Screening device for plansifters for fractionating ground cereal products

Abstract

The plansifter has at least one screening compartment with an arrangement of a plurality of screening elements with screens (23). The screening device (20) has a screen frame (21) and an insert frame (22) with the screen (23) fastened thereon, in particular clamped thereon. The screen frame (21) forms a circumferential side wall (30) and an - inwardly protruding - support on which the insert frame (22) rests, specifically in such a manner that the screen (23) lies within the circumferential side wall, - i.e. the circumferential side wall surrounds the screen on the outer side, along an outer boundary (edge or similar) of the screen. In addition, the screen lies below an upper edge of the circumferential side wall. The screen frame (21) therefore forms, as it were, a trough in which the insert frame with the screen lies.

Description

[0001] SCREENING DEVICE FOR PLAN SIFTS FOR

[0002] FRACTIONATION OF GRAIN MILLING PRODUCTS

[0003] The invention relates to machines, for example, plansifters, used for fractionating ground grain products. It particularly relates to a screening device for a plansifter.

[0004] Plan sifters are used to separate the components of a ground material into coarser and finer grained components and, depending on the case, also components of different

[0005] Densification and the removal of foreign matter from the ground material. The separation of the ground material into different granular components is also called "classifying" or "fractionating." Plan sifters are generally used in the milling industry to fractionate the ground grain products between and after passes through the roller mill of a grain mill. Also for a so-called

[0006] They can be used for control screening, ie the sifting of flour that is otherwise ready for sale.

[0007] Plan sifters have screening compartments, each containing a stack of plan screens, which are set into horizontal oscillating movements by a suitable drive mechanism, particularly in circular oscillations in the screening plane. The screens are each mounted on

[0008] Primary frames, so-called "inlay frames," are stretched across them, which in turn are inserted into screen frames (also referred to here as "secondary frames"). Between the stacked screen frames, seals, for example made of suitable felt, are provided at the level of the screen mesh to prevent the product from escaping undesirably from the sides. However, these seals are subject to deterioration due to compression and must be replaced regularly. Furthermore, the height of the inlay frame and the height of the structures within the screen frame in which the inlay frame is guided must be very precisely coordinated to ensure that the inlay frame sits securely and is properly sealed when stacked. A further disadvantage of felt seals is that a felt seal is installed between each screen frame. Typically, around 20-30 screen frames are stacked on top of each other. The screen frames are pressed together in the stack.As a result, the felt seals become compacted and thinner over time. Typically, they lose up to about half their original thickness. This causes the top screen frames to be relocated by up to several centimeters. This, in turn, can lead to their incorrect position relative to the schematic parts in the screen wall.

[0009] Another issue concerns space requirements. There is a constant need to maximize screening performance per volume used. An optimized height per screening device or the closest possible arrangement of screen stacks next to each other may be desirable in this regard.

[0010] Conventional plansifters require a so-called screen box around the screen stacks, which, firstly, entails certain disadvantages in terms of space requirements and, secondly, makes handling somewhat more difficult, especially since entire pre-assembled rows of screen boxes or drive modules are usually transported as pre-assembled units. Compatibility is another issue. Mills often contain plansifters of different generations. It can be disadvantageous for the operator of a mill if they have to maintain a separate warehouse containing the most important consumables – namely the screens – for each plansifter or different groups of plansifters. Therefore, a desirable feature of screening devices can be the ability to use screens that can also be used in other, older plansifters.In particular, the principle of attaching a screen to a primary frame, which can be replaced together with the screen if damaged, can be a desirable feature.

[0011] US 2009 / 0184031 A1 discloses a sieve with a rectangular container for use in a commercial kitchen. This sieve is intended to allow the reusable flour / powder to be sifted into the container after food has been floured or powdered. Such a sieve is neither intended for nor would it be suitable for a plansifter, simply because the sieve must be movable relative to the container, and therefore the necessary horizontally oscillating movements could not be incorporated into it.

[0012] FR 2.023.574 shows a plansifter with sieve compartments containing drawers into which sieve frames with mounted sieves are inserted. The drawers are formed by rails running along two opposite sides of the sieve frame.

[0013] It is an object of the present invention to provide a screening device for a plansifter and a plansifter that allows improvements at least with respect to one or more of the aforementioned aspects. The screening device should, in particular, be robust and flexible in use and preferably at least allow use as an open screen stack without the need for a screen box.

