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Industrial Metal Detection Ideas?

C

Christopher Ott

Jan 1, 1970
0
Hello 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
 
R

Robert Baer

Jan 1, 1970
0
Christopher said:
Hello 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
At least you have a partial "solution" using sound (the unique noise).

First dumb thought i had, is to add a "pre-chopper" that uses
flexible metal "bits" that do not get mangled by anything; their
function is to create that metallic noise before the junk gets to the
working chopper.
Naturally, there is a trade-off here, as the "flexible bits" need to
be strong enough to dig thru the wood, etc to "find" buried metal, but
flexible enough for minimal damage when they do hit metal.
So, they should be easily replaceable in the field, and sufficent
spares should be on site (presumes cheap "flexible bits").

Next dumb idea was to use sound (or RF) for determinimg density; an
engineering challenge.
 
A

Andy P

Jan 1, 1970
0
On the flexible "bit" front, as was mentioned earlier..why not use
chains? Beat the heck outta them with rotating chains akin to mine
clearing devices. Chances are that the dense metal of the contaminants
wont be damaged by the chains, but the wood sure will.

Another thought is a thermal camera. Run everything through a pseudo
induction heater (like put a heating coil above the conveyor for a few
feet) and then after that put a thermal camera. The metal pieces will
hold heat longer than the wood, and you should be able to pick up the
temperature differences and stop the feed before anyhting damaging gets
into the machine.
 
C

Christopher Ott

Jan 1, 1970
0
Actually, flail chains are used in a similar product, a debarker. The chains
pound the bark off the tree before it's fed into a chipper. The problem with
flail chains is that they work much, much slower than hardened bits. The
overall throughput of the system cannot be reduced (or no one would buy it.)

The temperature profiling idea is do-able, but would be a severe safety
hazard. Remember there's tons of dried organic material everywhere around
these machines. barkdust, gasoline, diesel fuel and acres of (quite
flammable) mulch piles everywhere around this equipment.

Good ideas, lets keep em coming,

Chris
 
J

Jim Douglas

Jan 1, 1970
0
OK, this might be off base but what about some type of XRAY equipment like
at the airports, have someone sitting there watching the crap going in at
the beginning. Another idea is a "large magnet" on one side of the box in
front so that anything
with metal within it would move to that side??

I remember seeing a demo movie of a large metal chipper\shredder, they were
dumping in cars, metal buildings, refridgerators, air conditioners, big
stuff and this thing chewed it up quicker than a dog that had missed a meal,
cool technology!
 
M

MG

Jan 1, 1970
0
Christopher Ott said:
Hello 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

A section of the magazine/shoot, far from the chipper blade, could be made
of wood or aluminum and improve the sensitivity to magnetic field.

The material could go through or above a coil which is part of an
oscillator, steel will detune the frequency which can be measured easily,
usually this method is very sensitive and frequency drift is proportional to
the quantity of steel, a threshold can be set. Still a window transparent
to magnetism is necessary, no steel structure near the coil.

Ultrasound (choose a frequency much above the rattle and vibrations) the
echo should be stronger from large metal than wood.

Let us know which solution will finally work.

MG
 
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