EP3857573B1 - Grinding media, device and method for producing said grinding media and use thereof - Google Patents

Description

The present invention relates to grinding media for use in an electromechanical comminution system (EMZ) and a corresponding device and a method for producing such grinding media.

In such a comminution plant, comminution, deagglomeration and/or dispersing of disperse substances and/or pumpable multiphase mixtures takes place. Such a crushing plant is, for example, in DE 10 2018 113 725 described.

Magnetic grinding media are used in DD 240 674 B1 , DE 41 13 490 A1 , EP 0510 256 B1 as well as U.S. 5,348,237 , which propose devices and methods for electromechanical comminution and/or deagglomeration or dispersion of disperse inorganic solids (silicates, oxide ceramics, pigments) or multiphase mixtures (dispersions), described as magnetic working bodies in order to generate intensive translational transverse movements and tumbling movements with electromagnetic fields of electrical excitation systems, and thus to generate sufficient mechanical stresses on the educt. These working bodies are made of hard magnetic material (e.g. hexaferrite), are spherical or barrel-shaped with a diameter or length of 1.0 to 4.0 mm and fill the process chamber of the electromechanical comminution system at least 40 to 90% by volume. . It is to be expected that such working bodies made of hard-magnetic hexaferritic materials in electromechanical comminution systems will wear out severely, so that the product will be contaminated with the wear.

In DE 32 33 926 A1 proposes an electromechanical comminuting, mixing or stirring device using ferromagnetic particles or bodies made of carbon steel or other materials having the necessary magnetic and/or electrical properties, suitably for fine comminution as pins of 15 mm and a diameter of 2 mm and which should have a higher magnetic conductance in the axial direction. Such working bodies are not suitable for the comminution, deagglomeration and dispersing of disperse substances, pumpable multi-phase mixtures, since the magnetic properties are far too low and their movement and the stresses triggered thereby are insufficient. In addition, foreign substances are introduced into the product as they wear out.

In DE 27 12 620 A1 are often proposed magnetically polarized working body to achieve an additional non-uniformity of the working body movement. However, multi-pole magnetization is very complex and technically feasible only on large working bodies (> 5 mm). But then, due to the large gap volume between the working bodies, no fine comminution or deagglomeration and dispersing of dispersions is possible.

In DE 198 55 219 B1 to support the disintegrating effect of low-frequency electromagnetic fields in biomass, the use of magnetized, hard-magnetic, inert working bodies, which consist of hard ferrite and are spherical, is proposed. Although hard ferrites are largely resistant to acids and alkalis, they have insufficient mechanical strength. In particular, the fracture toughness is too low. It can therefore be assumed that these working elements will wear out, contaminate the product and have to be replaced after only a short period of operation.

Patent applications are also known that describe the movement of the grinding media in mechanical mills (ball mill: PL382610A1 or. WO_2014/065680 A1 , RU 2 319 546 , mortar grinder: WO 86/01129 ) with magnet systems arranged on the outside of the grinding container and thus increase the efficiency of the grinding process (e.g. cement production: EP 2 128 107 A2 ) want to improve. Grinding or working bodies made of ferromagnetic material, primarily carbon steel, are used. In addition to the low magnetic properties, such materials heat up very strongly, since eddy currents are generated in them due to the changing magnetic fields due to their high electrical conductivity. On the one hand, this reduces the efficiency of the grinding process and, on the other hand, leads to additional heating of the product.

Likewise is off EP 0 434 985 A1 known to use secondary elements for mixing liquids or dispersing solids in liquids and/or grinding solids by means of linear motors, which are irregularly shaped on the outside to increase the mixing effect, e.g. by spikes, ribs, etc. and made of magnetizable metals (iron), a reaction metal (aluminum or copper), a compound reaction metal (iron/aluminium, iron/copper) or magnetisable plastic or magnetic rubber. The components are assembled in a sandwich construction, for example by gluing. In addition, such secondary elements can be encased with a non-magnetic material, eg plastic. None of the suggested Embodiments represents an EMZ grinding body and can be used as such in comminution plants (EMZ) for comminution, deagglomeration and dispersing of disperse substances, pumpable multi-phase mixtures.

In addition, magnetic working bodies—so-called magnetobeads—are known, which are mainly used in carrier technology for biocatalysis, immobilization, separation and/or analysis. A comprehensive overview is given in the Publication Pieters, BR; Williams, R.A.; Webb, C.: Magnetic carrier technology. In: Williams, RA (Ed.): Colloid and Surface Engineering: Applications in the Process Industries. Butterworth Heinemann, Oxford 1992, pp. 249-286 given. These known magnetobeads in the form of particles or spheres are made exclusively of magnetite or mixed with a polymer (=composite) and have dimensions in the range of 0.2-150 μm, depending on the application. They are therefore always soft-magnetic and therefore not suitable for the electromechanical comminution, deagglomeration and dispersing of disperse substances, pumpable multi-phase mixtures.

Magnetic polymer particles as carriers for enzymes, bacteria, cells, RNA and proteins are used in U.S. 5,814,687 called, which are produced by mixing a monomer with superparamagnetic particles and then polymerizing.

