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
  • 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
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G1/00—Calenders; Smoothing apparatus
  • D21G1/0066—Calenders; Smoothing apparatus using a special calendering belt

Definitions

• the present invention relates to a method for preventing the damaging of a polymer-coated belt in a calender and a calender.
• calenders can be located inside the paperma ing line as so- called intermediate calenders, in the final end as so-called on-line calenders or they can be so-called off-line calenders separate from the paper machine.
• calenders comprise superimposed rolls, between which a nip is formed.
• the nip can also be formed between a so-called shoe roll and its counter roll or between a belt loop travelling through the nip and its counter roll.
• the rolls may be unheated or heated, and they can have a hard or soft surface.
• a nip is formed which is longer than the nip formed by the hard rolls, and in which the treatment time of the web becomes longer than that in the nip formed by the hard counter surfaces, but the pressure exerted on the web per surface area unit is small.
• the shape of the surface such as a shoe, behind the polymer surface, and/or the elasticity of the polymer material, such as a belt, it is possible to affect the length of the nip.
• the web travels via the nip, and by means of this treatment for example the variations in the thickness of the web are reduced, the surface becomes smoother and the web becomes thinner.
• a calender in which the nip is formed between a heated roll and a belt is called a long nip calender.
• the nip pressure can be adjusted in the transverse direction of the machine, wherein it is possible to profile for example the thickness of paper or paperboard.
• the long-nip calender can be formed of a belt calender in which a belt is by means of auxiliary rolls guided around a second nipping roll that functions as a counter roll for thermo rolls.
• the long nip is formed between the thermo roll and the belt, which is loaded with a second nipping roll.
• the belt calender can be composed of a normal thermo roll, a belt loop and a counter roll of a soft calender, which counter roll can be either a hard roll or a soft roll.
• the belt rotates via the counter roll and guiding/tension rolls.
• the simple structure of the belt loop also enables the modernizing of old machine calenders and soft calenders into belt calenders. Without a belt the calender can be used as a conventional machine calender or a soft calender depending on the counter roll.
• the most common long-nip calender is a shoe calender in which the belt is arranged to travel around a stationary supporting structure, and in which the belt is loaded against the thermo roll by means of a loading shoe that rests on the supporting structure inside the belt loop.
• the long nip is formed between the thermo roll and the belt, which is loaded by the shoe.
• the loading shoe of the shoe calender defines the length of the nip.
• One example of the shoe calender is disclosed in the publication WO 9928551
• the shoe used in the press section is disclosed in the publication US 4705602.
• the concept of a polymer coating refers to a counter surface in which the surface that forms the nip is a polymer-coated belt.
• Such solutions are, for example, the polymer-coated belt of the shoe calender or a belt arrangement in which the polymer-coated belt travels around the rolls and via the nip.
• the polymer-coated belt is resilient and it is often pressed in the nip in such a manner that spreading of the belt takes place in the transverse direction of the web, wherein the section of the web that is exposed from underneath the web is easily damaged under the effect of heat and/or wear.
• the polymer-coated belt forms a rotating belt loop in the calender, and the damaging is facilitated by the fact that there is not enough time for the belt to cool down before it enters the nip again.
• a known solution for preventing the damaging of a polymer-coated belt in the nip between a polymer-coated belt and a thermo roll is for example a solution in which the width of the belt is dimensioned according to the smallest width of the paper web.
• the method according to the invention is characterized in that the polymer-coated belt is moved in the transverse direction of the web to be treated.
• the calender according to the invention is characterized in that the calender comprises means which are arranged to move the polymer-coated belt in the transverse direction of the web to be treated.
• the polymer-coated belt is arranged to be moved in such a manner that it moves in the transverse direction of the web to be treated. If neces- sary, the polymer-coated belt can be moved when the aim is to align the edge of the web with the edge of the counter surface. Thus, the polymer-coated belt can remain stationary in the transverse direction of the web to be treated after the adjustment when the rotating movement of the polymer-coated belt which is parallel to the travel direction of the web continues or its alignment with the edge can be monitored by means of a suitable monitoring device and adjusted, if necessary.
