Working HDPE

Oven

Bill Tindall, E.Tn.

I think the temperature is around 90 to 100C +/-. Start on the low end and work up if needed.

The problem is this stuff is a good insulator so it takes a long time to get the interior warm.

The bend is a combination of time and temperature. This stuff creeps. Given enough time you could slowly bend it at room temperature. Less time at 50C....etc your get the idea. From memory I think it melts around 100-110C. (There are so many varieties of PE I can't keep the properties of each straight.) The HDPE is crystalized so you will have to get the crystals melted to bend it in any short time and its this melting point I can't recall reliably. Success is melting the crystals without making it so hot the viscosity becomes too low and it gets runny.

Re: Oven

Mark Mandell - Gone Round In New Jersey

Piece is 48 x 32. Bend is across the short axis. Don't have that size oven

Guess I'll just have to work the heat gun . . .

patience

Bill Tindall, E.Tn.

The fact that this stuff creeps is your friend. Start the bend to stress the bend area. Use pieces of wood clamped on each side to keep the pieces flat and oriented and confining the heat to the bend area. Then start slowly heating, ideally both sides. It may take a half hour to get the piece heated to depth, uniformly, with uniformly being the key to success.

Re: Working HDPE

Keith Newton

Mark, I'm not sure what the maximum thickness for cold bending on a metal break, but I suspect 1/4" is over it. Back in my plastics days I made some bending strips using a trough which had two or three strands of nichrome wire stretched across it. The heat was controlled with a big reostat. However If you wanted to make your own, I would try to find and old toaster that had the coiled wire elements, and a good switch to re-purpose. There may be a wax crayon that you mark the top side that changes color when the heat gets high enough.

Re: Oven

Bill Howatt

What about making an "oven" from 2x4s with some flat stock on the sides and an opening in a bottom edge for the heat gun. Some vent holes on top.

We did similar using fire bricks around a huge piece of copper and heated it with a heat gun.

Bill

Re: Oven

Bruce, a MN Galoot

I made an oven to cure epoxied bow limbs from an insulated box heated by 100 watt light bulbs. I could regulate the temperature to an even 200F. Much higher temps are easily achieved with larger bulbs.

the problem....

Bill Tindall, E.Tn.

There may be a wax crayon that you mark the top side that changes color when the heat gets high enough.

The important temperature is the middle of the 1/4". the challenge is to get the temperature correct in the middle without overhearing the surface. Achieving this happy state is made difficult by the poor conductivity of this stuff.

Re: Oven

Alan Schaffter

Do you really need to bend it or could you just cut it and make a reinforced* butt joint?

*machine screws and tapped holes

Re: Working HDPE

Keith Newton

Another suggestion, might be to cut a V kerf in the inside, so maybe only the outside10-16th inch has to bend while the V closes.

The V

Mark Mandell - Gone Round In New Jersey

would then have to be welded together. I don't have a plastic welder or I would have just cut the two pieces and then welded the 90.

Thanks All

Mark Mandell - Gone Round In New Jersey

I'm going to try the heat-wall idea and it it doesn't work this will be a cut-n-bracket job with silicone caulk. This thing has to make a top and side enclosure for a heat pump compressor that is subject to icing up from a north-west snow blow.

Weld?

Tom Dunlap

As much as I love trees, wood and woodworking welding is so flipping fascinating!

Plastic welding has caught my eye. Not because I need to do it just that it brings on possibilities. Plenty to find on the 'net.

Harbor Freight has plastic welders that get decent reviews for the price point.

Re: Welder

Mark Mandell - Gone Round In New Jersey

I bought one of those HF welders that was comprised of a heating coil inside a handle attached to a compressor. It used the concentrated air stream to melt the plastic.

Never got it to work properly and s***-canned the whole rig. Wasted $$

Done

Mark Mandell - Gone Round In New Jersey

Patience and the heat gun got the sheet to bend to a 90, but it steadfastly insisted on springing back to a 45 so,

Flipped and cut the sheet (table saw - carbide blade) and then trimmed the other piece to remove the bend. Pieces joined with angle brackets and the seam and hardware sealed with silicone.

Installed over the condenser and should keep the snow and ice from fouling the fan and coils.

Re: Done

John K Jordan

>>>Installed over the condenser and should keep the snow and ice from fouling the fan and coils.

I have the same problem with the outside unit of my shop heat pump. I usually stand a sheet of plywood leaning against the side so one half angles up over and deflects the snow and freezing rain. This works well but it might be nice to have a more permanent solution and lighter-weight solution. I have some thin stainless steel sheet I could bend or weld. Or a piece of galvanized roofing.

JKJ

Material

Mark Mandell - Gone Round In New Jersey

I chose 1/4" recycled black HDPE. 4'x4' piece was $45. Cuts well on the table saw, but the bayonet saw leaves a lot of black "sand" that static-sticks to everything and the blade wasn't too happy cutting.

Freezing rain and sleet on tap tonight so the test is "on."