Abstrict
A screen for use with a vibrating screening machine to filter undesired
particles from a liquid uses a filter cloth having a substantially
rectangular mesh suitable for separating the undesired particles
from the liquid bonded in laminar relationship to a back-up having
a substantially coarser mesh. The substantially rectangular mesh
is formed by a lengthwise array of parallel individual wires woven
with a transverse widthwise array of parallel groups of at least
three wires. The individual wires are distorted from rectangular
proximate the ends of the rectangles by bows in the individual wires
at their area of intersection with each of the parallel groups of
wires. This configuration provides improved throughput and life
characteristics over known screens. A plastic grid of mesh substantially
greater than the back-up mesh may be fused to the bonded lamination
of the filter cloth and the back-up. The fused grid, cloth and back-up
may be corrugated in approximately triangular or sinusoidal fashion
with the apexes and nadirs of corrugation being parallel to the
groups of wires. The possibility of fracture and tearing at the
apexes and nadirs of corrugation and the midpoint bubbling is reduced
due to the distorted rectangular configuration. The screen in any
of its embodiments can also be secured to a perforated plate or
to a plurality of metal strips if additional strength is desired.
Claims
What is claimed is:
1. A screen for use with a vibrating screening machine to filter
undesired particles from a liquid comprising:
a filter cloth having a substantially rectangular mesh suitable
for separating the undesired particles from the liquid;
a back-up having a mesh substantially coarser than said filter
cloth mesh; and
means for bonding said filter cloth and said back-up in laminar
relationship;
said substantially rectangular mesh comprising an array of parallel
individual wires as lengths thereof and a transverse array of parallel
groups of at least three wires as widths thereof, said individual
wires of said substantially rectangular mesh when viewed in a direction
perpendicular to a surface of said cloth being distorted from rectangular
proximate ends of said lengths by bows in said individual wires
extending through each of said parallel groups of wires.
2. A screen according to claim 1, said bonding means comprising
a coat of epoxy applied to said back-up, said filter cloth being
bonded to said back-up by fusion in a heat press.
3. A screen according to claim 1, said back-up being calendared.
4. A screen according to claim 1, said bonded cloth and back-up
being bonded to a perforated plate.
5. A screen for use with a vibrating screening machine to filter
undesired particles from a liquid comprising:
a filter cloth having a substantially rectangular mesh suitable
for separating the undesired particles from the liquid;
a back-up having a mesh substantially coarser than said filter
cloth mesh;
means for bonding said filter cloth and said back-up in laminar
relationship; and
a plastic grid of mesh substantially greater than said back-up
mesh fused to a bonded lamination of said filter cloth and said
back-up;
said substantially rectangular mesh comprising an array of parallel
individual wires as lengths thereof and a transverse array of parallel
groups of at least three wires as widths thereof, said individual
wires of said substantially rectangular mesh when viewed in a direction
perpendicular to a surface of said cloth being distorted from rectangular
proximate ends of said lengths by bows in said individual wires
extending through each of said parallel groups of wires.
6. A screen according to claim 5, said bonding means comprising
a coat of epoxy applied to said back-up, said filter cloth being
bonded to said back-up by fusion in a heat press.
7. A screen according to claim 5, said back-up being calendared.
8. A screen according to claim 5, said fused cloth, back-up and
grid being bonded to a perforated plate.
9. A screen for use with a vibrating screening machine to filter
undesired particles from a liquid comprising:
a filter cloth having a substantially rectangular mesh suitable
for separating the undesired particles from the liquid;
a back-up having a mesh substantially coarser than said filter
cloth mesh;
means for bonding said filter cloth and said back-up in laminar
relationship; and
a plastic grid of mesh substantially greater than said back-up
mesh fused to a bonded lamination of said filter cloth and said
back-up;
said substantially rectangular mesh comprising an array of parallel
individual wires as lengths thereof and a transverse array of parallel
groups of at least three wires as widths thereof, said individual
wires of said substantially rectangular mesh when viewed in a direction
perpendicular to a surface of said cloth being distorted from rectangular
proximate ends of said lengths by bows in said individual wires
extending through each of said parallel groups of wires and said
fused grid, cloth and back-up being corrugated with apexes and nadirs
of corrugation being parallel to said groups of wires.
