EP0293426B1 - Installation and process for the dry-grinding of granular foodstuffs and feedstuffs - Google Patents

Abstract

PCT No. PCT/EP87/00747 Sec. 371 Date Sep. 22, 1988 Sec. 102(e) Date Sep. 22, 1988 PCT Filed Dec. 1, 1987 PCT Pub. No. WO88/04203 PCT Pub. Date Jun. 16, 1988.A size grading unit and a gravity grading unit in a grinding preparation installation form an oscillating unit and are arranged one above the other so that a V-shaped space exists between them. The product flow transfers as a carpet or veil falling from the size grading unit at the V apex to the gravity grading unit located below. Air flows through the V-shaped space but not through the size grading unit.

Description

Technical field :

The invention relates to a system for dry grinding preparation of grain-like food and feed, such as cereals, namely for cleaning, separating into different fractions and preferably for reading foreign material, such as sand, stones, scrolls, etc., which a size classification unit, for. For example, sieves, as well as a gravity classifying unit performing a throwing swing movement, e.g. For example, as a stone reader, light grain reader, etc.

State of the art :

A system of the aforementioned type is known from GB-A-2 040 190 (GEBRÜDER BÜHLER).

More recently, the number of special machines for dry grinding preparation, sometimes also called cleaning, in a mill system, sometimes also called a mill for short, has reduced significantly. In contrast, a group of standard units, such as screening devices and stone readers, more and more also light grain readers, can be found in almost every new mill system. Each unit or device is designed for its specific task and provided with exhaust air, vibrators, etc. The very specific one Training makes it possible to use both the required air and the vibration energy in a targeted manner with the least possible expenditure for construction and operation, so that an increased throughput and a higher quality of work can be achieved with the lowest possible system costs, compared to the even older practice.

The currently built mill systems mostly have four building complexes side by side, a first one for the silo, a second one for the grinding preparation, a third one for the grinding or mill and a fourth one for the finished products.

The preparation and grinding machines are distributed over four or five floors. Depending on the desired storage capacity, the storage silos usually tower above the mill building. What is, as it were, the most natural thing about the storage silos, namely the discharge through openings in the floor with the corresponding downward movement of the product by gravity, has also been used in the machines for dry grinding preparation for many decades. Here, too, the product is fed into the machines on the top floor, only to be moved by gravity, i.e. to move downwards from floor to floor or from machine to machine without the technical use of additional energy for transport.

Every milling specialist knows that the preparation for grinding, in particular the dry preparation (cleaning, separating, reading out, etc.) of the raw material should be given as much attention as the grinding itself. This manifests itself in the fact that in most Milling plants enough space is provided for the grinding preparation / cleaning machines, so that no immediate need for further concentration thereof is known.

A fundamental disadvantage of dry grinding preparation results from the floor-to-floor connection of the grinding preparation machines. For the sorting, classifying and separating process, the entire product or material flow in the respective machine is brought into a flat thin layer or a thin falling veil. For the transfer to the next machine, the product stream is then bundled again in order to then be spread over the area again after the transfer.

A specially designed inlet section is required for the uniform flat formation of a product bed. This is to prevent the initial part of the machine from being poorly used for the work it desires, based on the area.

In many cases the idea was played that one machine would be lined up on the same floor. Judging from the quality of work, this would be an advantage. However, since each machine requires different optimal conditions, there would be structurally very complex transition pieces, especially if the neighboring machines swing against each other. Process engineering shows time and again that machines with a large surface area are difficult to control. Malfunctions are recognized late, so that often a small malfunction in the previous stage can adversely affect the next stage over a longer period of time.

From CH-A-270 243 (GEBRÜDER BÜHLER) a semolina and fume cleaning machine is already known which has sieve layers inclined to one another, arranged one above the other and through which a common air flow flows. A vibrating drive common to all sieve layers keeps the sieves in motion. So-called passage monitors are used to control, in particular weaken the flow of the main air.

FR-A-711 465 (MEUNIER) describes a coal separation process for separation into different coal fractions. With this separation process, the product flow is guided by means of vibration and air forces over a sieving and then a weight classification, without constriction of the product flow up to the point of exit from the weight classification. The air is conducted in recirculation mode as follows: through the weight classification, the room above the weight classification and the room above the sieve, a subsequent common exhaust pipe, a fan, a dust separator and finally back to the weight classification.

