EP0363282B1 - Use of a nozzle having a convergent-divergent profile in an ejection device for a root-cutter - Google Patents

Use of a nozzle having a convergent-divergent profile in an ejection device for a root-cutter Download PDF

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Publication number
EP0363282B1
EP0363282B1 EP89402749A EP89402749A EP0363282B1 EP 0363282 B1 EP0363282 B1 EP 0363282B1 EP 89402749 A EP89402749 A EP 89402749A EP 89402749 A EP89402749 A EP 89402749A EP 0363282 B1 EP0363282 B1 EP 0363282B1
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EP
European Patent Office
Prior art keywords
nozzle
air
knives
use according
pressure
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EP89402749A
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German (de)
French (fr)
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EP0363282A1 (en
Inventor
Claude Chacoux
Gilles Schrevel
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Maguin SAS
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Maguin SAS
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    • C—CHEMISTRY; METALLURGY
    • C13—SUGAR INDUSTRY
    • C13B—PRODUCTION OF SUCROSE; APPARATUS SPECIALLY ADAPTED THEREFOR
    • C13B5/00—Reducing the size of material from which sugar is to be extracted
    • C13B5/06—Slicing sugar beet
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B26—HAND CUTTING TOOLS; CUTTING; SEVERING
    • B26D—CUTTING; DETAILS COMMON TO MACHINES FOR PERFORATING, PUNCHING, CUTTING-OUT, STAMPING-OUT OR SEVERING
    • B26D7/00—Details of apparatus for cutting, cutting-out, stamping-out, punching, perforating, or severing by means other than cutting
    • B26D7/08—Means for treating work or cutting member to facilitate cutting
    • B26D7/088—Means for treating work or cutting member to facilitate cutting by cleaning or lubricating

