The invention also relates to a wire part of a board or paper machine for manufacturing a continuous web, which wire part comprises a headbox, at least one forming wire, running in a loop, and at least one press, which comprises a first press member, arranged in the loop of the forming wire, a second press member, arranged outside the loop of the forming wire, which press members form at least one press nip with each other, and an outer clothing, running in a loop outside the forming wire through said press nip to carry and transfer the web after the press nip to a subsequent press section.

When the web is pressed in a press nip at the end of a wire part, large quantities of water are released, as the dry-solids content of the web is very low, typically between 10 and 20 per cent. Part of the water volume can be accumulated in the open volume of the forming wire, formed by-its voids. When the forming wire reaches the press nip, however, these voids are already filled with water to a greater or lesser extent from the draining of the web along the preceding forming zone. Considerable difficulties are therefore encountered in controlling the

volume available in the forming wire to receive the water pressed out of the web in the press nip.

When using one or two press felts in a single-felted or double-felted press nip, the press felt will absorb part of the released quantity of water, however, the absorbency of the press felt diminishes after a relatively short period of use as it is clogged by small fibres that accompany the water pressed out in the press nip and are deposited on the surface of the press felt as well as penetrating it. Even if the press felt has some elasticity in its thickness direction, this elasticity is exhausted because of the continuous compression to which the press felt is subjected in the press nip so that the thickness of the press felt decreases, which results in reduced absorbency. Continuous conditioning of the press felt is therefore also more difficult. If the press nip is single-felted and the clothing in contact with the web is an impermeable belt, the strain on the press felt is increased. The use of suction equipment to create a suction zone in the press nip to remove the water pressed out also entails disadvantages as explained below.

Obviously, the above-mentioned problems will be aggravated as running speeds increase. The problems must therefore also be viewed against the ever-increasing demands made by industry for higher running speeds. It would be possible to produce a wire for direct web contact with a greater open volume than presently existing forming wires. Such a solution is not available, however, when taking into account that the wire is designed to serve not only as a press clothing in the pre-press but also as a forming wire, it being important that the fibres are retained on the forming wire and do not accompany the drainage water and that the forming wire does not carry with it excessive quantities of water after the press nip, which water is physically retained

in said imagined greater open volume and burdens the forming wire in an undesirable way.

Consequently, there is a great need to develope a device that satisfactorily negotiates the handling of the large quantities of water released in a press nip, especially at increased running speeds.

US-5,389,205, EP-0 359 696 and WO 97/13030 may be mentioned as examples of patent specifications based on the techniques discussed above.

US-5,389,205 describes a wire part (see Figure 6A) with a pre-press, having a press nip, through which a forming wire passes together with outer and inner press clothings, which press nip is formed by an outer press roll with an open envelope surface and an inner suction roll. In another configuration of this patent (see Figure 6B), a shoe press roll has been substituted for the outer, open press roll and the inner press clothing has been removed. In both cases, the web is carried by the forming wire from the press nip to a pick-up point before the wire turning roll. Even if the inner press clothing, in the shape of a press felt, is able to absorb water through the forming wire, this ability is reduced after a relatively short period of use as fine fibres in the web will be sucked into the press felt by the suction roll so that the press felt becomes denser. This is an obstacle to achieving the demanded higher running speeds, at which the web will be crushed unless sufficient quantities of water have been removed from the web in the press nip. Further, each increase in speed necessitates a corresponding increase in the suction effect of the suction roll. A suction roll is an expensive installation and is also expensive to operate, with running costs that increase as running speeds increase. Further, suction rolls have a high noise level. Another problem with the

mentioned configuration is that the web is re-wetted by the forming wire before the pick-up takes place a considerable distance downstream of the press nip.

EP-0 359 696 describes a wire part with a pre-press, having a double-felted press nip, through which a forming wire passes together with outer and inner press felts.

The press nip is formed by an outer suction roll and an inner open roll. The outer press felt runs to a shoe press and carries the web on its underside to the extended press nip of the shoe press. The problem regarding re-wetting of the web remains with the suggested configuration, as do all the other above-mentioned problems. In addition, a further problem emerges in that there is a risk of the web not adhering sufficiently to the outer press felt after the press nip but, instead, adhering to and accompanying the forming wire. Using an open roll, as suggested in EP-0 359 696, also entails difficulties in keeping the roll clean from fibres accumulated in the open holes of the envelope surface.

