Granules (in industrial scale referred to as pellets) are the raw material for most plastic parts. A number of processes to turn these granules into plastic parts has evolved over time, ranging from die casting over film extrusion to 3D printing. But how do you get plastics that has reached its end of use back into granules of specified parameters in order to close the cycle?
That is what I am investigating in detail during this year's Hackaday price.
There is a number of challenges to reach the goal:
-The physical properties of plastic range from hard and brittle to soft and elastic. Each of these needs a special treatment.
-The properties of plastic change with temperature
-What about impurities?
My first approach to get grains smaller than 2mm from the mix coming out of a blender was to use a DIY sieve. The second one is a mixture of sieving and grinding:
The solution is made of 3mm steel with a 8.5mm hole drilled and a 8mm threaded rod.
The steel plate with a hopper is mounted on the base plate and the threaded rod is in the chuck of a drill press. By moving the drill up and down WITHOUT the drill rotating, the grains are forced down through the hole. Even at the highest point, the threaded rod is still in the hole of the steel plate, so that only grains of a certain size, fitting in the gap between threaded rod and hole can be squeezed through. Larger grains will get crushed by this process, so that this is a combination of sieving and grinding.
Of course, the raw material filled into the hopper must first be crushed into small pieces with a blender. The advantage is, that larger particles coming out of the blender can also be processed in one run. There is no need to put the large granules back into the blender.
To get raw material for my Direct Granules Extruder, I am using a commercial blender and a DIY sieve to get the raw material needed. The main property the granules must fulfill is a size of no more than 2mm. This is critical, because larger sized granules lead to clogging of my existing extruder design. This must be relatively small to be able to extrude plastics in small quantities as required in 3D printing.
To get the correct grain size, I have drilled 2mm holes on the bottom of a tin can.
I was going to comment something about grinding and plastic recycling. But when looking for a reference found -- it's complicated.
So, I don't know. You might find this an interesting read: