Extended nip press

Abstract

 It includes an extended press nip between a rotatable roll shell (10) and a shoe (11) having a concave surface (12) facing the nip with a piston (16) and cylinder (17) support for the shoe and a stationary shaft (26) extending through the roll shell (10) and a piston (32) and cylinder (33) support opposite the nip between the roll shell (10) and shaft (26) with the shoes (11, 29) being essentially the same area and providing opposed equal and opposite forces and the ends of the shafts being supported on a universal bearing (27, 28) so as to permit bending of the shaft (26) with the shell (10) being driven by a gear (38) on the shell and drive gears (39, 40) laterally of the nip and spaced diametrically opposite to each other.

Description

[0001] The present invention relates to improvements in press mechanisms for dewatering fibrous webs, and more particularly to an extended nip press with an improved unique construction for arrangement and support of the elements that allows for a straight nip and improved support for the mechanisms which apply forces to the nip for dewatering the traveling web.

[0002] Developments in the field of papermaking machines recently have included a breakthrough in the field of presses which has resulted in a press arrangement which is capable of removing greater amounts of water from a traveling paper web. This removal of water has accomplished a very marked and important saving in thermal energy in that less water has to be removed in the dryer section of the paper machine, thus saving the energy needed to provide steam to the dryer drums. This innovation is generally called an extended nip press wherein the web passes through a nip which maintains the web under pressure for a longer period of time than the conventional press which merely passes the web through the nip between two opposed rolls. A basic concept which is employed in commercial extended nip presses is shown in US Patent 3,783,097, Justus, wherein a web is supported on a support roll and an extended nip press is provided by a slipper bearing shoe which is concave to face the nip and is provided with lubricating fluid and the leading edge of the shoe. An endless belt passes through the nip, along with the felt adjacent the web, to receive water expressed from the web. By the web being subjected to a pressing pressure over a substantial duration of travel through the extended nip, more water is expressed from the web, less rewetting occurs, all resulting in a drier web traveling to the dryer section of the paper machine.

[0003] The increased efficiency and effectiveness of water removal from the web is accompanied by uniformity of dewatering of the web and to this end, it is expedient to insure that the web is pressed uniformly along the length of the nip which in modern paper machines can be on the order of 7,3 - 12,2 m.

[0004] It is accordingly an object of the present invention to provide an improved extended nip press which employs the principle of fluid or hydraulic pressure to press water from the web over a relatively extended length of travel through a press nip wherein an improved force arrangement is utilized that insures improved uniformity of pressure to the web and consequently an improved more uniform paper sheet.

[0005] A further object of the invention is to provide an improved extended nip press assembly which is capable of continued operation without requiring attention for repair or shutdown, and which is simplified in construction to reduce the cost of parts and insure continued operation at a minimal cost to the paper mill. An overall objective is to provide an improved extended nip press which embodies advantages and features which constitute improvements over presses heretofore available.

[0006] Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings, in which:

Figure 1 is a front elevational view showing an extended nip press embodying the principles and features of the present invention;

Figure 2 is an elevational view taken generally along line II-II of Figure 1;

Figure 3 is a horizontal sectional view taken substantially along line III-III of Figure 2; and

Figure 4 is a vertical sectional view taken substantially along line IV-IV of Figure 3.

[0007] The drawings illustrate an extended nip press with a continual traveling fibrous web W passing through an extended nip N. The nip is formed between a rotatable roll shell 10 and a shoe 11 which has a concave surface 12 facing the nip and a relieved leading edge 13. A lubricant is provided at the lead end of the shoe 11 at the leading edge 13 by a lubricant supply nozzle 14.

[0008] An endless belt B is trained through the nip and the web W passes through the nip with means for receiving the water expressed from the web, such as a pair of felts Fl and F2.

