US3303576A

US3303576A - Apparatus for drying porous paper

Info

Publication number: US3303576A
Application number: US459652A
Authority: US
Inventors: Sisson James Bryant
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1965-05-28
Filing date: 1965-05-28
Publication date: 1967-02-14
Anticipated expiration: 1984-02-14

Description

F 1967 J. B. slssoN 3,303,576

APPARATUS FOR DRYING POROUS PAPER Filed May 28, 1965 2 Sheets -Sheet l INVENTOR. James Bryant Sisson QRNEY Feb. 14, s sso APPARATUS FOR DRYING POROUS PAPER Filed ma 28, 1965 I; III N Ina...

i 3 a I\ u Q e Wm: MMMMMMM MMMWMMMMMMMMMMMMMMMMM wwm uw Ev n MMmmmmmmmlmmmmmmm W mm W. l mmmmmmmmmmmmmmmm nmmm I ml l l wv h m "0mm ohmmm mm uuwwwwmwMMMMMHMMHHMMMHH awn 8 o mm 5 3.5 p m NQ 1 u mm mm W mm 3 2% bmw S @N HHHHmWHHHHHHHHHHHHHHHHHHHHHHHHHHWHHHHHHHHHHHHW HHHHHHHm pmm MM A 7 1m II) II M Vm mm 0 mm 0 mm B 0 mm 0 mm INVENTOR. James Bryant Sisson ORNEY United States Patent M 3,303,576 APPARATUS FOR DRYING POROUS PAPER James Bryant Sisson, Hamilton, Ohio, assignor to The Procter & Gamble Company, Cincinnati, Ohio, a corporation of Ohio Filed May 28, 1965, Ser. No. 459,65

17 Claims. (Cl. 34115) This invention relates to apparatus for drying porous webs at very high throughput rates and more particularly to apparatus for high speed drying of porous, lightweight paper or tissue.

In the drying of paper, textiles and other like sheet materials it has been determined that if the heat available in a drying process is adequate, the rate of drying is determined by the ability of the system to transfer heat to the material being dried and to remove the liquid being evaporated. When a moist web is dried by means of conventional tunnel or drum dryers, a stagnant layer of moist air travels with the web, providing substantial resistance to the flow of heat and water vapor. Thus, the quantity of moisture or vapor that can be discharged from the material and absorbed by the contacting air is greatly reduced.

In an attempt to overcome the problem presented by the stationary layer of supersaturated air, various devices have been developed by means of which hot or cold air is blown upon or through the web being dried so as to disperse the stagnant layer and permit the removal of further moisture from the web. Along these lines, certain machines continuously feed or apply the web to be dried to the periphery of a rotating, penforated drum or roll. Heated air at a pressure greater than atmospheric is admitted to the drum interior :by means of an axially located pipe or inlet duct. Due to the pressure difference between the drum interior and the atmosphere surround- 4 ing it, the heated air is forced through the peripheral aperair is delivered to the exterior of the rotating, perforated roll and the interior of the roll placed in communication with a source of vacuum through an axial outlet. The pressure differential forces the air to flow through the web being carried on the roll periphery and through the apertures underlying it to the axial outlet.

While equipment such as that described above may be perfectly satisfactory in connection with low speed drying or where control of uniformity of moisture removal is not important, it has been found unsatisfactory when applied to the drying of lightweight porous paper webs at high rates of speed, for example, up to about 2000 feet per minute, utilizing a practical range of roll diameters. The principal problem in connection with drying by means of the priorart devices described above is that the same invariably promote non-uniform drying across the width of the web being dried due to the fact that the flow pattern of the drying air varies greatly from side to side. While the adverse effects of this problem could be minimized in low speed drying by using cooler air, high speed dryers must, of necessity, use air having a temperature as high as possible consonant with the ability of the web material to withstand heat at the moisture levels contemplated. Thus, if the dryer is designed to dry a paper 3,303,576 Patented Feb. 14, 1967 web to an consistency (.25 pound of water per pound of fiber) the heated air can have a temperature at least as high as 700 F., whereas if the Web is to be brought to bone dry condition, the temperature of the air used should not exceed about 450 F. to avoid damaging the web fibers. If a high speed dryer is to reduce the level of moisture in a web to an 80% consistency and one edge of the web should dry substantially faster than the other edge or the center thereof, it is likely that the high temperature air used would severely damage the fibers in the areas which are prematurely dried While the balance of the web is brought to the moisture level contemplated.

