AU661152B2 - A flotation machine - Google Patents

Description

661152

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S F Ref: 241669 r Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Industrial Equipment Company Limited Qual De Lile 1211 Geneva 1

SWITZERLAND

Robert Anthony Shelston, Anthony Wyndham Mandy Sive, Bruce Andrew Firth Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia A Flotation Machine ASSOCIATED PROVISIONAL APPLICATION DETAILS [311 Application No(s) [333 Country PL2621 AU [323 Application Date 26 May 1992 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815/3 '1 f 2 TECHNICAL FIELD The present invention relates to flotation machines and more particularly to the impeller and baffle assembly construction of such flotation machines. In this regard it should be appreciated that the impeller is also known as the rotor, and the baffie assembly as the stator, BACKGROUND TO THE INVENTION Flotation machines are described in Australian patents 606216 and 562457, as well as Australian applications 23458/88 and 68647/91.

Various baffle assemblies and impeller constructions are illustrated in the above specifications.

Specification 575102 has the baffle assembly supported on a plate directly mounted on the bottom of the flotation tank. The baffle blades project vertically upwardly from this plate and surround the impeller.

1 5 The impeller consists of vertical blades which depend from a plate g extending generally transverse of the direction of rotation. A similar baffle assembly and impeller are described in specification 571281.

The baffle assembly and impeller of specification 562475 is again of similar construction as is that illustrated in specification 23548/88.

20 Specification 68647/91 however is slightly different in that the baffle blades depend from a mounting plate which is positioned slightly above the plate of the impeller. The two plates co-operate to provide a -3channel into which air is directed.

Some impellers have passages which deliver air adjacent to the impeller fins. For example one known impeller has passages extending to the extremities of the fins. Another impeller has passages extending to the base of the fins. However in all these previously known impellers, the blades depend from a plate which extends radially outwardly a similar radial distance to the impeller blades.

The above discussed impellers and baffle assemblies are, at least in some instances, energy inefficient.

Still further, those previous designs which have bottom mounted baffle assemblies and upward pumping impellers have the disadvantage of restricting the flow under the impeller. This restriction in flow can allow sanding to occur around the bottom mounted devices, reducing the effective volume of the tank.

o* 15 Some previous designs with top mounted baffle assemblies have utilised down pumping impellers to avoid bottom sanding. The down pumping impeller requires expensive wear linings in the base of the tank to prevent erosion.

Some previous designs with top hung baffle assemblies and upward pumping impellers have included slurry slots and impeller covers. The up flow of material into the slurry has resulted in blocking of the slots.

o• oo SUMMARY OF THE INVENTION According to the invention there is provided a flotation machine comprising: an impeller assembly comprising a vertically extending drive shaft and a plurality of radially extending impeller blades at the lower extremity of said shaft, said blades each having an exposed upper edge and an exposed lower edge, vertically extending free flow passages being defined between adjacent blades; a baffle assembly including an annular baffle plate extending generally radially outwardly relative to said shaft, a plurality of baffle blades depending from said plate and surrounding the impeller blades, and a central aperture in said plate through which said drive shaft projects and through which air under pressure will be directed in use; and a sleeve surrounding the drive shaft and connected at its lower end to the radially inner edge of the annular baffle plate, said sleeve being adapted to convey air under pressure to said central aperture, the arrangement between the impeller and the baffle assembly being such that a gap is formed between said upper edge of the blades and the underside of the baffle plate and air under pressure which in use passes through said central aperture is directed into that gap past the exposed upper edges of the impeller blades and directly into the spaces between the impeller blades, and fluid and entrained particles aze drawn 9 0* 0• 0 *e o *o IN:\lIbttI00525:HRW in use, as the impeller rotates upwardly past the exposed lower edges of the blades through the vertically extending free flow passages so as to mix with the air that has been introduced into the impeller blades.

It is preferred that the impeller blades be connected to the drive shaft through a hub, the hub having a diameter which is substantially less than the diameter of the impeller.

