CH669337A5 - - Google Patents

Description

DESCRIPTION

The invention relates to a grinding plant with at least one impact mill according to the preamble of claim 1.

In the case of impact mills, the fineness of the final product is largely determined by a sieve which, in most known designs, surrounds the rotor of the mill. Theoretically, such a mill should function in such a way that every regrind particle in the grinding chamber remains exposed to the impacts of the rotor until it is fine enough so that it can pass out through the sieve. In practice, there are numerous reasons why this beautiful theory does not work. This is mainly due to the rotor, which - actually undesirable - sets the particles in motion. On the one hand, this rotational movement means that the heavier particles tend to reach the outside of the sieve and thus block the way outwards for the lighter, already finely ground particles.

While this effect of the rotational movement can still be controlled by appropriate dimensioning of the aspiration (suction) applied to the outside of the grinding chamber, another effect also comes into play: with sieves it is known that the selectivity also depends on the size of the relative movement between the sieve surface and sieving particles depends, ie with the same hole size of the

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Sieves will only be able to get through the finer particles at a higher relative speed, and coarser particles at a lower relative speed that will just fit through the sieve hole. In a beater mill, however, the speed ratios are not fully defined: particles that have just been accelerated by a club will fly through the grinding chamber at a higher speed than particles that just happened to be slowed down by a collision with another particle. However, this means that a narrow grain spectrum can no longer be obtained under the conditions prevailing in an impact mill, which is often not necessary, but is sometimes desired.

For this reason, it has already been proposed in EP-OS 53 755 to separate the screening process from the grinding process. The product to be milled was introduced into the beater mill, the grinding chamber of which was surrounded by essentially imperforate walls, and left it through one of several exits. The particles drawn off from the grinding chamber were then fed via a conveying device to a separating device which carried out the separation under more favorable conditions than could be done within the grinding chamber. This conveyor could either be a pneumatic line or was formed by a screw conveyor and an elevator.

The declared goal, which led to the training according to EP-OS 53 755, was primarily to improve the efficiency of the system. For this purpose, several exits were provided from the grinding chamber, which should ensure a relatively short stay of each particle in it, so that the rotor did not have to carry the already fine particles with it. From this point of view, the concept also had to work, but the energy gained (and even a good amount more) had to be used for the conveyor, because pneumatic conveyors have a relatively low efficiency, while a succession of mechanical conveyors also has the energy for the Drive of each individual conveyor is used up. As a result, overall efficiency remained below expectations and the problem remained unsolved.

Attempts in this direction had been made long before, as the DE-PS 699 100 proves. An attempt was made to avoid the energy expenditure caused by a conveyor by using the impact energy imparted to the particles to convey them to a sieve connected to a tangential centrifugal channel leading out of the grinding chamber. The particles were thrown through the centrifugal channel onto the sieve, which bounded the underside of the centrifugal channel itself, the particles passing through the sieve being discharged to the outside while the sieve repulsion trickled down the sieve surface or down through the centrifugal channel. However, the sieve rejection was moving towards the thrown material, braking its energy and guiding it back into the grinding chamber before it could reach the sieve. This not only restored the energetic situation as before, it could also easily happen (as an effect with positive feedback) that the grinding chamber was simply blocked, because the more particles were first thrown onto the sieve, the more the next wave fell against the thrown up material and tore it into the grinding chamber, where the ground material accumulated and therefore the effect mentioned got worse and worse. In this way, no energy savings could be obtained.

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The invention has for its object to improve the energy balance of a system of the type mentioned in the preamble of claim 1 and known from DE-PS 699 100, and this is done in a surprisingly simple manner by the features of the characterizing part of claim 1 Separation device of any kind per se, although it is preferred if the features of claim 2 are realized.

Further details emerge from the following description of exemplary embodiments shown schematically in the drawing. Show it:

Figure 1 shows an embodiment of a system according to the invention in perspective view, wherein a deflection bend to the screen is provided.

