Tag: melt

It’s the return of HDPE! I was recently at IKEA and grabbed a metal baking pan. I gave up on glass after the last episode, and while people suggested Silicone, I never got around to buying a Silicone pan.

Now, it’s important to remember this is recycled HDPE, and it’s not virgin material. Also, some foreign matter may get mixed in. The HDPE for this batch came from a few sheets I asked John McGeen to plane for me. He swept up the shreds and bagged it and returned it to me to re-melt. (The sweeping from the floor is probably why some foreign matter gets in.)

The bottom (the part that was touching the metal pan) shows a bit more of a “burny” look to it, being yellow, and such. That may be the difference between glass and metal. I’ll experiment more to find out.

Like the other pieces I pressed the hot HDPE between some pieces of wood. Removing the plastic from the metal pan was much easier than the glass pan. You could even consider skipping the pressing and just let it cool in the metal pan. It should shrink a little bit and pop right out.

My most recent HDPE adventure did not turn out well. While I got a nice sized sheet, I managed to slice my finger open and wasn’t sure why, until I investigated more closely…

If you can see those shiny pieces, those are pieces of glass. But since I’m personally cutting up all the HDPE scraps and putting them in the oven, where did this glass come from?

Oh yeah, I put it in the oven in a glass baking pan. The HDPE actually tore some layers from the bottom of the pan when I was removing it! The HDPE doesn’t exactly fall out of the pan, and requires some coaxing to come out. I typically pry it out with a screwdriver, then pull it out. (I wear gloves the entire time, as that stuff is HOT!)

Obviously the glass baking pan isn’t ideal for this. I’ve gone back to using the smaller glass loaf pan. I’m hoping the smaller surface area will help prevent this from happening again.

The glass pan is pretty beat anyway, and with pieces missing from the bottom, I guess I’ll just scrap it. (Unless someone wants to melt it down!)

Our latest experiment in recycling HDPE into sheets uses material that one of the guys in the shop got from Craigslist. It’s a giant bag of shredded HDPE scrap. It’s all white, and very clean. I think it was used for archery targets or something.

Here’s a photo of one of the bags with a one gallon jug on top of it. (We’ve got three of these bags!)

I thought this would be the perfect material, and it is good, but it takes a while to melt down. With jugs I could cut them up into small flat pieces and fill the baking pan, but with the shreds it’s mostly a matter of trying to stuff as much as I could into the pan, then heating it until it melted flat, and then adding more. It’s not a fast process.

Despite the time involved, the results were good. I may have rushed things a bit, as the, plastic did not seem completely pliable when I put it on the board (aka “The Press”) but I decided to go for it anyway.

The results were ok, but it’s definitely not as smooth (or shiny) on the surface as the last attempt. Getting it the right plasticity is important in this process.

The size of this (oval shaped) piece is about 8″ x 7.5″, which should yield a square sheet of 6.5″ x 6.5″. I’ll probably go back to using the larger square glass pan next time instead of the loaf pan.

In our last experiment recycling HDPE into usable form, we created a brownie pan full of plastic. While this looked impressive, it wasn’t the best idea for something that was going to be milled. It ended up being much thicker than needed, and finding a cutting bit with the proper LOC (Length of Cut) proved to be an issue. I was all set to mill a thicker piece, but we blew a fuse on the Shapeoko.

I decided that I needed sheet material of a uniform thickness, so I ended up creating a simple press using two pieces of wood, with some spacers. Once I warmed up the HDPE block I got it out of the pan, onto the wood, and stood on it until it was squished flat(ish.) I then put some weights on it until it cooled.

It turned out well! It’s a pretty uniform thickness now, and this was just under 1/3rd of a bread loaf pan, so I may need a bigger press if I want to do bigger melts. I can also make different presses with different thicknesses as well.

Funky!

I’m calling these “HDPE Brownies” because I find it slightly amusing. Here’s what’s going on: I’m taking HDPE scrap and putting it in an 8″x8″ glass baking pan (a brownie pan) and popping it in the toaster over at about 270° F for a bit, them smashing it down and repeating the process.

So why am I doing this? Well, at the museum we sometimes mill sheets of HDPE for exhibits, and it creates a lot of chips/sawdust, and I gathered it up remembering that I’ve seem some people heat up HDPE and press it into a mold. Oh, and check out this video for lots more info on melting HDPE.

Once I got a full pan I took it out and cut off the sloped sides on the band saw to create a (mostly) squared-off slab. There are some air bubbles and what not, but for a first attempt, it’s pretty good. And what am I going to do with this stuff? I’d like to mill it using a CNC machine, probably a Shapeoko2 to start with. The HDPE cuts well, and shapes well, similar to working with wood. You can sand it, and whittle it too.

The white you see is from milk jugs and cat litter jugs, and the yellow and blue are from laundry soap jugs. All the black and pinkish-red are the sawdust bits from the milling of HDPE slabs we purchased. I think the sawdust bits caused more air bubbles than the cut up jugs, but more experimentation is needed.

Besides milling this piece, my plan is to keep collecting HDPE by gathering old jugs and cutting them up and making more blocks. Just making more of these should help me refine the process and work out the bugs, or the bubbles, as it were.