GB2263944A

GB2263944A - Pump having magnetic coupling.

Info

Publication number: GB2263944A
Application number: GB9302328A
Authority: GB
Inventors: Jurgen Ahlfeldt
Original assignee: QVF GLASTECH GmbH
Current assignee: QVF GLASTECH GmbH
Priority date: 1992-02-05
Filing date: 1993-02-05
Publication date: 1993-08-11
Also published as: DE9201412U1; FR2687740A1; GB9302328D0

Abstract

In a magnetically coupled pump more particularly for conveying aggressive and environmentally harmful media, the pump having a rotor (3) which is part of an inner rotor (10) around which an outer rotor (18) extends, magnetic parts (22a, 22b) which are disposed in a common transverse plane being disposed on the inner rotor 10 and outer rotor 18, the inner rotor 10 being sealed by a separating can 13 whose peripheral wall extends in the annular gap between the inner rotor 10 and the outer rotor 18. A supporting or casing wall 25 extends around the outer rotor. One or both of those facing zones of the outer rotor 18 and support wall 25 and/or, of the outer rotor 18 and separating can 13 which may contact one another in the event of a defect are made of a spark-proof material. Examples of such materials described include bronze, beryllium bronze, copper or brass. <IMAGE>

Description

A MAGNETICALLY COUPLED PUMP MORE PARTICULARLY FOR CONVEYING AGGRESSIVE AND ENVIRONMENTALLY HARMFUL MEDIA The invention relates to a magnetically coupled pump as set out in the preamble of claim 1.

The main function of such a pump is to provide a sealing-tight enclosure of the pump delivery chamber to prevent the egress of the medium being conveyed, such medium usually being one which is aggressive and hostile to the environment. The magnetic coupling transmits the drive through the encapsulation, the same being embodied by a separating can whose hollow cylindrical peripheral wall extends in the gap between the magnet elements, the same being disposed on an inner rotor and on an outer rotor.

In a conventional pump of this kind the sealing means described are at risk when the bearing carrying the outer rotor wears and the clearance for the outer rotor becomes so large that the magnet elements or parts disposed on its inner generated surface contact the separating can, so that the same splits open and the medium being conveyed can issue from the encapsulation or enclosure. To obviate this disadvantage magnetically coupled pumps have been devised wherein the free gap between the outer rotor and the can is greater than a gap between the outer rotor and a casing therearound. In such a construction the outer rotor cannot contact the can in the event of damage to the bearing since the outer rotor is bounded radially on the outside by the casing wall and so cannot wobble in a manner likely to cause damage.

Another problem with magnetically coupled pumps is that many liquids and/or gases which have to be conveyed are not only aggressive and hostile to the environment but also, or merely, fire and explosion hazards. There is therefore a double fire and explosion risk with magnetically coupled pumps, first because flammable gases or liquids may enter the casing and second because in the case of a disturbance hereinbefore described flammable medium may issue from the pump chamber.

When the outer rotor contacts the can or casing, sparking occurs as a result of friction or striking or grazing and may ignite a flammable medium.

It is the object of the invention so to devise a pump of the kind described that ignition in the pump casing is obviated.

This problem is solved by the features of claim 1.

The sub-claims disclose advantageous developments of the invention.

In the pump according to the invention, one or both of those surface zones between, on the one hand, the outer rotor and/or, on the other hand, the casing and/or the inner rotor, which may contact one another are made of a spark-proof material, so that if in the event of damage, for example, of bearing damage previously described, the outer rotor contacts the casing or inner rotor while in movement, no sparking occurs or sparking or partial heating is reduced considerably. This protection against explosion applies not only to the case in which a flammable medium passes from the pump chamber to the casing chamber but also to the case in which a flammable medium enters the casing chamber from outside.

Advantageously, therefore, in a development of the invention a shaft seal or secondary seal sealing the drive shaft is provided and prevents any medium from entering the pump casing from outside. It is preferred to use for this purpose a shaft seal of the kind providing two-way sealing tightness and thus also preventing any passage of medium from the inside to the outside, for example, in the event of the separating can leaking.

Other sub-claims describe other advantageous features which help to solve the problem and which lead to a simple construction which is economical to produce and which can be assembled and demounted readily and rapidly.