[0014] According to one aspect of the present invention, a screening device for plansifters is provided, which comprises a screen frame and an insert frame with a screen attached thereto, in particular clamped thereon. The screen frame has a circumferential side wall and an inwardly projecting support on which the insert frame rests, specifically such that the screen lies within the circumferential side wall—i.e., the circumferential side wall surrounds the screen on the outside, along an outer boundary (edge ​​or similar) of the screen and the insert frame. Furthermore, the screen lies below an upper edge of the circumferential side wall.

[0015] The sieve frame essentially forms a tub in which the insert frame with the sieve lies.

[0016] On the one hand, this has the advantage that the position of the insert frame and the screen is freely defined. The surrounding side wall and the insert frame are coordinated in such a way that the insert frame fits perfectly and, for example, without any play in the tray formed by the screen frame.

[0017] In particular, the insert frame is immobile in horizontal directions relative to the screen frame, due to the aforementioned precision fit and / or a clamping frame that clamps the insert frame against the screen frame. Secondly, there is an advantage with regard to sealing: According to the state of the art, a seal must be created between the screening device and the screening device above it at the level of the screen. This is possible with appropriate seals. However, it is not entirely unproblematic, not least because the plane of the screen is the plane in which the hydrostatic pressure (if the screening material is approximately characterized as a fluid) is greatest - the seal must therefore counteract the hydrostatic pressure of the screening material. In contrast, with the inventive approach, no screening material can escape sideways due to the circumferential side wall.A labyrinth seal prevents leakage past the outside of the insert frame without any additional measures. For this purpose, the support can run continuously along the circumference of the insert frame, i.e., the insert frame rests on the support along its entire circumference.

[0018] Thirdly, the inventive approach also enables a design that is advantageous with regard to the relationship between the height of the screening device, on the one hand, and the cross-sectional area of ​​the lateral opening (slot opening), on the other. As is known per se, the screening device can have a collecting tray below the screen, which is formed, for example, by the screen frame. The collecting tray delimits a collecting area below the screen, wherein the collecting area is open on at least one side, in that the screening device has the aforementioned slot opening through which the permeate (the screening material passing through the screen) can be removed. The efficiency of the screening process depends not least on the size of this slot opening.The inventive design enables the use of a particularly flat insert sieve, which allows for a particularly favorable ratio between the height of the slotted opening and the height of the entire sieve device. For example, the height of the slotted opening can be at most 20%, in particular at most 15%, smaller than the distance between the collecting tray and the sieve. Additionally or alternatively, the condition can be met that the height of the slotted opening is smaller than the distance between the collecting tray and the sieve by at most the thickness of the insert frame plus the thickness of an inwardly projecting projection, which is formed, for example, by an intermediate plate.

[0019] In particular, the collecting floor can form the bottom of the sieve frame, ie the collecting floor can be arranged entirely at the bottom of the sieve frame, and the sieve frame can therefore be free of walls or other structures projecting downwards from the level of the collecting floor (possibly except for small projections which form the stack structures described below).

[0020] This also means that an inlet area above the screen, between the screen and the collecting tray of the screening device above, is formed entirely by the trough-like structure created by the screen on the one hand and an upper section of the surrounding side wall on the other (possibly together with the clamping frame, see the description below). The trough-like structure formed by the screen frame thus collects the screening material hitting the screen from above.

[0021] The collecting tray below the sieve can be formed, in particular, by the sieve frame. It can be metallic and / or particularly thin, having a thickness of no more than 3 mm, in particular no more than 2 mm, and, for example, approximately 1 mm. The collecting tray, together with the side wall, can be formed by pieces of sheet metal or possibly a suitably folded sheet metal.

[0022] The surrounding side wall can be constructed from multiple wall elements. For example, if it is metallic, such wall elements can be made of sheet metal, and the resulting gaps between surface sections, i.e., between wall elements or, if applicable, between surface sections resulting from the folding of a sheet metal wall element, can be filled with a thermally insulating filler material to prevent condensation on the inner surfaces of the side wall.

[0023] An intermediate floor, also made of sheet metal, for example, can form the support.

[0024] The surrounding side wall can accommodate passage channels, whereby depending on the configuration there can be one row, two rows or no row of passage channels per side.

[0025] Passage channels are generally vertical channels located on the side of the screen frame through which screenings can fall downwards into a lower screen frame or an outlet line.

