Sorting discs by weight

I'd like to sort a large quantity of disks by weight. They're 0.75" in diameter and the two type have a mass of either 3.1 grams, or 2.5 grams. Little to no deviation of those two values from sample to sample. I can think of a couple ways to do this in an automated fashion, but I'm interested to know how a problem like this has been solved previously.

Alternately, the disks in question have a different density - SG of one is around 9.0, SG of the other is around 7.0 - is there a reasonable substance with a SG of 8-ish, that I could use to differentiate them by which ones float? I'm thinking not, but...

Reply to
Dave Hinz
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Depending on how many and how often the need will come up, if you had enough funds to devote to the project you might think about this:

Use a vibratory feeder and a "one at a time" escapement mechanism to let the disks slide down a track and over a very lightweight "trap door".

That door would be spring loaded so that it would deflect under the weight of the heavier disks (but not the lighter ones) and let them shoot under the remainder of the track, while the lighter ones would continue sliding down the track a bit further and fall off its end into a different pile.

Jeff

Reply to
Jeff Wisnia

I see that iron powder has a density of 7.9 which is right in the middle.

Yup, pennies. Copper is way up, and bullion value of a penny is near 2 cents. The zinc ones would float on a vibratory bed of iron powder, the copper ones will sink. No clue if it's legal to recycle pennies or who I'd take 'em to, this is more a mind experiment than anything else at the moment.

Reply to
Dave Hinz

-- Attach some solenoids and a digital scale to a computer, and sequence the solenoids to move pennies onto the scale and then to different hoppers depending on the measurement.

-- Have the pennies fall between two plates, with a constant sideways airflow; the lighter pennies will deflect sideways more.

-- Conductivity of zinc is somewhat lower than that of copper (but the copper coating on the zinc pennies might make it hard to measure the difference). I haven't found any references for diamagnetic properties of zinc (except that it has them) so don't know if that property would help in a sorter.

-- Have a "ski jump" to roll the pennies down, or a ballistic launcher to deliver constant specific impulses, and put bins at the right distances to catch each variety.

-- Use your mass spectrometer to sort them out ...

-jiw

Reply to
James Waldby

Molten zinc or tin? Or molten iron, but it'll probably destroy your discs. I can only think of molten metals which have a density that high.

Are these coins by any chance? If so, it might be worth looking at how vending machines work. Some have rather novel ways of sorting coins.

Chris

Reply to
Christopher Tidy

You are attempting to export sensitive nuclear technology with these statements! Please report to the FBI at your earliest convenience...

Dave

Reply to
spamTHISbrp

That's an interesting thought. I don't know if the vibration will disturb the floating effect, but I suspect not. You'll need pretty fine iron powder (maybe with a variety of different particle sizes) to get a density above 7, otherwise the air spaces will take up too much room.

Chris

Reply to
Christopher Tidy

I wonder if they could be slid down a ramp with a gap in it. Direct an air blast up through the gap. Adjust the air so that the heavy pennies drop through while the zinc ones pass on an air cushion. Use a vibratory feeder to feed the pennies one at a time. Or, use image recognition and look at the date as they roll or slide past and use a solenoid to kick the bad ones out. ERS

Reply to
Eric R Snow

Sounds like a good application for the "ramp, launch and catch" sorting method used in some coin sorters. Anything easy to build will likely be slow to use, but that's normal.

Electrical properties probably also vary a lot - could probably use (old hard disk drive - strong) magnets along the ramp to slow them down differently via eddy currents, causing a wider variation in where they land than mass alone would.

Reply to
Ecnerwal

Dave Hinz wrote: ...

Umm - there's 175 pennies in a pound, IIRC. That makes bullion $3.50/lb. A couple of weeks ago I priced copper stock at $3.25. What a dealer would pay for scrap would be considerably less.

I think that sorting is not the biggest problem. Quantity is a bigger problem, I think. Haven't copper pennies been filtered out of circulation, mostly? Or do you already have a whole bunch? It would have to be a *whole* bunch to be worth while. Even 100% profit requires some volume.

And what of the smelting? I haven't melted copper, but I hear it's a PITA for home casters.

Do you have a scrap dealer who will take the ingots, relying on your word for the purity of them? Or take the pennies themselves, again relying on your word that they're gen-u-wine copper?

But then you weren't really serious, were you? It's just an interesting problem: how to sort them.

Bob

Reply to
Bob Engelhardt

"Dave Hinz" wrote in message news: snipped-for-privacy@individual.net...

This problem is solved on a daily basis in industry by the use of check weighers. They are used to sort all sorts of packed products by weight. The product is fed ,one at a time, onto a belt weigher. a load cell weighs each item, then a pneumatically driven arm flicks under weight and over weight items off the sides of the belt. They are able to cope with a rate of about 100 items per minute without much effort.

Reply to
Tom Miller

Actually, a simple analog threshhold circuit with a strain gage could work.

This is similar to my thought of a solenoid with a known mass - the heavier pennies will fly less far, Newton's laws and all that.

Sounds tricky, and surface slag could give false readings.

That's the idea we were just talking about here - hotwheels track type thing.

Nope, can't. The roughing pump bit the dust so right now it's just a really cool, large paperweight.

Reply to
Dave Hinz

Ah. To McGuyver this a bit further, I have a bank-type coin cointer with the rotating plate, so I can get pennies one at a time at a rate of about 7 per second, slower if I change pullies.

I'm hoping for low-tech physics type method but if I still worked at GE, I know exactly which store-room I'd have to raid to pull that sort of thing off.

Reply to
Dave Hinz

Ah. That is a very interesting suggestion, I was playing with coins through the gap of hard-drive magnets just the other day. Should try that & see how I can use it. Get some distance, ramp 'em between the magnets to make the effect subtle enough to use, and have two catching bins.

Reply to
Dave Hinz

[ ... ]

Or -- you could set up something like the coin mechanisms in pay phones or other machines which have to distinguish between them.

Roll the disk on edge down a slot and let it shoot across a gap and hit a solid hardened chunk of steel. Play with the angle of the steel, and then set up secondary chutes where the two different styles bounce, and route them to different bins.

While you're about it, you could set up optical sensors, or low force switches to count the ones of each weight as they go rolling past in their respective chutes.

Enjoy, DoN.

Reply to
DoN. Nichols

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