EP1049115A1 - Method and device for demagnetizing pieces of small thickness - Google Patents

Abstract

The system uses very short pulses of reducing magnitude to achieve demagnetization. The process for demagnetization of thin ferromagnetic products includes placement of the products within a free zone which surrounded by an electrical coil. Current is applied to the coil in a series of pulse trains (T1, T2, ... Tn). Each train compri the same integer number of pulses (N) which are very short and of the same polarity within a train. Positive pulse trains (T1, T alternate with negative pulse trains (T2, T4..). The intensities of the pulse trains decrease with time from the largest amplitu initial pulse train (T1) to the last pulse train (Tn).

Description

The present invention relates to a method for demagnetization of thin ferromagnetic products, or thin walls, but able to occupy a large volume, such as containers, mechanically welded frames, metal boxes or strips alloys electrically isolated from each other, in which the Eddy currents cannot develop. This invention also relates to a device for demagnetizing such products, putting in implements said process.

In the mechanical and metallurgical industry in particular, it is necessary, in certain cases, to carry out these operations of demagnetization, in order to obtain magnetic neutrality of products, parts or components, so as to eliminate any risk of attraction and retention of ferromagnetic filings or dust, harmful to good functioning or proper presentation of these products, parts or organs.

The most typical example concerns ball bearings, which could be polluted during assembly, but we can also cite diesel engine injectors that keep metal particles when machine cleaning, and clogging up in service.

In addition, if such products, parts or components are grouped and transported in containers, these products, parts or organs are are re-magnetized if the container is itself magnetized, hence the usefulness to also be able to demagnetize containers.

All metallic elements welded by bombardment electrons must also be perfectly demagnetized, otherwise the jet of electrons is deflected and the solder is moved.

Also before electroplating decorative, it is better to demagnetize the parts to treat, because otherwise ferromagnetic dust can be retained and create unsightly iridescence ....

Generally, to suppress residual magnetism also called remanent magnetism, there are so-called devices demagnetizers which all proceed according to the same principle, namely generate decreasing hysteresis cycles in the magnetized matter, by alternating and declining magnetic fields. On an industrial level, demagnetization devices fall into two categories main, namely the demagnetizing plates and the demagnetizing tunnels.

In a demagnetizing tray, a laminated magnetic circuit made of silicon sheets contains a coil of enamelled copper wire, supplied by the alternating current of the network. The magnetic field of the plate is therefore alternative and has a maximum intensity at the center of its nucleus metallic. The part to be demagnetized is moved laterally on the face upper part of the magnetic circuit, so that each part of this part passes through the field's maximum intensity zone, then distant. The material is thus subjected to alternating magnetic fields and decreasing, which causes its demagnetization. Such devices demagnetizers are suitable for parts up to a thickness 40 to 50 mm. However, these devices are not suitable for products large volume units, or to grouped products representing total a significant volume.

A demagnetizing tunnel includes a coil of enamelled wires supplied with alternating current, which creates an alternating magnetic field important in its section, but decreasing very quickly as soon as one moves away from the device. Any part that passes through the tunnel, or is brought to the center of its reel then out, undergoes a field declining alternative and demagnetizes.

• D'une part, ils consomment une énergie réactive très importante, et les ampérages sont prohibitifs dès que l'on dépasse une section de 0,5 m².
• D'autre part, ils ne démagnétisent pas les pièces ferreuses massives, en raison de la naissance de courants de Foucault, en réponse à la variation de flux magnétique ; seul l'extérieur d'une pièce massive est démagnétisé, mais jamais l'intérieur (effet de peau).

Demagnetizing tunnels powered by the network have two drawbacks:

• On the one hand, they consume a very high reactive energy, and the amperages are prohibitive as soon as one crosses a section of 0.5 m ² .
• On the other hand, they do not demagnetize massive ferrous parts, due to the birth of eddy currents, in response to the variation in magnetic flux; only the outside of a massive piece is demagnetized, but never the inside (skin effect).

