Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Dave Hinz
 
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Default 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...


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Jeff Wisnia
 
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Default Sorting discs by weight

Dave Hinz wrote:

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...




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

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."
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Dave Hinz
 
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Default Sorting discs by weight

On Tue, 18 Apr 2006 22:36:21 +0000, Christopher Tidy wrote:
Dave Hinz wrote:
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.


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.


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

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.


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.

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James Waldby
 
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Default Sorting discs by weight

Dave Hinz wrote:
... Christopher Tidy ...wrote:
Dave Hinz wrote:
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.

....
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.


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.


-- 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
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Christopher Tidy
 
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Default Sorting discs by weight

Dave Hinz wrote:
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...


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



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Default Sorting discs by weight


James Waldby wrote:

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


-- 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.

-jiw


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

Dave

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Christopher Tidy
 
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Default Sorting discs by weight

Dave Hinz wrote:
On Tue, 18 Apr 2006 22:36:21 +0000, Christopher Tidy wrote:

Dave Hinz wrote:

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.



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.



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


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.



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.


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

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Eric R Snow
 
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Default Sorting discs by weight

On 18 Apr 2006 20:26:51 GMT, Dave Hinz wrote:

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...

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
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Ecnerwal
 
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Default Sorting discs by weight

In article ,
Dave Hinz wrote:

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.


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.

--
Cats, coffee, chocolate...vices to live by
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Bob Engelhardt
 
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Default Sorting discs by weight

Dave Hinz wrote:
....
Yup, pennies. Copper is way up, and bullion value of a penny is near 2
cents. ...


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


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Dave Hinz
 
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Default Sorting discs by weight

On Tue, 18 Apr 2006 16:34:57 -0600, James Waldby wrote:
Dave Hinz wrote:


this is more a mind experiment than anything else at
the moment.


-- 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.


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

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


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.

-- Conductivity


Sounds tricky, and surface slag could give false readings.

-- 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.


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

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


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

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Dave Hinz
 
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Default Sorting discs by weight

On Tue, 18 Apr 2006 21:48:45 -0400, Bob Engelhardt wrote:
Dave Hinz wrote:
...
Yup, pennies. Copper is way up, and bullion value of a penny is near 2
cents. ...


Umm - there's 175 pennies in a pound, IIRC. That makes bullion
$3.50/lb.


It's at like $3.05 or so today, but yeah.

A couple of weeks ago I priced copper stock at $3.25. What a
dealer would pay for scrap would be considerably less.


Right, like I said, this is more a mind-game than anything at the
moment. If copper keeps doing what silver and gold have been doing,
though, I'd like to have a workable method in my pocket.

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 a bank willing to be your source... Yup, there are logistical
issues to work out. But even if it's "sort now, store in 5 gallon pails
until it hits 5" or something, well, like I say, more of a mind-game
than anything. THing is, though, the silver coins we took out of
circulation in 1964, are selling for 11 times face value today.

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


Yeah, wouldn't want to do that part, finding a place that takes a known
alloy is the key - or, like I say, use the 5 gallon pails of copper as
thermal mass for a few decades, and leave it for my kids to either laugh
about, or cash in on.

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.


A bit of each. With such a dramatic mass and density difference, it
should be easy...on paper. Where can I get a few gallons of iron
filings, I wonder, without doing it the hard way?

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Dave Hinz
 
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Default Sorting discs by weight

On Tue, 18 Apr 2006 16:46:35 -0700, Eric R Snow wrote:
On 18 Apr 2006 20:26:51 GMT, Dave Hinz wrote:

I'd like to sort a large quantity of disks by weight.


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.


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.

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.


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.
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Dave Hinz
 
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Default Sorting discs by weight

On Wed, 19 Apr 2006 00:43:59 GMT, Ecnerwal wrote:
In article ,
Dave Hinz wrote:

I'd like to sort a large quantity of disks by weight.


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.


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.

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