INCLINED-WIRE FORMER AND METHOD OF PRODUCING A FIBROUS WEB

Abstract

An inclined-wire former for producing a fibrous web, in particular a long-fibered paper or wet-laid nonwoven web, includes a wire that runs over a breast roll, subsequently runs inclined at an angle with respect to the horizontal, before it is deflected at a deflection point into a substantially horizontal direction. A headbox in the inclined section of the wire applies a fibrous suspension to the top side of the wire. At least one dewatering element is arranged on the bottom side. The headbox has a front wall which defines, together with the wire, an outlet gap for the at least one fibrous suspension. The front wall of the headbox extends in the wire running direction beyond the deflection point of the wire, such that the outlet gap is arranged above the substantially horizontally extending portion of the wire.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2022 121 105.3, filed Aug. 22, 2022; the prior application is herewith incorporated by reference in its entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to an inclined-wire former for producing a fibrous web, in particular a long-fibered paper or wet-laid nonwoven web, from at least one fibrous suspension. In the device, a wire runs over a circumferential region of a breast roll and subsequently runs in a wire running direction, at least for some distance, inclined at an angle with respect to the horizontal before it is deflected at a deflection point into a substantially horizontal direction. In the inclined section of the wire, at least one headbox applies at least one portion of the at least one fibrous suspension to the top side of the wire, and at least one dewatering element for dewatering the at least one portion of the at least one fibrous suspension applied to the wire is arranged on the bottom side. The headbox has a front wall which, together with the wire, defines an outlet gap for the at least one fibrous suspension.

The invention also relates to the implementation of such an inclined-wire former in a method for producing a long-fibered paper or wet-laid nonwoven web, in particular a battery separator paper web or an aramid paper web or a capacitor paper web.

Such an inclined-wire former is known, for example, from the commonly assigned German published patent application DE 10 2004 047 518 A1. The inclined-wire former is produced and sold by the applicant, Voith of Germany under the name “HydroFormer.” It is used primarily to produce long-fibered papers and wet-laid nonwovens, which sheet formation involves the use of fibers and fiber mixtures of various materials with a length of 1 to 40 mm.

Some long-fibered paper and wet-laid nonwoven webs, such as battery separator paper webs or aramid paper webs or capacitor paper webs, have very high quality requirements. Generally, they should have the lowest possible grammage but should be free from what are known as “pinholes”, i.e., small holes. This requires a very good formation. Agglomerations of fibers are to be avoided and the web should have the most uniform thickness possible and the most uniform mass per unit area transverse profile possible. At this point, the known inclined-wire formers still have further potential for improvement.

SUMMARY OF THE INVENTION

It is the object of the present invention to improve an inclined-wire former of the type mentioned in the introduction in such a way that the high quality requirements of particular long-fibered paper or wet-laid nonwoven webs, such as battery separator paper webs or aramid paper webs or capacitor paper webs, can also be achieved.

With the above and other objects in view there is provided, in accordance with the invention, an inclined-wire former for producing a fibrous web from at least one fibrous suspension, the inclined-wire former comprising:

• • a wire disposed to run over a breast roll and, subsequently in a wire running direction, to run in an inclined section of said wire that is inclined relative to a horizontal before said wire is deflected at a deflection point into a substantially horizontally extending section of said wire;
  • at least one headbox disposed at the inclined section of said wire and configured to apply at least one portion of the at least one fibrous suspension to a top side of said wire;
  • said headbox having a front wall which, together with said wire, defines an outlet gap for the at least one fibrous suspension, said front wall extending in the wire running direction beyond said deflection point of said wire and forming said outlet gap above said substantially horizontally extending section of said wire; and
  • at least one dewatering element disposed at a bottom side of said wire for dewatering the at least one portion of the at least one fibrous suspension applied to said wire.

In other words, the objects of the invention are achieved by means of a generic Fourdrinier former described in the introduction, in which the front wall of the headbox extends in the wire running direction beyond the deflection point of the wire, such that the outlet gap is arranged above the substantially horizontally extending portion of the wire.

