EP0774302B1 - Method and device for separating a material comprising particles of different form, size and/or density in at least two components - Google Patents

Abstract

The separating process can separate solid particles differing in form, size or thickness. In the case of material consisting of flakes of different thickness, the material is fed onto a sieve (4). The sieve is vibrated, causing the particles below a certain thickness to pass through angled slits in the sieve. The endface or narrow side surfaces of the particles are directed at an angle to the sieve plane. The sieve slits are of a known width to sort the material as required. A further sorting by density can be achieved by blowing air onto the sieve from below.

Description

The invention relates to a method and an apparatus for Separation of solid particles of different shapes, Size and / or density of existing goods in at least two Components according to the preamble of claims 1 and 6 respectively.

A variety of methods and devices are known those for the separation of solid particles according to certain differentiation criteria be used. For example, find Vibrating sieves and separation processes using vibrating sieves already at the classification, i.e. when separating a good in different grain sizes, use, the of which Vibratory drives vibrations introduced into the sieve bottom one serve to throw the particles up to repeat them close to the sieve openings and secondly to the particles in horizontal or slightly inclined sieve trays to be transported from the task to the discharge by micro-throws. In order to achieve the micro-throws, the particles are known vibrating screens excited in the same way by the vibrating drive one vertically upwards away from the sieve plate and the other in Direction of transport, i.e. in the direction from task to Discharge, accelerated.

DE-AS 1 193 345 describes a method and a device known for the classification of difficult screenings. That there disclosed vibrating screen has a lower, more inclined Section and an upper, more steeply inclined section on and is alternately excitable and opposite, which means that opposite excitation on the steeper inclined section for the most part consisting of Unterkorn and Grenzkorn of the good is moving upwards, while the excitement is constant it is avoided that unscreened material leaves the vibrating screen.

For sorting, i.e. for separating according to material properties in contrast, predominantly other methods and devices used, such as setting for density separation or views on typesetting machines or in wind or Cross flow sifters, these procedures under certain Conditions also for separation according to the shape of the solid particles can be used, for example cross-flow sighting in the Water bed for separating fibrous flat material and granular material of the same density. However, this is suitable last-mentioned method only for the separation of goods with Water may come into contact.

The separation of a good into two or more components is mostly associated with difficulties when the to separating components from each other only slightly, for example the same or similar physical properties and have comparable dimensions, such as Mixed shredded plastic waste almost the same density as recycling plastic parts of motor vehicles or plastic housings from electrical or electronic devices. These platelet or disc-shaped snippets differ in essential only in terms of their thickness, this difference in thickness often with different material properties is linked, due to the previous purpose of the Plastics. The separation of such a good with the help of a Air cooker is in processing technology 36 (1995) No. 7 p. 314-320 described, but this known method none large throughputs allowed.

The same difficulties arise when the goods to be separated from sliced dried fruits, mushrooms Vegetables or aromatic plants are made with foreign matter particles similar size and / or density, but with a different shape, such as for example small clay lumps, pebbles or broken glass, especially thin plate-shaped lamp glass fragments are contaminated and cleaned before use have to.

A separation of platelets of different thicknesses or disc-shaped particles by sieving is known with Vibrating sieves, their sieve openings in the plane of the sieve bottom are arranged, not possible because platelet or disk-shaped particles predominantly in their most stable position move on the sieve bottom, in which they lay flat on the The sieve bottom rests, so that all the particles Screen openings face their broad sides.

For classifying tobacco leaf parts is from DE-OS 35 05 502 already a sieve with an inclined sieve bottom and a vibration exciter known per se, in which the Sieve openings between two up or down over the Protruding protrusions are arranged so that they are too open diagonally upwards. The good is there through the Vibrations of the vibrating screen from one at the lower end of the Sieve bottom arranged task to one at its upper end ordered discharge transported. The over the top bulges Pieces of tobacco leaf transported away either fall directly into the screen openings or on the bevels arranged in front of them the lower bulges, whereby only the tobacco leaves through the Sieve openings fall, whose dimensions are smaller than that Hole width is the same. Thickness sorting is with the known classification device not possible.

