The present invention concerns an on-machine- procedure in connection with the surface sizing of a paper web for conducting the web that has been surface-sized on both sides and thereby has been wetted, through the surface-sizing steps to the after-drying section of the paper machine.

Furthermore, the invention concerns a paper machine drying section intended for carrying out the procedure of the invention, comprising a pre-drying group constituted by drying cylinders, following there- after a size press, an after-drying group disposed thereafter, this latter comprising a plurality of drying cylinders.

The invention also concerns paper manufactured by a procedure and/or means according to the invention, in particular newsprint paper.

The greater part of fine paper that is produced is surface-sized or coated. Surface sizing is a comparatively simple and inexpensive method of quality improvement. Surface sizing is usually carried out in an on-machine size press provided on the paper machine. Surface sizing of fine paper brands containing mechanical pulp is being increasingly applied, particularly towards offset uses. In addition, it is known in the art to surface size or to pre-coat in a size press: kraft liner, cardboards and various base papers. The ranges of appli¬ cation of size presses known in the art, presented in the foregoing, can be subdivided into four groups:-

(1) surface sizing of writing and printing papers;

(2) surface sizing and precoating of base papers;

(3) pigmenting and coating of paper; and (4) manufacturing of special brands.

s known in the art, the paper web is run through the roll nip of

the size press. The sizing is supplied in the press in contiguity with the paper by creating before the nip a pool, where the web is wetted and adsorbs sizing onto itself. Between the rolls of the size press, sizing is urged into the paper web by action of hydro- dynamic pressure. At the same time, owing to the hydrodynamic pressure, a sizing film is formed between the paper and the roll, this film being split in the exit throat of the roll and leaving behind it a layer of sizing on the surface of the paper. The amount of sizing that remains on the paper depends on viscosity of the sizing, machine speed, roll diameter, surface characteristics of the roll, lineal pressure and factors introduced by the roll deformation.

Oldest among size presses known in the art is the so-called vertical press, wherein the rolls are positioned one above the other and the paper runs horizontally between the rolls. In the horizontal press of prior art, the rolls lie in one horizontal plane and the paper runs vertically through between the rolls. The third size press known in the art is the so-called oblique press where the rolls are disposed one above the other at an angle about 45 . This is considered the best problem solution in view of web conduction at high running speeds.

The diameters of the size press rolls are important in view of run- ability. In size presses of prior art, one has arrived in the case of the nip rolls at diameters in order of 800 to 1500 mm at running speeds between 10 and 17 m/sec. Increasing the roll diameter with increasing speed is an expedient applied in the art in an attempt to avoid splashing in the pool throat, because this would interfere with uniform wetting of the paper web.

Rubber has mostly been used for coating material of the size press rolls. Such presses are also known in the art in which the hard roll is of metal and the soft roll of rubber. It is thus understood that softer and harder pressing zones are used. At higher speeds rolls with larger diameter are used than at low speeds.

Achievement of good surface sizing implies not only a long enough wetting time but also high pressure, between 20 and 50 kN/m.

Regarding the state of art associated with size presses, reference is made as an example to the Finnish Patent No. 28686 (Class 55 f 15/20, published March 15, 1957, Combined Locks Paper Co., U.S.A.). Through this Finnish patent is known in the art a paper coating machine comprising a hard central roll and in its conjunction two nips through which the paper web is passed that one desires to coat. The sizing, or other coating substance, is introduced first from a trough over a plurality of applicator rolls onto said hard-surfaced roll, from which it is pressed into the web in the first nip. The other side of the web is coated by introducing from a trough by mediation of a plurality of applicator rolls the coating substance onto the latter nip roll, from which it is pressed onto the surface of the web in the second nip defined in conjunction with the hard central roll. As taught by this Finnish patent, the nip rolls define nips together with the hard central roll in such manner that these nips are disposed in conjunction with the central roll substantially symmetrically with reference to the vertical plane passing through the axis of the central roll under a central angle about 45 with reference,to said vertical plane.

As taught by said Finnish Patent, the coating substance is intro- duced by the aid of small-diameter applicator rolls, in contrast with which the present invention concerns size presses in which the sizing, or other coating substance, is introduced by means of nozzles, to form a pool located between the paper web and the roll.

Regarding the size presses associated with the present invention, reference is made to the Finnish patent application No. 803710 (filed Nov. 28, 1980, applicants: Valmet Oy and Kymi Kymmene Oy) . The said patent application discloses a size press comprising three coating rolls which between themselves, two and two, define two press nips through which the paper web to be treated has been passed to run so that both sides of the web will receive treatment in said nips.

