How to Make a Vacuum Flask

That should be that. GA, Ky.

The final sealing could be performed while inside a vacuum chamber.

The sealing may be like a brazing operation where the filler is placed at the joint and put in an oven that is under vacuum. When the item comes up to temperature the filler melts and due to joint design or flux the filler bridges the components. On cooling you have a seal, then you release the chamber's vacuum but you still have a vacuum in your item.

Looking at the specs I'd say the company you work with has this down pat and have it nailed.

Hi HangWaiter,

As a fellow 'struggling inventor' I can relate only too well. But if it was JUST idle curiosity and not something you need to figure out for your invention, then a careful, thoughtful, detailed, thorough very observant deconstruction and reverse engineering of something that is that low in cost, I would suggest doing it even if you do find out how it was done, though I would suggest waiting to see if you can find out before you do it to give you a better idea of where, what and how it was done and sealed.

There are so many high tech and sophisticated welding processes now, including some that work in conjunction with other 'mechanical means such as forming, extreme pressure. Fusion welding, 'gap welders' such as they use to make up continuous band saw blades with spot welding, etc that it is not surprising. While working in various machine shops, I encountered one very highly trained welder that specialized in manual TIG welding and was capable of some phenomenal fine, manual welding; but couldn't do larger stick welding worth a damn (to boring for his tension span). LoL (< 8) He had studied fusion beam welding in a university in Asia amongst many other things. He worked in the R&D division of McDonald Douglas in central Canada for a while (an AeroSpace company). He is the only welder in the western half of Canada that is licensed to weld the actual turbines blades etc of huge commercial jets as well as high performance military planes. I went to see him one day to get some specialty welding done where he was working in a small shop. There was an upcoming trade show in our vicinity that the owners wanted some impressive demonstration work pieces for. I watch him run a bead across the bottom of an aluminum pop can, VERY thin, though heavier than the sides. He ran a beautiful bead across the bottom freehand in a perfectly straight line on this thin concave surface that was so thin I could barely feel any height of the bead, and as a machinist, I CAN feel a 0.001" difference in height and tell you which one is higher! He invited me to try it. I laughed it off as we both knew what would happen: not only would the bottom of the can be gone but most of the body as well. But THE most amazing part was that we got a flashlight and looked at the bottom of the inside of the can. Not only had the bead not even burned through the bottom of the can anywhere at all on the inside of the can, there was NOT even any discoloring or change on the inside due to the heat of the welding !!! There was absolutely nothing visible on the inside of the can that showed it as having been welded! This is NOT hearsay, I watched and saw everything that I am testifying to with my own eyes and fingers! When it was slow at MD in the R&D department, they used to have welding contests. They would take a mass produced cigarette and using a very fine needled would poke a very tiny hole on opposite sides of the cigarette about ¼" from the end of it. They would then very gently roll the cigarette between their fingers with the smoking end down and get the tobacco (mostly hundreds of chemicals )< 8( out of the end of it. They would then take a very fine gold wire about 0.003" in diameter, about half the thickness of a human hair and stick a short piece in from both sides through the holes so that they were almost butted up against each other within the now empty cylindrical cigarette recess with it's very thin and highly flammable paper. They would then 'reach inside of the end of the cigarette' and weld the two pieces of very fine gold wire together without burning them away or even discoloring the paper. All by hand!

Still think it can't be done (almost invisibly), especially with automated welding equipment with active feedback and computer controlled?

Even if you do know where and how they do it before you 'reverse engineer it', good luck trying to find any evidence of it!

What field/type of invention(s) are you working on?

Good luck with all of these things and let me know what you find out and how it turns out please.

Regards, (< 8)

Doug

Hi Doug

Thanks a lot for the insight. I´m also not foreign to welding and have done some pretty fine TIG welds on firearms parts. But nowhere near the intricacy which you describe here.

My invention involves heat insulation of a metal tube, where durability and low cost are some of the criteria. I just found that a metal thermos flask keeps the coffee hotter for longer than any filigrane glass thermos. Plus, I can drop it and whack it without running the risk of fragmenting the inner vessel. therefore I presume that a similar setup would serve my purpose much better than any foam, Styrene or ceramic wrapping of the said metal tube. the working temp of the tube is between 80 and 115 degrees C

Will keep you posted if the concept works, but estimate about 6 months before proto can be field tested.

Kind regards

Hangwaiter

Hi Hangwaiter

A few years ago there was a story on TV here in Minnesota about a couple that had a problem with a metal thermos used for coffee & such. The thermos had broken & released very fine particles of carbon. These particles of carbon trashed the entire house. I have never heard of the use of carbon in a flask like this before. I believe the flask was a brand name.

Good luck on your project.

Doug

i also dont know how they make the final seal on vacuum flasks but i do know that applying a vacuum to a fish tank would suck the water out of the fish tank, as a vapour. as the pressure started to drop the water in the tank would start to boil. the pressure would remain stable untill all the water had boiled off and then start to drop again.

You are correct. This explains why we must use brazing alloys that have lower vapor pressure than the pressure we braze in. Zinc is a common component of several braze alloys, but is generally not used in vacuum brazing applications because of its relatively high vapor pressure.