Machine for fractionating ground cereal products

Abstract

The plansifter or the grain purifying machine includes at least one sieve compartment with an arrangement of several sieve elements with sieves. The sieve compartments can be brought into oscillations in the form of circling movements. At least one of the sieves is designed as a flat body. The sieve holes are present as though-holes. The sieve can be present as a metal sieve with etched through-holes or the metal sieve can be manufactured by way of an additive method. The flat body sieve with through-holes significantly improves the efficiency of the fractionating process.

Claims

1. A machine for fractionating ground cereal products, comprising at least one sieve compartment with a plurality of sieves, a sieving product inlet and a sieving product outlet, wherein the machine is configured to bring the sieve into oscillation movements, in order to assist in the at least partial passage of the sieving product through the sieve, said sieving product being in through the sieve inlet, wherein at least one of the sieves is designed as a flat body with through-holes, wherein for webs which are formed between adjacent through-holes, it is the case that: 0.5*d<bst<1.6*d, wherein d is the thickness of the flat body and bst is the width of the webs at their narrowest location.

2. The machine according to claim 1, wherein the flat body is metallic.

3. The machine according to claim 2, wherein the metallic flat body is magnetic.

4. The machine according to claim 1, wherein the sieve is fastened to a primary frame.

5. The machine according to claim 4, wherein the primary frame comprises an outer frame part which runs along a periphery of the sieve, as well as rods over which the sieve is spanned, and wherein the sieve is fastened to the outer frame part as well as to the rods.

6. The machine according to claim 4, wherein the sieve is welded to the primary frame.

7. The machine according to claim 1, wherein the through-holes of at least one of the sieves form a hexagonal arrangement.

8. The machine according to claim 1, wherein the through-holes of at least one of the sieves have a hexagonal shape.

9. The machine according to claim 1, wherein the flat body forms an edge around the through-holes.

10. The machine according to claim 1, which is free of adhesive in contact with the sieve.

11. The machine according to claim 1, wherein the through-holes are created by way of etching.

12. The machine according to claim 1, wherein the sieve is manufactured by way of an additive manufacturing method.

13. The machine according to claim 1, which is configured to bring the sieves into oscillations in a horizontal sieve plane, whereby the machine is a plansifter.

14. The machine according to claim 1, which is configured to bring the sieves into oscillations such that a sieve plane is subjected to oscillations, whereby the sieves act as throw sieves.

15. The machine according to claim 1, wherein at least one of the sieves is equipped for an automatic detection of sieve breakages by comprising a strip conductor which is formed in electrically insulating material, wherein the strip conductor forms an electrode each at two locations, whereby one can ascertain whether the strip conductor between the electrodes runs in an uninterrupted or interrupted manner.

16. A sieve element for fractionating ground cereal products, the machine comprising at least one sieve compartment with a plurality of sieves, a sieving product inlet and a sieving product outlet, wherein the machine is configured to bring the sieve into oscillation movements, in order to assist in the at least partial passage of the sieving product through the sieve, said sieving product being in through the sieve inlet, the sieve element comprising a flat body with an area of at least 100 cm.sup.2 with a regular arrangement of through-holes, as well as a primary frame, to which the flat body is fastened, wherein for webs which are formed between adjacent through-holes, it is the case that: 0.5*d<bst<1.6*d, wherein d is the thickness of the flat body and bst is the width of the webs at their narrowest location.

17. A machine for fractionating ground cereal products, comprising at least one sieve compartment with a plurality of sieves, a sieving product inlet and a sieving product outlet, wherein the machine is configured to bring the sieve into oscillation movements, in order to assist in the at least partial passage of the sieving product through the sieve, said sieving product being in through the sieve inlet, wherein at least one of the sieves is designed as a flat body with through-holes, wherein at least one of the sieves is equipped for an automatic detection of sieve breakages by comprising a strip conductor which is formed in electrically insulating material, wherein the strip conductor forms an electrode each at two locations, whereby one can ascertain whether the strip conductor between the electrodes runs in an uninterrupted or interrupted manner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiment examples of the invention are hereinafter described by way of drawings. In the drawings, the same reference numerals denote equal or analogous elements. The drawings show elements which partly correspond to one another in sizes which differ from one another from figure to figure. There are shown:

