METHOD FOR PRODUCING A ROTATIONALLY SYMMETRICAL, IN PARTICULAR CYLINDRICAL SCREENING DEVICE

Abstract

Method for producing a rotationally symmetrical screening device with a plurality of profile bars and screen basket for a pressurizable screen. The method includes producing bent bar holders having a radius of curvature of smaller than a radius of curvature of a finished screening device and having cut-outs open at an edge of an exterior circumference of the bent bar holders. The method also includes inserting profile bars parallel to one another into the cut-outs, and forming rings from the bar holders with inserted profile bars by enlarging the radius of curvature of the bar holders, thereby narrowing the cut-outs and clamping the profile bars. The forming of rings includes transferring bending forces to at least two locations on sides of the bar holders not provided with the cut-outs. The method also includes fixedly connecting respective ends of the bar holders to one another.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 10 2006 008 172.2, filed on Feb. 22, 2006, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for producing a rotationally symmetrical, in particular, cylindrical screening device with a plurality of profile bars.

2. Discussion of Background Information

A known example for the use of screening devices that can be produced according to the method of this type is the screening of fibrous suspensions, as carried out in pressurized screens of the paper-producing industry. The fibers contained in the suspension are thereby to pass through the screen, whereas the undesirable solid components are rejected at the gap and guided out of the screening device again. Since the openings have an essentially oblong shape, i.e., are slots or gaps, fibrous particles are let through more easily than the cubic ones, even if both types should be present in a similar magnitude. A very good elimination effect of non-fibrous contaminants from fibrous suspensions is thus rendered possible with a screening technology of this type. A use for separating different fiber components, the so-called fiber fractionation, is also conceivable. A high precision of the slot shape over the entire screen surface is, however, a prerequisite. With high demands, cylindrical screening devices, so-called screen baskets, are generally used.

DE 39 27 748 A1 shows a possible method for producing screen baskets of this type, in which method the profile bars are clamped by plastic deformation of the support rings provided with recesses for the bars. Profile bars particularly suitable for production methods of this type are used for this. By this method it was possible to make production considerably cheaper. The method is used with screen baskets where the bars are inserted on the interior edge of the support rings. A bar arrangement of this type is chosen if the suspension is to pass through the slots from the inside outward (centrifugal mode of operation). For the centripetal mode of operation, i.e., with a suspension flow from the outside inward, e.g., screening devices according to DE 44 35 538 A1 can be used.

Screening devices produced by the use of the method according to the invention are preferably used in pressurized screens of the paper-producing industry. It is thereby important that the dimensions of the screen openings are maintained with very low tolerances. In order to keep them unclogged, scrapers are generally necessary, which are moved past the screen surface at a narrow distance and which generate hydraulic impulses. Screening devices for use in pressurized screens must therefore be manufactured very precisely and must withstand high stresses.

SUMMARY OF THE INVENTION

The invention provides a method with which screening devices can be produced in an even more favorable economical manner. It is also to be usable for different sizes of screening devices without any great expenditure. The screening devices produced are to be of high precision and strength, so that they can be used in pressurized screens.

According to the invention, bent bar holders are produced having a radius of curvature smaller than that of the finished screening device and cut-outs open at the edge of the exterior circumference. The shape of the cut-outs essentially corresponds in a complementary manner to the bar bases of the profile bars. The profile bars are inserted parallel to one another into the cut-outs open at the edge of the bar holders that have a radius of curvature smaller than that of the finished screening device. Rings are produced from the bar holders provided with the profile bars, such that the radius of curvature of the bar holders is enlarged by forming while the cut-outs narrow and clamp the profile bars. The bending forces required for the forming are transferred at at least two locations on the sides of the bar holders not provided with cut-outs, and the bar holders are fixedly connected to one another at their two abutting ends after forming.

