US3287822A

US3287822A - Drying apparatus

Info

Publication number: US3287822A
Application number: US340684A
Authority: US
Inventors: Jr William Howard Beasley; Hogan James Raymond
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1964-01-28
Filing date: 1964-01-28
Publication date: 1966-11-29
Anticipated expiration: 1983-11-29
Also published as: DE1629026B1

Description

2 Sheets-Sheet 1 DRYING APPARATUS W. H. BEASLEY, JR., ETAL.

Nov. 29, 1966 Filed Jan. 28, 1964 INVENTORS WILLIAM HOWARD BEASLEY, JR JAMES RAYMOND HOGAN K m/6mm ATTORNEY Nov. 29, 1966 w. H. BEASLEY, JR., ETAL 3,287,822

DRYING APPARATUS Filed Jan. 28, 1964 2 Sheets-Sheet 2 FIG 4 c0MPARAT0R SERVO 4|-M|PLIFIER 42 43 COHPARATOR SERVO Hi-AMPLIFIER 48 INVENTORS JAMES RAYMOND HOGAN BY 75MM I ATTORNEY WILLIAM HOWARD BEASLEY, JR.

United States Patent fiFice 3,287,822 Patented Nov. 29, 1966 3,287,822 DRYING APPARATUS William Howard Beasley, Jr., and James Raymond Hogan, both of Brevard, N.C., assignors to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed Jan. 28, 1964, Ser. No. 349,684 2 Claims. (Cl. 34-157) This invention relates to a process and apparatus for drying of continuous webs. More particularly, this invention relates to such apparatus for drying coated, festooned webs.

Photographic films and papers are usually made by coating continuous rolls of flexible base material with an aqueous dispersion of silver halides in a water permeable colloid, chilling and setting the liquid emulsion, and drying the emulsion layer in a convection type drier where the wet bulb temperature of the conditioned air is lower than the melting point of the set emulsion. Drying of the web is often accomplished by festooning it over sticks and moving the sticks through a drying chamber. Within the drying chambers, the air velocities and the drying conditions are usually moderate and, depending upon coating weight, drying times of 30 to 90 minutes may be required.

With the increased speeds which photographic emulsions are now coated, it has become necessary to accelerate the drying rate so that the period for drying the coated web will be reduced. The rapidity of drying generally depends upon a combination of the temperature and velocity of the supply air. It has been found in festoon type driers that if an overhead air distribution system, with the conditioned air being directed onto the loops from above at a high velocity, is utilized, the drying rate will be accelerated. This system will permit the use of web driers of shorter length with the resulting saving in installation and maintenance costs. However, in the drying of photographic emulsions, the drying rate must be uniform over the entire area of the web so that a product having good photographic qualities is obtained. If the drying is not uniform, the web may contain some of the following defects: stickmarks, emulsion runs, drying lines or mottle. Also, it is known that the sensitivity of a photographic product is affected by the drying rate and an uneven drying rate will produce uneven sensitivity.

It has been found that the directing of conditioned air from overhead onto festooned loops creates some problems with respect to the uniformity of the drying rate. The area of the web that is directly supported by the stick and closest to the air supply will receive a direct impingement of air. This causes stick marks and more seriously, it dries this area of the web at a much faster rate than the area of the web in the loops.

Accordingly, it is an object of this invention to provide improved drying apparatus that can be used to obtain optimum air distribution in the loops of a festooned web. Another object is to provide apparatus that will provide a uniform drying rate in a festooned web drier. Another object is to provide apparatus for obtaining an accelerated drying rate in a festooned web drier in combination with the uniform drying of the web. A still further object is to provide apparatus for a festoon drier that allows the drier to be constructed with reduced length and with the resulting savings in cost. Still further objects will be apparent from the following description of the invention.

The improved drying apparatus of this invention comprises (1) A drying chamber,

(2) Means for feeding a coated Web into and from the chamber,

(3) Means for forming the coated web into festoons and moving the festoons in the chamber, and

(4) Meansfor directing drying air onto the festooned web while it is so moving in the chamber, said apparatus being characterized in that spaced baffles are placed above the festooned web and prevent the drying air from impinging directly on the festoons at the uppermost parts of the festoons and said baffles travel at the same speed and in the same direction as said uppermost parts.

