Screen device comprising screen rollers for preventing oversize grain from jamming

Abstract

A screen device for sorting screening material into one or more fine grain fractions and one or more oversize grain fractions. The screen device includes a frame and a roller screen including screen rollers which are arranged, such that they can be rotary-driven about a roller axis each, next to each other and which are supported on the frame and which each comprise a roller body and one or more screen structures which protrude radially relative to the roller body. There is a fine grain screen gap between the roller bodies of respectively adjacent screen rollers, through which a fine grain fraction falls, while an oversize grain fraction is conveyed on the roller screen in the axial direction of the rollers when the screen rollers are rotary-driven. The roller body of at least one of the screen rollers widens radially in the axial direction of the rollers in an axial widening portion and the width of the fine grain screen gap which the widening roller body forms with the roller body of an adjacent screen roller decreases in the axial direction of the rollers along the widening portion.

Claims

1. A screen device for sorting screening material into one or more fine grain fractions and one or more oversize grain fractions, the screen device comprising: a frame; and a roller screen comprising screen rollers which are arranged, such that they can be rotary-driven about a roller axis each, next to each other and which are supported on the frame and which each comprise a roller body and one or more screen structures which protrude radially relative to the roller body, wherein there is a fine grain screen gap between the roller bodies of respectively adjacent screen rollers, through which a fine grain fraction falls, while an oversize grain fraction is conveyed on the roller screen in the axial direction of the rollers when the screen rollers are rotary-driven, wherein the roller body of at least one of the screen rollers widens radially in the axial direction of the rollers in an axial widening portion, and the width of the fine grain screen gap which the widening roller body forms with the roller body of an adjacent screen roller decreases in the axial direction of the rollers along the widening portion, wherein the one or more screen structures of the respectively adjacent screen rollers interlock as viewed in a plan view onto the roller screen.

2. The screen device according to claim 1, wherein a virtual envelope which is placed against the outer circumference of the one or more screen structures of the at least one screen roller comprising the widening portion tapers in the axial direction of the rollers along the widening portion.

3. The screen device according to claim 1, wherein the widening portion of the screen roller further comprises one or more screen structures which protrude radially from the roller body.

4. The screen device according to claim 1, wherein the widening portion widens to a maximum width gradually in the axial direction of the rollers in a first sub-portion and, in a second sub-portion which adjoins the first sub-portion in the axial direction of the rollers, is at least substantially cylindrical and preferably exhibits the maximum width.

5. The screen device according to claim 1, wherein the widening portion widens in the axial direction of the rollers in a first sub-portion and, in a second sub-portion which adjoins the first sub-portion in the axial direction of the rollers, exhibits a maximum width and is at least substantially cylindrical, and wherein the one or more protruding screen structures extend(s) in the axial direction of the rollers up to the second sub-portion at most and preferably into the first sub-portion.

6. The screen device according to claim 1, wherein the widening portion of the roller body comprises a transverse and/or reverse conveying structure on its outer circumference in order to exert a conveying effect, transverse to the axial direction of the rollers and/or counter to the axial direction of the rollers, on oversize grain conveyed into the widening portion.

7. The screen device according to claim 6, wherein the transverse and/or reverse conveying structure is a toothed or ribbed structure comprising teeth or ribs which are axially linear or extend at an inclination with respect to the axial direction of the rollers.

8. The screen device according to claim 1, wherein the widening portion of the roller body widens in a continuously differentiable way over a length of at least several centimeters.

9. The screen device according to claim 1, wherein the widening portion of the roller body widens conically, in the shape of a trumpet or in the shape of a bell, over a length of at least several centimeters.

10. The screen device according to claim 1, wherein the one or more screen structures exhibit an inclination of more than 0° and less than 90° with respect to the axial direction of the rollers in a plan view onto the roller screen, in order to convey at least some of the oversize grain fraction in the axial direction of the rollers when the screen rollers are rotary-driven.

11. The screen device according to claim 1, wherein the roller body which comprises the widening portion can be axially moved.

12. The screen device according to claim 1, wherein an axially elastic element is arranged on at least one of the side-faces of the roller body which comprises the widening portion, and the roller body can be axially moved, counter to the restoring force of the elastic element.

13. The screen device according to claim 1, wherein the screen rollers are rotatably mounted on the frame at both axial ends.

14. The screen device according to claim 1, wherein a frame wall protrudes beyond an upper side of the roller screen at an end of the screen rollers which is a downward end in the axial direction of the rollers, and at least some of the roller bodies are attenuated at the ends facing the frame wall or terminate at an axial distance in front of the frame wall, such that the screen rollers each comprise a slender roller portion at the ends facing the frame wall, and the clear distance between respectively adjacent slender roller portions is at least twice as large as a maximum width of the fine grain screen gap between adjacent roller bodies, such that the slender roller portions form a peripheral strip which extends transverse to the axial direction of the rollers and adjoins the frame wall and in which oversize grain conveyed up to and into the peripheral strip can fall down between the screen rollers.

15. The screen device according to claim 1, wherein the roller body comprises an additional widening portion and widens in the additional widening portion, either likewise in the axial direction of the rollers or preferably counter to the axial direction of the rollers.

