US2188091A - Process for making permanent magnets and products thereof - Google Patents

Description

Jan. 23, 1940. M. BAERMANN, JR 2,188,091.

PROCESS FOR MAKING PERMANENT MAGNETS AND PRODUCTS THEREOF Filed July 8, 1935 Z .1 v 21 y i l i 1 4 :l m m rfir I I I I I l l" I 9 ll 11 K ATTORNEY Patented Jan. 23, 1940 AYES Max Baermann, In, Cologne, Germany Application July 8, 1935, Serial No. 80,329 In Germany July 11, 193% 6 Claims.

This invention relates to a process for making permanent magnets.

Permanent magnets are made of iron alloys with high carbon content and greater or smaller additions of chromium, cobalt, copper and so forth. These alloys are distinguished by high coercivity and remanence, but the high carbon content and the addition of the mentioned metals result in great hardness of these magnetic steels so that working of them, in particular machining, as well as shaping by forging or pressing involves considerable difiiculty and may only be possible in unhardened condition. These dimculties of working and shaping are increased by the circumstance that the steels must be hardened before magnetislng because only by hardening do they acquire the requisite properties for permanent magnets. In this hardened condition, final working which is often necessary because of the distortion and changes of form resulting from the hardening process, can only be effected by grinding. Further, hardening fissures often. occur, which make the magnet unusable.

Much greater difiiculties as regards working are met with owing to their great hardness and crystalline structure, inthe case of nickel-aluminium steel alloys whose coercive force is above 240 gauss (oersted). These magnet steels in. any case can only be cast in bar form, so that for use in apparatus separate soft iron limbs or pole shoes must be attached to the magnets. A further obstacle to the use of these high value magnet steel alloys is that owing to the high percentage of waste necessarily produced in their preparation and working, they are very expensive, especially since the waste cannot be used again and is therefore almost worthless.

The above mentioned disadvantages which arise in the production and working of permanent magnets are avoided by the present new process, because according to this process any desired form of magnet can readily be made independently of the hardnem of the magnetic material used and such substances can also be used with full magnetic efiect which hitherto had to be regarded as waste.

The process consists in reducing a permanent magnetic alloy, such as an alloy of nickel, aluminum and steel having high coercivity and high remanence to powdered condition, followed by mixing the powder with a binding medium such as phenol formaldehyde resin, followed by molding or otherwise forming the mixture of the powder and the binding medium, followed by magnetizing the material.

The use according to the invention of ferromagnetic materlals with a coercive force of more than 240 oersted has been found particularly suitable for this process, and the considerable waste material produced through pipe formation or the like in the making of these alloys leads to the same technical result as the goodmaterial so that the invention provides a use for this waste material.

Any material can be used as the binding me- 10 dium which affords the mixture in cooled or pressed condition a solid and lasting shape and form. In particular among fluid materials, dissolved resin, synthetic resin and pressable artificial substances of all kinds are suitable. 16

In further development of the invention the mixture consisting of ferromagnetic particles of high coercive force and a binding medium is directly cast or pressed into the desired form, so that all supplementary working is avoided. Hold- 20 ing clips, securing eyes, bushes and the like can be incorporated at the same time.

In. many cases it is desirable for protecting the magnetic pressing, for it to be surrounded by a sleeve of resistant non-magnetic material. According to the invention therefore, it is proposed in the making of a pressing which is particularly resistant to mechanical or shock stresses to pro ceed by putting the mixture into a sleeve of non magnetic material of sufiicient strength and so pressing or fusing it therein.

It has further been found that the coercive force of pressed magnets in this manner reaches a still higher value if according to the invention the mixture of ferromagnetic materials and binding medium is subjected to a magnetic field during the actual making or pressing operation. The explanation of this fact is that exactly the high value ferromagnetic alloys of more than 240 oersted particularly suitable for the 40 process, consist of crystallites which are anisotropic, that is their permeability is different in different axial directions of the crystallite. The same applies to the other magnetic properties.

The preliminary magnetisation proposed according to the invention of the mixture of metal grains and binding medium while still in a condition in which the grains are free to move therefore to some extent effects a pre-orientation of the crystallites in an advantageous axial direction for the subsequent location of the poles.

