FIELD OF THE DISCLOSURE

The present disclosure relates to a transmission assembly for a slurry mixer. The present disclosure further concerns a flotation cell comprising such a transmission assembly.

BACKGROUND OF THE DISCLOSURE

In slurry mixers, a slurry mixer shaft connected to a slurry mixer head is rotated for mixing the slurry. Commonly a fluid flow, such as an airflow is introduced to the slurry via the slurry mixer shaft, most often from the slurry mixer head. Rotating the slurry mixer requires a great amount of torque, and hence, power from a motor is transmitted to the slurry mixer shaft via a transmission device.

A gear transmission device provides a robust and compact solution for converting a highspeed rotation of a motor into a high torque rotation of the slurry mixer shaft. However, as the gear transmission device cannot slip, there is no mechanical overload protection, and thus, excessive mixing forces may cause damage to the transmission device or the motor running it. Excessive mixing forces may be caused by a very heterogenous particle size distribution of the slurry or even single oversized objects being introduced into the slurry. Such excessive mixing forces may cause mechanical failure of the transmission device, motor, or both. Moreover, it is not feasible to repair a damaged transmission device or motor.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a transmission assembly in which a mechanical failure due to excessive mixing forces does not damage the transmission device.

The objects of the disclosure are achieved by a transmission assembly and a flotation cell which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of providing a discontinuity on the mechanical structure of the slurry mixer shaft, arranged to exhibit a local maximum on internal stresses caused by mixing forces, when in use.

An advantage of the disclosure, is that a predetermined failure point is defined on the slurry mixer shaft, which is easy to replace on site. Moreover, the risk of mechanical failure on the transmission device due to excessive mixing forces are minimized, regardless of the type of the mixing force, i.e. whether the mixing force is torsional or radial.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawing, in which Fig. 1 is a schematic cut-view illustration of transmission assembly according to the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Fig. 1 illustrates a schematic cut-view of a transmission assembly 1 according to an embodiment of the present disclosure. The transmission assembly 1 comprises a gear transmission device 2 having an input shaft 3 and a hollow tubular output shaft 4. The square boxes marked with an X surrounding the output shaft denote two separate support bearings 7 rotationally supporting the output shaft 4. A slurry mixer shaft 5 having an axial inner passage 5a has a portion 5c at least partially nested within the output shaft 4 for coupling the output shaft 4 with the slurry mixer shaft 5. Moreover, the slurry mixer shaft has a portion 5b not nested within the output shaft 4, and extending in slurry mixer direction from said output shaft. The slurry mixer shaft 5 also has a portion 5d not nested within the output shaft 4, and extending into a direction opposite to the slurry mixer direction.

The slurry mixer shaft 5 has a discontinuity on the mechanical structure thereof. Namely, the outer cross-sectional dimension thereof is different on the portion 5c at least partially nested within the output shaft 4 with respect to the portion 5b not nested within the output shaft 5 and extending to the slurry mixer direction therefrom. This forms a shoulder 5b' providing the discontinuity on the mechanical structure of the slurry mixer shaft 5.

Although not illustrated in Fig. 1 , the shoulder 5b' may be arranged to abut the slurry mixer side end 4a of the output shaft so as to form a part of the axial locking arrangement therebetween. Moreover, the portion 5d of the slurry mixer shaft not nested within the output shaft and extending in a direction opposite to the slurry mixer direction may equipped with an attachment means abutting against the corresponding end 4b of the output shaft so as to form another part of the axial locking arrangement between the outputs haft and the slurry mixer shaft 5.

The transmission assembly 1 is also equipped with a rotational coupling 6 for introducing a fluid flow from a stationary coupling portion into the inner passage 5a of the slurry mixer shaft 5, rotating when in use. Fig. 2 illustrates a schematic cut-view of a slurry mixer, more specifically a flotation cell 8, equipped with the transmission assembly 1 of Fig. 1 . Particularly, transmission assembly 1 is provided above a flotation tank 9 of a flotation cell 8, such that the slurry mixer shaft 5 extends within said flotation tank 9. The slurry mixer haft 5 is equipped with a mixer head 5 for agitating the slurry within the flotation tank 8.

