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The correct CHOICE is (b) Metal

To EXPLAIN I would say: Metal is the most USED material to make patterns for a PROCESS of SHELL moulding.

The correct option is (a) True

To explain: 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.

The CORRECT option is (a) True

To explain I would say: 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.

Right choice is (a) True

Explanation: In Co2 moulding, over-gassing and under-gassing can affects the properties of cured sand ADVERSELY. When the continuous passing of Co2 is done for long time, this may results into sticking of pattern with the mould which cannot be REMOVED easily, so proper CARE should be TAKEN while passing of Co2 GAS.

Correct choice is (a) True

Easy explanation: In CENTRIFUGAL casting, the AXIS of rotation of the mould can be horizontal, vertical or any angle in between. Generally, very long pipes are cast with a horizontal axis, WHEREAS SHORT pieces are more conveniently cast with a vertical axis, as it requires less area for the casting operation.

The correct answer is (a) True

The explanation is: Rapid SOLIDIFICATION rates of the casting can avoid the oxidation of the material in the vacuum DIE casting (VDC). This is accomplished by providing very thin WALLS (1 to 12 mm) of mould to the casting with close tolerances. Then the PROPERTIES of casting approach to that of wrought product, and with relatively short cycle times.

The correct choice is (c) TIGHT TOLERANCES

The explanation: In vacuum die casting, the part is EXPOSED to atmospheric AIR only after solidification, and oxidation of the material is avoided as much as POSSIBLE. This can be achieved by processing of parts with tight tolerances and also by faster cooling rate which results into fine microstructure nature of castings.

Correct choice is (a) True

To explain I would SAY: The die LIFE is less for higher melting TEMPERATURE alloys such as copper and grey cast iron. Very HIGH temperature of molten metal in contact with the moulding surface damages it and may cause surface erosion. This can be avoided by using die material of highly RESISTANT to the temperature of molten metal.

The CORRECT option is (b) False

To explain I would SAY: Air cooling is not sufficient except for thin and small castings. Generally, air cooled dies are provided with fins on the outer surfaces to increase the heat extraction. And cooling water can be ALSO circulated through the portions of the mould that are likely to have LARGE heat CONCENTRATION.

The correct choice is (b) False

Easiest explanation: The mould CAVITY should be simple WITHOUT any undesirable DRAFTS or undercuts because these interfere with the ejection of the solidified castings and makes the casting weak and less durable. And care should be taken to SEE that progressive solidification occurs toward the riser, in the designing of permanent MOULDS.

Correct OPTION is (a) True

The explanation: As CONTROL of grain size and its orientation is POSSIBLE in INVESTMENT castings, so it makes the casting ready for use WITHOUT any requirement of machining. This is particularly useful for those hard to machine materials such as nimonic alloys. So this process saves time and money both, which is usually spent on machining for other processes.

Right ANSWER is (b) False

The best explanation: Complex SHAPES which are DIFFICULT to produce by any other method are possible in the precision investment castings since the pattern is withdrawn by melting it. And the thin sections with complexities can ALSO be produced because the mould is heated before pouring of molten metal.

Correct option is (b) Molten wax

To ELABORATE: An expendable pattern, around which the mould is PREPARED. For the preparation of the pattern for every casting to be made, molten wax is used as the pattern material, which is injected under PRESSURE of about 2.5 MPa into a metallic DIE, which has the cavity of the casting to be made. After the solidification of wax, it would PRODUCE the pattern.

The correct ANSWER is (a) True

Explanation: For the curing of the shell mould, it is kept in an electric or gas fired oven. The curing of the shell should be done as PER REQUIREMENTS only because over-curing can cause the mould to break down as the resin would burn out. And under-curing may result in BLOW holes in the CASTING or the shell may break during handling.

The correct option is (b) False

The best explanation: When after the achieving of a desired thickness of the SHELL, the dump BOX is rotated backward by 180 degrees so that the excess of sand falls back into the box, leaving the formed shell intact with the PATTERN. Thickness of the shell depends on the TEMPERATURE of the pattern and the coating time of sand in contact with the heated pattern.

Correct answer is (b) False

To explain: 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.

Correct choice is (a) True

To explain: In squeeze CASTING, the die temperature has to be monitored within close limits, because too LOW preheating temperature of die may result in quick solidification and cold laps in the castings. And too high temperature may CAUSE the surface defects and welding of the die with casting.

Correct choice is (a) True

Easy explanation: GENERALLY, squeeze casting has two TYPES of WAYS for performing casting operation. Direct and in-direct, in direct squeeze casting, PRESSURE is directly applied to the metal, while in in-direct squeeze casting; pressure is applied on the molten metal through an INTERMEDIATE feeding part.

Correct OPTION is (d) Squeeze casting

To ELABORATE: Squeeze casting is also known as the LIQUID metal forging, which combines the advantages of casting and forging processes. This PROCESS is widely used for the production of quality castings; this is mainly achieved by improving the CONTACT between the molten metal and the die by pressurization.

The correct choice is (d) Centrifugal casting

To explain: Specifically, true centrifugal casting is generally used for the making of hollow pipes and tubes, which are axi-symmetric with a CONCENTRIC hole. MOLTEN metal is accumulated at the inward surface of the MOULD by the ROTATION of the mould and then the solidification of a MELT is taking place.

