GB2116373A - Coupled drive - Google Patents

Abstract

A coupled drive for producing rotary motion within a sealed vessel, for example for stirring the contents of an autoclave comprises a stator (16) outside a container (5) producing a rotating magnetic field within the container and a rotor (10) located within the container responding to the rotating magnetic field. The container (5) is secured to the sealed vessel (3) at its open end. The coupling may act as an induction or synchronous motor. <IMAGE>

Description

SPECIFICATION Coupled drive The present invention is concerned with a coupled drive, whereby a rotary mechanical action may be produced within a sealed vessel.

When materials are put together in a vessel, for mixing, co-reaction or any other purpose, it is often desired to rotate a mechanical component within the vessel. Thus in mixing devices or in chemical reactors, for example, a stirrer or agitator may be rotated within the vessel to enhance the intermingling of its contents.

Difficulties arise, however, when it is necessary or desired to use a sealed vessel.

For example, if the vessel is an autoclave wherein materials are chemically reacted under elevated pressure, the provision of a directlydriven stirrer entails transmitting the drive from outside to inside the vessel while avoiding any pressure leakage past the drive transmission. At highly-elevated pressures in particular, it is difficult to devise an adequate seal for this purpose. Similarly, if it is necessary to isolate the vessel contents because of their noxious nature, an appropriate rotary seal must be adopted.

It has been proposed to provide the desired rotary action within a sealed vessel, while simultaneously preserving the integrity of the contents, by using a magnetic coupling arrangement. Thus a magnet (or series of magnets) is rotated outside the vessel and a second magnet (or series of magnets) located within the vessel or in direction communication with the interior of the vessel is thereby caused to rotate. In this way, an agitator or stirrer mechanically linked to the second magnet is rotated within the vessel by means of an external drive via the magnetic coupling between the magnets. Typical such magnetically-coupled drives are described and illustrated in US Patent Specifications Nos. 2,996,363 and 3,050,646.

A disadvantage of such prior art drives is the space which they may require. Thus the devices illustrated in the above US Specifications require, in addition to the external parts of the coupling unit, a separate motor to drive those parts via a transmission comprising belt and pulleys. If the vessel is a small one, for example a laboratory autoclave, then the drive mechanism may be as large as the vessel.

It would therefore be advantageous if a suitable drive could be devised, which lends itself to a more compact design.

The coupled drive according to the present invention, for producing a rotary mechanical action within a sealed vessel, comprises a container, a stator surrounding at least a part of said container and designed to produce a rotating magnetic field within said container, and a rotor located at least in part within said container and designed to rotate in response to the rotation of said rotating magnetic field.

The container may be the sealed vessel itself but advantageously it may be an open-ended generally cylindrical container, adapted to be secured to the vessel adjacent said open end so as to be in direct communication with the interior of said sealed vessel. Thus the vessel may, for example, be a reaction vessel such as an autoclave to which the container forms a branch.

The container dimensions and material of construction may be selected taking into account the particular purpose for which the vessel is to be used. Thus if the vessl is to contain materials at significantly elevated or significantly reduced pressure, the container is necessarily of more robust construction than is required if the vessel is to be used at amospheric pressure. If the vessel contents are corrosive and the container is likely to come into contact with those contents, then the container material should be chosen with that in mind. Typically, the container may be made from a 31 6 stainless steel.

The coupled drive according to the present invention may be more readily understood if it is thought of as a conventional electric motor, with the important difference that the stator and rotor are located on opposite sides of the wall of the container. This "motor" may be of the induction or synchronous type and the electrical characteristics of the stator may be those of a conventional induction or synchronous motor.

Thus the stator will have a multiple-phase winding, for example a two-phase winding, fed by an appropriate electrical supply. The latter supply may usefully be a multlphase supply but if such is not available then a stator design may be adopted of the type which generates a rotating field from a single-phase supply. The stator core may consist of an axial stack of laminates of conventional type. The electric supply to the stator may be at a fixed frequency or alternatively the frequency may be variable, for example as a means of varying the rotor speed.