To overcome this effect, which comes from the speed with which the demagnetizing field alternates, we can use a lower frequency, but large power frequency converters are expensive. We can also create, in the coil of the demagnetizer tunnel, a succession of alternating and declining voltages, each of a sufficiently long time so that the current is established in continuous mode. In the latter case, the part to be demagnetized is immobilized, and this is the adapted value of voltages that decrease the magnetic field.

In the case of thin products, such as sheets or strips, or of structures formed of thin components such as sheets or angles, the eddy currents cannot develop. However, the classic design of demagnetizing tunnels does not allow, with a reasonable power, to interest a bulky unit product, or grouped products, the whole of which is large, taking into account the limitation of the passage section of these demagnetizing tunnels, already indicated above.

The German utility model No. 87.02843 describes a demagnetization, which is presented as a transportable case, with a passage capable of being crossed by the parts to be demagnetized, and a coil surrounding this passage. Such a device remains analogous to a tunnel conventional demagnetizer: the parts to be demagnetized must be moved relative to the device, and the coil of it is simply powered by alternating current. In addition, this known device is also limited, in its applications, to the demagnetization of small parts dimensions, in particular of timepieces.

The present invention aims to overcome these drawbacks, and it has therefore aim to provide a method and a device for the demagnetization of thin products that can occupy a large volume, this in an efficient way, with implementation of economic means.

To this end, the invention essentially relates to a process for the demagnetization of thin ferromagnetic products, the method consisting in sending, in at least one winding surrounding a free zone where the product (s) to be demagnetized are placed, pulses of electric current distributed in successive pulse trains which each include a whole number of successive pulses very short and of the same sign, alternating pulse trains positive and negative pulse trains, the intensities of the trains of pulses decreasing in time, from the first train up to the last train of pulses.

It should be noted that this process cannot be assimilated to known methods, using similar pulses but serving to demagnetize fixed magnets in electro-permanent devices used for holding parts on machine tools, bodies (magnets) to demagnetize being massive and of small volume, and being permanently surrounded by the windings without any free space remaining the inside of these coils, while the coercive field is strong - see the European patent application No. 0834890.

The invention also relates to a device for the demagnetization of thin ferromagnetic products, for the implementation of the demagnetization process defined above.

This device is of the "demagnetizing tunnel" type, and it includes at least one winding surrounding a free zone provided for receive said products to be demagnetized, the or each winding being connected to a power supply group, itself connectable to a network of AC distribution, and designed to send to the or each winding of electric current pulses distributed in trains successive pulses which each include an integer very short successive pulses of the same sign, alternating positive pulse trains and negative pulse trains, the pulse train intensities decreasing in time, since the first pulse train to the last pulse train.

The power supply of such a demagnetizer tunnel is thus performed by a group that controls the moments and the directions of passage of the current, and also the intensity of the current, creating pulses of high intensity current, for example of the order of 300 amperes (for the first pulses), but with so many passage times short that a 32 amp circuit breaker, for example, does not trip. he thus becomes possible to make a large demagnetizer tunnel section, allowing to activate at once, during a cycle of demagnetization with a duration for example of the order of 20 seconds, a full pallet loaded with products. The construction of such a tunnel, including including its power pack, is economical (low weight of copper) and the results, as demonstrated by the tests carried out by the Applicant, are very satisfied. In addition, the use of the process and demagnetization device, objects of the invention, is done with the products to be demagnetized kept immobile.

Figure 1 est une vue d'ensemble, très schématique, d'un tunnel démagnétiseur conforme à la présente invention, à bobinage unique ;

Figure 2 est un diagramme général montrant les trains d'impulsions envoyés dans le bobinage d'un dispositif selon l'invention, lors d'un cycle de démagnétisation ;

Figure 3, 4 et 5 sont des diagrammes montrant, de façon "dilatée", les formes des impulsions envoyées respectivement en début de cycle de démagnétisation, en milieu de cycle et en fin de cycle ;

Figure 6 est un diagramme général, similaire à la figure 5 mais illustrant le processus inverse de magnétisation ;

Figure 7 est une vue d'ensemble, très schématique, d'une autre forme de réalisation du dispositif démagnétiseur selon l'invention, à bobinages multiples.

The invention will in any case be better understood with the aid of the description which follows, with reference to the appended schematic drawing illustrating this process of demagnetization, and representing a device for its implementation, as well as a variant of this device .

