US3176411A - Paper drying hood - Google Patents

Description

April 6, 1965 M. D. JEPSON ETAL 3,175,411

PAPER DRYING HOOD Filed Sept. 26, 1960 8 Sheets-Sheet 1 FIG. 7.

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April 1965 M. D. JEPSON ETAL 3,176,411

PAPER DRYING HOOD 8 Sheets-Sheet 3 Filed Sept. 26. 1960 INVENTORS L mm JW a/nd/ S W 7Za /mw/u 3r 6W?) 2 71 0/; WWW

April 1965 M. D. JEPSON ETAL 3,176,411

PAPER DRYING HOOD 8 Sheets-Sheet 4 Filed Sept. 26. 1960 VIE mvzmons F IG. 4. v filo/lad) WW 4014,

April 1965 M. D. JEPSON ETAL 3,176,411

I PAPER DRYING HOOD Filed Sept. 26, 1960 8 Sheets-Sheet 5 a} Q ///r/ a INVE NTORS 72:14am 9% W April 1965 M. D. JEPSON ETAL 3,176,411

PAPER DRYING HOOD Filed Sept. 26, 1960 8 Sheets-Sheet 6 INVENTORS mklmbJz/rw a nd/ WW MW B Y ZZZWW x WW April 6, 1965 M. D. JEPSON ETAL 3,176,411

PAPER DRYING HOOD Filed Sept. 26, 1960 8 Sheets-Sheet 7 F IG. 5.

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April 6, 1965 Filed Sept. 26, 1960 M. D. JEPSON ETAL 3,176,411

PAPER DRYING HOOD 8 Sheets-Sheet 8 X INVENTORS mm @W 472/ W W 952 4 14a .BY aldwm) W ZZZM FIG. 9.

United States Patent 3,176,411 PAPER DRYING HOOD Michael Denis Jepson, Ilkley, and George Flaxman Underhay, Weybridge, England, assignors to The Bowater Research and Development Company Limited, London, England, a company of the United Kingdom- Filed Sept. 26, 1960, Ser. No. 58,265 Claims priority, application Great Britain, Sept. 2, 1960, 30,426/ 60 7 Claims. Cl. 34-422) The present invention relates to papermaking machinery and more particularly to drying sections of papermaking machines.

It is the principal object of the invention to provide an improved method and means for evaporating the moisture from the web and for increasing the rate of drying in papermaking machines.

In conventional machines the distribution of moisture in the web is somewhat uneven and in wide machines this may be very marked. For example, if paper is taken from the machine at an average moisture content of 6% it is not uncommon to find that the actual moisture content transversely of the web varies from 4% at one part to 8% at another part at the dry end of the drying section. Thus, if it were necessary not to have a moisture content of more than 6% at any part in the paper some of the paper would have to be overdried to reduce the moisture content of those parts of the paper having 8% of moisture down to 6% and the parts having 4% would be further over-dried. Moreover, the whole process of drying might have to be slowed up to allow the wetter portions to be dried down to the maximum permissible moisture content.

It is a further object of the present invention to provide a control of the moisture distribution across the paper web.

According to one aspect of the present invention, in a papermaking process wherein the web is dried by entrainment around one or more heated drying cylinders and by directing gaseous drying medium directly on to the outer surface of the web about the drying cylinder in such manner that evaporation of moisture from the web surface and transference of heat from the drying cylinder are enhanced at drying zones arranged transversely of the web, individual control of the drying rate in each zone is achieved by adjustment of the velocity of the drying medium directed onto the web at that zone or the temperature of the drying medium so directed or the humidity of the drying medium so directed or any combination of two or all of such adjustments, the gaseous medium, after flowing over and away from the outer surface of the web being caused to flow transversely of the web and then to flow in a direction away from the surface of the cylinder.

By the use of the invention it is possible to control the rate of drying transversely of the web to a degree sufficient to ensure that the web may be dried down to an overall pre-determined moisture content without any part of the paper being overdried or without any remoistening or conditioning of the paper after drying being necessary.

In order to avoid any tendency for the web to lift from the surface of the drying cylinder the velocity of the gaseous medium flowing away from the outer surface of the web is preferably substantially lower than the velocity of the gaseous drying medium directed onto the outer surface 3,176,411 Patented Apr. 6, 1965 a drying hood for a drying cylinder of a paper-making machine comprises a plurality of pressure chambers disposed in side by side relationship transversely of the direction of paper travel, each pressure chamber having an arcuate face adapted to the periphery of the drying cylinder and containing nozzle orifices for the direction of gaseous drying medium onto a web of paper on the periphery of said drying cylinder, and means for supplying gaseous drying medium to said pressure chambers and for enabling the drying rate achieved by the drying medium directed from the nozzle orifices of each pressure chamber to be individually controlled, by adjustment of the humidity of the drying medium supplied to each pressure chamber, or the temperature of the drying medium supplied to each pressure chamber, or the rate of supply of drying medium to each pressure chamber, or any combination of two or all of such adjustments, and exhaust passageways spaced apart transversely of the direction of paper travel by which the gaseous medium after flowing over and away from the surface of the web can flow in a direction away from the periphery of the drying cylinder.

