Marine Applications for A.E.I. Products and Technologies

Interconnect Product Showcase

Lloyd Murray

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A Harsh Environment for Electrical Interconnect Systems

The commercial and military aerospace industry is a harsh testing ground for electrical systems. Airborne electronics require faultless performance in environments where even minor failures can result in loss of life and property. Aerospace standards for the manufacture and supply of electrical and optical componentry are some of the most rigid found in any industry, and for good reason: aircraft electrical systems are subjected to extremely harsh environmental conditions which include destructive extremes in vibration, shock, temperature, pressure, water/chemical emersion, as well as electromagnetic and radio frequency interference. It should come as no surprise that the world's major aerospace manufacturers conduct aggressive ongoing research on new designs and materials which can deliver stronger, lighter and more durable component parts for their airborne avionic systems.

No where is the research more active than in the portion of the aerospace industry responsible for the interconnection of electronic systems. The designers and manufacturers of electrical and optical cabling, conduit, connectors, connector accessories (backshells), braided shielding and other "interconnect" components are at the forefront of the innovative use of such materials as composite thermoplastics, titanium, and optical fiber to extend the life and reduce the weight of aircraft avionics. In many cases, their challenges are identical to those faced by their counterparts in ship and boat design, especially those designing for high performance commercial and naval applications such as fast ferries or submarines. These design challenges include:

Commercial-off-the-Shelf

While much of the innovation taking place in the aerospace interconnect industry has occurred as a result of military and proprietary commercial programs, the overall trend in the last three years has been in the development of Commercial-off-the-Shelf (COTS) componentry. Aircraft manufacturers are increasingly insisting that certain classes of components be "standardized" in terms of form, fit and function, and be stocked in standing inventories to provide faster turn-around (and lower costs) for new production, retrofit and repair activities. The improved availability of these aerospace calibre components is serving a growing number of ship designers and builders who are incorporating these technologies for marine use.

Geo-Marine® Connectors and Cable

As this "cross-over" market matures, more aerospace vendors and suppliers are optimizing their product offerings for use in marine applications. One such company is Glenair, Inc. which began operations in 1956 as the first company specifically founded to produce connector accessories for the aerospace industry. Headquartered in Glendale, California USA, Glenair has already enjoyed considerable success in the marine marketplace with its Geo-Marine® harsh environment connectors and cable assemblies used in oil and gas drilling, seabed exploration and pipeline inspection systems. Using materials such as nickel aluminum bronze and stainless steel, and insulators made from glass and thermoplastic, these connectors are designed to withstand hydrostatic pressures up to 5,000 PSI and exposure to temperature extremes and corrosive chemicals. Glenair is at the forefront of innovations in a number of other areas of interest to the marine industry, including the following:

Weight Savings and Corrosion Protection

Composite Thermoplastics

Perhaps no other single area carries such potential for technology "cross-over" between space and sea as composite thermoplastics. Newly popular in both the aerospace and marine industries, the weight savings and corrosion protection provided by composites have already led to many radical changes in ship design and construction in both environments.

In the electrical interconnect industry, electrical connectors and accessories, ranging from simple wire bundle strain reliefs, circular and rectangular backshells, dummy stowage receptacles and protective covers, to more advanced devices for electromagnetic shielding, are conventionally constructed from brass, nickel aluminum bronze, aluminum, stainless steel, and more recently, from titanium. This complete range of products is now evolving to include composite thermoplastics as a major alternative material.

New uses for composite materials, such as for cable junction boxes, connectors, connector backshells, conduit junctions and transitions are being developed almost daily. Tom Young, Glenair's senior composite product engineer heads up the company's research and development into composite component design, manufacturing, and plating. Mr. Young explains that "the thermoplastic resins used in composite component manufacture are divided into two basic groups, amorphous and semi-crystalline. Amorphous resins such as PPA (trade name Amodel) and PEI (Ultem) are generally easy to mold into tubular shapes and have a good "knit" or weld line strength coefficient. Amorphous resins, which can be reinforced with glass, mineral and carbon fibers, have good dimensional stability and exhibit even mold shrinkage with low stress. Semi-crystalline resins such as PPS (Ryton), PAI (Torlon), PEEK (polyetheretherketone) and LCP (Zydar/Vectra) are relatively more difficult to mold, but accept reinforcement fibers more readily than amorphous resins and exhibit greater resistance to chemicals.

