More specifically, the present invention relates to a suction roll with internal vanes for regulating the air flow through the suction roll.

BACKGROUND OF THE INVENTION Suction rolls are widely used in papermaking machines for guiding movement of a paper web and for drying the web. A suction roll includes a cylindrically shaped porous shell that defines an internal chamber that is connected to a vacuum for drawing air though the shell into the chamber. In one known type of suction roll, the vacuum is connected to one end of the suction roll such that all air is evacuated though the one end. The opposite end of the suction roll is usually a driving end, at which is attached a driving assembly for rotating the suction roll.

As the suction roll is evacuated, air flows into the suction roll through the shell, thus drawing the web toward the outer surface of the shell. As the suction roll rotates, it transports the web and simultaneously draws air through the web, thus holding the web against the roll (which might be desirable for handling reasons) and also having a drying effect on the web.

Within the shell is an internal structure that supports the suction roll. For example, a series of rings are placed so that the central axis of each ring is colinear with the central axis of the shell. These rings are connected to one another with a network of cross bracing. Typically, this internal structure remains stationary as the shell rotates.

One problem that is frequently encountered with the described suction roll is that drying can occur nonuniformly over the suction roll surface. In particular,

air flow through the web can be greater near the tending side of the suction roll where the air is evacuated and lesser at the driving side. This flow disparity is thought to occur because of the greater resistance the air flowing into the suction roll at the driving side encounters compared to that encountered by the air flowing in near the tending side of the suction roll. This greater resistance is thought to be caused at least in part by the internal support structure of the suction roll.

Consequently, the web may experience relatively more drying and/or holding effect near the tending side than at the driving side of the suction roll.

SUMMARY OF THE INVENTION The present invention provides a suction roll comprising a porous cylindrical shell and an internal structure that includes vanes within the shell near the inner surface thereof. The vanes are arranged so that, as the shell rotates, the vanes disrupt the boundary layer of air on the inner surface of the shell. It has been found that the spacing between a vane and the shell impacts the degree to which the vane augments the air flow into the shell in the vicinity of the vane. If the vanes are located close to the shell, they will tend to draw more air through the shell than if there is a wide gap between the vanes and shell. Therefore, the vanes are placed at varying distances from the shell so that the flow profile across the length of the suction roll can be controlled. More particularly, in preferred embodiments of the invention, the vanes are spaced from the shell by distances that vary along the lengthwise direction of the shell.

In one embodiment, the suction roll has a vacuum connection at a first end of the suction roll. A plurality of vanes extend from near the first end of the suction roll to a location near the opposite second end of the suction roll. The vanes are spaced apart in a circumferential direction of the suction roll. The vanes are spaced relatively closer to the inner surface of the shell near the second end of the suction roll, and relatively farther from the shell near the first end of the suction roll. Preferably, the vanes are curved or cambered, with convex faces of the vanes facing generally toward the shell inner surface.

In a suction roll having vacuum connections at both ends of the suction roll, the vanes can be closest to the shell near the midpoint of the shell and can be

spaced farther from the shell near the opposite ends of the shell. Other variations are also possible in accordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: Figure 1 is a view of the suction roll as seen in the direction of the central axis of the suction roll.

Figure 2 is a section view of the suction roll as seen from the plane A-A as defined in Figure 1.

Figure 3 is a cut-away perspective view of the suction roll.

DETAILED DESCRIPTION OF THE INVENTION The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

A suction roll according to the present invention is shown in Figures 1 and 2. Referring first to Figure 1, it can be seen that the suction roll 1 has a circular cross-section. A porous shell 2 defines an internal space through which air is evacuated from the suction roll 1. Within the space are located a plurality of vanes 5, which are arranged in eight rows in this embodiment. In other embodiments, the vanes 5 may be arranged in any number of rows and/or not all of the vanes 5 may be colinear with one another. Each vane 5 has an inner surface 10 that faces generally in a direction toward the center of the roll, and an outer surface 11 that opposes the inner surface 10. Each vane 5 also has a leading edge 8 that is located proximate to the shell 2 and a trailing edge 9 that is opposite to the leading edge 8.

