TECHNICAL FIELD

The present invention relates to a method for control¬ ling or regulating shrinking and/or stretching of a paper web transversely to the transport direction of the web in the drying section of a paper machine in the form of a cylinder drier and/or a fan dryer.

The invention also relates to arrangements for control ling shrinkage and/or stretching of a paper web in the drying section of a paper machine in the form of a cylinder dryer and/or a fan dryer, transversely to the transport direction of the web.

BACKGROUND ART

A number of mutually different drying sections inten- ded for paper machines are known to the art, the majority of which sections incorporate a cylinder dryer and/or a fan' dryer with which to effect drying of the web. It has long been known that when drying a paper web in the drying sec¬ tion of a paper machine the web tends to shrink in both the longitudinal and transverse directions thereof.

—It-is.also known that shrinking of the web in its transport direction or machine direction can be controlled by driving mutually adjacent drying means in the drying sec¬ tion at different speeds. It is also known that improved values, or an improved index, can be achieved with regard to the strength properties of paper, by controlled reduction of shrinkage of the paper web in its axial or transport direction.

It is also known that control reduction in web shrinkage transversely to the web axis cannot be achieved in dryers of the aforesaid kind.

It has been shown, however, that a small force of certain magnitude acts across the whole width of the paper web, from the centre of the web outwards, as a result of the friction prevailing between the peripheral surface of a drying cylinder and the web. In connection with the known art there is described and illustrated in U.S. Patent Specification 3,650,043 an arrangement designed to stabilize a dried paper web, by blowing air thereonto in a manner to stretch the web.

The U.S. Patent Specification No. 3,452,447 also describes an arrangement for stabilizing a dried paper web, by blowing streams of air thereonto, so that the web is s-tretched.

It should be emphasized here that these paper webs have a dryness in excess of 75 % and preferably about 95 %.

DISCLOSURE' OF THE PRESENT INVENTION

TECHNICAL PROBLEMS

With regard to the prior technical standpoint in this art, the realization that the final s.trength properties of a dried paper web are dependent on the extent to which the finished paper has been permitted to shrink in different directions and that different degrees of shrinkage will result in varying properties in different directions, means that a technical problem must be considered to exist in the provision of conditions, with the aid of simple means, which enable all strength properties of a dried paper to be control led or regulated, such as flexural rigidity, tensile strength tensile rigidity and compression strength in the various directions. It must also be considered a more qualified technical problem to take such measures that the strength properties can be regulated in a simple fashion transversely to the

transport direction of a paper web to be dried.

Another technical problem in this regard is one of providing with the aid of simple means conditions which enable shrinkage of a paper web to be dried to be control- led and counteracted transversely to the transport direc¬ tion of the web, and also to provide conditions whereby the web can be stretched in said transverse direction..

When considering the fact that a varying degree of stretch, to counteract shrinkage or elongation in different directions, will impart varying properties to the finished paper in different directions, it must be considered a technical problem ^' with view to the present standpoint of. the art to create with the aid of simple means conditions which enable these properties to be substantially equalizied in the various directions.

Another technical problem is one of enabling measures to be taken which ensure that the paper web in the dryer section is dimensionally more stable.

A further qualified technical problem is one of ensuring that a paper web dried in the drying section of a paper machine obtains a uniform transverse profile, thereby to reduce the occurrence of so-called margin or edge effects, by which is meant marginal dried-web portions of lower strength properties.' A still further technical problem relates to the use of the specific peculiarity that variations in the extent to which stretching is effected, to counteract shrinkage or to produce elongation in different directions, will result in a finished paper- having varying properties in said different directions, such that these properties can be adapted to pre-determined requirements with the aid of simple means.

Another technical problem is one of providing a simple, inexpensive and operationally reliable arrangement which affords a solution to the aforementioned technical problems and which can be adapted for ready installation in existing drying sections.

A further technical problem is one of providing ways

and means whereby stretching of the paper web transversely to its longitudinal axis can be adapted so as not to result in a reduction of the mechanical properties desired in the paper web in its transport direction. It must also be considered problematic from a tech¬ nical aspect to obtain, with the aid of simple means, a dried paper web of improved quality, so as to enable there¬ by the selection of a lower surface weight and an increased filler mixture or an admixture of cheaper fibres to be used while maintaining the properties of the paper.