16. The screen device according to the preceding claim, wherein the widening portions collectively form a contiguous widening portion in which the roller body widens in the axial direction of the rollers and then tapers again.

17. The screen device according to claim 1, wherein the widening portion forms an axial conveying end of the at least one screen roller and preferably exhibits a maximum width at the conveying end.

18. The screen device according to claim 1, wherein the roller body comprises a roller body portion which is an upward roller body portion in relation to the axial direction of the rollers, a roller body portion which is a downward roller body portion in relation to the axial direction of the rollers, and the widening portion axially between the upward and downward roller body portions.

19. The screen device according to claim 18, wherein the one or more protruding screen structures of the at least one screen roller comprising the widening portion exhibit an inclination of more than 0° and less than 90° with respect to the axial direction of the rollers in a plan view onto the roller screen, and the inclination is positive in the upward roller body portion up to or up to and into the widening portion and negative in the downward roller body portion up to the widening portion at most, in order to convey at least a first portion of the oversize grain fraction in the axial direction of the rollers and at least a second portion of the oversize grain fraction counter to the axial direction of the rollers and to remove it transverse to the axial direction of the rollers in the region of the widening portion.

20. The screen device according to claim 1, wherein the roller screen comprises multiple screen rollers which widen radially.

21. The screen device according to claim 1, wherein at least every second screen roller in a plan view onto the roller screen respectively widens radially.

22. The screen device according to claim 1, wherein two or more screen rollers of the roller screen which are arranged immediately next to each other in a plan view respectively widen radially, and the widening portions of adjacent screen rollers are arranged next to each other and widen in the same direction, such that the width of the fine grain screen gap between the adjacent widening portions is reduced from both sides.

23. The screen device according to claim 20, wherein the widening portions of the screen rollers are arranged such that in a plan view onto the roller screen, they collectively form a linear strip of widening portions which is oblique or orthogonal with respect to the axial direction of the rollers.

24. The screen device according to claim 23, wherein the widening portions of the screen rollers are arranged next to each other and level in the axial direction of the rollers.

25. A screen device for sorting screening material into one or more fine grain fractions and one or more oversize grain fractions, the screen device comprising: a frame comprising a frame wall; and a roller screen comprising screen rollers which are arranged, such that they can be rotary-driven about a roller axis each, next to each other and which are supported on the frame and which each comprise a roller body and one or more screen structures which protrude radially relative to the roller body, such that there is a fine grain screen gap between the roller bodies of respectively adjacent screen rollers, through which a fine grain fraction falls, while at least one oversize grain fraction is conveyed on the roller screen in the axial direction of the rollers towards the frame wall when the screen rollers are rotary-driven, wherein the screen rollers are rotatably mounted on the frame at both axial ends, and the frame wall limits the roller screen at an end which is a downward end in relation to the axial direction of the rollers, and protrudes beyond an upper side of the roller screen, such that oversize grain cannot be conveyed over the frame wall in the axial direction of the rollers, and wherein at least some of the roller bodies are attenuated at the upward ends or terminate at an axial distance in front of the frame wall, such that the screen rollers each comprise a slender roller portion at the ends facing the frame wall, and the clear distance between respectively adjacent slender roller portions is at least twice as large as a maximum width of the fine grain screen gap between adjacent roller bodies, such that the slender roller portions form a peripheral strip which extends transverse to the axial direction of the rollers and adjoins the frame wall and in which oversize grain conveyed up to and into the peripheral strip can fall down between the screen rollers.

26. A screen roller for a screen device for sorting screening material into a fine grain fraction and an oversize grain fraction, the screen roller comprising: a roller body comprising an outer roller body circumference; a bearing journal for rotary-mounting the roller body about a roller axis; and one or more screen structures which is/are connected to the roller body, such that torque is transmitted, and protrude(s) radially from the roller body circumference and is/are formed by a winding structure which helically encircles the roller body circumference or by multiple screen discs which are axially spaced from each other, wherein the roller body circumference widens radially in the axial direction of the rollers in an axial widening portion, wherein a virtual envelope which is placed against the outer circumference of the one or more screen structures of the at least one screen roller comprising the widening portion tapers in the axial direction of the rollers along the widening portion.

27. A screen roller for a screen device for sorting screening material into a fine grain fraction and an oversize grain fraction, the screen roller comprising: a roller body comprising an outer roller body circumference; a bearing journal for rotary-mounting the roller body about a roller axis; and one or more screen structures which is/are connected to the roller body, such that torque is transmitted, and protrude(s) radially from the roller body circumference and is/are formed by a winding structure which helically encircles the roller body circumference or by multiple screen discs which are axially spaced from each other, wherein the roller body circumference widens radially in the axial direction of the rollers in an axial widening portion, wherein the widening portion of the roller body comprises a transverse and/or reverse conveying structure on its outer circumference in order to exert a conveying effect, transverse to the axial direction of the rollers and/or counter to the axial direction of the rollers, on oversize grain conveyed into the widening portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Example embodiments of the invention are described below on the basis of figures. The features disclosed by the example embodiments, each individually and in any combination of features, advantageously develop the embodiments of the invention described above and in particular the subject-matter of the claims and the subject-matter of the aspects, respectively. There is shown:

