FIELD OF THE INVENTION

The present invention relates to a a drum filter apparatus according to the preamble of claim 1 . BACKGROUND OF THE INVENTION

Filtration is a widely used process whereby a slurry or solid liquid mixture is forced through a media, with the solids retained on the media and the liquid phase passing through. Examples of filtration types include depth filtration, pressure and vacuum filtration, and gravity and centrifugal filtration.

Both pressure and vacuum filters are used in the dewatering of mineral concentrates. Pressure filtration is based on the generation of an overpressure within a filtration chamber. Consequently, solids are deposited onto the surface of the filter medium and filtrate flows through the filter medium into the filtrate channels. Pressure filters often operate in batch mode because continuous cake discharge is more difficult to achieve.

Vacuum filtration is based on producing a suction within the filtrate channels and thereby forming a cake of mineral on the surface of the filter medium. The most commonly used filter types in vacuum filters are filter cloths and ceramic filters. There exists several types of vacuum filters, ranging from belt filters to drums. The invention is, however, related to rotary vacuum drum filters.

Rotary vacuum drum filters are used for the filtration of relatively free filtering suspensions on a large scale, such as the dewatering of mineral concentrates. The dewatering of mineral concentrates requires large capacity in addition to producing a cake with low moisture content. The vacuum drum filter may comprise a cylindrical support structure rotating around a longitudinal shaft forming a centre axis for the drum. There are a plurality of filter plates arranged on the outer surface of the cylinder. Each filter plate forms a portion of the cylindrical outer surface of the cylinder. Each filter plate is during each revolution of the shaft displaced for a certain period into a slurry basin situated below the shaft. The filter plate rises out of the basin when the revolution of the shaft proceeds. When the filter plate is submerged in the slurry basin a cake forms onto the outer surface of the filter plate due to the vacuum within the filter plate. Once the filter plate comes out of the basin, the pores are emptied as the cake is deliquored for a predetermined time which is essentially limited by the rotation speed of the drum. The cake can be discharged by a back- pulse of air or by scraping, after which the cycle begins again. The filter plates are advantageously made of porous ceramic.

The filter plates are in prior art solution attached with bolts to the drum. There are fastening points provided with holes passing through the filter plate. A fastening flange is positioned into each hole in the filter plate. The fastening flange comprises a hole passing through the fastening flange. The filter plate is fastened by bolts passing through the hole in the fastening flange in the filter plate. The holes passing through the filter plate will reduce the filter area in the outer surface of the filter plate. The holes and the bolts passing through the filter plate will also increase the risk of leakage.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to present a drum filter apparatus with an improved fastening arrangement for the filter plates in the appa- ratus.

The object of the invention is achieved by a fastening arrangement in a drum filter apparatus according to the independent claim 1 . Preferred embodiments of the invention are disclosed in the dependent claims.

The drum filter apparatus comprises a cylindrical drum that is sup- ported with a rim structure on a rotatable shaft having a centre axis, an outer surface of the drum comprises a number of individual filter plates forming an essentially continuous cylindrical filter surface, each filter plate comprises an inner surface and a curved outer surface forming the filter surface of the filter plate, each filter plate is attached through at least three fastening points to the rim structure. The fastening arrangement at each of the at least three fastening points comprises:

a first recess extending from the inner surface of the filter plate into a portion of the filter plate so that the outer surface of the filter plate remains unbroken,

a fastening flange positioned at least partly in the first recess and being firmly attached to the filter plate,

a longitudinal fastening member comprising a first end portion and a second opposite end portion, the first end portion being attached to the fastening flange and the second end portion being attached to the rim structure, at least one snap locking means positioned in the fastening flange or in the rim structure or in both and providing snap locking of the fastening member to the filter plate or to the rim structure or to both, wherein

the filter plate is mounted on the drum by pressing the filter plate ra- dially to the drum so that the snap locking means locks the filter plate to the rim structure of the drum.

The fastening arrangement in the drum filter apparatus according to the invention will eliminate the holes passing through the filter plate. The outer surface of the filter plate will thus be unbroken, which leads to a bigger effec- tive filter area in the filter plate. It is only the outer surface of the filter plate that functions as the filter surface in the filter plate. The inner surface and the edge surfaces of the filter plate are impervious to water.

The fastening arrangement in the drum filter apparatus is identical in all fastening points in the filter plate. This fact will lower the production costs of the fastening arrangement compared to a situation where the fastening arrangements in the different fastening points are different.

