quartz seal

[durcan]

HI,
Trying to seal a quartz tube with stainless steel flange, this is in a furnace which can operate at 500 deg C, I was going to use a hight temp oring, with water & gas cooling in the stel flange.
Does anybody know of a ,metal seal i could use??

Thanks

 

[IRstuff]

You might wish to consult with semiconductor diffusion furnace tube suppliers. While the standard diffusion furnace uses a glass end cap, there are other processes, particularly those involving low pressure that used metal flanges.

TTFN

 

[durcan]

Thanks
have you any idea where i can find such a supplier, any web site? can find any.

P

 

[IRstuff]

I would start by doing a websearch for "diffusion furnace"

TTFN

 

[strokersix]

If you have a means of applying axial force to the quartz tube an effective seal can be achieved as follows: Lap the end of the tube into a spherical shape using diamond compound in a spherical copper pocket. Machine a conical pocket in the stainless flange. When the sperical end of the tube is inserted into the conical pocket and held there it will seal, especially if the final operation is to lap the two surfaces to each other with very fine diamond. An advantage to this configuration is the joint is flexible; the tube does not need to be perfectly square to the flange. Another, perhaps greater, advantage is the joint flexibility eliminates the problem of thermal expansion mismatch between quartz and stainless. An obvious disadvantage is the continuous applied force to maintain contact. I have sucessfully used this configuration in ceramic materials from inches of water up to 1500 psi.

Mike

 

[hacksaw]

there are a number of methods you can use, but you'll have to be more specific about your physical arrangement

 

[durcan]

i have a quartz tube dia 238mm and i have to seal it both ends, i can add quartz flanges etc if needs be. There is a 500 C operating temp in the center of the quartz tube, the tube is 850 long.
Is there a metal seal that can take some expansion?

 

[hacksaw]

it is a solvable design

couple of things:

you can use a "compression fitting" on the tube with grafoil lantern rings. tfe won't take the full temperature, but realize that your fitting temps will be considerably cooler.

500 C is not that hot, but you may need to think about radiation baffles to keep the heat off the end-connections.


a good glass shop can also fix you up with ground quartz/glass fittings that will take expansion

your actual and final MOC will depend on the gases in the hot zone.

you don't want to cool your metal fitting over much. that will only maximize the thermal stresses, but you do want to account for differential expansions as the system heats.

there are vacuum (metal/glass, metal/ceramic)feed-throughs that are available with materials of construction that account for the differential expansion and use of matched materials (cte matching).