The invention relates to a method for manufacturing multi-ply web, presented in the preamble portion of Claim 1, as well as to an apparatus for accomplishing the method, presented in the preamble portion of Claim 10.

Bonding power between various layers has been a problem in the multi-ply web manufacture. The problem is aggravated when a web with a poor fine substances content is run, because the fine substances contribute to the bonding of the layers to each other, and further when such machine constructions are used where the webs are joined together to form a multi-ply product after the dry lines of the individual webs. For improving the peeling strength, various solutions have been developed, among which starch sprays, feed of fine substances between the layers, adjustment of the dry matter content of various layers to an optimum value before the combining of the webs, use of a reinforcing stock, as well as increasing the beating degree of the stocks used in webs can be mentioned as examples.

The influence of the starch sprays on the peeling is significant, but the solution is economically expen¬ sive and requires additional equipment. Further, the solution causes soiling problems. Also the feed of fine substances between the layers requires additional equipment. The optimization of the dry matter content of various layers requires precise dewatering control within the dewatering zone situated before the joining point of the webs. The feed of fine substances requires for its part a separate headbox of its own with respective pipes of circulation resulting to a compli¬ cated and expensive solution. The beating of the stock helps to increase the amount of the fine

substances, but on the other hand, the physical properties of a finished sheet will be inferior. Further, increased beating leads to increased energy consumption.

Swedish publication laid open to public inspection No. 394,700 ( atanabe) discloses further a method and device for forming a multi-ply product wherein a second layer is brought on top of a first layer travel- ling on a transport felt by means of an open roll and wire wrapping it. After the wire and transport felt have passed with the joined web layers therebetween round the open roll within a certain sector, they are transferred onto the periphery of another roll opposite to the roll, and soon after the point of transfer, the wire diverges from the top of the web, and the transport felt and the web continue their travel forward guided by the roll. The publication mentions that the latter roll is a press roll. It is apparent that this describes more the structure of the roll than its purpose. At this point the other roll does not have an effect on the dewatering of the web, and even if some pressing were present at this location, the water would be drained quite uniformly on both sides of the web towards the open roll and towards the water-absorbent transport felt.

Further, Finnish application laid open to public inspection No. 71377 discloses a method and apparatus for manufacturing of multi-ply web. In this publica¬ tion, an intermediate layer is formed between the outermost layers of the web by feeding stock of higher consistency from a special high-consistency headbox. The improving of the bonding power according to this traditional method requires thus the feed of stock of a higher consistency and makes consequently the machine construction more complicated.

The purpose of the invention is to provide a new method and an apparatus for accomplishing the method by means of which the peeling strength of a multi-ply product can be improved without increasing energy consumption or without recourse to expensive solution involving additional equipment. For achieving the purpose, the method according to the invention is mainly characterized by what is presented in the characterizing portion of Claim 1. The apparatus according to the invention is characterized by what is presented in the characterizing portion of Claim 10.

The invention is based on the finding that in the couching operat: n of the webs, the fine substances can be caused to move with the water with the help of mechanical pressing, contrary to the effects when only suction is applied. A firm connection can be accomplished without suction and surfaces sweeping the wire.

The solution can be easily realized also in present machine constructions for example by assembling an additional roll with a suitable surface structure beneath a normal open couch roll to form a press nip that urges the fine substances to move between the layers at as early a stage as possible, usually at a dry matter content below 12%.

The invention will be described in the following more closely with reference to the accompanying drawings, wherein

Fig. 1 shows a traditional joining point of the web layers in a paper or cardboard machine in a side view,

Fig. 2 shows the joining point of tne layers in accordance of the invention,

Fig. 2a illustrates the principle of the invention in a larger scale compared with Fig. 2,

Fig. 3 shows the point of Fig. 2 in another operating position,

Fig. 4 shows the point of Fig. 2 in a third operating position,

Fig. 5 shows a joining point according to another modification,

Fig. 6 shows the point of junction according to a third modification,

Fig. 7 shows the entire wire section of a paper or cardboard machine that includes the apparatus according to the invention,

Fig. 8 shows another possible construction of a machine including the apparatus according to the invention,

Fig. 9 shows the joining points of the machine of Fig. 8 in a larger scale, and

Figs. 10 and 11 show some additional devices for improving the bonding power.

