Reversible foil blade having multi-activity zones

Abstract

A reversible foil blade for a papermaking machine providing for a plurality of activity zones wherein the drainage and sheet activity characteristics of the blade can be independently and separately predetermined, established, and controlled. The shape of the foil blade is designed to provide both leading and trailing edges that each form an angle less than 90° with the horizontal, the paper sheet and conveying forming fabric, thereby providing different drainage and sheet activity characteristics when the blade is reversed and installed in a reverse orientation.

Description

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The present invention relates generally to activity and drainage devices for formation sections of paper manufacturing machines and, more particularly, to a foil blade for manipulating activity of a pulp suspension sheet in the formation section of a paper machine.

[0003] (2) Description of the Prior Art

[0004] Definitions

[0005] It is relevant and instructive to define those areas of a foil blade as done by the applicant for the purposes of describing the prior art and the present invention; these terms are as follows:

[0006] Activity zone or acceleration zone is the location on the blade where a change in direction is forced upon the fabric/sheet over an acceleration distance;

[0007] Approach angle is the angle at which the fabric/sheet enter the foil blade moving in the machine direction;

[0008] Exit angle is the angle at which the fabric/sheet exit the foil blade moving in the machine direction.

[0009] Drainage angle is the divergent angle that follows the flat surface that contacts the fabric/sheet.

[0010] Drainage nip length is the sustended length of the drainage angle.

[0011] For example, in FIG. 1B of the prior art, activity zone 1 of foil blade B has an approach angle (&thgr;1), an exit angle (&agr;2), and an acceleration distance (F); also, foil blade B has a drainage angle (&agr;2), and a drainage nip length (L).

[0012] Typically, foil blades are known to be used in the formation sections of paper machines and, in particular, are commonly employed on the wet end of Fourdrinier paper machines to extract water from the pulp fiber and water mixture or slurry and to induce activity of the sheet during its formation. The controlled extraction of water and the manipulation of activity levels of the sheet by using foil blades in the forming section of the paper machine are the preferred methods for controlling fiber distribution within the sheet. Additionally, manipulation of activity in the sheet can impact the quality of the finished paper sheet, most importantly in terms of its uniformity or formation.

[0013] Prior art foil blades commonly include a blade surface for contacting the sheet in the forming section of the paper machine; generally, the prior art blades are constructed so as to have a leading flat surface for contacting the sheet and the conveying fabric across the divergent surface so provided. This movement of the pulp sheet and the conveying fabric across the divergent surface introduced by the leading flat surface of the foil blade produces a vacuum effect on the sheet; it is this vacuum effect and the surface disruption created by the foil blade leading flat edge that are commonly recognized in the prior art to control the extraction of water and the sheet activity levels, thereby impacting the final paper sheet uniformity. However, while the prior art does include means for adjusting the foil blade position, if the foil blade leading flat surface is not properly and precisely positioned, conveying fabric wear and sheet discontinuity usually occur. Thus, there is little or no capacity to make adjustments to the prior art foil blades in order to attempt to manipulate and control the sheet activity and water extraction by adjusting the foil blade position. Furthermore, the foil blade surface also experiences wear during use and must be discarded or serviced repeatedly over time; this surface wear can also negatively impact sheet uniformity by affecting the sheet activity and introducing variation thereof.

[0014] By way of further background of the prior art generally, the following brief description of the operational principles and features of conventional foil blades follows. FIG. 1A shows an arrangement of three conventional or prior art foil blade designs as they function on a paper machine interactively with the conveying fabric and sheet. The fabric travel direction is shown, also known as the machine direction. In each case, it is important to note that the foil blade has a flat leading edge that forms an angle greater than 90° with the paper sheet and conveying forming fabric as they move in the machine direction. Formerly prior art has not effected the use of the concept of “activity zones”; however, for the comparison with the present invention, the concept and related terminology set forth hereinabove is employed. The activity zones are identified with the dotted circles, Activity zone 1 and 2, respectively, on foil blade B; these activity zones are affected by the flat leading edge F and the entry and exit angles of the sheet and conveying fabric with respect to the horizontal, &thgr;1 and &thgr;2, respectively, as shown in FIG. 1B, which is a close-up view of the foil blade B of FIG. 1A.

[0015] Importantly, the flat of the foil blade supports the conveying fabric and creates a water seal that enables vacuum to be generated and sustained by the motion of the conveying fabric and slurry over the divergent surface of the foil blade; thus, the leading flat edge of prior art foil blades is a critical feature to their function and operation. The water extracted from the sheet by the foil blade B is subsequently removed by a doctoring action of the foil blade C that immediately follows foil blade B in the machine direction.

