Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
  • D21G1/0073—Accessories for calenders

Definitions

• the present invention relates to a calender according to the preamble of claim 1
• a calender of this kind comprises at least two rolls arranged in nip contact, between which the web being calendered is arranged to travel, and at least one belt arranged to travel outside the edge of the web between the nip formed by the rolls, to prevent the rolls from touching each other.
• the invention also relates to a method for calendering a paper or board web.
• the surface of a paper or board web is smoothed and glazed in a calender.
• the web travels through calender nips formed by rolls set on top of each other.
• Some of the rolls are heatable, hard-surfaced thermo rolls, which can be heated by, for example, water, steam, oil, or induction.
• Some of the other rolls are soft-surfaced rolls, with surfacing made generally of polymers, for example, thermoplastic or thermoset plastic.
• rolls covered with surfacings made from natural fibres raw material were more common than rolls surfaced with polymers.
• thermo roll can even exceed 300°C.
• a soft-surfaced roll can be damaged at a temperature as low as 120°C.
• the web being calendered prevents the rolls from touching each other and thus protects the soft-surfaced roll from overheating.
• the web conducts the heat from the thermo roll away from the nip.
• the web being calendered is generally narrower than the covers of the rolls forming the nip, so that the rolls may touch each other in places that are not covered by the web being calendered. A soft- surfaced roll can then overheat and be damaged.
• the overheating problem referred to above usually appears in all types of calenders that have a nip formed by a thermo roll heated to a high temperature and a soft-surfaced roll.
• a thermo roll heated to a high temperature
• a soft-surfaced roll there is a great danger that the high temperature may damage the belt.
• the surface of the belt is usually rubber or polymer, which will not withstand the surface temperatures of a thermo roll.
• the belt can easily come in contact with the thermo roll, for example, if the width of the web varies or the web vibrates, when the shoe regulating the nip load, or some other member will press the parts of the belt outside the edges of the web onto the thermo roll.
• the edge parts of soft-surfaced rolls can be cooled by compressed air.
• the power requirement of the compressor may be several hundreds of kilowatts.
• the blast of air does not prevent the thermo roll and the polymer roll from touching each other.
• Patent publication EP 792 966 discloses a calender, in which the rolls forming the nip are prevented from touching each other by means of belts running through the nip.
• the belts cover the areas outside the web being calendered, so that the hot thermo roll and the soft-surfaced roll cannot touch each other. If the width of the web being calendered varies, the web and the belt may go on top of each other, or else a large gap, which the belt does not cover, may remain between the web and the belt.
• the calender must then be stopped and the nip through which the belts run, must be opened to allow the belts to be moved to the desired distance from the edges of the web. Stopping the calender to change the position of the belts increases the number of production breaks and reduces the calendering capacity.
• the invention is intended to eliminate the defects of the state of the art disclosed above and for this purpose create an entirely new type of calender and a calendering method, in which the distance from the edge of the web being calendered to the belt running outside the edge of the web and protecting the soft- surfaced roll can be altered while the calender is running.
• the invention is based on using a guide device at the end of the roll to change the distance of the belt from the edge of the web while the calender is running, one embodiment of which device includes a belt guide, in which the belt is set to run at least more or less horizontally between continuations of the centrelines of the rolls forming the nip.
• the belt guide is attached to a carrier secured to the frame of the guide device. By moving the carrier in the direction of the width of the web being calendered, the distance of the belt from the edge of the web can altered even while the calender is running.
• the distance between the edge of the web and the belt is measured, for example, by means of photoelectric cells attached to the belt guide.
• the calender according to the invention is characterized by what is stated in the characterizing portion of claim 1.
• the calendering method according to the invention is characterized by what is stated in the characterizing portion of claim 10.