Figure 1 shows a traditional apparatus for the manufac¬ ture of a multi-ply cardboard web. On top of a pre- filtered first web Wl lying on a first wire 3 is brought a web W2, also pre-filtered, lying on a second wire 4, in such a manner that the wires 3, 4 are brought against each other by means of a reversing roll 2, which is situated on the side of the second wire 4 and can have an open surface. After the joining point the wires travel with the multi-ply web there-

between to a transfer suction box 5, on which the second wire 4 is separated from the first wire 3. The multi-ply web W formed of both webs Wl, W2 continues its travel forward on the first wire 3. The operation above is the so-called normal couching.

The wires 3, 4 transporting the webs Wl, W2 shall be understood in this context to mean such continuous water-permeable conveyors in which the water-perme- ability is based on their structural openness, that is, they are manufactured of a material that is not water-absorbent per se.

Figure 2 shows an apparatus according to the invention in which an additional roll 1 is placed opposite to the reversing roll 2 at the location where the wires 3, 4 travel together on the periphery of the reversing roll 2 with the web therebetween. The rolls 1 and 2 form therebetween a press nip N which helps to improve the joining of the webs Wl, W2 to form the multi-ply web. By means of the rolls 1 and 2, a desired line pressure can be provided in the press nip N, said pressure being adjustable in a stepless manner, depend¬ ing on the products that are run.

The position of the press nip N caused by the roll 1 with regard to the common run of the wires 3 and 4 on the periphery of the roll can vary. In Fig. 2, the first wire 3, guided by a wire roll 6, is deviated from its usual plane of travel slightly downward before it joins the wire 4, and it joins the _.re 4 travelling on the roll 2 a little bit before the lowermost point of the roll 2, at which point the nip N caused by the additional roll 1 is situated. The rolls are thereby so situated that their axes of rotation are in align¬ ment in a vertical plane. After the nip N, the wires travel again a little bit further on the periphery of the roll 2 and are directed thereafter slightly upward

toward the suction box 5. Figure 3 shows a situation where said nip N is situated after the lowermost point of the roll 2 owing to the fact that the roll 1 is shifted a little bit to the right compared with Fig. 2. Correspondingly, Fig. 4 shows a situation where the nip N caused by the additional roll 1 is situated before the lowermost point of the roll 2 at the joining point of the wires 4 and 3, that is, the roll 1 is shifted to the left compared with the position of Fig. 2. It is appreciated that the ad¬ ditional roll 1 is preferably movable both in a horizontal and vertical direction for achieving the most suitable position and an optimum line pressure in the nip N. The additional roll l is preferably movable to the suitable point during the run, that is, the position of the nip N can be changed in machine direction when desired.

A suitable dry matter content of the webs for joining them is that present after their dry lines, usually over 6%, most preferably 8-12%. Within said range both webs Wl and W2 are at an optimum dry matter content for the effect of the invention. The invention has no importance at lower dry matter contents, and in addition, there will be the risk of spattering at the nip, and at higher values the desired effect is not reached because of the reduced water content. Moreover, the dry matter contents influence the choice of the modifications shown in Figs. 2-4 in such a way that if the dry matter contents of the webs to be joined are high, the pressing can be applied at an early stage, which means that the nip N can be right at the joining point of the webs 3 and 4 in order to influence the webs in good time as their water content still lies within a suitable range. Correspondingly, when wet webs of low dry matter contents are run together, the nip N can be situated as far as at the point where the wires 3 and 4 depart from the reversing

roll 2 where the webs have had enough time to loose water in course of normal couching during their travel between the wires 3 and 4 on the roll 2 in such an extent that they have a suitable water content when entering the nip N and there will thus be no risk of spattering. It can be stated as a general rule that the thicker the webs are that are run, the farther the nip N should be from the joining point of the wires 3 and 4, because the thicker grades have a larger total water content at the joining point of the webs. After the nip N, the wires 1 and 2 travel the web W there¬ between still over some length guided by one of the rolls, either by the reversing roll 2 (Figs. 2 and 4) or by the additional roll 1 or the surface of any other additional member (Fig. 3) . For ensuring the transfer, this section is followed by a special suction zone lying against the wire 3 for retaining the web W on the wire 3.

