EP3431209B1 - Method and installation for the production of a starting material for producing of rare earth magnet - Google Patents

Description

Starting material for the production of rare earth magnets and a system for producing a starting material for the production of rare earth magnets.

State of the art

A permanent magnet (also: permanent magnet) is a piece of a magnetizable material, for example iron, cobalt or nickel, which maintains its static magnetic field without the need for an electrical current flow (unlike electromagnets). A permanent magnet can be created by applying a magnetic field to a ferromagnetic material.

The name rare earth magnets refers to a group of permanent magnets that essentially consist of ferrous metals (iron, cobalt, more rarely nickel) and rare earth metals (especially neodymium, samarium, praseodymium, dysprosium, terbium, gadolinium). They are characterized by the fact that they simultaneously have a high magnetic remanent flux density and a high magnetic coercive field strength and thus a high magnetic energy density.

An alloy of neodymium, iron and boron (NdFeB), for example, enables the production of very strong magnets at a relatively low cost. They are manufactured using powder metallurgy processes, but today they are also sometimes produced using plastic-bonded magnets. For a long time, operating temperatures were limited to 60-120 °C. In some newer developments with additional additions of other rare earth elements, in particular dysprosium or terbium, the temperature stability can be increased to over 200°C. To To increase corrosion stability, other alloy components such as cobalt are often added.

Permanent magnets are made from crystalline powder. The magnetic powder is pressed into a mold in the presence of a strong magnetic field. The crystals align themselves with their preferred magnetization axis in the direction of the magnetic field. The compacts are then sintered. During sintering, the pulverized components of the powder are bonded together or compacted by heating, but none or at least not all of the starting materials are melted. The compacts are heated - often under increased pressure - in such a way that the temperatures remain below the melting temperature of the main components, so that the shape (shape) of the workpiece is retained.

At sintering temperatures above 1000 C, the externally effective magnetization is lost because the thermal movement of the atoms leads to the elementary magnets in the crystals being aligned largely antiparallel. However, since the orientation of the grains in the sintered composite is not lost, the parallel alignment of the elementary currents can be restored after the magnets have cooled down by a sufficiently strong magnetization pulse.

The magnetic powder is produced in particular by grinding the corresponding alloys or components, for example in fluid bed jet mills or similar grinding systems. In fluid bed jet mills, in particular, defined fine grinding takes place, with an exact upper grain limit, but with a not insignificant proportion of fine particles. The comminution energy is provided by gas jets.

A method for producing a permanent magnet from an alloy is described in EP 0 414 376 A2 described, whereby the alloy is coarsely and finely pulverized. From the finely pulverized powder, the finest particles and coarse particles are sorted out using a “particle-size classifier machine”. The powder of the defined size is then pressed into a molding and sintered.

The disclosure document EP 2 273 513 A1 describes a method for producing an RTB sintered magnet. For this purpose, a metal alloy is first provided as the starting material, which is initially coarse and then Is finely pulverized. After obtaining the desired particle size, the further process steps “compression”, “sintering” and “heat treatment”, “surface treatment” and “magnetization” etc. take place.

The document US 2002/0129874 describes a process for producing a rare earth magnet. Here, an alloy is first pulverized coarsely and finely, with a classifying rotor being assigned to the pulverizer in order to separate particles of a predetermined size. The particles with a predetermined size are then fed to a cyclone classifier, whereby the finest particles are separated.

The WO published publication 2007/045320 A1 also describes a process for producing a rare earth magnet. Here, an alloy provided is first coarsely pulverized and then finely pulverized. To obtain the desired particle size, the finely pulverized powder is sieved.

Practice has shown that magnetic powders, which can be produced using processes known from the prior art, are chemically very reactive and for this reason react with the oxygen or nitrogen from the environment even at low oxygen concentrations. As a result, further processing of the magnetic powder can result in powder fires. Practice has also shown that magnets that are manufactured using magnetic powders known from the prior art can often be oriented very poorly, which means that the remanence of the magnets manufactured from the already known magnetic powders is impaired. Such disadvantages can be associated, in particular, with or with a high volume percentage of fines in the magnetic powder.

Furthermore, it may be that magnets made from the magnetic powders already known from the prior art have an opposing field stability or coercive field strength that requires improvement due to a high volume percentage of coarse content.

