This invention relates to an apparatus and method for removing fluid from a fibrous web. More particularly, this invention relates to an apparatus and method in which a formed web is subjected for an extended period to increased pressure and temperature such that fluid within the web is removed.
In the papermaking art, as much water as possible is removed from the web in the press section because mechanical removal of fluid at this stage is more economical than subsequent removal of fluid in the drying section of the papermaking machine.
Such a prior art proposal is disclosed in DE-C-575,453 which shows a press member A with a web B extending therearound. A metal band C extends around a nip roll D and sandwiches the web B between the band C and the press member A. The band C continues around the press member and extends through a further nip defined between a further nip roll D and the press member A. A second band F moves continguously with the metal band C around the press member A such that the band C is sandwiched between the web and the second band F. The web is heated by heating means I and K during passage of the web through the pressing section.
In the aforementioned DE-C-575 453 there is described an apparatus according to the preamble of claim 1. More specifically, DE-C-575 453 teaches the provision of an apparatus for removing fluid from a fibrous web, the apparatus including a press member, a blanket means cooperating with the press member for defining therebetween an elongate pressing section such that the web is pressed between the press member and the blanket means during passage through the pressing section, and heating means disposed adjacent to the press member. A method for removing fluid from a fibrous web according to the preamble of claim 18 is also known from DE-C-575 453.
Difficulties are encountered with an appartus of the type described in DE-C-575 453 with respect to the application of high pressures to the web. In particular, delamination of the formed web can occur if the web is subjected to high temperatures and high pressures within the pressing section.
EP-A-0 258 169 published on March 2, 1988 falls under Article 54(3) EPC and thus is not relevant to the question of inventive step. In the aforementioned EP-A-0 258 169, a so-called "high temperature pressing apparatus and method" is disclosed in which the paper web is subjected to a press drying operating for removing most of the water from the fibrous web. The high temperature pressing technique involves the application of high temperatures and pressure to the paper web for an extended period of time. In one embodiment of the high temperature pressing (HTP) process, the web to be dried extends through a press which includes an elongate shoe and a cooperating backing roll. A blanket extends, together with the web, through a pressing section defined between the shoe and the backing roll (or pressing member). The pressing member is inductively, or otherwise, heated such that during passage of the web through the pressing section, fluid within the web is vaporized to force fluid remaining in the liquid phase away from the web.
Because of the very high temperatures employed in the aforementioned HTP process coupled with the extremely high pressures, delamination of the formed web has been experienced. Such delamination occurs primarily as the result of the rapid evolution of vapor within the pressing section with such vapor blowing the web apart as the web exits from the pressing section.
It is a primary objective of the present invention to overcome the aforementioned problems associated with the aforementioned press drying apparatus and techniques and to provide an apparatus and method which contributes significantly to the press drying art.
To achieve this, the apparatus of the invention is characterized by the features claimed in the characterizing portion of claim 1 and the method of the invention is characterized by the features set forth in the characterizing portion of claim 18. According to the invention a pressing shoe urges the blanket means towards the press member such that when the web passes through the pressing section, fluid is removed from the web. The heating means are disposed upstream relative to the pressing section for heating the press member and structured such that when the web passes through the pressing section, the web is subjected for an extended period to increased pressure and temperature so that water vapour generated within the pressing section during passage through the pressing section forces the fluid in the liquid phase away from the web.
Advantageous embodiments of the invention are claimed in the subclaims.
In accordance with an aspect of the present invention there is provided an apparatus for removing fluid from a fibrous web in which the press member defines a pressing surface which is porous.
In a specific embodiment the present invention provides an apparatus for removing fluid from a fibrous web in which the press member includes a first and a second coaxial layer with the second coaxial layer extending around the first layer, the second layer defining a cylindrical pressing surface.
Another feature of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the second layer is sintered and has a pore size of at least 2 microns.
Another feature of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the second layer has a thickness of at least .0127 centimeters (.005 inches).
Another feature of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the sintered layer is spray-coated onto the first layer which is a backing roll of an extended nip press.
Another embodiment of the present invention provides an apparatus for removing fluid from a fibrous web in which the apparatus includes a fiber metal felt disposed between a press roll and the web such that in operation of the apparatus, the metal felt passes with the web through the press section and in which the metal felt is heated immediately prior to the passage of the felt through the pressing section.