According to a further feature of the present invention, a drying hood for a drying cylinder of a drying section of a papermaking machine comprises a manifold, fan means for supplying gaseous medium to said manifold, heating means for heating the said gaseous medium, a plurality of pressure chambers disposed in side-by-side relationship transversely of the direction of paper travel, each pressure chamber communicating with said manifold for receiving heated gaseous medium therefrom and having an arcuate face adapted to the periphery of the drying cylinder and containing nozzle orifices for the direction of heated gaseous medium onto a web of paper on the periphery of said drying cylinder so as to hold the web in close non-adhesive contact with the cylinder, valve means for individually controlling the flow of gaseous medium from said manifold to each pressure chamber, and exhaust passageways spaced apart transversely of the direction of paper travel by which the gaseous medium after flowing over and away from the surface of the web can flow in a direction away from the periphery of the drying cylinder.

Preferably the pressure chambers are spaced-apart and the spaces between them provide at least some of the exhaust passageways.

Preferably the manifold lies directly adjacent said pressure chambers and on the opposite side thereof to their arcuate faces and said valve means conveniently comprises shutters controlling ports in a wall between the manifold and the pressure chambers.

Since the gaseous medium must be brought into direct contact with the web entrained around the cylinder no dryer felt is employed. The invention is applicable to any type of drying section and can be used with machines employing a number of small cylinders, a single large cylinder such as is generally used for the production of glazed or creped paper, or a combination of both large and small cylinders. In the case of a multi-cylinder drying section when the web is maintained in non-adhesive contact with the cylinders, the necessary pressure to maintain contact, and which, in conventional machines is produced by the dryer felts, is generated by the pressure of the gaseous medium directed onto the web or any longitudinal tension which may be applied to the web or both.

In a preferred arrangement the drying hood has an outer casing for collecting spent gaseous medium flowing away from the periphery of the drying cylinder, the fan means communicating by its inlet side with the interior of said casing whereby to re-supply spent gaseous medium to said manifold. The preferred drying medium is predominantly air, but it will be appreciated that in general a proportion of water vapour from the web is present and is beneath the exhaust openings.

. I a r to avoid Saturation of the drying generally made for exhausting some of the spent air thecasing and supplying fresh make-up air thereto. The

medium provision is from;

pressure chambers,;the manifold and the fan means can.

all'be disposed withinthe outer casing with the heating;

means situated at the entry or entries to a supplychamber which is formed between the manifold and the wall of The inlet of the fan means can thus lie within the supply'chamberand the outlet.

the casing opposite thereto.

within the manifold. This is most conveniently achieved if the fan means comprises at least one axial flow fan driven by a motor which maybe situated outside the cas- V from'a common manifold 42.

ing. In the preferred arrangement the arcuate faces of the pressure chambers are contiguous and exhaust channels extendinglongitudinally of the drying cylinder but at the opposite side of the arcuate faces to the cylinder communicate with'the-exhaust passageways, said arcuate I faces having exhaust openings to permit thespent 3.11 to flow into the exhaust channels.

The total area of the exhaust openings is preferably-subst-antially greater than that of'the nozzle orifices so that the velocity of the air flowing away from the cylinder is substantially less than the velocity of the drying air d1- 7 be necessary thata positive :pressure be maintained' beneath the exhaust openings and even aslrght negative pressure may not, in certain circumstances, bGdlSfiKlVQIltageous." v V I Itis generally preferred however that'the lowestpressure of the gaseous medium under the'hood is sufficient" to avoidthe uncontrolled inflow of ,air at ambient condi-. tions from outside the hood under its bottom'edges.

The invention will be further. described by way of example "with reference to the accompanying drawings, in

which:

FIG. 1 is a diagrammatic side elevation oflpart of-a.

multi-cylinder drying section of a paper making machine incorporating a dryinghood constructed according to the present invention; a i FIG. 2 is a front elevation of the drying hood of FIG. 1; FIGS is a cross section on the line III-III'of FIG. 2

. to a larger scale, the section line III- 1H also being in dicated in FIG. 4;.

FIG. 4 is a section on, 7 section line IV-IV also being indicated in FIG. .5;

FIG. 5 is'a detailed section on the line V-V of FIG. 4;.

FIG. 6 ,is a detailed cross section on the line VI VI of FIG. 3 to a still larger scale, the section line VI VI also being indicated in FIG. 5; I I FIG. 7 is an enlarged detail of the section shown 1n FIG. 4 forcomparison with. FIG. 6; v

FIG. 8 is a section on the line ;VIII--VIII of FIG. 3,

the nae rv-i-rv ofFIG. s, the

"T he drying hood 2% contains six pressure chambers 30,. 32, 34, 36,38 and deployed axially of the cylinder in the positions indicated by dotted lines in FIG. 2. The

'- pressure chambers are individually supplied with gaseous drying medium, which'in the embodiment shown is air,

FIGS. 3 to 8 show the construction of the drying hood in more detail. Referring to FIG. 4, the pressure chambers 38 and 40 are spaced apart so that their longitudinal partition'walls 39 and 41 define an exhaust passageway 44 by which spent air can flow in adirection away from the surface of the cylinder 22. ,Allthe other pressure chambers are likewise spaced apart: I

