DE3324408A1 - Process and equipment for the press treatment of a fibrous material web, in particular a paper web or cardboard web - Google Patents

Abstract

In a process and equipment for the press treatment of a paper web and cardboard web, a press nip formed by two press rollers being used, through which the web to be dried by pressing is passed, borne by one or two cloths. In addition, an elastic press carpet, which is substantially thicker than the said press cloths, or a plurality of part carpets is passed through the press nip. The material and/or the structure of the said press carpet is chosen such that, due to hysteresis, such a delay for the restoration, taking place after the centre line of the press nip, to the previous thickness of the said carpet is obtained that the press force in the nip, compared with the distribution of the symmetrical nip force, decreases relatively steeply. Owing to the said delay after the centre line of the nip, the cloth or the press cloths can be taken off as quickly as possible, so that renewed moisture absorption of the web is substantially reduced. The press carpet is pressed at the centre line of the nip to a thickness which amounts to about 30...90% of the normal unpressed thickness of the said press carpet. In the unpressed state, the thickness of the press carpet is, for example, 8...20 mm. The press carpet is made of plastic material and/or rubber material, which was selected with allowance for the abovementioned hysteresis. The carpet has reinforcements or other appropriate constructions which increase the strength.

Description

- Gräms - StfIuif

Valmet Oy Helsinki / Finland Dipl.-Ing. H. Tiedtke Dipl.-Chem. G. Bühling Dipl -Ing. R. Kinne Dipl.-ing R Group Dipl.-Ing. B. Pellmann Dipl.-Ing. K. Grams Dipl.-Chem. Dr. B struif

Bavariaring 4, Postfach 8000 Munich 2 Tel .: 089-5396 Telex: 5-24 845 tipat Telecopier: 0 89-537377 cable: Germaniapatent Münc July 6, 1983

DE 3145

case FI 822425

Method and device

for the press treatment of a fibrous web, especially paper or cardboard web

d "!? 'Ba ^ k iMu-che'- KIo 3939 6«

iMuncher KIO 508 94t (Munich »KIc 670-13-βΟ4

description

The invention relates to a method for the press treatment of a fibrous web, in particular paper or Cardboard web, in a soft process one of two press rollers Formed pressboard is used, through which the web to be dried by pressing is carried by a cloth or is passed between two cloths and through which also an elastic press carpet, which is much thicker is as mentioned press cloths, or several partial carpets out we r d e η.

The invention also relates to a pressing device to carry out the method according to the invention, which consists of two the press nip forming press rolls, one of which is expediently a roll provided with a smooth surface and the second expediently one with a height 1 profiled surface provided roller is, and which continues to consist of an or consists of several press cloths, which through said press nip

0 are performed _; and that continues from one

There is a press carpet which is passed through said press nip and is much thicker than said press cloths.

The most common type of drainage known to date of fibrous webs, in particular of paper and

Cardboard webs, takes place in that the web through one out two opposing 1 lying rollers existing press nip out will. As is known, in the drainage crevices used a press cloth or two to get this off track Remove removed water and serve as a rail transport sheet.

When increasing the production speed of Paper machines formed the one designed as a hot press Drainage the crucial bottleneck, which is the speed limited. This is because the area of the a pair of rollers formed press nips is short, so that the dwell time of the web at high speeds in these Press gaps is only small. However, the railway drainage is increasing especially because of the flow resistance of the fiber structure the railway takes a certain amount of time for the Water from the web to the hollow profiled surface of the roller or can step over the presscloth.

As is known, there were several consecutive Press nips used, either so-called compact press sections, what the "Sym-Press" (trademark) press section of the Applicant or several separate successive press nips Examples are. However, press nips require a relatively large space, especially if consecutive Press nips are used. A compact construction of the press sections in turn brings difficulties in the optimal arrangement of the individual parts and in operation z. B. when removing paper scrap with itself. In Nip presses are generally used for suction rolls are relatively expensive components and consume suction energy. Perforated jackets must be used in suction rolls, which have problems with the mechanical durability of the Cause rolling.

When the dewatering performance of gap presses

should be increased by increasing the press nip pressure, with a certain line pressure you come to a limit where the increase in the nip pressure no longer brings in anything, because the web structure can no longer withstand the pressure.

The extension of the nip of the nips can through the use of rollers of larger diameter and are sought after by soft press cloths, but here too one quickly reaches the limits of economic efficiency.

