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The CORRECT answer is (a) True

To explain I would SAY: Bentonite is a type of CLAY which used as a bonding MATERIAL because bentonite can absorb more water, which increases its bonding power, so that it can be used for drilling MUD, purification and as a binder, absorbent, groundwater barrier etc.

The correct OPTION is (b) False

To explain: Solidification is GREATLY affected by the geometrical shape of the mould cavity; variation in geometry causes the change in heat flow which leads to altering of solidification. In the condition of progressive solidification, there is ALWAYS a chance of shrinkage defects. So it cannot be better than DIRECTIONAL solidification.

Correct OPTION is (a) True

To ELABORATE: A primary requirement for high TEMPERATURE structural applications is an adequate oxidation resistance at temperature more than 1000 ⁰C. So, ATTENTION must be focused on those alloys which have a high concentration of aluminium and silicon, however, these elements produce protective oxide scales of alumina and silica respectively to protect the material.

Right choice is (c) Cylindrical

Explanation: The shape of an OPEN RISER is GENERALLY cylindrical. The top of the CYLINDER is open, causing the molten METAL direct exposure to the atmosphere.

The correct answer is (d) Magnesium

Best explanation: EXOTHERMIC materials are those which GENERATE a lot of heat because of exothermic chemical reactions. Exothermic materials do not include OXIDES of magnesium.

Right answer is (d) Type of riser

To EXPLAIN I would say: For the most PROPER functioning of the gating SYSTEM, all the above factors should be TAKEN into considerations, but not the type of riser.

Correct option is (a) Screening test

Easiest explanation: Screening test is PERFORMED by taking a fixed sample weight of sand and screening it through STANDARD sieves. It is accomplished by SHAKING the sieves. The amount of sand that COLLECTS in the different sieves is then plotted, and then a DISTRIBUTION of grain size is computed.

The correct option is (d) More than 1600 ⁰C

Best explanation: To ACHIEVE USEFUL strengths at the temperatures of 1000-1600 ⁰C, melting points in EXCESS of 1600 ⁰C are required. Most of the MATERIALS retain SIGNIFICANT strength to approximately 0.5-0.6 of their absolute melting temperature, but for high strength, high melting point temperature is preferred.

The correct answer is (a) True

The explanation is: In the production of composite castings by DIRECTIONAL SOLIDIFICATION of eutectics, this allows the components are to be PRODUCED from the melt in a single stage PROCESS, by which there is intrinsic thermodynamic stability and also the CHEMICAL compatibility between the matrix and reinforcement of the casted composite component.

The correct OPTION is (d) Zinc

Easy explanation: For making chills, steel, cast IRON and copper is widely USED. But zinc metal is not used for this. Copper is used even more for CHILLING, as it provides the highest conductivity.

The correct option is (C) Mould contains moisture

Explanation: Green sand mould contains 3-6 % of water, due to containing of moisture it is termed as green sand. Green sand has enough strength so that the constructed mould retains its SHAPE. Moisture makes the sand more FEASIBLE and 95% REUSABLE.

Correct answer is (d) Optical floating ZONE furnace

Explanation: The drop cast INGOTS are directionally solidified using an optical floating zone furnace, in which radiation is EMITTED from a xenon lamp and focused on the specimens enclosed in a quartz tube which is basically evacuated FIRST and BACK filled with the argon gas. And then drop-cast rods are used as the feed material for the performing of other operations.

Right option is (b) False

Easiest explanation: In the casting system, the RISERS should be located at the heaviest sections to achieve a better casting with fewer DEFECTS, and because the HEAVIER sections, themselves act as FEEDERS for the thin sections. And variations in volume of riser must be DONE if the size of casting sections also varies.

The correct choice is (a) By increasing riser height

To explain: If riser height is reduced, the pipe will extend to CAST cavity. Similarly, if less no of the riser is used it will not SATISFY feeding distance. Open riser alone can’t help in REDUCTION of the cavity. But by increasing length of the riser, the pipe can be controlled in riser itself eliminating shrinkage cavity in CASTING.