- 'As can be seen from FIGS. 3 to 7, a series of flow passage means formed as channels 46 extend along the cylin-. der 22 ,behind'aperforated arcuate bottom wall' or face 48 of each pressurechamber, the arcuate faces substantially'conforming to the periphery of the cylinder in ra-' dially outwardly spaced'relation tothe latter; Drying air in thepressure chamber 38 :has access to nozzle orifices '54 in the form of holes arranged in the arcuate face 48 for the projection or air towards the webof paper on the sur-'- face of the cylinder 22.. This is indicated in FIGS. 3 and 6 by arrows 52. I I I Although the following description refers for the most part to the pressure chambers 38 and 40, it will be. appre,

V ciated that all thepres'sure chambers 30, 32, 34,36, 33

. and 40 are of similar construction.

i As can be seen in FIGS. 6 and 7,.the arcuate faces of the pressure chambers are contiguous although the press surechamber walls 39 and 41 are spaced apart. The chan- 1 nels 46 extend the full length ofthe contiguous arcuate "faces 48 but are open to the exhaust passageway44 at their facesopposite the arcuate faces 48, as can be seen in FIG. 7; 'The gaps betweenthefchannels provide access to. the'ndz-zle orifices for the airin the pressure chambers and are isolated from the exhaustpassageway 44by plates 7 3 4'7 1 as can be seen in FIGS. 5 and 6 Intercommunication between the'pressure chambers along the gaps between ,thechannels 46 is prevented by plates 54 (see FIG. 6).

fThe flow passage channels 46 lead spent air flowing 7 from the space between'th'e arcuate faces 48 and the cylin- V der through larger size openings-56 to the exhaust passageway 44, mean he se'en from FIG; 4. Although only a few 'no'zzle orifices 50'and exhaust openings 56 are shown, it will be appreciated that'these :extend over subf stantially thewhole of the arcuate faces 48of thepressure the sectionline VIII-VIII also being'indicated in FIG. '4;

' FIG. 9 is a cross section similar to that shown inFIG.

4, but of another embodiment of drying hood according, l

to the invention; and I FIG. 10 is a detail section on the line X-eXiof FIG. 9.

Referringnow to th drawings, and'm'ore particularly to FIGS."1 and 2, adrying hood 20 constructed accord ng to the present invention is disposed about anv upper cylinder 22 of faImulti-cylinder drying section of a paper makk 24 to be dried passes al-,

ing machine; A web of, paper chambers. The path of the spent airis indicated by arrows 58 in FIGS. 3, 4, 5 and 7. Ascan be seen from these figures, the spent air,'after issuing through the nozzle orifices 50, flows only to a limited extent circumferentially of the cylinder before .flowing away from the cylinder through the exhaust openings 56. The spent air then flows transversely of the web along the channels 46 to the exhaust passageway 44 or one of the other'exhaust'passageways between the pressure chambers or to an end exhaust passageway '45 (FIG. 4), whereupon it can fiow freely through gaps 45b (FIGURE 5) inthe transverse walls 450: and away from the drying cylinder 22.1 The exhaust passageways L are circumferentially coextensive about the cylinder with thepressure chambers, and'are spaced apart axially'of the cylinder. 7

.The drying hood'20 is provided with an outer casing. 60v having sidewalls 62 transverse to the direction of movement of the'web, end walls 64 longitudinal tothe direction of movement, ofythe' web and'a top 'wall66 j formed of heat insulating panelling (see FIGS. '3 and 4).

Two spaced inner walls 45a, transverse to the direction of f ,t-raveliof the web, extend from'the'bottom wall 48 to the manifold 42, one at each side of the arcuate part of the bottom wall 48 Thetransverse walls 45a are spaced from ternately round cylinders in :an upper row a cylinders in alower row, those 1n thei'upperrow, other than the by 26 and those in.the lower cylinder 22, being indicated row by 28 in FIG. I. I I

the respectively adjacent outer transverse walls 62 to define "the end exhaust passageways 45. A supply chamber 68 1 (FIG. 3) is formed between the manifold 42 and the top wall 66 of the casinggand main fans 70 are arranged between the supply chamber 68 and the manifold 42. Spentto the manifold 42 by the main fans 70, which are driven by motor 72. The spent air flowing into the supply chamber 68, passes through heaters 74 in the form of a plurality of finned steam pipes 76, supplied with steam th oughvinlets-78, and having steam outlets 80.

The mainfans 70 are axial flow fans having their inlets 82 disposed directly in the supply chamber 68 and their outlets 84, having a diffuser 86, directly within the manifold 42. This construction avoids the use of any ducting between the supply chamber and the manifold 42 and leads to a compact space-saving arrangement.

