U.S. patent application number 10/097918 was filed with the patent office on 2002-07-11 for apparatus for repairing or refurbishing a filtering screen.
Invention is credited to Bailey, Arthur Robert, Cook, Gordon James, Hartnup, George Charles, Hughes, Andrew, Stewart, Dugald.
Application Number | 20020088747 10/097918 |
Document ID | / |
Family ID | 26311102 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020088747 |
Kind Code |
A1 |
Cook, Gordon James ; et
al. |
July 11, 2002 |
Apparatus for repairing or refurbishing a filtering screen
Abstract
apparatus for repairing or refurbishing a filter screen (of the
type defined in the specification) is described. The apparatus
comprises a tray for accommodating a filter screen frame from which
worn wirecloth has been stripped. Wirecloth stretching means
surrounds the tray which includes attachment means for securing to
edges of a sheet of wirecloth laid over an upper surface of the
frame in the tray. Tensioning means is provided for exerting
tension on the wirecloth in at least two mutually different
directions so as to stretch it over the frame, and heating means is
provided for heating the frame to soften the uppermost edges of a
matrix of struts and periphery of the frame. Forcing means serves
to force the wirecloth into the softened edges such that after
cooling, the wirecloth remains bonded to the frame. Thereafter the
wirecloth can be trimmed back to the edges of the frame. A second
attaching means and tensioning is provided to enable at least a
second sheet of wirecloth to be secured over the first wirecloth
for bonding to the frame, at the same time as the first wirecloth
is bonded to the frame. Additional means is provided for applying
plastics material along each of the surfaces to which the new
wirecloth is to be attached, prior to, or after, wirecloth has been
stretched over the support frame, so as to increase the amount of
plastics material available to bond the wirecloth to the frame.
Inventors: |
Cook, Gordon James;
(Newtonhill, GB) ; Hughes, Andrew; (Edinburgh,
GB) ; Bailey, Arthur Robert; (Sutton Coldfield,
GB) ; Hartnup, George Charles; (Gorebridge, GB)
; Stewart, Dugald; (Edinburgh, GB) |
Correspondence
Address: |
Lee, Mann, Smith, McWilliams, Sweeney & Ohlson
P.O. Box 2786
Chicago
IL
60690-2786
US
|
Family ID: |
26311102 |
Appl. No.: |
10/097918 |
Filed: |
March 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10097918 |
Mar 13, 2002 |
|
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09367379 |
Nov 1, 1999 |
|
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Current U.S.
Class: |
210/499 ;
156/160; 156/229 |
Current CPC
Class: |
B07B 1/4627 20130101;
B29C 45/14336 20130101; Y10T 428/12361 20150115; B01D 29/012
20130101; B07B 1/4618 20130101; B01D 29/05 20130101; B01D 29/445
20130101; B07B 1/4672 20130101; Y10T 428/12347 20150115; B07B
2201/02 20130101; Y10T 428/12444 20150115; B29C 70/82 20130101;
B07B 1/4645 20130101; B29C 2045/14442 20130101; B29L 2031/737
20130101; Y10T 428/298 20150115; B07B 1/48 20130101; Y10T 29/49895
20150115; B07B 1/4663 20130101; Y10T 29/49616 20150115; Y10T
428/12965 20150115; B07B 1/46 20130101; B29C 70/56 20130101; B29C
70/885 20130101; B29L 2031/14 20130101; Y10T 428/249923 20150401;
Y10T 29/4962 20150115 |
Class at
Publication: |
210/499 ;
156/229; 156/160 |
International
Class: |
C09J 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 1997 |
GB |
9704332.7 |
Sep 19, 1997 |
GB |
9719850.1 |
Claims
1. An apparatus for refurbishing a filter screen of the type
described, from which worn wirecloth has been stripped, the
apparatus comprising: (a) a tray for accommodating a stripped
filter screen frame, (b) wirecloth stretching means surrounding the
tray including attachment means for securing to edges of a first
sheet of wirecloth laid over an upper surface of the frame in the
tray, (c) tensioning means for exerting tension on the wirecloth in
at least two mutually different directions whilst it is so
stretched over the frame, (d) heating means for heating the frame
to soften the uppermost edges of a matrix of struts and periphery
of the frame, and (e) forcing means for forcing the wirecloth into
the softened edges such that after cooling, the wirecloth remains
bonded to the frame so that the wirecloth can be trimmed back to
the edges of the frame.
2. An apparatus according to claim 1 further comprising attaching
means and tensioning means to enable at least a second sheet of
wirecloth to be secured over the first wirecloth for bonding to the
frame.
3. An apparatus according to claim 1, wherein additional means is
provided for applying plastics material along each of the surfaces
to which the wirecloth is to be attached prior to, wirecloth being
stretched over the support frame, so as to increase the amount of
plastics material available to bond the wirecloth to the frame.
4. An apparatus according to claim 1 wherein additional means is
provided for applying plastics material along each of the surfaces
to which the wirecloth is to be attached after wirecloth has been
stretched over the support frame, so as to increase the amount of
plastics material available to bond the wirecloth to the frame.
Description
FIELD OF INVENTION
[0001] This invention concerns screens for use as filters in
vibratory filtration equipment such as shakers that are used in the
oil drilling industry for separating solids from the liquid phase
of oil and water based muds retrieved from drilling operations. In
particular the invention is concerned with the construction of
apparatus by which such a screen can be repaired or refurbished to
enable new woven wire cloth to be stretched over and secured to a
support frame from which worn or damaged wire cloth has been
removed, to thereby enable the support frames of such screens to be
re-used.
BACKGROUND
[0002] Examples of filtering machines in which such screens are
used are contained in UK 2237521 and UK 2229771.
[0003] One such screen is described in PCT/GB95/00411
(WO95123655).
[0004] The earlier design of screen extends the life of a screen by
providing a sacrificial support cloth of woven wire below an upper
woven wire cloth of harder wearing material than that of at least
the surface of the wire from which the lower cloth is woven, so
that wear due to rubbing and vibration during use occurs to a
greater extent in the lower cloth than in the upper cloth. The
specification also describes an improved design of frame across
which woven wire cloths can be tensioned and bonded by adhesive, to
form a sifting screen, in which the frame is proposed to be formed
from glass reinforced gas blown polypropylene with elongate metal
reinforcing elements or rods buried in the GRP. The improved frame
construction is shown in FIGS. 3 to 8 of the earlier
specification.
