Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-12-11
2003-03-25
Dunn, Tom (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S437000, C164S490000, C164S113000, C164S312000, C164S259000, C164S066100, C164S337000, C164S133000, C222S590000, C222S594000, C222S596000
Reexamination Certificate
active
06536508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a molten metal supply system and, more particularly, a continuous pressure molten metal supply system and method of operating the same.
2. Description of the Prior Art
The metal working process known as extrusion involves pressing metal stock (ingot or billet) through a die opening having a predetermined configuration in order to form a shape having a longer length and a substantially constant cross-section. For example, in the extrusion of aluminum alloys, the aluminum stock is preheated to the proper extrusion temperature. The aluminum stock is then placed into a heated cylinder. The cylinder utilized in the extrusion process has a die opening at one end of the desired shape and a reciprocal piston or ram having approximately the same cross-sectional dimensions as the bore of the cylinder. This piston or ram moves against the aluminum stock to compress the aluminum stock. The opening in the die is the path of least resistance for the aluminum stock under pressure. The aluminum stock deforms and flows through the die opening to produce an extruded product having the same cross-sectional shape as the die opening.
Referring to
FIG. 1
, the foregoing described extrusion process is identified by reference numeral
10
, and typically consists of several discreet and discontinuous operations including: melting
20
, casting
30
, homogenizing
40
, optionally sawing
50
, reheating
60
, and finally, extrusion
70
. The aluminum stock is cast at an elevated temperature and typically cooled to room temperature. Because the aluminum stock is cast, there is a certain amount of inhomogeneity in the structure and the aluminum stock is heated to homogenize the cast metal. Following the homogenization step, the aluminum stock is cooled to room temperature. After cooling, the homogenized aluminum stock is reheated in a furnace to an elevated temperature called the preheat temperature. Those skilled in the art will appreciate that the preheat temperature is generally the same for each billet that is to be extruded in a series of billets and is based on experience. After the aluminum stock has reached the preheat temperature, it is ready to be placed in an extrusion press and extruded.
All of the foregoing steps relate to practices that are well known to those skilled in the art of casting and extruding. Each of the foregoing steps is related to metallurgical control of the metal to be extruded. These steps are very cost intensive, with energy costs incurring each time the metal stock is reheated from room temperature. There are also in-process recovery costs associated with the need to trim the metal stock, labor costs associated with process inventory, and capital and operational costs for the extrusion equipment.
Attempts have been made in the prior art to design an extrusion apparatus that will operate directly with molten metal. U.S. Pat. No. 3,328,994 to Lindemann discloses one such example. The Lindemann patent discloses an apparatus for extruding metal through an extrusion nozzle to form a solid rod. The apparatus includes a container for containing a supply of molten metal and an extrusion die (i.e., extrusion nozzle) located at the outlet of the container. A conduit leads from a bottom opening of the container to the extrusion nozzle. A heated chamber is located in the conduit leading from the bottom opening of the container to the extrusion nozzle and is used to heat the molten metal passing to the extrusion nozzle. A cooling chamber surrounds the extrusion nozzle to cool and solidity the molten metal as it passes therethrough. The container is pressurized to force the molten metal contained in the container through the outlet conduit, heated chamber and ultimately, the extrusion nozzle.
U.S. Pat. No. 4,075,881 to Kreidler discloses a method and device for making rods, tubes, and profiled articles directly from molten metal by extrusion through use of a forming tool and die. The molten metal is charged into a receiving compartment of the device in successive batches that are cooled so as to be transformed into a thermal-plastic condition. The successive batches build up layer-by-layer to form a bar or other similar article.
U.S. Pat. Nos. 4,774,997 and 4,718,476, both to Eibe, disclose an apparatus and method for continuous extrusion casting of molten metal. In the apparatus disclosed by the Eibe patents, molten metal is contained in a pressure vessel that may be pressurized with air or an inert gas such as argon. When the pressure vessel is pressurized, the molten metal contained therein is forced through an extrusion die assembly. The extrusion die assembly includes a mold that is in fluid communication with a downstream sizing die. Spray nozzles are positioned to spray water on the outside of the mold to cool and solidify the molten metal passing therethrough. The cooled and solidified metal is then forced through the sizing die. Upon exiting the sizing die, the extruded metal in the form of a metal strip is passed between a pair of pinch rolls and further cooled before being wound on a coiler.
An object of the present invention is to provide a molten metal supply system that may be used to supply molten metal to downstream metal working or forming processes at substantially constant working pressures. It is a further object of the present invention to provide a molten metal supply system incorporating a plurality of molten metal injectors adapted to generate relatively high working pressures with correspondingly low amounts of stored energy, and further exhibit improved wear resistance.
SUMMARY OF THE INVENTION
The foregoing objects are accomplished with a molten metal supply system and method of operating the same in accordance with the present invention. The molten metal supply system includes a molten metal supply source, a plurality of molten metal injectors, and a gas supply source. The plurality of molten metal injectors each include an injector housing and a piston reciprocally operable within the housing. The injector housing is configured to contain molten metal and is in fluid communication with the molten metal supply source. The piston is movable through a return stroke allowing molten metal to be received into the housing from the molten metal supply source, and a displacement stroke for displacing the molten metal from the housing to a downstream process. The piston has a pistonhead for displacing the molten metal from the housing. The gas supply source is in fluid communication with the housing of each of the injectors through respective gas control valves. During the return stroke of the piston of each of the injectors, a space is formed between the pistonhead and the molten metal and the corresponding gas control valve is operable to fill the space with gas from the gas supply source. During the displacement stroke of the piston of each of the injectors, the corresponding gas control valve is operable to prevent venting of gas from the gas filled space, such that the gas in the gas filled space is compressed between the pistonhead and the molten metal received into the housing and displaces the molten metal from the housing ahead of the piston.
The molten metal supply system may further include a control unit connected to each of the injectors and configured to individually actuate the injectors, such that the pistons move substantially serially through the return and displacement strokes thereby providing a substantially constant molten metal flow and pressure to the downstream process. The control unit may be configured to control the injectors such that at least one of the pistons moves through its displacement stroke while the remaining pistons move through their return strokes to provide the substantially constant molten metal flow and pressure to the downstream process. The piston of each of the injectors may include a piston rod having a first end and a second end. The first end may be connected to the pistonhead and the second end may be connected to an actuator fo
Chabal Ronald G.
Paola Vincent A.
Reighard Scott E.
Sample Vivek M.
Alcoa Inc.
Dunn Tom
Lin I.-H.
Pearce-Smith David W.
Schuster Christian E.
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