The vanes 5 are shown to be curved, but they may instead be straight. In this

embodiment, the vanes 5 are said to be concave-inward because the inner surface 10 is concave. Also, it can be seen that the vanes 5 do not extend from the shell 2 directly inward toward the center of the suction roll 1 but rather are angled toward the tangential direction of the shell 2. In this embodiment, the leading edges 8 of the vanes 5 are said to lead when the shell 2 rotates clockwise because, as the shell 2 rotates, a plane extending in the radial direction from the center of the roll 1 to a point on the shell 2 will intersect the leading edge 8 of the vane 5 before the trailing edge 9. In this embodiment, each of the vanes 5 has a similar curvature and angle, but in other embodiments, either or both of the curvature and angle may differ from one vane 5 to another.

As the shell 2 rotates, it transports a web 6 that is wrapped about a section of the perimeter of the suction roll 1. Because of the rotation of the shell 2, air near the shell 2 within the suction roll 1 tends to move with the shell 2. Due to the shell's motion relative to the vanes 5, for example in a clockwise direction in Figure 1, the vanes 5 interfere with the boundary layer of air against the inner surface of the shell 2.

Figure 2 shows a section view of the suction roll 1 as seen in the direction A-A as indicated in Figure 1. It can be seen from Figure 2 that the suction roll 1 has a driving side 3 and a tending side 4, which are opposed. A driving means 12 is attached to the driving side 3 and rotates the suction roll 1. At the tending side 4 a vacuum means 13 evacuates air from the suction roll 1. It can also be seen from Figure 2 that the vanes 5 are not oriented uniformly relative to the shell 2. Instead the vanes 5 that are farther from the tending side 4 are closer to the shell 2.

The arrangement of the vanes 5 is also apparent in Figure 3, a cutaway perspective view of the suction roll 1. Three of the rows of vanes 5 can be seen in Figure 3. Again, the vanes 5 furthest from the tending side 4 are closest to the shell 2. Therefore, vane 5a is located closest to the shell 2, and vane 5b is furthest from the shell 2. In this embodiment, the vanes 5 are of varying length (defined as the generally radial dimension of the vane), but in other embodiments the vanes are of similar length so that the vanes 5 furthest from the shell 2 extend further toward the center of the suction roll 1 than those vanes 5 closest to the shell 2. Also, the vanes 5 are shown to be generally trapezoidal in shape, but a variety of other

shapes are possible. For example, the vanes 5 may be of generally rectangular shape.

The vanes 5 are held in place by bracing members 7. The bracing members are most apparent in Figure 3 on those vanes that are located closest to the tending side 4 of the suction roll 1. The bracing members 7 provide support to the vanes 5 and maintain the appropriate spacing between the vanes 5 and the shell 2. In some embodiments, the bracing members 7 are adjustable so that the vanes 5 can be moved. The vanes 5 can be moved to different locations in the roll 1, or the space and angle between the vanes 5 and the shell 2 can be changed. In other embodiments, the vanes 5 may be of sufficient strength that no bracing members 7 are required to maintain the integrity and placement of the vanes 5. For example, each vane 5 may extend the entire length of the shell 2.

Because the vanes 5 are located at varying distances from the shell 2, there is a varying degree to which each vane 5 interrupts the boundary layer of air near the shell 2. Those vanes 5 that are located closer to the shell 2 will tend to have a greater interference with the boundary layer. In a suction roll 1 that has only one tending side 4 where evacuation takes place, the air flow profile tends to vary over the length of the roll 1 so that air flow is greatest near the tending side 4. In the accompanying figures, the vanes 5 have been configured to counteract that nonuniformity in the flow profile. Thus, the vanes 5 farthest from the tending side 4 interfere with the boundary layer and increase the flow of air through the shell 2.

Conversely, the vanes 5 nearest to the tending side 4 interfere with the boundary layer to a lesser extent.

Through appropriate tuning of the number, shape, placement, and orientation of the vanes, a desired flow profile can be achieved. In many instances, the desired flow profile will be a uniform profile. The vane assembly that is required to achieve that flow profile may depend on such factors as the number and location of points of evacuation, the rate of evacuation, the dimensions of the suction roll, the rotational speed of the shell, the type and moisture content of the web, and ambient conditions. For example, in a suction roll that is evacuated from both sides, the air flow profile will likely tend to be greatest near the ends and lower towards the center. A suction roll according to the present invention might

have vanes closer to the shell at the midpoint of the shell, and vanes spaced farther from the shell at the two ends thereof. In addition, the spacing between the vanes 5 and the shell 2 may be quite different than that illustrated, which has been drawn for ease of illustration.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.