A good friend of mine is rebuilding a 1913 Overland. He's run into a problem with a bronze spring. It was part of an assembly that included a shaft and cast iron wing nut. He used heat to tackle the frozen wing nut and has annealed part of the spring.
He's wondering on how to harden/temper it back.
I suggested he anneal the entire spring, beyond that, I've not much to tell him. Any ideas?
Copper alloys, such as bronze, can only be hardened by work-hardening. Thus, I expect some sort of re-forming of the spring will be required, but I don't know how you'd replicate what was done in the factory without knowing what they did (in terms of the state of the bronze) to form it in the first place. That is, I don't know how you'd figre what state (half-hard, say) the spring was in before the final forming to it's final shape. Hopefully it's not too critical, or someone has the details available.
Work hardening is the only way, as you've heard elsewhere in this thread.
I wouldn't be hopeful that the strength could be restored. Annealing is exactly the *opposite* of what you'd want to do, unless you're just after uniform strength. The strength would be lower than the original part by some unknown amount.
You could look into shot-peening. It is used on bronze to increase fatigue strength, or at least on aluminum-bronze alloys.
Your friend should lay off using heat on parts of a rare vehicle. Almost anything else is preferable. He's going to wreck something if he keeps that up.
-- Ed Huntress
Find a new spring. The old one is F***ed.
If a new spring cannot be found, find a source for bronze spring wire, search out the nomographs (to determine the mandrel size required) and wind the new one.
Or sub in a steel spring that fits.
Work hadening is the only way to get bronze harder. Heat makes it soft and it stays that way.
Cheers Trevor Jones
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