Note: Descriptions are shown in the official language in which they were submitted.
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SEALING MEANS FOR ELECTRICALLY DRIVEN WATER
PURIFICATION UNITS AND METHOD OF MANUFACTURING THEREOF
Field of the Invention
The present invention relates to electrically driven water purification
devices and,
in particular, to novel sealing means to facilitate sealing of 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 chambers bounded by ion exchange membranes. Typically,
each of
the chambers is defined on one side by a membrane disposed to the preferential
permeation of dissolved cation species (cation exchange membrane) and on an
opposite
l 0 side by a membrane disposed to the preferential penneation of dissolved
anion species
(anion exchange membrane).
Water to be purified enters one chamber commonly referred to as a diluting
chamber. By passing a current through the device, electrically charged species
in the
diluting chamber migrate towards and through the ion exchange membranes into
adjacent
chambers commonly known as concentrating chambers. As a result of these
mechanisms, water exiting the diluting chamber is substantially demineralized.
Electrically charged species which permeate through the ion exchange membranes
and
into a concentrating chamber are flushed from the concentrating chamber by a
separate
aqueous stream flowing through the concentrating chamber.
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To this end, the above-described devices comprise alternating diluting and
concentrating chambers. In addition, cathode and anode chambers, 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 chamber.
For maintaining separation of associated cation and anion exchange membranes,
spacers are provided between the alternating cation and anion exchange
membranes of
the above-described water purification devices. Therefore, each of the
diluting chambers
and concentrating chambers of a typical electrically-driven water purification
device
comprise spacers sandwiched between alternating cation and anion exchange
membranes.
To prevent any appreciable leakage from diluting chambers and concentrating
chambers of such devices, the above-described arrangement of spacers
sandwiched
between ion exchange membranes must form a substantially water-tight seal. To
this
end, the spacers and the ion exchange membranes are pressed together and fixed
in
position with known connectors. Unfortunately, this alone has not provided
adequate
sealing characteristics.
Various attempts have been made to improve the sealing characteristics of
electrically driven water purification devices. For instance, it is known to
use an
adhesive to bond the ion exchange membranes to either side of a spacer.
Unfortunately,
as a result of exposure to typical operating conditions, the seal formed
thereby is prone
to leakage, thereby causing the loss of valuable product water. This arises
from the
intrinsic moisture permeability of the IX membranes and because of poor
mechanical
sealing characteristics.
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Alternatively, it is known to provide spacers having resilient o-ring type
sealing
members on either side of the spacer for engaging an opposing planar surface
of adjacent
spacers. A cation exchange membrane and an anion exchange membrane are pressed
against opposite sides of the spacer and function as permselective barriers.
In this
arrangement, the spacer, its o-ring type sealing member, and ion exchange
membranes
define a space wherein ionic species in aqueous fluid media contained therein
can migrate
in a direction substantially orthogonal to the plane of the spacer and
permeate through
either of the ion exchange membranes. Unfortunately, during assembly of the
device, it
is known to be difficult to maintain ion exchange membranes in a desired
alignment
relative to associated spacers. Further, during operation and consequent
exposure to
relatively high internal pressure or differential pressures within the device,
ion exchange
membranes may move and become displaced from a desired position relative to
their
associated spacers. Failure to maintain such a desired position may compromise
the
sealing of the associated chamber.
In an attempt to limit movement of ion exchange membranes during assembly of
the water purification device, ion exchange membranes have been provided with
alignment holes which receive fixed rod-like structures. However, this
provides a further
potential source for leakage and, therefore, compromises sealing of the
device.
The material of construction of known spacers is also known to be detrimental
to
the sealing characteristics of this arrangement. To facilitate mass production
by injection
moulding, spacers are typically manufactured from thermoplastic materials,
such as
polypropylene. Unfortunately, such thermoplastic materials are prone to stress
relaxation
or compression set. As a result, over time, because of exposure to the
relatively high
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internal pressures, such spacers, and particularly their o-ring type sealing
members, lose
their resiliency, thereby compromising their ability to maintain adequate
seals with
adjacent surfaces.
Summary of the Invention
According to one aspect, the present invention provides an electrically driven
membrane process apparatus comprising a first spacer having a perimeter having
a
surface with an inner peripheral edge defining an opening, and a recess formed
on the
inner peripheral edge, and an ion exchange membrane having an outer edge
fitted within
the recess. The recess can be continuous along the inner peripheral edge. The
ion
exchange membrane can have a top surface wherein the top surface is vertically
disposed
no lower than the surface of the perimeter when the ion exchange membrane is
fitted in
the recess. The spacer can be comprised of material selected from the group
consisting
ofthermoplastic vulcanizates, thermoplastic elastomeric olefins and
fluoropolymers. The
spacer can be a concentrating chamber spacer (C-spacer) or a diluting chamber
spacer (D-
spacer).
