What is Gravity Casting?
Among the many forms of casting that see use in modern industry, gravity die casting is one of the earlier processes developed. Though relatively simple compared to other casting methods, gravity castings have been refined over time and remain useful for the right applications throughout the industry.
How Gravity Casting Works
Gravity casting, as the name suggests, relies on the force of gravity to drive the process. Metal placed in a crucible is heated until molten, then poured into a reusable mold or die to cool in the desired shape. This contrasts with methods such as sand casting that use temporary molds. The process is similar to pressure casting save for the reliance on gravity versus high-pressure injection. Modern die casts feature finely-designed sprues, gates and risers to control the metal’s flow into all parts of the mold, as well as vents that allow trapped gases to escape; this ensures sufficient material feeding to the entire mold and minimizes the risk of void formation within the product.
Applications of Gravity Casting
Parts manufactured from ferrous alloys generally require pressure casting, but gravity casting is suitable for working with copper, zinc and aluminum alloys, as well as some applications with cast iron. In particular, die casting is the go-to method for working with aluminum alloys; thus, these castings are common in the automobile and aerospace industries where aluminum alloys are prized for a good strength-to-weight ratio. Gravity casting is preferred over pressure casting when short cycle times are not a high priority—upfront costs are lower, since pressure casting requires more advanced equipment and dies made to withstand the high pressures employed. Additionally, gravity castings feature more uniform, less porous internal structures. The primary drawback is that the molten metal may not properly flow into thinner sections in time to cool, so pressure casting becomes necessary.