).
Water to be purified enters one compartment commonly referred to as a diluting
compartment. By passing a current through the device, electrically charged
species in the
diluting compartment migrate towards and through the ion exchange membranes
into adj acent
compartments commonly known as concentrating compartments. As a result of
these
mechanisms, water exiting the diluting compartments is substantially
demineralized. Electrically
charged species which permeate through the ion exchange membranes and into a
concentrating
compartment are flushed from the concentrating compartment by a separate
aqueous stream
flowing through the concentrating compartment.
CA 02451256 2003-11-27
-2-
To this end, the above-described devices comprise alternating diluting and
concentrating
compartments. In addition, cathode and anode compartments, housing a cathode
and an anode
respectively therein, are provided at the extreme ends of such devices,
thereby providing the
necessary current to effect purification of water flowing through the diluting
compartments.
For maintaining separation of opposing canon and anion exchange membranes,
spacers
axe provided between the alternating cation and anion exchange membranes of
the above-
described water purification devices. Therefore, each of the diluting and
concentrating
compartments of a typical electrically-driven water purification device
comprise spacers
sandwiched between alternating canon and anion exchange membranes.
Spacers for maintaining separation of opposing ion exchange membranes for
defining a
concentrating compartment which is not filled with ion exchange resin
typically include a mesh
structure to support the ion exchange membranes and to assist in preventing
the opposing ion
exchange membranes from moving closer to one another or, in the extreme,
coming into contact
with one another. When excessive forces are applied to these ion exchange
membranes from
within the diluting compartments, the ion exchange membranes have a tendency
to move closer
to one another, and thereby potentially impede or obstruct flow in the
concentrating
compartment. Under these conditions, there is an increased risk that the
interaction between the
membrane and the mesh causes pinhole formation in the membrane. Further, there
is a tendency
for the membrane to deform into the gaps provided in the mesh. Such
deformation of the
membrane could compromise sealing engagement between the membrane and the
spacer
structures it is associated with, thereby creating the potential for leakage
between the
concentrating and diluting compartments.
CA 02451256 2003-11-27
-3-
Summary of the Invention
The present invention provides a spacer mesh configured to separate a first
ion
conducting membrane from a second ion conducting membrane to define a space
between the
membranes, comprising a plurality of strands consisting essentially of a
polymer having a heat
distortion temperature of at least 90 °C at 66 psi, and a melt flow
index within the range of 3 g/
min to 6 g/ 10 min, and being chemically stable at pH >13 or pH <2.
In one aspect, the polymer is substantially a multicomponent co-polymer having
at least
two co-monomers, wherein at least one of the co-monomers is halogenated. At
least one of the
co-monomers can be ethylene.
In another aspect, the polymer has a crystallinity of at least 50%.
In yet another aspect, the plurality of strands are configured to define a
netting. The
plurality of strands can include a first plurality of spaced apart
substantially parallel strand
elements, and a second plurality of spaced apart substantially parallel strand
elements, wherein
the first plurality of strand elements and the second plurality of strand
elements are connected to
provide a netting. The netting can be non-woven or woven. Further, the netting
can be a
diagonal netting.
The present invention also provides a spacer mesh configured to separate a
first ion
conducting membrane from a second ion conducting membrane to define a space
between the
membranes, comprising a plurality of strands consisting essentially of a
polymer having a heat
distortion temperature of at least 90 °C at 66 psi, and a melt flow
index within the range of 3 g/
CA 02451256 2003-11-27
-4-
min to 6 g/ 10 min, and being chemically stable when in contact with the first
or second ion
conducting membranes.
The present invention also provides a spacer mesh configured to separate a
first ion
conducting membrane from a second ion conducting membrane to define a space
between the
membranes, comprising a plurality of strands consisting essentially of a
halogenated polymer
having a melt flow index within the range of 3 g/ 10 min to 6 g/ 10 min.
Further, the present invention provides a spacer mesh configured to separate a
first ion
conducting membrane from a second ion conducting membrane to define a space
between the
membranes, comprising:
a first plurality of spaced apart substantially parallel strand elements, and
a second
plurality of spaced apart substantially parallel strand elements, wherein the
first plurality
of strand elements and the second plurality of strand elements are connected
to define a
netting having a plurality of apertures, each of the apertures having a
plurality of vertices
defined by a pair of intersecting strands, and a distance between non-adjacent
vertices in
an aperture is less than 10/1000 of an inch.
