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Correct ANSWER is (a) True

To elaborate: Centrifugal casting is a technique which works on the principle of centrifugal force. Centrifugal force is a force that draws a rotating body away from the axis of ROTATION. This is basically caused by the inertia of the body. In this method of casting, molten METAL is poured in the horizontal MOULD which rotates at high speed to FORM hollow castings.

The correct choice is (a) True

Explanation: In mould making process, after placing of CORES in the mould, the mould parts are closed and clamped together by a clamping operation. It is very ESSENTIAL that the mould parts remain closely clamped together to PREVENT any LOSS of molten metal. Clamping is a very IMPORTANT operation and must be performed with great care.

Correct CHOICE is (c) IRON Oxide

The BEST I can EXPLAIN: In the formation of the compound fayalite (FeOSiO2), Iron oxide reacts with silica to give out the compound fayalite or iron chrysolite.

The correct answer is (C) Turn-over method MOLDING

Best EXPLANATION: For both the PATTERNS to be produced, that is solid and split patterns, turn-over method of molding can be used.

The CORRECT OPTION is (B) SiO2

Explanation: NONE.

The CORRECT choice is (a) True

For EXPLANATION I would say: Friability and crumbling are the PROPERTIES of the core material which helps in breaking and removing of core from the solidified casting part. So, these two properties are important in breaking of cores. Removal of the cores becomes EASIER when the friability and crumbling properties of the core sand is better.

The correct answer is (a) True

The explanation: During pouring operation, the molten metal is POURED into the MOULD by the application of ladle. The filling time of molten metal should be kept short in order to avoid early solidification of any part of the casting COMPONENT. The filling of melt through the ladle can be PERFORMED manually or by an automated MACHINE.

The correct choice is (a) True

Easy explanation: The coarse sand GRAINS of the core MATERIAL are USED so that the better refractoriness of the core can be achieved. Sometimes special binders are also used in the core MAKING process to induce better mechanical and THERMAL properties in the core like hot strength which is very important because core experiences extreme thermal load.

Right answer is (b) False

The best I can explain: Thermal load experienced by the core is much greater than that of experienced by the mould WALLS. So it is required that the core is able to BEAR the MECHANICAL loading as well as the thermal loading. So, refractoriness required in the core should be higher than that required in the moulding SAND.

The correct answer is (a) True

To elaborate: Venting at the runner side can DECREASE the air pressure because the air inside the sprue is EJECTED instead of COMPRESSING it into the mould cavity. Bernoulli’s principle states that an INCREASE in velocity of fluid occurs simultaneously with a decrease in pressure. According to this law, the velocity of air flowing through the runner RESULTS in air suction from the mould cavity to the runner.

The CORRECT choice is (b) Sprue PIN

The best I can explain: The hand molding equipment here is a sprue pin. A tapering is provided to the pin, that is, the diameter of the pin KEEPS INCREASING from one end to ANOTHER.

Right choice is (c) Sand SLINGING

Easiest explanation: Sand slinging is DEFINED as the combination of jolt and squeeze METHOD of ramming, in which jolt-squeeze MACHINES are used for the more uniform ramming. This is the method which is widely used in the ramming process, but the processes are expensive due to the application of various machines.

The correct answer is (c) 40%

Best explanation: In a typical dry sand molding mixture, the total content of FLOOR sand is approximately about 40%, for MAKING non-ferrous CASTINGS.

Correct option is (b) False

To EXPLAIN: The method of jolt ramming is very severe on the MOULDING equipment because the LIFTING and dropping operations can affect the mould layers due to the impact forces, which ABRUPTLY disturb the mould material by the high magnitude of force, this can even lead to cracking and BREAKING of mould.

Correct answer is (a) True

To EXPLAIN: JOLT and squeezing is a combination of jolting and squeezing. First of all jolting is done followed by squeezing. If the height of mold is LESS than 200 mm, throughout the depth of mold uniform strength is achieved. If the height of mold is more than 200 mm, the FORCE will not transmit to the MIDDLE portion of mold hence, less strength at center.

The correct choice is (a) True

To explain: For keeping the HIGH viscosity of molten metal, the TEMPERATURE of the melt should be kept low, but GREATER than its melting point. High viscosity generally reduces the pouring speed which takes more time to complete the process. This may be done for venting but it will cause defects in the casting such as cold cracks, INCOMPLETE sections, shrinkages etc.

Correct answer is (b) Direct contact between GAS and METAL

The explanation: For MOLD – metal reaction to take place, the CONDITION is that there has to be direct contact between the gas and the metal.

The CORRECT ANSWER is (b) False

The explanation is: Dry sand molding, as compared to green sand molding is a bit expensive process, as it INVOLVES more time as WELL as labour.

The correct option is (b) False

The best explanation: When the mould cavity is filled with MOLTEN METAL and during its solidification, the final shape of the casting PART is formed. The mould cannot be opened until the cooling time has elapsed. The desired cooling or solidification time can be ESTIMATED by considering the wall thickness and the TEMPERATURE of the casting metal.

Correct answer is (B) False

For explanation: Collapsibility of the core material is very important and required in the core making process because after the solidification the core is pressurized from all the SIDES due to contraction of molten metal in the MOULD. So, the core is expected to COLLAPSE under these situations. And if it does not collapse then it causes defects like HOT tearing and cracks in the castings.

Correct choice is (B) False

Explanation: The compensation for liquid and solidification shrinkage of the molten casting is BASICALLY done by setting up RISERS in the casting system. Venting is a process which ALLOWS the escaping of gases from the molten METAL during the solidification. For the venting process, a vent is provided in the casting system through which gases escape out.