The patent specification DE 196 38 591 describes magnetic particles that are constructed as 50-1500 nm large monodisperse SiO2 spheres with a magnetic particle layer < 60 nm thick.

In JP 0830 8570 it is suggested to mix porous ceramics with 0.01-100 µm fine paramagnetic particles, shape the mixture and then sinter. The carriers are suitable for immobilization in the field of fermentation, biochemistry and environmental technology.

US2010/046323 and US2006/133954 show hard-magnetic bodies that are coated with polymers and intended for mixing liquids.

JP H09 325656 shows how polymer coatings are applied to toner particles using a fluidized bed process.

The object of the present invention is to provide grinding bodies with low grinding body wear and high product compatibility, which have appropriate magnetic and mechanical properties, and a corresponding device and a method for producing such grinding bodies.

This object is solved by the independent patent claims.

A grinding body according to the invention is characterized in particular by the fact that the grinding body has a hard-magnetic core and at least one wear-resistant coating surrounding it. Such coated, hard-magnetic grinding media are used in comminution plants for comminution, deagglomeration and/or dispersing, in particular of active ingredients that are required in pharmacy, biotechnology and/or the food industry.

There were, for example, attempts in the EMZ after DE 10 2018 113 725 carried out in which the corresponding coated hard magnetic cores showed no gravimetrically detectable loss of mass after 10 minutes in batch operation.

In the case of uncoated grinding media, however, a relative loss in mass of 1 to 10% by weight was determined under the same conditions. Such grinding media lead to higher operating costs due to wear and tear and are not product-compatible with products from the pharmaceutical, biotechnology and/or food industry and are therefore not permitted in corresponding comminution plants.

The hard-magnetic cores of such grinding bodies can have a coercive field strength of at least 50 kA/m, preferably at least 70 kA/m and particularly preferably at least 100 kA/m. Furthermore, they can have a remanence of >50 mT, preferably >70 mT and particularly preferably >100 mT.

The wear-resistant layer is a polymer layer, for example. This has corresponding physical and/or chemical properties which are advantageous when the grinding bodies are used as mentioned above.

The hard-magnetic core is spherical and can be correspondingly magnetizable.

Furthermore, depending on a core size, in particular core diameter, the coating can have a thickness of 5 μm to 500 μm and preferably from 10 μm to 300 μm. The spherical shape of the hard-magnetic cores has a diameter of 0.1 mm to 10 mm.

As a rule, the polymer layer or coating can be closed and/or at least one primer layer can be arranged between the polymer layer and the hard-magnetic core as an adhesion-promoting layer. In addition, the surface of the coating can be smoothed. In the production of the grinding media, the hard magnetic cores are first treated mechanically and/or chemically on their surface to improve the physical and/or chemical adhesiveness in order to increase the surface roughness. Then can the hard-magnetic cores are magnetized and then fed to a device according to the invention for the production of the grinding media.

Such a device has at least one reactor, which is divided by a gas-permeable floor into a lower, material-free area and an upper, material-carrying area. The material-carrying area serves to accommodate fluidized, disperse coating material and fluidized, hard-magnetic cores. Furthermore, the material-carrying area is surrounded by a magnet system for fluidizing the hard-magnetic cores.

In this case, the pretreated hard-magnetic cores, see the above statements, are fed to the reactor in which the coating material is already in dispersed form. Before being fed in and/or in the reactor, the hard-magnetic cores are heated to a temperature that is higher than a melting point of the coating material but lower than a Curie temperature of the hard-magnetic cores.

In the material-carrying area of the reactor, the hard-magnetic cores are then fluidized by the magnet system or the magnetic field generated by it, so that particles of the coating material come into contact with the surfaces of the hard-magnetic cores and melt there due to the temperature. By removing the heat of fusion, the particles of the coating material solidify. After a sufficient residence time in the reactor, the hard-magnetic bodies are preferably completely and evenly coated with the coating material.

The hard-magnetic cores with their coating can then be removed from the reactor as finished grinding media, cooled and optionally post-treated. These grinding media are then very well suited for use in electromechanical comminution systems in the magnetized state or also demagnetized in mechanical comminution systems for comminution, deagglomeration and/or dispersing of disperse substances and/or pumpable multi-phase mixtures, also in areas of application in the field of pharmacy and the like and are characterized characterized by low material wear and high product compatibility.

Furthermore, the grinding media according to the invention are characterized in that, in the demagnetized state, they can also be used in ball mills, such as agitator ball mills or the like, for comminuting, deagglomerating and/or dispersing active substances or organic materials in general.

Compared to known grinding media, the grinding media according to the invention are also characterized by a higher density, so that a higher processing intensity is possible with the same operating parameters of ball mills.

The device according to the invention for producing such grinding bodies has a gas-permeable base in the corresponding reactor. Furthermore, the reactor can have a gas inlet opening below this floor. As a result, a gas flow can be introduced into the material-carrying area, which supports, for example, the fluidization of the particles of the coating material and also the fluidization of the hard-magnetic cores. However, the main fluidization of the hard-magnetic cores takes place through the magnet system surrounding the reactor.

In order to be able to feed or remove material from the reactor in a simple manner, at least one closable opening for feeding cores, coating material and/or for removing the finished grinding media can be formed above the base. Of course, the arrangement of several openings for the separate supply of corresponding substances is also possible.

It has already been pointed out that the magnet system, which completely surrounds the reactor above the gas-permeable floor, enables corresponding fluidization of heated, magnetized, hard-magnetic cores. For this purpose, the magnet system can have at least one coil that completely surrounds the reactor.

In order to be able to heat the hard-magnetic cores sufficiently, a heatable and in particular funnel-shaped container can be assigned or arranged in particular in an upper end region of the reactor, in which previously magnetized hard-magnetic cores can be arranged for heating. The hard magnetic cores are heated to a temperature which is lower than a corresponding Curie temperature of the hard magnetic cores and higher than a melting temperature of the coating material.

There is also the possibility of arranging another magnet system in the area of a connection between the reactor and the funnel-shaped container. This is preferably operated periodically in pulses with a current. Current pulse height and duration can be selected in such a way that hard magnetic cores arranged at least in a lower area of the funnel-shaped container are briefly influenced in such a way that their mutual magnetic attraction is canceled and thus, as a result of the magnetic pulling force through this additional magnet system and gravity, a certain amount of Cores in the material-carrying area of the reactor falls. The amount of hard-magnetic cores supplied can be adjusted by current pulse height and pulse duration.

Appropriate openings in the reactor have already been pointed out, with at least one lateral opening for removing coated hard-magnetic cores, i. H. the finished grinding media, can be arranged.

It is possible that already preheated and magnetized hard magnetic cores are fed into the reactor. In this context, however, it can prove to be advantageous if a further heating device is arranged in the material-carrying area. The coating material can be heated by this, although heat losses or direct heating of the fluidized, hard-magnetic cores can also be compensated or ensued.

An example of a heating device is heating with microwaves, in which case a corresponding microwave antenna, which is connected to a controllable microwave generator, can be arranged in the material-carrying area. In this connection, the reactor above the gas-permeable tray should be formed of a microwave-non-absorbent material.

At least one temperature sensor can preferably be provided in particular above the gas-permeable floor and in particular in the material-carrying area. This can be used to record the mean temperature in the reactor and/or the coating material and/or the hard-magnetic cores. Of course, several temperature sensors are also conceivable, which can be assigned to different areas of the reactor, for example.

In terms of the method, it must be ensured that the device according to the invention, for example, magnetizes the hard-magnetic cores and heats them to a temperature above the melting point and below the Curie temperature. These magnetized and heated hard-magnetic cores are then fluidized by the corresponding magnetic field of the magnet system that changes over time and location. The likewise fluidized, powdery coating material is then melted on the surfaces of the heated, hard-magnetic cores, so that a coating can form.

When a preferably closed coating has formed and a certain target layer thickness has also been reached, the grinding media produced in this way can be removed and cooled to room temperature.

A magnetic field that changes over time and location is generated in the reactor by an additional magnet system. This magnet system has at least one coil and surrounds the reactor above the gas-permeable floor. Alternating currents flow through the magnet system and, for example in the middle of the gas-permeable floor, has a magnetic flux density with an effective value of at least 5 mT, with the frequencies of the alternating currents having to be adapted to the mass of the hard-magnetic cores. Such a magnetic field is used, for example, to fluidize the hard-magnetic cores in the material-carrying area of the reactor.

In order to achieve sufficient magnetization of the hard-magnetic cores before they are fed into the reactor, appropriate magnetization can take place outside the reactor, preferably by pulse magnetization. Before such a magnetization outside of the reactor, it can prove advantageous if the surfaces of the cores are roughened by mechanical and/or chemical methods. This improves the adhesion of the coating material.

According to the invention, there is also the possibility that the hard-magnetic cores are already completely or at least partially heated after they have been magnetized and still outside the reactor. It is also possible for the hard-magnetic cores in the reactor to be heated in the fluidized state by means of a heating device and, for example, by microwaves.

In order to further improve adhesion, there is also the option of coating the hard-magnetic cores with an adhesion promoter. This can be done before magnetization.

Furthermore, externally pre-coated and magnetized hard-magnetic cores that are fed into the reactor can be heated with the microwave and completely coated.

According to the invention, there is also the possibility of removing correspondingly finished grinding media from the reactor and essentially simultaneously feeding an equivalent amount of magnetized hard-magnetic cores back into the reactor. As a result, essentially the same quantity of such cores can always be stored for further treatment in the reactor.

The removal of the finished grinding bodies from the reactor or their feeding can optionally be done manually. Correspondingly finished grinding bodies can be smoothed after they have been removed from the reactor, for example by tumbling (vibratory grinding).

It is also possible to sort the grinding media by size and, if necessary, to re-magnetise them.

The device according to the invention for producing the grinding media is also suitable for recoating grinding media that have already been used. For this purpose, any residual coating present on such grinding bodies can be removed and the core surfaces can also be pretreated using the methods already described (mechanical and/or chemical roughening and/or application of a primer layer). These can then be returned to the device according to the invention in the form of the remaining hard-magnetic cores.

It has already been pointed out that the grinding media according to the invention can be used in electromechanical comminution systems for comminution, deagglomeration and/or dispersing of active ingredients which are required in pharmacy, biotechnology and/or the food industry. This also applies to ball mills, in which case the grinding media can be demagnetized beforehand.

Figur 1:

eine Anzahl von hartmagnetischen Kernen;

Figur 2:

für ausgewählte hartmagnetische Kerne ermittelte Hysteresekurven;

Figur 3a:

einen unbehandelten hartmagnetischen Kern;

Figur 3b:

einen oberflächenbehandelten hartmagnetischen Kern;

Figur 4a:

eine elektronenmikroskopische Aufnahme einer Oberfläche eines unbehandelten hartmagnetischen Kerns;

Figur 4b:

eine behandelte Oberfläche eines hartmagnetischen Kerns analog zu Fig. 4a;

Figur 5a:

eine lichtmikroskopische Aufnahme eines Querschliffs eines beschichteten hartmagnetischen Kerns;

Figur 5b:

eine Aufnahme analog zu Fig. 5a mit anderer Schichtdicke der Beschichtung;

Figur 6:

ein Diagramm zur Darstellung unterschiedlicher Schichtdicken in Abhängigkeit von der Temperatur des fluidisierten Beschichtungsmaterials;

Figur 7:

ein erstes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung;

Figur 8:

ein zweites Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung;

Figur 9:

ein drittes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung;

Figur 10:

ein viertes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung;

Figur 11a:

einen Mahlkörper mit Beschichtung; und

Figur 11b:

einen Mahlkörper analog zu Fig. 11a nach Glätten der Oberfläche.

Advantageous exemplary embodiments of the invention are explained in more detail below with reference to the attached figures. Show it

Figure 1:

a number of hard magnetic cores;

Figure 2:

hysteresis curves determined for selected hard magnetic cores;

Figure 3a:

an untreated hard magnetic core;

Figure 3b:

a surface-treated hard magnetic core;

Figure 4a:

an electron micrograph of a surface of an untreated hard magnetic core;

Figure 4b:

a treated surface of a hard magnetic core analogous to Figure 4a ;

Figure 5a:

an optical micrograph of a cross section of a coated hard magnetic core;

Figure 5b:

a recording analogous to Figure 5a with a different layer thickness of the coating;

Figure 6:

a diagram showing different layer thicknesses as a function of the temperature of the fluidized coating material;

Figure 7:

a first embodiment of a device according to the invention;

Figure 8:

a second embodiment of a device according to the invention;

Figure 9:

a third embodiment of a device according to the invention;

Figure 10:

a fourth embodiment of a device according to the invention;

Figure 11a:

a grinding media with a coating; and

Figure 11b:

a grinding media analogous to Figure 11a after smoothing the surface.

1 shows a number of hard-magnetic cores 6, which in the illustrated embodiment are ball-shaped or spherical and have a diameter of 1-1.6 mm. Other diameters can also be used. In the illustrated embodiment, the hard-magnetic cores are made of strontium hexaferrite (SrFe ₁₂ O ₁₉ ). Other materials can be used, which in particular have coercive field strengths 21, see 2 , of, for example, >50 kA/m and remanences 22 of >50 mT. Such materials are rare earth magnets from the material systems Nb-Fe-B, Pr-Fe-B or Sm-Co, AlNiCo materials and also Fe-CrCo, PtCo and MnAlC alloys.

In the 1 The cores shown with the appropriate sizes were produced from a stable slurry containing strontium hexaferrite particles using a drop-forming process, followed by drying and sintering. Other sizes of hard magnetic cores smaller than 1.0 mm or larger than 1.6 mm and other shaping processes such as pressing, briquetting, spray drying, fluidized bed granulation or simple pelleting of the starting materials with subsequent temperature treatments up to sintering are also possible. Such forming processes determine the feasible sizes, shapes and strengths as well as the surface morphology of the hard magnetic cores.

2 shows a diagram with hysteresis curves determined by a sample vibration magnetometer for various selected hard magnetic cores from a total of three batches. These are made of strontium hexaferrite. The corresponding coercivity 21 and the magnetic polarization or remanence 22 of the hard-magnetic cores can be seen. In addition note that the remanence 22 corresponds to the magnetic polarization at H=0. In this case, the magnetic characteristics are coercivity 270 - 340 kA/m and remanence 162 - 200 mT. These are in the range preferred according to the invention.

In the Figure 3a and 3b different surfaces 24 of the hard magnetic cores 6 are shown. The illustrations are electron micrographs of an untreated ( Figure 3a ) and a surface-treated ( Figure 3b ) hard magnetic core with a diameter of 29. The surface treatment after Figure 3b was carried out chemically using 14.8 molar phosphoric acid (H ₃ PO ₄ ) at 120° C. for 30 minutes. This etching resulted in an increase in the surface roughness, which enables better mechanical adhesion of further layers. Etching is also possible with other acids such as hydrochloric acid, aqua regia or the like. A volume ratio of hard magnetic cores to solvent was 1:50 to 1:100 in these chemical treatments in order to avoid concentration of the solvates.

Instead of chemical surface treatment, mechanical roughening, for example by grinding, sandblasting or the like, is also possible.

The surface treatment according to the invention leads to a mass loss of less than 20% by weight, so that a corresponding change in size of the hard-magnetic cores is less than 5%.