10. A screen according to claim 9, said bonding means comprising
a coat of epoxy applied to said back-up, said filter cloth being
bonded to said back-up by fusion in a heat press.
11. A screen according to claim 9, said back-up being calendared.
12. A screen according to claim 9, said corrugated grid, cloth
and back-up being bonded to a perforated plate along said nadirs.
13. A screen for use with a vibrating screening machine to filter
undesired particles from a liquid comprising:
a filter cloth having a substantially rectangular mesh suitable
for separating the undesired particles from the liquid;
a back-up having a mesh substantially coarser than said filter
cloth mesh;
means for bonding said filter cloth and said back-up in laminar
relationship;
a plastic grid of mesh substantially greater than said back-up
mesh fused to a bonded lamination of said filter cloth and said
back-up;
said substantially rectangular mesh comprising an array of parallel
individual wires as lengths thereof and a transverse array of parallel
groups of at least three wires as widths thereof, said individual
wires of said substantially rectangular mesh when viewed in a direction
perpendicular to a surface of said cloth being distorted from rectangular
proximate ends of said lengths by bows in said individual wires
extending through each of said parallel groups of wires, said fused
grid, cloth and back-up being corrugated with apexes and nadirs
of corrugation being parallel to said groups of wires; and
a perforated plate, said corrugated grid, cloth and back-up being
bonded to said plate along said nadirs of corrugation.
14. A screen according to claim 13, said bonding means comprising
a coat of epoxy applied to said back-up, said filter cloth being
bonded to said back-up by fusion in a heat press.
15. A screen according to claim 13, said back-up being calendared.
16. A screen for use with a vibrating screening machine to filter
undesired particles from a liquid comprising:
a filter cloth having a substantially rectangular mesh suitable
for separating the undesired particles from the liquid;
a back-up having a mesh substantially coarser than said filter
cloth mesh;
means for bonding said filter cloth and said back-up in laminar
relationship;
a plastic grid of mesh substantially greater than said back-up
mesh fused to a bonded lamination of said filter cloth and said
back-up;
said substantially rectangular mesh comprising an array of parallel
individual wires as lengths thereof and a transverse array of parallel
groups of at least three wires as widths thereof, said individual
wires of said substantially rectangular mesh when viewed in a direction
perpendicular to a surface of said cloth being distorted from rectangular
proximate ends of said lengths by bows in said individual wires
extending through each of said parallel groups of wires, said fused
grid, cloth and back-up being corrugated with apexes and nadirs
of corrugation being parallel to said groups of wires; and
a plurality of metal strips aligned transversely and bonded to
said nadirs.
17. A screen according to claim 16, said bonding means comprising
a coat of epoxy applied to said back-up, said filter cloth being
bonded to said back-up by fusion in a heat press.
18. A screen according to claim 16, said back-up being calendared.
Description BACKGROUND OF THE INVENTION
This invention relates generally to screens for use with vibrating
screen machines and more particularly concerns an improvement in
screen structure resulting in increased life and throughput of such
screens.
The development of vibrating screen technology leading up to the
present invention can be appreciated by review of a few of the patents
that have issued related to that technology in recent years, including
U.S. Pat. No. 4,575,421 issued on Mar. 11, 1986, U.S. Pat. No. 5,221,008
issued on Jun. 22, 1993 and U.S. Pat. Nos. 5,417,793, 5,417,858
and 5,417,859 issued on May 23,1995, all assigned to Derrick Manufacturing
Corporation, and U.S. Pat. Nos. 5,256,291 and 5,256,292 issued on
Oct. 26, 1993 and U.S. Pat. No. 5,370,797 issued on Dec. 6, 1994
to the present inventor.
Prior to the '421 patent, most screens for vibrating machines consisted
of one or more layered filter cloths spanning an open area, sometimes
within a frame and, in some instances, on a perforated plate. The
vibratory motion of the screen in the pressure head of the screened
material caused the cloths to pulsate. As a result, in a very short
time, the cloths would tear near their periphery or the uppermost
cloth would be so seriously abraded by the filtered material as
to render the screen useless. Faster pulsation and greater pressure
heads, desirable conditions in order to increase the throughput
of the screen, resulted in greater amplitudes of pulsation which,
in turn, accelerated the destruction of the screen.
