US2484676A - Apparatus for drying paper - Google Patents

Description

Oct. 11, 1949. e. L. BIDWELL APPARATUS FOR DRYING PAPER 2 Sheets-Sheet 1 Filed Nov. 21, 1946 INVENTOR GEORGE l .BlDWEl L.

ATTORNEYS Oct, 11, 1949. e. BIDWELL 9 5 APPARATUS FOR DRYING PAPER Filed Nov. 21, 1946 2 sheets-sheet 2 INVENTOR GEORGE L. BIDWELL BY mu, Ema

ATTORNEYS Patented Oct. 11, 1949 UNITED STATES PATENT OFFICE 6 Claims. 1

This invention relates to the manufacture of paper and more particularly to a novel apparatus for so drying a continuous running paper web as to inhibit lateral shrinkage of the web while it is being dried.

It is an object of the present invention to provide an apparatus for drying a running 'web of paper in such manner as to eifect certain economies in the drying process and at the same time produce an improved product.

Another object of the invention is to provide 1 an apparatus for drying a running paper web that substantially eliminates the lateral shrinkage of such a web that normally occurs when it is dried by conventional means.

It is still another object of the invention to provide an appartaus for drying a paper web that produces paper of more nearly uniform thickness across its width.

Another object of the invention is to provide a transparent paper in which the product has improved uniformity of transparency across the width of the sheet.

A still further object of the invention is to provide an apparatus for drying a paper web to produce a grease proof paper in which the yention is concerned are commonly made by causing a paper stock comprising a pulp suspension to flow on to a moving screen, causing the water of the suspension to flow through the holes in the screen to form a mat or web of fibers on the screen, removing this web from the screen and passing it over heated drying rolls to dry the web, and then passing the dried sheet or web over a series of calender rolls to apply a an apparatus for drying a paper web to produce One of the problems that has been encountered in the operation of such a drier arises out of the fact that there is a tendency for the paper web to shrink as it passes over the drier rolls and water is removed from the web. Since the web is normally under tension inthe direction of its motion, this shrinkage occurs, for the most part, in a lateral direction, that is to say, the running :web becomes narrower as it passes over the drying rolls. This reduction in width of the web of the paper as it is being dried may amount to form 5 to 20% of the initial width of the web, depending upon the degree of hydration of the fibers composing the web of paper. In a typical standard drier section of a paper machine if the paper web entering the'drier is 100 inches wide it may be only 90 inches on leaving the drier, or, in cases of extreme hydration, may be as narrow as 80 inches. One result of this shrinkage, other than reduction in width, is that the center of the web becomes more dense than the side edges of the web and hence the web becomes non-uniform in thickness across its width.

This shrinkage, which normally occurs in the drying step of conventional paper making processes, is disadvantageous for a number of rea- "sons. In the first place, the reduction in the width of the web as it is being dried means a corresponding reduction in the amount, 1. e., the area or yardage, of paper that can be made from a given weight of paper stock. Thus shrinkage represents a serious economic loss to the paper maker. Furthermore as previously pointed out when shrinkage occurs the sheet becomes nonsuitable finish to the surface of the paper. The

uniform across its width as a result of which the product produced is of varying thickness.

'Also, since the side edges of the web are thinner than the center of the web, there is a greater tendency for these edges to tear and thus produce a break in the web in the paper machine.

Shrinkage of the character described is particularly undesirable in cases where certain special papers, such as transparent or grease proof papers, are being made. In the case of transparent papers the transparency is developed in the calender section of the paper machine wherein the paper web is'subjected to moisture, heat and pressure. When the paper web is of nonuniform thickness it is diflicult to adjust these factors in such manner that the transparency of the sheet will be uniform, and in some cases-the desired transparency cannot be developed at all in the ,central portions of the sheet.

In the case of grease proof papers a similar difficulty is encountered Shrinkage causes the web to have a non-uniform density and as a result of this non-uniform density the grease proof qualities of a grease proof paper produced from such a web will be non-uniform, that is to say, the grease Proof qualities of the central portions of the web will be inferior to those of the edge portions of the web.

I have found that the shrinkage that occurs in standard drier sections of paper machines is, in some measure, due to the tension that exists in the paper as it passes between the heated drums or rolls of the drier. Because of this tension the sheet cannot shrink in the direction of its motion through th machine, and all of the shrinkage that occurs must take place in a lateral direction. By utilizing the method of the present invention this shrinkage of the paper web is in all cases significantly reduced, and in some cases substantially eliminated. This result may be achieved, in general, by causing the paper web to pass over a series of freely rotatable, heated rolls between two endless fibrous blankets that are in contact with the opposite sides of the paper web. The two fibrous blankets are firmly held against the paper web so that as the web passes from one drying roll to the other it is supported and held against shrinkage. By using freely rotatable drying rolls the tension in the web is maintained more nearly uniform and at a relatively low value. Because of the fact that the web is held between two blankets the web does not come in direct contact with the heated surfaces of the drying rolls and hence it is usually desirable that the blankets be preheated before they come in contact with the web in order to effect the desired transfer of heat to the web for evaporation of moisture therefrom.

