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Improving recyclebot concepts
| By Michigan Tech's Open Sustainability Technology Lab.
Wanted: Students to make a distributed future with solar-powered open-source 3-D printing.
For main page see: recyclebot and latest version RepRapable Recyclebot: Open source 3-D printable extruder for converting plastic to 3-D printing filament
These ideas were generated from the study: Shan Zhong, Pratiksha Rakhe and Joshua M. Pearce. Energy Payback Time of a Solar Photovoltaic Powered Waste Plastic Recyclebot System. Recycling 2017, 2(2), 10; doi: 10.3390/recycling2020010 open access
- Three heating sections with varied temperature are helpful, which can be obtained by changing the coil density.
- Heating section-2 is in the middle of the heating tube. The temperature on the section-2 should be at a point where the plastic can be totally melted.
- Heating section-1 is on the feeding side and heating section-3 is on the extrusion side. The temperatures on section-1 and section-3 should be slightly lower than that on section-2 . Heating section-1 is for pre-heating the plastic. Plastic after heating section-3 should have enough viscosity to form filament, and the viscosity is varied with temperature for the same plastic.
- The temperature on the nozzle should be close to the temperature on heating section-3. It is important to keep the nozzle with a stable temperature because the nozzle easily loses heat.
- The two main purposes for driving system are to deliver plastic and compress plastic.
- To reduce the degradation of the plastic during recycling, it is necessary to decrease the residential time for plastic in the heating tube. It is better to use long heating tubes and rather high auger speeds, which can decrease the residential time and enable the plastic to be heated more consistently. The normal screw rotation speed is 45-210 rpm    .
- If the size of the auger on the nozzle end is slight bigger than other parts, it’s better for the auger to compress the plastic in the tube.
- Uniform feeding rate is important for keeping stable temperature and pressure in the heating tube.
- Fluctuating temperature would lead to degradation of the plastic and unstable pressure in the heating tube would result in the variation of the filament diameter which is bad for accurate 3-D printing.
- To recycle the plastic which is easy to degrade, using a chain extender can increase the viscosity of plastic and make it easy to form filament. However, the amount of the chain extender used is usually tiny, so it is difficult but important to make uniform distribution of chain extender in the plastic pellets.
- Some examples of chain extenders for PET cited in the literature are diepoxides, diisocyanates, dianhydrides, bis-oxazolines, carbodiimides, bis-dihydrooxazines    .
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