Fig. 2 essentially the same system in cross section; 3 shows a further embodiment, without a deflection bend, using a ballistic classifier;

4 shows a possible design in the area of a deflection bend; the

5 and 6 each another embodiment in perspective and in plan view; the

7 and 8 each show a possible embodiment variant for the formation of the outlet of the centrifugal channel from the grinding chamber (detail A in FIG. 2); and

FIG. 9 shows a control device that can be used in a corresponding or similar embodiment of FIG. 8.

1 and 2, a hammer mill 1 has a rotor 3 which can be driven by a motor 2. The rotor 3 rotates within a grinding chamber 4, which is preferably delimited at least for the most part by imperforate walls 5, although it would also be possible to provide the walls 5 with a perforated sieve at least in part, so as to remove part of the material to be ground Crushing to allow the exit. In this case, for example, the sieve forming part of the walls 5 could have a relatively small hole size in order to actually allow only the finest fraction of the ground material to exit.

The still unmilled regrind is supplied in a known manner, for example EP-PS 98 441, which can be seen along an arrow 6 (FIG. 2), the aspiration control described in this EP-PS for the embodiment shown also being shown for reasons which will become apparent later can be advantageous. The quantity of the material fed along the arrow 6 is expediently regulated by a pivoting slide 7, the position of which is preferably determined by a control circuit (not shown) which contains a measuring element for the power consumed by the motor 2 and throttles the supply if the power (Current) consumption of the motor 2 is too large.

A tangentially branching centrifugal channel 8 leads out of the grinding chamber 4 and is preferably directed obliquely upwards. The angle enclosed between a vertical plane and the centrifugal channel 8, which is not named in FIGS. 1 and 2, is preferably 10 ° to 50 °, in particular 15 ° to 45 °. If the feed opening 6 'according to FIG. 2 is arranged almost exactly at the top of the mill 1, there is an angle between the feed opening 6' and the centrifugal channel 8 with respect to the axis 9 of the rotor 3, which is in the range from 220 ° to 350 ° and in particular from 225 ° to 345 °. This angle determines the average residence time of each regrind particle within the grinding chamber 4. Of course, one is in no way restricted to this angular range, since, for example, the feed opening can also be on the side, as will be seen later with reference to FIG. 3. Practical tests have shown that even at an angle of only 90 ° between the feed opening and the centrifugal channel, the greater part of the ground material is at least once from one of those on the rotor 3

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strikers 11 or hammers fastened to one axis 10 each, so that this angular range may be sufficient for some applications. In most cases, however, 90 ° is not sufficient, and it is preferred if the angle between the feed opening 6 'and the centrifugal channel 8 is at least 180 °, in particular at least 270 °. As will be shown later with reference to FIG. 5, even angles of more than 360 ° are possible and preferred. On the other hand, the invention is not limited to the fact that the feed opening is arranged on the circumference of the grinding chamber, although, as can be seen, the residence time within the grinding chamber can thereby be predetermined with greater accuracy; as such it would also be possible to provide the feed opening in a manner known per se on an end face of the rotor 3.

As can be seen, the centrifugal channel 8 can be made relatively long. The reason for this is that it is completely free from structural obstacles and the energy imparted to the regrind particles by the beater 11 can thus be used undiminished for conveying. Tangential channels on impact machines have already been proposed for a wide variety of purposes, for example in DE-OS 3 406 285 or DE-AS 1 272 091, but no conveying function should be performed there, rather there were cross-tangent channels Sieves are provided on which the material should be thrown. In any case, the particles provided with considerable energy content are flung relatively far upwards until they expediently reach a deflection bend 12 at the end of the centrifugal channel 8. This deflection bend 12 then forms the entrance to a separating device, in particular to a sieve 13, the exit of which is connected to the feed opening or a further feed opening 6 ″ of the mill 1.

From the above explanation it is understandable that the energy content communicated to the regrind particles depends not least on the type and size of the product to be ground. It can therefore prove to be advantageous to adapt the throwing energy of the particles to the particular circumstances by changing the speed of the rotor 3. For this purpose, a speed setting device 55 is connected to a control stage 54 (main switch, contactor) for the motor 2, which can be designed in a manner that can be reversed, depending on the type of the motor 2. For example, in the case of a synchronous or asynchronous motor 2, the device 55 can be formed by a frequency converter whose output frequency can be preselected with the aid of an adjusting wheel 56. For other motors, on the other hand, a resistance circuit or a phase control can be provided, such as is used for the motors of electric locomotives, for example.

