Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
  • D21G1/006—Calenders; Smoothing apparatus with extended nips
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
  • D21G1/0066—Calenders; Smoothing apparatus using a special calendering belt
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
  • D21G1/02—Rolls; Their bearings
  • D21G1/0233—Soft rolls

Definitions

• the invention concerns a calendering method, in which the material web to be calendered, in particular a paper or board web, is passed through the calender, in which at least one calendering nip is formed by means of two rolls provided with resilient roll coatings, which rolls are loaded towards each other so that, owing to the resilient nature of the roll coatings, the nip between the rolls becomes an extended nip.
• the invention also concerns a calender that makes use of the calendering method, which calender comprises at least one calendering nip, which is formed by means of two rolls provided with resilient roll coatings, and through which calendering nip the material web to be calendered, in particular a paper or board web, has been passed, in which connection the rolls provided with resilient roll coatings are loaded towards each other so that, owing to the resilient nature of the roll coatings, the nip between the rolls becomes an extended nip.
• the paper to be calendered is passed by means of an endless belt into a preliminary contact with a hot calender roll, in which case it is possible to create a steep temperature gradient, which is favourable from the point of view of calendering.
• the effective length of the nip is increased, owing to the preliminary contact and because, as the belt material, it is possible to use considerably softer polymers than in roll coatings without problems arising from deformations related to heat.
• the press impulse applied to the paper can be increased so that the pressure peak does not become excessively high and that the bulk does not start decreasing.
• FIG. 1A is a schematic illustration of a prior-art calender, in which the calendering nip N is formed between a heatable hard roll 1 and a calendering belt, in particular a metal belt 5, supported by a roll 2 with resilient coating.
• the metal belt 5 is an endless belt, and its material can be, for example, steel.
• the belt is passed over a nip roll 2 provided with a resilient coating 3 and over a reversing roll 4.
• the calendering nip N is, thus, formed between a heatable hard roll 1 and said metal belt 5, which is supported by a calender roll 2 provided with a resilient coating.
• Fig. IB illustrates a further development of the prior-art calender as shown in Fig. 1A.
• the calender has been extended to be a calender with two nips, so that the calender comprises two heatable hard-faced calender rolls 1A and IB, two calender rolls 2A, 2B provided with resilient roll coatings 3A, 3B, and an endless metal belt 5.
• the endless metal belt 5 is passed over said rolls 2A, 2B with resilient coatings, and said rolls with resilient coatings form calendering nips Ni , N 2 with the heatable hard-faced rolls 1A, IB. More correctly, the calendering nips are formed, in each particular case, between the heatable hard-faced roll 1A, IB and the metal belt 5. which metal belt 5 is loaded by
• ISA/EP means of a corresponding roll 2A, 2B with a resilient coating against the heatable hard-faced roll 1A, IB.
• the paper web W is passed through the first nip Ni , after which the web is spread and reversed by means of the take-out leading rolls 4A, 4B and guided into the second nip N 2 .
• the construction and the operation of the rolls 2A,2B with resilient coatings are similar to the illustration in Fig. 1A.
• the prior-art calenders as shown in Figs. 1A and IB are suitable for use with paper grades that do not require a long nip time to be glazed. Such paper grades are, for example, coated grades in which the glass transition temperature of the coating paste is low and in which, therefore, the glazing is rapid.
• a belt calender provides a significant advantage, among other things, in respect of the clear and linear running of the paper web, which again permits tail threading taking place at a high speed.
• the nip is formed between an endless belt and a steel roll. Owing to the glide shoe, the press zone becomes wider than in the belt calender described above.
• the maximal pressure remains lower than in other present-day calenders, for which reason it is best suitable for paper grades in which retaining of the bulk has a high importance.
• such a shoe calender is quite extensively similar to extended-nip presses, which have already been in use for a rather long time.
• ISA/EP surface portions of the web to be finished are first moistened to a high degree of moisture (dry solids content 50%...70%), and the web is then passed, on support of a belt, into a long finishing zone of low pressure, which zone comprises more than one roll nips.
• prior-art paper machine fabrics are employed, such as felts, wires or polymer belts, while the surface treatment proper is applied exclusively to the side of the web placed facing the backup roll.
• a long belt circulation and a roll nip involve a similar basic problem.