Another technical problem is one of providing means which enable those forces which are applied to the edge por¬ tions of a paper web to counteract the shrinking tendencies of the paper or which, when increased slightly cause the paper web to stretch in its transverse direction, to be applied to the web at the lowest possible dry solids content thereof, i.e. preferably in or immediately downstream of the press section, preferably when the dry solids content of the paper web is somewhat above 30 %. As will readily be understood, those fcrces applied to the edge portions of a paper web of low dry solids content, to counteract shrinkage, will not be as high as the forces applied to a web of higher dry solids content for the same purpose, and consequently a further technical problem is one of providing means whereby the forces applied to the said edge portions can be controlled identically or substan¬ tially identically and/or mutually differently, in dependenc on the properties desired, in order to counteract the latera shrinkage tendency of the paper web.

SOLUTION

The present invention relates to a method and an arrangement for regulating or controlling the shrinkage and/ or stretching of a paper web which is to be dried in the drying section of a paper machine, in the form of a cylinder dryer and/or fan dryer, transversely to the feed direction of the web.

It is proposed herewith, in accordance with the inven¬ tion, that means capable of co-acting with an edge portion or edge portions of the paper web is, or are, located along the whole or part of the drying section where the dry solids content of the paper web is at most 75%; and that said means are arranged to exert on the paper web an outwardly or trans¬ versel directed resisting force adapted to counteract sub¬ stantially shrinkage of the paper web and even to stretch said web. Preferably, the forces are adapted to counteract shrinkage to an equal or substantially equal extent through¬ out the whole drying interval. The means generating the aforesaid forces are preferably arranged in pairs on respec¬ tive sides of the paper web, such that the edge portions of the web are subjected to outwardly acting forces which are effective throughout the whole or a part of a given drying interval.

In accordance with one particular embodiment of the invention stretching of the paper web transversely to its transport direction with the aid of externally applied for- ces is effected at a location where the dry solids content of the web exceeds 30 %, such that the web need not be substantially stretched at remaining locations in the drying section at which the dry solids content is in excess of 75 %. Although the means which apply the aforesaid outward lateral force to the paper web, and particularly to the edge portions thereof, may have many different forms, it is proposed that said means comprise devices adapted to direct streams of pressurized air against the edge portions of the web, so as to create outwardly acting frictional forces against the paper. The aforesaid means may also comprise a device which will produce forces which counteract shrinkage and/or induce stretch in the transverse direction of the web through frictional and/or clamping forces. Alternatively, the said means may comprise an arrangement which is effec- tive to create forces on the web in a manner to counteract shrinkage and/or induce stretching in the transverse direc¬ tion thereof, through a combination of pressurized air/streams

and mechanical devices.

Because large forces are required to stretch a wide paper web, and because the magnitude of the forces required to effect a given degree of stretch increases greatly with increasing dry solids content of the web, it is proposed thatone or more strip-like members are arranged along respec¬ tive edge portions of the web for co-action therewith, and that there is provided a number of air boxes adapted to produce air streams which can be caused to press the edges of the web against respective strip-like members. Alterna¬ tely, the edge portions of the web can be pressed against a respective strip-like member with the aid of purely mecha¬ nical means, preferably with the aid of rotating brushes or opposing strip-like devices. In this latter case, it is proposed that the strip-like members are highly permeable to air and readily plastically deformed. The strip-like members may also be embossed or profiled to provide well-defined co- action with said edge portions without appreciable relative movement therebetween, therewith to provide an arrangement which creates forces which act substantially outwardly, such as to compensate fully for any tendency of the web to shrink, while simultaneously increasing the magnitude of said forces with increasing dry solids contents of the web.

Although the strip-like members may be made of rubber, plastics or textile material, they are preferably made of metal, such as stainless steel.

In order to obtain forces sufficient to counteract or resist the tendency of the web to shrink at high dry solid contents, the aforesaid embossments suitably have the form of depressions made in the strip so as to perforate same, thereby enabling relatively high forces to act in respec¬ tive directions relative to the transport direction of the paper web. Conditions are also created hereby which enable the paper web to stretch in its transverse direction, so that it can also be extended in said direction.

