Fibrous Web Press Nip Structure Including Nonporous Belts Backed By Pistons Supported With Fluid Pressure

Abstract

An extended nip press device for removing fluids from a fibrous web and including a pair of endless looped non-porous belts positioned to define a nip of at least 6 inches in length. A porous belt or felt is positioned to pass through the nip and is used as a web carrying device. The pressure exerted in the nip is caused by a piston positioned inside the loop of each of the nonporous belts having a force transmitting surface contacting the nonporous belts substantially across the width and length of the nip. Lubrication lines are provided for each piston so as to lubricate the surface contacting the nonporous belt. Deflection control structure defining a fluid reservoir and positioned to accept one of the pistons in each reservoir is further provided, and includes feed lines for supplying fluid to the reservoir in an amount sufficient to support the piston in the reservoir. Force supplied by the piston on the nonporous belt is balanced by the deflection control structure so as to prevent deflection of the piston.

Description

BACKGROUND OF THE DISCLOSURE

A factor which is believed to be limiting the amount of water removal from the processing and manufacturing of fibrous webs is the flow property of the fluid in the fibrous web. In the manufacture of paper, one of the important economic considerations justifying a satisfactory return on investment is the operation of the paper machine at the fastest speed possible consistent with good paper formation. At the present time, in a normal paper making operation in which the paper is formed on a wire, pressed, dried and thereafter processed, the press section is seen to represent a speed limiting portion of the process. If it is possible to increase the amount of fluid removed from the fibrous web during the press section, increased speeds are possible with existing equipment, thereby increasing the production per hour and the return on investment.

It has been known for quite some time that a long term static application of mechanical pressure to a web can reduce the amount of moisture in that web to below 40 percent. However, under the dynamic short term mechanical pressing in a paper machine press section, an extensive amount of effort is necessary to retain moistures at or below 60 percent. It has been found that a hydraulic pressure or wedge effect develops during the passage of the wet web through the wet press nip. The hydraulic pressure that develops substracts from the applied load and reduces the mechanical compacting pressure. The result is this above noticed loss in dryness. Naturally, as machine speeds increase, the compacting rates are higher and result in higher hydraulic pressures within the mat. It is a generally accepted conclusion that these hydraulic pressures are the primary factor in press performance on those machines operating at the highest speeds. Significant improvement in high speed press performance could be achieved if the time of application of the pressure could be significantly extended. By allowing more time for the flow of the fluid within the web, the hydraulic pressure would dissipate and more efficient use of the compacting pressure would be achieved.

Many devices have been composed to increase the efficiency of the press section. As paper machine speeds increased, at one point in the history of the paper making process, the use of grooved rolls provided areas for the water to be expressed into, and resulted in an improvement in the operating speed of press sections. However, as the desirability of ever increasing the speed of the machine becomes more important to the paper maker, even this improvement becomes limited, due to the hydraulic wedge or resistance to flow of the water being pressed.

The obvious solution to this problem is to extend the period of time that the web is subjected to pressing forces. This can be done by increasing the number of press nips through which the web must pass, since each succeeding press nip treats a web with less and less water initially present. However, due to the significant capital investment in each press section, a limit is soon reached whereby the capital investment for additional press nips is a greater cost than the benefit gained by operating at faster speeds. To counteract this, it has been proposed to extend the amount of time which the web spends in each press nip, thereby requiring fewer nips and decreasing the capital investment. However, short of slowing down the machine speed to increase residence time in conventional nips, no satisfactory device has yet been proposed which would increase the residence time of the web without decreasing the speed.

A number of methods have been proposed for extending the length of the nip in the press section, such as by the use of inflatable bags which would deform to the contour of a hard roll in nip defining relationship therewith, but these proposed devices have been unable to apply significant compaction pressures to the web. The result is that although a longer nip is experienced, a lower pressure is used and little if any benefit is achieved.

OBJECTS OF THE INVENTION

Accordingly, it is an object of this invention to provide a device which is capable of operating at high pressure while simultaneously extending the nip length by a significant amount.

