Abstrict
A vacuum or gas pressure clamp prevents movement of an elongate
filter cloth used in a horizontal vacuum filter. The clamp includes
a support frame and a planar supporting device having a perforated
support surface for supporting the filter cloth. The vacuum clamp
is mounted on the frame and is adapted for connection to a vacuum
source so that vacuum can be applied to numerous holes in the support
surface. An imperforate sealing sheet extends over the support surface
and in close proximity thereto. The filter cloth can be drawn between
the supporting device and the sealing sheet. A vacuum can be applied
to the filter cloth in order to prevent its movement in the longitudinal
direction. Preferably the support surface forms a rectangular grid
comprising rows of closely spaced holes. This grid is surrounded
by a sealing surface. In the gas pressure clamp, an enclosure extends
around the supporting device and the sealing sheet and a positive
air pressure can be provided in this enclosure. In this version,
the perforated support surface can be vented to atmosphere.
Claims
I therefore claim:
1. A vacuum clamp for preventing movement of an elongate, movable
filter cloth comprising:
a support frame;
a supporting device having a perforated support surface for supporting
said filter cloth, said supporting device being mounted on said
support frame and being adapted for connection to a vacuum source,
so that a vacuum can be applied to numerous holes in the support
surface;
an imperforate sealing sheet extending over said support surface
and in close proximity thereto, and
a number of weights on said sealing sheet
wherein said elongate filter cloth can be drawn between said supporting
device and said sealing sheet and a vacuum can be applied to said
filter cloth by said supporting device in order to prevent movement
of said filter cloth in its longitudinal direction, said sealing
sheet being pulled against said filter cloth by the vacuum and thereby
preventing air from passing through the filter cloth in the area
of said perforated support surface.
2. A vacuum clamp according to claim 1 wherein said support surface
forms a planar rectangular grid comprising rows of closely spaced
holes and said grid is surrounded by a sealing surface positioned
below said sealing sheet.
3. A vacuum clamp according to claim 2 including said elongate
filter cloth which is formed into a continuous loop, said cloth
having a width corresponding approximately to the dimension of said
rectangular grid which is perpendicular to the direction of movement
of said filter cloth.
4. A vacuum clamp according to claim 2 wherein said supporting
surface is formed substantially from a grid made of polypropylene.
5. A vacuum clamp according to claim 2 wherein said weights are
positioned on said sealing sheet above said sealing surface and
comprise a number of flat tile-like members arranged in rows adjacent
the periphery of the sheet.
6. A vacuum clamp for preventing movement of an elongate, movable
filter cloth comprising:
a support frame;
a supporting device having a perforated support surface for supporting
said filter cloth, said supporting device being mounted on said
support frame and being adapted for connection to a vacuum source
so that a vacuum can be applied to numerous holes in the support
surface;
an imperforate sealing sheet extending over said support surface
and in close proximity thereto, and means for introducing water
to a side of said filter cloth facing said sealing sheet, said water
being drawn through said filter cloth during operation of the supporting
device in order to remove solids entrained in said filter cloth.
7. A filtering machine comprising an endless belt of filter cloth
arranged to have a horizontally extending, upper reach and a lower
reach; at least one vacuum tray disposed beneath said upper reach;
means for feeding material to be filtered onto said upper reach;
means for intermittently advancing said upper reach of the belt
by a predetermined distance in a selected direction; a vacuum clamp
for preventing lengthwise movement of at least a section of said
lower reach of the belt by clamping a portion of said lower reach,
said clamp operating when said advancing means is used to advance
said upper reach and including a perforated, planar support surface
for holding said filter cloth during operation of said clamp, air
passage means for applying vacuum to numerous holes in said support
surface, and an impervious sealing sheet extending over said support
surface and in close proximity thereto; means for connecting a vacuum
source to said vacuum clamp; and means for supporting said vacuum
clamp in a position adjacent said lower reach of the endless belt,
wherein said belt extends between said support surface and said
sealing sheet and a vacuum can be applied to said filter cloth by
said clamp, thereby pulling said sealing sheet against said filter
cloth.
8. A filtering machine according to claim 7 wherein said support
surface forms a planar rectangular grid comprising rows of closely
spaced holes and said grid is surrounded by a sealing surface positioned
below said sealing sheet.
9. A filtering machine according to claim 8 including said vacuum
source, means for connecting said vacuum source to said at least
one vacuum tray, valve means for operatively connecting said vacuum
source to said at least one vacuum tray, and further valve means
for operatively connecting said vacuum source to said vacuum clamp.
10. A filtering machine according to claim 8 including a number
of weights on said sealing sheet which is made of flexible fabric.
11. A filtering machine according to claim 8 wherein said filter
cloth has a uniform width corresponding approximately to one dimension
of said rectangular grid which is perpendicular to the direction
of advancement of said filter cloth.
