Machine for fractionating crushed grain products

Abstract

The planshifter or grain refiner comprises at least one sieve section with an arrangement of several sieve elements with sieves (23). The sieve section can be vibrated, for example in the form of a swirling movement. At least one of the sieves (23) is designed as a flat body, in particular a metal sheet. Here, the sieve holes are present as through-holes. According to a first option, the sieve can be present as a metal sieve with etched through-holes. According to a second option, the metal sieve can be manufactured by additive methods. It has been found that by providing the sieve as a flat body with through-holes, the efficiency of the fractionation process can be significantly improved compared to woven sieves.

Description

[Technical field]

[0001] The present invention relates to a machine for fractionating a ground grain product, such as a planshifter or grain refiner. [Background technology]

[0002] Machines for fractionating milled grain products serve to separate the constituents of the milled product into coarser or finer granular constituents, and under certain circumstances also into constituents of different densities, and to remove foreign bodies from the milled product. The separation of the milled product into different granular constituents is also called "grading" or "fractionation". In particular, planshifters and so-called grain refiners ("cleaners") are known as machines for fractionating milled grain products. Planshifters are generally used in the flour milling industry to fractionate milled grain products during and after passing through roller mills in grain mills. Planshifters can also be applied in the so-called controlled sifting, i.e. the sieving of flours that are ready for sale as such. Grain refiners serve to separate grain constituents after the milling process or even in steps during the milling procedure.

[0003] The procedure of fractionating the ground grain product should not be confused with a previous washing procedure in which the grain kernels are subjected to, and similarly relatively coarse sieves are used, in order to separate straw, stones, foreign matter, seedlings or sand from the grain.

[0004] The planshifter comprises a sieve section, each of which comprises a stack of sieves acting as a planar sieve. The sieves are each suspended on a primary frame, a so-called "loom", which is inserted into a sieve frame (herein called "secondary frame"). The sieve sections are subjected to a horizontal vibration movement, in particular a circular vibration in the sieve plane, by means of a suitable drive mechanism. Generally, so-called sieve cleaners, i.e. mobile elements driven by the movement of the sieve sections and the movement of the sieve sections relative to the respective sieves, which free the respective sieves from clogged sieving product portions, are also applied to the planshifter.

[0005] As regards grain refiners, the applied sieves are likewise arranged in several layers and are likewise vibrated. However, in contrast to plane sieves such as those used in planshifters, they are classified as throwing sieves, since they do not (simply) vibrate in the sieving plane. Furthermore, as regards grain refiners, an air flow is generated to which the sieved product is exposed during the sieving procedure.

[0006] Generally, sieves of various mesh sizes are applied in a machine for fractionating the ground grain product, thereby allowing fractionation into three or more constituents, which are suitably packaged for sale or subjected to further processing steps, for example a new pass through a roller mill.

[0007] Woven fabrics from plastic threads or filaments, e.g. PET or polyamide, are known as such plansifters or grain refiner sieves. Woven fabrics of metal wires are also available, especially for pre-sieving at larger mesh widths, as the high wear caused by this procedure must often be taken into account. Since the sieves are designed as woven fabrics, each mesh is square. Mesh width is defined here as the distance between adjacent filaments or wires.

[0008] For fixing, the sieves are placed on wood, plastic or metal looms envisaged for this purpose, pretensioned and glued in the tensioned state, for example by means of cyanoacrylate. The use of such adhesives, which may come into contact with the food to be processed, is increasingly considered to be disadvantageous.

[0009] So-called "shale shakers" capable of removing solid residues from excavated sludge, as occurs in the extraction of shale oil, are known from the crude oil industry. WO 2017 / 019580 proposes using metallic perforated plates as sieves, and it is claimed that all common methods by which metallic perforated plates can be created, such as laser drilling, chemical etching, spark erosion, water jet cutting, punching and further methods, can be considered for the size of the holes in an extremely wide range from 1 μm to 5000 μm. Such shale shakers are in no way suitable for the processing of crushed grain products.

[0010] DE 3041270 and FR 9851710 each teach a sieve for hammer mills or generally for grain products. The sieves are designed as metal sheets with elongated sieve slots. Due to the design of their elongated sieve slots, these sieves may not be suitable for machines in which a number of sieves form sieve sections, for example arranged one above the other, and in which the sieve sections are vibrated. Generally, the sieve sections in machines of the type described herein are subjected to a swiveling movement, so that generally sieve holes should be used that have a length essentially the same size as their width.

[0011] US 2,166,367 relates to a method for producing metal screens, i.e. screen structures for use in sieves, but also to a printing method. The method according to US 2,166,367 creates significantly more regular holes than the simple etching of holes into a metal sheet. The method consists of several steps and involves the galvanic deposition of a material on a specially manufactured matrix with protrusions. The method is relatively complex and laborious. For this reason alone, screen structures produced according to US 2,166,367 may not be suitable as sieves for industrial applications in machines such as planshifters or grain refiners.

[0012] In contrast, to date it is exclusively woven screens that have proven their worth for use in planshifters or grain refiners.