[0026] From the through-channels, the screenings falling through them either reach a screen of the (correspondingly differently configured) screening device below, or into a through-channel of the screening device below, or possibly into an outlet line. Through-channels that simply pass the screenings from the next upper screening device to the next lower screening device without a lateral slot opening are also called "drop channels." The lateral slot opening, through which the screenings are transported away from the collection area, opens into one of the through-channels.

[0027] In embodiments, the screening device has at least one screen cleaner, i.e. an element that is movable relative to the screen and is subject to more or less random movements due to the movements of the screen. As is known per se, such a screen cleaner can move on the collecting tray, the height of the screen cleaner being only slightly less than the height of the collecting area, which is why it repeatedly hits the screen with its movements. Since - as described above - the height of the lateral slotted opening(s) can be relatively large, the collecting tray can have retaining structures, e.g. in the form of thin pins, which limit movements of the screen cleaner to a desired area - they can in particular prevent the screen cleaner from passing through the slotted opening or from becoming wedged in it.

[0028] As an alternative to or in addition to at least one sieve cleaner, the collection area can also have one or more baffles which promote or promote the conveyance of the perforation in the collection area through the lateral slot opening.

[0029] The support can be formed as a shoulder of the circumferential side wall, at least in some areas - for example with the exception of the side(s) which have / have the slotted opening.

[0030] The insert frame can be metallic – for example, it can be designed as a flat metallic body (thin plate) with at least one large-area recess spanned by the screen. The insert frame can, for example, have an outer frame section that is essentially rectangular overall, with dimensions adapted to the support. In addition to the outer frame section, a system of bars can also be present to stabilize the screen, with at least one bar, e.g., rectangular in cross-section, spanned by the screen. The insert frame can be relatively thin, with a maximum thickness of, for example, 3 mm.

[0031] The screen can be designed as a flat body, particularly as a metal sheet, with the screen openings as through holes. If the screen is made of a suitable material (e.g., if both the insert frame and the screen are metal), the screen can be welded to the insert frame.

[0032] A "flat body" is a film or plate, i.e. a continuous object extending in two dimensions with a constant thickness (extension in the third dimension), which is at least one order of magnitude smaller than the extensions in the other two dimensions (length and width). Depending on the thickness, such a flat body is perceived more as a film or a plate. As described in detail in patent application CH 000837 / 2022, it has surprisingly been shown that the design as a flat body with through-holes - instead of the prior art as a web of threads or wires - significantly increases effectiveness. The time required to process a certain amount of the sieved material (flour, dust, semolina, grit, etc.)) through a certain sieve area when all other relevant parameters (mechanical excitation, size of the sieve holes, number of sieve holes) are the same can be significantly reduced.

[0033] It also turns out that such flat-body screens are particularly advantageous in combination with features of the present invention. For example, the sealing effect of the trough described above is particularly advantageous due to the greater mobility of the material being screened on such flat-body screens, and a slot opening that is larger in relation to the screen height optimally interacts with the improved screening effectiveness (screening performance).

[0034] However, with a design according to the invention, screens with filaments (threads / wires) made of plastic, e.g., nylon screens, can also be readily used. A further advantage of the inventive approach is that the thickness of the insert frame with screen is not predetermined by the design of the screen frame (only the height of the clamping frame, see below, may need to be adjusted). Therefore, different screens can be used flexibly in a mill system and, under certain circumstances, in one and the same plansifter.

[0035] In addition to the screen frame and the insert frame, some embodiments of the screen device also include a clamping frame. The clamping frame is arranged so that the insert frame is fixed between the support and the clamping frame. The clamping frame can fit precisely into the recess formed within an upper section (above the support) of the surrounding side wall.

[0036] In embodiments, the clamping frame can be shaped so that its inner surface is flush with the inner surface of the lower section (below the clamping frame) of the surrounding side wall. Additionally or alternatively, the clamping frame can be flush with the upper edge of the surrounding side wall, i.e., its height can correspond to the height of the upper section of the surrounding side wall, minus the thickness of the insert frame.

[0037] The clamping frame can, for example, be shaped like a rectangular profile. The clamping frame can also be made of metal, possibly with a thermally insulating filler material.