Brief Descriution of Drawings
The present invention will be better understood with reference to the appended
drawings
in which:
Figure 1 is an exploded perspective view of an electrodeionization of the
present invention;
Figure 2 is a schematic illustration of an electrodeionization apparatus of
the present invention;
CA 02451256 2003-11-27
-5-
Figure 3 is a plan view of one side of a C-spacer of the present invention;
Figure 4 is a sectional elevation view of the C-spacer;
Figure 5 is an illustration of a sample of mesh of the C-spacer;
Figure 6 is an illustration of an unclamped mold having mesh interposed
between its cavity
and core plates for purposes of injection molding;
Figure 7 is a plan view of the exterior side of the cavity plate of the mold
shown in Figure 6;
Figure 8 is a plan view of the interior side of the cavity plate of the mold
shown in Figure 6;
Figure 9 is a plan view of the interior side of the core plate of the mold
shown in Figure 6;
Figure 10 is an illustration of second unclamped mold having mesh interposed
between its
cavity and core plates for purposes of injection molding a spacer of the
present
invention;
Figure 11 is a plan view of the interior side of the cavity plate of the mold
shown in Figure 10;
Figure 12 is a plan view of the interior side of the core plate of the mold
shown in Figure 10;
and
Figure 13 is a plan view of the exterior side of the cavity plate of the mold
shown in Figure 10.
Description of The Preferred Embodiment
Unless otherwise indicated, all numbers expressing quantities of ingredients,
properties
such as distance, operating conditions, and so forth used in the specification
and claims are to be
CA 02451256 2003-11-27
-6-
understood as being modified in all instances by the term "about."
Accordingly, unless indicated
to the contrary, the numerical parameters set forth in the following
specification and attached
claims are approximations that may vary depending upon the desired properties
sought to be
obtained by the present invention. At the very least, and not as an attempt to
limit the application
of the doctrine of equivalents to the scope of the claims, each numerical
parameter should at least
be construed in light of the number of reported significant digits and by
applying ordinary
rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the
broad scope
of the invention are approximations, the numerical values set forth in the
specific examples are
reported as precisely as possible. Any numerical value, however, inherently
contain errors
necessarily resulting from the standard deviation found in their respective
testing measurements.
The present invention provides a spacer 50 of a filter press type
electrodeionization
apparatus 10. An electrodeionization apparatus includes product and waste
liquid flow passages
defined by opposing flexible ion exchange membranes 28, 30. Spacers are
provided to maintain
spacing between opposing ion exchange membranes 28, 30 to facilitate liquid
flow between the
opposing ion exchange membranes 28, 30.
Refernng first to Figure 1, an electrodeionization apparatus 10 in accordance
with the
present invention comprises an anode compartment 20 provided with an anode 24
and a cathode
compartment 22 provided with a cathode 26. A plurality of cation exchange
membranes 28 and
anion exchange membranes 30 are alternately arranged between the anode
compartment 20 and
the cathode compartment 22 to form diluting compartments 32 and concentrating
compartments
18. A suitable cation exchange membrane 28 is SELEMION CMETM. A suitable anion
CA 02451256 2003-11-27
exchange membrane 30 is SELEMION CMETM. Both are manufactured by Asahi Glass
Co. of
Japan. Each of the diluting compartments 32 is defined by anion exchange
membrane 30 on the
anode side and by a cation exchange membrane 28 on the cathode side. Each of
the
concentrating compartments 18 is defined by a canon exchange membrane 28 on
the anode side
and by an anion exchange membrane 30 on the cathode side. Electrolyte
solutions are supplied
to the anode compartment 20 and to the cathode compartment 22 via flow streams
36 and
38 respectively.
Ion exchange material designated by numeral 40 is provided in diluting
compartments 32.
Such media enhance water purification by removing unwanted ions by ion
exchange. Further,
such media facilitate migration of ions towards membranes 28 and 30 for
subsequent permeation
therethrough, as will be described hereinbelow. The ion exchange material 40
can be in the form
of an ion exchange resin, an exchange fibre or a formed product thereof
Water to be treated is introduced into the diluting compartments 32 from
supply stream
S0. Similarly, water or an aqueous solution is introduced into the
concentrating compartments
18 and into the anode and cathode compartments 20, 22 from a supply stream 44.