The strip-like member may suitably extend along the whole of the intended drying part, and is then conveniently

divided into sections. The aforesaid ^' means comprises a box¬ like structure provided with an. air inlet and having channel which are directed obliquely outwards towards the edges of the paper web, placed on a respective side of the web. In accordance with the .invention, several such box-like struc¬ tures are placed in the free draw of the drying section, by which is meant the distance between two adjacent drying cylinders.

Alternatively, the aforesaid means may comprise suc- tion boxes located on. respective ^" sides of the web in the proximity of the edge portions thereof, and including chan¬ nels which are directed towards the centre of the web. An auxiliary strip-like member may be arranged to accompany the paper web in a manner to increase the friction between the web and the air stream.

^• The aforesaid means may alternatively have the form of mutually spaced grooves which are formed in the wire accompanying the paper web and into which the edge portions of the web are pressed so as to hold the web firm. This downward pressing of the web edge-portion is preferably effected with the aid of one or more jets of pressurized air exiting from one or more nozzles associated with respec¬ tive grooves.

The web edge-portions may also be pressed into the grooves with the aid of one or more rings mounted on a roller, or may be effected with the aid of strip-like devices.

As a further alternative, the aforesaid means may comprise strip-like members which are arranged on each side of the web edge and positionally fixed over drying cylinders, and which accompany the paper web continuously through a plurality of drying cylinders. The strip-like member is thus fixed to the cylinders through the agency of grooves formed therein, and a further strip-like member, e.g. a drying felt, is arranged between the two aforesaid mutually spaced strip¬ like members. The strip-like members can be secured by means of a ring fitted to the roller. Finally, the edge portions

of the paper web may be fastened between two superimposed strip-like members, of which one member has provided on one surface thereof elongated beads or punctiform studs which are adapted to mate with corresponding recesses or grooves in the facing surface of the other strip-like member.

ADVANTAGES

Those advantages primarily afforded by a method and arrangement according to the invention reside in the possi- bility of controlling the strength properties of a dried paper web in the transverse direction thereof, by applying to the web during the drying process, at a location therein where the web has a dry solids content of 75 %, stretching or resisting forces such as to counteract shrinking tenden- cies of the web. In this way there is obtained a dried paper web of improved and controllable properties, e.g. such properties as flexural rigidity, tensile rigidity, tensile strenght and compression strength, in all directions. The main characteristic features of the method according to the invention are set forth in the characteri¬ zing clause of Claim 1 , while the main characteristic fea¬ tures of the arrangement according to the invention are set forth in the characterizing clause of Claim 15.

Other advantages afforded by the invention are dis- closed in the claims appended to the aforesaid claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Proposed embodiments at present preferred and exhi¬ biting the significant features of the invention and capable of being used to advantage in a method according to the invention will now be described in more detail with reference to the accompanying drawings,in which

Figure 1 illustrates schematically and in side view a drying section forming part of a paper machine; Figure 2 is a plan view of an arrangement having two members for producing laterally directed forces relative to the transport direction of a paper web, with the aid of air under pressure;

Figure 3 is a plan view of the arrangement illustra¬ ted in Figure 2;

Figure 4 is a sectional view of a slalom wire having grooves provided along the edges thereof; Figure 5 illustrates a slalom wire arrangement in which a cylinder is provided with two peripheral rings, which engage corresponding grooves in the wire, to press the paper web into said grooves;

Figure 6 illustrates a slalom wire arrangement in which the web is pressed into two grooves and held therein with the aid of strip-like members;

Figure 7 illustrates schematically and in side view a drying section which forms part of a drying machine and which has arranged therein means for generating forces which are directed laterally relative to the transport direction of the web and which are adapted to take-up shrinkage depen¬ dent forces;

Figure 8 illustrates an arrangement in which an edge strip is located on either side of the web edge portions and holds the edge portions firmly to the cylinder in grooves located therein;

Figure 9 illustrates an arrangement in which edge strips are held to or guided against the cylinder with the aid of two rings; Figure 10 illustrates an arrangement which incorpo¬ rates edge strips having two longitudinally extending flanges, such that the flanges of two similarly located edge strips will co-act with and be held against recesses -formed in the peripheral surface of •the cylinder, preferably adjacent to the end walls thereof;

