On Thu, 26 Mar 2015 10:46:13 -0700, mike wrote:

On 3/26/2015 10:01 AM, wrote:
On Wed, 25 Mar 2015 19:46:37 -0700 (PDT), "
wrote:

On Monday, March 23, 2015 at 3:01:02 PM UTC-4, wrote:
All,
I have been looking online and have found lots of info but I would
also like to hear from anyone here who has actually done what I want
to do. The goal is to magnetise a heat treated to 40 Rc steel rod that
is .200 in diameter in the radial direction. The area to be magnetised
needs to be about .350" from the end of the rod. The magnetism can be
pretty weak, it only needs to hold a steel sleeve in place for a few
seconds. But the end of the rod must have a very weak magnetic
strength, weak enough that it won't even hold a straight pin.
Thanks,
Eric

I tried to find some information on plain carbon steel, and failed. For four hundred series stainless , the hardened condition retains a lot more magnetism than the annealed condition. Exactly what steel are you planning on using.

It also might make a difference if you have more than two poles when you magnetise the steel.

And when you say straight pin, I assume you are talking about the pins one finds among the sewing supplies.

Dan
Greetings Dan,
You are correct about the pins. I will be using probably 4340 steel
because I can get it in the heat treated condition so that it is
already pretty hard and tough. I only need two poles so that's no big
deal. I think I need to just build a C shaped magnetiser out of some
steel rod, wind some wire around it, and try discharging a cap through
it. Maybe use an old flash unit from a disposable camera since I have
a few of them in a drawer somewhere.
Eric

I'd like to hear some discussion on how this might be done.

If you connect a charged cap to an inductor, you're gonna get a damped
sinusoid determined by R, L and C of the series circuit.
Isn't that exactly what happens with a demagnetizer as you move the
piece being demagnetized away?

If magnetization is a mechanical process that takes time to perform,
there should be some interaction between that process time and the frequency
of the damped oscillation??

The more I think about this the more questions I have.
Seems like you need to maintain current for some minimal time
to allow the magnetic domains to rearrange, then interrupt the
current in a manner that does not allow the inductor current to reverse?????
You know, I think you're right. It seems like the coil and cap would
ring. I'll have to look again at some sites that mentioned discharging
a cap into a coil to make a pulse magnetizer. I know that a lot of
magnetizers work this way, dumping current into a coil. Some turn the
coil on for a brief period using some sort of switch. Others use a
charged capacitor for the power pulse. If a cap and a rectifier are
used in series that would stop the ringing, right?
Anyway, I'll check.
Eric