EP0418317B1 - Verfahren zur schrumpflosen trocknung einer papierbahn - Google Patents

Verfahren zur schrumpflosen trocknung einer papierbahn Download PDF

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Publication number
EP0418317B1
EP0418317B1 EP89907445A EP89907445A EP0418317B1 EP 0418317 B1 EP0418317 B1 EP 0418317B1 EP 89907445 A EP89907445 A EP 89907445A EP 89907445 A EP89907445 A EP 89907445A EP 0418317 B1 EP0418317 B1 EP 0418317B1
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EP
European Patent Office
Prior art keywords
web
dryer
sheet
felt
cross
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP89907445A
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English (en)
French (fr)
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EP0418317A1 (de
EP0418317B2 (de
Inventor
Borgeir Skaugen
Gregory L. Wedel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Beloit Technologies Inc
Original Assignee
Beloit Corp
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Application filed by Beloit Corp filed Critical Beloit Corp
Publication of EP0418317A1 publication Critical patent/EP0418317A1/de
Publication of EP0418317B1 publication Critical patent/EP0418317B1/de
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Publication of EP0418317B2 publication Critical patent/EP0418317B2/de
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    • 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
    • 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
    • D21F5/042—Drying on cylinders on two or more drying cylinders in combination with suction or blowing devices
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
    • D21G9/00—Other accessories for paper-making machines
    • D21G9/0063—Devices for threading a web tail through a paper-making machine