' Another problem experienced with the prior art apparatus is that either the inlet or the outlet ducts of such devices are restricted so as to prevent high air flow rates 'therethroughanother factor which detracts from the ability of the machines to perform drying at high speeds.

It is an object of the present invention to obviate the above problems.

Another object of the present invention is to provide high speed drying apparatus adapted to cause the web being dried to lose moisture uniformly across the width of the sheet whereby maximum temperatures can be utilized in the drying operation.

It is another object of the present invention to provide a machine in which the web being treated is uniformly dried across its width and in which the ratio of air outlet and air inlet to roll length is constant.

It is a further object of the present invention to provide apparatus of partial drying of a porous, lightweight paper web utilizing temperatures of air substantially above those heretofore used in drying such webs.

Briefly stated, in accordance with one aspect of this invention the subject dryer comprises a sieve roll mounted for rotation and having a foraminous sidewall. There is an infeed station at which point a moist web having a width which is the same as the length of the roll is placed contiguous to the periphery of the rotatable roll. An outlet station is also provided and is thelocation at which the dried web is removed from the sidewall of the roll. The outlet station is spaced peripherally from the infeed station so that the'web covers a major portion of the periphery of the sidewall and that a full length-minor portion of the roll periphery intermediate the infeed andoutlet stations is not covered by the web. The major portion is exposed externally to uniform air pressures along its length. A source of a moving stream of drying air at a pressure slightly above that of the air surrounding the major portion is connected to an air inlet duct or plenum located intermediate the web infeed and web outfeed stations, adjacent the uncovered minor portion. The inlet duct directs the moving stream of drying air into the roll through substantially the length of the uncovered full length minor portion of the roll periphery in a substantially radial direction so that a uniform flow path is established for the drying air.

While the-specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it

is believed that the invention will be better understood FIGURE 4 is a fragmentary perspective view illustrating a honeycomb material suitable for use as the roll periphery.

Referring to FIGURE 1, a two-stage air drying system is disclosed for removing moisture from a porous lightweight paper web 11 issuing from the end of a papermaking machine. The web 11 is carried by a Fourdrinier wire 12 and at this point has a consistency of about 20%, or in other words, contains 4 pounds of water per pound of fiber. The web 11 and wire 12 proceed around the periphery of idler 13 toward the idler 14, which starts the Fourdrinier wire on its return loop. Intermediate the papermaking machine idlers 13 and 14, the porous lightweight paper web 11 is contacted by and transferred to reticulated fabric carrier 16 as the carrier is drawn about suction roll 17. The carrier 16 provides the means for conveying or transporting the web 11 to, from and through the dryer at a substantially constant speed.

The carrier 16 may be endless and constructed of syn-' thetic plastics or other suitable non-corrosive materials, including metals. For the purpose of the present invention the carrier must have at least 15% projected open area in order to avoid high pressure drops in the drying cycle to be described hereinbelow and the mesh should be such as to provide more than 8 openings per inch to prevent holes from being blown in the fragile web being dried and must contain less than 100 openings per inch for good durability in view of the carrier materials used. Preferably, for drying lightweight paper or tissue the carrier should have from about 20 to about 45 openings per inch, both longitudinally and laterally.

As the carrier 16 proceeds around suction roll 17, the suction pulls the web 11 into contact with the carrier 16, thereby elfecting the transfer of the web 11 from the papermaking machine to the subject dryer. The Fourdrinier wire 12, of course, continues its movement to idler 14 and thence returns to the paper-forming end of the machine. The carrier 16 with the Web 11 on the underside thereof passes under idler 18 and to the inlet or infeed station I whereat the moist Web 11 is placed in contact with the periphery of the freely rotatable sieve roll 21. An idler 19 provides the means for feeding the continuous length of moist web 11 and carrier 16 concurrently onto the foraminous sidewall of the sieve roll 21 as the roll rotates past the station I. At this point it will be noted that the carrier 16 overlies the web 11, urging it into contact with the foraminous periphery of the roll 21 and providing the necessary back-up for the web to prevent the 111pt-ure thereof during the drying process.

As the roll 21 revolves, it carries the web 11 and carrier 16 in a circular path to the other side of the dryer at which is located an outlet station 0. At the outlet station 0, the dried 'web is removed from contiguity with the roll 21 periphery, the superposed web and carrier passing around idler 22, the means effecting such removal, as the second stage of drying is approached. The outlet sta- 'tion is spaced peripherally so that the web covers a major portion, preferably about 65% to about 85%, of the foraminous roll periphery.

