Method of making a shaker screen

Abstract

A shaker screen for attachment to a bed of a shaker includes a screen frame having at least one mesh screen attached to the top side of the screen frame, wherein the screen frame is preferentially bowed prior to attaching the mesh screen to the screen frame.

Claims

1. A shaker screen for attachment to a bed of a shaker, the shaker screen comprising: a screen frame having a total length, a total width and a total height, the total height is defined between a top surface of the screen frame and an opposite bottom surface of the screen frame, the top surface of the screen frame is movable from a first position to a second position, the first position of the top surface being an initial and intentionally bowed shape such that the screen frame is bowed upward or downward along at least one selected from the total length and the total height of the screen frame; wherein the screen frame, with the top surface in the second position, has a substantially flat shape after at least one pre-tensioned mesh screen is attached to the top side of the screen frame; and the at least one pre-tensioned mesh screen attached to the top side of the screen frame such that spring back forces of the pre-tensioned mesh screen pull the screen frame from the initial and intentionally bowed shape toward the substantially flat shape, wherein the pre-tensioned mesh screen maintains tension along at least one of the total width and the total length of the screen frame.

2. The shaker screen of claim 1 further comprising a reinforcement structure provided within the screen frame adjacent or near the top surface of the screen frame.

3. The shaker screen of claim 2, wherein the reinforcement structure is a steel structure adjacent or near the top surface of the screen frame that provides the initial and intentionally bowed shape.

4. The shaker screen of claim 3, wherein the steel structure is thermally stable.

5. The shaker screen of claim 1 further comprising a sealing surface about a perimeter of the screen frame.

6. The shaker screen of claim 5, wherein the sealing surface is on the bottom surface of the screen frame.

7. The shaker screen of claim 1, wherein the screen frame comprises a composite material.

8. The shaker screen of claim 1, wherein the at least one mesh screen is configured to pull the screen frame from being bowed into a substantially flat shape when the mesh screen is attached to the top side of the screen frame.

9. The shaker screen of claim 8, wherein the substantially flat shape of the screen frame comprises a center of a side of the screen frame being substantially horizontally aligned with two ends of the side of the screen frame when the at least one mesh screen is attached to the top surface.

10. The shaker screen of claim 8, wherein the bowed configuration of the screen frame comprises a center of a side of the screen frame being substantially vertically higher than two ends of the side of the screen frame prior to attaching the mesh screen to the screen frame.

11. An apparatus comprising: at least one tensioned mesh screen; a screen frame comprising: a top surface configured to receive the at least one tensioned mesh screen thereon, the top surface movable from a first position comprising a bowed shape without the at least one tensioned mesh screen disposed on the top surface to a second position comprising a substantially flat planar shape with the at least one tensioned mesh screen attached to the top surface; a total height defined between the top surface and an opposite bottom surface of the screen frame; and a reinforcing structure disposed within the screen frame adjacent or near the top surface of the screen frame such that the bowed shape of the top surface is provided by unequal placement of the reinforcing structure adjacent or near the top surface wherein the tensioned mesh screen is pre-tensioned prior to attachment to the top surface of the screen frame and the substantially flat planar shape of the second position is configured to seal the screen frame with a shaker screen bed.

12. The screen frame of claim 11, wherein the substantially flat planar shape of the screen frame comprises a center of a side of the screen frame being substantially horizontally aligned with two ends of the side of the screen frame when the at least one tensioned mesh screen is received on the top surface.

13. The screen frame of claim 11, wherein the bowed shape of the screen frame comprises a center of a side of the screen frame being substantially vertically higher than two ends of the side of the screen frame prior to receiving the at least one tensioned mesh screen.

14. The screen frame of claim 13, wherein the bowed shape is provided along at least one of a total length of the screen frame and the total width of the screen frame.

15. The screen frame of claim 11, wherein the reinforcing structure is configured to restrict a contraction of the screen frame mold above a neutral axis of the screen frame, and wherein the neutral axis is located halfway between the top surface and a bottom surface of the screen frame.

16. A shaker system comprising: a shaker screen bed configured to receive a shaker screen, wherein the shaker screen comprises a screen frame comprising: a neutral axis; a reinforcing structure disposed within the screen frame above or below the neutral axis such that a bowed shape of the screen frame is provided by unequal placement of the reinforcing structure above or below the neutral axis; and at least one tensioned mesh screen disposed on a top surface of the screen frame, and wherein the screen frame in a first position comprises the bowed shape without the at least one tensioned mesh screen disposed on the top surface, wherein the screen frame comprises a substantially flat shape, substantially parallel to the neutral axis, in a second position with the at least one tensioned mesh screen attached to the top surface, and further wherein the at least one tensioned mesh screen is pre-tensioned before attachment to the top surface of the screen frame.

