Metal founding – Means to shape metallic material – Including ladle or crucible type melt receptacle
Patent
1996-10-09
1998-06-02
Lin, Kuang Y.
Metal founding
Means to shape metallic material
Including ladle or crucible type melt receptacle
164133, B22D 3504
Patent
active
057587124
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a casting device for counter-gravity casting with a light-metal alloy.
BACKGROUND ART
Such a casting device is known from the international patent application WO 93/11892. In this specification, the holding furnace is placed at a lower level than the moulds to be cast, and the electromagnetic pump can be connected to each of these moulds by means of a heated ceramic tube terminating in a nozzle which may be tight-fitting pressed around the bottom inlet in the side of the mould. Moreover, this publication describes measures for closing the bottom inlet in the mould after the casting of same, making it possible to remove the nozzle from the mould after casting with a view to casting a subsequent mould in a mould string in a mould-string plant, without the cast metal flowing out from the mould.
In this known casting device, the heated ceramic tube connecting the pump to the casting nozzle has an internal cross-section approximately corresponding to that of the bottom inlet of the mould, and a relatively large length as compared to the length of the inlet system in the mould.
As the moulds in the mould-string plant are to be cast rather rapidly, viz. within the period during which the mould string is stationary while a new mould part is being made, during the casting of the mould the metal moves at a relatively high velocity through the ceramic tube and the inlet system of the mould into the mould cavity and consequently, this moving molten mass has a rather high kinetic energy and is braked suddenly, if the flowing metal in the mould encounters a constriction, and in any case when the mould eventually is filled. While the first situation gives rise to a continuous increase of pressure within the flowing metal upstream of the constriction, the eventual filling of the mould gives rise to a momentary increase of pressure within the metal cast into the mould, a so-called "pressure surge" or "impact", which may partly effect local expansions of the mould cavity causing incorrect dimensions and shapes of the resulting casting, partly cause the metal to penetrate into the interstices between sand grains in the mould wall causing the sand grains to "burn on" to the surface of the casting, and partly may such impact cause the nozzle to be forced away from its pressure sealing abutment around the inlet, so that molten metal leaks out at this location and may cause difficulties in the closing of the bottom inlet of the mould.
DISCLOSURE OF THE INVENTION
It is the object of the invention to provide a casting device of the kind referred to initially, with which the amplitude of both the first-mentioned pressure rise and the impact at mould filling may be reduced considerably with a view to avoiding the drawbacks mentioned.
This object may be achieved in accordance with this invention by forming a reservoir in the conduit between the furnace and bottom inlet of the moulds with a cross-sectional area A substantially greater than the cross-sectional area a of the bottom of the inlet of the mould.
The effect of this is a corresponding reduction of the velocity of the flowing metal within the reservoir, while the mass of the latter correspondingly increases. This means that the kinetic energy of the flowing melt within the reservoir is approximately reduced in the ratio a:A between the two cross-sectional areas as compared to the known casting device, in which the communicating conduit is a ceramic tube with approximately the same cross-sectional area as that of the inlet system of the mould. As the length of the communicating conduit is rather large as compared to the length of the inlet system of the mould, and as the reservoir extends along a major proportion of the distance between the pump and the mould, this means a considerable reduction of the total kinetic energy of the moved melt to be braked, i.e. converted into pressure energy, at a constriction in or at filling of the mould and, consequently, of the amplitude of the resulting pressure surges or impacts.
Advantageous
REFERENCES:
patent: 3761218 (1973-09-01), Portalier
patent: 4076070 (1978-02-01), Lefebvre et al.
patent: 4733714 (1988-03-01), Smith
Georg Fischer Disa A/S
Lin Kuang Y.
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