(2) FIG. 1 a view of a plansifter;

(3) FIG. 2: a sieve stack;

(4) FIG. 3 an exploded representation of a sieve element with sieve, primary frame and secondary frame;

(5) FIG. 4 a primary frame with a sieve;

(6) FIG. 5 schematically, a detail of a sieve with a hexagonal structure;

(7) FIG. 6 likewise schematically, a detail of a sieve with a square grid arrangement;

(8) FIG. 7 a cross section through the sieve according to FIG. 5;

(9) FIG. 8 a cross section through a sieve according to the state of the art;

(10) FIG. 9 schematically, an alternative cross-sectional shape;

(11) FIG. 10 a cross section through a sieve which was manufactured with an additive manufacturing method;

(12) FIG. 11 a measurement of the grade efficiency curve for a sieve which is designed as a flat body with etched through-holes, in comparison to a sieve according to the state of the art;

(13) FIG. 12 a horizontal section through a sieve with an automatic sieve breakage recognition; and

(14) FIG. 13 a detail of a cross section through the sieve according to FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

(15) FIG. 1 as an example of a machine for fractionating ground cereal products shows a plansifter 1 as is applied in cereal mills. The plansifter includes a plurality of sieve compartments 3 which via a common suspension device 4 are assembled in a space such that common horizontal oscillating movements are possible. A drive (not visible in FIG. 1) is configured to bring the assembly of sieve compartments into for example horizontally circling oscillations. Moreover, the plansifter includes flexible feed conduits 6 as the sieving product inlet as well as likewise flexible outlet conduits 7 as the sieving product outlet.

(16) Each sieve compartment 3 includes a stack of sieve elements 11 which are represented schematically in FIG. 2 and which are each with a sieve, wherein the sieves can have different mesh widths. Furthermore, a sieving product guide which for example is lateral with respect to the sieve is present, by way of which guide shares of the sieving product which are not sieved (which for example are led away laterally and for example to another sieve element which lies further below) and possibly also sieving product shares which are sieved are transported further, this being the case with each sieve. As a whole, the sieve compartments are designed such that a selection of the fed sieving product into sieved sieving product shares of a different grain size is effected, so thatdepending on the fed sieving productthe sieving product shares which are fed into the different sieve product discharge conduits 7 have different characteristics.

(17) This principle which is known per se, according to the present invention is implemented such that at least some of the applied sieves are present as for example metallic flat bodies with through-holes, for example as etched or additively manufactured sieves.

(18) Concerning grain purifying machines, as with plansifters, likewise several sieve elements which can be arranged above one another are present. Concerning grain purifying machines, one generally does not speak of sieve stacksthe number of sieves which are arranged above one another is often smaller than with plansiftersbut rather of sieve decks. In contrast to plansifters, the oscillation movement, to which the sieves are subjected, is different, which is why the sieves act as throw sieves. The subsequent explanations on the nature of the sieve elements and sieves generally relate to machines for fractionating ground cereal products, amongst such plansifters as well as grain purifying machines.

(19) FIG. 3 schematically shows an exploded representation of a sieve element 11. A sieve frame 21 (secondary frame) acts as a supporting structure. It can moreover include a structure which is not represented in FIG. 3, for guiding so-called sieve cleaners which are likewise not represented in the drawings and which can be present as an option, in order to beat the sieve for example from below. The actual sieve 23 is fastened to a primary frame 25 which can be placed into the sieve frame 21 and be guided by this.

(20) The primary frame 25 includes an outer frame part 26 which forms a rectangle, as well as rods 27, over which the sieve 23 is spanned. The frame elements of the outer frame part 26 as well as the rods 27, over which the sieve is spanned, can each have a rectangular or also other cross section.

