US3201305A - Sheet forming method and apparatus - Google Patents

Description

1965 D. R. WEBSTER 3,201,305

' SHEET FORMING METHOD AND APPARATUS Filed Nov. 5, 1962 2 Sheets-Sheet 1 IN VEN TOR David R. WEBSTER Aug. 17, 1965 D. R. WEBSTER SHEET FORMING METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed Nov. 5, 1962 E1162 VIBRATOR INVENTOR David R. WEBSTER ATTORNEY United States Patent Filed Nov. 5, 1962, set. No. 235,325 in Claims. (11. 162-203) The present invention relates to sheet forming and more particularly to a method and apparatus for forming a continuous sheet of paper from fibres in liquid suspension.

Paper is made currently by either of two main processes, the cylinder machine, and Fourdrinier machine.

The cylinder machine has the main difiiculties, firstly of the sheet tending to rinse off the cylinder because of immersion in a vat, and secondly of the sheet tending to peel olf the cylinder before formation is complete because of centrifugal force. Thirdly, the differential pressure forcing drainage is weak, being limited to the difference in liquid level inside and outside the cylinder. These and other dilficulties restrict the cylinder machine to relatively slow speeds and small capacity.

The Fourdrinier machine has the main difficulties, firstly of themesh dragging across stationary suction boxes, which requires a strong pull on the mesh thereby causing an abrasive creep at the drive roll. The suction-box drag and the drive-roll creep abrade the mesh quickly to where it cannot withstand the strong pull. Mesh replacement therefore is frequent and costly.

Secondly, a further difiiculty is that the table rolls of a Fourdrinier by their pumping action draw down the mesh after the crest of each roll, and let the mesh rebound with such force that the free surface of the liquid becomes fractured thus spoiling formation. A main result is that a Fourdrinier sheet is only as strong as a sheet made by ancient hand methods. This agitation or vibration caused by the table roll has not only kept down the quality of the machine-made product, but the table roll also has been discovered by widespread research to impose a practical speed limit on the Fourdrinier of approximately 2,500 ft./rnin.

A third difiicultyis that a negligible amount of liquid is removed between table rolls, whereby the mesh between rolls is merely a conveyor, and thus the drainage process is halted for most of the space occupied by the Fourdrinier. These and other difficulties restrict the quality and quantity of product off a Fourdrinier.

The present invention is aimed to avoid the above mentioned difiiculties of cylinder and Fourdriner machines by departing from some of their basic actions and constructions. In avoiding these difficulties the present invention provides a method and means, which firstly improve the quality, and secondly the quantity of paper produced per unit width.

The improvement in paper quality is achieved mainly by eliminating liquid disturbances and controlling fibre vibration. The improvement in quantity is achieved mainly by intensifying the drainage process necessary in pulp and paper sheet formation.

The present invention is an improvement on my United States Patent 3,056,719, issued October 2, 1962, Continuous Web Forming Machine, the present invention being adapted to use existing headboXes delivering a horizontal jet, and to control flocculation and interlocking of fibres by a control of vibration.

More specifically, the method of the present invention comprises the steps of: delivering a substantially-horizontal and ribbon-like jet of fibres in liquid suspension to a substantially-horizontal mesh means; supporting said fibres on said mesh means; driving said horizontal-mesh means in the same direction as said jet; controlling said horizontal-mesh means according to the physical laws for a taut string, with regard to frequency, wave length, wave velocity, mesh tension, and mass per unit length, as a way to control fibre vibration; guiding said jet of fibres from said horizontal means directly around a vertical curve of substantial angle; draining said fibres in suspension around said vertical curve to leave a formed layer of fibres on said mesh means; and removing said layer of fibres from said vertical curve as a continuous selfsupporting sheet. i

The method of the invention may be carried out by a preferred apparatus which embodies in combination: a substantially-horizontal segment of an endless-mesh means adapted to travel with and support a ribbon-like layer of fibres in liquid suspension; carrying rolls for the mesh means including a drum mounted for rotation about a horizontal axis with the drum tangent to the horizontal segment of mesh; another segment of the mesh means comprising a loop wrapped around a substantial are of said drum and adapted to guide the layer of fibres around the arc against centrifugal force; a first tension-control means including a carrying-roll portion with mounting means of the floating type cooperating with a tension regulator adapted to maintain a substantially-constant tension throughout the loop thereby providing a constant mesh-pressure against centrifugal force; during deflections of said mesh from drum by said layer of fibres; a second tension-control means including another carrying-roll portion with loading means adapted to set a magnitude of said constant tension, said magnitude of tension being for an optimum vibration of said horizontal segment of mesh as derived from physical laws fora vibrating string,

said laws including the variables of frequency, wave length, wave velocity, mesh tension, and mass per unit length of mesh; whereby said apparatus includes control means for the amount of agitation of fibres in forming a sheet of paper.

Having thus generally described the nature of the invention, particular reference will be made to the accompanying drawings, and in which FIGURE 1 is a somewhat diagrammatic showing in side elevation and partially in cross section of a preferred construction of an apparatus capable of carrying out the method of the invention with a plain drum, in which a horizontal segment of mesh, and an upward-curving segment of mesh are segments of a single endless mesh.

FIGURE 2 is a corresponding showing in side elevation and partially in cross section of an alternative construction with a plain drum, in which a horizontal segment of mesh, and a downward-curving segment of mesh are segments of two separate endless meshes.

FIGURE 3 is a corresponding showing in side elevation in cross section of an alternative construction with suction drum and box, in which a horizontal segment of mesh, and an upward-curving segment of mesh are segments of a single endless mesh. The suction drum and box are surrounded by a separate mesh to keep fibres from entering the drum.

FiGURE 4 is a side elevation in cross section of an alternative construction with suction drum and box, in which a horizontal segment of mesh and a downwardcurving segment of mesh are segments of two separate endless meshes. The suction drum and box are surrounded by the same mesh which has the horizontal'segment, and which also keeps the fibres from entering the drum.