12. A filtering machine according to claim 7 including a cloth
wash box for washing said filter cloth, said wash box being mounted
along said lower reach of said belt and said vacuum clamp being
mounted in the vicinity of said wash box, wherein in use of said
machine, said filter cloth moves from said wash box to said vacuum
clamp.
13. A filtering machine according to claim 7 including said vacuum
source which is connected to both the vacuum clamp and said at least
one vacuum tray.
14. A gas pressure operated clamp for preventing movement of an
elongate, movable filter cloth comprising:
a supporting device for supporting an area of said filter cloth,
said device having a supporting surface arranged to extend along
one side of said filter cloth,
an imperforate pressure sheet extending over said supporting surface
and in proximity thereto;
a number of weights mounted on top of said pressure sheet; and
means for applying gas pressure to one side of said sheet so as
to press said sheet towards said supporting surface over said area
of the filter cloth,
wherein during use of said clamp, said elongate filter cloth is
drawn between the other side of said pressure sheet and said supporting
device and gas pressure is applied to said sheet to clamp the filter
cloth between said pressure sheet and the supporting surface to
prevent movement of said filter cloth in its longitudinal direction.
15. A gas pressure clamp according to claim 14 wherein said supporting
device comprises a planar rectangular grid having rows of closely
spaced holes surrounded by a sealing surface positioned below said
pressure sheet.
16. A gas pressure operated clamp according to claim 15 wherein
said applying means includes an enclosure extending around said
supporting device and said pressure sheet and a pressurized air
space is provided above said pressure sheet.
17. A gas pressure operated clamp according to claim 16 wherein
said applying means includes means for maintaining an air pressure
exceeding atmospheric pressure in said enclosure and the holes in
said rectangular grid are vented to atmosphere.
18. A gas pressure operated clamp for preventing movement of an
elongate, movable filter cloth comprising:
a supporting device for supporting an area of said filter cloth,
said device having a supporting surface arranged to extend along
one side of said filter cloth,
an imperforate pressure sheet extending over said supporting surface
and in proximity thereto;
means for applying gas pressure to one side of said sheet so as
to press said sheet towards said supporting surface over said area
of the filter cloth, and
means for introducing a cleaning liquid to a side of said filter
cloth-facing said pressure sheet, said cleaning liquid being forced
under pressure through said filter cloth during operation of the
clamp in order to remove solids entrained in said filter cloth.
19. A cleaning device for an elongate, movable filter cloth comprising
a support frame, a supporting device having a support surface with
numerous perforations formed therein, said supporting device being
mounted on said support frame and being adapted for connection of
said perforations to a vacuum source or atmosphere, an imperforate
sealing cover extending over said support surface and in close proximity
thereto, means for introducing and distributing a cleaning liquid
between said cover and said filter cloth when the latter is drawn
between said cover and said supporting device, and means for forcing
said cleaning liquid through the filter cloth and into said supporting
device, wherein at least a peripheral region of said cover is caused
by said forcing means to be pressed against an adjacent surface
of the filter cloth, thereby sealing the peripheral region of the
cover against the filter cloth.
20. A cleaning device according to claim 19 wherein said forcing
means includes an air pressurizing enclosure extending around said
supporting device and said sealing cover, said enclosure permitting
a positive air pressure above atmospheric pressure to be provided
on a side of said sealing cover facing away from the filter cloth.
21. A cleaning device according to claim 19 wherein said introducing
and distributing means comprises a number of side- by-side distribution
channels extending across a substantial portion of the width of
the sealing cover in the transverse direction of the filter cloth
and pipe connectors extending through and attached to the sealing
cover, said pipe connectors opening into said channels.
22. A cleaning device according to claim 19 wherein said supporting
device comprises a planar rectangular grid having rows of closely
spaced holes surrounded by a sealing surface positioned below said
sealing cover.
23. A cleaning device according to claim 22 wherein said forcing
means includes a number of weights arranged in rows about the perimeter
of said sealing cover.
24. A cleaning device according to claim 19 wherein said forcing
means is a vacuum pump and pipe means for connecting said supporting
device to said vacuum pump.
25. A method for filtering a material using a horizontal vacuum
filter, said method comprising:
providing a filtering machine having an endless belt of filter
cloth with a horizontal upper reach and a lower reach and at least
one vacuum tray disposed beneath said upper reach;
feeding material to be filtered onto said upper reach and applying
a vacuum to said material by means of said at least one vacuum tray
in order to filter same;
intermittently advancing said upper reach of the belt in a forward
lengthwise direction by a predetermined distance; and
preventing said lower reach of the belt from moving in said forward
lengthwise direction during the advancing step by clamping a portion
of said lower reach with a clamping mechanism after filtered material
has been discharged from said portion of the filter cloth, said
clamping mechanism comprising a supporting device for supporting
said filter cloth and an imperforate sealing sheet extending over
said supporting device and in close proximity thereto, said belt
extending between said supporting device and said sealing sheet,
said clamping step being carried out by applying a vacuum to said
filter cloth by said supporting device, said sealing sheet being
pulled against said filter cloth by the vacuum.