The fastening arrangement in the drum filter apparatus according to the invention makes the connection and the disconnection of the filter plates to the drum fast and efficient. The connection and the disconnection of the filter plates to the drum could be done e.g. by a vacuum lifter.

The fastening arrangement in the drum filter apparatus according to the invention makes it easy to regulate the rigidity of the fastening of the filter plate to the drum. This can be done by changing the snap locking means. The snap locking means is in one advantageous embodiment a spring ring posi- tioned in a second groove within the second recess. The spring load is proportional to the cross sectional area of the spring ring. The rigidity of the fastening of the filter plate can thus be altered by changing the cross sectional area of the spring ring.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of example embodiments with reference to the accompanying drawings, in which

Figure 1 is a perspective top view of a drum filter apparatus, wherein the inventive fastening arrangement may be applied, Figure 2 is a perspective top view of the drum of figure 1 with some of the upper filter plates being removed,

Figure 3 is a cross section of the drum of figure 2,

Figures 4 is a cross section of a filter plate showing a prior art fas- tening arrangement to the right in the figure and a fastening arrangement according to the invention to the left in the figure,

Figure 5 shows the fastening flange of the inventive fastening arrangement in figure 4,

Figure 6 shows the fastening member of the inventive fastening ar- rangement in figure 4,

Figure 7 shows the fastening flange of figure 5 and the fastening member of figure 6 in an assembled form,

Figure 8 is a cross section of a filter plate showing a second embodiment of a fastening arrangement according to the invention,

Figure 9 shows the fastening flange and the fastening member in a disassembled form.

Figure 10 shows a third embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figure 1 is a perspective top view illustrating a drum filter apparatus in which the inventive fastening arrangement may be applied. The drum filter apparatus 10 comprises a frame 8, a cylindrical drum 20 supported within the frame 8, a slurry basin 9 under the drum 20. The drum 20 comprises a shaft 25 that is supported at both ends with bearings 1 1 , 12 on the frame 8. The shaft 25 and thereby also the drum 20 is rotatated by an electric motor 7 through a gear. The drum 20 rotates around a centre axis X-X forming the longitudinal centre axis X-X of the shaft 25.

Figure 2 is a perspective top view illustrating the drum of figure 1 and figure 3 is a cross section of the drum 20 of figure 1 . The drum 20 is supported with a rim structure 21 at the axial X-X middle point of the drum 20 and at both ends of the drum 20. The rim structure 21 can be supported on the shaft 25 e.g. by a disc structure or by spokes. The rim structure 21 comprises further a plurality of support members 22 attached to each rim 21 . The support members 22 are formed of straight bars having a rectangular cross section. The support members 22 are attached to the rim 21 by axially X-X directed bolts passing through the support members 22 and being screwed into holes in the side surface of the rim structure 21 . The support members 22 are arranged on the circumference of a circle having the centre on the centre axis X-X. Each ceramic filter plate 23 is attached to two opposite support members 22 so that an outer surface 23B of the filter plates 23 forms the cylindrical outer filter sur- face of the drum 20. The axial X-X length of the drum 20 is divided into two sections. A first ring R1 of filter plates 23 is positioned on the first section of the drum 20 and a second ring R2 of filter plates 23 is positioned on the second section of the drum 20. The filter plate 23 comprises a planar inner surface 23A, a curved outer surface 23B and edge surfaces connecting the side edges of the inner surface 23A and the side edges of the outer surface 23B of the filter plate 23. The curvature of the outer surface 23B of the filter plates 23 coincides with the circumference of the outer surface of the drum 20. The centre of the radius R forming the circumference of the outer surface of the drum 20 is on the longitudinal centre axis X-X of the drum 20.

The number of the ceramic filter plates 23 on the drum 20 may vary depending on the size of the drum 20. The diameter of the drum 20 may be in the order of 1 to 5 meter and the length of the drum 20 may be in the order of 2 to 10 meter. The filtering area of the filter plates 23 may be in the order of 10 to 200 m ² . A lower portion of the drum 20 is submerged in the slurry basin 9. The outer surface 23B of the ceramic filter plate 23 has a microporous structure so that water can enter into the filter plate 23. The interior of the filter plate 23 is porous so that water can travel within the filter plate 23. The inner surface 23A of the filter plate 23 and the edge surfaces of the filter plate 23 are impervious to water. This means that water can penetrate into the filter plate 23 only through the outer surface 23B of the filter plate 23.

