metal casting

Question 1

in expendable mold processes, the mold must be …

Answer 1

destroyed to remove the part

Question 2

a pro and con of expendable mold processes

Answer 2

more complex shapes possible
lower production rates [limited by time to make the mold rather than casting itself]

Question 3

a pro and con of permanent mold casting

Answer 3

higher production rates
limited geometries since need to open mold

Question 4

most widely used casting process… what materials can be used?

Answer 4

sand casting
almost all alloys, incl metals with high melting temps like steel, nickel, titanium

Question 5

2 metals with high melting temperatures

Answer 5

steel, nickel, titanium

Question 6

steps in sand casting:
pour { } into the {} mold

allow time for metal to {}

break up {} to remove {}

clean and {} casting

seperate {} and {} system

Answer 6

molten metal, sand
solidify
mold, casting
inspect
gating, riser

Question 7

heat treatment of casting is used to improve

Answer 7

(metallurgical) properties

Question 8

the {} in the sand mold, is formed by packing sand around a pattern, then separating the molding into { } and removing the {}

Answer 8

core
2 halves
pattern

Question 9

is sand casting a permanent or expendable mold process?

Answer 9

expendable, new sand mold must be made for each part produced

Question 10

purpose of gating and rising

Answer 10

gating–directs flow of molten metal into the mold
riser–compensates for solidification shrinkage

Question 11

for sand mold, a {} and {} system must be included. If the casting is to have internal surfaces, a {} must be included in the mold.

Answer 11

gating, riser
core

Question 12

The pattern is the {…} slightly enlarged to account for {} and machining {} in the casting

Answer 12

model of the part, to scale
shrinkage
allowance

Question 13

2 pattern materials and a fact

Answer 13

wood–easy to work with, warps
metal–more expensive to fabricate, lasts longer
plastic–compromise between wood and metal

Question 14

the supports used to hold core in position in the mold cavity during pouring is called…

Answer 14

chaplets

Question 15

3 desirable mold properties

Answer 15

strength–maintain shape & resist erosion

permeability–allows hot air and gases to pass through voids in sand

reusability–can sand from broken mold be reused to make other molds

thermal stability– resist cracking on contact with molten metal

Question 16

why is the sand damp in sand casting

Answer 16

enhance strength and plasticity
moisture– improve sand particles bond together– mold hold its shape under the pressure of the molten metal

sand more easily compacted around the pattern, ensuring a detailed and accurate mold

allows gases to escape more easily during the pouring process–reduces defects

Question 17

Foundry Sand:
smaller grain sizes are better for {…}, while larger grain sizes are more ideal for {…}. Irregular grain shapes {weaken, strengthen} the molds due to {1}. compared to round grains. This {1} will reduce {}

Answer 17

{…}: surface finish on cast part
{…}: permeability, allowing gases to escape during pouring
strengthen
interlocking
permeability

Question 18

what’s foundry sand

Answer 18

silica (SiO2) or silica mixed with other minerals e.g. bentonite clay

Question 19

foundry sand is held together by a mixture of {} and {}

Answer 19

water, bonding clay

Question 20

additives such as {} are sometimes combined with the foundry sand mixture to increase {s } and {p }

Answer 20

organic resins
strength, permeability

Question 21

green sand molds are composed of {}, {}, and {}
the name green meaning…

Answer 21

sand, clay, water
the mold contains moisture at time of pouring (recall green timber)

Question 22

the sand mold is baked to improve {}

Answer 22

strength

Question 23

during pouring, buoyancy of the molten metal tends to {} the core, which can cause the {} to become {}

Answer 23

displace
casting
defective

Question 24

force tending to life core= weight of displaced liquid less the weight of the core itself, i.e. equation for buoyancy is:

Answer 24

Fb=Wm-Wc

{Wm: W molten metal displaced}

Question 25

another expendable mold process

Answer 25

plaster mold and ceramic mold casting
investment casting

Question 26

heat of fusion meaning

Answer 26

heat energy required to transform metal from solid to liquid state

Question 27

How does solidification of alloys differ from solidification of pure metals?

Answer 27

alloys (exception of eutectic) start to solidify at liquidus and complete solidification at solidus
pure metals solidify at single temp equal to melting point

Question 28

disc volume formula

Answer 28

V=piD**2h/4

Question 29

velocity in this context (g,..) equals

Answer 29

v=Sqrt[2gL] (i.e. L=length)

Question 30

time to fill cavity formula (T_MF)

Answer 30

T_MF=V/Q

Question 31

volume flow rate formula

Answer 31

Q=vA (v: velocity)

Question 32

linear contraction, given shrinkage value as a %…
shrinkage rule elongation therefore is…

Answer 32

LC=1-S(%)
SE=1/LC=1/(1-S(%)) per m length

Question 33

for a 100cm ruler, and a shrinkage rule elongation of 1.02, the value for ruler length is now

Answer 33

L’=LSE=1001.02=102cm

Question 34

for a volumetric solidification shrinakge of 6%, and initial volume=1,000,000 ; the new volume is…

Answer 34

V’=V_0*(1-S)=940,000

Question 35

volume formula for a disk

Answer 35

V = πD**2*t/4

Question 36

surface area formula for disk

Answer 36

A=(2πD**2)/4 + πDt

Question 37

surface area of cube

Answer 37

A=6 (sides)*L

Question 38

cylinder volume

Answer 38

V = πD**2 * L/4

Question 39

surface area cylinder

Answer 39

2πD**2/4 + πDL

Question 40

sphere volume and surface area formula

Answer 40

V=piD**3/6
A=piD^2