Said solution has created a considerable improvement for the bonding power compared with traditional couching. The advantages of the press couching accord¬ ing to the invention are due to the possibility to move the fine substances in a transverse direction with regard to the interface between the layers formed of the webs Wl, W2 by means of mechanical pressing. The advantageous effect of the fine substances on the bonding power is achieved by causing the movement of the water present in the layers and the movement of the fine substances with the water towards one of the rolls at the interface of the web layers. The direction of movement is so chosen that the transfer takes place from the layer at an immediate vicinity of the interface of the webs in which the fine substances content is higher. In the case of a two-ply web, this operation is performed from a web with a higher total fine substances content across the interface to the web with a poorer total content.

By means of the structure of the rolls 1 and 2 situated against each other, a desired movement of the fine substances together with the water can always be accomplished from one web layer to the other one with the movement of the water occurring across the inter¬ face of the web layers. This can be ensured by making the structures of the rolls and wires such that one of the rolls together with the wire lying over it will collect the most, preferably over 90% of the water that is pressed out of the webs Wl and W2 at the press nip N. In practice, the surface of this other roll can be made considerably more open than the surface of the opposite roll. This can be achieved most safely and simply in such a way that one of the rolls is a roll having an open surface and the other of the rolls is a roll having a smooth surface. The surface of the smooth-surface roll is advantageously soft, over 30 PJ, most preferably over 50 PJ. The unit PJ is a unit of hardness in common usage for the coatings of paper machine rolls. The unit of hardness is preferably below 300 PJ. A normal rubber-coated lump-breaker roll, "lumper-roll", can be used as such a soft roll, but of course any other suitably soft roll can be used at this point. By virtue of the above-defined hardness values of the roll, a sort of "longitudinal nip" will be present at the nip N and said structure helps to avoid the crushing of the web. It should be further noted that the term "line pressure" can be used also in this context, because at this kind of points the pressure is always defined in terms of the line pressure, which can be always determined with standard methods.

In the construction of Figs. 2-4, the reversing roll 2 is an open-surface roll and an additional roll 1 is a roll with a smooth surface, the movement of the water at the nip N thus being directed from both layers

formed of the webs Wl and W2 towards the roll 2 into the open spots of the surface of the roll 2, also fine substances being thus entrained by the water from the web Wl across the interface to the web W2. If the roll is a blind-drilled roll, the water pressed out of the web into the bores can be collected by means of centrifugal force to a collecting trough situated after the roll 2.

Figure 5 further shows another possibility to make the gathering of the water by the roll 2 more effect¬ ive. The reversing roll with an open surface is a suction roll whose suction sector S extends at least up to the nip N. Moreover, the suction sector is situated in the roll 2 before the nip N, as seen in its direction of rotation, which makes it possible to still adjust the dry matter content of the web W2 travelling at the suction sector and entering the joining point to have a suitable value, when desired.

Figure 2a illustrates the movement of the water and fine substances according to the invention in more detail. The figure shows the nip of Fig. 2 in a larger scale in a section taken perpendicularly to the axes of rotation of the rolls 1 and 2. The web Wl lying on the wire 3 on the side facing the roll 1 is thicker in grammage, and because of the preliminary filtering taken place through the wire 3, its fine substances distribution is such that the fine substances content increases in direction z towards the upper surface forming the future interface W12 and the content is highest in the vicinity of the surface. The fine substances content is illustrated by dots. The web W2 thinner in grammage, which is brought by the wire 4 to the joining point from the side of the water- receiving roll 2, is poorer in total fine substances content compared with the web Wl, although for the above-mentioned reason it has also the highest fine

substances content in the vicinity of its upper surface, that is, the future interface W12. At the press nip N, the fine substances accumulation of the web Wl is urged to the interface W12 of the webs on both sides thereof by means of the water (arrows A) that is moved by the pressing, also into the web W2 of poor fine substances content. Also the fibre bonds are strengthened by virtue of the pressing at the water contents prevailing at the pressing point.

