Web material test stand having a laminar airflow development device

A laminar air flow development device for use with stationary web material testing equipment is disclosed. The laminar air flow development device has a machine direction, a cross-machine direction orthogonal thereto, and a Z-direction orthogonal to both the machine and cross-machine directions. The stationary web material testing equipment has a first web material support having a Z-direction thickness, D. The device has first and second surfaces contactingly and matingly engaged to form an airfoil having a machine direction length, L, a cross-machine direction width, a leading edge, and a trailing end. The airfoil has a chord disposed between the first and second surfaces. The trailing end has a width equal to the Z-direction thickness, D. The device has a ratio of L/D ranging from about 1 to about 70 and provides machine direction laminar air flow to at least one surface of the first web material support.

FIELD OF THE INVENTION

The present disclosure relates to devices suitable for the development of laminar air flow for web material test stands. The present disclosure more particularly relates to devices suitable for the development of laminar air flow for testing web materials disposed upon test stands that more suitably simulate real-time web material handling in typical operating environments.

BACKGROUND OF THE INVENTION

Wind tunnels are used in aerodynamic research to study the effects of air moving past solid objects. A wind tunnel can generally consist of a passage with the object under test disposed and/or mounted therein. Air is made to move past the object by a fan system or other means. The test object, sometimes called a wind tunnel model, can be provided with instruments having suitable sensors to measure aerodynamic forces, pressure distribution, or other aerodynamic-related characteristics observed by the test object.

Referring toFIG. 1, in the world of consumer products, such as paper toweling, bath tissue products, and facial tissue products, wind tunnel10tests can be used to suitably measure simulated air velocities, forces, and/or pressures exerted upon a web material18while the web material18is conveyed from one location to another. Such conveying is known to those of skill in the art as converting.

Referring to the exemplary prior art wind tunnel10ofFIGS. 1 and 2, air32(or airstream32) is blown or sucked through a duct equipped with instrumentation where an object (here presented as web material test stand12) is positioned for study. Typically the air32is moved through the wind tunnel10using a wind generating device14in the form of a fan30. For very large wind tunnels that are several meters in diameter, a single large fan may not be practical, and so instead an array of multiple fans30can be used in parallel to provide sufficient air flow through the wind tunnel10.

In a typical web material18wind tunnel10set-ups, a test stand12can provide for a web material18to be attached to a web material support16. The web material support16will typically be provided as a roller, turn bar, or the like having a nominal diameter, or Z-direction thickness, D. In most applications, the web material support16will be provided to represent typical web material18handling equipment used in the production of consumer products such as paper toweling, bath tissue, facial tissue, as well as web materials18suitable for the production of assembled articles such as diapers, catamenial devices, and the like.

During wind tunnel testing of web materials18, any turbulence34present in air32has a deleterious effect upon the analysis of the web material18disposed upon test stand12. Thus, in order to suitably test web materials18disposed upon test stand12it is preferred that the air32moving through the wind tunnel10be relatively turbulence-free and laminar.

Web materials18, including web materials18having high surface texturing, such as unusual or complicated shapes are generally analyzed in wind tunnels10in order to understand boundary layer air (i.e., air located proximate to web material18). Such testing can provide the necessary design analysis to help in the development of equipment for the handling of web materials18, especially web materials18that preferably move at high rates of speed during converting operations.

However, it is a common problem experienced by those of skill in the art that the air32provided by the wind generating device14becomes turbulent34upon contact with the relatively blunt leading edge surface of web material support16. This turbulent air32negatively impacts the analysis of web materials18. This includes those web materials18having high surface texturing.

Another issue that can arise with such test stands10as described supra, is the effect of the application of a tension, T, to the web material18attached to the test stand10. One of skill in the art will understand that typical web materials18used in the production of the articles mentioned supra are typically subjected to high tensions in order to secure the most efficacious winding, effect a complimentary registration of the web material18relative to a particular portion of the manufacturing operation, or even the registration of one web material18to another web material18. Applying a tension to the web material18disposed upon the test stand10assists the analysis of the web material in conditions that more accurately simulate actual manufacturing conditions.

