Patent Application
20070125687
The invention relates to screens and in particular to a screen assembly for a vibratory separator such as a shale shaker.
Drilling mud is used while drilling oil and natural gas wells on a drilling rig to control subsurface pressures, lubricate the drill bit, stabilize the wellbore, and carry cuttings and other debris to the surface, among other functions. The drilling mud is pumped through a drill string and out of a drill bit, then returned to the surface through the annular space between the drill string and the wellbore. At the surface, cuttings and other solids that are entrained in the mud are typically separated from the mud by a vibrating screen separator called a shale shaker.
Shale shakers include a lower stationary base, called an under flow pan, and an upper vibratable basket that has connected to it a high frequency linear angular motion or rotary vibratory motor. Mounted generally horizontally in 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 screen deck and solids retained by the screening material are conveyed by vibratory action to the other end where they are discharged. Fluids and small particles pass through the screening material and are collected in a tank system for further processing and reuse in the active system.
Screen assemblies can be distinguished by the way that they provide tensioned screening material. One system is to use hook strips on the basket sides of the screening material in association with tensioning mechanisms on the shale shaker. Alternatively, pretensioned screen assemblies include tensioned screening material attached to a rigid perforated plate, which is in turn attached to a generally rectangular structural frame. The perforated plate supports the screening material and contains a plurality of openings to permit the screened fluid to collect beneath the screening assembly. The frame is used to mount the screen assembly onto corresponding support rails of the basket and the sides of the screening assembly are secured thereto. For example, wedge blocks can be wedged between the top periphery of the screen assembly and wedge angles extending radially inwardly from sides of the screen basket. The sides of the screening assembly are thereby securely sandwiched between the support rails and the wedge blocks.
In one type of construction, the screening material layers are bonded to the perforated plate, which is in turn bonded to the top surface of the frame to form an integral screen assembly. The screen assembly is subject to tremendous stresses caused by the vibratory machinery. In particular, upward and downward stroking motion of the vibratory motor causes the screen assembly to oscillate between the secured sides. In other words, the unsecured area of the screening assembly can vibrate at greater amplitude than the sides, thereby causing out of plane flexing. Such flexing eventually results in failure of the bonding of the perforated plate to the frame and the screen material, as well 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 drilling mud flows over the screens, the upward stroking motion drives the mud into the screen with the impinged mud creating additional reactive force against the downward stroking motion.
Flexing of the screening assembly is a major cause of early deterioration of pretensioned screens, such as separation of components of the screening assembly, contributing greatly to increased operational costs of the shale shaker due to the man-hours required to replace the screen, loss of rig operating time, and cost of replacement screens. To increase the rigidity of the screening assembly for withstanding flexing forces, pretensioned screens are typically made of thick structural tubing and thick perforated plates. This construction, however, results in high manufacturing costs and makes the screening assembly heavy and difficult to handle. While texturing of the bonding surface of perforated plate has been used to increase the bonding strength between the perforated plate and the frame, this approach has not proven to be totally adequate.
There is, therefore, a need in the art for an improved screen for a vibratory separator.
A screen assembly for a vibratory separator is provided whereby a perforated plate for supporting screening material is more securely attached to a frame as compared to conventional screen assemblies. Consequently, the screen assembly is more resistant to damage caused by out of plane flexing of the screen assembly when subjected to high frequency vibratory forces in the vibratory separator.
In a broad aspect of the invention, the perforated plate of the 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 particular at least to sides of frame members that are most susceptible to flexing. The attachment of the perforated plate to sides of the frame thereby provides for more secure attachment, and also structurally reinforces the frame members to which the perforated plate is attached.
Accordingly, in an embodiment of the invention there is provided a screening assembly comprising a generally rectangular outer frame section, a perforated plate attached to the frame, and one or more layers of screening material supported on and attached to the perforated plate. The outer frame 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 to be securely mounted on a vibratable basket of a vibratory separator. The perforated plate includes a substantially planar portion for supporting the screening material, with the planar portion having a plurality of openings formed 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 planar portion of the perforated plate is supported on and attached to a top of the frame with the vertical portion of the tabs extending along and attached to a side of the transverse end members.
The tabs can be further configured to be L-shaped tabs which additionally extend along a bottom of the transverse end members.
Additional aspects relating to the construction of the frame are also disclosed.