26. A method according to claim 25 including pressing said sealing
sheet against said belt by providing a number of weights distributed
over and attached to said sealing sheet.
27. A method according to claim 25 wherein said supporting device
forms a planar rectangular grid comprising rows of closely spaced
holes, said grid being surrounded by a sealing surface positioned
below said sealing sheet.
28. A method according to claims 25 including introducing water
to a side of said filter cloth facing said sealing sheet, said water
being drawn through said filter cloth during operation of the supporting
device in order to remove left-over solids entrained in said filter
cloth.
29. A method according to claim 25 including washing said filter
cloth with a wash box mounted along said lower reach of said belt,
said clamping mechanism being mounted in the vicinity of said wash
box, said belt being moved during use from said wash box to said
clamping mechanism.
30. A method for filtering a material using a horizontal vacuum
filter, said method comprising:
providing a filtering machine having an endless belt of filter
cloth with a horizontal upper reach and a lower reach and at least
one vacuum tray disposed beneath said upper reach;
feeding material to be filtered onto said upper reach and applying
a vacuum to said material by means of said at least one vacuum tray
in order to filter same;
intermittently advancing said upper reach of the belt in a forward
lengthwise direction by a predetermined distance;
preventing said lower reach of the belt from moving in said forward
lengthwise direction during the advancing step; and
discharging the filtered material from said filter cloth at one
end of said upper reach, wherein said lower reach is prevented from
moving by clamping a portion of said lower reach with a clamping
mechanism after the filtered material has been discharged from said
portion of the filter cloth, said clamping mechanism comprising
a supporting device for supporting said filter cloth and an imperforate
pressure sheet extending over said supporting device and in close
proximity thereto, said belt extending between said supporting device
and said pressure sheet, said clamping step being carried out by
applying gas pressure to one side of said pressure sheet so as to
press said sheet towards said supporting device and against an area
of said filter cloth.
31. A method for filtering a material according to claim 30 wherein
said supporting device has a perforated supporting surface arranged
along one side of said filter cloth and said pressure sheet is pressed
towards said supporting surface.
32. A method of filtering a material according to claim 30 including
providing an enclosure extending around said supporting device and
said pressure sheet, and applying said gas pressure by pressurizing
an air space located in said enclosure and above said pressure sheet.
Description BACKGROUND OF THE INVENTION
This invention relates to restraining devices for preventing movement
of a filter cloth, also to filtering machines that employ a movable
filter cloth and a restraining device for this cloth, and to a method
of filtering a material using a horizontal vacuum filter.
Horizontal vacuum filtering machines employing a movable belt filter
have come into wide spread use for precise, continuous liquid/solid
separation, cake washing and drying. A horizontal belt filter is
described in U.S. Pat. No. 3,870,641 which issued Mar. 11, 1975
to H. G. Pierson. This machine employs an endless belt of filter
cloth, this belt having an upper reach that extends over a series
of vacuum trays. Each tray is connected by vacuum pipes to a vacuum
pump. At the end of the upper reach, the belt passes over a movable,
terminal discharge roller which can be moved by rams to an extended
position. On the return reach of the belt, it passes through a belt
washer wherein jets of water remove traces of any filter cake. The
belt then passes over a drive roller and a drive contact roller,
each of which is provided with a ratchet so that they can rotate
only in the forward direction. It is important to prevent the lower
reach of the filter belt from being pulled back by the outward movement
of the discharge roller.
In the current versions of the above filtering machine, the vacuum
is removed from the vacuum trays before the discharge roller is
moved. The discharge roller acts now as the drive roller and its
movement to the extended position causes the filter cloth to advance
over the series of vacuum trays, one tray at a time. Vacuum is applied
to the vacuum trays again before the discharge roller is caused
to retract.
Although the method of restraining backward movement of the filter
cloth described in the above-mentioned U.S. patent is generally
satisfactory, it can fail under some filtration conditions that
leave the filter cloth surface soiled. If the filter cloth is still
soiled when it is passing over the drive roller, the cloth can slip
causing the filter to operate in an unpredictable manner and possibly
preventing operation of the filtering machine.
Although modifications have been attempted to the aforementioned
driver roller and drive contact roller in these horizontal vacuum
filters, these modifications have not been very successful. One
such previous modification involved trapping the filter cloth between
a fixed member and a movable member which applied pressure generated
by an air actuated cylinder or similar device. This known clamp
roll can cause damage to the filter fabric because it applies a
relatively high point force to the filter cloth.
