The technique can be used to obtain a very lightweight composite product with high mechanical resistance. The reinforcement material is positioned in a hermetically sealed mould and a vacuum is generated. The resin is then introduced into the mould where it impregnates and catalyses around the reinforcement material. The process is used to make medium to large objects with improved product quality and reduced labour costs.
The Vacuum Infusion process is frequently employed in the automotive, aerospace and shipbuilding sectors as well as in the construction of wind turbines.
Zhermack produces a range of RTV2 poly-addition silicones formulated exclusively for this application:
- ZA 22 WT 3 SPRAY
- ZA 22 WT 20 THIXO SPRAY
Zhermack liquid silicones for this application have a Shore A hardness of about 20.
The first formula has low viscosity, making it suitable for use with a spray machine, while the second version is slightly thixotropic and ideal for combined application with spray machine and brush.
The silicone "bags" are reusable and give finished objects with perfectly formed surfaces. They also have excellent mechanical characteristics, short working times and good elasticity and are compatible with a range of resins (polyester and epoxy). They are ideal for making large numbers of objects, keeping costs down and reducing duplication times as the vacuum mould is ready for use.
The silicone must be spread in the mould and the vacuum applied before the resin is added. The vacuum serves to shape the composite material, guide the resin and impregnate the material. When total vacuum is achieved, the resin is sucked into the mesh of glass fibres and spreads evenly through the mould.