| 摘要 |
In the apparatus (1), the ladder rung (13) is positioned between centre supports (9a, 9b), after which a shoulder (23) is forced at both ends simultaneously by utilizing the material of the rung (13). A simultaneous operation of forcing means (7a, 7b) is provided by means of an unelastic beam (4) connected to be moved by power units (5a, 5b).
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