The invention relates to a method for forming a seam in a wire weave, wherein a seam structure is formed in an interwoven wire weave with at least two layers by folding the wire weave double and by joining the free end of the folded wire weave together by a bonding stitch, the folded threads at the folded edge forming bonding loops at the folded edge.

The invention also relates to a wire weave, woven into a uniform wire weave with at least two layers, the wire weave being provided with a seam structure by folding the wire weave double, the folded threads at the folded edge forming bonding loops at the folded edge.

Various filter apparatuses, such at disc filters and drum filters, are used for removal of liquid, usually water, from a mixture of liquid and dry sol¬ ids.

Typically, a disciform filter comprises a plurality of filter segments inserted into filter bags, and the installation openings in the filter bags have been closed. The filter disc is placed rotatably into a basin into which the mix¬ ture of water and dry solids is introduced. The liquid in the mixture is allowed to permeate through the filter bag, which is permeable to liquid, to the inside of the body of the filter segment from where the liquid is led out in a suitable manner. Doctor blades or water jets are disposed against the surfaces of the disk for removing dry solids remaining on the surfaces of the disc, whereby the filtering capacity can be continuously retained good.

A drum filter is a commonly used filtering apparatus in forestry, mining and other industries. In section, a drum filter is a round tube, on the surface of whose mantle openings extending through the mantle have been arranged in a certain manner, e.g. by drilling, to allow liquid to flow through the mantle of the drum filter from the periphery of the drum filter into its inner parts. In most cases a filter wire, woven of threads that shrink when exposed to heat, is positioned at the periphery of the drum filter and is then shrunk tightly against the outer mantle of the drum filter by means of heat. When the drum filter is subsequently subjected to a rotational movement, the filter gauge ro¬ tates firmiy with the drum. Thread that shrinks when exposed to heat refers to thread that it used for producing filter wire and can be shortened in the longi¬ tudinal direction by means of heat to the extent that the change in length can be utilized as desired for e.g. tightening the filter wire firmly in place. Typically, a drum filter is placed rotatably into a basin containing a mixture of liquid and

dry solids. When rotating with the mixture, the water in the mixture permeates through the filter cloth which is permeable to liquid. The water is further carried to the interior parts of the drum filter through small openings in the drum filter mantle and led out therefrom. Dry solids attached to the filter wire are me- chanically removed from the surface of the filter wire by special doctor blades or water jets, the filtering capacity of the drum filter remaining continuously good.

Drum filters use almost solely two-layer filter wires, as filter wires have to be sufficiently stiff to stay tightly around the drum filter in spite of the forces it is subjected to. Furthermore, the filtering capacity has to be sufficient.

In most cases the two-layer filter wires used in drum filters are formed of two superimposed weave structures, both comprising transverse weft threads and warp threads in the longitudinal direction of the wire, i.e. the weaving direction, the weave layers being bonded together during weaving. Various bond structures or combinations thereof may be used for producing the weave, by means of which the weave is supplied with desired characteris¬ tics according to the purpose of use. Furthermore, the sectional shape of weft and warp threads may be round, elliptic, rectangular, or a combination thereof according to the purpose of use and the weave structure. For efficient removal of water from the mixture of water and dry solids mass, the liquid permeability and the dry solids holding capacity of the filter wire should be in appropriate proportion to each other. Furthermore, dimensional stability and durability un¬ der demanding circumstances are required of a filter wire.

The seams of different wires, such as drying and filter wires, are usually formed by reducing the thickness of the wire ends in a suitable man¬ ner, and by folding the reduced part double. A seam spiral for fastening the wire ends together is then attached to the loops formed by the folded threads. The folded wire end is usually stitched together by thread stitches in the trans¬ verse direction of the wire for forming a substantially continuous wire part. Wire weave seams may also be formed without any special reduc¬ tion, the wire weave being simply folded at a suitable point and a bonding stitch being sewn through the fold. A seam spiral for joining the wire ends to¬ gether may be attached to the warp thread loops formed at the edge of the fold. A wire weave seam may also be produced by weaving a weave portion at the seam backwards in the travel direction, whereby the edge of the

fold is provided with warp thread loops into which a seam spiral may be threaded.

