METHOD OF SHEET TRANSFER

Abstract: It includes an intermediate press nip (N-I) formed between first and second press members (21, 22) with a porous felt (20) on one surface of the web (W) and a nonpervious looped smooth surface belt (15) of nonextensible material impervious to water passing through the nip in direct contact with the other surface of the web so that the web follows the belt (15) downstream of the nip (N-I) with the web first being pressed between an earlier press (N) upstream of the intermediate press (N-I), and the web being removed from the belt (15) following the intermediate press (N-I) with rewetting of the web (W) on the offrunning side of the intermediate nip due to contact with the impervious belt (15) being eliminated.

Description: Description for the following Contracting States: FR, IT The invention relates to a mechanism for positive web transfer in a press section of a papermaking machine as summarized in the preamble of claim 1. The invention also relates to a method of positively transferring a web through a press section of a papermaking machine as summarized in the preamble of claim 9. In the transfer of a web between presses or from a press to a dryer, different structures and method have been employed. One arrangement, is to carry the web across an open draw. However, since the sheet is unsupported, the open draw often limits the maximum machine speed due to the strength of the sheet. With types of webs made of short fibres of pulp such as bagasse, and with constructions wherein the sheet is unusually wet and heavy, breakage can occur much too easily in an open draw due to sheet flutter or normal stresses so that the use of open draws is limited to lower speeds and certain types of webs. US―A―2 653 523 or DE―B―1 108 060 discloses another form of sheet transfer, in which a press section having a first nip and a second nip disposed downstream relative to the first nip is employed, and in which the web is carried on a felt through the nips. This arrangement eliminates the problems of sheet breaks at an open draw, but there is a disadvantage in that a considerable amount of rewetting is counter-productive inasmuch as the function of the press is to remove as much moisture as possible to reduce the thermal energy expenditure necessary in the paper machine dryer section. Another form of sheet transfer is on a press roll and although this eliminates the disadvantages of both the open draw and the rewetting of the sheet in felt transfer, there are geometric problems involved in having enough space around the roll to install all the associated press equipment for such transfer. The location and transfer space is determined by the location of the surface of the press roll. It is accordingly an object of the present invention to provide an improved method and mechanism for the transfer of a web between presses or from a press to a dryer in a papermaking machine which eliminates the disadvantages accompanying open draw transfer, felt transfer or direct roll transfer, wherein the web is under complete control to avoid breakage, wherein rewetting from a felt is eliminated, and wherein space problems are not limiting as to where the transfer is to take place. As far as the mechanism is concerned, the object of the invention is achieved by applying the features stated in the characterizing portion of claim 1 to a mechanism as summarized in the preamble of claim 1. As far as the method is concerned, the object of the invention is achieved by applying the features stated in the characterizing portion of claim 9 to a method as summarized in the preamble of claim 9. Various embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic elevational view showing a press section of a papermaking machine constructed and operating in accordance with the principles of the present invention; Figure 2 is another schematic elevational view showing another form of the invention; Figure 3 is another schematic elevational view showing still another form of the invention; and Figure 4 is a further schematic elevational view showing a still further form of the invention. As illustrated in Figure 1, a web W is formed on a forming wire 10 which passes down over a couch roll 11 and a turning roll 12. On the downrunning transfer run of the wire, the web is picked off the wire by a pick-up felt 13 passing over a pick-up roll 14 having a suction gland therein. The web is carried on the underside of the felt to a (second) press nip N formed between an upper press roll 17 and the lower press roll 16. Water is transferred from the web into the felt 13 in the press nip N with the upper press roll 17 being a suction roll with a gland therein or being another form of open roll such as a grooved roll. On the offrunning side of the nip N a guide roll 19 leads the felt 13 away from the nip and away from the web. On the underside of the felt in the nip N, the web is sandwiched between the felt 13 and an endless traveling impervious belt 15. The belt has a smooth upper surface and has a smoothness and a hardness or density generally similar to a plain press roll cover, and therefore the belt acts like an expanded press roll carrying the sheet onwardly to the next press. The belt surface preferably has a hardness in the range of between 10 and 200 P&J (Pusey and Jones). Since the belt surface is impervious to water, there is no rewetting of the sheet when carried on the belt, on the