Learn: Quiz 3 (Castings)

Casting of metals

Process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity

Two Categories of Casting Processes

1. expendable mold processes

2. permanent mold processes

Expendable Mold Processes

use an expendable mold which must be destroyed to remove casting

Permanent mold processes

use a permanent mold which can be used to produce many castings

cope

upper half of mold

drag

bottom half of mold

Gating System

channel through which molten metal flows into cavity from outside of mold

Riser

reservoir in the mold which is a source of liquid metal to compensate for shrinkage of the part during solidification

Total Solidification Time

time required for casting to solidify after pouring

Mold Constant (Cm)

Depends on mold material and thermal properties of casting metal

Pattern Shrinkage Allowance

Amount by which mold is made larger relative to final casting size

Riser Design

- Riser is waste metal that is separated from the casting and remelted to make more castings

- To minimize waste in the unit operation, it is desirable for the volume of metal in the riser to be a minimum

- Since the shape of the riser is normally designed to maximize the V/A ratio, this allows riser volume to be reduced to the minimum possible value

Types of Patterns

Solid pattern, split pattern, match-plate pattern, cope and drag pattern

Types of Sand Mold

Green sand molds, dry sand molds, and skin-dried mold

Expendable Mold Processes

*sand casting

• Shell Molding

• Expanded Polystyrene Process

• Investment Casting

• Plaster Mold and Ceramic Mold Casting

Permanent Mold Casting Types

Basic permanent mold casting, die casting, and centrifugal casting

General Defects

misrun, cold shut, cold shot, shrinkage cavity

Sand Casting Defects

Sand Blow, pinholes, penetration, and Mold shift