Description

The object of the invention is to further optimize the production of the starting mixture for the production of rare earth magnets in order to be able to produce improved rare earth magnets.

The above task is solved by the objects having the features in the independent claims. Further advantageous embodiments are described in the subclaims.

The invention relates to a method for producing a powdery starting material intended for the production of rare earth magnets.

A first step of the method involves comminution of an alloy comprising at least one rare earth metal, with a powdery intermediate product being formed from the alloy comprising at least one rare earth metal. Grinding includes coarse grinding and fine grinding. In particular, particles with an average particle size between d50 = 2µm to 5µm are produced.

A further step provides for carrying out at least one particle size-oriented classification for the powdery intermediate product, with a fraction of the powdery intermediate product formed by means of the at least one classification forming the starting material intended for the production of rare earth magnets. The powdery intermediate product is initially fed to at least a first static classifier. Following this, a portion separated from the powdery intermediate product by means of the at least one static classifier can be fed to the at least one dynamic classifier, which at least one dynamic classifier carries out at least one particle size-oriented classification for the portion separated from the powdery intermediate product by means of the at least one static classifier and thereby separates the fraction from the portion that forms the starting material intended for the production of rare earth magnets. Within the fraction forming the starting material, particles are formed in a target size range between 1µm and 10µm.

In the method, at least two temporally successive classifications, each based on the particle size, are implemented via the at least one dynamic classifier.

Here, coarse material is separated from the powdery intermediate product by the at least one dynamic classifier as part of a first classification based on the particle size. Furthermore, as part of a second classification based on the particle size, fine material is separated from the powdery intermediate product by the at least one dynamic classifier. A portion of the powdery intermediate product separated from the fine and coarse material is then provided as a fraction, which forms the starting material intended for the production of rare earth magnets.

With the method mentioned, a starting material is produced in which a proportion of particles > 8µm is ≤ 2 percent by volume and in which a proportion of particles < 2 µm is ≤ 2 percent by volume. Preferably, a proportion of particles >8µm is in a range between 0.1 percent by volume and a proportion of particles <2µm is in a range between 0.05 percent by volume and 2 percent by volume.

Furthermore, it is provided that the dynamic classifier comprises a classifying rotor and the static classifier is designed by a cyclone classifier.

It can also be that the at least one dynamic classifier sifts the powdery intermediate product and also disperses it, from which the fraction is separated from the powdery intermediate product, which forms the starting material intended for the production of rare earth magnets.

Embodiments have proven useful in which the first classification based on particle size and/or density and the second classification based on particle size and/or density are carried out via exactly one dynamic classifier. Furthermore, the alloy comprising at least one rare earth metal can preferably be comminuted mechanically in two separate steps, with the powdery intermediate product being formed from the comminutements in separate steps.

It may be that the at least one dynamic classifier implements the at least one classification based on particle size and/or density for the powdery intermediate product under a protective gas atmosphere.

Not part of the present invention is a starting material intended for the production of rare earth magnets, which was produced by a method according to one of the previously described embodiments. In the starting material according to the invention, a proportion of particles > 8 μm is ≤ 2 percent by volume, in particular in a range between 0.1 percent by volume and 1 percent by volume and / or a proportion of particles < 2 μm is ≤ 2 percent by volume and in particular in a range between 0. 05 percent by volume and 2 percent by volume.

• Herstellen eines Ausgangsmaterials mittels eines Verfahrens gemäß einem Ausführungsbeispiel der vorhergehenden Beschreibung,
• Einbringen des Ausgangsmaterials in Formen und Verpressen des Ausgangsmaterials in den Formen, wobei Rohlinge aus dem Ausgangsmaterial entstehen,
• Sintern der Rohlinge und Beaufschlagen gesinterten Rohlinge mit einem Magnetisierungsimpuls, so dass hieraus resultierend die gesinterten und mit einem Magnetisierungsimpuls beaufschlagten Rohlinge als Seltenerd-Magnete ausgebildet sind, optional können die Rohlinge einer mechanischen Bearbeitung unterzogen werden.