In another aspect, the present invention provides an electrically driven
membrane
process apparatus comprising a spacer with a plurality of bosses and an ion
exchange
membrane having a corresponding plurality of apertures for receiving the
bosses. The
spacer can further comprise a perimeter having a surface with an inner
peripheral edge
defining an opening, and a recess formed on the inner peripheral edge for
fitting an ion
exchange membrane, wherein the bosses extend from the recess substantially
perpendicular thereto.
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In yet another aspect, the present invention provides a spacer of an
electrically
driven membrane process apparatus comprising a plastic mesh consisting
essentially of
polypropylene or polyethylene, and a perimeter surrounding the plastic mesh,
the
perimeter comprising material selected from the group consisting of
thermoplastic
vulcanizates and thermoplastic elastomeric olefins.
In a further aspect, the present invention provides an electrically driven
water
purification apparatus having a first spacer and a frame member separated by
an ion
exchange membrane, the first spacer having an upstanding seal member depending
therefrom and the frame member having a groove for receiving the seal member.
The
seal member can be an o-ring or a sealing bead. The frame member can be a
second
spacer, or cathode or anode end frames.
In another aspect, the present invention provides an electrically driven
membrane
process apparatus having a first spacer and a frame member separated by an ion
exchange
membrane, the first spacer comprising a first surface having a first
throughbore for
flowing an aqueous liquid, the frame member comprising a second surface, a
second
throughbore extending through the second surface and communicating with the
first
throughbore, and a continuous flange depending from the second surface and
surrounding
the second throughbore, the flange pinching a portion of the first surface
surrounding the
first throughbore. The second throughbore can facilitate D-flow.
In a further aspect, the present invention provides an electrically driven
membrane
process apparatus comprising an electrically driven membrane process apparatus
comprising a first spacer having a first perimeter having a surface with a
first inner
peripheral edge defining a first opening, a recess formed on the first inner
peripheral
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edge, and a mesh extending across the first opening and joined to the first
inner
peripheral edge, a second spacer having a second perimeter having a surface
with a
second inner peripheral edge defining a second opening, an ion exchange
membrane
fitted within the recess and extending across the first opening and having a
surface
portion engaged to the second perimeter inwardly of the first inner peripheral
edge, and
a ridge depending from the second perimeter of the second spacer and
compressing the
surface portion of the ion exchange membrane against the mesh, thereby
preventing or
reducing likelihood of buckling of the mesh.
In yet another aspect, the present invention provides a method of injection
molding a thin plastic part comprising a perimeter having an inner peripheral
edge and
a mesh joined to said inner peripheral edge, including the steps of (a)
providing a mold
having a cavity and a core, the cavity having a first interior surface and a
first continuous
ridge depending from the first interior surface, the core having a second
interior surface
and a second continuous ridge depending from the second interior surface; and
(b)
pinching opposite side of the mesh between the ridges to form a flow barrier.
The cavity
can further include hanging pins depending from the first interior surface. In
this respect,
the method would then further include, after step (a) and before step (b), the
step of
suspending the mesh from the hanging pins.
Brief Description of Drawings
The present invention will be better understood with reference to the appended
drawings in which:
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Figure 1 is an exploded perspective view of an electrically driven water
purification unit of the present invention;
Figure 2a is a plan view of one side of a C-spacer of the present invention;
Figure 2b is a sectional elevation view of the C-spacer of Figure 2a taken
along lines A-A;
Figure 3 is a perspective view of an ion exchange membrane of the present
invention;
Figure 4a is a plan view of one side of a D-spacer of the present invention;
Figure 4b is an elevation view of the D-spacer shown in Figure 4a;
Figure 5 is a plan view of one side of a D-spacer of the present invention,
partly in section, illustrating flow channels formed therein;
Figure 6 is a plan view of one side of an anode end frame of the present
invention;
Figure 7 is an illustration of an unclamped mold having mesh interposed
between its cavity and core plates for purposes of injection
molding;
Figure 8 is a plan view of the exterior side of the cavity plate of the mold
shown in Figure 7;
Figure 9 is a plan view of the interior side of the cavity plate of the mold
shown in Figure 7;
Figure 10 is a plan view of the interior side of the core plate of the mold
shown in Figure 7;
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Figure 11 is an illustration of a second unclamped mold having mesh
interposed between its cavity and core plates for purposes of
injection molding a spacer of the present invention;
Figure 12 is a plan view of the interior side of the cavity plate of the mold
shown in Figure 11;
Figure 13 is a plan view of the interior side of the core plate of the mold
shown in Figure 11;
Figure 14 is a plan view of the exterior side of the cavity plate of the mold
shown in Figure 11;
Figure 15 is an illustration of an embodiment of a boss of a C-spacer;
Figure 16 is an illustration of another embodiment of a boss of a C-spacer;
and
Figure 17 is an illustration of an embodiment of a secondary seal member of
a C-spacer.