[0038] In one group of embodiments, the screening device has an upper stacking structure on the top side and a lower stacking structure on the bottom side at the identical horizontal position (x-y position if a coordinate system is defined whose z-axis corresponds to the vertical), wherein the upper stacking structure and the lower stacking structure are coordinated with one another such that when several of the screening devices are stacked, the upper screening device is defined in its horizontal position relative to the lower screening device. The upper stacking structure has a first ramp, and the lower stacking structure has a second ramp, wherein the first and second ramps abut one another in a force-transmitting manner when a lower and an upper screening device are stacked on top of one another.

[0039] A ramp in the sense of this text is formed by a surface section which is flat in some areas and inclined to the horizontal and vertical.

[0040] Because the first and second ramps rest against each other in a force-transmitting manner, the upper screening device is not only supported in relation to the lower screening device on which it rests, but is also aligned in its horizontal position, without the need for precisely matched groove and rib structures with the disadvantages discussed above. There is also an advantage in terms of the sealing effect, particularly in combination with the principle described below of providing the screen attached to an insert frame which is inserted into a trough-like structure of the screen frame, which is why the superimposed ramps are not arranged on the screen level, but above it. In particular, it can be provided that the upper screening device rests only on ramps (sloping surfaces) of the lower screening device and that there is therefore no force-transmitting contact of horizontal surfaces on top of each other.

[0041] In particular, the first ramp can slope outward and the second ramp inward. It has been shown that this approach can solve another problem: The screening device can be removed from a stack by slightly lifting it on one side and then pulling it toward that side (assuming there are no screening devices above it that rest their full weight on the screening device to be removed). In many embodiments, this can be done without the use of tools. This is a substantial advantage, because screening stacks are often not equally accessible from all sides.

[0042] It is particularly advantageous if the first ramp and the second ramp have an angle of between 25° and 65°, in particular between 30° and 50°, to the horizontal.

[0043] In addition to the first and second ramps, the upper stacking structure may also have an upper, inwardly sloping third ramp and the lower stacking structure may have a lower, outwardly sloping fourth ramp, whereby the slopes of the third and fourth ramps also correspond to each other (they may correspond to the slope of the first and second ramps, but this does not have to be the case).

[0044] Optionally, the clamping frame can form the third ramp or a region (part) thereof by having a bevel on the top inside. In addition to the screening device, the present invention also relates to a plansifter comprising at least one stack of screening devices of the type described here, in addition to a drive mechanism that imparts horizontally oscillating movements, e.g., circular movements, to this stack.

[0045] Embodiments of the invention are described below with reference to the drawings. In the drawings, like reference numerals denote like or similar elements. The drawings show partially corresponding elements in different sizes from figure to figure. They show:

[0046] Fig. 1 : a view of a plansifter with closed sieve compartments;

[0047] Fig. 2: a plansifter with open sieve stacks;

[0048] Fig. 3 : an exploded view of a screening device with screen, primary frame, clamping frame and insert frame;

[0049] Fig. 4: a view of two partially cut screening devices stacked on top of each other;

[0050] Fig. 5 shows the screening devices of Fig. 4 in plan, elevation and side view;

[0051] Fig. 6 is an enlarged detail of Fig. 5; and

[0052] Fig. 7 is a schematic sectional view of an edge area of ​​two stacked screening devices, with screening cleaners.

[0053] Figure 1 shows a plansifter 1 as used in grain mills. The plansifter comprises a plurality of screening compartments that are mounted in a space via a common suspension device 4 so that common horizontal oscillating movements are possible. A drive (not visible in Fig. 1) is designed to set the ensemble of screening compartments into, for example, horizontal circular oscillations. In addition, the plansifter has flexible feed lines 6 as the screening material inlet and likewise flexible outlet lines 7 as the screening material outlet. Each screening compartment has a stack of screening devices arranged one above the other. In the embodiment of Fig. 1, the screening compartments are provided in screening boxes 3, each of which forms a housing for the screening compartments. In such embodiments, the screening devices arranged one above the other in a stack can be guided and, under certain circumstances, also held by corresponding structures of the housing.

[0054] As an alternative to the sieve compartments provided in sieve box 3, sieve compartments can also be formed by open sieve stacks, in which a housing surrounding the sieve stacks is omitted.

[0055] Figure 2 shows an embodiment of such a plansifter with open sieve stacks in a particularly space-saving arrangement, although some elements (suspension device, feed lines, some outlet lines) are not shown. A frame 11 serves as the mechanical support structure. It forms a supporting frame for the upper sieve stacks 12 and the lower sieve stacks 13 and, in the illustrated embodiment, also accommodates drive modules not visible in the figure. The sieve stacks are attached directly or indirectly to the frame 11, for example, by means of a clamping system consisting of rods and / or belts and / or other means; the clamping system is not shown in Fig. 2.