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It has been considered a novelty in the size press of the said application: that of said coating rolls the one which is the middle roll as regards its position in altitude has been arranged to be the central roll of the size press, in conjunction with which both coating nips are formed so that the first coating nip has been disposed at an appropriate angular distance above the horizontal plane placed to pass through the axis of said central roll; that the second coating nip is defined by the third coating roll, placed at an appropriate central-roll angular distance downward from said horizontal plane; and that to precede the first nip have been provided, with reference to the web run on the central roll side, sizing supply means, which supply a first pool or layer of sizing into the cleft between the central roll and the web, and that the second nip has been arranged to be preceded in the throat defined by the central roll and the third coating roll by second sizing supplying means, which provide a second pool or layer of sizing on the side opposite with reference to the first sizing pool or layer, said means having been arranged to cooperate in such manner that when the web runs from its principal direction downwardly from above, it is supported by the roll surface while the sizing operation is going on.

Since the size press, constituting an important functional unit within the present invention, is an on-machine apparatus to be connected to the drying section of a paper machine, it must be possible with this means, and likewise with the guide and drying means subsequent thereto, to run an equally high speed as that at which the paper machine is being run. In many instances, in fact, the size press and the pieces of equipment immediately succeeding have constituted a bottle-neck restricting the speed of the paper machine. The primary object of the present invention is to eliminate this drawback.

Furthermore, regarding size presses, reference is made to the U.S. Patent No. 4.108.110.

Although in the foregoing the talk has been about size presses, it

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should be understood that in this context the word "sizing" has been used in the broad sense to encompass also other substances known in themselves, serving the treatment of a paper or cardboard web, which are suited to be applied in means of the type concerned here.

The size press is an important aid for the papermaker, and it has enabled the paper quality to be improved and new paper qualities, or brands, to be developed, as well as new combinations of raw materials to be adopted. However, one of the difficult problems has been that surface sizing of paper could not heretofore be applied in connection with high speeds and/or with thin paper brands, in particular not with those containing groundwood and fillers, and/or paper brands made of short-fibre pulp stock.

The size press is placed in the drying section of the paper machine at a point where the water content of the paper web prior to the size press is about 4 to 17%. The size press should be so located in the drying section that the widest possible range of brands can be run at maximum production rate in a manner ensuring that the drying capacity will be no bottle-neck before nor af er the size press. However, the problem has frequently been that the water . ^• content of the paper after the size press varies greatly: within 15 to 55%.

After the last nip of the size press the web follows along with the hard roll, and it is to advantage to detach it therefrom as soon as possible. After the press the web expands as a result of increased water content. Since the said expansion requires a given minimum time, it is known in the art that the distance from the last sizing nip to the next drying cylinder has to be arranged to be long enough. A long free draw between the last sizing nip and the drying cylinder following thereupon is highly problematic for the reason that on this free draw is manifested a high amplitude, uncontrolled fluttering of the web, which frequently causes web breaks for the reason that on said free draw the web has quite a high water content: up to about 55%. Therefore, in fact, it has not been possible to use a size press on thin webs and/or webs made of raw materials giving- a

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web which is not strong enough in view of the surface sizing operation and of the subsequent web treatment steps. These problems have become accentuated with the increase of paper machine speeds that has taken place.

In prior art also a paper spreading roll has been used, interposed between the size press nip and the after-drying section following thereafter, with a view to preventing wrinkles.

As known- in the art, the drying of the paper after the size press has taken place on a standard multiple cylinder dryer, in which the first drying cylinder after the size press operates without felt. It has been necessary in addition to keep the surface temperatures of the two cylinders following closest after the size press at a comparatively low level, e.g. about 70 to 80 C because higher drying temperature would damage the surface of the paper, and the sizing, and the fibres along with it, would adhere to the cylinder and the paper would give off dust in spite of the surface sizing. In the manufacturing of pigment-coated paper endeavours have been made in prior art to avoid these drawbacks by drying the coated surface with warm air immediately after the size press.

