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The correct choice is (a) The sand grains are not adequately bonded

To EXPLAIN: Sand mould crumbles because moulding sand is not adequately compacted in the flask. Clay, TOGETHER with water acts as a bonding AGENT and the organic additives also save the mould from crumbling by burning out at HIGH temperatures and make room for the moulding sand to expand.

The CORRECT choice is (d) Insulation CLIP

The BEST explanation: For delaying the solidification in risers, insulation is done. Insulation powder, insulation sleeve and insulation pad can be USED, but not an insulation clip.

Right choice is (B) WEDGE gate

Easy explanation: Among the FOLLOWING, edge gate, ring gate and finger gate, are not used for the MAKING of stove plate castings. A wedge gate is used when a stove plate casting has to be MADE.

Correct choice is (b) When POURING basins are made LARGE

Explanation: The metal could be stopped from entering the SPRUE, and would cause the DROSS and slag to float on the metal surface, when the pouring basins are made large.

Right choice is (a) Feeding distance is low

For explanation I would say: If feeding distance is high, number of the isolated zone in casting will be less THUS less number of RISERS REQUIRED. For high THERMAL conductivity, the metal will solidify faster and high FLUIDITY molten metal will flow over a long distance which will result in less number of risers. If feeding distance is low, we have to use more risers to overcome isolated liquid pools.

Correct ANSWER is (a) True

The best EXPLANATION: External chills can be USED over and over again many TIMES. But the same cannot be SAID for internal chills.

The correct answer is (c) Whirl GATE method

Explanation: Whirl gate method utilizes the principle of centrifugal ACTION to throw the dense metal to the periphery and retain the lighter SLAG at the CENTRE. Also, the metal revolves 270 degree before reaching the exit gate so as to gain ENOUGH time for separating the impurities.

The correct option is (b) W/dtC√2gh

Easiest explanation: Choke area (A) = W/dtC√2gh, It is the main control area which meters the metal FLOW into the mould cavity so that the mould is completely filled within the calculated pouring time. Its unit is mm².

Where, W = CASTING mass (KG), t = pouring time (second), d = mass density (kg/mm³),

 h = Sprue height (mm), G = Acceleration due to GRAVITY (mm/s²), C = Efficiency factor.

Correct answer is (d) GREATER dimensional stability of the casting

The explanation is: Uniform ramming of SAND is very necessary for green sand MOULDING process. Uniform ramming of sand during mould preparation improves mould strength, and makes it dimensionally STABLE. Uniform ramming done to obtain a smooth and hard casting SURFACE which prevents break out.

Correct choice is (b) Feeding aids

Easy explanation: At the time of solidification, the shrinkages are produced in the castings which are eliminated by the use of a RISER. The metal in riser should be in liquid FORM for a long PERIOD of time as to feed the casting till it SOLIDIFIES. So feeding aids are used for this purpose, they can be either exothermic materials or INSULATORS.

The correct option is (a) ts = k(V/SA)^2

For explanation I would say: Chvorinov scientist has shown that the solidification time of a CASTING is directly proportional to the square of the ratio of VOLUME-to-SURFACE area of the casting and the constant of proportionality is KNOWN as mould constant. His RELATION is given by:ts = k(V/SA)^2, where ts = solidification time, V = volume, SA = surface area, k = mould constant.

Right choice is (b) False

The best EXPLANATION: Feeding distance is more implies MOLTEN metal can flow for a longer distance. This will result in very few mushy ZONES in the CASTING. Hence, if the mushy zone is less, the number of risers required will also be less.

Right answer is (c) SHAPE factor

To EXPLAIN: Modulus is used for designing of riser using modulus method. The FREEZING ratio is a key parameter when we design riser using Caine’s method. SHRINKAGE volume is used when we use the shrinkage volume method. For Novel research method, we use shape factor and CORRESPONDING to this we find Y from casting databook which is the ratio of the volume of casting to the volume of the riser.