The present invention both as to method and as to apparatus, may be most conveniently described in connection with the accompanying drawings which illustrate a preferred embodiment of apparatus capable of carrying out the method of the invention and wherein:

Fig. 1 is a semi-diagrammatic elevation view of a paper machine drier section incorporating my apparatus invention and capable of carrying out my method invention;

Fig. 2 is a top plan view, partly in section, of the drier section of Fig. 1; and

Fig. 3 is a horizontal section taken on the line 3-3 of Fig. 1.

Referring to the drawings and more particularly to Fig. 1 the drier section there shown comprises four horizontal tiers of heated rotatable rolls or drums, the drums of the four tiers being designated respectively by the numerals Ill, I2, I4 and I6. The drums I2 and I4 of the second and third tiers are mounted for free rotation, preferably in suitable roller hearings or the like, and are rotated by the passage of the paper web and its associated blankets thereover. All of the rolls I 0, I2, I4 and I 6 are heated by steam in any suitable manner well known in the art.

The moist paper web I! enters the drier at the right-hand end thereof (as shown in Fig. 1), passes alternately .over the rolls I2 and I4 of the second and third tiers of rolls, and leaves the drier at the left-hand end thereof. During its passage over therolls I2 and I4 the web I! is held firmly between a pair of endless fibrous blankets I8 and I9 that are preferably woolen blankets of a type well known in the art. As web I1 and blankets I8 and I3 pass over the rolls I2 and I4 moisture is removed from the web to dry the web in a manner that will now be described in detail.

The desirability of preheating the blankets I8 and I9 before they come into contact with web I1 8 to improve heat transfer to the web has been pointed out, and rolls III of the top tier of rolls and rolls I6 of the bottom tier or rolls perform this function. The rolls III of the top tier are positively driven. Each of the rolls III (see Fig. 2) is provided with a large gear 20 which is connected to an adjacent and similar large gear 22 by a 'relatively small pinion or idler gear 2I to form a gear train interconnecting the rolls of the series. Power to operate the gear train 2lI2I and rotate the rolls I0 is supplied by an electric motor 22 which is connected by a shaft 24 to one of the idler gears 2| of the gear train. The idler gears 2I serve to it power to the large Sears 20 that are connected to each of the rolls III, and also provide for rotation of each of the rolls III in the same direction. The motor 22 may be connected to any of the idler gears 2I but is preferably connected to an idler gear close to the center of the train.

The rolls I 6 of the lowermost tier (see Fig. 3) are provided with large gears 26 interconnected by the small idler gears 28 that are similar to the large gears 20 and small idler gears 2| respectively, and the gear train 26-28 is driven by an electric motor 38 similar to the motor 22 to cause the rolls I8 to be rotated in the same direction. It should be noted that the rolls I8 rotate in a direction opposite to the direction of rotation of the rolls l0.

Referring again to Fig. 1, the rolls I0 and I6 function to preheat the endless fibrous blankets I8 and I8 between which the paper web is held during its passage over the drier rolls I2 and I4. The blanket I8 moves over the rolls I8 from left to right (as shown in Fig. 1). Tension or carrier rolls 32 are provided between the rolls I II, and also at the ends of the series of rolls I0, to hold the blanket against the heating surfaces of the drums. After leaving the last preheating roll III blanket I8 passes downwardly to the first roll I4 of the series of rotatable rolls I4, where it comes in contact with the upper surface of paper web I! and thereafter passes alternately over the rolls I2 and I4 of the second and third tiers. Upon leaving the last roll I 2 the blanket I8 passes around the upper roll 34 of a, pair of ress rolls 34-38 and then passes through a blanket stretcher 38, which may be of suitable and wellknown construction, to the first roll III of the top tier of rolls.

In like manner the blanket I9 passes over the rolls I6 of the bottom tier of rolls, and carrier rolls 48 are provided to hold the [blanket I3 against the heating surfaces of rolls I6. After leaving the last roll I6 of the bottom tier of rolls the .blanket I9 passes upwardly over a tension roll 42 and thence to the first roll of the series of rotatable rolls I4, where it comes in contact with the undersurface of the paper web II. Thereafter the blanket I9 passes alternately over the freely rotatable rolls I2 and I4 and upon leaving the last roll I2 passes around the lower press roll 36. From the press roll 36 the blanket passes through a blanket stretcher 44, simila to the blanketstretcher 38, and then returns to the first roll I 6 of the lowermost tier of rolls. As the blankets I8 and I9 pass over the rolls I0 and I8 respectively they are heated to such an extent that they are appreciably hotter than the web II when they come in contact with the web.