[0009] The web is pressed throughout its travel between the concave surface 12 of the shoe and the rotating roll shell 10. The shoe functions as a slipper bearing with a hydraulic wedge building up along the inner surface of the shoe between the belt and the shoe. The shoe is pivotally supported about an axis parallel to the nip by being supported on a roll pin 15. The roll pin is carried on the top of a piston 16 mounted in a cylinder 17 and a pressurized fluid such as hydraulic liquid is supplied to the chamber 18 beneath the piston. The assembly of the shoe 11, roll pin 15 and piston 16 are sufficiently flexible to allow a limited bending without changing the nip pressure along the nip, but in accordance with the present invention, the roll shell and shoe are supported so as to maintain a straight nip and thereby avoid any possibility of inducing unequal forces along the nip due to bending of the roll shell 10 or the shoe 11.

[0010] The cylinder is supported on a beam 19 which is supported on its ends from an upper frame 24. For supporting the beam, pivotal links 20 and 21 depend downwardly and are connected to the frame such as by pivot pins 21a and connected to the beam such as by pivot pins 21b, Figure 1. These links 20 and 21 at the front end of the machine and similar links 23 at the rear end of the machine provide a support for the beam, but also interconnect the beam with a stationary shaft 26 passing through the center of the roll shell. As will become clear, the stationary shaft 26 provides support for the roll shell and equal and opposite forces are applied at the location of the nip so as to maintain a straight nip.

[0011] Supported on the upper frame 24 are end plates 25, Figures 1 and 3, which support a universal bearing support for the stationary shaft 26 with the bearing support including a first part 27 on the end of the shaft and a second mating part 28 carried on the plate 25. This universal bearing with its curved mating surfaces permits bending of the beam due to the reaction forces created when the roll shell is supported opposite the nip.

[0012] For supporting the roll shell opposite the nip, a sliding shoe 29 is positioned within the inner smooth surface of the roll shell, and the shoe 29 is positioned equal and opposite the shoe 11 and preferably has a sliding surface area 29a which slides against the inner surface lOa of the roll shell, which is of the same area as the supporting surface 12 of the shoe 11. The shoe 29 has a relieved leading edge 30 and lubricant within the roll shell maintains a hydraulic dynamic film between the shoe 29 and the inner surface lOa of the roll shell. The shoe 29 is pivotally supported about an axis parallel to the nip on a roll pin 31 which is carried on a piston 32 mounted in a cylinder 33 in the shaft 26. Pressurized fluid in a chamber 34 beneath the piston supports the piston, and the combined roll shell 10, shoe 29, and piston 32 have sufficient flexibility to allow for a slight bending without inducing unequal forces in the nip, but with the arrangement illustrated and described, the.nip can remain straight so that no bending is necessary. In a preferred form, the piston 32 for the shoe 29 is the same size as the piston 16 for the shoe 11, so that when the chambers beneath the pistons are pressurized to the same pressure, the forces in the nip will be equal and opposite. For this purpose, a common source of fluid pressure 37 is connected through lines 35 and 36 to the chambers 34 and 18. While a preferred arrangement is shown, it will be appreciated that in some instances, it may be desirable to have the shoe 29 in the roll shell either larger or smaller than the shoe 11 opposite the nip. In any event, in accordance with the principles of the invention, the shoe 29 applies a force equal and opposite to the force applied by the shoe 11. If a smaller support piston 32 is used for the shoe within the roll, then increased hydraulic pressure in the chamber 34 will accomplish the same equal and opposite force.

[0013] To allow for bending of the shaft due to application of force to the shoe 29, the shaft is supported on the universal bearing 27, 28, and to avoid complications in the drive, a drive is provided which is positioned laterally of the nip. That is, the drive is preferably approximately 90° from the nip, and as illustrated, a dual drive is arranged with a ring gear 38 being attached to the roll shell. The rinq qear is driven by pinions 39 and 40 driven bv shafts 41 and 42, Figures 1 and 3.

[0014] The drive shafts and pinions are supported in suitable bearings in the plate assembly 25 which is supported from the frame 24 and from downwardly extending brackets 22 and 23 on which the links such as 20, 21 and 23 are suspended.

[0015] Thus, it will be seen that we have provided an improved extended nip press assembly which meets the objectives and advantages above set forth and provides a more simplified mechanism capable of continued pressing operation through an extended nip which applies a uniform extended pressure for improved dewatering of a web.

