Method and material mixture for producing plastic-bonded permanent magnets from recycled powdery magnetic material

Abstract

The invention relates to a method for producing polymer-bonded permanent magnets from recycled, powdered magnetic material (2) derived from waste magnets (1) from various applications. The magnetic material (2) is mixed with an epoxy resin (6b) and a pressing aid, compacted into a powder pellet in a powder press, and subsequently cured in an oven. According to the invention, the epoxy resin (6b) is a powder and is dry-mixed with the magnetic material (2) before compaction. This simplifies the process and allows for pre-batch testing to verify the quality of the magnetic material. The invention further relates to a mixture (4) for producing polymer-bonded permanent magnets according to the method.

Description

[0001] The invention relates to a method for producing polymer-bonded permanent magnets from recycled, powdered magnetic material derived from waste magnets originating from various applications, wherein the magnetic material is mixed with an epoxy resin and a pressing aid, compacted into a powder pellet in a powder press, and subsequently cured in an oven. The invention further relates to a mixture of materials for carrying out the method.

[0002] Recycling old permanent magnets is becoming increasingly important in light of the ever-decreasing resources of rare earths and their extremely limited geographical distribution on Earth.

[0003] Above all, polymer-bonded neodymium-iron-boron (NdFeB) magnets are technically very relevant because they have a significantly higher magnetic performance than hard ferrites, which in turn allows for smaller permanent magnets. At the same time, they are mechanically very robust. Polymer-bonded magnets can be manufactured in complex shapes, and their magnetization is freely selectable. In polymer-bonded permanent magnets, the epoxy resin is the polymer in which the powder particles of the magnetic material are bound. The epoxy resin melts in the oven, fills the spaces between the powder particles, and acts as an adhesive.

[0004] Recycled magnetic material is characterized by fluctuating magnetic properties because the origin of the scrap magnets from which it is produced varies. The recycled magnetic material also regularly exhibits a wider range of components and impurities, as the scrap magnets used are composed of diverse materials. These scrap magnets come from a variety of applications, such as wind turbine generators or electric vehicle motors. However, whether the quality of the recycled magnetic material is sufficient to produce new permanent magnets with specified characteristics can only be determined after the new permanent magnets have been manufactured, specifically after they have been magnetized following curing in an oven.An entire batch of recycled magnetic material may be unusable if even a few of the permanent magnets produced from it exhibit insufficient magnetic properties. This is particularly problematic if the manufacturer of the magnetic material and the manufacturer of the permanent magnets are different companies. In this case, the delivered magnetic material must be returned, resulting in additional logistical effort.

[0005] It should be noted that the quality of the batch cannot be easily improved due to the standard manufacturing process, as the magnetic material powder particles are coated with epoxy resin. This coating is achieved through a "wet mixing" process, in which the recycled magnetic material powder is stirred into acetone as a solvent, in which a liquid epoxy resin has been dissolved. Subsequent vacuum drying removes the acetone, resulting in epoxy-coated magnetic material powder. Both process steps take place in a vacuum stirred dryer.

[0006] It is possible to miniaturize this manufacturing process by wet-mixing only a small amount of recycled magnetic material with the epoxy resin and producing test magnets from this small quantity, the quality of which is then examined. However, this requires a parallel manufacturing process and also new machinery, namely a smaller vacuum stirred dryer.

[0007] Furthermore, the described wet mixing of the magnetic material powder in acetone is complex, expensive, and poses safety concerns.

[0008] It is therefore an object of the present invention to overcome the aforementioned disadvantages and to improve and simplify a process of the type mentioned at the outset, without wasting recycled magnetic material, thereby eliminating the use of acetone, avoiding the purchase of new machines, and enabling batch pre-production for testing purposes. Furthermore, it is an object of the invention to provide a mixture of materials that enables the production of permanent magnets using the improved process.

[0009] This problem is solved by a method having the features of claim 1 and a mixture having the features of claim 10. Advantageous embodiments are specified in the respective dependent claims and are explained below.

[0010] According to the invention, the method mentioned in the introduction is further developed in such a way that the epoxy resin is a powder and is dry-mixed with the magnetic material before compaction. The proposed mixture for producing polymer-bonded permanent magnets according to the proposed method is, overall, a powder mixture of recycled, powdered magnetic material produced from waste magnets originating from various applications, an epoxy resin in powder form, and a pressing aid.

