The present invention relates to a method for pressure filt¬ ering of the kind, which is disclosed in the preamble of claim 1.

The invention also relates to a means for bringing about said method according to the preamble of the first means claim.

The invention especially relates to the solution of the pro¬ blem to loosen and discharge the filter cake as well as the washing and cleaning of the filter cloths at such a filter.

There are previously known pressure filters, for instance fro DE-C3.341.636 and DE-A3.527.735 , at which pressure filters the suspension means of the filter cloths in both cases are suspended by from the press plates of the pressure filter pro truding, hinged brackets and springs, while the lower ends of the filter cloths are substantially rigidly affixed to the press plates. The filter cloths are vibrated by means of a travelling vibration device, which is acting directly on the suspension rods of the filter cloths. At these previously known devices the filter chambers of the pressure filter are discharged one at a time, which results in very long dis¬ charge and cleaning times. Especially at short cycle times and great filter cake capacity this results in uneconomically and unreasonably long discharge times for such a pressure fil ter. The fixation of the filter cloths in the lower part of the press plates also results in severe strains and increased wear of the filter cloths.

From DE-A3.527.735 there is also known a pressure filter with a travelling, vertically movable cleaning device, which is cleaning the filter cloths in one filter chamber at a time. This also results in very long cycle times for the filter cloth cleaning operation.

FR-A1.33 .850 describes a pressure filter comprising weights at the lower edge of the filter cloths for the tension thereo

However, this filter does not comprise- any means for the vib¬ ration of the filter cloths. Futhermore, also in this case the cake discharge is effected one filter chamber at a time, which results in the disadvaπtagous long cycle times men- tioned above.

In order to overcome these problems of the Prior Art, a pres¬ sure filter has been developed, which is able to discharge the filter cakes in all the filter chambers at the same time and also is able to flush and clean all the filter cloths at the same time. This means of course a considerable improve¬ ment compared to the old technique, however, especially for short cycle times and great filter cake capacity, the time used for cake discharge and filter cloth cleaning remains a problem.

In order to elucidate this previously known pressure filter and the drawbacks and disadvantages thereof reference is made to "Book of Instruction Manual for urita Automatic Filter Press, KUF-10", September 1983, published by Sala Inter¬ national AB , Sala, and to the appending figures 1-3, which during various process stages discloses a section of such a filter press, in which section irrelevant components are excluded.

Such a previously known pressure filter 1 comprises a frame 2, a stationary end or head plate 3, a movable end or head plate

4, as well as press plates 5, 6 arranged therebetween (see also fig. 4). At least every second press plate 5 is provided with a membrane 7 on at least one side thereof. Through a supply conduit F the underside of said membrane can be supp¬ lied with a pressurized medium, for instance a hydraulic liquid or pressurized air. Between themselves the press plates

5, 6 and/or the end plates 3, 4 are in pairs forming pressure chambers 8. In each pressure chamber 8 there are arranged two filter cloths 9. Outside the filter cloths, the walls of the

pressure chambers exhibit drain channels 10 arranged in the plates 3-6 and the membrane 7 respectively, said channels through conduits 12 being connected to holes 14 passing through the plates. Also between the press plate 5 and the membrane 7 there are arranged distribution channels 16 cor¬ responding to the drain channels 10 for said pressurized medium. Some of the holes 14 constitute outlets B, E for separated liquid, while others C, D serve both as outlet for separated liquid and as inlet for pressurized gas, as will be explained in detail below.

