Recycling in favor of building boomerangs is not a new topic for the blog, 3 articles have already been published. It was time to take it up a notch. By dint of making boomerangs, we see that the scraps associated with the cuts are numerous and that the plastics to be recycled are abundant. More generally, the problem of plastic waste which is struggling to be recycled is increasingly present in people's minds. I was looking for a solution to re-use these scraps and why not other abandoned plastics to give them a second life. The primary objective is not to make a 100% finished boomerang (with the profiles) but to be able to hand-mold boomerang blanks in original materials, not often used. Through research, I discovered the Precious plastics initiative which allowed me to evolve in my approach. Instead of finding material slabs and carving boomerangs out of them like I had done previously, I was going to be able - thanks to the machines they offer - to melt scrap plastic into boomerangs. The first step was to build the injection machine, the second to make a mold. The objective is not to detail here all the stages of the construction of the injection machine, the video below does it very well. On the other hand, I explain how to simply make a mold (you still need a little tooling) and some preliminary results of my experiments.
The Precious Plastics website
Precious Plastic's tutorial for making the injection machine This video explains in detail how to build a plastic injection machine, this realization requires an advanced level of DIY and a minimum of equipment.
Making the mold Once the injection machine is ready, you need a mold. The form reproduced here is a Manicosaurus, boomerang by Nico FastNico [Courtesy of his close friends]. If you have access to a machine that can do water or laser cutting, it will make the job even easier, but these machines are truly attached to the world of heavy industry. The mold was cut from flat, smooth metal plates 4 mm thick. The mold is composed of 3 elements The central element that will receive the molten plastic and will form the future boomerang The lower element that closes the mold The upper element, which receives the connector allowing connection to the injection machine The steel plates here were cut with a grinder. The boomerang's imprint is in the centerpiece. Central element of the mold The outer contours of the future boomerang are traced on the central element, - Be careful, the plastic retracts more or less as it cools, make the mold a little larger (the shrinkage depends on the type of plastic) - then they are pointed with a pointerolle so that the drill does not rip when drilling. A margin of two centimeters is provided around the outline of the future boomerang to be able to drill the holes allowing the passage of the tightening bolts. Make holes all along the inside of the outline. Connect the holes together to remove the inside. This operation can be done with a round file, with a hacksaw blade ...
It is necessary to file the irregularities to arrive at the final contours of the future injected boomerang. The surface finish of the edges will be reproduced on your molding. Fine sanding (180 grit) is recommended to have a nice finish appearance.
Drill holes which will allow the 3 elements of the mold to be assembled. I don't know what is the minimum number of tightening points to put in place, maybe less is possible but I wanted to insure it for the first try.
Lower mold element To make the lower part of the mold, take the exterior outline of the central element and cut the plate along the same outline. Transfer the holes of the central element of the mold to the lower element and proceed to drill the fixing holes of the elements between them (outer holes).
Upper part of the mold These are the same steps as the lower element. Once this element is done, drill a hole in its center to weld the nipple that is screwed onto the injection machine.
Once the 3 elements have been drilled, the connector welded and the central element cut out, the mold is finished. Here's another mold fro trick catch:
Injection Before molding, the plastic must be prepared for injection, i.e. cut it into small pieces (or better to reduce it to granules) so that it can enter the heated part of the injection machine, where it will melt.
Switch on the machine, let it heat up for 5 minutes until it reaches the desired temperatures (around 200 degrees C) Place the plastic fragments in the tube. Leave to heat (depends on the type of plastic, the quantity, etc.) for about 5 minutes
Screw the mold to the machine then the actual injection phase. I choose to leave the assembly under pressure for around 10 seconds, because industrial processes also leave injections under pressure for a few seconds. I don't know what is the benefit of this operation, but I do it too.
At first, the injection may not be complete. Either you have not put in enough material, or the plastic is not melted enough / not hot enough, or the mold is too cold (this problem disappears after the second consecutive injection).
If all went well, well done you have your draft to profile Some tests:
Simple polypropylene assemblies from different origins (gray pp plates for boomerangs, but also blue pp bottle caps, a little pp from broken pink plastic chair).
ASA, Rigid and quite heavy (more than pp but less than pp + gf40) Plastic similar to ABS but resistant to UV
Remember to put a dust collection bin when sanding your blanks, to be able to recast them into boomerangs.
The flight test Here is a test video of a speed made in Polypropylene TD20 (Talc 20%) from recycled auto parts. Wind conditions between 10 and 15km / h. [This boomerang was used during the Moirans tournament on August 29 and 30, 2020 to take second place in FC and fourth in endurance (51 catches)]
Another fast catch test Polypro fast catch test with 40% fiberglass
Warning // Security. Protect yourself, pay attention to your health, respect the safety instructions of the machines you use. Wear a mask, goggles and gloves, the mold is hot after injection (over 100 degrees C) Vacuum all plastic dust for recycling, do not throw your plastic waste in nature, put it in the recycling circuits provided for this purpose. Watch out for vapors from hot plastics.