GB2221638A - Making structural component by lost foam casting - Google Patents

Abstract

A method of producing a structural component comprises preparing a heat destructible model or former having a plurality of layers with each such layer comprising webs (1) separated by spaces (2). The layers are arranged such that the spaces (2) between the webs (1) of a particular layer are partially overlaid by the webs in adjacent layers. The former is embedded in a refractory particulate such as sand, and molten metal is cast and allowed to solidify so that the model is destroyed and there is produced a structural component of generally honeycomb-like configuration. A filling material such as carbon fibre may be incorporated within the model so as to become encast in the metal. Examples of possible applications and metals used are given. <IMAGE>

Description

IMPROVEMENT RELATING TO CASTING The present invention relates to the production of structural components by use of the lost foam casting process.

As is known, the lost foam casting process comprises producing a model in a heat destructable material (usually a plastic such as polystyrene), embedding the model in a refractory powder (usually sand), and then casting molten metal into the sand to destroy the model and produce a metal component having the shape of the model.

It is an object of the invention to provide a method of producing structural components (e.g.

honeycomb) by the lost foam casting process.

According to the present invention there is provided a method of producing a structural component comprising preparing a heat destructable model or former having a plurality of layers with each such layer having a plurality of spaced webs disposed such that the spaces between the webs are partially overlaid by the webs in adjacent layers, embedding the model in a refractory powder, and casting molten metal to destroy the model or former and produce the refractory component.

When the sacrificial model or former is embedded in the refractory powder, the latter occupies the spaces between the webs. After moulding and removal of sand there remains a structural component of for example honeycomb type configuration in which the taperturesw are defined by those areas in the model into which the sand was able to penetrate and the "body" is defined by the original polystyrene. These "apertures" may subsequently be filled with a secondary material for imparting desired properties to the component, e.g. carbon fibre. It is also within the scope of the invention to provide such secondary material within the polystyrene of the former so that such material is incorporated in the metal of the component.

Preferably each such layer is an identical moulding comprising webs angled at about 450 to the length of the layer, and the adjacent layers are orientated at 1800 to each other so that the webs in one layer overlie the spaces in adjacent layers.

The invention will be further described, by way of example only, with reference to the accompany drawings, in which: Fig. 1 illustrates a polystyrene moulding used for forming a layer in a sacrificial mould; Fig. 2 illustrates two of the layers shown in Fig. 1 superimposed on and orientated by 1800 with respect to each other.

The layer of Fig. 1 is of polystyrene and comprises webs 1 at 450 to the length of the layer and separated by spaces 2. Fig. 2 illustrates two such layers orientated at 1800 relative to each other. The assembly of Fig. 2 forms the destructable former. During moulding, the refractory sand penetrates the spaces 2. The final cast component is of the shape depicted in Fig. 2 but, of course, those parts of the mould of Fig. 2 which are of polystyrene are of cast metal. Although the model of Fig. 2 has been formed by joining two layers, clearly there will be no 'joints" between the metal in the cast article.

The basic design of the structural component is a series of equi-sided triangles, formed by 450 webs joining parallel plates giving the opportunity to produce systems of varying complexity and density (Fig. 1).

By reversing each segment (building block) the 450 webs described equi-sided triangles in relation to each other to give optimum structural strength and rigidity (Fig. 2).

The basic advantages of this structure over a continuous extrusion is that the interrupted webs reduce the volume of metal between face plates by approximately 50% and give the situation of allowing continuous interfill of secondary material in all directions to permit three axis interaction to form a practical composite.

Modules of building blocks of foamed polystyrene or similar plastic suitable for use in the full mould process, are produced with the basic design concept (Fig. 1).

There modules are glued or fastened together to form the sacrificial model of the desired structure or heat or abrasive component which may or not as desired by modified prior to casting or after casting depending on the heat resistance of the infill secondary material by filling the foam model with the secondary material.

If the nature of the secondary material precludes its use prior to casting, the resultant cast component may be filled at a later more convenient time either before or after incorporation into a larger assembly. Examples of structural components are: 1. Main spar cast structure in aluminium or stainless steel with carbon fibre infill).

2. A yacht or boat keel or lower hull cast in S.G. iron or stainless steel and infilled with lead to eliminate lead/water contamination problems.

3. A structure having its prime material of aluminium and filled with lead on other high density material. The purpose of this structure is to provide shielding from radiation, i.e. hospital x-ray units.

4. Heat and wear resistant plates and blocks, for use in handling equipment. Cyclones for the removal of solids from air or liquid. Furnace structures, power station, fly ash, handling systems and air and water pollution control equipment.

In this application the cast weldable structure is filled with a liquid ceramic which cools to give a solid infill of hot secondary material.

The advantage is that conventional blocks of the infill ceramic need to be retained in a dedicated fabricated structure and repairs can be time consuming and expensive.

With the composite material, structures can be fabricated initially from honeycomb filled plates and sections welded together. In use the top layer of cast steel is eroded over periods of three months to two years to reveal the matrix of the composite with the secondary infill ceramic being firmly embedded in the cast structure. Ceramic alloys and mixes are now available which would give life expectancy of five to fifteen years in the various applications listed.

In maintenance and emergency repair situations plates of honeycomb material can be welded directly to a damaged structure giving immediate long term repair.

5. A further advantage with the honeycomb filled composite is that experimental secondary materials which provide the inf ill can be tested in hazardous or potentially expensive situations, with the basic cast material providing the safety barrier or back up.

Claims (6)

1. A method of producing a structural component comprising preparing a heat destructible model or former having a plurality of layers with each such layer having a plurality of spaced webs disposed such that the spaces between the webs are partially overlaid by the webs in adjacent layers, embedding the model in a refractory powder, and casting molten metal to destroy the model or former and produce the structural component.

2. A method as claimed in Claim 1 wherein the heat destructible model if of polystyrene.

3. A method as claimed in Claim 1 or Claim 2 wherein a secondary material is incorporated in the polystyrene.

4. A method as claimed in any one of Claims 1 to 3 wherein each layer is an identical moulding comprising webs angled at about 450C to the length of the layer, and the adjacent layers are orientated at 1800C to each other so that the webs in one layer overlie the spaces in adjacent layers.

5. A method as claimed in any one of Claims 1 to 4 wherein the refractory material is refractory sand.

6. A method of producing a structural component substantially as hereinbefore described with reference to the accompanying drawings.