casting fundamentals

Question 1

with expendable mold presses, the mold must be..

Answer 1

destroyed to remove casting

Question 2

example of expendable mold material

Answer 2

sand, plaster

Question 3

permanent mold can be… And is made from e.g. …

Answer 3

reused
metal, sometimes ceramic refractory materials

Question 4

an advantage and disadvantage of expendable mold processes

Answer 4

allows more intricate geometries
more expensive than permanent mold when high productions needed

Question 5

part shapes in permanent mold casting processes are limited by…

Answer 5

need to open the mold

Question 6

define pattern in this context

Answer 6

replica of object to be cast

Question 7

For sand casting, the mold cavity is formed by {1} sand around a {2}, which has the shape of the part. When the {2} is removed, the remaining cavity of the packed sand has {…}

Answer 7

1: packing
2: pattern
desired shape of cast part

Question 8

the pattern is usually {under, over}-sized to allow for {1} during {…}. Sand for the mold is {dry, moist} and contains a binder to {…}

Answer 8

over
shrinkage
metal during solidification and cooling
moist
maintain its shape

Question 9

in sand casting, cores are made from…

Answer 9

sand

Question 10

what does the core do in sand casting

Answer 10

internal features of the casting, i.e. any holes, channel, geometries that can’t be formed by the mold alone
after casting is removed, core is broken down and removed, leaving behind desired internal features

Question 11

the mold {1} provides the external surfaces of the cast part, while the {2} provides the internal geometries

Answer 11

1: cavity
2: core

Question 12

heating furnaces heat the metal to {1} temperature sufficient for {2}.

Answer 12

1: molten
2: casting

Question 13

in a heating furnace, the heat required is the sum of… (3 things)

Answer 13

…: heat to {raise temp to melting point+ of fusion convert from solid to liquid+ raise molten metal to desired pouring temp}

Question 14

For the step of pouring molten metal to be successful, the metal must… most importantly the … before…

Answer 14

flow into all regions of the mold,
main cavity
solidifying

Question 15

2 factors determining success of pouring molten metal

Answer 15

pouring temp and rate
turbulence

Question 17

from bernoulii’s, we find that v equals

Answer 17

v=sqrt(2gh)

Question 18

by continuity law, the volume flow rate Q is equal to

Answer 18

Q=v1A1=v2A2, A: cross section area of flow

Question 19

from v1A1=v2A2, the equation implies the sprue should be tapered, as the liquid metal {1} the cross sectional channel area must be {2}, otherwise air can be {…}

Answer 19

1: accelerates
2: reduced
aspirated into the metal, conducted into mold cavity

Question 20

mould filling time equation T_MF=f(Q,?)

Answer 20

T_MF=V/Q
V: volume

Question 21

from Chvorino’s Rule, the mold constant, Cm can depend on {1} and {2}

Answer 21

mold material
casting metal’s thermal properties
pouring temp relative to melting point

Question 22

even if shape of part is very different, the Cm value for a given cast operation can be used provided the same {1,2,3} are used

Answer 22

same mold material, metal and pouring temp

Question 23

Chvorino’s Rule tells us that casting with a higher volume:surface area ratio will cool and {1} , more {2} than a lower ratio. This is due to…

Answer 23

1: solidify
2: slowly
…:higher ratio has more material relative to the surface area, i.e. less surface area available to dissipate the heat, less surface area exposed to the cooling environment

Question 24

why does shrinkage occur, is it common in metals?

Answer 24

solid phase has a higher density than the liquid phase, very common

Question 25

Solidification causes an increase in {1} per unit {2} of metal, with the exception of {3} with a high {4} content. Graphitization during the final stages of {5} causes {6} that counteracts the volumetric decrease associated with {7} changes

Answer 25

1: mass
2: volume
3: cast iron
4: carbon
5: freezing
6: expansion
7: phase

Question 26

to counteract solidification shrinkage and { 1 } , patternmakers by …

Answer 26

1: thermal contraction
…: making the mold cavity oversized

Question 27

what’s meant by thermal contraction?

Answer 27

reduction in volume as material cools down

Question 28

During thermal contraction, when a material loses {1}, its particles move { 2 }, resulting in a size {reduction, enlargement}, the opposite of thermal {3}

Answer 28

1: heat
2:closer together
reduction
3: thermal expansion

Question 29

the amount by which the mold is larger relative to the final casting size is the…

Answer 29

shrinkage allowance

Question 30

a material with a relatively high shrinkage allowance… and one with a low…

Answer 30

high–steel, magnesium
low–cast iron, aluminium alloy

Question 31

2 negative impacts of shrinkage

Answer 31

dimensional inaccuracy, deviating for intended design e.g. not fitting/functioning
crack formation–uneven S induces internal stresses
distortion–uneven cooling and contraction causes casting to warp/distort impacting shape and structural integrity

Question 32

describe a riser

Answer 32

risers are reservoirs of molten metal, attached to the mold, compensate for shrinkage, placed a points shrinkage likely to occur, ensuring molten metal flows into these areas

Question 33

describe a feeder

Answer 33

provides additional molten metal to casting, as it cools and contracts, designed to solidify after main casting