EP0291780A1 - Pump with a magnetic drive - Google Patents

Abstract

In the pump according to the invention which in particular comprises a body (20) having two parts (22, 36) forming a tight assembly, two apertures (32, 34) for the admission and outlet of a liquid to be pumped and means of connection (46, 48) to allow pipes (42, 44) to be connected in the vicinity of these apertures, and a rotary device (2), for example a screw, fixed inside this body, to draw the liquid in through one aperture and deliver it through the other, the two assembled parts of the body and the rotating device are made of a ceramic, composed mainly of aluminium (Al2O3), zirconium oxide (ZrO2), silicon nitride (Si3N4) or silicon carbide (SiC). Such a pump may be made without any joint and will convey virtually any type of liquid at either high or low temperature. <IMAGE>

Description

The subject of the present invention is a magnetic drive pump which comprises a body comprising two parts assembled in a sealed manner, two openings for the inlet and outlet of a liquid to be pumped and connection means for enabling pipes to be connected at the locations of these openings; a rotary device mounted inside this body for sucking the liquid through one of the openings and discharging it through the other; at least one permanent motor magnet placed outside the body; a motor for driving this magnet in rotation about an axis; at least one permanent follower magnet linked to the rotary device for transmitting to the latter the rotational movement of the motor magnet; and fixing means for making the body integral with a fixed part of the engine.

Pumps of this kind, in which the rotary device can be a propeller, a disc with fins on one of its faces or a gear, are currently used in many fields such as chemistry, medicine, mechanics (for example for polishing with a liquid loaded with abrasive particles), heating and refrigeration or the food industry. They also have more specific applications such as, for example, the supply of fresh or sea water to an aquarium.

In a conventional pump, direct drive, it is necessary to provide a mechanical seal to seal the pump body at the point where it is crossed by the motor shaft or the speed reducer which drives the device rotating and, due to the rotation of this shaft, the seal wears out, which inevitably causes liquid leaks which can damage the components of the motor and / or the gearbox if there is one. On the other hand, there is necessarily friction between the shaft and the seal, which leads to a drop in pump efficiency.

With magnetic drive these problems are solved. In addition, this drive acts as a clutch and avoids overloads which could damage the engine.

Magnetic drive pumps therefore have great advantages over direct drive pumps, but we can still blame them for at least two things.

The first is that, given the way they are currently made, they would not be waterproof if we did not provide at least one static joint between the parts of the body which are assembled and if we did not replace this joined more or less frequently.

The second is that the same pump can generally only be used to transport certain liquids and not others and this mainly because of the materials which were used to manufacture the body of this pump and the elements which it contains. For example, a pump specially designed to transfer or circulate very corrosive liquids or abrasive liquids may very well not be suitable for more harmless products such as food or pharmaceutical products.

The object of the invention is to provide a magnetic drive pump which does not require any seal and therefore practically no maintenance.

Another object of the invention is to provide a pump which can be used to pump a wide variety of liquids, both at high and at low temperatures, which is often not the case for pumps of the same kind which currently exist.

These aims are achieved thanks to the fact that in the pump according to the invention the assembled parts of the body as well as the rotary device are each made of a ceramic formed mainly of one of the following compounds: alumina (Al₂O₃), zirconium oxide ( ZrO₂), silicon nitride (Si₃N₄) and silicon carbide (SiC).

Indeed, it has been discovered that by using such a ceramic to manufacture the assembled parts of the pump body, it was possible, by correct machining, to make them present perfectly polished contact surfaces and that it was then sufficient to press these surfaces one against the other so that they adhere to each other and to obtain a completely sealed junction between these parts of the body.

In addition, since the ceramics which are based on these compounds are very resistant to wear and the rotary device is also made up of one of them simple holes or simple raised parts inside the body can often serve as bearings for this device. However, if this is not the case or if this makes it possible to improve the qualities of the pump (efficiency, operating speed, longevity, etc.) it is possible to use bearings, in particular ball bearings which are also made entirely in one ceramic which is one of those just indicated. Such bearings already exist commercially.