Definitions

  • the invention relates to the cleaning of root cutters used in the sugar industry, by blowing compressed air in the direction of the knives of the root cutters.
  • the beets are cut into strips or cossettes in a device called root cutter, of the tray or drum type.
  • the latter consists of a drum with a horizontal axis rotating in a fixed casing.
  • the rim of the drum is formed by a succession of cells in which knife holders are fixed. The knives are oriented parallel to the generators, towards the inside of the drum.
  • a vertical base of the drum is hollowed out and allows the beets to access, from a hopper, inside the drum in which they accumulate in the lower half.
  • the beets are driven by the drum until they come up against a fixed part which pushes them back against the knives. They are then cut into pods, projected outside, and collected by the casing from where they are routed to the diffuser.
  • an intermittent spraying of compressed air is usually carried out, in the direction of the knives, during the operation of the root cutter.
  • the air takes off the fibrous materials from the blades, and drives them outwards where they are entrained with the chips.
  • the blowing ramp which is slit-shaped, is arranged on the fixed part of the device, inside the drum. It extends along a generator parallel to the knives.
  • the ramp consists of a tubular distributor, supplied with pressurized fluid at one end, which opens along its axis on a converging nozzle.
  • the lips of the nozzle provide between them a very small opening so as to distribute the flow as uniformly as possible over its entire length.
  • such a device requires a relatively high pressure, of the order of 15 to 20 bars in current installations.
  • the injection lasts a few seconds and is repeated at regular intervals.
  • the frequency is determined based on the amount of fibrous material entrained with the beets.
  • the present invention proposes to improve the efficiency of the cleaning of root cutters by blowing air under pressure, while reducing costs.
  • the subject of the invention is the use, for the cleaning of a root cutter, of a device comprising a compressed air blowing ramp arranged on the fixed part of the root cutter and having at least one nozzle. ejection of compressed air towards the knives of the root cutter.
  • the nozzle has a convergent-divergent profile suitable for obtaining isentropic expansion up to a pressure close to atmospheric pressure; the nozzle is supplied with air at a supply pressure such that the ratio of supply pressure to atmospheric pressure is greater than the critical pressure ratio of air so that the speed of ejection of air by the nozzle is supersonic; and the nozzle is placed at such a distance from the trajectory of the cutting edges of the knives that the potential core has a length (4D) substantially equal to this distance, so that the air jet at the outlet of the nozzle retains substantially parallel current lines until it reaches the cutting edges of the knives.
  • the nozzle By pressure close to atmospheric pressure, we understand a pressure whose value is at most greater or less than 20% of the latter. So, the nozzle will be shaped so as to ensure isentropic expansion up to a pressure between 0.8 and 1.2 times atmospheric pressure.
  • the invention results from the observation that for existing embodiments where the nozzle, or nozzle, is simply convergent with a small opening - of the order of a millimeter - and a high supply pressure, the pressure of the jet, immediately downstream of the outlet section, remains strong compared to its value before expansion in the nozzle and is not adapted to atmospheric pressure. It follows a brutal relaxation giving a flared shape to the jet whose effectiveness decreases rapidly with distance.
  • the usable energy represented by the product of the momentum (QV) by the length of the potential nucleus (4D), is therefore limited by the ejection speed, which is at most sonic, and the short distance over which it is kept.
  • Q is equal to the flow rate of the fluid, V to its speed at the outlet of the nozzle, D to the hydraulic diameter of the latter.
  • D corresponds to the diameter in the case of a circular nozzle and to twice the distance E separating the lips in the case of a two-dimensional nozzle.
  • the length of the potential core 4D corresponds, as is known, substantially to the distance separating the outlet section of the nozzle from the section of the jet for which the maximum speed of the fluid becomes lower than the initial speed of ejection.
  • the hydraulic diameter of the nozzle will be equal to at least one-eighth and preferably close to a quarter of the distance separating the nozzle from the path of the cutting edges of the knives.
  • supply pressure is understood the total pressure of the air immediately upstream of the nozzle.
  • the pressure supplied by the air supply means will generally be higher due to the pressure losses generated in the conduits up to the nozzle itself, and which will have to be overcome.
  • the nozzle is preferably two-dimensional. It is supplied from a tubular distributor along a generator from which it is mounted. The distributor, meanwhile, is connected to a supply pipe by one end.
  • the distributor comprises a means of standardizing the speed profile along the nozzle in the case where it is two-dimensional, or alternatively from one nozzle to the other in the case of a plurality of nozzles. Indeed, it is desirable that the air acts with the same efficiency from one edge to the other of the knives.
  • this means consists of a flow distributor disposed inside the chamber formed by the distributor upstream of the nozzle.
  • the flow distributor advantageously consists of a cylindrical tube pierced with calibrated orifices, of diameter smaller than the diameter of the tube.
  • this means can be constituted by the supply chamber itself which will then have a volume sufficient to slow the air coming from the supply pipe.
  • the root cutter 1 of which appears in FIG. 1 only the part surrounding the blowing ramp 2, comprises a stator 3 inside the drum. This is shown schematically by the knives 4 only.
  • the drum rotates around an axis perpendicular to the plane of the figure, in the direction of arrow F.
  • the beets taken between the drum and the stator are cut into chips by the knives 4.
  • This type of root cutter, with drum, is well known in the sugar industry, it is not necessary to develop its description. It is also known to have a ramp 2 for blowing fluid, usually compressed air but also water vapor if necessary, in the upper part of the device, inside a cavity formed in the stator. , as shown in the drawing.
  • the ramp injects the fluid substantially radially, in the direction of the path traveled by the knives.
  • the purpose of the fluid jet is to take off the fibrous elements which are deposited astride the edge of the latter.
  • the ramp 2 is subject to the stator, inside the cavity, by any appropriate means, for example stirrups 5.
  • the ramp consists of a tubular distributor 21 of circular or other section - see also the proud 2.
  • the distributor is open at one end 21a, and closed at its other end 21b by a plug.
  • the wall of the tube 21 has a longitudinal opening parallel to its axis, which opens onto a nozzle 22 integral with it.
  • the nozzle is two-dimensional.
  • This nozzle is shaped, according to the invention, as a function of the total supply pressure of the system prevailing immediately upstream of said nozzle itself, so as to obtain through it an isentropic expansion of fluid up to ambient pressure at the nozzle outlet.
  • the ejection speed is supersonic
  • the profile corresponds to a ratio of the upstream pressure to the atmospheric pressure greater than the critical pressure ratio of the fluid. This last ratio is, for air for example, 1.89.
  • the nozzle has a first converging part 22a, connected to a second diverging part 22b by a neck 22c.
  • the section variation along the radial flow lines is defined according to well-known laws of fluid mechanics so that the expansion is isentropic up to atmospheric pressure at the outlet of the nozzle. It thus allows the fluid to accelerate continuously to the outlet section passing through a sonic speed at the neck 22c.
  • the fluid reaches the distributor through the end 21a, passes through the distributor tube 23, fills the annular balancing chamber, and is ejected in the direction of the knives by the nozzle 22.
  • the potential core length is substantially equivalent to the distance separating the nozzle from the knives. Indeed this distance is of the order of 40 mm in known drum devices. We will therefore have optimal efficiency.
  • the invention can be applied to other types of root cutters including the tray root cutter.

Description

L'invention se rapporte au débourrage de coupe-racines utilisés dans l'industrie sucrière, par soufflage d'air comprimé en direction des couteaux des coupe-racines.The invention relates to the cleaning of root cutters used in the sugar industry, by blowing compressed air in the direction of the knives of the root cutters.

Avant l'étape d'extraction du jus sucrè par diffusion, on découpe les betteraves en lanières ou cossettes dans un appareil appelé coupe-racines, du type à plateau ou à tambour. Ce dernier est constitué par un tambour à axe horizontal tournant dans un carter fixe. La jante du tambour est formée d'une succession d'alvéoles dans lesquelles sont fixés des porte-couteaux. Les couteaux sont orientés parallèlement aux génératrices, vers l'intérieur du tambour.Before the stage of extraction of the sweet juice by diffusion, the beets are cut into strips or cossettes in a device called root cutter, of the tray or drum type. The latter consists of a drum with a horizontal axis rotating in a fixed casing. The rim of the drum is formed by a succession of cells in which knife holders are fixed. The knives are oriented parallel to the generators, towards the inside of the drum.