offrunning side of the nip N as in the case of when a felt is used and the sheet transfer is accomplished on a felt. The web or paper sheet follows the belt 15 following the press nip N since the belt has a smoother or more dense surface. Also, the web is not in contact with a felt between presses, as it travels to an intermediate (first) press nip N―I so that rewetting does not occur during the travel time between press nip. While the presses shown as N and N―I are illustrated as conventional roll presses, extended nip presses may be employed, and the same advantages of the use of the impervious belt occur. Extended nip presses, as will be recognized by those versed in the art, are presses utilizing elongated press nips where the pressing pressure may be obtained such as from a dynamic layer of hydraulic liquid. The press nip N―I which may be termed an intermediate nip is formed between a first press member 21 and a second press member 22 defining a pressing zone therebetween through which the web is carried subject to a dewatering pressure. A porous felt 20 which may be termed an intermediate felt is on one surface of the web carrier on the first press roll 21 which may be a grooved roll or a suction roll. The second press roll 22 is a solid roll and may be an extended press nip as indicated symbolically by the rectangle 23 or the rectangle 23 may be designate a controlled crown support shoe which runs inside of a hollow roll shell 22. Following the nip N―I, the felt 20 is separated from the nip over a guide roll 24, and the web W is pulled off of the impervious belt 15 by suitable mechanism, not shown, and the web will follow the belt on the offrunning side of the nip N―I. The web at this location in travel will have been dewatered sufficiently to gain strength to be drawn off of the belt. In the arrangement of Figure 2, similar to Figure 1, a web W is carried through a (second) press nip (N) before passing through an intermediate (first) press nip (N―I), and in the intermediate press nip, one side of the web is supported by a nonporous smooth belt. In Figure 2, there is a closed transfer from the press to the dryers, rather than an open draw as illustrated in Figure 1. Referring to Figure 2, a web is formed on a forming wire 30 which passes down over a couch roll and a turning roll in a downrunning transfer run. In the transfer run, the web is transferred to a first felt 33 which passes in pick-up relation to the wire 30 over a pick-up roll 34 with a pick-up gland therein. An intermediate felt 35 is brought up under the web, guided by a roll 36, and the web is carried through a double felted (second) press nip N. The press nip N is formed between an upper press roll 37 and a lower press roll 38 which may be of various forms, and as illustrated the lower press roll 38 is an open roll such as a grooved roll or roll shell with a suction gland therein. The suction gland transfers the web to the lower felt 35, and the upper felt is guided away from the nip N by a roll 39. The web is then carried to an intermediate (first) press nip N―I formed between the first press member 41 and a second press member 42. The first press member may be a supported controlled deflection roll or an extended press type of roll as indicated by a schematic shoe 48 within the roll shell. In each of the arrangement of Figures 1 and 2, the solid impervious belt 15 and 40 respectively will function as a web carrying member preventing rewetting and can also function as the belt as part of an extended nip arrangement with a sliding shoe therein indicated respectively at 23 and 48. In the sliding shoe arrangement, as in conventional with one form of extended nip, the shoe will be shaped to conform to the roll on the opposite side of the nip and will have a relieved leading edge with means for delivering a hydraulic liquid to the leading edge so that a film of dynamic hydraulic liquid builds up between the belt 40 and the shoe. In Figure 2 on the offrunning side of the nip N―I, the lower felt 35 is separated from the web by being led away by a roll 43. The web will follow the smooth impervious belt 40 to a last nip formed between an upper roll 44 and a lower roll 45. The last nip may be merely be a transfer nip with the web transferring onto the smooth lower roll 45 to be carried through a dryer section with successive dryer drums 47, and additional supporting felts are led onto the web in a conventional manner. In Figure 3, a web W is formed on a forming wire 50 led down through a pickup run over a couch roll 51 and a turning roll 52. The web is picked off the wire 50 by pick-up felt 53 running over a pick-up 54 with a pick-up gland therein. A lower felt 55 is brought up underneath the upper felt 53 to sandwich the web therebetween and carry it through a double felted (second) nip N. The nip N is formed between an upper roll 56 and a lower roll 57 which has a gland therein to transfer the web to the lower felt on the offrunning side of the nip N. The web is picked off the lower felt by a pick-up roll 59 having a gland therein supporting a porous intermediate felt 58. A non-porous looped impervious belt 60 is brought up beneath the web to carry it through an intermediate (first) nip N―I formed between an upper roll 61, which may be an open roll such as a grooved roll, and a lower press roll 62. The lower roll may be an extended nip press arrangement having a shoe 63 or a controlled deflection roll. The