US3221416A - Heat treating method and apparatus for sheet or web material - Google Patents

Description

Dec. 7, 1965 H. L. SMITH, JR HEAT TREATING METHOD AND APPARATUS FOR SHEET OR WEB MATERIAL Filed May l5, 1962 vtm mmv

INVENTOR Horace L.Smi1h, dr. Wwf@ ATTORNEYS United States Patent O 3,221,416 HEAT TREATING METHD AND APPARATUS FR SHEET R WEB MATERIAL Horace L. Smith, Jr., Richmond, Va., assigner to Hnpp Corporation, Cleveiand, Ohio, a corporation of Virginia Filed May 15, 1962, Ser. No. 194,879 6 Claims. (Cl. 3i-41) This invention relates to a method of, and apparatus for, the heat treating and drying of continuous sheet, or web, material, and more particularly to a method and apparatus for drying paper base materials while under lateral tension. It has particular applicability in drying relatively thick paper products such for example, as paper base box board and the following description will be made in this connection although the invention has general applicability as hereinafter set folth.

Box board or the like is normally made on cylinder machines in which a conventional arrangement of rotating cylinder driers receives and dries the newly produced wet sheet material while maintaining continuous Contact with the smooth surface of the driers to prevent wrinkles, cockle, etc. In such apparatus the sheet material is under considerable longitudinal tension, i.e., tension in the direction of travel, and under no appreciable laterial tension, i.e., tension in the sheet material at right angles to the direction of sheet travel. Lateral shrinkage is therefore disproportionately large in relation to longitudinal shrinkage and the resultant product does not exhibit optimum physical strength and durability in service.

Previous drying methods have also been undesirably slow in production and many have failed to uniformly heat the entire surface of the wet sheet sufficiently to produce a completely satisfactory Ihigh quality, yet low cost, product.

These and other disadvantages are overcome by my present invention involving maintenance of lateral tension in the wet sheet material after it has been dried to withstand the tension, and applying heat uniformly over the entire width of the sheet, preferably by radiation as set forth below. As a result, primarily of the lateral tension established in the wet sheet during drying, a product having properties superior to similar products heretofore produced, is achieved without substantial, if any, increase in manufacturing costs. The physical or chemical mechanism by which the lateral tension produces the improved product over conventional drum drying processes is not known at this time although it is lthought that the results are due to a resultant unique libre orientation, due perhaps to a balancing of the lateral versus longitudinal shrinkage differential, possibly with the combination of relatively fast, uniform heating by radiation which, for best results is by peak radiation in the wave length most readily absorbed by the wet sheet.

The lateral tension created in the wet sheet should be of sufficient magnitude to prevent wrinkling or cockling, and permit substantially no lateral sagging. Beyond this however, the limits of tension magnitude for optimum process results can be established by test 4runs for each material being treated since this will vary basically, according to the organic composition and thickness of the sheet material, and the degree of wetness upon entering the dryer. The tension if desired, may be maintained throughout subsequent treating phases such as cooling or during application of finishing materials such as treating liquids, although this is not necessary.

The most pertinent art of which I am aware is not in the paper drying art, but has to do with the heat treatment of textiles, where it has been the practice for a number of years in the iinishing of some types of cloth, to mount wet cloth on a tentering machine having edge-gripping clips on opposed chains which grip its opposite longitudinal edges whereby the cloth is stretched transversely while it 3,22 l ,4 l 6 Patented Dec. 7, 1 965 ICC travels in a longitudinal direction through the tentering machine. During such travel of the cloth on the machine it is usually heated to dry, set, and cure. The object of lateral tensioning the cloth is to suitably stretch knit goods, prevent weave deformation, maintain absolute uniformity in width, and to promote uniformity of treatment to reduce the possibility of streaking or shading. Thus, while the tenter apparatus is somewhat similar to the apparatus disclosed herein, the present invention differs significantly from the tenter treating methods in that the primary purpose here is to produce a product of improved physical strength, yand having other advantages, as well as to promote uniformity and economy of heat treatment. Prior to this invention it has not been thought desirable, or possible to dry paper base materials in a tenter-like apparatus, primarily because the advantages of drying under lateral tension were not realized and since it has not heretofore been realized that paper base materials not having the fiber strength of textiles could be handled for drying on such apparatus.