[0056] Drive modules for a modular structure, which can be accommodated in a frame 11 of the type shown in Fig. 2, are described in Swiss patent application 000722 / 2022. However, the present invention is independent of the design of the plansifter drive and also works for plansifters with a central drive device, as is often found, and as is present centrally between the screen boxes 3 in a plansifter of the type shown in Fig. 1.

[0057] The upper sieve stacks 12 and lower sieve stacks 13 in Fig. 2 are each formed from a plurality of sieve devices 20 of the type described below, wherein the sieve devices are stacked directly on top of one another, and wherein a closing element 14 and 15, respectively, is present on the top side of the upper sieve stack 12 and on the bottom side of the lower sieve stack, through which the material to be sieved is fed in or removed. The sieves can have different mesh sizes, and the configuration of the sieve stacks can be selected by the user as required. A plansifter with closed sieve compartments as shown in Fig. 1 can also have sieve devices 20 according to the description below.

[0058] Figure 3 shows an exploded view of a screening device 20. Figure 4 shows a view of two partially sectioned, stacked screening devices 20. Figure 5 shows a top view of the screening devices 20 of Figure 4, as well as sections through planes AA and BB in the top view, i.e., Figure 5 shows a plan view, elevation view, and side view of the arrangement of Figure 4. Figure 6 shows detail D from section AA in Figure 5.

[0059] A sieve frame 21 forms a mechanical support structure of the sieve device 20. An insert frame 22 (primary frame) carries the sieve 23. For example, the sieve 23 can be designed as a metallic foil with perforations as sieve holes, as shown in the Swiss patent application 000837 / 2022, wherein the foil is welded onto the - also metallic - insert frame 22. In addition to the sieve frame 21 and the insert frame 22 with the sieve 23 attached thereto, the sieve device also has a clamping frame 24, which the - flat

[0060] - Insert frame 22 and the sieve 23 relative to the sieve frame 21.

[0061] The sieve frame has a circumferential side wall 30 and, towards the sides, two rows or one row or no rows of at least one passage channel 31 each, so that the side wall forms wall sections on the very outside, the very inside, and optionally between the passage channels 31. In the illustrated embodiment, two rows each with two passage channels 31 are present on two opposite sides (top and bottom in the plan view according to Fig. 5), while the other two opposite sides each have one row with two passage channels 31. The arrangement of passage channels can vary from sieve device to sieve device in order to guide fractions of the sieved material fed in through the feed lines and separated by the sieves as intended.

[0062] The insert frame 22 has an outer frame part 26, which forms a rectangle with rounded corners, as well as bars spanned by the screen 23, which can be seen in Fig. 3. The frame elements of the outer frame part as well as the bars spanned by the screen can each have rectangular or other cross-sections.

[0063] Below the sieve 23, a collection area is formed for each screening device, which is closed off at the bottom by a collecting base 33 of the sieve frame 21. The collection area is open on at least one side in order to discharge fine particles of the screening material that have passed through the sieve (the so-called through-fall) through a laterally arranged slotted opening 37 that opens into a passage channel 31. On the other sides, the collection area is closed off by a lower section 38 of the circumferential side wall 30 formed by the sieve frame. The other passage channels 31 of the upper screening device shown in the figures serve as drop channels, i.e. for passing screening material that comes from a screening device or a screening material inlet located higher up to lower down.

[0064] From the passage channel 31, into which the slot opening 37 opens, the fallout either reaches a passage channel 31 (more precisely: a fall channel) of the underlying screening device, as shown in the drawn configuration, or it reaches the screen of the underlying screening device.

[0065] This applies very generally to passage channels 31: A passage channel 31 either opens into an outlet line 7 (applies in particular to the lowest screening device), a passage channel 31 of the screening device below or, if applicable, a drive module arranged between screening devices 20, or the screen of the screening device below extends below the passage channel 31, so that the screening material passes from the passage channel onto the screen of the screening device below.