The motive power for moving web l1 and blankets l8 and I! over the rolls l2 and I4 is supplied by the press rolls 34 and IS. The lower press roll 36 is driven by an electric motor 46 and the two press rolls are interconnected in any suitable and well-known manner such as by gears or by a mule drive," Le, a belt drive including a tightener mechanism 35, all of which is well known in the paper industry. The rolls 34 and 36 are pressed together, the pressure between the rolls being controlled and maintained at such a value as to produce the desired frictional contact with the blankets I8 and I9 and the web H to cause the web and blankets to be drawn over the rolls i2 and I4 as the press rolls 84 and 36 are rotated. As previously described the endless blankets l8 and is separate after passing between the press rolls, and return to the top and bottom tiers of rolls Ill and I6 respectively to be again preheated. The pap r web IT, after leaving the press rolls, passes over a tension roll 48 and on to a series of calender rolls, or to another drier or to some other portion of the paper machine.

It will be understood that the driving motors 22, 30 and 46 should be synchronized to produce that speed of rotation of the various heated rolls which will give the desired uniform linear speeds of the web and blankets. may be effected by standard methods utilized in conventional paper machine driving mechanisms. Furthermore it is desirable that the drier section be provided with a conventional vapor absorption system, including hood and exhaust fans, to remove vapors arising from the drier as moisture is removed from the web and blankets by the heated rolls.

The operation of the apparatus shown in the drawings is largely apparent from the foregoing description. The moisture laden paper web l1 coming from the web-forming portion of the machine or from a previous drier section or other portion of the machine pames over a tension roll 50 to the first roll of the series of rolls l4. As it comes in contact with the first roll l4 the web is embraced by the two preheated blankets l8 and I9 and held firmly therebetween. The rolls l2 and I4 are preferably of relatively small diameter to provide a sharp nip" which im proves the firmness with which the blankets II and I9 hold the web against shrinkage. The web is fully supported by the two blankets l8 and I9. as it passes over the rolls l2 and I 4, and, more particularly, as it pass% between successive rolls. This complete support of the web by the two blankets as it passes between successive rolls is an important feature of the present invention.

During its passage over the rolls l2 and I4 heat is supplied to the blankets and web to remove moisture therefrom and the blankets hold the web firmly against lateral shrinkage. Since the rolls l2 and H are freely rotatable the blankets and web are maintained in uniform and relatively low tension during their passage over these rolls. After leaving the last roll l2 the blankets and web pass between the press rolls 34 and 3G and as previously described the blanket l8 passes around press roll 34, the blanket I9 around press roll 36 and the paperweb I! over tension roll 48 to another section of the paper machine.

From the foregoing description it will be evident that I have provided an effective method and apparatus for inhibiting lateral shrinkage of a continuous running web of paper while it is being dried and thereby increasingthe area of paper Such synchronization ent drier.- However in most cases it will be de-' that can be prdduccd from. a given weight of paper stock and at the same time providing a 1 product that is more nearly uniform in thick-' ness. The paper web is fully supported throughout the entire period that it is passing through the drier by the two blankets which are in contact with opposite sides of the web and firmly hold the web against shrinkage. Since the blankets are preheated, effective heat transfer and moisture removal is achieved notwithstanding the fact that one or the other of the blankets is interposed between the web and the heating surfaces of the drying rolls. Since the drying rolls are freely rotatable excessive tension of the web in the direction of its motion is avoided during the drying period.

It is to be understood that the foregoing description is illustrative only and that numerous changes can be made in both the method and apparatus without departing from the spirit of the invention. The number of drying rolls in each tier of the drier shown in the drawings and described above may be varied widely. It is a common practice in paper machines to arrange the drying rolls in a number of different sections through which the paper web passes in series. It is evident that the drier of the present invention may be used as one section of a plurality of drier sections and connected to a conventional drier section through which the paper web passes either before or after it passes through the pressirable where more than one drier section is used to incorporate the present invention in all of the drier sections so that the advantages of the present method and apparatus may be more fully achieved.

1 claim:

" 1. In a paper machine drier for drying a continuousrunning web of paper, in combination, a series of heated drying rolls over which said web passes, a pair of endless fibrous blankets in contact with opposite sides ofsaid web as it passes over said drying rolls, said drying rolls being freely rotatable to equalize tension in said web in the direction of movement of said web as it is being dried, a plurality of driven heatedrolls for preheating said blankets before they come in contact with said web, and means for drawing said blankets with said web therebetween over said heated drying rolls to hold said blankets firmly against said web and thereby prevent latenal shrinkage of said web while it is being dried.