17. The system of claim 16, wherein the substantially flat shape of the screen frame comprises a center of a side of the screen frame being substantially horizontally aligned with two ends of the side of the screen frame when the at least one tensioned mesh screen is disposed on the top surface.

18. The system of claim 16, wherein the bowed shape of the screen frame comprises a center of a side of the screen frame being substantially vertically higher than two ends of the side of the screen frame prior to the at least one tensioned mesh screen being disposed thereon.

19. The system of claim 16 further comprising a sealing surface disposed on the shaker screen, wherein the sealing surface is configured to seal with at least a portion of the shaker screen bed.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a prior art vibratory shaker.

(2) FIG. 2 is a shaker screen with a screen frame and wire mesh screen in accordance with embodiments of the present disclosure.

(3) FIG. 3A is an assembly view of a screen frame before installation of the mesh screen in accordance with conventional methods.

(4) FIG. 3B is an assembly view of a screen frame after installation of the mesh screen in accordance with conventional methods.

(5) FIG. 4A is an assembly view of a screen frame prior to installation of the mesh screen in accordance with embodiments of the present disclosure.

(6) FIG. 4B is an assembly view of a screen frame after installation of the mesh screen in accordance with embodiments of the present disclosure.

(7) FIG. 5A is a section view of a screen frame mold prior to injection of a screen frame material into the screen frame mold in accordance with conventional methods.

(8) FIG. 5B is a section view of a screen frame after injection of a screen frame material into the screen frame mold in accordance with conventional methods.

(9) FIG. 6A is a section view of a screen frame mold prior to injection of a screen frame material into the screen frame mold in accordance with embodiments of the present disclosure.

(10) FIG. 6B is a section view of the screen frame after removal from the screen frame mold of FIG. 6A in accordance with embodiments of the present disclosure.

(11) FIG. 7A is a perspective view of a screen frame with a preferential bow along a length of the screen frame in accordance with embodiments of the present disclosure.

(12) FIG. 7B is a perspective view of a screen frame with a preferential bow along a width of the screen frame in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

(13) In one aspect, embodiments disclosed herein relate to pre-tensioned composite screens for an oilfield shaker. More specifically, embodiments disclosed herein relate to methods for manufacturing pre-tensioned composite shaker screens.

(14) Referring to FIG. 2, embodiments disclosed herein generally include a screen frame 202 and at least one filtering element 208 attached to screen frame 202. Screen frame 202 may be formed from any material and by any method known in the art. In certain embodiments, screen frame 202 may be a composite frame formed from a frame sub-structure including high-strength steel beams, having a hollow cross-section, and high strength steel rods 204. The frame sub-structure may be enclosed in a high-strength, glass reinforced plastic outer frame 206, wherein the frame sub-substructure forms part of both cross-members and/or transverse ribs (not shown). The composite material may include high-strength plastic, mixtures of high-strength plastic and glass, high-strength plastic reinforced with high-tensile-strength steel rods, and any combination thereof. One of ordinary skill in the art will appreciate that the frame sub-structure and the outer frame may be formed in any configuration and from any material or combination of materials known in the art. Alternatively, screen frame 202 may be formed by injection molding, gas-assisted injection molding, extrusion, and/or any other process known in the art.

(15) In embodiments using injection molding, a molten material is injected at a high pressure into a mold having an inverse shape of a desired grid. The mold may be formed by a toolmaker or mold maker from metals (e.g., steel or aluminum) and precision-machined to form smaller, more detailed features. Once the mold is filled with molten material, the molten material is allowed to cure and is then removed from the mold. The grid may be filled with any molten material known to one of ordinary skill in the art. Further processes of forming composite frames are discussed in U.S. patent application Ser. No. 11/859,223, assigned to the present assignee and fully incorporated herein by reference.