(2) In FIG. 1, a screen device comprising screen rollers in a first example embodiment, is shown in an isometric representation;

(3) In FIG. 2, screen rollers arranged next to each other, are shown in a plan view;

(4) In FIG. 3, the screen device of the first example embodiment, is shown in a plan view;

(5) In FIG. 4, the screen device of the first example embodiment, is shown in a section;

(6) In FIG. 5, a screen roller of a second example embodiment, comprising a widening portion at an axial conveying end, is shown;

(7) In FIG. 6, a widening portion comprising a transverse and reverse conveying structure is shown;

(8) In FIG. 7, a screen roller of a third example embodiment, comprising two widening portions as a middle roller portion, is shown;

(9) In FIG. 8, two widening portions, comprising a transverse conveying structure, for a middle roller portion, are shown; and

(10) In FIG. 9, multiple screen rollers of the third example embodiment, arranged next to each other, are shown in a plan view.

DETAILED DESCRIPTION OF THE INVENTION

(11) FIG. 1 shows a screen device comprising a roller screen 1 consisting of screen rollers 10, in a first example embodiment. In order to form the roller screen 1, the screen rollers 10 are arranged next to each other and mounted at both roller ends in a frame of the screen device, such that they can rotate about a rotational axis each. The screen rollers 10 are each rotatably mounted at one roller end on a frame wall 2 and at the other roller end on a frame wall 3 and thus supported on both sides. The frame walls 2 and 3 protrude beyond an upper side of the roller screen 1 and enclose the roller screen 1 at the two roller ends. Together with the roller screen 1, they form a channel for a screening material which is to be sorted into different fractions by means of the screen device. The screen device also comprises a drive means for rotary-driving the screen rollers 10 in the same direction. In FIG. 1, only couplings 4 of the drive means, for attaching drive motors, and a traction drive for coupling the screen rollers 10, for rotary-driving them collectively in the same direction of rotation, can be seen. The traction drive comprises multiple traction mechanisms—in the example embodiment, chains—and drive wheels 5—in the example, toothed wheels—which are non-rotationally connected to the screen rollers 10. The traction mechanisms each enclose only the drive wheels of two adjacent screen rollers 10. The drive wheels 5 are correspondingly formed as twin-drive wheels, such that the screen rollers 10 driven via the traction mechanisms are each driven via one of the twin-drive wheels and output onto the next screen roller 10 via the other of the twin-drive wheels.

(12) FIG. 2 shows a small detail of the roller screen 1, in a plan view onto its upper side. The screen rollers 10 each comprise a roller body 11 and a screen structure 12 which is formed as a winding structure and encircles an outer circumferential surface of the roller body 11. Accordingly, the screen structure 12 protrudes radially from the roller body 11 of the respective screen roller 10 in the form of a helical line. When the screen rollers 10 are rotary-driven, their screen structures 12 exert a screw action and accordingly a conveying effect in the axial direction of the rollers X.

(13) In the first example embodiment, the roller bodies 11 are each cylindrical over their entire length; they are preferably, but merely by way of example, circularly cylindrical over their entire length. A fine grain screen gap remains between the roller bodies 11 of respectively adjacent screen rollers 10 and exhibits a constant gap width w over the entire length of the roller bodies 11. The screen structures 12 of respectively adjacent screen rollers 10 extend axially offset with respect to each other in relation to the axial direction of the rollers X, such that the helical line of each respective screen roller 10 engages the flight of the screen structure of the respectively adjacent screen roller 10, i.e. the screen rollers 10 are embodied and arranged such that their screen structures 12 interlock. The rotational axis of one of the screen rollers 10 arranged in parallel is denoted by R in FIG. 2.

(14) During sorting operations, a screening material which is introduced onto the upper side of the roller screen 1 in an introducing region 7 is separated into several different grain fractions. A fine grain fraction falls downwards through the screen gaps, preferably onto a conveying means, such as for example a conveyor belt, arranged below the roller screen 1 in order to remove the fine grain fraction from the region of the roller screen 1. The maximum grain size of the fine grain fraction is determined by the gap width w and the axial distances between the interlocking screen structures 12. The oversize grain which does not fall through the screen gaps is conveyed on the roller screen 1 by the screen rollers 10 which are rotary-driven in the same direction. The screen structures 12 of the screen rollers 10 exert a conveying effect in the axial direction of the rollers X and also a conveying effect in the transverse direction Y tangential to the outer circumferential surface of the roller bodies 11 on the oversize grain, wherein the oversize grain is separated into a first oversize grain fraction and a second oversize grain fraction. The first oversize grain fraction substantially contains compact, comparatively heavy parts which due to their outer dimensions protrude into the depressions formed over the respective screen gap between adjacent roller bodies 11, to such a depth that the flanks of the screen structures 12 can act on this oversize grain to an extent which is sufficient to convey the oversize grain in the depressions, or distributed among multiple consecutive depressions, in the axial direction of the rollers X into the peripheral region formed with the frame wall 3. A second oversize grain fraction, which in particular contains larger, for example elongated, and/or lighter parts, is conveyed primarily in the circumferential direction of the screen rollers 10, i.e. in the transverse direction Y, to an output region 9 situated at the end of the roller screen 1 which is the downward end in the transverse direction Y. In simple embodiments which not least for this reason are preferred embodiments, the second oversize grain fraction falls downwards from the roller screen 1 in the output region 9, preferably onto a remover, such as for example a conveyor belt, arranged below the roller screen 1 in the output region 9.

