Open Source Waste Plastic Granulator

The plastic cutting system consists of four separate components (plus mounting hardware). Two blade arms will connect to the cutting rotor shaft (shown in Figure 2 ) and will spin with the shaft. Connected to either end of each blade arm in the configuration shown below are two fly knives, which will contact the plastic within the cutting chamber and shear through it. To help with the cutting of the plastic granules, there are two more pieces in this system that both interact with the rotating fly knives, the granulation screen and the bed blade. As the fly knives rotate in the granulation chamber, they will pass very close to the fixed bed blade on the right side of Figure 2

This is where the large pieces entering the cutting chamber will be sheared for the first time. In the design, all stress-bearing components related to this large cutting force were designed to be able to cut 22.2 mm cubes of nylon mill stock. Once large pieces have been cut for the first time by the bed blade, they will accumulate on the surface of the granulation screen. The clearance between the tip of the fly knives during rotation and the inside of the screen in 3 mm, which means that any larger granules will get pinched between the screen and the blade and be sheared to a smaller size. Once the granules are smaller than 6 mm in all dimensions, they are pulled through the holes located in the granulation screen and into a collection chamber by a vacuum. Thus, the vacuum is used for the collection of the granules of cut plastic. In order to make the blade arms rotate, as described in Section 2.1 , weld-on hubs attached to the shaft were bolted onto the blade arms. For the cutting system fly knife blades were manufactured from O1 tool steel and a Bridgeport was used to manually face fill the stock down to dimension. Once block was dimensioned down an end mill was used to cut slots and pockets needed to attach the bolts. Finally, an angle vise was used to face mill the bevel for the cutting edge all to the specifications with the drawings [ 63 ]. After machining the blades were heat-treated using an electric furnace and quenched in oil in order to harden the tool steel following standard protocols. For the granulation screen, a seamless pipe cut to width was used as the starting material, but due to manufacturing methods the pipe had internal stresses. Heat treating the pipe in an electric furnace and then letting it air cool relieved the internal stresses. This step is not required if tools are not available as one could continue to cut the pipe, but stress may not be relieved, and it will spring open. After the stress relief heat treatment, an angle grinder is used to cut a straight line down the length of the pipe and then cut the other side of the pipe to provide equal halves, which are then subsequently drilled as shown in the Figures.