Patent Application
20060278360
The present invention relates to devices for handling web materials that require support and control. In particular, the present invention relates to a device that supports a web on a cushion of air. Further, the present invention relates to devices capable of removing dust generated by a moving web in a web-handling process.
Various devices for forming fluid cushions or fluid bearings have been used for the contactless support of a web as the latter changes directions during its course of travel. These running webs may be required to pass through a number of different processes or directed in different directions. By way of example, webs resulting from a papermaking process may be directed through contactless supporting devices to downstream converting operations to produce absorbent paper products such as diapers, facial tissues, and the like. Such contactless support devices are described as generally partially cylindrical surfaces through which pressurized air is introduced through various slots, holes, apertures, or the like.
However, it should be realized that web materials handled under such processes are generally planar with a thickness much smaller than the dimensions of the material. Such webs are likely to include paper, cloth, plastic film, woven, non-woven, and metal films. These web materials are known to present unique process challenges. For example, it is known that typical flexible web materials are easily damaged, and can result in final products that are unacceptable.
Such thin materials that are produced into wound webs are also known to have fluctuations in the wound web tension throughout the length and width of the web. Such fluctuations can be problematic as the web is unwound and transported by processing equipment during the conversion of large rolls of web material into finished products. Such web tension fluctuations may result in wrinkled, broken webs, webs of varying widths, a loss of control of the web material during processing, and ultimately provide for a loss of quality and/or productivity.
Thus, in most applications, it is desirable, if not imperative, to keep the web material from coming into direct contact with handling surfaces. The web material may be recently imprinted, and, thereby, carrying a wet image on at least one surface. Alternatively, the web material may be delicate and have a relatively low basis weight. Yet still, the web material may be wet. Therefore, preventing contact of the web material with a control surface can be beneficial, for example, if the control surface is dirty or greasy. Additionally, mechanical flaws in the surface of conventional control systems may cut or severely scar the surface of the web material. Further, it can be difficult to provide conventional web handling equipment to be surface speed matched to the speed of the web. This can be especially true if the process requires the web material speed to be variable, or if velocity fluctuations are caused by out of round or non-uniform supply rolls.
Additionally, moving and/or tensioned web materials may have inherent properties that provide additional difficulty in handling. For example, a material may have a lateral contraction when the material is subjected to an applied elongation. Such lateral contraction in a tensioned web material is known as the “Poisson lateral contraction effect.” Also, it has been seen that the stress and/or strain characteristics of the web material may vary laterally to a considerable extent. This may cause one portion of the web substrate to be tight and another portion of the web substrate to be loose. Additionally, low basis weight materials, because of their ability to stretch, can easily become wrinkled as the unconstrained web material moves over traditional supports. This can lead to wrinkles in the finished product. Typically, wrinkles can lower the product functionality by reducing absorbency of cellulose-based web materials and detract from the appearance of the finished product if it is formed from tissue paper.
Previous air-driven web handling equipment has been provided to frictionlessly, aerodynamically, and/or hydrodynamically support a moving web material on a cushion of fluid, such as air or gas, as the moving web passes over the control surface. Such devices are described in U.S. Pat. Nos. 4,043,495; 4,197,972; 5,775,623; 6,004,432; and 6,505,792. However, such devices as described do not reduce the Poisson lateral contraction that inherently occurs in a moving and/or tensioned web material as it passes through a converting process. Additionally, it is possible for these described devices to utilize excessive air flows. Excessive air flow can cause loss of control of the web material due to excessive lift. Further, the described devices do not provide the ability to remove dust generated by the moving web material.
Therefore, a device that provides contactless support of a moving web material that is capable of reducing the Poisson lateral contraction in a moving and/or tensioned web material is required. Such a device would be capable of controlling or turning a web material without wrinkling or significant stretching. Further, it is also a benefit to be able to provide such a device with the ability to remove dust from the web material as the web material progress through a web handling or converting process.
