US3807056A

US3807056A - Device for the contact-free support of a web of material

Info

Publication number: US3807056A
Application number: US00204203A
Authority: US
Inventors: D Norfolk
Original assignee: Polytype AG
Current assignee: Polytype AG
Priority date: 1970-12-04
Filing date: 1971-12-02
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30
Also published as: IT951649B; NL7116548A; DE2160131B2; CA969352A; AU3647171A; DE2160131A1; CH536772A; GB1340000A; BE776229A; AU462166B2; FR2114934A5; AT316982B

Abstract

For supporting a web of material in a contact-free manner and also for drying the material, a U-shaped box-like member is arranged so that its open side faces toward the surface of the web to be supported. An air baffle plate is positioned in the open side of the box-like member and has a curvilinear shape along each of its edges located closely adjacent to the opposite closed sides of the box-like member. The spacing between the opposite sides and the curvilinear surfaces of the air baffle provide openings through which air is directed so that it follows the curvilinear surface of the air baffle and provides a cushion between the air baffle and the web. The air baffle can be formed in various ways, for example, by a pair of spaced tubular members joined by a plate member, by an oval shaped member and by a plate member with curved edges joined by a flat or undulating section.

Description

United States Patent [191 Norfolk Apr. 30, 1974 DEVICE FOR THE CONTACT-FREE SUPPORT OF A WEB OF MATERIAL [75] Inventor: Douglas J. Norfolk, Koniz BE,

[21] Appl. No.: 204,203

[30] Foreign Application Priority Data Dec. 4, 1970 Sweden 16475/70 June 1, 1971 Sweden 7059/71 [52] US. Cl. 34/156, 226/97 [51] Int. Cl. F26!) 13/20 [58] Field of Search 34/156, 10; 308/DIG. l; 226/97, 7; 239/DIG. 7, 590.5; 302/29 [56] References Cited UNITED STATES PATENTS 3,622,058 11/1971 Vits 226/97 3,549,070 12/1970 Frost 34/156 3,452,447 l/l969 Gardner 34/156 3,448,907 6/1969 Otepka et al.. 34/156 3,384,282 5/1968 Vits 34/156 3,041,739 7/1962 Mgier-Windhorst... 34/156 3,367,581 2/1968 Kizilos et a1. 239/D1G. 7

FOREIGN PATENTS OR APPLICATIONS 1,145,572 3/1963 Germany 34/156 OTHER PUBLICATIONS Scientific American, June 1966, pg. 84-92, Vol. 214, No. 6, Applications of the Coanda Effect.

Germany 34/156 Primary Examiner-Meyer Perlin Assistant ExaminerPaul Devinsky Attorney, Agent, or Firm-Toren and McGeady ABSTRACT For supporting a web of material in a contact-free manner and also for drying the material, a U-shaped box-like member is arranged so that its open side faces toward the surface of the web to be supported. An air baffle plate is positioned in the open side of the boxlike member and has a curvilinear shape along each of its edges located closely adjacent to the opposite closed sides of the box-like member. The spacing between the opposite sides and the curvilinear surfaces of the air baffle provide openings through which air is directed so that it follows the curvilinear surface of the air baffle'and provides a cushion between the air baffle and the web. The air baffle can be formed in various ways, for example, by a pair of spaced tubular members joined by a plate member, by an oval shaped member and by a plate member with curved edges joined by a flat or undulating section.

6 Claims, 15 Drawing Figures III PATEHTED MR 30 I974 SHEET 1 BF 5 PATENTEBAPRBO I974 3; 807 058 SHEET 3 0F 5 Fig. 8

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zlw m/roz v 0006148 I Mae/0m DEVICE FOR THE CONTACT-FREE SUPPORT OF A WEB OF MATERIAL SUMMARY OF THE INVENTION The present invention is directed to a device for contact-free support and drying of a web of material and, more particularly, it concerns the configuration of the device for directing air so that it provides the necessary support without any direct mechanical contact or influence on the web of material.

Various apparatuses are known for supporting webs of material, mainly such apparatuses use nozzles which blow air directly against the web of material either perpendicularly or obliquely to it and frequently also include mechanical means for supporting the web.

Further, it has been known to arrange nozzle boxes on the opposite sides of the material web. In the German Auslegeschrift l,l93,468 a suspension drier is described which employs staggered nozzle boxes and an undulating web guide to avoid curving or warping of the web in the transverse direction.

