US2892263A

US2892263A - Paper machine dryer

Info

Publication number: US2892263A
Application number: US515635A
Authority: US
Inventors: Hornbostel Lloyd
Original assignee: Beloit Iron Works Inc
Current assignee: Beloit Iron Works Inc
Priority date: 1955-06-15
Filing date: 1955-06-15
Publication date: 1959-06-30
Anticipated expiration: 1976-06-30

Description

June 30 1959 HQRNBOSTEL- 2,892,263

' PAPER MACHINE DRYER 2 Sheets-Sheet 1 Filed June 15, 1955 June 30. 1959 L HORNBOSTEL 2,892,263

PAPER MACHINE DRYER 4 2 Sheets-Sheet 2 Filed June 15, 1955 f7 V227 2232'" 40 yo bOPA/BOST'EL fUflitCd S s, Pa en PAPER MACHINE DRYER 5 Lloyd H ornbostel, Beloit, Wis., assignor to Beloit Iron 7 Works, Beloit, Wis., a corporation of Wisconsin Application June 15, 1955, Serial No. 515,635

6 Claims. (Cl. 34120) This/invention relates to an improved apparatus and method for the formation of paper webs, and more particularly, to an improved paper making machine of the type generally referred to as a Yankee Dryer machine and an improved method of treating a paper web therein.

" As a rule, machine glazed papers are made in a Yankee dryer niachineor Yankee machine; and such a machine may have a cylinder or Fourdrinier wet end and it may also have a number of presses or auxiliary dryers of thetusual type. The characteristic feature of the Yankee machine is the large Yankee dryer drum, having a diameter of from about nine feet to about fifteen feet, that is made of cast iron or steel and has a very high polish imparted to the outside cylindrical surface. 'Soft material, such as a paper web, will develop a fine glazed,

smooth surface if it is pressed against the heated finely polished dryer drum surface during the drying of the web. There are certain limitations or difiiculties in con: nection with the operation of machines of this type, however. 1 If the paper contains too little moisture when it comes in contact with the dryer drum, often it will not too Wet for use with a dryer drum maintained at the conventional dryer drum temperatures. In general, the temperature of the dryer drum must be carefully controlled, since it must be cool enough to take thepaper from the felt at the initial transfer nip and it must be hot. enough to dry the paper in about three-quarters of a revolution of the dryer drum. ,If the capacity of the machine was to be increased heretofore, presses had to be' positioned ahead of the dryer drum; but this was not a complete solution to the problem, since it is necessary to havea certain amount of moisture in the paper web when and this moisture must be removed while the web is moving on the dryer drum. Since the maximumtempera ture of the dryer drum is limited by the necessity .for. having a cool enough temperature to permit initial pickup of the wet web, the total amount of moisture which may be driven out of the web by the heat from the dryer drum is limited and the capacity or operating'speed is limited, accordingly. v V

The instant invention provides a unique answer to the 30 problems heretofore involved in the operation 'of Yankee machines. In accordance with the teachings of the instant invention, a plurality of successive Yankee dryer" drums are mountedin a paper machine, so as to permit partial casting of the Web on the first of such drums to 65 receive the web and final casting of the Web on the last of such drums to receive the Web. By this arrangement, the

first drum to receive the web can be operated at less than the conventional dryer drum temperature, if desired, so as to pickup a wetter web than could ordinarily be cast 7 on conventional Yankee dryer drums, and only partial drying of such web is accomplished on the first drum. Successsive drums may be employed in like manner or only a second drum may be employed. The last drum in the machine must, however, receive the web in wet enough condition to adhere to the drum surface and effect casting thereof on such drum surface; but it has been found that the moisture content of the web thus used can be much less than the moisture content of the web that is cast onto a single Yankee dryer drum in conventional operation.

It is, therefore, an important object of the instant invention to provide an improved paper machine and an improved method of making paper. 7

It is a further objectof the instant invention to provide an improved method of drying paper that comprises casta ing the web onto a first smoothly polished heated travelretaining the web thereon until it is dewatered to 93-95% dryness, the same side of the web being cast against both said travelling surfaces.

