CA2158728A1 - Traction-free web transport in a compression section - Google Patents
Traction-free web transport in a compression sectionInfo
- Publication number
- CA2158728A1 CA2158728A1 CA002158728A CA2158728A CA2158728A1 CA 2158728 A1 CA2158728 A1 CA 2158728A1 CA 002158728 A CA002158728 A CA 002158728A CA 2158728 A CA2158728 A CA 2158728A CA 2158728 A1 CA2158728 A1 CA 2158728A1
- Authority
- CA
- Canada
- Prior art keywords
- felt
- press
- roll
- web
- nip
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 230000006835 compression Effects 0.000 title abstract 4
- 238000007906 compression Methods 0.000 title abstract 4
- 239000002657 fibrous material Substances 0.000 claims abstract description 110
- 230000013011 mating Effects 0.000 claims description 20
- 239000010438 granite Substances 0.000 claims description 12
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 230000000284 resting effect Effects 0.000 claims description 2
- 239000002250 absorbent Substances 0.000 claims 1
- 238000000926 separation method Methods 0.000 description 13
- 238000000034 method Methods 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 230000008569 process Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 238000001035 drying Methods 0.000 description 3
- 238000007789 sealing Methods 0.000 description 3
- 238000007664 blowing Methods 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
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
- D21F3/04—Arrangements thereof
- D21F3/045—Arrangements thereof including at least one extended press nip
-
- 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
- D21F3/04—Arrangements thereof
Landscapes
- Paper (AREA)
Abstract
A compression section of a machine to produce webs of fibrous materials, preferably paper webs, has the following characteristics: (a) a smooth cylinder (4.1) in contact with the web forms a first nip (I) together with a first counter-cylinder (5.1) or with a compression band that runs on a shoe, and forms a second nip (II) with a second counter-cylinder (6.1); (b) an endless, water-absorbing felt (F1) runs together with the web through both consecutive nips; (c) the second counter-cylinder (6.1) is designed as a suction cylinder with an internal stationary seal support that forms a suction zone (7, 8) that lies at least for the most part downstream of the second nip.
The compression section is characterized in that a second endless felt (F2) takes over the web from the first felt (F1) in a manner known per se and conveys it through a third nip (III).
The compression section is characterized in that a second endless felt (F2) takes over the web from the first felt (F1) in a manner known per se and conveys it through a third nip (III).
Description
21~728 Draw-free web transfer in a press section The invention relates to a device and a method for the draw-free web transfer of a web of fibrous material, preferably a paper web, in the press section of a paper machine.
Reference is made to the German Utility Model G 92 06 340.
In the case of previously known web transfers in press sections, it has always been attempted to separate the press felt and the paper web as far as possible directly after the press nip, in order to avoid rewetting of the paper web. For this reason, the press felt is separated from the paper web as rapidly as possible adjacent to the press nip, as a result of which, however, tensions and ~YpAn~ions in the paper web are produced which have a negative effect on the quality of the paper produced.
In the case of a design corresponding to the document EP 0 364 114 Al, therefore, in a single-felt press unit, the guidance of the web of fibrous material together with the press felt is carried out on the mating roll as far as a pick-up roll which forms a nip with the mating roll. There, the pick-up of the web of fibrous material and, furthermore the transfer to a second felt are carried out, said second felt being designed, however, as a transfer felt from which 215872~
the web is led away in a free draw for further treatment.
It is therefore the object of the invention to describe a method for guiding the paper web and a device in which expansion of the paper web is avoided, the dryness content of the paper web not being negatively influenced at the same time, however. That is to say, therefore, the additional transfer felt which is normally present between two presses is made superfluous, but in spite of this the web of fibrous material is still intended to come into contact with both its sides consecutively with a smooth press roll in each case and still intended to be transferred without a free web draw from the first to the second felt.
The achievement of this object, according to the invention, is characterized by the characterizing features of claim 1 and of claim 18. Advantageous refinements are reproduced in the subclaims.
The achievement of the object according to claims 1 and 18 is based on the knowledge that the final dryness content downstream of a second press nip, which is designed as a long press nip, virtually does not change if the input dryness content in this second press nip is slightly different - that is to say with or without previous rewetting of the web of fibrous material by the first press felt. A separate transfer felt can thus be dispensed with, so that the first press felt virtually represents the transfer felt at the same time. This 21~728 therefore means, presupposing that the following press nip is formed by a long nip press, that the immediate separation of the press felt from the web of fibrous material at the press nip lying upstream can be dispensed with and the press felt can be used as transfer felt.
Accordingly, the achievement of the object is based on the knowledge that a high final dryness content because of the utilization of a high-capacity press unit, for example a long nip press, as second press nip can also be achieved even if rewetting of the web of fibrous material takes place on the first felt downstream of the first press nip. This results from the long common run of the paper web and the first felt downstream of the first press nip. This long common run is necessary in order to transfer the web of fibrous material to the second felt by means of the first felt, that is to say dispensing with a separate transfer felt and an open draw in the web of fibrous material.
In press sections having a press unit which comprises a rotating body which forms a ring, preferably a roll, and a mating element - which can be described as a roll or by a press belt running over a shoe -, which together form a press nip through which at least one endless felt belt (first felt belt), together with the web of fibrous material, is guided, for this purpose there is assigned to the rotating body forming a ring, downstream of the press nip in the running - 21587~8 direction of the web of fibrous material, a pick-up roll which forms with said body a further second nip at which the web of fibrous material is transferred with the first felt belt to the pick-up roll. The web of fibrous material with the first felt belt thus wraps around, downstream of the press nip, part of the circumference of the rotating body forming a ring, that is to say the web of fibrous material is guided with the first felt belt along part of the circumference of the rotating body forming a ring. The guiding of the first felt belt is carried out in this case along part of the circumference of a rotating body forming a ring, the pick-up roll and further felt guiding elements. As a result of guiding in this manner, the web of fibrous material is further supported by the felt belt adjacent to the press nip, which proves to be advantageous above all in the case of a design of the rotating body forming a ring as a granite roll. The complicated transfer, carried out manually, of the web of fibrous material during the start up phase by means of blast air in the free draw to the next press unit can be omitted. The necessary pivoting of a press roll in the subsequent press unit can be dispensed with.
In addition, according to the invention, the web of fibrous material can be picked up from the first felt belt by means of a second felt belt and fed with the latter through a third press nip which is designed as a high-capacity 21~728 dewatering nip. As a result of the provision and feeding of the web of fibrous material with the second felt belt through a high-capacity dewatering gap, the final dryness content downstream of the latter remains virtually unchanged if the input dryness content in this third press nip is slightly different - that is to say with or without previous rewetting of the web of fibrous material by the first press felt.
The rotating body forming a ring can be designed, for example, as a roll or granite roll. The first mating element can likewise be designed as a smooth roll or as a shoe roll, according to the requirements of use.
The invention allows the use exclusively of conventionally proven components, while similar arrangements according to DE 40 26 021, for example, must use either smooth press belts contacted by the web or smooth press covers contacted by the paper, in each case with the high-risk direct web transfer, or must use a paper suction and blow roll. In this case there is the risk that the web of fibrous material gets wound around the felt guide rolls and "wraps them up".
In addition, by means of the arrangement and web guidance according to the invention, there is the possibility that the problems, occurring in press units of press sections adjacent to nips in whose formation a granite roll is involved, with the pick-up of the web of fibrous material - 215 8~ 28 from the smooth surface and the transfer to subsequent press units can be avoided, especially in the start up phase. Here, it was previously necessary to realize the transfer by means of additional aids such as, for example, blast air and the opening of the subsequent press nip by pivoting away one of the elements forming the nip.
In the case of the use of shoe press units, where the guiding of the web of fibrous material is essentially determined by the guiding of the felt belts, the problems of rewetting of the web of fibrous material after passing through the press nip and the damage occurring to the web of fibrous material during its transport away with the felt on the shoe side as a result of the drawing of the felt over the edge of the shoe was previously especially relevant. This disadvantage and the wear on the felt belts and the loading of the web of fibrous material with respect to conventional web guiding after the press nip can be virtually avoided, since felt and web of fibrous material are no longer drawn over the shoe, especially the exit radius of the shoe, at the exit from the press nip when the web of fibrous material is being carried away by means of the felt on the shoe side.
First and second press unit can be designed as single-felt or double-felt press units.
