Test: Casting Processes - 1 - Mechanical Engineering MCQ

Moulds can be classified on the basis of material i.e. green sand mould, plastic mould and metal mould.

Permeability: It is expressed as the gas flow rate through the specimen under a specified pressure difference across it.
Strength: It refers to compressive strength.
Deformation: It indicates the change in length of a standard specimen at the point of failure.
Flowability: it refers to the ability of the sand to flow around and over the pattern when the mould is rammed.
Refractioness: It measures the ability of the sand to remain solid as a function of temperature.

The optimum temperature after melting is decided by a property, called fluidity, of the metal. Fluidity refers to the relative ability of the liquid metal to fill in the mould at a given temperature. Fluidity is higher when viscosity is lower.

Gating ratio = Sprue area: Runner area: Ingate area
If total ingate area is not greater than the area of sprue, gating systems are known as pressurised gating system.
Option (a), (c) and (d) represents unpressurized gating system.

Following are the suggested methods to reduce turbulence in liquid metal flow in mould:
(i) Keep the system filled by proper design of pouring basin and a tapered spure.
(ii) Use a sprue base or well.
(iii) Reduce metal velocity by an enlarged runner.
(iv) Use a streamlined system by providing radius for sprue entrance and exit, runners and ingates.

Solidification time 
Shapes having highest surface area will solidify fastest.

Investment casting employs a shell made of ceramic, plaster, or plastic that is formed around a wax pattern. The wax pattern is melted and removed in a furnace and metal is poured into the shell to create the casting.