The process of this invention for uniformly drying a festooned web, especially a coated web, eg, a continuous coated photographic film or paper base, comprises directing a gaseous medium, e.g., drying air from above onto moving festoons of such a web; said process being characterized in that during movement of the festoons the uppermost looped portions thereof are shielded from direct impingement of high velocity currents of the gaseous medium while the gaseous medium flows past the upper surfaces of the festooned web.

The process, as well as the apparatus of the invention, will be exemplified below with respect to the drying by means of air, which may be at room temperature or below or heated to an elevated temperature, e.g., 40180 F of a photographic film or paper base that has been coated with an aqueous gelatin coating solution, for instance, an

aqueous silver halide dispersion and festooned with the coated surface uppermost. The process and. apparatus, however, are not limited to such use as webs of paper, metal foil, cloth and films coated and/ or impregnated with various other solutions can be treated in like manner to set or dry the treated web uniformly.

The invention will be further explainedwith reference to the attached drawings which are part of this specification and in which:

FIG. 1 is a side elevation of a festoon drier embodying the traveling bafile and air distribution chamber of the invention;

' FIG. 2 is an end elevation of the drier taken along the line 2-2 of FIG. 1;

FIG. 3 is an isometric view, with sections broken away, of a preferred bafile element;

FIG. 4 is a cross-section of an alternative baflle element,

FIG. 5 is a cross-section of another alternative baffle element,

FIG. 6 is a cross-section of yet another alternative baflie element, and

FIG. 7 is a block diagram of a suitable electrical drive and circuit for the drier.

With reference to the drawings wherein similar reference numerals refer to similar parts throughout the several views, practical embodiments of the invention will now be described. These embodiments are primarily concerned with apparatus suitable for coating photographic films and papers. The apparatus comprises a suitable light-tight chamber 11.- If the material being dried is not light-sensitive, a light-tight chamber will not be necessary. A web 12 of coated material enters the chamber through a narrow entrance slot 13 in an end Wall of the chamber. The web then passes over a driven roll 14 and then is fed downwardly where it is successively taken up by sticks 15 of a continuous conveyor. The downward passage of air within the chamber, the motion and interval of the stick and the movement and weight of web cause it to festoon itself over the sticks and form loops 16. The sticks extend between and are supported on two parallel and laterally-spaced, inclined, endless chain conveyors 17 and which pass around lower sprockets 18 mounted on a suitable shaft (not numbered) and around upper sprockets 19. The sticks are held on the conveyors by projecting lugs or dogs 20 attached to the conveyors at regular intervals, the spacing of which determines the depth of the festooned loops. The conveyors are moved in an upward inclined path upon rotation of the lower sprocket which is fasten-ed to the shaft. The shaft in turn is rotated by means of sprocket 21 fastened thereto which latter sprocket meshes with endless chain 22 which in turn meshes with sprocket 21' that is mounted on, and driven by, motor 23. The motor speed is synchronized with the speed of the web and insures that the sticks are supplied at regular intervals.

The festooned web is propelled upward until it reaches the maximum elevation of the inclined conveyors. At this point, the sticks are transferred to another pair of parallel and laterally spaced endles chain conveyors 24 which are mounted on spaced sprockets 25. Upon transfer, the path of the sticks is changed from an inclined to a horizontal path. The speed of the conveyors is that which is necessary to give the film the required period in the housing for adequate drying. The conveyors transport the festooned web through the housing where the web is subjected to the drying action of conditioned air. At the exit end, the dried web 12 is removed from the sticks by passing the web to, and partly around, guide roller 26 near narrow exit slot 27 in the end wall of the chamber. The web'can then be acted on by supplemental processes or operations. As the sticks pass around end sprockets 25, they fall into a suitable hopper (not shown) and are returned to the point where they are disposed on chain 17.

Within the drying chamber 11 and supported to the frame thereof in any suitable manner are lengthwise disposed plenum supply ducts 28 which are closed at their outer ends. Conditioned air that is supplied to the ducts enters the drying chamber through lateral nozzles 29. The entrance end of the plenum ducts are joined through an accordion fold flexible connector 30 to the short ducts 30' extending from the supply duct 31 which passes through a sidewall of the chamber 11. Air can be removed from said chamber through outlet ducts 32 and recirculated to the supply ducts after the air has been reconditioned. The ducts can be supported by the frame of the chamber in any suitable manner, e.g., mounted on cross-braces.

In the drying of photographic emulsions, the air will usually have a dry bulb temperature between 75 F. and 120 F. The air exits from the nozzles at a high velocity, in the order of 3,000 to 5,500 feet per minute. This high velocity accelerates the drying rate. After leaving the nozzles, the conditioned air is directed downward onto the traveling festooned loops by a gullwing-shaped bafile 33 that is disposed between the lateral nozzles of the plenum supply ducts.

