MACHINE FOR MANUFACTURING A PAPER OR CARDBOARD WEB AND PRESS SECTION THEREIN

Abstract: A machine for manufacturing a paper or cardboard web (1) comprises a press section (5) with first, second and third presses (52, 60, 63), which each have first and second press elements (53, 54; 61, 62; 64, 65), in which the first press element of the second press is a smooth press roll, with a smooth envelope surface, and the third press has a press felt (66), running around a roll (68) and the second press element in the third press, besides which an impermeable transfer belt (69) runs in contact with the press roll of the second press and the press felt of the third press to transfer the web from the second press to the third press. In accordance with the invention, the press section includes a wet calender, arranged between the second press and the third press and including a first roll nip, formed by a first calender roll (79), arranged in the loop of the transfer belt, and a second calender roll (80), arranged outside the transfer belt (69). The invention also relates to such a press section.

Description: Machine for manufacturing a paper or cardboard web and press section therein The present invention relates to a machine for manufacturing a continuous paper or cardboard web, comprising - a forming section, - a press section that includes at least a first press, a second press and a third press, which presses each have first and second press elements co-operating with each other to form a press nip, in which the first press element of the second press consists of a smooth press roll, with a smooth envelope surface, and in which the third press has a press felt, running in a loop around a roll and the second press element in the third press, - a drying section, and - an impermeable transfer belt, running in a loop around a plurality of guide rolls and in contact with said smooth press roll of the second press and in contact with said press felt of the third press to transfer the web from the second press to the third press. The invention also relates to a press section in a machine for manufacturing a continuous paper or cardboard web, comprising at least a first press, a second press and a third press, which presses each have first and second press elements co-operating with each other to form a press nip, in which the first press element of the second press consists of a smooth press roll, with a smooth envelope surface, and in which the third press has a press felt, running in a loop around a roll and the second press element in the third press, and - an impermeable transfer belt, running in a loop around a plurality of guide rolls and in contact with said smooth press roll of the second press and in contact with said press felt of the third press to transfer the web from the second press to the third press . In the following, the expression "top side" refers to the side of the paper or cardboard web that is suitable for printing and requires a specific surface smoothness or gloss for each printing quality of the paper or cardboard. To obtain a paper or cardboard web having very high printing quality on its top side the web must be treated so that its top side will display a very high surface smoothness or gloss. The requirements regarding surface smoothness can even be extremely high. A paper machine of the kind described by way of introduction is known through US-5, 647, 960, in which the transfer belt runs around a portion of the smooth roll to form an encompassing zone, the sector angle of which with respect to the smooth roll can be regulated by parallel displacement of a guide roll, around which the transfer belt runs, located upstream. The web runs through said encompassing zone enclosed between the smooth roll and the transfer belt without the web being subjected to any external pressure. The web is pressed in the last press nip with its top side facing the transfer belt. Although the surface smoothness of the top side can be improved in such a press nip, it is not sufficient to conduce to the attainment of a paper or cardboard web of very high printing quality. The object of the present invention is to provide a paper or cardboard machine that enables the manufacture of paper or cardboard webs with improved surface smoothness that conduces to the attainment of a web with very high printing quality. The paper or cardboard machine in accordance with the invention, as well as the press section, is characterized in that - the press section comprises a wet calender, arranged between the second press and the third press and including a first roll nip, formed by a first calender roll, arranged in the loop of the transfer belt, and a second calender roll, arranged outside the loop of the transfer belt, the transfer belt and the web running together through said first roll nip in the wet calender. The invention will be described further in the following with reference to the drawings. Figure 1 shows in outline schematically parts of a cardboard machine with a press section in accordance with a first embodiment. Figure 2 shows schematically parts of a cardboard machine with a press section similar to the one in Figure 1, but with a forming section of a different design from the one included in the cardboard machine in accordance with Figure 1. Figure 3 is a cross-section along the line III-III in Figure 2. Figure 4 shows the press section in accordance with Figure 1 (or Figure 