Installation of a mixer in a receptacle

Abstract: The present invention relates to an apparatus for mixing fluids, and especially to a mixer shaft which is provided with a mixing means at the end thereof and which extends from the exterior side of a mixing tank deep into the interior thereof. According to the invention, the mixing shaft is mounted on bearings at a point near the mixing means, and the housing construction of the mixer shaft, including a shield, forms a shape convergent towards the mixing means, which shape contributes to flowing of fluid. For purposes of servicing, the mixer shaft with its drive means may be displaced out of the tank without the necessity of emptying the tank. The above has been achieved in such a manner that the shaft housing (18) with bearings and sealings is disposed inside a shield (56), which extends inside the mixing tank (80) and is attached to a wall thereof so that the mixer is detachable from the tank (80) in such a way that, of the moving parts of the mixer, only the mixing means (64, 66) remain inside the tank (80), whereby emptying the tank is avoided.

Description: The present invention relates to an apparatus for mixing fluids, and especially to a mixer shaft which is provided with a mixing means at the end thereof and which extends from the exterior of a mixing tank deep into the interior thereof. Mixing apparatuses, called mixers, are generally used in the wood-processing industry and other chemical industry for mixing various fluids with each other and for mixing solid materials with fluids. These means are constructed with an aim of achieving the greatest possible mixing efficiency with the lowest possible power consumption. Another aim is to construct the equipment so that the greatest possible reliability in operation is achieved and that the maintenance or replacement of the shaft sealing and bearings may be effected without the necessity of emptying the mixing tank. In generally used mixers which are inserted in the mixing tank from the side thereof, the reach of the mixing means inside the tank is fairly short, but in spite of that, the shaft is supported at a point which is relatively far from the point of loading caused by the mixing means. In other words, it has been attempted to arrange the supporting of the shaft either entirely outside the tank or at least near the wall thereof to facilitate repairs which may possibly be needed. This results in the use of a thick mixer shaft for minimizing deflections caused by different strains. Consequently, big shaft sealings are needed and, in spite of the thickness of the shaft, deflections of the shaft result which are harmful to the sealing. An example of the construction roughly described above is an arrangement according to DE-A-31 50 537, in which the mixer is mounted on a flange installed in the wall of the mixing tank so that the entire mixing unit can be extracted from the tank. However, the most distinct drawback of the apparatus according to the above application is that the mixer cannot be totally removed unless the mixing tank is emptied at least to the lower edge of the opening reserved for the mixer. Another drawback is the great thickness of the shaft, which is also well seen in the figures, and the purpose of which is to prevent deflections of the shaft and further stresses subjected to the bearing system and the sealings. Another construction to the prior art is a mixer disclosed in US-A-3,539,155 in which the mixing tank itself is totally closed and the drive of the mixer is arranged by means of powerful magnets through the cover part of the tank. What makes this patent specification interesting, is a tapered shell around the mixer shaft, in connection of which shell the bearings are arranged both next to the mixing means and near the "magnet switch". In this manner, ideal support of the mixing shaft has been provided, but the service of the apparatus has not at all been considered. Naturally, as a mixer installed in the cover of a mixing tank is concerned, the entire mixer may be removed from the tank without the necessity of emptying the tank. Such principle is, of course, not possible with such an arrangement if the mixer is installed in a sidewall of the tank. In this case, a great number of different factors have to be taken into account, starting from the shaft being deflected by gravity and ending with different sealing problems occurring both during the drive and the servicing of the apparatus. None of these problems have been considered in connection with said prior art publication because there has been no need therefor. In very many cases, however, there is no chance of choosing the location of the mixer relative to the mixing tank, and the mixer has to be disposed at the side of the tank no matter how many problems it may cause. In some installations of the mixer at the side of the mixing tank, the servicing has been performed successfully due to the mixer shaft being provided with an additional sealing which can be closed during service. In that case, it is possible to replace the shaft sealing if the sealing is of a replaceable type. Bearings and such sealings that cannot be divided may be replaced in some type of shafts by dismantling all drive equipment and support structures of bearings and by temporarily supporting the shaft. In FR-2613792 there is disclosed a mixing device wherein a propeller shaft 7 extends through