A developmental wind-turbine blade is likely to be the longest RIM polyurethane part ever molded. Designed for what counts as a "small" wind turbine-up to 65 ft diam. and generating less than 100 kw of electricity-the blade will be around 216 in. (7.5 meters) long and weigh 6 to 7 lb.
The blade is the project of a consortium headed by Dr. Woody Stoddard of Amherst, Mass., a wind-energy expert and senior engineer at the primary contractor, Composite Engineering, Inc. (CEI), Concord, Mass. Backed by a $1.5-million grant from the U.S. Dept. of Energy, the consortium aims to mold the first blade in the first quarter of 2005.
The blade is a spar covered with airfoil skins. The skins will be made of microcellular, integral-skin PUR foam and will be about 36 in. wide and 8 in. thick at the tip. Bayer MaterialScience in Pittsburgh will provide the formulation, which may include fillers like mica or wollastonite to add stiffness.
The primary stress loads are handled by the spar, which is to be made of unidirectional carbon fibers impregnated with epoxy by an RTM-type process. Older blades were produced by fiberglass hand-lay up with unsaturated polyester or epoxy-a labor-intensive process.
According to plastics consultant and consortium member David Wright, the new blade could be made in under an hour versus two to three days for an older FRP blade. He estimates that about 200 top or bottom skins could be produced per day. Mass-produced RIM blades could significantly lower the cost of wind power.
Art Mold Corp. of Roselle, N.J., will build the RIM tooling in three segments bolted together. The free-standing molds will have their own clamping systems. This year's goal is to build a prototype of the 79-in. middle section of the mold. It will have runners and a "peanut" aftermixer feeding a single long fan gate.
The molder is GI Plastek of Newburyport, Mass., which has experience in making large structural RIM parts such as panels and fenders for agricultural equipment.