| 摘要 |
<p>The foot piece is used in support structures in galleries in underground mines. It is used in conjunction with steel bars or rails of 'I' section. A piston-type prop foot is displaceable in a tube by means of a spring, pref. volute spring, and stands under pressure. It can be connected to an additional tube to accommodate the end of the gallery arch. Foot and second tube may be sealed on the first tube with an intervening annular chamber produced. This can contain a return valve opened from outside. Feet can absorb and give off forces, and prevent gallery arches from bending and sagging.</p> |