Correct answer is (d) Non-pressurized gating system

Explanation: Non-pressurized gating system has CHOKE at the bottom of the SPRUE base, have total RUNNER area and in-gate areas higher than the sprue area. In this system, there is no pressure existing in the metal FLOW system and thus it helps to reduce turbulence. Hence this system can be used for casting drossy alloys such as ALUMINUM and magnesium alloys.

Correct choice is (b) ZIRCON sand

The explanation is: It has low coefficient of thermal expansion. Due to HIGH density and high chilling power, zircon sand has high thermal conductivity. These properties of the zircon sand MAKE it very USEFUL in controlling zircon sand, which is used as refractory BEDDING material.

Right OPTION is (a) Top gate

The best I can explain: When a NON FERROUS casting is made to drop from the top gate, there is a TENDENCY of it to form dross. HENCE, top gates are not favourable for non ferrous castings.

The correct option is (c) 4

The explanation is: ACCORDING to the exothermic REACTION, when 4 MOLES of IRON OXIDE would react with 8 moles of aluminium, 4 moles of aluminium oxide and 8 moles of iron atoms will be formed.

Right option is (B) Decrease

The explanation: WEIGHT of the sprue and the yield of the CASTING are inversely proportional to each other, that is, with an increase in sprue, yield will decrease.

Correct CHOICE is (a) Increase

The EXPLANATION is: According to Chvorinov’s rule, freezing time is directly proportional to the square of the VOLUME. THEREFORE, an increase in the volume of the casts will cause a lot of increase in the freezing time.

Right ANSWER is (a) True

For explanation: In the casting of massive RING shaped bodies, the bore area is very small, so the bore experiences very HIGH temperature that can damage or destroy the bore material, so in maximum cases, the designs are made to eliminate the use of cores or the highly refractory core MATERIALS are used to RESIST the high temperature.

Correct choice is (b) False

Best explanation: Freezing ratio GREATER than UNITY is always preferred for the ability to feed the casting. Sphere could be used as a riser as its surface area to volume ratio is very low. But in sphere, the hottest METAL being at CENTRE, it is very difficult to use it for feeding to the casting, so a cylindrical TYPE is always preferred.

Correct option is (b) Increase fluidity

The EXPLANATION: Feeding distance REDUCES by reducing molten METAL temperature and using a low thermal CONDUCTIVE mold. For sand casting, feeding distance will be low because HEAT extracted by sand is very less compared to metals. By increasing fluidity, metal can flow over a long distance which results in higher feeding distance.

Right answer is (b) 4.5√T

For EXPLANATION: Feeding distance will be EQUAL to 4.5√T + 2 if we are USING chill for a plate. For a bar, feeding distance will be 6√T without chill and 6√T +2 with chill. Thus, feeding distance will be equal to 4.5√T if we are not using chill during casting a plate.

The correct option is (a) INSULATION POWDER

The best I can explain: Insulation powder is USED for slowing down the process of RETARDATION of radiation losses from the surface of the METAL in the riser.

Correct answer is (c) High temperature resistant

The best explanation: Refractoriness is the ability of the MOULDING material to withstand the high TEMPERATURES of the molten METAL to be poured so that it does not get fused with the metal. The refractoriness of the silica sand is highest. Refractoriness is MEASURED by the sinter point of the sand.

The correct CHOICE is (b) DECREASE in permeability

The best I can explain: A decrease in permeability usually indicates a closed structure in the RAMMED sand, and if the decrease continues, it will lead to TIGHTER packing and fewer voids hence increase in hardness of the green sand mould. This increase in hardness can be measured by mould hardness tester.

Right ANSWER is (a) True

The explanation is: In grey cast iron, while solidification the process of GRAPHITIZATION occurs, this increases the VOLUME of the CASTING and counteracts the metal shrinkage, so risers can be eliminated for the casting of grey cast iron. But for some metals like aluminium and STEEL, the volumetric contraction is very high, so elaborate risering is required.

Correct choice is (d) METAL to be casted

To explain: When directional solidification is taken into consideration, the SIZE of the riser and its LOCATION are the FACTORS, but the metal to be casted is not a factor of directional solidification.

