EP0034552A1 - Method and device for multipole magnetization of a sheet material - Google Patents

Abstract

The invention relates to a device for magnetizing materials in the form of sheets or strips such as magnetic rubber. This device consists of one (or two) stack (s) formed of flat main magnets (1) adjacent to ferromagnetic pole pieces (2) in the vicinity of which (or between which) the strip to be magnetized ( 3). The main magnets adjacent to the same pole piece have opposite magnetizations as well as the magnets located face to face in each of the stacks. The device can be supplemented by field magnets (8) and intermediate magnets (9).

Description

The present invention relates to a device for carrying out the multipolar magnetization of a magnetizable material in the form of sheets or strips, more particularly flexible strips of relatively small thickness of the magnetic rubber type.

It is known to print alternating polarity magnetic poles on the surface of a magnet strip by passing the strip of material to be magnetized in the immediate vicinity of the active part of a magnetizing device, or in the air gap of such an apparatus producing a sufficient magnetic field. The multipolar magnetization obtained can be through; which means that the two faces of the strip or of the sheet exert a magnetic attraction of substantially the same value. On the contrary, it can be non-traversing, and, in this case, only one of the faces of the sheet or of the strip mainly exerts magnetic attraction, the other face being reserved for other uses and able to receive for example a decoration, a paint or an adhesive, or a sheet of soft magnetic material.

To magnetize a material, you must apply an adequate magnetic field to it: the intensity of which depends on the intrinsic coercive field of the material and the direction of which depends on the field lines that you want to print in this material.

In known magnetization processes (see for example "Permanent Magnets and Magnetism" edited by D. HADFIELD, Iliffe Books 1962, London, chapter 9) this magnetic field can be generated in two ways:

1 °) or the field is produced by direct electric currents, possibly impulsive, using for example electromagnets, coils (solenoids), or the discharge of capacitors. Such specific devices for magnetizing sheets or strips are described in French patents 1,471,725, 2,106,213 or 2,211,731 or US 3,127,544.

However, these systems are essentially intended for one-side magnetization (except US 3,127,544). But they are expensive because they are complex, often fragile, subject to overheating and large consumers of energy. and possibly dangerous.

They are also limited in number of poles and possible active surfaces due to the problems of insulation of the conductors and the electromagnetic forces which are applied to them.

In addition, production rates are often limited to a strip speed of less than 1 m / min, and even much less in the case of double-sided multipolar magnetization.

• - d'une très faible consommation énergétique limitée à l'énergie mécanique nécessaire à l'extraction de là bande de l'appareil,
• - d'une grande fiabilité de fonctionnement,
• - d'une grande sécurité d'emploi (absence de haute tension),
• - de la suppression des efforts internes à l'appareillage.

2 °) Or the magnetic field is produced by permanent magnets; in this case, we benefit:

• - very low energy consumption limited to the mechanical energy required to extract the strip from the device,
• - high operating reliability,
• - great job security (absence of high voltage),
• - the elimination of internal forces in the apparatus.

• - la production d'un champ magnétique relativement faible, donc la difficulté d'obtenir une aimantation des matériaux fortement coercitifs,
• - la difficulté d'obtention d'aimantation multipolaire de matériaux magnétiques sous forme de feuille,tels.que décrits ci-dessus.

However, the main drawbacks of permanent magnet systems like Alnico or ferrite are:

• - the production of a relatively weak magnetic field, therefore the difficulty of obtaining a magnetization of strongly coercive materials,
• - The difficulty of obtaining multipolar magnetization of magnetic materials in the form of a sheet, as described above.

The object of the present invention relates to a device for magnetizing sheet or strip materials which eliminates all the drawbacks mentioned above, in which the magnetic field is created by permanent magnets capable of magnetizing at technical saturation. highly coercive materials to make a mul _t ipo- lar magnetization of greatly varying shape and allow a scroll speed of the high band, for example several tens of meters per minute.