In the case of designing the first press unit as a double-felt press unit, for example, the web of fibrous - 21~ ~728 material is guided between two felt belts, the first felt belt and a further third felt belt, through the press nip and is subsequently guided between both felts with the latter along part of the circumference of the rotating body forming a ring, that is to say the guiding of the felt belts is carried out in such a way that the first felt belt contacts the mating element at least directly, the rotating body forming a ring at least over part of its circumference adjacent to the press nip as far as to the nip directly, and downstream of the nip wraps around the pick-up roll once more on part of its circumference, while the third felt belt wraps directly around the rotating body forming a ring over part of its circumference in the press nip and adjacent to the press nip. The separation of the two felt belts from each other is carried out at the pick-up roll which is arranged in the running direction of the web of fibrous material downstream of the press nip and in relation to the rotating body forming a ring in such a way that said pick-up roll and said body form a nip with each other. In this arrangement, the separation can be carried out directly in the region of the nip or on the circumference of the pick-up roll adjacent to the nip. In the first case, the pick-up roll is preferably designed as a suction roll. The web of fibrous material is in this case sucked on to the first felt belt. The second felt belt is guided in such a way that it is separated from the 21~8~28 web of fibrous material in the free draw and from the first felt belt in the nip.
In the second case, the pick-up roll can be designed as a full-cover roll. The pick-up roll is wrapped around over part of its circumference by the first felt belt. The guiding of the third felt belt is then carried out in such a way that the third felt belt likewise wraps around the pick-up roll over part of its circumference downstream of the nip, the wrap angle of the third felt on the pick-up roll being smaller than the wrap angle of the first felt belt in relation to the pick-up roll. Because of the guidance of the felt belt, the third felt belt is drawn off from the web of fibrous material in the free draw and is preferably ventilated on both sides, while the web of fibrous material remains on the first felt belt. The web of fibrous material and the felt belt on the shoe side, that is to say the felt belt which wraps directly around the mating element at least over part of its circumference, are not drawn over the exit radius of the shoe in this case, as a result of which damage to the web of fibrous material as a result of pressure/draw loading is avoided.
Press units of this type can be arranged in press sections of various designs, for example in press sections of machines for the production of tissue, the second press unit being able to be designed as a single-felt press unit. A
21~872g design of the second press unit as a double-felt press unit is likewise conceivable. For the purposes of closed web guidance within the press section, in this case the web of fibrous material is transferred from the first felt belt to a second felt belt which is guided with the web of fibrous material through the press nip of the second press unit. The transfer can in this case be carried out either exactly on the pick-up roll or on a further felt guiding element of the first felt belt. For this purpose it is necessary that the second felt belt likewise wraps around the pick-up roll or the felt guiding element in the regions of the pick-up roll or of the felt guiding element which are wrapped around by the first felt belt. The felt guiding element is preferably likewise constructed as a blow roll.
In the case of the transfer on the pick-up roll, the latter preferably has a suction zone directed toward the rotating body forming a ring and a blowing zone directed toward the second felt belt. The blowing zone can extend over the entire width transversely to the running direction of the web of fibrous material or can be constructed only in the edge regions of the roll.
From an economic standpoint, the pick-ups are preferably designed in accordance with the patent application P 44 40 948.6, which is not a prepublished document, with a variably adjustable suction zone width across the machine width.
In a further aspect of the invention, it is conceivable to realize a draw-free web guidance between two press units, the pick-up of the first felt belt and the web of fibrous material being carried out adjacent to the first press nip by means of a suction device in the form of a rigid suction box.
The guiding of a web of fibrous material, according to the invention, is explained hereinafter with reference to figures, in which:
Figure 1 shows a guiding of a web of fibrous material, according to the invention, between the first press nip and a long nip press;
Figure 2 shows a device like figure 1, but with an additional felt guide roll;
Figure 3 shows a guiding of a web of fibrous material, according to the invention, downstream of a double-felt shoe press unit with separation in the press nip of the mating element, using a simple pick-up roll;
Figure 4 shows a guiding of a web of fibrous material, according to the invention, downstream of a double-felt shoe press unit with separation at a suction roll;
Figure 5 snows a guiding of a web of fibrous material, according to the invention, downstream of a double-21c~8~28 felt shoe press unit with separation on a suctionblower roll and subsequent transfer of the web of fibrous material on to a further felt belt;
igure 6 shows a guiding of a web of fibrous material, according to the invention, downstream of a press unit with a granite roll;
igure 7 shows a draw-free web transfer from a press nip to a long nip press, having a felt guide roll which is variable in its width to which suction is applied;
igure 8 shows a felt guide roll corresponding to Figure 7;
igure 9a shows a draw-free web transfer from a press nip to a subsequent long nip press with the aid of a suction box;
igure 9b shows a view in cross section through the contact pressure strips of the suction box, with a spray pipe as cleaning device;
igure 9c shows a longitudinal section through the suction box according to the invention.
Figure 1 shows a section of a press section having draw-free web transfer from a press nip I of a press unit 1, via a press nip II to a third press nip III, which is designed as a high-capacity dewatering nip and, as in the case shown, is formed by a long nip press 3. The first press nip I is formed by a rotating body 4 forming a ring and a first mating roll 5, in the case shown a pair of rolls, comprising a central - 21S8~28 roll 4.1 and a profiled roll 5.1. An endless first felt belt, here the press felt F1, runs over a felt guide roll into the press nip I on the side of the profiled roll 5.1, while at the same time on the side of the central roll 4.1 the web of fibrous material B which is to be dewatered runs in. Adjacent to the press nip I, the pressed web of fibrous material B, resting on the central roll 4.1, together with the press felt F1 lying thereon, wraps around the central roll 4.1 by an angle ~, until it is finally picked up by a pick-up device 6 in the form of a pick-up roll, together with the felt F1, from the central roll 4.1. In this case the pick-up roll is represented by a suction roll 6.1 which, in this example, has two suction zones, the suction zone 7 which is first in the running direction of the web of fibrous material being equipped with a higher vacuum than the second suction zone 8.
The pick-up roll forms the second press nip II with the central roll 4.1.
The suction roll 6.1 leads the press felt F1, together with the web of fibrous material B which remains thereon, to a second opposite suction roll 9 which is designed as a felt guide roll for a second felt F2 which leads through the long nip press 3. The felt F2 takes over the web of fibrous material B, supported by the vacuum of the suction guide roll 9, and guides the web of fibrous material B into the press nip III of the long nip press, which is formed by a profiled 2158~28 roll 10.1 and a shoe roll 11.1, comprising a rotating jacket which can be pressed against the profiled roll by means of a shoe.
In the case of a design corresponding to Figure 1, the pick-up roll 6.1 also serves for transferring the web of fibrous material on the part of the first felt F1.
Figure 2 shows a press section similar to Figure 1. The corresponding reference symbols have been used. The difference consists in the fact that the transfer device in this case comprises a first roll 6.2 to which suction is applied and a subsequent simple felt guide roll 12, the transfer of the paper web on to the felt F2, which is guided over the suction guide roll 2, being carried out between the roll 6.2 and the roll 12. According to the invention, the roll 6.1 shown in Figure 1 is of pivotable design, so that the paper web can, for example in the case of a break of the web of fibrous material, be guided along the roll surface of the roll 4.1 to a doctor 13 and lands in the broke pit. It is likewise possible, in the case of Figure 2, to pivot the two rolls 6.2 and 12 of the pick-up and transfer device away from the roll 4.1 coupled to each other.
In Figures 1 and 2, the pick-up roll is also a component of the transfer device for transferring the web of fibrous material to the second felt F2.
Figure 3 illustrates the further possibility of closed 215872~
web guidance according to the invention in a section of a press section. A press unit 1, including a press element designed here as a shoe roll 5.2, forms with a rotating body forming a ring, here a roll 4.2, an extended press nip I
through which a web of fibrous material B is led. The web of fibrous material B is guided between two endless felt belts, a first felt F1 and a further felt F3, through the press nip I and is there dewatered under the action of pressure. After the exit from the press nip I, the web of fibrous material B
is fed between the first felt F1 and the felt F3 over part of the circumference 15 of the roll 4.2, according to the invention. For this purpose, the felt F3 is guided in such a way that it wraps around the roll 4.2 over part of its circumference 15 and around at least one felt guiding element, not shown here. The first felt F1 wraps around the circumference 16 of the press element 5.2, at least in the region of the press nip I, and after the exit from the press nip I is guided together with the felt F3 and the web of fibrous material B over part of the circumference 15 of the roll 4.2 and then wraps around a suction roll 6.3 over part of its circumference 17 and around further felt guiding elements, not shown here. The suction roll 6.3 is arranged opposite the roll 4.2 in such a manner that the two form a nip II with each other. At the exit from the nip II, because of the suction effect of the suction roll 6.3, the web of 21~8728 fibrous material B is separated from the felt F3 and is guided together with the felt Fl along part of the circumference 17 of the suction roll 6.3 and is transferred at a felt guiding roll 18 to a further endless felt belt F2.
