Cost-effective Resin Infusion
a report by Philip Lunn
European Technical Manager, Airtech Europe Sarl
Vacuum bagging for resin infusion can be time-consuming and understanding how and why can save a lot of time and money. As the use of the process has become more widespread, the range of techniques employed and products offered has greatly expanded. Greater choice provides greater opportunities for improved performance and more cost-effective manufacture.
For over 35 years the Airtech Advanced Materials Group – located in Huntington Beach, California; Differdange, Luxembourg; Rochdale, England; and Tianjin, China – has specialised in the manufacture of vacuum bagging and composite tooling materials. Founded by William Dahlgren in 1973, Airtech is still family owned and operated, with a renowned technical and sales team who have had decades of experience in all forms of composite processing.
The resin infusion process is long established in the manufacture of parts and tooling. Many composite fabricators have recognised the advantages of the process and it is now employed successfully in a broad range of industries such as marine, wind energy, automotive and aerospace. Simply explained, the process involves the placement of dry fabrics in a mould, which are then vacuum bagged. The applied vacuum creates a pressure differential which is used to draw resin from a bucket into the dry fabric lay-up achieving full fabric wet-out.
As a specialist in vacuum bagging and composite tooling, Airtech has continued to make progress in the development of new materials for all aspects of the process, including fabric and core positioning adhesives, peel ply fabrics, release films, resin flow media, vacuum bag films, sealant tapes and resin flow channels. Significantly, Airtech has also developed custom-engineering capabilities to provide pre-shaped, combination and kitted materials that offer substantial reductions in labour to the composite fabricator.
Typically, the process starts with the positioning of dry fabrics and core materials on a mould or master model. When they are being placed on vertical surfaces, the Airtech Airtac 2 spray adhesive provides enough tack to hold fabrics in position (recent additions to the Airtech range include Econotac, a lower-cost alternative to Airtac 2). Alternatively, Tac-Strip is an open-weave glass mesh with adhesive applied to both sides; this double-sided adhesion holds dry fabrics in place. Tac-Strip prevents excessive application of spray adhesive, which could affect laminate properties.
After a dry fabric stack has been completed, the laminate is covered with a combination of materials to promote resin flow and provide easy removal off the cured laminate. Typically, this is a peel ply fabric, and then a resin distribution mesh. The mesh provides enhanced resin flow over the laminate, enabling transport of resin to the whole tool
© TOUCH BRIEFINGS 2011
surface. The peel ply provides a means of removing the mesh after cure, good resin flow into the tool laminate and a textured surface for a subsequent bonding of a support structure. The use of a perforated release film between the peel ply and resin flow mesh will aid removal further by allowing the resin-saturated flow mesh to be removed separately from the saturated peel ply. Some core materials available on the market promote the flow of resin through the laminate, and the use of a resin distribution mesh can be avoided.
Peel ply fabrics are lightweight, tightly woven fabrics of either nylon or polyester construction. They can be supplied coated with release agent for easier removal after cure, or uncoated. Typically, release agent coating of the fabrics aids removal on complex shapes or aggressive resin systems. The development of new peel plies for resin infusion – such as the Airtech Econoply range and Econostitch – has provided low-cost products for large structures in the marine and wind energy industries. Econostitch peel ply includes a red tracer to give better visibility and aid easy removal off the cured laminate. Most recently, Econostitch 5445 & Econostitch G have been introduced to provide an easier removal after cure without the need for a release agent coating.
Low-cost release films and their perforation styles have seen significant development effort over recent years. The resin infusion process is typically a low-temperature process, not requiring the high-temperature performance of Teflon films used in pre-preg vacuum bag applications. The development of release films such as Airtech’s WL3700 and WL3900R offers a cost-effective performance that is ideal for low-temperature resin infusion applications. Perforations in the film are essential to provide the resin flow required by the process. The size and number of perforations is critical in providing enough open area to achieve the resin flow required to wet-out the laminate – but not so open that the film becomes mechanically locked onto the laminate. A wide choice of perforation styles, such as MP22, MP25, P16 and P is available to match the requirements of individual applications.
A number of resin distribution meshes are available, offering different properties – flow, drape and ease of placement being the main criteria for selection. The range offers meshes suitable for shaped and flatter
Philip Lunn, European Technical Manager for the Airtech Advanced Materials Group, has specialised in the field of vacuum bag processing of composite materials for the last 12 years and has 23 years of composite engineering experience. Airtech has a worldwide team of engineers developing solutions locally, applying and developing the materials and techniques for a variety of processes in a range of industries including aerospace, wind energy and automotive.
E:
p.lunn@
airtech.lu
53
Wind – Composite
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