Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2002-05-09
2004-06-29
Stoner, Kiley (Department: 1725)
Metal founding
Process
Shaping a forming surface
C164S522000, C164S132000, C164S138000, C164S369000
Reexamination Certificate
active
06755238
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for manufacturing a disintegrative core for high pressure casting, such as die casting or squeeze casting. More particularly, the present invention relates to the manufacture of complex disintegrative cores from water-soluble salts. Also, the present invention relates to such water-soluble salt cores. In addition, the present invention is concerned with a method for extracting such water-soluble salt cores.
PRIOR ART
Generally, a core preparation technique is necessary to prepare cast articles which have complex internal structures or are undercut.
In the case of gravity casting, a disintegrative core made of hard sand or ceramic powder or a water-soluble salt core is positioned inside a mold, and then a molten metal is introduced and solidified in the mold. After that, the disintegrative core is removed by mechanical and chemical methods or the salt core is melted-out with water or steam.
In the case of a piston for an internal combustion engine, the salt core preparation technique is useful in forming a circular oil cooling gallery inside of the piston.
U.S. Pat No. 3,645,491, the content thereof being incorporated herein by reference, discloses a core preparation technique in which a powdered water-soluble salt is combined with about 10% of synthetic resin as a binding agent U.S. Pat. No. 4,629,708, the content thereof being incorporated herein by reference, discloses a core preparation technique in which a water-soluble salt, such as sodium chloride and potassium chloride, is mixed with ceramics, such as alumina, and silicone resin as a binding agent and sintered.
Under actual circumstances, however, a piston is subjected to high pressure casting, such as die casting and squeeze casting, in order to prepare a high performance aluminum alloy or composite material piston.
In such a high press casting, a conventional disintegrative core made of sand or a conventional salt core cannot be applied to a high pressure casing method because the molten metal penetrates into the inside of the core by cast pressure or the core is collapsed by high pressure.
Recently, there are developed several kinds of core preparation techniques capable of being used where high pressure casting is required. For instance, U.S. Pat. No. 3,963,818, the content thereof being incorporated herein by reference, discloses a core preparation technique in which a powdered water-soluble salt, such as sodium chloride and potassium chloride, is added with about 1% of water, molded under a high pressure of 1.8~4.0 ton/cm
2
, then sintered at 100~300° C. for 20 minutes.
U.S. Pat. No. 4,438,804, the content thereof being incorporated herein by reference, discloses a core molding method in which a water-soluble salt powder is mixed with hard powder such as Zircon sand, and molded, along with potassium carbonate, barium carbonate or alkali silicate as a binding agent, under a high pressure.
U.S. Pat. No. 3,407,864, the content thereof being incorporated herein by reference, discloses a core molding method in which a water-soluble salt powder, such as sodium chloride and potassium chloride, is mixed with 3 wt % of borax, 1 wt % of magnesium oxide and 1 wt % of talc, and molded under a high pressure.
G.B. Pat. No. 2,156,720, the content thereof being incorporated herein by reference, discloses a core preparation technique in which a powdered water-soluble salt is hydrostatic-pressurized.
In these preparation methods using high pressures or hydrostatic pressures, voids between particles are minimized and their bonding force is strengthened so as for the core to keep its shape unchanged at a cast pressure of 5,000~20,000 psi and so as to prevent the molten metal from penetrating into the inside of the core.
However, these conventional methods suffer from disadvantages in that their application is restricted by the size and shape of cores and the production cost is increased because particle sizes of salt powders are required to be finely controlled.
In addition, it takes a significant amount of time to completely remove cores from the high pressure cast articles because the cores are dissolved with water.
Meanwhile, U.S. Pat. Nos. 4,446,906, 4,875,517, and 5,303,761, the contents thereof being incorporated herein by reference, disclose core preparation methods in which a water-soluble salt such as sodium chloride and potassium chloride are heated, melted, and subjected to die casting, optionally in combination with hard particles, such as silica and alumina.
Somewhat superior as it is to molding methods in core shape and productivity, these conventional methods are limited in their application by the size of the core. In addition, the conventional methods require a significant amount of time to completely remove cores from high pressure cast articles when water is used to dissolve the cores.
U.S. Pat No. 4,840,219, the content thereof being incorporated herein by reference, discloses a method in which a molten salt of a mixture comprising 40% by weight of NaCl and 40% by weight of Na
2
CO
3
is added with 10~50% of hard powder to give a slurry which is introduced into a mold. U.S. Pat. No. 3,459,253, the content thereof being incorporated herein by reference, discloses a method in which wire or glass fiber is added to the molten mixture salt comprising sulfate salt and carbonate salt to give a slurry which is introduced into a mold.
These methods have more variety in shape and size of the core than does the pressurization method or the die cast method. Meanwhile, because the used salts are as high as above 660° C. in melting temperatures, cracks are easily caused owing to the shrinkage upon solidification so that the cores become brittle and are difficult to handle. Additionally, a substantial period of time is required to remove the cores of high pressure cast articles because the cores must be dissolved by use of water, and the core salts thus obtained cannot be re-used.
DISCLOSURE OF THE PRESENT INVENTION
In view of the aforementioned problems and considerations, it is an object of the present invention to provide a method for manufacturing a disintegrative core for high pressure casting, capable of simply manufacturing a core of a complex shape and obtaining a core for high pressure casting by use of a re-usable aluminum alloy or a magnesium alloy.
It is another object of the present invention to provide a disintegrative core for high pressure casting.
It is a further object of the present invention to provide a method for extracting the core.
In one embodiment, one of the objects of the present invention is realized by the method for manufacturing the disintegrative core for high pressure case wherein a water-soluble salt, alone or in combination with a fine hard powder, is melted and solidified in a core mold; or processed into a fine powder and molded in a core mold under pressure, said water soluble salt ranging from 280 to 520° C. in melting point and from 9.8×10
−2
to 1.2×10 W/m·° C. in heat transfer coefficient (&kgr;) with a high latent heat, whereby the disintegrative core is manufactured from the water-soluble salt.
In another embodiment, another object of the present invention is embodied by the disintegrative core for high pressure casting manufactured through the said method.
In a further embodiment, the other object is realized by the method for extracting the disintegrative core for high pressure casting from a high pressure cast article, wherein the core is heated to a melting temperature at which the high pressure cast article is not thermally deformed, the core melt is extracted, and the cast article is washed with water.
BEST MODES CARRYING OUT THE PRESENT INVENTION
Hereinafter, the present invention describes a disintegrative core for high-pressure casting, and methods for manufacturing and extracting the same.
A disintegrative core for high pressure casting is manufactured from a water-soluble salt, wherein the water-soluble salt, alone or in combination with a fine hard powder, is melted and solidified in a core mold;
Lin I.-H.
Lowe Hauptman & Gilman & Berner LLP
Stoner Kiley
Technology Union Co., Ltd.
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