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heat colouring stainless steel

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marcros

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Is is possible to colour stainless steel in the home workshop, ie using a propane or mapp gas blow torch? I want to achieve a blue colour, similar to the image. I need two pieces to be similar, the actual colour isn't vital.

material will be 40mm stainless steel pipe, 50mm long, wall thickness 3mm.

how resilient/stable is the finish to scratches and handling?

the only proper of stainless steel that I need is the lack of corrosion (generally, and in the presence of dry table salt) and lack of staining to oak.
 

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Lazurus

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Have you a spare length you could experiment with heat and time exposed etc. I know exhausts can take on that hue but I think a bit of experimentation may assist.
 

TFrench

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If I get a chance tomorrow I'll stick a mapp torch on a bit of stainless at work. Personally I think you will struggle to get a consistent colour. Mapp is about 3600F and tig welding is 11000F.
 

marcros

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are there any alternatives to get a colour other than shiny silver? cold bluing is one possible, but I believe it needs oiling to maintain.
or even an alternative material I could use
 

TFrench

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I take it back, according to a chart on google stainless goes dark blue at about 1100F which is definitely doable with Mapp. If I get a chance tomorrow I'll have a go, its got me curious now!
 

TFrench

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Ok, I did science. Normal Mapp torch, first is a bit of 0.5mm bright stainless. Very hard to control the heat with it being so thin - but the back side went a very consistent shade of purple. Tried it on a bit of tube and it's much more controllable but it takes a lot longer. If you're doing a large piece it will take a lot of gas I think. Scratch wise, it marks relatively easily - it's only a surface colour.


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Bm101

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All coloured finish after heat treating is surface based. Microns. If you want a lasting effect with any contact at all you will need to find a different solution. (Sorry.)
Regards
Chris
 

hawkeyefxr

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Possible but hard to control. You picture seems to show something that has been TIG welded, intense heat in a very small area.
 

sunnybob

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Stainless steel exhaust pipes are common nowadays on cars and motorcycle engines, they all go coloured with engine heat.
But its not a durable finishas far as shine is concerned, although trying to get it back to pristine stainless is impossible.
If you just want it to look nice but not be subject to handling or abuse, then its a very easy job.
 

marcros

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Thanks all. I should explain the application a little more. I need a band of colour about 10mm wide, the rest will be hidden from view. 30mm would be even better. The exact colour is not that important, but I would like a dark blue/purple to replicate gun bluing and would like pairs to almost match each other. it needs to be fairly resistant to corrosion, because there is dry salt not far from it, and needs to be food safe.

https://www.christian-masche.de/epages/ ... ducts/2270

I have ordered some tube to try a few things. If the heat is not resilient enough, the back up plan is to polish to a satin finish. It is difficult in that if I were making hundreds, it would be worth looking at different options at a sensible unit price, but to do a couple of sets makes a subcontracted process prohibitively expensive.
 

Bm101

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Ahhh, that makes more sense now.
I reckon timing is everything to get a uniform colour as the wall thickness will be even.
I've found generally that getting an even grind on round stock (by hand) for example it's always a more even result if you apply a rotating material to the finisher. Same principle as a lathe. You apply the tool to the lathe. It's the rotation between fixed centres that keeps it all aligned eh?
Rather than move the torch, mount the pipe on a flat wheel of some variety. Bit of scrap centred 18mm mdf with a bearing jammed into it, whatever. Bit of threaded bar in a vise, couple of nuts. Some canny means of work holding too keep the pipe centred over the bearing in place and you're off.
Light your torch and get spinning. 8)

If it's for those salt and pepper grinders, (very smart) it's not going to get a lot/any wear being recessed. What about a few coats of summat like this spray laquer? Should be plenty of protection in that situation.
https://www.toolstation.com/industrial- ... gLfe_D_BwE
This one is food safe.
https://www.zoro.co.uk/shop/lubricants- ... id=&pgrid={groupid}&ptaid=pla-656563121450&gclid=EAIaIQobChMIpL2FytCv4gIVhuFRCh2UKg01EAQYAyABEgKtI_D_BwE
I wouldn't pretend to dip a toe into finishing but shellac or some other solution might well do.
I'd use a spray because I'm lazy and you could do it without taking the pipe off the wheel to get a perfect finish :wink:
Cheers,
Chris
 

TFrench

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I wouldn't worry too much about scratching - its quite protected in that design.
 

Bm101

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Actually... Just had an idea.
Why not just temper it? It will be totally uniform. #-o



I did this in my kitchen oven Mark. Highest possible temp with an aluminum tray filled with sand in the bottom to act as a heat sink.



Did I get my oven raise the max temp 30c with the sink from 280?
Dunno.
It cuts well though and never needs sharpening. (Witchcraft!)
Sometimes, if I leave the shed windows open in the summer, I go down and there's woodland creatures and such lying about it peacefully. Rabbits and Badgers and stuff.
Lambs bleating and that. Busty Virgins. Maybe. No. There's no Busty Virgins so far. I live in hope.
Who knows.
 

Eric The Viking

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I don't know what the exhaust temp of my old BMW R80 should be, but it has a Keihan all-stainless exhaust, and the downpipes go a horrid muddy brown after a while (They all do that , sir.)

You can polish it out (thankfully the pipes are thick enough so that repeated polishings don't matter too much), but they will always end up brown again.

On most bigger bikes with stainless systems, or even bright chrome, wherever it's on show, they cheat nowadays by putting a sleeve over the downpipes. Harleys are a good example.

If you do find a reliable way of heat-treating it to get a colour, I'd suggest counterintuitively that you polish first (Autosol, Brasso or the graded polishing waxes, with a selection of mops), before colouring, because the heat treatment colour will be pretty thin and you'd most likely remove it again, otherwise.

You might also have a word with one of the plating companies or anybody who builds choppers, etc. There are a variety of interesting colours available nowadays, and I don't think it's just for anodizing aluminium any more.
 
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