Detailed Description of The Preferred Embodiment
The present invention provides a spacer of a filter press type electrically
driven
water purification apparatus, such as an electrodyalisis unit or an
electrodeionization unit.
Electrodeionization units include those with ion exchange resin in the
concentrating
chamber. The spacer of the present invention can also be used in other
electrically driven
membrane process apparati of the filter press type. An example of another
electrically
driven membrane process which falls within the purview of this invention is
salt splitting.
The invention will hereafter be explained with reference to an electrically
driven water
purification apparatus.
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Referring to Figure 1, a typical electrically driven water purification
apparatus 2
comprises alternating anion exchange membranes 4 and cation exchange membranes
6.
Spacers 10 and 100 are provided in between the alternating cation and anion
exchange
membranes to help define alternating diluting chambers ("D-chambers") and
concentrating chambers ("C-chambers"). Electrode chambers, namely a cathode
chamber with a cathode 230 and an anode chamber with an anode 232, are
provided at
terminal ends of the unit, and are each bound on one side by a spacer 10 and
on an
opposite side by an end plate 200a or 200b. To assemble the water purification
apparatus, each of the anion exchange membranes, cation exchange membranes,
and
associated spacers and end plates 200a and 200b are forced together to create
a
substantially fluid tight arrangement.
Different spacers are provided for each of the D-chambers and C-chambers. In
this respect, the D-chamber spacer, or "D-spacer", helps define the D-chamber.
Similarly, the C-chamber spacer, or "C-spacer", helps define the C-chamber.
Referring to Figures 2a and 2b, the C-spacer 10 comprises a continuous
perimeter
12 of thin, substantially flat elastomeric material, having a first side
surface 14 and an
opposite second side surface 15, and defining an opening 16. In this respect,
the C-spacer
has a picture frame-type configuration. The C-spacer 10 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. In particular,
the C-spacer
material should possess acceptable electrical insulation properties and be
chemically
resistant to high and low pH levels. In this respect, an example of suitable
materials
include thermoplastic vulcanizates, thermoplastic elastomeric olefines, and
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fluoropolymers. The C-spacer 10 can be manufactured by injection moulding or
compression moulding.
The first side surface 14 can be pressed against an ion exchange membrane,
such as
a cation exchange membrane 6. Similarly, the opposite second side surface 15
can be
pressed against a second ion exchange membrane, such as an anion exchange
membrane 4.
In one embodiment, the ion exchange membrane associated with a side surface of
the C-
spacer 10 is also associated with a side surface of the D-spacer 100 (see
Figure 4) in the
manner described below. Figure 3 shows one side surface of an ion exchange
membrane 4
or 6, and it is understood that the features of one side surface are the same
as those of the
opposite side surface. Further, Figure 3 is representative of either an anion
exchange
membrane 4 or a cation exchange membrane of the present invention. In another
embodiment, the ion exchange membrane associated with a side surface of the C-
spacer 10
is also associated with a side surface of an electrode end plate 200 (see
Figure 6), such as a
cathode end plate or an anode end plate (anode end plate is shown in Figure
6), in the
manner described below.
Notably, pressing first and second ion exchange membranes against the first
and
second sides of the C-spacer 10 forms a C-chamber. The inner peripheral edge
18 of the
C-spacer 10 perimeter helps define a space (or opening 16) which functions as
a fluid
passage for aqueous liquid flowing through the C-chamber.
First and second spaced-apart throughbores are provided in the C-chamber to
facilitate flow in and out of the C-chamber. In one embodiment, first and
second
throughbores can be formed in one or both of the first and second ion exchange
membranes (see Figure 3) to facilitate flow in and out of the C-chamber. In
this respect,
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flow is introduced in the C-chamber via the first throughbore 4a or 6a and is
discharged
from the C-chamber via the second throughbore 4b or 6b (supply flow to and
discharge
flow from C-chamber hereinafter referred to as "C-flow").
It is understood that other arrangements could also be provided to effect flow
in
and out of the C-chamber. For instance, the C-spacer perimeter 12 could be
formed with
throughbores and channels wherein the channels facilitate fluid communication
between
the throughbores and the C-chamber. In this respect, aqueous liquid could be
supplied via
an inlet throughbore in the C-spacer perimeter, flow through a first set of
channels formed
in the C-spacer perimeter into the C-chamber, and then leave the C-chamber
through a
second set of channels formed in the C-spacer perimeter which combine to
facilitate
discharge via an outlet throughbore formed in the C-spacer perimeter.