web will follow the impervious belt on the offrunning side of the nip N―I, and the upper felt 58 is led away from the nip by a roll 68. The web is picked off the smooth impervious belt by a felt 64 travelling over a pick-up roll 65 having a pick-up gland therein, and the roll 65 is adjustable in position to bring it into pick-up touch contact with the belt. The felt 64 then carries the web through a series of dryer drums such as 67. In this arrangement, the web is under supportive control at all locations and rewetting at the final nip N―I is prevented by the one-piece impervious belt 60. In Figure 4, a web W is formed on a traveling forming wire 70 which is guided down over a couch roll 71 and a turning roll 72 in a pick-up run. The web is picked off of the wire by an upper felt guided into a pick-up relationship with the web by pick-up roll 74 having a pick-up gland therein. A lower felt 75 is brought up under the web so that it is carried in double felted arrangement through a (second) press nip N. The nip N is formed between an upper press roll 76 and a lower press roll 77 which is a suction roll with a gland therein to transfer the web to the lower felt 75. On the offrunning side of the nip, a plain surfaced roll 78 carrying a one-piece smooth belt 86 is pressed into the felt to transfer the web W. The web will transfer to the smooth surfaced belt from the felt, and roll 78 will be adjusted for this purpose. A lower porous felt 79 is brought up beneath the web to carry it through an intermediate (first) nip N―I formed between an upper press roll 80 and a lower press roll 81. The upper roll may be an extended nip roll with a shoe 82 therein, or a controlled crown roll or similar suitable support roll for the nip N―I. The web will follow the smooth-surfaced belt 86 on the offrunning side of the nip N―I, and will automatically transfer to a smooth surface roll 83 which is pressed into the belt a controlled amount by a movable belt guide roll 87. On the downrunning side of the smooth surface roll 83, the web is lifted off of the roll onto a felt 85 which carries it through a series of dryer drums 84. In operation, various arrangements are used for the intial press, but generally speaking an intermediate press nip is utilized formed between a first press member and a second press member defining a pressing zone therebetween with a porous felt on one surface of the web and an impervious nonporous smooth surfaced belt on the other side so that the web follows the belt on the offrunning side of the nip and is not rewetted by the belt at the downside of the nip or while the web is being carried on the belt. Thus, it will be seen that we have provided an improved mechanism for positive web transfer in a press of a papermaking machine which meets the objectives and advantages above set forth and accomodates improved handing with space conservation and enabling higher speed secure transfer of a web without rewetting. Description for the following Contracting States: DE, GB, SE The invention relates to a mechanism for positive web transfer in a press section of a papermaking machine as summarized in the preamble of claim 1. The invention also relates to a method of positively transferring a web through a press section of a papermaking machine as summarized in the preamble of claim 9. In the transfer of a web between presses or from a press to a dryer, different structures and method have been employed. One arrangement, is to carry the web across an open draw. However, since the sheet is unsupported, the open draw often limits the maximum machine speed due to the strength of the sheet. With types of webs made of short fibres of pulp such as bagasse, and with constructions wherein the sheet is unusually wet and heavy, breakage can occur much too easily in an open draw due to sheet flutter or normal stresses so that the use of open draws is limited to lower speeds and certain types of webs. US―A―2 653 523 or DE―B―1 108 060 discloses another form of sheet transfer, in which a press section having a first nip and a second nip disposed downstream relative to the first nip is employed, and in which the web is carried on a felt through the nips. This arrangement eliminates the problems of sheet breaks at an open draw, but there is a disadvantage in that a considerable amount of rewetting is counter-productive inasmuch as the function of the press is to remove as much moisture as possible to reduce the thermal energy expenditure necessary in the paper machine dryer section. Another form of sheet transfer is on a press roll and although this eliminates the disadvantages of both the open draw and the rewetting of the sheet in felt transfer, there are geometric problems involved in having enough space around the roll to install all the associated press equipment for such transfer. The location and transfer space is determined by the location of the surface of the press roll. It is accordingly an object of the present invention to provide an improved method and mechanism for the transfer of a web between presses or from a press to a dryer in a papermaking machine which eliminates the disadvantages accompanying open draw transfer, felt transfer or direct roll transfer, wherein the web is under complete control to avoid breakage, wherein rewetting from a felt is eliminated, and wherein space problems are not limiting as to where the transfer is to take place. As far as the mechanism is