While each material has its own specific structural properties, the starting point in materials selection is generally either the temperature range of the target application or the specification of conductive versus non-conductive fillers and platings to address both electromagnetic and radio frequency shielding requirements as well as required electrical performance characteristics."

Composite Connector Accessories

One of the most appealing attributes of composites is their enhanced corrosion protection (as compared to metal), when used in exposed environments such as above-deck ship board applications. This is because conventional metal interconnect components are extremely susceptible to corrosion due to galvanic coupling. In short, galvanic coupling causes the less nobel metals, such as aluminum, to become "sacrificed" to their nobel metal platings when exposed to an electrolyte, such as salt spray. In aluminum interconnect components, for example, the primary cause of corrosion is due to galvanic coupling with the cadmium/nickel plating that provides wear resistance and improved permeability and conductivity. The essential difference between thermoplastic and aluminum in this scenario is that high-temperature plastic is not sacrificial to plating.

Composit Junction Boxes

Next to their anti-corrosive capabilities, composites are increasingly being specified in interconnect systems as a weight reduction measure. The typical weight savings for composites over aluminum is approximately 40% (depending on component design), which translates to direct savings in the targeted application as well as potential additional weight savings in supporting structures. Weight savings versus other materials are even more pronounced: 60% for titanium, 80% for stainless steel, and 80% for brass. Component design is a critical factor in weight reduction efforts, as established part configurations and dimensions must be accommodated while providing for strength differences over metal materials. But given the potential benefits in improved durability and reduced weight, the additional design and engineering required to transition to composites is easily justified.

Exotic Material Conduit Systems

Plastic convoluted tubing, used throughout both ships and planes as a durable, light weight enclosure for wiring systems, is also a target for considerable research and development in the interconnect industry. Ongoing improvements in the protective capabilities of conduit systems, and significant weight reductions for both plastic conduit as well as metal-core conduit systems have been accomplished through extensive experimentation with manufacturing processes, wall thicknesses, and hybrid metal-plastic materials configurations.

Ralph Hays, Glenair's Conduit Business Unit Director, summarizes the principal challenge of designing conduit systems as "ensuring a high degree of physical, environmental and radiation protection while still meeting the customer's requirements for weight savings, ease of assembly and maintainability." He further states that the art of conduit system design is "to exactly match material selections for tubing, braiding, jacketing and fittings with the intended application."

Plastic Convoluted Tubing Systems:
Two basic tubing construction types, "Annular" (ring) and "Helical" (spiral) are commercially available in shielded and jacketed configurations to address a range of electromagnetic and environmental protection requirements. User and factory installable adapters, equipped with Glenair's unique style of coupling nut captivation, are available to accommodate both circular and rectangular connectors. Bulkhead fittings, adapters, feed-throughs and transitions provide flexibility in cable routing and electrical system architecture. These individual component elements are generally specified as part of the complete interconnect system design, as accessory component selection can directly affect final electromagnetic shielding values, as well as ease of assembly and maintenance.

Convoluted Tubing Materials

Convoluted tubing is constructed from a wide range of materials including PTFE, Tefzel, PFA, FEP, Kynar and PEEK and is available in a range of standard diameters and wall thicknesses. Braided shielding is available in tin plated copper, nickel plated copper and tin plated iron/copper (SnCuFe). Protective coverings, such as black dacron and jacketings made from Neoprene (Polychloroprene) and Hypalon (Chlorosulfonated polyethylene) provide additional mechanical and environmental protection.

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 gamma radiation.

PTFE - Polytetrafluroethylene is stable up to 260°C, and is available in opaque black and transparent clear. One of the more expensive materials, it provides one of the highest temperature ratings available in an exotic plastic.

ETFE - Also known by the trade name Tefzel, ethylene tetraflouroethlene provides the highest tensile strength and lubricity available. It is produced in opaque black and transparent clear.

