US1873949A - Paper drying means - Google Patents

Description

Aug. 30, 1932. H. R. WILLIAMS PAPER DRYING MEANS Filed Jan. 29, 1930 INVEJYIZOR Harv/s0 A. wll/lams BY ATTORNEYS Patented Aug. 3%, 1932 PATENT OFFICE HARRISON a. WILLIAMS, on NEW YORK, 1v. 1.

PAIER DRYING MEANS Application filed. January 29, 1930. Serial No. 424.,145.

This invention relates to the drying of paper webs and more particularly to web drying means including web engaging belts corresponding with the drier felts heretofore in use. a.

In paper machines each web of paper, after complete formation thereof and preferably a partial drying thereof, is finally dried by "passing it over the surfaces of a series of v heated drying cylinders or rollers which are driven in any suitable manner. The cylinders are so placed that both surfaces of the Web are alternately in contact with the heating surfaces, and the rollers of what may be called the upper and lower groups are encased, at the portions of their surfaces engaged by the paper web, by continuous traveling felts.

Heretofore it has been the theory in regard to the conventional type of drier felt that the felt itself carried off a considerable quantity of the moisture from the sheet or web of paper during the drying thereof in the driers or drier section pf the paper ma chine. However, in connection with certain types of drying systems, I have found that this theory is based upon a mistaken idea of the actual conditions. It will be apparent that any moisture absorbed by the felt while in contact with the wet sheet or web should be driven out before the felt (which is really a belt) returns into contact with the paper or web. Actually an important function of the drier felt is to insulate the web of paper while in contact with the drier cylinder to enable the temperature to be brought up to or maintained at a higher degree, thereby causing the web, after passing out of engagement with a drying cylinder and the drier-felt cooperating therewith, to give off in the form of vapor a greater percentage of its moisture.

In a drier felt wherein absorption takes place rapidly, a larger percentage of the heat passes directly through the felt and the temperature is lowered accordingly. Consequently a lesser proportion of the water or moisture in the paper is converted into vapor.

Another function of a drier felt is to hold the paper closely against the hot surface of a 50 drier cylinder, thereby pressing out as much air as possible and causing a greater area of the paper web to be in direct contact with the heated surface of the cylinder.

In connection with machines equipped with felts or webs of the type heretofore in use it has been the general custom or practice, when the paper ceases to dry properly in the machine, to remove one or more of the drier felts and replace the same with a new felt. The assumption was that the newer the felt the greater would be the amount of water or moisture which the felt would absorb directly from the paper web. It has, however, been conclusively proven that the opposite is true, namely, the new felt is to a large degree water repellent and becomes more ab- "sorben't as it ages.

It has also been assumed heretofore that the driers which carry variable steam pressure, averaging from 15 to 20 pounds, drive off a large part of the moisture directly through the drier felts. In view of the fact that a new felt, which, as above stated, is to a degree water repellent, produces a better drying v effect than an older and more porous felt, it is evident that, even if moisture is driven off through the drier felts, the results are not so desirable as with felts or belts which are water proofed. The felts or belts heretofore in use are subject to rapid deterioration in that the wetting by absorption of water from the paper web causes the woof threads to expand so that the warp threads, which pass back and forth aroundwoof threads, will be displaced further from the central plane of the fabric and thus tend to decrease the length of the belt. Eventually the warp threads, due to repeated drying and wetting of the belt will be stressed to their elastic limit and fail to respond, thus causing the belt to loosen. The belt is then generally shortened by cutting out a portion of its length. This results in uneven tension on the warp threads, a condition which tends 05. to lessen the life of the belt. A new felt is more tightly drawn than an old felt, and the older the felt the more open the mesh thereof. This causes 'more rapid radiation of the heat so that the temperature 160 of the paper falls and the drying is greatly retarded.

An important object of the present invention is to provide drying means whereby more rapid drying of paper webs will be effected. Another important object ofthe invention is to provide improved drying belts. A further object is to provide drying means whereby an improved finish of the surface of the paper web is obtained."

The above objects can be attained by replacing felts of the type heretofore in use by belts which are resistant to heat and water so as to act as insulators over the portions of the paper in contact with the faces or surfaces of the drier rolls or cylinders. The better the insulation obtained in this way, the more rapid will be the increase of temperature during the fraction of time taken y a short portion of a sheet in passing between a cylinder and the belt cooperating therewith, and the higher willbe the temperature to which said portion of the sheet is raised. It will be obvious thatthe higher the temperature obtained from passing the web or'sheet between a drier roll and a belt, the greater the amount of moisture which will pass ofl in the form of steam or vapor when the sheet is freed from the roll in its passage to the next roll at which the operation is repeated. This action of the driers and the felts is the same in principle as the pressing action in which a hot fiat iron is placed in contact with a damp piece of cloth. The heat of the fiat iron brings the temperature up to a point where the water is vaporized and upon withdrawing the iron the moisture will pass away in the form of vapor.

For the purpose of providing the paper web with a better surface, the drier belt or felt of the present invention is made with a smooth face-to engage the paper web at the face opposite tothat engaged by the cooperating rolls or cylinders. With a smooth surface which is impervious to moisture and is heat insulating, the effect is to bring the water trapped in the paper quickly to the vaporizationpoint and, by preventing the water from entering the belt, avoiding rotting which occurs in connection with the former type of belt or felt.