concerned, the object of the invention is achieved by applying the features stated in the characterizing portion of claim 1 to a mechanism as summarized in the preamble of claim 1. As far as the method is concerned, the object of the invention is achieved by applying the features stated in the characterizing portion of claim 9 to a method as summarized in the preamble of claim 9. In view of the disclosure of earlier British application No. 8324 755 (GB-A-2 127 448) German application P 33 33 040 (DE-A-3 333 040) and Swedish application No. 83 04 926-2, the patentee has voluntarily limited the scope of the patent, and submitted separate claims for Contracting States GB, DE and SE. Various embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic elevational view showing a press section of a papermaking machine constructed and operating in accordance with the principles of the present invention; Figure 2 is another schematic elevational view showing another form of the invention; Figure 3 is another schematic elevational view showing still another form of the invention; and Figure 4 is a further schematic elevational view showing a still further form of the invention. As illustrated in Figure 1, a web W is formed on a forming wire 10 which passes down over a couch roll 11 and a turning roll 12. On the downrunning transfer run of the wire, the web is picked off the wire by a pick-up felt 13 passing over a pick-up roll 14 having a suction gland therein. The web is carried on the underside of the felt to a (second) press nip N formed between an upper press roll 17 and the lower press roll 16. Water is transferred from the web into the felt 13 in the press nip N with the upper press roll 17 being a suction roll with a gland therein or being another form of open roll such as a grooved roll. On the offrunning side of the nip N a guide roll 19 leads the felt 13 away from the nip and away from the web. On the underside of the felt in the nip N, the web is sandwiched between the felt 13 and an endless traveling impervious belt 15. The belt has a smooth upper surface and has a smoothness and a hardness or density generally similar to a plain press roll cover, and therefore the belt acts like an expanded press roll carrying the sheet onwardly to the next press. The belt surface preferably has a hardness in the range of between 10 and 200 P&J (Pusey and Jones). Since the belt surface is impervious to water, there is no rewetting of the sheet when carried on the belt, on the offrunning side of the nip N as in the case of when a felt is used and the sheet transfer is accomplished on a felt. The web or paper sheet follows the belt 15 following the press nip N since the belt has a smoother or more dense surface. Also, the web is not in contact with a felt between presses, as it travels to an intermediate (first) press nip N―I so that rewetting does not occur during the travel time between press nip. While the presses shown as N and N―I are illustrated as conventional roll presses, extended nip presses may be employed, and the same advantages of the use of the impervious belt occur. Extended nip presses, as will be recognized by those versed in the art, are presses utilizing elongated press nips where the pressing pressure may be obtained such as from a dynamic layer of hydraulic liquid. The press nip N―I which may be termed an intermediate nip is formed between a first press member 21 and a second press member 22 defining a pressing zone therebetween through which the web is carried subject to a dewatering pressure. A porous felt 20 which may be termed an intermediate felt is on one surface of the web carrier on the first press roll 21 which may be a grooved roll or a suction roll. The second press roll 22 is a solid roll and may be an extended press nip as indicated symbolicaly by the rectangle 23 or the rectangle 23 may be designate a controlled crown support shoe which runs inside of a hollow roll shell 22. Following the nip N―I, the felt 20 is separated from the nip over a guide roll 24, and the web W is pulled off the impervious belt 15 by suitable mechanism, not shown, and the web will follow the belt on the offrunning side of the nip N―I. The web at this location in travel will have been dewatered sufficiently to gain strength to be drawn off of the belt. In the arrangement of Figure 2, similar to Figure 1, a web W is carried through a (second) press nip (N) before passing through an intermediate (first) press nip (N―I), and in the intermediate press nip, one side of the web is supported by a nonporous smooth belt. In Figure 2, there is a closed transfer from the press to the dryers, rather than an open draw as illustrated in Figure 1. Referring to Figure 2, a web is formed on a forming wire 30 which grasses down over a couch roll and a turning roll in a downrunning transfer run. In the transfer run, the web is transferred to a first felt 33 which passes in pick-up relation to the wire 30 over a pick-up roll 34 with a pick-up gland therein. An intermediate felt 35 is brought up under the web, guided by a roll 36, and the web is carried through a double felted (second) press nip N. The press nip N is formed between an upper press roll 37 and a lower press roll 38 which may be of various forms, and as illustrated the lower press roll 38 is an open roll such as a grooved roll or roll shell with a suction gland therein. The suction gland transfers the web to the lower felt 35, and