Recess Plate and Method for Manufacturing the same TECHNICAL FIELD

The invention relates in general to filtering and in particular to a recess plate and to a method for manufacturing the same.

BACKGROUND ART

Recess plates are commonly known, inter alia from DE 10 2007 027 033 A1 . Recess plates must be capable to take unavoidable differential pressure, and to return back to original shape after deflection due to differential pressures. They must take huge closing and sealing forces and full process pressures, without being compressed. Machining must be possible to ensure dimensional accuracy, and installing sealing rings and membranes. Fixing and supporting areas must be sufficiently strong, and they must provide opportunity to include internal channels for filtrate, washing media, air etc. These days, such recess plates are mostly molded from polypropylene (PP), or even from steel, and subsequently machined to the final shape.

Both the limited number of PP plate manufacturers and limited size of molding presses technically and economically constrains both manufacturing and application of filter devices. PROBLEM TO BE SOLVED

It is an object of the invention to suggest an alternative recess plate.

SUMMARY OF INVENTION

The invention suggests a recess plate designed for use in a filter device for filtering a suspension, the filter device having a stationary head piece and a movable end piece, and a pack including copies of the recess plate, having a filter

CONFIRMATION ^' COPY chamber inside the pack, adjoining the recess plate, having a first pipe for filling the suspension into the filter chamber, having a filter cloth for collecting a solid content out of the suspension, and having a second pipe for discharging a liquid fraction of the suspension out of the filter chamber as a filtrate, wherein the filter device may be closed before filtering by forcing the end piece in direction of the head piece, and opened after filtering by releasing the end piece, and moving the end piece away from the head piece for removing the filter cake from the filter cloth, and wherein the recess plate has a first surface at the filter chamber and a second surface vis-a-vis the first surface, the first surface and the second surface are formed by sheets, and the recess plate has a rigid body between the sheets. Using the recess plate according to the invention, both manufacturers and users of filter devices are no longer dependent on PP plate manufacturers, and on their limited manufacturing capacities, and limited size molding presses. The recess plate according to the invention provides very high strengths against differential pressures, low weight recess plates, fully automated manufacturing without need for huge and expensive presses, short manufacturing cycles.

Preferably, in a recess plate according to the invention the rigid body is from hardened foam. Using foam allows for lightweight construction of the recess plate. Alternatively, the rigid body may be from any hardening matter, e.g. PP or aluminum, or machined from solid matter, e.g. steel or wood.

In a favored recess plate according to the invention, the sheet is from fabric.

Fabric surfaces provide for high resistance against bending stress. Alternatively, the sheet may be a plastic film, or a steel panel.

In such recess plate, the fabric is preferably reinforced by fibers. Resistance of the surface against bending stress is thus even increased.

Further in such recess plate, the fibers are preferably fiber-glass. A huge variety of fiber-glass reinforced fabrics is commercially available, and processing the same is well known. Alternatively, the fibers may be e.g. carbon fibers, ceramic fibers, or metal fibers. In such recess plate having a sheet from fabric, the fabric is preferably penetrated with a hardened resin. Soaking with a hardening resin is well known for giving both dimensional stability and impermeability to a fabric. As an alternative to giving the fabric itself dimensional stability, a mold may be lined by a flexible fabric, and subsequently filled with hardening matter for forming the rigid body.

Further in such recess plate, the resin preferably is polyethylene. Using

polyethylene (PE) for impregnating fabrics is well known, and PE is a highly competitive material, for this purpose.

The invention further suggests a method for manufacturing a recess plate to be used in a filter device for filtering a suspension, the filter device having a stationary head piece and a movable end piece, and a pack including copies of the recess plate, having a filter chamber inside the pack, adjoining the recess plate, having a first pipe for filling the suspension into the filter chamber, having a filter cloth for collecting a solid content out of the suspension, and having a second pipe for discharging a liquid fraction of the suspension out of the filter chamber as a filtrate, wherein the filter device may be closed before filtering by forcing the end piece in direction of the head piece, and opened after filtering by releasing the end piece, and moving the end piece away from the head piece for removing the filter cake from the filter cloth, wherein a first sheet is formed to provide a first surface of the recess plate at the filter chamber, and a second sheet is formed to provide a second surface of the recess plate vis-a-vis the first surface, and a spacing between the first sheet and the second sheet is filled by a rigid body. The method according to the invention provides for manufacturing the recess plate according to the invention, and features the above mentioned advantage over the state of the art. Alternatively, the rigid body may be formed by molding, and subsequently lined with the sheets.

