Note: Descriptions are shown in the official language in which they were submitted.
NS-632
TILED SCREEN CLOTH
FIELD OF THE INVENTION
The present invention relates generally to a tiled screen cloth particularly
useful for vibrating screens for screening oversize objects in a material such
as
an oil sand slurry.
BACKGROUND OF THE INVENTION
Vibrating, rotating and/or stationary screens are used in the oil sand
industry, in particular, in oil sand slurry preparation plants. Oil sand, such
as is
mined in the Fort McMurray region of Alberta, generally comprises water-wet
sand grains held together by a matrix of viscous bitumen. It lends itself to
liberation of the sand grains from the bitumen by mixing or slurrying the oil
sand
in water, allowing the bitumen to move to the aqueous phase.
As-mined or pre-crushed oil sand is generally mixed with warm or hot
water to yield an oil sand slurry.
The slurry is then conditioned in a
hydrotransport pipeline and subsequently introduced into a large, open-topped,
conical-bottomed, cylindrical vessel commonly termed a primary separation
vessel (PSV) where the more buoyant aerated bitumen rises to the surface and
forms a bitumen froth layer.
It may be desirable to remove the larger aggregates present in oil sand
slurry prior to pipelining in order to avoid blockage or damage of downstream
equipment, e.g., pump component wear.
Thus, vibrating, rotating and/or
stationary screens may be used at various points during slurry preparation to
reject larger lumps of oil sand, rocks and other aggregates, which are large
enough to block or damage downstream equipment, prior to pipeline
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conditioning. Screens may also be used to further screen oil sand tailings
slurry
prior to treating/disposing same.
However, oil sand slurry is extremely heavy and abrasive due to the large
amount of sand, gravel and crushed rock contained therein. Further, in
particular
.. with primary vibrating screens, these screens are generally vibrating with
an
acceleration of approximately 4-5 g, so that all oil sand slurried material
passes
over and through the screen cloths of the vibrating screen. This results in
the
rapid spalling and eventual wearing through of the screen cloths of the
vibrating
screen ("hole-throughs"), which can lead to production interruption and an
unplanned maintenance event.
Currently, screen cloths comprising chromium white iron (CWI)
longitudinal and transverse ligaments having two passes of plasma transferred
arc welding tungsten overlays (9 mm in thickness) are the best available
design
for oil sands vibrating screens. However, the whole screen has a weak area in
the transverse ligaments, which area wears first to expose the mild steel
underneath to the erosive oil sand slurry. Because of this weakness, the
screen
cloths require repair in mid life, which limits the mission run of the whole
plant.
Canadian Patent Application No. 2,992,665 discloses a screen segment
useful in screening oil sands comprising a substantially screen-shaped base
plate whereon a plurality of support plates having a plurality of plate-shaped
anti-
wear element thereon are joined to the base plate, e.g., by substance-to-
substance bonding. However, such screens are very heavy and would weigh
down a vibrating screening device.
Thus, it is desirable to have a screen cloth that can withstand the
abrasiveness of oil sand slurry while being light enough to be used on a
vibrating
screening devise.
SUMMARY OF THE INVENTION
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It was discovered that the currently used screen cloths for vibrating
screening devices that are used to screen oil sand lumps, which are often
frozen,
rocks and the like from oil sand slurry were wearing through much quicker than
desired due to the abrasive nature of the slurry. In particular, it was
discovered
that screen cloths of vibrating screening devices were suffering from
localized
wear phenomena resulting from the slurry flow distribution.
The current application is directed to screen cloths useful for screening an
oil sand slurry having oversize reject material. Use of the present invention
extends the running time of a vibrating screening device so that the operator
does not have to shut down the screening device as frequently to replace the
impact screen cloths. It is understood, however, that the screen cloths of the
present invention can also be used with rotating and/or stationary screening
devices.
Broadly stated, in one aspect of the present invention, a screen cloth for
use in a screening device for screening out oversize objects, including oil
sand
lumps and rocks, is provided, comprising:
= a supporting structure comprising two mutually opposing lateral
attachment elements and a plurality of transverse stiffeners
extending therebetween; and
= a plurality of screen segments, each screen segment having a
plurality of openings, and each screen segment comprising a steel
base and a plurality of anti-wear tiles attached thereon;
whereby the plurality of screen segments are attached to the support
structure to form a screening portion of the screen cloth.
In one embodiment, the plurality of screen segments are first attached to
one another prior to being attached to the support structure. In
another
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embodiment, the anti-wear tiles are sintered tungsten carbide tiles. In
another
embodiment, the screen cloth further comprises at least two attachment
segments having a plurality of anti-wear tiles attached thereon for attaching
to
the two lateral attachment elements, respectively.
In one embodiment, the plurality of anti-wear tiles are attached to the
screen segments and the attachment segments by means of brazing.