Correct option is (c) To remove SLAG and dross from the metal

The best I can explain: The metal which moves FIRST into the gating system is likely to contain slag and dross which should not be allowed to get into the mould cavity. This could be ACHIEVED by extending the runner beyond the in-gate so the clean metal can be expected to GO into the mould after completely FILLING the runner extension.

Right choice is (a) Non-ferrous material

For explanation: For nonferrous material, a longer pouring time would be beneficial since they lose heat SLOWLY and also tend to form dross if a METAL is poured too quickly, this dross MAKES the quality of the material POOR and further defects induced in the material.

The correct option is (d) Grey CAST iron

Easiest EXPLANATION: Different materials have different volumetric shrinkage, in which grey cast iron is the material which sometimes may have a negative shrinkage. This mainly occurs because of high carbon and silicon CONTENTS in the grey cast iron, which results in occurring of GRAPHITIZATION which increases the VOLUME.

Correct choice is (b) False

Easiest explanation: BASICALLY, the main objective of the riser is to feed the casting during solidification so that no any kinds of shrinkage cavities are formed in the casting. Type of METAL poured and the COMPLEXITY of the casting is responsible for the requirement of RISERS in the casting system to produce castings.

The CORRECT CHOICE is (b) False

Best explanation: An OPEN riser is connected at the top of the cope, but may ALSO have a connection at the side of the parting LINE.

Right CHOICE is (b) False

The explanation: According to the CONSERVATION of mass, weight remains constant until occurring of any reaction in the process. So, in some CASES of materials, weight loss can occur by evaporation when the vapour pressure is very high. For EXAMPLE, vapour pressure of chromium is relatively high, about ten TIMES the vapour pressure of silicon at the processing temperatures.

Right choice is (a) True

Explanation: YES, Modulus method can be used for DETERMINING height and diameter of the riser. In this method, we find modulus of casting and riser which is the ratio of VOLUME and AREA. The ratio of modulus of the riser to that of casting is 1.2, and the ratio of riser height to its diameter is 1.5. By using these two equations DIMENSION of the riser is estimated.

Right OPTION is (d) Chvorinov’s rule

The explanation is: Shrinkage volume consideration METHOD, Modulus method, and NOVEL research method are USED for riser design. For calculation of SOLIDIFICATION time, Chvorinov’s Rule is used. The Same rule can be modified for riser design called as Caine’s method.

The CORRECT option is (c) Gate

Easy explanation: ONE or more than one gates can be employed in the apparatus, as these gates are the links connecting the runner and the MOLD cavity.

Right option is (b) False

Explanation: Directional solidification of binary or pseudo-binary eutectics is able to produce well ALIGNED regular structures CONSISTING of FIBROUS constituents. Such structures may offer a substantial hike in high-temperature strength and creep resistance. So EASILY, there can be a replacement of super-alloys by the directionally solidified eutectics.

The correct choice is (d) Positive temperature gradient towards the riser

Explanation: If the temperature gradient is not there, the metal will not solidify. Same will HAPPEN in case of the UNIFORM temperature gradient. In case of the negative THERMAL gradient, the metal will first solidify near riser which results in unsound casting. Hence positive thermal gradient is required so that metal will solidify near WALLS first hence FEEDING distance will be increased.

Correct answer is (B) 70%

Best EXPLANATION: The use of exothermic materials causes to INCREASE the efficiency by around 70%. The use of exothermic materials ALSO causes the RISER to be of only one-third its regular size.

The correct choice is (b) False

Easiest explanation: In DIRECTIONAL solidification, material can be controlled over a wide range from well aligned to finely dispersed PARTICLES or fibers at microstructure level by the adjusting the various solidification conditions, in which several eutectic TYPES are analyzed as potential materials for HIGH temperature APPLICATIONS.

The correct CHOICE is (b) DECREASE

The best I can explain: Weight of the RISER and the yield of the casting are inversely proportional to each other, that is, with an increase in the riser, yield will decrease.