Abstract: The straightening jaw comprises a cubical chuck with a plane face end. The face end has an intake element and an exit element of a straightening groove. Between them is an opening arranged perpendicular to the face end. A straightening insert made of hard metal is inserted into the opening loosely but insured against twisting. On the face end, the straightening insert has a of saddle-shaped straightening indentation that connects the intake and exit elements. Because of this structure, long service lives of the straightening jaw and shorter down times of the straightening device causing low production costs are achieved.

Abstract: Stiffening elements are welded between the three rods (T1, T2, T3) of three-rod girders in uderground drift construction. Such stiffening elements consist of thee triangular wire polygons (10, 20, 30) connected to form one piece. Two of the polygons meet at the top rod (T3) to form a wire pyramid. The third wire polygon (30) is perpendicular to the plane determined by the axes of the lower rods (T1, T2). Since neither this third wire polygon (30) nor the adjacent polygon (10), which is one side of the pyramid, needs a cross-strut between the lower rods (T1, T2), a significant saving in materials combined with high resistance to bending is achieved.

Abstract: The frame girder for underground drift construction comprises three or more retainer bars (3a, 3b) whose cross sections form a polygon, the retainer bars being affixed to one another by stiffener elements (4). Each stiffener element (4) comprises a number of cross struts (5) bent in their centers and inclined with respect to the retainer bars. The outer ends (9) of the struts (5) are each attached to one of the retainer bars. The stiffener element may be formed symmetrically with respect to a central plane extending obliquely to the retainer bars. The frame girder may be made from conventional round irons. It resists bending, torsion and buckling at very high loads, and no undesirable injection shadows are produced during concreting.

Abstract: The frame girder for underground drift construction comprises three or more retainer bars (3a, 3b) whose cross sections form a polygon, the retainer bars being affixed to one another by stiffener elements (4). Each stiffener element (4) comprises a number of cross struts (5) bent in their centers and inclined with respect to the retainer bars. The outer ends (9) of the struts (5) are each attached to one of the retainer bars. The stiffener element may be formed symmetrically with respect to a central plane extending obliquely to the retainer bars. The frame girder may be made from conventional round irons. It resists bending, torsion and buckling at very high loads, and no undesirable injection shadows are produced during concreting.