Each of the pressure chambers is individually supplied with air from the manifold 42. As can be seen in FIGS. 3 and 4, the top Wall 88 of each pressure chamber is intermediate each pressure chamber and a top inner wall 42a. The inner transverse walls 45a, together with the I top innerwall 42a and the intermediate wall 88, define the manifold 42. The top wall' 88, which forms the bottom wall of the manifold 42, is provided with ports 90 to permit the air to flow into the pressure chambers. The ports 90 are controlled by shutters 92, each of which is individually slidable by means of a Bowden cable 94 to enable individual adjustment of the flow through the ports 90 to be made.

As can be seen more clearly in FIG. 8, each of the ports 90 is cusp shaped and in particular comes to a point at one end to enable a fine control of the quantity of air flowing from the manifold 42 to each pressure chamber to be obtained. For ease of manipulating the shutters, the shutters are provided with runners 96 which run in channels 98, as can be seen in FIGS. 4 and 8.

It will be appreciated that the drying air is circulated along a substantially enclosed endless path, which comprises the manifold 42, one of the pressure chambers, the nozzle orifices 50, the exhaust openings 56, the flow passage channels 46, one of the exhaust passageways and the supply chamber 68 whence it is re fed to the manifold 42 by the main fans 70.

In order to prevent the drying air so circulated becoming saturated with, water vapour, some of the air and evaporated water, so circulated is withdrawn through exhaust ducts 100 and fresh air is supplied through ducts 102 (see FIGS. 1 to 5). As can be seen more clearly from FIGS. 1 and 2, there are two exhaust ducts 100 which, are joined into a single duct 101, within which, is disposed an exhaust fan 104, of the axial flow type, driven by amotor 106 (indicated diagrammatically in broken lines in FIG. 2). The exhaust fan 104 withdraws spent air from within the casing. 60 and the spent air is discharged,for example, into a flue (not shown). The quantity of spent air withdrawn is controlled by a damper 112. The make-up air ducts 102, which are also two in number, are supplied, from a common duct 103, within which there, is disposed a fresh-air fan 108, also of the axial flow type, driven by a, motor 110 (indicated diagrammatically in broken lines in FIG. 1). The fresh-air fan 1'08- draws fresh air in from the atmosphere through a filter 114. and supplies such fresh air to the supply chamber. The quantity of fresh or make-up, air is controlled by adamper 116 (FIG. 2).

Cooling air for the motors 72 driving the main fans 70 is also supplied by the fresh-air fan 108. For this purpose ducts 118 leading-to the motors 72, are also connected to the common duct 103, as shown in FIG. 2. It can conveniently be arranged that cooling air after cooling the motors 72, flows through the fan centres and is discharged just before the fan rotor'blades of the main fans so as to mix with the drying air being circulated. If desired, the make-up air can be heated, for example by steam or electrical heaters (not shown). If the make-up air is also used to cool the motors 72 as shown, then the temperature to which such air is heated is limited by the temperature rating of the motors 72. This temperature may, for example, be 160 F. If it is desired to heat the make-up air to a higher temperature, then a separate supply of cooling air for the motors 72 is preferred. It is not essential that the make-up air be heated before supplying to the supply chamber; the make-up air can obtain heat by admixture with the air being circulatedthrough the heaters 74.

The rate of supply of drying air to each of the pressure chambers can be individually controlled, thereby enabling the drying rate at six zones contiguously arranged transversely of the web to be separately controlled. The- Bowden cables 94 attached to the shutters 92 (FIGS. 3 and 8) lead to a control panel 128 (FIG. 1) fitted with cranks or handles 130 for adjusting the shutters. The control panel 128 also has further handles 132 operating Bowden cables 134, which control the dampers 112 and 116 in the exhaust air and makeup air ducts (FIG. 2).

The shutters are adjusted in order to obtain as even a moisture distribution, transversely of the finished web, as possible. Should the moisture profile transversely of the web vary during operation of the paper making machine, for example due to uneven wear of the calender or press rolls, then appropriate corrective action may betaken at the control panel 128.

In order to provide access to the surface of the cylinder 22, for example when threading the web through the machine, or when removing torn paper should a break occur in the web, the drying hood 20 is pivoted to a fnamework 120 situated at one end of the cylinder 22 and to a piston rod 122 of a pneumatic piston and cylinder mechanism 124 situated at the other end of the cylinder 22, as can be seen in FIGS. 1 and 2. The upper end of the mechanism 124 is mounted on the framework 126. The make-up air duct 103 is provided with a flexible portion 128 to avoid having to disconnect this duct when lifting the drying hood away from the surface of the cylinder.

The drying cylinders 22, 26 and 28 are internally steamheated in the conventional manner, the means for this purpose being omitted from the drawings for the sake of clarity.

More than one of the cylinders of the upper row may be provided with drying hoods according to the present invention, if so desired. Where adjacent cylinders in the same row have such drying hoods then the supply chambers, possibly the manifold and possibly also the pressure chambers, as well as the outer casing, may be arranged to be common to said adjacent cylinders. Moreover, drying hoods according to the present invention may also be adapted to the drying cylinders of the lower row. In order to increase the drying capacityof the drying section, a large number of drying hoods may be used. In this case it is not necesary that all the hoods be provided with shutters for individually controlling the drying rate transversely of the Web, but it is desirable that they be so provided so that a substantially uniform moisture profile may be obtained through as large a part of the drying section as possible. Thus a uniform moisture profile transversely of the web may be obtained substantially throughout the drying section. This reduces the risk of wrinkles developing in the web.