The felt guide roll 18 is primarily wrapped around by the felt belt F2 and is preferably designed as a suction roll which sucks on the web of fibrous material B. The felt F2 serves to guide the web of fibrous material B through a third and extended press nip III of a second press unit 3, which is formed by a second shoe roll 10.2 and a second mating element 11.2. The guiding of the web of fibrous material is carried out in this region of the press section without a free draw, that is to say the web of fibrous material is supported during its passage through the press section in each case by at least one felt.
The arrangement, shown in the figure, of the pick-up roll 6.3 and of the roll 18 for the purposes of transferring the web of fibrous material B from the felt Fl on to the felt belt F2, however, generally has the effect, during transfer, of an elongation of the web of fibrous material - shown here as a broken line - as a result of which, in the region between the felt guide roll 18 and the press nip III, a separation of the web from the felt belt F2 can result, for which reason the transfer of the web of fibrous material from the felt Fl on to the felt F2 should preferably be carried out as described in the following figures.
Figure 4 likewise illustrates a section of a press section of a machine for the production of endless webs of fibrous material, having two press units, as described in Figure 3, for which reason identical reference numbers are used for identical elements. The web of fibrous material B is also guided here through the extended press nip I of the press unit 1 between the felt F3 and the felt F2. After the exit from the press nip I, felt F1 and felt F3 with the web of fibrous material lying between them are guided together on part of the circumference 15 of the roll 4.2. The further guidance of the web of fibrous material B with the felt Fl is carriéd out by picking up by means of the suction roll 6.3 in the nip II in a manner similar to Figure 3. The web of fibrous material B is guided with the felt F1 over a further second roll 19 (felt guiding element of the felt Fl), which is wrapped around over part of its circumference 20 by the felt Fl and is designed as a blow roll. The transfer of the web of fibrous material B to the endless felt belt F2, which is guided with the web of fibrous material B through the extended press nip III to a second press unit 3, is carried out on this blow roll 19. The felt belt F2 does not only touch but wraps around the blow roll 19 indirectly over part of its circumference 20.
Figure 4 shows a possibility for guiding the web of fibrous material, in which the felt F3 is guided downstream of the extended press nip I over part of the circumference of the roll 4.2 and along part of the circumference 17 of the pick-up roll 6.3, which forms a nip II with the roll 4.2. The web of fibrous material B is likewise guided with the felt Fl. However, the separation of felt Fl and F3 is carried out in this design only downstream of the nip II on the circumference 17 of the pick-up roll 6.3. Because of its guiding by means of felt guiding elements, not shown here, the felt F3 is drawn off from the felt Fl and ventilated on both sides downstream of the nip II in the free draw in the wrap-around region of the felt Fl with the pick-up roll 6.3.
Separation of the felts Fl and F3 in the nip II is likewise conceivable but not shown here.
Figure S illustrates the possibility of guiding the web of fibrous material downstream of a first press unit 1, designed as a shoe press unit, with a supporting element acting in the direction of gravity in the installed position and with an adjoining second press unit 3, the transfer of the web of fibrous material B on to the felt belt F2 being carried out after the separation of the felts Fl and F3 on a pick-up roll 6.4, which is designed as a suction blow roll.
The shoe press unit comprises a rotating body forming a ring, for example in the form of a roll 4.3, which forms with a - 21~2~
mating element 5.3 a first press nip I through which the web of fibrous material B is led between a first endless felt F3, which wraps directly around the ring over part of its circumference 21, and a felt belt Fl, which wraps directly around or contacts the mating element 5.3 over part of its circumference. The separation of the two felt belts F1 and F3 is carried out in the nip II, which is formed by the pick-up roll 6.4 with the roll 4.3. The web of fibrous material B is in this case sucked on to the felt belt F1, for which reason the pick-up roll 6.4 has a suction part 22 directed toward the roll 4.3. The transfer of the web of fibrous material B
from the felt belt F1 to a felt belt F2, which is guided together with the web of fibrous material B through a further high-capacity dewatering press nip III of a second press unit 3, is likewise carried out on the pick-up roll 6.4. For this purpose, the latter is partly wrapped around by the felt belt F2 in the wrap-around region of the first felt belt F1 with the pick-up roll. The pick-up roll 6.4 has in this region a blast zone 23 which is preferably provided only in the end regions of the pick-up roll 6.4.
Figure 6 illustrates a possibility for carrying off the web of fibrous material directly downstream of the press nip of a single-felt press unit 1 which comprises two rolls, one roll being designed as a granite roll 4.4. After passing through a press nip 24, the web of fibrous material is guided to a double-felt press device, which is formed by a roll 25 and a mating element 26, along the circumference of the mating element downstream of the press nip 24, with a felt band 28 which wraps around the mating element over part of its circumference 27. For this purpose, the web of fibrous material B is already separated at the exit of the press nip 24 from a felt belt 30, which directly partly wraps around the roll 25 over part of its circumference 31 and is guided together with the felt belt 28 through the press nip 24. The roll 26 is designed as a suction press roll for this purpose.
The guidance of the individual felt belts - felt belt 28 and felt belt 30 iS carried out in such a way that the felt belt 28 is already separated from the felt belt 30 at the exit from the press nip 24 and, because of the design of the mating element 26 as a suction press roll, the web of fibrous material B is sucked on. The web of fibrous material B is guided with the felt belt 28 through a further press nip 29 which is formed by the roll 26 with a granite roll 4.4. After completing the dewatering process in the press nip 29, the web of fibrous material B is guided on its own further along the surface 32 of the granite roll 4.4 and led together with a felt belt F1 through a press nip I which is formed by the granite roll 4. 4 and a further press roll 5.4. The felt Fl and the web of fibrous material B, after passing through the press nip I, are guided together along the surface 32 of the granite roll 4.4 and through a second press nip II which is formed by the granite roll 4.4 with a pick-up roll 6.5, designed as a suction blow roll, in order then to be transferred to a felt belt F2 which wraps indirectly around the pick-up roll 6.5 over part of its circumference and is guided together with the web of fibrous material B to a further press unit 3. The pick-up roll 6.5 is constructed here as described in Figure 5. Said roll includes a suction region 33, directed toward the granite roll 4.4, and a blast region 34 which is preferably constructed only in the end regions of the roll and is directed toward the felt belt F2.
The sections from the press sections which are cited in the figures are only examples for a possible arrangement of press units. The significant fact here is that the transfer of the web of fibrous material on to a felt belt after passing through a press nip is essentially carried out in such a way that the web of fibrous material, after the exit from the press nip, is guided with the felt over part of the circumference of one of the press elements and passes through a nip which is formed with this press element by a pick-up roll which is at the same time guiding element of the felt.
According to the invention, it is essential that, following the draw-free web transfer from a previous press nip to a subsequent press nip, the subsequent press nip is designed as a high-capacity dewatering nip, for example in 21~8728 the form of a long nip press, since because of the properties of the long nip press the rewetting of the web of fibrous material as a result of the continuous contact with the felt downstream of the first press nip is compensated. On the other hand, it is of course possible according to the invention to design the previous or one of the previous press nips as a long nip press.
The possibilities of the transfer of the web of fibrous material for further transport to further press units can be used for the passage in press units of various designs; the press unit arrangements cited in the figures are therefore not compulsory.
Figure 7 illustrates a draw-free web guidance in a press section, in which the design of the pick-up roll on a first press unit is carried out in such a way that the latter is especially suitable for the problems of the start-up process, that is to say when the production of a paper machine begins to start up following a preceding standstill and a narrow strip of the still wet paper web is cut out from somewhere upstream of the drying section or at the beginning of the drying section (so-called tail) and this tail is initially fed through the entire drying section. The main part of the still wet paper web is, in contrast, diverted away at the point of separation into a pit underneath the paper machine in order to be converted, by means of stirring with the - 215~7~8 addition of water, once more into a stock suspension which is fed back once more to the stock circulation. This process is described in EP 0 584 492 Al. The so-called tail can be generated here by being already separated by a water jet on the paper machine wire from the remaining paper web just produced. However, said tail can also be cut out at a subsequent location, viewed in the machine direction, by cutting out from the already consolidated paper web. The separation of tail and remaining web is carried out, for example, at a press roll, for example at the central roll of a roll press having three press nips. At this location, the main part of the web - as mentioned above - is diverted into a catching pit, while the tail is transferred on to a suction roll. The suction roll can be equipped with two suction zones. The first of these two suction zones is located at one end of the suction roll, specifically where the tail is guided. This first suction zone is as narrow as the tail itself. The second suction zone extends over the remaining part of the suction roll width. In this arrangement, the first suction zone has vacuum applied to it first, in order to transfer the tail from the previous press roll to said suction roll. As soon as the tail has passed through the entire paper machine, the tip cutter is moved transversely to the running direction of the paper web, specifically in the direction in which the tail is continuously broadened, until 215~2~
the complete web width is reached. Vacuum must already be applied to the second suction zone at the beginning of this process, in order to seize the broadening web and to transfer it to the suction roll. However, in this process the following problem occurs: already from the first instant of making the web wider (= beginning of the movement of the tip cutter transversely to the running direction), the complete vacuum must be applied to the second suction zone. At this time, however, the perforations of the second suction zone are not yet covered by the web. This means that immense quantities of air must be sucked through the perforations, with the result that the energy consumption for applying the vacuum is very large. Accordingly, the vacuum pump must also be dimensioned to be correspondingly large.
