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PeterSibley
11-05-2003, 07:36 PM
Does anyone know the correct alloy or grade of bronze to use for bending? The project is a mainsheet horse .Thanks all.

Chris Gerkin
11-05-2003, 10:41 PM
I am at about the same point. How are you attaching the rod to the deck?

PeterSibley
11-06-2003, 03:03 AM
I have 2 cast collars which I will bore and tap and 2 cast nuts for under the deck.I'll run a thread on the rod with a die to suit ...however bending the bronze is the problem !

imported_Steven Bauer
11-06-2003, 07:33 AM
John Gardner tells how to do this in one of his books. I'll look it up tonight. Basically you just heat the rod where you want it to bend, but he gives more info on how hot, etc.

Steven

NormMessinger
11-06-2003, 08:12 AM
Sometimes ignoraance is a benifet and sometimes it aint. I didn't know there was a bending grade of bronze so when it came time to make the horse for Prairie Islander I just fired up my oxy-acetylene torch, clamped 1/2" bronze rod in the vise and applied heat until the rod yealded to make a 90 degree bend. The arc across the top of the horse was made without heat. I braze welded (http://www.esabna.com/EUWeb/OXY_handbook/589oxy14_1.htm) collars on where required and taped the ends for the nuts.

A MAP gas torch would have done the job.

The trouble with heating bronze (any copper alloy, I think) is it takes out the temper so one considers that when sizing the part.

So now that the job is done I'm still interested in how Gardner says it should be done.

megman
11-06-2003, 08:29 AM
You would probably want to use High-Silicone bronze A or Low-Silicon Bronze B. You could also go with an old propeller shaft for cheap if the diamater is right.

If you want it bent to a specific angle simple clamp the bar to a wood stock with the angle you want cut in one end of it with the bar hanging over the angled end.

Then simply heat it at the bending point with a torch, preferablly using a big blue flame. It will usually droop of it's own free will, or you could apply very light pressure on the end.

If you let it sit like this until cool, temper will not be a problem. Tempering will be a problem if you throw water on it. Let it air-cool naturally.

Jon Etheredge
11-06-2003, 10:34 AM
Peter,

There are a number of alloys that could be used. Silicon bronze (CA655) would be a good choice since it has excellent corrosion resistance and good capacity for cold or hot forming.

Bronze rod will typically be sold in a "half hard" condition. This may make the rod difficult to bend without causing cracks at the bend. So you need to anneal the rod. Just heat the rod to a red color and it will be annealed. You can then either let the bronze cool slowly in air or you can quench (cool) the rod with water. Either method of cooling will leave the rod in an annealed state. Bronze (or any copper) alloys are different from steels in that quenching the metal will not cause hardening. Hardening of copper alloys only occurs as a result of working (i.e. shaping or forming) the metal.

If you make the bend while the rod is red hot, it will remain in the annealed (soft) state after you are through. If you make the bend while the rod is cold, the act of bending the rod will cause it to work harden. I feel like it is better to cold form the bend but depending on the radius of the bend and the diameter of the rod you may have to anneal the rod several times while making the bend. Make the bend by hand and if the amount of force needed to make the bend starts to increase then you should stop and re-anneal the rod before continuing with the bend.

Jon

PeterSibley
11-07-2003, 01:23 AM
Thank you Jon, that was just what I was looking for. I've had a few unsuccessful attempts prior to this, resulting in an excellent supply of brass punches...and one success, which was purely accidental ! smile.gif

imported_Steven Bauer
11-07-2003, 07:47 AM
Accoding to John Gardner to work the bronze you must soften it by annealing it - heat it to a dull cherry red but no hotter then quickly quench it in cold water. Then after it's shaped, heat it again and let it cool slowly to stiffen and harden it again. He says if bronze is heated to a yellow or white heat the metal will crumble and go to pieces when it's worked on.

Steven

Moray MacPhail
11-13-2003, 08:05 AM
I have made about 300 horses in bronze over the years; this is how I do it (using phosphor bronze usually, but have also done the same with silicon bronze and aluminium bronze)

Get the camber into the horse by bending cold. You can do this by hand up to 1" diameter. Ideally you would get the bends in cold, but in practice you need some pretty epic equipment to do that in anything more than 1/2" bar.

So heat the area to be bent - ie the corners - to just below red. This bit is critical, if you heat to cherry red or yellow and bend the bronze will break. (Because all copper based alloys have a temperature at which they go "hot short" and lose strength between the grains. So they just crumble apart.)
The temperature you want is where there is just a hint of red below the surface - well that's what it looks like. I find it best to do this operation in a slightly gloomy light to see what is going on.
Put the bend in reasonably quickly, and water cool the bronze as soon as you can. Why water cool? at high temperatures for a period of time the bronze will anneal and soften. To get the bend in you need to work it at a high temperature, but to keep the hardness get it cool again as quickly as possible.

As for the deck collars, to minimise the heat input I pin these in place rather than weld them.

Hope this helps
BTW don't do the same trick with steel - if you water quench that it will become brittle, so air cooling is required.

NormMessinger
11-13-2003, 08:22 AM
Moray, that is about the best description of the proper method I've seen. I was not aware that time was a factor in heat and hardness. That's good to know. Thanks.

Jon Etheredge
11-13-2003, 03:36 PM
The temperature you want is where there is just a hint of red below the surface - well that's what it looks like. I find it best to do this operation in a slightly gloomy light to see what is going on.
Excellent description of how to spot the correct color.



Put the bend in reasonably quickly, and water cool the bronze as soon as you can. Why water cool? at high temperatures for a period of time the bronze will anneal and soften. To get the bend in you need to work it at a high temperature, but to keep the hardness get it cool again as quickly as possible.
Quenching with water will not cause most commonly encountered copper alloys (i.e. most brasses and bronzes) to harden or to keep any hardness that the material may have had prior to heating. The only way to harden most copper alloys is by cold working. There are exceptions (aren't there always), but these alloys aren't likely to be encountered.

But enough talk by us amateur metallurgists...

A web search turned up the publication "Fundamental Characteristics of Revere Copper and Its Alloys" available on the Busby Metals (http://www.busbymetals.com/lit_col.htm) web site which provides some nice info on annealing and the cold working of copper alloys.

Lion
11-13-2003, 07:49 PM
Moray,

What a really succinct summary of the best technique. Tallies with my vaguely remembered apprenticeship days and lessons. Thank you for sharing.

Lion

PeterSibley
11-14-2003, 02:55 AM
Thank you Moray...I should be able to get things right from now on ! Much appreciated smile.gif