In like manner, the superposed web 11 and carrier 16 are carried around corresponding idler 19' at the inlet 1 of the second stage dryer where the web 11 is placed on the foraminous periphery of second stage dryer sieve roll 21. Here, again, the carrier 16 overlies the web 11, maintaining it in contact with roll 21 and providing back-up during the drying process. The roll 21' freely revolves with the carrier 16 and the web 11 maintained on the periphery thereof, carrying the same to the outlet station at which point the web 11 leaves the drum periphery, the superposed web and carrier being trained about idler 22. Next, the web 11 and carrier 16 move to idler 23 :where the dried web 11 is separated from the carrier 16 and drawn to the next operation. The carrier 16 passes around idler 23 and returns to suction roll 17 through an overhead loop route, not shown, so as to be recycled through the dryer.

The overhead loop includes a drive roll, tensioning means and, if desired, a shower system and suction box for cleaning and drying the carrier 16. Suitable arrangements along this line are well known by those of ordinary skill in the art and therefore not described in detail herein. Due to the engagement of the web 11 and carrier 16 over a major portion of the sidewall or periphery of sieve rolls 21 and 21' the movement imparted to the carrier 16 by the drive roll causes the

sieve rolls

21 and 21 to rotate. Thus the peripheral velocity of the sieve rolls will be identical with the speed of movement of the carrier 16.

As shown schematically on FIGURE 1, ambient air is drawn into the inlet of a fan 24, forced at high velocity through a heater 25 to provide a source for a moving stream of low pressure drying air. The heated air is then carried through an appropriate duct arrangement to an inlet duct or plenum 26. If the first stage of the dryer is to take a web having a 20% consistency and 12 pounds of dry fiber/ 3000 square feet and dry it to a consistency of 50% at a speed of approximately 1200 feet per minute on a roll 21 which is 4 feet in diameter and 75% of the periphery of which is covered by the Web, the fan speed and capacity and the rate of heat transfer in the heater should be such as to result in the provision of air to the inlet plenum at approximately 450-500 F at a pressure range between about 2 to about 7 inches of Water above atmospheric in quantities of approximately 30 to 45 pounds of air per minute per square foot of dryer area covered by the Web 11 intermediate the inlet station I and outlet station 0. Thus, in accordance with the relationships hereinabove described, each square foot of web will have between about .23 to about .35 pound of heated air pass therethrough as it proceeds through the dryer. The flow rate, of course, will be dependent on the temperature of the air, the speed of the web and the infeed and outfeed Web consistencies. It is contemplated that the entry of the air through the foraminous wall of sieve roll 21 adjacent the inlet plenum will reduce the pressure to a range from about atmospheric to about 5 inches of water above atmospheric.

As will be noted in FIGURES 1, 2 and 3, the inlet plenum 26 has a flange around the outlet end thereof which conforms closely to the uncovered full length minor portion of the periphery of the sieve roll 21 intervening the inlet station I and outlet station 0 and which is close but not touching the web 11 carried on

idlers

19 and 22. The close fit of the flange along these areas tends to prevent the loss of heated air or the inward leakage of outside air between the

idlers

19 and 22, the roll 21 and the inlet duct or plenum 26. It is for this same reason that the pressure of the heated air is maintained at slightly above atmospheric in the inlet plenum 26 and approximately atmospheric in the interior of roll 21. Preferably the inlet plenum should have an arcuate width of about 2 to about 4 inches per foot of circumference of the sieve roll 21, although the drawing (FIG. 1) is not to scale and hence does not accurately reflect this relationship. If the plenum arcuate width is smaller than the specified range, the fan horsepower requirements increase substantially; if larger the required diameter of the sieve roll increases in order to effect drying at high rates.

As noted above, the air proceeds from the plenum 26 substantially radially through the apertures in the uncovered full length minor portion of the periphery of roll 21 into the interior thereof. Another fan 27, as shown schematically in the upper portion of FIGURE 1, has the inlet thereof connected with outlet duct 28 mounted on an enclosure 29 encompassing the major portion of the sidewall of the first stage sieve roll 21, the portion which underlies the web 11 and carrier 16 proceeding from the infeed station I to outlet station 0. Thus, the fan 27 provides a source of vacuum communicating with the enclosure interior. As the fan 27 operates, air is pulled out of the chamber C of enclosure 29, exposing the exterior of the above-described major portion of the sidewall of roll 21 and the overlying carrier 16 and web 11 to vacuum conditions. Preferably, the vacuum should be in the range of from about 5 to about 20 inches of water.

