Net shape steel and titanium castings
This one-off titanium valve body illustrates the quality of part that is rapidly produced from machined polystyrene by Titanium Castings UK
Castings technology international (Cti) can use precision machined polystyrene patterns to make short lead time, one-off and low-volume castings up to a 2m cube in size – even in titanium and zirconium.
As in the lost wax process, layers of ceramic are built up on the pattern, which is removed on firing to leave an inert ceramic shell mould. Cti and other uses have used this Replicast technology to manufacture numerous steel castings, such as those for pumps and valves, using this technique.
More recently, further development has resulted in the MEGAshell technology. This enables exceptionally large ceramic shell moulds to be produced to deliver the benefits of Replicast for one-off and low volume castings of a size and weight far greater than most casting manufacturers would have believed possible. So far, ceramic moulds with dimensions up to 2m by 2m by 2m have been produced so that, for example, heavy section valve castings weighing several tonnes can be manufactured that are more than 20% lighter than the sand cast equivalent. Machining cost reductions of 50% or more can be achieved along with all the other benefits of the Replicastprocess.
To date, more than 3,500 ceramic moulds have been manufactured by the MEGAshell® technology, proving its capability to meet the market demand for large, near net shape castings, especially in costly alloys of steel and nickel – and latterly, Cti has refined the technology so that it can be used for reactive alloys of titanium and zirconium.
Titanium Castings (UK) Ltd, a wholly owned subsidiary of Cti which offers this service, also uses the Replicast® process – in which the polystyrene patterns are formed in an aluminium die – for volume production of complex, thin-wall titanium castings. The polystyrene patterns are a cost-competitive substitute for the wax patterns that would otherwise be used, and provide the precision, quality of surface finish and integrity that are normally associated with the lost wax process.
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