[0013] In the flour milling industry, there is a constant need to increase the efficiency of the fractionation process. The total per sieve area of ​​a defined mesh size depends on the number of meshes per sieve area. This number can be optimized by further increasing the ratio between the open sieving area and the total sieving area by using thinner filaments or wires, or it can be more precisely defined between the open sieving area and the net sieving area (the area of ​​the sieve minus the loom and possible rods, i.e. the area on which the sieve is freely suspended). However, due to the fact that stability must be maintained, limits are imposed on the optimization, which in practice sets a minimum limit for the permissible filament or wire diameter for each applied material. Other optimization possibilities, for example the use of optimized sieve cleaners, only lead to further improvements in efficiency to a limited extent. Summary of the Invention

[0014] It is therefore an object of the present invention to provide a machine for fractionating crushed cereal products, and a sieve element for such a machine, which overcomes the drawbacks of the state of the art and makes the screening process of milled products carried out in cereal mills more efficient.A further object of the present invention is to further develop the machine for fractionating crushed cereal products, so that it has additional functions and / or is suitable for new applications.

[0015] Machines of the type described herein comprise at least one sieve section, often arranged next to one another, each of which comprises an arrangement of several sieve elements with sieves. Typically, the sieve section comprises a stack of sieve elements. The machine is configured to vibrate the sieve elements, for example in the form of a gyratory vibration actuated by an unbalanced rotation, and actively induced movements are also conceivable. When speaking of "vibration" in the context of this document, this also includes circular movements, regardless of the method of their excitation. Typically, the sieve section is vibrated as a whole, i.e. the stack of sieve elements is subjected to a common, in particular gyratory, movement.

[0016] According to the invention, the sieve is designed as (at least one) flat body, for example of metal. Here, the sieve holes are present as through holes. Non-metallic materials are also conceivable, in particular materials with adequate dimensional stability suitable for etching and / or additive manufacturing methods, for example ceramic materials suitable for 3D screen printing methods, or hard thermoplastic or hardening (duroplastic) plastics.

[0017] A "flat body" is a foil or sheet, i.e. a consistent body that extends in two dimensions and has a particularly constant thickness (extension in the third dimension) that is at least an order of magnitude smaller than the extension in the two other dimensions (length and width). Such flat bodies tend to be recognized more as foils or as sheets, depending on the thickness. In particular, a flat body can also be a sheet in the broader sense of the term, and in certain embodiments, a flat body in this context is also a sheet in the narrower definition of the term, i.e. a metal product produced by rolling.

[0018] Surprisingly, it has been found that the design, not of woven filaments or wires as in the state of the art, but of flat bodies with through holes, significantly increases the effectiveness: the time required to pass a given amount of sieving product (flour, Dunst, semolina, grits, etc.) through a defined sieving area, all other relevant parameters being equal (mechanical excitation, size of sieve holes, number of sieve holes) can be significantly reduced.

[0019] It may be particularly advantageous if a defined edge around each through hole is formed between the upper and, for example, even the lower surface of the sieve on the one hand and the wall of the through hole on the other hand, the angle being about 90°. Such a pronounced edge is present when the upper surface merges with the wall of the through hole without a continuous curvature, i.e. when the average radius of curvature of the transition area, while still visible when considered microscopically, is much smaller than half the thickness of the flat body, for example smaller than one-fifth, one-eighth or one-tenth of the thickness of the flat body.

[0020] As known per se from sieves according to the state of the art, the through holes differ from slot-like holes in that they are essentially equal in width and length in the plane of the sieve. In particular, they are circular or have the shape of an approximately regular polygon. The average ratio of the longest extension of the through holes in the sieve plane to their smallest extension in the sieve plane can therefore be relatively small, for example not more than 1.5, in particular not more than 1.3, 1.2 or 1.1. Through holes with this property are suitable for machines in which the sieve elements in the plane are subjected to a uniform, for example swirling, movement. Moreover, they allow a good discrimination of the sieved product particles, even if these are not spherical, as is almost certainly the case with crushed cereal products.

[0021] In a first group of embodiments, starting from a metal sheet or a foil / plate of a different material, the sieve is produced by a material removal method. Among the material removal methods, in particular parallel methods are suitable, in which a material removal procedure is carried out simultaneously for all through-holes or for large groups of through-holes, for example for a complete consistent area of ​​the sieve. Such a method is in particular etching. Thus, the sieve element may comprise an etched metal sieve.

[0022] Etching creates through holes with walls that are approximately perpendicular to the sieve surface.

[0023] In a second group of embodiments, the sieve is manufactured by an additive process, thus a manufacturing method in which the sieve material is deposited layer by layer to create the sieve.

[0024] Also among additive manufacturing methods, essentially parallel methods are particularly well suited. For these essentially parallel methods, at least the hardening procedure is carried out in layers in parallel over the entire surface of the sieve, or at least over a partial surface. This is in contrast to methods in which the laser beam hardens selectively locally and therefore must move over the entire sieve surface. Essentially parallel methods can in particular be methods from the category of extrusion methods in the broadest sense, for which 2D forms are used, by which the material to be hardened is printed.

