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Ralph Hays and Dick Holden Introduction High-performance conduit systems may be specified for virtually every application environment: from the interconnection of laboratory test equipment to hostile environments involving above-deck shipboard use, vehicular and heavy machinery, as well as airborne and submarine applications. Appropriate wire protection solutions may also be designed to address virtually every physical, environmental and electromagnetic protection requirement. Because the range of performance requirements is so broad in high-reliability application environments, the industry has come to rely on an equally broad range of wire enclosure products: from plastic convoluted tubing to various forms of metal-core conduit, braided shields, jacketing and fittings. High-performance conduit systems provide compatibility with virtually every type of electrical connector and interconnect system, and can be supplied completely wired or as component elements. Understanding the performance properties of the materials which go into these products is the key to selecting the best system for each application. This white paper presents a complete overview of one of the most important materials used in the manufacture of high-performance protective wire enclosures: plastic. Performance Requirements The first step in conduit system design is to identify the critical performance requirements of the wire enclosure. Or in other words, to determine what exactly the conduit system is supposed to do. For general duty applications these requirements might range from protecting the wires and terminations from moisture to preventing physical damage due to rough handling. In high-performance settings, additional requirements such as protection from electromagnetic interference, extreme temperatures and radiation are commonly considered. In harsh environmental conditions, the ability of chosen materials to resist damage from hydraulic fluids, fuels, lubricating oils, solvents and decontaminating agents comes into play. From Monomers to Polymers
The various plastic materials used in the manufacture of the tubing are referred to as polymers. Polymers are carbon based compounds built up from a series of smaller units, or monomers. Which monomers are used, how they are joined together (rings, strings, etc.) and the overall molecular weight of the compound are the three variables which determine the mechanical and physical properties of the resultant material. Polyetheretherketone (PEEK), for example, consists of ether, ketone and phenyl monomers. The ability to form PEEK into specific shapes using heat is a property provided by the ether groups. PEEK's high temperature tolerance and excellent mechanical strength are due to the structure of the ketone and phenyl groups. Every one of the plastic polymers used in the fabrication of convoluted tubing has unique properties due to its distinctive molecular make-up. The following summaries provide an overview of material properties for all of the commercial polymers used in Glenair's line of plastic convoluted tubing: Kynar- Kynar is the trade name for polyvinylidene, an opaque black, thermally stable material used in the standard manufacture of annular plastic tubing. It is highly resistant to UV light and gamma radiation. KynarŽ is extremely resistant to oxidizing agents and halogens and is almost completely resistant to allphatic, aromatics, alcohols, acids and chlorinated solvents. Kynar is mechanically strong, abrasion resistant and features high dielectric strength. Kynar is also thermally stable, resistant to low temperatures, self-extinguishing and nontoxic.
PTFE- Polytetrafluroethylene, one of the more expensive polymer tubings, provides one of the highest temperature ratings available in an exotic plastic (260°C). PTFE is inert to virtually all chemicals and insoluble in all solvents below 300°C. PTFE is considered the most slippery material in existence and has very low friction and adhesiveness coefficients. PTFE's moisture retention is less than 0.01% and it has an infinite shelf life. The material also has very good electrical (high resistance) and dielectrical (very low dielectric number and loss factor) properties.
ETFE- Also known by the trade name TefzelŽ, ethylene tetraflouroethlene provides the highest tensile strength and lubricity available. It is produced in opaque black and transparent clear. ETFE resin is a meltcut thermoplastic which combines mechanical toughness with outstanding chemical, dielectric and thermal properties. Its other main features include ease of processing, a lower density than TeflonŽ and improved radiation resistance. ETFE is suitable for continuous exposure at a maximum service temperature of 155°C. PFA and FEP- Perfluoralkoxy (PFA), and fluorinated ethylene propylene (FEP) are two of the lower cost materials to provide relatively high thermal stability. These TeflonŽ copolymers provide continuous service temperatures up to 260°C for PFA and 205°C for FEP. Both have excellent dielectric properties and are unaffected by virtually all solvents and chemicals. As with PTFE, they also have excellent low temperature toughness and good resistance to adhesion. PEEK- Polyetheretherketone is halogen free, extremely light weight and crush resistant. PEEK is semi-crystalline, with both crystalline and amorphous regions. The material is very tough under an extreme range of conditions. Melting occurs at about 340° C, continuous use is rated at 250° C, with short-term excursions to 300° C (572° F). PEEK far outperforms other plastics in this regard, and has a V-O flammability rating down to 0.057 inches without the use of additives. The mechanical and high temperature properties of this material make processing and manufacturing of PEEK tubing more costly than other polymers. PEEK combines strength, toughness, chemical resistance, purity, lubricity/wear resistance, and USP Class VI biocompatibility. This material maintains its properties under sustained pressure, elevated temperature, water, steam, and most chemical environments. Gamma Processed ETFE - Ethylene tetrafluoroethylene provides a durable, highly flexible protective enclosure for wiring systems used in harsh application environments. The material provides exceptional flexibility in cable routing and electrical system architecture and has a higher operating temperature range than non-processed ETFE of -55° C to 200° C. The tubing also withstands temperature excursions to 300° C and is both crush resistant and cut resistant at elevated temperatures. The irradiated material provides outstanding resistance to hydraulic fluids, fuels, lubricating oils, solvents, and decontaminating agents. Application Notes As you can see from the summaries and also from Table 1 (next page), each material has certain advantages over the rest, but there is also a great deal of overlap in terms of the most basic physical properties. In fact, some of the performance measures are so close that final selection is usually based on other factors such as ease of manufacture, price, color and so on. Two of DuPont's most popular materials, TelflonŽ PFA and TeflonŽ PTFE, for example, are so close in most major performance areas that selection has little to do with differences in performance. Both materials show outstanding chemical properties for resistance to corrosive agents, nonsolubility, and nonflammability. Both are virtually identical in terms of their electrical properties for dielectric and volume resistivity. Even in critical service temperature ratings, both materials have identical properties. In fact, it is only in three areas, cold flow, folding endurance and cost that these virtually identical fluoropolymer resins differ significantly. Because PFA is melt extruded, it exhibits better cold flow values than PTFE, which translates to better long-term sealing and reduced loosening of fittings. PTFE, on the other hand, exhibits better folding endurance than PFA, but at 500,000 bends before failure, PFA is well within the operational tolerances of most applications. In terms of cost, PFA convoluted tubing is typically the better performer, as the melt extruded product is less costly to fabricate and can be produced in any length, effectively eliminating the scrap associated with PTFE.