Moreover, a suspension drier is disclosed in German Auslegeschrift 1,729,222 in which the nozzle boxes are staggered in the direction of the web and also have a convex curvature in the same direction and baffle plates are arranged on the transverse walls and form slotted nozzles for the moving web. However, a vibration-free guidance of the web is not assured with such suspension driers. Therefore, it is the primary object of the present invention to eliminate the disadvantages experienced in the prior art and to provide a device for contact-free support of a web which is relatively free of vibrations.

In accordance with the present invention, a web of material is supported in a contact-free manner by means of box-like members which direct air between a baffle plate and the web for supplying an air cushion and also for using the air to dry the web. Preferably, the box-like member has a U-shaped configuration with its open side facing toward the web and with the air baffle positioned within the open side and spaced along its edges from the adjacent sides of the box-like member. The edges of the air baffle adjacent the sides of the boxlike member have a curvilinear shape and are spaced from the adjacent side surfaces to provide narrow elongated slot-like openings through which air can be directed. Because of the curvilinear configuration of the baffle at the slot-like openings, air discharged from the boxlike member flows over the curved surfaces and is directed across the baffle toward the opposite opening.

Various arrangements of the air baffle can be provided such as a pair of spaced tubular members interconnected by a plate member, an oval shaped member and a plate member having either a flat or undulating surface between the curvilinear surfaces defining one side of the slot-like openings from the box-like member.

Preferably, the box-like members from which the air is directed are arranged across the opposite surfaces of the web with the air baffles arranged in staggered relationship. The invention is intended primarily for use in the paper, film and foil industries where piece material or a web of material is coated on one or both sides or where several webs are combined and subsequently transported through a passageway, tunnel or similar structure for drying, polymerization, fusion, baking, material changes, and the like.

The device in accordance with the present invention, can be adapted individually or in groups to meet the requirements of the individual operation being effected on the web, for instance, drying, cooling, heating and supporting.

Unlike many known devices, the present invention affords a device which provides vibration-free guidance in the longitudinal or transverse direction of a stationary material web or of a web moving at any desired speed.

By arranging the device both above and below the web, the web tension can be varied within a wide range, that is by the range of tension produced by the air flowing from the nozzle-like openings in the device, and such variation can be altered without impairing the supporting or carrying properties of the device.

Since the device can be used for webs of thin foils or of thick cardboard and in instances where the overall height of the device must be'limited, numerous tests have indicated that the device yields optimum results in accordance with the intended use.

The various features of novelty which characterize the invention are pointed out with particularly in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a sectional view of one embodiment of the present invention taken along the line A-B in FIG. 3;

FIG. 2 is a schematic view of a plurality of devices such as shown in FIG. 1 arranged in staggered relationship on the opposite sides of a web of material;

FIG. 3 is a top view of the embodiment of the present invention shown in FIG. 1; 7

FIG. 4 is a longitudinal sectional view taken along the line C-D in FIG. 3;

FIG. 5 is a longitudinal sectional view taken along the line E-F in FIG. 3;

FIG. 6 is a side view of another embodiment of the present invention; 1

FIG. 7 is a schematic side view of a device embodying the arrangement shown in FIG. 6 with the device for supporting the web being located above and below its surface;

FIG. 8 is a view, similar to FIG. 6, of still another embodiment of the present invention;

FIG. 9 is a side view, similar to that in FIG. 7, of devices embodying the arrangements of FIG. 8 arranged opposite both surfaces of a web of material;

FIG.

S

10,11 and 12 are views similar to FIGS. 6 and 8 showing still further embodiments of the present invention;

FIG. 13 is a side view of devices embodying the arrangement as shown in FIG. 12 for supporting the opposite surfaces of a web; FIG. 14 is a view of yet another embodiment of the present invention; and