In order to further improve the adhesive strength, a primer layer can be applied, for example by silanizing the surface of the hard-magnetic cores. This allows the formation of strong bonds between the core material and the coating material.

If the coating takes place with a polymer, organofunctional silanes are preferably used. These have a functional group -X, which connects to the polymer layer. The connection to the organic material takes place via a hydrolyzable functional group. This combines with the -OH groups, which are always found on inorganic materials. This creates covalent bonds with the inorganic substrate via a condensation reaction. In selecting the organofunctional silane, an appropriate -X functional group is selected. This depends on the polymer used. Possible groups are amino (-NH ₂ ), sulfur (-S), glycidol (-C ₃ H ₆ O ₂ ) and metacryloxy (-C ₄ H ₅ O ₂ ). Aminosilanes are suitable for a polymer coating with polyamide.

Figure 4a and 4b show electron micrographs of surfaces 24 of an untreated ( Figure 4a ) and a silanized ( Figure 4b ) Hard magnetic core 6. A 5 vol% silane-acetone solution was used used. A continuous layer can be seen in the upper part of the electron micrograph 4b. On the rest of the image, this layer is covered by particles that are tightly bound to the surface. Other solvents that can be used are water and ethanol. As a rule, the hard-magnetic cores should be washed with the solvent used after silanization, dried in air and then baked in an oven, for example at 105°C for 1 hour.

Figure 5a and 5b show light micrographs of cross sections of hard magnetic cores coated with a polyamide as the coating material, see coating 28. These were reproduced in a device according to the invention 7 manufactured. In Figure 5a is a coating of corresponding thickness 23 less than thickness 23 in Figure 5b educated.

After 6 different layer thicknesses result, for example depending on a powder temperature of the coating material, see Figures 7 - 10 .

Other coating materials that can be used are polymers that have a melting temperature below the Curie temperature of the hard magnetic cores and can harden by cooling or by reactive components. The corresponding polymer powders can consist of a pure substance, mixed with additives and used as a mixture (master batches) to achieve certain properties. Coating materials can be based on the following polymers: polyamide, polypropylene, polystyrene, polyether, ketone, polyurethane, epoxy resin and the like. The coating materials are selected in particular according to the fact that they can be melted below the Curie temperature of the selected hard magnetic core material, are sufficiently wear-resistant after curing and are approved for the processing of corresponding products (see the preceding statements).

In the Figures 7 to 10 different exemplary embodiments of a corresponding device for the production of grinding media according to the invention are shown. The same reference symbols identify the same parts and some of them are only explained in connection with one figure.

7 shows such a device with a reactor 1, through which coated hard-magnetic cores, ie grinding bodies according to the invention, can be produced. The reactor itself consists of a non-ferromagnetic material and has an upper opening 2 . Hard-magnetic cores can be supplied via the upper opening 2 . Furthermore, the reactor 1 has a gas-permeable base 4, which has a lower material-free area 26, see also 8 , separated from a material-carrying area 27 . The material-free area 26 extends from the gas-permeable floor 4 to a lower opening 3. The material-carrying area 27 extends above the Gas-permeable floor 4 and is essentially limited by the height of the reactor, so that it can be larger than in the Figures 7 to 10 shown. The gas-permeable base 4 also consists of a non-ferromagnetic material.

The embodiment after 7 suitable for a batch coating of hard magnetic cores 6.

The hard-magnetic cores 6 to be coated are preferably magnetized to saturation using a magnetizing device (not shown). The magnetization can be done by pulse magnetization. The magnetized cores are then heated, e.g. B. in an electrically heated oven, to a temperature that in the reactor 1 in contact with particles of a coating material 7 can melt them. However, the temperature is lower than a corresponding Curie temperature of the hard magnetic cores.

The opening 2 is used for the addition of coating material, the heated and magnetized hard magnetic cores and the removal of finished coated hard magnetic cores, i. H. the finished grinding media.

A gas stream can be introduced through the lower opening 3 , which gas stream is distributed uniformly over the reactor cross section from below when it passes through the gas-permeable base 4 and supports fluidization of the disperse coating material 7 .

The coating material is, for example, polyamide powder with a particle size of d ₅₀ =50 μm and a melting point of 176.degree.

Above the gas-permeable floor 4 is a magnet system 5 with two coils 30 surrounding the reactor. The magnet system and its time- and location-dependent magnetic field result in a field gradient that changes over time and location, which fluidizes the heated and magnetized hard-magnetic cores 6 that are fed in via the opening 2 .

The disperse coating material 7 is also fluidized by the movement of the hard-magnetic cores 6, as well as by the gas flow already described above. The coating material melts on contact with surfaces 24 of the heated, hard-magnetic cores.

There is also the possibility of additionally heating the coating material, for example by using a gas stream 8 fed in via the opening 3 and/or a further heater 10 in the corresponding area (see Fig 7 ) and/or the disperse coating material directly, for example with an infrared radiator (in Figure 7-10 not shown) is heated.

The overall resulting temperature of the disperse coating material 7 determines a thickness 23 of the coating 28 on the hard magnetic cores 6 with a constant dwell time of the hard magnetic cores in the reactor 1, see also 6 .