A drying hood according to the present invention can be fitted to an existing machine in order to improve the uniformity of the moisture content of the finished web and in order to increase the capacity of the drying section.

It is at present common practice to over-dry the web in the drying section of -a paper making machine and then to subsequently re-moisten the web in a separate operation, so that the finished product will have a moisture content which is in keeping with the humidity of the surcylinder.

rounding atmosphere, in order to obtain a. moisture distribution which is as uniform as possible throughout the web. By providinga drying hood according to the in ventionlover at leastone of the cylindersof a multi cylinder drying section, the "web can be dried to a substantially uniform wetness in keeping with thehurnidity In the embodiment of the drying hood shown, the total of the surrounding'atmosphere, thus avoidingthe nec'es--f Y sure chambers, by means not shown. The pressure chamhere may also be provided with thermometers, if desired.

The humidity of the drying air being circulated is controlled by the dampers 112 and 11s (FIG. 2), and samples of the spent air flowing through the exhaust duct 101 then-there-would be arisk of-the web being lifted from may bejtaken'for the purpose of assessing thelmoisture" content of the "drying air being circulated. I 3 I In operation, heat istransferred to theweb' on the drying cylinder 22 not only from the drying cylinder but also from the heated air directed onto the web. Morecrossasectional area of the exhaust openings is approximately twenty-eight times thetotal cross-sectional area of the nozzle orifices. ;Thus the velocity of the spent air flowing awayfrom the web 'through' the exhaust openings is very muchlower than the velocityofthe air flowing towards the web through the nozzle orifices. Moreover,

I there issome resistance to the flow of the spent air flowing through the exhaust channels and through, the exhaust over, the rate of heat transfer from the drying cylinder-to the web is enhanced by'bl'owing air on to the web for by taking away the evaporated'moisture in th'cspcnt air the rate ofevaporation is increased thereby increa'singthe temperature difierencebetween theweb land thedrying Although a to -amulti-cylinder drying section of a paper-making maf dryinghood according to-the present chine it can also be applied to'a paper-making machine having one large drying cylinder only, whether that cylinder is an M.G. cylinder or not; -Where an-M.G. cylinder is'used the" web usually pressed intoadhesiye; contact with the cylinder; Where an unpolished cylinder, whether of large or small diameter, is used the web is held close but non-adhesive contact with'thecylinder'. In

this latter case, the drying :air issuing from the nozzle.

orifices of a drying hood according to the present invention creates a force acting on the outer surface of the web, thusQat least assisting in maintaining theweb in close'but non-adhesive contact with the cylinder. Where passageways, so that a slight positive pressure may be still maintained beneath the exhaust openings. 1

It will be appreciated that the provision of a large number'of exhaust channelsat fairly. closely spaced intervals enables the spent air to be removed fromthe surface ofthe web without the surface of the webbeing presented to large openings extending transversely of the web. If the web were exposed to such large openings,

the s'urface'of-the drying cylinder beneath such openings,

" and .be'ing drawn into. the machinery within the drying hood. In the drying hood of thepresent invention there are large exhaust openings, namely at the exhaust pas sageways', but theseextend circumferentially of thedrying cylinder, i.e'. longitudinally of the web, and they com-' rnunicate witlr' theexhaust channclsand not directly with the exposed surface ,of the web. Thus the risk of the web being broken. and drawn' intothe exhaust passageways isfreducedto'aminimum.

' The perforated arcuate faces of the pressure chambers present a substantially smooth surface to the web abou'tthe drying cylinder so that should a break-occur in the web there is little risk of the broken web being caught up o'nthe drying hood and damaging the hood.

It will be appreciated-that although the drying hood in'gs. Princip'alparts which are like those of the ema paper-making machine-liasa drying section with an M.G. cylinder and one or more pro-drying cylindersa drying hood according to the present invention may be applied to some or all of the pro-drying cylinders. It'is envisaged further-more that drying hoods according to the present invention can be applied to, drying sections hav-' ing few, large diameter drying cylinders compared with. conventional multi-cylinder drying sections having a large numberof .small,.e.g. 5 ft.,diameter, drying cylinders.

In a multi-cylinder. drying section, the web is main;

bodimentof FIGS. '1 to 8 are indicated by like reference numerals; The embodiment of FIGS. 9 and 10 differ from that of the previous embodimentfprin'cipally in i that the pressure chambers, of which 238 and 240 are seenin the drawings, instead of being spaced apart, adjoin one another. Exhaust passageways 244, which extend circumferentially of the drying cylinder 22, are arranged within the pressure chambers themselves. The arrows 258- indicatethepassage-of spent air-from thesurface of the web through the exhaustopenings 56, and

- the flow'passagechannels 46 'and exhaustpassageways 45 and 244 through gaps 455 into the-casing 60. The

tained in closev but non-adhesive contact with the drying cylinders, in order topermit amaximum rate "of heat transfer from the cylinder. to the web. If the Web is sufiia ciently strong, then maintain such contact, 7 However, if -the' Web is very weak, then it is usual to provide felts in order to press the web into close non-adhesive contact with the drying cylinders. The felts, however, hinder the flow of moisture away between'the channe1s46 to completely the tension in the web canbe. used tO' 7 sure "chambers from one another.