To increase screen life, the '421 patent layered a pair of filter
cloths over a supporting screen or back-up of heavier gauge wire
and considerably more open mesh and a plate having apertures considerably
larger than the mesh of the back-up. The cloths, the back-up and
the plate were secured together by adhesive applied at the perimeter
of the plate so that the abutting filter cloths could still move
laterally and vertically with respect to each other in order to
prevent clogging. By reducing the size of the opening spanned by
the filter cloths, the amplitude of pulsation was reduced, increasing
the life of the screen. However, tearing along the mesh perimeters,
though taking longer than tearing along the frame perimeter, still
occurred. Furthermore, abrading of the finer outer filter cloth
remained a serious problem. Given these deficiencies, as is pointed
out in the '008 patent, screens of the '421 type still failed after
only 5 hours of use.
The '008 patent sought to increase screen life beyond that of '421
screens by further reducing pulsation amplitude and by addressing
the abrading of the uppermost fine cloth of the screen in a different
fashion. To accomplish this, a third filter cloth of mesh not as
fine as that of the finest cloth was layered as the uppermost cloth.
This heavier cloth protected the finer cloth from abrading and also
reduced the amplitude of pulsation. The '008 patent indicates that
the resulting screen was found to last about 30 hours. Moreover,
by applying a drop of epoxy to the screen at the center of each
plate aperture, the filter cloths can be bonded together as well
as to the back-up to stabilize the layers against flexing and further
reduce pulsation amplitude and border tearing. However, this inhibits
relative lateral and vertical motion of the cloths and reduces open
screen area, thus reducing the screen throughput and increasing
the possibility of clogging.
The basic approach of the '421 and '008 patents was the use of
additional filter cloths and back-ups to overcome inherent cloth
deficiencies. Unfortunately, those solutions also result in increased
screen cost and lower screen throughput with each added layer. While
increased screen life is a desired result, increased screen throughput
and reduced screen cost are very important. Subsequent to those
patents and in a totally different approach to the problem, the
'291, '292 and '797 patents address the life and throughput characteristics
of the individual filter cloths. The structural arrangements of
shute and warp wires or filaments disclosed in those patents provide
greater screen life and product throughput as characteristics of
the filter cloth, thus enhancing any known screen structure in which
they might be incorporated.
Thereafter, the '793, '858 and '859 patents again addressed the
problem by modifying the screen structure to an undulating configuration.
'858 type screens employ at least one and preferably two filter
cloths and a back-up bonded to each other at every intersection
by adhesive such as epoxy and then triangularly or sinusoidally
corrugated to form parallel apexes and nadirs with connecting walls
therebetween, the corrugated assembly being adhered to an apertured
plate along its nadirs. '793 and '859 type screens bond the filter
cloths and the back-up to each other by use of heat and pressure
applied to a fused plastic grid layered with them to permeate all
the filter cloths and the back-up. The resulting assembly is then
corrugated and may also be applied to an apertured grid as was the
'858 type of screen. These types of screens are said to increase
throughput by increasing screen surface area. They are said to reduce
damage to the screen caused by pulsation and abrading of the uppermost
filter cloth because impinging particles are generally not striking
the screen in a path normal to its surface. They are said to still
permit the filter cloths to yield relative to each other so as to
obviate blinding. However, these types of screens also introduce
new problems because the stress in the filter cloths resulting from
the bends at the apexes and nadirs of the corrugation increases
the occurrence of fracture or tearing at these points, thus reducing
screen life. In addition, in screens of this type, the cloth tends
to bubble at approximately the midpoint between the apexes and the
nadirs, shortening the life of the screen. Furthermore, these types
of screens not only require extra layers of cloth to compensate
for inherent cloth deficiencies, but each layer requires greater
lengths of cloth due to the corrugation, further increasing costs.
Thus, the benefits of corrugation to the throughput, anti-clogging
and life characteristics are mitigated by both old and new problems.
