WO2011025402A2

WO2011025402A2 - Magnetizer/demagnetizer with a chopped magnetic field

Info

Publication number: WO2011025402A2
Application number: PCT/RS2009/000025
Authority: WO
Inventors: Obrad Aleksic; Milomir Djukic; Branislav Zlatkov; Lazar Lukic
Original assignee: IRITEL AD
Current assignee: IRITEL AD
Priority date: 2009-08-26
Filing date: 2009-11-09
Publication date: 2011-03-03
Anticipated expiration: 2012-02-26
Also published as: RS20090381A

Abstract

A magnetizer/demagnetizer with a chopped magnetic field is based on a continual stream of magnetic impulses and minor magnetic loops SM and SD used for sequential progressive hysteresis-less magnetization and demagnetization of magnetically hard materials (sintered cores). Moreover it is used for magnetic alignment of powder particles during powder molding injection and orientation of groups of grains of polycrystalline magnetically hard materials during annealing. Magnetizing and demagnetizing is performed using current impulses in a solenoid SL embedded in the injection tool or magnetic circuit MC. Moreover, the value of the chopped magnetic field is adjusted to be as high as the coercive force EU of the magnetically hard material, or higher. The magnetizer /demagnetizer with a chopped magnetic field includes a generator of square impulses CC adjustable for the number of impulses per second, impulse height and width, IGBT module (group of power transistors), active cooler C and snubber circuit SS for protection of self inductance impulses, a magnetic circuit made of dynamo sheets MC with a large air gap, equipped by an axial A, radial R, diametrical B and multi polar M adapters. The magnetizer/demagnetizer is power supplied by a group of batteries in serial / parallel connection; it is mobile, safe for work, saves a lot of energy and has low dissipation.

Description

MAGNETIZER/DEMAGNETIZER WITH A CHOPPED MAGNETIC FIELD Technical Field

The invention belongs to the field of electromagnetism: magnetic circuits for magnetization and demagnetization of magnetically hard materials. The unit is also used for magnetic alignment of particles of hard magnetic materials in molds for powder injection molding with melted feedstock (PIM technology), then for annealing of polycrystalline magnets in a magnetic field and final magnetization of sintered (finished) cores for permanent magnets. The type of magnetization is hysteresis-less, asymmetrical, impulse, progressive and sequential, e.g. it applies the inner -minor loops of magnetization and demagnetization generated by a dense continual stream of quadratic magnetic impulses. Magnetization /demagnetization with a chopped magnetic field has the same summary effect as DC magnetization, but the energy consumption is many times smaller, dissipation is smaller and as a consequence it requires much shorter cooling, a smaller cross section of copper conductors (windings) and smaller solenoid dimensions.

This chopper power magnetizer is powered by kA currents from a block of parallel/serially connected batteries controlled by an IGBT switch (group of transistors). The currents flow in a dense continual stream of quadratic impulses: their width, height, spacing and number per second are adjustable. Magnetization is quite safe for workers and it lasts during feedstock injection, as programmed. The achieved impulse magnetic fields in it are in the range from 400 to 1000 kA/m and higher, depending on the air gap of the magnetic circuit, number of windings in the solenoid, chosen gate current of the IGBT, voltage selection in the block of batteries (parallel/serial connection of batteries). Battery charging is performed in a serial connection with the mains 220 Vac when the magnetizer is switched off. The magnetizer is mobile and can safely and autonomously work for many hours.

According to the international classification of patents it can be classified in groups:

and

Background Art

A magnetizer is a unit designed for magnetization/demagnetization of magnetically hard materials and it generally consists of a power current source, and magnetic circuit with air gap and adapters (pole legs) for focusing the magnetic flux.

Today magnetizers for magnetizing cores for permanent magnets are produced in many variants depending on the type of magnetization (axial, radial, diametrical, multipole) and core shape (adapter with pole legs). Generally they can be classified in two groups: DC current magnetizers and capacitive discharge (impulse) magnetizers. DC magnetizers use high intensity currents and a certain number of windings in solenoids to produce the magnetic field. The windings are cooled by air, oil or water. The magnetic fields produced by DC currents are used for the alignment of particles of magnetically hard materials during powder pressing e.g. compact formation. DC magnetic fields of increasing/decreasing intensities are used in hysteresis graphs for magnetic measurements.

