Dosing conveyor for conveying and dosing a solid mixture

Description

[0001] The invention relates to a dosing conveyor for solid mixtures, i.e., a device for conveying and dosing a solid mixture, such as municipal waste and natural rock. The solid mixture contains solids of different sizes and weights, optionally also of different types. The solid mixture can be a pure dry mixture, but can also contain significant amounts of water or other liquids.

[0002] When conveying mixtures of solids of different shapes, sizes, and weights, blockages can easily occur, limiting the amount of solid mixture that can be conveyed per unit of time. However, for the efficient operation of solid mixture treatment facilities, it is essential that the mixture is fed to the facility in question as evenly as possible at an appropriate flow rate.

[0003] In the treatment of municipal waste, excavated soil, natural rock, and much more, the respective solid mixture is fed into a receiving device, for example, by an excavator, and from there to a downstream treatment facility. For example, EP 2 914 386 B discloses a device with a roller screen, to which the solid mixture to be treated is fed via a conveyor belt. Conveyor belts convey the solid mixture to the downstream treatment device in approximately the same way as it was fed to the conveyor belt. To achieve more uniform conveyance, the respective conveying device can be set to vibrate, but this requires additional drive and bearing costs.

[0004] DE 39 26 451 C1 discloses a roller grate for screening and classifying bulk materials. The roller grate comprises several grate rollers with grate discs mounted in a grate frame and driven in the same direction. The grate rollers are spaced apart such that the grate discs of adjacent grate rollers form classification openings through which smaller bulk materials can fall. These smaller bulk materials fall onto an inclined grate underpass beneath the roller grate and slide over the grate underpass to a grate discharge.

[0005] US 731 073 A discloses a dosing conveyor according to the preamble of claim 1.

[0006] It is an object of the invention to convey solid mixtures and discharge them in metered quantities and to provide a conveying and metering device suitable for this purpose, a "metering conveyor".

[0007] Another or further task is to discharge a solid mixture that is fed into the device in uneven quantities over time at a more uniform conveying rate.

[0008] These objects are achieved by a dosing conveyor according to claim 1.

[0009] According to the invention, a roller screen and a collecting tray extending beneath the roller screen serve in combination as a dosing conveyor for conveying and simultaneously dosing a solid mixture that can be fed into the roller screen. As mentioned above, the solid mixture can be, for example, municipal waste, excavated soil, natural rock such as rubble, but also, in principle, crops.

[0010] The roller screen comprises several screw rollers arranged side by side. When the screw rollers are rotated, an oversize fraction of larger solid particles is conveyed from the solid mixture fed onto the top of the roller screen in a conveying direction parallel to the rollers' longitudinal axes into a screen discharge area, while an undersize fraction of smaller solid particles falls downwards through the screen gap between adjacent screw rollers and the intermeshing, spirally rotating coils of the screw rollers. The collecting tray extends directly beneath the roller screen in the roller longitudinal direction and transversely to the roller longitudinal direction over several, preferably all, screw rollers of the roller screen. The collecting tray extends in the conveying direction to a downward soil discharge edge. The soil discharge edge is preferably a free end of the feed tray.During conveying and dosing operations, the collecting tray catches the undersize fraction falling through the screen gaps in the overlapping area of ​​the roller screen and the collecting tray.

[0011] The collecting tray extends so close to the screw rollers on the underside of the roller screen that the screw rollers, with their rotating helices, convey the undersize fraction on the collecting tray in the conveying direction to the bottom discharge edge. The screw rollers push the undersize fraction on the collecting tray in the conveying direction up to and over the bottom discharge edge. The collecting tray can be designed along the bottom discharge edge in such a way that the undersize fraction simply falls freely downwards when pushed over the bottom discharge edge. Alternatively, the collecting tray can form a kind of chute at the bottom discharge edge, along which the undersize fraction conveyed over the bottom discharge edge slides downwards due to gravity.

[0012] The roller screen can consist of two screw rollers. However, in many applications, it is advantageous to have three or more screw rollers. The screen discharge area is located at one axial roller end. In such designs, the conveying direction is at least substantially parallel to the longitudinal direction of the roller; preferably, the conveying direction and the longitudinal direction of the roller are the same. In principle, however, the screen discharge area can also be formed along an outer peripheral edge of an outer screw roller of the roller screen, so that the conveying direction of the oversize fraction conveyed on the roller screen also has at least a significant directional component transverse to the longitudinal direction of the roller.

[0013] To ensure uninterrupted, even conveyance of the undersize fraction on the collecting tray, it is advantageous if the collecting tray forms a collecting tray that is impermeable to the undersize fraction and is continuously smooth in the conveying direction. Particles of the undersize fraction can become stuck on uneven surfaces and in holes and complicate conveyance towards the bottom discharge edge. This can lead to uneven conveyance or, at the very least, to increased power requirements for driving the screw rollers. For example, undersize particles trapped in holes or other types of passages are literally shaved off by the spirals of the rotating screw rollers. This can be counteracted by an impermeable collecting tray that is continuously smooth on its surface facing the roller screen in the conveying direction, preferably in the longitudinal direction of the roller.