Accordingly, it is the primary object of this invention to provide a novel method for the production of paper base sheet materials of improved physical properties.

Another object is to provide a novel method of producing improved paper board sheet material such as used in the manufacture of boxes and like mat-erials, by establishing lateral tension in the sheet material while it is being heated in a suitable heating zone, the source of heat in which is preferably, although not necessarily, radiant heaters.

Still another object is to provide novel apparatus and methods for producing paper board sheet and like materials by establishing laterial tension in the sheet While in a relatively wet state, but after physical production thereof and preliminary drying by conventional apparatus, and thereafter or during application of the laterial tension passing the wet sheet under tension through a heating zone heated preferably, by radiant heaters emitting radiations of peak wave length in the range most readily absorbed by said wet sheet.

Other object-s and advantages of the present invention will become apparent to those skilled in this art from the appended claims `and following description of the preferred embodiment of the present invention taken in connection with the accompanying drawing in which:

FIGURE l is a plan view of a drying apparatus constructed according to the present invention;

FiGURE 2 is a front elevation View of the apparatus illustrated in FIGURE l;

FIGURE 3 is a detail front elevation view, of larger scale than FIGURES l and 2 of a wet sheet gripping device attached to a piece of sheet material and utilized in the apparatus illustrated in FIGURES l and 2; and

FIGURE 4 is a plan view of a series of gripping devices illustrated as being attached to a sheet of material passing through the apparatus illustrated in FIG- URES l and 2.

Referring to the drawing, a conventional box board making machine 10 is diagrammatically illustrated by phantom lines producing a continuous sheet of wet paper base material 14. A large preheating drum 18 receives the wet paper emerging from machine 10 to remove a sufficient amount of moisture to enable the wet material to be laterally tensioned and dried in accordance with this invention. Drum 18 is associated with a pair of guide rollers 22, 23 which direct the wet sheet onto and off of drum 18, and onto another pair of guide rollers 24, 28.

Drum 18, pivoted about shaft 32, may be of any suitable drying apparatus, for example, a conventional Yankee drier or the like. However, it is preferred that such drying drum be constructed in accordance with the principles of the invention set out in my copending application Serial No. 118,439, tiled June 20, 1961 for Heat Transfer and Pressure Applying Apparatus and Method of Manufacture Thereof (now Patent No. 3,181,605) wherein a drum is described having a unidirectional, or countercurrent channels, set up therein forreceiving a heated fluid. The latter is preferably a high boiling hydrocarbon liquid capable of being heated to temperatures in the order of S50-700 F., without substantial increase in pressure. This rhas considerable advantage over similar prior art devices in which steam has normally been used as the heating medium requiring construction of heating equipment capable of withstanding relatively high pressures and yet producing only moderately high temperatures at practical operating pressures.

As the wet sheet material enters the tensioning and drying zone, it is passed between radiant heating panels 40 and 42 which are preferably provided with the heated, low boiling point liquid which may also be circulated therein in a unidirectional manner, or in channels which direct the liquid in opposite, countercurrent directions to thereby achieve a more uniform temperature over the surface of the panel. A plurality of panels may be connected in series or one single large panel may be used. However, if a large panel is used, it is desirable that the countercurrent liquid iiow be utilized inasmuch as the temperature drop over a large panel will be substantial. The heating iiuid medium supplied to the panels is suitably heated and pumped in a system in which the panel constitutes a part thereof and the liquid is circulated through the panels and recirculated back to the heater and pumped continuously so that the heat may be maintained relatively constant if desired. Any suitable system which accomplishes this result may be utilized and it is nota part of this invention.

The radiating panels are preferably, although not necessarily spaced approximately equal distances from the opposite sides of wet sheet 14. The radiating surfaces of the panels facing the sheet are coated with a highly emissive material so that the panels may radiate at optimum efficiency. Such emissive material may be for example, a glass frit coating, or other suitable composition.

Many materials absorb radiation of predetermined wave lengths much more readily than radiation of other wave lengths. The more radiation absorbed by a material, the less it reflects, the more heat is generated therein, and the quicker the material will be dried to the desired degree. Accordingly, the radiating surface of the panels are provided with a coating, and are operated at a temperature, which will emit radiant energy at the wave length range most readily absorbed by the particular wet sheet material being processed. The selection of a suitable wave length will be dependent on the nature of the wet content of the sheet material, and the composition of the sheet material itself. If wave lengt-h data is unknown, the optimum wave length range can readily be determined by known testing methods.

