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Wednesday, December 21, 2011

Type of FRC Moulds : Split Mould

     Where deep draw mouldings or ones with undercuts are to be produced which would be difficult or impossible to remove from a one-piece mould, split moulds can be used. Here a temporary barrier should be fitted to the pattern so that the first half of the mould can be made with a flange (image below). 

      The flange area should be about 50% thicker than the mould shell to ensure adequate life. The first half of the mould is left in place, the temporary barrier removed and the second half of the mould manufactured using the suitably released flange as former. A metal plate can then be laminated onto either side of the flange to assist in supporting the bolts used to clamp the flange halves together. Once the resin has cured, holes can be drilled to take fixing bolts. These should be spaced at about 150 mm intervals.

     The mould should not be removed from the pattern until all necessary work has been carried out. Mould release can be assisted by using compressed air carefully applied between the mould and the pattern. Release can also be assisted by filling the gap between the mould and the pattern with water to soften and dissolve the polyvinyl alcohol release agent. If the mould has to be struck in any way, extreme care should be taken to ensure that this does not result in star patterns forming in the gelcoat.

     Any imperfections in the mould surface can be removed by rubbing with fine abrasive such as grade 600 wet emery paper followed by a fine cutting paste or by using a metal polish. Before use, the mould surface must be thoroughly polished to a high gloss finish using a silicone-free wax polish applied in several thin coats.

Method of  Constructing a Split Mould
PVA Release Agent