2) somewhat enlarged, illustrating an operating position before threading of the web. Figure 5 shows the press section in accordance with Figure 4, illustrating an operating position after threading of the web. Figure 6 shows a press section in accordance with a second embodiment . Figures 1 and 2 show schematically parts of a cardboard machine for manufacturing a cardboard web 1 that consists of a first layer 2 and a second layer 3. As is shown in Figure 3 , the first layer 2 forms the core of the finished two-layer cardboard web, whilst the second layer 3 forms its surface layer. Alternatively, a cardboard web consisting of three or more layers, one of which being said core and another being said surface layer, is manufactured. The surface layer 3 forms the top side 42 of the web that is to be treated so that as high a surface smoothness as possible is achieved. Each of the cardboard machines shown comprises a forming section 4, a press section 5 and a drying section 6. The forming section 4 includes a first forming unit 7 for manufacturing the core 2 and a second forming unit 8 for manufacturing the surface layer 3. In the embodiment shown in Figure 1, the two forming units 7, 8 consist of a first fourdrinier former, located upstream, and a second fourdrinier former, located downstream, whilst in the embodiment in accordance with Figure 2, they consist of a first twin-wire former or gap former, located upstream, and a second twin-wire former or gap former, located downstream. In this context, the expressions "upstream" and "downstream" refer to the relative positions of the forming units as seen in the machine direction. The first fourdrinier former 7, located upstream in accordance with Figure 1, is extended in the machine direction and has a fourdrinier wire 9, which runs in a loop around an upstream breast roll 10, a downstream suction couch 11, a wire-turning roll 12 and a plurality of other types of guide rolls 13, such as alignment and tension rolls. Between the breast roll 10 and the suction couch 11, the fourdrinier wire 9 has a plane and horizontal upper run 14, where the stock is dewatered and the layers and web are formed. Further, the first upstream fourdrinier former 7 includes a headbox 15, arranged near the breast roll 10 to emit a jet of stock onto the upper run 14 of the fourdrinier wire 9, and dewatering members 16 for dewatering the stock to form the core 2. The second fourdrinier former 8, located downstream in accordance with Figure 1, has a fourdrinier wire 17, which runs in a loop around a breast roll 18, an upper guide roll 19 and two lower guide rolls 20, which lower guide rolls are arranged closely adjacent to the upper run 14 of the fourdrinier wire 9 of the first fourdrinier former 7 to couch the formed second layer together with the formed first layer. The second fourdrinier former 8 includes a headbox 21, arranged near the breast roll 18 to emit a jet of stock onto the upper, plane run 22 of the fourdrinier wire 17, and dewatering members 23 for dewatering the stock to form the second layer. The first twin-wire former 7, located upstream in accordance with Figure 2, has first and second forming wires 25, 26 that run together in a forming zone. The first forming wire 25 runs in an upper loop around a plurality of guide rolls 27. The second forming wire 26 runs in a lower loop around an upstream forming roll 28 and a downstream suction couch 29, a wire-turning roll 30 and a plurality of other guide rolls 31, including alignment and tension rolls. The lower forming wire 26 is extended up to the press section so that the suction couch 29 is located downstream of the second twin-wire former 8. In the loop of the firs forming wire 25, dewatering means 32 are arranged within said forming zone. A headbox 33 is arranged to emit a jet of stock into a gap formed by the forming roll 28 and a guide roll 27 located adjacent to the same in the upper wire loop 25. The second twin-wire former 8, located downstream in accordance with Figure 2, has first and second forming wires 34, 35 that run together in a forming zone. The first forming wire 34 runs in a loop around a plurality of guide rolls 36 and has a lower, straight run 37, running along the lower forming wire 26 of the first twin-wire former 7 to form a couching zone . The second forming wire 35 runs in a loop around a forming roll 38 and two guide rolls 39. In the loop of the first forming wire 34, dewatering means 40 are arranged within said forming zone. A headbox 41 is arranged to emit a jet of stock into a gap formed by the forming roll 38 and a guide roll 36 located adjacent to the same in the first wire loop 34. The first, upstream forming unit 7 is arranged to provide a core 2, whilst the second, downstream forming unit 8 is arranged to provide a top layer or surface layer 3, which forms the top side 42 of the finished cardboard web suitable for printing, which surface layer 3 encounters the core 2 so that the two layers are couched together with each other to a unitary two-layer cardboard web, see Figure 3, which leaves the forming wire 9, 26 of the first forming unit 7 with the surface layer 3 facing upwards . Each press section 5 includes a first press unit 50, including two press nips, and a second press unit 51, including one press nip. The first press unit 50 includes a first, double-felted press 52, having an upper press element 53 and a lower press element 54, which press elements 