EP3857573A1

EP3857573A1 - Grinding media, device and method for producing said grinding media and use thereof

Info

Publication number: EP3857573A1
Application number: EP19773020.3A
Authority: EP
Inventors: Bernd Halbedel; Mathias May; Rolf Baudrich
Original assignee: Rti Rauschendorf Tittel Ingenieure GmbH
Current assignee: Baudrich Rolf; HALBEDEL, BERND; May Mathias
Priority date: 2018-09-24
Filing date: 2019-09-17
Publication date: 2021-08-04
Anticipated expiration: 2039-09-17
Also published as: EP3857573B1; DE102018216190A1; WO2020064430A1; EP3857573C0

Abstract

The invention relates to grinding media (20) for use in an electromechanical comminution plant and a corresponding device and a method for production of such grinding media (20). According to the invention, grinding media (20) having low grinding media wear and high product compatibility, which have corresponding magnetic and mechanical properties, are provided. Such grinding media have a magnetically hard core (6) and at least one wear-resistant coating (28) surrounding said core. According to the invention, such coated, magnetically hard grinding media (20) can be used in grinding plants for comminution, de-agglomeration and/or dispersion, in particular of substances which are required in the pharmaceutical, biotechnology and/or food industry.

Description

Grinding media, device and method for producing the grinding media and use

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

In a comminution system of this type, comminution, deagglomeration and / or dispersion of disperse substances and / or pumpable multiphase mixtures takes place. Such a shredding system is described for example in DE 10 2018 1 13 725.

Magnetic grinding media are described in DD 240 674 B1, DE 41 13 490 A1, EP 0510 256 B1 and US 5 348 237, the devices and methods for electromechanical comminution and / or deagglomeration or dispersion of disperse inorganic solids (silicates, oxide ceramics, Propose pigments) or multi-phase mixtures (dispersions), described as magnetic working bodies, in order to generate intensive translational transverse movements and wobble movements with electromagnetic fields, generated by electrical excitation systems, and thus sufficient mechanical stress on the educt. These working bodies are made of hard magnetic material (eg hexaferrite), have a spherical or barrel shape with a diameter or a length of 1.0 to 4.0 mm and fill the process chamber of the electromechanical comminution system to at least 40 up to 90 vol%. It is to be expected that such working bodies made of hard magnetic hexaferritic materials will wear out heavily in electromechanical comminution systems, so that the product becomes contaminated with the wear.

DE 32 33 926 A1 proposes an electromechanical comminution, mixing or stirring device which uses ferromagnetic particles or bodies made of carbon steel or other materials which have the required magnetic and / or electrical properties for fine comminution, they have to be designed as pins with a length 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 dispersion of disperse substances, pumpable multiphase mixtures, since the magnetic properties are far too low and therefore their movement and the stresses they cause are insufficient. In addition, foreign substances are entered into the product with their wear. DE 27 12 620 A1 often proposes magnetically polarized working bodies in order to achieve an additional nonuniformization of the working body movement. However, a multi-pole magnetization is very complex and technically only possible on large work pieces (> 5 mm). Then, due to the large gap volume between the working bodies, no fine comminution or deagglomeration and dispersion of dispersions is possible.

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

Furthermore, patent applications are known which support the movement of the grinding media of mechanical mills (ball mill: PL 382610 A1 or WO_2014 / 065680 A1, RU 2 319 546, mortar mill: WO 86/01 129) with magnetic systems arranged on the outside of the grinding container and thus with it want to improve the efficiency of the grinding process (eg cement production: EP 2 128 107 A2). Grinding or working bodies made of ferromagnetic material, primarily carbon steels, are used. In addition to the low magnetic properties, such materials heat up very strongly because eddy currents are generated in them due to their high electrical conductivity due to the changing magnetic fields. On the one hand, this lowers the efficiency of the grinding process and, on the other hand, leads to additional heating of the product.

