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Beefing up shredder for wire & circuit boards

This topic contains 5 replies, has 3 voices, and was last updated by  mike 3 weeks ago.

mike kde5fan

Beefing up shredder for wire & circuit boards

23/03/2019 at 18:56

I’m looking into building some version of your shredder, it would be much wider (probably 18-30″ wide and maybe 4 rows of cutting blades) and I’d beef up the hex rod. I’d also be able to control change the speed of the shredder and slow it down for things like circuit boards and heavy wire.

It Depending upon how small the final product needs to be I might create a secondary shredder to create a finer grind. This should need much less “beefyness”.

I’m wondering if anyone has tried to do 2 levels of shredders, one to get coarser pieces and then one underneath that one (or a separately fed one with the larger peices).

I am thinking about using 1/4″ stock, possibly spring steel (which will be hardened then heat treated/normalized) because I can get it almost free. For the larger machine I’m thinking of doing 1/2″ thick blades by welding the two pieces together (maybe drill a hole in the blades & place a metal rod in the hole, then weld it and grind it till flat). I’d also weld the edges and grind till flat.

For the larger machine, I’m thinking 3/4″, 7/8″ or even 1″ hex rod. IDK if 1″ is overkill though.

What I’m most curious about is for the smaller shredder when working with plastics, wire, circuit boards and maybe some other things, is if there is a way to make the bits smaller without using that screen. Is it possible to change the design to allow for more fine shredding? IDK what your standard blade width is, I thought I saw 6mm ( just under 1/4″), but have you tried using ~3.5mm (1/8″ here) for the blades? That would give smaller pieces I think

I’ve seen some new paper shredders that are called “micro-cut” shredders that make little squares of paper that are about 6mm ^2. I’ve seen these items being sold, but I’ve never seen the insides of these or what the blades look like. This micro shredding would be ideal for plastics and wire (help separate the insulation).

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24/03/2019 at 13:37

Smaller teeth (width and height) will shred into smaller pieces without using a screen.

For the larger shredder you are talking about, 1″ hex rod will be no way near big enough, the standard shredder uses 27mm hex (1.062″) and that’s just about adequate, the end turned down to 20mm can shear with a powerful motor if it jams.

24/03/2019 at 14:42

Wow, thanks for the information!  I was going off the stats from another YT video where they were using 13mm or 16mm hex as the drive shaft, but that was strictly for plastic.

Yeah, it makes sense that the shaft needs to be beefy, especially the longer it is because there is more cumulative force put on the end where it connects.

I’m wondering if using square stock would work as well with the difference being how the blades are cut.  The hole would have to be cut at different angles to allow for the blades to be offset by X degrees.   So if you wanted each blade off set by 30 degrees from the next one, then the same size square would be cut into the blade but it would be rotated by 30 degrees from the previous one.

I’ll have to check out torsion strengths of different types of steel.

I’m wondering if anyone has played around with heat treating their blades, like what you do with knife edges.  It’s possible to harden only the cutting area and then allow the rest of it to be something like standard spring steel.  This would allow the edges to retain their sharpness (for much longer)  and not allow the blades to crack under high twisting pressure.

As for a source of metal for this project, I suggest people take a look at an automotive junk yard and look for a heavy duty truck.  Most all have leaf springs, many of which are pretty thick, maybe 3/16 to 5/16  (or 4.75mm to  8mm) – there might be heavier ones on Semi’s (tractor trailers) and buses.  Those would also be wider.  The springs come in layers, each layer getting shorter with anywhere from 3-4 layers up to 7-10 – it all depends upon the weight it needs to support.

Now these might be rusty (and HEAVY) but they always clean up really nicely, it can look horrible, but it’s usually just surface rust.  An angle grinder (with sand paper) works well as well as a wire brush to remove the rust .  Sand/bead blasting is an option. Then there is electrolysis.

Cleaning up the old springs – Electrolysis
This uses electricty to clean two metals and does an excellent job when done correcly probably the best method for a good finish). You will need an elctrolysis tank, which can be a simple 5gal bucket or similar (it depends on size of item).

You need a DC power supply preferably about 4-8v but 12v will also work, though it doesn’t give as nice a finish (satin smooth). The current of the supply will determine how long the cleaning takes, higher current, the faster it wor until you REALLY high currents (like 50-100A on small pieces) then you start having other problems.  Look for a power supply that does 2-20A unless doing a lot at one shot.
You then need an electorlyte, washing soda is suggested (sodium carbonate, Na2CO3) and baking soda (sodium bicarbonate, NaHCO3) will also work but not as well.  You can find washing soda in the laundry detergent isle (usually yellow box – arm & hammar symbol on it).  You can make washing soda by putting baking soda in the oven at 400-500F (about 2 hours for 2lbs) and stir it under a fan every 15-20 mins – it stirs like water even though it’s a powder.

To set up the cell, take the metal to be cleaned and connect the negative wire to it (VERY IMPORTANT) and then with a scrap piece, connect the positive.  If you reversed this, the piece you were cleaning would get more rust on it.  Any piece of scrap steel will work, it should be 20-60% the surface area of the piece you are cleaning (that much/% needs to be under water – it is fine for both to stick out of the water and maybe beter as you can connect your leads out of the water.

As far as the the electrolyte, I’m just guessing but i would say add 1-1.5  cups to ~4 gallons of water (warm to hot water is fine, the cell works better at warmer temps like around 120-140

Here is a site that gives a decent explanation of the process:

If you are looking for a really nice finish, then you can’t use a high voltage (it’s like pressure washing with higher PSI, higher voltage will “eat away” at the metal).  It is safe to run the cell overnight and unattended.  I’d put a circuit breaker on the line (use one of those power strips with one built in) or a ground fault detection breakers (like in bathrooms so you don’t electrocute yourself).

The nasty red “slime” in the picture is just the rust floating inside bubbles.  This is the same rust they use to color bricks, pottery, pavement, paint and thousands of other things. All of this is non-toxic.

If you have any questions, feel free to ask!

25/03/2019 at 13:37

Yes, I hardened and tempered my blades, I made smaller ones though. I used ground tool steel as it’s a very accurate thickness and not that expensive, any small differences in the blades adds up across the whole stack so you’d need to be careful reusing old truck springs. That said they are a good source of steel.

26/03/2019 at 18:31

Just curious. What do you do with shredded circuit boards? Also I thought wire was usually stripped for recycling rather than shredded. How do you use the shredded cable?

28/03/2019 at 05:23

If you have a whole mass of wire consisting of copper, aluminum and some steel bits (connectors) or even steel grounding wire, a shredder can chop it all up and in the process much, if not all the insulation comes off and if it doesn’t come off it can be put back through or there are some other processes for that which aren’t too difficult.  Then the metals are seperated.

So instead of getting $.10 per lb for mixed metal wire with insulation & ferrous material, you can get full price of #1 copper & pure aluminum (both top prices for the metal)  Copper is around $2.90/lb and pure Al $.50-.80+ (and copper was pushing $5 a few years back) so separating it can be profitable,especially if not labor intensive.

As for the circuit boards, well it is similar to the wire, and you have to find yards that want shred and trust that you aren’t giving them gutted boards.  Some people build their own kiln/forges and separate metals out, or do it chemically or via electrolysis.  Some people are after the precious metals like gold, platinum, silver and a few others, others are happier with copper, tin, lead, etc – but it’s all in there and comes out much easier when it is shredded.

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