[0016] Referring to FIG. 1B, discussing the general principles of operation of foil blades in the art using formulas and acceleration terminology developed and discovered by the applicant that are not taught in the prior art, foil blade B has a flat length (F), a divergent surface having an angle (&agr;2) and such angle having a sustended length (L). The drainage from foil blade B is substantially proportional to the divergent angle (&agr;2) and the sustended length of that angle (L). The activity imparted to the sheet by foil blade B is proportional to the acceleration of the fabric/sheet as it deflects and conforms to the surface of the foil blade. For example, referring again to FIG. 1B, the fabric/sheet approaches foil blade B at an approach angle (&thgr;0), traverses the flat of foil blade B and diverges down the divergent surface at an angle (&agr;2). The fabric leaves foil blade B and approaches foil blade C at angle (&thgr;2). The conveying fabric/sheet experience an acceleration at two zones of activity as they traverse the foil blade B. The conveying fabric sheet enters the first activity zone at an approach angle (&thgr;1), changes direction, and leaves the first activity zone at an exit angle (&agr;2). This change in fabric direction takes place over a distance that is established by the length of the flat (F). Thus, the acceleration imparted to the sheet at activity zone 1 can be described by the following equation:

Acceleration at zone 1=(fabric speed)2×(&thgr;1+&agr;2)/F

[0017] Similarly, the conveying fabric/sheet enters a second activity zone at an approach angle (&agr;2) and leaves the second activity zone at an exit angle (&thgr;2). Thus, the acceleration imparted to the sheet at activity zone 1 can be described by the following equation:

Acceleration at zone 2=(fabric speed)2×(&agr;1+&thgr;2)/d

[0018] where d is the distance over which the change in direction of the fabric/sheet takes place; this distance d is on the order of about ¼ inch.

[0019] It is the acceleration of the sheet at activity zones 1 and 2 of the foil blade B that determines the activity imparted to the sheet as it traverses foil blade B. FIG. 1B of the prior art shows activity zone 1 of foil blade B having an approach angle (&thgr;1), an exit angle (&agr;2), and an acceleration distance (F); also, foil blade B has a drainage angle (&agr;2), and a drainage nip length (L). The drainage of the foil blade B is approximately &agr;2*L. Conventional foil blade shapes such as those illustrated in FIGS. 1A and 1B have inherent drawbacks. For example, as shown in FIG. 1B, the exit angle of activity zone 1 and the entry angle of activity zone 2 is the angle (&agr;2), which is also the drainage angle of the foil blade. Thus, the primary foil blade angle that characterizes the activity of the foil blade is the same angle that characterizes the drainage of the foil blade; this linkage between activity imparted to a sheet and the drainage for a given foil blade is undesirable because it is not possible to affect changes to sheet activity and the drainage separately by modifying the foil blade. Often it is desirable to impart a substantial activity to the sheet without a corresponding increase in sheet drainage.

[0020] Thus, it is desirable to have a foil blade wherein the activity and drainage characteristics associated with it can be substantially separately and independently established. Furthermore, a conventional foil blade cannot be used in reverse orientation relative to the travel direction of the conveying fabric as set forth by the present invention. Such a reversible feature of the present foil blade invention is beneficial, as for example, when a substantial change in machine speed or sheet weight is made; the foil blade could be reversed and such reversal would present to the sheet a new set of drainage and activity characteristics beneficial to and consistent with the production change. Also, this type of reversible quality would be beneficial to make the foil blade suitable for use at different forming table locations, where the blade is presented with a wetter or drier sheet. Another benefit of the reversible feature may be to extend the useful life of the blade as with plastic blades.

[0021] Specifically, prior art foil blades are set forth in the following references:

[0022] U.S. Pat. No. 3,874,998 issued Apr. 1, 1975 to Johnson for an AGITATOR BLADE FOR USE BELOW FORMING WIRE OF PAPER MAKING MACHINE teaches a foil blade for use in the forming section of a paper machine that has a flat leading edge and an agitating channel or depression between the leading edge and the trailing edge, wherein both the leading and trailing edges form an angle greater than 90° with the paper sheet and conveying forming fabric.

[0023] U.S. Pat. No. 4,789,433 issued Dec. 6, 1988 to Fuchs for a SKIMMING BLADE WITH WAVE-SHAPED TROUGHS FOR A PAPERMAKING MACHINE teaches a foil blade with a flat leading edge forming an angle greater than 90° with the paper sheet and conveying forming fabric and a wavy-shaped dewatering surface that follows the flat leading edge.