Definitions

  • the present invention relates to a process for the restrained drying of a paper web extending successively through a wet end and a dry end of a dryer section of a papermaking machine, said process comprising the steps defined in the preamble of the claim.
  • the afore-mentioned article indicates that a high vacuum of 1 kPa is produced by the vacuum transfer roll to hold the web to the fabric around the roll, thereby restraining the web against cross-machine directional shrinkage.
  • a single-tier dryer section of the kind disclosed in the afore-mentioned article has been used at the wet end of the dryer section.
  • the afore-mentioned article suggests to extend the single-tier concept through the entire dryer section.
  • the shrinkage of the sheet is very low as it is dried from 40 to 60 percent dry. Once the sheet reaches 60 percent dry, the shrinkage increases and continues at a high rate until the sheet is essentially dry.
  • US-A-3868780 discloses a dryer section in which there are long felt draws between adjacent guide rolls so that cross-machine directional shrinkage is permitted.
  • the guide rolls may have a perforated shell so as to permit them to operate as traverse flow dryers when a vacuum is generated within the loop of the felt which is guided alternately around drying cylinders and guide rolls. Since the felt has long spans uncovered by the web, air will be drawn through such uncovered felt spans, thereby reducing the level of the vacuum acting on the web significantly. As a result the vacuum is inadequate to inhibit cross-machine directional shrinkage both at the wet end and the dry end of the dryer section.
  • An object of the present invention is to restrain the web positively against cross-machine directional shrinkage during drying of the web in the dry end of the dryer section.
  • the object of the invention is achieved by applying a vacuum level of 1.49 to 1.99 kPa (6 to 8 inches WC) in the vacuum roll so that cross-machine directional shrinkage of the web during drying of the web in the dry end of the dryer section is inhibited.
  • An advantage of the invention is that cross-machine direction shrinkage is not only inhibited during passage of the web around the dryer but also around the vacuum guide roll. Furthermore, the vacuum guide roll being of a diameter considerably less than that of the dryer results in a joint run of the web and felt between the dryers and the guide rolls which is minimal so that the web is restrained against cross-machine direction shrinkage throughout most of the passage through the dryer section.
  • the aforementioned sheet restraint reduces edge curl and cockle and the graininess of the resultant sheet at the edges thereof. Furthermore, by the provision of such sheet restraint, the slice opening in the headbox is able to be more uniform and the cross direction fiber orientation profile is improved.
  • nonuniform cross directional sheet shrinkage which occurs during conventional drying processes.
  • the aforementioned nonuniform shrinkage is responsible for nonuniformities in headbox slice profiles, in fiber orientation, and in the sheet elongation and tensile energy absorption.
  • TEA Tensile energy absorption hereinafter referred to as TEA is defined in "The Dictionary of Paper” Fourth Edition, published 1980, as the energy absorbed when a paper specimen is stressed to rupture under tension. It is expressed in energy units per unit area eg kg-cm/cm 2. It is useful in evaluating packaging materials subject to rough handling.
  • the continuous drying restraint has a direct effect on the finished sheet properties by controlling the cross-directional elongation and TEA profiles. Additionally, such reduced shrinkage reduces the cockles and graininess of the sheet edges.
  • graininess is defined in the afore- mentioned dictionary as small variations in the surface appearance of a paper or board, resulting from any of a variety of causes, such as impressions of wires or felts, irregular distribution of color, and uneven shrinkage in drying.
  • the opening of the slice lip of the headbox may be maintained more uniform and an improved cross direction fiber orientation profile is obtained as stated more particularly hereinafter.
  • the process according to the invention provides a transfer of the web between dryers with positive support and restraining the sheet with fabric pressure and roll vacuum.
  • the combination of the aforementioned arrangement has improved sheet threading, machine runability, and sheet properties.
  • the wet paper is dried by intermittent contact with cast-iron, steam heated dryers.
  • the thermal contact between the paper and the dryer is maintained by tensioned dryer fabrics which apply a pressure to the paper as it wraps the dryer.
  • the aforementioned fabric pressure not only improves the drying contact, but also applies a restraint to the paper to prevent shrinkage from occurring. Such restraint, however, is repeatedly released as the sheet passes through the open draws between conventional dryer cylinders as described hereinbefore.
  • the fabric pressure continues to provide some restraint in the machine direction by maintaining a machine direction draw, but in the cross-machine direction, the paper is virtually unrestrained.
  • the paper shrinks freely in the cross direction particularly at the edges and somewhat less so near the center of the web where the sheet is at least partly restrained by the outer portions.
  • nonuniform cross-machine shrinkage gives rise to nonuniform cross-directional sheet properties such as stretch, TEA and tensile.
  • Stretch is defined in the aforementioned dictionary as "the elongation corresponding to the point of rupture in a tensile strength measurement; it is usually expressed as a percentage of the original length.”
  • the high cross-directional edge shrinkage also aggravates the susceptibility of the sheet to edge cockle, curl and graininess.
  • Hygroexpansivity is defined in "The Dictionary of Paper” as "the change in dimension of paper that results from a change in the ambient relative humidity; it is commonly expressed as a percentage and is usually several times higher for the cross direction than for the machine direction. This property is of great importance in applications where the dimensions of paper sheets and cards or construction board (wallboard, acoustical tile, etc.) are critical.”
