... purpose: for mine tunnel, mine tunnel secondary support, and mountain tunnel support .U25,U29,U36 type steel frame.U25/U29/U36 Steel ... Arch Support for Mining:1.Spec.: 25U, 29U, 36U 2.Standard:GB/QB 3.Materials: 20MnK, Q275 4.Length ... is mainly used for mine laneway, mine laneway secondary support, and the support of the mountain tunnel in supporting purposes.Feature of ...