PROPERTIES OF MOULDING SAND

 Contents - Silica (70 - 85%), clay (10 - 20%), water (2 - 8%)

    Fine-grain - less permeability

    Silica grain - no bonding property

    clay acts as a bonding agent.

    Two types of clay material

1. NATURAL CLAY MATERIAL:    

               Bentonite, Kaxlonite - Available in the form of powder.

       2. SYNTHETIC OR ORGANIC MATERIAL:

             Clay is present between two silica grain and this provide the sufficient bonding property of sand and to activate this bonding property water is used.

            River sand can not be used as moulding sand because it is formed by the disintegration of rocks.

PROPERTIES OF MOULDING SAND:

1. REFRACTORINESS:

    The ability of the moulding sand to withstand the high temperature of the liquid metal.

2. PERMEABILITY:

    Gas evolving capability of moulding sand is known as permeability. It is expressed by permeability number

        Pn = VH

where

    Pn = Permeability number

    V = Volume of the air passing through the specimen = 2000cc

    H = Height of the standard cylindrical specimen

    P = Difference of pressure through the edge passing through the specimen gm/cm

    A = Cross-sectional area of the cylindrical specimen

    T = Time taken by the air to pass through the standard cylindrical specimen

3.STRENGTH:

    To retain the shape and size of the cavity strength is required. Also to avoid the expanding of the cavity.

    

    Greensand - contain moisture

    Dry sand - Wen hot metal poured, the moisture evaporated and dry sand obtained.

    Hot sand - Due to the temperature of liquid metal the sand becomes hot

    Thus moulding sand requires all types of strength i.e., green strength, dry strength, and hot strength.

    UNIVERSAL SAND STRENGTH TESTER

 

    To retain the shape and size of the mould cavity, strength is required for the mould. To resist the forces applied by the liquid metal, strength is required for the amount. 

    The strength required by green sand is known as green strength.

    The strength required by dry sand is known as dry strength.

    The strength required by hot sand is known as hot strength.

4. MOULD HARDNESS

Mould hardness number - 0 to 100.

    MOULD HARDNESS TESTER

    Hardness means resistance to the external force. It is a surface property. Hardness is expressed by mould hardness number.

    The average value of this number is 60 - 70.

    If the Hardness is less than 60, the dimension of the mould cavity will be distributed.

    If hardness is more than 70, permeability will be decreased and gas defects will be found.