Still another object of the instant invention is to provide an improved paper machine section for drying a wet Web that comprises a pluralityof successive Yankee dryer drums, a looped felt extending between a pair of such drums receiving the wet Web from the first of the pair and guiding the web to the second of the pair, and a press roll within the loop of said felt defining a nip with the second drum to effect transfer of the web to the surface of said second drum.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure of preferred embodiments thereof and the attached drawings which are made a part hereof.

On the drawings:

Figure 1 is essentially a diagrammatical view of. a"

paper machine showing an embodiment of the instant invention;

Figure 2 is essentially a diagrammatical view of apaper machine showing a fourth embodiment of the instant invention.

As shown in the drawings:

In Figure l, the press and dryer section of a paper machine, indicated generally by the reference numeral 10, is shown comprising a first Yankee dryer drum 11, a first press roll 12 defining a first nip N-13 with the underside of the first drum 11, a first felt 14 running through the first nip N-l3 for effecting transfer of a wet web W thereat onto the first drum 11, a suction pickup roll 15 (with the suction area at 15a) lapped by the first felt 14 transferring the web W from a travelling surface (in this case a travelling forming wire F trained over a suction couch roll 16 and a turning roll 17), the suction pickup roll 15 transferring the web W from the travelling surface F onto the first felt 14, a second Yankee dryer drum 18, a second press roll 19 defining a second nip N-20 with the underside of the second drum 18, and a second felt 21 running from adjacent the first drum ll through the second nip N-20 to receive the web W from the first drum 11 and transfer the web W to the second drum 18 at the second nip N-20.

As. is indicated diagrammatically, the first Yankee having suitable heating means, as indicated by a source of steam 22 connected by suitable lines 23 leading through a hollow trunnion or axle 24 to the interior of the drum 11, which is also provided with a suitable drain line 25 leading to the drain 26 to remove condensate. All of the Yankee dryer drums indicated in Figures 1-4, inclusive, are provided with comparable heating means (not shown) 'as is conventional with the Yankee dryer drum. Also, all of the Yankee dryer drums shown in the instant drawings have smooth polished surfaces suitable for casting the web thereon; and these various Yankee dryer drums 11, 18, etc. may be of different sizes (or diameters) to suit the particular designer, although the drums will all be of substantial size, much greater in diameter than the ordinary press roll, for example. These sizes are in the range of about nine feet to about fifteen feet in diameter.

The first felt 14 is a looped felt trained about a plurality of

guide rolls

27, 28, 29. and 30; and as indicated the suction pickup roll and the first press roll 12 are within the loop of the first felt 14. The transfer of the web W is accomplished at the first nip N-13 between the first drum 11 and the first press roll 12, which preferably has asuction area 12a at the oncoming side of the nip N-13 to assist in dewatering of the web W at the first nip N-13 just prior to casting of the web W onto the polished surface of the drum 11. Press rolls (not shown) may also be associated with the first felt 14 to assist in dewatering of the web before it reaches the first nip N-13. For example, the suction pickup roll 15 could be a suction press roll and it could accomplish the transfer of the web W from another felt (not shown) rather than the specific travelling surface here shown, namely, the wire F.

