US 3284285 A
Description (OCR text may contain errors)
Nov. 8, 1966 G. R. HOLDEN 3,284,285
APPARATUS FOR DEWATERING OF FIBROUS WEBS V IN PAPERMAKING AND SIMILAR MACHINES Filed March 18, 1965 4 Sheets-Sheet 1 Nov, 8, 1966 G. R. HOLDEN APPARATUS FOR DEWATERING OF FIBROUS WEBS IN PAPERMAKING AND SIMILAR MACHINES 4 Sheets-$heet 2 Filed March 18, 1965 4 Sheets-Sheet 3 Nov. 8, 1966 Momma APPARATUS FOR DEWATERING OF FIBROUS WEBS IN PAPERMAKING AND SIMILAR MACHINE! Filed March 18, 1965 Nov, 8, 1966 G. R. HOLDEN 33%45285 APPARATUS FOR DEWATERING OF FIBHOUS WEBS IN PAPERMAKING AND SIMILAR MACHINES Flled March 18, 1965 4 Sheets-$heet 4.
United States Patent APPARATUS FOR DEWATERING 0F FIBRUUS WEBS IN PAFERMAKING AND SIMILAR MACHINES Grenville R. Holden, New Canaan, Conn., assignor to Huyclr Corporation, Rensselaer, N.Y., a corporation of New York Filed Mar. 18, 1963, Ser. No. 265,833 2 Claims. (Cl. 162-2d7) The present invention relates to the dewatering of Webs of freshly laid paper, paperboard, pulp and the like all of which will be referred to herein as paper. At the time a web of paper leaves the Fourdrinier screen the water contents thereof typically will lie in the range of from about 80% to about 90%. A paper web in this condition consists of a structure of some predetermined thickness made up of interlaced or felted fibers having voids between the fibers which are not entirely filled with water in a continuous liquid form whereby the web of paper is essentially porous to air. Stated otherwise, the web at this point has reached a porous condition such that the rate at which further water may be removed by the suction devices of the type ordinarily associated with a Fourdrinier screen is no longer satisfactory from a practical standpoint. Accordingly, a paper web in this condition is customarily transferred to a press or series of presses, usually associated with a relatively thick and absorbent papermakers felt, in which some of the remaining water is removed by a squeezing action. It will be recognized that squeezing of a paper web in this condition will temporarily reduce the thickness thereof and thus may reduce the total volume of voids within the structure of the web to or below the volume of thewater contained in the web, with the result that the water reassumes a continuous liquid form. The presses customarily used utilize such squeezing action to express liquid water from the paper web into an absorbent felt or into suction press rolls.
The present invention is directed particularly to removal of water from a paper web by establishing in the web one or more streams of air or other gas which will flow generally vertically through the thickness of the web to dislodge water from the web. This is accomplished by exposing a substantial area of one surface of the web to a body of gas at superatmospheric pressure while the opposite surface of the web is supported on a porous member such as a screen or felt having gasand water-permeable openings therethrough into which the gas and dislodged water may flow toward a zone of lower gaseous pressure. The body of pressurized air or gas will squeeze the web against the porous member and this may be supplemented by mechanical squeezing if so desired. Such squeezing with consequent reduction in thickness and void volume of the web will cause an increase in proportion of volume of water to total volume of the web. If the water in the web is subdivided it will tend to form into larger subdivisions which will be more readily dislodged by the gas. In many cases the water will form a continuous body which will be literally stripped from the web by the gas flowing therethrough.
Studies, initiated as a result of the concept of the present invention, have revealed that paper webs subjected to a stream of gas at superatmospheric pressure can be effectively dewatered by removal of a substantial amount of water from the interstices of the web either by stripping water therefrom when the Water is in continuous liquid form or by entraining particles of liquid water when the water is in subdivided form, or both. While a large portion of the water can be removed in a very short time by a stripping action, the additional amount which can be removed by entrainment of particles in such a stream of air or gas which penetrates through the web over a fairly extended period of time is well worth while as contrasted with the substantial ineffectiveness of suction means upon subdivided water particles. However, neither stripping nor entrainment of substantial value can be achieved in the extremely short period of time which is taken by an increment of a paper web to pass through the nip of press rolls in a high speed papermaking machine. For example, at a machine speed of 1,000 feet per minute an increment of the paper web will traverse a one inch nip length (measured longitudinally of the web path) in 0.005 second. The studies referred to above have shown that an increment of paper web, the interstices of which are filled with water (whether this condition exists because the web is naturally filled or has been squeezed as discussed above) must be exposed to a gas stream under particular conditions which will be disclosed hereinbelow, for at least about 0.05 second to permit the stream to penetrate the thickness of the web while setting the water ahead of it into motion and expelling it from the opposite surface of the web in a stripping action. At the machine speed aforesaid the web will travel at least ten inches in such period of time.
When the interstices of the web are not filled with water, as would be the case after it had been stripped as described above or as would be the case, for example, if the web had already been subjected to the action of one or more presses particular conditions can be established under which very substantial dewatering can be achieved with an exposure of each web increment to the air or gas stream for periods of time such as about one second. At the machine speed aforesaid the web will travel about two hundred inches in such period of time.
The present invention has for its object the provision of apparatus and methods by the use of which a traveling web of paper may be subjected to a stream or streams of air or gas for a period or periods of time suificient to achieve useful amounts of dewatering, in accordance with the principles discussed above, and under conditions such that the web will not be disrupted and will not be objectionably marked or crushed. The invention may be used for further dewatering of webs which have already passed through conventional presses, or it may be used to supplant one or all of the presses. In particular cases the present invention may be used to dewater webs while still on the screen on which they were formed.
Other and further objects of the present invention will become apparent from the following detailed disclosure of preferred, but not necessarily the only, embodiments of the present invention taken in connection with the accompartying drawings in which:
FIGURE 1 is a somewhat diagrammatic elevational view of one form of apparatus embodying the present invention;
FIGURE 2 is a view, similar to FIGURE 1, showing a d ferent form of apparatus;
FLGURE 3 is a view, similar to FIGURE 1, showing still a different form of apparatus;
FIGURE 4 is a somewhat diagrammatic elevational view of a papermaking machine with web forming, dewatering and drying apparatus associated in according with the present invention; and
FIGURE 5 is a somewhat diagrammatic sectional view taken along the line 5-5 in FIGURE 4.
Referring now to the drawings, in FIGURE 1 there is diagrammatically shown the major elements of a simple form of apparatus embodying the present invention. The illustrated apparatus constitutes a single unit and it Will be understood that a plurality of similar or identical units ordinarily will be placed in series for successive operation upon a web of paper. For example, a plurality of units such as shown in FIGURE 1 may be substituted for the series of presses customarily provided in a papermaking 3 machine. When apparatus such as shown in FIGURE 1 is used in place of the first press in a papermaking machine, it will receive the paper from the Fourdrinier screen whereas when used in place of the second and subsequent presses it will receive the paper from a preceding unit or from a preceding press as may be desired.
As shown in FIGURE 1, a paper web is moving from the left toward the right. When the illustrated unit is used as the first in a series in which it receives the paper web 10 from the couch roll of the papermaking machine, the moisture content of the-web 10 may be in the order of from about 80% to about 90% water by weight which is distributed through the web in subdivided form. When the unit is positioned to receive paper from a preceding similar unit or from a press or other device, the moisture content may be different.
