Manufacturing Technology I Set 3

Answer: true

Explaination:
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.

Answer: true

Explaination:
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

Answer: false

Explaination:
not only sand moulds, the metallic moulds can also be used in the centrifugal casting process for large scale production. as inducing of high temperature of metallic mould can be avoided by water circulation through it and sticking problem can also be solved by casting of non-sticking materials.

Answer: true

Explaination:
there is no need for the gates and runners in the centrifugal casting process, which saves a lot of molten metal. this

Answer: true

Explaination:
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.

Answer: false

Explaination:
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.

Answer: co2 moulding

Explaination:
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

Answer: 2 to 6 %

Explaination:
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:

Answer: false

Explaination:
continuous passing of co2 always results in a strong and hard mould. more the passing of co2 more will be the strength of the mould. only the drawback is the decrease in permeability and collapsibility of the mould. much passing of co2 gas

Answer: one

Explaination:
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.

Answer: true

Explaination:
in co2 moulding, over-gassing and under-gassing can affects the properties

Answer: true

Explaination:
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.

Answer: aluminium oxide

Explaination:
after the preparation of the sand mixture by adding sodium silicate to the

Answer: true

Explaination:
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.

Answer: false

Explaination:
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.

Answer: true

Explaination:
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.

Answer: run out

Explaination:
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.

Answer: pin hole porosity

Explaination:
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.

Answer: moulding material defect

Explaination:
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.

Answer: run out

Explaination:
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.

Answer: misrun & cold shut

Explaination:
fluidity is a very important consideration in metal casting. cold shuts and misruns can be caused by a lack of fluidity in the metal.

Answer: hot spots

Explaination:
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.

Answer: slag

Explaination:
slag is said to be refuse produced as a result of melting nonferrous material which have a high melting point, it is

Answer: blow holes

Explaination:
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.

Answer: shrinkage cavity

Explaination:
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,