McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 51. |
In centrifugal casting, a movable pouring basin is employed for the pouring of molten metal. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: the molten metal is poured into the mould in requisite quantity through a movable pouring basin. the thickness of the pipe determined by the amount of metal poured into the mould. then after the completion of pouring, mould is rotated at its operational speed till it solidifies to form the requisite tubing. | |
| 52. |
The speed of rotation is almost double in semi centrifugal casting as compared to the true centrifugal casting. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: in semi-centrifugal casting method, complicated but axi-symmetric shapes of casting can be possible to make and this is accomplished by pouring of molten metal into the mould, which is rotated about a vertical axis. and the rotating speeds used in this process are not as high as in the case of true centrifugal casting. | |
| 53. |
Which of the following moulds or moulding is also known as sodium silicate process. |
| A. | shell moulding |
| B. | permanent moulding |
| C. | slush moulding |
| D. | co2 moulding |
| Answer» D. co2 moulding | |
| Explanation: carbon dioxide moulding is also known as sodium silicate process is one of the widely used processes for preparing of moulds and cores. basically, sodium silicate is used as a binder, but it binds the sand | |
| 54. |
How much percentage of sodium silicate (Na2SiO3) is added to the sand mixture in Co2 moulding? |
| A. | 0 to 2 % |
| B. | 2 to 6 % |
| C. | 6 to 10 % |
| D. | 10 to 14 % |
| Answer» B. 2 to 6 % | |
| Explanation: no other things like clay, water and resins are added to the sand except sodium silicate, which reacts with the sand mix to increase the flow-ability to fill up corners and intricate contours. then the co2 is supplied to the mould and reaction takes place as follows: | |
| 55. |
How much time (in a minute) is usually required for the passing of Co2 through the mould? |
| A. | one |
| B. | two |
| C. | five |
| D. | seven |
| Answer» A. one | |
| Explanation: in co2 moulding, mould of sand is hardened by passing of co2 for about one minute. the co2 gas forms a weak acid that hydrolyzes the sodium silicate (na2o, sio2) solution to form amorphous silica gel which acts as the bond and sodium silicate itself also provides some bonding action. | |
| 56. |
It is very safe to use Co2 in Co2 moulding, so it eliminates the use of any shielding apparatus. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: in co2 moulding, the process uses relatively safe carbon dioxide gas and it does not cause any of the sand disposal problems or any kind of odour while mixing and pouring. so the using of carbon dioxide gas is very safe to human operators. and so, no any equipment is required for the shielding. | |
| 57. |
Which of the following additives are added to the sand in Co2 moulding for the improvement in collapsibility of the sand? |
| A. | copper oxide |
| B. | wood flour |
| C. | aluminium oxide |
| D. | oil |
| Answer» C. aluminium oxide | |
| Explanation: after the preparation of the sand mixture by adding sodium silicate to the | |
| 58. |
Co2 moulding process is an ideal process, where speed and flexibility is the prime requirement. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: in co2 moulding, moulds and cores of varied sizes and shapes can be formed, this is mainly achieved by the using of binder sodium silicate that can binds the sand in any shape and size, and that is further tightened by the passing of co2 gas. this makes the moulding process very fast and flexible, so this process is more economical, where speed and flexibility is the prime requirement. | |
| 59. |
Moisture from the mould can be removed by using of dryer or heater in Co2 moulding. |
| A. | true |
| B. | false |
| Answer» B. false | |
| Explanation: in co2 moulding, water is never added while preparing a sand mixture. instead of water, sodium silicate is added to act as a binder. hence the moisture is completely eliminated from the mould. so, this process provides great dimensional tolerances and high accuracy in the production of castings. | |
| 60. |
Co2 moulding is a kind of sand moulding, but it is not economical than the green sand moulding. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: better surface finish of castings with close tolerances are produced by co2 moulding, but it is still not economical than the green sand moulding because this process uses expensive devices like co2 cylinder, hoses, regulator, hand held applicator gun or nozzle etc., and the processes in green sand moulding are simple and no expensive devices are required, due to this, green sand moulding is more economical. | |
| 61. |
Which of the following defect is not a gas defect? |
| A. | blow holes |
| B. | air inclusions |
| C. | run out |
| D. | pin hole porosity |
| Answer» C. run out | |
