Metal Casting and Material Science Fundamentals

Casting Fundamentals

Casting is a process where molten metal flows into a mold to solidify. Key components include:

• Gating system: The channel through which molten metal flows.
• Riser: A reservoir used to compensate for shrinkage.
• Shrinkage: Occurs during solidification and cooling.
• Mold cavity: The shape of the final part.

Casting Diagram Components

• Pouring cup: Where molten metal is poured.
• Downsprue: The vertical channel.
• Runner: The horizontal channel.
• Core: Creates internal holes.
• Cope: The upper part of the mold.
• Drag: The lower part of the mold.
• Parting line: Separates the cope and drag.
• Flask: The external mold structure.

Material Properties

Engineering materials consist of metals, ceramics, polymers, and composites. Metals are characterized by high strength, hardness, toughness, and conductivity.

Pouring and Solidification

Pouring: The pouring temperature and rate affect filling. Turbulence must be avoided to prevent oxides and erosion. Superheat is the difference between pouring temperature and freezing temperature.

Solidification: Consists of nucleation and growth. Pure metals solidify at a constant temperature, while alloys solidify over a range (liquidus–solidus). The cooling rate affects grain size: slow cooling produces large grains, while fast cooling produces small grains.

Shrinkage Types

• Liquid contraction: Occurs before solidification.
• Solidification shrinkage: Occurs during phase change.
• Thermal contraction: Occurs after solidification.

Formulas

v = √(2gh)
Q = vA
t = V/Q

Polymers and Crystal Structures

Polymers: Long-chain molecules made of repeating units (monomers).

• Thermoplastics: Can be reheated and reshaped.
• Thermosets: Cannot be reheated.
• Elastomers: Exhibit elastic properties.

Crystal Structure

Crystalline structures feature atoms arranged regularly. The three primary types are BCC, FCC, and HCP.

Alloys

An alloy is a mixture of two or more elements. Substitutional solid solutions replace atoms, while interstitial solid solutions insert small atoms. Alloying is primarily used to increase strength.