[0025] Such an essentially parallel method is the 3D screen printing method. In this regard, the suspension with the particles of the material that constitutes the object to be manufactured, and therefore here the sieve, is pressed in layers by a squeegee through a screen provided with a stencil, the so-called screen printing screen (which should not be confused with the screen (sieve) of the machine to be manufactured). The stencil here thus serves as a printing form in the context of the extrusion method and defines (in two dimensions) the shape of the body to be manufactured. Each layer is hardened before the next layer is deposited. After all layers have been deposited, further sintering can be performed for compaction. Thus, with regard to the application to the manufacture of sieves, a screen printing screen with a stencil representing the negative of the sieve to be manufactured is created and is subsequently used for additive manufacturing.

[0026] Manufacturing sieves using such additive methods also produces through holes having walls that are nearly perpendicular to the sieve surface and significant, well-defined edges between the sieve surface and the walls.

[0027] Thus, sieves of the type according to the invention, which apply to both groups of embodiments, have webs between the sieve holes, said webs being rectangular in cross section (i.e. essentially rectangular, as will be explained in more detail below) in contrast to the circular cross section of the filaments or wires of a woven sieve. Furthermore, in contrast to a woven sieve, the sieves form a planar structure, in respect of which the filaments or wires overlap one another at their intersections.

[0028] Geometrical differences can represent a way to explain the higher efficiency of the procedure according to the invention compared to the state of the art. In particular, the edges that occur on the upper side of the web with the sieve of the invention can have a significant effect. On the one hand, the edges make it less likely that particles subjected to random motion will collide with the surface and get stuck there, and more likely to collide with the edge of the etched sieve. Secondly, the edges can make it less likely that the temporarily stable structures that arise from the sieving product, such as structures that extend beyond the sieve holes, will occur.

[0029] However, the findings of the present invention do not depend on any particular explanation for the observed beneficial effects.

[0030] A further characteristic of etched sieves or sieves produced by additive manufacturing is the fact that there are no structures protruding beyond the plane of the sieve. This differs from punched structures such as the well-known coarse perforated plates, each of which has a sharp burr on one side while tapering conically from the other side. It has been found that the absence of such structures has a positive effect on the efficiency of etched sieves.

[0031] A further advantage is the fact that, compared to the state of the art, sieves as flat bodies with through holes are easier to clean, in particular by ultrasound.

[0032] The through holes can be arranged in a hexagonal structure, thus offset from one another row by row. This exploits a further advantage of the procedure according to the invention, which allows the arrangement of the sieve holes to be freely selected and is no longer limited to a rectangular arrangement. The hexagonal structure has the advantage that, for a given minimum web width, it is possible to arrange as many sieve holes as possible per sieve area. This again increases the efficiency gain.

[0033] This also applies to the shape of the sieve holes, which can also be freely determined within the limits dictated by the etching or additive manufacturing process, so that the shape as well as the arrangement of the sieve holes can be approximately hexagonal, which allows the ratio of open sieving area to net sieving area to be maximized for a given minimum web width.

[0034] For example, it can be assumed that the perforations of a very fine sieve of a machine, for example up to a mesh width of about 0.3 mm, are generally circular, whereas larger perforations are hexagonal.

[0035] The use of etched sieves or sieves produced by additive manufacturing, i.e. sieves with through holes produced by etching, is particularly advantageous with a mesh size of 0.08 mm to about 1 mm. Thus, the machine according to the invention comprises, for example, at least one sieve with through holes with a mesh width of 0.08 mm to 1 mm. In particular, the machine according to the invention may have at least one sieve with a mesh width of more than 0.3 mm and hexagonal through holes.

[0036] For non-square through holes, the mesh width is defined in this document as the square root of the area of ​​the through hole in a horizontal cross section.

[0037] The width of the web between the through holes may correspond to just short of the flat thickness. For webs with a non-constant width, this applies to the width at the narrowest point. In this specification, "approximately corresponding to the flat thickness" means that the web width is 40% or more or 50% or more of the flat thickness, and 160% or less or 130% or less of the flat thickness, and in particular may be between 60% and 100% of the flat thickness.

[0038] The manufacture of the sieves in the first group of already mentioned embodiments is carried out by etching (the industrial etching process is also referred to by the term "chemical milling", and in this document "etching" should generally be understood as a material removal method using a substance that attacks the material). Etching, in contrast to, for example, laser processing, has the advantage that the process is parallel, which can determine the efficiency of the manufacture, especially in the case of fine-mesh sieves. In particular, the sieve holes (through holes) can be etched from both sides, i.e. from above and below.

[0039] In the first group of embodiments, the sieve is designed so that the etching from above and below is asymmetric, with more material being removed from below, so that the narrowest place of the through-hole is located above the mid-plane of the flat body, which minimizes the possibility of particles of the sieving product becoming stuck in the through-hole.

[0040] In a second group of embodiments, in the case of additively manufactured sieves, in particular the layers from which the sieve is built are parallel to the two large surfaces ("upper and lower") of the flat body. In the second group of embodiments, the sieve is also in particular made of metal. In the second group of embodiments, there is not necessarily a defined narrowest point between the planes of the sieve defined by the large surfaces.