  • the first phase of such study was directed at quantifying the nonuniformity on commercial paper machines and then determining the effect that the nonuniform shrinkage has on the machine operation and on the finished sheet properties.
  • the cross-directional sheet shrinkage was determined by metering fine drops of ink onto the stock as it discharged from the slice lip of the headbox. The distance between marks at the wet end were then compared to the distances at the dry end to determine the cross-directional shrinkage profile.
  • Tensile strength is defined in the aforementioned dictionary as "the maximum tensile stress developed in a specimen before rupture under prescribed conditions; it is usually expressed as force per unit width of the specimen.”
  • the machine direction tensile was fairly uniform, again being affected in part by the machine direction draw which does not vary in the cross direction.
  • the cross direction tensile profile is nonuniform and exhibits a slight hyperbolic configuration. The lowest tensile occurs near the sheet edges, again where the cross-direction shrinkage was the greatest.
  • the tensile ratio is the ratio of the tensile in the cross direction to the tensile in the machine direction and will be discussed in detail hereinafter.
  • the TEA profiles were also measured for the sample.
  • the cross-direction profile reflected the nonuniformity in cross-direction stretch.
  • the TEA profile does not exhibit quite as much variation as the cross-direction stretch, because the loss in stretch near the machine center is greatly offset by the increase in tensile strength.
  • the increased shrinkage which occurs near the edges also has an adverse effect on headbox performance.
  • the slice opening In order to produce a level basis weight profile at the reel, the slice opening must be closed down near the edges. Such closing down near the edges of the slice opening reduces the basis weight at the edges to compensate for the higher shrinkage which occurs near the edges. Such reduction in basis weight causes the paper to go through the press section and earlier dryer sections with light edges which eventually heavy up as the edges shrink.
  • Basis weight is defined in the aforementioned dictionary as "the weight in pounds of a ream cut to a specified basis size. The number of sheets in a ream is usually 500.”
  • the aforementioned nonuniform slice opening is known to cause a distortion of the fiber orientation by inducing cross flows.
  • the fiber orientation was determined for the aforementioned sample by measuring the sonic modulus profile as discussed hereinafter.
  • the fiber orientation is indicated as the angle of the primary axis of the modulus envelope from the machine direction. A positive angle indicates the fibers are oriented towards the back side of the web and a negative angle indicates the fibers are oriented towards the front side.
  • the fibers are all oriented towards machine center line as would be expected because the slice opening is closed down near the edges to compensate for edge shrinkage.
  • a vacuum level of 1.49 to 1.99 kPa (6 to 8 inches water column) in the vacuum rolls is essentially equal to the restraint which is applied by the dryer fabric. Such vacuum level is also the level which is required for positive sheet restraint.
  • FIG. 1 is a side-elevational view of a typical double-felted dryer section generally designated 10 including dryers 11 and 12 of an upper tier generally designated 13.
  • the dryer section 10 also includes lower dryers 14 and 15 of a lower tier generally designated 16.
  • the web W extends in sinusoidal configuration past dryers 14, 11, 15 and 12 respectively so that alternate sides of the web are dried as they come into contact with the respective external surfaces 17, 18, 19 and 20 of dryers 14, 11, 15 and 12.
  • An upper felt 21 extends around a guide roll 22 and then around dryer 11. The upper felt 21 then extends around a further guide 23 and the upper dryer 12.
  • a lower felt 24 after extending around dryer 14 extends around a lower guide roll 25 and dryer 15 and then around a further lower guide roll 26.
  • Figure 2 is a graph showing the results for a fine paper machine wherein the shrinkage was found to be highly nonuniform with the graph being almost parabolic. As expected, the highest shrinkage was found to occur at the edges where the sheet has the least cross-directional restraint and the sheet shrinkage was the lowest near the center where the paper was at least partly restrained by the outer portion.
  • the x axis includes readings taken from the front edge to the back edge of the sample web and the amount of shrinkage is shown as a percentage of the initial width.
  • Figure 3 is a graph showing a cross-directional paper sample tested in the laboratory to determine the variations in sheet properties. As shown in figure 3, the machine direction and cross-machine direction sheet strength profiles are demonstrated. The machine direction stretch is very uniform in the cross direction because it is controlled by the machine direction draws. However, the cross-machine direction stretch is very nonuniform as shown by the graph. From a comparison of the graph 28 with the graph 29 of the machine direction, it appears there is a direct reflection of the cross-direction shrinkage, that is the highest stretch occurs at the edges where the sheet has experienced the greatest shrinkage.
  • the graph shown in figure 4 includes a graph of the sheet tensile strength profiles for the cross-machine direction 30 and the graph for the machine direction 31.
  • the machine direction tensile as shown in figure 4 is fairly uniform again being affected in part by the machine direction draw which does not vary in the cross-direction.
  • the cross-direction tensile profile is nonuniform. It exhibits a slight "frown" or hyperbolic shape. The lowest tensile occurs near the sheet edges again where the cross-machine direction shrinkage was the greatest.
  • Figure 6 shows two graphs 33 and 34.