[0024] U.S. Pat. No. 4,838,996 issued Jun. 13, 1989 to Kallmes for a HYDROFOIL BLADE FOR PRODUCING TURBULENCE teaches a foil blade having a flat leading edge forming an angle greater than 90° with the paper sheet and conveying forming fabric and a plurality of angulated surfaces for producing turbulence in the paper sheet to control dewatering thereof.

[0025] U.S. Pat. No. 6,030,501 issued Feb. 29, 2000 to Neun, et al. for a PAPER FORMING ACTIVITY BLADE teaches a foil blade having a flat leading edge forming an angle greater than 90° with the paper sheet and conveying forming fabric and an elevator-type device for adjusting the leading edge vertical position with respect to the substantially horizontal surface of the paper sheet and conveying fabric.

[0026] None of the prior art foil blades, particularly where a convergent nip is used to redirect water back into the sheet, as with U.S. Pat. No. 4,447,296 issued May 8, 1984 to Cruse for DOUBLE NIP HYDROFOIL permit the reversal of the orientation of the blade with respect to the conveying fabric running or machine direction, much less to change the sheet drainage and activity characteristics thereby.

[0027] Thus, there remains a need for a foil blade having a modifiable leading surface that can be varied for introducing different activity levels to the sheet without increasing the wear to the conveying fabric. Also, there remains a need for a foil blade that can be reversible with respect to its orientation and that of the sheet and conveying fabric direction, or machine direction. Furthermore, there remains a need for a foil blade that can separately and independently predict, establish, and control the drainage and activity characteristics of the sheet.

SUMMARY OF THE INVENTION

[0028] The present invention is directed to a foil blade having different and modifiable leading and trailing edges for manipulating and controlling the sheet activity and water extraction or drainage in the forming section of a paper machine, such that reversal of the foil blade produces different drainage and activity characteristics of the sheet. Such a reversible feature is advantageous when a substantial change is made, e.g., a change in machine speed or sheet weight. Additionally, the reversible nature of the foil blade advantageously permits the foil blade to be positioned and used at a different forming table location, where the sheet moisture level may be wetter or drier. Furthermore, the reversible nature and design of the foil blade according to the present invention provides for extended useful life of the blade, particularly for plastic foil blades, since the reorientation of the foil blade could effectively double the life of the blade.

[0029] In the preferred embodiment, a foil blade having reversible characteristics for controlling and manipulating sheet activity and drainage includes both leading and trailing edges that each form an angle less than 90° with the horizontal, the paper sheet and conveying forming fabric. The foil blade of the present invention is used to impact the sheet activity in a precise and controlled manner based upon the leading and trailing edge design, in particular the angle that each forms with respect to the horizontal. Additionally, the present invention improves and enhances sheet properties, e.g., sheet formation or uniformity, due to the activity it imparts to the sheet. The present invention may advantageously be configured to extract water from the sheet as well. However, notably, the present invention is capable of being configured such that the foil blade imparts activity to the sheet but does not drain the sheet.

[0030] Preferably, the present invention is reversible and has a different leading and trailing or exit edge configuration so that the reversing of the blade with respect to the machine direction changes the sheet activity and drainage while the paper machine is running. Furthermore, the present invention is preferably configured to provide for separate and independent establishment of the drainage characteristics and activity characteristics of the foil blade; this is provided by the reversibility of the foil blade and the different angles of the leading and trailing edges, which when the foil blade is reversed produce different activity and drainage characteristics in the sheet. Advantageously, the desired drainage and activity characteristics in the sheet can be calculated and the foil blades of the present invention can then be designed to produce those desired characteristics by varying the leading and trailing edge angles, and with the introduction of additional activity-producing zones within the foil between the leading and trailing edges.

[0031] The present invention is further directed to a method for using foil blades having such angled leading and trailing edges and additional activity zones, which collectively produce predictable and controlled activity and drainage characteristics in the sheet, and which, when the foil blade is reversed, produce different predictable and controlled activity and drainage in the sheet.

[0032] Thus, the present invention provides for a reversible foil blade having angled leading and trailing edges that can be different for providing different predictable and controlled activity and drainage characteristics in the sheet when the foil blade is reversed, and additional activity zones between the leading and trailing edges for providing predictable and controlled activity and drainage characteristics in the sheet, which can also be different if the foil blade is reversed, i.e., the operative set of drainage and activity characteristics relating to the sheet are predicted, established, and controlled by the leading and trailing edge designs, the design of additional activity zones therebetween, and the orientation of the foil blade with respect to the travel or machine direction of the conveying fabric.