It is an object of the present invention to provide a relatively
simple, inexpensive means for preventing movement of a filter cloth
in a vacuum filtering machine when this is required.
It is a further object of this invention to provide a vacuum clamp
capable of preventing movement of an elongate filter cloth, which
clamp has a perforated support surface for supporting the filter
cloth and a sealing sheet that extends over this support surface.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a vacuum clamp for preventing
movement of an elongate, movable filter cloth comprises a support
frame and a supporting device having a perforated support surface
for supporting the filter cloth. The supporting device is mounted
on the support frame and is adapted for connection to a vacuum source
so that vacuum can be applied to numerous holes in the support surface.
An imperforate sealing sheet extends over the support surface and
is in close proximity thereto. A number of weights are arranged
on the sealing sheet. The elongate filter cloth can be drawn between
the supporting device and the sealing sheet and a vacuum can be
applied to the filter cloth by the supporting device in order to
prevent movement of the filter cloth in its longitudinal direction.
The sealing sheet is pulled against the filter cloth by the vacuum
and thereby prevents air from passing through the filter cloth in
the area of the perforated support surface.
Preferably the support surface forms a planar rectangular grid
comprising rows of closely spaced holes and this grid is surrounded
by a sealing surface positioned below the sealing sheet.
According to a further aspect of the invention, a filtering machine
comprises an endless belt of filter cloth arranged to have a horizontally
extending, upper reach and a lower reach and at least one vacuum
tray disposed beneath the upper reach. There are also means for
feeding material to be filtered onto the upper reach and means for
intermittently advancing the upper reach of the belt by a predetermined
distance in a selected direction. This machine includes a vacuum
clamp for preventing lengthwise movement of at least a section of
the lower reach of the belt by clamping a portion of the lower reach.
The clamp operates when the advancing mechanism is used to advance
the upper reach. The clamp includes a perforated, planar support
surface for holding the filter cloth during operation of the clamp.
The clamp has air passage means for applying vacuum to numerous
holes in the support surface and an imperforate sealing sheet extending
over the support surface and in close proximity thereto. Means for
connecting a vacuum source to the clamp and means for supporting
the vacuum clamp in a position adjacent to the lower reach of the
filter cloth the lower reach are provided. The belt extends between
the support surface and the sealing sheet. A vacuum can be applied
to the filter cloth by the clamp, thereby pulling the sealing sheet
against the filter cloth.
In a preferred version of the machine there is a cloth wash box
for washing the filter cloth running along a lower reach of the
belt. The vacuum clamp is mounted near this wash box so that the
cloth moves from the wash box to the vacuum clamp.
According to another aspect of the invention, a gas-pressure operated
clamp for preventing movement of an elongate movable filter cloth
comprises a supporting device for supporting an area of a filter
cloth, this device having a supporting surface arranged to extend
along one side of the filter cloth. An imperforate pressure sheet
extends over the supporting surface and in proximity thereto. A
number of weights are mounted on top of the pressure sheet. The
clamp includes means for applying gas pressure to one side of the
sheet so as to press the sheet towards a supporting surface over
the area of the filter cloth. During use of the clamp, the elongate
filter cloth is drawn between the other side of the pressure sheet
and the supporting device and gas pressure is applied to the sheet
to clamp the filter cloth between the pressure sheet and the supporting
surface, thereby preventing movement of the filter cloth in its
longitudinal direction.
According to still another aspect of the invention, a cleaning
device for an elongate, movable filter cloth comprises a support
frame, a supporting device having a support surface with numerous
perforations formed therein, said supporting device being mounted
on said support frame and being adapted for connection of said perforations
to a vacuum source or atmosphere, an imperforate sealing cover extending
over said support surface and in close proximity thereto, means
for introducing and distributing a cleaning liquid between said
cover and said filter cloth when the latter is drawn between said
cover and said supporting device, and means for forcing said cleaning
liquid through the filter cloth and into said supporting device,
wherein at least a peripheral region of said cover is caused by
said forcing means to be pressed against an adjacent surface of
the filter cloth, thereby sealing the peripheral region of the cover
against the filter cloth.
According to still another aspect of the invention, a method for
filtering a material using a horizontal vacuum filter comprises
providing a filtering machine having an endless belt of filter cloth
with a horizontal upper reach and a lower reach and at least one
vacuum tray disposed beneath said upper reach; feeding material
to be filtered onto said upper reach and applying a vacuum to said
material by means of said at least one vacuum tray in order to filter
same; intermittently advancing said upper reach of the belt in a
forward lengthwise direction by a predetermined distance; and preventing
said lower reach of the belt from moving in said forward lengthwise
direction during the advancing step by clamping a portion of said
lower reach with a clamping mechanism after filtered material has
been discharged from said portion of the filter cloth, said clamping
mechanism comprising a supporting device for supporting said filter
cloth and an imperforate sealing sheet extending over said supporting
device and in close proximity thereto, said belt extending between
said supporting device and said sealing sheet, said clamping step
being carried out by applying a vacuum to said filter cloth by said
supporting device, said sealing sheet being pulled against said
filter cloth by the vacuum.