Braiding materials used at Glenair include bare copper, tin-plated copper-covered steel, copper plated with tin, nickel or silver, bronze, stainless steel, copper-covered steel, aluminum, nylon, DacronŽ, NomexŽ, KevlarŽ, monofilament PEEK, TeflonŽ, RytonŽ, HalarŽ, and polyester. Glenair's newest addition to our braid products is the extremely light weight AraconŽ braid for EMI/RFI shielding applications. For special applications, other materials may be selected.
 Glenair's metal braid is offered in tubular and flat configurations in a variety of sizes ranging from 1/32 inch (0.8 mm) to 2 1/2 inches (63.5 mm). Glenair's tubular metal braid is manufactured to afford excellent flexibility for a variety of EMI shielding applications. Its flexibility allows the braid to easily be slipped over convoluted tubing, or to be used directly with wire bundles or cables. Glenair's standard tubular braid is constructed of 34 or 36 AWG copper stranding and is available in bare copper, or plated with tin, nickel, or silver. Glenair's flat metal braid is produced from tin-plated copper and rolled flat. This highly conductive flat braid construction provides excellent flexibility and is recommended for bonding and grounding applications. Typical applications include bonding strips in vehicles and aircraft to assist in eliminating ignition interference.
Glossary of Performance Terms
Brittle Temperature: The temperature below which a material becomes brittle as measured by cold impact tests.
Standard Materials Configurations Glenair's wide selection of tubing, braided metal coverings and jackets may be combined to meet virtually any electromagnetic shielding requirement from H and E field shielding to Tempest, EMP and lightning. The two tables below define standard combinations of tubings, coverings, internal and external shielding for Glenair's Series 72 Annular Convoluted Tubing and Series 74 Helical Convoluted Tubing. Other combinations, including stainless steel reinforcement support wire may be specified to match material properties to the environment and the intended use of the system. Glenair's engineering staff can provide assistance in selecting the right combination of component elements for virtually any high-performance application, including solutions for:
  About Glenair: Glenair has been the leading manufacturer and supplier of commercial and Mil-Spec connector accessories since 1956. Building on that foundation, the company offers a dozen, full-spectrum product lines designed to meet every interconnect requirement. From hermetic connectors to fiber optics, from conduit systems to Micro-D assemblies, from composite enclosures to assembly tooling. And throughout the years, we've made outstanding customer service our approach to maintaining our position as the industry's best-value interconnect supplier:
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Glenair's plastic convoluted tubing is available in the widest range of materials and constructions in the industry - the right weight, duty, and protection level for every application. Glenair's Series 74 (helical) convoluted tubing, for example, is available in PTFE, TefzelŽ (regular and irradiated), PFA, FEP, KynarŽ and PEEK. The tubing is fabricated in annular, helical, close convolutions, thin wall, dual wall and reinforced versions and can be supplied in random lengths (Glenair standard packaging) as well as specific lengths or spools.
In most wire protection applications, the appropriate choice of plastic tubing is combined with various braids and jackets to meet the application's exact electromagnetic radiation, electromagnetic pulse or advanced weather-proofing requirements. Glenair offers both its Series 72 Annular Convoluted Tubing and Series 74 Helical Tubing unshielded or in a standard range of shielded configurations to meet the most common environmental requirements (see Tables 2 and 3).
Glenair's in-house braiding production capacity includes more than 50 braiders, ranging from 16 to 96 carriers, and provides the capability to produce large quantities of precise metal and nonmetallic braid and expandable sleeving in tubular, tapered, and flat configurations - in virtually any material and length necessary to suit customer requirements.