Correct choice is (b) Draw spike

The explanation is: The HAND molding equipment which is SHOWN in the figure is a draw spike. It is a sharp tapered rod, that is, the diameter of the rod GOES on INCREASING from the TIP till the end.

Right CHOICE is (d) OXYGEN

Explanation: Iron when reacts with Oxygen gas, it PRODUCES the compound, ferrous oxide. Ferrous oxide is an inorganic compound and possesses BLACK colored appearance.

Correct choice is (B) False

The best EXPLANATION: An overflow system includes extra material or metal which is WASTED after every shot, overflow cutting operation and additional space requirements. This decreases the material or CASTING yield in the production of casting COMPONENTS. This further increase the cost involved in material handling.

Right option is (a) True

To explain I would say: During solidification, the material from the channels in the MOULD solidifies and joined to the casting part. This excess material should be TRIMMED from the casting part, for which a trimming press is used that REMOVES excess material very FINELY. The time needed for trimming the excess material can be estimated from the SIZE of the casting’s envelope.

The correct option is (a) Open sand method molding

To elaborate: AMONG the FOLLOWING, open sand method molding is the EASIEST and simplest of the three GREEN sand molding METHODS.

Correct option is (C) FLAT

For explanation I would say: In the bedded-in MOLDING METHOD, the upper surface of the casting, which has to be smoothened, can be any other SHAPE, but not flat.

Right option is (b) False

For explanation I would say: Sand SLINGING is a very fast method of ramming, it is DONE by throwing sand into the FLASK rapidly with the GREAT FORCE. This process develops uniformly high mould hardness. Sand slinging is the best method comparatively, but the cost of equipment used in this method is very high as compared to the other methods of ramming.

The CORRECT option is (a) True

Best explanation: During sand SLINGING, sand is thrown with a higher amount of force into the mold box and will hit the projection present on the pattern. This will RESULT in the DAMAGE of the pattern. Thus, the sand slinging OPERATION is used only for a simple pattern without any projection or extension.

Right answer is (b) FeOSiO2

The explanation is: The CHEMICAL REPRESENTATION of the compound fayalite is given by FeOSiO2. Fayalite is also KNOWN by the name, IRON CHRYSOLITE.

The correct answer is (a) True

Easiest explanation: In general, the strength of the green sand CORE is LESS. So it cannot be used in the production of CASTINGS with deep or complex features, MEANS it is normally used for producing the shallow features in the casting components. Because when the castings are made with deeper features, then the cores will have tendency to get break. So for limited features, green sand cores are preferred.

Right answer is (a) Sand SLINGING

For EXPLANATION: In sand slinging, we will obtain uniform strength throughout the mold because localized RAMMING of sand takes place because of THROWING the small-small amount of sand into the mold box at the same amount of force. But in other processes strength will be more at the top or BOTTOM or middle.

Right answer is (b) False

The explanation: Vacuum technology for venting process includes removing of gases from the cavity before the pouring of MOLTEN metal. This actually generates a vacuum INSIDE the cavity for which the cavity must be sealed completely. And ALTHOUGH vacuum technology may solve gases problems, it is not EFFECTIVE in dealing with gas produced during pouring, so this process is not ECONOMICAL and cannot be used conventionally.

Correct answer is (c) Diesel effect

To elaborate: PROPER mould venting is very important and necessary for producing quality casting parts. During the moulding process, the gases INCLUDED in the mould needs a way to escape, or else the MOLTEN metal will compress and TRAP those gases in the mould cavity. A combination of high melt pressure and temperature will then ignite the oxygen and will cause an effect that is called a diesel effect.

Right answer is (B) False

To explain I would say: It is not always POSSIBLE to USE pattern for generating internal FEATURES to the casting. Any kind of internal features of the casting which cannot be produced by the application of pattern are produced by using the separate cores which are mostly formed by the sand that can be green sand or dry sand, depending on the PURPOSE.

The CORRECT choice is (B) False

The explanation is: In LIGHT alloy, metal – bond reaction can be suppressed, but not by using Helium, but by using Boric acid and ammonium bi-fluoride.

Right choice is (a) True

Explanation: In the mould, the core is surrounded by the MOLTEN METAL, so it experiences more thermal LOAD as compared to the mould wall. The mould wall experiences the HEAT which is exposed to the molten metal from one side only, but in the case of the core it is surrounded from all the sides. So, the heat experienced by the core is MUCH severe.

Right option is (a) True

The explanation is: In squeeze ramming, a plate smaller than the inside DIMENSIONS of the moulding flask is fitted with the moulding sand. Then a uniform pressure is applied by the DOWNWARD movement of a plate or by the UPWARD movement of the flask itself, so this method avoids the DAMAGE to the moulding equipment.

Correct option is (a) True

The EXPLANATION: In the jolt method of ramming, impact FORCE is generated by the application of overhead HOPPER, this impact force compact the sand uniformly in the MOULD. This is achieved by continuous lifting and dropping of hopper and then the required hardness is achieved by the mould. Horizontal SURFACES are mostly compatible or preferred for the optimization of this method.

Correct option is (b) False

The best explanation: Squeeze ramming is suitable for SMALL castings and is generally suitable for shallow flasks which are of little depth. In this METHOD of ramming, it is also possible to use a diaphragm to PROVIDE DIFFERENTIAL ramming force which is generally required for the contour of the pattern.

Right option is (a) More than 1%

For explanation I WOULD say: In the mold metal reactions, there is EXTREMELY less amount of magnesium used. APPROXIMATELY more than 1% of magnesium is used in the reactions CONTAINING light alloys.