| 摘要 |
A derrick crane has a jib pivoted by way of a horizontal pivot to the movable member of a bearing device supported by a vertically extending mast and includes devices for raising and lowering a load, luffing the jib and slewing the jib about the mast. The bearing device comprises a single ring of free running balls which are a running fit in part circular registering grooves formed in inner and outer bearing rings. The bearing device is located on the mast in such a position that the line of thrust of the jib passes within the pitch circle diameter of the ring of balls. |
