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MET166 > ppt 5 > Flashcards

ppt 5 Flashcards

1
Q

mold is sacrificed to remove part

A

expendable mold process

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2
Q

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

A

permanent mold process

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3
Q

[expendable mold process] advantage (shape)

A

more complex shapes are possible

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4
Q

[permanent mold process] advantage (production rate)

A

higher production rates

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5
Q

[expendable mold process] disadvantage (production rate)

A

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

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6
Q

[permanent mold process] disadvantage (shape)

A

geometries limited by need to open mold

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7
Q

They are employed for casting low melting point materials.

A

permanent mold

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8
Q

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

A

expendable mold

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9
Q

they are costly

A

permanent mold

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10
Q

they are cheaper

A

expendable mold

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11
Q

they are employed to produce objects smaller in size

A

permanent mold

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12
Q

they are employed to produce objects bigger in size

A

expendable mold

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13
Q

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

A

permanent mold

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14
Q

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

A

expendable mold

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15
Q

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

A

mold

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16
Q

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

A

suitable quality; re-used

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17
Q

Desirable mold properties

A

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

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18
Q

withstand the liquid metal temperature while it is poured.

A

refractoriness

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19
Q

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

A

rejection

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20
Q

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

A

chemical resistivity

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21
Q

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

A

strength with proper binder

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22
Q

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

A

strength with proper binder

23
Q

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

A

permeability

24
Q

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

A

surface finish

25
Q

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

A

flowability

26
Q

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

A

collapsibility

27
Q

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

A

reusability

28
Q

why SiO2

A

-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

29
Q

disadvantage of SiO2

A

interlocking tends to reduce permeability

30
Q

typical mix of mold

A

90% sand, 7% clay and 3% water

31
Q

other binding agents also used in sand molds

A

-organic resins
-inorganic binders

32
Q

organic resins

A

phelonic resins

33
Q

inorganic binders

A

sodium silicate and phosphate

34
Q

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

A

additives

35
Q

Types of Sand Mold

A

green sand molds
dry- sand mold
skin- dried mold

36
Q

mixture of sand, clay, and water

A

Green Sand Mold

37
Q

organic binders rather than clay

A

dry- sand mold

38
Q

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

A

skin dried mold

39
Q

_______ means mold contains moisture at
time of pouring

A

Green

40
Q

defines the total surface area of grains contained in unit mass

A

the grain shape and size of molding sand

41
Q

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

A

Specific surface; amount of binder

42
Q

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

A

permeability, flowability, refractoriness, surface fineness and strength

43
Q

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

A

the finer

44
Q

Fine grain sands give good _________ but possess low permeability.

A

surface finish

45
Q

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

A

green strength

46
Q

_________________imparts high permeability, good
refractoriness and high flowability

A

Coarse and uniformly graded sand

47
Q

Normally the foundry sand possess the grain size between ____________

A

0.1 to 1.0 mm

48
Q

The fine grained sands are used to make _________________.

A

intricate and small size castings.

49
Q

Coarse grained sands are used to make ______________.

A

large castings

50
Q

Grain shape is defined in terms of _______________.

A

angularity and sphericity

51
Q

Sand grains vary from ____________________.

A

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

52
Q

Within each angularity band, grains may haveee..

A

high, medium or low sphericity.

53
Q

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

A

good flowability and permeability with high strength

54
Q

Classification of Foundry Sands

A

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

MET166 (9 decks)

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