Liquid purification or separation – Filter – Movable medium
Reexamination Certificate
2001-03-14
2003-06-17
Walker, W. L. (Department: 1723)
Liquid purification or separation
Filter
Movable medium
C210S402000, C210S404000, C210S484000, C210S485000, C210S492000, C210S494200, C210S497010, C210S497300, C210S232000, C029S896620
Reexamination Certificate
active
06579458
ABSTRACT:
This application claims the priority of German Patent Application Ser. No. 198 42 042.0, filed Sep. 14, 1998, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a screening device for screening fiber suspensions, and more particularly, to a screening device which can be applied in the paper industry, for example with pressurized sorters.
Screening devices typically include a substantially cylindrical screening element with a screening surface in the form of a slotted hole screen mat or a screen plate provided with drilled or milled/sawn screening slots. Such screening device has to withstand high static and dynamic loads, particularly in sorter applications. Hence, a spacer element is typically associated with the cylindrical screening element. The cylindrical screening element with the spacer element is supported on a reinforcing element with a radial clearance. The reinforcing element can have the form of, for example, a reinforcing jacket. Terminal elements, for example, in the form of end rings, can be provided on the axial ends of the screening device to aid in positioning of the screening device. In typical arrangements, the respective terminal element is welded to the reinforcing element and the screening element, whereby the screening element is assembled first and the reinforcing element is subsequently positioned from the outside over the screening element and thereafter secured. Finally, the ring-shaped terminal elements are connected with the cylindrical screening element along the circumference of the reinforcing element. The welding seams of the weld connection are accessible only from one side. The high static and dynamic loads can introduce notch stress, so that the durability of such screening device depends strongly on the integrity of the weld connection.
In typical applications, the screening element in particular is subjected to severe wear, with the reinforcing element having a much longer service life. Because the manufacture of the screening device requires a weld connection between the screening element with the spacer element and the reinforcing element, the entire screening device has to be exchanged when the screening element wears out, which is expensive and complex.
European Pat. No. EP-0 471 195 A1 as well as U.S. Pat. No. 5,200,072 discloses screen plates, screen cylinders and methods for manufacturing the same. The cylindrical screening device is designed so that the screening element and the screening units forming the screening element are releaseably and interchangeably connected to a support cylinder that forms the reinforcing element. The manufacturing cost and the manufacturing time is reduced in that only a worn-out screening element has to be replaced, whereas the reinforcing element, in particular the support cylinder, can be reused. The releaseable connection between the screening element and the jacket-shaped reinforcing element is formed by making the outside diameter of the screening element slightly greater than the inside diameter of the support cylinder. The screening element and the reinforcing element are non-positively secured to one another by a temperature-dependent shrink-on process. This connection can optionally be secured by an additional step, for example, by welding, riveting, with screws, adhesives, solder and the like.
U.S. Pat. Nos. 4,954,249 and 5,023,986 disclose a modular screen basket with several small ring-shaped cylindrical screening elements. The individual cylindrical screening modules are interchangeable and are positively connected with reinforcing rings via notches. The axial end rings are tensioned with respect to one another by a plurality of tension rods. The axial tension rods are simultaneously guided through bores provided in the reinforcing rings.
European Pat. No. EP-A-0 724 037 discloses a screen basket wherein the profile rods are positively connected with reinforcing rings.
German Pat. No. DE 39 42 484 A1 describes a sorter with a screen basket which is supported on the sorter housing by support rings. The design of the support structure is quite complex and the axially spaced apart support locations can absorb only radial forces, but no torsion forces. Since the sorter housing provides the main support function, it requires modifications to accommodate different types of screen baskets or screening elements, since there are no additional reinforcing elements aside from the sorter housing that can be adapted to support the screen basket.
J & L Fiber Services, Inc., Waukesma, USA, supplies screening cylinders, wherein a plurality of short rod-shaped elements is positively located in grooves of reinforcing rings and fixed in position by tension rods, which is time-consuming and expensive. The entire screening cylinder has to be disassembled to exchange any damaged and worn elements.
It would therefore be desirable to provide a screening device of simple design which can be applied, in particular, with fiber suspensions in the paper industry, and which permits an economical and cost-effective reuse of those elements of the screening device that are not severely worn, such as the reinforcing element. In addition, the screening element and the reinforcing element should be reliably connected to one another so as to support both dynamic and static loads.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a screening device, in particular for fiber suspensions in the paper industry, is provided which has a substantially cylindrical screening element forming a screening surface, with the screening element being radially supported on a reinforcing element by spacers with clearance therebetween. The screening element can be interchanged as one unit and is non-positively secured to the reinforcing element by a frictionally engaging clamping connection.
In this way, the screening element forming the screening surface can be released from the reinforcing element when the screening element is consumed. The reinforcing element, on the other hand, can be reused with the screening device after insertion of a new screening element. The design of the screening device according to the invention is based on the observation that the actual screening and/or sorting function is mainly performed by the screening element with the screening surface, possibly in cooperation with the spacer elements, whereas the reinforcing element provides the actual support for the screening element and facilitates insertion of the screening device in the respective machine. The clamping connection between the screening element and the spacer elements, on one hand, and the reinforcing element, on the other hand, distributes the clamping force uniformly over the entire circumference of the screening device and the reinforcing device. The clamping forces of the frictionally engaging clamping connection alone can reliably secure the screening element against rotation with respect to the reinforcing element. Since this connection is releaseable, the screening device can be removed from the reinforcing device without damaging the reinforcing device. Accordingly, the invention permits the reinforcing element to be reused repeatedly, while the screening element itself, which is subject to wear even if the screening device is used as intended, can be exchanged as an entire unit.
Advantageously, the entire screening device can be pre-fabricated and unit exchanged as a single unit. In particular, the reinforcing element, which can be fabricated separately and independently of the screening device, provides the actual support function and ensures the proper fit of the screening device to the machine, such as a sorter. By separating the screening and support functions and/or the fit, the respective components of the screening device, i.e., the screening element and/or the reinforcing element, can be designed and constructed to take into account the desired properties, without requiring tradeoffs for the purpose of a matching these elements.
The screening de
Baier Maximilian
Gassmann Hubert
Mickelat Thomas
Feiereisen Henry M.
Heinrich Fiedler GmbH & Co. KG
Ocampo Marianne
Walker W. L.
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