Casting of light metal alloys

Details Casting of light metal alloys Casting of light metal alloys

1995-03-21

1998-04-07

Batten, Jr., J. Reed

Metal founding

Process

Shaping liquid metal against a forming surface

164136, 164167, 164323, 164337, B22C 1110, B22C 4702

Patent

active

057353344

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to the casting of light metal alloys for example of aluminium or magnesium.
2. Description of Prior Art
Existing casting techniques for the production of light metal alloy castings are unsatisfactory because of low production rates and casting defects resulting from turbulence during pouring of the molten metal. In order to avoid the filling problems when casting light alloys the low pressure die casting process uses a liquid metal reservoir which is pressurised to displace the metal up a riser tube into the metal die. Although this process results in an improvement in the casting quality it has two main disadvantages: firstly, poor control of upwards displacement of the metal sometimes results in the turbulence which the process is intended to avoid; secondly, production rates are low because of the long cycle time (typically 4-6 minutes) of the metal die.
In the Cosworth process as described for example in UK Patent No. 2187984 sand moulds are filled by a low pressure technique and improved control over filling is achieved by the use of an electromagnetic pump having no moving parts which is effectively a linear motor. The sand mould has a horizontal parting line to facilitate bottom feeding. The moulds are made from chemically bonded sand at a rate dependent upon the time taken by the chemical reactions required to bind the sand. Although the cycle time is considerably reduced compared to low pressure die casting a casting may nevertheless take some 40 to 60 seconds to produce.
Ferrous casting processes using sequentially produced green sand moulds are known to have a shorter cycle time but have been disregarded for the casting of light metal alloys because of the filling problems described above. For example U.K. Patent No. 848604 by Disa describes the commercially well-known ferrous metal casting apparatus in which green sand mould halves are continually formed in a compaction zone and arranged one behind the other to provide a succession of moulds with vertical parting lines. The moulds are moved under a top filling station from which molten ferrous metal is gravity poured into the successive mould cavities. In a modification of the Disa process described in U.K. Patent No. 1357410 by Gravicast Patentverwertungsgesellschaft m.b.H., which as far as the applicants are aware has had no commercial application, the sand moulds are bottom filled but the velocity and pressure of the in-flowing melt cannot be controlled to the extent required for casting of light metal alloys.


SUMMARY OF THE INVENTION

It is an object of the present invention to further improve the casting of light metal alloys, in particular by increasing the rate at which castings may be made.
According to one aspect of the present invention there is provided a method of casting light alloy metal products, comprising introducing the molten metal into a sand mould having a vertical parting line, by bottom filling in a manner permitting control of flow velocity and pressure.
Preferably, bottom filling of the mould involves introducing liquid metal into the mould at a mould inlet (which may be on a side or bottom wall of the mould) and below the level of the mould cavity, introducing the metal into the mould cavity by a cavity inlet at or closely adjacent to the bottom of the mould cavity, and interconnecting the mould inlet with the cavity inlet by a passageway which preferably has a positive gradient throughout its length so that the metal always travels against gravity.
By using a vertically parting sand mould use can be made of high speed green sand moulding techniques in which sand is bonded by a clay/water binder capable of forming an instant bond on the application of pressure, thereby substantially reducing cycle times (typically to 10-15 seconds). By bottom filling of the sand mould, preferably using an electromagnetic pump for pumping molten metal from an unpressurised reservoir below the level of the mould, filling problems are reduced and casting quali

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