GB2265099A - Consumable cluster of patterns at several layers; precision casting - Google Patents

Abstract

A casting installation for use in precision casting of metal alloy parts comprises a mould (1) formed of a cluster of (10) of patterns (2) embedded in a granular material (3), the patterns (2) forming several levels (4, 5). The installation has application to massive parts and/or a large number of parts. Each level has an independent metal feed through downgates 6, 7 so that the flow to each level can be controlled by correct dimensioning of each of the downgates. The levels may be fed with metal from a single casting pouring basin. <IMAGE>

Description

METHOD AND INSTALLATION FOR CONSUMABLE PATTERN CASTING AND USE OF THE INSTALLATION This invention relates to the precision moulding of consumable patterns for metal alloy parts. It relates primarily to a method in which a mould consisting of a cluster comprising among other things several consumable patterns embedded in a granular material is used.

The technique of precision moulding in which consumable patterns embedded in a granular material are used as a mould (see FR-A-2 647 379 in the name of the applicant) is particularly advantageous in the context of casting in moulds with hollow cavities for casting metal alloy parts. Among its advantages may be mentioned the fact that the pattern, which is consumed by conversion into a gas, has the precise shape of the part being cast without the need for the use of cores.

It makes great accuracy possible, in contrast with a good many conventional casting procedures.

It makes recovery of the granular material, to which no binder is added, a possibility. However, because of the processes inherent in casting, in some cases the number of parts which can be obtained at the same time is limited because a sufficient metal flow has to be ensured when filling a part, particularly if the material forming the pattern has rapid degradation kinetics, this problem being accentuated for parts of large volume, which may then have an adverse effect on the manufacture of the parts, particularly when it is desired to increase the number of parts in a cluster.

The object of this invention is to overcome this limitation and to benefit from the advantages of consumable patterns which can be used to cast parts with great accuracy and to recover the binder-free granular material and cast a large number of parts in one mould at the same time.

This problem is overcome by the method of casting a part in the characterising clause of claim 1 in which the cluster is fed with liquid metal by gravity, causing gasification of the consumable pattern or patterns, with the result that metal alloy parts are obtained on several levels.

The method according to the invention is characterised by an independent metal feed to each of the levels by means of downgates, each one of which only feeds a single level.

Then, depending on the casting conditions (size of the parts, nature of the pattern, head of metal, etc.) the flow to each level can be controlled by correct dimensioning of each of the downgates.

With this flow control it is possible to avoid the conventional defects in the process of casting which uses a consumable pattern, e.g. a defect such as collapse of the granular material, or a cold shut with carbon inclusions.

The ability to ensure a sufficient flow per level in relation to the rate of degradation of the pattern makes it possible both to cast long parts which have to be filled, such as e.g. massive parts, and to increase the number of parts per level.

In order to increase the yield of metal and to fill all the levels in the mould with hot liquid metal simultaneously, the levels are fed by metal from a single casting pouring basin.

The invention also relates to a casting installation for the use of such a method. This installation comprises a mould consisting of patterns of consumable material and feeds thereto forming several levels to obtain cast parts.

The metal feed system comprises gravity downgates each feeding a single level, for rapid filling of a multilevel mould. In particular the consumable patterns may be of polystyrene, as a sufficient flow of metal is obtained.

More specifically, every gravity downgate consists of a hollow revolution member of refractory material.

The installation includes a liquid metal casting pouring basin which together with the gravity downgates forms one assembly of refractory material, and the downgates can be rapidly filled with a sufficient flow of metal with the result that a large number of parts can be obtained per level on several levels for a single melt.

The granular material consists of sand without binder, so that it can be recovered.

A further object of the invention is the use of an installation in accordance with the above description for casting massive metal parts. The parts are of cast iron.

Example embodiments of the invention will now be described with reference to the appended drawing, in which the single figure shows a casting installation according to the invention diagrammatically.

The installation illustrated in the drawing comprises a mould 1 consisting of a cluster 10 of several levels 4, 5 of consumable patterns of expanded material 2 embedded in a granular material 3 without binder. Mould 1 is designed to mould cast iron parts, and for this purpose the installation includes a pouring basin 8 and downgates 6, 7 which feed levels 4, 5 respectively. Level 4 is located higher in the mould than level 5, and each of levels 4, 5 form cluster 10. The granular material is held in a shell 9. It is compacted by vibration.

Each downgate 6, 7 is of a diameter appropriate to the position and composition of level 4, 5 which it feeds so that it is filled with hot metal as rapidly as possible and thus ensures an adequate flow of metal.

Downgate 6 passes through level 4 without contact with patterns 2 in that level. A greater number of levels can be added on the same principle.

Casting pouring basin 8 and downgates 6, 7 are constructed of a fibrous refractory material.

The downgates are hollow frusta of cones with a diameter which decreases downwards.

Levels 4 and 5 take the form of cast parts such as e.g. pipe parts.

During casting the liquid metal is run out from pouring basin 8 into downgates 6, 7, fills these, then gasifies patterns 4 and 5 and fills the space left by the pattern before granular material 3 collapses. After cooling the cluster of parts is separated from granular material 3.

This installation is suitable for casting many massive cast iron parts in a short time with a low metal consumption. For a given number of parts the metal yield is improved in comparison with the technique of casting in a single level.

Claims (10)

1. A method for the precision casting of metal alloy parts with a consumable pattern in which a mould formed of a cluster comprising among other things several consumable patterns embedded in a granular material is used, characterised in that the mould is fed with liquid metal by gravity, causing gasification of the consumable patterns and thus making it possible to obtain metal alloy parts on several levels.

2. A method according to claim 1, characterised in that the metal is fed by downgates, each of which only feed one level.

3. A method according to claim 1 or 2, characterised in that the levels are fed with metal from a single casting pouring basin.

4. A casting installation for implementing the method according to any one of the foregoing claims, characterised in that it comprises a mould formed of patterns of consumable material embedded in a granular material and means for feeding the mould with metal, the consumable pattern or patterns forming several levels in order to obtain cast parts.

5. An installation according to claim 4, characterised in that the feed system consists of gravity downgates, which each feed only a single level.

6. An installation according to claim 4 or 5, characterised in that each gravity downgate is formed of a hollow revolution member of refractory material.

7. An installation in particular according to claim 6, characterised in that a casting pouring basin for liquid metal forms an assembly made of refractory material together with the gravity downgates.

8. An installation according to any one of claims 4 to 7, characterised in that the granular material is sand without binders.

9. Use of an installation according to any one of claims 4 to 8 for casting massive metal parts.

10. Use of an installation according to any one of claims 4 to 9 for casting cast iron parts.