Aluminum Recycling Micro Factory

So, most of the parts for the Aluminum Recycling Micro Factory are in!

I haven't posted much because I took three weeks off this July but now that I'm back most of what I need has arrived in the mail. Will be posting more updates soon.

Updated the FreeCAD model.

Removed the 20 lb propane tank. Will use that for an accessory resistance heating forge.

I've ordered 4x hot swappable HP 750 Watt Server Power supplies (PN: 660183-001) and will instead be using induction heating to melt aluminum in a crucible instead.

The general idea is going to be that I can use a crucible which can raise and lower into the work coil, melting the aluminum and using 3D printing hardware, dump the molten contents of the crucible.

One potential issue is that the baking ingot trays would need to be heated. However, what if they didn't need to be? What if a steel pipe was used instead?

The steel pipe would obviously get quite hot. But, a steel pipe could also radiate quite a bit of heat naturally. One issue with molten aluminum is that it is possible to trap moisture and steam causes an explosion.

But, if the only direction that the molten aluminum had to go was up, would it splash out of a confined steel cylinder?

I've decided to take a different approach for melting the aluminum.

This is based on a couple of factors. The first is that we can use the principle of induction heating to raise the temperature of the aluminum well past it's melting temperature.

The effect that this has on the aluminum is that any impurities are burned away in the process. This is important as we don't need a separate heater for removing the BPA epoxy liner and the paint on the aluminum soda cans.

It also allows for a much safer method of melting. Raising and lowering a graphite curcible within the work coil means we can effectively create a system that requires no human interaction.

Remember that the whole the whole point of this project is to build something that an operator can dump a bag of aluminum cans into the hopper, turn the unit on and leave unattended. The system should ideally be capable of taking care of every step in the process on it's own.

A Raspberry Pi and/or an Arduino controls the shredder, feeds the shredded aluminum into the crucible, and turns the induction heater on and off, all while monitoring current to detect jams and the state of the metal in the crucible.

An interesting phenomenon exists with the induction heating method. Once the shredded aluminum is dumped into the crucible, the current rises until a certain point. When the aluminum melts, the current drops. This can be used as a signal to feed more shredded aluminum into the crucible.

In order to detect when there's enough molten aluminum to fill an ingot, a load cell will be needed to detect the tare weight of the crucible before being filled and once that point is reached, stepper motors will lower the crucible platform and tip it in order to dump the contents into a mold.

This process is quite a bit safer in terms of semi-automated operation,

This is a brief description of the electronics requirements:

First, we'll need a Raspberry Pi or an Arduino to control things. Among the system's being controlled by the Raspberry Pi or Arduino will be a UL listed voltage relay and PID controller to supply power to the kiln heating wire inside the forge. This will have it's own temperature sensor to measure the temperature inside the forge during operation.

Next, a motor controller will need to supply power to the Windshield Wiper motor shredder and it will need to have a sensor to detect the current being drawn by the windshield wiper motor. The current sensor will need to periodically measure for a surge in current which would indicate a jam. The motor controller will need to go through a jam clearing process that involves reversing polarity to go into reverse and back to forward and repeat this several times until the jam is cleared. The Arduino or Raspberry Pi will need to raise an alarm condition if the jam cannot be cleared automatically and user interaction is needed to clear the jam. Safety features will need to be setup so that in the process of clearing a jam any operator of the system is not put in danger of losing fingers or electrocution.

Additionally, two stepper motors will be needed. One will be for moving a conveyor belt or gate for the shredded pop can material into the forge inlet and another stepper motor will be needed in order to raise and lower a lead screw that tilts a graphite crucible inside the forge and dumps the content of the crucible into a steel spigot that the molten aluminum pours into a revolving tray of bread pan baking trays at aluminum recycling miro factory at it's base. This might need to be another stepper motor, but it can also likely be accomplished using a more affordable low RPM DC motor and a position sensor.

The entire system operation would entail pre-heating the forge with the PID controller, dumping the contents of a plastic bag full of popcan's into the hopper, turning the system on and the shredder would begin shredding and the stepper motor conveyor belt or gate would direct the contents into the forge inlet where it's dropped into the crucible where the contents are melted, it's likely that the stepper motor can be installed on some form of load cell to detect the weight of contents inside the crucible and once a certain threshold is reached, the lead screw can dump the contents onto the spigot plate and be directed into a series of the baking trays revolving at the system's base.

It's likely that additional safety precautions are needed as well. However, the whole system should be able to have a camera and web based monitoring system, a physical warning bell/siren and other safety features involved.

The Precious Plastic project has a number of CAD designs as part of their starter kit.

Included in their starter kit is a design for a plastic material shredder.

The Aluminum Recycling Micro Factory project will be borrowing a number of the design choices from there with a couple of exceptions.

The first is that the first motor to be tested will be the nearly ubiquitous windshield wiper motor. It runs on 12 VDC and has enough torque to hopefully shred popcans.

Since we're going a bit smaller scale than the plastic shredder used by Precious Plastic, the blades will be smaller but the overall design will still utilize plasma cut mild steel.

The first iteration of this backyard recycler design will also use threaded steel rod instead too.

We need to shred pop cans.

The reason we need to shred soda cans first is because melting tiny shredded bits of aluminum is quite a bit easier than it is to melt the soda cans as they are. There is also the BPA epoxy spray on liner inside the can and the paint on the exterior of the can that we need to get rid of first as well.

I've decided that a form factor that is approximately the size of a 3D printer is necessary because getting the materials for doing this means the parts can be sent via regular mail.

We will also be using 2020 aluminum extrusion for the "Aluminum Recycling Micro Factory" because it's commonly available for prototyping.

However, rather than rushing forward and ordering parts it makes sense to first identify what we need to cram into a small volume of space first.

1. A hopper is needed to dump a single large plastic bag full of soda and beer cans
2. The hopper needs to be directly above a shredder
3. A conveyor belt or some form of conveyance needs to direct a stream of shredded aluminum into a stage that involves cooking the BPA liner and the paint off of the aluminum cans
4. Both of the above stages will need to be controlled by an Arduino microcontroller or Raspberry pi
5. Once enough shredded and pre-processed material is collected, it needs to be dumped into a graphite crucible
6. The graphite crucible then needs to be heated to approximately 800 degree's celsius using resistive heating using kiln wire and a PID controller with a high temperature probe
7. Once the aluminum is melted, it needs to be tipped over and dumped into a form of some kind, the most likely choice will be a conventional baking tray to create an ingot