EP1210520B1 - Magnetically driven pump - Google Patents

Abstract

A magnetically driven pump comprises a sealing partition 48 whereof the central portion forms the rotational axis of the rotating portion of the pump, that central portion being itself supported and centered by a rotating connection piece 42 linked to or integral with drive shaft 41 of the motor 29.

Description

• un élément de pompe pourvu d'un premier rotor entraíné en forme de roue montée à rotation dans un corps associé à des tuyauteries d'aspiration et de refoulement,
• une première série d'aimants solidaires du premier rotor,
• un moteur d'entraínement doté d'un arbre de transmission sur lequel est monté un deuxième rotor d'entraínement portant une deuxième série d'aimants, les deux séries d'aimants étant disposées concentriquement pour réaliser un couplage magnétique en rotation,
• et un dispositif d'étanchéité ayant une cloison fixe s'étendant dans l'entrefer entre les deux séries d'aimants en assurant une séparation étanche entre l'élément de pompe et le moteur.

The invention relates to a magnetic drive pump comprising:

• a pump element provided with a first rotor driven in the form of a wheel rotatably mounted in a body associated with suction and discharge pipes,
• a first series of magnets secured to the first rotor,
• a drive motor provided with a transmission shaft on which is mounted a second drive rotor carrying a second series of magnets, the two sets of magnets being arranged concentrically to achieve a magnetic coupling in rotation,
• and a sealing device having a fixed partition extending in the gap between the two sets of magnets providing a sealed separation between the pump element and the motor.

The sealing wall is particularly important when the pumped liquid corrosive character, which is frequently the case in chemistry or electroplating.

For these applications, which do not support the stops, it is also important that maintenance interventions are as small as possible, or even deleted.

State of the art

• les pompes à garniture d'étanchéité ( figure 1), comportant des pièces en frottement montées en partie fixe d'une part, et en partie tournante d'autre part, la nature des matériaux en présence et la qualité de leur état de surface permettant d'obtenir une étanchéité satisfaisante ;
• les pompes à entraínement magnétique (figure 2), qui ont été conçues pour remédier aux inconvénients précités, assurant l'étanchéité, non plus par des pièces en frottement, mais par une cloison continue. De part et d'autre de cette cloison, se trouvent un rotor d'entraínement lié au moteur, et un rotor entraíné lié à la roue de la pompe. Les deux rotors portent des aimants disposés de telle sorte qu'ils assurent un couplage magnétique entre les deux rotors.

Pumps currently used can be classified into two broad categories:

• seal-filled pumps (FIG. 1), comprising friction parts mounted in fixed part on the one hand, and partly rotating part, on the other hand, the nature of the materials present and the quality of their surface state allowing to obtain a satisfactory seal;
• magnetic drive pumps (Figure 2), which were designed to overcome the aforementioned drawbacks, ensuring the seal, no longer by friction parts, but by a continuous partition. On either side of this partition, there is a drive rotor connected to the motor, and a driven rotor connected to the pump impeller. Both rotors carry magnets arranged so that they provide a magnetic coupling between the two rotors.

In FIG. 1, the motor 1 is connected to the centrifugal wheel 2 by an axis 3 and a rigid coupling device 4. The wheel 2 rotates in the pump body 5 which communicates with the suction pipe 6 and the discharge pipe. pump body at the passage of the axis 3 is ensured by the friction seal 8.

The first flaw that can be blamed on this type of pump is that the parts in This seal is subject to wear and must be replaced. periodically, resulting in maintenance shutdowns. This operation replacement is all the more delicate as the seal 8 is located in an area not very accessible.

A second potential defect concerns the sealing itself which can not be guaranteed in a perfect way, because of the small surface defects that can be meet on the rubbing support faces, and the inevitable creation of a film liquid between these surfaces.

FIG. 2 shows the motor 11, the wheel 12, the pump body 15, the suction pipes 16 and discharge 17. The sealing is here ensured by the continuous partition 18 assembled rigidly and hermetically between the body of pump 15 and the spacer 19 providing the connection with the motor flange 11. On the axis of the motor 11 is rigidly mounted the drive rotor 20 in which is inserted, for example by overmoulding, a series of magnets 21.