CH-A-96 318 (WIEDMER) discloses an installation and a method for the dry grinding preparation of granular food and feed with several size classifying units, namely sieves, which are subjected to a common vibration. The screens are arranged one above the other and form a fork or. V-shaped rooms. The product flow is transferred from one screen to the other at some transfer points between two screens in the manner of a falling product carpet or veil. At the second transfer point, an air stream blows through the lower end of the one sieve and removes the light bodies according to the principle of wind separation.

The invention is concerned with the problem of improving the dry grinding preparation, preferably in such a way that it is possible to concentrate the work processes, but preferably while maintaining the manageability of each step, the possibility of influencing each step, particularly preferably achieving an at least the same Throughput and quality of work as before.

The solution according to the invention is characterized in that the size classification unit and the weight classification unit form an oscillating group in the grinding preparation system mentioned at the outset, and are arranged one above the other in the form of a fork or V, so that a fork or respectively between the underside of one and the top of the other unit. V-shaped space is created; Means for transferring the product flow in the manner of a product carpet or veil falling from the size classification unit at the fork position to the heavy classification unit underneath and finally means for generating an air flow through the fork or V-shaped space, but not provided by the size classification unit.

• ― der der Größenklassierung (Siebung)
• ― der Schwereklassierung, hier
• ― ― der Teilung von leicht und schwer und
• ― ― der Steinauslesung

vollständig wegfällt. Nur an der (ersten) Eintrittsstelle des Produktes in die erfindungsgemäße "Kompaktvorrichtung" muß eine flächige gleichmäßige Produktschicht erzeugt werden. Danach muß sie nur noch aufrechterhalten werden.It is often the case with new inventions that you no longer understand why the simplest and most optimal solution was not used long before. You look for reasons why others working in the field did not come up with the idea of the inventor. Heavy class requires a very strong ventilation to form a fluid bed. In contrast, the actual sieves can now be easily aspirated, otherwise parts will easily stand out and on the Float the surface of the flowing bulk layer. The fork-shaped arrangement of the size classification unit and the weight classification unit results in two decisive advantages. The product transfer from the upper size classifier (sieve) to the heavy classifier underneath takes place evenly over the entire width of the sieve; This means that the multiple change between the flat product flow and the tubular product flow described above is now within all (three) basic functions, ie

• - that of size classification (screening)
• - the severity classification, here
• - - the division of light and heavy and
• - - the stone reading

completely disappears. A flat, uniform product layer only has to be produced at the (first) entry point of the product into the “compact device” according to the invention. After that it just has to be maintained.

The invention thus enables an impressive solution to the problem mentioned with the simplest measures and, in addition, even better use of the work surfaces.

In principle, a separate vibratory drive can be provided for the size classification unit and for the weight classification unit. However, the vibration group formed by the size and weight classification unit preferably has a common vibration drive, so that an identical vibration (identical direction, frequency and amplitude) is impressed on both units. Preferably, the vibratory drive is arranged on both sides of the vibrating group with an angle of incidence to a horizontal plane of gravity, such that a throwing vibration for upward conveyance is generated for the weight classification, while a throwing vibration for downward conveyance is generated for the size classification. All work surfaces therefore perform an optimal swinging movement. Experiments have confirmed that the new idea enables a sharp separation process even at high throughput rates.

In a further advantageous embodiment, the means for generating the air flow have a bottom that closes the size classification unit (sieve device), a suction fan preferably being connected to the expanded side of the aspiration space between the size classification unit and the weight classification unit. By placing the closed bottom underneath the sieve, the sieve section can easily be separated from the fluidized bed in relation to the air.

The aspiration space expanded on one side is very particularly preferably divided into at least two extraction chambers, namely an upper and lower extraction chamber, with adjustable air throttles being assigned to each extraction chamber.

This allows the air distribution to the gravity classifier to be regulated in a very simple manner with any desired accuracy, without any negative influence on the size classifying unit located above. In this way, each individual function can be set to the desired maximum requirement.