The multipolar magnetization device of a strip material on one face or on two faces, object of the present invention, consists in producing one or two stacks on their large parallel faces, of flat prismatic elements, these elements being alternately permanent magnets with high coercive force, referred to herein as "main magnets" and polar material in Magnemite parts ^q uement soft, the direction of magnetization of the main magnets having a nerpendiculaire component to the large faces of the elements in opposite directions for the two magnets principal adjacent to the same pole piece; to magnetize a strip, it is scrolled in the immediate vicinity or against a stack or, in the same way, in an air gap between two stacks, preferably in a direction substantially parallel to the large faces of the flat elements and the plane of the strip being generally in a plane perpendicular to the large faces of the elements.

As main magnets, preference is given to magnets made of cobalt-rare earth alloys such as the samarium-cobalt Sm CoS; the magnetically soft material used for the pole pieces is preferably soft iron or an iron-cobalt alloy, but it is also possible to use permalloy, iron-nickel alloys, silicon or carbon steels, soft ferrites, according to the required magnetic permeability.

To obtain a through magnetization, the strip is passed through the air gap defined by two stacks placed face to face. On the other hand, to obtain a non-traversing magnetization, it suffices to use a single stack or to replace the second with a block of soft iron (or other ferromagnetic material) or any other non-magnetic device ensuring for example the displacement and the guiding of the strip or sheet.

The flat elements are delimited by two large parallel faces and the stacking takes place on these large faces. When the strip runs in the air gap or in the vicinity of the active part of the magnetizer, it is generally in a plane perpendicular to these large faces and it advances in a direction called the running axis, which is substantially parallel in terms of the large faces. In the case where the strip has, in the immediate vicinity of the magnetizer or in the air gap, a certain curvature, in the longitudinal direction, the term “plane of the strip” and “axis of travel” respectively mean the tangent plane to the strip on the generatrix of the strip closest to the magnetizer and the tangent to the advance curve of a point of the strip located in the previous tangent plane.

The direction of magnetization of the main magnets is not parallel to the large faces of these magnets and of the adjacent pole pieces. For two main magnets located on either side of the same pole piece, the directions of magnetization NS are opposite. The pole pieces used to channel towards the air gap or the surface of the magnetizer the magnetic flux produced by the opposing magnets, we have, at the outlet of the pole pieces on the surface of the magnetizer, an alternation of the North and South poles separated by zones neutral, located on the same width of the strip.

In the case where it is desired to obtain a through magnetization, the two stacks are placed facing each other, so that the elements of the same nature of each stack are facing each other and that the directions of magnetization NS of two facing main magnets are in opposite directions.

The device according to the invention may include several non-limiting variants of the scope of the invention.

In a first variant, the stacked flat elements have a lateral surface which narrows in the vicinity of the strip, for example a trapezoidal section whose small base is located on the side of the strip, so as to orient and concentrate the magnetic flux towards this one. These sections do not necessarily determine a prismatic lateral surface of the stack.

In a second variant, the stacked pole pieces have the shape of circular discs, having a cylindrical outer surface of revolution, movable around a non-ferromagnetic axis, which eliminates any sliding of the strip relative to the magnet when these discs rotate at an appropriate speed; the main magnets then have a base inscribed in (or equal to) the base of the pole pieces. Depending on the case, these discs can be driven and / or mounted idly on their axis. In order to limit the leakage field in the stack, it is preferable that the inside diameter of the pole pieces be greater than the inside diameter of the main magnets.

It is possible that, despite the high coercive field of the magnets of the stack, the field available on the surface (or in the air gap) of the magnetizer is still insufficient and that it should be increased. In a third variant, the invention also relates to an improved device compared to the previous device, characterized in that the pieces of the stack are brought, in addition, into contact with one or or several permanent magnets, called field magnets, located at the periphery of the stack and whose direction of magnetization NS is parallel to the running axis of the strip and in the same direction. Therefore, the direction of magnetization of the field magnets is parallel to the plane of the large faces of the stack and perpendicular to the direction of magnetization of the permanent magnets of the stack.

In this case, the pole pieces have a larger section than that of the main magnets and they enclose them completely; they alone are in contact with the field magnets and have a general form of "comb".

