pole piece

[sminica]

Newest member here, I've enjoyed looking through your threads--great feedback on alot of topics so I had to join.

My question is related to pole pieces to "bridge" two magnets together. I have a weight sensitive application for magnets and I need to stretch or lengthen one NdFeB grade N50 magnet that is 1/4" dia x 1/2" long to 1/4" dia x 1" long, while trying to keep the increase in weight to a minimum and magnetic strength to a maximum. So my thought is to use two magnets with a pole piece between them. What's the best material to use? Is there a rule of thumb for how long the pole piece can be compared to your magnets and still be effective? What kind of losses should I expect?

 

[MagMike]

I'm just taking a guess here, but can you go with a hollow (magnetic) steel tube to connect the magnets? The steel in the tube will hold to the magnets pretty well. I'd recommend matching the OD of the tube to the diameter of the magnets. The wall thickness of the steel tube isn't too critical from a magnetic standpoint (the mechanical strength will probably be more important).

In the situation you describe, I'm not aware of a rule of thumb for optimum length of the pole piece. An N50 magnet is pretty potent, even without the benefit of a pole piece. I wouldn't worry too much about the losses.

 

[sminica]

Yes, good idea and that's what I planned to do. I will keep the steel tube OD at .250 and will play with reducing the internal diameter up to the point it is "saturated" (from what I've been told!). But I'm not sure how long of a pole piece I can have relative to my magnets and still have desired effect.

This is a real challenge for me becasue the .250 x .500 long magnet is already too heavy for my application. It works, but I'd like it to be lighter. But at this point it's more important that I go longer, but I absolutely have to minimize any additional weight.

So is any ferrous steel a good choice or should I try the mumetals I have heard about? Thanks.

 

[prex]

Why not putting the two magnets together?
You should describe how is the full magnetic circuit to allow us for proposing something.
Plain carbon steel is generally good if the cross section is the same as that of the magnets, because it saturates at a fairly higher flux (close to 2 T).
Along the length of any pole pieces there will be additional losses, so you should simply use the minimum length compatible with your geometry.

prex

http://www.xcalcs.com

Online tools for structural design

 

[sminica]

I'm trying to save weight by using pole piece that I can have a thinner wall than the magnets.

My application is pretty complicated (for me at least, maybe not for you guys), but it's certainly complicated to describe. Actually it's an idea and product out of my hobby that I'm trying to make improvements on. If I needed to post a drawing or picture to show the applications, what's the easiest way?

 

[nbucska]

sminica:
If you post it, you can't patent it !!!!


Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[sminica]

nbucska, thanks for the warning, but actually, you get one year to patent it after public show. You just have to hope that nobody beats you to it in the first year! But no worries tho, it is patented, with others still pending.

Is there a way to private message somebody here to get one or two quick opinions before posting to the world?

 

[Skogsgurra]

Have a look at faq238-1161. There are instructions on how to post pictures.

Gunnar Englund

http://www.gke.org