AN APPARATUS FOR FORMING A WEB

Abstract: An apparatus (10) is disclosed for forming a web from paper stock ejected from a headbox (12). The apparatus includes a first and a second forming wire (14,16) which cooperate together to define therebetween a forming sec­ tion (18) having a first and a second end (20,22). The first end (20) of the forming section (18) is disposed adjacent to the headbox (12) such that the stock ejected from the headbox (12) enters the first end (20) of the forming section (18) so that the stock is dewatered du­ ring passage from the first (20) towards the second end (22) of the forming section (18). A first turning bar (24) is disposed adjacent to the first end (20) of the forming sec­ tion (18) for guiding the first forming wire (14) such that the first wire is disposed between the first turning bar (24) and the stock. A second turning bar (26) is dis­ posed adjacent to the first (20) end of the forming sec­ tion (18) for guiding the second forming wire (16) such that the second wire is disposed between the second tur­ ning bar (26) and the stock. The turning bars (24,26) de­ fine respectively a first and a second convex surface for slidingly engaging the respective wires (14,16) such that the headbox (12) is disposed in close proximity to the first end (20) of the forming section (18) so that dis­ turbance of the stock between the headbox (12) and the first end (20) of the forming section (18) is minimized.

Description: The present invention relates to an apparatus and method for forming a web from paper stock ejected from a headbox. More particularly, this invention relates to a twin-wire forming section in which the headbox is disposed in close proximity to a first end of the forming section. A typical paper web forming section includes a headbox for ejecting paper stock onto a moving flat screen known as a fourdrinier wire. The stock from the headbox impinges against the moving fourdrinier wire and water within the stock is drained downwardly through the wire so that a fibrous web is formed on the upper surface of the fourdrinier wire. However, due to the downward drainage of water from the web, the resultant web has an upper surface which displays different surface characteristics from the lower surface of the web. Such two-sidedness, or lack of uniformity between the upper and lower surfaces of the web, has caused problems in the finished product when used for printing in which uniformity of the surfaces is desirable. A forming machine which enables the web to be dewatered upwardly as well as downwardly is known from DE 35 01 312 A1. This so-called twin-wire machine includes an upper wire loop which cooperates with the lower fourdrinier wire such that the stock entering a forming section is dewatered through the upper and lower wires for removing a further portion of water from the web upwardly through the second wire. In Figure 8C of DE 35 01 312 A1 (D1) a first 63 and a second turning bar 62 are shown. These turning bars are disposed facing each other between the forming section and the first and second breast roll respectively. However, the rotating breast rolls are of a diameter such that it is not possible to position the slice lip of the headbox very close to the first end of the forming section. Therefore, the slice lip of the headbox is disposed at a considerable distance from the forming section. It is evident that the wires 20 and 10 are very close to each other at the downstream edge of the turning bars 63 and 61 and the slice lip is not positioned in the gap between the turning bars, but it is positioned outside this gap between the breast rolls. This distance between the slice lip and the gap causes the stock ejected from the headbox to contact the wires in the region of the turning bars and the jetted stock is splashing against the wires upstream relative to the turning bars. This splashing causes disturbance of the stock between the headbox and the first end of the forming section. Experiments have indicated that when the slice lip of the headbox is moved nearer to the first end of the forming section, less disturbance and breaking up of the stock occurs between the headbox and the first end and the uniformity of the resultant web is improved. Furthermore, less streaking occurs when the slice lip is brought up very close to the first end as the angle at which the stock impinges, or first contacts the lower wire is minimized. US-3 440 136 (D2) discloses also an apparatus for forming a web from paper stock ejected from a headbox. In Figure 2 two turning bars disposed close to the first end of a forming section are shown However, the stock from the headbox contacts both forming wires simultaneously at a point on the turning bars Therefore, it is an object of the present invention to minimize the disturbance of the stock between the headbox and the first end of the forming section. This object of the invention is achieved by incorporating the features stated in the characterizing portion of claims 1 and 13 into the apparatus and the method defined in the precharacterizing portion of these claims respectively. The present invention reduces the distance between the headbox and the first end of the forming section by using stationary turning bars in place of the aforementioned rotatable breast rolls. Additionally, by the provision of the aforementioned turning bars, the present invention, when combined with the extended trailing elements as taught by U.S. patent number 4,141,788 assigned to Beloit Corporation, provides a layered sheet having enhanced layer purity. All the disclosure of the aforementioned U.S. patent number 4,141,788 is incorporated by reference into the subject application. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which Figure 1 is a side-elevational view of a horizontal twin-wire forming section according to the present invention including stationary turning bars. Figure 2 is an enlarged side-elevational view of the invention shown in figure 1 showing a first and second stationary turning bar in place of rotating breast rolls. Figure 3 is a similar view to that shown in figure 2 but shows the headbox adjusted so that the stock impinges the first wire between the first turning bar and the shoe, Figure 4 is a side-elevational view of another embodiment of the present invention in which the forming section is vertical, and Figure 5 is a side-elevational view of a further embodiment of the present invention including a CONVERFLO headbox with extended trailing elements as shown in U.S. patent number 4,141,788. Similar reference characters refer to similar parts throughout the various embodiments of the present invention. Figure 1 is a side-elevational view of a horizontal BEL BAIE forming apparatus generally designated 10 according to the present invention. The apparatus 10 forms a web W from paper stock ejected from a headbox 12. The apparatus 10 includes a first and a second forming wire 14 and 16 respectively which cooperate together to define therebetween a forming section 18 having a first and a second end 20 and 22 respectively. The first end 20 of the forming section 18 is disposed adjacent to the headbox 12 such that the stock ejected from the headbox 12 enters the first end 20 of the forming section 18 so that the stock is dewatered during passage from the first towards the second end 20 to 22 respectively of the forming section 18. A first turning bar generally designated 24 is disposed adjacent to the first end 20 of the forming section 18 for guiding the first forming wire 14 such that the first wire 14 is disposed between the first turning bar 24 and the stock. A second turning bar generally designated 26 is disposed adjacent to the first end 20 of the forming section 18 for guiding the second forming wire 16 such that the second wire 16 is disposed between the second turning bar 26 and the stock. Figure 2 is an enlarged detailed view of the first end 20 of the forming section 18 showing the first and second turning bars 24 and 26 respectively. The first and second turning bars 24 and 26 define respectively a first and second convex surface 28 and 30 for slidingly engaging the first and second wires 14 and 16 respectively such that the headbox 12 is disposed in close proximity to the first end 20 of the forming section 18 so that disturbance of the stock between the headbox 12 and the first end 20 of the forming section 18 is minimized. As shown in figure 2, the stock 32 ejected from the headbox 12 enters the forming section 18 centrally such that the stock 32 first contacts the first and second wires 14 and 16 respectively at approximately the same distance D from the headbox 12. As shown in figure 3, the angular disposition of the headbox 12 relative to the first end 20 of the forming section 18 is adjustable so that a first distance D1 between the headbox 12 and the point P1 at which the stock 32 first contacts the first wire 14 is adjustable relative to a second distance D2 between the headbox 12 and a second point P2 at which the stock 32 first contacts the second wire 16. As shown in figures 2 and 3, the first turning bar 24 is disposed downstream relative to the second turning bar 26 and the first convex surface 28 defines a leading and a trailing edge 34 and 36 respectively. The trailing edge 36 of the first convex surface 28 is disposed almost parallel to the stock 32. As shown in figures 2 and 3, the second convex surface 30 defines a forward and a rearward portion 38 and 40 respectively with the rearward portion 40 being disposed almost parallel to the stock 32. Preferably, the convex surfaces 28 and 30 are ceramic for reducing wear between the respective wires 14 and 16 and the turning bars 24 and 26. In one embodiment of the present invention, the convex surfaces 28 and 30 are fabricated from zirconia and in another embodiment of the present invention, these surfaces are of aluminum oxide. Figure 2 further shows a solid shoe 42 which is disposed downstream relative to the first turning bar 24 such that the first wire 14 is disposed between the shoe 42 and the stock 32. More particularly, the solid shoe 42 defines an upstream and a downstream end 44 and 46 respectively such that the stock 32 first contacts