FITTER MADE OF PLATES COATED WITH INFLATABLE MEMBR ANES AND FILTERING CLOTHS

Technical Field My invention relates to a filter made of plates coated with inflatable membranes and filtering cloths. The invention finds particular, even though not exclusive, application as a system for the filtration of liquids, in which after the filtration it is possible to extract the solid conglomerated particles remaining between the plates after the compression in the form of "cakes".

Background Art In the prior art, the filtration systems utilizing quadrangular plates are well known and include a plurality of plates which, are hollowed and disposed on guides at the four corners, and which are free to move so as to be pressed or loosened like an accordion. Said plates have a wide hole in a median position for the flow of the liquid that must be filtered afler having pressed all the plates together to form a single tight block. Each plate is coated on its opposite surfaces through the perimetrical -. insertion of a ' bossed and perspiring elastic rubber membrane that in turn is coated with a filtering cloth like a real filter. Air immission holes are provided between the membranes and

the surface of the plates, in order lo carry out the final compression of the solid material that has accumulated between the filtering cloths, or in the chambers defined by the opposite hollows of said plates. In the final filtration phase, while the plates are always tightly pressed between them in pack, and after having completed the passage of the liquid to be filtered between the plates and the filtering cloths, an amount of solid material will then have accumulated in said chambers. The compressed air immission will then be carried out always under the membranes, in order lo force the membranes to detach from the plates, consequently realizing a greater compacting of the solid material between the filtering cloths which, when opening the plates (loosening of the clamping and spacing between them), will look like pats or cakes which are indeed commonly known as "cakes". The drawbacks of such a system substantially derive from the limited durability of said elastic membranes which, being inserted perϊpherically and necessarily lightly flanged in juxtaposition in connection with the hole for the passage of the liquid in filtration. frequently tend to break owing both to the repeated elastic movement of detach and adherence to the plate, and to the wear caused by the material in filtration together with the action of removal of the - cakes and the respective cleaning, which are necessary for each filtering operation. The greater drawbacks derive in particular from the flanging in the hole for the passage of the filtering liquid. Said flanging is realized by means of two opposite flanges that clamp strongly by means of bolts passing the opposite membranes on the plate to realize said seal.

The area of such intermediate flanging which is made of a substantially rigid material just like the plates (metallic material or non-flexible plastic material), is then the one of greater danger for the breaking and consequently i t is the one which causes the greater danger of breaking. The construction of two flanges, the holing of the plate and the use of clamping bolts, involve evident costs which cannot apparently be reduced since, while the filtering cloths can be made to pass in their half through said hole, this is not possible for said membranes, so that consequently the membranes must always be made in couple to be clamped on thei r respective plate in juxtaposition through said flanging.

Disclosure of Invention The object of the present invention is to obviate the above mentioned drawbacks. This and other scopes are reached as claimed by means of a filter made of plates coated with inflatable membranes and filtering cloths, of the type in which there is at least one median hole of passage for the liquid to be filtered in said plates, membranes and filtering cloths, characterized in that: • said membranes are realized in a single membrane for each plate which covers both opposite faces of the respective plate and passes without solution of continuity through said median hole; " the membrane portion that passes through said hole is more rigid than the flat portion interested in the filtration which extends in the surrounding inflation area in such a way that, when letting in the compressed ai r between said membrane and said plate,

1 substantially only the portion interested in the filtration that

2 extends in the area surrounding said hole is detached from said

3 plate.

4 In this way the advantage is obtained of having a single cake

5 compression membrane which does not need any flanging in the

6 area of said supply hole, and it is avoided the restriction of the hole

7 itself in compression during the membrane inflation which would

8 occlude the passage for the downflow of the squeezed liquid. Advantageously, the grcaicr stiffness of said membrane 0 . portion passing through said hole is obtained by means of a greater I thickness, if compared to the adjacent filtration areas. In this way a greater stiffening is obtained in a simple and less expensive way. The continuity of said membrane is realized through welding, sticking or vulcanization of two half membranes in connection with said hole. In this way the half membranes can be built sufficiently rigid, there being no need for at least one of them to be passed through said hole. Advantageously, the continuity of said membrane realized by means of welding, sticking or vulcanization of iwo half membranes in connection with said hoIe _v takes place with the aid of a flanged sleeve made of the same material, which is previously inserted into said hole and is then intended to make up a whole with said two half membranes by means of two respective opposite annular junctions, so as to form a single reinforced membrane in said hole area. In this way the advantage is obtained of making it always possible, if a membrane face has deteriorated, to cut it in connection

