Patent Publication Number: US-6656325-B1

Title: Machine for manufacturing paper or board

Description:
This application is a continuation of International Application No. PCT/SE99/00768, filed May 7, 1999, currently pending, which claims the benefit of Swedish Application No. 9801741-1, filed May 15, 1998. 
    
    
     The present invention relates to a machine for manufacturing a continuous web of paper or board, comprising a wet section, a press section and a drying section, said wet section including a forming fabric, and said press section comprising 
     a first press including a first press member, a second press member, said press members forming a first press nip with each other, a first press felt running in a loop through the first press nip, and a second press felt running in a loop through the first press nip, the first press member being situated in the loop of the first press felt and the second press member being situated in the loop of the second press felt, and 
     a second press including a first press member, a second press member, said press members forming a second press nip with each other, a first press felt running in a loop through the second press nip, and a second press clothing running in a loop through the second press nip, the first press member being situated in the loop of the first press felt and the second press member being situated in the loop of the second press clothing. 
     BACKGROUND OF THE INVENTION 
     A paper machine of the type described above is known through U.S. Pat. No. 4,483,745. In the first press of the known paper machine, the lower press felt passes around the suction roll for a long distance that is more than twice as long as the actual suction zone. The pressed paper web is transferred to the upper press felt of the second press by means of a suction roll forming a transfer nip with the suction roll of the first press. Suction means cannot therefore be arranged before the transfer of the paper web to the second press to remove water from the lower press felt of the first press downstream of the first press nip. The paper web is therefore rewetted by the wet lower press felt when the paper web and the lower press felt run in intimate contact with each other around the suction roll said long stretch after the suction zone. Furthermore, the known construction lacks steam boxes before the press nip to increase the temperature in the press nip. Neither is it provided with blow boxes to improve running of the paper web. 
     U.S. Pat. No. 4,561,939 describes a paper machine having a press section consisting of two presses. However, both the first and the second presses lack suction rolls. Suction shoes are used to ensure that the paper web accompanies the desired press felt after the press nip, which makes the construction more expensive. A similar paper machine, having a press without suction press roll, is also described in U.S. Pat. No. 5,389,205. 
     EP-0 803 605 describes a paper machine with three presses, the middle one of which is located above the other two presses. The first press has a lower shoe press roll and an upper suction press roll around which the upper press felt runs some considerable distance to be deflected more than 90° after the press nip. The suction press roll has a first suction zone situated opposite the press shoe, and a longer suction zone following the first suction zone and extending to the point where the upper press felt and the paper web leave the suction press roll in vertically upward direction. The upper press felt of the first press also forms the press felt in the first press nip of the middle press. A shoe press with a similar suction press roll and similar large deflection of the web-supporting press felt is described in DE-29701948-U1. In both cases the second press has only one clothing, namely a press felt, but lacks a second clothing, so that the paper web runs a longer distance around one press roll of the second press. A drawback with such configurations as those described in the latter two patent specifications is that the web runs in an open draw from the last press to the drying section and a considerable difference in speed is necessary there in order to remove the web from the smooth roll. This limits the speed of the machine to about 1700-1800 m/min. 
     Each of the known paper machines constitutes a specific configuration offering very limited opportunity or none at all, for choosing positions for the clothings and press members of the presses, and web run in accordance with the customer&#39;s desires and specific machine spaces in each individual case. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an improved paper or board machine designed so that rewetting of the web is avoided, which is free from open draws that limit the speed of the paper or board machine, which offers ample opportunity to apply various types of equipment such as suction boxes, blow boxes and steam boxes at suitable points along the web run, and which allows the positions of the press clothings and press members, as well as web run, to be chosen in accordance with the customer&#39;s desires and specific machine spaces in each individual case. 
     The machine according to the invention is characterized by the combination 
     that the first press member of the first press is a suction roll with a suction zone, within which the first press nip is situated and which has an upstream end and a downstream end, said downstream end being situated downstream and spaced from the first press nip, the second press felt being arranged to be separated from the first press felt at a separation point situated upstream and spaced from the downstream end of the suction zone, 
     that the first press felt of the first press is situated either in a lower or an upper position, and the first press felt of the second press is situated in a reversed relationship in an upper position and lower position, respectively, 
     that the first press felt of the first press is arranged to carry the web from the first press nip to the second press, 
     that the first press member of the second press is a shoe press roll, 
     that the first press felt of the second press is arranged to carry the web from the first press felt of the first press to the second press nip, which is an extended press nip, 
     that a pickup suction roll is arranged in the loop of the first press felt of the second press, close to the first press felt of the first press for transfer of the web from the first press felt of the first press to the first press felt of the second press, 
     that the first press felt of the first press is arranged to leave the suction roll at a point situated at or close to the downstream end of said suction zone, 
     that suction means are arranged in the loop of the first press felt of the first press at at least one point downstream of the suction roll before the transfer of the web to the first press felt of the second press, and 
     that heat-supply means are arranged on the outside of the loops of said press felts situated in an upper position at points where one side of the web is exposed and the other side adheres to said press felts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in more detail in the following with reference to the drawings. 
