EP0098502A2 - Belt for use in wet presses of paper machines - Google Patents

Abstract

A belt to be used in paper-machine wet-pressing, in particular in a machine with an extended pressing gap, includes a flexible, liquid-impermeable belt stratum which is smooth on its back side. This belt is improved by providing the front side of the belt stratum (2,12,25,36) with a structured surface with open longitudinal and/or transverse channels (9,14,30,41), for the purpose of water drainage, which cannot be squeezed, or only insignificantly, under press compression.

Description

The invention relates to a belt for use in wet presses of paper machines, in particular with an extended press nip, which has a flexible, liquid-impermeable belt layer that is smooth on the back.

In wet presses of paper machines, a substantial part of the liquid still in the paper web is pressed out. For this purpose, pressure rollers are used, which form a press nip through which the paper web is passed with a rotating felt cloth. Due to the pressure in the press nip, the liquid is pressed out of the paper web into the felt cloth and removed there.

More recently, wet presses with an extended press nip, so-called "extended nip presses", have been developed in which the paper web is exposed to high press pressure over a longer distance and thus for a correspondingly longer time, so that it dryer runs out of the wet press. Such wet presses are for example in DE-AS 23 38 414, DE-AS 24 13 280, US-PS 3 808 092, US-PS 3 970 515 and DE-AS 23 26 980 and DE-OS 29 35 630. Two fundamentally different embodiments have emerged.

In one embodiment, the paper webs and one or two felt cloths are guided into the press nip between two liquid-impermeable belts. This consists of two pressure chambers lying on the back of these belts, which are acted upon hydraulically and in this way exert pressure from both sides on the belts and the paper webs and felt towels guided between them.

In the other embodiment, the paper web is guided over a portion of the circumference of one or more pressure rollers, pressure being exerted in the direction of the pressure roller via this portion. This is also done here via a hydraulically actuated pressure chamber, which acts on a flexible and liquid-impermeable belt running with the paper web and the felt cloth.

Flexible tapes which are smooth on both sides are used as tapes for the aforementioned purpose, the plastic being resistant to the pressure fluid used in the pressure chambers and having a high abrasion resistance. These tapes cannot absorb the water pressed out of the paper web, so that the entire amount of water must be removed from the felt cloth or felt cloths. Because of the high pressure and the comparatively long way on which this pressure acts, this amount is even greater than at the wet presses without an extended press nip.

The invention has for its object to find a way to improve the drainage in wet presses of paper machines, in which tapes of the type mentioned are used, in particular in wet presses with an extended press nip.

This object is achieved according to the invention in that the front of the band layer, of which the band essentially consists, has a structured surface with open longitudinal and / or transverse channels for water drainage that cannot be compressed or cannot be compressed to any significant extent.

This solution is based on the idea already belonging to the invention of assigning a double function to the belt that is already running along, namely once the pressure transfer to the paper web and once the discharge of the water pushed out of the paper web. It has been shown that this structuring of the front side of the strip layer, which causes only a small additional cost, can substantially improve the dewatering. The front side means the side of the tape which faces the paper web or the felt cloth or cloths, while the back is acted upon by the pressure-exerting medium.

In an embodiment of the invention, it is provided that the structured surface is constructed from a multiplicity of intermeshing wire helices with alternating clockwise and counterclockwise pitch, which are partially embedded in the strip layer. Such structures formed from wire spirals are as Wire link belts from DE-OS 24 19 751 known per se. In the present combination, they are characterized by the fact that, depending on their orientation, they form longitudinal or transverse channels that are open at the top and thus ensure good water drainage. They are so stable that they are not compressed under the prevailing pressures in wet presses with an extended press gap, so that the channels always remain open.

If the turns of the wire spirals each consist of two substantially straight turn legs and head arches connecting them, the surface formed by the wire spirals is so flat that markings are prevented and felt abrasion is reduced to a minimum.

To improve the stability of the structured surface consisting of the wire coils, the wire coils should be connected to one another in the overlapping regions by means of coupling wires. Multi-filaments and / or monofilaments can also be inserted into the wire coils, which are then expediently embedded in the strip layer. They increase the stability of the tape in the direction of its orientation and also improve the hold of the wire coils in the tape layer.