Une base verticale du tambour est évidée et permet l'accès des betteraves, depuis une trémie, à l'intérieur du tambour dans lequel ils s'accumulent dans la moitié inférieure. En fonctionnement, les betteraves sont entrainées par le tambour jusqu'à buter sur une pièce fixe qui les repousse contre les couteaux. Elles sont alors découpées en cossettes, projetées à l'extérieur, et recueillies par le carter d'où elles sont acheminées vers le diffuseur.A vertical base of the drum is hollowed out and allows the beets to access, from a hopper, inside the drum in which they accumulate in the lower half. In operation, the beets are driven by the drum until they come up against a fixed part which pushes them back against the knives. They are then cut into pods, projected outside, and collected by the casing from where they are routed to the diffuser.

Les betteraves, malgré leur nettoyage préalable, entrainent avec elles des déchets fibreux : herbes cu radicelles, qui ne sont pas découpés par les couteaux et qui se déposent en travers du tranchant des lames. Ils finissent par obstruer l'espace entre les couteaux avec pour conséquence une réduction du débit de l'appareil.Beets, despite their prior cleaning, carry with them fibrous waste: herbs or rootlets, which are not cut by the knives and which are deposited across the cutting edge of the blades. They end up obstructing the space between the knives resulting in a reduction in the flow rate of the device.

Pour éliminer ces déchets indésirables, on procède usuellement à la projection intermittente d'un jet d'air comprimé, en direction des couteaux, pendant le fonctionnement du coupe-racines.To eliminate this undesirable waste, an intermittent spraying of compressed air is usually carried out, in the direction of the knives, during the operation of the root cutter.

L'air décolle les matières fibreuses des lames, et les chasse vers l'extérieur où elles sont entrainées avec les cossettes. La rampe de soufflage, qui est en forme de fente, est disposée sur la partie fixe de l'appareil, à l'intérieur du tambour. Elle s'étend le long d'une génératrice parallèle aux couteaux.The air takes off the fibrous materials from the blades, and drives them outwards where they are entrained with the chips. The blowing ramp, which is slit-shaped, is arranged on the fixed part of the device, inside the drum. It extends along a generator parallel to the knives.

Dans une solution connue, la rampe est constituée d'un distributeur tubulaire, alimenté en fluide sous pression à une extrémité, qui débouche le long de son axe sur une tuyère convergente. Les lèvres de la tuyère ménagent entre elles une très faible ouverture de manière à répartir le flux le plus uniformément possible sur toute sa longueur.In a known solution, the ramp consists of a tubular distributor, supplied with pressurized fluid at one end, which opens along its axis on a converging nozzle. The lips of the nozzle provide between them a very small opening so as to distribute the flow as uniformly as possible over its entire length.

Un tel dispositif nécessite, pour pouvoir désobstruer avec quelque efficacité les couteaux, une pression relativement élevée, de l'ordre de 15 à 20 bars dans les installations actuelles. L'injection dure quelques secondes et est répétée à intervalles réguliers. La fréquence est déterminée en fonction de la quantité de matières fibreuses entrainées avec les betteraves.To be able to unclog the knives with some efficiency, such a device requires a relatively high pressure, of the order of 15 to 20 bars in current installations. The injection lasts a few seconds and is repeated at regular intervals. The frequency is determined based on the amount of fibrous material entrained with the beets.

Ce dispositif ne donne pas entièrement satisfaction, d'une part, parce que le niveau élevé de la pression d'alimentation òblige à l'emploi de compresseurs spéciaux, onéreux en soi, d'autre part, parce que la force d'impact produite par le jet n'est pas toujours suffisante pour éliminer rapidement tous les déchets. On est alors amené à augmenter soit la durée du soufflage, soit sa fréquence. Tout ceci a une incidence défavorable sur le coût d'exploitation de l'installation.This device is not entirely satisfactory, on the one hand, because the high level of the supply pressure forces the use of special compressors, which are expensive in themselves, on the other hand, because the impact force produced by the jet is not always sufficient to quickly eliminate all the waste. It is then necessary to increase either the duration of the blowing, or its frequency. All this has an unfavorable impact on the operating cost of the installation.

