DE102010042425A1 - Cleaning and passivating solution, useful for cleaning a workpiece, preferably magnet, comprises a water soluble salt of phosphoric acid, a water soluble salt of nitric acid, and an anionic surfactant e.g. sodium dodecyl sulfate - Google Patents

Abstract

Cleaning and passivating solution (6) comprises at least one water soluble salt of phosphoric acid, at least one water soluble salt of nitric acid, and at least one anionic surfactant, where the pH of (A) is 1.5-4. Independent claims are included for: (1) cleaning a workpiece comprising providing the workpiece, providing the cleaning and passivating solution, completely or partially contacting the workpiece in the cleaning solution for a given period, and removing the cleaned workpiece from the cleaning solution at the end of the given period; and (2) preparing and cleaning a magnet comprising providing a magnetic raw material, producing a workpiece to be cleaned by grinding the magnetic raw material and cleaning of the workpiece.

Description

The invention relates to a cleaning solution and a cleaning method. If, for example, magnets based on rare earths (SE), such as Nd ₂ Fe ₁₄ B, SmCo ₅ or Sm ₂ Co ₁₇ , are mechanically processed in aqueous cooling lubricants, this produces magnetic grinding sludge which adheres slightly magnetically to the surface of the processed sintered magnet and which is therefore difficult to remove using conventional cleaning processes. As a rule, first a pre-cleaning in an alkaline cleaning bath in a temperature range of about 60 ° C to 70 ° C is required, followed by an acid treatment, which removes the magnetic surface and at the same time dissolves the abrasive slurry particles. Passivation of the pickled magnets must be carried out after the process in order to prevent corrosion (red rust) during subsequent rinsing and drying. In this process, the dimensions of the magnets are slightly changed, which increases the spread. As a result, it may happen that the dimensions of the finished magnet are outside a predetermined tolerance band.

Although it is not possible to change the dimensions of the magnet too unintentionally, if one uses as a cleaning process on ultrasonic cleaning in aqueous alkaline cleaning baths, but this process is difficult to perform in SE permanent magnets and also very time consuming. To safely remove the magnetic sludge particles, special process conditions must be observed, such. B. changing ultrasonic frequencies, movement of the magnets to be cleaned in the bathroom, high flooding of the magnets, subsequent spraying with water under pressure, etc. For the purpose of corrosion protection must also be followed by a passivation to protect the cleaned magnets from corrosion.

The corrosion protection may, for example, be a conversion layer treatment such as phosphating or chromating. Alternatively, the cleaned magnets may be oiled or anticorrosive may be dried. All of these processes are not suitable for linking the cleaning process with the grinding processes. For example, a grinding treatment with subsequent continuous cleaning can not be meaningfully integrated into a production line, as both the pickling process with passivation and the ultrasonic cleaning process are too complex and take too much time with a treatment time of about 10 minutes. A combined production line would require a lot of space and would be unprofitable due to the high investment costs compared to the classical concept with locally separated processes.

In classical production, the magnets are first ground in a machining center and then cleaned in a separate electroplating plant in a drum process. In between, the magnets must be dried due to the extended service life and preserved from corrosion.

The object of the present invention is to provide a cleaning solution which is generally suitable for cleaning soiled articles, in particular for cleaning ground magnets. A further object of the invention is to provide a cleaning method for cleaning soiled articles, and a method for producing and cleaning magnets, in which the processes grinding, cleaning, passivation and drying can be combined in a single pass process in the simplest possible way to create a significantly cheaper and faster alternative to the conventional processes.

These objects are achieved by a cleaning and passivation solution according to claim 1, by a cleaning method according to claim 15 or by a method for processing and cleaning a magnet according to claim 26. Embodiments and developments of the invention are the subject of dependent claims.

For the intended cleaning process, the use of an acidic phosphate-based cleaning and passivation solution is provided, by means of which the magnets can be both cleaned and protected against corrosion. In the following, for the sake of simplicity, the term "cleaning solution" is used in abbreviated form of the term "cleaning and passivation solution". The cleaning and corrosion protection process can optionally be carried out in the form of an ultrasonic bath treatment, in which the magnet to be processed is inserted into said cleaning solution. As a result, within a very short period of time of, for example, less than two minutes, an optimum cleaning result in terms of particle freedom and corrosion protection is achieved by growing on the surface of the workpiece a phosphate layer which can extend over the entire surface of the workpiece. This phosphate layer may, for example, have a thickness of at least 100 nm. It is important in this context that during the treatment there is no surface damage to the magnetic material by hydrogen uptake or by other chemical attacks. The phosphate layer forms a passivation layer which protects the surface of the magnet on the one hand against corrosion, on the other hand it serves as a bonding agent for a subsequent coating and / or gluing.

BASIC STRUCTURE OF THE CLEANING SOLUTION

The cleaning solution comprises at least one water-soluble salt of phosphoric acid, at least one water-soluble salt of nitric acid and at least one anionic surfactant, and a pH in the range of pH 1.5 to pH 4.

The adjustment of the pH to said range can be achieved by adding an acid, e.g. As nitric acid or phosphoric acid, or by adding an alkali, for. As sodium hydroxide or potassium hydroxide solution, take place.

The at least one anionic surfactant may, for example, be any selection of exactly one or any two or more of the following anionic surfactants: a long-chain alkyl sulfate, such For example, sodium dodecyl sulfate; an ethoxylate of long chain aliphatic alcohols, such as. Nonylphenol ethoxylate or isotridecanol ethoxylate; a long-chain aliphatic or aromatic sulfonate, such as. B. dodecylbenzenesulfonate; a carboxylate of fatty acids (soaps); a secondary alkyl sulfonate (SAS): C _n H _{2n + 1} -SO ₃ ^- Na ⁺ . For the purposes of the present invention, an aliphatic surfactant is considered long-chain if it has at least one chain of 6 carbon atoms.

The anionic surfactants having a negatively charged functional group have a polar and a nonpolar component. The polar, functional group is -COO ^- (carboxylate) or -SO ₃ ^- (sulfonate) or -SO ₄ 2 ^- (sulfate), as the nonpolar part is an alkyl radical.

OPTIONAL COMPONENTS OF CLEANING SOLUTION

(a) cations

As an optional component (s), the cleaning solution may have, in addition to the base components, one type or any combination of several types of metal cations that are not yet included in the base components. Suitable metal cations are, for example, cations of the elements of the first main group (alkali metals: lithium, sodium, potassium, rubidium, cesium, francium) and second main group (alkaline earth metals: beryllium, magnesium, calcium, strontium, barium, radium) of the Periodic Table, the rare earth metals and the Transition metals (ie the metals with atomic numbers 21 to 30, 39 to 48 and 57 to 80), which form water-soluble phosphate salts or water-soluble salts in the pH range from pH 1.5 to pH 4, for example with at least one of the following anions: Chromat , Molybdate, tungstate, chlorate, perchlorate, manganate, vanadate, niobate, tantalate, titanate, sulfate, borate and others. In addition, organic anions are also suitable, for. For example: carboxylate, alkyl sulfonate, arylsulfonate, but also other organic anions.

(b) anions

As another optional component (s), the cleaning solution may have, in addition to the basic components, one type or any combination of several types of anions not yet contained in the basic components. Suitable anions are, above all, not nitrate-oxidizable anions, for example: chromate, molybdate, tungstate, chlorate, perchlorate, manganate, vanadate, niobate, tantalate, titanate, sulfate, borate and others. In addition, organic anions are also suitable, for. For example: carboxylate, alkyl sulfonate, but also other organic anions.

Also suitable as anions are hydrotropes, of which the cleaning solution may contain one or more in addition to the basic components. These hydrotropes are a precursor of surfactants and serve as anionic solubilizers. Examples of suitable hydrotropes are: arylsulfonate, cumene sulfonate, xylene sulfonate or toluenesulfonate.

A cleaning solution, as has been explained above, may have the following constituents in, for example, the concentration ranges indicated in each case: Phosphate: 10 g / l to 300 g / l; Nitrate: 10 g / l to 500 g / l; anionic surfactants: 0.1 g / l to 100 g / l;

The following concentration ranges can be particularly advantageous: Phosphate: 50 g / l to 200 g / l; Nitrate: 50 g / l to 300 g / l; anionic surfactants: 5 g / L to 50 g / L;

The pH of the finished cleaning solution is adjustable in the range of pH 1.5 to pH 4. Particularly advantageous is a pH in the range of pH 1.6 to pH 2.4, since in this area, the growth of the passivation layer is particularly fast.

For cleaning and / or passivation, a workpiece to be cleaned or passivated is placed in the cleaning solution for a certain time, for example 45 seconds to 90 seconds. In this case, the required treatment duration can increase with degree of contamination. Basically, treatment times of less than 45 seconds or more than 90 seconds are possible. The working temperature of the cleaning solution during the cleaning process may, for. B. 5 ° C to 95 ° C, or 40 ° C to 80 ° C. During the cleaning process, the workpiece can be completely or only partially immersed in the cleaning solution.

The invention will now be described by way of concrete examples with reference to the accompanying figures. The values or ranges given in the examples and the constituents of the cleaning solution used are by no means to be understood as limiting. In the described method steps, the order of individual method steps can be interchanged, unless a step necessarily requires that another step has previously been carried out. In addition, a method according to the present invention does not necessarily have to include all of the explained steps.

Show it

the 1A to 1E various steps of a method in which a magnetic blank is ground and then cleaned;

2 a flow chart illustrating the basis of the 1A to 1E explained method steps.

example 1

There were ten prepared block magnets as blanks 1' with dimensions of 50 mm × 13 mm × 3 mm made of Nd ₂ Fe ₁₄ B with diamond discs with the aid of an aqueous cooling lubricant on a continuous grinding machine 3 ground in length, width and thickness ( 1A ), causing magnetic grinding dust 2 on the surface of the ground blanks 1 clung.

The ground blanks 1 were the grinding system 3 when wet, initially rinsed briefly with tap water to remove the mildly alkaline coolant, and then immediately onto a stainless steel screen 4 placed with the mesh size 8 mm ( 1B ).

That with the blanks 1 occupied grid 4 was placed in a commercial laboratory ultrasonic pan 5 (Ultrasonic frequency 35 kHz, 215 W ultrasonic power, internal dimensions of the tub 300 mm × 300 mm × 300 mm) with coupled ultrasonic transducer 7 hanged, in which a cleaning liquid 6 was filled, so that the magnets 1 about 3 cm below the surface of the cleaning fluid 6 and thus completely from the cleaning fluid 6 covered ( 1C ). Alternatively, the cleaning fluid 6 even after the blanks 1 occupied grid 4 into the laboratory ultrasound pan 5 be filled. According to another alternative, the blanks 1 also individually without the use of a grid 4 in the laboratory ultrasound pan 5 placed and treated.

As a cleaning fluid 6 a solution of the following composition was used: phosphate content: 100 g / l; Nitrate content: 125 g / l; Surfactant content: sodium lauryl sulfate 20 g / l. The pH was adjusted to pH 2 with 10% sodium hydroxide solution.

After insertion into the cleaning fluid 6 became the block magnets 1 at a temperature of 65 ° C for a period of 1 minute with ultrasound 8th acted upon with the help of the ultrasound generator 7 generated and in the cleaning fluid 6 was coupled. After that they were on the grid 4 located blanks 1 the cleaning fluid 6 taken ( 1D ) and rinsed first with tap water and then with demineralized water ("DI water"). By treating the block magnets 1 in the cleaning fluid 6 has sic on the surfaces of the block magnets 1 a phosphate layer 1'' formed, which the block magnets 1 on the one hand protects against corrosion and on the other serves as a bonding agent for any intended subsequent painting and / or gluing. The phosphate layer 1" is in the enlarged section in 1D shown in cross section. The thickness d1 '' of this phosphate layer 1'' , with increasing residence time of the block magnets 1 in the cleaning fluid 6 may increase, for example, at least 100 nm.

After rinsing, the block magnets became 1 on the grid 4 in a convection oven 9 dried at 80 ° C. The magnetic grinding dust 2 stayed in the cleaning fluid 6 back.

In the cleaning fluid 6 , during rinsing and during the drying process were the block magnets 1 always on the stainless steel grid 4 , At the dried block magnets 1 The cleaning success was checked by means of transparent adhesive tape, which was applied to the block magnets 1 glued on, peeled off and then and for visualization of the residual dirt particles removed with the adhesive tape, ie above all of the remaining magnetic grinding dust 2 , was glued on white paper. It was found that the treated block magnets 1 free of adhering dust particles 2 and grinding mud residues. The dried magnets 1 were visually impeccable and coated with a blue iridescent conversion protective layer of Nd / Fe phosphate (detection by scanning electron microscopy / EDX). At the support points of the block magnets 1 on the stainless steel grid 4 no dry spots occurred.