• the quality of the belt face and a homogeneous inner structure are an unconditional requirement in order that a uniform quality of web surface could be achieved, and, moreover, keeping the long belt loops, which are made of a more or less elastic material and which often comprise more than one belt alignment rolls, in their position in the cross direction of the web requires the construction of a regulation system of remarkable complexity in connection with the finishing device.
• the present invention concerns a calendering method and in particular a calendering method that makes use of a metal belt calender, in which, by means of endless metal belts, a calender with a very long nip is provided so that attempts are made to create all stages of the calendering process in one and the same calendering nip without unnecessary additional operations.
• the object of the invention is to provide a calendering method that has been improved substantially, as compared with the prior art, and a calender that operates in accordance with this improved method, by means of which calender the calendering process can be made readily controllable and by means of which method the construction of the calender that carries out the method can be made relatively simple.
• the method in accordance with the invention is mainly characterized in that a flexible calendering belt, which is non-compressible in comparison with the roll coatings, which has been formed into an endless loop by means of alignment or reversing rolls or of equivalent rolls, and which runs through the nip, is passed over the calendering rolls provided with resilient roll coatings at each side of the nip.
• the calender in accordance with the invention is mainly characterized in that a flexible calendering belt, which is non-compressible in comparison with the roll coatings, which has been formed into an endless loop by means of alignment or reversing rolls or of equivalent rolls, and which runs through the nip, has been passed over the calendering rolls provided with resilient roll coatings at each side of the nip.
• a flexible, thin and substantially non-compressible belt is used in a novel way together with rolls provided with compressible or non- compressible coatings, a very wide range of regulation of pressure is obtained together with a simultaneous range of high running speeds.
• a substantially non-compressible belt whose material can be metal or, for example, a hard polymer, such as a fibre-reinforced resin, and a roll that is provided with a resilient coating and that supports said belt at the nip are employed, a resilient finishing zone is obtained which has a face of very high quality and which is adapted against the web face very well in compliance with the loading.
• a finishing device in which the overall length of the web treatment zone is very long and, if necessary, includes a number of zones with different pressure ranges.
• An essential feature of a calender in accordance with the present invention is the hardness of the calendering belt that is used, as compared with the roll coating. This provides the highly significant advantage that tail threading is free of problems and easy, for the leader end of the web can be passed through the calender as of full width without a risk that the web that is possibly wrinkled or clodded during the threading might cause permanent damage to the resilient coatings.
• FIG. 1A is a schematic illustration of a calendering nip which has been provided by means of a heatable hard roll and an endless metal belt that is supported by a roll provided with a resilient coating.
• Fig. IB is a schematic illustration of a calender with two nips, in which the calendering nips are formed between hard rolls and a metal belt supported by rolls provided with resilient coatings.
• Figure 2 is a schematic illustration of a calendering nip in accordance with the invention, which nip is formed between metal belts supported by means of rolls provided with resilient coatings at both sides of the nip.
• FIG. 3 illustrates a calender alternative to that shown in Fig. 2, in which calender the calendering nip is likewise formed between two metal belts supported by rolls provided with resilient coatings.
• Figure 4 is a schematic illustration of a calender that has been developed further from Figs. 2 and 3 and by whose means a glazing in two stages can be carried out.
• the necessary pressing in the calendering nip is produced mainly by means of the rolls that support the calendering belts and partly by regulating the tension of the calendering belt.
• the calendering belt can be supported either by hard rolls or by rolls provided with resilient coatings.
• the effect of a calendering belt supported by hard steel rolls on the paper is similar to that in a machine calender, which means that variations in thickness of the paper are calibrated efficiently.
• ISA/EP with resilient coatings are employed, the risk of damaging of the roll coatings is considerably lower than in a supercalender or soft calender, for the rolls are not in direct contact with the paper to be glazed, but the calendering belt protects the coatings efficiently from marking in the event of possible web breaks.
• the use of a calendering belt in a nip between the paper and a roll with resilient coating permits efficient cooling of the roll with resilient coating, which contributes to permitting a high running speed.
• the face of the paper to be calendered ought to be heated to a temperature higher than the glass transition temperature of the paper either before the calendering nip or, in an ideal case, in the nip itself. If the face of the paper has been heated in this way to the desired temperature, the face that presses the paper does not have to be hot any more, but the face can be preferably relatively cool, in which case, at the same time as the paper face in the soft state is pressed against the calendering face and becomes smooth, its temperature becomes lower, and the reversing of the deformation after the pressing is reduced.
• Such a solution involves a certain contradiction, i.e.