Each filter plate 23 is also provided with a tube connector 29 in order to provide a fluid duct from the interior of the the filter plate 23 to a collector piping 30 provided in the drum 20. The tube connector 29 in each filter plate 23 is connected to a radial inner tube 31 supported on the support member 22 and passing through the support member 22. The inner end of the radial inner tube 31 is connected to an axial tube 32 passing in the axial X-X direction through the drum 20. The axial tubes 32 are at one end of the drum 20 connected to radial outer tubes 33. The radial outer tubes 33 extend from the outer edge of the drum 20 to the shaft 25 of the drum 20. The radial outer tubes 33 are connected to a distributing valve 13 disposed on the shaft 25 of the drum 20. The distributing valve 13 transmits vacuum or overpressure to the filter plates 23. The distributing valve 13 may comprise zones such that a part of the filter plates 23 are subjected to a higher vacuum or overpressure and a part of the filter plates 23 are subjected to a smaller vacuum or overpressure. If a long drum 20 is used, it can be advantageous to have a distributing valve 13 at both ends of the drum 20.

The vacuum system providing the vacuum through the collector piping 30 to the filter plates 23 is not shown in the figures. The pump for removing the filtrate from the collector piping 30 is also not shown in the figures. It is possible to arrange reverse flushing or backwash either such that some of the filtrate or clean water from an external water source is led back to the collector piping 30 by means of a backwash system, such as a backwash pump.

As the drum 20 rotates, the filter plates 23 move into and through the basin 9. Each filter plate 23 goes through different process phases during one revolution of the drum 20. In a cake forming phase, the liquid is passing through the outer surfaces 23B of the filter plate 23 into the interior of the filter plate 23 when it travels through the slurry, and a cake is formed on the outer surface 23B of the filter plate 23. The filter plate 23 enters the cake drying phase after it leaves the basin 9. If cake washing is required, it is done in the beginning of the drying phase. In the cake discharge phase the cake is scraped off from the outer surface 23B of the filter plate 23 by ceramic scrapers so that a thin cake is left on the outer surface 23B of the filter plate 23. There is thus a small gap between the scraper and the outer surface 23B of the filter plate 23. In the backflush phase of each rotation, water (filtrate) is pumped in a reverse direction from the inside of the filter plate 23 through the filter plate 23 to the outside of the filter plate 23. The backflush water washes off the residual cake and cleans the pores of the filter plate 23.

Figure 2 shows that each filter plate 23 comprises fastening points P1 , P2, P3 comprising holes passing through the filter plate 23 in a radial direction. The filter plates 23 are attached to the support members 22 by bolts 70 passing through the holes in the fastening points P1 , P2, P3. Two fastening points P1 , P2 are positioned at the axial X-X outer edge of the filter plate 23 and one fastening point P3 is positioned at the axial X-X inner edge of the filter plate 23.

Figures 4 is a cross section of a filter plate showing a prior art fas- tening arrangement 50 to the right in the figure and a fastening arrangement 100 according to the invention to the left in the figure. The prior art fastening arrangement 50 shown to the right in figure 4 comprises at each fastening point P1 , P2, P3 a first hole 45 passing through the filter plate 23, a fastening flange 60, a rubber bushing 80 and a bolt 70. The fastening flange 60 comprises an upper portion 61 forming essentially a cylinder and a second lower portion 62 forming essentially a collar. The upper portion 61 is fitted within the first hole 45 in the filter plate 23 and the collar like lower portion 62 is fitted against the inner surface 23A of the filter plate 23. The fastening flange 60 can be attached by glue to the filter plate 23. The fastening flange 60 comprises further a second hole 63 extending through the fastening flange 60 from the upper portion 61 to the lower portion 62. The second hole 63 has a first diameter within the upper portion 61 and a second smaller diameter within the lower portion 62 of the fastening flange 60. A landing 64 is thus formed within the second hole 63. The end part 71 of the bolt 70 will thus seat against the landing 64 when the bolt 70 is tightened. A first end of the cylindri- cal rubber bushing 80 extends partly into the lower portion 62 of the fastening flange 60. A second opposite end of the cylindrical rubber bushing 80 is seated against the upper surface of the support member 22. The exterior threads at the outer end 72 of the bolt 70 are received by corresponding interior threads in a hole in the support member 22. Tightening of the bolt 70 will press the filter plate 22 tightly against the upper surface of the support member 22. The first hole 45 passing through the filter plate 23 at each fastening point P1 , P2, P3 will reduce the effective filtering area of the filter plate 23. The upper curved filtering surface 23B of the filter plate 23 is broken at each hole 45.