Figure 1 is an overall view, very schematic, of a demagnetizer tunnel according to the present invention, single coil;

Figure 2 is a general diagram showing the pulse trains sent in the winding of a device according to the invention, during a demagnetization cycle;

Figure 3, 4 and 5 are diagrams showing, in a "dilated" manner, the shapes of the pulses sent respectively at the start of the demagnetization cycle, in the middle of the cycle and at the end of the cycle;

Figure 6 is a general diagram, similar to Figure 5 but illustrating the reverse process of magnetization;

Figure 7 is an overall view, very schematic, of another embodiment of the demagnetizer device according to the invention, with multiple windings.

In FIG. 1 is shown schematically a demagnetizing tunnel, which comprises a single coil 1, of rectangular section and horizontal axis A, composed for example of about 50 turns 2 of electrically conductive cable having a section of 6 mm ² . The winding 1 surrounds a free zone 3 of the "tunnel" type, forming a parallelepiped volume which can receive a standard pallet loaded with products to be demagnetized over a height of 2 meters maximum, for example.

The winding 1 is connected by conductors 4 to a group power supply 5, itself connectable to a network of distribution of alternating current, and intended to send in this winding 1 current pulse trains capable of demagnetizing products concerned.

Figure 2 illustrates, in the form of a general diagram, the characteristics of the pulse trains sent successively in the winding, during a complete demagnetization cycle, the time t being plotted on the abscissa and intensity I on the ordinate.

Demagnetization is achieved by sending, in the winding 1, a succession of pulse trains in predefined number, i.e. first pulse train T1, a second pulse train T2, ....., a last pulse train Tn, the total number of pulse trains can be of the order of ten to twenty. Each train of pulses T1, T2, ...., Tn itself includes an integer N successive current pulses, all of the same sign, this number N can be between two and ten pulses. However, the sign of pulses alternate, from one train of pulses to the next: thus the N pulses of the first train T1 are all of positive sign, the N pulses of the second train T2 are all of negative sign, the N pulses of the third train T3 are again all of positive sign, and and so on. In addition, the intensities I1, I2, I3, ..., In (in value absolute) current pulses are decreasing depending on the time t, from those of the first train T1 to those of the last train Tn, according to a predefined decay law, for example a linear law or a parabolic law. Depending on the decreasing values of the pulses current flowing through it, winding 1 thus generates fields magnetic which are themselves declining.

The successive pulse trains T1, T2, ..., Tn result from network alternations, received and processed by the power supply unit 5. In particular, the trains of positive impulses can come from alternations successive positive from the network, either directly or by rectification, and similarly, the negative pulse trains can come from successive negative alternations from the network. In each half-cycle, the sampling times of the alternating voltage of the network are controlled by the power supply group 5, in particular by being degressive from one pulse train to the next, so that obtain the pulse trains having the characteristics described previously, with reference to Figure 2.

More particularly, as shown in Figure 3, at the beginning of the demagnetization cycle so for the first train of pulses, the alternating voltage sampling time is practically equal to the half-period T / 2 of the alternating voltage of the network. As the Figure 4, in the middle of the demagnetization cycle, the sampling time of the alternating voltage is of the order of half of the half-period T / 2 of the alternating voltage of the network. Finally, as shown in Figure 5, in end of the demagnetization cycle, the time for drawing the voltage alternative is weak, relative to the half-period T / 2 of the voltage network alternative, and it tends to zero.

The use of the demagnetizer tunnel is as follows: the operator deposits the pallet, carrying the product or products to be demagnetized, in the free zone 3 of the tunnel, and it starts the demagnetization cycle previously defined, which can last a total of about 20 seconds, each pulse train having itself a duration of the order of a tenth second. At the end of this cycle, the pallet can be extracted from zone 3, all the products she carries then being demagnetized.

Referring to Figure 6, note that with the same device, but by triggering only the first train of pulses T1, reverse complete magnetization possible some products.

The demagnetization device, previously described, gives complete satisfaction with the demagnetization of products such as sheets, frameworks, wires or strips, arranged so that they form an angle between 0 ° and 60 °, relative to the direction of the magnetic field of winding 1, therefore with respect to axis A. However, this device can be insufficient or unsuitable for differently oriented products, for example vertically arranged products, or oriented products transversely.