[0041] If the flats from which the sieve is produced are metallic, there is also the option for the flats to be produced from a magnetic (i.e. magnetizable, and therefore ferromagnetic or ferrimagnetic) material, for example magnetic steel. Ferromagnetic stainless steels (in particular martensitic or ferritic steels or steels with corresponding parts) are known as steels with hard magnetic and soft magnetic properties. The use of magnetizable materials has the advantage that in the event of a break in the sieve, which may occur over time, there is the possibility of removing the magnetic sieve fragments from the sieving product by exposing the area with the fragments to a magnetic field.

[0042] The use of metals or certain plastics as the material of the flat body has the further possible advantage that the sieve can be fixed to the primary frame by welding. This makes the use of adhesives unnecessary. A prerequisite for weldability is the design of the sieve as a flat body with through holes. Only with this design can the forces acting on the web between the through holes be sufficiently distributed over the entire periphery of the sieve and from there onto the primary frame. As is known from the state of the art, welding of the wires forming the woven wire sieve is theoretically possible as well, but can be cumbersome and unrealistic.

[0043] Apart from the primary frame, to which the sieves are directly connected and which can therefore also be considered as part of the sieve, the sieve element may comprise a secondary frame on which the primary frame is placed or which otherwise holds and / or receives the primary frame. The secondary frames of the sieve sections may be stacked on top of each other and / or held by the sieve section housing and may function as modules of such a housing. However, a secondary frame in addition to the primary frame is not essential. It is also possible that the primary frames are directly attached to the sieve section housing and / or stacked on top of each other and thus function as sieve frames. In that case, the sieve element consists only of the primary frame on which the sieves are fixed.

[0044] Apart from machines for fractionating comminuted cereal products, such as planshifters or grain refiners, sieves for use in such machines, the use itself and methods for manufacturing sieves for such machines are also the subject of the present invention. In many embodiments, sieves for machines for fractionating comminuted cereal products have a mesh size of 100 cm 2 More than 0.35m, most at least 2 It has a relatively large area.

[0045] The sieve according to the method according to the invention can be in one piece, i.e. produced with a single flat body, however it is also possible to use two or more flat bodies, for example two or more flat bodies as strips or parts can be placed next to each other and fixed to the primary frame.

[0046] Apart from the outer frame part which fits the area of ​​the sieve, the primary frame to which the sieve is directly fixed can also comprise rods on which the sieve is suspended, in which case the sieve is for example not only fixed to the outer frame part but also to the rods.

[0047] With respect to the sieves of the first group of embodiments, the manufacturing method includes providing a flat body and creating through holes from both flat sides in a material removal process, for example etching.

[0048] For the sieves of the second group of embodiments, these steps are replaced by additive manufacturing methods. This involves the provision of a suspension, which has particles, in particular metallic (or made of another suitable, for example weldable, material) suspended in a solvent, and under certain circumstances further components, such as binders or other additives. In a further step, the method involves depositing the suspension in layers, each layer having a shape corresponding to the shape of the flat body with the through-holes (horizontal cross section) to be made. This can be done using a stencil (in 3D screen printing) or, in the case of non-parallel methods, also by selective hardening with a laser beam. In the former case, in particular, each layer after deposition is at least partially hardened before the next layer is deposited. This hardening can also be done as an actively induced step, for example by irradiation with electromagnetic radiation (infrared or possibly visible and / or UV) or by the inflow of hot air by a hot air blower, or and / or by another mode of energy supply. Alternatively, in principle, it is also conceivable that the step is carried out passively by the hardening of the material itself, for which sufficient time is allowed.

[0049] What the methods according to the first group and the methods according to the second group have in common is the fact that between the surfaces (i.e. upper and lower) on the one hand and the walls of the through-holes on the other hand a very flat surface with pronounced edges results, and this is true despite the very small size of the through-holes due to the application. For the methods according to the first group, the pronounced edges result from the properties of the applied material-removing etching process. For the methods of the second group, the pronounced edges result from the fact that the successively deposited layers are always relatively thin compared to the overall sieve thickness and that the specificity of the method allows each layer to have exactly the same dimensions.

[0050] This sharp edge characteristic distinguishes the sieves produced by the described procedure, firstly, from the woven sieves known in the state of the art, and secondly, they also differ from the sieves known from US Pat. No. 2,166,367, in which the sieves are formed by molding techniques and in addition to the rounding already present in the applied mould, a rounding of the edges occurs due to the surface tension of the still flowable mass during the moulding process and also due to the mould removal process.

[0051] Moreover, this applies to both groups of embodiments, the method may include fixing the flats to the primary frame, for example by welding, in particular laser welding or spot welding. A particular advantage of the procedure according to the invention is that here it is not necessary to clamp the flats particularly tightly, but it may be sufficient to place them on the primary frame with the correct dimensions and then fix them to this. This makes it possible to avoid the use of disadvantageous adhesive and clamping devices.

[0052] The sieve according to the second group of embodiments may optionally be configured to allow automatic detection of a sieve break. For this purpose, apart from the electrically insulating material, the sieve comprises a strip conductor, in particular embedded in the electrically insulating material. The strip conductor forms electrodes in at least two places, in particular at the two ends of the strip conductor. The machine is then configured to determine, by means of a suitable sensor, whether an electrical contact exists between the two electrodes. If not, the strip conductor is interrupted, which is an indication of a sieve break. The machine can display the sieve break to the user, thus allowing the sieve to be replaced in time without causing damage due to the passage of unscreened sieved product through the sieve surface or sieve fragments arising in the sieved product.

