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David W Pratt
01-03-2010, 02:43 PM
I have a bent boathook and I want to straighten it out. Cold bending, hot bending, annealing? I'm lost, so any help will be appreciated.
Thanks in advance.

john welsford
01-03-2010, 02:52 PM
I have a bent boathook and I want to straighten it out. Cold bending, hot bending, annealing? I'm lost, so any help will be appreciated.
Thanks in advance.

Depends, some bronzes go from solid to liquid all of a sudden when heated so you dont want to heat them, some go gradually and would accept enough heat to soften them a little. Unless you know which of the many varieties of bronze that you have you wont know which technique to use.

But I'd suggest that if the thing got bent while cold, it should bend back, take it gently.

John Welsford

Tobago
01-03-2010, 02:53 PM
Ask the people or do a search over at iforgeiron.com. It's a blacksmiths' forum with smiths who have expertise in other metals.

Ted

Gold Rock
01-03-2010, 06:34 PM
But I'd suggest that if the thing got bent while cold, it should bend back, take it gently.

John Welsford

Sorry John, I'm going to contradict your suggestion. The fellow who owns the foundry which employs me never bends a copper based alloy cold. I can't illuminate the exact metallurgical reasons why, but he's been fabricating top shelf hardware for over thirty years and no one knows his business better. Heat the metal to a dull red. I would define this as the first perceptable evidence of redness in a normally lit room. Then bend away. Let it cool at room temp. (Though I've water quenched a number of things with no ill affect. The boss disagrees, but my research of experts on line says quenching is fine). He does this with everything from heavy bar stock to chain plates to thin sheet stock.

Chuck

PeterSibley
01-03-2010, 06:44 PM
Chuck ,what alloy does he use as bending stock ?

donald branscom
01-03-2010, 06:49 PM
Just heat it up to 300-400 degrees and try to bend it.

Kitchen oven at 450
Heat will help.
I would NOT repeat- NOT heat it to red hot

Better have a good vise or hole in the concrete. Be careful.
Use a long lever.

seo
01-03-2010, 09:05 PM
One method of annealing bronze parts that aren't very thick (say 1/2" thick max, maybe 2 Lbs) is to use an acetylene torch with the oxygen turned off. Play the very smoky acetylene flame over the part until it's completely covered with soot. Then turn up the oxygen to a normal heating flame, of course a rosebud tip would be best, but who actually owns one? Anyway, keep the flame moving on the workpiece until it gets hot enough to burn the soot off. The guy who taught me this technique said that this was hot enough to anneal bronze, and if you're careful to not heat it beyond the point where the soot burns off you won't be in danger of melting the piece.
Then let the piece cool, or quench it? Dunno. I had always cooled it in bucket of ashes, but then read on this site that quenching it was all right. I tried it on a sample piece, and it worked okay on that piece...
The way I learned it, copper alloys are what's called "hot short," which means that if you try to bend them when they're red hot they'll break, which has been my experience. But if the metal is annealed and cooled, it can be bent and shaped pretty easily, but after a bit of bending it begins to work harden, which shows up as getting stiffer and more resistant. Keep bending and it will break. Anneal it again, and you can keep bending it.
Last winter I had some special little mounting brackets to make with brass flat bar (1/4" X 2" X 12") and 3/8" everdure round stock. I used my shop's coal stove with a good hot bed of coal to do the annealing, and it worked fine.
A good pair of welding gloves is an essential accessory, and I even splurged on the kind of torch glasses that have a safety-glass inner pane, and a flip-up shade on the outside.
A few years ago I was given a 150 Lbs hollow anvil, and it makes this kind of work a lot easier. But as a stopgap a couple feet of railroad rail will work all right.
If you haven't done this sort of stuff before, it might be a good idea to find a few pieces of junk bronze to practice on.

Gold Rock
01-03-2010, 10:48 PM
I would NOT repeat- NOT heat it to red hot


That's a bold declarative. Would you educate us as to why you feel this to be valid advice? Cold forming of many copper based alloys yields strength increases of a normally unstable nature. The stablility breaks down with sustained elevation of atomic movement at quite low levels. Direct heat can be a source, but so also can work cycles imparted by force loads. Heat applied prior to bending mitigates stress instabilities in the formed workpiece. Aside from the physical properties of the formed metal, have you ever tried bending a piece of 5/8" x 3" manganese bronze plate cold? I'm guessing not. At a certain point of cross sectional dimension, cold forming isn't possible without equipment of an industrial scale beyond the individual.
Pete, we've bent stem bands as thick as 1" x 4" and round stock as large as 1 1/2" dia. for sheet horses. Both usually Si Brz. or AlNi brz.

john welsford
01-04-2010, 02:24 AM
Fair enough, perhaps I've just been lucky so for.
JohnW


Sorry John, I'm going to contradict your suggestion. The fellow who owns the foundry which employs me never bends a copper based alloy cold. I can't illuminate the exact metallurgical reasons why, but he's been fabricating top shelf hardware for over thirty years and no one knows his business better. Heat the metal to a dull red. I would define this as the first perceptable evidence of redness in a normally lit room. Then bend away. Let it cool at room temp. (Though I've water quenched a number of things with no ill affect. The boss disagrees, but my research of experts on line says quenching is fine). He does this with everything from heavy bar stock to chain plates to thin sheet stock.

Chuck

David W Pratt
01-04-2010, 08:41 AM
With copper washers I've always heated them red and water quenched to soften them before reinstalling them.
Thanks for all the advice.

PeterSibley
01-04-2010, 09:03 AM
Pete, we've bent stem bands as thick as 1" x 4" and round stock as large as 1 1/2" dia. for sheet horses. Both usually Si Brz. or AlNi brz.

Thanks Chuck always good to know ...Ihave few jobs where I will need to bend stock .


Mang Br is hard and stiff .I cut up my 2" thick ingots with an abrasive saw because the 80 ton shear at the supplier won't do it !