EP0940253A1 - Magnetic mounting for a permanent magnet in a screen printing device - Google Patents

Abstract

The magnetic rule, for use on a continuous silk screen printer with a perforated cylinder containing a solid roller (3) or tube of a magnetic material attracted by the rule, comprises a grille (14) of a non-magnetic material with a series of lengthwise cells for permanent magnets (16) with alternating directions of magnetization. The magnets are able to slide inside a fixed part of a lower sole (7) of a magnetic material, and the rule also has two lateral spacers and an upper polar plate (8) with pole pieces (11) positioned opposite the magnets to prevent short circuiting of the magnetic flux.

Description

The present invention relates to a strip magnetic with permanent magnets, intended for a device continuous screen printing, including a industrial fabric printing device by screen printing.

The industrial impression of fabrics derives from the traditional screen printing technique, in which we push the ink or the dye using a squeegee, through a sieve or stencil, some areas of which have been made waterproof with ink. In print industrial repetitive pattern, the stencil is consisting of a rotating cylinder, with a diameter of around 200 mm, made of nickel sheet metal pierced with small holes with a diameter of approximately 0.2 mm. The fabric to be printed, supported by a carpet, scrolls so continues on a hearth placed under the perforated cylinder, which turns while rolling on the fabric. Printing ink or dye, brought inside the cylinder by a ramp food, is traditionally distributed to through cylinder holes by means of a squeegee, placed inside the cylinder and supported on the lower generator of this cylinder.

To get an even distribution of ink on the entire width of the fabric, so a uniform impression on the width of this fabric which can be between about 2 meters and about 3.5 meters, it is necessary that the pressure of the squeegee is uniform at all points of the length of the cylinder, which is not easy to achieve.

To avoid this difficulty, we have already considered replace the sole with a shaped magnetic generator strip, permanent magnets or electromagnets, and the squeegee by a full roller or by a weak tube section, made of magnetic material, placed inside the perforated cylinder. The magnetic generator attracts the roller or tube, which rolls in the cylinder while the latter turns itself, and which pushes the ink or dye to the fabric, through the holes of said cylinder. This principle is revealed, among other things, by French patents N ° 2284447 and N ° 2321447, the application International No. WO 8903256, Swiss Patent No. 426711 and European Patent No. 0369540.

In the case of magnetic generators with electromagnets, there is the advantage of easy adjustment of the force of attraction of the roller or tube, by variation of the electric supply voltage which can go up to a zero value. . On the other hand, these electromagnetic generators are very expensive, because of the weight of copper required and the time required by the winding operations. In addition, their consumption of electrical energy is not negligible. Thus, a medium-sized magnetic strip consumes 600 watts of power, and each screen printing machine is equipped on average with ten strips, one strip per color. If such a machine works 300 days a year, operating for 16 hours each day, its annual energy consumption is: 0.6 x 10 x 16 x 300 = 28,800 Kwh / year

Magnetic generators with permanent magnets obviously don't have this drawback but they must use sufficiently strong magnets. It is around 1985 that new permanent magnets at "rare earths" have been produced industrially. These magnets have a volume energy such that they can advantageously replace the electromagnets with copper or aluminum windings, to create fields sufficiently strong magnetic, usable in particular in strips for screen printing devices rotary as specified above.

However, both the force setting of attraction is easy in the case of generators electromagnetic, by variation of voltage power supply, this variation and its cancellation are difficult to obtain when using strips with permanent magnets including magnetization by definition, is permanent.

The system of the aforementioned European patent N ° 0369540 uses, for the variation of the force of attraction magnetic, a longitudinal displacement of a part sliding bearing a series of permanent magnets cylindrical, arranged at constant intervals. This part is mounted and moves under an upper plate of non-magnetically conductive material, provided with circular pads made of magnetically material conductor, arranged in the same pitch as the magnets and forming pole pieces. How the device here requires that the distance between said magnetically conductive pads be greater than diameter of permanent magnets. This condition reduces the flow section of the magnetic flux and, therefore, the efficiency and power of the device. In addition, the European patent N ° 0369540 proposes, for the cancellation of the force of attraction, a complementary device consisting of a rotary assembly of all the magnets permanent around a longitudinal axis, allowing this together to describe a 90 ° rotation that keeps the magnets on the top plate. This solution complicates structure, comes at an additional cost, and it increases the size of the magnetic strip. She also complicates the use of this strip, forcing with two separate controls, one for the variation of the force of attraction and the other for the cancellation of this force, by prohibiting a continuous variation between the maximum attraction force and zero force. In addition, the longitudinal movement of the workpiece sliding is difficult and causes wear and seizures, because the magnets are strongly attracted by the upper plate, thus causing friction under said plate.