Other features will become apparent from the following detailed
description. It should be understood, however, that the detailed description
and
the specific embodiments, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will become
apparent to
those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the drawings wherein like reference numerals indicate similar
parts throughout the several views, several aspects of the present invention
are
illustrated by way of example, and not by way of limitation, in detail in the
following figures. It is understood that the drawings provided herein are for
illustration purposes only and are not necessarily drawn to scale.
FIG. 1 is a bottom view of a supporting structure of a screen cloth of the
present invention.
FIG. 2A is a perspective view of a screen segment having anti-wear tiles
attached thereon for use in a screen cloth of the present invention.
FIG. 2B is a perspective view of an attachment segment having anti-wear
tiles attached thereon for use in a screen cloth of the present invention.
FIG. 3 is a perspective view of an embodiment of a screen cloth of the
present invention, viewed from the bottom.
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FIG. 4 is an end view of the screen cloth of FIG. 3.
FIG. 5 is an illustration as to how screen and attachment segments are
arranged on a supporting structure to form a screen cloth of the present
invention.
FIG. 6 is a perspective view of an embodiment of a screen cloth of the
present invention, viewed from the top.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The detailed description set forth below in connection with the appended
drawings is intended as a description of various embodiments of the present
invention and is not intended to represent the only embodiments contemplated
by the inventor. The detailed description includes specific details for the
purpose
of providing a comprehensive understanding of the present invention. However,
it will be apparent to those skilled in the art that the present invention may
be
practiced without these specific details.
The present invention relates generally to a light weight screen cloth with
improved wear properties for use in screening raw materials such as crushed
oil
sand, ores and the like, and, in particular, screening oil sand slurry using a
vibrating screening device comprising the screen cloths.
FIG. 1 illustrates a supporting structure of an embodiment of a screen
cloth of the present invention. Supporting structure 10 comprises two mutually
opposing lateral attachment elements, first lateral attachment element 12 and
second lateral attachment element 14. Lateral attachment elements 12, 14 have
at least one fastening hole 16 drilled therethrough for attaching the lateral
attachment elements to, for example, a vibrating screening device's cross
beams
by means of bolts, screws and the like. In FIG. 1, each lateral attachment
element has four fastening holes 16.
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Extending between and attached at each end to the first and second
lateral attachment elements 12, 14 are a plurality of transverse stiffeners
18.
Generally, the transverse stiffeners 18 are attached to the lateral attachment
elements 12, 14 by means of welding. Each of the lateral attachment elements
and the transverse stiffeners are made of a mild steel, a corrosion resistant
steel
such as stainless steel, or other wear resistant steel. The supporting steel
structure forms the base of the screen cloths of the present invention.
FIG. 2A is a perspective view of a screen segment 20 of the present
invention. Screen segment 20 is comprised of base plate 22, generally made of
a mild steel, a corrosion resistant steel such as stainless steel, or other
wear
resistant steel, having a plurality of screen openings 26, made by plasma cut
or
machining, therethrough. The screen segment 20 shown in FIG. 2A comprises
five such screen openings 26. Attached to the upper surface of base plate 22
are a plurality of anti-wear tiles 24 made from a hard metal such as cemented
or
sintered tungsten carbide, chrome carbide, titanium carbide or ceramic. In one
embodiment, the anti-wear tiles 24 are attached to base plate 22 by brazing,
usually accomplished by using a filler metal with a melting temperature above
450 C (840 F), mechanical fasteners or using an industrial adhesive (glue)
such
as epoxies. In one embodiment, the anti-wear tiles 24 are square or
rectangular
in shape and are comprised of about 89 to 91 % tungsten carbide. In one
embodiment, the anti-wear tiles 24 are about 6 to 12 mm in thickness, however,
the anti-wear tiles can be greater than 12 mm in thickness. In one embodiment,
the screen segment 20 is rectangular, 32 mm in thickness and about 175x659
mm in dimension.
FIG. 2B is a perspective view of an attachment segment 28 of the present
invention. Attachment segment is comprised of base plate 30, generally made of
steel, having a plurality of attachment holes 34 therethrough. The attachment
segment of FIG. 2B has two such attachment holes. The attachment holes 34
correspond to fastening holes 16 in supporting structure 10 of FIG. 1.
Attached
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to the upper surface of base plate 30 are a plurality of anti-wear tiles 32
made
from a hard metal such as sintered tungsten carbide. In one embodiment, the
anti-wear tiles 32 are attached to base plate 30 by brazing. In one
embodiment,
the anti-wear tiles 32 are rectangular in shape and are comprised of about 89
to
91% tungsten carbide. In one embodiment, the anti-wear tiles 32 are about 6 to
about 12 mm in thickness. It is understood that the anti-wear tiles can be
greater
than 12 mm in thickness. In one embodiment, the attachment segment 28 is
rectangular, 32 mm in thickness and about 175x659 mm in dimension.