Pressure of
water flowing through the compartments 18, 32 can range from 140 psi to over
200 psi. Water
temperature in the concentrating compartment is typically 38 °C, but
can go as high as 65 °C to
80 °C during thermal sanitation operations. A predetermined electrical
voltage is applied
between the two electrodes whereby anions in diluting compartments 32 permeate
through anion
exchange membranes 30 and into concentrating compartments 18 while canons in
streams in
diluting compartments 32 permeate through cation exchange membranes 28 and
into
concentrating compartments 18. The above-described migration of anions and
cations is further
facilitated by the ion exchange material 40 present in diluting compartments
32. In this respect,
_ __..___~.. ~.._..~__~ ____._ _
CA 02451256 2003-11-27
_8_
driven by the applied voltage, rations in diluting compartments 32 migrate
through ration
exchange resins using ion exchange mechanisms, and eventually pass through
ration exchange
membranes 28 which are in direct contact with the ration exchange resins.
Similarly, anions in
diluting compartments 32 migrate through anion exchange resins using ion
exchange
mechanisms, and eventually pass through anion exchange membranes 30 which are
in direct
contact with the anion exchange resins. Aqueous solution or water introduced
into concentrating
compartments 18 from stream 44, and anion and ration species which
subsequently migrate into
these compartments, are collected and removed as a concentrated solution from
discharge stream
48, while a purified water stream is discharged from diluting compartments 32
as discharge
stream 42.
To assist in defining the diluting compartments 32 and the concentrating
compartments
18, spacers 50, 52 are interposed between the alternating ration and anion
exchange membranes
28, 30 so as to maintain spacing between opposing ration and anion exchange
membranes 28, 30
and thereby provide a flowpath for liquid to flow through the compartments 18,
32. The anode
and cathode compartments 20, 22 are provided at terminal ends of the apparatus
10, and are each
bound on one side by a spacer 50 and on an opposite side by end plates 200a,
200b, respectively.
To assemble the apparatus 10, each of the anion exchange membranes 30, ration
exchange
membranes 28, and associated spacers 50, 52 and end plates 200a, 200b are
forced together to
create a substantially fluid tight arrangement.
Different spacers are provided for each of the concentrating and diluting
compartments
18, 32. In this respect, the spacer 52 helps define the diluting compartment
32, and is referred to
as a "D-spacer". Similarly, the spacer 50 helps define the concentrating
compartment 18, and is
referred to as a "C-spacer".
CA 02451256 2003-11-27
-9-
Referring to Figure 2, the C-spacer SO comprises a continuous perimeter 54 of
thin,
substantially flat elastomeric material, having a first side surface 56 and an
opposite second side
surface 58, and defining a space 60. In this respect, the C-spacer 50 has a
picture frame-type
configuration. The C-spacer perimeter 54 is comprised of a material which is
not prone to
significant stress relaxation while able to withstand typical operating
conditions in an electrically
driven water purification unit with a view to maintaining sealing engagement
with adjacent
components, such as the membranes 28, 30, to mitigate leakage between the
compartments 18,
32. In this respect, an example of suitable materials include thermoplastic
vulcanizates,
thermoplastic elastomeric olefines, and fluoropolymers. The C-spacer 50 can be
manufactured
by injection moulding or compression moulding.
The first side surface 56 is pressed against an ion exchange membrane, such as
a ration
exchange membrane 28. Similarly, the opposite second side surface 58 is
pressed against a
second ion exchange membrane, such as an anion exchange membrane 38. In one
embodiment,
the ion exchange membrane associated with a side surface of the C-spacer 50 is
also pressed
against a side surface of the D-spacer 52. In another embodiment, the ion
exchange membrane
associated with a side surface of the C-spacer 52 is also pressed against a
side surface of an
electrode end plate 200a, 200b, such as a cathode end plate 200b or an anode
end plate 200a.
Pressing the ration and anion ion exchange membranes 28, 30 against the first
and
second sides of the C-spacer 10 forms a concentrating compartment 18. The
inner peripheral
edge 62 of the C-spacer 50 perimeter helps define the space 60 which functions
as a fluid
passage for aqueous liquid flowing through the concentrating compartment 18.