By the invention, it is rendered possible to carry out in particular the process of forming in a precise and relatively simple manner. The bending forces required for forming are applied to parts lying radially inside on the circumference of the bar holders. In this stage of the production process, i.e., before the final forming into a closed cylinder is to be carried out, the as yet unfinished screening device is composed of a bent part, the radius of curvature of which is smaller than the radius of curvature of the finished screening device. The bar holders are thus still open at their butt joints lying outside, which makes it easy to insert or slide in the profile bars. The butt joints mentioned are brought into contact by the final forming process, or at least brought close enough for a fixing to be possible, e.g., by welding. The shape of the formed component is determined by the bending forces and/or bending moments introduced on the circumference. The counterforce customarily hitherto applied with the aid of a mating shape, e.g., a so-called bending mandrel, acting on the component can be omitted. As is known, a mating shape of this type has a surface that is complementary to the desired shape of the component to be bent. Overall, the bending machine, which is a large, expensive apparatus, is simplified considerably. Furthermore, the bending machine can easily be reset to screening devices of different diameters, since as a rule only the control program needs to be changed.

The present invention is directed to a method for producing a rotationally symmetrical screening device with a plurality of profile bars. The method includes producing bent bar holders having a radius of curvature of smaller than a radius of curvature of a finished screening device and having cut-outs open at an edge of an exterior circumference of the bent bar holders. The method also includes inserting profile bars parallel to one another into the cut-outs, and forming rings from the bar holders with inserted profile bars by enlarging the radius of curvature of the bar holders, thereby narrowing the cut-outs and clamping the profile bars. The forming of rings includes transferring bending forces to at least two locations on sides of the bar holders not provided with the cut-outs. The method also includes fixedly connecting respective ends of the bar holders to one another.

According to a feature of the invention, the rotationally symmetrical screening device can be cylindrical.

In accordance with another feature, the profile bars may include base portions, and the cut-outs may be shaped to essentially correspond in a complementary manner to the base portions of the profile bars.

Further, a location for introducing the bending forces can essentially extend over an axial extension of the screening device. The location may be fixed on the bar holders during the forming.

According to still another feature of the invention, the bending forces may act both radially outwardly and in the circumferential direction.

In accordance with a further feature of the present invention, during the forming, no forces influencing the forming are transferred to the exterior circumference of the bar holder being formed.

According to another feature, no mating shape is used during the forming.

The method can further include applying the bending forces during the connecting of the respective ends of the bar holders. Further, complete rings can be formed by the connecting of the respective ends of the bar holders.

The method may also include clamping the bar holders during the forming in bending devices applying the bending forces.

According to still another feature, the bending forces can be introduced at a maximum of four locations, and four bending devices can be used to introduce the bending forces at the maximum of four locations. Further, respectively two bending devices may form a bending group which, in interaction, transfers a bending moment to the bar holders.

In accordance with another feature of the invention, the bending forces can be introduced at six locations, and four bending devices and two backing rolls may be arranged to introduce the bending forces at the six locations. Moreover, respectively two bending devices and one backing roll can form a bending group which, in interaction, transfers a bending moment to the bar holders.

According to another feature of the instant invention, the respective ends of the bar holders can be fixedly connected to one another by welding.

Further, the forming and the fixedly connecting of the bar holders may be carried out with a same machine.

According to still another feature, the bar holders can be assembled from segments before the forming.

In accordance with still yet another feature of the present invention, a screen basket for a pressurized screen usable in the paper-producing industry, is produced by the above-noted method.

Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIGS. 1a and 1b illustrate a principle of forming in accordance with the method of the invention;

FIG. 2 diagrammatically illustrates the forming;

FIG. 3 illustrates a perspective view of a finished screen basket;

FIG. 4 illustrates a part of a slotted screen produced according to the invention;

FIG. 5 diagrammatically illustrates a bending machine carrying out a step of the method according to the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

FIGS. 1a and 1b show the principle of deformation in two sketches. FIG. 1a indicates a bar holder 1 in a state in which the radius of curvature of this bar holder 1 is smaller than the radius of curvature of the finished screen basket. Further, as ends 6 and 7 of bar holder 1 are arranged to overlap, thereby forming a circumference of bar holder 1, i.e., from end 6 to end 7, larger than 360° by an angle α. In this state, cut-outs 4 (see FIG. 4) lying outside are open far enough for profile bars 2 to be inserted or slid in. This described shape of bar holders 1 can be produced, e.g., by plastic deformation, either on a one-piece bar holder or on segments, if it is a screening device assembled from segments. As noted above, the joined, preferably welded, segments can then have a total circumference larger than 360° before forming, i.e., by an overlap angle α.

