GB2185203A

GB2185203A - Sieve/choke for casting of metals

Info

Publication number: GB2185203A
Application number: GB08629254A
Authority: GB
Inventors: Michael Keith Jackson
Original assignee: SVENSKA HALLAM Ltd
Current assignee: SVENSKA HALLAM Ltd
Priority date: 1986-01-14
Filing date: 1986-12-08
Publication date: 1987-07-15
Also published as: GB8629254D0; GB8600734D0

Abstract

For use in the casting of metals such as aluminium and its alloys, a sieve/choke comprises a flat perforated sheet (1) of an inorganic, relatively high melting point material, preferably phlogopite mica, formed into a laminated construction. The flexibility is determined by the number of laminations and will be selected to allow the sieve/choke to be bent to whatever shape is required for a given use. The diameter and density of perforations may also be chosen to provide various porosities. <IMAGE>

Description

SPECIFICATION Casting of metals This invention relates to the casting of metals and is particularly, but not necessarily exclusively, concerned with the casting of metals such as aluminium and its alloys.

Aluminium and its alloys are frequently used for high precision components employed in critical areas such as component parts of aircraft. It is therefore most important that the integrity of such castings is assured, i.e. they must be free from surface defects and free from internal inclusions.

Conventionally, aluminium and its alloys are cast into sand moulds, and consequently control over the entry of the metal into the mould must be provided to prevent the metal from washing mould material from its walls, and to prevent any materials picked up from the runner system from reaching the mould cavity.

Thus it is already known to strategically locate at the entrance to a mould a combined sieve/choke member. In one known construction, a combustible sponge-like material is formed to the required shape, and loaded with a suitable ceramic material, following which the sponge-like material is burned away to leave a honeycomb, ceramic sieve/choke member. However, such constructions are expensive and particularly so with larger castings where multiple inlets to the mould cavity are provided, each requiring a sieve/choke member.

In an alternative construction, the sieve/choke member is formed as a perforated plate, usually of tin-plated steel. When the mould inlet so permits, a flat perforated plate can be used, but frequently the plate needs to be bent or otherwise shaped to suit a particular mould inlet, adding noticeably to the cost of production. Perforated metal plate sieve/chokes whilst of themselves less expensive than honeycomb ceramic sieve/chokes, even when there is the need to form the plate to a specific shape, have the disadvantage that on solidification of the casting, the plate-like sieve/choke becomes fused into the stringer of solidified metal extending from the ingate to the mould cavity to the inlet to the mould, and the stringer once severed from the casting, cannot simply be returned for re-melting.

The fused-in plate must be cut from the metal, adding noticeably to the cost of scrap recovery, and causing an inevitable loss of recoverable scap material.

The object of the present invention is to provide a sieve/choke member that avoids the disadvantages mentioned above.

According to the present invention, a sieve/choke member for use in the casting of molten metals, comprises a flat perforated sheet of an inorganic, relatively high melting point, material. Preferably, the inorganic material is mica, and the sheet formed as a laminated construction. Thus the grade of mica and the number of laminations can generate a relatively inflexible plate-like construction, or can provide a relatively flexible construction that can readily be bent or curved (e.g.

formed to conical shape), to suit a particular mould inlet. It is still further preferred that the mica is phlogopite mica.

A perforated, laminated mica sheet is less expensive than either honeycomb-ceramic or tin-plated steel sheet constructions, with the added major advantage that the stringer severed from the casting and in which the laminated mica sheet is embedded can be returned as such for re-melting, in the knowledge that the embedded mica will float to the surface following re-melting, and from where it can readily be removed.

Three embodiments of the invention are illustrated in the following schematic drawings in which each of Figs. 1, 2 and 3 shows a sieve/choke member 1 in accordance with the invention with a different size and distribution of perforations to generate different required porosities.

Each of Figs. 1, 2 and 3 shows a sieve/choke member 1 in accordance with the invention, formed from phlogopite mica paper.

Each member is formed as a laminate of a number of sheets of the phlogopite mica paper secured together by an appropriate, preferably inorganic, adhesive material, the number of sheets of phlogopite mica paper employed to a large extent determining the rigidity or the flexibility of the member. However, it will be understood that the precise number of sheets employed to provide a required degree of rigidity or flexibility will be influenced by the number of and size of the perforations 2 forming each member.

The size and number of the perforations 2 have the principle effect of dictating the porosity of the sieve/choke member 1. Thus, as is shown in Fig. 1, the size of the perforations is 1.5mm and the number employed on the member combining with the diameter of each to generate a porosity of 42%. In Fig. 2 the diameter of the perforations is 1.8mm and that plus the number of perforations employed producing a porosity of 30%. To illustrate the wide range of design parameters available to the user, Fig. 3 also shows a member with a porosity of 30% here employing perforations of a diameter of 3.0mm.

It will be readily understood that having once selected the diameter of perforation and the number of perforations to be employed both to suit the flow characteristics of the metal to be cast and the required degree of porosity it is simply a case of securing together a required number of sheets of phlogopite mica paper to produce the required degree of rigidity or flexibility of the member.

Claims

1. A sieve/choke member for use in the casting of molten metals, comprising a flat perforated sheet of an inorganic relatively high melting point material.

2. A sieve/choke member as in Claim 1, wherein the inorganic material is mica.

3. A sieve/choke member as in Claim 1 or Claim 2, wherein the member is formed as a laminated sheet construction.

4. A sieve/choke member as in any of Claims 1 to 3, wherein the inorganic material is phlogopite mica.

5. A sieve/choke member substantially as hereinbefore described with reference to the accompanying drawings.