US 2281496 A
Description (OCR text may contain errors)
April 1942- H. H. HANSON 2,281,496
AIR DRIER FOR PAPER Filed April29, 1940 primary drying cylinders and the named A r.--z s, -1942 umreo STATES PATENT Fi?lE AIItD ration of Pennsylvania Application April 29,1940, Serial No. 332,348 Claims. (01. 34155) This invention relates to the art of finishing paper, and especially to the production of a cockle finish which is characteristic or high grade bond and similar air-dried stock.
In the paper making and finishing art, the term air dried distinguishes that class of papers having a uniformly puckered surface, known as cockle, from the machine dried type wherein the paper has an overall fiat level surface.
The distinguishing characteristics between the two processes reside in the air dried paper being dried under minimum restraint while the ma chine dried paper is dried under relatively great restraint. v
In thecase of the air dried paper, drying is effected by contact therewith of flowing air while the paper is supported and maintained under the least possible degree of longitudinal and transverse tension; whereas in the case of the machine dried paper, it passes around and is maintained under a high :degree of lengthwise and crosswise tension on the peripheral surfaces of heated cylinders. The paper is dried by its direct contact with the heated surfaces of the cylinders.
In either case, the paper web, after it leaves the final press rolls of the web forming machine in awet condition, passes around a set or nest of primary drying cylinders. From the primary drying cylinders the web passes tl ough a sizing solution in a suitable tub located between the finishing apparatus.
In the case of the machine finished papers, the initially partly dried web passes from the sizing tub to a finishing set" composed of a second series of heated cylinders, around which the a web passes successively. Throughout a. substantial portion of the travel of the web on the face of each heated finishing cylinder the web is pressed firmly against the smooth peripheral surface of the cylinder by a blanket which travels concurrently with the cylinder and holds the web against shrinkage. Drying of the web under the above noted conditions prevents the paper from shrinking naturally, thus the paper dries fiat with a more or less smooth surface.
In the case of air dried papers, the web coming from the primary set of drying cylinders and passing through the solution in the sizing tub, passes into a long drying chamber in whichthe web is loosely supported and through which it is advanced by a series of rotating rolls. Supporting and advancing the web in this manner re- R FOB PAPER assignor to Miquon, Pa., a corpolieves the web of tension, tothe'greatestpossrble extent. The web resting on and sagging between the supporting rolls is therefore under no restraint against natural shrinkage, except that which is produced by its, own weight in resting on and hanging loosely between the advancing rolls.
The mechanism at the delivery end of the drying chamber is regulated to take up the web at a rate commensurable with the rate at which the wet sized web is fed into the receiving end of the drying chamber, less the rate at which the web shrinks longitudinally in its drying-transit through the chamber.
Under the air drying processes previously known to the art, the drying rate has been relatively low, therefore an extremely long chamber" has been required. The low rate of drying has been due to the fact that the temperature of the drying .air considered safe for drying without scorching the web, did not exceed 240 F. and in chamber heretofore required under prior art practices, air dryers were usually installed in a room separate from that in which the paper making machine and primary set of drying rolls was installed. This necessitated the use of turnover rolls, conveying rolls, and idlers, etc. to support and advance the web along'a course deviating from a straight line path in alignment with the travel of the web through the primary set and sizing tub.
One object of the present invention is to provide an air dryer capable of rapidly drying a web, in transit, at such a relatively high rate that the length of the air dryer can be reduced to approximately the overall length of an ordinary set of machine finishing cylinders.
. Another object of the invention is to produce an air dryer which can be installed and operated in superposed relation to an ordinary set of mainder or cylinders, up to the point where shri'nkage of the web would normally begin and then to pass the preheated web immediately into the feed end of the air drier.
Another object of the invention is to arrange the air-heating and circulating means of th air drier in such relation to the path of travel of the web that temperatures up to approximately 280 F. or 300 F. may be employed without fear of scorching the web, and by which the evaporation of the moisture from the web is made so rapid that the web is kept relatively cool and safely below scorching temperature. Such extremely fast drying permits the length of the drier to be reduced to the extent noted above.
The single figure of the accompanying drawing diagrammatically illustrates the air drier of the present invention in superposed relation to a conventional set of machine drying cylinders commonly employed to produce the smooth finished paper noted above.
In the drawing, a web a: in an initially dried state as it comes from the primary drying set (not shown) is illustrated as passing into a sizing solution y contained in a conventional type of size-tub I. The tub is provided with the usual squeeze rolls 2 and 3 for removing excess sizing solution from the web.
From the squeeze rolls 2 and 3 the web :1: passes around carrying rolls 4 and 5 to a normal set, A, of finishing cylinders, one only of which is shown at 6.
