Finally, a hand-laminated high resin content chop mat layer known as a skin coat should be applied consistently and cured to full Barcol hardness. Like the barrier coat, the skin coat prevents fiber and core print through and protects the gel coat from pre-releasing by adding stiffness and strength while the dry laminate stack is applied to the mold. For the best cosmetics, a one-ounce to three-ounce per square foot skin is recommended depending on the part size and laminate schedule.
Following the coat layers are the dry reinforcement and core layers. Many companies utilize customized multilayer reinforcements to reduce print through and additional finishing time. An example of a customized print-blocking reinforcement includes a flexible foam core, glass or polyester veil, continuous filament mat (CFM) and a flat stitch-bonded fabric combined.
Core fit and resin flow through the core are also critical considerations in achieving superior cosmetics. To ensure consistent core fit and flow, producers can utilize a kit cutter – a pre-marked, ready-to-place reinforcement and core kit cut and shaped specifically for the mold they are to be used in.
Finally, additional layers of reinforcement fabrics should be added after the core and tucked into radiuses with minimal wrinkles. Knitted fabrics provide better flow in the z-direction and typically lay flatter than woven fabrics, which reduces resin usage and opportunities for bridging. When multiple layers are used, staggering the overlaps one to one-and-a-half inches helps reduce prerelease, shrinkage and resin-rich areas. This step is crucial when infusing thick laminates in vacuum infusion processing.
With the dry lay-up complete and the part ready to be infused, it is important to work through a final pre-infusion checklist. The temperature should be above 60 degrees Fahrenheit (mold, reinforcement and resin), and a second drop test should confirm less than two-inch mercury (inHg) loss over five minutes. All material should be tucked into place, and feed and vacuum lines should be in the proper layout.
Having an established preproduction process can make the difference between good and great results. From before material is loaded into the mold until the part is ready to be infused, attention to detail is key and these steps can lead to better, more efficient and highly cosmetic products.
Scott Phillips is marketing manager for Vectorply. Email comments to firstname.lastname@example.org.
For more information on mold release and preparation, visit www.compositesmanufacturingmagazine.com, click on the Tech Talk tab and search “mold release.”