| Explanation: blow holes, air inclusions and pin hole porosity are known as “gas defects” in casting. blow holes and open blows are spherical, flattened or elongated cavities present inside the casting or on the surface of the casting. these are caused b moisture left in the mold and core. air inclusions are due to absorption of gases by the molten metal in the furnace, they cannot escape and weaken the mold during casting. these are due to high pouring temperatures. pinhole defects are a form of gas porosity. they are usually small, elongated holes at or immediately below the casting surface with the long axis of the pinhole perpendicular to the casting surface. | |
| 62. |
Which gas defect is caused by hydrogen in molten metal? |
| A. | blow holes |
| B. | air inclusions |
| C. | open blows |
| D. | pin hole porosity |
| Answer» D. pin hole porosity | |
| Explanation: as hydrogen is such a small atom, it can diffuse rapidly once it is absorbed, creating pinholes. hydrogen being absorbed by the molten metal inside the furnace and inside the cavity. this is the main reason for the evolution of pinhole porosity. | |
| 63. |
Cuts, washes, swell, drop etc. are the examples of which of the following casting defects? |
| A. | gas defect |
| B. | pouring material defect |
| C. | moulding material defect |
| D. | metallurgical defect |
| Answer» C. moulding material defect | |
| Explanation: moulding material defects are caused by the characteristics of molding materials. cuts, washes, swell, drop etc. are some known examples of this type. these are caused by poor strength of moulding sand or molten metal flowing at high velocity. | |
| 64. |
When the molten metal leaks out of mould which defect occurs? |
| A. | run out |
| B. | misrun |
| C. | fusion |
| D. | drop |
| Answer» A. run out | |
| Explanation: a run out occurs when molten metal leaks out of the mould during pouring. this is caused by defecting moulding boxes, faulty clamping and weighing and by casting too near the edge of the box. this defect is avoided by modifying the moulding system, providing proper line and providing proper gating system. | |
| 65. |
The lower fluidity of molten material causes |
| A. | misrun |
| B. | cold shut |
| C. | misrun & cold shut |
| D. | fusion |
| Answer» C. misrun & cold shut | |
| Explanation: fluidity is a very important consideration in metal casting. cold shuts and misruns can be caused by a lack of fluidity in the metal. | |
| 66. |
Defects caused by the chilling of the casting are known as? |
| A. | hot spots |
| B. | hot tears |
| C. | shrinkage cavity |
| D. | swell |
| Answer» A. hot spots | |
| Explanation: hot spots are the thick sections, those cool slower than other sections causing abnormal shrinkage. defects such as voids cracks and porosity are created at these hot spots. | |
| 67. |
During melting process flux is added to react with impurities to form? |
| A. | cavity |
| B. | slag |
| C. | cold shut |
| D. | blow holes |
| Answer» B. slag | |
| Explanation: slag is said to be refuse produced as a result of melting nonferrous material which have a high melting point, it is | |
| 68. |
Which defect is caused due to the conversion of moisture to steam because of the heat of molten metal? |
| A. | blow holes |
| B. | open blows |
| C. | air inclusions |
| D. | cold shut |
| Answer» A. blow holes | |
| Explanation: blow holes are entrapped gases, which are formed as a result of gases from mould, molten metal and stream sand. further these are caused due to the conversion of moisture to steam because of the heat of molten metal. | |
| 69. |
Defect which occurs due to the solidification of casting is known as? |
| A. | swell |
| B. | misrun |
| C. | metal penetration |
| D. | shrinkage cavity |
| Answer» D. shrinkage cavity | |
| Explanation: shrinkage cavity is a void on the surface of the casting caused mainly due to uncontrolled and haphazard solidification of the metal. these can be of two types, | |
| 70. |
The direction of rmf when a single phase supply is given to stator of three phase induction motor is? |
| A. | zero |
| B. | ns |
| C. | 2ns |
| D. | -ns |
| Answer» A. zero | |
| Explanation: there will be no rmf generated as a single phase is only fed to the three phase of induction motor. | |
| 71. |
The direction of rmf when a three phase supply is given to stator of three phase induction motor is? |
| A. | zero |
| B. | ns |
| C. | 2ns |
| D. | -ns |
| Answer» B. ns | |
| Explanation: there will be rotating magnetic field will be produced causing the emf to be induced and the current will flow in the rotor at a speed of synchronous speed. | |
| 72. |
Two three phase induction motors A and B are identical in all respects except that motor A has a larger air-gap than motor B. Which motor will have more no load current? |
| A. | a |
| B. | b |
| C. | both a and b |
| D. | neither a nor b |
| Answer» A. a | |
| Explanation: as the air gap of motor a is more, it will require more flux to excitation and so the no load current. | |
| 73. |
Two three phase induction motors A and B are identical in all respects except that motor A has a larger air-gap than motor B. Which motor will have poorer power factor? |
| A. | a |
| B. | b |
| C. | both a and b |
| D. | neither a nor b |
| Answer» A. a | |
