Inclined screen former

Description

[0001] The present invention relates to an inclined wire former for producing a fibrous web, in particular a long-fiber paper or wet-laid nonwoven web, from at least one fibrous suspension, with a wire which runs over a circumferential region of a breast roll and then runs at least partially at an angle to the horizontal in the wire running direction before being deflected into a substantially horizontal direction at a deflection point, wherein in this inclined section of the wire at least one headbox applies at least a portion of the at least one fibrous suspension to the top of the wire, and at least one dewatering element is arranged on the bottom side for dewatering the at least a portion of the at least one fibrous suspension applied to the wire, wherein the headbox comprises a front wall which, together with the wire, defines an outlet gap for the at least one fibrous suspension.

[0002] The invention further relates to the use of such an inclined wire former for producing a long fiber paper or wet-laid nonwoven web, in particular a battery separator paper web or an aramid paper web or a capacitor paper web.

[0003] Such an inclined wire former is known, for example, from German patent application DE 10 2004 047 518 A1 and is manufactured and marketed by the applicant under the name "hydroformer." It is primarily used for the production of long-fiber papers and wet-laid nonwovens. Fibers and fiber blends of various materials with a length of 1 to 40 mm are used in this type of sheet formation.

[0004] Some long-fiber paper or wet-laid nonwoven webs, such as battery separator paper webs, aramid paper webs, or capacitor paper webs, have very high quality requirements. Generally, they should have the lowest possible basis weight while remaining free of pinholes. This requires excellent formation. Fiber agglomerations must be prevented, and the web should have the most uniform thickness and a cross-sectional area profile possible. In this area, there is still room for improvement with conventional inclined wire formers.

[0005] It is an object of the present invention to improve an inclined wire former of the type mentioned above in such a way that the high quality requirements of certain long fiber paper or wet-laid nonwoven webs, such as battery separator paper webs or aramid paper webs or capacitor paper webs, can also be achieved.

[0006] This object is achieved by an inclined screen former according to independent claim 1 and the use of such an inclined screen former according to independent claim 10. The subclaims relate to advantageous developments of the present invention.

[0007] Specifically, the problem is solved by a generic fourdrinier former as described above, in which the front wall of the headbox extends in the direction of wire travel beyond the deflection point of the wire, so that the outlet gap is arranged above the substantially horizontally extending section of the wire.

[0008] The inventors are credited with recognizing that the quality of a long-fiber paper or wet-laid nonwoven web produced on a conventional inclined wire former is negatively affected by the fact that a portion of the fiber suspension exiting the outlet gap flows back along the inclined section of the wire due to gravity. By arranging the outlet gap above the essentially horizontally extending section of the wire, such backflow can be reliably prevented.

[0009] For the purposes of the present invention, by "substantially horizontally extending section of the sieve" is meant that this section of the sieve either extends exactly horizontally or has only a small angle to the horizontal, namely an angle of less than 20°, preferably less than 10°, more preferably less than 5°. In any case, the angle to the horizontal that the "substantially horizontally extending section of the sieve" has is, in magnitude, smaller than the angle to the horizontal that the inclined sieve section has.

[0010] One could also say that the present invention is a special combination of an inclined wire former and a fourdrinier wire former, wherein the fiber suspension is applied to the wire by the special former largely in the region of the inclined wire section and only to a small extent in the substantially horizontally extending wire section.

[0011] Preferably, the at least one dewatering element arranged under the inclined section of the screen extends in the direction of screen travel beyond the deflection point of the screen, so that it ends below the substantially horizontally extending section of the screen. This ensures that dewatering by the at least one dewatering element through the screen also takes place in all areas where fiber suspension is applied to the screen.

[0012] It has proven advantageous if the front wall of the headbox has a curve or a kink or the like in the area of ​​the wire deflection point, so that the distance between the front wall of the headbox and the wire tapers, preferably continuously, in the direction of wire travel. Due to the distance tapering in the direction of wire travel, the flow velocity of the fiber suspension to be applied to the wire can be kept approximately constant.

[0013] It is also advantageous if a suction fixation device is arranged beneath the essentially horizontally extending screen section, by means of which the position of the waterline of the at least one fiber suspension on the essentially horizontally extending screen section can be fixed. Immediately after the outlet gap, there is enough fiber suspension on the screen that a high proportion of the stock suspension can continue to move on the forming fiber web. The fibers still possess turbulence energy from the headbox and can thus, while still in motion, be deposited in the sheet structures. The watery state in this sheet formation area is clearly illustrated by the side view of the essentially horizontally extending screen section, where a shiny, reflective surface can be seen. This phenomenon breaks off almost abruptly at the so-called "waterline," and the surface subsequently appears relatively matte in the direction of screen travel.The position of the waterline can be adjusted using the suction cup.