A vibrating sieve device is already known from US-A-4,351,719 for separating wood chips on the one hand and over and Undersize on the other hand with the features of the generic term of Claim 6 known, in which the acceleration of the Particle against the direction of transport serves the Extend the dwell time of the coarser particles on the sieve, until the entire undersize is separated.

One also intended for the separation of wood chips similar screening device is known from US-A-4,802,591. This screening device has a vibrating screen, the Sieve openings in relation to the direction of transport of the wood chips are slanted to the wood chips with their narrow sides align in front of the openings so that only those cutlets pass through, the thickness of which is a predetermined value falls below. A simultaneous density sorting of flakes, slices or platelet-like flat particles is known with the However, devices are not possible.

Proceeding from this, the invention is based on the object Process and an apparatus of the type mentioned in the foregoing to improve that they're not just separating one from flat solid particles existing after the Allow particle thickness but also according to the particle density.

This object is achieved by the characterizing Part of claim 1 for the method or in the characterizing Part of claim 6 characterized for the device Features resolved. Preferred embodiments for the method are in the subclaims 2 to 5 and for Device set out in the subclaims 7 to 9.

Accordingly, the method according to the invention is characterized by this from that the sieve openings from below with an air flow are applied while the device according to the invention by means of loading the sieve openings of is marked below with an air flow.

While the particles of the component to be screened at known Separation processes mostly perpendicular to the sieve plate level and thus in through their most stable position with their broad sides If the sieve openings pass through, they slide when inventive method with their forehead or Narrow side faces advance into the screen openings when they are in their most stable position on the sieve plate in the direction of the discharge move down and in front of the slanted screen openings come to rest. The bottom through the sieve openings flowing air acts as an entry of the flake, disc or platelet-shaped particles in the sieve openings because they face or narrow side surfaces facing the sieve opening the particle flows. The flow velocity of the air is expediently set so that only those particles in the sieve openings can enter, where the Slope downforce in the direction of the screen openings is greater than the air and friction resistance, which is generally for the specifically heavier particles.

The invention takes advantage of the fact that the particles be aligned before entering the sieve openings that their front or narrow side surfaces always flow against become. Because the relationship between slope downforce on the one hand and aerodynamic drag on the other hand in the specific heavier particles are larger, they slide or fall against the air flow into the sieve openings, while the specifically lighter particles are blown upwards.

By combining this feature with an inclined one Sieve bottom, a transport direction of the material to be sieved from above below and a vibratory drive with an upward, vibration component opposite to the transport direction causes the flake, disc or rotate platelet-shaped particles in the course of the micro-throws and repeated with their front or narrow side surfaces in the direction the sieve openings are aligned, the opening width so is chosen that only those particles pass through, at which the dimensions of the front or narrow side surface falls below the predetermined value, in other words the thinner particles.

The particles can thus be placed in one in front of the sieve openings Align position in which a separation of two components Shape properties is possible.

In addition, the opposite to the direction of transport Vibrations of the vibrating sieve each a part of the particles, namely those who are just at the time when the Sieve plate moved upwards, in contact with it come and do not pass through the sieve openings, in a direction opposite to the transport direction accelerated and from the swinging sieve bottom towards the Task thrown back.

According to a preferred embodiment of the invention, this is done Throwing back the particles in the method according to the invention in that the vibrations of the sieve plate cause forces in the particles are introduced, which consist of two Assemble power components, one of which is vertical to the sieve bottom and the other parallel to Sieve bottom in an opposite to the transport direction Direction points so that a single, unobstructed on the Particle lying on the sieve floor along a parabolic path thrown up towards the task.

To ensure that despite the acceleration of the particles against the direction of transport, a transport of the goods in Direction of discharge is preferred Embodiment of the invention, the loading of the sieve plate as large chosen that only part at a time the particle comes into contact with the sieve bottom and the Particles the sieve bottom preferably in several layers one above the other cover, which means that the one with the sieve bottom in Coming into contact and not through the sieve openings passing particles after their acceleration at least partly collide with particles above and partly give their energy to them. In addition, the inclination of the Sieve bottom chosen relatively steep, so that the slope downforce despite the opposing force component due to the vibratory drive a transport of the screenings towards the discharge causes.