CA 02451256 2003-11-27
-10-
First and second spaced-apart openings are provided in the concentrating
compartment 18
to facilitate flow in and out of the concentrating compartment 18. In one
embodiment, first and
second throughbores 62, 64 can be formed in one or each of the canon and anion
ion exchange
membranes 28, 30 to facilitate flow in and out of the concentrating
compartment 18. In this
respect, flow is introduced in the concentrating compartment 18 via the first
throughbore 62 and
is discharged from the concentrating compartment 18 via the second throughbore
64 (flow
through the concentrating compartment 18 hereinafter referred to as "C-flow").
It is understood that other arrangements could also be provided to effect flow
in and out
of the concentrating compartment 18. For instance, the C-spacer perimeter 54
could be formed
with throughbores and channels wherein the channels facilitate fluid
communication between the
throughbores and the concentrating compartment 18. In this respect, aqueous
liquid could be
supplied via an inlet throughbore in the C-spacer perimeter 54, flow through a
first set of
channels formed in the C-spacer perimeter 54 into the concentrating
compartment 18, and then
leave the concentrating compartment 18 through a second set of channels formed
in the C-spacer
perimeter 54 which combine to facilitate discharge via an outlet throughbore
formed in the C-
spacer perimeter 54.
The first and second throughbores 62, 64 extend through the surface of the C-
spacer
perimeter 54. The first throughbore 62 provides a fluid passage fox purified
water discharging
from the diluting compartments 32, the second throughbore 64 provides a fluid
passage for water
to be purified supplied to the diluting compartments 32 (flow through the
diluting compartment
32 hereinafter referred to as "D-flow"). As will be described below, means are
provided to
isolate C-flow from D-flow.
CA 02451256 2003-11-27
- 11 -
In one embodiment, throughgoing holes 66, 68, 70, 72 are also provided in the
perimeter
of the C-spacer 50. Holes 66, 68 are adapted to receive alignment rods which
assists in aligning
the D-spacer 52 when assembly the water purification apparatus. Holes 70, 72
are adapted to
flow aqueous liquid discharging from the anode and cathode compartments.
The C-spacer SO further includes a plastic screen or mesh 74 joined to the
inner
peripheral edge 62 of the perimeter 54 and extending through the space 60
defined by the inner
peripheral edge 62 of the perimeter 54. The mesh 74 can be made integral with
or encapsulated
on the inner peripheral edge 62 of the perimeter 54. The mesh 74 assists in
spacing and
maintaining a desired spacing between opposing membranes 28, 30, which are
pressed against
the C-spacer 50, by supporting the membranes 28, 30 between which the mesh 74
is interposed.
In other words, the mesh 74 assists in preventing the opposing membranes 28,
30 pressed against
the C-spacer 50 from moving closer to one another or, in the extreme, from
coming into contact
with one another. As opposing membranes 28, 30 pressed against the C-spacer 50
move closer
to one another or come into contact with one another, flow through the
concentrating
compartment 18 defined between these opposing membranes 28, 30 would be
impeded or
obstructed. In this respect, the mesh 74 mitigates the creation of such flow
impediments or
obstructions.
The mesh 74 can be a bi-planar, non-woven high flow mesh. Alternatively, the
mesh 74
can be woven.
In one embodiment, the mesh 74 consists of a plurality of layers. The layers
include at
least one inner layer interposed between the outer layers. Each of the two
outer layers are
adjacent to one of the membranes 28, 30. Each layer includes a plurality of
strands configured to
CA 02451256 2003-11-27
-12-
define a netting. In this respect, the plurality of strands includes a first
plurality of spaced apart
substantially parallel strand elements and a second plurality of spaced apart
substantially parallel
strand elements. The first plurality of strand elements and the second
plurality of strand
elements are connected to provide this netting. The netting can be non-woven
or woven. In the
embodiment illustrated in Figure 5, the netting is a diagonal netting (or
"diamond-shaped"
configuration).
