EP2004329A1

EP2004329A1 - Method for the production of very fine particles by means of a jet mill

Info

Publication number: EP2004329A1
Application number: EP07722207A
Authority: EP
Inventors: Roland Dr.-Ing. Nied
Original assignee: Nied Roland Dr-Ing
Current assignee: NIED, ROLAND
Priority date: 2006-04-13
Filing date: 2007-04-13
Publication date: 2008-12-24
Anticipated expiration: 2027-04-13
Also published as: US20100065668A1; JP5463138B2; DE102006017472A1; BRPI0710652B1; JP2009533207A; EP2004329B1; CN101421044A; CN101421044B; ES2773730T3; BRPI0710652A2; WO2007118460A1; US8177149B2

Abstract

The invention relates to a method for producing very fine particles by means of a jet mill (1). The relative distance a/dDüse between at least approximately concentric milling jet inlets (5) whose center lines intersect at least approximately in one point is adjusted in accordance with the pressure of the working medium, a representing the jet length and dDüse representing the nozzle diameter.

Description

Method for producing finest particles by means of a jet mill

description

The present invention relates to a method for producing finest particles by means of a jet mill.

The material to be sighted or ground consists of coarser and finer particles which are entrained in an air stream and form the product stream which is introduced into a housing of a jet mill wind miller. The product flow passes in the radial direction into a classifying wheel of the air classifier. In the classifying wheel, the coarser particles are eliminated from the air stream and the air stream leaves the classifying wheel with the fine particles axially through a discharge pipe. The air flow with the fine particles to be filtered out or produced can then be supplied to a filter in which a fluid, such as air, and fine particles are separated from each other.

From DE 198 24 062 Al such a jet mill is known, in the grinding chamber further at least one high-energy jet of hot steam with high flow energy is introduced, the grinding chamber except the inlet device for the at least one grinding jet an inlet for the material to be ground and an outlet for the Product, and in which rich of the coincidence of regrind and at least one grinding jet of hot steam and millbase have at least about the same temperature.

Furthermore, a corresponding air classifier is particularly suitable for a jet mill, e.g. from EP 0 472 930 Bl. This air classifier and its operating methods are basically extremely satisfactory.

From DE 31 40 294 C2 a method and an apparatus for separating a good mixture in components of different grindability are known. To separate a good mixture of components of different grindability into a more easily grindable and a heavier grindable component, the mixture of good is introduced by introduced steam or gas jets in a fluidized state and thereby subjected to an impact crushing. The intensity of the impact crushing is adjusted by the choice of operating pressure, speed and direction of the jets so that only the easier grindable component of the good mixture is crushed. Subsequent to the impact crushing, the mixed material is exposed to a centrifugal force separation, by which the easier grindable component as fine material and the heavier grindable component as coarse material are separated from the unground material mixture. In this case, a fluidized-bed jet mill with a centrifugal force classifier arranged above the fluidized bed is used, wherein the mill housing has an annular gap opening into a discharge chamber in the peripheral area of the centrifugal force-classifier. The annular gap is designed to be adjustable in width over a guided in the mill housing concentric ring. The axes of the jet nozzles of the fluidized bed jet mill lie in one plane and intersect at one point and the mutually facing nozzle orifices lie on a circle concentric with the mill housing.

DE 38 25 469 A1 discloses a process for dispersion, comminution or deagglomeration and the screening of solids. With a classifier jet mill, where a jet mill and a spiral current classifier are combined. The product is supplied via the product feed via injector gas into a dispersion chamber, which is delimited by a lid, a grinding ring and a base plate. A grinding gas, which is also visual gas, is passed through a distributor space and nozzles arranged in the grinding ring in a dispersing space and there depending on the form, gas quantity and nozzle geometry for a targeted solids stress, residence time and separation limit. Dwell time and separation limit can be further varied by supplying secondary gas, which is divided by a cone and flows through a concentric gap, within wide limits. By supplying the adjustable secondary gas flow through the gap, a targeted influencing of the solids residence time and stress is possible. The secondary flow changes the probability of penetration into a collecting container and shifts the separation limit within the dispersion space to coarser values. Due to the concentric gap of variable width continuous withdrawal of coarse or difficult to disperse shares in the collection container is possible. By varying the Mahlgasdruckes, the Mahlgasvolumenstromes through the Mahlring and different nozzle geometries and the supply of more or less secondary gas, the Zer- reduction and separation result can be influenced.

