The invention relates to a flexible coupling for compensating the differences in alignment between two rotary bodies which are rigidly connected in their axial and rotational direction. Such flexible couplings are generally known. As an example, the known universal joint is mentioned here. Often, flexible couplings are applied in cases in which the exact alignment of the rotational axes of the connected rotary bodies is not guaranteed.

This may be caused by the fact that differences in alignment are accepted beforehand, for instance if small variations in the mutual position of the rotary bodies should be accounted for. Such a situation may occur for instance with an axle which is rotatably supported by means of three bearings. The support at three points of the axle is statically overdetermined, in such a way that, due to an incorrect position of the bearings transverse with respect to the axle, a bending moment is introduced therein. Such a bending moment constantly changes its sign upon rotating the axle, which generates the danger of fatigue. Furthermore, such a bending moment leads to extra high bearing forces, which negatively influence the usefull life thereof.

An example of such a case is the mixing screw of a conical mixing device. At its upper end, the mixing screw is supported on a drive axle situated at the end of a swinging arm, which axle is supported by means of two bearings. The mixing screw itself at its lower end is rotatably supported in the vessel. Both the faults in alignment of the bearings mentioned above, as well as the loadings exerted by the mixing goods on the mixing screw may give rise to unacceptable bending moments in the mixing screw respectively the drive axle. These undesirable bending moments may be prevented by connecting the mixing screw and the drive axle by means of a flexible coupling such as described before.

In this respect however the known universal joint has disadvantages, due to the fact that it is exposed to the goods to be mixed. In the case of specific types of mixing goods, it is necessary to protect the universal joint, which in practice however appears to be difficult. Examples are finely drained mixing goods, gasses or liquids.

Furthermore, the mixing good may contain materials which are chemically or mechanically aggresive, and which could deteriorate the

coupling.

As a consequence of its construction the known coupling has a shape which promotes the gathering of mixing goods in specific hollow spaces and slids. The mixing goods thus gathered are very difficult to remove. This leads to the risk that the mixing goods get polluted by the non- removed rests. As a consequence thereof, the mixing goods may be bacteriologically contaminated.

In particular in mixing devices which are applied in the dairy and foodstuff industry as well as in the pharmaceutical industry, this risk is however unacceptable.

A coupling which is contaminated with a bacterial focus is difficult to clean. As a consequence, a coupling once contaminated may contaminate many new charges and render the complete mixing device useless. The object of the invention is therefore to provide a flexible coupling of the type described before which on the one hand provides a solution for the undesirable bending moments and which on the other hand is suitable for applications in which every risk of pollution should be prevented. . This object is achieved in that the coupling comprises a ball-and- socket joint for transferring axial loads and transverse loads, as well as a bellows surrounding it for transferring torsional loads which bellows consist of a material with a high modulus of elasticity and at each end is connected, with high torsion stiffness, to always one of the rotational bodies. The ball-and-socket joint according to the invention allows mutual rotary movements of the two rotary bodies, in such a way that in case of faults in alignment between the different bearings, or in case of high transverse loads on the rotary bodies, no large bending moments will occur. The construction of the bellows allows such limited bending movements. However, with respect to torsional loads it is rigid, in εuch a way that the driving couple in rotary direction between both bodies may be transmitted very well.

This combination of torsional stiffness on the one hand, as well as the allowability of bending movements on the other hand is obtained due to the fact that the bellows at each end has a mounting flange between which flange there is a sleeve the axial ends of which are provided with inwardly facing edges which are each connected to a flange. Such a sleeve with stiff end flanges has a high torsional rigidity, whereas by means of the curved shape of the wall of the sleeve yet mutual rotational

movements of the flanges in a plane through the centre line of the bellows may occur. Preferably, the sleeve has an essential V-shaped or U- shaped cross-section in an axial plane, in such a way that the tips of the legs of the V respectively U are each connected to a flange and the bottom of the V respectively U is directed radially outwardly. In this embodiment the part of the sleeve composed of the legs of the V respectively U provides the flexibility for the bending movement.

In a practical embodiment the sleeve may consist of two axial house which are welded together. In order to prevent that at the side of the welding seam, the fatigue stresses would be too high, the part of the axial halve of the sleeve which borders the welding seam has an enlarged thickness.

According to a partically preferred embodiment the wall parts of the sleeve which extend between the parts with an enlarged wall thickness and the flanges have a relatively small wall thickness, in such a way that these wall parts are able to deform according to an S for compensating non-alignment. Due to the fact that the differences in alignment are always small, this S-shaped deformation is very small, in such a way that also over a length of wall which is small in radial direction, the radius of curvature which corresponds to the deformations may stay limited.

The embodiment of the coupling may be simplified in case the halves of the sleeve are symmetrical with respect to a radial plane running through the welding seam. In this embodiment, one need to manufacture only one sleeve halve, which favourably influences the costs of manufacturing.

