|Publication number||US3622058 A|
|Publication date||Nov 23, 1971|
|Filing date||Sep 25, 1967|
|Priority date||Nov 23, 1966|
|Also published as||DE1499078A1, DE1499078B2|
|Publication number||US 3622058 A, US 3622058A, US-A-3622058, US3622058 A, US3622058A|
|Original Assignee||Vits Gmbh Maschf|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Referenced by (39), Classifications (14)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent The portion of the term of the patent subsequent to May 21, 1985, has been discialmed.
[ 54] CONTACT-FREE HOLDING OF A WEB OF SHEET MATERIAL GUIDED IN A FLOATING MANNER 7 Claims, 9 Drawing Figs.
 U.S. Ci 226/7, 226/97,101/228,101/416 A, 302/31, 34/156 [51 Int. Cl B65h 17/32, F26b 13/20  Field of Search 101/232, 228, 416 A; 302/31, 63; 226/7, 97; 34/10, 57, 156,
[ 56] References Cited UNITED STATES PATENTS 2,176,093 10/1939 Merrill 117/64 Primary Examiner.l. Reed Fisher Attorney-Michael S. Striker ABSTRACT: A web of sheet material, such as paper is held free from contact with mechanical supports by providing a floating support system. Nozzles on a support side of the web send air from a blowing chamber through at least one slitshaped orifice that is set to deliver air to the web at an angle. The wall of the nozzle which faces away from the web is shaped to provide a convex domelike profile. which preferably is perforated to provide a novel effect on suction forces there. There may be two slit-shaped orifices at each nozzle, both set at an angle to the web and shaped as mirror images of each other, both orifices having adjacent perforated domelike profiles. The device and method are applicable to paper driers, multicolor offset and gravure presses, and to climatic treatment of paper.
PATENTEnunv 23 I97! 3, 622 058 sum 3 or a Pressure J, D min. n M m Distance from Nozz/e- F lg. 9
Inventor: H/L MAI? VI T5 BY 00m ZA J M A r 705w; vs
CONTACT-FREE HOLDING OF A WEB OF SHEET MATERIAL GUIDED IN A FLOATING MANNER The invention relates to the contact-free holding of a web of sheet material by guiding it in a floating manner through an interspace between the nozzles of blowing chambers. It applies both to single-coated and the double-coated webs, especially of paper, as in coating machines, color presses, and climatic treatments machines.
It is known to guide webs which are to be dried in contactfree manner by nozzles which form a gap in the direction of the width of the web, between which air exhaust spaces are provided, directing the issuing air, half in the direction of movement and half counter to the direction of movement of the web, into flow channels which directly follow on to the noule exit.
When drying sensitive materials that are in a web form, it is important to avoid contact between the web and the nozzles at any point. The danger of such contact is heightened by the tendency of the edges of the web to flap, and the stronger the stream of air blown against the. web,.the greater the tendency to flap. Thus the need to limit the velocity of airstreams in order to prevent flapping has, in turn, limited the drying capacity of prior art floating driers, so that relatively long channels have been required in order to achieve the requisite drying.
Webs of material treated on only one side, such as paper coated on one side, have hitherto been run over rollers in a drier, the coated side facing upwards, and the drying air could then be blown against the web at relatively high pressure and at high speed, and the drying channel could be short. However, the guiding of single-side treated webs of material over rollers had numerous disadvantages. One difficulty was that the rollers had to be relatively close together and had to be precisely machined, chromium-plated and polished, all of which resulted in high plant costs. The drive mechanisms for the rollers also were quite expensive since in most cases several rollers were grouped together for each drive, and many groups of rollers then had to be synchronized with each other. The drive.devices also impeded the accessibility of the drying channel.
A further disadvantage that resulted from the use of rollers was that contaminations of the rollers were transferred to the web of material. Also, when coating ink passed through a defective patch in the web of material on to one of the rollers, the ink would dry solid there and form a small raised area which with each revolution of that roller pressed a corresponding recess into the web.
Furthermore, it is difficult to prevent creases from forming in the web when using support rollers. On taking up moisture, a web of paper expands both lengthways and widthways. In order to prevent creases from being rolled in, the web has therefore been stretched widthways by special so-called spreader rollers. Nevertheless the tendency of paper webs to form creases has still presented difliculties, which became greater as the web ran more rapidly, as the web was broader, and as the web was thinner.