FIG; 15 is a side view of a pair of oppositely disposed devices embodying the arrangement shown in FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION In FIGS. 1 to a device is shown for supporting a web of material. The device includes a U-shaped box-like member 4 open on its face or side directed toward the web 14. Supported within the U-shaped member 4 are a pair of laterally spaced tubular members 1,2 arranged so that their outer surfaces are spaced closely from the adjacent inner surfaces of the legs 9 of the U-shaped member. Due to the relative arrangement of the tubular members 1 and 2 and the adjacent inner surfaces of the box-like member 4, a pair of chambers 3 extend along each of the legs 9 of the box-like member. The tubular members 1,2 combine with a supporting plate 5 to provide an air baffle facing toward the web 14. The supporting plate 5 has a flattened V-shaped configuration in a plane extending in parallel relationship with the legs of the box-like member, note FIG. 5. The point or apex of the V-shaped plate is located intermediate the ends of the plate, approximately midway between the ends of the tubular members 1,2, and is located more remotely from the web 14 than the surfaces of the plate which extend from the point to the opposite ends of the box-like member. The surfaces of the plate 5 converge toward the web as they extend outwardly toward the ends of the tubular members. Each of the surfaces of the plate 5 extending from its point has a longitudinally extending slot 6 extending generally in parallel relationship with the axes of the tubular members. The sides of the slots diverge from one another as the slot extends toward the ends of the tubular members. At the ends of the box-like member 4, cover plates 7 form closures for the ends of the tubular members and for the chambers 3. Accordingly, narrow elongated slot-like openings 10 are provided between the inner surface of the free ends of the legs 9 and the juxtaposed surface of the tubular members 1,2.

As shown in FIGS. 1 and 4, inlet lines 11 and 12 extend through the wall of the box-like member into the tubular members 1 and 2 for supplying air therein. Each of the tubular members has a slot-like opening 13 for communicating the interior of the tubular member with one chamber 3. Accordingly, air flows through the inlet lines 11 and 12 into the tubular member 1,2 and then flows from each tubular member through the slotlike openings 13 into the chambers 3 and then through the nozzle or slot-like openings 10 toward the web and along the outer periphery of the tubular members. As can be seen in FIG. 1, the air flows over the curvilinear surface on the exterior of the tubular members after its passage through the nozzles 10 and flows inwardly toward the other tubular member and is removed through the slots 6.

METHOD OF OPERATION (FIGS. 1 THROUGH 5) The flow of air from the nozzles or slot-like openings 10 passes, for aerodynamic reasons, over the curvilinear surfaces on the exterior of the tubular members and combines to provide an air cushion between the web and the baffle provided by the tubular members 1,2 and the plate 5. The pattern of the flow of air is shown in FIGS. 1 to 5 and the greatest pressure is provided in the center of the device. Due to the lateral flow the web of material is smoothed out in the transverse direction. Additionally, the rapidly flowing air contacts the web over a considerable distance and leads to effective utilization, particularly for drying action. The portion of the air which does not flow along the curvature of the tubular members contributes a drying effect as it contacts the web. Accordingly, the air is excellently utilized from its issuance from the slot-like openings 10 until it is sucked off or returned for circulation on the side of the web.

If webs of different widths are used, the lateral outflow of air presents problems with increasing web width. To avoid this problem, the outwardly widening slots 6 are provided in the support plate 5. The air passing through these slots is drawn into the circulation system from the chamber between the plate 5 and the wall of the box-like member 4 by means of an exhaust system (not shown).

Based on the arrangement illustrated in FIGS. 1 to 5 and using the effect of the air on the web without any direct mechanical influence or contact, it has been found that different arrangements are possible, depending on the intended use for the device. The embodiment shown in FIGS. 1 to 5 is characterized in that the air bafile is arranged between at least two oppositely disposed walls of a box-like member and the curvilinear surfaces of the baffle and the side walls of the box-like member provide a pair of nozzles or slot-like openings for directing the air outwardly so that it follows the curvilinear surface of the air baffle located at the opening. Due to the arrangement of the curvilinear surfaces of the baffle, the air from each of the nozzles or openings flows toward the other and provides the desired air cushioning effect.

The shape or configuration of the air baffles is selected in accordance with the type of material forming the web and several typical embodiments are shown in the drawings in FIGS. 6 to 15.

In FIG. 6 another embodiment of the device is illustrated in which the oval shaped baffle plate 4A is positioned within the open side of a U-shaped box-like member 3A with the baffle plate extending between the free ends of the side walls lA,2A so that the

curvilinear surfaces

7A,8A of the plate project outwardly from the ends of the side walls toward the web 9A. The curvilinear ends of the baffle plate 4A and the free ends of the

adjacent side walls

1A,2A form elongated nozzles or slot-

1ike openings

5A, 6A for directing air supplied into the boxJike member 3A. Due to the curvilinear configuration of the end surfaces 7A,8A of the baffle plate, the air flows from the

openings

5A,6A are directed toward each other. Hot or cold air supplied into the box-like member 3A flows in the direction of the arrows at a high speed passing through the

openings

5A, 6A and is directed toward the web of material 9A with a portion of the air following along the surface of the baffle plate 4A and providing the boundary layer effect or cushioning for the web.

