Metal founding – Means to shape metallic material – Pressure shaping means
Reexamination Certificate
2000-08-03
2002-11-19
Dunn, Tom (Department: 1725)
Metal founding
Means to shape metallic material
Pressure shaping means
C164S312000, C164S317000, C164S318000
Reexamination Certificate
active
06481489
ABSTRACT:
TECHNICAL FIELD
This invention relates to a reinforced casting intended for use in hot chamber die casting processes.
BACKGROUND ART
Die casting machines generally utilize one of two classifications of casting material pumping systems, either a hot chamber system or a cold chamber system. Hot material chamber die casting machines include parts that are partially submerged in a vat containing the molten metal and thus operate at the temperature of the metal bath. Cold chamber die casting machines are unheated except for the die member which receives the molten metal during the casting process. Hot chamber systems are used primarily for the casting of metals having low melting points such as tin, zinc and lead alloys. Cold chamber machines can be used for die casting most metals, however, they are most commonly used for aluminum, magnesium and copper alloys.
The portions of the hot chamber die casting machine that come in contact with the molten metal must have good wear resistance, hardening resistance and softening resistance at the operating temperature of the machine. This is particularly true with the nozzle, nozzle seat and gooseneck sections of hot chamber machines. These components must be able to withstand the continuous washing action of the heated molten metal and maintain their dimensional and structural integrity in spite of the corrosive properties of the molten metal and the extreme temperature and pressure gradients to which they are exposed. The nozzle, nozzle seat and gooseneck of the machine are exposed to injection pressures commonly ranging from 2,000 to 6,000 psi, but can vary with injection pressures sometimes ranging as high as 30,000 psi. Hardening occurs from repeated crystallization and failure results from cracking.
The industry has lavished great care in choosing materials for the construction of hot chamber die casting machines. Improved materials for the various parts have led to enhanced resistance against wear, hardening and softening. The industry, however, has had little success in overcoming failure problems resulting from the high operating pressures present in the hot melt die casting process.
DISCLOSURE OF INVENTION
This invention is generally related to a reinforced casting and specifically related to a reinforced gooseneck and related components for use with a hot chamber die casting machine. The invention provides for the selected reinforcement of the gooseneck, nozzle, and nozzle seat. The preferred embodiment of the invention focuses on reinforcing the gooseneck as this is the location where most pressure-caused failures occur. The reinforcement structure is generally made of steel wire. The wire may be a solid or braided wire. The reinforcements generally have a shape or a combination of shapes. For example, the preferred embodiment is a combination of shapes, one of them being a U-shape with a tail and the other an inverted U-shape.
A gooseneck is commonly known to the casting industry as a unit designed to increase the pressure of a molten non-ferrous metal before it is forced or flowed into a die. Goosenecks are most commonly cast from molten grey iron such as cast iron, alloyed cast iron, and semi-steel. They may also be cast from molten steel or alloyed steel. In rare instances, Goosenecks are machined from a block of steel or alloyed steel.
Grey iron goosenecks have many advantages when compared to steel goosenecks. Grey iron is generally more stable when subjected to the heat levels found in hot melt die casting processes. The internal channel of the gooseneck cast from grey iron can also be cast, thereby allowing for the creation of a smooth path having gentle curves for the molten non-ferrous metal to flow through to the die. A smoothly flowing molten metal has less turbulence and therefore the final die cast product is denser and has less porosity. The preferred internal channel of a grey iron gooseneck is also preferably cast to have a gradually reducing diameter in the direction of fluid flow. However, a major disadvantage of grey iron goosenecks lies in the low tensile strength of grey iron as compared to steel and resultant failures when the goosenecks are subjected to regular and sustained high pressure levels.
Goosenecks cast or machined from steel, on the other hand, have greater strength than grey iron castings. Steel goosenecks, however, have several disadvantages. The internal channel must be machined or drilled, thereby creating sharp angular corners which tend to interfere with the smooth flow of molten metal creating considerable turbulence and frothing of the molten metal. Such turbulence and frothing lowers the pressure of the molten metal entering the die cavity and increases the porosity of the metal flowing into the die cavity. Further, plugs must be installed where the channels were machined or drilled and the plugs create an area of weakened structure in the gooseneck, thus creating an enhanced chance of failure of the gooseneck, as well as additional maintenance.
The present invention provides a cast grey iron gooseneck having steel reinforcements fused with the grey iron around the internal channel. The reinforced gooseneck of this invention offers the strength advantages of steel combined with the positive advantages of grey iron goosenecks. The invention provides a high strength gooseneck with a smooth internal channel, preferably having a gradually reduced diameter and having gentle curves, and a good stability when exposed to the extreme heat of the hot melt die casting process.
The same principals discussed above are applicable to the nozzle and nozzle seats. Other embodiments envision bimetallic components using an expensive or exotic metal, such as austenitic stainless steel as a core surrounding the internal channel of the gooseneck, nozzle and nozzle seat with the reinforced casting surrounding the exotic metal core. Finally, it is envisioned that other embodiments of the invention will provide reinforced cast steel goosenecks for certain desired applications.
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Republic “Endurs” Stainless Steels, Republic Steel Corp. Jul. 1952, pp. 6-9, 67-68, 79-86.*
Republic “Endurs” Stainless Steels, pp. 6-9, 67-68, 79-86 (no date available).
Dunn Tom
Emch, Schaffer, Schaub & Porcello & Co., L.P.A.
Lin I.-H.
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