Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1982-06-02
1985-11-12
Bernstein, Hiram H.
Metal founding
Process
Shaping liquid metal against a forming surface
164132, B22D 700
Patent
active
045521980
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the removal of refractory material from components. The invention finds particular application in removing refractory cores from cast components such as blades for use in gas turbine engines, the cores defining, for example, openings such as cavities or passages required for cooling purposes.
Typically in the casting of such blades, a core defining the cooling passages is inserted into a mold, molten blade material is introduced into the mold, the blade is solidified and the core is removed from within the blade.
Fused silica is most commonly used as the core material because of its good chemical removability. However, considerable problems occur with this material due to bowing and distortion of the core, which problems are due to the relatively poor refractory properties of the material. In particular, directional solidification techniques (which are necessary or desirable in many applications to produce high strength, long life blades) may impose excessively severe conditions for fused silica to be used as the core material. Hence, in such applications the use of fused silica as the core material precludes the use of directional solidification techniques and results in blades being relatively weak and having a relatively short life.
It has long been recognised that other materials might be used as core materials and considerable effort has been expanded in looking for materials, other than fused silica, of high strength and high refractoriness which can be easily removed. High temperature fired, recrystallised alumina has the required properties of high strength and high refractoriness but, until this invention, such alumina has been considered generally unsuitable as a core material because of the difficulty of removing the material at practically useful rates. Indeed, much effort has gone into devising structural forms of alumina which present an increased surface area to a dissolving agent and so dissolve more quickly. An example of such a structural form of fired alumina is disclosed in U.S. Pat. No. 4,184,885.
The inventors have made the surprising discovery that high-temperature fired, re-crystallised alumina can, in fact, be readily removed from components at a practically useful rate. The method of the invention has also been found to be applicable to removing other refractory material such as magnesia, steatite and spinel, which were previously thought to be generally unsuitable as core materials because of the difficulties of removing the materials at pratically useful rates. It is believed that the method of the invention may also be applicable to the removing of other refractory materials which were previously considered unsuitable as blade core materials and which have not yet been tried in the present invention.
According to a first aspect of the invention, a method of removing refractory material from a component comprises contacting the material with a reduced concentration aqueous solution of dissolving agent at an elevated temperature and an elevated pressure.
The present invention is thus distinguished from previous attempts to remove refractory oxide materials such as alumina from components since, whereas these previous attempts have sought to dissolve the material directly, the present invention first reacts a chemically reactive agent with the refractory material to convert it to a substance which is more easily removable and then removes this substance.
According to a second aspect of the invention, a method of casting a component having an opening therein comprises the steps of: method according to the first aspect of the invention.
One method of casting blades having internal cooling passages for use in a gas turbine engine will now be described, by way of example only.
Into a blade mold of known type is inserted a core of pure substantially 100% dense recrystallised alumina. The alumina is of tubular, preferably extruded, form and is shaped to define the cooling passages required in the blade to be cast in the mold. In its simplest form the core may c
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Kington Alan D.
Mills David
Bernstein Hiram H.
Rolls-Royce Ltd.
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