US3359643A - Production of paper - Google Patents

Description

Dec. 26, 1967 lcLEBELT ETA'L 3,359,643

PRODUCTION OF PAPER Filed March 22, 1965 ive 730A;

am zwg United States Patent 3,359,643 PRODUCTION OF PAPER John C. Leihelt and Leslie F. Newby, Jr., Wisconsin Rapids, Wis; said Newby assignor to Consolidated Papers, Inc., Wisconsin Rapids, Wis., a corporation of Wisconsin Filed Mar. 22, 1965, Ser. No. 441,579 9 Claims. (Cl. 34-25) This invention relates to the production of paper and more particularly to novel method and means for controlling the uniformity of a newly formed paper web in a continuous papermaking process.

More specifically, the present invention relates to novel method and means for controlling the caliper (thickness) or variations in caliper across the width of the traveling paper web, such as for example reduction of hard and/ or soft spots, ridges, wavy edges, rough printability due to corrugations in the cross or transverse direction of the sheet and similar roll defects, with the end in view of producing paper of enhanced uniformity and thickness and concomitant physical properties such as uniform porosity, improved subsequent coating pickup, enhanced smoothness, opacity and print quality.

Non-uniformity of caliper has been particularly noticed in the newly formed paper web after it leaves the first machine calender, this machine calender comprising a plurality of vertically aligned steel rolls, the web passing through one or more pairs or nips of these rolls, which serve to density the web while hot just after it leaves the last of the conventional series of drier drums but prior to coating and further calendering or supercalendering.

The newly formed paper web, which can have an average temperature on the order of about 150-180 F. as it enters the first nip of the calender stack, by heat transfer causes the steel rolls thereof to become heated, resulting in heat expansion of the calender rolls and bringing the peripheries of adjacent rolls closer to each other and causing enhanced densification of the paper web. It is known, however, that the heated rolls do not expand uniformly throughout their length resulting in a web being more highly densified in some areas than in others and as a matter of fact resulting very often in production of a series of transverse corrugations extending longitudinally of the paper web. Such irregular expansion of the calender rolls can be minimized by subjecting unduly heated high spots to cooling, and conversely by subjecting relatively low spots to heating to cause them to expand.

It has been found in accordance with the present invention that the cross direction temperature of the moving paper web entering the aforesaid machine calender stack can vary across the web while its cross direction profile remains quite stable in the longitudinal or machine direction of the paper. It is further found that temperature differences in certain areas of the web could transfer to the steel rolls of the calender stack thereby expanding these calender rolls in the areas corresponding to those of the higher paper temperature. In turn, these expanded areas of the calender rolls in the stack were found to then compress the paper passing through it in the same areas of high paper temperature more than in the areas of lower paper temperature. Conversely, cooler paper areas could contract or diminish areas of these calender rolls and said areas would compress the paper passing through to less than those areas of higher temperatures. It was furthermore found that the cross direction caliper profile after or following this first calender stack was inversely proportional to the cross direction temperature profile of the paper entering the stack.

It was therefore found that in accordance with the present invention by thermally treating selected areas of the newly formed forwardly moving heat dried web prior to subjecting it to calenderin-g, that the effects of the heat variations longitudinally of the rolls could be minimized. That is to say, by thermally treating selected areas of one or both faces of the heated web, such as by impinging, blowing or showering gas, for example air, against selected areas of the web in heat exchange relationship correlated to the said expansion or lack of expansion, the eifeots of heat variations longitudinally of the rolls could be minimized and paper webs produced of more uniform cross directional caliper. For example, impinging cooled air at a given distance from a moving web of paper by means of a plurality of orifices or nozzles disposed transversely of the web and individually controllable, a transfer of heat from the moving web of paper and disruption of the moisture and heat laden layers of air which normally follow the moving web, may be effected. This disruption and cooling effect of the air on the paper web in turn causes the transfer of heat from the hot calendering rolls to the cooler web causing the rolls to locally cool and decrease in diameter and thereby inversely increasing the caliper of the moving web in the selected areas in which the air was applied.