Dans la demande de brevet EP-A-251 122, on propose, pour opérer le décollement des fibres des couteaux et leur évacuation vers l'extérieur, la combinaison de deux rampes de projection agissant en opposition : une première rampe est orientée vers la trajectoire des couteaux en formant un angle aigu avec la direction de leur déplacement, tandis que la deuxième forme un angle obtus. Cette dernière a pour objet d'assurer l'entrainement des fibres vers l'extérieur, une fois qu'elles ont été décollées par le jet de la première rampe. Cette solution n'est toutefois pas moins économique que la première, car elle doit faire appel également à des pressions de fluide élevées.In patent application EP-A-251 122, it is proposed, to operate the separation of the fibers from the knives and their evacuation towards the outside, the combination of two projection ramps acting in opposition: a first ramp is oriented towards the trajectory knives forming an acute angle with the direction of their movement, while the second forms an obtuse angle. The purpose of the latter is to ensure the entrainment of the fibers towards the outside, once they have been detached by the jet from the first ramp. This solution is however not less economical than the first, because it must also use high fluid pressures.

La présente invention se propose d'améliorer l'efficacité du débourrage de coupe-racines par soufflage d'air sous pression, tout en réduisant les coûts.The present invention proposes to improve the efficiency of the cleaning of root cutters by blowing air under pressure, while reducing costs.

L'invention a pour objet l'utilisation, pour le débourrage d'un coupe-racines, d'un dispositif comprenant une rampe de soufflage d'air comprimé disposée sur la partie fixe du coupe-racines et présentant au moins une buse d'éjection d'air comprimé en direction des couteaux du coupe-racines. Selon l'invention:
   la buse présente un profil convergent-divergent adapté à l'obtention d'une détente isentropique jusqu'à une pression voisine de la pression atmosphérique;
   la buse est alimentée en air sous une pression d'alimentation telle que le rapport de la pression d'alimentation à la pression atmosphérique soit supérieur au rapport de pression critique de l'air de façon que la vitesse d'éjection de l'air par la buse soit supersonique; et
   la buse est placée à une distance telle de la trajectoire des bords de coupe des couteaux que le noyau potentiel ait une longueur (4D) sensiblement égale à cette distance,
   de façon que le jet d'air à la sortie de la buse conserve des lignes de courant sensiblement parallèles jusqu'à atteindre les bords de coupe des couteaux.The subject of the invention is the use, for the cleaning of a root cutter, of a device comprising a compressed air blowing ramp arranged on the fixed part of the root cutter and having at least one nozzle. ejection of compressed air towards the knives of the root cutter. According to the invention:
the nozzle has a convergent-divergent profile suitable for obtaining isentropic expansion up to a pressure close to atmospheric pressure;
the nozzle is supplied with air at a supply pressure such that the ratio of supply pressure to atmospheric pressure is greater than the critical pressure ratio of air so that the speed of ejection of air by the nozzle is supersonic; and
the nozzle is placed at such a distance from the trajectory of the cutting edges of the knives that the potential core has a length (4D) substantially equal to this distance,
so that the air jet at the outlet of the nozzle retains substantially parallel current lines until it reaches the cutting edges of the knives.

Par pression voisine de la pression atmosphérique, on comprend une pression dont la valeur est au plus supérieure ou inférieure de 20 % de cette dernière. Ainsi, la buse sera conformée de façon à assurer une détente isentropique jusqu'à une pression comprise entre 0,8 et 1,2 fois la pression atmosphérique.By pressure close to atmospheric pressure, we understand a pressure whose value is at most greater or less than 20% of the latter. So, the nozzle will be shaped so as to ensure isentropic expansion up to a pressure between 0.8 and 1.2 times atmospheric pressure.

L'invention résulte de la constatation que pour les réalisations existantes où la buse, ou tuyére, est simplement convergente avec une faible ouverture - de l'ordre du millimètre - et une pression d'alimentation élevée, la pression du jet, immédiatement en aval de la section de sortie, reste forte par rapport à sa valeur avant détente dans la buse et n'est pas adaptée à la pression atmosphérique. Il s'ensuit une détente brutale donnant une forme évasée au jet dont l'efficacité diminue rapidement avec la distance. L'énergie utilisable, représentée par le produit de la quantité de mouvement (QV) par la longueur du noyau potentiel (4D), est de ce fait limitée par la vitesse à'éjection, qui est au plus sonique, et la faible distance sur laquelle celle-ci est conservée.The invention results from the observation that for existing embodiments where the nozzle, or nozzle, is simply convergent with a small opening - of the order of a millimeter - and a high supply pressure, the pressure of the jet, immediately downstream of the outlet section, remains strong compared to its value before expansion in the nozzle and is not adapted to atmospheric pressure. It follows a brutal relaxation giving a flared shape to the jet whose effectiveness decreases rapidly with distance. The usable energy, represented by the product of the momentum (QV) by the length of the potential nucleus (4D), is therefore limited by the ejection speed, which is at most sonic, and the short distance over which it is kept.

Q est égal au débit du fluide, V à sa vitesse en sortie de buse, D au diamètre hydraulique de cette dernière.Q is equal to the flow rate of the fluid, V to its speed at the outlet of the nozzle, D to the hydraulic diameter of the latter.

