Process for formation of high strength aluminum ladder structures
AssigneeAlumax Extrusions, Inc.
InventorJoseph C. Benedyk
Life of this patent
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Abstract
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.
Claims12
A method for forming aluminum ladders with strengthened ladder rung structures in position within co-operating ladder stile members, the method consisting of the steps of:
- age hardening a plurality of tubular, formed ladder rung components to a hardness ranging from 13 to 18 Webster;
- selectively softening the opposing ends of each of said plurality of formed ladder rungs to a hardness falling within the range of 0 to 12 Webster through the application of localized and regionally confined heating means while isolating the transmission and conducted migration of said heating means from the regions of ladder rungs between said opposing ends;
- closely controlling said application of confined heat means through quickly elevating the temperature of same for a substantially brief time period, to facilitate said isolation of the transmission and conducted migration of same so as to heat only said desired opposing end portions;
- said application of confined heat means being controlled by elevating the temperature of each said ladder rung end to a range of from 600.degree. to 1100.degree. F. over a period of time ranging from one-half second to ten seconds;
- said accelerated application of generated heat during said substantially brief time period serving to control said selective softening of said ladder rung ends to said isolated region while further controlling against the inadvertent and undesired migration of conducted heat from beyond said confined localized region;
- forming collar and upset flanging into each said respective ends of said plurality of ladder rungs for positioning through and into respectively aligned apertures in said ladder stile members;
- restrainably affixing the collar and upset flanging portions of said ladder rungs, positioned at opposite ends thereof, in attached spacial relationship about the inner and outer surfaces of each said ladder stile respectively;
- and
- exposing the ladder structure so formed and particularly the treated ladder rung ends and juxtaposed portions of said ladder stiles to ambient room temperatures, so as to alternatively age harden treated ladder rung ends softened to a hardness below 8 Webster to a hardness ranging from 8 to 13 Webster, and maintain treated ladder rung ends softened to a hardness ranging between 8 and 13 Webster within said respective range.
Dependencies are inferred from the claim text.