It is also known from EP 0 434 985 A1 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, for example by serrations, ribs or Ä. and consist of magnetizable metals (iron), a reaction metal (aluminum or copper), a composite reaction metal (iron / aluminum, iron / copper) or magnetizable plastic or magnetic rubber. The components are assembled in a sandwich construction, for example by gluing. In addition, such secondary elements can be coated with a non-magnetic material, such as plastic. None of the proposed embodiments represents an EMZ grinding media and can be used as such in comminution systems (EMZ) for comminution, deagglomeration and dispersion of disperse substances, pumpable multiphase 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 of this is given in the publication Pieters, B. R .; Williams, R. A .; Webb, C .: Magnetic carrier technology. In: Williams, R. A. (Ed.): Colloid and Surface Engineering: Applications in the Process Industries. Butterworth Heinemann, Oxford 1992, pp. 249-286. These known magnetobeads in the form of particles or spheres are made exclusively of magnetite or mixed with a polymer (= composite) and, depending on the application, have dimensions in the range from 0.2-150 μm. They are therefore always soft-magnetic and therefore not suitable for the electro-mechanical comminution, deagglomeration and dispersion of disperse substances, pumpable multi-phase mixtures.

Magnetic polymer particles as carriers for enzymes, bacteria, cells, RNA and proteins are mentioned in US Pat. No. 5,814,687, which are produced by mixing a monomer with superparamagnetic particles and then polymerizing.

The patent specification DE 196 38 591 describes magnetic particles which are constructed as 50-1500 nm large monodisperse SiO 2 balls with a magnetic particle layer of <60 nm thickness.

JP 0830 8570 proposes mixing porous ceramics with 0.01-100 pm fine paramagnetic particles, shaping the mixture and then sintering. The carriers are suitable for immobilization in the field of fermentation, biochemistry and environmental technology.

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

This problem is solved by the independent claims.

A grinding element according to the invention is characterized in particular by the fact that the grinding element has a hard magnetic core and at least one wear-resistant coating surrounding it. Coated, hard magnetic grinding media of this type are used in comminution plants for comminution, deagglomeration and / or dispersion, in particular of active ingredients which are required in the pharmaceutical, biotechnology and / or food industry.

For example, tests were carried out in the EMZ according to DE 10 2018 1 13 725, in which the corresponding coated hard magnetic cores showed no gravimetrically demonstrable loss of mass after 10 minutes in batch operation.

In the case of uncoated grinding media, however, a relative mass loss of 1 to 10 wt% was found under the same conditions. Such grinding media lead to higher operating costs due to wear and tear and are not 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 media can have a coercive field strength of at least 50 kA / m, preferably at least 70 kA / m and particularly preferably of 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, for example, a polymer layer. This has corresponding physical and / or chemical properties, which is advantageous when the grinding media are used.

The hard magnetic core can be spherical and can be magnetized accordingly.

Depending on a core size, in particular core diameter, the coating can furthermore have a thickness of 5 pm to 500 pm and preferably of 10 pm to 300 pm. The spherical shape of the hard magnetic cores can have 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 as an adhesion-promoting layer between the polymer layer and the hard magnetic core. In addition, the surface of the coating can be smoothed.

In the manufacture of the grinding media, the hard magnetic cores are first treated mechanically and / or chemically on their surface in order to improve the physical and / or chemical adhesion, in order to increase the surface roughness. Then you can the hard magnetic cores are magnetized and then fed to a device according to the invention for producing the grinding media.

Such a device has at least one reactor which is subdivided by a gas-permeable bottom into a lower, material-free area and an upper, material-carrying area. The material-carrying area is used to hold 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.

The pretreated hard magnetic cores, see the explanations above, are fed to the reactor in which the coating material is already in disperse form. The hard magnetic cores are heated up to a temperature higher than a melting temperature of the coating material, but lower than a Curie temperature of the hard magnetic cores, before being fed in and / or in the reactor.

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 uniformly 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, if necessary, post-treated. These grinding media are then very good for use in electromechanical comminution systems in a magnetized state or also demagnetized in mechanical comminution systems for comminution, deagglomeration and / or dispersion of disperse substances and / or pumpable multiphase mixtures, even in fields of application in the field of pharmacy and the like suitable and are characterized by low material wear and high product compatibility.

Furthermore, the grinding media according to the invention are distinguished in that, in the demagnetized state, they can also be used in ball mills, such as, for example, agitator ball mills or the like, for comminution, deagglomeration and / or dispersion of active ingredients or general organic materials. Compared to known grinding media, the grinding media according to the invention are further characterized by a higher density, so that a higher machining intensity is possible with the same operating parameters of ball mills.