[0005] It is an object of the present invention to provide an
improved method of constructing such a frame and an improved frame
for use as the support for layers of woven wire cloth, an improved
screen formed from such a frame, and a frame which can be re-used
under some circumstances.
SUMMARY OF THE INVENTION
[0006] The method of repair or refurbishment which can be performed
by the apparatus embodying the invention, is applicable to a
filtering screen formed from a support frame which is formed from
glass reinforced plastics material, the faces of peripheral edge
regions of the support frame over which woven wirecloth is overlaid
and to which the cloth be bonded by heating, wherein the peripheral
edge regions are formed with a plurality of closely spaced apart
parallel ridges so that when the surface is heated, the crests of
the ridges soften, and the woven wirecloth laid thereover and
tensioned can, under an appropriate downward loading, penetrate and
become embedded in the softened crests. Such a filter screen will
hereinafter be refreed to as a filter screen of the type
described.
[0007] According to the present invention apparatus for repairing
or refurbishing a filter screen from which worn wirecloth has been
stripped comprises a tray into which the stripped frame is
inserted, wirecloth stretching means surrounding the tray including
attachment means for securing to the edges of a sheet of wirecloth
laid over the upper surface of the frame in the tray, tensioning
means for exerting tension on the wirecloth in at least two
different directions whilst it is so stretched over the frame,
means for heating the frame to soften the uppermost edges of the
matrix of struts and periphery of the frame, and means for forcing
the wirecloth into the softened material such that after cooling,
the wirecloth remains bonded to the polymer frame, and can be
trimmed back to the edges of the frame. Apparatus as aforesaid may
also comprise further attachment means and tensioning means to
enable at least a second sheet of wirecloth to be secured over the
first for bonding to the frame, preferably at the same time as the
first.
[0008] In such apparatus additional means may be provided for
applying plastics material along each of the surfaces to which the
wirecloth is to be attached prior to or after wirecloth has been
stretched over the support frame, so as to increase the amount of
plastics material available to bond the wirecloth to the frame.
[0009] Apparatus according to the invention enables screens of the
type described to be repaired or refurbished in accord with the
following method, namely stripping worn or damaged wirecloth from
the surface of a polymer frame, placing fresh cloth over the frame
and tensioning it as appropriate, applying heat to soften the
surfaces of the frame over which wirecloth is stretched, so that
the latter can penetrate the softened plastics material and become
embedded therein, after which the assembly is allowed to cool, the
tensioning force is removed, and the wirecloth edges are trimmed
back to the surrounding flange of the frame.
[0010] In a method of repair or refurbishment as aforesaid plastics
material may be applied to the surface of the frame which is to
receive the wirecloth before the latter is fitted thereover, to
provide additional plastics material for bonding the wirecloth to
the frame.
[0011] The stripped support frame may be inserted in a mould and
fresh polymer material injected into the mould so as to reform on
the surfaces of the frame ridges similar to those which existed
when the frame was first manufactured, before the wirecloth is
applied thereto.
[0012] Using apparatus embodying the invention thus enables the
repair or refurbishment of a filter screen of the type described
wherein worn or damaged wirecloth is replaced by fresh wirecloth in
accordance with the above method.
[0013] A method of repair or refurbishment using apparatus as
aforesaid, may also involve the steps of removing worn or damaged
wirecloth from a support frame, placing a plastics sheet, similar
in size and pattern of openings to the support frame when viewed in
plan, over the frame which is to be repaired, in alignment
therewith, before or after new wirecloth is stretched thereover and
before heat and pressure is applied, to provide additional plastics
material to bond the new wirecloth to the frame.
[0014] A method of constructing a polymer support frame for use in
a filter screen of the type described, over which woven wire cloth
is to be stretched and secured to form the sifting screen,
comprises the steps of locating in a mould tool a wire frame
assembly comprising two parallel spaced apart arrays of reinforcing
wires, closing the tool, injecting liquid polymer so as to wholly
encapsulate the wire frame and to form an article having an open
central region crisscrossed by intersecting orthogonal ribs bounded
on all sides by a rigid flange, in which each of the ribs includes
two parallel spaced apart wires of the said wire frame assembly,
permitting the polymer to cure, and opening the tool, and removing
the moulded article.
[0015] By arranging for two parallel spaced apart wires to extend
through each of the ribs, one near one edge and the other neaer to
the opposite edge of the rigs, each rib has the stiffness of a
beam, and the resulting frame has high rigidity and resistance to
bending, yet remains relatively lightweight.
[0016] Preferably the wire frame is selected so as to impart
sufficient structural rigidity to the support frame as to prevent
deflection thereof and consequent changes in the tension in the
wire cloth when fitted thereto.
[0017] Additionally the wire frame is selected so as to impart
sufficient strength to the support frame as to allow the latter to
withstand shear stresses introduced as the frame is clamped into a
vibratory screening machine.
[0018] Typically the wire frame is formed from high tensile
straightened steel wire, bent as required, and in a preferred
arrangement the wire is of 2.5 mm diameter.
[0019] A reinforcing wire frame for use in making a support frame
as aforesaid, may be formed by the steps of:
[0020] equally spacing apart cut lengths of wire in a jig to form a
first array,
[0021] locating thereover a second equally spaced array of cut
lengths of wire at right angles to the first array,
[0022] resistance welding the wires of the two arrays at all the
points of intersection so as to form a first rectilinear matrix
[0023] similarly positioning two similar arrays of similarly cut
lengths of wire in a jig and resistance welding the points of
intersection of the orthogonal wires so as to form a second,
similar rectilinear matrix,
[0024] bending in a press break the protruding lengths of wire on
at least two of the four sides of one of the rectilinear matrices,
so as to bend each protruding section first in a generally upward
sense and then at a point nearer to its end in a downward sense so
that the end region of each protruding length extends parallel to
the plane containing the matrix, but is displaced therefrom,
and
[0025] and thereafter resistance welding the displaced ends of the
protruding wires of the said one matrix to the protruding ends of
the wires of the other matrix.
[0026] The welding may be in part effected through the intermediary
of transversely extending filler wires, so that intersections are
provided where welds are to be formed between parallel protruding
ends of the reinforcing wires, and the filler wires facilitate the
resistance welding of the parallel protruding ends.
[0027] Preferably the wire frame fabrication is assembled so that
each matrix is bowed in an outward sense, opposite to the
other.
