Bending bronze..does it work harden?

[jerrytug]

Hi folk, my old sailing boat got some impact damage, some solid bronze stanchions got bent. About 1 1/4" diameter.
They are important safety items as they stop people falling in the sea.

I was wondering if I can just remove them and batter them straight again, or if doing that would introduce a dangerous weak spot?
And, if it's safe to straighten them, should I heat them up to bend them back, or do them cold?

Thanks a lot Jerry

 

[MattF]

Heat & straighten.

 

[jerrytug]

Thanks Matt. What would you say, cherry red?

 

[Seadog]

I wouldn't heat to cherry red, too much risk of it melting since you don't know the composition. Bending in a press may be better. The issue, of course, is that it's a safety device. A marine engineer might be the best person to ask. Where are you berthed btw?

 

[Paul.]

I would be careful about getting it too hot, if it is bronze then you could do more harm than good, it needs a controlled gentle push in a press rather than battering them with a hammer, proper bronze (copper alloyed with tin) is quite ductile and may push back without any problems, without knowing the exact alloy its really impossible to say,
you could try annealing it up to about 400 deg without damaging the structure, But I would try it cold initially

 

[jerrytug]

Very intersting replies, mucho appreciado. @Seadog: I'm near Mandal in the far south of Norway on my old wooden gaff cutter. She got battered about due to a random incident, and I must repair her locally, with the very limited facilities where I am.

 

[nickk]

That's interesting to hear the comments,the small amount of bronze fabrication I've done has been mainly on yachts TRESSANG was the one raced by Blonde hasler,I learnt how it worked hardened quickly.
Since then I've made railings with mama,I had to pre heat so much ,my bench split in two.

 

[Seadog]

I assume you're cruising then, and doing it in style? It looks like a fantastic location. Norway is definitely somewhere I'd like to go one of these days.
When you get sorted maybe you could post a couple of pictures of the boat?

There's a lot of conflicting information on the various boat forums. It depends on the alloy composition. One suggestions was to coat the bend in soot using just acetylene and then to heat with O/A until the soot burnt off, at which point the alloy should be annealed, then straighten.

http://weldingweb.com/showthread.php?242311-Please-help-with-bent-bronze-marine-parts

 

[fizzy]

Please can we see a picture of your boat?

 

[gt6s]

Straighten that in a press.

Laurence

 

[fizzy]

I straightened something similar to that. I just stuck it in the end of some railings around the harbour and bent it back into shape. Gently does it!

 

[jerrytug]

Please can we see a picture of your boat?

Yes, Marihøna ( Norwegian for ladybird) was built in Moen, Norway in 1957. She is a traditional double-ender, with a lineage going back to the Vikings.
Construction is pitch pine planking on an oak keel and skeleton.
Fastened together with iron rivets. Wrought iron keel bolts.
She weighs about 12 tons ( there is no way to weigh her, unless she is hoisted by a crane with a load cell) and of that 12, 3 is internal ballast in the form of lead ingots, and 3 is external, in the form of a cast-iron ballast keel.
The rig is gaff cutter, with modifications (compared to a Colchester oyster smack gaff cutter, for example) for very long distance sailing.
Motor is a 1973 36hp Volvo 3-pot 1.5 litre diesel, old-skool with individual decompressors and a big flywheel like a steam engine. On its last legs so being swapped out for a sensible but boring Kubota ( Jap).

I dont really have many good photos of her, but she is a real head turner although looking somewhat battered right now..

Thanks for the interest. I've had a few boats and worked as a (civilian) sailor, Marihona is my last, I will keep her until Im past it. She wan't expensive, just the price of a modest, 2nd hand fibreglass yacht or a minging, small rustbucket narrowboat.

(The bronze fairlead was salvaged from a sunken post-war RAF target towing launch, it was covered in about 20 layers of Admiralty grey when it came into my possession..if you cant drink it , paint it )

 

[fizzy]

That is a stunning boat. I bet she heaves to like a dream with that keel.
Very jealous!

 

[jerrytug]

Yeah she heaves-to like a champion, steady as Stonehenge..

 

[MattF]

That's interesting to hear the comments,the small amount of bronze fabrication I've done has been mainly on yachts TRESSANG was the one raced by Blonde hasler,I learnt how it worked hardened quickly.
Since then I've made railings with mama,I had to pre heat so much ,my bench split in two.

That's the main problem with cupreous metals; They both work and age harden. Personally, I wouldn't risk doing it cold. It could be anywhere from ductile to on the point of cracking/snapping. Anneal first, or heat and bend. Cherry red is the general annealing colour. Needs to be done in dim light to see the colouring properly, else just look for the silvery surface sheen which appears around then, if done in brighter light. I always let my pieces air cool too, rather than quenching. I find it slightly more forgiving if you overcook the heat slightly.

 

[Screwdriver]

I'd be tempted to do a quick make do and mend with a new length of steel bar. Not ideal for a number of reasons but in the meantime you could send the original item off to be repaired properly or wait until you find somewhere that can do a repair. While you probably could straighten it hot or cold, you won't know if it's a good repair unless it snaps, at which point you'll realise it wasn't. Ideally that happens during the repair, not when someone gets washed overboard...

Some alloys are really very weird. Look at the history of Duralumin for example.