Further, EP 1 080 786 A1, which is based on the present inventor, discloses a fluidized bed jet milling method, an apparatus therefor, and a plant with the latter. In this case, a fluidized bed is enclosed by a housing which rotates on the fluidized bed in the region of at least one high-energy fluid jet entering the fluidized bed about an axis which is at least approximately perpendicular to the at least one fluid jet, which essentially counteracts the centrifugal force to generate a centrifugal force is. As a result, it is advantageously achieved that the energy exchange between the solid particles, which become parts of the high-energy fluid jets, already takes place immediately after the The high-energy radiation into the fluidized bed begins and in general the concentration of the solid particles within the fluid jets is improved.

The aim of the present invention is to further optimize a process for the production of very fine particles by means of a jet mill.

This object is achieved by a method for producing very fine particles according to claim 1.

Accordingly, a method for producing very fine particles by means of a jet mill is characterized in that the relative distance a jet length _nozzle ; and _{nozzle nozzle} diameter nozzle, of at least approximately concentrically arranged grinding jet inlets 5, whose center lines meet at least approximately at one point, is adjusted in dependence on the operating medium pressure.

This advantageously creates a process for the energy-optimized operation of a jet mill by means of compressed gases.

It is preferred if each grinding jet inlet is formed by an inlet nozzle or grinding nozzle.

Another preferred embodiment is that 3 or 4 Mahlstrahleinlässe are present.

Preferably, a fluidized bed jet mill is used.

It is also preferred to use a dynamic air classifier integrated in the jet mill. In this case, it is preferably further provided that the air classifier contains a classifying rotor or a classifying wheel with a clear height increasing with decreasing radius, so that the area of the classifying rotor or wheel through which flows is at least approximately constant during operation. Al Alternatively or additionally, it may be provided that the windscreen contains a classifying rotor or a classifying wheel with a particularly exchangeable immersion tube which is designed such that it rotates when the classifying rotor or the classifying wheel rotates.

Yet another preferred embodiment of the method is that a fine-material outlet chamber is provided, which has a cross-sectional widening in the flow direction.

Preferred and / or advantageous embodiments of the invention will become apparent from the claims and their combinations as well as the entire present application documents.

The invention will be explained in more detail by way of example only with reference to exemplary embodiments, with reference to the drawings, in which:

Fig. 1 diagrammatically shows an embodiment of a jet mill in a partially sectioned schematic drawing,

Fig. 2 shows an embodiment of an air classifier

Jet mill in a vertical arrangement and as a schematic central longitudinal section, wherein the classifying wheel is associated with the outlet pipe for the mixture of classifying air and solid particles,

Fig. 3 shows a schematic representation and a vertical section of a classifying wheel of an air classifier, and

4 is a graphical representation of the relation between the gas pressure p _{0 in} front of the nozzle and the relative jet length a _rel . With reference to the embodiments and examples of application described below and illustrated in the drawings, the invention is explained only by way of example, that is, it is not limited to these embodiments and applications or to the respective feature combinations within individual embodiments and applications. Process and device features result analogously also from device or process descriptions.

Individual features that are indicated and / or illustrated in connection with specific embodiments are not limited to these embodiments or the combination with the other features of these embodiments, but may in the context of the technically possible, with any other variants, even if they in the documents are not treated separately.

The same reference numerals in the individual figures and illustrations of the drawings designate the same or similar or identical or similar components. On the basis of the representations in the drawing, those features are also clear, which are not provided with reference numerals, regardless of whether such features are described below or not. On the other hand, features that are included in the present description but are not visible or illustrated in the drawing will be readily understood by those skilled in the art.

In the method for producing finest particles by means of a jet mill, the new steps provided by the present invention are so clear and understandable that a graphical representation of the individual steps is unnecessary.

