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"Camilo" <camilogil@[EMAIL PROTECTED]
> wrote in message
news:4037f2ec-b634-4257-a330-007f3e002add@[EMAIL PROTECTED]
everybody! Speaking about industrial electromagnets, like this one:
http://www.coolmagnetman.com/images/em500a.jpg
¿Is an electromagnet like this, strong for attract nearby
ferromagnetic objects? ¿How closer they need to be to get attracted
strongly? or ¿are they strong just for holding ferromagnetic objects?
(particulary, at the webpage where shows this electromagnet, they say
that it can hold 500 lb just using a 1,5 v "D" size cell, so it´s
obvious that this class of electromagnets are too good for holding
ferromagnetic objects; what i need to know is how good are the to
attract and how strong they attract nearby objects)
The attractive force depends on the ampere turns in the winding, the
cross-section and length of the air gap and the geometry of the magnet and
gap. Ignoring the iron, for a total air gap length g and area A, with N
turns and current I, the force is (mu0/2 )N^2I^2A/g^2. In the magnet
shown,
there are two air gaps, preferrably of the same area. (use 2g instead of
g)
muo is the permeability of free space and fringing of flux is ignored.
This is not valid at a gap very near 0 as the iron will limit the flux.
You can then use force =1/2 BHA where B is the maximum flux density with
no
gap. Then B is determined by H=NI/L where L is the iron path length and B
is generally found from a B-H curve for the material rather than using
B=muH
because u is so variable.
--
Don Kelly dhky@[EMAIL PROTECTED]
the X to answer
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