To note, it should be readily understood that web materials18used in the production of paper toweling, bath tissue, or facial tissue are typically thin (e.g., have a caliper ranging from about 0.005 inches to about 0.020 inches) and have a very low basis weight (e.g., about 5 pounds/3,000 ft2to about 30 pounds/3,000 ft2). In other words, the web materials18used in the production of paper toweling, bath tissue, or facial tissue are really quite delicate. Additionally, the rolls of web materials used in the production of paper toweling, bath tissue, or facial tissue typically have large cross-machine direction widths—typically in the order of 100 inches. When these thin, low basis weight, and large width web materials18are moved at typical manufacturing speeds (e.g., about 2,000 ft/min to about 4,000 ft/min) and at typical manufacturing web tensions (e.g., about 30 g/inch to about 120 g/inch), the web handling equipment used to manufacture these products (such as web material support16) are designed to have low inertia.

Low inertial components are necessary to avoid breaking or otherwise damaging these otherwise delicate web materials18. Designing low inertial equipment suitable for the above described converting operations requires that such equipment be manufactured from materials that have good mechanical (e.g., structural) strength and are light weight (i.e., low mass). Designing such low inertia equipment from traditional construction materials (such as steel) or from modern high-strength materials (such as carbon fiber), combined with the lengths of the equipment necessary to handle these high-width web materials results in web handling equipment having a high bend modulus (or bending moment).

One of skill in the art would understand that bending moment is the reaction induced in a structural element when an external force or moment is applied to the element causing the element to bend. The internal reaction loads in a cross-section of the web material support16can be resolved into a resultant force and a resultant couple. For equilibrium, the moment created by external forces (and external moments) are balanced by the coupling induced by any internal loads. This resultant internal coupling is called the bending moment.

Such is the typical case when a web material support16is caused to support a web material18having a low basis weight and large width, under high tension in a typical converting application. In principle,FIG. 3shows a beam (here web material support16) which is simply supported at both ends. In other words, each end of the web material support16can rotate but has little to no bending moment. This means that the ends of the web material support16only react to a shear load. As shown, when a wide web material18is subjected to an applied tension, T, it is not uncommon for a low inertia web material support16to deform in the manner of web material support16′ in the direction of the applied tension, T. This is akin to a beam structural element that is subjected to a bending moment.

Additionally, the web material support16experiences deformation caused by the external load applied to the web material support16by the air moved within the wind tunnel10as it impacts the leading edge of the web material support16. The deformation is generally caused by a strain or a stress field induced by the impact of air upon the low inertia device (e.g., web material support16). In most cases, the deformations experienced by the web material support16can be elastic. This can cause erroneous measurements due to a changing deformation in the web material support16due to changes in the tension applied to the web material18, the changing geometry of the web material support16, or even changes in the velocity or volume of air impinging upon the leading edge of web material support16. Additionally, deformations in the web material support16can cause variations in both the MD and CD length of the web material18. In other words, a first portion of the web material18can have a displacement relative to an adjacent portion of the web material disposed in either of the MD, CD, or combinations thereof.

Thus, there is a need to provide a device for such web material test stands that provides laminar air flow at the leading edge of a web material support or at the point of attachment of the web material to a web material support. There is also a need to provide a device that can effectively reduce the deformation experienced by a web material support positioned within a wind tunnel. There is also a need to provide a device that can effectively reduce the deformation experienced by a web material disposed upon a web material test stand positioned within a wind tunnel.

SUMMARY OF THE INVENTION

The present disclosure provides for a laminar air flow development device for use with stationary web material testing equipment. The laminar air flow development device has a machine direction, a cross-machine direction orthogonal thereto, and a Z-direction orthogonal to both the machine and cross-machine directions. The stationary web material testing equipment has a first web material support having a Z-direction thickness, D. The device has first and second surfaces contactingly and matingly engaged to form an airfoil having a machine direction length, L, a cross-machine direction width, a leading edge, and a trailing end. The airfoil has a chord disposed between the first and second surfaces. The trailing end has a width equal to the Z-direction thickness, D. The device has a ratio of L/D ranging from about 1 to about 70 and provides machine direction laminar air flow to at least one surface of the first web material support.

