Wet lay-up/wet spray-up
Hand lay-up is the simplest of composite moulding processes, where the reinforcing mat is laid onto an open mould and resin applied by brush or roller. In spray lay-up, the reinforcing fibres are chopped and applied to the open mould together with the resin via a spray gun. In both processes to ensure a high quality surface finish, a gel coat (often reinforced with a surfacing veil) is used. The surfacing veil reduces cracking or crazing in the gel coat, ensures a coherent bond between the gel coat and reinforcing mat and reduces print through of the reinforcing mat onto the surface of the composite.
For simple shaped mouldings a light weight veil can be used, for mouldings with complex curvatures a heavier weight conformable needle-punched veil can be used.
Pultrusion of constant section profiles
Pultrusion of composites is similar to the extrusion of metals or plastics. Both processes are used to produce components of constant profile. Whereas extrusion pushes deformable materials through a static die, pultrustion is a process whereby reinforcing fibres are passed through a resin bath and pulled through a heated die to produce a composite component of constant profile. As the process is dynamic, the inclusion of a surfacing veil is the optimum method used to impart a wide range of properties to the surface of the pultruded profile.
In addition to the enhanced properties of the pultruded profile, the surfacing veil also improves the pultrusion process itself by increasing process speeds and reducing die wear.
For more information on the use of synthetic non-wovens in pultrusion processes, please click to enlarge:
Filament winding of pipes and tanks
Filament winding is a process used to manufacture composite pipes and tanks typically used in industries such as the chemical and petrochemical, power generation, water storage and treatment etc. Reinforcing fibres and resin are wound onto a rotating mandrel in orientations controlled by the winding mechanism and the rotation of the mandrel where the resin is cured using infra-red heaters. During the process technical non wovens are wound onto the mandrel and onto the outside of the formed pipe or tank to improve properties such as corrosion resistance, wear resistance, resistance to UV degradation etc.
For more information on the use of synthetic non-wovens in filament winding processes please click to enlarge:
In the vacuum infusion process layers of reinforcement are laid onto an open mould face, covered with a sealed flexible vacuum bag, a vacuum applied and resin allowed to flow into the laminate. As a gel coat is rarely used non-woven surfacing veils are used to improve the surface finish of the laminate reducing surface cracking and crazing and print-through of the reinforcment pattern.
Resin transfer moulding (RTM)
As in the vacuum infusion process layers of reinforcement are laid onto a "female" mould. A second "male" mould is clamped over the first and resin injected into the mould cavity under pressure. Vacuum can also be applied to the mould cavity to assist resin infusion (vacuum assisted resin transfer moulding or VARTM). RTM produces a component with a moulded finish on both the inner and outer faces. Again, as a gel coat is rarely used, surfacing veils can be incorporated on both top and bottom faces to improve surface finish and impart specialist surface finishes.
Continuous laminating is a low cost process for manufacturing flat or corrugated composite sheet and honeycomb core materials. Reinforcing mats combined with resin are sandwiched between a carrier and shaped with forming rollers or on a continuous belt press. Alternatively, chopped fibres and resin can be deposited directly onto a carrier and again the laminate formed continuously using rollers or continuous belt press. Depending on the application, surfacing veils can be used to impart higher quality surface finish, coloured or decorative finishes or electrical conductivity/antistatic properties.