Rolls-royce Corporation

Rolls-royce (1971) Limited

Rolls-royce Power Engineering Plc

David William Mills

Daniel Clark

Alan D Kington

John Goddard

Anthony T Lindahl

Rodney J Close

Ian Michael Bunce

Hubert D Sellars

Ivan J Birch

Matthew Charles Blake

Michael F Ford

Nigel Alastair Town

Alan J Moulden

Mark Alwyn Thomas Causton

Philip J Lovell

A steam generator comprising a vessel having an inlet and an outlet, and in use a primary fluid flow enters the vessel through the inlet and exits the vessel through the outlet. A plurality of modules are connected in series and at least partially housed within the vessel, and each module comprises at least one tube. The modules are arranged such that at least one tube of one module is coaxial with at least one tube of an adjacent module so as to define a conduit through which a secondary fluid can flow from one module to an adjacent module.

Steam generator

The article together with the alumina core in situ is placed in a sealable vessel containing a concentrated aqueous potassium hydroxide leaching liquor at a temperature immediately below its normal atmospheric boiling point. The vessel is sealed and the pressure within the vessel is reduced to less than atmospheric pressure so as to induce boiling and agitation of the leaching liquor within the passage in the article. The pressure in the vessel is raised to atmospheric pressure and finally spent leaching liquor together with leached alumina core is removed from within the article.

Leaching of ceramic materials

A ceramic material for making ceramic moulds and core for metal casting is described comprising basically granular or bubble refractory material, e.g. alumina or mullite, bound together by hardened ceramic slurry. Moulds for lost wax casting are built-up by dipping a wax pattern in ceramic slurry and then applying granules of bubble alumina in an all over coating. A plurality of such coats may be applied by allowing the slurry to harden between applications. The moulds are more insulating than those using tubular alumina grits, for example, and produce castings with smoother surface finishes.

Ceramic mould material

Complex shapes, e.g. for ceramic cores, can be produced by bonding components with simpler shapes together without the use of glue or cement, thus permitting high precision and avoiding problems caused by excess of cement. The components are formed of curable binder (preferably thermosetting) and a filler (generally a ceramic powder). At least one of the components to be bonded is not completely cured. It is placed in close contact with another component. Heating to cure the uncured component(s) gives a bonded assembly which is then fired.

Production of articles from curable compositions

A reinforced tubular core for casting gas turbine engine blades with cooling air passages therein is disclosed. A method of casting is also disclosed in which the blades are directionally solidified to produce columnar grained or single crystal blades and in which non-linear passages can be produced. The problem in producing such articles is that the moulds and cores used in the casting process are held at temperatures in excess of 1500.degree. for long periods and presently used Silica cores deform during the process. Stronger cores of Alumina or Silicon Nitride cannot be easily bent were believed to be non-leachable from the casting. The present invention provides a core having a tubular silica sheath with a solid alumina rod inside it for support. The sheath can be bent and the straight alumina rods can be inserted from opposite ends of the sheath.

Component casting

The present invention provides a method for manufacturing a thin-walled ceramic casting mould which is particularly suitable for casting directionally solidified articles in which rapid cooling of the cast material is required. The mould is transfer moulded around a disposable pattern material and includes an integral core. The mould has an outer wall thickness of the order of 0.5 mm to 2.0 mm. The mould and core may be made of the same or different ceramic materials chosen for their strength or thermal conductivity. The method further provides for a series of high temperature disposable supports embedded in the disposable pattern material, providing support for the outer wall of the mould during the firing process. The disposable supports are disposed of at a temperature at which the mould has acquired self-supporting strength.

Ceramic casting mould and a method for its manufacture

A method for moulding multiple castings in which each mould is fed from a source of molten metal through a thin slit the width of which lies in the range 1.25 mm down to 0.25 mm. The cast articles can easily be removed from the runner and riser system after casting without a machining operation so that the casting moulds can be packed closer together and more castings can be produced from each mould assembly. The thin slit also acts as a filter. A particular mould assembly seen in FIG. 2 is cylindrical and comprises a plurality of wedge-shaped mould segments 2 having mould cavities 4 in abutting faces. A central runner passage 6 is formed when the mould segments are assembled and the metal flows into the mould cavities through narrow slits 10 in one edge of each mould. After casting and removal of the mould the narrow flashing formed in the slits can easily be broken to remove the cast articles from the metal formed in the central runner passage.