Further features and advantages will become apparent from the following
detailed description taken in conjunction with the drawings.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation of a horizontal vacuum filtering machine
constructed in accordance with the invention with some of the lines
and components connected thereto being shown schematically for ease
of illustration;
FIG. 2 is a plan view of a vacuum clamp employed in the filtering
machine of FIG. 1;
FIG. 3 is a rear end view of the vacuum clamp of FIG. 2;
FIG. 4 is a side elevation of the vacuum clamp of FIG. 2;
FIG. 5 is a plan view of a further embodiment of a vacuum clamp
with means for introducing a cleaning liquid to a side of the filter
cloth facing the sealing sheet;
FIG. 6 is a cross-sectional elevation taken along the line VI-VI
of FIG. 5; and
FIG. 7 is a rear end view of a clamp for a filter cloth employing
positive air pressure above the sealing sheet.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The horizontal vacuum filtering machine 10 of FIG. 1 is of standard,
known configuration except for the use of a vacuum clamp 12 constructed
in accordance with the invention and the associated vacuum supplying
devices. The vacuum clamp 12 takes the place of a non-return roller
that is provided with a ratchet so that it can rotate in only the
forward direction of a filter belt 14. The belt 14 is an endless,
elongate belt of filter cloth. An upper reach 16 of this belt extends
horizontally over a series of vacuum trays at 17, 18 and 19. Each
tray is connected by vacuum pipes 20 to a vacuum pump 21 or pumps.
Preferably the individual pipes 20 are connected to main vacuum
supply pipe 23 which itself is connected to a filtrate receiving
tank 25. It is this tank which is connected to the vacuum pump 21
and also a filtrate pump 27 for removing collected filtrate from
the tank.
At the discharge end of the upper reach 16, the belt passes over
a movable terminal discharge roller 22 which can be moved by rams
24 to an extended position indicated at 26 in broken lines. The
upper end of the ram arm is connected to a connecting arm 28 which
is able to pivot at pin or shaft 30. Pivotable movement of the arm
28 causes a corresponding pivotable movement of supporting arm 32
on which one end of the roller 22 is mounted. It is the roller 22
which also functions as a drive roller to advance the filter cloth.
After passing over the roller 22, the lower reach of the belt passes
through a cloth wash box 34 wherein jets of water can be arranged
to play on the belt to remove any filter cake that remains after
discharge. The aforementioned vacuum clamp 12 is mounted in the
vicinity of the wash box 34 and is preferably mounted as close to
the wash box as possible in order that it will catch any dripping
from the belt before this occurs. As shown in FIG. 1, the filter
cloth moves from the wash box to the vacuum clamp, the construction
of which is described hereinafter. The belt next passes over a fixed
roller 36. The clean filter cloth is accumulated and tensioned by
a movable, horizontally extending roller 40 which is free to move
up and down along vertical guide members 42 and 44. The belt then
passes over fixed guide rollers 46, 48 and 50 before passing again
along the upper reach 16 of the machine.
In the operation of the machine of FIG. 1, a slurry to be filtered
is fed onto the belt 14 through a continuous feeding device 15 and
the slurry is evenly distributed over a predetermined area which
extends across the width of the belt. The device 15, which is known,
constitutes means for feeding the material to be filtered. In order
to advance the belt, the rams 24 are operated and they cause the
roller 22 to be pushed out to the position at 26. As the operation
of the vacuum clamp 12 (in a manner described below) prevents pulling
back of the belt 14, the movement of the roller 22 pulls the belt
to the right in FIG. 1 along the upper reach. The slurry placed
on the belt by the chute is pulled along until it lies over the
first vacuum tray 17. When this movement is completed, the vacuum
trays are switched on, that is, their suction becomes active, and
removal of liquid from the slurry commences. Vacuum is released
from the vacuum clamp 12 allowing the filter cloth 14 to be tensioned
by tension roller 40. Fluid pressure is then reversed in the rams
24 causing the roller 22 to retract. Tension on the filter cloth
is maintained by tension roller 40 which accumulates the cleaned
filter cloth. The slack increases at the roller 40 so that the latter
is able to return to its lowermost position.
As this cycle is carried out, the feed slurry is continuously delivered
to the belt by the device 15. It is delivered to a pool or non-vacuum
section on the upper reach of the belt. The vacuum trays are switched
"off" at each pulling forward stage and "on"
during each retensioning stage.
