US2928185A - Drier for sheet material - Google Patents

Description

E. G. DREW 2,928,185

DRIER FOR SHEET MATERIAL March 15, 1960 Filed March 19, 1956 4 Sheets-Sheet 1 4 INVENTOR. Evere H 6. Drew March 15, 1960 E. G. DREW 2,923,185

DRIER FOR SHEET MATERIAL Filed March 19. 1956 4 Sheets-Sheet 2 IN VEN TOR. fverci'i 6: Drew March 15, 1960 E. G. DREW 2,928,185

DRIER FOR SHEET MATERIAL Filed March 19, 1956 4 Sheets-Sheet a 'IIIIIIIIIIIIIIIIII/ D 6 INVENTOR. "3 Evrezz G.Drew

March 15, 1960 Filed March 19, 1956 E. s. DREW 2,928,185

DRIER FOR SHEET MATERIAL 4 Sheets-Sheet 4 INVENTOR. .Evcrc H 6. Drew 'type of drier is termed in -this type of machine,

, jets,

Un S ates P flf0 2,928,185 DRIER FOR SHEET MATERIAL Everett G. Drew, Portland, Oreg.

' Application March 19,1956, Serial No. 572,406

12 Claims. (or. 34-43 vThis invention relates-'general-ly to the drying of a sheet of material as it lies uponand is carried by a'heated surface and has air impinged uponit, which air flows over the upper or exposed surface to provide additional drying of said sheet.

This invention is particularly concerned with the formation of a sheet of paper in a paper making machine or drier having a single large drum or cylinder. This the art as a Yankee type, although it is sometimes known as an MG machine. In a continuous, moist paper-web is plastered against the peripheral surface of a heated drum or cylinder and is held thereto by the surface tension of the moisture lying at the interface of the peripheral surface of the drum or cylinder and the contacted surface of the sheet of paper being formed and dried thereon.

In order to accelerate .the drying of the paper, the air which flows over the distant surface of the sheet of paper, that is, the one spaced most distantly from the heated peripheral surface of the drum, is'projected 'by'jets directed from perforated orslotted pipes which are spaced some distance from the path of the moving web.

In all such apparatus with which I am familiar, the

conduits have a fixed spacial-relaperforated or slotted tionship to the peripheral surface ofthe -drum. This is usually between three to six inches from said surface. Experiments have been performed to vary the velocity of said jets, the temperature thereof, and the angle. of incidence of said jets with the opposed surface of the sheet of paper. The greatest difficulty is breaking an overlying stratum of steam or vapor which forms and collects immediately above said sheet and clings to and moves with the upper or outer surface.

This sheathes said sheet and from the sheet as it is produced blankets the flow of vapor 'by the vaporization of the moisturecontent, by the heated drum upon which said sheet is plastered.

The spacial relationship has been dictated by the fact that it has generally been assumedthat it is necessary to retain a substantial working space or clearance because, requently, the sheet being formed; and dried ruptures,

and inasmuch as the sheet is formed and dried'with the sheet moving at high lineal velocity, rupturing of the sheet while it passes through the drier causes it to crumple and mass up in said space. This can lodge so tightly in the space that it produces disruptive pressures and scorchingaof the drum, due to the friction of the massed and crumpled paper as it conduits and rubs against the peripheral surface ofthe drum. In that event, it is necessary to provide some type of device for prying and pulling said massedand crumpled sheet from said space. A minimal distance of three inches has thus been maintained for this purpose.

'Another factor which has limited the proximity of the jets or perforations to the peripheral surface of the drum, the volumes of air impinged and directed over said sheet being dried, and the effective placement of orifices or nozzles is that his necessary that the air carrying off said vaporsmust befree to flow quickly paper being is restrained .by the overlying .eachother.

2,928,185 rtenrea Mar. retrace ice away from said sheet and to be exhausted so as torer'nove moisture from thedrier. Efforts have been made to increase the number of nozzles without restricting thedischarge of said moisture laden air.