One of the flanges may have a housing for containing the outer ring of the ball-and-socket joint, and the other flange may have a pin for supporting the inner ring of the ball-and-socket joint. In such a way, a compact construction is obtained, the bellows enclosing the rings of the ball-and-socket joint hermetically.

Furthermore, the invention is related to a mixing device provided with a conical mixing vessel as well as a mixing screw which at its upper end is suspended from a drive axle situated at the free end of a swinging arm, and supported at the vessel at its lower end. According to a preferred application, the flexible coupling as described before is applied between mixing screw and drive axle. In such a way the bearing of the drive axle may be saved largely, even when there are differences in alignment between on the one hand the support at two points of the drive

axle and on the other hand the support of the lower end of the mixing screw. However, also in case the mixing screw is bending under the influence of the loadings exerted thereon by the mixing goods, the bearing loads may be kept limited as a consequence of the presence of the flexible coupling.

Preferably, each flange has a sealing ring for providing a sanitary or aseptic sealing with respect to the mixing screw or the drive axle. This embodiment is εuitable for application in the food industry or the pharmaceutical industry. The coupling has a shape which on the outside is completely smooth, without having corners or slits which are difficult to reach and in which dirt could gather. The risk of the formation of focusses of bacteries is thereby largely prevented. The mixing device with a coupling is very suitable for materials which are mechanically or chemically aggressive. Having regard to the sealed character of the coupling, it is also suitable for mixing vessels in which an overpressure or underpressure occurs during mixing.

This means that in the internal space for instance a nitrogen atmosphere may be maintained, which further decreases the danger of contamination. The sealing consists of a known and accepted type, which also ensures that no contaminations may occur due to capillairy action. Thereby, in a temperature range of -20° upto 200°C, aseptic conditions may be assured.

The invention will explained further with reference to an embodiment shown in the figure.

The figure shows a flexible coupling which in its entirety is indicated with number 1. This flexible coupling is on the one hand connected to a drive axial (not shown) such as e.g. figuring at the end of the swinging arm of a conical mixing vessel. On the other hand, coupling 1 is connected to a mixing screw 3t comprising a central axle as well as a screw 5 _* The central axle 4 is equipped with a mounting flange 6 onto which ultimately the coupling is connected.

The flexible coupling according to the invention encompasses a ball-and-socket joint 7- comprising an outer ball-and-socket joint ring 22 as well as an internal ball-and-socket joint ring 8. The outer ball- and-socket joint ring 22 is contained in a housing 9 forming part of the mounting flange 10 of coupling 1. The inner ball-and-socket joint ring 8 is positioned around a hollow pin 11 which internally has a screw thread. This hollow pin 11 has a ring 12, onto which the inner ball-and-socket

joint ring rests. This ball-and-socket joint ring 8 also rests on a rim 13 which is solid with flange Ik of the coupling. By means of bolt 15 the hollow pin 11 may be mounted, in such a way that the inner ball-and- socket joint ring 8 is clamped between a rim 12 and a rim 13. The head of bolt 15 is situated in the supporting axle (not shown) of the mixing screw 3- In a known manner, it is covered with a cap. Due to the fact that the complete support construction of mixing screw 3 is contained in the interior of the swinging arm (not shown) of the mixing device, the danger of pollution is excluded. Due to this way of connecting, the coupling situated in the mixing vessel is completely smooth on the outside, without emerging bolt heads.

By means of balls, the flanges 10 and 13 are furthermore, in a known manner, fixed to the rotary axle 2 or to the mounting piece 6. Thereby, a very good seal is ensured, in case recesses are provided for sealing rings 16, in εuch a way that an aseptic or sanitary seal of the coupling may be obtained.

The flanges in a cross-section, are always provided with a leg of the bellows 17- Both legs 18, 19 of the bellows together with the thickened bottom part 20 have a U- respectively V-form. The parts 20 with enlarged thickness are connected by means of welding seam 21. Due to the fact that the parts 20 are relatively thick, the stresses in the welding seam 21 are limited such that the danger of fatigue is largely avoided here. In case small differences in alignment occur between the centre line of the axle 2 on the one hand and the centre line of the mixing screw on the other hand, the ball-and-socket joint rings 22 and 8 rotate a little bit with respect to each other. The wall parts 18, 19 of the bellows 17 thereby deform very slightly according to an S-shape depending on the direction of the angular rotation, which is made possible by the relatively small wall thickness of these wall parts 18, 19.

On the other hand, due to the high modulus of elasticity of the material of the wall parts 18, 191 as well as due to the rotational symmetry it is guaranteed that the torsional loadings almost without deformations are transmitted via the wall parts 18, 19, the parts 20 with enlarged thickness, as well as the welding seam 21.

As the mixing screw constantly rotates, it is guaranteed that the ball-and-socket joint 7 is loaded regularly in consecutive radial planes. This means that the ball-and-socket joint 7 is loaded very regularly, which leads to only very limited wear. Furthermore, the very small

rotation of the ball-and-socket joint rings 8, 22 with respect to each other already ensures a long useful life of the ball-and-socket joint.