The present invention relates to an apparatus for, reducing the Poisson lateral contraction in a tensioned web substrate. The apparatus comprises a surface having a machine direction, a cross-machine directional orthogonal to the machine direction, and a z-direction orthogonal to both the machine direction and the cross-machine direction. The apparatus is provided with a plurality of holes disposed upon the surface, each of the holes being operatively connected to a source of positive pressure. The holes provide fluid communication of the positive pressure through the surface to the web substrate passing proximate thereto. Each of the holes has a longitudinal axis associated thereto. The longitudinal axis of a first of the holes has a first inclination relative to the z-direction and the longitudinal axis of a second of the holes has a second inclination relative to the z-direction. Further, the first and second inclinations are different.
The present invention also relates to an apparatus for reducing the Poisson lateral contraction in a machine direction moving web substrate. The apparatus comprises a surface having a machine direction, a cross-machine directional orthogonal to the machine direction, and a z-direction orthogonal to both the machine direction and the cross-machine direction. A plurality of holes are disposed upon the surface and each hole is operatively connected to a source of positive pressure so that the holes provide a fluid communication of the positive pressure through the surface to the web substrate passing proximate thereto. Each of the holes has a longitudinal axis associated thereto and the longitudinal axis of a first of the holes has a first inclination relative to the z-direction and the longitudinal axis of a second of the holes has a second inclination relative to the z-direction. The longitudinal axis of a third of the holes has a third inclination relative to the z-direction. Further, the first and second inclinations are different. Additionally, the third hole is spaced from the first and second holes in the cross-machine direction and, the first and second inclinations are directed toward a first edge of the web substrate and the third inclination is directed toward a second edge of the web substrate.
The present invention further relates to an apparatus for reducing the Poisson lateral contraction in a machine direction moving web substrate. The apparatus comprises a surface having a machine direction, a cross-machine directional orthogonal to the machine direction, and a z-direction orthogonal to both the machine direction and the cross-machine direction. A plurality of holes are disposed upon the surface so that each of the holes is operatively connected to a source of positive pressure. The holes provide a fluid communication of the positive pressure through the surface to the web substrate passing proximate thereto. Each of the holes has a longitudinal axis associated thereto. The longitudinal axis of a first of the holes has a first inclination relative to the z-direction and the longitudinal axis of a second of the holes has a second inclination relative to the z-direction and the longitudinal axis of a third of the holes has a third inclination relative to the z-direction. The first and second inclinations are different. The third hole is spaced from the first and second holes in the machine direction and, the first, second, and third inclinations are directed toward a first edge of the web substrate.
As shown in
It would be apparent to one of skill in the art that web control device 10 can be provided in geometries other than a cylindrical hollow bar. By way of non-limiting example,
Returning again to
Inner portion 16 of web control device 10 can function as a central plenum that is supplied with air under pressure. Such pressurized air can be blown through holes 14 that provide fluid contact between inner portion 16 and outer portion 18 of web control device 10. Each of the plurality of holes 14 disposed in web control device 10 is provided with a longitudinal axis 20. In a preferred embodiment, the longitudinal axis 20 of each hole 14 is provided with a vector component, or inclination, relative to the z-direction of web control device 10.
As shown in the cross-section view of
In other words, as shown in
In yet still another preferred embodiment, the longitudinal axis 20 of the holes 14 disposed upon a respective side of center C of web control device 10 are provided with vector components in both the CD and z-direction so that holes 14 disposed proximate to the center C of web control device 10 have a larger z-direction component than holes 14 disposed proximate to an edge of web control device 10. This means that the longitudinal axis 20 of holes 14 disposed proximate to an edge of web control device 10 have a larger CD component than holes 14 disposed proximate to the center C of web control device 10.