If a multi-ply web, such as for example a two- or three-ply web, is run, the web is consequently pressed according to the invention as early as at the joining point applying a larger pressing force than in "tra- ditional couching" where the pressing is brought about only by the tension of the wires. The main principle is to aim to move fine substances by means of a controlled pressing and at the same time to accomplish a stronger fibre bond at as early a stage as possible when the dry matter contents of the webs are suitable for the purpose. In a traditional two-ply run (two Fourdrinier wires) the water is sucked away within a dewatering zone only to one direction and the fine substances have remained close to the upper surface and the surface lying against the wire has become poor in fine substances content. Also after the joining, water has been subjected only to suction within the wire section and it has been no longer possible to move the fine substances and consequently the bonding power has remained poor.

The pressing can be chosen according to the product that is run. It can be stated as a rule of thumb that lower line pressures can be used at lower fine sub- stances contents, because there is more water that can be moved. A lower line pressure is also preferable because of the spattering risk. A suitable line pressure lies in a range of 0 to 30 kN/m.

An additional roll 1 can be easily mounted in existing multi-ply cardboard and multi-ply paper machines without any greater changes in machine constructions. The invention is therefore applicable in renovating old multi-ply cardboard and paper machines. A rubber- coated roll of a suitable hardness can be used as the additional roll 1 and it can be fixed under the wire 3 using suitable provisions such that it can be trans- ferred in the machine direction during the run and it can be loaded against the roll 2 using a desired force in all its positions. Alternatively, the loading adjustment for effecting the desired line pressure can be accomplished by means of the reversing roll 2, in which case the additional roll 1 has no loading adjustment. The additional roll 1 needs no driving, but it can be driven if desired.

Also other members having a press surface suitable for the objects of the invention and thrusting the wire 3 against the nip N can be used as a member lying against the reversing roll 2.

Figure 6 further shows an alternative where the reversing roll 2 on the side of the second wire 4 is a roll providing the movement of the water from the webs towards the additional roll 1. In this case the roll 2 is a smooth roll and the roll 1 is an open roll. The alternative is advantageous in the cases where it is advisable to make the water and fine substances therewith to move from the web W2 of a richer fine substances content, brought by the second wire 4, to the web Wl of a poorer fine substances content, brought by the first wire 3. This is usually the case when a thinner back of a two-ply product is run on the lower wire l and the thicker body is brought by the upper wire.

However, the thickness of the web is not always the determining factor as to the side from which the water and fine substances are preferably moved. In two-ply webs, the layers bounded by the interface W12 are constituted of the surface layers of separate webs Wl and W2 being formed in the same way in principle. In this case the layer bounded by the interface W12, containing more fine substances, is the surface layer of the thicker web. Yet, in some cases the surface layer of a web thicker in grammage can have a poorer fine substances content than the surface layer of a thinner web that is run against it. For example, when a three-ply web is run where the back is run on the lower wire, that is, on the first wire 3, and a thicker web formed of the body layer and the surface layer is brought from above by the second wire 4, in which web the upper surface forming the interface has also been against a water-permeable wire due to the fact that it is formed of a body layer brought by a third wire on top of the surface lying on the second wire and has therefore a poor fine substances content, the moving of the fine substances is preferably carried put from the thinner web Wl lying on the lower wire 3 towards the web W2 brought by the upper wire 4. In this case, the roll receiving the water lies on the side of the thicker web W2, thus it is the reversing roll 2.

Further, it has been noted in the experiment results that when the webs of equal grammages have been run together, the bonding power has also been improved by means of the invention. The movement of the water and fine substances caused in accordance with the invention across the interface W12 is advantageous also in this case in improving the bonding power even if it can be assumed that the layers have differ¬ ing fine substances contents after the treatment. A more prominent improvement in the strength is, however,

achieved when webs of different grammages are run together.

