An extended nip press dewaters a wet paper web by applying a pressing force to the web across a wide area, or extended nip, rather than at a narrow point contact. This application of force increases the quality of the finished paper product.

Optimization of the pressing operation is a function of the machine speed, the nip load applied, the pressure profile of the nip, and the grade of the paper being produced. The optimal pressure profile at a given machine speed and nip load ensures that the finished paper product is of superior quality.

A typical extended nip press includes a rotating cylindrical backing roll and a rigid press shoe having a complementary curved concave facing surface. The press shoe is pivotally mounted and is hydraulically actuated to apply pressure against the backing roll.

To dewater the paper web, the web is passed between the press shoe and the rotating backing roll.

A felt is normally provided on each side of the web, and a rotating belt is provided between the surface of the press shoe and the felt, if provided, or the web surface. Lubricant is sprayed between the belt and the press shoe so that the belt provides a sliding contact with the press shoe surface. Thus, the rotating belt, the felt (s), and the web travel through the extended nip between the surface of the press shoe and the surface of the backing roll.

U. S. Patent No. 4,425,190 (Cronin) discloses an extended nip press in which the press shoe is pivotally

supported by a single pivot rod and actuated by a single piston. While this press generally operates well and provides dewatering over an extended nip, the optimal pressing operation is limited due to the rigid geometry. of the press shoe and its range of movement or adjustability, relative to the backing roll when in operation. The pressure profile on the web is optimized at a given combination of machine speed and nip loading force. If the machine speed or the nip load changes so that the pressure profile is not optimal, however, the press shoe cannot be adjusted to return to an optimal condition due to the single fixed pivot.

U. S. Patent No. 4,973,384 (Cronin) discloses an extended nip press having some flexibility at setting an optimal pressure profile. In this press, the press shoe has a plurality of parallel grooves serving as adjustable pivot points for the press shoe. The single pivot rod supporting the press shoe can be positioned in any of these grooves to change the pressure profile.

This adjustment is time-consuming and costly. Also, this press has limited flexibility because the pressure profile at each pivot point is fixed and cannot be adjusted to overcome non-optimal conditions while the machine is in operation.

U. S. Patent No. 5,167,768 (Cronin et al.) discloses an extended nip press having increased flexibility at setting an optimal pressure profile. In this press, the rigid press shoe is pivotally supported on two parallel rods, each of which is supported by a separate piston. The pistons operate to apply different forces to the pivot rods to bias the facing surface of the press shoe with different forces. By being able to apply force to the press shoe at two points, the pressure profile can be altered so that a more controlled application of pressure is provided.

This control is achieved independently of maximum nip load, machine speed, or paper grade. The press

establishes a variable, more gentle pressure profile providing increased flexibility in operating the machine at a greater speed while maintaining the optimization of the pressing operation.

SUMMARY OF THE INVENTION While the extended nip press disclosed in U. S.

Patent No. 5,167,768 provides increased flexibility at setting an optimal pressure profile, the optimization of the pressing operation is still limited by the fixed pivot locations and the rigid press shoe. The present invention provides an improved extended nip press which overcomes the limitations of earlier extended nip presses. The extended nip press of the present invention provides greater flexibility in optimizing press operating conditions.

More particularly, the invention provides an extended nip press comprising a backing roll, a shoe, a belt and one or more felts for passing between the shoe and the backing roll with the web. The extended nip press also comprises a pressure applying apparatus for selectively forcing the shoe toward the backing roll at any of at least first, second and third points on the shoe, the first, second and third points being spaced in the machine direction. The belt, the felts and the web are urged against the backing roll to establish a pressure zone between the shoe and the backing roll.

The pressure profile of the pressure zone can be varied by the pressure applying apparatus. In the preferred embodiment, the pressure applying apparatus includes first, second and third hydraulic assemblies. Also, the hydraulic assemblies are preferably independently controlled by a control system including a corresponding valve for each hydraulic assembly.

The invention also provides an extended nip press comprising a flexible shoe having a stiffness value in the range of five million to fifty million mm4/meter width. The pressure applying apparatus is selectively

operable to flex the shoe and thereby vary the pressure profile of the pressure zone. In the preferred embodiment, the shoe has a length of approximately twenty inches, and the pressure profile is substantially constant along a substantial portion, e. g. at least one-third, of the length of the shoe.

Additionally, the invention provides an extended nip press including a pressure applying apparatus for selectively forcing the shoe toward the backing roll at any one or more of a plurality of points on the shoe, the pressure applying apparatus including a corresponding plurality of pressure applying devices that exert non-parallel forces on the shoe.

Preferably, the pressure applying devices each exert a force in a respective plane including the backing roll axis of rotation, such that the force is perpendicular to the surface of the backing roll.