Furthermore, as will be seen below, it can be arranged so that the liquid to be pumped is only in contact with ceramic parts and, as this kind of material is practically inert to all chemical agents, in in this case it is not only a very large number of liquids that the pump according to the invention makes it possible to transfer, but almost all of them.

As is known, there are currently several techniques for manufacturing ceramic parts. Those which are most suitable for obtaining the elements of a pump according to the invention are firstly the pressing of granules produced from a very pure powder of the base compound with the addition of organic binders and optionally other compounds (oxides, metals, etc.) and sintering, with machining before or after this last operation, and on the other hand injection. In one case as in the other one is obviously obliged to proceed in addition to a rectification to arrive at the perfectly polished contact surfaces which have been mentioned previously.

On the other hand, if one chooses to use an alumina ceramic the best is to opt for a white ceramic which contains at least 96% by weight of alumina, especially if one calls upon the technique sintering because this operation is then easier than with ceramics whose alumina concentration is lower and especially if the pump must convey products such as pharmaceutical liquids which must in no way lose their purity.

Among the white alumina ceramics which currently exist and which can be used, mention may be made, for example, of those which have the following compositions:
Al₂O₃: 96%, SiO₂: 3%, other oxides: 1%
Al₂O₃: 99.4%, MgO: 0.3%, other oxides: 0.3%
Al₂O₃: 99.9%, impurities: 0.1%

Naturally, the third solution is the one that is best for the products we just talked about.

That said, it is quite clear that other alumina ceramics can also be used. This is the case for example of red, green or blue ceramics which respectively contain chromium (Cr₂O₃), nickel (Ni nickelO₃) and cobalt (Co₃O₄) oxides and black ceramics which contain several metallic oxides other than that of aluminum, in varying proportions.

Finally, among the ceramics which are not based on alumina and which may also be suitable for producing the parts of a pump according to the invention, there may be mentioned, by way of example, those which have the following compositions, with percentages by weight:
ZrO₂: approximately 94.5% Y₂O₃, Al₂O₃, SiO₂, Fe₂O₃: approximately 5.5%
Si₃N₄: around 95% SiO₂, Al₂O₃, AlN, Y₂O₃: around 5%
SiC: about 98% Al, B, SiO₂: about 2%

• - la figure 1 est une vue en coupe axiale, partielle, ce cette forme d'exécution;
• - les figures 2 et 3 sont des vues en coupe respectivement selon les plans II-II et III-III de la figure 1;
• - les figures 4, 5 et 6 sont des vues en coupe axiale et partielles des trois variantes en question; et
• - la figure 7 est une vue en plan de l'arrière de l'hélice montrée à la figure 6.

Other characteristics and advantages of the invention will appear on reading the following description of a particularly advantageous embodiment and of three possible variants thereof. This description refers to the attached drawing in which:

• - Figure 1 is an axial sectional view, partial, this embodiment;
• - Figures 2 and 3 are sectional views respectively along the planes II-II and III-III of Figure 1;
• - Figures 4, 5 and 6 are views in axial and partial section of the three variants in question; and
• FIG. 7 is a plan view of the rear of the propeller shown in FIG. 6.

The pump which has been chosen as an example to illustrate the invention and which can be seen in FIGS. 1 to 3 is a pump whose rotary device is a propeller 2, for example made of alumina ceramic, which the 'is also commonly called a turbine and which could have been produced by using one or the other of the two manufacturing techniques which we discussed above.

As shown in FIG. 1, this propeller 2 has a bell-shaped shaft 4 which has a hollow cylindrical part 6, surrounded at one of its ends by blades 8, and which is extended on the other side by a part full frustoconical 10 and two successive cylindrical parts 12 and 14, also full, of increasingly smaller diameter, the smallest of which 14 is intended to constitute a pivot for the propeller and the largest 12 a range for this pivot.