As indicated above, the baffle plates 4A shown in both FIGS. 6 and 7, are represented as oval shaped members or bodies so that a curvilinear surface is provided at each of the nozzles or openings from the boxlike member. In FIG. 7 an arrangement is shown with a box-like member 10A located on the opposite sides of the surface of the web 9 and the openings in the boxlike members containing the nozzle plates are staggered or offset on the opposite sides of the web. As the web 9A passes between the two box-like members A, it is supported and spaced from the baffle plates by the flow of air conducted through the box-like members and outwardly through the openings extending along the curvilinear surfaces of the baffle plates.

In FIGS. 8 and 9 another embodiment of the baffle plate is shown which consists of a pair of laterally spaced cylindrical bodies 11A joined together by a plate 12A fixed to and extending along the surfaces of the cylindrical bodies which are located more closely to the web 9A. As in FIG. 7, the openings from the boxlike members 10A on the opposite sides of the web 9A in FIG. 9 are offset relative to one another to effect the desired support arrangement. In FIGS. 8 and 9, the free ends of the

side walls

1A,2A are directed inwardly toward the

curvilinear surfaces

7A, 8A of the cylindrical bodies 11A forming a constricted opening and directing the air flowing from the

nozzles

5A, 6A over the

curvilinear surfaces

7A,8A.

In FIG. 10 a baffle plate is provided with an undulating or wave-shaped configuration having the

curvilinear surfaces

7A and 8A located adjacent the nozzle or slot-

like openings

5A,6A from the box-like member and with an additional wave-shaped section extending between the two

curvilinear surfaces

7A,8A. As with the other embodiments discussed above, the

curvilinear surfaces

7A,8A direct the air from the

openings

5A,6A so that it flows toward the web and in a cushionlike effect between the baffle plate and the web.

In FIG. 11 the baffle plate has the

curvilinear surfaces

7A, 8A located adjacent the slot-

like openings

5A,6A from the box-like member, however, instead of the undulating form of section joining the curvilinear surfaces, a flat planar section is provided which is recessed inwardly toward the box member, that is away from the

curvilinear surfaces

7A, 8A and the surface of the web.

In FIG. 12 another embodiment of the baffle plate is shown similar to that set forth in FIG. 11, but the flat planar section which connects the

curvilinear surfaces

7A, 8A extends in a plane containing the ends of the curvilinear surfaces located closer to the web. In the embodiments of FIGS. 10, 11 and 12, the air flows outwardly from the box-like member through the restricted nozzle or slot-

like openings

5A, 6A and then passes at least in part over the

curvilinear surfaces

7A, 8A along the opposite edges of the baffle plate for providing the air cushion between the baffle plate and the web 9A.

In FIG. 13 a pair of box-like members are positioned on the opposite sides of the web 9A and are provided with baffle plates formed in the same manner as the baffle plates in FIG. 12. As in the arrangements shown in FIGS. 7 and 9, the openings from the box-like members 10A in which the baffle plates are located are offset relative to one another on the opposite sides of the web.

Still another embodiment of the invention is shown in FIGS. 14 and 15 in which inverted L-shaped sections 15A are located on the interior surfaces of the

sides

1A,2A adjacent their free ends. In combination with the ends of the

sides

1A, 2A, the L-shaped sections 15A form elongated grooves or pockets into which the edges of the baffle plate extend and from which the

curvilinear surfaces

7A,8A project toward the surface of the web. As with the embodiment of the baffle plate shown in FIGS. 12 and 13, a flat planar section extends between the ends of the

curvilinear sections

7A, 8A. As indicated in FIGS. 14 and 15, the air entering the boxlike members flows outwardly through the

grooves

13A, 14A formed between the ends of the sides IA, 2A and the L-shaped sections 15A, reversing direction about the ends of the

curvilinear sections

7A, 8A and being directed outwardly over the curvilinear surfaces for passage between the flat surface of the baffle plate and the opposed surface of the web. In FIG. 15 the boxlike members 10A are provided on the opposite sides of the webs with multiple openings containing baffle plates of the type shown in FIG. 14. As with the other box-like members 10A containing multiple openings for the baffle plates, the openings are offset relative to one another on the opposite sides of the web.

