PAPERMAKER'S SCREEN CYLINDER WITH HELIX SCREEN ELEMENT

Abstract: A papermaker's screen cylinder (10) has a screen body (11) formed as a helical strip (15) of sheet material being joined along marginal edges to form lock seams (18), and mounted on end rings (12, 13). The strip (15) may be perforated with openings therein such as holes or may have openings or holes formed therein after being helically wound. The strip (15) is preferably corrugated transversely of its width with corrugations (21, 22) that extend parallel to the edges of the strip so as to enhance the beam strength of the strip. The end rings may be formed of stainless steel or may be formed of a polymer or composite material (36) bounded on the ends of the cylindrical screen body and retained by embedded anchors (40) extending through the screen body and into the material of the rings.

Description: PAPERMAKER'S SCREEN CYLINDER WITH HELIX SCREEN ELEMENT Background of the Invention Paper pulp mills and paper mills for many years have made extensive use of pressure screening apparatus for cleaning paper making stock. The paper making stock suspension may contain new fibers or may contain a large amount of reclaimed fiber material, or both. The screening apparatus commonly employed uses a generally cylindrical perforated screening member in a closed pressure housing. The screening member divides an internal chamber of the pressure housing into an inlet chamber and an accepts chamber respectively on opposite sides of a perforated screen. The inlet chamber may be considered as the high pressure side of the screen and the accepts chamber, the low pressure side of the screen. Such pressure screening apparatus commonly employs a rotor that operates to move vanes, foils or other impulse members at high speed along one of the surfaces of the screen, usually at the high pressure side, to keep the screening perforations open and free from plugging or blinding with solid material. Commonly, the stock suspension, or "furnish" as it is called, is delivered to the inlet chamber adjacent one end of a screening cylinder, and the material rejected by the screening cylinder is collected and discharged at its opposite end. Prior patents that disclose such apparatus including screening cylinders and impulse foils for this purpose are shown for example in the U.S. patent of Hatton et al. 4,017,387 issued April 12, 1997 and Lehman 4,276,159 issued June 30, 1981, and additional examples are shown in the references cited in Lehman '159 in column 1, lines 18-23. In the pressure screening apparatus of the kind described, the rotor, as previously mentioned, has impulse members or vanes, preferably of an airfoil cross section, that move in closely spaced but non-contacting relation with a surface of a cylindrical screen member, preferably, an inner inlet high pressure surface. These vanes create alternating positive and negative pressure waves that are effective on the perforations in the screening cylinder to prevent plugging thereof, and to permit the pressure screen apparatus to operate at high capacity. This common screening process imposes a great deal of stress on the screening member, and it has been found that it is desirable to make such screens out of a solid cylinder of approximately at least 3/16 inch stainless steel, which cylinder is reinforced by end rings and sometimes by encircling rings intermediate the end rings. The screen cylinder perforations may be either slots or holes. For example, screening holes are shown in Martindale U.S. patent 2,835,173, and machined slots are shown in Lehman 4,276,159. Additionally, laser cutting has been used to form either slots or holes in the screening material, as shown in the U.S. patent of Chupka 4,795.360. The necessity of using a screen having a wall thickness of about 3/16 inch or greater has resulted in a high materials and manufacturing costs. For example, a 24 inch diameter screen cylinder, approximately 24 inches high, may weigh up to 150 pounds or more. The screening surface may be precision machine cut or laser cut, or combinations of both, including in some cases EDM cutting, to provide the closely spaced openings in the form of holes or slots in order to provide a screen with a desired openness. The thickness of the screening wall has necessitated tedious, time consuming, and expensive slotting and cutting techniques, adding to the labor cost of preparing such screen cylinders. Therefore, a need exists for lighter weight and lower cost screen cylinder member for papermaker's closed pressure screening apparatus, for screening slurries or suspensions of papermaker's stock. Summary of the Invention This invention is directed to an improved lighter weight and lower cost cylinder screen member for use in pressure screening apparatus for screening papermaker's stock, in which the screening portion includes a generally cylindrical tubular section of helically wound, endless strip or strips of sheet material, joined along the edges. The strip sheet material is preferably transversely corrugated so that the axes of the corrugations extend generally parallel to the length of the strip for imparting radial stiffness. The wall thickness of the corrugated strip is substantially thinner than that required by conventional screen cylinders, as outlined above, and may, for example, have a thickness of about .060 inch or less. Further, the screening openings or perforations therethrough may be made by pre- perforating the strip material or by perforating the screen wall by cutting, drilling, or laser cutting, after the same has been formed into a cylinder. Therefore, the screen cylinder of this invention is not necessarily limited to punched perforations or holes, and screening slots may be cut therein as well. Surprising and unobvious advantages accrue from the use of helically wound strip material, such as stainless steel sheet metal. When the strip material is corrugated along its length, a substantial gain in strength or radial stiffness is imparted to the completed cylindrical section. Also strength is imparted by the creased interlocking seams formed at the respective marginal edges of the strip material. Preferably lock seams are formed in which the edges are interlocked, folded and pressed flat against each other. The seams also may be resistance welded during the forming process. The seams may be welded with or without flux. The seams may be rolled into a relationship with a cylinder so that they may be either "inside" or "outside." It is preferred, in the construction of the cylinders according to this invention, to form the seams so that the major portion of the seam thickness extends inwardly in relation to the inlet surface, as the case may be. In this manner, the seams tend to form a spiral guideway that augments the flow of the rejects along the screen surface to the rejects outlet. The axes of the corrugations, which extend parallel to the seams, similarly induce a flow of the stock slurry and rejects toward the screen outlet. These effects depend upon selecting the direction of the helix in relation to the direction of rotation of the rotor such that paper stock material not accepted by the screen moves generally in the axial direction toward the accepts outlet of the pressure screening apparatus. Stainless steel end rings may be welded in place to the ends of the screen section, for fitting and supporting the screen in the screening cavity of the screening apparatus. This application further describes a new and novel arrangement using polymer, plastic or composite retainer rings molded in place over the exposed ends of a cylindrical section of helically wound screen material. Pins or other retainer members may be inserted through the openings in the screen material to be embedded in the ring material to serve as anchors for retaining the ends of the screen in the polymer or composite rings. The invention may be characterized as a screen cylinder member for screening papermaker's stock in pressure screening apparatus in which the screening surface is formed as a helix or as a helically wrapped sheet metal strip welded or joined at the margins. The helix cylinders may be supported by end rings. Preferably, the strip material is also corrugated transversely of its width to impart additional strength to the strip. One or two end rings may be used, positioned at one or both ends of a cylindrical screen plate made according to this invention, for the purposes of mounting in a paper making screen and/or for providing a seal between the spaces which extend at each side of the plate. Such rings accommodate the diametrical variations that result from the seams and/or the corrugations, and serve to center an enveloping screen cylinder surface of the screen cylinder plate at the center of rotation of the screen rotor apparatus. As a further feature and characterizing object of the invention, one or more of the end rings are formed of a molded polymer, fiberglass or composite material in which the ends of a helically wound screen are embedded in such material and retained therein by anchoring elements. In a further aspect of the invention, a papermaker ' s screen member is formed with a screening member defined as a helix of a continuous sheet metal strip, joined by interlocking edges, and in which the sheet metal strip is corrugated in a direction along its length to increase the strength, and in which the strip is perforated or otherwise formed with screening openings either in the form of holes or slots. The slots may extend longitudinally or transversely of the direction of the strips and the perforations or openings may be formed in the strip prior to processing into helix tubing, or during the processing, such as by concomitant punching or cutting, or subsequent to forming the tubing, such as by cutting, punching, drilling, or ablading such as by laser or EDM. The screen by this invention also provides a further and unexpected advantage over conventional screen plates used in papermaker's pressure screen apparatus. That is, the thinness of the screening wall reduces to at least 50% or more the usual thickness through which accept fibers must pass through openings or slots and reduces the chance of hole plugging compared to that of conventional screen plates, at least without expensive profiling of the plate surface or surfaces in order to reduce the effective length of the opening. Thus, the thinner plate can screen fibers with reduced friction or pressure drop as compared to plates of convention thickness, and therefore exhibits a higher throughput and efficiency. It is accordingly an important object or the invention to provide a lightweight screen cylinder member for screening papermaker's stock that requires less metal and material as compared to conventional screens, and which may be manufactured with reduced labor and overhead costs. An important advantage of the invention is that it provides the ability of using pre-perforated material in the manufacture of a paper stock screening member. A further advantage of the invention is that the screening material may be helically formed in long tubes and stored for future use and then sections cut off of the tubes, to form a screening member for a screen plate. A still further object of advantage resides in a method for manufacturing a screen cylinder element for paper making screens, as described above, including the steps of forming a very long cylindrical tube from long and substantially flat strip or perforated strip material, and then cutting the tube into cylindrical segments of the desired axially length. Such segments may be formed from a continuously formed spiral tube in which the segments are cut off as the tube is made. These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. Brief Description of the Drawings Fig. 1 is a top plan view of a screen made according to this intention; Fig. 2 is a partially broken away side elevation view of a screen of Fig. 1; Fig. 3 is an enlarged fragmentary detail looking generally along line 3- -3 of Fig. 1 showing the manner in which the screen portion is attached to a metal end ring such as by welding; Fig. 4 is an enlarged fragmentary' cross-sectional detail of a transverse portion of the corrugated strip of sheet material; Fig. 5 is an enlarged plan view of a typical hole pattern that may be used with this invention; Fig. 6 is a fragmentary section of a strip of sheet metal showing one arrangement or pattern by which the screen may be slotted; Fig. 7 is an enlarged fragmentary view showing the manner in which a polymer, fiberglass or other composite ring may be attached to the screen strip material, at one or both of the end rings; and Fig. 8 is a enlarged sectional view through one of the seams joining the marginal edges of a helix wound strip, the view showing the seam connection prior to rolling and welding. Detailed Description of Preferred Embodiments Referring the figures of the drawings, which illustrate preferred embodiments of the invention, a cylindrical screen cylinder element made according to this invention is illustrated generally at 10 in Figs. 1 and 2. In Fig. 2, reference numeral 11 referres to a helically wound screen section or body, generally cylindrical in shape, with circumferential ends respectively received in mounting rings 12 and 13. At least one of the mounting rings, such as the ring 13 in Fig. 1, is provided with conventional bolt openings 14 by which the screen cylinder element 10 may be received and mounted within the pressure screening apparatus. The cylindrical screen body 11 is made or rolled as a helix tube from a single continuous length or substantially flat strip of sheet metal by helix tube forming apparatus, such as that shown in U.S. patent 5,609,055. The helix screen body 11 has a plurality of side-by-side joined strip sections 15 formed as a continuous strip 16 (Fig. 4) of sheet material that has been rolled and welded in a helix over a mandrel to a cylindrical shape, with the butting edges interlocked, rolled and optionally welded, at helical seams 18, as shown in Fig. 8. The lateral space of the strip 16 between the seams is preferably corrugated in an approximate sinusoidal manner such as by rolling or forming a flat sheet metal strip. As shown in the fragmentary transverse section of Fig. 4, a corrugation pattern consists of reverse partial cylindrical arcuate sections joined with radii as shown so as to form a continuous pattern of ridges 21 and valleys 22 extending across the width of the strip, such that the axes 23 (Fig. 2) of the corrugations extend parallel to the length of the strip. However, the invention is not intended to be limited to the particular form of corrugation as illustrated in Fig. 4. The purpose of the corrugations is to provide high radial stiffness to the co-joined strip segments. The waviness provided by the corrugations, as illustrated in Fig. 4. as well as the seams 18 provide a further unexpected advantage. The waviness and the marginal seams produce, with the rotating foils, regions of microturbulence that assist in maintaining the perforations or openings in the body 11 in an open state. A pattern of perforations or openings 24 may be preformed in the strip material, from a common roll of stainless steel of, as example, a thickness of 0.60 inches as noted above. Fig. 5 illustrates a preferred 60° pattern of perforations forming cylindrical openings 24 that may be as small as 0.008 inches or smaller or larger. It is not intended that the invention be limited to a particular hole pattern or sizes. Fig. 6 diagrammatically illustrates how a pattern of slots 25 may be formed in the strip material. It is also within the scope of the invention to employ unperforated or unslotted strip material in making the helix screen body 11 and thereafter forming the desired openings through the formed cylindrical body by laser cutting, by EDM machining, by high pressure water cutting, or other equivalent means including mechanical cutting and drilling. A particular advantage of the screen cylinder of this invention resides in the fact that the material used for the strip 16 has a thickness permitting high speed perforation at relatively low cost. Preferably, the seams or continuous seam 18 are formed in interlocking manner in which each of the adjacent edges form interlocking loops 26 which loops are then rolled tight with pressure applied as shown by the arrows 30 of Fig. 8. If desired the seams may be continuously heat welded such, as by using arc or high intensity electricity, with or without flux, to form an integral and continuous seam. The seam 18 as shown in Fig. 8, consisting essentially of four thickness of the material of the strip 16, may be located on the "inside" or "outside" circumference of the cylinder as dictated by the rolling equipment. In the case of the screen cylinder 10. it is preferred that the seam be placed at the inlet surface, usually the inner surface, of the screen. In this manner, the slightly elevated helically rib that is formed by the seams can, together with the undulating corrugations, serve as spiral channels leading from one axial end of the screen to the other, as the impulse foils are rotated. By selecting the helix and direction of rotation so as to lead the rejects to the outlet, efficiency can be provided by assuring in this manner that a component of the rotary motion of the material is in an axial direction that assists in carrying the rejects to the rejects outlet and away from the inlet surface of the screen. The seams also act as turbulence inducing bars that cooperate with the rotating foils to keep open the screen perforations. Fig. 3 illustrates a preferred method by which the helix screen bod)' section 11 may be attached to one of the end rings, such as the end ring 13. The end ring 13 is formed of metal and provided with an L-shaped slot or opening 32. The cylindrical edges of the section 11 are inserted into the slot and welded in place such as by the weld 35. The opposite end ring 12 may be attached by the same method. As an example of a preferred embodiment, a 24 inch diameter, a 24 inch high screen according to this invention was instructed using stainless steel strip material having a wall thickness of 0.060 inches (16 gauge). The screen was transversely corrugated so that the axis of the corrugations extended parallel to the edges of the screen, and the lead angle of the helix was about 20°, as shown in Fig. 2. The pitch of the corrugations, between ridges 21 was 0.625 inches. The strip 15 was pre-perforated with holes 24 of about 0.062 inches in diameter at a hole spacing of about 0.14 inches to provide an approximately 12% open area. A corrugated strip 16 was nominally 6 inches wide providing an effective width of about 5.6 inches after seaming thereby providing seams 18 at about 5.6 inch spacings. The radius of curvature of the corrugations was approximately 0.19 inches (measured to the surface of the plate) and when taken together with the thickness of the plate, provided an effective thickness dimension "d" as shown in Fig. 4 of 0.25 inches. A radial thickness of the screen at the seams was about 0.24 inches. The perforated openings were on a 60° pattern, on 0.170 centers, dimension A as illustrated in Fig. 5. The end rings were made of stainless steel and attached as shown in Fig. 3. The screen weighed 60 pounds. It is within the scope of the invention to utilize low cost and lighter weight support rings made of polymer, fiberglass, filled or composite material, as illustrated in Fig. 7. The ring 36 is formed of such composite or polymer material and is molded in place about each of the axial ends of the body 11. Locking anchors in the form of pins 40 may be inserted through perforations formed in the marginal edges or the ends of the screening sheet material to be molded into and engage the material forming the ring 36 prior to curing. In the matter, the ring, which may have the general overall configuration of the ring shown in Fig. 3, can be bonded to each of the ends of the body 11. The use or a polymer of composite material for the rings permits an additional substantial savings in cost, and the use of such support rings is possible due to the inherent strength of the helically wound corrugated screening body 11. Apparatus for forming a strip of sheet material into a continuous helix as well known in the art as shown in U.S. patent 5,604,055, and equipment for this purpose may be acquired from a number of companies including Spiral-Helix, Inc. at 999 Dearfield Parkway, Buffalo Grove, Illinois 60089 USA. A helix tube formed in this manner may have indefinite length and predetermined diameter, and after forming may be cut in lengths to correspond to the proposed height of the cylindrical screening body 11 taking into account the dimensions of the end rings to be applied. Therefore, screening material can be helically wound and formed, as described above, and then cut to desired axial lengths as needed for particular machines. It will be necessary to supply the cylinders in a plurality of diameters, with 24 inch diameter being typical but not exclusive, and is a simple matter of choice in setting up the helix tube forming machine. Also, the seamed tube may be continuously formed with cylindrical segments being cut off as the tube is made.