The inclination of the screen openings at an angle to Sieve plate level and its orientation towards the task facilitates the entry of the thinner particles into the Sieve openings, as a result of the micro-throws on the sieve bottom particles hitting above the sieve openings on the Slide the sieve bottom down towards the sieve openings, with their broad sides on the sieve bottom rest and their front or narrow side surfaces in the direction of the sieve openings. While the thicker particles oppose push the edge of the sieve openings and through the Vibration movement of the sieve bottom opposite to Direction of transport, i.e. up towards the task be accelerated so that they separate from the sieve openings move away and create space for new particles, they slide thinner particles, the thickness of which is smaller than the opening width of the Sieve openings is, with their front or narrow side surfaces ahead through the screen openings and are screened out.

With the features of the invention is therefore both Separation of thinner and thicker particles as well Separation of specifically heavier from specifically lighter ones Particles possible. Overall, this can be done by sieving separate thin, heavy particles, their thickness below the opening width of the slit-shaped sieve openings lies and their specific weight a predetermined value which is very close to that of the discharge transported remaining good may be because the flow velocities adjust very precisely in the sieve openings to let.

Another advantage of loading the screen openings with air is that it is a fluidized form Particle bed causes on the sieve bottom, so that the turbulent movement of the particles is calmed. With sieve openings, which are inclined with respect to the sieve plate level the airflow emerging from the sieve openings a certain braking of the material to be screened, so that the particles more often in front of the screen openings on their way to discharge reach. With the help of an extractor hood arranged above the sieve bottom the air flow can also be used to remove dusty components from coarse screenings, such as abrasion to dissipate upwards. A particularly good separation effect can be achieved e.g. at a Screenings from dried, sliced or in Form of flakes of vegetables, such as dried mushrooms or onion slices with an inclination angle of the sieve bottom over the horizontal of more than 20 degrees, preferably between 30 and 40 degrees, an oscillation frequency between 3 and 20 Hz, preferably between 5 and 10 Hz, an oscillation amplitude between 5 and 40 mm, preferably between 20 and 40 mm, one completely covering the sieve openings, preferably two to three-layer good loading and one Air flow velocity in the sieve openings between 5 and 10 m / s. With such a choice of parameters adjusts itself when the supply of goods is interrupted some time a steady state in which either a Part of the goods at a constant height on the sieve bottom bounces up and down or even back towards the task is moved upwards.

According to a further advantageous embodiment of the invention are the slot-shaped sieve openings between each two adjacent angle bars arranged, one of which A plurality arranged one behind the other transversely to the transport direction and forms the step-shaped sieve bottom in longitudinal section. The angle strips essentially consist of two legs, their tops towards the task or towards of the discharge point, the feed-side leg is usually narrower than the discharge side leg. The two legs make a right or acute angle one that opens towards the sieve bottom. Are preferred the opening widths of those adjacent between the free ends Leg openings arranged according to the shape and Size of the components of the material to be separated adjustable.

The method according to the invention and the device according to the invention enable the processing of large quantities of a Good thing that consists of a main component intended for use and one or more, in much less There are quantities of foreign substance components present with Using the invention quickly, effectively and practically completely can be separated. An example of such Well, that with the method and the device according to the present Invention can advantageously be sorted is in Sliced dry vegetables such as Onions or mushrooms that contain small amounts of foreign substances, such as for example fragments of glass from incandescent lamps or fluorescent tubes, included, which are due to their matching Do not have color separated with color sorters and in a wind sifting due to their small thickness of 0.3 to 0.8 mm with the onion or two to three times as thick Mushroom pieces of the same size compete because they are exposed to the flow of the largest areas due to their different Have density comparable hover speeds. These foreign substances are eliminated with the help of the present invention mechanically removed quickly and almost completely, being on a vibrating screen with a width of less than 1 m and a sieve tray length of less than 3 m throughput of several tons per day can be achieved. On in this way e.g. dried onion slices or flakes, dried horseradish and / or dried mushroom slices quickly and effectively from lamp break or other Foreign objects are freed, what with other mechanical or optical separation process not or only with a disproportionate high cost is possible.

