Lecture 1 Flashcards
(23 cards)
What is casting?
Transforming liquids into solid form
What is forming?
Transfoming solids into other solid form
What is finishing?
Changing properties of the surface
How does casting work?
1 - pour molten metal into a mould
2 - allow it to solidify
3- remove part from mould
Disadvantages of casting
Dangerous
skill intensive
prone to errors
advantages of casting
Capable of complex shapes
capable of making large parts in one piece
The mould
Flask: outer container
Upper half: cope
Lower half: drag
Mould features
Designed to allow for escape of gas and material shrinkage
what is a sprue
in a mould: molten metal poured through this
What is a gate
in a mould: after sprue; ensures uniform metal flow into mould
what is a riser
in a mould: allows air to escape, indicates a full mould
How can dissolved gases be removed from mould
flushed with inert gas or melted and poured under vacuum
how does mould take into account material shrinkage
- usually oversized use risers to supply extra metal (avoiding porosity)
describe pure metal cast structure
columnar areas (grains nucleate at cool mould walls)
what is the mush zone
in alloy solidification: dendrites surrounded by liquid
Which cools faster sand or chill??
Chill (metal mould)
What happens to properties as grain size decreases?
- Increased strength and ductility
- Tendency to crack decreases
What does an inoculant do?
provides a nucleation site to promote grain isotropy
Why are hot tears formed
because casting cannot shrink freely during cooling
What are chills
increase cooling rate at critical points to avoid porosity - internal or external
What does time to solidify depend on
volume and surface area
what equation is used to measure time to solidify
Chvorinov’s rule - T = C(V/A)^n
C = constant for process V = volume A = surface area n = constant between 1.5 and 2.5
Sphere, Cube, Cylinder - what solidifies fastest and slowest?
Sphere - slowest
Cube - fastest