The driven rotor 22 integral with the wheel 12 is equipped with a series of magnets 23. The magnets 21, 23 are organized so that a north pole side drive is in face of a south pole driven side, and vice versa. We thus obtain a coupling magnetic field without mechanical contact, which must be sufficient to withstand without stalling the maximum torque absorbed by the wheel.

• à minimiser l'épaisseur de la cloison, ce qui suppose qu'on ne la sollicite pas trop sur le plan mécanique, et/ou qu'on la réalise dans un matériau présentant une bonne rigidité ;
• à réduire les jeux, ce qui suppose une bonne maítrise dimensionnelle des pièces concernées, ainsi que de leur positionnement.

Good coupling efficiency requires that the gap between the two families of magnets be as small as possible. This gap being constituted by the thickness of the partition 18 and the games present on either side of it, we see that we must look for:

• to minimize the thickness of the partition, which supposes that it is not stressed too much mechanically, and / or that it is made of a material having good rigidity;
• to reduce the games, which assumes a good dimensional control of the parts concerned, as well as their positioning.

On the first point, there may be a contradiction between the mechanical strength of the bulkhead and its chemical compatibility with the pumped liquid, with which it is contact by its internal face.

• extérieurement, une partie métallique amagnétique fournissant précision et rigidité.
• intérieurement, une partie en matériau synthétique chimiquement compatible.

A commonly used solution consists in producing this partition by juxtaposing two materials:

• externally, a non-magnetic metal part providing precision and rigidity.
• internally, a part made of chemically compatible synthetic material.

• augmentation de l'épaisseur, et donc de l'entrefer.
• présence de courants de Foucault dans la paroi métallique, ces courants étant induits par la rotation du flux des aimants. Ces courants de Foucault constituent une source d'échauffement qui peut devenir prohibitive, notamment pour de grosses unités.

This arrangement solves the problem quite well, but it has two significant disadvantages:

• increase of the thickness, and therefore of the gap.
• presence of eddy currents in the metal wall, these currents being induced by the rotation of the flux of the magnets. These eddy currents are a source of heating that can become prohibitive, especially for large units.

• d'un axe fixe 24, monté avec rigidité et précision sur la cloison 18,
• d'une bague fixe 25 solidaire de l'axe 24,
• et d'une bague tournante 26 solidaire de la roue 12.

To address the second point, namely the games, the device for positioning and guiding the rotation of the wheel 12 according to FIG. 2 consists of:

• a fixed axis 24 mounted rigidly and precisely on the partition 18,
• a fixed ring 25 integral with the axis 24,
• and a rotating ring 26 secured to the wheel 12.

• un dimensionnement aussi large que possible des surfaces en contact.
• un choix judicieux des matériaux (céramique, carbure de silicium, graphite....) et de leur état de surface.
• une utilisation judicieuse du liquide pompé pour assurer la lubrification
• une évacuation aussi bonne que possible des calories générées par le frottement.

The quality and arrangement of the rings 24, 25 are obviously essential for the holding of the pump, including:

• as large a dimensioning as possible of the surfaces in contact.
• a judicious choice of materials (ceramic, silicon carbide, graphite ....) and their surface condition.
• judicious use of the pumped liquid to ensure lubrication
• an evacuation as good as possible of the calories generated by the friction.

The examination of Figure 2 clearly shows the inherent disadvantages of mounting of the axis 24 with regard to the precision, therefore the control of the games. His positioning with respect to the motor axis (with which it must theoretically be aligned), passes by two pieces whose precision and rigidity can pose problem: the spacer 19 and especially the partition 18. We saw indeed that this last must be thin to go into the air gap and not produce too much eddy currents.

It will therefore be very difficult to obtain a good embedding of the axis 24. It has been proposed improve the mechanical strength by installing an additional bearing at the other end of the wheel, but this solution significantly increases the complexity without solving perfectly the problem.