The invention also relates to a method for producing rare earth magnets. The procedure includes the following steps:

• Producing a starting material by means of a method according to an exemplary embodiment of the preceding description,
• Introducing the starting material into molds and pressing the starting material into the molds, creating blanks from the starting material,
• Sintering the blanks and applying a magnetization pulse to the sintered blanks, so that as a result the sintered blanks subjected to a magnetization pulse are designed as rare earth magnets; optionally, the blanks can be subjected to mechanical processing.

It may also be the case that a starting material is produced according to the previous description using the described method for producing rare earth magnets and that this starting material is introduced into the molds and pressed.

The invention also relates to a system for producing a powdery starting material intended for the production of rare earth magnets. Features that have already been described previously for various embodiments of the method can also be provided in the system described below and are therefore not mentioned redundantly. Features described below, which relate to various embodiments of the system according to the invention, can also be provided in the methods already described above.

The system for producing a powdery starting material intended for the production of rare earth magnets comprises at least one comminution device, which is aimed at producing a powdery intermediate product by comminuting an alloy comprising at least one rare earth metal. The size reduction includes coarse grinding and fine grinding. In particular, particles with an average particle size between d50 = 2µm to 5µm can be produced.

The system further comprises at least one separating device, which can separate a fraction from the powdery intermediate product via at least one particle size-oriented classification or sifting, which forms the starting material intended for the production of rare earth magnets.

It is envisaged that the at least one separating device comprises at least one static classifier in the form of a cyclone classifier, to which the powdery intermediate product can be fed. Furthermore, the system includes at least one dynamic classifier with a classifying rotor, which can separate the fraction from the powdery intermediate product, which forms the starting material intended for the production of rare earth magnets, via a classification based on particle size.

Here, the at least one static classifier and the at least one dynamic classifier are connected to one another in such a way that a portion separated from the supplied intermediate product by means of the at least one static classifier can be fed to the at least one dynamic classifier. The at least one dynamic safe can then, if necessary, separate the fraction from the supplied portion that forms the starting material intended for the production of rare earth magnets.

The system produces a starting material in which a proportion of particles > 8µm is ≤ 2 percent by volume and in which a starting material < 2µm is ≤ 2 percent by volume. In particular, a proportion of particles >8µm is in a range between 0.1 percent by volume and 1 percent by volume and a proportion of particles <2µm is in a range between 0.05 percent by volume and 2 percent by volume.

The dynamic classifier is connected to a control and/or regulating unit, in which control and/or regulating unit an algorithm is stored, via which the control and/or regulating unit sets a speed of the as part of the classifying rotor, which is designed at least one dynamic classifier, independently regulates or controls.

It may be that the at least one dynamic classifier is designed to classify and disperse the supplied powdery intermediate product.

It can also be that the at least one comminution device comprises two successive comminution machines, each of which is designed for preferably mechanical comminution of the alloy comprising at least one rare earth metal and interacts with one another to produce the powdery intermediate product from the alloy comprising at least one rare earth metal.

Embodiments in which the at least one dynamic filter can implement the classification based on particle size and/or density under a protective gas atmosphere have also proven successful.

The starting material, which can be produced within the framework of the previously described methods or by means of the previously described system, can essentially comprise particles of a target size range and hardly have any contamination with particles that are smaller than particles of a target size range. These are also referred to below as fine particles. Furthermore, the starting material produced within the framework of the previously described methods or by means of the previously described system can essentially hardly contain any contamination with particles that are larger than the particles of the target size range. These are also referred to below as coarse particles.

With a method or a system according to the previous description, it can in particular be possible to produce a starting material which essentially only comprises particles with a size within the target size range in a substantially homogeneous mixture. With regard to the starting material, which can be produced with the previously described methods or by means of the previously described system, embodiments have proven successful in which the starting material has particles in the target size range between 1µm and 10µm, in particular in a target size range between 2µm and 8µm. When comminuting an alloy containing at least one rare earth metal, in practice it cannot be avoided that a proportion of fine particles are created that are smaller than the target size range. In addition, there is usually a proportion of coarse particles that have not been sufficiently comminuted. A good compromise always has to be found here. Further grinding of the starting material would lead to a reduction in the proportion of coarse particles, but at the same time the proportion of fine particles, which are also undesirable, would increase. A high volume percentage of fine particles and/or coarse particles in the starting material is associated with undesirable properties of the respective rare earth magnets produced or manufactured from the starting material.