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

In order to be able to supply or remove material from the reactor in a simple manner, at least one closable opening can be formed above the base for the supply of cores, of coating material and / or for the removal of the finished grinding media. 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 a corresponding fluidization of heated, magnetized, hard magnetic cores. For this purpose, the magnet system can have at least one coil which 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 to 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.

It is also possible to arrange a further magnet system in the area of a connection between the reactor and the funnel-shaped container. This is preferably operated periodically with a pulse. The current pulse level and duration can be selected such that hard magnetic cores arranged briefly at least in a lower region of the funnel-shaped container are influenced in such a way that their mutual magnetic attraction is canceled and thus as a result of the magnetic tensile force by this further 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 adjustable by means of the current pulse height and pulse duration.

Attention has already been drawn to corresponding openings in the reactor, preferably at least one lateral opening in the upper end region of the reactor for the removal of coated hard magnetic cores, ie. H. the finished grinding media can be arranged.

There is the possibility that preheated and magnetized hard magnetic cores are fed to the reactor. In this context, however, it can prove to be advantageous if a further heating device is arranged in the material-carrying area. These can be used to heat the coating material, although heat losses or direct heating of the fluidized, hard magnetic cores can also be compensated for or carried out.

An example of a heating device is heating with microwaves, it being possible for a corresponding microwave antenna, which is connected to a controllable microwave generator, to be arranged in the material-carrying region. In this context, the reactor above the gas-permeable bottom should be made of a microwave non-absorbent material.

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

In terms of the method, care must be taken that the device according to the invention magnetizes, for example, the hard magnetic cores and heats them to a temperature above the melting temperature 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. Subsequently, the likewise fluidized, powdery coating material is melted on surfaces of the heated hard magnetic cores, so that a coating can form.

If a, preferably closed, coating has formed and a certain target layer thickness has additionally been reached, the grinding media produced in this way can be removed and cooled to room temperature. Another magnetic system generates a magnetic field that changes in time and location in the reactor. This magnet system has at least one coil and surrounds the reactor above the gas-permeable bottom. Alternating currents flow through the magnet system and, for example, have a magnetic flux density in the middle of the gas-permeable base with an effective value of at least 5 mT, the frequencies of the alternating currents being 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 to the reactor, a corresponding magnetization can take place outside the reactor, preferably by pulse magnetization. Before such magnetization outside the reactor, it can prove to be 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 completely or at least partially heated after their magnetization and outside of the reactor. There is also the possibility that the hard magnetic cores in the reactor are already heated in the fluidized state by means of a heating device and, for example, by microwaves.

In order to further improve the adhesion, there is also the possibility that the hard magnetic cores are coated with an adhesion promoter. This can be done before magnetization.

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

According to the invention, there is also the possibility of removing appropriately 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 amount of such cores can always be stored for further treatment in the reactor. If necessary, the finished grinding media can be removed from the reactor or can be fed in manually. Completed grinding media can be smoothed after they have been removed from the reactor, for example by tumbling (vibratory grinding).

There is also the option of sorting the grinding media by size and, if necessary, re-magnetizing them.

The device according to the invention for producing the grinding media is also suitable for recoating grinding media already used. For this purpose, an existing residual coating can be removed from such grinding media 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 fed back 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 for use in electromechanical comminution systems for comminution, deagglomeration and / or dispersion of active ingredients which are required in the pharmaceuticals, biotechnology and / or food industry. This also applies to ball mills, in which case the grinding media can be demagnetized beforehand.

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;

FIG. 2: hysteresis curves determined for selected hard magnetic cores;

Figure 3a: an untreated hard magnetic core;

Figure 3b: a surface-treated hard magnetic core;

FIG. 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;

FIG. 5a: an optical micrograph of a cross section of a coated hard magnetic core;

FIG. 5b: an image analogous to FIG. 5a with a different layer thickness of the coating; FIG. 6: a diagram to show 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 1 1 a: a grinding media with coating; and

Figure 1 1 b: a grinding media analogous to Fig. 1 1 a after smoothing the surface.

Fig. 1 shows a number of hard magnetic cores 6, which are spherical or spherical in the embodiment shown and have a diameter of 1-1.6 mm. Other diameters can also be used. In the exemplary embodiment shown, the hard magnetic cores consist of strontium hexaferrite (SrFe ^ Oig). Other materials can be used which in particular have coercive field strengths 21, see FIG. 2, of, for example,> 50 kA / m and remanence 22 of> 50 mT. Such materials are rare earth magnets made of the material systems Nb-Fe-B, Pr-Fe-B or Sm-Co, AINiCo materials and also Fe-CrCo, PtCo and MnAIC alloys.

