US2783546A - Apparatus for drying - Google Patents

Description

March 5, 1957 E. T. ARMSTRONG APPARATUS FOR DRYING 3 Sheet-s-Sheet 1 Filed Nov. 19, 1954 INVENTOA 1I ARMSTRONG ATTORNEYS EDWARD BY A@MLM 0@ March 5, 1957 E. T. ARMSTRONG 2,783,546

APPARATUS FOR DRYING Filed Nov. 19, 1954 s sheets-sheet 2 FIG. 2

INVENTOR. :'.DWARD T. ARMSTRONG lex/(9% 0% ATTORNEYS March 5, 1957 E. T. ARMSTRONG APPARATUS FOR DRYING 3 Sheets-Sheet 3 Filed NOV. 19, 1954 lON INVENToR. EDWARD T. ARMSTRONG ATTORNEYS 2,783,546 APPARATUS FOR DRYING Edward T. Armstrong, Wanaque, N. J., assigner to Toscony Fabrics, Inc., New York, N. Y., a corporation of New York Application November 19, 1954, Serial No. 469,935 9 Claims. (Cl. 34-51) This invention relates to methods and apparatus for drying web material and the like, and, more particularly,

is concerned with improved means and methods for drying printing, coatings or the like, on endless, continuously moving web material, or in drying the web material high a percentage of explosive solvent in the drier discharge, may be objectionable because of high horsepower requirements on blowers for moving the air through the drier, may have diiculties in establishing proper temperature conditions upon the web material being treated, the temperatures being so high that the web material may soften and rupture, or being so =low that the web material or the Solvent present in any printing or coating is not properly vaporized, or may have ditlculties of threading the web material through the apparatus or in providing for the passage of knots therethrough.`

tates Patent l It is the general object of my invention to avoid and overcome the foregoing and other diiculties of and objections to known drying mechanisms for web material, and particularly printed or coated web material, by the provision of improved methods and apparatus for rapidly drying web material, and specically printed or coated web material, the method and apparatus functioning with a minimum of attention, cost and horsepower` with no danger of rupture to the web material, and with the apparatus being rapidly threaded, and allowing the passage of knots. t

Another object of my invention is to provide methods and apparatus for drying printed webs and in which the web itself is heated and the air is not, and with a plurality of throats being established through which the air is moved at high velocity adjacent the surface of the web material having the printing or coating thereon, and followed by sharply divergent portions in which the air speed rapidly drops and the air ow is made turbulent.

Another object of my invention is the provision of` methods and apparatus for drying web material in which the drying characteristics of the air are enhanced by maintaining its density high and its viscosity low, which follows when the air is not heated, and with the heat in the process and apparatus being concentrated upon the solvent to be removed to eiect the vaporization thereon.

Another object of my invention is to provide methods and apparatus of the character described wherein the fan means for moving air through the drier is provided with a discharge nozzle having divergent sides positioned at angles not more than 3 so as to avoid too rapid a decel- 2,783,546 Patented Mar. 5, 1,957

explosive characteristics thereof so that the solvent iny the discharged air never exceeds 50% of the lower eX- plosive limit.

Another object of my invention is to provide improved heating means for progressively heating the film or web material, the heating means employing condensed steam,

usually at'less than atmospheric pressure, to provide substantially constant temperatures below the boiling point 3 of water, which temperatures are required for certain iilm material, such as polyvinyl chloride. i

Another object of my invention is to provide in apparatus ,such as set forth above movable covers for the drying tunnel and in the region of the high velocity throats, which movable covers facilitate threading of the web material through the apparatus, or which allow for the passage of splices or knots, and with the movable covers, in one form of my invention, comprising a ilexible diaphragm which automatically adjusts itself under the differential pressures inside and outside offthe tunnel to providera throat passage of elticient dimension.

