FIELD OF THE INVENTION

The present invention relates to a filter cloth, and more particularly to a filter cloth as defined in the preamble of independent claim 1 . BACKGROUND OF THE INVENTION

The invention relates to pressure filters for separation of solids from fluids and especially to filter cloths used in pressure filters. Pressure filters comprise filter plates which are stacked vertically or horizontally. Filter cloth zigzags between the filter plates and transports the cakes formed during filtration out from the pressure filter chamber. Moving filter cloth is exposed to frictional wear and pressure water sprays to remove the solids so the filter cloth has to be durable. In general the filter cloth is a continuous cloth having at least one seam. The seam part is normally the weakest point of the filter cloth because the seam is weaker than the cloth itself. So in very heavy loading conditions seam is limiting the durability of the cloth.

Publication US 2010/0297386 discloses a belt having a seam which said seam is formed from clippers for joining the ends of the belt. The clippers are connected by interdigitated staples which are looped about a pintle and provide barbs on their remote ends to penetrate into the material of the belt. Each end is covered by an edge strip of vinyl by radio frequency welding, and a flap is attached to one end on the low pressure side of the belt by a portion, and folded over to cover the seam on the low pressure side by means of a flap which extends beyond the seam area of the other end. A central area to each side of the seam is impregnated with polyurethane to resist abrasion which tends to concentrate in this area.

One of the problems associated with the above seam is that the clippers tend to pull out the belt so that the belt will break in the area next to the seam where the clippers are connected to the belt. The strip of marine vinyl is radio frequency welded to the belt but it requires additional work phases. The marine vinyl is kind of a material that is waterproof and is flexible but does not have the required special strength property.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a seam so as to alleviate the above disadvantages. The object of the invention is achieved by a seam which is characterized by what is stated in the independent claim. The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of increasing the strength of the seam to be more durable. A filter cloth in a pressure filter has to take a lot of tensile stress and the seam of the filter cloth has much less resistance than the rest of the cloth. The purpose of the reinforcement structure in the end of the filter cloth, which the reinforcement structure has a high modulus, is to transfer and share the tension caused by the point load of the metal brackets on the seam to a larger area in the filter cloth in a way that increases the tensile strength of the seam.

The invention relates to a filter cloth for a pressure filter, said filter cloth having a seam for connecting the ends of the filter cloth to form a continuous filter cloth to be used in a pressure filter. The seam comprises at least two binder members and a hinge member arranged through the binder members for binding the ends of the filter cloth together. The ends of the filter cloth comprise a reinforcement structure for increasing strength of the seam, said reinforcement structure having a higher modulus than the filter cloth. This higher modulus means the ratio of the tensile force and the tensile strain.

In one embodiment of the invention the reinforcement structure comprises a reinforced fabric arranged to a surface of the filter cloth. The reinforced fabric may be arranged on one surface of the filter cloth or on both surfaces of the filter cloth in the end area of said filter cloth in which the seam is produced. I.e. preferably in both ends of the filter cloth, which the ends of the filter cloth are to be connected to form a seam. The reinforced fabric comprises at least one of the following: aramid fibre, carbon fibre, fibreglass, ultra high modulus polyethylene or their combination. The reinforced fabric may be Kevlar, i.e. the reinforced fabric may comprise para-aramid synthetic fibre.

In another embodiment of the invention the reinforcement structure is a sewn thread which is sewn in the ends of the filter cloth. If the thread is sewn to the filter cloth such that the thread covers a large area of the filter cloth in the end of the filter cloth it suffices alone to increase the tensile strength. In another embodiment of the invention the thread is combined with the reinforced fabric such that the reinforced fabric is sewn to the filter cloth with the thread and they together form the reinforcement structure. So the reinforcement structure comprises a reinforced fabric arranged on the surface of the filter cloth with the thread sewn through said reinforced fabric and said filter cloth.

