Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1991-10-01
1993-10-26
Rosenbaum, Mark
Metal founding
Process
Shaping liquid metal against a forming surface
164 97, B22D 1904, B22D 1914
Patent
active
052557308
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for producing a casting consisting of a primary piece and a secondary piece using the casting-on technique. With the casting-on technique, a special kind of precision casting, a second metallic body (secondary piece) is cast onto the first metallic body (primary piece) with great accuracy in the production of cast fittings. The primary piece can be cast too, and the secondary piece fits to it. Such fittings find application in the field of dental technology in the production of tooth replacement anchors, such as attachments and double crowns. The casting-on technique can however in other areas of precision mechanics also rationalize expensive deformation and adjustment work in the production of fittings, such as for example in the casting-in of complicated movements in paste jewellery which are not accessible to pinning, or very generally in the casting-in of all those space maintainers in precision casting technology which are later to be removed.
The traditional process used in the production of cast fittings consists of preparing from the primary piece which was made first a duplicate pattern which is resistant to the casting effects of the subsequent secondary casting, and of casting onto this, within a mould, the secondary melt.
However with this indirect procedure, especially in the case of high-melting alloys with a high surface melting loss, disturbing variations have to be tolerated, even when there is an optimal harmony of the expansion and contraction behaviour of the casting mould and the cast metal. Even with noble metal casting or the working, in the vacuum casting process, of cast metals threatened by the formation of oxides or nitrides, this indirect method of producing a cast fitting will still always produce a disturbing, methodically conditioned variation even when modern controllable mounting materials are used for the precision casting.
It was therefore attempted to increase the precision of the fitting by the direct casting-on of one fitting partner onto the other. This technique of direct casting-on is termed the casting-on technique. One difficulty of this technique lies in the fact that frequently the primary and secondary pieces during casting bond inseperably to one another. For this reason the primary piece and the secondary piece must be isolated from one another in order that they may be separated from one another after casting.
In the state of the art numerous methods of isolation have been developed for the casting-on technique, but they all possess considerable disadvantages. An attempt was made, for example, to restrain diffusion processes between the primary and secondary pieces by selecting different alloys for the primary and secondary pieces. However electrical potential differences arise between alloys which are greatly different from one another, and these can lead to destruction of the cast fitting by corrosion.
The provision beforehand of autogenous oxidic interlayers on the primary piece as well as on the surface of the molten secondary alloy leads often in practice to inadequate isolation. The reason for this can lie in the chemical reactions which take place when there is contact of the secondary alloy with the surface of the primary piece during casting-on at higher temperatures.
The provision beforehand of an exogenous interlayer which is applied mechanically using the PAC method (Precision Attachment Casting-On Technique) leads in the case of sheet structures to inadequate isolation, for example, with conical and telescopic crowns or with locks. The formation of a surface film which is high-temperature resistant and slightly soluble from a special ceramic mass by means of the CVD method leads to good results. However the high working temperatures involved in the CVD method restrict its applicability to alloys with solidus temperatures above ca. 1100.degree. C.
The known application of colloidal graphite is limited to low-melting gold alloys and shows no constancy in its effect.
The known blowing of lycopodium (club foot moss
REFERENCES:
patent: 3899324 (1975-08-01), Corbett
patent: 4060120 (1977-11-01), Takahashi et al.
patent: 4703806 (1987-11-01), Lassow et al.
Puknys Erik R.
Rosenbaum Mark
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