D correspond au diamètre dans le cas d'une buse circulaire et à 2 fois la distance E séparant les lèvres dans le cas d'une tuyère bidimensionnelle.D corresponds to the diameter in the case of a circular nozzle and to twice the distance E separating the lips in the case of a two-dimensional nozzle.

La longueur du noyau potentiel 4D correspond, comme cela est connu, sensiblement à la distance séparant la section de sortie de la tuyère de la section du jet pour laquelle la vitesse maximale du fluide devient inférieure à la vitesse initiale d'éjection.The length of the potential core 4D corresponds, as is known, substantially to the distance separating the outlet section of the nozzle from the section of the jet for which the maximum speed of the fluid becomes lower than the initial speed of ejection.

Pour obtenir une meilleure action du fluide, on peut certes essayer de rapprocher la buse de la trajectoire des couteaux, mais il est évident qu'il existe une distance minimale que l'on ne peut réduire pour des raisons techniques. Cette distance est de l'ordre de 40 mm dans la pratique pour les coupe-racines à tambour.To obtain a better action of the fluid, one can certainly try to bring the nozzle closer to the trajectory of the knives, but it is obvious that there is a minimum distance that cannot be reduced for technical reasons. This distance is around 40 mm in practice for drum root cutters.

Pour un même débit, en autorisant, conformément à l'invention, une détente isentropique du fluide jusqu'à la pression atmosphérique, au moyen d'une buse à profil convergent-divergent avec une pression d'alimentation supérieure à la pression critique de l'air, on obtient un jet qui n'éclate pas et qui conserve des lignes de courant sensiblement parallèles. En outre, la vitesse d'éjection étant maintenant supersonique et la section à la sortie du fluide supérieure à celle du col, l'énergie disponible du jet est augmentée en proportion.For the same flow rate, by authorizing, in accordance with the invention, isentropic expansion of the fluid to atmospheric pressure, by means of a nozzle with a convergent-divergent profile with a supply pressure greater than the critical pressure of l 'air, a jet is obtained which does not burst and which maintains substantially parallel streamlines. In addition, the ejection speed now being supersonic and the section at the outlet of the fluid greater than that of the neck, the available energy of the jet is increased in proportion.

De préférence, le diamètre hydraulique de la buse sera égal au moins au huitième et de préférence voisin au quart de la distance séparait la buse de la trajectoire des bords de coupe des couteaux.Preferably, the hydraulic diameter of the nozzle will be equal to at least one-eighth and preferably close to a quarter of the distance separating the nozzle from the path of the cutting edges of the knives.

Par pression d'alimentation, on comprend la pression totale de l'air immédiatement en amont de la buse. La pression fournie par le moyen d'alimentation en air sera généralement supérieure du fait des pertes de charge engendrées dans les conduits jusqu'à la buse elle-même, et qu'il faudra vaincre.By supply pressure is understood the total pressure of the air immediately upstream of the nozzle. The pressure supplied by the air supply means will generally be higher due to the pressure losses generated in the conduits up to the nozzle itself, and which will have to be overcome.

Afin d'assurer un balayage sur toute la longueur du tranchant des couteaux, la buse est de préférence bidimensionnelle. Elle est alimentée à partir d'un distributeur tubulaire le long d'une génératrice duquel elle est montée. Le distributeur, quant à lui, est relié à une canalisation d'alimentation par une extrémité.In order to ensure scanning over the entire length of the cutting edge of the knives, the nozzle is preferably two-dimensional. It is supplied from a tubular distributor along a generator from which it is mounted. The distributor, meanwhile, is connected to a supply pipe by one end.

Au lieu d'une buse bidimensionnel produisant un jet d'air en forme de lame, on peut envisager la disposition, le long du distributeur, d'une pluralité de buses à contour circulaire, ou autre, produisant une rangée de jets d'air couvrant toute la longueur des couteaux.Instead of a two-dimensional nozzle producing an air jet in the form of a blade, it is possible to envisage the arrangement, along the distributor, of a plurality of nozzles with circular contour, or other, producing a row of air jets. covering the entire length of the knives.

Conformément à un second aspect de l'invention, le distributeur comporte un moyen d'uniformisation du profil de vitesse le long de la buse dans le cas où elle est bidimensionnelle, ou bien d'une buse à l'autre dans le cas d'une pluralité de buses. En effet, il est souhaitable que l'air agisse avec la même efficacité d'un bord à l'autre des couteaux.In accordance with a second aspect of the invention, the distributor comprises a means of standardizing the speed profile along the nozzle in the case where it is two-dimensional, or alternatively from one nozzle to the other in the case of a plurality of nozzles. Indeed, it is desirable that the air acts with the same efficiency from one edge to the other of the knives.

Selon un mode de réalisation, ce moyen est constitué par un répartiteur de débit disposé à l'intérieur de la chambre formée par le distributeur en amont de la buse.According to one embodiment, this means consists of a flow distributor disposed inside the chamber formed by the distributor upstream of the nozzle.