As apparent in Figs. 2-6, the reversing roll 2 is run in course of the operation to a normal position slightly inside the wire 3, that is, below the plane of the wire 3, a small curve thus being created in the travel of the wire 3 between the wire roll 6 and the suction box 5. Within this section, the wires 3 and 4 wrap the roll 2 in a certain sector having the webs Wl and W2 to be joined therebetween.

Figure 7 shows a complete wire section of a multi-ply cardboard or paper machine wherein the apparatus according to the invention can be applied. The machine is a twin-wire machine where the stock forming the web Wl is fed onto the lower wire 3 from a headbox Hi and the stock forming the web W2 is fed from a head¬ box H2 onto the horizontal section of a loop consti- tuted of the wire 4 above the wire 3. The webs are joined together in the above-described manner at a point where the loop formed of the wire 4 is turned guided by the reversing roll 2 onto the lower wire 3. In the case of Fig. 7, the web Wl forms the h-dγ of the finished product and the web W2 forms the surface thereof. The webs Wl, W2 are joined together at -er the dry lines of the webs, that is, the joining point is preceded by relatively long pre-filtering zones on both wires 3 and 4.

Figure 8 shows another multi-ply machine, a so-called three-wire machine. Stock forming a web W3 is fed from a headbox H3 onto the horizontal section of a loop formed of the second wire 4, and after the point where the horizontal section of the wire 4 is directed downwards guided by a reversing roll 8 towards the first wire 3, a web W4 lying on a third wire 7 that wraps a roll 9 is guided by means of the roll 9 on

top of the web W3 lying on the wire 4. The wire 7 travels above the lower wire 3 in the same direction therewith and the stock is fed thereon from a head¬ box H3. The webs W3, W4 on top of each other form the joined web W2 after the joining point of the wires 4 and 7. Both surfaces of the web have a poor fine substances content. The web W2 is guided by means of the wire 4 on top of the thinner web Wl brought by the lower wire 3, and the joining operation is carried out in the above-described manner. The surface of the three-ply product is thus formed of the web W3, and the web W4 and Wl constitute the body and back thereof, respectively.

Figure 9 shows in a larger scale the points where the wires 3, 4 and 7 of the machine of Fig. 8 come to lie against each other. As shown by the figure, the construction according to the invention can be used also at the point where the third wire 7 transfers the web W4 on top of the web W3. At a point where the wire 7 travels round the roll 9, there is an additional roll 10 on the side of the second wire 4, said roll making the effect according to the invention possible also at this point between the webs W3 and W4. Because the web W4 has a greater grammage at this point, it is advisable that the additional roll is the more open roll, the water moving then towards the wire 4 and the web W3.

In the press nip N formed of the rolls 9 and 10 in Fig. 10, the second wire 4 as well as the web W2 travelling thereon correspond functionally to the first wire 3 and the web Wl present in the press nip N of Figs. 1-6, and the third wire 7 and the web W4 travelling thereon correspond for their part to the second wire 4 and the web W2 travelling thereon present at the point illustrated by Figs. 1-6. The invention can be applied in all such points in

multi-ply machines where a web is transferred on top of another web by means of two wires guided against each other.

Figures 10 and 11 show further one advantageous modification for improving the bonding power. Fig. 10 shows a steam-box 11 that is placed as close to the nip N as possible. Steam nozzles open on the box surfaces facing the wires 3 and 4. Saturated steam is blown from the nozzles at a suitable speed on the surfaces of the webs Wl and W2 to be joined. In this way the surfaces of the webs are moistened and the bonding capability of the fibres is consequently improved. The fibres are also softened by means c the heat which improves the bonding capability. The distance of the surfaces of the steam-box 11 from the wires _s preferably ca. 10-20 mm. Fig. 11 shows another alternative where the heating and moistening is effected at different stages. Heaters 12 face the webs Wl and W2 before the nip N and after them before the nip N there is a separate atomizer 13 that is provided to spray water as a fine mist onto the surfaces of the webs to be joined together. The water used can be also warmed up. Of course, only one of the surface of the webs Wl, W2 to be joined together can be subjected to the above-mentioned treatments if desired.

