EP1118707A1 - Vorrichtung und Verfahren zum Schutz eines Stützgewebes - Google Patents

Vorrichtung und Verfahren zum Schutz eines Stützgewebes Download PDF

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Publication number
EP1118707A1
EP1118707A1 EP00300524A EP00300524A EP1118707A1 EP 1118707 A1 EP1118707 A1 EP 1118707A1 EP 00300524 A EP00300524 A EP 00300524A EP 00300524 A EP00300524 A EP 00300524A EP 1118707 A1 EP1118707 A1 EP 1118707A1
Authority
EP
European Patent Office
Prior art keywords
fabric
cooling liquid
dryer
edges
carrying
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.)
Ceased
Application number
EP00300524A
Other languages
English (en)
French (fr)
Inventor
Richard A. Parker
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.)
Valmet Inc
Original Assignee
Valmet Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Valmet Inc filed Critical Valmet Inc
Publication of EP1118707A1 publication Critical patent/EP1118707A1/de
Ceased legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
    • F26B13/10—Arrangements for feeding, heating or supporting materials; Controlling movement, tension or position of materials
    • F26B13/14—Rollers, drums, cylinders; Arrangement of drives, supports, bearings, cleaning
    • F26B13/16—Rollers, drums, cylinders; Arrangement of drives, supports, bearings, cleaning perforated in combination with hot air blowing or suction devices, e.g. sieve drum dryers
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F1/00—Wet end of machines for making continuous webs of paper
    • D21F1/30—Protecting wire-cloths from mechanical damage
    • 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
    • D21F5/18—Drying webs by hot air
    • D21F5/182—Drying webs by hot air through perforated cylinders
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
    • F26B13/007—Treating a particular portion of the web or plate, e.g. the edge