As an alternative to the wire helices, the structured surface can also be achieved by means of an at least double-layer fabric with a fabric bond forming the longitudinal and / or transverse channels, the fabric being partially embedded in the strip layer. Pressure-resistant screen fabrics, such as those found in the wet end of paper machines, are particularly suitable for this purpose come into use.

So that the longitudinal and / or transverse channels are formed, the threads running in one direction of the fabric can be made considerably thicker than the threads running in the other direction. In order to keep the channels open, the number of threads in the outer layer of the fabric should be considerably less than that in the inner layer.

In a particularly preferred embodiment, the band according to the invention is open-ended and has seam webs which can be joined together in the paper machine. This considerably simplifies the assembly of the tape in the paper machine. The seam webs should overlap in the longitudinal direction so that the pressure acting on the tape in the area of the overlap acts as a seal. In addition, one of the seam webs on the side facing the other seam web can have at least one profiling, for example a transverse groove, into which a matching counter-profiling, for example a transverse rib, surrounds on the other seam web. In this way, a positive seam connection is made. The thickness of the seam webs should be such that it has the same thickness as the strip layer when lying on top of each other. In addition, at least one of the seam webs on the side facing the other seam web can have a sealant or adhesive. Furthermore, the front edge should be beveled at least one of the seam webs and lie on the inside against a corresponding bevel of the other seam web.

If the structured surface of the band according to the invention is formed by the wire spirals running in the transverse direction, the wire spirals abutting the seam can be connected to one another in a simple manner be connected so that their structure does not change in the area of the seam. Coupling wires can additionally stabilize the connection in this area. In the case of the formation of the structured surface by a fabric or longitudinally extending wire spirals, a fine special seam is provided, by means of which the fabric or the wire spirals can be closed in addition to the band layer, so that a continuously structured area is also formed in this area Surface results.

• Fig. 1 ein Querschnitt durch ein Band für Naßpressen von Papiermaschinen;
• Fig. 2 eine Teildraufsicht des Bandes gemäß Fig. l;
• Fig. 3 ein Längsschnitt durch die Enden eines anderen Bandes für die Naßpresse von Papiermaschinen;
• Fig. 4 der Längsschnitt gemäß Fig. 3 in einer Zwischenstellung vor der Kupplung der Bandenden;
• Fig. 5 der Längsschnitt gemäß Fig. 3 und 4 in Kuppelstellung der Bandenden;
• Fig. 6 ein Querschnitt durch ein weiteres Band für die Naßpresse von Papiermaschinen und
• Fig. 7 ein Querschnitt durch ein anderes Band für die Naßpresse von Papiermaschinen.

In the drawing, the invention is illustrated in more detail using exemplary embodiments. Show it:

• Figure 1 is a cross section through a belt for wet pressing of paper machines.
• Fig. 2 is a partial plan view of the tape of FIG. 1;
• Figure 3 is a longitudinal section through the ends of another belt for the wet press of paper machines.
• 4 shows the longitudinal section according to FIG. 3 in an intermediate position before the coupling of the band ends;
• 5 shows the longitudinal section according to FIGS. 3 and 4 in the coupling position of the band ends;
• Fig. 6 is a cross section through another belt for the wet press of paper machines and
• Fig. 7 is a cross section through another belt for the wet press of paper machines.

The band shown in Fig. 1 is shown in a cross section transverse to the running direction, while Fig. 2 shows a partial plan view. The band 1 consists of a band layer 2, in the front of which a wire structure 3 is embedded, for example cast, with its lower part.

The wire structure 3 is composed of a multiplicity of individual wire helices 4 arranged parallel to one another in the running direction of the strip 1, which are flattened in such a way that 5 semicircular head arches 6 and then straight turn legs 5 are connected to straight turn legs 5. The straight winding legs 5 provide an open but relatively smooth surface, which prevents markings and felt abrasion.

The head bends 6 of the individual wire coils 4 overlap with one another in such a way that coupling wires 7 can be inserted through them for the positive connection of the individual wire coils 4. In addition, longitudinal wires 8 running in the longitudinal direction are provided, which run between the winding legs 5 and are embedded in the strip layer 2. It improves the strength of the band 1 in the longitudinal direction.