However, the idea according to the invention permits various further very advantageous configurations. So z. B. open the lower end of a light grain reader directly into a vertical aspiration channel in order to be able to read a light fraction from the rejection of the gravity classifier.

This combination shows the advantages of the invention particularly well, since the product is brought into a flat layer when it enters the compact device according to the invention. This flat product layer is now maintained on the entire processing path through the compact device, that is to say on its way from the screen of the size classifier via the concentrator and finally via the stone reader, without interruption. Correspondingly, the dust air can also be routed via a duct into the aspiration duct, which also works flatly. For the viewer, an image is created as if a textile web was pulled through a printing press and the corresponding work processes were carried out step by step on the belt.

As a particularly interesting further development idea, the invention allows the aspiration space, which widens to one side, to be provided with an air suction system which, via a dust separator, leads the air back to the suction side of the stone reader in recirculation mode.

This idea brings great progress in many applications, especially in small and medium-sized milling plants. The invention thus enables the plant for dry grinding preparation, which previously consisted of several individual machines, in which each individual machine A good aspiration for the intensive ventilation and the whole system needs a central air filter system to build now as a closed, compact machine.

The new invention allows all work steps to be operated in one unit, in many cases without a filter, with circulating air.

The weight classification unit very particularly preferably consists of two classification tables arranged one above the other and through which the same air flows. It is possible that the upper classification table as a concentrator. Light grain reader or as a stone reader and the lower classification table is designed as a stone reading table. Furthermore, it is also possible to form the size classification unit from two identical sieve tables arranged one above the other (two parallel runs) or to use two or more different sieve tables one above the other. Furthermore, the classification tables are preferably arranged parallel to one another in the same classification unit.

The invention further comprises a method for the dry grinding preparation of a product stream from grain-like foods and feedstuffs, such as cereals, namely for cleaning, separating in different fractions and, preferably for reading out foreign material, such as sand, stones, rolls, etc., the product stream being oscillated - resp. Air forces are promoted via at least one size classification (screening) and then at least one gravity classification (stone reading, light grain reading) that causes a swinging movement. Such a method is known from GB-A-2 040 190 (GEBRÜDER BÜHLER) already mentioned.

According to the invention, the known method is further developed in such a way that the product flow in the size classification and in the weight classification of a common one Vibration is subjected, the flow and the inclination direction in the size classification opposite to the flow and inclination direction in the severity classification is selected and the product flow without entering the size classification.

Constriction (spread out like a carpet) up to the exit of the respectively read fraction from the respective classification unit, at the latest from the weight classification unit.

Fig. 1

zeigt den Grundaufbau einer Lösung gemäß der Erfindung;

Fig. 2

zeigt im wesentlichen den Aufbau gemäß Fig. 1 jedoch kombiniert mit einer Aspirationsstufe;

Fig.3

zeigt im wesentlichen eine Lösung entsprechend Fig. 2, jedoch mit Umluftbetrieb und einem zusätzlichen Abscheider;

Fig. 4

zeigt im wesentlichen eine Lösung gemäß Fig. 1, jedoch mit zwei übereinander angeordneten Steinauslesetischen und einem Parallellauf für die Siebung;

Fig. 5

zeigt eine weitere Ausführungsvariante für die Schwereklassierung mit einem oberen Konzentrator resp. Leichtkornausleser und einem unteren Steinauslesetisch.

The air flow is preferably only guided by the weight classification and the space located directly above it, but not by the size classification. However, this means that the new invention not only permits a very strong further concentration of the work functions while maintaining controllability, but also an optimization of the individual process steps, since the next work step in each case benefits from the previous one due to the flat transfer. A product transfer through a short free fall as a product curtain or carpet also helps to loosen up the good parts, so that parts that stick together are released again.

Fig. 1

shows the basic structure of a solution according to the invention;

Fig. 2

shows essentially the structure of Figure 1 but combined with an aspiration level.

Fig. 3

shows essentially a solution corresponding to Figure 2, but with recirculation mode and an additional separator.

Fig. 4

shows essentially a solution according to Figure 1, but with two stacked stone reading tables and a parallel run for the screening.

