What is braid? Why is braid unique? Which materials are used to make braid? What is a "hybrid braid?" What are some common braid uses? What are current braid capabilities? What advantages are there in using braid to make composites? Which composite manufacturing processes use braid? What is "overbraiding?" What are some common braid forms? What are some common braid architectures? Is braid cost effective?

Why is braid unique?

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Braided fiber architecture resembles a hybrid of filament winding and weaving. Like filament winding, tubular braid features seamless fiber continuity from end to end of a part. Like woven materials, braided fibers are mechanically interlocked with one another. The combination, however, is quite extraordinary. When functioning as a composite reinforcement, braid exhibits remarkable properties because it is highly efficient in distributing loads. Because all the fibers within a braided structure are continuous and mechanically locked, braid has a natural mechanism that evenly distributes load throughout the structure. With regard to strength and stiffness, properly molded biaxial braided composites exhibit properties that are essentially identical to unidirectional tape laminates of the same orientation and fiber volume. Because of the load distributing feature inherent in braided reinforcement, there is no knock down due to fiber crimp. This phenomenon is limited to triaxial constructions that have significant fiber volume in the axial direction. The laid in axial yarns force added crimp in the bias yarns, causing the biases to lose in-plane properties. The axial fibers also tend to inhibit the distribution of loads within the laminate, yielding lower breaking strength. However, triaxial constructions are very cost effective in a myriad of applications because the automated formation of complex net shape preforms frequently affords more savings than the additional cost associated with the fiber needed to meet design loads. When used with biaxial braid, A&P Technology's patented UnimaxTM sleeving overcomes this property loss problem while maintaining all the ease of manufacturing cost advantages of braid in triaxial preforms. Braid's efficient distribution of loads also make braided structures very impact resistant. Since all the fibers in the structure are involved in a loading event, braid absorbs a great deal of energy as it fails. This is why braid is used as fan blade containment in commercial aircraft and in energy absorbing crash structures in formula one racing cars. Braided structures are also excellent with regard to fatigue. Like a filament wound structure, braided fibers are coiled into a helix just like wire in a spring. The difference, however, is the mechanical interlocking. As a structure is exposed to high fatigue cycles, cracks will propagate through the matrix of filament wound or unidirectional prepreg laid-up structures. While micro-cracking will occur in a braided structure, the propagation is arrested at the intersections of the reinforcing yarns. This is why braid is the reinforcement choice for aircraft propellers and stator vanes in jet engines. Braid greatly improves interlaminar shear properties when nested together with other braids. While interlaminar adhesion is no different from other reinforcement products, the layers move together. As a result, it is very rare for cracks to form and propagate between layers of braided reinforcement. Since braids are woven on the bias, they provide very efficient reinforcement for parts that are subjected to torsional loads. Braid is an ideal reinforcement for drive shafts and other torque transfer components such as flanged hubs.

Which materials are used to make braid?	Back to Top
Virtually any fiber with a reasonable degree of flexibility and surface lubricity can be economically braided. Typical fibers include: Aramid Carbon Ceramics Fiberglass Natural Fibers Synthetic Fibers Thermoplastics

What is a "hybrid braid?"

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Hybrid braid is formed using different raw materials to tailor the ultimate properties and optimize the reinforcement costs. Hybrids can also be made using different yarns to create aesthetically pleasing patterns within the fabric that compliments braid's naturally attractive symmetry. In addition to utilizing a wide array of raw materials, braid can be made in a virtually infinite variety of diameters or widths, fiber angles and areal weights. However, each of these parameters are interdependent so certain combinations of product characteristics are sometimes impractical or impossible.

What are some common braid uses?

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Braid is currently the reinforcement of choice in components that serve a wide variety of market applications utilizing an exhaustive list of composite processing techniques. Examples include: Aerospace - braid is used in aerospace applications like aircraft engine containment, aircraft propeller blades, missile nose cones and bodies, self-lubricating bearings, control surfaces, aircraft engine stator vanes, aircraft ducting and tubing and satellite components. Industrial - braid is the primary, load bearing reinforcement in automobile cross beams, automobile air bags and restraint devices, commercial furniture, industrial rollers, lamp and utility poles. It is a partial reinforcement in structures like shipping containers and boat hulls. Medical - braid is being used extensively for prosthetic limbs and orthotic braces, surgical devices like endoscopes and catheters and implantable devices such as splints and stents. Recreational - recreational equipment utilizing braided reinforcement include wind surfing masts, snow boards, water skis, snow skis, wake boards, sail masts, boat hulls, hockey sticks, golf shafts, bicycle components, baseball bats, tennis and other racquets, and kayak and canoe paddles.

What are current braid capabilities?

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Current capabilities in braiding include freestanding biaxial and triaxial sleevings from .05" to 48" in diameter. Biaxial and triaxial flat tapes can be made up to 36" wide and braided slit fabrics (broad goods) can be produced up to 8' wide depending on fiber architecture and raw material input. Braid angles for sleevings and tapes can range from approximately 15° to 75°. By overbraiding, angles closer to 90° can be achieved and true 90° hoop wraps can be added with winding equipment fully integrated with the braid process. Areal weights can range from .5 to 200 ounces per square yard. Overbraiding can be done on objects up to 8' in diameter and 15' in length. Our business is all about expanding the envelope on braided products. If your requirements do not fall into our current capabilities, we would appreciate the opportunity to discuss your requirements.