53, 54 co-operate with each other to form a press nip between them. In the embodiments shown, the first press 52 is a roll press, in which, thus, the upper and lower press elements 53, 54 are press rolls. The upper press roll 53 which, in the embodiments shown, is a suction roll, can be grooved and/or blind-drilled, whilst the lower press roll 54 can be smooth, grooved or blind-drilled. In another embodiment (not shown) , the first press 52 is a shoe press, in which the lower press element 54 is a shoe roll. The first press 52, the roll press, includes an upper, endless press felt 55, running in a loop through the first press nip, around a plurality of guide rolls 56 and around a pick-up suction roll 57, arranged adjacent to the fourdrinier wire 9 to form a transfer zone with the same in which the formed web is transferred from the fourdrinier wire 9 to the upper press felt 55. The roller press 52 has a lower endless press felt 58, running in a loop through the first press nip around a plurality of guide rolls 59. Further, the first press unit 50 includes a second press 60, having an upper press element 61 and a lower press element 62, which press elements 61, 62 co-operate with each other to form a second press nip between them. The second press 60 is a roll press, in which, thus, the two, upper and lower press elements 61, 62 are press rolls. The lower press roll 62, which in the embodiments shown is a suction roll, can be grooved and/or blind-drilled. In the embodiment shown, the upper press roll 53 of the first press 52 also forms the lower press roll 62 of the second press 60, i.e. the two presses 52, 60 have a common press element. Thus, the upper press felt 55 of the first press 52 also runs through the second press nip. The upper press roll 61 of the second press 60 is smooth, so that the web will accompany this smooth press roll 61, which has a smooth envelope surface, after the second press nip and not the upper press felt 55. The press roll 62 is not a suction roll, as the two presses 52, 60 are separated, i.e. they have no common press roll. The second press unit 51 includes a press 63, which has an upper press element 64 and a lower press element 65, which press elements 64, 65 co-operate with each other to form a press nip between them. In the embodiments shown, the last-mentioned press 63 is a shoe press, its upper press element 64 being a counter roll and its lower press element 65 being a shoe roll . In the embodiment in accordance with Figure 4, the counter roll 64 always has a smooth envelope surface, whereas in the embodiment in accordance with Figure 6, the counter roll 64 can have a smooth or grooved envelope surface, a grooved envelope surface providing an improved air-handling function. In the embodiment shown in Figure 1, the shoe press 63 includes a lower endless press felt 66, running in a loop through the press nip, which thus is an extended press nip, around a plurality of guide rolls 67 and a pick-up suction roll 68, arranged upstream of the extended press nip and a distance from the upper smooth press roll 61 of the second press 60. To eliminate an open draw for the web, a transfer belt 69, is arranged to transfer the web from the upper smooth press roll 61 of the second press 60 to the lower press felt 66 of the shoe press 63. The transfer belt 69 runs in an endless loop around a plurality of guide rolls 70, one of which is arranged downstream of the pick-up suction roll 68 to co-operate with the lower press felt 66 in a transfer zone. In accordance with the present invention, the press section is provided also with a wet calender, arranged between the second press 60 and the third press 63 and including a first roll nip, formed by a first calender roll 79, arranged in the loop of the transfer belt 69, and a second calender roll 80, arranged outside the loop of the transfer belt 69. The transfer belt 69 and the web 1 thus run together through the first roll nip in the wet calender. In the preferred embodiment shown of the wet calender, the first roll nip is arranged in close proximity to the upper smooth press roll 61 of the second press 60 so that this press roll 61 forms the second calender roll 80, whilst the first calender roll 79 is arranged in the loop of the transfer belt 69 opposite said smooth press roll 61. The first calender roll 79 is pivotably mounted to assume an elevated inactive position in accordance with Figure 4 and a lowered active position in accordance with Figure 5. The transfer belt 69 runs into the roll nip of the wet calender, while encompassing a portion of the first calender roll 79 and thus does not encounter the web until said roll nip. The transfer belt 69 is arranged such that it departs from the smooth second calender roll 80 with the web adhering to it immediately after the exit from the roll nip of the wet calender. Accordingly, the transfer belt 69 is in contact with the smooth second calender roll 80 only in the roll nip. The nip pressure in the roll nip of the calender is at least 30 kN per metre of web width. Downstream of the roll nip of the calender, a doctor 72 is arranged for scraping the web 1 from the smooth press roll 61 to divert the web down to a broke section. This takes place before and during threading in connection with start up or re-start after a web rupture, the first calender roll 79 being elevated to the inactive operating position in accordance with Figure 4. The counter roll 64 