Thanks to the field magnets, the main magnets, which then play the role of anti-leakage magnets, work mainly in the third quadrant of the hysteresis cycle, which makes it possible to increase the magnetomotor force which they generate and, consequently, the field of the air gap (or near the poles).

As for simple stacking, the comb system can also consist of a stack of discs and be rotatable about an axis, but in this case, only the main magnets and the ends of the combs located between the main magnets, are mobile, the field magnets and the contiguous polar part remaining fixed and as close as possible to the mobile parts.

The field obtained in the air gap can be further increased by inserting between two main magnets adjacent to the same pole piece and replacing a part of said pole piece, an intermediate magnet attached to these two main magnets and located alternately at the before and at the rear of the stack in the direction of the axis of travel of the strip, the direction of magnetization NS of these intermediate magnets being parallel to the axis of travel of the strip and in the opposite direction.

When all the main magnets have the same thickness (a) and all the pole pieces have the same thickness (b), except possibly the main end magnets, the value (p = a + b) is called "not polar". However, it is also very easy to construct systems with variable polar pitch. The advantage of keeping neutral zones not magnetized is to close the field lines at a distance from the sheet, therefore to have a significant attraction force for non-zero work gaps.

The invention will be better understood thanks to the appended drawings which only represent specific non-limiting embodiments.

Figures 1 and 2 show in cross section a magnetic strip respectively through and non-through magnetization.

Figures 3 and 4 show respectively in section, along aa '- (fig.4) and bb' (fig.3), a through magnetization device with simple stack of trapezoidal contour elements.

Figures 5 and 6 respectively show a sectional view, along cc '(fig. 6) and dd' (fig.5), of a through magnetization device with simple stack of elements in the form of circular discs.

Figure 7 shows a side view and in partial section, along cc '(fig.9), a non-through magnetization device with combs.

FIG. 8 represents the lower part of a comb device for through magnetization comprising a movable stack in the vicinity of the strip, seen in section.

FIG. 9 is a plan view of the device shown in FIG. 7.

A strip of magnetizable material has a through magnetization as shown in Figure 1 when it has on the two faces in the width direction a succession of South poles and alternating North poles separated by neutral zones; when this arrangement is periodic, the distance between two neighboring poles defines the polar pitch of the magnetization. In this case, the field lines cross the thickness of the strip, being approximately perpendicular to the faces.

For against, the magnetization is not overall length, as shown in Figure 2, when on the same width of the strip and on one of the faces, there is a ^p alternating succession oles North and South separated by neutral zones, lines field closing on this face and not practically not crossing the thickness of the strip.

The device represented in FIGS. 3 and 4 comprises two stacks on their large faces, of flat elements which are alternately permanent magnets (1), for example made of cobalt-rare earth alloy, with high coercive field and ferromagnetic pole pieces (2 ), for example in iron-cobalt alloy with 35X cobalt. The large faces of these flat elements have a profile which, in the vicinity of the strip (3) is trapezoidal as it appears in FIG. 4, the small base (4) of the trapezium facing the strip (3). Each of the stacks is held by supports (5) made of soft iron or any other magnetically soft material. Two magnets (1) located on either side of the same pole piece (2) have overall magnetization directions preferably perpendicular to the plane of the large faces of the stack and in opposite directions. The strip (3) runs in a plane substantially perpendicular to the large faces of the stack and in a direction (or running axis) substantially parallel to the small bases (4) of the trapezoidal flat elements. The two stacks delimit an air gap (6). Each main magnet (1) and each pole piece (2) of one of the stacks is respectively located opposite a magnet and of a pole piece of the other similar stack. In addition, for two magnets facing each other on the air gap (6), the magnetization directions are in opposite directions. One thus obtains in the air gap to the right of the pole pieces, a succession of field lines and alternating directions, represented by the arrows which will print on the width of the strip (3) running in the air gap (6), a alternating succession of North and South poles separated by neutral zones.