As indicated, the "motor" may be of induction or synchronous type; the rotor is designed accordingly. Thus the rotor may if desired have induction windings or may carry magnets. In a preferred form, the motor is a synchronous motor in which permanent magnets are uniformly distributed about the circumference of the rotor.

The magnets may be orientated radially or circumferentially or in some intermediate position. If desirsd, the rotor, while carrying permanent magnets, may also carry induction windings, for example a squirrel-cage, to assist starting of rotation.

The invention will now be further described with reference to the accompanying drawing, -, which is a vertical section through a coupled drive unit according to the present invention, mounted in position on an autoclave.

Referring to the drawing, a coupled drive unit designated generally by the numeral 1 is located at one end within a bore 2 within the outer face of the wall 3 of an autoclave and is secured in place by means of a retaining nut 4. The body of the unit 1 consists of a cylindrical container 5 closed at its upper end by a bearing housing 6 and end cap 7.

Within the container 5 and supported for rotation in bearings 8, 9 is a rotor 10 comprising permanent magnets 11 mounted upon a shaft 12 between end plugs 13, 14. The magnets 11 and end plugs 13, 14 are sealed as a single unit within a stainless steel tube 1 5. Upon an extension of the shaft 1 2 into the interior of the autoclave is mounted a stirrer or agitator blade (not shown), for example in the form of paddles. That part of the container 5 located adjacent to the magnets 11 is surrounded by a stator 16, comprising conventional stator windings wound to give two phases.

The magnets 11 on the rotor are sixteen in number and are mounted in four groups of four along the axis. Each magnet is mounted in a generally circumferential orientation and circumferentially adjacent magnets are magnetised in alternate directions, giving two North pole positions and two South pole positions alternately about the circumference of the rotor.

Axially adjacent groups of magnets are similarly magnetised.

Thus the coupled drive according to the present invention may be understood as a form of two-phase synchronous motor, with the significant difference that the stator is mounted outside the autoclave while the rotor is "within" the autoclave (in the sense that the container 5 is in direct communication with the latter). Thus rotation of the shaft 12 and associated agitator is achieved within the autoclave without the need to transmit a rotary drive directly through a mechanical seal in the autoclave wall and by use of a device which is adapted to a more compact design than that of the hitherto conventional coupled drives.

Claims (11)

Claims

1. A coupled drive for producing rotary mechanical action within a sealed vessel, comprising a container, a stator surrounding at least a part of said container and designed to produce a rotating magnetic field within said container, and a rotor located at least in part within said container and designed to rotate in response to the rotation of said rotating magnetic field.

2. A coupled drive as claimed in claim 1, wherein said container is open-ended and is adapted to be secured to said vessel adjacent said open end.

3. A coupled drive as claimed in claim 1 or claim 2, wherein the electricity supply to the stator is at a variable frequency.

4. A coupled drive as claimed in any of claims 1 to 3, wherein the rotor and stator together form a synchronous motor

5. A coupled drive as claimed in any of claims 1 to 3, wherein the rotor carries and stator together form a synchronous motor.

6. A coupled drive as claimed in claim 5, wherein the rotor carries a plurality of permanent magnets uniformly distributed about its circumference.

7. A coupled drive as claimed in claim 6, wherein the permanent magnets are disposed about the rotor in a generally circumferential orientation.

8. A coupled drive as claimed in claim 6 or claim 7, wherein the magnets are sealed within a tube.

9. A coupled drive as claimed in any of claims 5 to 8, wherein the rotor also carries induction windings.

10. A coupled drive for producing rotary mechanical action within a sealed vessel, said coupled driving being substantially as hereinbefore described with reference to the accompanying drawings.

11. A coupled drive as claimed in any of the preceding claims, wherein the rotor drives a stirrer or agitator.