[0053] A further aspect of the invention relates to the use of a sieve of the type described in this document and designed as a flat body with through holes as a sieve in a machine for fractionating crushed grain products, in particular in a machine of the described type, the sieve forming a sieve section (open or closed) in which a vibrating movement is brought about.

[0054] Yet another aspect of the invention relates to a new type of use of a machine for fractionating a ground grain product using sieves which are provided with a movement, e.g. a swiveling movement, to assist at least partial passage of the fractionated sieved product, at least one of the sieves being designed as a flat body with through holes.

[0055] This new type of application is the fractionation of spent grain. "Spent grain" here refers to the by-product that remains as a residue after dissolving the malt raw material in the production of beer or similar processes. Spent grain is a ground grain product, since cereals, such as barley, are crushed after malting and drying and before mashing, and thus subjected to a (relatively coarse) milling process.

[0056] Apart from the insoluble protein fraction and further substances, spent grain usually contains the husks of the applied grain, as is generally intended in practice. Due to these husks, spent grain is not suitable for further fractionation, due to the fact that the husks quickly clog the sieves of plan-sifters and similar machines. For this reason alone, spent grain is mainly used as animal feed. However, due to its richness in protein, spent grain may also be suitable for the production of nutritional foods for humans, such as meat substitute products. Therefore, an efficient method for sieving husks and other coarse constituents from spent grain would be desirable.

[0057] In tests it was found that, in contrast to known types of machines (plan sifters or even throwing sifters, and other sieves with conventional woven sieves), with respect to machines designed according to the invention as flat bodies with through holes, and in particular with sieves with pronounced edges between the surface and the wall of the through holes, no clogging was observed when the spent grain was sieved. In contrast, and indeed surprisingly, it was found that this type of machine with flat sieves is suitable for fractionating the spent grain without further ado. This solved a problem that could not be solved by the state of the art.

[0058] Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings, in which the same reference numerals refer to the same or similar elements, and the drawings show elements that are different sizes from one drawing to another, but partially correspond to one another. [Brief description of the drawings]

[0059] [Figure 1] FIG. 1 is a diagram of a planshifter. [Diagram 2] A stack of sieves. [Diagram 3] FIG. 2 is an exploded view of a sieve element having a sieve, a primary frame, and a secondary frame. [Figure 4] It is a primary frame having a sieve. [Diagram 5]1 is a schematic detail of a sieve having a hexagonal structure. [Figure 6] Also shown is a schematic detail of a sieve having a square grid arrangement. [Figure 7] FIG. 6 is a cross-sectional view through the sieve according to FIG. [Figure 8] FIG. 2 is a cross-sectional view through a sieve according to the state of the art. [Figure 9] 11A-11C are schematic diagrams of alternative cross-sectional shapes. [Figure 10] FIG. 1 is a cross-sectional view through a sieve produced by additive manufacturing. [Figure 11] FIG. 1 shows the measured grade efficiency curves of a sieve designed as a flat body with etched through holes compared to a sieve according to the state of the art. [Figure 12] FIG. 13 is a horizontal section through a sieve with automatic sieve break recognition. [Figure 13] FIG. 13 is a detailed view of a section through the sieve according to FIG. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Figure 1 shows a planshifter 1 applied in grain mills as an example of a machine for fractionating crushed grain products. The planshifter comprises a number of sieve sections 3 assembled in space such that a common horizontal oscillatory movement is possible by means of a common suspension device 4. A drive device (not visible in Figure 1) is configured to oscillate the assembly of sieve sections, for example in a horizontal direction. Furthermore, the planshifter comprises a flexible feed conduit 6 as a sieved product inlet and a flexible outlet conduit 7 as a sieved product outlet.

[0061] Each sieve section 3 comprises a stack of sieve elements 11, which are shown diagrammatically in Fig. 2 and each have a sieve, which can have different mesh widths. Furthermore, there is a sieve product guide, which is for example transverse to the sieves, by means of which a part of the sieved product that has not been sieved (for example guided transversely to another sieve element, for example further below) and possibly even a part of the sieved product that has been sieved is further conveyed, this being the case for each sieve. Overall, the sieve sections are designed in such a way that a selection of the sieved product fed into sieved product parts of different grain sizes is achieved, whereby depending on the sieved product fed into the different sieve product discharge conduits 7, the sieve product parts have different properties.

[0062] According to the invention, this principle, which is known per se, is implemented in such a way that at least some of the applied sieves are present, for example as etched or additively manufactured sieves, for example as metallic flat bodies with through holes.

[0063] As for grain refiners, there are several sieve elements that can be arranged one above the other, similar to planshifters. As for grain refiners, the number of sieves arranged one above the other, generally a "stack of sieves", is often less than in planshifters, rather they do not speak of a sieve deck. In contrast to planshifters, the vibration movement to which the sieves are subjected is different, which is why they function as throwing sieves. The subsequent description of the sieve elements and the nature of the sieves generally relates to machines for fractionating crushed grain products, among such planshifters, and to grain refiners.