[0014] The collecting tray can be shaped to fit snugly against the underside of the roller screen. If the roller screen is flat, or at least flat on its underside, the collecting tray can also be flat and arranged at a short distance below the screw rollers. If the roller screen curves upwards on one or both side edges, the collecting tray can also be curved accordingly, so as to advantageously have only a small distance from the roller screen at the side edge of the roller screen. In such designs, the collecting tray can form a collecting surface that is smooth all around, either simply flat or curved, composed of flat sections, which is only a short distance from an enveloping surface applied to the screw rollers on the underside of the roller screen. In such designs, the collecting tray can have a smallest distance in the longitudinal direction of the rollers only in a line to the lowest points of the helices of the screw rollers.

[0015] The distance between the roller screen and the collecting tray is large enough to ensure free rotation of the screw rollers or the spirals of the screw rollers, preventing the spirals from dragging on the collecting tray. On the other hand, the distance is small enough to prevent a permanent undersize layer from forming on the collecting tray while the screw rollers are rotating.

[0016] In a further development, the collecting tray comprises wrap-around sections extending in the longitudinal direction of the roller or is composed entirely of wrap-around sections running alongside one another, with each wrap-around section wrapping around one of the screw rollers on its underside. The collecting tray can be channel-shaped on its surface facing the roller screen. In particular, the collecting tray can comprise tubular, upwardly open wrap-around sections running directly alongside one another, which also includes configurations in which the collecting tray consists entirely of such wrap-around sections. Adjacent wrap-around sections each protrude upward between adjacent screw rollers.Due to the wrap sections, the effective engagement length with which the screw rollers engage the undersize fraction located on the collecting tray and act on the undersize fraction in the conveying direction can be increased. In such designs, as explained above, an advantageously small distance can be maintained over the angular extent of the wrap.

[0017] The wrap sections can, viewed in cross-sections of the roller screen and collecting tray, each extend over a wrap angle, measured around the axis of rotation of the respective screw roller, of at least 20°, at least 30°, or at least 40°. In such embodiments, the collecting tray has the shape of adjacent channels that are open towards the roller screen. The channels can, in particular, be cylindrical in the longitudinal direction of the roller. If, on the other hand, the diameter of the screw rollers varies in the longitudinal direction, the radii of the channels can vary accordingly to adapt to the local screw roller cross-section in order to maintain a uniformly small distance. In advantageous embodiments, the wrap angle is equal to or greater than 60° and can easily be up to 150°. The wrap angle is preferably 90° or more.

[0018] The collecting tray can, in particular, be a flat structure and accordingly have a length measured in the longitudinal direction of the roll and a width measured transversely to the longitudinal direction of the roll, each of which is significantly greater than a thickness of the collecting tray measured orthogonally to the length and width. The collecting tray can, for example, be a sheet-like flat structure.

[0019] The dosing conveyor conveys the fed solid mixture in two material streams in the conveying direction: one material stream, the undersize fraction, along the underside of the roller screen to the bottom discharge edge, and the other material stream, the oversize fraction, along the top of the roller screen to the screen discharge area. The undersize fraction can be conveyed to its respective discharge area largely free from interference from the oversize fraction, and the oversize fraction can be conveyed to its respective discharge area largely free from interference from the undersize fraction. Fluctuations in the feed rate when feeding the solid mixture onto the roller screen, for example, when fed by an excavator, are largely compensated for, and the feed rates at the bottom discharge edge and at the screen discharge area are evened out.

[0020] A rotary drive for the screw rollers can be configured to change the feed rate of the dosing conveyor depending on the rate at which the solid mixture is fed to the roller screen and to flexibly adjust it by increasing or decreasing the rotational speed of the screw rollers accordingly. In principle, however, the dosing conveyor according to the invention compensates for fluctuations in the rate at which the solid mixture is fed within wide limits, even with a drive with only a constant rotational speed.

