Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-01-10
2003-02-18
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S136000, C164S323000
Reexamination Certificate
active
06520243
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of foundry operations and more particularly to the casting of molten metal in a production line environment. In greater particularity the present invention relates to a technique for casting molten metal in a production process utilizing a conveyable string of molds that define a series of mold cavities. In still further particularity, the present invention relates to an apparatus and method for preventing the premature introduction of molten metal into a mold cavity formed by a conveyable string of molds as the mold string is advanced stepwise along a conveying system in a metal casting process.
BACKGROUND OF THE INVENTION
The art of casting metal objects in sand molds is ancient. Numerous advances have been made in the art, and metal casting may now be accomplished by complex, automated production techniques utilizing a conveyable string of closely juxtaposed molds that are advanced along a production line. A mold string used in well known production casting systems typically comprises multiple adjacent molds, each distinct mold defining a mold cavity and at least one passageway, referred to as a downsprue, leading from the mold cavity to a surface of the mold. In the production method, castings are formed by introducing molten metal into the downsprue of a mold to fill the mold cavity and thereafter allowing the molten metal to cool to form a solid casting. Economic constraints require increasing efficiency in the casting process, and it is well known in the art that it is desirable that individual castings be formed in relatively short time intervals without having an adverse impact on the quality of the metal casting.
Metal casting production techniques utilizing a conveyable mold string require a source of molten metal and a method of transferring selective quantities of molten metal from a molten metal source to individual molds. In the production line casting of molten metal, molten metal is typically provided in batches stored in a large reservoir or ladle. An efficient and commonly used method of transferring molten metal into individual molds from the source of molten metal is to pour molten metal from a source into the downsprue of a mold. Utilization of this method of transferring requires positioning the source of molten metal, such as a reservoir or ladle, above the mold string.
A common method of pouring molten metal from a molten metal reservoir is to selectively open and close an outlet located in the bottom portion of a molten metal reservoir, such as with the use of a stopper rod positioned within the reservoir that can be raised to open the outlet and lowered to close the outlet. This method of transferring molten metal into individual molds often involves aligning the downsprue of an individual mold directly below the effluent outlet of a molten metal reservoir for the receipt of the molten metal poured from the reservoir outlet.
Production methods of the type utilizing a source of molten metal disposed directly above a conveyable mold string typically utilize a specific type of mold string having downsprues extending from the top surface of the mold string. In the casting process, the mold string of this type is indexed to position a first individual mold beneath the molten metal source so that the downsprue in the top surface of the mold string is aligned directly below the outlet. In a typical production casting process, the mold string remains in a stationary position as the outlet is opened to fill the mold with molten metal. After the selected amount of molten metal has been poured into the mold, the outlet is closed to cease the transfer of molten metal. The mold string is then indexed, or advanced, along a conveying system to a next stationary position in which a next mold being adjacent to the first individual mold is aligned directly beneath the outlet of the molten metal source. This next mold is then filled with molten metal and this process is repeated in sequence to progressively fill adjacent molds with molten metal.
Various techniques for producing a mold string defining a series of mold cavities and downsprues extending from the top surface of the mold string are commercially available and widely utilized. A mold string of this general type may be manufactured in connection with metal casting in vertically-parted green sand molds, and in connection with molds produced utilizing the well known Disamatic machine. Other similar methods of such production of mold strings are well known in the art.
Without regard to the specific manner in which a particular mold string is produced, mold strings typically utilized in production line casting techniques comprise a series of vertically parted molds wherein each mold defines a mold cavity and a downsprue extending from the top surface of the mold string. There is a continual problem relating to the use of vertically parted molds such as those produced by a Disamatic molding machine and other common production techniques. Such molds are in relatively close proximity to adjacent molds, and in actual operation molten metal intended for introduction into specific mold cavities may instead be ultimately deposited on the top surface of a mold string. This can result in the unintended and premature introduction of molten metal into an empty mold cavity, which causes serious defects in the resulting quality of produced castings. Molten metal prematurely introduced into an empty mold cavity cools to form small droplets of metal commonly referred to as “shots.” The casting process is typically not designed for the random and unintended introduction of shots into an empty mold cavity prior to filling the mold cavity with molten metal. Instead, the casting process is designed to fill mold cavities that are entirely empty. This allows the molten metal introduced into the mold cavity to have substantially uniform metallurgical properties.
The premature introduction of shots into an empty mold cavity can result in the production of castings having significant defects. The shot produces an inclusion in the casting causing scrap or, worse, resulting in the failure of a safety part. The molten metal poured into the mold may not adhere properly to the shot or the shot may otherwise adversely influence the cooling properties of the molten metal proximate the shot. The premature introduction of even small droplets of molten metal forming shot into an empty mold cavity results in serious defects in the quality of produced castings. Therefore, methods of preventing the premature introduction of shot into molds in a casting process is needed.
One manner in which this quality control problem initially occurs is by the splashing of molten metal from one mold to an adjacent mold during pouring of molten metal. Methods of preventing this type of manufacturing problem are disclosed in the prior art. Sorrell et al., U.S. Pat. No. 4,749,019 discloses the utilization of a splash guard in a metal casting process for preventing molten metal from splashing into the downsprue of a mold as molten metal is poured into an adjacent mold cavity. The Sorrell et al. device is a solid object that is selectively placed between adjacent molds during the pouring of molten metal. In a manual casting process, a portion of the Sorrell et al. device physically contacts a portion of the top surface of the mold string and remains in this position as molten metal is poured. After molten metal has been poured into a cavity, the splash guard disclosed in the Sorrell et al. patent is then raised from the top surface of the mold string. The Sorrell et al. device remains in a raised position as the mold string is indexed to the next position.
A second embodiment of the device disclosed in the Sorrell et al. patent is directed for use in an automated production process. In the second embodiment, the splash guard remains in a fixed raised position above the top surface of the mold string. These and other conventional methods of preventing the premature introduction of molten metal into an emp
Lin Kuang Y.
Smith , Gambrell & Russell, LLP
Vulcan Engineering Company, Inc.
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