Industrial Metal Detection Ideas?

[Christopher Ott]

Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal wood
recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

These are generally 500 to 1000 HP diesel units made by many several
different companies. They run debris through a rotor/grating assembly and
produce chips on the other end. They are used for a number of other
applications (compacting roofing shingles for landfill, chipping railroad
ties, etc.), but the most typical use is by landscaping suppliers who turn
yard debris and slash piles into landscaping mulch.

The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth and
other large, heavy objects will break the teeth off the rotor and blow out
bearings. This causes several hours to several days of downtime.

I'm looking into methods of detecting this contamination before it hits the
rotor. This is complicated by the fact that the hopper is steel, as is the
drag chain used to pull the material into the rotor. Non-metallic drag belts
are far too fragile and are not commonly used on the infeed side. Also the
loader bucket which dumps material into the hopper does tend to confuse
traditional metal detection technology.

Here's what's been tried:

Traditional metal detection coils. The large amount of steel on three sides,
and drag chain made the output virtually worthless. This technology could
not determine a difference between a tin can (which can safely pass through
the rotor and be picked out with a magnet) and sledgehammer head.

Vibration sensors on the bearings: This does work to a certain extent.
Sometimes (like with a railroad spike in a tie) the high frequency ticking
of the rotor bits hitting the metal can be sensed and the load can be
reversed and dumped out the back to be sorted. However what more commonly
happens (with loose metal) is the system simply senses the hit milliseconds
before the contamination gets pulled in and destroys the bits.

What I'm curious about is if anyone out there has seen this problem solved
before. Perhaps in a different application which I can leverage to this one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to any
input...

Thanks!

Christopher Ott
Ott Electronics Corp.
Chandler, AZ, USA

 

[Larry Brasfield]

"Christopher Ott" <spamtrap@ottelectronics.com> wrote in
message news-mdnXil-JFSSO7fRVn-iA@giganews.com...

Hi Folks,
Hi.
I'm exploring the feasibility of inline metal detection for horizontal wood recyclers. Here is a link to a photo of a typical
recycler.

http://www.ottelectronics.com/images/recycler1.jpg

These are generally 500 to 1000 HP diesel units made by many several different companies. They run debris through a rotor/grating
assembly and produce chips on the other end. They are used for a number of other applications (compacting roofing shingles for
landfill, chipping railroad ties, etc.), but the most typical use is by landscaping suppliers who turn yard debris and slash piles
into landscaping mulch.

The metal contaminations occurs when large pieces of steel get into the piles. Axes, sledgehammers, rebar, railroad spikes,
loader-bucket teeth and other large, heavy objects will break the teeth off the rotor and blow out bearings. This causes several
hours to several days of downtime.

I'm looking into methods of detecting this contamination before it hits the rotor. This is complicated by the fact that the hopper
is steel, as is the drag chain used to pull the material into the rotor. Non-metallic drag belts are far too fragile and are not
commonly used on the infeed side. Also the loader bucket which dumps material into the hopper does tend to confuse traditional
metal detection technology.

Here's what's been tried:

Traditional metal detection coils. The large amount of steel on three sides, and drag chain made the output virtually worthless.
This technology could not determine a difference between a tin can (which can safely pass through the rotor and be picked out with
a magnet) and sledgehammer head.

Vibration sensors on the bearings: This does work to a certain extent. Sometimes (like with a railroad spike in a tie) the high
frequency ticking of the rotor bits hitting the metal can be sensed and the load can be reversed and dumped out the back to be
sorted. However what more commonly happens (with loose metal) is the system simply senses the hit milliseconds before the
contamination gets pulled in and destroys the bits.

What I'm curious about is if anyone out there has seen this problem solved before. Perhaps in a different application which I can
leverage to this one. Also, any thoughts on sensors which might work. Other ideas? I'm open to any input...

I once developed a metal detection scheme that I
believe could be adapted to your requirement. It
would need some post-processing of its output to
handle the varying aspects of the metal legitimately
in the equipment. But it can readily be made to
ignore constantly present metal and respond to
changes with good sensitivity and low drift. The
changes could, I believe, be processed together
with chain movement information to filter out the
changing component due to the chain links moving
through the detection field.

The basic idea is pretty simple, amounting to a
way of detecting minute changes in the portion
of an AC magnetic field reflected from targets,
where the excitation field is produced by a fixed
arrangement of coils.

Please feel free to contact me if interested in a
detailed discussion of this. I'm in the Seattle metro
area phonebook.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Dan Mills]

Christopher Ott wrote:

Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal
wood recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

<Snip>

The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth
and other large, heavy objects will break the teeth off the rotor and blow
out bearings. This causes several hours to several days of downtime.

Look at the mining industry which has exactly the same problem.