[0064] Figure 3 shows diagrammatically an exploded view of the sieve element 11. A sieve frame 21 (secondary frame) serves as a support structure. Furthermore, structures not shown in Figure 3 can be provided for guiding a so-called sieve cleaner, which is also not shown in the drawing and can be present as an option, for example to tap the sieve from below. The actual sieve 23 is fixed to a primary frame 25, which can be placed in and guided by the sieve frame 21.

[0065] The primary frame 25 comprises an outer frame portion 26 forming a rectangle and rods 27 over which the sieve 23 is suspended. The frame elements of the outer frame portion 26 and the rods 27 over which the sieve is suspended may each have a rectangular or other cross section.

[0066] The primary frame 25 on which the sieve 23 is fixed is depicted in Fig. 4. An advantage of the invention is that the fixing can optionally be performed by a welded connection, for example a spot welded connection. The corresponding weld spots 31 are shown diagrammatically in Fig. 4.

[0067] In an embodiment, the screen is not only welded onto the outer frame part 26 but also onto rods 27, onto which the screen 23 is suspended, for example also by means of spot welded or laser welded connections.

[0068] The metal sheet has a moderate degree of elasticity in the plane of the metal sheet. This property is particularly advantageous in the context of the present invention, since the sieve can be fixed to the loom 25 without the need to use means for tensioning along the plane, said means being specifically envisaged for this and known for woven sieves. In contrast, the flat body with the through holes only needs to be placed on the frame and then connected to it, for example by the above-mentioned spot welded connection or laser welding. The use of adhesives is also eliminated, which should be considered as an advantage for components that come into direct contact with food.

[0069] FIG. 5 shows a schematic detail of the sieve 23. The through holes 42 are present in a hexagonal arrangement. Moreover, the shape of the through holes 42 is approximately hexagonal. Depending on the size of the through holes 42, such a hexagonal shape as a matter of manufacture can be achieved to a greater (given larger through holes, i.e. when the sieve is of a relatively large mesh) or to a lesser extent, for example if the sieve is manufactured by etching. In very fine mesh sieves, the shape of the through holes is approximately circular depending on the manufacturing method. However, the advantages of the hexagonal arrangement continue to exist regardless of the actual shape.

[0070] Although hexagonal arrangements and shapes are particularly advantageous, the sieve can in principle have any, generally regular arrangement and any shape of through holes. Figure 6 shows a square lattice arrangement with square through holes, which occurs automatically in the case of woven sieves and can optionally be present in the sheet metal or other flat-body type sieves described herein. Figure 6 also shows the definition of the mesh width w, which is defined as the width of the intermediate space between adjacent filaments (not, for example, the distance between the axes of the filaments), and if the lattice is non-planar, this definition applies to the projections on the sieve surface.

[0071] For a sieve having non-square perforations, such as that of FIG. 5, the mesh width can be defined as the square root of the area a of the perforations in horizontal cross section, i.e., the mesh width that would result if the perforations had area a but were square.

[0072] Depending on the shape of the through-hole, it can be assumed that the area is deliberately selected to be somewhat smaller or even somewhat larger than that of a square through-hole in order to achieve the same grain size. For example, very small through-holes, for example with a diameter of less than 0.3 mm, can be etched to give a roughly circular through-hole, and even additive methods can produce a slightly rounded shape of a very fine structure, selecting a diameter that gives an area of ​​only about 95% of the area a, which results in approximately the same selection as for a square through-hole with a mesh width √(a). Hexagonal through-holes can also be made by etching a sieve to have a somewhat larger mesh width, for example at least 0.3 mm, and the through-holes can also have an area a slightly smaller than the corresponding square through-hole with the same grain size effect.

[0073] A comparison of Figs. 5 and 6 also shows that for a given web width b st It has been shown that the ratio of open sieve area (an important variable for throughput through the sleeve) to net sieve area (which is generally given by the size of the sieve elements and cannot be influenced) is better for a given hexagonal arrangement and for a given approximately hexagonal through-hole than for a given conventional square arrangement, using mesh width and mesh width. For example, it has been found that for hexagonal through-holes, the open sieve area can be increased by about 4% when compared to a woven steel fabric, and by about 11% when compared to a woven plastic fabric (which requires somewhat thicker filaments), which represents a very significant increase in efficiency in industrial processes such as those carried out in grain mills.

[0074] Furthermore, however, tests have shown that, compared to the state of the art, the sieving throughput through sieves of the type according to the invention can be increased even more than could be explained by a larger open sieve area, as will be explained further below.

[0075] A vertical section of a sieve of the type according to the invention produced by etching is shown in FIG. 7. FIG. 7 also shows the web width b stcorresponds for example approximately to the thickness d of the flat body, i.e. the web has an aspect ratio of approximately 1. In FIG. 7 it can also be seen that the cross section of the web 41 is rectangular, for example approximately square, and considering the production by etching, in particular the etching is carried out from both sides and therefore from above and below, which is why a very slight narrowing of the through holes occurs towards the mid-plane, but without any significant negative effect on the result that can be achieved.

