This set of Manufacturing Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Metal Solidification and Fluid Flow”.
1. Grains created when a metal solidifies rather slowly in the presence of a steep temperature gradient fall in the category of?
a) equiaxed grains
b) columnar grains
c) elongated grains
d) planer grains
Explanation: Columnar grains are long, thin, coarse grains created when a metal solidifies rather slowly in the presence of a steep temperature gradient. Relatively few nuclei are available when columnar grains are produced.
2. Vacancies are _____________
a) planer defects
b) line defects
c) point defects
d) volume defects
Explanation: Vacancy defect is the simplest point defect. In this system, an atom is missing from its regular atomic site, vacancies are formed during solidification due to vibration of atoms.
3. Scanning tunneling microscope is a tool usually used to analyze an image at ____________
a) sub-atomic level
b) atomic level
c) micro level
d) macro level
Explanation: Scanning tunneling microscope (STM) is a technique that has been used for the surface study of nanostructures using the chemical composition of atoms and molecules in NPs to image surfaces at the atomic level. High-resolution material contrast has been successfully demonstrated in STM photon emission maps that correlate closely with the topographi image.
4. What are the examples of line defect?
d) stacking faults
Explanation: Line imperfections, or dislocations, in crystalline solids are defects that cause lattice distortion centered around a line.
5. A mixture of a metal(s) and a non-metal(s) is called?
Explanation: A mixture of metal and non-metal is termed as an alloy, whereas a combination of two different materials (may not have metal in it) is called as composite.
6. If there are 930 grains per mm2 on a photomicrograph of a metal at 2X, what is the ASTM grain size number of the metal?
Explanation: If there are 930 grains per mm2 at 2X, then at 1X we will have
N‘ = (2/1)2 (930 grains/mm2) = 3720
therefore, N = N‘/15.5 = 3720/15.5 = 240
240 = 2n-2
log 240 = (n-1)(log 2)
2.380 = (n-1)(0.301)
n = 8.91.
7. An ASTM grain size determination is being made from a photomicrograph of a metal at a magnification of 1X. What is the ASTM grain size number of the metal if there are 992 grains per square mm?
Explanation: N = 2n-1
where, N = no of grains per square inch at 100X
n = ASTM grain size number
and N is obtained using the following expression:
N = N‘/15.5 where N‘ = no. of grains per square mm at 1X
Thus, N = 992/15.5 = 64
or, 64 = 2n-1
log 64 = (n-1)(log 2)
n = 7.
8. Risers are also called __________
Explanation: Risers also called feeders serve as reservoirs of molten metal to supply any molten metal necessary to prevent porosity due to shrinkage during solidification.
9. In a free-falling liquid, the cross-sectional area of the stream?
c) remains constant
d) first increases and then decreases
Explanation: In a free falling liquid, the cross sectional area of the stream decreases as the liquid gains velocity downward.
10. If the pouring basin has a much larger cross-sectional area than the sprue bottom, then the velocity of the molten metal is?
d) either high or low
Explanation: The molten metal flows through a sprue to a runner and a gate and fills the mold cavity. If the pouring basin has a much larger cross sectional area than the sprue bottom, then the velocity of the molten metal at the top of the pouring basin is very low and can be taken to be zero.
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