Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper
  • D21F5/02—Drying on cylinders
  • D21F5/04—Drying on cylinders on two or more drying cylinders
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F7/00—Other details of machines for making continuous webs of paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G9/00—Other accessories for paper-making machines
  • D21G9/009—Apparatus for glaze-coating paper webs

Definitions

• the invention concerns a method for drying a paper to be surface-treated, in particular fine paper, in an after-dryer in a paper machine, in which method the paper web is first dried in the forward dryer section of the paper machine by means of a number of successive groups with single-wire draw that are open downwards on support of a drying wire, after which the paper web is finished in a finishing section, in which finishing section the web is surface-sized or coated.
• the invention concerns an after-dryer that makes use of the method of the invention for drying a paper to be surface-treated, in particular fine paper, in which paper machine, before the after-dryer, there is a forward dryer section, in which there are a number of successive groups with single-wire draw that are open downwards, and after which forward dryer section a finishing section is placed, in which there are devices for surface-sizing or coating of the paper web.
• twin- wire draw and/or single-wire draw is/are employed.
• twin- wire draw the groups of drying cylinders comprise two wires, which press the web one from above and the other one from below against heated cylinder faces. Between the rows of drying cylinders, which are usually horizontal rows, the web has free and unsupported draws, which are susceptible of fluttering, which may cause web breaks, in particular so when the web is still relatively moist and, therefore, of low strength.
• each group of drying cylinders includes just one drying wire, on whose support the web runs through the whole group so that the drying wire presses the web on the drying cylinders against the heated cylinder faces, whereas on the reversing cylinders or rolls between the drying cylinders the web remains at the side of the outside curve.
• the drying cylinders are placed outside the wire loop, and the reversing cylinders or rolls inside said loop.
• the tendency of curling of paper is already affected in connection with the web formation, in particular at the sheet formation stage by means of selection of the difference in speed between the slice jet and the wire, and by means of other running parameters.
• a suitable initial curl form is regulated for the sheet in order that the curling of the paper after one-sided or double-sided copying could be optimized.
• the reactivity of curling i.e. the extent to which curling occurs per unit of change in moisture content, is affected to a greater extent by means of a multi-layer structure of the paper, which is produced in connection with the web formation in the wet end.
• the method in accordance with the present invention is mainly characterized in what is stated in the characterizing part of claim 1 , 2 or 3.
• the after-dryer of a paper machine that carries out the method in accordance with the present invention is mainly characterized in what is stated in the characterizing part of claim 10, 11 or 12.
• the after-dryer is started with a dryer group that applies an inverted single-wire draw, in which case, in view of the tendency of curling of paper, the desired ratio of upper cylinders to lower cylinders is obtained.
• the drying is started by means of an inverted group with single-wire draw, and said group is followed by either normal or inverted groups with single-wire draw or by dryer groups based on twin- wire draw.
• the paper web is brought from the coating device or equivalent onto an upper or lower cylinder, and after this there follows the inverted dryer group.
• the most important advantage of this arrangement in accordance with the present invention is formation of a ratio of upper cylinders to lower cylinders that is correct in view of the tendency of curling of paper, without additional length of the dryer section. Owing to this, no additional arrangements are needed to supply additional heat to provide unequalsidedness.
• moist air is introduced in appropriate locations inside the hood, in which case the moisture levels in the different pocket spaces formed by the cylinders, rolls and wires in the dryer groups can be controlled. In the supply of moisture, it is possible to use air supply devices, ventilators, blow pipes, etc. fitted in the after-dryer.
• hot moist air is supplied into the desired upper/lower pockets, in which connection the control of curling takes place so that evaporation taking place from the wrong side of the paper is restrained by means of the supply of hot moist air.
• the necessary moist air is obtained, for example, from the exhaust air from the hood or from suction rolls.
• appropriately selected moisture levels of air are employed in order to achieve the desired distribution of moisture.
• the air moisture levels at all of the different moisture supply points can be regulated separately, and so also the exhaust quantities of all the air exhausts can be regulated separately if necessary.
• the supply of hot dry air onto the side of the web from which evaporation is to be promoted is included in the scope of the present invention.
• Figure 1 is a schematic illustration of an embodiment of a solution of the dry end of a paper machine, showing the forward dryer section and the following finishing section.