• the paper face can be heated in a cold nip if radiation energy is used for the heating and if the nip has been made of a material penetrable by said radiation.
• Calendering can also be carried out as a so-called friction calendering, which is based, besides on the pressing of the paper placed between the faces, also on different speeds of the faces and the paper and on glide friction arising from said differences in speed.
• a normal copying arising from a press tension is intensified, besides owing to the rising of the temperature caused by the friction, also because the friction between the glazing face and the paper has been converted from static friction to kinetic friction, which is, as is well known, the lower one of these two.
• gliding takes place in the machine direction only, the movement of the polymers is also facilitated in the cross direction because of the transition from the static friction to the kinetic friction.
• Friction calendering can also be employed in an extended-nip calender that makes use of a calendering belt. In such a calender, even with a very little difference in speed between the faces, the gliding to which the paper is subjected is considerably large because of the extended nip. Such gliding can be produced, for example, by rotating the opposite calendering belts at slightly different speeds.
• Fig. 2 is a fully schematic illustration of a calender, in which the calendering nip N has been formed between two calendering belts 15A,15B supported by rolls provided with resilient coatings.
• the calendering belts 15A,15B are preferably metal belts, in particular steel belts, but it is an essential feature of the invention that the belts are flexible and smooth belts non-compressible in comparison with the roll coatings 13A,13B on the rolls 12A,12B with resilient coatings.
• the material of the belts is preferably steel, but it is also possible to contemplate that, as the material of the belt, for example, a fibre-reinforced, hard polymer belt or an equivalent belt material is used.
• each of the endless calendering belts 15A,15B is passed over a roll 12A,12B provided with a resilient roll coating 13A,13B and over a reversing roll 14A,14B.
• the rolls 12A,12B with resilient coatings 13A,13B, or at least one of them can be, for example, a self-loaded roll 12A adjustable in zones, in which the roll mantle 16A is arranged to revolve around a stationary roll axle 17A, the roll mantle 16A being loaded in relation to said axle towards the nip N by means of loading elements 18 A.
• the load in the nip N can be made uniform in the cross direction of the web, and, if desired, the load can be regulated if necessary. If one of the rolls with resilient faces is, for example, a self-loaded roll 12A adjustable in zones, in which the roll mantle 16A is arranged to revolve around a stationary roll axle 17A, the roll mantle 16A being loaded in relation to said axle towards the ni
• a roll 12A adjustable in zones the roll 12B placed at the opposite side of the nip N does not necessarily have to be adjustable in zones in a similar way.
• the calendering belts 15A,15B in view of achieving the desired calendering effect, must be heatable, because the rolls 12A,12B provided with resilient roll coatings 13A,13B cannot be made heatable in a corresponding way.
• the heating of the calendering belts 15A,15B can be carried out in a number of different ways, and as one of such ways, for example, induction heating can be mentioned. Induction heating can be employed if the belts are made of a metal material.
• the heating devices, in particular induction heaters, which heat the calendering belt 15A are illustrated fully schematically and denoted with the reference numeral 19A. Other modes of heating are, however, not excluded.
• the paper web W is subjected to an equally high press impulse as in a soft calender.
• it is an advantage of the present invention as compared with a soft calender, that at both sides of the paper there is a smooth hot metal face placed against the paper face, against which metal face the glazing can take place.
• the primary function of the soft roll is just to make the nip longer and, thus, to increase the nip time. Glazing proper does not take place at the side of the soft roll almost at all, and therefore, in order to avoid unequalsidedness, in a soft calender at least two nips are needed, in which the roll positions are reversed in relation to one another.
• a straight nip N provides an advantage, for in it the calendering belt 15A, 15B just becomes straight when it enters into the nip N, and the curve direction is not reversed, as it is reversed in the case of Figs. 1A and IB.
• the improvement is significant in comparison with the prior art.
• Fig. 3 shows a calender in which the calendering nip N through which the paper web W is passed is likewise formed between two calendering belts 15A,15B supported by rolls with resilient faces.
• Fig. 3 differs from the solution of Fig. 2 in the respect that the calendering belts 15A, 15B are guided by means of alignment rolls 16A',16A" and 16B',16B", respectively, so that said calendering belts 15A,15B are in contact with the resilient roll coating 13A,13B in the nip N only.
• Such a solution is needed in particular if the formation of heat in the soft roll coatings 13A,13B causes problems.