[0014] At least one further dewatering element, in particular a suction box, can be arranged downstream of the fixing suction device below the essentially horizontally extending screen section, by means of which the fibrous web can be further dewatered. The aim is to achieve a predetermined dry content of the fibrous web before it is removed from the screen.

[0015] To achieve the dry content as quickly and efficiently as possible, at least one steam blow box can be arranged above the essentially horizontally extending screen section. The steam can reduce the viscosity of the water in the fibrous web, which promotes dehumidification of the fibrous web, for example, by means of suction boxes arranged below the screen.

[0016] Additionally or alternatively, at least one upper wire can be arranged above the essentially horizontally extending wire section for this purpose. This allows the fibrous web to be dewatered both downwards through the wire and upwards through the upper wire. This not only shortens the required dewatering distance but also improves the surface of the fibrous web.

[0017] The fabric can have a low air permeability of less than 0.193 m³ / s (410 CFM) and / or a high retention value of more than 100 FSI. This allows for reliable production and transport of fibrous webs even at low stock consistency.

[0018] In order to prevent the fiber suspension emerging from the discharge gap, which is still very mobile until the water line is reached, from flowing down laterally from the substantially horizontal sieve section, it is advantageous if the substantially horizontally extending section of the sieve is at least sectionally surrounded laterally by edge limiters.

[0019] Another aspect of the present invention relates to the use of a previously described inclined sieve former according to the invention for producing a long fiber paper or wet laid web, in particular a battery separator paper web or an aramid paper web or a capacitor paper web. Especially for these webs with their high quality requirements, the advantages of the inclined sieve former according to the invention come into play.

[0020] The inclined screen former according to the invention is preferably operated such that the water line of the at least one fiber suspension is positioned on the substantially horizontally extending screen section. This prevents the fiber suspension from flowing back.

[0021] The consistency of the at least one fiber suspension can be less than 0.3%, preferably less than 0.02%. Low consistency is particularly advantageous for battery separator paper webs, aramid paper webs, or capacitor paper webs. The same applies if the long-fiber paper or wet-laid nonwoven web has a basis weight of less than 20 g / m².

[0022] The invention is further explained below with reference to the schematic and not-to-scale drawings. They show: Figure 1 shows an embodiment known from the prior art, and Figure 2 shows an embodiment according to the present invention.

[0023] Figure 1 shows a schematic of an inclined wire former 10' known from the prior art with a headbox 20' and a wire 30'. During normal operation, the wire 30', designed as an endless wire loop, moves clockwise over a series of rollers. One of these rollers is designed as a breast roll 32'. In the direction of wire travel, the wire 30' moves upwards from the breast roll 32' at an angle oblique to the horizontal direction. In this inclined wire section, the headbox 20' applies a fiber suspension to the top of the wire 30'. To dewater the fiber suspension, a dewatering element 40' is arranged on the bottom of the inclined wire section.

[0024] The headbox 20' has a front wall 22', which, together with the wire 30', defines an outlet gap 24' for the fiber suspension. Behind the dewatering element 40' is a suction fixation device 50', by means of which the water line of the fiber suspension can be adjusted. Both the outlet gap 24' and the dewatering element 40' and the suction fixation device 50' are arranged here in the inclined region of the wire 30'. Only then is the wire 30' deflected in a substantially horizontal direction by means of a first deflection roller 34'. In the wire travel direction, in an area between the first deflection roller 34' and a second deflection roller 36', in which the wire 30' moves substantially horizontally, further dewatering elements 60' are arranged below the wire 30' to further dewater the fiber web.

[0025] Figure 2now schematically shows an embodiment of an inclined screen former 10 according to the invention. Similar or identical components as those shown in Figure 1 shown and described above, are provided with the same reference numerals, but without a prime. In the following, we will primarily discuss the differences between the two embodiments and otherwise refer to the explanations above regarding Figure 1 referred to.

[0026] The inclined wire former 10 according to the invention is particularly characterized in that the outlet gap 24 is already arranged above the essentially horizontally extending section of the wire 30. For this purpose, the front wall 22 of the headbox 20 extends over a deflection point at which the wire 30 transitions from an inclined wire section into the essentially horizontally extending wire section. This reliably prevents part of the fiber suspension emerging from the outlet gap from flowing back onto the wire 30, which is detrimental to the quality of the fibrous web to be produced. The front wall 22 is curved in the region of the deflection point such that its distance from the wire 30 tapers, preferably continuously, in the direction of wire travel.