As is indicated, the felt covered first press roll 12 transfers the web W to the uprunning underside of the Yankee dryer drum 11 at the nip N-13 in the conventional manner of casting a web on a dryer drum. The web W is carried along on the surface of the first dryer drum 11 over the top thereof and most of the way down on the downrunning side ofthe drum 11 Whereat the Web is finally removed from the surface of the drum 11. In certain instances (which will be explained hereinafter) the web may fall free from the surface of the drum 11- to be received by the second felt 21, or means may be provided to assist the second felt 21 in receiving the web W' from the first drum 11. As shown in Figure 1, in the case of the dryer drum 11 having a highly polished metal surface (which is wetted by water in the web W), it is preferable to employ a doctor 31 on the downrunning side of the first drum 11 to remove the web therefrom and transfer the web W to the second felt 21. A third felt 32 may also be provided beneath. the bottom run 21a of the second felt 21 for initially receiving the web W from the first drum 11 (as it is removed from the drum surface by the doctor 31) for transfer of the web W to the second felt 21. The third felt 32 urges the web W against the underside of the bottom run 21a of the second felt, so as to assist in supporting the webW (although the second felt 21 could be used alone to guide the web W in its travel) and also to assist in smoothing out the web W. The first dryer 11, as mentioned, has a rather substantial drying area (and it maybe of any dryer drum size up to perhaps twelve feet or overin. diameter depending upon the operating speed and steam pressure available for the machine), but it is important that complete drying should not bev accomplished on the dryer drum 11. The precise extent of drying which should be accomplished on the dryer drum 11 will bev discussed, hereinafter, but it is sufiicient to note that the web W is still fairly wet when. it is taken away from. the; downrunning side of the dryer 11. This perrnits thev use ofa very sharp creping doctor 31' which may be. used to put a minimum of crepe in the web W. A sharp.

doctor 31 may be used because of the moisture content 75 be undesirable smoothing of both sidesof the web);

I of the web W which will cool the same so as to avoid burning which might take place using such a sharp doctor for dry creping. The sharpness of the doctor minimizes the creping of the paper and what little crepe, if any, that is put into the paper is pulled out in the draw between the bottom run 21a of the second felt and the top run 32a of the third felt, thus leaving a reasonably smooth finish on the web and enough moisture in the web to permit adherence of the web. to the surface of the second dryer 18. As shown, the second felt 21, passes over

guide rolls

33, 34 and 35 and it is a looped felt running over the guide roll 35 adjacent the drum 11 and, back through the nip N-20 defined by the second press roll 19 within the loop of the second felt 21 and having preferably a suction area 19a at the oncoming side of the nip N-20 to assist to a limited extend in further dewatering of the web W. Because the web W is quite dry by the time it reaches the nip N-20 (in the neighborhood of 50-70% dryness) only a relatively minor amount of dewatering can be accomplished at the nip N-20 by mechanical means.

The web W is cast onto the surface of the dryer drum 18 at the nip N-20 on the uprunning underside of the drum 18 and the web W passes on around to the downrunning side of the drum 18 (as indicated by the arrow) whereat the web W is taken from the surface of the dryer drum 18. At this point the web may be removed from the dryer drum 18 merely by drawing the,

web away from the surface so as to obtain a smooth web, or the web may be dry creped with a doctor 36', as here shown. Dry creping of the finally dried web (i.e. 93-95% dryness) gives a very soft sheet which is desira; ble for certain purposes. In contrast, substantial creping of the wet web W at the doctor 31 on the first drum 11 may be undesirable for most purposes, since the creped wet web will not cast well on the second drum 1'8 (and glazing as well as drying efiiciency is reduced). Forthis reason the sharp doctor 31 is preferred and also the draw between the second felt 21 and, the third felt 32 is preferred to effect maximum smoothness. The, third felt 32 is mounted on adjustable guide rolls 37 and 38 supporting the upper run 32 thereof so as to adjustably urge the upper run 32 against the lower run 21 of the second felt.