• the measurement of temperature is arranged in the edges of the polymer-coated belt and the motion of the polymer- coated belt is arranged to start when the temperature exceeds a certain set value.
• the calender is provided with members suitable for this purpose.
• the members can, for example, be suitable pushers which push the roll frame in the axial direction at a speed suitable for the pur- pose.
• the pusher can be for example a hydraulic cylinder or a pneumatic cylinder, or a screw arrangement that initiates movement in the transverse direction of the web to be treated.
• the polymer-coated belt can be moved in the axial direction.
• the belt On the other side of the belt, for example on the so-called driving side, the belt is aligned very accurately with the edge of the paper web.
• overheating of the polymer coating can be avoided, because the paper web protects the polymer-coated belt.
• the problem still remains on the other edge of the belt, on the so-called tending side. Said problem can be solved for example by means of the solution explained in the following.
• the other edge of the polymer- coated belt is thinner in a set area in the lateral direction of the web than the rest of the area in the lateral direction of the belt. Part of the normal thickness of the belt is removed for example by abrading. A sufficient change in the thickness can be for example 2 mm.
• the other edge of the polymer-coated belt is aligned very accurately with the edge of the paper web, and in the other edge the substantially thinner edge of the polymer-coated belt remains outside the width of the paper web.
• Damaging of the section of the polymer-coated belt that remains outside the width of the paper web is, however, prevented because in said section the polymer-coated belt is thinner, and thus it does not touch the heated counter surface that functions as a second counter surface of the nip.
• the invention can be applied in the shoe calender in such a manner that the belt forming the shell of the shoe roll is oscillated continuously back and forth in the axial direction of the roll in such manner that the roll moves a fixed length of path in the axial direction.
• the belt of the shoe roll is arranged rotatable by fixing the same from its ends to the end plates of the shoe roll that rotate around a stationary shaft and are joumalled on the shaft.
• the belt of the shoe roll is typically a polymer surface, which is loaded from inside the shell by means of zonally adjustable loading elements.
• the edges of the belt are for some time covered by the paper, wherein the thermo roll does not conduct heat on the belt, and, on the other hand, the paper also cools down the belt if the temperature of the belt is higher than that of the paper web.
• the shoe calender By means of the shoe calender it is possible to measure the temperature in the edge areas of the belt for example by means of an infrared thermometer and the oscillation is switched on when the temperature exceeds the set value. It is also possible that the edge of the paper web and the edge of the belt of the shoe roll are aligned with each other on the other edge of the paper web and the temperature of the polymer- coated section of the belt extending over the edge of the paper web in the axial direction of the roll is monitored and said section is cooled down.
• both the polymer-coated belt and the gliding shoe and/or roll frame of the shoe roll are moved. It is, for example possible to act in such a manner that the gliding shoe and/or the roll frame of the shoe roll are moved towards a so-called driving side, and the polymer-coated belt is moved towards a so-called tending side, in other words, the gliding shoe and/or roll frame of the shoe roll are transferred in opposite directions with respect to each other in the axial direction of the shoe roll.
• the other edge of the paper web and the edge of the polymer-coated belt are in alignment with each other, and the other edge of the polymer-coated belt is protected by means of the edge area of the above- described belt that is abraded thinner.
• the transfer of a polymer-coated belt in the transverse direction of the paper web to be treated can also be utilized to prevent the wearing of the polymer-coated belt. If, for example a web treated by means of a zone-controlled roll has to be profiled locally due to a profile error in the paper, this may cause wearing in the belt or local reduction in the surface roughness, which reduces the sen/ice life of the belt.
• a polymer-coated belt such as the belt formed by the shell of the shoe calender or the belt loop of a belt calender is moved in the trans- verse direction of the web to be treated by means of the method according to the invention, uneven wearing can be reduced.
• Figs. 1 and 2 show the principles of some embodiments of the invention, a shoe calender and a belt calender, in a side-view
• Fig. 3 shows a side-view of a nip formed by a shoe roll and a thermo roll, and
• Fig. 4 shows the cross-section of the edge of the shoe roll on the tending side of the belt.
