Abstract:
An apparatus transfers a lead strip of a paper web, in particular the beginning of a still wet lead strip or tail, from a press roll of a paper-making machine to a following section of that machine. An air jet device peels off the beginning of the tail from the press roll and transfers it across a paper roll to an infeed area of a felt which guides the web into the following section. On an infeed area of the felt, an air cushion is created by an air table having a plurality of tiny holes delivering air from a low pressure plenum to the air cushion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for transferring a lead strip of a paper-web from a first traveling surface (e.g., of a press roll or of a press belt) of a paper-making machine to a following section (e.g., a further wet press or drying section) of that machine. In particular, the beginning of a still wet lead strip (or “tail”) is transferred according to the invention. This is to facilitate the threading of the paper web into the machine. 
     2. Description of the Related Art 
     In a dewatering press section of a papermaking machine, as disclosed in FIG. 1 of U.S. Pat. No. 5,404,811, a still wet paper web 9 travels from a wire belt 8 of a forming section through three press nips 16/17, 1/2 and 2/3 and thereafter via a paper roll 59 to a further dewatering press 60; then the still wet web is transferred to a drying section (not shown). When the machine is started up or after a web break, the web is threaded into the machine in a known manner: 
     Initially the web (having the full web width) is running behind the third press nip downwardly and is guided by a doctor 14 into a broke pulper (not shown, positioned below the machine). The web includes a small edge strip, namely the so-called lead strip or “tail”, severed from the web by a water jet positioned in the forming section. This tail is now transferred across paper roll 59 and via a bottom press felt through press 60 as well as through the following drying section. Then the width of the tail is increased up to the full width of the web. 
     During the threading operation, the web is already running with the full machine speed which may be more then 1000 m/min, in modem high speed machines up to about 2000 m/min. Therefore, the transfer of the tail from press roll 2 to the press felt of press 60 is a very difficult step of the threading operation. Sometimes this is done manually by means of an air jet being directed onto the surface of roll 2, thusly severing the tail and forming a new beginning of the tail guided across paper roll 59 to the further press 60. 
     A modem high speed paper-making machine normally comprises an apparatus for carrying out this difficult step. One known apparatus of this type is disclosed in FIG. 2 of U.S. Pat. No. 5,635,030. Here again, a paper web 1 is traveling downwardly across a press roll 5 from a press nip toward a doctor 7. A blast nozzle 6 (or “separating blow pipe”) is provided to peel off the tail from press roll 5 and to transfer the tail to paper roll 2. A further blast nozzle 3 is arranged between the two rolls 5 and 2, which blast nozzle creates an air stream, the velocity of which is greater than the velocity of paper roll 2. Due to the Coanda-Effect, the air stream adheres to the rotating shell of paper roll 2 and guides the tail up to a stationary guide plate 9 which deflects the air stream and the tail toward subsequent press unit 8. 
     The method and the apparatus disclosed in the &#39;030 patent have some disadvantages. Among others, two blast nozzles are needed, one being positioned between the press roll 5 and the paper roll 2. Also, there is a large distance between the paper roll 2 and the infeed area of the press felt 17 of the following press 8. As a result, the tail transfer to the following press may not always be successful in a reliable manner. 
     In another concept, only a short distance has been provided between the paper roll and the infeed area of the following press felt. In other words, a felt roll guiding the following press felt to the following press has been arranged relatively close to the paper roll (as shown in FIG. 1 of the &#39;811 patent). Also, an air cushion has been created onto the infeed area by means of a series of blast nozzles. However, this design also does not always operate satisfactorily. Also, a so-called pony roll has been suggested to be arranged on the infeed area instead of an air cushion, however this is mechanically complicated and therefore not desirable. 
     SUMMARY OF THE INVENTION 
     The present invention significantly improves the transfer of a tail from a first traveling surface to a following machine section by use of a novel method and by use of an improved apparatus which operates more reliably than previous proposals. 
     The method requires little operator skill. Thus, inexperienced personnel are able to start the threading operation without a lot of practice. 
     The threading operation is easily started by a reliable transfer of the tail, even with different paper grades (e.g., different basis weight) and with different machine speeds, including extremely high speed (e.g., more than 2000 m/min). 
     A lead strip or ‘tail’b of a paper web is transferred from a first traveling surface of an element of a paper-making machine to an infeed area of a second traveling surface which guides the tail into a following machine section. 