One more disadvantage of guiding single-coated paper on rollers was that adjacent rollers had to be set extremely accurately if the tendency of the web to drift sideways was to be prevented; once it has drifted the web cannot be returned to the center of the track even with the aid of control devices. When a new roller-equipped drying channel was started up many tons of paper were regularly lost as a result of the web drifting sideways, until finally all the rollers were precisely set.
Despite the above-mentioned numerous disadvantages, roller-supporting of webs has hitherto been standard in driers handling single-side treated webs of material, in order to enable use of the strongest possible streams of air. Guiding a web exposed to strong stream of drying air was believed to require such rollers. However, the present invention solves the problem of floating by supporting a web of material which has strong streams of drying air blown against it. I have found that by use of a novel nozzle structure on the underside of the web of material, it becomes possible to support the web of material free of contact and furthermore to quiet manner.
The invention comprises providing on the support side of the web material nozzles having a slit-shaped blowing orifice which delivers a stream of air directed against the web at an angle, and having an outer wall facing away from the web and extended to form a profile that domes convex to the web, in the manner of a support surface, though it does not actually touch the web. 1 have found that a stream of air which is blown by the nozzle over a nozzle wall which is thus domed forms a cushion, a kind of air lubrication, for the web of material, and although the web comes very close to the nozzle under the pressure of the drying air blown on to it from above, it does not mechanically touch the nozzle. Furthermore, even with very thin webs of material and high airspeeds, the guiding is especially quiet if the domed nozzlewall is provided with perforations through which air can stream.
On this last-mentioned feature, one phenomenon to be considered is that when a stream of air flows over a support surface, both pressure and suction forces are generated. With a nozzle constructed in accordance with the invention, the pressure forces arise in the vicinity of the nozzle and the suction forces predominate at a distance from the nozzle. The suction force on the part of an unperforated domed wall remote from the nozzle opening can, if the web of material is close to the wall, become sov great that the web begins to flap. However, such flapping is avoided by the perforation of the domed nozzle wall, the perforated domelike structure producing the surprising effect that the suction force remains practically unchanged as the distance from the web to the wall changes, but that it changes to a pressure force when the distance is very small. With nonperforated support surfaces, the changeover from suction to pressure takes place only after touching, i.e., where the distance is zero, and changes from pressure to suction at a distance about equal to the width of the nozzle; in contrast, the changeover in the case of my perforated surface takes place at a distance which is approximate ly equal to the width of the nozzle, in both directions. Hence, while with a nonperforated wall, the web must flap and swing because of this property, it lies quiet in the case of my perforated nozzle wall.
This surprising phenomenon appears to be based on the fact that when the distance between the web and the wall is very small, the excess pressure which produces the pressure force becomes even greater in front of the narrowest position between the web and the wall and can only be compensated by the perforation to a very small extent, while behind this narrowest position a significant pressure reduction is produced under whose influence air is sucked through the perforation, thereby preventing a further increase in the suction force by disturbance of the boundary layer. Thus the web of material cannot touch the domed surface. Instead, a surprisingly stable equilibrium is set up between the various forces. The consequence is that the web of material is guided in an exceptionally quiet manner.
l have further found that nozzles which, relative to a vertical plane running at right angles to the direction of travel of the web, have two slit-shaped blowing orifices arranged as mirror images to one another, with extensions, adjoining thereto, of the nozzle defining perforated walls which are domed in the manner of a support surface and face away from the web, are particularly suitable for supporting webs of material which are dried from the top surface by blowing strong currents of air at it.
Nozzles constructed in accordance with the invention can also be used for many other purposes. For example, it has surprisingly been found that a long unsolved problem met in roller offset printing technology and other wet on wet" printing processes can be solved by using a device according to the invention provided with slit nozzles facing towards one side only.