is provided with a doctor 73, arranged to loosen the leader from the smooth surface of the counter roll 64 in connection with threading, a blowing device (not shown) being arranged to guide the leader in the direction of the drying section 6. Reference number 82 denotes a guide roll that is arranged between the press section and the drying section to support the web when this runs therebetween, the top side 42 of the web facing away from this guide roll. In an alternative embodiment (not shown) , the first roll nip of the wet calender is formed by a separate pair of calender rolls arranged in a suitable location downstream of the smooth upper press roll 61. In another alternative embodiment (not shown) , the wet calender has a second roll nip, in which case the first roll nip can correspond to what is shown on the drawings and the second roll nip is formed by a pair of calender rolls arranged in a suitable location downstream of the first roll nip, the transfer belt running through both the roll nips of the wet calender together with the web. The drying section 6 includes a plurality of drying cylinders 74 and a drying clothing 75, running in a loop around the drying cylinders 74 and a plurality of guide rolls 76, of which the guide roll located nearest the press section 5 is arranged such that the drying clothing 75 is deflected in the direction towards the first drying cylinder 74. A blowing box 83 generating a partial vacuum to retain the web against the drying clothing 75 is mounted before the first drying cylinder 74 in the loop of the drying clothing. When a threading has been performed, the web is widened to full width and the calender roll 79 is swivelled down to its operational position adjacent to the smooth press roll 61 to form the wet calender roll nip, as illustrated in Figure 5. The press section in accordance with Figure 6 is similar to the one in accordance with Figure 5, but with the difference that the transfer belt 69 is extended so that it runs through the shoe press nip and around a guide roll 70 located downstream of the shoe press nip so that the transfer belt 69 also supports the web after the shoe press nip. In this case, the roll 68, located upstream in the loop of the press felt 66, does not need to have suction function. From this roll 68, the web runs enclosed between the press felt 66 and the transfer belt 69. The press section is combined with the drying section by way of a permeable transfer clothing 77, running in a loop around a plurality of guide rolls 78, one of which being a pick-up suction roll, enabling the web to be transferred to the permeable transfer clothing 77. The first guide roll 76 of the drying section is designed as a pick-up suction roll that co-operates with the transfer clothing 77 to transfer the web to the drying clothing 75. Thus, the press sections described in accordance with the invention cause the web to be pressed in the two last press nips with the top side in direct contact with a smooth surface in each press nip, namely first in the additional press nip in the shape of the wet calender roll nip and then in the press nip of the third press, the embodiment in accordance with Figure 5 providing a somewhat finer top side, by comparison with the embodiment in accordance with Figure 6 , as the top side of the web in the last press nip is in contact with a counter roll 64 the envelope surface of which being somewhat smoother than the web-contacting surface of the transfer belt 69. The invention contributes to the attainment of webs with top sides having an extremely high smoothness. The press sections shown eliminate an open draw before the last press. In the press section in accordance with Figure 6, an open draw is also eliminated after the last press. Examples of cardboards with high requirements regarding printing quality are the ones commercially known as "White Top Liner" and "Phote Base paper". 0000628 P1392SE TP1

Claims: C A I M S 1. A machine for manufacturing a continuous paper or cardboard web (1) , comprising - a forming section (4) , - a press section (5) that includes at least a first press (52) , a second press (60) and a third press (63) , which presses (52, 60, 63) each have first and second press elements (53, 54; 61, 62; 64, 65) co-operating with each other to form a press nip, in which the first press element (61) of the second press (60) consists of a smooth press roll, with a smooth envelope surface, and in which the third press (63) has a press felt (66) , running in a loop around a roll (68) and the second press element (65) in the third press (63) , - a drying section (6) , and - an impermeable transfer belt (69) , running in a loop around a plurality of guide rolls (70) and in contact with said smooth press roll (61) of the second press (60) and in contact with said press felt (66) of the third press (63) to transfer the web (1) from the second press (60) to the third press (63) , characterized in - that the press section (5) includes a wet calender, arranged between the second press (60) and the third press (63) and including a first roll nip, formed by a first calender roll (79) , arranged in the loop of the transfer belt (69) , and a second calender roll (80) , arranged outside the loop of the transfer belt (69) , the transfer belt (69) and the web (1) running together through said first roll nip in the wet calender. 