If we now refer to Figure 3 we see that the blades 8 are four in number, which is of course only a possibility, that they are both short, straight and fairly thick, their ends are rounded so as to form portions of the same circle centered on the axis of the shaft 4 and that they are oriented approximately tangentially with respect to another circle with the same center as the previous one, which means that the pump we are describing is not reversible.

On the other hand, returning to Figure 1 we see that the cylindrical part 6 has inside a recess 16 which serves as a housing for a permanent magnet also cylindrical 18, for example of ferrite or samarium-cobalt, whose l thickness is equal to the depth of this recess and which is fixed to the propeller by gluing.

Naturally, this cylindrical magnet 18 could very well be replaced by several small magnets in the form of rings and placed side by side.

One could also provide a thinner magnet and hold it in place not by sticking it but by simply squeezing it between the bottom of the recess and a deformable plastic ring inserted therein.

If we continue to look at Figure 1 we see that the propeller 4 that we have just described is placed in a body 20 which includes a tank 22 externally cylindrical and fairly thick, which could also be produced made of alumina ceramic, preferably by the pressing and sintering method, and which has both a very flat and perfectly polished edge 24, a bottom 26 with inside a central blind hole 28, in which is engaged the pivot 14 of the propeller, and a wall 30 pierced with two frustoconical holes 32 and 34 which have a decreasing diameter when passing from the inside to the outside of the tank and a turn also perfectly polished and which constitute two openings respectively for the entry and exit of a liquid to be pumped.

As shown in the drawing, the wall 30 has an internal surface which is composed of a cylindrical part located on the edge side 24 and a slightly less frustoconical part which is located on the bottom side 26 and which corresponds to that 10 of the propeller shaft but it is quite clear that this surface could also be completely cylindrical.

Likewise, it is not compulsory for the openings 32 and 34 to be located in the same diametral plane and opposite one another as in the figure.

On the other hand, for the pump to function properly, it is necessary, on the one hand, that the diameter of the cylindrical part of the internal surface of the wall is only very slightly greater than that of the circle circumscribed by the blades of the propeller and, on the other hand, that the outlet opening 34 is close enough to the edge 24 to be in front of these blades and that the opening 32 is more distant so as to open into the free space and sufficiently large that the propeller shaft leaves between it and the wall of the tank. This inlet opening can be located, for example, approximately halfway up the tank.

That said, the body 20 also includes a round cover 36, substantially the same diameter as the tank 22 and which closes the latter completely, simply by being pressed against its edge 24 by assembly means which will be described later.

This cover 36, which could have been manufactured using the same technique and preferably the same ceramic as for the tank, has the shape of an inverted cap with a wide and flat edge 38 whose thickness is about the same than that of the upper part of the wall of the tank and a cylindrical cap 40 much thinner than this edge 38, which serves as a hub for the propeller 2. It is in fact seen that the hollow cylindrical part 6 of the latter completely surrounds this cap.

Naturally, for the closure of the tank to be truly sealed, it was also necessary to polish the inner surface of the edge 38 or at least the periphery thereof so that this edge can adhere perfectly to that of the tank.

Before specifying by what means pipes can be connected to the body 20, there is one more thing to say. It is that, for a reason which will be indicated later, it is advantageous to produce the tank 22, the cover 36 and the propeller 2 so that the latter has a fairly large clearance and as well axial than radial.

In the embodiment that we are describing, the means which make it possible to connect pipes 42 and 44 to the pump consist of two identical and entirely removable devices 46 and 48.

Each of these connection devices consists of a tube 50, respectively 52, also made of ceramic, which has at one of its ends a collar 54, respectively 56, the surface of which has been polished and the frustoconical shape of which corresponds exactly to that of the opening 32, respectively 34, of the wall of the tank 22, in which this collar is engaged and of a mechanical system, placed outside the tank, to exert a substantially axial traction on this tube .

As can be seen by looking at Figures 1 and 2, this system consists of three elements.

