Made some experiments with an Air Fryer this morning. My observation so far is that it works but it might be best in combination with another form of heating, either pre-melting smaller batches on the sandwich toaster and combining them in the air fryer, or placing the air fryer on a saucepan which is on a hob. The plastic seems to melt more readily when in contact with a hot surface than just hot moving air.
Also was amazed at how small 50 caps look once melted together!
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I did another experiment, this time with the caps on baking paper in the bottom of the air fryer bowl. It kinda worked, and using my half-finished press I was able to make my biggest useless splodge so far at about 200mm diameter. However, I’m not convinced that the air fryer is going to be very useful for my needs. The heating is too uneven and the base is like a big heatsink, so the bottoms of the caps don’t melt properly. I tried lifting the caps up on the wire shelf, which helped, but overal the sandwich toaster was much faster and easier. Direct conduction of heat is way faster than convection in air.
The plastic definitely benefits from being mixed so I can see why the screw extruder works well. Kitchen appliances are promising though as they are so widely available. Has anyone tried a tossing a ball of melted plastic in a meat mincer? I haven’t got one or I’d try today. I imagine what would come out would be like mincemeat, if the output were connected to a heated tube maybe it could make a crude extruder? The screw inside a meat grinder has a decreasing pitch to increase meat pressure towards the blades. Maybe without the blades it would be enough to move the plastic along the tube?
Although the airfryer may not be useful in the end, these experiments have really helped me appreciate the nature of the material. I can see now that it really prefers to be about 3-5mm thick, any thicker and it moves around like crazy, and if it’s really thick it gets voids and bubbles inside. I had planned to create large billets of HDPE and turn them on a lathe, but I can see now that it would be much less effort and use less energy to make a really good mould where the wall thickness is consistent throughout. I can also see a serious advantage in controlling the temperature of the mould itself, by preheating in an oven at the very least.
Not having an extruder, I have not found reason to make flakes smaller than postage stamp size. I can turn a one gallon jug down to that size pretty quickly manually. Your pancake looks pretty. Might be worth cutting it up to confirm that there are no voids.
These flat splodges might be a way of making bottle caps and milk bottles easier to turn into flakes without a shredder- I’m going to try planing the edge with an electric planer. It would be great to make small, uniform flakes with just a sandwich press and a planer. Can’t test it now though as its the middle of the night.
Thanks for trying this. Yeah, I think for these to be useful, the airflow wants to be managed, I think several mesh shelves may be helpful (kind of like a dehydrator). For my application, if it could preheat the plastic prior to my putting it into the injector, and reduce the melt time, it may be worth it.