Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02528542 2005-12-01
1 "SCREEN ASSEMBLY FOR A VIBRATORY SEPARATOR"
2
3 FIELD OF THE INVENTION
4 The invention relates to screens and in particular to a screen
assembly for a vibratory separator such as a shale shaker.
6
7 BACKGROUND OF THE INVENTION
8 Drilling mud is used while drilling oil and natural gas wells on a
9 drilling rig to control subsurface pressures, lubricate the drill bit,
stabilize the
wellbore, and carry cuttings and other debris to the surface, among other
11 functions. The drilling mud is pumped through a drill string and out of a
drill bit,
12 then returned to the surface through the annular space between the drill
string
13 and the wellbore. At the surface, cuttings and other solids that are
entrained in
14 the mud are typically separated from the mud by a vibrating screen
separator
called a shale shaker.
16 Shale shakers include a lower stationary base, called an under flow
17 pan, and an upper vibratable basket that has connected to it a high
frequency
18 linear angular motion or rotary vibratory motor. Mounted generally
horizontally in
19 the basket is one or more screen assemblies having one or more layers of
tensioned screening material. In use, solids-laden mud flows onto one end of
the
21 screen deck and solids retained by the screening material are conveyed by
22 vibratory action to the other end where they are discharged. Fluids and
small
23 particles pass through the screening material and are collected in a tank
system
24 for further processing and reuse in the active system.
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1 Screen assemblies can be distinguished by the way that they
2 provide tensioned screening material. One system is to use hook strips on
the
3 basket sides of the screening material in association with tensioning
mechanisms
4 on the shale shaker. Alternatively, pretensioned screen assemblies include
tensioned screening material attached to a rigid perforated plate, which is in
turn
6 attached to a generally rectangular structural frame. The perforated plate
7 supports the screening material and contains a plurality of openings to
permit the
8 screened fluid to collect beneath the screening assembly. The frame is used
to
9 mount the screen assembly onto corresponding support rails of the basket and
the sides of the screening assembly are secured thereto. For example, wedge
11 blocks can be wedged between the top periphery of the screen assembly and
12 wedge angles extending radially inwardly from sides of the screen basket.
The
13 sides of the screening assembly are thereby securely sandwiched between the
14 support rails and the wedge blocks.
In one type of construction, the screening material layers are
16 bonded to the perforated plate, which is in turn bonded to the top surface
of the
17 frame to form an integral screen assembly. The screen assembly is subject
to
18 tremendous stresses caused by the vibratory machinery. In particular,
upward
19 and downward stroking motion of the vibratory motor causes the screen
assembly to oscillate between the secured sides. In other words, the unsecured
21 area of the screening assembly can vibrate at greater amplitude than the
sides,
22 thereby causing out of plane flexing. Such flexing eventually results in
failure of
23 the bonding of the perforated plate to the frame and the screen material,
as well
24 as a loss of structural integrity of the screen material, the perforated
panel and
the frame. In general, greater flexing occurs with greater g-forces. Further,
as
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CA 02528542 2005-12-01
1 drilling mud flows over the screens, the upward stroking motion drives the
mud
2 into the screen with the impinged mud creating additional reactive force
against
3 the downward stroking motion.
4 Flexing of the screening assembly is a major cause of early
deterioration of pretensioned screens, such as separation of components of the
6 screening assembly, contributing greatly to increased operational costs of
the
7 shale shaker due to the man-hours required to replace the screen, loss of
rig
8 operating time, and cost of replacement screens. To increase the rigidity of
the
9 screening assembly for withstanding flexing forces, pretensioned screens are
typically made of thick structural tubing and thick perforated plates. This
11 construction, however, results in high manufacturing costs and makes the
12 screening assembly heavy and difficult to handle. While texturing of the
bonding
13 surface of perforated plate has been used to increase the bonding strength
14 between the perforated plate and the frame, this approach has not proven to
be
totally adequate.
16 There is, therefore, a need in the art for an improved screen for a
17 vibratory separator.
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CA 02528542 2005-12-01
1 SUMMARY OF THE INVENTION
2 A screen assembly for a vibratory separator is provided whereby a
3 perforated plate for supporting screening material is more securely attached
to a
4 frame as compared to conventional screen assemblies. Consequently, the
screen assembly is more resistant to damage caused by out of plane flexing of
6 the screen assembly when subjected to high frequency vibratory forces in the
7 vibratory separator.