2. A machine as claimed in claim 1, characterized in that the nip pressure in the first roll nip is at least 30 kN per metre of web width. 3. A machine as claimed in claim 1 or 2, characterized in that the first press roll (61) of the second press (60) forms second calender roll (80) in the first roll nip, the first calender roll (79) being arranged in the loop of the transfer belt (69) opposite said first press roll (61) . 4. A machine as claimed in claim 3, characterized in that the first calender roll (79) is pivotably mounted to assume an elevated inactive position and a lowered active position, in which active position said first roll nip is maintained. 5. A machine as claimed in any one of claims 1-4, characterized in that one of said guide rolls (70) , around which the transfer belt (69) runs, is arranged adjacent to the press felt (66) of the third press (63) upstream of the press nip of the third press (63) , so that the transfer belt (69) is deflected away from the press felt (66) , and that the first press element (64) of the third press (63) is a smooth or grooved press roll. 6. A machine as claimed in any one of claims 1-4, characterized in that the transfer belt (69) is arranged to run in contact with the press felt (66) of the third press (63) and through the press nip of the third press (63) and thereafter in contact with the first press element (64) of the third press (63) . 7. A machine as claimed in any one of claims 1-6, characterized in that the third press (63) is a shoe press, its second press element (65) being a shoe press roll. 8. A machine as claimed in any one of claims 1-7, characterized in that the first press (52) is a roll press or shoe press. 9. A machine as claimed in any one of claims 1-8, characterized in that it includes a plurality of forming units (7, 8) for forming several layers that are couched together with each other, one of which layers being a surface layer (3) , forming a top side (42) of the multi-layer web (1) , and that the wet calender is arranged to act against said surface layer (3) of the multi-layer web. 10. A press section (5) in a machine for manufacturing a continuous paper or cardboard web (1) , comprising at least a first press (52) , a second press (60) and a third press (63) , which presses (52, 60, 63) each have first and second press elements (53, 54; 61, 62; 64, 65) co-operating with each other to form a press nip, in which the first press element (61) of the second press (60) consists of a smooth press roll, with a smooth envelope surface, and in which the third press (63) has a press felt (66) , running in a loop around a roll (68) and the second press element (65) in the third press (63) , and - an impermeable transfer belt (69) , running in a loop around a plurality of guide rolls (70) and in contact with said smooth press roll (61) of the second press (60) and in contact with said press felt (66) of the third press (63) to transfer the web (1) from the second press (60) to the third press (63) , characterized in - that the press section (5) includes a wet calender, arranged between the second press (60) and the third press (63) and including a first roll nip, formed by a first calender roll (79) , arranged in the loop of the transfer belt (69) , and a second calender roll (80) , arranged outside the loop of the transfer belt (69) , the transfer belt (69) and the web (1) running together through said first roll nip in the wet calender. 11. A press section as claimed in claim 10, characterized in that the nip pressure in the first roll nip is at least 30 kN per metre of web width. 12. A press section as claimed in claim 10 or 11, characterized in that the first press roll (61) of the second press (60) forms the second calender roll (80) in the first roll nip, the first calender roll (79) being arranged in the loop of the transfer belt (69) opposite said first press roll (61) . 13. A press section as claimed in claim 12, characterized in that the first calender roll (79) is pivotably mounted to assume an elevated inactive position and a lowered active position, in which active position said first roll nip is maintained. 14. A press section as claimed in any one of claims 10-13, characterized in that one of said guide rolls (70) , around which the transfer belt (69) runs, is arranged adjacent to the press felt (66) of the third press (63) upstream of the press nip of the third press (63) , so that the transfer belt (69) is deflected away from the press felt (66) , and that the first press element (64) of the third press (63) is a smooth or grooved press roll. 15. A press section as claimed in any one of claims 10-13, characterized in that the transfer belt (69) is arranged to run in contact with the press felt (66) of the third press (63) and through the press nip of the third press (63) and thereafter in contact with the first press element (64) of the third press (63) . 16. A press section as claimed in any one of claims 10-15, characterized in that the third press (63) is a shoe press, its second press element (65) being a shoe press roll. 17. A press section as claimed in any one of claims 10-16, characterized in that the first press (52) is a roll press or shoe press. 0000628 P1392SE TP1

Inventors: LEANDERSSON PER ANDERS ARTUR, LEANDERSSON, PER, ANDERS, ARTUR
Applicants: LEANDERSSON PER ANDERS ARTUR, VALMET KARLSTAD AB, LEANDERSSON, PER, ANDERS, ARTUR, VALMET-KARLSTAD AB
Application year: 2001
Main classification: D21F9
IPC codes: D21F3, D21F9, D21F11, D21G1, D21G9