• the distance of the belt, protecting the soft-surfaced roll, from the edge of the web being calendered can be changed even while the calender is running, so that the calender need not be stopped to position the belt, which increases the calendering capacity considerably.
• the photoelectric cells measuring the distance between the edge of the web and the belt allow the belt to be repositioned extremely precisely and rapidly, if the width of the web changes.
• the solution according to the invention can also be used in multinip calenders, in which there are many rolls one on top of the other, because the belt runs between continuations of the centrelines of the rolls forming the nip.
• the guide device according to the invention has a simple construction and is economical to manufacture. In addition, the guide device can be easily installed in both new and existing calenders and can be applied in all types of calenders.
• the concept 'roll' refers not only to conventional rolls used in calenders, but also to other devices, such as the shoe of a long-nip calender, or a belt, that can be used to form the nip of a calender.
• the embodiment shown in the drawing comprises two rolls 1, 2, arranged in nip contact, one of which is a heatable thermo roll and the other is a soft-surfaced roll.
• the web 5 being calendered is arranged to run through the nip formed by the rolls 1, 2.
• the web 5 is narrower that the covers of the rolls 1, 2 forming the nip.
• an endless belt 3 is arranged to run through the nip, beside at least one of the edges of the web 5.
• the distance between the belt 3 and the edge of the web 5 can be altered while the calender is running, by means of the guide device 11 at the end of the nip, which is attached, for example, to the frame of the calender.
• the guide device 11 comprises a fixed frame 8, to which a carrier 7, which moves in the cross-direction of the web 5, is attached.
• the belt 3 travels between the continuations of the centrelines of the rolls 1 , 2 forming the nip, in at least almost horizontal direction according to the drawing, guided by pulley-wheels 6 fitted to the belt guide 4 attached to the carrier 7.
• the belt 3 is driven by one of the rolls 1, 2 forming the nip.
• the distance between the edge of the web 5 and the belt 3 is checked by means of two photoelectric cells 10 attached to the belt guide 4 close to each other.
• the photoelectric cells 10 are fork-shaped, so that the transmitter and the receiver are on opposite sides of the web 5 being calendered.
• the measurement points of the photoelectric cells 10 are at various distances from the edge of the web 5.
• the belt 3 is positioned by moving the carrier 7 and the belt guide 4 attached to it, by means of operating devices 9. If the web 5 does not intersect the beam of either photoelectric cell, the carrier 7 is moved closer to the edge of the web 5. Correspondingly, when the web 5 intersects the beams of both photoelectric cells 10, the carrier 7 is moved farther from the edge of the web 5. If the web 5 intersects only the beam of the photoelectric cell 10 nearer to the web 5, the carrier 7 is held in place, for example, with the aid of a delay, so that the edge of the web 5 remains at least approximately in the area remaining between the beams of the photoelectric cells 10. During calendering, the distance between the edge of the web 5 and the belt 3 is typically about 0 - 3 mm.
• the belt 3 is thinner than the web 5 being calendered, the thickness of the belt 3 being preferably about 0,12 - 0,4 mm.
• the belt 3 is manufactured from a material, such as Teflon, that will withstand the temperature of the therm-roll, giving it a heat-resistance of about 260°C.
• the belt 3 can also be manufactured from a metal strip or mesh.
• the distance between the edge of the web 5 and the belt 3 can also be monitored by means of, for example, ultrasound, laser, or pneumatic measurement devices.
• pneumatic measurement there are holes in the surface of the roll and compressed air inside the roll. The web covers some of the holes, making it possible to determine the location of the edge.
• Air nozzles can be installed in the belt guide 4, from which air is blown to cool the belt 3 that has become heated in the nip.

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Priority Applications (1)

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Publications (1)

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Family Applications (1)

Country Status (3)

Citations (3)

• 2000
  • 2000-02-15 FI FI20000330A patent/FI20000330A0/sv not_active IP Right Cessation
• 2001
  • 2001-02-14 AU AU37466/01A patent/AU3746601A/en not_active Abandoned
  • 2001-02-14 WO PCT/FI2001/000142 patent/WO2001061106A1/en active Application Filing

Patent Citations (3)

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