The first plurality of strand elements and the second plurality of strand
elements are
connected to define the netting having a plurality of apertures. Each of the
apertures has a
plurality of vertices defined by a pair of intersecting strands. It has been
found that the spacing
between the strands in each of the outer layers of mesh which are closest to
the ion exchange
membranes, when the mesh is interposed between the ion exchange membranes, is
preferably
less than 10/1000 of an inch. In one embodiment, the distance between non-
adjacent vertices is
less than 10/1000 of an inch. By configuring the mesh 74 in this manner, it
has been found that
the membranes 28, 30, are more effectively supported by the mesh 74 and are
less likely to be
susceptible to pinhole formation during normal operation of the
electrodeionization apparatus 10.
As well, by virtue of this design, it is found that the membranes 28, 30 are
less likely to deform
into the apertures of the outer layers of mesh 74 and interfere with flow
through the
concentrating compartment.
In one embodiment, the mesh 74 consists of three substantially parallel
layers, where a
single inner layer is interposed between two outer layers. Each of the layers
has a bi-planar
diagonal or diamond-shaped configuration. The diamond-shape mesh configuration
is illustrated
in Figure 5. Each of the outer layers of mesh is characterized by a strand
density of 32 strands
per inch, wherein each of the strands has a diameter of 20/1000 of an inch.
The inner strand
CA 02451256 2003-11-27
-13-
layer is characterized by a strand density of 9 strands per inch, wherein each
of the strands has a
diameter of 40/1000 of an inch. Preferably, the strand density of the outer
layers of a mesh 74
having three or more layers is no less than 32 strands per inch.
The mesh 74 comprises a plurality of strands consisting essentially of a
polymer having a
heat distortion temperature of at least 900C at 66 psi, and a melt flow index
within the range of
3g/10 min. to 6g/10 min. The mesh 74 is chemically stable when in contact with
either of the
membranes 28, 30. Other materials may be present in the composition in amounts
not
sufficiently significant to detract from the desired properties of the
composition, such as
mechanical strength properties, melt processibility; or chemical resistance.
Other materials may
also be present to enhance these or other properties, in which case the
polymer is referred to as
being "compounded". Such materials include slip agents, anti-oxidants, and
fillers.
Heat distortion temperature is a measure of a tendency of a material to
deflect in response
to an applied mechanical force at elevated temperatures. In this context, the
heat distortion
temperature is measured in accordance with ASTM D648.
Melt flow index is a measure of the degree to which a material is capable of
being melt
processible. In this context, the melt flow index is measured in accordance
with ASTM D1238
(Procedure A).
As explained above, in the electrodeionization apparatus, when assembled, the
spacer S0,
including the mesh 74, is in contact with ion exchange membranes. Ion exchange
membranes
include functional groups capable of entering into acid-base reactions. The pH
in a typical
environment immediately adjacent to anion exchange membrane 30 in an
electrodeionization
apparatus 10 can approach 13-14. The pH in the typical environment immediately
adjacent to
CA 02451256 2003-11-27
-14-
the canon exchange membrane 28 in an electrodeionization apparatus 10 during
normal
operation can be as low as 0-2. Additionally, high pH and low pH cleaning
solutions are
typically flowed through the concentrating compartments 18 when the
electrodeionization
apparatus 10 is not operational so as to mitigate biofouling and scaling. The
mesh 74 is
configured so as to be chemically stable in these pH environments such that
electrochemical
performance and/or service life of the electrodeionization apparatus 10 is not
compromised.
In one embodiment, the polymer is a co-polymer consisting essentially of
alternating
ethylene co-monomers and chlorotrifluoroethylene co-monomers. It is understood
that departure
from perfect alternation of the ethylene and chlorotrifluoroethylene co-
monomers is permitted,
and impurities may be present in the polymer molecule, so long as the degree
of departure, or the
impurities, do not detract form the desired properties of the composition,
such as mechanical
strength properties, melt processibility and chemical resistance. An example
of a suitable
commercially available ethylene chlorotrifluoroethylene co-polymer is HALARTM
manufactured by Ausimont USA. The HALAR polymer is characterized by a heat
distortion
temperature at 66 psi of 92 °C, a melt flow index of 4g/10 min., and a
crystallinity of 50%
measured by X-Ray diffraction.
The material comprising the perimeter 54 must be compatible with the material
comprising mesh 74 in regard to the manufacture of a unitary component
comprising both the
perimeter 54 and mesh 74. In this respect, to facilitate melt processing of
the C-spacer 50, the
perimeter 54 is preferably comprised of material which is melt processible at
temperatures which
would not cause degradation of the mesh ?4. In one embodiment, the material is
a thermoplastic
elastomer such as a thermoplastic vulcanizate.