Figure 7 shows a section from a paper machine, prefer-ably a section from a wire section and a subsequent press section, having a suction roll picking up the web of fibrous material at the first press unit and having an adjustable suction zone width corresponding to the increase of the tail width.
The wire section 40 comprises a wire 41. The wire section 40 has a row of built-in parts, for example a suction means 42, deflection rolls 43 and 44. A water jet nozzle 45 directs a water jet against the paper web which is in the course of production, in order to cut out herefrom a narrow 21~872~
strip, the so-called tail, at the beginning of starting up the paper machine. The wire section is followed by a press section. The latter has a plurality of press felts, for example the felt F1, which wraps around a pick-up roll 46, and which picks up the paper web (or the tail) from the wire 41. The pick-up roll 46 is followed by a first press unit 1 having press rolls 4.5 and 5.5. The first press unit 1 is followed by a second press unit 3 having the press rolls 47 and 48. Both the press units are designed as long nip presses and the press rolls 5.5 and 48 are designed as shoe rolls.
As already explained, in the case of conventional installations there is the following problem: if the tail is being fed, it must be picked up at the suction roll. The suction roll in the case of conventional installations is therefore divided into a first suction zone for the tail and into a second suction zone for the main part of the paper web. At the beginning of broadening the paper web, the second suction zone is still not covered, but vacuum must already be applied to this second zone, energy being lost - as mentioned above - or great quantities of air having to be sucked through the perforations of the second zone.
Hence, it is to be recommended to configure in accordance with the invention all those suction rolls in which there is a risk that the said disadvantages occur during feeding of the paper web, in the figure this is in 215872~
particular the pick-up roll 6.6.
Furthermore, the following combination of the definitive elements can be seen from Figure 7: the water jet nozzle 45 has a drive 54 assigned to it. Likewise, a drive 55 is assigned to the adjustment device for varying the sucked width in the suction roll 6.6. A switch 56 is provided which serves for the purpose of driving the two drives 54 and 55 simultaneously. The drives 54 and 55 are connected to each other via electric lines 57, 58. Furthermore, an actuating device 59 for varying the control signal in line 58 relative to the control signal in line 57 is provided. The result achieved is that the two drives 54 and 55 have one and the same speed.
Finally, a delay unit 60 is provided. This has the effect, if required, that the drive 55 starts later than the drive 54, to be specific by the time interval ~t.
The value of ~t depends on the machine speed, and in addition on the distance which is covered by the web between the water jet nozzle 45 and the suction roll 6.6.
The suction roll 6.6 is shown in Figure 8. Said roll has, on the front side, a vacuum connection 61 and a sealing plate 62, perpendicular to its axis, in its internal space.
The sealing plate 62 can be moved in the longitudinal direction of the suction roll by means of a threaded spindle 63 which can be rotated about its own axis. During the moving
Reference is made to the German Utility Model G 92 06 340.
In the case of previously known web transfers in press sections, it has always been attempted to separate the press felt and the paper web as far as possible directly after the press nip, in order to avoid rewetting of the paper web. For this reason, the press felt is separated from the paper web as rapidly as possible adjacent to the press nip, as a result of which, however, tensions and ~YpAn~ions in the paper web are produced which have a negative effect on the quality of the paper produced.
In the case of a design corresponding to the document EP 0 364 114 Al, therefore, in a single-felt press unit, the guidance of the web of fibrous material together with the press felt is carried out on the mating roll as far as a pick-up roll which forms a nip with the mating roll. There, the pick-up of the web of fibrous material and, furthermore the transfer to a second felt are carried out, said second felt being designed, however, as a transfer felt from which 215872~
the web is led away in a free draw for further treatment.
It is therefore the object of the invention to describe a method for guiding the paper web and a device in which expansion of the paper web is avoided, the dryness content of the paper web not being negatively influenced at the same time, however. That is to say, therefore, the additional transfer felt which is normally present between two presses is made superfluous, but in spite of this the web of fibrous material is still intended to come into contact with both its sides consecutively with a smooth press roll in each case and still intended to be transferred without a free web draw from the first to the second felt.
The achievement of this object, according to the invention, is characterized by the characterizing features of claim 1 and of claim 18. Advantageous refinements are reproduced in the subclaims.
The achievement of the object according to claims 1 and 18 is based on the knowledge that the final dryness content downstream of a second press nip, which is designed as a long press nip, virtually does not change if the input dryness content in this second press nip is slightly different - that is to say with or without previous rewetting of the web of fibrous material by the first press felt. A separate transfer felt can thus be dispensed with, so that the first press felt virtually represents the transfer felt at the same time. This 21~728 therefore means, presupposing that the following press nip is formed by a long nip press, that the immediate separation of the press felt from the web of fibrous material at the press nip lying upstream can be dispensed with and the press felt can be used as transfer felt.
Accordingly, the achievement of the object is based on the knowledge that a high final dryness content because of the utilization of a high-capacity press unit, for example a long nip press, as second press nip can also be achieved even if rewetting of the web of fibrous material takes place on the first felt downstream of the first press nip. This results from the long common run of the paper web and the first felt downstream of the first press nip. This long common run is necessary in order to transfer the web of fibrous material to the second felt by means of the first felt, that is to say dispensing with a separate transfer felt and an open draw in the web of fibrous material.
In press sections having a press unit which comprises a rotating body which forms a ring, preferably a roll, and a mating element - which can be described as a roll or by a press belt running over a shoe -, which together form a press nip through which at least one endless felt belt (first felt belt), together with the web of fibrous material, is guided, for this purpose there is assigned to the rotating body forming a ring, downstream of the press nip in the running - 21587~8 direction of the web of fibrous material, a pick-up roll which forms with said body a further second nip at which the web of fibrous material is transferred with the first felt belt to the pick-up roll. The web of fibrous material with the first felt belt thus wraps around, downstream of the press nip, part of the circumference of the rotating body forming a ring, that is to say the web of fibrous material is guided with the first felt belt along part of the circumference of the rotating body forming a ring. The guiding of the first felt belt is carried out in this case along part of the circumference of a rotating body forming a ring, the pick-up roll and further felt guiding elements. As a result of guiding in this manner, the web of fibrous material is further supported by the felt belt adjacent to the press nip, which proves to be advantageous above all in the case of a design of the rotating body forming a ring as a granite roll. The complicated transfer, carried out manually, of the web of fibrous material during the start up phase by means of blast air in the free draw to the next press unit can be omitted. The necessary pivoting of a press roll in the subsequent press unit can be dispensed with.
In addition, according to the invention, the web of fibrous material can be picked up from the first felt belt by means of a second felt belt and fed with the latter through a third press nip which is designed as a high-capacity 21~728 dewatering nip. As a result of the provision and feeding of the web of fibrous material with the second felt belt through a high-capacity dewatering gap, the final dryness content downstream of the latter remains virtually unchanged if the input dryness content in this third press nip is slightly different - that is to say with or without previous rewetting of the web of fibrous material by the first press felt.
The rotating body forming a ring can be designed, for example, as a roll or granite roll. The first mating element can likewise be designed as a smooth roll or as a shoe roll, according to the requirements of use.
The invention allows the use exclusively of conventionally proven components, while similar arrangements according to DE 40 26 021, for example, must use either smooth press belts contacted by the web or smooth press covers contacted by the paper, in each case with the high-risk direct web transfer, or must use a paper suction and blow roll. In this case there is the risk that the web of fibrous material gets wound around the felt guide rolls and "wraps them up".