• Fig. 1 shows the principle of a shoe calender in a side-view.
• the calender contains a shoe roll 5, which comprises a rotating belt shell and a stationary central shaft.
• the belt forming the belt shell can be made of a suitable resilient polymer, such as polyurethane, and inside the belt there is a texture that strengthens the same.
• the shoe roll 5 is arranged to be loaded zonally by means of loading elements inside the roll. against the rotating shell of the shoe roll 5 there is a gliding shoe inside the roll, which keeps the belt shell in its shape in a nip N2.
• the length of the shoe can be even 275 mm.
• the shoe nip enables the standardization of the nip width irrespective of the loading, roll diameters and properties of the belt. This enables the optimization of the variables which are important in the calendering, completely irrespec- tive of each other.
• the counter surface of the shoe roll 5 in the nip N2 is a thermo roll 6, which is a hard-faced, heated roll.
• the surface temperature of the thermo roll that functions as a counter roll for the shoe roll is typically in the order of 80 to 350°.
• the belt forming the shell of the shoe roll 5 is moved back and forth in the axial direction of the roll, i.e. in the transverse direction of the paper web W to be treated.
• both edges of the belt have to be moved equally in the same direction, so that an axial strain does not occur in the belt.
• the shoe roll can be made to oscillate continuously for example ⁇ 50 mm during one minute, and to prevent the wearing of the belt it is possible e.g. to oscillate the polymer surface between the driving side and tending side, in practice for example by means of shoe rolls within a distance of 200 mm, which corresponds to the zone distribution of some multi-zone rolls.
• the os- dilation can be implemented for example in such a manner that the set value of an electric belt controller is changed by means of a program approximately 1 mm per hour, wherein the belt slowly moves in the lateral direction.
• Fig. 2 shows the principle of a belt calender in a side-view.
• a polymer- coated belt 10 is arranged to rotate around rolls 9, said belt forming a soft counter surface in the nip N3.
• the paper web W to be treated travels between the belt 10 and a hard-faced roll 8.
• the nip N3 is thus formed by two hard-faced rolls 8, of which at least one is heated, and by a polymer-coated belt 10 travelling therebetween.
• the belt 10 is moved in the lateral direction, i.e. in the axial direction of the rolls 8 and in the transverse direction of the web W to be treated.
• the nip time (nip length) and the nip pressure depend on the linear loading and on the coefficient of elasticity of the belt.
• the hardness of the belt is typically in the order of 80 to 100 ShA.
• the length of the nip varies approximately between 10 to 275 mm, and the nip pressure between 5 to 20 MPa.
• Fig. 3 illustrates en embodiment of the invention.
• Fig. 3 shows a nip N2 formed by a shoe roll 5 and a thermo roll 6 in a side-view.
• the paper web W to be run is equal in width with the polymer-coated belt 11 , the paper web W protects the polymer surface.
• both the polymer-coated belt 11 and the gliding shoe and/or the roll frame 12 of the shoe roll are transferred.
• the frame 12 of the roll and the polymer-coated belt 11 are transferred in a manner described hereinbelow.
• the frame 12 of the roll is transferred 25 mm towards the driving side in the direction of ar- row U by sliding the shaft of the roll on bearings located in the brackets 13 of the shaft.
• the polymer-coated belt 1 1 is transferred 25 mm towards the tending side in the direction of arrow S by transferring the flange 14 of the tending side.
• a part of the thickness of the polymer- coated belt 11 is abraded off from a fixed area A in the lateral direction of the belt on the edge of the belt on the driving side of the calender (shown in Fig. 4), in the case according to the example from an area of 100 mm in width. The area continues around the entire belt loop in the edge of the belt.
• the thickness of the abraded layer may be for example 2 mm, wherein the contact between the thermo roll and the polymer-coated roll is prevented.
• the invention is not restricted to the description above, but it may vary within the scope of the claims.
• the means for transferring the polymer surface in the transverse direction of the paper web to be treated can differ from each other.
• the main aspect of this invention is that the damaging of a polymer-coated belt can be prevented by moving it in the calender in the transverse direction of the web to be treated.

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Cited By (3)

Citations (3)

• 2000
  • 2000-04-05 FI FI20000799A patent/FI113675B/fi not_active IP Right Cessation
• 2001
  • 2001-04-04 WO PCT/FI2001/000323 patent/WO2001075225A1/en active Application Filing
  • 2001-04-04 AU AU2001252297A patent/AU2001252297A1/en not_active Abandoned
  • 2001-04-04 DE DE10196029T patent/DE10196029T1/de not_active Withdrawn

Patent Citations (3)

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