Another object of my invention is to provide apparatus of the type described wherein sealing means are positioned between the tunnel and the web material in the region of the introduction of the web material to the tunnel to reduce the ow of air around the web material and into the tunnel.

The foregoing object of my invention, and other obwith one side of the tunnel and at longitudinally spacedl points a plurality of narrow throats, each throat having on its upstream side gradually converging sides forming a nozzle to give relatively high throat velocities to any` air passing the throat, and on its downstream sidey having relatively sharply'diverging sides to create turbulence of the air after passing the throat, and fan means for drawing the air by suction through the tunnel in a direction opposite to the travel of the web. The amount ofV air passed through the tunnel is such that the air never contains more solvent than 50% of the lower explosive limit, and usually the fan means is provided with a discharge diffuser on the exhaust side of the fan which diffuser has side angles not exceeding 3. The web is usually heated by roller means engaging the unprinted or uncoated side of the web, and with the roller means being heated by condensed steam at less than atmospheric pressure. The height of the tunnel means is less than the width of the web material, and it usually is considerably less, and means are provided for reducing substantially to a minimum the ow of air around the web in the region of the introduction of the web to the tunnel. Also, movable cover means are usually provided on the tunnel in y the region of each throat.

In accord with thermethod of theim'ention thenweb material to be dried is continuously moved in a path, the web is heated, at spaced points along the path cool air is directed with high velocity over the surface of the partially brokenaway in Section. fone typical. iapparatus embodiment of my invention;l l

,Fia 2 is. a. plan .View Ot @neemt cttheapparatust FlgS- 1A. 1BJ and 1C, talscnsubstantially..inlhereson f1r1Q2 -.2;

Fig. 3 is a horizontal cross sectional viewtakensub-` Staatiallypalinef-. of Fig.i 1A;.

Eig. 4 is al pian view` of amoditicationof Ithe mot/able.

clasureatliacent the. throatofthe. tunnel; and.`

Eis- Sfis @enlarged dross, sectional viewtaken,sub-V stantially on line, =ST-Sof Fig. V4,.V

Ijiayingreference `to the drawings, andrparticularly to Figs. 1A, 1B, lC andZ, the numerall indicatesgenerally a tunneL, usually constructed of sheet metal or Slillliamaierial, andwhich doesnot have Lto be insulated, inasmuch as the air passing..therethrough. isA not heated. The tunnelv lll is relatively long, forexample, in one embodiment having a length of forty feet, isrelatively shallou/in vertical Vdirection, forexample', in one embodiment being 8 inchesrhigh andv` is of,f a width toY receive the widestwebmaterial to be dried, forexample, inv one embodiment being approximately. 56 inches wide. In

order to maintain the ,air velocities throughout .the tunnel, such as: hereinafter described, it is preferable, in order to achieve highest efficiencies, that the web material W being dried in the tunnel be substantially the full' width of theinside @of the tunnel. However, web material o f materiallyless width than that Vof the tunnel can be successfully dried but with lower e'iciencies.

`flietunllfl l@ is mountedY in any suitable manner and 1n any convenient position in the factory in which the drying4 operation is to he performed, it being remembered that vthe tunnel should be positioned so as to facilitate threadingofthe Vweb material W. therethrough. Suitable frantemeans 12 are indicated Vin the drawing for supporting ,the tunnel in a typical installation.

Nearone end 'of thetunnel .'10, as shown in Fig. lA, the web material W. is adapted to be introduced .and this is `pijeferablyachieved by. introducing theweb material froml beneath thc.tunuel, the web material W- passingVA over albanll having a at arcuate curve over its length,"` `andwith thebar 14 engaging with the side of the web" material W, opposite to the `printing or coating thereon.

