| 摘要 |
A jib or tower crane has a jib or boom (3), a main block (1) and a light block (not shown). In order to secure the main block (1) to the boom (3) when the main block (1) is not in use, the main block (1) is provided with pulley wheels (2), two on each side of the main block (1), which wheels (2) engage in guide rails (4) provided on the boom (3). Angled brackets (5) are provided in the end of each guide rail (4) to direct the pulley wheels (2) into engagement with the guide rails (4) the boom (3) being nearly vertical. Oscillation of the main block (1) with consequential possible damage is thus prevented when the light block is in use, the main block (1) sliding up and down in the guide rails (4) when the boom (3) is lowered or raised. When the main block (1) is to be used again the boom (3) is raised nearly to the vertical position and the main block (1) lowered out of the guide rails (4), when it is ready for use. <IMAGE> |