FIGURE 5 is a side elevation in cross section of the preferred construction of FIGURE 1, with the optional equipment of adjustable forming board, drainage tray, doctor-blade damper, table-roll damper, drum decklebelts, horizontal deckle-belts, vibrator, plus a suction-Y transfer roll and an extra mesh-carrying roll.

Patented Aug. 17, 1965.

URE 1 is shown a preferred construction in which a layer 12 of fibres in liquid suspension is supported on a horizontal segment It) of an endless mesh 40. The horizontal segment It) is tangent to a plain drum 14 at an entry nip 16.

From tangency at entry nip 16, another segment 18 of mesh 4i is in tight wrap against drum 14, for a substantial arc to an exit nip 29. Mesh 49 is supported in tension as a free loop at drum 14 by an entry roll 3 i and an exit roll 26, and in a return circuit by intermediate rolls 2 8, 39 and 32. A greater or lesser number of carrying rolls, and shape of mesh circuit, may be used as is found convenient.

The horizontal mesh segment til, the fibre in liquid suspension 12 and arcuate mesh-segment 18- all travel in unison throughout the wrap on drum 14- because mesh tension causes a frictional non-sliding contact between arcuate mesh-segment 18 and drum 1 through the medium of fibre layer 12 trapped between mesh and drum from entry nip 16 to exit nip 24B. It is preferred to drive drum 14 by conventional drive means not shown. Alternatively, the drive may be applied by conventional drive means at any other roll or mesh part.

The fibre layer 12 is of ribbon-like shape as delivered by a headbox 36 of conventional form and utilizing conventional slice regulation 38. Take-up of the mesh 40, as the'mesh stretches normally during its life is by conventional take-up means (not shown) at any convenient roll, for example at roll 30. Guiding also is by conventional guide means (not shown), for example at roll 32.

Tension-control means may be any of several conventional types, and in the preferred construction shown in FIGURE 1 hastwo portions, firstly a floating portion 22 which imparts a given thrust to roll 28, and secondly a loading portion 24- which determines the thrust at roll 28 and thus the tension in mesh 40. Floating portion 22 is secured to a paper-machine frame (not shown) by pivotal means 42, and to roil728 by journal means 44, whereby roll 28 can deflect in a way to be described.

. In some known types of tension regulator, the floating portion 22 for example might be replaced by pistonrod means, and the loading portion 24 might be replaced by a pneumatic or hydraulic means regulating pressure at the piston.

As another alternative, it is possible to use for example a non-moving pressure-sensitive support at roll 28, and to use conventional take-up means mentioned above for the floating function. Other alternative means of tension control will be apparent to those skilled in the art.

In operation, the mesh 49 directly touches drum 14- at startup, and the mesh is deflected from the drum by the fibre layer 12 forcing its Way into entry nip 16. Fibre layer 12 thereby separates mesh from drum throughout arcuate mesh-segment 18 and is squeezed by tension in mesh 40 causinga radial pressure of mesh toward drum throughout are 18.

The fibre layer 12 thereby has drainage expressed through the mesh, while the fibres are felted together, and the fibres then emerge at exit nip 2t! as a self-supporting and continuous sheet 46 to be treated further in a conventional way. The drainage is re-cycled in a conventional manner.

The arcuate mesh-segment 18 is provided as a tensioned loop free to conform to any deflection or rate-oftaper of mesh from drum during the decrease of thickness of fibre layer 12 by drainage in advancing along are 13-. This feature of mesh-segment 18 being free flexing derives firstly from the elimination of a vat wall, and thus of fixed taper as found in cylinder machines, and secondly from the provision of a floating roll 2%.

The floating roll 28 permits having a constant tension in mesh 40, and thus a constant mesh pressure against the drum in the forming zone throughout are 155, regardless hoW far the fibre layer 12 may deflect the mesh from 4t drum. The initial deflection at entry nip 16 depends on variables, such as the layer thickness at slice 38, and the kinetic energy of fibre layer 12.

The rate-of-taper around mesh are 18 depends as mentioned on rate-of-drainage. It is well known that fibres in liquid suspension drain at varying rates depending on variables such as quality of raw materials, fibre size, proportion of fines, liquid surface tension, and additives. This seepage of liquid is according to the laws of filtration. Thus, the rate-of-drainage depends also on pressure and time.

Pressure from mesh tension has been shown to be made virtually constant via floating roll 28 although there is some fluctuation from most controllers. Also there is a change in hydrostatic pressure from any difference in elevation between entry nip 16 and exit nip 2t). Concerning time, the period to traverse are 18 depends on machine speed, and thus the uniformity of traverse time depends on uniformity from the papermachine speed controller.

A main advantage of having a free-flexing arcuate mesh-segment 13 is that the mesh can conform exactly to the decreasing thickness of the fibre layer 12, including conforming instantly to variations in rate-of-taper of that thickness, whereby the present invention keeps the entire thickness of the fibre layer 12 at a fixed speed and ther by prevents having liquid-shear planes harmful to formation.

An experimental paper machine has made paper both without a floating roll, and with the floating roll fixed in one position, and the lack of this floating feature left a partial lack of control over controlling machine operation and paper quality. Thus the floating feature of roll 28 is a means of helping to control sheet quality. a

The magnitude of mesh tension, determined by loading means 24, also determines the unit pressure at are 18 and thereby the drainage rate. The stronger the pressure the faster the drainage rate.

The magnitude of mesh tension also determines the manner in which fibre layer 12 enters nip 16. For example, the kinetic energy of fibre layer 12 would normally be strong enough to force its way into entry nip 16, but if loading means 24 increases mesh pressure substantially, then a limit is reached where kinetic energy of fibre layer 12 is insufficient to deflect mesh it enough to admit all stock into entry nip 16. Some stock then is rejected at the nip as an overflow. Up to this limit, the greater the pressure the greater the drainage capacity.

Means to control the magnitude of mesh tension therefore provide a means of helping to increase drainage rate and thereby to increase the machine speed and the quantity of sheet produced.

Simultaneously with setting the magnitude of mesh tension for drainage rate, this same tension also helps to determine the natural frequency of horizontal mesh-segment lib according to the law for standing waves to be described. The effect of mass will also be explained.