The functiooof the bar14` is vtojsmooth the .webmatev rial ,laiallytoremove wrinkles or waves, and withvth' webmaterial after `leaving the bar 14 Vpassing througlf a curved opening 16 Vin a pan-shapedY housing 13 extendmg1 jlLaltterally o and secured to theunderside of the tunne* H TheY curved opening 16 in the housing 18 is delined on one side, namely the left side in Fig. l, by the housingY itself, and4 at the'o'th'er side by'a'door'Zf) hinged at 22y tomaintain the opening 16 with the smallest possible clearances, butf without the web material W touching either;- theihou'sing 13 or thel door 29. The bar14 is mounted tobe adjustably rotated about itsaxisto bring thedhat curv'emof the web IW into close proximitytothe sides of the opening 16. By maintainingthese,clearanCcSl..

' example.

small the loss of'air through the opening 16 is maintained to a minimum. Y

A spring 28 fastened at one end of the door 20 and to its opposite end at a bracket 30 resiliently holds the door 2lb-in the position illustrated but allows the door to yield against the action of the spring 2,8 should a knot or heavy splice occur in the web material during its passage into the tunnel 10.

Positioned in the housing 18 and vextending also through an opening in the bottom of the tunnel lilis a hollow heating drum 34 which is journalled at its ends on .suitable bearing plates 36 carried by the ends of the housing 18, and With the drum. being of a length equal tothe inside width of the tunnel. A flexible strip of nylon or other suitable material, and indicated by the numeral 58, is secured to the bottom of the tunnel 10 adjacent one edge of the drum 34 and in a position to wipe on the rsurface of the drum so as to effectively seal oft the passageof `air between. the drum and the bottom 0in-the tunnel. A door 40 hinged at fi?. vto a plate #i2 is mounted.

at the other side of the drum 34 on the bottom of the tunnel 10, and in a positionv tojust clear the surface of.k

An important part of the invention is the heating ofv drum 34, by condensing steam passed to the interior of the drum through its journals. The arrangement is such that the steam condenses inside of the drum 34 so as .to createtherein pressures of less than atmospheric and with the temperature of the drum being maintained at not .higher than n190" F. for polyvinyl chloride nlm, tor Thecondensed steam is removed inknown mannerfrom the. interior of the drum 34, and additional steam is supplied to the drum by tempcratureresponsive means, and the result is that very constant and uniformtemperatures can be maintained inside ofthe drum.34,in themanner described andbecause of the condensing steam action at temperatures below normal steam temperatures, and without going to the considerably greater expense of electric heating.

Theweb material W in passing over the drum 34 through thearcuate contact illustrated in Fig. 1A is strongly heated by means of the drum so that the temperature of the Aweb material itself is raised substantially tothe temperature .of the roller, for example, tol F. for polyvinyl chloride film material, this being `substantially theupper temperature limitrbeyond which the unsupported lilm may softenk and become distorted., lm is heated substantially uniformly throughout its entirethickness and the solventv material presentin any printin'g'inl; Aor coating on the film is rendered volatile.

Leaving the drum 34 the web material W passes through l the .tunnellU towards the opposite end thereof, and. in this. passageV is so positioned as to provide a plurality of areas producing relatively narrow throats .and alternate areas `of relatively sharp diffusion. More specifically, and having particular reference Vto Figs. 1A, 1B and 1C, the Web material leaving the heating drum 34, passes to rolle1u44 journalled between the sides ot' the tunnelV 10- with;the insidetof the'top of the tunnel provides a grado-- The.

and as hereinafter explained in relation to the airtiow, a diverging passage is provided terminating in the relatively narrow throat provided between the top of the web material immediately above the roller 44 and the inside of the top of the tunnel 10. A hinged cover 48 is provided on the top of the tunnel above the roller 44, the cover 48 yielding about its hinge point 50 to allow the passage of knots or heavy splices in the web material lengthwise of the tunnel, but normally forming a sealed closure for the top of the tunnel 10.