After profile bars 2 have been inserted or slid in, bar holders 1 are formed, i.e., expanded far enough for ends 6 and 7 to abut or come into contact with each other. Thus, cut-outs 4 become narrower and clamp profile bars 2. To achieve this forming of bar holder 1, bending forces are transferred to bar holder 1 at locations 8 and 9. Forces directed radially inward, forces in the circumferential direction or bending moments can be applied individually or in combination as bending forces—as indicated here by the vectors illustrated in FIG. 1b. Moreover, bending devices used in the technical implementation of the instant method are to be moved during the forming such that ends 6 and 7 come closer to each other or abut or come into contact with each other, as illustrated in FIG. 1b. After this forming is finished and the bending forces are removed, the screening device has a cylindrical shape, the projection of which is the circle 5.

As shown in somewhat more detail in FIG. 2, bar holder 1 can be composed of several (e.g., three) segments 21, 22, and 23, which have already been connected to one another, e.g., welded, in a process step carried out previously. Some of profile bars 2 are also shown drawn in this representation, which have been inserted on the exterior circumference of bar holder 1. With respect to this representation, it is to be noted that a screening device must be provided with at least two bar holders 1 (usually more) and that only a single bar holder is visible here on account of the representation in top view. In order to be able to transfer forces as well as, if required, bending moments to bar holders 1 in a technical embodiment of the method according to the invention, four bending devices 10, 11, 12, and 13 are used in the exemplary embodiment of FIG. 2, i.e., the bending forces are transferred to bar holders 1 at four locations. Bending devices 10, 11, 12, and 13 can advantageously be equipped such that a projecting part of bar holder 1 is clamped during the bending process. Respectively, two bending devices, e.g., 10 and 11, or 12 and 13, can thereby interact such that they jointly produce a bending moment. As already mentioned, it is advantageous to move the bending devices during forming such that bar holders 1 come together at their ends 6 and 7 to form a butt joint. In other cases, they can rotate slowly and thus bring the ends 6 and 7 together in a butt joint. It is advantageous to design the ends 6 and 7 such that the required dimensioning of the screening device is ensured in particular when the two ends come into contact at a butt joint. A very precise manufacturing is thus possible.

It can be expedient to provide one or more nip rolls 14 on the exterior contour, which rolls support the clamping of bar holders 1 in the bending devices and/or form a counter hold for bending devices 12 and/or 13. They are usually not designed to apply bending forces for forming bar holders 1.

The subsequent process step, in which a fixed connection of the ends 6 and 7 forming a butt joint is produced, e.g., by welding, is not shown in this representation. Advantageously, the bending forces are only withdrawn after the connection has been made at the butt joints.

A finished screen basket produced according to the invention is shown diagrammatically and in perspective in FIG. 3. As shown in this exemplary embodiment, four bar holders 1 can be used in this case, in which profile bars 2 (of which only a few are illustrated) can be clamped on the exterior circumference of the bar holders 1. Profile bars 2 are thereby aligned in an axially parallel manner.

As shown in FIG. 4, profile bars 2 can be inserted into cut-outs 4 of bar holders 1 with their bar bases 3. They can be arranged such that a slot-shaped screen opening 20 is respectively located between them. In practice, slots of this type have a width between 0.08 and 2 mm. EP 0 499 154 shows examples of screen baskets that can be produced according to this method. But it is also possible to produce drilled screen baskets with the aid of the method according to the invention. A similar screening device is described, e.g., in DE 196 35 189. With respect to FIGS. 4 and 5 it is to be noted as well that the curvature of the bar holders 1 is not visible in these partial representations.