In a favored method according to the invention, the first surface and/or the second surface are formed by pressing the respective first sheet and/or second sheet to a solid mold. Forming the sheet in a reusable solid mold provides for reproducible shapes and large-scale production. In such method, a protective sheet is preferably arranged between the respective first sheet and/or the second sheet and the solid mold, and removed from the first surface and/or the second surface, after forming. Such protective sheets may be used to avoid soiling of both the mold, and of the pressing agent with resin from the first and/or second sheets.

Preferably, in a method according to the invention, the first surface and the second surface are formed by arranging the first sheet and the second sheet between two solid molds, and inserting a pressing agent between the first sheet and the second sheet. Simultaneously forming both surfaces allows for streamlining the

manufacturing process of the recess plate, and avoiding warehousing.

Alternatively, only one sheet may be formed between a solid mold an a solid lid, closing the recess, or two independent sheets may be formed by combining two independent solid molds.

In a further favored method according to the invention, a fluid is used for pressing the first sheet and/or the second sheet to the solid mold. A fluid always adapts to, and thus in independent of the shape of the solid mold. Alternatively, a male mold (or "positive mold") may be used for pressing the sheets to the mold. Such male mold may be either rigid, or flexible.

In such method, the fluid preferably is hot water. Hot water may assist in hardening the resin soaking the sheets.

Further preferred, in a method according to the invention, the rigid body is glued to at least one of the first sheet and the second sheet. Gluing provides for a durable connection of the rigid body to the sheet(s).

Even further preferred, in a method according to the invention, a foam is injected between the first sheet and the second sheet, that after hardening forms the rigid body. A foam, similar to a fluid for pressing, adapts to, and thus is independent of the shape of the rigid body. Alternatively, another fluid material may be filled between the sheets. Further alternatively, a prefabricated honeycomb composite rigid body may be arranged between the sheets. BEST MODE FOR CARRYING OUT THE INVENTION

The recess plate according to the invention and the associated method are subsequently described in more detail with reference to the drawing figures, showing schematic cuts through the sheets, molds, and the resulting recess plate during four steps in the manufacturing process.

In manufacturing a recess plate 1 according to the invention, as shown in fig. 1 , a stack of two sheets 2, 3 from glass-fiber reinforced fabric, soaked with liquid PE, each lined by two protective sheets 4, 5 - here: plastic foils - is inserted between two female solid molds 6.

The solid molds 6 are then pressed, and clamped (clamps not shown) together, to ensure sealing of the recesses 7 inside, as shown in fig. 2.

As shown in fig. 3, hot water 8 is then fed between the two sheets 2, 3, pressing the same into the recesses 7. After hardening of the PE, the hot water 8 is discharged, the solid molds 6 are opened. Until now, the first surface 9 of the first sheet 2 and the second surface 10 of the second sheet 3 are facing each other.

The sheets 2, 3, now having the shape of the respective recesses 7, and being dimensionally stable, are removed from the solid molds 6. The protective sheets 4 are removed from the flip sides 1 1 of the sheets 2, 3, and, as shown in fig. 4, and the sheets 2, 3 reversed to have the flip sides 1 of the sheets 2, 3 facing each other. The sheets 2, 3 are mounted to a prepared frame 12, containing all the drills and bores required for filtrate, wash water, air etc. Then the hollow space 13 between the sheets 2, 3 is filled with a structural foam 14 core material using a SAN polymer base featuring high toughness and impact resistant characteristics, e.g. available under the trade name Corecell™ M from Gurit Holding AG,

Wattwil/Switzerland. After hardening, together with the frame 12, the foam 14 forms the rigid body 15 of the recess plate 1.

The protective sheets 5 remain on the first surface 9 and on the second

surface 10, until delivery. In the figures are

1 recess plate

2 first sheet

3 second sheet

4 protective sheet

5 protective sheet

6 solid mold

7 recess

8 water

9 first surface

10 second surface

1 1 flip side

12 frame

13 hollow space

14 foam

15 rigid body