Fig. 5

shows a further embodiment for the gravity classification with an upper concentrator, respectively. Light grain reader and a lower stone reading table.

The invention will now be explained in more detail with reference to the drawing using the exemplary embodiments shown there:

In the following, reference is now made to FIG. 1. The entire system consists of a compact machine 1 which contains a screening device 2 as a size classification unit and a concentrator 3 and a stone reader 4 as a weight classification unit. An arrow 5 symbolizes a vibration exciter. Whose direction of oscillation is angularly aligned with the sieving device 2 as well as with the concentrator 3 and the stone reader 4 in accordance with the setting angle α to the horizontal plane of gravity 6. The direction of vibration is simultaneously parallel to the drawing plane of FIG. 1 or parallel to the main product flow direction. The machine 1 is supported on vibration bearings 7 via a frame 8 on the floor 9. A product feed line 10 is attached above the sieve device 2 and is firmly connected to the non-vibrating ceiling 12 via a suspension 11. Between the product feed line 10 and the screening device 2 is a flexible Cuff 13 attached, which serves as a transition from the non-vibrating parts of the machine 1 to the vibrating parts. The area of product entry into the screen box 2 is designed as a distribution box 14, so that the product stream bundled in the tube in the product feed line 10 is spread out as a fluffy, uniform product carpet on the top screen layer or the coarse screen 15. The coarse sieve 15 is preferably used to remove coarse additives and disruptive, large foreign bodies, such as cords, pieces of wood, etc., which are removed from the product stream via an outlet 16. The space above the coarse screen 15 is completely closed off from the outside by sheet metal cladding 17, so that no dust escapes and no air exchange takes place to the outside. At a distance below the coarse sieve 15 there is a selection sieve 18. This has a relatively fine sieve mesh in order to obtain fine constituents such as fine sand, grain fragments etc. as sieve diarrhea. The sieve diarrhea is carried away via a closed, essentially air-impermeable bottom 19 and an adjoining sand outlet 20, that is to say it is separated from the product stream. The rejection of the sieve 18 flows directly across the entire width of the table through a discharge channel 21 and continues to be distributed evenly over the entire width onto the concentrator 3 through which there is a large amount of air. Fluid bed on the concentrator 3 has a double function. On the one hand, the product parts are loosened, for example dirt that is only slightly adhering to a grain or shell parts, which facilitates the subsequent division into fractions.

• ― vor der Übergabestelle in einer Produktschicht auf einer nicht-luftdurchströmten Siebfläche (Auslesesieb 18)
• ― nach der Übergabestelle in einer klassischen stark luftdurchströmten Wirbelschicht (Konzentrator 3).

The other advantageous function is that - unlike before - the product carpet is retained in its entirety, but the significantly different physical effects or forces required for the respective treatment of the product carpet sections before and after the transfer point can still be used in full:

• - in front of the transfer point in a product layer on a screen surface through which no air flows (read-out screen 18)
• - After the transfer point in a classic fluidized bed with high air flow (concentrator 3).

On the non-air-flowed screen surface there are pure mechanical impact forces from particle to particle. Similar to the process of concrete vibration, the vibrated product layer looks for the greatest possible bulk density, whereby the smallest parts immediately tend to move into the cavities of the bottom layer of larger grains. However, since the sieve bottom is permeable to the small particles, they fall through and are screened off. Large parts, even larger parts, strive for the surface of the product layer. The main forces or effects that are used on the sieve result from the different size of the particles.

In contrast, the main forces in the fluidized bed are the air forces. Accordingly, a very stressed stratification takes place within the fluidized bed according to the severity. Cereal grains move within a fluidized bed upwards, stones down, provided similar sizes.

Due to the vertical discharge from the reading screen 18 onto the concentrator 3 and the reversal of the flow direction, the shifting from the pure shake seal into a fluidized bed stratification takes place quickly, i.e. on a very short distance instead. Neither short-term performance increases nor throughput fluctuations - even within relatively large limits - have a negative impact on the quality of the redeployment. This is an essential point of the surprising success of the new invention.