The inventors' achievement is to have discovered that the quality of a long-fibered paper or wet-laid nonwoven web produced on a conventional inclined-wire former is adversely affected by the fact that a portion of the fibrous suspension, which exits the outlet gap, flows back on the inclined section of the wire on account of gravity. By virtue of the outlet gap being arranged above the substantially horizontally extending portion of the wire, such backflow can be reliably prevented.

In the context of the present invention, “substantially horizontally extending portion of the wire” means that this portion of the wire either extends exactly horizontally or has only a small angle with respect to the horizontal, namely an angle of less than 20°, preferably of less than 10°, further preferably of less than 5°. In any case, the angle that the “substantially horizontally extending portion of the wire” has with respect to the horizontal is of smaller magnitude than the angle that the inclined wire portion has with respect to the horizontal.

It would also be possible to say that the present invention is a special combination of an inclined-wire former and a Fourdrinier former. The special former applies the fibrous suspension to the wire largely in the region of the inclined wire portion and only to a small extent in the substantially horizontally extending wire portion.

Preferably, the at least one dewatering element arranged on the bottom side of the inclined section of the wire extends in the wire running direction beyond the deflection point of the wire, such that it ends under the substantially horizontally extending portion of the wire. This makes it possible to ensure that, in all regions in which fibrous suspension is applied to the wire, dewatering also takes place through the wire by means of the at least one dewatering element.

It has proven to be favorable for the front wall of the headbox to have, in the region of the deflection point of the wire, a curvature or a bend or the like, such that the spacing between the front wall of the headbox and the wire narrows, preferably continuously, in the wire running direction. Due to the narrowing spacing, or taper, in the wire running direction, the flow rate of the fibrous suspension to be applied to the wire can be kept approximately constant.

It is also advantageous for a fixing suction device to also be arranged under the substantially horizontally extending wire portion, said fixing suction device being able to be used to determine the position of the water line of the at least one fibrous suspension on the substantially horizontally extending wire portion. Directly downstream of the outlet gap, there is so much fibrous suspension on the wire that a high proportion of stock suspension is able to move forward on the fiber nonwoven being formed. The fibers still have turbulence energy from the headbox and may thus be deposited, still in motion, in the sheet structures. The lateral view from above of the substantially horizontally extending wire portion clearly illustrates the aqueous state in this sheet forming region, and a glossy, reflective surface can be seen. This phenomenon stops quite abruptly at what is known as the “water line” and the surface subsequently has a relatively matt appearance in the wire running direction. The fixing suction device can be used to set the position of the water line.

In this case, downstream of the fixing suction device, at least one further dewatering element, in particular a suction box, can be arranged under the substantially horizontally extending wire portion and can be used to further dewater the fibrous web. The aim is to achieve a predefined dry content of the fibrous web before same is removed from the wire.

In order to achieve the dry content as rapidly and efficiently as possible, provision may be made for at least one steam blower box to be arranged above the substantially horizontally extending wire portion. The steam makes it possible to reduce the viscosity of the water located in the fibrous web, which promotes dehumidification of the fibrous web, for example by means of suction boxes arranged below the wire.

For this purpose, it is additionally or alternatively also possible for at least one top wire to be arranged above the substantially horizontally extending wire portion. This makes it possible for the fibrous web to be dewatered both downward through the wire and upward through the top wire. This not only shortens the required dewatering section but also leads to an improvement in the surface of the fibrous web.

The wire may have a low air permeability of less than 410 CFM (cubic feet per minute) and/or a high retention value of more than 100 FSI (fiber support index). In this way, fibrous webs with low consistency can also be reliably generated and transported.

In order to prevent the fibrous suspension which exits the outlet gap and which is still very mobile until the water line is reached from flowing laterally down from the substantially horizontal wire portion, it is advantageous for the substantially horizontally extending portion of the wire to be surrounded laterally, at least in certain portions, by edge limiters.

A further aspect of the present invention relates to the use of an inclined-wire former according to the invention as described above for producing a long-fibered paper or wet-laid nonwoven web, in particular a battery separator paper web or an aramid paper web or a capacitor paper web. The advantages of the inclined-wire former according to the invention come into effect especially for these webs with their high quality requirements.

