Stress relieving question

[jpigg55]

Is it possible to stress relieve bearing bronze ?
If so, is it done as an annealing process, tempering process, or some other heat treat procedure ?

I'm wanting to use bearing bronze to make Clupet rings for a Stirling engine project.

[Jake Parker]

While steel is annealed by heating to red and being allowed to cool slowly, metals which crystalize in the “Face-centered Cubic” system—which includes the copper alloys as well as gold and silver—will reharden if they are treated this way. The crystals, given time, will form a more organized structure, without the molecular “vacancies” which make the metal malleable. In fact, one can take advantage of this tendency to “heat-harden” non-ferrous metals, holding sterling silver, for instance, at 280° C (536° F) for 2½ hours.

To soften metals of this type, they should be brought to a medium red color, then quenched in water to cool quickly. I would be careful not to overheat it though—some bronzes will suddenly go from solid to falling-apart when hot.
Copied and pasted from Juxtamorp.com

[jpigg55]

Thanks Jake,
I looked on Juxtamorp.com trying to find this to see if there was any more info or links, but couldn't find it.
I wondered if you could post the link where you found this ?

[jpigg55]

I found some additional info after changing search terms to "Heat treatment of copper alloys" instead of bronze.
Still didn't find much, but here's a video link for anyone else interested: https://www.youtube.com/watch?v=V4nGpSC1oVw

[Carpenter84]

Jimmy, search for a heat treating facility and call them up. See if you can speak to the journeyman. Maybe they'll offer some advice.

I know the facility I use, the owner is a gem, old school, but super nice guy. He'll talk your ear off. I'm sure they're not all like that, but you could get the info you need right from the horses mouth.

[Jake Parker]

Thanks Jake,
I looked on Juxtamorp.com trying to find this to see if there was any more info or links, but couldn't find it.
I wondered if you could post the link where you found this ?

I posted everything it had. There were no more links, sorry.

[jpigg55]

No worries Jake.
After noticing the site dealt with jewelry makers, I started looking at some of the videos I'd previously discounted.
While they didn't answer all my questions, they did provide a lot of answers. I learned quite a bit about how heat treating non-ferrous metals differs from ferrous metals.

[4GSR]

I've never heard of stress relieving bearing bronze, and I've cut lots of it over the years without ever noticing any issues with warpage.  I must be missing something here.

[jpigg55]

I've never heard of stress relieving bearing bronze, and I've cut lots of it over the years without ever noticing any issues with warpage.  I must be missing something here.

From what I've watched, as I understand it, non-ferrous metals like silver and copper alloys harden when hammered or deformed causing them to become hardened and brittle  requiring annealing to restore them back to a pliable soft state.

[4GSR]

I believe this is a non-issue with bar and tube stock in most copper alloys including brass and bronze.  Most are extruded into bar and tubes when hot.  Now, I can understand with pure copper, it work hardening from cold working into bar or sheet form.  But I don't believe the hardness is anything that would make it non-machineable.  Would it deform when machined? Maybe, I've never encountered it myself.

To stress relieve materials like copper, you may change the temper state of the material and make it way too soft to machine.  I'm no expert here, just saying.

[RayH]

The video shows the complete manufacturing process for a cast Iron Clupert ring.
The presenter makes it look as simple as possible, step by step, but machinists will recognize the attention to detail required.
Very challenging project (piece) Jimmy. What seems sort of weird to me is that the finished ring looks so simple which belies the difficulty to create it.

https://www.youtube.com/watch?v=pquXx5JBFfM

[jpigg55]

Thanks for the video link Ray.
I've already watched that one and this one: https://www.youtube.com/watch?v=80jzsNM6olE

Clupet rings seemed ideal for use in Stirling engines being basically a double ring with no gap. I considered cast iron, but wasn't sure how to go about dealing with lubrication.
I wondered if using either oil impregnated bearing bronze or graphite impregnated bearing bronze would work without lubrication and ordered some to give them a try. Not sure if either will have the springiness to act like a cast iron piston ring, but thought it worth a shot.
Generally speaking, small Stirling engine pistons don't require rings for the Beta & Gamma types, just a tight fit, but Alpha types do require rings.