| 摘要 |
In the separation of materials of different sizes and specific gravities, such as in the cleaning of coal, by stratifying the mixed materials, previously graded by screening into batches of limited size range, under the action of an upwardly directed air current, a preliminary winnowing operation is performed on the materials for the purpose of carrying off the smallest particles of the lighter products and facilitating the subsequent screening and separating operations. In the example described, raw coal ranging in sizes from 1/2 " to 0" is first treated in apparatus such as described in Specification 338,119, [Class 117], for removing the lighter particles up to 1/32 ". The remainder is then divided into batches ranging from 1/2 "-/ba1/8 " and 1/8 "-/ba1/32 " respectively by screening, and treated on pneumatic separators appropriate thereto. The product that passes through the second screen consists mainly of the small size denser constituent, e.g. shale, of the original material and is thus removed from the action of the pneumatic separators. |