the upper felt is guided away from the nip N by a roll 39. The web is then carried to an intermediate (first) press nip N―I formed between the first press member 41 and a second press member 42. The first press member may be a supported controlled deflection roll or an extended press type of roll as indicated by a schematic shoe 48 within the roll shell. In each of the arrangement of Figures 1 and 2, the solid impervious belt 15 and 40 respectively will function as a web carrying member preventing rewetting and can also function as the belt as part of an extended nip arrangement with a sliding shoe therein indicated respectively at 23 and 48. In the sliding shoe arrangement, as in conventional with one form of extended nip, the shoe will be shaped to conform to the roll on the opposite side of the nip and will have a relieved leading edge with means for delivering a hydraulic liquid to the leading edge so that a film of dynamic hydraulic liquid builds up between the belt 40 and the shoe. In Figure 2 on the offrunning side of the nip N―I, the lower felt 35 is separated from the web by being led away by a roll 43. The web will follow the smooth impervious belt 40 to a last nip formed between an upper roll 44 and a lower roll 45. The last nip may be merelv be a transfer nip with the web transferring onto the smooth lower roll 45 to be carried through a dryer section with successive dryer drums 47, and additional supporting felts are led onto the web in a conventional manner. In Figure 3, a web W is formed on a forming wire 50 led down through a pickup run over a couch roll 51 and a turning roll 52. The web is picked off the wire 50 by pick-up felt 53 running over a pick-up 54 with a pick-up gland therein. A lower felt 55 is brought up underneath the upper felt 53 to sandwich the web therebetween and carry it through a double felted (second) nip N. The nip N is formed between an upper roll 56 and a lower roll 57 which has a gland therein to transfer the web to the lower felt on the offrunning side of the nip N. The web is picked off the lower felt by a pick-up roll 59 having a gland therein supporting a porous intermediate felt 58. A non-porous looped impervious belt 60 is brought up beneath the web to carry it through an intermediate (first) nip N―I formed between an upper roll 61, which may be an open roll such as a grooved roll, and a lower press roll 62. The lower roll may be an extended nip press arrangement having a shoe 63 or a controlled deflection roll. The web will follow the impervious belt on the offrunning side of the nip N―I, and the upper felt 58 is led away from the nip by a roll 68. The web is picked off the smooth impervious belt by a felt 64 travelling over a pick-up roll 65 having a pick-up gland therein, and the roll 65 is adjustable in position to bring it into pick-up touch contact with the belt. The felt 64 then carries the web through a series of dryer drums such as 67. In this arrangement, the web is under supportive control at all locations and rewetting at the final nip N―I is prevented by the one-piece impervious belt 60. In Figure 4, a web W is formed on a traveling forming wire 70 which is guided down over a couch roll 71 and a turning roll 72 in a pick-up run. The web is picked off of the wire by an upper felt guided into a pick-up relationship with the web by pick-up roll 74 having a pick-up gland therein. A lower felt 75 is brought up under the web so that it is carried in double felted arrangement through a (second) press nip N. The nip N is formed between an upper press roll 76 and a lower press roll 77 which is a suction roll with a gland therein to transfer the web to the lower felt 75. On the offrunning side of the nip, a plain surfaced roll 78 carrying a one-piece smooth belt 86 is pressed into the felt to transfer the web W. The web will transfer to the smooth surfaced belt from the felt, and roll 78 will be adjusted for this purpose. A lower porous felt 79 is brought up beneath the web to carry it through an intermediate (first) nip N―I formed between an upper press roll 80 and a lower press roll 81. The upper roll may be an extended nip roll with a shoe 82 therein, or a controlled crown roll or similar suitable support roll for the nip N―I. The web will follow the smooth-surfaced belt 86 on the offrunning side of the nip N―I, and will automatically transfer to a smooth surface roll 83 which is pressed into the belt a controlled amount by a movable belt guide roll 87. On the downrunning side of the smooth surface roll 83, the web is lifted off of the roll onto a felt 85 which carries it through a series of dryer drums 84. In operation, various arrangements are used for the intial press, but generally speaking an intermediate press nip is utilized formed between a first press member and a second press member defining a pressing zone therebetween with a porous felt on one surface of the web and an impervious nonporous smooth surfaced belt on the other side so that the web follows the belt on the offrunning side of the nip and is not rewetted by the belt at the downside of the nip or while the web is being carried on the belt. Thus, it will be seen that we have provided an improved mechanism for positive web transfer in a press of a papermaking machine which meets the objectives and advantages above set forth and accomodates improved handing with space conservation and enabling higher speed secure transfer of a web without rewetting.

