A known type of twin-wire or twin-fabric former is the Bel Bond former, which is designed as a retrofit to an existing fourdrinier wire. Bel Bond is a registered trademark of Beloit Corporation. A Bel Bond former includes a looped top wire cooperating with the existing fourdrinier or bottom wire. The Bel Bond former also includes a curved inverted vacuum box positioned within the loop of the top wire.

The curved inverted vacuum box typically includes a box that is made from stainless steel or the like and that defines an enclosure connected to a source of partial vacuum. The box includes a base having a convex curved surface for guiding the top wire. A plurality of dewatering blades, usually ceramic, extend in the cross machine direction and are spaced in the machine direction along the curved surface of the curved inverted vacuum box. The top and bottom wires sandwich the web, and dewatering takes place due to tension of both wires, combined with centrifugal force. The vacuum source urges water upwardly out of the web through the top wire. A portion of water is removed from the formed web downwardly through the bottom wire during movement of the wires and the web over the blades.

SUMMARY OF THE INVENTION Known prior art curved inverted vacuum boxes do not allow changing the drainage pressure from one blade to the next so as to allow experimentation with formation and sheet strength. The invention provides a curved inverted vacuum box in which each blade is loaded independently, thus providing the ability to change the drainage pressure at each blade location. With the consistency of the web or sheet changing along the curved surface of the curved inverted vacuum box, a controlled induced drainage curve can be achieved to follow consistency changes along the curved surface.

More particularly, the invention provides an apparatus for removing fluid from a fibrous web in a papermaking machine, the apparatus comprising a plurality of generally parallel supports that extend in the cross machine direction and that are spaced in the machine direction. Each support has mounted thereon a respective blade extending in the cross machine direction. The blades are spaced in the machine direction along a convex path for movement of the web and, in the preferred embodiment of the invention, the fabrics, over the blades. Each blade is movable relative to its respective support in a direction perpendicular to the web such that outward movement of the blade relative to the support presses the blade against the web. The apparatus also comprises a control system for exerting, on each of the blades, a force in the direction toward the web so as to press the blade against the web. The control system is operable to vary the force exerted on each of the blades independent of the force exerted on the remaining blades.

Preferably, the supports are tee bars extending in the cross machine direction. An air loaded tube is saddled in each tee bar between the tee bar and the base of the respective blade. When the tube is pressurized, a force

is exerted, pushing the blade into the fabrics and the web, changing the drainage pressure at the leading and trailing edges of the blade. A control panel equipped with gauges, regulators and air lines connected to the individual air tubes is provided for independent air pressure regulation.

Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings.

DESCRtPTION OF THE DRAWINGS Fig. 1 is a partial side elevational of a papermaking machine embodying the invention.

Fig. 2 is an enlarged portion of Fig. 1, partially in section.

Fig. 3 is a further enlarged portion of Fig. 2.

Fig. 4 is a partial view taken along line 4-4 in Fig. 3.

0 Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT A papermaking machine 10 embodying the invention is partially illustrated in Fig. 1. More particularly, the portion of the papermaking machine 10 illustrated in Fig. 1 is a Bel Bond former 14. As is known in the art, the Bel Bond former 14 comprises a frame 18 supporting a looped

bottom fabric or wire 22 moving in the machine direction (from left to right in Fig. 1). A secondary headbox 26 is mounted on the frame 18 above the bottom fabric 22. A fibrous web 30 (see Fig. 3) is supported on top of and moves with the bottom fabric 22. Mounted on the frame 18 downstream of the secondary headbox 26 is (see Fig. 1) a looped top fabric or wire 34 positioned such that the web 30 is sandwiched between and moves with the top fabric 34 and the bottom fabric 22. A curved inverted vacuum box 38 is mounted on the frame 18 within the endless loop of the top fabric 34. The curved inverted vacuum box 38 includes a box 42 defining an enclosure connected to a source 46 of partial vacuum. The base of the box 38 has a convex curved surface. The Bel Bond former 14 and the curved inverted vacuum box 38 as thus far described are conventional and will not be described in further detail.