The difference in pressure between the roll 21 interior and the chamber C, i.e., in the range of from about 5 to about 25 inches of Water, causes the heated air to be forced through the enclosed and covered major portion of the roll 21 and through the interstices of web 11 and carrier 16. While passing through the web, the air transfers heat to the web 11 and removes moisture therefrom, carrying the same in vapor form to the chamber C. Then, as indicated by the arrows, the air and entrained water vapor are pulled from chamber C into the fan 27, forced through the second stage heater and into the inlet plenum 26 of the second stage in which a similar air flow pattern is established, the fan 31 providing vacuum in the range of about 5 to about 15 inches of water within the chamber C of second stage enclosure 29'.

If the web 11 is to be dried in the second stage dryer to a consistency of about 80%, at the same speed and utilizing a roll diameter as described above in connection with the first stage, the temperature of the air at inlet plenum 26' should be approximately 250 to 350 F. at a pressure range between about 2 and about 7 inches of water and should be supplied in quantities of from about 30 to about 45 pounds per minute per square foot of dryer area covered by the web between inlet station I and outlet station O. The entry of the air into the sieve roll 21' reduces the pressure to a range from about atmospheric to about 5 inches of water above atmospheric to thereby give a difference in pressure between the interior of the roll 21 and the chamber C of from about 5 to about 20 inches of water. The heated air in the second stage is thus forced through the roll 21, the web 11 and carrier 16 into the chamber C and exhausted through fan 31 in a manner similar to that described above in connection with roll 21.

The sieve roll 21 is constructed as shown most clearly in FIGURE 3. The roll is closed at each end by a circular, substantially imperforate head 32. An annular support ring 33 is attached to the inner periphery of each of the heads 32 by machine screws or other suitable fastening device thereby providing the means for mounting the foraminous material 34 which forms the sidewall of the roll 21. The foraminous material 34 must have at least about 60% open area to promote uniform drying and preferably comprises at least about 75% open area. One suitable material 34 is -a honeycomb material currently available commercially and known to those skilled in the art. As most clearly shown in FIGURE 4, a

sembly of metal strips, preferably Monel or extra low carbon stainless steel, which possesses substantial rigidity in all directions and has a thickness and diameter matching the thickness and diameter of ring 33. The thickness of the ring and the depth of the honeycomb will depend upon the length of roll 21 and the stiflness of the honeycomb material. Such dimensions can be readily determined for any specific application and therefore are not described in detail herein.

It will be seen that the honeycomb includes a number of straight members 36 between which are fastened strips 37 which have a length which approximates the width of the web 11 and which are bent to form a repetitive pattern of hemihexagonally shaped offsets. The bent strips 37 alternate so that staggered rows of hexagonally shaped patterns 37' are formed therebetween, the intervening straight members bisecting the patterns. The members 36 and strips 37 are appropriately fastened together in a rigid manner for example by welding or silver soldering two adjacent strips 37 to the intervening member 36 in the contacting areas between the patterns 37 in each row thereof.

The side edges of the strips 37 are spaced inwardly of the side edges of members 36 and it is the outwardly projecting portions of the members 36 which are fastened to the support ring 33. In this connection, the support rings each have a multiplicity of equally spaced radial slots along the inner edge thereof, the spacing and width of the slots matching the spacing and the thickness of the members 36 and having sufiicient depth to accept the projecting portion thereof. The projecting portions at each end of the honeycomb are telescoped and fixed within the slots of the corresponding support rings, as shown in FIGURE 3, by suitable means such as welding whereby to complete the basic assembly of the roll 21.

A trunnion 38 is axially aflixed at each end of roll 21 by bolting an integral flange ring 38a to the central outer side of each of the heads 32. The trunnions 38 are mounted for free rotation within roller bearings housed in flange bearings 39 which are telescoped within a hub 40 and maintained in position by bolts. A shoulder 38b on each trunnion casting is contiguous to the inner side of flange bearing 39 and prevents lateral movement of the roll 21 in operation.

Each hub 40 is integrally formed with a circular support plate, the rear support plate 41 on the left side of FIGURE 3 and the front support plate 42 on the right side of FIGURE 3. It should be noted that the diameter of rear support plate 41 exceeds the roll 21 diameter, preferably by about 2" to 4", while the front support plate 42 has approximately the same diameter as roll 21. The reasons for the differences in diameter of the support plates will be apparent from the description to follow. Each of the hubs 40, and therefore the

support plates

41 and 42, is rigidly attached to a cradle 43 by welding or the like and the cradle is bolted to a plate 44 welded to the top of gusseted pedestal 46 anchored to the floor by means not shown. Referring to FIGURE 1, the corresponding cradle 43', plate 44' and pedestal 46' for the second stage illustrate the general arrangement described above.

