Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F3/00—Press section of machines for making continuous webs of paper
  • D21F3/02—Wet presses
  • D21F3/0209—Wet presses with extended press nip
  • D21F3/0218—Shoe presses
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
  • D21F11/14—Making cellulose wadding, filter or blotting paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F3/00—Press section of machines for making continuous webs of paper
  • D21F3/02—Wet presses
  • D21F3/0281—Wet presses in combination with a dryer roll

Definitions

• the invention relates to a machine for producing a fibrous web, in particular tissue or tissue paper web, with a main press comprising a pressing unit and a drying cylinder.
• DE-A-42 24 730 describes various embodiments of a hygiene paper machine of the type mentioned at the outset.
• One of these known embodiments comprises a total of three press points, namely two pre-presses between two upper rolls and two lower shoe press rolls with a flexible roll casing, and a main press with a pressure roll and a drying cylinder.
• the paper web is produced on a roll former between a dewatering screen and an upper belt.
• Lower belts designed as permeable felts are passed through the two pre-presses together with the paper web and the upper belt.
• an upper belt removes the paper web from a former in order to then pass it through a pre-press between an upper roller and a lower roller with a bottom felt to a main press between a pressure roller and a drying cylinder.
• the pressure roller is a shoe pressure roller.
• the upper felt is very dense and the lower felt is very water-absorbent.
• the bottom roller is designed as a suction roller.
• the blind bores or grooves in the surface of the press shell cannot absorb the entire amount of water due to their production-related limited depth. This should be a reason for the fact that in most of the embodiments described in DE-A-42 24 730 two pre-presses and in one case an additional suction pressure roller are provided in the main press.
• the known embodiments of the two-felt machine take up a relatively large amount of space, especially since in the cases mentioned two pre-presses and a main press are provided which do not remove any water from the creping cylinder.
• the aim of the invention is to provide a machine of the type mentioned at the outset, in which the disadvantages mentioned above are eliminated and the press pulse generated, defined by the sum of all line forces divided by the web running speed, is optimally produced in high paper quality, high production output and low Operating costs is implemented and with which the use of any suction press rollers is unnecessary.
• the contact pressure unit of the main press and / or a press unit assigned to a pre-press is formed by a shoe press unit to form a respective shoe press with a press nip extended in the direction of web travel, and in that the first shoe press, viewed in the direction of web travel, is designed such that the pressure profile generated in the press nip over the nip length has a progressive pressure rise which begins in the area of the nip beginning and extends over at least one third, preferably at least half of the nip length.
• the special pressure distribution is achieved through a special shape of the respective press shoe, taking into account the radius of the counter roll, the press jacket and felt thickness and the dynamic compressibility of the press felts used. Since the felt compressibility decreases with the operating time, the chosen shape of the press shoe is a compromise.
• the values previously specified for the pressure profile are intended in particular apply to one new or two new press felts intended as upper and lower felt at the beginning of their operating time in the first two to four days of use.
• the respective shoe press unit is advantageously formed by a shoe press roll.
• a second shoe press is provided in the web running direction behind the first shoe press, the length of the press nip of the first shoe press being greater than or equal to 100 mm and the length of the press nip of the second shoe press in a range from about 60 to is about 130 mm.
• a preheating and / or predrying device is preferably provided in front of this first press in the web running direction in order to pre-dry or preheat the fibrous web, whereby the dewatering of the fibrous web is significantly improved.
• the preheating and / or predrying device advantageously comprises at least one heat radiator and / or at least one steam blower box.
• this preheating and / or predrying device can also comprise at least one suction unit.
• This suction unit in turn can be formed, for example, by at least one suction box and / or at least one suction roller.
• the length of the press nip of the main press is in a range from about one third to about two thirds of the length of the press nip Pre-press.
• the length of the press nip of the pre-press is in a range from about 100 to about 250 mm and the length of the press nip of the main press is in a range from about 50 to about 100 mm.
• the pressure roller of the main press can be a conventional pressure roller provided with blind holes with a soft rubber cover with a hardness of preferably about 25 to 45 P&J.
