ME 3351
Manufacturing
Processes
Tutorial 2
Eng. Ahmad Aljazea
What is a factory that performs
casting operations usually
called?
• Answer. A foundry.
Open mold & Closed mold
What is the difference between an open
mold and a closed mold?
• Answer. An open mold is open to the atmosphere at the top; it is
an open container in the desired shape which must be flat at the
top. A closed mold has a cavity that is entirely enclosed by the
mold, with a passageway (called the gating system) leading from
the outside to the cavity. Molten metal is poured into this gating
system to fill the mold.
Pattern and Core
What is the difference between a pattern
and a core in sand molding?
• Answer. The pattern determines the external shape of the
casted part, while a core determines its internal geometry.
What is meant by the term
superheat?
• Answer. Superheat is 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.
Why should turbulent flow of molten metal into
the mold be avoided?
• Answer. Turbulence causes several problems: (1) accelerates
formation of oxides in the solidified metal, and (2) mold
erosion or gradual wearing away of the mold due to impact of
molten metal.
What is the continuity law as it applies
to the flow of molten metal in casting?
• Answer. The continuity law, or continuity equation, indicates
that the volumetric flow rate is constant throughout the liquid
flow.
What are some of the factors affecting the
fluidity of a molten metal during pouring
into a mold cavity?
• Answer. Factors include: (1) pouring temperature, (2) metal alloy
composition, (3) viscosity of liquid metal, and (4) heat transfer to
the surroundings.
What does heat of fusion mean in
casting?
• Answer. Heat of fusion is the amount of heat energy required
to transform the metal from solid state to liquid state.
How does solidification of alloys
differ from solidification of pure
metals?
• Answer. Pure metals solidify at a single temperature equal to
the melting point. Most alloys (exceptions are eutectic alloys)
start to solidify at the liquidus and complete solidification at
the solidus, where the liquidus is a higher temperature than
the solidus.
What is a eutectic alloy?
• Answer. A eutectic alloy is a particular composition in an alloy
system for which the solidus and liquidus temperatures are
equal. The temperature is called the eutectic temperature.
Hence, solidification occurs at a single temperature, rather
than over a temperature range.
H.W
• Sand casting is which of the following types? (a) expendable mold,
or (b) permanent mold.
• The upper half of a sand casting mold is called which of the
following? (a) cope, or (b) drag.
• In casting, a flask is which one of the following? (a) beverage bottle
for foundrymen, (b) box which holds the cope and drag, (c)
container for holding liquid metal, or (d) metal which extrudes
between the mold halves.
• In foundry work, a runner is which one of the following? (a) channel in
the mold leading from the downsprue to the main mold cavity, (b)
foundryman who moves the molten metal to the mold, or (c) vertical
channel into which molten metal is poured into the mold.
• 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, or (d) time to give up
the heat of fusion.
• During solidification of an alloy when a mixture of solid and liquid
metals are present, the
• solid-liquid mixture is referred to as whic h one of the following? (a)
eutectic composition, (b) ingot segregation, (c) liquidus, (d) mushy zone,
or (e) solidus.
• Chvorinov's Rule states that total solidification time is proportional to
which one of the following quantities? (a) (A/V)n, (b) Hf, (c) Tm, (d) V, (e)
V/A, or (f) (V/A)2; where A = surface area of casting, Hf = heat of fusion,
Tm = melting temperature, and V = volume of casting.
• A riser in casting is described by which of the following (may be more than
one answer)? (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, and (e) waste
metal that is usually recycled.
• A riser in casting is described by which of the following (may be
more than one answer)? (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, and (e) waste metal that is usually
recycled.
• In a sand casting mold, the V/A ratio of the riser should be which
one of the following relative to the V/A ratio of the casting itself? (a)
equal, (b) greater, or (c) smaller.
• A riser that is completely enclosed within the sand mold and
connected to the main cavity by a channel to feed the molten metal
is called which of the following (may be more than one)? (a) blind
riser, (b) open riser, (c) side riser, and (d) top riser.