In roller offset printing, multicolored prints are produced on both sides by bringing pairs of rollers inked with various colors guide it in a surprisingly successively into contact, in all cases on both sides simultaneously, with the paper web passing between them. It is usual to print in four colors, and in order for the print to appear clear and clean, it is necessary for the individual colors printed over one another to correspond exactly to register. An exact overlap of the register marks is however not possible because of the differential stretching of the paper on taking up the printing ink and the water, if the sets of printing rollers run identically. The printing rollers must therefore be subsequently adjusted. This is done by optically examining the register marks. An optical system is therefore provided ahead of each printing roller, which views the register mark which has been printed by the preceding roller, and on the basis of its position the optical system gives a signal which corrects the subsequent printing roller, if necessary. However, the paper web frequently vibrates strongly between the printing rollers, since it frequently detaches itself somewhat too late from the preceding roller as a result of the adhesive action of the wet printing ink. Since both sides of the paper are printed, the paper web alternately adheres for a brief moment to the upper and for a brief moment to the lower roller. The vibrations resulting therefrom are very harmful to the subsequent optical system which is intended to view the register mark, since each optical system has a relatively small depth of focus, and the control cannot be sensed to give proper control if the mark moves out of the focusing range. Despite the use of optical and automatic control devices it was therefore necessary always to provide a manual override for the register control, and these overriding corrections could only be carried out by the operator in an approximate manner and on the basis of a finished print at the end of the machine. Manual regulation takes place too late and produces poor printing images and high waste.
This difiicult problem can be solved by use of the nozzle of the invention, which blows air to one side and is provided with an extension in the shape of a domed support surface. When such a nozzle is provided underneath the paper web, opposite an optical sensing device for register control, the web remains stable in this region, apart from very high slight vibrations. The optical system can therefore always sharply focus on the register marks which are on the very rapidly running paper. This method also solves the hitherto particularly great difficulties in sensing the yellow color especially on glossy paper.
My new nozzle can also be employed with equal success in four-color gravure printing technology, where the problems are similar.
Another problem has related to changes in direction of movement of the web. As a result of the particular flow conditions which are established between the web of material and the nozzle of the invention, the web of material is drawn towards the perforated domed surface, which is an extension of the nozzle wall, and is kept in this position even if the web is under relatively great longitudinal tension. Thus, changes of direction of the web can be made with the aid of the nozzle of the invention; direction changes of up to about deviation from rectilinear travel of the web are attainable in both sideways directions.
A further new application of the nozzle of the invention arises in the climatic treatment of material in a web form. Coated paper, after passage through the drier, is often given a climatic treatment, i.e., it is brought to a normal moisture content and normal temperature after drying. The climatic treatment takes place by blowing on the paper air which corresponds to the temperature and humidity of the climate with which the paper is to be in equilibrium. In climatic treatment the webs of material have hitherto also been transported on driven rollers. The disadvantages which result are the same as those discussed above. Using the nozzle of this invention, it is now possible to guide the web in a floating manner during climatic treatment, the air supplied for the floating process being taken directly from the climatic treatment chamber or from an air pretreatment unit of the chamber.
Other objects and advantages of the invention will appear from the following detailed description of some preferred embodiments.
In the drawings:
FIG. 1 is a simplified view in side elevation and in partial section through a floating drier employing a nozzle embodying the principles of the invention for supporting a web of material subjected to drying air from above.
FIG. 2 is a partial view in vertical section through the edge zone of a web of material, the three broken line portions indicating three alternative positions of the edge.
FIG. 3 is a schematically represented view of a portion of a so-called polygonal roller drier.
FIG. 4 is a schematic side view of a fourcolor roller-type offset printing machine, employing the principles of the present invention.
FIG. 5 is a somewhat diagrammatic view in side elevation of a nozzle according to the invention as incorporated into the machine of FIG. 4.
FIG. 6 is a diagrammatic view in side elevation of nozzles according to the invention as used for changing the direction of webs of material.
FIG. 7 is a front view of the nozzle of FIG. 5.
FIG. 8 is a schematic sectional representation of a two-stage drier with subsequent climatic treatment device, embodying the principles of this invention.
FIG. 9 is a graph showing certain characteristics of the nozzle of FIGS. I and 5.
The nozzle N of the invention, represented on the left in FIG. 1, is used with a blowing cabinet 1, which extends over the entire width of a drier. A plate 2, which is slightly concave in cross section and is perforated at 2a, is provided between sidewalls 3, the upper part of which is bent over in both directions, so as to form two slit-shaped nozzle portions 2b blowing in opposite directions to one another. The sidewalls 3 are extended beyond the nozzle opening and form a profile in the shape of a support surface, which is domed, i.e., curved convex to the web of material W. Openings or perforations 3a are provided in that part of the side walls 3 which is in the shape of a support surface and which projects beyond the mouths 2b of the noule N, and there are unperforated end sections A. A directly blowing nozzle 4 for increasing the drying capacity may be provided, in the case of porous paper, between each pair of successive nozzles N. Conventional nozzles 5 of any desired construction serve to dry the web of material W from the top side.