(21) The primary frame 25 with the sieve 23 which is fastened thereto is drawn in FIG. 4. It is an advantage of the invention that the fastening can be effected optionally by way of a weld connection, for example a spot weld connection. Corresponding weld spots 31 are schematically represented in FIG. 4.

(22) In embodiments, the sieve is not only welded onto the outer frame part 26, but also onto rods 27, over which the sieve 23 is spanned, for example likewise by a spot weld connection or laser weld connection.

(23) Metal sheets in their plane have a certain moderate elasticity. This characteristics is particularly advantageous in the context of the present invention: the sieve can be fastened to the loom 25 without having to use means for applying a tension force along the plane, such means being envisaged especially for this and being known for woven sieves. In contrast, the flat body with the through-holes merely needs to be placed onto the frame and then connected to this, for example by way of the mentioned spot weld connection or by way of laser welding. The use of an adhesive also becomes superfluous, which is to be seen as being advantageous for a component which comes into direct contact with foodstuff.

(24) FIG. 5 schematically shows a detail of a sieve 23. The through-holes 42 are present in a hexagonal arrangement. Furthermore, the shape of the through-holes 42 is approximately hexagonal. Depending on the size of the through-holes 42, such a hexagonal shape inherently of the manufacture can be accomplished to a greater (given larger through-holes, i.e. when the sieve is comparatively large-meshed) or lesser extent, for example if the sieve is manufactured by way of etching. With very finely meshed sieves, an approximately round shape of the through-holes results depending on the manufacturing method. The advantages of the hexagonal arrangement however continue to exist independently of the real shape.

(25) Even if a hexagonal arrangement and shape are particularly advantageous, the sieve in principle can have arbitrarygenerally regulararrangements and arbitrary shapes of through-holes. FIG. 6 shows a square grid arrangement with square through-holes as automatically results in the case of woven sieves, and as can be present optionally with sieves of the type described here of a sheet metal or other flat bodies. FIG. 6 also shows the definition of the mesh width w which is defined as the width of the intermediate space between adjacent filaments (and not for instance for example the distance between the axes of the filaments); if the grid is non-plane, this definition applies to a projection onto the sieve surface.

(26) Concerning a sieve with non-square through-holes such as that of FIG. 5, the mesh width can be defined as the square root of the area a of the through-holes in the horizontal section, i.e. the mesh width which would result if the through-holes have the area a, but were to be square.

(27) Depending on the shape of the through-holes, one can also envisage the area being deliberately selected somewhat smalleror possibly somewhat largerthan with square through-holes, in order to achieve the same grading. For example, given approximately round through-holessuch result for example on etching very small through-holes of for example less than 0.3 mm diameter; with additive methods too, a slightly rounded shape arises with very fine structuresone can select a diameter which results in an area of approx only 95% of the area a, which then results in roughly the same selection as with square through-holes of the mesh width (a). With hexagonal through-holes toosuch can be produced with a somewhat larger mesh width of for example at least 0.3 mm with etched sievesthe through-hole can also have a little smaller area a than the corresponding square through-hole with the same grading effect.

(28) The comparison between FIGS. 5 and 6 also illustrates than with a given web width b.sub.st and mesh width, the ratio between the open sieve area (the variable of importance for the throughput through the sleeve) and the net sieve area (which is generally given by the dimensions of the sieve element and cannot be influenced) is better given a hexagonal arrangement and given approximately hexagonal through-holes than given a conventional square arrangement. It has been found that for example in the case of hexagonal through-holes, the open sieve area when compared to steel woven fabrics can be enlarged by roughly 4% and compared to plastic woven fabrics (which necessitate somewhat thicker filaments) by about roughly 11%, which with industrial processes such as those which take place in cereal mills signifies a very significant increase in efficiency.

(29) Additionally, in trials it has however been found that the sieve throughput through a sieve of the type according to the invention in comparison to the state of the art can be increased even further than that which could be explained by a larger open sieve area, which is yet explained hereinafter.