In addition, by means of the arrangement and web guidance according to the invention, there is the possibility that the problems, occurring in press units of press sections adjacent to nips in whose formation a granite roll is involved, with the pick-up of the web of fibrous material - 215 8~ 28 from the smooth surface and the transfer to subsequent press units can be avoided, especially in the start up phase. Here, it was previously necessary to realize the transfer by means of additional aids such as, for example, blast air and the opening of the subsequent press nip by pivoting away one of the elements forming the nip.
In the case of the use of shoe press units, where the guiding of the web of fibrous material is essentially determined by the guiding of the felt belts, the problems of rewetting of the web of fibrous material after passing through the press nip and the damage occurring to the web of fibrous material during its transport away with the felt on the shoe side as a result of the drawing of the felt over the edge of the shoe was previously especially relevant. This disadvantage and the wear on the felt belts and the loading of the web of fibrous material with respect to conventional web guiding after the press nip can be virtually avoided, since felt and web of fibrous material are no longer drawn over the shoe, especially the exit radius of the shoe, at the exit from the press nip when the web of fibrous material is being carried away by means of the felt on the shoe side.
First and second press unit can be designed as single-felt or double-felt press units.
In the case of designing the first press unit as a double-felt press unit, for example, the web of fibrous - 21~ ~728 material is guided between two felt belts, the first felt belt and a further third felt belt, through the press nip and is subsequently guided between both felts with the latter along part of the circumference of the rotating body forming a ring, that is to say the guiding of the felt belts is carried out in such a way that the first felt belt contacts the mating element at least directly, the rotating body forming a ring at least over part of its circumference adjacent to the press nip as far as to the nip directly, and downstream of the nip wraps around the pick-up roll once more on part of its circumference, while the third felt belt wraps directly around the rotating body forming a ring over part of its circumference in the press nip and adjacent to the press nip. The separation of the two felt belts from each other is carried out at the pick-up roll which is arranged in the running direction of the web of fibrous material downstream of the press nip and in relation to the rotating body forming a ring in such a way that said pick-up roll and said body form a nip with each other. In this arrangement, the separation can be carried out directly in the region of the nip or on the circumference of the pick-up roll adjacent to the nip. In the first case, the pick-up roll is preferably designed as a suction roll. The web of fibrous material is in this case sucked on to the first felt belt. The second felt belt is guided in such a way that it is separated from the 21~8~28 web of fibrous material in the free draw and from the first felt belt in the nip.
In the second case, the pick-up roll can be designed as a full-cover roll. The pick-up roll is wrapped around over part of its circumference by the first felt belt. The guiding of the third felt belt is then carried out in such a way that the third felt belt likewise wraps around the pick-up roll over part of its circumference downstream of the nip, the wrap angle of the third felt on the pick-up roll being smaller than the wrap angle of the first felt belt in relation to the pick-up roll. Because of the guidance of the felt belt, the third felt belt is drawn off from the web of fibrous material in the free draw and is preferably ventilated on both sides, while the web of fibrous material remains on the first felt belt. The web of fibrous material and the felt belt on the shoe side, that is to say the felt belt which wraps directly around the mating element at least over part of its circumference, are not drawn over the exit radius of the shoe in this case, as a result of which damage to the web of fibrous material as a result of pressure/draw loading is avoided.
Press units of this type can be arranged in press sections of various designs, for example in press sections of machines for the production of tissue, the second press unit being able to be designed as a single-felt press unit. A
21~872g design of the second press unit as a double-felt press unit is likewise conceivable. For the purposes of closed web guidance within the press section, in this case the web of fibrous material is transferred from the first felt belt to a second felt belt which is guided with the web of fibrous material through the press nip of the second press unit. The transfer can in this case be carried out either exactly on the pick-up roll or on a further felt guiding element of the first felt belt. For this purpose it is necessary that the second felt belt likewise wraps around the pick-up roll or the felt guiding element in the regions of the pick-up roll or of the felt guiding element which are wrapped around by the first felt belt. The felt guiding element is preferably likewise constructed as a blow roll.
In the case of the transfer on the pick-up roll, the latter preferably has a suction zone directed toward the rotating body forming a ring and a blowing zone directed toward the second felt belt. The blowing zone can extend over the entire width transversely to the running direction of the web of fibrous material or can be constructed only in the edge regions of the roll.
From an economic standpoint, the pick-ups are preferably designed in accordance with the patent application P 44 40 948.6, which is not a prepublished document, with a variably adjustable suction zone width across the machine width.
In a further aspect of the invention, it is conceivable to realize a draw-free web guidance between two press units, the pick-up of the first felt belt and the web of fibrous material being carried out adjacent to the first press nip by means of a suction device in the form of a rigid suction box.
The guiding of a web of fibrous material, according to the invention, is explained hereinafter with reference to figures, in which:
Figure 1 shows a guiding of a web of fibrous material, according to the invention, between the first press nip and a long nip press;
Figure 2 shows a device like figure 1, but with an additional felt guide roll;
Figure 3 shows a guiding of a web of fibrous material, according to the invention, downstream of a double-felt shoe press unit with separation in the press nip of the mating element, using a simple pick-up roll;
Figure 4 shows a guiding of a web of fibrous material, according to the invention, downstream of a double-felt shoe press unit with separation at a suction roll;
Figure 5 snows a guiding of a web of fibrous material, according to the invention, downstream of a double-21c~8~28 felt shoe press unit with separation on a suctionblower roll and subsequent transfer of the web of fibrous material on to a further felt belt;
igure 6 shows a guiding of a web of fibrous material, according to the invention, downstream of a press unit with a granite roll;
igure 7 shows a draw-free web transfer from a press nip to a long nip press, having a felt guide roll which is variable in its width to which suction is applied;
igure 8 shows a felt guide roll corresponding to Figure 7;
igure 9a shows a draw-free web transfer from a press nip to a subsequent long nip press with the aid of a suction box;
igure 9b shows a view in cross section through the contact pressure strips of the suction box, with a spray pipe as cleaning device;
igure 9c shows a longitudinal section through the suction box according to the invention.
Figure 1 shows a section of a press section having draw-free web transfer from a press nip I of a press unit 1, via a press nip II to a third press nip III, which is designed as a high-capacity dewatering nip and, as in the case shown, is formed by a long nip press 3. The first press nip I is formed by a rotating body 4 forming a ring and a first mating roll 5, in the case shown a pair of rolls, comprising a central - 21S8~28 roll 4.1 and a profiled roll 5.1. An endless first felt belt, here the press felt F1, runs over a felt guide roll into the press nip I on the side of the profiled roll 5.1, while at the same time on the side of the central roll 4.1 the web of fibrous material B which is to be dewatered runs in. Adjacent to the press nip I, the pressed web of fibrous material B, resting on the central roll 4.1, together with the press felt F1 lying thereon, wraps around the central roll 4.1 by an angle ~, until it is finally picked up by a pick-up device 6 in the form of a pick-up roll, together with the felt F1, from the central roll 4.1. In this case the pick-up roll is represented by a suction roll 6.1 which, in this example, has two suction zones, the suction zone 7 which is first in the running direction of the web of fibrous material being equipped with a higher vacuum than the second suction zone 8.
The pick-up roll forms the second press nip II with the central roll 4.1.
The suction roll 6.1 leads the press felt F1, together with the web of fibrous material B which remains thereon, to a second opposite suction roll 9 which is designed as a felt guide roll for a second felt F2 which leads through the long nip press 3. The felt F2 takes over the web of fibrous material B, supported by the vacuum of the suction guide roll 9, and guides the web of fibrous material B into the press nip III of the long nip press, which is formed by a profiled 2158~28 roll 10.1 and a shoe roll 11.1, comprising a rotating jacket which can be pressed against the profiled roll by means of a shoe.
In the case of a design corresponding to Figure 1, the pick-up roll 6.1 also serves for transferring the web of fibrous material on the part of the first felt F1.
Figure 2 shows a press section similar to Figure 1. The corresponding reference symbols have been used. The difference consists in the fact that the transfer device in this case comprises a first roll 6.2 to which suction is applied and a subsequent simple felt guide roll 12, the transfer of the paper web on to the felt F2, which is guided over the suction guide roll 2, being carried out between the roll 6.2 and the roll 12. According to the invention, the roll 6.1 shown in Figure 1 is of pivotable design, so that the paper web can, for example in the case of a break of the web of fibrous material, be guided along the roll surface of the roll 4.1 to a doctor 13 and lands in the broke pit. It is likewise possible, in the case of Figure 2, to pivot the two rolls 6.2 and 12 of the pick-up and transfer device away from the roll 4.1 coupled to each other.
In Figures 1 and 2, the pick-up roll is also a component of the transfer device for transferring the web of fibrous material to the second felt F2.