As can be seen from FIG. I, the web of material W rests on an air cushion in the zone of the double nozzle N, which is provided with the extensions in the manner of a support surface. These air cushions form between the concave plate 2 and the underside of the web of material W in the space C. The web of material W is pressed downwards by the stream of air from the upper nozzles 5. As a result, the interspace between the web of material W and the nozzle walls 3 narrows slightly, approximately at the positions marked B. Since the stream of air flowing between the walls 2 and 3 and/or the part of the air which issues through the perforations 2a in the plate 2 has its outflow impeded, air accumulates in the space C above the plate 2; this lifts the web of material W and improves the possibility of outflow of the air at the positions B. The web W of material assumes a surprisingly stable position above the nozzle N of the invention, corresponding to the pressure of the air blown onto it by means of the nozzles 5 and the weight of the web W.
It follows from FIG. 1 that the web W is not guided in a rectilinear manner but is guided in long waves as a result of the aerodynamics of the nozzles. This manner of guiding the web prevents the rolling-up or tuming-over of the edges of the web which is otherwise familiar.
FIG. 2 reproduces a section through the side zone of a web W. In the dry state, i.e., before applying the coating ink, the edge lies in the part R and in the same plane as the remainder of the web W. If the coating ink is now applied, the web extends on its upper side and the edge zone bends over downwards as shown by R,. On subsequent drying the upper side shrinks more rapidly and more strongly than the middle and lower part of the web of material. As a result the edge tends to roll up in an upwards direction as shown on R;,. In
order to prevent this objectionable phenomenon of rolling up, the prior art resorted to so-called polygonal roller driers, wherein the web'of material W is guided over rollers 6 which are not arranged rectilinearly behind one another but over a track which is curved concave towards the underside. It will be readily appreciated that if the web W is guided in this way, it is kept plane even if the side edges have a tendency to roll upwards. Even if the web W is tightly tensioned longitudinally in driers with average fan capacity, the aerodynamics of nozzles N according to FIG. 1 are more powerful than. the rollingup force at the edges of the web, even if papers and coatings giving a particularly great tendency to rolling-up are being run. Hence polygonal driers need not be used in the nozzles of this invention.
FIG. 4 shows a series of nozzles N and N according to the invention; in principle the nozzles N correspond to the nozzle N of FIG. 1 but the nozzle N only blows in one direction. This can be used in order to keep quite a web P of paper which is to beprinted in several colors by the offset printing process as it moves between the printing rollers 7a, 7b, 7c and 7d. This is necessary in order to be able to sense optical register marks on the paper web P and thereby to be able to adjust the control of the subsequent printing roller as required.
A roller offset printing machine for four-color printing is usually constructed in accordance with the principle represented in FIG. 4. In this, the first pair of rollers 7a prints in a yellow color, the second roller pair 7b in a red color, the third roller pair 70 in a blue color and the fourth roller pair 7d in a black color. The paper web P thenruns into a drier T in which the printing ink is dried.
Since the paper web P extends longitudinally on printing as a result of taking up moisture, and since theextension depends on the moisture taken up in the particular case, which varies according to the surface being printed, difficulties are caused if the web tension is relaxed between the printing rollers. The mechanical elastic tension of the web P decreases as the tension-free extension due to moisture increases, and this affects the machine's ability to print the colors precisely over one anotherin the desired manner. The register of the print of the subsequent printing rollers withthat of the preceding rollers must therefore always be rechecked. Optical sensing devices 9 are therefore provided close to the web P to sense register marks printed by the preceding roller. However the paper web P does not run quietly between the successive rollersbut executes relatively large vibrations atright angles to the plane of the web, because the paper web-P issuing from one pair of rollers continues to adhere for a brief moment to the upper or lower roller, depending on the printing ink which has just been applied, and only detachesitself when it has accompanied the roller for a short distance of its rotary movement. Since the positions at which these sticking phenomena occur are displaced relative to one another in the longitudinal direction of the 'web as far as the upper and lower rollers are concerned, corresponding to'the printed image, the web P alternately swings upwards and downwards. In order to be able to transmit precise control impulses, the optical sensing devices 9 must be able to focus sharply, in their field of view, on to the marks which pass by at very high speed. The depth of focus of these optical devices 9 is very low because of the short distance from them to the paper web P. The marks provided on the paper web therefore leave the focusing zone of the optical sensing device even if the web swings upwards or downwards a relatively slight amount. Attempts have therefore been made to bring the sensing device as close as possible to the infeed 8 of the subsequent roller. The web P is of course relatively quiet just in front of the new roller. However, this arrangement does not really solve the problem, since the device 8 is in the region of soiling-by the inking rollers. Cleaning the optical equipment requires stopping the machine because of the danger of accidents due to the immediate vicinity of the rapidly rotating rollers.