Further, the invention provides a method for controlling the pressure profile in an extended nip press. The method includes the following steps: providing the shoe with a stiffness value in the range from five million to fifty million mm"/meter width; selectively forcing the shoe toward the backing roll at any one or more of at least first, second and third points on the shoe, the first, second and third points being spaced in the machine direction, such that the belt, the one or more felts and the web are urged against the backing roll to establish a pressure zone between the shoe and the backing roll, the pressure zone having a pressure profile in the machine direction; and controlling the force applied at each of the first, second and third points so as to flex the shoe and vary the pressure profile.

An advantage of the extended nip press of the present invention is that the press provides greater flexibility in optimizing the pressing operation. The improved extended nip press provides a longer and more gradual pressure profile. The pressure profile can be

varied by the selective application of two or more loads to the press shoe. Additionally, the pressure profile can be varied by the flexing of the flexible press shoe.

Another advantage of the extended nip press is that the press is adjustable"on the run", during pressing operations. This increases the efficiency of the pressing operation.

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.

DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial cross-sectional view of an extended nip press embodying the invention.

Fig. 2 is a graph of the pressure profile achieved by the extended nip press shown in Fig. 1.

Fig. 3 is a partial cross-sectional view of an extended nip press that is a second embodiment of the invention.

Fig. 4 is a partial cross-sectional view of an extended nip press that is a third embodiment of the invention.

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 the 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 An extended nip press 10 embodying the invention is partially illustrated in Fig. 1. The extended nip press 10 is part of a papermaking machine (not otherwise shown) having a machine direction (right to left in Fig. 1) and a cross-machine direction (into and out of the paper in Fig. 1). The extended nip press 10 dewaters a wet paper web W by applying pressure to the web W in a pressure zone or extended nip P. The web W moves generally in the machine direction and in a direction of travel indicated by arrow 12.

It should be understood that the extended nip press 10 can be either an open extended nip press or a closed extended nip press. In an open extended nip press, the longitudinal ends of the extended nip press are open so that the operating elements, such as the press shoe and pressure applying apparatus described below, are open to the surrounding work area. In a closed extended nip press, the longitudinal ends of the extended nip press are closed by a suitable cover so that the operating elements are substantially sealed to contain operating fluids and to protect the operating elements from any environmental contaminants.

The extended nip press 10 includes a rotating cylindrical backing roll 14 having an axis of rotation 18. The backing roll 14 is mounted on a frame 19 for rotation in the direction indicated by arrow 20. The backing roll 14 is driven by a drive mechanism (not shown).

The extended nip press 10 also includes a press shoe 22 having a concave upper surface 26. The surface 26 is complementary to the surface of the backing roll 14 and faces the backing roll 14. Grooves 30a, 30b and 30c are defined in the lower surface of the press shoe 22. The grooves 30a, 30b and 30c are spaced apart in the machine direction and are parallel to each other and to the axis 18. The grooves 30a, 30b and 30c extend in the cross-machine direction. In the

illustrated construction, the grooves 30b and 30c are defined by flexible locators 31b and 31c fixed to the underside of the shoe 22. Pivot rods 32a, 32b and 32c are positioned in respective grooves 30a, 30b and 30c.

The locators 31b and 31c allow relative movement in the machine direction between the pivot rods 32b and 32c and the shoe 22. This is explained more fully below.

The grooves 30a, 30b and 30c and corresponding pivot rods 32a, 32b and 32c provide respective pivot lines 33a, 33b and 33c for the press shoe 22. In the illustrated construction, the central pivot line 33a is in a generally vertical plane including the axis 18 of the backing roll 14.

The press shoe 22 is made from a suitable material such as mild steel having a stiffness value (or"I" value) such that small deflections of the press shoe 22 are possible over its length. In the preferred embodiment, the press shoe 22 has a length'of approximately 20 inches in the machine direction, and the press shoe 22 can be deflected up to 1 mm. In other constructions, the length of the press shoe 22 is preferably between 10 and 30 inches, although it can be greater or less. The preferable range of stiffness values for the press shoe 22 is from 5X106 to 107 mm4/meter width, although it can be greater or less.

The flexing of the press shoe 22 allows the profile of the pressure applied to the web W to be varied. This is discussed below in greater detail.

The press shoe 22 is supported by a pressure applying apparatus for selectively forcing the press shoe 22 towards the backing roll 14. The pressure applying apparatus includes pressure applying devices or extendable assemblies 34a, 34b and 34c engaging respective pivot rods 32a, 32b and 32c. The extendable assemblies 34a, 34b and 34c are spaced apart in the machine direction. The extendable assemblies 34a, 34b and 34c are parallel and exert parallel forces. In

other embodiments, the extendable assemblies 34 may be non-parallel.

