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Glass/metal joining?

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Cornish Jack09/07/2013 18:58:23
1218 forum posts
171 photos

G'day all.

I'm messing about trying to construct a hot air engine, using a glass test tube as the displacer and mounting it in a brass or copper flange base for attachment to the central support. Has anyone any proven methods for making heat resistant joins between these materials, please? A similar join, between a brass flange and copper tube for the power cylinder, I'm considering soldering ... but, soft or silver???

Any suggestions appreciated. TIA



Peter G. Shaw09/07/2013 20:11:11
1313 forum posts
44 photos

My oven door has a glass panel glued onto a formed metal flange on the inner panel. I have successfully used RTK "High Temperature Adhesive and Sealant" from Intek Adhesives for this purpose. It is expensive though, £18-66 this time last year for a normal sized cartridge - and it doesn't appear to keep. Also, to carry the weight of glass, which I imagine is considerably heavier than for your purpose, the adhesive had to be about 2mm thick.

Depending on the temperature range expected, I wonder of a normal temperature rating silicone adhesive would be suitable.

Usual disclaimer.


Peter G. Shaw

jason udall09/07/2013 21:36:02
2030 forum posts
41 photos
If , as I think you mean the testube is the displacer cylinder not displacer..and the closed end to be the hot end....The open end is usually "cold"..the point is that glass allows you to keep the two ends at maximum temperature difference.

In any case o rings are often used to provide the seal..epoxy is some times used as an alternative
Jens Eirik Skogstad09/07/2013 21:50:00
400 forum posts
22 photos

You can use clue for windscreen for vehicle if the parts is not to be dismantled in future. The clue is very strong to hold the glass and metall togheter.

Ian S C10/07/2013 12:36:03
7468 forum posts
230 photos

I'v put a question on another web site, to someone who builds your type of motor, well see what he comes up with. Ian S C

Cornish Jack10/07/2013 12:45:16
1218 forum posts
171 photos

Peter, Jason, Jens and Ian, thank you all.

Peter - RTK sounds as though it might be good.

Jason - yes, you're correct - certainly temperature differential end-to-end but even so, the cool end is still quite warm!

Jens - yes, I had considered that until I remembered my late sister's Ford rear side window which was glued to the opener ... and disappeared with no warning while en-route!!angry

Ian - would much appreciate that.



Hopper11/07/2013 04:29:30
5505 forum posts
137 photos

Jan Ridders makes a lot of these glass-tube Stirlings.

His drawings call for silicone glue to glue the displacer on to an aluminium plug that goes screws on to the connecting rod. There is a groove in the plug so I would assume fill the groove with silicone glue or high temp silicone if you want to be sure.

To secure his glass displacer cylinder to its aluminum flange, he uses a groove ofr step in the flange and a rubber o-ring that is compressed when the flange bolts are tightened. If you wanted to use glue instead, I guess you could use high temp epoxy. That end of a glass displacer or cylinder is not going to get madly hot.

Take a look at Jan Ridders's website for more ideas. He is happy to email you plans etc.

John Haine11/07/2013 08:13:14
4186 forum posts
242 photos

Search "glass - metal seals" on Wikipedia. Common problem making vacuum tubes.

Ian S C11/07/2013 11:50:06
7468 forum posts
230 photos

I meant to say last night, E-mail Jan Ridders, from what I'v heard from others he is only too glad to pass on information on hot air motors, or any other of his models, but I see Hopper has got there first, thanks. Ian S C

Cornish Jack11/07/2013 12:19:12
1218 forum posts
171 photos

Hopper, JH and Ian - thank you. I do have one of Jan Ridders's plans so will dig it out and check.



Phil Whitley13/07/2013 17:04:17
1375 forum posts
147 photos

Google Sikaflex, and see if it will meet the temperature range, I have fitted windscreens with this stuff (volvo estate) and they don't budge!


David Jupp14/07/2013 09:12:19
787 forum posts
17 photos

If you are feeeling adventurous, do a web search on 'housekeeper joint'.

Cornish Jack14/07/2013 12:44:43
1218 forum posts
171 photos

Thank you Phil and David, good possibilities and David's suggestion might be very helpful with the arthritis!!smileythumbs up

For anyone else similarly interested in joining things to things, the loctite site **LINK** could be useful. I think I may well give Loctite Glass a whirl.



Gordon W14/07/2013 14:54:17
2011 forum posts

An old way to seal glass / metal was Sodium Silicate (water glass ) It is used in wood stoves as seal glue and glass fixing. It certainly makes a good high temp. joint, but not sure of mechanical strength.

Cornish Jack15/07/2013 12:16:06
1218 forum posts
171 photos

Thank you, Gordon and M W.

Update - Have now joined the brass flange and test tube - two methods; initially used super glue (common or garden variety) with the tube just resting in place on a polythene 'underlay'. Once that had set, I mixed up some Araldite 2-part and 'filleted' the join. Appears to be a solid join but temperature resistance remains to be seen.

The brass/copper join was done to make allowance for my total lack of expertise! - brass flange and tube end were coated with thick flux 'ointment' and positioned correctly (inverted) on a suitably sized bolt held in the vice. The top (as positioned) side of the flange was then generously covered with Fry's solder paste. Butane torch applied to the copper tube until the 'witches' brew' bubbled and then left to cool. Result: the neatest solder join ever ... for me!!smileythumbs up

Now need to 'pickle the solder joint and intending to use Citric acid. Should be able to get crystals at local chemist but what is the ratio of crystals/powder to water for 'pickling'. please?



Stub Mandrel15/07/2013 20:23:26
4311 forum posts
291 photos
1 articles

Hi Bill,

Citric is good for cleaning off silver solder flux. The various fry's fluxes seem to come off with plenty of water and detergent. Quite dilute citric will clean the brass/copper of surface oxide where teh flux wasn't (if you get my drift) nicely though.


frank brown16/07/2013 06:29:26
436 forum posts
5 photos

High temperature silicon sealant is used to seal the joints in wood burning stove flues. Its very cheap. warning its also very fluid and will run and drip and is "very soft and flexible " when its cured.


Cornish Jack16/07/2013 11:54:56
1218 forum posts
171 photos

Thank you, Neil and Frank.

I've just finished washing off the pickle and the tube certainly looks nice and clean (the non-soldered bits). I made up a solution with 2 heaped teaspoonsful of crystals with about a quarter pint of water. Seems to work OK.

I have a couple more of these things to make up so will probably try at least one of the suggestions for the next one.

Thanks to all who replied



Ian S C17/07/2013 13:06:47
7468 forum posts
230 photos

Keep your used citric acid in a screw top jar if only using small amounts, with larger amounts, like a bucket full, put a lid on it, and as it evaporates you just add a bit of water, it lasts for ages, and its safe to flush down the drain when you'r finished with it. Ian S C

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