The filter cloths 9 are sewn together at the top and fast¬ ened to suspension bars. Furthermore, the filter cloths 9 exhibit feed port fixtures 20 which, when the plates 3-6 are brought together, sεalingly connect to a feed supply con¬ duit A. The feed port fixture exhibits passages 22, which connect the feed supply conduit A with respective pressure chamber 8. The suspension bar is suspended by two pulling wire ropes 24 connected at the other end with wire rope drums 26. The wire rope drums are non-rotary and axially ov- ably arranged on two hexagonal shafts 28 connected to a lif¬ ting and descending motor. At their lower ends the filter cloths pass guide members 30 and then the filter cloths are two and two rolled onto spring-loaded cloth rollers 32 si - ilar to a roller blind roller. Futhermore, there are pipe- shaped members 34 constituting supply means G for washing liquid and exhibiting nozzles 36 intended for spraying wash¬ ing liquid onto the obliquely opposed filter cloth 9. The guide members 30, cloth rollers 32 and the pipe-shaped member 34 are arranged to simultaneously being brought along during movements with he press plates 5, 6 and the movable end plate 4.

The function of the press filter is as follows. The press plates 5, 6 and the movable end plate 4 are initially brought together with the aid of at least one hydraulic cylinder 38.

Then a for moisture removal intended suspension of solid particles in a liquid, for instance a water suspension of ore" concentrate with 65 % solids is introduced through the feed supply conduit A and the passage 22 of respective feed port fixture 20 in between the two filter cloths 9 of each pressure chamber 8, said filter cloths forming a filter ele¬ ment. The suspension is introduced under high pressure, for instance 4 bars. The main portion of the liquid is already now driven through the filter cloths and the moisture is al- ready at this stage reduced; for ore concentrate to 86-88 % STxL±ds. When the pressure chambers have been filled the sus¬ pension Is removed from the feed supply conduit A by flush¬ ing with pressure air and clean liquid. A pressurized medium is now introduced through a supply conduit F between the press plates 5 and the membranes 7, such that the membranes compress the filter cakes 40. In doing so, the moisture con¬ tent is further reduced in the filter cake. During these process stages the separated liquid is removed through both the outlets B, E and the combined inlets and outlets C, D. After that the membranes are releaved from pressure and a pressurized gas, for instance pressure air, is introduced through the inlets C, D and blown through the filter cakes under continued reduction of the moisture cσnteπt. In this way a maximally demoisturized filter cake is produced, which for an ore concentrate typically may contain a remaining mois¬ ture content of for instance 6,0-6,5 % water.

When the moisture removal is finished the press plates 5, 6 are brought away from each other by means of the hydraulic cylinders 38, such that gaps 44 defined by distance limiting means 42 are created therebetween. The filter cloths are low¬ ered through the bottom gap by unrolling the pulling wire ropes 24 from the rope drums 26. The spring-loaded cloth rol¬ lers 32 are then rolling up the lower portions of the filter cloths and are holding the filter cloths tensioned. The filter cakes formed are released from the filter cloth at the passage of the guide members 30. When the filter cake removal is fin-

ished the filter cloths are lifted up again. The filter cloths are cleaned at least periodically by bringing a drip pan 46 (fig. 5) under the filter press 1 and introduce wash¬ ing liquid as obliquely upwardly directed spray jets 48 during a repeated lowering of the filter cloths. Only one of the filter cloths 9 in each chamber can be washed at the same time, since the spray jets 48 otherwise would interfere with each other.

This previously known system for filter cloth suspension and filter cake removal has several drawbacks. In spite of the washing there occur obstacles and other troubles during the rolling -Jp of the cloth on the cloth rollers because of remaining particles on the filter cloths. Furtheron, the rinsing and cleaning effect is unsatisfactory since the wash¬ ing liquid is spread on in an upward direction, and con¬ sequently directed in counter-current to the washing liquid leaving the filter cloths. Other drawbacks with the spring- loaded cloth rollers is a big building height of the machine, a mechanically vulnerable design and that long time periods have to be sp-ent for cloth change and repair. ^' Changes are _■ quite frequent, since holes in the filter cloths often occur during operation. Also the arrangement of wire rope drums on hexagonal shafts is connected with disturbances, for instance derailment of the wire ropes. This design is also contribu¬ ting to increased, building height. However, the most important drawback connected with this design is that the repeated lif¬ ting and lowering of filter cloth for filter cake removal and filter cloth cleaning considerably contribute to a long cycle time for this previously known pressure filter and conse¬ quently to a low production capacity.

