Patent Application
20160271691
The invention relates generally to molding techniques, and more particularly to a system and method for reducing hydrogen in a casting, for example, an aluminum casting.
Fabrication processes are used to shape, machine, and join metals or metal alloys. One fabrication process involves using a molding process to produce the desired shape of the metal or metal alloy. The molding process involves heating metal to a molten state, pouring the molten metal into a mold, and allowing the molten metal to cool and solidify in the shape of the mold. Castings obtained by the molding processes may be used in areas such as transportation, aerospace, defense, mining, construction, maritime, fluid power, and domestic household, and the like.
A sand molding process involves using a pattern, which is a replica of the finished casting. The pattern is slightly larger to allow for material shrinkage during solidification and cooling. The pattern (made of wood, plastic, or metal) can either be disposed loose or attached to a plate. A flask is disposed around the pattern to contain the prepared, free-flowing molding sand that is placed on the pattern. Pressure is applied to the sand to compact the sand firmly against the face of the pattern. When the sand is compacted, the sand exhibits physical properties that allow holding the exact shape of the pattern after the pattern is drawn from the mold. When the casting is solidified, the sand is removed from the casting.
In foundries, inert gases are purged through molten melt to scavenge hydrogen and to improve the quality of the casting. Such a process is referred to as “hydrogen degassing”. After degassing treatment, the molten metal tends to re-pickup hydrogen by reacting with surrounding hydrogen-containing gases during metal transfer and mold filling processes. Such a hydrogen re-pickup may not be undesirable to the quality of the casting but may be truly detrimental to cryogenic applications where cast components may outgas and impact the cryogenic system performance.
It is desirable to have a system and method for reducing hydrogen in a casting.
In accordance with one exemplary embodiment, a method is disclosed. The method involves filling a hydrogen-lean molten material in a crucible and closing a lid of the crucible and then feeding a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the hydrogen-lean molten material. The method further involves feeding a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly and transferring the hydrogen-lean molten material via an opening of the lid of the crucible to a mold cavity of the mold assembly. The method further involves cooling the hydrogen-lean molten material to form a casting.
In accordance with another exemplary embodiment, a system is disclosed. The system includes a crucible with a lid, the crucible utilized to store a hydrogen-lean molten material. The system further includes a mold assembly comprising a mold cavity, the mold cavity receiving the hydrogen-lean molten material from the crucible and cooling the hydrogen-lean molten material to form a casting. The system further includes a gas source to feed a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the molten material and to feed a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In accordance with certain embodiments of the present invention, a method for molding a hydrogen-lean molten material is disclosed. The method involves filling a hydrogen-lean molten material in a crucible and then closing a lid of the crucible. The method further involves feeding a first quantity of a compressed dry gas via the crucible to form a dry gas blanket on a surface of the hydrogen-lean molten material. The method also involves feeding a second quantity of the compressed dry gas to a mold assembly to purge the mold assembly. Further, the method involves transferring the hydrogen-lean molten material via an opening of the lid of the crucible to a mold cavity of the mold assembly and cooling the hydrogen-lean molten material to form a casting. The exemplary method involves minimizing a hydrogen content in the casting by controlling environment within the crucible and the mold assembly. In one embodiment, the casting is a low cryogenic magnet coil former. In such an embodiment, outgassing of hydrogen from the low cryogenic magnet coil former during storage and transportation is minimized. In accordance with certain other embodiments of the present invention, a system for molding a hydrogen-lean molten material is disclosed.
The mold assembly 16 has a mold cavity 30 for molding the hydrogen-lean molten material 12 to form a casting. In one embodiment, the casting may be a low cryogenic magnet coil former. In the illustrated embodiment, a fill pipe 32 is coupled to the mold cavity 30. The mold cavity 30 may be optionally coupled to a vacuum source 33 for applying a vacuum force to the mold cavity 30. The gas source 18 includes two containers 34, 36 filled with a compressed dry gas 38. The compressed dry gas 38 may include at least one of argon, air, nitrogen, or the like. The gas source 18 further includes connecting pipes 40, 42 coupled respectively to the two containers 34, 36. The pipes 40, 42 are further provided with regulators 44, 46 respectively for controlling flow of the compressed dry gas 38 through the pipes 40, 42. The gas source 18 is used to feed the compressed dry gas 38 to the crucible 14 and the mold assembly 16.
