Backyard Aquaponics
A place to discuss aquaponics

Hello everyone...

Before I get started I'm wondering if anyone has attempted to stretch the bottom of a 30 gallon (115 L) poly drum?

It seems easy to me that I could:

1) Hang/ support the drum
2) Drill the cent of the bottom to the size of the eye bolt
3) Add the 3" washers, nuts, and push the eye hook through the hole
4) Add a constant weight to eye hook
5) Heat the "future cone area" with a hot air gun. As the sides get soft it should pull down the cone.

Anyone ever tried this?

Never tried it; but, thermoforming styrene storm trooper armor and molding kydex has taught me a few things.

I personally would heat in concentric rings from the washers first and probably hand pull. Static weight may elongate the heated area too fast and cause excess thinning or breaking. The areas for this most likely to happen is at the cone and barrel transition, and the washers edges.

If you have a long armed companion and two heat guns I would try to heat the rings from both the inside and outside at the same time. I would not put someone in the barrel with a heat gun. Barrels are a lot thicker than what I have experiences with, but even heating is critical.

Go slow, be happy with a 22.5-30 degree and relatively shallow cone/bowl/spherical shape, and I see you being successful.

oh, forms help a whole heck of a lot. Can be anything. In this case a big metal kitchen bowl with some rocks placed inside might may work well with slow even heating via the concentric ring method.

Hope it helps. Looking forward to seeing this in action.

J.B.

Thanks for the input. I will put some 2x4 cross forms just to stop the max drop. I don't think the plastic will move that fast if at all, and I just might pull the eye down and not use the weight. I'm actually wondering if the thickness will even get soft or just bubble.

Well, like most things in life... you don't know until you do it.

You may try a shop vac and just blow it out. Could use regulated compressed air just go easy on the psi.

There is a point that heated plastics go from slow, low, and droopy, to OMG! stretch, drip, tear, flame on.

Probably won't reach it with a heat gun, but, just be aware.

I've thought about doing this myself. Considering that blue drums are typically polyethylene, and polyethylene is a thermoplastic, I don't see why it wouldn't work. I think the biggest challenge will be stretching the bottom without pulling the bolt through.

The more I think on this, the more I think a plug mold is the way to go. I am getting to the obsessive point that I may need to try this



I bet a post, a preheated metal bowl, heat gun and gravity would do this!

1. Preheat bowl to 200-250
2. Heat poly to 1-1.5" droop in center
3. Put bowl on post
4. Put barrel on plug

Definitely going to have to give this a go

How would you get the mold inside the barrel without cutting a big hole?

I probably should have paid attention to the type of barrel

However, I tired it just now with a HDPE bucket, as I never have molded Polyethelene, and I learned a few things.

1. It takes a lot of heat and a much higher temp to get PE malleable.
2. Even heating is very hard, I had thick and thin spots.
3. PE went from the right temp to over heated/melting very quickly
4. My plug sucked
5. This thread is going to bug me, lol.







Time for a beer. My head hurts. Probably from the fumes... or the failure.

Looking forward to seeing where this topic goes! I've seen acrylic sign faces molded with a wooden mold. Maybe wood would be a better plug?

So, that was what I was worried about... the bubbles.

Do you know how hot you needed to get the plastic? I think it would be around 130°C, but if it is less than 100°C, it might be possible to get boiling water w/ a big pot and your bowl form to make it work. Or if we need more heat, veg oil will work... that stuff can get crazy hot without boiling.

And yes, if anyone else tries this... go outside the fumes are very toxic.

I did it outside. It was snowing at the time and dark so I took pics inside.

Temp was more than 250 F, so, definitely above 100 C. I had to get out the propane burner and a sheet of metal to help radiate the heat better. I estimate being about 330-360 F. Much hotter than I am use too with styrene and kydex.

Never even thought of the veg oil and submersion.

Edit: I did find this gem that is worth a read. Backs up my temp estimates.
http://thermoformingdivision.com/wp-con ... -paper.pdf