Right answer is (c) surface AREA to VOLUME ratio

Easiest explanation: Solidification is basically OCCURRED by losing HEAT from the surfaces and the AMOUNT of the heat is given by the volume of the casting, and the cooling characteristics of casting are given by the surface area to volume ratio. Riser is also similar to the casting in its solidification nature; hence the riser characteristics can also be given by the ratio of its surface area to volume.

Correct option is (a) turbulency

Best explanation: In the case of a PRESSURIZED gating system, DUE to the smallest in-gate AREA it maintains a back PRESSURE throughout the gating system. Because of this back pressure in the gating system, the metal is more turbulent and generally flows full.

The correct OPTION is (a) 24.98

For explanation I WOULD say: Pouring time(t) = K[ 1.41 + T/14.59]√W SEC.

where K = Fluidity of IRON in inches/40

Pouring time(t) = 32/40[ 1.41 + 25/14.59]√100 = 24.988 sec.

Right OPTION is (a) Gate basin

For EXPLANATION I WOULD say: A gate basin PLAYS a very vital role in stopping the liquid metal flow. A gate basin does not allow the turbulently flowing liquid metal to ENTER the gate.

The correct answer is (c) c

The explanation: There is optimum WATER content for the permeability considerations. At a lower water content, DRY clay POWDER, being finer than sand grains, fills up the voids between the sand PARTICLES, and thus reduces the permeability. Beyond the optimum water content, water itself fills up the voids and reduces the permeability.

The correct answer is (a) True

Easiest explanation: Directional solidification is always started from the farthest end of the casting and finishes at the sprue part of the casting system. ANOTHER TERM is the PROGRESSIVE solidification, in which solidification STARTS from the WALLS of the casting that is also known as parallel solidification.

Correct choice is (b) False

For EXPLANATION: A blind riser can be made anywhere in the MOLD, and it OCCUPIES MINIMUM area and VOLUME, hence it is smaller as compared to an open riser.

The correct answer is (c) Latent heat

The EXPLANATION is: Heat DIFFUSIVITY DEPENDS on thermal conductivity, specific heat and the density of the material, by the FORMULA heat diffusivity = (kcp)1/2. Hence, heat diffusivity does not depend on latent heat.

Right OPTION is (a) Fluidity

Explanation: Fluidity is the property of molten metal, which is USED to DESCRIBE the capability of the molten metal to FILL mould CAVITIES. Solidification interval, viscosity and surface tension are the factors which help in determining the fluidity of the molten metal.

The correct choice is (a) True

Best explanation: The MAIN reason for the formation of VOIDS inside the castings is that the liquid METAL in the centre which solidifies in the end is not fed during the solidification of the castings; hence the liquid shrinkage ends up as a void. This can be avoided by proper design of the riser in the casting SYSTEM.

Right choice is (c) Turbulent FLOW

Easiest explanation: Too less pouring time is caused by turbulent flow of nature of the molten metal. The mixing and collisions of molecules make the CHANGE in momentum and molecules get accelerated and hence HIGH velocity, that CAUSE the less pouring time of molten metal in the mould.

Right answer is (c) 4:1

For explanation I WOULD say: In-gates are generally made WIDER compared to the depth, up to a ratio of 4. This facilitates in the severing of gating from the casting after solidification. And it reduces the actual connection between the in-gate and the CASTINGS so that the REMOVAL of the gating is simplified.

Right option is (c) very less

To explain: Tapered sprues are invariably used with an unpressurized system. Casting yield of a non-pressurized gating system gets REDUCED because of the LARGE metal INVOLVED in the runner and gates. This makes the WASTAGE of material, to AVOID this, a pressurized gating system is used.

The correct option is (c) Copper

The EXPLANATION is: When there is an addition of a powdered form of CHARCOAL, graphite or out hulls, there is an INSULATION effect in the RISER, but not by the addition of copper.

The correct answer is (a) True

The BEST explanation: Ring gates hinder the FALL of LIQUID with a core. These ring gates are observed to RETAIN slag.

Right option is (d) Higher permeability

To EXPLAIN: Low bulk density of sand mix results in equal size of GRAINS with SMOOTH round shape, this further results in increase in volume of voids due to less bulk density and hence a higher permeability which permits an EASY outflow of the gases from the molten metal.