European patent application No. 0732199 describes another magnetic strip with permanent magnets, for screen printing machine, which has a succession of permanent magnets mounted on a support mobile. The attraction force is adjustable here by more or less significant distance from all of the magnets, thanks to a "parallelogram" type mounting deformable ". This solution also remains complicated and cumbersome because it requires a certain number joints, as well as the space required for deflection of the deformable parallelogram. In addition, she does not allow total force cancellation of magnetic attraction.

The present invention aims to remedy the whole of the disadvantages previously exposed, by providing a magnetic strip with permanent magnets for device screen printing, which allows a variation continues to attract until it is canceled practically total, with a simple and compact solution, while making it easier to move the mobile part.

To this end, the invention relates to a strip magnetic permanent magnet for device continuous screen printing, including a perforated rotary cylinder inside which is placed a solid roller or scraper tube, made of material magnetic, able to be attracted by the magnetic strip placed under the cylinder, this magnetic strip comprising in a known manner a fixed part with plate upper in non-magnetic material comprising a longitudinal succession of cells filled with parts mild steel fleeces arranged at a constant pitch, and a movable part arranged under the upper plate and movable in longitudinal translation, the mobile part comprising a longitudinal succession of magnets permanent, not equal to that of the pieces polar of the fixed part, the magnets being all vertically magnetized but with magnetization directions alternating, the strip being characterized in that said mobile part includes a grid made of non-magnetic material, comprising a longitudinal succession of cells receiving permanent magnets, the spacing between two cells or consecutive magnets being significantly lower the longitudinal dimension of said cells or magnets, the movable part being slidably mounted in a cavity of the fixed part itself composed of a sole lower magnetic material, two spacers slightly thicker than that of the movable part including the grid and the magnets permanent, and the upper pole plate whose alveoli and pole pieces, disposal corresponding to that of the magnets, also have a spacing significantly less than the dimension longitudinal of said cells and pole pieces.

A magnetic strip with magnets is thus obtained permanent, which can be in particular magnets with "rare earths", belonging to a moving part of relatively thin, which slides freely in a slightly higher cavity, determined by the thickness of the side struts of the fixed part which forms a hollow body. The magnets of the moving part are simultaneously drawn upwards by the pole pieces of the top plate, and towards the bottom by the bottom sole of the fixed part, so that they find themselves in a relatively neutral situation and that their friction, whether under the top plate or on the sole, is particularly weak. According to a another essential aspect of the invention, the spacing between the permanent magnets of the moving part is clearly smaller than the longitudinal dimension of these magnets, and the same is true for pole pieces, the arrangement corresponds to that of the magnets. So the movable part is movable in translation, relative to the fixed part, between a walking position in which the magnets coincide with the pole pieces, and a offset position in which the center of the magnets found in agreement with the middle of the space which separates two pole pieces inserted in the plate upper part of the fixed part. In the first position, which is the walking position, the pole pieces conduct the magnetic flux from the magnets to the solid roller or the scraper tube, which is thus subjected to a vertical attraction force, directed down. In the second position, which is the position stop, two neighboring magnets of opposite polarities find under the same pole piece, which short-circuits most of the magnetic flux coming out of magnets, the residual scent only interesting then very weakly the roller or the scraper tube which is generally about 4 mm above the face top of the polar plate.

So a simple translational movement of the mobile part, obtained without significant effort, allows a adjustment with continuous variation of the force of attraction of the scraper element, and in particular a reduction of this force until the residual force of attraction is negligible, from a practical point of view.

The previously explained operation can be obtained with permanent magnets and pole pieces circular, respecting the dimensional relationship indicated above. However, in one embodiment preferred of the invention, the permanent magnets inserted in the grid of the moving part, and the pole pieces inserted in the upper plate of the fixed part, have a rectangular or oblong shape, their most large dimension extending in the direction longitudinal of the magnetic strip. This special configuration, with magnets and parts polar with relatively small transverse extension, provides positional stability of the roller or tube forming a scraper, in the direction perpendicular to that of vertical attraction.

The spacing of the permanent magnets inserted in the grid of the mobile part, and the spacing corresponding pole pieces inserted in the plate upper part of the fixed part, for example equal to about 0.4 times the longitudinal dimension of these magnets and these pole pieces, which is about 0.3 times the pitch of said magnets and pole pieces.