An endless porous belt 12 having substantial tensile strength is conducted over a guide roll 14, a guide roll 16, a return guide roll 18, a tensioning roll 20, and return guide rolls 22 and 24 to establish an endless path of adjustable length through which the belt. 12 may move. The width (not shown) of the belt 12 as well as the axial length of the rolls over which it passes is commensurate with the width of the papermaking machine. The belt 12 also is conducted over a roll 16, into a nip between the roll 26 and a relatively large perforated roll 28 and beneath the perforated roll 28 to a nip between the perforated roll 23 and a roll 30. The roll 28 is rotatable upon a hollow shaft 32 which preferably is fixed against rotation. The bearings for the roll 28, as well as the closures for the op posite ends thereof, have not been illustrated, it being understood that the construction in this respect may be similar to that of the conventional suction press roll. The interior of the roll 28 is partitioned by a chamber-forming element 34 fixed to the hollow shaft 32 to provide a chamber 36 which extends axially of the length of roll 23 and which communicates with the interior of the shaft 32 as by one or more passageways 38. The partitioning element 34 is provided with sealing strips 40 and 42 which are pressed against the inner cylindrical surface of the perforated roll 28 and also is provided with end sealing means, not shown, to isolate the chamber 36 from the remainder of the interior of the perforated roll 28. The sealing strips 40 and 42 are preferably positioned approximately opposite the points at which the pressure rolls 26 and 30 engage the exterior surface of the perforated shell of roll 28. The roll 28 is provided with a. very large number of closely spaced perforations 44, the opposite ends of which are open into the outer and inner surfaces of the cylindrical shell thereof. The perforations 44 may be radially drilled holes and, if so desired, they may be flared to larger diameter at their outer ends (not shown) in a manner which is well known in the construction of suction press rolls.
The web 10 is brought into contact with the upper surface of the belt 12, usually in the vicinity of the guide roll 14, and is carried by the belt 12 into fiatwise engagement with the portion of the perforated roll 28 which. lies be tween the rolls 26 and 30.
A receiver 46 is positioned inside the path of the belt 12 and is provided with a bottom wall 48, side walls 50 and 52, as well as with end walls not shown. The receiver 46 is positioned beneath and throughout the axial length of the perforated roll 28 and it encompasses the pressure rolls 26 and 30 as well as that portion of the perforated roll 28 which extends between these pressure rolls. The receiver 46 serves to collect water discharged from the web 10 and through the porous belt 12 as well as any water that might be thrown from the surfaces of the rolls 26 and 30. The upper edges of the side walls 50 and 52 of the receiver 46 need not engage the lower or inner surface of the endless belt 12, but preferably are positioned rather closely thereto in order to catch substantially all of the water that may be discharged in the vicinity of the perforated roll 28. The receiver 46 is provided with a drain 54 through which accumulated water is discharged along with the air or other gas which passes through the apparatus as will be described hereinbelow.
The endless belt 12 may be a papermakers felt of suitable strength and porosity or it may be a suitable screen-like or perforated structure made from metal or plastic sheet materials or woven from synthetic yarns or metal Wires. The relative merits of these various materials will be discussed below. However, an illustrative preferred form of belt 12 is a screen-like fabric woven from synthetic yarns, such as multifilament or monofilament yarns of suitable size and construction. Such yarns preferably are woven into an endless tubular structure, the circumference of which is equal to the length of the endless path through which the belt is to be conducted in use. When woven in this manner the belt will be devoid of seams. The endless belt 12 may be woven from material such as polyamides which are known as various types of nylon or polyesters such as Dacron, or combinations thereof, as well as other synthetic materials which have great tensile strength and resistance to abrasion, whether wet or dry, and preferably are made in accordance with US. Patent No. 2,903,021. When so made the yarns which extend longitudinally of the belt 12 are preferably set in relatively straight configuration while the crosswise yarns are set in curved condition so as to present knuckles as disclosed in said US. Patent 2,903,021. Also preferably, the endless belt 12 is impregnated or coated, or both, with a suitable heat-settable, resinous or other material which serves to enhance its dimensional stability. In any event, it is preferred that the weave of the endless belt 12 be stabilized by heat or other suitable treatment of the woven belt which will set either or both of any settable fiber-forming material incorporated in the yarn and any coating or impregnating material therein. It will be understood that an endless belt made of synthetic fabric and treated as just described, is a relatively incompressible screen-like structure which is non-absorbent of water and which is extremely stable in weave and dimensions. Such a structure has substantially uniform porosity throughout its area and the porosity as well as the void volume thereof is virtually unaffected by mechanical or other pressure applied generally in the direction of the thickness of the woven fabric.
For use with fine papers wherein marking of the paper would be objectionable, the belt 12 may be a fine screenlike fabric, or a duplex fabric with a fine screen-like surface for contact with the paper. Also, a felt may be used. For coarser grades of paper or board or for lap pulp where marking is of less consequence or of very little consequence, the fabric may be woven from coarser yarns and may have proportionately larger openings between adjacent yarns. For the purposes of the present invention, the fabric or felt used for the belt 12 should be readily permeable to water and air.
In FIGURE 1 it will be observed that the web of paper 10 is supported throughout its width upon the upper surface of the belt 12 and is held in contact with the exterior surface of the perforated roll 28. The belt 12 or perforated roll 28, or both, are driven by means, not shown, at such speeds relative to the linear speed of the paper web 10 as to permit substantially no slippage between the paper web 10 and the belt 12 and roll 28 between which the web 10 is sandwiched. It will be apparent that the paper web 10 remains in contact with a substantial portion of the perforated surface of the roll 28 as the web moves from the roll 26 to the roll 30.
As is customary in the construction of paper machine presses, the perforated roll 28 may be carried by a structure which provides downward force or adjustment in vertical directions whereby to vary the amount of pressure exerted upon the web 10 and belt 12 in the nips formed between the roll 28 and the rolls 26 and 30. Alternatively, a similar result may be achieved by mounting the roll 28 on an immovable axis and providing ad justable mountings for the rolls 26 and 30 whereby the latter may be moved generally radially of the axis of rotation of the roll 28. The latter alternative is particularly useful in instances wherein the paper web is held in contact with a greater portion of the periphery of the perforated roll 28. For instance, the rolls 26 and 30 may be positioned in a horizontal plane passing through or passing well above the axis of the roll 28 in which event the chamber 36 would span a correspondingly larger portion of the inner surface of roll 28. It will be appre ciated that while the pressure exerted upon the web and 12 in the nips may be varied as discussed above, such adjustment of nip pressures will have little or no effect upon the tightness of confinement of the web 10 against the surface of roll 28 in that portion of the path of the web 10 which lies between the pressure rolls 26 and 30. For the purposes of the present invention it is desirable at least that the web 10 be held firmly against the surface of the roll 28 throughout the portion of the path just discussed to resist billowing away from the roll 28 when the dewatering gas is discharged through the perforations 44 in the surface of the roll 28. Furthermore, as pointed out above, air blast dewatering efficiency is increased by squeezing the web to reduce its void volume with attendant increase in size or proximity of discrete water particles therein. When the water content of the web 10 is high enough, as may be the case with a paper web coming directly from the forming screen or couch roll, it is practicable in the form of the invention illustrated in FIGURE 1 to squeeze the web 10 in at least a portion of the path of travel from roll 26 to roll 30 to such an extent as to fill the voids of the web 10 with water in substantially continuous, liquid form.
The amount of pressure exerted by the belt 12 upon the web 10 in directions radially inward of the perforated roll 28 is dependent upon the amount of tension that may be placed longitudinally upon the belt 12 in at least that portion thereof which, at any given instant, extends from the nip of roll 26 to the nip of roll 30. In the form of apparatus shown in FIGURE 1 the tensioning roll is positioned between the guide rolls 18 and 22 in the return portion of the path of belt 12. Movement of the tensionin'g roll 20 in the direction of the arrows will cause a greater or lesser amount of tension to be placed upon the belt 12. It has been found that when the belt 12 is Woven from suitably selected synthetic yarns as discussed above, its tensile strength in a longitudinal direction is adequate for the application thereto of very substantial amounts of tension, quite sufficient to hold the paper web 10 tightly in contact with the perforated roll 28 and, where desirable, to squeeze the paper web for the purposes mentioned above.