A main advantage of such vibration is to prevent fibre flocculation, and to interlock the fibres for sheet strength. Also the span of horizontal mesh-segment 10 is so short compared to the length of a Fourdrinier, that the vibra tions are small and mild compared to the violent impulses at table rolls.

The combinationof parts in the present invention thus provides a method and means for improving paper quality, byeliminating liquid disturbances and controlling fibre agitation, and for improving paper quantity by in tensifying the drainage action.

in FIGURE 2 is shown an alternative construction in which the vibration and pressure controls are effected through two separate endless meshes. A layer 112 of fibres in liquid suspension is supported on a horizontal segment 110 of an endless mesh The mesh segment 110 is tangent to a plain drum 114 at a point 116.

From tangency at point 116 mesh 150 is in tight wrap against drum 114 for a substantial are to an exit point 154. Mesh 150 is supported in a return circuit at any number of rolls such as roll 132 and breast roll 134. At least one roll, such as roll 132 is fitted with conventional guide and tension-control means (not shown). Tension in mesh 150 is adjusted by such tension control means to control the horizontal mesh-segment 110 according to the physical laws for standing waves.

Another endless mesh 1% has an arcuate segment 118 in tight Wrap overlying the mesh 15% from tangent point 116 to an exit point 120. The overlying mesh 140 can have a lesser are on driving drum 114 than mesh 15% if desired. Mesh 14%) is supported as a free loop in tension at drum 114- by an entry roll 126 and an exit roll 148, and in a return circuit by intermediate rolls 128, 130 and 152. A greater or lesser number of carrying rolls, and a variance in shape of mesh circuit, may be used as is found convenient.

The horizontal mesh-segment lit}, the fibre in liquid suspension 112, and the arcuate mesh-segment 118 all travel in unison throughout the wrap on drum 114 by frictional non-sliding contact with one another. The layer of fibres in liquid suspension 112 makes its own way, by deflecting arcuate mesh-segment 118 from drum 114, while mesh 15d remains tightly against the drum 114.

Fibre layer 112 thereby is squeezed between meshes 149 and 115i], throughout arc 118 from entry 116 to exit 120, by mesh Mt) being tensioned to create a radial pres sure toward drum 1114.

Takeup of the mesh 149, as the mesh stretches normally during its life, is by conventional takeup means (not shown) at any convenient roll. Guiding also of mesh Mill is by conventional guide means (not shown) as at roll 152.

Tension control is by any conventional means for example firstly by a floating portion 122, secured to the paper machine frame by pivot 142 and to roll 128 by shaft 144, and secondly a loading portion 124. The floating portion 122 accommodates various mesh deflections instantly, thereby to maintain constant tension, and the loading portion 124 sets the magnitude of the constant tension as previously described for FIGURE 1.

The fibre layer 112 is of ribbon-like shape as delivered by any headbox 136 and conventional slice regulation 13%. Drainage is expressed through mesh 140 while the fibres are felted together and emerge at exit 129 as a self-supporting and continuous sheet 3146.

Operation is similar to theoperation per FIGURE 1 except that control of horizontal mesh-se ment 110 is operated separately from the rate-of-drainage control by tension in mesh Mil. As previously described, vibration control is to prevent fibre flocculation, and to interlock fibres for sheet strength in a way not possible at high speed with cylinder and Fourdrinier machines.

In FIGURE 3 is shown an alternative construction in which the plain drum of FIGURE 1 is replaced by a suction drum. A layer 212 of fibres in liquid suspension is supported on a horizontal segment 2143 of an endless mesh 240. The mesh segment 210 is tangent to a suction drum 214 at an entry nip 2%.

From tangency at entry nip 1216, another segment 218 of mesh 240 is in tight wrap toward drum 214 for a substantial arc to an exit nip 2 2d. Mesh 24% is supported in tension as a free loop at drum 214 by an entry roll 234 and an exit roll 226, and in a return circuit by iniermediate rolls 223, 234i and 2.32. A greater or lesser number of carrying rolls, and shape of mesh circuit, may be used as is found convenient Another endless mesh 260 also is in tight wrap about the same substantial are as segment 218, and more, and mesh 26% lies between the periphery of suction drum 214 and mesh 24%. Endless mesh 26% has a return cir cuit supported by any number of rolls, for example roll 256 and roll 25?, and mesh 26% encircles a suction box 262 which transmits suction throughout arcuate segment 21%.

This suction roll 214, with suction box 262, rolls 25-6 and 258, mesh 260, and headbox 236-233 is in accordance with my United States Patent 3,057,402, issued October 9, 1962, Silent Suction Roll. Other types of porous roll using vacuum or pressure may be used from known art.

Takeup of mesh 24%, as the mesh stretches normally during its life, is by conventional takeup (not shown) at any convenient roll for example roll 230. Guiding also is by conventional guide means (not shown) for example at roll 232.

Tension control is by any conventional means for example firstly by a floating portion 222, secured to paper-machine frame by pivot 242 and to roll 228 by shaft 244, and secondly by a loading portion 224. The floating portion 222 accommodates various mesh deflections instantly, thereby maintaining constant tension, and the loading portion 224 sets the magitude of the constant tension as described for FIGURE 1.

The horizontal mesh-segment 216, the fibre in liquid suspension 212, and the arcuate mesh-segment 218 all travel in unison throughout the wrap on drum 214 by frictional non-sliding contact with one another.

Fibre layer 212 is of ribbon-like shape as delivered by any headbox 236 and conventional slice regulation 238. Drainage is expressed through mesh 24%, and simultaneously through mesh 260, at arcuate segment 213 while the fibres are felted together and emerge at exit 220 as a self-supporting and continuous sheet 246.

As in FIGURE 2, fibre layer 212 makes its own way between meshes 249 and 264) from entry 216 to exit 220, whereby mesh 240 is deflected as a free loop, and mesh 26% remains in tight contact with drum 2114.