Another conventional arrangement used with Yankee dryer drums may also be used with the instant drums 1-1' and 18. This involves the application of hot air to the exposed surface of the web W on the dryer drums 11- and- 18. Hot air from a suitable source 39' is directed to an arcuate header 40 surrounding a substantial portion of the periphery of the drum 11 carrying the web. W so as to direct streams of hotair against the exposed surface of the web, and the hot air from the source 39 is. also directed to a second header 41 that is arcuate i'n shape surrounding a substantial portion of the periphery of the second drum 18 carrying the web W so as to direct a multiplicity of streams of hot air against the exposed surface of the web W. It will further be noted a that the exposed surface of the web W is the same on both. the dryer drums 11 and 18 and the cast side of the paper web Wis also the same on both dryer drums- 11 and: 18. The: net effect of this is to provide aYankee machine in which the flexibility of operation is increased and also the actualjcapacity. is increased whilestill producing a papersheet of the type which is obtained on. a single Yankee dryer drum machine. The advantages: in texture that are obtained by casting on only one sideofa web and keeping the other side open during, the entire drying operation are thus obtained in a machine of increased capacity. It will be notedthat the instant. machine affords numerous advantages in this respect. The increased dryer drum capacity avoids the necessity for using additional dewatering press assemblies which; may tend to crush the web (and also to effect What may The instantmachine affords the advantage that press ing of'the web W takes place only at the nips N-13 and N-20 and such pressing, if desired, need be only the amount necessary to effect transfer of the web W and not necessarily crushing of the web W. The first felt 14 may be used to effect direct pickup from the forming surface F and immediate transfer to a dryer drum surface, on the drum 11. The second felt 21 minimizes the open draw of the web between the drums 11 and 18 by extending from adjacent the drum 11 to the drum 18 and guiding the web W therebetween. In another embodiment of the'instant invention (shown in Figure 4) it will be seen that the open draw can be eliminated completely. And it will be noted that the second felt 21 contacts the open and not the smoothed or cast side of the web W in effecting transfer of the same. As previously indicated the third felt 32 may be omitted so that no felts or rolls engage the smoothed or cast surface of the web from the first nip N-13 until the web W is completely dry. If a third felt 32 is used, it is preferably made of very fine wool; and the first and second felts 14, 21 are also preferably made of a fine wool.

Referring now to Figure 2, wherein elements shown that have functions comparable to elements in Figure 1 are indicated by corresponding reference numerals in the 100 series, it will be noted that the paper machine 100 comprises a first Yankee dryer drum 111, first press roll 112 defining a first nip N-113 with the underside of the first drum 111, a first felt 114 (on guide rolls 127, 128, 129 and 130) running through the first nip N-113 for effecting transfer of the wet web W thereat onto the first drum 111, a suction pickup roll 115 (with the suction area 115a) lapped by the first felt 114 transferring'the web from a travelling surface F onto the first felt 114, the travelling surface F being a forming wire trained over a suction couch roll 116 and a turning roll 117, a second Yankee dryer drum 118, a second press roll 119 defining a second. nip N-120 with the underside of the second drum 118, a second felt 121 (on guide rolls 133, 134 and 135) running from adjacent the first drum 111 through the second nip N-120- to receive the Web W from the first drum 111 and transfer the web to the second drum 118 at the second nip N-120, a third felt 132 beneath the second felt 121 urging the web W against the underside of the second felt 121, and a doctor 131 on the downrunning side of the first drum 111 removing therweb -W' therefrom to transfer the web W to the secondfelt 121, via the third felt 132 (mounted on adjustable guide rolls 137 and 138). The first and second press rolls 112 and 119 also preferably have suction areas 112a and 119a at the oncoming side of their respective nips N-113 and N-120. A doctor 136 is also preferably used to remove the web W from the downrunning side of the second dryer drum 118 and to dry crepe the web W.

The instant machine 100 is an arrangement which affords adequate drying in a Yankee machine using a minimum size first Yankee dryer drum 111. Larger sized dryer drums could, of course, be used in this arrangement, but an advantage of the arrangement is that it permits the use of a minimum size dryer drum 111, by incorporating in the device a felt covered third press roll 150 defining a nip N-151 with the first drum 111 (above the nip N-113 and the doctor 131) so as to eifectdewatering of the web W on the surface of the first drum. 111. The press roll 150 preferably has a suction area 150a which is lapped by a fine wool press felt 152 mounted on guide rolls 153, 154, 155 and 156.

The machine 100 preferably also includes a first press 157 defined by an upper press roll 158 (with the suction area 158a within the loop of the first felt 114) and a lower press roll 159 covered by a felt 160 trained over guide rolls 161 and 162. The first press 157 assists in dewatering of the web W as it is carried by the first felt 114 to the first nip,N-113 and this also reduces the amountof preliminary drying which the dry er drum 111 must carry out. The felt covered press roll 150 in nip defining relationship with the first dryer drum 111 also reduces the amount of drying which the dryer drum 111 must carry out.