Impulse magnetizers usually contain large electrolytic capacitors for high voltages (2kV-3kV/5-50 mF, paper in oil). They are charged several seconds from the mains 220Vac and discharged by thyristors to form a triangular impulse of high intensity such as 10-100 kA with for example a duration of 20 ms. A half sine wave can also be used as an impulse source directly from the mains 220 Vac through the thyristor. The currents generated by a half sine wave directly from the mains 220 Vac are usually limited to IkA. Moreover it is a source of high conductive noise. It is used for final magnetization of magnetic cores for permanent magnets.

DC demagnetization is performed by unidirectional currents, but in the opposite direction to magnetization currents. The opposite current intensity must be close to a third of the magnetization current to achieve a reverse coercive force that decreases residual induction of the permanent magnet to zero. In practice a slightly higher reverse magnetic field is needed than the coercive force H_Cb- The coercive force H_cb is defined on the demagnetization curve in quadrant II of the B-H diagram.

The second method is demagnetization by a capacitor discharge impulse magnetizer but not through the thyristor but through the solenoid (RLC -circuit). In this free discharge of the loaded capacitor transient periodical oscillations occur and perform demagnetization (known as AC demagnetization).

Besides the described methods of magnetization a hysteresis-less magnetization - or asymmetric AC magnetization is sometimes in use. It is a combination of a unidirectional magnetic field and an alternating magnetic field (sine wave) caused by AC current. The result of the superposition of two fields is an asymmetrical field that changes from zero to a certain positive value of the magnetic field. This causes magnetization by minor loops up to remanent induction B_r without passing the full magnetization curve up to the saturation induction in the first quadrant on the B-H diagram.

There are many producers of DC and impulse magnetizers, for example:

1. MAGNET-PHYSIK.De, Dr Steingroever, GmbH, www.magnet-phyzsik.de

K,U,X- series magnetizers, demagnetizers.

2. ASC SCIENTIFIC, Impulse magnetizer, model EVI-IO, www.ascscientific.com

3. MAGNETIC INSTRUMENTS, Magnet charger model 942A, www.maginst.com

4. ELECTROSINESYSTEMS, Magnetizers for magnetizing multipolar magnet based magnets required in automobiles, www.electiOsine.com 5. METIS INSTRUMENTS & EQUIPMENT, Magnetizers, modular energy sources for magnetizing systems, www.metis.be

90

6. M-PULSE, Magnetizers, magnetisiergerate von pulse - energie fur magnete, www.m-pulse.biz

The disadvantage of DC magnetizers/demagnetizers is larger currents, larger 95 cross section of windings, cooling of windings by oil or water.

^"The disadvantage of capacitive discharge impulse magnetizers is large pauses between the impulses (several seconds) used for charging the capacitor, so they can't be used for alignment of a magnetic powder during pressing, injection molding of green cores or extruding plastomagnets.

100 In the patent literature magnetizers/demagnetizers depend on the permanent magnet core geometry and type of magnetization, as mentioned above. Generally, they apply unidirectional DC currents or impulses including half-sine wave impulses, for example:

105 1. US Patent 3,969,657 (13.07.1976), Oettinghaus; Dieter (Hohenlimburg, DT), Magnetizing and demagnetizing electrical circuit

2. US Patent 4,381,492 (26.04.1983), Steingroever; Erich (53 Bonn, DE),

Steingroever; Dietrich (Bergisch-Gladbach), Apparatus for magnetizing

^{1 10} multipolar permanent magnets

3. US Patent 4,920,326 (24.04.1990), Agarwala; Ashok K. (Penfield, NY), Method of magnetizing high energy rare earth alloy magnets

^{1 15} 4. US Patent 5,055,813 (08.10.1991), Johnson; Terry R. (Newport News, VA)

Magnetization/demagnetization device

5. US Patent 5,469,321 (21.11.1995), Stupak, Jr.; Joseph J. (Portland, OR), Magnetizing device having variable charge storage network and voltage control

6.US Patent 5,852,393 (22.12.1998), Reznik; Svetlana (Rochester, NY), Furlani; Edward P. (Lancaster, NY), Schmidtmann; William E. (Naples, NY), Apparatus 125 for polarizing rare-earth permanent magnets

7.US Patent 6,026,718 (22.02.2000), Anderson; Wayne (Northport, NY), High energy magnetizer and selective demagnetizer integral with driver tool .

8. US Patent 6,310,532 (30.10.2001), Santa Cruz; Cathy D. (Reno, NV), Henry; Gregory L. (Sparks, NV)...et alt., Multipurpose magnetizer/demagnetizer 9. US Patent 6,621,396 (16.09.2003), Leupold; Herbert A. (Eatontown, NJ),

Permanent magnet radial magnetizer

130

In US patents and EU patents many magnetizers/demagnetizers described are based on DC currents and impulse currents (triangular and half-sine impulses). As far as we know there are no chopper power magnetizers with a dense continual stream of quadratic current impulses from batteries to generate the same shape chopped 135 magnetic field in the solenoid and magnetic circuit made of dynamo sheets. The chopped magnetic field in magnetizing sample generates small or minor magnetic loops sequentially and performs progressive magnetization /demagnetization e.g., hysteresis-less magnetization based on a chopped magnetic field.

140 Disclosure of the invention

A magnetizer/demagnetizer based on a chopped magnetic field is a new unit designed for hysteresis-less, sequential, progressive magnetization and demagnetization of hard magnetic materials (finished, sintered cores), for magnetic alignment of magnetic

145 particles in high intensity magnetic fields during magnetic powder pressing and powder injection molding with a melted organic binder (PIM technology), and finally for alignment of polycrystalline grains of magnetic materials during annealing at high temperatures.

The magnetization is based on a chopped magnetic field in a solenoid (SL) or in a

150 magnetic circuit (MC) with an intensity equal or slightly higher than the coercive force H_cb of the hard magnetic material injected by PIM technology or magnetized as a sintered core e.g. the new magnetizer applies inner small or minor loops of magnetization (SM) or demagnetization (SD). The chopped current in the magnetic circuit with air gap generates progressive magnetization by minor loops in the

155 magnetically hard material. In the magnetizer with chopped current e.g. in the continual stream of dense narrow quadratic impulses the height, width, spacing or number of impulses per second are adjustable. The unit consists of an adjustable impulse generator-control circuit (CC), group of parallel/serially connected batteries (BG), battery charger (BC), chopper transistor module (IGBT) with self control logic

1^0 (CL) for driving power transistors and a power transistor output module (TR), a module for active cooling (C) and a snubber circuit (SS) for suppressing induced impulses during switching off magnetizing impulses. The unit consists of an adjustable impulse generator-control circuit (CC), group of parallel/serially connected batteries (BG), battery charger (BC), chopper transistor module (IGBT) with self

1^5 control logic (CL) for driving power transistors and a power transistor output module (TR), a module for active cooling (C) and a snubber circuit (SS) for suppressing induced impulses during switching off magnetizing impulses.

The peripherals of the chopper power magnetizer are: solenoid embedded in the injection mold (SL) and magnetic circuit made of dynamo sheets (MC) with air gap in

170 the middle and adapters for final magnetization of sintered cores - axial (A), 175 radial (R), diametrical (D), multipole (M). The procedure of magnetization and demagnetization by a dense continual stream of quadratic current impulses e.g., the same shape of magnetic field (for example 10 impulses per second and impulse/pause = 1/10) belongs to the asymmetrical, hysteresis-less magnetization. Opposite of DC magnetizers and impulse capacitive discharge magnetizers that depend full operating

180 time on mains 220 Vac, a chopper power magnetizer discharges the battery group by IGBT power through a magnetic circuit to generate minor magnetic loops and progressive magnetization. The chopper power magnetizer saves a lot of power, has a lower dissipation in the same proportion, is a mobile unit, autonomous and safe for work (operating).

185

Brief description of drawings

- Figure 1 represents a block scheme of a magnetizer/demagnetizer with a chopped magnetic field.

- Figure 2 represents a solenoid SL to be embedded in the injection mold - 190 serves for magnetic alignment of particles during injection of melted feedstock.

Figure 3 represents a magnetic circuit MC with an air gap - serves for magnetization by a chopper magnetizer; MC is made of dynamo sheets.

Figure 4 represents an axial adapter A designed to be inserted in MC

195 - Figure 5 represents a diametrical adapter D designed to be inserted in MC

Figure 6 represents a radial adapter R designed to be inserted in MC

- Figure 7 represents a multipolar adapter M designed to be inserted in MC

- Figure 8 represents minor magnetization loops (SM) caused by chopped power magnetic field- hysteresis -less magnetization.

200 - Figure 9 represents minor demagnetization loops (SD) caused by reverse chopped power magnetic field- hysteresis-less demagnetization.