[0021] According to the invention, the roller screen protrudes in the conveying direction beyond one or more sections of the bottom discharge edge. The roller screen preferably protrudes over its entire width, measured transversely to the longitudinal direction of the roller, along the bottom discharge edge beyond the collecting tray in the longitudinal direction of the roller. The screening discharge area of ​​the roller screen is thus located downwards in the conveying direction from, i.e. behind the one or more sections of the bottom discharge edge or preferably everywhere behind the bottom discharge edge. At least some of the undersize fraction thus leaves the collecting tray in the conveying direction before the screening discharge area of ​​the roller screen. A distance, measured in the conveying direction, between the screening discharge area and the bottom discharge edge is sufficiently large that the oversize fraction, if it falls from the roller screen in the screening discharge area, can be collected separately from the undersize fraction.If the roller screen only protrudes above the collection tray in one or more sections of the bottom discharge edge, this applies to that portion of the undersize fraction that falls from the collection tray in one or more sections of the bottom discharge edge that are set back in relation to the conveying direction. When we talk here about the oversize fraction falling from the roller screen and the undersize fraction falling from the collection tray, this is initially only intended to characterize the distance between the screen discharge area and the bottom discharge edge in terms of size. In actual designs of the dosing conveyor, the oversize grain does not have to fall from the roller screen and / or the undersize grain does not have to fall from the collection tray or be collected separately; here only the distance is intended to characterize the size. The fractions can, for example, slide downwards on downstream conveying structures or be collected by a common conveyor.However, designs are preferred in which the oversize fraction actually falls freely from the roller screen and the undersize fraction falls freely from the collecting floor and is collected and conveyed separately by different conveying devices, an oversize conveyor and an undersize conveyor.

[0022] With regard to the distance between the screen discharge area and the discharge edge, in preferred embodiments in which several or all screw rollers protrude in the longitudinal direction of the rollers, the respective screw rollers protrude in the conveying direction by at least 1 / 5 of the effective length LW of the respective screw roller for conveying the oversize grain beyond the one or more sections of the discharge edge, preferably beyond the entire discharge edge of the collecting tray. The effective length LW for each of the screw rollers is the length over which a helix extends, i.e., the roller length over which a conveying effect is exerted in the longitudinal direction of the roller when the respective screw roller is driven by rotation. If LF denotes the length of the effective length LW by which the respective screw roller protrudes beyond the collecting tray, i.e., the axial projection, then in advantageous embodiments at least one of the following relationships applies to the ratio LF / LW: L F / L W ≥ 1 / 5 order L F / L W ≥ 1 / 4 order L F / L W ≥ 1 / 3 .

[0023] On the other hand, it is advantageous for a locally defined discharge of the undersize fraction if at least one of the following relations applies: L F / L W ≤ 3 / 4 order L F / L W ≤ 2 / 3 order L F / L W ≤ 1 / 2 .

[0024] For a large proportion of solid mixtures, a ratio LF / LW in the range of at least 1 / 4 and at most 1 / 2 is favorable.

[0025] The screw rollers and the collecting tray overlap in the conveying direction up to at least the tray discharge edge and, as mentioned above, in the longitudinal direction of the rollers. The overlapping length of the collecting tray and the respective screw roller is referred to collectively as the "overlap length" LA. According to the invention, the screw rollers, as also mentioned, each protrude beyond the tray discharge edge in the conveying direction parallel to the longitudinal direction of the rollers. If the length by which the respective screw roller protrudes is referred to as the "clearance length" LF, in the sense of "clear from the collecting tray," then, with regard to the distance measured in the longitudinal direction of the rollers between the screen discharge area and the tray discharge edge, the following applies according to the invention for the ratio of clear length to overlap length, alternatively or in addition to the previous paragraph: LF / LA ≥ 1 / 5 or preferably LF / LA ≥ 1 / 4 or LF / LA ≥ 1 / 3

[0026] On the other hand, it is advantageous for a locally defined discharge of the undersize fraction if at least one of the following relations applies: L F / L A ≤ 3 order L F / L A ≤ 2 order L F / L A ≤ 1 .

[0027] In particular, 1 / 4 ≤ LF / LA ≤ 3 / 2, preferably LF / LA = 1 / 2.

[0028] The overlap length and / or the free length can vary from screw roller to screw roller, i.e., they do not have to be the same for all screw rollers, but they are preferably the same for all screw rollers. It is preferred if the respective screw roller conveys the oversize fraction over its entire free length in the longitudinal direction of the roller to the screen discharge area.

[0029] According to the invention, the screw rollers cannot be supported at both axial ends. In such embodiments, the screen discharge area extends in the longitudinal direction of the rollers over an axial roller section, for example an axial end section of the screw rollers, in which the screw rollers are, for example, slimmer than over the rest of their length(s). According to the invention, however, the screw rollers are only supported on one side and protrude freely axially from the respective bearing. With only one-sided support, the screen discharge area can be located directly at the free axial ends of the screw rollers and accordingly be a free screen discharge edge, with the oversize particles in the screen discharge area or screen discharge edge falling or possibly slipping off the roller screen at the free roller ends.

[0030] The dosing conveyor may include a boundary structure as a further functional component. The boundary structure may include a right boundary wall along a right side edge of the roller screen and / or a left boundary wall along a left side edge of the roller screen, wherein the respective boundary wall prevents the oversize fraction from being conveyed by the roller screen transversely to the conveying direction, i.e., transversely to the longitudinal direction of the roller.

[0031] In further developments, the boundary structure can have a right boundary wall along the right side edge of the roller screen, a left boundary wall along the left side edge of the roller screen and a rear boundary wall over which the screw rollers protrude in the conveying direction, preferably in the longitudinal direction of the rollers, wherein the boundary structure frames the roller screen on three sides, but is open in the conveying direction, preferably in the longitudinal direction of the rollers.