In operation compressed air or other gas is continuously supplied to the chamber 36 within the perforated roll 28 for discharge through the perforations 44 therein within the area bounded by the sealing elements 40 and 42 and the pressure rolls 2 6 and 30. The air discharged from the perforations 44 in this zone is brought directly into contact with the closely confined upper surface of the paper web 10 and will be directed through the web 10 to strip or to entrain water within the web for discharge through the lower surface of the web 10 and through the belt 12 into the receiver 46. The water and air discharged into the receiver 46 may be permitted to flow outwardly through the drain 54 and the water may be separated from the air for disposal or reuse as may be desired. It will be apparent that the drain 54 also may be connected through suitable conduits to a suction pump and water separation device, if so desired, to enhance scavenging of water from the receiver 46. The suction pump may also be used to reduce back pressure in the receiver 46 or even to lower the pressure therein to a su'batmospheric pressure, if so desired.
The differential in gaseous pressure between the high pressure chamber 36 in the perforated roll 28 and the receiver 46 may be selected from a wide range of pressures dependent to a great extent upon the type and the moisture content of the paper being dewatered. For light and/0r porous grades of paper differentials as low as from about 4 p.s.i. to about 15 p.s.i. will be effective, particularly when the major portion, at least, of the differential is established by use of gas at superatmospheric pressures. It has been found that differentials as great as from about 15 p.s.i. up to about 60 p.s.i. may be used with many grades of paper containing as much as to moisture particularly when such selection is accompanied by appropriate selection of texture and weave of the endless belt 12. Differentials in the higher portion of this range can be used with almost any type of paper or similar felted product when the moisture content thereof is somewhat lower, for example in the range of from about 60% to 7.5%, which frequently is the lowest moisture content that can be established by conventional presses.
The supplying of air or other gas at superatmospheric pressure to the chamber 36 to establish the entire differential, or at least a major portion of the differential, has been found to be greatly preferable for the purposes of the present invention over any attempt to rely entirely upon the establishment of a su-batmospheric pressure in the receiver 46 to work against atmospheric pressure in the chamber 36. While there are several practical reasons for this preference, including the fact that differentials in excess of about 15 p.s.i. may be readily established by a compressor, it should be pointed out that a major reason for preferring superatmospheric pressure for dewatering a web in which the water is in subdivided form is the avoidance of rarification of air which occurs when a substantial differential is set up by suction means. For a given differential the rarified air which may be sucked through the torturously small passageways in a paper web has much less power to entrain discrete water droplets than the densified air or other gas which may be forced through the same web by an air compressor.
The amount of time during which the paper web 10 is subjected to the fiow of air for dewatering purposes is, as indicated above, a function of the linear speed of the web and the length of the circumferential path from roll 26 to roll 30. A relatively large number of suction press rolls now in use in the paper industry have a diameter of about 32 inches. Rolls of such diameter are used on machines of relatively great width, that is, a width of perhaps 20 feet to 30 feet, and the 32 inch diameter is provided primarily to minimize deflection due to the weight of the roll and the pressure applied at the nip. In a suction press, however, only a very small fraction of the circumference of the suction roll comes into contact with the paper and felt assembly because such contact occurs only in the nip which is of very limited length. For the purposes of the present invention a perforated roll such as is customarily used in a suction press may be used as the roll 28 shown in FIGURE 1. For example, if such a roll having a diameter of 32 inches is used the circumference thereof will be approximately inches. In FIGURE 1 the roll 26 is at approximately the eight oclock position and the roll 30 is at approximately the four oclock position with respect to the roll 28, whereby circumferential distance from the roll 26 to the roll 30 is about one-third the circumference of the roll 28, or about 33 inches. At an assumed machine speed of 1,000 feet per minute, each increment of the web 10 will take approximately 0.165 second to traverse the distance between the rolls 26 and 30. As noted above, a very substantial amount of water may be expelled from a web by compressed air, especially when the voids of the web are filled with liquid water, in as little a 0.05 second. Thus, a 0.165 second period afforded by the particular arrangement shown in FIGURE 1, with the dimensions assumed above, is sufiicient to assure the stripping of liquid water from the paper web as well as to provide some additional time in at least some cases for dewatering by entrainment of the water particles left in the web after the initial sripping.
When the rolls 26 and 30 are positioned at the eleven oclock and one oclock positions, respectively, of a roll 28 the web 10 and belt 12 will wrap about five-sixths of the circumference of the roll 28. Thus, with a roll 28 having a diameter of 32 inches each increment of the web 10 and belt 12 will traverse about 83 inches from the roll 26 to the roll 30. At an assumed machine speed of 1,000 feet per minute this will take about 0.415 second.
'Thus, it will be apparent that the form of the invention shown in FIGURE 1 making use of a perforated roll 28 of typically, commercially available, diameter can provide the relatively extended periods of time needed for effective dewatering of a peper web by air blasting. For example, for the first, second and third presses frequently provided in a large high speed papermaking machine, there may be substituted respectively, a first air press such as shown in FIGURE 1 with the rolls 26 and 30 at the eight oc-lock and four oclock positions, and second and third air presses with the rolls 26 and 30 at the eleven oclock and one oclock positions. At the assumed machine speed of 1,000 feet per minute these air presses will provide almost exactly one full second of exposure of the web 10 to air blasting. It has been found that in this amount of time paper webs of types and caliper including a major percentage of commercial production can be dewatered from the usual moisture content, say 80% to 90%, at which time they leave the forming screen or couch roll, down to about 50% or less. The latter moisture content is considerably below that which is achieved at best by the use of three suction presses.
Optimum results which can be achieved by taking into account the principles of the present invention in connection with the specific paper product being produced usually will be considerably better than what is broadly indicated above. The variables introduced by the type of paper and type of finish required are too numerous to be covered in this specification and are not essential to the present disclosure. However, in a general sense, it will suffice to point out that when the web 10 is squeezed between the belt 12 and perforated roll 28 to such an extent as to fill the interstices or voids therein with liquid water, the air pressure in the chamber 36 needs only to be high enough to push the liquid water out of the web 10 in the time available, whereas in those cases wherein the web is not compressed to such an extent, the web remains porous and higher air pressures, with attendant higher velocities and air densities, can be used to promote more efficient entrainment of subdivided water particles. Also, longer periods of time of exposure at each air press or longer total periods of time of exposure may be provided by using perforated rolls of proportionately larger diameter or by using a larger number of air press units such as shown in FIG- URE 1. The latter procedures are available in any instance wherein the air pressure must be reduced to avoid damage to or marking of the paper or where relatively weaker, extremely fine fabric belts 12 must be used to minimize screen marking of the web.
' While it has been stated above that relatively high air or other gaseous pressures of from about p.s.i. up to about 90 p.s.i. or even more, may be applied, in accordance with the present invention, to paper for dewatering it, it should be pointed out that substantially lower pressures may be used. For example, pressure of from 3 or 4 p.s.i. to about 15 p.s.i. may be used, particularly when the moisture content of the paper is relatively high. Also, while reference has been made to the difierential in pressure on opposite sides of the Web 10 it is not intended to imply that the entire pressure drop occurs within the web. The water pushed ahead by the air, when the web is full, leaves the web at a high velocity as does the air and entrained water particles when the web is porous. Accordingly, neither the paper web 10 nor the fabric belt 12 is actually subjected to a mechanic-a-l loading corresponding numerically per unit area with the pressure per unit area under which the air or gas is supplied to the pressure chamber 36.
Similarly, it is not believed to be essential or practicable to set forth the specific amount of mechanical pressure to which a paper Web must be subjected to reduce its thickness to such an extent as to result in the water therein filling the voids in liquid form. It .will be apparent, however, that the very moist web which leaves the couch roll of a papermaking machine will require relatively little compression for this purpose, whereas a web containing only about 50% to 60% moisture would require a very substantial reduction in thickness for this purpose. Dependent upon the thickness of the web and the freeness, among other things, of the pulp or furnish from which it is made, there is a limit to the amount of compression which any particular web can withstand without crushing. This is well known in the art and it has been one of the limiting factors with respect to the amount of moisture that can be removed by any form of mechanical squeezing device such as the plain presses and suction presses heretofore used. Accordingly, in the use of the present invention it is intended that the web be compressed to a condition wherein the voids are filled with water, only when this can be done without crushing the paper. It can be safely done with substantially any type of paper having the to water content dis cussed above, and because of the remarkably large amount of water that can be expelled by the air blast disclosed herein when the water is in liquid form it is not likely that such a degree of compression is needed or desirable in any air press succeeding the first air press of the form shown in FIGURE 1. It is for this reason that it is suggested herein that the first air press may provide a substantially shorter exposure to the air blast than the subsequent air presses in which subdivided water must be dislodged by entrainment. I
The amount of mechanical pressure exerted by the belt 12 upon the web 10 in the zone between the rolls 26 and 30 may be calculated in accordance with the following formula:
Unit pressure Pressure (#/square inch on paper) Tension on fabric (pounds per lineal in. of width) X2 Roll diameter (in inches) Since fabrics of the type discussed above are available having an ultimate tensile strength of from about 40#/ lineal inch to about 1,000 or more #/lineal inch, it will be recognized that a very Wide range of pressures may be applied to a paper web 10 by tensioning the belt 12 within the limits of its tensile strength. For example, with a fabric having a tensile strength of such that one may safely put it under a tension of 300 pounds per lineal inch the pressure which can be exerted by the belt 12 on the web 10 in a direction normal to the surface thereof is 600 divided by the diameter (in inches) of the roll 23. When the roll diameter is 32 inches the pressure will be about 18.7 pounds per square inch which is well within the range in which various papers with moisture contents in the 80% to 90% level discussed above will be sufficiently compressed to fill the remaining void volume thereof with water in substantially continuous liquid form. The example just given is merely illustrative inasmuch as for each type of paper and for each specific moisture content it is necessary to determine the unit pressure required to compress the paper to the desired degree.
As stated above, the illustration in FIGURE 1 is deliberately made very simple in order to avoid obscuring of the principles of this invention by the illustration of various details and refinements, within the skill of the art, which could be utilized to advantage. For example, the perforated roll 28 has been shown as a shell with the perforations 44 therein opening directly into contact with the paper web. It will be apparent that, when the finish requirements of the paper demand it, the perforated roll may be provided with a finely woven cylindrical jacket overlying the perforations, or with a spirally wound closely spaced hoe covering made of metal wire or the like, all as is well known in the construction of suction press rolls. Also, instead of a cylindrical covering for the roll 28, there may be provided a second endless belt of fabric, metal screen or the like arranged to run above the web 10, as viewed in FIGURE 1, and thus to lie between the upper surface of the web 119 and the outer surface of the perforated roll 28 in the portion of the web path which lies between the rolls 26 and 30. The provision of any of the structures just described serves, in effect, to substitute a very large number of closely spaced holes (the openings between yarns or wire-s) for the relatively large and widely spaced apertures 44 illustrated herein. The relatively more diffused pattern of impingement of air upon the surface of the web thus provided may be advantageous in any case wherein the uncovered apertures 44 present a problem or wherein, for reasons of economy or strength requirements, it is desired to use a shell 28 with a reduced number of perforations 44.
Similarly, the path or direction of travel of the web 10 as it approaches and leaves the air press shown in FIG- URE 1 may be varied or selected to meet special requirements which might be imposed by the moisture content of the web or by the limited space within an existing papermaking machine in which one or more such air presses is to be installed. When the web has a high moisture content, such as the 80% or 90% content discussed above, and when the web is travelling at a high rate of speed, it is preferable to minimize the sharpness or extent of changes in direction of travel there-of. This is one reason for preferring, as noted above, the positioning of the rolls 26 and 31) at the eight oclock and four oclock positions relative to roll 28 as shown is FIGURE 1 for use with webs of high moisture content and which are resultantly subject to disruption by centrifugal force. It will be apparent that, with a roll 26 of a given diameter positioned at eight oclock, as illustrated, the change in direction of the web 10 as it progresses around the roll 26 into contact with the roll 28 is much less extensive than it would be with a roll 26 of the same diameter positioned at eleven oclock. The latter positioning is entirely suitable, how ever, for webs of lower moisture content or which are travelling at a lower linear speed.
In many cases the selection of the superatmospheric pressure in view of the particular type and moisture condition of the paper web 111 and in view of the particular construction of the belt 12 can be so made as to expel the water from the web and through the openings or passageways in the belt 12. However, there are many combinations of factors such as those just mentioned wherein it may be preferable to dislodge water from the web 10 and to move such water into the passageways of the belt 12 without necessarily blasing all of the dislodged water all the way through the belt 12. For example, to minimize disruption of fiber formation in the web 1d or to minimize impression in the web of the pattern of the belt 12 the belt may be so constructed as to present a closely woven fine screen-like pattern to the paper. Alternatively the belt 12 may be a felt similar to the press felts heretofore used in plain or suction presses. In such cases the fine screen will afford a very large number of small passageways and the felt will present smaller or even capillary passageways. In either event it is not always necessary to provide a superatmospheric pressure sufficient to blast all of the dislodged water through the fine passageways of the belt 12. Instead, advantage may be taken of the capacity of the belt 12 to retain a substantial quantity of water which will be carried away from the paper web 10 when the latter and the belt 12 are separated. The retained water may be dislodged if so desired from the belt 12 by any suitable means, not shown, such as air showers, wringers, suction wringers and the like located in the return path of the belt 12 whereby the successive portions of the belt 12 which enter the apparatus of the present invention may be free or relatively free of water.
In the form of the invention shown in FIGURE 1 the apertures or perforations 44 each constitute an orifice across which a portion of the travelling web is confined while air or other gas is supplied at superatmospheric pres sure through the orifice. When the perforated roll 28 is covered by a jacket or is supplied with an apron as discussed above the openings in the screen, fabric or wire windings which form the apron or jacket serve as orifices for the same purpose. In either event the orifices move with the paper web 10 whereby a particular portion of the web remains in communication with each orifice during the purging operation and since the belt .12 also moves with the web it serves to confine the paper web against the orifices and to support the portions of the web which span each orifice. The forms of the invention to be described below provide rnuch larger orifices across which a paper web, supported by a porous member is: progressively moved and illustrative sealing devices which permit such progressive movement while maintaining a surface of the paper web sealed with respect to the orifice and the gas supplied thereto will be described.
Referring now to FIGURE 2 there is shown a modification of the present invention which provides in a simple and inexpensive manner for the dewatering of a paper web by passing compressed air or other gas through it over an extended period of time. In this form of the invention the paper web is supported upon, or backed-up by a porous belt which is maintained in a flat supportive position primarily by tension exerted longitudinally of the belt as the latter moves through an endless path.
As shown in FIGURE 2, a web of paper or similar felted fibrous material is guided from a source such as the Fourd-rinier screen or couch roll of a papermaking machine or from a set of press rolls or from an air press such as that shown in FIGURE 1, into engagement with the upper surface of a porous belt 112 which may be of the type described above in connection with FIGURE 1. The web 110 and supporting belt 112 are conducted into an enclosure comprising an upper chamber 114 and a lower chamber 116.
The upper chamber 114 is provided with an inlet 118 through which air or other gas may be supplied at a superatmospheric pressure. The inlet 118 may comprise a manifold or a plurality of spaced pipes as desired, and may be positioned in the upper wall 120 of the chamber 114, as shown, or may be positioned in one or both of the side walls 122 as will be more fully described hereinbelow.