(15) The roller screen 1 and the two frame walls 2 and 3 together form a conveying channel for the oversize grain. Problems can arise in particular in the peripheral region of the roller screen 1 near the frame wall 3, since the screen rollers 10 continually exert a conveying effect in the axial direction of the rollers X and therefore towards the frame wall 3 on the oversize grain. The first oversize grain fraction can accumulate in this peripheral region, which can jam screen rollers 10 and therefore interrupt sorting operations, or even damage the roller screen 1.

(16) To counter the risk of jamming, the screen rollers 10 are attenuated in roller end portions near the frame wall 3, such that a peripheral strip 8 is obtained along the frame wall 3, in which the gap width w between respectively adjacent screen rollers 10 is significantly larger than in the other regions of the roller screen 1. The peripheral strip 8 can advantageously extend, as shown in FIG. 1, over the entire length of the roller screen 1 as measured in the transverse direction Y. The breadth of the peripheral strip 8 as measured in the axial direction of the rollers X can vary over the length of the roller screen 1. Expediently, however, the peripheral strip 8 exhibits a constant breadth. The slender roller portions of the screen rollers 10, which extend over the breadth of the peripheral strip 8, do not comprise any protruding screen structure, such that the screen rollers 10 do not exert any conveying effect in the axial direction of the rollers X in the peripheral strip 8. The screen rollers 10 can in particular each exhibit a smooth, non-structured outer circumference over the lengths of their slender roller portions. Optionally, the attenuated roller portions of individual screen rollers 10 or of each of the screen rollers 10 can comprise transverse conveying structures on their outer circumference, in order to be able to exert a conveying effect in the transverse direction Y on oversize grain conveyed into the peripheral strip 8.

(17) FIG. 3 shows a part of the screen device, in a plan view onto the roller screen 1. A partial region of the peripheral strip 8, formed by slender roller end portions 14 of the screen rollers 10, can in particular be seen. The slender roller portions 14 are each smoothly cylindrical—in the example embodiment, circularly cylindrical—as is preferred but merely by way of example. The length l of the slender roller portions, as measured in the axial direction of the rollers X, corresponds to the breadth of the peripheral strip 8. A clear distance d remains between respectively adjacent roller portions 14. The distances d are larger than, and advantageously at least twice as large as, the width w of the screen gaps for the fine grain. The distances d are preferably at least three times and even more preferably at least five times as large as the gap width w. The lengths l of the slender roller portions 14 and therefore the breadth of the peripheral strip 8 are/is larger than, and advantageously at least twice as large as, the width w of the screen gaps for the fine grain and advantageously at least as large as the distance d. In simple embodiments which not least for this reason are preferred embodiments, the distances d and also the lengths l are constant over the entire peripheral strip 8. The distances d and/or the lengths l can however in principle vary. If the distances d are variable, the lengths l are preferably each at least as large as the largest of the distances d. In preferred embodiments, the distances d are as large as is possible in the design, i.e. in preferred embodiments, the slender roller portions 14 are slender and long enough that the resultant “mesh size” of the roller screen 1 in the peripheral strip 8 is large enough that all the parts of the oversize grain fraction which pass into the peripheral strip 8 and are not conveyed in the transverse direction Y by the rotational movement of the slender roller portions 14 in the region of the peripheral strip 8 can fall downwards between respectively adjacent roller portions 14.

(18) FIG. 4 shows the screen device in a section along the rotational axis R of one of the screen rollers 10. The screen rollers 10 each comprise a central shaft 13 which extends through the frame walls 2 and 3 and is rotatably mounted on each of the frame walls 2 and 3 and therefore supported on both sides. The roller bodies 11 of the screen rollers 10 are sleeve-shaped and non-rotationally connected to the shaft 13 of the respective screen roller 10 in a coaxial arrangement with respect to the shaft 13. The shaft 13 of each of the screen rollers 10 extends through the roller body 11 and protrudes beyond the roller body 11 at both ends of the roller body 11, whereby the shaft 13 forms a bearing journal at each of the two ends for the roller body 11 of the same screen roller 10. The winding screen structure 12 is non-rotationally connected to the corresponding roller body 11 and encircles the roller body 11 at its outer circumference as a helical line. The frame walls 2 and 3 enclose the roller screen 1 on the left and right in a seal, such that screening material cannot be conveyed axially past one of the two frame walls 2 and 3, in particular the frame wall 3.