I have discovered that I am able to minimize said spacing almost two thirds by arranging jetsapproximately one inch, and in some instances less, from the peripheral surface of the drum and to direct a multiplicity of small size jets at said optimum spacing, which provides an adequate flow of air over said sheet, and to pinpointit at closely spaced intervals to make the carry-off of vapors more effective. I do this by providing a multiplicity' of conduit sections arranged generally parallel totheaxis of rotation of the drum or cylinder and providingeach conduit section with a face that is plane. Insaid plane face which is arranged in opposition'to the peripheral surface of the drtun, I provide a multiplicity of, closely spaced orifices, each carrying a streamlined nozzle through which air or other drying fluid may be directed against the sheet of paper being dried upon said peripheral surface. I arrange a plurality of said conduits in a bank, generally two in number, and each bank is adjustably mounted with respect to the sweep of the peripheral surface of the drum. Said banks may be moved quickly by power means to space said conduits, arranged in bank, from the peripheral surface, so that access may be had in case of breakage and wadding up of a sheetof dried. I have also discovered that this retraction ofthe jets from close proximity to the peripheral surface of'the drum, and to the sheet carried thereby, may be done automatically by providing sensing devices which produce said retraction immediately following a break or rupture of the sheet, so as to provide a substantially greater .working clearance. ance may be had ina matter of seconds.

For example, eight inches of clear- By providing such additional space,'the machine maybe stopped before damage is doneeither by production of wedging pressures or by scorching produced by friction ofthe wad of paper against the peripheral surface of the drum.

Other and important objects of my invention'are:

(1) To arrange nozzles inithe conduits so that the dischargeapertures of said nozzles are in close proximity to the sheet of paper and are in closely spaced pattern, so that the impingement of the air upon the sheet of paper will pierce the overlying stratum of vapor which. normally overlies the sheet and flows therewith, and thus break up said stratum and carry it away with the drying air and thus eliminate the blanketing effect of said stratum. i 5

, (2) Producing a plurality of closely spaced "impact jets directed downwardly upon said sheet of paper with pinpoint effect and in generally uniform pattern which overlies the entire area of the sheet of. paper over which air is flowed. This not only aids the drying ofa sheet of paper stock, but also produces a hold-downeifect to said sheetto augment the so-called plastering of, said sheet produced by surface tension of themoisturecon tent upon the surface of the drum, or to supplant it if said surface tension is relaxed; v

, (3) To perform these effects without increasing the number of hot air conduits. and without conversely decreasing the areaof the passageways necessary'tolaccommodate discharge of'vapor laden air from the drier.

deflected by impact with the surface of the sheet of paper and as they mushroom over the sheet. and collide with ,(i) It argues .sqaztew 'su smal 291; a the will produce high velocity directed flow, but which nozzles in total will permithigh quantitative flow of air .pr ether drying .fluid -without increasing the power re- ,gui merits of the blower system for flowing said air through saideonduitsand over said sheet.

(6) To provide a patterned flow of air or other drying flnid .from said nozzles which discharge close to said sheet, impinge ,upon it at high velocity, and yet which iinzzles are retractable quickly to provide access to the ispaee adjacent said sheet-in case of breakage or other fifl i i (7, To provide ready adjustment of said conduits and the nozzles carried thereby, so as to vary the spacing of ghe ischargefoutlets of said nozzles with relation to said 3. r b n d ed 8.) To proyide quick acting power means for retracting-said nozzles and automatic sensing and operating :devi'c for quickly enlarging the space adjacent the pery of the drum or cylinder to prevent damage to the .dri r- {These and other-features ofrmy invention, the operation ther eof, and the results that flow therefrom are e1nafterdescribedin greater detail with reference to accompanying drawings, in which: i

, ig. 1 isan end elevation of a machine embodying my in, cation, shown somewhat diagrammatically with respect {in the ducts through which drying air flows thereto;

Fig. 2 is ,a foreshortened elevation of said machine,

' showing somewhat diagrammatically the ducts for supplying air to the hood and nozzles arranged therein;

Fig. 3 is ;an enlarged sectional detail view, showing -;sornewhatdiagrammatically .the nozzles, the jets of dryingair emitted therefrom, and the path of flow of said air glgwnwardlyi toward a sheet of paper, mushrooming thereoyer, and the production of turbulence induced by im- -p act: of saidmushroomin'gjets with respect tceach other it) :p dduce ntermediate impingement against a sheet-of paperrand theproduction of an increased number of pressure points upon saidsheet of paper;

fig. 4 is 'a'graphicshowing of test data, illustrating the relative. amplitude of the pressure points and their locations with respect to the jets from the nozzles and the intermediate. pressure points developed by collision of the spreadingair between the jets to produce turbulence nhddownward pressure upon the sheet of stock;