The three-roll and two-nip size presses mentioned allow comparatively high speed to be used in two-sided surface sizing of the web, and they are therefore well applicable on modern paper machines with high running speeds. In such case however — as has been made obvious in the foregoing - the bottle-neck has moved to the treatment steps following after the surface sizing. In addition to the drawbacks already stated, these treatment steps are encumbered by the detriment that in connection with the first drying cylinders after the size press no felt can be used, and this in itself results in reduced drying capacity and in a tendency of breaks to occur at the free draws between drying cylinders. It has moreover been unavoidable in prior art to use at least as first drying cylinder after the size press a chromium-surfaced, or other quite expensive cylinder in order to prevent adhesion of the sizing to this cylinder.

Regarding the state of art most closely associated with the present invention, reference is made by way of an example to a paper in Tappi/June 1974, Vol. 57, No. 6: Donald . Lawton, "Airflow Floater Drying after a Size Press", p. 105-107. Reference is made in parti- cular to Fig. 4 of said article, displaying a typical floater dryer of prior art, mounted in oblique position after a single-nip size press. Differing from our present invention, the arrangement of this reference provides after the size press nip and before the floater dryer a return roll. The drawbacks of said return roll have been acknowledged in the article, but the writer fails to recognize by which means it could be eliminated; use of such a return roll has been considered indispensable in view of practical considerations of runability. Most often, however, this return roll destroys the surface-sized wet surface. It is a further drawback that when using floater dryers known in the art, which specifically aim to achieve high drying efficiency, the opposed nozzles of the floating dryer are too closely spaced and therefore by their aid no controlled wave action is obtained which would have an amplitude large enough for web stabilization, and a suitable wavelength. The risk is also present that owing to the said small dimension the web may in floating dryers of prior art easily come in contact with the nozzle surfaces, thereby causing a web break. A further drawback is that floating dryers of prior art allow no substantial variations of the angle under which the web enters, without risk of contact and breakage, and they do not spread the web in the cross-machine direction. The object of the invention is to avoid these drawbacks.

The object of the invention is provide a combination of size press and subsequent web treating means in which the drawbacks mentioned can be avoided. The main object of the invention is therefore to provide a combination of size press and after-treatment means en¬ abling even thin webs to be treated at high running speeds without incurring any excessive risk of their breakage and, furthermore, webs which have been made of papers containing groundwood and/or fillers and/or of short-fibre pulp stock.

It is a further object of the invention to provide a procedure and

an apparatus combination in which it is possible in the treatment step following after the surface sizing to run the web with a lower tension allowing transversal deformation of the web to take place in sufficient amount.

In order to achieve the aims presented above, and others which will be apparent later on, the procedure of the invention is mainly characterized in that the procedure comprises in combination the following steps:-

the web arriving from the pre-drying section of the paper machine is surface-sized on both sides in one or several size press nips;

the web is after the surface sizing step, or steps, conducted either directly or by mediation of a contact-free turning, supporting and/or spreading means to a stabilizer means, by an effect of which the web is supported in contact-free manner and its running is stabilized;

the web is subsequent to the preceding step conducted either directly or over a contact-free turning, supporting and/or spreading roll to the after-drying group of the paper machine; and

said contact-free stabilizer means and other potential web con¬ ducting means are so disposed that the free draws of the run will not be too long in view of the fluttering phenomenon, and so that the web is allowed to spread out in its transversal direction.

The means of the invention, again, is mainly characterized in that the means comprises a stabilizer means acting on the web from both sides and based on the use of gas flows, placed after the size press? and before the after-drying group.

The paper of the invention, again, is mainly characterized in that said paper is such newsprint or equivalent of which the printability properties have been achieved mainly by two-sided surface sizing of the web.

The procedure and means of the invention afford advantages which are important in practice, and they eliminate a number of drawbacks. Most important among said advantages is: that thinner and weaker webs than before can be run in a stabilized manner and free of fluttering, and therefore without excessive risk of breaks, at higher speeds than heretofore and can be surface-sized and after the surface sizing treated in such manner that the web can be conducted to a standard multiple cylinder dryer on which it is possible directly to apply fabric conduction and full efficiency drying.

It is a highly important advantage of the invention that the invention enables completely new paper brands to be manufactured on modern fast-running paper machines, in particular newsprint paper machines. It is thus possible, thanks to the invention, to manu¬ facture surface-sized newsprint from more versatile and advantageous raw materials than before and, in addition, by virtue of the two- sided surface sizing to obtain newsprint which has better printa- bility characteristics than before. Furthermore, the runability of the paper machine is improved. The need for such paper is obvious indeed, e.g. in view of the newspapers' advertisement sales and of their multiple colour printing.