Leaving the roller 46 the web material W rises on a relatively sharp angle to pass over roller 52 positioned, like roller 44, near the top of the tunnel, and with the web material W then extending at a relatively long liat angle to pass beneath roller 54. Thence the web material rises sharply to pass over roller 56 and then at a long flat angle to pass under roller 58, again rising sharply to pass over vroller 69 and thence out of the tunnel by way of a bottom opening 62 near the other end ot" the tunnel, a roller 64 being provided in association with the opening 62 to facilitate removal of the web material from the tunnel.

From the foregoing description it will be evident that during the passage of the web material W lengthwise of the tunnel in the manner described that a plurality of relatively narrow throats are provided in the region of rollers 44, 52, 56 and 60, these throats being dened by the gradually narrowing distance between the web material and the inside of the upper portion of the tunnel, each throat being followed by relatively rapidly diverging diffusion areas formed between the web material W and the top of the tunnel. Each of the rollers 52, 56 and 60 is provided with an associated hinged cover or door 66, 68 and 70 similar to the door 48 and for purposes previously described. All of the doors 48, 66, 68 and 70 are of low mass and serve as means to blow open to minimize ydamage due to explosion, which might occur because of power failure or other shutdown in case of an air raid,

Vfor example. Incidentally, my improved apparatus is particularly explosion proof being a suction system and `can normally be started up without danger even though .the line has been stopped for some reason.

At the end of the tunnel 10 near which the web ma- Tterial W is introduced a blower 71 is provided upon the frame 12 for pulling air through the tunnel 10. Fig. 1A and Fig. 2 illustrate that the blower 71 is connected by a funnel-shaped housing 72 with the end of the tunnel 10, the blower 71 being driven, for example, by belt 74 from a suitable prime mover. A exible connection 73 is usually provided between the blower 71 and the housing 72 to reduce vibration. The discharge side of the blower 71 is provided with a discharge diffuser 76 which is formed so that its side diverges at no greater than an angle of 3, and this notably minimizes the overall horsepower required for the operation of the blower 71, and also notably reduces the noise level of the exhaust system.

With the blower 71 in operation air is drawn in through the remote end of the tunnel in the manner shown by the arrows in Fig. 1C, and this air passing through the throat formed by the roller 60 is given a relatively high velocity during its movement through the throat but immediately after passing the throat the sharply diverging area between the web material and the inside of the top of the tunnel causes the air velocity to drop off sharply and induces turbulent mixing of the air and solvent from the printing or coating on the web material. This same action of inducing high velocity travel of the drying air througha throat followed by a zone of turbulence and diffusion is periodically repeated throughout the passage of the air through the tunnel, the throats being provided by the rollers 56, 52 and 44 in turn during the travel of the air, each period of high velocity air travel being followed by an interposed slowdown of the air travel plus turbulence and diffusionvwhereby a very effective removal. of the solvent from the printing, and/or terial W, is effected. g

It should be noted here that the several throats provided along the tunnel in the manner described are arranged to have substantially the same pressure drop. This means that the throat at roller 60 is slightly larger than the throat at roller 56, which is slightly larger than `the' throat at roller 52, which in turn is slightly larger than the throat at roller 44. v y

In previously known driers there has` always tended to be a concentration of vapor or solvent at the surface of the lm being dried which blankets the solvent within the boundary layer and inhibits proper drying or evaporating i and removal of Vthe solvent. Any such action in the present drier is eliminated due to the boundary layer 'removing actionof the several throats and-subsequent dif-` f fusion areas in the manner described.

The drier of the present invention dilers basically from.; most driers in that only the film and/or ink o rcoatingVIA thereon are heated, and the air is not. The advantage of- 1 this is that the drying characteristics of the air Vare enchanced by maintaining the density of the air high and its viscosity low, and this follows when the airis not heated. The vaporization of a solvent in the ink or coating is promoted 4because the temperature of the solvent is maintained at a high level. In fact it has been found that once the film `is heated by the drum 34 the film` cools down very slowly during its travel through the tunnel. This is because convective heat transfer from the film to the air is relatively poor. The amount of heat necessary to effect the drying action inthe present application is far less than that required in conventional apparatus so that the cost of operation is vnotably reduced, and the disadvantages of discharging large amounts of hot air are eliminated.