The lower chamber 116 may be similar in construction to the chamber 114 and may be provided with one or more outlets 124 positioned in the bottom wall 126, as shown, or end wall 128 thereof as may be desired. The lower chamber 116 is so positioned as to receive water discharged from the web 111] as well as to receive the air or other gas which is forced through the web 110' from the upper chamber 114-. The outlet 126 may be open directly to the atmosphere or may be connected with suitable watenseparating and fines-recovering systems. Also, the lower chamber 116 may be connected to a suction pump in such manner as to assist in scavenging of Water from the chamber and to maintain the gaseous pressure therein below atmospheric pressure, if so desired.
The incoming and outgoing ends of the upper and lower chambers 114 and 116 include end walls 130, 132, 134 and 136 in which are formed horizontally extending apertures of sufiicient width to receive the full width of the belt 112 and web 110 supported thereon. Positioned within the aperture in the incoming end wall 130 of the upper chamber 114 there is a roll 138 which has an axial length slightly less than the width of the porous belt 112. The aperture in the incoming end wall 134 of the lower chamber 116 has positioned thereon a roller 140 which is similar to the roll 138 and which is arranged directly beneath the roll 138. A similar pair of rolls 142 and 144 are positioned respectively in the outgoing apertures in the upper and lower chambers 114 and 116.
The upper rolls 138 and 142 preferably are arranged for vertical adjustment relative to the respective lower rolls 140 and 144 so that the sandwich consisting of the belt 112 and web 110 may be subjected to any desired degree of compressive force as they pass through the nip between the respective pairs of rolls. Suitable sealing means is provided to isolate the interior of the chamber 114 from the surrounding atmosphere. For example, a sealing strip 146 may be positioned between the end wall 130 and the upper peripheral surface of the roll 138. The sealing strip 146 preferably is made of rubber or similar elastomeric material whereby it may be tightly and yieldably pressed against the surface of the roll 138 throughout the length of the roll and the aperture within which the roll lies. Suitable similar sealing strips or devices (not shown) are provided at the opposite ends of the roll 138 to prevent egress air, and while such means has not been illustrated herein, it will be understood that any of the several known forms of sealing devices may be employed. The sealing strips just described for the roll 138 are also provided for the upper roll 142, the horizontal sealing strip 146 only being shown. While the lower chamber 116 may be open to the atmosphere as is the receiver 46 shown in FIGURE 1, it usually is preferred to seal the lower chamber and the same sort of means may be employed as is employed for the upper chamber 114. Thus, in FIGURE 2, sealing strips 146 are illustrated in contact with the lower peripheral surfaces of the rolls 140 and 144.
It will be apparent that sealing means also must be provided along the opposite edges of the belt 112 to prevent, or at least to minimize, escape of air laterally through the belt which, as described above, is preferably made of a woven fabric through which air may move in horizontal directions. While any suitable means may be utilized there is shown herein an endless sealing belt 143 which is conducted around relatively narrow, reduced diameter pulleys or shoulders 150 provided at the opposite ends of the rolls 138 and 142. The belt 148 is conducted over suitable guide rollers 152 and 154 positioned outside of and above the chamber 114 whereby to provide an endless path for the belt 148. The reach of the belt 148 which extends from the lower diametral portion of the roll 138 to the lower diame-tral portion of the roll 142 is so arranged as to press firmly against the lateral edge portion of the belt 112. The sealing belt 148 therefore preferably is made of a yieldable or elastomeric material. The lower reach of the belt 148 may be positioned directly beneath the lower edge of the side wall 122 in order to maintain the belt 148 firmly against the porous belt 112 throughout the length thereof which lies within the enclosure. (See sealing belt 448 and the slotted lower edge of side wall 422 in FIGURE 5.) A similar sealing belt 156 is provided for the lower chamber 116 and such a belt should be provided irrespective of whether the chamber 116 is otherwise open to the atmosphere. The upper reach of the belt 156 is positioned directly above the edge of the side wall 128 whereby the belts 148 and 156 will firmly and tightly engage the associated lateral edge portion of the porous belt 112.
In operation of the apparatus shown in FIGURE 2 the upper rolls 138 and 142 are appropriately weighted or vertically adjusted relative to the lower rolls 140 and 144 so as to exert upon the web 110 and porous belt 112 a desired degree of compressive force suitable for the particular paper of which the web is formed and suitable for the moisture content thereof. The surfaces of all of the rolls 138, 140, 142 and 144 are preferably smooth and imperforate and thus are similar to the plain press rolls heretofore used for dewatering of paper Webs carried by compressible papermakers felts. However, it will be recalled that the material from which the belt 112 is preferably constructed is substantially incompressible at any pressure which may reasonably be applied, whereby any compressive action exerted by the rolls is confined to compression of the paper web alone. Accordingly, any water which might be expressed from the paper in the nip of the incoming pair of rolls 138, 140, for example, will be received in the voids of the belt 112, the volume of which has not been reduced because of the substantial incompressibility of the structure. Care should be taken that the volume of voids in the belt 112 is sufficiently great to receive any quantity of water which might be expressed in the nip of the rolls 138, 140. Thus, if the belt 112 is a fabric having a limited amount of void volume the pressure applied at the nip of rolls'138, should not be sufficiently great to expel any more water from the web 110 than can be received and retained within the voids of the belt 112.
Immediately that each increment of the sandwich consisting of the belt 112 and web 110 passes beyond the nip of the incoming rolls 138, 140 the entire width of such increment will be exposed to the compressed air or other gas contained within the upper chamber 114. As a result of the compression of the paper in the nip of the rolls 138 and 14d and the fact that the web may not instantly recover its original thickness and porosity, there may be a brief period of time during which the voids of each incoming increment of paper web 110 are substantially filled with water in liquid form. In that event such liquid water will be rapidly and effectively stripped from the successively incoming increments of the web by the gaseous pressure exerted thereupon in the upper chamber 114. Thereafter, as each increment of the sandwich consisting of the belt 112 and paper web 110 progresses through the enclosure the pressurized air or gas from the upper chamber 114 will flow through the paper web and will entrain particles of water which are distributed through the web. The gas and entrained water particles will be propelled from the web through the porous belt 112 and into the lower chamber 116.
It will be apparent from the above that the apparatus shown in FIGURE 2 may provide any reasonable length of path for the sandwich consisting of the web 110 and supporting porous belt 112 through the zone in which the differential gaseous pressure exists. As indicated above, dewatering of a felted fibrous material such as paper can be effectively achieved by the flow of gas through the material provided that a sufficient period of time is permitted. For example, the studies referred to above have shown that very substantial amounts of water may be thus removed from a paper web in a period of time as short as 1 second. However, the studies have also revealed that extension of the time up to several seconds will result in even greater dewatering of the paper. The law of diminishing returns sets in rather early and at different times, depending upon the particular paper and initial moisture content thereof, 'but in a very general sense it has not been found to be worth-while to extend the time much beyond 5 to 10 seconds. It will be recognized that at a paper machine speed of 1,000 feet per minute each increment of the web will have travelled about 83 feet in a period of 5 seconds. The removal of water from the paper by means of evaporation on conventional steam-heated dryer drums is such an expensive procedure that, within reasonable limits, the installation of appropriately large tunnel-like equipment such as shown in FIGURE 2, which is simple in construction and which requires no heat and virtually 13 no maintainance, may be preferable to the capital investment and cost of steam dryer felts and maintenance of the portion of the conventional dryer equipment which can be supplanted.
In FIGURE 3 there is shown a modification of the invention which in many respects is very similar to that shown in FIGURE 2. Thus, there is an upper chamber 214 and a lower chamber 216 through which a web 210 of paper or other felted fibrous product is carried upon a porous screen-like belt 212 preferably woven from synthetic material as described above. The upper chamber 214 is provided with an inlet 218 and the lower chamber 216 is provided with an outlet 224. Upper press rolls 238 and 242 are positioned in apertures in the end walls 230 and 232 of the upper chamber 214 and sealing strips 246 are arranged to bear against the upper peripheral surfaces of the rolls 238 and 242. An endless sealing belt 248 is provided to bear upon the lateral edge portion of the porous belt 212.