Le répartiteur de débit est constitué avantageusement par un tube cylindrique percé d'orifices calibrés, de diamètre inférieur au diamètre du tube.The flow distributor advantageously consists of a cylindrical tube pierced with calibrated orifices, of diameter smaller than the diameter of the tube.

Toutefois, si l'encombrement est compatible avec la place disponible, ce moyen peut être constitué par la chambre d'alimentation elle-même qui présentera alors un volume suffisant pour ralentir l'air provenant de la canalisation d'alimentation.However, if the space is compatible with the space available, this means can be constituted by the supply chamber itself which will then have a volume sufficient to slow the air coming from the supply pipe.

La description qui suit se rapporte à un mode de réalisation non limitatif de l'invention, elle est accompagnée des dessins sur lesquels :

  • la figure 1 est une vue en coupe transversale d'une rampe de soufflage d'air comprimé, en position sur un coupe-racines à tambour représenté de façon partielle.
  • La figure 2 est une vue en coupe longitudinale de la rampe de la figure 1, selon II II.
The description which follows relates to a nonlimiting embodiment of the invention, it is accompanied by the drawings in which:
  • Figure 1 is a cross-sectional view of a compressed air blowing ramp, in position on a drum root cutter shown partially.
  • Figure 2 is a longitudinal sectional view of the ramp of Figure 1, along II II.

Le coupe-racines 1, dont n'apparait sur la figure 1 que la partie environnant la rampe de soufflage 2, comporte un stator 3 à l'intérieur du tambour. Celui-ci est représenté de façon schématique par les couteaux 4 seulement. Le tambour tourne autour d'un axe perpendiculaire au plan de la figure, dans le sens de la flèche F. Les betteraves prises entre le tambour et le stator sont découpées en cossettes par les couteaux 4.The root cutter 1, of which appears in FIG. 1 only the part surrounding the blowing ramp 2, comprises a stator 3 inside the drum. This is shown schematically by the knives 4 only. The drum rotates around an axis perpendicular to the plane of the figure, in the direction of arrow F. The beets taken between the drum and the stator are cut into chips by the knives 4.

Ce type de coupe-racines, à tambour, est bien connu dans l'industrie sucrière, il n'est pas nécessaire de développer sa description. Il est également connu de disposer une rampe 2 de soufflage de fluide, air comprimé le plus souvent mais aussi vapeur d'eau le cas échéant, dans la partie haute de l'appareil, à l'intérieur d'une cavité ménagée dans le stator, comme cela est figuré sur le dessin. La rampe injecte le fluide sensiblement radialement, en direction de la trajectoire parcourue par les couteaux. Le jet de fluide a pour objet de décoller les éléments fibreux qui se sont déposés à cheval sur le tranchant de ces derniers.This type of root cutter, with drum, is well known in the sugar industry, it is not necessary to develop its description. It is also known to have a ramp 2 for blowing fluid, usually compressed air but also water vapor if necessary, in the upper part of the device, inside a cavity formed in the stator. , as shown in the drawing. The ramp injects the fluid substantially radially, in the direction of the path traveled by the knives. The purpose of the fluid jet is to take off the fibrous elements which are deposited astride the edge of the latter.

La rampe 2 est assujettie au stator, à l'intérieur de la cavité, par tout moyen approprié, par exemple des étriers 5.The ramp 2 is subject to the stator, inside the cavity, by any appropriate means, for example stirrups 5.

La rampe est constituée d'un distributeur tubulaire 21 de section circulaire ou autre - voir également la fière 2. Le distributeur est ouvert à une extrémité 21a, et fermé à son autre extrémité 21b par un bouchon.The ramp consists of a tubular distributor 21 of circular or other section - see also the proud 2. The distributor is open at one end 21a, and closed at its other end 21b by a plug.

La paroi du tube 21 comporte une ouverture longitudinale parallèlement à son axe, qui débouche sur une buse 22 faisant corps avec lui. Dans l'exemple représenté la buse est bidimensionnelle.The wall of the tube 21 has a longitudinal opening parallel to its axis, which opens onto a nozzle 22 integral with it. In the example shown, the nozzle is two-dimensional.

Cette buse est conformée, selon l'invention, en fonction de la pression totale d'alimentation du système régnant immédiatement en amont de ladite buse elle-même, de manière à obtenir à travers elle une détente isentropique de fluide jusqu'à la pression ambiante en sortie de buse.This nozzle is shaped, according to the invention, as a function of the total supply pressure of the system prevailing immediately upstream of said nozzle itself, so as to obtain through it an isentropic expansion of fluid up to ambient pressure at the nozzle outlet.

Dans le mode de réalisation tel qu'illustré sur les dessins, la vitesse d'éjection est supersonique, le profil correspond à un rapport de la pression amont à la pression atmosphérique supérieur au rapport de pression critique du fluide. Ce dernier rapport est, pour l'air par exemple, de 1,89.In the embodiment as illustrated in the drawings, the ejection speed is supersonic, the profile corresponds to a ratio of the upstream pressure to the atmospheric pressure greater than the critical pressure ratio of the fluid. This last ratio is, for air for example, 1.89.