The tunnel 10 is preferably provided with bae means to assist in obtaining the alternate throat and diffusion regions as previously described even though `the width` of the web W should be considerably less than the width of the tunnel 10. Specifically, baffles 90 are provided for stead. Figs. 4 and 5 illustrate such a diaphragm,'the

diaphragm, for example of rubber sheeting, being indicated by the numeral and being sealed in a frame 82 hinged at 84 to the top of the tunnel 10. The frame 82 drops down to make sealing contact with the top of the tunnel, but can be lifted to facilitate threading of the tunnel with the web material W. The advantage of thev diaphragm 80 over the rigid doors heretofore described is that during the flow of air at high velocity through the throats of the tunnel the diaphragms 80 can adjust themselves in relation to the spacing from the web material to give the proper relation between air velocity and pressure drop in the region of each throat.

From the foregoing it will be recognized that4 the various objects of the invention have been achieved by the provision of relatively simple, highly eliicient and yet relatively inexpensive to voperate drying apparatus.A

The amount of air drawn through the tunnel is controlled so that at no time does the air discharge from the blower with no solvent being determinable in the tunnel in the region of the last diffusion area, and with the lilm leaving the drying tunnel at temperatures in the region of*V drying of the web mae 1 th-160 F., andewith the film being capable ot' being directly wound upon itself without smearing `of the ink.

While in accord'A with the patent statutes certain best knowneinbodiments of theinvention have been illustratedY and described in detail, Iit is to be particularly understood that the invention is not to be limited thereto or thereby, but that the scope of the inventionl is defined inY totherwidthof the web and a height less than the width` oftheweb, means'for directing the web into the tunnel near one end thereof,v meansffor reducing substantially to aminimum the owof air around the web in the region of the introduction of the web to the tunnel, hollow drum means adjacent the region ot introduction off-the webto the 'tunneland inside they tunnel-and progressively engaging with fthe unprinted'side of the web toeheat; the web, means for heating --the drum with condensed'istearn andat less than atmospheric pressure, roller means for directing the web through the` tunnel, said roller-'means being positioned so that the web forms with one-side oli-the tunnel a plurality of narrow throats each throat having on its upstream side gradually converging side-storming a nozzle to give relatively high throat velocities tn .any air passing the throat, and on its downstream side having relatively sharply diverging sides to create turbulence of the air after passing the throat, fanmeans for drawingair through the tunnel in a direction opposite tothe travel of the-web and in a Volume so..tha ti.the air never .contains more vsolvent vthan 50% ot thelowenexplosivelimit, adischargediiuser on the exhaust side of the fan means having sideangles not eXceeding3"- toreduce the horsepower requirements of thetanmeans, and movable cover means on the tunnel in the region of each throat.. e

2., Apparatus for drying printing and the like on endless,continuously moving webmaterial including a tunnel member having an yinside width substantially equal to the` width ofI the web and apheight less than the Width of the web, means for directing the web into the tunnel near one krend thereof, means for reducing substantially to a minimnrn theflow of air around the web in the region of` the introduction of the web to the tunnel, hollow drummeans adjacent the region of introduction of, the webztofthe tunnel and insidethe tunnel and progressively engaging `with the .unprinted side of the web to heat the web, means for heating the drum with condensed steam and atless thanatmospheric pressure, roller means for directing theu web Athrough the tunnel, said roller means beingpositioned so that the web formsV with one side'of the-tunnel. a plurality of narrow throats each throat having ,onf its y upstream side gradually vconverging sidesflforrnin g a nozzle to give relatively high throat velocities to anyV air passing the throat, and on its downstream side having relatively sharply diverging sides to create turbulence ofthe air after passing the throat, fan means for drawing air through the tunnel in a direction'opposite to the travel of the web and in a volume so that the air never contains more solvent than 50% of the lower explosive limit, and a discharge diffuser on the exhaust side .of the fan means having side angles not exceeding 3 to reduce the horsepower requirements or" the, fan means.

