Monday, December 20, 2010

Plastic Extruder - Continued

I was a bit surprised to received so many questions about my plastic extruder. Hopefully this info will answer some of these questions:

There are 3 sections: bearing chamber, hopper, and heating chamber. These are made with a section of ¾” black pipe (gas pipe) and ¾” wood auger bit fits nicely into the pipe. There is a little bit of gap between the auger and pipe. I was concerned the molten plastic would ooze back out of the chamber, but it was never a problem. This unit can consume virgin HDPE pellets or cut up milk bottles.

The bearing chamber is about 3.5” long and is mostly dead space. The shaft of the auger bit is long and I didn’t feel like turning it down shorter. At the end where the shaft comes out, there is a thrust bearing placed on it to minimize the friction.

The hopper has half of the black pipe cut away to expose the auger. This is 4.5” long and has a metal hopper which holds around 1 cup of pellets. As the auger turns, some pellets get forced into the heating chamber while some just sort of move to the front of the hopper. Between the hopper and heating chamber is ¼” of plywood…to act as a heat insulator to minimize the heat loss through the metal.

The heating chamber has two heating zones. The main reason was to attempt to heat the plastic evenly since I wasn’t sure how it would heat as it moved through the chamber. This chamber is 5 inches long. The first temperature sensor is placed about half way through and the auger bit ends just before it (so it won’t hit against the probe). The second reason was I didn’t want to run a high voltage through the Nickel Chromium wire…too dangerous and I had a couple of PC power supplies I could run 12 volts at 8 amps. The pipe is wrapped in Kapton tape which is heat resistant….but you can see in the photo it did eventually burn through. Each zone is independently controlled by a microprocessor to maintain a consistent temp.

The heating chamber has a flange on the end which allows different die plates to be bolted on to the end. Depending on the size of the “hole” in the die, the plastic will extrude at different speeds. For the 1/4” slot, the auger turns at about 18rpm and can produce a ribbon of material at roughly 200 feet/hour.


Joel Clemens said...

Thank you so much for posting a follow up. As you may know there has been a large group of people trying to figure out how to extrude recycled plastic at home for a long time.

Anonymous said...

At what temperature does the hdpe melt/turn clear?
I am very interested in trying this and the temperature is the only thing I can't figure out.

A very cool project, by the way.

Anonymous said...

Oops! I just found the answer to my own question on the other page! 120C

David said...

Where is the other page? Thanks