Best mode for carrying out of the invention

205 The magnetizer/demagnetizer with chopped magnetic field (fig.l) performs magnetic alignment of powder of magnetically hard materials during injection of green cores by melted feedstock- PIM technology, then during annealing in the magnetic field and finally performs magnetization and demagnetization of green and sintered cores. The chopper power magnetizer uses a continual and dense stream of narrow quadratic

210 current impulses and minor magnetic loops for progressive magnetization (SM) or demagnetization (SD) (figures 8 and 9). The intensity of the chopped magnetic field achieved by the continual and dense stream of quadratic current impulses has to be equal or higher than the coercive force H_Cb of the hard magnetic material being magnetized. Alignment of magnetic particles is performed in the mold by a solenoid

215 embedded in it. Magnetization of sintered cores is performed in the magnetic circuit with an air gap (MC) made of dynamo sheets using adapters e.g. pole legs for different cores and types of magnetization. Magnetization of magnetic cores made of 220 magnetically hard materials is performed by sequential progressive loops of magnetization SM (the first quadrant in the B-H diagram) generated by a chopped power magnetic field which is similar in intensity to the coercive force H_ct,.

Magnetization by a chopper magnetizer lasts as along as needed to achieve the remanent induction B_r in the magnetic circuit (MC) using for example 10 impulses

225 per second and an impulse width/pause = 1/10. Demagnetization is performed in the same magnetic circuit using demagnetization loops (second quadrant in the B-H diagram), e.g. the direction of the chopped current is reversed using a certain switch or mutually changing the output solenoid termination wires. The demagnetization duration time is limited to the number of impulses needed to demagnetize a sample

230 e.g. to lower the residual magnetization B_r* to a value as close to zero as possible. In contrary a higher number of impulses than needed can pre - magnetize a sample in the reverse direction. For adjusting the intensity of the magnetizing field the IGBT gate current is changed by a potentiometer and the IGBT input voltage is changed in steps of 12V by a serial connection of batteries (for example 12, 24, 36, 48..Vdc).

235 The magnetizer/demagnetizer with a chopped magnetic field (block scheme given in figure 1) consists of two units: impulse power current source and magnetic circuit. The impulse current source consists of a control circuit (CC), group of serially/parallel connected batteries (BG), battery charger (BC), power transistor switching module (IGBT), and with adapter -control logic (CL), an output module

240 e.g. group of power transistors (TR) (MOSFETs in parallel), electronic regulated cooler (C) and snubber circuit (SS) as a suppressor of self-induced impulses during switching.

The magnetizing part of the magnetizer/demagnetizer consists of a solenoid (SL) embedded in the injection mold (figure 2), which serves for alignment of

245 magnetic particles during powder injection molding and a magnetic circuit with an air gap (MC), made of dynamo sheets and copper windings. The magnetic circuit (MC) together with axial (A), radial (R), diametrical (D) and multipole (M) adapters (figures 4-7) serves for magnetization /demagnetization of finished cores (sintered samples).

250 The control circuit (CC) is an impulse signal generator with potentiometers for adjusting the number of impulses per second, their intensity, width and the impulse width/pause ratio. The circuit generates a continual dense stream of quadratic impulses of small intensity sufficient to open or close the IGBT (group of power output transistors). For example the width/pause ratio of impulses from the control

255 circuit (CC) can be 1/10, the gate impulse intensity on the IGBT gate of +12 Vdc for open state for passing IkA and -3 Vdc for closing the current to zero value in the pauses. Using gate impulse intensity in the range of 9-15 Vdc, for example, the control circuit regulates the output IGBT current from 0.1 to 1.5 kA.

The battery group (BG) is formed by a serial/parallel connection of lead.

260 batteries 12V/ 180 Ah/ 1200 A (DC). It serves as an ideal voltage source with gradually adjustable voltage such as 12, 24, 36, 48...Vdc with a very low self resistance, suitable for powering the IGBT module in kA. A couple of batteries with a lower capacity are connected in parallel to enlarge capacity and allow higher currents than IkA as the first step, and then couple by couple are connected in series to form a

265 gradually adjustable voltage source, as a second step.