The fastening arrangement according to the invention 100 shown to the left in figure 4 comprises at each fastening point P1 , P2, P3 a first recess 46 made into the filter plate 23, a fastening flange 1 10, a rubber bushing 130 and a fastening member 120. The first recess 46 extends from the lower surface 23A of the filter plate 23 into a portion of the filter plate 23. The opposite surface of the filter plate 23 remains unbroken at the first recess 46. The cylin- drical bushing 130 corresponds to the cylindrical bushing 80 in the prior art fastening arrangement. A first end of the cylindrical rubber bushing 130 extends partly into the lower portion 1 12 of the fastening flange 1 10. A second opposite end of the cylindrical rubber bushing 130 is seated against the upper surface of the support member 22 or extends partly into the support members 22. Figure 5 shows the fastening flange of the inventive fastening arrangement. The fastening flange 1 10 comprises a first portion 1 1 1 forming essentially a cylinder with a closed end and a second portion 1 12 forming essentially a collar. The first portion 1 1 1 is fitted within the first recess 46 in the filter plate 23 and the second portion 1 12 is fitted against the lower surface 23B of the filter plate 23. The fastening flange 1 10 can be attached by glue to the filter plate 23. The fastening flange 1 10 comprises further a second recess 1 13 extending from the second portion 1 12 towards the first portion 1 1 1 of the fastening flange 1 10 i.e. in the same direction as the first recess 46. There is fur- ther a circular second groove 1 14 extending radially into the inner surface of the second recess 1 13 within the first portion 1 1 1 of the fastening flange 1 10.

Figure 6 shows the fastening member of the inventive fastening arrangement. The longitudinal fastening member 120 has an essentially cylindrical form and comprises a first end portion 121 and an opposite second end portion 122 provided with an external thread. The first end portion 121 of the fastening member 120 comprises a first circular groove 123 extending radially into the outer surface of the first portion 121 of the fastening member 120. The second end portion 122 of the fastening member 120 comprises further a gripping portion 125 with two parallel planar side surfaces. The two parallel side surfaces form gripping surfaces for an adjustable wrench or fork wrench.

Figure 7 shows the fastening flange and the fastening member in an assembled form. This figure shows that first snap locking means 140 is fitted into the second groove 1 14 in the fastening flange 1 10.

The fastening member 120 can be attached to the support member 22 by threading the second end portion 122 of the fastening member 120 into a corresponding hole 75 in the support member 22. There are exterior threads at the second end portion 122 of the fastening member 120 and interior threads in the corresponding hole 75 in the support member 22. The hole 75 can either extend only into a portion of the support member 22 or pass through the support member 22. The cylindrical rubber bushing 130 can then be pushed on the fastening member 120. The filter plate 23 can then be fastened to the fastening members 120 protruding in a radial direction from the upper surface of the support member 22 by pushing the filter plate 23 on the fastening members 120 so that the first end portions 121 of the fastening mem- bers 120 glide into the corresponding second recesses 1 13 in the first portion 1 1 1 of the fastening flange 1 10. The filter plate 23 will be locked to the fas- tening member 120 by the spring ring 140 setting into the circular first groove 123 on the fastening member 120. A first end of the cylindrical rubber bushing 130 will extend partly into the lower portion 1 12 of the fastening flange 1 10 and a second opposite end of the cylindrical rubber bushing 130 will seat against the upper surface of the support member 22 or extend partly into the support member 22.

Figure 8 is a cross section of a filter plate showing a second embodiment of a fastening arrangement according to the invention and figure 9 shows the fastening flange and the fastening member in a disassembled form. Figure 9 illustrates the porous structure of the filter plate 23. The fastening flange 1 10 corresponds essentially to the fastening flange shown in figure 5. The fastening flange comprises a first portion 1 1 1 having essentially the form of a cylinder and a second portion 1 12 having essentially the form of a collar. The first portion 1 1 1 is within the recess 46 in the filter plate 23 and the second portion 1 12 is seated against the inner surface 23A of the filter plate 23. The longitudinal fastening member 120 forms advantageously an integral part of the fastening flange 1 10. The fastening member 120 is essentially cylindrical and comprises a first end portion 121 and a second end portion 122. The second end portion 122 of the fastening member 120 is incorporated with the second portion 1 12 of the fastening flange 1 10. The first end portion 121 of the fastening member 120 is provided with a first circular groove 123 extending radially into the outer surface of the fastening member 120. There is a third recess 1 15 extending in a direction opposite to the direction of the first recess 46 into the support member 22 in the rim structure 21 . The third recess 1 15 receives the first end portion 121 of the fastening member 120. The third recess 1 15 comprises a second circular groove 1 16 extending radially into the surface of the third recess 1 15. The second circular groove 1 16 is provided with second snap locking means 141 . The support member 22 is also provided with axial X-X holes 22A through which the support member 22 can be fas- tened to the rim 21 of the drum 20. The cylindrical rubber bushing 130 corresponds to the cylindrical rubber bushing 130 in figure 4. The rubber bushing 130 is positioned between the fastening flange 1 10 and the support member 22.