WO 97/13030 describes a wire part with a pre-press, having a press nip, through which a forming wire passes together with an impermeable transfer belt. The press nip is formed by a press roll or a press shoe roll and a lower press roll that has an envelope surface provided with openings and can consist of a suction roll. The transfer belt carries the web on its underside from the press nip to the clothing of a subsequent shoe press. The problem regarding re-wetting and the adhesion of the web to the transfer belt is solved by such a configuration.

In the alternative using a suction roll, the problems mentioned above for an installation in accordance with US-5,389,205 will arise. The use of a grooved roll, as suggested in WO 97/13030, results in the forming wire being subjected to considerable wear.

The efforts suggested so far to create a pre-press in a wire part that enables the water pressed out of the web in the press nip to be efficiently dealt with, especially at increasing running speeds, have not been successful.

The object of the invention is to considerably decrease the problems discussed above and to provide a press that enables the water pressed out of the web to be dealt with in an efficient and controllable way and that also enables increased running speeds.

The press in accordance with the invention is characterized in that it comprises a first water-receiving member in the shape of a non-compressible, inner belt, running in a loop inside the loop of the forming wire around the first press member and through the press nip and having water-receiving, evenly distributed voids that are open at least towards the side of the forming wire not carrying the web, that the voids of the belt, when the belt is the only water-receiving member, constitute an open volume that is substantially equal to or greater than the volume of water pressed out of the web in the press nip, and that the press comprises conditioning members arranged downstream of the press nip in proximity to the belt for removing the water, received in the press nip, from said voids in the belt.

The wire part in accordance with the invention is characterized in that the press comprises a first water-receiving member in the shape of a non-compressible, inner belt, running in a loop inside the loop of the forming wire around the first press member and through the press nip and having water-receiving, evenly distributed voids that are open at least towards the side of the forming wire not

carrying the web, that the voids of the belt, when the belt is the only water-receiving member, constitute an open volume that is substantially equal to or greater than the volume of water pressed out of the web in the press nip, and that the press comprises conditioning members arranged downstream of the press nip in proximity to the belt for removing the water, received in the press nip, from said voids in the belt.

Besides the advantages gained by a considerable alleviation, and, in most cases, a complete elimination, of the problems discussed above, there is a further essential advantage with the invention in that the separate belt with an open volume enables the use of more fine-meshed forming wires, which produce webs with improved formation and an accompanying reduced degree of wire marking on the surface of the web that is in contact with the forming wire.

The invention will be further described with reference to the drawings, in which Figure 1 is a side view of parts of a paper machine with a press in accordance with a first embodiment of the invention.

Figure 2 is a cut-out section of a water-receiving belt in the press in accordance with Figure 1.

Figure 3 is side view of parts of a paper machine with a press in accordance with a second embodiment of the invention.

Figure 1 shows, schematically, parts of a paper machine comprising a wet section 1 and press section 2. The wet section 1 comprises a wire part which in the shown embodiment consists of a fourdrinier former, comprising a

headbox 3 and a forming wire 4, running in an endless loop around a plurality of guide rolls, which comprise a breast roll 5, a wire turning roll 6, a wire roll 7, an alignment roll 8 and a tension roll 9. Stock is ejected from the headbox 3 onto the forming wire 4 and dewatered to form a continuous web 10. At the end of the fourdrinier former, a plurality of dry suction boxes 11 are arranged in the loop of the forming wire 4.

The fourdrinier former further comprises a press 12, which may be termed a pre-press, and which is arranged downstream of the dry suction boxes 11. The pre-press 12 comprises a first press member 13, arranged in the loop of the forming wire 4, a second press member 14, arranged outside the loop of the forming wire 4, which press members 13,14 co-operate with each other to form a press nip between them. The forming wire 4 runs through the press nip, whilst encompassing a pre-determined sector part of the first press member 13. Further, the pre-press comprises an outer impermeable belt 15, running in an endless loop around a plurality of guide rolls 16 and through the press nip whilst encompassing a pre-determined sector angle of the second press member 14. The impermeable belt 15 co-operates with a lower press felt 17 of a subsequent shoe press 18 in the press section, which shoe press 18 also has an upper press felt 19. The impermeable belt 15 has a smooth surface, which faces the forming wire 4 and to which the formed web 10 adheres after the web 10 has passed the press nip. In the embodiment shown in Figure 1, the pre-press 12 consists of a shoe press, in which the first press member 13 is a smooth counter roll and the second press member 14 is a shoe press roll.

In accordance with the concept of the invention, the press 12 does not have a suction device and suction zone in the press nip.