Figure 11 illustrates and arrangement in which one end strip is provided with a longitudinally extending groove and the mutually co-acting edge strip with a corresponding longitudinally extending bead; and Figure 12 illustrates an arrangement in which streams of pressurized air are directed through air-injection boxes onto the web, to produce outwardly acting forces on an edge strip co-acting with the edge portion of the web.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

Figure 1 illustrates schematically and in s ^' ide view a drying section which forms part of a paper machine and which includes upper drying cylinders 6, lower drying cylinders 6', upper felt-guide rolls 7, and lower felt- guide rolls 7'. The paper web to be dried is referenced 1. Extending over the upper drying cylinders 6 and the upper guide rolls 7 is an upper drying felt 8, while a lower drying felt 8 ' extends over the cylinders 6' and the rolls 7 ^« .

Located on either side of the paper web in the open draw between the cylinders 6 and 6' adjacent edge portions 1a and 1b of the web are box-like structures 2 and 2', so- called blow boxes, which are adapted to cover the edge portions of the web. The blow boxes 2 are shown more clearly in Figure 3.

Pressurized air is supplied to the blow boxes 2, 2a through a respective inlet 4 and 4a and is caused to flow therefrom at high velocity through channels 3 directed obliquely outwards towards and away from the paper web. The streams of air thus produced bear against the web and the resultant frictional forces acting outwardly on the web prevent the web from shrinking in its transverse direction, and may also result in a certain amount of stretch. For the purpose of increasing the frictional forces acting between the air streams and the web, it is proposed that friction- enhancing strips 9 and 9' are arranged on mutually opposite sides of the edge portion 1a of the web, and also the edge portion 1b thereof. The arrangement -illustrated in Figures 4 to 6 is intended for use in paper machine where the drying section incorporates a so-called slalom wire. In a drying section which incorporates a slalom wire, the paper web lies between drying cylinders and wire, over each alternate cylinder. Over the "next" alternate cylinder the wire lies between the drying cylinder and the web.

In the Figure 4 embodiment, the wire 11 has grooves 12,12' provided along the edges thereof. As illustrated in

the Figure, the edge portion 10a of the web 10 is pressed into the grooves 12 by a pressurized air jet 13 exiting from a nozzle, and is held in said groove by the jet. Simi¬ larly, the other edge portion 10b of the web 10 is pressed into a groove 12' and held therein by a pressurized air jet 13* exiting from a nozzle 14'.

As shown in Figure 5, the paper web 10 may also be held to the wire in the groove 12 or 12' during passage of the web 10 over the cylinder 6 with the aid of two rings 15 and 15' respectively, peripherally arranged on the cylinder and engaging the grooves 12, 12', to press the web there¬ into.

Figure 6 illustrates another variant in which the paper web is held pressed into respective grooves 12 and 12' with the aid of a respective strip-like member 16 and 16*, so as to hold the web to the wire 11.

Figures 7-11 illustrate other arrangements and devices for holding the edge portions of the paper web against the cylinders and therewith fix the edge portions of the web so that the web can be dried without shrinking in its transverse direction, by applying external forces along the edge portions of the web to counteract shrinking tenden¬ cies.

A certain amount of stretch may also be obtained in the transverse direction of the web, especially at low dry solids content.

A common feature of these arrangements is the use of a so-called edge strip ^" which is arranged to accompany the paper web 17 continuously through each drive group of drying cylinders.

Pairs of edge strips, such as those references 19, 19a, may be fixed in their mutual positions beyond the drying cylinders, in various ways.

The pair of edge strips 19,19a for one edge portion 17a of the paper web 17 and the pair of edge strips 19',

19a' for the other edge portion 17b are spaced axially at a given distance apart, and each pair of strips is intended to

exert a high -frictional force on a respective edge portion of the web.

In the Figure 8 embodiment, the edge-strip pairs 19, 19a and 19', 19a ¹ are located on either side of the edge portions of the paper web and are held against relative move¬ ment along the cylinder in grooves 21 , and 21 * formed at respective ends 18a and 18b of the cylinder 18.The effect can be further enhanced by providing a stiff or rigid drying felt 20 between the edge strips, this felt functioning as "precision block" therebetween and preventing .shrinkage of the web.

In the Figure 9 embodiment the pairs of edge strips and the edge portions 17a and 17b of the paper web are held and guided by respective rings 23 and 23' located around the cylinder 18. This embodiment also employs a.stiff or rigid drying felt 22, the defining edge surfaces of which are located adjacent the mutually facing surfaces of respective rings 23 and 23' .