Sheet 14 is carried through the radiant heating Zone by means of a tenter apparatus comprised of a pair of chain-like traveling sheet-gripping members indicated generally as 44 and 46 in FIGURE 1, As sheet 14 emerges from roller 28, travelling from left to right as viewed in FIGURE l, it is directed into gripping members 44 and 46 which grip the sheet material and carry it throughout the length of the heating zone and deliver it to a final guide roller 50 and product accumulator diagrammatically illustrated at 54.

Gripping members 44 and 46 are shown substantially parallel in FIGURE 1; however, they may be adjusted to converge or diverge as desired depending upon the degree of tension desired to be established in the sheet material as it proceeds through the drying zone. Each gripping member 44 and 46 is comprised of a continuous chain-like element driven by any suitable means, about sprockets located at the opposite ends of each of the gripping members.

The preferred construction of the tenter frame assembly is illustrated in more detail in FIGURES 3 and 4. FIGURE 3 is a detailed showing of the preferred means by which the gripping members engage and hold moving sheet 14 by a plurality of clamps each comprised of a pair of clamp arms 58 pivotally mounted on a U-shaped link body member 59. Clamp arms 58 have substantially flat parallel clamping surfaces which engage sheet 14 when the clamp is in the closed position as illustrated in full lines in FIGURE 3, and are biased toward a normal open position illustrated in dotted lines in FIGURE 3 by a spring member 62 and are closed by rotatable cam followers 66 mounted on each clamp arm 5S and adapted to bear against stationary cam tracks 68 and 70.

Cam tracks 68 and 70 are elongated members having recesses 74 at spaced intervals on the inner side thereof facing `sheet material 14. A guide wheel 76 and 78 is mounted for rotative movement on the top and bottom portions of each chain link body member 59. As the chain moves with the sheet material in its direction of travel, wheels 76 and 78 bear against the surface of cam tracks 63 and 'i0 respectively and thereby maintain the desired path of travel of the chain. Cam followers 66 rolling on the inner side of cam tracks 68 and 70 and being biased against the cam by springs 62, maintain clamp elements 58 in their closed position until a cam follower 66 arrives at a recess 74, at which time the particular clamp arms, associated with the cam, open to the dotted line position as shown in FIGURE 3, and as illustrated by the middle clamp in FIGURE 4 for example. Thus, during the travel of the sheet material throughout the length of the heating zone it will be engaged by a plurality of clamps which grip and tend to maintain the width of the sheet material the same throughout the drying zone even though it may tend to shrink due to drying. However, so that the sheet material will not be unduly stressed for too long a period of time the clamps are closed and released periodically throughout their travel through the heating zone according to the spacing of recesses 74 along cam tracks 68 and 70.

As the sheet material 14 enters the drying zone, it is initially gripped by a plurality of clamps and as the material proceeds through the drying zone increased tension will be progressively applied to the sheet material due to its drying and shrinking. Thus, when the gripping members 44 and 46 are maintained in a relatively parallel position as shown in FIGURE 1 the extent of tensioning will be directly proportional to the extent of shrinkage. By maintaining the same width of the material from the beginning to the end of the drying zone the forces of tension being applied from within the sheet material, a desirable fibre structure is established which produces the aforementioned superior product. However, if desired, the degree of tension may be applied by arranging the gripping elements so that they diverge or converge progressively through the drying zone. Alternatively, if a maximum tension is desired to be maintained after having once been achieved in the paper, the gripping elements may be parallel for a portion of the run and then may have intermediate sprockets or other suitable means for effecting divergence or convergence of the gripping elements throughout the remaining length of the drying Zone as desired.

The invention may be embodied in other specific forms without departing from the lspirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A method of producing box board and similar relatively thick paper products of improved quality, comprising the steps of:

(a) forming a wet, continuous web of the paper product;

(b) continuously moving the Wet web in at least one horizontal drying pass between radiant heaters baving emitting 4surfaces substantially parallel to, closely adjacent, and on opposite sides of the wet web to thereby dry said Web; and

(c) as the web moves between said radiant heaters,

periodically and alternately;

(d) applying tensile forces acting at right angles to the Webs direction of movement to said product to produce lateral tension therein; and

(e) releasing the lateral tension thereby produced in said web from the web.