• Fig. 3 shows a calender in which the calendering nip N through which the paper web W is passed is likewise formed between two calendering belts 15A,15B supported by rolls with resilient faces.
• Fig. 3 differs from the solution of Fig. 2 in the respect that the
• the calendering belts 15A,15B have to be provided with purposeful heating devices in order to achieve the desired temperature in the roll nip N.
• the heating devices it is possible to use, for example, induction heaters or equivalent. Since the roll coatings 13A,13B on the rolls 12A,12B that form the nip N are in contact with the hot calendering belt 15A,15B at the nip N only, the roll coatings 13A, 13B can be cooled efficiently almost over the entire length of the coating.
• the construction and the operation of the rolls 12A,12B can be, for example, similar to those described in connection with the preceding embodiment of the invention.
• the embodiments shown in Figs. 2 and 3 are best suitable for use as calenders substituted for a soft calender.
• Fig. 4 shows an embodiment of a calender in which there are two calendering nips N t and N 2 placed one after the other.
• the first nip N j is formed between two hard rolls 11A,11B, such as steel rolls. Said hard rolls 11A,11B are preferably heatable rolls.
• the second nip N 2 is formed between two rolls 12A,12B provided with resilient roll coatings 13A,13B, however, so that endless calendering belts 15A,15B have been passed over the hard rolls 11A,11B and over the resilient-face rolls 12A,12B placed at each side of the nips.
• the paper W runs between the nips N j and N 2 in a closed space between the calendering belts 15A, 15B.
• this solution provides a significant advantage in particular in the
• the pair of rolls in the second nip N 2 consists of rolls 12A,12B with resilient faces. Their function is, within a press zone wider than in the pair of rolls 11 A, 11B and with a lower linear load, to finish the calendering result by applying a glazing effect similar to soft- calendering to both faces of the paper.
• the calendering is almost exclusively based on compression of the paper. Between the nips N j and N 2 , shear forces between the paper faces and the calendering belts 15A,15B and the heat conducted from the calendering belts to the paper face are effective. In the portion of the paper web that has reached the area of the latter pair of rolls 12A,12B, a temperature gradient has had time to be formed, so that the faces of the paper have been heated beyond the glass transition temperature of the polymers contained in the faces, and the primary calendering mechanism is copying of the face of the smooth calendering belt to the face of the paper.
• the formation of the temperature gradient can be regulated by varying the nip length and by thereby acting upon the time of dwell and by regulating the temperature of the calendering belts.
• actuators 19 may have been fitted, by whose means the calendering belts are either cooled or heated or high-frequency oscillation is produced in the calendering belts 15A,15B.
• the calendering belt can be heated.
• the calendering belt can be, for example, cooled, moistened, etc., as required.
• Such a solution is very well suitable for one-sided calendering, in particular for calendering of board.
• one belt can be heated and the belt placed at the opposite side of the nip can be cooled, in which case a phenomenon is produced in which the moisture present in the material web to be calendered can be made to be transferred in the calendering nip from the heated side to the cooled side.
• one essential feature of the belt is its hardness in comparison with the roll coating. This provides the highly significant advantage that the threading is free from problems and easy, for the end of the web can be passed through the calender as of full width.

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• Paper (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Peptides Or Proteins (AREA)
• Preparation Of Compounds By Using Micro-Organisms (AREA)
• Reinforced Plastic Materials (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)
• Saccharide Compounds (AREA)
• Dowels (AREA)
• Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)

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• 1997
  • 1997-04-02 FI FI971342A patent/FI102304B1/fi not_active IP Right Cessation
• 1998
  • 1998-03-26 DE DE69802672T patent/DE69802672T2/de not_active Expired - Lifetime
  • 1998-03-26 AU AU65036/98A patent/AU6503698A/en not_active Abandoned
  • 1998-03-26 AT AT98910782T patent/ATE209727T1/de active
  • 1998-03-26 EP EP98910782A patent/EP0973971B1/en not_active Expired - Lifetime
  • 1998-03-26 JP JP54119098A patent/JP4008503B2/ja not_active Expired - Fee Related
  • 1998-03-26 CA CA002285291A patent/CA2285291C/en not_active Expired - Fee Related
  • 1998-03-26 US US09/402,212 patent/US6418840B1/en not_active Expired - Lifetime
  • 1998-03-26 WO PCT/FI1998/000269 patent/WO1998044195A1/en not_active Ceased

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