I have seen a setup in a old tin mine which actually went the other way and
used large electromagnets to trap ferrous junk (on the poles) before the
rock crushers.

Could you run the incoming feed over a pair of pole pieces which would both
attract any ferrous scrap and (by means of a small AC current riding on the
DC supply) detect the change in inductance when the ferrous scrap reduces
the air gap?

Just a thought.

Regards, Dan.

 

[Joerg]

Hello Christopher,

It seems that you would need a directional RF field that is applied on
one side and detected on the other. The steel hopper should not pose a
problem if the antennas are mounted in a flat and sturdy housing that is
sleek enough not to obstruct the passing materials, or recessed. The
drag chain could most likely be detected and ignored via a pattern
recognition algorithm. As an added benefit you might even be able to
detect damage (irregularity) to the chain before it is beyond repair.

The loader bucket is a problem but for this scheme to work you would
have to restrict loading to the far end anyway. Else there wouldn't be
enough time to stop the diesel or for the spin-down if using a clutch.
So you could mount the RF scheme just past that point. If you don't,
chance are someone drops a bucket tooth or sledge hammer piece just
beyond the sensors and it goes in undetected.

Distinguishing between a soda can and a bucket tooth will be the real
challenge. If you can't live with such false alarms this would probably
require some ultrasound.

Regards, Joerg

http://www.analogconsultants.com

 

Christopher Ott <spamtrap@ottelectronics.com> wrote:

The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth
and other large, heavy objects will break the teeth off the rotor and
blow out bearings. This causes several hours to several days of downtime.

Dump incoming material into a tank of hydric acid first and agitate it.
The hydric acid attacks the steel and causes it to separate from the
wood. The wood can then be retrieved and put into the recycler.
Unfortunately, I understand that for environmental reasons, hydric acid
is difficult to come by in Arizona.

Matt Roberds

 

[John Woodgate]

I read in sci.electronics.design that mroberds@worldnet.att.net wrote
(in <YU1de.323$gc6.23@okepread04&gt about 'Industrial Metal Detection
Ideas?', on Sun, 1 May 2005:

Christopher Ott <spamtrap@ottelectronics.com> wrote:
The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth
and other large, heavy objects will break the teeth off the rotor and
blow out bearings. This causes several hours to several days of downtime.

Dump incoming material into a tank of hydric acid first and agitate it.
The hydric acid attacks the steel and causes it to separate from the
wood. The wood can then be retrieved and put into the recycler.
Unfortunately, I understand that for environmental reasons, hydric acid
is difficult to come by in Arizona.

Hydric acid is extremely dangerous, especially when in concentrated

form. It is safe to drink if diluted with ethyl hydroxide.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Rene Tschaggelar]

mroberds@worldnet.att.net wrote:

Christopher Ott <spamtrap@ottelectronics.com> wrote:

The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth
and other large, heavy objects will break the teeth off the rotor and
blow out bearings. This causes several hours to several days of downtime.


Dump incoming material into a tank of hydric acid first and agitate it.
The hydric acid attacks the steel and causes it to separate from the
wood. The wood can then be retrieved and put into the recycler.
Unfortunately, I understand that for environmental reasons, hydric acid
is difficult to come by in Arizona.

Aah, the dreaded dihydrogen monoxide.
http://www.dhmo.org/

Rene

 

[Rich Grise]

On Sat, 30 Apr 2005 12:02:33 -0700, Christopher Ott wrote:

Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal wood
recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

[very good homework snipped]

What I'm curious about is if anyone out there has seen this problem solved
before. Perhaps in a different application which I can leverage to this one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to any
input...

Make the whole machine out of Inconel?

Good Luck!
Rich

 

[John Woodgate]

I read in sci.electronics.design that Rich Grise <richgrise@example.net>
wrote (in <pan.2005.05.01.19.53.29.210195@example.net&gt about
'Industrial Metal Detection Ideas?', on Sun, 1 May 2005:

What I'm curious about is if anyone out there has seen this problem solved
before. Perhaps in a different application which I can leverage to this one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to any
input...

You were given the answer in the post about 'hydric acid'.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Graham Orme]

In message <D-mdnXil-JFSSO7fRVn-iA@giganews.com>, Christopher Ott
<spamtrap@ottelectronics.com> writes

Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal wood
recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

(snip)
What I'm curious about is if anyone out there has seen this problem solved
before. Perhaps in a different application which I can leverage to this one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to any
input...

How about x-raying it. Video the fluorescent screen and use a threshold

detector on the video signal to pick out the solid objects.

--
Graham

 

[Christopher Ott]

This is the solution I'm currently looking at. An array of low power RF
transmitters on one side pulsing in sequence, and a receiver array on the
other side looking for shadows. The challenge is synching the TX and RX to a
very narrow time frame to ignore any signal reflections.