Figure 10 shows a third embodiment of the invention. This third em- bodiment corresponds to the second embodiment shown in figure 9 except that the fastening member 120 is in this embodiment fastened at both ends with snap lock means. The fastening member 120 has an essentially cylindrical form and comprises a first end portion 121 and an opposite second end portion 122. The first end portion 121 of the fastening member 120 is fastened with first snap lock means 140 to the fastening flange 1 10. The second end portion 122 of the fastening member 120 is fastened with second snap lock means 141 to support member 22. Both snap lock means 140, 141 are advantageously identical. The first snap lock means 140 comprises a first spring ring positioned in a circular groove 1 14 in a second recess 1 13 in the fastening flange 1 10. The second snap lock means 141 comprises a second spring ring posi- tioned in a circular groove 1 16 in a third recess 1 15 in the support member 22. The fastening member 120 comprises a first circular groove 123 in the first end portion 121 and a second circular groove 124 in the second end portion 122. The first circular groove 123 and the second circular groove 124 extend radially into the outer surface of the fastening member 120. The rubber bushing 130 is positioned between the fastening flange 1 10 and the support member 22. The support member 22 is also provided with axial X-X holes 22A through which the support member 22 can be fastened to the rim 21 of the drum 20.

The longitudinal fastening member 120 has advantageously an essentially cylindrical form with a circular cross section in all embodiments in the invention.

The cylinder hat like form of the fastening flange 1 10 is an advantageous form. The fastening flange 1 10 can be attached with glue from the cylindrical outer surface of the first portion 1 1 1 , from the outer bottom surface of the first portion 1 1 1 and from the planar lower surface of the second portion 1 12 to the filter plate 23. There is thus a fairly big fastening area for the glue between the fastening flange 1 10 and the filter plate 23. The fastening flange 1 10 could, however, also have some other form. The fastening flange 1 10 should comprise a second recess 1 13 or have the fastening member 120 fixedly attached to the second recess 1 13 and have a form that fits into the first recess 46 in the filter plate 23.

The fastening flange 1 10 and the fastening member 120 are advantageously made of acid-proof steel. The fastening flange 1 10 is naturally tightly fitted in the recess 46 in the filter plate 23. The outer diameter of the first portion 1 1 1 of the fastening flange 1 10 corresponds to the inner diameter of the recess 46 in the filter plate 23. The depth of the recess 46 in the filter plate 23 corresponds to the depth of the first portion 1 1 1 of the fastening flange 1 10. The fastening member 120 is also tightly fitted in the second recess 1 13 in the fastening flange 1 10 and/or in the second recess 1 15 in the rim structure 21 , 22.

The filter plate 23 comprises in the figures three fastening points P1 , P2, P3. Two fastening points P1 , P2 are at the outer ends of the drum 20 and one fastening point P3 is at the middle of the drum 20 in the axial direction. Three fastening points P1 , P2, P3 are needed in order to achieve a firm attachement of the filter plate 23. There could naturally be more than three fastening points P1 , P2, P3 if a need for further fastening points would for some reason arise.

The axial X-X length of the drum 20 is divided into two sections so that there are two rings R1 , R2 of filter plates 23 in the drum 20. There could naturally be more than two rings R1 , R2 of filter plates 23 on the drum 20 or only one ring of filter plates 23 on the drum 20. The appropriate number of rings R1 , R2 of filter plates 23 on the drum 20 depends on the length of the drum 20.

The fastening of the filter plates 23 to the drum 20 need not necessary be through the support members 22. It might be possible to fasten the filter plates 23 directly to the rims 21 of the drum 20. The inner surface 23A of the filter plates 23 would thus have to be curved. The fastening of the filter plates 23 would thus be to the curved outer surface 23B of the rims 21 .

In embodiments described herein, a material to be filtered is referred to as a slurry, but embodiments of the invention are not intended to be restricted to this type of fluid material. The slurry may have high solids concen- tration, e.g. base metal concentrates, iron ore, chromite, ferrochrome, copper, gold, cobalt, nickel, zinc, lead and pyrite.

Upon reading the present application, it will be obvious to a person skilled in the art that the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples de- scribed above but may vary within the scope of the claims.