Method and mould for casting metal articles

Cores made from Alumina and other non-Silica based refractories can be made readily leachable in fused anhydrous caustic alkalis by the addition to the core of a small quantity of a material containing a Hydrogen donor group. The Hydrogen donor group is one which produces uncombined, or nascent Hydrogen when the ceramic is contacted with the anhydrous caustic alkali. Such groups are Hydroxyl groups, Hydrides or chemically combined water. In one disclosed example Silica which contains traces of water is added to high fired Alumina to provide the Hydrogen donor group. Only 2% to 3% Silica addition is required to make the Alumina readily soluble in the fused alkali.

Method of casting using non-silica based ceramic cores for castings

Ceramic core materials are selectively dissolved from light metal, e.g. Aluminium or light alloy, e.g. Aluminium alloy castings which are themselves susceptible to attack by caustic alkali solutions, by providing the core material with a substance containing Hydrogen donor group which is capable of producing nascent hydrogen and contacting the core with fused anhydrous caustic alkalis. By this means Silica cores can be removed from Aluminium alloy castings, or a ceramic containing a hydrogen donor group can be selectively dissolved from one that does not, e.g. a Silica disposable pattern from within an Alumina mould containing an integral Alumina core.

Dissolving ceramic materials

The invention relates to a mould assembly including a plurality of individual moulds. The mould assembly of the present invention is made by separately transfer moulding a starter base 16, a plurality of moulds 12, a downpole 14 and pouring cup 19, providing each with mechanical locking features, such as screw threads, and joining them together into the assembly. Much greater flexibility is thereby achieved in materials and wall thicknesses, which can be different in different parts of the assembly to suit strength and heat transfer requirements, individual bits can be replaced, and the transfer moulding produces a compact homogeneous ceramic structure.

Mould assembly for casting metal articles and a method of manufacture

Removing refractory material from components

Apparatus for casting in a vacuum has a single evacuable furnace chamber 10 in which the charge melting and mould heating takes place. The charge is melted in a crucible 24 by an induction coil 20, while the mould is heated by resistance heaters 18 which are made from a FECRALLOY (Registered Trade Mark) material and can be operated in air or vacuum. In operation an empty mould 16 and a charged crucible 24 are positioned in the furnace 14 and the furnace chamber is sealed. The heaters 20 and 18 are operated while the furnace is pumped down. A control device 40 ensures that the charge is not melted until the appropriate vacuum level has been reached. After pouring the filled mould is withdrawn into a withdrawal zone 25 and as soon as the casting has solidified to the extent that air can be admitted to the chamber without detriment, the vacuum is released and the mould and charge replaced. The furnace described is relatively inexpensive, having no water cooled valves between chambers, and the process is relatively quick and inexpensive due to the heating of the mould during evacuation of the chamber.

Method of, and apparatus for, producing castings in a vacuum

A reinforced tubular core for casting gas turbine engine blades with cooling air passages therein is disclosed. A method of casting is also disclosed in which the blades are directionally solidified to produce columnar grained or single crystal blades and in which non-linear passages can be produced. The problem in producing such articles is that the moulds and cores used in the casting process are held at temperatures in excess of 1500.degree. for long periods and presently used silica cores deform during the process. Stronger cores of alumina or silicon nitride cannot be easily bent were believed to be non-leachable from the casting. The present invention provides a core having a tubular silica sheath with a solid alumina rod inside it for support. The sheath can be bent and the straight alumina rods can be inserted from opposite ends of the sheath.

In Titanium casting the surface of the casting is usually contaminated with a brittle oxide layer which has to be removed. Physical or chemical machining reduces the dimensions of the casting and adds to its cost. Chemical reagents may remove fine surface detail. In accordance with the invention the oxygen in the oxide layer is removed by contacting the surface of the casting with an oxide scavenge agent, notably Titanium, for a sufficient time and at a sufficient temperature to allow diffusion of the oxygen from the surface into the scavenge agent.

Surface oxide layer treatment

In a process for making refractory articles, such as cores and moulds for use in casting metals, the articles are formed from dies using a refractory material mixed with a thermosetting resin. The articles are formed with the mixture heated to a softened state and the resin is cured. Thereafter the article has to be fired and problems have arisen with deformation of the articles during the firing process. With the present invention, the articles, 8, which as can be seen in FIG. 2 are mould segments, are bound into an assembly with a flexible refractory tape (15) which shrinks on firing to a greater extent than the articles, and thus pulls the assembly tightly together whereby each article provides support for the adjacent article and prevents distortion. The joint faces between the mould segments are thus held in tight abutment and for pouring metal into the mould, the firing cup is fitted and a coating of refractory slurry is brushed on without removing the tape to seal the assembly. The process is also applicable to the manufacture of cores to prevent bending during firing.

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Derby, United Kingdom

David William Mills