A first aspect of the present disclosure concerns a transmission assembly 1 for a slurry mixer providing fluid addition via a mixer shaft 5. That is, a fluid may be introduced into the slurry via the mixer shaft 5 either directly form the mixer shaft 5, and / or from a slurry mixer head whereto the fluid is directed via the mixer shaft 5.

The transmission assembly 1 comprises a gear transmission device 2 for converting an input rotation to an output rotation, the input rotation being relatively high-speed and low- torque with respect to the output rotation, whereas the output rotation is relatively low- speed and high-torque with respect to the input rotation. The transmission device 2, in turn, comprises an input shaft 3 for receiving the input rotation and an output shaft 4 for providing the output rotation to a slurry mixer shaft 5. Particularly, the output shaft 4 of the transmission device 2 is a hollow tubular shaft arranged to nest a portion 5c of a slurry mixer shaft 5 therein. The transmission assembly 1 further comprises the slurry mixer shaft 5 fixed to the output 4 shaft of the transmission device 2, so as to extend towards a slurry mixer direction. The slurry mixer shaft is equipped with an axial inner passage 5a extending therethrough for conducting a fluid flow. It should be noted, that the slurry mixer shaft 5 may be composed of more than one separate section attached to each other so as to form the mixer shaft 5. In such a case, the consecutive mixer shaft sections could be attached to each other, for example, by flanged joints. Moreover, the mixer shaft 5 may comprise at a slurry mixer direction end thereof, a slurry mixer head 5d having a shape and dimensioning suitable for agitating slurry when the mixer shaft 5 is rotated.

It should be noted, that in the context of the present disclosure, the slurry mixer direction should be understood as the direction, with respect to the transmission assembly 1 , in which the slurry tank resides. That is, in a conventional situation where the transmission assembly 1 is positioned above a slurry tank, the slurry mixer direction would be downwards. However, other configurations are foreseeable within the scope of the present disclosure.

Moreover, the slurry mixer shaft 5 comprises, on a portion 5b not nested by the output shaft 4, in the slurry mixer direction, a discontinuity 5b' on the mechanical structure of the slurry mixer shaft 5. The discontinuity 5b' is arranged to exhibit a local maximum on internal stresses caused by mixing forces, when in use. Such an arrangement provides a pre-determined failure point that is located outside the transmission device. In other words, a mechanical failure caused by excessive mixing forces can be isolated outside the transmission device, on the slurry mixer shaft 5. Most importantly, the likelihood of excessive mixing forces causing failure of the transmission device 2 are minimized, as the failure will most likely occur at the discontinuity 5b'.

As a further consequnece, a mechanical failure caused by excessive mixing forces can be repaired by replacing the slurry mixer shaft 5 or a portion of it. Most importantly, this increases the reliability and reparability of the transmission assembly 1 and an associated slurry mixer.

Arranging a discontinuity 5b' on the mechanical structure of the slurry mixer shaft 5 provides a further advantage of simultaneously exhibiting a local stress maximum for radial and torsional mixing forces with respect to the slurry mixer shaft 5. This is particularly prominent when compared to arranging a pre-determined failure point at a flanged joint, where the bolts used for joining the flange are suitable for exhibiting a local stress maximum for a shear forces caused by torsional mixing forces but not so much for tensile forces caused by radial mixing forces. Moreover, it has been found that dimensioning such bolts to provide a suitable pre-determined failure point for an excessive radial mixing force will not result in a practical arrangement for withstanding ordinary, non-excessive torsional mixing forces.

According to an embodiment of the first aspect, the portion 5c of the slurry mixer shaft 5 nested within the output shaft 4 has a cross-sectional outer dimension differing from that of an adjacent portion 5b of the slurry mixer shaft 5 in the slurry mixer direction. Such a construction results in a shoulder 5b' being formed on the outer surface of the slurry mixer shaft 5. Moreover, the shoulder 5b' forms the discontinuity on the mechanical structure of the slurry mixer shaft 5.

In this context, the cross-sectional dimension of a shaft should be understood, for shafts having a round cross-section, as the diameter thereof, and for shafts having non-round cross-section, as the largest cross-sectional dimension thereof.