[0032] The boundary structure can be open at the top and widened in a funnel-like manner so that the solid mixture can be fed to the roller screen from above and, in plan view, within the boundary structure, falling onto the roller screen.

[0033] The boundary structure can extend down to the collecting tray or close to it to prevent the undersize fraction from falling off the collecting tray at the edges and / or the rear end of the roller screen. The respective boundary wall can be tightly connected to the collecting tray, for example, by a material bond, or can be loosely attached to the collecting tray in an overlapping manner.

[0034] An embodiment of the invention is explained below with reference to figures. Figure 1 shows a dosing conveyor in a perspective view of the top side of a roller screen, Figure 2 shows the dosing conveyor in a perspective view of the bottom side, Figure 3 shows the dosing conveyor in a frontal view of a screen outlet and a bottom outlet edge, Figure 4 shows part of the dosing conveyor in a cross-section orthogonal to the longitudinal direction of the roller, Figure 5 shows part of a modified dosing conveyor in a cross-section orthogonal to the longitudinal direction of the roller, Figure 6 shows the dosing conveyor in a vertical plan view of the top side of the roller screen, Figure 7 shows the dosing conveyor in a side view, Figure 8 shows the dosing conveyor with a downstream conveyor and Figure 9 shows the dosing conveyor with two downstream conveyors.

[0035] Figure 1shows a dosing conveyor 1 according to the invention. The dosing conveyor 1 comprises a roller screen 10 with several screw rollers 11 to 16 arranged next to one another. Figure 1 is a perspective view of the top of the roller screen 10. The screw rollers 11 to 16 are mounted next to one another so as to be rotatable about parallel axes of rotation D. The axes of rotation D each point in the longitudinal direction of the rollers X. The screw rollers 11 to 16 each have a central roller body and a radially projecting helix encircling this in a helical manner. Adjacent screw rollers 11 to 16 each intermesh with their helices, so that screen gaps are obtained which are delimited in the transverse direction Y to the longitudinal direction X of the rollers by the roller bodies and in the longitudinal direction X of the rollers by the intermeshing helices.

[0036] If a solid mixture is added to the top of the roller screen 10, an undersize fraction of smaller particles of the solid mixture falls downwards through the screen gaps of the roller screen 10, while an oversize fraction of larger particles is conveyed on the roller screen 10 in a conveying direction F to a screen discharge area 19, corresponding to the screen gaps. The conveying direction F coincides with the roller longitudinal direction X. The solid mixture can be natural rock, for example, rubble, excavated earth or construction rubble, or other types of municipal waste.

[0037] The roller screen 10 forms a screen surface that is convexly curved downwards in the transverse direction Y. To form such a screen surface, the screw rollers 11 to 16 are arranged such that the axes of rotation D rise from a roller screen center in the transverse direction Y to both sides. The roller screen 10 thus rises in the transverse direction Y from the screen surface center to both lateral longitudinal edges. The outer screw roller 15 on the right side of the screen forms a right side edge at its outer circumference, and the outer screw roller 16 on the left side of the screen forms a left side edge of the roller screen 10 at its outer circumference.

[0038] The dosing conveyor 1 comprises a rotary drive for the screw rollers 11 to 16. The rotary drive can be configured, in particular, to drive a right-hand roller group of screw rollers 11, 13, and 15 in one direction of rotation and a left-hand roller group of screw rollers 12, 14, and 16 in the other direction of rotation. Accordingly, the spirals of the left-hand roller group 11, 13, and 15 have the same first direction of rotation, and the spirals of the left-hand roller group 12, 14, and 16 have the same direction of rotation but opposite to the screw rollers 11, 13, and 15 of the right-hand roller group.The direction of rotation of the screw flights and the direction of rotation of the screw rollers of the respective roller group are selected such that the oversize fraction of the solid mixture fed to the roller screen 10 is conveyed on the screw rollers of the right-hand roller group 11, 13, 15 to the right-hand side edge and on the screw rollers of the left-hand roller group 12, 14, 16 to the left-hand side edge of the roller screen 10. Due to the rise of the roller screen 10 on both sides in the transverse direction Y at the side edges, the oversize fraction conveyed on the upper side of the roller screen 10 is pushed back towards the roller center by gravity, with the oversize particles conveyed into the lateral rise area falling back towards the roller center by gravity. This is advantageous for loosening the oversize fraction, for example, separating entangled oversize particles from one another or freeing oversize particles from adhering soil material.