(16) Still referring to FIG. 2, filtering element 208 may include, for example, a mesh, a fine screen cloth, combinations thereof, and/or any other materials known to one of ordinary skill in the art. Furthermore, filtering elements 208 may be formed from, for example, plastics, metals, alloys, fiberglass, composites and/or polytetrafluorethylene. In certain embodiments, multiple layers of filtering elements 208 may be used, and in such multiple layer filtering elements 208, filtering elements 208 with different size perforations may be used. While attaching filtering element 208 to composite screen 202, filtering element 208 may be pre-tensioned. Filtering element 208 may then be attached to screen frame 202 by, for example, heat staking, ultrasonic welding, mechanical fastening, chemical adhesion, and/or thermal bonding. One of ordinary skill in the art will appreciate that filtering element 208 may be attached to screen frame 202 with any method known in the art.

(17) Referring to FIG. 3A, an assembly view of a shaker screen 300 prior to installation of a wire mesh screen 310 on a screen frame 320 is shown. Shaker screen 300 includes a screen frame 320 which is made by molding a thermoplastic framework, and further includes a wire mesh screen 310 that is stretched and melted onto screen frame 320. Screen frame 320 is initially substantially flat and includes an integral welded wire grid (204 in FIG. 2) to provide strength as well as thermal stability for screen frame 320, which may be subjected to high temperatures when wire mesh 310 is melted onto it.

(18) Referring now to FIG. 3B, as assembly view of shaker screen 300 after stretching and melting wire mesh screen 310 on screen frame 320 is shown. Wire mesh screen 310 may be tensioned on a stretching fixture (not shown) and melted onto screen frame 320 using a hot plate or other devices known to those skilled in the art. When the tension is taken off of the stretching fixture, wire mesh screen 310 may spring back causing a bow in screen frame 320 as shown. On shaker screens where a seal is required on an underside periphery, or where there may be structural support on the underside at a center of the shaker screen, the bow may prevent an adequate seal from being achieved. Furthermore, because the periphery of the shaker screen may not properly seat in a shaker screen bed, excess vibrations or whipping may occur in these areas due to the vibratory forces of the shaker. Therefore, a method to form a shaker screen to control the bowing or to provide a preferential bow of the shaker screen is now described.

(19) Referring to FIG. 4A, an assembly view of a shaker screen 400, prior to installation of wire screen mesh 410 onto screen frame 420, is shown in accordance with embodiments of the present disclosure. Screen frame 420 may initially be molded with a preferential bow incorporated into it. As used herein, the preferential bow may be defined as an initial and intentional bow incorporated into screen frame 420 to compensate for tension caused by wire screen mesh 410 once released from the stretching machine. Once wire screen mesh 410 has been released from the stretching machine, spring back forces of the tensioned wire screen mesh 410 may pull the bowed screen frame 420 back toward a more planar or flat configuration as shown in FIG. 4B.

(20) As described above, the tendency of the screen frame material to shrink or contract after molding and cooling may be used to configure a preferential bow in the screen frame. As previously described, the molding process requires a molten plastic or other suitable material to be injected into a mold or die cavity. After injecting the plastic material, the mold is then cooled, usually via waterways machined in the mold tool, so that the part may be handled upon removal from the mold. Because the shape is formed at a high temperature and then cooled, the plastic may naturally want to contract due to its natural thermal expansion/contraction properties. When the part is removed from the constraints of the mold, it is then free to contract.

(21) Referring to FIG. 5A, a section view of a conventional screen frame mold 500 before injecting the frame material to form the screen frame is shown. A steel structure 502 is positioned in mold 500 above and below a neutral axis 504 prior to injecting the plastic material. Neutral axis 504 may be defined as the axis passing through the geometric center of screen frame mold 500. Steel structure 502 provides added strength as well as thermal stability to the screen frame when formed, which is subjected to high temperatures when the mesh screen is melted onto it. FIG. 5A shows the near symmetrical geometry of steel structure 502 above and below neutral axis 504 of screen frame mold 500.

(22) Referring now to FIG. 5B, a section view of a screen frame 510 is shown after having been removed from screen frame mold 500 (FIG. 5A). In existing molding processes, the amount of contraction observed may be very small because of steel structure 502 placed in screen frame 510. Steel structure 502 restricts frame material 506 from contracting as much as it would without the added steel structure 502, which means any contractions of frame material 506 may be equal or close to equal above and below neutral axis 504. Because of the placement of steel structure 502, the contraction of frame material 506 may be restricted equally above and below neutral axis 504, which results in a substantially flat molded screen frame 510.