It is, therefore, an object of this invention to provide a screen
for a vibrating screen machine having longer life than presently
known screens. Another object of this invention is to provide a
screen for a vibrating screen machine having improved throughput
over presently known screens. It is also an object of this invention
to provide a screen for a vibrating screen machine having greater
resistance to fracture or tearing than presently known screens.
Still another object of this invention is to provide a screen for
a vibrating screen machine using fewer filter cloths than presently
known screens having similar throughput and life characteristics.
It is a further object of this invention to provide a screen for
a vibrating screen machine which is less expensive over its life
span than presently known screens. And it is an object of this invention
to provide a screen for a vibrating screen machine having greater
resistance to fracture or tearing when corrugated than presently
known corrugated screens.
SUMMARY OF THE INVENTION
In accordance with the invention, a screen is provided for use
with a vibrating screening machine to filter undesired particles
from a liquid. A filter cloth having a substantially rectangular
mesh suitable for separating the undesired particles from the liquid
is bonded in laminar relationship to a back-up having a substantially
coarser mesh, preferably by applying a coat of epoxy to the back-up
and fusing the filter cloth to the back-up in a heat press. The
substantially rectangular mesh is formed by a lengthwise array of
parallel individual wires woven with a transverse widthwise array
of parallel groups of at least three wires. The individual wires
are distorted from rectangular proximate the ends of the rectangles
by bows in the individual wires at their area of intersection with
each of the parallel groups of wires. This configuration provides
improved throughput and life characteristics over known screens.
To further enhance the life of the screen with minimal impact on
throughput, a plastic grid of mesh substantially greater than the
back-up mesh is fused to the bonded lamination of the filter cloth
and the back-up. The grid further reduces the possibility of separation
between parallel individual wires which would shorten the life of
the screen.
Finally, to further increase throughput, the fused grid, cloth
and back-up are corrugated in approximately triangular or sinusoidal
fashion with the apexes and nadirs of corrugation being parallel
to the groups of wires. By using distorted rectangular mesh filter
cloth, the possibility of fracture and tearing at the apexes and
nadirs of corrugation and the midpoint bubbling experienced with
known corrugated screens is reduced. Thus, the use of corrugated
screen with a filter cloth of distorted rectangular mesh increases
both screen life and throughput.
The screen, in any of its embodiments, can also be secured to a
perforated plate or to a plurality of metal strips if additional
strength is desired. In the corrugated embodiment, the plate or
strips are bonded to the nadirs of the corrugated screen.
Preferably, the back-up is a calendared 8 mesh mill grade cloth
and the plastic grid has 1.times.1" or 2.times.2" openings,
but the particular back-up and grid configuration will be determined
by the screen application. In the corrugated embodiment, it is preferred
to align the grid openings diagonally in the screen.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent
upon reading the following detailed description and upon reference
to the drawings in which:
FIG. 1 is a perspective view of a segment of one embodiment of
a distorted rectangular filter cloth for use in a vibrating screen;
FIG. 2 is a top plan view of a segment of a preferred embodiment
of the distorted rectangular filter cloth at approximately 140 magnification;
FIG. 3 is a sectional view of a back-up embodiment of a screen
using a distorted rectangular filter cloth;
FIG. 4 is a sectional view of a gridded embodiment of a screen
using a distorted rectangular filter cloth;
FIG. 5 is a sectional view of a corrugated embodiment of a screen
using a distorted rectangular filter cloth; and
FIG. 6 is a sectional view of a perforated plate embodiment of
a screen using a distorted rectangular filter cloth.
While the invention will be described in connection with a preferred
embodiment, it will be understood that it is not intended to limit
the invention to that embodiment. On the contrary, it is intended
to cover all alternatives, modifications and equivalents as may
be included within the spirit and scope of the invention as defined
by the appended claims.