Operation is similar to the operation per FIGURE 1, except that drainage is reclaimed from two sources instead of one, namely drainage issues away from drum 21 through mesh 24!) at arcuate segment 218, and drainage issues into drum 214 through mesh 26% at arcuate segment 218. Drainage from the two sources is recycled in a conventional way.

As previously described, the vibration control is to prevent fibre flocculation and to interlock the fibres for sheet strength in a way not possible at high speed with cylinder machines and F ourdriniers.

In FIGURE 4 is shown an alternative construction in which the vibration and pressure controls are effected through two separate endless meshes. A layer 312 of fibres in liquid suspension is supported on a horizontal segment 310 of an endless mesh 3%. The mesh segment 315i is tangent to a suction drum 314 at point 31 .6.

From tangency at point 316, mesh 3% is in tight wrap against drum 314, for a substantial arc to an exit point 354. Mesh 350 is supported in a return circuit at any number of rolls such as roll 332 and breast roll 334. At least one roll, such as roll 33?; is fitted with conventional guide and tension-control means (not shown). Tension in mesh 350 is adjusted by such means in order to control the horizontal mesh segment 310 according to the physical laws for standing waves as described for FIG- URE 2.

Another endless mesh 34% has an arcuate segment 318 in tight wrap overlying mesh 350 from tangent point 316 to an exit point 3%. The overlying mesh 34-0 can have a. lesser are on drum 314- than mesh ?:fitl if desired. Mesh 340 is supported as a free loop in tension at drum 314 by an entry roll 326 and an exit roll 348, and in a return circuit by intermediate rolls 328, 330

and 352. A greater or lesser number of carrying rolls,

and shape of mesh circuit, may be used as is found conven-ient.

Mesh 35% also circuits around a suction box 362 which transmits suction to fibre layer 312 from entry 336 to exit 354 in accordance with my United States Patent 3,057,402, issued October 9, 1962, Silent Suction Roll.

The horizontal mesh-segment 314), the fibre in liquid suspension 312, and the arcuate mesh-segment 318 all travel in unison throughout the wrap on drum 314 by frictional non-sliding contact with one another. The layer of fibres in liquid suspension 312 make their own Way, by deflecting arcuate mesh-segment 318 from drum 3114 While mesh remains tightly against drum 314 as for FIGURE 2.

Fibre layer 312 thereby is squeezed between meshes 3 th and 356 from entry 316 to exit 32%, and simultaneously is drained by suction from entry 316 to exit 354.

Talteup of the mesh 3449, as the mesh stretches normally during its life, is by conventional takeup means (not shown) at any convenient roll. Guiding also of mesh is by conventional guide means (not shown) as at roll 352.

Tension control is by any conventional means for example firstly by a floating portion 322 secured to paper-machine frame by pivot 342 and to roll 323 by shaft 34 and secondly a loading portion 324. The floating portion 322 accommodates varying mesh deilections instantly, thereby maintaining constant tension, and the loading portion 324 sets the magnitude of the constant tension as described in FIGURE 1.

The fibre layer 312 is of ribbon-like shape as delivered by any headbox 336 and conventional slice regulation 33S. Drainage is expressed through mesh 340 at arcuate segment 318, and simultaneously through mesh 35%, while the fibres are felted together and emerge at exit 354 as a self-supporting continuous sheet 346.

Operation is similar to operation per FIGURE 1 except that drainage is recovered from two sources instead of one, namely the drainage issues per FIGURE 3 away from drum 314 through mesh 340 at arcuate segment 318, and drainage issues into drum 314 through mesh 3% at arcuate segment 318. Drainage from the two sources is re-cycled in a conventional way.

As previously described, the vibration control is to prevent fibre flocculation and to interlock the fibres for sheet strength in a way not possible at high speed with cylinder machines and Fourdriniers.

Suction box 362 can be used for damping vibrations by raising it slightly against horizontal mesh-segment 310, in the nature of a forming board.

In FIGURE 5 is shown the preferred construction of FIGURE 1 in which are added: the optional structures of adjustable forming-board 68, drainage tray 70, doctorblade damper '72, table-roll damper 74, drum deckle-belt 76, horizontal deckle-belt 78, adjustable apron 8d, and vibrator 82. Although decides 76 and 78 are shown with a gap between them, they can be extended toward each other to effect a more complete seal at the mesh edges.

Also in FIGURE 5, the exit roll 26 is replaced by optional suction-transfer roll 64. An extra mesh-carrying roll 66 helps to provide room for tray in. Any, or all these optional structures may be used, as desired. Other conventional accessories for Fourdriniers may be added if desired. All these optional parts are fitted to the papermachine frame (not shown) by adjustable means well known in the art.

In operation, the suction roll 64, the carrying roll 66, the tray 7% and the deckles '76 and 7S operate in a conventional way also well known in the art. The adjustable forming-board 68, the adjustable-doctor damper 72, the adjustable-roll damper 7 adjustable apron 8d, and vibrator 82 are each adjusted to control vibration of horizontal mesh-segment it as described in an example folthus whatever the string shape.

lowing to provide vibration control, thereby to prevent fibre flocculation and to interlock the fibres for sheet strength in a way not possible at high speed with known methods and means.

The method for adjusting mesh tension, mass per unit length, wave length, frequency and wave velocity by these structures will be described.

In order that the basic concept of the present invention may be more clearly understood, reference will be made to the following theory and example.

Theory In the apparatus of the present invention the use of a substantial]y-horizontal segment of an endless meshmeans, adapted for vibration control, according to the physical laws for standing waves is based on the following theoretical considerations.

It is well known that a transverse wave travelling in a string may be analyzed by visualizing a string, with a tension T and mass per unit length M, being pulled rapidly at velocity V through a glass tube having the shape of any curve for example one phase of a sine curve. At any point where the radius-of-curvature of the tube is R, the pressure against the tube or force per unit length is being greater the sharper the curve.

Considering a unit length of the string, it is travelling in a circular path and must be subject to a centripetal force That is MV =T.

