Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1998-10-28
2001-03-13
Pyon, Harold (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S134000, C164S358000, C164S362000, C164S363000, C164S337000
Reexamination Certificate
active
06199619
ABSTRACT:
TECHNICAL FIELD
The invention relates to an arrangement of an ingate system with a feeding reservoir for feeding castings.
BACKGROUND ART
It is commonly known that metals, both in the liquid and the solid state, when cooled undergo a reduction in volume, a so-called thermal contraction. In casting moulds, in which a non-uniform heat distribution reigns in the mould cavity after the pouring, and in which for this reason all parts of the casting do not solidify at the same time, this causes the parts of the casting solidifying last to give off liquid metal to compensate for the contraction of the parts of the casting having solidified earlier, leading to faults in the casting, commonly called “shrinkage holes” appearing in the form of depressions in the surface of the casting or cavities (macroscopic or microscopic holes) within the casting. In order to avoid these casting faults, the skilled person can have recourse to a series of expedients, of which the most common is the use of feeding reservoirs, i.e. cavities in the mould being filled with metal during the pouring and having such dimensions that the metal in them solidifies later than the parts of the casting solidifying last, being connected to the latter through ducts having a relatively large cross-sectional area, thus being able to post-feed these parts with liquid metal to compangate for the contraction. U.S. Pat. No. 1,410,775 describas an example of this method.
In the method described in U.S. Pat. No. 1,410,775, the full flow of the melt passes through the feeding reservoir. As the latter will necessarily have a considerable volume in order to be able to accommodate all the melt required for feeding, this means that the melt will flow through the feeding reservoir in a turbulent manner. If the melt is of an easily oxidizable material, such as aluminium or maqnesium or their alloys, such an arrangement entails the risk of relatively large quantities of oxide being formed, causing a loss of metal and possibly contamination of the castings.
DISCLOSURE OF THE INVENTION
It is the object of the invention to provide an arrangement of an ingate system that does not present the disadvantages of the prior art referred to above, and according to the invention, this object is achieved by the features set forth hereinafter.
With this arrangement, the feeding reservoir is separated from the duct carrying the flow of melt by a permeable partition having a finite resistance to flow through it, and during the initial phase of the pouring, this partition will act like a wall restricting the flow to the duct only. If the latter is shaped in a manner supporting laminar or quasi-laminar flow, i.e. with a high ratio of circumference to cross-sectional area, such as a flat shape, then the risk of oxidization can be considerably reduced. During the later phases of the pouring, the back pressure from the casting cavity increases, causing melt in the duct to penetrate the permeable partition so as to gradually fill the feeding reservoir, and when the casting cavity is full, the reservoir will also be full and ready to supply feeding melt during the contraction of the casting in the cavity.
An additional advantage of using the permeable partition is that it has a braking effect upon the hydraulic surge occurring when the mould is full.
The present invention also relates to a method of making the arrangement of the invention.
Advantageous embodiments of the arrrangement and the method according to the invention, the effects of which—beyond what is obvious—are explained in the following detailed part of the present description, are set forth.
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Georg Fischer Disa A/S
Larson & Taylor PLC
Lin I.-H.
Pyon Harold
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