[0033] Accordingly, one aspect of the present invention is to provide a reversible foil blade for a paper machine wherein the operative set of drainage and activity characteristics relating to the pulp sheet are predicted, established, and controlled by the leading and trailing edge designs of the foil blade and the orientation of the foil blade with respect to the travel or machine direction of the conveying fabric.

[0034] Another aspect of the present invention is to provide a reversible foil blade for a paper machine wherein the operative set of drainage and activity characteristics relating to the pulp sheet are predicted, established, and controlled by the leading and trailing edge designs of the foil blade, the design of additional activity zones therebetween, and the orientation of the foil blade with respect to the travel or machine direction of the conveying fabric.

[0035] Still another aspect of the present invention is to provide a method of using a reversible foil blade for a paper machine wherein the operative set of drainage and activity characteristics relating to the pulp sheet are predicted, established, and controlled by the leading and trailing edge designs of the foil blade and the orientation of the foil blade with respect to the travel or machine direction of the conveying fabric. Also, another aspect of the present invention is to provide a method of using such a foil blade having additional activity zones located between the leading and trailing edges of the foil blade.

[0036] These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1A is a side view of a conventional PRIOR ART foil blade.

[0038] FIG. 1B is an expanded view of a section of FIG. 1A showing PRIOR ART.

[0039] FIG. 2A is a side view of an embodiment constructed according to the present invention.

[0040] FIG. 2B is the side view of FIG. 2A with additional activity zones indicated.

[0041] FIG. 2C is the side view of FIG. 2A with additional activity zones indicated.

[0042] FIG. 3 illustrates a side view of one embodiment of a foil blade according to the present invention.

[0043] FIG. 4 illustrates a side view of one embodiment of a foil blade according to the present invention.

[0044] FIG. 5 illustrates a side view of one embodiment of a foil blade according to the present invention.

[0045] FIG. 6 illustrates a side view of one embodiment of a foil blade according to the present invention.

[0046] FIG. 7 illustrates a side view of one embodiment of a foil blade according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as “forward,” “rearward,” “front,” “back,” “right,” “left,” “upwardly,” “downwardly,” and the like are words of convenience and are not to be construed as limiting terms.

[0048] Referring now to the drawings in general, the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. As set forth in the summary hereinabove, one object of the present invention is to provide a foil blade that can be installed on the paper machine in either of two opposite orientations with respect to the travel direction of the conveying fabric, or machine direction, for predicting, establishing, and controlling the sheet activity and drainage characteristics. As such, the following description of the embodiments of the present invention are presented in context of the orientation of the foil blade relative to the travel direction of the conveying fabric and sheet, or machine direction. To this end, descriptive terms such as first, second, entry and exit are intended to be taken in context of the travel direction of the conveying fabric and sheet relative to the foil blade as indicated for each drawing or representation and descriptions thereof.

[0049] As best seen in FIG. 2A, a foil blade according to the present invention is shown, generally referenced 1, having an orientation relative to the travel direction of the conveying fabrics, or machine direction, as illustrated by the travel direction arrow A. FIG. 2B shows the same embodiment of the present invention shown in FIG. 2A, and illustrating the path of the conveying fabric and sheet as they traverse the foil blade simultaneously. FIG. 2B also shows the foil blade activity zones and the foil blade drainage angle and the drainage nip length for the orientation shown in FIG. 2A. FIG. 2C shows the same embodiment of the present invention shown in FIG. 2A, but it illustrates a reversed blade orientation with respect to the travel direction of the conveying fabric and sheet; this direction shown in FIG. 2C is opposite that direction shown in FIG. 2A and FIG. 2B. FIG. 2C also shows the path of the conveying fabric and sheet as they traverse the foil blade simultaneously in the reversed orientation; a delineation of surface elements corresponding to those shown in FIG. 2A.

