| 摘要 |
In a sand classification tank for producing classified sand for concrete pouring purposes, i.e., sand containing predetermined fractions of sand grains of different sizes per unit of volume, a mixture of unclassified sand and water is introduced into a tank (1) partially filled with water, beneath the surface of the water, and the sand grains are deposited by sedimentation at the bottom of the tank at varying distances from the inlet, depending on their weight, such that the coarsest sand fraction will be deposited closest to, and the finest fraction or fines farthest from, the place where the sand/water mixture is introduced into the tank. For the purpose of retaining as much of the fines fraction as possible (i.e., sand grains of between 0.002 and 0.006 mm) as well as coarser sand fractions that are larger than conventional equipment can handle (up to about 12 mm), in order thereby to obtain a substantial savings of cement and substantially improved castability of the concrete as well as to reduce the water requirement considerably, the classification tank (1) is defined at the bottom thereof by a plurality of successive compartments (8,8a) each associated with one or more screw conveyors (9) for carrying off the sand from the respective compartments, said compartments (8,8a) communicating with the remainder of the tank (1) through slots (10) that preferably are adjustable. |
