Annealing

[Jon Nazareth]

Can anyone tell me how much heat to apply to a 23 though brass firebox wrapper in order to anneal it?  I've not done this before and fear it may distort or buckle.

Regards
Jon

[Andy B]

Jon,

What are you intending to use for heating the sheet?
Distortion would be more likely caused more by uneven heating, rather than too much heat (even with a big blow torch).
Experience has told me to ensure the plate is clean first, then use the colour as a guide - as described here: http://steamshed.com/annealing%20process.html.
I assume you have some offcuts to practise on first?

Andy

[Jon Nazareth]

Dear Andy

Thank you for that and yes, I've looked at the website and the instructions are duly noted.  I'm going to use a blow torch and start one end moving it along as the required colour is reached.  I still have one more concern.  There is an half etched edge to the two long sides measuring 10-11 thou thick and I'm wondering if this will burn out before the main part reaches temperature.  Do you think that the plum colour is of a low enough temperature that this won't occur?  I hope so.

I've annealed copper in the past simply by heating to a cherry red and quenching.  This was then beaten to form shapes and nothing near as delicate as to what I'm trying to achieve with the wrapper.  Fingers crossed for tomorrow 

Regards
Jon

P.S.  yes, I do have some scrap but only the waste from the etches

[Andy B]

.... and start one end moving it along as the required colour is reached.

That would be most likely to cause distortion.

I still have one more concern.  There is an half etched edge to the two long sides measuring 10-11 thou thick and I'm wondering if this will burn out before the main part reaches temperature.

I would keep playing the flame along / across the plate roughly following the lines of where the tightest bends will be, and keeping it away from the half-etched edges - you should be able to see the colour change creeping out to those edges by conduction.

Do you think that the plum colour is of a low enough temperature that this won't occur?  I hope so.

Should be. But as with copper boilersmithing, if/when the material is not soft enough or gets work hardened again you can just re-anneal it. If it's anything like forming the smokebox of my GRS 1F, the main 'circle' formed quite easily. It was the reverse curves at the bottom that were most difficult and these took a little extra heating to get them to match the ends.
Andy

[Jon Nazareth]

Dear Andy

Thanks for the reply, all tips taken on board.  The firebox has straight sides but the smokebox has quite strong tight reverse curves which may prove problematical.

Regards
Jon

[Jon Nazareth]

Well, I've done it.  I was a bit cautious with the first heating and that didn't work but the second did.  The big problem is that I managed to kink the very top where there is a hole for the safety valve cover.  I have gingerly pushed at it but it didn't go down.  I have thought of tapping it and may try that after I've given the firebox a good clean up.

Jon