[0066] The screen 23 and the insert frame have lateral screen passage openings 41 on the screen level, through which screening material portions not screened through the screen (the so-called reject or transition) can fall. The screen frame is designed such that the collecting tray does not extend below the screen passage openings 41. Rather, depending on the desired configuration, the reject passes through the screen passage openings - and possibly a shortened associated passage channel below the screen passage opening - either into a passage channel 31 of the underlying screening device, or, as shown in the configuration of the present figures, onto the screen 23 of this underlying screening device 2. In the example shown, rotating the screen frame by 90° or 270° can cause the reject from the screen passage opening 41 to fall into a passage channel 31 (fall channel) rather than onto the next screen below.This makes sense, for example, once the screening process is complete. This discharge can then be transferred from the screener to another roller mill via drop channels.

[0067] The sieve frame 21 forms a circumferential support for the insert frame 22. Where the collecting area is closed off at the sides by the lower section 38 of the circumferential side wall 30, the support can be formed by a shoulder 34, while elsewhere, above the lateral slot opening 37, it is formed by an inwardly projecting projection 35. The support is uninterrupted along the circumferential line of the insert frame 22.

[0068] In embodiments, the sieve frame is at least partially metallic. In such embodiments, the collecting base can be formed by a base plate and the surrounding side wall can be constructed in several parts, with several wall elements, for example with an outer wall element which forms the outer wall surface, a lower inner wall element which forms the inner wall surface of the lower section 38, an upper inner wall element which forms the inner wall surface of the upper section 39, and several passage channel wall elements which surround the passage channels. A thermally insulating filling material can be arranged in the spaces between the wall elements. The shoulder 34 and the projection 35, i.e. the support, can be formed by an intermediate base.

[0069] The dimensions of the screen frame 21 on the one hand and the clamping frame 24 on the other hand are coordinated so that the clamping frame fits exactly into the receptacle that is created within the upper part of the surrounding side wall.

[0070] In particular, the dimensions of the screen frame 21 and the clamping frame 24 are matched to one another in such a way that the inner surface of the lower part 38 is flush with the inner surface of the clamping frame 24, as can be clearly seen, for example, in Fig. 5 (sections AA and BB) or also in Fig. 6.

[0071] In addition, the height of the clamping frame 24 is adapted to the distance between the support and the upper edge 40 of the surrounding side wall as well as to the thickness of the insert frame 22, so that the upper edge of the clamping frame 24 is at the same height as the upper edge 40 of the surrounding side wall, so that the clamping frame 24 acts like a part of the sieve frame 21 when the sieve devices 20 are stacked and can be perceived.

[0072] In contrast to the prior art, no seal is required where the insert frame 22 rests on the support (shoulder 34, projection 35). This is due to the design of the sieve frame 21 with the circumferential (vertical) side wall 30, whereby the insert frame is inserted into a trough-like structure formed by the sieve frame. Due to this design, sieved material can only escape past the sieve 23 and the sieve passage openings 41 if it passes outwards between the clamping frame 24 and the insert frame 22, downwards along the outer edge of the insert frame 22, and then back inwards between the insert frame and support. This design acts like a labyrinth seal, which is sufficiently effective even if there is no separate seal with a sealing (e.g., elastic, elastically deformed) material, e.g., between the clamping frame and the insert frame.In particular, in Figure 6, it can be seen that the screening devices 20 have an upper stacking structure and a lower stacking structure at corresponding horizontal positions (xy positions), see the Cartesian coordinate system indicated in the upper and right panels of Figure 5. When the screening devices are stacked on top of each other as intended, the lower stacking structure of the upper screening device rests on the upper stacking structure of the lower screening device.

[0073] The upper stacking structure includes an outwardly sloping first ramp 61, upon which rests an inwardly sloping second ramp 62 of the lower stacking structure of the upper screening device 20. In the illustrated embodiment, the outwardly sloping first ramp 61 and the inwardly sloping second ramp 62 are flat and parallel to each other. They form an angle of between 25° and 65°, in particular between 30° and 50°, to the horizontal.

[0074] “Inside” and “outside” are to be understood in relation to the screening device as a whole, ie “inside” is the side of a wall facing the screen and the collection area, while “outside” is the opposite side, on the left in Figure 6.