Figure 1 est une vue en coupe transversale d'une réglette magnétique à aimants permanents conforme à la présente invention, avec indication de certains éléments du dispositif d'impression sérigraphique ;

Figure 2 est une vue en coupe horizontale de la réglette magnétique, suivant II-II de figure 1 ;

Figure 3 est une vue en coupe longitudinale de cette réglette magnétique, en position de marche ;

Figure 4 est une vue en coupe longitudinale de la même réglette magnétique, en position d'arrêt.

The invention will in any case be better understood with the aid of the description which follows, with reference to the appended schematic drawing representing, by way of example, an embodiment of this magnetic strip with permanent magnets for printing device. screen printing:

Figure 1 is a cross-sectional view of a magnetic strip with permanent magnets according to the present invention, with indication of certain elements of the screen printing device;

Figure 2 is a horizontal sectional view of the magnetic strip, along II-II of Figure 1;

Figure 3 is a longitudinal sectional view of this magnetic strip, in the on position;

Figure 4 is a longitudinal sectional view of the same magnetic strip, in the stopped position.

The magnetic strip, designated as a whole by the mark 1, belongs to a printing device continuous screen printing including a rotating cylinder perforated 2, partially shown in Figure 1, which overcomes the magnetic strip 1 and inside which a full roll 3 of small section is placed, magnetic material. The fabric 4 to be printed, placed on a belt 5, scrolls between the magnetic strip 1 and the perforated cylinder 2, whose peripheral speed is identical to the linear speed of the fabric 4. The roller 3, attracted by the magnetic strip 1, rests and rolls on the lower generatrix of the perforated cylinder 2, and there thus pushes ink or dye 6 through the holes of cylinder 2, to distribute it on fabric 4 according to a preset pattern. The force of attraction F, exerted by the magnetic strip 1, keeps the roller 3 in its lower position, and allows this roller 3 to exercise continuous pressure on the inside of the cylinder perforated 2 and, consequently, on the fabric 4, said roller 3 thus forming a scraper.

The magnetic strip 1 comprises a fixed part, which consists of a flat bottom sole 7, a upper pole plate 8, and two spacers longitudinal 9.

The lower sole 7, of rectangular shape elongated, is made of mild steel.

The upper pole plate 8, of shape and dimensions corresponding to those of sole 7, is made of non-magnetic material but it has a longitudinal succession of rectangular cells 10, furnished with rectangular pole pieces 11 made of mild steel, whose respective vertical axes are separated from each other of the others by a certain step P, the larger sides of the cells 10 and pole pieces 11 being parallel to the longitudinal direction of the strip 1. More in particular, the length of the cells 10 and of the corresponding 11 pole pieces is chosen such that the minimum spacing e, separating two cells 10 or two 11 consecutive pole pieces, that is to say clearly of value less than the length L of these cells 10 and parts polar 11. For example, the value of the spacing e is equal to 0.4 times the length L of cells 10 and pole pieces 11.

The two longitudinal spacers 9 hold the upper pole plate 8 at the desired distance above of the lower sole 7, by providing a cavity internal 12 of elongated rectangular section. These spacers 9 can be made indifferently by magnetic or not.

The assembly constituted by the lower sole 7, by the upper pole plate 8 and by both spacers 9 is assembled by means of screws 13 arranged laterally.

In the cavity 12 is slidably mounted, in longitudinal direction, a movable grid 14 made of material non-magnetic, comprising a longitudinal succession of cells 15 whose number, pitch P, shape rectangular and the dimensions correspond, respectively, to those of the cells 10 of the plate polar 8. The rectangular cells 15 of the grid 14 are filled with rectangular permanent magnets 16 of corresponding dimensions, all magnetized according to a vertical direction, but with feeding directions alternating, alternating polarities N, S, N, S ... being thus encountered on the upper face of the grid 14, as well as on its underside. Permanent magnets 16 are advantageously magnets of the "earth" type rare ".

The thickness of the grid 14 and the magnets permanent 16 is slightly less than the clear height of the cavity 12, so that the grid 14 can slide freely in relation to the fixed part of the magnetic strip 1. At least one end of the grid 14, there is a member 17 providing the coupling of this grid 14 with a device for control, not shown, which allows the grill to be moved 14 in translation in a controlled manner, relative to the fixed part of the strip, between two extreme positions, with possibility of immobilization in positions intermediaries.

The operation of this magnetic strip 1 is established as follows:

According to Figure 3, when the grid 14 with its permanent magnets 16 is in agreement with the pole plate 8 and its pole pieces 11, the flux magnetic from magnets 16 is freely driven, through pole pieces 11, towards the roller 3 forming scraper, which is then attracted strongly. The lines of magnetic field strength close by the sole lower 7.