8 In a broad aspect of the invention, the perforated plate of the
9 screening assembly is attached not only to a top of the frame, as with
conventional screening assemblies, but also to sides of the frame, and in
11 particular at least to sides of frame members that are most susceptible to
flexing.
12 The attachment of the perforated plate to sides of the frame thereby
provides for
13 more secure attachment, and also structurally reinforces the frame members
to
14 which the perforated plate is attached.
Accordingly, in an embodiment of the invention there is provided a
16 screening assembly comprising a generally rectangular outer frame section,
a
17 perforated plate attached to the frame, and one or more layers of screening
18 material supported on and attached to the perforated plate. The outer frame
19 section includes a pair of spaced apart longitudinal side members and a
pair of
spaced apart transverse end members, where the longitudinal side members are
21 to be securely mounted on a vibratable basket of a vibratory separator. The
22 perforated plate includes a substantially planar portion for supporting the
23 screening material, with the planar portion having a plurality of openings
formed
24 therein. The perforated plate further includes a pair of opposing tabs
extending
downwardly from the planar portion, with the tabs having a vertical portion.
The
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1 planar portion of the perforated plate is supported on and attached to a top
of the
2 frame with the vertical portion of the tabs extending along and attached to
a side
3 of the transverse end members.
4 The tabs can be further configured to be L-shaped tabs which
additionally extend along a bottom of the transverse end members.
6 Additional aspects relating to the construction of the frame are also
7 disclosed.
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1 BRIEF DESCRIPTION OF THE DRAWINGS
2 In drawings which are intended to illustrate embodiments of the
3 invention and which are not intended to limit the scope of the invention:
4 Figure 1 is a perspective view of one embodiment of a screen
assembly according to the present invention, with part of the screening
material
6 removed for viewing the perforated plate and the frame;
7 Figure 2 is a cross-sectional side view taken along lines II-II of Fig.
8 1 and with the cross members removed;
9 Figure 3 is an exploded view of Fig. 1;
Figure 4 is a cross-sectional side view of another embodiment of a
11 screen assembly according to the present invention;
12 Figure 5 is a partial perspective and exploded view of the frame and
13 perforated plate of Fig. 4;
14 Figures 6A is a top view of an outer frame section of the screen
assembly of Fig. 1;
16 Figure 6B is a top view of the hollow structural tubing used to form
17 the outer frame section of Fig. 6A;
18 Figure 6C is a close-up view of a notched area of Fig. 6B;
19 Figure 6D is a sectional view taken along lines VI-VI of Fig. 6A;
Figure 7 is an exploded partial perspective view of intersecting
21 cross members of the frame of the screen assembly of Fig. 1; and
22 Figure 8 is a cross-sectional side view of yet another embodiment
23 of a screen assembly of the present invention.
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1 DESCRIPTION OF THE PREFERRED EMBODIMENT
2 With reference to Figs. 1-3, an embodiment of a screen assembly
3 10 for a vibratory separator generally comprises a frame 12, a perforated
plate 14
4 and one or more layers of screening material 16. The screening material 16
is
supported on and attached to the perforated plate 14, with the perforated
plate 14
6 in turn being supported on and attached to the frame 12. As described below,
7 the perforated plate 14 includes features that provide for more secure
attachment
8 to the frame 12 as compared to conventional perforated plates, thereby
9 enhancing the structural integrity of the screen assembly 10 against
vibratory
forces.
11 In further detail, the frame 12 comprises a generally rectangular
12 outer frame section 18 having a pair of spaced apart longitudinal side
members
13 20 and a pair of spaced apart transverse end members 22. In use, the
screening
14 assembly 10 is mounted horizontally in a vibratable basket of a vibratory
separator (not shown), with the longitudinal side members 20 being clamped or
16 otherwise secured to the basket. Linear angular or rotary vibratory forces
are
17 applied to the basket, and hence the screening assembly 10, to cause
material
18 on a top 24 of the screening material 16 to move generally longitudinally
19 therealong from one end 26 of the screening assembly 10 to another end 28.
As with conventional perforated plates, the perforated plate 14
21 comprises a planar portion 32 for supporting the screening material 16
22 thereupon, with the planar portion 32 having a plurality of holes or
perforations 34
23 punched or otherwise formed therein. The perforations 34 can be of any
suitable
24 shape and size to permit sufficient flow-through of screened fluid, while
maintaining structural integrity of the perforated plate 14, as would be
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1 appreciated by one skilled in the art. In addition, the perforated plate 14
includes
2 a pair of opposing tabs 36 having a vertical portion 38 extending downwardly
3 from transverse edges 40 of the planar portion 32. The tabs 36 may be
formed,
4 for example, by downwardly bending a non-perforated periphery 42 of the
planar
portion 32.
