New Vacuum Bagging System
A new system available through Bentley Chemicals that features re-usable silicone bags for moulding composites under vacuum is already bringing major production benefits. The process is much faster, cheaper and greener than the traditional methods widely used in aerospace, automotive and marine composite moulding.
The silicone bags are more resistant to heat and chemical attack from resins, the process is non-hazardous and has no odour and the bags can be used over and over again with a comparatively long shelf life. It has been estimated that the new process is already saving up to 90% of labour costs.
The Company has already helped to pioneer its use in motor racing. Working closely with a racing team, it has been able to help them dramatically reduce the time taken to mould complex composite parts. It is also now working with a major marine manufacturer to research how the system can benefit its production processes.
The silicone has been developed by Smooth-On in the United States and the bags are created by either spraying or brushing the special silicone onto a composite profile already sitting inside the mould. Once it has cured, the bag is simply peeled away and stored ready for use in the vacuum process.
Vacuum bagging is a technique that creates mechanical pressure onto a laminate during its cure cycle. Pressurising a composite laminate serves several functions. First, it removes trapped air between layers; secondly, it compacts and strengthens the fibre layers; thirdly, it reduces humidity and finally, it optimises the fibre-to-resin ratio in the composite part. Composite mouldings produced by the process have a very high strength to weight ratio.
Traditionally vacuum bags have been made out of polypropylene. The materials are expensive, the bags can only be used once and are quite time consuming and fiddly to apply. They also quite commonly leave marks on the surface of the moulding where the bag has not completely vacuumed flat.
“We know that this new silicone bag system has major potential for many composite moulding applications currently using the vacuum process,” commented Richard Watson from Bentley, “we are looking forward to working closely with fabricators to see them reap the major benefits that it can bring.”