The first element is a plastic plate, for example round, 62, respectively 64, which has a notch 66 and which is placed around the tube, between its frustoconical collar 54, respectively 56, and another collar 68, respectively 70, for example cylindrical, which it has in its central part and whose diameter is obviously less than the minimum diameter of the opening 32, respectively 34, of the wall of the tank.

The other two elements are screws 72, respectively 74, also made of plastic, which pass through two tapped holes 76, respectively 78, of the plate, located on either side of the tube and whose truncated points come to bear against the wall 28 when the tube is in place.

Of course, when the connection devices are mounted, these screws must continue to be tightened after the plate has come up against the collars 68 and 70 to force the surfaces of the other collars 54 and 56 of the tubes to adhere perfectly to the towers holes 32 and 34. Otherwise, the body 2 of the pump would not be waterproof.

Furthermore, still with regard to these connection devices, it should also be noted that the frustoconical collars 54 and 56 of the tubes are also provided so as not to exceed the internal surface of the tank. For the output device 48 this is a necessity.

We will now talk about the means of assembly of the tank 22 and the cover 36 to which we alluded previously.

As shown in Figures 1 and 3 these means comprise two circular metal flanges 80 and 82, of diameter greater than that of the body 20, which are placed at each end thereof and which are connected together by several bolts 84 which cross and which carry at their ends tightening nuts 86.

In Figure 3 these bolts are three in number but there could also be only two, diametrically opposite, or on the contrary there may be more, for example four or five regularly distributed around the body.

In addition, if we look at Figure 1, we see that the facing faces of the two flanges 80 and 82 have two respective shallow recesses 88 and 90, the same diameter as the body and in which are engaged the bottom of the tank 22 and cover 36. This makes it possible to easily ensure perfect coaxiality of these elements when the pump is mounted and to prevent them from then shifting with respect to one another when this pump is operating.

Finally, still according to FIG. 1, it can be seen that, in this embodiment, the means for assembling the tank and the cover are also those which make it possible to mount the body in front of a unidirectional electric motor. 94.

To simplify, this part is simply shown in a part of a fixed element 96 of this motor, for example of a part of a casing or of a chassis, to which the flange 80 is fixed, by suitable means not visible which can be screws, and its output shaft 98 which is surrounded at its end by a permanent magnet cylindrical motor 100, substantially the same length as the follower magnet 18 carried by the propeller and which passes through a central hole 92 of this flange to penetrate inside the cap cylindrical 40 of the cover 36, the axis of this shaft 98 of course coinciding with that of the body 20.

Thus, when the motor turns in the direction of arrow F, the motor magnet 100 can, thanks to the relative thinness of the cap 40 of the cover, easily drive the follower magnet 18 of the propeller in the same direction.

On the other hand, since, as already indicated, the helic has a certain play both radial and axial inside the body, as soon as the motor starts to rotate it positions itself automatically so that its axis of rotation coincides exactly with that of the shaft 98 and that the median planes, perpendicular to these axes, of the magnets do the same and if the pump is carried out correctly it is possible that there is no longer then no contact between the propeller and the body and that the latter turns by floating in the pumped liquid.

In this case there is friction between the propeller and the body only at the time of starting and stopping the pump, which means that its performance is very good and that it only wears very slowly.

In addition to this, the pump just described has the following advantages:
- the parts that make it up are simple and easy to manufacture;
- As the connection tubes 46 and 48 are held in place mechanically there is no bonding or brazing operation to be carried out to fix them to the tank;
- it is easy to dismantle it completely, for example for cleaning or sterilization; and
- it is also easy to change the motor or to add a speed reducer to it.

One can however criticize him for one thing: it is that its field of application can be somewhat restricted by the fact that the follower magnet 18 is in contact with the liquid which is pumped.

To avoid this, it is enough to modify it slightly to arrive at the variant of FIG. 4.