1, an embodiment of a jet mill 1 for carrying out the method explained above is shown schematically. As already explained above, the method according to the invention can be carried out manually or automatically. which has no fundamental influence on the usefulness of the procedure. The automated variant of course allows a further reduction of the effort and is readily implemented with facilities and means that are known to those skilled in and by itself, which should not be expressed that the skilled person would also be aware of the individual steps of the method that was recreated by the present invention. In any case, dealing with the sensor, measuring, processor, storage and control devices and control in general and in particular unnecessary, since this device implementation of the method according to the invention does not require its own inventive steps in the knowledge thereof.

The jet mill 1 according to FIG. 1 contains a cylindrical housing 2 which encloses a grinding chamber 3, a grinding material feed 4 approximately half the height of the grinding chamber 3, at least one grinding jet inlet 5 in the lower region of the grinding chamber 3 and a product outlet 6 in the upper region of FIG Milling chamber 3. There, an air classifier 7 with a rotatable classifying wheel 8 is arranged, with which the material to be ground (not shown) is classified in order to discharge only material to be ground below a certain grain size through the product outlet 6 from the grinding chamber 3 and ground material having a particle size above the selected Supply value to another grinding process.

The classifying wheel 8 may be a classifying wheel which is common in air classifiers, whose blades (see later eg in connection with FIG. 3) delimit radially extending blade channels, at whose outer ends the classifying air enters and particles of smaller particle size or mass to the central outlet and to the product outlet 6 entrains, while larger particles or particles of larger mass are rejected under the influence of centrifugal force. In particular, the air classifier 7 and / or at least its classifying wheel 8 are equipped with at least one design feature according to EP 0 472 930 B1. - Q _

For example, for purposes of illustration and ease of understanding, grinder jet inlets 5, e.g. each provided from a radially directed inlet opening or inlet nozzle 9, which may also be referred to as a grinding nozzle 9, each impinge a grinding jet 10 on the Mahlgutpartikel that pass from the Mahlgutaufgäbe 4 in the area of the grinding jet 10, with high energy and the To allow regrind particles to be broken down into smaller sub-particles, which are sucked in by the classifying wheel 8 and, insofar as they have a correspondingly small size or mass, are conveyed through the product outlet 6 to the outside. By arranging the Mahlstrahleinlässe 5 or more appropriately arranged inlet nozzles or grinding nozzles 9, such that the Mahlstrahleinlässe 5 are arranged at least approximately concentric and meet their center lines at least approximately at a point, is achieved that such colliding grinding jets 10 are formed effect the particle decomposition more intensively. In particular, a better effect is achieved than is possible with only one grinding jet 10, in particular if several grinding jets, and particularly preferably 3 or 4 grinding jets, are produced.

In order to provide a method for the energetically optimized operation of a jet mill 1, such as a fluidized bed jet mill, by means of compressed gases, the relative distance a / d _nozzle , with a for the jet length and d _nozzle for the nozzle diameter, of at least approximately concentric arranged Mahlstrahleinlässen 5, the center lines meet at least approximately at one point, adjusted depending on the operating medium pressure. It is not absolutely necessary, even if the above condition is satisfied by the fact that the Mahlstrahleinlässe 5 are in particular directed in pairs against each other. Preferably, 3 or 4 Mahlstrahleinlässe 5 are present. It is further preferred if each grinding jet inlet 5 is formed by an inlet nozzle or grinding nozzle 9. Furthermore, both Manual as well as automated operations and controls are used, with appropriate detection means for detecting the operating medium pressure and the relative distance of each Mahlstrahleinlasses 5 are provided. Such devices for the detection, determination and comparison of values and for the corresponding control and displacement of Mahlstrahleinlässe 5 to adjust their relative distances are known in the art and he know the present invention readily select and use without having to be inventive yourself , One _. Closer attention to such devices for detecting, determining and comparing values as well as for the corresponding control and displacement of the grinding jet inlets 5 for setting their particular relative distances is therefore unnecessary.

Furthermore, for example, the processing temperature can be influenced by using an internal heat source 11 between the grinding material feed 4 and the area of the grinding jets 10 or a corresponding heating source 12 in the region outside the grinding material feed 4 or by processing particles of an already warm grinding material, avoiding Heat losses in the Mahlgutaufgabe 4 passes, including a feed tube 13 is surrounded by a temperature-insulating jacket 14. The heating source 11 or 12 may, when used, be basically arbitrary and therefore purposely operational and selected according to market availability, so that further explanation is not required.