In a roughly diagrammatic manner, FIG. 5 shows a bending machine 17 suitable for carrying out the method. A view that looks outward from the center of a screen cylinder to be manufactured at its interior surface has thereby been chosen here. The operating principle and the situation in the course of production corresponds approximately to what is represented in FIG. 2. The bending machine 17 according to FIG. 5 illustrates four bending devices 10, 11, 12, and 13, which can also be referred to as bending towers with a perpendicular arrangement of the machine. They can be constructed such that it is possible to intermittently clamp the projections of bar holders 1. Bending machine 17 has a frame 18 with support elements (merely roughly indicated) for the components to be bent. Advantageously, the bending devices 10, 11, 12, and 13 are laterally moveable in this frame, so that the method according to the invention can be carried out in the manner already described. Expediently, the bending devices 10, 11, 12, and 13 have a height that renders it possible to introduce the bending forces over the entire axial extension A of the finished screening device.

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

1. A method for producing a rotationally symmetrical screening device with a plurality of profile bars, comprising:

producing bent bar holders having a radius of curvature of smaller than a radius of curvature of a finished screening device and having cut-outs open at an exterior circumference edge of the bent bar holders;

inserting profile bars parallel to one another into the cut-outs;

forming rings from the bar holders with inserted profile bars by enlarging the radius of curvature of the bar holders, thereby narrowing the cut-outs and clamping the profile bars, wherein the forming of rings includes transferring bending forces to at least two locations on sides of the bar holders not provided with the cut-outs; and

fixedly connecting respective ends of the bar holders to one another.

2. The method in accordance with claim 1, wherein the rotationally symmetrical screening device is cylindrical.

3. The method in accordance with claim 1, wherein the profile bars include base portions, and the cut-outs are shaped to essentially correspond in a complementary manner to the base portions of the profile bars.

4. The method in accordance with claim 1, wherein a location for introducing the bending forces essentially extends over an axial extension of the screening device.

5. The method in accordance with claim 4, wherein the location is fixed on the bar holders during the forming.

6. The method in accordance with claim 1, wherein the bending forces act both radially outwardly and in the circumferential direction.

7. The method in accordance with claim 1, wherein, during the forming, no forces influencing the forming are transferred to the exterior circumference of the bar holder being formed.

8. The method in accordance with claim 1, wherein no mating shape is used during the forming.

9. The method in accordance with claim 1, further comprising applying the bending forces during the connecting of the respective ends of the bar holders.

10. The method in accordance with claim 9, wherein complete rings are formed by the connecting of the respective ends of the bar holders.

11. The method in accordance with claim 1, further comprising clamping the bar holders during the forming in bending devices applying the bending forces.

12. The method in accordance with claim 1, wherein the bending forces are introduced at a maximum of four locations.

13. The method in accordance with claim 12, wherein four bending devices are used to introduce the bending forces at the maximum of four locations.

14. The method in accordance with claim 12, wherein respectively two bending devices form a bending group which, in interaction, transfers a bending moment to the bar holders.

15. The method in accordance with claim 1, wherein the bending forces are introduced at six locations.

16. The method in accordance with claim 15, wherein four bending devices and two backing rolls are arranged to introduce the bending forces at the six locations.

17. The method in accordance with claim 15, wherein respectively two bending devices and one backing roll form a bending group which, in interaction, transfers a bending moment to the bar holders.

18. The method in accordance with claim 1, wherein the respective ends of the bar holders are fixedly connected to one another by welding.

19. The method in accordance with claim 1, wherein the forming and the fixedly connecting of the bar holders are carried out with a same machine.

20. The method in accordance with claim 1, wherein the bar holders are assembled from segments before the forming.

21. A screen basket for a pressurized screen usable in the paper-producing industry, produced by the method of claim 1.