JNTU Hyderabad B.Tech II PRODUCTION TECHNOLOGY Previous Question Paper (December 2017 - R15)

Moulding sand is primarily composed of silica sand (silicon dioxide), which provides the necessary refractory properties and strength. To achieve the required bonding and plasticity, it is mixed with clay (typically bentonite or kaolinite) as a binder, water to activate the clay, and sometimes additives such as coal dust, wood flour, or dextrin to improve surface finish and collapsibility.

A pressurized gating system is one in which the total cross-sectional area of the gating system decreases towards the mold cavity. This restriction creates back pressure in the system, ensuring that the sprue and runners remain completely filled with molten metal during the pouring process.

Key characteristics include:

• The gating ratio is typically expressed as Sprue area : Runner area : Ingate area, where the ratio is less than 1:1:1.
• The restricted flow prevents the aspiration of air and gases into the mold cavity, which helps in reducing oxidation and turbulence.
• It is commonly used for non-ferrous metals to ensure a steady, controlled flow of metal into the mold.