Facts & Figures Book - KPI-JCI

CLASSIFICATION METHODSAPPLIED TO FINE AGGREGATESINTRODUCTIONClassification is the sizing of solid particles by means ofsettling. In classification, the settling is controlled so thatthe very fines, silts and clays will flow away with a streamof the water or liquid, while the coarse particles accumulatein a settled mass.Washing/classifying equipment is manufactured inmany different configurations depending on the naturalmaterial characteristics and the end product(s) desired.Although the general definition of aggregate classifyingcan be applied to coarse material (+ 3 ⁄8”), it is mostcommonly applied to the material passing 3 ⁄8”. Includedin the fine material classifying equipment are the sandscrews, counter-current classifiers, sand drags and rakes,hydro-cyclones, hydro-classifiers, bowl classifiers, hydroseparators,density separators, and scalping/classifyingtanks.All the above-mentioned classifiers, except the scalping/classifying tank, are generally single product machineswhich can only affect the gradation of the end producton the very fine side (the overflow separation size). Thisseparation size, due to the mechanical means employed,is never a knife-edge separation. However, the aim ofmodern classification methods is to approach a clean-cutdifferentiation. Many material specifications today call formultiple sizing of sand with provisions for blending backto obtain the gradations required. It is rare to find theexact blend occurring naturally or to economically manufacturethe blend to exact specifications. In either case,the accepted procedure is to screen out the fine materialfrom which the sand specifications will be obtained. Thismaterial is processed in a water scalping/classifying tankfor multiple separation by grain sizes or particle specificgravity.There is no mystery connected with classifying tanks.They are merely long settling basins capable of holdinglarge quantities of water. The water and sand mixWashin g/Classifyin g113