Further description of the filtering machine herein is believed
unnecessary because, except for the vacuum clamp described hereinafter,
such machines are known in the art and are available from such companies
as Komline-Sanderson Limited of Brampton, Ontario, Canada.
Turning now to FIGS. 2 to 4 of the drawings wherein the construction
of the vacuum clamp 12 is illustrated, the clamp includes a support
frame 52 and a planar supporting device 54 having a perforated support
surface 56 for supporting the filter cloth of the belt 14. The supporting
device is mounted on the support frame and is adapted for connection
to a vacuum source so that a vacuum can be applied to numerous holes
60 in the support surface. Preferably the support surface forms
a rectangular grid comprising rows of closely spaced holes 60. This
grid is surrounded by a sealing surface 62. Preferably the sealing
surface extends along all four sides of the rectangular grid and
this surface should be sufficiently wide to ensure an adequate seal
is created. The rectangular drainage grid 54 is preferably made
of low-friction polypropylene. This grid itself can be made in a
similar fashion to the known vacuum trays 17 to 19 used to carry
out the filtering operation in the machine 10. The grid can be made
from a drilled or otherwise perforated plate. It can also be made
by injection moulding process. A bottom section 64 of the device
54 is open and communicates with all of the holes 60 formed in an
upper section of the device. Thus, the bottom section 64 acts as
a vacuum plenum for the device. This plenum can be connected via
downwardly extending pipe 66 to a vacuum source which preferably
is the same vacuum source that is connected to vacuum trays 17 to
19.
The clamp includes an imperforate sealing sheet 70 that extends
over the support surface 56 and is in close proximity thereto. The
sheet 70 should be supple to allow the vacuum (or possibly pressure
forces--see below) to form a secure seal between the underside of
the sheet and the sealing surface 62. One suitable material for
the sheet 70 is Neoprene. In order to hold this sealing sheet in
place, a support bar 72 extends across the path of the belt 14 and
is supported above the level of the device 54 by means of upright
frame members 74 and 76. These frame members can be supported at
the bottom by the above-mentioned support frame 52. The bar 72 preferably
has a circular cross-section so that the forward end of the sealing
sheet 70 can be wrapped around the bar as indicated in FIG. 4. An
end section 78 of the sealing sheet is secured to a transversely
extending frame member 80 by a number of bolts 82.
In order to provide better sealing, it is preferred that a number
of weights 84 be provided at the edges or periphery of the sealing
sheet. These weights are positioned on top of the sealing sheet
and are secured thereto. The weights are located above the sealing
surface 62 and preferably comprise a number of flat tile-like members
arranged in four rows 85 to 88 around the perimeter of the grid
of holes 60. Although the use of the weights is optional, these
weights help ensure close contact between the sealing sheet, the
filter cloth and the sealing surface 62. By using small dense tile-like
weights, this allows the sealing sheet to close tightly even when
the bulky seal section of the belt 14 is passing through the vacuum
clamp. A heavy metal, such as stainless steel, can be used to make
the weights 84.
It will be understood that the belt 14 of filter cloth as indicated
in FIG. 4 is drawn between the supporting device 54 and the sealing
sheet 70. Then, when one wishes to prevent backward movement of
the belt, vacuum can be applied to the filter cloth in the area
of the perforated support surface 56 in order to prevent movement
of the cloth. When this vacuum is applied, the sealing sheet is
pulled against the filter cloth by the vacuum and thereby prevents
air from passing through the filter cloth in the area of the perforated
support surface. The filter cloth has a width corresponding substantially
to or slightly greater than the dimension of the rectangular grid
56 which is perpendicular to the direction of movement of the filter
cloth.
A three-way valve 100, of which there can be several on the machine,
is mounted on the side of the machine near the upper reach of the
belt 14 as shown in FIG. 1. The valve can be constructed in the
manner illustrated and described in U.S. Pat. No. 4,857,194 which
issued Aug. 15, 1989 to H. G. Pierson, the disclosure of which is
incorporated herein by reference. Other known actuated three-way
valves can also be used for this purpose of controlling the application
of vacuum to the vacuum trays. The three-way valves 100 are connected
to downwardly extending pipes of the vacuum trays. The valves alternately
connect the plenums of these vacuum trays to the vacuum source,
for example, vacuum pump 21 or to atmosphere.