Another object of this invention is to provide an extending nip device which is capable of uniform compacting pressure and will expell fluids from the web being treated without a major capital investment.

Yet another object of this invention is to provide a method for compacting webs to remove fluids therefrom in an extended nip while simultaneously extending the nip pressure across the entire width of the web in a uniform manner.

Other objects will appear hereinafter.

THE INVENTION

It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Basically, it has been discovered that an extended nip press device can be manufactured without a substantial capital investment which will permit increase of the length of the nip to that which is necessary to dewater at the high speeds which represent economical paper making. The device of the present invention includes a pair of endless looped nonporous belts positioned in a nip defining relationship with each other so that the nip is at least 6 inches in length. Depending upon the optimum speed at which the paper machine is to be operated, these belts are positioned to define a nip which may be 10 or 12 inches or even more in length. By designing the nip length for the maximum rate at which the machine will operate, it is possible to achieve maximum efficiency of water removal at all speeds.

As a means for carrying the web to be dewatered through the nip, and as a means for carrying the water thus expressed from the web away from the press device, at least one porous web carrying belt is positioned to pass through the nip. Normally, a felt will carry the web from the forming zone through the extended nip and on to the dryer section. Conventional methods for removing water from the felt or felts at a point remote from the press can be employed to insure a consistent reservoir for the fluid being expressed at the press nip.

Positioned inside the loop of each of the nonporous belts are piston means having a force transmitting surface contacting the nonporous belt at a point substantially across the width and length of the nip. It is these piston means which transmit the force to the nonporous belts to give the nip pressure. Force transmitting means are provided which are capable of forcing the piston against the nonporous belt through the force transmitting surface.

Since the piston means is stationary and the nonporous belts are moving, lubrication means must be provided for each piston means to eliminate buildup of heat and friction as the force transmitting surface is urged against the nonporous belt. Thus lubrication means may include an external source of water or other lubricating fluid which would be transferred to the nonporous belt at a point just prior to contact of the belt with the force transmitting surface, so that an amount of fluid sufficient to form a fluid layer between the surface and the belt would be provided. A preferred means for lubricating the force transmitting surface as it contacts the moving nonporous belt will be described hereinafter.

Due to the substantial width of paper machines and the extensive forces ranging up to as much as 1,000 lbs. per sq. inch in the nip, it is necessary to provide a deflection control means for each of the piston means. These deflection control means include means defining a fluid reservoir so that the piston means is accepted or positioned within the reservoir. Means are provided to supply fluid to the reservoir in an amount sufficient to support the piston in the reservoir. Therefore, force supplied by the piston on the nonporous belt is balanced by a uniform force throughout the fluid. Since the deflection control means defining the reservoir is fixed, all of the deflection caused by the force into the nip is taken up by the deflection control means. The piston means, since it is essentially floating in a fluid, does not appreciably deflect and uniform pressure across the width of the machine is exerted on the web. The pressure which the piston exerts on the nonporous belt to define the nip pressure may be obtained by a means for transmitting fluid under pressure to the reservoir, whereby the fluid pressure on the piston forces the force transmitting surface of the piston against the nonporous belt. As mentioned above, the piston receives a uniform fluid pressure across its entire width and length to transmit uniform pressure to the nip, while the deflection caused by such tremendous total load is taken up by the deflection control means without deflecting the piston means.

For a more complete understanding of the present invention, reference is hereby made to the drawings, in which:

FIG. 1 represents a schematic view showing one embodiment of the present invention; and

FIG. 2 represents a detailed view of a preferred part of the present invention.

As shown in FIG. 1, a web 12 is carried by a porous belt or felt 10 through a nip shown generally in FIG. 1. A pair of looped nonporous belts 14 and 22 are positioned about support rolls 15 and 23 respectively to define a nip such that the nip length is at least 6 inches. Although the distance between the rolls 15 is substantially greater than the above mentioned 6 inches, the portion of the nip which passes over the forced transmitting surface hereinafter described is considered to be that portion of the nip in which nip pressure is applied. Accordingly, for the purposes of this disclosure, the nip length and width is considered to be defined by the force transmitting surface of the piston means which is in contact with the nonporous belts.