Also in FIGURE 3 lower press rolls 240 and 244 are positioned in apertures formed in the end walls 234 and 236 of the lower chamber 216 and they are sealed by strips 246. An endless sealing belt 256 is provided to cooperate with the endless sealing belt 248 in sealing the lateral edge portions of the porous belt 212. As in the case of FIGURE 2, the apparatus shown in FIGURE 3 is also provided with suitable sealing devices for cooperation with the opposite ends of each of the rolls 238, 240, 242 and 244, although such sealing means is not shown.
The apparatus shown in FIGURE 3 differs from that shown in FIGURE 2 in that each of the rolls 238, 240, 242 and 244 are hollow perforated shells having a plurality of generally radially extending openings 258 extending throughout the thickness of the shells. Each of the hollow perforated rolls or shells 238, 241 242 and 244 is provided with an inner chamber 260 comprising generally radially disposed walls 262 and 264 having sealing strips 266 and 268 arranged to bear resiliently against the inner surface of the associated shell. A wall 261 having a sealing strip 263 bearing on the inner surface of the shell serves to prevent communication through the shell between the surrounding atmosphere and the chambers 214 and 216. Each of the chambers 260 communicates with a centrally disposed conduit 270 which is accessible outside the associated shell. The chambers 260 are essentially fixed against rotation although as is usual in the construction of suction press rolls, the circumferentail position of the walls 262 and 264 may be adjusted relative to the shells and to each other in order to vary the circumferential length of the inner surface of the shell which is encompassed between said walls.
In operation of the apparatus shown in FIGURE 3 air or other gas under pressure is supplied to the upper chamber 214 and the lower chamber is maintained at a lower gaseous pressure as by permitting discharge to the atmosphere or by application of a suction pump, all as described above in connection with FIGURE 2. However, the apparatus shown in FIGURE 3 not only provides for the squeezing and releasing of the paper as it passes through the nips between rolls 238, 24th and 242, 244 respectively, but it also provides for the blasting of air or other gas through the paper at the time it is under squeezing pressure.
To the latter end, air or other gas at a superatrnospheric pressure which may be the same as or less than but preferably is greater than the gaseous pressure maintained in the upper chamber 214, is supplied to the chambers 261) located in the upper press rolls 233 and 242. Gaseous pressure which is lower than that in the chambers 260 in the upper press rolls, and which preferably is also lower than that in the lower chamber 216, is maintained in the chambers 26% in the lower press roils 240 and 244. This may be achieved by permitting the lower chambers 260 to discharge to the atmosphere but preferably is achieved by connecting such chambers with a suction pump or pumps.
The upper press rolls 238 and 242 are weighted or are vertically adjustable relative to the associated lower press rolls whereby to apply to the web 210 and belt 212 a compressive force of desired magnitude. Also, the press rolls in each pair, 238 and 240, and 242 and 244 are preferably geared together for rotation at the same peripheral speed, and the apertures therein are preferably so located as to register at the nip as shown in FIGURE 3.
Under the mechanical pressure exerted by the upper rolls upon the paper web 210, the latter will be made thinner and there will be a nip of predetermined length, measured lengthwise of the paper web, in which the paper web 210 and belt 212 will be held in intimate contact with the perforated shells of the mated press rolls. The walls 262 and 264 of each of the chambers 260 are so adjusted relative to one another and the length of the nip that the chambers 260 will open only into that portion of the paper web 210 or fabric belt 212, as the case may be, as is confined in the nip.
Because the paper web 216 is backed up, not only by the fabric 212 but also by the mating surfaces of the upper and lower press rolls, a very substantial differential in gaseous pressure may be safely applied to the paper at the press roll nips. Thus, as stated above, it is desirable to utilize air or other gas at a higher pressure in the upper chambers 260 than is utilized in the upper chamber 214.
It Will be appreciated that the matter of shell marking must be considered when utilizing the apparatus shown in FIGURE 3. The pattern of openings 258 in the lower press rolls 240 and 244 will tend to show in the paper, much as in suction press. However, the presence in the nip of the fabric belt 212 will serve to minimize such shell marking because of the diffusion of the exiting air or gas through the finely woven pattern thereof before the air reaches the openings 258 in the lower press rolls 240 and 244. Thus, by proper choice of fabric for the belt 212 and by selection of pressure differentials the problem of shell marking can be obviated.
The very brief squeeze and air blast to which the web is subjected in the nips of the press rolls will be effective to reduce the void volume of the paper web and to discharge any water in excess of that required to fill the voids of the compressed paper into the voids of the fabric. Any water in excess of that required to fill the voids in both paper and fabric will be discharged into the openings 258 in the lower press rolls 240. and 244. Beyond this, the air blast at least will initiate downward migration of water in the web 210, overcoming inertia and thus conditioning the web for eifective dewatering as it passes through the zone between the upper and lower chambers 214 and 216. Also, since the paper is reduced in thickness at the nips and it requires some time for it to expand the water therein will be in more consolidated form at least for a brief period of time after the web leaves the nip. As pointed out above, this too, leads to more effective dewatering by air blast.
The apparatus shown in FIGURE 3 may be utilized as a single unit, as shown, with any desinable or practical length of path for the web 210 and supporting belt 212 from the incoming press rolls 238 and 241] to the outgoing press rolls 242 and 244. Alternatively, a plurality of individually complete units such as shown in FIGURE 3 may be arranged in series to provide a total path. of desired length while also providing repeated squeezing and relaxing of the paper web 219. Also, one or more additional pairs of press roll may be enclosed within the upper and lower chambers 214 and 216 of a unit such as shown in FIGURE 3 to provide more frequent squeezing of the web if so desired.
The devices shown in FIGURES 2 and 3, like that shown in FiGURE 1 may be used instead of or ahead of or behind other dewatering devices such as conventional presses. Also, as described above in connection with FIGURE 1 any suitable provision may be made for removing or reducing the quantity of any water that might remain in the belts 112 or 212 after they have been separated from the paper.
In the forms of the invention shown in FIGURES 2 and 3 a felt such as or similar to a conventional press felt may be used as the endless belt 112 or 212 instead of a relatively incompressible screen-like material. The factors to be taken into consideration when determining whether to use a felt or a screen in these forms of the invention are similar to those discussed above in connection with the form of the invention shown 'in FIGURE 1. Thus, to the extent that a felt or similar material may be relatively compressible the squeezing action which favors dislodgin-g of water from the paper web usually will cause reduction in void volume and permeability of the belt on which the :paper web is supported and this must be taken into account. For example the nip pressures between the plain press rolls 138, 140 and 142, 144 in FIGURE 2 must be so selected with regard to machine speed, moisture content of the web and any residual moisture content of the belt 112 as to avoid compressing the belt 112 to such an extent that the volume of water in the compressed paper web 110 and belt 112 substantially exceeds the void volume thereof. Substantial excess of water at this point would present danger of damage to the paper. Similarly the nip pressures for the perforated press rolls 238, 24d and 242, 244 in FIGURE 3 should be selected with due regard for the capacity of the press rolls to carry away water in excess of the combined void volume of the compressed paper web 210 and belt 212 at the nip.
In FIGURE 4 t ere is shown an illustrative embodiment of the present invention in which air presses of the type herein disclosed are arranged to operate upon a web of paper while it continues to be supported by a screen, such as a Fourdrinier screen, upon which the web was formed. By incorporating one or more such air presses into a Fourdrinier section which is provided with a Fourd-rinier screen of suflicient length, the paper which is formed upon the Fourdrinier screen may be so thoroughly dewatered before it leaves the same that it may be conducted directly from the screen or couch roll to a dryer drum.