[0028] During moulding it has been found that the pressure within
the mould tool can distort the framework so that the outward bowing
of the opposite faces of the framework can be replaced by
significant inward bending - so destroying the alignment of the
long rods within the upper and lower edges of the interstices of
the moulded frame. To avoid this it is proposed that at least one
spacer is located within the framework, so that if there is any
tendency for the rod arrays to collapse inwards, the spacer will
present this collapse occurring.
[0029] Preferably a plurality of spacers are located within the
wire frame fabrication, each attached to one or other of the
matrices so as to extend towards the other, whereby any tendency
for the matrices to collapse inwards during moulding, is resisted
by the spacers.
[0030] In one embodiment each spacer comprises a length of wire
bent to form a shallow U with its two ends bent outwards to form
two in-line lugs by which it can be welded to the underside of one
of the wires which form one of the matrices, with the crest of the
U section in close proximity to one of the wires of the other
matrix, whereby the spacer will maintain a given dimension between
the two matrices if the fabrication is subjected to a collapsing
force during moulding, so causing the crest to engage the said wire
of the other matrix.
[0031] A method of moulding a support frame in a mould tool as
aforesaid around a wire frame fabrication as aforesaid involves
exerting an inward force on opposite faces of the fabrication
within the mould tool by fingers protruding inwardly from the
inside faces of the tool, to externally engage the opposite
matrices of the fabrication when the tooling closes. The fingers
sandwich the fabrication in position and produce just the required
inward movement of the two oppositely bowed matrices to render them
parallel and spaced apart by the desired distance.
[0032] Typically the fingers comprise inwardly projecting pegs
which align with crossing points of wires in the upper and lower
reinforcing matrices, to space the matrices from the corresponding
upper and lower internal surfaces of the mould tool and ensure that
the matrices are buried within the plastics material which is
injected into the mould tool during the manufacturing process.
[0033] Preferably the ends of the pegs taper to an edge, or a
point.
[0034] After the mould tool is opened and the protruding pegs
disengage from the struts, openings are left in the polymer.
Preferably therefore the method further comprises plugging the
openings with plastics material or filler.
[0035] Typically the wire frame fabrication is supported within the
tooling by means of retractable pins which protrude through the
tooling wall to engage the fabrication and accurately locate it
within the tooling.
[0036] The pins may be retracted as the tooling opens after the
moulding step has been completed.
[0037] Conveniently the pins align with protruding ends of wires
making up the fabrication and are separably joined to the ends of
the wires by means of sleeves of plastics material opposite ends of
which receive the pins and the reinforcing wire ends
respectively.
[0038] Preferably the passage through each sleeve is blocked so as
to form two coaxial blind bores, and each sleeve becomes embedded
in the polymer during moulding and remains in the polymer as the
pin which engages it is retracted as the tooling is opened, the
blocked passage serving to encapsulate the end of the wire end
located in the inner end of the sleeve.
[0039] Prior to moulding the tool may be fitted with pegs formed
from a plastics material which is compatible with or is the same as
the polymer material which is to be injected into the mould to
encapsulate the wire frame fabrication, and the pegs become
integrally bonded therein during moulding so that when the tool is
opened, the pegs separate from the tool, and remain in the
frame.
[0040] Protruding portions of each peg may be removed by grinding
or filing or cutting.
[0041] It is generally desirable for the wires of the cloths to be
taut and under tension in the finished product and it is for this
purpose that the wirecloth wires are put in tension whilst the
plastics material is allowed to cool and set hard, to bond the
woven wire cloths to the frame. This aspect is of particular
advantage in that by using a suitable polymer for the frame
material and heating the surfaces in contact with the wire cloths,
so the need for an adhesive is obviated as is the step of applying
the adhesive.
[0042] It is of course necessary to select a plastics material
which is suitable to serve as a bonding medium for woven wire cloth
and it has been found that polypropylene and polyethylene are
suitable plastics materials although the repair apparatus of the
invention is not limited to the use of support frames of
polypropylene and polyethylene material.
[0043] Whether polyethylene or polypropylene is used, it has been
found advantageous for either material to be gas blown and glass
fiber reinforced.
[0044] In a preferred arrangement, the wirecloth which is first
fitted over the support frame has a coarser mesh than any
subsequent layer of wirecloth fitted thereover.
[0045] In general, filtering screens will have two layers of woven
wirecloth fitted thereover and bonded thereto, in which the lower
wirecloth has a coarser mesh than the upper wirecloth and in which
the tension in the wires forming the upper wirecloth is less than
the tension in the wires forming the lower wirecloth.
[0046] A wire frame reinforcing fabrication for a support frame as
aforesaid, may be formed from resistance welded steel wire matrices
arranged in two parallel spaced apart planes and themselves welded
together along at least two edge regions by welds between
protruding ends of the wires of the two matrices.
[0047] In a method of forming a wire frame reinforcing cage for
incorporating in a mould tool for moulding a polymer material
therearound to form a support frame for a filter screen of the type
described, the cage may be constructed from two similar rectilinear
arrays of resistance welded wires, and the method involves bending
protruding wires along at least two sides of one of the arrays and
welding the ends of the bent portions of the wires of the one array
to the protruding ends of the wires in the other array, so as to
maintain separation between the two matrices.
[0048] A method of constructing a filter screen of the type
described comprises the steps of forming a polymer support frame
having therein a plurality of similarly sized rectilinear apertures
defined by an integral rectilinear matrix of wire reinforced struts
of polymer material, in which the upper edge of each strut, and the
upper surface of each boundary of the support frame, is ridged, and
in which the woven wirecloths are fitted over the ridges,
tensioned, and secured in place by heating at least the ridges so
as to soften the polymer material therein sufficiently to allow the
wirecloths to penetrate the crests thereof and upon cooling to
remain embedded therein, so as to maintain tension in the wires of
the wirecloths after cooling.
[0049] The method may also involve the step of differentially
tensioning the wires in one wirecloth relative to those in the
other, so that different tensions exist in the wires of the two
cloths after bonding to the polymer support frame.