For the temperature, in particular the temperature of the grinding jet or the grinding jets 10 is relevant and the temperature of the material to be ground should at least approximately correspond to this grinding jet temperature.

To form the grinding jets 10 introduced into the grinding chamber 3 by grinding jet inlets 5, for example, superheated steam can be used but also any other suitable fluid can be used. When using superheated steam, it can be assumed that the heat content of the steam after the inlet nozzle 9 of the respective Mahlstrahleinlasses 5 is not significantly lower than in front of this inlet nozzle 9. Because the energy required for the impact crushing is primarily to be available as flow energy, on the other hand Pressure drop between the inlet 15 of the inlet nozzle 9 and the outlet 16 be considerable (the pressure energy will be largely implemented in flow energy) and also the temperature drop will not be negligible. In particular, this temperature drop is to be compensated so far by the heating of the ground material that regrind and grinding jet 10 in the region of the center 17 of the grinding chamber 3 at least two colliding grinding jets 10 or a multiple of two grinding jets 10 have the same temperature.

For the design and implementation of the preparation of the grinding jet 10 from superheated steam, in particular in the form of a closed system, reference is made to DE 198 24 062 A1, the full disclosure of which is fully incorporated by reference herein to avoid mere identical adoption by the present reference. By a closed system, for example, a grinding of hot slag as regrind with optimum efficiency is possible.

In the representation of the present embodiment of the jet mill 1 is representative of any supply of a resource or medium B, a reservoir or generating means 18, such as a tank 18 a shown, from which the resource or operating medium B via line devices 19 to the Mahlstrahleinlass 5 or the Mahlstrahleinlässen. 5 to the formation of the grinding jet 10 and the grinding jets 10 is passed. Instead of the tank 18 a, for example, a compressor can be used to provide appropriate operating medium B available. In particular, starting from a jet mill 1 equipped with such a windscreen 7, the relevant embodiments being intended and to be understood here only as an example and not as a limitation, with this jet mill 1 with an integrated dynamic air classifier 7 a method for the production of very fine particles carried out . As the resource B, a fluid is generally used, preferably the water vapor already mentioned, but also hydrogen gas or helium gas or simply air.

Furthermore, it is advantageous and therefore preferred if the sifting rotor 8 has a clearing height which increases with decreasing radius, that is to say towards its axis, wherein in particular the throughflow area of the sifting rotor 8 is constant. Additionally or alternatively, a fine-material outlet chamber (not shown) may be provided which has a cross-sectional widening in the flow direction.

A particularly preferred embodiment of the jet mill 1 is that the sifting rotor 8 has an exchangeable, co-rotating dip tube 20.

Only to explain and to deepen the overall understanding will be discussed below on the particles to be produced from the preferably processed material. For example, these are amorphous SiO ₂ or other amorphous chemical products which are comminuted with the jet mill. Other materials include silicic acids, silica gels or silicates or materials based on or containing carbon black.

2 and 3 further details and variants of exemplary embodiments of the jet mill 1 and its components are explained below. The jet mill 1 contains, as the schematic representation in FIG. 2 shows, an integrated air classifier 7, which is, for example in types of the jet mill 1 as a fluid bed jet mill, a dynamic air classifier 7, which is advantageously located in the center of the grinding chamber 3 Jet mill 1 is arranged. Depending on the grinding gas volume flow and the classifier speed, the desired fineness of the material to be ground can be influenced.

In the air classifier 7 of the jet mill 1 according to FIG. 2, the entire vertical air classifier 7 is surrounded by a classifier housing 21, which consists essentially of the upper housing part 22 and the lower housing part 23. The upper housing part 22 and the lower housing part 23 are provided at the upper or lower edge, each with an outwardly directed peripheral flange 24 and 25 respectively. The two peripheral flanges 24, 25 are in the installation or functional state of the air classifier 8 to each other and are fixed by suitable means against each other. Suitable means for fixing are, for example, screw connections (not shown). As releasable fastening means may also serve brackets (not shown) or the like.