The magnet system 5 after 7 has two coils 30 concentrically surrounding the reactor, through which alternating currents flow. These generate a temporally and spatially changing magnetic flux density distribution in the material-carrying area 27 of the reactor 1, preferably with an effective value of at least 5 mT on the gas-permeable floor 4. The frequency of the alternating currents in the coils 30 of the magnet system 5, which determine the flux density changes over time, should not exceed a frequency at which the hard-magnetic cores 6 can no longer follow the changes in flux density due to their inertia. For example, frequencies greater than 10 Hz and less than 400 Hz should be set for cores with a size of >0.5 mm and densities of around 4 to 5 kg/dm ³ .

In the case of the coils 30 of the magnet system 5, care must be taken to ensure that their number, arrangement, number of turns and design are determined by the cross-sectional shape and size of the reactor and the distribution of the magnetic vector gradient required for fluidizing the hard-magnetic cores 6. For example, solenoidal coil systems can be used for cylindrical reactors. In this context, it has proven to be advantageous if the coils are designed in the manner of disks.

8 shows a second embodiment of a device according to the invention or a reactor 1 according to the invention. This differs from the first embodiment 7 by heating the magnetized, hard-magnetic cores 6 to a required process temperature via a heating device 37 in the area of a funnel 9. The heating device 37 can be designed to be controllable in order to achieve the corresponding temperature of the hard-magnetic cores in a reproducible manner.

The heating device 37 is in front of a reactor opening 32 (see also 8 ) and serves to feed the heated, magnetized, hard-magnetic cores 12 into the reactor 1. The feed is carried out magnetically with another magnet system 11 operated in a pulsed manner. This enables a quasi-continuous process control of the coating. Completely coated, hard-magnetic cores can be removed from the reactor 1 via an opening 13 with a rod-like holding magnet or the like when the magnet system 11 is not electrically active.

A further opening 14 is arranged as an exhaust gas opening opposite the opening 13 .

The opening 32 of the reactor, in the upper end region 31, is in the exemplary embodiment 8 via a connection 33 in a heatable funnel-shaped container 9 over. In this, the previously magnetized, hard-magnetic cores are heated by means of the heating device 37 to a temperature lower than the Curie temperature of the cores and higher than the melting point of the coating material. Other heating devices are also possible, such as infrared radiators, induction heating, magnetrons or the like.

The magnet system 11 comprises an ironless coil which is periodically pulsed with a current. Current pulse height and duration are selected in such a way that a short-term magnetic field is created which penetrates the lower area of the bed of heated, magnetized, hard-magnetic cores 12 and which cancels out the magnetic holding forces between the cores in this area. As a result of the magnetic pulling force of the magnet system 11 and the force of gravity, a corresponding quantity of hard magnetic cores falls through the opening 32 as an exit into the reactor 1, with the cores remaining in the funnel 9 slipping down. The amount of hard magnetic cores supplied can be adjusted by the current pulse height and pulse duration.

In all exemplary embodiments of the device according to the invention, the corresponding finished grinding bodies are removed from the reactor 1 after a residence time required for coating the fluidized, hard-magnetic cores 6 . The coating process can also be carried out periodically.

9 12 shows a third exemplary embodiment of the device or of the reactor 1. This differs from the exemplary embodiments according to FIG 7 and 8th in that the magnetized, hard-magnetic cores are heated to the required process temperature by coupling in microwave power as a heating device 34 (see figure 10 ) by means of at least one antenna 15 directly on the reactor 1. The reactor 1 thus consists of a non-microwave-absorbing material, such as Teflon, silica glass or the like, at least in the region where the microwave radiation acts. Furthermore, the reactor 1 is surrounded by a metallic grid 18 in the region where the microwave radiation acts, so that the microwave radiation is negligible and prescribed limit values are observed (<50 W/m ² at a distance of 5 cm).

A water-cooled microwave generator 16 based on semiconductors with a power of up to 1000 W at 2.45 GHz, which can be controlled depending on the size of the process container and how it is filled, can be used to generate microwaves.

The supplied microwave power can be controlled by measuring, fiber-optically, pyrometrically or the like, a surface temperature of the hard-magnetic cores 6 .

A corresponding design of a reactor 1 ensures, on the one hand, a coating of very small (<1 mm) hard magnetic cores 6, since such cores would cool down too quickly when heated before and during entry into the reactor 1 as a result of their low heat storage capacity, and, on the other hand, a better and reproducible coating quality for all core sizes. Furthermore, externally pretreated, in particular precoated, non-magnetized hard magnetic cores, which were precoated in a preliminary stage with a coating material/binder suspension and to which further layers were applied as solid films using known coating methods, can then be fed magnetized to the reactor. Thereafter, without further addition of disperse coating material, the layers already present in the reactor can be melted in order to improve the homogeneity and/or the surface quality. The cores can also be pretreated prior to the precoating, see for example the surface treatment described above.

10 represents a fourth exemplary embodiment of a device or a reactor 1 according to the invention.