As can easily be seen from FIG. 1, the fork-like (or V-shaped) arrangement of sieve device 2 and concentrator 3 creates an expanding space 22, which is connected to an aspiration line 24 via a suction nozzle 23. The desired amount of air for the operation of the machine 1 can be set by an adjusting flap 25. The expanding space 22 is divided into sections 22 ', 22˝ by at least one wall 26. This allows throttle valves 27 and 28 in one or the other sector 22 'or 22˝ depending on need (either in the upper or lower part of the fluidized bed) to set more or less large air flows. A flexible sleeve 29 is in turn attached between the suction nozzle 23 and the aspiration line 24.

The concentrator 3 has the task of layering the product stream and concentrating the specifically heavy parts in the area immediately above its table surface. Just before the bottom end of the concentrator table surface, which is air-permeable up to this point, but is impermeable to the product, there is a section 30 with large product outlet openings. Through this section, the lower layer, enriched with the heavy parts, in particular with stones, is drained directly onto a chute 31 extending underneath and from there to a central region of the stone reader 4. With an adjustable product storage bar 32, the percentage portions of the product flow - portion of the gravity concentrate on stone reader 4 and portion of the light fraction - can be determined according to the particular task. The fraction of the light fraction is fed directly to a corresponding outlet 33. There is also the possibility of adding a medium-weight fraction via the additional diarrhea openings symbolized by the arrow 34 at the very bottom of the concentrator 3 into an outlet 35 for the heavy goods, ie for the good, heavy grains.

The stone reader 4 has a rough surface, usually a mesh. The heaviest parts lying directly on the table surface of the stone reader 4 are conveyed to the upper left end of the table by the rough table surface and the throwing vibrations of the vibration exciter and then fed to a stone outlet 36. In contrast to the stone reader 4, the concentrator 3 has a table with a smooth surface (sheet with fine perforations), so that the concentrator table surface exerts a conveying effect only on the heavy product layer closest to the table surface, despite its oscillation identical to the stone reader 4. Due to the fluid bed effect, the product flows downward like a liquid. The one Concentrator 3 and the stone reader 4 common direction of vibration is also correct for the screening device 2. The product is conveyed downwards by the vibration of the sieve table surface.

This shows that all three classifying units, that is to say the screening device 2, the concentrator 3 and the stone reader 4, can be provided as one oscillating unit with the same oscillating drive 5, and nevertheless each work process can be carried out optimally. However, only the stone reader 4 and the concentrator 3 are aerated with the same air.

All three machine parts 2, 3 and 4 are arranged directly one above the other according to the invention. By fully utilizing the many combinatorial effects of the invention, the entire machine 1 is only about man-high, so it can be installed in any room of normal height. The experts involved rate the surprisingly successful interplay between the screening device 2 and the concentrator unit 3 as being particularly advantageous.

However, the invention allows further design ideas.

2, the embodiment of the machine 1 shown in FIG. 1 can also be used in combination with a vertical aspiration channel 40. In the widening space 22, the wall 26 is preferably made adjustable, so that both the air quantity distribution on the concentrator surface within certain limits, but in particular the air required in the aspiration channel 40, are adjusted separately by means of a throttle 41 can. The amount of air that is extracted from the higher part of the room 22 can be adjusted by a control flap 42.

In the solutions according to FIGS. 1 and 2, the bottom of the stone reader 4 is permeable to air, so that the air can freely flow in and through the stone reading table from below. Both solutions work in the so-called suction mode, which is also a very big advantage for easy control of the air flows.

The solution of FIG. 3 has the structural elements of the solution according to FIG. 2, but is further developed in a basic function. It enables the machine 1 to be operated entirely with circulating air and has a light-weight separator for this purpose.

The exhaust air from the aspiration channel 40 is passed directly into a rotary cutter 50. In the rotary cutter, dust and shell parts are separated from the air with a very high degree of separation and can be discharged via a dust lock 51. The working air is returned to the classifying section through a duct 52 and a return line 53. For this purpose, the space below the stone reader 4 is completely closed to the outside by an air distribution box 54. The air distribution box 54 is part of the vibrating unit and is connected to the return line 53 via a flexible sleeve 55. The stone reader is constructed in the sandwich construction known per se, which at the bottom has a plate 56 with very fine perforations, so that there is a guarantee of good air distribution on the table surface of the stone reader 4.

