MFE 2010 - Casting Quiz
The upper half of a sand casting mold is called which of the following?
Cope
Shell molding is which one of the following?
casting process in which the mold is a thin shell of sand bonded by a thermosetting resin
A riser in casting is not described by which of the following ?
casting that inhibits buoyancy of the core
Which of the following molds is more suited for casting of high melting point metals
ceramic
In foundry work, a runner is which one of the following?
channel in the mold leading from the down spruce to the main mold cavity
The micro structure of the metal adjacent to mold cavity tends to be
chilled fine grans randomly oriented
Chvorinov's Rule states that total solidification time is proportional to which one of the following quantities?
(V/A)^n
Based on Chvorinov's Rule
-A good shape for a riser would one with a small area per unit volume -To the pattern maker and mold designer the best practical shape for a casting riser would probably be a cylinder with height approximately equal to the diameter
The advantages of shell molding process include:
-Close tolerance of 0.002 to 0.005 inch per inch. -Low cleaning costs. -Smooth surfaces
Limitations of die-casting include the following
-High cost of equipment and die. -Rapid reduction in die life as metal temperature increases. -Metal having a high coefficient of contraction must be removed as soon as possible.
Design of gating involves a number of factors like :
-Metal should enter the cavity with as little turbulence as possible. -Erosion of passageways should be avoided. -Directional solidification should be observed.
During pouring of molten metal oxides forming
-are dross or slag -can be reduced or eliminated by use of flux -can be reduced or eliminated by use of vacuum
the best designed risers are
-as close as possible to being spherical in shape -located in extremities of the mold
Identify some of the important advantages of casting processes
-complex part geometries are possible; -some casting operations are net shape processes, meaning that no further manufacturing operations are needed to accomplish the final part shape; -very large parts are possible; -applicable to any metal that can be melted;
The sources of contraction in a metal casting after pouring.
-contraction of the molten metal after pouring, -solidification shrinkage during transformation of state from liquid to solid
Alloys with large freezing range of solidification
-give more troubles because it makes compensation through risers difficult -the resultant structure contains numerous small shrinkage pores
Cast iron is the most used casting metal because of its
-good fluidity -good strength
The following methods use expendable molds
-green and dry sand mold casting -plaster and ceramic mold casting
if the molten metal speed
-is high it may cause erosion of mold wall -is low it may cause miss runs and cold shuts
Sand grain size and shape has direct influence on the quality of the casting
-large grains give good permeability -angular shaped grains give better green strength
The limitations and disadvantages of casting?
-limitations on mechanical strength properties; -porosity; -poor dimensional accuracy -Safety hazards and environmental problems.
The factors affecting the fluidity of a molten metal during pouring into a mold cavity?
-pouring temperature -heat transfer to the surroundings.
Alloys with high melting point temperature generally uses
-short gating system -open gating system
Shape, length and size of cross sections of feeding channels are critical
-short spruces are desirable -rectangular pouring cups spruces prevent vortex formation
to slow the cooling rate
-switch from blind to open risers -place insulators in the vicinity of the mold cavity
Sand casting is which of the following types?
Expendable mold
Silica sand has which one of the following compositions?
SiO2
In sand casting, the volumetric size of the pattern is which of the following relative to the cast part?
bigger
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)?
blind riser side riser
In casting, a flask is which one of the following?
box which is composed of cope and drag
Cupolas are furnaces used to melt which of the following metals (choose one best answer)?
cast iron
Which one of the following casting metals is most important commercially?
cast iron
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?
greater
Which of the following qualifies as a precision casting process ?
investment casting
Investment casting is also known by which of the following names (may be more than one)?
lost-wax process
Which of the following casting processes is not an expendable mold operation ?
low pressure casting
A misrun is which one of the following defects in casting?
metal solidifies before filling the cavity
poor fluidity can lead to
miss runs cold shuts
Which of the following casting processes is most widely used?
shell casting
Which of the following casting processes is not a permanent mold operation?
shell molding
Which of the following is not an advantage of die-casting over sand casting?
suitable for casting higher melting temperature metals
Runner extensions can be used to
trap first metal
semicentrifugal casting is normally used for parts in which the center is to be removed
true
true centrifugal casting is used for symmetrical objects
true
Which of the following metals would not typically be die casted?
tungsten