US2929153A

US2929153A - Drying apparatus for sheet material

Info

Publication number: US2929153A
Application number: US549650A
Authority: US
Inventors: Jr Horace P Fry; Lester B Cundiff
Original assignee: American Viscose Corp
Current assignee: Akzo Nobel UK PLC
Priority date: 1955-11-29
Filing date: 1955-11-29
Publication date: 1960-03-22
Anticipated expiration: 1977-03-22

Description

March '22, 1960 H. P. FRY, JR., DRYING APPARATUS FOR SHEET MATERIAL Filed Nov. 29 1955 name APPARATUS non snnnr MATERIAL Horace P. Fry, Jan, West Chester, Pa., and Lester B.

Candid, Wilmington. Del., assignors to American Viscose (Iorporation, Philadelphia, Pa., a corporation of Delaware Application November 29, 1955, Serial No. 549,650

16 Claims. (Cl. 34-72) The present invention relates to a novel and improved drying apparatus for continuous sheet material such as cellophane. T

With present day procedure, running lengths of continuous sheet material are dried by passing the sheet material over a series of heated drying rolls. This drying procedure has been used for years and years with little improvement incorporated therein. This established and long-used drying system has many disadvantages. The main disadvantage with such a system is that the sheet is not dried uniformly across its width. The edges of the sheet dry before the central sheet portions are dried' because the end surface portions of the drum are apparently maintained at a higher temperature than the central portions of the drums and because of non-uniform moisture conditions across and immediately adjacent the drying rolls. This uneven drying pattern produces a final sheet of uneven strength and strain whereby the sheet has varying shrinkage and stretch characteristics across its width. In addition, the final sheets have floppy edges. This non-uniform pattern is especially noticeable in cellophane sheets which have been dried on the abovedescribed type dryer.

Many attempts have been made to alleviate this nonuniform drying condition, but none have proved to be entirely satisfactory.

Another disadvantage with this roll drying system, especially in cellophane and other plastic film manufacture, is that no provision is made to recover the large amount of film plasticizer, such as ethylene glycol'or glycerine, which escapes from the film in vapor form during the drying of the film. As the film is dried on the heated rolls, the plasticizer within the film vaporizes and escapes into the room atmosphere. A great saving in expense to the film producers would result if this escaping plasticizer could be recovered and used again.

It is therefore oneobject of our invention to provide a novel and improved method and apparatus for drying traveling continuous sheet material which will uniformly dry the sheet material both lengthwise and widthwise of the sheet.

Another object of our invention is to provide a novel and improved film drying method and apparatus where-.

in a substantial amount of any film plasticizer being released from the film during the drying stage may be recovered. 7

Other objects and advantages of the present invention will become apparent from a study of the following description and drawing wherein:

' Figure 1 is a side view of a portion of our novel and improved drying apparatus; and

Figure 2 is a section'taken' along the lines II--II of Figure 1.

'Briefly, our invention comprises an. upper and lower deck of heated drying rolls over which the continuous sheet material to be dried travels in an alternating patterm from the upper deck to the lower deck. The roll decks are enclosed within a housing, the top of which hinged along its longitudinal center line whereby it may be raised so that access may be had to the drying rolls. Atfixed to the inside of the top and bottom housing walls are channel-forming partitions which extend longitudinally of the direction of sheet travel. Means are provided for introducing a gaseous medium such as heated air intoboth the upper and lower channels at one end of the housing whereby air streams are formed'within the channels which fiow above, below and between the roll surfaces of eachroll deck in a direction countercurrent to the direction of film travel to pick up and remove moisture escaping from the film being dried.. Means are provided for regulating the amount or volume 1 of air entering the channels. A recirculation and reconditioning system is provided for the air escaping from both the upper and lower set of channels whereby the air is returned to the entrance end of the channels after being reconditioned. A recovery apparatus is installed within each recirculation system of the drying apparatus whereby vaporized plasticizer escaping from the film may be recovered.

In general, the continuous sheet material passes in an alternatingover and under path through a plurality of drying rolls which are enclosed in a housing. A heated moving air mass is introduced into the housing immediately above and below the rolls at the sheetv discharge end of the housing, which air mass is confined to a single path or is broken up into a plurality of separate, partially-confined air streams. These separated air streams are directed or guided through the housing in a path immediately above and below the heated drying rolls in the plane of travel and countercurrent to the direction of sheet travel. The moving air streams pick up and remove from the area immediately adjacent the drying rolls the moisture escaping from the traveling sheet material being dried. The moisture-laden air streams are then discharged at the sheet entrance end of the housing to be reconditioned and recirculated to the housing. During the recirculation cycle, any vaporized plasticizer for the sheet material which has escaped from the sheet material being dried and which is present in the discharged air streams is recovered.