[0039] In a modification, the screening surface can also be flat, for example by arranging the rotational axes D of the screw rollers 11-16 in one plane. The screw rollers of a flat roller screen can all rotate in the same direction of rotation, and the intermeshing helices can accordingly have the same sense of rotation. Alternatively, an outer right-hand roller group and an outer left-hand roller group can have helices with groups rotating in opposite directions to one another, and the rotary drive can be configured to drive the left-hand roller group and the right-hand roller group in opposite directions. For a flat roller screen, it is expedient if the left and right-hand roller groups are driven with respect to the direction of rotation such that they convey the oversize particles floating in the respective roller group primarily in the longitudinal direction of the rollers, but also towards the center of the roller screen.

[0040] The dosing conveyor 1 comprises a boundary structure 2 that surrounds the roller screen 10 in a rear screening area remote from the screening discharge area 19. The boundary structure 2 comprises a right boundary wall 3, a rear boundary wall 4, and a left boundary wall 5. The boundary walls 3, 4, and 5 project upwards beyond the roller screen 10 on both side edges and at the rear of the latter. The boundary walls 3, 4, and 4 can advantageously form a receiving hopper together, which widens away from the roller screen 10 at the top and is open at its front facing the screening discharge area 19. The oversize material is fed to the roller screen 10 in the area of ​​the boundary structure 2, i.e., in the rear area of ​​the roller screen 10.

[0041] The screw rollers 11 to 16 are supported only at their rear ends and protrude freely from the rear roller ends in the longitudinal roller direction X. Due to this only one-sided support, the screen discharge area 19 is maintained at the free roller ends of the roller screen 10 in the form of a screen discharge edge. The oversize grain falls downwards over the free roller ends in the screen discharge area 19. In a modification, a chute or the like can be connected to the screen discharge area 19, for example, so that the oversize grain does not fall freely downwards, but can slide down the chute or the like.

[0042] In addition to the roller screen 10, an essential component of the dosing conveyor 1 is also a collecting tray 20 for the undersize fraction. The collecting tray 20 is arranged directly below the roller screen 10, here accordingly directly below the screw rollers 11 to 16. The collecting tray 20 can be sufficiently tightly connected at its side edges to the boundary walls 3 and 5 and at its rear edge to the rear boundary wall 4 to prevent undersize from being conveyed over the rear edge or the side edges of the collecting tray 20. The collecting tray 20 and boundary structure 2 can thus jointly form a retention container for the undersize fraction, although this retention container is open in the conveying direction F. At its downstream end with respect to the conveying direction F, the collecting tray 20 has a free soil discharge edge 29, still below the screw rollers 11-16, through which the undersize is discharged.

[0043] Figure 2 shows the dosing conveyor 1 in a perspective view of the underside of the roller screen 10 and the collecting tray 20 arranged there. The bottom discharge edge 29 forms the free front end of the collecting tray 20. The undersize grain is conveyed by the screw rollers 11 to 16 accordingly over the bottom discharge edge 29 so that it can fall freely downwards from the collecting tray 20 at the bottom discharge edge 29. In a modification, a chute or the like can be formed directly adjacent to the bottom discharge edge 29 in the conveying direction F so that undersize grain conveyed over the bottom discharge edge 29 cannot fall freely downwards but can slide down on the chute or the like.

[0044] To improve the conveyance of the undersize layer, the collecting floor 20 comprises several wrapping sections 21 to 26 extending in the roller's longitudinal direction X, which are arranged next to one another in a manner corresponding to the screw rollers 11-26. In the corresponding arrangement, the wrapping section 21 wraps around the screw roller 11, the wrapping section 22 wraps around the screw roller 12, the wrapping section 23 wraps around the screw roller 13, the wrapping section 24 wraps around the screw roller 14, the wrapping section 25 wraps around the screw roller 15, and the wrapping section 26 wraps around the screw roller 16.

[0045] In Figure 3 the dosing conveyor 1 is shown in a frontal view of the screen discharge area 19 and the bottom discharge edge 29, so that the wrapping of the roller undersides by the collecting bottom 20 can be clearly seen.

[0046] Figure 4shows the right part of the dosing conveyor 1 with the right roller group 12, 14, 16, the associated wrap sections 22, 24 and 26 and the right boundary wall 5 in a cross-section orthogonal to the roller longitudinal direction X. The arrangement of the left roller group 11, 13, 15, associated wrap sections 21, 23 and 25 and the left boundary wall 3 is mirror-symmetrically identical on the other side of the dosing conveyor (not shown).

[0047] The collecting floor 20 extends, as shown in the Figures 3 and 4 and also in Figure 2clearly visible, directly below the roller screen 10, in the exemplary embodiment accordingly directly below the screw rollers 11 to 16. Between the roller screen 10 and the collecting tray 20, i.e. between the spirals of the screw rollers 11-16 and the collecting tray 20, there remains a clear distance which ensures that the screw rollers 11-16 rotate freely from the collecting tray 20 and at the same time that the screw rollers 11-16 convey the undersize fraction which has fallen through the screen gaps of the roller screen 10 onto the collecting tray 20. The distance is so small that the spirals of the screw rollers 11 to 16 engage in the undersize fraction on the collecting tray 20 and convey this on the collecting tray 20 in the conveying direction F to the soil discharge edge 29 when the screw rollers 11-16 are rotated.In particular, the distance can be so small that no undersize layer can permanently form on the collecting tray 20 due to the engagement of the spirals, since the spirals push an overlying undersize layer, should it form locally and temporarily, onto the collecting tray 20 into conveyor F. On the other hand, this does not mean that no undersize particles can remain on the collecting tray 20, regardless of their size.