the first wire 14 between the upstream and downstream ends 44 and 46 of the shoe 42 as shown in figure 2. However, as shown in figure 3, the angular disposition of the headbox can be adjusted such that the stock 32 first contacts the first wire 14 between the first turning bar 24 and the solid shoe 42 such that a first portion of water is removed from the stock 32 upstream relative to the solid shoe 42. Figure 2 further shows a first shower 48 disposed upstream relative to the first turning bar 24 for spraying lubricating water between the first wire 14 and the first turning bar 24 for assisting movement of the first wire 14 relative to the first turning bar 24. Also, a second shower 50 is disposed upstream relative to the second turning bar 26 for spraying lubricating water between the second wire 16 and the second turning bar 26 for assisting movement of the second wire 16 relative to the second turning bar 26. Figure 4 shows a second embodiment of the present invention in which the forming section 18A is disposed vertical with the headbox 12A being disposed beneath the forming section 18A. This arrangement is known as the BEL BAIE III FORMER. BEL BAIE III is a registered trademark of Beloit Corporation. Figure 5 is a side-elevational view of a further embodiment of the present invention for the manufacture of a multi-ply board having enhanced outer layer purity which results in a web having improved printing characteristics. More specifically, as shown in figure 5, a headbox generally designated 12B is of the type shown in U.S. patent number 4,141,788 assigned to Beloit Corporation. The aforementioned headbox 12B is a CONVERFLO headbox. CONVERFLO is a registered trademark of Beloit Corporation. The headbox 12B includes trailing elements 52,53,54,55,56 and 57. The elements 53 and 56 extend downstream relative to the slice lip 62. The arrangement is such that during formation, the inner layer 64 of relatively low quality stock does not come into physical contact with the outer layers 66 and 68 which are of a relatively high quality stock until the outer layers 66 and 68 have been dewatered to a certain degree. This has the advantage that migration or diffusion of the relatively low quality stock of the layer 64 into the adjacent layers 66 and 68 is minimized thereby maintaining a very good outer layer purity. Such purity of the outer layers 66 and 68 improves the printability of the resultant board. In operation of all of the embodiments of the present invention, stock is ejected from a headbox such that the stock enters the forming section at the first end thereof. The first and second wires are guided respectively by first and second turning bars which define convex surfaces such that the slice lip of the headbox may be moved into close proximity to the first end of the forming section thereby minimizing disturbance and breakup of the stock between the slice lip and the first end 20 of the forming section thereby increasing the uniformity of the resultant web and inhibiting streaking thereof and enabling the angle at which the stock impinges against the first wire to be minimized. The present invention, by substituting stationary turning bars for rotatable breast rolls, enables the headbox to be positioned very close to the forming section thereby enhancing the uniformity of the resultant web by inhibiting disturbance, breaking up and streaking of the stock. Although the present invention is useful in the production of all grades of paper and board, the present invention is particularly useful and applicable to the production of fine paper grades and newsprint.

Claims: An apparatus (10) for forming a web (W) from paper stock ejected from a headbox (12), said apparatus (10) comprising: a first (14) and a second forming wire (16) cooperating together to define therebetween a forming section (18) having a first (20) and second end (22); said first end (20) of said forming section (18) being disposed adjacent to the headbox (12) such that the stock (32) ejected from the headbox (12) enters said first end (20) of said forming section (18) so that the stock (32) is dewatered during passage from said first (20) toward said second end (22) of said forming section (18); a first turning bar (24) disposed adjacent to said first end (20) of said forming section (18) for guiding said first forming wire (14) such that said first wire (14) is disposed between said first turning bar (24) and the stock (32); a second turning bar (26) disposed adjacent to said first end (20) of said forming section (18) for guiding said second forming wire (16) such that said second wire (16) is disposed between said turning bar (26) and the stock (32); and said first (24) and second turning bars (26) defining respectively a first (28) and a second convex surface (30) for slidingly engaging said first (14) and second wires (16) respectively, said first (24) and second turning bars (26) are substituted for rotable breast rolls enabling the headbox (12) to be positioned very close to the forming section (18); characterized in that a solid shoe is disposed downstream relative to said