Solidification of castings

- The mechanism of solidification of metal / alloys and control for sound projection to find the most important problem of the foundry men.

- Is the proper understanding of the essential solidification mechanism for defects caused contraction of the metal prevention.

- Once the molten metal is poured into a sand mold, solidification process begins.

- During solidification, develops the integration and gets cast form structural characteristics.

- Influences the properties of the castings solidification method because solutions get metallographic structure is determined during solidification.

- The structure consists of
● metallographic grain size, shape and orientation
● Distribution of alloying elements.
● Basic crystal structure and its imperfections.

- In addition to the structure, soundness depends on solutions along the solidification mechanism.

- Understanding the soundness of the amount of metallic real continuity and solutions be secure if shrinking volume to change the state of a solid melting liquid metal to compensate with the help of riser, etc.

- Volume contraction occurs or volume contraction during three phases and therefore shrinkage or contraction of three types.

● Liquid contraction (shrinkage): it occurs when the metal in a liquid state.
● Solidification Shrinkage (contraction) occurs during the transition from liquid (melting) a solid.
● Solid contraction (shrinkage): it occurs when solid metal ie after solidification. They do not influence shrinkage defects.

1) solidification: In pure metals and eutectic alloy is held at a constant temperature. In solid solution alloys proceeds over a temperature range.

2) takes the nucleation solidification By the very small crystals. A growing under thermal conditions and existing crystallographic during solidification. Grain growth stops when complete melt has solidified. The relative rates of nucleation and growing presence within the melting phenomenon determines the final structure of the solid and establishes the directional solidification or that it takes place on isolated way throughout the melt.

The changes occur: i) Superheat must be removed from the metal. Super heat is basically heat that must be removed before solidification. There ii) latent heat has also melted; this must be transferred to the surrounding mold before achieving complete solidification. iii) Finally solid metal transfers heat to the mold, and then to the atmosphere as it cools to room temperature.