The sieve 13 only needs one sieve layer 15 per se in order to fulfill its function, namely to separate the already ground ground particles from those to be ground again, as can be seen from FIG. 1. In the embodiment shown in FIG. 2, however, three screen layers 15, 16 and 17 are provided, the screen 16 being finer than the screen 15, but coarser than the screen 17. The benefit of this application is clear: Whereas in the past the sieve surrounding the grinding chamber 4 had to be replaced relatively laboriously after switching off the mill and observing a certain safety time until the rotor 3 had run out, in order to convert a striking machine to a different grain size, it is now sufficient to Flaps 18, 19 and 20 provided on the sieve exit 14 are to be changed over in order to feed the relevant sieve push-off either to the feed opening 6 "or a line 21 for the finished product. Normally the flap 18 will be set so that the sieve push-off of the sieve layer 15 of the Feed opening 6 "is supplied, but it may be sufficient for a desired broad grain spectrum to also feed the screen rejection of the screen layer 15 to the output line 21. The diarrhea of the sieve layer 17, however, is always fed to the outputs 21.

In order to ensure the accessibility of the grinding chamber 4,

are in a known manner on the impact mill 1 side doors 22, 23 (Fig. 2) are provided which are rotatable about pivot bearing 24. The construction can optionally be designed such that only the door 23 is provided, whereas the grinding chamber 4 is not accessible at all from the side of the centrifugal channel 8. However, in order to enable the attachment of a door 22, the centrifugal channel 8 can be connected to a short tangential piece 25 of the grinding chamber 4, for example being supported on the door 22 by means of a flange 26 or held in this position by a fastening device (not shown) is.

At the other end, the centrifugal channel 8 is pivotally held on an axis 27, which is held stationary in a manner not shown, so that it can be pivoted about the axis 27 after loosening the fastening device holding it on the door 22, whereupon the door 22 is free to open.

It was mentioned above that it is expedient to provide an aspiration, in particular regulated according to EP-PS 98 441. The reason for this will be particularly evident in the later description of FIG. 4, but it is understood that a slight suction via an aspiration tube 28 (FIG. 1) supplies the regrind particles ejected up the centrifugal channel 8, which in particular (additionally or instead of the speed change of the rotor 3 via the stage 15) can be used to adapt the energy of the particles to the respective circumstances. Since the adjustment of the energy of the regrind particles can be important in certain cases, it is clear that regulation according to EP-PS 98 441 is of particular advantage here.

It can be seen particularly from FIG. 2 that such a configuration results in a cycle for those regrind particles which have not yet reached the desired degree of fineness. The ground material first passes through the feed opening 6 ', each particle receiving only a limited number of strokes from the clubs 11 and then being ejected by these clubs 11 in the manner of a golf ball into the tangentially leading centrifugal channel 8. Since the centrifugal channel 8 is not only free of any built-in components, but is additionally ensured by the circuit via the sieve 13 and the feed opening 6 ″ that material that is not flowing in the opposite direction could also stop the flight of the ground material particles thrown upwards, the ground material arrives at to the deflection bend 12. It has already been mentioned that the centrifugal duct 8 can be pivoted about the axis 27, this axis 27 expediently being located exactly in the center of a circle, the curvature of which corresponds to the curvature of the deflection arch 12. This allows the upper end of the centrifugal duct 8 when swiveling, immerse in the appropriately curved sieve housing 29. However, the radius given by the distance of the axis 27 from the curved sieve housing 29 should preferably be selected such that the particles lose as little energy as possible. if the aspiration via the suction tube 28 located near the deflection bend 12 g e is performed, which will then develop a particularly pronounced effect in the region of the deflection bend 12. However, if the radius of curvature is chosen too small, there is a risk that

that individual regrind particles collide with the curved wall and are robbed of their energy. This can