At a virtually arbitrary point of the flange circumference, both circumferential flanges 24 and 25 are connected to one another by a hinge 26 so that the upper housing part 22 can be pivoted upward in the direction of the arrow 27 after loosening the flange connecting means relative to the lower housing part 23 and the upper housing part 22 from below and the lower housing part 23 are accessible from above. The lower housing part 23 in turn is formed in two parts and it consists essentially of the cylindrical Sichtraumgehäuse 28 with the peripheral flange 25 at its upper open end and a discharge cone 29, which tapers conically downwards. The discharge cone 29 and the Sichtraumgehäuse 28 are at the upper and lower ends with flanges 30, 31 to each other and the two flanges 30, 31 of Austragkonus 29 and Sichtraumgehäuse 28 are like the peripheral flanges 24, 25 by releasable fastening means (not shown) connected to each other. The thus assembled classifier housing 21 is suspended in or on support arms 28a, of which a plurality of evenly spaced around the circumference of the classifier or compressor housing 21 of the air classifier 7 of the jet mill 1 are distributed and attack the cylindrical Sichtraumgehäuse 28.

An essential part of the housing installations of the air classifier 7 is in turn the classifying wheel 8 with an upper cover plate 32, with an axially spaced lower downstream cover plate 33 and arranged between the outer edges of the two cover plates 32 and 33, fixedly connected to these and evenly around the circumference of Classifying wheel 8 distributed blades 34 with appropriate contour. In this air classifier 7, the drive of the classifying wheel 8 is effected via the upper cover disk 32, while the lower cover disk 33 is the outflow-side cover disk. The storage of the classifying wheel 8 comprises a positively driven forcibly Sichtradwelle 35, which is led out with the upper end of the classifier housing 21 and rotatably supports the classifying wheel 8 with its lower end within the classifier housing 21 in flying storage. The removal of the Sichtradwelle 35 from the classifier housing 21 takes place in a pair of machined plates 36, 37 which close the classifier housing 21 at the upper end of an upwardly frustoconical housing end portion 38, the Sichtradwelle 35 lead and seal this shaft passage without obstructing the rotational movement of the Sichtradwelle 35 , Conveniently, the upper plate 36 can be rotatably associated with the Sichtradwelle 35 as a flange and rotatably supported via pivot bearings 35a on the lower plate 37, which in turn is associated with a housing end portion 38. The underside of the downstream cover disk 33 lies in the common plane between the peripheral flanges 24 and 25, so that the classifying wheel 8 is arranged in its entirety within the hinged housing upper part 22. In the region of the conical housing end portion 38, the upper housing part 22 also has a tubular product feed nozzle 39 of the Mahlgutaufgabe 4, the longitudinal axis of which is parallel to the axis of rotation 40 of the classifying wheel 8 and its drive or Sichtradwelle 35 and as far away from this axis of rotation 40 of the classifying wheel 8 and its drive or Sichtradwelle 35, located on the upper housing part 22 radially outboard.

The classifier housing 21 receives the coaxial with the classifying wheel 8 arranged tubular outlet nozzle 20 which lies with its upper end just below the downstream cover plate 33 of the classifying wheel 8, but without being connected thereto. At the lower end of the tube formed as a discharge nozzle 20, an outlet chamber 41 is attached coaxially, which is also tubular, but whose diameter is substantially greater than the diameter of the outlet nozzle 20 and in the present embodiment, at least twice as large as the diameter of the outlet nozzle 20. At the transition between the outlet nozzle 20 and the outlet chamber 41 so there is a significant diameter jump. The outlet nozzle 20 is inserted into an upper cover plate 42 of the outlet chamber 41. Below the outlet chamber 41 is closed by a removable cover 43. The assembly of outlet nozzle 20 and outlet chamber 41 is held in a plurality of support arms 44 which are evenly distributed star-shaped around the circumference of the unit, connected with their inner ends in the region of the outlet nozzle 20 fixed to the unit and secured with their outer ends on the classifier housing 21.