A first throughbore 20 and a second throughbore 22 extend through the surface
of
the C-spacer perimeter. The first throughbore 20 provides a fluid passage for
purified
water discharging from the D-chambers, the second throughbore 22 provides a
fluid
passage for water to be purified supplied to the D-chambers (supply flow to
and discharge
flow from D-chamber hereinafter referred to as "D-flow"). As will be described
below,
means are provided to isolate C-flow from D-flow.
Throughgoing holes 24, 25a and 25b are also provided in the perimeter of the C-
spacer 10. Holes 24a, 24b are adapted to receive alignment rods which assists
in aligning
the D-spacer when assembling water purification apparatus. Holes 25a and 25b
are
adapted to flow aqueous liquid discharging from the anode and cathode
chambers.
In one embodiment, the C-spacer 10 can further comprise a plastic screen or
mesh
26 joined to the inner peripheral edge 18 of the perimeter 12 and extending
through the
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space 16 defined by the inner peripheral edge 18 of the perimeter 12. The mesh
26 can
be made integral with or encapsulated on the inner peripheral edge 18 of the
perimeter
12. The mesh 26 further assists in spacing the anion exchange membrane from
the cation
exchange membrane. The mesh 26 can be a bi-planar, non-woven high flow mesh.
Alternatively, the mesh 26 can be woven. Suitable materials include
polypropylene and
polyethylene. It is understood that, where ion exchange resin is provided in
the
concentrating chamber, no mesh would be required as the resin itself would
provide a
spacing function.
In one embodiment, mesh 26 comprises three co-planar layers of polypropylene
mesh wherein the first and third layers have a thickness of 20/1000 of an inch
and are
characterized by 16 strands per inch, and the second layer, interposed between
the first
and third layers, has a thickness of 30/1000 of an inch and is characterized
by 15 strands
per inch. Preferably, the first and third layers of mesh are thinner and
characterized by
a tighter weave than the second layer. In this way, desirable hydraulic
characteristics can
be achieved (as the water flows primarily across the middle second layer)
while the
thinner outer layers with the tighter weaver provide desired support to the
membrane.
In another embodiment, the second layer is characterized by a different colour
or shading
than the first and third layers to permit easier identification and
differentiation between
the second and the first and third layers, thereby facilitating assembly.
Where the C-spacer 10 includes mesh 26 for spacing anion exchange membranes
from cation exchange membranes, the mesh 26 must be comprised of material
which are
stable at high temperatures and chemically resistant to high and low pH
environments.
The material comprising the perimeter 12 must also be compatible with the
material
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comprising mesh 26 in regard to the manufacture of a unitary component
comprising
both the perimeter 12 and mesh 26. In this respect, to facilitate melt
processing of the C-
spacer 10, the perimeter 12 is preferably comprised of material which is melt
processible
at temperatures which would not cause degradation of the mesh. In this
respect, where
the mesh is comprised of polypropylene or polyethylene, acceptable materials
include
thermoplastic vulcanizates and thermoplastic elastomeric olefines.
In the embodiment illustrated in Figure 2, discontinuities or gaps 28 may be
provided between the mesh 26 and the perimeter 12 wherein such discontinuities
28
correspond with the first and second throughbores of an ion exchange membrane.
Such
l0 discontinuities 28 provide visual assistance in properly aligning the ion
exchange
membrane in relation to the C-spacer 10 during assembly of the water
purification unit.
A side surface of the C-spacer further has a recess 30 formed therein which is
adapted for fitting an ion exchange membrane. When the ion exchange membrane
is
fitted in the recess 30, the exposed surface of the ion exchange membrane is
planar with
the surface of the perimeter 12 or slightly raised above the surface of the
perimeter 12.
In one embodiment, a continuous recess 30 is provided along the inner
peripheral edge
18 of the perimeter 12 and on both the first and second side surfaces of the
perimeter 12.
During assembly of the water purification apparatus, the outer edge of ion
exchange
membrane is fitted in the recess 30 on the first side of the perimeter 12 and
a cation
exchange membrane is positioned in the recess 30 on the second side of the
perimeter 12.
The recesses 30 are sized to facilitate a relatively tight fitting arrangement
between the
ion exchange membranes and the perimeter and the ion exchange membranes and
the
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mesh, once the ion exchange membranes and C-spacer 10 are forced together and
once
the ion exchange membranes become hydrated and swell.
A side surface of the C-spacer 10 further includes a plurality of bosses 32
which
can be fitted within corresponding apertures 8 of an ion exchange membrane.