As FIG. 1 shows in particular, longitudinal channels 9 are formed by the wire coils 4, which serve to drain water when the belt 1 is used in wet presses, in particular with an extended press nip. In this application, pressure is usually exerted on the smooth back of the belt 1 via a hydraulically operated pressure chamber. This pressure is passed on to a felt cloth and a paper web via the wire helices 4. This is based either directly or via another felt cloth on a roller. Due to the pressure, the water in the paper web is pressed out into the felt cloth. From this it can then be discharged via the longitudinal channels 9 formed from the wire helices 4. In the present exemplary embodiment, this is done in the longitudinal direction. The stability of the wire coils 4 is created so that they are not compressed under the pressure load.

Fig. 2 shows that the longitudinal channels 9 are so open by the distance between the individual winding legs 5 upwards that the water coming from the felt cloth can get into the longitudinal channels 9 without any significant resistance and can drain from there.

3 to 5 show another embodiment of the tape lo according to the invention in a sectional view in the running direction of this tape lo, specifically in the seam area. This band lo differs from the band 1 shown in FIGS. 1 and 2 only in that the wire structure 11, which is otherwise of identical design, is embedded here in the band layer 12 in an orientation rotated by 90 °, so that the wire coils 13 of the wire structure 11 Form transverse channels 14 extending in the transverse direction. The water squeezed out of the paper web and the felt cloth is thus discharged to the sides of the belt 10 in this case.

In this embodiment, the coupling of the ends of the band lo is particularly simple. For this purpose, the tape 10 has seam webs 15, 16 at both ends. The seam web 15 of the left end of the band lo in this view is on its upper side 17th so far except that the wire structure 11 is exposed. Its underside is also excluded, in such a way that a transverse web 18 is formed, which extends over the entire width of the seam web 15 and protrudes downward. The seam web 15 runs towards the belt 10 in a slope 19.

The seam web 16 of the right end of the band lo in this view is only excluded on its upper side. There it has a transverse groove 2o which is suitable for receiving the transverse web 18 of the other seam web 15. To the free edge, the seam web 16 ends in a slope 21 which corresponds to the slope 19.

3, the seam webs 15, 16 are still at a distance from one another. Above the seam webs 15, 16, a bridging wire structure 22 is shown, which consists of three wire coils 13. This bridging wire structure 22 is connected via coupling wires 23 to the wire structure 11 embedded in the strip layer 12, so that it is closed.

Then the seam webs 15, 16 - as shown in Fig. 4 - are brought together and placed on top of each other, so that the cross web 18 fits into the transverse groove 2o and the bevels 19, 2o come to lie together with the mutually facing sides of the seam webs 15, 16 . In operation, these surfaces are pressed together by the press pressure, so that there is automatically a liquid-tight connection. The tightness of this connection can be further improved by previously applying adhesive to at least one of the mutually facing sides of the seam webs 15, 16. Since the seam webs 15, 16 are so coordinated in their thickness that the total thickness does not change in the superimposed state changes, there are no discontinuities.

6 shows a further exemplary embodiment of the invention. The band 24 shown in cross section here consists of a band layer 25 and a pressure-resistant fabric 26 embedded in it with its lower part.

The fabric 26 is constructed in two layers. The lower layer 27 is located within the band layer 25 and the upper layer 28 at a distance from the front surface of the band layer 25. Both layers 27, 28 are formed by relatively thick warp threads 29 running in the running direction of the band 24, the number of warp threads 29 in the lower layer 27 is twice as large as that in the upper layer 28. Only over every second warp thread 29 in the lower layer 27 is a warp thread 29 in the upper layer 28 here, so that the fabric 26 is very open towards the top and wide longitudinal channels 30 are formed between the warp threads 29.

The warp threads 29 of the lower layer are bound by weft threads 31 which run exclusively in the strip layer 25. The integration takes place in such a way that the weft threads 31 run alternately over the upper side of a warp thread and the underside of the next warp thread, etc.