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trigger the chain reaction discussed at the beginning of DE-PS 699 100 by positive feedback, in that not only individual particles are thrown down the centrifugal channel, but in turn slow down other particles and throw them back into the grinding chamber. On the other hand, if the radius of curvature is chosen too large, the path to be traveled by the particles increases, along which of course they also lose energy continuously, so that the same effect can result as if the radius is too small. These relationships will be examined in detail later with reference to FIG. 4. It should only be noted here that tests have confirmed that the inner radius, i.e. the distance of the axis 27 from the boundary wall of the curved part of the centrifugal channel 8 or the sieve housing 29 which is initially located for most construction applications (so small laboratory mills are excluded here) is in the range from 30 cm to 100 cm.

Of course, the question arises as to whether such a deflection bend 12 which returns the material by almost 180 ° cannot be avoided, and in fact such a construction will be described with reference to FIG. 3. The advantage of the deflection bend 12 - and this will be shown by the exemplary embodiment according to FIG. 3 - lies in the fact that it enables a relatively compact arrangement of the impact mill 1 and separating device 13, so that the space requirement can be kept limited.

Although the use of a sieve according to FIGS. 1 and 2 is preferred, the invention is in no way restricted to this. Especially with high throughput of regrind, it may either be necessary to use a larger sieve, or it may prove advantageous to use several separating devices, e.g. also interconnect an air classifier (into which, for example, the centrifugal channel 8 opens). On the other hand, such separation devices can, if desired, also be provided without the use of a sieve. This is illustrated using the exemplary embodiment according to FIG. 3. The angle <1> between a line 30 through the center of the feed opening 6 ″ (into which the feed opening 6 ′ opens) and a line 32 through the center of the centrifugal channel 108, on its axis 31, is approximately 240 with respect to the rotor axis 9 The axis 31 of the centrifugal channel 108 is inclined at an angle 0 to the vertical 33, which here is approximately 15 °.

In this exemplary embodiment, the centrifugal channel 108 does not have a deflection curve leading back to the impact mill 101, but is only slightly curved in the upper region in accordance with a parabola. The centrifugal channel 108 opens into a ballistic separating device 113, which is equipped with three sections 34 to 36, for example, for classifying the ground material in three sizes. In the illustrated embodiment, a screen layer 115 is additionally provided in each of the departments 34 and 35 in order to be able to carry out a further separation, whereas fastening means 37 for a screen layer are probably provided in the compartment 36, but this is removed. Of course, the screen layers 115 can also be removed if desired.

The connection of the outputs 114, 214 from the compartments 34, 35 to the discharge line 21 on the one hand or to the feed opening 6 "on the other hand, which is designed here as a relatively long channel, is not shown, but the connection of the compartment 36 via its outlet 314 may be the same Lines serve as an example.

In the illustrated embodiment, each of the exits 114, 214, 314 is divided into two channels by a separating plate 38, one of which - in the case of attachment, a screen layer 115 - the screen rejection, the other the screen diarrhea. If one now assumes that the coarsest fraction obtained in compartment 36 is normally fed to the feed channel 6 "for renewed grinding, a switching flap 39 can be provided for the second coarsest fraction, which from the position shown in full line in FIG Since the associated sieve is detached from its fastenings 37 in the compartment 36, only particles of a uniform size class accumulate in this compartment 36, which is why the flap 39 is positioned such that all the goods accumulating in the compartment 36 enter the channel 6 ", although the dashed position could still make sense, since there will still be a separation between the coarsest and a less coarse fraction along the separating plate 38. In the hatched position of the flap 39, it feeds part of the material to the outlet line 21.

Since the throwing parabolas can be relatively wide, the embodiment according to FIG. 3 is of course not as space-saving as an embodiment according to FIGS. 1 and 2, whereby it must also be taken into account that the channel 6 "must also have a certain inclination in order to feed the regrind flowing through it without complaint to the mill 101 without gravity.

The deflection bend 12 can, however, also perform a further function, as is shown in FIG. 4. The deflection bend 12 is also used as a deflection sifter. The coarsest fraction is then thrown outwards relatively soon as it enters the deflection bend 12 due to the higher centrifugal force and falls into an outlet 40. The finest fractions, on the other hand, will move more along the inner radius R of the deflection bend 12 and can, if desired, also be cut 41 can be divided into further partial flows.