Fig. 5 .is a plan view of a plane face of a conduit secationiembodying my invention, showing the pattern of nozzles therein arranged in closely spaced arrangement over the plane surface. of said conduit, which surface lies in close proximity to the perpheral surface of the drum ;,or drying'cylinder;

Fig. 6 is a somewhat schematic view of the path of the jets of 'Iairas they impinge against the sheet of paper, mushroom thcreover,'and impinge against each other to produce the intermediate pressure points between jets, as is-rillustrated in Fig. 4, said section being taken on the line 6 -6 in Fig. 4; and Fig. 7' is adiagrammatic illustration of the sensing devices, controls and operating mechanism by which said seaming-in plural banks may be retracted in case of breakage of the sheet 'of stock, or otherwise.

invention is illustratedin connection with a machine which comprises a structural frame I mounted n a foundation 2. Within said frame is a rotatable i or'cylindef 3, over whose peripheral surface 3a eet of.material 4 is carried and is dried.

Said drum is hollow and is supplied with steam or other heating fluid through a conduit 5 entering the drum s1.1b s tantially atthe axis of rotation thereof. A hood .6 .o erlies approximately 180 degrees of said peripheral filtfeQq as is. shown inFig. 1. Intake conduits 7-'-7a QQmmUhiCate withthe interior of said hood and carry heating air into said hood.' Said conduits are bo ne ssence with adjustable couplings 8 to accommodate movement.

of said conduits reward"and"mayhem."ss'idursfiifss will hereinafter be described The air inflow conduits 77a are more or less diagrammatically illustrated in Fig. 2 and supply air to the two sides 6a of said hood.

A multiplicity of longitudinal jetting conduits 10 extend between the two sides of the hood. To facilitate assembly of said jet conduits'with the hood sides, I preferably arrange short .sections of conduitob upon the interfaces of said sides 6a and they terminate in flanges 6c. The jetting conduits are similarly flanged, and the flanges are used tojoin the jetting conduits between a pair of aligned'short sections 6b in the manner illustrated in Fig. 1. It is usual to join these'by studs-or bolts to facilitate repair and replacement. Air thus flows into said jetting conduits from both ends thereof. This is desirablebut not essential, but I have found that this produces suflicient volumes of air for the purpose intended and more uniform jet velocity over the entire portion of the drum and the sheet carried thereby to promote uniform drying of the latter. It is common .to heat the air flowing in through the conduits 9a under most conditions, and thus 'a heater is provided (not shown) for heating the air thus applied. Conventional practices may be observed to recirculate air and the eflicient utilization of the heat thus supplied to the drying air.

To aid in the retraction of said conduits and the jetting conduits carried thereby, I preferably support and join said conduits in two or more banks, as is illustrated in Fig. 2; thatis, one bank lies to one side of the centerline of said figure and the other bank lies at the opposite side thereof. Each bank of conduits is provided with parallel guides 1111a which are fixed to the structural frame 1. Rollers 12-12a engage the guides 11 11a, respectively, and each of said rollers is carried by its bank of conduits at each end thereof. That is to .say, one set of guides 11-11a lies at the end of a bank facing the viewer in .Fig. 2, and a companion set is arranged at the oposite end. A beam 1?: extends inter- -mediate the'ways of guide 11 and spans the entire length of the conduits togive structural strength and rigidity thereto. Pairs of power cylinders 1414a aligned with the guides 11 have their pistons 1515a joined to said beam at its opposite ends by means of piston rods 16-16a and connecting links 17--17a. The connecting links join the cylinder through' pad eyes 18.

In order that both banks of conduits will be retracted uniformly and the ends of each bank will be lifted equally, I join the pistons 15-154: by a shaft 19' which is rotated by connection with the pistons 17-1711, as is illustrated in Fig. 1. Intermediate the connection of said shaft with the cylinders, vI arrange a pairof arms 20, links v21 .andpad eyes 22. Thus, as the shaft 19 turns back and forth,.it will swing the pairs of arms secured thereto equal radial swings and will pick up and return each of the conduit banks equally and uniformly.

' Said banks of conduits carry the jetting conduits, as has been described, and thus when the banks of conduits are arranged as illustrated in Fig. 1, it is necessary that the conduits occupy. a correct spacial relationship with regard to the peripheral surface 3a of the rotatable drum.

This is accomplished by providing an adjusting screw 1duitsj that is, there are four adjusting screws, two of which engage the beam on the left hand bank of conduits, one' at each end, "anda similar arrangement is provided {for the right hand conduits,

lies viewed in Fig. 1 ,th'e'drum' or cylinder 3--rotates irra counterclockwise direction, as is indicated by arrows. The sheet of material 4 overlies the peripheral surface 3 a,thereof,and thus the paper enters at the lower right handfside of said figure and is-discharged at the lower left hand side. Supported by the guide 11a at said right hand side which forms a part of the fixed framework of the machine is a feeler or sensing device 25. It has a riding arm 25a which rests lightly upon the sheet of material and which is carriedalong by the drum. If said sheet of material breaks, the feeler or sensing device is tripped to cause the power cylinders to lift the jetting conduits more or less radially from the drum a distance of about eight inches, so as to provide a large working clearancebetweenthe peripheral surface of the drum andthe most closely adjacent surfaces of the jetting conduits 10. I have illustrated this somewhat diagrammatically in Fig. 7.1 1 1 e It is to be understood that the feeler or sensing .de-

, vice 25 and itsriding arm 25a is only exemplary'of any type of sensing device. The ultimate end which I have in mind is to provide a device which will sense a break or rupture in the sheet of material 4. This may be mechanical-electrical, as is illustrated and described, or it might be photoelectric in which the presence of the uninterrupted sheet of material intercepts the beam, and when said. sheet is broken, the maintenance of the beam will actuate the means for moving the jetting conduits 10 and their nozzles away from the peripheral surface of the drum in order to provide the desired clearance. The feeler or sensing device also might bear upon a span of paper'as it is discharged from the roller rather than to sense it at the point of entry of the moist stock under the hood. The advantage of the location selected and illustrated, however, is that it is at this point that any massing or crumpling of paper would be initiated, in all probabilities, and as the paper, following a break, would tend to mass up at this point and would produce pressure which'would be sensed by and transmitted to the operating mechanism, which would respond to the emergency condition thus created and the parts would be rapidly separated before damage occurred.

. As is shown in Fig. 7, the feeler or sensing device actuates a switch 26 in'thecontrol circuit 27. The actuation of said switch operates a hydraulicjvalve 28 by means of a solenoid 29 to supply fluid through the conduit system 30 to all four powercylinders 14-14a. The actuation; of said, cylinders causes the bank of conduits to be-quickly lifted, that is, retracted from the drum, as-hasbeen described. Said jetting conduits are quite massive and will return by gravity to the position they occupy in Fig. 1 when the sensing device 25 is returned into bearing relationship withthe sheet of material. I preferably provide a main control switch 31 in the electrical control circuit 27. Said main control switch or other control element can make the operation and retraction of said parts manual rather than automatic and also provide a safety factor for holding the parts spaced apart, if such is desirable. Referring now to Figs. 3 and 4: v

It is desirable thatthe face wall 32 of each of the conduits 10 ffOllOW generally the sweep of the peripheral surface 3a of the rotatable drum. Thus, said conduits 10 are arranged generally in acircular course surrounding and facing said peripheral surface, as is shown in Fig. 1. .Said conduits preferably are of rectangular section, as is shown in said figure, and in a typical installation said conduits are approximately twelve inches deep: They extend-the full width of, the paper, as is indicated in Fig.2.

Machines generally accommodate sheets of paper stock from about eight feet wide to about twenty feet wide, and thus each of the conduits 10 is of corresponding length.

.I-have-found-that I getthebest results byproviding nozzles 33, each having a discharge aperturepfqaboutoneover the surface of the sheet of paper.

each nozzle and they descend. quite sharply.

quarter inch, the nozzles being three-quarter's inch long. They preferably are of the reentrant type, that is, they lie inwardly of the face wall 32 "and terminate the exterior face of wall 32. I have found that nozzles of streamlined contour operate most efliciently. In alludrying machines with which I am familiar, in which air is directed by jets over a surface of a sheet to be dried, the apertures or discharge nozzles have either. been perforations through the wall of the conduit, or standrad mouth pieces, or else they have been reentrant tube discharge outlets or examples of Bordas mouthpiece. A Borda mouthpiece is one in which the reentrant'tube is of cylindrical form and is half as long as the diameter of the orifice. The reentrant tubes haveextended inwardly from the face fo the conduit a distance two or three times the diameter ofv the orifice. With a Borda mouthpiece, high velocities are attainable'on the order of an empirical scale of about 99', but the quantitative flowv is on the order of 54 onra similar scale. The reason is that the Borda mouthpiece contracts the jet as it flows over the relatively sharp entrance edge, which substantially restricts the volume to produce the higher velocity. On the other hand, a reentrant tube two .or 'three timesas long as the diameterof the orifice cuts down the velocity to about 72 on 'said scale and has a quantitave flow of about 72. i