[0050] The reinforcing matrix is preferably formed from high
tensile steel wire of nominally 2.5 mm diameter, and glass
reinforced gas blown polypropylene polymer is injected into the
mould tool under pressure and is left to cure for a given period of
time, and the moulded support frame then removed, a first woven
wirecloth of nominally 30 mesh formed from stainless steel wire of
nominally 0.28 mm diameter is fitted over the support frame and
tensioned, a second woven wirecloth is fitted over the first
wirecloth, the second cloth being formed from wire having a smaller
diameter and a finer mesh size than the first cloth, and is
likewise tensioned, a force is applied over the face of the support
frame carrying the overlaid wirecloths, heat is applied to soften
the crests of the ridges and to allow the two cloths to become
embedded in the crests of the ridges such that after the heating
and force is removed and the frame has cooled, the cloths remain
bonded to the crests of the ridges and residual tensions exist in
the wires forming the two cloths.
[0051] In a support frame which is to have woven wirecloth bonded
to the one face thereof by locally heating the frame material and
forcing the wirecloth wires into the softened material before it is
allowed to cool and harden again, and which is formed from glass
reinforced plastics material having embedded therein a reinforcing
wire frame constructed as aforesaid, preferably the thickness of
the plastics material between the reinforcing wires and the face of
the support frame members to which the woven wirecloth is to be
bonded is selected so as to be sufficient to enable the wirecloth
to be embedded therein without making contact with the reinforcing
wires.
[0052] Preferably the plastics material comprises a polypropylene
or a polyethylene, and may be gas blown and glass fiber
reinforced.
[0053] In a support frame which is formed from glass reinforced
plastics material, the faces of the peripheral edge regions of the
support frame which woven wirecloth is to overlay and to which the
cloth is to be bonded by heating, are formed with a plurality of
closely spaced apart parallel ridges so that when the surface is
heated, the crests of the ridges soften, and woven wirecloth laid
thereover and tensioned can, under an appropriate downward loading,
penetrate and become embedded in the softened crests.
[0054] In a method of constructing a filter screen using a support
frame as aforesaid the heat is preferably applied through the woven
wirecloth so as to preferentially heat the crests of the ridges as
opposed to the remainder of the support frame.
[0055] In a support frame as aforesaid, which is generally
rectangular, the ridges along each of the four sides run parallel
to the length dimension of each side so that the ridges in the
surfaces of the four edges of the frame run perpendicular to the
direction in which woven wirecloth is tensioned relative to those
edges.
[0056] Where the frame includes a matrix of wire reinforced struts
defining within the boundary of the frame a plurality of openings,
sufficient plastics material exists in each of the struts between
the internal wire reinforcement therein and the cloth engaging
surface thereof, to enable the strands of wire forming the
wirecloth also to become embedded in the struts when the frame is
heated and an appropriate force is applied, without the wirecloth
contacting the internal reinforcing wires, to prevent electolytic
action between wirecloth and reinforcing wires where different
metals are used.
[0057] In a support frame as aforesaid, constructed from glass
fiber reinforced plastics material over which wirecloth is to be
stretched and bonded thereto to form a sifting screen and which
includes a matrix of struts within a perimeter flange of the frame,
the thickness of the cloth engaging ends of the struts is
preferably less than that of the more remote regions of the
struts.
[0058] Preferably the wirecloth engaging edge of each strut is of
reduced section, and on heating the wirecloth wires become embedded
in the said reduced strut sections.
[0059] The reduced strut section is preferably created by forming a
ridge along the wire receiving edge thereof.
[0060] A support frame formed from glass fiber reinforced plastics
material over which wirecloth is to be stretched for bonding
thereto to form a sifting screen, preferably includes an outer
peripheral flange surrounding a central region occupied by an
integral matrix of interconnecting struts wherein the flange and
struts are ridged where they are to engage the wirecloth and the
ridges extend to different heights so that the crests lie in
different parallel planes.
[0061] Preferably the crests of the ridges of the struts defining
the integral matrix lie in a first plane, which is below a second
plane containing the crests of the ridges on the surrounding
flange.
[0062] When covering a support frame as aforesaid, heat is
preferably applied uniformly over the entire face of the support
frame by means of by a flat heated platen which forces the
wirecloth into the crests of the ridges and the wirecloth has to be
pressed into the crests of the ridges on the surrounding flange
before it can enter the crests of the ridges on the struts making
up the integral matrix.
[0063] In such a support frame, outer ridges on some or all of the
surrounding flange may extend to a greater height than inner ridges
on the flange, so that the crests of the outer ridges occupy a
third plane above the second plane, whereby there is a greater
volume of polymer to be melted and spread by the application of
heat and pressure to the wirecloth near the outer edges of the
peripheral flange, than is the case near the inner regions of the
flange.
[0064] By forming ridges along the wire cloth engaging edges of the
struts, so the area of the woven wire cloth which is actually
blinded by being embedded in plastics material is reduced to the
minimum necessary to achieve support for the cloths. Thus although
the struts may have a lateral width considerably greater than the
width of their crests, the area of the woven wire cloth which is
available for filtering liquid is only reduced by the narrow width
of the melted crests and is not reduced by the total area of the
struts, which would be the case if the width of the cloth engaging
face of the struts is the same width as the struts themselves.
[0065] The struts have so far been described as being ridged and in
general they will have a symmetrical cross-section in which the
crest is mid-way between two parallel sides of the strut, and the
ridge can be thought of as an isosceles triangulation at the upper
end of a rectangular cross-section of the remainder of the strut.
However this configuration is merely a preferred form, and the
triangular cross-section of the upper region of the strut may be
offset so that the crest of the ridge is displaced towards one side
or the other of the strut when viewed end on and if the triangle is
a right angled triangle the crest will be aligned with one side or
the other of the rectangular section of the strut, the hypotenuse
of the triangle forming a sloping surface between the crest of the
ridge and the other edge of the rectangular strut region.
[0066] In general the primary purpose of the ridging of the struts
is to reduce the width of the plastics material which is to engage
the woven wire cloth, and the ridging effect can be obtained simply
by reducing the width of the strut just below its face which is to
be bonded to the wire cloth. This width reduction may be achieved
by means of a step, so as to define a shoulder, (or two steps on
opposite sides to form two shoulders), and the reduced width region
above the shoulder(s) provides the reduced width plastics face for
engaging the woven wire cloth. The difference between such an
arrangement and a triangular ridge is that in the former case, the
underside of the woven wire cloth immediately to the left or right
of a bonded crest will be completely unobstructed at least down to
the shoulder(s) whereas in the case of a triangular ridge, a
sloping surface will be presented to liquid filtering through the
wire cloth. In practice however, the stronger triangular section is
preferred particularly since differential softening will occur down
the height of the ridge upon the application of heat to the
crests.
