This project is about making plastic sheets out of recycling flakes, mainly with low Invest machines. For heating the flakes, we use a normal kitchen oven. The Baking process is done in a metal mold with a clamping mechanism. If necessary, we a want to add a pressing process.
The first mold works, but it is costly to manufacture and relatively heavy due to the welded construction made of mild steel. In addition, fixing the frame and lid via 12 screws is not always that easy. The new approach does not require any welding at all. Instead of individual plates, a large stainless steel plate is now used for the base and lid, which we received last year from a household / workshop liquidation. The frame elements are sawn from simple aluminum profiles and screwed to the plate by drill holes. This form is again scalable, in which simply several frame elements can be arranged on top of each other. Pressing pressure is also generated in this form by pretensioned springs.
jiha, I finally managed to make recycling sheets with a good surface on both sides which are easy to remove from the mold. So weighing the material in andvance helps to get a good fillfactor. I just multiplied the mold volume with the density of the material and added 10% safety. Worked out well.
Got a big Flake-hill on my mold with the 5-8mm flakes. Smaller ones should work better.
okay, equipped both sides with thin galvanized metal sheets and rubbed them with silicon oil. Also lowered the temperature to 200 degree, the baking time to 1,5 hours and place a small indicator sheet with flakes on the mold to get an impression of the melting process.
This solution worked well, the plasticsheet was easy to remove and the surface of side 1 was very good. Unfortuanetly the amount of flakes was not sufficient to fill the whole mold with molten plastic. So side 2 was not so nice and looked like small trees would come out of the surface.
Then.....Fourth try will be with weighing the needed plastic amount in advance. Stay tuned
For the second try I raised the baking time to 2 hours and added a thin metal sheet on one side of the mold to prevent the plastic from sticking onto the surface. This worked well, but unfortunately, I had only one side equipped with the metalsheed. So the material baked solid on the second side and it was very hard to remove it. Nevertheless the way to go is cleat for the third try....
the first sheet which was made with the mold. Not that bad but the process needs some major improvements. For the second run, the mold will be filled with more material and the baking time will be 2hours instead of one.
Okay friends, deassembled the large metal-profiles because they appeared to massive. And yes, the mold had a better look afterwards. But guess what happened when I filled it with plastic flakes and screwed it together ? The mold bended, but with continuing of the baking process, it got back in the original shape. So the first attemp to make it more stable was not that wrong. Anyway, I will go in the direction of a lighter Verison, to reduce the thermal mass and the baking time. So stay tuned
The first mold is finished. Welded 4 Plates for each side together and reinforced it with an additional metal-profile. Two bore-holes on each side will hold screws and springs for applying pressure on the plate. After having the mold on the table, it seemed very heavy. So I will change the metal-profiles a little bit and start a testrun afterward.
The main challange with the low cost 4 Plate solution is bending of the material during the welding process.
Ordered 8 sheets 200x175mm. Four of these are welded together for one side. Found a few rods and welded them onto the plates to make them more stable in the pressing process and to prevent them from bending during the welding.