Applications of aramids

Aramid fibers are notorious for their application in bulletproof jackets, more generally addressed as ballistic resistant fabric articles. Less exciting applications of aramids are in automotive, electrical, and electronic fields. They are also used in medical devices. Specific uses are summarized in Table 13.3. 

To achieve this goal, two existing deep mining operations were considered for the application of aramid ropes. Management at these operations has provided the project team with the actual cost and production data as well as hoisting system configurations and parameters. Based on a mix of simulations and estimates, three case studies have been completed. The first two cases refer to mine A and the third case to mine B. This paper summarizes the results obtained from these case studies. 

In reinforcing materials double-dipped polyesters for improved tire durability, plasma-treated yams for improved bonding in tire, and increased usage of aramid fabric as belt and application of PEN are the areas where manufacturers are showing interest. Introduction of new styles of steel wire geometry for improved mbber to metal adhesion and new steel wire coating formulations for improved mbber to metal bonding are other focused areas of development. 

Aramid polymers are much more expensive than the aliphatic polyamides. The use of aramid polymers is limited to those applications that justify the high cost. The present... 

Perhaps the most widely utilized (and studied) lyotropic LCP is poly j -phenylene terephthalamide (PPTA), more commonly known as Kevlar (see Figure 1.70). Kevlar belongs to the class of aramids that are well known for their LCP properties. Because these polymers are crystalline in solution, they are often spun into filaments, from which the solvent is subsequently removed in order to retain the aligned polymer structure. The result is a highly oriented, strong filament that can be used for a wide variety of structural applications. Most thermotropic LCPs are polyesters or copolymers that can be melted and molded into strong, durable objects. 

Its strength and modulus are slightly lower than those of aramid fibers on a per-unit-weight basis, i.e. specific property values are about 30-40% higher than those of aramid. It should be pointed out that both polyethylene and aramid fibers, as is true of most organic fibers, must be limited to low temperature (less than 150°C) applications. 

Ropes, cables, coated fabrics for inflatables, architectural fabrics, and for ballistic protection fabrics. Ship to shore mooring lines are made of aramid fibers because of its resistance to saltwater corrosion. Vests made of Kevlar 29 are used by law enforcement agencies in many countries. Later we discuss this application in some detail. 

Wet layup consists of placing a layer of dry reinforcement inside a mold and then applying an uncured, low-viscosity thermoset resin as shown in Fig. 2. Woven glass fibers are the prevalent reinforcing preform utilized in layup processes, although carbon and aramid fibers are also used to a lesser extent. Typical fiber volume fraction of composites manufactured via wet layup range between 30% and 50%. The resin can be poured, sprayed, or brushed on top of the preform layer either by hand or by machine. The fiber preform layer is rolled on or pressed after the application of resin to evenly distribute the resin and remove air pockets. Resin is applied on top after each layer of fiber mats is properly placed. This process is repeated until the desired thickness is reached. To provide a smooth surface finish on the mold side, a thin layer of mold release is often applied prior to starting the layup. Thereafter, pressure and heat are applied to allow the composite to cure. Pressure can be applied... 

Table 4 compares the mechanical properties of various organic fibers, graphite/carbon fibers, ceramic fibers, and glass fibers, and lists commercially important applications. One major application of organic fibers, such as Spectra and aramid fibers, is in ballistic In contrast, graphite, ceramic fibers, and glass fibers are primarily used in structural applications. One of the reasons that organic fibers find little... 

For friction material applications, composite materials (qv) comprising glass or metallic fibers with other minerals have been developed. In such applications also, aramid and graphite fibers are effective, although the cost of these materials restricts their use to heavy duty or high technology applications (see Carbon fibers). 

Aramid polymers are much more expensive than the aliphatic polyamides. The use of aramid polymers is limited to those applications that justify the high cost. The present U.S. market is about 20 million pounds per year. The applications are those where one needs very high flame resistance (clothing for firefighters and welders, welder s protective shield, upholstery and drapes), heat resistance (ironing board covers, insulation film for electrical motors and transformers, aerospace and military), dimensional stability (fire hose, V- and conveyor belts), or strength and modulus (circuit boards, bulletproof vests, fiber optic and power lines, ship mooring ropes, automobile tire cord, puncture-resistant bicycle tires). 

Hydrophobically finished aramid fabric can be produced by a water-repellent agent. In addition, the application of an antistatic agent is advantageous. The water repellant agent is a mixture of fluoroacrylate pol5miers. 

Techniques for production of 3-D structures of high tenacity aramid fiber have also been developed, offering excellent fatigue resistance to abrasion, flexure, and stretching. One such system is on a wire frame basis, with mechanized frame building, and it is proposed as reinforcement for concrete pillars and other structures. As well as the strength of the fiber, this application exploits the high chemical resistance of aramid to acids, alkalis, and cement. 

Carbon/Aramid Fiber Sheet Jacketing Method. The application of carbon/aramid fiber sheet for the reinforcement of concrete pier is adopted when restricted conditions are present on site, such as no permit of sectional increase due to clearance limit or weight increase on the foundation. The sheet in longitudinal direction is effective to increase the flexural strength and the sheet in transverse direction acts as lateral reinforcement to raise the shear strength. Particularly the fiber sheet is concentrically bonded at the termination of longitudinal rebar at the mid-height. 

The broad range of properties of aramids is the main reason for their utility in diverse applications. Here we will attempt to illustrate how previously described properties of these fibers are exploited in their applications. 

Mechanical rubber goods include hoses, power transmission (PT) belts, and conveyor belts. Aramids compete with nylon, polyester, glass, and steel in these applications. Steel dominates the rubber hydraulic hose market and polyester is the reinforcement of choice in lower pressure thermoplastic hoses. Advantages of aramid vs. other textiles in hose applications include higher strength, which can lead to constructions with fewer plies and less weight, and better thermal stability, dimensional stability, and chemical resistance. When compared with steel, aramid will not corrode and can be fabricated into lower weight, more flexible hoses. 

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