The shaft plate may be generally flat, or concave or convex. The baffle blades may be generally vertical or may diverge radially outwardly from the plate.

The gap between the upper edge of the impeller blades and the undersurface of the baffle plate is preferably relatively small and may be between 5 and 20 mm.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. 1 is a schematic perspective view of an impeller and baffle assembly of a flotation machine; Fig. 2 is a schematic side elevation of the baffle assembly and impeller of Fig.

1; Fig. 3 is a schematic side elevation of a modification of 2~ [N:\lIbtt00525:HRW

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-6the baffle assembly and impeller of Figures 1 and 2; Fig. 4 is a schematic side elevation of a further modification of the baffle assembly and impeller of Figs. 1 and 2; and Fig. 5 is a schematic side elevation of a still further modification of the baffle assembly and impeller of Figs. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figs. 1 and 2 there is schematically depicted a baffle assembly (stator) 11 and an impeller assembly (rotor) 10 of a flotation machine.

The impeller 10 includes a drive shaft 12 which is rotatably driven. The lower end of the drive shaft 12 is provided with an impeller 13 consisting of a mounting hub 14 which supports a plurality of impeller blades 15. It will be noted that the diameter of the hub 14 is significantly less than the diameter of the impeller 13 so that the upper edges 23 of the blades 15 are to a large extent exposed. The blades 15 depend from the hub 14 and extend radially relative to the longitudinal and rotational axis of the shaft 12. As can be seen, particularly from Fig. 2, the blades 15 extend beyond the radial extremity of the hub 14. The spaces between adjacent blades form vertically extending free flow passages, as can be clearly seen from the figures.

The baffle assembly 11 includes a mounting sleeve or pipe 16 which in use is fixed to the body of the flotation tank. Fixed to the lower end of

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o *o *s rI r~f -7the sleeve 16 is an annular baffle plate 17. Depending from the outer periphery of the plate 17 are baffle blades 18 which are equally angularly spaced about the longitudinal axis 19. The blades 18, in this particular embodiment, diverge downwardly. However, as seen in Figure 4, the blades on opposite ides of the baffle plate may be parallel (ie, the blades are vertical).

Defined between the shaft 12 (hub 14) and the radially inner peripheral edge 20 of the plate 17, is a circular aperture 21 communicating with the passage 22 enclosed by the sleeve 16.

A gap 24 is defined between the underside 25 of the baffle plate 17 and the exposed upper edges of the impeller blades 15. That gap 24 should not be too wide to ensure effective operation of the machine, not too narrow which could result in excessive wear between the baffle plate and the blades 15. The preferred gap is about 6mm although a gap of 15 between 5mm and 20mm will be appropriate for different machines.

e e In operation o F the above described baffle assembly 11 and impeller 13, e I1 air under pressure is delivered to the passage 22 to exit via the aperture 21. The air then enters the gap 24 from where it is able to pass directly S-into the spaces 26 between the impeller blades 15. Since the upper 20 edges 23 of the impeller blades 15 are exposed, the air simply travels past those upper edges 23 into the spaces 26 and this ensures effective air entrainment with the material being mixed. Simultaneously, the shaft 12 is rotatably driven to cause rotation of the blades 15 about the longitudinal axis 19. This draws material upwardly from the tank and S: 2-5 propels it radially outward through the blades 18. The material is mixed -8 with the air. Essentially the output flow is radially from the axis 19.

Still further, above the plate 17 is a quiescent zone extending from the plate 17 upward into the flotation cell. Still further, the plate 17 inhibits the inward flow of slurry from a position above the baffle assembly 11.

Accordingly the impeller 10 draws mainly from beneath the baffle assembly 11, allowing the impeller 10 to be positioned higher in the tank while still inhibiting "sanding". Still further, the baffle assembly 11 protects the impeller 10 from settled solids if a power failure occurs.

As the impeller 10 has an "open bottom" a vortex is generated beneath the impeller 10. This greatly enhances the flow of heavy particles upwardly into the impeller 10. This also aids in inhibiting "sanding" (particle deposition). The improved air entrainment referred to above enhances the flotation of the material being treated.