The alternative according to Fig. 10 has been tested in practice. Mechanical stock having a grammage of 130 g constituted the web W2 brought by the wire 4, and chemical stock having a grammage of 60 g con¬ stituted the web Wl brought by the wire 3. Steam was blown only on the latter of the web surfaces in the experiment. The invention had some effect even in the normal couching of Fig. 1 in such a way that the bonding power was increased by 10%. The peeling took place in the web layer W2 brought from above and

formed of two separate webs, but the results show, in any case, that the provision had a positive influence on the total strength of the whole web. When the pressing according to the invention was used, said increase of the peeling strength was ca. 20%.

The steam used was saturated steam at ca. 100°C. By choosing the suitable heating and moistening speed, the process can be further optimized.

The advantages of the invention can be listed as follows:

Does not require the feed of additives (starch) .

- Does not require additional beating. - Simple and inexpensive construction.

- Is easily applicable also to old multi-ply machines.

- Does not require additional suction capacity, except for the case where a suction roll 2 is used instead of an open roll. - Does not limit the adjustment of dewatering within the pre-filtering section.

If the products run by means of the machine have a wide range of grammage, it is easy to adjust an optimum joining of the webs by means of the above press solution, either by using the press or not, in which case "normal couching" is carried out.

Some test runs performed in the apparatus according to the invention are described hereinbelow. The test runs were carried out without a preliminary moistening before the nip N.

PRESS TEST RUN IN A TEST MACHINE

1. OBJECT

The bonding power between various layers is a problem in multi-ply web forming. The problem will be

pronounced when a web which is poor in fine substances content is run and when machine constructions are used where the webs are joined together after the dry lines of the webs.

Various solutions have been developed to solve the problem: starch sprays

- feed of fine substances between the layers - optimizing the dry-matter contents of various layers before the couching

- use of a reinforcing stock

- beating in general.

Certain limitations and negative factors are common to these methods, i.a. the price, complicity of the construction, soiling, price of energy, limitations in the dewatering adjustment, etc.

New models have been planned, and here are shown preliminary results of one model.

The main idea is to make the fine substances to move in the couching operation of the webs by means of pressing without suction and surfaces that sweep the wire.

2. TEST RUNS

Stocks:

Vton sa broke (Macon Kraft)

The beating of the stock in a non-beated state was ca. 600 csf and it was beated to the value of ca.

480 csf. The same stock was used on both wires. During the test run, the values of the stock were within the range:

start middle end

Machine concept:

- lower wire Tamflo H (3-row)

- upper wire Tamflo R

- press section Tampress C+LNP-S

A lump-breaker roll having suitable surface properties was used as the additional roll. A rough egouter roll was the opposite couch roll, and the desired pressing was achieved by adjusting it vertically. The position of the lump-breaker roll was stationary and it was on the same vertical line as the couch roll. Because of the construction, the line loads used are not known.

Wires and felts:

Lower wire: Scapa & Porritt, 8150 m ³ / (m ² *h) Upper wire: Tamfelt Formtec DL HIFI T=120 Pick-up: Tamfelt Tambat 1210 g/m ² 1-lower Triaud Gauvain 1650 g/m ² LNP-S upper-lower Cofpa 1500 g/m ²

Test program:

The program was divided in four parts having each as variables: - normal couching

- press couching (minimum press)

- press couching (maximum press, however, in such a way that no spattering at the nip was present) .

Normal couching means that the lower lump-breaker roll was shifted away from the nip and the couch roll could be lowered in the lower wire by ca. 10 mm.

Because the run was a preliminary one, the aim was to keep the dry limits on the wires at constant positions, and they were ca. 8.0-8.5 m on the lower wire and ca. 6.0-6.5 m on the upper wire calculated from the head-box.

The couching consistencies were measured by means of a NDC instrument. The effect of the couching on the dry matter content after the wire suction roll was also monitored.