Materials which produce little friction when struck by a moving object are suitable as spark-proof material, such materials preferably being bronze, preferably beryllium bronze, or copper or brass.

Advantageously, these materials on the two contacting parts are paired with different material or materials.

Soft cast iron or steel is a suitable pairing material, preferably for the casing.

Shaft seals are known as secondary sealing means but their function is to prevent the passage of a medium from the inside to the outside.

The invention and other advantages it provides will be described in greater detail hereinafter with reference to an embodiment and to a drawing.

The drawing is a view in axial section of a magnetically coupled pump according to the invention, more particularly for liquids.

The main parts of the pump are a casing 1 which comprises two parts la, ib disposed in axially contiguous relationship. Disposed in the part la is a pump chamber 2 in which a pump rotor 3 is rotatably mounted on a coaxial pump shaft 4. The part la has an axial medium inlet port 5 and a radial or tangential outlet port 6 in the plane of rotation of the pump rotor 3 and the same has an axial intake duct 7 into which the port 5 merges and which in turn merges radially into a number of delivery channels 8 or into a delivery slot. The casing part B is flanged on to that side of the casing part la which is remote from the inlet port 5. The casing part Ib is a dished casing associated by way of its free dished edge 9 with the casing part la.A separating can 13 is secured with the interposition of disc-like bearing parts 11, 12 on the pump shaft 4 which extends from the rotor 3 as far as and into the casing part lb; the can 13 extends dish-fashion around the pump shaft end remote from the rotor 3 and the dish edge 14 of the can 13 is sealed on an annular member 15 disposed between the parts la and lb. If required, the can 13 forms a flywheel-like unit with attachments.

The shaft 4, rotor 3, bearing parts 11, 12 and can 13 form a single component, viz. an inner rotor 10, rotatably mounted in the casing 1. This component or unit can be combined from two or three components and be in one or two or three or more parts. Its length is such that the can 13 extends over much of its length into the dished casing part lb. That end wall 16 of the part 1b which is remote from the casing part la has mounted in it and extending through it a drive shaft 17 on whose inner end an outer rotor 18 is secured, the hollow cylindrical wall 19 of the rotor 18 extending around the can 13. On or near the free edge magnetic parts 22a are distributed around the periphery of the inner generated surface of the outer rotor 18 and cooperate with magnetic parts 22b which are of opposite polarity and disposed on or recessed in the periphery of the bearing member 11 disposed in the same transverse plane. The axial spacing between the magnet parts 22a, 22b is such that gaps S1, S2 are left between them and the can 13 disposed between them.

A hollow cylindrical ring 24 made of a spark-proof material is secured to the outer generated surface 23 of the hollow cylindrical wall 19 of the outer rotor 18 near or contiguous with the free edge of the rotor 18; the ring 24 can be so embedded in the wall 19 as to be flush with or placed on the surface 23. Between the same and the radially opposite inner generated surface of the casing wall 25, which is hollow cylindrical here, of the casing part lb there is a gap S3 smaller than the gap S1 or S2.

Preferably, an inner shoulder 26 of the wall 25 is disposed opposite the ring 24 so that the remainder of the casing wall 25 is at a greater radial distance from the outer rotor 18.

In the embodiment described the drive shaft 17 is mounted in a bearing bush 27 which is screwed to the end wall 16 and extends through an aperture therein.

Drive shaft bearing 28 has two axially spaced apart rolling bearings 29 between which a shaft seal 31 is disposed as secondary seal. The seal 31 seals the casing 1 internally and externally. To this end, two ring seals 32a, 32b, preferably radial or lip ring seals, are provided and are separated from one another by a space effective as a grease chamber 33 or grease lock. Preferably, the two ring seals 32a, 32b together with an inner ring 34 and outer ring 35 receiving them form a sealing component in the sense of a unit. The rings 34, 35 are sealed off from the bearing member 27 and shaft 24 preferably by means of radial ring seals, which can be 0-rings 34a, 35a received in annular grooves preferably in the outer generated surface of the outer ring 35 and in the inner generated surface of the inner ring.The space 36 in the casing part lb is therefore sealed by means of the shaft seal 31 and by means of the can 13.