La buse comporte une première partie convergente 22a, raccordée à une seconde partie divergente 22b par un col 22c. La variation de section le long des lignes d'écoulement radial est définie selon les lois bien connues de la mécanique des fluides de façon que la détente soit isentropique jusqu'à la pression atmosphérique en sortie de buse. Elle permet ainsi au fluide d'accélérer continuellement jusqu'à la section de sortie en passant par une vitesse sonique au col 22c.The nozzle has a first converging part 22a, connected to a second diverging part 22b by a neck 22c. The section variation along the radial flow lines is defined according to well-known laws of fluid mechanics so that the expansion is isentropic up to atmospheric pressure at the outlet of the nozzle. It thus allows the fluid to accelerate continuously to the outlet section passing through a sonic speed at the neck 22c.

Un tube répartiteur de débit 23, percé d'orifices calibrés 24 sur toute sa longueur, est disposé à l'intérieur du distributeur. Son diamètre est inférieur au diamètre intérieur de ce dernier, de manière à ménager une chambre annulaire d'équilibrage des pressions. Il a pour fonction d'assurer une pression d'alimentation immédiatement en amont de la buse 22, uniforme d'une extrémité à l'autre.A flow distributor tube 23, pierced with calibrated orifices 24 over its entire length, is disposed inside the distributor. Its diameter is less than the inside diameter of the latter, so as to provide an annular pressure balancing chamber. Its function is to ensure a supply pressure immediately upstream of the nozzle 22, uniform from one end to the other.

Le fluide parvient dans le distributeur par l'extrémité 21a, traverse le tube répartiteur 23, emplit la chambre annulaire d'èquilibrage, et est éjecté en direction des couteaux par la buse 22.The fluid reaches the distributor through the end 21a, passes through the distributor tube 23, fills the annular balancing chamber, and is ejected in the direction of the knives by the nozzle 22.

On a rassemblé dans un tableau les caractéristiques du jet obtenu conformément à l'invention, en comparaison avec un jet bidimensionnel obtenu selon un dispositif de l'art antérieur à même débit d'air et mêmes conditions initiales de température et de pression. Buse de l'art antérieur, convergente Buse adaptée, conforme à l'invention - Pression d'alimentation (bars) 18 18 - Température du fluide (°C) 50 50 - Débit du fluide : Q (kg/s) 1,4 1,4 - Ouverture de la buse à la sortie : D/2 (mm) 0,95 2,6 - Longueur de la buse (mm) 365 365 - Longueur du noyau potentiel : l = 4D (mm) 7,2 20,8 - Vitesse d'éjection m/s 329 618 - Quantité de mouvement : QV 460 865 - Energie disponible : QVl (joules) 3,7 19 The characteristics of the jet obtained in accordance with the invention have been collated in a table, in comparison with a two-dimensional jet obtained according to a device of the prior art at the same air flow rate and the same initial conditions of temperature and pressure. Prior art nozzle, converging Adapted nozzle, in accordance with the invention - Supply pressure (bars) 18 18 - Fluid temperature (° C) 50 50 - Fluid flow: Q (kg / s) 1.4 1.4 - Opening of the nozzle at the outlet: D / 2 (mm) 0.95 2.6 - Nozzle length (mm) 365 365 - Potential core length: l = 4D (mm) 7.2 20.8 - Ejection speed m / s 329 618 - Movement amount: QV 460 865 - Energy available: QVl (joules) 3.7 19

Il apparait que l'énergie disponible d'une buse adaptée est environ quatre fois supérieure à celle d'un système de l'art antérieur, l'efficacité de jet s'en trouve accrue d'autant.It appears that the available energy of a suitable nozzle is approximately four times that of a system of the prior art, the jet efficiency is thereby increased by the same amount.

On a effectué la même comparaison pour une pression d'alimentation de 6 bars, le débit de l'air comprimé et les conditions initiales de température et de pression étant les mêmes que précédemment. Buse de l'art antérieur, convergente Buse adaptée, conforme à l'invention - Pression d'alimentation (bars) 6 6 - Température (°C) 50 50 - Débit : Q (kg/s) 1,4 1,4 - Ouverture de la buse à la sortie : D/2 (mm) 2,85 4,2 - Longueur de la buse (mm) 365 365 - Longueur du noyau potentiel : l = 4D (mm) 22,8 33,6 - Vitesse d'éjection de l'air V (m/s) 329 521 - Quantité de mouvement : QV 460 730 - Energie disponible : QVl (joules) 11 24,8 The same comparison was made for a supply pressure of 6 bars, the flow rate of the compressed air and the initial temperature and pressure conditions being the same as above. Prior art nozzle, converging Adapted nozzle, in accordance with the invention - Supply pressure (bars) 6 6 - Temperature (° C) 50 50 - Flow: Q (kg / s) 1.4 1.4 - Opening of the nozzle at the outlet: D / 2 (mm) 2.85 4.2 - Nozzle length (mm) 365 365 - Potential core length: l = 4D (mm) 22.8 33.6 - Air ejection speed V (m / s) 329 521 - Movement amount: QV 460 730 - Energy available: QVl (joules) 11 24.8