Unfortunately this does still allow tin cans to fake out the system. How
would you use ultrasound to distinguish them?

Chris


"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:9mSce.3027$zu.2873@newssvr13.news.prodigy.com...

Hello Christopher,

It seems that you would need a directional RF field that is applied on one
side and detected on the other. The steel hopper should not pose a problem
if the antennas are mounted in a flat and sturdy housing that is sleek
enough not to obstruct the passing materials, or recessed. The drag chain
could most likely be detected and ignored via a pattern recognition
algorithm. As an added benefit you might even be able to detect damage
(irregularity) to the chain before it is beyond repair.

The loader bucket is a problem but for this scheme to work you would have
to restrict loading to the far end anyway. Else there wouldn't be enough
time to stop the diesel or for the spin-down if using a clutch. So you
could mount the RF scheme just past that point. If you don't, chance are
someone drops a bucket tooth or sledge hammer piece just beyond the
sensors and it goes in undetected.

Distinguishing between a soda can and a bucket tooth will be the real
challenge. If you can't live with such false alarms this would probably
require some ultrasound.

Regards, Joerg

http://www.analogconsultants.com

 

[Christopher Ott]

This would require a large swimming pool of acid be kept on site at
thousands of yard waste companies worldwide. We're talking about huge
volumes of debris being processed daily. One machine can fill a large semi
trailer in under an hour.

It would be quite a sight however, seeing hydric acid drenched mulch melt a
whole truck...

Think harder Homer...

Chris


<mroberds@worldnet.att.net> wrote in message
news:YU1de.323$gc6.23@okepread04...

Christopher Ott <spamtrap@ottelectronics.com> wrote:
The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth
and other large, heavy objects will break the teeth off the rotor and
blow out bearings. This causes several hours to several days of downtime.

Dump incoming material into a tank of hydric acid first and agitate it.
The hydric acid attacks the steel and causes it to separate from the
wood. The wood can then be retrieved and put into the recycler.
Unfortunately, I understand that for environmental reasons, hydric acid
is difficult to come by in Arizona.

Matt Roberds

 

[Christopher Ott]

Given the current cost of steel, it might actually be cheaper!

Chris


"Rich Grise" <richgrise@example.net> wrote in message
newsan.2005.05.01.19.53.29.210195@example.net...

On Sat, 30 Apr 2005 12:02:33 -0700, Christopher Ott wrote:

Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal
wood
recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

[very good homework snipped]

What I'm curious about is if anyone out there has seen this problem
solved
before. Perhaps in a different application which I can leverage to this
one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to
any
input...


Make the whole machine out of Inconel?

Good Luck!
Rich

 

[Christopher Ott]

Is it possible to safely x-ray material outside of an enclosure?

Chris


"Graham Orme" <xxx@xxx.xxx> wrote in message
news:2+dSSWDa69cCFwHF@ntlworld.com...

In message <D-mdnXil-JFSSO7fRVn-iA@giganews.com>, Christopher Ott
spamtrap@ottelectronics.com> writes
Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal
wood
recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

(snip)
What I'm curious about is if anyone out there has seen this problem solved
before. Perhaps in a different application which I can leverage to this
one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to
any
input...

How about x-raying it. Video the fluorescent screen and use a threshold
detector on the video signal to pick out the solid objects.

--
Graham

 

[John Woodgate]

I read in sci.electronics.design that Christopher Ott
<spamtrap@ottelectronics.com> wrote (in
<_LGdnUBEXOSL8uvfRVn-2A@giganews.com&gt about 'Industrial Metal Detection
Ideas?', on Mon, 2 May 2005:

This would require a large swimming pool of acid be kept on site at
thousands of yard waste companies worldwide. We're talking about huge
volumes of debris being processed daily. One machine can fill a large
semi trailer in under an hour.

It would be quite a sight however, seeing hydric acid drenched mulch
melt a whole truck...

Think harder Homer...

No, YOU think harder. 'Hydric acid' is one of the humorous chemical
names for WATER.

Separation by flotation is a very well-known technique for the sort of
operation you are involved in, from coal mining to gold mining.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Poul Bundgaard]

Christopher Ott wrote:

Is it possible to safely x-ray material outside of an enclosure?

Isn't that what they do at airport check-in ?

 

[Rich Grise]

On Mon, 02 May 2005 11:18:59 -0700, Christopher Ott top-posted:

This would require a large swimming pool of acid be kept on site at
thousands of yard waste companies worldwide. We're talking about huge
volumes of debris being processed daily. One machine can fill a large semi
trailer in under an hour.

It would be quite a sight however, seeing hydric acid drenched mulch melt a
whole truck...

Think harder Homer...

