Electronically Controlled Magnetic Stirrer

Abstract

A magnetic stirrer for stirring low viscosity media comprises a plurality of stationary electromagnets arranged in a housing on which a receptacle containing the medium to be stirred can be mounted. The receptacle also contains one or more freely movable stirring arms controlled by the electromagnets which produce a rotary magnetic field by corresponding consecutive energization of the individual electromagnets by means of an electronic control element.

Description

The invention relates to an electronically controlled magnetic stirrer for stirring media of low viscosity, wherein a rotating magnet which performs the stirring work is disposed in a housing, on which there is mounted a vessel container the medium to be stirred, there being freely movably disposed in the said vessel one or more stirring members which are driven by the rotating magnet and which stir the medium.

Since the stirring members in the vessel are driven by the rotating magnet lines of force pass through the vessel, the latter may consist of a material of any kind with the exception of a magnetic material. Such apparatus are employed primarily in chemical laboratories, so that the media to be stirred are primarily chemicals, and the stirring members are therefore preferably provided with an acid-resistant coating.

The object of the present invention is to provide a magnetic stirrer, wherein the field strength which acts on the stirring member and the speed of the later can be infinitely varied, and which has no mechanically or electrically moved parts and consequently requires no servicing and, in addition, has from the outset the properties of an explosion-proof apparatus.

Apparatus are already known in which a permanent magnet is rotated in some way within the housing during the operation. This permanent magnet transmits its rotational movement, by means of the magnetic field transmission, to a second permanent magnet situated in the stirring vessel, i.e. to the stirring member. In such cases, it is immaterial whether the permanent magnet in the housing of the stirrer is directly mounted on the shaft of the electric motor or is mounted on a shaft driven through a transmission system.

The disadvantage of such apparatus is that they are very costly by reason of the principle of their construction. From the physical viewpoint, they utilize two stators and two rotors.

The first stator and the rotor associated therewith form the driving motor, the second stator is the rotating permanent magnet, and the second rotor is the stirring member consisting of a permanent magnet and situated in the vessel.

In addition, stirring apparatus are known which employ an electric rotating-field generator within the housing. However, such apparatus operate only at a supply frequency of 50 c/s or 60 c/s and they therefore have no means for speed regulation.

The invention has for its object to provide an apparatus based upon a very simple principle and having no mechanically moving parts, which constitutes further development of the existing known apparatus, i.e. the apparatus is to operate silently, to be infinitely regulatable in speed and magnetic field strength, to have no wear and to be explosionproof.

In accordance with the invention, this object is achieved in an apparatus of the type mentioned at the beginning, by virtue of the fact that there are employed to drive the stirring member or members, instead of a rotating magnet, one or more fixed electromagnets disposed in the housing, which generate a rotating magnetic field, the speed of the magnetic field, by which the stirring frequency is determined, and the strength of the said field being infinitely variable within a wide range of limits by an electronic control element for feeding the electromagnets.

The electromagnets generate a rotating electromagnetic field, which in turn transmits this rotational movement to the stirring member situated in the stirring vessel and this initiates and maintains the stirring operation. In contradistinction to the known apparatus, the apparatus according to the invention requires only one stator and one rotor.

In consists of a fixedly mounted electromagnet within the housing constituting a stator and a soft-iron or permanent magnet, freely movable in the stirring vessel, constituting a rotor.

The intensity of the rotating magnetic field which is generated by the electromagnet makes it possible in accordance with the invention, to employ as stirring members in the vessel containing the medium to be stirred magnetizable soft-iron parts which are provided with blades or the like which promote the stirring action. In addition, it is possible in accordance with the invention to provide the described apparatus with heating means and thus to supply heat to the medium during the stirring operation without magnetization of the permanent magnets being disadvantageously influenced by the heating as might happen in the stirring apparatus hitherto operating with permanent magnets.

The advantages achieved by the invention consist more especially in that, with low cost of construction, an apparatus can be produced which employs no mechanically or electrically movable parts and thus has an unlimited useful life, and which operates silently and is explosionproof, since sparking, for example due to an electric motor, need not be given concern. In addition, the speed of rotation of the magnetic field and thus the speed and the magnetic field strength may be regulated and thus adapted to the particular purpose of use. Moreover, it is possible to make the overall height of the apparatus according to the invention substantially smaller, because no mechanical driving devices have to be accommodated therein.

In a convenient further development of the invention, instead of the vessel, there may be resiliently mounted upon the housing, in spaced relationship thereto, a soft-iron or permanently magnetic plate, which is in turn intended to receive a vessel and which performs a three-dimensional agitating movement with the vessel under the influence of the rotating magnetic field, whereby a further possibility of application of the apparatus is afforded.

Also, by switching over it is possible to alter the rotating magnetic field to an increasing and decreasing magnetic field and thereby amplify the agitating effect. It is also possible within the scope of the invention to reverse the direction of rotation of the magnetic field during the stirring operation by reversing the polarity of the magnet. This is of particular advantage whenever a stir spout is formed in the medium to be stirred.

Embodiments of the invention are illustrated by way of example in the accompanying drawings and more fully described in the following.

In the accompanying drawings:

FIG. 1 diagrammatically illustrates in section the construction of hitherto known magnetic stirrers,

FIG. 2 diagrammatically illustrates in section the principle of the invention,

FIG. 3 illustrates in section one embodiment of the invention, and

FIG. 4 illustrates in fragmentary form a stirring mechanism according to the invention with an attachment for vibrating the vessel.