(30) A vertical cross section through a sieve of the type according to the invention and which is manufactured by etching is shown in FIG. 7. FIG. 7 also illustrates the feature that the web width b.sub.st corresponds for example to roughly the thickness d of the flat body, i.e. the webs have an aspect ratio of roughly 1. In FIG. 7, one can also see that the webs 41 are rectangular in cross section, for example roughly square, wherein given a manufacture by way of etching, in particular one etches from both sides, thus from above and below, which is why a very slight narrowing of the through-hole results towards the middle plane, which however has no significant negative influence on the results which can be achieved.

(31) A corresponding section through a woven sieve according to the state of the art is shown in FIG. 8.

(32) A comparison between FIG. 7 and FIG. 8 shows that with sieves of the type according to the invention, edges 44 result along the webs, which is not the case with a woven sieve. The existence of such edges 44, in particular at the upper side, i.e. towards the product which is to be sieved represents one possible explanation for the efficiency with the approach according to the invention being so greatly increased. A flour or grit particle or a group of such particles would form part of a stable structure on the upper side of the sieve with a much lesser probability and at the edge would be deflected downwards in its movement with a much greater probability, than given a woven sieve with its round cross-sectional structures.

(33) FIG. 9 firstly schematically illustrates the principle of not having to etch equally deeply from both sides on manufacture by way of etching, but that asymmetrical configurations are also possible. In FIG. 9, one has etched roughly double as deeply from below as from above, so that accordingly the location with the greatest narrowing is above the middle plane. Such an asymmetrical configuration with the narrowest location above the middle plane can be advantageous, since on account of this the probability of the particles getting clogged in the through-hole is smaller. A potential further increase in the efficiency results from this.

(34) Secondly, FIG. 9 illustrates that the web width b.sub.st can also be smaller than the thickness d, which has already been discussed above.

(35) Thirdly, FIG. 9 also illustrates that even given the presence ofas mentioned, under certain circumstances advantageousa sharp edge, the angle between the upper-side surface of the sieve and the wall of the through-hole does not need to be exactly 90 but can also be somewhat smaller.

(36) FIG. 10 shows a vertical cross section, analogously to FIG. 7, through a sieve of the type according to the invention, said sieve not having been manufactured by etching, but by way of an additive manufacturing method. By way of dotted lines, it is indicated that the sieve is constructed from a multitude of layers 51, wherein the layers run horizontally. The layered structure can, but does not necessarily have to, be recognisable on the sieve. The considerations explained by way of FIG. 7 relating to the dimensions and the shape (with edges 44), and by way of FIG. 9 relating to the web width also apply to embodiments of the second group, of which one example is represented in FIG. 10.

(37) Example 1: Approx 100 g of commercially available wheat flour was given to a sieve which is manufactured by etching and is of the dimension 275 mm*175 mm (net sieve area) with a hexagonal arrangement of in total 427000 through-holes. The through-holes had an area which was measured out by way of CAD software, of a=0.05309 mm.sup.2, which corresponds to a mesh width of 0.23. The sieve was brought into horizontally circling movements (approx. 3 rotations per second; diameter of the movement circle: 5 cm). After in total approx. 25 s the flour has passed through the sieve with the exception of a small residual quantity.

(38) An equal quantity of the same flour was given to a comparable commercially available nylon sieve (mesh width 0.236 mm; number of through-holes 426000) and sieved through under the same conditions (same sieve dimensions and net sieve area). After 40 s, significant shares of flour has still not passed through the sieve, which is why additionally a sieve cleaner was placed upon the sieve to assist in the procedure. Only after a further 20 sthus in total 60 s had the flour passed through with the exception of a small remainder of a comparable residual quantity.

(39) In this example, therefore, the efficiency was increased by significantly more than a factor of 2.

(40) This example indeed corresponds to a realistic application situation. It is common for ready-for-sale flour to be sieved once again in so-called control sifters before delivery, in order to filter out possible foreign bodies. A sieve such as the commercially available nylon sieve with a mesh width of 0.236 mm can be applied with such procedures.