Fig. 1:

eine teilweise geschnittene schematische Seitenansicht einer erfindungsgemäßen Siebtrennvorrichtung;

Fig. 2:

eine Draufsicht auf einen Teil eines Siebbodens der Vorrichtung;

Fig. 3a:

einen Längsschnitt durch den Siebbodenteil aus Fig. 2 entlang der Linie 3a - 3a;

Fig. 3b:

einen Schnitt durch den Siebbodenteil aus Fig. 2 entlang der Linie 3b - 3b;

Fig. 4:

eine Draufsicht auf einen Teil eines anderen Siebbodens;

Fig. 5:

einen Längsschnitt durch den Siebbodenteil aus Fig. 4 entlang der Linie 5 - 5;

Fig. 6:

eine Draufsicht auf einen Teil eines Siebbodens mit spaltförmigen Sieböffnungen;

Fig. 7:

einen Längsschnitt durch den Siebbodenteil aus Fig. 7 entlang der Linie 7 - 7.

The invention is explained in more detail below with reference to an embodiment shown in the drawing. Show it:

Fig. 1:

a partially sectioned schematic side view of a screen separating device according to the invention;

Fig. 2:

a plan view of part of a sieve bottom of the device;

Fig. 3a:

a longitudinal section through the sieve bottom part of Figure 2 along the line 3a - 3a.

3b:

a section through the sieve bottom part of Figure 2 along the line 3b - 3b.

Fig. 4:

a plan view of part of another sieve plate;

Fig. 5:

a longitudinal section through the sieve bottom part of Figure 4 along the line 5-5.

Fig. 6:

a plan view of part of a sieve bottom with slit-shaped sieve openings;

Fig. 7:

a longitudinal section through the sieve bottom part of FIG. 7 along the line 7-7.

The screen separating device 1 shown in FIG. 1 is intended for this purpose are used, mainly from dried Onion flakes as the first component of existing screenings of small amounts of impurities as a second component to separate that inadvertently during manufacture Screenings have gotten. On the one hand, the impurities include thin glass fragments, especially thin lamp glass fragments, the hover speeds similar to those in the air classifier Part of the onion flakes has a similar color as they possess, so that they cannot be have it separated by a color sorter. Include further the impurities are small stones, lumps of clay or Plastic particles, the weight of which is also only insignificant differs from that of the smaller onion particles, whereby their dimensions are essentially the dimensions of the smallest Face or narrow faces of part of the onion flakes correspond.

The screen separator 1 consists essentially of a Vibrating screen 2, comprising one at an angle to the horizontal inclined sieve plate 4 with a plurality of sieve openings 6, one arranged at the upper end of the vibrating screen 2 Feed hopper 8 with a metering device for the dosed feeding of the screenings onto the upper end of the screen bottom 4, one at the lower end of the vibrating screen 2 or Sieve bottom 4 arranged discharge 10 for the first component of the screened material, one arranged below the discharge 10 Conveyor belt 12 for removing this component, one below the sieve bottom 4 arranged sump 16 for the through the screen openings 6 falling second component, and one Vibratory drive 18, which is coupled to the vibrating screen 2, to set the sieve plate 4 in vibration.

The vibrating screen 2 can, as shown in Fig. 1, as positively guided linear vibrating screen can be formed, alternatively however, this also includes the use of vibrating screens an elliptical oscillation movement possible. Corresponding applies to the vibration system, which is a two-mass vibration system can be formed, as shown in Fig. 1, but also in the form of a one-mass vibration system can be used. During the frequency of the vibrations of the oscillating drive 18 expediently in a range of 3 to 20 Hz and preferably 5 to 7 Hz, is Amplitude depending on the oscillation frequency and the Screen material between about 5 mm at high frequency and screen material with small particle size and about 40 mm at low frequency and coarser screenings so that the particles have time to settle in front of the sieve openings 6 so that their front or narrow side surfaces are facing.