A starting material produced in the context of the preceding processes or by means of the system described above contains ≤ 2 percent by volume of fine particles, in particular ≤ 1 percent by volume. Furthermore, it is envisaged that within the framework of the previous procedures or Starting material produced using the system described above comprises ≤ 2 percent by volume of coarse particles, in particular ≤ 1 percent by volume.

In particular, the starting material produced within the framework of the previously described processes or by means of the previously described system essentially or predominantly contains particles in the target size range between 2µm and 8µm, with a proportion of particles whose size is above 8µm being ≤ 2 percent by volume, in particular in a range between 0.1 percent by volume and 1 percent by volume and where a proportion of particles whose size is below 2 μm is ≤ 2 percent by volume, in particular in a range between 0.05 percent by volume and 2 percent by volume.

The previously mentioned at least one static classifier, which is provided in various embodiments of a method according to the invention or a system according to the invention, is formed by at least one cyclone classifier.

The at least one cyclone classifier can possibly achieve a reduction in the proportion of fine particles. A powdery mixture separated via the at least one static classifier or the at least one cyclone classifier, which is also referred to below as a powdery intermediate product, generally still contains up to 10 percent by volume of fine particles and/or up to 10 even after the fine particles have been separated Volume percent of coarse particles. The fine particles, which are necessarily always present in such a powdery intermediate product, have a detrimental effect on the properties of the rare earth magnets made from them in several respects.

In order to improve the particle composition even further, the ground powder intermediate product, which has possibly already been partially freed of fine particles via the at least one static classifier, is subjected to at least one further classifier process, implemented by at least one dynamic classifier. In order to be able to carry out this classifying process efficiently, embodiments have proven useful in which the powdery intermediate product is first dispersed and then a classification according to particle size is carried out for the dispersed powdery intermediate product. This dispersion and classification according to particle size can be carried out in exactly one dynamic classifier. Fine particles and coarse particles can then be separated from the powdery intermediate product using the at least one dynamic classifier or exactly one dynamic classifier.

• Dispersion des Zwischenproduktes UND/ODER
• erneute Abtrennung von Feinstpartikeln und Grobpartikeln.

This means that the process can include the following steps individually or in combination:

• Dispersion of the intermediate AND/OR
• renewed separation of fine particles and coarse particles.

It can therefore preferably be provided that the dispersion of the intermediate product and the renewed separation of fine particles and coarse particles are carried out within a single device, in particular within a single dynamic classifier. Due to the high chemical reactivity of fine particles that may be present in high concentrations in the powdery intermediate product, the only dynamic classifier can implement dispersion and/or classifying, if necessary under a protective gas atmosphere. Helium, argon, nitrogen, etc. are used as protective gases.

The at least one rare earth metal formed as a component of the alloy can be formed, for example, by iron and/or boron. For example, the alloy comprising at least one rare earth metal can be an NdFeB alloy. Using the process steps described above or by means of the system already described, a starting material can be produced from this alloy comprising at least one rare earth metal, which essentially only comprises particles in the target size range between 2µm to 8µm. The starting mixture preferably comprises ≥ 95 percent by volume, in particular ≥ 98 percent by volume, of particles in the target size range, which target size range is set from 2 μm to 8 μm.

The system already described includes a device for the coarse comminution of an alloy comprising at least one rare earth metal.

One under With the aid of the device for coarse comminution, the coarse powder fraction formed from the alloy comprising at least one rare earth metal is in a fine comminution device designed as part of the system is ground into a fine powder fraction, the fine powder fraction forming the powdery intermediate product. For example, the device for fine comminution can be designed as a fluid bed jet mill.