  • Graph 33 demonstrates the sheet TEA profile in a machine direction where graph 34 shows the sheet TEA profile for the cross-machine direction.
  • the TEA profiles also measured for the same sample.
  • the cross-machine direction profile shown in figure 6 reflects the nonuniformity in the cross-machine direction stretch.
  • the TEA profile does not exhibit quite as much variation as the cross-machine direction stretch because the loss in stretch near the machine center is partly offset by the increase in the tensile strength.
  • Figure 7 is a graph 35 showing the dry weight of a sample sheet from the front to the back edge thereof.
  • Figure 8 is a graph showing the slice profile required in order to obtain the result shown in figure 7. As shown in figure 8 the slice openings are reduced at the respective edges in order to obtain a relatively uniform resultant web after shrinkage.
  • the fiber orientation was determined for the sample by measuring the sonic modulus profile.
  • the profile is shown in figure 9 which is a graph from the front to the back of the sheet.
  • the graph indicates actual readings whereas the graph 36 shows the average orientation.
  • the fiber orientation is indicated as the angle of the primary axis of the modulus envelope from the machine direction. A positive angle indicates that the fibers are oriented towards the back side, and a negative angle indicates that the fibers are oriented towards the front side.
  • the fibers were all oriented towards the machine center line, as expected, because the slice opening was closed down near the edges to compensate for edge shrinkage.
  • the samples were manufactured on pilot two-wire machines at commercial speeds. These sheets were then freely dried on a dryer fabric which was supported by a vacuum box. Separate sheets were dried with different levels of vacuum in the box to provide different levels of sheet shrinkage restraint.
  • figure 10 shows the effect of sheet vacuum restraint on sheet shrinkage for machine directions as shown by graph 37 and for cross-machine direction as shown by graph 38.
  • a common commercial arrangement for eliminating open draws is the single felt or serpentine dryer section shown in figure 14.
  • dryers 100, 101 and 102 constitute a upper tier generally designated 103 whereas dryers 104 and 105 constitute a lower tier 106.
  • a joint run of the web WA and felt F extends in serpentine configuration respectively around the dryers 100, 104, 101, 105 and 102.
  • blow boxes 107 and 108 draw the web towards the felt during transit of the web between dryers, such vacuum is insufficient to cause any appreciable restraint of the web.
  • this arrangement does eliminate the open draws, it does not replace the open draws with positive restraint and it dries the sheet from one side only.
  • FIG 15 shows the TOTAL BEL RUN@ arrangement disclosed in EP-A-0345266 and EP-A-0345921 including dryers 200, 201 and 202 arranged as a single tier generally designated 203. Interposed between the dryers 200 and 201 is a vacuum guide roll 204. Furthermore, another guide roll 205 is disposed between the dryers 201 and 202. In this design the bottom ineffective dryers of the serpentine section shown in figure 14 have been eliminated and replaced with vacuum rolls 204 and 205. Two-sided drying is maintained in this arrangement by alternating between top-felted and bottom-felted single tier sections as shown in EP-A-0345266 and EP-A-0345921.
  • the intermediate vacuum rolls 204 and 205 of the aforementioned single tier section 203 act much like the fabric vacuum box used in the afore- mentioned laboratory studies. This vacuum maintains the restraint which is applied by the dryer fabric pressure as the sheet is transferred between dryers.
  • the vacuum which is induced by conventional serpentine blow boxes is typically only 24.9 to 49.81 Pa (0.1 to 0.2 inches water column) and is clearly inadequate to provide significant shrinkage restraint as shown from figure 9. Additionally, this low level vacuum does not extend around the entire bottom dryer. With the long sheet length between top dryers, the sheet is left unrestrained for a significant portion of the drying cycle in the conventional serpentine dryer section.
  • a vacuum level of 1.49 to 1.99 kPa (6 to 8 inches WC) in the vacuum rolls is essentially equal to the restraint which is applied to the dried fabric. It is also the vacuum level which is required for positive sheet restraint as indicated in figure 9.
  • the single tier dryer section should be applied near the dry end of the machine.
  • the single tier dryer section configuration should be applied to the entire dryer section.
  • a sheet which is dried under a restraint is significantly different from one which is dried freely.
  • FIG. 17 shows the effect of restraint on hygroexpansivity, the upper graphs 400, 401 and 402 representing freely dried sheets and the graphs 403, 404 and 405 representing sheets dried under restraint.
  • the photomicrographs shown in figures 18 and 19 compare the fiber surface characteristics of a sheet taken from the center of the machine that is under partial cross-machine direction restraint to a sheet taken from the edges with unrestrained cross-machine direction. These micrographs show the same reduction in fiber kinks and caliper as seen in laboratory dried samples.
  • the cross-directional sheet shrinkage which occurs during the drying process is highly nonuniform.
  • This nonuniform shrinkage directly affects the cross-machine direction stretch, tensile, modulus and TEA profiles.
  • the greatest shrinkage occurs near the edges.
  • the headbox slice opening In order to achieve a level basis weight profile at the reel, the headbox slice opening must be reduced near the edges to recompensate for the edge shrinkage.
  • the nonuniform shrinkage thereby indirectly affects fiber orientation and a single tier dryer section with intermediate vacuum rolls can be used to control the cross-machine direction shrinkage. Vacuum levels in the intermediate rolls or guide rolls in the range 1.49 to 1.99 kPa (6 to 8 inches WC) will continue the restraint applied by the dryer fabric pressure and substantially reduce the edge shrinkage.