The course of the coating process is controlled by means of a sequence of steps in a controller, for example a programmable logic controller 19 . Uncoated hard magnetic cores 6 are first magnetized, weighed and placed in the reactor 1. Then the magnet system 5 is switched on by a controller 35, which serves to move and fluidize the cores. At the same time, the microwave generator 16 for heating the hard-magnetic cores 6 is activated. This takes place via microwave antennas 15 and the delivery of corresponding microwaves. Measures the temperature sensor 17 reaching a target temperature of z. B. 176 ° C, is supplied by means of a heater 36 temperature-controlled air as a gas stream 8 for fluidization and also added the coating powder. The desired temperature is then maintained according to the temperature sensor 17, for example for 3 minutes. However, this time depends on the reactor size, the amount of hard magnetic cores filled in, the core size and the desired layer thickness. The target temperature is maintained until sufficient coating material has been melted onto the magnetized, hard-magnetic cores 6 . After the corresponding holding time has elapsed, the microwave generator 16 and the heater 36 are switched off. A corresponding supply of air as a gas stream 8 continues to be operated for cooling until the temperature sensor 17 falls below a corresponding setpoint value. The coated hard-magnetic cores are then removed via the opening 13 (see 8 ). This is advantageously carried out with a rod which is provided at the end with a permanent magnet or an activatable electric coil. Thereafter, the magnetic coils 30 are switched off by means of the controller 35 and the reactor 1 is completely emptied and cleaned and, if necessary, refilled.

Figure 11a and 11b show finished grinding media, ie coated, hard magnetic cores according to the invention. The coating on the hard magnetic cores is closed. After Figure 11a the coating has a corresponding roughness. A mechanical post-treatment to smooth the surfaces of the grinding media is possible. Drumming, magnetic fluidization in a reactor without coating material or targeted stressing ("grinding") in an EMZ system with an abrasive material, for example aluminum oxide, are suitable.

11 shows such a coated hard magnetic core after tumbling in water for one hour.

It has already been pointed out that the grinding bodies 20 can also be demagnetized if necessary. This succeeds in a decaying alternating field, which is operated by a coil that is operated with a controllable alternating current source - in the simplest case a regulating transformer. The alternating field must at least reach the saturation field strength of the hard-magnetic cores and then decay or be reduced to zero.

Another way to demagnetize is to determine the coercivity of the polarization of the hard magnetic nuclei, e.g. B. by recording the hysteresis curve with a vibration magnetometer, and then using a magnet system fed with direct current to build up an opposing field of this strength and to let it act briefly on the hard magnetic cores.

In both cases, the hard magnetic cores must be sufficiently mechanically fixed to prevent them from moving in the direction of the magnetic field generated for demagnetization.

Claims (15)

1. A grinding body (20) suitable for an electromechanical comminution plant for comminution, deagglomeration and/or dispersion of disperse materials and/or pumpable multiphase mixtures,
   wherein the grinding body (20) includes a hard-magnetic core (6) and at least one wear-resistant coating (28) at least partially surrounding the same, characterized in that the hard-magnetic core is spherical and has a diameter of 0.1 - 10 mm.
2. The grinding body according to claim 1, characterized in that the hard-magnetic core (6) has a coercive field strength (21) of at least 20 kA/m, preferably at least 40 kA/m and more preferably at least 50 kA/m,

   in particular the hard-magnetic core (6) has a remanence (22) of more than 20 mT, preferably more than 40 mT, and more preferably more than 50 mT, and

   preferably the wear-resistant coating (28) is a polymer coating.
3. The grinding body according to the preceding claims 1 or 2, characterized in that the hard-magnetic core (6) is spherically shaped and/or magnetizable,

   preferably, depending on the size of the core, in particular the diameter (29) of the core, the coating (28) has a thickness from 5 µm to 500 µm and preferably from 10 µm to 300 µm, and

   in particular a surface (24) of the hard-magnetic core (6) is roughened and in particular has an arithmetic average roughness (Ra) of 0.4 µm or more and preferably of 0.5 µm or more.
4. The grinding body according to any one of the preceding claims, characterized in that the coating (28) is closed and completely surrounds the hard-magnetic core and/or at least one force-transmitting layer (25) is arranged between the coating and the hard-magnetic core and/or the coating is smoothed.
5. An apparatus for producing grinding bodies (20) according to any one of the preceding claims comprising at least one reactor (1) divided into a lower region (26) devoid of material and an upper region (27) carrying material by means of a gas-permeable bottom (4) wherein the region (27) carrying material is configured for receiving fluidized disperse coating material (7) and fluidized hard-magnetic cores (6), and is surrounded by a magnetic system (5) for fluidizing the hard-magnetic cores (6) in the region (27) carrying material, wherein, in particular, the reactor (1) includes a gas inlet opening (3) underneath the bottom (4), and
   in particular above the bottom (4), at least one closable opening (2, 13) is formed for supplying cores (6) of the coating material (7) and/or for removing finished grinding bodies (20).
6. The apparatus according to claim 5, characterized in that the magnetic system (5) is made up of at least one coil (30) surrounding the reactor (1) above the gas permeable bottom (4),

   in particular, an upper end region (31) of the reactor (1) includes a container (9), in particular a heatable and funnel-shaped container for receiving magnetized hard-magnetic cores (6), with which a heating device (10) may be associated, and