Claims

1. Press mechanism for dewatering a traveling fibrous web,
characterised by an extended press nip for receiving an endless web (W) and being defined between a rotatable support roll shell (10) and a shoe (11) having a concave surface (12) facing the nip,
a pivoted support (15) for said shoe (11) having an axis parallel to the nip, an endless belt (B) trained through the nip to slide over the shoe (11) to carry a web (W) through the nip with water receiving means (F1,F2) passing through the nip to receive water expressed from the web, means (14) to deliver lubricant between said belt (B) and shoe (11), a pressure fluid support (16,17,18) for said shoe (11) providing pressure in the nip,
and a pressure fluid support (26,32,33,34) within the roll shell (10) opposite the nip providing a backing force within the shell opposite the force of the shoe (11).

2. Press mechanism as claimed in claim 1, characterised in that
said shoe (11) and said roll shell (10) are bendable along their axial length and said pressure fluid supports (16,17,18,26,32,33, 34) apply uniform force along said shoe and along said roll for maintining uniform nip pressure along the nip.

3. Press mechanism as claimed in claim 1 or 2, characterised in that the fluid support for said roll shell (10) includes a shaft (26) extending through the shell (10) with an expansible fluid support (32,33,34) between the shaft and shoe,
and a universal bearing (26,28) at each end of the shaft (26) accomodating bending of the shaft.

4. Press mechanism as claimed in any one of the claims 1 to 3,
characterised in that the forces applied by said fluid pressure supports (16,17,18,26,32,33,34) for the shoe (11) and the roll shell (10) are equal and opposite.

5. Press mechanism as claimed in claim 4, characterised in that
said pressure fluid supports each include a piston (16,32) and cylinder (17,33) with the fluid delivered to the cylinder for each support originating from the same source (37) and the pressures being substantially equal.

6. Press mechanism as claimed in any one of the claims 1 to 5,
characterised in that
said pressure fluid support (26,32,33,34) within the roll shell (10) includes a sliding second shoe (29) opposite the first shoe (11) with means for supplying lubricating fluid between the roll shell (10) and second shoe (29) and wherein said shoes are of substantially equal length in the direction of roll rotation.

7. Press mechanism as claimed in any one of the claims 1 to 6,
characterised in that
the pressure fluid support (26,32,33,34) within the roll shell (10) includes an axial shaft (26) extending through the roll shell and means (19 to 28) are provided mechanically interconnecting the ends of the shaft (26) and the pressure fluid support for said shoe (11).

8. Press mechanism as claimed in claim 7,
characterised in that
said means (19 to 28) includes an overhead frame (24), and hanger means (20 to 23) supported from said frame (24) connected to the ends of said shaft (26) and connected to support said pressure fluid support (16,17,18) for said shoe (11).

9. Press mechanism as claimed in any one of the claimes 1 to 8,
characterised by
a drive (38 to 42) for rotating the roll shell (10) comprising a driven gear (38) concentric with the roll shell (10) and a drive gear (39,40) positioned laterally of the nip to accommodate bending of the shell.

10. Press mechanism as claimed in claim 9, including a second drive gear (39,40) lateral of the nip and diametrically opposite the first drive gear (39,40).

11. Press mechanism for dewatering a traveling fibrous web, characterised by an extended press nip for receiving an endless web and being defined between a rotatable support roll shell (10) and an elongate fluid pressure supported press means (11,15,16,17,18) facing the nip;

a shaft (26) extending through the roll shell (10) ;

a shoe (29) within the roll shell (10) opposite the nip;

a fluid pressure support (32,33,34) between the shoe (29) and shaft (26) opposite the nip;

and a drive (38 to 42) for rotating the roll shell (10) comprising a driven gear (38) concentric with the roll shell (10) and a drive gear (39,40) positioned laterally of the nip to accommodate bending of the shell.

12. Press mechanism as claimed in claim 11, including a second drive gear (39,40) lateral of the nip and diametrically opposite the first drive gear (39,40).

Drawing