building a small sheetpress

If you look around the Precious Plastic website, you'll find three main methods for recycling plastic- injection molding, extrusion molding, and sheetpress. While we are very busy with our injection machines, we're also looking into the other options as well.

A sheetpress is- again- very simple in theory. You bring the plastic up to melting temperature in a specialized oven, and then squeeze it to get rid of the voids. What could be simpler?

In practice, though, it's much more complicated. The Precious Plastic sheetpress design is a complicated build, and our metal fabrication facilities are extremely limited. To put it another way, I'm our metal fabrication facility. I have a stick welder, but that's about it. There's no space to build such a machine, and no room at our Tybee Island shop to put the thing if I did build it. But on the other hand, a sheetpress can use a lot of plastic flake at a time, and we have a lot of flake to use.

So I wanted to try some kind of small-scale sheet press operation- something that is cutting board size or smaller. If we can find an oversize toaster oven that isn't too expensive, then we could match that with a small flat press to squeeze the "sheet." We still don't have the toaster oven, but I went ahead and designed & built a press that is slightly larger than a cutting board. 

The main thing I was after with this design was low cost. It's made mostly of angle steel and 1/8x3 flat bar. I had an old bed frame that I squirreled away some time ago that provided the angle steel, and I had about eight feet of flat bar from a previous project. The plywood for the bed was also scrap... someone was moving and cleaning out their woodshop, so that was another zero cost item. The only thing that I needed was a small auto jack, which I bought for around twenty five bucks. Even if you had to buy everything new, I'd guess the cost would come in at around a hundred dollars.

The photos below show the basic process. In order to speed up the operation of the jack, the hand crank was removed and replaced with a bolt. You use a battery-powered drill with a socket drive to raise and lower the bed.

The "mold" for this... I really shouldn't call it a sheet because it's so much smaller... is just four pieces of 3/8" square welded into a rectangle. I used 3/8" because it's what on hand. Some sheet aluminum from an old road sign forms the top and bottom surface of the sheet.

I can't tell you how well- or even if- this approach works, because we don't have a heat source large enough to accommodate the mold. Another trick of this approach is bowls using male and female molds. The trick is the molds- they need to be very accurately made in order to get consistent wall thickness. This is a back-burner project that I hope to get on shortly.

Look for an update soon.

Starting the press frame. I used angle and flat bar, but square tube would work as well.

The finished press.The plywood is attached with screws.

Halfway done, Some paint applied.

Welding a cutting board "mold." It's really just something to contain the flake while it melts, and to set the finished thickness of the sheet.