The shoe press 12 further comprises a first water-receiving member 20 in the shape of a non-compressible inner belt, running in a loop inside the loop of the forming wire 4 around a plurality of guide rolls 21 and around the counter roll 13 and three of the guide rolls of the forming wire 4. In the embodiment shown in Figure 1, the belt 20 is guided directly on the counter roll to meet the forming wire in or shortly before the extended press nip, where the forming wire 4 reaches the counter roll 13. The belt 20 is driven around its loop by its friction engagement with the forming wire and the counter roll in the press nip.

The belt 20 has water-receiving voids 22, open towards the outer side of the belt 20, which side, in the extended press nip, is in contact with the side of the forming wire 4 not carrying the web. The water-receiving voids 22 are visible to the naked eye and are evenly distributed in the longitudinal and transverse directions of the belt 20 in such a way that the water-receiving capacity is uniform or virtually uniform per unit of area along and across the belt 20. In one embodiment of the belt 20, the voids 22 are also open towards the inner side of the belt, which side, in the extended press nip, is in contact with the envelope surface of the counter roll. In other words, the voids 22 form through openings in the thickness direction of the belt 20. A preferred embodiment of such a belt is a wire, in which the through openings are defined by the intersecting threads 23,24 of the wire, see Figure 2.

In another embodiment (not shown), the belt 20 has straight, uniform through holes which give the belt a perforated appearance.

In a third embodiment (not shown), the belt has recesses on its outer side facing the forming wire, which recesses are preferably as deep as possible and have any shape, for instance round depressions and/or long grooves that are longitudinal, transverse or diagonal or which cross each other.

In a fourth embodiment (not shown), the belt 20 has voids 22 that consist of a combination of said second and third embodiments.

The belt 20 is thus either permeable or impermeable to water.

The thickness of the belt 20 and the design and number of the voids 22 per unit of area are chosen in such a way that the belt obtains an open volume equal to or substantially equal to or greater than the volume of water pressed out of the web in the press nip, for instance 1-100 per cent greater. To be able to ensure a constant open volume during an extended period of production it is consequently necessary that the belt is not compressed in the press nip so that its thickness is diminished. For a wire with suitable thickness and thread dimensions, the water-receiving capacity can be in the range 300-2,000 g/m2 and, normally, it can be 800-1,300 g/m2 (corresponding to a void volume of 300-2,000 cm3/m2 and 800-1,300 cm3/m2, respectively).

To ensure continuous operation with sustained removal of a constant quantity of water from the press nip and to be able to control this removal, it is an important property of the present invention that the press also comprises conditioning members arranged at suitable locations downstream of the press nip for continuous removal of water from the voids 22 of the belt 20, so that the belt is dry and free of fibres when it runs into the press

nip. In the embodiment shown, such conditioning members comprise a high-pressure squirter 25 for air and two suction boxes 26. One or both of the suction boxes can be replaced by at least one blow box.

Figure 3 shows parts of a press in accordance with a second embodiment of the invention. The press in Figure 3 is similar to the one in Figure 1 but comprises, additionally, a second water-receiving member in the shape of said first press member 13, which consists of an open counter roll, the shell of which has water-receiving, evenly distributed voids 27. The embodiment shown in Figure 3 uses a perforated counter roll 13, said voids 27 of which constitute radially extending openings. The water that flows through the openings 27 is collected in an inner trough 28, from which the water is drained through one of the end walls of the counter roll. When using an open counter roll, the water-receiving belt 20 is always permeable. The open counter roll can, alternatively, be a blind-drilled or grooved counter roll, which thus has water-receiving voids that are outwardly open but inwardly closed. When using an open counter roll 13, its voids 27 and the voids 22 of the belt 20 together have an aggregate open volume equal to or substantially equal to or greater than the volume of water pressed out of the web in the press nip.

In this context, it is suitable for the voids 22 of the belt 20 to constitute at least 50 per cent, preferably at least 60 per cent, of said aggregate open volume. If possible, it may be suitable to arrange some form of conditioning member by the open counter roll as well, when this helps in handling the press water.

The second press member can comprise two press rolls, arranged after each other in the loop of the impermeable belt 15 so that they form two roll press nips with the counter roll 13 and so that the belt 15 forms an extended

belt press zone with the counter roll between the two roll press nips.

The invention is not limited to a fourdrinier former but can involve any kind of wire part, for instance, a twin-wire section with a forming roll.

Experiments with presses in accordance with the invention have shown that, to obtain the best results as regards the handling of the press water, it is necessary that the open volume available in a wire and, alternatively in a wire and an open counter roll, must be essentially greater, for instance 50-100 per cent greater, than the volume of water pressed out of the web. This is presumably due to limitations of time which necessitate good accessibility of the open volume. This also means that the open volume must be evenly distributed over the surface.