I have discovered by measurement and test that with a bell-shaped reentrant tube of streamlinedcontour such as is illustrated in Fig. 3, the velocity is maintained at about 96 on said scale and the quantitative flow is about 96. Thus, jets of high velocity are emitted and there is little restriction to flow through the orifice. The emitted jet also seems to hold its cylindrical pattern or cross sec; tion better than one emitted by either of the other two orifices. That is to say, the angle of divergence seems slight, and thus the entire jet of air is directed throughspread out and mushroom and sweep over the surface of said paper. This is graphically shown'in Fig. 4.

The peaks x underlie the axis of the jet emitted from Lying intermediate said peaks are ones of lower amplitude y which develop when nozzles one-quarter inch in discharge aperture size, three-quarters inch long, belled as is shown, and

spaced apart one and a quarter inches apart are arranged approximately one inch away from the upper surface of a sheet of paper to be dried. I am unable to explain definitely why these intermediate peaks occur, but they do. It seems logical to suppose, as is illustrated diagrammatically in Fig. 3, that they are produced by the impinging of adjacent mushrooming jets as the jets flow They likewise rise and fall sharply. In said test, air velocities were maintained slightly above 13,000 feet per minute. When vthe spacing is increased above one inch, said intermediate peaks rapidly diminish and flatten out, and this is likewise true when a spacing of the nozzle to the paper is less than one-half inch. The amplitude of the major peaks xincreases substantially at the smaller spacing, but the intermediate peaks do not occur. This is critical between an orifice spacingfrom the sheet of from one-half inch to two inches and with jets having outlet diameters of from three-sixteenths inch to one-half inch -at -the attained velocities. I believe this to be an important factor in the efliclent drying of paper because the production of these numerous pressure points or applications of impact air to the sheet produces more rapid drying of said sheet.

My experience, further, has been that when an optimum relationship such as described is maintained, there is a substantially less tendency to rupture the sheet of paper being dried than previously. Certainly, the pressure a generated by said numerous impact points would tend to hold the sheet to the surface of the drum -more securely than li -they were not of the-attained amplitude and pattern. Nomial-l-y, .the,;paper I1's" plastered* to the peripheral surface of :the .drum :by the surface tension ,of the water content ofthe sheet where :itlies as ,-a film between the opposed .surfaces of the sheet and the drum. If the sheet dries .too rapidly at "the interface and said water film is .vaporized unevenly, the uniform surface tension is relaxed .andthe paper vtends to blow Off the peripheral surface f .the drum.

' The presence of the plurality of pressure points, say three-.fourthsinch apartover the entire area, would tend to :provide some force greater than a generally elevated air pressure'extending over the sheet, to preventdislodgment .of .the sheet from the peripheral surface of the drum. In anyevent, inmy experience, the rupturingof the sheet and the consequent stopping of the machine has beenmaterially diminished when .my invention has been .used, and my observation of the factors involved :leads .me' to the conclusion that this is produced by the uniform pattern of closely spaced pressure points over the entire sheet of. ;paper :being dried .under' the air hood.

:Infig. 6, Ihave shown somewhat schematically the flow lines producedwhen-a jet strikes the surfaceof the paper, which is arranged substantially normal to the jet, as isillustrated. The outward -flow orsplatter over the sheet of paper .quickly strikes the opposed outward flow from adjacent jets and the splatter produced by collision .with adjacent jets. The impact of two of said jets moving .in :opposite directions and of approximately equal .velocities wouldproduce a .downwardfiow, or at least a downward component ,of force, against the surface of the paper. This is evidenced by graphs developed bynumerfous tests. In other .words, said'midpoints y shown on the graphzinFig. .4 .do occur routinely, and it is for the reason, I believe, that I have just described.