En travaillant à cette pression d'alimentation avec le dispositif de l'invention, on constate que la longueur de noyau potentiel équivaut sensiblement à la distance séparant la buse des couteaux. En effet cette distance est de l'ordre de 40 mm dans les appareils à tambour connus. On aura de ce fait une efficacité optimale.By working at this supply pressure with the device of the invention, it can be seen that the potential core length is substantially equivalent to the distance separating the nozzle from the knives. Indeed this distance is of the order of 40 mm in known drum devices. We will therefore have optimal efficiency.

L'invention peut étre appliquée à d'autres types de coupe-racines dont le coupe-racines à plateau.The invention can be applied to other types of root cutters including the tray root cutter.

Claims (7)

  1. Use, for cleaning a root-slicer (1), of a device comprising a blower (2) for blowing compressed air disposed on the fixed part (3) of the root-slicer and having at least one nozzle (22) for ejection of compressed air in the direction of the knives (4) of the root-slicer, characterised in that
       the nozzle (22) has a convergent-divergent profile adapted to the obtaining of an isentropic expansion down to a pressure close to atmospheric pressure;
       the nozzle (22) is fed with air under such a supply pressure that the ratio of the supply pressure to the atmospheric pressure is greater than the critical pressure ratio of air so that the ejection speed of the air by the nozzle is supersonic; and
       the nozzle (22) is placed at such a distance from the trajectory of the cutting edges of the knives (4) that the potential core has a length (4D) substantially equal to this distance,
       so that the jet of air at the outlet from the noble retains substantially parallel lines of flow until reaching the cutting edges of the knives.
  2. Use according to Claim 1, characterised in that the hydraulic diameter of the nozzle (22) is at least equal to one eighth of the distance separating the nozzle from the trajectory of the cutting edges of the knives (4).
  3. Use according to Claim 1 or 2, characterised in that the blower (2) has a single bidimensional nozzle (22).
  4. Use according to Claim 1 or 2, characterised in that the blower (2) comprises a plurality of nozzles, particularly of circular cross-section, disposed in a row.
  5. Use according to Claims 1 to 3, characterised in that the nozzle (22) is fed from a tubular distributor (21) comprising a means (23) for rendering uniform the speed profile of the air along the nozzle (22).
  6. Use according to Claim 5, characterised in that the said means is constituted by a flowrate apportioner (23) disposed inside the distributor (21).
  7. Use according to Claim 6, characterised in that the flowrate apportioner is constituted by a tube (23) pierced with calibrated apertures (24), the external diameter of the said tube being smaller than the internal diameter of the tubular distributor (21).
EP89402749A 1988-10-05 1989-10-05 Use of a nozzle having a convergent-divergent profile in an ejection device for a root-cutter Expired - Lifetime EP0363282B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8813020 1988-10-05
FR8813020A FR2637295B1 (en) 1988-10-05 1988-10-05 ROOT CUTTER TRIMMING DEVICE

Publications (2)

Publication Number Publication Date
EP0363282A1 EP0363282A1 (en) 1990-04-11
EP0363282B1 true EP0363282B1 (en) 1994-04-20

Family

ID=9370701

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89402749A Expired - Lifetime EP0363282B1 (en) 1988-10-05 1989-10-05 Use of a nozzle having a convergent-divergent profile in an ejection device for a root-cutter

Country Status (4)

Country Link
EP (1) EP0363282B1 (en)
DE (1) DE68914767T2 (en)
ES (1) ES2051380T3 (en)
FR (1) FR2637295B1 (en)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR638579A (en) * 1926-12-14 1928-05-29 Alfred Maguin Soc Nouv Ets Drum Root Cutter Improvements
DE1164340B (en) * 1958-12-18 1964-02-27 Pierre Corbin & Cie Device for cleaning the knives of beet cutting machines
FR2600576B1 (en) * 1986-06-24 1988-10-21 Maguin Sa DEVICE FOR CLEANING THE KNIVES OF A ROOT CUTTER
DE8710000U1 (en) * 1987-07-22 1988-06-30 H. Putsch Gmbh & Co, 5800 Hagen, De

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Dubbel, Taschenbuch für Maschinenbau, 1974, p.322 *

Also Published As

Publication number Publication date
FR2637295A1 (en) 1990-04-06
ES2051380T3 (en) 1994-06-16
DE68914767D1 (en) 1994-05-26
DE68914767T2 (en) 1994-08-04
FR2637295B1 (en) 1990-12-14
EP0363282A1 (en) 1990-04-11

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