[0048] The collecting base is nestled with its wrap-around sections 21-26 against the screw rollers 11-16. The wrap-around sections 21-26 each have a surface on their upper sides facing the screw rollers 11-16, which forms a virtual envelope circumference applied to the outer circumference of the helix of the associated screw roller with the aforementioned small radial distance, which in Figure 4denoted by a, via a wrap angle. It is advantageous if the wrap angle is more than 20°, more than 30°, or more than 40°. Wrap angles in the range of 60° to 150° are preferred, with wrap angles of 90° and more being particularly advantageous.

[0049] In Figure 4 For the wrap section 26, it is indicated in dashed lines that the wrap on the outer peripheral edge can be extended, i.e., raised, compared to the middle wrap sections 21, 22, and 24, as well as the middle wrap section 23 (not shown). The outer wrap section 25 can be extended in the same way, mirror-symmetrically, on the other side. This even more reliably prevents oversize particles from becoming trapped on the outer side edges of the roller screen 10. For the two outer wrap sections 25 and 26, the wrap angle can easily be 180°.

[0050] The wrapping surface of the respective wrapping section 21-26 can be equidistant from the envelope circumference of the associated screw roller 11-16 over the wrap angle, so that the radial distance a is constant over the wrap angle of the respective wrapping section 21-26.

[0051] The wrap-around sections 21-26 are each shaped as an upwardly open tube. They can each be shaped as a circular ring section in cross-section. In the exemplary embodiment, they are cylindrical over their entire axial length. The wrap-around sections 21-26 can be manufactured individually and joined together in the arrangement of the exemplary embodiment, so that they collectively form the downwardly convexly curved collecting base 20. Overall, the collecting base 20 is thus obtained as a sheet-like flat structure. In the exemplary embodiment, the collecting base 20 consists of the wrap-around sections 21-26. The wrap-around sections 21-26 accordingly extend directly next to one another in the roller longitudinal direction X.

[0052] In a Figure 5 In the modification shown, the dosing conveyor 1 has a modified collecting floor 28, which consists of a flat right floor section, a Figure 5shown flat left base section and a likewise recognizable flat middle section. The right base section extends directly below the right roller group 11, 13, 15. The left base section extends directly below the left roller group 12, 14, 16. The middle section extends directly below the two middle screw rollers 11 and 12, of which screw roller 11 is counted as part of the right roller group and screw roller 12 as part of the left roller group.

[0053] Figure 6shows the dosing conveyor 1 in a plan view of the top of the roller screen 10. The effective length LW of the screw rollers 11-16 is entered, which in the exemplary embodiment are preferably of equal length. The effective length LW is the length with which the respective screw roller 11-16 comes into contact with the solid mixture and conveys oversize grain in the roller longitudinal direction X. In the exemplary embodiment, the screw rollers 11-16 protrude with the effective length LW in the roller longitudinal direction X over the rear boundary wall 4 to the free roller end, where the screen discharge area 19 is formed. LA designates the length over which the collecting tray 20 overlaps with the screw rollers 11-16 in the roller longitudinal direction X. The length LA is also the length of the collecting tray 20 measured in the roller longitudinal direction X, i.e.The collecting tray 20 extends at its rearward end in the roller longitudinal direction X to the rear end of the roller screen 10 and extends in the conveying direction F to the bottom discharge edge 29. In principle, the collecting tray 20 can extend beyond the rear end of the roller screen 10 against the conveying direction F; however, for comparison purposes, even in such modifications, only the length of the overlap LA is used and is referred to below as the "overlap length LA". LF is the length by which the screw rollers 11-16 project freely in the conveying direction F, here axially, beyond the collecting tray 20, i.e., beyond its bottom discharge edge 29. This length of free projection is referred to below as the "free length LF".

[0054] For the comparison of the lengths LW , LA and LF, Figure 6 assumes that the axes of rotation of the screw rollers 11-16 are horizontal. Figure 7shows the dosing conveyor 1 in a side view. In contrast to the arrangement of the Figure 6 the dosing conveyor 1 is in Figure 7 tilted about a horizontal tilting axis pointing in the transverse direction Y. The rotational axes D of the screw rollers of the roller screen 10 point at an acute angle, namely an inclination α, to the horizontal H. In simple designs, the dosing conveyor 1 can be arranged in or on a frame in a non-adjustable manner with a correspondingly fixed inclination α, where 0° ≤ α ≤ 50°. In further developments, the dosing conveyor 1 can also be arranged in or on the frame so that it can be adjusted about the tilting axis, so that the inclination α can be adjusted. Figure 7 are the same lengths LW , LA and LF as in Figure 6 , but entered according to the tilted orientation.