[0067] A vibratory screening machine will usually be fitted with
two screens of the type described, wherein one of the screens is
mounted so as to be substantially horizontal in use and the other
is mounted downstream of the first and is inclined upwardly in the
direction of movement of particulate material through the
machine.
[0068] The shorter ends of support frames as aforesaid are adapted
to interlock and sealingly engage with a corresponding edges of
adjoining similar support frames such that if two frames are slid
one towards the other, engagement and sealing occurs merely by the
sliding movement of the one frame relative to the other.
[0069] The sealing engagement of one frame to the other can be
arranged to occur when the two frames are in line, or when the two
frames are mutually angled.
[0070] It is an advantage to form screens in this way and to mount
a number of such screens in a supporting framework within a
vibratory screening machine with edges abutting so as to form a
larger area for filtering, for a number of reasons.
[0071] Firstly, as already indicated, some designs of shaker
require a first filtering area to be substantially horizontal and a
second area to be inclined upwardly in the direction of particulate
movement over the overall screen. This can be achieved by forming
the overall screen from two smaller screens, each constructed as
aforesaid and adapted to be joined edge to edge where the change in
inclination is required to occur.
[0072] Secondly, each individual screen can be of such a size and
weight as can be readily handled by one man.
[0073] Thirdly in the event of damage occurring in one such screen,
it can be simply removed and a fresh screen inserted (sometimes
without needing to disturb the undamaged screen(s)). The damaged
screen can be repaired using apparatus as provided by the present
invention.
[0074] In a support frame as aforesaid, preferably the cross
section of each strut is generally rectangular and the longer
dimension is generally perpendicular to the plane of the frame, and
a first reinforcing wire extends through each strut near the edge
thereof which is to be bonded to wirecloth, and a second parallel
reinforcing wire extends through each strut near to the opposite
edge thereof, and the wires are bonded to the plastics material by
the moulding step and form therewith a beam, thereby to impart
rigidity to the structure.
[0075] Furthermore, in a support frame as aforesaid, preferably the
struts intersect similar struts which extend at right angles and a
second assembly of parallel reinforcing wires is provided, running
perpendicular to the first assembly of wires in planes proximate
those containing the first said assembly, so that a pair of
parallel spaced apart wires extends through each of the struts.
[0076] In such a support frame each reinforcing wire which aligns
with the peripheral flange of the frame preferably extends into the
flange at each end thereof, thereby to increase the rigidity of the
flange.
[0077] Preferably the ends of the other wire of each pair are bent
so as also to become aligned with the flange of the frame, and the
bent ends thereof extend into the said flanges close to the ends of
the first mentioned wire to further assist in reinforcing the said
flanges.
[0078] Typically the wires touch at all points of intersection and
are preferably welded at all such points.
[0079] Preferably the ends of each pair of wires are welded where
they occupy the flange.
[0080] In a wireframe assembly for a support frame as aforesaid,
cross-point engagement may be introduced between parallel wires in
the flange by incorporating intermediate transversely extending
filler wire, or weld wire, between the wire ends.
[0081] Further reinforcing may be provided in the flange by means
of additional reinforcing wires extending parallel to the length
direction of the flange so as to overlie or underlie the protruding
reinforcing wires entering the flange from the struts, and the
additional reinforcing wires are welded to the protruding
reinforcing wire ends.
[0082] Filtering machines of the type into which screens as
aforesaid can be fitted, are described in UK Patent Specifications
Nos. 2237521 and 2299771, but these are intended as examples only
and the invention is not limited to the use of these screens in
such machines.
[0083] The invention will now be described by way of example, with
reference to the accompanying drawings, in which:
[0084] FIG. 1 is a plan view of a frame over which wire cloths are
to be stretched and secured to form a screen for use a filter in a
vibratory filtration equipment such as a shaker for separating
solids from the liquid phase of oil and water based muds;
[0085] FIG. 2 is a cross-sectional view at CC of FIG. 1;
[0086] FIG. 3 is a part section at BB in FIG. 1;
[0087] FIG. 4 is a part section on AA in FIG. 1;
[0088] FIG. 5 is a part end view at D of the frame of FIG. 1 to an
enlarged scale;
[0089] FIG. 6 is a plan view to a reduced scale showing two
screens, each constructed using a frame such as shown in FIG. 1, in
aligned edge abutting relation, to form a larger screening
area;
[0090] FIG. 7 is a side elevation in the direction of arrow VII of
FIG. 6;
[0091] FIGS. 8 or 9 show to an enlarged scale the two
inter-engaging edge regions of the two frames of FIGS. 6 and 7;
[0092] FIG. 10 shows to enlarged scale in cross-section the
abutting region of the two frames shown circled at VIII in FIG.
7;
[0093] FIG. 11 is a plan view from above of another frame similar
to that of FIG. 1, but adapted to be joined in edge abutting
relation with another similar frame so that the two frames are
angled relative to one another when viewed from the side;
[0094] FIG. 12 is an end view at "B" in FIG. 11;
[0095] FIG. 13 is a section on DD in FIG. 11;
[0096] FIG. 14 is a part end view (to an enlarged scale) at "B" in
FIG. 11;
[0097] FIG. 15 is a part section at AA of the left hand end of the
frame shown in FIG. 11;
[0098] FIG. 16 is a part section at AA of the right hand end of the
frame of FIG. 11 showing in more detail the wire reinforcing
structure, and where inserts are required to support it within a
mould tool;
[0099] FIG. 17 is a part section at CC (to an enlarged scale) of
the frame of FIG. 11;
[0100] FIGS. 17A and 17B show how the wire frame can be supported
within a mould tool by ferrules which become an integral part of
the moulded frame to cover the ends of the wires;
[0101] FIG. 17C shows a bent-wire spacer to prevent wireframe
collapse in the mould tool, as polymer is injected under
pressure.
[0102] FIG. 18 is a side edge view of two frames of the type shown
in FIG. 11, in edge abutting engagement;
[0103] FIG. 18A is a view of the join to an enlarged scale;
[0104] FIG. 19 is a side elevation partly in cross-section of an
intersection between row and column support members of a frame such
as shown in FIG. 1;
[0105] FIG. 20 is a top plan view of the frame part shown in FIG.
19;
[0106] FIG. 21 is an elevation of a support for locating the wire
reinforcing structure at a point of intersection as shown in FIGS.