Since the radius-of-curvature cancels out of the result, the speed at which pressure vanishes against the tube is the same whatever the radius-of-curvature may be, and That is, for a given mass and tension, there is a Critical Speed at which the inward and outward forces exactly balance.

If the string is pulled through at this Critical Speed, the glass tube may be made to vanish, and the bend in the string will remain unchanged. If the observer now moves along at this Critical Speed from left-to-right, the string will appear stationary and the bend will appear to travel right-to-left with a velocity V, where Formula (1) Thus we have a small force-vector acting on the where the wave travels at a velocity V and has wave length L and has frequency N is:

V=NL Formula (2) Below are three well known laws for a string based on this third formula and useful in operating the present invention.

(a) The number of vibrations per second made by a string under a given tension and mass per unit length is inversely proportional to the length of the vibrating segment. Thus if we half the length of segment, by damping it in the middle, we double the vibrations per second.

(b) The number of vibrations per second made by a string of a given length and mass per unit length is proportional to the square root of the tension. Thus if we quadruple the tension we double the vibrations per second.

(c) The number of vibrations per second made by a string of given length and tension is inversely proportional to the square root of the mass per unit length. Thus if we quadruple the mass per unit length we half the vibrations per second.

With a Fourdrinier the table-roll pumping action flexes the mesh into the shape of a crest at each table roll and a sump between rolls. This fixes the number of vibrations to the number of table rolls.

Compared to a wave, such crests would correspond to loops and such sumps to loops with a node between each crest and sump. Thus, there would be two nodes between adjacent table rolls and one wave length would be the centre-to-centre distance between rolls. As such table-roll loops are not free to vibrate vertically, but are of fixed curvature, a Fourdrinier mesh may be compared to the preceding analysis using the analogy of a string being pulled through a glass tube.

But a Fourdrinier is operated without regard to any Critical Speed of Wave at which mesh tension is just sufficient to supply the centripetal force. At such Critical Speed, a table roll for example could be made to vanish and the mesh would retain its table-roll loop unchanged, except for two practical considerations.

Firstly, removing a table roll would remove its pumping action and thereby would cause a mesh movement to a new equilibrium of forces. Secondly, liquid resting on the mesh comprises a major part of the mass per unit length and does not withstand tension except for a small contribution from liquid surface tension. This weakness in tension contributes for example to liquid escaping from the loop over table rolls in the familiar pattern of jumping, and in addition to loop curvature the jumping is aggravated by some drainage rimming the table roll and striking the mesh from underneath. Also the mesh vibrates more as a ribbon than as a string.

However, the instant invention introduces a way to eliminate the fixed pattern of vibrations at table rolls by introducing pressure drainage so strong around a vertical curve that table rolls are not needed for drainage. Also means are introduced for controlling vibration of the horizontal segment of mesh with adjustment to com- Formula (3) id promise between a big enough vibration to prevent flocculation of fibres and a small enough vibration to prevent damaging paper strength.

In accordance with the present invention the slower a layer of fibres traverses the horizontal segment of mesh the longer a time it is vibrated and thus the more times a fibre is vibrated. Therefore, one way to minimize the number of fibre agitations in the present invention is to speed the jet as much as possible. In contrast any speeding of a Fourdrinier increases the fibre agitations,

Upon reaching the Critical Speed where the mesh speed equals wave speed, and assuming that jet and mesh act together as a single mass for the present amplitudes, each fibre rides a frozen series of loops and follows in the same path as every preceding fibre.

The present invention therefore introduces a paperrnaking method and apparatus which controls vibration pattern, independently of table rolls, by control means for frequency, wave length, wave velocity, mesh tension and mass per unit length of mesh. More specifically, these separate but interrelated control methods and means are as follows.

Control 0 frequency Above are given three laws, based on Formula 3, for the effects on frequency from a change in any of the factors of wave length, tension, and mass. The resultant frequency is for a free vibration.

But we may also impress a forced vibration on a string is desired. If such forced frequency corresponds to the free or natural frequency, then a strong resonance results with great amplitude. But if the forced frequency does not correspond to the free frequency then waves advancing will interfere with waves reflecting. This is because the velocity in both directions is identical and equal to per Formula 1; and because the wave length is fixed from Formula 2 where wave velocity and frequency are fixed. When a wave length therefore is imposed by forcing an unnatura frequency, the resultant forced wave length would not be an even multiple of the free span and the reflecting waves would try to have a node where the approaching waves try to have a loop. The string would adopt a resultant shape from the two actions and the result is termed wave interference.

Various forced frequencies may be impressed at a paper-machine mesh unintentionally by such as screen and fan pump impulses in the jet, or slight eccentricity in carry rolls, and intentionally by special vibrators such as ultra-sonic devices. Thus it can be desirable in some papermaking conditions to impress a non-resonant frequency on the mesh thereby to interfere with waves from jet impulses and mechanical imbalances.

Control of wave length Except where there is a forced vibration, the wave length for free vibrations will be a multiple of the free span of mesh between breast roll and drum. This horizontal segment of mesh can be made to vibrate with any desired number of nodes and loops, without table rolls,

more than one mode of vibration at a time. For example, if a string is struck the distance from one end, it may vibrate not only as two loops but simultaneously as a single loop. From V=NL, these short loops will have twice the frequency of the long loops and if such frequencies are in the audible range they will sound an octave apart. The single loop provides the fundamental frequency and the double loops a harmonic frequency. Thus, tuning-up a paper machine takes on a literal meaning because an experienced papermaker is given a new and unexpected value to his sense of hearing through the present invention.

From Youngs law, when a string is struck at any point only those modes of vibration are set up which do not have nodes at that point. Conversely, when a string is touched at any point all vibrations are damped that do not have nodes at that point. It is clear from Youngs laws, that in order to stop all vibrations of a string, it should be damped at the same point where it is struck. This is done for example in the piano.

Therefore one way to change the wave length in a papermaking mesh is to touch the mesh with a doctor blade, or else some object such as a roll, where a node is wanted.

Another way to change Wave length is to change the free span of mesh by extending a forming board under the mesh. A forming board is especially effective in damping vibration, if we heed Y oungs law by placing the forming board to include the area where the jet strikes the mesh. If a Wave is not started there is no wave to transmit.