PFA - Perfluoralkoxy, like PTFE, is thermally stable to 260°C and is available in black and clear.

FEP - Fluorinated ethylene propylene is one of the lower cost materials to provide the relatively high thermal stability of 204°C.

PEEK - Ployetheretherketone is halogen free, extremely light weight and crush resistant. It is thermally stable to 200°C and is available in opaque black and transparent clear versions.

Plastic and Metal Core Conduit Systems

Flexible Metal Core Conduit Systems:
widely used in military applications, metal-core conduit systems provide state of the art EMI and mechanical protection, plus complete compatibility with virtually every type of electrical connector in use today. Designed for hostile applications which require superior crush resistance and weather proofing, such as above-deck shipboard use, cranes, heavy machinery, submarines and weapons systems, these reinforced conduit products are ideally suited for a broad range of commercial marine applications. Available materials include helically-wound brass, nickel-iron, and stainless steel; typically welded at each joint to insure a continuous air-tight seal.

Depending on the designer's EMI, mechanical or environmental requirements, a broad selection of overbraiding, shielding and jacketing is also available, from tin copper, nickel copper, phosphorous bronze, stainless steel, Neoprene, Nomex, Halar, Dacron, Kevlar and Aramid.

Fiber Optics

The use of optical fiber and interconnects is increasingly prevalent throughout the aerospace and communications industries. Fiber optic solutions are typically employed in computerized equipment and communications applications where weight savings and/or space constraints make the specification of traditional copper wiring systems inappropriate. As a data transfer technology, optical fiber is known for its outstanding speed and bandwidth capabilities and for its ability to provide reliable communication signals in systems which generate large amounts of electromagnetic radiation, such as fork lifts and cranes.

Fiber Optic Solutions

Greg Noll, Glenair's Fiber Optic Product Engineer, states that "the first practical uses of optical fiber were for military applications, such as the 1976 Airborne Light Optical Program in which the United States Air Force replaced the 40 kilogram wiring harness of the A-7 aircraft with a fiber optic system weighing just 1.7 kilograms. Many subsequent innovations took place in the telecommunications industry, which has expanded the use of fiber optics into 85% of the world's telephone systems. Glenair is focusing its effort on highly specialized aspects of the technology, such as hybrid fiber optic/electrical connectors, Kevlar reinforced fiber optic cable, and composite thermoplastic fiber optic connectors and backshells."

Glenair's fiber optic termini, for example, feature precision zirconia ceramic alignment sleeves inside corrosion-resistant stainless steel covers. The chosen materials provide for better dimensional stability, less wear and contamination during insertion and removal, and better overall optical performance than steel-only termini. The termini are a new addition to Glenair's fiber optic product line which includes single and multi-channel connectors, backshells, test probes and adapters, fiber optic cable and conduit as well as custom molded cable assemblies. The systems are being employed in high-speed magnetic levitation trains, in scientific laboratory hardware, in computerized industrial equipment and in hundreds of other applications where weight savings, large communications bandwidth and faultless data-link performance are required.

Aircraft on Ground

There is an expression in the aerospace industry, "Aircraft on Ground" (AOG) which conjures up painful images for owners and operators. It's used to describe a plane which is grounded from flying until a maintenance or repair problem can be addressed. Ship and boat owners of course have their equivalent concern when it comes to repair-yard dock fees. In fact, both industries are extremely similar when it comes to many of the most critical business and engineering issues which dictate electrical system design and architecture: issues such as enhanced durability and performance, standardized and regulated product quality, improved component part availability, and worldwide technical service and support.

Many aerospace companies, like Glenair, are already accustomed to providing service-levels acceptable to the marine industry based on their years of experience servicing their equally demanding aerospace customers. Cost containment in aerospace component design and manufacture, initiated with the Commercial-off-the-Shelf (COTS) model of production and stocking, has made many of the most beneficial aerospace innovations accessible at the general commercial level. And aggressive research into new manufacturing processes, materials and designs has led to the development of a new wave of lighter and stronger interconnect components. It is left to the ship designers and builders to take advantage of the many recent innovations in aerospace interconnect systems to advance electrical system designs for the next-generation of ships and boats.