The outlet nozzle 20 is surrounded by a conical annular housing 45 whose lower, larger outer diameter corresponds at least approximately to the diameter of the outlet chamber 41 and its upper, smaller outer diameter at least approximately the diameter of the classifying wheel 8. At the conical wall of the ring housing 45, the support arms 44 terminate and are firmly connected to this wall, which in turn is part of the assembly of outlet nozzle 20 and outlet chamber 41. The support arms 44 and the annular housing 45 are parts of a scavenging air device (not shown), wherein the scavenging air prevents the ingress of matter from the interior of the classifier housing 21 into the gap between the classifying wheel 8 or more precisely its lower cover disk 3 and the outlet nozzle 20. In order to get this scavenging air into the ring housing 45 and from there into the gap to be kept clear, the support arms 44 are formed as tubes, with their outer end portions passed through the wall of the classifier housing 21 and connected via a suction filter 46 to a purge air source (not shown) , The annular housing 45 is closed at the top by a perforated plate 47 and the gap itself can be adjusted by an axially adjustable annular disc in the area between perforated plate 47 and lower cover plate 33 of the classifying wheel 8.

The outlet from the outlet chamber 41 is formed by a fine-material discharge tube 48, which is led into the separator housing 21 from the outside and is connected in a tangential arrangement to the outlet chamber 41. The fine material discharge pipe 48 is part of the product outlet 6. The lining of the junction of the fine material discharge pipe 48 with the outlet chamber 41 serves as a deflecting cone 49.

At the lower end of the conical housing end section 38, a sighting air inlet spiral 50 and a coarse material discharge 51 are assigned to the housing end section 38 in a horizontal arrangement. The direction of rotation of the sighting air inlet spiral 50 is opposite to the direction of rotation of the classifying wheel 8. The coarse material discharge 51 is detachably associated with the housing end portion 38, wherein a flange 52 is assigned to the lower end of the housing end portion 38 and a flange 53 to the upper end of the coarse material discharge 51 and both flanges 52 and 53 are in turn releasably connected to each other by known means, if the Air classifier 7 is ready for use. The dispersing zone to be designed is designated 54. Flanges machined on the inner edge (chamfered) for a clean flow guidance and a simple lining are designated with 55.

Finally, a replaceable protective tube 56 is still applied to the inner wall of the outlet nozzle 20 as a wear part and a corresponding replaceable protective tube 57 may be applied to the inner wall of the outlet chamber 41.

At the beginning of the operation of the air classifier 7 in the illustrated operating state, view air is introduced into the air classifier 7 at a pressure gradient and at a suitably chosen entry speed via the sighting air inlet spiral 50. As a result of the introduction of the classifying air by means of a spiral, in particular in conjunction with the conicity of the housing end portion 38, the classifying air spirals upward into the region of the classifying wheel 8. At the same time, the "product" of solid particles of different mass is introduced into the classifier housing 21 via the product feed port 39. From this product, the coarse material, ie the particle fraction with greater mass counter to the classifying air in the range of Grobgutausträges 51 and is provided for further processing. The fine material, ie the particle fraction with a smaller mass is mixed with the classifying air, passes radially from outside to inside through the classifying wheel 8 into the outlet nozzle 20, into the outlet chamber 41 and finally via a fine material outlet pipe 48 into a fine material outlet or outlet 58, as well as from there in a filter in which the resources in the form of a fluid, such as air, and fines are separated. Coarser fines constituents are thrown radially out of the classifying wheel 8 and mixed with the coarse material in order to leave the classifier housing 21 with the coarse material or to circle in the classifier housing 21 until it has become fines of such a grain size that it is discharged with the classifying air. As a result of the abrupt cross-sectional widening from the outlet nozzle 20 to the outlet chamber 41, there is a significant reduction in the flow velocity of the fine-material-air mixture. This mixture will therefore reach the fine material outlet 58 via the fine-material outlet pipe 48 at a very low flow rate through the outlet chamber 41 and produce abrasion only to a slight extent on the wall of the outlet chamber 41. Therefore, the protective tube 57 is only a highly precautionary measure. However, the reasons for a good separation technology high flow velocity in classifying wheel 8 still prevails in the discharge or outlet nozzle 20, which is why the protective tube 56 is more important than the protective tube 57. Particularly significant is the diameter jump with a diameter extension in the transition from the outlet nozzle 20 into the outlet chamber 41st

Incidentally, the air classifier 7 can again be well maintained by the division of the classifier housing 21 in the manner described and the assignment of the classifier components to the individual sub-housings and defective components can be replaced with relatively little effort and within short maintenance times.