Because of the problems described above and for other reasons, so-called extended-nip presses have recently become available invented. Examples of this are given to the U.S. Patents 3,808,092, 3,808,096, 3,840,429, 3,970,515, 4 201 624 and 4 229 253 and GB application 20 57 027 note.

So far known are formed from a pair of rollers Presses, in which it was sought, the gap zone by elastic, z. B. to extend existing rubber roller coverings. The construction of a press of this type is simple, but the press nip is even with large rolls and moderate pressures of the pads not very long. Another disadvantage is that elastic coverings are deformed heat. This has led to this lately from rollers with rubber coating to rollers with polyurethane coating was passed over, in which the losses are lower and the damping constant is smaller than before. As an an example for a press in which a roller with an elastic covering is used reference is made to U.S. Patent No. 3,535,760 (The Polymer Corporation).

In addition, it is known in the above-mentioned rollers with an elastic covering to increase their elasticity different grooves and similar heights

To use constructions. In this regard, as See, for example, U.S. Patent No. 3,630,837 (Glupac Inc.).

It is also known to guide an elastic carpet, which extends the gap, through the gap.

In the presses mentioned, in which an elastic roller or an elastic pair of rollers or an elastic TeDpich is used However, it was already able to do so in traditional splitting presses Occurring disadvantage of the rebellion with you (rewettina) not eliminated will. This phenomenon is detailed below described. E.g. causes a time of about 20 ms in the middle zone of the press nip, where the press pressure is a falls below a certain limit, already an approx. 30% Re-humidification. This effect is a major disadvantage, the drainage ability even of press nips with wide press zones.

The object of the present invention is to provide a method and to provide a device with which the im the disadvantages mentioned above can be avoided. In particular, the invention is intended to provide a long-nip press, i.e. H. one Create press provided with an extended press zone in which the above-mentioned rewetting does not or at least not to a disadvantageous extent. We i terh i η The invention is intended to provide a press that is in construction is simple and reliable.

In order to achieve the objectives described above and which will become clear further below, the inventive Procedure essentially characteristic, that the material and / or the structure of said press carpet is chosen such that due to hysteresis for behind the center line of the press gap

gang to the previous thickness of said carpet such a delay is achieved that the pressure in the Gap, compared with the distribution of the syrrme t r ι see gap pressure drops relatively steeply and that the cloth or, thanks to the delay mentioned, remove the press cloths as quickly as possible behind the center line of the gap let re-illumination of the web be essential is r i nger t.

For the pressing device according to the invention is in turn mainly characteristic of the press carpet mentioned from an elastic carpet or an elastic There is a web, the material of which is chosen such that that behind the center line formed by said rollers Rough elastic return to the previous state of the carpet due to hysteresis to a suitable extent is delayed so that the Bahn is prevented.

The method and apparatus of the invention are based on the use of a special, relatively thick and elastic press carpet or a corresponding web. The material for this carpet is chosen so that it has a particularly large hysteresis, which means that the Deformations of the carpet, d. H. in this case changes the thickness, decrease relatively slowly behind the crevice zone. This ensures that the web can be removed from one or more felts quickly and in such a way that that the area in which rewetting could take place, stays very short.

In the invention, the heating of one or more press carpets does not cause an insurmountable problem, since the loops of the carpets are relatively long and, if necessary, special cooling

Devices such as bladder, water nozzle or water basin systems, can be arranged with which one or more carpets can be cooled.

That in the method and apparatus of the invention special press carpet used can be grooved, Layers of air or other equivalent devices be provided that the deformability and elasticity of the carpet. The carpet material leaves also complement each other with various reinforcement fabrics.

The inventive idea deviates from the usual Ways of thinking to the extent that the elastic roller coverings have recently been specifically chosen so that their Hysteresis and losses are as low as possible, and for this purpose Gurrmi is already laying I ices on polyurethane coverings is passed over for press rolls.

The following are the starting point of the invention Applicable prior art and some embodiments shown in the figures of the accompanying drawings of the invention described in detail.

Fig. A illustrates a double 1fι 1 ζ spa Itpres se according to the state of the art and their pressing

distribution.

Figure B illustrates a known double felt press and their pressure distribution to widen the gap a ver

relatively thick, elastic press belt is used.

Fig. 1 shows a method according to the invention corresponding press and its compression

division.

Fig. 2 shows a press roll according to the invention

combination in side view.

3A, 3B, 3C and 3D show alternative embodiments for the one in the invention

used press carpet.