In the illustrated embodiment, the vibrating screen comprises 2 shows a fixed rigid frame shown in simplified form 20 with three vertical arms 22, on their free upper At the end of a double rocker arm 24 is rotatably mounted, the upper end 26 articulated with the sieve bottom 4 supporting box-shaped collecting pan 16 is connected, which together form the first mass, while its lower end 30 also articulated with a counterweight 32 forming the second mass is connected, the oscillation movement of the oscillation movement is opposite to the first mass. The Vibrating drive 18 of the vibrating screen 2 comprises in the illustrated Embodiment an electric motor 36, the output shaft via a belt drive 38 with a rotatably mounted Flywheel 40 is connected, via which a crank pin 42 eccentrically protrudes, which is articulated with the lower one End of a push rod 44 is connected, the upper end articulated via a pivot joint 46 to the collecting trough 16 is. Alternatively, however, balancing drives can also be used or magnetic drives are used, but independently on the choice of the drive common to all vibrating screens is that they are excited in opposite directions, i.e. that one from Sieve tray 4 from upward direction vector X0 Main vibration direction X with a parallel to the sieve plate 4 Transport direction T from task 8 to discharge 10 one Includes angle γ of more than 90 degrees. As in Fig. 1 shown schematically again above the vibrating screen 2 , it means that this direction vector X0 from Sieve plate 4 from obliquely upwards in the direction of task 8 has. The term main swing direction was chosen because the direction of movement of the sieve plate in the course of a upward half-vibration can change. In which linear oscillator shown, this change results by the eccentric arrangement of the crank pin 42, the main swing direction X through the center of the flywheel 40 and the axis of rotation of the swivel joint 46 extends.

Such an arrangement of the oscillating drive 18 has the consequence that due to its vibration exciter in the Vibrating sieve 2 vibrations initiated acceleration forces K0 can be exercised on the screenings, which consist of two Assemble power components K1 and K2, one of which (K1) perpendicular to the sieve plate 4 and the other (K2) parallel to the sieve plate 4 in a direction of transport T. points in the opposite direction. Through these acceleration forces K0 become those particles of the screened material which just come into contact with the sieve plate 4 and do not pass through the screen openings 6, both in the direction of K1 as well as in the direction of K2 and thus in accelerates in a direction opposite to the transport direction T, causing them to be thrown up and repeated with their smaller front or narrow side surfaces in front of the slot-shaped sieve openings 6 are aligned.

By loading the sieve plate 4 with a sufficiently large amount Screening material in at least two or more layers one above the other as well due to the inclination of the sieve bottom 4 with respect to the horizontal at an angle of preferably 30 to 45 degrees depending the quality of the screened material ensures that the first component of the screened material despite the opposite Accelerating forces relatively quickly Discharge 10 is transported.

The one arranged over the drip pan 16 of the screen separating device 1 Sieve plate 4 can be made of stamped and deformed sheet steel 48 with hump-shaped projections 50, which after above to the steel sheet lying in the sieve plate level E. 48 survive and on her towards task 8 Side or flank to form the screen openings 6 open are. While the closed in the direction of the discharge 10 The protrusions 50 side is relatively flat to the one Projections 50 connecting flat section 52 of the sieve bottom 4 falls, the sieve opening 6 is from a feed side Punching edge 54 of the projections 50 enclosed in the illustrated Embodiment at an angle of 90 degrees the flat part 52 of the sieve bottom plate 48 inclined is.

The width b of the slot-shaped screen openings 6 is selected that all particles of the second component with their smaller forehead or in the direction of transport Narrow side surfaces essentially parallel to the sieve plate level can pass through the screen openings 6 if they in their most stable position, i.e. parallel to the sieve plate level E aligned broad side surfaces, through the screen openings 6 fit.

At the entry of the particles hitting the sieve plate 4 to facilitate the second component into the screen openings 6, the sieve bottom 4 can also be designed as in 4 and 5, where the projections 50 on the discharge side steadily up to the staggered below and behind arranged screen openings 6 in the adjacent projections 50 fall off, so that each above the sieve openings 6 arranged surface areas 60 of the sieve plate 4 steeper are inclined and thus the particles slide through them Promote component through the screen openings 6. How in particular 5 shows, are here also to the Sieve openings 6 towards falling edges of the projections 50 so shaped that the impacting solid particles to the screen openings 6 be directed.