{2. In a paper machine drier for drying a con-- tinuous running web of paper, in. combination, a series of heated drying rolls over which said web passes, a pair of endless fibrous blankets in con tact with opposite sides of said web as it passes over said drying rolls, said drying rolls being freely rotatable to equalize tension in said web in the direction of movement of said web as it is being dried, a plurality of driven heated rolls for preheating said blankets before they come in contact with said web, and a pair of driven press rolls for drawing said blankets with said web therebetween over said heated rolls to hold said blankets firmly against said web and thereby inhibit lateral shrinkage of said web.

3. In a paper machine drier for drying a continuous running web of paper, in combination, four tiers of heated rolls, said web of paper passign over the rolls of thesecond and third of said tiers, and the rolls' of said second and third tiers being arranged to confront opposite sides of said web, a first fibrous blanket passing over the rolls of said first, second and third tiers and positioned to contact one side of said web during its passage over said second and third tiers, a second fibrous blanket passing over the rolls of said second, third and fourth tiers and arranged to contact the other side of said web as it passes over the rolls of said second and third tiers, the rolls of said first and fourth tiers being heated to preheat said blankets before they come in contact with said web, and the rolls of said second and third tiers being freely rotatable to equalize tension in said web as it is being dried, and means for drawing said two blankets with said web therebetween over the rolls of said second and third tiers to cause said blankets to hold said web firmly and thereby inhibit lateral shrinkage of said web, the rolls of said second and third tiers being so positioned with respect to one another that the portions of said web and blankets extending between said second and third tier rolls are substantially parallel with on e another.

4. In a paper machine drier for drying a continuous running web of paper, a pluraltiy of free- 1y rotatable drying rolls over which said web passes, said drying rolls being arranged in two series, one side of said web confronting the rolls of one of said series and the other side of said web confronting the rolls of the other of said series, a pair of endles fibrous blankets in contact withopposite sides of said web together with a plurality of driven heated rolls for drying and preheating said blankets before they come in contact with said web and means for drawing said blankets with said web therebetween over said drying rolls to cause said blankets to be pressed against said web and thereby inhibit lateral shrinkage of said web, said rolls being of relatively small diameter to improve the firmness with which said web is held by said blankets and being so positioned with respect to one another that the portions of said web and blankets extending between the rolls are substantially parallel with one another.

5. In a paper machine drier for drying a continuous running web of paper, in combination, four tiers of heated rolls, said web of paper passing over the rolls of the second and third of said tiers, and the rolls of said second and third tiers being arranged to confront opposite sides of said web, a first fibrous blanket passing over the'rolls of said first, second and third tiers and positioned to contact one side of said web during its passage over said second and third tiers, a second fibrous blanket passing over the rolls of said second, third and fourth tiers and arranged to contact the other side of said web as it passes over the rolls of said second and third tiers, the rolls of said first and fourth tiers being heated to preheat said blankets before they comein contact with said web, and the rolls of said second and third tiers being freely rotatable to equalize tension in said web as it is being dried and being of relatively small diameter to improve the firmness with which said web is held by said blankets, and means for drawing said two blankets with said web therebetween over the rolls of said second and third tiers to cause said blankets to hold said web firmly and thereby inhibit lateral shrinkage of said web, the rolls of said second and third tiers being so positioned with respect to one another that the portions of said web and blankets extending between said second and third tier rolls are substantially parallel with one another.

6. In a paper machine drier for drying a continuous running web of paper,in combination,four tiers of heated rolls, said web of paper passing over the rolls of the second and third of said tiers, and the rolls of said second and third tiers being arranged to confront opposite sides of said web, a firstfibrous blanket passing over the rolls of said first, second and third tiers and positioned to contact one side of said web during its passage over said second and third tiers, a second fibrous blanket passing over the rolls of said second, third and fourth tiers and arranged to contact the other side of said web as it passes over the rolls of said second and third tiers, the rolls of said first and fourth tiers being heated to preheat said blankets before they come in contact with said web, and the rolls of said second and third tiers being freely rotatable to equalize tension in said web as it is being dried and being of relatively small diameter to improve the firmness with which said web is held by said blankets, and a pair of driven press rolls for drawing said blankets with said web therebetween over the rolls of said second and third tiers to cause said blankets to hold said web firmly and thereb inhibit lateral shrinkage of said web, the rolls of said second and third tiers being so positioned with respect to one another that the portions of said web and blankets extending between said second and third tier rolls are substantially parallel with one another.

GEORGE L. BIDWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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