Referring to Figure 3, wherein elements having functions comparable to elements previously disclosed have corresponding reference numerals in the 200 series, it will be seen that the paper machine 200 of Figure 3 comprises a first Yankee dryer drum 211, a first press roll 212 defining a first nip N-213 with the underside of the first drum 211, a first felt 214 running through the first nip N-213 for effecting transfer of the wet Web W" thereat onto the first drum 211, a second Yankee dryer drum 218, a second press roll 219 defining a second nip N-220 with the underside of the second drum 218, a second felt 270 running through the second nip N220, and means receiving the web W" from the first drum 211 and transferring the web W'-' to the second felt 270 for transfer therefrom to the second drum 218 at the second nip N-220', said means being in the form of a third felt 232 (mounted on adjustable guide rolls 237 and 238) and a guide roll 271 adjacent the first drum 211 for assisting in directing the web W onto the upper run 232a of the third felt 232, plus a turning roll 272 at the other end of the upper felt run 232a adjacent the second drum 218 for turning the web W" upwardly onto the second felt 270 (which is mounted on guide rolls 273, 274 and 275).

In Figure 3, a forming wire F is shown in its entirety with a suitable suction couch roll 216, a turning roll 217, guide rolls 276, 277 and 278 and breast roll 279. A suction pickup roll 215, with the suction area 215a, is lapped by the first felt 214 and the suction pickup roll 215 picks up the web W" from the forming wire F adjacent the couch roll 216, transferring the web W" to the first felt 214. A first press 257 is also preferably included in the machine 200 and is defined by an upper press roll 258, with suction area 258a, and a lower press roll 259, with suction area 259a, which 'is lapped bya felt 260 mounted on guide rolls 261 and 262. The first press 257 serves to accomplish'initial dewatering of the web W" before drying on a dryer drum surface is commenced. The first press 257 as well as the first press 157 (Figure 2) is used to advantage when, for one reason or another, it may be desirable to have more limited drying capacity in the two dryer drums than is obtained in the arrangement of, for example, Figure l. In the machine of Figure 2, a smaller size Yankee dryer drum 111 is employed to advantage: In the machine 100, the felt covered press roll in nip defining relationship with the first drum 111 may be capable in many cases of accomplishing the necessary dewatering of the web W which is required because of the reduced size of the drum 1.11; but if the felt covered press I011 150 cannot accomplish this necessary dewatering, then the first press 157 can be used to advantage. The first press 157 also affords greater flexibility of operation in themachine 160. i I V In the machine 200, however, the first press 257 may be used to a particular advantage, because it is one of the principal devices for accomplishing mechanical dewater ing in the machine 200; In the machine 200, the first drum 211 has a hydrophobe surface 211a in the form of a layer or coating covering the drum surface (or defining the casting surface) made of a hydrophobe (Le. a material that is not wetted by water). Materials of this type include rubber or other natural or synthetic plastic resins or elastomers; most preferably polytetrafiuoroethylene (Teflon) or similar heat resistant materials are used, because the material must be able to stand up under the operating temperatures of approximately 200 F. at which the dryer drum surface is maintained. Because the heat resistant hydrophobe coatings, such as polytetrafluoroethylene, are not very goodheat conductors, the coatings are applied in as thin a layer as possible. The advantage of using a hydrophobe surface on the first drum 211 is that it permits ready release of the partially dried web W on the downrunning side of the drum 211.