The extendable assemblies 34a, 34b and 34c are preferably hydraulic. Each extendable assembly 34 is a piston and cylinder assembly including a piston rod 38 and a cylinder 42. The cylinders 42 are supported on the frame 19, and the extendable assemblies 34 extend between the frame 19 and the press shoe 22. Each piston rod 38 engages the respective pivot rod 32 at a point on the corresponding pivot line 33.

The pressure applying apparatus also includes a control system 50 for controlling the supply of hydraulic fluid to each extendable assembly 34. The control system 50 includes valves 52a, 52b and 52c for independently controlling the supply of hydraulic fluid to extendable assemblies 34a, 34b and 34c, respectively. The extendable assemblies 34a, 34b and 34c are independently actuated so that the pressure applied to the press shoe 22 is varied dependent upon the amount of pressure applied by each of the extendable assemblies 34a, 34b and 34c and to the respective pivot rods 32a, 32b and 32c.

The extended nip press 10 also includes a felt 54 which is positioned on one side of the paper web W between the web W and the surface of the backing roll 14. A second felt (not shown) may be provided on the other side of the web W. The extended nip press 10 also includes a rotating belt 58 positioned between the surface 26 of the press shoe 22 and either the second felt, if provided, or the web W. A nozzle (not shown) is positioned at the upstream end of the press shoe 22 and sprays lubricant between the rotating belt 58 and the surface 26 of the press shoe 22.

In operation, the web W, the felt 54, and the rotating belt 58 travel at a machine speed between the backing roll 14 and the surface 26 of the press shoe 22. The press shoe 22 is forced towards the backing roll 14 by the extendable assemblies 34a, 34b and 34c

to apply a nip load pressure to the web W. The pressure zone or extended nip P is created by the pressure of the press shoe 22 and the backing roll 14.

The optimal pressure profile of the pressure zone P is shown in Fig. 2. By independently actuating the extendable assemblies 34 and by flexing the press shoe 22, the pressure profile can be adjusted so that the profile is substantially constant over a substantial portion of the length of the press shoe 22. In the preferred embodiment, the pressure profile is substantially constant along at least one-third of the length of the press shoe 22 at a pressure of approximately 3,000 kPa. It should be understood that in other embodiments of the invention the maximum pressure and the pressure profile can vary greatly depending on various factors.

In other embodiments, the pressure applying apparatus can include only two or more than three extendable assemblies 34 so that the press shoe 22 can be loaded at only two or more than three points.

As mentioned above, the flexible locators 31b and 31c allow relative movement between the pivot rods 32b and 32c and the shoe 22. Such relative movement can occur as a result of flexing of the shoe 22, thermal expansion of the shoe 22, or, in embodiments in which the assemblies 34 are not parallel, the angle of the assemblies 34.

An extended nip press 110 that is a second embodiment of the invention is illustrated in Fig. 3.

Except as noted below, the extended nip press 110 is substantially identical to the extended nip press 10 illustrated in Fig. 1, and common elements have been given the same reference numerals.

The extended nip press 110 includes a press shoe 122. The press shoe 122, like the press shoe 22, is flexible and is preferably 20 inches in length. The pressure applying apparatus includes pressure applying devices or extendable assemblies 134a, 134b and 134c

engaging respective pivot rods 32a, 32b and 32c. The extendable assemblies 134a, 134b and 134c are non- parallel and each exerts a force in a respective plane including the axis 18 of the backing roll 14, such that the force is perpendicular to the surface of the backing roll 14. In other words, the assemblies 134a, 134b and 134c extend radially of the backing roll 14.

An extended nip press 210 that is a third embodiment of the invention is illustrated in Fig. 4.

Except as noted below, the extended nip press 210 is substantially identical to the extended nip presses 10 and 110 illustrated in Figs. 1 and 3, and common elements have been given the same reference numerals.

The extended nip press 210 includes a press shoe 222. The press shoe 222, like the press shoe 22, is flexible and preferably 20 inches in length. Grooves 230a, 230b, 230c and 230d are defined in the lower surface of the press shoe 222. The grooves 230a, 230b, 230c and 230d are spaced apart in the machine direction, are parallel to each other and to the axis 18, and extend in the cross-machine direction. Pivot rods 232a, 232b, 232c and 232d are positioned in respective grooves 230a, 230b, 230c and 230d.

The pressure applying apparatus includes pressure applying devices or extendable assemblies 234a, 234b, 234c and 234d engaging respective pivot rods 232a, 232b, 232c and 232d. The extendable assemblies 234a, 234b, 234c and 234d are non-parallel and each exerts a force in a respective plane including the axis 18 of the backing roll 14.

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