Lecture 2 Flashcards
What are the two subgroups of casting?
Expendable mold and multiple-use mold.
What are the six steps of casting?
- Design and production of a container with a mold cavity,
- Melting process (proper temperature, quantity, quality & cost),
- Pouring technique (make sure air can escape),
- Solidification process (restraining means cracking),
- Mold removal,
- Cleaning, finishing and inspection.
What is a flask?
The rigid metal or wood frame that holds the molding aggregate.
What is a cope and drag?
The top and bottom halves of the pattern, flask, mold or core.
What is a parting line?
The interface between the cope and drag.
What is a core?
Sand or metal shape inserted inside a mold to produce internal features in casting.
What is a core print?
Region added to the pattern or mold to locate and support the core.
What is the purpose of a riser?
Compensate for the shrinkage experienced during solidification. Shrinkage voids should be located in the riser.
What is a gating system?
The network of channels used to deliver molten metal to the mold cavity.
What is a core box?
The mold or die used to produce cores.
The ability to remove heat depends on the exposed XXX through heat can be extracted and the XXX to the molten metal.
Surface area, surrounding environment.
What are the three zones in a cast structure?
Chill zone, columnar zone and equiaxed zone.
What is dross/slag and how to control it?
Metal oxides created by the exposition of liquid metal to the atmosphere. Can be trapped inside a casting and affect its properties. Controlled by the use of fluxes (to cover the pool of liquid metal) and melt under vacuum/inert atmosphere. OR use metal from below and use ceramic filters.
What causes gas porosity and how can it be controlled?
The dissolved gases in the liquid metal are expulsed as bubbles when it solidifies. Control by preventing gases to enter the liquid metal, by vacuum degassing or by gas flushing.
What does fluidity depend on?
Composition, melting point, freezing range and surface tension of films.
Where should the gating system be attached?
To the heaviest part of the casting (freezes last), to the bottom (avoid turbulence/splashing).
Why are rectangular pouring cups used?
To prevent vortex.
What is a sprue well and why is it used?
A small reservoir below the sprue. Used to dissipate energy and prevent splashing.
What is a choke?
Diminishing cross-sectional area in the runners to regulate metal flow.
What are the three stages of shrinkage? Which one can be controlled?
- Shrinkage of the liquid. CAN BE CONTROLLED (RISER).
- Solidification shrinkage as the liquid turns to solid.
- Solidification of the solid as it contracts while cooling.
What is the efficiency or yield of a casting?
Casting/Total Liquid Metal
What is the best theoretical shape for a riser?
Sphere, however not practical. Cylinders are widely used.
How should the riser be connected to the casting?
Using short connection close to casting. Should not be too small (or metal will freeze inside).
What are the types of riser?
Top, Side, Blind or Open.