Located between the gullwing baffle 33 and the festooned web on the conveyor chains 24 is the lower section of another spaced pair of endless conveyors 34. The conveyors pass around four spaced sprockets 35 one or more of which is driven. Inverted V-shaped battle 36 mounted on shafts 37 extend between these conveyors. The :bafiles can be welded or bolted to the shafts and the latter fastened to the chains by bolts 38 and angle irons 38, or by suitable means to prevent the shafts and baffles from rotating and to maintain the desired interval between successive bailies. The bat-lies preferably are spaced on these conveyors at the same interval that the sticks are spaced on conveyors 24. In operation they should be located directly over the sticks and their length is at least the width of the festooned web 12.

The drive for conveyors 24 is synchronized with the drive for conveyors 34 by suitable means. The synchronization of the two drives insures that the conveyors are moving at the same speed, and since they are also moving in the same direction, a baflie is always located between the area of the web supported directly on a stick and the source of the distributing air during the passage through the drier. As the air is directed downward into the loops, the traveling bafiles divert the flow of air from the tops of the loops and prevent a direct impingement of high velocity air. A relatively gentle air current is directed to the tops of the loops and this provide for uniform drying of the web and eliminates defects caused by nonuniformity.

The optimum design of the traveling bafiie depends upon many factors, e.g., the temperature and humidity of the conditioned air, direction of conditioned air, velocity of conditioned air, drying properties of the festooned web, size of the loops, spacing of the loops, and speed of the loops through the drier. It has been found experimentally that the most eifective shape for the traveling baffie 36 is essentially an inverted V, with slightly curved sides and an enclosed bottom. Referring to FIG. 3, when working with a web in loops 5 feet long, spaced 18" apart, it was found that if the height (H) of the baffle 36 was two times the width (W), optimum air distribution was obtained. Other types of baffles may be used, such as an inverted V with an open bottom, an inverted T, a flat baffie, or a semi-cylindrical bafile, but these are less preferred. Suitable shapes are shown in FIGS. 4, 5 and 6. These baffles can be fastened to the chain conveyors in any suitable manner. They may have projecting end shafts like those of the V-shaped battles. The baffles can be constructed out of many materials, e.g., metal, wood, plastic, etc. The bathe can be hollow as shown in FIG. 3 or it can be made in solid form.

FIG. 7 shows, schematically, a suitable method of electrically synchronizing the movement of the bafiles and sticks.

The desired speed for both conveyors is represented by a set reference voltage 2 This voltage is compared in a comparator or bridge 39 with a voltage e that is representative of the actual speed of conveyor 24. Voltage e is developed by a tachometer 40 that senses the speed of the conveyor and produces a voltage that varies proportionally with the speed. The difference between the two voltages e and e or the error voltage e is the output of the comparator and is sent to a servo amplifier 41. This servo amplifiers output e; is functional with some input voltage and it governs the speed of a motor 46 that drives conveyor 24. Another tachometer 42 senses the speed of the motor 46 and produces a feedback voltage e that con trols the acceleration rate of the motor during the startup and speed changes. Thus, the motor 46 will accelerate as long as e is smaller than the reference voltage e will decelerate when a is greater than e and when e equals e; the motor will run at the constant, desired speed. In some embodiments where there is no conveyor slippage, pulley sizes, bias, etc., only one tachometer will be necessary to sense the motor or conveyor speed.

Similarly, the voltage output e of tachometer 47 which senses the speed of conveyor 34 is compared with voltage e which as previously explained represents the speed of conveyor 24. The difference, if any, between the two input voltages is the output a of the comparator or bridge 43. This output is received by another servo amplifier 44 where a voltage 2 is produced that governs the speed of motor 45. Here also the rate feedback voltage c which controls the acceleration rate of the motor 45 is developed by a tachometer 48 that senses the speed of the latter motor. With the arrangement, motor 45 will accelerate if voltage e is greater than e decelerate if e is smaller than 12 and if E equals e the motor will run at a constant speed which is equal to the speed of motor 46. Thus, conveyor 34 becomes dependent upon conveyor 24 and assumes the same speed.