a housing secured to the interior of a vessel and a non-metallic support collar 2 is mounted in a ring 1/12 in the vicinity of the propeller, which is soldered to the housing. Sealing means 3,4,5 and 10,13,15 are provided in the housing between the shaft and ring. Otherwise, apart from the conical cover fixed to the vessel and its sealing means there is no other housing for shaft 7. Also FR-2613792 does not allow the shaft of the mixer with its bearings and sealing to be removed from the tank leaving the mixer rotor in the tank. The object of the invention is to provide a mixer with an improved ratio of mixing efficiency and power requirement and in which mixer the shaft extends a substantial distance into the tank and may be sealed substantially more economically by a small and non-leaking sealing structure. Furthermore, it is intended the mixing apparatus and its shaft may be quickly detached for maintenance or replacement without the necessity of emptying the tank, which is essential especially with big tanks. Because all moving parts of the mixer, except for the mixing means itself, are readily detachable, it is extremely rare that the tank would have to be emptied for the maintenance of the mixer. Actually, the only reason for emptying of the tank is the vane or blade of the mixing means being broken or the vane or blade coming off the hub, in which case the tank would have to be emptied to find the vane or blade in the fluid. According to the invention there is provided a mixer comprising drive means arranged in connection with a side wall of a mixing tank; a shaft to be mechanically driven by said drive means, extending inside the mixing tank and being surrounded by a separate shield or cover, and a mixing means attached to the end of said shaft, said separate shield or cover being attached to the wall of said mixing tank and extending into the tank to adjacent said mixing means, characterized by: a housing being attached to the drive means, said housing supporting and sealing said mixer shaft which extends deep into the interior of the tank, with said shaft being supported and sealed by means of bearings and sealings in the vicinity of the mixing means; and by said shield or cover supporting said mixing means there, and being spaced from and surrounding said housing for preventing the fluid contained in the tank coming into contact with the housing. The cover or shield preferably forms a shape convergent towards the mixing means, which shape contributes to flowing of fluid within the tank. For purposes of servicing, the mixer shaft with its drive means is displaceable out of the tank without the necessity of emptying the tank. A mixer according to the invention is further described below, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a side elevation with partial section of a mixer according to the invention in the operating position, and Fig. 2 is an elevation of the mixer of Fig. 1 in the position for service. In accordance with Figs. 1 and 2, the mixer of the invention comprises two main units, 10 and 50, namely, a drive motor and shaft unit 10 and a transfer support means, shield and mixing means unit 50. Unit 10 is movable. In other words, it may be extracted from extending into a tank 80 so as to make it possible to simply take all measures necessary for maintenance without need for the tank 80 to be emptied or for the mixer to be dismantled to an unnecessary extent. Unit 10 includes a bracket 12, drive motor 14 of the mixer, said motor being mounted on said bracket, gear means 16 (usually a gear reducer), housing 18 extending from gear means 16 towards the interior of the tank 80, said housing being provided with flanges 20 for fastening the housing to a wall of the tank 80. Furthermore, a drive shalt 22 of the mixer and driven via the gear means 16 is mounted on bearings to the tapering housing 18 in such a manner that an outer support bearing 24, i.e. the bearing at the outer end of the shaft remote from gear moans 16, is disposed as near the end of the shaft 22 as possible and thus also near the mixing means. The housing 18 is also provided with a shaft sealing 26 and a sealing cage 28. The shaft sealing 26 is so arranged as to prevent the fluid contained in the mixing tank 80 from looking along the shaft towards the housing 18. Should the sealing, however, fail at that point, the fluid will escape and leak as far as the end part of the housing 18. The sealing cage 28 is, however, provided with openings through which the fluid will flow onto the inner surface of cover or shield 56 and therealong further out or the tank and mixer without the risk of the bearings 24 of the mixer shaft being damaged. With the same arrangement, it has also been provided that the fluid to be mixed is inaccessible to leaks of greases and oils from the bearings, and any such flow out of the mixer along the path described above. Thus, it is easy to observe the equipment at the transition between the mixer and mixing tank to see if the equipment is completely in order and, in case of a leak, it is easy to see whether it is a seal or a bearing that has been damaged. At an end of the shaft 22, there is preferably machined a spiral-shaped tapering wedge part 30 in accordance with FI-A-864730 and EP-A-87117154.2 to which wedge part the mixing means is attached by means of a corresponding and cooperating wedge part. This type of wedge attachment makes it possible