L12 Casting Flashcards
(34 cards)
What is casting?
Casting processes involve the introduction of molten metal into a cavity where upon solidification the metal takes the shape of a cavity
What are some advantages of casting as compared to machining?
- Able to produce intricate shapes (including internal cavities) in a single piece
- Scalable from very small to very large
- A near net shape process with minimal waste and finshing
What are 4 Important Factors of Casting?
- Solidification
- Heat transfer
- Fluid flow
- Mold material
In what way does a pure metal solidify? ie. When it reaches a freezing point, does the temperature stay constant? What physical properties change as metal transforms from liquid to solid?
Pure metals have a clearly defined melting/freezing point.Solidification takes place at a constant temperature until all the metal has frozen.Volume decreases –> density changes
What is the difference between solidification of alloys compared with pure metals?
Unlike pure metals, alloyssolidify over a range of temperatures.
Solidification of alloys, where does freezing begin?
Freezing begins at theliquidus line and completes at the solidus line (TempL - TempS : Freezing range)
Within the 2 phase region, the alloy during solidifcation has a”blank” texture. How can its composition be approximated?
- “Mushy”
* The composition may be approximated by its phase diagram
As the alloymetal solidfies what forms?
- Dendrites are formed that interlock as the material cools
- Dendrites are crystals that develop with a multi branch tree like form
- Form between the liquid and solid phase (ie two phase region)
Name the following dendrites
- Columnar Dendrite
- EquiaxedDendrite
- EquiaxedNon-Dendrite
“____” is a strong fuction of cooling rate.What are the 3 types of cooling rates and their purposes?
Grain Size
- Slow Cooling (10^2 K/s) creates coarse dendrite structures
- Medium Cooling (10^4 K/s) creates a finer structure
- Fast Cooling (10^8 K/s) creates amorphic strucutres
What addition allowsequiaxed grains throughout the solid?
Nucleating agents allow equiaxed grains throughout the solid (Favourable mechanical properties)
What are the 3 compositions ofEquiaxed grains? Which is the most desired?
- We can have pure metal, solid solution, or heterogeneous nucleation
- Heterogeneous nucleation is the desired composition
Theflow of heat and molten metals has an affect on cast parts”___” and performance?
Cast part “properties”
3basic principles (math related) applied to begin analyzing fluid flow and mold geometry are…
- Bernoulli’s Theorem
- Mass Continuity
- Reynolds Theorem
What are thelaminar and turbulent conditions for Reynolds Number?
- Re
* Re > 20000 (Turbulent)
Fill in the blanks of this single gravity casting system (The pic shows up when you actually do the question, dont delete anything. If its too small, go to the lecture slides)
I am so proud of you for doing this
What is the purpose of the runner and gate system in thesingle gravity casting system?
To deliver metal to the mold and trap contaminants
What is a blind riser in thesingle gravity casting system?
Allows for extra metal to be added and replace material lost during shrinkage and cooling
What is the mold cavity?
Represents the final mold part
When is a core usedin the single gravity casting system?
If the part hasinternal cavities
What is fluidity?
Ability of a molten metal to fill a cavity
What are the materialproperties thataffectfluidity with regards to casting?
- Viscosity
- Surface Tension (ST)
- Inclusions
- Solidification Pattern
Explain how viscosityaffects fluidity
Viscosity
* Increase in vis. decreases fluidity
Explain how surface tensionaffects fluidity
Surface Tension (ST)
- Increase in ST decreases fluidity
- Metal oxides usually have higher ST
