This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Metal Composition Testing, Inspection of Materials”.
1. What is the disadvantage of wet analysis?
c) Not suitable for iron-carbon alloys
d) Causes fatigue
Explanation: Wet analysis is a method of testing for mechanical composition. This technique is accurate but is time-consuming. Wet techniques for iron-base and copper alloys are straightforward. However, there are difficulties measuring boron in boron-treated steels, magnesium in ductile iron, and for carbon contents less than 0.04%.
2. Which spectrometer allows analysis of carbon and sulfur?
a) Vacuum spectrometer
b) Airpath spectrometer
c) Tube spectrometer
d) Rayleigh spectrometer
Explanation: In a spectrometer, only selected wavelengths are recorded through entrance slits. These are dispersed by the grating and then go through exit slits for a particular set of elements. Airpath spectrometer does not allow determination and analysis of carbon and sulfur, whereas vacuum spectrometer does.
3. A ___________ is used to measure the blackness of lines in a spectrograph.
a) X-ray tube
Explanation: For a spectrograph, the complete spectrum is recorded on a black-and-white 35 mm film. Densitometer then measures the blackness of lines, from which the concentration can be calculated. A quantometer is a separate device used for automatic quantitative analysis in spectroscopy.
4. For a concentration of about 0.0001 to 2%, which method of analysis is used?
a) X-ray fluorescence
b) Optical emission spectroscopy
c) Surface spectroscopy
d) Laser fluorescence
Explanation: A metal to be analyzed by XRF or OES requires a specially poured, chill-cast sample to retain the elements in solution and maintain homogeneity. XRF is most accurate at concentrations of about 0.1-50% whereas OES is most accurate for concentrations of 0.0001-2%.
5. Visual inspection may be done for which of the following activities?
a) Internal shrinkage
d) Counterbalance weights
Explanation: Visual inspection is the simplest, fastest, and most commonly employed inspection technique. However, it requires greater skills of the inspector to identify the defects. It is mostly used for castings such as manhole covers, drains, counterbalance weights etc.
6. How can porosity of material be inspected?
a) Hammer test
b) X-ray radiography
c) Gamma-ray radiography
d) Liquid penetrant test
Explanation: Certain defects such as internal shrinkage, porosity, blowholes, and slag inclusions affect the casting soundness. These can be detected by a hammer test. Here, the casting is suspended above the floor, struck with a hammer at different places, and the sound produced is carefully noted.
7. What is used as the source of rays for radiography?
d) Manganese dioxide
Explanation: Radiography is done by exposing the components to short wavelength radiation in the form of x-rays or gamma-rays. These rays are derived from a source like an x-ray tube or cobalt-60.
8. The x-ray film showing light and dark areas is known as _________
c) Wilbur’s film
d) Smith’s film
Explanation: Most defects such as blow holes, porosity, cracks etc., possess less density than the sound of metal casting. As a result, they transmit x-rays better than the sound metal does. This gives the film a dark appearance where the defects are present. The exposed and developed x-ray film showing light and dark areas is termed as a radiograph or an exograph.
9. Which of the following holds true for gamma-ray radiography as compared to x-ray radiography?
a) Better detection of castings of uniform thickness
b) Better for detection of small defects
c) More rapid method
d) Used for thick castings
Explanation: Gamma-rays are used for detecting small defects in casting sections less than 50 mm as well as castings thicker than those in x-rays. Gamma-rays are better for examination of varying thickness due to less scatter. X-ray is a much quicker method requiring seconds or minutes, whereas gamma-ray method requires hours.
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