SJ Grinding Mills are developed by Shuangjin company base on the theory of high efficiency crusher, with multi-cylinder hydraulic technology and several patents technology referred to structure, material and craft, are new concept sand making equipments. The type of machines make sand based on the “rock grind rock” theory, different with the “rock impact rock” theory of traditional Vertical Shaft Sand Grinding Mill, from “to impact” to “to grind”, it is easier and more efficient to make sand. Mainly used in mine production line for making sand, and in ore production line for extracting metal powder.