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Spacer considerations

Fabric Basics | July 1, 2001 | By:

Manufactured in a wide range of forms, 3-D fabrics can be used for construction, soil retention or acoustic attenuation

Think of spacer fabric (also called 3-D fabric) as a sandwich, featuring two complementary slabs of fabric with a third layer tucked in between. The inner layer can take a variety of shapes, including tubes, pleats or other engineered forms (think egg salad, smoked turkey or peanut butter and jelly), which gives the entire three-layer fabric a wide and ever-expanding range of potential applications.

For example, some spacer fabrics are designed to be compressible; these are used in the inner soles of athletic shoes and the shoulder straps of backpacks. Other spacers are designed to be filled: with air (for inflatables), with sand (to surround buried gas tanks), or with concrete (to serve as part of a composite building structure).

These internal spacer spaces also can be designed to trap sound, which, when combined with surface yarns of certain densities and a middle, or “spacer” yarn, can give the spacer fabric acoustic-insulation properties. Spacer fabrics’ internal architecture can provide water and air filtration, as well. For example, the Huckaback textile from SI Corp., Gainesville, Ga., is composed of electrically charged polypropylene that’s layered on the bias to maximize the surface area, to which dust can adhere.

Add the various engineered properties of the face fabrics—water repellence or Velcro® compatibility, to name a few—to those of the internal architecture, and you start to get a better idea of spacer fabrics’ almost limitless potential.

Making spacers

Spacer fabrics can be made via two methods—warp knitted by the Raschel process or woven.

For woven spacer fabric, two to three spools of yarn are needed to produce a flat fabric that is subsequently heat-treated. Since one of the yarns used in this process is a “shrinker” yarn, it contracts when heated, producing the fabric’s characteristic architecture. The thicker or more intricate the architecture of the 3-D fabric, the more shrinker yarn is needed to make it. Synthetic Industries, for example, uses polyethylene shrinker yarns with polypropylene face yarns that give the material rigidity and height, says the company’s sales manager, Kevin Jung. Different manufacturers employ other fibers. Gehring Textiles Inc., New York City, knits its MSHR735 textile in one sequence with Kevlar® faces for impact resistance, with a 6.25-mm (.25-in.) middle layer that contributes additional resistance. These features enable the fabric to withstand sudden thrusts. In contrast, Gehring designed its spacer fabric MSHR730F to be highly compressible in order to withstand ongoing pressure. Gehring renders this monofilament polyester fabric more compressible by adding thickness to the middle layer (8.75 mm/.35 in.).

According to a company spokesperson, woven spacer fabrics offer greater dimensional stability than do those of the knitted variety. She adds that because it takes less yarn to make woven spacer fabrics than knitted fabric of equal compressibility, woven spacer fabrics generally are lighter and less costly to make than knitted spacers.

George Christmann, Gehring’s vice president of corporate development, says that there are upsides to Raschel-knit spacer fabrics, too. Most notably, he says, knitted spacers won’t run or ravel like their woven counterparts. However, SI Corp.’s Anderson says that raveling is controlled by cutting the fabric with machines that simultaneously heat-seal the freshly cut edges. Spacer fabrics can be seamed or sealed in a variety of ways, depending upon the fabric’s composition, thickness and end use. Methods include impulse-sealing, ultrasonic sealing, hot-air sealing, and radio- frequency (RF) sealing. Gehring’s Christmann notes that RF welding becomes a more appropriate choice as fabric increases in thickness and decreases in compressibility.

Outdoor spacers

Tek-Knit Industries, Montreal, Quebec, Canada, is another producer of spacer fabric. According to Tek-Knit’s Harry Glanz, the Raschel-knit monofilament polyethylene produced by his firm is a “sturdy fabric” that requires “no special handling” in cutting or seaming.

Tek-Knit’s polyethylene spacer fabric provides vertical filtration for construction applications. For example, when placed against a building, Tek-Knit’s fabric allows water to drain into the sub-grade. In a related application by McGill University professor emeritus Robert Broughton, a surface inlet for a subsurface drain pipe was double-wrapped with Tek-Knit’s R-2090 double-needle spacer fabric, which extended approximately 600mm(2 ft.) below ground. By using spacer fabric for this application, Broughton accomplished several goals—increased the inlet’s surface area, prevented debris from entering the pipe, and improved subsurface seepage—for less than it would cost to employ the more traditional method of backfilling with gravel and sand.

Another outdoor application for spacer fabric is provided by SI Corp.’s Pyramat®, woven of UV-stabilized monofilament polypropylene. Pyramat holds soil in place while vegetation grows through the fabric, and thus becomes a “permanent part of a permanent solution to erosion” in such places as landfill caps and storm water runoff channels, according to Lee Pierce, the company’s North American sales manager for erosion products. Pierce notes that Pyramat’s role in managing storm water dramatically reduces the amount of sediment in municipal water supplies, enabling cities to meet federal clean water guidelines.

Where the spacers are

3-D fabrics are available in a variety of fibers, compositions, widths and thicknesses, and they can be made fire retardant. Gehring offers stock knitted spacer fabric in thicknesses from 1.5 to 15mm (.06 to .6 in.) and widths up to 1.52 m (60 in.), with in-stock fabric available in minimum orders of 183 to 274 m (200 to 300 yds.). Custom widths are available (in 2,000-yd-minimum quantities) up to 2.02m (80in.).

SI Corp.’s woven 3-D fabrics are made from polypropylene and polyethylene, and are available in stock widths of 1.5 and 1.9m(60 and 76 in.), and in stock thicknesses of 3.1 to 12.5mm (1/8 to 1/2in.). Developmental orders are available in custom widths and thicknesses. While the minimum custom order is approximately 457m (500yds), the minimum order for a stock fabric is one roll, which can be 32 to 46m (35 to 50 yds.), depending upon the fabric’s thickness.

Tek-Knit currently produces one type of spacer fabric: a knitted polyethylene approximately 6 to 7 mm (.25 in.) thick, which can be custom-altered to be as thin as 3mm (.125 in.) thick and 3.75m (.150 in. wide). A minimum order of this fabric is 914m (1,000 yds).

Several sources offer machines capable of cutting woven spacer fabric. Branson Ultrasonics, Danbury, Conn., sells machines that ultrasonically cut and seam in one operation. Miller Weldmaster Corp., Navarre, Ohio, manufactures, sells and leases custom and standard machines that use heat, speed and pressure to cut and seam in one operation using the rotary hot-air-sealing method. Rosenthal Mfg. Co. Inc., Northbrook, Ill., leases and sells machines that use heat and air pressure to cut longitudinally while simultaneously fusing the edge of fabric, as well as machines that use a heated wire to transversely cut polyethylene and polypropylene.

Janet Cass is a Twin Cities-based contributing editor for Fabric Architecture.

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