Another feature of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which a cleaning means is provided for grassing a cleaning medium through the metal felt towards a surface of the metal felt contacting the web so that contaminants picked up by the metal felt during operation of the apparatus are ejected from the metal felt.
Another feature of the present invention is the provision of an apparatus for removing fluid from a fibrous web in which the first layer of the press member is vented.
Other features and advantages of the present invention will be apparent to those skilled in the art by consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.
In a more specific embodiment of the present invention, the pressing surface is cylindrical and the press member includes a first coaxial layer and a second coaxial layer which extends around the first layer with the second layer defining the cylindrical pressing surface.
The second layer is sintered and has a pore size of at least 2 microns and a thickness of at least .0127 cm (.005 inches). The second layer may be spray-coated onto the external surface of the first layer which may be an extended nip press backing roll.
In an alternative embodiment of the present invention, the apparatus includes a fiber metal felt which is disposed between the press member and the web such that in operation of the apparatus, the metal felt passes with the web through the press section, the metal felt being heated immediately prior to passage through the press section.
In the alternative embodiment of the present invention, the apparatus also includes cleaning means for cleaning the metal felt. The cleaning means includes means for passing a cleaning medium through the metal felt towards a surface of the metal felt contacting the web so that contaminants picked up by the metal felt during operation of the apparatus are ejected from the metal felt.
In another embodiment of the present invention, the first layer is vented such that fluid entering the porous layer passes through the second layer into the first layer.
In a further embodiment of the present invention, the hot roll includes a first, or inner, solid surface, a second, or outer, layer having a porosity of 20 microns and an intermediate third layer of 100 microns porosity disposed between the first and second layers such that the third layer assists in the ventilation of the roll.
Although the present invention has been described with a certain degree of particularity, it is to be understood by those skilled in the art that the present invention is not limited to the embodiments described in detail hereinafter.
More specifically, although the present invention provides a porous second layer for inhibiting delamination, it will be apparent to those skilled in the art that in the alternative embodiment of the present invention, the provision of the fiber metal felt may be sufficient to inhibit delamination of the formed web without the need of a porous outer layer on the press member.
Additionally, it will be appreciated by those skilled in the art that the second, or outer, layer may not necessarily be a separate layer but may be etched onto the first layer or otherwise provided by mechanically working the surface of the first layer.
Similar reference characters refer to similar parts throughout the various embodiments of the present invention.
Figure 1 is a side-elevational view of an apparatus generally designated 10 for removing fluid from a fibrous web W. The apparatus 10 includes a press member 12 and a blanket means generally designated 14 which cooperates with the press member 12 for defining therebetween an elongate pressing section generally designed 16 such that the web W is pressed between the press member 12 and the blanket means 14 during passage through the pressing section 16. An elongate means 18 such as an extended nip press shoe, urges the blanket means 14 towards the press member 12 as indicated by the arrow 20 such that when the web W passes through the pressing section 16 fluid is removed from the web W. Heating means generally designated 22 is disposed adjacent to the press member 12 for transferring heat to the web W such that when the web W passes through the press section 16, the web W is subjected for an extended period to increased pressure and temperature so that water vapor generated within the pressing section 16 during passage through the pressing section 16 forces the fluid in the liquid phase away from the web W. The press member 12 defines a pressing surface 24 which is porous for inhibiting delamination of the web W. More specifically, as shown in figure 1, the pressing surface is cylindrical.
Figure 2 is a similar view to that shown in figure 1 but shows a second embodiment of the present invention in which an apparatus 10A for removing fluid from a fibrous web WA includes a press member 12A in which the press member 12A has a first coaxial layer 26 and a second coaxial layer 28 extending around the first layer 26. The second layer 28 defines a cylindrical pressing surface 24A. The second layer 28, as shown in figure 2, may be a sintered layer having a pore size of at least 2 microns. The second layer 28 has a thickness of at least .0127 cm (.005 inches). Such second layer 28 may be applied to the first layer 26 by a spray-coating technique. The second layer 28 in the aforementioned spray-coating technique, is spray-coated onto the external surface 30 of the first layer 26, the first layer 26 being an extended nip press backing roll.
Preferably, the second layer 28 is applied to the first layer 26 by the aforementioned spray-coating technique in which the specification and performance of the resultant second layer 28 is equivalent to the specification and performance of a plate having a pore size of at least 2 microns and a thickness of at least .0127 cm (.005 inches).