from the Web as it is dried. .With the use of a drying hood according to the present invention the drying air issuing from the nozzle orifices'creates aforce acting on the outer surface of the web to'hold the web in close nonx adhesive contact the drying cylinder as disclosedin United States Patent No. 2,919,495.. -Drying hoods 'according to the present invention obviate thenecessity for pressure chambers 238' and 240 are in etfect separated by a longitudinal partition 239, which extendsat 241 isolate the pres- It'willbe-seenthat,in'the' embodiment of FIGS. 9 and 10-, the spent air, immediately after direction towards the surface of the web,'first flows only to a limited eX- tent circumferentially of the drying cylinder, then through the exhaust openings Sdinto the channels 46 and subsequently transversely'of. the web into the exhaust passageways 244 and 45, wherein'it'can how in a, direction away, from the surface of the-drying cylinder. The manner in'which the 'spentair is led away from the surface of-the' rcylinder is therefore substantially thesarne as that in'the embodiment of FIGS. 1 to 8. r

felts, except possibly at the wettest part of the dryingsection. However, it is. necessary that the risk of the web.

lifting from-the surface of the cylinder when beneath the exhaust openings be reduced to a minimum. To end the total cros's-sectionalarea of the exhaust opcning's is made very much larger thanthe totalcross-sectional are-a dof the nozzle orifices, preferably at least sixteen i Although the embodiments of the inventlon shown in the drawings employ steam heaters, other :forms of heating means could be employed such as. electrical heating elements and] gas and oil burners which may heat the circulated air either; indirectly or by admixture oftheir products of combustion withthe circulated air.

9 In the embodiment of drying hood illustrated in FIGS. 1 and 2 of the drawings, access to the surface of the drying cylinder is obtained by pivoting the hood about one end. It may, however, be preferable, according to the design of the frame of the drying section to which the hood is applied, to arrange for the hood to be liftable vertically, for example by four hydraulic or pneumatic piston and cylinder mechanisms or screw jacks arranged at its corners. The pneumatic piston and cylinder mechanism illustrated in FIGS. 1 and 2 may be replaced by a hydraulic piston and cylinder mechanism so desired.

7 In the illustrated embodiments of the invention, the shutters controlling the ports between the common manifold and the individual pressure chambers are manually operable using Bowden cables. However, the shutters could be operated by air or hydraulic cylinders or by screwed rods on each of which a nut is rotatable by "means of an air or electric motor.

It is envisaged that the moisture profile transversely of the finished web may be controlled automatically.

For this purpose moisture content sensing shoes, corresponding in number and transverse positions to the numher and transverse positions of the pressure chambers,

,may be arranged to meter the moisture content of the Web leaving the drying section, each of themoisture content sensing shoes being connected electrically or otherwise so as to control the shutter associated with the corresponding pressure chamber. Alternatively a single I moisture content sensing shoe may be arranged to traweb in six groups of three, the groups being spaced from one another to provide five exhaust passageways between adjacent pressure chambers. Such a structure is achieved by dividing each pressure chamber of the drying hood illustrated in FIGS. 1 to 8 into three, each one of which has its own shutter controlling the supply of heated air thereto from the common manifold. It is desirable that the spent air should flow through the exhaust channels with a significant velocity, the consequent pressure drop in the exhaust channels being used to maintain a slight positive pressure beneath the exhaust openings in the arcuate faces of the pressure chambers. If too many exhaust passageways were provided they would be a comparatively short distance apart so that the air velocity in the exhaust channels, which would be correspondingly shorter, would be negligible, leading to a negligible pressure drop in the exhaust channels which could not be used to maintain a positive pressure beneath the exhaust openings. Moreover, the provision of a comparatively few exhaust passageways transverse of the Web when a large number of pressure chambers is employed leads to a simplification in construction.

It is possible to obtain pressures ranging from 4 ins. to 16 ins. water gauge (measured at 60 F.) in the manifolds of the illustrated embodiments of the invention. Thus the pressure in each of the pressure chambers may be varied from zero to 16 ins. water gauge. By using more powerful fans or a greater number of fans higher pressures are, of course, possible. A static positive pressure (with respect to atmosphere) of from 0.1 in to 1 in. water gauge (measured at 60 F.) is obtainable immediately beneath the exhaust openings in the perforated arcuate faces of the pressure chambers.