Normally, in the above noted machine drying of paper the endless belt or blanket composed of felt or other suitable material is associated with the upper row of cylinders of the finishing set, and bears against segmental portions of the upper sides of the peripheral surfaces of these cylinders, said blanket or belt being held in contact with the cylinders and otherwise supported by a series of rolls.
A similar belt is associated with the lower row of cylinders of the finishing set and bears against the under segmental portions of these cylinders, under control of suitable guide rolls.
Normally the above noted belts travel concurrently with the peripheral surfaces of the heated cylinders, with the paper being held between the belts and the peripheral surfaces of the cylinders, as the web of paper travels around the cylinders.
Normally the web passes from the last cylinder of the finishing set around a guide or spring roll IE to a stack .of calenderlng rolls I1, l1, and from there to suitable reeling mechanism adapted to convert the'web into a roll 1:2.
The calendering rolls l1, I! are power driven and serve as a means for drawing the web through the finishing set A, the cylinders 6, etc. of which may also be driven by any suitable means, not shown, this being common practice in the art.
In accordance with the principles of the pres ent invention the air drier B is superposed above the finishing set of cylinders A, as indicated in the drawing. Under the principles of the present invention the web :1: passes around one or more of the heated cylinders of the finishing set A, employed in this instance merely to heat or preheat the web :1: prior to its entrance into the air drier B. r
In the present instance the web a: is shown as passing around only the first cylinder 6, it being found that usually the heat applied to the paper by this one cylinder is sufficient to bring the paper to a stage of moisture evaporation wherein the paper is about to begin normal shrinkage, upon further evaporation of the moisture there- 'from.
The preheated web :0 passes from the heating cylinder 6 to and around a series of guide rolls l9, l9, onto a series of supporting rolls 20, 20. The rolls 20, 20 support the web in a substantially horizontal plane between upper and lower air heating and impinging um'ts 2| and 22 respectively, the upper series 2| being designed to drive air downwardly into impinging contact with the upper surface of the web a: as it travels along horizontally over the rolls 20, 20, while the lower series 22 drives air upwardly into impinging contact with the under surface of the web a.
Between and as a result of the opposed currents of air the web :cis maintained in a more or less floating condition, free of restraint opposing its natural tendencies to shrink in all directions simultaneously.
,In the units 2| and 22, the air is driven downwardly and upwardly by high capacity impellers in the form of fans 23 and 24 respectively. These fans are driven individually by electric motors 25 and 26 respectively, or by any other suitable means. The fans 23 and 2B are adapted to move large volumes of air at relatively high velocity into impingement with the opposite surfaces of the web 2:.
Intermediate the air impellers 23 and 24 and the opposite surfaces respectively of the web 2:, air heaters 21 and 28 are provided. The air heaters 21 and 28 are preferably of the high heat transfer type such, for example, as the honeycomb type of radiator employed in automobiles and in other heating equipment.
Preferably the construction of the heaters 21 and 28 is such as to withstand an internal steam pressure of approximately 185 pounds per square inch, by which high temperatures upward to about 300 F. may be readily obtained in the airdriven through the honeycomb construction by theimpellers23 and 24.
Under the above conditions, the evaporation of moisture from the web a: is so rapid that the opposite surfaces of the web are maintained relatively cool and the web 1:, traveling at the rate of approximately 130 to 150 feet per minute, does not remain in contact with the high temperature air currents for a sufiicient length of time to scorch or otherwise damage the web. However, even at such relativelyhigh rate of travel of the paper the air currents by impinging upon substantially all points on bothsurfaces of the web from side to side thereof and from end to end of the unit B, simultaneously, effects completedrying of the web. During this drying, with the web in an unrestricted condition, said web attains the all-over puckered condition commonly known as cockle.
From the last of the supporting rolls 20, at the delivery end of the unit B, the web passes around a guide roll 29 to and around a drag roll 30 to which friction is applied by a shoe 3| under the influence of a weight 32 or other friction producing means.
From the roll 30 the web passes around additional drag rolls 33 to and around a retarding roll 35. At spaced intervals across the face of the roll 35, narrow endless belts or straps 36 pass around guide rolls 31, 31 which engage and press the web into firm contact with the peripheral surface of the roll 35 at laterally spaced intervals across the width of the paper throughout 30, 33 and 35, with the friction device 3! and spaced straps 36, act as a brake to permit the calender rolls l1 to place the web under tension after it leaves the air drying unit B, at which time it has attained its full amount of natural shrinkage, said tension being placed on the web in order that it may be properly calendered and wound into the roll 3:2 without wrinkling.
The web :2, as it leaves the size-tub I, is of web is heated on the cylinder 6 up to the point where evaporation of moisture and shrinkage of the web begins, after which the moisture is evaporated from the web during its travel through the unit B.
