... recovery operations, so that oil and gas cracked rock, support for propping fractures not close because of releasing force, thereby to ... , (174KN) angd 103Mpa four series, according to bulk density are divided into: low-density, medium density, high-density. Product specifications are :12-18 mesh ,12 ... .3552≤4.0>0.8MIDDLE DENSITY30MESH-50MESH≤1.80≤3.3569≤6.0>0.8LOW DENSITY30MESH-50MESH1.632.71524. ...