Patent Application
20130118704
The invention relates generally to electromagnetic stirring of metal castings. More particularly, the invention relates to a casting system, mold, and method for electromagnetically stirring sand castings.
Sand casting refers to a metal casting process that uses sand as the mold material. A binder such as, e.g., clay or resin, may be mixed with sand, and the mixture may be moistened. This produces an aggregate material having suitable strength and plasticity to form the mold. The sand material is packed around a pattern, and the pattern is subsequently removed, leaving a cavity in the mold.
In the casting process, molten metal is poured into the mold cavity through a gating system, and the molten metal is allowed to solidify in the mold. For large metal castings, such as steel components of, e.g., wind turbines, which may weigh upwards of 4,500 to 5,000 kg (about 10,000 to 11,000 pounds), the solidification process may take several days to a week or more. After the casting has cooled, it can be shaken out of the mold.
The lengthy cooling time associated with sand casting presents several challenges. Steel and other alloy castings may be susceptible to segregation of elements during the cooling process due to different reactions. The longer cooling takes, i.e., the longer the cycle time, the greater the risk of this occurring. Elemental segregation can produce defects in the resulting casting that weaken the structure. Shrinkage defects may also occur when feed metal is unavailable to compensate for shrinkage as the metal cools and solidifies. These may naturally concentrate in the thermal center of the casting, which may disproportionately weaken that area of the resulting casting.
A first aspect of the disclosure provides a mold including a mold body having a cavity therein; the mold body further including a passageway fluidly connecting the cavity with an exterior of the mold, wherein the passageway allows for introduction of a molten metal into the cavity; and at least one induction coil embedded in the cope, or top half, of the mold, and at least one induction coil embedded in the drag, or bottom half, of the mold.
A second aspect of the disclosure provides a casting system comprising a mold body and a molten metal introduced into the mold. The mold body may include: a cavity therein; a passageway fluidly connecting the cavity with an exterior of the mold body; and at least one fluid-cooled induction coil embedded in a cope of the mold body and at least one fluid-cooled induction coil embedded in a drag of the mold body. The at least one fluid-cooled induction coil may be embedded in a cope of the mold body, and the at least one fluid-cooled induction coil may be embedded in a drag of the mold body to generate an electromagnetic field for stirring the molten metal during solidification of the molten metal.
A third aspect of the disclosure provides a method including: preparing a metal for casting, the preparing including melting the metal; introducing the molten metal into a cavity within a mold body; and using at least one induction coil, applying an electromagnetic field to the molten metal during solidification of the molten metal in the mold.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.
As indicated above, aspects of the invention provide a casting system and mold structure for producing metal castings, shown in
Referring to
With reference to
Induction coils 150, 160 are fluid-cooled. In some embodiments, the fluid may be water. More specifically, in some embodiments, deionized water may be used. In further embodiments, induction coils 150 and 160 are low-frequency induction coils, operating at a frequency of, e.g., about 20 Hz to about 10 kHz. Induction coils 150, 160 may further have a cross-sectional diameter of between about 5 and about 30 mm, and may have either a round or a rectangular cross sectional shape. In further embodiments, induction coils 150, 160 are made of copper, and coated with ceramic, providing improved heat resistance.
Referring back to
Referring to
In this manner, electromagnetically stirred sand castings may be produced. As used herein, the terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 5,000 kg, or, more specifically, about 4,500 kg to about 5,000 kg,” is inclusive of the endpoints and all intermediate values of the ranges of “about 4,500 kg to about 5,000 kg,” etc.).
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