A circular labyrinth seal 47 is provided between rear support plate 41 and the adjacent head 32 and between the front support plate 42 and corresponding head 32. These labyrinth seals are each formed by concentric and interfitting ribs and grooves machined on contiguous surfaces of annular movable seal members 48 bolted to heads 32 'and annular stationary seal members 49 bolted to support

plates

41 and 42 respectively. The interfitting ribs and grooves, it will be noted, are close fitting but do not make contact. Thus air leakage iwardly to the chamber C of enclosure 29 alongside the heads 32 of the roll 21 is reduced by causing such air to follow a tortuous route.

The sieve roll 21' for the second stage is constructed and supported for free rotation in the same manner as described in connection with sieve roll 21. Where sec- 0nd stage parts corresponding to those described in connection with the first stage are shown in FIGURE 1, the same reference numerals are utilized with a prime appended thereto.

The embodiment shown is adapted to employ a carrier 16 which is endless and for this reason the

enclosures

29 and 29 are preferably constructed so as to be easily moved to facilitate maintenance and replacement of the carrier. As may be seen in FIGURES l and 3, the front wall 29a and 29a and the rear wall 2% and 29b of each enclosure are horseshoelike in shape to permit removal of the enclosures by sliding the enclosures axially of the corresponding rolls 21 and 21. (In FIGURE 3, the enclosure 29 is adapted to slide to the right.) Since the

rear walls

29b and 29b of each enclosure must move across the full length of the sieve rolls 21 and 21', respectively, the inverted U-shaped cutouts in the rear walls must be somewhat larger than the diameter of the rolls. The cutouts in the front walls 29 and 29a, of course, do not have to pass over the sieve rolls at all and hence must merely be large enough, to prevent interference with the front bearing pedestals 46 or 46', respectively, and their appendages.

When the enclosures are in the operative position the rear walls 2% and 2% are sealed against the peripheral portion of the inner faces of

rear support plates

41 and 41. Thus, it will be seen that the use of

plates

41 and 41 which are larger in diameter than the

rolls

21 and 21" is for the purpose of supplying a surface against which the rear wall may be sealed. Similarly, the front walls 29a and 29a are sealed against the peripheral portion of the outer faces of front support plates 42 and 42'. Each of the seals is effected by utilizing resilient strips 51, preferably constructed of silicone rubber or other compressible heat resistant material, intervening the surfaces to be sealed and attached to either the plate or enclosure wall by adhesive or the like.

The top walls 290 and 290' of the enclosures each have an outlet duct 28 or 28' attached thereto. The outlet ducts extend parallel to the respective sieve roll axes and each is at least as long as the sieve roll which it overlies. Preferably, the

outlet ducts

28 and 28 should have about 2-4 inches of width per foot of circumference of the sieve roll. In the embodiment shown, the lower portions of outlet ducts 28 and 28' are disengageable from the upper portion thereof by means, not shown, permitting the sliding movement mentioned above. This can be accomplished by disengaging contiguous flange extensions on the upper and lower portions of the ducts 28 and 28' or by other commonly used means for separating adjacent sections of ductwork.

The

enclosure side walls

29d and 29d each have an inwardly and downwardly extending lower section terminating with a chisel shaped lip, as shown most clearly in FIGURE 2, adapted to rest contiguous the surface of the adjacent inlet or outlet idler,

idlers

19, 19, 22 or 22' as the case may be, when the enclosure is in operative position. The chisel lips thus prevent entry of any substantial volume of ambient air into the chambers C and C through the narrow slit intervening the enclosure sidewall and the aforesaid idlers. If desired, a doctor blade type of seal, not shown, can be effected by the chisel lips or by doctor blades attached thereto, in which case the lips or the doctor blades lightly ride on the idlers to give a more positive seal. It should be noted that there is no interference between the sidewalls 29d and 29d and the balance of the dryer structure in an axial direction. Thus, the sidewalls are free to slide outwardly as required.

Means is provided to support the

enclosures

29 and 29 for the sliding movement described above. While any suitable arrangement can be used, as shown in FIGURES l and 3, a pair of hangers 52 are bolted to each of the

sidewalls

29d and 29d, each hanger being provided at its upper end with one or more wheels 53 which are grooved peripherally to accept one of the pair of tracks 54 extending parallel to the axis of each of the rolls 21 and 21'. The tracks 54 are each affixed to and supported by an I-beam 55 which is cantilevered from a position, not shown, at the rear of the dryer. It will be understood that the tracks extend across the full depth of the dryer and for a sufficient distance in front of the dryer to permit the enclosures to be brought far enough in front that the carrier 16 can be threaded through the dryer stages.