Finally, concerning the evacuation of the calories absorbed by the axis 24, it is necessary to note that it must be done through partition 18 which lends itself badly, always because of his thinness.

Document FR-A-2311201 describes a pump with magnetic drive, in which the turbine is equipped with a magnetic core and is driven by the magnetic crown through a watertight bulkhead. The rotary turbine is supported by a fixed shaft, which is guided by a pair of bearings on the magnetic ring in connection with the motor shaft. The presence of bearings in addition to the output bearing of the motor shaft gives the whole a door to fake important, and additional embedding. The axial size of the pump is important, and the positioning of the turbine shaft does not allow to achieve perfect alignment.

Object of the invention

The purpose of this patent is to propose a solution to remedy disadvantages above, that is to say to ensure on the one hand a perfect centering of the axis of rotation of the pump impeller while unloading the watertight bulkhead this function, and on the other hand by seeking effective evacuation of calories to a cooling element.

• le premier rotor entraíné tourillonne sur une portée cylindrique dont le positionnement et le soutien sont assurés par un embout axial s'étendant dans le prolongement de l'arbre du moteur,
• un palier cylindrique femelle sert de logement concentrique à l'embout pour obtenir un soutien mécanique et un centrage précis de la cloison et du premier rotor entraíné.

The pump according to the invention is characterized in that:

• the first rotor driven rotates on a cylindrical seat whose positioning and support are provided by an axial endpiece extending in the extension of the motor shaft,
• a cylindrical female bearing serves as a concentric housing at the end to obtain mechanical support and precise centering of the partition and the first driven rotor.

The axis of the motor is advantageously prolonged by a length sufficient for him allow to get into the heart of the driven rotor. It follows that the axis of the engine encompasses the axis of the wheel which, fixed, becomes turning. This is obviously not this rotation which is sought after, but the fact of having for the first rotor driven, a rigid support and perfectly aligned with the motor axis.

According to a preferred embodiment ,. the first driven rotor has a second ring which pivots on a first ring integral with the fixed partition. The bearing integrated in the partition comprises at least one self-lubricating ring constituting a thermal bridge for the evacuation of the calories generated by the trunnion of the first rotor driven to the radiator formed by the motor shaft.

The sealing partition must not be interrupted, so it is necessary to complicate a little shape to make it bypass the extended tip, which belongs to the area external to the pumping circuit, whereas the axis 24 according to FIG. 2 of the prior art belonged to the inner zone.

In addition to the cylindrical part in the air gap, the partition will have to present a second cylindrical part coming to engage on the end of the axis motor, with the interposition of a friction sleeve, made for example in self-lubricating material.

This axis now ensures the positioning of the rotor driven with precision and the rigidity wanted, this function does not have to be ensured by the partition sealing, which can be significantly lightened. In the embodiment the simplest, this partition can be made in one piece, in a material chemically compatible with the pumped liquid.

It should be noted, however, that the part must be able to withstand the pressure of the liquid around the driven rotor, a sizeable pressure since it can be close to the discharge pressure of the pump. In cases where this pressure is high, and where there is no chemically compatible material having the sufficient mechanical strength, one can be reduced to a solution of composite partition with a mechanically strong outer shell, and a chemically compatible inner shell.

However, we are not reduced to the same constraints as with pumps corresponding to Figure 2. In fact, the resistance to internal pressure is much easier to ensure than rigidity and precision.

• soit en métal amagnétique, comme dans la solution classique, mais en adoptant une épaisseur très faible, ce qui ramène les pertes par courants de Foucault à une valeur admissible ;
• soit en matériau synthétique (polyamide ou polycarbonate chargés par exemple), ce qui impose une augmentation modérée de l'entrefer, mais supprime totalement les courants de Foucault.