Referring now to the drawing, there is provided an upper deck A and a lower deck B of heated drying rolls which are afiixed to a horizontally extending support 11v in turn supported by vertically disposed supports 11',

11'. The top wall 8 may thereby be raised so that access may be had to the

drying rolls

2, 2 for lacing up the rolls, cleaning the rolls, etc. Both the top wall 8 and bottom wall 12 of the housing 6 are of irregular (preferably scalloped) shape so that their surfaces follow the contour of the

rolls

2, 2 of the upper and lower roll decks A and B. The reason for this irregular surface contour will be explained at a later point in the description.

. Secured to the inside. ofboth the top wall 8 and bottom wall 12 of the housing 6 are longitudinally-extend ing, spaced-apart partitions 1 5, 15 which extend longi-: tudinally of the housing 6. As seen in Figure 1 of: the,v drawing, the

partitions

15, 15 also have a line of curva-' ture along their length which corresponds to the PC 3 ripheries of the was 2, 2. When the top wall 8 of the housing is in its lowermost or operative position, the

partitions

15, 15 form

sepaiate channels

17, 17 which run lengthwise of the housing 6 The same is true with respect to the bottom wall 12 of the housing 6.

Heated air is supplied to the

channels

17, 17 at their entrance end C from 'a supply 'con'duit2 1 which leads from arcirculation fan 22. The air passes through 'a heater 23 installed in the conduit 21 where the temperature of the air may be regulated. The supply conduit is connected with a. nozzle 25 which flares outwardly from the supply conduit 21 to 'a Width substantially the same as that of the housing '6, The nozzle 25 is lc'on nected with the air entrance e'ndC of the

housing chaflnels

17, 17. As seen in FigureZ, longitudinally-

extendingpartitions

27, 27 arepo'sitioued within the nozzle interior whereby

channels

29,, 29 are formed which line up with the channels17, 17 of the top wall 8 of the housing 6. The air stream or lrfnass issuing from the supply conduit 21 is divided as it passes through the nozzle 25 to vform s cpariatefair streams through each of the channels 29, 29 e: the nozzle 25. These ,streams of air pass from the

individual channels

29, 29 into the mating channels '17, 17 'formedin the top wall 8 of the housing '6. As indicated by the arrows in Figure 1, these separated air streams pass through the housing in a counte'rcurrent direction to the directionof film travel.

Dampers

31, 31 are installed within the channels 29 2 9 of each nozzle 25 whereby the flow or volume of air passing through each

channel

29, 29 may be controlled. The purpose 'for these

control units

31, 31 will be explained more fully hereinafter.

The circulation fan 22 circulates the air through the supply conduit 21, the heater 23, the nozzle 25 and into and through the

channels

17, 17 of thethousing '6. The air is exhausted at the opposite end D (the sheet ontrance end) of the housing 6. v r

A duplicate air supply system is provided for feeding air to the

channels

17, 17 formed along the bottom housing wall 12. p H

As mentioned above, a recirculation system is provided for recirculating of the air which has traveled through the housing 6 back to the supply conduits 21. A return conduit 33 is mounted adjacent the discharge end D of the

channels

17, 17 and connects the channels 'with the fan 22. The return conduit 33 receives the air as it is exhausted from the discharge end D of the

channels

17, 17. The circulation fan 22 draws the 'air into the supply line 21 from which point the air is returned through the supply path described above 'to the 'entrance end C of the

channels

17, 17 of the top housing wall 8. A duplicate recirculation system is provided for recirculating the air being discharged from the

channels

17, 17 along the bottom housing wall 12.