     FIG. 1 shows schematically parts of a paper machine according to a first embodiment of the invention. 
     FIG. 2 shows schematically parts of a paper machine according to a second embodiment of the invention. 
     FIG. 3 shows schematically parts of a paper machine according to a third embodiment of the invention. 
     FIG. 4 shows schematically parts of a paper machine according to a fourth embodiment of the invention. 
     FIG. 5 shows schematically parts of a paper machine according to a fifth embodiment of the invention. 
     FIG. 6 shows schematically parts of a paper machine according to a sixth embodiment of the invention. 
     FIG. 7 shows schematically parts of a paper machine according to a seventh embodiment of the invention. 
     FIG. 8 shows schematically parts of a paper machine according to an eighth embodiment of the invention. 
     FIG. 9 is an enlarged view of a shoe press of the paper machine according to FIG. 1 or FIG.  2 . 
     FIG. 10 is an enlarged view of a shoe press of the paper machine according to FIG. 5 or FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention is described in connection with paper machines but is equally applicable to machines for manufacturing board. 
     FIGS. 1-4 show schematically parts of paper machines for manufacturing a paper web W. Each of the paper machines comprises a wet section  1 , a press section  2  and a drying section  3 . 
     The wet section  1 , of which only the downstream part is shown, includes a forming wire  4  which runs in a loop around guide rolls  5 . If desired a suction roll (not shown) may be arranged in the loop of the forming wire  4  immediately upstream of a pickup point. 
     The drying section  3  includes a plurality of drying cylinders  7  and rolls  8  having smooth shells or shells provided with openings or recesses. In the embodiments shown each roll  8  is a suction roll without internal suction box with seals, but with internal vacuum (“VacRoll”). The roll  8  may alternatively consist of an ordinary suction roll with an inner suction box with seals. 
     The press section  2  includes a first, double-felted press  9  and a second press  10  which may be a single-felted press as shown in FIGS. 1,  3 ,  5  and  7  or a double-felted press as shown in FIGS. 2,  4 ,  6  and  8 . 
     The first press  9  includes a first press member  11  and a second press member  12 , which press members  11 ,  12  cooperate with each other to form a first press nip between them. The first press  9  also includes a first endless press felt  13  running in a loop through the first press nip and around a plurality of guide rolls  14 . The first press  9  also includes a second endless press felt  15  running in a loop through the first press nip and around a plurality of guide rolls  16 . 
     In all the embodiments according to the present invention the first press member  11  is a suction roll situated in the loop of the first press felt  13 , and the first press felt  13  is arranged to carry the web W from the first press nip to the second press  10 . Blow boxes generating negative pressure or suction boxes  17  are also provided in the loop of the first press felt  13 , these being arranged downstream of the first press nip within the zone where the first press felt  13  carries the paper web W. 
     The second press member  12  of the first press  9  may be a shoe press roll, as is the case in the embodiments according to FIGS. 1,  2 ,  5  and  6 , or a blind-drilled or grooved roll, as is the case in the embodiments according to FIGS. 3,  4 ,  7  and  8 . 
     As is clear from the various embodiments, either one of the two press felts  13 ,  15  may be used as top felt, so that the press felt  13  or  15  of the first press  9 , arranged as top felt, also forms pickup felt and is provided in its loop with a pickup suction roll  18  arranged close to the forming wire  4  for transfer of the paper web W from the forming wire  4  to the top felt  13  is (see e.g. FIG. 5) alternatively  15  (see e.g. FIG.  1 ). 
     A steam box  19  is arranged close to the outer side of the top felt  13  alternatively  15 , downstream of the pickup suction roll  18  for advantageous treatment of the paper web W with steam prior to pressing in the first press nip. 
     In the embodiments according to FIGS. 1,  2 ,  3  and  4  the suction roll  11  is in the lower position and the first press felt  13  is therefore a bottom felt which contains in its loop said blow boxes for generating negative pressure or suction boxes  17 . In the embodiments according to FIGS. 5,  6 ,  7  and  8  the suction roll  11  is in upper position and the first press felt  13  is thus a top felt and has said pickup suction roll  18  in its loop, as well as said blow boxes generating negative pressure or suction boxes  17 . 