Corresponding apertures can be provided in a D-spacer 100 or an electrode end
plate 200
to receive insertion of the bosses 32. In one embodiment, the bosses 32 extend
along the
inner peripheral edge 18 of the perimeter 12 on both the first and second side
surfaces of
the perimeter 12. More preferably, the bosses 32 extend from the surfaces of
the
recessed portions 30 substantially perpendicular thereto. During assembly of
the water
purification apparatus, the bosses 32 on the first side of the perimeter 12
are matched
with corresponding mating apertures 8 in the anion exchange membrane 4 and the
D-
spacer 100 or electrode end plate 200. The apertures 8 of the anion exchange
membrane
4 and a first D-spacer 100 are then fitted over the corresponding bosses 32.
Similarly,
the bosses 32 on the second side of the perimeter 12 are matched with
corresponding
apertures 8 in the cation exchange membrane 6 and a second D-spacer 100 or an
electrode end plate 200. The apertures of the cation exchange membrane 6 and
the second
D-spacer 100 or electrode end plate 200 are then fitted over the corresponding
bosses 32.
The apertures 8 of the ion exchange membranes 4 or 6 are sized to be tightly
fitted over
the bosses 32. In one embodiment, the apertures 8 are sized to be no greater
than
approximately 75% of the diameter of the bosses 32.
Referring to Figures 15 and 16, in one embodiment, the bosses 32 include a
radially extending undercut 33. Further, sidewall surface 35 of the bosses 32
can be
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tapered or flared outwardly from top surface 37 towards undercut 33, to
facilitate
insertion of bosses 32 through apertures 8 in membranes 4 or 6.
An upstanding secondary seal member 34 is also provided on a side surface of
the
C-spacer 10 for fitting within a first corresponding groove of a D-spacer 100
or electrode
end plate 200. In one embodiment, the secondary seal member 34 is a continuous
0-ring
or bead extending from and integral with the surface of the C-spacer. The
secondary seal
member 34 depends from the surface of the perimeter 12. In one embodiment,
secondary
seal members 34 are provided on both the first and second side surfaces of the
perimeter
12. The secondary seal member 34 on the first side surface and the secondary
seal
member 34 on the second side surface each fit within grooves of a first D-
spacer 100 and
a second D-spacer 100 or electrode end plate 200 respectively. During assembly
of the
water purification apparatus, the secondary seal members 34 are fitted or
inserted into the
grooves of the D-spacers 100 and electrode end plates 200.
Referring to Figure 17, in one embodiment, secondary seal member 34 is
characterized by a ratio of width:height of about 3:2. In another embodiment,
the ratio
of width:height is from about 1.25:1 to 2:1.
Referring to Figure 4a and 4b, the D-spacer 100 comprises a continuous
perimeter
102 of a thin plastic material, having a first side surface 104 and an
opposite second side
surface 105 and defining an opening 106. In order to complement the sealing
features
provided on the above-described embodiment of the C-spacer 10, and therefore
improves
sealing of both the C-chamber and the D-chamber, the D-spacer 100 is made of
harder
material than the C-spacer 10. Suitable materials for the D-spacer 100 include
polyethylene and polypropylene.
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The first side surface of the D-spacer 100 can be pressed against an ion
exchange
membrane, such as a cation exchange membrane 6. Similarly, the second side
surface of
the D-spacer 100 can be pressed against a second ion exchange membrane, such
as an
anion exchange membrane 4. In one embodiment, one of the ion exchange
membranes
associated with a side surface of the D-spacer 100 is also associated with a
side surface of
the C-spacer 10 in the manner above-described.
Notably, pressing first and second ion exchange membranes against the first
and
second side surfaces of the D-spacer 100 forms a D-chamber. The inner
peripheral edge
108 of the D-spacer perimeter 102 helps define a space which functions as a
fluid passage
for aqueous liquid flowing through the D-chamber.
A first throughbore 110 and a second throughbore 112 are formed in the D-
spacer
and define fluid passages for the respective supply and discharge of aqueous
liquid in the
D-chainber. The positions of the first throughbore 110 and second throughbore
112 of the
D-spacer 100 correspond to those of the first throughbore 20 and second
throughbore 22 of
the C-spacer 10 respectively when the water purification apparatus is
assembled. In this
respect, the first throughbore 110 and second throughbore 112 of the D-spacer
100
communicate with the first throughbore 20 and second throughbore 22 of the C-
spacer 10
respectively. In operation, aqueous liquid is supplied from the first
throughbore 110 of the
D-spacer 100, flows through the D-chamber and becomes purified, and is then
discharged
via the second throughbore 112 of the D-spacer 100.
In one embodiment, the first and second throughbores 110 and 112 of the D-
spacer
100 are formed in the perimeter 102 of the D-spacer 100. To facilitate flow of
water to be
purified into the D-chamber via the first throughbore 110, a first plurality
of
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channels 114 are formed through the perimeter 102 and provides for
communication
between the first throughbore 110 and the D-chamber. Similarly, a second
plurality of
channels 116 are formed through the perimeter 102 and provides for
communication
between the second throughbore 112 and the D-chamber, thereby facilitating
discharge
of purified water from the D-chamber.