(19) The screen rollers 10 each comprise the described slender roller portion 14 at the ends axially facing the frame wall 3. The continuous shaft 13 forms the slender roller portion 14 directly, as is preferred but merely by way of example, i.e. the roller portion 14 is a portion of the shaft 13. The screen rollers 10 are attenuated in one stage from the comparatively large cross-section of the respective roller body 11 to the comparatively slender roller portion 14, in that the roller bodies 11 each terminate at the distance 1 in front of the frame wall 3 and the shafts 13 each protrude by this distance 1 beyond the axial conveying end of the respective roller body 11 up to the facing frame wall 3 and, for the purpose of rotary-mounting, through the frame wall 3. The screen rollers 10 are mounted on the outside of the frame walls 2 and 3, as viewed from the respective roller body 11. In the example embodiment, they are mounted directly on the frame walls 2 and 3. In modifications, the shafts 13 or other types of bearing journals of the screen rollers 10 can simply merely protrude through the frame walls 2 and 3 and be rotary-mounted on the frame in another way.

(20) The falling direction of the fine grain fraction which falls through the roller screen 1 and, in the peripheral strip 8, the falling direction of the first oversize grain fraction which is conveyed up to and into the peripheral strip 8 is indicated in FIG. 4 by directional arrows −Z.

(21) A partition wall 6 can expediently be arranged beneath the roller screen 1, in order to keep the oversize grain falling down between the slender roller portions 14 in the peripheral strip 8 away from the fine grain separated out beforehand.

(22) FIG. 5 shows a screen roller 20 of a second example embodiment, in a radial view. The screen roller 20 comprises a roller body 21 and a screen structure 22 which protrudes radially from the outer circumference of the roller body 21 and is formed, as in the first example embodiment, as a winding structure which helically encircles the roller body 21, in order to convey the first oversize grain fraction in the axial direction of the rollers X. The winding flanks of the screen structure 22 are inclined at an angle α with respect to the rotational axis R, i.e. exhibit a pitch in accordance with the inclination angle α.

(23) As in the first example embodiment, the roller body 21 can be sleeve-shaped and non-rotationally connected to a shaft 23 which extends axially through the roller body 21. A twin-drive wheel 5 is non-rotationally connected to the screen roller 20 at a drive end of the screen roller 20, as in the first example embodiment.

(24) Unlike the first example embodiment, one end of the roller body 21 comprises an axial widening portion 25 in which the roller body 21 widens uniformly in the axial direction of the rollers X over its entire circumference. The widening is rotationally symmetrical and, as is preferred but merely by way of example, conical. The widening portion 25 forms an end portion of the roller body 21 which is a downward end portion in relation to the axial direction of the rollers X. The roller body 21 is cylindrical, as in the first example embodiment, from its upstream end to the widening portion 25.

(25) In a modified roller screen 1, one or more or preferably all of the screen rollers 10 fitted in the first example embodiment with cylindrical roller bodies 11 is/are each replaced with a screen roller 20. In the roller screen 1 modified in this way, the respective fine grain screen gap exhibits the constant gap width w from the upward end of the roller body 21 to the widening portion 25, wherein in the widening portion 25, the gap width w is reduced in the axial direction of the rollers X to a smaller gap width—gradually, continuously and monotonically in the example embodiment. Because the outer circumference of the roller body 21 increases in the widening portion 25 and the screen gap width is accordingly reduced, the screen roller 20 and the adjacent screen roller or the adjacent two screen rollers together form a flatter depression over the respective screen gap than in the cylindrical roller body portion, wherein the depression flattens out gradually in accordance with the profile of the widening. The parts of the first oversize grain fraction which engage the depression are raised in the region of the widening portion 25; the relevant oversize grain is buoyed upwards, so to speak. The conveying effect exerted by the screen structure 22 in the axial direction of the rollers X is reduced accordingly. Also, the conveying effect exerted on this oversize grain fraction in the circumferential direction Y of the roller body 21 increases. Each of these effects counters the risk of jamming in the peripheral region of the modified roller screen 1 near the frame wall 3 (FIG. 1).

(26) Although the two advantageous effects with regard to reducing the risk of jamming, namely the buoying effect and the stronger conveying effect in the transverse direction Y as viewed over the roller screen 1, are achieved even if not all the screen rollers 10 of the first example embodiment but rather only a sub-group of the screen rollers 10 are replaced with screen rollers 20, for example every second screen roller 10, and although a positive effect is in principle also achieved by replacing even just one screen roller 10, it is preferred if multiple screen rollers 20 are arranged immediately next to each other in the modified roller screen 1 or, even more preferably, if the modified roller screen 1 is formed exclusively or at least predominantly by screen rollers 20.

(27) The modified roller screen 1 which comprises one or more screen rollers 20 instead of (respectively) one of the screen rollers 10 can comprise the peripheral strip 8 of the first example embodiment, even in embodiments in which all or most of the screen rollers 10 are replaced with screen rollers 20, as is preferred. This enables jamming by oversize grain conveyed in the axial direction of the rollers X to be even more reliably countered, in particular in embodiments in which the modified roller screen 1 also still comprises one or more of the screen rollers 10. This is not however required, since the second oversize grain fraction is buoyed upwards in the region of the widening 25, and the conveying effect in the axial direction of the rollers X decreases and the conveying effect in the transverse direction Y increases in the widening portion 25. The roller body 21 can accordingly extend immediately up to the frame wall 3. In the modified roller screen 1, a peripheral strip consisting of widening portions 25 arranged next to each other can replace the peripheral strip 8 of the first example embodiment which, aside from slender roller portions 14 (FIGS. 3 and 4), is vacant.