In Fig. A is a known double 1fi 1 ζ-Preßspa1t and its pressure distribution is shown. The gap will see between one with a height of 1 profiled surface 10 'provided Upper roller 10 and a smooth lower roller 11 are formed. The web W is supported by felt 12 and guided into the gap water between felts 12 and 13. The web W is removed from the felts 12 and 13 as immediately as possible behind the gap. According to the one shown in picture A below The curve is the pressure P to the center line K-K of the gap essentially so symmetrical that the pressure behaves from the starting point A of the gap to the center line K. increases steeply, after which the pressing pressure drops accordingly towards the end point C of the gap. In practice the pressure is not quite synmetrical to the center line K-K despite the use of felts 12 and 13. The press board area A-C remains relatively narrow. That's why the Water withdrawn from web W does not have enough time on the felts 12 and 13 to convert. A second disadvantage is the so-called Re-moistening that takes place in the cleavage zone B-C. In said Zone B-C both the web W and the felts 12, 13 expand and go under the influence of capital forces the water from the felt or felts 12, 13 over to web W, since the pores of the paper are smaller than those of the felts 12, 13 are. The re-illumination of the paper web W is all the more the smaller the narrower the gap, the greater the machine speed and the smaller the differences in pore sizes of web W and felts 12, 13 are. The rewetting is a particularly great night ι 1 for thin,

finely ground types of paper. To prevent rewetting was done so that the web W and the felts 12, 13 after the nip as immediately as possible from each other can be removed, but this also made it impossible to completely avoid re-illumination.

FIG. B shows a known widened press nip formed from the pair of rollers 11 and 11, which, compared to the press according to FIG. As can be seen from the curve of FIG. B, which shows the pressure distribution of the gap, the gap could be widened significantly by the cloth 14 in comparison to the gap in FIG. In Fig. B the gap area extends over the distance AC. A gap which is completely symmetrical with respect to the center line KK and which would extend to point D is shown by the dashed line P ^1. In practice, cloth is so slow, so to speak, that it does not quite happen to expand behind the middle II ι never KK at the same speed as the gap between the rollers 10 and 11 and the felts do, so that the gap pressure behind the Center line KK drops slightly more steeply than the curve P ¹ presupposes. In this known press, the re-moistening of the web described above takes place in the area BC. The invention described below provides a simple solution to this problem.

In Figs. 1 and 2, one embodiment is this Invention shown. According to the method according to the invention the paper web W is guided through an extended press nip between a surface with a higher profile 10 'provided upper roller 10 and a smooth lower roller 11 is formed. Web W is carried by felt 12 to the nip guided. Web W runs through the gap between two felts 12 and 13. The felts 12 and 13 can be commonly known ones

3 -S · <

- 13 -

Be pressfi.lze. Immediately behind the gap, the BaHr. W. removed from both felts 12 and 13, e.g. B. such that the acceptance angles and B are essentially the same size. This helps to ensure that the above-described Re-wetting is avoided. On the top roller 10 a catcher 16 and a Sarrme 1 basin 15 are attached, with those of the hollow profiled surface 10 'from f 1 i eating water se r ge sarrme 1 t wi rd.

It is found to widen the gap between the felt 13 and roller 11 a special, yielding and elastic carpet or ein.Bahn 20 carried out whose Material is deliberately chosen so that the elastic Decline somewhat delayed due to hysteresis. As a result, paper web W and felts 12, 13 can be almost immediately behind the center line K-K can be removed from each other and can in this way the remoistening described above the web W can be prevented. This advantage is illustrated by the pressure distribution curve according to FIG. Before the gap center K, d. H. in the area A-K, the pressure increase is essentially the same as that of the known press nip according to Fig. B. Behind the gap center K, the gap pressure falls due to the sufficiently large deceleration of the elastic The decline of the special carpet 20 is very steep.

In the pressure curve according to FIG. 1, a curve P ^{1 is} shown in dash-dotted lines, which represents a symmetrical gap pressure which would extend to point D. In the gap according to the invention, the re-humidification can only occur in the short area BC. The re-moistening of the web W is thus decisively reduced by the invention.

In Fig. 2, the thickness of the cloth in the normal uncompressed state is denoted by Sj. In the middle of the gap formed by the rollers 10 and 11, the carpet 20 is _{pressed to the thickness S 2} , which dimension z. B. is approx. 30 ... 90% of Sj.

