Many sand molding properties such as permeability, adhesiveness, surface fineness, strength. etc, depending on the grain size and distribution of sand particles. The finer the grain size, the finer the sand as a whole. Finely grained sand gives a good surface finish but possesses low permeability. Provides coarse grained sand surface finish less but taste good flow ability, good refractoriness and good permeability. The green strength of silky sand higher than the coarse sand with the same quantity of ingredients added. Has a significant impact on their properties such as flow capacity, coherence and strength of the shape of a grain of: Foundry Sand Grain Shape. In general, there are four types of grains present in the foundry sand were as follows. Grains
(I) rounded Sand: Rounded sand grains to poor bonding strength compared with angular sand grains. Too smooth and rounded sand grains resulting wash sand, sand crack and sand scales. On the sand also greater flow capacity.
(II) angular grains: The grains produced by breaking the rocks without moving the particles. They are also formed by frost and glacial action. There are plenty more angular grains bonding, flow capacity and low permeability smaller than sand grains round. Angular grains have sharp corners and more contact surface.
(III) Sub-angular Grains: As compared with rounded grains, that sub-angular grains better strength and lower permeability. Compared with angular grains, they would lower strength and better permeability.
(IV) compound Grains: grained sand stick compound when two or more grains of sand together and not separate either sawing or washing. Not the best sand and used in foundries.