Figure 3 illustrates the further possibility of closed 215872~
web guidance according to the invention in a section of a press section. A press unit 1, including a press element designed here as a shoe roll 5.2, forms with a rotating body forming a ring, here a roll 4.2, an extended press nip I
through which a web of fibrous material B is led. The web of fibrous material B is guided between two endless felt belts, a first felt F1 and a further felt F3, through the press nip I and is there dewatered under the action of pressure. After the exit from the press nip I, the web of fibrous material B
is fed between the first felt F1 and the felt F3 over part of the circumference 15 of the roll 4.2, according to the invention. For this purpose, the felt F3 is guided in such a way that it wraps around the roll 4.2 over part of its circumference 15 and around at least one felt guiding element, not shown here. The first felt F1 wraps around the circumference 16 of the press element 5.2, at least in the region of the press nip I, and after the exit from the press nip I is guided together with the felt F3 and the web of fibrous material B over part of the circumference 15 of the roll 4.2 and then wraps around a suction roll 6.3 over part of its circumference 17 and around further felt guiding elements, not shown here. The suction roll 6.3 is arranged opposite the roll 4.2 in such a manner that the two form a nip II with each other. At the exit from the nip II, because of the suction effect of the suction roll 6.3, the web of 21~8728 fibrous material B is separated from the felt F3 and is guided together with the felt Fl along part of the circumference 17 of the suction roll 6.3 and is transferred at a felt guiding roll 18 to a further endless felt belt F2.
The felt guide roll 18 is primarily wrapped around by the felt belt F2 and is preferably designed as a suction roll which sucks on the web of fibrous material B. The felt F2 serves to guide the web of fibrous material B through a third and extended press nip III of a second press unit 3, which is formed by a second shoe roll 10.2 and a second mating element 11.2. The guiding of the web of fibrous material is carried out in this region of the press section without a free draw, that is to say the web of fibrous material is supported during its passage through the press section in each case by at least one felt.
The arrangement, shown in the figure, of the pick-up roll 6.3 and of the roll 18 for the purposes of transferring the web of fibrous material B from the felt Fl on to the felt belt F2, however, generally has the effect, during transfer, of an elongation of the web of fibrous material - shown here as a broken line - as a result of which, in the region between the felt guide roll 18 and the press nip III, a separation of the web from the felt belt F2 can result, for which reason the transfer of the web of fibrous material from the felt Fl on to the felt F2 should preferably be carried out as described in the following figures.
Figure 4 likewise illustrates a section of a press section of a machine for the production of endless webs of fibrous material, having two press units, as described in Figure 3, for which reason identical reference numbers are used for identical elements. The web of fibrous material B is also guided here through the extended press nip I of the press unit 1 between the felt F3 and the felt F2. After the exit from the press nip I, felt F1 and felt F3 with the web of fibrous material lying between them are guided together on part of the circumference 15 of the roll 4.2. The further guidance of the web of fibrous material B with the felt Fl is carriéd out by picking up by means of the suction roll 6.3 in the nip II in a manner similar to Figure 3. The web of fibrous material B is guided with the felt F1 over a further second roll 19 (felt guiding element of the felt Fl), which is wrapped around over part of its circumference 20 by the felt Fl and is designed as a blow roll. The transfer of the web of fibrous material B to the endless felt belt F2, which is guided with the web of fibrous material B through the extended press nip III to a second press unit 3, is carried out on this blow roll 19. The felt belt F2 does not only touch but wraps around the blow roll 19 indirectly over part of its circumference 20.
Figure 4 shows a possibility for guiding the web of fibrous material, in which the felt F3 is guided downstream of the extended press nip I over part of the circumference of the roll 4.2 and along part of the circumference 17 of the pick-up roll 6.3, which forms a nip II with the roll 4.2. The web of fibrous material B is likewise guided with the felt Fl. However, the separation of felt Fl and F3 is carried out in this design only downstream of the nip II on the circumference 17 of the pick-up roll 6.3. Because of its guiding by means of felt guiding elements, not shown here, the felt F3 is drawn off from the felt Fl and ventilated on both sides downstream of the nip II in the free draw in the wrap-around region of the felt Fl with the pick-up roll 6.3.
Separation of the felts Fl and F3 in the nip II is likewise conceivable but not shown here.
Figure S illustrates the possibility of guiding the web of fibrous material downstream of a first press unit 1, designed as a shoe press unit, with a supporting element acting in the direction of gravity in the installed position and with an adjoining second press unit 3, the transfer of the web of fibrous material B on to the felt belt F2 being carried out after the separation of the felts Fl and F3 on a pick-up roll 6.4, which is designed as a suction blow roll.
The shoe press unit comprises a rotating body forming a ring, for example in the form of a roll 4.3, which forms with a - 21~2~
mating element 5.3 a first press nip I through which the web of fibrous material B is led between a first endless felt F3, which wraps directly around the ring over part of its circumference 21, and a felt belt Fl, which wraps directly around or contacts the mating element 5.3 over part of its circumference. The separation of the two felt belts F1 and F3 is carried out in the nip II, which is formed by the pick-up roll 6.4 with the roll 4.3. The web of fibrous material B is in this case sucked on to the felt belt F1, for which reason the pick-up roll 6.4 has a suction part 22 directed toward the roll 4.3. The transfer of the web of fibrous material B
from the felt belt F1 to a felt belt F2, which is guided together with the web of fibrous material B through a further high-capacity dewatering press nip III of a second press unit 3, is likewise carried out on the pick-up roll 6.4. For this purpose, the latter is partly wrapped around by the felt belt F2 in the wrap-around region of the first felt belt F1 with the pick-up roll. The pick-up roll 6.4 has in this region a blast zone 23 which is preferably provided only in the end regions of the pick-up roll 6.4.
Figure 6 illustrates a possibility for carrying off the web of fibrous material directly downstream of the press nip of a single-felt press unit 1 which comprises two rolls, one roll being designed as a granite roll 4.4. After passing through a press nip 24, the web of fibrous material is guided to a double-felt press device, which is formed by a roll 25 and a mating element 26, along the circumference of the mating element downstream of the press nip 24, with a felt band 28 which wraps around the mating element over part of its circumference 27. For this purpose, the web of fibrous material B is already separated at the exit of the press nip 24 from a felt belt 30, which directly partly wraps around the roll 25 over part of its circumference 31 and is guided together with the felt belt 28 through the press nip 24. The roll 26 is designed as a suction press roll for this purpose.
The guidance of the individual felt belts - felt belt 28 and felt belt 30 iS carried out in such a way that the felt belt 28 is already separated from the felt belt 30 at the exit from the press nip 24 and, because of the design of the mating element 26 as a suction press roll, the web of fibrous material B is sucked on. The web of fibrous material B is guided with the felt belt 28 through a further press nip 29 which is formed by the roll 26 with a granite roll 4.4. After completing the dewatering process in the press nip 29, the web of fibrous material B is guided on its own further along the surface 32 of the granite roll 4.4 and led together with a felt belt F1 through a press nip I which is formed by the granite roll 4. 4 and a further press roll 5.4. The felt Fl and the web of fibrous material B, after passing through the press nip I, are guided together along the surface 32 of the granite roll 4.4 and through a second press nip II which is formed by the granite roll 4.4 with a pick-up roll 6.5, designed as a suction blow roll, in order then to be transferred to a felt belt F2 which wraps indirectly around the pick-up roll 6.5 over part of its circumference and is guided together with the web of fibrous material B to a further press unit 3. The pick-up roll 6.5 is constructed here as described in Figure 5. Said roll includes a suction region 33, directed toward the granite roll 4.4, and a blast region 34 which is preferably constructed only in the end regions of the roll and is directed toward the felt belt F2.
The sections from the press sections which are cited in the figures are only examples for a possible arrangement of press units. The significant fact here is that the transfer of the web of fibrous material on to a felt belt after passing through a press nip is essentially carried out in such a way that the web of fibrous material, after the exit from the press nip, is guided with the felt over part of the circumference of one of the press elements and passes through a nip which is formed with this press element by a pick-up roll which is at the same time guiding element of the felt.
According to the invention, it is essential that, following the draw-free web transfer from a previous press nip to a subsequent press nip, the subsequent press nip is designed as a high-capacity dewatering nip, for example in 21~8728 the form of a long nip press, since because of the properties of the long nip press the rewetting of the web of fibrous material as a result of the continuous contact with the felt downstream of the first press nip is compensated. On the other hand, it is of course possible according to the invention to design the previous or one of the previous press nips as a long nip press.
The possibilities of the transfer of the web of fibrous material for further transport to further press units can be used for the passage in press units of various designs; the press unit arrangements cited in the figures are therefore not compulsory.