Within the loop of the nonporous belt 14, is a force transmitting means 16. Fluid pressure is supplied to the force transmitting means 16 through line 18 from pump 19 and supply reservoir (not shown) leading from line 20. The force transmitting means is supported on a beam 17. Likewise, within the loop of nonporous belt 22 is a force transmitting means 24 which receives a fluid under pressure through line 26, pump 27 and line 28 to cause nip pressure in the nip. This force transmitting means 24 is supported by frame 25.

As shown in FIG. 2, the force transmitting means is generally shown by the numeral 24 and mounted on beam 25. A force applying means in the form of a piston 33 is positioned to contact the belt 22 substantially across the width and length of the nip. This piston 33 contacts the moving belt 22 at surfaces 35. As will be apparent from the drawings and description herein, the surfaces 35 which seal the edges of a chamber 34a in the piston include a surface at the oncoming or leading edge of the chamber 34a, a surface shown at 35a at the trailing edge of the chamber, and surfaces at each side of the chamber with all surfaces slidably engaging the belt. These surfaces surround the opening of the chamber 34a which is exposed to the belt so that the pressure within the chamber is transmitted through the flexible belt to the web carried between the belts. As is indicated in FIG. 1, the force transmitting means 16 has the same construction as the force transmitting means 24 so that the chamber and its opening of the force transmitting means 16 are positioned exactly opposite the chamber 34a, and the sliding surfaces for the opposing chamber are directly opposite the sliding surfaces 35. Thus, fluid forces in said chambers will oppose each other and apply opposite balanced pressures against the web within the nip. The piston 33 is contained in a reservoir 31 which is defined by a deflection control means 30. Fluid through line 26 is supplied to the reservoir 31 in an amount sufficient to support the piston 33. As shown in FIG. 2, fluid under pressure through line 26 enters the reservoir 31 and then passes through a conduit means which may be in the form of a line or holes 34 in the piston 33. Seal means 32 insure no leakage of the fluid from the reservoir 31. As the fluid passes through holes 34 in piston 33, under substantial pressure, the fluid is forced against the nonporous looped belt 22 to create nip pressure. Optionally, a separate source of fluid could be provided for passage through line 34 to contact the belt 22 and create nip pressure.

Sufficient fluid is passed through the holes 34 in piston 33 to cause an escape of fluid along both surfaces 35 and 35A. If, for purposes of example, the belt 22 is seen to be moving from left to right as seen in the drawing, fluid will be carried by the belt 22 across surface 35A to lubricate the surface. However, since the fluid being passed through holes 34 of piston 33 is of sufficient pressure to create a significant nip pressure, this fluid will additionally be forced contrary to the direction of movement of belt 22 to thereby lubricate surface 35. If, as it may be occasionally necessary to do, additional lubrication of surface 35 is necessary, additional fluid can be added to the belt 22 at a point just prior to contact of the belt 22 with the force transmitting surface 35 through line 38

It will thus be seen that by a suitable pressure of fluid transmitted through 26 to reservoir 31, the piston 33 will be forced against the belt to create the desired nip pressure. Lubrication of the surfaces 35 and 35A which contact the moving looped nonporous belt 22 will be accomplished by escape of the fluid from the holes 34 of piston 33. Furthermore, since the pressure on piston 33 is uniform across the entire length and width thereof, the piston will be free from deflection. The force necessary to achieve a proper pressure in the nip will be balanced and accepted by the reservoir defining deflection control means 30. Deflection of the reservoir defining deflection control means 30, and possible deflection of beam 25, will not affect the piston 33. Therefore, all of the deflection caused by the forces necessary to achieve a suitable nip pressure will be balanced by the deflection control means without deflecting the piston means.