[0011] The use of epoxy resin in powder form offers numerous advantages. Firstly, it eliminates the need for acetone, and the dry mixing process also eliminates the need for a vacuum stirred dryer. This alone makes the manufacturing process simpler, more cost-effective, and less hazardous. However, a major advantage lies in the fact that only a small portion of a produced batch of recycled magnetic material needs to be mixed with the epoxy resin as a batch pre-mix. This pre-mix is ​​then used to produce samples of new permanent magnets, initially for testing purposes, and to examine their magnetic properties.Should it turn out that the magnetic properties are insufficient, the batch of recycled magnetic material can easily be improved, for example by altering the particle size distribution through sieving out excessive amounts of fines or oversize particles (coarse particles), or by adding further powder with a different chemical composition and better magnetic properties, since it is not yet mixed with epoxy resin. Thus, no magnetic material has to be discarded. The present invention is therefore resource-efficient and contributes to sustainability.

[0012] Preferably, the pressing aid is also in powder form and is added dry to the magnetic material together with the epoxy resin, i.e., simultaneously. Thus, unlike the prior art, two separate mixing processes for the epoxy resin on the one hand and the pressing aid on the other are not required, which also simplifies the manufacturing process.

[0013] Zinc stearate has proven particularly suitable as a pressing aid. It acts as a lubricant between the powder particles of the magnetic material and, with the same pressing force, results in a higher density of the magnetic material.

[0014] It is sufficient if the pressing aid is mixed with the magnetic material at a proportion of between 0.8 and 1.5 percent by weight, preferably approximately 1.0 or 1.2 percent by weight. The percentage by weight refers to the total quantity of the powder mixture consisting of the magnetic material powder, the epoxy resin powder, and the pressing aid. The pressing aid thus comprises between 1.0 and 1.5 percent by weight, preferably approximately 1.0 or 1.2 percent by weight, of the mixture.

[0015] In one embodiment, the epoxy resin can be mixed with the magnetic material at a proportion or dosage between 1.3 and 1.8 percent by weight, preferably 1.5 percent by weight. The epoxy resin thus constitutes a proportion of between 1.3 and 1.8 percent by weight, preferably 1.5 percent by weight, in the mixture. It has been shown that a proportion within this range is suitable for binding all of the magnetic powder without the epoxy resin leaching out of the outer surface of the compact. The value of 1.8 percent by weight can be understood in this context as a limit for a standard dosage of the epoxy resin.

[0016] In another embodiment, the extrusion of epoxy resin from the outer surface of the powder compact may be desirable, as the adhesive properties of the epoxy resin allow it to bond the permanent magnet being produced to a metal component immediately. Such a metal component could, for example, be a stainless steel sleeve encapsulating the permanent magnet. The epoxy resin can be mixed with the magnetic material at a proportion of between 1.8 and 2.5 percent by weight, preferably between 2.0 and 2.2 percent by weight. The epoxy resin then constitutes a proportion of between 1.8 and 2.5 percent by weight, preferably between 2.0 and 2.2 percent by weight, in the mixture. Furthermore, the powder compact is encapsulated in a stainless steel sleeve before curing. It is then placed in the oven along with the stainless steel sleeve to cure.Due to the higher dosage of epoxy resin used compared to the standard dosage, the resin oozes out of the surface of the powder compact because of the temperature in the oven and acts as an adhesive to the stainless steel sleeve. Since curing in the oven takes place at a relatively low temperature between 170°C and 190°C, preferably 180°C, the stainless steel sleeve survives the time in the oven without damage.

[0017] The stainless steel sleeve can, for example, have a wall thickness between 0.3mm and 0.8mm, preferably 0.5mm.

[0018] The magnetic material can be produced, for example, by centrifugal melting. In this process, shredded scrap magnets are melted down and extruded drop by drop onto a rotating roller or cylinder, from where they bounce off and cool into flakes.

[0019] The method according to the invention is particularly suitable for the production of ring-shaped permanent magnets.

[0020] The permanent magnets are preferably used in electric motors intended for driving centrifugal pumps.

[0021] Further features, properties and advantages of the inventive method and powder mixture are explained in more detail below with reference to specific exemplary embodiments and the accompanying figures.

[0022] It should be noted that, in the context of the present description, the terms "exhibit," "comprise," or "contain" in no way preclude the presence of other characteristics. Furthermore, the use of the indefinite article for an object does not preclude the plural of that object.

[0023] They show: Figure 1: A flowchart for the production of permanent magnets from recycled magnetic material according to the prior art. Figure 2: A flowchart for the production of permanent magnets from recycled magnetic material according to a first embodiment of the invention. Figure 3: A flowchart for the production of permanent magnets from recycled magnetic material according to a second embodiment of the invention.

[0024] The reference symbols in the figures retain their meaning from figure to figure. In the figures, the reference symbols always denote the same or equivalent process steps and materials, unless otherwise specified.