(41) Example 2: As Example 1 but with rye flour instead of wheat flour as the sieving product. Rye flour is highly agglomerating and therefore difficult to sieve. The increase in efficiency according to example 1 was confirmed.

(42) Example 3: Analogously to Example 1, but a sieve which is manufactured by etching with a square arrangement of approximately square sieve holes was used (the shape of the sieve holes is that of squares with significantly rounded corners due to the etching process). The effective area of the through-holes was re-measured by CAD. It corresponded to the area of the square with a mesh width 236, i.e. 0.236 mm. On account of the circling movements practically the complete quantity of the 100 g of wheat flour has passed through the sieve already after 16 s. A renewed comparison measurement with the same quantity of white flour and with the nylon sieve of Example 1 and of a mesh width 0.236 mm, but without the use of a sieve cleaner has still not resulted in a complete passage of the wheat flour even after 93 seconds; i.e. the remaining residue was greater than with the sieve according to the invention after already 16 s.

(43) Example 3 confirms that the arrangement and also the shape of the sieve holes tend to be secondary, and that the effect of the invention is due to the fact that the sieve intrinsically has a different structure than a woven sieve.

(44) FIG. 11 by way of a comparative measurement shows that the procedure according to the invention not only improves the efficiency of the sieving procedure, but also the fineness of the separation. The measurement was carried out with the sieve according to the invention and the commercially available nylon sieve according to Example 1.

(45) This ground cereal product was sieved with the parameters according to Example 1. The so-called discharge, thus that share of the sieving product which is not sieved through was analysed with the help of a commercially available laboratory device (manufacturer: Microtrac) which utilises the principle of dynamic picture analysis (ISO 13322-2). Specifically, what was determined was the size distribution of the ground cereal product particles, and specifically with the minimal diameter x.sub.C, min as the characteristic quantity. x.sub.C,min is the minimal dimension of the respective particleswith spherical particles, x.sub.C,min corresponds to the diameter, with ellipsoidal particles double the value of the smallest semi-axis. FIG. 16 shows the so-called grade efficiency curve, i.e. that share of the number of ground cereal product particles with an x.sub.C,min value which is smaller than the value specified on the abscissa. One can see that with the first curve 61 which is obtained with the machine according to the invention with the etched sieve, the delimitation is significantly sharper (steeper gradient) than with the second curve 62 which results for the machine with a conventional sieve. From this, it is directly evident that the machine according to the invention and the sieve element according to the invention not only entails an improved efficiency but also an improved discrimination quality.

(46) FIGS. 12 and 13 illustrate the possibility of providing a sieve element of the type according to the invention with an additional function, specifically an automatic sieve breakage recognition. This possibility specifically exists with sieve elements which are manufactured with additive manufacturing methods, in particular with the 3D printing method. The sieve element includes at least one embedded strip conductor 71 which runs between two contacts 74. In the shown embodiment example, the course of the strip conductor 71 is meandering. In the case of a sieve breakage 81, the strip conductor is interrupted and by way of this can be ascertained by a simple sensor or a simple measurement device, which examines whether an electrical connection exists between the two contacts 74.

(47) The strip conductor 71 runs in an embedded manner, i.e. there is no contact to the upper or lower surface of the flat body. In embodiments in which these surfaces are metallici.e. the sieve element is essentially metallicat least one electrically insulating layer 92 will be present between the strip conductor 71 and the metallic layers 81 on the surfaces; likewise, the layer with the strip conductor 71 can be filled out with electrically insulating material (i.e. be electrically insulating at those positions in the sieve element plane where there is no strip conductor). Suitable electrically insulating materials are the mentioned ceramic materials or hard thermoplastic or curable plastics.

(48) In the represented embodiment example, apart from the (first) strip conductor 71, a second strip conductor 72 is present in another layer and likewise runs in a meandering manner but with a different, in particular orthogonal primary direction. Sieve breakages such as the second represented sieve breakage 82 which run such that they do not sever the first strip conductor 71 can thus be ascertained. The second electrodes 75 for the second strip conductor are read out separately by the (first) electrodes 74 of the first strip conductor 71.