FI 88,944 discloses a seam structure in a paper machine weave, made by folding the reduced end of a drying wire double and by sewing the double wire part together. In accordance with the publication, the end of the wire weave is reduced by removing weave material from its wear side. Further, warp threads form ioops at the edge of the fold, whereby a seam spiral may be attached to said Ioops. In the seam structure according to the publication, a bonding stitch is sewn below the contact surfaces of the warp threads in the weaving direction, whereby the stitches are not exposed to wear. The above described seam structure is, however, possible only in said weave structure, and cannot consequently be used in a continuous multi-layer weave.

With known methods a wire weave is usually woven parallel to the final machine direction, the length of a finished weave being the entire length needed by the wire. This is ineffective and expensive from the point of view of production, as in this case a wire of a suitable width is woven according to the purpose of use, and if the width of the wire is less than that of the weaving machine, the entire weaving width of the machine cannot be utilized, part of the capacity of the weaving machine being wasted. The inability to utilize the weaving capacity optimally leads to a highly priced finished product.

It is an object of the present invention to provide an efficient and fast method for forming a wire seam structure, wherein the weaving width of a weaving machine is better utilized, and further, a wire weave produced with this method. The method of the invention is characterized in that the wire weave is woven in a direction transverse relative to its longitudinal direction when being used, that when weaving the wire weave, at least two separate super¬ imposed weaves are woven over a distance at both edges of the wire weave, and that for forming a seam structure at the ends of the finished wire weave, one of the separate superimposed weaves is folded double and sewn to¬ gether.

The wire weave of the invention is characterized in that the wire weave is woven in a direction transverse to its longitudinal direction when be¬ ing used, that at least two superimposed separate weaves are woven over a distance at both edges of the wire weave, and that for forming a seam struc¬ ture at the ends of the finished wire weave, one of the separate superimposed

weaves is folded double and sewn together.

It is an essential idea of the invention that a two-layer wire weave can be woven with a narrow weaving machine, and that the wire weave woven extends over the entire width of the machine such that two separate one-layer weaves for forming a seam structure are woven at both edges of the wire in the weaving direction. Owing to the seam structure, several wire parts can be combined into one long endless wire whose weaving direction is different from its machine direction.

It is an essential idea of the wire weave seam of the invention that the seam of a two-layer interwoven wire weave is formed of two woven sepa¬ rate superimposed one-layer weaves, whereby a part entirely lacking warp threads in the weaving direction is woven in one of the one-layer weaves, i.e. the seam weave. A fold is formed at this point by folding the seam weave dou¬ ble and by sewing the free end of the seam weave through the seam weave by a bonding stitch, whereby the folded weft threads form bonding Ioops at the folded edge of the seam weave, and a seam spiral or the end of another wire weave formed in a corresponding manner can be attached to these Ioops.

It is an advantage of the invention that the capacity of a weaving machine can be better utilized as a narrower weaving machine can be used for the weaving, in stead of a wider one, since the breaking length of a wire weave woven in accordance with the invention is determined according to the width of the filter drum. Another advantage is that preferably the entire width of the machine is used for weaving, resulting in considerably more efficient and inexpensive weaving. Another advantage of a preferred embodiment is that one of the separate one-layer weaves of the seam, i.e. the auxiliary weave, can serve as a cover flap for the seam, free at one end, protecting the seam against wear, whereby the seam wears well in use as long as does the actual wire weave, with the permeability of the seam being equal to that of the rest of the weave. This eliminates many stoppages due to damage to the seam structure. A cover flap covering the seam as a continuous weave ensures that filtration at the seam is as good as at other points of the wire, resulting in a better filtration result.