[0055] In the exemplary embodiment, the effective length LW is the sum of the overlap length LA and the free length LF . The length ratios can therefore be characterized by the ratio of the free length LF to the overlap length LA. Thus, it corresponds to preferred embodiments if the ratio of free length to overlap length is at least essentially that LF / LA = 1 / 2. In relation to the effective length LW, this means that the free length LF makes up one third and the overlap length LA two thirds of the effective length LW of the respective screw roller 11-16. Good results are achieved with regard to the uniformity of conveying and the associated metering of the conveyed quantities of undersize and oversize fractions, but also with regard to an optionally implemented separation of the two fractions, if the ratio LF / LA is at least 1 / 4 or, more preferably, at least 1 / 3. The lower limit for the ratio LF / LA is 1 / 5.The upper limit for the ratio LF / LA is considered to be 3. It is preferable if LF / LA is not greater than 2. The preferred range is 1 / 4 ≤ LF / LA ≤ 3 / 2, and even more preferably 1 / 3 ≤ LF / LA ≤ 1.

[0056] Figure 8shows the dosing conveyor 1 and a conveyor 7 arranged downstream of the dosing conveyor 1 in a plan view of the upper sides of the roller screen 10 and the conveyor 7. The conveyor 7 can, for example, be a simple belt conveyor. The conveyor 7 extends below the collecting tray 20 and is designed to collect the undersize fraction falling from the collecting tray 20 and also the oversize fraction falling from the roller screen 10 in the screen discharge area 19 and to convey them further in the conveying direction F. The dosing conveyor 1 serves only to dampen fluctuations in the conveyed quantities, which can arise from the fact that the solid mixture is fed to the roller screen 10 discontinuously and / or in varying composition and / or with other irregularities.

[0057] In the arrangement of the Figure 9The dosing conveyor 1 not only serves to reduce feed rate fluctuations, but also to separate the two fractions. Accordingly, an oversize grain conveyor 8 and an undersize grain conveyor 9 are arranged downstream of the dosing conveyor 1. The oversize grain conveyor 8 can, for example, be connected to the conveyor 7 of the Figure 8However, the oversize grain conveyor 8 now only extends below the screen discharge area 19 and no longer below the collecting tray 20. The oversize grain conveyor 8 therefore only collects the oversize grain fraction falling from the roller screen 10 in the screen discharge area 19. The oversize grain conveyor 8 conveys the oversize grain fraction further in the conveying direction F. The undersize grain conveyor 9 extends in the transverse direction Y over the entire width of the roller screen 10 and the collecting tray 20 and, in plan view, overlaps the bottom discharge area 29 over its entire length. The undersize grain conveyor 9 collects the undersize grain fraction discharged over the bottom discharge edge 29 and conveys it further in the transverse direction Y.

[0058] In the embodiment of the Figure 9the undersize conveyor 9 is arranged lower than the oversize conveyor 8. The oversize conveyor 8 is therefore at a distance from the bottom discharge area 29, measured in the conveying direction F. If the oversize conveyor 8 is impermeable to the smaller oversize particles of the oversize fraction, for example, designed as a dense conveyor belt, the undersize conveyor 9 can also extend in the conveying direction F to below the screen discharge area 19 or beyond. The oversize conveyor 8 and the undersize conveyor 9 can basically also be arranged at the same height without mutual overlap. In modifications, the oversize conveyor 8 can be arranged lower than the undersize conveyor 9. If the undersize conveyor 9 in such designs is impermeable even to the smaller particles of the undersize fraction, for example, designed as a closed conveyor belt, the oversize conveyor 8 can also reach below the collecting floor 20, while the undersize conveyor 9, as in Figure 9shown, should end in conveying direction F before the screen discharge edge 19. Reference symbols:

[0059] 1Dosing conveyor 2Boundary structure 3Boundary wall 4Boundary wall 5Boundary wall 6- 7Conveyor 8Oversize conveyor 9Undersize conveyor 10Roller screen 11Screw roller 12Screw roller 13Screw roller 14Screw roller 15Screw roller 16Screw roller 17- 18- 19Screen discharge area 20Collecting floor 21Wrapping section 22Wrapping section 23Wrapping section 24Wrapping section 25Wrapping section 26Wrapping section 27- 28Collecting floor 29Soil discharge edge aDistance αInclination DRoller rotation axis FConveying direction HHorizontal LA Overlap length LW Effective roll length LF Free length, axial projection XRoller longitudinal direction YTransverse direction