6 The perforated plate 14 is fit over the frame 12 with the planar
7 portion 32 being supported by an adjacent top 44 of the frame 12, and the
vertical
8 portion 38 of the tabs 36 adjacent outer sides 46 of the transverse end
members
9 22 of the frame 12. The perforated plate 14 is attached with bonding
material 48
to the adjacent surfaces of the frame 12 and the screening material 16 is in
tum
11 bonded with bonding material 48 to the perforated plate 14, thereby forming
an
12 integral screen assembly 10. As compared with conventional perforated
plates,
13 which are bonded or otherwise attached to only to the top surface 44 of the
frame
14 12, additional attachment of the perforated plate 14 to the outer sides 46
of the
transverse end members 22 by the tabs 36 provides for more secure attachment
16 of the perforated plate 14 to the frame 12. Consequently, the perforated
plate 14
17 is more resistant to vibratory detachment from frame 12 upon flexing of the
18 screening assembly 10 in response to upward and downward forces imposed by
19 the vibratory machinery. Further, the tabs 36 of the perforated plate 14
structurally reinforce or stiffen the transverse end members 22 of the frame
12,
21 thereby reducing the risk of bond failure between the frame 12 and the
perforated
22 plate 14, as well as between the perforated plate 14 and the screening
material
23 16. Notably, the structural and functional advantages provided by the tabs
36 do
24 not significantly increase the weight of the screening assembly 10.
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1 While the tabs 36 are preferably each a single tab 36 extending
2 along the entire transverse length of the perforated plate 14, the tabs can
also
3 extend partially along the transverse length of the perforated plate 14, and
can
4 also be a plurality of spaced apart tabs.
Tabs 36 extending along the longitudinal side members 20 can also
6 be provided, although this is generally not necessary as the sides of the
screen
7 assembly 10 are typically held in position by wedge blocks.
8 With reference to Figs. 4 and 5, to further improve the security of
9 the attachment of the perforated plate 14 to the frame 12, the tabs 36 can
be L-
shaped tabs 36 further having an inwardly directed horizontal portion 50 that
11 extends along a bottom 52 of the transverse end members 22. The horizontal
12 portion 50 thereby vertically clamps the perforated plate 14 onto the
transverse
13 end members 22 of the frame 12 and further structurally reinforces the
transverse
14 end members 22. While it is not necessary to attach the horizontal portion
50 to
the bottom 52 of the transverse end members 22, the overall process of bonding
16 the perforated plate 14 to the frame consequently results in bonding of the
17 horizontal portion 50, as described in detail below.
18 With further reference to Fig. 8, while the perforated plate 14 has
19 thus far been described as having the tabs 36 positioned to extend from the
transverse edges 40 of the perforated plate 14, the tabs 36 may be also be
21 inwardly offset from the transverse edges 40 to attach to the vertical
portion 38 to
22 an inner side 54 of the transverse end members 22. In this case, the tabs
36 can
23 be formed by welding or otherwise securely attaching the tabs underneath
the
24 perforated plate 14.
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1 The components of the screen assembly 10 can be of any suitable
2 fabrication and construction, as would be apparent to one skilled in the
art. For
3 example, the frame 12 and the perforated plate 14 can be made of rigid yet
4 malleable material, such as mild steel. The screening material 16 can be
made
of stainless steel and can also include a plurality of layers of screening
material
6 16, as particularly seen in Figs. 1-3. Such layers typically progress in
mesh size
7 whereby a finer-meshed top layer 16a is supported by more coarsely-meshed
8 lower layers 16b, 16c. The top layer 16a thereby acts as a sizing screen
while
9 the lower layers 16b, 16c act as structural layers to extend the life of the
top layer
16a. To reduce wear, the lower layers 16b, 16c can be calendared, i.e.
flattened
11 where the wires of the screening material 16 intersect.
12 Preferably, the bonding material 48 is an epoxy thermosetting resin,
13 which can be heated to reversibly transition from a solid state to a
flowable fluid
14 state for coating the surfaces of the components of the screen assembly 10.
