Halbach array plus steel extension

[SpaceRanch]

I am designing a 16-foot magnetic assembly that will be mounted on a trailer to collect steel wire and scraps off the ground. The long-range (10-inches) field strength is important due to many pieces being partially buried and having uneven ground. The basic idea involves a Halbach array of neodymium magnets enclosed in an aluminum housing. If I want to extend the field even farther would adding a steel bar to the strong side of the array increase the strength of the field farther out or would it cancel the advantages of the Halbach Array?

The additional steel would be mounted in the center of the array similar to the example here: Link

 

[aussiejohn2]

Hi SpaceRanch,
Free finite simulator femm would let you simulate. KJ is a great site by the way, one of my stickies. A lot of their images look to have been made in femm.
John.

 

[MagMike]

Adding a steel bar to the strong side would cancel the advantage of a Halbach array. The steel will absorb the flux.

It's going to be very difficult to design a permanent magnet assembly that can pull items that are 10 inches away. Magnetic field strength, even those of Halbach assemblies drop rapidly with distance.

A 'junkyard' electromagnet will perform better.

 

[MagBen]

If your main concern is to pull long distance subject, do not use Halbach design, donot use back steel. Alternative N/S/N... design is not recommended either. Use same N or S design for better penetration (deeper, large gap).

If the max pull force (zero to small gap) is your concern, you can use Halbach or alternative design with back steel. The steel will be placed to the opposite of functional (strong) side to focus the flux to maximize the field.

 

[IRstuff]

Don't people already do something like that? The electromagnets at wrecking yards I've seen in film can do the job, although they don't span the lateral distance you're asking for. The video below shows the electromagnet pulling brake rotors from about 10 to 15 inches.

https://www.youtube.com/watch?v=XBWy9gzGGd4

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[RyreInc]

If the permanent magnets are strong enough to pull the metal from out of the ground, who or what is strong enough to pull the metal back off the magnets once it attaches? Consider that the latter requires vastly more force than the former!

 

[MagBen]

There is often a DC-excited coil switched on the permanent-magnetic field, that neutralizes at the holding surface and the workpiece to be held can be taken off.

 

[RyreInc]

Fair enough; I doubt OP was planning on one though! I'm not too familiar with these - I would suspect considerable care must be taken to avoid demagnetizing the PMs.