The only difference between the embodiment of Figures 1 to 3 and this variant is that, in the latter, the recess 16 of the hollow cylindrical part 6 of the propeller 2 is deeper or that the permanent follower magnet 18 is thinner and that this magnet is entirely covered by a tube also made of ceramic 102 which is glued to it and which fills the recess in question.

Thus, the pumped liquid can only be in contact with ceramic, which means that it can be practically any.

The two other variants which are shown in FIGS. 5 to 7 are also very close to the embodiment of FIGS. 1 to 3.

In both cases the tank 22, the connection devices 46 and 48, the flange 82 which is not fixed to the motor 94, the external shape of the shaft 4 of the propeller 2 and the blades 8 remain unchanged.

In both cases also the cover 36 is no longer constituted by a disc of constant thickness and relatively small compared to that of the tank and the flange 80 in the recess 88 of which the cover is engaged has instead become more thick so that the shaft 98 of the motor 94 which has become much shorter and much larger does not leave the central hole 92 that this flange continues to have and that the end of this shaft is on the contrary at a certain distance of the cover.

In fact, in the variant of FIG. 5, the shaft 98 must be able to carry at its end a motor magnet in the form of a disc which continues to bear the mark 100 and which is glued inside a recess 104 in which it is only partially housed.

On the other hand, we see that in this same variant the cylindrical part 6 of the propeller is no longer hollow and that this propeller also has, on its face opposite the cover, a central recess 106 in which is stuck a permanent follower magnet also in the form of a disc, of diameter substantially equal to that of the motor magnet 100 and which is always designated by the reference 18.

In the variant of FIG. 6, this face of the propeller opposite the cover has, on the contrary, several small recesses 108, for example six (see FIG. 7), distributed regularly in a circle centered on the axis of this propeller and in which small follower magnets 18 are housed and as many small motor magnets 100 as the motor shaft 98 carries at its end.

Naturally, the invention is not limited to the embodiment and to the variants which have just been described.

One could imagine for example to make the liquid arrive by the bottom of the tank and provide inside of it an additional alumina ceramic plate, fixed, with a central hole for the pivot of the propeller and d other holes for the passage of the liquid, which would form a double bottom.

Without doing this we could also reverse the position of the tank and the lid. In this case it would be the latter which would be pierced with a blind hole for the pivot of the propeller and the bottom of the tank which would be thin or which would have a cylindrical recess in which the motor magnet would be located.

Another possibility would be to remove the flanges, to make the tank with a flange around its opening, to provide holes in this flange and in the cover, to assemble the latter and the tank by bolts and nuts and to use these same bolts and other nuts or to use other means to mount the body to the front of the engine.

Furthermore, it could be arranged, by slightly modifying the shape of the wall of the tank, so that the arrangement of the outlet tube 52 relative to the latter is not radial as in the embodiment which has been described. but tangential or between the two, which could facilitate the penetration of the liquid in this tube.

We could also replace the connection devices 46 and 48 with simple external nozzles made in one piece with the tank or design the pump differently so that the motor magnet is around the follower magnet, like this is already done in some existing magnetic drive pumps, or modify the shape of the propeller to make the pump reversible.

Finally, as has already been understood, the invention can also be applied to disc or gear pumps.

Claims (16)