   in particular, the heating device (10) heats the magnetized hard-magnetic cores (6) to a temperature lower than a Curie temperature of the hard-magnetic cores and higher than a melting temperature of the coating material (7).
7. The apparatus according to claims 5 or 6, characterized in that below an outlet (32) of the funnel-shaped container (9) another magnetic system (11) is located, which is made up of at least one coil and surrounds a connection (33) between the reactor (1) and the outlet (32) of the funnel-shaped container (9).
8. The apparatus according to any one of the preceding claims 5 to 7, characterized in that at least one opening (13), in particular a lateral opening, for removing coated hard-magnetic cores (6) is arranged in the upper end region (31) of the reactor (1),
   in particular, a heating device (36) is arranged above the gas-permeable bottom (4) and advantageously in the region (27) carrying material.
9. The apparatus according to any one of the preceding claims 5 to 8, characterized in that the reactor (1) consists of a microwave-permeable material above the gas-permeable bottom (4) and at least one microwave antenna (15) is arranged in the reactor (1) above the gas-permeable bottom (4), preferably in the region (27) carrying material or in the upper end region (31), in conjunction with a controllable microwave generator (16) as a heating device (34), and
   in particular at least one temperature sensor (17) is arranged in the reactor (1) above the gas-permeable bottom (4), preferably in the region (27) carrying material, for detecting an average temperature in the reactor and/or of the coating material (7) and/or of the hard-magnetic cores (6).
10. A method for producing grinding bodies (20) according to any one of claims 1 to 4, comprising an apparatus for producing grinding bodies (20) according to any one of claims 5 to 9,
    characterized by

    magnetizing hard-magnetic cores (6) and subsequently heating the magnetized hard-magnetic cores (6) to a temperature above a melting temperature of a coating material (7) and below a Curie temperature,

    fluidizing the heated, magnetized hard-magnetic cores (6) by means of a magnetic field varying in time and space,

    melting fluidized powdered coating material (7) onto surfaces of the heated magnetized hard-magnetic cores (6) and forming a wear-resistant coating (28) and

    subsequently discharging the finished grinding bodies (20) from the reactor (1) after reaching a target layer thickness and cooling to ambient temperature.
11. The method according to claim 10, characterized by generating the temporally and spatially varying magnetic field in the reactor (1) by means of a magnetic system (5) which encloses the reactor (1) above a gas-permeable bottom (4) and through which alternating currents flow, with a magnetic flux density with an effective value of at least 5mT in the region of the gas-permeable bottom (4) and an alternating current frequency of at most 300 Hz, wherein in particular a magnetization of the hard-magnetic cores (6) occurs even on the outside of the reactor (1), preferably by means of pulse magnetization and/or
    roughening of surfaces (24) of the hard-magnetic cores (6) outside the reactor (1) by means of mechanical and/or chemical processes.
12. The method according to any one of the preceding claims 10 or 11, characterized in that the hard-magnetic cores (6) are coated with an adhesion promoter (25) before being magnetized,

    in particular heating of the hard-magnetic cores (6) after their magnetization outside the reactor (1) and/or

    heating of the hard-magnetic cores (6) in the reactor (1), in particular by means of microwaves, take place during fluidization thereof.
13. The method according to any one of the preceding claims 20 to 26, characterized by detecting the temperature in the reactor by means of at least one temperature sensor (17) and controlling the average temperature in the reactor and/or of the coating material and/or of the hard-magnetic cores (6) as a function of the detected temperature, and

    in particular, supplying a respective amount of magnetized hard-magnetic cores (6) to the reactor (1) after removal of a corresponding amount of grinding bodies (20) from the reactor (1) and/or

    supplying the hard-magnetic cores (6) to the reactor (1) is effected by means of a magnetic system (11) which is made up of at least one coil surrounding a connection (33) between the reactor (1) and a funnel-shaped container (9) and is activated by means of current pulses, a magnetic field being generated by the current pulses, which reduces magnetic attraction between the magnetized hard-magnetic cores (6) located above the magnetic system (11) in such a way that the hard-magnetic cores (6) fall into the reactor (1) by gravity and are fluidized therein with the magnetic field of the further magnetic system (5).
14. The method according to any one of the preceding claims 10 to 13, characterized by smoothing the grinding bodies (20) after removing them from the reactor (1), in particular by tumbling or the like,

    in particular by sorting the grinding bodies (20) and/or re-magnetizing the grinding bodies (20) after removing them from the reactor (1), and/or

    removing a residual coating from used grinding bodies and feeding said grinding bodies to the reactor for recoating, and

    if necessary, performing an external pre-treatment, in particular precoating of non-magnetized hard-magnetic cores, which are subsequently magnetized and fed to the reactor, and/or

    pre-coating the pre-treated hard-magnetic cores, if any, by means of a suspension consisting of coating material and binding agent.
15. Use of the grinding bodies according to any one of the preceding claims 1 to 4 in an electromechanical comminution plant for comminution, deagglomeration and/or dispersion of active ingredients for use in the pharmaceutical, biotechnology and/or food industries, or
    in ball mills for comminution, deagglomeration and/or dispersion of active ingredients or inorganic materials for use in the pharmaceutical, biotechnology and/or food industries, wherein the grinding bodies are demagnetized.

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