(28) The roller body 21 can widen in the widening portion 25 from a minimum radial width, preferably a minimum circular diameter, to a maximum radial width, preferably a maximum circular diameter, and terminate immediately upon reaching the maximum width. More preferably, however, the widening portion 25 comprises a first sub-portion 26 and a second sub-portion 27 immediately adjoining it in the axial direction of the rollers X, such as can be seen in FIG. 5. In the example embodiment, the two sub-portions 26 and 27 alone form the entire widening portion 25. The widening from the minimum radial width to the maximum radial width of the widening portion 25 and of the roller body 21 as a whole occurs in the sub-portion 26. The sub-portion 27 is cylindrical and preferably circularly cylindrical. The sub-portion 26 exhibits an axial length a, and the sub-portion 27 exhibits an axial length b. If the widening portion 25 is composed of the two sub-portions 26 and 27, the overall length of the widening portion 25 therefore corresponds to the sum of the lengths a and b. The sub-portion 26 is preferably longer than the sub-portion 27 in order to distribute the widening over a correspondingly large length a and avoid an abrupt transition. The length a is preferably at least 1.5 times, even more preferably at least two times larger than the length b. Since the cylindrical or at least substantially cylindrical sub-portion 27 serves the purpose of exerting a conveying effect in the transverse direction Y on the oversize grain fraction conveyed up to and into the sub-portion 27, namely due to circumferential contact, the sub-portion 27 should however on the other hand exhibit a length b which is sufficient for this purpose. It is advantageous if the length b accounts for at least a tenth of the length of the widening portion 25 or an eighth of the length a. The length b is preferably at least an eighth of the length of the widening portion 25 and/or at least a sixth of the length a.

(29) In order to reduce the conveying effect in the axial direction of the rollers X in the region of the widening portion 25, the screen structure 22 can terminate in front of or at the widening portion 25. More preferably, however, the screen structure 22 extends into the widening portion 25—in the second example embodiment, into the sub-portion 26—and terminates a short distance in front of the downward end of the widening portion 25. The screen structure 22 preferably extends only up to the sub-portion 27 at most, which is advantageously free of any structures which convey in the axial direction of the rollers.

(30) The screen structure 22 can flatten out in the widening portion 25. An imaginary virtual envelope H placed against the outer circumference of the screen structure 22 is shown by a broken line in FIG. 5. The envelope H, which can in particular be cylindrical over the entire axial length of the roller body 21 up to the vicinity of the widening portion 25 or preferably up to the widening portion 25, tapers in the widening portion 25 due to the screen structure 22 flattening out, preferably uniformly over the entire circumference of the roller body 21.

(31) FIG. 6 shows a modified widening portion 25 which can replace the widening portion 25 shown in FIG. 5. The modified widening portion 25 comprises a transverse conveying structure 28 on the outer circumference of its sub-portion 27 which forms the end of the roller body 21, in order to further intensify the conveying effect in the transverse direction Y. The transverse conveying structure 28 can be formed as surface structuring, for example knurling or fluting, or a circumferentially extending outer denticulation or ribbing, which is flat as compared to the screen structure 22, i.e. radially short of the screen structure 22 of at least the cylindrical roller body portion. The outer denticulation or ribbing can be formed as a linear denticulation or ribbing comprising axial ribs or, in developments such as is shown in FIG. 6, as an oblique denticulation or with teeth or ribs which extend at some other inclination in relation to the rotational axis R and/or axial direction of the rollers X. If the teeth or ribs extend at an inclination with respect to the axial direction of the rollers X, the screen roller 20 also exerts a conveying effect counter to the axial direction of the rollers X in the sub-portion 27 and thus more reliably keeps the oversize grain away from the frame wall 3 or reduces a pressure which may be exerted by the oversize grain on the frame wall 3 in the axial direction of the rollers X.

(32) Wherever differences between the screen roller 20 and the screen roller 10 of the first example embodiment are not described or are not apparent from FIGS. 5 and 6, the screen roller 20 of the second example embodiment can correspond to the screen roller 10 of the first example embodiment, such that reference is additionally made to the statements regarding the first example embodiment.

(33) FIG. 7 shows a screen roller 30 of a third example embodiment, in a radial view. The screen roller 30 comprises a roller body 31 which comprises, in succession in the axial direction of the rollers X, an upward roller body portion 31a, a widening portion 35, an additional widening portion 35′ and a downward roller body portion 31b. The widening portion 35 directly adjoins the roller body portion 31a, the additional widening portion 35′ directly adjoins the widening portion 35, and the roller body portion 31b directly adjoins the additional widening portion 35′. The roller body portions 31a and 31b are axially outer roller body portions and form the two ends of the roller body 31. The roller body portions 31a and 31b can in particular each exhibit a cylindrical outer circumference over their entire length. A shaft 33 extends through the roller body 31 and serves as a bearing journal for mounting the screen roller 30 on both sides, as in the other example embodiments. The shaft 33 protrudes beyond the roller body 31 on both sides, in order to form a rotary bearing point with the frame, for example the frame walls 2 and 3, on each of the two sides of the screen roller 30, as in the other example embodiments. The roller body 31 can however in principle also comprise other types of roller journals for rotary-mounting.