The outer envelope can be much thinner, which allows to consider to achieve:

• either of non-magnetic metal, as in the conventional solution, but adopting a very low thickness, which reduces the eddy current losses to a permissible value;
• either of synthetic material (polyamide or polycarbonate loaded for example), which imposes a moderate increase in the air gap, but completely eliminates eddy currents.

Regarding the evacuation of the calories generated by the rotation, the configuration described above has an obvious advantage, as far as it is appear a thermal bridge of strong section and thin thickness between the bearing driven rotor and the motor shaft. Of course, this advantage is mitigated by the it is necessary to evacuate in addition the calories produced by the rotation of the mouthpiece additional engine shaft in its own landing, but we're out there of reaching the pumped liquid, which makes it possible to use components classic mechanicals, whose performance is excellent.

According to another characteristic of the invention, the sealing partition is shaped for chemical compatibility, while accuracy and mechanical strength are provided by an additional piece partially matching the shape of the partition, and made of a material having good mechanical strength. The room may be made of metal alloy, in particular steel stainless steel, and includes a ferrule inserted into the gap between the two series of magnets. The thickness of the ferrule is less than that of the envelope of the partition.

Brief description of the drawings

• la figure 1 représente une vue en élévation schématique d'un ensemble motopompe classique avec garniture d'étanchéité à frottement.
• la figure 2 représente une vue en élévation schématique d'un ensemble motopompe classique à entraínement magnétique.
• la figure 3 représente une vue en élévation et en coupe d'un entraínement magnétique selon l'invention.

Other advantages and features will emerge more clearly from the following description given in the appended drawings, given by way of non-limiting examples, and in which:

• Figure 1 shows a schematic elevational view of a conventional motor pump unit with friction seal.
• FIG. 2 represents a diagrammatic elevational view of a conventional motor pump unit with magnetic drive.
• Figure 3 shows an elevational view in section of a magnetic drive according to the invention.

Description of a preferred embodiment

• le moteur d'entraínement 29,
• la roue du premier rotor entraíné 32, équipée de la première série d'aimants 33 et d'un tube en acier 37,
• le deuxième rotor d'entraínement 30, équipé de la deuxième série d'aimants 31 et d'un tube en acier 38, les tubes 37 et 38 ayant pour fonction d'assurer le bouclage du flux magnétique des aimants permanents 31, 33. Les tubes 37, 38 et les aimants 31, 33 sont fixés respectivement sur le deuxième rotor 30 et sur la roue 32 par tout moyen approprié, notamment par surmoulage,
• la bague fixe 35 et la bague tournante 36 constituant le palier de rotation de la roue,
• le corps de pompe 45,
• et l'entretoise 49 assurant la liaison entre le moteur 29 et le corps de pompe 45.

This embodiment is illustrated by FIG. 3 in which we find:

• the drive motor 29,
• the wheel of the first driven rotor 32, equipped with the first series of magnets 33 and a steel tube 37,
• the second drive rotor 30, equipped with the second series of magnets 31 and a steel tube 38, the tubes 37 and 38 having the function of ensuring the looping of the magnetic flux of the permanent magnets 31, 33. tubes 37, 38 and the magnets 31, 33 are respectively fixed on the second rotor 30 and on the wheel 32 by any appropriate means, in particular by overmolding,
• the fixed ring 35 and the rotating ring 36 constituting the rotation bearing of the wheel,
• the pump body 45,
• and the spacer 49 providing the connection between the motor 29 and the pump body 45.

A tip 42 extends the motor shaft 41, which it can be an integral part, or on which it can be assembled with rigidity and precision. In addition to its function first, which is to support and center the pump impeller, the tip 42 is arranged to receive the fixing of the second drive rotor 30, this attachment being provided by any suitable mechanical means.

The sealing partition consists of a casing 48 made of material chemically compatible with the pumped liquid, and a cylindrical shell 52 made of mechanically resistant material, especially stainless steel. This ferrule makes it possible to bring the resistance to the internal pressure, insofar as the constituent material of the envelope 48 may be insufficiently resistant. The envelope 48 is extended inwards by a sheath portion, in which axially introduces the tip 42.