The object with the present invention is, therefor, to bring about a method and a means for pressure filtering of the kind described above, which gives a faster cycle time for the fil¬ tering operation, an improved cleaning of the filter cloths

by concurrent washing and a reduced time consumption for filter cloth changes and other repairs. Furtheron, the in¬ ventive pressure filter shall have a lower building height, a more simple construction with a smaller amount of moving parts and generally give an improved and more economic press filter construction.

According to the invention this can be achieved by a pressure filtering method of the kind mentioned above chiefly characterized by the features specified in the characterizing pia t Q-Γ claim 1. The inventive means for pressure filtering of ^~~ t er kind described above is above all characterized by the features specified in the characterizing part of the first means claim.

By the fact, that according to the invention, the suspension means of the filter cloths are longitudinally movably sup¬ ported separate from the press plates by guide rails being possible to vibrate instead of by protruding, hinged brackets, it is possible to discharge the filter cakes in all the filter chambers- at the same time with short cycle times. By vibra¬ ting the filter cloths with the aid of the guide rails it is possible to achieve a fast and effective filter cake dis¬ charge without the need of any time consuming lowering and rising movements of the filter cloths.

By spraying washing liquid on the filter cloths in this way for cleaning thereof, it is possible to further reduce the cycle times. By cleaning the filter cloths in this way ac- cording to the invention it is no longer necessary to lower the filter cloths for cleaning as described above for the most pertinent Prior Art. Compared to a travelling cleaning device as described in DE-A3.527.735 the time gains are of course even greater.

According to an advantageous embodiment of the invention the filter cloths are cleaned by spraying washing liquid

thereon through nozzles arranged on pipelike means being insertable between the filter cloths. Spray nozzles may also be arranged on pipelike means along the sides of the plates and/or pipelike suspension means for the filter cloths. In this way a fast cleaning of the filter cloths is achieved at the same time as washing liquid is sprayed on in concurrent with the flow of washing liquid leaving the filter cloths.

According to a further advantageous embodiment of the inven- tion the filter cloths are tensioned, and/or loaded by weights affixed to those parts of the filter cloths protruding under¬ neath the press plates, preferably by rods introduced in the bottom hem of the filter cloths.

According to another advantageous embodiment the filter cloths are tensioned with the aid of spring means, prefer¬ ably helical springs or rubber bands affixed to the parts of the filter cloths protruding underneath the press plates.

By the use of these two alternative filter cloth tension means the need for vulnerable and mechanically complicated spring- ^• loaded cloth rollers of roller blind-type is eliminated.

By the use of the measures described above it has been pos- sible to reduce the cycle time for the filter cake removal and washing of the filter cloth with about 40 % .

According to a further advantageous embodiment of the inven¬ tion the two on each side of respective press plate situated filter cloths are connected with each other underneath said press plate, said filter cloths exhibiting tension and load¬ ing means connected to each other and/or common tension and loading means. In this way there is no longer any need for separate guide means 30 for preventing the parts of the filter cloths hanging underneath from hindering the filter cake discharge .

According to further advantageous embodiments of the inven¬ tion the two filter elements forming filter cloths in each pressure chamber are made in one piece and are freely hang¬ ing over their suspension means separated from each other, exhibit one half each of a feed port fixture with passages to respective pressure chamber, and exhibit positioning aiding means, such as holes provided with eyelets, co-operating with positioning means arranged on the filter cloth suspension means. These arrangements together with the arrangements men- tioned above at the lower ends of the filter cloths contri¬ bute to a reduced time consumption for filter cloth exchange. It has been possible to reduce this time from about half an hour to only two minutes.

Further favourable features of the invention are disclosed in the following description and the attached patent claims.