Our apparatus is especially designed for drying film material such as cellophane. -In the initial formation of the cellophane sheet and prior to its being dried, an amount of a plasticizin'gsubstance is incorporated into the sheet. v Two such .film plasticizers which are commonly used are diethylene glycol and glycerine. "Some of this plasticizer escapes in vapor formffrom the sheet as it is being dried. Our apparatus provides forrecovering this plasticizer releas e d fromthe sheet material 4 during the drying stage. As the cellophane sheet 4 is heated by the drying rolls 2, 2, some of the plasticizer in the film vaporizes and passes into the air streams moving through the

housing channels

17, 17 to enter the return line 33. As seen in Figure l, a plasticizer recovery station '35 is installed in the-return line '33 whereby the exhausted as containing the vaporized "plasticizer will pass therethIough to be "relieved of its 'pla'stic'ize'r content. A duplicate recovery system 35 isprovidedjin the return line for the air exhausted from the bottom housing wall 'chan'nels 17, '17. No specific "form of recovery apparatus is shown; however, any suitable type or recovery apparatus may be used.

Several housings, air supply systems, recirculation systems and recovery systems may be provided for each drying machine. The number of these structures pro vided depends upon the length of the drying machine. The shorter the housings'are, the more efficient is the drying operation since the moisture escaping from the rolls should be removed from the housing as quickly as possible. In addition, the recirculation, recovery and reconditioning systems for the air supply will operate more efiiciently if the air is not over-saturated with moisture and vaporized plasticizer. V

As seen in Figure 1, booster heating pipes 37, 37 are installed within the

channels

17, 17 of, the top and bottom housing walls 8 and 12 whereby the temperature of the air traveling through the channels may be boosted asrequired, V H

To. furtherieg'ulate the humidity of the air entering the

channels

17, 17,

steam spray assemblies

39, 39 are installed within the nozzles 25 The amount of steam introduced within the nozzle 25 may be controlled externally of the nozzle 25 since the valves for the steam spray units are positioned externally of the conduit 25.

To sum up the operation, the film 4 enters the housing 6 at the right hand end jar the housing as seen in Figure iand 'travels in an alternating pattern over and under the

rolls

2, 2 of the upper deck A and lower deck B, The fil n 1 4 femerges from the housing at the left hand end thereof as seen in Figure l. The supply air is moved through supply conduit 21 by the circulation fan 22, into the heater 23, and "into the nozzle 25 where it is broken up into separate streams by the

nozzle partitions

27, 27 to'form separate streams of air. The heated air passes from the nozzle 25 into the

channels

17, 17 of the top housing wall 8 whichare aligned with the

channels

29, 29. The air streams are carried through the channels both by the push and pull of the circulation fan as exerted upon the streams through the supply conduit 21 and the return conduit 33. The air streams within the housing flow countercurrent to the direction of film travel and follow the corrugated pattern of the top and bottom housing walls 8 and 12. With this arrangement, the air streams flow into the pockets between the rollsto remove moisture laden air trappedin these pockets. From this point, the exhausted air containing the moisture and vaporized plasticizer released from the film or sheet is picked up by the return line 33, passed into the plasticizer recovery system, and into the circulation fan 22 after which the cycle is repeated. v H A p To prevent the film or sheet plasticizer, which has escaped from the film, from condensing on the hood, the top and bottom walls 8 and 12 of the housing 6 are preferably insulated to maintain their temperature above the dew point for the particular plasticizer used.

As mentioned in the opening paragraphs of our application, we stated that one disadvantage with the drying apparatus and methoddescribedtherein was that the final sheet had a non-un' dorm stretch and shrinkage pattern across its width. Such a non-balanced condition occurred because the edge portions of the sheet were dried faster than the central sheet portions. With our drying apparatus, this condition of non-uniform drying is elimlnated. To slow down the drying efiect along the edge portions of the sheet material 4 as it is being dried, the

dampers

31, 31 within the

channels

29, 29 of the nozzle's '25 may be partially closed to decrease the flow or volume of air entering these

individual channels

17, 17 of the upper 'and lower walls 8 and 12 of the housing 6, By closing thedampers 31, 3.1 in the outermost channels and thus decreasing the volume of air entering the

channels

17, 17 tliemois ture rising from the edge portions ofithe sheet willnotbc removed from the immediate'are'a rapidlyasthetnoisture rising from'the cenaaaanea tral sheet portion. The drying effect is therefore slowed down along the edge portions of the sheet 4 whereby the sheet material may be uniformly dried across its width.

Additional make-up air is received into the housing from the surrounding atmosphere through cracks or leaks within the housing structure. An exhaust pipe 41 is installed within the supply line 21 just below the circulation fan 22 through which a portion of the moisture-laden air is permitted to escape from the system. If desired, an air intake may be installed in the recirculation conduit. In this instance, the leaks and cracks will be sealed off as efficiently as possible.