What is claimed is: l. A drying hood for a drying cylinder of a. machine I for drying sheet material in continuous lengths to be entrained about said cylinder, comprising a casing having longitudinal walls, transverse walls, a top wall and a bottom wall, said bottom wall being at least in part of exteriorly concave arcuate shape adapted to the periphery Of the drying cylinder and having its axis substantially parallel to said transverse walls; a manifold within said casing, a supply chamber being defined between said top wall and said manifold; heating means disposed in said supply chamber for heating gaseous medium therein; fan means housed within said casing and having its inlet in said supply chamber and its outlet within said manifold for supplying heated gaseous medium from said supply chamber to within said manifold; two transverse partitions parallel respectively to the transverse walls and extending from said bottom wall to said manifold one at each side of said arcuate part of said bottom wall defining a path for return flow of exhaust gas to the supply chamber; longitudinal partitions extending between said transverse partitions to define a plurality of pressure chambers between the bottom of the manifold and the arcuate surface, and a plurality of exhaust passageways coextensive with the pressure chambers about the periphery of the cylinder, the face of said manifold facing said bottom well being provided with ports for the flow of heated gaseous medium from the interior of said manifold to each of said pressure chambers; shutters for closing said ports to a variable extent, each of said shutters being individual to one of said pressure chambers; and means for individually adjusting said shutters from without said casing, said arcuate part of said bottom wall being apertured for the direction of gaseous medium from said pressure chambers on to a Web of paper on said drying cylinder and further apertured to provde access to said exhaust passageways for gaseous medium flowing over and away from the outer surface of said web on said cylinder and said exhaust passageways communicating through said transverse partitions with said supply chamber for the return to said supply chamber of gaseous medium received in said exhaust passageways.

2. In drying apparatus including a drying cylinder about which sheet material in continuous lengths to be dried is entrained, the combination comprising a plurality of pressure chambers deployed axially of the cylinder, said pressure chambers having axially aligned arcuate faces substantially conforming to the periphery of the cylinder in radially outwardly spaced relation thereto and having nozzle orifices for directing gaseous drying medium from the pressure chambers onto sheet material entrained about said cylinder; exhaust passageways circumferentially coextensive about said cylinder with said pressure chambers and spaced apart axially of said cylinder, each exhaust passageway being separated from the next thereto by at least one of said pressure chambers; means communicating through said arcuate faces for directing said gaseous medium axially of said cylinder to said exhaust passageways after said gaseous medium has flowed over and away from the surface of said sheet material; means for supply ing gaseous drying medium to said pressure chambers; and means for enabling the drying rate of the sheet material achieved by said gaseous drying medium directed from each said pressure chamber to be independently controlled.

3. In drying apparatus including a drying cylinder about which sheet material in continuous lengths to be dried is entrained, the combination comprising a plurality of pressure chambers deployed axially of the cylinder, said pressure chambers having axially aligned arcuate faces substantially conforming to the periphery of the cylinder in radially outwardly spaced relation thereto and having nozzle orifices for directing gaseous drying medium from the pressure chambers onto sheet material entrained about said cylinder; exhaust passageways circumferentially coextensive about said cylinder with said pressure chambers and spaced apart axially of said cylinder; flow passage means radially outwardly beyond said arcuate faces extending axially of said cylinder and comalt e 11 municating with said exhaust passagewayasaid flow' paS? sage means also communicating through saidi arcuate i faces with the spaces between said arcuatei faces andts'aid' cylinder whereby gaseous medium'whichhas flowed over I and away from the surface of'said sheet material will flow outwardly through said arcuate ,faces into said flow pas sage means and will then flow axially of said cylinder within said flow'passage means to said exhaust passageways; means for supplying gaseous drying medium to, said pressure chambers; and means for .enabling 'the drying" I rate of the sheet material achieved by said gaseous drying rnediumdirected from each said pressure chamber to be independently controlled.

an enclosing casing having a bottom Wall' which provides said pressuretcharnber-arcuate faces; twospaoed apart 4. Drying r-apparatus according to claim "3 in which said exhaust passageways arev within, said pressure,

chambers. i

5. Drying apparatus according to claim} comprising an enclosing casing having a bottom wall which-provides saidpressure chamber arcuate faces; an intermediate wall spaced from said bottom Wall; two spaced apart transk verse walls parallel to the cylinder'axis on opposite sides thereof and extending between said intermediate and bottom Walls, said intermediate 'wall dividing the casing in;

terior into a lower space bounded by said bottom wall;

said transverse walls, and said' inte'rmediate' wall, and a collecting space; a plurality of sp'aced apart partitions inner transverse walls parallel'to the cylinder axis and onopposite sides thereof; an intermediate wall spaced irom said bottom wall and extending from oneof said transverse walls. tolthe other; a plurality of spaced apart partitions between said transverse walls extending parallel to thedirection of motion of sheet material entrained about said cylinder, said inner transverse walls, said bottom wall; said intermediatewall and said partitions defining-said pressure chambers andsaid exhaust passageways,

saidmeans for enabling the drying rate of the sheet ma- :te'rial to be independently controlled comprising separate independently operableinlet means between said manitold and the respective pressure chambers;