Although the D-spacer 100 has been described as being provided with first and
second throughbores 110 and 112, each associated with a plurality of channels
114 and
116, to effect fluid flow into and out of the D-chamber, it is understood that
other means
may be provided to supply and discharge aqueous liquid in and out of the D-
chamber.
For instance, water to be purified may be introduced directly into the D-
chamber via the
a first throughbore formed in an ion exchange membrane. Similarly, purified
water may
be discharged directly out of the D-chamber via a second throughbore formed in
an ion
exchange membrane. In this respect, flows in and out of the D-chamber would be
channelled in a manner similar to that above-described for the C-chamber.
A third throughbore 118 extends through the surface of the D-spacer perimeter
102 and provides a fluid passage for aqueous liquid discharging from a C-
chamber.
Further, a fourth throughbore 120 extends through the surface of the D-spacer
perimeter
for supplying aqueous liquid to a C-chamber. The positions of the third
throughbore 118
and fourth throughbore 120 of the D-spacer perimeter communicate with first
and second
throughbores respectively formed in a C-chamber for facilitating flow in and
out of such
C-chamber. In the embodiment illustrated in Figure 3, the third and fourth
throughbores
118 and 120 of the D-spacer perimeter 102 communicate with first and second
throughbores respectively formed in an ion exchange membrane pressed against a
C-
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spacer perimeter 112. In operation, aqueous liquid is supplied to a C-chamber
via the
third throughbore 118 of the D-spacer perimeter 102 and the first throughbore
in the ion
exchange membrane. Such aqueous liquid then flows through such C-chamber,
becomes
loaded with ionic species migrating through the ion exchange membranes pressed
against
the C-spacer 10, and is discharged from the C-chamber via the second
throughbore in the
ion exchange membrane and the fourth throughbore in the D-spacer perimeter
102.
Throughgoing holes 122a, 122b, 123a, and 123b are also provided in the
perimeter of the D-spacer 100. Holes 122a and 122b are adapted to receive
alignment
rod which assists in aligning the D-spacer 100 when assembling the water
purification
unit. Holes 123a and 123b are adapted to flow aqueous liquid discharging from
the
anode and cathode chambers.
As discussed above, a side surface of the D-spacer 100 is provided with
apertures
124 to receive insertion of bosses 32 associated with the C-spacer 10.
Further, a groove
126 is also provided in a side surface of the D-spacer perimeter 102 to
receive insertion
of the secondary sealing member 34. In one embodiment, the apertures 124 and
the
groove 126 is provided on both the first and second side surfaces of the D-
spacer
perimeter 102.
A first flange 128 and a second flange 130 can depend from a side surface of
the
perimeter 102 of the D-spacer 100 and surround the first throughbore 110 and
second
throughgoing bore 112 of the D-spacer 100 respectively. When the water
purification
apparatus is assembled, the first flange 128 engages and pinches a portion of
the C-spacer
perimeter 12 surrounding the first throughgoing bore 20 of the C-spacer 10.
Similarly,
the second flange 130 engages and pinches a portion of the C-spacer 10
surrounding the
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second throughgoing bore 22 of the C-spacer perimeter 12. In one embodiment,
first and
second flanges 128 and 130 are provided on both side surfaces of the D-spacer
100 to
engage and pinch adjacent C-spacers 10 on each side of the D-spacer 100.
A first upstanding shallow ridge 132 and a second upstanding shallow ridge 134
can be provided extending from a side surface of the perimeter 102 of the D-
spacer 100.
The first and second upstanding shallow ridges 132 and 134 are provided to
prevent or
reduce ingress of aqueous liquid from the D-chamber 101 and into the third and
fourth
throughbores 118 and 120 of the D-spacer 100. Aqueous liquid in the D-chamber
101
may leak into any of the third and fourth throughbores 118 and 120 if the ion
exchange
membrane adjacent to the D-spacer 100 disengages from the D-spacer perimeter
102,
thereby creating a flow path for liquid in D-chamber 101 to flow into any of
the third or
fourth throughbores 118 and 120, thereby providing a risk for mixing of D-flow
with C-
flow. To reduce the likelihood that the ion exchange membrane becomes
disengaged
from the D-spacer perimeter 102, one or more upstanding shallow ridges can be
strategically provided on the D-spacer perimeter 102 (two upstanding shallow
ridges 132
and 134 are provided in the embodiment illustrated in Figure 4) to engage and
compress
a side surface of ion exchange membrane against the C-spacer mesh 26 when the
unit is
assembled, thereby providing a more effective seal between the ion exchange
membrane
and the D-spacer 100.
