CompositesWorld
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75 CompositesWorld.com NEWS N E W S N S N E W S E N W S W When graphs of the scan generated for the unsanded primer- plus-clearcoat panel at 25°C were overlaid with the scans for unfnished panels, the curves revealed the similar periodicity, meaning the texture in the clearcoat could be explained by cooling of the substrate between 100°C and 25°C. When the panel is reheated, the substrate expands and the grooves disappear, only to return as the panel cools. Te diferential expansion of the substrate arises as a result of the resin-rich domains of epoxy that lie between non-homogeneously distributed carbon fber bundles at the substrate surface. Te carbon exhibits little to no thermal expansion, whereas the epoxy, with a CTE of 15 to 100 ppm/°C, diferentially expands and contracts with the changing temperature. As for the sanded panel, the same explanation holds, with one diference. Te baked primer is removed from the oven and sanded smooth at room temperature over the substrate, which also has cooled with its characteristic textured surface beneath the primer (Fig. 2, p. 73). After the clearcoat is applied and ramped to bake temperature, the substrate expands, causing ridges in the solidifed primer layer above. However, the still-liquid clearcoat fows to a smooth level over the ridges until it cures and sets at the bake temperature. But as the panel cools, the substrate shrinks, the ridges in the primer disappear, and the adhesion between the primer and clearcoat causes grooves in the clearcoat. Te same phenomenon reportedly explains why reverse texture Painting Carbon Fiber Body Panels www.wabashmpi.com Tel: 260-563-1184 wabashmpi@acscorporate.com WABASH MPI produces a wide range of hydraulic presses for com- pression molding in composites applications. We offer standard and custom designs from 15-1000 tons with various heated platen sizes and control options. Visit our website to learn more. WABASH, The Leader in Composites Molding ISO 9001:2008 Certifed 400 Tons Down-acting, 120" x 60" Platens