With the apparatus illustrated, as the web 11 and carrier 16 follow the path described above, heated air at a pressure slightly above atmospheric fiows from the inlet plenum 26 in a substantially radial direction through the minor portion of the foraminous periphery of sieve roll 21 intermediate the inlet station I and the outlet station and into its interior along the full length thereof. The pressure and flow rate of the air emanating from the inlet plenum is substantially uniform across the length and width of the outlet. Upon reaching the roll interior, the air is at approximately atmospheric pressure to about inches of water above atmospheric while the pressure in the chamber C of the enclosure is at least about 5 to about 20 inches of Water vacuum. Consequently, the heated air is forced radially outwardly through the apertures in the web-covered major portion of the periphery of the sieve roll 21 which is then within the chamber C, through the interstices in web 11 and carrier 16 and into the chamber C. As the air flows through the carrier 16 and web 11, it is not unusual for the central portions thereof to billow outwardly, slightly spacing the center of the web from the roll 21. Such will not adversely affect the dry ing process and is merely dependent upon the tension, elasticity, etc. of the carrier 16.

The air then flows to the outlet duct 28 which is connected to a source of vacuum such as the inlet of fan 27 of the illustrated embodiment. This exhaust arrangement is such as to pull a vacuum in the above stated range substantially uniform across the entire cross section of outlet duct 28. The flow pattern of the air is shown by means of arrows in FIGURES 1-3. Since both the inlet plenum 26 and the outlet duct 28 are full length of the sieve roll 21, and since both the air supply and air exhaust are uniform along the full length of the roll 21, the quantity of heated air flowing through the periphery of the sieve roll 21 (and therefore through the web 11) per square foot per unit of time will be constant along the roll length so as to obviate the possibility of nonuniform drying of webs of fairly uniform porosity and water content.

It will be understood, of course, that the abovedescribed first stage of the dryer apparatus can be used by itself and enjoy the benefits of the present invention. If a second stage is desired, the air issuing from the first stage can be recycled, following reheating, in substantially the same way as described above. In this connection, a multi-stage system, i.e., one employing two or more stages, is attractive from an efficiency standpoint and, in addition, permits an operation whereby the first or preliminary stages can utilize air at temperatures which might scorch the desired end product coming from the last stage. Thus, the instant apparatus can perform a preliminary drying operation, i.e., an operation in which the consistency of the web is increased up to about at temperatures of between about 450 to about 700 F. Subsequently, if desired, the web could be fully dried by air heated to a temperature at which the web fibers will not be damaged.

While the above embodiment utilizes a carrier because of the fragile condition of the web being dried (and although the nature of the carrier is extremely important in connection with such fragile webs) where the webbing dried is a self-supporting material such as a woven textile, the reticulated carrier can be dispensed with in connection with the dryer. In this case, the driving of the sieve rolls is accomplished by force applied to the web itself. Alternatively, the sieve rolls can be driven at the same speed as the web to obviate the need to transmit the drive through the web. Other means, for example, a suitable arrangement of idlers, turning bars and the like, can be used for conveying or transporting the web to and from the dryer.

Many modifications of the above invention may be used and it is not intended to hereby limit it to the particular embodiments shown or described. The terms used in describing the invention are used in their descriptive sense and not as terms of limitation, it being intended that all equivalents thereof be included within the scope of the appended claims.

What is claimed is:

1. A dryer for porous webs comprising:

(A) a rotatably mounted sieve roll closed at its ends and having a foraminous sidewall;

(B) an infeed station adjacent said sieve roll and incorporating means for feeding a continuous length of a moist web onto the foraminous sidewall of the sieve roll as the sieve roll rotates past said station,

said web having a Width matching the length of said foraminous sidewall;

(C) an outlet station adjacent said sieve roll and incorporating means for removing the continuous length of web from said foraminous sidewall following the drying thereof, said outlet station being spaced peripherally of the sieve roll from said infeed station so that said web covers a major portion of the periphery of said foraminous sidewall and that a full length minor portion of the foraminous sidewall intermediate said infeed and said outlet stations is not covered by the web;

(D) conveying means for transporting said web to said infeed station and from said outlet station;

(E) air supply means for providing a moving stream of low pressure drying air; and

(F) an air duct located adjacent the outer surface of said full length minor portion of said foraminous sidewall and in communication with said air supply means, said duct directing the moving stream of drying air into said sieve roll through substantially the length of said full length minor portion in a substantially radial direction and from the sieve roll interior through said major portion of said foraminous sidewall and the web covering it, whereby the moisture is uniformly removed from the web by the drying air passing therethrough.

