Patent Application
20240327165
Due to higher specific strength and stiffness, carbon fiber (CF) composites are widely used in many applications in aerospace, civil and military aircraft, boats, automobiles, wind energy and in many other areas. For the same reasons, in recent years CF composites have also made inroads into the converting industries, such as papers, plastics, textiles, etc., where CF composites are used to make winding/unwinding shafts. Traditionally, winding/unwinding shafts are made from steel and aluminum which have low specific strength and modulus. Steel has high modulus (30 million pounds per square inch (MSI)) compared to aluminum (10 MSI), but with three times higher density, steel is also heavier than aluminum. As a result, neither steel nor aluminum are ideal to make light weight shafts of high critical speed. Therefore, with its low density (about 0.06 lbs./in.3) and high modulus (up to 125 MSI), carbon fibers offer great opportunity to overcome the limitations of steel and aluminum shafts.
U.S. Pat. No. 5,379,964 describes the development of a winding shaft where a plurality of elongated CF composite rails are bonded to the outer surface of a CF composite tube. Such arrangement of the rails created elongated slots where the expandable bladder system could be mounted to hold the core on which web-materials were wound. Conceptually, such a construction was supposed to eliminate many disadvantages associated with steel and aluminum shafts. However, in practice, the construction did not show sufficient stability against buckling, and thus the expected benefits were not achieved. Such instability was addressed in a subsequent patent (U.S. Pat. No. 5,746,387), where an aluminum extrusion with multiple cavities filled with carbon fibers is used. The fibers are mostly oriented along the longitudinal axis of the extrusion, which maximizes the stiffness (modulus) of the hybrid (carbon-aluminum) structure. The combined modulus of the hybrid structure depends on the type of fiber used and its volume fraction. Generally, there are two different categories of carbon fibers available, namely PAN-based (polyacrylonitrile-based) and pitch-based. The PAN-based fibers have lower tensile modulus, but higher strength than the pitch-based fibers. Examples of some of the carbon fibers and their manufacturers are given in Table 1 below:
For example, at 54% (by volume) of 125 MSI fiber, the modulus of the 3-inch three cavities hybrid structure is expected to be 30 MSI. On the other hand, if the cavities are filled with 92 MSI carbon fiber at the same volume fraction, the modulus of the hybrid structure is expected to be around 24 MSI. In both cases, the shafts are lighter than aluminum and steel, and the modulus can approach that of steel (with 125 MSI fiber). However, there are some disadvantages with the prior art solutions.
Firstly, about 50% of the hybrid structure's cross-section is aluminum, which is the weakest link. As a result, the maximum potential benefits of CF composite are not realized. Such a shaft is also heavier than if the entire shaft is made with CF composite only.
Further, the fibers in the pultruded profile are uniaxially oriented, making it an anisotropic material. It is well known that the flexural (bending) modulus of uniaxially oriented fiber composites is sensitive to the span-to-thickness (L/D) ratio. Below a certain L/D ratio (also known as critical ratio), the shear component of the stress becomes dominant. It was shown that the maximum flexural modulus of uniaxially oriented composite can be achieved at L/D ratio of 60 or higher [L. A. Carlsson et al., “Experimental characterization of advanced composite materials”, Prentice-Hall, 1987]. In fact, the ASTM D-790 test standard for uniaxially oriented fiber composite material defines such critical ratio as 60. If the dimensions of the test specimen are not strictly followed as per ASTM standard, the critical ratio may change, but it follows the principle that the flexural modulus decreases as L/D decreases [A. Karmaker et al., “Effect of design parameters on the flexural properties of fiber-reinforced composites”, J. Mater. Sci. Letts., p. 663-665, 19 (2000)]. Based on theory, the flexural modulus of a 3-inch OD (outer diameter) shaft made with uniaxially oriented carbon fiber would be to its maximum at a span of 180 (3×60) inches.
To address these and other disadvantages of the prior art, a new winding shaft is provided for, where the shaft body is made only of CF composites, with the fibers being multi-directional. Generally, there are two types of expandable winding shafts: (a) single bladder type with buttons or discontinuous expanding elements (lugs), and (b) multi-bladder type with continuous expanding elements (ledges). The shaft of the present application is a combination of both types and is a multi-bladder shaft with discontinuous expanding elements. The shaft body is made with CF composites. The shaft comprises two tubes (inner and outer) and two types of profiles (cavity and ledge profiles). The shaft body components can be made of CF composites where the fibers are at least partially oriented to achieve quasi-isotropic character, meaning the orientation angle of the fibers in respect to the shaft length is greater than 0°. Such character makes the properties less dependent on the loading direction as opposed to the uni-axially oriented composite part. The inner and outer tubes can be made by filament winding, roll wrapping or any other method that would allow the fibers to be at least partially oriented in relation to the shaft's length. The cavity and ledge profiles can be made by various methods such as compression molding, resin transfer molding (RTM), vacuum assisted resin transfer molding (VRTM), Seeman composite resin infusion molding process (SCRIMP), structural reaction injection molding process (SRIMP), 3D-printing or any other suitable process.