By the procedure steps of the invention, known in themselves in the art, a synergistic effect is obtained because contact-free and stabilized guidance and support of the web is achieved such that fluttering and web breaks are prevented, and such that the web has enough time and travelling distance to be able to expand and spread in lateral direction, and that it is specifically actively spread out if required. The last-mentioned action is particularly advantageous because hereby the web draw length between the surface sizing operation and the after-drying can be reduced in itself.

As taught by the invention, one uses to greatest advantage a stabilizer means which guides the web free of contact on both sides so that by effect of air blown out through the stabilizer's conse¬ cutive nozzles the web runs with substantially sinusoidal and

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controlled wave motion in its longitudinal direction. By this controlled wave motion the free and indefinite fluttering of the web is prevented and potential wrinkles longitudinal to the web are removed or their forming is prevented. In the said stabilizer means heated gases may be used so that both sides of the surface- sized web are dried to a moisture content which is suitable with view to normal after-drying. The use of such drying is not indis¬ pensable, however.

It is furthermore possible by using apparatus according to the invention, to render the web run optimal on the portion between surface sizing and after-drying. Since the invention also allows a running of the web on the portion between surface sizing and after-drying in which it changes direction, it becomes possible to accommodate within a comparatively short machine hall length a long enough contact-free run of the web in view of its sidewise spreading, for instance.

The invention is described in detail in the following, reference being made to certain embodiment examples of the invention, presented in the figures of the attached drawing, to the details of which the invention is in no way narrowly confined.

Fig. 1 presents, in schematic elevational view, an apparatus combination implementing the procedure of the invention, comprising a three-roll and two-nip size press, thereafter an air-support means for turning and spreading the web, whereafter follows a contact-free stabilizer means.

Fig. 2 presents, in like manner as Fig. 1, an apparatus combination implementing the procedure of the invention, comprising a three-roll and two-nip size press, whereafter follows immediately a contact-free stabilizer means, which operates using heated drying gases.

Fig. 3 presents an apparatus combination implementing the procedure of the invention, comprising a single-nip size press, thereafter a contact-free stabilizer means, whence the web is conducted to a -

contact-free spreading and/or- return means.

Fig. 4 presents a favourable apparatus combination implementing the procedure of the invention and comprising a single-nip size press, whence the web is conducted in straight draw to a contact-free turning and spreading means, whereafter follows a contact-free stabilizer means.

Fig. 5 presents, in schematic elevational view, an example of the stabilizer means applied in the invention.

Fig. 6 shows the cross section of a nozzle in the stabilizer means of Fig. 5.

Fig. 7 shows the nozzle of the stabilizer means, as a perspective drawing.

Fig. 8 presents a more detailed implementation example of the web turning and spreading means employed in the invention.

Fig. 9 shows the carrying surface of the turning means of Fig. 8, on a larger scale.

The size press 100 depicted in Figs 1 and 2 comprises a frame part (not depicted), in connection with which have been provided a web guide roll 10 and the size press rolls proper 11,12 and 13, and the other pieces of equipment belonging to the size press 100. The arrival at the size press of the web co ing from the paper machine and which is going to be treated has been indicated by the reference symbol W. . The exit of the web W treated on both sides with a coating substance, such as sizing for instance, has been indicated with W, . The passage through the size press of the web W which is to be coated has been shown by a dotted line. The first of the size press rolls in the direction of travel of the web is the guide roll 10. The first coating nip N _χ is defined in conjunction with the coating rolls 11 and 12. The roll 12 is the central roll of the press and it has been rotatably carried e.g. in stationary bearing

stands (not depicted) . Th$ central roll 12 defines the second coating nip N„ together with the third and lowermost coating roll 13. In the size press 100 shown in Figs 1 and 2 two pools L. and L„ of the coating substance are formed. The coating substance supply means in conjunction with the first pool L, comprise a sizing supply tube 17 extending over the whole breadth of the web , this tube carrying a plurality of parallelly disposed nozzle tubes 17a, or an equivalent continuous slit nozzle. The first sizing pool L, is established in the throat defined by the central roll 12 and the web W, before the first nip N_.. From the pool L.,, the sizing, or other equivalent coating substance, is absorbed to the other side of the web , and the sizing is pressed into the web in the nip N, .

The size press 100 coπηprises a second sizing supply tube 18 disposed in conjunction with the third coating roll 13 and having in its connection a set of sizing supply nozzles 18a or an equivalent nozzle slit. The nozzles 18 supply sizing jets to a second sizing pool Ix _j . Hereby the second sizing pool L ₂ is formed before the nip ₂ , and from this pool „ is treated and impregnated the other side of the web W. After the nip N_, the web W follows e.g. the roll 12 on the sector o , whereafter the web ¥ is conducted to the subsequent wet-web treatment sføe s according to the invention, to be described later on.