Definitions

  • This invention relates to a device and method for extending the useful life of a carrying fabric in web processing as, for example, in the manufacture of paper and textiles. More specifically, this invention extends the life of a carrying fabric by applying a cooling liquid to those edges of the fabric which are uncovered by the web and which remain exposed to high operating temperatures during the drying operation.
  • drying means for example, dryers of the flat-bed type; a drying system in which a series of small diameter rolls is used to convey the product through a drying hood.
  • the products produced by this invention are widely used in home and industry and include, for example, kitchen towels, bathroom tissue and facial tissue.
  • This invention also has application in the treatment of nonwoven fabrics, that is, fabrics composed of fibers which are in random array. Included in this category are fibers obtained from any type of loose fibrous web, batt or sheet. Moreover, the fibers may be straight or crimped and may include fiber blends. Also included are combinations of textile fibers as for example, polyester, polypropylene, rayon, nylon and the like and papermaking fibers as, for example, wood pulp or cotton linters and the like.
  • carrier fabric as used herein is intended to include wires, screens, belts, and other web supporting means, typically made from plastics such as polyesters.
  • Carrying fabrics are often used in the dryer sections of paper machines or other web processes where the web is wet and lacks strength and must be supported.
  • a carrying fabric is expensive not only in capital cost but also in the downtime which results when the machine must be serviced and the fabric replaced.
  • heat-generating means is used to heat and dry the web as it passes over a roll.
  • air is drawn through the web (e.g., paper) as the result of a pressure differential across the web surface and moisture is removed by convective heat and mass transfer between the web and the air.
  • the roll in this system includes a cylindrical wall which is air permeable and which serves as a support for the carrying fabric.
  • the carrying fabric in turn, carries and supports the web. Two nip rolls hold the carrying fabric and determine the extent to which the web wraps around the roll.
  • the heated air for drying the web may flow from outside the cylinder to the inside as, for example, by passing the web under a heating hood or, alternatively, it may flow from inside the cylinder to the outside. In either case, the effect on the carrying fabric is the same because the heated air drawn through the roll exposes the edge of the carrying fabric to the degrading effects of unremittingly high operating temperatures.
  • the drying time for the web depends upon the desired degree of drying, the speed of the line, the amount of heat applied and the volume of air which is drawn through the fabric. Since it is more energy efficient and cost effective to heat air than move it, it is preferable to increase the operating temperature of the dryer and minimize air volume. Moreover, as the line speed increases, so does the need to remove water. Therefore, it is desirable to operate dyers at higher temperatures as the line speed increases.
  • hot air is supplied at temperatures in the range of from about 350-520°F; however, when this heated air passes through the wet web, it picks up moisture and the temperature is greatly reduced.
  • the air which passes through the web-covered fabric is in the range of about 190-250°F, whereas, the temperature of the air which passes through those fabric areas not covered by the web is usually within the 350-520°F range. Accordingly, those areas of the carrying fabric which are not covered by the web receive the impact of high heat and suffer its degrading effect. On the other hand, those areas of the carrying fabric which are web-covered are protected because the moisture in the web exerts a cooling effect which is transmitted to the fabric's interior.
  • Another method provides for the application of suction means to the edge of the roll so that ambient air can be drawn in from the side between the hood and roll. As the ambient air passes through the fabric, it cools the edge.
  • Still another method prevents suction from being drawn over the edge of the roll by placing a sleeve under the exposed edge of the fabric.
  • the reasoning is that, since the hot air which emanates from the hood is prevented from passing through the roll, it cannot pass through the carrying fabric. The convective heat transfer between the air and fabric is therefore less than it would be if the air were allowed to pass through the fabric. Consequently, the rate of rise of fabric temperature is less when this method is employed.
  • Another method for preserving the carrying fabric is simply to reduce the operating temperature of the dryer.
  • the use of ambient air to shield or cool the exposed edge of a fabric has limited value because air has a limited capacity to absorb heat.
  • the alternative is to reduce the temperature at which the dryer may operate; however, the result is a reduction in line speed.
  • This invention provides an apparatus and method for extending the useful life of carrying fabric in a dryer by maintaining the fabric edge at temperatures that minimize the effects of thermal degradation. This is achieved by applying a cooling liquid to the edge of the carrying fabric.
  • cooling liquids may be employed; however, the object of this invention is to cool by evaporation and, therefore, it is desirable to employ liquids which possess a relatively high latent heat value.
  • Latent heat is the quantity of energy absorbed or given off when a substance undergoes a change of state as, for example, from a liquid to a gas.
  • Water has an unusually high latent heat value (540 cal/g) and, therefore, it is particularly suitable as a cooling liquid because it can absorb appreciable amounts of heat and thus reduce the temperature of the fabric edge to moderate levels.
  • Organic liquids such as alcohols and the like also have a desirable latent heat levels but aqueous solutions comprised principally of water are preferred.
  • liquid i.e., water
  • the tendency is for both fabric and water to reach an equilibrium by arriving at a common temperature. Since the water which is applied has a temperature which is appreciably less than that of the fabric, it will draw heat energy from the fabric and continue to do so until it reaches evaporation temperature (212°F at sea level). Moreover, the water will remain at evaporation temperature until there has been a transfer of energy sufficient to convert the liquid water to its gaseous state.
  • the water which is applied to the fabric edge protects in two ways, first by absorbing heat energy at a rate which increases the water temperature to 212°F (evaporation temperature) and, secondly, by absorbing the additional energy needed to convert it from a liquid to a gas.
  • the object of this invention is to cool by evaporation, it is important that water be applied to the fabric edge in a manner which will ensure a thorough wetting of the fabric surface. This can be achieved by spray means or by the use of rolls and the like; however, spraying is preferred.
  • the liquid is applied by means of a nozzle which is positioned at the edge of the carrying fabric proximate to the dryer in such manner that the nozzle sprays the liquid onto the terminal end segment or fabric edge.
  • the liquid may be applied by utilizing a multiplicity of nozzles.
  • the cooling step may be applied prior to the dryer to ensure that the carrying fabric enters the dryer in a sufficiently wet condition.
  • This invention relates to a device and method for extending the useful life of a carrying fabric in a dryer by maintaining the edges of the carrying fabric at temperatures that serve to minimize thermal degradation. Functionally, this is achieved by applying a cooling liquid to the fabric edge.
  • This device has particular application in the dryer sections of a paper machine where high operating temperatures are typically encountered; however, it should be understood that this invention may also be employed in any system where a process web or film leaves a portion of the carrying fabric exposed to high temperatures.
  • the means by which the cooling liquid is brought into contact with the carrying fabric may be any device known in the art for applying either liquid or vapor to a moving surface.
  • this contact or application means comprises at least one nozzle positioned proximate to the dryer such that the nozzle sprays the liquid onto the edge of the fabric as it passes by.
  • FIGS 1 and 2 show a dryer for drying a web 4 and a carrying fabric 6 beneath the hood 3 .
  • the web and carrying fabric are supported by a roll 1 having a cylindrical outer wall 5 which is air permeable so that heated air 8 from the hood 3 may pass through the web 4 , through the carrying fabric and then through the cylinder wall 5 .
  • the hood 3 covers only a portion of the roll 1 so that, as a practical matter, the heated air 8 comes into drying contact only with those areas of the web and carrying fabric which are supported by the roll 1 .
  • Two nip rolls 10 and 11 hold the web and carrying fabric and determine the extent to which they are fed onto the roll. Once they are within the dryer, the heated air from the hood passes through the web 4 , through the carrying fabric 6 and through cylinder wall 5 before exiting via ducts in the sidewalls 7 . In known systems, this drying step exerts a degrading effect on those portions of the carrying fabric which are not covered by the web. Over a period of time, their exposure to high heat weakens the fabric fibers and causes it to degrade.
  • the present invention solves this problem by contacting the exposed portions of the fabric with a liquid (i.e., coolant) which has the ability to draw heat away from the carrying fabric and into the liquid. Moreover, the nature of the coolant is such that this heat transfer continues until the liquid absorbs whatever degree of latent heat is needed to convert it into a gas (i.e., vapor).
  • a liquid i.e., coolant
  • this liquid contacting step is achieved by mounting within the drying hood a multiplicity of nozzles 31 which are positioned proximate to the exposed edge of the fabric and along the perimeter of the roll as shown in Figure 2. As roll 1 and the carrying fabric 6 move into the hood, the nozzles 31 spray the liquid 34 onto the exposed edges 2 of the fabric and the spraying is continued at the frequencies needed to avoid thermal degradation.
  • the liquid 34 is supplied to the spray nozzles by the supply conduit shown as piping 33 in Figure 1.
  • Figure 3 shows an alternate type of conduit comprised of a pipe 51 which traverses the web 4 so as to provide nozzles on either side of web 4 .
  • a typical nozzle is shown in Figures 1, 2 and 3; however, it should be understood that other means may also be used to bring the cooling liquid into contact with the fabric.
  • Other typical means include, for example, a spout or a faucet that drips, pours or otherwise applies a stream of liquid onto the fabric edge as it passes through the dryer.
  • the application of liquid may also be achieved by bringing the application means and the fabric edge into intimate contact as, for example, by the use of an applicator roll which rolls the cooling liquid directly onto the carrying fabric.
  • Still another embodiment provides for positioning at least one nozzle prior to the dryer and proximate to each exposed edge of the carrying fabric. As the liquid is emitted, it comes into contact with the fabric and ensures that the fabric and fabric edges will enter the dryer in the wet state.
  • This invention cools the exposed edge of the carrying fabric and minimizes thermal degradation by exploiting the heat capacity of the cooling liquid.
  • the liquid absorbs heat and minimizes temperature increases on the fabric edge.
  • the ideal cooling liquid is one having a relatively high latent heat capacity, that is, the liquid should have the ability to absorb heat without significantly increasing the temperature of the coolant.
  • Typical of such liquids are, for example, those which exhibit a high latent heat of vaporization and, thus, have the ability to change from a liquid to a vapor with little or no change in temperature. Water is preferred, but it will be obvious to the artisan that other liquids such as aqueous mixtures of alcohols and the like may also be employed.
  • the contacting of the fabric with the liquid may result in an incidental 'wetting' of the web's edge; however, it should be noted that this does not impact negatively on the quality of the resulting product because the edge of the web 41 can be trimmed in a finishing step.
  • water in vapor form i.e., steam
  • steam has a significantly higher heat capacity than air and, therefore, it can be relied upon to remove more heat from the system without any comparable increase in temperature of its own.
  • the steam employed is saturated steam employed at low temperature and low pressure.