DETAILED DESCRIPTION
Turning first to FIG. 1, a segment of distorted rectangular filter
cloth is illustrated in which substantially rectangular openings
11 are defined by a weave of parallel individual wires 13 along
the lengths of the rectangular openings 11 with transverse parallel
groups 15 of five wires along the widths of the rectangular openings
11. As shown, the wires 21, 23, 25, 27 and 29 in each group 15 are
alternated over and under pairs of individual wires 13, the beginning
of the weave for the first group wire 21 starting at one of the
individual wires 13 and each successive group wire 23, 25, 27 and
29 starting at the next successive individual wire 13. However,
the number of wires in the groups 15 can be three or more and the
weave configuration can be any taught in U.S. Pat. Nos. 5,256,291,
5,256,292 and 5,370,797. It is important, however, that in weaving
the cloth, the tension forces in the weaving process cause the individual
wires 13 to be distorted out of rectangular proximate the lengthwise
ends of the rectangular openings 11.
The distorted rectangular relationship can best be understood in
relation to FIG. 2 illustrating an approximately 140 magnification
of a segment of a preferred embodiment of the distorted rectangular
filter cloth in which groups 31 include three wires 33, 35 and 37
interwoven with individual wires 39. In the weaving process, as
the individual wires 39 are sequentially drawn under tension between
the group wires 33, 35 and 37, the group wires 33, 35 and 37 force
the individual wires 39 into bows 41 which extend through each of
the groups 31. As sequential individual wires 39 are woven into
the cloth, the groups 31 lock the bows 41, resulting in the distorted
rectangular openings 43 in the cloth. It is believed that this distortion
of the rectangular openings affords a small amount of uniform stretch
in the cloth which reduces the damaging forces applied to the cloth
during use.
As shown in FIG. 3, in one embodiment of the screen the distorted
rectangular filter cloth 51 is bonded to a back-up 53. The back-up
53 is typically a square mesh cloth of mesh having coarser or substantially
larger openings than the filter cloth and, preferably and by way
of example, is an 8-mesh mill grade cloth. The filter cloth 51 can
be bonded to the back-up 53 by application of an epoxy coat to the
back-up 53 and fusion of the filter cloth 51 and the back-up 53
in a heat press. Such bonding processes and others are well known
in the industry. This bonding of the distorted rectangular filter
cloth 51 to the back-up 53 inhibits separation of the individual
wires and therefore increases the life of the screen.
Looking at FIG. 4, the bonded distorted rectangular filter cloth
51 and back-up 53 are fused with a plastic grid 55 of mesh substantially
coarser than the mesh of the back-up 53 to provide another embodiment
of the screen having even greater life. The grid will typically
be of 1.times.1" or 2.times.2" openings, though other
openings can be used depending on the particular screen application.
The process for fusing a filter cloth and a back-up with the grid
is known in the industry and explained in U.S. Pat. No. 5,417,793
and 5,417,859.
The screen of FIG. 4 is specially suited for approximately triangular
or sinusoidal corrugation as is illustrated in FIG. 5. In the embodiment
of FIG. 5, the screen of FIG. 4 is corrugated so that the apexes
61 and nadirs 63 of corrugation extend in a direction parallel to
the groups of wires in the distorted rectangular filter cloth as
was explained in relation to FIGS. 1 and 2. In this embodiment,
the throughput benefits of corrugation are gained without significant
diminishing of the screen life benefits gained by grid embodiment
of FIG. 4.
As shown in FIG. 6, the screen of FIG. 5 is bonded to a perforated
plate 65 to further increase its strength and life. In this embodiment,
the nadirs 63 of the corrugated screen are bonded to the plate 65
in any manner known in the industry, such as described in U.S. Pat.
No. 5,417,858. Alternatively, strips of metal bonded transversely
to the nadirs 63 of the corrugated screen may be used in lieu of
the plate 65. The screen embodiments of FIGS. 3 and 4 can also be
bonded to a plate or metal strips.
It may be desirable to use a calendared back-up in any of the embodiments.
Frames for the various embodiments and the attachment of connectors
such as hook strips to the screen or frame are well known in the
art.
Thus, it is apparent that there has been provided, in accordance
with the invention, a distorted rectangular filter cloth screen
for vibrating screening machines that fully satisfies the objects,
aims and advantages set forth above. While the invention has been
described in conjunction with specific embodiments thereof, it is
evident that many alternatives, modifications and variations will
be apparent to those skilled in the art and in light of the foregoing
description. Accordingly, it is intended to embrace all such alternatives,
modifications and variations as fall within the spirit of the appended
claims. |