Casting - Process

Question 1

What factors affect choice of technique?

Answer 1

Cost, shape limitations, material, quality (tolerances, finish, integrity), quantity (automation)

Question 2

What’s the outer fountained of a mould called?

Answer 2

Flask

Question 3

The upper half of a mould

Answer 3

Cope

Question 4

Lower half of mould

Answer 4

Drag

Question 5

What gives hollow features of a mould

Answer 5

Cores

Question 6

Purpose of a spruce

Answer 6

Pouring molten material

Question 7

Purpose of gate

Answer 7

Narrow to ensure uniform flow

Question 8

How to allow gases to escape a mould

Answer 8

Risers or vents

Question 9

Purpose of risers

Answer 9

Allow gas escape, indicate full,

Question 10

Issues in filling a mould may be caused by;

Answer 10

Low fluidity, low solidification time, gases not escaping

Question 11

Preventing gases entering the mould

Answer 11

Flushing with an inert gas or melting and pouring under a vacuum

Question 12

Why is porosity an issue with casting?

Answer 12

When materials are molten, gases are more soluble or may react

Question 13

What materials are used in casting?

Answer 13

Metals, polymers or ceramics

Question 14

What are the general steps in casting?

Answer 14

Pour molten metal into mould → solidify → remove

Question 15

Advantages to casting

Answer 15

Complex shapes (+internal cavities), large singular parts, inexpensive, competitive (sometimes exclusive) near net shape

Question 16

Disadvantages to casting

Answer 16

Dangerous, skill intensive, error prone, does not provide some properties

Question 17

Preventing material shrinkage

Answer 17

Cavity is slightly oversized

Riser supplies extra material

Question 18

If a mould causes too much restraint on a casting, this can lead to;

Answer 18

Hot tears as material shrinks as strength is low at high temperatures

Question 19

When grains nucleate at cool mould walls, what 3 characteristics are formed?

Answer 19

Chill zone, bulk zone, solidification fronts

Question 20

Describe the chill zone

Answer 20

Fine multi-axed grains

Question 21

Describe the bulk zone

Answer 21

Columnar grains, slowing cooling rate

Question 22

Describe the solidification front

Answer 22

During cooling they move away from the wall with time, the skin is therefore thinner at concave sections

Question 23

When can solidification fronts (during cooling) be utilised for casting

Answer 23

Slush casting (pouring it out before it’s set)
{hollow decorative objects}

Question 24

Effect on grain structure with fast cooling

Answer 24

Finer grains

Cored dendrites cause micro (conc surface to centre) and macro (tend to form at centre) segregation

Question 25

Effect on grain structure with slow cooling

Answer 25

Courses grain structure

Question 26

What affects cooling rate?

Answer 26

Mould material (chill metal), alloy used

Question 27

As grain size decreases

Answer 27

^strength and ductility, microporosity, hot tears decrease

Question 28

Reducing grain anisotropy when cooling materials

Answer 28

Use inoculates

Question 29

Reducing chance of hot tears

Answer 29

Placing exothermic compounds at critical areas

Question 30

Porosity during cooling can be caused by

Answer 30

In larger regions the surroundings solidify first

Question 31

Reduce porosity during cooling

Answer 31

Using chills to increase cooling rate at points (permanent or removable)

Question 32

What is a rough casting

Answer 32

Initial part removed from mould

Question 33

What is removed from the rough casting?

Answer 33

Sprue, runners, risers, gates and flash

Question 34

What can speed up post casting shrinkage?

Answer 34

Annealing

Question 35

Chovinov’s rule

Answer 35

T = C(V/A)ⁿ

1.5

Question 36

What helps with casting removal

Answer 36

Draft angles