In the use of a drum such as the drum 211, it is also preferable to employ a fourth felt 280 that is a very fine wool felt that is lapped over the web W" on the first drum 211 above the, first nip N-213 so as to retain the web, W" on the surface of the first drum 211 on the uprunning side and. to the extent desired on the downrunning side. Suitable guide rolls 281 and 282, respectively, apply the fourth felt 23.0 to the drum 2,11 and remove the felt 280 therefrom. The felt 28!! also assists in effecting controlled e en and slow evaporation of moisture, all of which is absorbed by the, felt 280.. Because of the moisture absorption of the felt 280 a pair of auxiliary dryer drums 283 and 284 are positioned adjacent the drum 211, and guide rolls 285 and 286 train the felt 280 over the dryer drum 28.3, and guide rolls 287 and 288 train the felt over the dryer drum 284 in order to accomplish drying of the felt 280 at spaced intervals during its travel along with the web W" on the surface of the drum 211.

When the guide roll 282 removes the Web 280 from the downrunning side of the drum 211 the web W can be easily stripped from the drum surface, in most instances it can be fed off manually around the turning roll 270 and it will continue to feed off the drum 11 merely on the basis of its own self-supporting strength. The web W" is then carried on the third felt 232 until it is passed around the turning roll 272, onto the second felt 270 and then onto the second drum 218, from which it may ultimately be removed, but preferably is dry creped to the doctor 236. In Figure 4, wherein elements functioning in a man: ner comparable to previously disclosed elements given corresponding reference numerals in the 300 series, it will be seen that the paper machine 300 comprises a first Yankee dryer drum 311, a first press roll 312 (with suction area 312a) defining a first press nip N-313 with the underside of the first drum 311, a first felt 314 running through the first nip N-313 for effecting transfer of the wet web W thereat onto the first drum 311, a second Yankee dryer drum 318, a second press roll 319 defining a second nip N-320 with the underside of the second drum 318, and a second felt 321 extending between the drums 311 and 318and receiving the wet web W from the first drum 311 and guiding the web W to the second drum 318. The second felt .321 is a looped felt (mounted onguide rolls 389, 39,0, 391, 392 and 393) having within its loop the second press roll 319 and also a suction transfer roll 394 defining a nip N-395 with the first drum 311 near the bottom of the downrunning side thereof. The'suction transfer roll 394 has a suction area 394a extending from the nip N-395 down to about the bottom of the roll 394 in order to effect web pickup from the surface ofthe drum 311 and to retain the web W on the second felt 321 as the felt 321 turns on the roll 394. A third felt (not shown) comparable to the

felts

32 and 132 may be used in conjunction with the second felt 321, if desired, but the felt 321 can adequately guide the web W" without the necessity for the third felt in many instances and the instant arrangement affords the advantage that the east side of the web W does not come in contact with anything but the surfaces of the dryer drums once drying has started. In other words, once the web W' has been cast onto the first drum 311 at the nip 181-313, this web W is not engaged on its cast side with any surface other than the surfaces of the

drums

311 and 318, until it is completely dry at which point it may be removed fromthe drum 318 on the downrunning side with or without dry creping using a doctor 336.

'Ihe first drum 311 prefe rably has a hydrophobe layer ngpuntedthereon defining the casting surface thereof, as a .311?! s t fa i at h Wet transfer at the i N-3951 As previously indicated, the hydrophobe layer is polytetrafiuoroethylene. In this arrangement, it is also preferable to. have a fourth very fine wool felt 380 lapped over the web W' on the first drum 311 above the suction transfer roll nip N-395 (and the casting nipv N-.-313.), to. retain the web W on the first drum 311. Guide rolls 381 (on the uprunning side) and 382 (on the downrun: ning side) suitably apply the fourth felt 38.0 to the web. W' and remove the same therefrom. Auxiliary dryers (not shown) may also be used with the fourth felt 380 in the manner described in connection with the machine 200.