It is still an advantage of the seam structure of the wire weave ac- cording to the invention that when an endless wire weave formed of several joined wire weaves is damaged, only the damaged wire weave part has to be

changed, resulting in considerable material savings.

It is still another advantage of the seam structure of the invention that bonding ioops are formed at both edges of the wire, eliminating the need for a separate seam spiral and avoiding several stages of operation. On the whole, the wire weave of the invention is faster and cheaper to produce than known wires.

The invention will be described in more detail in the attached draw¬ ings, in which

Figure 1 is a schematic sectional view of the edge of a wire weave according to the invention in the direction of weft threads, i.e. perpendicularly to the weaving direction,

Figure 2 is a schematic sectional view of the seam structure of a wire weave according to the invention in the direction of the weft threads,

Figure 3 is a schematic sectional view of the seam of two wire weaves according to the invention in the direction of the weft threads,

Figure 4 is a schematic sectional view of another seam structure of a wire weave according to the invention in the direction of the weft threads,

Figure 5 is a schematic sectional view of a third seam structure of a wire weave according to the invention in the direction of the weft threads, and Figure 6 is a schematic sectional view of a wire weave structure ac¬ cording to the invention, shrunk onto the periphery of a filter drum and com¬ bined into a continuous band of several separate wire weave parts.

Figure 1 is a schematic sectional view of an edge 1 of a wire weave according to the invention in the direction of weft threads 2. The wire weave of the invention is formed of an interwoven two-layer weave 3 consisting of warp threads 4 running in the weaving direction, and weft threads 2 running trans¬ versely to the weaving direction, the weft threads 2 being in two layers in the two-layer weave 3, the layers being interwoven by the warp threads 4 such that the different layers cannot be separated one from another without unrav- elling the entire weave structure. Two separate superimposed one-layer weaves, i.e. a seam weave 3a and an auxiliary weave 3b, are woven over a distance at both edges 1 of the wire weave in the weaving direction for the seam structure of the wire weave. The one-layer weaves 3a and 3b comprise weft threads 2 of one layer only, the weft threads being interwoven by means of the warp threads 4. A fold part 5 is woven into the seam weave 3a, totally lacking warp threads, whereby the weft threads 2 only are running at the fold 5

transversely to the weaving direction. The weaving of the wire weave is termi¬ nated at the edge 1 of the wire after the single weaves 3a and 3b by still weaving a bit of double closing weave 6 at the edge, and then the weaving is terminated in the width direction. This double closing weave 6 is not necessary per se; the weaving may also be implemented by arranging separate superim¬ posed layers furthest at the edge.

Figure 2 is a schematic sectional view of the seam structure of a wire weave according to the invention in the direction of the weft threads 2. The numbering of Figure 2 corresponds to that of Figure 1. A seam structure is formed of the edge 1 of the wire weave woven in accordance with the inven¬ tion by cutting off the two-layer closing weave 6 from the outer edge of the wire in the weaving direction. The edge 1 of the wire then consists of two separate one-layer weaves 3a and 3b, free at one end. The threads at the cutting point of the closing weave 6 are melted in connection with the cutting or as a separate step immediately after the cutting in order to prevent the weave structure from unravelling.

After the two-layer closing weave 6 has been cut off, the free end of the one-layer seam weave 3a is folded between the one-layer weaves 3a and 3b. The free end of the one-layer seam weave 3a is attached by a bonding stitch through the fold. Bonding loops 7 are formed at the edge of the fold, us¬ able when joining together the wire weaves. Corresponding structures are woven at both edges 1 of the wire weave, whereby seams are also formed at both edges of the wire. One end of the simple auxiliary weave 3b can be left as a free flap-like seam cover. Figure 3 is a schematic sectional view in the direction of the weft threads 2 of an embodiment of the seam structure according to the invention wherein two edges 1 of a wire weave produced by the same weaving tech¬ nique are joined together. The numbering of Figure 3 corresponds to that of the previous Figures. In Figure 3, the structure of the left-hand wire weave has been formed in accordance with the description of Figure 2, whereby bonding Ioops 7 have been formed at the fold of the left-hand wire weave, bonding Ioops 7 being formed in the same way in the right-hand wire weave and ar¬ ranged interlocked with the bonding loops 7 of the left-hand wire weave. The interlocked bonding Ioops 7 form a channel in the direction of the warp threads 4. A special seam thread 8, preventing the movement of the joined wire weaves in relation to each other in the direction of the weft threads 2, can be