• the values given are plastomer points measured with the Pussey & Jones device with a 1/8 "ball.
• the design given has the advantage that it is relatively inexpensive.
• the line force is limited to approximately 90 kN / m. Higher Line forces cannot be achieved or recommended with regard to the longest possible durability of the soft rubber covers of the pressure rollers.
• the pressure unit of the main press is formed by a shoe press unit, preferably a shoe press roller.
• a shoe press unit preferably a shoe press roller.
• Such a design has the great advantage of higher line forces and an asymmetrical pressure distribution with a steep pressure drop at the end of the press nip. As a result, a much higher final dry matter content is achieved.
• Both presses can be adjusted over a wide line force range as required. For example, the line force of one or both presses can be reduced by the Increase softness of the product at the expense of production output. Conversely, high line forces can be set for maximum production of mass products. In addition, old, already heavily compacted felts can continue to be used until the next planned machine standstill if the line force is somewhat reduced.
• the pressure unit of the main press is formed by a shoe press unit, preferably a shoe press roll
• the maximum line force generated in the press nip of the main press is preferably less than 250 kN / m and the pressure increase gradient in the area of the beginning of the nip is less than 50 kPa / mm.
• the pressure increase gradient in the first shoe press in the case of new felt in the area of the beginning of the gap is less than or equal to 30 kPa / mm.
• the falling average gradient at the end of the press nip should preferably be so steep that there is no substantial rewetting of the fibrous web due to the felt separating from it. According to a preferred embodiment in practice, provision is accordingly made for the mean gradient of the pressure drop at the end of the gap in the press nip of the respective shoe press to be in a range from approximately 400 to approximately 1000 kPa / mm.
• the line force in the first press formed by a pre-press is higher than that in the second press formed by the main press and the maximum pressure in the second press is higher than that in the first press.
• At least the press nip of the main press zone is simply felted.
• a felt belt can be passed both through the press nip of a pre-press and through the press nip of the main press.
• the press nip is double felted at least one pre-press.
• an upper felt belt is advantageously passed both through the press nip of the pre-press and through the press nip of the main press and additionally a lower felt belt through the press nip of the pre-press.
• Figure 1 shows the pressure profile in a press nip of an embodiment of a 1-felt tissue machine with new felt.
• the press nip in question is formed between a drying cylinder and a pressure roller.
• the pressing pressure p given in MPa is plotted over the length L of the press nip, which is given here in mm.
• the line force generated in the press nip is approximately 170 kN / m.
• a soft suction press felt with a basis weight of 1,350 g / m 2 was used as the felt.
• the old felt still had about a third of the compressibility of the new felt.
• the press jacket was 6.2 mm thick and provided with blind holes.
• the maximum pressure p max is approximately 2.5 MPa.
• Figure 2 shows the pressure profile in the press nip of a pre-press of an embodiment of a 2-felt tissue machine with new felts.
• the press pressure given in MPa is plotted over the length L of the press nip, which is given here in mm.
• the line force F L generated in the press nip is approximately 175 kN / m in the embodiment shown with a solid curve. In a further embodiment shown in dashed lines, this line force F L is approximately 120 kN / m.
• the gap length is less than in the first case.
• FIG. 3 shows the course of the press pressure in a press nip of the main press of the 2-felt tissue machine with a new top felt passed through this main press.
• the press pressure p given in MPa is plotted over the length L of the press nip, which is again given here in mm.
• the line force F L generated in the press nip is approximately 170 kN / m.
• the press nip of the main press is shorter than the press nip of the pre-press.
• the maximum pressure in the main press is higher than that in the pre-press.
• the pressure profile generated in the respective press gap over the gap length has a progressive pressure increase which begins in the area of the beginning of the gap and extends over at least one third, preferably at least half of the gap length.

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• Paper (AREA)
• Sanitary Thin Papers (AREA)

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Citations (2)

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• 1996
  • 1996-12-23 DE DE19654197A patent/DE19654197A1/de not_active Withdrawn
• 1997
  • 1997-11-05 EP EP97119333A patent/EP0854232B1/fr not_active Expired - Lifetime
  • 1997-11-05 DE DE59709775T patent/DE59709775D1/de not_active Expired - Lifetime
  • 1997-12-23 US US08/997,689 patent/US6083349A/en not_active Expired - Lifetime

Patent Citations (2)

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