Author Topic: Stainless Stays  (Read 3123 times)

Offline doubletop

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Stainless Stays
« on: May 25, 2020, 08:10:11 AM »
Iím making a small wobbler engine and boiler for my granddaughter The boiler will be horizontal  made from 16 gauge 2.5Ē copper tube about 7Ē long. It will be methylated spirit fired and is only going up to 25psi. Pretty much Mamod style. I want to put 2 or three stays in in the end plates. The smallest diameter copper rod I can get is 1/4Ē, I canít find small diameter bronze either. Monel is out of the question.

So what about stainless stays? The thermal expansion (Thermal Expansion (10-6 in/(in oF))) is 9.8 for copper, bronze ranges from 9.0 to 10.2 and Monel is7.8. Whereas stainless 316 is 8.8.

I would plan to use 3mm or 4mm stainless threaded with bronze bushes and silver soldered, however, I donít think Iíve seen stainless stays proposed in any boiler design is there any reason for this?

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline gadabout

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Re: Stainless Stays
« Reply #1 on: May 25, 2020, 08:21:47 AM »
Your local hobby shop might have a  KS metals display that has copper rod in 1/16, 3/32 or 1/8 ??
Mark

Offline doubletop

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Re: Stainless Stays
« Reply #2 on: May 25, 2020, 09:38:12 AM »
Your local hobby shop might have a  KS metals display that has copper rod in 1/16, 3/32 or 1/8 ??
Mark

Good suggestion but I've gone through all the NZ hobby shops that come up in Google and as far as their online inventory shows they all seem to have rod in brass aluminium and piano wire but not copper.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline gadabout

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Re: Stainless Stays
« Reply #3 on: May 25, 2020, 09:47:32 AM »
Worth a call maybe? Might just not have everything they have on their website, have seen that before.
Mark

Offline GWRdriver

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Re: Stainless Stays
« Reply #4 on: May 25, 2020, 02:13:03 PM »
What about using copper wire?  :thinking: Your local electrician should have scraps of various gauges of single conductor wire.

What about bronze welding (brazing) rod?  :thinking:  Your local welding shop should have some as small as 3mm.

I've used both as stay material in small boilers (and a few large ones.)

Online Jo

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Re: Stainless Stays
« Reply #5 on: May 25, 2020, 03:46:03 PM »
Over here copper rod is available on Fleabay. Are you trying to buy imperial sizes? Try quoting metric sizes.

Jo
Enjoyment is more important than achievement.

ChuckKey

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Re: Stainless Stays
« Reply #6 on: May 25, 2020, 05:17:19 PM »
Surprisingly, stainless steel is not suitable for boiler work, because of corrosion problems.

Offline Dan Rowe

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Re: Stainless Stays
« Reply #7 on: May 25, 2020, 05:38:09 PM »
stainless steel is not suitable for boiler work

This is true for every grade of stainless steel with the exception of duplex stainless steel.
See:
http://www.wirralmodelengineeringsociety.co.uk/Articles/DuplexSteelBoiler.pdf
http://www.smex.net.au/Store/Store_AALS-Codes.php

Cheers Dan
ShaylocoDan

Offline crueby

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Re: Stainless Stays
« Reply #8 on: May 25, 2020, 05:56:42 PM »
stainless steel is not suitable for boiler work

This is true for every grade of stainless steel with the exception of duplex stainless steel.
See:
http://www.wirralmodelengineeringsociety.co.uk/Articles/DuplexSteelBoiler.pdf
http://www.smex.net.au/Store/Store_AALS-Codes.php

Cheers Dan
Very interesting write-up on the duplex steel boiler!

Offline doubletop

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Re: Stainless Stays
« Reply #9 on: May 25, 2020, 08:38:05 PM »

Surprisingly, stainless steel is not suitable for boiler work, because of corrosion problems.


Now you mention that I know that's the case. There's still a major debate going on even about duplex boliers. (Promise I'll wake up soon)


Over here copper rod is available on Fleabay. Are you trying to buy imperial sizes? Try quoting metric sizes.

Jo

Jo
Good idea but, as you know, getting Ebay to deliver is a bit of a problem at the moment


What about bronze welding (brazing) rod?  :thinking:  Your local welding shop should have some as small as 3mm.


Good idea, I'll be calling the BOC depot later today, They are only about 15mins from the house.

Thanks for your input Team. Some great suggestions, and confirmation my question was a bit dumb.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline crueby

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Re: Stainless Stays
« Reply #10 on: May 25, 2020, 08:43:36 PM »
Rather than longitudenal stays, could also do ribs on the inside of the endcaps made from copper sheet stock and silver soldered inside the caps. Bit fussier to fit than stays but not bad.



Offline doubletop

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Re: Stainless Stays
« Reply #11 on: May 25, 2020, 08:58:41 PM »

What about bronze welding (brazing) rod?  :thinking:  Your local welding shop should have some as small as 3mm.


1/8" bronze rods now on order from BOC ;D. Delivery tomorrow, but most likely it won't be. No problem though as I can now move on knowing that particular problem is solved.

Thanks again

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: Stainless Stays
« Reply #12 on: May 25, 2020, 09:04:36 PM »
Rather than longitudenal stays, could also do ribs on the inside of the endcaps made from copper sheet stock and silver soldered inside the caps. Bit fussier to fit than stays but not bad.


Another great suggestion but I would be concerned that they could fall off when soldering the end caps into the main tube. I don't have gas welding gear to localise the heat so a lot more heat required on the interface which would migrate to the center of the end plate. 

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline crueby

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Re: Stainless Stays
« Reply #13 on: May 25, 2020, 09:33:23 PM »
Thats where the different grades of silver solder come in handy - do the inside parts with the 'hard' grade, then the final assembly with the 'easy' grade which takes a lower temperature. I usually put a small brass screw into the rib from the outside just in case too!
The says will work fine, just throwing out another option.   :cheers:

Offline doubletop

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Re: Stainless Stays
« Reply #14 on: May 25, 2020, 10:35:34 PM »
Thats where the different grades of silver solder come in handy - do the inside parts with the 'hard' grade, then the final assembly with the 'easy' grade which takes a lower temperature. I usually put a small brass screw into the rib from the outside just in case too!
The says will work fine, just throwing out another option.   :cheers:

I had considered different grades of solver solder but if using a propane torch the heat required to bring the main, double thickness, joint up to temp will spread to the centre of the end plate and could be high enough to release the high temp solder. After I posted my comment it did occur to me to flange the stay and use a couple of rivets to hold it in place and then solder it up.

BTW did you post your boiler build? I see you are using a central flue tube, what burner do you plan to use? Its been a few years since I did small boiler builds and I'm catching up.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss