Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
E21C27/00—Machines which completely free the mineral from the seam
E21C27/20—Mineral freed by means not involving slitting
E21C27/22—Mineral freed by means not involving slitting by rotary drills with breaking-down means, e.g. wedge-shaped drills, i.e. the rotary axis of the tool carrier being substantially perpendicular to the working face, e.g. MARIETTA-type