2 shows a flowchart illustrating the basis of the 1A to 1E explained method steps. According to the method, a magnetic blank 1' provided (step 10 ), ground (step 11 ) and then with tap water (step 12 ) and / or with deionised water (step 13 ). In addition, a cleaning fluid 6 provided (step 14 ). The ground and rinsed magnetic blank 1 is for a predetermined period in the cleaning fluid 6 introduced (step 15 ). Before, during or after insertion is by the ultrasonic transducer 7 an ultrasonic signal 8th generated in the cleaning fluid 6 coupled in (step 16 ), so that the ultrasonic signal 7 for a predetermined period of time, for example, 45 seconds to 90 seconds or 60 seconds to 90 seconds on the magnet blank 1 acts. Thereafter, magnetic blank 1 again from the cleaning fluid 6 taken out (step 17 ), rinsed with tap water and / or deionised water (step 18 ), and in a drying oven 9 dried (step 19 ).

The cleaned in the manner described, surface passivated and dried block magnets 1 were placed in deionized water for further testing for three days. Then the degree of corrosion became DIN 53210 certainly.

For comparison, the degree of corrosion of identically ground block magnets was determined, which had been conventionally cleaned and passivated by pickling and phosphating and then also placed in demineralized water for three days. As a result, the conventionally treated block magnets showed a rust attack of 10% to 30% of the surface at degrees of rust ranging from Ri 3 to Ri 4, while the surfaces of block magnets cleaned and surface-passivated in accordance with the present invention were rust-free or rusted showed a maximum of 1% of the surface at degrees of rust ranging from Ri 0 to Ri 1.

Example 2

Furthermore, block magnets were measured as blanks with dimensions of 12 mm × 10 mm × 2 mm, which were ground and cleaned and surface-passivated by the method of Example 1, for surface damage. The magnetic preferred direction of the block magnets was chosen in the direction of the long side (12 mm) of the block magnets. The assessment of the surface damage was carried out according to the method of R. Blank and E. Adler: "The Effect of Surface Oxidation on the Demagnetization Curve of Sintered Nd-Fe-B Permanent Magnets ", Appendix 3 (9th International Workshop to Rare Earth Magnets and Their Applications, Bad Soden, Germany, Sept. 1987 ). The condition of the surfaces was measured before and after the treatment. As a result, no surface damage could be detected on the block magnets. A change in the magnetic properties of the block magnets was also not observed.

Example 3

Block magnets of SmCo ₅ with the dimensions 7 mm × 5.5 mm × 4.1 mm were ground in aqueous cooling lubricant and cleaned and surface-passivated according to the method explained in Example 1 in a cleaning liquid with the composition described in Example 1. After treatment, the block magnets were free of adherent particles and had a yellowish iridescent phosphate layer.

In this example too, the wet block magnets could be dried absolutely stain-free after cleaning and passivation on the stainless steel grid. Since the material SmCo _{5 is} particularly susceptible to staining, it can not be treated effectively with the conventional cleaning method (ie ultrasonic cleaning in an alkaline cleaning medium or ultrasonic cleaning with pickling). In the conventional method, therefore, a targeted post-treatment (passivation) must be carried out, in which in addition the standing on the workpieces water is blown off, or in which the workpieces are dabbed dry with paper. It is also noticeable that no cobalt goes into solution when cleaning SmCo materials with the aid of the cleaning liquid according to the invention. In contrast, cobalt dissolves in conventional alkaline ultrasonic cleaning and the solution turns red. From the point of view of occupational safety, the new cleaning and passivation solution also offers advantages, since cobalt solutions can trigger allergies in humans when they come into contact with the skin.

Comparison to the prior art

Compared to the conventional cleaning methods, the present invention has significant advantages. The process sequence in the conventional method comprises the sequence of steps: ultrasonic cleaning in aqueous alkaline cleaning media (5 minutes to 10 minutes); Do the washing up; Pickling the magnets (1 minute) to dissolve magnetically adhering abrasive slurry particles; Do the washing up; Passivation of the magnets for the purpose of temporary corrosion protection (10 minutes to 20 minutes); Do the washing up; Dry.