Character description

• Figur 1 zeigt schematisch Verfahrensschritte zur Herstellung eines Ausgangsmaterials zur Fertigung von Seltenerd- Magneten, wie sie in diversen Ausführungsformen jeweils einzeln oder in der gezeigten Kombination vorgesehen sein können;
• Figur 2 zeigt einen Querschnitt durch einen dynamischen Sichter, wie er in diversen Ausführungsformen des erfindungsgemäßen Verfahrens sowie in diversen Ausführungsformen der erfindungsgemäßen Anlage vorgesehen sein kann.
• Figur 3 zeigt einen seitlichen Querschnitt durch den dynamischen Sichter nach Figur 2.
• Figur 4 stellt eine für diverse Ausführungsformen des erfindungsgemäßen Verfahrens bzw. der erfindungsgemäßen Anlage denkbare Partikelgrößenverteilung eines pulverförmigen Zwischenproduktes einer denkbaren Partikelgrößenverteilung eines zur Fertigung von Seltenerd-Magneten vorgesehenen Ausgangsmaterials gegenüber;
• Figur 5 zeigt eine rasterelektronenmikroskopische Aufnahme, wie sie für das pulverförmige Zwischenprodukt ausgebildet sein kann;
• Figur 6 zeigt eine rasterelektronenmikroskopische Aufnahme, eines Ausgangsmaterials, wie es mittels des erfindungsgemäßen Verfahrens bzw. der erfindungsgemäßen Anlage in diversen Ausführungsformen hergestellt werden kann.

In the following, exemplary embodiments will explain the invention and its advantages in more detail using the attached figures. The proportions of the individual elements in the figures do not always correspond to the real proportions, as some shapes are simplified and other shapes are shown enlarged in relation to other elements for better illustration. Features described below are not closely linked to the respective exemplary embodiment but can be used in a general context.

• Figure 1 shows schematically process steps for producing a starting material for producing rare earth magnets, as they can be provided individually or in the combination shown in various embodiments;
• Figure 2 shows a cross section through a dynamic classifier, as can be provided in various embodiments of the method according to the invention and in various embodiments of the system according to the invention.
• Figure 3 shows a side cross section through the dynamic classifier Figure 2 .
• Figure 4 compares a conceivable particle size distribution of a powdery intermediate product for various embodiments of the method according to the invention or the system according to the invention with a conceivable particle size distribution of a starting material intended for the production of rare earth magnets;
• Figure 5 shows a scanning electron micrograph as it can be designed for the powdery intermediate product;
• Figure 6 shows a scanning electron micrograph of a starting material, as can be produced in various embodiments using the method according to the invention or the system according to the invention.

Identical reference numbers are used for elements of the invention that are the same or have the same effect. Furthermore, for the sake of clarity, only reference numbers that are necessary for the description of the respective figure are shown in the individual figures. The illustrated embodiments merely represent examples of how the invention can be designed and do not represent a final limitation.

Figure 1 shows schematically process steps for producing a starting material AM for the production of rare earth magnets. The basis for this is a suitable RFeB alloy, which contains the components R = rare earth metal, Fe = iron and B = boron in the desired proportions. For example, an NdFeB alloy is used to produce a so-called neodymium magnet. Under certain circumstances, an alloy must first be produced from the elements in the desired proportions. In a first step, this alloy is subjected to coarse grinding. For example, in a mechanical grinding system or through embrittlement with hydrogen. In particular, particles with a size of up to a few mm are generated. The coarse powder fraction gPF obtained during coarse grinding is then subjected to fine grinding, with particles with an average particle size between d50 = 2 µm to 5 µm being or should be produced. This means that the d50 value of the fine powder fraction fPF is between 2µm and 5µm with a correspondingly broad particle distribution towards finer and also coarser particles, with the corresponding amounts of fine particles (d10 = approx. 1 - 2µm) or coarse particles (d90 = approx. 8-15µm). In contrast to the fine particles fP described below, the coarse particles gP are chemically stable and can also be easily oriented in magnetic fields, but they have negative effects on the opposing field stability of the magnet because these coarse particles gP remagnetize even in small magnetic opposing fields and thus worsen the opposing field stability (or the coercive field strength) of the entire magnet. For this reason it is advantageous to reduce the proportion of coarse particles To further reduce gP in the starting mixture for the production of sintered permanent magnets.

The particles fP of the fine fraction are chemically very reactive due to their fineness and react with the oxygen or even with the nitrogen from the environment even at the lowest oxygen concentrations. These fine particles fP can cause spontaneous powder fires during further processing of the powder. Another disadvantage of the finest particles fP is that these fine powder particles are very difficult to orient in the magnetic fields and pressing devices that are usually available (of the order of magnitude of approximately 10 - 20 kOe) and therefore worsen the remanence of the magnets made from them. For this reason, in a fourth or additional process step, fine particles, in particular particles with a diameter of ≤ 1-2 μm, are removed from the fine powder fraction fPF. For this purpose, following the coarse grinding and fine grinding according to numbers 1 and 2, the mixture is passed through a cyclone that carries the fines through a suitable gas stream and thereby separates it from the mixture. This forms the intermediate product ZP. However, this still contains a not insignificant proportion of up to 10% of fine particles smaller than approx. 1 µm to 2 µm.