Claims: Claims for the following Contracting States: FR, IT 1. Mechanism for positive web transfer in a press section of a papermaking machine comprising in combination: means forming a first press nip (N―I) between a first press roll (21;41;61;80) and a second press roll (22;42;62;81) and a porous felt means (20;35;58;79) on one surface of the web (W) passing through the nip (N―I) and receiving water pressed from the web (W) in the nip (N―I); characterized by a nonporous looped smooth surfaced belt (15;40;60;86) of nonextensible material impervious to water passing through said nip (N―I) in direct contact with the other surface of the web (W) in supporting relationship thereto; means guiding the belt (15;40;60;86) away from the nip (N―I); and means (45;64;83) receiving the web (W) from the belt (40;60;86) and separating the web (W) therefrom. 2. Mechanism according to claim 1, wherein means (33;35;53;55;73;75) carrying the web (W) to the felt means (35;58;79) and the belt (40;60;86) are provided. 3. Mechanism according to claim 1, wherein said means carrying the web (W) to the belt (40;60;86) includes a pickup felt (33;53;73) arranged to receive the web (W) from a forming wire (30;50;70) and a second felt (35;53;75) with a roll couple (37,38;56,57;76,77) forming a second press nip (N) pressing the web (W) between the pickup felt (33;53;73) and the second felt (35;55;75) prior to its delivery to said belt (40;60;86). 4. Mechanism according to claim 1, wherein means forming a second press nip (N) between a third (17) and a fourth press roll (16) are provided, said nonporous looped smooth surfaced belt (15) of nonextensible material impervious to water passing sequentially to said second and first nips (N―I, N) in direct supporting contact with the other surface of the web (W) so that the web (W) follows the belt (15) and is supported thereby in travel through the nips (N―I, N); said porous felt means (13,20) on said one surface (W) passing through said first and second nips (N―I, N) and receiving water pressed from the web, and said means receiving the web (W) from the belt (15) and separating the web (W) therefrom following the first nip (N―I). 5. Mechanism according to anyone of the preceding claims, wherein the belt (15;40;60;86) is of a material having a hardness between 10 and 200 P&J. 6. Mechanism according to claim 4 or 5, wherein said belt (15) passes beneath the web (W) in travel through the first and second nips (N―I, N). 7. Mechanism according to anyone of claims 4 to 6, wherein said felt means includes first and second felts (13,20) with the first felt (13) passing through the second nip (N) and separating from the web (W) on the offrunning side and second felt (20) passing through the first nip (N―I) and separating from the web (W) on the offrunning side of the first nip (N―I). 8. Mechanism according to anyone of claims 4 to 7, wherein an initial dewatering nip positioned in advance of said first and second nips (N―I, N) with means (10,13) carrying the web (W) through said initial nip and transferring the web (W) to said belt ( 15) are provided. 9. Method of positively transferring a web (W) through a press section of a papermaking machine between first and second press nips (N―I, N) each formed of a roll couple (21,22;41,42;61,62;80,81;17,16;37,38; 56,57;76,77,73,75) comprising the step of passing a porous felt means (13,20;33,35;53,55,58;73,75,79) through each of said nips (N―I, N) for receiving water pressed from the web (W), characterized by the step of carrying the web (W) on a nonporous looped smooth surfaced belt (15;40;60;86) of nonextensible material impervious to water and passing the belt through at least one of said first and second nips (N―I, N) in direct supporting relationship with the web (W), said porous felt means being on the side of the web opposite the belt (15;40;60;86). 10. Method according to claim 9, wherein the web (W) is first pressed between two opposed felts (33,35;53,55;74,75) upstream of the roll couples and thereafter transferred to the belt (15;40;60;86). Claims for the following Contracting States: DE, GB, SE 1. Mechanism for positive web transfer in a press section of a papermaking machine comprising in combination: means forming a first press nip (N-I) between a first press roll (21;41;61;80) and a second press roll (22;42;62;81), a porous felt means (20;35;58;79) on one surface of the web (W) passing through the first nip (N-I) and receiving water pressed from the web (W) in the first nip (N-I), a roll couple (16,17;37,38;56,57;76,77) forming a second press nip (N) upstream of said