A further way to change wave length is to change the distance between breast roll and drum. This is not easily done, and thus is not practical because it requires either sliding the breast roll and headbox with its piping, or else sliding the drive and drum which in some alternative constructions includes suction apparatus.

Of some further ways to change wave lengths, one is to move the point where the jet strikes the mesh by changing the trajectory, and another is to adjust an apron cloth in its mass and distance out from the bottom slice 1i One would choose any of these and other ways to change wave lengths according to whichever is suited to prevailing conditions.

Control of velocity of wave The velocity of a Wave in the mesh may be determined from Formula 1, namely Thus, for a fixed mass, if we quadruple the tension, We double the wave velocity. If we increase or decrease tension and mass simultaneously in equal proportions, the expression remains constant and there velocity.

From Formula 2, namely V :NL, for a fixed frequency, if we double the wave length we double the wave velocity. Also, for a fixed wave length if we double the frequency We double the wave velocity. If we increase the frequency in the same proportion as we decrease the wave length, the expression NL remains constant and there will be no change in Wave velocity. If we increase frequency and wave length together then We increase wave velocity very quickly.

We can thus change wave velocity 21 measured amount byimparting a measured change to any or all of the factors, frequency and wave length by means already will be no change in wave i2 explained, and tension and mass by means to be explained in detail later.

Also it has been shown that when the velocity of the wave reaches the Critical Speed, the bends in the mesh become frozen in place. It is of course possible to drive the mesh and fibres faster or slower than this Critical Speed if desired and to rush or drag the jet relative to the mesh according to usual papermaking practice. In such an event the mass M for Formulas 2 and 3 has its velocity made up of two parts, one part for the mesh, and one part for the fibres in liquid suspension.

Control OfijnCS/t tension Mesh tension is regulated directly at a carrying roll, by conventional belt take-up means, with provision for measuring the load. The effect of tension on vibration is seen in Formulas 1 and Sand has already been explained.

Control of mass per unit length For the small amplitude of vibration in this method and apparatus, the masses of mesh and overlying fibres in liquid suspension have been considered as one mass. This is not strictly correct, and it has been explained above that the liquid does not carry tension and thus does not supply centripetal force (as a mesh does) except for the liquid surface tension. Thus, the treatment of the combined mesh and liquid in this invention according to the physical laws of vibration in a string is an approximation, but a valuable one. Therefore in papermaking the various magnitudes would be set according to these laws and then adjusted to yield optimum results, according to the qualities wanted in a given grade of paper.

Mass may be changed in any of several ways including combinations of these ways. Firstly, the jet may be speeded while other conditions remain constant, whereby the mass per unit length of mesh will increase directly as the speed increases. That is, if the jet speed for example is doubled, the mass per unit length is doubled.

Secondly, the jet may be thickened by raising the top lip of the slice. For example doubling the jet thickness while other conditions remain constant, would double the mass per unit length of mesh.

As both methods would increase the quantity of fibres per unit length of mesh, these methods should be accompanied by usual means to lessen the concentration of fibres in the headbox in order to maintain a constant basis Weight. That is, we should provide the extra mass by adding Water only, not fibres.

Thirdly, an adjustable apron cloth has already been suggested above as one means of changing mass, for at least part of the mesh span.

Fourthly, the mesh may be speeded or retarded to change the distribution of mass per unit length. Of several other ways to change mass per unit length of mesh, one for example is to introduce additives to the liquid such as clay to make it heavier or air bubbles for example to make it lighter; another is to use a liquid of different specific gravity such as thickblack liquid from kraft pulping. Y

Example Having explained the theory and application of the instant invention, a typical calculation may be made as follows.

A Fourdrinier travelling at say 1800 ft./min. (30 ft./ sec.) with table rolls at 1.5 ft. centre-to-centre spacing produces table-roll impulses of equalling 20 vibrations/sec. It is well known that the combination of mesh speed, mesh tension and deflecting force at Fourdrinier table rolls is enough to bounce liquid off the free surface and across as many as 5 table rolls before landing. A table roll cannot drain liquid which is as droplets in mid air. Thus, table-roll vibrations hinder drainage and disrupt formation thereby weakening the sheet.

In contrast, to the Fourdrinier the present invention has no strong drag to cause an abrasive creep from differential tension at the drive roll and has no fiat boxes to abrade the mesh. Firstly, this elimination of drag and creep frees a part cross-sectional area of each tensile thread to be loaded for tension, instead of being reserved for abrasion. Secondly, this elimination of drag and creep frees the mesh from having a maximum tension between a last flat box and couch, and permits letting the maximum tension pervade the entire mesh circuit, especially pervading the former zone of table rolls previously a zone of weak rate or else the same number of vibrations as in the above Fourdrinier example merely by controlling the number of vibration loops.

. Firstly, for the same rate of 20 vibrations/see, at 1800 ft./min. we would merely set up the previous wave length of 1.5 it. Thus if we choose say a 6 ft. span for an example with the present invention, then we would need equalling four waves or eight loops. Such loops would be achieved by damping the mesh, by such as a doctor blade or roll, at i from the breast roll. If one wanted maximum vibration the jet should impinge at the centre of this .75 ft. loop. The height for a horizontal jet at .1800 ft./min. to impinge at half .75 ft. by free fall calculates to about .001"

' above the levelof the mesh. Such a flat trajectory needs to be adjusted for any air current induced by mesh movement and for the phenomenon of any ascended loop intercepting the jet at a point nearer the slice than a descended loop. The same vibration could be imparted by impinging the jet at the centre of the. second loop, in this example,.narnely- .75 ft. beyondthe point of damping.

As already explained, one of several ways of damping such vibration 'or flutter is to extend a forming board under the zone of impingement. In the instant invention, byduplicating the rate of vibration in the Fourdrinier example, the shorter length of the instant invention would result in fewer total vibrations than on the Fourdrinier.