     According to the present invention the second press  10  is a shoe press including a first press member  20  in the form of a shoe press roll and a second press member  21  in the form of a counter roll, said press members  20 ,  21  cooperating with each other to form a second, extended press nip. The shoe press  10  also includes a first endless press felt  22  running in a loop through the extended press nip around a plurality of guide rolls  23  and around a pickup suction roll  24  arranged close to the first press felt  13 , carrying the web, of the first press  9  so that the first press felt  22  of the shoe press  10  also acts as pickup felt to transfer the paper web W from the web-carrying first press felt  13  of the first press  9  to the first press felt  22  of the shoe press  10 . Blow boxes generating negative pressure or suction boxes  25  are also arranged in the loop of the first press felt  22  of the shoe press  10 , these being arranged downstream of the pickup suction roll  24  in order to retain the paper web W against the outer side of the first press felt  22  of the shoe press  10  before the extended press nip. 
     The shoe press  10  also includes a second endless press clothing  26  running in a loop in which the counter roll  21  is situated, through the extended press nip and round a plurality of guide rolls  27 . In the embodiments according to FIGS. 2,  4 ,  6  and  8  the second press clothing  26  is a press felt  26 a which, in the embodiments according to FIGS. 2 and 4, is arranged to carry the paper web W from the extended press nip, a suction roll  28  also being arranged in the loop of the press felt  26   a  containing the counter roll  21 , the suction roll  28  being located downstream of the extended press nip, followed by a blow box generating negative pressure or suction box  29 . In the embodiments according to FIGS. 1,  3 ,  5  and  7  the second clothing is a transfer belt  26   b  which is impermeable or substantially impermeable and which may have a smooth surface in contact with the web. 
     In the embodiments illustrated the counter roll  21  of the shoe press  10  is shown as a grooved roll or a blind-drilled roll. The counter roll may alternatively be a smooth roll (not shown). 
     In the embodiments according to FIGS. 1,  2 ,  3  and  4  the paper web W is transferred from the bottom felt  13  of the first press  9  to the top felt  22  of the shoe press  10 , whereas in the embodiments according to FIGS. 5,  6 ,  7  and  8  the paper web W is transferred from the top felt  15  of the first press  9  to the bottom felt  26   a  of the shoe press  10 . In the embodiments according to FIGS. 6 and 8 the bottom felt  26   a  of the shoe press  10  is also arranged to carry the paper web W after the extended press nip up to the drying section. In this case the loop of the bottom felt  22  which contains the shoe press roll  20  is also arranged to contain a suction roll  30  downstream of the extended press nip, followed by a blow box generating negative pressure or suction box  31 . 
     As can be seen from the various embodiments, the position of the first press felt  22  of the second shoe press  10  is determined by the position of the first press felt  13  of the first press  9 , the loop of the press felt  13  holding the suction roll  11 , so that the positions are always inverted, i.e. if the first press felt  13  of the first press  9  containing the suction roll  11  in its loop is in the lower position as in FIG. 1, for instance, then the first press felt  22  of the second shoe press  10  is always in the upper position, and vice versa, as in FIG. 5, for instance. 
     The drying section  3  includes an endless, permeable drying clothing  32  in the form of a drying wire or drying felt running in a loop around a plurality of guide rolls  33 , drying cylinders  7  and rolls  8  which may be grooved rolls or blind-drilled rolls as shown, or alternatively, smooth rolls. In the embodiments according to FIGS. 1,  2 ,  3 ,  4 ,  6  and  8  the drying wire or felt  32  also runs around a pickup suction roll  34  arranged close to the bottom clothing  22 , or alternatively  26   a  or  26   b , of the shoe press  10  so that the pressed paper web W is transferred from the bottom clothing  22 , or alternatively  26   a  or  26   b , to the drying wire or drying felt  32 . Blow boxes generating negative pressure or suction boxes  35  are arranged at suitable points in the loop of the drying wire or felt  32 . A separate, endless pickup clothing  36  is used in the embodiments according to FIGS. 5 and 7, which may be a wire or a felt running in a loop around a plurality of guide rolls  37  and a pickup suction roll  38  arranged close to the top clothing of the shoe press  10 , i.e. the transfer belt  26   b , for transfer of the pressed paper web W from the transfer belt  26   b  to the pickup clothing  36 . A blow box generating negative pressure or suction box  39  is arranged downstream of the pickup suction roll  38  in the loop of the pickup wire or felt  36 . The roll  8  of the drying section situated upstream is arranged close to the pickup wire or felt  36  so that the pressed paper web W is transferred from the pickup wire or felt  36  to the drying wire or felt  32 . 
