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Characterising neodymium magnets
Barry Hardhouse:
Hi All,
Got an oddball problem and would be interested in your thoughts.
We purchase neodymium magnets in an un-magnetised state. These are incorporated into an assembly and then magnatised ("charged").
We have noticed that after charging, some of these magnets are failing to produce the expected flux. Everything else is identical, so we suspect that the material is substandard.
I'm looking for possible ways to separate "good" magnets from "bad" prior to production (with a view obviously to getting the supplier to sort the issue out).
Does anyone have any ideas how this could be done?
I was hoping to measure some differences in permeability or see some hysteresis loops. However, it looks like the material has pretty much the same permeability as air - all my measurements are in the noise. Presumably you'd see the permeability jump as the magnetisation happened?
Thanks!
mendip_discovery:
There are a few bits of kit you can buy, a gauss meter is one.
A simple option might just be a fish scale and a ball bearing. Measure the force needed to remove the bearing and you are good.
I found that out just googling it the other day when I was asked about a magnet for catching metal particles put of a beer mix.
Barry Hardhouse:
Thanks Mendip.
Unfortunately, the Gauss meter is already reveling the problem. We can measure when the magnetised parts are weaker than expected, after magnetising, but by that point the entire assembly has been put together and must be thrown away if the magnet is no good.
I'm looking for a method that might reveal if the neodymium is good before it is permanently magnetised.
TomKatt:
Absolutely no experience in this field, but my first thought is what types of QC testing does the raw material manufacturer perform and what specifications you require of the raw materials you purchase.
Also, perhaps there is some kind of chemical analysis that could identify differences between known good and failed materials, such as spectrum analysis?
Edit - I'm assuming you've ruled out any possible variables in your processing? Are you certain it's the raw material, or could something affect manufacturing?
In any case, discussing this issue with the manufacturer / supplier would be on the top of my list - sometimes they have access to testing resources that you may not have available.
jmelson:
--- Quote from: Barry Hardhouse on February 28, 2023, 01:44:54 pm ---Thanks Mendip.
Unfortunately, the Gauss meter is already reveling the problem. We can measure when the magnetised parts are weaker than expected, after magnetising, but by that point the entire assembly has been put together and must be thrown away if the magnet is no good.
I'm looking for a method that might reveal if the neodymium is good before it is permanently magnetised.
--- End quote ---
Can't you charge the magnet before assembly? Maybe you can charge, test and then "erase" before the traditional procedure.
Jon
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