[0050] Referring now to FIGS. 2A and 2B, the foil blade of the present invention is illustrated with the foil blade (1) oriented relative to the travel direction of the conveying fabric as indicated by the direction arrow A. The foil blade (1) is constructed with a tee slot (2) to facilitate the mounting, installation and/or removal of the blade on the paper machine in the cross-machine direction such that the foil blade leading edge (13) is established substantially perpendicular to the conveying fabric and sheet. The tee slot (2) is constructed and configured to receive a tee bar (not shown) or other mounting means connected to the paper machine for installation of the foil blade on the machine; these mounting means are known to one of ordinary skill in the paper machine and foil blade art, and may employ mounting means such as a bar, dovetail mount, etc. The tee slot may be centered with respect to the foil blade, or it may be offset from the center such that reversal of the blade changes the amount of the blade that is positioned ahead of the tee slot. A first doctoring surface (3) is provided by the foil blade for deflecting the water that is carried on the underside of the approaching conveying fabric, which is illustrated by a dotted line in FIG. 2B, away from the conveying fabric thereby providing drainage of the fabric and the sheet. A second doctoring surface (4) is also shown; it assumes the same function as the first doctoring surface when the foil blade is oriented in a reverse direction, as shown in FIG. 2C. The second doctoring surface also serves to prevent fiber build-up at the back edge of the blade when the foil blade assumes the orientation shown in FIG. 2B; in this orientation, the second doctoring surface is presented as a trailing surface along with the trailing or exit edge (14). An entry surface (5) having an angle &agr;1 and a subtended length L1, which extends to form the angle &agr;1 with the horizontal line H, is established for the foil blade oriented as shown in FIG. 2B; this angle &agr;1 is less than about 90 degrees with the horizontal H, preferably between about 0 to about 10 degrees and functions to moderate the quantity of water doctored off the conveying fabric by the doctoring surface (3), thereby controlling the drainage characteristics associated with that orientation of the foil blade. A first flat surface (6) having a length F1, which defines the acceleration distance of activity zone 1, as shown in FIG. 2B is positioned directly following the entry surface (5). A first divergent surface (7) having an angle &agr;2 and a subtended length L2, which extends to form the angle &agr;2 with the horizontal line H, is established for the foil blade oriented as shown in FIG. 2B. A surface discontinuity (8) may be located following and establishes the first divergent surface (7); the location of the surface discontinuity establishes the maximum deflection of the conveying fabric as it conforms to the divergent surface when it exits activity zone 1 and enters activity zone 2. Angle &agr;2 is the exit angle of activity zone 1. The present invention does not necessarily need to employ any surface discontinuity between the foil blade leading and exit edges (13, 14 respectively for FIGS. 2A and 2B); the surface discontinuity is predetermined, selected, and employed only where additional activity of the sheet is desired.

[0051] For the first orientation shown in FIGS. 2A and 2B, the activity zone 1 or first activity zone is established and defined by the approach angle &agr;1, the acceleration distance F1, and the exit angle &agr;2. These parameters can be separately and independently predetermined and selected in such a configuration to achieve or produce a desired acceleration or sheet activity within the first activity zone. Furthermore, these parameters can be predetermined and selected in such a configuration without impacting drainage characteristics associated with the foil blade; rather, the foil blade drainage characteristics are predetermined, selected and established by the divergent surface (12), its drainage angle &agr;2 and its sustended length L5, where L5 is the drainage nip length, as shown in FIG. 2B. Thus, the first orientation produces a first activity zone or a first acceleration zone according to the following:

Acceleration at zone 1=(fabric speed)2×(&thgr;1+&agr;2)/F1

[0052] Similarly, activity zone 2 or the second activity zone is established and defined by the approach angle &agr;2, the acceleration distance d, and the exit angle &thgr;2. The exit angle &thgr;2 of the second activity zone is affected and is capable of being manipulated by the location of the first surface discontinuity (8), as shown in FIG. 2B, such that &thgr;2=L2/((L3+L4)×&agr;2). Thus, the first orientation produces a second activity zone or a second acceleration zone according to the following:

Acceleration at zone 2=(fabric speed)2×(&thgr;2+&agr;2)/d

[0053] Surprisingly, the location of the first surface discontinuity (8) has a material and important impact on the acceleration at the activity zone 2 when the foil blade is oriented as shown in FIGS. 2A and 2B, or the first orientation; however, when the foil blade is arranged in a reversed orientation as shown in FIG. 2C, the location of the surface discontinuity is inconsequential. In FIG. 2C, the conveying fabric and sheet are directed toward the flat (11). Also surprisingly, any surface discontinuity present between the leading edge (13) and the exit edge (14) of the foil blade essentially nullifies the effect of the following surfaces with respect to activity or acceleration of the sheet.

[0054] Referring once again to FIGS. 2A and 2B, the foil blade further includes a convergent surface (10) having an angle &agr;3 and a sustended length of that angle, L4. The sustended length L4 is established by the location of a second surface discontinuity (9). The convergent surface (10) and the second surface discontinuity (9) do not produce any significant effect for the first orientation shown in FIG. 2B. However, the location of the second surface discontinuity has a significant impact on the acceleration or activity at the activity zone 1 or first activity zone when the foil blade is positioned in the reverse orientation shown in FIG. 2C.