In this case, the inclined-wire former according to the invention is preferably operated such that the water line of the at least one fibrous suspension is set on the substantially horizontally extending wire portion. A return flow of the fibrous suspension is thus avoided.

The consistency of the at least one fibrous suspension may be lower than 0.3%, preferably lower than 0.02%. Low consistencies are advantageous in particular for battery separator paper webs or aramid paper webs or capacitor paper webs. The same applies if the long-fibered paper web or wet-laid nonwoven web has a grammage of less than 20 g/m².

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in an inclined-wire former, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a diagrammatic side view of an inclined-wire former according to the prior art; and

FIG. 2 shows an embodiment of the inclined-wire former according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail, FIG. 1 shows a diagrammatic illustration of an inclined-wire former 10′ which is known from the prior art. The device 10′ comprises a headbox 20′ and a wire 30′. During the intended operation, the wire 30′ in the form of an endless loop moves counter-clockwise over a series of rolls. One of these rolls is in the form of a breast roll 32′. In the wire running direction, the wire 30′ moves from the breast roll 32′ upward inclined at an angle with respect to the horizontal direction. In this inclined wire portion, the headbox 20′ applies a fibrous suspension to the top side of the wire 30′. For the dewatering of the fibrous suspension, a dewatering element 40′ is arranged on the bottom side in the inclined wire portion.

The headbox 20′ comprises a front wall 22′ which defines, together with the wire 30′, an outlet gap 24′ for the fibrous suspension. Located downstream of the dewatering element 40′ is a fixing suction device 50′ which can be used to set the water line of the fibrous suspension. Here, the outlet gap 24′, the dewatering element 40′ and the fixing suction device 50′ are arranged in the inclined section of the wire 30′. Only thereafter is the wire 30′ deflected in a substantially horizontal direction by means of a first deflection roll 34′. In the wire running direction, in a region between the first deflection roll 34′ and a second deflection roll 36′, the wire 30′ moving substantially in the horizontal direction in said region. Further dewatering elements 60′ are arranged underneath the wire 30′ in order to further dewater the fibrous web.

Referring now to FIG. 2, there is shown a diagrammatic view of an embodiment of an inclined-wire former 10 according to the invention. Here, components which are similar or identical to those shown in FIG. 1 and described above are provided with the same reference designations, but without an apostrophe. In the following we will primarily discuss the differences between the two embodiments and reference will otherwise be made to the explanations appearing above with reference to FIG. 1.

The inclined-wire former 10 according to the invention is distinguished in particular by the fact that the outlet gap 24 is already arranged above the substantially horizontally extending portion of the wire 30. In this respect, the front wall 22 of the headbox 20 extends beyond a deflection point at which the wire 30 transitions from an inclined wire portion to the substantially horizontally extending wire portion. It is thus possible to reliably avoid a portion of the fibrous suspension exiting the outlet gap being able to flow back on the wire 30, which is detrimental to the quality of the fibrous web to be produced. In this case, the front wall 22 is bent in the region of the deflection point in such a way that its spacing to the wire 30 narrows in the wire running direction. That is, the spacing tapers, preferably continuously, in the wire running direction.

The dewatering element 40 arranged underneath the wire 30 also extends beyond the deflection point to under the substantially horizontally extending wire portion. By virtue of the top side of the dewatering element 40 being of curved form, it guides the wire 30 and defines the deflection point. It is therefore possible to dispense with a deflection roll here.

Here, the fixing suction device 50, which follows the dewatering element 40 in the wire running direction, is thus arranged underneath the substantially horizontally extending portion of the wire 30. Consequently, the water line of the fibrous suspension exiting the outlet gap 24 is also located on the substantially horizontally extending portion of the wire 30. The wire 30 is preferably delimited laterally, at least in the region between the outlet gap 24 and the water line, by edge limiters (not illustrated in FIG. 2) which prevent the fibrous suspension from running laterally down from the wire 30.

It is optionally possible for a steam blower box 70 and/or a top wire 80 to be arranged above the substantially horizontal wire portion. In this way, downstream of the water line, the dehumidification of the fibrous web can be effected efficiently, or the structural length of the inclined-wire former 10 that is required in order to be able to transfer the fibrous web with a predetermined dry content to a production machine section adjoining the inclined-wire former 10 can be reduced. Preferably, further dewatering elements 60 are arranged under the wire in the region of the steam blower box 70 and/or the top wire 80.