[0025] Figure 1This document describes a state-of-the-art process for manufacturing permanent magnets from recycled magnetic material 2. In this process, waste magnets 1 made of a neodymium-iron-boron (NdFeB) alloy are first collected in step S1, then crushed in step S2, and finally melted in step S3. In step S4, powder particles in the form of flakes are extracted from the melt by centrifugal force. These flakes form the magnetic material 2, which is then further processed. The flakes have an average grain size of 150 µm.

[0026] According to the prior art, this magnetic material 2 is mixed with a liquid epoxy resin 6a dissolved in acetone (step S5). Since acetone is also liquid, this is referred to as "wet mixing." The powder particles are thereby coated with epoxy resin 6a. The magnetic material is then vacuum-dried (step S6) to remove the acetone, leaving behind the epoxy resin-coated magnetic material powder 3. The wet mixing in step S5 and the drying in step S6 are carried out in a vacuum stirred dryer.

[0027] The aforementioned steps S1 to S6 are carried out at the supplier of the magnetic material powder 3, who delivers the magnetic material powder 3 coated with epoxy resin 6a to the magnet manufacturer. It thus forms the starting material for magnet production.

[0028] The magnet manufacturer's initial step is to mix the magnetic material powder 3 with a powdered pressing aid, step S7a. This is done dry, i.e., without the addition of a liquid solvent.

[0029] This yields a powder mixture 4, which is then compacted into a powder pellet 5 in a powder press (step S8). This is done at a density of 10 t / cm², achieving 80% of the material's theoretical density and also 80% of the magnetic remanent flux density. The powder pellet 5 has the desired final shape of the permanent magnet to be produced. This powder pellet 5 is then placed in an oven to cure at a temperature of 180°C. During this process, the epoxy resin 6a polymerizes, causing the powder particles to bond together.

[0030] Not shown is in Figure 1The next step is magnetization, in which the manufactured permanent magnet is exposed to a strong electromagnetic field, which imprints its magnetic orientation. Only after magnetization can the magnetic properties or quality of the original magnet material 2 be determined. If the quality is insufficient, the entire batch of magnet material 3 mixed with epoxy resin 6a must be returned to the supplier for recycling.

[0031] Figure 2 A first embodiment of a method according to the invention is shown, which is significantly simpler than the prior art and enables the test production of permanent magnets from a batch. As a comparison of the Figure 2 with the Figure 1As shown, the process according to the invention does not involve wet mixing (step S5) and consequently no vacuum drying (step S6), so that neither acetone nor a vacuum stirred dryer is required. Instead, the magnetic material 2 obtained from the centrifugal melting process is delivered directly to the magnet manufacturer. However, not the entire batch of magnetic material 2 is delivered, but only a partial quantity, i.e., a preliminary batch.

[0032] It is now planned that the magnet manufacturer will mix the magnetic material 2, or the pre-drawn sample, with the epoxy resin 6b. This is done in step S7b by simultaneously adding the epoxy resin 6 and the molding aid to the magnetic material powder. Of course, the epoxy resin 6b and the molding aid can also be mixed with the magnetic material powder sequentially. The epoxy resin 6b is also a powder in this case, so the material mixture remains dry and in powder form, or in the form of powder mixture 4. In this mixture, the molding aid has a proportion of 1.2% by weight and the epoxy resin 6b a proportion of 1.5% by weight.

[0033] Zinc stearate is used as a pressing aid.

[0034] The subsequent steps differ from the procedure in Figure 1No. The powder mixture 4 is compacted in the powder press to form a powder pellet 5, step S8, which is then placed in the oven and hardens there, step S10. However, the polymerization of the epoxy resin is not triggered directly at this point. Rather, the powdered epoxy resin melts, thereby encapsulating the powder particles and filling the spaces between them.

[0035] The magnetization process then follows. If it turns out that the quality of the batch is insufficient, the remainder of the batch of magnetic material 2 does not need to be sent back to the supplier, as it has already remained with them. Instead, the supplier can immediately rectify the batch.

[0036] Figure 3 shows a further development of the procedure in Figure 2It differs from the first version only in that the epoxy resin powder 6b has a higher proportion in the powder mixture, namely between 1.8 and 2.5 percent by weight, for example, 2.2 percent by weight. Such a proportion, since it exceeds 1.8 percent by weight, is referred to as "overdosed." This results in epoxy resin oozing from the surface of the powder compact during curing in the oven. This is used to bond a stainless steel sleeve, which encapsulates the permanent magnet, to it. For this purpose, after the powder compact 5 has been produced, such a stainless steel sleeve is slid over the powder compact 5, or alternatively, the powder compact 5 is inserted into the stainless steel sleeve. The powder compact 5 then cures in the oven together with the stainless steel sleeve, where it is bonded to the permanent magnet by the epoxy resin 6b.