He I indungsgemäß the gap unsymmetrically such that the length is greater 5mA 1 AK of the gap in front of the center line (KK) about 2 ... as the gap length KC behind the center line. The thickness Sj of the carpet 20 is generally & ... 20 cubic meters. The normal thickness of the felts 12 and 13 is approx. 2 ... U mm and the felts are compressed in the gap in the direction of the thickness by approx. 1 mm.

Behind the center line KK of the gap, thanks to the special structure and / or the special material of the carpet 20, the thickness of the carpet 20 essentially only goes back _{to its original dimension at a distance l o} from the center line KK of the gap. A gap is thus achieved which is asymmetrical in the manner of the pressure curve of FIG. 1 and in which the pressure behind the center line KK is very ste i1.

In the known press according to FIG. A, the length of the gap is generally approx. 20 ... 50 mn. According to the invention reaches the length A-C of the gap when using ordinary diameters of the rollers 10 and 11 one size from approx. 100 rrm.

The following briefly describes the theoretical background to the behavior of the press carpet 20 and the hysteresis described. For the deformation ε after a time t, νiskoe1 is an astic material whose retardation λ is the following formula:

ε - E

ε = 2 ₍ Γ- e " ^{t / X} ) (I)

The following formula applies to the deformation c after a time t:

ι ε = ε ₎ + ε ₂ + ε ₃ (2)

in which Cj = elastic deformation = σ / Ej

^Z 2 ~ viscous deformation = σ _t / ri ^

σ 2 "

ε3 = delayed elastic deformation = - (I - e)

Equations (1) and (2) are the behavior model of so-called burger material, which corresponds to the behavior of the most common types of rubber. In the models shown, the terms λ and Ε2 / Π correspond to the sub-tangent of the exponential deformation, in this case the decrease in carpet 20 from thickness S2 to thickness Sj. With the designations from FIG. 2, l _o = v _o · t _o , where v _{o is} the speed of carpet 20 and web W and t _{o is} the time taken by the stretching distance l _o . Here, t ₀ = N. · Λ, where N is approximately 1.5 ... 3.

Referring now to Figures 3A-3D some embodiments of the carpet according to the invention 20 described. As I said, the thickness of the carpet is Sj usually 8 ... 20 rrm. According to Fig. 3A, the carpet 2OA reinforcing fabric 23. The side of the carpet 20 lying on the felt 13 is denoted by reference numeral 21 and that on the smooth surface of roller 11 overlapping side with reference numerals 22 designated. Located on side 22 of the carpet grooves 24 which are rectangular in cross section and which Allow deformation of the carpet as well as increase the elasticity of the carpet 20A.

According to Fig. 3B, carpet 20B has reinforcement fabric 23, the z. E}. made of plastic or metal. On the website 22 of the carpet 20B are grooves with substantially wedge-shaped cross section, which is described in the

serve a purpose. According to Fig. 3C, the carpet 2OC has called reinforcing fabrics 23. On the side 21 of carpet 2OC, d. H. on the side of felt 13, are relatively close to each other, parallel to the direction of travel of the Carpet running grooves 26 and on the opposite Page 22 further apart, much wider Grooves 27. The purpose of both grooves 26 and 27 is deformability and to increase the elasticity of the carpet.

According to Fig. 3D, the carpet has 2OD on the side 21,

the one on Filz 13anlieat, one with a dense one Reinforcement 23 provided layer 28. On the opposite Side of the carpet is a layer 29 that has a dense surface layer 31 lying on the surface of roller 11, followed by a layer, the air cells 30 has. These lines 30 ensure sufficient elasticity and deformability in the carpet 2OD.

For all carpets described above 2OA, 2OB, 2OC and 2OD the main material was chosen such that the above-mentioned decline time λ, the loss factor and the attenuation constant of the carpet compared to the corresponding tapes previously used for this purpose or carpets are larger on average to achieve the aforesaid hysteresis-based retardation.

As a material for the carpet 20 according to the invention may or may be rubber, or some other suitable elastomer Sandwich structures from it are used, as well 3A-3D grooves or other speci a 1einrichturigen to have.

Since the loss coefficient of the materials of the invention Carpet 20 is relatively large, he

If the carpet 20 hits the repeated run through the Press gap. However, this does not cause any in the invention Problems such as B. in known roller coverings because it a relatively long time is possible for the carpet 20 Arrange loop so that it cools down this way. In addition, special cooling systems, such as. B. Water nozzle devices or pools of water through which the carpet is passed for cooling purposes. Farther Instead of one carpet 20, two or more layers can be placed on top of one another Partial carpets are used, which increases the cooling surface. When using several partial carpets the material and / or the structure of each individual carpet can be selected so differently that one within the meaning of the invention the best possible end result is achieved.