The cavity and ledge profiles can be adhesively mounted around the outer surface of the inner tube in an alternating fashion, so that each profile (cavity or ledge) lies between two other profiles. This ensures that the profile axes (cavity or ledge) are 120° apart from each other. Ledge profiles hold the expandable bladders and lug assembly. In addition or alternative to adhesion, rivets can be used to attach the profiles to the inner tube. The outer tube can be created by applying layers of carbon fibers, fabrics (woven/unwoven) or prepregs by filament winding, roll wrapping or any other suitable method. The outer surface of the outer tube can be coated with hard and durable coating material to prevent fiber damage during the handling of the shaft in a manufacturing environment. Elongated discrete slots can be machined along the ledge profiles. When the bladders are inflated with air, the lugs are pushed outward through the discrete slots to engage the inner wall of the core. When deflated, an installed spring system pushes the lugs inward, enabling easy sliding of the core over the shaft. Inside each cavity profile a stiffening bar, made from CF composite, may be installed to enhance the rigidity of the shaft, if deemed to be necessary for some applications. The stiffening bars can be adhesively mounted inside the cavity profiles. In addition or alternative to the adhesive, rivets can also be installed to connect the bars with both inner and outer tubes.
In accordance with a first general aspect of the present application, a shaft is provided. The shaft comprises a first, inner tube made of a composite fiber material, and a second, outer tube also made of a composite fiber material. The shaft also includes a plurality of cavity profiles made of a composite fiber material disposed in between the inner and outer tubes. The shaft also includes a plurality of ledge profiles made of a composite fiber material and disposed in between the inner and outer tubes, the cavity profiles and the ledge profiles being arranged in an alternating manner, where one ledge profile is arranged in between two cavity profiles and one cavity profile is arranged in between two ledge profiles. Further, the composite fibers in the tubes and profiles of the shaft can be multi-directional.
In embodiments of the shaft of the first general aspect of the application, the shaft is an expandable shaft that may comprise: a plurality of elongated slots discontinuously distributed along the length of the outer tube; a plurality of protrusion elements, each protrusion element discontinuously positioned in one of the elongated slots; and a plurality of expandable elements located in one or more of the ledge profiles.
The plurality of protrusion elements and the plurality of expandable elements can be arranged in the plurality of ledge profiles. The plurality of protrusion elements may be lug assemblies, each comprising a lug and a lug support. The plurality of expandable elements may be bladder assemblies, each may include a bladder configured to be inflated with air, and a bladder support on which the bladder is disposed.
In various embodiments, the bladder support may be a single-part system and made of metal, composite, or plastics, or the bladder support may be a multi-part system and made of at least two different materials having different densities. The bladder is configured to push the lug outward when the bladder inflated with air, and when deflated, an installed spring system pushes the lug inward.
The composite fiber materials of the tubes and the cavity and/or ledge profiles may comprise one or more of glass, carbon, aramid, or graphite. The composite fiber material may comprise a matrix of a thermoset resin, including one or more of an epoxy, polyesters, phenolics, vinyl esters, bismaleimide or polyurethane.
The inner and outer tubes of the shaft may be made by filament winding, roll wrapping, pull-winding, resin transfer molding, vacuum assisted resin transfer molding, Seeman composite resin infusion molding process or structural reaction injection molding process. The ledge profiles and cavity profiles can be made by compression molding, filament winding, pull-winding, resin transfer molding, vacuum assisted resin transfer molding, Seeman composite resin infusion molding or structural reaction injection molding.
One or more of the plurality of cavity profiles can be hollow, or one or more of the plurality of cavity profiles may include stiffening bars therein.
One or more of the plurality of cavity profiles are one-part systems, or one or more of the plurality of cavity profiles can be multi-part systems, each including a top portion adhered to a bottom portion. In certain further embodiments of the shaft, the plurality of ledge profiles is defined laterally by a wall of each adjacent cavity profile and on a base by an outer diameter of the inner tube, and further may include a bridge element defining the top of the ledge profile. The ledge profile may include a curved upper surface, a curved lower surface, and parallel side walls between the curved upper surface and curved lower surface.
Referring to the Figures, cross-sectional views of a shaft body 100 of the present application are shown in
In the shaft body 100, three of each of a cavity profile 102 and a ledge profile 103 are arranged circumferentially on the outer surface of the inner tube 101. The outer diameter of the inner tube 101 matches with the outside smaller diameter of each cavity profile 102 and ledge profile 103. In other embodiments of the shaft body 100, more or less than three of each cavity profile 102 and ledge profile 103 can be provided. For example, in shafts having larger diameters, four or more (e.g., 4, 5, 6, 7, 8, 9, etc.) of each cavity profile 102 and ledge profile 103 can be provided.