Now referring to an exemplary method of casting, the hydrogen-lean molten material 12 is filled in the container 20 of the crucible 14 and the lid 24 is closed. As discussed earlier, the heating element 22 is used to maintain the material 12 in a molten state. Thereafter, a first quantity of the compressed dry gas 38 from the container 34, is fed via the crucible 14 to form a dry gas blanket 48 on a surface 50 of the hydrogen-lean molten material 12. The hydrogen-lean molten material 12 is separated from the external environment by the dry-gas blanket 48 over the surface 50 of the hydrogen-lean molten material 12. The first quantity of the compressed dry gas 38 may vary depending upon the application.
Then, a second quantity of the compressed dry gas 38 is fed from the container 36 to the mold assembly 16 to purge the mold cavity 30. Specifically, the second quantity of the compressed dry gas 38 is fed via the fill pipe 32 to the mold cavity 30 to purge the mold cavity 30. Such purging facilitates to maintain a positive in-mold pressure until at least 95% of hydrogen-containing gases are removed from the mold cavity 30.
The hydrogen-lean molten material 12 is fed from the container 20 via the fill pipe 32 to the mold cavity 30 of the mold assembly 16. In one embodiment, the hydrogen-lean molten material 12 is fed from to the mold cavity 30 under the influence of the counter gravity force by applying a vacuum force from the vacuum source 33 (shown in
The hydrogen content in the casting is linearly proportional to a relative humidity of the process atmosphere. In accordance with the embodiments of the present invention, hydrogen content is reduced in the casting by reducing a moisture content in casting process environment using the compressed dry gas 38.
The mold assembly 58 has a mold cavity 70 for molding the hydrogen-lean molten material 54 to form a casting. In the illustrated embodiment, the mold assembly 58 has a pour cap 72 provided with a stopper 74. The stopper 74 has a passage 71 provided with a stopper 73. The mold cavity 70 may be optionally coupled to a vacuum source 76 for applying a vacuum force to the mold cavity 70. The gas source 60 includes two containers 78, 80 filled with a compressed dry gas 82. The gas source 60 further includes connecting pipes 84, 86 coupled respectively to the two containers 78, 80. The pipes 84, 86 are further provided with regulators 88, 90 respectively for controlling flow of the compressed dry gas 82 through the pipes 84, 86.
Now referring to an exemplary method of casting, the hydrogen-lean molten material 54 is filled in the container 60 of the crucible 56 and the lid 64 is closed. Thereafter, a first quantity of the compressed dry gas 82 from the container 80, is fed via the crucible 56 to form a dry gas blanket 92 on a surface 94 of the hydrogen-lean molten material 54.
Then, a second quantity of the compressed dry gas 82 is fed from the container 78 to the mold assembly 58 to purge the mold cavity 70. Specifically, the stopper 73 is removed and a second quantity of the compressed dry gas 82 is fed via the passage 71 to the mold cavity 70 to purge the mold cavity 30. Such purging facilitates to maintain a positive in-mold pressure until at least 95% of hydrogen-containing gases are removed from the mold cavity 70.
In accordance with the embodiments of the present invention, hydrogen content and an unpredictable variation of the hydrogen content in the casting due to weather changes are reduced. Hence, hydrogen outgassing from the casting, for example, an aluminum coil former, during storage and transportation is reduced. Additionally, issues associated with different amount of hydrogen content in castings such as coil formers cast at different seasons are avoided, thereby enhancing overall system reliability. Moreover, there is no requirement for usage of expensive hydrogen removal materials, such as palladium oxide.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
