View Full Version : Welded polyethylene tanks

08-12-2008, 08:06 PM
I'm thinking of a small but oddly shaped polyethylene tank.
Is this a DIY project?
I'll need sources of materials, tools and how-to.


The Bigfella
08-12-2008, 08:48 PM
I need one too - but without an (is it) ultrasonic welder .....

I dont think they are too expensive to buy - the tanks that is.

08-12-2008, 09:24 PM
I don't remember what the tank plastic was (Probably Poly), but they used to make and repair tanks at a fish farm where I worked. They had these hot air welders that would trigger feed a stick of plastic into the hot air stream. Worked a bit like an arc welder. Here's one outfit (http://www.delviesplastics.com/welding.htm)that sells something similar to what we had.



08-12-2008, 09:27 PM
Have not thought about this for a while but I'll take a stab.
HDPE fuel tanks for automobiles are blow molded a multi-layer composite construction. Something like HDPE-EVOH-HDPE. Where the EVOH is in place for Hydrocarbon permeability reasons.

Building prototype fuel tanks. We bought sheets of HDPE with the EVOH thermoformed in place HDPE-EVOH-HDPE. That was 10+ years ago. To weld the tanks we used an HDPE had held extrusion welder. Production tanks our pulled off assembly lines and put through simulated hdyrocarbon leak tests. How important is the EVOH layer at the small boat owners level? I don't know. Skipping the EVOH layer. Not sure what the small tanks are made out of and if they even consider hydrocarbon permeability as design criteria.

Shaping the tanks. Crude thermoforming. Build a male and female mold if needed preheat the sheet and vacuum form. I'd not try to do deep draw thermoforming with a EVOH layer in place more like use the mold and a little vacuum assistance to get the shape. You'd be better off bending a U or a square and welding ends on with a fillet weld. Building your own tank you could place an in tank reservoir inside with a 12VDC fuel pump etc. I use one to empty the marine diesels end of the year.
Material can probably be found in CT at one of the commercial material suppliers. A new tank could be cut up and Frankenstiend into place--been there done that.

Joint design. You could overlap joints, heat,clamp,cool. 300-400 degrees F possibly cooler. You want intermolecular entanglement of the polymer. Stuff moves whens its hot. To much clamp travel and splat. A little R&D on your part would be required. You could bend right angles over heated pipe and extrusion weld end plates on. This you could have a fabricator do for a small fee. Build the structure and bring it to him to weld. Have fitting for a pressure test so you don't go home with leaks. You could build a card board mock up and bring it to a fabricator (a few in CT that work in plastics).

Rambling post. I have joint design manuals for this somewhere and material data sheets could scan to PDF form. I try to stay away from plastic.

Roger Cumming
08-12-2008, 10:39 PM
Kracor, Inc. of Milwaukee makes high quality polyethylene holding and fuel tanks for boats. They are made to order but they may have a shape that would work for you. Check their catalog. I have used one of their holding tanks and can recommend them highly.

08-12-2008, 10:53 PM
OK, I'll fess up. What I'm really contemplating is an oddly shaped wastebasket and I thought that PE would be a good material for it. I'm as much a tool-hoarder as the next guy, but I'm not ready to spend several hundred bucks for the necessary gear for such a piddly job.

So much for that idea.

It'll be 4mm. ply and some artful fillets.