The attachment of anti-wear tiles 24 and 32 to smaller base plates 22 and
30, respectively, to form screen segments 20 and attachment segments 28,
respectively, allows for better brazing quality as opposed to brazing anti-
wear
tiles to a larger base plate.
FIG. 3 is a perspective view of an embodiment of a screen cloth, screen
cloth 40, of the present invention viewed from the bottom and FIG. 4 is an end
view of screen cloth 40. In this embodiment, four attachment segments 28 and
twelve screen segments 20 are bolted and welded together, as shown in FIG. 3,
such that two pairs of attachment segments 28 are at laterally opposing ends
to
the twelve screen segments 20, which are arranged in two rows of six screen
segments each, as shown in FIG. 5. The thus joined segments are then bolted
to light supporting structure 10 to form light weight screen cloth 40. It is
understood, however, that the four attachment segments 28 and twelve screen
segments 20 can also be directly bolted to light supporting structure 10. FIG.
6 is
a perspective view of a fully assembled screen cloth as described in FIG. 5
viewed from the top.
As can be seen more clearly in FIG. 3 and FIG. 6, the reason screen cloth
40 is much lighter than the proposed screen cloth in Canadian Patent
Application
No. 2,992,665, is that for much of the screen cloth's area, the screen cloth
is only
comprised of two layers, namely, base plate 22 and anti-wear tiles 24, as
opposed to three layers, as in Canadian Patent Application No. 2,992,665. In
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Canadian Patent Application No. 2,992,665, the entirety of the screen cloth is
composed of a bottom base plate, a middle support plate and an anti-wear
element top layer. The use of the bottom base plate, which is made of steel,
adds extra weight, which, when the screen cloths are then attached to a
screening device, such as a vibrating screening device, the added weight
interferes with the screening device's operation, as, by virtue of the
device's
design, it goes through ultra high fatigue cycles, which is exponentially
sensitive
to stresses and, in turn, exponentially sensitive to extra weight.
Interpretation
The corresponding structures, materials, acts, and equivalents of all
means or steps plus function elements in the claims appended to this
specification are intended to include any structure, material, or act for
performing
the function in combination with other claimed elements as specifically
claimed.
References in the specification to "one embodiment", "an embodiment",
etc., indicate that the embodiment described may include a particular aspect,
feature, structure, or characteristic, but not every embodiment necessarily
includes that aspect, feature, structure, or characteristic. Moreover, such
phrases
may, but do not necessarily, refer to the same embodiment referred to in other
portions of the specification. Further, when a particular aspect, feature,
structure,
or characteristic is described in connection with an embodiment, it is within
the
knowledge of one skilled in the art to affect or connect such module, aspect,
feature, structure, or characteristic with other embodiments, whether or not
explicitly described. In other words, any module, element or feature may be
combined with any other element or feature in different embodiments, unless
there is an obvious or inherent incompatibility, or it is specifically
excluded.
It is further noted that the claims may be drafted to exclude any optional
element. As such, this statement is intended to serve as antecedent basis for
the
use of exclusive terminology, such as "solely," "only," and the like, in
connection
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with the recitation of claim elements or use of a "negative" limitation. The
terms
"preferably," "preferred," "prefer," "optionally," "may," and similar terms
are used
to indicate that an item, condition or step being referred to is an optional
(not
required) feature of the invention.
The singular forms "a," "an," and "the" include the plural reference unless
the context clearly dictates otherwise. The term "and/or" means any one of the
items, any combination of the items, or all of the items with which this term
is
associated. The phrase "one or more" is readily understood by one of skill in
the
art, particularly when read in context of its usage.
The term "about" can refer to a variation of 5%, 10%, 20%, or 25%
of the value specified. For example, "about 50" percent can in some
embodiments carry a variation from 45 to 55 percent. For integer ranges, the
term "about" can include one or two integers greater than and/or less than a
recited integer at each end of the range. Unless indicated otherwise herein,
the
term "about" is intended to include values and ranges proximate to the recited
range that are equivalent in terms of the functionality of the composition, or
the
embodiment.
As will be understood by one skilled in the art, for any and all purposes,
particularly in terms of providing a written description, all ranges recited
herein
also encompass any and all possible sub-ranges and combinations of sub-
ranges thereof, as well as the individual values making up the range,
particularly
integer values. A recited range includes each specific value, integer,
decimal, or
identity within the range. Any listed range can be easily recognized as
sufficiently
describing and enabling the same range being broken down into at least equal
halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each
range
discussed herein can be readily broken down into a lower third, middle third
and
upper third, etc.
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As will also be understood by one skilled in the art, all language such as
"up to", "at least", "greater than", "less than", "more than", "or more", and
the like,
include the number recited and such terms refer to ranges that can be
subsequently broken down into sub-ranges as discussed above. In the same
manner, all ratios recited herein also include all sub-ratios falling within
the
broader ratio.
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