(34) The screen structure 32, which in the third example embodiment is also a winding structure, comprises a first screen structure portion 32a which extends in a winding shape in the first roller body portion 31a, over its entire axial length as is preferred, and a second screen structure portion 32b which extends in a winding shape in the second roller body portion 31b, preferably over its entire axial length. An inclination angle α and therefore a pitch of the helical or winding screen structure 32 is selected such that the upward screen structure portion 32a exerts a conveying effect in the axial direction of the rollers X on the oversize grain. The helical line of the downward screen structure portion 32b extends in the opposite direction to that of the screen structure portion 32a. The inclination angle α and/or the pitch of the screen structure portion 32b can be as large, in terms of magnitude, as the inclination angle α of the screen structure portion 32a, but exhibit a negative polarity accordingly. The inclination angles of the two portions 32a and 32b can however in principle also differ in terms of their magnitude as well as their polarity. Because the screen structure portions 32a and 32b extend in opposite directions, the screen roller 30 exerts a conveying effect in the axial direction of the rollers X on the oversize grain in the roller body portion 31a and a conveying effect counter to the axial direction of the rollers X, i.e. in the −X direction, on oversize grain situated in the roller body portion 31b, when it is rotary-driven.

(35) The widening portions 35 and 35′ form a contiguous widening portion 35, 35′ axially between the roller body portions 31a and 31b. In the widening portion 35, the roller body 31 widens in the axial direction of the rollers X from the radial width of the roller body portion 31a to a maximum radial width. In the additional widening portion 35′, the roller body 31 widens counter to the axial direction of the rollers X from the radial width of the roller body portion 31b, again to a maximum radial width. The maximum radial width of the widening portion 35 and the maximum radial width of the additional widening portion 35′ are identical, as is preferred, but can in principle also be different.

(36) The cylindrical roller body portions 31a and 31b exhibit the same radial width; in principle, however, the radial widths of the roller body portions 31a and 31b can differ from each other. In the example embodiment, the roller body portions 31a and 31b exhibit the same length and/or the widening portions 35 and 35′ exhibit the same length. The roller body portions 31a and 31b can however in principle differ from each other in terms of their length, and/or the widening portions 35 and 35′ can differ from each other in terms of their length. In the third example embodiment, the uniform screen roller body 31 is however symmetrical in relation to a plane of symmetry which extends perpendicular to the rotary axis R between the widening portions 35 and 35′. Because the screen structures 32a and 32b extend in opposite directions, the screen structure 32 composed of the two screen structures 32a and 32b is likewise symmetrical with respect to the same plane of symmetry.

(37) The widening portion 35 itself corresponds to the widening portion 25 of the second example embodiment. Aside from the fact that it widens counter to the axial direction of the rollers X, the additional widening portion 35′ likewise corresponds to the widening portion 25 of the second example embodiment. Both widening portions 35 and 35′ comprise a cylindrical portion in their end regions which face each other axially and in which they directly abut against each other. As in the second example embodiment, the widening portion 35 comprises a first sub-portion 36a which widens and, adjoining it, the cylindrical sub-portion 37. This also applies, mirror-inverted, to the additional widening portion 35′ which widens in a first sub-portion 36b from the width of the roller body portion 31b to the maximum radial width and cylindrically extends, at the maximum radial width, in the second sub-portion 37 which it shares with the widening portion 35.

(38) An imaginary virtual envelope H placed against the protruding screen structure 32 is again indicated for the screen roller 30. The envelope H is cylindrical in the roller body portion 31a, narrows in the region of the widening portion 35 to the sub-portion 37, then widens mirror-symmetrically in the additional widening portion 35′ to the width of the screen structure portion 32b and is again cylindrical over the length of the roller body portion 31b.

(39) In order to relieve the protruding screen structure 32 in the event of jamming in the axial direction of the rollers X, the screen structure 32 can be arranged such that it can be axially moved to a minor extent. As is preferred, but merely by way of example, the axial mobility of the screen structure 32 is achieved by arranging the roller body 31 such that it can be axially moved. The roller body 31 is mounted on the shaft 33 such that it axially floats. The axially floating arrangement is realized by means of elastic elements 15, one of which is arranged on the left-hand end-face of the roller body 31 and one of which is arranged on the right-hand end-face of the roller body 31. The elastic elements 15 can in particular be elastomer elements or natural rubber elements. They are expediently annular in accordance with the sleeve shape of the roller body 31. Due to their elasticity, they enable the roller body 31 and the screen structure 32 which is immovably connected to it to yield elastically in and counter to the axial direction of the rollers X in the millimeter range, for example by 1 to 3 mm at most. The elastic elements 15 constantly force the deflected roller body 31 back towards an axial position corresponding to the relieved state by means of an elastic restoring force.

(40) The roller screen 1 of the first example embodiment can be modified by replacing one or more or preferably all of the screen rollers 10 with (respectively) a screen roller 30. The statements made regarding the second example embodiment apply in this respect. During sorting operations using the modified roller screen 1, oversize grain is conveyed in the axial direction of the rollers X to the widening portion 35 in the region of each screen roller 30 in the roller body portion 31a, and oversize grain is conveyed counter to the axial direction of the rollers, in the direction −X, to the additional widening portion 35′ in the region of each screen roller 30 in the roller body portion 31b. In the contiguous widening portion 35, 35′, the oversize grain experiences an intensified conveying effect in the transverse direction Y. The risk of jamming in a peripheral region near a frame wall, such as for example the frame wall 3, is countered in a particularly effective way.