[0076] The corresponding cross section of a woven sieve according to the state of the art is shown in Figure 8.

[0077] A comparison of Figures 7 and 8 shows that in sieves of the type according to the invention, edges 44 occur along the web, whereas in woven sieves this is not the case. The presence of such edges 44, especially at the top, i.e. towards the product to be sieved, represents one possible explanation for the very large increase in efficiency achieved by the approach according to the invention. In comparison with the case of woven sieves with a circular cross-sectional structure, the probability that a powder or coarse grain particle or a group of such particles will form part of a stable structure at the top of the sieve may be much lower, and at the edges the probability of a downward deflection of the movement may be much higher.

[0078] First, FIG. 9 shows, in a schematic way, the principle that etching does not require equal etching depths from both sides during fabrication, and asymmetric configurations are also possible. In FIG. 9, there is almost twice as much etching from below compared to etching from above, and therefore the narrowest location is above the mid-plane. Such an asymmetric configuration with the narrowest location above the mid-plane may be advantageous, since there is less chance of particles getting stuck in the through-hole. This may further increase efficiency.

[0079] Second, FIG. 9 shows the web width b st It is shown that it is also possible to make the thickness d smaller than that already mentioned above.

[0080] Third, FIG. 9 also shows that, as discussed above, the angle between the upper surface of the sieve and the wall of the through hole does not have to be exactly 90° and can be somewhat less, even if there is a sharp edge which may be advantageous in certain circumstances.

[0081] Figure 10, like figure 7, shows a vertical section through a sieve of the type according to the invention, which is not produced by etching but by additive manufacturing. The dotted lines indicate that the sieve is made up of a number of layers 51, which run horizontally. The layered structure may be visible on the sieve, but does not necessarily have to be. The considerations explained by figure 7 with respect to size and shape (with edges 44) and by figure 9 with respect to web width also apply to the second group of embodiments, an example of which is shown in figure 10.

[0082] Example 1: Approximately 100 g of commercial wheat flour was applied to a sieve of dimensions 275 mm x 175 mm (net sieve area) with a hexagonal array of a total of 427'000 through holes produced by etching. The through holes have a dimension of a = 0.05309 mm, measured by CAD software. 2 The sieve had an area of ​​0.23, which corresponds to a mesh width of 0.23. The sieve was subjected to a horizontal gyrating motion (approximately 3 revolutions per second, with a diameter of the motion circle of 5 cm). After a total of approximately 25 seconds, the powder had passed through the sieve, except for a small amount of residual material.

[0083] An equal amount of the same powder was applied to an equivalent commercial nylon sieve (mesh width 0.236 mm, number of holes 426'000) and sieved under the same conditions (same sieve dimensions and net sieve area). After 40 seconds, a significant portion of the powder had still not passed through the sieve, so an additional sieve cleaner was placed on the sieve to aid the procedure. Only after another 20 seconds, thus a total of 60 seconds, had the powder passed through, except for a small remnant of an equivalent amount.

[0084] Thus, in this example, the efficiency was increased by well over a factor of two.

[0085] This example corresponds quite literally to a real application situation: ready-to-sell powders are usually sieved once more in so-called control sieves before delivery in order to filter out possible foreign bodies. In such a procedure sieves such as commercially available nylon sieves with a mesh width of 0.236 mm can be applied.

[0086] Example 2: As in Example 1, but rye flour was used instead of wheat flour as the sieving product. Rye flour is highly agglomerated, which makes it difficult to sieve. The improved efficiency of Example 1 was confirmed.

[0087] Example 3: As in Example 1, but using a sieve with a square arrangement of nearly square sieve holes produced by etching (the shape of the sieve holes is square with significantly rounded corners due to the etching process). The effective area of ​​the through holes was measured again by CAD. This corresponds to a square area with a mesh width of 236, i.e. 0.236 mm. Due to the swirling motion, practically the entire amount of 100 g of flour passes through the sieve already after 16 seconds. A new comparative measurement with the same amount of white powder, the nylon sieve of Example 1 and a mesh width of 0.236 mm, but without the use of a sieve cleaner, results in the flour not passing completely through even after 93 seconds, i.e. the remaining residue is already more than with the sieve according to the invention after 16 seconds.

[0088] Example 3 confirms that the arrangement and even shape of sieve holes tends to be secondary and that the benefits of the present invention result from the fact that the sieve has an inherently different structure than a woven sieve.

[0089] 11 shows, as comparative measurements, that the procedure according to the invention improves not only the efficiency of the sieving procedure but also the fineness of separation. Measurements were carried out with a sieve according to the invention and with a commercial nylon sieve according to Example 1.

[0090] The ground cereal product was sieved with the parameters according to Example 1. The so-called rejection, and thus the proportion of the sieved product that was not sieved, was analyzed with the aid of a commercially available laboratory device (manufacturer Microtrac) that utilizes the principle of dynamic image analysis (ISO 13322-2). In particular, the size distribution of the ground cereal product particles, in particular the minimum diameter x C,最小値 was determined as the characteristic quantity. C,最小値 is the smallest dimension of each particle, and for spherical particles, x C,最小値 corresponds to the diameter, which for ellipsoidal particles is twice the value of the smallest semi-axis. Figure 16 shows the so-called grade efficiency curves, i.e. the curves with x smaller than the value specified on the abscissa. C,最小値 0.05%. It can be seen that in the first curve 61 obtained with the machine according to the invention with the etched sieve the limit setting is significantly steeper (steeper slope) than in the second curve 62 obtained with the machine with the conventional sieve. From this it is directly evident that the machine according to the invention and the sieve element according to the invention are not only associated with an improved efficiency but also with an improved discrimination quality.