The papermaking machine which is diagrammatically illustrated in FIGURE 4 includes a breast roll 380, a couch roll 382, a head box 384 and slice 336. An endless Fourdrinier screen 312 is conducted around the breast I011 381 beneath the slice 386, and over any desired arrangement of dewatering devices customarily used in a papermaking machine. For example, there may be provided a forming board 388, a plurality of table rolls 390 and a plurality of suction boxes 392. The Fourdrinier screen 312 also is conducted through one or more, for example three air press units 394 and then around the couch roll 382, a return guide roll 396 and a screen tension-i-ng roll 3% from which the screen 312 returns to the breast roll 380, thus completing its endless path. The papermaking machine shown in FIGURE 4 also includes a dryer drum 399 which may be of any conventional type. For example, the dryer drum 399 may be heated by steam and it may be a single dryer drum of large diameter, sometimes referred to as a yankee dryer, or it may comprise the first of a series of steam-heated dryer drums of the type customarily provided in a multiple drum dryer section.
In the use of the apparatus shown in FIGURE 4 a suspension of paper pulp, or similar fibrous material, in water is supplied to the head box 394 to flow beneath the slice 386 onto the continuously :moving Fourdrinier screen 312. The fiber suspension is carried by the screen 312 over the forming board 388 and then successively over the table rolls 3% which promote the drainage of water from the suspens-iDD hmll g h the screen 312. The ms pension is then carried by the screen 312 over the suction boxes 392 which may be of any conventional form, for example, they may be provided with perforated tops communicating with the underside of the screen 312 and with suitable suction, pump apparatus whereby additional water is withdrawn through the screen 312. The paper web 310 is substantially completed formed by the time it leaves the last suction box and 'it is in the form of a wet but porous fibrousstructure which contains les than enough residual water to fill all of the voids between the fibers. The condition just described usually occurs 'at or near the last suction box where the appearance of the surface of the paper changes from shiny and wet to relatively dull and flat due to the fact that air begins to strike through the thickness of the web. It is at this point that a paper web usually has a moisture content of anywhere from about to about water, and because of its porosity to air further removal of water by suction alone is relatively inefiicient. However, in accordance with the present invention, one or more air presses of any of the forms herein disclosed may be installed between the last suction box and the couch roll to provide effective further dewa'tering of the porous web while it is still carried by the screen on which it was formed. Such installation can be effective at least to reduce the moisture content of the web substantially below that at which it leaves the last suction box and the resultant increase in tensile strength of the web means that it can be transferred with greater safety from the couch roll to one or more air presses or conventional presses, as may be preferred. In other instances, one or more air presses such as disclosed herein may be used in the Fourdrinier section and may be of such size related to the speed of travel of the forming screen as to provide the relatively extended period of time needed for dewatering the web to a moisture content such that it can be transferred immediately from the couch roll to an evaporative drying device such as a dryer drum.
An installation of the latter type is shown in FIGURE 4 wherein there are three air presses 394 in series, each of which may be in either of the forms illustrated herein in FIGURES 2 or 3. The speed of travel of the forming screen 312 and the total length of the path of the screen 312 through the interior of the presses 3% may be so related as to provide in the neighborhood of 1 second or more of exposure of the web 310 to air blasting by the presses while the web remains supported upon the screen 312. In such event the moisture content of the paper web can be made suificiently low for direct transfer to the dryer drum 399 which, preferably is in tangential engagement with the couch roll 382.
FIGURE 5, which is a transverse sectional view taken along the line 55 in FIGURE 4, is more detailed than FIGURE 4 and it shows an arrangement of inlets and outlets which is equally adaptable to the forms of the invention shown in FIGURES 2 and 3. Thus, in FIG- URE 5 there is an upper chamber 414 and a lower chamber 416, an upper .press roll 438, a lower press roll 440 and sealing strips 446 which serve to seal the press rolls in the respective chambers. The porous belt 412 carries a web 410 of paper through the nip between the press rolls 438 and 440 into the enclosed Z0116 established by the upper chamber 414 and lower chamber 416. The lateral edges 413 and 415 of the belt 412 are firmly gripped between upper and lower sealing belts 448 and 456.
The apparatus shown in FIGURE 5 differs from that shown in FIGURES 2 and 3 only in that the upper chambers 414 and 416 are each provided with an inlet and outlet which may be regulated with respect to one another in such a manner as to maintain the particular gaseous pressure desired in each chamber. Since modern papermaking machines are quite wide such an arrangement is desirable because it affords uniform pressure throughout the width of the chambers. This arrangement may be found to be especially desirable when the air or other gas which is supplied for dewatering of the web is heated above atmospheric temperature or where dry steam, for example, is used as the gas for dewatering the web. It will be recognized that there are some advantages to be had from the use of hot gas or steam inasmuch as elevation in temperature of the water within the web serves to reduce the surface tension thereof and also may provide additional dewatering due to vaporization of the water. i
In the apparatus shown in FIGURE the dewatering gas is introduced into the upper chamber 414 through an inlet 418. The upper chamber 414 is also provided with an outlet 419 which in turn has located therein a pressure regulating valve 421. The rate of introduction of gas through the inlet 418 is so regulated with respect to the amount thereof which flows through the web 410 and belt 412, and with regard to the rate of withdrawal from the outlet 419, as to maintain a substantially uniform gaseous pressure throughout the interior of the upper chamber 414. When steam or hot air is used the withdrawal rate through the outlet 419 is so regulated as to maintain a substantially uniform temperature in the chamber 414. Regulation also may be utilized to prevent condensation of steam in the upper chamber.
The lower chamber 416 may be provided with a single outlet as shown in the preceding embodiments, and such outlet may be open to the atmosphere or may be con nected with a suction pump as desired. However, as shown in FIGURE 5, the lower chamber 416 is provided with an inlet 423 and an outlet 425 with a regulating valve 427 positioned in the latter. The outlet alone may be used and regulated to maintain the gaseous pressure in the lower chamber 416 at the desired level below that maintained in the upper chamber 414 in those instances wherein such operation is satisfactory. However, when desired, air or other gas may be supplied through the inlet 423 at such a rate, with regard to the differential desired between the upper and lower chambers, as to establish a circulation of gas within the lower chamber. The circulation in the lower chamber may be utilized to establish gaseous velocity or temperature, or both, to entrain water particles discharged from the web 410 or to carry water in vaporized form to the outlet 425. It will be apparent that the circulation of the gaseous atmosphere in the lower chamber 416 also will be effective to facilitate the maintenance of substantially uniform pressure throughout the width of the apparatus as discussed above in connection with the upper chamber 414. The conditions thus established by the circulatory systems for the upper and lower chambers of the apparatus shown in FIGURE 5, assure that the differential in pressure between opposite surfaces of the paper web 410 will be substantially uniform throughout that area of the web which extends between the upper chamber 414 and lower chamber 416. The resultant uniformity of velocity or velocity and temperature of the gas flowing through the web 419 brings about a highly desirable uniform dewatering action upon the web.
From a consideration of the foregoing description it will be apparent that the present invention does not contemplate the exposure of the freshly laid, wet paper web to jets or currents of rapidly moving gas directed toward a surface of the web from nozzles or hoods which are spaced from such surface. The confused gas flow patterns which would exist in the area of impact of a high-velocity jet or current upon the web surface would disrupt the web formation and still would not produce a high velocity flow through the web. In contrast with this the present invention involves the sealing of a substantial area or areas of the paper web across an opening or openings in a chamber in which gas is confined under pressure. The confined gas flows outwardly through the interstices of the web pushing the water ahead or entraining water particles and thus accelerating the water to a high velocity as the velocbelt.
ity of the gas increases in its movement toward the zone of lower gaseous pressure on the exit side of the web. The differential between the pressures on opposite sides of the web must be so chosen as not to result in such high exit velocities as to dislodge fibers from tthe web and drive them into the interstices of the supporting screen When the web is very high in moisture content total pressures in the order of from 5 to 15 pounds per square inch upon the web will be effective to squeeze the web to such a point that the water therein becomes substantially continuous and when, of this total pressure, the gaseous pressure is from about one pound per square inch up to about 15 pounds per square inch the continuous body of water will be ejected in a very short period of time. The pressure conditions upon the web thus do not differ greatly from those existing at the suction boxes and the problems of wire marking or other damage to the web are no greater. Stated otherwise, the present invention makes it possible to provide a dewatering action which can be a substantial repetition or duplication of the dewatering action performed by the suction boxes.
