Some welding...

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daniele
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Some welding...

Post by daniele » Mon Jul 08, 2002 7:36 am

Hi all,
I have just acquired the two 6" Conflats from MDC... (I had a heart attak whe I paid, anyway...)

I am asking if you please can give me some advice, for the preferred order for welding the flanges to the hemispheres. (bad english here)

What first ? big CF ? or smaller ?
I will have a friend of mine doing the job for me since I have no lab at the moment (changing house) and no TIG welder at all. So I will be present when he'll do the job.
I'd like to hear from you a reasonable order of welding the components.

thank you all
ciao
Daniele

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Richard Hull
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Re: Some welding...

Post by Richard Hull » Mon Jul 08, 2002 4:40 pm

The order of weld is not too terribly important. All Conflats are figured for size to help avoid thermal warping across their span.

More important is the job assembly methodolgy. Are some parts harder to reach and hold in place if other parts are welded first? This kind of decision and planning process should preceed all welding or asssembly effort. In general small stuff is put on first.

However, I prefered to put on my large flanges first on fusor III and IV. The reason for this was that I was worried about the hemispheres warping to destroy the plane lip of the hemisphere if I stuck on a lot of ports and other stuff prior to making the big weld. Most well equipped facilities would put on the small stuff and then surface grind the hemisphere lip to a flat plane. Regardless, it is important to protect all knife edges throughout the assembly process from being damaged or dented.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Richard Hull
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Re: Some welding...

Post by Richard Hull » Mon Jul 08, 2002 4:49 pm

I will admit that silver soldering those thin skirted base pieces into the conflat was one of the toughest silver solder jobs I ever have undertaken.

I started by silver tinning the flange area of contact on the conflat and then silver tinned the insulator's skirt lip. I then placed the skirt onto the conflat and re-heated the conflat only until the hole thing was near red heat and the insulator just nestled down into the silver tining via gravity and reflow of the silver solder did the rest without ever applying any extra silver solder.

I was really worried that I would destroy the seal intergrity at the skirt/insulator interface, I worried enough to put a light bead of vacuum epoxy externally at that seal after cleaning up following the job. The seal and or my epoxy job turned out to be fine.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

daniele
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Re: Some welding...

Post by daniele » Tue Jul 09, 2002 7:25 am

These are my worries too !!!
But I'd like to hear the way you machined the FT to the right diameter before silver soldring stage...
In effect I really don't know how to "grab" the Ft to machine it.

Can you please explain the way you did it ?

tnx again
Daniele

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Richard Hull
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Re: Some welding...

Post by Richard Hull » Tue Jul 09, 2002 2:28 pm

I just cut, with a hacksaw, the insulator (flush) from its base. This left, the insulator and a thin metal, conical skirt. I chucked the insulator in a lathe and turned the skirt true. I hacksawed well, so this took off little metal.

I measured the diameter of the skirt base. I next chucked up a 1.5" holded, 2.75" conflat flange. I simply bored out the back of the flange to a depth of .25" to match the skirt diameter +.005".

From here I just pre-tinned the flange and skirt with silver solder as I have stated and finally sweated the two into a reflow state for the final silver solder connection.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

daniele
Posts: 144
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Re: Some welding...

Post by daniele » Tue Jul 09, 2002 2:55 pm

tnx for accurate description !

ciao
Daniele

daniele
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Re: Some welding...

Post by daniele » Mon Jul 15, 2002 8:18 am

what about the possibility of brazing ?
could it be a clever alternative ?

tnx

Richard Hester
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Re: Some welding...

Post by Richard Hester » Mon Jul 15, 2002 4:44 pm

Brazing will probably work as long as you use a brazing alloy without any zinc or cadmium. Ideally, it should be a pure silver-copper alloy. Harris Safety-Silv 72 is a good example. Jewelers also use silver-copper solders that would work.

daniele
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Re: Some welding...

Post by daniele » Tue Jul 16, 2002 6:57 am

tnx,
brazing could be a good solution here, because of the lower temps involved.
The alloy is critical as you suggest...
It's amazing how the welding technology has evolved.
I have a friend working in a welders shop.
They have almost everything from small arc welders to big stuff for the hard workers...
(not so much fun there) Asking for something to him can become an 1/2 hour briefing :-)



ciao & tnx
Daniele

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