(23) Referring now to FIG. 6A, a section view of a screen frame mold 600 before injecting plastic material to form the screen frame is shown in accordance with embodiments of the present disclosure. Steel structure 602, or other appropriate reinforcement material, is positioned in mold 600 above neutral axis 604 prior to injecting plastic material. In certain embodiments, a trial and error method to determine a proper positioning of steel structure 602 in a screen frame to induce a certain preferential bow may be used as understood by those skilled in the art.

(24) Referring to FIG. 6B, a section view of a screen frame 610 is shown after having been removed from screen frame mold 600 (FIG. 6A), in accordance with embodiments of the present disclosure. As shown, the natural contraction of the plastic material in combination with the placement of the steel structure, creates a preferential bow in screen frame 610 after it is removed from mold 600. Contraction of the plastic material above neutral axis 604 is restricted by placement of steel structure 602 near the top of the mold, while the material below the neutral axis 604 is free to contract due to the lack of steel structure 602 in this region. The unequal placement of steel structure 602 above and below neutral axis 604 is thus used to induce the preferential bow.

(25) In alternate embodiments, the preferential bow may initially be designed as a part of the molded screen frame. The mold or die tool used to form the screen frame may be machined to incorporate the preferential bow. As such, the mold may be configured to produce a screen frame with the preferential bow. Further, the steel structure forming the internal reinforcing grid may be machined or formed in the preferentially bowed shape and positioned in the screen frame mold prior to injecting plastic material. Therefore, the mold tool may already be configured with the preferential bow requiring only the plastic material to be injected. After the material is cooled, the screen frame may be removed from the mold tool with a molded preferential bow.

(26) In still further embodiments, a combination of embodiments already described may be used. A mold tool used to form the screen frame may be machined to incorporate the preferential bow with steel structure to form the internal reinforcing grid also machined to form the preferential bow. Steel structure may then be positioned in the screen frame mold only above the neutral axis before injecting the plastic material to form the screen frame. The molded screen frame may then be removed from the mold and the natural contraction of the plastic material creates a preferential bow in the screen frame. Contraction of the plastic material above the neutral axis is restricted by placing the steel structure at the top, while the material below the neutral axis is free to contract due to the lack of steel structure in this region. The unequal placement of the steel structure above and below the neutral axis is used to induce the preferential bow.

(27) Referring now to FIG. 7A, a perspective view of a screen frame is shown in accordance with embodiments of the present disclosure. As shown, in certain embodiments, the screen frame 720 may be configured so that the screen frame preferentially bows along the length of the screen frame only. Now referring to FIG. 7B, a component view of the screen frame is shown in accordance with embodiments of the present disclosure showing the preferential bow along a width 722 of screen frame 720 only. In still further embodiments, the screen frame may be configured to have the preferential bow along both the length and the width (not shown). The screen frame may be configured having a preferential bow as described in various embodiments above depending on sealing requirements, structural requirements of the shaker assembly or screen, or others known to those skilled in the art.

(28) After the screen frame has cooled and contracted, the preferential bow is formed in the screen frame. The wire mesh screen may then be applied by stretching it and melting it on the screen frame. As described above, when the stretching fixture used to stretch the wire mesh screen is removed from the wire mesh screen, the tension in the mesh may cause the screen to bow. However, in embodiments disclosed herein, because of the initial preferential bow in the screen frame, the screen frame may be forced into a flatter configuration, or slightly convex bow. A convex bow of the screen frame may be defined as when the screen frame is set on the shaker bed, the screen frame will be bowed upward towards the center, creating more of a dome configuration. In embodiments disclosed herein, when assembled, the screen frame may have a flat to slightly convex configuration when attached to the shaker bed. In alternate embodiments, the screen assembly may be attached in a concave configuration in which the screen frame is bowed downward towards the center, forming more of a bowl. Further, the screen frame may be configured with a sealing surface about a perimeter to form a seal with the corresponding shaker bed.

(29) Advantageously, embodiments of the present disclosure for the screen assembly may provide a method to use the natural contraction and consequential bowing of the composite screen frame. By using the preferential bow, a screen assembly may be configured to provide adequate sealing between the screen assembly and shaker frame, and therefore reduce of prevent materials from passing around the screen perimeter. Further, the preferential bow may provide improved and more secure seating between the screen assembly and the shaker frame, thereby preventing excessive rattling and vibrations during operation. Any reduction in excessive vibrations between the screen assembly and the shaker frame may also reduce wear on components and increase the life of the entire shaker assembly.

(30) While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.