It will be understood that a similar three-way valve 103 can be
connected to the vacuum clamp 12 in order to operate same. In such
case, one arm or connection of the valve is connected to the pipe
66 of the vacuum clamp and another arm or connection is connected
to the vacuum source. A suitable commercial valve to operate the
clamp 12 is a Durco 3 way plug valve with actuator, available from
The Duriron Company Inc. For small applications, an Asco 3 way solenoid
valve can be used. By a simple control arrangement, one can operate
the valves for the vacuum trays 17, 18, 19 in an alternating fashion
with the valve for the vacuum clamp. With such an arrangement, it
is possible to use the same vacuum source for both the operation
of the vacuum trays of the filtering machine and the operation of
the vacuum clamp as illustrated in FIG. 1. When the valves for the
vacuum trays are in one position causing the vacuum trays to be
vented, the valve 103 for the vacuum clamp is in the opposite position
causing the vacuum clamp to operate and hold the filter cloth firmly
against movement. Similarly, when the valves 100 for the vacuum
trays are in another position causing vacuum to be supplied to the
trays, the valve 103 for the clamp is in a different position so
that its supporting device 54 is vented.
An optional, added feature of the vacuum clamp is the possible
inclusion of means for introducing water to the side of the filter
cloth facing the sealing sheet 70. This added water is then drawn
through the filter cloth during operation of the vacuum clamp in
order to remove solids that may be still entrained in the filter
cloth. Not only water, but other suitable cleaning liquids, can
be introduced in this manner. Back flushing the filter cloth in
this way can provide very effective cleaning of the cloth which
cannot be achieved by spraying onto the filter cake side of the
cloth. This back flushing technique may be utilized in the filtering
machine 10 independently of the need to clamp the filter cloth,
if desired.
Shown in FIGS. 5 and 6 is another embodiment of a vacuum clamp
101 for an elongate, movable filter cloth. Except as described hereinafter,
the vacuum clamp 101 is constructed in a similar fashion to the
vacuum clamp 12 shown in FIGS. 2 to 4 of the drawings. The vacuum
clamp 101 is equipped with means for introducing a cleaning fluid,
such as water, to a side of the filter cloth 14 facing an imperforate
sealing cover or sealing sheet 102. The cleaning liquid or water
is drawn through the filter cloth during operation of the clamp
101 in order to remove solids entrained in the filter cloth. The
sealing cover 102 extends over the support surface 104 and in close
proximity thereto. There are means for introducing and distributing
the cleaning liquid or water between the cover 102 and the filter
cloth when the latter is drawn between the cover and the supporting
surface 104. The preferred means includes a number of side-by-side
distribution channels 106. As shown in FIG. 6, these channels have
an inverted V shape in cross-section and they are closed at each
end so that water in the channels tends to be forced through the
filter cloth by the cover. As illustrated in FIG. 5, the channels
cover a rectangular area that is substantially the same in its dimensions
as and located directly over the rectangular grid that forms the
perforated support surface 104. The channels are cut or otherwise
formed in a relatively thick, flexible central pad 108 which is
waterproof. Extending along side edges of this central pad are flexible,
sealing side pads 110 and 111. Extending across the top of the central
and side pads and helping to connect these pads together is a rectangular,
flexible top sheet 112 which can be made of a suitable plastics
or rubber material. The side pads 110 and 112 can be covered with
bottom sheets or pads 114 and 116 with the bottom sheet 116 extending
around the support bar 72. In order to provide for a better and
more even distribution of the water over the adjacent surface of
the filter cloth, there is preferably provided a thin distribution
membrane 120 which extends across the bottom of all of the channels
and across the bottom of sheets or pads 114 and 116. The membrane
120 is covered with rows of small slits or slots 122 which permit
the even flow of the cleaning fluid through the membrane from the
channels. The membrane is bonded or otherwise firmly secured to
the bottom sheets 114 and 116.
In order to deliver water or cleaning fluid to the channels, there
can be provided a series of metal or plastic pipe connectors 124.
These pipe connectors extend through the top sheet 112 and through
the central pad 108 so that they each open into two or more adjacent
channels 106 in the manner illustrated in FIG. 6. The pipe connectors
can be distributed diagonally across the sealing cover in the manner
illustrated in FIG. 5, if desired. It will also be understood that
the relatively short, rigid pipe connectors 124 will normally be
connected to flexible rubber or plastic hose to a source of water
or other cleaning fluid (not shown) which is fed under a suitable
pressure. It will be understood that the flow of water or cleaning
fluid will be shut off when the clamp is not operating and the vacuum
source is not connected to the clamp. The flow of water is resumed
by a suitable control device when the clamp is used to stop movement
of the filter cloth.
There are means for forcing the cleaning liquid through the filter
cloth of the belt 14 and into the supporting device or grid. If
the vacuum clamp 101 is in fact acting as a clamp and vacuum is
being applied to the downwardly extending pipe 66, then the vacuum
will act as said forcing means, in effect pulling the cleaning liquid
from the channels 106, through the membrane 120 and through the
filter cloth. The rows of weights 84 about the perimeter of the
cover will also act to press the cover down against the sealing
surface 62 and this action will also tend to force the water or
cleaning liquid through the filter cloth.
