JEC COMPOSITES MAGAZINE - Issue #67 - August/September 2011 - 29

Alan Harper has been involved in closedmould composite production techniques for the last 41 years. The Alan Harper Composites consultancy and technology company was established in October 2010.

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Compare this to the time to actually manufacture a reusable silicone membrane – in the example this would be approximately 2 hours plus 10 minutes for placement and removal of the finished reusable silicone bag for each of the 20 cycles. The sum of these times is therefore 120 + (20 x10) = 5.3 hours Here, labour cost is significantly reduced, by well over 60%, when employing silicone infusion membranes. It must also be emphasized that silicone bags are moulded to fit even the most complex mould geometry, while the use of conventional infusion bagging materials requires further time to set up, with increasing complexity leading to many pleats, and postmoulding time to clean up the B surface of the part.

manufacture. This brings, by default, more effective and reliable seal engagement. An example of reusable silicone bag is shown in Figure 3.

spray application. The compact machine example shown in Figure 5 features easy manoeuvrability with

Seals, inserts and resin delivery channels
Reusable silicone bags now have the advantage of including built-in seals, connection fittings and resin runners uniquely designed for the application. The edge seal is in fact a moulded shape in the bag edge, so the builder simply uses a reusable profile precursor when spraying the bag. Vacuum connection and resin fittings are designed with pre-bonded reinforcing cloth “roots” providing a permanent mechanical bond and perfectly sealed features.

when the reusable silicon membrane is employed. When labour costs are compared, there are further savings of almost greater significance. For example, consider the time to bag up using conventional film infusion materials for the 2m part in the preceding example. Labour time starting from a point at which the fibre pack is already in position upon the face mould, the operator’s tasks include cutting from roll and placement of peel ply, infusion mesh and film. Further, he must add tacky tape to the mould flange perimeter, in this case approximately 7 m of peripheral run, in order to attach and seal the infusion film and vacuum take-off tubing. Thereafter, careful attachment of the film edge after exposing tacky tape and pleating before vacuum is applied and leak tests are carried out. An estimated time of 40 minutes per production cycle for these tasks is reasonable, which also includes the postmoulding clean-up work and disposal of the consumables. The above labour tasks carried out for 20 cycles amount to 20 x 40 minutes = 13.4 hours.

Fig. 2: Pleat in bag at flange edge

The common resin delivery spiral wrap of consumable A significant technical bags is replaced with a advantage of reusable bags is reusable keyhole channel the elimination of pleats. It is section that also features a well-known fact that bagging pre-bonded reinforcing films are more susceptible to cloth “roots” to ensure vacuum leaks where the film better bonding to the bag. has to be pleated to Fig. 3: Moulded net-shape accommodate doubleLiquid platinum-cure reusable silicone bag curvature mould geometry. In silicone membrane materials these cases, the need to are most include up-standing pleats efficiently with tacky tape off the flange applied using 2will undoubtedly be more component prone to vacuum sealing spraying/ a difficulties. Figure 2 illustrates dispensing a typical film pleat. machine with an output of There are no pleats in a between 0.5 to 3 reusable silicone bag as the fit kg/minute. This c is achieved through a ensures good, perfectly-matched moulded bubble-free Fig. 4: Keyhole resin runner section (a) net shape during bag mixing and rapid Precursor seal section (b)and insert (c)

Technical advantages

No67 August - September 2011 / jec composites magazine b

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

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