Referring to the front end of the machine 300, it will be noted that the forming wire F is mounted in the manner described in connection with Figure 3 on a sue.- tion couch roll 316, turning roll 317, guide rolls 376, 377 and 378 and a breast roll 379. A suction pick p roll 315 with suction area 315a is suitably mounted with: in the loop of the first felt 314 and urged against the forming wire F between the couch roll 316 and the turn-v ing roll 317 to pick up the web W' therefrom and trans: fer the same onto the first felt 314 which is a looped felt (here shown incompletely) mounted on guide rolls such as the

rolls

396 and 397 and passing through the first nip N313. A first press 357 carrying out the same function as the press 257 of Figure 3 may also be used in the machine 300 and this press 357 is defined by an upper suction roll 358 with suction area 358a within the loop of the first felt 314 and a lower suction roll 359 with suc: tion area 359a within the loop of still another felt 3.6. on guide rolls 361 and 362. The press 357 may be used to assist in dewatering and to compensate for less effective heat transfer which may be obtained on the first dryer drum 311 because of the hydrophobe layer 311a. On the other hand, the press 357 may be omitted in instances where a minimum handling of the web W is desired, or at least a minimum mechanical crushing of the web is desired; and in such instance, the W' will pass through only three nips N-313, N-395 and N-320 (in that order) and each of such nips is defined only for purposes of transfer and not necessarily for excessive pressing or crushing of the Web.

In general, the web on the forming surface which is picked up by the suction pickup roll will have a consistency of about 12% (i.e. about 12% of the web is equivalent to the weight of the fibers therein suspended in the aqueous medium, if such fibers are bone dry). The web coming off the forming wire thus has about 12% dryness. Ordinarily the web that is cast onto the surface of a Yankee dryer drum in a single dryer drum machine has a dryness of about 30 to 35% which is made possible by initial pressing of the web after it is removed from the wire. The pickup felt will also assist in dewatering of the web, On the dryer drum of a single dryer drum machine, the web is converted from about 30%' dryness when cast onto the dryer surface to approximately 93 to 95% dryness when removed from the dryer surface. Because of the increased drying capacity afforded by the use of a plurality of dryer drums in the instant invention, the web may be cast onto the first dryer drum at a dryness of as low as 20-25%, if such is desired, and in such instances the dryer drum surface may be maintained at temperatures slightly lower than the conventional temperature of about 200 F. As will be appreciated, the temperature of the dryer drum surface should not be maintained above 212 F., or a layer of steam would be created between the dryer drum surface and the web. The usual temperature is around 200 F. and air is ordinarily removed at the initial casting nip so that the web will be cast cleanly onto the drum surface. The web should have a dryness of at least about 20% in order to be sufliciently integrated to'be retained on the dram surface; and the drum surface of the first drum may be maintained at perhaps 180-190 F. in instancesinvolving' the casting of webs of 20-2 5.% dryness. The dryness of the web should, however, not be increased as high as 70% on the-first dryer drum, or the web will be too dry to be cast onto a second dryer drum. Preferably the web is dried on the first dryer drum to a dryness of at least as much as 50, but not as much as 70%. About 55% dryness is preferred for the dryness of the web that is to be cast onto the last dryer drum in the machine. As will be appreciated, if more than two dryer drums are to be used, the web leaving the next to the last dryer drum and cast upon the last dryer drum should have a dryness of at least 50% but not as much as 70%. The web on each of the other drums in such machine would then have correspondingly less dryness. For present paper machine capacities, two drums are usually enough and the dryness figures just indicated are the figures which should be used in the operation of the two drums.

It will also be appreciated that it is not necessary to cast extremely wet webs on the first dryer drum and, instead, webs of the conventional dryness of 2535% used in a single Yankee dryer drum machine can be cast onto the first drum and, in such situation, pressassemblies before the first drum may be used to create this higher dryness in the web. In such instances, of course, the function of the two or more dryer drums then be comes that of speeding up the operation of the machine so that the machine may operate at a speed much faster than a single dryer drum machine can operate. In such instances, the web cast onto the first dryer drum may have a dryness of 30% and coming off the first dryer drum may have a dryness of 55%. In such instances, also, the surface temperatures of both of the dryer drums would be maintained at the maximum surface temperature of about 200 P. so that maximum drying is accomplished on both dryer drums and the only reason that the dryness of the web is not increased beyond 55% on the first drum (or some other figure below 70%) is that the drum speed is so great that the web does not have adequate time to dry to this extent on the first drum.