The press loads were kept at a constant value:

1-nip: 80 kN/m

2-nip: 120 kN/m

3-nip: 500 kN/m (shoe)

3. DISCUSSION

Determination of the laboratory results: The peeling, i.e. bond, was the most important para¬ meter. Because there is usually a large deviation m the bond, the determinations were carried out for two strips in each of four sheets, and thus the average value of 40 measurement results was obtained. The other determinations are normal average values of five measurements.

The laboratory results are shown in Tables 1-4.

Bond:

In all part-runs the press couching had a positive effect on the peeling compared with the normal couch¬ ing:

3,3 m/s ca. 170 + 50 g/m ² 127 -> 176 J/m ² = 38,6%

5,0 m/s ca. 150 + 50 g/m ² 146 -> 174 J/m ² = 19,2%

8,3 m/s ca. 50 + 50 g/m ² 91 -> 99 J/m ² = 8,8%

8,3 m/s ca. 100 + 50 g/m ² 94 -> 115 J/m ² = 22,3%

When the grammage of the body was above 150 g/m ² , an optimum peeling was obtained with a minimum pressing, whereas maximum pressing was the optimum below 150 g/m ² .

On the other hand, it should be noted that even if remarkable improvement in the bond level was achieved in the press couching, the bonds of the 2-ply sheets were only 45-57% of those of the l-ply sheet.

Other physical properties of the sheet: There was no clear systematic correlation to be seen when running at an optimum pressing, as far as the bond is concerned, which is clearly exemplified by the appendices.

Dry matter contents:

Calculated according to the NDC measurements, the dry matter contents were relatively constant before the couching:

- on the lower wire 8.3 - 10.0 %, average 9.0 %

- on the upper wire 11.0 - 12.0 %, average 11.3 %

The measurements by NDC before the wire suction roll and the samples of dry matter content after the suction roll showed that the dry matter content increased in the press couching by ca. 0.5-1.0 percentage units compared with normal couching.

4. OBSERVATIONS

No technical problems were noticed in the run.

The lump-breaker roll rotated well in a wet state and no kind of soiling was to be seen.

Even if the pressing was not accurately determined, it can still be stated that for the heavy grades above 200 g/m ² press load was very small, but also in this case it was greater than in normal couching. At light grammages below 200 g/m ² , much higher pressure could be applied.

The improvement in the peeling even after a light press was due to the fact that even in light pressing, part of the free water and fine substances is urged towards the open roll, because the lump-breaker roll has a closed surface structure. Even during runs with a light press, it could be clearly seen that water was removed into the open roll.

The lump-breaker roll was not driven during the test run, which presented no problems.

Table 1, COUCHING PRESS TEST RUN LABORATORY RESULTS

Test point Speed

Headbox consistency

- lower wire

- upper wire

Gap consistency

- lower wire ca. 9.0 ca. 10.0 ca.10.0

- upper wire ca. 12.0 ca. ll.O ca.11.0

Dry matter content after suction roll 19.0 20.7 21.2

Table 2. COUCHING PRESS TEST RUN LABORATORY RESULTS

Test point Speed

Headbox consistency

- lower wire

- upper wire

Gap consistency

- lower wire

- upper wire

Dry matter content after suction roll 19.7 19.4 20.0

Table 3. COUCHING PRESS TEST RUN LABORATORY RESULTS

Test point Speed

Headbox consistency

- lower wire

- upper wire

Gap consistency

- lower wire

- upper wire

Dry matter content after suction roll 18.6 18.5 19.3

Grammage

- total

- lower wire

- upper wire

Density Porosity (G-H)

Tensile index

- machine dir.

- transverse dir.

- md/td

- geometric average

Elongation

- machine dir.

- transverse dir.

Scott Bond Bursting index

RCT

- machine dir.

- transverse dir.

Table 4. COUCHING PRESS TEST RUN LABORATORY RESULTS

Test point Speed

Headbox consistency

- lower wire

- upper wire

Gap consistency

- lower wire

- upper wire

Dry matter content after suction roll 20.9 21.3 22.0