[0027] The dewatering element 40, located below the screen 30, also extends beyond the deflection point to below the essentially horizontally extending screen section. Since the upper side of the dewatering element 40 is curved, it guides the screen 30 and defines the deflection point. A deflection roller is therefore unnecessary here.

[0028] The fixing suction device 50, which follows the dewatering element 40 in the direction of the screen travel, is thus arranged here below the substantially horizontally extending section of the screen 30. Consequently, the waterline of the fiber suspension emerging from the outlet gap 24 is also located on the substantially horizontally extending section of the screen 30. The screen 30 is preferably laterally supported by Figure 2not shown, which prevent the fiber suspension from running down the side of the screen 30.

[0029] Optionally, a steam blow box 70 and / or an upper wire 80 can be arranged above the essentially horizontal wire section. In this way, the dehumidification of the fibrous web can be carried out efficiently downstream of the waterline, or the overall length of the inclined wire former 10 can be reduced, which is required to transfer the fibrous web with a predetermined dry content to a section of the production machine following the inclined wire former 10. Preferably, additional dewatering elements 60 are arranged below the wire in the area of ​​the steam blow box 70 and / or the upper wire 80. List of reference symbols:

[0030] 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 cup 60, 60' Other dewatering elements 70 Steam box 80 Top wire

Claims

1. Inclined-wire former (10) for producing a fibrous web, in particular a long-fibre paper or wet-laid non-woven web, from at least one fibrous suspension, having a wire (30) which runs over a circumferential region of a breast roller (32) and then runs in the wire running direction at least in places at an angle, obliquely to the horizontal, before being deflected at a deflection point in a substantially horizontal direction, wherein in this oblique section of the wire (30) at least one headbox (20) applies at least one part of the at least one fibrous suspension to the upper side of the wire (30), and disposed on the lower side is at least one dewatering element (40) for dewatering the at least one part of the at least one fibrous suspension applied to the wire (30), wherein the headbox (20) comprises a front wall (22) which conjointly with the wire (30) defines an outlet gap (24) for the at least one fibrous suspension, characterized in that the front wall (22) of the headbox (20) extends in the wire running direction beyond the deflection point of the wire (30) in such a way that the outlet gap (24) is disposed above the substantially horizontally extending portion of the wire (30).

2. Inclined-wire former (10) according to Claim 1, characterized in that the at least one dewatering element (40) disposed on the lower side of the oblique section of the wire (30) extends in the wire running direction beyond the deflection point of the wire (30) in such a way that it ends under the substantially horizontally extending section of the wire (30).

3. Inclined-wire former (10) according to Claim 1 or 2, characterized in that the front wall (22) of the headbox (20) in the region of the deflection point of the wire (30) has a curvature or a kink so that the spacing between the front wall (22) of the headbox (20) and the wire (30) tapers, preferably continuously, in the wire running direction.

4. Inclined-wire former (10) according to one of the preceding claims, characterized in that a fixing suction device (50) is furthermore disposed below the substantially horizontally extending wire portion, by means of which fixing suction device the position of the water line of the at least one fibrous suspension on the substantially horizontally extending wire portion is able to be set.

5. Inclined-wire former (10) according to Claim 4, characterized in that, after the fixing suction device (50), below the substantially horizontally extending wire portion, is disposed at least one further dewatering element (60), in particular a suction box, by means of which the fibrous web is additionally dewaterable.

6. Inclined-wire former (10) according to one of the preceding claims, characterized in that at least one steam blower box (70) is disposed above the substantially horizontally extending wire portion.

7. Inclined-wire former (10) according to one of the preceding claims, characterized in that at least one upper wire (80) is disposed above the substantially horizontally extending wire portion.

8. Inclined-wire former (10) according to one of the preceding claims, characterized in that the wire (30) has a low air permeability of less than 0.193 m3 / s and / or a high retention value FSI (fibre support index) of more than 100.

9. Inclined-wire former (10) according to one of the preceding claims, characterized in that the substantially horizontally extending portion of the wire (30) is at least partly surrounded laterally by peripheral delimiters.

10. Use of an inclined-wire former (10) according to one of the preceding claims for producing a long-fibre paper or wet-laid non-woven web, in particular a battery separator paper web or an aramid paper web or a capacitor paper web.

11. Use according to Claim 10, characterized in that the inclined wire former (10) is operated in such a way that the water line of the at least one fibrous suspension appears on the substantially horizontally extending wire portion.

12. Use according to Claim 10 or 11, characterized in that the substance density of the at least one fibrous suspension is less than 0.3%, preferably less than 0.02%.

13. Use according to one of Claims 10 to 12, characterized in that the long-fibre paper or wet-laid non-woven web has a weight per unit area of less than 20 g / m2.