Pipes and tubular conduits – Distinct layers – Reinforced
Reexamination Certificate
2001-06-14
2004-11-23
Hook, James (Department: 3752)
Pipes and tubular conduits
Distinct layers
Reinforced
C138SDIG001, C428S036910
Reexamination Certificate
active
06820654
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates generally to the design and manufacture of high performance, composite, tubular structures. More specifically, the invention relates to high performance, composite, tubular structures that utilize an integral pattern of reinforcing ribs on the inner diameter (“ID”) or outer diameter (“OD”) surface of the tube.
2. Background of the Prior Art
Thin-walled, high performance, tubular structures have a wide variety of practical uses, such as for graphite composite golf shafts, arrows, bats, ski poles, hockey sticks, bicycle parts and many other applications. Current state of the art, high performance, tubular structures are constructed by various methods and from various materials. Designers of such tubular structures satisfy certain design criteria (such as strength, stiffness, weight and torsional behavior) by varying material types (fibers/resins), orientations of fiber directions and geometric proportions of the tube itself Another way designers have sought to improve high performance tubes is by developing new manufacturing techniques.
Using one manufacturing method, tubular structures are made by rolling material, such as pre-impregnated sheets of fiber/resin (“prepreg”), onto a “mandrel.” The rolled layers of prepreg are then consolidated against the outer surface of the mandrel (called the “ID control surface”) by wrapping the prepreg layers with shrink tape and curing via elevated temperature.
FIG. 1
is a simplified diagram of this method, which involves wrapping layers of prepreg
108
around a mandrel
102
and wrapping a layer of shrink wrap material
104
around the layers of prepreg
108
. Through the application of heat, the shrink wrap material
104
contracts, providing external compaction pressure
106
such that the layers of prepreg
108
are consolidated and cured to form a tubular structure.
FIGS. 2
a
and
2
b
are copies of magnified, cross sectional photographs of “flag wrapped” (
FIG. 2
a
) and “filament wound” (
FIG. 2
b
) high performance tubular structures made by the method described in FIG.
1
.
FIGS. 2
a
and
2
b
readily demonstrate wall irregularities
202
,
204
in tubular structures which frequently result from conventional manufacturing techniques.
The standard flag wrapping and filament wound processes for manufacturing high performance tubes have several drawbacks due to the fact that, during consolidation/curing, the diameter of the tube is reduced. This reduction in diameter typically makes the final OD surface rough and irregular, thus requiring secondary finishing by centerless grinding and sanding. Grinding and sanding make the OD surface of the tubular structure uniform and smooth so that it can be painted to yield a cosmetically acceptable finish. However, the grinding/sanding process also typically cuts and abrades the outermost fibers of a tubular structure. Because these outermost fibers are the most highly stressed due to their location (i.e., &sgr;max=MC/I, where “C” is the distance to the outside layer), the grinding/sanding process usually reduces the structural integrity of a tubular structure.
One variation on the flag wrapping and filament wound techniques for making high performance tubular structures is to consolidate them from the inside, rather than the outside, thus yielding a “net molded” outer surface. This technique uses a female mold, rather than a grinding/sanding process, and the resulting outermost fibers are less distorted during consolidation/cure and are also not cut or abraded during grinding/sanding. The net molding technique also allows for the use of higher, more uniform, consolidation pressures than the conventional, shrink-wrap, flag wrapping and filament wound techniques. Higher consolidation pressures result in higher integrity laminates with fewer voids and, therefore, greater tubular strength.
Though the net molding technique may be an improvement over the shrink wrapping techniques, prior art methods for producing high performance, composite, tubular structures are still limited. One problem, aside from the wall irregularities discussed above, is the inability of prior art tubular structures to attain optimal wall thinness while retaining sufficient tubular strength. Whichever technique is chosen for manufacture, a designer typically strives to produce a tubular structure with a uniform, consistent, well-consolidated wall thickness, with undamaged, undistorted composite fibers. A designer also typically tries to make the wall of the tubular structure as thin as possible, to decrease the weight of the tube, while attaining sufficient wall stiffness and strength to enable the structure to be used for its intended purpose. For example, as the wall of a tubular structure is made thinner, its overall stiffness and strength usually decrease. A fundamental failure mode, such as buckling, of a tubular structure may result if the wall of the structure is too thin. A tube that buckles (typically from compression) cannot achieve its maximum strength. Buckling, in turn, usually leads to further structural failures, such as local fiber breaking and premature catastrophic structure failure.
Structural failure is especially likely if a tubular structure is bent when used for its intended purpose.
FIGS. 3
a
and
3
b
, for example, show a tubular structure
302
with arrows representing tension
304
and compression
306
forces which might occur with bending
308
. The combination of tension
304
on one side and compression
306
on the other side of a tubular structure
302
may cause deflection
310
of the structure, as shown in
FIG. 3
b
. The stiffness of the wall of a tubular structure
302
, determined by such factors as the material used to make the tube and the thickness of the wall of the tube, determines how much deflection
310
occurs when the tubular structure is loaded with bending forces. If deflection
310
reaches a certain point, a situation of exponential decay is reached, wherein the stresses present at the wall section increase exponentially until the wall eventually buckles catastrophically. Because instability is inherent in ultra-thin walls of tubular structures, designers generally must use thicker walls than are desirable, in order to achieve adequate stiffness (which translates to adequate stability). Therefore, using prior art methods to produce high performance, composite, tubular structures, the goal of optimal lightness is sacrificed somewhat to achieve requisite stiffness and strength. Accordingly, a long-felt need exists for a high performance, composite tubular structure, and a method for producing that structure, which will combine optimal wall thinness with optimal resistance to buckling and buckling-related stress.
SUMMARY OF THE INVENTION
The present invention satisfies the needs described above by providing high performance, composite, tubular structures that are lighter and/or more resistant to buckling-related stress than conventional tubes. In general, the present invention incorporates features into the design of tubular structures to enhance performance.
For example, in accordance with one preferred embodiment of the present invention, tubular structures are enhanced by incorporating small, stabilizing, raised ribs on the ID or OD of the tubes. These ribs enable designers to optimize the tubes' inertial properties (area mass moments of inertia) to achieve lighter weight, greater stiffness, increased strength or some combination of all three. The ribs may be configured in a variety of shapes and sizes, but are typically helical or circular, parallel or non-parallel, and/or may travel in opposite directions and cross over one another. In accordance with various aspects of the present invention, the ribs may also be hollow. Hollow ribs optionally allow specific materials that are different from the rest of the tubular structure to be included within the ribs. Thus, it will be readily apparent to one skilled in the art that countless combinations and variations of ribs ac
Hook James
Snell & Wilmer LLP
Vyatek Sports, Inc.
LandOfFree
High performance composite tubular structures does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High performance composite tubular structures, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High performance composite tubular structures will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3362854