• deux bobinages 6 d'axe vertical B, situés respectivement à la base et au sommet du "tunnel", et couplés entre eux ;
• deux bobinages 7 d'axe transversal C, situés respectivement sur les deux côtés du "tunnel", et eux aussi couplés entre eux.

To resolve this difficulty, it is also proposed in the context of the present invention, as shown in FIG. 7, a demagnetization device which comprises a plurality of coils surrounding the free zone 3, of the "tunnel" type, designed to receive the or the products to be demagnetized. The device comprises a first winding 1 of horizontal axis A longitudinal, at least one other winding 6 of vertical axis B, and at least one other winding 7 of transverse axis C. As regards more particularly the additional windings, it can be expected:

• two windings 6 of vertical axis B, located respectively at the base and at the top of the "tunnel", and coupled together;
• two windings 7 of transverse axis C, located respectively on the two sides of the "tunnel", and they also coupled together.

For the use of this variant of the device, the operator still places the pallet carrying the products to be demagnetized in the area free 3, and it controls, successively in the three windings 1, 6 and 7, the repetition of a demagnetization cycle as previously defined.

One would not depart from the scope of the invention, such as defined in the claims by modifying the total number of trains of pulses, or the number of pulses in each train, or the number of windings in which the pulse trains are sent. Similarly, the invention is applicable to demagnetization of all unitary or grouped products, thin or manufactured in from thin constituents.

Claims (6)

Method for demagnetizing products ferromagnetic thin, characterized in that it consists of send, in at least one coil (1, 6, 7) surrounding a free zone (3) where the product (s) to be demagnetized are placed, current pulses distributed in successive pulse trains (T1, T2, ...., Tn) which each include an integer (N) of successive pulses very short and of the same sign, alternating pulse trains positive (T1, T3, ...) and negative pulse trains (T2, T4, ....), the intensities (I1, I2, ..., In) of the pulse trains decreasing in time (t), from the first pulse train (T1) to the last train of pulses (Tn). Demagnetization method according to claim 1, characterized in that each pulse train (T1, T2, ..., Tn) comprises an integer (N) of successive pulses, of the same sign, included between two and ten pulses. Demagnetization process according to claim 1 or 2, characterized in that the current pulses result from the alternations from the network, the positive pulse trains (T1, T3, ...) coming successive alternations from the network, and trains negative pulses (T2, T4, ...) from negative alternations successive from the network, the voltage sampling times network alternative in each alternation, for the formation of said pulses, being declining from one train of pulses to the next. Device for the demagnetization of products ferromagnetic thin, for the implementation of the process of demagnetization according to any one of claims 1 to 3, the device being of the "demagnetizing tunnel" type, characterized in that it includes at least one coil (1, 6, 7) surrounding a free zone (3) scheduled to receive the product (s) to be demagnetized, the or each winding (1, 6, 7) being connected to a supply group (5), itself connectable to an alternating current distribution network, and designed to send current pulses to the or each winding (1, 6, 7) distributed in successive pulse trains (T1, T2, ..., Tn) which each include an integer (N) of successive pulses very short and of the same sign, alternating pulse trains positive (T1, T3, ...) and negative pulse trains (T2, T4, ...) intensities (I1, I2, ...., In) of the pulse trains decreasing the time, from the first train, of pulses (T1) to the last train of pulses (Tn). Demagnetization device according to claim 4, characterized in that it comprises a single winding (1), in particular of axis horizontal (A), surrounding the free area (3), of the "tunnel" type, provided for receive the products to be demagnetized. Demagnetization device according to claim 4, characterized in that it comprises a plurality of coils (1, 6, 7) surrounding the free area (3), of the "tunnel" type, intended to receive the products to be demagnetized, in particular with a winding (1) with a horizontal axis (A) longitudinal, at least one other winding (6) of vertical axis (B), and at at least one other winding (7) with transverse axis (C), the power unit (5) being provided for successively sending pulses, according to the cycle previously defined, in the different windings (1, 6, 7).

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