US2837830A - Method and apparatus for drying flexible sheet material - Google Patents

Description

'June 10, 1.958 H. P. FRY, JR.; ET AL METHOD AND APPARATUS FOR DRYIN FLEXIBLE SHEET MATERIAL Filed June 19, 1956 United tates METHOD AND APPARATUS FOR DRYING FLEXIBLE SHEET MATERIAL Horace P. Fry, Jr.,West Chester, Pa., and Lester B.

Cunditr, Wilmington, Del., assignors to American `Viscose Corporation, Philadelphia, Pa., a corporation of Delaware Application June 19, 1956, Serial No. 592,338

21 Claims. (Cl. 34-23) tinuous sheet material are dried by passing the sheet material over a series ofY heated drying rolls. This drying procedure has been used for years and years with little improvement incorporated therein. This established and 1ongused drying system has many disadvantages. The main disadvantage with Such a system is that the sheet is not dried unifo-rmly across its width. The edges of the sheet dry before the central sheet portions are dried because the end surface portions of the drum have, when heated, a higher temperature than the central portions of the drums and because of non-uniformlmoisture 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 varyingA shrinkage and stretch characteristics across its width. In addition, the final sheets have floppy edges.` This nonuniform pattern is especially notable in cellophane sheets which have been dried on the above-described dryer.

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

Another disadvantage with the 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 vapo-rizes 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 one object 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 wherein a substantial amount of any film plasticizer being released from the film during the drying stage may be recovered.

Still another object of our invention is to provide a novel and improved film drying method and apparatus wherein means are provided for directing separated and partially confined streams of air having different humidities longitudinally over the film or sheet material being dried whereby different transverse portions of the film or sheet will be subjected to varying atmospheric conditions to vary the rate of drying across the width of the traveling sheet or film.

Another object of our invention is to provide a novel and improved film drying method and apparatus wherein .different humidities are set up within the separate air atent ice streams traveling over the film by independent temperature and/ or other humidity control means supported within each stream of air.

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 our novel and improved drying apparatus; and

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

Briefiy, 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 pattern between the rolls of the upper and lower deck. Preferably, the roll decks are enclosed within a housing, the top of which is hinged along its longitudinal center line whereby the top may be raised so that access may be had to .the drying rolls. Afiixed to the inside of the top and bottom Walls are channel-forming partitions which extend longitudinally of the direction of sheet travel. A pair of nozzles are provided at one end of the housing for introducing heated air into both the upper and lower channels whereby air streams are formed within the channels which flow above and below the roll surfaces of each roll deck in a direction countercurrent to the direction of film travel to pick up and remove mois.- ture-laden air from the area immediately surrounding the drying rolls. Each nozzle contains a plurality of channelfroming partitions which partitions are aligned with the channel-forming partitions along the bottom and top walls ofthe housing. Each channel formed by the partitions within the nozzles supports means for controlling the humidity of the air stream passing through the channel. A recirculation system is provided for each upper and lower set of channels whereby the air traveling through the channels is discharged and returned to the nozzles after being reconditioned. In addition, a recovery apparatus is installed within each recirculation system of the drying apparatus whereby any vaporized plasticizer escaping from a film may be recovered.

In general, our method for drying the sheet material comprises passing the continuous sheet material in an alternating over 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 sheet discharge end of the housing, which air mass is broken up into separate, confined air streams. The humidity of each air stream is adjusted and controlled independently of the other streams as the streams enter the housing. These separated air streams are directed or guided through the housing in a path immediately above and below 4the 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 bereconditioned 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 2, 2. The rolls 2, 2 in the lower deck areralternately spaced with respect to the rolls of the upper deck so that the sheet material 4, such as cellophane, travels in an overV and under pattern over the upper and lower deck rolls 2, 2. As seen more clearly in Figure 2 of the drawing, the

rolls 2, 2 are completely enclosed within a housing 6 having'a separate top wall 5. The housing top wall 8 is n J hinged longitudinally along its center by hinges 1t), 10 which are axed yto a -horizontally extending-bar '11 supported by overhanging vertically disposed supports 11', 11. The sections of the top wall S may therefore be raised or folded back toward the wall center to provide access to .-therolls `for lacing -up the rolls, cleaning, etc. Both the top wall 8 and bottom wall 120i Vthe housing 6 are .ofrirregular surface in Vthat their surfacesV vfollow the contour of the rolls 2, 2 of the upper and lower roll `decks A and B. will 'oe explainedat a later point in the description.