19 and 20;
[0107] FIG. 22 is an end view to an enlarged scale of the lower end
of the support of FIG. 21;
[0108] FIG. 23 shows to a larger scale the preferred engagement of
the chisel end of the stand off support with a reinforced rod;
and
[0109] FIG. 24 shows part of a completed screen.
DETAILED DESCRIPTION OF THE DRAWINGS
[0110] FIG. 1 illustrates a frame across which woven wire meshes
are to be stretched and bonded in the manner herein described. The
frame is generally designated 10 and includes a large number of
similarly sized rectangular openings, one of which is denoted by 12
formed by a rectilinear matrix of orthogonally intersecting
cross-members one of which is designated by 14 and another of which
is designated by reference numeral 16.
[0111] On two opposite sides, namely 18 and 20, the frame includes
a relatively wide flange the upper surface of which is corrugated
so as to form ridges and furrows 22. The other two edges 24, 26 and
28 are relatively narrow and include just two or three ridges 30,
32. By forming at least the ridges from a plastics material which
can be softened on heating and which sets hard on cooling, woven
wire meshes (not shown) can be stretched over the ridged peripheral
regions of the frame and embedded in the ridges by heating the
peripheral edges of the frame and pressing the wire meshes into the
softened crests of the ridges. By allowing the plastics material to
cool, so the wire meshes will be held firmly in place and if they
are tensioned in both directions prior to the heating step and the
tensions are maintained throughout, thereafter the plastics
material has cooled, residual tensions will remain in the stretched
layers of wire cloth. If as is usually preferred, the wire cloths
have been differentially tensioned so that the tension in one is
higher than that in the other, the differential will remain in the
residual tensions retained in the wire cloths.
[0112] By forming similar ridges along the top of each of the
orthogonal cross-members, and arranging that the ridges of the
cross-members are engaged by the wire cloth after the latter have
become embedded in the ridges of the surrounding flanges, by
heating over the whole surface area of the frame, so the woven wire
meshes will become secured to the crests of the crossing members
which when the assembly cools, will hold the woven wire cloths
firmly in place, and provide additional support therefor.
[0113] In a typical example, the first wirecloth will have a mesh
size of approximately 30 and the second cloth a mesh size in the
range 100-300. Each is made from annealed stainless steel
wire--that making up the first cloth typically having a diameter of
the order of 0.28 mm.
[0114] In accordance with a preferred aspect of the invention, the
frame is formed from a plastics material which may be reinforced
with glass fibers or similar reinforcing material and the edge
regions and the crossing members of the frame are all reinforced
with elongate steel wires which are welded together to form a wire
frame reinforcing structure in a manner which will be described
later. Typically steel wire of 2.5 mm diameter is used to construct
the reinforcing wire frame.
[0115] A frame such as shown in FIG. 1 is typically formed by
inserting the reinforcing framework into a suitable mould tool and
injecting plastics material under pressure into the tool so that
the wire reinforcing frame becomes completely encased within
plastics material (typically reinforced with glass fiber) so that
on release from the mould, the reinforcing wires are totally
encased within plastics material.
[0116] The section at CC in FIG. 2 shows the cross member 14 in
section and the orthogonal cross member 16 is seen extending on
either side of 14. The edge regions 18, 20 are reinforced by frame
members 34 and 36.
[0117] The cross-section at BB in FIG. 1 is shown in FIG. 3. The
cross member 14 is still visible but the orthogonal cross member 38
is now shown intersecting 14 and the opening intersected by BB is
denoted 40.
[0118] Ridges such as 24 in the upper surface of the relatively
wide edge flange 20 can be seen, as can also the inner of the two
ridges along the narrower edge 28, namely ridge 42 which is also
identified in FIG. 1 for reference purposes. The ridged end 28 is
cut away at opposite ends at 44, 46 as shown in FIG. 1.
[0119] Also shown in FIG. 3 are some of the metal reinforcing rods
forming the reinforcing framework. Two rods designated 48 and 50
extend through the upper and lower regions respectively of the
cross member 38.
[0120] Similar pairs of rods extend through the upper and lower
regions of each of the parallel cross members such as 16.
[0121] Through each of the orthogonally extending cross members
designated 14 and 52 respectively, extend two similar pairs of rods
designated 54 and 56, and 58 and 60 respectively. At the points of
intersection between the rods they are welded together as by
electric resistance welding.
[0122] Further reinforcing rods 62 and 64 extend parallel to rods
54 and 58 through the edge region 20, and this is resistance welded
to the extended ends of the rods 48 etc where they extend into the
flange 20.
[0123] The extensions of the lower rods such as 50 are bent
upwardly as shown at 66 so as to extend co-extensively with or in
contact with the underside of the upper rod of the pair eg
extension of rod 48 and are resistance welded thereto. In this way
the upper layer of intersecting and welded rods such as 48, 54, 58,
62, 64 is secured to the lower layer of rods such as 50, 56, 60, to
form a unitary reinforcing structure.
[0124] FIG. 4 is a part section on AA to a larger scale than FIG. 1
which allows the ridges 30 and 32 to be seen in section at the ends
of the frame which are to be butt-joined.
[0125] FIG. 4 also shows detail of the male and female locking
arrangement at opposite ends of the frame. Thus at the left hand
end an elongate protrusion 68 stands off from the left hand end
face 70 and extends across the entire width of the frame, whilst at
the other end of the frame the end face 72 is cutaway to define a
rebate 74 to receive the protrusion 68 of an abutting frame.
[0126] The end face 72 also includes an upstand 76 which cooperates
with the opposite end region of the end face 70 of the abutting
frame, to space the two end faces from each other by the thickness
of the upstand 76. This also assists in seating the rebate 78 in
the protrusion 68 correctly below the lp 80 along the upper edge of
the rebate 74.
[0127] FIG. 4 also shows the small openings which can be left above
the intersection point of the reinforcing grid, if stand-off pits,
or stools, are used in the mould tooling to position the
reinforcing grid within the tooling. Two of these are visible at 82
and 84.
[0128] FIG. 5 is a part end view in the direction of arrow D in
FIG. 1 and shows the upstand 76 and the end face 72 of the right
hand end of the frame as depicted in FIG. 4. Likewise the lip 80 is
also shown together with the undercut 86 in the underside of the
shoulder created by the rebate 74.