The main characteristic of the present invention incorporated into each of its embodiments is the curvilinear surfaces provided along the edges of the baffle plate adjacent the sides of the box-like member through which the air flows prior to passing between the baffle plate and the web. The baffle plate is spaced from the sides of the box-like member so that nozzles or slot-like openings (in FIG. 1 reference numeral 10, in FIGS. 6 to 15

reference numerals

5A,6A) are provided so that the jets of air issuing through the openings follow the curvilinear surfaces of the air baffle and flow toward each other. After the air has been introduced between the baffle and the web, it must continue to flow because of the continuous supply of air from thebox-like members. Accordingly, there are two possibilities for the discharge of the air from between the baffle plate and the web, in one instance the air must reverse itself by 180 degrees and flow out in the opposite direction from which it came. Alternatively, the air being supplied forces the air ahead of it in the axial direction of the device from the center toward the sides.

In fact, the outflow of air from between the baffle and the web combine both of the above types of flow, however, they are slightly mixed at the ends of the device.

Since it is difficult for the air to either reverse itself by l or to push the cushion of air ahead of it, both of these air flows encounter some resistance. In accordance with the invention, a chamber is formed for the length of the nozzles or slot-like openings having the dimension of the distance between the baffle plate and the web and also the width of the web and in the chamber the pressure is higher than atmospheric pressure so that it places the web of material under tension and carries it in a contact-free manner. In accordance vgith the tension acting on the web and the lift which results from the amount of air supplied between the web and the baffle plate, thedistance from the web to the baffle plate adjusts itself automatically to a dynamic equilibrium which has highly balanced flow conditions and, as a result, ensures a practically vibration-free support of the web.

If the process in which the web is involved is stopped for production reasons, the amount of air can be reduced to about 5 percent of the usual amount used, because it has been found that this amount is sufficient for supporting the web so that it does not touch the structure from which the air flows. This arrangement leads to an economical consumption of air and prevents overdrying of the web during short work stoppages.

While specific embodiments of the invention have been shown and described in detail to illustrate the ap- 7 plication of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A device for supporting a web of material in a contact-free manner so that it is maintained in a spaced position from the device, comprising a box-like member open at least on the side directed toward the web to be supported and closed along two opposite sides which extend along the open side and with the closed sides extending angularly from the open side away from the web, an air baffle positioned within and extending across the open side of said box member and closely spaced along two of its opposite edges from said two opposite sides of said box-like member and forming therebetween narrow elongated slot-like openings, each of said two opposite edges of said air baffle extending along said slot-like openings having a curvilinear form from a first location at which it forms one side of said slot-like opening to a second location spaced angularly from said first location and located in a plane disposed angularly to the plane of the adjacent said opposite side and extending in the general direction of the web to be supported, inlet means for supplying air internally of said box-like member with the air flowing outwardly through said slot-like openings and over the curvilinear surface of said baffle so that at least a part of the flow of air from each said slot-like opening is directed toward the other along the surface of said baffle facing toward the web, said air baffle comprising a pair of tubular members having their axes disposed in substantially parallel relationship with one another and with said opposite sides of said box-like member, said inlet means comprises an inlet sleeve extending into each of said tubular members at a point spaced from the open side of said box-like member and each of said tubular members having a narrow elongated opening arranged to open within said box-like member for supplying air to said slot-like openings from said box-like member.