2. The method as defined in claim 1, together with the step of removing from the newly formed wet web before it reaches said horizontal drying pass a minor proportion of the water in said product.

3. The method as defined in claim ll, wherein the lateral tension applied to the product is progressively increased as the web moves through said horizontal drying pass.

4. The method as dened in claim 1, wherein the lateral tension applied to said sheet is prevented from exceeding a predetermined maximum as said web pro gresses through the drying pass.

5. Apparatus for drying box board and similar relatively thick paper products under lateral tension to produce products of improved quality, comprising:

(a) means for forming a continuous wet web of the paper product;

(b) preliminary drying means for removing a minor amount of the moisture from the newly formed product;

(c) drying means comprising radiant heaters adapted to have the web being dried passed therebetween; and

(d) means for conveying the wet Web from the preliminary drying means through the drying means between said radiant heaters, including:

(e) means for, concomitantly with the passage of the web between said radiant heaters, alternately:

(f) applying tensile forces acting at right angles to the webs direction of movement to said product to produce lateral tension therein; and

(g) releasing the lateral tension thereby produced in said web from the web;

(h) said last-na1ned means including means for pe riodically applying said tensile forces to and releasing the lateral tension from said web as it passes between said radiant heaters.

6. Apparatus for drying box board and similar relatively thick paper products under lateral tension to produce products of improved quality, comprising:

(a) means for forming a continuous wet web of the paper product;

(b) preliminary drying means for removing a minor amount of the moisture from the newly formed product;

(c) drying means comprising radiant heaters having parallel, closely spaced, horizontally Ioriented emitting surfaces at least equal in width to the width of the web of newly formed product;

(d) means for conveying the newly formed product from the preliminary drying means through the heated zone between the radiant energy emitting surfaces and for maintaining lateral t-ension in said web as it moves through said zone including means gripping both edges of said web product and maintaining a predetermined distance between said edges, said conveying means comprising:

(e) endless members on both sides of the heated zone supported for movement therealong and gripping means comprising:

(f) co-operating upper and lower clamp arms pivotally fixed to said endless members at predetermined intervals;

(g) spring means biasing said clamp arms apart;

(h) co-operating upper and lower cam tracks extending the length of the heated zone on opposite sides thereof; and

(i) cam followers fixed to said upper and lower clamp arms and engaging said upper and lower cam tracks;

(j) said cam tracks being contoured to force said clamp arms against said web against the bias of; the spring means to secure the web therebetween as it moves through the heated zone.

References Cited by the Examiner UNITED STATES PATENTS 2,094,111 9/1937 Willis 34-158 2,103,110 12/1937 Dickhaut 34-158 2,569,713 7/1951 Dunski BIL-158 2,621,422 12/1952 Deck 34-158 2,760,410 8/1956 Gillis 34-18 2,788,841 4/1957 Hockett 34--158 WILLIAM F. ODEA, Primary Examiner. NORMAN YUDKOFF, Examiner,

Claims (1)

1. A METHOD OF PRODUCING BOX BOARD AND SIMILAR RELATIVELY THICK PAPER PRODUCTS OF IMPROVED QUALITY, COMPRISING THE STEPS OF: (A) FORMING A WET, CONTINUOUS WEB OF THE PAPER PRODUCT; (B) CONTINUOUSLY MOVING THE WET WEB IN AT LEAST ONE HORIZONTAL DRYING PASS BETWEEN RADIANT HEATERS HAVING EMITTING SURFACES SUBSTANTIALLY PARALLEL TO, CLOSELY ADJACENT, AND ON OPPOSITE SIDES OF THE WET WEB TO THEREBY DRY SAID WEB; AND (C) AS THE WEB MOVES BETWEEN SAID RADIANT HEATERS, PERIODICALLY AND ALTERNATELY; (D) APPLYING TENSILE FORCES ACTING AT RIGHT ANGLES TO THE WEB''S DIRECTION OF MOVEMENT TO SAID PRODUCT TO PRODUCE LATERAL TENSION THEREIN; AND (E) RELEASING THE LATERAL TENSION THEREBY PRODUCED IN SAID WEB FROM THE WEB.

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