Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1983-03-07
1985-06-18
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164503, B22D 2702
Patent
active
045236275
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for high-speed vertical continuous casting of aluminium and alloys thereof, in particular in the form of billets and plates, the smallest dimension of which does not exceed 150 mm.
The man skilled in the art has long had knowledge of the vertical casting process wherein a metal in a liquid condition is continuously moulded by passing downwardly through a cooled, bottomless mould, to form billets or plates of greater or lesser length.
As the decades have passed, that process has been improved for the purposes of enhancing the levels of performance thereof, both from the point of view of production capacity and from the quality aspect.
In seeking to achieve higher casting speeds, problems relating to surface defects have been encountered, being both physical, namely an irregular skin, and chemical, namely inverse segregation phenomena, which at first have been overcome in a rather unsatisfactory manner, by carrying out intermediate scalping operations on the castings. Then, different measures concerning the materials used for the moulds and the lubrication thereof, cooling devices, and the casting programme made it possible to reduce and in some cases even omit the scalping operation.
More recently, and particularly in order in particular to obtain products which can be used directly for transformation operations, recourse has been had to particular shaping equipment, such as for example the HOTTOP wherein a top feeder head is disposed above the ingot mould, being a sort of reservoir of liquid metal which is similar in section to the section of the cast product and which is variable in height, being formed by a refractory and insulating material.
Such an apparatus results in products which are improved in regard to the surface condition, but, depending on the type of alloy cast, it is found that there is an optimum speed which is not to be exceeded, as otherwise the skin or surface layer of the casting suffers from tearing effects. Although it is possible to restrict that defect by associating the top feeder heads with moulds which are of small height, nonetheless such a coupled assembly cannot be used in relation to plates which are close to 150 mm in thickness because, by virtue of deformation thereof at the moment of starting to move, they may cause damage to the feeder head, in particular when the diameter of the feeder head is less than that of the ingot mould.
Under these conditions, it is found that, if there is a need to cast high-quality billets with a diameter of 100 mm, even with a mould which is 1.5 cm in height, the best speed which can be attained, with the most suitable alloy, is 300 mm/min, which is also confirmed by French Pat. No. 2,249,728.
Another way of reducing the occurrence of defects at the surface of the castings comprises carrying out the moulding operation without any contact with a mould. This can be achieved by passing the liquid metal through the centre of an induction means which creates an electromagnetic field and thus generates forces which contribute to imparting a properly defined shape to the liquid. That shape is then maintained by causing the metal to solidify, by spraying it directly with a heat exchange fluid.
It is beyond all doubt that such a process made it possible substantially to improve the surface condition of the castings and substantially to reduce the occurrence of inverse segregation, but it does suffer from some disadvantages. Thus, using that process necessitates maintaining a constant height of liquid metal above the interface with the solidified metal. In order to achieve the aim, use is made of a nozzle-float assembly which is somewhat bulky and which is particularly difficult to set in position when the aim involved is that of casting components, one of the dimensions of which does not exceed 150 mm. In addition, if the speed of casting is to be increased beyond certain values, turbulence is caused at the location of the nozzle-float assembly, and such turbulence results in deformation of the meniscus of th
REFERENCES:
patent: 4236570 (1980-12-01), Gaule et al.
Cans Yves
Gonda Richard
Tavernier Marc
Lin Kuang Y.
Societe de Vente de l'Aluminium Pechiney
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