| 摘要 |
PROBLEM TO BE SOLVED: To determine the location of a crack to be generated at a boom in earliest stages even during operation of a construction machine, and to repair the damage of the boom before it becomes larger. SOLUTION: A lower flange 35 and a bulkhead plate 40C both forming a boom are fixed to each other by a welding bead 42 which is coated with a semi-solid paint 44. Further, compressed air is supplied into hollow chambers 41B, 41C defined by the plates. Thus, if a crack C is generated during operation of a construction machine, the semi-solid paint 44 in a color different from the color of a surface paint of the boom seeps through the crack C. As a result, the operator can determine the location of the generated crack C in earliest stages.
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