Figure 3 is a side-elevational view of a third embodiment of the present invention and shows an apparatus 10B for removing fluid from a fibrous web WB. The apparatus 10B includes a fiber metal felt 32 which is disposed between a press member 12B and the web WB such that in operation of the apparatus 10B, the metal felt 32 passes with the web WB through the press section 16B. The metal felt 32 is heated as indicated by the heater 22B immediately prior to passage of the metal felt 32 through the press section 16B. The porosity, void volume and heat transfer specification of the metal felt 32 is equivalent to the specification and performance of a sintered plate having a pore size of at least 2 microns and a thickness of at least .0127 cm (.005 inches).
Figure 3 also shows cleaning means generally designated 34 disposed downstream relative to the press member 12B for cleaning the metal felt 32. The cleaning means 34 includes means 36 such as a pump for passing a cleaning medium through the metal felt 32 towards a surface 24B of the metal felt 32 contacting the web WB so that contaminants picked up by the metal felt 32 during operation of the apparatus 10B are ejected from the metal felt 32.
Figure 4 is a side-elevational view of a fourth embodiment of the present invention and shows an apparatus 10C in which the first layer 26C of the press member 12C is vented such that fluid entering the pressing surface 24C passes through the second layer 28C into the first layer 26C. As shown in figures 4 and 5, the first layer 26C is grooved as shown particularly in figure 5 which is a section on the line 5-5 of figure 4. Figure 5 shows a plurality of axially-spaced grooves 38, 39 and 40 defined by the external surface 30C of the first layer 26C.
Figure 6 is a similar view to that shown in figures 4 and 5 but shows a fifth embodiment of the present invention in which the first layer 26D is blind-drilled as indicated by the holes 41, 42 and 43.
In a further embodiment of the present invention as shown in figure 7, the heated roll, or press member, 12E includes a first layer 26E which is solid and an outer, or second, porous layer 28E having a pore size within the range 5-50 microns and preferably of 20 microns. An intermediate third layer 44 is disposed between layers 26E and 28E, the third layer 44 having a pore size within the range 50-100 microns and preferably of 100 microns such that ventilation of the second layer and the web WE is assisted.
In operation of the apparatus 10, as shown in figure 1, the web W is conducted through the press section 16 and heat is applied, for example by induction heating, through th heater 22 such that the press member 12 is heated. Pressure is applied as indicated by the arrow 20 such that the blanket 14 is pressed towards the pressing member 12 thereby exerting pressure on the web W as the web W passes through the pressing section 16. The combination of high pressure and high temperature for an extended period results in fluid from within the fibrous web W being vaporized such that this vapor forces fluid in the liquid phase away from the web W. Although there exists a tendency for the aforementioned force of such pressurized vapor to cause delamination in the pressed web, the present invention overcomes this problem by the provision of a porous layer 24 on the outer surface of the press member 12 such that the vapor pressure is relieved and the amount of heat transferred through the press member 12 to the web W is reduced thereby inhibiting delamination of the web.
The operation of the embodiment shown in figure 2 is similar to that shown in figure 1, however, figure 2 shows a simple means of applying a porous layer 28 to the external surface of a conventional backing roll of an extended nip press.
In operation of the embodiment shown in figure 3, a fiber metal felt 32 is used to convey thermal energy from the heater 22B towards the pressing section 16B such that the web WB is subjected to heat and pressure during passage through the pressing section 16B. The advantage of the embodiment shown in figure 3 is that the pressing surface which effectively is the surface 24B of the metal felt 32 may be cleaned by means of the cleaning means 34. Also, the metal felt can be replaced more easily than a porous surface roll. Another advantage derived from use of a metal felt is that the press member or roll will run significantly cooler thereby alleviation problems associated with heating a controlled crown type roll.
The operation of the embodiment shown in figures 4, 5, 6 and 7 is similar to that of the embodiment shown in figures 1 and 2, however, the provision of a grooved (or blind-drilled) first layer permits further reduction in the force applied by the vapor in removing fluid in the liquid phase away from the web in the case of the embodiments of figures 4-6. Similarly, with the embodiments of figure 7, the third layer 44 assists in the ventilation of the outer layer 28 and the web WE. Although this may reduce the overall amount of fluid removed from the web, such arrangements avoid the problem of delamination and thus provides a very practical and economic means for press drying a fibrous web.