SPECIAL SECTION Russian patent published in 1995 - IPC

FIELD: mining. SUBSTANCE: special section has straight bottom 1, inclined side walls 2 and flanges 3. Made at the level of conjunction of inner surface of side walls 2 with bottom 1 is smooth turn with outer radius R= , where d₁ is thickness of section wall; γ is angle of turn equalling 1-5 deg. Walls on the area from turn to flanges are made with same thickness. EFFECT: higher efficiency. 2 dwg