Secured to the inside of both the top wall 3 and bottom .wall 1'... of the housing 6 are longitudinally-extending7 spaced- apart partitions 15, 15. As seen in Figure l of the drawing, Vthe- partitions 15, 15 also'have a `line of curvature along their length which corresponds to the peripheries of `the 'rolls' 2, 2. When the top wall 8 of the housing is loweredinto operative position, the partitions 1S, l5 form separate `channels 17, 1.7'which run lengthwise of .ther-housing 6. spect tothe bottom wall 12o?? the housing 6.

Heated air is supplied to the channels 17, 17 at their entrance end VC from a supply conduit 21 which-leads `from a circulation fan 22. .The air passes through a heater 23 installed in the conduit 21 where the temperature of the air maybe regulated. The supply conduit 2i is connected with anozzle 25 which flares outwardly from the supply conduit 21 to a width substantially the saine as that of the housing 6. The nozzle 25 is connected with the airen'trance end C of the housing channels 17, 17. As seen .in Figure 2, longitudinally-extending partitions 27, 27 are supported within the nozzle interior whereby channels 29, 29 are formed which line up with the channels 17, 17 of the top Wall 8 of the housing 6.

The air stream or mass issuing from the supply conduit 21 is divided as it passes through the nozzle 25 to form separate air streams through each of the channels 29, 29 of the nozzle 25. These streams of air pass from the Vindividual channels 29, 2.9 into the mating channels i7,

duced withineach channel may be controlled whereby r the humidity of each air stream may be adjusted and controlled independently of the other streams as the streams enter the housing 6.

Also .contained within each nozzle channel 29 is a heating unit 37 which may be used independently of or in cooperation `with the spray nozzles 33, 33 to independently control the relative humidities of the air stream. The temperature of each unit 37 is independently controlled whereby the temperature of each stream of air passing from the nozzle channels 29, 29 into the housin; channels 17, 17 may be adjusted iand controlled.

It should be pointed `out tha-t the temperature regulating unit 23 in the supply conduit 21 sets the temperature of the undivided air stream to correspond approximately -to the lowest temperature setting maintained by anyV single heating unit 37 within the nozzle 25.

The circulation fan 22 circulates the air through'the supply conduit 21, the heater 23, the nozzle 2S and into and through the channels 17, 17 of the housing 6. The air is exhausted at the opposite end D (the sheet entrance end) of the housing 6.

A duplicate system is provided for channeling, conditioning and feeding `air to the housingchannels 17, 17 formed along the bottom housing Wall 12.

The independently controlled spray nozzles 35, and

The reason for this irregular surface con-tour The same'is vtrue -with re- 4 the independently controlled heating units 37, 37 form `an limportantfeatureV VofV our invention. As mentioned above, a great disadvantage with the roll system now used for drying lilms and sheets is that the edge portions of the sheet dry faster than the more central portions of the sheet. With our invention, this disadvantage may be completely eliminated by adjusting andrcontrolling the humidity of the separate air streams vpassing longitudinally of the film being dried.` To control the drying of the sheet material solely through lthe use of the spray nozzles 33, 33, the Valves 35, 35 for the spray nozzles 33, 33 located within the outer channels 29, 29 'are adjusted to permit rather large amounts of humidifying medium to enter the air streams passing through these outer channels. Progressing toward the more central channels, the valves 35,735of ythe spray" nozzles 33, 33 are adjusted to permit gradually decreasing amounts of humidifying liquid to pass into the .air streams. With this arrangement, the humidity `of the atmosphere over and under the sheet being dried will be gradually decreased from the edge portions of the sheet toward the more central portions of -thesheet The heavier atmosphere over and below the edge portions of the sheet lli) being dried will, in addition to the moisture .beingemib ted from the sheet material, create a heavy moisture laden atmosphere surrounding the iilrn edge portions to retard the drying of the sheet material along its edge portions as it passes ove-r the rolls 2, 2. The atmosphere surrounding the more central portions of the sheet is less humid and therefore the drying will occur -at a slightly faster rate. By slowing down the rate of .drying ad jacent the edge portions of the film which normallydry at rapid rates and increasing the rate of drying adjacent the central portions of the film which normally .dry `at slower rates, the drying of the sheet across its width may be brought into equilibrium whereby the sheet is dried at a uniform rate across its width.