Suitable epoxy includes, for example 10-7010 Corvel Gray (Rohm and Haas,
16 Philadelphia, PA) and Nap-Guard (DuPont, Mississauga, Ontario, Canada). As
17 an example of an assembly process, each of the frame 12 and the perforated
18 plate 14 can be separately coated with epoxy powder by pre-heating each
19 component in an oven to a suitable temperature and suspending the heated
component into a fluidized epoxy powder bed as necessary to develop a coating
21 thereon. Upon return to ambient temperature, the fluid coating re-
solidifies and
22 firmly adheres to the surfaces of the components. The epoxy-coated
perforated
23 plate 14 is fit over the frame 12 and screening material 16 is placed over
the
24 perforated plate 14. The entire assembly 10 is then subjected to a heat
press at
a suitable temperature to firmly bond the surfaces together to form an
integral
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1 screen assembly 10. To provide a better surface texture for bonding, the
2 surfaces can be abrasive grit blasted prior to epoxy powder coating.
3 Where L-shaped tabs 36 are used and with particular reference to
4 Fig. 5, prior to coating and bonding with epoxy, it may be desired to first
fit the
perforated plate 14 over the frame 12 by inserting a longitudinal side member
20
6 into channels 58 defined by the L-shaped tabs 36 and further sliding the
frame 12
7 into the channels 58 to form a perforated plate-frame unit. The fitted
perforated
8 plate 14 can then be attached to the frame 12 by coating the perforated
plate-
9 frame unit with epoxy thermosetting resin, such as described above.
Preferably,
the epoxy has sufficient flow characteristics to enter between tightly
adjacent
11 surfaces, such as 10-7010 Corvel Gray.
12 Although it is particularly contemplated to use bonding material 48
13 for attaching the screen assembly 10 components to form an integral unit,
other
14 attachment means can be used alternatively or in addition to the bonding
material
48, as would be appreciated by one skilled in the art. Other attachment means
16 can include, for example, tack welding, spot welding, screws, rivets, etc.
As an
17 example, where L-shaped tabs 36 are used, it may be desired to spot weld
the
18 fitted perforated plate 14 to the frame 12 prior bonding, where in the
bonding
19 process the epoxy or other bonding material may enter spaces between the
tabs
36 and the frame 12 to effect bonding.
21 With reference to Figs. 6A-D, the outer frame section 18 can be
22 constructed of single piece of hollow structural tubing 60 having four
spaced-
23 apart corner notches 62, with each notch 62 forming an angle of about
ninety
24 degrees extending from an outer wall 64 of the tubing 60. The outer frame
section 18 is completed by inwardly bending the tubing 60 around the notches
62
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1 to form a generally rectangular shape and securing the ends 66 together by
2 welding. The notches 62 are preferably formed by punch-cutting such that a
top
3 edge 68 of each notch 62 is downwardly deformed, as shown in Fig. 6D.
4 Consequently, the corners 70 of the completed outer frame section 18
advantageously form a top pocket 72 for containing bonding material 48 used to
6 bond the perforated plate 14 to the frame 12, thereby making a more secure
7 bonding connection. In this case, welding on the top pocket 72 should be
8 avoided as welding material may fill the top pocket 72 that would otherwise
9 contain bonding material 48. Further, welding material on any top surface 44
of
the frame 12 would potentially interfere with the fitting of the perforated
panel 14
11 on the frame 12 if excess welding material is not removed.
12 With particular reference to Fig. 3, the frame can also include at
13 least one transverse or longitudinal cross member 74, 76 positioned within
the
14 outer frame section 18. The cross member or members 74, 76 thus provide
additional structural rigidity to the frame 12 and further support for the
perforated
16 plate 14. The cross members 74, 76 can be fabricated from hollow structural
17 tubing, with the cross members 74, 76 being secured such as by welding to
the
18 outer frame section 10 or to an oppositely oriented cross member 74, 76.
19 With further reference to Fig. 7, where both transverse cross
members 74 and longitudinal cross members 76 are used, the cross members
21 74, 76 can be interlocked by complementary upward- and downward-facing
22 notches 80, 82 formed such as by punch-cutting.
23 Other suitable forms of the frame are also contemplated, as would
24 be apparent to one skilled in the art. For example, rather than having a
generally
rectangular outer frame, the frame can comprise a pair of spaced apart
opposing
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1 longitudinal sides that are connected by at least one transverse cross-bar
to form
2 an H- or a ladder-type arrangement.
3 Although preferred embodiments of the invention have been
4 described in some detail herein above, those skilled in the art will
recognize that
various substitutions and modifications of the invention may be made without
6 departing from the scope of the invention as defined by the claims as
defined
7 herein.
13