[0055] Furthermore, as shown in FIGS. 2A and 2B, the foil blade includes a second flat (11) having a length F2; this second flat is predetermined and selected to define the acceleration distance of activity zone 3 or the third activity zone. A divergent surface (12) is predetermined, selected and configured to produce an angle &agr;4 and a sustended length L5, which establish the drainage angle of the foil blade and drainage nip length of the foil blade, respectively, when the foil blade is arranged in the first orientation shown in FIGS. 2A and 2B. Thus, the drainage associated with the foil blade for the first orientation is substantially established according to the following:

Drainage˜&agr;4×L5

[0056] Referring now to FIG. 2C, a reverse orientation of the foil blade is shown. This reverse orientation is established by reconfiguring the foil blade on the paper machine such that it is installed or mounted in the opposite or reverse direction to that shown in the first orientation of FIGS. 2A and 2B. For this reversed orientation, the foil blade has drainage and activity characteristics that are materially different than those for the same foil blade when it is configured in the first orientation. As with the first orientation, the drainage and activity characteristics of the foil blade are predetermined, selected, and established by the components of the foil blade; for the first orientation, as shown in FIGS. 2A and 2B, these drainage and activity characteristics are set forth as follows:

Acceleration at zone 1=(fabric speed)2×(&thgr;1+&agr;2)/F1

Acceleration at zone 2=(fabric speed)2×(&thgr;2+&agr;2)/d

Acceleration at zone 3=(fabric speed)2×(&thgr;2+&agr;4)/F1

Acceleration at zone 4=(fabric speed)2×(&thgr;3+&agr;4)/d

Drainage˜&agr;4×L5

[0057] where d is the acceleration distance or the distance over which the fabric changes direction, which is essentially constant approximately about ⅜ to about ¼ inch, and &thgr;1 is the angle of the fabric with the horizontal H at activity zone 1, &thgr;2 is the angle of the fabric with the horizontal H at activity zone 2, and &thgr;3 is the angle of the fabric with the horizontal H at activity zone 4. Note that for convenience, d is approximated as being about equal to the distance of a flat, e.g., F2.

[0058] Significantly, for the reverse orientation from that shown in FIGS. 2A and 2B, which is shown in FIG. 2C, these drainage and activity characteristics are set forth as follows:

Acceleration at zone 1=(fabric speed)2×(&thgr;1+&agr;3)/F2

Acceleration at zone 2=(fabric speed)2×(&thgr;2+&agr;3)/d

Acceleration at zone 3=(fabric speed)2×(&thgr;2+&agr;1)/F1

Acceleration at zone 4=(fabric speed)2×(&thgr;3+&agr;1)/d

Drainage˜&agr;1×L1

[0059] where d is the acceleration distance or the distance over which the fabric changes direction, which is essentially constant approximately about ⅜ to about ¼ inch, and &thgr;1 is the angle of the fabric with the horizontal H at activity zone 1, &thgr;2 is the angle of the fabric with the horizontal H at activity zone 2, and &thgr;3 is the angle of the fabric with the horizontal H at activity zone 4.

[0060] The formulas set forth hereinabove are applicable for reversible foil blade configurations of the present invention having those components shown and illustrated in FIGS. 2A, 2B and 2C. These figures are used for illustrative purposes and are not intended to be limiting as to the range of embodiments properly considered within the scope of the present invention.