[0129] FIG. 6 shows how two frames 10 and 10' each similar to that
shown in FIG. 1 can be joined, with the two edges 26', 28
abutting/engaged as will be described more fully with reference to
later figures of the drawings.
[0130] In use the wider flanges 18 and 20, 18' and 20' and one end
flange 28' are gripped in an appropriate manner within the basket
of a shaker assembly. The end flange 20 may in fact only be
supported on its underside in order to permit solids material to
progress over that edge unimpeded during shaking.
[0131] An inflatable grip seal may be used along the edges 20, 20',
28', 18' and 18.
[0132] As shown in FIG. 7, the two frames 10 and 10' may be aligned
and in some shakers advantageously the aligned frames are mounted
so as to be inclined to the horizontal so as to describe an uphill
slope up which the mud which is to be filtered climbs as a result
of the shaking movement. Typically the shaking movement has
components generally in the direction of the alignment of the two
frames and generally perpendicular thereto.
[0133] The two separate parts forming the abutment are shown to an
enlarged scale in FIGS. 8 and 9, and detail of the engagement is
shown in FIG. 10. FIG. 9 shows the edge 28 which includes the
protruding nose generally designated 68 which extends across the
width of the frame and fits below the shoulder 80, of the rebate 74
of the cooperating frame 10.
[0134] The upstand 76 may comprise a separate member in the form of
a seal which may be of plastics material or rubber or a composite
thereof. Alternatively as shown it may simply comprise a protruding
ridge formed during moulding, in the material from which the rest
of the frame is constructed.
[0135] When mounting the two frames in a shaker, frame 10' is first
introduced into the shaker basket and thereafter frame 10. By
raising the right hand end of frame 10 (as viewed in FIG. 6) so
that the frame 10 is angled relative to the plane of frame 10', the
nose 68 can be inserted below the shoulder 80 into the undercut 86
of the rebate 74 so that the ridge 88 of the protrusion 68 engages
in the undercut 86 behind the shoulder 80. Once 88 is within 86,
the frame 10 can be lowered so as to be in alignment with 10' and
by choosing the dimensions carefully, in that condition only, the
inclined surface 90 engages the inclined underside 92 and the
upstand 76' makes contact with the face 70 of the other frame end.
This is more clearly shown in FIG. 10.
[0136] By dimensioning thus any fluid trapped between the ends of
the frame as the two frames are pushed together, can be squeezed
through the gap left between the surfaces to facilitate drainage
through the lowermost gap visible in FIG. 10.
[0137] In some shakers, it is preferred that the two screens such
as shown in FIG. 6, (each formed by a frame with woven meshes
stretched thereover) are inclined relative one to the other instead
of being aligned as shown in FIG. 7. To this end an alternative
edge configuration may be incorporated, by arranging that one frame
end can be fitted into the other with a small step between the two
upper surfaces.
[0138] FIG. 11 is a plan view of such a frame.
[0139] FIGS. 12, 13 and 14 provide edge and section views to an
enlarged scale of the case of FIG. 14, of the frame shown in FIG.
11.
[0140] Essentially the construction of the central area of the
frame is similar to that of the frame of FIG. 1. Thus the meshes
are secured to external flanges 100, 102, 104 and 106 and to the
upper edges of intersecting orthogonal cross members such as 108,
110, 112 etc.
[0141] The relatively wide flanges 100 and 102 are visible in FIGS.
12 to 14, together with the cross members 110, 112.
[0142] Each of the intersecting cross members is ridged along its
upper edge as best seen from the hidden detail of items 110, 112 in
FIG. 14. The ridges are identified by reference numerals 114, 116
and it will be noted that the peaks of the ridges 114, 116 are just
below the peak of the ridges 118 along edge 106 (see FIG. 11). This
ensures that when the GRP material is heated to accommodate the
wire meshes, the heating and welding of the meshes to the outer
regions 100 to 106 of the frame occurs prior to that over the
central region made up of intersecting cross members 108, 110
etc.
[0143] The ends 104, 106 are designed to be capable of
interengagement and accordingly the end 106 is formed with a pair
of jaws 120, 122 which extend across the entire width of the frame
end and can receive the opposed end 104 of a second frame (not
shown). This opposed end comprises an extended flange 124 having
three ridges 126 formed in its upper surface, the height of the
flanges combined with the thickness of the flange 124 being equal
to the internal spacing between the upper and lower jaws 120, 122,
so that an end 124 can be pushed into the elongate slot formed by a
pair of jaws 120, 122.
[0144] At 128 the underside of the upper jaw diverges upwardly away
from the lower jaw, to assist in entering the end 124 therein.
Being formed from a plastics based material, the ridges 126 are
deformable, and by dimensioning the gap between the jaws 120, 122
accurately, so the flange 104 can become firmly wedged in the gap
between those jaws, the ridges 126 forming a partial seal between
the flange 124 and the underside 128 of the upper jaw 120 of end
flange 106.
[0145] As with the frame illustrated in FIGS. 1 to 10, the frame of
FIG. 11 includes a grid of reinforcing rods, welded or otherwise
joined at the interstices of the grid, and constructed from upper
and lower layers--generally designated 130, 132 respectively--see
FIG. 15. The ends of the lower layer of rods are bent upwardly as
at 134 in FIG. 16 to be welded to the aligned rods of the upper
layer in the end flange 104.
[0146] The upper and lower layers of rods terminate without
converging at the other end of the frame as can be seen from the
part section of FIG. 15.
[0147] The two edges 100 and 102 are reinforced in the same way as
is end flange 104, and the ends of the rods 136 of the lower layer
are bent upwardly as at 138 in FIG. 17, to merge with and be welded
or otherwise joined to the upper rods 140.
[0148] All the rods are wholly contained within the rectilinear
array of intersecting cross members except at the flanged edges of
the frame.
[0149] The part section of FIG. 17 is taken on the line CC in FIG.
11 and cross members 110 and 112 are denoted in both figures.
[0150] FIG. 18 shows how two frames such as shown in FIGS. 11 to 17
can be fitted so that one lies at a shallow angle relative to the
other. The one frame is denoted 14.
[0151] FIG. 18A shows a modified interengagement possibility
similar to the engagement of an end such as 126 in an elongate
"socket" between jaws such as 120, 122--but in which both ends are
"female" (ie equivalent to end 106), and the upper flange of the
one can be received and wedged, into the socket of the other and a
good seal is maintained. Similar reference numerals are employed to
denote items in common as between FIG. 18A and earlier and later
figures.