Maybe if you looked up "hydric acid":
http://www.dhmo.org/msdsdhmo.html

Cheers!
Rich

mroberds@worldnet.att.net> wrote in message
news:YU1de.323$gc6.23@okepread04...
Christopher Ott <spamtrap@ottelectronics.com> wrote:
The metal contaminations occurs when large pieces of steel get into the
piles. Axes, sledgehammers, rebar, railroad spikes, loader-bucket teeth
and other large, heavy objects will break the teeth off the rotor and
blow out bearings. This causes several hours to several days of downtime.

Dump incoming material into a tank of hydric acid first and agitate it.
The hydric acid attacks the steel and causes it to separate from the
wood. The wood can then be retrieved and put into the recycler.
Unfortunately, I understand that for environmental reasons, hydric acid
is difficult to come by in Arizona.

Matt Roberds

 

[Christopher Ott]

Oops.

Regardless of my failure as a chemist, separating large debris piles in
water is not practical. This would add a considerable amount of time to the
process and the added weight of the processed mulch would reduce the amount
which could be trucked around. It would have to be dried first adding even
more complexity. We can already find metal by pre-processing the material
through a separate detector. What I'm looking for is methods of detecting
in-process on the existing machine.

Hydric Acid.... (smart ass)

Chris


"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:uclf$Reu0ndCFwvu@jmwa.demon.co.uk...

I read in sci.electronics.design that Christopher Ott
spamtrap@ottelectronics.com> wrote (in
_LGdnUBEXOSL8uvfRVn-2A@giganews.com&gt about 'Industrial Metal Detection
Ideas?', on Mon, 2 May 2005:
This would require a large swimming pool of acid be kept on site at
thousands of yard waste companies worldwide. We're talking about huge
volumes of debris being processed daily. One machine can fill a large semi
trailer in under an hour.

It would be quite a sight however, seeing hydric acid drenched mulch melt
a whole truck...

Think harder Homer...

No, YOU think harder. 'Hydric acid' is one of the humorous chemical names
for WATER.

Separation by flotation is a very well-known technique for the sort of
operation you are involved in, from coal mining to gold mining.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Rich Grise]

On Mon, 02 May 2005 11:23:13 -0700, Christopher Ott top-posted:

Is it possible to safely x-ray material outside of an enclosure?

They seem to do it at the airport.

Cheers!
Rich

Chris


"Graham Orme" <xxx@xxx.xxx> wrote in message
news:2+dSSWDa69cCFwHF@ntlworld.com...
In message <D-mdnXil-JFSSO7fRVn-iA@giganews.com>, Christopher Ott
spamtrap@ottelectronics.com> writes
Hi Folks,

I'm exploring the feasibility of inline metal detection for horizontal
wood
recyclers. Here is a link to a photo of a typical recycler.

http://www.ottelectronics.com/images/recycler1.jpg

(snip)
What I'm curious about is if anyone out there has seen this problem solved
before. Perhaps in a different application which I can leverage to this
one.
Also, any thoughts on sensors which might work. Other ideas? I'm open to
any
input...

How about x-raying it. Video the fluorescent screen and use a threshold
detector on the video signal to pick out the solid objects.

--
Graham

 

[Joerg]

Hello Christopher,

This is the solution I'm currently looking at. An array of low power RF
transmitters on one side pulsing in sequence, and a receiver array on the
other side looking for shadows. The challenge is synching the TX and RX to a
very narrow time frame to ignore any signal reflections.

Time domain will be really tough. I'd start with reflectivity
measurements, very high frequencies etc. But you would have to stay in
an ISM band, else the goons show up some day ;-)

Unfortunately this does still allow tin cans to fake out the system. How
would you use ultrasound to distinguish them?

I am not very familiar with ultrasound through air. My home turf is
medical ultrasound. There we can echo through thin walls whereas hard
calcifications are tough to penetrate. But we are able to see, for
example, two layers of calcification, something that can indicate a
dangerous condition in the medical world (if one flies off it can cause
an obstruction and that can lead to a stroke).

I'd research this in the NDT field, they deal with that all the time. In
the soda can case it would boil down to detecting the cavity. IOW, if
the beam passes metal and there is no detectable cavity then the
probability that it is a large and dangerous chunk of metal is high.

You probably also need some magnetic field measurements. It's not only
the occasional soda can but also a hard fresh piece of manzanita that
could fool the system or a full water bottle that got dropped in there.

Magnetic fields can't really be realized with loops in this case because
of the loader bucket. You need a more defined field such as the one
between separated transformer core halves.

Another thought to keep in mind is materials. Teeth from a bucket will
usually be of a good quality steel whereas soda and beer cans are mostly
aluminum. Unless someone throws away a Campbell's soup can but that's
rather rare these days except maybe around clandestine camping areas.

Regards, Joerg

http://www.analogconsultants.com