[0061] Alternative embodiments having additional angles, surfaces, and predetermined discontinuities may be similarly predetermined, calculated, and designed based on appropriate modifications to the formulas as will be obvious to those skilled in the art upon review of the foregoing description. By way of example, not limitation, FIGS. 3, 4, 5, 6, and 7 illustrate some alternative embodiments of the present invention. FIG. 3 illustrates a foil blade (1) having a leading edge angle &agr;1 with the horizontal line H and an exit angle &agr;2 with the horizontal line H, where angle &agr;1 affects the sheet activity and angle &agr;1 affects the sheet drainage for the foil blade orientation similar to FIGS. 2A and 2B, where the conveying fabric and sheet first meet the leading edge angle &agr;1 as they traverse the foil blade and later pass over exit angle &agr;2 in the direction of arrow A. No surface discontinuity is included for the foil blade configuration shown in FIG. 3; the fabric/sheet essentially follow the surfaces without substantial deflection therefrom but deflecting from the horizontal H along with the surface. FIG. 4 shows a foil blade with the same orientation and construction as that shown in FIG. 3, and further includes a groove surface discontinuity (15) with a following surface length VL3. FIG. 4 shows the location of a groove surface discontinuity that does not have a significant impact when the fabric/sheet travel in the direction A, but do have a significant impact when the blade is positioned in a reverse orientation, since the surface discontinuity limits the fabric deflection from the horizontal as the fabric follows the divergent angle surface until it meets with the surface discontinuity, i.e., the surface discontinuity interrupts the fabric, which is otherwise following the blade surface. In this way, the introduction of a surface discontinuity provides for controlled fabric deflection, and therefore controlled sheet activity. FIG. 5 shows a foil blade with the same orientation and construction as that shown in FIG. 3, and further includes a recessed surface discontinuity (16). FIG. 6 shows a foil blade with the same orientation and construction as that shown in FIG. 3, and further includes a first groove surface discontinuity (17) and a second groove surface discontinuity (15) with a following surface length VL3. FIG. 7 shows a foil blade with the same orientation and construction as that shown in FIG. 3, and further includes a first recessed surface discontinuity (19) and a second recessed surface discontinuity (16) with a convex surface therebetween (18), wherein the first and second recessed surface discontinuities form the entry and exit angles, &agr;1 and &agr;2, respectively, with the horizontal H, which is the configuration set forth in the foregoing detailed description of the FIGS. 2A, 2B, and 2C. The convex surface discontinuity (18) provides a truncated first and second recessed surfaces (19) and (16), respectively, which creates another surface discontinuity itself. It is important to note that the reversible function of the foil blade is effective for each of these illustrations used as examples in the foregoing.

[0062] Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. By way of example, as set forth in the foregoing, alternative embodiments of the present invention may not employ any surface discontinuity between the foil blade entry and exit edges. Also, an offset tee slot may be used with the foil blade according to the present invention. An offset tee slot changes the angles, in particular the &thgr;1 or the angle of the fabric with the horizontal H at the first activity zone, creating a shorter distance and corresponding greater sheet activity; reversing the blade affects that distance as well, and therefore affects the acceleration and activity associated therewith. All modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.

Claims

1. A foil blade for paper machines comprising

a first orientation of the foil blade having a leading edge angle &agr;1 that is less than 90 degrees from the horizontal;

an entry surface positioned at the angle &agr;1;

and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine, such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity.

2. The foil blade according to claim 1, wherein reversing of the blade with respect to the machine direction changes the sheet activity and drainage associated with the blade while the paper machine is running.

3. The foil blade according to claim 1, wherein the leading edge angle &agr;1 is between about greater than zero and 10 degrees.

4. The foil blade according to claim 1, further including an exit angle &agr;2 that is less than 90 degrees from the horizontal and is formed by an exit surface positioned at the opposite end of the blade from the entry surface.

5. The foil blade according to claim 1, wherein the exit angle &agr;2 is between about greater than zero and 10 degrees.

6. The foil blade according to claim 1, further including at least one surface discontinuity following the entry surface, wherein the at least one surface discontinuity produces separate and independent drainage and activity characteristics for the blade.

7. The foil blade according to claim 6, wherein the surface discontinuity is at least one groove surface.

8. The foil blade according to claim 6, wherein the surface discontinuity is at least one recessed surface.

9. The foil blade according to claim 6, wherein the surface discontinuity is at least two groove surfaces.

10. The foil blade according to claim 6, wherein the surface discontinuity is at least two recessed surfaces forming the entry and exit of a convex surface.

11. The foil blade according to claim 1, wherein the tee slot is centered.

12. The foil blade according to claim 1, wherein the tee slot is offset from the center of the blade.

13. The foil blade according to claim 1, further including a first flat surface that defines the acceleration distance of the first activity zone.

14. The foil blade according to claim 13, wherein the first flat surface is between about 0.25 inches to about 3 inches.

15. The foil blade according to claim 13, wherein reversal of the blade makes the first flat surface define the acceleration distance of a different activity zone.

16. The foil blade according to claim 1, further including a first divergent surface having an angle between about 0 to about 15 degrees, which defines the exit angle of the first activity zone and produces a first activity zone exit drainage.

17. The foil blade according to claim 16, wherein reversal of the blade makes the first divergent surface define a convergent nip of a different activity zone.

18. The foil blade according to claim 16, wherein the first divergent surface further includes a surface discontinuity to define fabric deflection at the exit angle of the first activity zone.

19. The foil blade according to claim 1, further including a first convergent surface having an angle between about 0 to about 15 degrees, which defines an entry nip into a second flat surface.

