When discussing materials used in Aluminum Foundries, graphite occupies an important spot, especially when referring to aluminum smelting operations.
Graphite Degassing Units are systems used for degassing hydrogen from molten aluminum. During the smelting process of aluminum, or aluminum alloys, hydrogen is produced through a chemical reaction with steam. Diffused throughout the aluminum, it creates voids, and ultimately cause structural defects. It will effectively weaken the casting. To combat this unwanted effect, most aluminum foundries will inject an inert gas, such as nitrogen or argon, which draws the hydrogen out from the aluminum / aluminum alloy.
The Graphite Degassing Units are assemblies of a graphite rotor and a graphite degassing tube (shaft). The rotor is designed and machined specifically to be capable of stirring uniformly the molted aluminum, and to disperse the gas. For that to happen, there is need for precision machining. The machining process, must strictly conform to customers drawing and tolerances. The rotor and the shaft must match perfectly, and the concentricity's must be high. These parameters are necessary to avoid creating unwanted disturbances throughout the molted material, as well as avoiding damage caused by mechanical stress.
Special treatment applied to the graphite components: An impregnation anti-oxidation treatment is usually applied to the system's components. In some instances an anti-oxidation coating is applied as well. These treatments are done in order to extend the service life of the graphite. The main improvement comes in the form of increased heat resistance.
Why graphite? Although other materials are used in the manufacturing of degassing systems, graphite is generally recognized as the material of choice. This is due in large part to its physical properties, but also due to good machinability and reduced costs, when compared to other materials. Graphite is an excellent heat resistant material, with good compressive and flexural strength. Also, anti-oxidation properties are excellent, when the impregnation treatments discussed prior, are applied.
In conclusion, graphite is the one material that stands out, as a choice in manufacturing of Degassing Systems for aluminum smelting operations. It's physical properties, machinability and cost recommend it.
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