The cores with corresponding sizes shown in FIG. 1 were produced by means of a dropletization process from a stable slurry which contains strontium hexaferrite particles, 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 or fluid bed granulation or simple pelleting of the raw materials with subsequent temperature treatments up to sintering are also possible. Lich. Such shaping 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 different selected hard magnetic cores from a total of three batches. These are made from strontium hexaferrite. The corresponding coercive field strength 21 and the magnetic polarization or remanence 22 of the hard magnetic cores can be seen. To it should be noted that the remanence 22 corresponds to the magnetic polarization at H = 0. In this case, the magnetic characteristics of the coercive force are 270-340 kA / m and the remanence is 162-200 mT. These are in the preferred range according to the invention.

Different surfaces 24 of the hard magnetic cores 6 are shown in FIGS. 3a and 3b. The representations are electron micrographs of an untreated (FIG. 3a) and a surface-treated (FIG. 3b) hard magnetic core with a diameter of 29. The surface treatment according to FIG. 3b was carried out chemically using a 14.8 molar phosphoric acid (H3PO4) 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. The volume ratio of hard magnetic cores to solvent was 1: 50 to 1: 100 in these chemical treatments in order to avoid a concentration of the solvates.

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

The surface treatment according to the invention leads to a loss in mass 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 is carried out 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 basically on inorganic materials. This creates covalent bonds with the inorganic substrate via a condensation reaction. When selecting the organofunctional silane, a suitable functional group -X is selected. This depends on the polymer used. Possible groups are amino (-NH2), sulfur (-S), glycidol (-C3H6O2) and metacryloxi (-C4H5O2). Aminosilanes are suitable for a polymer coating with polyamide.

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

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 produced in a device according to the invention according to FIG. 7. In FIG. 5a, a coating with a corresponding thickness 23 is formed less than a thickness 23 in FIG. 5b.

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

Other coating materials that can be used are polymers which have a melting temperature below the Curie temperature of the hard magnetic cores and can harden by cooling or by reactive constituents. 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 produced on the basis of the following polymers: polyamide, polypropylene, polystyrene, polyether, ketone, polyurethane, epoxy resin and the like. The coating materials are selected in particular so 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 preparation of corresponding products (see the preceding explanations).

7 to 10 show different exemplary embodiments of a corresponding device for producing grinding media according to the invention. The same reference numerals designate the same parts and are only partially explained in connection with a figure.

7 shows such a device with a reactor 1 by means of which coated hard magnetic cores, ie grinding media 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 fed through the upper opening 2. Furthermore, the reactor 1 has a gas-permeable bottom 4 which separates a lower material-free area 26, see also FIG. 8, from a material-carrying area 27. The material-free area 26 extends from the gas-permeable bottom 4 to a lower opening 3. The material-carrying area 27 extends above the gas-permeable bottom 4 and is essentially limited by the height of the reactor, so that it can be larger than shown in FIGS. 7 to 10. The gas-permeable bottom 4 also consists of a non-ferromagnetic material.

7 is suitable for a batch coating of hard magnetic cores 6.

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

The opening 2 serves the addition of coating material, the heated and magnetized hard magnetic cores and also the removal of coated hard magnetic cores, ie. H. the finished grinding media.

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

The coating material is, for example, polyamide powder having a particle size of d _ö o = 50pm and a melting temperature of 176 ° C.

Above the gas-permeable bottom 4 there is a magnet system 5 with two coils 30 which surround the reactor. The magnet system and its time and location-dependent magnetic field result in a field gradient which changes in time and place and which fluidizes the heated and magnetized hard magnetic cores 6 which are supplied, heated and magnetized 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. Upon contact with surfaces 24 of the heated hard magnetic cores, the coating material melts.

There is also the possibility of additionally heating the coating material by, for example, a gas stream 8 supplied via the opening 3 and / or in the corresponding area a further heater 10 (see FIG. 7) and / or the disperse coating material directly, for example is heated with an infrared radiator (not shown in FIGS. 7-10). The overall temperature of the disperse coating material 7 determines a thickness 23 of the coating 28 on the hard magnetic cores 6 with a constant residence time of the hard magnetic cores in the reactor 1, see also FIG. 6.

