Demagnetiser Design.

Check here

https://www.google.com/search?q=demagnetizer+coil&rlz=1T4PRFF_enUS585US585&tbm=isch&imgil=S68K2WQyvFmYHM%253A%253BKWreHCEhXx6ISM%253Bhttp%25253A%25252F%25252Fgould-bass.net%25252Fmagnetic-particle-inspection-systems%25252Fdemagnetizers&source=iu&usg=__If0hzoT6dvBk4_iFz7mSdQNVUAk%3D&sa=X&ei=dAvbU_f9OKri8gHsuYHoCQ&ved=0CFIQ9QEwBg&biw=1264&bih=544#facrc=_&imgdii=_&imgrc=S68K2WQyvFmYHM%253A%3BKWreHCEhXx6ISM%3Bhttp%253A%252F%252Fgould-bass.net.temp.realssl.com%252Fwp-content%252Fuploads%252F2010%252F11%252FDemagnetizertoo-300x277.jpg%3Bhttp%253A%252F%252Fgould-bass.net%252Fmagnetic-particle-inspection-systems%252Fdemagnetizers%3B300%3B277

Interesting, many years ago when I ran a flat bed grinder with a magnetic bed, the bed had a built-in demagnetize function when you turned it off.

Same for the ones I used. Its many years ago, but I'm fairly sure they were made by Eclipse.

Here is a link to what we use in our NDT department after magnetic inspection.

http://www.ndtunlimited.com/magenetic-particle-equipment (scroll to bottom of page)

There are a couple of other manufacturers out there.

Good luck ;)

800 turns of #22 enameled wire will do it.

Remember,it is for intermittent use,and must have a short duty cycle,not for

continuous,repetitive production-line type use.

You will need a very good momentary switch switch or push button to handle the

initial inrush current.

An automatic circuit could be designed to automatically taper down the current to

the coil,which is desired,to prevent a sudden turn off from re magnetizing the object

of interest.

If you need more info, let me know.