Said peaks are developed by impact of the jets upon asurface of theisheet of stock being dried. They are of relatively high amplitude and tend topierce the stratum of .vapor which is possibly a thousandths or two-thousandths of an inch in thickness. Said stratum is developed by the heat of the drum in the paper stock, and

tends .to blanket the stock and to inhibit the outward flow of following vaporous moisture from the stock. By piercing this blanket in numerous places and sweeping it ina turbulent flow from proximity with a sheet of stock, I eliminate said blanketing influence and ac tolerate the rate at which vapor is absorbed by the air and carried out of the drier and, correspondingly, increase the :rate at which the stock is dried. As'has been point out, the sum of the number of peaks x and y is double that of the nozzles in each row and is augmented between successive'rows. Thus, with the-same number of nozzles or orifices, the pressure points are patterned more closely and are increased substantially 'in'number without the addition of other nozzles, which was heretofore considered necessary.

The provisionof bell-shaped reentrant tubes, or socalled streamlined contour nozzles, permits the orifices of the several nozzles to be diminished in diameter and the number of nozzles to be increased without correspondingly decreasing the volume of flow of air through said nozzles. This permits me to use nozzles of from three-sixteenths inch to approximately one-half inch diameter rather'than from five-eighths inch to one inch in diameteiy -as was previously done. I believe this to be a matter of consequence because resistance to fiow through an aperture is substantially inversely in proportiontoithe square of area of the aperture. Thus, when apertures one-half inch in diameter are used rather than those of one inch in diameter, the area of said apertures is diminished three quarters. When air-is forced through an aperture one-quarter inch in diam- 'cter, ithas a'cross'sectional'area of only one-sixteenth that 'ofan inch diameter aperture. The volume of air whichnecessarily must be flowed through driers 'of this %type and'capacity=require blowers of largesize to be erupts io csa s zb m anss t am 2. ili-i I91 Q0Ji-P- It i thusss snt a tha -.theai W rpugsa dp rtu e at hi h e oc ty and minim m es ri t cn p i u a y a a as yq me ric flow is concerned. Said bell-shaped reentrant tubes or streamlined orifices perform this function well and produce @jetshaving the desirable characteristics vto which I have hereinabove referred. 1

I .have not illustrated the encompassing hoodtoriroom into which the discharged moisture laden airflows from the hood becausethis .is more or less conventional-andis well ;known in the art. In any event, this air is-sometimes wholly wasted to the atmosphere, sometimes-wholly recirculated, and at other times it isintermixed with proportionate make-up air and returned to the machine '1. A paper-making machine for drying a continuous sheet of material directed .over the peripheral surface of a rotatable drum which is maintained at a temperature substantially above atmospheric, comprising a hollow hood member partially encircling the :periphery of said drum, means for directing air under pressure ;;to the .interior .of said hood, a series of longitudinally disposed conduits arranged in a circular sweep generally concentric with the'peripheral surface of said'drum, and streamlinedbore bell-shaped nozzles arrangedin each of said conduits and having discharge outlets directed toward the peripheral surface of said drum, where the nozzle:diameter is less than approximately one-half inch, the nozzles are spaced less than approximately two and .one-half inches apart, and said nozzles terminate less than approximately two inches from the drum surface.

2. A paper-making machine for drying a continuous sheet of material directed over the peripheral surface of a rotatable drum which is maintained at a temperature substantially above atmospheric, comprising a hollow hood member partially encircling the periphery of said drum, means for directing air under pressure to -the.interior of said hood, a series of longitudinally disposed conduits each having a wall arranged in a circular sweep generally concentric with the peripheral surface of said drum, and reentrant-type streamlined-bore bell-shaped nozzles arranged in each of said conduits and having discharge-outlets terminating at the exterior face of said wall and directed toward the peripheral surface of said drum, where the nozzle diameter is less than approximately one-half inch, the nozzles are spaced less than approximately two and one-half inches apart, and :said

nozzles terminate less than approximately two inches' of a rotatable drum which is maintained at a temperature substantially above atmospheric, comprising a hollow hood member partially encircling the periphery of said drum, means for directing air under pressure to the interior of said hood, a series of longitudinally disposed conduits each having a wall arranged in acircular sweep generally concentric with the peripheral surface of said drum, each of said conduits having a generally plane exterior face carrying a plurality of equidistant rows of nozzles including a plurality of nozzles spaced a predetermined distance apart in each row and terminating at-the exterior face of said wall, where the nozzles are less than one inch in diameter, are spaced apart in each row less than approximately two inches and terminate less than approximately two inches from the drum-surface.

