Determination Of Permeability Of Given Sand Sample Using Permeability Tester

Permeability is that property which allows gas and moisture to pass through the moulding sand. It is determined by measuring the rate of flow of air through A.F.S. standard rammed specimen under a standard pressure. The volume of air in cm3 / min. passing through a specimen of length 1 cm. and cross sectional area of 1 cm2 under a pressure difference of 1 cm. water gauge is called Permeability Number.

1. Permeability Number:

The volume of air passing through a sand specimen 1 sq. cm area and 1 cm. in height at a pressure of 1 gram per square centimeter in 1 min. is called the Permeability Number and is computed by the formula:

P = (v x h) / (p x a x t)

Where,

P = Permeability Number
v = Volume of air passing through the specimen (cubic centimeter or in mil)
h = Height of specimen (centimeters)
p = Pressure difference between upper and lower surfaces of test specimen (in centimeter of water column)
a = Cross-sectional area of specimen (square centimeter)
t = time (minutes)

1. Permeability Meter:

The body of the Permeability Meter is an aluminum casting of a water tank and base. Inside water tank floats a balanced air drum carefully weighed and designed to maintain constant pressure of 10 cm during its fall.
The outlet from the air drum is connected to a centre post in the base via three way air valve. The centre post incorporates a pipe for measuring pressure, which is connected to the water manometer and an expandable “O” ring for sealing the specimen tube. It also accommodates the orifices.

Equipment:

• Sand Permeability Tester
• Testing sand specimen

1. Standard Permeability Test:
   

1. Test Procedure:

1. Check that the open orifice is in the position in the centre
2. Prepare an A.F.S. standard specimen of sand. Before stripping from tube place in position on the centre post and seal by rotating the knurled ring anti-clockwise.
3. Check water level in the tank. Turn air valve to “NENT” and slowly raise drum until it is out of water.
4. Allow the air drum to descend by turning the air valve to a position midway between “CLOSED” and “VENT”.
5. Time the descend of the air drum between zero and 2000 ml mark with a stop watch and record the pressure indicated on the manometer during the descend of the drum.
6. Calculate the permeability by applying the given formula.

1. Dry Permeability Test:

The permeability of a moulded mass of sand dried at 105oC to 110oC is called Dry Permeabilty. It is used for dried, baked or cured sand specimens.

1. Test Procedure:
   

• Place split specimen tube on pedestal, and insert steel ring in bottom of tube.
• Tighten clamp on split specimen tube.
• Weigh out sufficient sand to produce a test specimen of standard dimensions, and ram according to standard procedure.
• Release clamp on specimen container, remove the tube, and place specimen on drier. The clamp is then release and the core is stripped.
• Place core in an oven and dry at 105oC to 110oC for one hour or until dry.
• Remove the specimen from oven, and place it in a desiccator to cool.
• When cool, place specimen in a core permeability tube. Clamp the specimen firmly in position.
  
• Place permeability tube in position in permeability meter, and determine permeability in usual way, as described above.