As shown in Fig. 1, the web W laps the first coating roll 11 on a suitable angle *, before the nip N. ; this arrangement is important also for the reason that thereby the web W is backed up by the surface of the roll 11 in the region of the pool L-, . The angle α.. has a magnitude preferably about 45°.

The roll geometry of the size press 100 is such that the middle roll in altitude direction, 12, is the central roll and the extreme rolls 11 and 13 are so disposed that the first nip N _χ and the second nip „ become substantially symmetrical with reference to the horizontal plane placed to pass through the central axis of roll 12. The angle ct„ cxτi the central roll between the nips N.. and N_ is preferably about

90 ^L

It is known from experience that it is to advantage to have in a size press nip a hard and a soft roll against each other, because in a nip between two hard rolls there is a tendency for holes to appear in the paper. In one favourable embodiment of the invention, the central roll 12 is the hardest roll, for instance a so-called "mickro rock" coated roll, which has a hardness in the range of 0 to 1 P&J hardness degress. The first press nip N, is defined together with this roll 12 by a softer "mikromate" coated roll having a surface with hardness e.g. in the range 20 to 30 P&J degrees. The second press nip N~ is formed together with the central roll 12 by the other extreme roll 13 having a surface equivalent to that of roll 11.

In the roll disposition just presented, the initial requirement is fulfilled that a hard roll and a soft roll define the nips N, and N„ in such manner that the central roll 12 is hardest and against this roll are urged two softer rolls 11 and 13. The same aim may be accomplished by having a soft-surfaced central roll 12 and arranging two harder rolls to work against it.

The moisture content of the paper web arriving at the size press is 3 to 8%. Paper having lower moisture content is brittle and pre¬ sents poor abosrptivity. If the moisture content is higher, the moisture is non-uniformly distributed and the abosrptivity of the paper is too high. The line pressure in the nips N, and N~ is between 10 and 50 kN/m, preferably about 30 to 40 kN/m. At least two of the rolls 11,12 and 13 require deflection compensation above all in a size press with which various paper types are run. Deflection compensation is more urgently required on wide than on narrow machines. The diameters 2 ₁₅ 2R„ and 2R ₃ of the rolls 11,12 and 13 are selected to be all equal e.g. with a view to easier maintenance, or the roll 11 is selected to be smaller than the other two, as shonw in Figs 1 and 2. In both nips N, and N„ one of the two rolls has to be a soft roll also in order to make the pressure area have a great enough width in the nips N, and N„. Each one of the three rolls 11,12, and 13 has its own controllable drive 14,15 and 16 respectively. The peripheral velocities of the rolls equal the web

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As shown in Fig. 1, after the two-sided surface sizing of the web in the nips N- and N„ the web follows along with the central roll 12 of the size press through a small angle α,. The web is thereafter carries straight draw W. to the turning means 20, in the region of which the web changes direction, turning upwards through the angle β. In the region of the turning means 20, the web W„ is carried without contact by air blown in between the nozzle surface, to be described later on, and the web, said air being conducted into said gap through nozzle slits transversal of their longitudinal direction to the direction of travel of the web W„ and opening to the carrying surface.

In the region of the turning means 20, the web may also spread out, and a favourable turning means 20 to be described later on is in fact characterized in that the air jets operating in the region of the carrying surface acutally actively spread the web, thereby preventing the forming of wrinkles and ensuring contact-free conduction of the web.

After passing over the turning means 20, the web „ is carried in substantially straight draw W, to the stabilizer means, which consists of two mutually opposed components 40 and 41 provided with nozzles 50. In the region of the stabilizer means 40,41, the web W, is carried free of contact and it is guided in stabilized fashion by the air jets discharging from the nozzles 50 so that the web may even directly be conducted to a standard drying cylinder 61, where additionally may be employed a drying felt, either in single- felt or in double-felt conduction. The web W,- „ is hereby throughout its run, from the last size nip N~ and from the size press roll 12 up to the first drying cylinder 61, subject to stabilized, contact- free supporting action in such manner that the web may freely spread out in lateral direction or is even actively spread, and so that on the said run W..-W of the web there are no excessively long free draws where a free, indefinite and uncontrollable high-amplitude fluttering could build up.