The invention will now be described in detail with the aid of explanatory examples and with reference to the attached draw- ing. In order to make the drawing more easily understandable the figures are made substantially to schematic form, and features irrelevant to the invention have been excluded. In the figures shows:

Fig. 1 a partial sectional view of a previously known press filter during filtering exhibiting a lifting and low¬ ering means, Fig. 2 a section corresponding to the section of fig. 1 show¬ ing the same filter press during a filter cake dis- charge sequence and also exhibiting cloth uprolling means and guide means for filter cloths, Fig. 3 a section corresponding to fig. 2 showing the washing of the filter cloths, Fig. 4 a schematic elevated view of a press filter according to the invention in open and closed position,

Fig. 5 a cross-sectional view of the press filter of fig. 4 in open position, the filter cloth being removed in the sectional plane shown,

Fig. 6 a view corresponding to fig. 5 of an alternate em¬ bodiment of a press filter according to the inven¬ tion,

Fig. 7 a schematic, partial cross section through a press filter according to the invention showing filter cloth suspension, feed port fixtures for a particle suspen¬ sion and the lower portion of the filter cloths in closed position,

Fig. 8 a sectional view corresponding to fig. 7 in open posi¬ tion also showing a vibrator, and

Fig. 9 a partial cross sectional view showing a guide rail for the filter cloths suspension means with appending console.

Referring now to fig. 4 ther is shown a general side view of an inventive press filter 1 comprising a frame 2, a station¬ ary end or head plate 3, a movable end or head plate 4, and intermediate press plates 5, 6.

The movable press plates 5, 6 and the movable head plate are slidably mounted on guide bars 50 of the frame and are pos¬ sible to bring apart and together respectively with the aid of two double action hydraulic cylinders 38. The end or head plates 3, 4 and the press plates 5, 6 exhibit distance limi- ting means 42 in the shape of only in fig. 6 shown roller chains said distance limiting means being used for bringing apart the plates and limiting the distance therebetween when the press filter is opened. Under the press filter there is a drip pan 46 which is removable on guide and run rolls 52 or slide rails. Under the press filter there is a receiving opening 54 for dried material and two collecting launders 56 for washing liquid and particles washed away.

On the frame and the stationary end or head plate there are connections for inlet conduits as well as outlet conduits A, B, C, D, E, F. The inlet connection F is connected to connec¬ tions F on the membrane-provided press plates 5 through flex-

ible tubing, not shown in detail. The construction of the end or head plates 3, 4, the press plates 5, 6 and the membranes 7 coincide with the previously known technique as described above and as shown in fig. 1-3.

The arrangement and suspension of the filter cloths 9 are best shown in fig. 7 and 8 showing partial sections through the press plates as well as the filter cloths and their sus¬ pension means. The press plates 5, 6 including their membranes are only shown by their outside contour. In each pressure chamber 8 there are two substantially vertical filter cloths 9 which are forming a filter element. The cloths are made in one piece and are suspended over a pipelike suspension rod 58. The position on the suspensions rod 58 of the two cloths is fixed by protrusions 60 which are engaging holes in the filter cloths provided with eyelets 62. This fixation of the position is necessary, because the two filter cloths 9 are not sewn together with each other at the top. The feed port fixture 20 of the filter cloths is separated in two separate halves 20' and 20" respectively, which are affixed to one each of the filter cloths in level with the feed supply con- ^" duit A of the press plates. By this arrangement it Is possible to separate the two halves 20' , 20" and consequently the filter cloths 9 from each other, when the press plates 5, 6 are brought apart. In the through flow passages 22 of the feed port fixtures the two halves exhibit distance strips 64 in¬ tended to prevent the feed port fixture to be compressed to¬ gether by membrane pressure or pressure from flowing-through air. The distance strips may be arranged right opposite each other as shown in the figures, or alternatively be arranged at the side of and overlapping each other, in which case they in closed position are abutting the opposite wall 66 of respective feed port fixture half 20' , 20".

