| 摘要 |
An improved process by which heavy duty aluminum ladder rungs are easily manufactured with the central stepping portion of the rung itself possessing qualities of exceptionally high yield strength, while the ends of the ladder rung are easily formable such that they are readily crimped and secured to the end rail or stile during the ladder assembly process-without cracking or fracturing. In order to maintain high strength at the central portion of the ladder rung while providing for adequate deformability at the ladder rung ends, the invention uses a selective localized heat treating process whereby high frequency induction heating is applied selectivley to the ladder rung ends prior to collar and upset formation.
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