• Figure 2 is a schematic illustration of an after-dryer of the present invention.
• Figures 3A...3C are illustrations in part of different variations of the after-dryer as shown in Fig. 2, which variations are included in the scope of the invention.
• Figures 4A...4B are further illustrations of an embodiment of an after-dryer in accordance with the present invention.
• Figures 5A...5B are schematic illustrations of some test results related to curling of the paper web in the after-dryer.
• Figure 6 is a schematic illustration of a further embodiment of the invention.
• the paper web is passed into the forward dryer section Dl from the press section onto the drying wire of the first group R j with single-wire draw, to which wire the web is made to adhere by the effect of the vacuum in the suction boxes.
• R j N normal groups
• All the single-wire groups R, ...R N are so-called normal groups, in which the, for example, steam- heated smooth-faced drying cylinders 110 are placed in the upper horizontal row and the reversing suction cylinders 111 are in the lower horizontal row. The web has closed draws over the gaps between the dryer groups.
• Each normal group RJ ...R N has a drying wire 115 of its own, which is guided by guide rolls 118.
• the drying wires 115 press the web W to be dried on the drying cylinders 110 against the smooth heated cylinder faces, and on the reversing cylinders 111 the web W remains on the outer face of the wire 115 at the side of the outside curve.
• the web W is kept reliably on support of the wire 115 against the effect of centrifugal forces by the effect of the vacuum present on the grooved faces of the reversing cylinders 111 or on the perforated mantle of an equivalent suction roll, by means of which effect cross-direction shrinkage of the web W is also prevented.
• suction cylinders 111 particularly favourably the suction cylinders are used which are marketed by the applicant with the trade mark "VAC-ROLL”TM and which have no inside suction box, and with respect to the details of the constructions of said cylinders reference is made to the applicant's FI Patent No. 83,680 (equivalent to US Patents Nos.
• the support contact between the web and the drying wire 115 is also kept adequate on the straight runs between the drying cylinders 110 and the reversing cylinders 111 by, at least on the runs from the drying cylinders 110 to the reversing cylinders 111, employing blow suction boxes, by whose means formation of pressures induced by the wire 115 in the closing wedge-shaped nip spaces between the wire 115 and the cylinder 111 mantles is prevented.
• Blow suction boxes are understood as blow boxes whose blowing of air produces a vacuum, and said boxes do not communicate with sources of vacuum.
• blow boxes are also used in the gaps between the reversing cylinders 111 , by means of which boxes said intermediate spaces are air-conditioned and evaporation from the web is promoted.
• the faces of the drying cylinders 110 can be kept clean by means of doctors.
• broke removal by means of gravity can be applied, for the groups R j ...R N with single-wire draw are open downwards so that, in the event of a web break, the removal of paper broke can be carried out below the dryer groups R ⁇ ...R N that are open downwards, substantially by the effect of gravity, onto the broke conveyor placed underneath.
• a finishing unit D2 which includes, among other things, a surface-treatment or surface-coating device, an after-dryer, a calender, and a machine reel-up, for example a Pope type reel-up.
• the machine reel that is being produced by means of the reel-up 150 is denoted with the reference MR Q , and one complete machine reel is denoted with the reference MR.
• the coating device includes two opposite coating rolls 11 and 12, in connection with each of which there are size feed devices so that the paper web is coated from both sides in the coating nip between the rolls 11 and 12. After this the web W is passed into the after-dryer.
• the web W is passed over the guide roll 13 onto the first drying cylinder 14 in the after-dryer, on which cylinder the top side of the web W is placed against the cylinder face of the drying cylinder 14, and after this there follows a second drying cylinder 15, on which the bottom face of the web is placed against the cylinder face of the drying cylinder 15.
• the web is passed into the inverted dryer group R k with single-wire draw, in which the drying cylinders 20 are placed in the lower row and the reversing rolls or cylinders, preferably rolls 25 that are marketed by the applicant with the trade mark VAC-ROLL and that have no inside suction box, in the upper row.
• the wire 24 that supports the paper web W to be dried enters from below the group R k , guided by the guide rolls 21,22, onto the drying cylinder 20, and after this the wire runs meandering from the drying cylinders 20 onto the reversing roll 25 in the upper row so that on the drying cylinder 20 the web W is placed between the heated cylinder face and the wire 24.
• the web W is passed on the wire 24 of the inverted group onto the drying cylinder 31 in the lower row in the following dryer group R 2 2, with twin-wire draw, in which group the web W runs from the drying cylinder 31 in the lower row onto the drying cylinder 32 in the upper row so that between the rows of cylinders the web has a free draw W, and both the drying cylinders 32 in the upper row and the drying cylinders 31 in the lower row have drying wires 36,35, respectively, of their own as well as wire guide rolls 34,33, respectively, of their own.