Figure 7 illustrates a draw-free web guidance in a press section, in which the design of the pick-up roll on a first press unit is carried out in such a way that the latter is especially suitable for the problems of the start-up process, that is to say when the production of a paper machine begins to start up following a preceding standstill and a narrow strip of the still wet paper web is cut out from somewhere upstream of the drying section or at the beginning of the drying section (so-called tail) and this tail is initially fed through the entire drying section. The main part of the still wet paper web is, in contrast, diverted away at the point of separation into a pit underneath the paper machine in order to be converted, by means of stirring with the - 215~7~8 addition of water, once more into a stock suspension which is fed back once more to the stock circulation. This process is described in EP 0 584 492 Al. The so-called tail can be generated here by being already separated by a water jet on the paper machine wire from the remaining paper web just produced. However, said tail can also be cut out at a subsequent location, viewed in the machine direction, by cutting out from the already consolidated paper web. The separation of tail and remaining web is carried out, for example, at a press roll, for example at the central roll of a roll press having three press nips. At this location, the main part of the web - as mentioned above - is diverted into a catching pit, while the tail is transferred on to a suction roll. The suction roll can be equipped with two suction zones. The first of these two suction zones is located at one end of the suction roll, specifically where the tail is guided. This first suction zone is as narrow as the tail itself. The second suction zone extends over the remaining part of the suction roll width. In this arrangement, the first suction zone has vacuum applied to it first, in order to transfer the tail from the previous press roll to said suction roll. As soon as the tail has passed through the entire paper machine, the tip cutter is moved transversely to the running direction of the paper web, specifically in the direction in which the tail is continuously broadened, until 215~2~
the complete web width is reached. Vacuum must already be applied to the second suction zone at the beginning of this process, in order to seize the broadening web and to transfer it to the suction roll. However, in this process the following problem occurs: already from the first instant of making the web wider (= beginning of the movement of the tip cutter transversely to the running direction), the complete vacuum must be applied to the second suction zone. At this time, however, the perforations of the second suction zone are not yet covered by the web. This means that immense quantities of air must be sucked through the perforations, with the result that the energy consumption for applying the vacuum is very large. Accordingly, the vacuum pump must also be dimensioned to be correspondingly large.
Figure 7 shows a section from a paper machine, prefer-ably a section from a wire section and a subsequent press section, having a suction roll picking up the web of fibrous material at the first press unit and having an adjustable suction zone width corresponding to the increase of the tail width.
The wire section 40 comprises a wire 41. The wire section 40 has a row of built-in parts, for example a suction means 42, deflection rolls 43 and 44. A water jet nozzle 45 directs a water jet against the paper web which is in the course of production, in order to cut out herefrom a narrow 21~872~
strip, the so-called tail, at the beginning of starting up the paper machine. The wire section is followed by a press section. The latter has a plurality of press felts, for example the felt F1, which wraps around a pick-up roll 46, and which picks up the paper web (or the tail) from the wire 41. The pick-up roll 46 is followed by a first press unit 1 having press rolls 4.5 and 5.5. The first press unit 1 is followed by a second press unit 3 having the press rolls 47 and 48. Both the press units are designed as long nip presses and the press rolls 5.5 and 48 are designed as shoe rolls.
As already explained, in the case of conventional installations there is the following problem: if the tail is being fed, it must be picked up at the suction roll. The suction roll in the case of conventional installations is therefore divided into a first suction zone for the tail and into a second suction zone for the main part of the paper web. At the beginning of broadening the paper web, the second suction zone is still not covered, but vacuum must already be applied to this second zone, energy being lost - as mentioned above - or great quantities of air having to be sucked through the perforations of the second zone.
Hence, it is to be recommended to configure in accordance with the invention all those suction rolls in which there is a risk that the said disadvantages occur during feeding of the paper web, in the figure this is in 215872~
particular the pick-up roll 6.6.
Furthermore, the following combination of the definitive elements can be seen from Figure 7: the water jet nozzle 45 has a drive 54 assigned to it. Likewise, a drive 55 is assigned to the adjustment device for varying the sucked width in the suction roll 6.6. A switch 56 is provided which serves for the purpose of driving the two drives 54 and 55 simultaneously. The drives 54 and 55 are connected to each other via electric lines 57, 58. Furthermore, an actuating device 59 for varying the control signal in line 58 relative to the control signal in line 57 is provided. The result achieved is that the two drives 54 and 55 have one and the same speed.
Finally, a delay unit 60 is provided. This has the effect, if required, that the drive 55 starts later than the drive 54, to be specific by the time interval ~t.
The value of ~t depends on the machine speed, and in addition on the distance which is covered by the web between the water jet nozzle 45 and the suction roll 6.6.
The suction roll 6.6 is shown in Figure 8. Said roll has, on the front side, a vacuum connection 61 and a sealing plate 62, perpendicular to its axis, in its internal space.
The sealing plate 62 can be moved in the longitudinal direction of the suction roll by means of a threaded spindle 63 which can be rotated about its own axis. During the moving
- 2 15 ~
of the sealing plate 62 in the figure from left to right, the roll width X to which vacuum is applied is increased and the roll width Y to which suction is not applied is decreased to the same extent. This is carried out once more at the same time and to the same extent as the water jet nozzle moves transversely to the paper web in accordance with Figure 7.
Figures 9a to 9c likewise illustrate a draw-free web transfer from a first press nip I to a further press nip III
which is designed as a long nip press, in this case a stationary suction box 67 being provided to support the web guidance and picking up the felt F1 from the cover of the central roll 4.6 of the first press unit 1. The stationary suction box 67, as shown in Figures 9b and 9c, is subdivided into a plurality of suction zones Z1, Z2 and Z3, at least one of the contact pressure elements 68-71, according to the invention, being suspended resiliently on the felt.
Furthermore, Figure 9b shows a possible arrangement of a spray pipe S for cleaning the felt or for separating the paper web from the felt F1 if a transfer of the paper web into the broke pit is desired.
According to the invention it is essential that, adjacent to the draw-free web transfer between two press units, the second press unit is designed as a long nip press since, because of the properties of the long nip press, the rewetting of the web as a result of the continuous contact of 215~8 the felt downstream of the first press nip is compensated. On the other hand, it is of course possible according to the invention to design the preceding or one of the preceding press nips as a long nip press.
In conclusion, it is established that the advantages of the invention described are:
- closed web guidance and thus avoidance of any extension of the web;
- no paper draw for separating the web from a smooth press roll and, as a result, no expansion of the paper web, no loss of strength and the maintenance of a greater elasticity of the paper web;
- reduction of web breaks in continuous operation;
- high dryness content;
- high dryness content even in the case of rewetting after passing through the first press nip.
of the sealing plate 62 in the figure from left to right, the roll width X to which vacuum is applied is increased and the roll width Y to which suction is not applied is decreased to the same extent. This is carried out once more at the same time and to the same extent as the water jet nozzle moves transversely to the paper web in accordance with Figure 7.
Figures 9a to 9c likewise illustrate a draw-free web transfer from a first press nip I to a further press nip III
which is designed as a long nip press, in this case a stationary suction box 67 being provided to support the web guidance and picking up the felt F1 from the cover of the central roll 4.6 of the first press unit 1. The stationary suction box 67, as shown in Figures 9b and 9c, is subdivided into a plurality of suction zones Z1, Z2 and Z3, at least one of the contact pressure elements 68-71, according to the invention, being suspended resiliently on the felt.
Furthermore, Figure 9b shows a possible arrangement of a spray pipe S for cleaning the felt or for separating the paper web from the felt F1 if a transfer of the paper web into the broke pit is desired.
According to the invention it is essential that, adjacent to the draw-free web transfer between two press units, the second press unit is designed as a long nip press since, because of the properties of the long nip press, the rewetting of the web as a result of the continuous contact of 215~8 the felt downstream of the first press nip is compensated. On the other hand, it is of course possible according to the invention to design the preceding or one of the preceding press nips as a long nip press.
In conclusion, it is established that the advantages of the invention described are:
- closed web guidance and thus avoidance of any extension of the web;
- no paper draw for separating the web from a smooth press roll and, as a result, no expansion of the paper web, no loss of strength and the maintenance of a greater elasticity of the paper web;
- reduction of web breaks in continuous operation;
- high dryness content;
- high dryness content even in the case of rewetting after passing through the first press nip.