As shown in Figs. 2 and 3, a plurality of generally parallel supports 50 are mounted on the curved surface of the box base. The supports 50 extend in the cross machine direction and are spaced in the machine direction. Preferably, as shown in Fig. 3, the supports 50 are tee bars that are generally T-shaped in cross-section. Each tee bar 50 has therein an outwardly or downwardly opening recess 54 extending in the cross machine direction, and each tee bar 50 includes opposed flanges 58 and 62 extending in the machine direction on opposite sides of the recess 54.

Each tee bar 50 is secured to the box base by a plurality of bolts 66, as best shown in Figs. 3 and 4.

The tee bars 50 have mounted thereon respective blades 70 extending in the cross machine direction. The blades 70 are preferably ceramic, as is known in the art. The blades 70 are spaced in the machine direction along a convex path, as best shown in Fig. 2. The blades 70 face generally downwardly such that the fabrics 22 and 34 and the web 30

pass beneath the blades 70, with the blades 70 pressing against the top fabric 34. Each blade 70 is movable relative to its respective tee bar 50 in a direction generally perpendicular to the web 30 (vertically in Fig. 3) such that outward movement of the blade 70 relative to the tee bar 50 (downward movement in Fig. 3) presses the blade 70 against the top fabric 34 and the web 30. To this end, each of the blades 70 is secured to a respective blade base 74 which extends in the cross machine direction and which is generally C-shaped in cross-section. The blade base 74 has therein an inwardly or upwardly opening channel 78 receiving the flanges 58 and 62 of the respective tee bar 50 such that the flanges limit vertical movement of the blade 70 relative to the tee bar 50. Each blade 70 is movable relative to its tee bar 50 between an uppermost position and a lowermost position. In Fig. 3, the left-hand blade 70 is shown in its uppermost position, the right-hand blade 70 is shown in its lowermost position, and the middle blade 70 is shown in an intermediate position between the uppermost and lowermost positions. Each blade base channel 78 and the respective tee bar recess 54 define (see Fig. 4) a variable volume chamber 82 extending substantially the entire length of the blade 70. The chamber 82 has a volume that changes in response to movement of the blade 70 toward and away from the web 30. Specifically, the volume increases in response to downward movement of the blade 70 and decreases in response to upward movement of the blade 70.

The curved inverted vacuum box 38 also includes (see Fig. 2) a control system 86 (shown schematically) for exerting, on each of the blades 70, a downward force so as to press the blade 70 against the fabrics 22 and 34 and the web 30. The control system 86 is operable to vary the force exerted on each of the blades 70 independent of the force exerted on the remaining blades 70. The control system 86 includes, for each blade 70, a respective flexible conduit or air tube 90 (Figs. 3 and 4)

saddled in the tee bar 50 between the tee bar 50 and the base 74 of the blade 70 (i. e., in the variable volume chamber 82). Each tube 90 extends substantially the entire length of the respective blade 70 and has a closed end (not shown) and an opposite open end (the left end in Fig. 4). The control system 86 includes a source 94 of variable pressure connected to the open end of each tube 90. The control system 86 also includes (see Figs. 2 and 4) air lines 98 connected between the pressure source 94 and the individual air tubes 90. The control system 86 is operable to vary the pressure in each of the tubes 90 independent of the pressure in the remaining tubes 90. In the preferred embodiment of the invention, the control system 86 includes a control panel (not shown) equipped with gauges, regulators and a manually adjustable control for each tube 90.

When a tube 90 is pressurized, the tube 90 expands, increasing the volume of its chamber 82 and pushing the blade 70 downwardly into the fabrics 22 and 34 and the web 30, thereby changing the drainage pressure at the leading and trailing edges of the blade 70.

Various features of the invention are set forth in the following claims.