The velocity and temperature of the impinging approximately 25 to 30% moisture content. The l0 air may be regulated to deliver the web from the unit B in any state desired from a bone dry condition to a condition having any percentage of moisture content that may be desired.
From the time the web 2: leaves the heating cylinder 6, until itarrives at the brake roll 30, or at least the roll at the delivery end of 'the unit B, it is under no tension except that produced by its own weight in passing around the various rolls and this lack of restraint is controlled by providing a differential in the speeds of the driven rolls 5 and 35 which will compensate for the reduction in the over-all length of the web by shrinkage as it dries in transit in passing through the unit B.
If desired, the air heating and impelling units of the air dryer B may be confined within any suitable casing with or without insulated'walls and with a slot adjacent each end roller 20 for the ingress and egress of the paper relative to the chamber formed within the casing, such casing being diagrammatically illustrated in broken lines and indicated at at.
From the foregoing it will be clear that b31 40 creating a zone of relatively high temperature adjacent each of the opposite faces of the unrestrained paper simultaneously, rapid evaporation of moisture from the paper can be effected,
and because of the paper being free to shrink in 5 all directions simultaneously the entire area of the paper within the zone will assume an allover substantially uniform puckered condition providing the desired cockle finish on the paper.
It will be further noted that the rapid evaporation of the moisture from the paper will maintain the surface of the paper relatively cool;
number of air passages, said .air-heaters being arranged in opposed spaced and substantially parallel relationship providing a paper-receiving channel therebetween, means for advancing a continuous web of paper longitudinally through v said channel, and means for driving air through channel and disposed adjacent the faces of said heaters lying opposite those between which said channel is formed for driving air through the air passages of said heaters directly into contact with the opposite faces respectively 9! the moving web, said air normallymaintaining said web in spaced relation to said heaters.
3. Ina paper-finishing apparatus, a pair oi? horizontally disposed naked foraminous' air-heaters each'having a large number of vertical air passages, said air-heaters being arranged in opposed vertically spaced and substantially parallel relationship providing a horizontal paper-receiving channel therebetween, means for advancing a continuous web of paper longitudinally through said channel, and means distributed over the areas of said heaters which define said channel and disposed adjacent the faces of said heaters .lying opposite those between which said channel is formed for driving'airthrough the airnpas sages of said heaters directly into contactwith the opposite faces respectively of the moving web,
said air normally maintaining said web in relation to said heaters.
4. In' a paper-finishing apparatus, a pair of horizontally disposed naked foraminous air-heaterseach having a large number of vertical air passages, said air-heaters being arranged in opposed vertically spaced and substantially parallel relationship providing a horizontal paper-receivspaced 5 ing channel therebetween, means for advancing thereby permitting the use of high temperatures heretofore considered unsafe in the drying of paper. s
= It will be further noted that by preheating thewet paper to a. point where shrinkage of the paper would normally begin, the time necessaryvto-evaporate the moisture from thepaper to the point where the puckering has advanced to the desired extent can be reduced to a minimum, v..thus requiring a relatively short air dryer. an example, with the temperatures noted above, (m
i. e.'from280 Fvto 300 F. or better, rather "complete evaporation of moisture from the paper may be eflectedin 5 seconds, thus with the paper.
traveling at approximately-130 to 150 feet per Iclaim: I 1. In a paper-finishing apparatus, a pair of to keep the paper in the high temperature zone minute the length of theair dryer need only r be approximately 12 feet long, the average length ..of a finishing set 'of machine dryingcylinders.
. a continuous web of paper longitudinally through said channel, means distributed over the areas of said heaters which define said channel and disposed adjacent the faces of said heaters lying opposite those between which said channel is formed for driving air through the air passages of said heaters directly into contact with the opposite faces respectively of the moving web,
said air normally maintaining said web-in spaced relation to said heaters, and meansjwithin said channel to maintain the web out of contact with the heaters;
5. In 'a paper-finishing apparatus, a pair ofv naked foraminous air-heaters of predetermined length and breadth respectively, operating at a temperature having a'minimum or 280' F., each air-heater having a large number of air passages uniformly distributed over its area, said air-heaters being arranged inopposed spaced 'substan- 1 tially parallel relationship toprovide a paperreceiving channel of predetermined length therebetween, means for advancing a'continuous web of paper containing a maximum of 30% moisture through said channel lengthwise thereof at a naked foraminous air-heatersieach having abuse 7 ra f Speed ha a m nimum'offeet per minute to eflect travel of the web from end to end or the channel within a period 0! time having a maximum of substantially 5 seconds,
. at a velocity predetermined to reduce the moisture content-oi the paper to substantially o in a single passage or the web through said channel, said air normally maintaining the web in spaced relation to the heaters within said channel.
11060 H. HANSON.