In known stirrers, there is provided within a housing 6, as diagrammatically illustrated in FIG. 1, an electric motor which is schematically represented by the stator 1 and the rotor 2. The said electric motor drives, for example through a belt pulley 7 and a V-belt 8, a belt pulley 10 mounted on a shaft 9, which is in some way mounted in the housing 6. Secured to that end of the shaft 9 which is further from the belt pulley 10 is a permanent magnet 3 which rotates at a particular speed when the shaft 9 is rotated by the electric motor. The speed regulation of the motor and thus of the permanent magnet 3 is effected through a potentiometer 5. Mounted on the upper side of the housing 6 is a vessel 11 which contains the medium 12 to be stirred. Situated on the base of the vessel 11 is a permanent magnet 4 which serves as a stirring member and which is driven by the rotation of the permanent magnet 3 and stirs the medium 12.

In the construction of the stirrer according to the invention, as diagrammatically illustrated in FIG. 2, there is disposed in the housing 13 an electromagnet consisting of a core 14 and a coil 15. The coil 15 receives current through the conductors 16, 17 from an electronic control device 18 which generates in the electromagnet a rotating magnetic field, the strength and speed of rotation of which are infinitely variable by the control device 18. Mounted on the housing 13, as in known stirrers, is the stirring vessel 11 containing the medium 12 to be stirred. A stirring member 19 consisting of a permanent magnet of a soft-iron member is situated on the base of the vessel 11. The said stirring member is driven by the rotating magnetic field of the electromagnet formed of the core 14 and the coil 15 and stirs the medium 12.

In the embodiment of the invention as illustrated in section in FIG. 3, the stirrer housing is denoted by 21, the coils of the electromagnets installed therein by 22 and the cores of the electromagnets by 23. The coils 22 of the electromagnets receive current from the electronic control device 26, through supply conductors 24, 25 illustrated by way of example for the right-hand coil in FIG. 3. The adjustment of the control device 26 for regulating the strength of the magnetic field and its speed of rotation is effected through operating elements, of which there is shown in FIG. 3, by way of example, a button 27. In the illustrated form of construction, the upper covering wall of the housing 21 is apertured for the passage of the cores 23 of the electromagnets. A cover plate 28 consisting of a nonferrous metal for receiving the vessel 29 containing the medium 30 rests on pillars 31 on the upper peripheral region of the housing 21. Situated on the base of the vessel 29 is a stirring member 32 which, in the illustrated form of construction, is provided with blades 33 to intensify the stirring movement. Provided within the cover plate 28 supporting the vessel 29 are heating bars 34 by means of which the medium 30 may be heated during the stirring.

In FIG. 4, the parts are denoted by the same reference numerals as corresponding parts in FIG. 3. Instead of the heatable cover plate 28, there is here merely provided a simple cover plate 35. Instead of the vessel 29 of FIG. 3, there is here mounted on the cover plate 35 a ring 37 which encircles the said cover plate and is held in position by an indentation 36. A frame 39 is resiliently suspended within the ring 37 by means of springs 38 to receive a vessel 40, which may be secured to the frame 39 and secured against displacement, for example by resilient bands 41. Situated on the lower side of the frame 39 is a soft-iron part or permanent magnet 42, which lies at a distance above the cover plate 35 and thus above the cores 23 of the electromagnets. The soft-iron part or permanent magnet 42, and thus the vessel 40, are given a three-dimensional vibrational movement by the rotating magnetic field.

Claims

I claim:

1. A magnetic stirrer for stirring low viscosity media, comprising a housing on which a receptacle containing the medium to be stirred can be mounted, a plurality of electromagnets in said housing for effecting stirring, at least one freely movable stirring arm in said receptacle controlled by the electromagnets, said stirring arm being free from axial restraint, and an electronic control element for energizing said electromagnets independently in succession, said electromagnets being independently operatively associated with said control element and arranged inside the housing to produce a rotary magnetic field within the receptacle upon corresponding consecutive energizing of the individual electromagnets by said electronic control element, whereby the speed of rotation of the magnetic field intensity are infinitely variable within a broad range and the direction of rotation of the magnetic field can be reversed at will by the electronic control element.

2. A magnetic stirrer according to claim 1 wherein said stirring arm comprises magnetizable soft-iron parts which are provided with blades to promote the stirring action.

3. A magnetic stirrer according to claim 1 comprising heating means in said housing in the region of the receptacle by which the medium may be heated during the stirring.

4. A magnetic stirrer for stirring low viscosity media, comprising a housing n which a receptacle containing the medium to be stirred can be mounted, a plurality of electromagnets in said housing for effecting stirring, and an electronic control element for energizing said electromagnets independently in succession, said electromagnets being independently operatively associated with said control element and arranged inside the housing to produce a rotary magnetic field within the receptacle upon corresponding consecutive energizing of the individual electromagnets by said electronic control element, whereby the speed of rotation of the magnetic field determining the stirring speed and the magnetic field intensity are infinitely variable within a broad range and the direction of rotation of the magnetic field can be reversed at will by the electronic control element, and further including means on said housing for resiliently supporting said receptacle in spaced relation from the housing, the latter means including a magnetic plate on which said receptacle is adapted to be supported to provide a three dimensional vibrating movement for said receptacle under the action of the rotating magnetic field.

5. A magnetic stirrer according to claim 4 wherein said means for resiliently supporting the housing further comprises an indented ring extending upwardly from said housing, a frame for said receptacle, springs secured to said frame and to said indented ring, and resilient bands connected to said frame for engaging the receptacle to hold the same against said frame, said magnetic plate being mounted on the frame on the underside to face said electromagnetic.