Design of conveyor belt for extruding thin-gauge stripe of plastic (in progress)

To produce rapidly Plastic@Bay face-shield designs, one solution is to attach an open mould to the extruder, the other is to produce the stripe continuously and then punch it. Being unable to make a mould right now, we are designing a conveyor belt to pull the plastic into an even stripe of plastics.

Choose your weapon

Aluminium doesn’t stick to plastic but copper is actually also very good for that. Our friend is a plumber and cut some lengths for us.

22mm coper pipes, cut to 150 mm lengths

Bearings

Of course we didn’t plan to be in this situation so we had to improvise bearings. The first thing was to try in wood as you would need to have a strong supporting frame. Using a flat bit, you can drill 22 into a plank. If you try to fit the pipe, it will not be able to turn. So we used an old technique to clean the hole, widen it and harden the wood, fire!

It is all well and good but it is not exactly ideal in terms of friction. So we looked into all the piping that washed up over the last years as 22 mm is a standard. We found this, that could be used in the middle to stretch the plastic or at least to maintain tension while cooling. It comes from a pipe extension link

Ideal to make a roller in the middle of the conveyor belt to keep the tension.

So clearly plastic was the best thing we could do at the moment. We thus decided to make the bearings using the fish farm feeder pipes we got 100s m of meter in stock. Cut of a 15 cm section and split it in 4 bits. There should be a overlapping of two bits on each side with one locking the lower roller and one locking the upper roller. Later on when we will know how to space the bearings better, the lower roller will be passive and shorter and the upper one will have the transmission. It is pretty hard to set but you can use ring joints to adjust it in tension.

To avoid deforming the pipes, you need to fill them, The best being sand so went to the beach, got some sand and plugged the pipe with it. You can make an end fill with foil or you can shape a piece of wood. No need to be very tight. That’s some heavy roller you got. Sand is very interesting as it is non-newtonian, the more it is deformed, the more it resists. Other solutions might be too soft (sylicon or foam) or too corrosive (cement)

Then try to make the frame to keep the spacing right. Motor will be a driller with a flat bit. Transmission will need to be thought through. later.

Ready to go on the bench

The overall concept works and we can theoretically produce 1 shield attachment every 2 minutes (29 an hour with the current system).

Here 29 HDPE stripes made in less than an hour

However, it demands an operator permanently keeping the tension right. The copper is really good as the plastic really slides on it. The down side is that even when you rotate with the drill the barrel, you don’t get grip on the hot plastic.

We have redesigned the bench to get more rollers and more tension while the plastic cools. Then we will need to setup some motorization.

The new bench geometry with the motorization at the back where plastic is cooler … to be tested

We have ordered BMX bearings and metal sheets to make the frame adjustable, easier to align and stronger.We will update the page as we progress