To obtain a non-traversing magnetization, it suffices to use only one half of the magnetizer, that is to say a single stack, the other half being either removed or replaced by a block of soft iron or other magnetically soft material, either by a non-magnetic device ensuring for example the movement and the guiding of the sheet or the strip.

In the variant shown in Figures 5 and 6, the stacks are formed of flat elements, main magnets (1) and pole pieces (2), in the form of circular discs, movable around an axis (7) and having a surface single right cylindrical lateral and rotating at a speed such that any slippage of the strip relative to the magnet is eliminated.

In the comb device shown in Figures 7, 8 and 9, there is a stack of main magnets (1) and pole pieces (2) of trapezoidal shape in the vicinity of the strip (3), the netite base (4) of the trapezoid facing the strip.

The pole pieces (2) have a larger section than that of the magnets (1) and extend beyond the stack, completely surrounding the magnets (1) to form a sort of comb. These pole pieces (2) are in contact with field magnets (8) which give them a certain magnetic potential.

The direction of magnetization of these field magnets (8) is parallel to the running axis (11) of the strip (3), that is to say also parallel to the large faces of the stack and to the plane of the strip and, therefore, perpendicular to the magnetization directions of the magnets (I), as shown in Figure 9.

The presence of the field magnets (8) makes it possible to increase the magnetomotive force generated by the magnets (1) and, therefore, the field of the air gap. In addition, the flux created by the field magnets (8) is forced, because of the presence of the main magnets (1), to pass through the strip (3).

The active part of this system can be in the form of a stack of circular discs rotating around an axis, but the field magnets (8) and the adjacent polar part remain fixed, as shown diagrammatically in FIG. 8.

To further reduce leakage between the two combs, part of the pole piece located between two main magnets (1) is replaced by an intermediate magnet (9). This intermediate magnet has the form of a bar perpendicular to the plane of the strip (3), attached to the two main magnets (1) and located, relative to the axis of travel of the strip, alternately at the front and at the back of the stack. As shown in FIG. 9, one thus obtains an S-shaped succession of main magnets (1) and intermediate magnets (9), the latter being arranged staggered at the ends of the adjacent magnets (1).

The direction of magnetization of these intermediate magnets (9) is parallel to that of the field magnets (8) but in the opposite direction or even parallel and in the opposite direction to the running axis (11) of the strip (3). A concentration of the magnetic flux is thus obtained in the parts of the pole pieces located in the center of the stack, this flux being directed by the pole pieces towards the small base (4) of the trapezoidal contour in the vicinity of the strip.

In a plane parallel to the plane of the strip, there is alternately, at the center of the pole pieces of the stack, a concentration of North and South poles in the zones (10).

To obtain a through magnetization, a magnetizer is used comprising two similar stacks located one opposite the other and delimiting an air gap in which the strip (3) runs. Here again, the main magnets (1) of each of the stacks face each other, as do the pole pieces, and the directions of magnetization of two magnets face to face on either side of the air gap are not parallel to the faces. and their results are in opposite directions. To obtain a non-crossing magnetization, only half of the magnet is used, the other half being removed or replaced by a soft iron roller, or by a non-magnetic device ensuring the movement and guiding of the sheet. or tape.

The results obtained using the method and the device according to the invention are illustrated by the following examples:

Example! ::

A stack of fixed magnets made of SmCo ₅ alloy 2.5 mm thick and pole pieces made of Fe-Co alloy 2 mm thick is produced. An induction of 0.4 Tesla (4000 Gauss) is obtained in the air gap with a thickness of 3 mm. non-through magnetization and 0.65 Tesla (6500 Gauss) through magnetization for a flexible strip 3 mm thick.

Example 2:

A stack of 20 mm diameter discs is made, movable around of an axis, these discs being alternately SmCo ₅ magnets of thickness 1.3 mm and pole pieces of Fe-Co alloy of thickness 1.2 mm. Such a device makes it possible to magnetize at saturation a magnetic rubber band with barium ferrite of thickness less than or equal to 1 mm in through or non-through magnetization.

The value of the field in the air gap (in the air) is 380 kA / m for a distance of 4 mm and reaches 1000 kA / m for a distance of 0.8 mm.