Thus, as can be seen in the exemplary embodiment of web control device 10 of
By providing such a progressive angular appearance of the orientation of each longitudinal axis 20 of each hole 14 from the center C to the respective edge of web control device 10, it is believed, without desiring to be bound by theory, that the air fluidly transmitted from the inner portion 16 through holes 14 to the surface of the web material 12 passing proximate to web control device 10, provides a spreading effect on the web material 12. This spreading effect is believed to reduce the effect of Poisson lateral contraction in the CD due to a MD tension upon web material 12 because the discharge of fluid from such a progressively angled series of holes 14 can facilitate the application of a force component on the web material 12 that is directed towards the respective edge of the web material 12. In other words any effects upon web material 12 due to a Poisson lateral contraction are counteracted to some degree by a momentum transfer from the discharged fluid to the web material 12 through viscous coupling.
Without desiring to be bound by theory, it is also believed that providing progressively angled holes 14, as described supra, can minimize strain on the web material 12. In other words, by avoiding any sudden changes in CD strain of web material 12, CD tension variations within web material 12 can be minimized. By gradually increasing the vectored angle the longitudinal axis 20 of each hole 14 from the center C of web control device 10 to a respective edge of web control device 10, a smaller and more uniform viscous force is applied to the web material 12. Forces applied to a web material 12 that has CD stress and/or strain differences, CD elastic modulus changes (i.e., stress-strain variations), CD caliper differences in web material 12, lateral differential MD unit lengths, and the like, can cause localized wrinkling in the web material 12. Thus, it is believed that such a vectored angle approach as described herein can effectively remove wrinkles present upon web material 12 that are related to such lateral contraction effects.
Further, as would be known to one of skill in the art, the number of holes 14, the apparent size of the holes 14, the air pressure provided to inner portion 16 of web control device 10, and the like, can be varied according to the porosity, density, web wrap angle, nominal tension, and other physical characteristics present in the web material 12 and by the requirements of the relevant processing system. Without desiring to be bound by theory, it is believed that the web control device 10 is capable of providing support for web material 12 as well as providing control for web material 12 because web control device 10 operates as a circular air foil. One of skill in the art will be able to utilize mathematical modeling systems to show the presence of a viscous drag upon the surface of the web control device 10 for a portion of the surface. In conventional air bar/handling devices for handling a web material, as the MD speed of web material 12 increases, the amount of air proximate to the web material 12 (i.e., the boundary air) increases, resulting in a loss of control of web material 12. Since one of skill in the art will appreciate that these conventional air bar/handling devices lose control of the web material because air reflected by the web material 12 follows the Knox-Sweeny equation. In other words, a web substrate controlled by a conventional air bar/handling device will float over the device and track to the neutral axis of the CD stress/strain characteristics of the web material. Since the CD stress/strain characteristics of the web material can changes quite dramatically (±30% normally) the web material will tend to steer from one side to another of a conventional air bar/air handling device and result in a loss of control and weave of the web material, and causing Holdovers.
Contrastingly, the vectored air handling approach as described herein can reduce the volume of fluid necessary to maintain support of a web material 12 traversing proximate web control device 10 while at the same time maintain better control of a traversing web material 12. By directing and limiting the amount of reflected air evoluted from holes 14 as described herein, the web control device 10 does not fully lift the web material 12 while providing small regions of drag disposed between each hole 14. Thus, the web material 12 tends to remain ‘wetted’ to the surface of web control device 10 thereby providing web control device 10 with heretofore unrealized control of a web material 12 passing proximate web control device 10.
Returning again to
As shown in
Without desiring to be bound by theory, it is believed that providing the longitudinal axis 20 of holes 14 with a vector component in the MD can provide a MD thrust component to a web material 12 traversing proximate the outer portion 18 of web control device 10. It is believed that an MD momentum is transferred from the fluid to web material 12 though viscous coupling of the web to the air by providing holes 14 having a longitudinal axis 20 with a vector component in the MD. In a preferred embodiment, the thrust component is applied to web material 12 in the direction of web material 12 motion to overcome the effect of drag over the web handling device 10. Thus, any force vectoring in the MD can overcome the viscous form drag and add a motive force to the web material 12. Likewise, if more drag upon web material 12 is desired and/or required by the process, one of skill in the art will appreciate that the longitudinal axis 20 of holes 14 can be provided with a vector component in a direction opposing the MD of web material 12.
