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Answers provided by Steve Nolet on wind turbine blade design

Daniel_Melo's picture

Questions and answers:

1) How do you bond the two halves together including the material and curing?

Utility scale blades, molded in two primary halves (Pressure Side Skin and Suction Side Skin) are bonded (most often) using epoxy bond pastes. These pastes are formulated from the same resins and amine hardeners used in the primary infusion matrix but blended with rheological agents (think cabosil and others) to create a high viscosity paste. The resins are mixed with various compatible amine hardeners that allow us to tailor the working time of the paste with the time needed for dispensing, bead shape formation, and closing (bringing mold halves together). In addition to epoxy bond pastes, the industry also uses Methyl-methacrylates as well as Polyurethanes adhesives. What material is chosen is based upon experience, physical properties (shear strength/stiffness, toughness or elongation, etc.). Epoxies, while providing the highest level of shear capability suffer from in tolerance of off ratio mixing, need for very careful adherend surface preparation and a lack of toughness which has led to several classic industry headaches for manufacturers. Room temperature curing MMA's and Polyurethanes address all of these issues with better tolerance to off ratio mixing, tenacious bonding characteristics that are less sensitive to bond prep and much higher fracture toughness and elongation. Lower shear characteristics are sighted for lower market penetration, but in practice, this has not been a significant problem.

2) What finishing/coating do you put on and how?
Blade coating vary from manufacturer to manufacturer, however a brief review can be discussed. Primary external coating serve to provide a uniform appearance but more importantly protect the blade materials from exposure to ultra-violet light that degrades the epoxy and causes rapid deterioration of laminate properties. In addition, leading edge protection for the outer one third span of the blade is essential to mitigate rain erosion, slow down fouling and shed icing all of which significantly degrades blade performance and results in lower energy yield. The range of coatings used include epoxy and polyurethane paints (primarily) although a number of polyester gel coats have also been formulated to provide good surface finish (tie layers are needed to bond to epoxy matrix laminates). This implies that some finishes are applied as in mold coatings that are either sprayed or rolled onto the surface of the mold prior to layup of the dry reinforcements for infusion. Leading edge coatings are evaluated and developed to improve erosion protection and this includes paints of all types (epoxy, polyurethane, loaded epoxy systems, etc.) also systems that are applied as "decals" to the leading edge. The choice is designer dependent and usually a result of varying experience.