The size press 100' depicted in Fig. 2 is substantially as that shown in Fig. 1. After the last nip N ₂ of the size press 100', the web _. W..

follows along with the central roll 12 through the angle α ' , where- straight to the stabilizer means 40',41', in the region of which the web is supported free of contact and, in addition, the nozzles of the floater dryer 40',41' blow heated air (reference H) so that in the region of the stabilizer means the web , ' dries out and requires a high enough dry matter content. It is also possible to apply radiation drying. The web „ is conducted over a guide roll or out spreading roll 42 to a multiple cylinder dryer, where single-felt conduction is applied. The felt 43 has been conducted over the cylinders 61' and 62', guided by the guide roll 44, in a manner known in itself in the art. For drying cylinders 61' and 62' may be used standard drying temperatures, and a felt 43, from which follow the advantages mentioned above.

Fig. 3 shows a variant of the invention wherein has been used an oblique size press 100a constituted by a pair of rolls 11a and 12a and provided with two nips N.. . This type of oblique size press 100a is known in itself in the art and has been used rather commonly in fast-running machines for the reason of the easy passage of the paper. The top roll 11a of the size press 100a is a hard-surface roll, and therefore the web W.. follows along with the top roll 11a through the angle α , whereupon on the horizontal run of the web there is a stabilizer means 40a,41a, the air blown through its nozzles 50 providing contact-free and stabilized support of the web W, . After the stabilizing means 40a,41a follows a turning means 20. The web is conducted to a conventional multiple cylinder dryer, the first among its cylinders, 61a and 62a, being visible in Fig. 3.

The conduction of a surface-sized web shown in Fig. 4 is substantially similar to that presented in Fig. 1, except that here is employed a single-nip, oblique size press 100b like that in

Fig. 3, its sole nip N-, being defined between a hard roll lib and a rubber-coated lower roll 12b. After the surface sizing nip N.., , the web is carried to the turning means 20b, whereafter follows a stabilizer means 40b,41b, whence the web W is conducted to a

' out multiple cylinder dryer 61b,62b known in itself in the art.

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Fig. 5 displays the more detailed construction of the stabilizer means 40,41 and the passage of the web therethrough. The stabilizer means consists of two mutually opposed housings 46,47, into which the blowing air is carried by tubes 45. The housings 46 and 47 extend across the web W in its transversal direction. The opposed walls 48 of the housings 46 and 47 carry transversal nozzles 50 extending over the whole web breadth, the nozzles on opposite walls 48 having a phase shift so that the nozzles on one side lie mid between on the other side. Hereby the web , will pass in stabilized fashion, and with a substantially sinusoidal wave motion, supported by the air flows discharging through the nozzles 50.

It is of essential importance from the viewpoint of the invention that the web runs in wavy fashion in the stabilizer means 40,41. The wavelength of the undulation of web W, , which equals the centre-to- centre spacing of the nozzles on one side of the web, is in the invention advantageously within 200 to 800 mm, preferably in the range from about 400 to 500 mm. The distance between the surfaces of the nozzles 50 facing the undulating web, Δ, is in the invention advantegously within 15 to 50 mm, preferably 20 to 30 mm. The said distance Δ is substantially larger than the corresponding dimension used in floater dryers known in themselves in the art. Hereby is achieved an amplitude of the wave motion which is large enough with a view to the stabilizing effect sought in the invention, and that there is no excessive risk of such occurrence that the web , comes

4 into contact with the surfaces of the nozzle 50. In floater dryers, which are used e.g. in the manufacturing of coated paper, the corresponding value of Δ is that at most about 10 mm, but in that case the aim is of course, above all, achieving of efficient drying action, not so much the obtaining of such stabilizing action as is the object of the present invention. The guided and controlled wave motion of the web W, eliminates or precludes wrinkles in longitudinal direction of the web. Furthermore, the controlled wave motion efficiently eliminates the free and detrimental fluttering. The gas jets discharging through the nozzles 50 of the stablizer 40,41 also spread the web out in its transversal direction and thereby straighten out any longitudinal wrinkles occurring in the web, and

they have the result that the transversal expansion resulting from the wetting of the web does not consume too much time.

The construction of the nozzles 50 according to the invention, to be . described more closely later on, is characterized in that said nozzles 50 permit a larger than before spacing Δ of the opposed nozzles 50 and larger than before variation of the angle under which the web W» enters. The variations of this angle of entry are caused e.g. by the circumstance that according to the invention the web may be conducted with a comparatively low tension and hereby the point where the web W.. is detached from the central roll 12 of the three-roll size press, or from the top roll 11a;lib of an oblique size press, is variable. A- similar favourable property is presented by the turning means 20;20a;20b of the invention, to be described later on.