4. Claim 3 modified inthat said nozzles-are less than ones-halfinch in diameter-and arespaced apart from adjacent nozz es a distance lessthan twoinchesf aud morc thanone-half inch.

5. Claim 3 modified in that said nozzles are less than one-half inch in diameter and are spaced apart from adjacent nozzles a distance less than two inches, and that the discharge outlets of said nozzles are spaced from the peripheral surface of said drum a distance less than two inches, and more than one-half inch.

6. Claim 3 modified in that said nozzles have discharge outlets approximately one-quarter inch in diameter, are spaced approximately one and one-quarter inches from adjacent nozzles over the generally plane face of each conduit, and are spaced from the peripheral surface of web of paper directed over the peripheral surface of a rotatable drum, which drum is maintained at a temperature substantially above atmospheric, comprising a hollow hood member comprising plural units, each unit occupying about 90 of the circumference of said drum, individual means for directing air under pressure to each of said hood units, a conduit carried by each of said hood units into which said means discharges, each conduit having a wall arranged upon a circular sweep generally concentric with and adjacent the peripheral surface of said drum, plural guideways for each of said units delining a path of travel toward and from said drum, which path is substantially radial to the circular sweep of the unit being guided, said pathways thereby diverging with respect to each other, sensing means responsive to web breakage, means activated by said sensing means upon web breakage for moving said plural units simultaneously toward and from said rotatable drum, each along its a rotatable drum which'is maintained at a temperature.

substantially above atmospheric, comprising a hollow hood member above and partially encircling the periphery of said drum, said hood comprising plural sections mounted for movement along diverging substantially radial separate paths, means for directing air under pressure to the interior of said hood, a series of longitudinally disposed conduits arranged in a circular sweep generally concentric with the peripheral surface of said drum,

nozzles arranged in each of said conduits and having dis charge outlets directed toward the peripheral surface of said drum, sensing means responsive to web breakage and operating means activated by said sensing means upon web breakage to lift said nozzles from the peripheral surface of said drum as units to provide access to a space of substantially uniform breadth between the conduits and the peripheral surface of said drurn.

9. Claim 8 modified in that said pressure-sensitive operating means are power actuated.

10. A paper making machine for drying a continuous web of paper directed over the peripheral surface of a rotatable drum, which drum is maintained at a temperature substantially above atmospheric, comprising a hollow hood member comprising plural units, each unit occupying about 90 of the circumference of said drum, individual means for directing air under pressure to each of said hood units, a conduit carried by each of said hood units into which said means discharges, each conduit having a wall arranged upon a circular sweep generally concentric with and adjacent the peripheral surface of said drum, plural guideways for each of said units defining a path of travel toward and from said drum, which path is substantially radial to the circular sweep of the unit being guided, said pathways thereby diverging with respect to each other, sensing means responsive to web breakage, and means activated by said sensing means upon web breakage for moving said plural units simultaneously toward and from said rotatable drum, each along its respective path.

11. A paper making machine for drying a continuous respective path, said means moving each of said head units over a predetermined range of movement along its path between preselected limits.

12. A paper making machine for drying a continuous web of paper directed over the peripheral surface of a rotatable drum, which drum is maintained at a temperature substantially above atmospheric, comprising a hollow hood member comprising plural units, each unit occupying about of the circumference of said drum, individual means for directing air under pressure to each of said hood units, a conduit carried by each of said hood units into which said means discharges, each con- I duit having a wall arranged upon a circular sweep generally concentric with and adjacent the peripheral surface of said drum, plural guideways for each of said units defining a path of travel toward and from said drum, which path is substantially radial to the circular sweep of the unit being guided, said pathways thereby diverging with respect to each other, sensing means responsive to web breakage, and means activated by said sensing means upon web breakage for moving said plural units simultaneously toward and from said rotatable drum, each along its respective path, each conduit wall of a hood unit having nozzles terminating in a common sweep at the surface of said wall adjacent said drum, the means moving said head units a'substantially uniform distance along said path,.thereby to provide access to a I space of substantially uniform breadth between all of the conduit walls and the peripheral surface of said drum.

Germany Sept. 11, 1941

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