The present disclosure also provides for a laminar air flow development device for use with stationary web material testing equipment having a machine direction, a cross-machine direction orthogonal thereto, and a Z-direction orthogonal to both the machine and cross-machine directions. The stationary web material testing equipment has a first web material support having a Z-direction thickness, D. The device has first and second surfaces having a machine direction length, L, and a cross-machine direction width. The first and second surfaces are symmetrically disposed about a plane formed in the machine and cross-machine directions. The device has a leading edge and a trailing end. The trailing end has a maximum and minimum thickness equal to the Z-direction thickness, D, of the first web material support and is cooperatively disposed proximate thereto. The first and second surfaces are contactingly and matingly engaged at the leading edge to form a parabolic shape relative to the machine direction. The device has a ratio of L/D ranging from 1 to about 70 and provides machine direction laminar air flow to at least one surface of the first web material support.

DETAILED DESCRIPTION

As used herein, “Machine Direction” (MD) means the direction parallel to the path or flow of a web material18through product manufacturing equipment. “Cross-Machine Direction” (CD) means the direction perpendicular to the machine direction in the plane of the web material18. “Z-direction” is the direction orthogonal to both the machine- and cross-machine directions.

FIGS. 1-3provide a schematic view showing an exemplary prior art wind tunnel measurement apparatus10. As shown, a wind tunnel10can include walls50and test stand12. Each of the two walls50has a flat surface parallel to the machine direction. The two walls50are preferably arranged at a predetermined distance from each other in the cross-machine direction. The space between the walls50defines an area for placement of the test stand12.

The test stand12is arranged so that during web material18testing, the test stand12is disposed within the flow path or air32generated by a fan30that is provided in fluid communication with wind tunnel10within the area defined by walls50. Test stand12is typically secured (anchored) or otherwise attached to a mounting surface26though web material support mount22that is operatively connected to web material support16and through a second web material support mount24that can be operatively connected to a second web material support20if it is so needed.

Operatively, a fluid (e.g., air32) generated by fan30flows through the wind tunnel10defined by walls50around test stand12and over a surface of a web material18that is operatively attached to a surface of test stand12. It was found that any air32that impacted the leading edge of web material support16immediately became turbulent34. This means that the air32impacted the leading edge of web material support16and then failed to provide laminar flow over the surface of web material18contactingly engaged and attached to web material support16at a first edge. This negatively impacted the ability to study the behavior of web material18.

Additionally, when web material18was subjected to an applied MD tension, T, it was observed that web material support16would tend to deflect and deform in the MD. If the applied MD tension, T, was sufficient, the web material support16would assume a deformed, arcuate-shaped web material support16′ thereby causing MD deformation in web material18as well as the generation of an induced CD deformation as well as a CD tension. The arcuate shaping16′ of web material support16was further exacerbated by the presence of high velocity air32. Without desiring to be bound by theory, while it is believed that the majority of arcuate deformation16′ of web material support16was due to the applied tension, T, some contribution to the deformation of web material support16was due to the MD contact of air32generated by fan30with the leading edge of web material support16.

Referring toFIGS. 4-5, it was surprisingly found that the placement of a laminar airflow development device38proximate to, and in some circumstances in contacting engagement with, the leading edge of web material support16effectively eliminated the presence of any turbulence34in favor of laminar air flow40over the surface of laminar airflow development device38, web material support16, and any web material18operatively and fixably attached thereto.

Without desiring to be bound by theory, the underlying principle of the laminar airflow development device38is a “body designed to provide a desired reaction force when in motion relative to the surrounding air”. Although this definition can be generally applied to aircraft airfoils that are in motion relative to the surrounding air, it can also apply to an airfoil that is stationary and the air is in motion relative to the airfoil. This is because in both cases, the reaction force results from the physical act of displacing the air from the path it had been on and re-directing it.

The laminar airflow development device38can be of almost any shape and be manufactured from almost any material and still reduce the generation of a reaction force of some magnitude. For example, a suitable laminar airflow development device38can be constructed from high tensile strength iron, stainless steel, composite fiber, and/or the like. Additionally, a suitable laminar airflow development devices38can range from a simple flat plate (e.g., similar to the panels of box-kite), to a curved plate (e.g., the sail on a sailboat), to a complex shape (e.g., the wing on an aircraft) which has some finite thickness resultant from the combination of upper and lower surfaces of different curvature. A reaction force can be generated by either changing direction of the airstream32(i.e., by the conservation of momentum) or by splitting an airstream32into two parts and forcing each of these streams to take a path of a different length to get past the airfoil (here laminar airflow development device38) before reuniting to form a single airstream32again. Using the Bernoulli principle, the use of a desired shape that prevents the generation of a reactive force by reducing any changes in direction of an impinging airstream32and providing a divided airstream32that has equal path lengths can reduce the development of turbulence34observed by test stand12as well as the web material18attached thereto.