Another particularly advantageous embodiment of a Sieve plate 4 is shown in Figures 6 and 7. Here are the screen openings 6 each between two parallel ones Angle strips 55 arranged transversely to the transport direction T, i.e. in the horizontal direction over at least one Part and preferably over the entire width of the sieve plate 4 extend. The angle strips 55 can, depending on the material to be screened Aluminum, a resistant and abrasion-resistant plastic or other suitable material. In the Transport direction T angular strips arranged one behind the other 55 each have two legs 51 and 53, which are different are wide, the narrower legs 53 on the feed side are arranged and only about half as wide as that discharge leg 51 are. The two legs 51, 53 each angle bar 55 close an acute or right An angle β, which extends to the underside of the sieve plate 4 opens. The slot-shaped sieve openings 6 are located in each case between the free ends of the legs 51, 53 adjacent Angle strips 55, on the one hand by the for Discharge 10 facing top of the leg 51 and on the other hand by a parallel to the top of the leg 51, in Distance from this arranged end face of the task side Leg 53 are limited. The opening width is b generally set so that all particles of the sieved second component with its front or narrow side surface fit through the sieve openings 6.

In all of the sieve trays shown in FIGS. 2 to 7 4, the sieve openings are designed so that they are essentially perpendicular to the above the screen openings arranged surfaces of the sieve plate, i.e. your The direction of passage is essentially parallel to these surfaces and parallel or at an acute angle to the sieve plate level aligned, with the sieve openings in vertical Top view of the sieve plate level are not visible and therefore have no pass component in this direction.

The alignment of elongated flat particles in the direction of transport T can protrude from such sieve trays parallel webs 58 take place on the top of the Sieve bottom 4 at a distance from each other in the transport direction T are arranged (Fig. 7).

Because the cut onion flakes are partly the same thickness like the larger stones or other foreign bodies of the first Component can, which is under the sieve bottom 4th arranged drip pan 16 via a supply line, not shown pressurized with compressed air, which as a result of the loading of screenings evenly distributed through the sieve openings 6 flows upwards and there is a wind sifting through the Sieve openings 6 passing particles of the first and second component causes.

This prevents the flow to the top of the sieve plate 4 Air through the thinner onion flakes the sieve openings 6, while the specifically heavier particles the second component against the air resistance of the air flowing down through the sieve openings 6 into the Catch pan fall because they act on it downward forces (essentially downhill force) the upward forces (essentially air resistance and sliding friction), for example because of the smaller sliding friction due to a more rounded shape Pebbles or clay lumps, because of the very small inflow area of thin lamp glass fragments, which are very small drag, or because of the larger Weight or downward slope of specifically heavier particles same particle size and thus inflow area.

That is, with a pure separation according to the thickness, that is Opening width b of the sieve openings selected so that only the thinner particles of the component to be screened with their Front or narrow side surfaces through the screen openings 6 fit through, but not the thicker particles of the to be discharged Component, while in a combined thickness and density separation is such that the thinner and at the same time, specifically heavier particles of the sieved Component and the thinner particles of the to be discharged Fit component, with the passage of the latter prevented by the air flow in the screen openings 6 becomes.

The upward flow of air also over a fluidized fluidized bed is formed in the sieve tray 4, in specifically the lightest, of heavier foreign bodies free onion flakes "float" and become proportionate move quickly down to the discharge 10, as they neither pass through the sieve bottom 4 still substantially counter to the air flow the transport direction T can be accelerated. These particles are therefore no longer subjected to the actual separation, which immediately above and in front of the sieve plate 4 the sieve openings 6 takes place where next to specifically heavier onion slices also the foreign bodies to be sifted out find again. These are located near the sieve plate 4 The opposite vibrations cause particles to become particles and supported by the upward flowing air repeatedly via the projections 50 or the tips of the angle strips 55 conveyed upwards and then slide on the surfaces 60 or the legs 53 in front of the sieve openings 6, whereby they to turn their front or narrow side surface.