Of course, the reverse of the foregoing can also be done, either alone or in combination with cooling air in adjacent areas, by the foregoing means to deliver relatively heated air to selected areas to thereby increase the temperature of the moving web and thereby, in turn, increasing the temperature of the calendering rolls in these related areas. This in turn causes expansion of the calender rolls in selected areas and as a result decreases caliper of the moving web in the thus expanded areas.

It will thus be seen that the newly formed, dried paper web while still warm can display a relatively fixed or stable cross direction temperature profile which it can transfer to the calender rolls of the first machine or calender stack disposed adjacent the last paper drying drum. This transfer temperature profile in turn can distort the calender rolls by developing relatively expanded or contracted areas, dependent upon the temperature profile, which in turn can calender the paper web passing through more or less strongly according to the roll areas involved. By employing the air showering method and means of this invention one can eliminate what has been found to be the main variable, and surprisingly the greatest contributor, of calender variations, namely that of paper web temperature differences in the cross or transverse direction of the moving web. This air shower technique has been found to provide a more rapid and sensitive control than has heretofore been available and has provided means not only for controlling variable longitudinal expansion in the rolls after their being heated but has also provided means to correct or compensate for varia tions inherent in the rolls. As a result, air pipes directed onto the rolls or heater strips on the rolls can very often be eliminated by directing relatively heated and/or relatively cooled air to selected spots or areas of the forwardly moving paper web in a direction transversely thereof.

The practice of the present invention can be employed in combination with and correlated to an on-the-machine traversing caliper instrument such as described in the copending application of John B. Kahoun, Ser. No. 313,476, filed Oct. 3, 1963, in engagement with the paper web as it leaves the aforesaid calender stack to provide prompt and continuous control of the paper caliper.

Other objects and advantages of the present invention, and the details of construction and arrangement of parts of the means for carrying out the method thereof, will be apparent from a consideration of the following specification and accompanying drawings, wherein FIG. 1 is a diagrammatic side elevational view of the arrangement of apparatus for carrying out the present invention.

FIG. 2 is a fragmentary plan view thereof with the top calender roll removed.

FIG. 3 is an enlarged fragmentary detail on the line 33 of FIG. 2, showing a solenoid valve actuated highpressure, low-volume air nozzle.

FIG. 4 is a plan view of a pair of optional low-pressure, high-volume air nozzles.

FIG. 5 is a diagrammatic View of remote control means for operating the air shower nozzles disposed adjacent a thickness profile graph recorder whereby the control means may be actuated in a manner correlated to the graph.

Referring to the drawings, the reference numeral generally indicates a machine calender stack comprising a plurality of vertically aligned steel rolls 11 through which the paper web 12 passes. The paper web may pass through a single nip, i.e., between an adjacent pair of rolls 11,11 or may pass between a plurality of nips such as the five indicated in the drawing.

The paper web leaves the last drying drum 13 at a temperature on the order of about 220 F. and it approaches the stack at about the roll 14 at a temperature on the order of ISO-180. The top roll temperature of the calender stack becomes heated by contact with the web to a temperature of about 160180 and the bottom roll temperature becomes heated to approximately 135- 145 F.

As previously explained, the web 12 as it leaves the last drier drum 13 and enters the steel rolls of the calender stack 10 has been found to be heated to varying degrees in a transverse direction, thereby causing the rolls 11 of the calender stack-to be non-uniformly expanded in a longitudinal direction, resulting in non-uniform density of the issuing web after it leaves the calender.