Example 3:

• est de : 1,2 N à une distance nulle
• 0,75 N à une distance de 1 mm
• 0,35 N à une distance de 2 mm

^* marques déposées de la Société AIMANTS UGIMAG SAA magnetizer is made up of two cylinders comprising CO-RAMAG magnets (SmCo _S structure) 4 mm thick and mild steel pole pieces 6.25 mm thick (a pole pitch of 10.25 mm The device was used to magnetize a strip of "FERRIFLEX 3" ^* 55.0 mm wide and 2 mm thick, according to the configuration shown in FIG. 10 at the speed of 30 m / min, which is moreover only characteristic of the belt drive system, the magnetization device not constituting a limit The force of attraction measured on a magnetic contact key placed in a hole in this band, - in function of the distance from the head of the latter to the magnetic strip

• is: 1.2 N at zero distance
• 0.75 N at a distance of 1 mm
• 0.35 N at a distance of 2 mm

^* trademarks of AIMANTS UGIMAG SA

which is at least equal to values obtained on a strip of the same thickness magnetized on an electromagnetic device whose pole pitch was 11.5 mm, but at a considerably lower speed of travel (V = 1 m / min), limited by recharging the capacitor bank and the forces to which the electromagnetic saturator is subjected.

Example 4:

A comb system with intermediate magnets is produced, having the same characteristics as the simple stack system of example l. The field in the air gap is then increased by 10%. In all of the previous examples, it is possible to magnetize "through" a strip essentially consisting of ferrite of Ba, Sr and / or Pb over a thickness close to that of the height of the pole pieces (b), when their diameter is much higher than their height.

Claims (12)

1. Method for multipolar magnetization of a hard magnetic material in the form of a strip or sheet (3) characterized in that it is scrolled in the direction (11) in the immediate vicinity of at least one stack consisting of elements dishes resting on their large parallel bases, these elements being alternately main permanent magnets (1) with high coercive field and pole pieces made of soft magnetic material (2), the permanent magnets having a magnetization component perpendicular to the large bases, these components having opposite directions for two main magnets adjacent to the same pole piece (2). 2. Device for implementing the method according to claim 1, characterized in that it consists of two stacks separated by an air gap (6) in which the strip (or the sheet) (3) moves, the elements of the same nature - magnet (1) or pole piece (2) - of each stack being located opposite each other, and in that the components of the magnetization on a perpendicular to the large bases of two main magnets (1) opposite, are of opposite direction. 3. Device according to claim 2, characterized in that the main magnets (1) are made of a cobalt-rare earth type alloy. 4. Device according to one of claims 2 or 3, characterized in that the pole pieces (2) are made of soft iron or an iron-cobalt alloy. 5. Device according to one of claims 2 to 4, characterized in that all or part of the stacked flat elements have a lateral surface which tapers in the vicinity of the strip (3). 6. Device according to claim 5, characterized in that the base of the flat elements is trapezoidal, the small base of the trapezoid (4) being in the vicinity of the strip (3). 7. Device according to claim 5, characterized in that the base of the flat elements is circular and that these are movable about their axis (7). 8. Device according to claim 7, characterized in that all of the flat elements have the same cylindrical lateral surface. 9. Device according to one of claims 7 or 8, characterized in that the inside diameter of the pole pieces is greater than that of the inside diameter of the main magnets. 10. Device according to one of claims 2 to 9, characterized in that the pole pieces are connected by means of a magnetically soft material (or directly in contact) with at least one permanent field magnet (8 ) located at the periphery of the stack and the direction of magnetization of which has a component in the same direction as the axis of travel of the strip (11). 11. Device according to claim 10, characterized in that the (or) stack (s) is (are) movable (s) about an axis (7). 12. Device according to claim 10, characterized in that a part of each fixed pole piece is replaced by an intermediate magnet (9) attached to two main magnets (1), the latter being placed alternately at the front and at the rear of the stack in the direction of travel of the strip (17), the direction of magnetization of these intermediate magnets having a component of direction opposite to the travel axis of the strip (11).

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