Here, too, it may be expedient to carry out suction in the area located directly on the deflection bend 12 with the aid of a suction blower 42 which is connected to an aspiration tube 128. An advantageous measure can be to provide an air supply opening 43 in the region of the deflection bend 12 or just after it, which exerts a suction on a middle fraction 44 in the manner of an injector nozzle. The cross section of this opening 43 can, if desired, be adjusted with the aid of a slide 45. The middle fraction 44 will then enter behind the deflection bend 12 into an enlarged space 46, where the flow energy is thus reduced, so that this fraction 44 can settle and exit at the lower end of the space 46 via an outlet 47. The aspiration tube 128 is expediently covered by flaps 48, which only leave upwardly directed channels between one another and thus effectively prevent the fraction 44 from entering the tube 128.

As can be seen more clearly from FIG. 4, the centrifugal channel 8 is suspended on a plate 49 which can be rotated about the axis 27 and which holds the channel 8 on the holding frame 50. The inner radius R has already been mentioned that it expediently lies in a range between 30 cm and 100 cm. Of course, it is possible, if desired, to further subdivide the fractions obtained with the aid of the deflection sifter on the deflection bend 12 with the aid of a sieve or another separating device. The connections to the line 21 or the feed opening 6 "(see the previous figures) can then be made in the manner desired in each case analogously to the description of the previous exemplary embodiments.

It has already been mentioned above that at an angle ® of 90 ° a large part, i.e. more than half of the regrind particles from at least one racket

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11 were hit. Of course, this depends on the design of the mill itself, i.e. of their speed, the radius and the number of clubs. As such, it would be possible to find the length at 90 ° (or even less), even though one accepts that a relatively large amount of material is circulated between the centrifugal channel 8 and the feed opening 6 ". This is not always the case be expedient, especially since this can result in energy losses within the centrifugal channel 8. On the other hand, the angle ® is not restricted to a mere 360 °, as shown in Fig. 5. The mill 201 shown here has two grinding rooms 4, 4 'connected in series. A rotor with beaters according to the previous exemplary embodiments is provided in each of these grinding rooms 4, 4 ', both rotors being driven by a common drive shaft 9' via the motor 2. According to the illustration in FIG. 4 'a space, but this is not absolutely necessary.

The material coming from a silo or a feed device, not shown, falls according to arrow 6 into the grinding chamber 4, from which it is thrown into a curved transfer duct 51, which opens out tangentially from the grinding chamber 4 in the same way as the centrifugal duct 8. The transfer duct 51 is, however, relatively short, so that despite its curvature the transfer of the regrind particles emerging from the grinding chamber 4 into the grinding chamber 4 'is ensured. The ground material thus passes through approximately 270 ° in the grinding chamber 4 and then again approximately 240 ° in the grinding chamber 4 'before it enters the centrifugal channel 8 connected to the grinding chamber 4'. In principle, this centrifugal channel 8 is designed in exactly the same way as described with reference to FIG. 1, and a screen 13 of this type is also provided. However, this sieve 13 is directed in such a way that its outlet (cf. FIG. 14 in FIG. 2) faces the grinding chamber 4 and is connected to a feed opening (cf. 6 "in FIG. 2) of this grinding chamber 4, so that it is not yet sufficient crushed regrind is in turn fed to the first grinding chamber 4.