In still another embodiment of the invention the reinforcement structure further comprises an impregnation or a coating layer. In one embodiment of the invention the impregnation or coating is applied on the surface of the reinforced fabric which is attached on the surface of the filter cloth. So the impregnation or coating is arranged on top of the reinforced fabric. If the reinforced fabric is on both sides of the filter cloth the impregnation or coating is applied on both sides as well. In another embodiment of the invention the impregnation or coating is applied on the surface of the reinforced fabric which is sewn with thread on the surface of the filter cloth. One of the purposes of the impregnation is to extend the bond strength between high-modulus reinforcement and the cloth in addition to the sewn thread. Said bond strength or adhesion is an important parameter when moving the strain between the reinforcement and the cloth. The reinforced fabric is sewn through with thread extending from one side of the filter cloth to another side of the filter cloth and the impregnation or the coating layer is arranged on top of the reinforced fabric.

A breakage or other damage of the filter cloth near the seam is prevented by a sewn thread texture in the end of the filter cloth. The thread texture may be for example a Kevlar ribbon which is sewn to the filter cloth with high strength thread. The sewn thread texture prevents the cloth from tearing when high pressure is applied to the cloth.

A preferred embodiment of the invention is that a high modulus reinforcement structure is applied to the end of the filter cloth which the reinforcement structure is achieved by thread texture. The thread texture can be further covered with impregnation material or other coating material.

An advantage of the seam is that the filter cloth is more durable and the binder members of the seam do not tear the seam so the filter cloth can be changed more seldom. BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a filter cloth according to one embodiment of the invention; Figure 2 shows the filter cloth shown in figure 1 from another view; Figure 3 shows a filter cloth according to another embodiment of the invention; and

Figure 4 shows the filter cloth shown in figure 3 from another view. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a filter cloth 1 according to the invention in which the filter cloth 1 is not yet arranged as a continuous filter cloth 1 and said filter cloth 1 is preferably a rubber cloth. One binder member 4 is already arranged in contact with the filter cloth 1 and a reinforcement structure that comprises in this embodiment a reinforced fabric 6 and thread 7 sewn through the reinforced fabric 6 and the filter cloth 1 . The reinforced fabric 6 is arranged on both sides of the filter cloth to cover the surfaces of the filter cloth 1 in the end area of the filter cloth 1 in which the binder member 4 is arranged. The thread 7 can be used to connect the reinforced fabric 6 as the only connect member or the reinforced fabric can be also connected by means of gluing or impregnation with a polymeric material some other way.

Figure 2 shows the same filter cloth 1 as figure 1 but from another viewing angle. In figure 2 the filter cloth 1 is connected to form a continuous filter cloth 1 with seam 2. The binder members 4 in different ends of the filter cloth 1 are connected together with a hinge 5 arranged through the binder members 4. The reinforced fabric 6 is sewn to the filter cloth 1 with thread 7 such that the thread is sewn in densely along the sides of the reinforced fabric 6 and back and forth in the centre area of the reinforced fabric 6.

Figure 3 shows another embodiment of the invention in which the filter cloth 1 is arranged as a continuous filter cloth 1 by combining the binder members 4 with a hinge 5 arranged through the binder members 4 so that a seam 2 is formed. The ends 3a, 3b of the filter cloth 1 is covered with the reinforced fabric 6 sewn through with at least one thread 7. An impregnation layer or a coating layer 8 is arranged on top of and inside the reinforced fabric 6. I.e. the filter cloth 1 and the reinforced fabric 6 are sewn through with at least one thread 7and the impregnation/coating layer 8 is arranged on top of and inside the layers. So the reinforced fabric 6 arranged on the filter cloth 1 is sewn through with thread 7 extending from one side of the filter cloth 1 to another side of the filter cloth 1 .

Figure 4 shows the embodiment shown in figure 3 from another viewing angle. The coating or the impregnation layer 8 preferably extends further in the filter cloth 1 than the reinforced fabric 6 underneath it. The impregnation or the coating layer 8 is preferably resin, but it may be some other suitable material as well.

As shown in all the figures the ends 3a, 3b of the filter cloth 1 comprise a reinforcement structure for increasing strength of the seam 2 and the binder members 4 are in contact with the filter cloth 1 and the reinforcement structure, said reinforcement structure having a higher modulus than the filter cloth 1 .

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.