A ring seal 36 co-operating with the drive shaft 4 can be disposed in a bearing cap piece 27a to protect the outer bearing 29. The ring seal 36 can be a conventional radial ring seal.

If because of damage to the pump, for example, in the event of wear of the bearing 28, the driven outer rotor 18 suffers from radial play, the relatively narrow gap S3 ensures that the magnet parts 22a cannot contact the can 13 and damage it or split it open, an event which would destroy the enclosure of the pump chamber 2 and allow the medium being conveyed to enter the space 36. In the event of such damage there is no risk of ignition in the casing 1 because the ring 24 is made of a spark-proof material and so no sparking occurs when the outer rotor 18 grazes the casing wall 25. An advantageous spark-proofing of the can against grazing is therefore provided. Also, the shaft seal 31 prevents the medium being conveyed from issuing from the space 36 to atmosphere.

The spark-proof protection against grazing is operative when the pump is disposed in a room where there is a risk of an explosion and a fault in the shaft seal 31 would allow flammable medium (gas, liquid) to enter the space 36. If a damage of the kind hereinbefore described, viz. damage to the bearing, also occurs, no ignition occurs in the space 36 because no sparking occurs in this case either, should the outer rotor 18 graze the casing wall 25.

The pump 1 hereinbefore described is lined with plastics in its pump chamber 2 and in chambers open there towards in order to protect the corresponding chamber walls against corrosion.

Claims

CLAIMS:

1. A magnetically coupled pump more particularly for conveying aggressive and environmentally harmful media, the pump having a rotor which is part of a rotating unit comprising the rotor, a pump shaft and an inner rotor, an outer rotor extending around the inner rotor, magnetic parts which are disposed in a common transverse plane being disposed on the inner rotor and outer rotor, the inner rotor being sealed by a separating can whose peripheral wall extends in the annular gap between the inner rotor and the outer rotor, a supporting or casing wall extending around the outer rotor, characterised in that, adjacent surface zones of the outer rotor and support wall and/or, adjacent surface zones, of the outer rotor and separating can which may contact one another in the event of a defect are made of a spark-proof material.

2. A pump according to claim 1, characterised in that the spark-proof material is disposed on the outside generated surface of the outer rotor, preferably adjacent or near the free edge thereof.

3. A pump according to one or more of the previous claims, characterised in that the spark-proof material is disposed near the transverse plane of the magnetic parts.

4. A pump according to one or more of the previous claims, characterised in that the spark-proof material is embedded in the surface zone supporting it, preferably in a groove.

5. A pump according to one or more of the previous claims, characterised in that a shoulder is disposed opposite the spark-proof material.

6. A pump according to one or more of the previous claims, characterised in that the spark-proof material is embodied by a ring, more particularly a hollow cylindrical ring, placed on or in the outside generated surface of the outer rotor.

7. A pump according to one or more of the previous claims, characterised in that a drive shaft connected to the outer rotor extends through and is mounted on a casing wall and the bearing is sealed by secondary sealing means against a flow of media from the outside to the inside and/or from the inside to the outside.

8. A pump according to claim 7, characterised in that the secondary sealing means take the form of a ring seal, more particularly a radial ring seal or a lip ring seal.

9. A pump according to one or more of the previous claims, characterised in that two ring seals which are preferably spaced apart axially from one another and/or which bound a grease chamber between them are provided.

10. A pump according to claim 9, characterised in that the ring seals are disposed between common outer and inner rings and form a single component therewith.

11. A pump according to claim 9 or 10, characterised in that the outer and inner rings are sealed off from the bearing carrier and drive shaft, preferably by way of radial ring seals.

12. A pump according to one or more of the previous claims, characterised in that the spark-proof material is bronze, preferably beryllium bronze, or copper or brass.

13. A pump according to one or more of the previous claims, characterised in that the spark-proof materials of the contacting parts are different from one another.

14. A pump according to claim 13, characterised in that the material of the particular other part concerned, more particularly the material of the casing wall, is soft cast iron or steel.

15. A pump according to one or more of the previous claims, characterised in that there is present between the outer rotor, more particularly between the spark-proof material thereon, and the supporting or casing wall a radial gap smaller than the radial gap between the outer rotor and the inner rotor.

16. A pump substantially as herein described with reference to the accompanying diagrammatic drawings.