with said hole and to stick another one by means of said flanged sleeve. In the substantially advantageous solution : • said plates arc made of reinforced resin; • said membranes arc made of rubber; • said membranes are stuck peripherically on the surface of said plate in an inflated area which is intended to be clamped in compression of said plates. In this way, the surfaces of said membranes being stuck to the surface of the plate, they will not undergo any slippings during the inflation, such slipping being made possible by the thinning of the thickness of the membrane in traction, in spite of its compression between the plates.

These and other advantages will appear from the following description of preferential solutions of realization with the aid of the included drawings, the execution details of which must not be considered as limitative but only as supplied by way of example. Figure 1A is a view of the plate on one of its faces. Figure IB represents the flanged sleeve made of the same material of the membranes, which is intended to . connect the two opposite membranes in order to form a single reinforced membrane in the hole area. Figure 2 is a view in section of a set of filtering plates forming the fil ter.

With reference to the figures, it is noticed that the invention concerns a filter (3 ) made o f plates coated with inflatable

membranes (5) and filtering cloths (6). of the type in which there is at least one median hole for the passage of the liquid to be filtered (7) in said plates, filtering membranes and cloths, wherein: • said membranes (5) are realized in a single membrane for each plate (3), which covers both opposite faces of the respective plate (3) and passes without solution of continuity (54) through said median hole (7); • the membrane portion (52-54) that passes through said hole is more rigid than the flat portion interested in the filtering (55) which extends in the surrounding inflation area in such a way that, when letting in the compressed air between said membrane (5) and said plate (3), substantially only the portion interested in the filtering (55) that extends in the area surrounding said hole (7) is detached from said plate. The greater stiffness of said membrane portion passing through said hole (7) is obtained by means of a greater thickness (54), if compared to the adjacent filtration areas (55). The continuity ■ of said membrane is realized by means of welding, sticking or vulcanization of two half membranes in connection with said hole (7) with the aid of a flanged sleeve which is intended to make up a whole with said two half membranes to form a single reinforced membrane in said hole area (52-53). Said plates (3) are made of reinforced resin; Said membranes (5) arc made of rubber; Said membranes (6) arc stuck periphcrically (51 ) on the surface of said plate (3) in an inflated area which is intended to be clamped in compression of said plates (3). The plate 3 arc clamped by two end pressing plates (1-2)

similarly holed 4 for the passage of the liquid to be filtered. In the filtration area the external surface of the membranes is duly bossed in order to allow the passage of the liquid to be filtered. Each plate also has four holes at its corners (8) for the slipping of the same in the corresponding cylindrical guides of the press between the clamping plates 1 ,2. In figure 2 are also shown the branch holes 8' for the passage of the filtered liquid under the filtration cloth (6) and over the membrane (5), passing through said bossings down to said discharge holes (8'). The pressure air between the membranes (5) and ^' the plate surface (3) takes place in a technically known way which is not sh own . The rubber flanged sleeve 56, before being integrated in the membrane by means of sticking (53,52), must obviously be inserted into the corresponding hole (7) of the respective plate. The edges can conveniently be of tapered thickness in order to obtain a sticking overlap or vulcanization (first time) without any thickness v ari ation . The flanged sleeve can be further loaded in order to be tougher (e.g. greater sulphur and other substances amount), it will have an U-shaped conformation suitable for fitting conveniently into the plate hole (7). The greater thickness on the tubular section of the plate will increase its stiffness, while at least one flange will be sufficiently flexible for being bent in order to pass through the hole (7) before

the definitive junction with the other portion of opposite membrane. Advantageously, said flanged sleeve can be obtained directly in one of the two half membranes, while the other has only the hole for the connection with the opposite flange in the welding area (52). Alternatively, both the half membranes can have a sleeve portion (53) that enters the hole (7) so as to have one mouth of a sleeve portion inside ihc other where the respective sticking will be carried out, thus obtaining the double object of not having any thickening on the filtering surface, and only a thickening in the hole area (53).