In drawings which are intended to illustrate embodiments of the invention and which are not intended to limit the scope of the invention:
With reference to
In further detail, the frame 12 comprises a generally rectangular outer frame section 18 having a pair of spaced apart longitudinal side members 20 and a pair of spaced apart transverse end members 22. In use, the screening assembly 10 is mounted horizontally in a vibratable basket of a vibratory separator (not shown), with the longitudinal side members 20 being clamped or otherwise secured to the basket. Linear angular or rotary vibratory forces are applied to the basket, and hence the screening assembly 10, to cause material on a top 24 of the screening material 16 to move generally longitudinally therealong from one end 26 of the screening assembly 10 to another end 28.
As with conventional perforated plates, the perforated plate 14 comprises a planar portion 32 for supporting the screening material 16 thereupon, with the planar portion 32 having a plurality of holes or perforations 34 punched or otherwise formed therein. The perforations 34 can be of any suitable shape and size to permit sufficient flow-through of screened fluid, while maintaining structural integrity of the perforated plate 14, as would be appreciated by one skilled in the art. In addition, the perforated plate 14 includes a pair of opposing tabs 36 having a vertical portion 38 extending downwardly from transverse edges 40 of the planar portion 32. The tabs 36 may be formed, for example, by downwardly bending a non-perforated periphery 42 of the planar portion 32.
The perforated plate 14 is fit over the frame 12 with the planar portion 32 being supported by an adjacent top 44 of the frame 12, and the vertical portion 38 of the tabs 36 adjacent outer sides 46 of the transverse end members 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 turn bonded with bonding material 48 to the perforated plate 14, thereby forming an integral screen assembly 10. As compared with conventional perforated plates, which are bonded or otherwise attached to only to the top surface 44 of the frame 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 of the perforated plate 14 to the frame 12. Consequently, the perforated plate 14 is more resistant to vibratory detachment from frame 12 upon flexing of the screening assembly 10 in response to upward and downward forces imposed by 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, thereby reducing the risk of bond failure between the frame 12 and the perforated plate 14, as well as between the perforated plate 14 and the screening material 16. Notably, the structural and functional advantages provided by the tabs 36 do not significantly increase the weight of the screening assembly 10.
While the tabs 36 are preferably each a single tab 36 extending along the entire transverse length of the perforated plate 14, the tabs can also extend partially along the transverse length of the perforated plate 14, and can also be a plurality of spaced apart tabs.
Tabs 36 extending along the longitudinal side members 20 can also be provided, although this is generally not necessary as the sides of the screen assembly 10 are typically held in position by wedge blocks.
With reference to
With further reference to
The components of the screen assembly 10 can be of any suitable fabrication and construction, as would be apparent to one skilled in the art. For example, the frame 12 and the perforated plate 14 can be made of rigid yet 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 16, as particularly seen in
Preferably, the bonding material 48 is an epoxy thermosetting resin, which can be heated to reversibly transition from a solid state to a flowable fluid 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, Philadelphia, Pa.) and Nap-Guard® (DuPont, Mississauga, Ontario, Canada). As an example of an assembly process, each of the frame 12 and the perforated plate 14 can be separately coated with epoxy powder by pre-heating each 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 thereon. Upon return to ambient temperature, the fluid coating re-solidifies and firmly adheres to the surfaces of the components. The epoxy-coated perforated plate 14 is fit over the frame 12 and screening material 16 is placed over the 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 screen assembly 10. To provide a better surface texture for bonding, the surfaces can be abrasive grit blasted prior to epoxy powder coating.
Where L-shaped tabs 36 are used and with particular reference to
Although it is particularly contemplated to use bonding material 48 for attaching the screen assembly 10 components to form an integral unit, other 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 can include, for example, tack welding, spot welding, screws, rivets, etc. As an example, where L-shaped tabs 36 are used, it may be desired to spot weld the fitted perforated plate 14 to the frame 12 prior bonding, where in the bonding process the epoxy or other bonding material may enter spaces between the tabs 36 and the frame 12 to effect bonding.
With reference to FIGS. 6A-D, the outer frame section 18 can be constructed of single piece of hollow structural tubing 60 having four spaced-apart corner notches 62, with each notch 62 forming an angle of about ninety 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 to form a generally rectangular shape and securing the ends 66 together by welding. The notches 62 are preferably formed by punch-cutting such that a top edge 68 of each notch 62 is downwardly deformed, as shown in
With particular reference to
With further reference to
Other suitable forms of the frame are also contemplated, as would 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 longitudinal sides that are connected by at least one transverse cross-bar to form an H- or a ladder-type arrangement.
Although preferred embodiments of the invention have been 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 departing from the scope of the invention as defined by the claims as defined herein.
