ppt 5

Question 1

mold is sacrificed to remove part

Answer 1

expendable mold process

Question 2

mold is made of metal and can be used to make many castings

Answer 2

permanent mold process

Question 3

[expendable mold process] advantage (shape)

Answer 3

more complex shapes are possible

Question 4

[permanent mold process] advantage (production rate)

Answer 4

higher production rates

Question 5

[expendable mold process] disadvantage (production rate)

Answer 5

production rates are often limited by the time to make mold rather than casting itself

Question 6

[permanent mold process] disadvantage (shape)

Answer 6

geometries limited by need to open mold

Question 7

They are employed for casting low melting point materials.

Answer 7

permanent mold

Question 8

since they are made of refractory sands, the temporary refractory molds employed for casting high melting point materials

Answer 8

expendable mold

Question 9

they are costly

Answer 9

permanent mold

Question 10

they are cheaper

Answer 10

expendable mold

Question 11

they are employed to produce objects smaller in size

Answer 11

permanent mold

Question 12

they are employed to produce objects bigger in size

Answer 12

expendable mold

Question 13

they produce casting with better surface finish, quality, and dimensional accuracy.

Answer 13

permanent mold

Question 14

the surface finish, quality and dimensional accuracy of the casting produced by temporary mold is poor.

Answer 14

expendable mold

Question 15

The basic tool for casting liquid metal to attain the
required shape is __________.

Answer 15

mold

Question 16

Once a mold of ___________ is made and poured
with liquid metal, it cannot be ________.

Answer 16

suitable quality; re-used

Question 17

Desirable mold properties

Answer 17

-refractoriness
-chemical resistivity
-strength with proper binder
-permeability
-surface finish
flowability
-collapsibility
-reusability

Question 18

withstand the liquid metal temperature while it is poured.

Answer 18

refractoriness

Question 19

without sufficient refractoriness, the sand partially
melts and fuses with the liquid metal giving rise to very
rough sand-fused casting surface

Answer 19

rejection

Question 20

mold should be inert and not react chemically with metal/ alloy being poured into it

Answer 20

chemical resistivity

Question 21

mold should develop adequate cohesion among its grains to be able to form and stay as a mold.

Answer 21

strength with proper binder

Question 22

It should also adhere to the mold-box or other container
when rammed, and withstand movement and handling of
molds before pouring.

Answer 22

strength with proper binder

Question 23

to allow hot air and gases to pass through voids in sand.

Answer 23

permeability

Question 24

surface smoothness of a casting is necessary for appearance as well as avoiding costly finishing operations.

Answer 24

surface finish

Question 25

capacity of molding sand to flow to different corners and intricate details in mold without much special effort to ram.

Answer 25

flowability

Question 26

ability to give way and allow casting to shrink without cracking the casting

Answer 26

collapsibility

Question 27

"can sand from broken mold be reused to make other molds?"

Answer 27

reusability

Question 28

why SiO2

Answer 28

-Good refractory properties - capacity to endure high temperatures -Small grain size yields better surface finish on the cast part - Large grain size is more permeable, allowing gases to escape during pouring - Irregular grain shapes strengthen molds due to interlocking, compared to round grains

Question 29

disadvantage of SiO2

Answer 29

interlocking tends to reduce permeability

Question 30

typical mix of mold

Answer 30

90% sand, 7% clay and 3% water

Question 31

other binding agents also used in sand molds

Answer 31

-organic resins -inorganic binders

Question 32

organic resins

Answer 32

phelonic resins

Question 33

inorganic binders

Answer 33

sodium silicate and phosphate

Question 34

are sometimes combined with the mixture to increase strength and/or permeability

Answer 34

additives

Question 35

Types of Sand Mold

Answer 35

green sand molds dry- sand mold skin- dried mold

Question 36

mixture of sand, clay, and water

Answer 36

Green Sand Mold

Question 37

organic binders rather than clay

Answer 37

dry- sand mold

Question 38

drying mold cavity surface of a green-sand mold to a depth of 10 to 25 mm, using torches or heating lamps

Answer 38

skin dried mold

Question 39

_______ means mold contains moisture at time of pouring

Answer 39

Green

Question 40

defines the total surface area of grains contained in unit mass

Answer 40

the grain shape and size of molding sand

Question 41

________ gives rough idea of ________ needed to coat the grains of molding sand

Answer 41

Specific surface; amount of binder

Question 42

The grain size and distribution influences many sand properties such as ________________________.

Answer 42

permeability, flowability, refractoriness, surface fineness and strength

Question 43

________ the sand grains, the finer is the molding sand as whole.

Answer 43

the finer

Question 44

Fine grain sands give good _________ but possess low permeability.

Answer 44

surface finish

Question 45

For same clay content, the _________ is higher in case of fine sands as compared to coarse sands.

Answer 45

green strength

Question 46

_________________imparts high permeability, good refractoriness and high flowability

Answer 46

Coarse and uniformly graded sand

Question 47

Normally the foundry sand possess the grain size between ____________

Answer 47

0.1 to 1.0 mm

Question 48

The fine grained sands are used to make _________________.

Answer 48

intricate and small size castings.

Question 49

Coarse grained sands are used to make ______________.

Answer 49

large castings

Question 50

Grain shape is defined in terms of _______________.

Answer 50

angularity and sphericity

Question 51

Sand grains vary from ____________________.

Answer 51

well rounded, rounded, sub-rounded, sub-angular, angular, and very angular.

Question 52

Within each angularity band, grains may haveee..

Answer 52

high, medium or low sphericity.

Question 53

The best foundry sands have grains which are rounded with medium to high sphericity giving _________________ at lower binder additions.

Answer 53

good flowability and permeability with high strength

Question 54

Classification of Foundry Sands

Answer 54

-silica sands -zircon -olivine -chromite -aluminum silicates (chamotte sand)