Claims (18)
original claim 1 changed; all further claims unchanged (4 pages)]
1. A press section in a machine for the production of webs of fibrous material, preferably paper webs, having the following features:
a) a rotating stiff roll cover forms, with a first mating roll (or with a press belt running over a shoe), a first press nip and, with a second mating roll, a second press nip;
b) an endless, water-absorbent felt runs together with the web of fibrous material in turn through the first press nip, then over part of the circumference of the roll cover along to the second press nip and through the latter, the felt coming into contact with the second mating roll;
c) the second mating roll is designed as a pick-up roll having an internal stationary seal support that forms a suction zone that lies at least for the most part downstream of the second press nip;
d) a second endless felt takes over the web of fibrous material from the first felt;
which comprises the following feature:
e) the second endless felt guides the web of fibrous material through a third press nip which is designed as a high-capacity dewatering nip.
a) a rotating stiff roll cover forms, with a first mating roll (or with a press belt running over a shoe), a first press nip and, with a second mating roll, a second press nip;
b) an endless, water-absorbent felt runs together with the web of fibrous material in turn through the first press nip, then over part of the circumference of the roll cover along to the second press nip and through the latter, the felt coming into contact with the second mating roll;
c) the second mating roll is designed as a pick-up roll having an internal stationary seal support that forms a suction zone that lies at least for the most part downstream of the second press nip;
d) a second endless felt takes over the web of fibrous material from the first felt;
which comprises the following feature:
e) the second endless felt guides the web of fibrous material through a third press nip which is designed as a high-capacity dewatering nip.
2. The press section as claimed in claim 1, wherein the third press nip, to which said second felt is assigned, is part of a long nip press.
3. The press section as claimed in claim 2, wherein said second felt is the only felt of the long nip press.
4. The press section as claimed in one of claims 2 or 3, wherein the long nip press has a shoe press unit located inside the loop of the second felt and a smooth press roll which is contacted by the web of fibrous material.
5. The press section as claimed in one of claims 1 to 4, wherein the second felt wraps around the pick-up roll over part of its circumference in the wrap-around region of the first felt with the pick-up roll.
6. The press section as claimed in claim 5, wherein the pick-up roll has a suction zone acting in the direction of the rotating body forming a ring and a blast zone in the direction of the second felt belt.
7. The press section as claimed in claim 5, which comprises the following features:
7.1 the pick-up roll is arranged downstream, in the running direction of the web of fibrous material, of a felt guide roll for the first felt belt;
7.2 the felt guide roll is designed as a blow roll;
7.3 the second felt belt wraps around the felt guide roll over part of its circumference in the wrap-around region of the first felt belt with the felt guide roll.
7.1 the pick-up roll is arranged downstream, in the running direction of the web of fibrous material, of a felt guide roll for the first felt belt;
7.2 the felt guide roll is designed as a blow roll;
7.3 the second felt belt wraps around the felt guide roll over part of its circumference in the wrap-around region of the first felt belt with the felt guide roll.
8. The press section as claimed in one of claims 1 to 7, wherein the rotating body forming a ring represents a rotating press belt.
9. The press section as claimed in one of claims 1 to 7, wherein the rotating body forming a ring is designed as a granite roll.
10. The press section as claimed in one of claims 1 to 7, wherein the rotating body forming a ring is designed as a roll with a smooth surface.
11. The press section as claimed in claim 10, wherein said suction roll is pivotably supported and can be pressed against the smooth roll (which forms the two press nips) or can be lifted away from the latter.
12. The press section as claimed in one of claims 1 to 11, wherein, at the exit from the first press nip (I) in the region of each of the two edges of the web of fibrous material, there is arranged a blast nozzle which presses the edges of the web of fibrous material on to the felt belt at the exit from the press nip.
13. The press section as claimed in claim 12, wherein the blast nozzle can be moved from a working position, which is located in the vicinity of the first press nip (I), into a remote resting position and back again.
14. The press section as claimed in one of claims 1 to 13, wherein the second felt belt picks up the web of fibrous material from the first felt belt by means of a second suction roll.
15. The press section as claimed in claim 14, wherein there is only a small distance (of the order of magnitude of 50 mm) between the roll covers of the two suction rolls.
16. The press section as claimed in one of claims 1 to 14, which comprises the following features:
16.1 a further, third endless felt belt is provided;
16.2 the web of fibrous material, together with the first felt belt and the third felt belt, is guided through the first and second press nip;
16.3 the third felt belt is guided away from the pick-up roll in the region of the second press nip.
16.1 a further, third endless felt belt is provided;
16.2 the web of fibrous material, together with the first felt belt and the third felt belt, is guided through the first and second press nip;
16.3 the third felt belt is guided away from the pick-up roll in the region of the second press nip.
17. The press section as claimed in one of claims 1 to 16, wherein the suction zones of the first and/or second suction roll can be variably adjusted in terms of their width over the machine width.
18. A press section in a machine for the production of webs of fibrous material, preferably paper webs, having the following features:
a) a rotating body (cover) forming a ring forms with a first mating roll (or with a press belt running over a shoe) a first press nip;
b) an endless, water-absorbing felt runs together with the web of fibrous material through the press nip;
d) a second endless felt takes over the web of fibrous material from the first felt;
which comprises the following features:
c) the rotating body forming a ring is assigned downstream, seen in the running direction of the web of fibrous material, of the first press nip of a pick-up device having an internal stationary seal support that forms a suction zone that lies at least for the most part downstream of the second press nip;
e) the second endless felt guides the web of fibrous material through a further press nip which is designed as a high-capacity dewatering nip.
a) a rotating body (cover) forming a ring forms with a first mating roll (or with a press belt running over a shoe) a first press nip;
b) an endless, water-absorbing felt runs together with the web of fibrous material through the press nip;
d) a second endless felt takes over the web of fibrous material from the first felt;
which comprises the following features:
c) the rotating body forming a ring is assigned downstream, seen in the running direction of the web of fibrous material, of the first press nip of a pick-up device having an internal stationary seal support that forms a suction zone that lies at least for the most part downstream of the second press nip;
e) the second endless felt guides the web of fibrous material through a further press nip which is designed as a high-capacity dewatering nip.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4401519.4 | 1994-01-20 | ||
| DE19944401519 DE4401519A1 (en) | 1994-01-20 | 1994-01-20 | Wet press section is for paper machine - and has a second continuous felt that takes over paper from first felt |
| DEP4402629.3 | 1994-01-31 | ||
| DE19944402629 DE4402629A1 (en) | 1994-01-31 | 1994-01-31 | Papermaking machine press section |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2158728A1 true CA2158728A1 (en) | 1995-07-27 |
Family
ID=25933144
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002158728A Abandoned CA2158728A1 (en) | 1994-01-20 | 1995-01-19 | Traction-free web transport in a compression section |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0689627A1 (en) |
| JP (1) | JPH08509274A (en) |
| CA (1) | CA2158728A1 (en) |
| FI (1) | FI954412A (en) |
| WO (1) | WO1995020068A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19654325A1 (en) * | 1996-12-24 | 1998-06-25 | Voith Sulzer Papiermasch Gmbh | Press section of a paper-making machine |
| DE19713645A1 (en) * | 1997-04-02 | 1998-10-08 | Voith Sulzer Papiermasch Gmbh | Papermaking machine web transfer |
| DE19741425B4 (en) * | 1997-09-19 | 2007-04-19 | Voith Patent Gmbh | roll press |
| DE102009029686A1 (en) | 2009-09-23 | 2011-04-07 | Voith Patent Gmbh | Stabilizing device for guiding a fibrous web and drying device with such a stabilizing device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4026021C2 (en) * | 1990-08-17 | 1995-10-12 | Voith Gmbh J M | Press section of a paper machine |
| DE4401519A1 (en) * | 1994-01-20 | 1994-06-16 | Voith Gmbh J M | Wet press section is for paper machine - and has a second continuous felt that takes over paper from first felt |
| DE4402629A1 (en) * | 1994-01-31 | 1994-07-14 | Voith Gmbh J M | Papermaking machine press section |
-
1995
- 1995-01-19 JP JP7519341A patent/JPH08509274A/en active Pending
- 1995-01-19 WO PCT/EP1995/000196 patent/WO1995020068A1/en not_active Application Discontinuation
- 1995-01-19 EP EP95908208A patent/EP0689627A1/en not_active Withdrawn
- 1995-01-19 CA CA002158728A patent/CA2158728A1/en not_active Abandoned
- 1995-09-19 FI FI954412A patent/FI954412A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FI954412A0 (en) | 1995-09-19 |
| EP0689627A1 (en) | 1996-01-03 |
| JPH08509274A (en) | 1996-10-01 |
| WO1995020068A1 (en) | 1995-07-27 |
| FI954412A (en) | 1995-09-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19980120 |