first turning bar (24) such that said first wire (14) is disposed between said shoe (42) and the stock (32); said first turning bar (24) is disposed downstream relative to said second turning bar (26) such that the stock (32) first contacts said first wire (14) between said first turning bar (24) and said solid shoe (42); said first (14) and second wires (16) are guided so that the angle at which the stock (32) first contacts the first wire (14) is minimized. An apparatus as set forth in claim 1 wherein said forming section (18) is disposed vertically, the headbox (12) being disposed beneath said forming section (18). An apparatus as set forth in claim 1 wherein said forming section (18) and the headbox (12) are disposed horizontally. An apparatus as set forth in claim 1 wherein stock (32) ejected from the headbox (12) enters said forming section (18) centrally such that the stock (32) first contacts the first (14) and second wire (16) respectively at approximately the same distance (D) from the headbox (12). An apparatus as set forth in claim 1 wherein the angular disposition of the headbox (12) relative to said first end (20) of said forming section (18) is adjustable so that a first distance (D1) between the headbox (12) and the point (P1) at which the stock (32) first contacts said first wire (14) is adjustable relative to a second distance (D2) between the headbox (12) and a second point (P2) at which the stock (32) first contacts said second wire (16). An apparatus as set forth in claim 1 wherein said first convex surface (28) defines a leading (34) and a trailing edge (36), said trailing edge (36) of said first convex surface (28) being disposed almost parallel to the stock (32). An apparatus as set forth in claim 1 wherein said second convex surface (30) defines a forward (38) and rearward portion (40), said rearward portion (40) being disposed almost parallel to the stock (32). An apparatus as set forth in claim 1 wherein said first (28) and second convex surfaces (30) are ceramic for reducing wear between the respective wires (14, 16) and the turning bars (24, 26). An apparatus as set forth in claim 8 wherein said first (28) and second convex surfaces (30) are fabricated from zirconia. An apparatus as set forth in claim 8 wherein said first (28) and second convex surfaces (30) are of aluminum oxide. An apparatus as set forth in claim 1 further including: a first shower (48) disposed upstream relative to said first turning bar (24) for spraying lubricating water between sold first wire (14) and said first turning bar (24) for assisting movement of said first wire (14) relative to said first turning bar (24); a second shower (50) disposed upstream relative to said second turning bar (26) for spraying lubricating water between said second wire (16) and said second turning bar (26) for assisting movement of said second wire (16) relative to said second turning bar (26). An apparatus as set forth in claim 1 comprising a headbox including: a slice lip (62), and a first (53) and a second trailing element (56) extending from within the headbox (12B) to downstream relative to said slice lip (62) such that during the manufacture of a multi-ply board, a layer of relatively poor quality stock (74) flows between said first and second trailing elements (53, 56) and is separated from outer layers (66, 68) of the stock until said outer layers (66, 68) have been subjected to partial dewatering thereby inhibiting diffusion and migration of said inner layer (64) into said outer layers (66, 68) of relatively high quality stock thereby enhancing the printability of the resultant board. A method for forming a web from paper stock (32) ejected from a headbox (12), that method including the steps of: ejecting the stock from the headbox (12) between a first (14) and second forming wire (16) which cooperate together to define therebetween a forming section (18) having a first (20) and a second end (22); guiding the first wire (14) around a first turning bar (24) such that the headbox (12) is disposed in close proximity to the first end (20) of the forming section (18); and guiding the second wire (16) around a second turning bar (26) disposed upstream relative to the first turning bar (24), the first (24) and second turning bars (26) defining respectively first (28) and second convex surfaces (30) for slidingly engaging the first (14) and second wires (16) respectively, characterized by guiding the first wire (14) around a solid shoe (42) disposed downstream relative to said first turning bar (24) such that said first wire (14) is disposed between said shoe (42) and the stock (32); directing the jet of the stock (32) first to contact said first wire (14) between said first turning bar (24) and said solid shoe (42); removing a first portion of water from the stock (32) upstream relative to said solid shoe (42); and guiding the wires (14, 16) such that the angle at which the stock (32) first contacts the first wire (14) is minimized.

Inventors: NORTH, MERLE WAYNE
Applicants: BELOIT CORPORATION
Application year: 1989
Main classification: D21F9
IPC codes: D21F9, D21F1