US 3577653 A
Description (OCR text may contain errors)
United States Patent Inventors John A. McClenathan;
Donald L. Nielsen, Beloit, Wis. 4,293
Jan. 20, 1970 May 4, 1971 Beloit Corporation Beloit, Wis.
Appl. No. Filed Patented Assignee WEB DRYING TUNNEL 7 Claims, 4 Drawing Figs.
US. Cl. 34/156 Int. Cl F261 13/00 FieldofSearch 34/156, 10
References Cited UNITED STATES PATENTS 12/1907 Cohen 3,287,821 11/1966 Schregenberger 3,324,570 6/1967 Flaithetal Primary Examiner-Carroll B. Dority, Jr. Attorneys-Dirk J Veneman, John S. Munday and Gerald A.
Mathews ABSTRACT: An elongate moving web passing through a drying tunnel is supported along a slightly arched path by pressurized air directed against its concave lower face. The arched path of the web tends to prevent it from bowing transversely, thereby facilitating maintaining it in central relation to the tunnel by means of the air escaping upwardly around its edges. Additionally, the resulting profile of the web inherently reduces its tendency to wrinkle or sag, thus allowing it to be drawn through the tunnel under relatively low longitudinal tension.
PATENTED m 4mm SHEET 1 [IF 2 JOHN A. McCLENATHAN DONALD L. NIELSEN PATENTEDMAY 415m 3577.653
' same or 2 v JOHN A. MCCLENATHAN DONALD L. NIELSEN INVENTORS iii am WEB DRYING TUNNEL BACKGROUND OF THE INVENTION I 1. Field of the Invention 1 The present invention relates to web-dryers and more particularly to dryers in which a moving elongate web is supported by air cushion means as it passes through a dryer tunnel.
2. Description of the prior Art It is well known in the prior art to support an elongate moving web by air cushion means as it is drawn through a drying chamber, thereby avoiding physical contact between the web and the dryer structure to eliminate the attendant possibility of scratching or otherwisedamaging the web. In such prior art dryers, however, a web has either been supported in a flat plane as it moves through an elongate tunnel or has been draped in vertical loops supported by semicylindrical air cushion devices as it passes through an analogous-drying chamber.
If the web being dried is very thin and flexible, for example a web of recording tape comprising a plastic film base coated with a layer of magnetic material, the former type of dryer tunnel is not entirely satisfactory for drying the magnetic coating because of the coating difficulty in maintaining the very flexible web in'central relation to the tunnel without bringing it into physical contact with structural guide means or subjecting it to excessive longitudinal tension. In other words, if the tape tends to drift sideways in the tunnel, the 'flow of air around its edges in'such prior art dryers will simply flex or ripple the web transversely rather than restoring it to its initial central path unless the web is under relativelygreat longitudinal tension. Furthermore, such-transverse flexing or rippling of the web is very apt to promote permanent wrinkling, creasing or localized stretching, which is totally unacceptable in the finished product.
In the other above-mentionedtype of dryer device,the difficulty encountered in centering the web is reduced because of the fact that it is bowed quite abruptly around the air cushion support members above and below its draped vertical portions and therefore resists transverse deformation in its supported arcuate areas. However, this approach is likewise undesirable for drying magnetic tape or the like, which requires that the web be maintained in a relatively horizontal plane to prevent the web coating from running or sagging during the initial stage of the drying process.