arranged in said channel. The Figure further shows that the one-layer auxiliary weave 3b, that was left free, can be cut off in one of the wire weaves, in this case the right-hand wire weave, since it is sufficient that the auxiliary weave 3b of only one of the wire weaves to be joined together provides a cover for the seam as a kind of cover flap with one free end.

Figure 4 is a schematic sectional view of another seam structure of a wire weave according to the invention in the direction of the weft threads 2. The numbering of Figure 4 corresponds to that of the previous Figures. When produced with the method of the invention, the seam structure of the wire weave edge 1 in the weaving direction can be provided with a seam spiral 9, known per se, arranged in the bonding Ioops 7 formed of the weft threads 2 of the seam.

Figure 5 is a schematic sectional view of a third seam structure of a wire weave according to the invention in the direction of the weft threads 2. In the arrangement of the Figure, the bonding loop 7 of a wire weave seam pro¬ duced according to the invention has been provided with a seam spiral 9, and a special seam thread 8 has been arranged to pass through a channel formed by the bonding loop 7 and the seam spiral 9, resulting in an extremely firm and durable joint between the bonding loop 7 and the seam spiral 9. Figure 6 is a schematic sectional view of an endless two-layer wire weave comprising several wire weave parts, joined together onto the periphery of a filter drum 10 by seam structures according to the invention, and seen from the end of the drum filter 10. The Figure shows how e.g. three separate wire weave can be joined together by seam structures according to the inven- tion to form one continuous wire weave covering the periphery of the drum filter 10. It should also be noted that the weaving direction of the wire weave is parallel to the axle of the drum filter 10, whereby the lengths of separate wire weaves to be joined together must be of the width of the drum filter 10. The drum filter 10 rotates around its axle, whereby the wire weave arranged on its periphery has to rotate with the drum filter 10. At least the weft threads of the wire weave are made of material that shrinks when exposed to heat, whereby the wire weave, consisting of one or more wire weaves with seam structures according to the invention, and arranged on the periphery of the drum filter to cover the entire filter drum periphery, is shrunk tightly around the drum filter by means of heat.

The drawings and the related description are only intended to illus-

trate the idea of the invention. The details of the invention may vary within the scope of the claims. This means that various bond structures and combina¬ tions thereof may be used for weaving the wire weave according to the inven¬ tion. Furthermore, weft and warp threads of different materials may be used according to the need, affecting the characteristics of the wire weave. Still further, weft and warp threads with different sectional shapes may be se¬ lected, e.g. round, elliptic, and rectangular, or some other shape. Still another alternative seam structure of a wire weave may be a wire weave comprising more than two woven layers, e.g. three layers, with separate one-layer parts being woven at the edges in accordance with the idea of the invention, in this case three superimposed one-layer weaves. A part lacking warp threads is woven to e.g. the middle seam weave; the middle one-layer seam weave in the part lacking warp threads being folded according to the idea of the inven- tion, whereby the folded weft threads form bonding Ioops at the folded edge, and the two unfolded one-layer auxiliary weaves may provide a cover for the seam, one from one side of the wire and the other from the other side. Fur¬ thermore, if desired, warp threads do not have to be woven in the auxiliary weave if it is not intended to be used as a cover flap for the seam, leading to thread material savings. The seam structure according to the invention is in no way restricted to be used in the wire weaves of drum filters only.