to extract unit 10 from projecting into the tank so that the actual mixing means will remain inside the tank 80. This spiral-wedge attachment is of reliable construction and capable of transferring heavy torques. Yet it does not become tightly locked by the effect of the torque like ordinary wedge attachments in which the wedge tends to become cut. If an ordinary threaded connection were used, it would also tend to jam so tightly that merely by drawing from the shaft it would be impossible to open the attachment. The housing 18 and the bracket 12 are equipped with rollers 32 for transferring the unit 10 outwards from the tank 80 for service. The second unit 50 comprises parts fixedly installed in the wall of the tank 80 or parts remaining inside the tank even if the apparatus is in the service position. The only part outside the tank 80 is a transfer support means 52, which substantially comprises two rails 54, arranged to function together with rollers 32 of the unit 10 for transferring the unit 10 outwards away from the tank 80 to the service position. The transfer support means 52 is attached to a fastening flange 82 on the wall of tank 80. To said fastening flange 82 is also attached a cover or shield 56 by means of flange 58 of said shield. Said shield 56 extends towards the interior of the tank 80, converges towards the mixing means referred to below and its shape and dimensions contribute to flowing of fluid. At the opposite end of the shield a securing or fastening flange 60 is disposed. To the fastening flange 60 there is still attached a sliding flange 62 for ensuring that the mixing means cannot at any stage fall into the tank. Such a risk would otherwise arise if, for some reason, the drive motor even momentarily rotates in a wrong direction, whereby the spiral-wedge attachment according to the above-mentioned patent application would tend to open and cause the mixing means to come off its shaft 22. The mixing means itself is, for example, a propeller whose blades 64 are attached to or formed with a hub 66. The hub 66 has a center hole 68 provided with a spiral-shaped keyway corresponding to the wedge part 30 of the shaft 22. The hub 66 also has a stepped protrusion 70, the radius of which is longer than the inner radius of the sliding flange 62, and a second stepped protrusion 72, the most important task of which is to serve as a sealing countersurface of O-rings 76 arranged in two sealing grooves 74 machined on the cylindrical outer surface of the sealing flange 60. The end of the center hole 68 of the hub 66 on the side of the tank wall has been broached and enlarged to a substantially tapered hole so that the shaft 22 is readily guided into its hole 68 in the installation stage. When the mixer is in operation, the fluid flow conforms to that illustrated in Fig. 1. It has been established in the tests that both the fluid flow and the mixing efficiency bound thereto increase intensively according to the reach of the mixing means into the tank until the value of the reach will be 0.5 x radius of mixing tank. With the tank geometries in practice, the reach should in most cases be within the range 1 to 1.5 m. However, in the previously known arrangements, in which the mixing means was installed at the end of the mixer shaft and the shaft bearing on the mixer side had been installed directly in the vicinity of the tank wall, the mixer shaft was strained by torsional and deflection loads caused by the weight of both the mixing means and shaft and the blade torque caused by uneven loading of the mixing means. The deflection of the shaft at the sealing, caused by deflection load, results in leaks at the seal or of sealing, wearing thereof in a short time, and consequential damage to the sealing, and very expensive special sealings or sealing arrangements have to be used if the distance between the bearing support and the mixing means is long. The construction according to the invention provides a small shaft deflection, whereby it will be safe to use, for example, small slide ring sealings or equivalent also used in the pump industry, which sealings have the advantages of series production. Correspondingly, also other stresses on the mixing unit are reduced to such an extent that a thinner shaft and consequently smaller and less expensive bearings of series production may be employed. Mixer parts wearing or susceptible to damages are the drive means, gear, bearings of the secondary shaft and shaft sealings. In the mixer of the present invention, the parts enumerated above and especially the shaft sealing have been constructed so as to make them durable. Should there, however, appear any operating disturbances in the mixer, it may be either dismantled or replaced by a similar mixer quickly and without the necessity to empty the mixing tank. Dismantling and reassembly of the apparatus itself is carried out as follows: The mixer is stopped and the nuts on the thread stubs (not shown) of the fastening flange 82 are loosened. Thus, the unit 10 of the mixer becomes displaceable in the axial direction and is supported by rollers 32 on rails 54. The mixer is displaced outwards in the axial direction away from tank 80 by means of transfer screws (not shown either) inserted in the fastening flange 82 or by some other suitable means. Then, the slide surface of the sealing cage 28, i.e. the cylindrical surface external to the case, is displaced relative to