The air supply to the sump 16 is when the sieving material set at the beginning so that the flow rate in the sieve openings 6 between 5 and 10 m / s and preferably about 7 and 9 m / s.

Removing the screened second component from the with Compressed air collecting tray 16 can for example via a lock, not shown.

By attaching two or more different sieve trays 4 in the transport direction one behind the other on the vibrating screen 2, and if necessary by applying different amounts to the individual sieve trays 4 with air, i.e. via separate drip pans 16, there are also several different components sieve one after the other from the screenings. Can continue the vibrating sieve 2 also as a preparative sieve for a subsequent one Air separation or optoelectronic color sorting be used.

Claims (9)

1. Process for separating a material which comprises solid particles of different shape, size and/or density into at least two components, in which the material is conveyed downwards over a screening plate (4), which is inclined with respect to the horizontal, of a vibrating screen (2) which is set in vibration, some of the particles being accelerated in the opposite direction to the conveying direction (T) by the vibrations and the particles of one component being discharged at the lower end of the screening plate and the particles of the other component being screened out through screening openings (6) in the screening plate (4), a material comprising large-area particles of different thickness in the form of flakes, leaves or platelets being applied, which particles, as a result of the vibrations of the vibrating screen (2), are oriented with their end faces or narrow side faces in front of the slot-like screening openings (6), which are inclined at an angle with respect to the screening-plate plane (E) and the width (b) of which is dimensioned in such a way that only those particles whose thickness is below a predetermined value pass through the screening openings (6), characterized in that the screening openings (6) are acted on by an air flow from below.
2. Process according to Claim 1, characterized in that the air flow is diverted by the screening openings (6) at least partially into a direction which is opposite to the conveying direction (T).
3. Process according to Claim 1 or 2, characterized in that a flow quantity of the air flow is set in such a way that at least some of the material is fluidized on the screening plate (4).
4. Process according to one of Claims 1 to 3, characterized in that a flow velocity of the air flow in the screening openings (6) is set in such a way that of the particles of the material which pass through the screening openings (6) substantially only those whose relative density is above a predetermined value emerge through the screening openings (6).
5. Process according to one of Claims 1 to 4, characterized in that the material used is dried fruit or vegetables or other substantially dry or dried foodstuffs which contain small quantities of foreign particles which are to be separated off and the thickness and possibly density of which differs from that of the foodstuffs.
6. Appliance for separating a material which comprises solid particles of different shape, size and/or density and which contains large-area particles which are of differing thickness and are in the form of flakes, leaves or platelets, into at least two components, comprising at least one vibrating screen (2) having a screening plate (4) which is provided with screening openings (6), is inclined with respect to the horizontal and has slot-like screening openings (6) which are inclined at an angle with respect to the screening-plate plane (E), a material feed (8) which is arranged in the region of an upper end of the vibrating screen (2), a discharge (10), which is arranged at the lower end of the vibrating screen, for one component, a collection device (16), which is arranged beneath the screening plate (4) for the other component, a vibratory drive (18), which is coupled to the screening plate (4) and accelerates some of the particles in the opposite direction to the conveying direction, so that the particles are oriented with their end faces or narrow side faces in front of the screening openings (6) and those particles whose thickness is smaller than the width (b) of the screening openings pass through the screening openings (6), characterized by devices for applying an air flow to the screening openings (6) from below.
7. Appliance according to Claim 6, characterized in that a flow velocity of the air flow in the screening openings (6) can be set in such a way that, of the particles of the material which are passing through the screening openings (6), substantially only those whose relative density exceeds a predetermined value emerge through the screening openings (6).
8. Appliance according to Claim 6 or 7, characterized in that the screening plate (4) is inclined at an angle α of from 20 to 45 degrees with respect to the horizontal.
9. Appliance according to one of Claims 6 to 8, characterized in that the screening openings (6) are in each case arranged between two limbs (51, 53) of two adjacent angle bars (55) which run parallel to one another and transversely with respect to the conveying direction (T).

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