It should also be understood that the device 101 of FIGS. 5 and
6 can also be used simply as a cleaning device for a filter cloth
and it need not be employed as a vacuum clamp. In this case, the
vacuum force, if any, applied by the supporting device 54 will be
substantially less so that it does not prevent further forward movement
of the belt 14. The device 101 then simply acts to apply a cleaning
liquid or water to the upper surface of the belt where either the
pressure of the water or a mild vacuum pushes or pulls the cleaning
liquid through the filter cloth. After passage through the cloth,
the liquid drains out through the pipe 66.
Instead of using a vacuum clamp in order to effectively prevent
movement of the filter cloth, it is also possible to use positive
air or gas pressure, particularly in a filtering machine that uses
positive pressure to carry out the filtering operation. These known
filtering machines are sealed in their upper section through which
the belt extends so that a positive pressure can be built up above
the filter cloth. This positive pressure is then used to push the
filtrate through the material being processed.
A gas pressure operated clamp for an elongate, movable filter cloth
is illustrated in FIG. 7. Except as specifically described hereinafter,
this clamp 130 constructed in the same manner as the vacuum clamp
12 described above. This clamp also includes a planar supporting
device 54 which preferably forms a rectangular grid having numerous
perforations arranged in rows. This device supports an area of the
filter cloth on its perforated support surface arranged to extend
along one side of the filter cloth. An imperforate pressure sheet
132 extends over the supporting surface and in proximity thereto.
There are means for applying gas pressure to one side of the sheet
132 so as to press the sheet towards the supporting surface over
said area of the filter cloth. This gas pressure applying means
can include a separate enclosure 136 indicated in dotted lines in
FIG. 7. This sealed enclosure extends around the supporting device
54 and the pressure sheet 132 and it can include a top 138, sidewalls
140 and 142 and a bottom wall 144. The top extends over the pressure
sheet and is spaced therefrom to provide an air space 146 between
the top and the pressure sheet 132. There can be means for maintaining
a positive air pressure, that is one exceeding atmospheric pressure
in the enclosure 136. This maintaining means can comprise an air
compressor 148 connected to the enclosure by means of suitable piping
150. If the enclosure 130 is maintained under sufficient positive
air pressure when a clamping force is to be applied to the filter
cloth, the holes in the rectangular grid at 54 can simply be vented
to atmosphere through the pipe 66. It will be understood that during
use of the clamp 130, the elongate filter cloth is drawn between
the pressure sheet 132 and the supporting device 54 and the positive
gas pressure above the sheet is applied to the sheet 132 to clamp
the filter cloth between this sheet and the supporting surface to
prevent movement of the filter cloth in its longitudinal direction.
Instead of a separate enclosure 136 for the clamp, it is also possible
to place the clamp in the same enclosure that is used for the filtering
machine as a whole, when this machine is one that uses positive
pressure to carry out the filtering operation. In this version,
the rectangular grid 54 can still be vented to atmosphere through
a suitable pipe 66.
The gas pressure clamp 130 can also, if desired, be provided with
means for introducing water to a side of the filter cloth facing
the pressure sheet 132. This water or cleaning liquid is forced
through the filter cloth during operation of the device in order
to remove solids entrained in the cloth. The means for introducing
the water or cleaning liquid can be constructed in the same manner
as illustrated for the vacuum clamp of FIGS. 5 and 6. The water,
again, is introduced through short pipe connectors 124 that project
upwardly from the pressure sheet 132. In this embodiment, it is
the pressure of the water entering the channels in the sheet 132
which forces the water through the filter cloth and into the support
device 54. Because the positive air pressure acting downwardly on
the sheet 132 holds the sheet firmly against the top of the filter
cloth, the water in the channels has nowhere to go except through
the filter cloth.
The advantages of the vacuum clamp and gas-pressure operated clamp
of the invention will be readily apparent to those skilled in the
use of horizontal vacuum filtering equipment. With such clamps,
it is possible to restrain the filter cloth across its entire width,
and thus distribute the forces that act on the cloth. These clamps
can be used with both lightweight and heavy weight filter cloth.
It is possible to operate the clamp using the vacuum pump or the
air compressor that is already provided with the filtering machine
for purposes of the filtering process. The clamping force can be
applied whether the filter cloth is clean or dirty. In the case
of a vacuum clamp constructed in accordance with the invention,
any residual moisture which is in the filter cloth when it enters
the clamp will be removed as part of the clamping process and this
may eliminate the requirement for drip trays underneath the filter
machine.
It will be obvious to one skilled in this art that various modifications
and changes can be made to the vacuum clamp, filtering machine and
gas-pressure operated clamp described herein without departing from
the spirit and scope of this invention. Accordingly, all such modifications
and changes as fall within the scope of the appended claims are
intended to be part of this invention.
|