SAND TESTING

SAND TESTING

WHY SAND TESTING IS NECESSARY?

Sand testing is necessary for moulding sand for a number of reasons. Properties moulding
sand changes due to the following factors:
a) Contamination of foreign matters.
b) Washing actions.
c) Gradual change and distortion of grain.
d) High temperature.
So periodic tests of moulding sand is necessary to determine the essential qualities of
foundry sand.

PERMEABILITY TEST

Permeability is a condition of porosity and thus is related to the passage of gaseous
materials through the sand. It is expressed as the volume of air in cubic centimetres that
will pass per minute under a pressure of 10 kg/m2 thorough a specimen of sand 1 square
centimetre of cross-sectional area and one centimetres in height.
There are four conditions of permeability
a) Base permeability: It is the permeability measured in a specimen of packed dry
sharp sand.
b) Green permeability: It is the permeability measured in a specimen made of moist
moulding sand.
c) Dry permeability: It is the permeability measured in a specimen made of
moulding sand and dried at about 100 to 110o C.
d) Baked permeability: It is the permeability measured in a specimen made of sand
with thermo-setting binder and backed at some temperature above 105oC.

PERMEABILITY NUMBER

The permeability number P can be found mathematically by the following formula:
P= v×h
p×a×t
P = permeability number to be determined
v = volume of air passing through the specimen in cm3
h = height of the specimen in cm (5.08 cm)
p = pressure of air in gm/cm2 (10 gm/cm2)
a = cross-sectional area of specimen in cm2. (A standard value of 20.26 cm2 is
generally adopted)
t = time for air to pass in minutes
P=200×5.08×60
10×20.26×t
= 3007.2