In further development of the invention the procedure in making the pressed permanent magnet is such that the mixture of ferromagnetic material of high coercive force and binding 5 medium is first preliminarily pressed while under the action of a strong magnetic field, then the magnetic briquette is obtained finish pressed under high pressure and advantageously simultaneous heating, and thereupon final magnetisation effected maintaining the same field direction as in the preliminary magnetisation. In the preliminary operation in which the mixture is included in a closed magnetic circuit, the pressure is made so high that the metal grains and the binding medium adhere firmly together and in particular the former cannot change their magnetically advantageous positions taken up under the influence of the magnetic field. These positions of the metal grains remain unchanged in the finish pressing, which on account of the high pressure is effected in an apparatus (mould) of steel.

A similar procedure is adopted according to the invention if neither synthetic resin nor easily mouldable plastic nor pulverulent artificial materials are used as the binding medium, but a metal with a lower melting point than the magnetic alloy is used, the preliminary magnetisation being effected before the solidification of the fluid binding medium. The melting of the mixture, which advantageously takes place under pressure so that excess metal is pressed out, can take place in the same apparatus as is employed for the preliminary pressing with the use of synthetic resins and artificial materials.

In order to collect the magnetic fiux effectively at the poles of these synthetic magnets and to produce a satisfactory passage thereof, the magnet bodies are provided, according to the invention, with a material of high permeability at the poles. In particular, an iron alloy of high permeability is proposed for this purpose.

The adhesion of these pole plates at the poles -is advantageously increased by providing these plates with extensions or projections of preferably non-magnetic material, which project into the pressed magnet body. The projections are made of non-magnetic material in order not to short circuit the crystals in the interior of the magnet body with which they come into contact, as the magnetic eiTect would thereby be considerably weakened.

According to the invention the whole process of production can be further simplified by the forming of the mixture by pressing or casting with heating of the mould as well as the insertion of the pole plates in the magnet body being effected in a single operation.

With extremely fine subdivision of the magnetic material and using very high pressure a coherent pressing can be made without the addition of a separate binding medium.

To carry out the process according to the invention an apparatus is proposed in which the mixture is introduced into a hollow body of nonmagnetic material bounded by two steel plungers, a magnetic fiux being caused to fiow in a magnetic circuit closed by the ferromagnetic mix ture to be pressed, either by supplying a magnetic fiux from outside through the steel plungers or by means of a winding in the hollow body, traversed by a direct current, an external magnetic bridge being applied across the steel plungers. Of the two plungers advantageously one is stationary and the other movable. The two plungers are externally connected magnetically by a short circuiting bow of soft iron. The production of the magnetic flux by means of a magnetising coil can also be effected by mounting the coil on the short circuiting bow.

For the production of the pressed magnet a mixture of ferromagnetic material has been found particularly suitable which is characterised by the grain mixture obtained by reducing larger magnetic pieces consisting of grains of very varying sizes, so that grains of all sizes from say 0.01 mm. to for example 1 mm. are present in the mixture. A grain mixture between the limits of 0.5 to 1 mm. has been found particularly effective. This choice of grains of various sizes results in better filling of the space occupied and close contact of the grains one with another, so that within the permanent magnet pressed from these grains, there is a far reaching magnetically con ductive connection among the individual ferromagnetic particles. The result of this measure shows itself particularly in a further increase in coercive force. The said advantages are still more apparent if according to the invention before sorting of the grains the non-magnetic particles are removed by treating by the methods known in connection with ores and coal.

The new pressed magnet, which with the use of a suitable binding medium has considerable strength, can easily be shaped and is relatively cheap to produce. Having regard to its high coercive force, which equals that of the basic material used, it is able to replace other high value iron alloys, such as carbon, chromium or cobalt steels, as well as nickel-aluminium steels in all places and all apparatus in which the latter alloys have hitherto been exclusively used. As against these high value magnetic alloys, the new pressed magnet in addition has the very important advantages that it is insensitive to vibration and does not rust.

Example gms. of finely powdered ferromagnetic material are mixed with about 10 gms. of powdered artificial material, put into a mould and preliminarily pressed, advantageously under heat and under the action of a magnetic field. Thereupon the pressing with its oriented magnet crystals is finished pressed in the same or another mould under such high pressure that the excess artificial material not necessary for binding is squeezed out. After cooling of the pressing it is removed from the mould and magnetised in the usual way in a strong magnetic field.

The percentage of necessary binding medium is the less the finer the alloy material is reduced and the higher the available pressure.

Examples of apparatus for carrying out the process of the invention and products made according to the invention are illustrated by way of example in the accompanying drawing.