[0037] The inventive method according to the Figure 2 or 3 is preferably used to manufacture ring-shaped permanent magnets, in particular permanent magnets for electric motors that drive centrifugal pumps.

[0038] It should be noted that the foregoing description is given merely as an example for illustrative purposes and in no way limits the scope of protection of the invention. Features of the invention that are indicated as "may," "exemplary," "preferred," "optional," "ideal," "advantageous," "if applicable," "suitable," or the like are to be considered purely optional and likewise do not limit the scope of protection, which is defined exclusively by the claims. Insofar as the foregoing description mentions elements, components, process steps, values, or information that have known, obvious, or foreseeable equivalents, these equivalents are also encompassed by the invention.Likewise, the invention includes any changes, alterations or modifications of embodiments which involve the replacement, addition, modification or omission of elements, components, process steps, values ​​or information, as long as the basic idea of ​​the invention is retained, regardless of whether the change, alteration or modification leads to an improvement or deterioration of an embodiment.

[0039] Although the foregoing description of the invention mentions a multitude of physical, intangible, or process-related features relating to one or more specific embodiments, these features can also be used in isolation from the specific embodiment, at least insofar as they do not necessarily require the presence of further features. Conversely, these features mentioned in relation to one or more specific embodiments can be combined arbitrarily with one another and with further disclosed or undisclosed features of illustrated or unillustrated embodiments, at least insofar as the features do not mutually exclude each other or lead to technical incompatibilities.

Claims

1. Method for producing plastic-bonded permanent magnets from recycled, powdered magnetic material (2) produced from waste magnets (1) from different applications, wherein the magnetic material (2) is mixed with an epoxy resin (6b) and a pressing aid, compacted in a powder press to form a powder pellet and subsequently cured in an oven, characterized by the fact that the epoxy resin (6b) is a powder and is dry mixed with the magnetic material (2) before compaction.

2. Method according to claim 1, characterized by the fact that the pressing aid is in powder form and is mixed dry with the epoxy resin (6b) into the magnetic material.

3. Method according to claim 2 or 3, characterized by the fact that the pressing aid is mixed with the magnetic material (2) in a proportion between 1.0 and 1.5 percent by weight, preferably 1.0 or 1.2 percent by weight.

4. Method according to any of the preceding claims, characterized by the fact that the epoxy resin (6b) is mixed with the magnetic material (2) in a proportion between 1.3 and 1.8 percent by weight, preferably 1.5 percent by weight.

5. Method according to any one of claims 1 to 3, characterized by the fact that the epoxy resin (6b) is mixed with the magnetic material in a proportion between 1.8 and 2.5 percent by weight, preferably between 2.0 and 2.2 percent by weight, and the powder compact is encapsulated in a stainless steel sleeve before curing.

6. Method according to claim 5, characterized by the fact that The stainless steel sleeve has a wall thickness between 0.3mm and 0.8mm, preferably 0.5mm.

7. Method according to any of the preceding claims, characterized by the fact that The curing process takes place in the oven at a temperature between 170°C and 190°C, preferably 180°C.

8. Method according to any of the preceding claims, characterized by the fact that The magnetic material is produced by centrifugal melting.

9. Method according to any of the preceding claims, characterized by the fact that the permanent magnets are ring-shaped.

10. Mixture (4) for the production of polymer-bonded permanent magnets according to the method of any one of claims 1 to 9 comprising a mixture of - recycled, powdered magnetic material (2) produced from waste magnets (1) from different applications, - an epoxy resin (6b) and - a pressing aid, characterized by the fact that the epoxy resin (6b) is a powder and the mixture (4) is a powder mixture overall.

11. Mixture (4) according to claim 10, characterized by the fact that The pressing aid is zinc stearate in powder form.

12. Mixture (4) according to claim 10 or 11, characterized by the fact that The pressing aid comprises a proportion of between 1.0 and 1.5 percent by weight, preferably 1.2 percent by weight, of the mixture.

13. Mixture (4) according to claim 10, 11 or 12, characterized by the fact thatthe epoxy resin (6b) comprises a proportion of between 1.3 and 1.8 percent by weight, preferably 1.5 percent by weight of the mixture.

14. Mixture of substances according to claim 10, 11 or 12, characterized by the fact that the epoxy resin (6b) comprises a proportion of between 1.8 and 2.5 percent by weight, preferably between 2.0 and 2.2 percent by weight of the mixture.

Images