In order to remove these remaining portions of fine particles fP ≤ 1 µm to 2 µm and/or coarse particles gP between 10 µm and 15 µm as completely as possible, the intermediate product ZP is subjected to at least one further sifting process in order to remove unwanted fine particles fP and coarse particles gP and thus ensure the homogeneity of the To further improve particles in the target size ZG, in particular in order to obtain a powder mixture as the starting material AM, which essentially only comprises particles with particle sizes in a target range between approximately 2µm to 8µm, since these particles represent the best powder fraction in magnetic terms. All further steps, which in terms of time follow the step according to number 4, are carried out with the help of a dynamic classifier 10 (cf. Figures 2 and 3 ) or a high-performance classifier.

The particles with the target size ZG between 2µm to 8µm are chemically sufficiently stable so that they do not cause any additional oxidation in the normal manufacturing process. They also work well with the usual magnetic fields orientate. They therefore contribute significantly to achieving a high remanence of the magnets produced and are therefore desirable, necessary and useful. The more powder particles of this target size ZG are present, the better the magnetic values (remanence Br and opposing field stability HcJ) of the magnets made from them.

In a further, or in this case 5th, process step, the powdery intermediate product ZP is dispersed in order to produce the most homogeneous distribution of the different particles of the intermediate product ZP. In particular, molecular and magnetic attractive forces between the particles are overcome and subsequent sifting and separation of fine particles and/or coarse particles following dispersion is possible. A dynamic classifier 10 is also used for this process step (cf. Figures 2 and 3 ) or high-performance classifiers are used.

The dispersed powdery intermediate product ZP is sifted again and particles of the fine fraction and/or particles of the coarse fraction are removed. This creates an optimized separation of the finest and coarse particles to achieve the desired target particle size ZG. The fine proportion of particles whose size is less than 1µm is reduced to a proportion of less than 1%. In addition, the coarse proportion of particles whose size is over 10µm can also be reduced to a proportion of less than 1%.

This at least one additional classifying process is preferably carried out under a protective gas atmosphere, for example helium, argon, or nitrogen, although this is not intended to represent an exhaustive list of possibilities. The protective gas atmosphere particularly prevents spontaneous powder fires due to the fine particles fP.

Particularly preferably, the fifth and sixth process step or the last two process steps, ie the dispersion and the separation of fine particles fP and/or the separation of coarse particles gP, can be carried out in a dynamic classifier 10 according to Figures 2 and 3 done together.

With regard to the embodiment of a dynamic classifier 1 according to Figures 2 and 3 The powdery intermediate product is added via product addition 1 ZP is fed to the classifier device or the dynamic classifier 10 from above. The necessary process air VL is supplied through the classifier air inlet 2, which takes the powdery intermediate product ZP supplied via the product addition 1 and leads it through a large number of adjustable guide vane gaps of the static guide vane basket 3, whereby the intermediate product ZP is dispersed. In the present case, a protective gas is used as the process air VL.

The intermediate product ZP dispersed in this way is passed through a classifier wheel 4 whose speed can be continuously adjusted, with the particle sizes being separated either into target and coarse material or into target and fine material.

The optimized classifier wheel design ensures that very high fineness levels can be achieved with just one classifier wheel 4, even at high throughputs. The finest particles fP leave the classifier device 10 via the classifier wheel 4, which is installed with a horizontal shaft 8, in the center of the classifier device or the dynamic classifier 10. The coarse particles gP are rejected by the classifier wheel 4 and through the helically designed machine housing 9, which is provided with a partition 5, at the back discharged via the coarse material outlet 6 on the underside of the machine housing 9. The position of the coarse material flap 7 can be used to regulate the discharge of the coarse particles gP in difficult separation tasks, and thus the cleanliness of the coarse particles gP can be influenced. The particles of the target size ZP leave the dynamic classifier 10 together with the coarse material via the coarse material outlet 6. The fine particles fP were separated from the particles of the target size ZP and therefore do not form part of the fraction that leaves the dynamic classifier 10 via the coarse material outlet 6.