More particularly, the upstanding shallow ridges 132 and 134 are positioned on
the D-spacer perimeter 102 to compress a portion of the first side surface of
ion exchange
membrane at a location opposite to that of the location of the second side
surface portion
which is not seated against the C-spacer perimeter 12 but which is engaged to
D-spacer
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perimeter 102 (hereinafter, surface portion). Further, the upstanding shallow
ridges must
necessarily compress that part of surface portion which is disposed between
throughbore
of ion exchange membrane and the inner peripheral edge of the D-spacer
perimeter 102.
When the unit is assembled, portions of the second side surface of ion
exchange
membrane are firmly pressed against C-spacer perimeter 12, and particularly
against the
recess portion 30 of the C-spacer perimeter 12, by virtue of contact between
the first side
surface of ion exchange membrane and a side surface of the D-spacer perimeter
102.
Those portions of the ion exchange membrane which are not firmly pressed
against the
C-spacer perimeter recess 30 are disposed against the C-spacer mesh 26.
Because the
mesh 26 is subject to buckling or other deformation, the ion exchange membrane
disposed against the mesh 26 is more likely to disengage from the surface of
the D-spacer
perimeter 102 than that portion of the ion exchange material pressed against
the recess
30. Where this disengagement occurs at the inner peripheral edge of the D-
spacer
perimeter 102, and continues along the D-spacer perimeter surface to either of
throughbores 118 or 120, fluid communication is established between D-chamber
101
and throughbores 118 and 120, creating a potential for mixing of D-flow and C-
flow. By
positioning upstanding shallow ridges 132 and 134 as above-described, buckling
ofinesh
26 is prevented or reduced, and the risk that this flowpath becomes
established is
mitigated. Preferably, the upstanding shallow ridge traverses the entire
surface portion
between opposite edges of ion exchange membrane.
In one embodiment, upstanding shallow ridges 132 and 134 are provided on both
the first and second sides of the D-spacer perimeter 102 at positions as above-
described.
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In this way, ion exchange membranes are compressed against both sides of the C-
spacer
mesh 26, thereby resisting buckling of the C-spacer mesh 26.
Flanges 136 and 138 are also provided and extend from a side surface of the D-
spacer perimeter 102 and surround holes 123a and 123b. Similarly, flanges 140
and 142
are also provided extending from the D-spacer perimeter 102 about throughbore
118 and
120. When the water purification device is assembled, flanges 128, 130, 140
and 142
engage and pinch a portion of C-spacer 10. In this manner, flanges 128 and 130
prevent or
reduces the mixing of D-flow with C-flow in the event that ion exchange
membrane
disengages from D-spacer perimeter 102 surface, as above-described, thereby
providing a
flow path from the D-chamber. On the other hand, flanges 140 and 142
facilitate better
sealing of flanges 128 and 130 against C-spacer perimeter 12. Without flanges
140 and
142, the sealing features about throughbores 110 and 118 or 112 and 120 may
not be
perfectly vertically aligned, which could compress sealing of these
throughbores.
Where the water purification apparatus is an electrodeionization unit, ion
exchange
resin is provided in the D-chamber and positioned between the anion and cation
exchange
membranes provided on either side of the D-spacer 100. Alternatively, where no
ion
exchange resin is required, such as in the case of an electrodyalisis unit, a
mesh can be
provided in much the same manner as provided in the above-described C-spacer
10, for
purposes of spacing ion exchange membranes disposed on either side of the D-
spacer 100.
It is understood that the above-described embodiments of a D-spacer 100 could
be
used as C-spacers 10 in electrically driven water purification units.
Similarly, the
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above-described embodiments of a C-spacer 10 could be used as D-spacers 100 in
such
units.
Referring to Figure 6, an electrode end plate 200, such as a cathode end plate
200a or an anode end plate 200b, (an anode end plate 200b), comprises a hard,
solid
plastic material, having a first side surface 202 and an opposing second side
surface (not
shown). The first side surface 200 comprises a perimeter 204 having an inner
peripheral
edge 206 which defines an interior recessed portion 208. The second side
surface can be
substantially planar. In order to complement the sealing features provided on
the above-
described embodiment of the C-spacer 10, and therefore improves sealing of the
C-
chamber and the electrode chamber, the electrode end plate 200 is made of
harder
material than the C-spacer 10. Suitable materials for the electrode end plate
200 include
polyethylene and polypropylene.
The first side surface 202 can be pressed against an ion exchange membrane,
such
as a cation exchange membrane 6 or an anion exchange membrane 4. In one
embodiment, the ion exchange membrane pressed against the first side surface
202 is also
pressed against a side surface of a C-spacer 10. Notably, pressing an ion
exchange
membrane against the first side surface of the electrode end plate 200 forms
an electrode
chamber, such as a cathode chamber or an anode chamber.