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

In the case of the coils 30 of the magnet system 5, care must be taken to ensure that the 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. Solenoidal coil systems, for example, can be used for cylindrical reactors. In this context, it has proven to be advantageous if the coils are disc-like.

FIG. 8 shows a second exemplary embodiment of a device according to the invention or a reactor 1 according to the invention. This differs from the first exemplary embodiment according to FIG. 7 in that the magnetized, hard magnetic cores 6 are heated to a required process temperature by means of a heating device 37 in the region of a Funnel 9. The heating device 37 can be designed to be adjustable in order to reproducibly reach the corresponding temperature of the hard magnetic cores.

The heating device 37 is arranged in front of a reactor opening 32 (see also FIG. 8) and serves to supply the heated, magnetized, hard magnetic cores 12 into the reactor 1. The supply takes place magnetically with a further, magnetically operated magnet system 1 1. 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 in magnetically inactive times of the magnet system 11.

A further opening 14 is arranged opposite the opening 13 as an exhaust gas opening. In the exemplary embodiment according to FIG. 8, the opening 32 of the reactor, in its upper end region 31, merges into a heatable funnel-shaped container 9 via a connection 33. 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 temperature of the coating material. Other heating devices are also possible, such as infrared heaters, induction heating, magnetron or the like.

The magnet system 1 1 comprises an ironless coil which is periodically operated with a current in a pulsed manner. The current pulse height and duration are selected such that a magnetic field penetrating the lower region of the bed of the heated magnetized hard magnetic cores 12 is briefly generated, which in this region cancels out magnetic holding forces between the cores. As a result of the magnetic tensile force of the magnet system 11 and the force of gravity, a corresponding amount of hard magnetic cores falls through the opening 32 as an outlet into the reactor 1, with the remaining cores slipping in the funnel 9. The amount of hard magnetic cores supplied can be adjusted by the current pulse height and pulse duration.

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

FIG. 9 shows a third exemplary embodiment of the device or of the reactor 1. This differs from the exemplary embodiments according to FIGS. 7 and 8 in that the magnetized hard magnetic cores are heated to the required process temperature by coupling in microwave power as the heating device 34 (see FIG. 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 area of exposure to the microwave radiation. Furthermore, the reactor 1 is surrounded by a metallic grating 18 in the area of exposure to the microwave radiation, so that the microwave radiation is negligibly low 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 controllable output of up to 1000 W at 2.45 GHz depending on the size of the process container and its filling can be used to generate microwaves. The microwave power supplied can be controlled via a measurement, fiber optic, pyrometric or the like, of 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 would cool 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 pre-coated, non-magnetized, hard magnetic cores, which were precoated in a preliminary stage with a coating material-binder suspension and onto which further layers were applied as solid films by means of known coating methods, can then be supplied magnetized to the reactor. Thereafter, the layers already present can be melted in the reactor without further addition of disperse coating material in order to improve the homogeneity and / or the surface quality. The cores may also have already been pretreated before the precoating, see for example the surface treatment described above.

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

The sequence of the coating process is controlled by means of a sequencer 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 is activated to heat the hard magnetic cores 6. This is done using microwave antennas 15 and emitting appropriate microwaves. The temperature sensor 17 measures the reaching of a target temperature of e.g. B. 176 ° C, 36 heated air is supplied as a gas stream 8 for fluidization by means of a heater and the coating powder is added. The setpoint temperature according to temperature sensor 17 is then maintained, for example for 3 minutes. However, this time depends on the reactor size, the quantity of hard magnetic cores, 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 air supply as gas stream 8 is continued to cool down until the temperature sensor 17 falls short of a corresponding setpoint. The coated hard magnetic cores are then removed via the opening 13 (see FIG. 8). This is advantageously carried out with a rod which is provided at the end with a permanent magnet or an activatable electrical coil. Thereafter, the magnetic coils 30 are switched off by means of the control 35 and the reactor 1 is completely emptied and cleaned and, if necessary, a new charge is made.

Fig. 1 1 a and 1 1 b show finished grinding media, d. H. coated, hard magnetic cores according to the invention. The coating on the hard magnetic cores is closed. According to Fig. 1 1 a, the coating has a corresponding roughness. A mechanical post-treatment for smoothing 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.