To control the sheet drying through temperature control alone, the temperature of the heating . units 37, 37 within each channel 29 is adjusted so that .the'temperature of the air streams traveling longitudinally `of Vthe iilm or sheet 4 being dried is gradually or lprogressively increased as the streams extend inwardly from the edge portions of the sheet to the more central portions of the sheet. The temperature of the heating units affectsthe relative humidity ofthe air streams whereby -thel'air streams traveling along the central portions of .thesheet are of lower humidity than the air streams traveling along the edge portions `of the sheet. 'With this arrangement, the atmosphere :adjacent the iilm edges is motel-humid than that adjacent the more central portions kof the sheet so that the edge portions of the sheet dry at approximately the same rate as the central sheet portions.

For maximum flexibility of the drying pattern control transversely of the sheet, both the spray nozzles 33, 33 and the4 heating units 37, 37 are used together in various combina-tion settings. For instance, both the heating unit and the spray nozzle within one or several of the channels can be operated simultaneously at controlled settings while only the heating unit or only the spray nozzle may be operating within the remaining channels. The manner in which the settings of the heating units and humidifying nozzles are combined is, of course, determined by the transverse drying pattern of the sheet ma terial as desired by-the manufacturer.

As mentioned above, a recirculation system is provided for recirculating the air Awhich has traveled through the housing 6 back to the supply conduit 2?.. A return conduit 39 is mounted adjacent the discharge end D of the channels 17, 17 and connects the channels with the tan 22. As seen in Figure 1, the Vreturn conduit 39 receives the air as it is exhausted from the discharge endD of the channels 17, 17 andthe circulation fan 22 draws-the discharged air vinto 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 plasticizing substance is incorporated into the sheet. Two such iilm plasticizers which are commonly used are ethylene glycol and glycerine. Some of this plasticizer escapes in vapor form from the sheet as it is being dried. Our apparatus provides for-recovering this plasticizer released from the sheet materialV 4 during the drying stage. As the cellophane sheet 4 is heated by the drying rolls 2, 2, some of the plasticizer in the lm vaporizes and passes into the air streams moving through the housing channels i7, 17 to enter the return line 39.

, As seen in Figure l, this plasticizer recovery station di is installed in the return line 59 whereby the exhaustedair containing the vaporized plasticizer will pass therethrough to be relieved of its plasticizer content. A duplicate recovery system il is provided in the return line for the air exhausted from the bottom housing 'wall channels i7, 17.

Several housings, air supply systems, recirculation systems and recovery systems may be provided for each drying machine. The number orP these structures provided depends upon the length ofthe drying machine. The shorter the housings are, the more efticient 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 efficiently if the air is not Vover-saturated with moisture and vaporized plasticizer.

As seen in Figure l, booster heating pipes 43 are installed within the channels i7, 17 of the top and bottom housing walls 8 and i2 whereby the temperature of the air traveling through the channels may be boosted as required to further adjust the humidity of the moving airstreams. n

To sum up the operation, the iilm 4 enters thev housing 6 at the right hand end of the housing as seen in Figure l and travels in an alternating pattern over and under the rolls 2, 2 of the upper deck A and lower deck B. rI'he film 4 emerges 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 humidity of each stream is adjusted as described above after which the air passes from the nozzle channels 29, 29 into the housing channels i7, 17 of the top and bottom housing walls which channels are aligned with the nozzle 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 39. The air streams within the housing flow countercurrent to the direction of lm travel and follow the corrugated pattern of the top and bottom housing walls E5 and i2. With this arrangement, the air streams ow into the pocketsbetween the rolls to remove moisture laden air trapped in 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 39, passed into the plasticizer recovery system, and into the circulation fan 22 after 'which the cycle is repeated.

To prevent the iilm or sheet plasticizer, which has escaped from the Iilm, from condensing on the hood, the top and bottom walls 8 andV El of the housing 6 are preferahly insulated to maintain their temperature above the dew point for the particular plasticizer used.