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  • Paper (AREA)
  • Drying Of Solid Materials (AREA)

Claims (1)

1. Verfahren zum schrumpfbehinderten Trocknen einer Papierbahn, die sich der Reihe nach durch ein nasses Ende und ein trockenes Ende einer Trockenpartie einer Papiermaschine erstreckt, wobei das Verfahren die folgenden Schritte aufweist:
Bewegen der Papierbahn und eines Trockenfilzes in Anlage miteinander derart, daß die Bahn und der Filz einen Abschnitt einer erhitzten Oberfläche eines drehbaren Trockenzylinders derart umschlingen, daß die Bahn zwischen dem Filz und der erhitzten Oberfläche angeordnet ist;
danach Führen der Bahn und des Filzes in Anlage miteinander um eine stromabwärts bezüglich des Trockenzylinders angeordnete Saugleitwalze herum, derart, daß die Bahn von dem Filz während des Laufs der Bahn zwischen dem Trockenzylinder und der Leitwalze gestützt wird, wobei die Anordnung so ist, daß der Filz zwischen der Bahn und der Leitwalze angeordnet ist, wenn die Bahn und der Filz einen Abschnitt der Oberfläche der Leitwalze umschlingen;
Verbinden der Leitwalze mit einer Unterdruckquelle derart, daß ein Unterdruck an der Bahn durch den Filz hindurch angelegt wird, wenn die Bahn und der Filz die Leitwalze umschlingen, derart, daß die Bahn in engem Formschluß an den Filz gezogen wird, wenn die Bahn und der Filz die Leitwalze umschlingen; und
Leiten der Bahn und des Filzes in Anlage miteinander um eine stromabwärts bezüglich der Leitwalze angeordneten weiteren Trockenzylinder herum, wobei der Trockenzylinder und der weitere Trockenzylinder ein Teil einer einreihigen Trockenpartie zum Trocknen der Bahn während der Bewegung der Bahn stromabwärts in bezug auf das nasse Ende der Trokkenpartie ist;
dadurch gekennzeichnet, daß
ein Unterdruckniveau von 1,49 bis 1,99 kPa (6 bis 8 Zoll Wassersäule) in der Saugleitwalze angelegt wird, so daß eine Schrumpfung der Bahn in Querrichtung der Maschine während des Trocknens der Bahn im trockenen Ende der Trockenpartie unterbunden ist.
EP89907445A 1988-06-02 1989-05-23 Verfahren zur schrumpflosen trocknung einer papierbahn Expired - Lifetime EP0418317B2 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US20170588A 1988-06-02 1988-06-02
US201705 1988-06-02
PCT/US1989/002230 WO1989012138A1 (en) 1987-02-13 1989-05-23 A process for the restrained drying of a paper web

Publications (3)

Publication Number Publication Date
EP0418317A1 EP0418317A1 (de) 1991-03-27
EP0418317B1 true EP0418317B1 (de) 1994-03-09
EP0418317B2 EP0418317B2 (de) 1999-05-19

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ID=22746955

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89907445A Expired - Lifetime EP0418317B2 (de) 1988-06-02 1989-05-23 Verfahren zur schrumpflosen trocknung einer papierbahn

Country Status (10)

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EP (1) EP0418317B2 (de)
JP (1) JP2639736B2 (de)
CN (1) CN1019406B (de)
AU (1) AU639414B2 (de)
BR (1) BR8907449A (de)
CA (1) CA1335473C (de)
DE (2) DE418317T1 (de)
ES (1) ES2015693A6 (de)
FI (1) FI107548B (de)
WO (1) WO1989012138A1 (de)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE9301512L (sv) * 1993-05-03 1994-11-04 Fibertech Ab Sätt och torkvira vid papperstorkning
DE19506778A1 (de) * 1995-02-27 1996-08-29 Bhs Corr Masch & Anlagenbau Verfahren zum Herstellen von Wellpappe
CN112609504A (zh) * 2020-12-10 2021-04-06 上海东升新材料有限公司 一种评估低氯湿强剂在生活纸中应用效果的纸样制作方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2537129A (en) * 1945-10-05 1951-01-09 Beloit Iron Works Structure for web transfers
FI53333C (fi) * 1972-11-13 1978-04-10 Valmet Oy Torkningscylindergrupp i en flercylindertork foer en materialbana i synnerhet foer papper
US4359827B1 (en) * 1979-11-05 1994-03-29 Keith V Thomas High speed paper drying

Also Published As

Publication number Publication date
CN1039460A (zh) 1990-02-07
EP0418317A1 (de) 1991-03-27
DE68913738T2 (de) 1994-09-08
FI905932A0 (fi) 1990-11-30
DE418317T1 (de) 1992-01-16
JP2639736B2 (ja) 1997-08-13
DE68913738T3 (de) 1999-09-16
WO1989012138A1 (en) 1989-12-14
CN1019406B (zh) 1992-12-09
AU639414B2 (en) 1993-07-29
FI107548B (fi) 2001-08-31
EP0418317B2 (de) 1999-05-19
AU3773389A (en) 1990-01-05
JPH03501395A (ja) 1991-03-28
BR8907449A (pt) 1991-04-30
DE68913738D1 (de) 1994-04-14
ES2015693A6 (es) 1990-09-01
CA1335473C (en) 1995-05-09

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