Infrastructure Made of Composites Nearly a Cost-Saving Reality
An array of economic, environmental, and other benefits offered by power transmission towers made of composite materials has impressed a major U.S. utility so much that it may trade in its metal towers and wood poles for an all-composites infrastructure. The conversion would mark a watershed in the commercial use of composites—hybrid materials typically consisting of a resin and fiber reinforcements—which are strong, lightweight, and corrosion resistant but, until now, expensive to manufacture for structural applications. Ebert Composites Corp. of San Diego, Calif., reduced the costs through two types of innovations. First, the towers were designed with interlocking joints to enable a “snap and build” assembly process that eliminates the need for adhesives, bolts, or other conventional fasteners. This design reduced at-site construction time but would be expensive to fabricate were it not for a second innovation. With support from NIST's Advanced Technology Program (ATP), Ebert designed and demonstrated an affordable manufacturing system that reduced production time for composite towers by 90 percent by combining pultrusion and computer numerical control (CNC) machining. Pultrusion is a process in which fibers are impregnated with a liquid resin and pulled through a heated die, which shapes and hardens the part. The ATP funding was used to design a CNC workstation with a five-axis machining head that performs intricate detailing on pultruded parts. Designs for different parts can be stored in the computer and produced with high accuracy in any quantity and sequence without interrupting the pultrusion. The CNC machine substantially reduces labor costs and human error. Southern California Edison (SCE) Co., which operates three demonstration towers made by Ebert, has found that the structures cost about the same as steel towers initially but require far less effort to install and save about $700 per tower on annual maintenance. SCE now plans to install and test power-transmission and distribution poles made of composites instead of wood. If these tests are successful, the company may convert entirely to composite structures in the future, according to the research project manager. Many other organizations, including a New Zealand utility and firms in other industries, also have expressed interest in using the composite structures or CNC machine. ATP funding: $1,032,000 March 1998 |