first press nip (N-I), and a pickup felt (13;33;53;73) arranged to receive the web (W) from a forming wire (10;30;50;70) and to carry the web (W) to said second press nip (N), characterized by a nonporous looped smooth surfaced belt (15;40;60;86) of nonextensible material impervious to water passing through said first nip (N-I) in direct contact with the other surface of the web (W) in supporting relationship thereto; means guiding the belt (15;40;60;86) away from said first nip (N-I); and means (45;64;83) receiving the web (W) from the belt (40;60;86) and separating the web (W) therefrom on the offrunning side of said first nip (N-I), wherein the web is dewatered in the first nip (N-I) sufficiently to gain strength to be separated from the belt on the offrunning side of said first nip (N-I). 2. Mechanism according to claim 1, wherein means (33,35;53,55;73,75) carrying the web (W) to the felt means (35;58;79) and the belt (40;60;86) are provided. 3. Mechanism according to claim 2, wherein said means carrying the web (W) to the belt (40;60;86) includes said pickup felt (33;53;73) and a second felt (35;53;75), and said second press nip (N) presses the web (W) between the pickup felt (33;53;73) and the second felt (35;55;75) prior to its delivery to said belt (40;60;86). 4. Mechanism according to claim 1, wherein said roll couple forming the second press nip (N) comprises a third (17) and a fourth press roll (16), said nonporous looped smooth surfaced belt (15) of nonextensible material impervious to water passing sequentially to said second and first nips (N-I, N) in direct supporting contact with the other surface of the web (W) so that the web (W) follows the belt (15) and is supported thereby in travel through the nips (N-I, N); said porous felt means (13,20) on said one surface of the web (W) passing through said first and second nips (N-I, N) and receiving water pressed from the web, and said means receiving the web (W) from the belt (15) and separating the web (W) therefrom following the first nip (N-I). 5. Mechanism according to anyone of the preceding claims, wherein the belt (15;40;60;86) is of a material having a hardness between 10 and 200 P&J. 6. Mechanism according to claim 4 or 5, wherein said belt (15) passes beneath the web (W) in travel through the first and second nips (N-I, N). 7. Mechanism according to anyone of claims 4 to 6, wherein said felt means includes first and second felts (13,20) with the first felt (13) passing through the second nip (N) and separating from the web (W) on the offrunning side and second felt (20) passing through the first nip (N-I) and separating from the web (W) on the offrunning side of the first nip (N-I). 8. Mechanism according to anyone of claims 4 to 7, wherein an initial dewatering nip positioned in advance of said first and second nips (N-I, N) with means (10,13) carrying the web (W) through said initial nip and transferring the web (W) to said belt (15) are provided. 9. Method of positively transferring a web (W) through a press section of a papermaking machine sequentially between a second press nip (N) and a first press nip (N-I), each nip being formed of a roll couple (21,22;41,42;61,62; 80,81;17,16;37,38;56,57;76,77,73,75), comprising the steps of passing a porous felt means (13,20;33,35;53,55,58; 73,75,79) through each of said nips (N-I, N) for receiving water pressed from the web (W), said porous felt means including a pickup felt (33; 53;73), and carrying said web on said pickup felt from a forming wire (10;30;50;70) to said second nip (N), characterized by the step of carrying the web (W) on a nonporous looped smooth surfaced belt (15;40;60;86) of nonextensible material impervious to water and passing the belt through at least one of said first and second nips (N-I, N) in direct supporting relationship with the web (W), said porous felt means being on the side of the web opposite the belt (15; 40;60;86), dewatering the web (W) in the first nip (N-I) sufficiently so that it gains strength in order for it to be separated from the belt on the offrunning side of the first nip (N-I), and separating the web (W) from the belt on the offrunning side of said first nip (N-I). 10. Method according to claim 9, wherein the web (W) is first pressed between two opposed felts (33,35;53,55;74,75) upstream of the roll couples and thereafter transferred to the belt (15;40;60;86).

Inventors: CHANCE, JAMES LARRY, CRONIN, DENNIS CALLAHAN, WICKS, LAURIE DAVID
Applicants: BELOIT CORP, BELOIT CORPORATION
Application year: 1983
Main classification: D21F2
IPC codes: B65H20, D21F3, D21F1, D21F2