While in the schematic illustration of FIG. 2, the classifying wheel 8 with the two cover disks 32 and 33 and the blade ring 59 arranged therebetween with the blades 34 is shown in already known, conventional form with parallel and parallel-sided cover disks 32 and 33 Fig. 3 shows the classifying wheel 8 for a further embodiment of the air classifier 7 of an advantageous development.

This classifying wheel 8 according to FIG. 3 contains, in addition to the blade ring 59 with the blades 34, the upper cover disk 32 and the lower downstream cover disk 33 spaced axially therefrom and is rotatable about the axis of rotation 40 and thus the longitudinal axis of the air classifier 7. The diametrical extent of the classifying wheel 8 is perpendicular to the axis of rotation 40, ie to Longitudinal axis of the air classifier 7, regardless of whether the axis of rotation 40 and thus the said longitudinal axis is vertical or horizontal. The lower downstream cover disk 33 concentrically encloses the outlet nozzle 20. The blades 34 are connected to both cover disks 33 and 32. Deviating from the prior art, the two cover disks 32 and 33 are conically shaped and were preferably such that the distance of the upper cover disk 32 from the outflow side cover disk 33 from the rim 59 of the blades 34 increases inwards, ie towards the axis of rotation 40 is preferably continuously, such as linear or non-linear, and with further preference so that the surface of the flow-through cylinder jacket for each radius between the blade outlet edges and outlet nozzle 20 remains constant. The decreasing due to the decreasing radius in known solutions outflow rate remains constant in this solution.

Apart from the variant of the design described above and in FIG. 3, the upper cover plate 32 and the lower cover plate 33, it is also possible that only one of these two cover plates 32 or 33 is conical in the manner explained and the other cover plate 33 or 32 is flat, as in the context of the embodiment shown in FIG. 2 for both shields 32 and 33 is the case. In particular, the shape of the non-parallel-sided cover disk may be such that at least approximately so that the surface of the cylinder jacket through which flows through remains constant for each radius between blade outlet edges and outlet nozzle 20.

Below, for further explanation and as the basis of further inventive aspects, the optimum jet length for jet mills will be discussed

From observations of test results in the low-pressure range (p ₀ <4 bar (abs)) a dependence of the optimal paint the jet length from the grinding gas pressure. The following is an approach to quantify this dependency. At the same time, a theoretical prediction is made as to whether such a dependence also exists on the grinding gas temperature.

In order to describe the processes during the beam expansion, it is initially assumed that both the pressure conditions at the blasting jacket through which the solid particles to be comminuted enter the jet to be accelerated and comminuted there, as well as at the "storage area", where appropriate two or more rays hit, should be constant.

Furthermore, it is assumed that these pressure ratios correlate with the momentum current density in the beam:

^{1 ~} A _Smhl ^{~ C} ld ⁾

in which mean

A- _strah i [m ² ] the area of the beam

C ₁ constant

I ^* [N / m ² ] Impulse current density m _L [kg / s] Gas mass flow v _ad [m / s] Adiabatic gas velocity downstream of the nozzle.

(It can be counted with the mass flow and the speed at the nozzle exit, since the momentum flow in the jet is preserved.)

Assuming that the beam propagates in a cone shape and the beam opening angle α is independent of pressure and temperature (at least the former was in the investigations of Hagele, Joachim: Experimental investigations on aerosol jets from micronozzles, - News from the Max Planck Institute for Flow Research No .72, 1981, for continuously tapered nozzles as well as for the pressure ratio. fitted Laval nozzles found), both surfaces can be according to the geometric relationship

Λ-s _t rahi = C ₂ - π - a ² (2)

With

C ₂ = βa) (3)

in which mean further

C ₂ constant a [m] beam length.

