JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011 - 30

productivity
Fig. 7: Racing car seat pre-calibrated for final part offset thickness and seal profile fixed to mould flange edge

excellent feed pipe flexibility for operator spraying comfort. Platinum-cured silicones can be formulated to react within 90 seconds. However, when making an infusion bag, it is preferable to use a 20-30 minute gel time material as this allows the operator time to place reinforcing mesh within the sprayed skins to give robust handling features in the final bag. To manufacture a reusable silicone bag, the face mould is normally calibrated with an offset thickness equal to that of the final part thickness using calibration wax. Some use an original part, placed back into the face mould, having a relatively smooth rear surface onto which the silicone is sprayed. To produce an effective seal at the edge, a cost-effective method employs a seal profile section prepositioned on the mould flange so that the cured silicone forms the correct seal shape (see Figure 6).

Fig. 6: Racing car seat precalibrated for final part offset thickness and seal profile fixed to mould flange edge

Fig. 5: Equipment: compact machine

on-board transparent material tanks and lightweight spray head with

jec composites magazine / No67 August - September 2011
For the mould illustrated in Figure 7, a spray-up time of approximately 40 minutes is normal, full cure being achieved in 3-4 hours. During spray-up, fabric reinforcement can be embedded to provide extra strength. Moreover, inserts are applied and bonded into the final membrane bag. There is no need for any form of release agent, as the silicone will not adhere to

any surface other than itself. Once cured, the reusable bag is demoulded and edge excess trimmed off, leaving the bag ready for instant use. If spray-up has to stop for extended periods during manufacture, it is possible to continue hours later without concern for each new layer of silicone delaminating. However, absolutely no contamination must be allowed to affect the virgin surface between layers. For a 2-m flat mould, it is possible to spray down the required thickness in less than 10 minutes, but the 40minute time previously mentioned allows for detailed spraying on this compound and complex shape with vertical walls and time to place fabric reinforcement and inserts. The finished bag incorporates all the features required for infusion production, including the edge seal, resin delivery paths and inserts. Reusable silicone bags are not limited to film infusion

but are also used for debulking and prepreg manufacture.

Conclusion
There exists today a totally viable alternative to wasteful consumable film infusion materials by adopting the use of reusable silicone bags. In addition to the time saved during bag up and improved quality, the part’s B surface needs little or no clean up. These features alone provide a strong argument for change. Not only does the moulder make more money, but he is able to reduce the industrial waste associated with conventional film bagging.
More information: www.rtmharper.com Acknowledgements Alan Harper Composites would like to thank SmoothOn (USA) and Bentley Creative Chemicals (UK) for their technical help and continued support in advancing this new technology.

http://www.rtmharper.com

JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011