| Explanation: due to larger air gap of motor a, it will need more of exciting current. so the no load angle will increase and power factor will deteriorate. | |
| 74. |
Two three phase induction motors A and B are identical in all respects except that motor A has a larger air-gap than motor B. Which motor will have better full-load power factor? |
| A. | a |
| B. | b |
| C. | both a and b |
| D. | neither a nor b |
| Answer» B. b | |
| Explanation: at full load conditions, the excitation current is not very high and so the power factor improves. | |
| 75. |
A three phase induction motor is sometimes calles a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is equal to stator frequency? |
| A. | it will not operate |
| B. | it will operate as induction motor only |
| C. | it will operate as induction generator |
| D. | it will operate in braking mode |
| Answer» A. it will not operate | |
| Explanation: as the rotor and stator | |
| 76. |
and the rotor current I2 are zero at |
| A. | ns |
| B. | 2ns |
| C. | zero |
| D. | slip of 50% |
| Answer» A. ns | |
| Explanation: the rotor emf and current are zero at the speed of synchronous speed of the machine. | |
| 77. |
If use auto transformer method starting to start an induction motor to replace star-delta method, then the required tapping on the transformer will be |
| A. | 57.73% |
| B. | 86.7% |
| C. | 57% |
| D. | 66.66% |
| Answer» A. 57.73% | |
| Explanation: k = 1/1.73 = 57.73%. | |
| 78. |
The starting method for a 3-phase squirrel-cage induction motor which is inferior in view of poor starting torque per ampere of line current drawn is? |
| A. | series-inductor method of starting |
| B. | direct-on-line starting |
| C. | auto-transformer method |
| D. | star-delta method |
| Answer» A. series-inductor method of starting | |
| Explanation: due to inductor method, reactance increases and the starting torque decreases. | |
| 79. |
volts, I = 200 A, and the cross-sectional area of the weld bead is 30 mm2. Estimate the welding speed if the workpiece and electrode are made of (a) aluminum, (b) carbon steel, and (c) titanium. Use an efficiency of 75%. |
| A. | 35 mm/s |
| B. | 34.5 mm/s |
| C. | 36 mm/s |
| D. | 46 mm/s |
| Answer» B. 34.5 mm/s | |
| Explanation: for aluminum, the specific energy required is u = 2.9 j/mm3 therefore, | |
| 80. |
Upon which of the following parameters does the current intensity in arc welding depend? |
| A. | stability of arc |
| B. | electrode diameter |
| C. | gap between the electrode and parent metals |
| D. | thickness of parent metals |
| Answer» B. electrode diameter | |
| Explanation: electrodes for consumable arc- welding processes are classified according to the following properties: | |
| 81. |
In which of the following welding processes we use two non-consumable electrodes? |
| A. | mig |
| B. | tig |
| C. | atomic hydrogen |
| D. | submerged arc |
| Answer» C. atomic hydrogen | |
| Explanation: non consumable electrodes are the ones that are not consumed during the process of welding. gtaw (gas tungsten arc welding)/tig (tungsten inert gas welding), ahw (atomic hydrogen welding), caw (carbon arc welding) processes use non-consumable electrodes. | |
| 82. |
Which of the following brazing process is good for mass scale joining? |
| A. | furnace |
| B. | induction |
| C. | dip |
| D. | torch |
| Answer» A. furnace | |
| Explanation: furnace brazing is a semi- automatic used widely in industries and are best suited to large scale production operations. | |
| 83. |
For grey cast iron, which of the following welding methods is preferable? |
| A. | mig |
| B. | submerged arc |
| C. | gas flame |
| D. | electric arc |
| Answer» A. mig | |
| Explanation: as the percentage of carbon in grey cast iron is less, therefore mig welding is preferable. | |
| 84. |
Due to which of the following reasons, flux is not used in atomic hydrogen welding? |
| A. | the burning hydrogen shields the molten metal |
| B. | two electrodes are coated which gradually release the flux |
| C. | the filler rod is coated with flux |
| D. | one of the two electrodes is coated which releases the flux |
| Answer» A. the burning hydrogen shields the molten metal | |
| Explanation: separate flux/ shielding gas is not required in atomic hydrogen welding. the | |
| 85. |
In resistance welding, between the electrodes, the nature of current and voltage parameters being used? |
| A. | high current, high voltage |
| B. | low current, high voltage |
| C. | low current, low voltage |
| D. | high current, low voltage |
| Answer» D. high current, low voltage | |
| Explanation: high current produces more heat. when we use a low voltage power source, it allows a welder to have some reasonable over the small lighting bolts we use to fuse metal together. | |
| 86. |
Which of the following welding process in which heat is produced for welding by a chemical reaction? |
| A. | resisting welding |
| B. | thermit welding |
| C. | forge welding |
| D. | gas welding |
| Answer» B. thermit welding | |
| Explanation: the thermite process is a chemical reaction in which a metal oxide (preferably molten) is displaced by another molten metal which is more reactive than the metal in the metal oxide, releasing a lot of heat. example: | |
