Woven narrow fabrics can serve as structure or substrate for components in critical customer applications that require superior properties. End product designers and engineers should understand weaving technology and how it differs from other textile production so they can correctly select a textile construction method that ensures end item performance.
Weaving of narrow fabrics – the basics
Weaving is a method of creating a structural textile by interlacing fibers and yarns in a way that maximizes specific fiber properties. Weaving yarns are interlaced in a perpendicular manner, with both longitudinal yarns (x-direction), and horizontal yarns (y-direction). Known respectively as warp and weft or filling yarns, they are oriented at 90 degrees to each other.
Weaving produces a stable construction in both the x and y directions. In fact, of all the available methods used to create textile material, weaving provides the most stable and versatile construct. Key properties include high strength, elongation, energy absorption, optimum strength to weight ratios, flexibility, and sewability.
Narrow fabrics are generally divided into two types: webbing and tape. Webbing, narrow fabrics 12 inches wide or less, refers to fabric with a longitudinal strength equal to or greater than 1000 pounds per inch of width. Tape refers to narrow fabrics with a longitudinal strength of less than 1000 pounds per inch of width.
Both shuttle looms and needle looms are used to manufacture both structural webbing and tape. The needle loom is designed for speed and is the best option for large runs of production material. A shuttle loom enables more weave design versatility and provides structural, uniform, and woven edges that results in more even loading across the webbing’s width. This method is preferred for applications requiring maximum weave design flexibility. Flat woven, tubular material and 3-D fabrics can all be produced with perfect symmetry on both edges of the woven substrate. This provides uniform edge loading during, for example, high-speed deployment of parachutes.
Weave design options
Several weave designs are available to meet specific application requirements.
Plain weave is the simplest form of weaving. The filling/weft is inserted up and down every other warp yarn. Edge binding and reinforcement tapes utilize plain weave designs due to their need for high structural stability and minimum surface abrasion.
Twill weave involves passing the filling/weft yarn over or under two more warp yarns. It is generally softer and more pliable than a plain weave and has increased tensile and decreased elongation properties. Twill constructions are used to bind edges with complex curves and tight corners and for high strength applications that require maximum strength of the woven warp yarns.
Tubular weave joins two sets of warps yarns at the edges. When woven on a shuttle loom, the fabric created is completely seamless, resulting in a fabric with a uniform water porosity and air permeability property. Often designed into filtration and other medical device applications, tubular webbings are also utilized for their hoop strength in inflatable vessel constructions.Stuffer yarn constructions are those with a tubular weave to which astufferyarn and abinderyarn is added to multilayer woven fabrics to add strength. One example is industrial belting applications that use woven thermoplastic fibers around aramid stuffer yarns used for its high tensile properties. The method is also used in parachute harness webbing to improve webbing strength and stiffness. The binder yarns act as woven sewing type stitches that help to stabilize the weave and lock in the jacket fibers with the stuffer yarns.
Many variables affect the success of a specific webbing. Questions to consider during the design process include:
- What performance properties will be required in the final weave design?
- What is the stiffness requirement? How should it feel when held?
- What type of hardware will be required?
- What termination method will be used?
- Does the end-use application require specific consideration?
- For composite applications, what are the specific properties of different fibers required?
- Fiber size and strength
Weaving yarns are composed of bundles of individual filaments of a specified number. When these filaments have long continuous lengths, it gives the yarn optimum strength and tensile resistance.
All types of manmade fibers are specified for size. Comparisons are made among fibers by referring to their denier, which equals the mass in grams of 9000 meters of weaving yarn. For example, a 220 denier nylon is composed of a smaller bundle of continuous filament fibers and has less mass than a 440 denier nylon, so it is less strong. The strength to mass ratio is in direct proportion; for example, 440 denier nylon 6.6 has 2-times the strength as 220 denier nylon 6.6 from the same batch of fiber.
Fiber producers publish tenacity values that can be valuable for comparison purposes, but actual tensile strength yields of woven fabrics will be less than these published numbers. This is due to a concept known as translational strength, defined as a comparison of the properties of a fabric to that of the input base fiber. Due to many weaving process variables, translational tensile strength yields are typically 20-40 percent less than published fiber tensile strengths. It is critical to understand the many trade-offs needed to achieve performance characteristics and the relationship between variables and performance.