2. A device for supporting a web of material in a contact-free manner so that it is maintained in a spaced position from the device, comprising a box-like member open-at least on the side directed toward the web to be supported and closed along two opposite sides which extend along the open side and with the closed sides extending angularly from the open side away from the web, an air baffle positioned within and extending across the open side of said box member and closely spaced along two of its opposite edges from said two opposite sides of said box-like member and forming therebetween narrow elongated slot-like openings, each of said two opposite edges of said air baffle extending along said slot-like openings having a curvilinear form from a first location at which it forms one side of said slot-like opening to a second location spaced angularly from said first location and located in a plane disposed angularly to the plane of the adjacent said opposite side and extending in the general direction of the web to be supported, inlet means for supplying air internally of said box-like member with the air flowing outwardly through said slot-like openings and over the curvilinear surface of said baffle so that at least a part of the flow of air from each said slot-like opening is directed toward the other along the surface of said baffle facing toward said web, said box-like member is U- shaped with the legs of said U-shaped member forming said two opposite sides thereof, and said air baffle comprises a pair of hollow cylindrically-shaped members having their axes disposed in substantially parallel relationship with one another and with said opposite sides of said U-shaped box-like member, and wherein said cylindrically shaped members define said curvilinear form, said cylindrically-shaped members being spaced apart and forming an open space therebetween, and a plate member extending between and forming a closure for the open space between said cylindrically-shaped members.

3. A device as set forth in claim 2, wherein said cylindrically-shaped members are tubular members, said plate member has a shape of a flattened V in a plane extending parallel to the axis of said tubular members with the point of its V shape located intermediate the ends of said tubular members and its surfaces extending from the point sloping toward the location of the web.

4. A device, as set forth in claim 2, wherein said plate member is a flat plate section fixed to and extending between said cylindrically-shaped members and being located in a plane which includes the surfaces of said cylindrically-shaped members spaced most closely from the web.

5. A device, as set forth in claim 3, wherein each of said surfaces of said plate member extending from its point having a slot therein extending in parallel relationship with the axes of said tubular members whereby the flow of air from said slot-like openings between said box-like member and the web enter said slot in said plate member.

6. A device, as set forth in claim 5, wherein said slots and said plate member having the longitudinally extending sides thereof disposed in diverging relationship as they extend away from the point of said V-shaped plate member.

Claims

1. A device for supporting a web of material in a contact-free manner so that it is maintained in a spaced position from the device, comprising a box-like member open at least on the side directed toward the web to be supported and closed along two opposite sides which extend along the open side and with the closed sides extending angularly from the open side away from the web, an air baffle positioned within and extending across the open side of said box member and closely spaced along two of its opposite edges from said two opposite sides of said box-like member and forming therebetween narrow elongated slot-like openings, each of said two opposite edges of said air baffle extending along said slot-like openings having a curvilinear form from a first location at which it forms one side of said slotlike opening to a second location spaced angularly from said first location and located in a plane disposed angularly to the plane of the adjacent said opposite side and extending in the general direction of the web to be supported, inlet means for supplying air internally of said box-like member with the air flowing outwardly through said slot-like openings and over the curvilinear surface of said baffle so that at least a part of the flow of air from each said slot-like opening is directed toward the other along the surface of said baffle facing toward the web, said air baffle comprising a pair of tubular members having their axes disposed in substantially parallel relationship with one another and with said opposite sides of said box-like member, said inlet means comprises an inlet sleeve extending into each of said tubular members at a point spaced from the open side of said box-like member and each of said tubular members having a narrow elongated opening arranged to open within said box-like member for supplying air to said slot-like openings from Said box-like member.

2. A device for supporting a web of material in a contact-free manner so that it is maintained in a spaced position from the device, comprising a box-like member open at least on the side directed toward the web to be supported and closed along two opposite sides which extend along the open side and with the closed sides extending angularly from the open side away from the web, an air baffle positioned within and extending across the open side of said box member and closely spaced along two of its opposite edges from said two opposite sides of said box-like member and forming therebetween narrow elongated slot-like openings, each of said two opposite edges of said air baffle extending along said slot-like openings having a curvilinear form from a first location at which it forms one side of said slot-like opening to a second location spaced angularly from said first location and located in a plane disposed angularly to the plane of the adjacent said opposite side and extending in the general direction of the web to be supported, inlet means for supplying air internally of said box-like member with the air flowing outwardly through said slot-like openings and over the curvilinear surface of said baffle so that at least a part of the flow of air from each said slot-like opening is directed toward the other along the surface of said baffle facing toward said web, said box-like member is U-shaped with the legs of said U-shaped member forming said two opposite sides thereof, and said air baffle comprises a pair of hollow cylindrically-shaped members having their axes disposed in substantially parallel relationship with one another and with said opposite sides of said U-shaped box-like member, and wherein said cylindrically shaped members define said curvilinear form, said cylindrically-shaped members being spaced apart and forming an open space therebetween, and a plate member extending between and forming a closure for the open space between said cylindrically-shaped members.