An important advantage arising from the feature of providing the belt of the present invention with a smooth face to engage the Web is that by applying a pressure roll to the back of a drier belt the paper is pressed more strongly against the drying surface of the drier roll, this making the action more like that of a fiat iron and producing a smoother finish. A series of such pressure rolls may be applied in connection with a series of drier rolls and the pressure gradually increased from the wet end to the dry end. By applying a suflicient number of such pressure rolls, the paper may be calendered to a certain degree without goingthrough the conventional type of calender stack. Where the sheet of paper is formed on a Fourdrinier wire, it is possible to detect the surface of the paper which was in engagement with the wire. By using one or more pressure rolls, both surfaces of the sheet are made to appear alike and a smoother surface is obtained, thus permitting finer and faster results in printin ne form of drier belt embodying the present invention can be obtained by rubberizing one face or side, which would be used to engage the paper web or sheet, or by rubberizing both sides of the type of felt heretofore 1n use. The rubberizing of the side to contact with the paper fills the valleys formed by the warp and woof and a smooth surface is obtained, thus eliminating the small pockets in which steam would otherwise be formed and trapped.

Other objects and advantages will hereinafter appear.

In the drawing forming part of this speci- Fig. 1 is a diagrammatic view of a drier including drier belt or felts embodying the present invention; and

Fig. 2 is a detail section of the drier belt.

In the diagrammatic showing of Fig. 1, l designates a moist web of fpaper which, after passing over a roll 2 (pre erably heated), is carried alternately under lower heated rolls or cylinders 3 and over upper heated rolls or cylinders 4. The lower parts of the cylinders 3 where engaged by the moist paper web-1 are encased by a continuous traveling web 5 of which the upper stretch passes over a guiding roll 6 beneath the roll 2 and then alternately beneath the heated rolls or cylinders 3 and over additional guide rolls 6 located above the rolls 3 and beneath the upper heated rolls 4, two of said additional guide rolls 6 being located, respectively, between the first and second rolls 3 (counting from the right in Fig. 1), and a third and last roll at the left of the third heated cylinder rollers 3. Beneath the heated cylinders 3 the lower stretch of the belt 5 is guided below the heated rolls 3 by means of guide rolls 7 arranged below the end rolls 6.

The upper parts of the cylinders 4. where engaged by the moist paper web 1 are encased by a continuous traveling web 8 which (beginning at the right in Fig. 1) passes alternately under guide rolls 9 and over the heated cylinders 4. In the arrangement illustrated. the belt 8 as it leaves thethird cylinder or roll 4 passes beneath and upwardly around a roll 10 which, as here shown, is higher than the top of the last rollA; and permits the web 1 to be discharged substantially horizontally from the 'top of the last roll 4. The

upper part of the belt extends rearwardly from the top of the roll 10 over an intermediate guide roll 11 and over a guide roll 12 (at the front end of the drier) from which it passes downwardly to the first guide roll 9.

' In Fig. 2 the belt 5 is illustrated as comprising a woven fabric made up of warp threads 13 and woof threads 14 and a heat resisting and water repellent surface layer 15 preferably of rubber. The surface layer 15 engages the web 1 and is made with a smooth surface so as to avoid the formation and trapping of steam at the adjacent face of the paper Web, and to assist in producing a smooth face at the adjacent side of the paper web. It should be understood that the belt 8 is of the same material as of the belt 5.

Due to the provision of drier belts or felts having water and heat resisting faces to engage the paper web, the temperature of the portions of the web passing between each heated cylinder and the corresponding drier belt is raised to such an extent that, upon passing from the cylinder, moisture in the paper Web passes from the web in the form of vapor.

By supplying a pressure roll 13 at the upper part of the first roll 4 (located at what may be called the wet end of the drier), the smooth surface of the upper belt or felt 8 will be pressed tighter against the paper thus producing an action more nearly that of a flat iron and tending to produce a smoother surface at both sides of the paper. As here shown the pressure rolls 13 may be journaled in blocks 14 which are slidable vertically and are urged downwardly by suitable springs 15. To improve the effect due to the pressure roll 13, there is provided a pressure roll 16 at the top of the second cylinder 4. This cylinder 16 is journaled in vertically slidable blocks 17 by springs 18 which are stronger than springs 15. If desired, a pressure roll can be applied to the third heated cylinder 14. It should be understood that by using a sufliv cient number of such pressure rolls and gradually increasing the pressure towards the dry end of the machine the paper may be calendered without going through the conventional type of calender stack.

While I have illustrated and described in detail one embodiment of the invention, it is to be understood that changes may be made therein. 1 do not, therefore, desire to limit myself to the specific construction illustrated but intend to cover my invention broadly in whatever form its principles may be utilized.

I claim:

1. In a drier for paper-making machines, the combination with a heated cylinder arounda portion of which passes a moist paper web, of a traveling belt engaging the outer surface of the paper web where it is supported by the cylinder, said belt having a water impervious and heat insulating webengaging surface to insulate the portion of the web between the cylinder and the belt,

thereby increasing the heating efiect of the cylinder.

2. In a drier for paper-making machines, the combination with a heated cylinder around a portion of which passes a moist paper web, of a traveling belt engaging the outer surface of the paper web where it is supported by the cylinder, said belt having a smooth heat insulating and water impervious web-engaging surface to enable the heat of the cylinder to be used to advantage.

In testimony whereof I have aflixed my signature to this specification.

HARRISON R. WILLIAMS.

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