The process according to the present invention, however, comprises the sequence of steps: rinsing of cooling lubricant, cleaning (eg 45 seconds to 90 seconds) including application of a temporary corrosion protection (phosphating) with the aid of a cleaning agent according to the present invention, optionally by means of ultrasound support ; Do the washing up; Dry.

Completely surprising in the discovery of the new cleaning solution was the enormous shortening of the process times compared to the conventional process in the aqueous-alkaline cleaning medium by a factor of 5 to 10. This is due to the fact that the removal of the magnetic dust is the rate-determining step to achieve particle freedom. Abrasive sludge consists of many small individual magnets with a grain size of typically less than 5 microns. Some of these particles are still hard magnetic and adhere relatively strongly magnetically to the surface of the magnet to be cleaned. In order to remove these particles, a high ultrasonic power and a very good rinsing of the parts (ie rapid movement of the magnets in the cleaning bath) is necessary.

In contrast, in the method of the present invention, a very thin non-magnetic phosphate layer rapidly grows on the magnetic particles and on the magnets to be cleaned. The layer thickness of such thin-layer phosphates is in the range of the wavelength of visible light. This betrays the iridescent and in many colors iridescent phosphate coating on the magnet after the process. As a result of the phosphate layer, the distance between the surface of the magnet to be cleaned and the magnetic particles increases with increasing duration of treatment, so that a distance r of the order of magnitude of 0.5 μm to 1 μm rapidly forms. Since the magnetic attraction decreases very sharply with increasing distance r (proportional to r ⁴ ), this causes the tiny particles with grown phosphate layer to not magnetically adhere so much and behave substantially like normal dust particles, so that they are within less Seconds are removable, the cleaning effect can be optionally increased by the application of cleaning liquid with ultrasound.

The invention has been described above by way of example with reference to magnets as workpieces to be processed, cleaned and passivated. In principle, the invention can be used in conjunction with all types of magnets such. As sintered magnets, magnets made of rare earth alloys, magnets with or from ferrous magnetic materials, magnets with or from ferromagnetic magnetic materials, magnets for magnetocalorics, etc. are also used. Suitable magnets may also comprise one or more soft magnetic hard magnetic, antiferromagnetic, diamagnetic, paramagnetic, permanent magnetic or magnetocaloric materials or may be formed from one or more of these materials. Magnetic or magnetizable materials may be mentioned by way of example of iron-based magnet alloys, such as, for example, B. materials that consist of NiFe or CoFe or at least one of these alloys. In principle, materials are suitable irrespective of whether they are crystalline or rapidly solidified. All workpieces made of a magnetizable material can be cleaned in both the non-magnetized and the magnetized state by the method according to the present invention. In addition, non-magnetic or non-magnetizable workpieces can also be treated in the same way with a cleaning fluid and / or a cleaning method according to the present invention, as has been described using the example of magnets.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• DIN 53210 [0031]
• R. Blank and E. Adler: "The Effect of Surface Oxidation on the Demagnetization Curve of Sintered Nd-Fe-B Permanent Magnets", Appendix 3 (9th International Workshop to Rare Earth Magnets and Their Applications, Bad Soden, Germany, Sept. 1987 [0033]

Claims (26)