     A steam box  40  is arranged in a free space existing between the bottom felt of the first press  9  and the bottom clothing of the second shoe press  10 , close to either the top felt of the first press  9  as shown in FIG. 5, for instance, or to the top clothing of the second shoe press as shown in FIG. 1, for instance, where the lower side of the paper web is exposed. 
     FIG. 9 shows parts of the shoe press  10  included in the embodiments according to FIGS. 1-4. The shoe press roll  12  has a flexible shell  41  and a press shoe  42  which has a concave surface over which the flexible shell  41  runs and which is substantially concentric with the suction roll  11 . The pressure of the shoe press against the suction roll  11  is regulated by jack devices  43  extending in two rows transversely to the machine direction. The suction roll  11  has a form stable shell  44  provided with radial suction apertures  45 , and an inner vacuum chamber  46  defined by walls  47  extending transversely to the machine direction and having sealing bodies  48  at their upper ends, these bodies being in sliding, sealing contact with the cylindrical inner side of the shell  44 . The two sealing bodies  48  define a suction zone  49  between them, which acts on the outer side of the shell  44  and encompasses a sector angle c which is in the range of 10°-30°. A press shoe  42  is situated within this suction zone  49 . The suction zone  49  has an upstream end  50  and a downstream end  51 , which upstream and downstream ends  50 ,  51  extend across the machine direction. The two press felts  13 ,  15  run together upstream of the extended press nip at the upstream end  50  of the suction zone  49 , enclosing the paper web W between them. Downstream of the extended press nip the top felt  15  leaves the bottom felt  13  and the suction zone  49  at a separation point P. This separation point P and the downstream end  51  of the C suction zone  49  between them define a downstream area  52  of the suction zone  49  which encompasses a sector angle d which is in the range of 0°-10°, preferably 1°-7°. After the separation point P the top felt  15  forms an angle a with the horizontal line  53  which is in the range of 0°-20°, preferably 5°-13°. The bottom felt  13  continues to run in contact with the shell  44  of the suction roll  11  in said downstream area  52  of the suction zone  49 , thus ensuring that the paper web W adheres firmly to the bottom felt  13  and is carried by this. The bottom felt  13 , and thus the paper web W, leaves the suction roll  11  at or close to the downstream end  51  of the suction zone  49  forming an angle b to the horizontal line  53  which is in the range of 5°-30°, preferably 8°-20°. It will be understood that the angle b is always greater than the angle a in each individual case. This difference is preferably at least 5°, i.e. b−a≧5°, taking into account said angle areas for a and b. It will also be understood that the angle c is always greater than the angle d in each individual case. This difference is preferably at least 5°, i.e. c−d≧5°, taking into account said angle areas for c and d. When the bottom felt  13  leaves the suction roll  11  exactly at the downstream end  51  of the suction zone, the angle b−c will be equal to the angle d. 
     FIG. 10 shows parts of the shoe press included in the embodiments according to FIGS. 5 and 6 and having the shoe press roll in the lower position instead. It can therefore be described in the same way as above, except that the reference numbers for the top and bottom felts are changed. 
     The suction roll  11  of the first press  9  may have an ordinary stainless steel shell or a shell made of metal powder in order to obtain high strength, which shell is suitable for a shoe press  9  operating under high load. The suction roll  11  of the first press  9  may also have a clothing, i.e. a rubber or polyurethane clothing, with suction apertures or suction apertures and blind-drilled holes or grooves. Masking of the suction roll can thus be avoided. 
     The reference number  54  denotes suitable equipment for conditioning the press felts  13 ,  15 ,  22 ,  26   a.    
     As is clear from the drawings, the press section has closed web run from the wet section to the drying section, thus allowing good running for all grades of paper and board as well as high running speed for paper with low weight. The press section has two optimized press nips to achieve good running and dry solids content. The first nip is a roll nip with a suction roll as press roll. The suction roll and blow boxes after the first nip result in good running and the risk of rewetting the web is reduced to a minimum after the first press nip. The second press nip is a shoe nip where extremely high nip load can be used and extremely high dry solids content can be obtained. Better dry solids content can be achieved and the dry solids content profile can be regulated by using a steam box before the first press nip, and especially after the second press nip.