The magnitude of a reaction force can be related to five factors: (1) the shape of the laminar airflow development device38; (2) the angle of the laminar airflow development device38relative to the air32(i.e., the so-called angle of attack); (3) the velocity of the airstream32; (4) the area of the laminar airflow development device38: and (5) the density of the air. In applying these factors to the task of managing the somewhat fragile tissue web material18that happens to be traveling at high speed, the variability and influence of each of these factors should be considered. Since an objective of the present disclosure is to manage the flow of air32traversing the surface of a web material18, a laminar airflow development device38can used to redirect a boundary layer airstream, since a portion of this airstream32impacts the flexible tissue web material18that is the object of desired study.

One embodiment of a suitable laminar airflow development device38design is that of a flat plate. The forces generated on either side of a flat plate laminar airflow development device38can be neutral if there is no realized increase in relative airstream32velocity on one side of the laminar airflow development device38over the other due to the Bernoulli effect. Any change in the angle of attack of the flat plate laminar airflow development device38relative to the direction of the air32produced by fan30will generate some additional force. As such, it is believed that a flat plate is limited to relatively low angles of attack (i.e., the angle of the flat plate laminar airflow development device38relative to the reference line or entering airstream32) in order to keep the airstream32from breaking away from the surface of the flat plate laminar airflow development device38and becoming turbulent, resulting in the reaction force being greatly diminished.

Another embodiment of an exemplary laminar airflow development device38design is the shape depicted inFIGS. 8-9. Such a curved plate design for laminar airflow development device38would likely derive most of its reaction force from any angular changes in direction of the airstream32. In other words, little force is generated by the Bernoulli effect. This is because as the only increase in airstream32velocity on the side farthest from the reference line is due to the lengthened path parallel to, and outwardly stepped from, the radius of curvature of the upper surface of the curved plate. The curved plate laminar airflow development device38is a more stable airfoil design than the flat plate laminar airflow development device38because the entry and exit airstreams32are generally tangent to the curvature of the laminar airflow development device38. This tangential flow avoids having the air32change direction abruptly and therefore reduces the potential of the airstream32separating from the surface of the laminar airflow development device38attached thereto.

As shown inFIG. 9, the exemplary laminar airflow development device38having an overall length, L, provides first and second surfaces that are contactingly and matingly engaged and disposed about the chord of the laminar airflow development device38. In a preferred embodiment the first and second surfaces that are contactingly and matingly engaged and symmetrically disposed about the chord of the laminar airflow development device38. Here the camber mean line is the same as the chord due to the symmetrical nature of the laminar airflow development device38shown. The maximum thickness (as well as the trailing end) of the laminar airflow development device38shown has a maximum and minimum thickness equal to the Z-direction thickness, D, of the desired first web material support16of test stand12. Preferably, the laminar airflow development device38has a leading edge that has a parabolic shape disposed symmetrically about a plane formed in the Z-direction and the CD. Preferably, the length, L, of laminar airflow development device38is provided relative to the Z-direction thickness, D, of the first web material support16and ranges from about 1 to about 70, or from about 2 to about 50, or from about 4 to about 30, or from about 5 to about 25, or about 7 to about 20, or from about 10 to about 15. As shown inFIG. 10, a cross-sectional view of an exemplary preferred embodiment of the laminar airflow development device38that extends in the CD is provided with a leading edge having a parabolic shape that satisfies the equation y=185x2where the x and y Cartesian coordinates correspond to the Z-direction and MD, respectively.

Additionally, it is believed that airfoils developed by the National Advisory Committee for Aeronautics (NACA) can be suitable for use as laminar airflow development device38. An exemplary formula for designing a suitable symmetric NACA foil is:

yt=t0.2⁢c⁡[0.2969⁢xc+(-0.1260)⁢(xc)+(-0.3516)⁢(xc)2+0.2843⁢(xc)3+(-0.1015)⁢(xc)4],where:c is the chord length,x is the position along the chord from 0 (leading edge) to c,ytis the half thickness at a given value of x (centerline to surface), andt is the maximum thickness as a fraction of the chord.

