Do a search in this forum for 1018 steel (which is close enough to 1020).  This question comes up every few months.

I graphed the data I found searching for 1018 steel. Can you check the attached excel graph and see if that fits an actual graph for the steel?  

• http://files.engineering.com/getfile.aspx?folder=b48d12d9-bc4f-48f1-a5ae-d9

The curve appears to be a bit generous.

Try getting a 2D FEA package such as Infoytica's Magnet to solve your problem.

Or post enough information such that we can make reasonable comments.

Mike

Sorry about the delay, my password got messed up and they haven't responded to my request for help. Anyway

The curve came from data in the 1018 thread you referred me to . I converted the units into CGS and graphed them in excel. That is why I wanted to double-check the values I got.

As for information, I need the info for a question I posted in an adjacent thread. I'm looking to put a covering around the sides, not the poles, on a 1 inch cubic n38 magnet, with the intention of containing all the flux not on, or in front of, the poles.

I tried looking at the cap formulas in Moskowitz's book, but they didn't involve size. That is why I'm asking here.

thanks for the help

You can better be helped now.
1018 steel will begin to saturate at about 16,000 gauss. So for a conservative design that minimizes flux being driven outside it would be best to stay below that level.

The Br for N38 will be about 12300 gauss or 6150 measured on the surface. A one inch cube then has about 15600 lines of flux. To keep most of your flux in will require a bit more than 0.5 square inches of steel or a 1/8 inch wrap. More will be a little better.

Fringe flux will still exist.

Mike

Can you please tell me the formula(s) and data sources to make such calculations?

For the project I'm working on, variables such as magnet size, grade, and proximity to other flux sources aren't set yet, so I expect to need more calculations such as the permeance of the cap so I can figure a safe distance from other fluxes.

It might also be easier for both of us if you could refer me to where I could learn such things instead of having to ask for help every time I come up with a new difficulty.

thanks!

 

Typically on the face of the magnet you will measure a field strength of about one-half the Br. That's a quick and rough number.

Gauss is number of lines of flux per square centimeter.

You want to 'short' the flux lines to return to the other end of your magnet. You do that by placing the steel wrap. However having the ends open allows some of the flux to spread out. That is what is causing the fringe field.

If those flux lines run into saturated steel they will travel in air. Make your steel thick enough to not be saturated.

There are calculators for permanent magnets on the web. There are free 2D FEA packages. With reasonable accuracy and creativity this problem may be reduced to 2D.

Mike