class 5

Question 1

3 advantages of shape-casting processes

Answer 1

1) complex part geometries
2) large parts possible
3) applicable to any melt-able metal
4) some suited to mass production

Question 2

T or F for shape casting processes:
no further manufacturing operations needed to accomplish final part shape for net shape processes

Answer 2

True (why?)

Question 3

What’s a foundry?

Answer 3

factory performing casting operations

Question 4

difference between open and closed mold

Answer 4

open: mold open to atmosphere at top, open container in desired shape, must be flat at top
closed: mold has cavity entirely enclosed by the mold with passageway (gating system) leading from outside to the cavity

Question 5

What’s a gating system and what does it entail?

Answer 5

passage way, in enclosed mold area, leading from outside to the cavity
molten metal poured into this to fill the mold

Question 6

Two basic mold types that distinguish casting processes

Answer 6

expendable molds
permanent molds

Question 7

which casting process is most commercially important?

Answer 7

sand casting

Question 8

why is sand casting the most commercially important mold process?

Answer 8

-offers blend of versatility, cost effectiveness, adaptability
-withstand high temperatures, manages metal flow, gas venting & thermal contraction to prevent defects and impurities during process

Question 9

what does sand casting allow?

Answer 9

formation of intricate shapes difficult to achieve with other methods

Question 10

difference between pattern and core in sand molding?

Answer 10

pattern: determines external casting part shape
core: determines casting parts internal geometry if cavity involved/contained within

Question 11

what’s superheat?

Answer 11

temp difference above melting point at which molten metal is poured
// amount of heat removed from molten metal between pouring and solidification

Question 12

what flow of molten metal is favoured

Answer 12

laminar

Question 13

why should turbulent flow of molten metal into mold be avoided?

Answer 13

issues such as accelerating formation of oxides in solidified metal
causes mold erosion or gradual wearing away of mold, due to impact of molten metal

Question 14

gradual wearing away of mold can be caused by (think of flow types)

Answer 14

impact of turbulent molten metal flow

Question 15

what’s the continuity law?

Answer 15

//continuity eqn; indicates volumetric flow rate is constant throughout liquid flow

Question 16

what are some factors affecting molten metal fluidity during pouring into mold cavity?

Answer 16

1) pouring temp above melting point
2) metal alloy composition
3) viscosity of liquid metal
4) heat transfer to surroundings

Question 17

how does pouring molten metal at a temperature above its melting point impact fluidity

Answer 17

increased fluidity- keeps metal in liquid state for longer period, reducing viscosity of fluid, enhancing ability to flow into intricate mold cavities

Question 18

why is it ideal to have molten metal at a temperature above its melting point?

Answer 18

-molten metal fills mold more completely, reducing likelihood of defects e.g incomplete filling or cold shuts
-elevated temps lower surface tension of molten metal, further aiding flow and filling efficiency
-metal remains liquid for longer, allowing more time to flow and fill mold before solidification

Question 19

what does excessive high temperatures lead to (in terms of molten metal pouring)

Answer 19

increased oxidation
damages the mold

Question 20

how does increased oxidation and mold damage occur with very high temps in metal casting?

Answer 20

oxidation- metal more readily reacts with oxygen in air, forming oxides on surface, degrades quality of cast metal, causes defects
mold damage-thermal shock to mold, leads to cracks or erosion, impacts lifespan and defects in cast part

Question 21

example of common oxidation reaction

Answer 21

rusting

Question 22

what’s rusting?

Answer 22

oxidation of iron, oxygen and moisture react with iron, degrading the surface overtime

Question 23

Iron oxide is more {1} and {2} than iron. The resulting material lacks the {3} integrity of iron. The rust will {4} and fall off. This then {5} the iron ‘new’ surface to further oxidation, continuing the cycle of this {6}.

Answer 23

1: brittle, flaky
2: flaky, brittle
3: structural
4: crumble
5: exposes
6: degradation

Question 24

how does composition of metal alloy impact its fluidity?

Answer 24

impurities–e.g. oxides, obstruct flow of molten metal, reducing fluidity
alloying elements–certain elements enhance/reduce fluidity
freezing range–alloys with short freezing range generally have higher fluidity

Question 25

why do alloys with short freezing range e.g. eutectic alloys have a higher fluidity?

Answer 25

uniform solidification--solidify at a single temperature, leading to uniform, rapid solidification (minimizes dendrites--tree like crystal structures that obstruct flow) consistent flow--eutectic alloys quickly transition from liquid to solid, they maintain a consistent flow without interruptions caused by partial solidification

Question 26

example of alloying element that enhances fluidity, and one that reduces

Answer 26

adding silicon to aluminium increases, making it easier to cast complex shapes magnesium reduces

Question 27

what's a eutectic alloy?

Answer 27

two+ metals that solidify at single, sharp temperature (which is lower than the individual melting points of metals)

Question 28

At eutectic composition, the alloy forms a {1} mixture

Answer 28

1: uniform

Question 29

applications of eutectic alloys include

Answer 29

soldering (e.g. tin-lead solder) brazing casting (excellent fluidity and predictable melting behaviour)

Question 30

why are eutectic alloys ideal in casting?

Answer 30

excellent fluidity and predictable melting behaviour

Question 31

what does heat of fusion mean in casting?

Answer 31

amount of heat energy required to transform the metal from solid state to liquid state

Question 32

how does alloy solidification differ from that of pure metal?

Answer 32

most allows (exception of eutectic!!) start to solidify at the liquidus and complete solidification occurs at the solidus, where liquidus is a higher temp than solidus pure metals--solidify at a single temperature equal to the melting point

Question 33

A eutectic alloy is a particular {1} in an alloy system, where solidus and liquidus temps are {2}. The temp is called the {3} temperature. Hence, solidification occurs at a {4} temperature, as opposed to over a temperature range.

Answer 33

1: composition 2: equal 3: eutectic 4: single

Question 34

Chvorino's rule; T_TS=C_m(V/A)^2 what does each component represent?

Answer 34

T_Ts: total solidification time C_m: mold constant V: casting volume A: casting surface area

Question 35

identify 3 sources of contraction in metal casting after pouring

Answer 35

1) liquid contraction- contraction of molten metal after pouring 2) solidification shrinkage during transformation of state from liquid to solid 3) thermal contraction in the solid state

Question 36

what is meant by contraction in a metal casting?

Answer 36

reduction in volume, that occurs as metal cools and solidifies

Question 37

liquid contraction

Answer 37

occurs as molten metal cools from the pouring temperature, down to its solidification point, not super significant for casting design, but impacts overall volume of metal required

Question 38

solidification contraction

Answer 38

liquid-to-solid shrinkage, when metal transition from liquid to solid state

Question 39

why is the solidification contraction stage critical?

Answer 39

can lead to voids or defects if not properly managed

Question 40

to counteract issues with solidification contraction...

Answer 40

(proper riser design and placement) by feeding additional molten metal into the mold

Question 41

solid contraction

Answer 41

solidified metal cools to room temp, 'patternmakers shrinkage'

Question 42

solid contraction must be {1} for in the {2} of the mold or pattern, to ensure { 3 } meets the desired {4}

Answer 42

1: accounted 2: design 3: final casting 4: dimensions

Question 43

what's a chill

Answer 43

heat sink

Question 44

what's the purpose of a chill

Answer 44

to encourage rapid freezing in certain regions of casting

Question 45

what's a riser/feeder and it's purpose

Answer 45

provide a reservoir of molten metal that compensates for shrinkage as casting solidifies, designed to solidify last