Thus, it will be seen that the web passes between first and second web pressing means, one on each surface with the pressing means pressing the web therebetween. In a preferred embodiment which is illustrated, each pressing means is shown as being of the same construction, and each is shown as including a belt and a confined fluid backing chamber, as described above.

By installation of a device according to the present invention in a paper making process, it is now possible for the capital investment of only one press nip to achieve as much dewatering at the press section as is possible. Residence time of the web being pressed, even at extremely high speeds, will be sufficient to overcome the hydraulic wedge effect and dewater the web sufficiently. The web then passed to the dryer section will contain no more water than was previously contained during slower speed operations. No deflection will occur in the nip, thereby providing uniform pressing across the entire width of the paper machine.

Claims

Having thus described the invention, what is claimed is:

1. An extended nip press for removing water from a traveling fibrous web comprising:

first and second looped nonporous flexible belts positioned in a nip defining relationship with each other;

guide means within the belts guiding the travel of the belts to form said nip;

a first stationary force applying means defining a pressure chamber

with an opening exposed to the inner surface of the first belt at said nip,

said force applying means having sealing surfaces surrounding said opening at the leading and trailing edges of the opening and at each side thereof sealingly engaging said belt,

a second stationary force applying means defining a pressure chamber with an opening exposed to the inner surface of the second belt at said nip,

said second force applying means having sealing surfaces surrounding said opening at the leading and trailing edges thereof and at each side thereof sealingly engaging said belt and positioned opposite the sealing surfaces of the first force applying means so that the fluid forces in said chambers will oppose each other and apply opposite balanced pressures along said nip,

means supporting each of said force applying means;

water receiving means for passing through the nip with the web to receive water pressed from the web;

and means for delivering pressurized fluid to each of said chambers.

2. An extended nip press for removing water from a traveling fibrous web constructed in accordance with claim 1:

wherein said means supporting each of said force applying means includes deflection control means including a fluid pressure backing chamber means for the force applying means extending laterally of the direction of belt travel across the force applying means and applying a fluid pressure backing thereto at uniform force across the force applying means so that substantial bending of the force applying means is prevented.

3. An extended nip press for removing water from a traveling fibrous web constructed in accordance with claim 2:

wherein said force applying means is in the form of a piston, and the deflection control means is in the form of a reservoir with the piston slidably mounted in the reservoir, with means to pressurize the reservoir to provide said fluid pressure backing to the piston.

4. An extended nip press for removing water from a traveling fibrous web constructed in accordance with claim 3:

wherein conduit means are provided communicating between said reservoir and said chamber for each of said first and second force applying means.

5. An extended nip press for removing water from a traveling fibrous web constructed in accordance with claim 3.

wherein said means for delivering pressurized fluid to the chambers is connected to said reservoir and said chambers are supplied by conduit means communicating between said reservoir and said chamber of each of said stationary force applying means.

6. An extended nip press for removing water from a traveling fibrous web constructed in accordance with claim 1:

and including lubricating means for the sealing surfaces of the force applying means.

7. An extended nip press for removing water from a traveling fibrous web constructed in accordance with claim 1:

wherein said water receiving means comprises a looped traveling belt passing through the nip between said belts with the web.

8. An extended nip press for removing water from a traveling fibrous web comprising:

first and second web pressing means on each side of the web forming a nip supporting and pressing water from a web carried therebetween,

at least one of said pressing means including: a looped nonporous flexible belt, guide means within the belt guiding its travel to said nip,

a stationary force applying means defining a pressure chamber with an opening exposed to the inner surface of the belt at said nip,

said force applying means having sealing surfaces surrounding said opening at the leading and trailing edges of the opening end at each side thereof sealingly engaging said belt,

means for delivering pressurized fluid to said chamber so that fluid pressure is applied at said opening to the belt to be transmitted to the web,

deflection control means including a fluid pressure backing chamber means for the force applying means extending laterally of the direction of belt travel and applying a fluid pressure backing to the force applying means at a uniform force;

and water receiving means for through the nip with the web to receive water pressed from the web.