The example according to FIG. 5 also shows that the regrind that has not yet been sufficiently comminuted does not necessarily have to be returned to the grinding chamber from which it emerged through the centrifugal channel. After all, in the embodiment according to FIG. 5 the grinding rooms 4 and 4 'can be considered as one unit. 6 is no longer the case in this sense. Here, too, the motor 2 expediently drives a continuous shaft 9 ', preferably via a coupling 52. In this embodiment, the material first passes through the feed opening 6' into a grinding chamber 4, exits through a centrifugal channel 8a and is in a first sieve 13a separated into two fractions, one of which enters the discharge line 21, while the other is fed to a feed opening 6 "of a further grinding chamber 4a provided below the sieve 13a. The grinding material exits this grinding chamber 4a via a centrifugal channel 8b Another sieve 13b can be connected to the centrifugal channel 8b, which is connected on the one hand again to the discharge line 21 and on the other hand to the feed opening 6 "of a grinding chamber 4b. If desired, this grinding chamber can also be connected to a further separating device in a manner not shown, or it has a sieve which surrounds the rotor in a known manner. Since only a part of the material is fed to the grinding chamber 4a or 4b below this sieve by dividing into two fractions with the aid of the respective sieve 13a or 13b, these grinding chambers 4a, 4b (in contrast to the illustration in FIG. 6 ) can be made smaller or shorter in the axial direction than the previous one.

The embodiment according to FIG. 6 is not preferred, however, because depending on the type of material to be ground, a differently large residual fraction will result for the passage through the grinding rooms 4a or 4b, so that these grinding rooms 4a, 4b will be utilized to different extents. This can be remedied by the fact that they are also equipped with a feed opening 6 'for fresh regrind, the pivoting slide 7 being able to provide a corresponding feed for uniform use. However, it will then be expedient to assign a separate motor to each of the grinding chambers 4, 4 a, 4 b, the current consumption of which is to form the input signal for the control circuit for adjusting the slide 7. However, all these problems can be mastered more easily if, for example, an arrangement according to FIG. 2 is selected in which the material emerging from the grinding chamber 4 via the centrifugal channel 8 is returned to the same grinding chamber 4 in a circuit via the feed opening 6 ".

The tests carried out by the applicant with a system according to FIG. 2 have led to an unexpected and therefore surprising finding in the strength of its effect. The proportion of the finer and coarser fractions resulting after the sieve 13 changes not only depending on the speed of the motor 2 set via the device 55, not only depending on the size of the angle <D (cf. FIG. 3) but to a very large extent also depending on the training in areas A (FIG. 2), ie in the transition from the grinding chamber into the centrifugal channel. Above all, the grain size can be influenced by the free cross section of the centrifugal channel 8. This effect is now used in the embodiments discussed below according to FIGS. 7 to 9.

FIG. 7 shows a preferred variant for forming area A of FIG. 2. The essentially cylindrical, non-perforated wall 5 surrounding the grinding chamber 4 is connected to a vertical housing wall 53 either by welding or another type of fastening, or also in one piece . The vertical wall 53 is interrupted by an opening 57 which represents the discharge opening from the grinding chamber 4 and at the same time the confluence with the centrifugal channel 8. The centrifugal channel 8 now has on the side facing the mouth 57 a double flange 58 with two mutually parallel legs, the leg 59 facing the grinding chamber 4 engaging in a recess 60 of the vertical wall 53.

The double flange 58 is now dimensioned such that it rests on the underside against the wall 53, whereas it can be displaced upwards. For example, the leg 59 can be elastically flexible, the double flange 58 first being inserted at the top of the opening 57 and then being inserted at the bottom in order to insert the centrifugal channel 8 into the opening 57.

However, it can be seen that, according to FIG. 7, the double flange 58 is longer on the top than on the bottom. It thus covers part of the opening 57 and only leaves the passage cross section of the centrifugal channel 8 free. If a broader grain spectrum or a higher proportion of coarser grain sizes is now desired, the centrifugal channel 8 can be replaced by a centrifugally indicated centrifugal channel 8 'of larger cross section.

The replacement of the centrifugal channel 8 or 8 'according to FIG. 7 is associated with a certain effort. 8 shows an embodiment of how an adaptation of the centrifugal channel cross section, possibly also automatically, can be carried out with less work. The spin

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channel 8 connected by means of its flange 26 (see FIG. 2) and bolts 61 inserted therein, a door 62 possibly being provided below wall 5 to achieve access to the bolts. With these bolts 61, the centrifugal channel 8 is screwed to the vertical wall 53. A guide slot 63 is provided within the wall 53, in which a diaphragm 64 is slidably guided. The aperture 64 can e.g. with the aid of an eccentric inserted into an opening (not shown) in this diaphragm, can be moved up and down by hand from the outside in order to change the free cross section of the opening 57. However, a motorized adjusting device can also be provided, in particular in the case of an automatic adjustment, as will be described later with reference to FIG. 9.