I have found that by incorporating a nozzle N, which is shown in more detail in FIG. 5, at the location shown in FIG. 4
and 5, the paper web P is kept sufficiently quiet in the region of the optical sensing device 9, and the optical sensing device 9 remains accessible during the running of the machine.
As FIG. 5 shows, the nozzle N has a slit opening I1 pointing sideways and upwards provided on a tube-shaped box or cabinet 10, with two nozzle walls 12 and I3 curved in a clockwise direction starting from the side edges of the opening 11. The left-hand nozzle wall 12 is significantly shorter than the right-hand nozzle wall 13, which corresponds to a domed or convex profile in the shape of a support surface and is extended in the running direction of the web P. The nozzle wall 13 is again provided with perforations 13a. The air supplied from the nozzle box 10 flows along the underside of the paper web P, partly counter to its direction of running and partly parallel to the direction of running of the web. The air redirected thereby causes the pressure cushion, and the air which basically continues to flow along the wall 13 in the original direction causes the suction efiect in conjunction with the curvature of the support surface. A reduced pressure is thereby produced under whose influence the web P retains the position indicated in the drawing even if vibrations are transmitted to the web.by the printing rollers working further forward. Since the web P lies practically completely quiet in the region of the sensing device 9, the optical system contained in the device 9 can sharply focus on the register marks provided on the rapidly moving web P. The control impulses trans mitted bythe device 9 for adjusting the subsequent pair of rollers if necessary are therefore reliable and precise.
As has been mentioned in conjunction with FIGS. 1, 4 and 5, a suction effect is produced at the nozzles represented in these figures, which urges the web P against the nozzle wall I3 where it curves in the manner of a support surface, but at a certain distance. This holding effect of the nozzle N can, according to FIG. 6, also be utilized for changing the direction of webs of material W of any kind. It has been found that it is possible both to change direction in accordance with the upper part of FIG. 6, in which the web of material W runs concave to thenozzle, and also to change direction in a way such that, according to the lower part of the representation in FIG. 6, the web of material travels convex to the nozzle. In this case it is advantageous to use double-channelled nozzles 10' whose outward-bent walls, in the manner of a support surface, are marked 12 and 13'.
FIG. 7 shows a nozzle N according to FIG. Sin a front view. The nozzle N formed by the curved walls 12 and I3 is mounted on an air box 10, which is tubular in the present case, and to which compressed air is supplied from the side by means of a blower 14. The air flows through the broad gapshaped opening as shown in FIG. 5, with the perforations 13a in the nozzle wall 13 serving to quieten the airflow.
The nozzles represented in FIGS. 4-7 can, according to FIG. 8, also serve for the climatic treatment of a web P passed through a drier. In the plant represented schematically in FIG. 8, V is the supply roll from which a paper web P which is to be provided with coating ink on both sides is drawn. The web P is first coated on its upper face in the device 8,. The web then travels fromv left to right through a drier T, which may for example be constructed like the drier of FIG. I. After the first passage through the drier T, paper web P is redirected over appropriate rollers 15, 16 and 17 and is fed to a second coating device S which provides the hitherto uncoated side of the paper P with coating ink. Thereafter the web P passes through the drier T for a second time, preferably in another portion thereof, this time with the initial underside facing upwards.
Since the paper always becomes heated in a drier T of this type, it is necessary subsequently to give the material a climatic treatment, i.e., to bring it to a normal temperature and a normal moisture content. This takes place in a climatic treatment zone Z in which cold, appropriately moist, air is blown over the material. Here again nozzles N according to FIGS. I and 6 (or nozzles N of FIG. 5) have proved successful for guiding the web P free of contact. Instead of having to provide expensive guide rollers and devices for supplying the climatic treatment air, as hitherto, the nozzles N according to the invention fulfill both tasks simultaneously, i.e., they carry the web and the air expelled at the same time serves for the climatic treatment of the material.