The blades 18 are inclined to the axis 19 by an angle of up to 450, but preferably by an angle of 150 to 20. The downwardly diverging configuration of the blades 18 aids in the formation of the above o• described vortex.

i S.In Figure 3, there is schematically depicted a modification of the above described impeller 10 and baffle assembly 11. In this prticular 20 embodiment the plate 17 (stator cover) is concaved upwardly so as to be Sgupwardly inclined away from the axis 19. The plate may conform to the surface of a cone or may be a portion of a sphere. The inclination of the major surfaces of the plate 17, if conical, may be up to 45' Preferably the inclination would be from 5' to *oo I" 1.

-9- The embodiment shown in Figure 4 has proved to be particularly effective, at least in some applications. The vertically aligned baffle plates 18 and the generally constant gap 24 are considered to be contributing factors in this effective performance. The parallel relationship between the surface 25 and the upper edges 23 of the blades ensures that air is drawn efficiently into the spaces 26 between the blades In Figure 5 the plate 17 is again modified so as to be concaved downwardly. The inclination of the major surfaces, if conical, may be up to 45°. Preferably the inclination would be from 50 to 150. Again the plate 17 may conform to the surface of a cone or a sphere.

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Claims (7)

1. A flotation machine comprising: an impeller assembly comprising a vertically extending drive shaft and a .'rality of radially extending impeller blades at the lower extremity of said shaft, said 0lades each having an exposed upper edge and an exposed lower edge, vertically extending free flow passages being defined between adjacent blades; a baffle assembly including an annular baffle plate extending generally radially outwardly relative to said shaft, a plurality of baffle blades dependirig from said plate and surrounding the impeller blades, and a central aperture in said plate through which said drive shaft projects and through which air under pressure will be directed in use; and a sleeve surrounding the drive shaft and connected at its lower end to the radially inner edge of the annular baffle plate, said sleeve being adapted to convey air under pressure to said central aperture, the arrangement between the impeller and the baffle assembly being such that a gap is formed between said upper edge of the blades and the underside of the baffle plate and air under pressure which in use passes through said central aperture is directed into that gap past the exposed upper edges of tb, impeller blades and directly into the spaces between the impeller blades, and fluid and entrained particles are drawn in use, as the impeller rotates upwardly past the exposed lower edges of the blades through the vertically extending free flow passages so as to mix with the air that has been introduced into the impeller blades.

2. A flotation machine according to claim 1 wherein the impeller blades are connected tot he drive shaft through a hub, the hub having a diameter which is 25 substantially less than the diameter of the impeller measured perpendicular to the axis of rotation of the impeller.

3. A flotation machine according to either preceding claim wherein the S baffle plate is flat, concave upwardly, or concave downwardly.

4. A flotation machine according to any preceding claim wherein the gap between the upper edge of the impeller blades and the undersurface of the baffle plate is between 5 and 20 mm.

5. A flotation machine according to any preceding claim wherein the baffle blades diverge downwardly.

6. A flotation machine according to any one of claims 1 to 4 wherein the b 35 baffle blades are vertical. •0 o (N:\llbttIO0525:HRW -11-

7. A flotation machine substantially as hereinbefore described with reference to Figs. 1 and 2, or any one of Figs. 3 to DATED this Thirteenth Day of Apfil .1995 Industrial Equipment Company Limited Patent Attorneys for the Applicant SPRUSON FERGUSON AL S. 4 1NA11btt1GU.25:HRW A Flotation Machine Abstract of the Disclosure A flotation machine including an impeller assembly The impeller assembly (10) is associated with a baffle assembly The impeller assembly (10) includes a drive shaft (12) provided at its lower end with a moLnting hub (14) upon which there is fixed impeller blades The blades (15) extend radially beyond the hub A sleeve (16) surrounding the shaft (12) provides a passage (22) through which air under pressure is delivered to the impeller assembly S, Figure 1. o0 e 5989W/GMM