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Drying Of Solid Materials (AREA)
EP00300524A 1999-12-14 2000-01-25 Vorrichtung und Verfahren zum Schutz eines Stützgewebes Ceased EP1118707A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US4659799P 1999-12-14 1999-12-14
US46597P 1999-12-14

Publications (1)

Publication Number Publication Date
EP1118707A1 true EP1118707A1 (de) 2001-07-25

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Family Applications (1)

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EP00300524A Ceased EP1118707A1 (de) 1999-12-14 2000-01-25 Vorrichtung und Verfahren zum Schutz eines Stützgewebes

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2063206A2 (de) * 2007-11-22 2009-05-27 Herbert Olbrich GmbH & Co. KG Vorrichtung zum Behandeln einer Substratbahn
CN102808348A (zh) * 2012-08-21 2012-12-05 金红叶纸业集团有限公司 烘缸装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3849904A (en) * 1973-04-04 1974-11-26 Aer Corp Horizontal flat bed through drying system
US4484981A (en) * 1982-07-26 1984-11-27 Feldmuhle Aktiengesellschaft Papermaking dewatering apparatus having wire support means with cooling water feed means
US5588223A (en) * 1994-06-14 1996-12-31 Asea Brown Boveri Inc. Restrained paper dryer

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3849904A (en) * 1973-04-04 1974-11-26 Aer Corp Horizontal flat bed through drying system
US4484981A (en) * 1982-07-26 1984-11-27 Feldmuhle Aktiengesellschaft Papermaking dewatering apparatus having wire support means with cooling water feed means
US5588223A (en) * 1994-06-14 1996-12-31 Asea Brown Boveri Inc. Restrained paper dryer

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2063206A2 (de) * 2007-11-22 2009-05-27 Herbert Olbrich GmbH & Co. KG Vorrichtung zum Behandeln einer Substratbahn
EP2063206A3 (de) * 2007-11-22 2014-04-02 OLBRICH GmbH Vorrichtung zum Behandeln einer Substratbahn
CN102808348A (zh) * 2012-08-21 2012-12-05 金红叶纸业集团有限公司 烘缸装置

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