While preferred embodiments of the invention have been shown and described, it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A drying apparatus for drying traveling continuous flexible sheet material comprising an upper deck of spacedapart heating drying rolls, a lower deck of spaced-apart heated drying rolls, the rolls of said lower deck being alternately spaced with respect to the rolls of upper deck whereby the sheet material travels over and under the rolls of the upper and lower decks in an alternating pattern, a housing for the drying roll decks for closing off the drying rolls from the surrounding atmosphere, a plurality of spaced-apart channel-forming partitions atfixed to the underside of the top housing wall which partitions extend longitudinally of the housing and of the direction of sheet travel over the rolls, and means for continuously supplying and introducing air into the channels formed by the partitions to set up within each channel a continuous stream of air which streams fiow through the housing in a countercurrent direction to the direction of sheet travel, said traveling air streams picking up and removing from the area immediately above the rolls and the traveling sheet the moisture-laden air escaping from the wet sheet material being dried.

2. A drying apparatus for drying traveling continuous flexible sheet material according to claim 1 comprising a damper adjacent the entrance end of each channel as formed by the partitions to control the volume of air introduced within each channel.

3. A drying apparatus for drying traveling continuous flexible sheet material according to claim 1 wherein the top of the housing is hinged along its longitudinal center line whereby the housing top may be raised out of posi tion so that access may be had to the drying rolls.

4. A drying apparatus for drying traveling continuous flexible sheet material according to claim 1 comprising a steam spray assembly connected with the air supplying and introducing means whereby the humidity of the air entering the channels can be adjusted.

5. A drying apparatus for drying traveling continuous flexible sheet material according to claim 1 comprising booster heating pipes installed within the housing in the channels formed by the partitions for boosting the temperature of the air streams during their travel through the channels.

6. A drying apparatus for drying traveling continuous flexible sheet material according to claim 1 comprising a plurality of spaced-apart channel-forming partitions affixed to the inside of the bottom wall of the housing which partitions extend longitudinally of the housing and of the direction of sheet travel over the rolls, and means for continuously introducing air into the channels formed by the partitions of the bottom housing wall to set up within each channel a continuous stream of air which flows countercurrent to the direction of sheet travel, said traveling air streams picking up and removing from the area immediately below the lower deck of drying rolls and the traveling sheet material the moisture-laden air escaping from the wet sheet material being dried.

7. A drying apparatus for drying .travelingcontinuous flexible sheet materialcomprising an upper deck of space apart heated drying rolls, a lower deck of spaced-apart heated drying rolls, the rolls of said lower deck being alternately spaced with respect to the rolls of the upper deck whereby the sheet material travels over and under the rolls of the upper and lower decks in an alternating pattern, a housing for the drying roll decks for closing off the drying rolls from the surrounding atmosphere, a plurality of spaced-apart channel-forming partitions affixed to the underside of the top wall of the housing which partitions extend longitudinally of the housing and of the direction of sheet travel over the rolls, means for continuously supplying and introducing air into the channels formed by the partitions to set up within each chan-, nel a continuous stream of air which streams flow through the housing in a countercurrent direction to the direction of sheet travel, said traveling air streams picking up and removing from the area immediately above the traveling sheet the moisture-laden air escaping from the wet sheet material being dried, and a recirculaiton conduit for receiving the air streams as they are exhausted from the channels which conduit connects the exit end of the channels at one end of the housing with the air supplying and introducing means at the air entrance end of the channels.

8. A drying apparatus for drying traveling continuous flexible sheet material according to claim 7 comprising a plasticizer recovery apparatus installed in the recirculation conduit for recovering sheet plasticizer material which has escaped from the film in vapor form and which R has been picked up by the traveling air streams.

9. A drying apparatus for drying traveling continuous flexible sheet material according to claim 7 comprising a plurality of spaced-apart channel-forming partitions affixed to the inside of the bottom housing wall which partitions extend longitudinally of the housing and of the direction of sheet travel through the housing, and means for continuously supplying and introducing heated air into the channels formed by the partitions to set up within each channel a continuous stream of heated air which streams fiow through the housing in a countercurrent direction to the direction of sheet travel, said traveling air streams picking up and removing from the area immediately below the lower deck of drying rolls and the sheet material traveling thereover the moisture-laden air escaping from the wet sheet material being dried.