     The first traveling surface is the surface of a rotatable shell of a press roll which directly contacts the still wet paper web and which is part of a web dewatering press. It may also be the surface of a press belt traveling through a press nip of a web dewatering press. 
     The second traveling surface is the web-carrying surface of a dewatering press felt which guides the web through a subsequent dewatering press. However, the second traveling surface may also be the surface of a subsequent press roll or of a subsequent press belt. In another embodiment of the invention, the second traveling surface is the surface of a dryer fabric which guides the web through a part of a dryer section following the press section of the paper-making machine. 
     The method of the present invention includes providing at least one air jet for peeling off of the tail from the first traveling surface and for transferring it across a rotating paper roll to the infeed area of the second traveling surface. More particularly, the air jet initially severs the tail running with the first traveling surface, thereby forming a new beginning of the tail which is now transferred to the second traveling surface. 
     An air cushion is provided on the infeed area of the second traveling surface. The air cushion is created by an air table having a plurality of tiny orifices delivering air from an air plenum to the air cushion. According to the invention, the air cushion a created by a large number of tiny orifices which connect the air plenum to the air cushion and which are distributed substantially equally on the air table. This results in a significant advantage, namely that the oncoming tail (including its new beginning) is forced to lay on the second traveling surface with only a small amount of air moving with the second traveling surface. Therefore, the tail, which is running at the high machine speed together with the second traveling surface, is reliably pressed onto the second traveling surface. In other words, the air does not bounce off the second traveling surface and the tail is not lifted with the air. Such an undesirable behavior would result from creating an air cushion by use of a series of blast nozzles which deliver too much air at a too high pressure. 
     Too much air is also not directed into the following machine section, e.g., into a further dewatering press. Therein the press nip (or a similar wedge-like gap) would cause the air to flow sideways and to take the tail with it. This could happen both before the beginning of the tail has arrived in the press nip and thereafter. 
     In summary, the method of the invention results in a very easy and reliable transfer of the tail so that the transfer does not need much operator skill. Also, the transfer works well with different paper grades and with different machine speeds including the high speed of modem paper machines. 
     The present invention also includes an apparatus for transferring the tail as described above. The apparatus includes a peeling jet device for providing the at least one air jet as mentioned above. The peeling jet device is arranged close to the first traveling surface (e.g., the surface of the press roll). 
     The apparatus further includes a conventional paper roll which guides the web between the first and second traveling surfaces. The most important element of the apparatus of the invention is a so-called air table having a large number of tiny holes which connect an air plenum with the infeed area of the second traveling surface, thereby creating an air cushion which is almost stationary on the second traveling surface. This results in the advantages described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic side view of two dewatering presses of a paper-making machine including an air table; 
     FIG. 2 is a schematic view along arrow II of FIG. 1; and 
     FIG. 3 is a side schematic view of a segmented air table. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, the normal path of a paper web to be dewatered in two presses  11  and  21  is shown as a broken line and designated  9 ′. Web  9 ′ is traveling through the nip of a top-felted press  11  including a bottom press roll  12  (which directly contacts the web) and a top press roll  13  positioned in the loop of an endless dewatering felt  14 . Bottom press roll  12  includes a (downwardly) “first traveling surface”  15 . Close to it, a peeling jet device  16  and a conventional doctor  17  are arranged. 
     A subsequent dewatering press  21  is bottom felted. It includes a top press roll  22  (which directly contacts the web) and a bottom felt  24  guided by felt rolls  28  and  29 , one ( 28 ) of which is positioned near the bottom press roll  12  of press  11 . The part of felt  24  traveling from felt roll  28  to the nip of press  21  forms a so-called “second traveling surface”  25  including a so-called “infeed area” (positioned on felt roll  28 ) wherein the web comes into contact with felt  24 . Web  9 ′ is guided by a paper roll  20  from the first ( 15 ) to the second ( 25 ) traveling surface. There is a short distance between surface  15  and roll  20  as well as between roll  20  and surface  25 . 
     Behind press  21 , web  9 ′ is traveling across a further paper roll  30  to a dryer fabric  34  running across a fabric toll  33  transferring the web to a first drying cylinder  32  of a drying section  31 . 
     Normally, at least one further press nip (not shown) may be arranged upstream of press  11 . Typically, press  11  forms a third press nip of a complete press section; then press  21  forms a fourth press nip. 