Additional make-up air is received into the housing 6 from the surrounding atmosphere through cracks or leaks within the housing structure. An exhaust pipe 45 is installed within the supply line 21 just below the circulation fan 22 .through which a portion ot 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 embodimen-ts or 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:

l. A drying apparatus for drying continuous traveling flexible sheet material comprising an upper deck of spaced-apart heated drying rolls, a lower deck of spacedapart heated drying rolls, the rolls of said lower deck being alternately spaced with respect to the rolls of the upper deck whereby Ithe sheet material travels over and under the rolls of the two 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 channel-forming partitions aixed to at least the underside of the top housing wall which partitions extend longitudinally of the housing and of the direction of sheet travel, a nozzle at one end of the housing for introducing air into the housing channels to set up within each channel a moving stream of air, a plurality of channel-forming partitions supported within the nozzle which parti-tions are aligned with the partitions within the housing, said traveling air streams picking up and removing from the area above the rolls and traveling sheet material the moisture-laden air escaping from thewet sheet material being dried, and means supported within at least one nozzle channel formed by the partitions for independently .controlling the humidity of the air stream passing through said channel.

2. A drying apparatus according to claim l compris- 4 ing through said channels.

3. A drying apparatus according to claim l comprising means supported within each nozzle channel formed by the partitions for independently controlling the humidity of the air streams passing through each channel.

4. A drying apparatus according to claim 3 wherein the humidity control means within each nozzle channel comprises a water or steam spray.

5. A drying apparatus according to claim l comprising a recirculation conduit for receiving the air streams as they are exhausted from the housing channels, said `conduit connecting the exit end of the channels at one end of the housing with the nozzle.

6. A drying apparatus according to claim 5 comprising a vplasticizer recovery unit installed in the recirculation conduit for recovering sheet plasticizing material which has escaped-from the iilm in vapor form and which has been picked up by the traveling air streams.

7. A drying apparatus for drying continuous traveling flexible sheet material Vcomprising an upper deck of spaced-apart heated drying rolls, a lower deck of spacedapart 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 two 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 channel-forming partitions affixed to at leastV the underside of the top housing wall which partitions extend longitudinally of the 'housing and of Vthe direction of sheet travel, a nozzle at one end ot the housing for introducing air into the housing channels to set within each channel a moving stream of air, a plurality of channel-forming partitions supported within the `nozzle which partitions are alignedV with the partitions Within the housing, said traveling air streams picking up and removing from the area above the rolls and traveling sheet material the moisture-laden air ascaping from the wet sheet material being dried, and heating means supported within at least one of the nozzle channels for controlling the humidity of the stream of air passing through said nozzle channel.

8. A drying apparatus according to claim 7 wherein heating means having an independent control is positioned Within each of the nozzlechannels.

9. A drying apparatus according to claim 8 comprising a recirculation conduit for receiving the air streams as they are exhausted from the housing channels, said conduit connecting the exit end of the channel at one end of the housing with the nozzle, and a plasticizer recovery unit installed in the recirculation conduit for recovering sheet plasticizing material which has escaped from the film in vapor form and which'has been picked up by the traveling air streams.

1.0. A drying apparatus for drying continuous traveling flexible sheet material comprising an upper deck of spaced-apart heated drying rolls, a lower deck of spacedapart heated drying rolls, the rolls of said lower deck` being alternately spaced Withrespect to the rolls of the upper deck whereby the sheet material travels over and under the rolls of the two decks in an alternating pattern, a housing for the drying roll decks for closing olf the drying rolls from the surrounding atmosphere, a plurality of channel-forming partitions aihxed to the underside of the top housing wall which partitions extend longitudinally of the housing and of the direction of sheet travel, a plurality of similarly disposed channel-forming partitions aixed to and extending along the inside face of the bottom housing wall, a pair of nozzles at one end of the housing for introducing yheated air into both the upper and lower housing channels formed by the partitions to set up within each channel a stream of air, a plurality of channel-forming 'partitions supported within each nozzle which vpartitions are aligned with the channel-forming `partitions Within the housing, said traveling air streams picking up and removing from the area adjacent the rolls and traveling sheet material the moisture-laden air escaping from the Wet sheet material' being dried, a Water or steam spray nozzle supportedwithin at least one of the nozzle channels for controlling the humidity of the air stream travelingthrough each channel, and-heating means supported within said channel for supplementing the control of the humidity of the lair stream traveling therethrough.