The aforementioned weft thread system alternates with weft threads 32, 33, 34, which produce the connection between the lower layer 27 and the upper layer 28 of the fabric 26. These wefts 32, 33, 34 run such that they alternate every sixth warp 29 of the lower layer 27 and then every third Integrate the warp thread 29 of the upper layer 28, whereby they are each offset by one warp thread in the upper layer 28 in the manner of an atlas weave in the weft direction. A fabric 26 constructed in this way practically does not compress under pressure, so that the longitudinal channels 3o remain open for water drainage.

7 shows a band 35, in the band layer 36 of which a somewhat differently constructed tissue 37 is embedded with its lower part.

This fabric 37 is also constructed in two layers, the lower layer 38 being located within the strip layer 36 and the upper layer 39 being at a distance from the front surface of the strip layer 36. 6, both layers 38, 39 are also formed by relatively thick warp threads 40 running in the running direction of the belt 35, the number of warp threads 40 in the lower layer 38 being twice as large as in the upper one Layer 39. However, the warp threads 40 in the upper layer 39 are offset such that they are in each case above the space between two warp threads 40 in the lower layer 38. The warp threads 40 of the upper layer 39 form wide longitudinal channels 41 for the water removal from the paper web and the felt cloth.

A separate weft thread system with weft threads 42, 43, which run in the band layer 36, is provided for the integration of the warp threads 40 in the lower layer 38. The warp threads 42, 43 each bind two warp threads 40 arranged next to one another on one side before they change sides. They are also in good shape thread direction offset by two warp threads 40 to each other.

The connection between the lower layer 38 and the upper layer 39 is made by further weft threads 44, 45. Each of these weft threads 44, 45 binds first a warp thread 40 in the upper layer 39 and then two warp threads 40 in the lower layer 38 before it goes up again. In addition, the weft threads 44, 45 are also offset from one another in the weft thread direction, in each case by a warp thread 40 of the upper layer 39.

This fabric 37 is also pressure-resistant, so that the longitudinal channels 41 are retained even in the press nip. Water drainage is therefore ensured in this critical area.

The material for the tape layers 2, 12, 25, 36 is predominantly elastic, but also thermoset or thermoplastic polymers, the polymeric substance depending on the intended use. Examples include polyurethane, butadiene-styrene resins, epoxy resins, chlorinated rubber, PVC, polyacrylates and the like. a. commercially available polymers.

The wire structure 3, 11 can be made of synthetic polymers such as PES or PA.

Claims (10)

1. Belt for use in wet presses of paper machines, in particular with an extended press nip, which has a flexible, liquid-impermeable, smooth strip layer on its back, characterized in that the front of the strip layer (2, 12, 25, 36) has a structured surface with an open surface , under or not significantly compressible longitudinal and / or transverse channels (9, 14, 3 ₀ , 41) for water drainage. 2. Band according to claim 1, characterized in that the structured surface of a plurality of interlocking wire helices (4, 13) is constructed with alternating right and left rotating pitch, which are partially embedded in the band layer (2, 12). 3. Band according to claim 2, characterized in that the turns of the wire helices (4, 13) each consist of essentially straight turn legs (5) and head arches (6) connecting them. 4. Band according to claim 2 or 3, characterized in that in the wire helices (4) additional multi and / or monofilaments (8) are inserted to absorb the longitudinal forces. 5. Band according to claim 4, characterized in that the multi- and / or monofilaments (8) are embedded in the band layer (2). 6. Tape according to claim 1, characterized in that the structured surface of an at least double-layered fabric (26, 37) is formed, which is partially embedded in the tape layer (25, 36). 7. Belt according to claim 6, characterized in that the threads running in one direction of the fabric (29, ₄₀ ) are considerably thicker than the threads running in the other direction (31, 33, 34; 42, 43, 44, 45) are. 8. Belt according to one of claims 1 to 7, characterized in that the belt (lo) is open-ended and has seam webs (15, 16) which can be joined together in the paper machine. 9. Band according to claim 8, characterized in that one of the seam webs (16) on the other seam web (15) facing side has at least one profiling (2o), in each of which a matching counter-profiling (18) on the other seam web (15th ) borders. lo. Belt according to claim 8 or 9, characterized in that the thickness of the seam webs (15, 16) is dimensioned such that in the superimposed state it has the same thickness as the belt layer (12).

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