[0091] 12 and 13 show the possibility of providing a sieve element of the type according to the invention with additional functions, in particular automatic sieve break recognition. This possibility exists in particular for sieve elements manufactured by additive manufacturing, in particular 3D printing. The sieve element comprises at least one embedded strip conductor 71 which passes between two contacts 74. In the example of the embodiment shown, the path of the strip conductor 71 is serpentine. In the case of a sieve break 81, the strip conductor is interrupted, which can be checked by a simple sensor or a simple measuring device that checks whether an electrical connection exists between the two contacts 74.

[0092] The strip conductors 71 extend in a recessed manner, i.e. do not contact the upper or lower surfaces of the flats. In embodiments where these surfaces are metallic (i.e. the sieve elements are essentially metallic), there will be at least one electrically insulating layer 92 between the strip conductors 71 and the metal layer 81 on the surface, and likewise the layer carrying the strip conductors 71 can be filled with an electrically insulating material (i.e. can be electrically insulating at positions in the sieve element plane where no strip conductors are present). Suitable electrically insulating materials are the ceramic materials mentioned above or rigid thermoplastic or hardenable plastics.

[0093] In the example embodiment shown, apart from the (first) strip conductor 71, a second strip conductor 72 is present in another layer and also runs meanderingly, but has a different, in particular orthogonal, main direction. Thus, sieve breaks can be seen, such as the second shown sieve break 82, which runs so as not to cut the first strip conductor 71. The second electrode 75 for the second strip conductor is read out separately by the (first) electrode 74 of the first strip conductor 71.

Claims

1. A machine (1) for fractionating a pulverized grain product, comprising at least one sieving compartment (3) having a plurality of sieves (23), a sieving product inlet (6), and a sieving product outlet (7), wherein the machine is configured to vibrate the sieves (23) to assist in the passage of at least a portion of the sieving product through the sieves, and the sieving product enters through the sieving inlet, wherein at least one of the plurality of sieves (23) is designed as a flattened body having through holes (42).

2. The machine (1) according to claim 1, wherein the flattened body is made of metal.

3. The machine (1) according to claim 2, wherein the metal flattened body is a magnetic material.

4. The machine (1) according to any one of claims 1 to 3, wherein the sieve (23) is fixed to the primary frame (25).

5. The machine (1) according to claim 4, wherein the primary frame comprises an outer frame portion (26) extending along the periphery of the sieve and a rod (27) over which the sieve is stretched, and the sieve is fixed to the outer frame portion (26) and the rod (27).

6. The machine (1) according to claim 4, wherein the sieve (23) is welded to the primary frame (25).

7. The machine (1) according to any one of claims 1 to 3, wherein at least one of the through holes (42) of the plurality of sieves forms a hexagonal arrangement.

8. The machine (1) according to any one of claims 1 to 3, wherein at least one of the plurality of sieves has a hexagonal shape.

9. For the web (41) formed between multiple adjacent through holes (42), 0.5 * d < b ｓｔ < 1.6 * d, where d is the thickness of the flattened body, and b ｓｔ However, the machine (1) according to any one of claims 1 to 3, wherein the width of the web (41) is the width at its narrowest point.

10. The machine (1) according to any one of claims 1 to 3, wherein the flattened body forms an edge (44) around the through hole (41).

11. The machine (1) according to any one of claims 1 to 3, wherein it does not contain an adhesive that comes into contact with the sieve (23).

12. The machine (1) according to any one of claims 1 to 3, wherein the through hole is created by etching.

13. The machine (1) according to any one of claims 1 to 3, wherein the sieve is manufactured by an additive manufacturing method.

14. The machine (1) according to any one of claims 1 to 3, wherein the plurality of sieves (23) are configured to vibrate within the horizontal sieve plane, thereby the machine is a plan shifter.

15. The machine (1) according to any one of claims 1 to 3, wherein the plurality of sieves (23) are configured to vibrate so that the sieve surface is subjected to vibration, and thereby the sieves function as throwing sieves.

16. The machine (1) according to any one of claims 1 to 3, wherein at least one of the plurality of sieves (23) is equipped for automatic detection of sieve breakage by comprising strip conductors (71, 72) formed in an electrically insulating material, the strip conductors each forming electrodes (74, 75) at two locations, thereby allowing it to be confirmed whether the strip conductors (71, 72) between the electrodes (74, 75) are continuous or intermittent.

17. A regular arrangement of through holes (42) at least 100 cm ２ A sieve element for a machine according to any one of claims 1 to 3, comprising a flattened body having an area and a primary frame (52) to which the flattened body is fixed.

18. Use of a sieve designed as a flattened body with through holes (42) as a machine sieve (23) for fractionating the milled pulverized product.

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