Applying the silicone by hand to create a vacuum bag.
Applying the silicone by hand to create a vacuum bag.
Removing the silicone bag.
Removing the silicone bag.

According to Bentley Creative Chemicals of Kidderminster, UK, 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. The company estimates that the new process is already saving up to 90% of labour costs.

Bentley has been working with a motor racing team to implement the process. The racing team is reported to have been able to dramatically reduce the time taken to mould complex composite parts. A major marine manufacturer is now investigating how the system can benefit its production processes.

The silicone has been developed by Smooth-On in the USA 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.

Traditionally vacuum bags have been made out of polypropylene. The materials are expensive, the bags can only be used once and are time consuming and difficult to apply, explains Bentley. They can also 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, and we are looking forward to working closely with fabricators to see them reap the major benefits that it can bring,” says Richard Watson from Bentley.

Bentley Creative Chemicals specialises in silicones, polyurethanes, polyester resins, plasters and epoxies for use across a wide range of sectors.