When the moisture content of the web is lower, as it would be when entering a second or third dewatering device of one of the types disclosed herein, it will be necessary to apply greater mechanical pressure or greater gaseous pressure or both to squeeze the web to a condition of continuous water content. It may or may not be practical or desirable to squeeze the web to such an extent in any particular case, but as pointed out above, the lower moisture content web is much more capable of withstanding squeezing and high gas velocities. Also, the supporting screen for the higher consistency webs may be coarser and thus have the greater tensile strength which is needed for the application of higher mechanical pressure by screen tension, as in FIGURE 1 or for resisting the higher gaseous pressure differentials which may be used in any of the forms of the invention.
As indicated above it is generally preferred to use as the belts 12, 112, 212, 312 or 412 a screen-like textile fabric made of suitable synthetic materials although fabrics such as or similar to papermalrer felts may be preferable under certain conditions. Such screens or felt-like fabrics may be of single-ply construction, having a single set of warps and a single set of wefts woven in any suitable pattern in which event the more closely woven constructions employing relatively fine yarns will have less tensile strength than more open weave coarse yarn constructions. In any case wherein great tensile strength is required along with a fine smooth paper contacting surface, the screens or felts may be woven duplex with coarse strong yarns in one system of yarns away from the paper side of the fabric and fine closely spaced yarns in a second system on the paper side of the fabric. With such duplex fabric great tensile stress may be placed on the fabric either to squeeze the paper web or as a result of great pressure differentials and the paper nevertheless will be supported on a fine smooth surface with little danger of wire marking. Furthermore two fabrics, one inside the other, may be run through any of the devices disclosed herein. A relatively fine fabric may be arranged to engage the paper and a coarser stronger fabric may be run inside the paper supporting fabric to afford requisite tensile strength. Arrangements of the latter type are disclosed in copending application SN. 159,415 filed December 14, 1961, now Patent No, 3,222,246, by C. A. Lee and assigned to the assignee of the present application.
It will be understood that the dewatering action provided by the invention as described in connection with various suggested embodiments thereof is to be distinguished from the drying of paper by currents of warm or hot air in which the reduction of moisture content is achieved primarily, at least, by evaporation. Also it is to be distinguished from the use of jets or currents of air or other gas, usually at relatively high temperature, for the scavenging of steam or moisture vapour from webs of paper as is sometimes practiced'in the dryer sections of papermaking machines. The present invention provides dewatering primarily by the purging of water in liquid form, whether in continuous phase or in finely divided or distributed form and such evaporation as may occur, although beneficial, is usually relatively small. The purging action on any unit volume of a portion of the paper web is accomplished principally because such portion of the web is confined across and in contact with the periphery of an orifice from which the purging gas is directed through the paper. In some forms of the invention successive increments of the paper are individually confined against a plurality of relatively small orifices with each increment remaining in fixed relationship with a particular orifice for a substantial period of time. The form of the invention shown in FIGURE 1 is illustrative of this procedure. In other instances, such as illustrated in FIGURES 2 through 5, successive increments are brought progressively into sealing relationship with a large orifice and move progressively across it while being purged. Also, as shown in FIGURE 5, the web is successively brought into sealing engagement with a series of orifices whereby to extend the total time of purging to the desired amount.
1. In apparatus for dewatering a web of paper being manufactured in a papermaking machine by purging of water therefrom in liquid form the combination of an endless belt of porous material having gasand waterpermeable openings therethrough, means for driving said belt through an endless path at the linear speed at which a web of paper is being manufactured in said machine, means for guiding said web of paper to position one surface thereof in face to face contact with one surface of said endless belt for movement with said belt through a portion of the path of said belt, a stationary housing having a substantially rectangular opening extending transversely and longitudinally of said portion of the path of said belt through which the interior of sa-idhousing is in communication with the opposite surface of the entire width and a longitudinally extending portion of said web as said web moves progressively through said portion of said path, first sealing means for forming substantially gas-tight seals of the transversely extending edges of said opening with respect to said opposite surface of said web, second sealing means for forming substantially gas-tight seals of the longitudinally extending edges of said opening with respect to said opposite surface of said web, means for supplying gas at substantial superatmospheric pressure to the interior of said housing for passage through the thickness of said web of paper to dislodge water from said web and to discharge said water into the openings in said belt, said first sealing means comprising two pairs of pressure rolls disposed transversely of the path of travel of said endless belt and web to form two spaced nips through which said belt and the web in contact therewith pass successively upon entering and leaving said portion of the path of said belt, at least the pair of pressure rolls at the entering end of said portion of the path of said belt having perforated cylindrical outer shells, and means for supplying gas at substantial superatmospheric pressure through the perforations in the nip zone only of the roll which is in contact with said opposite surface of said web.
2. In apparatus for dewatering a web of paper being manufactured in a papermaking machine by purging of water therefrom in liquid form the combination of an endless belt of porous material having gasand waterpermeable openings therethrough, means for driving said belt through an endless path at the linear speed at which a web of paper is being manufactured in said machine, means for guiding said web of paper to position one surface thereof in face to face contact with one surface of said endless belt for movement with said belt through a portion of the path of said belt, a first stationary housing having a substantially rectangular opening extending transversely and longitudinally of said portion of the path of said belt through which the interior of said first housing is in communication with the opposite surface of the entire width and a longitudinally extend-ing portion of said web as said web moves progressively through said portion of said path, a second stationary housing having a substantially rectangular opening extending transversely and longitudinally of the same portion of the path of said belt through which the interior of said second housing is in communication through said screen-like belt with said one surface of said web, first sealing means for forming substantially gas-tight seals of the transversely extending edges of said openings with respect to said web, second sealing means for forming substantially gas-tight seals of the longitudinally extending edges of said openings with respect to said web, means for supplying gas at substantially superatmospheric pressure to the interior of said first housing for passage through the thickness of said web of paper to dislodge water from said web into the openings in said belt and to discharge water from the openings in said belt into the interior of said second housing, means for maintaining a gaseous pressure within the interior of said second housing which is lower than said superatmospheric pressure, said first sealing means comprising two pairs of pressure rolls disposed transversely of the path of travel of said endless belt and web to form two spaced nips through which said belt and the web in contact therewith pass successively upon entering and leaving said portion of the path of said belt, at least the pair of pressure rolls at the entering end of said portion of the path of said belt having perforated cylindrical outer shells, and means for supplying gas at substantial superatmospheric pressure through the perforations in the nip zone only of the roll which is in contact with said opposite surface of said web.
References Cited by the Examiner UNITED STATES PATENTS 1,748,224 2/1930 Hinde 162-313 1,870,971 8/1932 Sundstrom et al. 162-208 1,881,404 10/1932 Hadley 162-208 2,428,555 10/1947 Cummins et al 162-208 2,441,169 5/1948 Roman 162-297 2,684,019 7/1954 Hart 162-297 2,716,927 9/ 1955 Sullivan 162-297 2,737,858 3/1956 Simpson 162-297 2,753,766 7/1956 Simpson 162-297 2,903,021 9/1959 Holden et al.
3,058,519 10/ 1962 Weiser 162-297 3,087,538 4/1963 Newman 162-297 DONALL H. SYLVESTER, Primary Examiner. J. H. NEWSOME, Assistant Examiner.