Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1991-10-18
1995-01-17
Bradley, P. Austin
Metal founding
Process
Shaping liquid metal against a forming surface
164122, B22D 1804
Patent
active
053818512
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a low pressure chill casting method for casting metal castings such as cylinder heads or engine blocks of combustion engines or the like, which cast components have walls which are considerably thinner in some regions than in their remaining regions, in which method by means of gas pressure liquid metal is forced from a melt container through a riser tube into a mold.
While in known gravity chill casting methods during charging metal is allowed to fall over the entire mold height, whereby strong turbulence occurs in the mold with the known disadvantageous consequences for the metal structure, in known low pressure chill casting methods by introducing the metal into the mold from beneath and allowing it to rise in the mold quieter metal flow is achieved, the molding speed being adaptable at each phase to the desired mold filling. According to previously generally accepted teaching, in known low pressure casting methods the casting molds are so arranged that the thickest wall parts of the cast component lie in the vicinity of the gating, while the thin walled regions lie spaced therefrom. This takes place with a view to enabling feeding of the cast component during its solidification exclusively by melt subsequently pressed from the riser tube, i.e. the solidification should begin in the regions of the cast component remote from the gating and propagate to the gating (see handbook "Kckillen fur Leichtmetallguss" by Professor Philipp Schneider, Giesserei-Verlag 1986, pages 205 and 206). Since in such a situation for the mold the predominantly thick walled regions of the cast components in the vicinity of the gating solidify relatively slowly in the mold, the formation of coarse crystalline structure with precipitation of coarse inter-metallic compounds in this region of the casting is the result. This has however proved to be very unsatisfactory with cast components which in use are subject to high loading in the region of their predominently thicker wall portions, as is for example the case in cylinder heads in the combustion region. A further disadvantage of these known methods of operation arises in that to achieve trouble free mold filling into the thin wall regions it is necessary to work with correspondingly increased casting temperatures which in turn must act disadvantageously on the overall solidification time, i.e. the duration of a casting cycle and also on the casting quality.
OBJECTS AND SUMMARY OF THE INVENTION
A principal object of this invention is preventing the disadvantages of the known low pressure chill casting method. This is achieved according to the invention in that in this casting method the mold is so arranged that its mold cavity regions forming the thicker wall portions of the cast component lie remote from the gating and its mold cavity regions forming the thinner wall portions lie near the gating, the liquid metal being introduced at or near the region of the mold lying near the gating into the mold cavity regions forming the thinner wall portions.
Normally, in this connection the regions of the mold cavity remote from the gating are uppermost and the regions of the mold cavity near the gating are underneath. It has proved that with this method of operation contrary to previously well-established and strictly maintained practice, particularly fault free cast components can be obtained under advantageous production conditions. Using the turbulence-free mold filling given in the low pressure casting method, in this connection foam formation and oxide inclusions are prevented and altogether favorable prerequisites for the production of high quality cast components are created.
By the introduction of the liquid metal into the regions of the mold cavity lying near the gating and forming the thinner wall portions of the cast component and thus having smaller cross-section, the introduced metal is cooled in this region of the mold as it rises within the mold so that with relatively low temperatures it reaches the larger mold cavi
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DE-Z. "Giesserei-Praxis" Niederdruck-Kokillenguss--Heutiger Stand der Technik by A. W. Plume, Nov. 1986, S. 294-298.
DE-Z. "Giesserei" Das Niederdruck-Kokillengiessverfahren fur Leichtmetallegierungen by V. E. Bertram, 49 (1962), S. 332-341.
"Kokillen fur Leichtmetallguss", Professor Dr.-Ing. Philipp Schneider, Handbuch der Konstruktion, Herstellung und Verwendung von Kokillen fur die Leichtmetallgisserei, Giesserei-Verlag, 1986, pp. 205 and 206.
Bilz Georg
Dobner Alfred
Lammermann Hans
Riess Klaus
Sterner Klaus
Alcan Deutschland GmbH
Bradley P. Austin
Puknys Erik R.
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