In accordance with the present invention this difference in density is minimized by showering as desired cooling or heating gas, preferably air, against selected areas of one or both faces of the moving web just before it enters the calender stack 10. For this purpose, a plurality of nozzles 15 are disposed in a series extending transversely of the web and in a direction parallel thereto, these nozzles 15 being connected to a header or common supply source of gas or air 16 suspended and supported in suitable manner as by the means 17. These nozzles 15 can be adapted to direct a compressed gas such as air essentially at high pressure and low volume a given distance above the moving web of paper so that the gas may cool by expansion and cool the web by transfer of heat from the paper to the roll and by disruption of the heat and moisture-laden boundry layers of air which normally follow the moving web. In the alternative, nozzles 18 may be employed to deliver a high volume of cooled gas, i.e., air. at a low-pressure from a suitable source directed through the nozzles disposed at a given distance from the moving web of paper. Again, the combined low tempera ture plus high velocity air promotes a transfer of heat from the web of paper and disrupts the moisture and heatla'den layers. of air which normally follow the moving web.

These nozzles are provided with suitable valve means such as ball valves as at 19 which may be provided with manual control means 20 or by remote-controlled solenoid means 21, individually controllable by, for example, the control buttons 22, on the panel 23. One or more of these valves may be actuated to deliver relatively cool or relatively heated air correlated to the high or low spots on the paper web to provide the effects previously described. This operation may be conveniently carried out in correlation to the caliper gauge means generally indicated as 24 which engages and traverses the web 12 as it leaves the calender stack 10 and provides a thickness profile graph 25 by means of an x-y recorder. Thus, where low spots are shown on the graph 25 a suitable valve 19 may be actuated either by means of the manual lever 20 or by remote-controlled buttons 22, to cool the web at the areas conforming to the low spots on the graph 25 thereby cooling the web and thus providing less heat to be transferred to the rolls 11 reducing their expansion, or conversely delivering heated air to areas of the web corresponding to the high spots on the graph 25 thereby to transfer heat to the rolls 11 to a degree substantially equal to adjacent areas whereby to induce expansion of the rolls at such areas and to minimize differences in expansion of the roll longitudinally thereof and to consequently provide a web of enhanced uniform thickness in its transverse direction, and to thus provide an improvement in the quality of the paper which is subsequently coated and further calendered or supercalendered.

Although we have shown and described the preferred method and means of our invention, it will be understood by those skilled in the art that changes may be made in the details thereof without departing from their scope as comprehended by the following claims.

We claim:

1. In a papermaking process wherein a newly formed, forwardly moving, heat dried web is subjected to densification between metallic calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, the improvement which comprises thermally treating selected areas on at least one face of said heated web by blowing gas thereagainst in heat exchange relationship correlated to said expansion whereby to minimize expansion variation prior to calendering thereof, by blowing relatively cool air against a portion of the web which is at a relatively higher temperature than other portions of the web and by blowing relatively warm air against a portion of the web which is at a relatively lower temperature than other portions of the web whereby to minimize the effects of said heat variations longitudinally of said rolls.

2. In a papermaking process wherein a newly formed, forwardly moving, heat dried web is subjected to densification between metallic calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, the improvement which comprises thermally treating selected areas of said heated web, prior to calendering thereof by blowing relative cool air against a portion of the web which is at relatively higher temperature than other portions of the web, whereby to minimize the effects of said heat variations longitudinally of said rolls.

3. In a paperrnaking process wherein a newly formed, forwardly moving, heat dried web is subjected to densification between metallic calendering rolls While retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, the improvement which comprises thermally treating selected areas of said heated web, prior to calendering thereof by blowing relatively warm air against a portion of the web which is at a relatively lower temperature than other portions of the web whereby to minimize the effects of said heat variations longitudinally of said rolls.

4. In a papermaking process wherein a newly formed, forwardly moving, heat dried web is subjected to densification between metallic calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said Web to said rolls resulting in variable expansion longitudinally of said rolls, the improvement which comprises periodically calipering said web in a transverse direction as it leaves said calendering rolls and thermally treating selected areas of said heated web, prior to calendering thereof by blowing streams of air thereagainst at temperatures inversely proportional to the thickness of the web as determined by said calipering,

whereby to minimize the effects of said heat variations longitudinally of said rolls.

