AFS Foundry Sand Testing Equipment Operating Instructions Manual

RIDSDALE-DIETERT PERMEABILITY METER (AFS)IGENERAL PRINCIPLESPermeability is defined by the AFS as that physical property of moulded sand which allowsgas to pass through it. It is determined by measuring the rate of flow of air through the AFSstandard rammed specimen under a standard pressure.The general formula for the calculation of permeability may be expressed as follows :-P = v x h Where P = Permeability numberp x a x t v = Volume of air in ml passing through thespecimenh = Height of test specimen in cm.p = Pressure of air in cm of water.a = Area of cross-section of specimen incm 2 .t = Time in seconds.Since the standard method requires that 2000 ml of air should be forced through a specimen2 inches (5.08 cm) and 2 inches diameter (20.268 cm 2 area), by substituting these values forv, h, and a, and measuring the time in seconds, the formula becomes :-P =____________30072____________________air pressure in cm of water x time in secondsTo determine permeability it is, therefore, only necessary to measure accurately the timetaken for 2000 ml of air at a known pressure to pass through a standard test specimen.For example, if p = 9.6 cm and t = 36 sP = _______________30072____________________ = 879.6 x 36By means of this instrument a measured volume of air can be passed through a rammedsand specimen and the permeability of the sand determined by recording the time taken forthe air at a measured pressure to pass through the specimen.Alternatively, for routine control purposes, calibrated orifices may be used to meter the rateof flow of air to the sand specimen and by measuring the pressure between the orifice andthe specimen, the permeability may be obtained by referring to the attached table or usingthe transparent direct reading scale.63