It will be understood that the edge strips and co- acting edge-strip pairs may differ in form, so as to pro¬ vide sufficiently reliable co-action with the edge portions of the paper web to withstand outwardly acting forces due to shrinkage, and so as to be able to co-act with the end parts of the cylinder without being unduly displaced towards one another by said forces, but remain firm at a given set distance apart.

The Figure 10 embodiment incorporates pairs of edge strips 40, 40a and 40', 40a' provided with longitudinally extending flanges 41, 42, 43 and 44, where the edge strips 40a and 40a' co-act with and are firmly held in a respec¬ tive recess 45 and 46 formed in end-wall parts of the cylinder 47.

The edge strips can be attached to and caused to co-act with the edge portions of the paper web 17 in various ways.

Figure 11 illustrates an arrangement in which a first edge strip 28 is provided with a longitudinally extending groove 27,.while a second strip is provided with a corres-

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When the edge portions of the web are clamped rigidly, the forces produced therewith will resist or counteract the shrinkage forces occurring, so as to prevent, shrinkage of the web either completely or to a very substantial extent. The edge portions of the paper web may be clamped with varying degrees of firmness, so as to obtain grea.ter or smaller frictional forces, so that the resultant out¬ wardly directed forces permit shrinkage of the web to an extent determined by the magnitude of the frictional force created.

It also lies within the scope of the invention to adapt the outwardly directed forces in a manner such as to stretch the paper web in its transverse direction. This is effected to particular advantage during that part of the drying interval when the dry solids content is low, for example between 30 and 50 %.

In this case blow-boxes or other means are suitably used in the free draw.

Since the forces acting on the edge portions of the paper web to effect the same degree of stretch increase with an increasing dry solids content, it is suggested that these forces are increased along the drying interval, so that the whole of the drying sequence is effected with substantially identical inner stresses in the transverse direction of the paper web.

The extent to which the paper web is stretched in its longitudinal direction can also be regulated in accordance with known methods, independently of the stretch significant to the invention. By way of example it can be mentioned that stretching of the paper web in its transverse direction by 1% at a dry solids content of 40% improves the tensile index of the paper by about 30%, its tensile rigidity index by 23% and its compression index by 34%. The following conclusions can be drawn from other experiments carried out. All strength properties of the paper in its transverse direction are greatly increased when

shrinking is prevented or. reduced. The strength properties are further improved, when the paper, web is. wet. stretched in its transverse direction, this stretching being preferably effected at the lowest possible dry solids content, prefer- ably in the press- section or immediately downstream thereof. When stretching is effected at low dry solids content, lower shrinkage forces shall be counteracted, meaning that the stretching devices need not be equally as robust as those used for stretching the web at higher dry solids contents. The strength properties are also greatly improved, when the paper web is allowed to dry for free shrinkage at dry solid contents in excess of 75 %.

Consequently, the drying interval or drying path shal be located within the region where the dry solids content of the paper web exceeds 30%, preferably between 40 and 75%. As will be understood, the edge portions of the paper web may also be pressed against the strip-like members with the aid of mechanical means other than the previously illustra¬ ted means, preferably rotating brushed or opposing strip-lik members.

When the strip-like members arranged on a respective side of the drying cylinder have the form of steel strips, it is proposed that embossments are formed in mutual spaced relationship therealong, these embossments advantageously having the form of impressions which perforate the strip. In contact with the embossed strips are strips having rela¬ tively soft surfaces, such as to enable the embossments to penetrate therein in a resilient fashion, therewith to clamp respective edge portions of the paper web between the utual ly facing surfaces of a respective pair of strip-like member In this, and also other embodiments, pairs of edge strips may be caused to diverge in the transport direction of the web on each side thereof, to provide conditions whereby the web can be stretched in its transverse direction The strip-like members may extend along the whole of a given drying path or interval and may be divided into sections.

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paper web into said groove, therewith to stretch the. web transversely to its transport direction. This guarantees that active forces are distributed substantially uniformly across the whole width of the web. It will be ^" understood that the invention is not restricted to the aforedescribed embodiments given by-way of example, and that modifications can be made within the scope of the following claims.