Right choice is (b) Centrifugal force

The best I can EXPLAIN: In centrifugal CASTING, mould is rotated rapidly about its central axis as the metal is poured into it. Because of the centrifugal force, continuous pressure is applied to the metal as it SOLIDIFIES. The slag and the other inclusions being lighter gets separated from the metal and segregates toward the CENTRE.

The correct option is (a) True

For EXPLANATION I would say: In low-pressure die casting, due to the application of RISER tube, MOLTEN metal flows upward in direction against the gravity. This makes the metal to flow into the mould slowly as compared to the die casting with LESS TURBULENCE, so the casting quality is also improved by eliminating the defects.

The correct answer is (a) below -38 ⁰C

To explain I would say: If MERCURY is used as a pattern material in place of wax, then the process is known as MERCAST, the mercury is kept under -57 ⁰C where the mercury is frozen. And the complete mould preparation is to be UNDERTAKEN at a TEMPERATURE below -38 ⁰C to keep the mercury in solid state.

Correct option is (a) True

Explanation: In DIE casting, as the metal is forced in under PRESSURE compared to the permanent MOULD casting, it is also known as pressure die casting. Because of involvement of high pressure in die casting, any type of complex SHAPES, narrow sections and FINE surface details can easily be produced.

Right OPTION is (d) Increase the heat transfer rate

For explanation: The moulds are coated with a REFRACTORY material to increase the mould life by preventing the soldering of metal to the mould, by controlling the direction and rate of the casting SOLIDIFICATION and also by minimizing the thermal shock to the moulding material. Coatings can be a mixture of sodium silicate, clay, soap, stone, talc etc.

The correct ANSWER is (d) Additives

To explain: Generally, additives are added to the sand mixture to improve the SURFACE FINISH and also for the avoiding of any THERMAL crack during pouring. Some of the additives used are coal dust, manganese dioxide, calcium carbonate, pulverized slag and AMMONIUM boroflouride.

The correct choice is (d) Continuous casting

Explanation: To produce continuously long length METALLIC objects in mass production directly from the liquid metal this technique can be used. Liquid metal is allowed through the die OPENING and the OUTPUT of the die is a solid CRUST on which water will be sprayed to cool the MATERIAL at a faster rate.

Correct answer is (a) True

The explanation is: The wall THICKNESS of the CASTING part not only determined by the thickness of the metallic wall of the mould, but it can also be OBTAINED by considering the other factors like length of time the mould is preheated, and the amount and type of molten metal are used in the process of SLUSH casting.

The correct option is (b) 50 to 140

To EXPLAIN I would say: In squeeze casting, the punch portion of the upper die is forced into the cavity by displacing the molten METAL under pressure until it fills the annular SPACE between the die and the punch. Normally, the metal is KEPT under pressure of 50 to 140 MPa to avoid the formation of shrinkage defects.

The correct CHOICE is (a) True

Explanation: When after the proper ramming of sand to CONFIRM to the outer contour of the PIPE to be made, dry sand cores may be introduced for the provision of end details such as SPIGOT ends, or flanged ends to the casting. Meanwhile there is no requirement of any cores for the making of the hollow section of the castings.

Correct CHOICE is (b) Hollow pipes

Explanation: True centrifugal CASTING METHOD is USUALLY used to make ‘hollow pipes and tubes’.

Right ANSWER is (b) False

To elaborate: In Co2 moulding, POOR COLLAPSIBILITY of the mould is a major disadvantage. Although some additives are used for the improvement in the properties of ferrous METAL castings, these additives which are added to the sand mixture, cannot be applicable for the non-ferrous APPLICATIONS.

Right answer is (B) False

Best EXPLANATION: In centrifugal casting, there is no requirement of any core for the making of the concentric hole. As the metal is always pushed outward because of the centrifugal force, application of core is eliminated. Only the OXIDES and slag part separate from the metal and segregate at the centre.

Right choice is (b) False

To EXPLAIN: Proper cooling is very essential in low-pressure die casting to produce CASTINGS of high strength. So, care needs to be exercised during DESIGNING of the mould to provide proper cooling circuits, so that the heavier sections of the casting are located close to the FEEDING path to MAKE it act as a riser.

The correct answer is (d) Ejector PINS

For explanation I would say: The ejector pins, which move through the moving die to free the CASTING from the ejector die. The number of ejector pins should be sufficient so as to remove the HOT casting WITHOUT any DISTORTION. And the position of ejector pins should be like so that the pins marks remain on the casting are not objectionable.

Correct option is (c) Grey cast IRON

The explanation: GENERALLY, metal patterns with the associated gating are used. The metal used for preparing patterns is grey cast iron; it is mainly used because of its easy availability and good stability at the temperatures involved in the process. Sometimes, ADDITIONAL risers are ALSO required as the cooling in SHELL moulds is slow.

Correct option is (C) Mueller

To explain: Mueller is the MACHINE used to mix mould particles THOROUGHLY.

Right option is (c) Both Ethyl and Sodium silicate

To EXPLAIN I would SAY: The SLURRY in which prepared pattern is dipped into is MADE by suspending FINE ceramic particles in ethyl silicate or sodium silicate.

Right answer is (d) Slush casting

For explanation: Slush casting is an excellent METHOD for producing of OPEN and hollow objects like boots, shoes, toys and AUTOMOTIVE products, such as protective skin coatings on arm rests, head rests and CRASH pads. This method is very simple and widely used for the production of ORNAMENTAL objects.