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 calender provided with an extended nip for calendering of a paper or board web, which calender comprises at least one calendering nip, which is formed between a heatable hard roll, on one hand, and a calendering belt which has been formed as an endless loop and which is loaded against the heatable hard roll by means of a backup roll or a press shoe, on the other hand, the paper or board web to be calendered being arranged to run through said calendering nip.
• shoe calenders as a rule, the technique very well known from extended-nip presses is employed, according to which the extended nip is produced so that the paper web is pressed against the backup roll by means of a shaped glide shoe and an endless belt running over the shoe.
• a belt calender by means of the belt, attempts are made to provide the necessary resilience in the calendering nip when the paper web is pressed between the rolls that form the calendering nip.
• Belt calenders in themselves are relatively new constructions, and they can also be formed so that the paper to be calendered is passed, by means of the endless belt, into a preliminary contact with a hot calender roll, in which case it is possible to provide a steep temperature gradient, which is favourable from the point of view of calendering.
• the effective length of the nip is increased because of the preliminary contact and because, as the belt material, it is possible to employ 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 is not reduced.
• the belt and shoe calenders that have been used so far have involved quite a signi- ficant problem, which has arisen from the structure of the belt that has been used.
• the belts that have been used have been almost completely non-compressible, and, as a rule, their structure has been such that there is a support fabric in the middle of the belts, and a polyurethane layer at both sides of the support fabric. Even though the belt in itself may have been elastic, its volume has not been compressible.
• Such a belt of substantially non-compressible volume behaves in a calendering nip, in which it is pressed with a high pressure to make it thinner, so that the material of the belt has to flow parallel to the face of the belt away from the nip.
• the object of the present invention is to provide an essential improvement over the existing calenders provided with extended nips.
• the invention is mainly characterized in that, through the nip, at the side of the backup roll or of the press shoe, respectively, in relation to the web, a belt has been passed which is, in respect of at least a part of its thickness, made of a material of compressible volume.
• the belt that is used in the calender is made of a material of substantially compressible volume.
• a calendering belt favourably a conventional polyurethane belt, is passed, and additionally a separate, substantially fully compressible support belt is passed, which performs the major part of the compression work in the nip.
• a solution with two belts can be accomplished very easily, because, in the manufacture, it is possible to employ conventional prior-art techniques, in particular in the case that a polymer belt is used as the calendering belt and the support belt is made of a felt material.
• the support belt it is also possible to use other compressible materials, for example, cellular rubbers, cellular plastics, and equivalent. Uniform thickness can be achieved easily in a unit composed of a calendering belt and of a support belt in particular made of a felt material.
• Figure 1 is a fully schematic side view of a single-nip calender in which a calender- ing belt is employed.
• Figure 2 shows an enlarged detail from the area of the calendering nip in a calender as shown in Fig. 1.
• Figure 3 is an illustration corresponding to Fig. 1 of a shoe calender.
• Figure 4 is an enlarged detail from the nip area in a calender as shown in Fig. 3.
• Figure 5 is a schematic side view of a belt calender in which, in accordance with the second embodiment of the invention, a combination consisting of a calendering belt and a support belt is employed.
• Figure 6 shows an enlarged detail from the area of the calendering nip in a calender as shown in Fig. 5.
• FIGs. 1 and 2 illustrate a belt calender, in which the calendering nip N is formed between a hot calender roll 1 and a backup roll 3. Further, through the nip N, a calendering belt 10 has been passed to provide the nip N with the necessary elasticity so that the paper web W runs through the nip N between the calendering belt 10 and the face of the hot roll 1.
• Fig. 2 is a more detailed illustration of the conduct of the calendering belt 10 in the nip, whose length is denoted with the reference a.
• the calendering belt 10 consists of a support layer 12 of compressible volume and of a tight polymer layer 11 fitted on one face of said support layer 12.
• the polymer layer 11 is placed on the face of the support layer 12 placed facing the paper web W.
• the support layer 12 itself is placed against the backup roll 3.
• the structure of the support layer 12 is such that it can be compressed in the nip N, i.e. its volume is reduced, in which case no wave of the sort formed in prior- art solutions can be formed ahead of the nip.
• the support layer 12 of compressible volume is favourably a felt, even though other materials can also be employed in the support layer 12. Of these other materials can be mentioned, for example, cellular rubbers, cellular plastics, and equivalent which are compressible.
• the material of the tight polymer layer to be placed against the paper is, for example, thermosetting or thermoplastic resin, favourably polyurethane.
• Figs. 3 and 4 illustrate a shoe calender, in which the extended calendering nip N is formed between a hot hard roll 1 and a shoe roll 2.
• the shoe roll 2 again comprises a press shoe 24 supported by a stationary beam 25 as well as a calendering belt 20, which has been passed around the press shoe 24 and the beam 25 and which has been formed as an endless loop.
• the press shoe 24 the necessary load is produced in the nip N.
• the calen- dering belt 20 consists of three layers fitted one above the other, i.e. of a support layer 22 of compressible volume placed in the middle and of tight polymer layers
• the polymer layers are preferably of polyurethane, and felt, cellular rubber, cellular plastic, or equivalent is employed as the support layer 22 of compressible volume.
• a tight polymer layer 23 is also required at the side of the press shoe 24, because it must be possible to make the friction between the press shoe 24 and the calendering belt 20 sufficiently low.