11. A drying apparatus according to claim 10 comprising a water or steam spray nozzle within each nozzle channel for independently controlling the humidity of each air stream traveling-through the channels, and independently controlled heating means within each nozzle channel for supplementing the control of the humidity of each air stream traveling through the channels.

l2. A drying apparatusaccording to claim ll comprising a recirculation conduit for receiving the air streams as they are exhausted from the channels, said conduit connecting the exit end of the channels at one end of the housing with the nozzles.

13. A drying apparatus according to claim 12 comprising a plasticizer recovery unit installed in the `recirculation conduit for recovering sheet plasticizing material which has escapedfrom the film in vapor form and which has been picked up by the traveling air stream.

14. A..me'tho l of vdrying traveling continuousA iiexible sheetzmaterial comprising the steps of passing the con- Lil) its

tinuous sheet through a drying area, discharging the sheet from the drying area, supplying a moving air mass to a point adjacent the discharge point of the sheet material, breaking up the air mass into separate partiallyconfined air streams, guiding the separate air streams through the drying area along a surface of the sheet material longitudinally of the sheet material whereby the moisture escaping from the heated traveling sheet material being dried is picked up by the air streams moving through the drying area and removed from the area, independently adjusting the humidity of at least one of the air streams before the air streams enter the drying area, and discharging the moisture-laden air from the drying area.

l5. A method of drying traveling flexible sheet material according to claim 14 comprising independently adjusting the humidity of each air stream before the streams enter the drying area.

16. A method of drying traveling continuous flexible sheet material according to claim l5 comprising recirculating the air streams.

17. A method of drying traveling continuous flexible sheet material according to claim 16 comprising removing vaporized sheet material plasticizer from the air streams being recirculated.

18. A method of drying traveling continuous ilexible sheet material comprising the steps of passing the continuous sheet through a drying area, discharging the sheet from the drying area, supplying a moving air mass to a point adjacent the point of discharge of the sheet material, breaking up the air mass into separate confined air streams, guiding the separate air streams through the drying area along a surface of the sheet longitudinally of the sheet material whereby the moisture escaping from the heated traveling sheet material being dried is picked up by the air streams and removed from the area, and controlling the temperature of at least one of the streams to control the humidity of said air stream prior to the streams passing into the drying area.

19. A method of drying traveling continuous flexible sheet material according to claim 18 comprising recirculating the air streams through the drying area, and removing vaporized sheet material plasticizer from the air streams being recirculated.

20. A method of drying traveling flexible sheet material comprising the steps of passing the sheet in an alternating overand under pattern through a drying area, discharging the sheet from the area, supplying a moving mass of air to a point adjacent the discharge point of the sheet material, breaking up the air mass into separate coniined streams, guiding the separate air streams through the area along both surfaces of the sheet longitudinally of the sheet whereby the moisture escaping from the heated traveling sheet material being dried is picked up by the air streams and removed from the area, independently controlling the temperature of each stream to control the humidity of each stream prior to the pas 'ng of the streams into the area, and adding moisture to each stream in varying amounts prior to the passing of the streams into the area to supplement the humidity control of each stream.

21. A drying apparatus for drying continuous traveling ilexible sheet material comprising at least one deck of spaced-apart heated drying rolls along which the sheet material travels in an alternating over and under pattern, a housing for the drying roll deck for closing ott the drying rolls from the surrounding atmosphere, a plurality of channel-forming partitions aflixed to at least the underside of the top housing wall which partitions extend longitudinally of the housing and of the direction of sheet travel, a nozzle at one end of the housing for introducing air into the housing channels to set up within each`channel a moving stream of air, a plurality of channel-forming partitions supported within the nozzle which partitions are aligned with l e partitions within the housing, said traveling air streams picking up and removing from the area above the rolls and traveling sheet material the moisture-laden air escaping from the wet sheet material being dried, and means supported within at least one nozzle channel formed by the partitions for independently controlling the humidity of the air stream passing through said channel.

References Cited in the iile of this patent UNITED STATES PATENTS Bassler Oct. 16, 1923 Hess et al. Ian. 6, 1942 Butterworth et al Nov. 10, 1942 Bradner Ian. 2, 1945

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