Figure 1 is an elevation partly in section of a pressing and magnetising apparatus having a winding around the magnet being pressed.

Figure 2 is an elevation partly in section of a pressing and magnetising apparatus in which the magnet being pressed is magnetised by means of a magnet yoke.

Figure 3 is a side view of Figure 2.

Figure 4 is a plan of a ring shaped pressed magnet.

Figure 5 is a longitudinal section of Figure 4.

Figure 6 is a longitudinal section of a bar form pressed magnet with lateral recesses for securing screws.

Figure '7 is a plan view of the magnet of Figure 6.

plungers.

Figure 8 is a longitudinal section of a disc form pressed magnet with pressed on pole plates.

Figure 9 is a plan of the magnet of Figure 8.

The pressing apparatus shown in Figure 1 comprises a hydraulic press i with two plungers 2 and 3 which enter a non-magnetic sleeve 6. The permanently magnetisable material mixed with a binder is put into the sleeve and compressed by means of the plungers. The sleeve 4 is surrounded by a magnetising winding 5 which is connected to a source of direct current through a rheostat 6 and an ammeter i. When a direct current flows through the winding a strong magnetic flux is produced in the magnetic circuit which is closed through the bolts 9, the crossmembers 50, ii and the plungers 2, 3, by which the pressing is magnetised in'the direction of the axis of the sleeve, in such a way that poles are produced at the surfaces in contact with the In the construction shown in Figures 2 and 3, the winding i3 is upon a yoke it of soft iron which is in magnetic connection with the fixed plunger i5 supported in the cross member it and the moving plunger i7! guided in the cross member it. The magnetic circuit is in this case completed through the pressing 99, the plungers i5, i'i and the yoke it so that the flux induced by a direct current flowing in the winding, flows through the pressing and magnetises it.

The ring form pressed magnet shown in Figures e and 5 has a bore 2i moulded in the body.

The bar magnet 2 of Figures 6 and '7 has lateralrecesses 23 for receiving screws, which recesses are moulded in the pressing operation.

In the disc shaped magnet 25 shown in. Figures 8 and 9, the pole plates 25 of soft iron, are intimately connected with the pressed body by proiections 2% of non-magnetic material, whereby firm attachment of the plates to the body is ensured.

I claim:

1. In aprocess for making permanent magnets, the steps which consist in preparing a mixture of a binding medium and finely divided magnetic material having high coercive force and remanence, preliminarily agglutinating said mixture by pressure while under the influence of a direct magnetic field and at a temperature at which the material retains its magnetic qualities, finish pressing said agglutinated mixture to final form under very high pressure and magnetising the body thus formed in the same direction as that efiected by said magnenc field.

2. In a process for making a permanent magnet the steps which consist in assembling a finely divided magnetic material having high coercive force and remanence, and pole pieces of magnetic material having high permeability said pole pieces having non-magnetic inserts, and agglutinating the whole into a coherent solid body with said inserts extending into the body of finely divided magnetic material.

3. In a process for making a permanent magnet, the steps which consist in making a mixture of a binding medium and a finely divided magnetic material having highcoercive force and remanence, charging said mixture into a mould bounded by a pair of steel plungers, and simultaneously applying pressure and a direct magnetic field through said plungers at a temperature at which the material retains its magnetic qualities.

4. A body for a permanent magnet consisting of a binding medium, grains of magnetic material of high coercive force and remanence agglutinated in said medium, pole pieces of magnetic material of high permeability in close contact with the agglutinated mass, and non-magnetic securing means projecting into said mass and engaging said pole pieces.

5. In a process for making permanent magnets, the steps which consist irr reducing a permanent magnetic nickel-aluminium steel alloy of high coercive force and remanence to powder, mixing the powder consisting principally of grains sized within the range from about 0.01 mm. to 1 mm. in average external diameter and having a high coercive force of at least 240 oersted with a binder and agglutinating the mixture under pressure to the desired form at a temperature below 400 C. 6. In a process for maldng permanent magnets, the steps which consist in reducing nickelaluminium steel alloyof high coercive force and remanence to powder, mixing the powder consisting principally ofgrains sized within the range from about 0.01 mm. to 1 mm. in average external diameter and having a high coercive force of at least 240 oersted with a binder and agglutinating the mixture to the desired form at a temperature below 400 C under pressure high enough to bring the particles into close contact and squeeze out all excess binder.

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