Pumps – Processes
Reexamination Certificate
1999-10-31
2001-09-25
Freay, Charles G. (Department: 3746)
Pumps
Processes
C164S312000
Reexamination Certificate
active
06293759
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to the field of pumps for pumping molten metal and, in particular, to using a pump for pumping molten metal into a shot sleeve for die casting metal parts. More specifically, the invention is directed to an apparatus for die casting high melting point alloys containing aluminum or magnesium, and the like.
BACKGROUND OF THE INVENTION
Metal parts may be produced using “cold chamber” and “hot chamber” die casting apparatuses. Cold chamber apparatuses employ a molten metal reservoir that is separated from the casting machine. Enough metal for one just casting is normally ladled by hand through a port of a small chamber referred to as a shot sleeve. Since this is done by hand it undesirably results in variation in the quantity of molten metal that is fed into the shot sleeve. A hydraulically actuated ram moves in the shot sleeve to force the molten metal under pressure into a die. As the ram advances, it seals the port and forces the charge into the die at pressures which may range from several psi to 60,000 psi or more. The molten metal cools in the chamber prior to injection into the die, thereby lending itself to description as a “cold chamber” process.
The hot chamber process is used for low melting point alloys such as zinc alloys and, may employ, for example, a machine comprising a fixed cylinder having a spout firmly connected to a nozzle locked against a die cavity. A piston operating in the cylinder is raised to uncover an inlet port below the molten metal level in the pot. After the molten metal fills the interior of the cylinder, the piston is forced downward, which causes the molten metal to flow through the spout and into the die. Once the metal solidifies in the die the piston is withdrawn, the die is opened and the casting is removed. The die is then closed and the process repeated.
It is generally believed that better metallurgical castings result from use of the hot chamber process since the molten metal is not cooled as in the cold chamber process. However, numerous attempts have been made to develop a hot chamber apparatus for casting high melting point aluminum without widespread success. In view of difficulties presented in the hot chamber process, the industry could benefit from a cold chamber die casting apparatus which eliminates the risk of workers having to carry out the dangerous task of ladling molten metal, and from a process which produces an accurate charge of molten metal into the shot sleeve.
SUMMARY OF THE INVENTION
An apparatus for pumping molten metal includes a pump base comprised of non-metallic, heat resistant material and adapted to be submerged in a bath of molten metal. The pump base includes a molten metal inlet opening; a molten metal valve chamber in communication with the inlet opening; a molten metal pumping chamber; a passageway that communicates the valve chamber and the pumping chamber and a molten metal outlet opening that communicates with the pumping chamber. A first piston made of non-metallic, heat resistant material is adapted for reciprocal movement in the valve chamber. A second piston made of non-metallic, heat resistant material is adapted for reciprocal movement in the pumping chamber. A first connecting member extends upwardly from the first piston and a second connecting member extends upwardly from the second piston. At least one actuator is in communication with the first and second connecting members. The at least one actuator acts upon the first and second connecting members to effect the reciprocal movement of the first and second pistons. When used in a die casting apparatus, preferably of the cold chamber type, also featured is a shot chamber disposed near the discharge opening for receiving molten metal discharged from the conduit. A ram is disposed in the chamber and adapted to direct molten metal in the chamber to a die for casting the molten metal.
In particular, support structure is connected to the base outside the bath. At least one removable stop member is disposed between the support structure and the second piston, the at least one stop member being configured and arranged so as to restrict movement of the second piston by a distance corresponding to at least one of a size and location of the stop member. At least one annular gasket comprised of refractory material is disposed around the second piston. The apparatus may also include an annular sealing member disposed around the second piston. The sealing member includes radial outlet openings therethrough. A drain opening is located near the outlet openings and extends to an exterior of the base.
The present invention advantageously enables an accurate charge of molten metal to be transferred to the shot chamber, which improves the die casting process. In addition, the risk associated with ladling the molten metal by hand, is avoided. The charge may be accurately varied as well, using stop member sleeves, a vertically movable stop plate and the like. The valve of the pump is advantageous in that it is a reliable and efficient way to facilitate the charge into the pumping chamber.
The present invention is especially adapted for use in the cold chamber process, to replace the hand ladling that is often used. However, the present apparatus may be used in a hot chamber die casting process, by connecting the conduit with the shot sleeve or directly to a die without using a shot sleeve. A seal would be disposed around the plunger that is suitable to enable sufficient pressure to be generated in the pumping chamber. In addition, the conduit may be heated or suitably insulated so as to prevent chilling of the molten metal prior to entering the die.
A method of pumping molten metal using the pump base includes a molten metal feed stage comprising positioning the first piston at a location that enables molten metal to enter the valve chamber through the inlet opening, and positioning the second piston in the pumping chamber so as to permit molten metal to enter the pumping chamber. A molten metal pumping stage includes positioning the first piston so as to prevent molten metal from entering the valve chamber, and moving the second piston so as to discharge molten metal from the pumping chamber and to direct molten metal from the outlet opening through a conduit into the shot chamber. The molten metal is then injected from the shot chamber into a cavity of a die.
In cold chamber die casting the molten metal that is received in the shot chamber is exposed to external air while passing from the conduit to the shot chamber. In the case of hot chamber die casting, molten metal is passed from the conduit to the shot chamber without exposing the molten metal to external air or from the conduit directly to the die.
Molten metal may be sealed in the pumping chamber using the annular sealing member disposed around the second piston. Pressure is relieved by passing molten metal out through radial exit openings in the sealing member and through the drain hole to the exterior of the base.
In particular, one embodiment of the invention is directed to a method of die casting molten metal comprising moving a piston in a pumping chamber within a bath of molten metal to inject the molten metal into a die and then casting the molten metal. The pumping chamber is sealed using an annular sealing member disposed around the piston, and relieving pressure by passing molten metal outwardly through radial exit openings in the sealing member and through a drain hole to an exterior of the base. The pumping chamber may be further sealed using at least one annular gasket formed of refractory material around the piston. The at least one gasket and sealing member may be compressed to improve the sealing effect.
Many additional features, advantages, and a fuller understanding of the invention will be had from the accompanying drawings and the detailed description that follows.
REFERENCES:
patent: 274104 (1883-03-01), Ayers
patent: 350761 (1886-10-01), Neff
patent: 1689698 (1928-10-01), Tornberg
patent: 1736188 (1929-11-01), Daeson et al
Freay Charles G.
Gray Michael K.
Watts Hoffmann Fisher & Heinke
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