(41) Another advantage of the screen rollers 20 and 30 and in particular the screen roller 30 is that a peripheral strip 8 (FIGS. 1, 3 and 4), which cannot be used for sorting purposes, can be omitted. A screen device comprising screen rollers 20 and/or screen rollers 30 can be shorter in the axial direction of the rollers X while still retaining the same screening quality. Alternatively, the separating precision of the roller screen 1 can be improved while still retaining the same breadth of the screen device, and/or the throughput can be increased, since the effective surface of the roller screen 1 can be increased while still retaining the same overall length in the transverse direction Y. Also, oversize grain does not have to be transported away below the roller screen.

(42) FIG. 8 shows just the contiguous widening portion 35, 35′ of the screen roller 30. The axial lengths a of the sub-portions 36a and 36b are identical, but can in principle also differ from each other. The sub-portion 37 connects the sub-portions 36a and 36b and exhibits the length b. It is circularly cylindrical, as is preferred but merely by way of example. The roller body 31 can be smooth over its entire exterior in the widening portion 35, 35′. It can also comprise a transverse conveying structure in the widening portion 35, 35′. If provided, the transverse conveying structure can in particular be provided in the sub-portion 37 and preferably only in the sub-portion 37. The roller body 31 can thus comprise a transverse conveying structure 38 in the form of surface structuring, such as for example knurling or fluting, or a more prominently shaped outer denticulation or ribbing on an outer circumferential surface in the widening portion 35, 35′, such as can be seen in FIG. 8, in order to intensify the transverse conveying effect. A transverse and reverse conveying structure can also be formed in the sub-portion 37. With regard to an optional transverse and/or reverse conveying structure and the widening portions 35 and 35′, reference is made to the statements regarding the second example embodiment, i.e. the screen roller 20. Wherever differences between the screen roller 30 and the screen rollers 10 of the first example embodiment and/or the screen roller 20 of the second example embodiment are not described or are not apparent from FIGS. 7 and 8, the screen roller 30 of the third example embodiment can be embodied in the same way as one of the screen rollers 10 of the first example embodiment and/or the screen roller 20 of the second example embodiment, such that reference is made to the respective embodiments.

(43) FIG. 9 shows a plan view of a detail of a modified roller screen which is formed from screen rollers 30 of the third example embodiment or at least comprises a screen region comprising multiple screen rollers 30 arranged next to each other. As already described, the screen rollers 30 each comprise the contiguous widening portion 35, 35′ in an axially middle roller portion, such that oversize grain is conveyed in the direction X and −X from a right-hand outer roller screen strip and a left-hand outer roller screen strip to the respectively assigned widening portion 35 and 35′. Because the respective screen roller 30 widens on both sides in the contiguous widening portion 35, 35′, the gap width w of the fine grain screen gaps respectively formed between adjacent screen rollers 30 is reduced in the contiguous widening portion 35, 35′. The relevant oversize grain is buoyed upwards in the contiguous widening portion 35, 35′ and experiences an increasing conveying effect in the transverse conveying direction Y as it is buoyed upwards. For the sake of completeness, it may be remarked that in many applications, batches of screening material comprise an oversize grain fraction which by its very nature is also conveyed substantially to the left and right of the contiguous widening portion 35, 35′, substantially in the transverse conveying direction Y only, i.e. is not conveyed to any practically relevant extent in or counter to the axial direction of the rollers X. This oversize grain fraction is substantially conveyed only in the roller screen strips to the left and right of the contiguous widening portion 35, 35′, in the circumferential direction and/or transverse conveying direction Y, while the oversize grain fraction which is substantially conveyed axially is conveyed in the transverse direction Y in the middle roller screen strip by the widening portions 35 and 35′ which are consecutive, preferably immediately consecutive, in the transverse direction Y.

REFERENCE SIGNS

(44) 1 roller screen 2 frame wall 3 frame wall 4 coupling 5 drive wheel 6 partition wall 7 introducing region 8 peripheral strip 9 output region 10 screen roller 11 roller body 12 protruding screen structure 13 shaft 14 slender roller portion 15 elastic element 16 - 17 - 18 - 19— 20 screen roller 21 roller body 22 protruding screen structure 23 shaft 24 - 25 widening portion 26 sub-portion 27 sub-portion 28 transverse conveying structure, transverse and reverse conveying structure 29 - 30 screen roller 31 roller body 31a roller body portion 31b roller body portion 32 protruding screen structure 32a screen structure portion 32b screen structure portion 33 shaft 34 - 35 widening portion 35′ widening portion 36a sub-portion 36b sub-portion 37 sub-portion 38 transverse and/or reverse conveying structure R rotational axis X axial direction of the rollers Y transverse direction Z vertical direction a length of first sub-portion b length of second sub-portion d distance l breadth of the peripheral strip w gap width α inclination angle