As discussed above, and in likewise manner with the D-spacers 100 of the first
side surface 202 of the electrode end plate 200 is provided with apertures 210
to receive
insertion of bosses 32 associated with C-spacer 10. Further, a groove 212 is
also
provided in the first side surface of the electrode end plate 200 to receive
insertion of the
secondary sealing member 34.
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Where throughgoing bores 214 and 216 are provided in the electrode end plate
to facilitate D-flow, as is the case in the electrode end plate 200
illustrated in Figure 6,
a first flange 218 and a second flange 220 can extend from the first side
surface 202 of
the perimeter 204 of the electrode end plate 200 and surround the throughgoing
bores 214
and 216 of the electrode end plate 200. When the water purification apparatus
is
assembled, the first flange 218 engages and pinches a portion of the C-spacer
10
perimeter surrounding the first throughgoing bore 20 of the C-spacer 10.
Similarly, the
second flange 220 engages and pinches a portion of the C-spacer 10 surrounding
the
second throughgoing bore 22 of the C-spacer perimeter 12. This serves to
prevent or
reduce mixing of D-flow with C-flow.
Referring to Figure 2, the embodiment of the spacer illustrated therein can be
manufactured by injection moulding. Where the perimeter 12 is comprised of a
high
temperature melt processible plastic such as a thennoplastic vulcanizate, the
perimeter
is preferably overmolded on the mesh by injection molding.
Where the C-spacer 10 is formed by overmolding mesh 26 with perimeter 12, the
mesh 26 is first formed by conventional methods and then interposed between
cavity
plate 302 and core plate 304 of mold 300. Referring to Figure 7, while
interposed
between plates 302 and 304, and immediately before the mold 300 is clamped
together,
mesh 26 is subjected to tensile forces such that the mesh 26 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 are
absent,
the mesh 26 may become convoluted and remain in this shape when the mold 300
is
clamped together. This may result in a C-spacer 10 having a convoluted mesh
portion
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26, which makes it more difficult for the C-spacer 10 to form effective seals
with adjacent
structural components.
Referring 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 machine 316 is provided to inject feed material through sprue
308 in
sprue/runner plate 306. The sprue 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 plate 302 through a
plurality of gates
314 (see Figure 9) drilled through cavity plate 302.
When the individual plates 302, 304 and 306 of mold 300 are clamped together,
feed material injected by injection mold machine 316 through sprue 308 flows
through the
runner system 310 and is directed via gates 314 into impressions 318 and 320.
Once inside
cavity plate 302, injected feed material fills the impressions 318 and 320
formed in the
interior surfaces 322 and 324 of cavity plate 302 and core plate 304
respectively, such
impressions being complementary to the features of C-spacer perimeter 12. In
filling the
impressions, feed material flows through mesh 26 which is clamped between core
and
cavity plates 302 and 304.
To help define inner peripheral edge 18 of C-spacer 10, 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
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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 18 of C-
spacer
perimeter 12, to which mesh 26 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 26
therebetween.
Conventional injection mold machines can be used, such as a Sumitomo SH22OAT"^
injection mold machine. To begin injection molding, material used for
manufacturing
the C-spacer perimeter, 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 3 80 F where the material enters the screw to 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 10 by overmolding mesh 26 with perimeter 12. Mesh 26 is first
formed
by conventional methods and then interposed between cavity plate 402 and core
plate 404
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of mold 400. In particular, mesh 26 is suspended on hanging pins 401 which
depend from
interior surface 422 of cavity plate 402. To this end, mesh 26 is provided
with
throughbores which receive hanging pins 401. In one embodiment, mesh 26 is die
cut to
dimensions such that mesh 26 does not extend appreciably into perimeter 12
once
perimeter 12 is formed within impression 418 and 420 by injection molding
using mold
400. In this respect, in another embodiment, mesh 26 does not extend across
feature on the
impressions 418 and 420 which cause the formation of the secondary seal member
34.
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 11, 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 inject 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 plate 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 12. In
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filling the impressions, feed material flows through the perimeter of mesh 26
which is
clamped between core and cavity plates 402 and 404.
To help define inner peripheral edge 18 of C-spacer 10, 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 of core plate 404 to abut the opposite
side of mesh
26, 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
t 0 together, opposed conterminous ridges 426 and 430 pinch opposite sides of
mesh 26,
thereby creating a barrier to flow ofinjected feed material. In doing so, such
arrangement
facilitates the creation of inner peripheral edge 18 of C-spacer perimeter 12,
to which
mesh 26 is joined.
Using mold 400, injection molding of the C-spacer embodiment 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.
