|Michael Gilligan||26/10/2021 19:30:33|
19258 forum posts
If we knew what you were trying to make, John … People might be able to offer useful comment, based on their experience.
But as it’s all confidential : “Tricky stuff, eh?” is probably a good summary.
|Dave S||26/10/2021 19:51:09|
|256 forum posts|
I’m not sure I agree with “Tricky Stuff”.
Possibly “narrow specialism, niche application stuff”
Magnetic properties of materials is a specific area of materials science, and a well studied one at that.
The information is available, it’s just not actually that critical to most applications.
|John Smith 47||28/10/2021 01:23:11|
|271 forum posts|
You could probably say the exact same thing about doing surgery on the human brain or about sending a rocket to the moon. In fact.. just a wild guess, Dave, but... maybe you do! ;^P
|John Haine||28/10/2021 10:14:36|
|4259 forum posts|
Hmmm. How close you can get to saturation depends on the flux density produced by a given magnetic field, and so on the permeability. So for the unmagnetized polepiece of a latch you want a material that has high permeability but also a reasonable saturation flux density, but low remanence so it doesn't itself get magnetised. There's a distinction between field and flux, which roughly speaking correspond to voltage and current. But in the end mild steel is probably a reasonable compromise and for most simple magnetic devices is as good as you need.
|John Smith 47||30/10/2021 02:05:14|
|271 forum posts|
[See how "tricky" this topic is!]
And in this regard the best ferromagnetic steels available don't perform all that much better than mild steel. From memory the uplift in magnetic pull was only something like +30% or +40% (??) and meanwhile the costs started to escalate.
"magnetic field" and "magnetic flux"
One thing I have noticed is that even though when you separate the steel from the magnets, the steel do not stay significantly magnetised, if you leave the magnets in place for a few seconds the magnetic pull SEEMS to gradually get quite a lot stronger in a matter of say a few seconds. This may be some kind off illusion I'm not sure, but I as far as I can tell it doesn't appear to be caused by the magnets slowly moving closer to each other. Either way if the magnetic pull is good enough immediately and if it gets say twice as strong in a few seconds that's fine by me.
|John Sykes 1||18/11/2021 09:46:04|
|10 forum posts|
The "pull" of the magnet is actually calculated from the incremental change in stored energy in the air gap as the pole piece (or whatever) is moved towards or away from the magnet. Many non-linearities will render precise calculations of absolute magnetic flux somewhat futile, but the general principle is there, and tells is that the pole piece should have a high saturation figure and should be adequately thick to handle the total flux generated by the magnet (if the objective is to obtain the maximum force). You can observe this phenomena using a magnetic dial-guage holder, first on thick cast iron, and then on a thin plate, where the force is much reduced. The surface roughness / flatness also comes into play when considering the maximum "pul-off" force, as any residual air gap when the parts are touching will impact on the "closed loop" flux density.
BTW, 1.3mm is very close to 16 AWG !
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