2. The dryer of claim 1 in which the full length minor portion of the foraminous sidewall intermediate the infeed and outlet stations has an arcuate width of about 2 to about 4 inches per foot of sieve roll circumference.

3. The dryer of claim 2 in which said foraminous sidewall has at least about 75% open area.

4. The dryer of claim 3 in which said means for feeding and said means for removing the continuous length of moist web each comprises an idler adjacent to and parallel with said sieve roll.

5. The dryer of claim 1 in which said conveying means comprises a porous reticulated carrier adapted to be fed onto and removed from said sieve roll concurrently with said web, said carrier overlying the web on the sieve roll and maintaining the web in position adjacent the sieve roll periphery as the web and carrier move between the infeed and outlet stations.

6. The dryer of claim 5 in which said reticulated carrier has a projected open area of at least about 15%.

7. The dryer of claim 6 in which said reticulated carrier is a mesh having about 25 to about 45 openings per inch of width and length.

8. A dryer for porous webs, comprising:

(A) a rotatably mounted sieve roll having substantially imperforate heads and a periphery which is foraminous;

(B) an enclosure encompassing a major portion of the periphery of said sieve roll and leaving a full length minor portion thereof which is not so encompassed;

(C) cooperating seal means on said sieve roll and enclosure to restrict the passage of air between the contiguous surfaces of said sieve roll and said enclosure;

(D) an air outlet duct leading to a source of vacuum and communicating with the interior of said enclosure externally of said sieve roll, the cross section of said outlet duct within said enclosure being axially aligned with and full length of the foraminous periphery of said sieve roll;

(E) conveying means for transporting said web to and from said sieve roll;

(F) an inlet station and an outlet station at opposite ends of said major portion of the periphery of said sieve roll, said infeed station incorporating means to feed a continuous length of moist web onto the periphery of the said sieve roll as it enters said enclosure, said outlet station being adapted to remove the continuous length of web from the periphcry. of the sieve roll as it leaves said enclosure, said web having a width generally matching the length of the foraminous periphery of said sieve roll and cover ing said major portion thereof;

(G) air supply means for providing a moving stream of low pressure drying air; and

(H) an air inlet duct located adjacent the outer surface of said minor portion of the periphery of said sieve roll and in communication with the air supply means, said inlet duct directing the moving stream of drying air into said sieve roll through substantially the length of said minor portion in a substantially radial direction and from the interior of said sieve roll through the said major portion of the periphery of said sieve roll and the web thereon, whereby a uniform flow path is established for the drying air.

9. The dryer of claim 8 in which said minor portion has an arcuate width of about 2 to about 4 inches per foot of sieve roll circumference.

10. The dryer of claim 9 in which said foraminous sidewall has at least about 75% open area.

11. The dryer of claim 8 in which said cooperating seal means comprises a labyrinth formed between concentric and interfitting ribs and grooves on contiguous annular surfaces of said enclosure and sieve roll at each end of said sieve roll.

12. The dryer of claim 11 in which idler rolls are employed for feeding the web onto said sieve roll at one longitudinal side of said major portion and for removing the web from said sieve roll at the other longitudinal side of said major portion, said idler rolls being adjacent to and parallel with said sieve roll, and said sealing means includes a longitudinally extending lip at each side of the enclosure which is contiguous to one of said idler rolls whereby to restrict passage of air therebetween at each side of said major portion.

13. The dryer of claim 12 in which said enclosure is axially slideable with respect to said sieve roll whereby to facilitate maintenance.

14. The dryer of claim Sin which said conveying means comprises a porous reticulated carrier adapted to move in superposed relationship with said web and to overlie the web on the sieve roll to maintain the web in position adjacent the sieve roll periphery as the web and carrier move through said enclosure on said roll.

15. The dryer of claim 14 in which said reticulated carrier has a projected open area of at least about 15%.

16. The dryer of claim 15 in which said reticulated carrier is a mesh having about 25 to about 45 openings per inch of width and length.

