Replica moulding

Replica Moulding. A PDMS stamp is cast against a conventionally patterned master. Polyurethane is then moulded against the secondary PDMS master. In this way, multiple copies can be made without damaging the original master. 

A silver replica of a holly leaf is to be made by investment casting. (A natural leaf is coated with ceramic slurry which is then dried and fired. During firing the leaf burns away, leaving a mould cavity.) The thickness of the leaf is 0.4 mm. Calculate the liquid head needed to force the molten silver into the mould cavity. It can be assumed that molten silver does not wet the mould walls. 

Fig. 4.11 (a) A photograph of the Australian greengrocer cicada. SEM images of (b) the nanotemplate of the cicada wing nanostructures (the scale bar is 500 nm), (c) the inverse h-PDMS mould, (d) an optical fiber exhibiting the polymer nanostructure replica, (e) the replica coated in silver, and (f) a macroscopic image of the imprinted fiber (Reproduced with permission from [29])... 

Electron micrograpns (Pt/C surface replicas) of the surfaces of polymethyl methacrylate lenses produced by casting into optically worked moulds a) low quality, b) high quality. 

Investment Casting. A process for the casting of small metal components to a close tolerance. In the usual process a wax replica of the part to be cast is coated ( invested ) with refractory powder, suitably bonded, and the whole is then warmed (150°C) to melt out the wax - hence the alternative name Lost-wax Process the refractory mould is then bred at 1000-1100 C. The refractory used may be powdered sillimanite or alumina, or specially prepared cristobalite the latter is particularly used in the application of the process in dentistry. B.S 1902 Pt 10 specibes methods for the determination of resistance to deformation at elevated temperatures permeability and standard air bow capacity at elevated temperatures thermal proble determination, for refractories for investment casting shell mould systems prefabricated brickwork, in which reinforcement is provided by steel rods running horizontally across perforations in the blocks. 

Fig. 3.13. A mould manufactured from low consistency (RTV) silicone elastomer is used in the epoxy encapsulation of capacitors. (Replica Materials Ltd...

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