In order to obtain a trouble-free transition from the cross section of the opening 57 into the centrifugal channel 8, which cross section is reduced by the aperture 64, and thus to avoid a vortex formation which could result in energy loss of the regrind particles, the side of the aperture 64 facing the centrifugal channel 8 is preferred an elastic apron 65 is provided. This apron 65 is resiliently biased in such a way that it always lies against the upper wall of the centrifugal channel 8 and thus forms a smoothly running guide surface for the regrind particles. The length of this apron in the direction of the axis 31 is adapted to the respective circumstances, and it is also conceivable and possible that its end is attached to the upper wall of the centrifugal channel or forms this wall itself. In the latter case it does not have to be elastic, it is sufficient if it is simply flexible.

Although this is not absolutely necessary, the screen 64 can be opposite a screen which can be moved from below and which then expediently has not only an apron projecting into the centrifugal channel 8, but also an apron to the side of the wall 5 in order to be able to move from there to ensure a smooth transition. In this case, the wall 5 expediently has a recess which receives at least the end of the apron and preferably extends as far as the end of the wall 5 which is connected to the wall 53, so that the apron has space in the said recess. Another possibility is that, additionally or alternatively, laterally movable panels are provided.

If a certain ratio between the coarse material repelled by the sieve 15 and the material let through the sieve 15 is now desired, the diaphragm 64 can form the actuator in a control loop whose

Input variable from a measuring arrangement for the ratio of the quantities occurring at the two outputs 14a, 14b of the sieve 13 is given. Such a measuring arrangement has already become known from US Pat. No. 3,716,196, in which a balance is used in each case. However, it is simpler if a flow meter is provided as the measuring device, each with a pivotable flap 66a or 66b, which is hit by the flow of the millbase flowing through and experiences a stronger or weaker deflection depending on the intensity of this millbase stream. The forces that occur can be measured on a measuring transducer 67a or 67b, which is connected to terminals A, A 'and B, B' in a control loop. Similar flow meters are known in numerous designs, for example from US Pat. No. 4,543,835.

FIG. 9 illustrates how the measurement signal of such transducers 67a, 67b can be used to adjust the aperture 64 and, for example, also a correspondingly opposite aperture 164. Here, a Wheatstone bridge 68 is provided, in one bridge branch of which the connections A, A 'and in an opposite bridge branch the terminals B, B'. The two transducers 67a and 67b are therefore in a differential circuit. In addition, the bridge 68 also has an adjusting resistor R 'as a setpoint generator and an adjusting resistor R ". The terminals 68 are connected to a voltage source via terminals C, whereas their output terminals are connected to the inputs of an operational amplifier 69 for controlling an adjusting motor 70. The motor 70 is shown here as a direct current motor, but any other adjustment drive can also be used - via corresponding converter stages. The motor 70 drives a drive gear 71 on each side of the screen 64, which is preferably still guided by free-running guide wheels 72. For this purpose, the Aperture 64 is toothed on both edges, whereas the aperture 164 is connected on both sides to racks 73 which are connected to the other side of the respective drive gear 71 and are therefore driven in the opposite direction to the aperture 64. The two apertures 64, 164 move with it towards or away from each other.

It goes without saying that the embodiment shown in FIG. 9 merely represents an example of the design and the drive of such diaphragms. In principle, however, a wide variety of aperture constructions, which are also known, for example, in photography and cinematography, can be used.