• the mode of reduction of friction that is known best and that is employed most commonly is producing an oil film between the press shoe and the calendering belt 20.
• the face of the calendering belt 20 that is placed against the press shoe 24 must be tight, in which case a polymer layer 23 is necessary.
• a similar belt can, of course, also be employed in connection with the embodiment shown in Figs. 1 and 2.
• the support layer 12; 22 can be compressed over the length a of the nip N without causing any wave ahead of the nip.
• FIGs. 5 and 6 illustrate a belt calender, in which the calendering nip N is formed between a hot calender roll la and a backup roll 3a.
• a calendering belt 30 as well as a support belt 40 of a material of compressible volume have been passed so as to provide the nip N with the necessary resilience, so that the web W runs through the nip N between the calendering belt 30 and the face of the hot roll la.
• Both the calendering belt 30 and the support belt 40 have been formed as endless loops by means of alignment and tensioning rolls.
• the calendering belt 30 and the support belt 40 are passed into the nip N between the calendering rolls la and 3a by means of a first alignment roll 4, and similarly they are passed out of the nip N by means of a second alignment roll 5, said first and second alignment roll 4 and 5 being, thus, common of the calendering belt 30 and of the support belt 40.
• the calendering belt 30 and the support belt 40 run from the first alignment roll 4 through the nip N to the second alignment roll 5 as a joint run and while fitted one above the other.
• the second alignment roll 5 the calendering belt 30 and the support belt 40 are, however, separated from one another so that they form separate loops of their own.
• the support belt 40 is, thus, guided onto the alignment roll 6 of the support belt, from it onto the support belt tensioning roll 7, and from it further onto the first alignment roll 4, which is common of the support belt and the calendering belt, as was already described above.
• the calendering belt 30 is guided from the second alignment roll 5 onto the belt align- ment roll 8, from it further onto the belt tensioning roll 9, from which the calendering belt 30 is passed, in the case shown in Fig. 5, onto the support belt 40 at the support belt tensioning roll 7.
• the arrangement can. however, also be such that the calendering belt 30 is passed from the belt tensioning roll 9 directly onto the first alignment roll 4 common of the calendering belt 30 and of the support belt 40.
• Fig. 6 illustrates the conduct of the calendering belt 30 and of the support belt 40 in the nip N in more detail, the length of the nip being denoted with the reference a.
• the non-compressible calendering belt favourably a polymer belt 30, and the support belt 40 of compressible volume, favourably a felt or a support belt of a similarly compressible material, are passed.
• the polymer belt 30 has been arranged in the nip N at the side of the heatable calendering roll la, i.e. at the side of the web W to be calendered.
• the material of the polymer belt 30 is favourably polyurethane.
• the structure of the calendering belt 30 is such that it is provided with a thin fibre reinforcement and with a polyurethane layer at least at the side placed facing the heatable calendering roll la.
• the structure of the belt can also be such that the fibre reinforcement is placed, in relation to the thickness of the calendering belt 30, in the middle of the belt, and the smooth polyurethane layers are placed at each side of the calendering belt.
• the support belt that runs through the nip N favourably a felt 40 or equivalent, is placed in the nip against the backup roll 3a.
• the belt 40 or equivalent can be compressed in the nip N, in other words, its volume is reduced, in which case a wave corresponding to that formed in the prior-art solutions cannot be formed ahead of the nip N.
• a felt material it is also possible to use other materials, e.g. cellular rubbers, cellular plastics, and equivalent which are compressible.
• the web W to be calendered is introduced into the nip N so that it does not enter into contact with the calendering belt 30 until in the nip N, and similarly the web W is taken out from the nip N so that it is separated from the calendering belt 30 directly.
• the web W can also be passed into the nip so that it is brought onto the calendering belt 30 before the nip N, and similarly, after the nip, the web is transferred on the calendering nip 30, from which it is taken to further processing.
• the running of the web W can be accomplished as a what is called closed draw.
• a calendering belt of compressible volume in accordance with the invention, and similarly in an arrangement in which a tight calendering belt, in particular a polymer belt, and a support belt of compressible volume, such as a felt or equivalent, are employed, by means of a calender a thicker and stiffer paper or board can be calendered so that the gloss and smoothness of the calendered web are at an equally high level as with a non-compressible calendering belt alone. Also, it can be established that the runnability with a felt or equivalent of compressible volume is better, because, in particular with thin paper grades, the frequency of web breaks is substantially lower than earlier. In the case of a compressible multi-layer belt, the improved runnability was ascertained in test runs. It can be suggested as a reason for this that, when a non-compressible calendering belt is used alone, the flow of the belt material parallel to the belt face strains the paper to such an extent that the frequency of web breaks becomes higher.

Landscapes

• Paper (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)
• Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)
• Medicines Containing Antibodies Or Antigens For Use As Internal Diagnostic Agents (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=8549725

Family Applications (1)

Country Status (8)

Families Citing this family (6)

Family Cites Families (5)

• 1997
  • 1997-10-14 FI FI973954A patent/FI115985B/fi active IP Right Grant
• 1998
  • 1998-10-14 AU AU94450/98A patent/AU9445098A/en not_active Abandoned
  • 1998-10-14 CA CA002274820A patent/CA2274820C/en not_active Expired - Fee Related
  • 1998-10-14 EP EP98947590A patent/EP0944761B1/de not_active Expired - Lifetime
  • 1998-10-14 AT AT98947590T patent/ATE286171T1/de not_active IP Right Cessation
  • 1998-10-14 WO PCT/FI1998/000801 patent/WO1999028551A1/en active IP Right Grant
  • 1998-10-14 JP JP52769199A patent/JP2001512539A/ja not_active Ceased
  • 1998-10-14 DE DE69828376T patent/DE69828376T2/de not_active Expired - Fee Related

Non-Patent Citations (1)

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