17. A multi-stage dryer for lightweight porous paper webs, each stage of which comprises:

(A) a rotatably mounted sieve roll having substantially imperforate heads and a foraminous sidewall;

(B) an enclosure encompassing a major portion of the foraminous sidewall and leaving a full length minor portion thereof which is not so encompassed;

(D) an air outlet duct leading to a source of vacuum and communicating with the interior of said enclosure externally of said sieve roll, the cross section of said outlet duct within said enclosure being axially aligned with and full length of the foraminous sidewall of said sieve roll;

(E) infeed means to concurrently feed a continuous length of a moist web and a superposed porous reticulated carrier onto the foraminous sidewall of said sieve roll with the carrier overlying the web and maintaining the web in position on the sieve roll;

(F) outlet means to concurrently remove the superposed carrier and web from said sieve roll, said infeed means and said outlet means effecting said feeding and said removal at opposite longitudinal sides of said major portion of the for-aminous sidewall whereby the superposed carrier and web are carried by said sieve roll only in the enclosed portion thereof;

(H) an air inlet duct located adjacent the outer surface of said minor portion of the foraminous sidewall of said sieve roll and closely fitted to said sieve roll and said infeed and outlet means to prevent leakage of air therebetween, said inlet duct being in communication with the air supply means and directing the moving stream of drying air into said sieve roll through substantially the length of said minor portion of the forarninous sidewall in a substantially radial direction and from the interior of said sieve roll through the said major portion of the periphery of said sieve roll and the web thereon, whereby a uniform flow path is established for the drying air.

References Cited by the Examiner UNITED STATES PATENTS 1,718,573 6/1929 Millspaugh 162207 1,870,971 8/1932 Sundstrom 162207 1,881,404 10/1932 Hadley 162297 2,061,976 11/1936 Merckens 3413 2,174,744 10/1939 Hill 34-122 2,753,766 7/1956 Simpson 162297 3,084,447 4/ 1963 Fleissner 34122 3,196,555 7/1965 Friedel 34-115 References Cited by the Applicant UNITED STATES PATENTS 340,335 4/1886 Lindsay.

347,3 6O 8/ 1886 Lorimer.

920,351 5/ 1909 Layland et a1. 2,074,455 3/ 1937 Carleton.

WILLIAM J. WYE, Primary Examiner.

Claims

1. A DRYER FOR POROUS WEBS COMPRISING: (A) A ROTATABLY MOUNTED SIEVE ROLL CLOSED AT ITS ENDS AND HAVING A FORAMINOUS SIDEWALL; (B) AN INFEED STATION ADJACENT SAID SIEVE ROLL AND INCORPORATING MEANS FOR FEEDING A CONTINUOUS LENGTH OF A MOIST WEB ONTO THE FORAMINOUS SIDEWALL OF THE SIEVE ROLL AS THE SIEVE ROLL ROTATES PAST SAID STATION, SAID WEB HAVING A WIDTH MATCHING THE LENGTH OF SAID FORAMINOUS SIDEWALL; (C) AN OUTLET STATION ADJACENT SAID SIEVE ROLL AND INCORPORATING MEANS FOR REMOVING THE CONTINUOUS LENGTH OF WEB FROM SAID FORAMINOUS SIDEWALL FOLLOWING THE DRYING THEREOF, SAID OUTLET STATION BEING SPACED PERIPHERALLY OF THE SIEVE ROLL FROM SAID INFEED STATION SO THAT SAID WEB COVERS A MAJOR PORTION OF THE PERIPHERY OF SAID FORAMINOUS SIDEWALL AND THAT A FULL LENGTH MINOR PORTION OF THE FORAMINOUS SIDEWALL INTERMEDIATE SAID INFEED AND SAID OUTLET STATIONS IS NOT COVERED BY THE WEB; (D) CONVEYING MEANS FOR TRANSPORTING SAID WEB TO SAID INFEED STATION AND FROM SAID OUTLET STATION; (E) AIR SUPPLY MEANS FOR PROVIDING A MOVING STREAM OF LOW PRESSURE DRYING AIR; AND (F) AN AIR DUCT LOCATED ADJACENT THE OUTER SURFACE OF SAID FULL LENGTH MINOR PORTION OF SAID FORAMINOUS SIDEWALL AND IN COMMUNICATION WITH SAID AIR SUPPLY MEANS, SAID DUCT DIRECTING THE MOVING STREAM OF DRYING AIR INTO SAID SIEVE ROLL THROUGH SUBSTANTIALLY THE LENGTH OF SAID FULL LENGTH MINOR PORTION IN A SUBSTANTIALLY RADIAL DIRECTION AND FROM THE SIEVE ROLL INTERIOR THROUGH SAID MAJOR PORTION OF SAID FORAMINOUS SIDEWALL AND THE WEB COVERING IT, WHEREBY THE MOISTURE IS UNIFORMLY REMOVED FROM THE WEB BY THE DRYING AIR PASSING THERETHROUGH.