how to fabricate an air tight compartment!??
how to fabricate an air tight compartment!??
(OP)
hi!
i am currently working on an air tight compartment by using 2mm thk mild steel. Say i have 5 pieces of 2mm mild steel being cut to size to build up the perimeter and base of the box, anyone have any ideas on how to join them together into a seamless air tight box??
been checking out on existing machines where they manage to join metals together and from outside it looks exactly as if it is bended instead of metals joined together, while from inside it is obvious metals are put together.
really urgently need solution to this,
hope that i have asked my questions comprehensively. :)
Best regards!
i am currently working on an air tight compartment by using 2mm thk mild steel. Say i have 5 pieces of 2mm mild steel being cut to size to build up the perimeter and base of the box, anyone have any ideas on how to join them together into a seamless air tight box??
been checking out on existing machines where they manage to join metals together and from outside it looks exactly as if it is bended instead of metals joined together, while from inside it is obvious metals are put together.
really urgently need solution to this,
hope that i have asked my questions comprehensively. :)
Best regards!





RE: how to fabricate an air tight compartment!??
Well you could weld them using oxyacetalene welding torch, however as with any welding you might get unwanted distortion, but its the only way I know to get it airtight.
How will you test for air tighness?
desertfox
RE: how to fabricate an air tight compartment!??
Use GTAW (TIG) welding process. Lap the corners rather than trying to butt them...fitup is easier. Then fillet weld all sheet edges. Lapping will cut down some of the distortion, but you'll probably still have some.
RE: how to fabricate an air tight compartment!??
you could use separate splice pieces, bent as needed, welded or bolted in place. an advantage being you could use two pieces on each corner (one inside, one outside, the corner) to help minimise distorsion if you're welding. of course no distorsion if you're bolting them together, but you'll need need a seal of some sort ...
plenty of ways to skin a cat ...
RE: how to fabricate an air tight compartment!??
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: how to fabricate an air tight compartment!??
Why are you using 5 pieces when you could use only 2?
Brazing or soldering.
RE: how to fabricate an air tight compartment!??
Even steel cans are "air-tight" for food protection...
If so, I agree: Start with a rectangular four-sided bent shape of your thin-walled sheetmetal. Your vertical seam should overlap both ends. Weld this vertical seam. (Sheetmetal fab shops have automatic folding machines to make seams like this for ducts and vents all the time, but 2 mm thick steel is a bit thick for most duct bending rollers and benders. The duct builders use a "Z" type fold, two doubled "U" bends would also work. A single "U" with the second sheet going into the "U" and being welded on both sides is an option.)
Fold the end tab's of the four walls at the bottom up at 90 degrees to make four "seats" or flanges that will overlap your bottom sheet.
place the bottom sheet onto the seat, weld all seams around the bottom.
fold the upper walls of your walls also into a seat and weld it up. Add your inlet/outlet/opening/access/lid ...
Optional: Fold the walls as above, but then fold a second rectgular shape one well thickness smaller. Nest the second into the first to eliminate the bottom joints - you'll still need to weld, but there are fewer seams but a heavier (more expensive for material, less expensive to weld ?) assembly might be acceptable.
What is this for? What are your design limits? What goes inside? What must be kept outside?
RE: how to fabricate an air tight compartment!??
A lap joint means touching the outside edge of one sheet to the inside edge of the adjacent sheet, then running a TIG torch along the exposed sheared face to melt the sheets together. For mild steel, the weld can be mostly autogenous, i.e. with a minimum of filler metal added. The weld would require minimal grinding to look like a bend on the outside.
Accounting for real shearing tolerances, you are mostly working with a half-lap joint, where you have to add some filler metal, but not an entire sheet thickness' worth.
I've seen it done in production for aircraft battery boxes, in 16 and 18 gage mild steel, assembled over a frame made of aluminum rectangular bar, which kept the steel in alignment and served as a nonconsumable backer and heat sink. Without the frame, you'd have to weld an inch at a time and work in alternation on all the welds at once to distribute the heat and distortion.
Mike Halloran
Pembroke Pines, FL, USA
RE: how to fabricate an air tight compartment!??
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: how to fabricate an air tight compartment!??
racookpe1978, your assumption is absolutely correct, the compartment is actually the filtration compartment for a dust collector, and i'm confused between the lap joint and butt joint, i think my current planning is a butt joint if not mistaken. with attachment is a full drawing and a corner section detail, please advise.
RE: how to fabricate an air tight compartment!??
To get the effect of a radiused corner after welding, most sheet metal shops will do what is called a half butt corner.
They will place the metal one half thickness over the other at the corner, then do an autogenous weld with a TIG torch. If the operator is skilled enough this will result in a smooth weld requiring little or no cleanup afterwards.
Unless your box exceeds standard sheet sizes, common manufacturing practice would be to miter the top and bottom flanges and bend at least two of the corners to avoid welding. If the finish does not have to look that good, a MIG welder may be used instead.
B.E.
RE: how to fabricate an air tight compartment!??
As for the design, those above have given you some good tips for the welding the seams. I would suggest talking with your sheet metal fabricator as to what their capabilities are. Often times you just need to give them the dimensions of the final component and define the material and they will use their discretion and your input on the best way to fabricate the box.
Personally, I would see if their break press has the clearances to make this out of one piece so there is only one weld seam. Then they can weld the miters on the corners. This will get you the best chance of holes lining up post assembly and a better seal along the top face. As for the miters, give some room between where the two faces come together. Typically I would give 0.025-0.050" so that when they bend everything, there is room for tolerances.