The desired target particle size ZG is regulated in particular by regulating the gas flow of the process air VL and/or the speed of the classifier wheel 4. A higher gas flow and/or a lower speed lead to a coarser product, while a lower gas flow and/or a higher one speed lead to a finer product.

Additionally shows the Figure 3 the at least two cracked gas feeds (11), these are necessary to flush the gap between the fine material outlet and the classifier wheel (4) with so-called cracked gas. However, designs with only one cracked gas supply (11) are also possible. This flushing prevents... Particles settle in the classifier wheel (4) and/or the gap between the fine material outlet and the classifier wheel (4) and clog it. The flushing is carried out using a suitable fluid, in a preferred embodiment using protective gas.

Figure 4 shows the particle size distribution in the intermediate product ZP and in the starting material AM. In particular, the diagram plots the particle size in µm against the proportion of the volume density of the respective mixture in %. It is clearly visible here that through the additional process step of dispersing the intermediate product ZP and sifting with subsequent separation of the finest particles fP ≤ 1µm and/or coarse particles gP ≥ 10 via a dynamic sifter 10, a more homogeneous particle mixture in the starting material AM can be achieved, in which the proportion of fine particles fP is ≤1% of the volume density and in which the proportion of coarse particles gP is also ≤1% of the volume density. In particular, the hatched portions of fine particles fP and coarse particles gP are removed from the powdery intermediate product ZP.

The starting material AM produced in this way is particularly suitable for the production of sintered rare earth magnets due to the particle size between 1µm and 10µm, in particular between 2µm and 8µm, since particularly good magnets can be achieved with these particle sizes of the starting material AM. In particular, with this starting material AM for the production of permanent magnets, high (improved) remanence values BR and good (improved) opposing field stability HcJ as well as a significant improvement in the squareness of the demagnetization curve are achieved.

Figure 5 shows a scanning electron microscope image of the powdery intermediate product ZP and Figure 6 shows a scanning electron micrograph of the starting material AM, as it is produced in various embodiments of the method according to the invention and can be used for the production of rare earth magnets. While the intermediate product ZP represents a highly inhomogeneous mixture of different particle sizes and in particular also contains a high proportion of fine particles fP Figure 6 It is clear that the double-screened starting material AM mainly only contains particles of a target size ZG between 1µm and 10µm, in particular between 2µm and 8µm.

The invention has been described with reference to preferred embodiments. It will be conceivable to a person skilled in the art that modifications or changes may be made to the invention without departing from the scope of the following claims.

Reference symbol list

1

Product addition

2

Classifier air inlet

3

Guide vane basket

4

sifter wheel

5

partition wall

6

Coarse material exit

7

Coarse material flap

8th

Wave

9

Machine housing

10

Classifying device

11

Fission gas supply

AT THE

Source material

fP

finest particles / finest particles

fPF

fine powder fraction

GP

coarse particles coarse particles

gPF

coarse powder fraction

VL

Process air

ZG

Target size

ZP

intermediate product

SG

fission gas

Claims (8)

1. A method used to produce a powdered starting material (AM) intended for the manufacture of rare-earth magnets, the method comprising the following steps:

   - comminuting an alloy that comprises at least one rare-earth metal, wherein the comminuting comprises a coarse grinding and a fine grinding, wherein a powdered intermediate product (ZP) is formed from the alloy that comprises at least one rare-earth metal; and

   - carrying out at least one particle size classification for the powdery intermediate product (ZP), wherein a fraction of the powdered intermediate product (ZP) formed by means of the at least one classification constitutes the starting material (AM) intended for the manufacture of rare-earth magnets,
   the method being characterised in that

   - the powdered intermediate product (ZP) is first supplied to at least one first static classifier, and wherein subsequently hereafter a portion separated from the powdered intermediate product (ZP) by means of the at least one first static classifier is supplied to at least one dynamic classifier (10), which at least one dynamic classifier (10) carries out at least one particle size classification for the portion separated from the powdered intermediate product (ZP) by means of the at least one static classifier, and in this context separates that fraction from the portion that constitutes the starting material (AM) intended for the manufacture of rare-earth magnets and has particles in a target size range between 1µm and 10µm,