1. Magnetic drive pump comprising a body (20) comprising two parts (22, 36) tightly assembled, two openings (32, 34) for the entry and exit of a liquid to be pumped and connection means (46, 48) to allow connection of pipes (42, 44) at the locations of these openings; a rotary device (2) mounted inside the body for sucking the liquid through one of the openings and discharging it through the other; at least one permanent motor magnet (100) placed outside the body; a motor (94) for driving this motor magnet in rotation about an axis; at least one permanent follower magnet (18) linked to the rotary device for transmitting to the latter the rotational movement of the motor magnet; and fixing means (80, 86) for making the body integral with a fixed part (96) of the engine, characterized in that the assembled parts (22, 36) of the body (20) as well as the rotary device ( 2) are each made of a ceramic formed mainly from one of the following compounds: alumina (Al₂O₃), zirconium oxide (ZrO₂), silicon nitride (Si₃N₄) and silicon carbide (SiC). 2. Pump according to claim 1, characterized in that said ceramic contains at least 96% by weight of alumina. 3. Pump according to claim 1, characterized in that said ceramic is based on alumina and also contains another metal oxide. 4. Pump according to claim 1, characterized in that said ceramic is based on alumina also contains several other metal oxides. 5. Pump according to any one of the preceding claims, characterized in that the two parts (22, 36) of the body (20) have respective contact surfaces which are polished and that these parts are assembled in a sealed manner simply by pressing these surfaces together. 6. Pump according to claim 5, characterized in that the rotary device is a propeller (2) which comprises a shaft (4), whose follower magnet (18) is integral, and several blades (8) arranged around this tree. 7. Pump according to claim 6, characterized in that the two assembled parts of the body (20) are constituted respectively by a tank (22) which has a bottom (26), a wall (22) and an edge (24) and by a cover (36) which closes this tank by being only pressed against its edge. 8. Pump according to claim 7, characterized in that the tank (22) and the cover (36) are assembled by means of two flanges (80, 82) which bear respectively on this cover and on the bottom of this tank and which are interconnected by bolts (86) and clamping nuts (86) arranged around the body (20). 9. Pump according to claim 8, characterized in that the flanges (80, 82) have two respective recesses (88, 90) in which the cover (36) and the bottom (26) of the tank (22) are engaged , to allow positioning this cover and this tank relative to each other. 10. Pump according to claim 8 or 9, characterized in that one (80) of the flanges (80, 82) is fixed to the fixed part (96) of the motor (94) so that these flanges also constitute said means fastening with the bolts (84) and the nuts (86) which connect them. 11. Pump according to any one of claims 7 to 10, characterized in that the bottom (26) of the tank (22) has inside a central blind hole (28) in which is engaged a pivot (14 ) that the shaft (4) of the propeller (2) has at one of its ends and that the blades (8) of this propeller are at the other end of this shaft. 12. Pump according to claim 11, characterized in that the shaft (4) of the propeller (2) has opposite the pivot (14) a hollow cylindrical part (6) with inside a recess (16) in which is housed the follower magnet (18), also cylindrical, that the cover (36) also has, in its center, a hollow cylindrical part (40) which penetrates inside that of the propeller shaft to serve as a hub for the latter, and that the motor magnet (100) also cylindrical, is placed coaxially inside this hollow part of the cover. 13. Pump according to claim 12, characterized in that the follower magnet (18) is entirely covered by a tube (102) also made of a ceramic based on alumina, zirconium oxide, silicon nitride or silicon carbide. 14. Pump according to any one of the preceding claims, characterized in that the openings (32, 34) of the body (20) are surrounded by respective bearing surfaces oriented towards the inside thereof and that the connection means comprise, for each of the pipes, a tube (50, respectively 52) also made of a ceramic based on alumina, zirconium oxide, silicon nitride or silicon carbide, which presents to the one of its ends a bearing surface oriented towards the outside of the body and complementary to that of the opening in which this end is engaged, and a mechanical system (62, 72, respectively 64, 74) placed outside of the body to exert a substantially axial tensile force on this tube and maintain its bearing surface applied against that of said opening. 15. Pump according to claim 14, characterized in that the bearing surfaces which surround the openings (32, 34) of the body (20) and the bearing surfaces of the tubes (50, 52) are frustoconical. 16. Pump according to claim 14 or 15, characterized in that said mechanical system comprises a plastic plate (62, respectively 64) which is removably placed around the tube (50, respectively 52) with which this system is associated and which is pierced by two tapped holes (76, respectively 78) located on either side of this tube and two screws also made of plastic (72, respectively 74) which pass through the holes in the plate and which, taking support against the body (20) by their tip, force this plate to come to press against a collar (68, respectively 70) that also has said tube.

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