Asymmetric NACA foils may also be suitable for use as laminar airflow development device38. An asymmetric NACA foil may use the same formula as that used to generate a symmetric NACA foil, but with the camber mean line bent. The formula used to calculate the mean camber line of an asymmetric NACA foil is:

yc={m⁢xp2⁢(2⁢p-xc),0≤x≤pcm⁢c-x(1-p)2⁢(1+xc-2⁢p),pc≤x≤cwhere:m is the maximum camber (100 m is the first of the four digits), andp is the location of maximum camber.

Because the thickness of an asymmetric NACA foil needs to be applied perpendicular to the camber line for a cambered laminar airflow development device38, the coordinates (xU, yU) and xL, yL), of respectively the upper and lower airfoil surface, become:
xU=x−ytsin θ,yt′=yc+ytcos θ,
xL=x+ytsin θ,yL=yc−ytcos θ,where:

Referring again toFIGS. 6-7, a preferred test stand12suitable for use with web material18and positionable within wind tunnel10and incorporating an exemplary laminar airflow development device38is shown. Here, a web material support16and a second web material support20are juxtaposed one in front of the other to form a point of attachment for a web material18. The web material support16and a second web material support20can be positioned into fixed alignment by the attachment of both the web material support16and the second web material support20by the physical attachment to a pair of spaced rails36forming an alignment frame42. Further, the rails can be attached to each respective rail36forming alignment frame42through a respective load cell44.

If desired, a temporary alignment frame46can be provided for attachment to alignment frame42. Temporary alignment frame46can be used to ensure that the pair of spaced rails36remain parallel to each other and can ensure symmetrical flow patterns around the test stand12that could otherwise have a negative effect on any physical measurements performed upon a web material18attached thereto.

In one embodiment, web material support16and second web material support20are constructed from high tensile strength iron, stainless steel, composite fiber, and/or the like. In this embodiment, web material support16and second web material support20are preferably provided in the form of a rod, square bar or rectangular bar, or other shapes to provide test stand12with increased stiffness.

In yet another embodiment, web material support16and a second web material support20are constructed from a high stiffness carbon fiber material or other high strength to weight ratio materials to eliminate gravitational sagging of the web material support16and second web material support20in the Z-direction. One of skill in the art would appreciate that a high degree of stiffness in the MD can be easy to achieve but stiffness in the Z-direction can require a high impact geometry thus exacerbating the need for such preferable high strength to weight ratio materials such as carbon fiber and the like.

In one preferred but non-limiting embodiment, laminar airflow development device38can be positioned in contacting and fixed relationship to the trailing edge of web material support16. Such an arrangement would be useful to one of skill in the art for understanding the impact of MD airflow upon a web material transfixed between two points such as web material support16and a second web material support20. Such an arrangement also can provide for the added benefit of reducing the bending moment (i.e., bending modulus) of web material support16. As discussed supra, web material support16can undergo significant bending in the event a tension, T, is applied to web material18or due to the impact of air32generated by fan30upon the leading edge of web material support16. Thus, laminar airflow development device38can provide a beneficial duality of laminar air flow40over a web material18fixably attached to web material support16as well as decrease the bending moment of web material support16due to a tension, T, that may be applied to a web material18disposed thereon by providing increased rigidity to web material support16.

In other words, the first material support16can be considered to have a first machine direction flexural rigidity. When the first web material support16is provided in cooperative, adhered, connective engagement with the trailing end of the laminar airflow development device38, the first web material support16can be now provided with a second machine direction flexural rigidity. Preferably, the second machine direction flexural rigidity is greater than the first machine direction flexural rigidity.

In another preferred but non-limiting embodiment, laminar airflow development device38can be spaced proximate to, but in spaced relationship with, the trailing edge of web material support16. Such an arrangement would allow for the transportation and/or introduction of web material18into the space between web material support16and laminar airflow development device38and into contacting engagement with the web material support16. By way of non-limiting embodiment, such an arrangement way be useful to one of skill in the art for understanding the impact of airflow upon a web material18that may be undergoing a translational positional movement from a direction relative to the Z-direction to a direction relative to the MD.

All publications, patent applications, and issued patents mentioned herein are hereby incorporated in their entirety by reference. Citation of any reference is not an admission regarding any determination as to its availability as prior art to the claimed invention.

The dimensions and/or values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension and/or value is intended to mean both the recited dimension and/or value and a functionally equivalent range surrounding that dimension and/or value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”.