Nozzle sealing

What is the best method of sealing a screw on brass nozzle from leaking around the threads?

Further info:- I have previously made the nozzles for my 4 printers as on the section on the left in the drawing below. My next printer will have 5 or more hot ends and quick changing of the whole hot end is no longer a viable option so I have opted to use a more standard threaded nozzle as shown on the right

Thanks for any input,

Mike.

I would guess Teflon tape, limited to 250C nozzle temperature. However, I believe that according to your diagram, the joint would be self sealing, as the surfaces would expand with heat to seal the thread. No? Have you tested it yet?

To cover a wide range of materials I need a maximum temperature as high as I can get it, or at least 300C which precludes PTFE tape. With the coefficients of expansion of brass at 18ppm and stainless steel at 17.3ppm I don't think that the joint would be reliably self sealing.
Has anybody used a soft metal gasket as marked in red in the drawing below.


The best material for this would be 24kt gold, but I think you can understand my reticence to use that here.
Mike.

If you really want to use a ring seal as in your latest diagram, then a simple copper ring would work fine imho. And these are available just about anywhere in standard sizes and very inexpensive too.

However, I still believe that heat expansion of the steel/brass thread joint will probably provide a good enough seal for the relatively viscous molten filament - I mean, we are not talking about a gas tight seal here.

Again, a simple 10 minutes test would demonstrate whether I am right or wrong.

... for UHV sealing we regularly used aluminium rings ... gold rings only for special problems, where the costs were negligible

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Viktor
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Thanks Andrew, I didn't know that copper ring seals were available: Can you tell me of any stockists of small ones in small quantities? The reason that I am getting a bit paranoid is that with 5 or more hot ends something like 5 times the opportunity exists for something to leak.

Picture below of one of the hot end assemblies.



Mike

Hi VDX, I used to work on a Kratos mass spectrometer which had gold ring seals and was baked out at 350C but at 6 grams per kit were not trivial - especially since somebody would contaminate it at least once a month.

Do you know where I could get aluminium O rings?

Mike

I bought 10 small copper sealing rings at a local hardware store here in Barcelona, Spain, a few weeks ago. They had them in various sizes, and unit cost was about $0.20. As Viktor wrote above, failing copper, you could use aluminum rings, I don't think it would make any difference in your particular application and cost should be about the same. However, I would expect aluminum rings to be a little bit harder to find.

... here's a check at ebay Germany - should be the same at your location too:

[www.ebay.de]

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Thanks AndrewBCN and VDX. Unfortunately the size of 'O' rings that I wanted were not available on any web site I could find. 3mm OD, 2mm ID is about half the size of their smallest so I had to make my own. Cut from K&S tubing with a 22mm circular saw blade in a Proxxon micromot mounted in a 10" lathe. Cut to 0.6mm lengths in both copper and aluminium - the copper is annealed to dead soft just before installation. Initial trials show they seal don't leak with 200kPa of air pressure.

Metal 'O' rings compared to a U.K. 5p coin.

Mike

Looks good!