The parts of the filter cloths 9 protruding -under the lower edαe of the press plates exhibit in their lower hem introduced through rods 68. With the aid of their weight they load the

filter cloths and keep them tensioned. The rods belonging to the cloths on each side of respective press plate 5, 6 are connected in pairs with each other at each end by connecting means, such as rubber bands 70 arranged in grooves. Because the rods are hold together in pairs no special guide members 30 are required for keeping the filter cloths 9 apart during the filter cake discharge and the filter cloth wash. In order to further improve the filter cloth tension and the loading of the filter cloths 9 elastic spring means may be arranged at the rods 68. An example is shown in fig. 8 in the shape of a helical spring 72 affixed to a console 74 protruding downwards from the associated press plate. Such elastic means prevent the rods and the lower parts of the cloths from swinging sidewards.

The parts of the filter cloths 9 protruding under the press plates 4, 5 and their rods 68 may also be free from each other. The thickness of the suspension rods 58 will bring them apart when the press plates are separated. Therefor, relatively thick suspension rods are preferred. Du.ring vibra.- tion, as described below, the rods will jump and jerk, thus stretching and cracking the filter cloth and removing the filter cake therefrom. The free lower ends also provides for a very fast filter cloth exchange, especially if all filter cloths are exchanged at the same time as described below.

The suspension rods 58 are pipe-shaped and are provided with downwards directed spray nozzles 36 for washing liquid intro¬ duced through a supply conduit G. At one of the ends they exhibit a connection 76 which via a flexible, only by its central line shown hose 78 connects to a distribution pipe 80. The pipe 80 is supported by posts82, which are anchored to the frame 2 or the near-by floor or similar 84.

The suspension rods 58 are supported movably in the longi¬ tudinal direction of the filter press on guide rails 86. In order to reduce the friction they may be provided with ball

bearings 88 or other bearings. In order to position the sus¬ pension rods 58 with their protrusions 60 directed upwards they exhibit rectangular guide or distance plates 90 which are abutting guide lists 92. The plates 90 are also defining the positioning of the suspension rods 58, when the press plates are in their closed position. The various suspension rods 58 are linked together by distance means 94 which are defining the distance between the suspension rods, when the press plates are situated in open or brought apart position. In the embodiment shown the distance means 94 comprise roller chains, of the bicycle chain type, but they may also comprise other flexible and/or articulated means.

The guide rails 86 are supported at both ends by vibration dampers 100 and consoles 102, which are connected to the frame 2 in appropriate way. The two guide rails 86 are provided with at least one vibrator 98, preferably one at each end. According to a first embodiment shown with full lines in fig. 4 each guide rail is provided with such at least one vibrator and the guide rails are vibrated independently. According to second embodiment, shown with dashed lines, the two guide rails are connected at the ends by two yokes 96, thus form¬ ing a frame. On at least one of the yokes there Is provided a vibrator 98 for vibrating the guide rails in unison.

The suspension rod 58 situated closest to the movable end or head plate is through the distance or connection means 94 connected to the movable plate 4, for instance with posts 104 protruding from said plate and only shown in fig. 4. Said posts 104 comprise abutment surfaces for abutting the guide and distance plates 90 of the nearest suspension rod 58. Con- quently, with the aid of the post 104 the suspension rods 58 and, consequently, the filter cloths 9 can be brought to follow the press plates 5, 6 in their movements when the press plates are brought apart and together.

For the cleaning of the filter cloths there are provided pipe¬ like means 106 and, preferably, downwardly directed spray

nozzles 36 connected to distribution pipes 108 which in turn are connected to a supply conduit G for washing liquid. The distribution pipes 108 and the pipelike means 106 are fastened to posts 110 which are protruding from the drip pan 46 and are following the drip pan in its movements. In this way it is possible to at the same time as the drip pan is moved in below the press filter introduce the pipelike means 106 with its spray nozzles between the filter cloths 9 in each pressure chamber 8 for spray cleaning of the filter cloths. It is pos¬ sible to arrange an arbitrary amount of pipelike means 106 at different levels in order to achieve a wished or necessary clean-washing effect. It is possible to provide downwardly directed spray jets 48 of washing liquid for concurrent washing, but also spray jets directed sideways or upwardly if one wishes to do this. Alternatively, the pipelike means 106 may be affixed to separate guide and run rolls or sliding rails and be moved independent of the drip pan 46.