5. In a papermak-ing apparatus comprising metallic calendering rolls disposed adjacent the last paper drying drum wherein a newly formed, forwardly moving, dried web is subjected to densification between said calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, means for thermally treating selected areas of said heated web, prior to calendering thereof, whereby to minimize the effects of said heat variations longitudinally of said rolls.

6. In a papermaking apparatus comprising metallic calendering rolls disposed adjacent the last paper drying drum wherein a newly formed, forwardly moving, dried web is subjected to densification between said calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, means comprising a series of selectively actuatable air jets disposed adjacent and parallel to said rolls for thermally treating selected areas of said heated web, prior to calendering thereof, whereby to minimize the effects of said heat variations longitudinally of said rolls.

7. In a papermaking apparatus comprising metallic calendering rolls disposed adjacent the last paper drying drum wherein a newly formed, forwardly moving, dried web is subjected to densification between said calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said Web to said rolls resulting in variable expansion longitudinally of said rolls, means for thermally treating selected areas of said heated web, prior to calendering thereof, comprising a series of selectively actuatable air jets disposed between and parallel to said drying drum and calendering rolls and adjacent to at least one web surface, whereby to minimize the eifects of said heat variations longitudinally of said rolls.

8. In a papermaking apparatus comprising metallic calendering rolls disposed adjacent the last paper drying drum wherein a newly formed, forwardly moving, dried web is subjected to densification between said calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, means for thermally treating selected areas of said heated web, prior to calendering thereof, comprising a series of selectively actuatable air jets disposed between and parallel to said drying drum and calendering rolls and adjacent to at least one web surface, and remote control means for said jets, whereby to minimize the effects of said heat variations longitudinally of said rolls.

9. In a papermaking apparatus comprising metallic calendering rolls disposed adjacent the last paper drying drum wherein a newly formed, forwardly moving, dried web is subjected to densification between said calendering rolls while retaining heat in varying degree transversely of the web, and wherein heat is transferred from said web to said rolls resulting in variable expansion longitudinally of said rolls, transversably reciprocable calipering means embracing said web disposed after passage of the web through said cellular rolls, and means for thermally treating selected areas of said heated web by blowing streams of air thereagainst at temperatures inversely proportional to the thickness of said web as determined by said calipering means comprising a series of selectively actuatable air jets disposed between and parallel to said drying drum and calendering rolls and adjacent to at least one web surface, pr-ior to calendering thereof, whereby to minimize the efiects of said heat variations longitudinally of said rolls.

References Cited UNITED STATES PATENTS 2,012,115 8/1935 Woodruff 34160 X 2,091,805 8/1937 Chuse 34-18 X 2,370,811 3/1945 Osgood 34 160 X 3,071,865 1/1963 Faeber 34 31 X 3,161,482 12/1964 Gschwind et al.

OTHER REFERENCES Paper Trade Journal, Lockwood Trade Journal Co., Inc., New York, June 10, 1963, pages -43.

KENNETH W. SPRAGUE, Primary Examiner.

Claims (1)

1. IN A PAPERMAKING PROCESS WHEREIN A NEWLY FORMED, FORWARDLY MOVING, HEAT DRIED WEB IS SUBJECTED TO DENSIFICATION BETWEEN METALLIC CALLENDERING ROLLS WHILE RETAINING HEAT IN VARYING DEGREE TRANSVERSELY OF THE WEB, AND WHEREIN HEAT IS TRANSFERRED FROM SAID WEB TO SAID ROLLS RESULTING IN VARIABLE EXPANSION LONGITUDINALLY OF SAID ROLLS, THE IMPROVEMENT WHICH COMPRISES THERMALLY TREATING SELECTED AREAS ON AT LEAST ONE FACE OF SAID HEATED WEB BY BLOWING GAS THEREAGAINST IN HEAT EXCHANGE RELATIONSHIP CORRELATED TO SAID EXPANSION WHEREBY TO MINIMZE EXPAN-

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