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Introduction to Casting - Lesson Summary

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The key points for this module are:

Metal casting is a shape obtained by pouring liquid metal into a mold or cavity and allowing it to freeze and thus take the form of the mold.

Casting can be classified by the following:

The type of mold material (sand, permanent)
The manner in which the molten metal is introduced into the cavity (gravity, pressure)
The state of the metal (percent which is liquid)
The state of the mold cavity itself (air, vacuum, gas)

Patterns are the replica of the part to be cast, used to prepare the mold cavity. Patterns are made of either wood or metal and are larger than the final job to be produced.

The total contraction of casting takes place in three stages:

The contraction of the liquid from the pouring temperature to the freezing temperature.
The contraction associated with the change of phase from liquid to solid.
The contraction of the solid casting from the freezing temperature to the room temperature.

There are four types of patterns;

Single-piece pattern: This is the simplest and least expensive. It is used when only a limited number of casting is required.
Split pattern: This is the permit molding of more complex shapes in moderate numbers.
Match - plate pattern: It is obtained by attaching two halves of a split pattern on opposite sides of a match plate. It can be used for a large number of castings.
Cope and drag patterns: These are two halves of split patterns mounted on two match plates. It is usually preferred for heavy casting.

A good gating design ensures the distribution of metals in the mold cavity at a proper rate without excessive temperature loss, turbulence, and entrapping gases and slags.

Bernoulli's theorem states that "the sum of the energies (head, pressure, kinetic, and friction) at any two points in a flowing liquid are equal".