What advantages are there in using braid to make composites?

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Braid is commonly used in composites simply because it enables lower finished composite costs. Braided reinforcements present composite fabricators a variety of opportunities to be more cost effective because of its unique combination of attributes. The vast majority of fabricators realize substantial savings in lay-up cost. Because of its "Chinese finger trap" feature, biaxial braid easily and repeatably expands open to fit over molding tools or cores, accommodating straight, uniform cross-section forms as well as non-linear, irregular cross section components. Braid is, in essence, a near net-shape preform. Just as socks rolled up in a drawer do not look like feet, braids shipped on reels or festooned in cartons do not look like net shape preforms. However, just like pulling socks on your feet, braids slip onto tools and cores with speed, ease, and a high degree of repeatability.

Which composite manufacturing processes use braid?	Back to Top
Composite processes using braided materials include the following: Autoclave Compression Molding Resin Transfer Molding Reaction Injection Molding Open Molding Pultrusion VARTM

What is "overbraiding?"

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Braid can be manufactured directly onto a molding tool or core. This allows for an automated lay-up of multiple plys as well as greater flexibility as to braid angle compared to approaches utilizing free-standing braid. Overbraiding is commonly used for complex or large shapes where lay-up of freestanding sleeving would be impractical. As with tailored sleevings, overbraiding can achieve constant thickness or constant angles on part with a complex shape.

What are some common braid forms?

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There four main braid forms include: Sleevings - the bias weaving process produces two sets of continuous yarns, one clockwise and the other counterclockwise, where each fiber from one set is interwoven with every fiber from the other set in a continuous spiral pattern. Flat Braids - there is only one set of yarns, where each yarn in the set is interwoven with every other yarn in the set in a zig-zag pattern from edge to edge of the fabric. Wide Braided Fabrics (a.k.a. Braided Broadgoods) - A&P Technology's large braiding machinery allows for the production of sleevings in excess of six inches that can be slit open to create a line of wide braided fabrics. These fabrics can be produced with a biaxial architecture such as +45°, -45° or a triaxial architecture, such as 0°, +45°, -45° or 0°, +60°, -60° within one layer. A&P Tech's ability to provide a quasi-isotropic architecture within a single layer of fabric eliminates quality problems associated with the current lay-up of woven fabric that requires a layering of multiple fabrics. Furthermore, the propensity for delamination is reduced dramatically with quasi-isotropic braided fabric. Since a 0°, +60°, -60° architecture guarantees that a fabric has the same mechanical properties in every direction, the possibility for a mismatch in stiffness between layers is eliminated. Overbraids - Although freestanding preforms commonly meet all requirements of a composite design due to the predictability of braid's behavior, some specific cases require a process called overbraiding which consists of braiding fibers directly onto cores or tools that will be placed within molding processes. This is often used when the preform design calls for very high bias angles, contoured triaxial design, or when it is desirable to include circumferential windings in the preform architecture.

What are some common braid architectures?

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Each of the four main braid forms is available in one of four main braid architectures. They include: Biaxial - the biaxial form is the most common form of braid and is often chosen by composite manufacturers since it allows for predictable, consistent lay-up and conforms to any shape. This typical braid construction is most often a basket weave with two yarns crossing over and under each other. Braids are commonly defined as a ± 45° orientation, but are often used at lower angles. When this sleeving is pulled over a mandrel with changing cross-sections the fiber orientation, the thickness, and the yield of the braid vary at each point along the mandrel. These variations are predictable and repeatable and, therefore lend themselves to easy and precise manufacture of composite parts (see Braid Calculator). Triaxial - the triaxial form involves adding a third set of yarns in the axial direction. This multi-directional braid achieves unidirectional and off-axis reinforcement within one layer. The introduction of the third set of axial yarns in a sleeving locks the diameter and stops the braid's natural tendency to expand and contract. Tailored - a tailored braid is desirable when a constant thickness or a constant angle is required in a reinforcement. A constant thickness or constant angle within discreet lengths of sleeving is achieved by programming A&P Tech braiding machinery to vary fiber orientation on the fly. The manufacture of tailored sleeving is a low cost method used for many closed molding processes. UnimaxTM - in order to provide a solution to the limitation of conformability within a triaxial construction, A&P Technology created a unidirectional sleeving called UnimaxTM that can be used in conjunction with biaxial sleeving in order to create a triaxial design. UnimaxTM is composed of small elastic bias yarns with all of the reinforcing fibers in the axial direction. The small elastic bias yarns in UnimaxTM allow for the even distribution of the axial fibers over changing cross-sections.

Is braid cost effective?

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Compared to other reinforcements, braid is cost competitive and is often identified as the least expensive once an overall cost analysis is performed. There are three main factors that contribute to braid's competitive price -- advancements in technology, braid's conformability, and the predictability of braid's architecture. In particular, braid's unique architecture, best understood as a "Chinese finger trap," offers natural conformability. This quality makes braid the ideal preform since it takes on the exact shape of the part that it is reinforcing. Therefore, cutting, stitching, or manipulation of fiber placement is not needed, as in the use of woven fabric. Not only does this allow for consistent repeatability and scrap reduction, the use of braided reinforcements reduces the labor hours necessary for manufacturing. Each of these factors contribute to the cost effectiveness of braid. Overall, braiding process technology has become dramatically less expensive due to recent advances in braiding machinery and advances in braid architecture have yielded new cost effective reinforcement options.