• the web W is passed from the last suction roll 25 in the inverted group R k onto a suction cylinder 37 fitted in connection with the upper wire in the group R 22 with twin-wire draw, which suction cylinder 37 is placed substantially at the same level as the lower cylinders 31 in the group R 22 with twin-wire draw.
• the web is passed from the last drying cylinder 20 in the inverted group R k directly onto the first cylinder 32 in the upper row in the group with twin-wire draw.
• the after-dryer is composed of one inverted dryer group R k only.
• a drying cylinder 41 is placed, in connection with which cylinder a calender nip has been formed by means of the roll 44. Below the cylinder 41 there can be a doctor 42.
• the schematic test results illustrated in Figs. 5A...5B are related to a test in which the effects of modes of running of the forward dryer and after dryer on the tendencies of curling of paper were examined.
• the machine that was used in the test comprised a former, a press, a forward dryer section, in which there was, in the beginning, one single-wire group followed by three twin-wire groups, a coating device, and an after-dryer, which consisted of two twin- wire groups.
• the paper grade was copying paper 76 grams per sq.m.
• the three points of comparison in the test were:
• R23 normal running mode of the machine all cylinders in the forward dryer are open; in the after-dryer slightly more heat is supplied to the top face of the paper than to the bottom face,
• Figs. 5 A and 5B The results of one method of curl measurement are illustrated in Figs. 5 A and 5B.
• a number in this case 16
• the curling of said pieces is examined and measured under conditions constructed for the purpose.
• graphs that illustrate the cross-directional curl profile as shown in Figs. 5 A and 5B, can be drawn.
• the profiles of the points R20 and R23 are compared with one another, it cannot be said that there is a difference between them. Between these points, the difference in the running mode is present in the forward dryer section: in R20 the steam supply into the lower cylinders is closed, in R23 open.
• the group R 21 with single-wire draw comprises heated drying cylinders 230 in the upper row and reversing rolls 231 in the lower row.
• the wire of the group with single-wire draw is denoted with the reference numeral 235.
• the wire guide rolls 238 guide the run of the wire 235.
• the group R 22 with twin-wire draw comprises two horizontal rows of steam-heated drying cylinders 230A and 230B, and the web has free draws W 0 on the runs between said rows.
• the group R 22 includes an upper wire 235A, which runs as guided by the guide rolls 238 and by the guide rolls 239 placed in the gaps between the upper cylinders 230A.
• the group R 22 includes a lower wire 235B, which runs as guided by the guide rolls 238 and by the guide rolls 239 placed in the gaps between the lower cylinders 230B.
• air blow boxes 237 are employed in the vicinity of the wire guide rolls 239, at the inlet side of the web W and the drying wire 235A and 235B.
• air jets of appropriate directions and blow velocities are applied into connection with the runs of the drying wire 235A,235B and with the free sectors of the wire guide rolls 239, placed in the vicinity of said blow boxes, by means of which air jets the support contact between the drying wires 235A,235B and the web W is promoted, the formation of detrimental differences in pressure is prevented, and fluttering of the web W on the free draws W 0 is prevented.
• Said blowings can also be applied through the drying wires 235A,235B, by means of which ventilation of the pocket spaces P formed in the gaps between the drying cylinders 230A,230B can be promoted.
• blow-suction boxes 217 On the runs from the drying cylinders 230 onto the reversing cylinders 231 , there are blow-suction boxes 217, by whose means formation of pressures induced by the wire 235 is also prevented in the closing wedge-shaped nip spaces between the wire 235 and the cylinder 231 mantles.
• the blow-suction boxes 217 are understood as blow boxes whose air blowing produces a vacuum, and said boxes 217 do not communicate with sources of vacuum.
• URO RUN BLOW BOX With respect to the details of the constructions of these blow-suction boxes 217, which are marketed by the applicant with the trade mark "UNO RUN BLOW BOX"TM, reference is made to the applicant's FI Patents Nos.
• blow boxes 216 by whose means said intermediate spaces are air-conditioned and evaporation from the web W is promoted.
• each air supply device 237,217,216,222 can be regulated separately, and so also the evacuation efficiency of the moisture removing points 221 can be regulated separately.
• Fig. 6 the arrangement of control of the moisture state of the dryer groups in this after-dryer is illustrated quite schematically, but it can be accomplished by means of principles and devices in themselves known to a person skilled in the art.

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Citations (4)

• 1996
  • 1996-07-31 FI FI963024A patent/FI101487B/fi active
• 1997
  • 1997-07-29 DE DE19781902T patent/DE19781902T1/de not_active Withdrawn
  • 1997-07-29 WO PCT/FI1997/000459 patent/WO1998004777A1/en active Application Filing
  • 1997-07-29 AU AU35446/97A patent/AU3544697A/en not_active Abandoned

Patent Citations (4)

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