| 87. |
The maximum diameter of electrodes being used in submerged arc welding? |
| A. | 30 mm |
| B. | 20 mm |
| C. | 15 mm |
| D. | 10 mm |
| Answer» D. 10 mm | |
| Explanation: a consumable electrode can be used by the submerged arc welding which is a loop of bare round wire with 1.5 mm to 10 mm diameter. it can be fed routinely throughout the welding gun, and the submerged arc welding electrode composition depends on the welded material. | |
| 88. |
Which of the following gases are used in Tungsten inert gas welding? |
| A. | helium and neon |
| B. | hydrogen and oxygen |
| C. | argon and helium |
| D. | carbon dioxide and hydrogen |
| Answer» C. argon and helium | |
| Explanation: in the tig welding process the arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium. | |
| 89. |
Which of the following materials necessitates preheating in welding? |
| A. | copper |
| B. | aluminium |
| C. | cast iron |
| D. | stainless steel |
| Answer» C. cast iron | |
| Explanation: as the weldability of cast iron usually decreases as the amount of free carbon in cast iron increases, so it is preheated to a dull red and then welded. | |
| 90. |
Which of the following is also called “gas welding”? |
| A. | oxy fuel gas welding |
| B. | metallic welding |
| C. | arc welding |
| D. | fuel gas welding |
| Answer» A. oxy fuel gas welding | |
| Explanation: gas welding is also known as oxy fuel gas welding. in gas welding, fuel gases are used to generate high amount of heat and melt the metal. | |
| 91. |
How many types of flames are there in welding? |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» C. 3 | |
| Explanation: there are three basic flame types: neutral (balanced), excess acetylene (carburizing), and excess oxygen (oxidizing) as shown below. | |
| 92. |
In which of the following type of flame, oxygen is in excess proportion with acetylene? |
| A. | neutral flame |
| B. | oxidizing flame |
| C. | carburizing flame |
| D. | both oxidizing flame and carburizing flame |
| Answer» B. oxidizing flame | |
| Explanation: oxidizing welding flames are produced when slightly more than one volume of oxygen is mixed with one volume of acetylene. oxidizing welding flames are commonly used to weld zinc, copper, manganese steel, cast iron, etc. | |
| 93. |
In which of the following type of flame, oxygen is deficient in proportion with acetylene? |
| A. | neutral flame |
| B. | oxidizing flame |
| C. | carburizing flame |
| D. | both oxidizing flame and carburizing flame |
| Answer» C. carburizing flame | |
| Explanation: the carburizing flame has excess acetylene then oxygen. reducing flame is used for the welding of low carbon and alloy steel. | |
| 94. |
For brazing, soldering and flame hardening which of the following flame is used? |
| A. | neutral flame |
| B. | oxidizing flame |
| C. | carburizing flame |
| D. | both oxidizing flame and carburizing flame |
| Answer» C. carburizing flame | |
| Explanation: for brazing, soldering and flame hardening carburizing flame is used. | |
| 95. |
The inner cone of the flame in welding has the following nature? |
| A. | highest temperature |
| B. | coldest temperature |
| C. | moderate temperature |
| D. | uncertain |
| Answer» A. highest temperature | |
| Explanation: the inner cone of the flame has the highest temperature (3500°c). the outer flame has the lowest temperature. | |
| 96. |
The oxy acetylene gas welding is a type of? |
| A. | endothermic reaction |
| B. | exothermic reaction |
| C. | neutral reaction |
| D. | both endothermic reaction and exothermic reaction |
| Answer» B. exothermic reaction | |
| Explanation: the oxy acetylene gas welding is a type of exothermic reaction. 1 mole of acetylene can produce kj/mol of heat. | |
| 97. |
The chemical formula of acetylene is? |
| A. | c2h4 |
| B. | c2h6 |
| C. | c2h5oh |
| D. | c2h2 |
| Answer» D. c2h2 | |
| Explanation: the chemical formula of acetylene is c2h2. 1 mole of acetylene can produce kj/mol of heat. | |
| 98. |
Amount of time during which the transformer will be used for welding under normal loading condition is known as? |
| A. | hold time |
| B. | off time |
| C. | weld time |
| D. | duty cycle |
| Answer» D. duty cycle | |
| Explanation: amount of time during which the transformer will be used for welding under normal loading condition is known as the duty cycle. | |
| 99. |
Amount of voltage required to generate the arc under no load condition is called? |
| A. | open circuit voltage |
| B. | closed circuit voltage |
| C. | short circuit voltage |
| D. | arc voltage |
| Answer» A. open circuit voltage | |
| Explanation: amount of current required to generate the arc under no load condition is called short circuit current (scc). | |
| 100. |
In which of the following gas welding process a non-consumable electrode is used? |
| A. | submerged arc welding |
| B. | tungsten inert gas welding |
| C. | stud welding |
| D. | gas metal arc welding |
| Answer» B. tungsten inert gas welding | |
| Explanation: in tungsten inert gas welding process a non-consumable electrode is used, which is made of tungsten. | |
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