Forum Etiquette inquiryIs it rude to ask how to design a home project?

[mikedunbar]

Hello... I'm trying to figure out how many magnets I need to put on one side of a piece of sheet metal in order to sufficiently magnetize all the surface area of the other side to a specific attractive force to other pieces of steel in contact with the sheet. It has been too long since college. I can't remember how to calculate this.

Is it rude to ask here?

It's not for commercial use. I want to magnetize a big piece of sheet metal, hang it in my garage, and keep tools on it, wrenches and sockets and such.

 

[mikedunbar]

I guess the gist of my question is: Does the attractive force of the magnet diminish with distance regardless of whether a ferrous or non-ferrous material occupies that intervening distance?

 

[Danger]

Welcome to PF, Mike. It's not rude at all. That's what we're here for. Unfortunately, your particular subject matter is not within my arena of knowledge. Someone else will be along to help you, though.

 

[Bobbywhy]

mikedunbar, Welcome here to Physics Forums!

Since there are so many unknown variables it appears not useful to try to calculate "how many magnets..." My suggestion is get yourself lots of magnets, put up the sheet metal, and hang up your tools using the trial and error method.

 

[mikedunbar]

mikedunbar, Welcome here to Physics Forums!

Since there are so many unknown variables it appears not useful to try to calculate "how many magnets..." My suggestion is get yourself lots of magnets, put up the sheet metal, and hang up your tools using the trial and error method.

That's kind of what I did. I found a magnet vendor who had a calculator which showed pull from various sized magnets at various distances. It turns out that the reason you don't see big magnetic walls is that the magnets required are not cheap at all.

Unless there is a way to make a big flat electromagnet, and I think there is not, this is another of my ideas which has come and gone.

The only way it could still possibly work with neodymium magnets is if steel somehow amplifies their power, and that question is still open.

I've sent twenty emails to members of university physics clubs with this question, and I'll wait on more astute replies from this august body, as well.

Thanks for your reply.

 

[Bobbywhy]

I would recommend against hoping steel is going to amplify magnets' power! Our revered conservation laws prohibit getting a "free lunch".

 

[mikedunbar]

I would recommend against hoping steel is going to amplify magnets' power! Our revered conservation laws prohibit getting a "free lunch".

Yes, but look at this...

<i>Magnetic strength can be multiplied by up to 32 times by using steel armatures to concentrate magnetic flux. Such armatures may take the form of backing plates, channels or cups. The maximum increase in power is obtained when magnets are sandwiched between two plates.

Channel Magnet Assemblies, Industrial MagnetsFor example: A 0.187" thick x 0.750" wide x 1" long rubber magnet has 4 oz. of pull strength. The same magnet bonded to a channel (assembly #RMCH-10) will pull 5 Ibs., which is 20 times greater. Furthermore, the same magnet sandwiched between two plates (assembly #RMSA-10) will pull 8 Ibs.—32 times more than the magnet alone!</i>

 

[sophiecentaur]

The magnetic supports I have seen consist of strips of steel / iron with magnets between them. This is like a horseshoe magnet, in essence. A set of strips with alternating polarity (N S N S N S) would provide an area which would hold your tools. I reckon that only one of these little high strength magnets would be needed between each pair of strips.

=============== strip
N
S
=============== strip
S
N
=============== strip
N
S
=============== strip

etc.

Magnetised tools are not always what you want, though, and they are sure to become that way.

 

[tiny-tim]

velcro

(then you could just chuck 'em at the wall! )