3. Apparatus. for drying printing and the like on end less continuously moving web material including a tunnel member having an inside width substantially equal to the Width of the web and a height less than the width of thejweb., means forA directing the web into the tunnel near; onegendthereof, means for reducing substantially to,Vl a minimum the flow of air around the ,web in the region .ofuthe .introduction of theweb to the tunnel, hollossyl d runr) means adjaeentmtheregion of introduction ot.

the. web to thetunnel and'finside thel tunnel andv prof gressively engaging-withrthe unprrinted `side of the web toi heat theY web, means forheating the drum with condensedV steam and at'less than atmospheric pressure, roller meansfor directing* the web through theY tunnel, said rollen means Vbeing" positioned -so that the web forms with onev side of the Ytunnel a-plurality of'narrow-throats each throat having on its vupstream side gradually converging sides forming a nozzle to give relatively rhigh throatvelocities toranyair passing the throat, andton its down stream side having relatively sharply diverging sidestocreate turbulence of the air after passingv the throat, and fan means for drawing air vthrough the tunnel.

4.V Apparatus vfor drying printing and the like on endless, continuously moving vweb material includinga .tun-

nel `member having an insidewidthsubstantially equal to. v

the width ofthe web and a Vheight less thanfthe width of the web, means for directingthe webn into -the tunnelv near one end thereof, means for lreducing substantiallyv to a minimum. the ilow of air around the web in the region of the introduction of the wel;I to thetunnel, hollow drum means adjacent the region .of introduction of the` web to the tunnel and inside the tunnel and progressively engagingvwith vtheunprinted side of theweb to heat theweb, roller means for directingy the web through the tunnel, said roller means` beingpositioned so that the.

the` throat, and fan, means .for drawingair through the.l

tunnel,

5.- Apparatus for dryinga continuously moving web ofsheet materiahsaid apparatus comprising atunnel, means for directing a weby progressivelyinto one end ofthe tunnel, means atsaid end ofthe tunnell for progressively heatingfrtherweb, a series of rollers located entirely within.. the tunnel to direet the web along the tunnelsaid rollers being positioned-alternately nearopposite walls of theV tunnel to direct theaveb in a sinuous path with a wall of said tunnel and said web providing therebetween a series of narrow throats, each throat having at its upstream reach gradually convergingsides forming a nozzle to provide 'high velocities to-air passing the ,throat andA at its downstream reach vsharply diverging sides to create` turbulence of air passing said throat, means providing aflow of air alongV said tunnel4 in a direction opposite to the direction of travel or".y the web, openings in at least,v

one wall of said tunnel adjacent the narrow throats provided by close proximity of some of said rollers and said last-named wall, andy coversover said, openings for closing them, said covers being displaceable outwardly of saijdm tunnel to permit passagevof knots or splices and-under.V

excess pressure in said tunnel.,

6. n Apparatusl for drying a continuously moving web of sheet material said apparatus comprising a tunnel, means for directing av web progressively into one end of the tunnel, means at said end of the tunnel for progressively heating the web, a series of rollers located entirely within` the tunnel to direct the web along the tunnel said rollers being positioned .alternately near opposite walls of the tunnel to direct the web ina sinuons path with a wall of said tunnel andisaid web providing therebetween aseries of narrow throats, each throat having at its upstream reach gradually converging sides forming a nozzle to providerhigh velocities to air passing the throat and at its downstream reach sharply diverging sides to createA turbulence of air passing said throat,` means providingA a flow of air along said tunnel in a direction opposite to theY directionrof travelof the web, openings in at least one wall of .saidr tunnel.. adjacent the narrow throats pro vided .by close-proximityof some of said rollers and said..`

lastfnamed wall andlcovers overwsaid-openings forclosm` ing them, said covers being displaceable outwardly of said tunnel to permit passage of knots or splices and under excess pressure in said tunnel, said covers each comprising a frame supporting a exible diaphragm providing a displaceable wall portion of the tunnel at one of the throats.