The gas mass flow through a nozzle results in too

the adiabatic jet exit speed becomes

in which mean also

Nozzle In] Nozzle diameter m _L [kg / s] Gas mass flow

Pl [bar (abs)] expansion pressure

Po [bar (abs)] gas pressure in front of the nozzle

R [kJ / kgK] gas constant

T ₀ [K] Gas temperature in front of the nozzle

K isentropic exponent ψ _max outflow coefficient.

If equations 2, 4 and 5 are used in Equation 1, we obtain

With

Cz = Tt ₂ ⁽ 7 ⁾

and

^ max = T ^ r ^• (ir) ^ά (8)

wherein additionally means

C ₃ constant.

Finally, you put

With

constant

so you get after reshaping

which means finally

a _rel relative beam length

Accordingly, the jet length a _re i depends only on the grinding gas pressure p ₀ , the pressure ratio Pi / p ₀ and K, but not on the grinding gas temperature. From experiments (see also Nied, R.: jet milling in the fluid bed counter jet mill tiz 109 (1985) 1, p 23 ff) is known that

• for a grinding gas pressure of pθ = 7 bar (abs)

• a pressure ratio of and

• K = 1.4

the relative beam length a _rel = 20.

This allows the value of the constant C to be calculated

C = 9.922 (11).

In FIG. 4, the relation between the gas pressure p ₀ in front of the nozzle and the relative beam length a _re i plotted on the basis of the plot of Equation 10 with Equation 11 to C.

The invention is illustrated by way of example only and not by way of example in the description and the drawing, but includes all variations, modifications, substitutions and combinations that the skilled person the present documents in particular in the context of the claims and the general representations in the introduction this description and the description of the embodiments and their representations in the drawing and combine with his expert knowledge and the prior art. In particular, all individual features and design options of the invention and its variants can be combined. LIST OF REFERENCE NUMBERS

Jet Grinder Cylindrical housing Grinding chamber Grinding area Grinding jet inlet Product outlet Air classifier Screen wheel Inlet opening or inlet nozzle or grinding nozzle Grinding jet Heating source Heating source Supply pipe Temperature-insulating jacket Inlet Outlet Center of grinding chamber Reservoir or generating unit Line fittings Outlet Sifter housing Upper part of housing Lower part of housing Peripheral flange Peripheral flange Joint Arrow Sighting housing a support arms

discharge cone

flange

cover disc

shovel

Clearwheel shaft a pivot bearing upper machined plates lower machined plate

housing end

Product feeding connection

axis of rotation

Exit chamber upper cover plate removable cover

Support arms conical ring housing

Suction

perforated plate

Feingutaustragrohr

deflection cone

Air inlet spiral

coarse material

flange

Dispersion zone on the inner edge machined (chamfered) flanges and lining interchangeable protective tube replaceable protective tube

Fines outlet / outlet

blade ring

Claims

claims

1. A method for producing very fine particles by means of a jet mill (1), characterized in that the relative distance a / drase / with a for the jet length and nozzle for the nozzle diameter of at least approximately concentrically arranged Mahlstrahleinlässen (5) whose center lines are at least approximately at one point, depending on the resource pressure is set.

2. The method according to claim 1, characterized in that each Mahlstrahleinlass (5) by an inlet nozzle or grinding nozzle (9) is formed.

3. The method according to claim 1 or 2, characterized in that 3 or 4 Mahlstrahleinlässe (5) are present.

4. The method according to any one of the preceding claims, characterized in that a fluidized bed jet mill is used.

5. The method according to any one of the preceding claims, characterized in that in the jet mill (1) integrated dynamic air classifier (7) is used.

6. The method according to claim 5, characterized in that the air classifier (7) includes a classifying rotor or a classifying wheel (8) having a decreasing radius increasing clear height so that during operation, the flowed through surface of the classifying rotor or wheel (8) at least is approximately constant.

7. The method according to claim 5 or 6, characterized in that the air classifier (7) includes a classifying rotor or a Sichtrad (8) with a particular interchangeable dip tube (20) which is designed so that it rotates when the Classifying rotor or the sighting wheel (8) rotates.

8. The method according to any one of the preceding claims, characterized in that a fine material outlet chamber (41) is provided which has a cross-sectional widening in the flow direction.