Metal founding – Process – Shaping a forming surface
Patent
1998-08-05
2000-09-12
Ryan, Patrick
Metal founding
Process
Shaping a forming surface
164519, 164516, B22C 700, B22C 904, B22C 102
Patent
active
061163279
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF INVENTION
This invention relates to making a metal shape by casting.
It is well known to make a metal shape by a centrifugal casting process in which molten metal is poured into a hollow mould which is rotating. Centrifugal casting provides the advantage of achieving segregation of impurities towards the axis of rotation and away from the external surface of the casting since impurities generally encountered are of lower density than the metal of the casting. Moreover, centrifugal casting enables the production of hollow cast shapes of controlled wall thickness without the need for central cores although, if desired, the rotating mould can be filled sufficiently so as to provide a shape without a central cavity. In either case the part of the casting containing the impurities can be removed, for example by machining.
Hitherto such centrifugal casting has been used with permanent moulds for metal shapes of relatively simple external surface configuration such as generally cylindrical. By providing a sand mould of appropriate shape within a container, generally made of steel, the external surface of the casting may be provided with a more complex configuration, within constraints imposed by the difficulty, complexity and expense of removing rigid patterns, typically of wood, for producing the sand mould, even when the rigid patterns are made collapsible to facilitate removal.
There is a demand for metal shapes, particularly hollow shapes such as gas turbine engine casings, having an external shape of relatively high complexity and precision than it has hitherto been possible, or economically possible, to manufacture by centrifugal casting.
Objects of the invention are to provide a method of making a metal shape in which the above mentioned problems are overcome or are reduced together with a method of making a mould capable of use in such a method and a method of making a pattern capable of use in making such a mould as well as apparatus capable of use in these methods.
According to one aspect of the present invention we provide a method of making a pattern of flexible elastically deformable material comprising the steps of moulding said material in a master mould of a required shape and removing the pattern from the master mould, after the pattern has set, by elastically deforming the pattern.
The method may include the step of moulding the material in a master mould which has a mould cavity defined between inner and outer parts and removing the inner part from within the outer part after the pattern has set and then removing the pattern from the outer part by elastically deforming the pattern.
The mould cavity may be of generally tubular configuration.
The inner part may comprise at least two portions and the method may include the step of separating said portions to remove the inner part from within the outer part.
The inner part may be provided with a plurality of retaining elements which extend into the mould cavity from the surface of the inner part so as to be embedded in the pattern.
The retaining elements may be releasably mounted on the inner part and the method may include the step of releasing the retaining elements from mounting relationship with the inner part.
The method may include the step of providing closure members at opposite ends of the mould cavity, at least one of said closure members being movable relative to at least one of said inner and outer parts.
The pattern may have a high elastic deformation memory so as to regain its shape within .+-.0.01 mm after elastic deformation up to 10.times. its original size.
The pattern may comprise a silicone rubber.
According to a second aspect of the present invention we provide a method of making a ceramic shell mould comprising providing a pattern of flexible elastically deformable material of a required shape and supported on a mandrel, applying at least one coating of hardenable refractory material to said pattern to form a rigid shell and removing the mandrel from supporting relationship with the pattern and subsequently rem
REFERENCES:
patent: 4682643 (1987-07-01), Bernhardt et al.
patent: 5630465 (1997-05-01), Feagin
patent: 5712435 (1998-01-01), Feagin
patent: 5738819 (1998-04-01), Feagin
Dey Anjan
F.V.C. Limited
Ryan Patrick
LandOfFree
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