An outer tube 109 is provided circumferentially around the cavity profiles 102 and ledge profiles 103. The outer tube 109 comprises a plurality of elongated slots along its length, in which a plurality of protrusion elements, such as lug assemblies 106 comprising lugs 108 are positioned.
The cavity profiles 102 and ledge profiles 103 can be fabricated as one or multi-part systems. In a one-part system, shown for example in
The cavity profile 102 is a longitudinal structure defined by a cross-sectional profile having a curved upper surface separated from a curved lower surface with opposing wall segments connecting the upper surface and the lower surface, as shown for example in
The ledge profile 103 is a longitudinal structure defined by a cross-sectional profile having a curved upper surface separated from a curved lower surface with opposing and parallel wall segments connecting the upper surface and the lower surface, as shown for example in
In some embodiments, as shown for example in
Alternatively, multiple longitudinal sections of a one-part cavity profile 102a can be connected via inserts 102e to cover the entire length of the shaft body 100, as shown in
In the configuration of
In the shafts of
A ledge profile 103 comprises therein the bladder 105, the bladder support 104, and the lug assembly 106. The bladder 105 can be made of any suitable material that is durable and flexible. When expanded by air or any other medium, the bladder 105 will radially push the lug assembly 106 outward through slots in the ledge profile 103 and outer tube 109 so that the lugs 108 can engage with the core on which web materials are wound. The ledge profile 103 may alternatively comprise other expandable elements other than a bladder 105, such as expandable hollow structures of various cross-sectional shapes such as circular, rectangular, or square.
An example of a lug assembly 106 is shown in
The bladder 105 rests on a bladder support 104. The bladder support 104 can be made of plastic or fiber composite materials, and can be made as a single-part bladder support 104 or a multi-part bladder support 114, as shown in
In a multi-part bladder support 114, each part 114a, 114b can be two to three inches in length. However, some applications may require a different length of each part 114a, 114b. The parts 114a, 114b are then connected to each other to the required length for the bladder support 114. For example, each part 114a, 114b can have holes 114c along two sides (
The lug support bar 107 of the lug assembly 106 is placed on top of the bladder 105. Each lug 108 is positioned in an individual slot along the length of the shaft body 100. When the bladder 105 is inflated, the lugs 108 move radially upward without any restriction to engage with the core. As shown for example in
To each end of the shaft body 100, a journal 115 can be connected, an example of which is shown in
The shaft body 100 of the winding shaft of the present application can be made using any type of fibers, including those listed in Table 1. The matrix resins can be of various thermosets such as epoxy, polyesters, phenolics, vinyl esters, bismaleimide and polyurethane, or thermoplastics such as polyamides, polypropylene, polyether ketone, polysulfone and polyphenyle sulfide.
Comparative properties of shafts with the following dimensions are listed in Table 2: Total length: 84 inches; Body length: 72 inches; Steel journal: 2 inches OD×6 inches length (each end); and Supports distance=77 inches.
Body designs for the aluminum extrusion with or without carbon inside can be found in U.S. Pat. No. 5,746,387, which is incorporated by reference in its entirety. Shaft bodies 100A and 100B represent the body designs of the present application. Both shaft bodies 100A and 100B can have designs as shown in
As used herein, directional or positional terms such as “front”, “rear”, “upper”, “lower”, “top”, “bottom”, etc., are used for explanatory purposes and are not limiting.
As can be seen, a shaft body 100A of the present application, if made with low modulus carbon fiber, can increase the first critical speed and specific modulus by 25 and 67% respectively, while reducing the weight by about 31%, compared to aluminum extrusion itself. Further increase of the first critical speed (by 75%) and specific modulus (by 417%) is expected, if the shaft is made with higher modulus carbon fiber (shaft body 100B). Compared to the carbon-aluminum hybrid design of the prior art, shaft body 100B of the present application is expected to reduce the weight by about 43% while increasing the specific modulus by about 67%.
A prototype shaft (shaft body 100A) of the present application was made, using low modulus (33 MSI) carbon fiber. Critical speed of the prototype shaft was determined using a balancing machine (CEMB, VibraSys, Inc.). The 1st critical speed was found to be 2373 rpm which is about 90.4% of the calculated value listed in Table 2. The test results were in good agreement with the calculated values.
In summary, the expandable shaft of the present application is a multi-bladder shaft with discontinuous expanding elements. The shaft body comprises two CF composite tubes and plurality of CF composite profiles securely placed between the tubes. Some of the profiles contain assemblies of various elements that are expanded with the help of air or other media.
Although the present application describes the system in reference to expandable winding shafts, it is noted that the shafts and shaft bodies described herein can be used in other shaft applications. For example, non-expandable shafts can be provided with the structures disclosed therein, include the tube and profile features shown and described herein, but no expanding elements.
While there have been shown and described and pointed out fundamental novel features of the invention as applied to embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice.
The present application claims the benefit of U.S. Provisional Patent Application No. 63/455,352 filed Mar. 29, 2023, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63455352 | Mar 2023 | US |