     Before the web  9 ′ is traveling along its normal path it runs across press roll  12  and doctor  17  downwardly into a broke pulper (not shown). For threading the web into the bottom felted press  21  (and further to dryer section  31 ) an edge strip on “tail  9 ” of the web is severed by peeling jet device  16 , peeled off from the first traveling surface  15  and transferred to the second traveling surface  25 . An air table  40  extends along the infeed area of the second traveling surface  25  of felt  24 . The air table also extends from paper roll  20  across the gap between paper roll  20  and felt  24  at felt roll  28 . The width of air table  40  is slightly larger than the width of the tail  9  (see FIG.  2 ). 
     The air table  40  includes a box  41  connected to an air pressure source  43  providing a relatively low air pressure, the box  41  thusly forming a so-called air plenum, wherein the air pressure is preferably between 5 and 20 psi. 
     Box  41  includes a convex wall  42  facing towards felt  24 , the convex wall having a plurality of tiny holes  44  or orifices. The diameter of each hole may be about 0.5 to 2 mm; the percentage of open area, i.e., the total of the cross-sectional areas of throughholes  44  as a percentage of the surface area of the perforated surface of the air table, is about 0.03% to 0.1%. Thereby a stable air cushion is created between air table  40  and the traveling surface  25  of felt  24  pressing the tail onto felt  24  without moving much air toward the nip of press  21 . As a further improvement, box  41  is arranged in such a way that the air cushion formed between box  41  and surface  25  is converging with respect to the web travel direction. Close to paper roll  20 , an air jet pipe  45  is mechanically connected to box  41 , the pipe  45  being connected to a high pressure source  46 . Peeling jet device  16  may also be connected (not shown) to high pressure source  46 . 
     Air jet pipe  45  may provide an air jet approximately tangential to the shell or outer surface of paper roll  20  contrary the travel direction of the shell. At most one further air jet or air curtain may be directed from pipe  45  or from an additional pipe  67  (FIG. 3) toward the infeed area, i.e., toward felt roll  28 . Peeling jet device  16  produces an air jet approximately perpendicular to the first traveling surface  15 . If needed, jet device  16  may additionally create an air jet toward paper roll  20 . 
     In order to further improve the reliable transfer of the tail to the second traveling surface  25  or  34 , it may he helpful to provide suction devices ( 70 - 73 ) in the area of the tail within roll  28  and/or within roll  33  and/or beneath felt  24  and/or fabric  34 . 
     In order to facilitate the transfer of tail  9  from press roll  30  to the drying fabric  34 , a further peeling jet device  26  is arranged close to the surface of press roll  22 . Also, a further air table  50  may be arranged below fabric roll  30 . In this case, press roll  22  forms the first traveling surface and the drying fabric  34  forms the second traveling surface. 
     FIG. 2 shows the peeling jet device  16  air the air table  40  in their operating position held during a threading operation. During the normal operation of the paper-making machine, the peeling jet device  16  is removed to the outside of the machine. For this purpose, a pneumatic cylinder (not shown) or a similar equipment is provided which moves the device  16  automatically into or out of its operating position, as indicated by a double arrow. If needed, the air table  40  may also be connected to a pneumatic cylinder. 
     FIG. 3 shows a further developed air table  60 . It is divided into various (e.g., three) segments  61  through  63 . Each segment is formed as a box similar to box  41  of FIGS. 1 and 2. One ( 61 ) of the boxes is mechanically connected to a supporting device  65  which supports the complete air table  60  and which may be connected (if needed) to a pneumatic cylinder (not shown) of the type explained above. The segments  61  and  62  as well as the segments  62  and  63  are mechanically connected one to the other by a pivot  64 . Also, the outer end of the third segment  63  is connected to support  65  by a spindle  66  (or threaded bolt). Therefore, the distance between the outer end of segment  63  and support  65  may be changed. In other words, the average radius R of the curvature of the complete air table  60  may be changed. This allows the user to change the form of the complete air table  60  in order to adapt the same to various operating conditions, e.g., to various paper grades or to various machine speeds. As an example, the form of the complete air table may be approximately flat. The segments  61 - 63  may be provided with equal air pressure or with different air pressures. Finally, it is possible to create air tables of different size by using a different number of segments (e.g., two or three or four, etc.). 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.