According to Figure 4, when subjected to the grid 14 a longitudinal translation of half a step (P / 2), the axes of the magnets 16 are brought into agreement with the midpoints of the spacings of value e which separate two successive pole pieces 11. Considering the dimensional relationship between the e value of these spacings, on the one hand, and the length L of the parts 11 and 16 magnets, on the other hand, there are then necessarily a partial recovery of each magnet 16 by two successive pole pieces 11. So, each pole piece 11 partially overlaps a magnet permanent 16 whose upper face has a polarity N, and a permanent magnet 16 close to the previous one but of which the upper side has an S polarity. Each part polar 11 thus short-circuits the magnetic flux from magnets 16, which previously was aimed at the roller 3. As before, the lines of force of the magnetic field is closed again here by the sole lower 7. In this position of the grid 14, the rod 3 forming a scraper is no longer magnetically attracted.

Intermediate positions of the grid 14 allow obtaining a force of attraction intermediate of the roller 3 forming a scraper, with a continuous variation of this force.

Note that all permanent magnets 16 are naturally attracted to both the sole lower 7, and by the mild steel parts 11 of the pole plate 8, the attractive forces exerted by the sole 7 on the one hand and by the pole pieces 11 on the other share being of opposite directions. The permanent magnets 16 are therefore maintained in a state of relative equilibrium, which considerably reduces their attraction towards the wall upper or the lower wall of the cavity 12. From this done, the longitudinal displacement effort of the grid 14 remains of very acceptable value.

The rectangular shape of the magnets 16 and pole pieces 11 not only provides overlap important in the stop position (figure 4), to then cancel the force of attraction of the roller 3, but it also guarantees, in the running position, good stability of the position of the roller 3 forming a scraper in the direction perpendicular to its vertical attraction F (see figure 1 - arrows f indicating the return force of the roller 3).

As is obvious, and as is clear from what precedes, the invention is not limited to the single form of this magnetic strip with magnets permanent for screen printing device which has been described above, by way of example; she in embraces, on the contrary, all variants of realization and application respecting the same principle. It is thus, in particular, that one would not stray from the scope of the invention by modifying the form of magnets and pole pieces, or by choosing a type magnets other than those with "rare earths", or replacing the full roller forming a scraper with a tube magnetic material having the same function.

Claims (4)

Magnetic strip with permanent magnets for continuous screen printing device, in particular industrial fabric printing device, comprising a rotary perforated cylinder (2) inside which is placed a solid roller (3) or a scraper tube, made of magnetic material, able to be attracted by the magnetic strip (1) arranged under the cylinder (2), this magnetic strip (1) comprising a fixed part with upper plate (8) made of non-magnetic material comprising a longitudinal succession of cells ( 10) furnished with pole pieces (11) made of mild steel arranged at a constant pitch (P), and a movable part disposed under the upper plate (8) and movable in longitudinal translation, the movable part comprising a longitudinal succession of permanent magnets (16) arranged at a pitch (P) equal to that of the pole traps (11) of the fixed part, the magnets (16) being all magnetized vertically but with directions of mentation (N, S) alternated, characterized in that said movable part comprises a grid (14) of non-magnetic material, comprising a longitudinal succession of cells (15) receiving the permanent magnets (16), the spacing (e) between two consecutive cells (15) or magnets (16) being significantly smaller than the longitudinal dimension (L) of said cells (15) or magnets (16), the movable part being slidably mounted in a cavity (12) of the fixed part, it - even composed of a lower sole (7) made of magnetic material, two longitudinal spacers (9) of thickness slightly greater than that of the movable part comprising the grid (14) and the permanent magnets (16), and the upper pole plate (8) of which the cells (10) and the pole pieces (11), of arrangement corresponding to that of the magnets (16) also have a spacing (e) markedly less than the longitudinal dimension (L) of said cells (10 ) and polar pieces es (11). Magnetic strip with permanent magnets according to claim 1, characterized in that the spacing (e) permanent magnets (16) inserted in the grid (14) of the movable part, and the corresponding spacing (e) pole pieces (11) inserted in the plate upper (8) of the fixed part, is equal to about 0.4 times the longitudinal dimension (L) of these magnets (16) and of these pole pieces (11). Magnetic strip with permanent magnets according to claim 1 or 2, characterized in that the permanent magnets (16) inserted in the grid (14) of the movable part, and the pole pieces (11) inserted in the upper plate (8) of the fixed part, have a rectangular or oblong shape, their largest dimension (L) extending in the longitudinal direction of the magnetic strip (1). Magnetic strip with permanent magnets according to any one of claims 1 to 3, characterized in what the permanent magnets (16) inserted in the grid (14) of the moving part are magnets rare ".

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