   - in which method at least two temporally successive classifications, each according to particle size, are carried out via the at least one dynamic classifier (10), wherein

   - the at least one dynamic classifier (10) separates coarse material (gP) from the powdered intermediate product (ZP) in the context of a first particle size classification, and wherein

   - the at least one dynamic classifier (10) separates fine material (fP) from the powdered intermediate product (ZP) in the context of a second particle size classification,

   - whereafter a portion of the powdered intermediate product separated from the fine material and the coarse material provides the fraction that constitutes the starting material (AM) intended for the manufacture of rare-earth magnets,

   - in which starting material (AM) a portion of particles > 8µm is at
   ≤ 2 volume percent, in particular, in a range between 0.1 volume percent and 1 volume percent,

   - and in which starting material (AM) a portion of particles < 2µm is at ≤ 2 volume percent, in particular, in a range between 0.05 volume percent and 2 volume percent;

   - wherein the at least one dynamic classifier (10) comprises a classifier rotor and the at least one static classifier is formed by a cyclone classifier.
2. The method according to claim 1, in which the at least one dynamic classifier (10) classifies and moreover disperses the powdered intermediate product (ZP), with the result that the fraction, which constitutes the starting material (AM) intended for the manufacture of rare-earth magnets, is separated from the powdered intermediate product.
3. The method according to claim 1 or 2, in which the first particle size classification and the second particle size classification are carried out via exactly one dynamic classifier (10).
4. The method according to one of the claims 1 to 3, in which the at least one dynamic classifier (10) carries out the at least one particle size classification for the powdered intermediate product (ZP) under inert gas atmosphere.
5. A method for the manufacture of rare-earth magnets, the method comprising the following steps:

   - producing a starting material (AM) by means of a method according to one of the claims 1 to 4,

   - placing the starting material (AM) into moulds and pressing the starting material (AM) in the moulds, wherein blanks are formed from the starting material (AM),

   - sintering the blanks and applying a magnetizing pulse to the sintered blanks such that the sintered blanks with the magnetizing pulse having been applied to are as a result formed to be rare-earth magnets.
6. A facility to produce a powdered starting material (AM) intended for the manufacture of rare-earth magnets, the facility comprising

   - at least one comminution device, which is adapted to produce a powdered intermediate product (ZP) by comminution of an alloy that comprises at least one rare-earth metal, wherein the comminution comprises a coarse grinding and a fine grinding, and

   - at least one separating device, which, via at least one particle size classification, can separate a fraction from the powdered intermediate product (ZP), which fraction constitutes the starting material (AM) intended for the manufacture of rare-earth magnets,
   the facility being characterised in that

   - the at least one separating device comprises at least one static classifier in the form of a cyclone classifier to which the powdered intermediate product (ZP) is suppliable, and

   - in that the at least one separating device comprises at least one dynamic classifier (10) with a classifier rotor, which, via a particle size classification, can separate that fraction from the powdered intermediate product (ZP) that constitutes the starting material (AM) intended for the manufacture of rare-earth magnets,

   - and wherein the at least one static classifier and the at least one dynamic classifier (10) are connected to one another in such a manner that a portion separated from the supplied powdered intermediate product (ZP) by means of the at least one static classifier is suppliable to the at least one dynamic classifier (10), and

   - wherein the at least one static classifier and the at least one dynamic classifier (10) are configured to produce a starting material (AM), in which starting material (AM) a portion of particles > 8µm is at ≤ 2 volume percent, in particular, in a range between 0.1 volume percent and 1 volume percent,

   - and in which starting material (AM) a portion of particles < 2µm is at ≤ 2 volume percent, in particular, in a range between 0.05 volume percent and 2 volume percent; wherein the dynamic classifier (10) is connected to a control unit and/or regulating unit, in which an algorithm is stored via which the control unit and/or regulating unit independently and in consideration of the particular desired particle size distribution for the starting material to be produced regulates or controls a rotational speed of the classifier rotor formed as a part of the at least one dynamic classifier.
7. The facility according to claim 6, in which the at least one dynamic classifier (10) is configured to classify and disperse the supplied powdered intermediate product (ZP).
8. The facility according to one of the claims 6 or 7, in which the at least one dynamic classifier (10) can carry out the particle size classification under inert gas atmosphere.

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