the fastening flange 60, and the stepped protrusion 72 of the hub 66 of the mixing means is transferred into the opening of the fastening flange 60. Due to double sealing 74, 76, for example O-rings 76, of the sealing flange 60, the sealing against the tank 80 is always tight. The mixer is transferred as long as it will be stopped by the limiters of hub 66 in connection with the slide flange 62. An arrangement may be made for reading the length of transfer, for example, from markings made on the transfer support means 52. Thereafter, the hub 66 is locked in place by means of a locking device 78 by winding the locking device, for example, through a winding rod. The eccentric ring disposed in the locking device 78 winds into a groove in the hub 66 of the mixing means and becomes tight relative to the hub 66. If the spiral-wedge attachment 30, 58, as described in the above-mentioned patent application, is used, the mixer shaft 22 is wound, for example, by the coupling of gear 16, whereby the shaft 22 becomes detached from the hub 66 and the unit 10 may be further transferred. According to the experience gained of spiral-wedge arrangements in practice, the shaft becomes easily detached from the hub. When the shaft is completely loose, the unit 10, supported by rails 54 of the transfer support means 52, is transferred to the limiters or stops. The transfer may be effected by an arm of a transfer wheel (not shown) or by some other suitable means. The mixer is then in the service position and, for example, a sealing or a bearing may be replaced or the entire mixing unit be transferred to the workshop for repairs and replaced by equivalent mixing unit. Sealing against tank 80 is maintained during the whole service operation. The flange ring 58 of the shield 56 is all the time fixed to the flange ring 82 of the tank 80 and the hub 66 is inside the sealing flange 60 of the shield 56. The hub 66 is locked to the sealing flange 60 and furthermore, the hub 66 is affected by the force dependent on the hydrostatic or other pressure of the tank 80 and on the diameter of the hub. When the service and other similar measures have been carried out, the unit is returned to the operating position in the opposite order.

Claims: A mixer comprising drive means (14,16) arranged in connection with a side wall of a mixing tank (80); a shaft (22) to be mechanically driven by said drive means (14,16) extending inside the mixing tank (80), and being surrounded by a separate shield or cover (56) and a mixing means (64,66) attached to the end of said shaft (22), said separate shield or cover (56) being attached to the wall of said mixing tank, and extending into the tank to adjacent said mixing means, characterized by: a housing (18) being attached to the drive means, said housing (18) supporting and sealing said mixer shaft (22) which extends deep into the interior of the tank, with said shaft (22) being supported and sealed by means of bearings and sealings in the vicinity of the mixing means (64,66); and by said shield or cover supporting said mixing means there, and being spaced from and surrounding said housing (18) for preventing the fluid contained in the tank coming into contact with the housing (18). The mixer as claimed in claim 1, characterized in that the housing (18) with bearings and sealings is disposed inside the shield or cover (56) so that the drive means (14,16), shaft (22) and housing (18) are detachable from the tank (80) in such a manner that, of the moving parts of the mixer, only the mixing means (64,66) remains inside the tank (80), whereby emptying of the tank is avoided. The mixer as claimed in any of claims 1 or 2 characterized in that the end of the shield or cover (56) on the side of the mixing means (64,66) is equipped with a sealing flange (60), in connection with which at least one sealing means (76) is disposed, said sealing means sealing the space inside the shield or cover (56) relative to the mixing tank (80). The mixer as claimed in claim 3, characterized in that the sealing flange (60) together with the sealing means (76) and a sealing cage (28) arranged at the end of the shaft housing (18) seals the space inside the shield or cover (56) relative to the mixing tank (80) when the mixer is in the operating position. The mixer as claimed in claim 3, characterized in that the sealing flange (60) together with the sealing means (76) and the hub of the mixing means (64,66) seal the space inside the shield or cover (56) relative to the mixing tank (80) when the mixer is in the service position. The mixer as claimed in any of claims 1 to 5, characterized in that, in connection with a wall of the mixing tank (80), a transfer support means (52) is provided to support the mixer unit (10) when said unit is being extracted from the tank. The mixer as claimed in claim 6, characterized in that the upper edges of the transfer support means (52) on both sides of the mixer (10) comprise rails (54) on which the mixer (10) rests supported by rollers (32). The mixer as claimed in any of claims 1 to 7, characterized in that the shield (56) forms a cone having its apex in the vicinity of the mixing means for guiding the flow with the reach of said cone inside the tank (80) being about 0.5 x radius of tank.

Inventors: KOSKINEN OLAVI, KOSKINEN, OLAVI
Applicants: AHLSTROEM OY, A. AHLSTROM CORPORATION
Application year: 1990
Main classification: B01F15
IPC codes: B01F7, B01F15