Referring now to fig. 6 pipelike means 112 with substantially sideways directed spray nozzles 36 can be also arranged along the sides of the plates. The pipelike means are connected to • a supply conduit G for washing liquid and can distribute such washing liquid on to the filter cloths 9 from the sides, when the press plates are in their open or brought apart position. Of course, it is possible to combine one or several of the above described ways of washing the filter cloths 9 with washing liquid; viz. by spray nozzles 36 arranged on the pipe¬ like suspension rods 58 for the filter cloths and or arranged on pipelike means 106 insertable between the filter cloths and/or arranged on pipelike means 112 arranged along the sides of the plates.

The function and the working mode of the inventive filter press are as follows: Initially, the press plates 5,6 and the end or head plates 3,4 are brought together, then a suspension of fine particles in a liquid is introduced and is demoisturized as described above for the previously known

technique with reference to fig. 1-3. When the demoisturiz- ing is finished the plates are brought apart by the hydrau¬ lic cylinders 38. Simultaneously, with the aid of the dis¬ tance limiting means 94 the suspension rods 58 are brought to take central positions over the intermediate gaps 44 created between the ^' plates of the filter press. The filter cloths 9 are brought apart from each other by the tension and loading effect of the weight of the rods 68 and/or separate spring means, such as helical springs 72 or rubber bands:.. After that, the guide rails 86 are vibrated during a short: time period in vertical direction by the vibrators 98. The guide rails in their turn vibrate suspension rods 98 with the filter cloths 9, thus the filter cakes 40 swiftly and completely are disengaged from the filter cloths 9 and fall down through the receiving opening 54. Next, the drip pan 46 is pushed over the receiving opening 54 by an hydrau¬ lic cylinder 114, at the same time as possibly provided pipelike means 106 are inserted between the filter cloths 9 in respective pressure chamber 8. After that, the filter ^" cloths 9 are washed clean from solid particles by spraying with liquid from the spray nozzles 36. At the end of the washing, the filter cloths are subjected to another short vibration by the vibrators. In this way, the filter cloths are releaved from most of the washing liquid, and this is prevented from dripping down into the receiving opening 54. After the washing, the pipelike means 106 if any, are re¬ moved and the plates of the press filter are brought to¬ gether again. A new filtering cycle can begin.

According to a especially favourable embodiment of the in¬ vention, the guide rails 86 are connected at their ends by yokes 96 to form a frame, said frame being disconnectable from its flexible and resilient suspension means 100. This makes it possible to remove and exchange the entire filter cloth package comprising said frame, with all the suspension rods 58 and their filter cloths 9. All that is needed is to open the press filter and disconnect the power supply means for the vibrating means and the flexible connection conduits

78 for washing liquid to the pipelike suspension means 58. Then the rods 68 at the lower end of the filter cloth 9 are disconnected from each other and from the spring means 72 if such are provided. In this case it is especially favourable if the rods 68 are free from each other as described above. After the disconnection of the guide rails from the flexible vibration dampers 100 the entire package can be lifted out. In order to facilitate the lifting out and replacement of the frame with the filter cloths vertical guide means (not shown) may be inserted in holes in the end or head plates 3, 4 and pass through suitable guide rings arranged in the frame formed by the guide rails and the yokes. In this way the filter cloths 9 can be exactly guided in between the respective gaps 44 between the press plates.

In this way it is possible to replace the entire filter package for an exchange unit. This is especially favourable when there is a need for a periodical cleaning of all fil¬ ter cloths. This is the case in some chemical and industrial processes where a chemical precipitation may occur in the - filter cloths. The entire package can then be placed in a bath and treated with suitable solutions for dissolving the precipitates. In the meantime the press filter is working at full capacity with the exchange unit.

The invention is not limited to the embodiments described above and shown in the figure, but can be modified in many various ways within the limits of the inventive concept and the following patent claims.