Claims: -CLAIMS- 1. A screen cylinder for use in pressure screening apparatus of the kind having rotating impulse members, for the purpose of screening papermaker's stock, comprising a generally cylindrical screen body formed of a strip sheet metal material wound in the form of a helix, lock seams formed at the marginal edges of said strip, said strip being formed with apertures therein for screening the papermaker's stock. 2. A screen cylinder according to claim 1 further comprising said strip being formed with corrugations transversely of its width in which the axes of the corrugations extend generally parallel to each other and generally parallel to said strip marginal edges. 3. A screen cylinder according to claim 1 or 2 in which said strip marginal edges are interlocked with adjacent marginal edges of the strip in the helix forming a locked seam having a thickness of about four times the thickness of the strip and imparting beam strength to the cylinder. 4. A screen cylinder according to claim 3 in which the strip marginal edges are welded at said seam. 5. A cylinder according to any preceding claim in which the end rings are formed of stainless steel. 6. A screen cylinder according to any one of claims 1-4 in which the end rings are formed of a non-metal composite or polymer material, and ring locking anchors extending through a said strip aperture at the marginal ends of the screening member and embedded in said rings for retaining said rings on said screen body. 7. A screen cylinder according to any one of claims 2-6 in which one of the generally cylindrical surfaces of the screen body is an inlet surface, and the pitch of said corrugations in relation to the direction of flow through the pressure apparatus causes rejects materials to move circumferentially toward a rejects outlet. 8. A screen cylinder for use in pressure screening apparatus of the kind having rotating impulse members that move adjacent to a screen surface, for screening papermaker's stock, comprising a generally cylindrical screen body, said body being formed of a single strip of sheet material wound in the form of a helix, seams formed at the marginal edges of said strip locking said strip edges together, said strip being corrugated with corrugations running generally parallel to the length of the strip material, said strip having apertures therethrough formed as perforations through said strip material for screening such papermaker's stock. 9. A metallic cylindrical screen plate for screening papermaking stock made from one or more long, substantially flat strips of perforated material wound in spiral helical fashion, with corresponding spiral seams joining the marginal edges of the strip or strips including a portion of the strip or strips forward to provide radial stiffness and strength to resist the forces exerted on the screen plate during the screening operation. 10. The screen plate according to claim 6, wherein the spiral seam or seams comprise crimped, locked connections of the neighboring edges of the strip or strips, whereby the resulting thickness of the seam is about 4 times the thickness of said strip of perforated material. 11. The screen plate of claim 9 or 10, wherein the edge of the seams are fastened together by welding or brazing. 12. The screen plate of claim 9, wherein the spiral seams are joined together by crimping and also welding or brazing. 13. The screen plate according to claims 9-12 in which said portion to provide radial stiffness comprising corrugated ridges and valleys which extend substantially parallel to the edges of said strip or strips and said seams. 14. The screen plate according to claim 9, including one or two end rings positioned at one or both ends of said cylindrical screen plate for purposes of mounting in a papermaking screen and/or for providing a seal between the spaces which extend of each side of said plate, said rings accommodating the diametrical variations which result from the seams and/or the corrugations and serving to center an enveloping cylindrical surface of said cylindrical screen plate on the center of rotation of the screen rotor. 15. The screen plate according to claim 14, wherein said end rings are metallic and connected to said cylindrical screen plate by weld, brazed, or glued bond. 16. The screen plate according to claim 14, wherein said end rings are metallic and mechanically connected by pin, screw, or rivet means, and including rubber or plastic material between the said cylindrical screen plate and said end rings, to provide a seal between said spaces which extend on each side of the screen plate. 17. The screen plate according to claim 14, wherein said end rings are made of a non-metallic composite or polymer material and connected to the screen plate by rivets, strips, pins, anchors, or glue bond. 18. The method of making a screen cylinder for papermaking screens according to claim 9-17, including the steps of forming a very long cylindrical tube from said long substantially flat strip of perforated material and then cutting the tube into cylindrical segments of the desired axial length. 19. The method of making a screen cylinder according to claims 9- 17, including the steps of substantially continuously forming a spiral tube and cutting cylindrical segments off, as the tube is made.

Inventors: CHUPKA DAVID E, WEATHERLY STEPHEN M, WILLIAMSON GARY S, CHUPKA, DAVID, E., WEATHERLY, STEPHEN, M., WILLIAMSON, GARY, S.
Applicants: CHUPKA DAVID E, THERMO BLACK CLAWSON INC, WEATHERLY STEPHEN M, WILLIAMSON GARY S, CHUPKA, DAVID, E., THERMO BLACK CLAWSON INC., WEATHERLY, STEPHEN, M., WILLIAMSON, GARY, S.
Application year: 1999
Main classification: B07B1
IPC codes: B01D29, B03B5, B07B1, D21D5