7. Drying apparatus according to claim 6 in which f independently operable inlet tmeans comprises cusp respectively extending from one of said transverse walls to the other in the direction'ofrnotion ofsheet material entrained about said cylinder, said transverse walls, said bottom wall, said intermediate wall and said partitions defining said' pressure chambers and said exhaust passageways, one of saidtintermediate and transverse walls-having a pluralityof ports separately providing communica tion between said collecting space and the respective pressure chambers and at least one other of, said intermediate and transverse walls having gaps' providingv communication between said exhaust passageways and said collect ing space, said meansfor supplying gaseous drying me dium to said pressure chambers including a heater within said casing, and said means for enabling the drying rate of the sheet material to be controlled comprising means within said casing but operable from the exteriorthere'of for controlling the flow of drying medium from said collecting space through said ports individually to difierent x ones of said pressure chambers. r a. ,6. Drying apparatus according to-claim 3 comprising shaped ports in said intermediate wall between said manifoldand respective pressure chambers; movable shutters respeotivelyta'ssociated.with said ports; and means con- 2,012,115, 8/35 Woodrutf "34-23 2,837,830 6/58 'Fry 34* '114 X 1 2,919,495 1/60 Underhay 34l60 X 2,929,153 3/60 Fr 34' 114 X f ronnro'n PATENTS 727,058 3/55 Great Britain. 7 1 773,908 5/57 Great'Britain;

fne cted to said shutters, respectively and beingro'perable 7 from the exterior of said enclosing casing.

, References'Cited by the-Examiner UNITED STATES PATENTS NORMAN YUDKOFEPr'imary Examiner,

"GEORGE/D. MITCHELL, CHARLES OCONNELL,'

: j BENJAMIN BENDETT, Examine

Claims (1)

1. A DRYING HOOD FOR A DRYING CYLINDER OF A MACHINE FOR DRYING SHEET MATERIAL IN CONTINUOUS LENGTHS TO BE ENTRAINED ABOUT SAID CYLINDER, COMPRISING A CASING HAVING LONGITUDINAL WALLS, TRANSVERSE WALLS, A TOP WALL AND A BOTTOM WALL, SAID BOTTOM WALL BEING AT LEAST IN PART OF EXTERIORLY CONCAVE ARCUATE SHAPE ADAPTED TO THE PERIPHERY OF THE DRYING CYLINDER AND HAVING ITS AXIS SUBSTANTIALLY PARALLEL TO SAID TRANSVERSE WALLS; A MANIFOLD WITHIN SAID CASING, A SUPPLY CHAMBER BEING DEFINED BETWEEN SAID TOP WALL AND SAID MANIFOLD; HEATING MEANS DISPOSED IN SAID SUPPLY CHAMBER FOR HEATING GASEOUS MEDIUM THEREIN; FAN MEANS HOUSED WITHIN SAID CASING AND HAVING ITS INLET IN SAID SUPPLY CHAMBER AND ITS OUTLET WITHIN SAID MANIFOLD FOR SUPPLYING HEATED GASEOUS MEDIUM FROM SAID SUPPLY CHAMBER TO WITHIN SAID MANIFOLD; TWO TRANSVERSE PARTITIONS PARALLEL RESPECTIELY TO THE TRANSVERSE WALLS AND EXTENDING FROM SAID BOTTOM WALL TO SAID MANIFOLD ONE AT EACH SIDE OF SAID ARCUATE PART OF SAID BOTTOM WALL DEFINING A PATH FOR RETURN FLOW OF EXHAUST GAS TO THE SUPPLY CHAMBER; LONGITUDINAL PARTITIONS EXTENDING BETWEEN SAID TRANSVERSE PARTITIONS TO DEFINE A PLURALITY OF PRESSURE CHAMBERS BETWEEN THE BOTTOM OF THE MANIFOLD AND THE ARCUATE SURFACE, AND A PLURALITY OF EXHAUST PASSAGEWAYS COEXTENSIVE WITH THE PRESSURE CHAMBERS ABOUT THE PERIPHERY OF THE CYLINDER, THE FACE OF SAID MANIFOLD FACIONG SAID BOTTOM WALL BEING PROVIDED WITH PORTS FOR THE FLOW OF HEATED GASEOUS MEDIUM FROM THE INTERIOR OF SAID MANIFOLD TO EACH OF SAID PRESSURE CHAMBERS; SHUTTERS FOR CLOSING SAID PORTS TO A VARIABLE EXTENT, EACH OF SAID SHUTTERS BEING INDIVIDUAL TO ONE OF SAID PRESSURE CHAMBERS; AND MEANS FOR INDIVIDUALLY ADJUSTING SAID SHUTTERS FROM WITHOUT SAID CASING, SAID ARCUATE PART OF SAID BOTTOM WALL BEING APERTURED FOR THE DIRECTION OF GASEOUS MEDIUM FROM SAID PRESSURE CHAMBERS ON TO A WEB OF PAPER ON SAID DRYING CYLINDER AND FURTHER APERTURED TO PROVIDE ACCESS TO SAID EXHAUST PASSAGEWAYS FOR GASEOUS MEDIUM FLOWING OVER AND AWAY FROM THE OUTER SURFACE OF SAID WEB ON SAID CYLINDER AND SAID EXHAUST PASSAGEWAYS COMMUNICATING THROUGH SAID TRANSVERSE PARTITIONS WITH SAID SUPPLY CHAMBER FOR THE RETURN TO SAID SUPPLY CHAMBER OF GASEOUS MEDIUM RECEIVED IN SAID EXHAUST PASSAGEWAYS.

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