According to another embodiment of the first aspect, the discontinuity, preferably provided as the shoulder 5b', is formed on the slurry mixer shaft 5 at a level of a slurry mixer side end 4a of the output shaft 4. That is, in this particular embodiment the discontinuity 5b' does not necessarily need to abut the slurry mixer side end 4a, but should be located in the immediate vicinity thereof. According to a further embodiment of the first aspect, the discontinuity, preferably provided as the shoulder 5b' on the slurry mixer shaft 5, is arranged to abut the slurry mixer side end 4a of the output shaft 4, thus forming a part of an axial coupling arrangement between the slurry mixer shaft 5 and the output shaft 4.

Suitably, at least the portion 5c of the slurry mixer shaft 5 nested within the output shaft 4 has an outer cross-sectional dimension of preferably between 30 - 190 mm, more preferably between 40 - 140 mm. For the mixer shaft materials conventionally used, such dimensions have been found to provide a pre-determined failure point suitable for conventional applications of slurry mixing and the transmission devices used therewith. Moreover, suitably at least the portion 5c of the slurry mixer shaft 5 nested within the output shaft 4 has an outer cross-sectional dimension differing from that of an adjacent portion 5b of the slurry mixer shaft 5 in the slurry mixer direction, such that the dimension of said adjacent portion 5b is preferably 5 - 60 %, more preferably 10 - 50 %, most preferably 20 - 40 % greater than that of the nested portion 5c.

According to further embodiment of the first aspect, a portion 5d of the slurry mixer shaft 5 extends at least a distance from the output shaft 4 in a direction opposite to the slurry mixer direction. Such an arrangement facilitates both providing an axial locking arrangement between the output shaft 4 and the slurry mixer shaft 5, and providing a fluid flow to the inner passage 5a of the flotation mixer shaft 5.

Moreover, the portion 5d of the slurry mixer shaft 5 extending from the output shaft 4 in a direction opposite to the slurry mixer direction may be equipped with a fastener element for abutting against a side end 4b of the output shaft 4 opposite to the mixer side end 4a, the output shaft 4 being thus axially locked between the shoulder 5b' and the fastener element of the flotation mixer shaft 5. Such an arrangement facilitates the replacement of the slurry mixer shaft 5 in order to repair a mechanical failure thereof, for example.

Alternatively, or additionally, the portion 5d of the slurry mixer shaft 5 extending from the output shaft 4 in a direction opposite to the slurry mixer direction may be connected to a rotary coupling 6 for providing a fluid flow to the inner passage 5a of the slurry mixer shaft. Particularly, such a rotary coupling 6 provides a sealed fluid connection between a stationary coupling portion and the rotating slurry mixer shaft 5, when in use. This kind of arrangement provides a coupling for a fluid flow via the slurry mixer shaft 5, which coupling does not hinder the replacement of a slurry mixer shaft 5, for example in order to repair a mechanical failure thereof. The transmission assembly according to the any of the embodiments of the first aspect of the disclosure, as discussed above, may preferably, but not necessarily, be provided a transmission assembly 1 for a flotation cell.

According to second aspect of the present disclosure, a flotation cell 8, being a specific example of a slurry mixer, is provided. The flotation sell may be used, for example, separating valuable minerals from ore. The flotation cell comprises a flotation tank 9 for receiving a slurry, and a slurry mixer head 5e arranged within the flotation tank for mixing the slurry. The flotation cell 8 further comprises a transmission assembly 1 according to any of the embodiments of the first aspect of the disclosure, as discussed above. The slurry mixer shaft 5 is coupled with the slurry mixer head 5e for rotating said slurry mixer head and for introducing a fluid flow into the slurry via the slurry mixer shaft 5 and the slurry mixer head 5a.

The use of a transmission assembly 1 according to the present disclosure is particularly advantageous in flotation applications, because excessive mixing forces are a particularly prominent risk in a flotation process. This is due to the fact that a malfunction or failure upstream of the flotation process may result in oversized particles being introduced into the flotation cell, which in turn may result in excessive mixing forces or even jamming the mixer head suddenly. Even without a malfunction or failure upstream of the flotation process, particularly in in connection with flotation application in the mining industry, excessive mixing forces are a prominent risk. In mining applications, flotation is commonly the first process after the mineral ore has been mechanically crushed, resulting in a fairly heterogenous slurry, which in turn results in an increased risk of excessive mixing forces.