In Fig. 1, a means 20" has been indicated before the turning means 20. The means 20" serves exactly the purpose that its carrying surface provided with nozzles permits the above-mentioned variations of the direction in which the web W enters, i.e., of the angle α~. Throat-resembling means equivalent to the means 20" may also be used on the entry margin of the stabilizer means 40,41.

In the following is described, with reference to Figs 5,6 and 7, a favourable structural example referring to the nozzles 50 of the stabilizer means 40,41.

The nozzle of Figs 5,6 and 7 comprises a nozzle box, the gas which is to be blown from its interior through apertures 51 being conducted into the side volumes 52 and 53 of the nozzle, defined between the inner walls 54,55 and outer walls 60 and 61 of the nozzle. The inner walls 54 and 55, in their upper part, curve towards each other e.g. substantially in the shape of a circular arc (R„) . Hereby is formed a carrying surface 56, over which the wet web W^ passes at the smallest distance Δ.. The planar parts 62,63 of the outer nozzle walls 60,61 pointing towards each other define together with the curved portions (radius R) of the inner wall 54,55

nozzle slits 57 and 58, which are preferably located on the curved portions of the walls 54 and 55, in the region of the angle α . The angle α is the angle subtended by the starting direction s, of the gas jets discharging through the slits 57 and 58 and the plane of the web W,, and it is at the same time the angle at which the gas-jet guiding surface curves, starting at the mouth of the nozzle slits

57,58 and up to the plane L-L. The imaginary plane L- at the same time confines underneath itself a depression 59 serving as calming volume, where the gas jets v.. flowing opposite directions meet and constitute an air cushion supporting the web W and extending a considerable distance in the direction of travel of the web W..

4

Adjacent to the depression 59, the radius of curvature of the carrying surface 56, R_, is preferably substantially larger than the radius of curvature R.. of the guiding surfaces.

The said angle is advantageously selected so that no separation of the flows from the curved surface 56 takes place before the jets v- have been deflected to be fully parallel with the web W, . The jets v_ _j flowing against each other in the region of the depression 59 meet, and over the carrying surface 56 is established a compara¬ tively extensive air cushion supporting the web W, . If the nozzles 50 are used towards drying, it is significant that the heat transfer coefficient remains good, as a result of the vortex produced adjacent to the depression 59, also in the region between the nozzle slits 57 and 58. The angle α mentioned before, which is associated with the guiding surface, ^" is at the most 70 and preferably about 40 to 60°.

In Fig. 6 has been indicated the vertical centre-plane A-A of the nozzle, passing through the bottom of the depression 59 in the carrying surface 56. The construction of the over-pressure nozzle shown in Figs 6 and 7 is symmetrical with reference to its central plane A-A. The nozzles 50 may of course equally be carried out using asymmteric designs.

In the following is described, with reference to Figs 8 and 9, an advantageous design example of the turning and spreading means 20

employed in certain embodiments of the invention.

The contact-free turning and spreading means 20 for the web W», presented in Figs 8 and 9, consists of a curved surface 32 upon a frame, the web . running over said surface. As shown in Figs 8 and 9, the means 20 consists of an interior volume 20', confined by a planar walls 24 and by end walls 26. Through the passage 25, the air, or other treatment or supporting gas, is conducted through the curved, perforated wall 23 into said interior volume 20', whence it is further conducted to give support to the web „, through the nozzle slits 36 in a manner which will become apparent later on.

As shown in Fig. 8, the direction of the web W ₂ is altered on the carrying surface 32 through the angle 8, which is at the same time the sector over which the curved carrying surface 32, which preferably has a constant radius of curvature, extends. The surface 32 is composed of pressure surface laths 34 and spacer surface laths 35, which leave nozzle apertures 36 between themselves. The air is blown through these nozzles towards the web W _? from the interior volume 20' of the means, where it is introduced with the aid of a blower (not depicted), in such manner that the web W ₂ is carried at a suitable distance M from the carrying surface. The nozzle slits 36 are defined between the laths 34 and 35 in that the edges of the lath serving as pressure surface 37 are angulated inward over a curved surface 38, and the edges of the lath serving as spacer surface 39 join this first surface over a sharp edge 21. The edge 21 extends in the direction of flow of the jet to such distance that it imparts together with the rounded surface 18 to the jet a starting direction subtending with the the angle β.. at the site of the slit. Since the aim is to achieve that the air jets S follow without separation the curved surface 38 up to the pressure surface 37 so that as efficient and stable support as possible might be obtained for the web W„, the width a_ of the slit in the nozzle 36, the radius of curvature R and the angle α are dimensioned with specific conside- ration of this requirement. Reference is made in this connection to the study by D. . McGlaughlin and J. Greber, "Experiments on the Separation of a Fluid Jet from a Curved Surface", American .

