Metal founding – Process – Shaping a forming surface
Patent
1987-07-27
1989-02-14
Jordan, M.
Metal founding
Process
Shaping a forming surface
164119, 164246, 164365, B22C 904, B22D 1804
Patent
active
048040320
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of making metal castings using the full mould process, namely providing an in situ destroyable pattern of, for example, expanded polystyrene, embedding the pattern in unbonded sand, consolidating the sand to form a mould in which is defined a mould cavity, feeding molten metal into the cavity, permitting the metal to solidify within the cavity to form a casting, interrupting the feed of metal to the cavity and removing the casting from the cavity. The pattern may be destroyed in situ either by the metal as it is fed into the cavity, or by the application of heat prior to introduction of the metal into the cavity.
Problems of lack of accuracy and poor surface finish have been encountered when using the full mould process to produce high quality castings of an aluminium or an aluminium alloy.
An object of the present invention is to overcome this problem.
In accordance with the present invention I provide a method of making metal castings comprising the steps of providing an in situ destroyable pattern, then embedding the pattern in unbonded sand and consolidating the sand to form a mould in which is defined a mould cavity, then feeding molten metal into the cavity and permitting the metal to solidify within the cavity to form a casting and interrupting the feed of metal to the cavity and removing the casting from the cavity, wherein the metal is aluminum or an aluminum alloy and at least part of the mould being formed of said which comprises at least 50% sand as herein defined, by weight of sand.
Said part may comprise at least one moulding feature, made of unbonded sand, as hereindefined.
Said part may comprise unbonded sand and comprise the whole or substantially the whole of the mould.
Said mould cavity may comprise at least one preformed moulding feature which is included in said pattern.
Said part may comprise at least one preformed moulding feature which is included in said pattern.
Said preformed moulding feature may be as hereindefined.
The whole of the mould, except the or each preformed moulding feature may comprise unbonded sand which comprises at least 50% sand, as hereindefined, by weight.
The invention also provides, according to another aspect, a method of making metal castings comprising the steps of providing an in situ destroyable pattern, then embedding the pattern in unbonded sand and consolidating the sand to form a mould in which is defined a mould cavity, then feeding molten metal into the cavity and permitting the metal to solidify within the cavity to form a casting and interrupting the feed of metal to the cavity and removing the casting from the cavity, wherein the mould cavity comprises a moulding feature as hereindefined, made of at least 50% sand, as hereindefined, by weight of sand.
The moulding feature may be formed of unbonded sand, or the moulding feature may be preformed of sand bonded with a bonding agent.
In either aspect of the invention, the unbonded sand may comprise wholly or substantially wholly zircon sand, except for usual impurities, whilst the bonded sand may comprise wholly or substantially wholly zircon sand and bonding agent except for usual impurities.
By virtue of using at least 50% zircon sand and preferably wholly, or substantially wholly, zircon sand, I have found an unexpected improvement in the quality of the casting produced compared with castings produced using the full mould process to cast such metals, particularly where a moulding feature as hereinbefore is provided in the mould cavity, when the mould is made of other sand, such as silica sand.
Analysis of the system in the light of this unexpected result leads to the belief that the improvement is due to the density of the sand being substantially the same as the density of the molten metal being cast. It is believed that this minimises the hydrostatic forces acting on the moulding feature thereby greatly improving mould stability during casting and hence greatly improving the final accuracy of the casting.
Because the mould when comprising a moulding feature, a
REFERENCES:
patent: 3222738 (1965-12-01), Carter
patent: 4291739 (1981-09-01), Baur
patent: 4693292 (1987-09-01), Campbell
Dieter, H. B. et al. "Sand Without Binder For Making Full Mold Castings" In Modern Casting, vol. 51, No. 6, June 1967, pp. 133-146, 164-34.
Batten, Jr. J. Reed
Cosworth Research & Development Limited
Jordan M.
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