Secondly, for the same total number of vibrations as in the Foui'drinier example, we would need 20 vibrations in the 6 ft. span between breast roll and drum. Thus we would need to increase from the above 4 waves to 20 waves. Such a fivefold increase would require dividing each of the 4 waves into 5 sub-waves, whereby the new Wave. length would be equalling .3 ft., and each loop length would be t l i 6 ft.

after the 2nd loop of 40, the wire could revert to 20 loops, being 10 waves instead of the desired 20 waves.

Thus we could damp in this example after the lst, 3rd, 7th, 9th, 11th, 13th, 17th and 19th loops and maintain the desired 20 waves. l

The present invention however is not restricted to reproducing either the same total rate or else the same number of vibrations as on a Fourdrinier, and instead may be adjusted to any frequency desired, including a virtual elimination of vibration by means above described. The present invention thus introduces a new wide range of vibration to papermaking with means to control that vibra'- tion all achieved with simple and rugged equipment.

In the above example, if one Wanted to set the wave velocity to equal the jet velocity, then one would proceed to set the tension for this Critical Velocity something as follows. Assume as above that liquid and mesh act to gether as a single mass, because the amplitude is so small, and then calculate Wave velocity from the vibration formulas.

Firstly calculate the mass per unit length of mesh. For a 1 ft. width of mesh, and a jet thickness of the order of say 1 inch, the mass including mesh is approximately 5.2 lb./ft. of the travel direction or span.

Secondly at the Critical Speed, velocity of the combined mesh and jet mass equals velocity of'wave, which in the above example requires causing the velocity of wave to be 1800 ft./min. being 30 ft./sec.

V: ft./ sec.

G=32.2 ft./sec./sec.

G: gravitational constant T=total tension of the wire in lbs.

M =mass of wire and slurry combined For 1 ft. Width T= lb. For 1 inch width T: 12.1 lb.

30 ft./sec.

N= =25 cycles/sec.

V=velocity of a wave L=length of a wave or cycle.

These calculations thus indicate that using the same jet speed as the Fourdrinier, namely 1800 ft./min., the present invention provides a way and means whereby it also may travel at the same 1800 ft./min., and at the same time make vibrations advance also at 1800 ft./min. merely by tightening the mesh to 12.1 lb./ inch including adjustments for the theoretical considerations of mesh and liquid acting as a single mass. This is the Critical Speed where the mesh waves will follow a curved path stationary relative to the ground, and the waves thereby appear frozen in position. The time for traversing the 6 ft; span of the example, at 1800 ft./min.tis only /5 sec. and therefore high-speed techniques would be needed to see the phe-y nomenon. Some correction coefficients are needed also t because the tangent point of the horizontal mesh-segment r to drum is ill-defined, when the stock layer has the mesh deflected from the drum during normal operation. In practice a papermaker can adjust to values which are found to produce the best results for given grades of paper.

It is possible for example to quadruple the above 12.1 lb./inch to 48.4 lb./inch and double the wave velocity. This would double the number of vibrations from 2.5/ sec. to 5 sec. while the mesh speed remains unchanged. Also, one could damp the mesh at a quarter point and quadruple the number of vibrations.

4 It is preferable, but not obligatory, in the present invention to eliminate all table rolls. Alternatively, table rolls also may be spaced to cause wave interference. Those skilled in the art will appreciate that the minimum free span between breast roll and drum will always be suificient to permit flexure of the mesh for controlled entry of ribbon of stock. The maximum free span will be limited by the acceptable amount of mesh sag depending on mesh tension and mass and velocity of stock. All the above on vibration is directed toward controlling fibre flocculation and alignment and thereby to controlling paper strength and quality.

Drainage capacity Paper quantity on the other hand may be increased by a method and means, explained below, which is in combination with and acts as an integral part of the vibration-control-part.

The present invention increases drainage capacity over known methods, and especially over the cylinder machine and Fourdrinier, by intensifying the drainage action necessary in pulp and paper sheet formation. This increase is achieved by having a mesh part wrapped around a substantial arc of a drum, whereby mesh tension causes a pressure radially toward the drum periphery, and a layer of fibres in liquid suspension is squeezed between mesh and drum. A fibrous sheet thereby is felted together and formed while liquid is squeezed through the mesh part.

Besides papermaking, this method and means for sheet forming is useful also for draining pulp to make laps or board, and treating fibrous or finely-divided materials which are suspended in chemical liquors.

Examples would be the separation of bleach and cooking liquors from pulp, the removal of precipitates such as lime in kraft pulping liquors, the separation of liquids from food mashes, and the separation of solids from oily and tar-like mixtures.

This structural combination introduces the new results of solids in liquid suspension being agitated controllably, for controlled sheet strength, and being drained intensively for quick formation and big capacity.

I claim:

1. Apparatus for forming a sheet from fibres in liquid suspension comprising in combination: a first substantiah ly-horizontal segment of an endless-mesh means for traveling with and supporting a ribbon-like layer of fibres in liquid suspension; carrying rolls for said mesh means including a drum mounted for rotation about a horizontal axis with the outer surface of said drum tangent to said horizontal segment of mesh; a second segment of said endless mesh means formed in a loop wrapped around a substantial arc of said drum for guiding said layer of fibres around said drum outer surface against centrifugal force; tension-control means acting on at least one of said carrying rolls and adjustably maintaining a substantiallyconstant tension throughout said mesh for providing a constant mesh-pressure acting on said fibres resisting centrifugal force and providing a magnitude of tension T in said horizontal segment of mesh; stock delivery means to set a magnitude M of fibre mass distributed on said horizontal segment of mesh; said horizontal segment of mesh having a magnitude N of frequency; and span adjustment means to set a magnitude L of wave length in said first segment of mesh; whereby any three of said T, M, N, and L are chosen magnitudes and the remaining fourth'magnitude is derived from the general wave formula in which each side of said formula represents wave velocity, and thereby is a means to predetermine the amount of vibration and thus fibre interlocking and quality of a selfsupporting sheet.

2. An apparatus as claimed in claim 1 wherein said tension-control means includes a tension regulator operatively connected to said one roll and includes variable pressure loading 'means.

