| 摘要 |
<p>Apparatus for enlarging or removing irregularities in an underground duct comprises first and second expandable segmented nose and intermediate shell portions (10, 20) each comprising a respective set of shell parts (14, 18) arranged around a longitudinal axis (16). The shell parts (14) of the nose portion (10) are pivotally connected to a nose cone (12) and to the front ends of the shell parts (18), while the shell parts (18) are pivotally connected at their rear ends to a rear pivot assembly (22). Expansion of the duct is achieved by repeatedly driving the joints between the shell parts (14) of the nose portion (10) and the shell parts (18) of the intermediate portion (20) outwards so as to force the wall of the duct outwards, returning the shell parts (14, 18) to a contracted configuration, and moving the apparatus forward in the duct. In accordance with the invention, ingress of loose particles of material from the duct wall into the apparatus is reduced by arranging for the shell parts (14, 18) of each portion to be overlapping, each shell part having a recessed border surface (34, 64) over which the edge of a neighbouring shell part slides.</p> |