The battery charger (BC) charges batteries connected in series with 10 % of the battery full capacity, for example, batteries of 12 V/180Ah are charged by 20Adc. The battery charger charges batteries when the chopper magnetizer/demagnetizer unit is in the off state. The fully charged batteries in the regime of 10 impulses per second

270 and ra£io impulse /pause = 1/10 can operate continually for 2 hours. In the powder alignment process during injection molding the chopper magnetizer operates sequentially: 10 seconds of magnetizing and after that a pause of few minutes to the next injection, so in this regime the full battery capacity lasts around 60 hours to the next charging.

275 The switching module of power transistors (IGBT) contains several blocks of parallel connected power transistors in a sealed housing. They are powered and controlled by control logic (CL), a small PCB card with electronics mounted onto the housing of the power transistor group (TR) or near it, depending on the producers.

The housing has a metal substrate used as a heat sink to cool transistor

280 groups, and heat is conducted to a larger cooler (C) made of aluminum, with a thermometer and a fan that revolves faster as the housing gets warmer.

The snubber circuit (SS) is a block for protecting the IGBT from self- induction e.g. induced impulses during switching off high currents. It is connected between the IGBT collector and the ground. In the normal operating mode current

285 power impulses pass the snubber protection and go through the solenoid to magnetize the magnetic circuit. The snubber circuit is a HF (EMI) filter made of a group of high voltage polyester capacitors, for example 10 x 10 uF/600V connected in parallel to the output copper ribbons or bars of the IGBT module to conduct the DC power current and to absorb self-induced impulses back from the solenoid to the IGBT when

290 the power current is switched off.

The solenoid that should be embedded into the injection mold (SL) (figure 2) is connected practically in parallel with the filter (SS) as a return-impulse protected output of the IGBT module. The solenoid has several dozen windings (22) made of a copper ribbon of a rectangular profile or copper tubes, which surround the iron part of

295 the injection mold where a high intensity magnetic field is needed for powder magnetic alignment.

The injection orifice (In) in the mold (24) serves for injection of melted feedstock made of magnetic powder and organic binder: the front steel plate (25) moves forward (mold opening), and the hardened injected sample is ejected from the

300 nonmagnetic cylinder (23) axially by the ejector (28). The mold parts marked as (25), (26), (27) are made of a magnetically soft material to enable flow of magnetic flux of the magnetic field generated by the solenoid (22). The direction of the magnetic field through the magnetic circuit is marked with arrows in figure 2. 305 The magnetic circuit with an air gap (MC) (figure 3) is made of dynamo sheets (32) and a solenoid with windings of copper tubes (31) or copper ribbon with a rectangular profile. Solenoid cooling is performed by water or oil circulation through the copper tubes (windings). Magnetizing adapters (33) (pole legs in MC) are made of dynamo sheets or of annealed soft iron.

310 The axial adapter (A) (figure 4) consists of two pole legs made of dynamo sheets (41) and two side holders of aluminum plates (42). The adapter is designed to be inserted in the large air gap in the middle of the magnetic circuit (MC). It is used for magnetizing sintered samples made of a magnetically hard material as flat (plate) cores and small height cylinders (flat pills).

315 The diametrical adapter (D) (figure 5) consists of two pole legs made of dynamo sheets (51) and two side holders made of aluminum plate (52). The adapter is inserted in the large air gap (MC) to magnetize diametrically cylindrical magnetic cores made of magnetically hard materials.

The radial adapter (R) (figure 6) consists of two pole legs made of

320 magnetically soft iron (61) and two side holders made of aluminum plate (62). The adapter is inserted into the large air gap of the magnetic circuit (MC) to magnetize radially cores made of magnetically hard materials such as torroids and cylinders with axial holes (63).

The multipole adapter (M) (figure 7) is designed for magnetizing a couple of

325 poles (N, S) on the cylindrical core (73) in the first step. It consists of two wedge pole legs made of dynamo sheets (71) and two side holders made of aluminum plate (72). The adapter is inserted into the large air gap of the magnetic circuit (MC) for lateral multipolar magnetization of cylinders made of magnetically hard materials. After rotation of the cylinder for 90° round the main axis another couple of poles (N, S) is

330 magnetized, until magnetization of four couples of poles is achieved.

Minor loops of sequential magnetization (SM) (figure 8) partially follow the magnetization curve caused by increasing the unidirectional magnetic field (DCM) in the first quadrant of the B-H diagram up to the coercive force value H_cb, as the

335 intensity of the chopped magnetic field caused by current impulses (IGBT) is adjusted near to that value. The stream of impulses is adjustable by intensity (impulse height), number of impulses per second and impulse width. In figure 8 left of the area limited by the dashed line +H_Cb, asymmetrical small or minor loops of hysteresis-less magnetization occur. They are caused by a continual dense stream of quadratic

340 impulses generated by the chopped current source and they cause progressive magnetization up to remanence B_r using 10 impulses (1 second) for example.