SUMMARY OF THE INVENTION The present invention involves the discovery that only a relatively slight arched curvature need be imposed on a web of very thin flexible material supported. by air cushion means in a horizontal tunnel type dryer in order to achieve a very signifi cant improvement in the smoothness and self centering action of the web while at the same time reducing the longitudinal tension to which it must .be subjected during the drying process. Accordingly, a dryer tunnel according to the invention is provided with a permeable support member which is slightly arched toward the center of the tunnel and through which pressurized air is blown against the lower face of the web to support the web along a correspondinglyarched path. By reason of its longitudinal curvature, transverse movement of the web is discouraged and stabilized to the extent that the air passing upwardly around the edges of the web suffices to keep it centered in the tunnel without resort to elaborate air control or pressure regulating'means. Due to the relatively slight longitudinal and transverse curvature encountered by the web. the invention also substantially eliminates the problem of gravitational sagging or flow of the liquid coating on the top surface thereof. Furthermore, by virtue of the absence of internal moving mechanical elements and because of the simplified air curtain means employed for preventing leakage of solvent vapors and drying air out of the ends of the,
dryer unit, the extremely versatile and economical construction of such a dryer tunnel is particularly suitable for apble solvents or the like.
Various means for practicing the invention and other advantages and novel features thereof will be apparent from the following detailed description of an illustrative preferred embodiment of the invention, reference being made to the accompanying drawings in which like reference numerals denote like elements. I
In the accompanying drawings:
FIG. I is a schematic front elevational illustration of a typical web drying tunnel installation according to a preferred embodiment of. the present invention;
v FIG. 2 is a fragmentary front elevational view of one of the sections of the dryer tunnel depicted schematically in FIG. 1;
.FIG. 3 is a cross-sectional end view taken along 3-3 of FIG.
2; and v FIG. 4 is a fragmentary cross-sectional plan view taken along line 440i" FIG. 2.
' DESCRIPTION 01% THE ILLUVSTRATIVIE'PREFIERRED I .EMBODIMENT Referring first to FIG. I of the drawings, the illustrative dryer tunnel will be seen to comprise six generally similar boxlike sections I] through l6 joined together between similar endsections 17 and 18.to provide an elongate arched tunnel structure through which web l9 moves from left to right as indicated by arrows 21. As shown in FIGS. 2, 3 and 4, each of the dryer sections is of generally rectangularcross section and is provided with slightly sloped end flanges 22 by which the sections are bolted to each other and to end sections I7 and I8, whereby the assembled unit is in effect a single selfsupporting unitary structure. v
An aperture plate 23, provided with narrow elongate transverse slots 24. is supported within each of the tunnel sections by angle members 25 along the sidewalls thereof. Each aperture plate is bent downwardly at one end to provide a lip 26, which is overlapped by the opposite end of the similar plate in the next tunnel section. A curtain plate 27 is sandwiched between the connected flanges of sections 13 and 14 at the centerof the tunnel and is provided with a horizontal slot 28 which accommodates the moving web. Similar curtain members are also provided at the ends of sections 17 and 18, as indicated by numeral 29. Accordingly, it will be seen that the portion of the tunnel between curtain plates 29 comprisessix separate lower chambers-30 in the corresponding tunnel sections, whereas the upper portion of the tunnel is divided into only two chambers or zones 31 and 32 definedbetween the central curtain plate 27 and the similar plates 29 at the ends of tunnel sections I1 and I6. 7
Each of the two zones of the dryer tunnel is connected with a corresponding air supply and exhaust system comprising a main heating and filtering blower 33 which delivers heated air into one end of its corresponding zone through an inlet duct 34 so that the drying air passes along the upper face of the moving web before being exhausted at outlet duct 36 connected to exhaust blower 37. Part of the exhaust air is reir ttroduced into the main heating and filtering blower for humidity control purposes, as is well known in the dryer art. A
supplemental blower 38 derives heated air fromthe corresponding main'blower unit and feeds it into the lower tunnel chambers 29 through a manifold 39 and inlet ducts 40 at a 4-, the web is somewhat wider than slots 24 in the aperture I plates but narrower than the tunnel itself so that the pressurized air impinging on the lower web surface escapes upwardly around the edges of the web into the drying zones and thereby tends to center the web in the tunnel.
in a typical. embodiment of the invention adapted to handle a web approximately 2 feet wide, the overall tunnel was longer and comprised more tunnel sections than the illustrative-embodiment shown in FIG. 1, having a total length of about 80 feet and effective radius of approximately 200 feet. in other words, the moving web within the tunnel was elevated approximately 4%feet at its center along a substantially arcuate arch path subtending an angle of approximately ll'r from each ideof a vertical line rassing through the center of the tunnel.
