US 3324570 A
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llnited StatesPatent The present invention relates generally to apparatus for drying continuous webs and relates more particularly to drying apparatus wherein a web is freely suspended orfloated between cushions of air directed against the surfaces thereof, such apparatus beingknown as a float dryer.
The present float dryer has been developed for drying fabric webs immediately after passage thereof through a screen printing machine. However, the apparatus-may be used with other types of dyeing or processing equipment and may be employed for drying natural or synthetic fiber webs, paper webs, or webs of any other material wherein contact with the web is to be avoided during the drying process and wherein uniform tension must be maintained on the web.
In screen printing, for example, the dyes pass through the fabric and it is essential that the dyed web upon leaving the printing machine not come into contact with any solid object such as a supporting roller until the design has dried sufficiently so as not to be blurred or in any way disturbed by such contact. It is, in addition, important that the printed fabric not be subjected toexcess or uneven tension after leaving the printing machine as this would tend to pull the design out of register.
Attempts previously made to develop a satisfactoryfloat dryer have not been wholly successful. A common shortcoming of previous designs has been the use of slots transverse to the directionof trav'elof the Web to receive the return air. In such arrangements, the Web tends to be sucked into the slots along with the air causing a fluttering of the web in these regions and contact of the web with the dryer. Not only does this mar the finish of the web, but the resulting uneven tension tends to pull the design pattern out of register.
In the present invention, this problem is overcome by the novel use of small, staggered perforations to receive the return air. It has furthermore been discovered that a significantly improved floating of the cloth is achieved by the reduction of the area of these perforations to one quarter to one half the area of the air inlet nozzles. Such a structure provides a cushion of air both above and below the fabric web which supports the Web and prevents any fluttering of the web.
In view of the above, it is a primary object of the present invention to provide apparatus for drying continuous webs by floating the web between cushions of air to prevent web contact with elements of the dryer.
A further object of the invention is to provide an apparatus as described having a novel air return arrangement which dispels any tendency of the web to diverge from its normal course in the vicinity thereof.
An additional object of the invention is to provide an apparatus as described wherein the area of the air return openings are of a substantially smaller area than the air inlet nozzles to provide a significantly improved floating of the web.
Additional objects and advantages of the invention will be more readily apparent from the following detailed description of an embodiment thereof when taken together with the accompanying drawings in which:
FIG. 1 is a typical cross-sectional view of a float dryer embodying the present invention;
FIG. 2 is a sectional view taken along line 22 of FIG. 1 showing the air inlet nozzles and the outlet perto Proctor and Schwartz,
forations and the flow pattern of the air currents passing therethrough;'and
FIG. 3 is a view taken along line 3-3 of FIG. 2shoW- ing the staggered pattern of the air outlet perforations.
Referring to the drawings, FIG. 1 shows a dryer 10 embodying the present invention which includes an elongated housing 12 having insulated side walls 14 and an insulated top wall 16. Spaced interiorly of and parallel to each of the side walls 14 are vertical partitions 18, between which extends the horizontal panel 20 which, in
conjunction with the partitions 18, top wall 16'and end walls (not shown) forms an air return chamber 22; Motor driven fans 24 mounted'on the side walls 14 and extending through the partitions 18 with their suction sides opening in'tothechamber'ZZare adapted to draw air'from the chamber 22 and from the atmosphere through inlet ports 26 in the top wall 16 and direct the air under pressure into the conditioning chambers 28 between the partitions 18,. side walls 14 and bottom partitions 29. Heaters and humidity control devices may'be employed in the conditioning chambers in COllJllIlCtlOl'l with the fans to provide the proper conditioning of the gaseous drying medium, which is normally air.
Opening into the conditioning chambers are a plurality of upper and lower distribution boxes 30 and'32 which extend substantially the distance titions 18, terminating at their closed ends at side panels 33. The 'distribution boxes are disposed in longitudinally spaced relation and are connected alternately with the two conditioning chambers 28.
Between the upper and lower distribution boxes is a longitudinally extending drying chamber 34 adapted for the longitudinalpassage of acontinuous Web 36therethrough. The drying chamber is defined in part by spaced, parallel floor and ceiling surfaces 38 and 40 below and above which the lower and upper distribution boxes are respectively mounted in spaced relation thereto. The distribution boxes are connected with the drying chamber by upper and lower inlet nozzles 42 and 44 which are located in opposed relation across the drying chamber. The drying chamber is enclosed at the sides by the side panels 33 of the upper and lower distribution boxes 30 and 32.
