NIST Industrial ImpactCompany: Ebert Composites Corporation, San Diego, California Steel and wood are getting some attractive competition in infrastructure applications. The promise of composite materials is turning into a practical reality that could be worth billions of dollars to U.S. companies and consumers, thanks in part to an affordable system for making composite structures designed with support from NIST's Advanced Technology Program (ATP). Extensive tests on three composite transmission towers made by Ebert Composites Corp. have demonstrated better corrosion resistance, much lower installation and maintenance costs, and smaller magnetic fields than steel towers. This success has prompted Southern California Edison Co. (SCE), which operates the towers, to take delivery of 15 transmission and distribution poles made of composites instead of wood for additional tests. "If this proves successful, I think we'll be going toward all composites in the future," says Joe Simpson, research project manager for SCE, one of the largest U.S. electric utilities and the owner of some 20,000 steel towers and millions of wooden poles. SCE is impressed by the following benefits:
SCE's conversion to composites well may signal a trend. Trade journal articles about the towers, which are located only 180 meters (200 yards) from the ocean yet have resisted any salt-water corrosion, have prompted calls to SCE and Ebert from all over the world. A New Zealand utility, for example, hopes the composite towers will resist acid damage from a combination of humidity and hydrogen sulfide emanating from local hot springs, according to Simpson. This type of enthusiasm for composites was precisely the purpose of the ATP support, which was intended to promote U.S. capabilities for producing vast amounts of affordable, high-performance composites for large-scale commercial applications. Traditional infrastructure materials, despite their drawbacks, are so entrenched that the private sector generally has avoided the risk of introducing alternatives, even when new materials are superior. Affordable processes for making composite structures are expected to open new markets worth tens of billions of dollars annually. Composites--hybrids of two or more materials--typically combine the light weight and corrosion resistance of a polymer with the stiffness and strength of reinforcing fibers made of glass or other materials. The engineering performance often exceeds that of steel while the installation and maintenance costs are lower. In the past, however, high manufacturing costs have limited composites to military, aerospace, and niche applications. As a result of the ATP project, Ebert has cut its production time by an estimated 90 percent and expects to receive at least two patents related to the work. "We are a perfect example of what ATP is meant to do," says Walter Warner, Ebert president, who credits the program with giving the small company and its composite products an opportunity to compete with conventional materials. Without the ATP funding, the company might not have had access to the resources and expertise needed to design and prototype its novel manufacturing system, which combines pultrusion and machining in one unit. Pultrusion is a continuous method of manufacturing composite shapes with uniform cross sections. The reinforcing fibers are impregnated with a liquid resin and then pulled through a heated die, which shapes and hardens the part. When Ebert first began production, a pultruded part weighing 45 kilograms to 90 kilograms (100 pounds to 200 pounds) had to be carried across the factory for hand detailing. The complex details are part of Ebert's proprietary "snap and build" tower design, which eliminates the need for adhesives, bolts, or other conventional fasteners. This design reduces on-site construction time but would be expensive to fabricate were it not for the manufacturing innovation. The challenge was to achieve in-line machining. The ATP funding was used to design a computer numerical control (CNC) workstation with a five-axis machining head that performs intricate detailing on pultruded parts exiting the die. Designs for different parts can be stored in the computer and produced accurately in any quantity and sequence without interrupting the pultrusion. The CNC machine substantially reduces labor and other factory costs as well as human error. To control the process, Ebert used commercially available software that can be customized for different manufacturing applications. A contractor, W. Brandt Goldsworthy & Associates, helped with mechanization, electronics, and computerization. "It's a huge advance just in the transmission of power alone," Brandt Goldsworthy says of the Ebert technology, noting that steel always has been a problem in transmission towers because it conducts electricity. Composites are electrical insulators, allowing the transmission of more power in a given amount of space and reducing magnetic fields. Ebert developed a lightning and grounding system that further enhances insulation. The Electric Power Research Institute performed mechanical and electrical tests on the 25-meter-tall (84-foot) SCE towers, which carry high voltages (220 kilovolts), prior to their installation in March 1996. The composite structures cost about the same as steel counterparts but, because they weigh only one-third as much, are much less expensive to install. Precise cost comparisons are difficult to make because different installations vary in many respects. Simpson says the towers, instrumented for electrical and environmental monitoring, have resisted both ultraviolet radiation and weather or salt damage without the periodic washing steel towers require. He predicts that the composite structures will last 80 years, perhaps twice the life span of steel and wood. Composites also attenuate shock better than traditional materials, a potential benefit in earthquake-prone areas. Ebert is focusing initially on utility applications and is negotiating with prospective partners, investors, and licensees. The technology has many additional potential uses. Composite structures might be designed for use as bridge truss supports or towers for microwave antennas, and the CNC workstation might be adapted to make composite airframe parts, for example. Goldsworthy, who invented the first pultrusion machine and now serves on Ebert's board of directors, predicts that composites will eventually dominate the nation's infrastructure and that Ebert's innovations will promote the transition. "The fastening technique is applicable across the board in civil engineering applications," he says. "I think that's going to have a long-term impact." March 1998 |