[0152] As also shown in FIG. 17, plastics support inserts or stools
such as denoted by 142, 144 may be located in the mould tool so as
to engage the interstices of the intersecting rods, thereby to
correctly space the framework within the mould tool when the latter
is closed.
[0153] In an alternative spacing arrangement, the spacing and
positioning may be achieved by fingers protruding from the inside
surfaces of the mould tool, and any openings in the plastics
moulding may be filled by appropriate material after the tool has
been opened and the moulded component has been removed, or may be
filled by the plastics material from which the struts are formed
when the frame is subjected to heat and pressure during the
manufacturing process.
[0154] Preferred arrangements utilise stand-off supports or stools
since these can be used not only to centre the reinforcing
framework within the mould tool, but where the framework has been
constructed so as to bow slightly upwardly and downwardly, they
will redefine the correct spacing between the upper and lower
arrays of rods, when the mould tooling is closed. A preferred form
of such stand-off support is illustrated and described with
reference to FIGS. 19 to 23.
[0155] In order to prevent moulding pressure within the tooling
from forcing the upper and lower walled arrays of rods/wires
together so as to reduce the spacing therebetween, spacers 143
(typically bent wires, formed to one or other of the two arrays and
permitting relative movement towards each other beyond a critical
dimension defined by the spacers) are provided, as shown in FIG.
17C.
[0156] In a similar way, plastic ferrules such as that shown in
FIG. 17 and denoted by 146, can be inserted into the mould tool so
as to cover the ends of the rods which might otherwise be left
exposed.
[0157] In a preferred mould tool, the welded reinforcing framework
is supported in one part of the tooling by four retractable pins
(145), two on opposite sides of the framework, by means of double
ended plastics ferrules (146) which are each fitted at one end onto
an end of one of the rods (140) making up the framework, and at the
other end onto one of the retractable pins. After moulding, the
pins (145) are retracted from the blind holes in the ferrules (146)
which will have been embedded in the GRP during moulding, to permit
the moulded article to be removed from the tooling.
[0158] An example is shown in FIGS. 17A and 17B.
[0159] Where support inserts or ferrules protrude after moulding,
they can be removed by cutting or filing.
[0160] As mentioned in relation to FIGS. 11 et seq, the crests of
the ridges in the edge flanges of the frame shown in FIGS. 1 to 10
may also lie in a different plane from the crests of the ridges on
the cross members such as 14 and 16, and in a preferred arrangement
one or more of the outer ridges along the flanges such as 18, 20,
26 and 28 extend(s) above the plane containing the crests of the
crests of the cross members such as 14, 16. In this way the
peripheral regions of the frames contain a greater amount of
plastics material to be heated and softened before the woven wire
mesh cloth can be forced thereinto, than exists along the
cross-members. Bonding of the peripheral regions therefore has to
occur before the cloths can come into contact with, and become
bonded into the crests of the cross members 14, 16 etc.
[0161] FIGS. 19 to 23 show, to different, and generally an enlarged
scale, the location of preferred stand off supports for the
reinforcing rods. Here each support comprises a tapering
chisel-ended metal pin 148 as shown in FIG. 19. The chisel end 150
is best seen in FIG. 21.
[0162] As shown in FIG. 23, the pins are arranged so that each
chisel end 150 extends generally perpendicularly to the length
dimension of the rod 48 which it will engage in the mould tool.
[0163] By virtue of the chisel end 150, and the taper 152, liquid
plastic material flows around the tapering, chisel ends in such a
way as to leave similarly tapering recesses such as 154 in the
crests of the cross members of the frame when the tool is opened
and the chisel ends are extracted from the moulding. Each recess
left by a pin 148 therefore only exposes a tiny area 156 of the
wire (see FIG. 20).
[0164] When woven wire cloths are stretched over the crests of the
frame and the cloths and frame are heated, the plastics material
flows into the lower end of each recess left by a chisel end, such
as 150. This fills the tiny area to provide a barrier between the
wire mesh(es) and the reinforcing rods such as 48 (see FIG. 3).
[0165] FIG. 24 is a perspective view of the female end of the frame
10' of FIG. 9.
[0166] The sealing ridge 76 can be seen above the groove 74 into
which the elongate male "nose" 68 (see FIG. 9) fits.
[0167] Across the frame are stretched woven wire cloths, the upper
one of which is shown in part at 158 and the lower, in part, at
159. Two such cloths, one above the other, are stretched over the
frame, the mesh of the lower cloth being coarser than that of the
upper cloth, and with the tension in the lower cloth being greater
than that in the upper.
[0168] By heating at least the upper surface of the frame, and
applying uniform downward pressure on the cloths, the crests of the
plastics frame will soften and allow the wire cloths to sink into
the crests, which will also become flattened into the process. On
cooling the plastics material hardens and secures the wire cloths
in place.
[0169] The crests of the outermost ridges 160 on the flange extend
upwardly above the crests of the inner ridges of the same
flange.
[0170] The land area at the junction between two screens such as
shown in FIGS. 7 and 18 should be as small as possible so as not to
impede the progress of particulate material from one screen to the
next.
[0171] Likewise the front edge of the screen where solids traverse
over and off the edge, for example into a skip, should also be as
small in area as possible.
[0172] The joint provided by intermitting ends such as shown in
FIGS. 18, 18A, causes the edge 120 of the upper frame to overlie
wire mesh of the lower frame. The non-screening dead area is
thereby reduced to the minimum, ie the ridged end 120.
[0173] The joint provided by the engagement such as shown in FIGS.
18, 18A also seals the joint and prevents fluid leakage, and has
been found to reduce the risk of bounce between one frame and the
other across the joint. This appears to be achieved due to the
formation of a structural member by the reinforcing wires and where
these are tensioned, as is the case when the framework is pushed
from above and below in the mould tool, the framework and plastics
material will significantly resist bending and therefore minimise
any tendency to bounce.
[0174] Flash heating is preferably-used to bond the wire cloths to
the crests.
[0175] Weld wires are conveniently employed between overlying
parallel rods such as 48, 66 (see FIG. 3) as designated by
reference numeral 49.
[0176] The drawings and related description of UK Patent
Specifications 2237521 and 2299771 are referred to as illustrating
filtering machines of the type in which screens as described herein
may be mounted.
* * * * *