CA 02451256 2003-11-27
-IS-
In the embodiment illustrated in Figure 2, discontinuities or gaps 76 may be
provided
between the mesh 74 and the perimeter 54 wherein such discontinuities 76
correspond with the
first and second throughbores of the cation and anion exchange membranes 28,
30. Such
discontinuities 76 provide visual assistance in properly aligning the ion
exchange membrane in
relation to the C-spacer 50 during assembly of the apparatus 10.
Referring to Figure 2, the embodiment of the spacer illustrated therein can be
manufactured by injection moulding. Where the perimeter 54 is comprised of a
high temperature
melt processible plastic such as a thermoplastic vulcanizate, the perimeter is
preferably
overmolded on the mesh by injection molding.
Where the C-spacer 50 is formed by overmolding mesh 74 with perimeter 54, the
mesh
74 is first formed and then interposed between cavity plate 302 and core plate
304 of mold 300.
This mesh 74 is extruded using a single screw extruder with a counter rotating
die. The mesh 74
is extruded as a bi-planar mesh. Referring to Figure 7, while interposed
between plates 302, 304,
and immediately before the mold 300 is clamped together, mesh 74 is subjected
to tensile forces
such that the mesh 74 is substantially planar and not slack when the mold 300
is clamped
together. In this respect, tension should be provided along the axis indicated
by arrow 301.
Where such tensile forces axe absent, the mesh 74 may become convoluted and
remain in this
shape when the mold 300 is clamped together. This may result in a C-spacer 50
having a
convoluted mesh portion 74, which makes it more difficult for the C-spacer 50
to form effective
seals with adjacent structural components.
Refernng to Figures 7, 8, 9, and 10, in one embodiment, the mold 300 is a
three-plate
mold comprising a sprue plate 306, a cavity plate 302, and a core plate 304:
An injection mold
CA 02451256 2003-11-27
-16-
machine 316 is provided to inject feed material through spree 308 in
sprue/runner plate 306. The
spree 308 comprises a throughbore which communicates with a runner system 310
(see Figure 8)
formed as an exterior surface 311 of cavity plate 302. The runners communicate
with an interior
of cavity 302 through a plurality of gates 314 (see Figure 9) drilled through
cavity plate 302.
When the individual plates 302, 304, 306 of mold 300 are clamped together,
feed
material injected by injection mold machine 316 through spree 308 flows
through the runner
system 310 and is directed via gates 314 into impressions 318, 320. Once
inside cavity plate
302, injected feed material fills the impressions 318 and 320 formed in the
interior surfaces 322,
324 of cavity plate 302 and core plate 304 respectively, such impressions
being complementary
to the features of C-spacer perimeter 54. In filling the impressions, feed
material flows through
mesh 26 which is clamped between core and cavity plates 302, 304.
To help define inner peripheral edge 62 of C-spacer 50, a continuous ridge 326
depends
from interior surface 322 of cavity plate 302 defining a space 328 wherein
feed material is
prevented from flowing into. Similarly, a complementary continuous ridge 330
depends from
interior surface 324 of core plate 304, defining a space 332 wherein feed
material is also
prevented from flowing into space 328. To this end, when cavity plate 302 and
core plate 304
are clamped together, ridges 326 and 330 pinch opposite sides of mesh 26,
thereby creating a
barrier to flow of injected feed material. In doing so, such arrangement
facilitates the creation of
inner peripheral edge 62 of C-spacer perimeter 54, to which mesh 74 is joined.
To injection mold the C-spacer embodiment illustrated in Figure 2, the core
and cavity
plates 302 and 304 are clamped together, thereby pinching mesh 74
therebetween. Conventional
injection mold machines can be used, such as a Sumitomo SH220ATM injection
mold machine.
CA 02451256 2003-11-27
-17-
To begin injection molding, material used for manufacturing the C-spacer
perimeter 54, such as a
thermoplastic vulcanizate, is dropped from an overhead hopper into the barrel
of the machine
where it is plasticized by the rotating screw. The screw is driven backwards
while the material
itself remains out in front between the screw and the nozzle. Temperature
along the material
pathway varies from approximately 193 °C (380 °F) where the
material enters the screw to 204°C
(400 °F) immediately upstream of the mold 300.