Many other methods of synchronizing the movement of the baffles with the sticks are possible and will be obvious to those skilled in. the art, e.g., using a common drive and mechanical means to connect the drive to both conveyors. Also, if desirable, only one conveyor need be used and the conveyors 24 could be omitted. In this embodiment the baffies can be attached to the single conveyor by suitable means, this conveyor could have two chains or one with cantilevered sticks. Each baffle should then have means for picking up the festooned sticks from the inclined conveyors 17 and transporting them the length of the drier, e.g., a hook extending from the shaft on each end of the baffle. At the exit end of the drier, another conveyor could receive the sticks and transport them for further operations.

The invention has many advantages, one of which is the fact that it leads to drying uniformity Without increasing drying time. The machine of the invention is of simple construction and can be successfully operated over long periods of time. The invention overcomes the problem of defects in the final product that are caused by direct overhead air impingement. Additionally, the invention provides means for controlling the uniformity of air distribution, a condition that was not obtainable by prior art apparatus. Additional advantages will be apparent from the foregoing specification.

We claim:

1. A drying apparatus which comprises (a) a drying chamber,

(b) means for feeding a coated web into the drying chamber,

(0) means for forming the web into festoons in said chamber,

((1) means for directing a drying gaseou medium from above the festoons onto the festooned Web while the latter is moving in a longitudinal direction in said chamber, and

(e) means for directing the dried web from said chamber;

said apparatus being characterized in that (i) above the festooned web, the drying chamber contains two spaced longitudinally disposed plenum supply ducts having a plurality of lateral nozzles for the gaseous medium and a longitudinal deflector between said ducts and nozzles for deflecting the gaseous mediumdownwardly onto the festooned web,

(ii) wedge-shaped baflles are disposed above the festooned web and beneath the deflector to prevent a drying gaseous medium from impinging directly upon the uppermost parts of the festooned web, said baffles being wedge-shaped, having a closed bottom, being spaced apart the same distance as the uppermost parts of the festooned web and adapted to travel at the same speed and in the same direction as said parts.

2. An apparatus according to claim 1 wherein the gaseout medium is air.

References Cited by the Examiner UNITED STATES PATENTS 1,599,797 9/ 1926 Stacey 2668 2,269,169 1/ 1942 Van Derhoef et a1. 2,290,053 7/1942 Hurxthal 34157 2,333,236 11/1943 Dreisel 34-24 X 3,118,583 1/1964 Haas 34157 X 3,214,274 10/1965 Ohyama et al. 117-119.8 X

FREDERICK L. MATTESON, JR., Primary Examiner. C. R. REMKE, Assistant Examiner,

Claims

1. A DRYING APPARATUS WHICH COMPRISES (A) A DRYING CHAMBER, (B) MEANS FOR FEEDING A COATED WEB INTO THE DRYING CHAMBER, (C) MEANS FOR FORMING THE WEB INTO FESTOONS IN SAID CHAMBER, (D) MEANS FOR DIRECTING A DRYING GASEOUS MEDIUM FROM ABOVE THE FESTOONS ONTO THE FESTOONED WEB WHILE THE LATTER IS MOVING IN A LONGITUDINAL DIRECTION IN SAID CHAMBER, AND (E) MEANS FOR DIRECTING THE DRIED WEB FROM SAID CHAMBER; SAID APPARATUS BEING CHARACTERIZED IN THAT (1) ABOVE THE FESTOONED WEB, THE DRYING CHAMBER CONTAINS TWO SPACED LONGITUDINALLY DISPOSED PLENUM SUPPLY DUCTS HAVING A PLURALITY OF LATERAL NOZZLES FOR THE GASEOUS MEDIUM AND A LONGITUDINAL DEFLECTOR BETWEEN SAID DUCTS AND NOZZLES FOR DEFLECTING THE GASEOUS MEDIUM DOWNWARDLY ONTO THE FESTOONED WEB, (II) WEDGE-SHAPED BAFFLES ARE DISPOSED ABOVE THE FESTOONED WEB AND BENEATH THE DEFLECTOR TO PREVENT A DRYING GASEOUS MEDIUM FROM IMPINGING DIRECTLY UPON THE UPPERMOST PARTS OF THE FESTOONED WEB, SAID BAFFLES BEING WEDGE-SHAPED, HAVING A CLOSED BOTTOM, BEING SPACED APART THE SAME DISTANCE AS THE UPPERMOST PARTS OF THE FESTOONED WEB AND ADAPTED TO TRAVEL AT THE SAME SPEED AND IN THE SAME DIRECTION AS SAID PARTS.