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

It has already been pointed out that the grinding media 20 can also be demagnetized if necessary. This is achieved 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 control transformer. The alternating field must at least reach the saturation field strength of the hard magnetic cores and then decay to zero or be reduced.

Another possibility for demagnetization is to determine the coercive field strength of the polarization of the hard magnetic cores, e.g. B. by recording the hysteresis curve with a vibration magnetometer, and then with a magnet system fed with a DC system to build up an opposing field of this strength and to act briefly on the hard magnetic cores.

In both cases, the hard magnetic cores must be mechanically fixed sufficiently, which prevents their movement in the direction of the magnetic field generated for demagnetization.

Claims

Expectations

1. grinding media (20), in particular for use in an electromechanical comminution system, EMZ, for comminution, deagglomeration and / or dispersion of disperse substances and / or pumpable multiphase mixtures, characterized in that the grinding media (20) has a hard magnetic core (6) and at least one wear-resistant coating (28) at least partially surrounding it.

2. Grinding body according to claim 1, characterized in that the hard magnetic core (6) has a coercive field strength (21) of at least 50 kA / m, preferably at least 70 kA / m and particularly preferably of at least 100 kA / m.

3. Grinding body according to claim 1 or 2, characterized in that the hard magnetic core (6) has a remanence (22) of> 50 mT, preferably> 70 mT and particularly preferably of> 100 mT.

4. grinding body according to one of the preceding claims, characterized in that the wear-resistant coating (28) is a polymer coating.

5. Grinding body according to one of the preceding claims, characterized in that the hard magnetic core (6) is spherical and magnetized.

6. Grinding body according to one of the preceding claims, characterized in that the coating (28), depending on a core size, in particular a core diameter (29), has a thickness of 5 pm to 500 pm and preferably from 10 pm to 300 pm .

7. Grinding body according to one of the preceding claims, characterized in that a surface (24) of the hard magnetic core (6) is roughened and in particular an average roughness (Ra) of> 0.4 pm and preferably of> 0.5 pm having.

8. Grinding body according to 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 hard magnetic core and / or the coating is smoothed.

9 Device for producing grinding media (20) according to one of the preceding claims, which device has at least one reactor (1) which passes through a gas-permeable base (4) into a lower material-free area (26) and an upper material All leading area (27) is subdivided, the material leading area (27) being designed in particular for receiving fluidized, disperse coating material (7) and fluidized, hard magnetic cores (6), and in the material leading area (27) by one Magnet system (5) for fluidizing the hard magnetic cores (6) is surrounded.

10. The device according to claim 9, characterized in that the reactor (1) below the bottom (4) has a gas inlet opening (3).

11. The device according to claim 9 or 10, characterized in that above the bottom (4) at least one closable opening (2, 13) for feeding cores (6) of the coating material (7) and / or for removing finished grinding media (20) is formed.

12. Device according to one of the preceding claims 9 to 11, characterized in that the magnet system (5) is formed from at least one coil (30) which surrounds the reactor (1) above the gas-permeable bottom (4).

13. Device according to one of the preceding claims 9 to 12, characterized in that an upper end region (31) of the reactor (1) has a particularly heatable and funnel-shaped container (9) for receiving magnetized hard magnetic cores (6), which if necessary, a heating device (37) is assigned.

14. The apparatus according to claim 13, characterized in that the heater (37) heats the magnetized hard magnetic cores (6) to a temperature lower than a Curie temperature of the hard magnetic cores and greater than a melting temperature of the coating material (7).

15. Device according to one of the preceding claims 9 to 14, characterized in that a further magnet system (11) is arranged below an outlet (32) of the funnel-shaped container (9), which is formed in particular from at least one coil and a connection (33) between the reactor (1) and outlet (32) of the funnel-shaped container (9).

16. Device according to one of the preceding claims 9 to 15, characterized in that in the upper end region (31) of the reactor (1) at least one in particular since Liche opening (13) for removing coated hard magnetic cores (6) is arranged.

17. Device according to one of the preceding claims 9 to 16, characterized in that a heating device (10) is arranged above the gas-permeable bottom (4) and in particular in the material-carrying area (27).

18. Device according to one of the preceding claims 9 to 17, characterized in that the reactor (1) above the gas-permeable bottom (4) is formed from a microwave-permeable material and in the reactor (1) above the gas-permeable bottom (4th ), preferably in the material-carrying area (27) or in the upper end area (31), at least one microwave antenna (15) is arranged in connection with a controllable microwave generator (16) as the heating device (34).