The characteristics of the twin nozzle N according to FIG. 1 and the single nozzle N according to FIG. 5 are represented in FIG. 9. Herein, the impact force D, i.e., the excess pressure acting upwards, and the suction force, i.e., the reduced pressure acting downwards, are plotted vertically, whilst the nozzle distance is plotted to the right. The paper web P assumes its position in accordance with the large pressure reduction D,,,,,,. In the case of an air supply on the scale of currently usual nozzle driers and of a strength corresponding to currently justifiable economic, the maximum impact force D,,,,, is several kilograms per square meter, and the suction force is a few kilograms per square meter. Thus a web of material can also be guided suspended at a distance below the nozzles of the invention, but after switching off and again switching on the air, the web will only reassume the position D if the initial distance does not exceed the suction distance S, which in the case of individually arranged twin nozzles can be up to about 30 times the slit width.
The impact force of vertically blowing nozzle systems and the weights of webs of material to be finished, together with the coating, are small in relation to the maximum or minimum pressure of the nozzles according to the invention, so that given the steep slope of the pressure curve in the region of D,,,,,,, i.e., in the usual working region, the dependence of the distance from the nozzle on the load is, in practice, neither perceptible nor such as to require consideration. The distance of material to the nozzle at the normal working position D,,,,,, is in practice somewhat smaller than the nozzle slit width.
Where the nozzles according to the invention follow each other very closely, an impact force overlaps, as a result of which the line of origin of the pressure may be displaced from 0 to 0, and possibly even to 0". This can be useful if the weight of the goods is exceptionally large, as in the case of soft floor coverings, or where the excess pressure on the other side of the nozzle is exceptionally large.
To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.
1. Apparatus for guiding a web movable in longitudinal direction in a floating and stable manner comprising, in combination, at least one nozzle means arranged beneath the bottom face of the web for blowing a stream of air at an acute angle against said bottom face, said nozzle means having at least one slit-shaped blowing orifice defined by a pair of spaced walls, one of which having an inner surface facing said bottom face, and including wall means forming an integral stepless continuation of said one wall, said wall means having a face facing said bottom face of said web and extending convexly curved toward said bottom face spaced from and closely adjacent thereto and being formed in the apex region thereof with a plurality of openings therethrough spaced from each other in longitudinal direction of said wall means.
2. Apparatus as defined in claim 1 wherein said nozzle means comprises two slit-shaped blowing orifices each defined by a pair of said spaced walls and each including said wall means formed with said plurality of openings therethrough, the pairs of spaced walls and wall means being arranged mirror symmetrically with respect to each other.
3. Apparatus as defined in claim 2 and including a blowing box and passage means extending substantially normal to said web and connecting said blowing box to said pairs of said spaced walls defining said blowing orifices, said passage means having an end facing said bottom wall of said web and including a perforated plate extending over said end of said passage means.
4. Apparatus as defined in claim 2, and including a pair of blowing nozzles arranged on the other side of said web and respectively spaced in opposite direction from a plane of symmetry of said nozzle means.
5. A method of guiding a web movable in longitudinal direction in a floating and stable manner comprising the steps of providing at least one nozzle means arranged adjacent one face of the web, said nozzle means having at least one slitshaped blowing orifice defined by a pair of spaced walls, one of which having an inner surface facing said one face, and including wall means forming an integral stepless continuation of said one wall, said wall means having a guide face facing said one face of said web and extending convexly curved toward said one face spaced from and closely adjacent thereto and being formed in the apex region thereofwith a plurality of openings therethrough spaced from each other in longitudinal direction of said wall means; blowing through said nozzle means a stream of air at an acute angle against said one face of said web; guiding said stream of air on the side thereof distant from said one face in a continuous and stepless manner along said convexly curved guide face toward said one face to form a continuously confined turbulent free stream of air and to thus produce downstream of said apex of said convexly curved guide face suction forces in said airstream tending to draw the web against said guide face; and passing air from the outside through said plurality of openings toward said one face of the web to thereby reduce the suction forces to thus guide the web in a floating and stable manner.
6. A method as defined in claim 5, comprising the step of blowing the air in two airstreams against said one face of said web, said two airstreams being arranged mirror symmetrically with respect to each other.
7. A method as defined in claim 6, and comprising the step of blowing a third airstream between said two airstreams and in a direction substantially normal to the web against said one face of the latter.
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|U.S. Classification||226/7, 34/641, 101/424.1, 226/97.3, 101/228|
|International Classification||B65H23/04, F26B13/20, F26B13/10, B65H23/24|
|Cooperative Classification||B65H23/24, F26B13/104, B65H2406/112|
|European Classification||B65H23/24, F26B13/10B4|