If there is no aspiration system available, the machine can also be assigned a small filter (not shown) behind an extraction nozzle 61. With a fan 58, which is preferably arranged after the rotary cutter 50, the desired pressure distribution in the system can be regulated via corresponding air flaps 59 and 60, as indicated by the + and _ signs in circles as symbolic pressure values.

If the machine 1 is not to be operated with circulating air, the corresponding parts are not required. The rotary cutter 50 can nevertheless be used, and the exhaust air can be sucked off, for example, via an aspiration system (not shown) via the suction nozzle 61.

4 shows a very particularly advantageous combination of the new invention. For the size classification, two parallel sieve runs 70 and 71 are provided, the sieve diarrhea (very fine sand and grain fragments) via the outlets 16 and. 20 are led away from the corresponding closed floors.

For the weight classification, in particular for stone selection, two stone selection table surfaces 72, 73 are provided, each of which has a good support in the form of a mesh. The swinging movement gives that directly on the upper resp. lower table surface 72, 73 heavy goods lying on top have a strong conveying effect after the higher table end. The light material is lifted by the strong, evenly distributed air flow from the two table surfaces, swims in the direction of the lower table ends and is via the spouts 33 and. 35 carried out.

It is now interesting that on the upper of the two stone reading tables 72, 73 a heavy fraction, e.g. For example, 30 to 60% of the total amount of goods flows under an inlet plate 74, and from there flows into a transfer point 75, in order then to fall directly onto the lower table surface 73. The upper table surface 72 only produces a mixture with all heavy goods, which, for. For example, when 50% of the total quantity is transferred to the lower table near the upper end of the table. Experts' concerns that feeding the goods close to the upper table end of the gravity classification automatically leads to poor stone selection could be refuted by tests. It can be seen that the very strong stratified flow indicated by circulation lines 76 achieves a stone selection quality that has hitherto hardly been achieved. In the area near the table there is a strong upward flow, but above that a strong downward flow.

The actual stone secretion takes place only between the lower table surface 73 and a guide plate 77 provided above the upper end of this table. Because of the air flow in this area which runs counter to the movement of material, the stones are transferred here with only a small fraction of grain and are finally discharged through the rubber hose lock 36.

A particularly great advantage of the embodiment variant according to FIG. 4 is that the throughput through the different process zones can be adapted very precisely to the specific requirements of the individual machine parts. Since all tables have an approximately equal working area, the sieve area is doubled and the actual stone reading area doubled, as the bottom one Table area only receives a subset of the total. This allows a very high screening and stone selection quality with high product throughput.

5 shows a further advantageous idea compared to FIG. 1. The lowest table surface is used for stone selection. An overlying table 81 has a slightly less rough table surface, so that some of the stones can be conveyed upwards with a small amount of grain and fall directly onto the stone reading table 4 via a passage opening 80. The upper table 81 of the weight classification serves primarily as a shift table and has a "good swamp" 82 in the lower part, i.e. a trough-shaped depression, in which all the heavy goods (heavy grains) collect together with the stones. The gravity fraction from the material swamp 82 is drained through the bottom openings 30 and fed to the stone reading table 4 via the chute 31.

The great advantage of this variant lies in addition to the very high stone selection quality, also in a very good separation, e.g. For example, in a heavy grain that is discharged through the outlet 35 and in a light cereal that is discharged through the outlet 33.

Overall, the invention encompasses both a method and a machine (1) for the dry cleaning of grain-type foods and animal feed, such as cereals. The material to be cleaned is separated into the different fractions in a single vibration group. This has an upper size classification (2), which can consist of any sieve combination (15, 18; 70, 71), preferably has a closed lower floor and directly above a weight classification (3, 4; 72, 73; 81) is arranged, in such a way that the two classification units to each other fork or. Are arranged in a V-shape. The weight classification (3, 4; 72, 73; 81) can also be combined in different versions, for example as a single or double-layer table, as an upper layer and lower stone reading table. The fork-shaped space (22) is used to guide the air for the heavy class tables. An important idea lies in the fact that the goods to be cleaned are passed from the entry into the machine 1 to the exit without interruption across the area, in the manner of a spread textile web and transferred from machine part to machine part (classifying unit to classifying unit). In contrast to the concept of the known cleaning systems or systems for dry grinding preparation constructed from individual machines, according to the invention a single compact machine without bundling of goods is provided.