As shown in
As would be known to one of skill in the art, a web material 12 can be produced from a papermaking machine or the like. The web material 12 produced from a former, through-air dryer, or pressing section, can be transported by a press felt or fabric to a press roll that transfers the web material 12 to a Yankee dryer roll. The web material 12 can then be brought into intimate engagement with the surface of a Yankee dryer whereby the web is rapidly dried by heat transfer from the dryer and from an air cap generally positioned over the top of the dryer. The resulting web material 12 can be scraped off the surface of the dryer by a doctor blade.
In a preferred embodiment, after the web material 12 is removed from the dryer surface by the doctor blade, the web control device 10 described herein can then be used to direct the web material 12 through a calendar. The web material 12 exiting such a calendar can then again be redirected by a second web control device 10 as described herein to a reel or winding device wherein the web material 12 is wound onto reels as would be known to those of skill in the art.
As shown in
As shown in
It is also believed that by providing holes 14 with a generally cylindrical geometry, a pressurized fluid contained within inner portion 16 of web control device 10 and transported to the outer portion 18 of web control device 10 through holes 14 can provide a uniform cushion pressure. Thus, the web material 12 can be supported more uniformly and can maintain a more stable float condition. Such a cylindrical hole 14 design can allow for reduced pressure requirements and thus, reduced air supply fan horsepower, resulting in energy savings. Further, by providing rows of holes 14 that are collinear in the CD but not in the MD of web material 12, coated web materials 12 are not adversely affected with lane modeling of the wet coating or heat streaking due to the drying aspect of the high velocity of a cylindrical hole 14 discharge design. It is known that high-pressure hole discharge velocities from conventional designs on many lightweight web substrates can cause corrugation or fluttering within the web material 12. Providing holes 14 in an alternating pattern, as described herein, can provide for a lightweight web to remain substantially flat with substantially no flutter.
Pressurized gas, preferably air, can be supplied to the inner portion 16 of the web control device 10 by a suitable supply such as a fan. The inner portion 16 of web control device 10 is preferably in fluid communication with a cavity or plenum disposed within inner portion 16 of web control device 10. As would be known to those of skill in the art, a cushion pressure tap can be used to measure web support pressure. Fan supply pressure (the pressure from the fan that builds within the inner portion 16 of the web control device 10) can be measured as required. However, the air pressure can be provided as required and can depend upon the characteristics of the web material 12 and the configuration and design of the web control device 10 or any other web material 12 processing equipment being used.
For porous web materials 12, the impact of the fluid passing through the web material 12 can release debris (i.e., loose fibers, dust, lint, and the like), or cause debris to be released, from the region proximate to web material 12 or from the web material 12 itself. In this manner, web control device 10 can be used with, or be incorporated into, a dust capture apparatus (not shown). An exemplary, but non-limiting, embodiment of a dust capture device suitable for use with the web control device 10 of the present invention provides for the placement of a hood opposing the web control device 10 that can capture such debris released from web material 12 due to any impingement of fluid from web control device 10 upon web material 12. Additionally, individual web control devices 10 can be successively alternated above and below web substrate 12 in the MD in order to facilitate the removal of debris from both faces of web material 12. In any case, it has been surprisingly found that the amount of fluid exiting web control device 10 should equal the amount of fluid impinging a dust capture apparatus fluidly associated with web control device 10. This can result in an overall mass balance of fluid thereby increasing the control of web material 12 by web control device 10 and provide for the effective removal of debris from web material 12.
It should also be understood that the present invention is not limited to the particular construction and arrangement of components herein illustrated and described, but embraces such modified forms thereof as come within the scope of the following claims. For example, where reference is made to holes, slots could be used in place of holes.
All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this written document conflicts with any meaning or definition of the term in a document incorporated by reference, the meaning or definition assigned to the term in this written document shall govern.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