To begin filling the mold 300, screw rotation is stopped, and molten plastic
is thrust
forward in the direction of the screw axis through the nozzle 334, sprue 308
and mold gates.
Once the mold 300 is filled, injection pressure is maintained to pack out the
part: Material
shrinkage occurs inside the mold 300 as the temperature is relatively lower
than inside the barrel.
As a result, pressure must be continuously applied to fill in any residual
volume created by
shrinkage. When the part is adequately packed and cooled, mold 300 is opened.
The ejector
pins 336 are actuated, thereby releasing the part.
Figures 11, 12, 13 and 14 illustrate a second mold 400 which could be used to
form C-
spacer 50 by overmolding mesh 74 with perimeter 54. Mesh 74 is first formed
and then
interposed between cavity plate 402 and core plate 404 of mold 400. Mesh 74 is
extruded using
a counter-rotating die in a single screw extruder (having an L/D = 24) to
produce a bi-planar
mesh. The temperature profile from the feed section to the die is 475
°F - 485 °F - 500 °F - 510
°F. In particular, mesh 74 is suspended on hanging pins 401 which
depend from interior surface
422 of cavity plate 402. To this end, mesh 74 is provided with throughbores
which receive
hanging pins 401. In one embodiment, mesh 74 is die cut to dimensions such
that mesh 74 does
not extend appreciably into perimeter 54 once perimeter 54 is formed within
impression 418 and
420 by injection molding using mold 400. In this respect, in one embodiment,
mesh 74 does not
CA 02451256 2003-11-27
- Ig -
extend across feature on the impressions 418 and 420 which cause the formation
of a sealing
member or one embodiment of the C-spacer 50. Interior surface 424 of core
plate 404 is
provided with depressions 405 to receive and accommodate hanging pins 401 when
mold 400 is
clamped together.
Referring to Figures 1 l, 12, 13 and 14, in one embodiment, the mold 400 is a
three-plate
mold comprising a sprue plate 406, a cavity plate 402, and a core plate 404.
An injection mold
machine 416 is provided to inj ect feed material through sprue 408 in sprue
plate 406. The sprue
408 comprises a throughbore which communicates with a runner system 410 (see
Figure 14)
formed as an exterior surface 411 of cavity plate 402. The runners communicate
with an interior
of cavity 402 through a plurality of gates 414 (see Figure 12) drilled through
cavity plate 402.
When the individual plates 402, 404 and 406 of mold 400 are clamped together,
feed
material injected by injection mold machine 416 through sprue 408 flows
through the runner
system 410 and is directed via gates 414 into impressions 418 and 420. Once
inside cavity plate
402, injected feed material fills the impressions 418 and 420 formed in the
interior surfaces 422
and 424 of cavity plate 402 and core plate 404 respectively, such impressions
being
complementary to the features of C-spacer perimeter 54. In filling the
impressions, feed material
flows through the perimeter of mesh 74 which is clamped between core and
cavity plates 402
and 404.
To help define inner peripheral edge 62 of C-spacer 50, a continuous ridge 426
depends
from interior surface 422 of cavity plate 402 to abut a side of mesh 26
defining an interior space
428 wherein feed material is prevented from flowing thereinto. Similarly, a
complementary
continuous ridge 430 conterminous with continuous ridge 426 depends from
interior surface 424
CA 02451256 2003-11-27
-19-
of core plate 404 to abut the opposite side of mesh 74, defining an interior
space 432 wherein
feed material is also prevented from flowing into space 432. To this end, when
cavity plate 402
and core plate 404 are clamped together, opposed conterminous ridges 426 and
430 pinch
opposite sides of mesh 74, thereby creating a barrier to flow of injected feed
material. In doing
so, such arrangement facilitates the creation of inner peripheral edge 62 of C-
spacer perimeter
54, to which mesh 74 is joined.
Using mold 400, injection molding of the C-spacer 50 illustrated in Figure 2
can be
accomplished much in the same manner as when using above-described mold 300.
It will be understood, of course, that modification can be made in the
embodiments of the
invention described herein without departing from the scope and purview of the
invention as
defined by the appended claims.
