Die casting is a casting procedure for metal, which is characterized by the use of molten metal forced under high pressure into a mold cavity. This cavity is created by use by two hardened steel dies, machined into exact shapes, and are used similar to injection molding. Most die casting uses non-ferrous metals, particularly zinc, copper, aluminum, lead, magnesium, pewter, and tin-based alloys. Depending on the metal-type being cast, a cold- or hot- chamber machine is used.
Die castings are among the highest volume, mass-produced items manufactured by the metalworking industry, and they can be found in thousands of consumer, commercial and industrial products. Die cast parts are important components of products ranging from automobiles to toys. Parts can be as simple as a sink faucet or as complex as a connector housing.
Die casting is particularly suited for a large quantity of small to medium sized castings, which is why this process produces more castings than any other casting process. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency. The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high volume production.
The die casting process has evolved from the original low-pressure injection method to techniques including high-pressure casting - at forces exceeding 4500 pounds per square inch - squeeze casting and semi-solid die casting. These modern processes are capable of producing high integrity, near net-shape castings with excellent surface finishes.
In order to use metal in die casting, it needs to be melted into a liquid form. Reverberatory furnaces are the most common type of furnace used in aluminum die casting foundries. Reverberatory furnaces use wall mounted burners to radiate heat from the refractory wall to the metal inside. Though typically fired by natural gas, electric reverberatory furnaces are available, and are primarily used as holding furnaces. Many foundries have more than one furnace, one used for melting metal and another for holding molten metal. The same types of furnace can be used for both purposes, but furnaces that are designed for efficient melting are less efficient at holding molten metal. Other techniques allow optimization of furnaces for the two functions. For example, it is recommended to keep melt furnaces at near capacity for efficiency.
Energy requirements for holding furnaces are typically much lower than for melting furnaces, simply due to the high energy requirements of melting metals. An average melting furnace has an efficiency around 40%, requiring 2.5 times more than the theoretical minimum to melt the metal. This is in agreement with other published gas-fired furnace efficiencies for melting aluminum.
If you are considering radiant roof electric holders and plan to deliver metal less often than once an hour and the draw down between deliveries is greater than 5 inches, then you should specify gas fired furnaces instead. The electric elements will not keep the temperature up because the metal gets too far away from the heat source and the electric elements cannot go on "high fire" like gas burners can. On the other hand, if you plan to have filtered and degassed metal delivered to the holding furnace, and the metal will be at or above the holding furnace temperature, then electric powered furnaces may be the right choice since there is no further contamination of the metal using electric elements. Some gas fired furnaces that use burners whose flame comes in contact with the metal will contaminate the previously clean metal. Other gas fired holding furnaces that use flat flame roof burners, in which the flame pattern never touches the metal, minimize this contamination. It is also true that gas fired furnaces are generall
(Sources: Wikipedia, Diecasting.org, Dalquist, Gutowski)
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