20. The foil blade according to claim 19, wherein the second flat surface is between about 0.25 to about 3 inches.

21. The foil blade according to claim 19, wherein reversal of the blade makes the first convergent surface become a divergent surface and defines an exit angle of the first activity zone and produces a first activity zone exit drainage.

22. The foil blade according to claim 1, further including a first doctoring surface to doctor water at the entry of the fabric to the blade and second doctoring surface to prevent fiber build-up at the exit of the fabric from the blade.

23. The foil blade according to claim 22, wherein reversal of the blade changes the first doctoring surface to prevent fiber build-up at the blade exit and the second doctoring surface to doctor water at the blade entry.

24. A foil blade for paper machines comprising

a first orientation of the foil blade having a leading edge angle &agr;1 that is less than 90 degrees from the horizontal;

an entry surface positioned at the angle &agr;1;

and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine, such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity and wherein reversing of the blade with respect to the machine direction changes the entry angle from affecting activity to function as an exit angle affecting drainage.

25. The foil blade according to claim 24, wherein reversing of the blade with respect to the machine direction changes the sheet activity and drainage associated with the blade while the paper machine is running.

26. A foil blade for paper machines comprising

a first orientation of the foil blade having a leading edge angle &agr;1 that is less than 90 degrees from the horizontal;

an entry surface positioned at the angle &agr;1 having a first flat surface F1;

an angle &thgr;1 of the conveying fabric with the horizontal at fabric entry to the blade and an angle &thgr;3 of the conveying fabric with the horizontal at fabric exit from the blade;

a second entry surface positioned at the angle &agr;3 having a second flat surface F2;

wherein a first activity zone is produced according to the formula

acceleration (a)=(fabric speed)2×(&thgr;1+&agr;2)/F1;

and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine, such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity.

27. The foil blade according to claim 26, wherein reversing of the blade with respect to the machine direction changes the sheet activity and drainage associated with the blade while the paper machine is running such that a reverse first activity zone is produced according to the formula

acceleration (a)=(fabric speed)2×(&agr;4+&thgr;3)/d,

where d is the distance over which the fabric changes direction and &agr;4 is the angle that the fabric forms with the blade when it enters the reversed orientation.

28. The foil blade according to claim 26, wherein the drainage and activity characteristics of the blade are set forth as follows:

Acceleration at zone 1=(fabric speed)2×(&thgr;1+&agr;2)/F1 Acceleration at zone 2=(fabric speed)2×(&thgr;2+&agr;2)/d Acceleration at zone 3=(fabric speed)2×(&thgr;2+&agr;4)/F1 Acceleration at zone 4=(fabric speed)2×(&thgr;3+&agr;4)/d Drainage˜&agr;4×L5

where d is the distance over which the fabric changes direction, and &thgr;1 is the angle of the fabric with the horizontal H at activity zone 1, &thgr;2 is the angle of the fabric with the horizontal H at activity zone 2, and &thgr;3 is the angle of the fabric with the horizontal H at activity zone 4.

29. The foil blade according to claim 27, wherein the drainage and activity characteristics of the blade are set forth as follows:

Acceleration at zone 1=(fabric speed)2×(&thgr;1+&agr;3)/F2 Acceleration at zone 2=(fabric speed)2×(&thgr;2+&agr;3)/d Acceleration at zone 3=(fabric speed)2×(&thgr;2+&agr;4)/F1 Acceleration at zone 4=(fabric speed)2×(&thgr;3+&agr;1)/d Drainage˜&agr;4×L1

where d is the distance over which the fabric changes direction, and &thgr;1 is the angle of the fabric with the horizontal H at activity zone 1, &thgr;2 is the angle of the fabric with the horizontal H at activity zone 2, and &thgr;3 is the angle of the fabric with the horizontal H at activity zone 4.

30. A method for using a foil blade for paper machines comprising the steps of:

providing a foil blade having a leading edge angle &agr;1 that is less than 90 degrees from the horizontal; an entry surface positioned at the angle &agr;1; and a tee slot to facilitate the mounting, installation and/or removal of the blade on the paper machine;

installing the foil blade in a first orientation such that when the foil blade is installed on a paper machine in the first orientation the leading edge angle is the first portion of the foil blade that is traversed by a conveying fabric and by a sheet being formed on the paper machine, thereby providing a predetermined and controlled effect of the blade on drainage and sheet activity.

31. The method according to claim 30, further including the step of removing the foil blade from the machine, reversing its direction with respect to the conveying fabric travel direction, and reinstalling the blade on the machine.