Although the illustrated individual aperture plates are flat, it will be obvious that they could be slightly curved to define a perfectly arcuate surface, but the essential requirement is not that the support surface be a perfect are but rather that either the true or approximate arc of the moving web be of sufficient curvature to stabilize it without sloping it out of a relatively horizontal path. As illustrated in FIG. 3, the edges of the web will droop slightly notwithstanding the longitudinal web curvature, but this effect actually tends to improve rather than detract from the tendency of the web to center itself in the tunnel. Although the longitudinal curvature of the web can vary considerably, depending on the flexibility and thickness of the particular web material being processed, it would generally not exceed an arc subtending an angle of more than 20 at either side of the vertical centerline nor would the effective radius of curvature of the support surfacedefined by the aperture plates generally be less than 25 times the width dimension of the web support surface.
The end sections 17 and 18 of the dryer, which are of the same type of construction as tunnel sections 11 through 1.6, are provided with respective entrance and exit curtain plates 41 and 42 similar to the corresponding plates 27 and 29. In these end sections, the previously described aperture plates are omitted so that the web itself serves to divide each end section into upper and lower chambers 43 and 44 in communication with each other along the edges of the web. Each of the end sections is associated with an input blower 45 which forces unheated air into the upper and lower chambers of that section through respective upper and lower inlet ducts 46 and 47 and with exhaust blower 37 which removes air from the same upper and lower chambers through respective upper and lower exhaust ducts 48 and 49. Accordingly, a relatively high volume of unheated air flows within the end sections along flow paths indicated generally by arrows 51, thereby providing air curtain sealing means to prevent solvent vapors or the like from escaping into the surrounding environment from the ends of the dryer.
The invention has been described in detail with particular reference to an illustrative preferred embodiment thereof but it will be apparent that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.
1. An apparatus for drying a longitudinally moving flexible web, said apparatus comprising:
a. means defining an elongate tunnel through which said web travels longitudinally,
b. permeable support plate. means defining an air penneable support surface within said tunnel, said support surface being generally flat in transverse relation to said tunnel and arched longitudinally of said tunnel approximately along an imaginary arc subtending an angle of less than 20 at either side of an imaginary vertical radius of that arc,
c. first air supply means for supplying pressurized heated dryi g air to and exhausting such air from said tunnel above said support plate means, and Y second air supply means for supplying web supporting air to said tunnel below said support plate means at a pressure greater than that of said heated drying air, whereby said web supporting air blows upwardly through said support plate means and impinges on the lower face of the portion of said web moving through said tunnel to thereby support that portion of said web out of contact with the physical structure of said tunnel along an arched web path generally parallel to said support plate surface.
2. An apparatus according to claim 1 including air curtain means at opposite ends of said tunnel providing barriers to the flow of said heated drying air out of said tunnel through said opposite ends thereof. 'I
3. An apparatus according to claim 1 including internal baffle means dividing the portion of said tunnel above said support plate means into a plurality of drying zones, said second air supply means being adapted to deliver heated drying air to and exhaust such air from each of said zones independently of one another.
4. An apparatus according to claim 1 in which said imaginary radius approximately defining the longitudinal curvature of said support surface is at least 25 times larger than the width of said support surface within said tunnel. v
5. An apparatus according to claim 1 in which said support plate means is provided with a plurality of narrow parallel air conductive slots disposed transversely of said tunnel.
6. An apparatus according to claim 1 in which said tunnel comprises a plurality of straight tunnel sections provided with respective substantially flat support plate means, said tunnel sections including slightly angled end flanges which are adapted to be joined together to establish a polygonally arched tunnel profile and a corresponding polygonally arched support surface approximating the curvature of said imaginary arc.
7. The invention defined by claim 6 in which said tunnel sections joined together by said end flanges thereof provide a rigid self-supporting tunnel structure.