10. A drying apparatus for drying traveling continuous flexible sheet material comprising an upper deck of spaceapart heated drying rolls, a lower deck of spaced-apart heated drying rolls, the rolls of said lower deck being alternately spaced with respect to the rolls of the upper deck whereby the sheet material travels over and under the rolls of the upper and lower decks in an alternating pattern, a housing for the drying rolls decks for closing off the drying rolls from the surrounding atmosphere, the top of said housing being hinged along its center line whereby the housing top may be raised for access to the drying rolls, a plurality of spaced-apart channel-forming partitions affixed to the underside of the top and bottom housing walls which partitions extend longitudinally of the direction of sheet travel over the rolls, a plurality of spaced-apart channeLforming partitions affixed to the inside of the top and bottom housing wall which partitions extend longitudinally of the housing and of the direction of sheet travel through the housing, means for continuously supplying and introducing heated air into the channels formed by the partitions to set up within each channel a continuous stream of heated air which streams flow countercurrent to the direction of sheet travel, said traveling air streams picking up and removing from the area immediately adjacent the rolls any moisture-laden air escaping from the wet sheet material being dried, a recirculation conduit for each set of upper and lower channels which connect the exit end of the channels at one end of the housing with the air supplying--and introducing means at the opposite housing end,

air supplying means, and booster heating pipes installed within the channels formed by the partitions within the housing for boosting the temperature of the air streams within the channel.

11. .A-dryingapparatus for drying traveling continuous flexiblesheet materialaccording to claim 10 Whereinthe air supplying and introducing means for the upper and lower setof channels comprises a supply conduit through which the air is directed by the circulation fan, a nozzle secured t'o'th'e discharge end of the supply conduit, said nozzle'fiaring outwardly from the discharge end of the supply "conduit to a'width equal to that of the housing, a plurality of channel-forming partitions supported within the nozzle which partitions extend longitudinally of the nozzle and which connect with the channel-forming partitions within the housing, and a damper within each channel of the nozzle for controlling the volumeof air introduced within each channel.

12. A dry ing apparatus for drying traveling continuous flexible sheet material comprising a plurality of drying rolls over which the sheet material travels, a housing within -which the drying rolls are supported, a plurality of channel forming partitions extending from and along the top wall of the housing in the direction of the path of the material traveling over the rolls, said partitions extending down from said top wall into close proximity with said dryingrolls so as to direct a heating medium into contact with the sheet material, and means for introducing a gaseous medium into the channels formed by the partitions to set up a flowing stream of the gaseous medium within and through said channel.

13. A drying apparatus according to claim 12 comprising a discharge conduit leading from one end of the housing and from the ends .of the channels which lie opposite the gaseous medium introduction end of the channel, and a gaseous imedium recirculation system joining the discharge conduit and the means for introducing the gaseous medium into the channels.

.14. A drying-apparatus according to claim 13 wherein a plasticizer recovery 'system is incorporated Within the recirculation system.

15. A drying apparatus fordrying traveling continuous flexible sheet material comprising a plurality of drying rolls over which the sheet material travels, a housing within which the drying rolls are mounted, a plurality of channel forming partitions extending from the top wall of the housing in the direction of the path of the material traveling over the rolls, said partitions extending down from said top wall into close proximity with said :dry'ing rollsso'as to direct a heating medium into contact with the sheet material, means for introducing a gaseous medium into the channels formed by the partitions to set up a flowing stream of the gaseous medium within-and through the channels, and means cooperating with the introducing means for controlling the volume of gaseous medium entering each channel.

16. A'drying apparatus for drying traveling continuous flexible sheet material comprising a plurality of heated drying rolls over which the sheet material travels, a housing within which the drying rolls are ,mounted, a plurality of partitions extending from the top wall of thehousing'which partitions form a plurality of channels which 'extendin the direction of the path of the material traveling :over therolls,'means for introducing a'gaseous medium into the channels-to set up a flowing stream of the medium-within and through the channels, and means positionedwithin each channel and cooperating with the introducing means for adjusting the volume of gaseous medium-entering each channel.

References Cited in the file ofthis patent UNITED STATES PATENTS 1,738,641 Cowan Dec. 10, 1929 2,301,249 Butterworth et al. Nov. 10, 1942 2,330,395 Sullivan Sept. 28, 1943 2,366,484 Bradner Jan. 2, 1945 2,837,830 Fry et al. r June 10, 1958