Society of Mechanical Engineers _r Advances in Fluids, 1976, p. 14-29, which reveals that at the flow velocities which come into question in a construction of this kind the jet is able to follow the curved surface through about 45 to 70°. The sharp edge is so positioned with reference to the rounded surface 38 that in the cross section the normal on the line connecting the edge and the centre of the rounded surface subtends with the direction of travel of the web an angle which is 70° at the most. The lenghs 1.. and L_ of the pressure surface and spacer surface, respectively, are then preferably chosen such that the ratio of their combined length L-i+L ^an( i ^tne width a of the nozzle apertures is between about 20 and 200.

The spacer surfaces 39 lie substantially in the same plane as their adjacent pressure surfaces 37. The spacer surfaces 39 have on both sides a sharp edge 21. Said sharp edge 21 prevents the jets dis¬ charging through the nozzle slit 36 from turning in over the spacer surfaces. The effect on the jets S from the curved guiding surfaces 38 based on the Coanda phenomenon is so powerful that not even the moving web is able to change the direction of the jets. The blowing air or other equivalent gas discharging from the nozzle elements is able to escape only from the sides of the web W», because the guiding, pressure and spacer surfaces block all other air exit paths. The flowing of air above/below the web out to the' sides produces an active effect spreading the web ₂ out, an action which is important for instance in preventing wrinkling of the web that has been wetted in the surface sizing step.

With the web supporting, spreading and/or turning means 20, a highly stable carrying force is obtained with low energy consumption, and it is well appropriate for the treatment of widely different types of webs. As the air escapes from under the web through its sides, this gives rise to a force spreading the web tø. , and this is advantageous from the viewpoint of the invention in many respects.

An embodiment of the invention in which specifically the active web spreading action by the aid of means 20 and/or 40,41 is applied, e.g. by using air flows which turn to be transversal, is favourable

also in the respect that the-web will then require less time for expansion caused by the water introduced in connection with the size pressing. It follows that owing to this, already, the length of the draw between surface sizing and after-drying can be reduced. If to this is added that contact-free stabilizing means as taught by the invention are used, it is clear that a favourable synergistic effect is obtained.

Moreover, with the stabilizer means 40,41 shown in Figs 5,6 and 7 and with its nozzle 50 is prevented toppling of the blow jets and decrease of the heat transfer coefficient between nozzles. The nozzle slits 57,58 are so disposed on the curved nozzle that the jets (V-, v ₂ ) follow without separating the nozzle surface 56, which is given a curved shape such that between the nozzle slits 57 and 58 is formed a depression 59, a kind of calming region, whence the jets (v.. and v„) flowing in opposite directions meet, constituting an air cushion supporting the web , and extending far in the longitudinal direction of the web W, . The heat transfer coefficient can be made quite favourable also in the area between the nozzle slits 57 and 58 as taught by the invention. Since no sharp air jets impinge on the web W, and since toppling of the jets (v.. ,v ₂ has been prevented by the perfect aligning, the travel of the web W, can be made smooth and flutter-free by employing nozzles 50 as taught by the invention; this is of essential significance with a view to achieving the overall aims of the present invention.

The apparatus combination of the invention, i.e., the combination of a size press, in which capacity preferably is used a three-roll and two-nip size press, and of the subsequent contact-free stabilizing and guiding means, is placed in the drying section of the paper machine for instance so that about 2/3. of the drying cylinders operate before the apparatus combination of the invention and 1 3 after the apparatus combination of the invention.

It is to advantage regarding the use of a stabilizing means 40,41 as taught by the invention if the web , passes therethrough in a direction as nearly vertical as possible because in that case

removal of broke from between the nozzles 50 is easier than in case the space between the nozzles 50 and the components 40 and 41 were substantially horizontal.

In the following are stated the claims, various details of the invention being allowed to vary within the scope of the inventive idea thereby defined.