The floor and ceiling surfaces of the drying chamber are perforated between the inlet nozzles, the apertures 48 therein providing outlet means for the gaseous medium in the drying chamber. The drying medium passing through the apertures passes upwardly into upper outlet chambers 50 and downwardly into lower outlet chambers 52. The upper outlet chambers 50 communicate directly with openings 54 in horizontal panel 20. The air from lower outlet chambers 52 passes laterally to either side and Upwardly through the passageways 55 defined by side panels 33 and partitions 18 between the air distribution boxes. Thus, both upper and lower outlet chambers 50' and 52 communicate with the return air chamber 22 by means of the openings 54 in the horizontal panel 20', which openings are provided with lint screens 56.
As shown in FIG. 3, the apertures 48 comprise annular, spaced perforations which are arranged in a staggered manner and which extend over substantially the entire area of the floor and ceiling surfaces of the drying chamber between the outlet nozzles. The total area of the apertures between two inlet nozzles should be approximately 20% to 70% of the area of one of the inlet nozzles for reasons presented hereinafter.
In operation, the fans 24 provide a pressurized supply of drying medium such as air to the distribution boxes from which the air is directed into the drying chamber through the nozzles 42 and 44. A continuous web is introduced to the drying chamber and is suspended between the ceiling and floor surfaces of the drying chamber by the high pressure air directed by the nozzles against the between the par-'- web surfaces. By providing the outlet means for the air in the form of the spaced apertures 48, the removal of air from the drying chamber takes place in a diifused manner such that there are no low pressure regions to which the web might be abruptly exposed.
1 It has furthermore been discovered that the restricting of the area of the outlet apertures to the range of 20% to 70% of the area of the inlet nozzles provides a greatly im'proved floating of the web by effectively establishing cushions of air both above and below the web throughout the length of the drying chamber. Fluttering of the web or movement of the web into contact with the floor or ceiling surfaces of the drying chamber are prevented by the formation of air cushions by use of this construction. The transverse movement of the web is prevented by the connection of the distribution boxes alternately with the two conditioning chambers such that the air flow from successive opposed pairs of distribution boxes will be in opposite directions.
A dryer construction in accordance with the invention, for example, might typically be characterized by inlet nozzles having openings spaced 12" on centers, V2" diameter outlet apertures 3" apart in three rows spaced 3" on centers, and floor and ceiling surfaces of the drying chamber spaced 6" apart. With such a unit, the ratio of the outlet aperture area to the nozzle area is 1/3.75 or 27%. Nozzle velocities ranging from 900 to 2000 feet per minute have proven satisfactory although these are not operating limits.
The invention, by eliminating concentrated low pressure areas in the drying chamber, provides a smooth, non-fluttering passage of the web without contact with the drying chamber surfaces, cushions of air both above and below the web providing additional web stabilization.
Manifestly, changes in details of construction can be effected by those skilled in the art without departing from the spirit and the scope of the invention as defined in and limited solely by the appended claim.
.A float dryer for the drying of continuous webs comprising a longitudinally extending drying chamber adapted for the longitudinal passage of a continuous web therethrough, means defining horizontal floor and ceiling surfaces of said chamber between which a web is adapted to be continuously moved in suspended, spaced, substantially parallel relation thereto, opposed longitudinally spaced inlet nozzles in said floor and ceiling surfaces opening into said chamber, said nozzles extending transversely substantially the full width of said drying chamber, means for directing a gaseous drying medium under pressure into said chamber through said inlet nozzles, outlet means on said floor and ceiling surfaces between said inlet nozzles, and means associated with said outlet means for removing the gaseous drying medium from said chamber, said outlet means comprising a staggered array of spaced apertures in said ceiling and floor surfaces between said inlet nozzles, said apertures being substantially uniformly spaced throughout the areas between said inlet nozzles, the area of said apertures being 20% to of the area of said inlet nozzles, the introduction of a gaseous drying medium under pressure to said chamber through said opposed inlet nozzles providing a cushion of gaseous medium above and below a web passing through said chamber for supporting said web in spaced parallel relation to said chamber ceiling and floor surfaces, said spaced apertures of said outlet means providing a diflused removal of said gaseous medium from said chamber to maintain said spaced parallel disposition of the web throughout the drying chamber.
References Cited UNITED STATES PATENTS 2,351,549 6/1944 Schwartz 34-23 2,952,078 9/1960 Litzler 34156 X 3,012,335 12/1961 Allander et al. 34160 X 3,199,224 8/1965 Brown 34160 X FREDERICK L. MA'ITESON, JR., Primary Examiner.
JAMES W. WESTHAVER, Examiner.
D. A. TAMBURRO, Assistant Examiner.