Q. Determine the size of grains using fineness test of sand?
Fineness test : Fineness test of sand specimen determines the size of grains and the distribution of grains of different sizes in the moulding sand. The test is performed on completely dry and clay free sand. The test apparatus consists of a set of graded sieves placed one above the other, with the coarsest sieve at the top and the finest sieve at the bottom, next to the pan. The sand is put in the top sieve and the set of sieve is shaken continuously for 15 minutes with the help of an electric motor. At the end of a shaking operation, the sieves are taken out and the sand retained on each is carefully weighed. Each weight is converted to percentage basis. Each percentage is multiplied by a weighting factor and these are added to get the sum of products. Then the grain fineness number (GFN) is given as,
GFN = Sum of products / Sum of percentage of sand retained on each sieve and pan