Chapter 5 - Fundamentals of Metal Casting

Question 1

Identify some of the important advantages of shape-casting processes.

Answer 1

Complex part geometries are possible . Some casting operations are net shape processes. Very large parts are possible. Applicable to any metal that can be melted. Some casting processes suited to mass production.

Question 2

What are some of the limitations and disadvantages of casting?

Answer 2

Limitations on mechanical strength properties. Porosity. Poor dimensional accuracy. Safety hazards due to handling of hot metals. Environmental problems.

Question 3

What is a factory that performs casting operations usually called?

Answer 3

Foundry.

Question 4

What is the difference between an open mold and a closed mold?

Answer 4

Open Mold: simply a container in the shape of the desired part. Closed mold: mold geometry us more complex and requires a gating system leading to the cavity.

Question 5

Name the two basic mold types that distinguish casting processes.

Answer 5

Expendable and permanent.

Question 6

Which casting processes is the most important commercially?

Answer 6

Sand casting.

Question 7

What is the difference between a pattern and a core in sand molding?

Answer 7

The pattern determines the external shape of the cast part, while a core determines its internal geometry if the casting includes a cavity.

Question 8

What is meant by the term superheat?

Answer 8

The temperature difference above the melting point at which the molten metal is poured. The term also refers to the amount of heat that is removed from the molten metal between pouring and solidification.

Question 9

Why should turbulent flow of molten metal be avoided?

Answer 9

It accelerates the formation of oxides in the solidified metal. It causes mold erosion or gradual wearing away of the mold due to impact of molten metal.

Question 10

What are some of the factors that affect the fluidity of a molten metal during pouring into a mold cavity?

Answer 10

Pouring temperature above the melting point. Metal alloy composition. Viscosity of the liquid metal. Heat transfer to the surroundings.

Question 11

What doe heat of fusion mean in casting?

Answer 11

The amount of heat energy required to transform the metal from solid state to liquid state.

Question 12

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

Answer 12

Pure metals solidify at a single temperature equal to the melting point. Most alloys start to solidify over a temperature range rather than a single temperature.

Question 13

What is the relationship known as Chvorinov’s Rule in casting?

Answer 13

TST = Cm(V/A)^n where TST = total solidification time Cm = mold constant V = volume of casting A = surface area of casting n = normally 2

Question 14

Sand casting is which of the following types:

a) expendable mold
b) permanent mold

Answer 14

A

Question 15

The upper half of a sand casting mold is called which of the following:

a) Cope
b) Drag

Answer 15

A

Question 16

In casting, a flask is which of the following:

a) Beverage bottle
b) Box which holds the cope and drag
c) Container for holding liquid metal
d) Metal which extrudes between the mold halves

Answer 16

B

Question 17

In foundry work, a runner is which one of the following:

a) Channel in the mold leading from the downsprue to the mold cavity
b) Foundryman who moves the molten metal
c) Vertical channel into which molten metal is poured into the mold

Answer 17

A

Question 18

Turbulence during pouring of the molten metal is undesirable for which of the following reasons:

a) It causes discolouration of the mold surfaces
b) It dissolves the binder used to hold together the sand mold
c) It increases erosion of the mold surfaces
d) It increases the formation of metallic oxides that can become entrapped during solidification
e) It increases the mold filling time
f) It increases total solidification time

Answer 18

C, D

Question 19

Total solidification time is defined as which one of the following:

a) Time between pouring and complete solidification
b) Time between pouring and cooling to room temperature
c) Time between solidification and cooling to room temperature
d) Time to give up the heat of fusion

Answer 19

A

Question 20

A riser in casting is described by which of the following:

a) An insert in the casting that inhibits buoyancy of the core.
b) Gating system in which the sprue feeds directly into the cavity.
c) Metal that is not part of the casting
d) Source of molten metal to feed the casting and compensate for shrinkage during solidification.
e) Waste metal that is usually recycled.

Answer 20

C, D, E

Question 21

In a sand casting mold, the V/A ratio of the riser should be:

a) equal to
b) greater than
c) smaller

than the V/A ratio of the casting itself?

Answer 21

B

Question 22

Which of the following riser types are completely enclosed within the sand mold and connected to the main cavity by a channel to feed the molten metal?

a) Blind riser
b) Open riser
c) Side riser
d) Top riser

Answer 22

A, C