In general, it is preferred to operate the second or last dryer drum under conditions which effect maximum drying and the operating conditions for the last dryer drum are thus substantially constant, except the drum speed. The drum speed may be varied in accordance with the amount of drying which is carried out on the first dryer drum with or without the assistance of separate presses or felt wrapped press rolls cooperating with the first drum. The use of separate presses and/or felt lapped press rolls cooperating with the first dryer drum, and/or a suction transfer roll cooperating with the first drum will serve to determine the particular type of paper which is ultimately obtained at the downrunning side of the last dryer rum.

It will be understood that modifications and variations may be efiected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. In a paper machine section for drying a wet Web, a

' first Yankee dryer drum, a first press roll defining a first nip with the underside of said first drum, a first felt running through said first nip for effecting transfer of the wet web thereat onto the first drum, a second Yankee dryer drum, a second press roll refining a second nip with the underside of said second drum, a second felt running from adjacent said first drum through said second nip, a third felt beneath said second felt urging the web against the underside of said second felt, and a doctor on the downrunning side of the first drum removing the web therefrom to transfer the web to said second felt.

2. In a paper machine section for drying a wet web, a first Yankee dryer drum, a first press r011 defining a first nip with the underside of said first drum, a first felt running through said first nip for effecting transfer of the wet web thereat onto the first drum, a suction pickup roll lapped by said first felt transferring the web from a travelling surface onto the first felt, a second Yankee dryer drum, a second press roll defining a second nip with the underside of said second drum, a second felt running from adjacent said first drum through said second nip, a third felt beneath said second felt urging the Web against the underside of said second felt, and a doctor on the downrunning side of the first drum removing the web therefrom to transfer the 'Web to said second felt.

3. In a paper machine section for drying a wet web, a first Yankee dryer dnum, a first press roll defining a first nip with the underside of said first drum, a first felt running through said first nip for effecting transfer of the wet web thereat onto the first drum, a second Yankee dryer drum, a second press roll defining a second nip with the underside of said second drum, a second felt rimning through said second nip, and a third felt beneath said second felt receiving the web from the first drum surface for transfer of the web to the second felt, whereby the web is placed on the second drum at the second nip.

4. In a paper machine section for drying a wet web, a first Yankee dryer drum, a first press roll defining a first nip with the underside of said first drum, a first felt running through said first nip for effecting transfer of the wet web thereat onto the first drum, a second Yankee dryer dnum, a second press roll defining a second nip with the underside of said second drum, a second felt running through said second nip, and means beneath said second felt receiving the web from the first drum surface and transferring the web to said second felt for transfer therefrom to the second drum surface at the second nip.

5. In a paper machine section for drying a wet web, a first Yankee dryer drum, said first drum having a hydro phobe surface engaging the web, a first press roll defining a first nip with the underside of said first drum, a first felt running through said first nip for effecting transfer of the wet web thereat onto the first drum, a second Yankee dryer drum, a second press roll defining a second nip with the underside of said second drum, and a second felt running (from adjacent said first drum through said second nip to receive the web from the first drum and transfer the web to the second drum at said second nip, and means lifting the web from the first drum and placing the web on the underside of the second felt.

6. In a paper machine section for drying a wet web, a first Yankee dryer drum, said first drum having a hydrophobe surface engaging the web, a first pressed roll defining a first nip with the underside of said first drum, a first felt running through said first nip for effecting transfer of the wet web thereat onto the first drum, a second Yankee dryer drum, a second press roll defining a second nip with the underside of said second drum, a second felt running from adjacent said first drum through said second nip to receive the web from the first drum and transfer the web to the second drum at said second nip, and a suction roll within the loop of the second felt lifting the web from the first drum and placing the web on the underside of the second felt.

References Cited in the file of this patent UNITED STATES PATENTS 340,335 Lindsay Apr. 20, 1886 1,167,029 Stickle Jan. 4, 1916 2,433,122 Hornbostel Dec. 23, 1947 FOREIGN PATENTS 233,493 Great Britain. nu. May 14, 1925 769,833 France June 18, 1934