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Claims (1)

TeDTKE - BOHUN0>: Kl M / dU ^ SSfJS If Pellmann - GffAMS -; $ rRuiF- ^: --- ^: SSS ^ HSn ₁ , Dipl.-Ing. R. Kinne 3324408 "Dipl.-Ing P Grupe Dipl.-Ing. B. Pellmann Dipl.-Ing. K. Grams Dipl.-Chem. Dr B. Struif Bavariaring 4. P.O. Box 8000 Munich 2 Tel .: 0 89-53 9653 Telex: 5-24 845 tipat Telecopier: 0 89-537377 cable: Germaniapatent Mür July 6, 1983 DE 3145 case FI822425 Claims !. ^ Process for the press treatment of a fibrous web, in "s ~ t3e special paper or cardboard web (W), in which process a press nip formed from two press rolls (10, 11) is used, through which the web to be dried by pressing (W ) is carried by a cloth or guided between two cloths (12, 13), and through which an elastic press carpet (20), which is considerably thicker than the said press cloths, or several partial carpets are guided, characterized in that the material and / or the structure of said press carpet (20) is chosen such that due to hysteresis for the decrease to the previous thickness of said carpet behind the center line (KK) of the press nip, such a delay is achieved that the press pressure in the nip, compared with the distribution (P ¹ ) of the syrrmet ri see Spaltdrukkes, drops relatively steeply and that the cloth or the press cloths (12, 13) thanks to said delay behind the center line Let the gap (KK) decrease as quickly as possible in such a way that renewed moisture absorption of the web is significantly reduced. 2. The method according to claim 1, characterized in that that the said press carpet is on the center line (K-K) of the gap is pressed to a thickness (S2) that is approx. 30 ... 90% of the normal uncompressed thickness (Sj) of said one Press carpet. 3. The method according to claim 1 or 2, characterized in that shows that the web is guided between two press cloths (12, 13) through a press nip and essentially immediately behind the center line (K-K) of the gap between the two press cloths (12, 13) in Angles (α, 8) are taken, which are essentially the same big s i nd. k. Apparatus for carrying out the method according to Claims 1 to 3, consisting of two presses forming the press nip rolls, of which one expediently a roller (Ii) provided with a smooth surface and the second expediently a roller (10) provided ^{with a higher profile surface (10 1} ) is ty the "furthermore one or more press cloths (12, 13) includes 1 through said press nip be led and continue to be one Has a press carpet (20) which is passed through the said press nip and is significantly thicker than the said press cloths (12, 13), characterized in that said press blanket Pressed carpet made of an elastic carpet or an elasti see web, the material is chosen such that the elastic decline occurring behind the center line (K-K) of the gap formed by said rollers (10, 11) in the previous state of the carpet as a result of hysteresis is delayed to a suitable extent, so that a renewed damp tigkeitsaufnähme the web is prevented. 5. Pressing device according to claim 4, characterized in that the thickness (Sp of said press belt (20) in the uncompressed state is 8 ... 20 nrm. 35 6. Pressing device according to claim k or 5, characterized marked that they have two press cloths (12, 13) comprises _t between which the web (W) is guided through the press nip, and that said press carpet (20) is arranged between one of the press blankets (13) and a press roll (11) provided with a smooth surface and that the The second press roll is a press roll (10) provided with a higher profile surface (10 '). 7. Pressing device according to one of claims 4 to 6, characterized in that the press carpet (20) made of plastic and / or rubber material i a I is made, taking into account the aforementioned hysteresis effect was chosen and that said carpet reinforcements (23) or other equivalent, increasing its strength Has constructions. 8. Pressing device according to one of claims 4 to 7, characterized in that one or both sides of said press carpet have grooves (2k; 25; 26, 27) which improve the elasticity and deformability of said press carpet (20A, 2OB, 20C) increase. • 9. Pressing device according to one of claims 4 to 7, characterized characterized in that said press carpet (20D) has air cells (30), which give the carpet sufficient elasticity and sufficient deformability. 10. Pressing device according to one of claims 4 to 9, characterized in that on the loop of the press carpet (20) or several partial carpets cooling devices are arranged, such as B. air bubble, water nozzle and / or water basin devices through which the press carpet (20) or the Tei1 carpets for the purpose of cooling. 35