• extérieurement, la bague fixe 35, sur laquelle vient tourillonner la roue 32, par l'intermédiaire de sa bague solidaire 36.
• intérieurement, un fourreau en acier 53, dans lequel viendront s'emmancher les bagues autolubrifiantes 54, 54' qui s'engagent elles-mêmes sur l'embout 42.

In this central zone, the envelope 48 carries:

• externally, the fixed ring 35, on which is journalled the wheel 32, through its integral ring 36.
• internally, a steel sleeve 53, into which the self-lubricating rings 54, 54 'engage, which engage themselves on the end piece 42.

The ring 35 and the sleeve 53 may advantageously be overmoulded in the envelope of the partition 48 during the molding thereof.

The centering of the ring 35, and the rotor wheel 32, is now provided with precision by the tip 42. This results in a good concentricity of the parts 35, 53, 54, 54 ', and the clearance between the tip 42 and the sockets 54, 54' is very small.

The sealing partition is therefore completely discharged from the centering function, and no longer has to be very rigid. On the contrary, it is desirable that it presents a minimum flexibility, so as not to upset the centering imposed by the tip 42.

In addition to the centering function, the device of FIG. evacuation to the outside of the calories generated by the rotation of the rotor wheel 32, the motor shaft 41 acting as a radiator via the nozzle 42. The calories pass successively through pieces 35, 48, 53, 54 and 54 'but all these transfers involve small thicknesses and large sections, which leads to a sufficiently efficient thermal bridge.

Alternatively, it is conceivable to replace the bushings 54, 54 'by bearings with needles. This solution will be particularly interesting if a large resistance and a long life are sought. However, she will be less effective under the thermal bridge aspect. Mixed solutions combining sockets with friction and needle bearings are also possible.

Claims (8)

1. A magnetically driven pump comprising:

   a pump element fitted with a first driven rotor (32) in the form of a wheel mounted to rotate in a body (45) connected to the suction and discharge piping,

   a first series of magnets (33) integral with the first rotor (32),

   a driving motor (29) fitted with a drive shaft (41) on which is mounted a second driving rotor (30) carrying a second series of magnets (31 ), both series of magnets (33, 31) being laid out concentrically to provide rotation magnetic coupling,

   a sealing device having a fixed partition (48) extending in the gap between both series of magnets (33, 31) while providing tight separation between the pump element and the motor (29),

   and a connection piece (42) of the shaft (41) on which is mounted the second driving rotor (30),

   characterized in that the rotating connection piece (42) linked to the shaft (41) is continued axially by a sufficient length to insert it inside a female cylindrical bearing in the core of the first driven rotor (32) to provide mechanical support and accurate centering of the partition (48) and of the first driven rotor (32).
2. A pump according to claim 1, characterized in that the first driven rotor (32) comprises a second ring (36) which rotates on a first ring (35) integral with the fixed partition (48).
3. A pump according to claim 1 or 2, characterized in that the bearing integral with the partition (48) comprises at least one self-lubricating ring (54, 54') forming a thermal bridge for the evacuation of the calories generated by the rotation of the first driven rotor (32) towards the heater formed by the motor shaft (41 ).
4. A pump according to claim 1 or 2, characterized in that the bearing comprises the needle bearings resting on the connection piece (42).
5. A pump according to the claim 1, characterized in that the partition (48) is a monobloc part in a material that is chemically compatible with the pumped liquid, and possesses sufficient mechanical stability to sustain notably the pressure of the pumped liquid.
6. A pump according to claim 1, characterized in that the partition (48) is formed for better chemical compatibility, while precision and mechanical stability are provided by an additional part matching partially the shape of the partition (48) and made of a material with good mechanical stability.
7. A pump according to claim 6, characterized in that the additional part is made of metal alloy, notably stainless steel, and comprises a ferrule (52) engaging into the gap provided between both series of magnets (31, 33).
8. A pump according to claim 7, characterized in that the thickness of the ferrule (52) is smaller than that of the envelope of the partition (48).

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