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Claims (11)

669337 PATENT CLAIMS 1. Grinding plant with at least one impact mill with a housing forming at least one grinding chamber, in which a rotor provided with projecting impact tools is rotatably mounted with its shaft about a geometric axis, and which has at least one opening for the supply and discharge of the grinding stock, wherein the discharge opening is designed as a centrifugal channel free from structural obstacles, approximately tangentially leading away from the rotor, into which the regrind particles can be thrown under the centrifugal force exerted by the rotating rotor, and with at least one separating device for separating the regrind particles according to their size is connected, which has at least two outlets for regrind particles each of coarser and finer grain size, characterized in that the centrifugal channel (8; 108; 8a, 8b) at an input of the separating device (13; 113) and that over the sling canal l (8; 108; 8a, 8b) and the input to the separating device (13; 113) of regrind of coarser grain size can be fed via an outlet (6 ") to a grinding chamber (4; 4a, 4b) to which the outlet (6") is connected. 2. Plant according to claim 1, characterized in that the separating device (13; 113) has at least one sieve layer (15; 16; 17; 115), and that there are preferably a plurality of sieve ducts (6 ", 21) that can be connected via switching elements and / or that the separating device acts as a ballistic classifier ( 113) is formed using the throwing energy of the grinding material particles in the centrifugal channel (108). 3. Plant according to claim 1 or 2, characterized in that - in the case of several grinding chambers (4,4a, 4b) connected in series in the flow direction of the ground material - each separating device with an input to a different grinding chamber (4,4a, 4b) than with its output (6 ") is connected, preferably to the input to the preceding grinding chamber (4 or 4a), to the output to the subsequent grinding chamber (4q or 4b) (Fig. 6). 4. Plant according to claim 1 or 2, characterized in that the separating device (13; 113) with output (6 ") and separate input is connected to the same grinding chamber (4). 5. Plant according to one of the preceding claims, characterized in that the centrifugal channel (8; 108; 8a, 8b) connected to the input separated from the outlet (6 ", 21) of the separating device (13; 113) at a predetermined angle (0 ) runs obliquely upwards to the vertical (3), and that this angle (0) is preferably in a range from 10 ° to 50 °, in particular from 15 ° to 45 °. 6. Installation according to one of the preceding claims, characterized in that the centrifugal channel (8) has at its upper end a downward deflection bend (12) pointing back towards the impact mill (1), and that this deflection bend (12) preferably has an inner radius (R) in the range from 30 cm to 100 cm and / or as a deflection sifter (FIG. 4) with at least one radially outer channel for the coarser ground material particles and at least one radially inner channel for the finer regrind is formed. 7. Plant according to one of the preceding claims, characterized in that the rotor (3) of the impact mill (1; 101) receiving grinding chamber (4; 4a, 4b) is at least largely limited by imperforate walls (5), and that the ground material can preferably be removed from the grinding chamber (4; 4a, 4b) exclusively via the centrifugal channel (8; 108; 8a, 8b). 8. Installation according to one of the preceding claims, characterized in that the cross section of the centrifugal channel, e.g. by changing, but in particular by changing its opening (57) from the grinding chamber (4) by means of a diaphragm arrangement (64, 164) with a variable opening cross-section, and that the diaphragm arrangement (64) is preferably used to achieve a smooth transition with at least one movable boundary wall (65 ) of the centrifugal channel (8) and / or that a measuring device (67a, 67b) is provided for the portion of at least one fraction emerging from the separating device (13), which is connected to a control device (68-71) which is connected via a Setpoint generator (R ") a setpoint signal can be fed and the output signal of an actuator (70, 71) for automatic adjustment of the cross section of the centrifugal channel (8) can be fed (Fig. 7-9). 9. Plant according to one of the preceding claims, characterized in that the centrifugal channel (8; 108; 8a, 8b) relative to, in particular on the circumferential side of the rotor (3) opening, supply opening (6 'or 6 ") and with respect to Axis (9) of the rotor (3) is offset by at least 90 °, preferably at least 180 °, in particular at least 270 °. 10. Plant according to one of the preceding claims, characterized in that the regrind is helically guided in the axial direction through the centrifugal channel (8; 8a, 8b) and expediently passes through two grinding chambers (4,4 ') connected in series before it leaves the Centrifugal channel (8) emerges, and that preferably the rotors of these grinding chambers (4,4 ') have a common shaft (9'). 11. Plant according to one of the preceding claims, characterized in that the throwing energy of the regrind particles can be adjusted by changing the number of revolutions of the rotor (3) with the aid of a speed setting device (55, 56) (Fig. 1).