To obtain a neat sand casting operation, all the critical points must be evaluated in terms of engineering. After the cope, drag, mold cavity, gating systems are obtained, two halves of sand casting system are clamped to each other. In this situation, system is ready to pouring of liquid metal. Cores are also placed into the mold sand to obtain internal shapes of metal parts.
In this extent, the term must be considered in the design of cores and placement of cores. When the core is placed inside sand and the liquid metal is poured, buoyancy effect of must be considered. In here, we will explain this buoyancy effect and how to eliminate it in casting operations.
What Is Bouyancy Effect Of Cores In Sand Casting Operations?
In sand casting, buoyancy is applied to the cores from the liquid metal that is poured inside the mold cavity. As you know from the Archimedes’ buoyancy law that, the lifting force applied to an object equals, the weight of liquid is replaced by the volume of this object minus weight of object. So, if the density of molten metal is bigger than the core’s density, the lifting force originates from this situation can damage the mold structure.
So, these bouyancy forced must be considered in the design of core and core placement. The placement places must withstand to these buoyancy forces to prevent sand damaging.
These are the densities of some metals in liquid form. You can easily calculate the buoyancy forces to eliminate the damagings inside core placement zones;
- Cast Iron(Gray): 7.16 g/cm^3.
- Pure Copper: 8.73 g/cm^3.
- Steel: 7.82 g/cm^3.
- Pure Aluminum: 2.70 g/cm^3.
- Aluminum-Copper(92%Al): 2.81 g/cm^3.
- Aluminum-Silicon: 2.65 g/cm^3.
- Pure Lead: 11.30 g/cm^3.
- Brass: 8.62 g/cm^3.
If you know the density and the volume of your core that you used in mold cavity, you can easily calculathe bouyancy forces that placement of core must withstand. And you can do required reinforcements for these areas to prevent damaging.
The general explanation of bouyancy for cores and elimination of damages results from it can be like above. Do not forget to leave your comments and questions about bouyancy of cores in liquid metals in sand casting below.
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