Gravity Casting of Metals

gravity casting Solves Sand Holes Theoretical Principle 1:

Porosity and oxidation inclusion are produced by Die Casting because of the high injection speed. The lower injection speed of die casting usually exceeds 10m/S or even reaches 120m/S. When the flow rate of liquid aluminium exceeds 2m/S, the flow will become surge flow, which will generate swirls, encapsulate the air and the cold alloy which enters the cavity first, resulting in a large number of small voids and defects of oxidation inclusions in the castings. The gravity casting process is slow to enter from the gate, and the normal flow rate is less than 2m/s. At this time, the flow of liquid aluminium is laminar and no vortexes will occur, and the liquid aluminium is not easy to produce defects of oxidation inclusions.

Gravity Casting Solves Sand Holes Theoretical Principle 2:

In the Die Casting Process, the liquid aluminium solidifies very fast in the die, but in fact it is impossible to shrink, which makes the casting easy to produce small shrinkage holes and shrinkage. The thicker the wall of the casting, the more serious the defect is. Therefore, die casting is generally only suitable for castings with wall thickness below 6mm. In gravity casting, the solidification rate of liquid aluminium in the die is very slow. During solidification, the casting solidifies layer by layer from bottom to top. Under the action of gravity, the upper layer shrinks to the lower layer. The solidification position is at the riser of the upper layer. The riser part is removed by cutting to obtain a compact casting from the surface.