19. Device according to one of the preceding claims 9 to 18, characterized in that in the reactor (1) above the gas-permeable bottom (4), preferably in the material-carrying area (27), at least one temperature sensor (17) for detecting an average temperature in the reactor and / or the coating material (7) and / or the hard magnetic cores (6) is arranged.

20 A method for producing grinding media (20) according to one of claims 1 to 8 with a device for producing grinding media (20) according to one of claims 9 to 19, characterized by

Magnetizing hard magnetic cores (6) and then 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 temporally and locally changing magnetic field,

Melting in particular fluidized, powdery coating material (7) on surfaces of the heated, magnetized hard magnetic cores (6) and forming a wear-resistant coating (28) and then removing the grinding media (20) produced after reaching a desired layer thickness from the reactor (1) and cooling to ambient temperature.

21. The method according to claim 20, characterized by generating the temporally and spatially changing magnetic field in the reactor (1) with a magnet system (5) surrounding the reactor (1) above a gas-permeable bottom (4), which is made up of alternating currents. is flowed through, with a magnetic flux density with an effective value of at least 5mT in the area of the gas-permeable bottom (4) and an alternating current frequency of maximum 400 Hz.

22. The method according to any one of claims 20 or 21, characterized by magnetizing the hard magnetic cores (6) already outside the reactor (1), preferably by pulse magnetization.

23. The method according to any one of claims 20 to 22, characterized by roughening surfaces (24) of the hard magnetic cores (6) outside of the reactor (1) with mechanical and / or chemical methods.

24. The method according to any one of the preceding claims 20 to 23, characterized in that the hard magnetic cores (6) are coated with an adhesion promoter (25) before their magnetization.

25. The method according to any one of the preceding claims 20 to 24, characterized by heating the hard magnetic cores (6) after their magnetization outside the reactor (1).

26. The method according to any one of the preceding claims 20 to 25, characterized by heating the hard magnetic cores (6) in the reactor (1) during their fluidization by means of microwaves in particular.

27. 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 the coating material and / or the hard magnetic cores (6) depending on the recorded temperature.

28. The method according to any one of the preceding claims 21 to 27, characterized by supplying a corresponding amount of magnetized hard magnetic cores (6) to Reactor (1) after removal of a corresponding amount of grinding media (20) from the reactor (1).

29. The method according to any one of the preceding claims 20 to 28, characterized by feeding the hard magnetic cores (6) into the reactor (1) by means of a magnet system (11) which is formed from at least one coil which forms a connection (33) between the reactor (1) and a funnel-shaped container (9) and is activated by means of current pulses, the current pulses generating a magnetic field which generates magnetic attraction forces between the magnetized hard magnetic cores (6) which are located above the magnet system (11), reduced so that the hard magnetic cores (6) fall into the reactor (1) as a result of gravity and are fluidized there with the magnetic field of the further magnet system (5).

30. The method according to any one of the preceding claims 20 to 29, characterized by smoothing the grinding media (20) after their removal from the reactor (1) in particular by drums or the like.

31. The method according to any one of the preceding claims 20 to 30, characterized by sorting the grinding media (20) and / or re-magnetizing the grinding media (20) after they have been removed from the reactor (1).

32. The method according to any one of the preceding claims 20 to 31, characterized by removing a residual coating of used grinding media and / or modifying the surfaces of their cores and feeding these cores thus recycled to the reactor for new coating.

33. The method according to any one of the preceding claims 20 to 32, characterized by an external pre-treatment, in particular pre-coating of non-magnetized hard magnetic cores, which are then magnetized and fed to the reactor.

34. The method according to claim 33, characterized by precoating the optionally pretreated hard magnetic cores by means of a coating material-binder suspension.

35. Use of the grinding media according to one of the preceding claims 1 to 8 in an electromechanical comminution system, EMZ, for comminution, deagglomeration and / or dispersion of active ingredients for use in pharmacy, biotechnology and / or the food industry.

36. Use of the grinding media according to one of the preceding claims 1 to 8 in ball mills for comminution, deagglomeration and / or dispersion of active ingredients or inorganic materials used in pharmacy, biotechnology and / or the food industry, the grinding media being demagnetized.