[0075] The upper and lower stack structures are designed such that the first and second ramps 61, 62 rest on one another in a force-transmitting manner. Therefore, there is generally no force-transmitting contact with the upper edge 40 - the surface of the screen frame runs horizontally there, or is curved in alternative embodiments. Rather, a distance a results between the upper edge 40 and the lower counter surface 50, whereby the distance a can be very small under certain circumstances - depending on manufacturing tolerances - and can amount to 1-2 mm or even less. In the illustrated embodiment, the upper stack structure, in addition to the outwardly sloping first ramp 61, also has an upper, inwardly sloping third ramp 63, and correspondingly, the lower stack structure has a lower, outwardly sloping fourth ramp 64.Therefore, the centering effect of the ramps also acts locally, for each pairing of a wall section of the upper screening device with a wall section of the lower screening device. This ensures that the stack structure is very stable even when the walls are only thin and therefore still slightly flexible.

[0076] Due to the passage channels 31, the sieve frames 21 have several wall sections depending on the configuration in vertical section (sections AA and BB in Fig. 5 and Fig. 6). In the illustrated embodiment, for example, there are two wall sections on each of two sides, and three wall sections on the other two sides, corresponding to the two rows of passage channels. With several wall sections per side, the stack structure shown is present at least on the outermost wall in each case, and for example on every wall. In the illustrated embodiment, each wall has a stack structure of the type described, which can also be seen in Fig. 5 in sections AA and BB and in Figure 6.

[0077] In the innermost wall section, the inwardly sloping third ramp 63 is not formed by the screen frame, but by the clamping frame 24, which is shown on the right in Fig. 6.

[0078] The inwardly sloping second ramp 62 of the lower stack structure and, if applicable, its outwardly sloping fourth ramp 64 are each formed in the illustrated embodiment by a downwardly projecting outer or inner rib 51 or 52 of the sieve frame 21, so that the walls of the sieve frame 21 are concave on the underside. Accordingly, the walls of the sieve frame are convex on the top. This has the advantage that residues cannot accumulate in a groove (or other concave upper structure) over time. However, a reverse configuration is not excluded - also due to the very good sealing properties of the sieve frames. This means that it is also possible for the outwardly sloping first ramp of the upper stack structure to be formed by an upwardly projecting rib and, conversely, for the walls of the sieve frame to be convex on the underside.

[0079] Figure 7 shows a schematic cross-section through two stacked screening devices in an edge region (ie, the illustration is cut off) and with a schematically illustrated screening cleaner 51 in the collection area. The height s of the lateral slot opening 37 is practically the same as the height h. a of the collection area, ie, the distance between the collecting tray 33 and the screen 23 (more precisely: between the top of the collecting tray and the bottom of the screen). This allows the height h to be adjusted for a desired lateral screenings throughput away from the collection area through the lateral slotted opening 37 into the passage channel. aof the collection area, which leads to a reduction in the height of the screening device as a whole (and thus to the possibility of providing more screening devices for a given height of the plansifter or of reducing the height of the plansifter for a given number of screening devices) and / or of increasing the height s of the slotted opening 37 in order to achieve a higher throughput. This advantage is made possible, among other things, by the fact that the insert frame is designed as a comparatively thin plate, e.g. a metal plate with recesses for the surfaces spanned by the screen as well as the screen passage openings. The insert frame can have a thickness of, for example, at most 5 mm, in particular at most 4 mm or at most 3 mm and, for example, between 1 and 2.5 mm.Because the slotted opening 37 essentially covers the entire height of the collection area and thus also of any screen cleaners 51 present in the collection area, measures can be provided to prevent a screen cleaner 51 from passing through the slotted opening 37 and, for example, becoming jammed in a passage channel. In the illustrated embodiment, the screen frame has retaining structures 36 in the form of bars protruding from the collection base 33, the spacing of which is selected such that no screen cleaner can pass between them. The retaining structures are arranged at least along the slotted opening 37. In the illustrated embodiment, there are also retaining structures 36 that segment the collection area, ensuring that each segment retains its screen cleaner or cleaners.

[0080] Sieve cleaners are optional: depending on the design of the collection area, they may also be superfluous and omitted, especially since, as described, the height s of the lateral slot opening can be particularly large without the sieve device being too high.

[0081] Another optional feature of the screening device can also be seen in Fig. 7: the collecting tray 33 is particularly thin compared to the prior art, in that the collecting tray—and, for example, the entire screening frame—is metallic, e.g., made of a sheet metal, such as sheet steel. The thickness of the collecting tray can be, for example, a maximum of 2.5 mm, in particular a maximum of 2 mm, a maximum of 1.5 mm, or a maximum of 1 mm, and, for example, between 0.3 and 0.8 mm.

