Standard: AA GSC
GUIDELINES FOR ALUMINUM SOW CASTING AND CHARGING
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Bulk aluminum intended for remelting is often cast in the form of large shapes, weighing from 700 to 2000 pounds (320 to 900 kg), known as "sows." Because of the normal geometry of these sows and how they are cast, shrinkage cavities are frequently unavoidable. These shrinkage cavities can often become reservoirs for collecting large amounts of water depending on how the sows are stored. The sows are also subject to surface moisture and other contaminants.
The introduction of water into molten aluminum can result in an explosion ranging from a small one to a very violent one causing extensive equipment damage and endangering human life. Therefore every effort should be made to avoid charging sows that contain moisture, either entrapped or surface, into molten aluminum.
The sows must also be free of any surface contaminants such as oxidizing agents and hygroscopic salts which can cause explosions. Many oxidizing agents can act as catalysts that can create an explosion. Some of these may be nitrate bearing fertilizers, metallic oxides, rust and fluxing salts. This is why visual inspection is so important.
Specific guidelines on sow casting techniques, storage methods, preheating, charging and melting practices can help reduce the risk of explosions. Each facility should develop specific procedures and standard practices to ensure that sows are completely dry and free of all surface contaminants before charging them into a furnace that contains molten aluminum.
The Aluminum Association discourages the procedure of drying sows by placing them on sills of furnaces that contain molten aluminum because the risk is too great that a sow will slip into the molten bath before it is fully dry. There is also the possibility that water will condense between sows stacked on the furnace sill during the early stages of heating. Serious explosions have occurred because of this practice.
General safety practices are discussed in the Aluminum Association's Guidelines for Handling Molten Aluminum, Second Edition (ref. 1). The hazards that cause explosions with aluminum sow must be eliminated in the casting, storage, transport, charge preparation and charging of the material.
These Guidelines deal with practices to minimize or eliminate shrinkage cavities in aluminum sow as well as methods and procedures for storage, transportation, inspection, drying and charging.
|Organization:||The Aluminum Association Inc.|
|Document Number:||aa gsc|
|Most Recent Revision:||YES|