3. An apparatus as claimed in claim 1 wherein said drum is provided with an imperforate outer surface.

4. An apparatus as claimed in claim 1 wherein said drum is provided with a perforated outer surface, vacuum means connected to said drum, said endless mesh means consisting of a first endless screen surrounding said drum in said substantial arc and providing said substantially horizontal segment of said endless mesh, and a second endless screen having a portion disposed between said drum outer surface and said first screen, and a further portion extending in parallel spaced relationship to said first screen horizontal portion whereby, said ribbon-like layer of fibres is delivered between said first and second screens.

5. An apparatus as claimed in claim 1 wherein said drum is provided with a perforated outer surface, vacuum means connected to said drum, said endless mesh means consisting of a first endless screen surrounding said drum in said substantial arc and providing said substantially horizontal portion of said endless mesh, and a second endless screen having a portion overlapping said drum surrounding portion of said first screen whereby, said ribbonlike layer of fibres is delivered to said first screen horizontal portion and carried by said screen portion between said overlapped first and second screen portions.

6. An apparatus as claimed in claim 1 wherein a headbox including adjustable slice means is positioned to deliver said ribbon like layer of fibres in liquidsuspension to said mesh means horizontal segment, said headbox and slice means being disposed adjacent said horizontal segment of said mesh at a point spaced from said loop segment.

'7. An apparatus as claimed in claim 1 wherein deckle means are disposed at each side margin of the upper surface of said mesh horizontal segment and further deckle means are disposed at each side margin of and bearing against the exterior surface of said mesh loop segment surrounding said drum substantial arc.

An apparatus as claimed in claim 1 including vibrator means engaging said mesh horizontal segment to impart vibrational motion to said mesh segment for augmenting natural wave frequencies imparted thereto by the operational movements of said mesh during its travel about said carrying rolls and drum. 7

9. The method of forming a sheet from fibres in liquid suspension comprising the steps of: delivering a substantially-horizontal and ribbon-like jet of fibres in liquid suspension to a substantial-ly-horizontal free-span portion of an endless mesh means .and supporting the fibres thereon; driving said horizontal-mesh portion in the same direction as said jet; imposing a wave velocity V in said free-span to control flocculation and interlocking of fibres by adjusting mesh tension T to a chosen value by tensioncontrol means and mass M to a chosen value by mass control means, wherein said T and M values determine the vaiue of V according to the classic wave formula in which V is the wave velocity in ft./sec., G is the 1 7 gravitational constant 32.2, T is the total mesh tension in pounds, and M is the mass of the mesh and fibres in liquid suspension per linear foot, and draining said fibres to form a continuous fibre layer; and removing said layer from said mesh means as a self-supporting sheet.

10. The method of claim 9 including the step of imposing a supplemental vibration to said free-span portion to augment natural Wave frequencies imparted thereto when said free-span portion is driven.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS Canada. Great Britain. Great Britain. Germany. Germany.

DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner.

Claims (2)

1. APPARATUS FOR FORMING A SHEET FROM FIBRES IN LIQUID SUSPENSION COMPRISING IN COMBINATION: A FIRST SUBSTANTIALLY-HORIZONTAL SEGMENT OF AN ENDLESS-MESH MEANS FOR TRAVELING WITH AND SUPPORTING A RIBBON-LIKE LAYER OF FIBRES IN LIQUID SUSPENSION; CARRYING ROLLS FOR SAID MESH MEANS INCLUDING A DRUM MOUNTED FOR ROTATION ABOUT A HORIZONTAL AXIS WITH THE OUTER SURFACE OF SAID FRUM TANGENT TO SAID HORIZONTAL SEGMENT OF MESH; A SECOND SEGMENT OF SAID ENDLESS MESH MEANS FORMED IN A LOOP WRAPPED AROUND A SUBSTANTIAL ARC OF SAID DRUM FOR GUIDING SAID LAYER OF FIBRES AROUND SAID DRUM OUTER SURFACE AGAINST CENTRIFUGAL FORCE; TENSION-CONTROL MEANS ACTING ON AT LEAST ONE OF SAID CARRYING ROLLS AND ADJUSTABLY MAINTAINING A SUBSTANTIALLYCONSTANT TENSION THROUGHOUT SAID MESH FOR PROVIDING A CONSTANT MESH-PRESSURE ACTING ON SAID FIBRES RESISTING CENTRIFUGAL FORCE AND PROVIDING A MAGNITUDE OF TENSION T IN SAID HORIZONTAL SEGMENT OF MESH; STOCK DELIVERY MEANS TO SET A MAGNITUDE M OF FIBRE MASS DISTRIBUTED ON SAID HORIZONTAL SEGMENT OF MESH; SAID HORIZONTAL SEGMENT OF MESH HAVING A MAGNITUDE N OF FREQUENCY; AND SPAN ADJUSTMENT MEANS TO SET A MAGNITUDE L OF WAVE LENGTH IN

9. THE METHOD OF FORMING A SHEET FROM FIBRES IN LIQUID SUSPENSION COMPRISING THE STEPS OF: DELIVERING A SUBSTANTIALLY-HORIZONTAL AND RIBBON-LIKE JET OF FIBRES IN LIQUID SUSPENSION TO A SUBSTANTIALLY-HORIZONTAL FREE-SPAN PORTION OF AN ENDLESS MESH MEANS AND SUPPORTING THE FIBRES THEREON; DRIVING SAID HORIZONTAL-MESH PORTION IN THE SAME DIRECTION AS SAID JET; IMPOSING A WAVE VELOCITY V IN SAID FREE-SPAN TO CONTROL FLOCCULATION AND INTERLOCKING OF FIBRES BY ADJUSTING MESH TENSION T TO A CHOSEN VALUE BY TENSIONCONTROL MEANS AND MASS M TO A CHOSEN VALUE BY MASS CONTROL MEANS, WHEREIN SAID T AND M VALUES DETERMINE THE VALUE OF V ACCORDING TO THE CLASSIC WAVE FORMULA

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