Cleaning and passivation solution, which has the following constituents: at least one water-soluble salt of phosphoric acid; at least one water-soluble salt of nitric acid; at least one anionic surfactant; and a pH in the range of pH 1.5 to pH 4. A cleaning and passivating solution according to claim 1, wherein the at least one anionic surfactant comprises at least one of the following surfactants: an alkylsulfate; an ethoxylate of aliphatic alcohols; an aliphatic or aromatic sulfonate; a carboxylate of the fatty acids; a secondary alkyl sulfonate. A cleaning and passivating solution according to claim 2, wherein the at least one anionic surfactant comprises at least one of the following surfactants: sodium dodecyl sulfate; nonylphenol ethoxylate; isotridecanol; Dodecylbenzenesulfonate. Cleaning and passivating solution according to any one of the preceding claims, wherein the pH is in the range of pH 1.6 to pH 2.4. Cleaning and passivating solution according to one of the preceding claims, comprising at least one other type of metal cations. The cleaning and passivating solution of claim 5, comprising metal cations of at least one of the following metals: lithium; Sodium; Potassium; rubidium; cesium; francium; Beryllium; Magnesium; calcium; Strontium; Barium; Radium; a transition metal which in the pH range of pH 1.5 to pH 4 forms a water-soluble phosphate salt or a water-soluble salt having one of the following anions: chromate, molybdate, tungstate, chlorate, perchlorate, manganate, vanadate, niobate, tantalate, titanate, sulfate , Borate; carboxylate; Alkyl sulfonate. Cleaning and passivating solution according to one of the preceding claims, comprising at least one further type of anions. A cleaning and passivating solution according to any one of the preceding claims comprising non-nitrate oxidizable anions. A cleaning and passivating solution according to claim 8, wherein the non-nitrate oxidizable anions are of at least one of the following types: chromate; molybdate; Tungstate; chlorate; perchlorate; manganate; vanadate; niobate; tantalate; titanate; Sulfate; borate; carboxylate; alkyl sulfonate; Arylsulfonate. Cleaning and passivating solution according to one of claims 7 to 9, comprising at least one hydrotrope. A cleaning and passivating solution according to any one of the preceding claims comprising at least one of the following hydrotropes: arylsulfonate; cumene; xylene sulfonate; Toluenesulfonate. A cleaning and passivating solution according to any one of the preceding claims comprising phosphate at a concentration in the range of 10 g / l to 300 g / l or in the range of 50 g / l to 200 g / l. A cleaning and passivating solution according to any one of the preceding claims comprising nitrate at a concentration in the range of 10 g / l to 500 g / l or in the range of 50 g / l to 300 g / l. A cleaning and passivating solution according to any one of the preceding claims, wherein the total of anionic surfactants comprises a concentration in the range of 0.1 g / l to 100 g / l or in the range of 5 g / l to 50 g / l. Method for cleaning a workpiece ( 1' ) with the steps: providing a workpiece ( 1' ); Provision of a cleaning and passivation solution ( 6 ) according to one of the preceding claims; complete or partial introduction of the workpiece ( 1' ) into the cleaning solution ( 6 ) for a given period of time; Removing the cleaned workpiece ( 1 ) from the cleaning solution ( 6 ) after expiration of the given period. The method of claim 15, wherein the duration of the predetermined period is at most 90 seconds, or in the period of 45 seconds to 90 seconds. Process according to Claim 15 or 16, in which the temperature of the cleaning and passivation solution ( 6 ) is in the range of 5 ° C to 95 ° C or in the range of 40 ° C to 80 ° C for at least the predetermined time period. Method according to one of Claims 15 to 17, in which an ultrasonic signal is injected into the cleaning and passivating solution during a part of the predetermined time period or during the entire predetermined period of time ( 6 ) is coupled. Method according to one of claims 15 to 18, wherein the workpiece ( 1 ) is rinsed with tap water and / or demineralized water prior to complete or partial incorporation. Method according to one of claims 15 to 19, in which on the surface of the workpiece ( 1 ) a phosphate layer is grown. The method of claim 20, wherein the phosphate layer has a thickness of at least 100 nm. Process according to Claim 20 or 21, in which the phosphate coating covers the entire surface of the workpiece ( 1 ) covered. Method according to one of Claims 15 to 22, in which the workpiece ( 1 ) after removal from the cleaning and passivation solution ( 6 ) with tap water and / or with demineralized water. Method according to one of claims 15 to 23, wherein the workpiece ( 1 ) after removal from the cleaning and passivation solution ( 6 ) is dried. Method according to one of claims 15 to 24, wherein the workpiece ( 1 ) is a magnet composed of one or more of the following materials or comprising one or more of the following materials: a rare earth alloy; at least one soft magnetic material having rare earth contents; at least one ferromagnetic metal; Iron is an iron alloy; a soft magnetic iron alloy; a NiFe alloy; a CoFe alloy; at least one soft magnetic material; an iron-containing soft magnetic material; at least one magnetocaloric material. Method for processing and cleaning a magnet with the following steps: Providing a magnet blank ( 1' ); Producing a workpiece to be cleaned ( 1 by grinding the magnet blank; Cleaning the workpiece ( 1 ) according to a method according to any one of claims 15 to 25.

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