Claims

1. A dosing conveyor for conveying and dosing a mixture of solids, the dosing conveyor comprising: - a plurality of helical rollers (11-16) arranged next to each other such that they can be rotary-driven and forming a roller screen (10) onto which the mixture of solids can be introduced in order to obtain an undersize-grain fraction which falls through the roller screen (10) and an oversize-grain fraction which can be conveyed on the roller screen (10) in a conveying direction (F) as far as and into a screen output region (19) of the roller screen (10); and - a collecting floor (20), which extends below the roller screen (10) in the conveying direction (F) as far as a downward output edge (29) of the floor, for collecting the undersize-grain fraction which falls through the roller screen (10), - wherein the collecting floor (20) extends close enough to the helical rollers (11-16) on the lower side of the roller screen (10) that the helical rollers (11-16) convey the undersize-grain fraction situated on the collecting floor (20) in the conveying direction (F) to the output edge (29) of the floor, wherein - the helical rollers (11-16) and the collecting floor (20) overlap in the longitudinal direction (X) of the rollers as far as the output edge (29) of the floor over a total overlapping length (LA), and wherein - the helical rollers (11-16) each protrude freely beyond the output edge (29) of the floor by a free length (LF) in the conveying direction (F) which is parallel to the longitudinal direction (X) of the rollers, characterised in that - the ratio of the free length (LF) to the overlapping length (LA) is at least 1 / 5.

2. The dosing conveyor according to the preceding claim, wherein the roller screen (10) protrudes beyond the entire output edge (29) of the floor in the conveying direction (F).

3. The dosing conveyor according to any one of the preceding claims, wherein the ratio of the free length (LF) to the overlapping length (LA) is at least 1 / 4 or at least 1 / 3 and preferably 1 / 2.

4. The dosing conveyor according to any one of the preceding claims, wherein the ratio of the free length (LF) to the overlapping length (LA) is at most 3 or at most 2 or at most 1.

5. The dosing conveyor according to any one of the preceding claims, wherein the collecting floor (20) has a distance (a) from helices of the helical rollers (11-16) which is smaller than a radial height by which the helices protrude radially from a central roller body of the respective helical roller, wherein for helical rollers having a radial height of the helix which varies in the longitudinal direction (X) of the rollers, the mean radial height obtained as the geometric mean of the maximum and minimum height is adduced for the comparison.

6. The dosing conveyor according to any one of the preceding claims, wherein the collecting floor (20) comprises looping portions (21-26) which extend in the longitudinal direction (X) of the rollers and loop around the helical rollers (11-16) on the lower sides of the rollers, preferably over a looping angle of more than 60° in each case.

7. The dosing conveyor according to any one of the preceding claims, wherein all of the helical rollers (11-16) of the roller screen (10) protrude freely from a bearing side in the conveying direction (F) and form the screen output region (19) at the free end of the rollers.

8. The dosing conveyor according to any one of the preceding claims, comprising a boundary structure (2) comprising a right-hand boundary wall (3) on a right-hand side edge of the roller screen (10), a left-hand boundary wall (5) on a left-hand side edge of the roller screen (10), and a rearward boundary wall (4) from which the helical rollers (11-16) protrude in the conveying direction (F), wherein the boundary structure (2) encloses the roller screen (10) on three sides, but is open in the conveying direction (F) which coincides with the longitudinal direction (X) of the rollers.

9. The dosing conveyor according to the preceding claim, wherein the boundary structure (2) extends downwards as far as the collecting floor (20) or close to the collecting floor (20) in order to prevent the undersize-grain fraction from being able to fall from the collecting floor (20) at the edges and / or at the rearward end of the roller screen (10).

10. The dosing conveyor according to any one of the preceding claims, comprising an oversize-grain conveyor (8) which is arranged downstream of the roller screen (10) in the conveying direction (F) and extends as far as and below the screen output region (19) in order to collect and convey onwards the oversize-grain fraction which falls from the roller screen (10) in the screen output region (19), and / or an undersize-grain conveyor (9) which is arranged downstream of the collecting floor (20) in the conveying direction (F) and extends as far as and below the output edge (29) of the floor in order to collect and convey onwards the undersize-grain fraction which falls over the output edge (29) of the floor.

11. The dosing conveyor according to any one of the preceding claims, wherein the helical rollers (11-16) and the collecting floor (20) are fixedly arranged at an upward inclination (α) in the conveying direction (F) or can be adjusted into such an inclined position by being jointly tilted.

12. The dosing conveyor according to any one of the preceding claims, wherein the roller screen (10) rises transversely to the conveying direction (F) towards a right-hand side edge and / or left-hand side edge of the roller screen (10), so that particles of the oversize-grain fraction fall transversely to the conveying direction (F), preferably transversely to the longitudinal direction (X) of the rollers, from the respective side edge back towards a lower region of the roller screen (10) due to gravity.

13. The dosing conveyor according to any one of the preceding claims, wherein the roller screen (10) and the collecting floor (20), and optionally also the boundary structure (2) and / or the rotary drive, are embodied as an assembly unit which can be fully assembled.