< INVESTING A WAX PATTERN IN CERAMIC SHELL 4
INVESTING A WAX PATTERN IN CERAMIC SHELL 5
9. ADDITIONS TO THE SHELL
Although a ceramic shell mould is strong, and substantially lighter than an equivalent plaster and grog mould, founders often add reinforcements between the later back-up layers of slurry and stucco. Shell reinforcement can vary from the application of a final sealing coat containing shredded glassfibre, to the embedding of stainless steel mesh, wire and clips between applied layers. These various measures can significantly add to a mould’s overall strength, enabling surprisingly large scale moulds to be poured ‘free standing’ (ie not encased in sand or another fully supporting jacket). Where it is imperative that the shell wall be highly porous to casting gases, founders may add a large refractory beading such as vermiculite (a material similar in size, weight and texture to small expanded polystyrene balls) to the wetted assembly, in the place of one or two of the later stucco coatings.
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