[0082] This reduced thickness of the collecting base - which can be achieved independently of the reduced thickness of the insert frame - also contributes to the fact that for a given height h cof the inlet area between the screen 23 and the collecting floor of the overlying screening device, the screening device as a whole can be particularly flat, ie the height h of the screening device can be particularly low - and / or the height h c The inlet area (the “swallow”) can be larger than in the state of the art in order to further increase the absorption capacity of the screening device and thus ultimately the efficiency.

[0083] In sum, with a combination of these described concepts, the height h of the screening device can be adjusted in relation to the height s of the lateral slot opening and / or in relation to the height h cof the inlet area should be particularly low. This allows for optimization of the plansifter, whereby, depending on requirements, the number of screening devices per plansifter can be increased (by reducing the height h compared to the state of the art) and / or the throughput per screening device can be improved (increasing the height s of the slot and / or increasing the height h c of the inlet area). The optimization can be carried out depending on the properties of the material to be screened and can take these properties into account.

Claims

PATENT CLAIMS 1. Screening device for a plansifter, comprising a screen frame (21) and an insert frame (22) with a screen (23) attached thereto, wherein the screen frame has a circumferential side wall (30), characterized in that the screen frame (21) has a support on which the insert frame (22) rests, in such a way that the circumferential side wall (30) surrounds the screen and extends above the screen (23), so that the screen lies below an upper edge (40) of the circumferential side wall.

2. Screening device according to claim 1, wherein the support is formed at least in part by a shoulder (34) of the circumferential side wall (30).

3. Screening device according to claim 1 or 2, wherein the support runs along a circumference of the insert frame without interruption.

4. Screening device according to one of the preceding claims, wherein the screen frame (21) forms a collecting base (33) below the screen (23) onto which material screened through the screen (23) passes, wherein the collecting base (33) is formed by a metal sheet and / or wherein the collecting base (33) has a thickness of at most 2 mm, in particular at most 1.5 mm.

5. Screening device according to one of the preceding claims, wherein the screen frame (21) forms a collecting base (33) below the screen (23) onto which material screened through the screen (23) passes, wherein the collecting base (33) is arranged at the bottom of the screen frame (21).

6. Screening device according to one of the preceding claims, wherein a slotted opening (37) is formed in the circumferential side wall below the screen, through which slotted material present on the collecting base (33) can pass into a passage channel (31), wherein a height (s) of the slotted opening is at most 20% or at most 15% smaller than the distance (h a ) between the collecting base (33) and the sieve (23).

7. Screening device according to one of the preceding claims, comprising a plurality of retaining structures (36) projecting upwards from the collecting base (33) to limit the movement of screen cleaners (51).

8. Screening device according to one of the preceding claims, wherein the insert frame (22) is metallic and / or has a thickness of at most 3 mm.

9. Screening device according to one of the preceding claims, comprising a clamping frame (24) which is arranged above the insert frame (22) and within an upper part (39) of the circumferential side wall (30).

10. Screening device according to claim 9, wherein the clamping frame (24) is flush on the top side with an upper edge (40) of the circumferential wall of the screen frame (21).

11. Screening device according to one of the preceding claims, wherein the screen (23) is designed as a flat body with through holes. - TI - Screening device according to claim 11, wherein the screen (23) is metallic. Screening device according to one of the preceding claims, wherein the screen frame has an upper and lower stacking structure at corresponding positions on the upper side and lower side, respectively, wherein the upper stacking structure has a first ramp (61) and the lower stacking structure has a second ramp (62), wherein the first ramp (61) and the second ramp (62) bear against one another in a force-transmitting manner when a lower and an upper screen device are stacked on top of one another. Screening device according to one of the preceding claims, wherein two rows of passage channels (31) are formed on at least one side of the circumferential side wall (30).A screening device according to one of the preceding claims, wherein the circumferential side wall (30) is formed by a plurality of sheet metal pieces, with a thermally insulating filler material being present in the spaces between sheet metal surfaces. A plansifter for fractionating ground grain products for a grain mill, comprising at least one stack with a plurality of screening devices according to one of the preceding claims, as well as a screening material inlet (6) and a screening material outlet (7), wherein the plansifter is further configured to set the stack in oscillating movements in order to promote the at least partial passage of screening material introduced through the screening material inlet through the sieves (23) of the screening devices.

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