7. Apparatus for drying a continuously moving web of sheet material said apparatus comprising a tunnel means for directing a web progressively into one end of the tunnel, means at said end of the tunnel for progressively heating the web, a series of rollers located entirely within the tunnel to direct the web along the tunnel said rollers being positioned alternately near opposite walls of the tunnel to direct the web in a sinuous path with a wall of said tunnel and said web providing therebetween a series of narrow throats, each throat having at its upstream reach gradually converging sides forming a nozzle to provide high velocities to air passing the throat and at its downstream reach sharply diverging sides to create turbulence of air passing said throat, means providing a tlow o air along said tunnel in a direction opposite to the direction of travel of the web, openings in at least one wall of said tunnel adjacent the narrow throats provided by close proximity of some of said rollers and said last-named wall, and covers over said openings for closing them, said covers being displaceable outwardly of said tunnel to permit passage of knots or splices and under excess pressure in said tunnel, said covers each comprising a frame supporting a flexible diaphragm providing a displaceable wall portion of the tunnel at one of the throats, said frame being hingedly secured to said tunnel wall at one of said wall openings.

8. Apparatus for drying a continuously moving web of sheet material, said apparatus comprising a tunnel means for directing a web progressively into one end of the tunnel, means at said end of the tunnel for progressively heating the web, a series of rollers having faces extending within the tunnel entirely across the width of the web to direct the web along the tunnel, said rollers being positioned alternately near opposite walls of the tunnel to direct the web in a sinuous path with a wall of said tunnel and said web providing therebetween a series of narrow throats, each throat having at its upstream reach gradually converging sides forming a nozzle to provide high velocities to air passing the throat and at its downstream reach sharply diverging sides to create turbulence of air passing said throat, means providing a flow of air along said tunnel along the web, openings in at least one wall of said tunnel adjacent the narrow throats provided by close proximity of some of said rollers and said last-named wall, and covers over said openings for closing them, said covers being displaceable outwardly of said tunnel to permit passage of knots or splices and under excess pressure in said tunnel, said covers each comprising a flexible diaphragm providing a iiexiole wall portion of a throat of said tunnel opposite a face of one of said rollers and adapted to assume under a balance of elastic membrane and aerodynamic forces a position defining a stable minimum throat gap, said covers being hingedly secured to said tunnel wall at one of said wall openings.

9. Apparatus for drying printing and the like on endless, continuously moving Web material including a tunnel member having an inside width substantially equal to the width of the web and a height less than the width of the web, means for directing the web into the tunnel near one end thereof, means for reducing substantially to a minimum the liow of air around the web in the region of the introduction of the web to the tunnel, means adjacent the region of introduction of the web to the tunnel and inside the tunnel and progressively engaging with the unprinted side of the web to heat the web,

- roller means for directing the web through the tunnel,

said roller means being positioned so that the web forms with one side of the tunnel a plurality of narrow throats each throat having on its upstream side gradually converging sides forming a nozzle to give relatively high throat velocities to any air passing the throat, and on its downstream side having relatively sharply diverging sides to create turbulence of the air after passing the throat, and fan means for drawing air through the tunnel.

References Cited in the le of this patent UNITED STATES PATENTS 1,830,287 Ohlin Nov. 3, 1931 1,847,915 Bailey Mar. 1 1932 2,248,897 Presby July 8, 1941 2,376,207 Tetzlali et al May 15, 1945 2,571,815 Benoit et al Oct. 16, 1951 2,574,844 Roden Nov. 13, 1951 2,659,162 Katz Nov. 17, 1953

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