The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

• • 10, 10′ Inclined-wire former
  • 20, 20′ Headbox
  • 22, 22′ Front wall
  • 24, 24′ Outlet gap
  • 30, 30′ Wire
  • 32, 32′ Breast roll
  • 34′ First deflection roll
  • 36, 36′ Second deflection roll
  • 40, 40′ Dewatering element
  • 50, 50′ Fixing suction device
  • 60, 60′ Further dewatering elements
  • 70 Steam blower box
  • 80 Top wire

Claims

1. An inclined-wire former for producing a fibrous web from at least one fibrous suspension, the inclined-wire former comprising: a wire disposed to run over a breast roll and, subsequently in a wire running direction, to run in an inclined section of said wire that is inclined relative to a horizontal before said wire is deflected at a deflection point into a substantially horizontally extending section of said wire;at least one headbox disposed at the inclined section of said wire and configured to apply at least one portion of the at least one fibrous suspension to a top side of said wire;said headbox having a front wall which, together with said wire, defines an outlet gap for the at least one fibrous suspension, said front wall extending in the wire running direction beyond said deflection point of said wire and forming said outlet gap above said substantially horizontally extending section of said wire; andat least one dewatering element disposed at a bottom side of said wire for dewatering the at least one portion of the at least one fibrous suspension applied to said wire.

2. The inclined-wire former according to claim 1, wherein said at least one dewatering element is arranged on the bottom side of said inclined section of said wire, extends in the wire running direction beyond said deflection point of said wire, and ends below said substantially horizontally extending section of said wire.

3. The inclined-wire former according to claim 1, wherein said front wall of said headbox has, in the region of the deflection point of said wire, a curvature or a bend, which causes a spacing between said front wall and said wire to narrow in the wire running direction.

4. The inclined-wire former according to claim 3, wherein said spacing between said front wall and said wire tapers continuously in the wire running direction.

5. The inclined-wire former according to claim 1, further comprising a fixing suction device underneath said substantially horizontally extending section of said wire, said fixing suction device being usable for determining a position of a water line of the at least one fibrous suspension on said substantially horizontally extending section of said wire.

6. The inclined-wire former according to claim 5, further comprising at least one further dewatering element disposed downstream of said fixing suction device, underneath said substantially horizontally extending section of said wire, and configured to further dewater the fibrous web.

7. The inclined-wire former according to claim 6, wherein said at least one further dewatering element is a suction box.

8. The inclined-wire former according to claim 1, further comprising at least one steam blower box arranged above said substantially horizontally extending section of said wire.

9. The inclined-wire former according to claim 1, further comprising at least one top wire arranged above said substantially horizontally extending section of said wire.

10. The inclined-wire former according to claim 1, wherein said wire has at least one of a low air permeability of less than 410 CFM or a high retention value of more than 100 FSI.

11. The inclined-wire former according to claim 1, further comprising edge limiters disposed to laterally surround said substantially horizontally extending section of said wire, at least in certain portions thereof.

12. The inclined-wire former according to claim 1 configured for producing a long-fibered paper web or a wet-laid nonwoven web from the at least one fibrous suspension.

13. A method, comprising: providing the inclined-wire former according to claim 1; andproducing a long-fibered paper web or wet-laid nonwoven web with the inclined-wire former.

14. The method according to claim 13, which comprises forming a web selected from the group consisting of a battery separator paper web, an aramid paper web, and a capacitor paper web.

15. The method according to claim 13, which comprises operating the inclined-wire former to form a water line of the at least one fibrous suspension on the substantially horizontally extending section of the wire.

16. The method according to claim 13, which comprises setting a consistency of the at least one fibrous suspension to less than 0.3%.

17. The method according to claim 16, which comprises setting the consistency of the at least one fibrous suspension to lower than 0.02%.

18. The method according to claim 13, wherein the long-fibered paper or wet-laid nonwoven web has a grammage of less than 20 g/m2.