The powder particles are magnetically aligned during injection by 50 impulses (5 seconds), for example, using H_cb of the sintered material as the maximum excitation, which is a value twice or more higher than the powder saturation magnetic

345 field H_ps. Minor demagnetization loops (SD) (figure 9) caused by the reverse unidirectional chopped magnetic field (DCM) partially follow the demagnetization curve in the second quadrant of the B-H diagram up to the coercive force value -H_Cb, as the intensity of the chopped magnetic field caused by current impulses (IGBT) is adjusted close to that value. In figure 9 right of the area limited by the dashed line

8 350 -H_Cb, asymmetrical small or minor loops of hysteresis-less demagnetization occur. They are caused by the continual dense stream of quadratic impulses generated by the chopped current source and they perform progressive demagnetization up to zero residual remanence. After ten or less impulses (the number of impulses can be programmed in advance) demagnetization is close zero as always a little remanent

355 magnetization remains as the soft iron or dynamo sheets have their self residual magnetization (remanence).

Industrial applicability

360 The chopper magnetizer/demagnetizer is designed to perform magnetic alignment of the powder of magnetically hard materials during powder injection molding (PIM technology) for materials that have magneto crystalline anisotropy. It can be also used for annealing materials in a magnetic field that have shape anisotropy and finally it can be used for magnetization (SM) of sintered cores of

365 magnetic materials during manufacturing of permanent magnets (the first quadrant of the B-H diagram). In the demagnetization operating mode (reverse current) it can demagnetize green samples injected by powder injection molding (PIM technology) before ejecting from the mold and it can also demagnetize sintered magnetized samples using demagnetizing loops (SD) in the second quadrant of the B-H diagram.

370 The chopped power magnetizer is suitable for work in laboratories as it uses DC current from large capacity batteries; it is safe for operating as the input voltage is low and the operator can touch it by hand anywhere during switching. It saves a lot of power as it operates in impulse/pause regime of 1/10. The nominal impulse currents are several times smaller than the currents in the capacitive discharge magnetizers and

375 the magnetic field used (H_cb) is several times smaller than the saturation magnetic field H_s. In that way the chopper magnetizer achieves remanence B_r but it doesn't achieves saturation B_s. The impulse current intensity, number of impulses per second and impulse /pause ratio are adjustable: therefore the chopped current can be adjusted to generate the magnetic field H in the solenoid (SL) and magnetic circuit with an air

380 gap (MC) to be equal or higher than the coercive force of the magnetic material H_Cb-

A prototype of the chopper power magnetizer was realized in IRITEL AD, Belgrade in June 2008 and applied for magnetization of sintered samples and powder alignment during powder injection molding of magnetically hard materials. During the first year of exploitation all the properties and advantages described above in the

385 patent were proved.

Claims

1. The magnetizer/demagnetizer with a chopped magnetic field is a new unit which uses a continual dense stream of narrow quadratic impulses and minor magnetization SM and demagnetization SD loops for sequential progressive - hysteresis-less magnetization and demagnetization of magnetically hard materials, magnetic alignment of powder particles during powder injection

^molding and grain orientation during annealing of sintered samples of magnetic materials in furnaces, is characterized by the construction (figure 1) consisting of an input control circuit (CC), group of serially/parallel connected batteries (BG), battery charger (BC), switching transistor module (IGBT), with control logic (CL), group of power switching transistors (TR), cooling block (C), snubber circuit (SS), solenoid embedded in the injection mold (SL), magnetic circuit with a large air gap (MC) and different magnetizing adapters : axial (A), radial (R), diametrical (D) and multipole (M).

2. The magnetization and demagnetization procedure by a stream of current impulses from the chopper magnetizer using the magnetic circuit and adapters, as claimed in 1 , is characterized by using a chopped magnetic field and asymmetrical hysteresis-less magnetization in a solenoid (SL) or in a magnetic circuit (MC) with equal or higher intensity than the coercive force H_cb of the magnetically hard material and progressive minor magnetization (SM) and demagnetization (SD) loops generated by the continual dense stream of narrow quadratic magnetic impulses (figures 8 and 9).

10