Claims (14)

1. System for the dry preparation for milling of granular foodstuffs and feeds, namely for cleaning, separation into different fractions and, in particular, separation of foreign matter, such as sand, stones, clumps of earth etc., with

a) a size-classifying unit (2) (e.g. screen 15, 18; 70, 71) and

b) a gravitational classifying unit (e.g. stoner (4; 72, 73) performing a throwing oscillatory movement, characterised in that

c) the size-classifying unit (2) and the gravitational classifying unit

c. 1) form an oscillating group and

c. 2) are arranged one above the other in a fork- or V-shape, a fork- or V-shaped space (22) thereby being formed between the underside of the one and the top side of the other unit (2),

d) means for transferring the product stream in the form of a carpet or veil dropping from the size-classifying unit (2) onto the gravitational classifying unit situated beneath the latter and

e) means for generating an air flow through the fork- or V-shaped space (22) but not through the size-classifying unit (2) are provided.

2. Machine according to Claim 1, characterised in that the means for air-flow generation have a plate closing off the size-classifying unit (2) at the bottom.

3. Machine according to one of the preceding claims, characterised in that the oscillating group has an oscillatory drive (5) common to the size-classifying unit (2) and the gravitational classifying unit.

4. Machine according to one of the preceding claims, characterised in that the gravitational classifying unit comprises two classifying tables arranged one above the other, through which the same air flows.

5. Machine according to Claim 4, characterised in that the upper classifying table is designed as a concentrator (3, 81) or light-particle separator or as a stoner (72) and the lower classifying table is designed as a stoning table (4; 73).

6. Machine according to one of the preceding claims, characterised in that the size-classifying unit (2) consists of two identical screening tables arranged one above the other (two parallel runs (70, 71)).

7. Machine according to one of the preceding claims, characterised in that the classifying tables are arranged parallel to one another in the same classifying unit.

8. Machine according to one of the preceding claims, characterised in that the oscillatory drive (5) is arranged on both sides of the whole oscillating group, with a setting angle (α) with respect to a horizontal plane of gravity, such that a throwing oscillation with an upward component for the gravitational classifying tables and with a downward component for the size-classifying tables is generated.

9. Machine according to one of the preceding claims, characterised in that the means for air-flow generation have a suction fan which is connected to the widened side of the space (22) between the closed plate and the gravitational classifying table.

10. Machine according to Claim 9, characterised in that the aspiration space (22) widening to one side is subdivided into at least one upper exhaust chamber (22˝) and one lower exhaust chamber (22′) and each exhaust chamber (22˝, 22′) is allocated adjustable air throttles (27, 28).

11. Machine according to Claims 9 or 10, characterised in that, for the purpose of separating a light fraction from the discharge of the concentrator deck, the lower end of the concentrator table opens directly into a vertical aspiration duct (40).

12. Machine according to one of the preceding claims, characterised in that the space (22) widening on one side has an air extraction facility which guides the air back in recirculatory fashion to the intake side of the stoner (4) via a dust separator (50, 51).

13. Method for the dry preparation for milling of a product stream of granular foodstuffs and feeds, such as grain, namely for cleaning, separation into different fractions and, in particular, separation of foreign matter such as sand, stones, clumps of earth etc., in which

a) the product stream is conveyed by means of oscillatory or air forces via at least one size classification (screening) and.

b) then via at least one gravitational classification (stoning, light-particle separation) performing a throwing oscillatory movement, characterised in that

c) the product stream in the size classification (2) and in the gravitational classification are subjected to a common oscillation;

d) the direction of flow and the direction of inclination in the size classification being selected to be opposite to the direction of flow and direction of inclination in the gravitational classification; and

e) from its entry into the size classification (2) the product stream being guided without constriction (spread out flat like a carpet) to the emergence of the particular separated fraction from the respective classifying unit, at the latest from the gravitational classification.

14. Method according to Claim 13, characterised in that the air flow is guided only through the gravitational classification and the space (22) directly above the latter.

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