Metal detecting

[perfectbite]

Bern, I have been thinking of common types of metals. In the normal recycling waste stream there are basically three kinds of metals used. Aluminium and a tinned mild steel. However there are a lot of other common metals. Copper, lead, brass, various pot metals, food grade 302 or 304 type stainless steel (chrome and nickel and steel), heavily plated chromed articles and, depending on the stream's tributaries, you could even have ground off flecks of carbide and tungsten (maybe with thorium, maybe not) and titanium and copper oxide and silver and gold and flecks of beryllium copper and the higher numbered stainless steel alloys and even magnesium alloys. Some metals are not as rare as they once used to be. Despite your best efforts you may have to accept a sizeable 'tailings' bin (hopefully more mixed metal than plastic) if your plastics stream is polluted with a mixed metal dust and you want your end product to be entirely metal free. Haklesup method may be the way to go. If you want the stuff to be absolutely metal free you'll have to wash the metal dust of it anyway so water or solvent is going to get in there somewhere. (Are these all different plastics?) <p>BTW. 1K# of fine sand, if it got even a little damp, would stand a good chance of clogging in an 1+1/4" pipe if there were the slightest resistance to its flow.<p>[ May 04, 2004: Message edited by: perfectbite ]<p>[ May 04, 2004: Message edited by: perfectbite ]</p>

[perfectbite]

It occurred to me that I did not finish my train of thought in listing some, but not all, commonly encountered metals. Some commonly used metals are toxic and, due to an applied electric field, if the metal particles (all with different electrical resonances) are so fine that gravity doesn't cause them to drop they will form a 'hanging' dust that should not be breathed or ingested.

[Bern]

Thanks for all the help, guys. Just thought I would let you know what direction I finally decided to go. I am using a small coil around a 1 ¼ inch D. plastic pipe. The coil is the tank circuit of an LC oscillator. I then measure the amplitude of the oscillations. It is quite simple to measure this, and see a decrease in amplitude whenever metal, ferrous or non-ferrous, goes through the pipe. As the conductors go through the magnetic field, eddy currents are generated, and this takes energy from the main field. Very simple then to trip an output, and the job is done.

[n7hqk]

How'a'bout using a radar (M/W) door opener? they are available on the surplus market cheap and will respond to a small metalic object passing in front of the antenna. Set up the sensitivity to activate for the size/distance to/through the plastic pipe... (I used a similar system to detect nails in wood...)

[Bern]

Thanks for the return, Ray. Could you pass on a little more info. on that radar system. Any sites I could look it up on? Thanks, Bern - KE7XD

[Bernius1]

Or you can run the conveyor through a heat source & detect it with an IR camera. But that won't sort it. For a waste station, the ballistic arc sounds best, and take the 'mostly metallic' dross, and run it through water, to float out the remaining plastic. You'll have alot less to drying to do.